0000950170-24-044508 | 10-K | XBRL Viewer

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Consolidated balance sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Statement of Financial Position [Abstract]
Convertible preferred stock, par value	$ 0.001	$ 0.001
Convertible preferred stock, shares authorized	5,000,000	5,000,000
Convertible preferred stock, shares issued	24,610	0
Convertible preferred stock, shares outstanding	24,610	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	45,000,000	45,000,000
Common stock, shares issued	4,885,512	4,541,167
Common stock, shares outstanding	4,885,512	4,541,167

Fair Value of Financial Assets

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets

4. Fair Value of Financial Assets

The following tables present information about the Company’s assets that are measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values:


	December 31, 2023
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	10,322	$	—	$	—	$	10,322
	$	10,322	$	—	$	—	$	10,322


	December 31, 2022
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	1,661	$	—	$	—	$	1,661
Investments:
Commercial paper		—		12,814		—		12,814
Treasury bills		—		3,234		—		3,234
	$	1,661	$	16,048	$	—	$	17,709

During the years ended December 31, 2023 and 2022, there were no transfers between levels.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Restructuring and Other Costs - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($) Employees	Dec. 31, 2022 Employees
Restructuring and Related Activities [Abstract]
Workforce reduction, remaining number of employees \| Employees	3	9
Restructuring charges \| $	$ 928

Accrued Expenses and Other Current Liabilities

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

9. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:


	December 31,
	2023		2022
External research and development services	$	1,110	$	533
Payroll and payroll-related costs		1,178		425
Professional fees		653		492
Other		206		181
Total accrued expenses and other current liabilities	$	3,147	$	1,631

Stock-Based Awards - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]
Number of Shares, Beginning balance	537,112
Number of Shares, Granted	10,900
Number of Shares, Exercised	0
Number of Shares, Forfeited/Canceled	(57,483)
Number of Shares, Expired	(58,886)
Number of Shares, Options assumed through business combination	1,780,459
Number of Shares, Ending balance	2,212,102	537,112
Number of Shares, Options exercisable	1,882,191	288,821
Number of Shares, Options vested and expected to vest	2,209,420	529,549
Weighted Average Exercise Price, Beginning balance	$ 29.77
Weighted Average Exercise Price, Granted	1.17
Weighted Average Exercise Price, Forfeited/Canceled	14.29
Weighted Average Exercise Price, Expired	27.35
Weighted Average Exercise Price, Options assumed through business combination	1.61
Weighted Average Exercise Price, Ending balance	7.42	$ 29.77
Weighted Average Exercise Price, Options exercisable	7.46	40.15
Weighted Average Exercise Price, Options vested and expected to vest	$ 7.41	$ 29.95
Weighted Average Remaining Contractual Term, Outstanding	6 years	7 years 10 months 24 days
Weighted Average Remaining Contractual Term, Options assumed through business combination	6 years 9 months 18 days
Weighted Average Remaining Contractual Term, Options exercisable	5 years 9 months 18 days	7 years 1 month 6 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	6 years	7 years 9 months 18 days
Aggregate Intrinsic Value	$ 2,905
Aggregate Intrinsic Value, Options assumed through business combination	200
Aggregate Intrinsic Value, Forfeited/Canceled	10
Aggregate Intrinsic Value, Options exercisable	2,631
Aggregate Intrinsic Value, Options vested and expected to vest	$ 2,904

Goodwill and Indefinite-Lived Intangible Assets - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2023 USD ($)
Indefinite-Lived Intangible Assets [Line Items]
Impairment of goodwill	$ 0
Impairment of indefinite-lived intangible assets	0
Goodwill	6,330,000
Indefinite-lived intangible assets acquired	$ 79,200,000

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References + Details

Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Oct. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Preferred stock, shares authorized			5,000,000
Preferred stock, par value			$ 0.001
Preferred stock, shares issued			0
Preferred stock, shares outstanding			0
Issuance costs		$ 893
Proceeds from the PIPE transaction		$ 741
Common stock, shares issued		4,885,512	4,541,167
Common stock, par value		$ 0.001	$ 0.001
Warrant [Member]
Class of Stock [Line Items]
Preferred stock, par value		$ 0.001
Lung Acquisition [Member]
Class of Stock [Line Items]
Common stock, shares issued	344,345	4,885,512
Common stock, par value	$ 0.001
Lung Acquisition [Member] \| Common Warrants [Member] \| Maximum [Member]
Class of Stock [Line Items]
Aggregate number of shares issued and sold	2,353,500
Series X Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized		5,000,000
Preferred stock, par value		$ 0.001
Preferred stock, shares issued		24,610
Preferred stock, shares outstanding		24,610
Gross proceeds from issuance of preferred stock		$ 18,429
Proceeds from issuance of preferred stock		16,795
Issuance costs		$ 855
Preferred Stock is convertible into common stock		1,000
Preferred stock, convertible, shares issuable beneficial ownership as a percentage		19.99%
Preferred stock, dividends declared		$ 0
Preferred stock, dividends paid		$ 0
Series X Preferred Stock [Member] \| Lung Acquisition [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	19,903
Series X Preferred Stock [Member] \| Lung Acquisition [Member] \| Purchase Agreement [Member]
Class of Stock [Line Items]
Aggregate number of shares issued and sold	4,707

Net Loss per Share - Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Numerator:
Net loss	$ (15,732)	$ (27,329)
Denominator:
Weighted average common shares outstanding - basic	4,598,715	4,539,318
Weighted average common shares outstanding - diluted	4,598,715	4,539,318
Net loss per share attributable to common stockholders-basic	$ (3.42)	$ (6.02)
Net loss per share attributable to common stockholders-diluted	$ (3.42)	$ (6.02)

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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-Publisher FASB
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Reference 24: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Subsequent Event

12 Months Ended

Dec. 31, 2023

Subsequent Events [Abstract]

Subsequent Event

18. Subsequent Event

On February 28, 2024, the Company held its 2023 annual meeting of stockholders (the “2023 Annual Meeting”) at which the stockholders of the Company approved an amendment (the “Plan Amendment”) to the Aileron’s 2021 Plan to increase the number of shares of common stock issuable under the 2021 Plan by 3,000,000 shares to 3,840,254. On January 17, 2024, upon the recommendation of the compensation committee and subject to stockholder approval, the Company’s Board of Directors adopted the Plan Amendment. Other than increasing the number of shares issuable under the 2021 Plan, the Plan Amendment does not make any changes to the 2021 Plan. The material terms of the 2021 Plan are described in the Company’s definitive proxy statement for the 2023 Annual Meeting filed with the Securities and Exchange Commission on January 29, 2024 (the “Proxy Statement”).

At the 2023 Annual Meeting, the Company’s stockholders approved an amendment to the Company’s Restated Certificate of Incorporation, as amended, to increase the number of authorized shares of common stock of the Company from 45,000,000 to 100,000,000 shares. The Company filed the Certificate of Amendment to implement

the increase in the number of authorized shares, which was effective upon filing, with the Secretary of State of the State of Delaware on February 28, 2024. The additional shares of common stock authorized by the Certificate of Amendment have rights identical to the Company’s currently outstanding Common Stock.

At the 2023 Annual Meeting, the Company’s stockholders also approved the issuance, in accordance with Nasdaq Listing Rule 5635(a), of shares of common stock, upon conversion of the Company's outstanding Series X Preferred Stock. Following approval of the conversion of outstanding Series X Preferred Stock, the Company had 29,495,512 shares of common stock issued and outstanding on a pro forma basis, which gives effect to the full conversion of the Series X Preferred Stock as of the date of the 2023 Annual Meeting, without regard to beneficial ownership limitations that may limit the ability of certain holders of Series X Preferred Stock to convert such shares to common stock as such time. On March 5, 2024, based upon existing beneficial ownership limitations, 12,087 shares of Series X Preferred Stock were automatically converted into 12,087,000 shares of common stock. The remaining approximately 12,523 shares of Series X Preferred Stock (which are convertible into 12,523,000 shares of common stock) will remain convertible at the option of the holder thereof, subject to certain beneficial ownership limitations.

On February 29, 2024, the Company received a letter from the Listing Qualifications Department of the Nasdaq Stock Market notifying the Company that it has regained compliance with the annual meeting requirement for continued listing on the Nasdaq Capital Market set forth in Nasdaq Listing Rule 5620.

On March 11, 2024, the Company and Manuel C. Alves-Aivado, M.D., Ph.D., agreed that his employment with the Company would cease and he would resign from his position as Chief Executive Officer of the Company, effective as of March 11, 2024 (the “Separation Date”). Dr. Aivado will remain a member of the Company’s Board. Dr. Aivado’s resignation from the Company was not the result of any disagreement with the Company on any matter relating to its operations, policies or practices.

In connection with Dr. Aivado’s separation from the Company, and in accordance with the severance agreement, dated as of September 6, 2018, between the Company and Dr. Aivado, Dr. Aivado is entitled to receive his base salary for eighteen months of $881 following the separation date, payments on Dr. Aivado’s behalf of the monthly premiums for medical insurance coverage under COBRA until the earlier of the date that is eighteen months following the separation date or the date on which Dr. Aivado becomes eligible to receive group health insurance coverage through another employer, a lump sum payment of $441 equal to one and one-half times Dr. Aivado’s target bonus for the 2024 calendar year, and acceleration in full of the vesting of any unvested equity awards. Dr. Aivado’s receipt of these post-separation benefits under the severance agreement is conditioned upon his execution of a severance and release of claims agreement with the Company.

Common Stock - Additional Information (Detail) $ / shares in Units, $ in Thousands			12 Months Ended
	Oct. 31, 2023 $ / shares shares	Nov. 10, 2022 shares	Dec. 31, 2023 USD ($) $ / shares shares	Dec. 31, 2022 $ / shares shares	Jan. 01, 2023 shares	Nov. 09, 2022 shares	Dec. 31, 2021 shares
Class of Stock [Line Items]
Common stock, shares authorized		15,000,000	45,000,000	45,000,000		300,000,000
Common stock, par value \| $ / shares			$ 0.001	$ 0.001
Common stock, shares outstanding			4,885,512	4,541,167
Common stock, shares issued			4,885,512	4,541,167
Preferred stock, shares issued				0
Shares issued, outstanding and reserved for issuance			36,095,427
Preferred stock, shares outstanding				0
Common stock, dividends declared \| $ / shares			$ 0	$ 0
Reverse stock split conversion ratio		0.05
Aggregate number of common stock shares issued and sold			2,353,500
Treasury stock			0
Issuance of warrants \| $			$ 741
Lung Acquisition [Member]
Class of Stock [Line Items]
Common stock, par value \| $ / shares	$ 0.001
Common stock, shares outstanding			4,885,512
Common stock, shares issued	344,345		4,885,512
Common stock reserved for issuance			1,780,459
Aggregate number of common stock shares issued and sold			726,437
Warrants exercise price \| $ / shares			$ 5.66
Warrants and Rights Outstanding, Maturity Date			May 20, 2029
Series X Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued			24,610
Common stock reserved for issuance			24,847,000
Preferred stock, shares outstanding			24,610
Series X Preferred Stock [Member] \| Lung Acquisition [Member]
Class of Stock [Line Items]
Preferred stock, shares issued	19,903
Aggregate number of common stock shares issued and sold	4,707
April 2019 Private Placement [Member]
Class of Stock [Line Items]
Aggregate number of common stock shares issued and sold			646,759
Warrants exercise price \| $ / shares			$ 40
Warrants and Rights Outstanding, Maturity Date			Apr. 02, 2024
Maximum [Member]
Class of Stock [Line Items]
Percentage of common stock share outstanding			19.99%
Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares outstanding			4,885,512	4,541,167			4,528,667
Stock remained available for future issuance			8,904,573
Outstanding Warrants [Member]
Class of Stock [Line Items]
Common stock reserved for issuance			3,726,696
Common Warrants [Member]
Class of Stock [Line Items]
Warrants exercise price \| $ / shares	$ 4.89
Common Warrants [Member] \| Maximum [Member] \| Lung Acquisition [Member]
Class of Stock [Line Items]
Aggregate number of common stock shares issued and sold	2,353,500
2017 Employee Stock Purchase Plan [Member]
Class of Stock [Line Items]
Common stock reserved for issuance			7,500		0
Stock remained available for future issuance			7,500
2021 Stock Incentive Plan [Member]
Class of Stock [Line Items]
Common stock reserved for issuance			416,617
Stock remained available for future issuance			840,254
Existing Equity Incentive Plans [Member]
Class of Stock [Line Items]
Common stock reserved for issuance			2,212,102

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Summary of Property and Equipment, Net

Property and equipment, net consisted of the following:


	December 31,
	2023			2022
Computer equipment and software	$	323		$	340
Furniture and fixtures		54			—
		377			340
Less: Accumulated depreciation and amortization		(358	)		(270	)
	$	19		$	70

Fair Value of Financial Assets (Tables)

12 Months Ended

Dec. 31, 2023

Fair Value Disclosures [Abstract]

Summary of Assets Measured at Fair Value on Recurring Basis


	December 31, 2023
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	10,322	$	—	$	—	$	10,322
	$	10,322	$	—	$	—	$	10,322


	December 31, 2022
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	1,661	$	—	$	—	$	1,661
Investments:
Commercial paper		—		12,814		—		12,814
Treasury bills		—		3,234		—		3,234
	$	1,661	$	16,048	$	—	$	17,709

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of U.S. Federal Statutory Income Tax Rate to Effective Income Tax Rate

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:


	Year Ended
	December 31,
	2023			2022
Federal statutory income tax rate		(21.0	)%		(21.0	)%
State taxes, net of federal benefit		108.1			(5.4	)
Research and development and orphan drug tax credits		31.5			(2.9	)
Other permanent items		2.4			0.9
Change in deferred tax asset valuation allowance		(444.9	)		28.4
Loss of federal net operating losses due to 382		323.9			—
Effective income tax rate		—	%		—	%

Schedule of Net Deferred Tax Liabilities

Net deferred tax liabilities as of December 31, 2023 and 2022 consisted of the following:


	December 31,
	2023			2022
Deferred tax assets:
Net operating loss carryforwards	$	12,387		$	64,959
Research and development and orphan drug tax credit carryforwards		7,825			6,606
Capitalized research and development expenses		9,797			4,380
Accrued expenses and reserves		251			61
Depreciation and amortization		—			—
Lease liability		10			9
Stock compensation		1,514			1,442
Total deferred tax assets		31,784			77,457
Valuation allowance		(18,506	)		(77,441	)
Net deferred tax assets	$	13,278		$	16
Deferred tax liabilities:
Depreciation and amortization	$	(16,594	)	$	(5	)
Right of use asset	$	(10	)	$	(11	)
Total deferred tax liabilities	$	(16,604	)	$	(16	)
Net deferred tax asset (liability)	$	(3,326	)	$	—

Schedule of Changes in Valuation Allowance

Changes in the valuation allowance were as follows:


	Year Ended December 31,
	2023			2022
Valuation allowance at beginning of year	$	(77,441	)	$	(69,680	)
Decreases/(increases) recorded to income tax provision		69,134			(7,761	)
Increases recorded to invested capital		(10,199	)		—
Valuation allowance at end of year	$	(18,506	)	$	(77,441	)

Other Asset

12 Months Ended

Dec. 31, 2023

Prepaid Expense and Other Assets [Abstract]

Other Assets

8. Other Assets

Other assets consisted of the following:


	December 31,
	2023		2022
Non-current prepaid research and development	$	2,140	$	—
Other assets		53		24
Total other non-current assets	$	2,193	$	24

Net Loss per Share - Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	30,548,798	1,183,871
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	2,212,102	537,112
Warrants To Issue Shares Of Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	3,726,696	646,759
Series X Preferred Stock Issued And Outstanding, As Converted [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	24,610,000	0

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Statement [Abstract]
Revenue	$ 0	$ 0
Operating expenses:
Research and development	3,991	17,967
General and administrative	11,357	9,680
Restructuring and other costs	928
Total operating expenses	16,276	27,647
Loss from operations	(16,276)	(27,647)
Other income (expense), net	544	318
Net loss	$ (15,732)	$ (27,329)
Net loss per share - basic	$ (3.42)	$ (6.02)
Net loss per share - diluted	$ (3.42)	$ (6.02)
Weighted average common shares outstanding - basic	4,598,715	4,539,318
Weighted average common shares outstanding - diluted	4,598,715	4,539,318
Comprehensive loss:
Net Income (Loss)	$ (15,732)	$ (27,329)
Other comprehensive gain (loss):
Unrealized gain on short-term investments, net of tax of $0	48	(35)
Foreign currency translation adjustments	(63)
Total other comprehensive loss	(15)	(35)
Total comprehensive loss	$ (15,747)	$ (27,364)

Nature of the Business - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Proceeds from collaboration agreement	$ 34,910
Cash and cash equivalents	17,313	$ 5,194
Accumulated deficit	(288,517)	(272,785)
Net loss	(15,732)	$ (27,329)
Lung Acquisition [Member]
Class of Stock [Line Items]
Proceeds from sales of stock	18,429
Issuance costs	893
Aggregate principal amount	$ 1,553
Lung Acquisition [Member] \| Series X Preferred Stock [Member]
Class of Stock [Line Items]
Percentage of discount to per share price	10.00%
Common Stock [Member]
Class of Stock [Line Items]
Proceeds from sales of stock	$ 145,467
Preferred Stock [Member]
Class of Stock [Line Items]
Proceeds from sales of stock	$ 131,211

Property and Equipment, Net - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 377	$ 340
Less: Accumulated depreciation and amortization	(358)	(270)
Property and equipment, net	19	70
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	323	$ 340
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 54

Prepaid Expenses and Other Current Assets

12 Months Ended

Dec. 31, 2023

Prepaid Expense and Other Assets, Current [Abstract]

Prepaid Expenses and Other Current Assets

5. Prepaid Expenses and Other Current Assets

Prepaid expenses and other current assets consisted of the following:


	December 31,
	2023		2022
Prepaid research and development	$	207	$	—
Other current assets		675		606
Total prepaid expenses and other current assets	$	882	$	606

Stock-Based Awards (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Valuation Assumptions of Stock Options Granted

The assumptions that the Company used to determine the grant-date fair value of the stock options granted to employees and directors during the years ended December 31, 2023 and 2022 and at the Lung Acquisition date were as follows, presented on a weighted average basis:


	Year Ended December 31,						October 31,
	2023			2022			2023
Risk-free interest rate		4.90	%		2.50	%	4.82-5.58%
Expected term (in years)		4.0			6.1		0.42-6.28
Expected volatility		94.4	%		94.2	%	75-91%
Expected dividend yield		0	%		0	%		0	%

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity since January 1, 2023:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2022		537,112		$	29.77		7.9	$	—
Granted		10,900			1.17		—		—
Exercised		—			—		—		—
Forfeited/Canceled		(57,483	)		14.29		—		10
Expired		(58,886	)		27.35		—		—
Options assumed through business combination		1,780,459			1.61		6.8		200
Outstanding at December 31, 2023		2,212,102		$	7.42		6.0	$	2,905

Options exercisable at December 31, 2023		1,882,191		$	7.46		5.8	$	2,631
Options vested and expected to vest at December 31, 2023		2,209,420		$	7.41		6.0	$	2,904
Options exercisable at December 31, 2022		288,821		$	40.15		7.1	$	—
Options vested and expected to vest at December 31, 2022		529,549		$	29.95		7.8	$	—

Summary of Stock Based Compensation Expense

The Company recorded stock-based compensation expense related to stock options in the following expense categories of its statements of operations and comprehensive loss:


	Year Ended December 31,
	2023		2022
Research and development expenses	$	277	$	600
General and administrative expenses		913		1,483
	$	1,190	$	2,083

Consolidated Statement of Changes in Convertible Preferred Stock and Stockholders' Equity (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Net of issuance costs	$ 893
Common Stock [Member]
Net of issuance costs	38
Series X Preferred Stock [Member]
Net of issuance costs	$ 855

Business Acquisition - Schedule of Unaudited Pro Forma Financial Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Business Acquisition, Pro Forma Information [Abstract]
Total net revenue	$ 153	$ 688
Net loss	$ (28,232)	$ (51,610)

Common Stock

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Common Stock

12. Common Stock

As of December 31, 2023 and 2022, the Company was authorized to issue 45,000,000 shares of common stock, par value $0.001 per share. As of December 31, 2023, the Company had 4,885,512 shares of common stock issued and outstanding. As of December 31, 2022, the Company had 4,541,167 shares of common stock issued and outstanding.

Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive dividends, as may be declared by the Company’s board of directors, if any. As of December 31, 2023 and 2022, no dividends had been declared.

In the event of liquidation or dissolution, the holders of the common stock are entitled to receive proportionately all assets available for distribution to stockholders after the payment of all debts and other liabilities and subject to the prior rights of any outstanding preferred stock.

Issuance of Common Stock

As disclosed above, on October 31, 2023, the Company issued to the stockholders of Lung 344,345 shares of the common stock of Aileron, par value $0.001 per share, under the terms of the Lung Acquisition Agreement. In addition, Aileron assumed (i) all Lung stock options immediately outstanding prior to the First Merger, each becoming an option for common stock subject to adjustment pursuant to the terms of the Lung Acquisition Agreement, and (ii) all warrants exercisable for Lung common stock immediately outstanding prior to the First Merger, each becoming a warrant to purchase common stock, subject to adjustment pursuant to the terms of the Lung Acquisition Agreement. Immediately following the closing of the Lung Acquisition, the Company had 4,885,512 shares of common stock issued and outstanding.

As disclosed in the Note 3 above, immediately following the closing of the Lung Acquisition, on October 31, 2023, Aileron entered into the Purchase Agreement with a group of accredited investors, pursuant to which Aileron issued and sold 4,707 shares of Series X Preferred Stock and warrants to purchase up to an aggregate of 2,353,500 shares of Aileron common stock. The exercise price of the Warrants is $4.89 per share, subject to certain price and share adjustments, including for stock splits, stock dividends, recapitalizations, subdivisions, combinations, reclassifications, noncash distributions, and cash dividends. The Warrants will be exercisable any time after the later of May 2, 2024, the date the requisite stockholder approval is obtained, and on or prior to May 2, 2027. Payment for Warrant shares upon exercise of the Warrants may be (i) in cash or (ii) in the event that there is no registration statement available for the resale of Warrant shares, by cashless exercise.

Under the terms of the Warrants, the Company shall not effect the exercise of any portion of any Warrant, and a holder shall not have the right to exercise any portion of any Warrant, to the extent that after giving effect to such exercise, the holder (together with its affiliates and any other persons acting as a group together with the holder or any of its affiliates), would beneficially own in excess of a percentage elected by the holder up to 19.99% of the number of shares of common stock outstanding immediately after giving effect to such exercise, as such percentage ownership is determined in accordance with the terms of the Warrants. However, any holder may, upon written notice to the Company, increase or decrease such percentage to any other percentage not in excess of 19.99%; provided that any increase or decrease in such percentage will not be effective until 61 days after such notice is delivered to the Company.

The Company has assessed the Warrants for appropriate equity or liability classification and determined the Warrants are freestanding instruments that do not meet the definition of a liability pursuant to ASC 480 and do not meet the definition of a derivative pursuant to ASC 815, Derivatives and Hedging (“ASC 815”). The Warrants are indexed to the Company’s common stock and meet all other conditions for equity classification under ASC 480 and ASC 815. Accordingly, the Warrants are classified as equity and accounted for as a component of additional paid-in capital at the time of issuance. The Warrants were initially recognized at their relative fair value in the amount of $741 at the time of issuance determined using Black-Scholes option-pricing model and will not be remeasured.

Reverse Stock Split

The Company’s stockholders approved a reverse stock split of the Company’s common stock on June 15, 2022. The Company effected the Reverse Stock Split on November 10, 2022. Pursuant to the Reverse Stock Split, every 20 shares of the Company’s issued and outstanding shares of common stock were automatically combined into one issued and outstanding share of common stock, without any change in the par value per share of the common stock. The Reverse Stock Split reduced the authorized number of shares of common stock from 300,000,000 to 15,000,000 and, pursuant to the certificate of amendment, such reduced authorized number of shares of common stock was subsequently multiplied by three, such that following the Reverse Stock Split the Company has 45,000,000 shares of

common stock authorized. The Reverse Stock Split affected all issued and outstanding shares of the Company’s common stock, and the respective numbers of shares of common stock underlying the Company’s outstanding stock options, outstanding warrants and the Company’s equity incentive plans were proportionately adjusted. All share and per share amounts disclosed give effect to the Reverse Stock Split on a retroactive basis.

As of December 31, 2023, 4,885,512 shares of common stock were issued and outstanding, no shares were held in treasury, and 24,610 shares of Series X Preferred Stock were issued and outstanding. In addition, as of December 31, 2023, there were:

•

24,847,000 shares of common stock reserved for issuance upon conversion of the Series X Preferred Stock;

•

2,212,102 shares of common stock issuable upon the exercise of options under existing equity incentive plans, of which 1,780,459 options were assumed through the Lung Acquisition;

•

416,617 and 7,500 shares of common stock reserved for issuance under the 2021 Plan and 2017 Employee Stock Purchase Plan, respectively, as well as any automatic increases in the number of shares of the common stock reserved under these plans; and

•

3,726,696 shares of common stock reserved for issuance upon exercise of outstanding warrants. The warrants consist of (i) warrants to purchase 646,759 shares of the Company’s common stock, with an exercise price of $40.00 per share, which were issued in the April 2019 private placement, which expire on April 2, 2024; (ii) warrants to purchase 726,437 shares of the Company’s common stock, with an exercise price of $5.66, which expire on May 20, 2029, which were assumed in connection with the Lung Acquisition, and (iii) warrants to purchase 2,353,500 shares of the Company’s common stock, which were issued and sold in the Financing as described above.

Accordingly, as of December 31, 2023, out of the 45,000,000 shares of common stock presently authorized, 36,095,427 shares are issued and outstanding or reserved for issuance and 8,904,573 shares of common stock remain available for future issuance.

- Definition

The entire disclosure for equity.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (h)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 505
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481004/946-505-50-6

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480237/815-40-50-6

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480008/505-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(e)(1))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 505
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//505/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-13

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-14

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
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-Paragraph 16
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Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Topic 505
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-Section 50
-Paragraph 18
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481112/505-10-50-18

+ Details

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Schedule of Property and Equipment Estimated Useful Lives

Depreciation and amortization expense is recognized using the straight-line method over the following estimated useful lives:

          Computer equipment and software
Furniture and fixtures

          3 to 5 years
7 years

Commitments and Contingencies - Schedule of Aggregate Future Service and Purchase Commitments with Manufacturer (Detail) $ in Thousands	Dec. 31, 2023 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2025 and thereafter	$ 2,312
Total purchase commitments	$ 2,312

Restructuring and Other Costs

12 Months Ended

Dec. 31, 2023

Restructuring and Related Activities [Abstract]

Restructuring and Other Costs

10. Restructuring and Other Costs

On February 16, 2023, the Board of Directors of the Company determined to reduce the Company’s remaining workforce from nine to three full-time employees. The determination to effect the workforce reduction was made in connection with the Company’s decision to terminate its Phase 1b breast cancer trial of ALRN-6924 and further development of ALRN-6924.

As a result of the above restructuring initiatives, the Company incurred restructuring-related charges of $928 for the year ended December 31, 2023. Restructuring-related charges were comprised of one-time termination costs in connection with the reduction-in-workforce, including severance, benefits, and related costs.

The Company paid all restructuring-related charges during the year ended December 31, 2023.

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Pay vs Performance Disclosure
Net Income (Loss)	$ (15,732)	$ (27,329)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Property and Equipment, Net

12 Months Ended

Dec. 31, 2023

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

6. Property and Equipment, Net

Property and equipment, net consisted of the following:


	December 31,
	2023			2022
Computer equipment and software	$	323		$	340
Furniture and fixtures		54			—
		377			340
Less: Accumulated depreciation and amortization		(358	)		(270	)
	$	19		$	70

Depreciation expense for the years ended December 31, 2023 and 2022 was $49 and $169, respectively. During the year ended December 31, 2023, the Company received payment for disposed, fully depreciated assets, resulting in a gain on sales of $42.

Stock-Based Awards

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Stock-Based Awards

13. Stock-Based Awards

As of December 31, 2023, the Company had five equity compensation plans, each of which was approved by its stockholders: 2006 Equity Incentive Plan, as amended (the “2006 Plan”), 2016 Stock Incentive Plan (the “2016 Plan”), 2017 Stock Incentive Plan (the “2017 Plan”), 2021 Stock Incentive Plan (the “2021 Plan”), and 2017 Employee Stock Purchase Plan (the “2017 ESPP”). The Company also assumed Lung’s 2013 Long-Term Incentive Plan (the “2013 Plan”) as a result of the Lung Acquisition.

As of December 31, 2023, the Company had 9,482 shares to be issued upon exercise of outstanding options under the 2006 Plan; 8,404 shares to be issued upon exercise of outstanding options under the 2016 Plan, and 130,903 shares to be issued upon exercise of outstanding options under the 2017 Plan. No outstanding options under the 2006 Plan, the 2016 Plan, or the 2017 Plan as of December 31, 2023. As such, no shares remained available for future issuance under the 2006 Plan, the 2016 Plan, or the 2017 Plan as of December 31, 2023.

Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards.

The exercise price for stock options granted may not be less than the fair market value of the common stock as of the date of grant.

2021 Stock Incentive Plan

The Company’s 2021 Plan was approved by the Company’s stockholders on June 15, 2021 and became effective on June 16, 2021. Under the 2021 Plan, the Company may grant incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, awards of restricted stock units and other stock-based awards. The

Company’s employees, officers, directors, consultants and advisors are eligible to receive awards under the 2021 Plan; however, incentive stock options may only be granted to employees. The 2021 Plan is administered by the Company’s Board of Directors (the “Board”) or, at the discretion of the Board, by a committee of the Board. The number of shares of common stock covered by options and the date those options become exercisable, type of options to be granted, exercise prices, vesting and other restrictions are determined at the discretion of the Board, or its committee if so delegated.

Stock options granted under the 2021 Plan with service-based vesting conditions generally vest over four years and may not have a duration in excess of ten years, although options have been granted with vesting terms of less than four years.

The total number of shares of common stock that may be issued under the 2021 Plan was 840,254 as of December 31, 2023, of which 416,617 shares remained available for grant. The Company initially reserved 625,000 shares of common stock, plus the number of shares of common stock subject to outstanding awards under the 2017 Plan, the 2016 Plan and the 2006 Plan that expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right up to 314,006 shares.

2017 Stock Incentive Plan

The 2017 Plan was approved by the Company’s stockholders on June 16, 2017, and became effective on June 28, 2017. Under the 2017 Plan, the Company could grant incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, awards of restricted stock units and other stock-based awards. The Company’s employees, officers, directors, consultants and advisors were eligible to receive awards under the 2017 Plan; however, incentive stock options could only be granted to employees. The 2017 Plan is administered by the Board or, at the discretion of the Board, by a committee of the Board. The number of shares of common stock covered by options and the date those options become exercisable, type of options granted, exercise prices, vesting and other restrictions were determined at the discretion of the Board, or its committee if so delegated.

Stock options granted under the 2017 Plan with service-based vesting conditions generally vest over four years and may not have a duration in excess of ten years, although options have been granted with vesting terms of less than four years. The exercise price for stock options granted may not be less than the fair market value of the common stock as of the date of grant.

As of the effective date of the 2021 Plan, the Board determined to grant no further awards under the 2017 Plan.

Shares that are expired, terminated, surrendered or canceled without having been fully exercised under the 2017 Plan will be available for future awards under the 2021 Plan. In addition, shares of common stock that are tendered to the Company by a participant to exercise an award are added to the number of shares of common stock available for the grant of awards under the 2021 Plan.

2017 Employee Stock Purchase Plan

On June 16, 2017, the Company’s stockholders approved the 2017 ESPP, which became effective on June 28, 2017. Under the 2017 ESPP, the number of shares of common stock that may be issued under the 2017 ESPP will automatically increase on each January 1, beginning with the fiscal year ended December 31, 2018 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2027, equal to the least of (i) 31,120 shares, (ii) 1% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s Board. On January 1, 2023 and January 1, 2024, no additional shares were reserved for issuance under the 2017 ESPP pursuant to this provision. 7,500 shares remained available for future issuance under the 2017 ESPP as of December 31, 2023.

2013 Stock Incentive Plan

The Company assumed the Lung’s 2013 Plan as a result of the Lung Acquisition. In October 2013, Lung’s Board of Directors (“Lung’s Board”) approved the 2013 Plan to provide long-term incentives for its employees, non-employee directors and certain consultants. As of December 31, 2023, 1,780,459 shares were reserved to be issued upon exercise of options outstanding under the 2013 Plan, and 726,437 shares to be issued upon exercise of outstanding warrants under Lung’s 2013 Plan. These options and warrants were assumed by the Company in connection with the Lung Acquisition.

Before the Lung Acquisition, the 2013 Plan was administered by the Lung’s Board or, at the discretion of the Lung’s Board, by a committee of the Lung’s Board. The exercise prices, vesting and other restrictions are determined at the discretion of the Lung’s Board, or its committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than ten years. The vesting periods for equity awards are determined by the Board, but generally are four years. The contractual term for stock option awards is ten years. The vesting periods for equity awards were determined by Lung’s Board, but generally are four years. The contractual term for stock option awards is ten years. Following the closing of the Lung Acquisition on October 31, 2023, no further awards can be granted under the 2013 Plan.

Stock Option Valuation


	Year Ended December 31,						October 31,
	2023			2022			2023
Risk-free interest rate		4.90	%		2.50	%	4.82-5.58%
Expected term (in years)		4.0			6.1		0.42-6.28
Expected volatility		94.4	%		94.2	%	75-91%
Expected dividend yield		0	%		0	%		0	%

Stock Options

The following table summarizes the Company’s stock option activity since January 1, 2023:


	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2022		537,112		$	29.77		7.9	$	—
Granted		10,900			1.17		—		—
Exercised		—			—		—		—
Forfeited/Canceled		(57,483	)		14.29		—		10
Expired		(58,886	)		27.35		—		—
Options assumed through business combination		1,780,459			1.61		6.8		200
Outstanding at December 31, 2023		2,212,102		$	7.42		6.0	$	2,905

Options exercisable at December 31, 2023		1,882,191		$	7.46		5.8	$	2,631
Options vested and expected to vest at December 31, 2023		2,209,420		$	7.41		6.0	$	2,904
Options exercisable at December 31, 2022		288,821		$	40.15		7.1	$	—
Options vested and expected to vest at December 31, 2022		529,549		$	29.95		7.8	$	—

The weighted average grant-date fair value of stock options granted during the year ended December 31, 2023 was $0.80. The weighted average grant-date fair value of stock options granted during the year ended December 31,

2022 was $7.32. The aggregate fair value of stock options that vested during the years ended December 31, 2023 and 2022 was $1,191 and $2,808, respectively.

The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. There were no options exercised during the year ended December 31, 2023. The aggregate intrinsic value of stock options exercised during the year ended December 31, 2022 was $0.

Stock-Based Compensation

The Company recorded stock-based compensation expense related to stock options in the following expense categories of its statements of operations and comprehensive loss:


	Year Ended December 31,
	2023		2022
Research and development expenses	$	277	$	600
General and administrative expenses		913		1,483
	$	1,190	$	2,083

As of December 31, 2023, the Company had an aggregate of $1,702 of unrecognized stock-based compensation expense, which it expects to recognize over a weighted average period of 1.73 years.

Other Asset - Schedule of Other Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Prepaid Expense and Other Assets [Abstract]
Non-current prepaid research and development	$ 2,140	$ 0
Other assets	53	24
Total other non-current assets	$ 2,193	$ 24

Commitments and Contingencies - Additional Information (Detail) $ / shares in Units, $ in Thousands			1 Months Ended		12 Months Ended		156 Months Ended	168 Months Ended
	Mar. 26, 2021 ft²	Feb. 06, 2015 shares	Mar. 31, 2018 USD ($) $ / shares shares	Jun. 30, 2013 shares	Dec. 31, 2023 USD ($) Milestone	Dec. 31, 2022 USD ($) Milestone	Dec. 31, 2022 USD ($)	Dec. 31, 2023 USD ($)	Aug. 16, 2021 ft²	Feb. 28, 2010 USD ($)
Other Commitments [Line Items]
Lease expiration date	Mar. 31, 2023
Operating lease, right-of-use asset						$ 40	$ 40
Operating lease, liability						48	48
Non-cancellable purchase obligations					$ 2,312			$ 2,312
Contract obligation, prepaid amount					1,432			1,432
Operating Lease Agreements [Member]
Other Commitments [Line Items]
Area of land \| ft²									6,455
Harvard and Dana-Farber Agreement [Member]
Other Commitments [Line Items]
Milestone payments					$ 0	$ 0
Milestones achieved \| Milestone					0	0
Additional liabilities for milestone payments					$ 0	$ 0	0	0
Non-refundable cash payment							$ 5,118	5,153
Harvard and Dana-Farber Agreement [Member] \| Therapeutic Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments										$ 7,700
Harvard and Dana-Farber Agreement [Member] \| Diagnostic Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments										$ 700
Harvard and Dana-Farber Agreement [Member] \| License and Maintenance [Member]
Other Commitments [Line Items]
Annual license maintenance fees					110
Harvard and Dana-Farber Agreement [Member] \| License [Member]
Other Commitments [Line Items]
Annual license maintenance fees					35	110
Umicore Agreement [Member]
Other Commitments [Line Items]
Milestone payments					$ 0	0
Milestones achieved \| Milestone					0
Additional liabilities for milestone payments					$ 0			$ 0
Umicore Agreement [Member] \| License [Member]
Other Commitments [Line Items]
Annual license maintenance fees					$ 50	$ 50
UTHSCT Agreement [Member] \| Common Stock [Member]
Other Commitments [Line Items]
Shares granted in consideration \| shares		4,000,000		2,000,000
UTHSCT Agreement [Member] \| Non-convertible preferred stock [Member]
Other Commitments [Line Items]
Shares granted in consideration \| shares		400,000		400,000
Vivarta Therapeutics LLC [Member]
Other Commitments [Line Items]
License fee on agreement effective date			$ 10,000
License fee on receipt of positive freedom to operate analysis from legal counsel			$ 40,000
Vivarta Therapeutics LLC [Member] \| Common Stock [Member]
Other Commitments [Line Items]
Issuance of Common Stock Warrant \| shares			75,000
Warrant per share \| $ / shares			$ 0.12
Boston, Massachusetts [Member] \| Operating Lease Agreements [Member] \| 285 Summer Street [Member]
Other Commitments [Line Items]
Area of land \| ft²	3,365

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation

The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and as amended by ASUs of the Financial Accounting Standards Board (“FASB”).

Principles of Consolidation

The accompanying consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Lung Therapeutics, LLC, Lung Therapeutics Australia Pty Ltd, and Lung Therapeutics Limited. All intercompany balances and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual for research and development expenses, the value of stock-based

compensation, the purchase price allocation for the Lung Acquisition, and the valuation of warrants. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from those estimates.

Foreign Currency Transactions

The functional currency for the Company’s wholly owned foreign subsidiary, Lung Therapeutics Australia Pty Ltd., is the United States dollar. All foreign currency transaction gains and losses are recognized in the consolidated statements of operations and comprehensive loss.

Concentration of Credit Risk and of Significant Suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. Periodically, the Company maintains balances in operating accounts above federally insured limits. The Company deposits its cash in financial institutions that it believes have high credit quality. The Company has not experienced any losses on such accounts and does not believe it is exposed to any significant credit risk on cash and cash equivalents.

The Company is dependent on third-party manufacturers to supply products for research and development activities of its programs, including preclinical and clinical testing. In particular, the Company relied on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could have been adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.

Cash and Cash Equivalents

The Company maintains cash balances in various accounts, including those insured by the Federal Deposit Insurance Corporation (FDIC). The FDIC provides insurance coverage up to applicable limits for deposits held in participating financial institutions.

The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at the acquisition date to be cash equivalents. The Company’s cash equivalents are comprised of funds held in money market accounts and are measured at fair value on a recurring basis.

Restricted Cash

As of December 31, 2023 and December 31, 2022, restricted cash of $25 consisted of cash deposited in a separate restricted bank account as a security deposit for the Company’s corporate credit cards.

Fair Value Measurements

Certain assets and liabilities are carried at fair value under GAAP. ASC 820, Fair Value Measurement (“ASC 820”), establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable.

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•

Level 2—Observable inputs (other than Level 1 quoted prices), such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.

•

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques.

To the extent that the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

The Company’s cash equivalents are carried at fair value, determined according to the fair value hierarchy described above (see Note 3). The carrying values of the Company’s accounts payable and accrued expenses approximate their fair value due to the short-term nature of these liabilities.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization expense is recognized using the straight-line method over the following estimated useful lives:

          Computer equipment and software
Furniture and fixtures

          3 to 5 years
7 years

Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation and amortization of assets disposed of are removed from the accounts and any resulting gain or loss is included in the consolidated statements of operations and comprehensive loss.

Leases

The Company accounts for leases under ASC Topic 842, Leases (“ASC 842”). Under ASC 842, at inception of a contract, the Company determines whether an arrangement is or contains a lease. For all leases, the Company determines the classification as either operating leases or financing leases. Operating leases are included in operating lease right-of-use assets and operating lease liabilities in the Company’s consolidated balance sheets.

Lease recognition occurs at the commencement date and lease liability amounts are based on the present value of lease payments over the lease term. The lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. If a lease does not provide information to determine an implicit interest rate, the Company uses its incremental borrowing rate in determining the present value of lease payments. Right-of-use (“ROU”) assets represent the Company’s right to use an underlying asset for the lease term, and lease liabilities represent the Company’s obligation to make lease payments under the lease. ROU assets also include any lease payments made prior to the commencement date and exclude lease incentives received. Operating lease payments are expensed using the straight-line method as a general and administrative expense over the lease term. The depreciable life of assets and leasehold improvements are limited by the expected lease term unless there is a transfer of title or purchase option reasonably certain of exercise. The Company has elected to apply the practical short-term expedient to leases with a lease term of 12 months or less, which does not subject the leases to capitalization.

The Company has an operating lease of office space, which has a remaining lease term of less than one year and includes one or more options to renew or terminate early. The Company determines if an arrangement contains a lease at inception. Operating lease right-of-use assets and lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. Certain adjustments to the right-of-use asset may be required for items such as prepaid or accrued lease payments, initial direct costs paid or incentives received. The Company’s leases do not contain an implicit rate, and therefore the Company uses an estimated incremental borrowing rate based on the information available at the lease commencement date in determining the present value of lease payments. Options to extend or terminate the lease are reflected in the calculation when it is reasonably certain that the option will be exercised. The Company has elected to account for lease and non-lease components as a single lease component, however non-lease components that are variable, such as common area maintenance and utilities, are generally paid separately from rent based on actual costs incurred and therefore are not

included in the right-of-use asset and operating lease liability and are reflected as an expense in the period incurred. Leases with an initial term of 12 months or less are not recorded on the consolidated balance sheet.

Goodwill and Indefinite-Lived Intangible Assets

Goodwill represents the excess of the purchase price of an acquired business over the amount assigned to the assets acquired and liabilities assumed. The Company's indefinite-lived intangible assets, which consist of in-process research and development ("IPR&D"), acquired in the Lung Acquisition were recorded at fair value on their acquisition date. Goodwill and indefinite-lived intangible assets are not amortized but are subject to impairment testing on an annual basis as of December 31 or more frequently if events or circumstances indicate a potential impairment. The Company accounts for goodwill and indefinite-lived intangible assets in accordance with ASC 350, Intangibles Goodwill and Other, and Accounting Standards Update, or ASU 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment. The Company’s goodwill and intangible assets are deductible for tax purposes.

Impairment of Long-Lived Assets

Long-lived assets consist of property and equipment, goodwill and intangible assets. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows.

In performing the Company’s annual goodwill impairment test, the Company is permitted to first assess qualitative factors to determine whether it is more likely than not that the fair value of the Company’s reporting unit exceeds its carrying amount, including goodwill. In performing the qualitative assessment, the Company considers certain events and circumstances specific to the reporting unit and to the entity as a whole, such as macroeconomic conditions, industry and market considerations, overall financial performance and cost factors when evaluating whether it is more likely than not that the fair value of the reporting unit exceeds its carrying amount. The Company is also permitted to bypass the qualitative assessment and proceed directly to the quantitative assessment. If the Company chooses to undertake the qualitative assessment and concludes that it is more likely than not that the fair value of the reporting unit is less than its carrying amount, the Company would then proceed to the quantitative impairment assessment. In the quantitative assessment, the Company compares the fair value of the reporting unit to its carrying amount, which includes goodwill. If the fair value exceeds the carrying value, no impairment loss exists. If the fair value is less than the carrying amount, a goodwill impairment loss is measured and recorded.

To date, the Company has not recorded any impairment losses on long-lived assets. For additional details regarding goodwill and intangible assets, refer to Note 7.

Series X Convertible Preferred Stock

The Company has classified its Series X convertible preferred stock, referred to as Series X Preferred Stock, as temporary equity in the accompanying consolidated balance sheets due to terms that allow for redemption of the shares in cash upon certain change in control events that are outside of the Company’s control, including sale or transfer of control of the Company as holders of the Series X Preferred Stock could cause redemption of the shares in these situations. The Company did not accrete the carrying values of the preferred stock to the redemption values since a liquidation event was not considered probable as of December 31, 2023. Subsequent adjustments of the carrying values to the ultimate redemption values will be made only when it becomes probable that such a liquidation event will occur.

Research and Development Costs

Research and development costs are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including stock-based compensation and benefits, facilities costs, costs of clinical trials, sponsored research, manufacturing, and external costs of outside vendors engaged to conduct preclinical development activities and trials.

Costs incurred in obtaining technology licenses are immediately recognized as research and development expense if the technology licensed has not reached technological feasibility and has no alternative future uses.

The Company has entered into various research and development and other agreements with commercial firms, researchers, universities, and others for provisions of goods and services. These agreements are generally cancelable, and the related costs are recorded as research and development expenses as incurred. Research and development expenses include costs for salaries, employee benefits, subcontractors, facility-related expenses, depreciation and amortization, stock-based compensation, laboratory supplies, and external costs of outside vendors engaged to conduct discovery, preclinical and clinical development activities, and clinical trials as well as to manufacture clinical trial materials, and other costs. The Company records accruals for estimated ongoing research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ materially from the Company’s estimates. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. Such prepaid expenses are recognized as an expense when the goods have been delivered or the related services have been performed, or when it is no longer expected that the goods will be delivered, or the services rendered.

Upfront payments, milestone payments and annual maintenance fees under license agreements are expensed in the period in which they are incurred in the consolidated statements of operations and comprehensive loss.

Patent Costs

All patent-related costs incurred in connection with filing and prosecuting patent applications are expensed as incurred due to the uncertainty about the recovery of the expenditure. Amounts incurred are classified as general and administrative expenses.

Accounting for Stock-Based Compensation

The Company measures all stock options and other stock-based awards granted to employees, directors and non-employee consultants based on the fair value on the date of the grant and recognizes compensation expense of those awards, net of forfeitures, over the requisite service period, which is generally the vesting period of the respective award. The Company applies the straight-line method of expense recognition to all awards with only service-based vesting conditions and applies the graded vesting method to all awards with performance-based vesting conditions or both service-based and performance-based vesting conditions.

The Company recognizes compensation expense for only the portion of awards that are expected to vest. The Company accounts for forfeitures as they occur. For performance-based awards, the Company does not recognize expense until the underlying vesting conditions are deemed to be probable of occurrence.

The Company classifies share-based compensation expenses in its statement of operations and comprehensive loss in the same manner in which the award recipient's payroll costs are classified or in which the award recipient's service payments are classified, either to general and administrative expenses or research and development expenses.

The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company estimates its expected stock volatility based on the historical volatility of its own traded stock price. For options with service-based vesting conditions, the expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of

stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The quoted market price of the Company’s common stock is used to estimate the fair value of the stock-based awards at grant date.

Income Taxes

The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse.

The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of the deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Changes in valuation allowances from period to period are included in the Company’s tax provision in the period of change. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies.

The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.

Inflation Reduction Act of 2022

On August 16, 2022, the Inflation Reduction Act of 2022 (the “IR Act”) was signed into federal law. The IR Act provides for, among other things, a new U.S. federal 1% excise tax on certain repurchases of stock by publicly traded U.S. domestic corporations and certain U.S. domestic subsidiaries of publicly traded foreign corporations occurring on or after January 1, 2023. The excise tax is imposed on the repurchasing corporation itself, not its shareholders from which shares are repurchased. The amount of the excise tax is generally 1% of the fair market value of the shares repurchased at the time of the repurchase. However, for purposes of calculating the excise tax, repurchasing corporations are permitted to net the fair market value of certain new stock issuances against the fair market value of stock repurchases during the same taxable year. In addition, certain exceptions apply to the excise tax. The U.S. Department of the Treasury (the “Treasury”) has been given authority to provide regulations and other guidance to carry out and prevent the abuse or avoidance of the excise tax.

Any redemption or other repurchase that occurs after December 31, 2022, in connection with a business combination, extension vote or otherwise, may be subject to the excise tax. Whether and to what extent the Company would be subject to the excise tax in connection with a business combination, extension vote or otherwise would depend on a number of factors, including (i) the fair market value of the redemptions and repurchases in connection with the business combination, extension or otherwise, (ii) the structure of a business combination, (iii) the nature and amount of any private investment in public equity (“PIPE”) or other equity issuances in connection with a business combination (or otherwise issued not in connection with a business combination but issued within the same taxable year of a business combination) and (iv) the content of regulations and other guidance from the Treasury. In addition, because the excise tax would be payable by the Company and not by the redeeming holder, the mechanics of any required payment of the excise tax have not been determined. The foregoing could cause a reduction in the cash available on hand to complete a business combination and in the Company’s ability to complete a business combination.

Segment Information

The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on developing novel therapies for the treatment of orphan pulmonary and fibrosis indications with no approved or limited effective treatments. All of the Company’s tangible assets are held in the United States. The Company views its operations and manages its business in one operating segment operating exclusively in the United States.

Comprehensive Loss

Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. The Company’s other comprehensive loss in all periods presented includes unrealized gains (losses) on available-for-sale investments and foreign currency translation adjustments.

Net Loss per Share

Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net loss attributable to common stockholders is computed by adjusting loss per share attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net loss per share attributable to common stockholders is computed by dividing the diluted net loss attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period, including potential dilutive common shares. For purpose of this calculation, outstanding options and warrants to purchase common stock are considered potential dilutive common shares.

Acquisition Accounting

The fair value of the consideration exchanged in a business combination is allocated to tangible assets and identifiable intangible assets acquired and liabilities assumed at acquisition date fair value. Goodwill is measured as the excess of the consideration transferred over the net fair value of identifiable assets acquired and liabilities assumed. The accounting for an acquisition involves a considerable amount of judgment and estimation. Cost, income, market or a combination of approaches may be used to establish the fair value of consideration exchanged, assets acquired, and liabilities assumed, depending on the nature of those items. The valuation approach is determined in accordance with generally accepted valuation methods. Key areas of estimation and judgment may include the selection of valuation approaches, cost of capital, market characteristics, cost structure, impacts of synergies, and estimates of terminal value, among other factors.

While the Company uses estimates and assumptions as part of the purchase price allocation process to estimate the fair value of assets acquired and liabilities assumed, estimates are inherently uncertain and subject to refinement. During the measurement period, which may be up to one year from the acquisition date, the Company may record adjustments to the assets acquired and liabilities assumed, with a corresponding offset to goodwill, to the extent that adjustments are identified to the preliminary purchase price allocation. Upon conclusion of the measurement period, or final determination of the value of the assets acquired and liabilities assumed, whichever comes first, any subsequent adjustments are recorded to results of operations.

Recently Adopted Accounting Pronouncements

On January 1, 2023, the Company adopted ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, for the fiscal year beginning January 1, 2023 using the modified retrospective approach, and no cumulative effect adjustment to accumulated deficit was needed as of the adoption date. Additionally, no prior period amounts were adjusted. The new standard adjusts the accounting for assets held on an amortized cost basis, including short-term investments accounted for as available-for-sale, and receivables. The standard eliminates the probable initial recognition threshold and requires an entity to reflect its current estimate of all expected credit losses. The allowance for credit losses is a valuation account that is deducted from the amortized

cost basis of the financial assets to present the net amount expected to be collected. The adoption of this standard did not have a material impact on the Company’s consolidated financial statements and related disclosures.

Accounting Pronouncements Not Yet Adopted

In October 2023, the FASB issued ASU 2023-06—Disclosure Improvements: Codification Amendments in Response to the SEC’s Disclosure Update and Simplification Initiative, to clarify or improve disclosure and presentation requirements of a variety of Topics. ASU 2023-06 adds 14 of the 27 identified disclosure or presentation requirements to the Codification. However, each amendment in the ASU will only become effective if the SEC removes the related disclosure or presentation requirement from its existing regulations by June 30, 2027. The effective dates of ASU 2023-06 will depend, in part, on whether an entity is already subject to the SEC’s current disclosure requirements. For such entities and those that must “file or furnish financial statements with or to the SEC in preparation for the sale of or for purposes of issuing securities that are not subject to contractual restrictions on transfer,” the effective date for each amendment will be the date on which the SEC’s removal of that related disclosure requirement from Regulation S-X or Regulation S-K becomes effective, with early adoption prohibited. For all other entities, the amendments will be effective two years after the date of such removal. The Company is currently assessing the effect of this ASU on its consolidated financial statements and related disclosures.

In November 2023, the FASB issued ASU 2023-07—Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, to improve the disclosures about a public entity’s reportable segments and address requests from investors for additional, more detailed information about a reportable segment’s expenses. All public entities will be required to report segment information in accordance with the new guidance starting in annual periods beginning after December 15, 2023. The Company plans to adopt the ASU for the fiscal year beginning January 1, 2024. Since the Company has only one reportable segment, the Company will need to disclose the title and position of the chief operating decision maker (“CODM”) and an explanation of how the CODM uses the reported measures of segment profit or loss in assessing segment performance and deciding how to allocate resources, as well as disclose, on an annual and interim basis, significant segment expenses that are regularly provided to the CODM. The Company is currently assessing the effect of this ASU on its consolidated financial statements and related disclosures.

In December 2023, the FASB issued ASU 2023-09—Income Taxes (Topic 740): Improvements to Income Tax Disclosures, to address investor requests for more transparency about income tax information through improvements to income tax disclosures primarily related to the rate reconciliation and income taxes paid information as well as certain other amendments to improve the effectiveness of income tax disclosures. The amendments in this update are effective for annual periods beginning after December 15, 2024. The Company does not expect adoption of this ASU to have a material impact on its results of operations, financial condition, and its consolidated financial statements other than adding new disclosures, which the Company is currently evaluating, as the Company has not recorded any net tax provision for the periods presented due to the losses incurred and the need for a full valuation allowance on net deferred tax assets.

Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s consolidated financial statements and related disclosures upon adoption.

Business Acquisition - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Oct. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Business Acquisition [Line Items]
Net proceeds from the Financing expected to be used to advance		$ 96	$ (0)
Lung Acquisition
Business Acquisition [Line Items]
Business acquisition, percentage of voting interests acquired	100.00%
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned		$ 1,553
Lung Acquisition \| Purchase Agreement [Member]
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	$ 1,553
Net proceeds from the Financing expected to be used to advance	17,536
Convertible Promissory Notes [Member] \| Lung Acquisition \| Purchase Agreement [Member]
Business Acquisition [Line Items]
Debt conversion, converted instrument, amount	$ 1,553
Common Stock [Member] \| Lung Acquisition
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	344,566
Common Stock [Member] \| Whole Shares [Member] \| Lung Acquisition
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	344,345
Common Stock [Member] \| Fractional Share [Member] \| Lung Acquisition
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	221
Series X Preferred Stock [Member] \| Lung Acquisition
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	20,141
Convertible Preferred Stock, Shares Issued upon Conversion	1,000
Series X Preferred Stock [Member] \| Lung Acquisition \| Purchase Agreement [Member]
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	4,707
Percentage of discount to per share price	10.00%
Convertible Preferred Stock, Shares Issued upon Conversion	1,000
Series X Preferred Stock [Member] \| Whole Shares [Member] \| Lung Acquisition
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	19,903
Series X Preferred Stock [Member] \| Fractional Share [Member] \| Lung Acquisition
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	238
Warrant [Member] \| Lung Acquisition
Business Acquisition [Line Items]
Business acquisition number of shares exercisable	(726,437)
Warrant [Member] \| Lung Acquisition \| Purchase Agreement [Member]
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	2,353,500
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	$ 18,429
Stock Options [Member] \| Lung Acquisition
Business Acquisition [Line Items]
Business acquisition number of shares exercisable	(1,780,459)
Common Stock and Series X Preferred Stock [Member] \| Lung Acquisition
Business Acquisition [Line Items]
Business acquisition cash in lieu of fractional shares	$ 290

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Payables and Accruals [Abstract]
External research and development services	$ 1,110	$ 533
Payroll and payroll-related costs	1,178	425
Professional fees	653	492
Other	206	181
Total accrued expenses and other current liabilities	$ 3,147	$ 1,631

Commitments and Contingencies - Summary of Lease Costs Recognized Under ASC 842 and Other Information Pertaining to Operating Leases (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Lease cost
Operating lease cost	$ 184	$ 125
Total lease cost	184	125
Other Information
Cash paid for amounts included in the measurement of lease liabilities	$ 192	$ 143
Weighted average remaining lease term (in years)	2 months 12 days	3 months 18 days
Weighted average discount rate	7.00%	12.00%

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Basic and Diluted Net Loss per Share Attributable to Common Stockholders

Basic and diluted net loss per share attributable to common stockholders was calculated as follows:


	Year Ended December 31,
	2023			2022
Numerator:
Net loss	$	(15,732	)	$	(27,329	)
Denominator:
Weighted average common shares outstanding—basic and diluted		4,598,715			4,539,318
Net loss per share attributable to common stockholders—basic and diluted	$	(3.42	)	$	(6.02	)

Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share

The following potential shares of common stock, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect:


	Year Ended December 31,
	2023		2022
Options to purchase common stock		2,212,102		537,112
Warrants to issue shares of common stock		3,726,696		646,759
Series X Preferred Stock issued and outstanding, as converted		24,610,000		—
Total		30,548,798		1,183,871

Business Acquisition - Schedule of Allocation of Purchase Price to Estimated Fair Values of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Oct. 31, 2023
Assets acquired:
Goodwill	$ 6,330
Indefinite-lived intangible assets	$ 79,200
Lung Acquisition [Member]
Assets acquired:
Cash and cash equivalents		$ 194
Prepaid expenses and other current assets		2,465
Property and equipment, net		3
Operating right-of-use assets		76
Goodwill		6,330
Indefinite-lived intangible assets		79,200
Other assets		27
Assets acquired		88,295
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract]
Accounts Payable		4,452
Accrued expenses and other current liabilities		1,899
Operating lease liabilities, current		80
Convertible notes payable		1,553
Deferred tax liability		3,326
Liabilities assumed		11,310
Net assets acquired		$ 76,985

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Basis of Presentation

Principles of Consolidation

Use of Estimates

Foreign Currency Transactions

Concentration of Credit Risk and of Significant Suppliers

Cash and Cash Equivalents

Restricted Cash

Fair Value Measurements

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•

Property and Equipment

          Computer equipment and software
Furniture and fixtures

          3 to 5 years
7 years

Leases

Goodwill and Indefinite-Lived Intangible Assets

Impairment of Long-Lived Assets

To date, the Company has not recorded any impairment losses on long-lived assets. For additional details regarding goodwill and intangible assets, refer to Note 7.

Research and Development Costs

Patent Costs

Accounting for Stock-Based Compensation

Income Taxes

Inflation Reduction Act of 2022

Segment Information

Comprehensive Loss

Net Loss per Share

Acquisition Accounting

Recently Adopted Accounting Pronouncements and Accounting Pronouncements Not Yet Adopted

Recently Adopted Accounting Pronouncements

Accounting Pronouncements Not Yet Adopted

Series X Convertible Preferred Stock [Member]

Accounting Policies [Abstract]

Convertible Preferred Stock

Net Loss per Share

12 Months Ended

Dec. 31, 2023

Earnings Per Share [Abstract]

Net Loss per Share

14. Net Loss per Share

Basic and diluted net loss per share attributable to common stockholders was calculated as follows:


	Year Ended December 31,
	2023			2022
Numerator:
Net loss	$	(15,732	)	$	(27,329	)
Denominator:
Weighted average common shares outstanding—basic and diluted		4,598,715			4,539,318
Net loss per share attributable to common stockholders—basic and diluted	$	(3.42	)	$	(6.02	)

The Company’s potential dilutive securities, which include stock options as of December 31, 2023 and 2022, have been excluded from the computation of diluted net loss per share attributable to common stockholders whenever the effect of including them would be to reduce the net loss per share. In periods where there is a net loss, the weighted average number of shares of common stock outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders is the same. The following potential shares of common stock, presented based on amounts outstanding at each period end, were excluded from the calculation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an anti-dilutive effect:


	Year Ended December 31,
	2023		2022
Options to purchase common stock		2,212,102		537,112
Warrants to issue shares of common stock		3,726,696		646,759
Series X Preferred Stock issued and outstanding, as converted		24,610,000		—
Total		30,548,798		1,183,871

Preferred Stock

12 Months Ended

Dec. 31, 2023

Equity [Abstract]

Preferred Stock

11. Preferred Stock

As of December 31, 2023, the Company had 5,000,000 shares of preferred stock, par value $0.001 per share, authorized, out of which 24,610 shares of Series X Preferred Stock were issued and outstanding. As of December 31, 2022, the Company had 5,000,000 shares of preferred stock, par value $0.001 per share, authorized, and no shares of preferred stock issued or outstanding.

On October 31, 2023 Aileron acquired Lung. Under the terms of the Lung Acquisition Agreement, at the closing of the Lung Acquisition, Aileron issued to the stockholders of Lung 344,345 shares of the common stock of Aileron, par value $0.001 per share, and 19,903 shares of Series X Preferred Stock.

Immediately following the closing of the Lung Acquisition, on October 31, 2023, Aileron entered into the Purchase Agreement with a group of accredited investors, pursuant to which Aileron issued and sold 4,707 shares of Series X Preferred Stock and Warrants to purchase up to an aggregate of 2,353,500 shares of Aileron common stock. Refer to Note 3 for more details on the Financing in connection with the Purchase Agreement.

Since the Series X Preferred Stock was sold as a unit with the Warrants according to the Purchase Agreement, the proceeds received were allocated to each instrument on a relative fair value basis. Total gross proceeds of $18,429 reduced by $893 of the issuance costs were allocated as follows: $16,795 to the Series X Preferred Stock and $741 to the Warrants. The Series X Preferred Stock and the Warrants issued in the Financing were recorded at par value of $0.001.

The Company evaluated the Series X Preferred Stock for liability classification in accordance with the provisions of ASC 480, Distinguishing Liabilities from Equity ("ASC 480"), and determined that equity treatment was appropriate because the Series X Preferred Stock did not meet the definition of the liability instruments. Specifically, the Series X Preferred Stock is not mandatorily redeemable and does not embody an obligation to buy back the shares outside of the Company’s control in a manner that could require the transfer of assets. The Company determined that the Series X Preferred Stock would be recorded as temporary equity, based on the guidance of ASC 480, given that it is contingently redeemable (see below).

Subject to stockholders’ approval, each share of Series X Preferred Stock is convertible into 1,000 shares of Common Stock. The preferences, rights, and limitations initially applicable to the Series X Preferred Stock are set forth in the Certificate of Designation.

The Series X Preferred Stock has the following characteristics:

Voting

Except as otherwise required by law, the Series X Preferred Stock does not have voting rights. However, as long as any shares of Series X Preferred Stock are outstanding, the Company will not, without the affirmative vote of the holders of a majority of the then outstanding shares of the Series X Preferred Stock, (i) alter or change adversely the powers, preferences or rights given to the Series X Preferred Stock or alter or amend the Certificate of Designation, amend or repeal any provision of, or add any provision to, the Certificate of Incorporation or by-laws of the Company, or file any articles of amendment, certificate of designations, preferences, limitations and relative rights of any series of preferred stock, if such action would adversely alter or change the preferences, rights, privileges or powers of, or restrictions provided for the benefit of the Series X Preferred Stock, (ii) issue further shares of Series X Preferred Stock or increase or decrease (other than by conversion) the number of authorized shares of Series X Preferred Stock, or (iii) enter into any agreement with respect to any of the foregoing. Additionally, the approval of the holders of a

majority of the Series X Preferred Stock is required for certain change of control transactions, provided that this approval right will terminate upon stockholders’ approval of the conversion proposal.

Dividends

Holders of Series X Preferred Stock are entitled to receive dividends on shares of Series X Preferred Stock equal, on an as-if-converted-to-common-stock basis, and in the same form as dividends actually paid on shares of the common stock. Such dividends are not cumulative. Since the Company’s inception, no dividends have been declared or paid.

Liquidation, dissolution or winding up

The Series X Preferred Stock does not have a preference upon any liquidation, dissolution or winding-up of the Company.

Upon liquidation, dissolution or winding up of the Company, the Series X preferred stockholders shall be entitled to receive an equivalent amount of distributions as would be paid on the common stock underlying the Series X Preferred Stock, determined on an as-converted basis, pari passu with any distributions to the common stock shareholders.

Conversion

Subject to stockholders’ approval of the conversion proposal, the Series X Preferred Stock is convertible into common stock at a rate of 1,000 shares of common stock for every one share of Series X Preferred Stock that is converted. The Series X Preferred Stock is subject to certain beneficial ownership limitations, including that a holder of Series X Preferred Stock is prohibited from converting shares of Series X Preferred Stock into shares of common stock if, as a result of such conversion, such holder (together with its affiliates and any other persons acting as a group together with the holder or any of its affiliates) would beneficially own more than a specified percentage (to be initially set at 19.99% and thereafter adjusted by the holder to a number not to exceed 19.99%) of the total number of shares of common stock issued and outstanding immediately after giving effect to such conversion.

At the 2023 Annual Meeting on February 28, 2024, the Company’s stockholders approved the issuance of shares of common stock, upon conversion of its outstanding Series X Preferred Stock. Refer to Note 18 for more details on the 2023 Annual Meeting.

Redemption

Shares of the Series X Preferred Stock are not redeemable at the election of the holder except for in the event the Company would have been unable to obtain an affirmative stockholder vote at the 2023 Annual Meeting to permit conversion, each holder of Series X Preferred Stock would have been entitled to elect, at the holder’s option, to have the shares of Series X Preferred Stock be redeemed by the Company and equal to the estimated fair value of the Series X Preferred Stock share at the time of redemption. Due to this redemption feature, as of December 31, 2023, the Series X Preferred Stock was classified within temporary equity on the consolidated balance sheet.

Maturity

The Series X Preferred Stock shall be perpetual unless converted.

Stock-Based Awards - Summary of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 1,190	$ 2,083
Research and Development [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	277	600
General and Administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 913	$ 1,483

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 1D
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480483/718-10-35-1D

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Paragraph 2
-Subparagraph (c)(1)(iv)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Paragraph 2
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Paragraph 2
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-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
-Name Accounting Standards Codification
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-Paragraph 2
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
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Reference 20: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480429/718-10-50-2

+ Details

Business Acquisition

12 Months Ended

Dec. 31, 2023

Business Combination and Asset Acquisition [Abstract]

Business Acquisition

3. Business Acquisition

On October 31, 2023, Aileron acquired 100% of Lung, pursuant to the Lung Acquisition Agreement. At the closing of the Lung Acquisition, Aileron issued to the stockholders of Lung 344,345 shares of its common stock (excluding 221 fractional shares from the total 344,566 shares pursuant to the Lung Acquisition Agreement) and 19,903 shares of its newly designated Series X Preferred Stock (excluding 238 fractional shares from the total 20,141 shares pursuant to the Lung Acquisition Agreement). Each share of Series X Preferred Stock is convertible into 1,000 shares of common stock. The Company paid $290 cash in lieu of fractional shares of both common stock and Series X Preferred Stock. In addition, Aileron assumed all Lung's stock options (1,780,459) and all warrants (726,437)

exercisable for Lung common stock immediately outstanding prior to the closing of the Lung Acquisition, each subject to adjustment pursuant to the terms of the Lung Acquisition Agreement.

Immediately following the closing of the Lung Acquisition, on October 31, 2023, Aileron entered into a Stock and Warrant Purchase Agreement (the “Purchase Agreement” or the "PIPE") with a group of accredited investors, pursuant to which Aileron issued and sold (i) an aggregate of 4,707 shares of Series X Preferred Stock, and (ii) warrants (the “Warrants”) to purchase up to an aggregate of 2,353,500 shares of Aileron common stock (the “Warrant Shares”), for an aggregate purchase price of approximately $18,429, which included the conversion of certain convertible promissory notes in the aggregate principal amount of $1,553 issued by Lung to Bios Partners, the majority stockholder of Lung prior to the closing of the Lung Acquisition, at a 10% discount to the per share price of the Series X Preferred Stock. The Financing closed on November 2, 2023. Subject to stockholder approval for the conversion rights of the Series X Preferred Stock, each share of Series X Preferred Stock is convertible into 1,000 shares of common stock.

The net proceeds from the Financing of approximately $17,536 are expected to be used to advance Aileron’s clinical development pipeline, business development activities, working capital and other general corporate purposes.

The Lung Acquisition was accounted for under the acquisition method of accounting under ASC 805. Under the acquisition method, the total purchase price of the acquisition is allocated to the net tangible and identifiable intangible assets acquired and liabilities assumed based on the fair values as of the date of the acquisition. Consideration transferred is the sum of the acquisition-date fair values of the assets transferred, the liabilities incurred by the acquirer to the former owners of the acquiree, and the equity interests issued by the acquirer to the former owners of the acquiree (except for the measurement of share-based payment awards). The total purchase price consideration consisted of the following:


Fair value of common stock issued to Lung stockholders	$	403
Fair value of Series X Preferred Stock issued to Lung stockholders		74,615
Cash in lieu of fractional shares		290
Fair value of the options assumed		1,050
Fair value of the warrants assumed		627
Total purchase price consideration	$	76,985

The Company recorded the assets acquired and liabilities assumed as of the date of the Lung Acquisition based on the information available at that date. The following table presents the allocation of the purchase price to the estimated fair values of the assets acquired and liabilities assumed as of the Lung Acquisition date:


Assets acquired:
Cash and cash equivalents	$	194
Prepaid expenses and other current assets		2,465
Property and equipment, net		3
Operating right-of-use assets		76
Goodwill		6,330
Indefinite-lived intangible assets		79,200
Other assets		27
		88,295
Liabilities assumed:
Accounts Payable		4,452
Accrued expenses and other current liabilities		1,899
Operating lease liabilities, current		80
Convertible notes payable		1,553
Deferred tax liability		3,326
		11,310
Net assets acquired	$	76,985

Pro Forma Financial Information

The following pro forma financial information reflects the consolidated results of operations of the Company for the years ended December 31, 2023 and 2022, as if the Lung Acquisition had taken place on January 1, 2022. The unaudited pro forma financial information is not necessarily indicative of the results of operations as they would have been had the transactions been effected on the assumed date.


	Year Ended December 31,
	2023			2022
Total net revenue	$	153		$	688
Net loss		(28,232	)		(51,610	)

The unaudited pro forma financial information above gives effect primarily to the following:

•

The exclusion of Lung Acquisition related transaction costs from the year ended December 31, 2023, and the addition of these items to the year ended December 31, 2022.

Related Party Transactions - Additional Information (Detail) - Lung Acquisition [Member] - USD ($) $ in Thousands	Oct. 31, 2023	Dec. 31, 2023
Related Party Transaction [Line Items]
Aggregate principal amount		$ 1,553
Series X Preferred Stock [Member]
Related Party Transaction [Line Items]
Aggregate number of shares issued and sold	20,141
Purchase Agreement [Member]
Related Party Transaction [Line Items]
Aggregate principal amount	$ 1,553
Purchase Agreement [Member] \| Series X Preferred Stock [Member]
Related Party Transaction [Line Items]
Aggregate number of shares issued and sold	4,707
Percentage of discount to per share price	10.00%
Purchase Agreement [Member] \| Warrant [Member]
Related Party Transaction [Line Items]
Aggregate number of shares issued and sold	2,353,500
Aggregate principal amount	$ 18,429
Maximum [Member] \| Purchase Agreement [Member] \| Warrant [Member]
Related Party Transaction [Line Items]
Aggregate number of shares issued and sold	2,353,500

Commitments and Contingencies - Schedule of Future Minimum Commitments under ASC 842 (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Commitments and Contingencies Disclosure [Abstract]
2024	$ 48
2025 and thereafter	$ 0
Total lease payments		$ 48
Less: imputed interest		0
Total operating lease liabilities		$ 48

Income Taxes - Schedule of Reconciliation of U.S. Federal Statutory Income Tax Rate to Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	(21.00%)	(21.00%)
State taxes, net of federal benefit	108.10%	(5.40%)
Research and development and orphan drug tax credits	31.50%	(2.90%)
Other permanent items	2.40%	0.90%
Change in deferred tax asset valuation allowance	(444.90%)	28.40%
Loss of federal net operating losses due to 382	323.90%
Effective income tax rate	0.00%	0.00%

Summary of Significant Accounting Policies - Additional Information (Detail)		12 Months Ended
	Aug. 16, 2022	Dec. 31, 2023 USD ($) Segment	Dec. 31, 2022 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Restricted cash		$ 25,000	$ 25,000
Impairment of long-lived assets		$ 0
Percentage of excise tax	1.00%
Percentage of fair market value of shares repurchased	1.00%
Number of operating segments \| Segment		1
ASU 2016-13 [Member]
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, ASU, Adopted [true false]		true
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect [true false]		true
Change in accounting principle, ASU, Adoption Date		Jan. 01, 2023
Security Deposit Related to Credit Card Accounts [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash		$ 25,000	$ 25,000

Prepaid Expenses and Other Current Assets (Tables)

12 Months Ended

Dec. 31, 2023

Prepaid Expense and Other Assets, Current [Abstract]

Schedule of Prepaid and other current assets

Prepaid expenses and other current assets consisted of the following:


	December 31,
	2023		2022
Prepaid research and development	$	207	$	—
Other current assets		675		606
Total prepaid expenses and other current assets	$	882	$	606

Consolidated statements of cash flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash flows from operating activities:
Net loss	$ (15,732)	$ (27,329)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	119	169
Net amortization of premiums and discounts on investments	32	(208)
Stock-based compensation expense	1,190	2,083
Gain on sale of property and equipment	(42)
Loss on disposition of property and equipment	6
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	51	1,613
Other assets	(3)
Accounts payable	(4,982)	510
Operating lease liabilities	(65)	(129)
Accrued expenses and other current liabilities	(382)	(1,574)
Net cash used in operating activities	(19,808)	(24,865)
Cash flows from investing activities:
Proceeds from sale of property and equipment	42
Purchases of investments		(21,850)
Proceeds from sales or maturities of investments	16,250	48,309
Acquisition, net of cash acquired	(96)	0
Net cash provided by investing activities	16,196	26,459
Cash flows from financing activities:
Proceeds from Financing	15,794
Net cash provided by financing activities	15,794
Effect of exchange rate changes on cash and cash equivalents	(63)
Net increase in cash, cash equivalents and restricted cash	12,119	1,594
Cash, cash equivalents and restricted cash at beginning of year	5,219	3,625
Cash, cash equivalents and restricted cash at end of year	17,338	5,219
Cash and cash equivalents at end of year	17,313	5,194
Restricted cash at end of year	25	$ 25
Supplemental disclosure of non-cash investing and financing activities:
Unrealized gain on short-term investments	48
Common Stock [Member] \| Lung Acquisition [Member]
Supplemental disclosure of non-cash investing and financing activities:
Fair value of stock issued in the Lung Acquisition	403
Series X Preferred Stock [Member] \| Lung Acquisition [Member]
Supplemental disclosure of non-cash investing and financing activities:
Fair value of stock issued in the Lung Acquisition	74,615
Stock Options [Member] \| Lung Acquisition [Member]
Supplemental disclosure of non-cash investing and financing activities:
Fair value of liabilities assumed in the Lung Acquisition	1,050
Warrant [Member] \| Lung Acquisition [Member]
Supplemental disclosure of non-cash investing and financing activities:
Fair value of liabilities assumed in the Lung Acquisition	$ 627

Nature of the Business

12 Months Ended

Dec. 31, 2023

Accounting Policies [Abstract]

Nature of the Business

1. Nature of the Business

Aileron Therapeutics, Inc. (“Aileron” or the “Company”) was a clinical stage chemoprotection oncology company. The Company's product candidate, ALRN-6924, was a MDM2/MDMX dual inhibitor that leverages its proprietary peptide drug technology. In February 2023, the Company decided to terminate further development of ALRN-6924. Refer to Note 10 for more details on the restructuring event in 2023.

On October 31, 2023, Aileron acquired Lung Therapeutics, Inc. (“Lung Therapeutics” or "Lung") pursuant to an Agreement and Plan of Merger, dated October 31, 2023 (the “Lung Acquisition Agreement”), by and among the Company, AT Merger Sub I, Inc., a Delaware corporation and its wholly owned subsidiary, or First Merger Sub, AT Merger Sub II, LLC, a Delaware limited liability company and its wholly owned subsidiary, or Second Merger Sub, and Lung. Pursuant to the Lung Acquisition Agreement, First Merger Sub merged with and into Lung, pursuant to which Lung was the surviving entity and became its wholly owned subsidiary, or the First Merger. Immediately following the First Merger, Lung merged with and into Second Merger Sub, pursuant to which Second Merger Sub was the surviving entity, such merger, together with the First Merger, the Lung Acquisition. Lung was incorporated on November 13, 2012 under the laws of the state of Texas. Its principal offices are in Austin, Texas. Following the Lung Acquisition, the Company shifted its operating disease focus to advancing a pipeline of first-in-class medicines to address significant unmet medical needs in orphan pulmonary and fibrosis indications with the potential to greatly improve patient outcomes over currently available treatments. Following expiration of the lease on March 31, 2024, the Company expects to operate virtually for the foreseeable future.

The Company is subject to risks and uncertainties common to clinical-stage companies in the biotechnology industry, including, but not limited to the risk that the Company never achieves profitability, the need for substantial additional financing, the risk of relying on third parties, risks of clinical trial failures, dependence on key personnel, protection of proprietary technology, and compliance with government regulations. The Company’s lead product candidate, LTI-03, is being developed for the treatment of Idiopathic Pulmonary Fibrosis (“IPF”) and has completed a healthy volunteer Phase 1a clinical trial. LTI-03 is currently in a Phase 1b clinical trial in IPF patients. The Company’s second product candidate, LTI-01, is in development for loculated pleural effusion (“LPE”). The Company has completed Phase 1b and Phase 2a clinical trials in LPE patients.

Liquidity and Going Concern

In accordance with Accounting Standards Update (“ASU”) No. 2014-15, Disclosures of Uncertainties about an Entity’s Ability to Continue as a Going Concern (Subtopic 205-40), the Company has evaluated whether there are conditions and events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date the accompanying consolidated financial statements were issued. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the consolidated financial statements are issued. When substantial doubt exists, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the consolidated financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. Generally, to be considered probable of being effectively implemented, the plans must have been approved before the date that the consolidated financial statements are issued.

The Company’s consolidated financial statements have been prepared assuming that the Company will continue to operate as a going concern, which contemplates the continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. Through December 31, 2023, the Company has financed its operations primarily through $145,467 in net proceeds from sales of common stock and warrants, $131,211 from sales of

preferred stock prior to its initial public offering (“IPO”), and $34,910 from a collaboration agreement in 2010, and $18,429 in gross proceeds, less issuance costs of $893, in connection with the financing following the Lung Acquisition, which included the conversion of certain convertible promissory notes in the aggregate principal amount of approximately $1,553 issued by Lung to Bios Partners prior to the closing of the Lung Acquisition at a 10% discount to the per share price of the Series X non-voting convertible preferred stock (“Series X Preferred Stock”), or the Financing, and collectively with the Lung Acquisition, the Transactions.

After the Lung Acquisition, management believes that, based on the Company’s current operating plan, the Company’s cash and cash equivalents of $17,313 as of December 31, 2023, will enable Aileron to fund its operating expenses and capital expenditure requirements for at least six months following the date of this Annual Report on Form 10-K. Since its inception, the Company has not generated any revenue from product sales and have never generated an operating profit. The Company has incurred significant losses on an aggregate basis. The Company’s net losses were $15,732 and $27,329 for the years ended December 31, 2023 and 2022, respectively. As of December 31, 2023, the Company had an accumulated deficit of $288,517. These losses have resulted primarily from costs incurred in connection with research and development activities, licensing and patent investment and general and administrative costs associated with the Company's operations. In February 2023, the Company discontinued development of ALRN-6924 which substantially reduced its operating expenses. Notwithstanding these events, management expects to continue to incur operating losses for the foreseeable future until the Company completes development and approval of its product candidates. The Company will continue to fund its operations primarily through utilization of its current financial resources and additional raises of capital.

These conditions raise substantial doubt about the Company’s ability to continue as a going concern for at least one year from the date those consolidated financial statements are issued. The Company plans to address these conditions by raising funds from its current investors, potential outside investors and other funding sources. However, there is no assurance that such funding will be available to the Company, will be obtained on terms favorable to the Company or will provide the Company with sufficient funds to meet its objectives. The Company’s funding estimates are based on assumptions that may prove to be wrong, and the Company could use its available capital resources sooner than it currently expects. The Company’s future viability is dependent on its ability to raise additional capital, enter into a financing, consummate a successful acquisition, merger, business combination, or a sale of assets or other transaction. If the Company becomes unable to continue as a going concern, it may have to liquidate its assets and the values it receives for its assets in liquidation or dissolution could be significantly lower than the values reflected in its consolidated financial statements.

Consolidated Statement of Changes in Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands	Total	Convertible Series X Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2021	$ 43,904		$ 91	$ 289,282	$ (13)	$ (245,456)
Beginning balance, shares at Dec. 31, 2021			4,528,667
RSUs vested, net of shares repurchased for tax, shares			12,500
Stock-based compensation expense	2,083			2,083
Unrealized gain (loss) on investments and short-term investments	(35)				(35)
Net loss	(27,329)					(27,329)
Ending balance at Dec. 31, 2022	$ 18,623		$ 91	291,365	(48)	(272,785)
Ending balance, shares at Dec. 31, 2022	4,541,167		4,541,167
Ending balance, shares at Dec. 31, 2022	0
Issuance of common stock in connection with business acquisition	$ 403			403
Issuance of common stock in connection with business acquisition, shares			344,345
Issuance of Series X preferred stock in connection with business acquisition	74,615	$ 74,615
Issuance of Series X preferred stock in connection with business acquisition, shares		19,903
Stock options assumed in connection with business acquisition	1,050			1,050
Common stock warrants assumed in connection with business acquisition	627			627
Issuance of Series X preferred stock in connection with the Financing, net of issuance costs	16,795	$ 16,795
Issuance of Series X preferred stock in connection with the Financing, net of issuance costs, shares		4,707
Issuance of common stock warrants in connection with the Financing, net of issuance costs	741			741
Stock-based compensation expense	1,190			1,190
Unrealized gain (loss) on investments and short-term investments	48				48
Foreign currency translation adjustments	(63)				(63)
Net loss	(15,732)					(15,732)
Ending balance at Dec. 31, 2023	$ 98,297	$ 91,410	$ 91	$ 295,376	$ (63)	$ (288,517)
Ending balance, shares at Dec. 31, 2023	4,885,512		4,885,512
Ending balance, shares at Dec. 31, 2023		24,610

Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Income Taxes

16. Income Taxes

On October 31, 2023, the Company acquired, in accordance with the terms of the Lung Acquisition Agreement, the stock of Lung Therapeutics ("Target"). In accordance with ASC 805-740-25-3, recognition of deferred tax assets and liabilities is required for substantially all temporary differences and acquired tax carryforwards and credits. The Company has computed estimated temporary differences and acquired tax carryforwards and credits as of the transaction date. The Company will not have tax basis in intangible assets recorded as part of the purchase. For accounting purposes, the intangible assets will not be amortized and subject to impairment review and testing. Though the tax effects may be delayed indefinitely, ASC 740-10-55-63 states that “deferred tax liabilities may not be eliminated or reduced because a reporting entity may be able to delay the settlement of those liabilities by delaying the events that would cause taxable temporary differences to reverse.” As such, the Company has recorded a deferred tax liability for the portion of the liability that cannot be offset with indefinite lived deferred tax assets.

The Company reported no income tax expense or benefit for the year ended December 31, 2023. The reported amount of income tax expense for the years differs from the amount that would result from applying domestic federal statutory tax rates to pretax losses primarily because of changes in valuation allowance.

A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:


	Year Ended
	December 31,
	2023			2022
Federal statutory income tax rate		(21.0	)%		(21.0	)%
State taxes, net of federal benefit		108.1			(5.4	)
Research and development and orphan drug tax credits		31.5			(2.9	)
Other permanent items		2.4			0.9
Change in deferred tax asset valuation allowance		(444.9	)		28.4
Loss of federal net operating losses due to 382		323.9			—
Effective income tax rate		—	%		—	%

Net deferred tax liabilities as of December 31, 2023 and 2022 consisted of the following:


	December 31,
	2023			2022
Deferred tax assets:
Net operating loss carryforwards	$	12,387		$	64,959
Research and development and orphan drug tax credit carryforwards		7,825			6,606
Capitalized research and development expenses		9,797			4,380
Accrued expenses and reserves		251			61
Depreciation and amortization		—			—
Lease liability		10			9
Stock compensation		1,514			1,442
Total deferred tax assets		31,784			77,457
Valuation allowance		(18,506	)		(77,441	)
Net deferred tax assets	$	13,278		$	16
Deferred tax liabilities:
Depreciation and amortization	$	(16,594	)	$	(5	)
Right of use asset	$	(10	)	$	(11	)
Total deferred tax liabilities	$	(16,604	)	$	(16	)
Net deferred tax asset (liability)	$	(3,326	)	$	—

As of December 31, 2023, the Company had net operating loss carryforwards for federal and state purposes of $56,518 and $8,197, respectively. $2,863 of the U.S. federal tax operating loss carryforwards will begin to expire in 2036. Approximately $53,655 of the U.S. federal tax operating losses can be carried forward indefinitely. Of this amount, $44,420 of federal net operating losses came over from the Lung Acquisition, of which $2,863 will begin to expire in 2036 and the remaining $41,557 can be carried forward indefinitely. The state tax operating loss carryforwards expire beginning in 2043. As of December 31, 2023, the Company also had available research and development tax credit carryforwards for federal income tax purposes of $1,094, which begin to expire in 2035. As of December 31, 2023, the Company also had available orphan drug credit carryforwards of $6,731 for federal income tax purposes, which begin to expire in 2039. Of this amount, $1,064 of research and development credit carryforwards and $6,574 of orphan drug credit carryforwards came over from the Lung Acquisition.

On December 22, 2017, the Tax Cuts and Jobs Act (the "TCJA") was signed into law. Under the TCJA provisions, effective with tax years beginning on or after January 1, 2022, taxpayers can no longer immediately expense research and development expenditures. Taxpayers are now required to capitalize and amortize these costs over 5 years for research conducted within the United States or 15 years for research conducted abroad. As a result, the Company capitalized $3,639 of research and development expenses for the year ended December 31, 2023 for tax purposes.

Utilization of the net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership changes that have occurred previously or that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50% over a three-year period. As of December 31, 2023, the Company has wound down its original business operations and entered into a merger in the year, which resulted in a significant shift in ownership. The Company expects to have all prior year net operating losses and tax credits of its legacy business to be completely limited going forward due to the lack of continuation in its legacy business. As such, all prior year net operating losses and tax credits have been written down to zero as of December 31, 2023. The remaining net operating losses and tax credits as of December 31, 2023 relate to post-merger activity in the year, as well as acquired attributes as part of the merger in the year. A study has been completed on the Target ownership shifts through December 31, 2023, and multiple ownership changes were determined. As a result, the Company has written down the $1,673 portion of the Target net operating losses expected to expire unutilized and include the $44,420 of remaining net operating losses and $7,638 of federal tax credits as part of its available attributes. As of December 31,

2023, the total federal net operating losses are $56,518 and federal research and development tax credits are $7,825, which could be subject to future limitations under these rules.

The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s cumulative net losses and its lack of commercialization of any products or generation of any revenue from product sales since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. The Company maintained a full valuation allowance on its net deferred tax assets as of December 31, 2023. Management reevaluates the positive and negative evidence at each reporting period. The decrease in the valuation allowance relates primarily to the deferred tax liability recognized as a result of the transaction as well as the reduction in prior year deferred tax assets due to Section 382 limitations. The increase in the valuation allowance for deferred tax assets during the year ended December 31, 2023 related primarily to an increase in net operating loss carryforwards. Changes in the valuation allowance were as follows:


	Year Ended December 31,
	2023			2022
Valuation allowance at beginning of year	$	(77,441	)	$	(69,680	)
Decreases/(increases) recorded to income tax provision		69,134			(7,761	)
Increases recorded to invested capital		(10,199	)		—
Valuation allowance at end of year	$	(18,506	)	$	(77,441	)

The Company has not recorded any amounts for unrecognized tax benefits as of December 31, 2023 or 2022.

The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. There are currently no pending tax examinations. The Company’s tax years are still open under statute from 2019 to the present. Earlier years may be examined to the extent that tax credit or net operating loss carryforwards are used in future periods. The Company’s policy is to record interest and penalties related to income taxes as part of its income tax provision. As of December 31, 2023 and 2022, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s consolidated statements of operations and comprehensive loss.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480678/235-10-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org//740/tableOfContent

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-14

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
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-URI https://asc.fasb.org//1943274/2147482685/740-10-50-21

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 270
-Name Accounting Standards Codification
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-Paragraph 1
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-URI https://asc.fasb.org//1943274/2147482526/740-270-50-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
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-Paragraph 17
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482685/740-10-50-17

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
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-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 6.I.5.Q1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-1

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SAB Topic 11.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479360/740-10-S99-2

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482603/740-30-50-2

+ Details

Related Party Transactions

12 Months Ended

Dec. 31, 2023

Related Party Transactions

17. Related Party Transactions

Immediately following the closing of the Lung Acquisition, the Company entered into the Purchase Agreement with a group of accredited investors led by Bios Partners, the majority stockholder of Lung prior to the closing of Lung Acquisition, and including Nantahala Capital, as well as additional undisclosed investors, pursuant to which the Company issued and sold (i) an aggregate of 4,707 shares of Series X Preferred Stock, and (ii) up to an aggregate of 2,353,500 Warrant Shares, as described in the Note 3, which included the conversion of convertible promissory notes in the aggregate principal amount of $1,553 issued by Lung to Bios Partners prior to the closing of the acquisition at a 10% discount to the per share price of Series X Preferred Stock. The Financing closed on November 2, 2023.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480990/946-20-50-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
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-URI https://asc.fasb.org//1943274/2147480990/946-20-50-6

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
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-URI https://asc.fasb.org//1943274/2147481062/946-235-50-2

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 235
-Name Accounting Standards Codification
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-Paragraph 2
-Subparagraph (e)
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
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-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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-Paragraph 1
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
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-URI https://asc.fasb.org//850/tableOfContent

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
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-URI https://asc.fasb.org//1943274/2147483326/850-10-50-6

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Topic 850
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-Name Accounting Standards Codification
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-Topic 850
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-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483326/850-10-50-1

+ Details

Accrued Expenses and Other Current Liabilities (Tables)

12 Months Ended

Dec. 31, 2023

Payables and Accruals [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:


	December 31,
	2023		2022
External research and development services	$	1,110	$	533
Payroll and payroll-related costs		1,178		425
Professional fees		653		492
Other		206		181
Total accrued expenses and other current liabilities	$	3,147	$	1,631

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Summary of Lease Costs Recognized Under ASC 842 and Other Information Pertaining to Operating Leases

The following table contains a summary of the lease costs recognized and other information pertaining to the Company’s operating leases for the years ended December 31, 2023 and 2022:


	Year Ended December 31,
	2023			2022
Lease cost
Operating lease cost	$	184		$	125
Total lease cost	$	184		$	125

Other Information
Cash paid for amounts included in the measurement of lease liabilities	$	192		$	143
Weighted average remaining lease term (in years)		0.2			0.3
Weighted average discount rate		7	%		12	%

Schedule of Future Minimum Commitments under ASC 842

As of December 31, 2023, future minimum commitments under the Company’s operating leases were as follows:


	2023
2024	$	48
2025 and thereafter		-
Total lease payments		48
Less: imputed interest		-
Total operating lease liabilities	$	48

Schedule of Aggregate Future Service and Purchase Commitments with Manufacturer

Aggregate future service and purchase commitments with manufacturer as of December 31, 2023 are as follows:


	2023
2024	$	-
2025 and thereafter		2,312
Total purchase commitments		2,312

Consolidated Statements of Operations and Comprehensive Loss (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2023 USD ($)
Income Statement [Abstract]
Unrealized gain (loss) on short-term investments, net of tax	$ 0

Business Acquisition (Tables)

12 Months Ended

Dec. 31, 2023

Business Combination and Asset Acquisition [Abstract]

Schedule of Total Purchase Price Consideration

The total purchase price consideration consisted of the following:


Fair value of common stock issued to Lung stockholders	$	403
Fair value of Series X Preferred Stock issued to Lung stockholders		74,615
Cash in lieu of fractional shares		290
Fair value of the options assumed		1,050
Fair value of the warrants assumed		627
Total purchase price consideration	$	76,985

Schedule of Allocation of Purchase Price to Estimated Fair Values of Assets Acquired and Liabilities Assumed

The following table presents the allocation of the purchase price to the estimated fair values of the assets acquired and liabilities assumed as of the Lung Acquisition date:


Assets acquired:
Cash and cash equivalents	$	194
Prepaid expenses and other current assets		2,465
Property and equipment, net		3
Operating right-of-use assets		76
Goodwill		6,330
Indefinite-lived intangible assets		79,200
Other assets		27
		88,295
Liabilities assumed:
Accounts Payable		4,452
Accrued expenses and other current liabilities		1,899
Operating lease liabilities, current		80
Convertible notes payable		1,553
Deferred tax liability		3,326
		11,310
Net assets acquired	$	76,985

Shedule of Unaudited Pro Forma Financial Information


	Year Ended December 31,
	2023			2022
Total net revenue	$	153		$	688
Net loss		(28,232	)		(51,610	)

Goodwill and Indefinite-Lived Intangible Assets

12 Months Ended

Dec. 31, 2023

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill and Indefinite-Lived Intangible Assets

7. Goodwill and Indefinite-Lived Intangible Assets

$6,330 of goodwill and $79,200 of indefinite-lived intangible assets acquired in the Lung Acquisition were recorded at fair value on the Lung Acquisition date (refer to Note 3 for more information). The Company performed a qualitative assessment of goodwill and indefinite-lived intangible assets for potential impairment as of December 31, 2023, and concluded that there was no goodwill or intangible assets impairment as of December 31, 2023.

Stock-Based Awards - Valuation Assumptions of Stock Options Granted (Detail)		12 Months Ended
	Oct. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Risk-free interest rate		4.90%	2.50%
Risk-free interest rate, minimum	4.82%
Risk-free interest rate, maximum	5.58%
Expected term (in years)		4 years	6 years 1 month 6 days
Expected volatility		94.40%	94.20%
Expected volatility, minimum	75.00%
Expected volatility, maximum	91.00%
Expected dividend yield	0.00%	0.00%	0.00%
Maximum [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term (in years)	5 months 1 day
Minimum [Member]
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Expected term (in years)	6 years 3 months 10 days

Stock-Based Awards - Additional Information (Detail)			12 Months Ended
Stock-Based Awards - Additional Information (Detail)	Oct. 31, 2023 shares	Jun. 16, 2017 shares	Dec. 31, 2023 USD ($) Plan $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Jan. 01, 2024 shares	Jan. 01, 2023 shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of equity compensation plans \| Plan			5
Number of shares, issued upon exercise of outstanding options			2,212,102	537,112
Number of options exercised			0
Number of options granted to employees or directors			10,900
Weighted average grant-date fair value of stock options \| $ / shares			$ 0.8	$ 7.32
Aggregate fair value of stock options vested \| $			$ 1,191,000	$ 2,808,000
Aggregate intrinsic value of stock options exercised \| $				$ 0
Aggregate unrecognized stock-based compensation expense \| $			$ 1,702,000
Unrecognized stock-based compensation expense, weighted average period expects for recognition			1 year 8 months 23 days
Outstanding Warrants [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock reserved for future issuance			3,726,696
2021 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option granted vesting period			4 years
Number of shares, available for grant			840,254
Number of shares remained available for grant			416,617
Stock reserved for future issuance			416,617
2021 Stock Incentive Plan [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option granted vesting period			4 years
Stock option expiration period			10 years
2017 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option granted vesting period			4 years
Number of shares, issued upon exercise of outstanding options			130,903
Number of shares outstanding options			0
Number of shares remained available for future issuance			0
Stock reserved for future issuance			625,000
2017 Stock Incentive Plan [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option granted vesting period			4 years
Stock option expiration period			10 years
2017 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, available for grant			7,500
Stock reserved for future issuance			7,500			0
Maximum annual increase in common stock reserved for future issuance		31,120
Percentage of common stock shares outstanding		1.00%
Stock incentive plan description			On June 16, 2017, the Company’s stockholders approved the 2017 ESPP, which became effective on June 28, 2017. Under the 2017 ESPP, the number of shares of common stock that may be issued under the 2017 ESPP will automatically increase on each January 1, beginning with the fiscal year ended December 31, 2018 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2027, equal to the least of (i) 31,120 shares, (ii) 1% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s Board. On January 1, 2023 and January 1, 2024, no additional shares were reserved for issuance under the 2017 ESPP pursuant to this provision. 7,500 shares remained available for future issuance under the 2017 ESPP as of December 31, 2023.
2017 Employee Stock Purchase Plan [Member] \| Subsequent Event [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock reserved for future issuance					0
2006 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, issued upon exercise of outstanding options			9,482
Number of shares outstanding options			0
Number of shares remained available for future issuance			0
Contractual repurchase right, shares			314,006
2016 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, issued upon exercise of outstanding options			8,404
Number of shares outstanding options			0
Number of shares remained available for future issuance			0
2013 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option granted vesting period			4 years
Number of options granted to employees or directors	0
2013 Stock Incentive Plan [Member] \| Lung Acquisition [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock option granted vesting period			4 years
2013 Stock Incentive Plan [Member] \| Options Outstanding [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, available for grant			1,780,459
Contractual terms of stock option awards			10 years
2013 Stock Incentive Plan [Member] \| Options Outstanding [Member] \| Lung Acquisition [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Contractual terms of stock option awards			10 years
2013 Stock Incentive Plan [Member] \| Outstanding Warrants [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, available for grant			726,437
2013 Stock Incentive Plan [Member] \| Maximum [Member] \| Options Outstanding [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Contractual terms of stock option awards			10 years
2013 Stock Incentive Plan [Member] \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of fair market value of common stock			100.00%

Subsequent Event - Additional Information (Detail) - USD ($) $ in Thousands			12 Months Ended
	Mar. 11, 2024	Mar. 05, 2024	Dec. 31, 2023	Feb. 28, 2024	Dec. 31, 2022	Nov. 10, 2022	Nov. 09, 2022	Dec. 31, 2021
Subsequent Event [Line Items]
Common stock, shares authorized			45,000,000		45,000,000	15,000,000	300,000,000
Common stock, shares issued			4,885,512		4,541,167
Common stock, shares outstanding			4,885,512		4,541,167
Conversion of Outstanding Series X Preferred Stock [Member]
Subsequent Event [Line Items]
Common stock, shares issued			29,495,512
Common stock, shares outstanding			29,495,512
Series X Preferred Stock [Member]
Subsequent Event [Line Items]
Conversion of stock shares issued			12,523
Preferred Stock is convertible into common stock			1,000
2021 Aileron's Stock [Member]
Subsequent Event [Line Items]
Increase in common stock			3,000,000
Common Stock [Member]
Subsequent Event [Line Items]
Common stock, shares outstanding			4,885,512		4,541,167			4,528,667
Preferred Stock is convertible into common stock			12,523,000
Subsequent Event [Member]
Subsequent Event [Line Items]
Common stock, shares authorized				100,000,000
Subsequent Event [Member] \| Dr. Aivado [Member]
Subsequent Event [Line Items]
Severance agreement description	On March 11, 2024, the Company and Manuel C. Alves-Aivado, M.D., Ph.D., agreed that his employment with the Company would cease and he would resign from his position as Chief Executive Officer of the Company, effective as of March 11, 2024 (the “Separation Date”). Dr. Aivado will remain a member of the Company’s Board. Dr. Aivado’s resignation from the Company was not the result of any disagreement with the Company on any matter relating to its operations, policies or practices.In connection with Dr. Aivado’s separation from the Company, and in accordance with the severance agreement, dated as of September 6, 2018, between the Company and Dr. Aivado, Dr. Aivado is entitled to receive his base salary for eighteen months of $881 following the separation date, payments on Dr. Aivado’s behalf of the monthly premiums for medical insurance coverage under COBRA until the earlier of the date that is eighteen months following the separation date or the date on which Dr. Aivado becomes eligible to receive group health insurance coverage through another employer, a lump sum payment of $441 equal to one and one-half times Dr. Aivado’s target bonus for the 2024 calendar year, and acceleration in full of the vesting of any unvested equity awards. Dr. Aivado’s receipt of these post-separation benefits under the severance agreement is conditioned upon his execution of a severance and release of claims agreement with the Company.
Base salary	$ 881
Group health insurance coverage amount	$ 441
Subsequent Event [Member] \| Series X Preferred Stock [Member]
Subsequent Event [Line Items]
Conversion of stock shares converted		12,087
Subsequent Event [Member] \| 2021 Aileron's Stock [Member]
Subsequent Event [Line Items]
Increase in common stock				3,840,254
Subsequent Event [Member] \| Common Stock [Member]
Subsequent Event [Line Items]
Preferred Stock is automatically convertible into common stock		12,087,000

Income Taxes - Schedule of Changes in Valuation Allowance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Abstract]
Valuation allowance at beginning of year	$ (77,441)	$ (69,680)
Decreases/(increases) recorded to income tax provision	69,134	(7,761)
Increases recorded to invested capital	(10,199)
Valuation allowance at end of year	$ (18,506)	$ (77,441)

Summary of Significant Accounting Policies - Schedule of Property and Equipment Estimated Useful Lives (Detail)	Dec. 31, 2023
Computer Equipment and Software [Member] \| Minimum [Member]
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful lives	3 years
Computer Equipment and Software [Member] \| Maximum [Member]
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful lives	5 years
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful lives	7 years

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Dec. 31, 2023
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
Rule 10b5-1 Arrangement Modified	false
Non-Rule 10b5-1 Arrangement Modified	false

Commitments and Contingencies

12 Months Ended

Dec. 31, 2023

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

15. Commitments and Contingencies

Operating Leases

On March 26, 2021, the Company entered into a sublease agreement (the “Sublease”) by and among the Company, Vittoria Industries North America, Inc. (the “Sublessor”) and Waterfront Equity Partners, LLC (the “Lessor”), under which the Company was leasing approximately 3,365 square feet of office space located at 285 Summer Street, Unit 101, Boston, Massachusetts (the “Premises”). The Sublease was subject and subordinate to a lease agreement, dated as of July 13, 2012, by and between the Sublessor and Lessor, pursuant to which the Sublessor is leasing the Premises from the Lessor. The Sublease expired March 31, 2023, and the Company did not renew the Sublease. Following expiration of the Sublease, the Company is operating virtually, and expects to do so in the foreseeable future.

On August 16, 2021, Lung Therapeutics entered into an operating lease agreement to rent approximately 6,455 square feet of office space for its corporate headquarters in Austin, Texas, beginning on October 1, 2021. The lease agreement is for a 30-month term that ended on March 31, 2024, and includes a rent escalation clause and a rent holiday. In addition to the base rent, the Company was also responsible for its share of operating expenses, electricity and real estate taxes, in accordance with the terms of the lease agreement. Following expiration of the lease, the Company expects to operate virtually for the foreseeable future.

The Company recognizes rent expense on a straight-line basis throughout the remaining term of the lease.

The following table contains a summary of the lease costs recognized and other information pertaining to the Company’s operating leases for the years ended December 31, 2023 and 2022:


	Year Ended December 31,
	2023			2022
Lease cost
Operating lease cost	$	184		$	125
Total lease cost	$	184		$	125

Other Information
Cash paid for amounts included in the measurement of lease liabilities	$	192		$	143
Weighted average remaining lease term (in years)		0.2			0.3
Weighted average discount rate		7	%		12	%

As of December 31, 2023, future minimum commitments under the Company’s operating leases were as follows:


	2023
2024	$	48
2025 and thereafter		-
Total lease payments		48
Less: imputed interest		-
Total operating lease liabilities	$	48

Legal Proceedings

The Company may from time to time be party to litigation arising in the ordinary course of business. As of December 31, 2023 and 2022, the Company was not party to any legal proceedings and no material legal proceedings are currently pending or, to the best of the Company’s knowledge, threatened.

Intellectual Property Licenses

Harvard and Dana-Farber Agreement

In August 2006, the Company entered into an exclusive license agreement with President and Fellows of Harvard College (“Harvard”) and Dana-Farber Cancer Institute (“DFCI”). The agreement granted the Company an exclusive worldwide license, with the right to sublicense, under specified patents and patent applications to develop,

obtain regulatory approval for and commercialize specified product candidates based on cell-permeating peptides. Under the agreement, the Company is obligated to use commercially reasonable efforts to develop and commercialize one or more licensed products and to achieve specified milestone events by specified dates. In connection with entering into the agreement, the Company paid an upfront license fee and issued to Harvard and DFCI shares of its common stock.

In February 2010, the agreement was amended and restated (the “Harvard/DFCI agreement”) under which additional patent rights were added to the scope of the license agreement and the annual license maintenance fees were increased. Under the Harvard/DFCI agreement, the Company is obligated to make aggregate milestones payments of up to $7,700 per licensed therapeutic product upon the Company’s achievement of specified clinical, regulatory and sales milestones with respect to such product and up to $700 per licensed diagnostic product upon the Company’s achievement of specified regulatory and sales milestones with respect to such product. In addition, the Company is obligated to pay royalties of low single-digit percentages on annual net sales of licensed products sold by the Company, its affiliates or its sublicensees. The royalties are payable on a product-by-product and country-by-country basis and may be reduced in specified circumstances. In addition, the agreement obligates the Company to pay a percentage, up to the mid-twenties, of fees received by the Company in connection with its sublicense of the licensed products. In accordance with the terms of the agreement, the Company’s sublicense payment obligations may be subject to specified reductions.

The Harvard/DFCI agreement requires the Company to pay annual license maintenance fees of $110 each year. Any payments made in connection with the annual license maintenance fees will be credited against any royalties due.

The Company incurred license maintenance fees of $35 and $110 during each of the years ended December 31, 2023 and 2022, respectively. In addition, the Company did not make any milestone payments during the years ended December 31, 2023 and 2022. During the years ended December 31, 2023 and 2022, no milestones were achieved and no liabilities for milestone payments were recorded in the Company’s consolidated financial statements. From 2010 through December 31, 2023 and December 31, 2022, the Company had made non-refundable cash payments, consisting of license and maintenance fees, milestone payments and sublicense fees, totaling $5,153 and $5,118, respectively.

As of December 31, 2023, the Company had not developed a commercial product using the licensed technologies and no royalties under the agreement had been paid or were due.

Under the Harvard/DFCI agreement, the Company is responsible for all patent expenses related to the prosecution and maintenance of the licensed patents and applications in-licensed under the agreement as well as cost reimbursement of amounts incurred for all documented patent-related expenses. The agreement will expire on a product-by-product and country-by-country basis upon the last to expire of any valid patent claim pertaining to licensed products covered under the agreement.

Umicore Agreement

In December 2006, the Company entered into a license agreement with Materia, Inc. (“Materia”), under which it was granted a non-exclusive worldwide license, with the right to sublicense, under specified patent and patent applications to utilize Materia’s catalysts to develop, obtain regulatory approval for and commercialize specified peptides owned or controlled by Materia and the right to manufacture specified compositions owned or controlled by Materia. In February 2017, Materia assigned the license agreement (the “Umicore agreement”) to Umicore Precious Metals Chemistry USA, LLC (“Umicore”), and Umicore agreed to continue to supply the Company under the agreement.

The Company incurred license fees of $50 during each of the years ended December 31, 2023 and 2022. The Company did not make any milestone payments during the years ended December 31, 2023 and 2022. During the year ended December 31, 2023, no milestones were achieved and no liabilities for additional milestone payments were recorded in the Company’s consolidated financial statements.

The Umicore Agreement terminated in July 2023 with the expiration of the last patent the Company had licensed.

Agreement with the University of Texas Health Science Center at Tyler

In June 2013, Lung entered into a patent and technology license agreement with the Board of Regents of the University of Texas System, or UT System, on behalf of University of Texas Health Science Center at Tyler, or UTHSCT. The patent and technology license agreement with UT System, or the UTHSCT Agreement, provides Lung access to patents and technology related to the development of LTI-01 and LTI-03. As part of the UTHSCT Agreement, Lung has (i) a royalty-bearing, exclusive license under the patent rights to manufacture, distribute, and sell certain intellectual property; (ii) a non-exclusive license under the technology rights to manufacture, distribute and sell the licensed product; and (iii) a sublicensing right that allows Lung to grant sublicenses to affiliates and third parties to use the licensed product in the field of use and approved territories outlined in the UTHSCT Agreement. In December 2013, the UTHSCT Agreement was amended and restated to include certain patents in all fields worldwide. In May 2017, the UTHSCT Agreement was amended and restated to modify the specific milestone criteria.

In consideration of the UTHSCT Agreement, Lung granted UT System (via UTHSCT and UT Horizon Fund affiliates) (i) 2,000,000 shares of Lung common stock and (ii) 400,000 shares of Lung non-convertible preferred stock. On February 6, 2015, UT System exchanged the 400,000 shares of Lung non-convertible preferred stock for 4,000,000 shares of Lung common stock. In addition, Lung agreed to pay past and ongoing patent expenses, and Lung owes UTHSCT sublicensing fees, assignment fees, and single digit royalties on worldwide net product sales, with fixed minimum royalty payments that started in 2015.

Pursuant to the UTHSCT Agreement, Lung is required to use diligent efforts to commercialize the licensed technology as soon as commercially practicable, including maintaining active research and development, regulatory, marketing and sales program, all as commercially reasonable.

The Company may terminate the UTHSCT Agreement for convenience with 90 days’ notice. UTHSCT may also terminate the UTHSCT Agreement, but only if the Company breaches the terms of the agreement.

Agreement with the University of Texas at Austin

In May 2015, Lung entered into a patent license agreement with UT Austin on behalf of the UT System. This license agreement with UT Austin, or the UT Austin 6607 Agreement, relates to the patent rights to polypeptide therapeutics and uses thereof. Pursuant to the UT Austin 6607 Agreement Lung has (i) a royalty-bearing, exclusive license under the patent rights to manufacture, distribute, and sell the licensed product; and (ii) a sublicensing right that allows Lung to grant sublicenses to affiliates and third parties to use the licensed product in the field of use and approved territories outlined in the agreement. The UT Austin 6607 Agreement was amended and restated in January 2017, November 2018, and June 2019. The amendments related to extension of milestone payment dates and specific terminology around the milestone achievement criteria.

In consideration of the UT Austin 6607 Agreement, Lung agreed to pay past and ongoing patent expenses, milestone fees upon certain development and regulatory milestone events, annual license fees, tiered sublicense fees, assignment fees, low single digit royalties on net sales and an FDA Priority Review Voucher fee if Lung sells or transfers this voucher.

Pursuant to the UT Austin 6607 Agreement, Lung is required to use diligent efforts to commercialize the licensed products, including maintaining active research and development, regulatory, marketing and sales program. Moreover, Lung is required to meet certain development and regulatory milestones by specific dates.

The Company may terminate the UT Austin 6607 Agreement for convenience with 90 days’ notice. UT Austin may also terminate the UT Austin 6607 Agreement, but only if the Company breaches the terms of the agreement.

Agreement with Medical University of South Carolina

In March 2016, Lung entered into a license agreement with Medical University of South Carolina Foundation for Research Development, or MUSC. Pursuant to this license agreement with MUSC, or the MUSC Agreement, Lung has patent rights related to protecting against lung fibrosis by up regulating Cav1. The MUSC Agreement granted (i) a royalty-bearing, exclusive license under the patent rights to make, use and sell the license product; and (ii) a sublicensing right that allows Lung to grant sublicenses to affiliates and third parties to use the licensed product in the field of use and approved territories outlined in the agreement. In September 2018, the agreement was amended and restated to include definitions of related methods, related products and related rights.

In consideration of the MUSC Agreement, Lung agreed to pay a non-refundable license fee, patent expenses, milestone fees upon certain development, regulatory and commercial milestone events, sublicense fees, assignment fees and low single digit royalties on net sales, with a fixed minimum royalty payment starting in 2019 and a transaction fee upon Lung's liquidation.

Pursuant to the MUSC Agreement, Lung is required to use diligent efforts to develop, manufacture and sell the licensed products.

The Company may terminate the MUSC Agreement for convenience by providing a written notice to MUSC effective 90 days following the receipt of notice, and either party may terminate the agreement for a breach of contract.

Agreement with Vivarta Therapeutics LLC

In March 2018, Lung entered into a license agreement with Vivarta Therapeutics, LLC, or Vivarta. This license agreement with Vivarta, or the Vivarta Agreement, relates to intellectual property relating to epithelial sodium channel inhibitors and methods to treat pulmonary disease. Pursuant to the Vivarta Agreement Lung has (i) a royalty-bearing, exclusive license under the intellectual property rights to make, use and sell the licensed product, and (ii) a sublicensing right that allows Lung to grant sublicenses to affiliates and third parties to use the licensed product in the field of use and approved territories outlined in the agreement.

In consideration for the Vivarta Agreement, Lung agreed to grant Vivarta a warrant to purchase an aggregate of 75,000 shares of Lung common stock for $0.12 per share, to pay a license fee of $10,000 upon the Vivarta Agreement effective date and $40,000 within 30 days of the receipt of a positive freedom to operate analysis from legal counsel. Lung also agreed to pay patent expenses, milestone fees upon certain development and regulatory milestone events, sublicense fees, assignment fees and low single digit royalties on net sales.

Pursuant to the Vivarta Agreement, Lung is required to use diligent efforts to develop, manufacture and sell the licensed products.

The Company may terminate the Vivarta Agreement for convenience by providing a written notice to Vivarta effective 90 days following the receipt of notice, and either party may terminate the agreement for a breach of contract.

Manufacturing Commitments

As of December 31, 2023, the Company has non-cancellable purchase obligations and a prepaid balance with its contract manufacturer in the amount of $2,312 and $1,432, respectively.

Aggregate future service and purchase commitments with manufacturer as of December 31, 2023 are as follows:


	2023
2024	$	-
2025 and thereafter		2,312
Total purchase commitments		2,312

Indemnification Agreements

In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it had not accrued any liabilities related to such obligations in its consolidated financial statements as of December 31, 2023 or December 31, 2022.

Document and Entity Information - USD ($) $ in Thousands	12 Months Ended
Document and Entity Information - USD ($) $ in Thousands	Dec. 31, 2023	Apr. 12, 2024	Jun. 30, 2023
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2023
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Trading Symbol	ALRN
Entity Registrant Name	Aileron Therapeutics, Inc.
Entity Central Index Key	0001420565
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
ICFR Auditor Attestation Flag	false
Entity Common Stock, Shares Outstanding		16,972,512
Entity Public Float			$ 6,587,576
Entity File Number	001-38130
Entity Tax Identification Number	13-4196017
Entity Address, Address Line One	12407 N. Mopac Expy.
Entity Address, Address Line Two	Suite 250
Entity Address, Address Line Three	#390
Entity Address, City or Town	Austin
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	78758
City Area Code	737
Local Phone Number	802-1989
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, $0.001 par value
Security Exchange Name	NASDAQ
Auditor Name	Marcum LLP
Auditor Location	New York, NY
Auditor Firm ID	688
Document Financial Statement Error Correction [Flag]	false
Documents Incorporated by Reference	Portions of the Registrant’s definitive proxy statement for its 2024 Annual Meeting of Stockholders, which the Registrant intends to file pursuant to Regulation 14A with the Securities and Exchange Commission not later than 120 days after the end of the Registrant’s fiscal year ended December 31, 2023, are incorporated by reference into Part III of this Annual Report on Form 10-K.

Fair Value of Financial Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Fair Value Disclosures [Abstract]
Fair Value, assets transfers into (out of) Level 3	$ 0	$ 0

Income Taxes - Schedule of Net Deferred Tax Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Deferred tax assets:
Net operating loss carryforwards	$ 12,387	$ 64,959
Research and development and orphan drug tax credit carryforwards	7,825	6,606
Capitalized research and development expenses	9,797	4,380
Accrued expenses and reserves	251	61
Depreciation and amortization	0
Lease liability	10	9
Stock compensation	1,514	1,442
Total deferred tax assets	31,784	77,457
Valuation allowance	(18,506)	(77,441)	$ (69,680)
Net deferred tax assets	13,278	16
Deferred tax liabilities:
Depreciation and amortization	(16,594)	(5)
Right of use asset	(10)	(11)
Total deferred tax liabilities	(16,604)	$ (16)
Net deferred tax asset (liability)	$ (3,326)

Investments - Summary of Fair Value of Available for Sale Investments (Detail) $ in Thousands	Dec. 31, 2022 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Investments, Fair Value	$ 16,048

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 49	$ 169
Gain (loss) on sale of property and equipment	(6)
Fully Depreciated Assets [Member]
Property, Plant and Equipment [Line Items]
Gain (loss) on sale of property and equipment	$ 42

Fair Value of Financial Assets - Summary of Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		$ 16,048
Recurring [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Fair Value of Financial Instruments	$ 10,322	17,709
Recurring [Member] \| Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Fair Value of Financial Instruments	10,322	1,661
Recurring [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total Fair Value of Financial Instruments		16,048
Recurring [Member] \| Commercial Paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		12,814
Recurring [Member] \| Commercial Paper [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		12,814
Recurring [Member] \| Treasury Bills [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		3,234
Recurring [Member] \| Treasury Bills [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		3,234
Recurring [Member] \| Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	10,322	1,661
Recurring [Member] \| Money Market Funds [Member] \| Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	$ 10,322	$ 1,661

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Income Tax Disclosure [Line Items]
Income tax expense (benefit)	$ 0
Capitalized research and development expenses	3,639,000
Uncertain tax position	0	$ 0
Unrecognized tax benefits	0	0
Accrued interest or tax penalties	0	$ 0
Internal Revenue Service (IRS) [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 1,673,000
Increasing the ownership of certain shareholders or public groups in the stock of a corporation period	3 years
Remaining net operating losses carryforwards	$ 44,420,000
Maximum [Member] \| Internal Revenue Service (IRS) [Member]
Income Tax Disclosure [Line Items]
Increasing the ownership of certain shareholders or public groups in the stock of a corporation	50.00%
Lung Acquisition
Income Tax Disclosure [Line Items]
Research and development tax credit carryforwards	$ 1,064,000
Orphan drug tax credit carryforwards	6,574,000
Federal [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	56,518,000
Tax operating loss carryforwards	2,863,000
Indefinitely operating loss carryforwards	$ 53,655,000
Net operating loss carryforwards, begin to expire	2036
Research and development tax credit carryforwards	$ 1,094,000
Research and development tax credit carryforwards, begin to expire	2035
Orphan drug tax credit carryforwards	$ 6,731,000
Orphan drug tax credit carryforwards, begin to expire	2039
Capitalize and amortize research and development costs performance period	5 years
Federal [Member] \| Internal Revenue Service (IRS) [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 56,518,000
Tax operating loss carryforwards	7,638,000
Research and development tax credit carryforwards	7,825,000
Federal [Member] \| Lung Acquisition
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	44,420,000
Tax operating loss carryforwards	2,863,000
Indefinitely operating loss carryforwards	$ 41,557,000
Net operating loss carryforwards, begin to expire	2036
State [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 8,197,000
Net operating loss carryforwards, begin to expire	2043
Foreign [Member]
Income Tax Disclosure [Line Items]
Capitalize and amortize research and development costs performance period	15 years

Business Acquisition - Schedule of Total Purchase Price Consideration (Detail) - Lung Acquisition [Member] $ in Thousands	Oct. 31, 2023 USD ($)
Business Combination, Consideration Transferred [Abstract]
Cash in lieu of fractional shares	$ 290
Fair value of options assumed	1,050
Fair value of warrants assumed	627
Total purchase price consideration	76,985
Common Stock [Member]
Business Combination, Consideration Transferred [Abstract]
Fair value of stock issued	403
Series X Preferred Stock [Member]
Business Combination, Consideration Transferred [Abstract]
Fair value of stock issued	$ 74,615

Other Asset (Tables)

12 Months Ended

Dec. 31, 2023

Prepaid Expense and Other Assets [Abstract]

Schedule of Other Assets

Other assets consisted of the following:


	December 31,
	2023		2022
Non-current prepaid research and development	$	2,140	$	—
Other assets		53		24
Total other non-current assets	$	2,193	$	24

Prepaid Expenses and Other Current Assets - Schedule of Prepaid and other current assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid research and development	$ 207
Other current assets	675	$ 606
Total prepaid expenses and other current assets	$ 882	$ 606

Consolidated balance sheets - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 17,313	$ 5,194
Investments		16,048
Prepaid expenses and other current assets	882	606
Restricted cash	25	25
Operating lease, right-of-use asset, current portion	46
Total current assets	18,266	21,873
Operating lease, right-of-use asset		40
Property and equipment, net	19	70
Goodwill	6,330
Intangible assets	79,200
Other non-current assets	2,193	24
Total assets	106,008	22,007
Current liabilities:
Accounts payable	1,190	1,720
Accrued expenses and other current liabilities	3,147	1,631
Operating lease liabilities, current portion	48	33
Total current liabilities	4,385	3,384
Deferred tax liability	3,326
Total liabilities	7,711	3,384
Commitments and contingencies (Note 15)
Convertible preferred stock, $0.001 par value, 5,000,000 shares authorized at December 31, 2023 and at December 31, 2022; 24,610 shares issued and outstanding at December 31,2023 and no shares issued and outstanding at December 31,2022	91,410
Stockholders’ equity:
Common stock, $0.001 par value; 45,000,000 shares authorized at December 31, 2023 and December 31, 2022; 4,885,512 shares and 4,541,167 shares issued and outstanding at December 31, 2023 and December 31, 2022, respectively	91	91
Additional paid-in capital	295,376	291,365
Accumulated other comprehensive loss	(63)	(48)
Accumulated deficit	(288,517)	(272,785)
Total stockholders’ equity	6,887	18,623
Total liabilities, convertible preferred stock and stockholders' equity	$ 106,008	$ 22,007