Sierra Oncology (SRRA) 10-Q 7 May 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2021	May 03, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Registrant Name	Sierra Oncology, Inc.
Entity Central Index Key	0001290149
Trading Symbol	SRRA
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	true
Entity Common Stock, Shares Outstanding		12,349,961
Entity Interactive Data Current	Yes
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common Stock, $0.001 par value
Entity File Number	001-37490
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-0138994
Entity Address, Address Line One	1820 Gateway Drive, Suite 110
Entity Address, City or Town	San Mateo
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94404
City Area Code	650
Local Phone Number	376-8679
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
CURRENT ASSETS:
Cash and cash equivalents	$ 107,658	$ 104,055
Prepaid expenses and other current assets	2,010	2,415
Total current assets	109,668	106,470
Property and equipment, net	42	52
Operating lease right-of-use asset	281	318
Other assets	572	647
TOTAL ASSETS	110,563	107,487
CURRENT LIABILITIES:
Accrued and other liabilities	6,364	7,148
Accounts payable	2,522	2,205
Total current liabilities	8,886	9,353
Operating lease liability	122	175
TOTAL LIABILITIES	9,008	9,528
Commitments and Contingencies (Note 7)
STOCKHOLDERS’ EQUITY:
Preferred stock, $0.001 par value; 10,000,000 shares authorized as of March 31, 2021 and December 31, 2020; nil shares issued and outstanding as of March 31, 2021 and December 31, 2020
Common stock, $0.001 par value; 500,000,000 shares authorized as of March 31, 2021 and December 31, 2020; 12,349,961 and 11,128,484 shares issued and outstanding as of March 31, 2021 and December 31, 2020	12	11
Additional paid-in capital	968,047	944,537
Accumulated deficit	(866,504)	(846,589)
TOTAL STOCKHOLDERS’ EQUITY	101,555	97,959
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 110,563	$ 107,487

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2021	Dec. 31, 2020
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	12,349,961	11,128,484
Common stock, shares outstanding	12,349,961	11,128,484
Series A Convertible Preferred Stock [Member]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating expenses:
Research and development	$ 13,953	$ 11,591
General and administrative	5,865	4,544
Total operating expenses	19,818	16,135
Loss from operations	(19,818)	(16,135)
Other income (expense), net:
Changes in fair value of warrant liabilities		(16,240)
Other income (expense), net	(29)	541
Total other income (expense), net	(29)	(15,699)
Loss before provision for income taxes, net	(19,847)	(31,834)
Provision for income taxes, net	68	78
Net loss and comprehensive loss	$ (19,915)	$ (31,912)
Net loss per common share, basic and diluted	$ (1.71)	$ (3.14)
Weighted-average shares used in computing net loss per common share, basic and diluted	11,667,967	10,156,628

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Series A Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]
Stockholders Equity, Beginning Balance at Dec. 31, 2019	$ 86,345	$ 1	$ 74	$ 851,957	$ (765,687)
Stockholders Equity, Beginning Balance, Shares at Dec. 31, 2019		103,000	1,867,176
Conversion of Series A convertible voting preferred stock to common stock		$ (1)	$ 8	(7)
Conversion of Series A convertible voting preferred stock to common stock, Shares		(103,000)	7,803,273
Reclassification of warrant liabilities to equity	62,175			62,175
Issuance of common stock in connection with an amendment to the asset purchase agreement	8,782		$ 1	8,781
Number of shares issued in connection with an amendment to asset purchase agreement			725,283
Issuance of warrant in connection with anamendment to the asset purchase agreement	3,188			3,188
Stock-based compensation	918			918
Reverse stock split adjustment			$ (73)	73
Net loss	(31,912)				(31,912)
Stockholders Equity, Ending Balance at Mar. 31, 2020	129,496		$ 10	927,085	(797,599)
Stockholders Equity, Ending Balance, Shares at Mar. 31, 2020			10,395,732
Stockholders Equity, Beginning Balance at Dec. 31, 2020	97,959		$ 11	944,537	(846,589)
Stockholders Equity, Beginning Balance, Shares at Dec. 31, 2020			11,128,484
Issuance of common stock	19,632		$ 1	19,631
Issuance of common stock, Shares			1,149,820
Issuance of common stock for exercise of common stock warrants	660			660
Issuance of common stock for exercise of common stock warrant, Shares			49,995
Issuance of common stock for exercise of common stock options	288			288
Issuance of common stock for exercise of stock options, Shares			21,662
Stock-based compensation	2,931			2,931
Net loss	(19,915)				(19,915)
Stockholders Equity, Ending Balance at Mar. 31, 2021	$ 101,555		$ 12	$ 968,047	$ (866,504)
Stockholders Equity, Ending Balance, Shares at Mar. 31, 2021			12,349,961

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (19,915)	$ (31,912)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	2,931	918
Depreciation and amortization	47	55
Changes in fair value of warrant liabilities		16,240
Securities issuance obligation		1,485
Other	(11)	2
Changes in operating assets and liabilities:
Prepaid expenses and other assets	406	429
Accrued, other and operating lease liabilities	(736)	(1,522)
Accounts payable	317	357
Net cash used in operating activities	(16,961)	(13,948)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock from At-The-Market equity offering, net of offering costs	19,632
Proceeds from exercise of common stock warrants	660
Proceeds from exercise of common stock options	288
Net cash provided by financing activities	20,580
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash	(16)	(46)
NET INCREASE (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	3,603	(13,994)
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — Beginning of period	104,355	147,828
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — End of period	107,958	133,834
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for income taxes, net	13	14
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Unpaid deferred financing costs in accounts payable and accrued and other liabilities	$ 110	45
Issuance of common stock and common stock warrant in connection with an amendment to the asset purchase agreement		11,970
Reclassification of warrant liabilities to equity		62,175
Unpaid property and equipment in accrued and other liabilities		$ 12

The Company and Basis of Presen

The Company and Basis of Presentation	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
The Company and Basis of Presentation	1. Organization and Description of Business Sierra Oncology, Inc. (together with its subsidiaries, collectively referred to as the “Company”), a Delaware corporation, is a late stage biopharmaceutical company focused on the Phase 3 execution, registration and potential commercialization of momelotinib, a novel drug that may address serious unmet needs in myelofibrosis. Momelotinib is a selective and orally-bioavailable JAK1 (Janus kinase 1), JAK2 (Janus kinase 2) and ACVR1 (Activin A receptor type 1) / activin receptor-like kinase-2 (ALK2) inhibitor with a differentiated mechanism of action that enables it to potentially address all three key drivers of myelofibrosis: anemia of inflammation, constitutional symptoms and enlarged spleen. More than 1,200 subjects have received momelotinib since clinical studies began in 2009, including more than 800 patients treated for myelofibrosis. Several of these patients remain on treatment for more than 10 years. The Company’s portfolio also includes SRA737, a selective, orally bioavailable small molecule inhibitor of Checkpoint kinase 1 (Chk1), an emerging target for the treatment of cancer which has a key role in the DNA Damage Response (DDR). The Company is currently focusing its resources on the development of momelotinib and exploring options to support any future continued development of SRA737. The Company’s primary activities since inception have been conducting research and development activities, conducting preclinical and clinical testing, recruiting personnel, performing business and financial planning, identifying and evaluating additional drug candidates for potential in-licensing or acquisition, and raising capital to support development activities. The Company has not generated any product revenue related to its primary business purpose to date, nor has it generated any net income, and is subject to a number of risks and uncertainties, which include dependence on key individuals, the need to identify and successfully develop commercially viable products, the need to obtain regulatory approval for its products and commercialize them, and the need to obtain adequate additional financing to fund the development of momelotinib. As of March 31, 2021, the Company had $107.7 million of cash and cash equivalents. The Company believes that its balance of cash and cash equivalents as of the date of the issuance of these condensed consolidated financial statements is sufficient to fund its current operational plan for at least the next twelve months, though it may pursue raising additional capital through equity financings or other arrangements.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) and applicable rules and regulations of the Securities and Exchange Commission regarding interim financial reporting. Accordingly, they do not include all the information and notes required for complete financial statements and should be read in conjunction with the Company’s audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on March 11, 2021. There were no significant changes to the accounting policies during the three months ended March 31, 2021 from the significant accounting policies described in Note 2 to the consolidated financial statements in the 2020 Form 10-K. The unaudited condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. These unaudited condensed consolidated financial statements and related disclosure have been prepared on the same basis as the annual consolidated financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair presentation of the Company’s condensed consolidated financial statements included in this report. The condensed consolidated results of operations for the three months ended March 31, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021, or for any other future annual or interim period. The condensed consolidated balance sheet as of December 31, 2020 included herein was derived from the audited consolidated financial statements as of that date. Use of Estimates The preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of expense during the reporting period. Significant estimates and assumptions made in the accompanying condensed consolidated financial statements include, but are not limited to the fair value of stock options and the warrant issued, the fair value of the securities issuance obligation, the probability of achieving performance-based milestones of stock options, accruals such as research and development costs, and recoverability of the Company’s net deferred tax assets and related valuation allowance. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates.

Net Loss Per Share

Net Loss Per Share	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	3. Basic net loss per share is calculated by dividing net loss by the weighted-average number of common stock outstanding during the period without consideration for common stock equivalents. Diluted net loss per share is computed by dividing net loss by the weighted-average number of common stock equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, stock options and warrants for common stock are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. The following shares of common stock equivalents were excluded from the calculation of diluted net loss per share for the periods presented because including them would have been antidilutive: March 31, 2021 March 31, 2020 Series A warrants for common stock 7,802,241 7,802,241 Series B warrants for common stock 2,524,732 2,574,727 Options to purchase common stock 4,667,173 1,738,827 Warrants for common stock 727,122 727,122 Total potential dilutive shares 15,721,268 12,842,917

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. The Company measures and reports its cash equivalents and restricted cash at fair value. The following table sets forth the fair value of the Company’s financial assets measured on a recurring basis by level within the fair value hierarchy: March 31, 2021 Level 1 Level 2 Level 3 Total (in thousands) Financial Assets Money market funds $ 106,126 $ — $ — $ 106,126 Restricted money market funds 300 — — 300 Total financial assets $ 106,426 $ — $ — $ 106,426 December 31, 2020 Level 1 Level 2 Level 3 Total (in thousands) Financial Assets Money market funds $ 101,919 $ — $ — $ 101,919 Restricted money market funds 300 — — 300 Total financial assets $ 102,219 $ — $ — $ 102,219 Money market funds and restricted money market funds are measured at fair value on a recurring basis using quoted prices and are classified as a Level 1 input. The Company’s cash and cash equivalents, restricted cash, other current assets, accounts payable and accrued and other liabilities approximate their fair values due to their short duration. There were no transfers between Levels 1, 2 or 3 during the three months ended March 31, 2021. Prior to reclassification to equity in January 2020, the Company’s warrant liabilities and securities issuance obligation contained unobservable inputs that reflected the Company’s own assumptions in which there was little, if any, market activity at the measurement dates. Accordingly, t were measured at fair value on a recurring basis using unobservable inputs a At January 22, 2020, Warrant A and Warrant B were no longer considered to be derivative instruments. The Company remeasured the fair value of the warrant liabilities at the time of reclassification to equity using the following assumptions: Series A Warrant Series B Warrant Expected term (in years) 5.0 2.1 Expected volatility 43 % 88 % Risk-free interest rate 1.57 % 1.53 % Expected dividend yield — % — % The Company recorded a $16.2 million non-cash expense relating to the change in fair value of warrant liabilities in other income (expense), net in the accompanying condensed consolidated statement of operations for the three months ended March 31, 2020. At January 31, 2020, the securities issuance obligation was settled by the issuance of common stock and a common stock warrant. The fair value of the common stock issuance obligation was remeasured based on the value of the common stock at the time of issuance. The fair value of the warrant issuance obligation was remeasured using the following assumptions: Warrant Issuance Obligation Expected term (in years) 5.0 Expected volatility 43 % Risk-free interest rate 1.57 % Expected dividend yield — % The Company recognized a $1.5 million non-cash research and development expense during the three months ended March 31, 2020, representing changes in fair value of the securities issuance obligation since December 31, 2019, in the condensed consolidated statement of operations.

Balance Sheet Components

Balance Sheet Components	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheet Components	5. Cash and Cash Equivalents Cash and cash equivalents consist of the following: March 31, 2021 December 31, 2020 (in thousands) Cash $ 1,532 $ 2,136 Cash equivalents: Money market accounts 106,126 101,919 Total cash and cash equivalents $ 107,658 $ 104,055 The following table provides a reconciliation of cash, cash equivalents and restricted cash reported in the condensed consolidated balance sheets to the amounts shown in the condensed consolidated statements of cash flows. March 31, 2021 March 31, 2020 (in thousands) Cash and cash equivalents $ 107,658 $ 133,534 Restricted cash included in other assets 300 300 Total cash, cash equivalents and restricted cash shown in the condensed consolidated statement of cash flows $ 107,958 $ 133,834 Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consist of the following: March 31, 2021 December 31, 2020 (in thousands) Prepaid insurance $ 572 $ 991 Prepaid software and subscription fees 362 376 Other receivables 214 311 Prepaid research and development project costs 186 321 Other 676 416 Total prepaid expenses and other current assets $ 2,010 $ 2,415 Property and Equipment, net Property and equipment, net consists of the following: March 31, 2021 December 31, 2020 (in thousands) Software $ 361 $ 361 Property and equipment, gross 361 361 Less: accumulated depreciation (319 ) (309 ) Total property and equipment, net $ 42 $ 52 Depreciation related to the Company’s property and equipment was $10,000 for the three months ended March 31, 2021 and $13,000 for the three months ended March 31, 2020. Accrued and Other Liabilities Accrued and other liabilities consist of the following: March 31, 2021 December 31, 2020 (in thousands) Accrued research and development costs $ 2,637 $ 1,715 Accrued employee related costs 1,917 4,359 Accrued professional fees 1,485 774 Operating lease liability 214 207 Other 111 93 Total accrued and other liabilities $ 6,364 $ 7,148

Leases

Leases	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Leases	6. The Company has an operating lease agreement to lease the office space in Vancouver, Canada that expires on February 28, 2023. In December 2020, the Company entered into an agreement to sublet the entire office premises to a third party until February 27, 2023. Pursuant to the sublease agreement, the subtenant will pay base rent of $0.2 million per annum to the Company and all operating costs related to the office space. The components of lease expense, which are recorded in general and administrative expense, and related cash flows for the three months ended March 31, 2021 and 2020 were as follows: Three Months Ended March 31, 2021 2020 (in thousands) Operating lease cost $ 43 $ 51 Short-term lease cost 7 22 50 73 Operating cash flows used for operating leases $ 57 $ 52 As of March 31, 2021, the weighted average remaining lease term and discount rate for the operating lease are 1.9 years and 6.5%, respectively. As of March 31, 2021, maturities of lease liability due under the lease agreement are as follows: Years Ending December 31: Operating Leases (in thousands) Remainder of 2021 $ 171 2022 183 Total lease payments 354 Less imputed interest (18 ) Total $ 336 These amounts have not been reduced by future base rent due under sublease of $0.4 million. In addition to base rent, the lease requires payment of operating costs. These costs are not included in the table above or the sublease amount. In December 2020, the Company entered into a 48-month operating lease agreement to lease office space in San Mateo, California. The lease has not commenced as of March 31, 2021. The Company’s obligation under this office lease is $0.1 million for 2021, $0.2 million for each of 2022, 2023 and 2024, and $0.1 million for 2025.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	7 . Asset Purchase Agreement In August 2018, the Company entered into an Asset Purchase Agreement with Gilead whereby the Company acquired worldwide rights to the pharmaceutical product, momelotinib, an investigational orally-bioavailable JAK1, JAK2 and ACVR1/ALK2 inhibitor together with all related intellectual property rights and certain other related assets. Pursuant to the agreement, the Company made a one-time upfront payment of $3.0 million in August 2018. In October 2019, the Company entered into an amendment to the Asset Purchase Agreement in which the Company agreed to issue, subject to certain conditions, shares of common stock and a warrant to purchase common stock to Gilead in consideration for meaningfully reduced royalty rates and elimination of a near term milestone payment in the Asset Purchase Agreement. Pursuant to the amended agreement, milestone payments of up to an aggregate of $190.0 million may become payable to Gilead upon the achievement of certain regulatory and commercial milestone events and the Company is now required to pay Gilead low double-digit to high-teens percent tiered combined royalties based upon net sales. License Agreements In September 2016, the Company entered into an exclusive license agreement with CRT Pioneer Fund LP (CPF) for worldwide rights, know-how and materials to develop SRA737, a small molecule inhibitor targeting Chk1, a promising therapeutic target to treat cancer. Pursuant to the agreement, the Company made a one-time upfront payment of $7.0 million to CPF in October 2016 and paid $2.0 million to CPF in January 2017 for the successful transfer of two ongoing Phase 1 clinical trials. Pursuant to the original license agreement, additional milestone payments of up to an aggregate of $319.5 million may have become payable to CPF upon the achievement of certain milestones. In November 2020, the Company entered into an amendment to the license agreement with CPF, which amended the terms and reduced the amounts of certain future milestone payments. Pursuant to the amended agreement, future milestone payments of up to an aggregate of $290.0 million may become payable to CPF upon the achievement of certain developmental, regulatory and commercial milestones, including a milestone payment of $2.0 million upon the dosing of the first patient of the first trial of SRA737 following the effective date of the amendment. These milestones will be accrued once they are considered probable of occurring. In addition, the Company is required to pay CPF, on a product-by-product and country-by-country basis, tiered high single-digit to low double-digit royalties on the net sales of any product successfully developed. In May 2016, the Company entered into an exclusive license agreement (Carna License Agreement) with Carna Biosciences, Inc. (Carna) for worldwide rights to develop and commercialize SRA141, a small molecule kinase inhibitor targeting Cdc7. In exchange for this exclusive right, the Company paid Carna an upfront payment of $0.9 million in June 2016. In June 2020, the Company entered into a collaboration agreement (Carna Collaboration Agreement) with Carna effectively terminating the Carna License Agreement. Pursuant to the Carna Collaboration Agreement, Carna paid an upfront fee of $0.3 million, which was recognized as collaboration revenue during the year ended December 31, 2020, for the exclusive worldwide rights for SRA141 and other transition services. In addition, the Company will be entitled to single-digit royalties on product sales, on a product-by-product basis, and low to mid-teen profit share on royalty and non-royalty income. Legal From time to time, the Company may become subject to other legal proceedings, claims and litigation arising in the ordinary course of business. In addition, the Company may receive letters alleging infringement of patent or other intellectual property rights. The Company is not currently a party to any other material legal proceedings, nor is it aware of any pending or threatened litigation that, in the Company’s opinion, would have a material adverse effect on the business, operating results, cash flows or financial condition should such litigation be resolved unfavorably. COVID-19 The full extent of the impact of the COVID-19 pandemic on financial markets, economies worldwide and our business is highly uncertain. Research and development expenses and general and administrative expenses may vary significantly if there is an increased impact from COVID-19 on the costs and timing associated with the conduct of clinical trials and other related business activities. The Company is carefully monitoring the pandemic and the potential length and depth of the resulting economic impact on its financial condition and results of operations. As of March 31, 2021, the Company was not aware of any contingencies and no related estimates were recorded on its financial statements as a result of COVID-19.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Stockholders' Equity	8 . At-The-Market Common Stock Offering In August 2020, the Company filed a prospectus supplement, pursuant to which it sold $20.0 million of its common stock in At-The-Market (ATM) offerings. In February 2021, the Company filed a prospectus supplement pursuant to which it can issue and sell an aggregate of up to an additional $30.0 million of its common stock from time to time in ATM offerings. During the three months ended March 31, 2021, the Company sold 1,149,820 shares under the ATM program for net proceeds of $19.6 million, net of commissions and offering expenses. There were no ATM sales during the three months ended March 31, 2020. On May 7, 2021, the Company filed a prospectus supplement, pursuant to which it can issue and sell an aggregate of up to an additional $50.0 million of its common stock from time to time in the ATM offerings. Common Stock Reserved for Issuance The Company is required to reserve and keep available out of its authorized but unissued shares of common stock a number of shares sufficient to effect the conversion of all outstanding options granted and available for grant under the incentive plans, shares reserved for issuance under the employee stock purchase plan and issued warrants. March 31, 2021 December 31, 2020 Shares reserved under Series A warrant 7,802,241 7,802,241 Shares reserved under Series B warrant 2,524,732 2,574,727 Shares reserved for future option grants under equity plans 1,521,028 1,117,796 Outstanding stock options under equity incentive plans 4,667,173 4,146,928 Outstanding warrants 727,122 727,122 Shares reserved under the 2015 employee stock purchase plan 17,500 17,500 Total common stock reserved for issuance 17,259,796 16,386,314 Preferred Stock On November 13, 2019, the Company completed an underwritten public offering whereby it issued 103,000 shares of Series A Convertible Voting Preferred Stock together with Series A warrants and Series B warrants for a combined purchase price of $1,000. The aggregate proceeds received by the Company was $97.7 million, net of underwriting discounts and commissions and offering expenses. Each share of Series A Preferred Stock was convertible into shares of the Company’s common stock equal to the stated value of the Series A Preferred Stock of $1,000 divided by the voting conversion price of $13.20. On January 29, 2020, all shares of Series A Preferred Stock converted into 7,803,273 shares of the Company’s common stock. Common Stock Warrants In connection with the Company’s November 2019 public offering of the Series A Preferred Stock, the Company issued Series A warrants to purchase up to 7,802,241 shares of common stock at an exercise price equal to $13.20, and Series B warrants to purchase up to 2,574,727 shares of common stock at an exercise price equal to $13.20. Both Series A and Series B warrants are exercisable following stockholder approval in January 2020 of an increase in authorized common stock sufficient to allow for the exercise of the warrants, subject to certain beneficial ownership limitations. The Series A warrants will expire five years from the date they first became exercisable or on January 22, 2025 and contain a cash and/or cashless exercise provision. The Series B warrants will expire on the 75 th In connection with obligations under the amendment to the Asset Purchase Agreement (See Note 7), the Company issued to Gilead 725,283 shares of the Company’s common stock and a warrant to purchase 725,283 shares of common stock at a price per share of $13.20 on January 31, 2020. The warrant is immediately exercisable, will expire on January 31, 2025 and contains a cash and/or cashless exercise provision. In August 2018, in connection with a Loan and Security Agreement (Loan Agreement) with Silicon Valley Bank (SVB), the Company issued a warrant to SVB to purchase 1,839 of the Company’s common stock at a price per share of $74.80. The warrant is immediately exercisable, will expire on August 21, 2028 and contains a cashless exercise provision.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	9 . In the accompanying condensed consolidated statements of operations, the Company recognized stock-based compensation expense for its employees and non-employees as follows: Three Months Ended March 31, 2021 2020 (in thousands) Research and development $ 1,663 $ 546 General and administrative 1,268 372 Total stock-based compensation $ 2,931 $ 918 Determination of Fair Value The fair values of the Company’s stock-based awards granted during the three months ended March 31, 2021 and 2020 were estimated as of the grant date using the Black-Scholes option pricing model, based on assumptions as follows: Three Months Ended March 31, 2021 2020 Expected term (in years) 5.5 – 7.0 5.7 – 6.7 Expected volatility 84 – 85 % 88 – 90 % Risk-free interest rate 0.5 – 1.1 % 0.6 – 1.2 % Expected dividend rate — % — % The fair value of each stock option grant was determined by the Company on the date of grant using the methods and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment and estimation by management. Expected Term— The expected term represents the period that stock-based awards are expected to be outstanding. As the Company’s historical share option exercise is limited due to a lack of sufficient data points, and does not provide a reasonable basis upon which to estimate an expected term, the expected term is derived by using the midpoint between the weighted-average vesting term and the contractual expiration period of the stock-based award. Expected Volatility— For the three months ended March 31, 2021, the expected volatility is derived from using the Company’s trading history for its common stock over a period equivalent to the expected term of the stock-based awards. For the three months ended March 31, 2020, the expected volatility was derived from a weighted volatility using both the Company’s trading history for its common stock and the historical stock volatilities of peer public companies within its industry that are considered to be comparable to the Company’s business over a period equivalent to the expected term of the stock-based awards. Risk-Free Interest Rate— The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the date of grant for zero-coupon U.S. Treasury notes with maturities approximately equal to the stock-based awards’ expected term. Expected Dividend Rate— The expected dividend is zero as the Company has not paid nor anticipate paying any dividends on its common stock in the foreseeable future. Forfeiture Rate— The Company accounts for forfeitures when they occur. Equity Incentive Plans 2018 Equity Inducement Plan In September 2018, the Company’s Compensation Committee approved the 2018 Equity Inducement Plan (2018 Plan). The number of shares available for awards under the 2018 Plan was set to 37,500. On June 30, 2020, the Company’s Board of Directors approved an amendment to the 2018 Plan to increase the authorized number of shares available for issuance by 500,000 shares. On February 3, 2021, the Company’s Compensation Committee approved an amendment to the 2018 Plan to increase the authorized number of shares available for issuance by 500,000. 2015 Plan The 2015 Equity Incentive Plan (2015 Plan) became effective on July 14, 2015. On January 21, 2020 the Company’s stockholders approved the following amendments to the 2015 Plan: (i) increase to the authorized number of shares available for issuance by 4,312,500 shares and proportionately increase the share limit related to incentive stock options, (ii) provide limits on the total value of compensation that may be granted to any non-employee director in each calendar year, and (iii) eliminate the annual individual grant limit to reflect changes to the tax law in 2017 tax legislation. As of March 31, 2021, 5,123,736 shares were reserved for issuance under the 2015 Plan. The number of shares reserved for issuance under the 2015 Plan will increase automatically on January 1 of each calendar year 2016 through 2025 by the number of shares equal to 4% of the total outstanding shares of the Company’s common stock as of the immediately preceding December 31. The Company’s Board of Directors or Compensation Committee may reduce the amount of the increase in any particular year. The exercise price of each stock-based award issued under the 2015 Plan is required to be no less than the fair value of the Company’s common stock. The vesting and exercise provisions of options or restricted awards granted are determined individually with each grant. Stock options have a 10-year life and expire if not exercised within that period or if not exercised within three months of cessation of employment with the Company or such longer period of time as specified in the option agreement, unless modified. 2008 Plan The Company granted options under the 2008 Stock Plan (2008 Plan) until July 2015 when it was terminated as to future awards, although it continues to govern the terms of options that remain outstanding under the 2008 Plan. The 2008 Plan provided for the granting of Incentive Stock Options (ISO), nonqualified stock options and stock purchase rights. In connection with the Board of Director’s approval of the 2015 Plan, all remaining shares available for future award under the 2008 Plan were transferred to the 2015 Plan, and the 2008 Plan was terminated. A summary of activity under the 2008 Plan, 2015 Plan and 2018 Plan and related information is as follows: Options Outstanding Shares Available for Grant Number of Shares Outstanding Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value of Outstanding Options (in thousands) Outstanding — December 31, 2020 1,117,796 4,146,928 $ 19.45 8.84 $ 12,227 Awards authorized 945,139 Options granted (650,460 ) 650,460 16.52 Options exercised - (21,662 ) 13.28 Options forfeited/cancelled 108,553 (108,553 ) 14.72 Outstanding — March 31, 2021 1,521,028 4,667,173 $ 19.18 8.76 $ 16,794 Exercisable — March 31, 2021 755,413 $ 46.18 5.66 $ 1,905 Vested and expected to vest — March 31, 2021 4,131,935 $ 20.09 8.67 $ 14,075 The weighted-average grant date fair values of options granted during the three months ended March 31, 2021 and 2020 was $11.73 and $9.81 per share, respectively. The aggregate intrinsic value of options exercised was $0.1 million for the three months ended March 31, 2021. No options were exercised for the three months ended March 31, 2020. The total grant date fair values of options vested for the three months ended March 31, 2021 and 2020 was $3.4 million and $1.6 million, respectively. In August 2020, the Company granted executives and employees 1,107,250 stock options with performance-based conditions. Vesting is achieved based upon the completion of pre-determined milestones. As of March 31, 2021, all of the performance-based options remain unvested. For the three months ended March 31, 2021, the Company has recognized approximately $0.8 million in stock-based compensation expense related to the options with performance-based criteria. No expense pertaining to performance-based options was recognized for the three months ended March 31, 2020. As of March 31, 2021, total unrecognized stock-based compensation related to unvested stock options with only service-vesting conditions was $27.7 million and are expected to be recognized over a remaining weighted-average period of 3.2 years. As of March 31, 2021, total unrecognized stock-based compensation related to unvested stock options with performance-based conditions was $7.9 million.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	1 0 . The Company did not record a provision for U.S. federal income taxes for the three months ended March 31, 2021 because it expects to generate a loss for the year ended December 31, 2021. The income tax provision for the three months ended March 31, 2021 represented foreign taxes. The Company’s net U.S. deferred tax assets continue to be offset by a full valuation allowance.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles (GAAP) and applicable rules and regulations of the Securities and Exchange Commission regarding interim financial reporting. Accordingly, they do not include all the information and notes required for complete financial statements and should be read in conjunction with the Company’s audited consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020, filed with the SEC on March 11, 2021. There were no significant changes to the accounting policies during the three months ended March 31, 2021 from the significant accounting policies described in Note 2 to the consolidated financial statements in the 2020 Form 10-K. The unaudited condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated in consolidation. These unaudited condensed consolidated financial statements and related disclosure have been prepared on the same basis as the annual consolidated financial statements and reflect, in the opinion of management, all adjustments of a normal and recurring nature that are necessary for the fair presentation of the Company’s condensed consolidated financial statements included in this report. The condensed consolidated results of operations for the three months ended March 31, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021, or for any other future annual or interim period. The condensed consolidated balance sheet as of December 31, 2020 included herein was derived from the audited consolidated financial statements as of that date.
Use of Estimates	Use of Estimates The preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of expense during the reporting period. Significant estimates and assumptions made in the accompanying condensed consolidated financial statements include, but are not limited to the fair value of stock options and the warrant issued, the fair value of the securities issuance obligation, the probability of achieving performance-based milestones of stock options, accruals such as research and development costs, and recoverability of the Company’s net deferred tax assets and related valuation allowance. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates.

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of Outstanding Shares of Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share	The following shares of common stock equivalents were excluded from the calculation of diluted net loss per share for the periods presented because including them would have been antidilutive: March 31, 2021 March 31, 2020 Series A warrants for common stock 7,802,241 7,802,241 Series B warrants for common stock 2,524,732 2,574,727 Options to purchase common stock 4,667,173 1,738,827 Warrants for common stock 727,122 727,122 Total potential dilutive shares 15,721,268 12,842,917

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of Fair Value Assets And Liabilities Measured On Recurring Basis	The following table sets forth the fair value of the Company’s financial assets measured on a recurring basis by level within the fair value hierarchy: March 31, 2021 Level 1 Level 2 Level 3 Total (in thousands) Financial Assets Money market funds $ 106,126 $ — $ — $ 106,126 Restricted money market funds 300 — — 300 Total financial assets $ 106,426 $ — $ — $ 106,426 December 31, 2020 Level 1 Level 2 Level 3 Total (in thousands) Financial Assets Money market funds $ 101,919 $ — $ — $ 101,919 Restricted money market funds 300 — — 300 Total financial assets $ 102,219 $ — $ — $ 102,219
Schedule of Fair Value Measurement Inputs and Valuation Techniques	At January 22, 2020, Warrant A and Warrant B were no longer considered to be derivative instruments. The Company remeasured the fair value of the warrant liabilities at the time of reclassification to equity using the following assumptions: Series A Warrant Series B Warrant Expected term (in years) 5.0 2.1 Expected volatility 43 % 88 % Risk-free interest rate 1.57 % 1.53 % Expected dividend yield — % — % At January 31, 2020, the securities issuance obligation was settled by the issuance of common stock and a common stock warrant. The fair value of the common stock issuance obligation was remeasured based on the value of the common stock at the time of issuance. The fair value of the warrant issuance obligation was remeasured using the following assumptions: Warrant Issuance Obligation Expected term (in years) 5.0 Expected volatility 43 % Risk-free interest rate 1.57 % Expected dividend yield — %

Balance Sheet Components (Table

Balance Sheet Components (Tables)	3 Months Ended
	Mar. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of Cash and Cash Equivalents	Cash and cash equivalents consist of the following: March 31, 2021 December 31, 2020 (in thousands) Cash $ 1,532 $ 2,136 Cash equivalents: Money market accounts 106,126 101,919 Total cash and cash equivalents $ 107,658 $ 104,055
Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported in the condensed consolidated balance sheets to the amounts shown in the condensed consolidated statements of cash flows. March 31, 2021 March 31, 2020 (in thousands) Cash and cash equivalents $ 107,658 $ 133,534 Restricted cash included in other assets 300 300 Total cash, cash equivalents and restricted cash shown in the condensed consolidated statement of cash flows $ 107,958 $ 133,834
Summary of Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consist of the following: March 31, 2021 December 31, 2020 (in thousands) Prepaid insurance $ 572 $ 991 Prepaid software and subscription fees 362 376 Other receivables 214 311 Prepaid research and development project costs 186 321 Other 676 416 Total prepaid expenses and other current assets $ 2,010 $ 2,415
Summary of Property and Equipment, Net	Property and equipment, net consists of the following: March 31, 2021 December 31, 2020 (in thousands) Software $ 361 $ 361 Property and equipment, gross 361 361 Less: accumulated depreciation (319 ) (309 ) Total property and equipment, net $ 42 $ 52
Schedule of Accrued and Other Liabilities	Accrued and other liabilities consist of the following: March 31, 2021 December 31, 2020 (in thousands) Accrued research and development costs $ 2,637 $ 1,715 Accrued employee related costs 1,917 4,359 Accrued professional fees 1,485 774 Operating lease liability 214 207 Other 111 93 Total accrued and other liabilities $ 6,364 $ 7,148

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Schedule of Components of Lease Expense and Related Cash Flows	The components of lease expense, which are recorded in general and administrative expense, and related cash flows for the three months ended March 31, 2021 and 2020 were as follows: Three Months Ended March 31, 2021 2020 (in thousands) Operating lease cost $ 43 $ 51 Short-term lease cost 7 22 50 73 Operating cash flows used for operating leases $ 57 $ 52
Schedule of Maturities Lease Liabilities under Leases Agreement	As of March 31, 2021, maturities of lease liability due under the lease agreement are as follows: Years Ending December 31: Operating Leases (in thousands) Remainder of 2021 $ 171 2022 183 Total lease payments 354 Less imputed interest (18 ) Total $ 336

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Schedule of Common Stock Reserved for Issuance	The Company is required to reserve and keep available out of its authorized but unissued shares of common stock a number of shares sufficient to effect the conversion of all outstanding options granted and available for grant under the incentive plans, shares reserved for issuance under the employee stock purchase plan and issued warrants. March 31, 2021 December 31, 2020 Shares reserved under Series A warrant 7,802,241 7,802,241 Shares reserved under Series B warrant 2,524,732 2,574,727 Shares reserved for future option grants under equity plans 1,521,028 1,117,796 Outstanding stock options under equity incentive plans 4,667,173 4,146,928 Outstanding warrants 727,122 727,122 Shares reserved under the 2015 employee stock purchase plan 17,500 17,500 Total common stock reserved for issuance 17,259,796 16,386,314

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Stock-based Compensation Expense for Employees and Non-employees	In the accompanying condensed consolidated statements of operations, the Company recognized stock-based compensation expense for its employees and non-employees as follows: Three Months Ended March 31, 2021 2020 (in thousands) Research and development $ 1,663 $ 546 General and administrative 1,268 372 Total stock-based compensation $ 2,931 $ 918
Schedule of Estimated Grant-date Fair Value of Stock-based Awards Using Black-Scholes Option Pricing Model Assumptions	Three Months Ended March 31, 2021 2020 Expected term (in years) 5.5 – 7.0 5.7 – 6.7 Expected volatility 84 – 85 % 88 – 90 % Risk-free interest rate 0.5 – 1.1 % 0.6 – 1.2 % Expected dividend rate — % — %
Summary of Stock-Based Compensation Activity	A summary of activity under the 2008 Plan, 2015 Plan and 2018 Plan and related information is as follows: Options Outstanding Shares Available for Grant Number of Shares Outstanding Weighted- Average Exercise Price Per Share Weighted- Average Remaining Contractual Term (Years) Aggregate Intrinsic Value of Outstanding Options (in thousands) Outstanding — December 31, 2020 1,117,796 4,146,928 $ 19.45 8.84 $ 12,227 Awards authorized 945,139 Options granted (650,460 ) 650,460 16.52 Options exercised - (21,662 ) 13.28 Options forfeited/cancelled 108,553 (108,553 ) 14.72 Outstanding — March 31, 2021 1,521,028 4,667,173 $ 19.18 8.76 $ 16,794 Exercisable — March 31, 2021 755,413 $ 46.18 5.66 $ 1,905 Vested and expected to vest — March 31, 2021 4,131,935 $ 20.09 8.67 $ 14,075

The Company and Basis of Pres_2

The Company and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Cash and cash equivalents	$ 107,658	$ 104,055	$ 133,534

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Outstanding Shares of Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potential dilutive shares	15,721,268	12,842,917
Series A Warrants For Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potential dilutive shares	7,802,241	7,802,241
Series B Warrants For Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potential dilutive shares	2,524,732	2,574,727
Stock options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potential dilutive shares	4,667,173	1,738,827
Warrants for Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total potential dilutive shares	727,122	727,122

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Fair Value of Financial Assets Measured on Recurring Basis (Detail) - Fair Value Measurements Recurring [Member] - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financial Assets
Total financial assets	$ 106,426	$ 102,219
Level 1 [Member]
Financial Assets
Total financial assets	106,426	102,219
Money Market Funds [Member]
Financial Assets
Total financial assets	106,126	101,919
Money Market Funds [Member] | Level 1 [Member]
Financial Assets
Total financial assets	106,126	101,919
Restricted Money Market Funds [Member]
Financial Assets
Total financial assets	300	300
Restricted Money Market Funds [Member] | Level 1 [Member]
Financial Assets
Total financial assets	$ 300	$ 300

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Fair Value of Financial Liabilities Assumptions (Detail)	Jan. 31, 2020yr	Jan. 22, 2020yr
Expected term [Member] | Series A Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input		5
Expected term [Member] | Series B Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input		2.1
Expected term [Member] | Warrant Issuance Obligation [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input	5
Expected volatility [Member] | Series A Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input		0.43
Expected volatility [Member] | Series B Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input		0.88
Expected volatility [Member] | Warrant Issuance Obligation [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.43
Risk-free interest rate [Member] | Series A Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input		0.0157
Risk-free interest rate [Member] | Series B Warrants [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input		0.0153
Risk-free interest rate [Member] | Warrant Issuance Obligation [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.0157

Fair Value Measurements - Addit

Fair Value Measurements - Additonal Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2020USD ($)
Fair Value Disclosures [Abstract]
Changes in fair value of warrant liabilities	$ 16,240
Securities issuance obligation	$ 1,485

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Cash And Cash Equivalents [Abstract]
Cash	$ 1,532	$ 2,136
Cash equivalents:
Money market accounts	106,126	101,919
Total cash and cash equivalents	$ 107,658	$ 104,055	$ 133,534

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Cash And Cash Equivalents [Abstract]
Cash and cash equivalents	$ 107,658	$ 104,055	$ 133,534
Restricted cash included in other assets	300		300
Total cash, cash equivalents and restricted cash shown in the condensed consolidated statement of cash flows	$ 107,958	$ 104,355	$ 133,834	$ 147,828

Balance Sheet Components - Su_3

Balance Sheet Components - Summary of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid insurance	$ 572	$ 991
Prepaid software and subscription fees	362	376
Other receivables	214	311
Prepaid research and development project costs	186	321
Other	676	416
Total prepaid expenses and other current assets	$ 2,010	$ 2,415

Balance Sheet Components - Su_4

Balance Sheet Components - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 361	$ 361
Less: accumulated depreciation	(319)	(309)
Total property and equipment, net	42	52
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 361	$ 361

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Property Plant And Equipment [Abstract]
Depreciation	$ 10,000	$ 13,000

Balance Sheet Components - Su_5

Balance Sheet Components - Summary of Accrued and Other Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued research and development costs	$ 2,637	$ 1,715
Accrued employee related costs	1,917	4,359
Accrued professional fees	1,485	774
Operating lease liability	$ 214	$ 207
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherCurrentLiabilitiesMember	us-gaap:OtherCurrentLiabilitiesMember
Other	$ 111	$ 93
Total accrued and other liabilities	$ 6,364	$ 7,148

Leases - Additional Information

Leases - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Vancouver [Member]
Loss Contingencies [Line Items]
Operating lease agreement expiration date	Feb. 28, 2023
Sublease base rent	$ 0.2
Weighted-average remaining lease term, operating lease (Year)	1 year 10 months 24 days
Weighted-average discount rate, Operating lease	6.50%
Sublease	$ 0.4
California [Member]
Loss Contingencies [Line Items]
Operating lease agreement term	48 months
2021	$ 0.1
2022	0.2
2023	0.2
2024	0.2
2025	$ 0.1

Leases - Schedule of Components

Leases - Schedule of Components of Lease Expense and Related Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Operating lease cost	$ 43	$ 51
Short-term lease cost	7	22
Total Lease Cost	50	73
Operating cash flows used for operating leases	$ 57	$ 52

Leases - Schedule of Maturities

Leases - Schedule of Maturities Lease Liabilities under Leases Agreement (Detail) $ in Thousands	Mar. 31, 2021USD ($)
Leases [Abstract]
Remainder of 2021	$ 171
2022	183
Total lease payments	354
Less imputed interest	(18)
Total	$ 336

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended			3 Months Ended
	Aug. 31, 2018	Oct. 31, 2016	Jun. 30, 2016	Mar. 31, 2021	Jan. 31, 2017
Carna Collaboration Agreement [Member]
Loss Contingencies [Line Items]
Upfront payment paid			$ 0.9
Upfront License Fee				$ 0.3
Asset Purchase Agreement [Member]
Loss Contingencies [Line Items]
Upfront payment paid	$ 3
Aggregate milestone payment				190
CPF License Agreements [Member]
Loss Contingencies [Line Items]
Upfront payment paid		$ 7
Milestone payment					$ 2
Additional milestone payment payable				319.5
CPF License Agreements [Member] | First patient first trial post amendment [Member]
Loss Contingencies [Line Items]
Milestone payment				2
CPF License Agreement Amendment [Member]
Loss Contingencies [Line Items]
Aggregate milestone payment				$ 290

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	Nov. 13, 2019	Jan. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	May 07, 2021	Feb. 28, 2021	Aug. 31, 2020	Jan. 29, 2020	Aug. 31, 2018
Class Of Stock [Line Items]
Issuance of common stock			$ 19,632,000
Proceeds from exercise of common stock warrants			$ 660,000
Silicon Valley Bank [Member] | Term Loans [Member] | Warrants to Purchase Common Stock [Member]
Class Of Stock [Line Items]
Excercise price of warrants or rights			$ 74.80
Warrant expiration date									Aug. 21, 2028
Warrants issued in connection with loan			1,839
Asset Purchase Agreement Amendment [Member] | Gilead [Member]
Class Of Stock [Line Items]
Issuance of common stock, Shares		725,283
Number of securities called by warrants and rights		725,283
Excercise price of warrants or rights		$ 13.20
Warrant expiration date		Jan. 31, 2025
Series A Warrants [Member]
Class Of Stock [Line Items]
Number of securities called by warrants and rights			7,802,241
Excercise price of warrants or rights			$ 13.20
Warrant expiration date			Jan. 22, 2025
Series B Warrants [Member]
Class Of Stock [Line Items]
Number of securities called by warrants and rights			2,574,727
Issuance of common stock for exercise of common stock warrant, Shares			49,995
Excercise price of warrants or rights			$ 13.20
Warrant expiration period after specified event			75 days
Number of Warrants exercised			151,500	0
Proceeds from exercise of common stock warrants			$ 700,000
Convertible Preferred Stock And Warrants And Underwritten Follow On Offering [Member]
Class Of Stock [Line Items]
Share issued price per share	$ 1,000		$ 1,000
Proceeds from issuance of convertible preferred stock and warrants net of issuance cost	$ 97,700,000
Series A Convertible Preferred Stock [Member]
Class Of Stock [Line Items]
Stock issued, shares	103,000
Share issued price per share			1,000
Preferred stock conversion price per share			$ 13.20
Preferred Stock converted into of the Company's common stock								7,803,273
At-The-Market Offering [Member]
Class Of Stock [Line Items]
Issuance of common stock, Shares			1,149,820	0
Issuance of common stock			$ 19,600,000
At-The-Market Offering [Member] | Maximum [Member]
Class Of Stock [Line Items]
Common stock reserved for issuance						$ 30,000,000	$ 20,000,000
At-The-Market Offering [Member] | Maximum [Member] | Subsequent Event [Member]
Class Of Stock [Line Items]
Common stock reserved for issuance					$ 50,000,000

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Common Stock Reserved for Issuance (Detail) - shares	Mar. 31, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Total common stock reserved for future issuance	17,259,796	16,386,314
Series A Warrants [Member]
Class Of Stock [Line Items]
Total common stock reserved for future issuance	7,802,241	7,802,241
Series B Warrants [Member]
Class Of Stock [Line Items]
Total common stock reserved for future issuance	2,524,732	2,574,727
Equity Incentive Plans [Member]
Class Of Stock [Line Items]
Total common stock reserved for future issuance	1,521,028	1,117,796
Awards outstanding	4,667,173	4,146,928
2015 Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Total common stock reserved for future issuance	17,500	17,500
Warrants to Purchase Common Stock [Member]
Class Of Stock [Line Items]
Outstanding warrants	727,122	727,122

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Stock-based Compensation Expense for Employees and Non-employees (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 2,931	$ 918
Research and development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	1,663	546
General and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 1,268	$ 372

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Estimated Grant-date Fair Values of Stock-based Awards Using Black-Scholes Option Pricing Model Assumptions (Detail)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, Minimum	84.00%	88.00%
Expected volatility, Maximum	85.00%	90.00%
Risk-free interest rate, Minimum	0.50%	0.60%
Risk-free interest rate, Maximum	1.10%	1.20%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 8 months 12 days
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	7 years	6 years 8 months 12 days

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Feb. 03, 2021	Jan. 21, 2020	Aug. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2020	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance				17,259,796				16,386,314
Total stock-based compensation				$ 2,931	$ 918
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Executives and employees stock options granted			1,107,250
Total stock-based compensation				800	$ 0
Total unrecognized stock-based compensation related to unvested stock options				7,900
Service Vesting Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized stock-based compensation related to unvested stock options				$ 27,700
Weighted-average period				3 years 2 months 12 days
2018 Equity Inducement Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance				1,037,500					37,500
Common shares authorized to be issued during the period	500,000					500,000
Stock option life in years							10 years
2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock shares reserved for issuance				5,123,736
Common shares authorized to be issued during the period		4,312,500
Stock option life in years				10 years
Percentage threshold of outstanding shares increased annually under the plan				4.00%
Stock option grants description				the number of shares equal to 4% of the total outstanding shares of the Company’s common stock as of the immediately preceding December 31.
2008 Plan, 2015 Plan and 2018 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common shares authorized to be issued during the period				945,139
Weighted-average grant date fair values of options granted				$ 11.73	$ 9.81
Issuance of common stock for exercise of stock options, Shares				21,662	0
Aggregate intrinsic value of options exercised				$ 100
Total grant date fair value of options vested				$ 3,400	$ 1,600

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock-Based Compensation Activity (Detail) - 2008 Plan, 2015 Plan and 2018 Plan [Member] - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Options Outstanding, Shares Available for Grant
Shares Available for Grant, Beginning balance	1,117,796
Shares Available for Grant, Awards authorized	945,139
Shares Available for Grant, Granted	(650,460)
Shares Available for Grant, forfeited/cancelled	108,553
Shares Available for Grant, Ending balance	1,521,028		1,117,796
Options Outstanding, Number of Shares Outstanding
Number of Shares Outstanding, Beginning balance	4,146,928
Number of Shares Outstanding, Options granted	650,460
Number of Shares Outstanding, Options exercised	(21,662)	0
Number of Shares Outstanding, Options forfeited/cancelled	(108,553)
Number of Shares Outstanding, Ending balance	4,667,173		4,146,928
Number of Shares Outstanding, Exercisable	755,413
Number of Shares Outstanding, Vested and expected to vest	4,131,935
Options Outstanding, Weighted-Average Exercise Price Per Share
Weighted-Average Exercise Price Per Share, Beginning balance	$ 19.45
Weighted-Average Exercise Price Per Share, Options granted	16.52
Weighted-Average Exercise Price Per Share, Options exercised	13.28
Weighted-Average Exercise Price Per Share, Options forfeited/cancelled	14.72
Weighted-Average Exercise Price Per Share, Ending balance	19.18		$ 19.45
Weighted-Average Exercise Price Per Share, Exercisable	46.18
Weighted-Average Exercise Price Per Share, Vested and expected to vest	$ 20.09
Options Outstanding, Weighted-Average Remaining Contractual Term (Years)
Weighted-Average Remaining Contractual Term (Years)	8 years 9 months 3 days		8 years 10 months 2 days
Weighted-Average Remaining Contractual Term (Year), Exercisable	5 years 7 months 28 days
Weighted-Average Remaining Contractual Term (Year), Vested and expected to vest	8 years 8 months 1 day
Options Outstanding, Aggregate Intrinsic Value of Outstanding Options
Aggregate Intrinsic Value of Outstanding Options	$ 16,794		$ 12,227
Aggregate Intrinsic Value of Outstanding Options, Exercisable	1,905
Aggregate Intrinsic Value of Outstanding Options, Vested and expected to vest	$ 14,075

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2021USD ($)
Income Tax Disclosure [Abstract]
Federal income tax provision, continuing operations	$ 0