Entasis Therapeutics (ETTX) 10-Q 4 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 01, 2021
Cover Abstract
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-38670
Entity Registrant Name	Entasis Therapeutics Holdings Inc.
Entity Central Index Key	0001724344
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	82-4592913
Entity Address, Address Line One	35 Gatehouse Drive
Entity Address, City or Town	Waltham
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02451
City Area Code	781
Local Phone Number	810-0120
Title of 12(b) Security	Common Stock, $0.001 par value
Trading Symbol	ETTX
Security Exchange Name	NASDAQ
Amendment Flag	false
Current Fiscal Year End Date	--12-31
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
Entity Common Stock, Shares Outstanding		47,637,629
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 44,124	$ 53,247
Grants receivable	2,967	1,890
Prepaid expenses	2,143	4,160
Other current assets	512	835
Total current assets	49,746	60,132
Property and equipment, net	213	222
Operating lease right-of-use assets	744	1,141
Other assets	63	63
Total assets	50,766	61,558
Current liabilities:
Accounts payable	1,130	660
Accrued expenses and other current liabilities	8,218	7,905
Total current liabilities	9,348	8,565
Operating lease liabilities, net of current portion	183	704
Total liabilities	9,531	9,269
Commitments (Notes 4 and 10)
Stockholders' equity:
Common stock, par value $0.001; 125,000,000 shares authorized and 47,310,254 and 36,637,357 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively	48	37
Additional paid-in capital	260,764	236,707
Accumulated deficit	(219,577)	(184,455)
Total stockholders' equity	41,235	52,289
Total liabilities and stockholders' equity	$ 50,766	$ 61,558

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
CONSOLIDATED BALANCE SHEETS
Common stock par value (in dollar per share)	$ 0.001	$ 0.001
Common stock authorized (in shares)	125,000,000	125,000,000
Common stock issued (in shares)	47,310,254	36,637,357
Common stock outstanding (in shares)	47,310,254	36,637,357

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating expenses:
Research and development	$ 9,282	$ 9,387	$ 28,638	$ 31,249
General and administrative	4,320	3,213	10,938	10,235
Total operating expenses	13,602	12,600	39,576	41,484
Loss from operations	(13,602)	(12,600)	(39,576)	(41,484)
Other income:
Grant income	1,208	1,458	4,444	1,519
Interest income	3	9	10	170
Total other income	1,211	1,467	4,454	1,689
Net loss	$ (12,391)	$ (11,133)	$ (35,122)	$ (39,795)
Net loss per share -basic and diluted (in shares)	$ (0.26)	$ (0.37)	$ (0.84)	$ (1.97)
Weighted average common stock outstanding-basic and diluted (in shares)	47,310,254	29,960,219	41,869,412	20,151,570
Other comprehensive loss:
Net loss	$ (12,391)	$ (11,133)	$ (35,122)	$ (39,795)
Comprehensive loss	$ (12,391)	$ (11,133)	$ (35,122)	$ (39,795)

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2019	$ 13	$ 176,103	$ (133,959)	$ 42,157
Balance (in shares) at Dec. 31, 2019	13,291,563
Stock-based compensation expense		2,199		2,199
Issuance of common stock in Private Placement, net of issuance costs	$ 22	57,653		57,675
Issuance of common stock in Private Placement, net of issuance costs (in shares)	22,183,878
Net loss			(39,795)	(39,795)
Balance at Sep. 30, 2020	$ 35	235,955	(173,754)	62,236
Balance (in shares) at Sep. 30, 2020	35,475,441
Balance at Jun. 30, 2020	$ 27	211,881	(162,621)	49,287
Balance (in shares) at Jun. 30, 2020	27,291,563
Stock-based compensation expense		664		664
Issuance of common stock in Private Placement, net of issuance costs	$ 8	23,410		23,418
Issuance of common stock in Private Placement, net of issuance costs (in shares)	8,183,878
Net loss			(11,133)	(11,133)
Balance at Sep. 30, 2020	$ 35	235,955	(173,754)	62,236
Balance (in shares) at Sep. 30, 2020	35,475,441
Balance at Dec. 31, 2020	$ 37	236,707	(184,455)	52,289
Balance (in shares) at Dec. 31, 2020	36,637,357
Stock-based compensation expense		2,669		2,669
Payment of financing costs		(352)		(352)
Issuance of common stock in Private Placement, net of issuance costs	$ 10	19,941		19,951
Issuance of common stock in Private Placement, net of issuance costs (in shares)	10,000,000
Exercise of warrants	$ 1	1,799		1,800
Exercise of warrants (in shares)	672,897
Net loss			(35,122)	(35,122)
Balance at Sep. 30, 2021	$ 48	260,764	(219,577)	41,235
Balance (in shares) at Sep. 30, 2021	47,310,254
Balance at Jun. 30, 2021	$ 48	260,198	(207,186)	53,060
Balance (in shares) at Jun. 30, 2021	47,310,254
Stock-based compensation expense		918		918
Payment of financing costs		(352)		(352)
Net loss			(12,391)	(12,391)
Balance at Sep. 30, 2021	$ 48	$ 260,764	$ (219,577)	$ 41,235
Balance (in shares) at Sep. 30, 2021	47,310,254

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net loss	$ (35,122)	$ (39,795)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	79	109
Stock-based compensation expense	2,669	2,199
Amortization and accretion of investments		(38)
Changes in operating assets and liabilities:
Grants receivable	(1,077)	(279)
Prepaid expenses	2,017	993
Other assets	720	460
Accounts payable	470	(698)
Accrued expenses and other liabilities	(436)	(662)
Net cash used in operating activities	(30,680)	(37,711)
Cash flows from investing activities:
Purchases of property and equipment	(70)
Proceeds from maturities of short-term investments		25,000
Net cash (used in) provided by investing activities	(70)	25,000
Cash flows from financing activities:
Proceeds from the issuance of common stock in Private Placement, net	19,951	57,867
Proceeds from the exercise of warrants	1,800
Payments of financing costs	(124)
Net cash provided by financing activities	21,627	57,867
Net (decrease) increase in cash and cash equivalents	(9,123)	45,156
Cash and cash equivalents at beginning of the year	53,247	16,034
Cash and cash equivalents at end of the year	44,124	61,190
Supplemental disclosure of non-cash investing and financing activities:
Financing costs included in accrued expenses and current liabilities	$ 228	$ 211

Organization and Description of

Organization and Description of Business	9 Months Ended
	Sep. 30, 2021
Organization and Description of Business
Organization and Description of Business	1. Organization and Description of Business Entasis Therapeutics Holdings Inc., or Entasis, or the Company, is an advanced, late clinical stage biopharmaceutical company focused on the discovery, development and commercialization of targeted antibacterial products that address high unmet medical needs to treat serious infections caused by multidrug-resistant pathogens. The Company has four subsidiaries: Entasis Therapeutics Limited; Entasis Therapeutics Inc.; Entasis Therapeutics Security Corporation; and Entasis Therapeutics (Ireland) Limited. On April 12, 2020, the Company entered into a securities purchase agreement, or the First Securities Purchase Agreement, with Innoviva, Inc., or Innoviva, pursuant to which the Company issued and sold to Innoviva, in a private placement, 14,000,000 newly issued shares of common stock of the Company at $2.50 per share, and warrants to purchase up to 14,000,000 shares of common stock with an exercise price per share of $2.50, resulting in an aggregate gross purchase price of approximately $35.0 million, collectively, the First Private Placement. As a result of the transaction, Innoviva acquired control of the Company, owning approximately 51.3% of the Company’s common stock without giving effect to the potential exercise of its warrants. ​ On August 27, 2020, the Company entered into a securities purchase agreement, or the Second Securities Purchase Agreement, with the purchasers named therein, or the Investors, which included existing stockholder Innoviva. Pursuant to the Second Securities Purchase Agreement, the Company issued and sold to the Investors in a private placement (i) 8,183,878 newly issued shares of common stock of the Company at $2.675 per share, (ii) warrants to purchase an aggregate of 9,345,794 shares of common stock with an exercise price of $2.675, and (iii) pre-funded warrants, in lieu of common stock, to purchase an aggregate of 1,161,916 shares of common stock with an exercise price of $0.001 per share, resulting in aggregate gross proceeds of approximately $25.0 million, collectively, the Second Private Placement. The closing of the Second Private Placement occurred on September 1, 2020. As a result of the transaction, Innoviva owned approximately 52.6% of the Company’s common stock without giving effect to the potential exercise of its warrants. ​ On May 3, 2021, the Company entered into a securities purchase agreement, or the Third Securities Purchase Agreement, with a subsidiary of Innoviva, pursuant to which the Company agreed to issue and sell to Innoviva, in a private placement up to 10,000,000 newly issued shares of common stock of the Company at $2.00 per share and warrants to purchase up to 10,000,000 shares of common stock with an exercise price per share of $2.00, collectively, the Third Private Placement. The warrants were exercisable immediately and have a five-year term. The Third Private Placement occurred in two tranches. At the closing of the first tranche, or the First Closing, which occurred on May 3, 2021, Innoviva purchased 3,731,025 shares of common stock and warrants to purchase up to 3,731,025 shares of common stock, for an aggregate purchase price of approximately $7.5 million. At the closing of the second tranche, or the Second Closing, which occurred on June 11, 2021, Innoviva purchased the remaining 6,268,975 shares of common stock and warrants to purchase up to 6,268,975 shares of common stock, for an aggregate purchase price of approximately $12.5 million. At the effective time of the Second Closing, Innoviva owned approximately 60.6% of the Company’s common stock without giving effect to the potential exercise of the warrants. If Innoviva were to have exercised of all of its warrants, as of such date Innoviva would have held approximately 75.5% of the Company’s outstanding common stock. ​ Going Concern Since its inception, the Company has incurred recurring net losses and negative cash flows from its operations. The Company has financed its operations primarily with proceeds from the sale of redeemable convertible preferred stock and the sale of its common stock. As of September 30, 2021, the Company had cash and cash equivalents of $44.1 million. The Company follows the provisions of Financial Accounting Standards Board, or FASB, Accounting Standards Codification, or ASC, Topic 205-40 , Presentation of Financial Statements Going Concern ​ Based on the Company’s available cash resources, management does not expect that its existing cash and cash equivalents as of September 30, 2021 will be sufficient to enable the Company to fund its operating expenses and capital expenditure requirements through the third quarter of 2022 however management believes it will be sufficient to fund its operating expenses and capital expense requirements into the second quarter of 2022. Management has concluded that substantial doubt exists about the Company’s ability to continue as a going concern for one year from the date these financial statements are issued. A failure to raise the additional funding or to effectively implement cost reductions could harm the Company’s business, results of operations and future prospects. The Company expects to seek additional funding to sustain its future operations and while the Company has successfully raised capital in the past, the ability to raise capital in future periods is not assured. If the Company is not able to secure adequate additional funding in future periods, the Company may make reductions in certain expenditures. This may include suspending or curtailing planned activities. The Company may also have to delay, reduce the scope of, suspend or eliminate one or more research and development programs or its commercialization efforts. ​ The consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates continuity of operations, the realization of assets and the satisfaction of liabilities and commitments in the normal course of business. The consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty. ​ Risks and Uncertainties As a late clinical stage company, Entasis is subject to a number of risks common to other life science companies, including, but not limited to, raising additional capital, development by its competitors of new technological innovations, risk of failure in preclinical and clinical studies, safety and efficacy of its product candidates in clinical trials, the risk of relying on external parties such as contract research organizations and contract manufacturing organizations, the regulatory approval process, market acceptance of the Company’s products once approved, lack of marketing and sales history, dependence on key personnel and protection of proprietary technology. The Company’s therapeutic programs are currently late clinical stage, spanning discovery through pre-NDA submission and will require additional research and development efforts, including the completion of Phase 3 registration trials and regulatory approval, prior to commercialization of any product candidates. These efforts require significant amounts of additional capital, adequate personnel, infrastructure, and extensive compliance-reporting capabilities. There can be no assurance that the Company’s research and development activities will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that products which have successfully completed clinical trials will obtain necessary regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate revenue from product sales. The Company may never achieve profitability, and unless and until it does, it will continue to need to raise additional capital or obtain financing from other sources, such as strategic collaborations or partnerships. The COVID-19 pandemic has, and will likely continue to have, a significant impact on the U.S. economy and businesses. The pandemic also has taxed healthcare systems both in the U.S. and around the world, resulting in disruption to or temporary suspension of certain clinical trials. The nature, extent and duration of the COVID-19 pandemic remains uncertain. Although vaccines are now being administered around the world, the time needed for businesses and healthcare systems to recover from the disruptions caused, and changes needed by businesses to adopt new working conditions remains unknown. The full impact of the pandemic on the economy, including the capital markets, remains uncertain. The prolonged adverse economic conditions could limit the Company’s access to financial resources from the capital markets and other sources. It is not possible to predict the full impact of the COVID-19 pandemic on the Company’s business and access to capital in the future. Despite these conditions, the Company was able to complete enrollment of patients in the SUL-DUR Phase 3 registration trial, or ATTACK trial in July 2021. The zoliflodacin Phase 3 registration trial continues to enroll patients and any future impact by the continued COVID-19 pandemic at clinical trial sites cannot be estimated at this time.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Significant Accounting Policies The Company’s significant accounting policies are disclosed in the audited consolidated financial statements for the year ended December 31, 2020 and the notes thereto, which are included in the Company’s most recent Annual Report on Form 10-K. Since the date of those consolidated financial statements, there have been no material changes to its significant accounting policies. Basis of Presentation and Consolidation The accompanying consolidated financial statements are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States, or U.S. GAAP, and pursuant to the instructions to Form 10-Q and Article 10 of Regulation S-X. The December 31, 2020 consolidated balance sheet was derived from audited consolidated financial statements. These interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements, which are contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020, filed with the Securities and Exchange Commission, or SEC, on March 23, 2021. The interim consolidated financial statements have been prepared on the same basis as the annual audited consolidated financial statements and, in the opinion of management, reflect all normal and recurring adjustments necessary for a fair statement of the Company’s financial position and results of operations. The accompanying consolidated financial statements include the Company’s accounts and those of the Company’s wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The results for the nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or any other future year or period. Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with U.S. GAAP requires management to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the recognition of revenue and the recognition of certain development costs. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from the Company’s estimates. Recently Adopted Accounting Pronouncements Effective January 1, 2021, the Company adopted the provisions of FASB ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2021
Fair Value of Financial Instruments
Fair Value of Financial Instruments	3. Fair Value of Financial Instruments The following tables set forth the Company’s assets that were accounted for at fair value on a recurring basis: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 ​ ​ Fair Value Measurement Using ​ Level 1 Level 2 Level 3 Total ​ ​ (in thousands) Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 39,134 ​ $ — ​ $ — ​ $ 39,134 Total ​ $ 39,134 ​ $ — ​ $ — ​ $ 39,134 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ Fair Value Measurement Using ​ Level 1 Level 2 Level 3 Total ​ ​ (in thousands) Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 49,125 ​ $ — ​ $ — ​ $ 49,125 Total ​ $ 49,125 ​ $ — ​ $ — ​ $ 49,125 ​ The Company classifies its money market funds as Level 1 assets under the fair value hierarchy, as these assets have been valued using quoted market prices in active markets without any valuation adjustment. The carrying amounts of the Company’s cash equivalents, grants receivable, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these amounts.

Leases

Leases	9 Months Ended
	Sep. 30, 2021
Leases
Leases	4. Leases The Company holds one significant operating lease consisting of 20,062 square feet of office and laboratory space in Waltham, Massachusetts that expires in December 2022 pursuant to a May 2015 lease with AstraZeneca, or the AZ lease, as amended in February 2018. Related Party Transactions, In calculating the present value of future lease payments, the Company utilized its incremental borrowing rate based on the remaining lease term at the date of adoption. One lease contains a renewal option that can extend the lease for three years. Because the Company is not reasonably certain to exercise this renewal option, the option is not considered in determining the lease term, and associated potential additional payments are excluded from lease payments. The Company elected to account for each lease component and its associated non-lease components as a single lease component and has allocated all of the contract consideration across lease components only. The Company has existing net leases in which the non-lease components (e.g., common area maintenance) are paid separately from rent based on actual costs incurred and therefore are not included in the operating lease right-of-use assets and lease liabilities and are reflected as an expense in the period incurred. The following table summarizes the presentation of the Company’s operating leases in its consolidated balance sheets (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ As of ​ ​ September 30, 2021 ​ ​ December 31, 2020 Assets ​ ​ ​ ​ ​ ​ ​ Operating lease right-of-use assets ​ $ 744 ​ ​ $ 1,141 ​ ​ ​ ​ ​ ​ ​ Liabilities ​ ​ ​ ​ ​ ​ ​ Operating lease liabilities, current ​ $ 681 ​ ​ $ 617 Operating lease liabilities, net of current portion ​ ​ 183 ​ ​ ​ 704 Total operating lease liabilities ​ $ 864 ​ ​ $ 1,321 ​ Future minimum lease payments under non-cancelable leases were as detailed below (in thousands): ​ ​ ​ ​ Fiscal Year ​ As of September 30, 2021 2021 (remaining 3 months) ​ $ 179 2022 ​ 737 2023 ​ 1 Total undiscounted lease payments ​ ​ 917 Less: imputed interest ​ ​ (53) Total operating lease liabilities ​ $ 864 ​ As of September 30, 2021, the weighted average remaining lease term was 1.3 years and the weighted-average incremental borrowing rate used to determine the operating lease right-of-use assets was 9.1%.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
	Sep. 30, 2021
Accrued Expenses and Other Current Liabilities.
Accrued Expenses and Other Current Liabilities	5. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ As of Accrued compensation and benefits ​ $ 3,215 ​ $ 2,935 Accrued contract manufacturing ​ ​ 2,270 ​ ​ 2,959 Accrued clinical ​ ​ 948 ​ ​ 504 Current portion of operating lease liabilities ​ 681 ​ 617 Accrued professional services ​ 644 ​ 435 Accrued research ​ ​ 365 ​ ​ 349 Other ​ 95 ​ 106 Total accrued expenses and other current liabilities ​ $ 8,218 ​ $ 7,905 ​

Funding Arrangements

Funding Arrangements	9 Months Ended
	Sep. 30, 2021
Funding Arrangements
Funding Arrangements	6. Funding Arrangements NIH In June 2020, the Company entered into a contract with the National Institute of Allergy and Infectious Diseases, or NIAID, part of the National Institutes of Health, or NIH, the NIH Contract, which was effective beginning July 1, 2020 and provides the Company with reimbursement of certain qualified expenses incurred The initial award consisted of approximately , with the potential to increase up to , and will be used to develop novel molecules from the Company’s non-β-lactam inhibitor, or NBP, platform. Funding from the contract will support research towards developing molecules with expanded Gram-negative spectrum against antibiotic resistant bacterial pathogens including E. coli, Acinetobacter, Pseudomonas and Klebsiella . I Through September 30, 2021, the Company has received $2.5 million in payments and recorded $3.4 million of grant income under this contract. The contract will be accounted for in a way that is consistent with the Company’s Government Contracts and Grant Agreements accounting policy. Summary of Significant Accounting Policies - Government Contracts and Grant Agreements Annual Report on Form 10-K filed with the SEC on March 23, 2021 ​ The Company recognized grant income in connection with the NIH contract of $0.8 million and $2.1 million during the three and nine months ended September 30, 2021, respectively, and $0.7 million during the three and nine months ended September 30, 2020. As of September 30, 2021, and December 31, 2020 the Company’s receivables for unreimbursed, eligible costs incurred under the NIH contract totaled $0.9 million and $0.7 million, respectively, including both billed and unbilled amounts. CARB-X In March 2017 and October 2017, the Company entered into funding arrangements with the Trustees of Boston University to utilize funds from the U.S. government through the Combating Antibiotic Resistant Bacteria Biopharmaceutical Accelerator, or CARB-X, program, in support of the Company’s ETX0282CPDP and ETX0462 programs. The amount of specified research expenditures of the Company that could be covered is $18.5 million from April 2017 through May 2023. Through September 30, 2021, the Company has received $11.0 million in payments and recorded $12.7 million of grant income under these funding arrangements. The remaining $5.8 million that could be received is related to the Company’s ETX0462 program. The Company recognized grant income in connection with the CARB-X agreements of $0.5 million and $2.4 million during the three and nine months ended September 30, 2021, respectively, and $0.8 million during the three and nine months ended September 30, 2020. As of September 30, 2021 and December 31, 2020, the Company’s receivables for unreimbursed, eligible costs incurred under the CARB-X agreements totaled $2.0 million and $1.1 million, respectively, including both billed and unbilled amounts.

License and Collaboration Agree

License and Collaboration Agreements	9 Months Ended
	Sep. 30, 2021
License and Collaboration Agreements
License and Collaboration Agreements	7. License and Collaboration Agreements ​ GARDP In July 2017, the Company entered into a collaboration agreement with the Global Antibiotic Research and Development Partnership, or GARDP, for the development, manufacture and commercialization of the product candidate zoliflodacin in certain countries. Under the terms of the collaboration agreement, GARDP will use commercially reasonable endeavors to perform and fully fund the Phase 3 registration trial, including the manufacture and supply of the product candidate containing zoliflodacin, in uncomplicated gonorrhea. The Phase 3 registration trial was initiated in September 2019 with activation of U.S. sites. The trial was negatively impacted by the COVID-19 pandemic, resulting in a 4-month pause in enrollment in mid-2020. Although GARDP resumed patient enrollment into the Phase 3 registration trial after the pause, any future impact by the continued COVID-19 pandemic at clinical trial sites cannot be estimated at this time. ​ In addition, under the collaboration agreement, the Company has granted GARDP a worldwide, fully paid, exclusive and royalty-free license, with the right to sublicense, to use its zoliflodacin technology in connection with GARDP’s development, manufacture and commercialization of zoliflodacin in low-income and specified middle-income countries. The Company has retained commercial rights in all other countries worldwide, including the major markets in North America, Europe and Asia-Pacific. The Company has also retained the right to use and grant licenses to its zoliflodacin technology to perform its obligations under the collaboration agreement and for any purpose other than gonorrhea or community-acquired indications. If the Company believes that the results of the Phase 3 registration trial of zoliflodacin would be supportive of an application for marketing approval, it is obligated to use its best efforts to file an application for marketing approval with the FDA within six months of the completion of the trial and to use commercially reasonable endeavors to file an application for marketing approval with the EMA. Each party is responsible for using commercially reasonable efforts to obtain marketing authorizations for the product candidate in their respective territories. ​ Zai Lab ​ In April 2018, the Company entered into a license and collaboration agreement with Zai Lab (Shanghai) Co., Ltd., or Zai Lab, pursuant to which Zai Lab licensed exclusive rights to durlobactam and sulbactam-durlobactam, or SUL-DUR, in the Asia-Pacific region, or the Zai Agreement. Under the terms of the Zai Agreement, Zai Lab will fund most of the Company’s clinical trial costs in China for SUL-DUR, including all costs in China for the Company’s Phase 3 registration trial of SUL-DUR, with the exception of Phase 3 patient drug supply. Zai Lab will conduct development activities and plan and obtain regulatory approval in a specified number of countries in the Asia-Pacific region beyond China after receipt of regulatory approval of a licensed product in China. Zai Lab is also solely responsible for commercializing licensed products in the Asia-Pacific region and will commercialize licensed products for which it has obtained regulatory approval. The Company is obligated to supply Zai Lab with the licensed products for clinical development, although Zai Lab may take over manufacturing responsibilities for its own commercialization activities within a specified time period following the effective date of the Zai Agreement. The Company received an upfront, non-refundable payment of $5.0 million, milestone payments of $7.0 million, research support funding of $0.6 million and certain other reimbursable registration trial costs of $5.4 million, less applicable taxes of $2.2 million, from Zai Lab through September 30, 2021. During the nine months ended September 30, 2021 and 2020, the Company recognized no revenue under the Zai Agreement. The Company is eligible to receive up to an aggregate of $91.0 million in additional research and development support payments and development, regulatory and sales milestone payments related to SUL-DUR, imipenem and other combinations with the licensed products. Zai Lab will pay the Company a tiered royalty equal from a high-single digit to low-double digit percentage based on annual net sales of licensed products in the territory, subject to specified reductions for the market entry of competing products, loss of patent coverage of licensed products and for payments owed to third parties for additional rights necessary to commercialize licensed products in the territory. Payments received for research support and reimbursable clinical trial costs are recorded as an offset to research and development expense during the period in which the qualifying expenses are incurred. The Company determined the $5.0 million non-refundable upfront payment was the entire transaction price at the outset of the Zai Agreement. All other future potential milestone payments were excluded from the transaction price as they were fully constrained as the risk of significant reversal of revenue had not yet been resolved. At the outset of the Zai Agreement, the achievement of the future potential milestones was not within the Company’s control and was subject to certain research and development success, regulatory approvals or commercial success and therefore carried significant uncertainty. The Company reevaluates the likelihood of achieving the future milestones at the end of each reporting period. Future development milestone revenue from the arrangement will be recognized as revenue in the period when it is no longer probable that revenue attributable to the milestone will result in a significant reversal of cumulative revenue. ​

Stockholders' Equity and Stock-

Stockholders' Equity and Stock-Based Compensation Expense	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity and Stock-Based Compensation Expense
Stockholders' Equity and Stock-Based Compensation Expense	8. Stockholders’ Equity and Stock-Based Compensation Expense Third Private Placement ​ On May 3, 2021, the Company entered into the Third Securities Purchase Agreement, with a subsidiary of Innoviva, pursuant to which the Company agreed to issue and sell to Innoviva up to 10,000,000 newly issued shares of common stock of the Company at $2.00 per share and warrants to purchase up to 10,000,000 shares of common stock, each with an exercise price per share of $2.00. Third Private Placement occurred in two tranches. At the First Closing, which occurred on May 3, 2021, Innoviva purchased 3,731,025 shares of common stock and warrants to purchase 3,731,025 shares of common stock, for aggregate gross proceeds of $7.5 million. At the Second Closing, which occurred on June 11, 2021, Innoviva purchased the remaining 6,268,975 shares of common stock and warrants to purchase 6,268,975 shares of common stock, for aggregate gross proceeds of $12.5 million. Second Private Placement ​ Under the Second Securities Purchase Agreement, the Company issued and sold to the investors, including Innoviva, in a private placement (i) 8,183,878 newly issued shares of common stock of the Company at $2.675 per share, (ii) warrants to purchase an aggregate of 9,345,794 shares of common stock with an exercise price of $2.675, and (iii) pre-funded warrants, in lieu of common stock, to purchase an aggregate of 1,161,916 shares of common stock, with an exercise price of $0.001 per share, resulting in aggregate gross proceeds of approximately $25.0 million. The closing of the Second Private Placement occurred on September 1, 2020. The exercise price and the number of shares of common stock issuable upon exercise of each warrant is subject to appropriate adjustments in the event of certain stock dividends and distributions, stock splits, stock combinations, reclassifications or similar events affecting the Company’s common stock. Each warrant is exercisable from the date of issuance and has a term of five years. First Private Placement Under the First Securities Purchase Agreement, the Company issued and sold to Innoviva 14,000,000 shares of common stock of the Company at $2.50 per share, and warrants to purchase up to 14,000,000 shares of common stock with an exercise price per share of $2.50. ​ Under the First Securities Purchase Agreement, the First Private Placement occurred in two tranches. At the closing of the first tranche, which occurred on April 22, 2020, Innoviva purchased 1,322,510 shares of common stock and warrants to purchase 1,322,510 shares of common stock, for aggregate gross proceeds of approximately $3.3 million. At the closing of the second tranche, which occurred on June 11, 2020, Innoviva purchased the remaining 12,677,490 shares of common stock and warrants to purchase 12,677,490 shares of the common stock for aggregate gross proceeds of approximately $31.7 million. At the closing of the first tranche, Innoviva and the Company entered into an investors rights agreement, or the Investor Rights Agreement, which provides that for so long as Innoviva and its affiliates hold at least 15% of the outstanding shares of the Company’s common stock on a fully-diluted basis, Innoviva shall have the right to designate two directors to the board of directors of the Company, or the Board; and for so long as Innoviva and its affiliates hold at least 8% of the outstanding shares of the Company’s common stock on a fully-diluted basis, Innoviva shall have the right to designate one director to the Board, subject to certain qualifications and conditions in the Investor Rights Agreement. The Investor Rights Agreement also provides for participation rights for Innoviva to participate pro rata in future offerings of securities by the Company. As a result of the closings of the three private placements, Innoviva owns approximately 60.6% of the Company’s outstanding common stock without the exercise of the warrants. ​ At-the-Market Facility In August 2021, the Company entered into a Controlled Equity Offering Sales Agreement, or Sales Agreement, with Cantor Fitzgerald & Co, or Cantor, for the offer and sale of up to $17.5 million of its common stock at the then current market prices in amounts to be determined from time to time. There were no sales under this program through September 30, 2021. ​ Warrants As of September 30, 2021, outstanding warrants to purchase shares of the Company’s common stock are as follows: ​ ​ ​ ​ ​ ​ Shares Underlying Outstanding Warrants Exercise Price Expiration Date 1,322,510 ​ $ 2.50 April 22, 2025 12,677,490 ​ $ 2.50 June 11, 2025 8,672,897 ​ $ 2.675 ​ September 1, 2025 10,000,000 ​ $ 2.00 ​ May 3, 2026 32,672,897 ​ ​ ​ ​ ​ ​ Aspire Common Stock Purchase Agreement In October 2019, the Company entered into a common stock purchase agreement, or CSPA, with Aspire Capital Fund, LLC, or Aspire, which provided that, upon the terms and subject to the conditions and limitations set forth therein, Aspire is committed to purchase up to an aggregate of $20.0 million of shares of the Company’s common stock over the 30-month term of the CSPA. In advance of the Company’s entry into the Sales Agreement with Cantor, the Company and Aspire agreed to terminate the CSPA. The CSPA was terminated without liability of either party to the other. Stock Incentive Plans In September 2018, the Company’s board of directors adopted, and its stockholders approved the 2018 Equity Incentive Plan, or the 2018 Plan, which became effective on September 25, 2018, at which point no further grants will be made under the 2015 Stock Incentive Plan, or the 2015 Plan. In June 2020, the Board adopted, and its stockholders approved an amendment to the 2018 Plan, to increase the number of shares available for stock-based awards by 500,000. Under the 2018 Plan, the Company may grant incentive stock options, or ISOs, non-statutory stock options, stock appreciation rights, restricted stock awards, restricted stock units and other stock-based awards. As of September 30, 2021, stock options to purchase an aggregate of 5,183,885 shares had been granted, restricted stock units, or RSUs, of 992,600 had been awarded, and 1,469,103 shares were available for future issuance under the 2018 Plan, as amended. The options issued under the 2018 Plan expire after 10 years from the grant date. At its inception, the aggregate number of shares of the Company’s common stock available for issuance under the 2018 Plan was 2,350,000. The number of shares of the Company’s common stock reserved for issuance under the 2018 Plan automatically increases on January 1 of each year, for a period of 10 years, from January 1, 2019 continuing through January 1, 2028, by 4% of the total number of shares of the Company’s common stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares as may be determined by Board. Accordingly, on January 1, 2021 and 2020, 1,465,494 and 531,662 shares were added to the number of available shares, respectively. The maximum number of shares that may be issued pursuant to the exercise of ISOs under the 2018 Plan is 7,500,000. The maximum number of shares of the Company’s common stock subject to awards granted under the 2018 Plan or otherwise during a single calendar year to any nonemployee director, taken together with any cash fees paid by the Company to such nonemployee director during the calendar year for serving on the Board, will not exceed $500,000 in total value, or, with respect to the calendar year in which a nonemployee director is first appointed or elected to the Company’s board of directors, $800,000. As of September 25, 2018, no additional stock awards have been or will be granted under the 2015 Plan. Although the 2015 Plan was terminated as to future awards in September 2018, it continues to govern the terms of options that remain outstanding under the 2015 Plan. Stock Option Activity Stock option activity under both plans during the nine months ended September 30, 2021 is summarized as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ ​ ​ ​ ​ ​ Weighted- ​ Average ​ ​ ​ ​ ​ ​ ​ Average ​ Remaining ​ Aggregate ​ ​ Number of ​ Exercise ​ Contractual ​ Intrinsic ​ Options Price Term (Years) Value (in thousands) Outstanding as of December 31, 2020 ​ 3,112,704 ​ $ 5.58 7.76 ​ $ 44 Granted ​ 1,463,376 ​ 2.44 ​ ​ ​ Forfeited and expired ​ (1,656,419) ​ 6.97 ​ ​ ​ Outstanding as of September 30, 2021 ​ 2,919,661 ​ $ 3.21 ​ 8.58 ​ $ 1,578 Exercisable as of September 30, 2021 ​ 923,730 ​ $ 3.86 ​ 6.75 ​ $ 115 ​ The aggregate intrinsic value of options is calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock for those options that had exercise prices lower than the fair value of the Company’s common stock. During the nine months ended September 30, 2021, the weighted-average grant date fair value per granted option was $4.07. As described below, on July 16, 2016, the Company completed a stock option exchange program that resulted in the termination of options to purchase 1,562,752 shares of the Company’s common stock with a weighted-average exercise price of $7.17 per share and in exchange issued stock options to purchase 1,148,572 shares of the Company’s common stock with an exercise price of $2.44 per share. Restricted Stock Unit Activity During the nine months ended September 30, 2021, the Company granted 597,500 RSUs to executives and directors, of which 254,750 contained a performance condition. As of September 30, 2021, the performance condition was not probable of being met. Restricted stock unit activity for the nine months ended September 30, 2021 is summarized as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ ​ ​ Average ​ ​ Number of ​ Grant Date ​ Units Fair Value Outstanding as of December 31, 2020 ​ 395,100 ​ $ 1.65 Granted ​ 597,500 ​ 2.57 Forfeited ​ (48,650) ​ 1.65 Outstanding as of September 30, 2021 ​ 943,950 ​ $ 2.23 ​ Employee Stock Purchase Plan In September 2018, the Company’s board of directors and its stockholders approved the 2018 Employee Stock Purchase Plan, or the ESPP, which became effective as of September 25, 2018. The ESPP is intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the U.S. Internal Revenue Code of 1986, as amended. The number of shares of common stock initially reserved for issuance under the ESPP was 140,000 shares. The ESPP provides for an annual increase on the first day of each year beginning in 2019 and ending in 2028, in each case subject to the approval of the board of directors, equal to the lesser of (i) 1% of the shares of common stock outstanding on the last day of the prior fiscal year or (ii) 250,000 shares; provided, that prior to the date of any such increase, the board of directors may determine that such increase will be less than the amount set forth in clauses (i) and (ii). Pursuant to the terms of the 2018 Employee Stock Purchase Plan, an additional 250,000 and 132,915 shares were added to the number of available shares effective January 1, 2021 and 2020, respectively. As of September 30, 2021, no shares of common stock had been issued under the ESPP and 654,163 shares remained available for future issuance under the ESPP. No offering period under the ESPP has been set by the Company’s board of directors. Stock-Based Compensation Stock-based compensation expense was classified in the consolidated statement of operations as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended Nine Months Ended ​ ​ September 30, ​ September 30, ​ 2021 2020 2021 2020 Research and development ​ $ 449 ​ $ 330 ​ $ 1,293 ​ $ 1,027 General and administrative ​ 469 ​ 334 ​ 1,376 ​ 1,172 Total stock-based compensation expense ​ $ 918 ​ $ 664 ​ $ 2,669 ​ $ 2,199 ​ The following table summarizes stock-based compensation by type of award (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended Nine Months Ended ​ ​ September 30, ​ September 30, ​ 2021 2020 2021 2020 Stock options ​ $ 717 ​ $ 664 ​ $ 2,061 ​ $ 2,199 Restricted stock units ​ 201 ​ — ​ 608 ​ — Total stock-based compensation expense ​ $ 918 ​ $ 664 ​ $ 2,669 ​ $ 2,199 ​ For the nine months ended September 30, 2021, the restricted stock units performance obligation was not probable of being met, and as such no expense was recognized. The following table summarizes unrecognized stock-based compensation expense as of September 30, 2021, by type of awards, and the weighted-average period over which that expense is expected to be recognized. The total unrecognized stock-based compensation expense will be adjusted for actual forfeitures as they occur. ​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2021 ​ ​ Unrecognized Expense ​ Weighted-average Recognition Period ​ (in thousands) (in years) Stock options ​ $ 2,229 ​ ​ 1.94 Restricted stock units ​ $ 774 ​ 0.89 ​ ​ ​ ​ ​ ​ Stock Option Exchange On June 17, 2021, the Company commenced a voluntary stock option exchange program, or the Exchange Program, to permit the Company’s eligible employees, directors and certain consultants to exchange some or all of their eligible outstanding options, or the Original Options, to purchase the Company’s common stock with an exercise price greater than or equal to $4.98 per share, whether vested or unvested, for a lesser number of new stock options, or the New Options. The New Options will be granted under the 2018 Plan on the date on which the Original Options accepted for exchange are cancelled. Participants must remain continuously employed by the Company or in continuous service to the Company through the New Option grant date. New Options will have a per share exercise price equal to the per share closing price of the Company’s common stock on the New Option grant date. The New Options will have the same vesting schedule as the Original Options for options with a remaining vesting period exceeding 12 months. For Original Options with a remaining vesting period of 12 months or less, including full vesting options, the replacement options will vest in full 12 months from the New Option grant date. In accordance with the terms and conditions of the Exchange Program, the Company closed the exchange program and accepted all exchanged outstanding options on July 16, 2021, at which time the Company’s common stock price per share was $2.44. The stock option exchange program was approved at the Company’s annual shareholder meeting on June 10, 2021. ​ Pursuant to the Exchange Program, 44 eligible participants elected to exchange, and the Company accepted for cancellation Original Options to purchase an aggregate of 1,562,752 shares of the Company’s common stock, representing approximately 97% of the total shares of common stock underlying the eligible Original Options. On July 16, 2021, immediately following the expiration of the exchange offer, the Company granted New Options to purchase 1,148,572 shares of common stock, pursuant to the terms of the exchange offer and the Company’s 2018 Plan. In addition to the grant date fair value of the original awards, the Company will recognize incremental expense of approximately $0.3 M over the remaining service periods of the replacement awards.

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2021
Net Loss per Share
Net Loss per Share	9. Net Loss per Share Basic net loss per share is calculated by dividing net loss by the weighted average number of shares of common stock outstanding for the period, without consideration for common stock equivalents. The Company’s potentially dilutive shares, which include outstanding stock options and warrants, 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 outstanding securities have been excluded from the computation of diluted weighted average shares outstanding for the three and nine months ended September 30, 2021 and 2020, as they would have been anti-dilutive: ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, ​ 2021 2020 Options to purchase shares of common stock ​ 2,919,661 ​ 3,107,671 Warrants to purchase shares of common stock ​ 32,672,897 ​ 24,507,710 Unvested restricted stock units ​ 943,950 ​ — ​ 36,536,508 27,615,381 ​

Commitments

Commitments	9 Months Ended
	Sep. 30, 2021
Commitments
Commitments	10. Commitments Lease Commitments The Company has an operating lease agreement for its office and laboratory space with AstraZeneca. See Note 4, Leases AstraZeneca Subscription Agreement In connection with the Company’s 2015 spin-out from AstraZeneca, the Company entered into a business transfer and subscription agreement with AstraZeneca pursuant to which the Company agreed to pay AstraZeneca a one-time milestone payment of $5.0 million within three months of achieving a specified cumulative net sales milestone for durlobactam. This milestone payment will be automatically waived should the Company’s common stock trade on The Nasdaq Global Market at or above a specified price at any time prior to achieving such specified cumulative net sales milestone for durlobactam. The Company is also obligated to pay AstraZeneca a one-time milestone payment of $10.0 million within two years of achieving the first commercial sale of zoliflodacin. At the Company’s election, either milestone payment may be paid in cash, common stock, or a combination of cash and common stock. Additionally, the Company is obligated to pay AstraZeneca tiered, single-digit, per-country royalties on the annual worldwide net sales of durlobactam and zoliflodacin.

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2021
Related Party Transactions
Related Party Transactions	11. Related Party Transactions AstraZeneca The Company was formed in May 2015 as a wholly owned subsidiary of AstraZeneca. Prior to the closing of the initial public offering on September 28, 2018, AstraZeneca was the sole series A preferred stockholder. Upon the closing of the initial public offering, all shares of preferred stock were converted into shares of common stock of the Company. AstraZeneca continues to maintain an ownership interest in the Company. The Company has an operating lease agreement for its office and laboratory space with AstraZeneca. See Note 4, Leases, Pharmaron Beijing Co., Ltd. (China) The Company contracts with Pharmaron Beijing Co., Ltd. (China), or Pharmaron, to provide various medicinal chemistry research, manufacturing development and clinical services related to the Company’s ongoing product candidates. The Company began utilizing Pharmaron as a service provider prior to the spin-out in 2015 (see Note 1, Organization and Description of Business,

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Summary of Significant Accounting Policies
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The accompanying consolidated financial statements are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States, or U.S. GAAP, and pursuant to the instructions to Form 10-Q and Article 10 of Regulation S-X. The December 31, 2020 consolidated balance sheet was derived from audited consolidated financial statements. These interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements, which are contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020, filed with the Securities and Exchange Commission, or SEC, on March 23, 2021. The interim consolidated financial statements have been prepared on the same basis as the annual audited consolidated financial statements and, in the opinion of management, reflect all normal and recurring adjustments necessary for a fair statement of the Company’s financial position and results of operations. The accompanying consolidated financial statements include the Company’s accounts and those of the Company’s wholly owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The results for the nine months ended September 30, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or any other future year or period.
Use of Estimates	Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with U.S. GAAP requires management to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the recognition of revenue and the recognition of certain development costs. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Changes in estimates are recorded in the period in which they become known. Actual results could differ from the Company’s estimates.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements Effective January 1, 2021, the Company adopted the provisions of FASB ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value of Financial Instruments
Schedule of assets that were accounted for at fair value on recurring basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 ​ ​ Fair Value Measurement Using ​ Level 1 Level 2 Level 3 Total ​ ​ (in thousands) Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 39,134 ​ $ — ​ $ — ​ $ 39,134 Total ​ $ 39,134 ​ $ — ​ $ — ​ $ 39,134 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ Fair Value Measurement Using ​ Level 1 Level 2 Level 3 Total ​ ​ (in thousands) Cash equivalents: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Money market funds ​ $ 49,125 ​ $ — ​ $ — ​ $ 49,125 Total ​ $ 49,125 ​ $ — ​ $ — ​ $ 49,125 ​

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2021
Leases
Schedule of operating lease balance sheet information	The following table summarizes the presentation of the Company’s operating leases in its consolidated balance sheets (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ ​ As of ​ ​ September 30, 2021 ​ ​ December 31, 2020 Assets ​ ​ ​ ​ ​ ​ ​ Operating lease right-of-use assets ​ $ 744 ​ ​ $ 1,141 ​ ​ ​ ​ ​ ​ ​ Liabilities ​ ​ ​ ​ ​ ​ ​ Operating lease liabilities, current ​ $ 681 ​ ​ $ 617 Operating lease liabilities, net of current portion ​ ​ 183 ​ ​ ​ 704 Total operating lease liabilities ​ $ 864 ​ ​ $ 1,321
Schedule of future lease payments	Future minimum lease payments under non-cancelable leases were as detailed below (in thousands): ​ ​ ​ ​ Fiscal Year ​ As of September 30, 2021 2021 (remaining 3 months) ​ $ 179 2022 ​ 737 2023 ​ 1 Total undiscounted lease payments ​ ​ 917 Less: imputed interest ​ ​ (53) Total operating lease liabilities ​ $ 864 ​

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Accrued Expenses and Other Current Liabilities.
Schedule of accrued expenses and other current liabilities	Accrued expenses and other current liabilities consisted of the following (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ As of ​ As of Accrued compensation and benefits ​ $ 3,215 ​ $ 2,935 Accrued contract manufacturing ​ ​ 2,270 ​ ​ 2,959 Accrued clinical ​ ​ 948 ​ ​ 504 Current portion of operating lease liabilities ​ 681 ​ 617 Accrued professional services ​ 644 ​ 435 Accrued research ​ ​ 365 ​ ​ 349 Other ​ 95 ​ 106 Total accrued expenses and other current liabilities ​ $ 8,218 ​ $ 7,905

Stockholders' Equity and Stoc_2

Stockholders' Equity and Stock-Based Compensation Expense (Tables)	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity and Stock-Based Compensation Expense
Summary of outstanding warrants to purchase shares of common stock	As of September 30, 2021, outstanding warrants to purchase shares of the Company’s common stock are as follows: ​ ​ ​ ​ ​ ​ Shares Underlying Outstanding Warrants Exercise Price Expiration Date 1,322,510 ​ $ 2.50 April 22, 2025 12,677,490 ​ $ 2.50 June 11, 2025 8,672,897 ​ $ 2.675 ​ September 1, 2025 10,000,000 ​ $ 2.00 ​ May 3, 2026 32,672,897 ​ ​ ​ ​ ​
Summary of Stock option activity under the 2015 and 2018 Plan	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ ​ ​ ​ ​ ​ Weighted- ​ Average ​ ​ ​ ​ ​ ​ ​ Average ​ Remaining ​ Aggregate ​ ​ Number of ​ Exercise ​ Contractual ​ Intrinsic ​ Options Price Term (Years) Value (in thousands) Outstanding as of December 31, 2020 ​ 3,112,704 ​ $ 5.58 7.76 ​ $ 44 Granted ​ 1,463,376 ​ 2.44 ​ ​ ​ Forfeited and expired ​ (1,656,419) ​ 6.97 ​ ​ ​ Outstanding as of September 30, 2021 ​ 2,919,661 ​ $ 3.21 ​ 8.58 ​ $ 1,578 Exercisable as of September 30, 2021 ​ 923,730 ​ $ 3.86 ​ 6.75 ​ $ 115
Summary of Restricted Stock Unit activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ ​ ​ Average ​ ​ Number of ​ Grant Date ​ Units Fair Value Outstanding as of December 31, 2020 ​ 395,100 ​ $ 1.65 Granted ​ 597,500 ​ 2.57 Forfeited ​ (48,650) ​ 1.65 Outstanding as of September 30, 2021 ​ 943,950 ​ $ 2.23
Schedule of stock-based compensation expense	Stock-based compensation expense was classified in the consolidated statement of operations as follows (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended Nine Months Ended ​ ​ September 30, ​ September 30, ​ 2021 2020 2021 2020 Research and development ​ $ 449 ​ $ 330 ​ $ 1,293 ​ $ 1,027 General and administrative ​ 469 ​ 334 ​ 1,376 ​ 1,172 Total stock-based compensation expense ​ $ 918 ​ $ 664 ​ $ 2,669 ​ $ 2,199 ​ The following table summarizes stock-based compensation by type of award (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended Nine Months Ended ​ ​ September 30, ​ September 30, ​ 2021 2020 2021 2020 Stock options ​ $ 717 ​ $ 664 ​ $ 2,061 ​ $ 2,199 Restricted stock units ​ 201 ​ — ​ 608 ​ — Total stock-based compensation expense ​ $ 918 ​ $ 664 ​ $ 2,669 ​ $ 2,199
Schedule of unrecognized stock-based compensation expense	​ ​ ​ ​ ​ ​ ​ ​ ​ As of September 30, 2021 ​ ​ Unrecognized Expense ​ Weighted-average Recognition Period ​ (in thousands) (in years) Stock options ​ $ 2,229 ​ ​ 1.94 Restricted stock units ​ $ 774 ​ 0.89

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Net Loss per Share
Schedule of anti-dilutive securities	​ ​ ​ ​ ​ ​ ​ ​ As of September 30, ​ 2021 2020 Options to purchase shares of common stock ​ 2,919,661 ​ 3,107,671 Warrants to purchase shares of common stock ​ 32,672,897 ​ 24,507,710 Unvested restricted stock units ​ 943,950 ​ — ​ 36,536,508 27,615,381

Organization and Description _2

Organization and Description of Business - General (Details) $ in Thousands	Sep. 30, 2021USD ($)subsidiary	Dec. 31, 2020USD ($)
Organization and Description of Business
Number of subsidiaries | subsidiary	4
Going Concern
Cash and cash equivalents | $	$ 44,124	$ 53,247

Organization and Description _3

Organization and Description of Business - Securities Purchase Agreement (Details) $ / shares in Units, $ in Millions	Jun. 11, 2021USD ($)shares	May 03, 2021USD ($)item$ / sharesshares	Aug. 27, 2020USD ($)$ / sharesshares	Jun. 11, 2020shares	Apr. 22, 2020shares	Apr. 12, 2020USD ($)item$ / sharesshares	Sep. 30, 2021$ / sharesshares	Dec. 31, 2020$ / shares
Common Stock
Common stock par value (in dollar per share) | $ / shares							$ 0.001	$ 0.001
Warrants to purchase common stock							32,672,897
Securities purchase agreement | Private Placement
Common Stock
Price per share | $ / shares						$ 2.50
Warrant exercise price | $ / shares						$ 2.50
Number of tranches | item						2
Percentage of outstanding shares of common stock						51.30%
Pro forma percentage of outstanding shares of common stock	75.50%
Securities purchase agreement | Second Private Placement
Common Stock
Shares issued (in shares)			8,183,878
Price per share | $ / shares			$ 2.675
Warrants to purchase common stock			9,345,794
Term of warrant			5 years
Warrant exercise price | $ / shares			$ 2.675
Proceeds from the issuance of common stock and warrants in private placements, net | $			$ 25
Percentage of outstanding shares of common stock			52.60%
Securities purchase agreement | Pre-funded Warrants
Common Stock
Shares issued (in shares)			1,161,916
Warrant exercise price | $ / shares			$ 0.001
Proceeds from the issuance of common stock and warrants in private placements, net | $			$ 25
Securities purchase agreement | Third Private Placement
Common Stock
Price per share | $ / shares		$ 2
Term of warrant		5 years
Warrant exercise price | $ / shares		$ 2
Number of tranches | item		2
Percentage of outstanding shares of common stock		60.60%
Securities purchase agreement | Closing of first tranche | Third Private Placement
Common Stock
Shares issued (in shares)		3,731,025
Aggregate purchase price of warrants | $		$ 7.5
Warrants to purchase common stock		3,731,025
Securities purchase agreement | Closing of second tranche | Third Private Placement
Common Stock
Shares issued (in shares)	6,268,975
Aggregate purchase price of warrants | $	$ 12.5
Warrants to purchase common stock	6,268,975
Securities purchase agreement | Minimum | Private Placement
Common Stock
Aggregate purchase price of warrants | $						$ 35
Securities purchase agreement | Minimum | Closing of first tranche | Private Placement
Common Stock
Shares issued (in shares)					1,322,510
Warrants to purchase common stock					1,322,510
Securities purchase agreement | Minimum | Closing of second tranche | Private Placement
Common Stock
Shares issued (in shares)				12,677,490
Warrants to purchase common stock				12,677,490
Securities purchase agreement | Minimum | Closing of second tranche | Third Private Placement
Common Stock
Shares issued (in shares)	6,268,975
Warrants to purchase common stock	6,268,975
Securities purchase agreement | Maximum | Private Placement
Common Stock
Shares issued (in shares)						14,000,000
Warrants to purchase common stock						14,000,000
Securities purchase agreement | Maximum | Third Private Placement
Common Stock
Shares issued (in shares)		10,000,000
Warrants to purchase common stock		10,000,000

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Company's assets that were accounted for at fair value on a recurring basis
Total	$ 39,134	$ 49,125
Level 1
Company's assets that were accounted for at fair value on a recurring basis
Total	39,134	49,125
Money market funds
Company's assets that were accounted for at fair value on a recurring basis
Cash equivalents	39,134	49,125
Money market funds | Level 1
Company's assets that were accounted for at fair value on a recurring basis
Cash equivalents	$ 39,134	$ 49,125

Leases - Lease Commitments (Det

Leases - Lease Commitments (Details) $ in Millions	Jan. 01, 2019ft²item	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)
Leases
Lessee, Operating Lease, Existence of Option to Extend	true
Renewal term	3 years
Waltham, Massachusetts lease
Leases
Number of significant operating leases | item	1
Significant operating lease space | ft²	20,062
Operating lease expense | $		$ 0.2	$ 0.2	$ 0.5	$ 0.5

Leases - Lease Balance Sheet (D

Leases - Lease Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Leases
Operating lease right-of-use assets	$ 744	$ 1,141
Operating lease liabilities, current	$ 681	$ 617
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Accrued Expenses And Other Current Liabilities	Accrued Expenses And Other Current Liabilities
Operating lease liabilities, net of current portion	$ 183	$ 704
Total operating lease liabilities	$ 864	$ 1,321

Leases - Operating Lease Maturi

Leases - Operating Lease Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Leases
2021 (remaining 3 months)	$ 179
2022	737
2023	1
Total undiscounted lease payments	917
Less: imputed interest	(53)
Total operating lease liabilities	$ 864	$ 1,321
Weighted average remaining lease term	1 year 3 months 18 days
weighted average incremental borrowing rate (as a percent)	9.10%

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accrued Expenses and Other Current Liabilities.
Accrued compensation and benefits	$ 3,215	$ 2,935
Accrued contract manufacturing	2,270	2,959
Accrued clinical	948	504
Current portion of operating lease liabilities	681	617
Accrued professional services	644	435
Accrued research	365	349
Other	95	106
Total accrued expenses and other current liabilities	$ 8,218	$ 7,905

Funding Arrangements (Details)

Funding Arrangements (Details) - USD ($) $ in Millions	Jul. 01, 2020	Jul. 31, 2021	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jul. 31, 2021	Sep. 30, 2021	Sep. 30, 2021	Dec. 31, 2020
CARB-X program
Funding Arrangements
Grant income recognized				$ 0.5	$ 0.8	$ 2.4	$ 0.8			$ 12.7
Funds received during the period										11
Grants receivable				2		2			$ 2	2	$ 1.1
ETX0462 program
Funding Arrangements
Grants receivable				5.8		5.8			5.8	5.8
National Institute of Allergy and Infectious Diseases
Funding Arrangements
Eligible amount receivable in research and development support payments and development, regulatory and sales milestone payments	$ 3	$ 2.9						$ 5.9
Reimbursable research expenditures									2.5
Grant income recognized				0.8	$ 0.7	2.1	$ 0.7		3.4
Grants receivable				$ 0.9		$ 0.9			$ 0.9	$ 0.9	$ 0.7
Maximum | CARB-X program
Funding Arrangements
Reimbursable research expenditures			$ 18.5
Maximum | National Institute of Allergy and Infectious Diseases
Funding Arrangements
Eligible amount receivable in research and development support payments and development, regulatory and sales milestone payments	$ 15.5

License and Collaboration Agr_2

License and Collaboration Agreements (Details) - License and collaboration agreement with Zai Lab - USD ($) $ in Millions	9 Months Ended		42 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021
License and Collaboration Agreement with Zai Lab
Upfront, non-refundable payment received			$ 5
Research support funding			0.6
Certain other reimbursable registration trial costs			5.4
Tax expense withheld			2.2
Eligible amount receivable in research and development support payments and development, regulatory and sales milestone payments			91
Revenue	$ 0	$ 0	$ 7

Stockholders' Equity and Stoc_3

Stockholders' Equity and Stock-Based Compensation Expense - Equity (Details) $ / shares in Units, $ in Thousands

Jun. 11, 2021USD ($)shares

May 03, 2021USD ($)item$ / sharesshares

Aug. 27, 2020USD ($)$ / sharesshares

Jun. 11, 2020USD ($)shares

Apr. 22, 2020USD ($)shares

Apr. 12, 2020USD ($)directoritem$ / sharesshares

Aug. 31, 2021shares

Oct. 31, 2019USD ($)

Sep. 30, 2020shares

Sep. 30, 2021USD ($)$ / sharesshares

Sep. 30, 2020shares

Dec. 31, 2020$ / shares

Common Stock

Common stock par value (in dollar per share) | $ / shares

$ 0.001

$ 0.001

Aggregate gross proceeds | $

$ 1,800

Warrants to purchase common stock

32,672,897

April 22, 2025 Expiration Date

Common Stock

Warrants to purchase common stock

1,322,510

Warrant exercise price | $ / shares

$ 2.50

June 11, 2025 Expiration Date

Common Stock

Warrants to purchase common stock

12,677,490

Warrant exercise price | $ / shares

$ 2.50

September 1, 2025 Expiration Date

Common Stock

Warrants to purchase common stock

8,672,897

Warrant exercise price | $ / shares

$ 2.675

Warrant May 3 ,2026 Expiration Date

Common Stock

Warrants to purchase common stock

10,000,000

Warrant exercise price | $ / shares

$ 2

Securities purchase agreement | Private Placement

Common Stock

Price per share | $ / shares

$ 2.50

Number of tranches | item

2

Percentage of Outstanding Shares Of Common Stock

51.30%

Warrant exercise price | $ / shares

$ 2.50

Securities purchase agreement | Second Private Placement

Common Stock

Shares issued (in shares)

8,183,878

Proceeds from the issuance of common stock and warrants in private placements, net | $

$ 25,000

Term of warrant

5 years

Price per share | $ / shares

$ 2.675

Percentage of Outstanding Shares Of Common Stock

52.60%

Warrants to purchase common stock

9,345,794

Warrant exercise price | $ / shares

$ 2.675

Securities purchase agreement | Pre-funded Warrants

Common Stock

Shares issued (in shares)

1,161,916

Proceeds from the issuance of common stock and warrants in private placements, net | $

$ 25,000

Warrant exercise price | $ / shares

$ 0.001

Securities purchase agreement | Third Private Placement

Common Stock

Term of warrant

5 years

Price per share | $ / shares

$ 2

Number of tranches | item

2

Percentage of Outstanding Shares Of Common Stock

60.60%

Warrant exercise price | $ / shares

$ 2

Securities purchase agreement | Closing of first tranche | Third Private Placement

Common Stock

Shares issued (in shares)

3,731,025

Aggregate purchase price of warrants | $

$ 7,500

Aggregate gross proceeds | $

$ 7,500

Warrants to purchase common stock

3,731,025

Securities purchase agreement | Closing of second tranche | Third Private Placement

Common Stock

Shares issued (in shares)

6,268,975

Aggregate purchase price of warrants | $

$ 12,500

Aggregate gross proceeds | $

$ 12,500

Warrants to purchase common stock

6,268,975

Securities purchase agreement | Minimum | Private Placement

Common Stock

Aggregate purchase price of warrants | $

$ 35,000

Securities purchase agreement | Minimum | Closing of first tranche | Private Placement

Common Stock

Shares issued (in shares)

1,322,510

Aggregate gross proceeds | $

$ 3,300

Warrants to purchase common stock

1,322,510

Securities purchase agreement | Minimum | Closing of second tranche | Private Placement

Common Stock

Shares issued (in shares)

12,677,490

Aggregate gross proceeds | $

$ 31,700

Warrants to purchase common stock

12,677,490

Securities purchase agreement | Minimum | Closing of second tranche | Third Private Placement

Common Stock

Shares issued (in shares)

6,268,975

Warrants to purchase common stock

6,268,975

Securities purchase agreement | Maximum | Private Placement

Common Stock

Shares issued (in shares)

14,000,000

Warrants to purchase common stock

14,000,000

Securities purchase agreement | Maximum | Third Private Placement

Common Stock

Shares issued (in shares)

10,000,000

Warrants to purchase common stock

10,000,000

Investor rights agreement | Scenario 1

Common Stock

Number of directors designated as board of directors | director

2

Investor rights agreement | Scenario 2

Common Stock

Number of directors designated as board of directors | director

1

Investor rights agreement | Minimum | Scenario 1

Common Stock

Percentage of Outstanding Shares Of Common Stock

15.00%

Investor rights agreement | Minimum | Scenario 2

Common Stock

Percentage of Outstanding Shares Of Common Stock

8.00%

Common Stock

Common Stock

Shares issued (in shares)

8,183,878

10,000,000

22,183,878

Aspire

Common Stock

Maximum amount committed to be purchased | $

$ 20,000

Term over which the purchase can be made

30 months

Cantor Fitzgerald & Co | Controlled Equity Offering Sale Agreement

Common Stock

Number of commitment shares purchased

0

Cantor Fitzgerald & Co | Controlled Equity Offering Sale Agreement | Maximum

Common Stock

Maximum number of shares that can be purchased under purchase notice

17,500,000

Stockholders' Equity and Stoc_4

Stockholders' Equity and Stock-Based Compensation Expense - Other (Details) - USD ($)	Jan. 01, 2021	Jan. 01, 2020	Sep. 25, 2018	Sep. 30, 2018	Sep. 30, 2021	Jun. 30, 2020
Incentive stock options
Stockholders' Equity and Stock-Based Compensation Expense
Annual increase in the number of shares to the shares of common stock (in shares)	1,465,494	531,662
2015 Stock Incentive Plan
Stockholders' Equity and Stock-Based Compensation Expense
Number of options granted (in shares)			0
Number of shares available for future issuance (in shares)			0
2018 Stock Incentive Plan
Stockholders' Equity and Stock-Based Compensation Expense
Increase in number of shares available for grant (in shares)						500,000
2018 Stock Incentive Plan | Non-employee directors
Stockholders' Equity and Stock-Based Compensation Expense
Maximum cash fee paid				$ 500,000
2018 Stock Incentive Plan | Board of directors
Stockholders' Equity and Stock-Based Compensation Expense
Maximum cash fee paid				$ 800,000
2018 Stock Incentive Plan | Options to purchase shares of common stock
Stockholders' Equity and Stock-Based Compensation Expense
Number of options granted (in shares)					5,183,885
Number of shares available for future issuance (in shares)					1,469,103
Number of shares available for grant (in shares)				2,350,000
Period of options				10 years	10 years
Percentage of annual increase to the total number of common stock outstanding (as a percent)				4.00%
2018 Stock Incentive Plan | Unvested restricted stock units
Stockholders' Equity and Stock-Based Compensation Expense
Number of options granted (in shares)					992,600
2018 Stock Incentive Plan | Incentive stock options
Stockholders' Equity and Stock-Based Compensation Expense
Maximum number of shares issued (in shares)				7,500,000

Stockholders' Equity and Stoc_5

Stockholders' Equity and Stock-Based Compensation Expense - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 01, 2021	Jan. 01, 2020	Jul. 16, 2016	Sep. 30, 2018	Sep. 30, 2021	Dec. 31, 2020
Employee Stock Purchase Plan
Stockholders' Equity and Stock-Based Compensation Expense
Number of shares available for future issuance (in shares)				140,000	654,163
Percentage of annual increase to the total number of common stock outstanding (as a percent)				1.00%
Annual increase in the number of shares to the shares of common stock (in shares)	250,000	132,915		250,000
Maximum number of shares issued (in shares)					0
2015 and 2018 Stock Incentive Plan
Number of Options
Outstanding, as of beginning of period (in shares)	3,112,704				3,112,704
Granted (in shares)			1,148,572		1,463,376
Forfeited (in shares)					(1,656,419)
Cancelled (in shares)			1,562,752
Outstanding, as of end of period (in shares)					2,919,661	3,112,704
Exercisable (in shares)					923,730
Weighted Average Exercise Price
Outstanding, as of beginning of period (in dollar per share)	$ 5.58				$ 5.58
Granted (in dollar per share)			$ 2.44		2.44
Forfeited (in dollars per share)					6.97
Cancelled (in dollar per share)			$ 7.17
Outstanding, as of end of period (in dollar per share)					3.21	$ 5.58
Exercisable (in dollar per share)					$ 3.86
Weighted Average Remaining Contractual Term (Years)
Options outstanding					8 years 6 months 29 days	7 years 9 months 3 days
Exercisable					6 years 9 months
Aggregate Intrinsic Value
Options outstanding					$ 1,578	$ 44
Exercisable					$ 115
Weighted average grant date fair value per share of options granted (in dollar per share)					$ 4.07

Stockholders' Equity and Stoc_6

Stockholders' Equity and Stock-Based Compensation Expense - AstraZeneca Shares Option and Incentive Plan (Details) - Unvested restricted stock units	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Number of Units
Outstanding, beginning balance (in shares)	395,100
Granted (in shares)	597,500
Forfeited (in shares)	(48,650)
Outstanding, ending balance (in shares)	943,950
Weighted Average Grant Date Fair Value
Outstanding, beginning balance (in dollars per share) | $ / shares	$ 1.65
Granted (in dollars per share) | $ / shares	2.57
Forfeited (in dollars per share) | $ / shares	1.65
Outstanding, ending balance (in dollars per share) | $ / shares	$ 2.23
Performance condition
Number of Units
Granted (in shares)	254,750

Stockholders' Equity and Stoc_7

Stockholders' Equity and Stock-Based Compensation Expense - Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Stockholders' Equity and Stock-Based Compensation Expense
Total stock-based compensation expense	$ 918	$ 664	$ 2,669	$ 2,199
Unrecognized compensation cost	300		300
Research and development.
Stockholders' Equity and Stock-Based Compensation Expense
Total stock-based compensation expense	449	330	1,293	1,027
General and administrative
Stockholders' Equity and Stock-Based Compensation Expense
Total stock-based compensation expense	469	334	1,376	1,172
Options to purchase shares of common stock
Stockholders' Equity and Stock-Based Compensation Expense
Total stock-based compensation expense	717	$ 664	2,061	$ 2,199
Unrecognized compensation cost	2,229		$ 2,229
Period for recognition			1 year 11 months 8 days
Unvested restricted stock units
Stockholders' Equity and Stock-Based Compensation Expense
Total stock-based compensation expense	201		$ 608
Unrecognized compensation cost	$ 774		$ 774
Period for recognition			10 months 20 days

Stockholders' Equity and Stoc_8

Stockholders' Equity and Stock-Based Compensation Expense - Stock Option Exchange (Details) - Stock Option Exchange Program	Jul. 16, 2021$ / sharesshares	Jun. 17, 2021item$ / sharesshares
Stockholders' Equity and Stock-Based Compensation Expense
Price per share | $ / shares	$ 2.44
Number of eligible participants | item		44
Aggregate number of shares cancelled | shares		1,562,752
Percentage of shares underlying eligible original options		97.00%
Number of options granted (in shares) | shares	1,148,572
Minimum
Stockholders' Equity and Stock-Based Compensation Expense
Common stock with an exercise price | $ / shares		$ 4.98

Net Loss per Share (Details)

Net Loss per Share (Details) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Net Loss per Share
Antidilutive securities excluded from computation of earnings per share (in shares)	36,536,508	27,615,381
Options to purchase shares of common stock
Net Loss per Share
Antidilutive securities excluded from computation of earnings per share (in shares)	2,919,661	3,107,671
Warrants to purchase shares of common stock
Net Loss per Share
Antidilutive securities excluded from computation of earnings per share (in shares)	32,672,897	24,507,710
Unvested restricted stock units
Net Loss per Share
Antidilutive securities excluded from computation of earnings per share (in shares)	943,950

Commitments (Details)

Commitments (Details) - AstraZeneca $ in Millions	1 Months Ended
	Apr. 30, 2018USD ($)
Commitments
Subscription agreement one-time milestone payment on net sales	$ 5
Term of the milestone payment on net sales	3 months
Subscription agreement one-time milestone payment on first commercial sale	$ 10
Term of the milestone payment on first commercial sale	2 years

Related Party Transactions (Det

Related Party Transactions (Details) - Pharmaron Beijing Co., Ltd. - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transactions
Expenses recorded	$ 1.5	$ 2.1	$ 3	$ 3.4
Owed to related party	$ 1		$ 1		$ 2