0001564590-21-056443 | 10-Q | XBRL Viewer

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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2021	Nov. 09, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Trading Symbol	ALRN
Entity Registrant Name	Aileron Therapeutics, Inc.
Entity Central Index Key	0001420565
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		90,573,597
Entity File Number	001-38130
Entity Tax Identification Number	13-4196017
Entity Address, Address Line One	285 Summer Street
Entity Address, Address Line Two	Suite 101
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02210
City Area Code	617
Local Phone Number	995-0900
Entity Shell Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Document Quarterly Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	DE
Title of 12(b) Security	Common Stock, $0.001 par value per share
Security Exchange Name	NASDAQ

Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 7,603	$ 7,046
Investments	44,629	6,759
Prepaid expenses and other current assets	2,166	1,928
Restricted cash	25	593
Total current assets	54,423	16,326
Operating lease, right-of-use asset	177
Other non-current assets	24
Property and equipment, net	144	15
Total assets	54,768	16,341
Current liabilities:
Accounts payable	1,035	1,596
Accrued expenses and other current liabilities	3,432	2,196
Paycheck Protection Program loan, current portion		168
Operating lease liability, current portion	93
Total current liabilities	4,560	3,960
Paycheck Protection Program loan, net of current portion		219
Operating lease liability, net of current portion	99
Total liabilities	4,659	4,179
Commitments and contingencies (Note 11)
Stockholders’ equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized and no shares issued and outstanding at September 30, 2021 and December 31, 2020, respectively
Common stock, $0.001 par value; 300,000,000 and 150,000,000 shares authorized at September 30, 2021 and December 31, 2020, respectively; 90,572,555 and 43,804,175 shares issued and outstanding at September 30, 2021 and December 31, 2020, respectively	91	44
Additional paid-in capital	288,674	231,412
Accumulated other comprehensive gain/(loss)	1	(2)
Accumulated deficit	(238,657)	(219,292)
Total stockholders’ equity	50,109	12,162
Total liabilities and stockholders’ equity	$ 54,768	$ 16,341

Condensed Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	300,000,000	150,000,000
Common stock, shares issued	90,572,555	43,804,175
Common stock, shares outstanding	90,572,555	43,804,175

Condensed Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Revenue	$ 0	$ 0	$ 0	$ 0
Operating expenses:
Research and development	4,278	2,684	12,447	9,241
General and administrative	2,513	2,344	7,342	7,063
Total operating expenses	6,791	5,028	19,789	16,304
Loss from operations	(6,791)	(5,028)	(19,789)	(16,304)
Interest income	21	5	54	77
Other income, net	66		370	66
Net loss	$ (6,704)	$ (5,023)	$ (19,365)	$ (16,161)
Net loss per share — basic and diluted	$ (0.07)	$ (0.13)	$ (0.22)	$ (0.49)
Weighted average common shares outstanding—basic and diluted	90,548,972	39,321,177	88,211,362	32,808,082
Comprehensive loss:
Net loss	$ (6,704)	$ (5,023)	$ (19,365)	$ (16,161)
Other comprehensive loss:
Unrealized gain (loss) on investments, net of tax of $0	(5)	1	3	(8)
Total other comprehensive gain (loss)	(5)	1	3	(8)
Total comprehensive loss	$ (6,709)	$ (5,022)	$ (19,362)	$ (16,169)

Condensed Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Statement [Abstract]
Unrealized gain (loss) on investments, tax	$ 0	$ 0	$ 0	$ 0

Condensed Statement of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2019	$ 16,048	$ 28	$ 214,148	$ 7	$ (198,135)
Beginning balance, shares at Dec. 31, 2019		27,810,358
Issuance costs	(28)		(28)
Stock-based compensation expense	505		505
Unrealized gain (loss) on investments	(8)			(8)
Net loss	(6,748)				(6,748)
Ending balance at Mar. 31, 2020	9,769	$ 28	214,625	(1)	(204,883)
Ending balance, shares at Mar. 31, 2020		27,810,358
Beginning balance at Dec. 31, 2019	16,048	$ 28	214,148	7	(198,135)
Beginning balance, shares at Dec. 31, 2019		27,810,358
Unrealized gain (loss) on investments	(8)
Net loss	(16,161)
Ending balance at Sep. 30, 2020	12,458	$ 40	226,715	(1)	(214,296)
Ending balance, shares at Sep. 30, 2020		39,874,847
Beginning balance at Mar. 31, 2020	9,769	$ 28	214,625	(1)	(204,883)
Beginning balance, shares at Mar. 31, 2020		27,810,358
Issuance of common stock	11,915	$ 11	11,904
Issuance of common stock, shares		11,425,118
Issuance costs	(1,186)		(1,186)
RSU's vested, net of shares withheld/repurchased for tax	(13)		(13)
RSU's vested, net of shares withheld/repurchased for tax, Shares		26,100
Stock-based compensation expense	560		560
Unrealized gain (loss) on investments	(1)			(1)
Net loss	(4,390)				(4,390)
Ending balance at Jun. 30, 2020	16,654	$ 39	225,890	(2)	(209,273)
Ending balance, shares at Jun. 30, 2020		39,261,576
Issuance of common stock	364	$ 1	363
Issuance of common stock, shares		606,747
RSU's vested, net of shares withheld/repurchased for tax	(3)		(3)
RSU's vested, net of shares withheld/repurchased for tax, Shares		6,524
Stock-based compensation expense	465		465
Unrealized gain (loss) on investments	1			1
Net loss	(5,023)				(5,023)
Ending balance at Sep. 30, 2020	12,458	$ 40	226,715	(1)	(214,296)
Ending balance, shares at Sep. 30, 2020		39,874,847
Beginning balance at Dec. 31, 2020	$ 12,162	$ 44	231,412	(2)	(219,292)
Beginning balance, shares at Dec. 31, 2020	43,804,175	43,804,175
Issuance of common stock	$ 59,088	$ 46	59,042
Issuance of common stock, shares		46,406,382
Issuance costs	(3,482)		(3,482)
Stock-based compensation expense	631		631
Unrealized gain (loss) on investments	(5)			(5)
Net loss	(6,975)				(6,975)
Ending balance at Mar. 31, 2021	61,419	$ 90	287,603	(7)	(226,267)
Ending balance, shares at Mar. 31, 2021		90,210,557
Beginning balance at Dec. 31, 2020	$ 12,162	$ 44	231,412	(2)	(219,292)
Beginning balance, shares at Dec. 31, 2020	43,804,175	43,804,175
Exercise of stock options, Shares	111,998
Unrealized gain (loss) on investments	$ 3
Net loss	(19,365)
Ending balance at Sep. 30, 2021	$ 50,109	$ 91	288,674	1	(238,657)
Ending balance, shares at Sep. 30, 2021	90,572,555	90,572,555
Beginning balance at Mar. 31, 2021	$ 61,419	$ 90	287,603	(7)	(226,267)
Beginning balance, shares at Mar. 31, 2021		90,210,557
Exercise of stock options	47		47
Exercise of stock options, Shares		67,357
Issuance costs	(24)		(24)
RSU's vested, net of shares withheld/repurchased for tax, Shares		250,000
Stock-based compensation expense	361		361
Unrealized gain (loss) on investments	13			13
Net loss	(5,686)				(5,686)
Ending balance at Jun. 30, 2021	56,130	$ 90	287,987	6	(231,953)
Ending balance, shares at Jun. 30, 2021		90,527,914
Exercise of stock options	27	$ 1	26
Exercise of stock options, Shares		44,641
Stock-based compensation expense	661		661
Unrealized gain (loss) on investments	(5)			(5)
Net loss	(6,704)				(6,704)
Ending balance at Sep. 30, 2021	$ 50,109	$ 91	$ 288,674	$ 1	$ (238,657)
Ending balance, shares at Sep. 30, 2021	90,572,555	90,572,555

Condensed Statement of Stockholders' Equity (Unaudited) (Parenthetical) $ in Thousands	3 Months Ended
	Sep. 30, 2020 USD ($)
Common Stock [Member]
Common stock, issuance costs	$ 159

Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
Condensed Statements of Cash Flows - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Cash flows from operating activities:
Net loss	$ (19,365)	$ (16,161)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	81	153
Net amortization of premiums and discounts on investments	212	(19)
Stock-based compensation expense	1,653	1,530
Forgiveness of Paycheck Protection Program loan	(387)
Gain on sale of property and equipment	(66)	(66)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(238)	(580)
Other assets	(24)	510
Accounts payable	(564)	(451)
Operating lease liabilities	(36)	(325)
Accrued expenses and other current liabilities	1,235	(378)
Net cash used in operating activities	(17,499)	(15,787)
Cash flows from investing activities:
Purchases of property and equipment	(157)	(5)
Proceeds from sale of property and equipment	66	66
Purchases of investments	(70,828)	(8,035)
Proceeds from sales or maturities of investments	32,751	14,742
Net cash provided by (used in) investing activities	(38,168)	6,768
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs	55,583	11,174
Proceeds from Paycheck Protection Program loan		384
Proceeds from exercise of stock options	73
Net cash provided by financing activities	55,656	11,558
Net increase/(decrease) in cash, cash equivalents and restricted cash	(11)	2,539
Cash, cash equivalents and restricted cash at beginning of period	7,639	5,904	$ 5,904
Cash, cash equivalents and restricted cash at end of period	$ 7,628	8,443	$ 7,639
Supplemental disclosure of non-cash financing activities:
Common stock issuance costs included in accounts payable and accrued expenses		$ 127

Nature of the Business and Basis of Presentation

9 Months Ended

Sep. 30, 2021

Accounting Policies [Abstract]

Nature of the Business and Basis of Presentation

1. Nature of the Business and Basis of Presentation

Aileron Therapeutics, Inc. (“Aileron” or the “Company”) is a clinical stage chemoprotection oncology company focused on fundamentally transforming the experience of chemotherapy for cancer patients. ALRN-6924, the Company’s first-in-class MDM2/MDMX dual inhibitor, is designed to activate p53, which in turn upregulates p21, a known inhibitor of the cell replication cycle. ALRN-6924 is the only reported chemoprotective agent in clinical development to employ a biomarker strategy, in which the Company exclusively focuses on treating patients with p53-mutated cancers. With this targeted strategy, ALRN-6924 is designed to selectively protect multiple healthy cell types throughout the body from chemotherapy without protecting cancer cells. As a result, healthy cells are spared from chemotherapeutic destruction while chemotherapy continues to kill cancer cells. By reducing or eliminating multiple chemotherapy-induced side effects, ALRN-6924 may improve patients’ quality of life and help them better tolerate chemotherapy. Enhanced tolerability may result in fewer dose reductions or delays of chemotherapy and the potential for improved efficacy.

The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations, uncertainties in the clinical development of product candidates and in the ability to obtain needed additional financing. ALRN-6924 will require significant additional research and development efforts, including preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance-reporting capabilities.

There can be no assurance that the Company’s research and development of ALRN-6924 will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that ALRN-6924 will obtain necessary governmental regulatory approval or that if approved, will be commercially viable. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its key employees and consultants.

The accompanying financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).

Liquidity

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), management must evaluate whether there are conditions or 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 that the financial statements are 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 financial statements are issued. When substantial doubt exists under this methodology, 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 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 financial statements are issued.

The Company’s interim financial statements have been prepared on a going concern basis, which contemplates the continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. Through September 30, 2021, the Company has financed operations primarily through $145,467 in net proceeds from sales of common stock, $131,211 from sales of preferred stock prior to its IPO, and $34,910 from a collaboration agreement in 2010.

As of September 30, 2021, the Company had cash, cash equivalents and investments of $52,232. The Company has incurred losses and negative cash flows from operations and had an accumulated deficit of $238,657 as of September 30, 2021. The Company expects to continue to generate losses for the foreseeable future.

The Company believes that, based on its current operating plan, its cash, cash equivalents and investments of $52,232 as of September 30, 2021 will enable the Company to fund its operating expenses for greater than twelve months from the date of issuance of these financial statements.

To execute its business plans beyond the next twelve months, the Company will need substantial funding to support its continuing operations and pursue its growth strategy. Until such time as the Company can generate significant revenue from product sales, if ever, it expects to finance its operations through the sale of common stock in public offering and/or private placements, debt financings or other capital sources, including collaborations with other companies or other strategic transactions. The Company may not be able to obtain financing when needed, on acceptable terms or at all. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its clinical programs, product portfolio expansion plans or commercialization efforts, which could adversely affect its business prospects. The interim financial statements do not include any adjustments that might result from the outcome of this uncertainty.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Use of Estimates

The preparation of financial statements in conformity with 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 financial statements include, but are not limited to, the accrual of research and development expenses and the valuation of common stock and stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.

Unaudited Interim Financial Information

The accompanying unaudited condensed financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021 and 2020 have been prepared by the Company pursuant to the rules and regulations of the United States Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 that was filed with the SEC on March 24, 2021.

The unaudited interim condensed financial statements have been prepared on the same basis as the audited financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of September 30, 2021, the results of its operations for the three and nine months ended September 30, 2021 and 2020 and its cash flows for the nine months ended September 30, 2021 and 2020. The financial data and other information disclosed in these notes related to the three and nine months ended September 30, 2021 and 2020 are unaudited. The results for the three and nine months ended September 30, 2021 are not necessarily indicative of results to be expected for the year ending December 31, 2021, any other interim periods, or any future year or period. The accompanying balance sheet as of December 31, 2020 has been derived from the Company’s audited financial statements for the year ended December 31, 2020 included in the Company’s Annual Report on Form 10-K that was filed with the SEC on March 24, 2021.

Cash Equivalents

The Company considers all short-term, highly liquid investments with original maturities of 90 days or less at acquisition date to be cash equivalents. Cash equivalents, which consist of money market accounts, corporate notes and commercial paper, are stated at fair value.

Restricted Cash

As of September 30, 2021 restricted cash consisted of $25 deposited in a separate restricted bank account as a security deposit for the Company’s corporate credit cards. As of December 31, 2020, restricted cash consisted of $568 deposited in a separate restricted bank account as a security deposit for the lease of the Company’s facility and $25 deposited in a separate restricted bank account as a security deposit for the Company’s corporate credit cards.

Investments

The Company classifies its available-for-sale debt security investments as current assets on the balance sheet if they mature within one year from the balance sheet date.

The Company’s investments are measured and reported at fair value using quoted prices in active markets for similar securities or using other inputs that are observable or can be corroborated by observable market data. Unrealized gains and losses on available-for-sale securities are reported as accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity (deficit). The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the statements of operations and comprehensive loss.

The Company evaluates its investments with unrealized losses for other-than-temporary impairment. When assessing investments for other-than-temporary declines in value, the Company considers such factors as, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general, among other factors. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be “other than temporary,” the Company reduces the investment to fair value through a charge to the statements of operations and comprehensive loss. No such adjustments were necessary during the periods presented.

Concentration of Credit Risk and of Significant Suppliers

Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents and investments. From time to time, the Company has maintained all of its cash, cash equivalents and investment balances at three accredited financial institutions, in amounts that exceed federally insured limits. The Company generally invests its excess cash in money market funds, commercial paper and corporate notes that are subject to minimal credit and market risks. Management has established guidelines relative to credit ratings and maturities intended to safeguard principal balances and maintain liquidity. The investment portfolio is maintained in accordance with the Company’s investment policy, which defines allowable investments, specifies credit quality standards and limits the credit exposure of any single issuer.

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 relies and expects to continue to rely 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 be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.

Fair Value Measurements

Certain assets and liabilities are carried at fair value under GAAP. 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.

The Company’s cash equivalents and investments 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.

Net Loss per Share

Basic net loss per share is computed by dividing the net loss by the weighted average number of shares of common stock outstanding for the period. Diluted net loss is computed by adjusting basic loss per share to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net loss per share is computed by dividing the diluted net loss 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, restricted stock units and warrants to purchase common stock are considered potential dilutive common shares. In periods in which the Company reports a net loss, diluted net loss per share is the same as basic net loss per share, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.

Risks and Uncertainties

In December 2019, an outbreak of respiratory illness caused by a strain of novel coronavirus, COVID-19, began in China. That outbreak has led to millions of confirmed cases worldwide, including in the United States and other countries where the Company is conducting clinical trials or activities in support thereof. The World Health Organization declared the outbreak a global pandemic on March 11, 2020. Recently, new variants of the virus that causes COVID-19 have been identified and are spreading in the United States and around the world, which may worsen or prolong the pandemic. In addition to those who have been directly affected, millions more have been affected by governmental efforts around the world to slow the spread of the virus. The outbreak and government measures taken in response have also had a significant impact, both direct and indirect, on businesses and commerce. The future progression of the pandemic and its effects on the Company’s business and operations are uncertain.

Potential impacts to the Company’s business include disruptions in supply of the Company’s product candidate and/or procurement of items that are essential for the Company’s research and development activities, including, for example, raw materials used in the manufacturing of ALRN-6924, medical and laboratory supplies used in the Company’s clinical trials or preclinical studies or animals that are used for preclinical testing, in each case, for which there may be shortages because of ongoing efforts to address the COVID-19 pandemic. While the Company believes that it currently has sufficient supply of its product candidate to continue the Company’s ongoing and planned clinical trials, its product candidate, or materials contained therein, come from facilities located in areas impacted by the COVID-19 pandemic.

Additionally, the Company has enrolled, and is seeking to enroll, cancer patients in the Company’s clinical trials at sites located both in the United States and Europe, which are areas that continue to be impacted by the COVID-19 pandemic. Enrollment at clinical trial sites has been and may continue to be disrupted as the effects of the COVID-19 pandemic persist. In the event that clinical trial sites close to enrollment in the Company’s trials or shift resources to address COVID-19, this could have a material adverse impact on the Company’s clinical trial plans and timelines. The Company may face difficulties recruiting or retaining patients in its ongoing and planned clinical trials if patients are affected by the virus or are fearful of visiting or traveling to the Company’s clinical trial sites because of the COVID-19 pandemic.

Any negative impact that the COVID-19 outbreak has on the ability of the Company’s suppliers to provide materials necessary for the Company’s product candidate or on recruiting or retaining patients in the Company’s clinical trials could cause costly delays to clinical trial activities, which could adversely affect the Company’s ability to obtain regulatory approval for and to commercialize the Company’s product candidate, increase the Company’s operating expenses, affect the Company’s ability to raise additional capital, and impact the Company’s operating and financial results. The capital markets have also experienced significant volatility as a result of the pandemic. Future disruptions in the capital markets could negatively impact the Company’s ability to raise capital in the future.

Recently Issued Accounting Pronouncements

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"). This standard requires that expected credit losses relating to financial assets measured on an amortized cost basis and available-for-sale debt securities be recorded through an allowance for credit losses. It also limits the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which carrying value exceeds fair value and also requires the reversal of previously recognized credit losses if fair value increases. The standard also establishes additional disclosure requirements related to credit risks. This guidance was originally effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption was permitted. In November 2019, the FASB subsequently issued ASU 2019-10, Financial Instruments—Credit Losses (Topic 326), Derivatives and Hedging (Topic 815), and Leases (Topic 842): Effective Dates, whereby the effective date of this standard for smaller reporting companies was deferred to annual reporting periods beginning after December 15, 2022, including interim periods within those annual reporting periods, and early adoption is still permitted. Accordingly, the Company will now adopt this standard effective January 1, 2023, and it is currently evaluating the potential impact that ASU 2016-13 may have on its condensed financial statements.

Fair Value of Financial Assets

9 Months Ended

Sep. 30, 2021

Fair Value Disclosures [Abstract]

Fair Value of Financial Assets

3. 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:

	Fair Value Measurements as of September 30, 2021 using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	5,174	$	—	$	—	$	5,174
Investments:
Commercial paper		—		36,217		—		36,217
Corporate notes		—		6,409		—		6,409
Treasury bills		—		2,003		—		2,003
	$	5,174	$	44,629	$	—	$	49,803

	Fair Value Measurements as of December 31, 2020 using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	4,190	$	—	$	—	$	4,190
Commercial paper		—		1,001		—		1,001
Investments:
Agency Bonds		—		3,511		—		3,511
Commercial paper		—		1,999		—		1,999
Treasury Bills		—		1,249		—		1,249
	$	4,190	$	7,760	$	—	$	11,950

As of September 30, 2021 and December 31, 2020, the Company’s cash equivalents and investments were valued based on Level 1 and Level 2 inputs. In determining the fair value of its corporate notes and commercial paper at each date presented above, the Company relied on quoted prices for similar securities in active markets or using other inputs that are observable or can be corroborated by observable market data. The Company’s cash equivalents have original maturities of less than 90 days from the date of purchase. All available-for-sale investments have contractual maturities of less than one year. During the nine months ended September 30, 2021 and the year ended December 31, 2020, there were no transfers in or out of Level 3.

- 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

Investments

9 Months Ended

Sep. 30, 2021

Investments Debt And Equity Securities [Abstract]

Investments

4. Investments

As of September 30, 2021 and December 31, 2020, the fair value of available-for-sale investments by type of security was as follows:

	September 30, 2021
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Commercial paper	$	36,215	$	2	$	—		$	36,217
Corporate notes		6,410		—		(1	)		6,409
Treasury Bills		2,003		—		—			2,003
	$	44,628	$	2	$	(1	)	$	44,629

	December 31, 2020
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Fair Value
Investments:
Commercial paper	$	1,999	$	—	$	—	$	1,999
Treasury bills		1,249		—		—		1,249
Agency bonds		3,511		—		—		3,511
	$	6,759	$	—	$	—	$	6,759

Property and Equipment, Net

9 Months Ended

Sep. 30, 2021

Property Plant And Equipment [Abstract]

Property and Equipment, Net

5. Property and Equipment, Net

Property and equipment, net consisted of the following:

	September 30, 2021			December 31, 2020
Computer equipment and software	$	340		$	181
Less: Accumulated depreciation and amortization		(196	)		(166	)
	$	144		$	15

Depreciation and amortization expense for the three months ended September 30, 2021 and 2020 was $15 and $14 respectively. Depreciation and amortization expense for the nine months ended September 30, 2021 and 2020 was $30 and $153 respectively. During the nine months ended September 30, 2021, the Company received payment for disposed, fully depreciated assets, resulting in a gain on sale of $66. During the nine months ended September 30, 2020, fully depreciated assets with a cost of $45 were sold for $66, resulting in a gain of $66. During the year ended December 31, 2020, assets with a cost of $640 were disposed of for $208 in proceeds, resulting in a gain on sale of $86.

Accrued Expenses and Other Current Liabilities

9 Months Ended

Sep. 30, 2021

Payables And Accruals [Abstract]

Accrued Expenses and Other Current Liabilities

6. Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:

	September 30, 2021		December 31, 2020
External research and development services	$	1,846	$	896
Payroll and payroll-related costs		1,150		922
Professional fees		420		135
Other		16		243
	$	3,432	$	2,196

Paycheck Protection Loan

9 Months Ended

Sep. 30, 2021

Debt Disclosure [Abstract]

Paycheck Protection Loan

7. Paycheck Protection Loan

On April 30, 2020, the Company received loan proceeds in the amount of approximately $384 under the Paycheck Protection Program (“PPP”). The PPP, established as part of the Coronavirus Aid, Relief and Economic Security Act (“CARES Act”), provides for loans to qualifying businesses for amounts up to 2.5 times of the average monthly payroll expenses of the qualifying business. The loan and accrued interest are forgivable after eight weeks if the borrower uses the loan proceeds for eligible purposes, including payroll, benefits, rent and utilities. The amount of loan forgiveness may be reduced if the borrower terminates employees or reduces salaries during the eight-week period. The unforgiven portion of the PPP loan is payable over two years at an interest rate of 1%, with a deferral of payments for the first six months. The Company used the proceeds for purposes consistent with the PPP.

The Company has determined to account for the PPP loan as debt under Accounting Standards Update (“ASC 470”), “Debt”, and allocated and recorded the loan proceeds between current and non-current liabilities.

The Company further determined that loan forgiveness would become probable of occurring upon acceptance by the Small Business Association of the Company’s forgiveness application. On May 20, 2021 the Small Business Administration notified the Company that the PPP loan had been forgiven in full. During the nine months ended September 30, 2021 the Company recognized income for debt extinguishment pursuant to ASC 470-50-15-4 as other income.

Lease

9 Months Ended

Sep. 30, 2021

Leases [Abstract]

Lease

8. Lease

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 is leasing approximately 3,365 square feet of office space located at 285 Summer Street, Unit 101, Boston, Massachusetts (the “Premises”). The Sublease is subject and subordinate to a lease agreement, dated as of July 13, 2012, by and between the Sublessor and Lessor (the “Prime Lease”), pursuant to which the Sublessor is leasing the Premises from the Lessor.

The term of the Sublease (the “Term”) commenced on April 1, 2021 and terminates upon the earliest to occur of (i) March 31, 2023, (ii) early termination of the Prime Lease or (iii) termination of the Sublease pursuant to the terms thereof. The Company is obligated to pay monthly base rent under the Sublease to the Sublessor in an approximate amount of $12 per month during the Term. The Company recorded a right of use asset of $228 and operating lease liabilities of $217 upon the inception of the Sublease.

Common Stock

9 Months Ended

Sep. 30, 2021

Equity [Abstract]

Common Stock

9. Common Stock

On January 6, 2021, the Company entered into a securities purchase agreement (the “2021 Purchase Agreement”) with certain institutional investors, pursuant to which the Company issued and sold, in a registered direct offering (the “Offering”), an aggregate of 32,630,983 shares of common stock, $0.001 par value per share, at a purchase price per share of $1.10 (the “Shares”). The aggregate gross proceeds of the Offering were $35,894, before deducting fees payable to the placement agent and other estimated offering expenses payable by the Company. The Offering closed on January 8, 2021. Between January 1, 2021 and January 28, 2021, the Company issued and sold an aggregate 7,174,993 shares of its common stock pursuant to its ATM Sales Agreement with JonesTrading Institutional Services LLC, resulting in net proceeds of $9,368. The Company terminated its ATM Sales Agreement with Jones Trading in January 2021.

On January 29, 2021, the Company entered into a Capital on Demand™ Sales Agreement (the “ATM Sales Agreement”) with JonesTrading Institutional Services LLC (“JonesTrading”) and William Blair & Company, L.L.C. (“William Blair” and, collectively with JonesTrading, the “Agents”), pursuant to which the Company may offer and sell shares of its common stock having an aggregate offering price of up to $30,000 from time to time through or to the Agents (the “ATM Offering”). On January 29, 2021, the Company filed a prospectus supplement with the SEC in connection with the ATM Offering under its Registration Statement. During the three and nine months ended September 30, 2021, the Company issued and sold an aggregate of 0 and 5,225,406 shares of its common stock, respectively, pursuant to the ATM Sales Agreement, resulting in net proceeds of $0 and $10,594, respectively.

During the three and nine months ended September 30, 2021, the Company issued and sold an aggregate of 0 and 1,375,000 shares of its common stock to Lincoln Park Capital, LLC pursuant to a purchase agreement entered into between Lincoln Park Capital, LLC and the Company in September 2020, resulting in gross proceeds of $0 and $2,614, respectively. During the three and nine months ended September 30, 2020, the Company issued and sold 588,235 shares to LPC under the Purchase Agreement for proceeds of $500.

In June 2020, the Company issued and sold in an underwritten public offering an aggregate of 10,162,059 shares of common stock, including an additional 1,071,149 shares of common stock upon the partial exercise of an option of the underwriter to purchase additional shares, for a purchase price to the public of $1.10 per share. The Company received aggregate gross proceeds from the public offering of approximately $11,178, before deducting underwriting discounts and commissions and offering expenses of $932.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 14
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496171-112644

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496171-112644

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496189-112644

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496158-112644

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/topic&trid=2208762

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
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-Section 50
-Paragraph 13
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Reference 15: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Stock-Based Awards

9 Months Ended

Sep. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Awards

10. Stock-Based Awards

2021 Stock Incentive Plan

The Company’s 2021 Stock Incentive Plan (the “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 board of directors or, at the discretion of the board of directors, 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 of directors, 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 12,756,267 as of September 30, 2021, of which 7,921,767 shares remained available for grant. The Company initially reserved 12,500,000 shares of common stock, plus the number of shares of common stock subject to outstanding awards under the Company’s 2017 Stock Incentive Plan (the “2017 Plan”), and the Company’s 2016 Stock Incentive Plan (“the 2016 Plan”) and the Company’s 2006 Stock Incentive Plan, as amended (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 6,280,135 shares.

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.

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 of directors or, at the discretion of the board of directors, 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 of directors, 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 of directors determined to grant no further awards under the 2017 Plan.

Shares that are expired, terminated, surrendered or canceled without having been fully exercised 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 Employee Stock Purchase Plan (the “2017 ESPP”), which became effective on June 28, 2017. A total of 150,000 shares of common stock were initially reserved for issuance under this plan. 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 ending 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) 622,408 shares, (ii) 1% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors. The compensation committee of the board of directors has determined that the number of shares of common stock that may be issued under the 2017 ESPP would not be increased on January 1, 2019 or January 1, 2020. The Company has not issued any shares under the 2017 ESPP.

Stock Option Valuation

The assumptions that the Company used to determine the grant-date fair value of the stock options granted to employees and directors during the nine months ended September 30, 2021 and 2020 were as follows, presented on a weighted average basis:

	Nine Months Ended September 30, 2021			Nine Months Ended September 30, 2020
Risk-free interest rate		0.96	%		1.19	%
Expected term (in years)		6.2			6.2
Expected volatility		91.0	%		76.0	%
Expected dividend yield		0	%		0	%

Stock Options

The following table summarizes the Company’s stock option activity since January 1, 2021:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding at December 31, 2020		4,665,586		$	2.39		8.1	$	622
Granted		5,371,900			1.30
Exercised		(111,998	)		0.62
Canceled, forfeited or expired		(536,280	)		2.27
Outstanding at September 30, 2021		9,389,208		$	1.79		8.7	$	444
Options exercisable at September 30, 2021		2,787,647		$	2.97		7.1	$	223
Options vested and expected to vest at September 30, 2021		9,141,869		$	1.81		8.7	$	437
Options exercisable at December 31, 2020		2,377,533		$	3.28		7.6	$	197
Options vested and expected to vest at December 31, 2020		4,592,729		$	2.41		8.1	$	606

The weighted average grant-date fair value of stock options granted during the nine months ended September 30, 2021 and 2020 was $0.97 and $0.48, respectively.

The aggregate fair value of stock options that vested during the nine months ended September 30, 2021 and 2020 was $918 and $1,694, 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. The aggregate intrinsic value of stock options exercised during the nine months ended September 30, 2021 and 2020 was $66 and $0, respectively.

Restricted Stock Units

The following table summarizes the Company’s stock option activity since January 1, 2021:

				Weighted-Average
				Grant Date
	Units			per Unit
Outstanding, non-vested at December 31, 2020		—		$	—
Issued		250,000			1.23
Vested		(250,000	)		—
Canceled/forfeited		—			—
Outstanding, non-vested at September 30, 2021		—			—

Stock-Based Compensation

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Research and development expenses	$	180	$	121	$	383	$	470
General and administrative expenses		481		344		1,270		1,060
	$	661	$	465	$	1,653	$	1,530

During the nine months ended September 30, 2021 and 2020 the Company recognized stock-based compensation expense of $0 and $160, respectively, included in the table above, related to performance-based awards for which achievement of such performance-based conditions were deemed probable.

As of September 30, 2021, the Company had an aggregate of $5,505 of unrecognized stock-based compensation expense, which it expects to recognize over a weighted average period of 3.1 years.

Net Loss per Share

9 Months Ended

Sep. 30, 2021

Earnings Per Share [Abstract]

Net Loss per Share

11. Net Loss per Share

Basic and diluted net loss per share was calculated as follows:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2021			2020			2021			2020
Numerator:
Net loss	$	(6,704	)	$	(5,023	)	$	(19,365	)	$	(16,161	)

Denominator:
Weighted average common shares outstanding—basic and diluted		90,548,972			39,321,177			88,211,362			32,808,082

Net loss per share —basic and diluted	$	(0.07	)	$	(0.13	)	$	(0.22	)	$	(0.49	)

The Company’s potential dilutive securities as of September 30, 2021 and 2020, which include stock options and warrants, have been excluded from the computation of diluted net loss per share 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 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 for the periods indicated because including them would have had an anti-dilutive effect:

	Nine Months Ended September 30,
	2021		2020
Warrants to purchase common stock		12,935,323		12,935,323
Stock options to purchase common stock		9,389,208		4,628,687
Total		22,324,531		17,564,010

Commitments and Contingencies

9 Months Ended

Sep. 30, 2021

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

12. Commitments and Contingencies

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 $145. 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 $0 and $145 during each of the three and nine months ended September 30, 2021 and 2020 respectively. The Company did not make any milestone payments during the three and nine months ended September 30, 2021 and 2020, respectively. As of September 30, 2021, no additional milestones had been achieved and no liabilities for additional milestone payments had been recorded in the Company’s financial statements.

As of September 30, 2021, 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.

Under the Umicore agreement, the Company is obligated to make aggregate milestone payments to Umicore of up to $6,400 upon the Company’s achievement of specified clinical, regulatory and sales milestones with respect to each licensed product. In addition, the Company is obligated to pay tiered royalties ranging in the low single-digit percentages on annual net sales of licensed products sold by the Company or its sublicensees. The royalties are payable on a product-by-product and country-by-country basis and may be reduced in specified circumstances.

The Umicore agreement requires the Company to pay annual license fees of $50. The Company incurred license fees of $0 and $50 during the three and nine months ended September 30, 2021 and 2020, respectively. The Company did not make any milestone payments during the three and nine months ended September 30, 2021 and 2020. As of September 30, 2021, no additional milestones had been achieved and no liabilities for additional milestone payments had been recorded in the Company’s financial statements.

The Umicore agreement expires upon the expiration of the Company’s obligation to pay royalties in each territory covered under the agreement.

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 is not aware of any claims for indemnification that would 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 financial statements as of September 30, 2021 or December 31, 2020.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2021

Accounting Policies [Abstract]

Use of Estimates

Unaudited Interim Financial Information

Cash Equivalents

Restricted Cash

Investments

The Company classifies its available-for-sale debt security investments as current assets on the balance sheet if they mature within one year from the balance sheet date.

Concentration of Credit Risk and of Significant Suppliers

Fair Value Measurements

•

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

•

Net Loss per Share

Risks and Uncertainties

Recently Issued Accounting Pronouncements

Fair Value of Financial Assets (Tables)

9 Months Ended

Sep. 30, 2021

Fair Value Disclosures [Abstract]

Summary of Assets Measured at Fair Value on Recurring Basis

	Fair Value Measurements as of September 30, 2021 using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	5,174	$	—	$	—	$	5,174
Investments:
Commercial paper		—		36,217		—		36,217
Corporate notes		—		6,409		—		6,409
Treasury bills		—		2,003		—		2,003
	$	5,174	$	44,629	$	—	$	49,803

	Fair Value Measurements as of December 31, 2020 using:
	Level 1		Level 2		Level 3		Total
Cash equivalents:
Money market funds	$	4,190	$	—	$	—	$	4,190
Commercial paper		—		1,001		—		1,001
Investments:
Agency Bonds		—		3,511		—		3,511
Commercial paper		—		1,999		—		1,999
Treasury Bills		—		1,249		—		1,249
	$	4,190	$	7,760	$	—	$	11,950

Investments (Tables)

9 Months Ended

Sep. 30, 2021

Investments Debt And Equity Securities [Abstract]

Summary of Fair Value of Available for Sale Investments

As of September 30, 2021 and December 31, 2020, the fair value of available-for-sale investments by type of security was as follows:

	September 30, 2021
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss			Fair Value
Investments:
Commercial paper	$	36,215	$	2	$	—		$	36,217
Corporate notes		6,410		—		(1	)		6,409
Treasury Bills		2,003		—		—			2,003
	$	44,628	$	2	$	(1	)	$	44,629

	December 31, 2020
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Fair Value
Investments:
Commercial paper	$	1,999	$	—	$	—	$	1,999
Treasury bills		1,249		—		—		1,249
Agency bonds		3,511		—		—		3,511
	$	6,759	$	—	$	—	$	6,759

Property and Equipment, Net (Tables)

9 Months Ended

Sep. 30, 2021

Property Plant And Equipment [Abstract]

Summary of Property and Equipment, Net

Property and equipment, net consisted of the following:

	September 30, 2021			December 31, 2020
Computer equipment and software	$	340		$	181
Less: Accumulated depreciation and amortization		(196	)		(166	)
	$	144		$	15

Accrued Expenses and Other Current Liabilities (Tables)

9 Months Ended

Sep. 30, 2021

Payables And Accruals [Abstract]

Summary of Accrued Expenses and Other Current Liabilities

Accrued expenses and other current liabilities consisted of the following:

	September 30, 2021		December 31, 2020
External research and development services	$	1,846	$	896
Payroll and payroll-related costs		1,150		922
Professional fees		420		135
Other		16		243
	$	3,432	$	2,196

Stock-Based Awards (Tables)

9 Months Ended

Sep. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Valuation Assumptions of Stock Options Granted

	Nine Months Ended September 30, 2021			Nine Months Ended September 30, 2020
Risk-free interest rate		0.96	%		1.19	%
Expected term (in years)		6.2			6.2
Expected volatility		91.0	%		76.0	%
Expected dividend yield		0	%		0	%

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity since January 1, 2021:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding at December 31, 2020		4,665,586		$	2.39		8.1	$	622
Granted		5,371,900			1.30
Exercised		(111,998	)		0.62
Canceled, forfeited or expired		(536,280	)		2.27
Outstanding at September 30, 2021		9,389,208		$	1.79		8.7	$	444
Options exercisable at September 30, 2021		2,787,647		$	2.97		7.1	$	223
Options vested and expected to vest at September 30, 2021		9,141,869		$	1.81		8.7	$	437
Options exercisable at December 31, 2020		2,377,533		$	3.28		7.6	$	197
Options vested and expected to vest at December 31, 2020		4,592,729		$	2.41		8.1	$	606

Summary of Restricted Stock Unit Activity

The following table summarizes the Company’s stock option activity since January 1, 2021:

				Weighted-Average
				Grant Date
	Units			per Unit
Outstanding, non-vested at December 31, 2020		—		$	—
Issued		250,000			1.23
Vested		(250,000	)		—
Canceled/forfeited		—			—
Outstanding, non-vested at September 30, 2021		—			—

Summary of Stock Based Compensation Expense

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Research and development expenses	$	180	$	121	$	383	$	470
General and administrative expenses		481		344		1,270		1,060
	$	661	$	465	$	1,653	$	1,530

Net Loss per Share (Tables)

9 Months Ended

Sep. 30, 2021

Earnings Per Share [Abstract]

Basic and Diluted Net Loss per Share

Basic and diluted net loss per share was calculated as follows:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2021			2020			2021			2020
Numerator:
Net loss	$	(6,704	)	$	(5,023	)	$	(19,365	)	$	(16,161	)

Denominator:
Weighted average common shares outstanding—basic and diluted		90,548,972			39,321,177			88,211,362			32,808,082

Net loss per share —basic and diluted	$	(0.07	)	$	(0.13	)	$	(0.22	)	$	(0.49	)

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 for the periods indicated because including them would have had an anti-dilutive effect:

	Nine Months Ended September 30,
	2021		2020
Warrants to purchase common stock		12,935,323		12,935,323
Stock options to purchase common stock		9,389,208		4,628,687
Total		22,324,531		17,564,010

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	51 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Proceeds from collaboration agreement	$ 34,910
Cash, cash equivalents and investments	52,232
Accumulated deficit	(238,657)	$ (219,292)
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

- Definition

The cumulative amount of the reporting entity's undistributed earnings or deficit.

+ References + Details

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Security Deposit Related to Credit Card Accounts [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 25	$ 25
Security Deposit Related to Lease Facility [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash		$ 568

Fair Value of Financial Assets - Summary of Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	$ 44,629	$ 6,759
Commercial Paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	36,217	1,999
Corporate Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	6,409
Treasury Bills [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	2,003	1,249
Agency Bonds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		3,511
Recurring [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	49,803	11,950
Recurring [Member] \| Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	5,174	4,190
Recurring [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	44,629	7,760
Recurring [Member] \| Commercial Paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	36,217	1,999
Recurring [Member] \| Commercial Paper [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	36,217	1,999
Recurring [Member] \| Corporate Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	6,409
Recurring [Member] \| Corporate Notes [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	6,409
Recurring [Member] \| Treasury Bills [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	2,003	1,249
Recurring [Member] \| Treasury Bills [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	2,003	1,249
Recurring [Member] \| Agency Bonds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		3,511
Recurring [Member] \| Agency Bonds [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		3,511
Recurring [Member] \| Money Market Funds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	5,174	4,190
Recurring [Member] \| Money Market Funds [Member] \| Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	$ 5,174	4,190
Recurring [Member] \| Commercial Paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents		1,001
Recurring [Member] \| Commercial Paper [Member] \| Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents		$ 1,001

Fair Value of Financial Assets - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Available-for-sale investments, maximum contractual maturity period	1 year
Fair value, assets transfers from Level 1 to Level 2	$ 0	$ 0
Fair value, assets transfers from Level 2 to Level 1	0	0
Fair Value, assets transfers into (out of) Level 3	$ 0	$ 0

Investments - Summary of Fair Value of Available for Sale Investments (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	$ 44,628	$ 6,759
Investments, Gross Unrealized Gain	2
Investments, Gross Unrealized Loss	(1)
Investments, Fair Value	44,629	6,759
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	36,215	1,999
Investments, Gross Unrealized Gain	2
Investments, Fair Value	36,217	1,999
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	2,003	1,249
Investments, Fair Value	2,003	1,249
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	6,410
Investments, Gross Unrealized Loss	(1)
Investments, Fair Value	$ 6,409
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost		3,511
Investments, Fair Value		$ 3,511

Property and Equipment, Net - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Less: Accumulated depreciation and amortization	$ (196)	$ (166)
Property, plant and equipment, net	144	15
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 340	$ 181

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Depreciation and amortization expense	$ 15	$ 14	$ 30	$ 153
Proceeds from property and equipment			66	66
Gain (loss) on disposal of property and equipment			66	66
Fully Depreciated Assets [Member]
Property Plant And Equipment [Line Items]
Disposal of property and equipment				45	$ 640
Proceeds from property and equipment				66	208
Gain (loss) on disposal of property and equipment			$ 66	$ 66	$ 86

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
External research and development services	$ 1,846	$ 896
Payroll and payroll-related costs	1,150	922
Professional fees	420	135
Other	16	243
Total accrued expenses and other current liabilities	$ 3,432	$ 2,196

Paycheck Protection Loan - Additional Information (Detail) - Paycheck Protection Program CARES Act [Member] $ in Thousands		9 Months Ended
	Apr. 30, 2020 USD ($)	Sep. 30, 2021
Debt Instrument [Line Items]
Proceeds from loan	$ 384
Number of times for loans to qualifying businesses average monthly payroll costs	2.5
Term of unforgiven portion of loan	2 years
Interest rate	1.00%
Term of deferral payments	6 months
Debt instrument, description		The PPP, established as part of the Coronavirus Aid, Relief and Economic Security Act (“CARES Act”), provides for loans to qualifying businesses for amounts up to 2.5 times of the average monthly payroll expenses of the qualifying business. The loan and accrued interest are forgivable after eight weeks if the borrower uses the loan proceeds for eligible purposes, including payroll, benefits, rent and utilities. The amount of loan forgiveness may be reduced if the borrower terminates employees or reduces salaries during the eight-week period. The unforgiven portion of the PPP loan is payable over two years at an interest rate of 1%, with a deferral of payments for the first six months. The Company used the proceeds for purposes consistent with the PPP.
Minimum [Member]
Debt Instrument [Line Items]
Term of loan and accrued interest forgivable	56 days

Lease - Additional Information (Detail) $ in Thousands	9 Months Ended
Lease - Additional Information (Detail) $ in Thousands	Sep. 30, 2021 USD ($)	Mar. 26, 2021 ft²
Lessee Lease Description [Line Items]
Operating lease, right-of-use asset	$ 177
Sublease [Member]
Lessee Lease Description [Line Items]
Lease commencement date	Apr. 01, 2021
Lease termination date	Mar. 31, 2023
Amount of obligated to pay monthly base rent to sub lessor during the term	$ 12
Operating lease, right-of-use asset	228
Operating lease, liability	$ 217
Sublease [Member] \| Boston, Massachusetts [Member]
Lessee Lease Description [Line Items]
Area of land \| ft²		3,365

Common Stock - Additional Information (Detail) - USD ($)			1 Months Ended		3 Months Ended				9 Months Ended		51 Months Ended
	Jan. 29, 2021	Jan. 06, 2021	Jan. 28, 2021	Jun. 30, 2020	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Common stock, par value					$ 0.001				$ 0.001		$ 0.001	$ 0.001
Stock issued during period, value						$ 59,088,000	$ 364,000	$ 11,915,000
Common Stock [Member]
Class Of Stock [Line Items]
Net proceeds from common stock shares issued and sold											$ 145,467,000
Stock issued during period, value						$ 46,000	$ 1,000	$ 11,000
Stock issued during period, shares						46,406,382	606,747	11,425,118
Underwritten Public Offering [Member]
Class Of Stock [Line Items]
Purchase price per share				$ 1.10				$ 1.10
Stock issued during period, shares				10,162,059
Additional shares of common stock issued upon partial exercise of option				1,071,149
Gross proceeds from issuance of common stock				$ 11,178,000
Common stock, issuance costs				$ 932,000
2021 Purchase Agreement [Member] \| Direct Public Offering [Member]
Class Of Stock [Line Items]
Aggregate number of common stock shares issued and sold		32,630,983
Common stock, par value		$ 0.001
Gross proceeds from common stock shares issued and sold		$ 35,894,000
2021 Purchase Agreement [Member] \| Direct Public Offering [Member] \| Common Stock [Member]
Class Of Stock [Line Items]
Purchase price per share		$ 1.10
Offering closed date		Jan. 08, 2021
ATM Sales Agreement [Member]
Class Of Stock [Line Items]
Aggregate number of common stock shares issued and sold					0				5,225,406
Net proceeds from common stock shares issued and sold					$ 0				$ 10,594,000
ATM Sales Agreement [Member] \| Jones Trading Institutional Services LLC [Member]
Class Of Stock [Line Items]
Aggregate number of common stock shares issued and sold			7,174,993
Net proceeds from common stock shares issued and sold			$ 9,368,000
ATM Sales Agreement [Member] \| Jones Trading Institutional Services LLC and William Blair & Company, LLC [Member] \| Maximum [Member]
Class Of Stock [Line Items]
Stock issued during period, value	$ 30,000,000
Purchase Agreement [Member] \| Lincoln Park Capital, LLC [Member]
Class Of Stock [Line Items]
Aggregate number of common stock shares issued and sold					0		588,235		1,375,000	588,235
Gross proceeds from common stock shares issued and sold					$ 0		$ 500,000		$ 2,614,000	$ 500,000

Stock-Based Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended		9 Months Ended
	Jan. 01, 2020	Jan. 01, 2019	Jun. 16, 2017	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average grant-date fair value of stock options						$ 0.97	$ 0.48
Aggregate fair value of stock options vested						$ 918	$ 1,694
Aggregate intrinsic value of stock options exercised						66	0
Recognized stock-based compensation expense				$ 661	$ 465	1,653	1,530
Aggregate unrecognized stock-based compensation expense				$ 5,505		$ 5,505
Unrecognized stock-based compensation expense, weighted average period expects for recognition						3 years 1 month 6 days
Performance-based Awards [[Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Recognized stock-based compensation expense						$ 0	$ 160
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				12,756,267		12,756,267
Number of shares remained available for grant				7,921,767		7,921,767
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
Stock reserved for future issuance				12,500,000		12,500,000
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
2006 Stock Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Contractual repurchase right, shares				6,280,135		6,280,135
2017 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares, available for grant				0		0
Stock reserved for future issuance			150,000
Maximum annual increase in common stock reserved for future issuance			622,408
Percentage of common stock shares outstanding			1.00%
Increase to shares authorized for issuance	0	0
Stock incentive plan description						On June 16, 2017, the Company’s stockholders approved the 2017 Employee Stock Purchase Plan (the “2017 ESPP”), which became effective on June 28, 2017. A total of 150,000 shares of common stock were initially reserved for issuance under this plan. 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 ending 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) 622,408 shares, (ii) 1% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors. The compensation committee of the board of directors has determined that the number of shares of common stock that may be issued under the 2017 ESPP would not be increased on January 1, 2019 or January 1, 2020. The Company has not issued any shares under the 2017 ESPP.

Stock-Based Awards - Valuation Assumptions of Stock Options Granted (Detail)	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	0.96%	1.19%
Expected term (in years)	6 years 2 months 12 days	6 years 2 months 12 days
Expected volatility	91.00%	76.00%
Expected dividend yield	0.00%	0.00%

Stock-Based Awards - Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance \| shares	4,665,586
Number of Shares, Granted \| shares	5,371,900
Number of Shares, Exercised \| shares	(111,998)
Number of Shares, Canceled, forfeited or expired \| shares	(536,280)
Number of Shares, Ending balance \| shares	9,389,208	4,665,586
Number of Shares, Options exercisable \| shares	2,787,647	2,377,533
Number of Shares, Options vested and expected to vest \| shares	9,141,869	4,592,729
Weighted Average Exercise Price, Beginning balance \| $ / shares	$ 2.39
Weighted Average Exercise Price, Granted \| $ / shares	1.30
Weighted Average Exercise Price, Exercised \| $ / shares	0.62
Weighted Average Exercise Price, Canceled, forfeited or expired \| $ / shares	2.27
Weighted Average Exercise Price, Ending balance \| $ / shares	1.79	$ 2.39
Weighted Average Exercise Price, Options exercisable \| $ / shares	2.97	3.28
Weighted Average Exercise Price, Options vested and expected to vest \| $ / shares	$ 1.81	$ 2.41
Weighted-Average Remaining Contractual Term, Outstanding	8 years 8 months 12 days	8 years 1 month 6 days
Weighted Average Remaining Contractual Term, Options exercisable	7 years 1 month 6 days	7 years 7 months 6 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	8 years 8 months 12 days	8 years 1 month 6 days
Aggregate Intrinsic Value \| $	$ 444	$ 622
Aggregate Intrinsic Value, Options exercisable \| $	223	197
Aggregate Intrinsic Value, Options vested and expected to vest \| $	$ 437	$ 606

Stock-Based Awards - Summary of Restricted Stock Unit Activity (Detail) - 2017 Stock Incentive Plan [Member] - Restricted Stock Units [Member]	9 Months Ended
	Sep. 30, 2021 $ / shares shares
Units
Issued	250,000
Vested	(250,000)
Weighted-Average Grant Date per Unit
Issued \| $ / shares	$ 1.23

Stock-Based Awards - Summary of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 661	$ 465	$ 1,653	$ 1,530
Research and Development [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	180	121	383	470
General and Administrative [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 481	$ 344	$ 1,270	$ 1,060

Net Loss per Share - Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net loss	$ (6,704)	$ (5,686)	$ (6,975)	$ (5,023)	$ (4,390)	$ (6,748)	$ (19,365)	$ (16,161)
Denominator:
Weighted average common shares outstanding—basic and diluted	90,548,972			39,321,177			88,211,362	32,808,082
Net loss per share —basic and diluted	$ (0.07)			$ (0.13)			$ (0.22)	$ (0.49)

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

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+ Details

Net Loss per Share - Summary of Potential Common Shares Excluded from Calculation of Diluted Net Loss per Share (Detail) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	22,324,531	17,564,010
Warrants to Purchase 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	12,935,323	12,935,323
Stock Options to Purchase 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	9,389,208	4,628,687

Commitments and Contingencies - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) Milestone	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) Milestone	Sep. 30, 2020 USD ($)	Feb. 28, 2010 USD ($)	Dec. 31, 2006 USD ($)
Harvard and Dana-Farber Agreement [Member]
Other Commitments [Line Items]
Milestone payments	$ 0	$ 0	$ 0	$ 0
Additional milestones achieved \| Milestone	0
Additional liabilities for milestone payments	$ 0		0
Payments for royalties			0
Harvard and Dana-Farber Agreement [Member] \| Therapeutic Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments					$ 7,700,000
Harvard and Dana-Farber Agreement [Member] \| Diagnostic Product [Member]
Other Commitments [Line Items]
Aggregate milestones payments					$ 700,000
Harvard and Dana-Farber Agreement [Member] \| License [Member]
Other Commitments [Line Items]
Annual license maintenance fees	0	0	145,000	145,000
Umicore Agreement [Member]
Other Commitments [Line Items]
Aggregate milestones payments						$ 6,400,000
Milestone payments	0	0	$ 0	0
Additional milestones achieved \| Milestone			0
Additional liabilities for milestone payments	0		$ 0
Umicore Agreement [Member] \| License [Member]
Other Commitments [Line Items]
Annual license maintenance fees	$ 0	$ 0	50,000	$ 50,000
Umicore Agreement [Member] \| License and Maintenance [Member]
Other Commitments [Line Items]
Annual license maintenance fees			$ 50,000