Rein Therapeutics (RNTX) 10-K 24 Mar 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 19, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
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	true
Entity Ex Transition Period	true
Entity Shell Company	false
ICFR Auditor Attestation Flag	false
Entity Common Stock, Shares Outstanding		90,210,557
Entity Public Float			$ 36,630,063
Entity File Number	001-38130
Entity Tax Identification Number	13-4196017
Entity Address, Address Line One	290 Pleasant Street
Entity Address, Address Line Two	Unit 112
Entity Address, City or Town	Watertown
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02472
City Area Code	617
Local Phone Number	995-0900
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
Documents Incorporated by Reference	Portions of the Registrant’s definitive proxy statement for its 2021 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, 2020, are incorporated by reference into Part III of this Annual Report on Form 10-K.

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 7,046	$ 5,311
Investments	6,759	12,967
Prepaid expenses and other current assets	1,928	1,247
Restricted cash	593	25
Total current assets	16,326	19,550
Operating lease, right-of-use asset		6,060
Property and equipment, net	15	295
Restricted cash, non-current		568
Total assets	16,341	26,473
Current liabilities:
Accounts payable	1,596	1,452
Accrued expenses and other current liabilities	2,196	3,941
Paycheck Protection Program loan, current portion	168
Operating lease liabilities, current portion		446
Total current liabilities	3,960	5,839
Paycheck Protection Program loan, net of current portion	219
Operating lease liabilities, net of current portion		4,586
Total liabilities	4,179	10,425
Commitments and contingencies (Note 9)
Stockholders’ equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized at December 31, 2020 and December 31, 2019; no shares issued and outstanding at December 31, 2020 and December 31, 2019
Common stock, $0.001 par value; 150,000,000 shares authorized at December 31, 2020 and December 31, 2019; 43,804,175 and 27,810,358 shares issued and outstanding at December 31, 2020 and December 31, 2019, respectively	44	28
Additional paid-in capital	231,412	214,148
Accumulated other comprehensive income/(loss)	(2)	7
Accumulated deficit	(219,292)	(198,135)
Total stockholders’ equity	12,162	16,048
Total liabilities and stockholders’ equity	$ 16,341	$ 26,473

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
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	150,000,000	150,000,000
Common stock, shares issued	43,804,175	27,810,358
Common stock, shares outstanding	43,804,175	27,810,358

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Revenue									$ 0	$ 0
Operating expenses:
Research and development	$ 1,925	$ 2,684	$ 2,488	$ 4,069	$ 4,709	$ 4,475	$ 4,305	$ 4,174	11,166	17,663
General and administrative	2,267	2,344	1,912	2,807	2,639	3,440	3,075	3,139	9,330	12,293
Total operating expenses	4,192	5,028	4,400	6,876	7,348	7,915	7,380	7,313	20,496	29,956
Loss from operations	(4,192)	(5,028)	(4,400)	(6,876)	(7,348)	(7,915)	(7,380)	(7,313)	(20,496)	(29,956)
Other income (expense), net	(738)	5	10	62	112	166	208	101	(661)	587
Net loss	$ (4,930)	$ (5,023)	$ (4,390)	$ (6,814)	$ (7,236)	$ (7,749)	$ (7,172)	$ (7,212)	$ (21,157)	$ (29,369)
Net loss per share—basic and diluted	$ (0.12)	$ (0.13)	$ (0.14)	$ (0.24)	$ (0.26)	$ (0.28)	$ (0.26)	$ (0.49)	$ (0.61)	$ (1.20)
Weighted average common shares outstanding—basic and diluted	40,997,759	39,321,177	31,221,139	27,810,358	27,810,358	27,810,358	27,526,065	14,816,253	34,866,690	24,535,454
Comprehensive loss:
Net loss	$ (4,930)	$ (5,023)	$ (4,390)	$ (6,814)	$ (7,236)	$ (7,749)	$ (7,172)	$ (7,212)	$ (21,157)	$ (29,369)
Other comprehensive gain (loss):
Unrealized gain (loss) on investments, net of tax of $0	(1)	1	(1)	(8)	(10)	(7)	24	5	(9)	12
Total other comprehensive gain (loss)	(1)	1	(1)	(8)	(10)	(7)	24	5	(9)	12
Total comprehensive loss	$ (4,931)	$ (5,022)	$ (4,391)	$ (6,822)	$ (7,246)	$ (7,756)	$ (7,148)	$ (7,207)	$ (21,166)	$ (29,357)

Statements of Operations and _2

Statements of Operations and Comprehensive Loss (Parenthetical) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Unrealized gain (loss) on investments, tax	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0

Statement of Stockholders' Equi

Statement of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock and Common Warrants [Member]	Pre-funded Warrants and Common Warrants [Member]	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Common Stock [Member]Common Stock and Common Warrants [Member]	Common Stock [Member]Pre-funded Warrants and Common Warrants [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]Common Stock and Common Warrants [Member]	Additional Paid-in Capital [Member]Pre-funded Warrants and Common Warrants [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member]Cumulative Effect, Period of Adoption, Adjustment [Member]
Beginning balance at Dec. 31, 2018	$ 19,600			$ (273)	$ 15			$ 188,083			$ (5)	$ (168,493)	$ (273)
Beginning balance, shares at Dec. 31, 2018					14,748,475
Accounting Standards Update [Extensible List]				ASU No. 2016-02 [Member]
Exercise of stock options	165							165
Exercise of stock options, shares					126,560
Stock issued during period, value		$ 23,796	$ 2,203			$ 12	$ 1		$ 23,784	$ 2,202
Stock issued during period, shares						11,838,582	1,096,741
Exercise of pre-funded warrants	11							11
Issuance costs	(2,213)							(2,213)
Stock-based compensation expense	2,116							2,116
Unrealized gain (loss) on investments	12										12
Net loss	(29,369)											(29,369)
Ending balance at Dec. 31, 2019	$ 16,048				$ 28			214,148			7	(198,135)
Ending balance, shares at Dec. 31, 2019	27,810,358				27,810,358
Stock issued during period, value	$ 16,897				$ 16			16,881
Stock issued during period, shares					15,961,193
Issuance costs	(1,494)							(1,494)
Stock-based compensation expense	1,893							1,893
RSUs vested, net of shares repurchased for tax	(16)							(16)
RSUs vested, net of shares repurchased for tax, shares					32,624
Unrealized gain (loss) on investments	(9)										(9)
Net loss	(21,157)											(21,157)
Ending balance at Dec. 31, 2020	$ 12,162				$ 44			$ 231,412			$ (2)	$ (219,292)
Ending balance, shares at Dec. 31, 2020	43,804,175				43,804,175

Statements of Cash Flows

Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities:
Net loss	$ (21,157,000)	$ (29,369,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	163,000	155,000
Net amortization of premiums and discounts on investments	(9,000)	(231,000)
Stock-based compensation expense	1,893,000	2,116,000
(Gain)/loss on disposition of property and equipment	(86,000)	5,000
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(682,000)	(206,000)
Other assets	6,060,000	1,318,000
Accounts payable	116,000	(277,000)
Operating lease liabilities	(5,033,000)	(370,000)
Accrued expenses and other current liabilities	(1,741,000)	385,000
Net cash used in operating activities	(20,476,000)	(26,474,000)
Cash flows from investing activities:
Purchases of investments	(10,034,000)	(27,237,000)
Proceeds from sales or maturities of investments	16,242,000	24,574,000
Purchases of property and equipment	(5,000)	(151,000)
Proceeds from sale of fixed asset	208,000	0
Net cash (used in) provided by investing activities	6,411,000	(2,814,000)
Cash flows from financing activities:
Proceeds from issuance of common stock, common warrants and pre-funded warrants, net of issuance costs	15,413,000	23,799,000
Proceeds from Paycheck Protection Program Loan	387,000
Proceeds from exercise of stock options		165,000
Net cash provided by financing activities	15,800,000	23,964,000
Net Increase (decrease) in cash, cash equivalents and restricted cash	1,735,000	(5,324,000)
Cash, cash equivalents and restricted cash at beginning of period	5,904,000	11,228,000
Cash, cash equivalents and restricted cash at end of period	7,639,000	5,904,000
Cash and cash equivalents, end of year	7,046,000	5,311,000
Restricted cash, end of year	$ 593,000	$ 593,000

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2020
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 biopharmaceutical company that is focused on transforming the experience of chemotherapy for cancer patients, enabling them to fight cancer without the fear or burden of chemotherapy-induced side effects. ALRN-6924, the Company’s first-in-class MDM2/MDMX dual inhibitor activating p53, is the only reported therapeutic 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 of treating patients with p53-mutated cancers, ALRN-6924 is designed to protect multiple healthy cell types throughout the body from chemotherapy while chemotherapy continues to kill cancer cells. In addition to potentially reducing or eliminating multiple side effects, ALRN-6924 may also improve patients’ quality of life and help them better tolerate chemotherapy, potentially allowing patients to complete their treatment without dose reductions or delays. The Company’s long-term vision is to provide chemoprotection for patients with p53-mutated cancers, which represents approximately 50% of cancer patients, regardless of cancer type or chemotherapeutic drug. 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. The Company’s product candidates are in development. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that any products developed will obtain necessary governmental regulatory approval or that any approved products 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 The Company’s 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 December 31, 2020, the Company has financed operations primary through $50,009 in net proceeds from its initial public offering, or IPO, $10,246 in net proceeds from a public offering in June 2020, $3,918 in net proceeds from “at the market” offerings, $1,801 in in net proceeds from sales pursuant to an equity line financing, $23,825 in net proceeds from a private placement in April 2019, $131,211 from sales of preferred stock prior to its IPO, $552 from the exercise of stock options and $34,910 from a collaboration agreement. As of December 31, 2020, the Company had cash, cash equivalents and investments of $13,805. The Company has incurred losses and negative cash flows from operations and had an accumulated deficit of $219,292 as of December 31, 2020. 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 $13,805 as of December 31, 2020, together with the net proceeds of approximately $33,091 from the issuance and sale of shares of common stock in a registered direct public offering on January 8, 2021, net proceeds of approximately $19,962 from the issuance and sale of shares of common stock in at-market-offerings under its Capital on Demand Sales Agreements between January 1, 2021 and the date of this Annual Report on Form 10-K , and net proceeds of approximately $2,614 from the issuance and sale of shares of common stock from its common stock purchase agreement with Lincoln Park Capital Fund, LLC between January 1, 2021 and the date of issuance of these financial statements date of issuance of these financial statements. To execute its business plans, 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, through debt financings or from other capital sources, including collaborations with other companies or other strategic transactions. The Company may not be able to obtain financing 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 research and development programs, product portfolio expansion plans or commercialization efforts, which could adversely affect its business prospects. The financial statements do not include any adjustments that might result from the outcome of this uncertainty.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
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. 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 December 31, 2020, current restricted cash of $593 consisted of cash deposited in separate restricted bank accounts as a security deposits for the lease of the Company’s facility in Watertown, Massachusetts (see Note 12) and for the Company’s corporate credit cards. As of December 31, 2019, current restricted cash consisted of $25 of cash deposited in a separate restricted bank account as a security deposit for the Company’s corporate credit cards. As of December 31, 2019, non-current restricted cash consisted of $568 of cash deposited in a separate restricted bank account as a security deposit for the lease of the Company’s facility in Watertown, Massachusetts (see Note 12). 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 classifies all of its investments as available-for-sale securities. 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, among other things, 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. 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. Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the offering. Should the planned equity financing be abandoned, the deferred offering costs would be expensed immediately as a charge to operating expenses in the statement of operations and comprehensive loss. During the year ended December 31, 2020, the Company received aggregate gross proceeds from the sale of common stock of approximately $16,881 before deducting placement agent fees and offering expenses of approximately $1,494. During the year ended December 31, 2019, the Company received aggregate gross proceeds from the private placement of approximately $26.0 million before deducting placement agent fees and offering expenses of approximately $2.2 million and excluding the exercise of any warrants. 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: Laboratory equipment 5 years Computer equipment and software Furniture and fixtures 3 to 5 years 7 years Building 30 years Leasehold improvements Shorter of 7 years or term of lease 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 statements of operations and comprehensive loss. Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. 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. To date, the Company has not recorded any impairment losses on long-lived assets. Research and Development Costs Research and development expenditures are expensed as incurred. Research and development expenses are comprised of salaries, stock-based compensation and benefits of employees, third-party license fees and other operational costs related to the Company’s research and development activities, including allocated facility-related expenses and external costs of outside vendors engaged to conduct both preclinical studies and clinical trials. Research Contract Costs and Accruals The Company has entered into various research and development contracts with research institutions and other companies. These agreements are cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. This process involves reviewing open contracts and purchase orders, communicating with personnel to identify services that have been performed and estimating level of service performed and the associated costs incurred for the services for which the Company has not yet been invoiced. Significant judgment and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs. 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 and directors based on the fair value on the date of the grant and recognizes compensation expense of those awards, net of estimated 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. In developing a forfeiture rate estimate, the Company has considered its historical experience to estimate pre-vesting forfeitures for awards with service-based vesting conditions. The impact of a forfeiture rate adjustment will be recognized in full in the period of adjustment, and if the actual forfeiture rate is materially different from the Company’s estimate, the Company may be required to record adjustments to stock-based compensation expense in future periods. The Company classifies share-based compensation expense 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. The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the 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. 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. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. 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. 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. Segment Data 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 a novel class of therapeutics for the treatment of cancer and other diseases. All of the Company’s tangible assets are held 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 only element of other comprehensive loss in all periods presented was unrealized gains (losses) on available-for-sale investments. Net Income (Loss) per Share The Company follows the two-class method when computing net income (loss) per share as the Company has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting income (loss) per share attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (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 to purchase common stock and shares of redeemable convertible preferred stock are considered potential dilutive common shares. The Company’s redeemable convertible preferred stock contractually entitled the holders of such shares to participate in dividends but contractually did not require the holders of such stock to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, 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 around the world, which may worsen or prolong the outbreak. 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 outbreak. 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 outbreak and its effects on our business and operations are uncertain. Potential impacts to the Company’s business include disruptions in supply of the Company’s product candidate and/or procuring 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 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 may 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 our 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 Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12, Income Taxes In February 2016, the FASB issued ASU No. 2016-02, Leases Leases The Company adopted the standard effective January 1, 2019. It has implemented the standard using the required modified retrospective approach and has also elected to utilize the package of practical expedients. The expedients used by the Company are as follows: (1) allowing an entity to not reassess the lease classification for any expired or existing leases, (2) allowing an entity to not reassess the treatment of initial direct costs as they related to existing leases, and (3) allowing an entity to not reassess whether expired or existing contracts are or contain leases. The Company elected to adopt the standard at the beginning of the period of adoption. As a result of the adoption of ASU 2016-02, the Company de-recognized $7,079 of the building asset and $81 of accumulated depreciation related to its former corporate headquarters at 490 Arsenal Way. Prior to the adoption of ASU 2016-02, the Company classified facility improvements associated with the 490 Arsenal Way building as a component of its building asset. Subsequent to the adoption of ASU 2016-02, these improvements were reclassified to leasehold improvements. 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 financial statements upon adoption.

Fair Value of Financial Assets

Fair Value of Financial Assets	12 Months Ended
	Dec. 31, 2020
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 December 31, 2020 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 4,190 $ — $ — $ 4,190 Corporate notes — — — — Commercial paper — 1,001 — 1,001 Investments: Corporate notes — — — — Treasury bills 1,249 1,249 Agency bonds 3,511 3,511 Commercial paper — 1,999 — 1,999 $ 4,190 $ 7,760 $ — $ 11,950 Fair Value Measurements as of December 31, 2019 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 4,208 $ — $ — $ 4,208 Corporate notes — — — — Commercial paper — — — — Investments: Corporate notes — 5,491 — 5,491 Commercial paper — 7,476 — 7,476 $ 4,208 $ 12,967 $ — $ 17,175 As of December 31, 2020 and 2019, the Company’s cash equivalents and investments were invested in money market funds, corporate notes and commercial paper and 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 years ended December 31, 2020 and 2019, there were no transfers between Level 1, Level 2 and Level 3.

Investments

Investments	12 Months Ended
	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Investments	4. Investments As of December 31, 2020 and 2019, the fair value of available-for-sale investments by type of security was as follows: December 31, 2020 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Corporate notes $ — $ — $ — $ — Treasury bills 1,249 — — 1,249 Agency Bonds 3,511 — — 3,511 Commercial paper 1,999 — — 1,999 $ 6,759 $ — $ — $ 6,759 December 31, 2019 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Corporate notes $ 5,489 $ 2 $ — $ 5,491 Commercial paper 7,470 6 — 7,476 $ 12,959 $ 8 $ — $ 12,967

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment, net consisted of the following: December 31, 2020 2019 Laboratory equipment $ - $ 451 Computer equipment and software 181 177 Furniture and fixtures - 189 181 817 Less: Accumulated depreciation and amortization (166 ) (522 ) $ 15 $ 295 Depreciation and amortization expense for the years ended December 31, 2020 and 2019 was $163 and $140, respectively. 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. During the year ended December 31, 2019, assets with a cost of $749 were disposed of for no proceeds, resulting in a loss on disposal of $5.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2020
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: December 31, 2020 December 31, 2019 External research and development services $ 896 $ 1,673 Payroll and payroll-related costs 922 1,281 Professional fees 135 635 Other 243 352 $ 2,196 $ 3,941

Paycheck Protection Loan

Paycheck Protection Loan	12 Months Ended
	Dec. 31, 2020
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 has 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. If and when the loan forgiveness becomes probable, the Company will recognize income for debt extinguishment pursuant to ASC 470-50-15-4. The Company submitted a loan forgiveness application in December 2020.

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Preferred Stock	8. Preferred Stock On July 5, 2017, in connection with the closing of the Company’s IPO, the Company filed its amended and restated certificate of incorporation, which authorizes the Company to issue up to 5,000,000 shares of preferred stock, $0.001 par value per share. As of December 31, 2020 and 2019, the Company had no shares of preferred stock issued or outstanding.

Common Stock

Common Stock	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Common Stock	9. Common Stock On July 5, 2017, the Company filed the amended and restated certificate of incorporation which increased the authorized number of shares of common stock from 143,500,000 shares of $0.001 par value common stock to 150,000,000 shares of common stock. 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, subject to the preferential dividend rights of the preferred stock. As of December 31, 2020 and 2019, no dividends had been declared. As of December 31, 2020, the Company had reserved 5,098,505 shares for the exercise of outstanding stock options and grant of future awards under the Company’s stock incentive plans (see Note 10).

Stock-Based Awards

Stock-Based Awards	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Awards	10. Stock-Based Awards 2017 Stock Incentive Plan The Company’s 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 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 2017 Plan; however, incentive stock options may 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 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 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 total number of shares of common stock that may be issued under the 2017 Plan was 4,701,056 as of December 31, 2020, of which 382,919 shares remained available for grant. The Company initially reserved 1,244,816 shares of common stock plus the number of shares equal to the sum of the number of shares of common stock then available for issuance under the 2016 Plan, which was 424,601 shares, and the number of shares of common stock subject to outstanding awards under the 2006 Plan and the 2016 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. The number of shares of common stock that may be issued under the 2017 Plan will automatically increase on January 1 of each year, 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) 1,244,816 shares of common stock, (ii) 4% of the outstanding shares of common stock on such date and (iii) an amount determined by the Company’s board of directors. For the year ended December 31, 2020, the Company’s compensation committee of the board of directors authorized an additional 1,112,414 shares that may be issued under the 2017 Plan. During the year ended December 31, 2020, pursuant to the terms of the 2017 Plan, the Company granted options to employees and directors to purchase 1,821,000 shares of common stock at a weighted average exercise price of $0.76 per share. 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 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. As of December 31, 2019, a total of 150,000 shares of common stock are reserved for issuance under the 2017 ESPP. The number of shares of common stock that may be issued under the 2017 ESPP automatically increase on each January 1 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 board of directors has not initiated any offerings under the ESPP. 2016 Stock Incentive Plan The Company’s 2016 Stock Incentive Plan (the “2016 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options, restricted stock, restricted stock units and other equity awards to employees, directors and consultants of the Company. The 2016 Plan was administered by the board of directors or, at the discretion of the board of directors, by a committee of the board. The 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 2016 Plan with service-based vesting conditions vest over four years and expire after ten years. After the effective date of the 2017 Plan, no stock options or other awards were made under the 2016 Plan. No shares remained available for future issuance as of December 31, 2017. Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards under the 2017 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 2017 Plan. 2006 Stock Incentive Plan The Company’s 2006 Stock Incentive Plan, as amended, (the “2006 Plan”) provided for the Company to grant incentive stock options or nonqualified stock options, restricted stock, restricted stock units and other equity awards to employees, directors and consultants of the Company. The 2006 Plan was administered by the board of directors or, at the discretion of the board of directors, by a committee of the board. The 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 2006 Plan with service-based vesting conditions generally vest over four years and expire after ten years, although options have been granted with vesting terms of less than four years. The 2006 Plan expired in 2016. No shares remained available for future issuance as of December 31, 2016. Shares that are expired, terminated, surrendered or canceled without having been fully exercised will be available for future awards under the 2017 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 2017 Plan. 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 year ended December 31, 2020 and 2019 were as follows, presented on a weighted average basis: Year Ended December 31, 2020 2019 Risk-free interest rate 1.17 % 2.35 % Expected term (in years) 6.2 6.2 Expected volatility 76.0 % 76.0 % Expected dividend yield 0 % 0 % Stock Options The following table summarizes the Company’s stock option activity since January 1, 2020: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding at December 31, 2019 3,320,706 $ 3.87 7.4 $ — Granted 1,821,000 0.76 Exercised — 0.00 Canceled (463,119 ) 6.59 Forfeited (13,001 ) 2.54 Outstanding at December 31, 2020 4,665,586 $ 2.39 8.1 $ 622 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 Options exercisable at December 31, 2019 1,415,900 $ 5.56 5.2 $ — Options vested and expected to vest at December 31, 2019 3,264,851 $ 3.89 7.4 $ — The weighted average grant-date fair value of stock options granted during the year ended December 31, 2020 and 2019 was $0.51 and $1.11, respectively. The aggregate fair value of stock options that vested during the year ended December 31, 2020 and 2019 was $2,099 and $2,236, 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 year ended December 31, 2020 and 2019 was $0 and $109, respectively. Restricted Stock Units On April 15, 2019, the Company granted restricted stock units under the 2017 Stock Incentive Plan. The following table summarizes the Company’s restricted stock unit activity during the year ended December 31, 2020: Weighted-Average Grant Date Units per Unit Outstanding, non-vested at December 31, 2019 50,000 $ 1.75 Issued — — Vested (50,000 ) $ 1.75 Canceled/forfeited — — Outstanding, non-vested at December 31, 2020 — — 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, 2020 2019 Research and development expenses $ 572 $ 524 General and administrative expenses 1,321 1,592 $ 1,893 $ 2,116 The Company used an estimated forfeiture rate of 2.43% to calculate its stock compensation expense for each of the years ended December 31, 2020 and 2019. As of December 31, 2020, the Company had an aggregate of $2,144 of unrecognized stock-based compensation expense, which it expects to recognize over a weighted average period of 2.14 years.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Loss per Share	11. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows : Year Ended December 31, 2020 2019 Numerator: Net loss $ (21,157 ) $ (29,369 ) Denominator: Weighted average common shares outstanding—basic and diluted 34,866,690 24,535,454 Net loss per share attributable to common stockholders—basic and diluted $ (0.61 ) $ (1.20 ) The Company’s potential dilutive securities, which include stock options as of December 31, 2020 and 2019, 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, 2020 2019 Warrants to purchase common stock 12,935,323 12,935,323 Stock options to purchase common stock 4,665,586 3,320,706 Restricted stock units to purchase common stock — 50,000 Total 17,600,909 16,306,029

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	12. Commitments and Contingencies Operating Leases 490 Arsenal Way On April 4, 2018, the Company entered into a lease agreement for office and laboratory space located in a building (the “Building”) at 490 Arsenal Way, Watertown, Massachusetts (the “490 Arsenal Way Lease”). Under the terms of the 490 Arsenal Way Lease, starting on August 21, 2018, the Company leases approximately 18,768 The Company occupied the Building from August 21, 2018 through November 11, 2020 when the 490 Arsenal Way Lease was terminated. The Company accounted for this lease under ASC 842 using its initial eight-year term through August 31, 2026. As part of its adoption of ASC 842, the Company de-recognized the building asset and corresponding financing obligation recorded on the Company’s consolidated balance sheets as of January 1, 2019, in accordance with the ASC 842 transition guidance. In applying the ASC 842 transition guidance, the Company classified this lease as an operating lease and recorded a right-of-use asset of $6,697 and lease liability of $5,401 on the effective date. The Company recognizes rent expense on a straight-line basis throughout the remaining term of the lease. On November 11, 2020, the Company entered into a lease termination agreement with respect to its former corporate headquarters at 490 Arsenal Way, Watertown, Massachusetts. In connection with the lease termination the right of use assets and operating lease liabilities associated with the lease were derecognized. The derecognition of these assets and liabilities resulted in a charge of $823. Summary of all lease costs recognized under ASC 842 The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the year ended December 31, 2020: Twelve Months Ended December 31, 2020 Lease cost (1) Operating lease cost $ 1,095 Total lease cost $ 1,095 Other Information Cash paid for amounts included in the measurement of lease liabilities $ 884 Weighted average remaining lease term (in years) — Weighted average discount rate — (1) Short-term lease costs and variable lease costs incurred by the Company for the twelve months ended December 31, 2020 were not material. As of December 31, 20 20 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 each year. Any payments made in connection with the annual license maintenance fees will be credited against any royalties due. The Company incurred license fees of $145 during each of the years ended December 31, 2020 and 2019. In addition, the Company did not make any milestone payments during the years ended December 31, 2020 and 2019. During the years ended December 31, 2019, no milestones were achieved and no liabilities for milestone payments were recorded in the Company’s financial statements. From 2010 through December 31, 2020 and December 31, 2019, the Company had made non-refundable cash payments, consisting of license and maintenance fees, milestone payments and sublicense fees, totaling $4,863 and $4,718, respectively. As of December 31, 2020, 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 $50 during each of the years ended December 31, 2020 and 2019. The Company did not make any milestone payments during the years ended December 31, 2020 or 2019. During the year ended December 31, 2020, no milestones were achieved and no liabilities for additional milestone payments were recorded in the Company’s financial statements. The 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 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 financial statements as of December 31, 2020 or December 31, 2019.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	13. Income Taxes There is no provision for income taxes because the Company has historically incurred operating losses and maintains a full valuation allowance against its net deferred tax assets. 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. On March 27, 2020, the previous U.S. President signed into law the Coronavirus Aid, Relief, and Economic Security Act (the CARES Act) in response to the U.S. COVID-19 pandemic, which, among other things, suspends the 80% limitation on the deduction for NOLs in taxable years beginning before January 1, 2021, permits a 5-year carryback of NOLs arising in taxable years beginning after December 31, 2017 and before January 1, 2021, and generally caps the limitation on the deduction for net interest expense at 50% of adjusted taxable income for taxable years beginning in 2019 and 2020. In addition, the CARES Act raises the corporate charitable deduction limit to 25% of taxable income and makes qualified improvement property generally eligible for 15-year cost-recovery and 100% bonus depreciation. The enactment of the CARES Act did not result in any material adjustments to the Company's income tax provision for the year ended December 31, 2020, or to its net deferred tax assets and related allowances as of December 31, 2020. 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, 2020 2019 Federal statutory income tax rate (21.0 )% (21.0 )% State taxes, net of federal benefit (5.9 ) (5.0 ) Research and development tax credits (2.6 ) (3.0 ) Other permanent items 0.6 0.6 Change in deferred tax asset valuation allowance 28.9 28.4 Effective income tax rate — % — % Net deferred tax assets as of December 31, 2020 and 2019 consisted of the following: December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 55,229 $ 50,240 Research and development tax credit carryforwards 4,979 4,449 Capitalized research and development expenses 57 63 Accrued expenses and reserves 265 312 Depreciation and amortization 462 435 Lease Liability — 1,368 Stock compensation 940 605 Total deferred tax assets 61,932 57,472 Valuation allowance (61,932 ) (55,825 ) Net deferred tax assets $ — $ 1,647 Deferred Tax Liabilities: Right of Use Asset $ — $ (1,647 ) Total Deferred Tax Liabilities $ — $ (1,647 ) Net Deferred Tax Asset (Liability) $ — $ — Since inception in 2001, the Company has not recorded any U.S. federal or state income tax benefits for the net losses the Company has incurred in any year or for its earned research and development tax credits, due to its uncertainty of realizing a benefit from those items. As of December 31, 2020, the Company had net operating loss carryforwards for federal and state purposes of $203,505 and $197,672, respectively. $129,596 of the U.S. federal tax operating loss carryforwards will begin to expire in 2029. Approximately $73,909 of the U.S. federal tax operating losses can be carried forward indefinitely. The state tax operating loss carryforwards expire beginning in 2030. As of December 31, 2020, the Company also had available research and development tax credit carryforwards for federal and state income tax purposes of $2,630 and $1,766, respectively, which begin to expire in 2025. As of December 31, 2020, the Company also had available orphan drug credit carryforwards of $954 for federal income tax purposes, which begin to expire in 2039. 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. The Company has not conducted a study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards would be subject to an annual limitation under Section 382, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed and any limitation is known, no amounts are being presented as an uncertain tax position. 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. Accordingly, a full valuation allowance has been established against the net deferred tax assets as of December 31, 2020 and 2019. Management reevaluates the positive and negative evidence at each reporting period. The increase in the valuation allowance for deferred tax assets during the years ended December 31, 2020 and 2019 related primarily to the increase in net operating loss carryforwards. Changes in the valuation allowance were as follows: Year Ended December 31, 2020 2019 Valuation allowance at beginning of year $ (55,825 ) $ (47,399 ) Increases recorded to income tax provision (6,107 ) (8,426 ) Valuation allowance at end of year $ (61,932 ) $ (55,825 ) The Company has not recorded any amounts for unrecognized tax benefits as of December 31, 2020 or 2019. 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 2017 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, 2020 and 2019, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s statements of operations and comprehensive loss.

401(k) Plan

401(k) Plan	12 Months Ended
	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
401(k) Plan	14. 401(k) Plan The Company has a 401(k) plan available for participating employees who meet certain eligibility requirements. Eligible employees may defer a portion of their salary as defined by the plan. Company contributions to the plan may be made at the discretion of the Company’s board of directors. The Company has not elected to make any employer contributions for the years ended December 31, 2020 or 2019.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (unaudited)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (unaudited)	15. Selected Quarterly Financial Data (unaudited) The following table contains selected quarterly financial information for 2020 and 2019. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period. Three Months Ended March 31, 2020 June 30, 2020 September 30, 2020 December 31, 2020 Revenue $ — $ — $ — $ — Operating expenses: Research and development 4,069 2,488 2,684 1,925 General and administrative 2,807 1,912 2,344 2,267 Total operating expenses 6,876 4,400 5,028 4,192 Loss from operations (6,876 ) (4,400 ) (5,028 ) (4,192 ) Other income (expense), net 62 10 5 (738 ) Net loss (6,814 ) (4,390 ) (5,023 ) (4,930 ) Net loss per share—basic and diluted $ (0.24 ) $ (0.14 ) $ (0.13 ) $ (0.12 ) Weighted average common shares outstanding— basic and diluted 27,810,358 31,221,139 39,321,177 40,997,759 Comprehensive loss: Net loss $ (6,814 ) $ (4,390 ) $ (5,023 ) $ (4,930 ) Other comprehensive gain (loss): Unrealized gain (loss) on investments, net of tax of $0 (8 ) (1 ) 1 (1 ) Total other comprehensive gain (loss) (8 ) (1 ) 1 (1 ) Total comprehensive loss $ (6,822 ) $ (4,391 ) $ (5,022 ) $ (4,931 ) Three Months Ended March 31, 2019 June 30, 2019 September 30, 2019 December 31, 2019 Revenue $ — $ — $ — $ — Operating expenses: Research and development 4,174 4,305 4,475 4,709 General and administrative 3,139 3,075 3,440 2,639 Total operating expenses 7,313 7,380 7,915 7,348 Loss from operations (7,313 ) (7,380 ) (7,915 ) (7,348 ) Other income (expense), net 101 208 166 112 Net loss (7,212 ) (7,172 ) (7,749 ) (7,236 ) Net loss per share attributable to common stockholders—basic and diluted $ (0.49 ) $ (0.26 ) $ (0.28 ) $ (0.26 ) Weighted average common shares outstanding—basic and diluted 14,816,253 27,526,065 27,810,358 27,810,358 Comprehensive loss: Net loss $ (7,212 ) $ (7,172 ) $ (7,749 ) $ (7,236 ) Other comprehensive loss: Unrealized loss on investments, net of tax of $0 5 24 (7 ) (10 ) Total other comprehensive loss 5 24 (7 ) (10 ) Total comprehensive loss $ (7,207 ) $ (7,148 ) $ (7,756 ) $ (7,246 )

Subsequent Event

Subsequent Event	12 Months Ended
	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Event	16. Subsequent Event 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 million, before deducting fees payable to the placement agent and other estimated offering expenses payable by the Company. The shares were offered by the Company pursuant to a shelf registration statement on Form S-3 (File No. 333-226650) that was filed with the United States Securities and Exchange Commission (“SEC”) on July 1, 2018, and declared effective by the SEC on July 15, 2019 (the “Registration Statement”), and a prospectus supplement thereunder. The Offering closed on January 8, 2021. In addition, between January 1, 2021 and January 28, 2021, the Company issued and sold an aggregate of 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. On January 29, 2021, the Company entered into a Capital on Demand™ Sales Agreement (the “ATM Sales Agreement”) with JonesTrading Institutional Services LLC and William Blair & Company, L.L.C. (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. Between January 29, 2021 and March 24, 2021, the Company issued and sold an aggregate of 5,225,406 shares of its common stock pursuant to the ATM Sales Agreement, resulting in net proceeds of $10,594. Between January 1, 2021 and March 24, 2021, the Company issued and sold an aggregate of 1,375,000 shares of its common stock to LPC pursuant to the Purchase Agreement, resulting in gross proceeds of $2,614.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Use of Estimates	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.
Cash Equivalents	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	Restricted Cash As of December 31, 2020, current restricted cash of $593 consisted of cash deposited in separate restricted bank accounts as a security deposits for the lease of the Company’s facility in Watertown, Massachusetts (see Note 12) and for the Company’s corporate credit cards. As of December 31, 2019, current restricted cash consisted of $25 of cash deposited in a separate restricted bank account as a security deposit for the Company’s corporate credit cards. As of December 31, 2019, non-current restricted cash consisted of $568 of cash deposited in a separate restricted bank account as a security deposit for the lease of the Company’s facility in Watertown, Massachusetts (see Note 12).
Investments	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 classifies all of its investments as available-for-sale securities. 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, among other things, 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. 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	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	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.
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the offering. Should the planned equity financing be abandoned, the deferred offering costs would be expensed immediately as a charge to operating expenses in the statement of operations and comprehensive loss. During the year ended December 31, 2020, the Company received aggregate gross proceeds from the sale of common stock of approximately $16,881 before deducting placement agent fees and offering expenses of approximately $1,494. During the year ended December 31, 2019, the Company received aggregate gross proceeds from the private placement of approximately $26.0 million before deducting placement agent fees and offering expenses of approximately $2.2 million and excluding the exercise of any warrants.
Property and Equipment	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: Laboratory equipment 5 years Computer equipment and software Furniture and fixtures 3 to 5 years 7 years Building 30 years Leasehold improvements Shorter of 7 years or term of lease 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 statements of operations and comprehensive loss.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Long-lived assets consist of property and equipment. 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. To date, the Company has not recorded any impairment losses on long-lived assets.
Research and Development Costs	Research and Development Costs Research and development expenditures are expensed as incurred. Research and development expenses are comprised of salaries, stock-based compensation and benefits of employees, third-party license fees and other operational costs related to the Company’s research and development activities, including allocated facility-related expenses and external costs of outside vendors engaged to conduct both preclinical studies and clinical trials.
Research Contract Costs and Accruals	Research Contract Costs and Accruals The Company has entered into various research and development contracts with research institutions and other companies. These agreements are cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. This process involves reviewing open contracts and purchase orders, communicating with personnel to identify services that have been performed and estimating level of service performed and the associated costs incurred for the services for which the Company has not yet been invoiced. Significant judgment and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual costs.
Patent Costs	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	Accounting for Stock-Based Compensation The Company measures all stock options and other stock-based awards granted to employees and directors based on the fair value on the date of the grant and recognizes compensation expense of those awards, net of estimated 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. In developing a forfeiture rate estimate, the Company has considered its historical experience to estimate pre-vesting forfeitures for awards with service-based vesting conditions. The impact of a forfeiture rate adjustment will be recognized in full in the period of adjustment, and if the actual forfeiture rate is materially different from the Company’s estimate, the Company may be required to record adjustments to stock-based compensation expense in future periods. The Company classifies share-based compensation expense 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. The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the 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.
Income Taxes	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. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. 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. 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.
Segment Data	Segment Data 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 a novel class of therapeutics for the treatment of cancer and other diseases. All of the Company’s tangible assets are held in the United States.
Comprehensive Loss	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 only element of other comprehensive loss in all periods presented was unrealized gains (losses) on available-for-sale investments.
Net Income (Loss) per Share	Net Income (Loss) per Share The Company follows the two-class method when computing net income (loss) per share as the Company has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting income (loss) per share attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (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 to purchase common stock and shares of redeemable convertible preferred stock are considered potential dilutive common shares. The Company’s redeemable convertible preferred stock contractually entitled the holders of such shares to participate in dividends but contractually did not require the holders of such stock to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.
Risks and Uncertainties	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 around the world, which may worsen or prolong the outbreak. 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 outbreak. 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 outbreak and its effects on our business and operations are uncertain. Potential impacts to the Company’s business include disruptions in supply of the Company’s product candidate and/or procuring 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 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 may 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 our 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 Accounting Pronouncements	Recently Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12, Income Taxes In February 2016, the FASB issued ASU No. 2016-02, Leases Leases The Company adopted the standard effective January 1, 2019. It has implemented the standard using the required modified retrospective approach and has also elected to utilize the package of practical expedients. The expedients used by the Company are as follows: (1) allowing an entity to not reassess the lease classification for any expired or existing leases, (2) allowing an entity to not reassess the treatment of initial direct costs as they related to existing leases, and (3) allowing an entity to not reassess whether expired or existing contracts are or contain leases. The Company elected to adopt the standard at the beginning of the period of adoption. As a result of the adoption of ASU 2016-02, the Company de-recognized $7,079 of the building asset and $81 of accumulated depreciation related to its former corporate headquarters at 490 Arsenal Way. Prior to the adoption of ASU 2016-02, the Company classified facility improvements associated with the 490 Arsenal Way building as a component of its building asset. Subsequent to the adoption of ASU 2016-02, these improvements were reclassified to leasehold improvements. 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 financial statements upon adoption.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Schedule of Property and Equipment Estimated Useful Lives	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: Laboratory equipment 5 years Computer equipment and software Furniture and fixtures 3 to 5 years 7 years Building 30 years Leasehold improvements Shorter of 7 years or term of lease

Fair Value of Financial Assets

Fair Value of Financial Assets (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Summary of Assets Measured at Fair Value on Recurring Basis	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 December 31, 2020 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 4,190 $ — $ — $ 4,190 Corporate notes — — — — Commercial paper — 1,001 — 1,001 Investments: Corporate notes — — — — Treasury bills 1,249 1,249 Agency bonds 3,511 3,511 Commercial paper — 1,999 — 1,999 $ 4,190 $ 7,760 $ — $ 11,950 Fair Value Measurements as of December 31, 2019 using: Level 1 Level 2 Level 3 Total Cash equivalents: Money market funds $ 4,208 $ — $ — $ 4,208 Corporate notes — — — — Commercial paper — — — — Investments: Corporate notes — 5,491 — 5,491 Commercial paper — 7,476 — 7,476 $ 4,208 $ 12,967 $ — $ 17,175

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Summary of Fair Value of Available for Sale Investments	As of December 31, 2020 and 2019, the fair value of available-for-sale investments by type of security was as follows: December 31, 2020 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Corporate notes $ — $ — $ — $ — Treasury bills 1,249 — — 1,249 Agency Bonds 3,511 — — 3,511 Commercial paper 1,999 — — 1,999 $ 6,759 $ — $ — $ 6,759 December 31, 2019 Amortized Cost Gross Unrealized Gain Gross Unrealized Loss Fair Value Investments: Corporate notes $ 5,489 $ 2 $ — $ 5,491 Commercial paper 7,470 6 — 7,476 $ 12,959 $ 8 $ — $ 12,967

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Summary of Property and Equipment, Net	Property and equipment, net consisted of the following: December 31, 2020 2019 Laboratory equipment $ - $ 451 Computer equipment and software 181 177 Furniture and fixtures - 189 181 817 Less: Accumulated depreciation and amortization (166 ) (522 ) $ 15 $ 295

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Summary of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: December 31, 2020 December 31, 2019 External research and development services $ 896 $ 1,673 Payroll and payroll-related costs 922 1,281 Professional fees 135 635 Other 243 352 $ 2,196 $ 3,941

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [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 year ended December 31, 2020 and 2019 were as follows, presented on a weighted average basis: Year Ended December 31, 2020 2019 Risk-free interest rate 1.17 % 2.35 % Expected term (in years) 6.2 6.2 Expected volatility 76.0 % 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, 2020: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding at December 31, 2019 3,320,706 $ 3.87 7.4 $ — Granted 1,821,000 0.76 Exercised — 0.00 Canceled (463,119 ) 6.59 Forfeited (13,001 ) 2.54 Outstanding at December 31, 2020 4,665,586 $ 2.39 8.1 $ 622 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 Options exercisable at December 31, 2019 1,415,900 $ 5.56 5.2 $ — Options vested and expected to vest at December 31, 2019 3,264,851 $ 3.89 7.4 $ —
Summary of Restricted Stock Unit Activity	On April 15, 2019, the Company granted restricted stock units under the 2017 Stock Incentive Plan. The following table summarizes the Company’s restricted stock unit activity during the year ended December 31, 2020: Weighted-Average Grant Date Units per Unit Outstanding, non-vested at December 31, 2019 50,000 $ 1.75 Issued — — Vested (50,000 ) $ 1.75 Canceled/forfeited — — Outstanding, non-vested at December 31, 2020 — —
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, 2020 2019 Research and development expenses $ 572 $ 524 General and administrative expenses 1,321 1,592 $ 1,893 $ 2,116

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 Numerator: Net loss $ (21,157 ) $ (29,369 ) Denominator: Weighted average common shares outstanding—basic and diluted 34,866,690 24,535,454 Net loss per share attributable to common stockholders—basic and diluted $ (0.61 ) $ (1.20 )
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, 2020 2019 Warrants to purchase common stock 12,935,323 12,935,323 Stock options to purchase common stock 4,665,586 3,320,706 Restricted stock units to purchase common stock — 50,000 Total 17,600,909 16,306,029

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
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 under ASC 842 and other information pertaining to the Company’s operating leases for the year ended December 31, 2020: Twelve Months Ended December 31, 2020 Lease cost (1) Operating lease cost $ 1,095 Total lease cost $ 1,095 Other Information Cash paid for amounts included in the measurement of lease liabilities $ 884 Weighted average remaining lease term (in years) — Weighted average discount rate — (1) Short-term lease costs and variable lease costs incurred by the Company for the twelve months ended December 31, 2020 were not material.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
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, 2020 2019 Federal statutory income tax rate (21.0 )% (21.0 )% State taxes, net of federal benefit (5.9 ) (5.0 ) Research and development tax credits (2.6 ) (3.0 ) Other permanent items 0.6 0.6 Change in deferred tax asset valuation allowance 28.9 28.4 Effective income tax rate — % — %
Schedule of Net Deferred Tax Assets	Net deferred tax assets as of December 31, 2020 and 2019 consisted of the following: December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 55,229 $ 50,240 Research and development tax credit carryforwards 4,979 4,449 Capitalized research and development expenses 57 63 Accrued expenses and reserves 265 312 Depreciation and amortization 462 435 Lease Liability — 1,368 Stock compensation 940 605 Total deferred tax assets 61,932 57,472 Valuation allowance (61,932 ) (55,825 ) Net deferred tax assets $ — $ 1,647 Deferred Tax Liabilities: Right of Use Asset $ — $ (1,647 ) Total Deferred Tax Liabilities $ — $ (1,647 ) Net Deferred Tax Asset (Liability) $ — $ —
Schedule of Changes in Valuation Allowance	Changes in the valuation allowance were as follows: Year Ended December 31, 2020 2019 Valuation allowance at beginning of year $ (55,825 ) $ (47,399 ) Increases recorded to income tax provision (6,107 ) (8,426 ) Valuation allowance at end of year $ (61,932 ) $ (55,825 )

Selected Quarterly Financial _2

Selected Quarterly Financial Data (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Schedule of Selected Quarterly Financial Information	The following table contains selected quarterly financial information for 2020 and 2019. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period. Three Months Ended March 31, 2020 June 30, 2020 September 30, 2020 December 31, 2020 Revenue $ — $ — $ — $ — Operating expenses: Research and development 4,069 2,488 2,684 1,925 General and administrative 2,807 1,912 2,344 2,267 Total operating expenses 6,876 4,400 5,028 4,192 Loss from operations (6,876 ) (4,400 ) (5,028 ) (4,192 ) Other income (expense), net 62 10 5 (738 ) Net loss (6,814 ) (4,390 ) (5,023 ) (4,930 ) Net loss per share—basic and diluted $ (0.24 ) $ (0.14 ) $ (0.13 ) $ (0.12 ) Weighted average common shares outstanding— basic and diluted 27,810,358 31,221,139 39,321,177 40,997,759 Comprehensive loss: Net loss $ (6,814 ) $ (4,390 ) $ (5,023 ) $ (4,930 ) Other comprehensive gain (loss): Unrealized gain (loss) on investments, net of tax of $0 (8 ) (1 ) 1 (1 ) Total other comprehensive gain (loss) (8 ) (1 ) 1 (1 ) Total comprehensive loss $ (6,822 ) $ (4,391 ) $ (5,022 ) $ (4,931 ) Three Months Ended March 31, 2019 June 30, 2019 September 30, 2019 December 31, 2019 Revenue $ — $ — $ — $ — Operating expenses: Research and development 4,174 4,305 4,475 4,709 General and administrative 3,139 3,075 3,440 2,639 Total operating expenses 7,313 7,380 7,915 7,348 Loss from operations (7,313 ) (7,380 ) (7,915 ) (7,348 ) Other income (expense), net 101 208 166 112 Net loss (7,212 ) (7,172 ) (7,749 ) (7,236 ) Net loss per share attributable to common stockholders—basic and diluted $ (0.49 ) $ (0.26 ) $ (0.28 ) $ (0.26 ) Weighted average common shares outstanding—basic and diluted 14,816,253 27,526,065 27,810,358 27,810,358 Comprehensive loss: Net loss $ (7,212 ) $ (7,172 ) $ (7,749 ) $ (7,236 ) Other comprehensive loss: Unrealized loss on investments, net of tax of $0 5 24 (7 ) (10 ) Total other comprehensive loss 5 24 (7 ) (10 ) Total comprehensive loss $ (7,207 ) $ (7,148 ) $ (7,756 ) $ (7,246 )

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	Jan. 08, 2021	Jan. 01, 2021	Jul. 05, 2017	Jul. 04, 2017	Jun. 30, 2020	Apr. 30, 2019	Mar. 24, 2021	Dec. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Net proceeds from sales to an equity line financing								$ 1,801
Net proceeds from issuance of private placement						$ 23,825
Proceeds from exercise of stock options								552
Proceeds from collaboration agreement								34,910
Cash, cash equivalents and investments								13,805
Accumulated deficit								(219,292)	$ (198,135)
ATM Sales Agreement [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Proceeds from sales of stock							$ 10,594
Common Stock [Member]
Class of Stock [Line Items]
Net proceeds from issuance of offerings			$ 50,009		$ 10,246
Common Stock [Member] | Purchase Agreement [Member] | LPC [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Proceeds from sales of stock		$ 2,614
Common Stock [Member] | At The Market Offering [Member]
Class of Stock [Line Items]
Net proceeds from issuance of offerings								$ 3,918
Common Stock [Member] | At The Market Offering [Member] | ATM Sales Agreement [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Proceeds from sales of stock		$ 19,962
Common Stock [Member] | Direct Public Offering [Member] | Subsequent Event [Member]
Class of Stock [Line Items]
Proceeds from sales of stock	$ 33,091
Preferred Stock [Member]
Class of Stock [Line Items]
Proceeds from sales of stock				$ 131,211

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, current	$ 593	$ 25
Restricted cash, non-current		568
Aggregate gross proceeds from sale of common stock	16,881
Placement agent fees	$ 1,494
Lease, practical expedients, package [true false]	true
ASU No. 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, ASU adoption date	Jan. 1, 2019
Change in accounting principle, ASU adopted	true
490 Arsenal Way [Member] | Operating Lease Agreements [Member] | ASU No. 2016-02 [Member]
Summary Of Significant Accounting Policies [Line Items]
De-recognized building asset			$ 7,079
De-recognition of accumulated depreciation			$ 81
Private Placement [Member]
Summary Of Significant Accounting Policies [Line Items]
Placement agent fees		2,200
Aggregate gross proceeds from private placement		26,000
Security Deposit Related to Lease Facilities and Credit Card Accounts [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, current	$ 593
Security Deposit Related to Credit Card Accounts [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, current		25
Security Deposit Related to Lease Facility [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash, non-current		$ 568

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Property and Equipment Estimated Useful Lives (Detail)	12 Months Ended
	Dec. 31, 2020
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful lives	5 years
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
Building [Member]
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful lives	30 years
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, estimated useful lives description	Shorter of 7 years or term of lease

Fair Value of Financial Asset_2

Fair Value of Financial Assets - Summary of Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	$ 6,759	$ 12,967
Corporate Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		5,491
Commercial Paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	1,999	7,476
Treasury Bills [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	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	11,950	17,175
Recurring [Member] | Corporate Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		5,491
Recurring [Member] | Commercial Paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	1,999	7,476
Recurring [Member] | Treasury Bills [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	1,249
Recurring [Member] | Agency Bonds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	3,511
Recurring [Member] | Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	4,190	4,208
Recurring [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total assets	7,760	12,967
Recurring [Member] | Level 2 [Member] | Corporate Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments		5,491
Recurring [Member] | Level 2 [Member] | Commercial Paper [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	1,999	7,476
Recurring [Member] | Level 2 [Member] | Treasury Bills [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	1,249
Recurring [Member] | Level 2 [Member] | Agency Bonds [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Investments	3,511
Money Market Funds [Member] | Recurring [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	4,190	4,208
Money Market Funds [Member] | Recurring [Member] | Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	4,190	$ 4,208
Commercial Paper [Member] | Recurring [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	1,001
Commercial Paper [Member] | Recurring [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cash equivalents	$ 1,001

Fair Value of Financial Asset_3

Fair Value of Financial Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
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 V

Investments - Summary of Fair Value of Available for Sale Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	$ 6,759	$ 12,959
Investments, Gross Unrealized Gain		8
Investments, Fair Value	6,759	12,967
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost		5,489
Investments, Gross Unrealized Gain		2
Investments, Fair Value		5,491
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	1,249
Investments, Fair Value	1,249
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Amortized Cost	1,999	7,470
Investments, Gross Unrealized Gain		6
Investments, Fair Value	1,999	$ 7,476
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 - S

Property and Equipment, Net - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 181	$ 817
Less: Accumulated depreciation and amortization	(166)	(522)
Property, plant and equipment, net	15	295
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross		451
Computer Equipment and Software [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross	$ 181	177
Furniture and Fixtures [Member]
Property Plant And Equipment [Line Items]
Property, plant and equipment, gross		$ 189

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 163,000	$ 140,000
Disposal of property and equipment	640,000	749,000
Proceeds from property and equipment	208,000	0
Gain (loss) on disposal of property and equipment	$ 86,000	$ (5,000)

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Summary of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
External research and development services	$ 896	$ 1,673
Payroll and payroll-related costs	922	1,281
Professional fees	135	635
Other	243	352
Total accrued expenses and other current liabilities	$ 2,196	$ 3,941

Paycheck Protection Loan - Addi

Paycheck Protection Loan - Additional Information (Detail) - Paycheck Protection Program CARES Act [Member] $ in Thousands	Apr. 30, 2020USD ($)	Dec. 31, 2020
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

Preferred Stock - Additional In

Preferred Stock - Additional Information (Detail) - $ / shares	Dec. 31, 2020	Dec. 31, 2019	Jul. 05, 2017
Equity [Abstract]
Preferred stock, shares authorized	5,000,000	5,000,000	5,000,000
Preferred stock, par value	$ 0.001	$ 0.001	$ 0.001
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Common Stock - Additional Infor

Common Stock - Additional Information (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Jul. 05, 2017	Jul. 04, 2017
Equity [Abstract]
Common stock, shares authorized	150,000,000	150,000,000	150,000,000	143,500,000
Common stock, par value	$ 0.001	$ 0.001		$ 0.001
Common stock, dividends declared	$ 0	$ 0
Stock reserved for future issuance	5,098,505

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Jun. 16, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2016	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for future issuance		5,098,505
Options granted		1,821,000
Options granted, weighted average exercise price per share		$ 0.76
Weighted average grant-date fair value of stock options		$ 0.51	$ 1.11
Aggregate fair value of stock options vested		$ 2,099	$ 2,236
Aggregate intrinsic value of stock options exercised		$ 0	$ 109
Share based compensation expense estimated forfeiture rate		2.43%	2.43%
Aggregate unrecognized stock-based compensation expense		$ 2,144
Unrecognized stock-based compensation expense, weighted average period expects for recognition		2 years 1 month 20 days
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, available for grant		4,701,056
Number of shares remained available for grant		382,919
Stock reserved for future issuance		1,244,816
Maximum annual increase in common stock reserved for future issuance		1,244,816
Percentage of common stock shares outstanding		4.00%
Increase to shares authorized for issuance		1,112,414
Options granted		1,821,000
Options granted, weighted average exercise price per share		$ 0.76
2016 Stock Incentive Plan [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
Number of shares, available for grant					0
2016 Stock Incentive Plan [Member] | Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock reserved for future issuance		424,601
2017 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
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%
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. As of December 31, 2019, a total of 150,000 shares of common stock are reserved for issuance under the 2017 ESPP. The number of shares of common stock that may be issued under the 2017 ESPP automatically increase on each January 1 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 board of directors has not initiated any offerings under the ESPP.
2006 Stock Incentive Plan [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
Number of shares, available for grant				0
Stock incentive plan termination year				2016
Maximum [Member] | 2017 Stock Incentive Plan [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
Maximum [Member] | 2006 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option granted vesting period		4 years

Stock-Based Awards - Valuation

Stock-Based Awards - Valuation Assumptions of Stock Options Granted (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	1.17%	2.35%
Expected term (in years)	6 years 2 months 12 days	6 years 2 months 12 days
Expected volatility	76.00%	76.00%
Expected dividend yield	0.00%	0.00%

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Beginning balance	3,320,706
Number of Shares, Granted	1,821,000
Number of Shares, Canceled	(463,119)
Number of Shares, Forfeited	(13,001)
Number of Shares, Ending balance	4,665,586	3,320,706
Number of Shares, Options exercisable	2,377,533	1,415,900
Number of Shares, Options vested and expected to vest	4,592,729	3,264,851
Weighted Average Exercise Price, Beginning balance	$ 3.87
Weighted Average Exercise Price, Granted	0.76
Weighted Average Exercise Price, Exercised	0
Weighted Average Exercise Price,Canceled	6.59
Weighted Average Exercise Price, Forfeited	2.54
Weighted Average Exercise Price, Ending balance	2.39	$ 3.87
Weighted Average Exercise Price, Options exercisable	3.28	5.56
Weighted Average Exercise Price, Options vested and expected to vest	$ 2.41	$ 3.89
Weighted-Average Remaining Contractual Term, Outstanding	8 years 1 month 6 days	7 years 4 months 24 days
Weighted Average Remaining Contractual Term, Options exercisable	7 years 7 months 6 days	5 years 2 months 12 days
Weighted Average Remaining Contractual Term, Options vested and expected to vest	8 years 1 month 6 days	7 years 4 months 24 days
Aggregate Intrinsic Value	$ 622
Aggregate Intrinsic Value, Options exercisable	197
Aggregate Intrinsic Value, Options vested and expected to vest	$ 606

Stock-Based Awards - Summary _2

Stock-Based Awards - Summary of Restricted Stock Unit Activity (Detail) - 2017 Stock Incentive Plan [Member] - Restricted Stock Units [Member]	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Units
Beginning balance | shares	50,000
Vested | shares	(50,000)
Weighted-Average Grant Date per Unit
Beginning balance | $ / shares	$ 1.75
Vested | $ / shares	$ 1.75

Stock-Based Awards - Summary _3

Stock-Based Awards - Summary of Stock Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,893	$ 2,116
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	572	524
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,321	$ 1,592

Net Loss per Share - Basic and

Net Loss per Share - Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Net loss	$ (4,930)	$ (5,023)	$ (4,390)	$ (6,814)	$ (7,236)	$ (7,749)	$ (7,172)	$ (7,212)	$ (21,157)	$ (29,369)
Denominator:
Weighted average common shares outstanding—basic and diluted	40,997,759	39,321,177	31,221,139	27,810,358	27,810,358	27,810,358	27,526,065	14,816,253	34,866,690	24,535,454
Net loss per share attributable to common stockholders—basic and diluted	$ (0.12)	$ (0.13)	$ (0.14)	$ (0.24)	$ (0.26)	$ (0.28)	$ (0.26)	$ (0.49)	$ (0.61)	$ (1.20)

Net Loss per Share - Summary of

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, 2020	Dec. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential common shares excluded from calculation of diluted net loss per share	17,600,909	16,306,029
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	4,665,586	3,320,706
Restricted Stock Units 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		50,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	Nov. 11, 2020USD ($)	Apr. 04, 2018USD ($)ft²$ / ft²	Feb. 28, 2010USD ($)	Dec. 31, 2020USD ($)Milestone	Dec. 31, 2019USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2020USD ($)	Jan. 01, 2019USD ($)	Dec. 31, 2006USD ($)
Other Commitments [Line Items]
Operating lease, right-of-use asset					$ 6,060,000	$ 6,060,000
ASU No. 2016-02 [Member]
Other Commitments [Line Items]
Operating lease, right-of-use asset								$ 6,697,000
Operating lease, liability								$ 5,401,000
Harvard and Dana-Farber Agreement [Member]
Other Commitments [Line Items]
Milestone payments				$ 0	0
Milestones achieved | Milestone				0
Additional liabilities for milestone payments				$ 0			$ 0
Non-refundable cash payment						$ 4,718,000	4,863,000
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 and Maintenance [Member]
Other Commitments [Line Items]
Annual license maintenance fees			$ 145,000
Harvard and Dana-Farber Agreement [Member] | License [Member]
Other Commitments [Line Items]
Annual license maintenance fees				145,000	145,000
Umicore Agreement [Member]
Other Commitments [Line Items]
Aggregate milestones payments									$ 6,400,000
Milestone payments				$ 0	0
Milestones achieved | Milestone				0
Additional liabilities for milestone payments				$ 0			$ 0
Umicore Agreement [Member] | License and Maintenance [Member]
Other Commitments [Line Items]
Annual license maintenance fees				50,000
Umicore Agreement [Member] | License [Member]
Other Commitments [Line Items]
Annual license maintenance fees				$ 50,000	$ 50,000
Watertown, Massachusetts [Member] | 490 Arsenal Way [Member]
Other Commitments [Line Items]
Charge of derecognition of assets and liabilities	$ 823,000
Watertown, Massachusetts [Member] | Operating Lease Agreements [Member] | 490 Arsenal Way [Member] | Building [Member]
Other Commitments [Line Items]
Area of land | ft²		18,768
Operating lease price per square foot per year | $ / ft²		52.55
Base rent per year		$ 986,000
Security deposit		568,000
Cost of construction and tenant improvements		$ 2,419,000
Period of contract				Aug. 21, 2018
Period of contract end date				Nov. 11, 2020
Lease initial term				8 years			8 years

Commitments and Contingencies_2

Commitments and Contingencies - Summary of Lease Costs Recognized Under ASC 842 and Other Information Pertaining to Operating Leases (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Lease cost
Operating lease cost	$ 1,095	[1]
Total lease cost	1,095	[1]
Other Information
Cash paid for amounts included in the measurement of lease liabilities	$ 884
Weighted average remaining lease term (in years)	0 years
[1]	Short-term lease costs and variable lease costs incurred by the Company for the twelve months ended December 31, 2020 were not material.

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	Mar. 27, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Provision for income taxes		$ 0	$ 0	$ 0
Research and development tax credit carryforwards		4,979,000	4,449,000
Uncertain tax position		0
Unrecognized tax benefits		0	0
Accrued interest or tax penalties		0	$ 0
Federal [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards		203,505,000
Tax operating loss carryforwards		129,596,000
Indefinitely operating loss carryforwards		$ 73,909,000
Net operating loss carryforwards, begin to expire		2029
Research and development tax credit carryforwards		$ 2,630,000
Research and development tax credit carryforwards, begin to expire		2025
Orphan drug tax credit carryforwards		$ 954,000
Orphan drug tax credit carryforwards, begin to expire		2039
State [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards		$ 197,672,000
Net operating loss carryforwards, begin to expire		2030
Research and development tax credit carryforwards		$ 1,766,000
Research and development tax credit carryforwards, begin to expire		2025
COVID 19 [Member]
Income Tax Disclosure [Line Items]
Percentage of limitation on deduction for net operating losses	80.00%
Net operating losses carryback term	5 years
Adjustable taxable income, deductible net interest expense percentage	50.00%
Corporate charitable deduction limit percentage	25.00%
Bonus depreciation percentage	100.00%
Cost recovery term	15 years

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of U.S. Federal Statutory Income Tax Rate to Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	(21.00%)	(21.00%)
State taxes, net of federal benefit	(5.90%)	(5.00%)
Research and development tax credits	(2.60%)	(3.00%)
Other permanent items	0.60%	0.60%
Change in deferred tax asset valuation allowance	28.90%	28.40%

Income Taxes - Schedule of Net

Income Taxes - Schedule of Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 55,229	$ 50,240
Research and development tax credit carryforwards	4,979	4,449
Capitalized research and development expenses	57	63
Accrued expenses and reserves	265	312
Depreciation and amortization	462	435
Lease Liability		1,368
Stock compensation	940	605
Total deferred tax assets	61,932	57,472
Valuation allowance	$ (61,932)	(55,825)	$ (47,399)
Net deferred tax assets		1,647
Deferred Tax Liabilities:
Right of Use Asset		(1,647)
Total Deferred Tax Liabilities		$ (1,647)

Income Taxes - Schedule of Chan

Income Taxes - Schedule of Changes in Valuation Allowance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Valuation allowance at beginning of year	$ (55,825)	$ (47,399)
Increases recorded to income tax provision	(6,107)	(8,426)
Valuation allowance at end of year	$ (61,932)	$ (55,825)

401(k) Plan - Additional Inform

401(k) Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Compensation And Retirement Disclosure [Abstract]
Employer contributions for the year	$ 0	$ 0
Defined Contribution Plan, Sponsor Location [Extensible List]	country:US
Defined Contribution Plan, Tax Status [Extensible List]	us-gaap:QualifiedPlanMember

Selected Quarterly Financial _3

Selected Quarterly Financial Data (Unaudited) - Schedule of Selected Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Revenue									$ 0	$ 0
Operating expenses:
Research and development	$ 1,925	$ 2,684	$ 2,488	$ 4,069	$ 4,709	$ 4,475	$ 4,305	$ 4,174	11,166	17,663
General and administrative	2,267	2,344	1,912	2,807	2,639	3,440	3,075	3,139	9,330	12,293
Total operating expenses	4,192	5,028	4,400	6,876	7,348	7,915	7,380	7,313	20,496	29,956
Loss from operations	(4,192)	(5,028)	(4,400)	(6,876)	(7,348)	(7,915)	(7,380)	(7,313)	(20,496)	(29,956)
Other income (expense), net	(738)	5	10	62	112	166	208	101	(661)	587
Net loss	$ (4,930)	$ (5,023)	$ (4,390)	$ (6,814)	$ (7,236)	$ (7,749)	$ (7,172)	$ (7,212)	$ (21,157)	$ (29,369)
Net loss per share—basic and diluted	$ (0.12)	$ (0.13)	$ (0.14)	$ (0.24)	$ (0.26)	$ (0.28)	$ (0.26)	$ (0.49)	$ (0.61)	$ (1.20)
Weighted average common shares outstanding—basic and diluted	40,997,759	39,321,177	31,221,139	27,810,358	27,810,358	27,810,358	27,526,065	14,816,253	34,866,690	24,535,454
Comprehensive loss:
Net loss	$ (4,930)	$ (5,023)	$ (4,390)	$ (6,814)	$ (7,236)	$ (7,749)	$ (7,172)	$ (7,212)	$ (21,157)	$ (29,369)
Other comprehensive gain (loss):
Unrealized gain (loss) on investments, net of tax of $0	(1)	1	(1)	(8)	(10)	(7)	24	5	(9)	12
Total other comprehensive gain (loss)	(1)	1	(1)	(8)	(10)	(7)	24	5	(9)	12
Total comprehensive loss	$ (4,931)	$ (5,022)	$ (4,391)	$ (6,822)	$ (7,246)	$ (7,756)	$ (7,148)	$ (7,207)	$ (21,166)	$ (29,357)

Selected Quarterly Financial _4

Selected Quarterly Financial Data (Unaudited) - Schedule of Selected Quarterly Financial Information (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Unrealized gain (loss) on investments, tax	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0

Subsequent Event - Additional I

Subsequent Event - Additional Information (Detail) - USD ($)	Jan. 29, 2021	Jan. 08, 2021	Jan. 06, 2021	Jan. 01, 2021	Jan. 28, 2021	Mar. 24, 2021	Mar. 24, 2021	Dec. 31, 2020	Dec. 31, 2019	Jul. 04, 2017
Subsequent Event [Line Items]
Common stock, par value								$ 0.001	$ 0.001	$ 0.001
Stock issued during period, value								$ 16,897,000
Common Stock [Member]
Subsequent Event [Line Items]
Stock issued during period, value								$ 16,000
Subsequent Event [Member] | Direct Public Offering [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Net proceeds from common stock shares issued and sold		$ 33,091,000
Subsequent Event [Member] | 2021 Purchase Agreement [Member] | Direct Public Offering [Member]
Subsequent Event [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			$ 35,894,000,000
Subsequent Event [Member] | 2021 Purchase Agreement [Member] | Direct Public Offering [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Purchase price per share			$ 1.10
Offering closed date			Jan. 8, 2021
Subsequent Event [Member] | ATM Sales Agreement [Member]
Subsequent Event [Line Items]
Aggregate number of common stock shares issued and sold						5,225,406
Net proceeds from common stock shares issued and sold						$ 10,594,000
Subsequent Event [Member] | ATM Sales Agreement [Member] | JonesTrading [Member]
Subsequent Event [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
Subsequent Event [Member] | ATM Sales Agreement [Member] | Jones Trading Institutional Services LLC and William Blair & Company, LLC [Member] | Maximum [Member]
Subsequent Event [Line Items]
Stock issued during period, value	$ 30,000,000
Subsequent Event [Member] | Purchase Agreement [Member] | LPC [Member]
Subsequent Event [Line Items]
Aggregate number of common stock shares issued and sold							1,375,000
Gross proceeds from common stock shares issued and sold							$ 2,614,000
Subsequent Event [Member] | Purchase Agreement [Member] | LPC [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Net proceeds from common stock shares issued and sold				$ 2,614,000