Eloxx Pharmaceuticals (ELOX) 10-K 12 Mar 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Mar. 08, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Trading Symbol	ELOX
Entity Registrant Name	ELOXX PHARMACEUTICALS, INC.
Entity Central Index Key	0001035354
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		40,214,867
Entity Public Float			$ 82,832,622
Entity Small Business	true
Entity Emerging Growth Company	false
Entity File Number	001-31326
Entity Tax Identification Number	84-1368850
Entity Address, Address Line One	950 Winter Street
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	577-5300
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Document Annual Report	true
Document Transition Report	false
Entity Incorporation, State or Country Code	DE
Title of 12(b) Security	Common Stock, $0.01 par value
Security Exchange Name	NASDAQ
Entity Interactive Data Current	Yes
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Certain information required by Part III, Items 10-14 of this Form 10-K is incorporated by reference to the Registrant’s definitive Proxy Statement for the 2021 Annual Meeting of Stockholders to be filed with the Securities and Exchange Commission pursuant to Regulation 14A not later than 120 days after the end of the fiscal year covered by this Form 10-K, provided that if such Proxy Statement is not filed within such period, such information will be included in an amendment to this Form 10-K to be filed within such 120-day period.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 24,668	$ 22,493
Marketable securities		33,783
Restricted cash	56	43
Prepaid expenses and other current assets	1,169	1,390
Total current assets	25,893	57,709
Property and equipment, net	133	201
Operating lease right-of-use asset	421	924
Other long-term assets	30	113
Total assets	26,477	58,947
Current liabilities:
Accounts payable	481	1,871
Accrued expenses	2,886	4,655
Current portion of long-term debt	5,239	4,336
Advances from collaboration partners	805	403
Current portion of operating lease liability	389	499
Taxes payable	38	43
Total current liabilities	9,838	11,807
Long-term debt	6,376	10,502
Operating lease liability	33	425
Total liabilities	16,247	22,734
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.01 par value per share, 5,000,000 shares authorized, no shares issued or outstanding as of December 31, 2020 and 2019
Common stock, $0.01 par value per share, 500,000,000 shares authorized, 40,350,922 and 40,186,469 shares issued, and 40,157,187 and 40,030,763 shares outstanding as of December 31, 2020 and 2019, respectively	404	402
Common stock in treasury, at cost, 193,735 and 155,706 shares as of December 31, 2020 and 2019, respectively	(1,828)	(1,703)
Additional paid-in capital	183,250	174,515
Accumulated other comprehensive income		18
Accumulated deficit	(171,596)	(137,019)
Total stockholders’ equity	10,230	36,213
Total liabilities and stockholders’ equity	$ 26,477	$ 58,947

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred Stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred Stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	40,350,922	40,186,469
Common stock, shares outstanding	40,157,187	40,030,763
Common stock, treasury shares	193,735	155,706

Consolidated Statements of Oper

Consolidated Statements of Operations and Comprehensive Loss - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating expenses:
Research and development	$ 14,590,000	$ 26,349,000	$ 20,489,000
General and administrative	14,847,000	24,206,000	26,482,000
Restructuring charges	4,018,000
Reverse merger related expenses			594,000
Total operating expenses	33,455,000	50,555,000	47,565,000
Loss from operations	(33,455,000)	(50,555,000)	(47,565,000)
Other expense (income), net	1,122,000	319,000	(502,000)
Loss before income taxes	(34,577,000)	(50,874,000)	(47,063,000)
Provision for income taxes	0	0	122,000
Net loss	$ (34,577,000)	$ (50,874,000)	$ (47,185,000)
Net loss per share, basic and diluted	$ (0.86)	$ (1.34)	$ (1.45)
Weighted average number of shares of common stock used in computing net loss per share, basic and diluted	40,124,953	38,063,173	32,436,506
Comprehensive loss:
Net loss	$ (34,577,000)	$ (50,874,000)	$ (47,185,000)
Other comprehensive income (loss):
Change in unrealized gain (loss) on available-for-sale securities	(18,000)	18,000
Comprehensive loss	$ (34,595,000)	$ (50,856,000)	$ (47,185,000)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Public Offering [Member]	At-the-market Sale Agreement [Member]	Common Stock [Member]	Common Stock [Member]Public Offering [Member]	Common Stock [Member]At-the-market Sale Agreement [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]Public Offering [Member]	Additional Paid-in Capital [Member]At-the-market Sale Agreement [Member]	Accumulated Other Comprehensive Income [Member]	Treasury stock [Member]	Accumulated deficit [Member]
Balance at Dec. 31, 2017	$ 21,361			$ 274			$ 60,047					$ (38,960)
Balance, shares at Dec. 31, 2017				27,527,738
Exercise of stock options	446			$ 14			432
Exercise of stock options, shares				1,334,522
Issuance of common stock upon Technion settlement				$ 6			(6)
Issuance of common stock Techion settlement, shares				569,395
Issuance of shares upon execution of warrants				$ 1			51				$ (52)
Issuance of shares upon execution of warrants, shares				60,989							(3,385)
Issuance of shares upon public offering		$ 53,573			$ 60			$ 53,513
Issuance of shares upon public offering, shares					5,899,500	201,100
Issuance of common stock from at-the-market sales agreement			$ 2,423			$ 2			$ 2,421
Repurchase of common stock	(31)										$ (31)
Repurchase of common stock, shares				(5,076)							(5,000)
Vesting of restricted stock units	(1,046)			$ 3			(3)				$ (1,046)
Vesting of restricted stock units, shares				271,946							(83,038)
Stock-based compensation expense	13,370						13,370
Net loss	(47,185)											(47,185)
Balance at Dec. 31, 2018	42,911			$ 360			129,825				$ (1,129)	(86,145)
Balance, shares at Dec. 31, 2018				35,860,114							(91,423)
Exercise of stock options	169			$ 1			168
Exercise of stock options, shares				116,327
Issuance of shares upon execution of warrants				$ 1			178				$ (179)
Issuance of shares upon execution of warrants, shares				44,814							(14,893)
Issuance of shares upon public offering		$ 32,172			$ 38			$ 32,134
Issuance of shares upon public offering, shares					3,833,334	35,362
Issuance of common stock from at-the-market sales agreement			$ 455						$ 455
Issuance of warrants	421						421
Vesting of restricted stock units	(395)			$ 2			(2)				$ (395)
Vesting of restricted stock units, shares				140,812							(49,390)
Stock-based compensation expense	11,336						11,336
Change in unrealized gain (loss) on investments	18									$ 18
Net loss	(50,874)											(50,874)
Balance at Dec. 31, 2019	$ 36,213			$ 402			174,515			18	$ (1,703)	(137,019)
Balance, shares at Dec. 31, 2019	40,030,763			40,030,763							(155,706)
Exercise of stock options	$ 71			$ 1			70
Exercise of stock options, shares	17,210			17,210
Vesting of restricted stock units	$ (125)			$ 1			(1)				$ (125)
Vesting of restricted stock units, shares				109,214							(38,029)
Stock-based compensation expense	8,666						8,666
Change in unrealized gain (loss) on investments	(18)									$ (18)
Net loss	(34,577)											(34,577)
Balance at Dec. 31, 2020	$ 10,230			$ 404			$ 183,250				$ (1,828)	$ (171,596)
Balance, shares at Dec. 31, 2020	40,157,187			40,157,187							(193,735)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (34,577)	$ (50,874)	$ (47,185)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	8,666	11,336	13,370
Depreciation	68	87	216
Loss (gain) on sales and disposals of property and equipment		(2)	12
Amortization of operating lease right-of-use asset	503	472
Amortization of debt discount	563	535
Amortization, net, of premiums and discounts on investments	15	(301)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	262	83	(1,121)
Accounts payable	(1,390)	1,124	(780)
Accrued expenses	(1,769)	(1,300)	3,999
Operating lease liabilities	(502)	(472)
Taxes payable	(5)	(79)	122
Net cash used in operating activities	(28,166)	(39,391)	(31,367)
Cash flows from investing activities:
Purchases of marketable securities		(67,214)
Proceeds from maturities of marketable securities	33,750	33,750
Purchase of property and equipment		(40)	(235)
Proceeds from sales of property and equipment		2	6
Cash received (paid) for long-term deposits	42	(22)	(88)
Net cash provided by (used in) investing activities	33,792	(33,524)	(317)
Cash flows from financing activities:
Proceeds from issuance of common stock		710	2,165
Proceeds from debt financing obligation	797	15,000
Payment of debt issuance costs		(276)
Repayment of term loan principal	(4,583)
Proceeds from exercises of stock options	71	169	446
Payment for settlement of taxes upon vesting of restricted stock units	(125)	(1,378)
Proceeds from advances from collaboration partners	402	403
Net cash (used in) provided by financing activities	(3,438)	46,800	56,184
Increase (decrease) in cash, cash equivalents and restricted cash	2,188	(26,115)	24,500
Cash, cash equivalents and restricted cash at the beginning of the year	22,536	48,651	24,151
Cash, cash equivalents and restricted cash at the end of the year	24,724	22,536	48,651
Reconciliation of cash, cash equivalents and restricted cash to consolidated balance sheet:
Cash and cash equivalents	24,668	22,493	48,606
Restricted cash	56	43	45
Cash, cash equivalents and restricted cash at the end of the year	24,724	22,536	48,651
Supplemental disclosure of cash flow activities:
Cash paid for interest	828	986
Cash paid for income taxes, net of refunds received	$ 5	36
Supplemental disclosure of non-cash financing activities:
Non-cash acquisition of treasury stock			1,129
Non-cash issuance of common stock upon exercise of warrants		179
Fair value of warrants issued in connection with long-term debt		421
Remeasurement of operating leases		176
Proceeds receivable from equity sales agreement			255
Underwritten Public Offering [Member]
Cash flows from financing activities:
Proceeds from issuance of common stock		$ 32,172	$ 53,573

Nature of the Business

Nature of the Business	12 Months Ended
	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business Eloxx Pharmaceuticals, Inc., together with its subsidiaries (collectively “Eloxx” or the “Company”), is a clinical-stage biopharmaceutical company developing novel ribonucleic acid (RNA)-modulating drug candidates, each designed to be a eukaryotic ribosomal selective glycoside (ERSG), formulated to treat rare and ultra-rare premature stop codon diseases. Premature stop codons are point mutations that disrupt the stability of the impacted messenger RNA (mRNA) and the protein synthesis from that mRNA. As a consequence, patients with premature stop codon diseases have reduced levels of, or no, protein from a gene whose product performs an essential function. This type of mutation accounts for some of the most severe phenotypes across genetic diseases. Nonsense mutations have been identified in over 1,800 rare and ultra-rare diseases. Read-through therapeutic development is focused on increasing functional protein synthesis by enabling the cytoplasmic ribosome to read through premature stop codons to produce full-length proteins is also conducting investigational drug (IND) enabling preclinical studies autosomal dominant polycystic kidney disease (ADPKD) and in by intravitreal administration The Company’s preclinical candidate pool consists of a library of novel ERSG drug candidates identified based on read-through potential and cytoplasmic ribosomal selectivity. The Company is headquartered in Waltham, Massachusetts Morristown, The Company’s research and development strategy is to target rare or ultra-rare diseases where a high unmet medical need exists, a nonsense mutation-bearing patient population is established, preclinical read-through can be established in predictive personalized medicine models, and a defined path through Orphan Drug development, regulatory approval, patient access and commercialization is identified. The Company believes patient advocacy is an important element of patient focused drug development and seeks opportunities to collaborate with patient advocacy groups throughout the discovery and development process. The Company’s current clinical program for its lead investigational drug product candidate, ELX-02, includes Phase 2 studies in cystic fibrosis in Europe, Israel and the United States. On March 25, 2020, the Company announced that enrollment in its Phase 2 clinical trials for ELX-02 in cystic fibrosis had been temporarily paused in response to the COVID-19 pandemic in order to avoid unnecessary exposure in at-risk populations, to maintain the integrity of study data and to support global healthcare providers in their commitment to ensure patient safety. On June 17, 2020, the Company announced that enrollment in its Phase 2 clinical trial in cystic fibrosis had been resumed in Israel and Europe, and on August 12, 2020, the Company announced that enrollment in its Phase 2 clinical trial in cystic fibrosis had been resumed in the U.S. The extent and severity of the impact of the current global health crisis on the Company’s business and clinical trials will be determined largely by the ability of patients and prospective patients in its clinical trials to access trial sites, the ability of personnel from clinical research organizations (“CROs”) to oversee the administration of the Company’s drug in accordance with trial protocols and the Company’s ability to monitor and communicate effectively with CROs, staff at clinical trial sites and principal investigators. In addition, the impact of the COVID-19 pandemic on the operations of the U.S. Food and Drug Administration (the “FDA”) and other health authorities may delay potential advancement of the Company’s product candidates. The Company cannot reasonably estimate the extent to which these potential disruptions may materially impact its consolidated results of operations or financial position. During 2019, the Company announced that the Cystic Fibrosis Foundation (the “CF Foundation”) is providing funding for a portion of the U.S. Phase 2 cystic fibrosis clinical trial and in December of 2020, expanded its support to include our global clinical trial program The Company has since formed On August 4, 2020, the Company announced that the FDA granted orphan drug designation for ELX- 02 for the treatment of cystic fibrosis. The FDA’s Office of Orphan Drug Products grants orphan status to support the development of medicines for underserved patient populations, or rare disorders, that affect fewer than 200,000 people in the U.S. Orphan drug designation qualifies Eloxx for certain benefits, including seven years of market exclusivity upon regulatory approval (if received), exemption from FDA application fees, tax credits on qualified U.S. clinical trials and eligibility for grant funding opportunities that can be used for clinical trial costs. ELX-02 had previously been granted orphan medicinal product designation for the treatment of cystic fibrosis by the European Medicines Agency. Liquidity and Going Concern The Company has a history of net losses and negative cash flows from operating activities since inception, and as of December 31, 2020, had an accumulated deficit of $(171.6) million. The Company expects to continue to incur net losses and use cash in its operations for the foreseeable future. To date, the Company has not generated revenue from the sale of any product or service and does not expect to generate significant revenue unless and until it obtains marketing approval for and commercializes one or more of its product candidates currently in development. Successful transition to profitable operations is dependent upon achieving a level of revenue adequate to support the Company’s cost structure. The Company has financed its operations primarily from the sale of equity securities and to a lesser extent, loans and grants. The Company may never achieve profitability, and unless and until it does, the Company will continue to need to raise additional capital to fund its operations. As discussed in Note 17, on February 24, 2020, the Company’s Board of Directors approved a leadership and organizational realignment, aimed at supporting the Company’s efforts to improve operating performance, and concentrate development efforts on core programs. The Company believes that its will enable it to meet the anticipated cash needs required to reach top line Phase 2 data in cystic fibrosis; however, this amount is not sufficient to maintain its current and planned operations for at least the next twelve months following the filing of this Annual Report on Form 10-K. Management intends to fund future operations through private or public debt or equity financing transactions and may seek additional capital through arrangements with strategic partners or from other sources. The availability of sufficient funding to alleviate the conditions that raise substantial doubt are not within management’s control and cannot be assessed as being probable of occurring.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The Company has prepared its consolidated financial statements in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) promulgated by the Financial Accounting Standards Board (“FASB”). Reclassification The Company has reclassified certain items from the prior year’s consolidated financial statements to conform to the current year’s presentation. Specifically, the Company allocated certain facilities and support costs between Research and development expenses and General and administrative expenses that were previously reported within General and administrative expenses only. For the year ended December 31, 2019, $0.5 million is reclassified from General and administrative expenses to Research and development expenses, which resulted in General and administrative expenses decreasing from $24.7 million to $24.2 million, and Research and development expenses increasing from $25.8 million to $26.3 million. This reclassification within the consolidated statements of operations and cash flows for the year ended December 31, 2019 had no impact on previously reported Total operating expenses, Loss from operations, Net loss, or Net cash used in operating activities. Principles of Consolidation The consolidated financial statements include the accounts of the Company and its subsidiaries. Intercompany balances and transactions have been eliminated upon consolidation. Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates, judgments and assumptions. The Company’s management believes that the estimates, judgments and assumptions used are reasonable based upon information available at the time they are made. These estimates, judgments and assumptions can affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of the consolidated financial statements, and the reported amounts of expenses during the reporting period. The Company evaluates estimates on an ongoing basis in light of changes in circumstances, facts and experiences. Actual results could materially differ from those estimates. Foreign Currency The functional currency of the Company and its subsidiaries is the U.S. dollar. Accordingly, monetary accounts maintained in other currencies are re-measured into U.S. dollars in accordance with ASC Topic 830, “Foreign Currency Matters”. All foreign currency transaction gains and losses arising from transactions denominated in foreign currencies, whether realized or unrealized, are recorded in the statements of operations as other income or expenses . Comprehensive Loss Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Comprehensive loss consists of net loss and other comprehensive loss. Other comprehensive loss consists of changes in unrealized gains and losses from available-for-sale securities. Cash and Cash Equivalents The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. The Company’s cash and cash equivalents include holdings in checking and overnight sweep accounts. The Company’s cash equivalents, which are money market funds held in a sweep account, are measured at fair value on a recurring basis. As of December 31, 2020 and 2019 the balances of cash and cash equivalents were $24.7 million and $22.5 million, respectively, which approximate fair value and were determined based upon Level 1 inputs. The sweep account is valued using quoted market prices with no valuation adjustments applied. Accordingly, these financial instruments are categorized as Level 1. Marketable Securities The Company classifies all investment instruments with an original maturity date, when purchased, in excess of three months but less than one year as current marketable securities. Marketable securities are classified as available-for-sale and are carried at fair value. The Company periodically assesses its portfolio of securities to determine whether to record any estimated allowances for credit losses in the statement of operations. This assessment includes considering whether the Company intends to sell a security, whether it is more likely than not that the Company will have to sell a security before recovery of its amortized cost, and whether a decline in a security’s fair value below its amortized cost is credit-related or non-credit-related. The Company records non-credit-related unrealized gains and losses on available-for-sale securities in upon sales of has recorded no allowances for credit losses, and Restricted Cash At December 31, 2020, and 2019, restricted cash consisted of bank guarantees related to Eloxx Limited’s corporate facilities lease and credit card program. Concentrations of Credit Risk and Off-Balance Sheet Risk Financial instruments that potentially subject the Company to credit risk consist primarily of cash and cash equivalents and marketable securities. The Company mitigates its risk with respect to cash and cash equivalents and marketable securities by maintaining its deposits and investments at high-quality financial institutions. The Company invests any excess cash in money market funds and U.S. treasuries, and the management of these investments is not discretionary on the part of the financial institution. The Company has no off-balance-sheet concentration of credit risk such as foreign exchange contracts, option contracts or other foreign hedging arrangements. Property and Equipment Property and equipment are recorded at cost, less accumulated depreciation. Leasehold improvements are amortized over the lesser of the estimated useful life or the expected term of the related lease. Costs associated with maintenance and repairs are expensed as incurred. Depreciation expense is computed on a straight-line method over the estimated useful lives of the respective assets, as follows: Estimated Useful Life Computers and software 3 years Office furniture and equipment 5 to 12 years Laboratory equipment 5 years Leasehold improvement Over the shorter of the expected remaining lease term or estimated useful life Upon sale or disposition of property and equipment, the cost and related accumulated depreciation are eliminated from the accounts and any resultant gain or loss is credited or charged to operations. Impairment of Long-Lived Assets Property and equipment subject to depreciation are reviewed for impairment in accordance with ASC Topic 360, “Accounting for the Impairment or Disposal of Long-Lived Assets,” whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds their fair value. The Company continually evaluates whether events or circumstances have occurred that indicate that the remaining useful life of its long-lived assets may warrant revision or that the carrying value of these assets may be impaired. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. Evaluation of recoverability of the asset or asset group is based on an estimate of undiscounted future cash flows resulting from the use of the asset or asset group and its eventual disposition. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the asset or asset group, the assets are written down to their estimated fair value. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. As of each balance sheet date presented, none of the Company’s long-lived assets were impaired. The Company has not recorded any impairment losses to date. Legal and Other Contingencies The Company accounts for its contingent liabilities in accordance with ASC Topic 450, “Contingencies”. A provision is recorded when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated. With respect to legal matters, provisions are reviewed and adjusted to reflect the impact of negotiations, estimated settlements, legal rulings, advice of legal counsel and other information and events pertaining to a particular matter. For the years ended December 31, 2020, 2019 and 2018 the Company was not a party to any litigation that was reasonably possible to have a material adverse effect on the Company’s business, financial position, results of operations or cash flows (see also Note 9, “Legal and Other Contingencies”). Legal costs incurred in connection with loss contingencies are expensed as incurred. Research and Development Expenses Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries, stock-based compensation and benefits for employees performing such activities, certain allocated facilities and support costs, depreciation, third-party license fees, and external costs of vendors engaged to conduct preclinical development activities and clinical trials. Research and development expenses are expensed as incurred and include the Company’s costs of performing services in connection with its collaboration agreements and research grants. Non-refundable prepayments for goods or services that will be used or rendered for future research and development activities are deferred and capitalized in prepaid expenses and other current assets. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered, or the services rendered. The Company enters into arrangements with contract research organizations in connection with clinical trials. Such arrangements often provide for payment prior to commencing the project or based upon predetermined milestones throughout the period during which services are expected to be performed. As part of the process of preparing the Company’s financial statements, management is required to estimate prepaid and accrued clinical trial expenses. The date on which services commence, the level of services performed on or before a given date, and the cost of such services are often determined based on subjective judgments informed by the facts and circumstances know to management from the terms of the contract and the Company’s ongoing monitoring of service performance. The Company makes these judgments based upon the facts and circumstances known to management based on the terms of the contract and the Company’s ongoing monitoring of service performance. Fair Value of Financial Instruments Fair value is determined based on the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal market for the asset or liability in an orderly transaction between market participants. U.S. GAAP specifies a hierarchy of valuation techniques based upon whether the inputs to those valuation techniques reflect assumptions other market participants would use based upon market data obtained from independent sources (observable inputs) or reflect the Company’s own assumptions of market participant valuation (unobservable inputs). The fair value hierarchy consists of three levels: Level 1 - Quoted prices (unadjusted) in active markets that are unadjusted and accessible at the measurement date for identical, unrestricted assets or liabilities. Level 2 - Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Financial assets and liabilities are classified within the fair value hierarchy based on the lowest level of input that is significant to the fair value measurement. The authoritative guidance requires the use of observable market data if such data is available without undue cost and effort. When available, the Company uses unadjusted quoted market prices to measure fair value and classify such items within Level 1. If quoted market prices are not available, fair value is based upon internally developed models that use, where possible, current market-based or independently-sourced market parameters, such as interest and currency rates and comparable transactions. Items valued using internally generated models are classified according to the lowest level input or value driver that is significant to the valuation. Thus, items may be classified in Level 3 even though there may be inputs that are readily observable. If quoted market prices are not available, the valuation model used generally depends on the specific asset or liability being valued. At December 31, 2020 and 2019, the Company’s financial assets valued based on Level 1 inputs consisted of cash, cash equivalents and, at December 31, 2019, marketable securities (U.S. treasuries). The Company did not have any transfers of financial assets between Level 2 and 3 during 2020 or 2019. Some assets and liabilities are required to be recorded at fair value on a recurring basis, while other assets and liabilities are recorded at fair value on a nonrecurring basis. The carrying amounts of current financial instruments, which include cash and cash equivalents, restricted bank deposits, accounts payable, accrued expenses, lease obligation liability and debt, approximate their fair values due to the short-term nature of these instruments. Stock-Based Compensation The Company accounts for stock-based compensation in accordance with ASC Topic 718, “Compensation-Stock Compensation” (“ASC 718”), which requires companies to estimate the fair value of equity-based payment awards on the date of grant using an option-pricing model. The Company recognizes compensation expenses for the value of its awards granted based on the straight-line method over the requisite service period of each of the awards or over the implicit service period when a performance condition affects the vesting, and it is considered probable that the performance condition will be achieved. The Company determines the fair value of each stock option award at its grant date using the Black-Scholes option pricing model for options awarded in 2020 and 2019 and using the . The Company determines the fair value of each stock unit, or RSU, at its grant date based on the closing market price of the Company’s common stock on that date. Income Taxes The Company accounts for income taxes in accordance with ASC Topic 740, “Income Taxes” (“ASC 740”), which prescribes the use of the asset and liability method whereby deferred tax assets and liability account balances are determined based on differences between financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to be recovered or settled. The Company provides a valuation allowance, if necessary, to reduce deferred tax assets to their estimated realizable value if it is more likely than not that a portion or all of the deferred tax assets will not be realized. The Company considers many factors when assessing the likelihood of future realization of deferred tax assets, including recent earnings results, expectations of future taxable income, carryforward periods available and other relevant factors. The Company records changes in the required valuation allowance in the period that the determination is made. Based on ASC 740, a two-step approach is used to recognize and measure uncertain tax positions. The first step is to evaluate the tax position taken or expected to be taken in a tax return by determining if the weight of available evidence indicates that it is more likely than not that, on an evaluation of the technical merits, the tax position will be sustained on audit, including resolution of any related appeals or litigation processes. The second step is to measure the tax benefit as the largest amount that is more than 50% likely to be realized upon ultimate settlement. As of December 31, 2020 and 2019, no liability for unrecognized tax positions has been recorded. Accordingly, no interest or penalties related to uncertain tax positions are recorded. The Company’s policy is to record any interest or penalties associated with unrecognized tax positions as a component of income tax expense. Net Loss per Share Basic loss per share is computed by dividing the loss for the period applicable to ordinary shareholders by the weighted average number of ordinary shares outstanding during the period. In computing diluted income per share, weighted average shares used in computing basic earnings per share are adjusted to reflect the potential dilution that could occur upon the exercise of outstanding stock options and upon conversion of restricted stock units and warrants issued to investors and service providers using the “treasury stock method”. Leases The Company adopted the provisions of ASC topic 842, “Leases”, on January 1, 2019. The Company has operating leases for its principal offices in the U.S. and Israel. Operating lease assets represent the Company’s right to use an underlying asset for the lease term and operating lease liabilities represent the Company’s obligation to make lease payments arising from its operating leases. Lease expense for these leases is recognized on a straight-line basis over the lease term, with variable lease payments recognized in the period those payments are incurred. In determining the length of the lease term to its long-term lease, the Company determined not to consider an embedded renewal option for one operating lease primarily due to the facts that (i) the renewal rate is at a future market rate to be determined, and (ii) the Company does not have significant leasehold improvements that would restrict its ability to consider relocation. The Company applied its incremental borrowing rate based upon information available in determining the present value of the lease payments. The Company’s incremental borrowing rate is determined using a secured borrowing rate for the same currency and term as the associated lease. The Company made an accounting policy election to not recognize assets or liabilities for leases with a term of less than twelve months. Recent Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement Although the FASB has issued several other ASUs for which adoption dates are pending, the Company does not expect any of them to have any impacts on its consolidated financial statements.

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	12 Months Ended
	Dec. 31, 2020
Prepaid And Other Current Assets [Abstract]
Prepaid Expenses and Other Current Assets	3. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2020 2019 Research and development $ 631 $ 448 Insurance 170 217 VAT receivables — 26 Other 368 699 Totals $ 1,169 $ 1,390

Property and Equipment, net

Property and Equipment, net	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Property and Equipment, net	4. Property and Equipment, net Property and equipment, net consisted of the following (in thousands): December 31, 2020 2019 Computers and software $ 124 $ 166 Office furniture and equipment 164 164 Leasehold improvements 158 158 Total property and equipment, at cost 446 488 Less: Accumulated depreciation (313 ) (287 ) Property and equipment, net $ 133 $ 201 Depreciation expense was $68 thousand, $87 thousand and $216 thousand

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued Expenses	5. Accrued Expenses Accrued expenses consisted of the following (in thousands): December 31, 2020 2019 Research and development $ 802 $ 1,560 Payroll, bonus and other employee-related expenses 1,315 2,200 Restructuring 258 — Professional services 415 664 Other 39 137 Interest on debt 57 94 Total $ 2,886 $ 4,655

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	6. Leases Operating lease costs under the leases for the year ended December 31, 2020 and 2019 were approximately $0.6 million and $0.5 million, respectively. The weighted average remaining lease term at December 31, 2020 was 0.86 years and the weighted average incremental borrowing rate was 8.0%. The following table summarizes the Company’s maturities of operating lease liabilities as of December 31, 2020 (in thousands): 2021 $ 404 2022 32 Total lease payments 436 Less: present value discount (14 ) Total operating lease liabilities 422 Less: current portion (389 ) Long-term portion $ 33

Debt

Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Debt	7. Debt Term Loan On January 30, 2019, the Company entered into a Loan and Security Agreement (the “SVB Loan Agreement”) in the amount of $15.0 million Outstanding principal on the loan accrues interest at a floating rate equal to the greater of (i) 5.25% per annum and (ii) the sum of 2.5% plus the prime rate, as published in the Wall Street Journal. Interest payments are payable monthly following the funding of the loan. On December 31, 2020, the rate was 5.75%. The Company commenced making principal which is payable In conjunction with the initial loan advance, the Company issued warrants (the “Warrants”) to SVB and WestRiver to purchase an aggregate of 40,834 shares of the Company’s common stock at a warrant exercise price of $11.02 (subject to certain adjustments), which price was calculated using the 10-day average bid price of the Company’s common stock prior to the date of the SVB Loan Agreement. The Company may prepay the outstanding principal balance of the loans advanced by SVB in whole but not in part, subject to a prepayment fee ranging from 1% to 3% of any amount prepaid, depending upon when the prepayment occurs. The Company will also pay a final payment fee equal to 6% of the total loans advanced, due upon the earlier of maturity or termination of the SVB Loan Agreement. Under the terms of the SVB Loan Agreement, the Company granted first priority liens and security interests in substantially all of the Company’s assets (excluding all of its intellectual property, which is subject to a negative pledge) and a pledge by the Company of the shares of one of its wholly-owned subsidiaries as collateral for the obligations thereunder. The SVB Loan Agreement also contains representations and warranties by the Company and SVB and indemnification provisions in favor of SVB and customary covenants (including limitations on other indebtedness, liens, acquisitions, investments and dividends, but no financial covenants), and events of default (including payment defaults, breaches of covenants following any applicable cure period, events relating to bankruptcy or insolvency, and a material adverse change, including a material impairment in the perfection or priority of SVB’s security interest in the collateral, a material adverse change in the Company’s business, or a material impairment of the prospect of repayment of any Obligations (as defined in the SVB Loan Agreement)). As of December 31, 2020, the carrying value of the outstanding loan consists of $10.4 million in principal less the unamortized debt discount of approximately $0.5 million. The debt issuance costs , the valuation of the Warrants, and the final maturity payment of $0.9 million, PPP Loan In April 2020, the Company entered into a loan agreement with SVB under the U.S. Small Business Administration (the “SBA”) Paycheck Protection Program (the “PPP”) pursuant to the Coronavirus Aid, Relief and Economic Security Act of 2020 (the “CARES Act”) and received loan proceeds of $0.8 million (the “PPP Loan”). The Company expects to use the loan proceeds for payroll and other covered costs in accordance with the relevant terms and conditions of the CARES Act. The Company issued a promissory note for the PPP Loan with a maturity date of April 21, 2022 and an interest rate of 1.0% per annum. Monthly payments of principal and interest will be due beginning on September 21, 2021, although interest accrues from the issuance date. The Company may prepay the PPP Loan without penalty or premium, and the promissory note provides for customary events of default. A PPP loan may be partially or entirely forgiven based on employee retention for the 24-week period starting on the loan date through October 2020, and the use of loan proceeds for payroll or other specified costs during the same period. Forgiveness is also based on the employer maintaining or restoring headcount and maintaining salary levels. Forgiveness is reduced if headcount declines or if salaries decrease. Any loan forgiveness will be made subject to SVB approval in accordance with SBA requirements. The Company’s scheduled future principal payments for the long-term debt are as follows (in thousands): December 31, 2020 2021 $ 5,398 2022 5,398 2023 417 Total future principal payments 11,213 Less: unamortized discount (498 ) Carrying value of long-term debt 10,715 Less: current portion (5,239 ) Add: final Term Loan fee due at maturity in 2023 900 Long-term portion $ 6,376

Related Parties

Related Parties	12 Months Ended
	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Parties	8. Related Parties On August 29, 2013, the Company entered into the Technion Agreement with TRDF, with respect to certain technology relating to aminoglycosides and the redesign of aminoglycosides for the treatment of human genetic diseases caused by premature stop mutations and further results of the research of the technology, in order to develop and commercialize products based on such technology. Under the Technion Agreement, TRDF is obligated to provide the Company with research services for an estimated annual payment of $0.1 million, the precise amount to be agreed by the parties prior to the beginning of each year of the research period. During the year ended December 31, 2020 no expenses were incurred and for the years ended December 31, 2019 and 2018, the Company recorded research and development expenses of $0.2 million and $0.1 million, respectively, in relation to the Technion Agreement for the reimbursement of costs incurred during the preparation, filing, prosecution and maintenance of the TRDF patents rights related to Eloxx Limited. As of December 31, 2020 no amounts were recorded in accrued expenses and December 31, 2019, amounts recorded in accrued expenses were $0.1 million. In addition, TRDF granted the Company a license to use, market, sell or sub-license the rights of the product developed under the TRDF research results (the “Licensed Product”), as fully defined in the Technion Agreement, for the following considerations: (i) milestone payments up to total consideration of $6.1 million, to be transferred upon meeting certain milestones as defined in the Technion Agreement; (ii) certain royalties in the low- to mid-single-digit percentage of net sales (subject to change in the case of (a) sublicensing to a big pharmaceutical or biotechnology company, or (b) payment of royalties to third parties, or (c) commercialization by a third party of an authorized generic to a licensed product), for a period until the later of (i) the expiration of a valid claim on the Licensed Product in each country the Licensed Product is sold to, or (ii) a certain amount of years from the date of the first commercial sale of the Licensed Product in such country; and (iii) a low- to mid-double-digit percentage of any non-royalty sub-license income received by the Company from a sub-licensed entity. During the year ended December 31, 2020, the Company made the first milestone payment of $0.1 million to TRDF.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies Royalty Commitments to the IIA To date, the Company has received research and development grants from the Israel Innovation Authority (the “IIA”) totaling $2.6 million. No grants were received for the years ended December 31, 2020, 2019 and 2018. Under the research and development agreements with the IIA and pursuant to applicable law, the Company is required to pay royalties at the rate of 3% on sales to end customers of products candidates developed with funds provided by the IIA, up to an amount equal to 100% of the IIA research and development grants received, plus interest based on the 12-month LIBOR rate. If the Company does not generate sales of products developed with funds provided by the IIA, the Company is not obligated to pay royalties or repay the grants. As of December 31, 2020, the Company has not commenced the payment obligation of the royalties and has a contingent obligation with respect to royalty-bearing participation received or accrued, amounting to $2.7 million, including accrued LIBOR interest. Commitments to TRDF Since August 29, 2013, the Company has had an ongoing agreement with TRDF. Refer to Note 8, “Related Parties”, for further information. Contingencies From time to time, the Company may become involved in various lawsuits and legal proceedings, which arise in the ordinary course of business. The Company is currently unaware of any material pending legal proceedings to which it is a party or of which its property is the subject. However, the Company may at times in the future become involved in litigation in the ordinary course of business, which may include actions related to or based on its intellectual property and its use, customer claims, employment practices and employee complaints and other events arising out of its operations. When appropriate in management’s estimation, the Company will record adequate reserves in its financial statements for pending litigation. Litigation is subject to inherent uncertainties, and an adverse result in any such matters could adversely impact its reputation, operations, and its financial operating results or overall financial condition. The Company accounts for contingent liabilities in accordance with ASC Topic 450, “Contingencies”. A provision is recorded when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated. With respect to legal matters, provisions are reviewed and adjusted to reflect the impact of negotiations, estimated settlements, legal rulings, advice of legal counsel and other information and events pertaining to a particular matter. As of December 31, 2020 and 2019, the Company was not a party to any litigation that is reasonably possible to have a material adverse effect on the Company’s business, financial position, results of operations or cash flows. Legal costs incurred in connection with loss contingencies are expensed as incurred. During 2019, the Company received a funding award from the Cystic Fibrosis Foundation and entered into an agreement relating to the award, which agreement was amended in December 2020 providing for an additional award amount. Payment of award amounts are subject to the achievement of certain milestones in connection with the Company’s global cystic fibrosis development program. The Company would be required to repay amounts received from the Cystic Fibrosis Foundation (or specified multiples of such amounts) in certain circumstances, pursuant to the terms of the agreement, as amended. In the event of a disposition transaction (as defined in the agreement), the Company would be obligated to use up to 5% of the amounts received to repay up to three times the award amount. The funding provided to the Company is accounted for as an advance from a collaboration partner within the scope of ASC Topic 730, “Research and Development.” As of December 31, 2020 and 2019, the Company had received payments of $0.8 million and $0.4 million, respectively, which are recorded as liabilities captioned 'Advances from collaboration partners'. Additional payments totaling $2.6 million were received in the first quarter of 2021, for a total of $3.4 million received to date.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Stockholders' Equity	10. Stockholders’ Equity As of December 31, 2020, the Company had 500,000,000 shares authorized of common stock, $0.01 par value, of which 40,157,187 shares were outstanding and 5,000,000 shares authorized of preferred stock, $0.01 par value, of which no shares were issued or outstanding. Common Stock Public Offerings On April 30, 2018, the Company closed an underwritten public offering of 5,899,500 shares of its common stock, including the exercise in full by the underwriter of its overallotment option to purchase an additional 769,500 shares, at the public offering price of $9.75 per share for gross proceeds of approximately $57.5 million, before deducting the underwriting discounts and commissions and offering expenses of approximately $3.9 million. The shares of common stock were offered by the Company pursuant to a shelf registration statement on Form S-3 (File No. 333-224207) that was filed with the U.S. Securities and Exchange Commission (the “SEC”) on April 10, 2018 and declared effective on April 20, 2018, which covers the offering, issuance and sale of up to $125 million of its common stock, preferred stock, debt securities or warrants and other securities, either individually or in combination (the “April 2018 Shelf”). On June 24, 2019, the Company completed an underwritten public offering of 3,833,334 shares of common stock of the Company at the public offering price of $ 9.00 per share and received net proceeds of approximately $ 32.2 million after deducting underwriting discounts and commissions of $ 2.1 million and estimated offering expenses of $ 0.2 milli on. Form S-3 and Equity Sales Agreement In November 2018, the Company entered into an Equity Distribution Agreement (the “Agreement”) with Citigroup Global Markets Inc. and Cantor Fitzgerald & Co. (collectively, the “Sales Agents”), pursuant to which the Company may sell and issue shares of its common stock up to an aggregate of $50 million through the Sales Agents. The shares were offered pursuant to the April 2018 Shelf. The Company agreed to pay the Sales Agents a commission of up to 3% of the gross proceeds of any sales of common stock pursuant to the Agreement. The Company incurred approximately $0.3 million related to legal, accounting and other fees in connection with the Agreement. For the year ended December 31, 2018, under the Agreement, the Company sold 201,100 shares of common stock and received net proceeds of $2.2 million. In January 2019, the Company sold 35,362 shares of common stock and received net proceeds of $0.7 million. On November 16, 2018, the Company filed a shelf registration statement (the “November 2018 Shelf”) on Form S-3 with the SEC. The November 2018 Shelf (File No. 333-228430) was declared effective on November 26, 2018 and covers the offering, issuance and sale of up to $200 million of the Company’s common stock, preferred stock, debt securities or warrants and other securities, either individually or in combination. Warrants Eloxx Limited issued warrants to purchase shares of common stock in conjunction with the Share Purchase Agreements prior to the December 2017 reverse merger between Eloxx Limited and Sevion Therapeutics, Inc. The Company also issued warrants to purchase shares of common stock in connection with the SVB Loan Agreement (further described above in Note 7, “Debt”). During the year ended December 31, 2020, transactions related to warrants were as follows: Shares Weighted average exercise price Weighted average remaining contractual life (years) Warrants outstanding at December 31, 2019 323,894 $ 4.32 3.74 Granted - Exercised - Forfeited (2 ) 520.00 Warrants outstanding at December 31, 2020 323,892 $ 4.31 2.74 Warrants exercisable at December 31, 2020 323,892 $ 4.31 2.74

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	11. Stock-Based Compensation Stock Incentive Plans On March 12, 2018, the Company’s Board of Directors (the “Board”) adopted the 2018 Equity Incentive Plan (the “2018 Plan”). The 2018 Plan became effective on April 20, 2018 upon approval by the stockholders of the Company with the outstanding options and shares available for future grant under any prior plans being assumed by the 2018 Plan. The initial total number of shares available under the 2018 Plan for awards to employees, non-employee directors and other key personnel was 5,000,000 shares. Stock options granted have a ten-year In 2017, the Company issued inducement awards outside of its stock plans to its former Chief Executive Officer in the form of options to purchase 663,212 shares of the Company’s common stock with an exercise price per share equal to $8.00, and awards of restricted stock units for 663,212 shares of the Company’s common stock. The employment of the grantee terminated in February 2020, as part of the organizational realignment, and the unvested portions of the awards were cancelled. Summary of Stock Option Activity Transactions during the year ended December 31, 2020 related to stock options granted to employees and directors were as follows: Shares Weighted average exercise price per Share Weighted average remaining contractual life (years) Aggregate intrinsic value Options outstanding as of December 31, 2019 4,737,670 $ 11.17 8.54 $ 3,629,073 Granted 1,400,010 3.52 Exercised (17,210 ) 4.08 Forfeited (2,317,409 ) (9.86 ) Options outstanding as of December 31, 2020 3,803,061 $ 10.16 8.20 $ 1,936,183 Options exercisable at December 31, 2020 1,766,009 $ 13.80 7.29 $ 1,266,440 As of December 31, 2020, the unrecognized compensation cost related to the outstanding options was $7.6 million and is expected to be recognized over a weighted-average period of 2.40 years. The weighted average grant date fair values of stock options granted during the years ended December 31, 2020, 2019, and 2018 were $2.29, $6.28 and $18.06 The following table presents the assumptions used to estimate the fair values of stock options granted in the periods presented: Year ended December 31, 2020 2019 2018 Dividend yield 0% 0% 0% Volatility 72%-80% 76%-92% 90%-92% Risk-free interest rate 0.36%-1.63% 1.51%-2.62% 2.55%-3.20% Expected term (years) 5.5-6.0 5.5-6.0 — Contractual term (years) 10 10 10 Forfeiture rate post-vesting — — 10% Suboptimal exercise — — 2.3 Summary of Restricted Stock Unit Activity Transactions during the year ended December 31, 2020 related to RSUs granted to employees were as follows: Shares Weighted average grant date fair value per share Unvested at December 31, 2019 463,945 $ 9.45 Granted 300,000 3.59 Vested (147,243 ) 10.32 Forfeited (266,977 ) 8.65 Unvested at December 31, 2020 349,725 $ 4.67 As of December 31, 2020, the unrecognized compensation cost related to the outstanding RSUs was $1.4 million and is expected to be recognized over a weighted-average period of 3.01 years. Stock-based Compensation Expense Stock-based compensation expense relates to stock options granted to employees, non-employee directors and consultants, time-based restricted stock units granted to employees and performance-based stock options and restricted stock units granted to an employee. The total equity-based compensation expense related to all of the Company’s equity-based awards was recognized as follows (in thousands): Year ended December 31, 2020 2019 2018 Research and development $ 979 $ 2,458 $ 1,745 General and administrative 5,563 8,878 11,625 Restructuring charges 2,124 — — Total stock-based compensation expense $ 8,666 $ 11,336 $ 13,370

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	12. Income Taxes The components of income (loss) before taxes on income are as follows (in thousands): Year ended December 31, 2020 2019 2018 U.S. $ (18,582 ) $ (22,242 ) $ (24,439 ) Israel (15,995 ) (28,632 ) (22,624 ) Loss before taxes on income $ (34,577 ) $ (50,874 ) $ (47,063 ) There were no taxes on income during the year ended December 31, 2020 or 2019. Taxes on income during the year ended December 31, 2018 resulted primarily from subsidiary income as a result of the implementation of an intercompany cost-plus arrangement. The current income tax provision consisted of the following (in thousands): Year ended December 31, 2020 2019 2018 Federal $ — $ — $ 94 State and local — — 28 Foreign — — — Income tax provision $ — $ — $ 122 The significant components of the Company’s deferred tax assets were comprised of the following (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 43,759 $ 38,357 Stock-based compensation 2,200 2,801 Reserves and allowances 431 615 U.S. tax credits and other credits 3,624 2,980 Research and development credits 2,511 1,831 Operating lease right-of-use assets (98 ) (169 ) Operating lease liabilities 98 169 Other 59 98 Total deferred tax assets 52,584 46,682 Valuation allowance (52,584 ) (46,682 ) Net deferred tax assets $ — $ — Deferred taxes are recognized for temporary differences between the basis of assets and liabilities for financial statements and income tax purposes. The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets. As of December 31, 2020 and 2019, based on the Company’s history of operating losses, the Company has concluded that it is more likely than not that the benefit of the deferred tax assets will not be realized. Accordingly, the Company has provided a full valuation allowance for deferred tax assets as of December 31, 2020 and 2019. As of December 31, 2020 and 2019, the Company provided valuation allowances of approximately $52.6 million and $46.7 million, respectively, on U.S. federal, U.S. state and Israeli tax jurisdiction deferred tax assets to reduce the carrying amounts of these assets to zero. The net changes in the Company’s valuation allowances were increases of $5.9 million and $10.8 million during the years ended December 31, 2020 and 2019, respectively. For the year ended December 31, 2020, the increase in the valuation allowance was primarily related to losses generated during the period and increases in research and development credits and other tax credits, partially offset by a reduction in the stock-based compensation deferred tax asset associated with cancelled awards. For the year ended December 31, 2019, the increase in the valuation allowance was primarily related to losses generated during the period, partially offset by a reduction in the stock-based compensation deferred tax asset associated with cancelled awards. For the years ended December 31, 2020, 2019 and 2018 the expected tax expense based on the federal statutory rate is reconciled with the actual tax expense as follows: Year ended December 31, 2020 2019 2018 U.S. federal statutory rate 21.0 % 21.0 % 21.0 % State tax rate, net of federal benefit 1.0 0.9 2.4 Permanent differences (2.0 ) (1.5 ) (3.0 ) Adjustment to deferred taxes — — (1.8 ) Tax credits 2.9 — — Effect of rate differences from statutory 0.9 1.1 0.8 Tax reform - federal tax rate change — — 0.1 Tax reform - change in valuation allowance — — (0.1 ) Change in valuation allowance (23.8 ) (21.5 ) (19.5 ) Other — — (0.2 ) Income tax provision 0.0 % 0.0 % -0.3 % The main reconciling item between the statutory tax rate and the Company’s effective tax rate is the recognition of valuation allowances in respect to deferred taxes related to accumulated net operating losses carried forward and temporary differences due to the uncertainty of the realization of such deferred taxes. As of December 31, 2020 and 2019, the Company had U.S. federal net operating loss (“NOL”) carryforwards of $108.9 million and $99.4 million, respectively. U.S. federal NOL carryforwards will begin to expire, if not utilized, beginning in 2021 through 2037. Included in the U.S. federal NOL carryforward as of December 31, 2020 are $34.9 million of NOLs generated after the effective date of the Tax Cuts and Jobs Act of 2017 (the “Tax Act”), which are not subject to expiration but may not be carried back and are only eligible to offset up to a maximum of 80% of taxable income generated in a given year. It is uncertain if and to what extent various U.S. states will conform their net operating loss rules to the Tax Act. As of December 31, 2020 and 2019, the Company had U.S. state NOL carryforwards of $13.7 million and $31.9 million, respectively, which may be available to offset future income tax liabilities. As of December 31, 2020 and 2019, the Company had federal research tax credit carryforwards of $3.6 million and $3.0 million, respectively, available to reduce future tax liabilities and which expire at dates beginning in 2026 through 2040. As of December 31, 2020 and 2019, the Company had Israeli NOL carryforwards of $86.9 million and $73.7 million, respectively, which carry forward indefinitely. The enactment of the Tax Act in December 2017, as further discussed below, resulted in the remeasurement of the Company’s net deferred tax assets due to the reduction in the corporate statutory rate from 35% to 21%. The effect on deferred tax assets and liabilities of a change in law or tax rates is recognized in income in the period that includes the enactment date. The Tax Act also includes a provision designed to currently tax global intangible low-taxed income (“GILTI”). The Company will record the U.S. income tax effect of future GILTI inclusions in the period in which they arise, if ever. After the enactment of the Tax Act, the SEC issued Staff Accounting Bulletin No. 118 (“SAB 118”) which provided guidance on accounting for the enactment effect of the Tax Act. SAB 118 addressed the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Tax Act. SAB 118 provided for a measurement period of up to one year from the Tax Act enactment date for companies to complete their accounting under ASC 740. The Company had calculated a provisional estimate of deferred tax expense of $10.2 million related to the remeasurement of its U.S. deferred tax assets in the future, which was fully and equally offset by a corresponding reduction in the valuation allowance. During the quarter ended December 31, 2018, the Company completed the accounting for the income tax effects of the Tax Act, which resulted in an immaterial change in the net deferred tax asset, before valuation allowance, as of the enactment date. Under the provisions of the Internal Revenue Code (“IRC”), the net operating loss and tax credit carryforwards are subject to review and potential adjustments by the Internal Revenue Service and state tax authorities. Under Section 382 of the Internal Revenue Code and corresponding provisions of state law, if a corporation undergoes an “ownership change,” which is generally defined as a greater than 50 percent change, by value, in its equity ownership over a three-year period, the corporation’s ability to use its pre-change NOL carryforwards and other pre-change tax attributes to offset its post-change income or taxes may be limited. The Company may have experienced ownership changes in the past, including the reverse merger of Sevion Therapeutics, Inc. on December 19, 2017 at which time the Company’s pre-change U.S. federal NOL carryforward was $77.2 million, and its research tax credit was $0.7 million. The Company may experience additional ownership changes in the future as a result of subsequent shifts in its stock ownership, some of which may be outside of its control. Although the Company has not completed its analysis, it is reasonably possible that its federal NOLs available to offset future taxable income could materially decrease. This reduction would be offset by an adjustment to the existing valuation allowance for an equal and offsetting amount. Additionally, the state NOLs available to offset future state income could similarly decrease, which would also be offset by an equal and offsetting adjustment to the existing valuation allowance. Given the offsetting adjustments to the existing valuation allowance, any ownership change is not expected to have an adverse material effect on the Company’s Consolidated Financial Statements. The Company is subject to income taxes in the United States and Israel. The Company files income tax returns in the U.S. and in several states. The federal and state tax returns are generally subject to tax examination by taxing authorities for tax years beginning in June 30, 2015 to present. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service or state tax authorities to the extent utilized in a future period

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Net Loss Per Share	13. Net Loss Per Share The loss and the weighted average number of shares used in computing basic and diluted net loss per share for the years ended December 31, 2020, 2019, and 2018, are as follows (in thousands, except share and per share data): Year ended December 31, 2020 2019 2018 Numerator: Net loss $ (34,577 ) $ (50,874 ) $ (47,185 ) Denominator: Weighted average number of shares of common stock used in computing net loss per share, basic and diluted 40,124,953 38,063,173 32,436,506 Net loss per share, basic and diluted $ (0.86 ) $ (1.34 ) $ (1.45 ) For the years ended December 31, 2020, 2019, and 2018, the totals of outstanding preferred stock, stock options, stock warrants and restricted stock units, as applicable, excluded from the calculation of the diluted net loss per share due to their anti-dilutive effect were 4,476,678, 5,525,509 and 4,163,107, respectively.

Other Expense (Income), net

Other Expense (Income), net	12 Months Ended
	Dec. 31, 2020
Other Income And Expenses [Abstract]
Other Expense (Income), net	14. Other Expense (Income), net Other Expense (income) consisted of the following (in thousands): Year ended December 31, 2020 2019 2018 Interest and other income $ (337 ) $ (1,072 ) $ (601 ) Foreign currency exchange losses (gains), net 35 76 92 Investment income, net 15 (301 ) — Interest and other expense 1,409 1,616 7 Total other expense (income), net $ 1,122 $ 319 $ (502 )

Segment and Geographic Informat

Segment and Geographic Information	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Segment and Geographic Information	15. Segment and Geographic Information Operating segments are defined as components of an enterprise (business activity from which it earns revenue and incurs expenses) about which discrete financial information is available and regularly reviewed by the chief operating decision maker in deciding how to allocate resources and in assessing performance. The Company’s chief operating decision maker is its Chief Executive Officer. The chief operating decision maker reviews consolidated operating results to make decisions about allocating resources and assessing performance for the entire company. The Company views its operations and manages its business as one operating segment; however, it operates in two geographic regions: the U.S. and Israel. Substantially all of the Company’s assets are located in the U.S.

Marketable Securities

Marketable Securities	12 Months Ended
	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Marketable Securities	16. Marketable Securities Below is a summary of cash, cash equivalents and marketable securities at December 31, 2020 (in thousands): Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents $ 24,668 $ — $ — $ 24,668 Marketable securities - U.S. treasuries — — — — Total cash, cash equivalents and marketable securities $ 24,668 $ — $ — $ 24,668 Below is a summary of cash, cash equivalents and marketable securities at December 31, 2019 (in thousands): Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents $ 22,493 $ — $ — $ 22,493 Marketable securities - U.S. treasuries 33,765 19 (1 ) 33,783 Total cash, cash equivalents and marketable securities $ 56,258 $ 19 $ (1 ) $ 56,276 As of December 31, 2020 and 2019, no credit losses were identified related to the cash equivalents or marketable securities.

Restructuring

Restructuring	12 Months Ended
	Dec. 31, 2020
Restructuring And Related Activities [Abstract]
Restructuring	17. Restructuring On February 24, 2020, the Company’s Board of Directors approved a leadership and organizational realignment aimed at supporting its efforts to improve operating performance and concentrate development efforts on its core programs. The organizational realignment reduced managerial layers and consolidated roles across the organization, resulting in the elimination of 13 full-time positions during the first quarter of 2020. This resulted in a one-time charge of $4.0 million, including $2.1 million in stock-based compensation expense, with the severance portion being paid out over a one-year Beginning Balance Additions Deductions Ending Balance Severance and related costs $ — $ 1,729 $ (1,471 ) $ 258 Contract termination costs — 165 (165 ) — Total restructuring charges $ — $ 1,894 $ (1,636 ) $ 258

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company has prepared its consolidated financial statements in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASUs”) promulgated by the Financial Accounting Standards Board (“FASB”).
Reclassification	Reclassification The Company has reclassified certain items from the prior year’s consolidated financial statements to conform to the current year’s presentation. Specifically, the Company allocated certain facilities and support costs between Research and development expenses and General and administrative expenses that were previously reported within General and administrative expenses only. For the year ended December 31, 2019, $0.5 million is reclassified from General and administrative expenses to Research and development expenses, which resulted in General and administrative expenses decreasing from $24.7 million to $24.2 million, and Research and development expenses increasing from $25.8 million to $26.3 million. This reclassification within the consolidated statements of operations and cash flows for the year ended December 31, 2019 had no impact on previously reported Total operating expenses, Loss from operations, Net loss, or Net cash used in operating activities.
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of the Company and its subsidiaries. Intercompany balances and transactions have been eliminated upon consolidation.
Use of Estimates	Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates, judgments and assumptions. The Company’s management believes that the estimates, judgments and assumptions used are reasonable based upon information available at the time they are made. These estimates, judgments and assumptions can affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of the consolidated financial statements, and the reported amounts of expenses during the reporting period. The Company evaluates estimates on an ongoing basis in light of changes in circumstances, facts and experiences. Actual results could materially differ from those estimates.
Foreign Currency	Foreign Currency The functional currency of the Company and its subsidiaries is the U.S. dollar. Accordingly, monetary accounts maintained in other currencies are re-measured into U.S. dollars in accordance with ASC Topic 830, “Foreign Currency Matters”. All foreign currency transaction gains and losses arising from transactions denominated in foreign currencies, whether realized or unrealized, are recorded in the statements of operations as other income or expenses .
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Comprehensive loss consists of net loss and other comprehensive loss. Other comprehensive loss consists of changes in unrealized gains and losses from available-for-sale securities.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. The Company’s cash and cash equivalents include holdings in checking and overnight sweep accounts. The Company’s cash equivalents, which are money market funds held in a sweep account, are measured at fair value on a recurring basis. As of December 31, 2020 and 2019 the balances of cash and cash equivalents were $24.7 million and $22.5 million, respectively, which approximate fair value and were determined based upon Level 1 inputs. The sweep account is valued using quoted market prices with no valuation adjustments applied. Accordingly, these financial instruments are categorized as Level 1.
Marketable Securities	Marketable Securities The Company classifies all investment instruments with an original maturity date, when purchased, in excess of three months but less than one year as current marketable securities. Marketable securities are classified as available-for-sale and are carried at fair value. The Company periodically assesses its portfolio of securities to determine whether to record any estimated allowances for credit losses in the statement of operations. This assessment includes considering whether the Company intends to sell a security, whether it is more likely than not that the Company will have to sell a security before recovery of its amortized cost, and whether a decline in a security’s fair value below its amortized cost is credit-related or non-credit-related. The Company records non-credit-related unrealized gains and losses on available-for-sale securities in upon sales of has recorded no allowances for credit losses, and
Restricted Cash	Restricted Cash At December 31, 2020, and 2019, restricted cash consisted of bank guarantees related to Eloxx Limited’s corporate facilities lease and credit card program.
Concentrations of Credit Risk and Off-Balance Sheet Risk	Concentrations of Credit Risk and Off-Balance Sheet Risk Financial instruments that potentially subject the Company to credit risk consist primarily of cash and cash equivalents and marketable securities. The Company mitigates its risk with respect to cash and cash equivalents and marketable securities by maintaining its deposits and investments at high-quality financial institutions. The Company invests any excess cash in money market funds and U.S. treasuries, and the management of these investments is not discretionary on the part of the financial institution. The Company has no off-balance-sheet concentration of credit risk such as foreign exchange contracts, option contracts or other foreign hedging arrangements.
Property and Equipment	Property and Equipment Property and equipment are recorded at cost, less accumulated depreciation. Leasehold improvements are amortized over the lesser of the estimated useful life or the expected term of the related lease. Costs associated with maintenance and repairs are expensed as incurred. Depreciation expense is computed on a straight-line method over the estimated useful lives of the respective assets, as follows: Estimated Useful Life Computers and software 3 years Office furniture and equipment 5 to 12 years Laboratory equipment 5 years Leasehold improvement Over the shorter of the expected remaining lease term or estimated useful life Upon sale or disposition of property and equipment, the cost and related accumulated depreciation are eliminated from the accounts and any resultant gain or loss is credited or charged to operations.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets Property and equipment subject to depreciation are reviewed for impairment in accordance with ASC Topic 360, “Accounting for the Impairment or Disposal of Long-Lived Assets,” whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If such assets are considered to be impaired, the impairment to be recognized is measured as the amount by which the carrying amount of the assets exceeds their fair value. The Company continually evaluates whether events or circumstances have occurred that indicate that the remaining useful life of its long-lived assets may warrant revision or that the carrying value of these assets may be impaired. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. Evaluation of recoverability of the asset or asset group is based on an estimate of undiscounted future cash flows resulting from the use of the asset or asset group and its eventual disposition. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the asset or asset group, the assets are written down to their estimated fair value. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. As of each balance sheet date presented, none of the Company’s long-lived assets were impaired. The Company has not recorded any impairment losses to date.
Legal and Other Contingencies	Legal and Other Contingencies The Company accounts for its contingent liabilities in accordance with ASC Topic 450, “Contingencies”. A provision is recorded when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated. With respect to legal matters, provisions are reviewed and adjusted to reflect the impact of negotiations, estimated settlements, legal rulings, advice of legal counsel and other information and events pertaining to a particular matter. For the years ended December 31, 2020, 2019 and 2018 the Company was not a party to any litigation that was reasonably possible to have a material adverse effect on the Company’s business, financial position, results of operations or cash flows (see also Note 9, “Legal and Other Contingencies”). Legal costs incurred in connection with loss contingencies are expensed as incurred.
Research and Development Expenses	Research and Development Expenses Research and development expenses are comprised of costs incurred in performing research and development activities, including salaries, stock-based compensation and benefits for employees performing such activities, certain allocated facilities and support costs, depreciation, third-party license fees, and external costs of vendors engaged to conduct preclinical development activities and clinical trials. Research and development expenses are expensed as incurred and include the Company’s costs of performing services in connection with its collaboration agreements and research grants. Non-refundable prepayments for goods or services that will be used or rendered for future research and development activities are deferred and capitalized in prepaid expenses and other current assets. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered, or the services rendered. The Company enters into arrangements with contract research organizations in connection with clinical trials. Such arrangements often provide for payment prior to commencing the project or based upon predetermined milestones throughout the period during which services are expected to be performed. As part of the process of preparing the Company’s financial statements, management is required to estimate prepaid and accrued clinical trial expenses. The date on which services commence, the level of services performed on or before a given date, and the cost of such services are often determined based on subjective judgments informed by the facts and circumstances know to management from the terms of the contract and the Company’s ongoing monitoring of service performance. The Company makes these judgments based upon the facts and circumstances known to management based on the terms of the contract and the Company’s ongoing monitoring of service performance.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Fair value is determined based on the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal market for the asset or liability in an orderly transaction between market participants. U.S. GAAP specifies a hierarchy of valuation techniques based upon whether the inputs to those valuation techniques reflect assumptions other market participants would use based upon market data obtained from independent sources (observable inputs) or reflect the Company’s own assumptions of market participant valuation (unobservable inputs). The fair value hierarchy consists of three levels: Level 1 - Quoted prices (unadjusted) in active markets that are unadjusted and accessible at the measurement date for identical, unrestricted assets or liabilities. Level 2 - Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 - Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Financial assets and liabilities are classified within the fair value hierarchy based on the lowest level of input that is significant to the fair value measurement. The authoritative guidance requires the use of observable market data if such data is available without undue cost and effort. When available, the Company uses unadjusted quoted market prices to measure fair value and classify such items within Level 1. If quoted market prices are not available, fair value is based upon internally developed models that use, where possible, current market-based or independently-sourced market parameters, such as interest and currency rates and comparable transactions. Items valued using internally generated models are classified according to the lowest level input or value driver that is significant to the valuation. Thus, items may be classified in Level 3 even though there may be inputs that are readily observable. If quoted market prices are not available, the valuation model used generally depends on the specific asset or liability being valued. At December 31, 2020 and 2019, the Company’s financial assets valued based on Level 1 inputs consisted of cash, cash equivalents and, at December 31, 2019, marketable securities (U.S. treasuries). The Company did not have any transfers of financial assets between Level 2 and 3 during 2020 or 2019. Some assets and liabilities are required to be recorded at fair value on a recurring basis, while other assets and liabilities are recorded at fair value on a nonrecurring basis. The carrying amounts of current financial instruments, which include cash and cash equivalents, restricted bank deposits, accounts payable, accrued expenses, lease obligation liability and debt, approximate their fair values due to the short-term nature of these instruments.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based compensation in accordance with ASC Topic 718, “Compensation-Stock Compensation” (“ASC 718”), which requires companies to estimate the fair value of equity-based payment awards on the date of grant using an option-pricing model. The Company recognizes compensation expenses for the value of its awards granted based on the straight-line method over the requisite service period of each of the awards or over the implicit service period when a performance condition affects the vesting, and it is considered probable that the performance condition will be achieved. The Company determines the fair value of each stock option award at its grant date using the Black-Scholes option pricing model for options awarded in 2020 and 2019 and using the . The Company determines the fair value of each stock unit, or RSU, at its grant date based on the closing market price of the Company’s common stock on that date.
Income Taxes	Income Taxes The Company accounts for income taxes in accordance with ASC Topic 740, “Income Taxes” (“ASC 740”), which prescribes the use of the asset and liability method whereby deferred tax assets and liability account balances are determined based on differences between financial reporting and tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to be recovered or settled. The Company provides a valuation allowance, if necessary, to reduce deferred tax assets to their estimated realizable value if it is more likely than not that a portion or all of the deferred tax assets will not be realized. The Company considers many factors when assessing the likelihood of future realization of deferred tax assets, including recent earnings results, expectations of future taxable income, carryforward periods available and other relevant factors. The Company records changes in the required valuation allowance in the period that the determination is made. Based on ASC 740, a two-step approach is used to recognize and measure uncertain tax positions. The first step is to evaluate the tax position taken or expected to be taken in a tax return by determining if the weight of available evidence indicates that it is more likely than not that, on an evaluation of the technical merits, the tax position will be sustained on audit, including resolution of any related appeals or litigation processes. The second step is to measure the tax benefit as the largest amount that is more than 50% likely to be realized upon ultimate settlement. As of December 31, 2020 and 2019, no liability for unrecognized tax positions has been recorded. Accordingly, no interest or penalties related to uncertain tax positions are recorded. The Company’s policy is to record any interest or penalties associated with unrecognized tax positions as a component of income tax expense.
Net Loss per Share	Net Loss per Share Basic loss per share is computed by dividing the loss for the period applicable to ordinary shareholders by the weighted average number of ordinary shares outstanding during the period. In computing diluted income per share, weighted average shares used in computing basic earnings per share are adjusted to reflect the potential dilution that could occur upon the exercise of outstanding stock options and upon conversion of restricted stock units and warrants issued to investors and service providers using the “treasury stock method”.
Leases	Leases The Company adopted the provisions of ASC topic 842, “Leases”, on January 1, 2019. The Company has operating leases for its principal offices in the U.S. and Israel. Operating lease assets represent the Company’s right to use an underlying asset for the lease term and operating lease liabilities represent the Company’s obligation to make lease payments arising from its operating leases. Lease expense for these leases is recognized on a straight-line basis over the lease term, with variable lease payments recognized in the period those payments are incurred. In determining the length of the lease term to its long-term lease, the Company determined not to consider an embedded renewal option for one operating lease primarily due to the facts that (i) the renewal rate is at a future market rate to be determined, and (ii) the Company does not have significant leasehold improvements that would restrict its ability to consider relocation. The Company applied its incremental borrowing rate based upon information available in determining the present value of the lease payments. The Company’s incremental borrowing rate is determined using a secured borrowing rate for the same currency and term as the associated lease. The Company made an accounting policy election to not recognize assets or liabilities for leases with a term of less than twelve months.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework-Changes to the Disclosure Requirements for Fair Value Measurement Although the FASB has issued several other ASUs for which adoption dates are pending, the Company does not expect any of them to have any impacts on its consolidated financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Summary of Useful Lives of Principal Classes of Assets	Depreciation expense is computed on a straight-line method over the estimated useful lives of the respective assets, as follows: Estimated Useful Life Computers and software 3 years Office furniture and equipment 5 to 12 years Laboratory equipment 5 years Leasehold improvement Over the shorter of the expected remaining lease term or estimated useful life

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	12 Months Ended
	Dec. 31, 2020
Prepaid And Other Current Assets [Abstract]
Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2020 2019 Research and development $ 631 $ 448 Insurance 170 217 VAT receivables — 26 Other 368 699 Totals $ 1,169 $ 1,390

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2020
Property Plant And Equipment [Abstract]
Property and equipment, net	Property and equipment, net consisted of the following (in thousands): December 31, 2020 2019 Computers and software $ 124 $ 166 Office furniture and equipment 164 164 Leasehold improvements 158 158 Total property and equipment, at cost 446 488 Less: Accumulated depreciation (313 ) (287 ) Property and equipment, net $ 133 $ 201

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2020
Payables And Accruals [Abstract]
Accrued expenses	Accrued expenses consisted of the following (in thousands): December 31, 2020 2019 Research and development $ 802 $ 1,560 Payroll, bonus and other employee-related expenses 1,315 2,200 Restructuring 258 — Professional services 415 664 Other 39 137 Interest on debt 57 94 Total $ 2,886 $ 4,655

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Summary of Maturities of Operating Lease Liabilities	The following table summarizes the Company’s maturities of operating lease liabilities as of December 31, 2020 (in thousands): 2021 $ 404 2022 32 Total lease payments 436 Less: present value discount (14 ) Total operating lease liabilities 422 Less: current portion (389 ) Long-term portion $ 33

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Future Principal Payments for Long-Term Debt	The Company’s scheduled future principal payments for the long-term debt are as follows (in thousands): December 31, 2020 2021 $ 5,398 2022 5,398 2023 417 Total future principal payments 11,213 Less: unamortized discount (498 ) Carrying value of long-term debt 10,715 Less: current portion (5,239 ) Add: final Term Loan fee due at maturity in 2023 900 Long-term portion $ 6,376

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Summary of Warrants Outstanding	Eloxx Limited issued warrants to purchase shares of common stock in conjunction with the Share Purchase Agreements prior to the December 2017 reverse merger between Eloxx Limited and Sevion Therapeutics, Inc. The Company also issued warrants to purchase shares of common stock in connection with the SVB Loan Agreement (further described above in Note 7, “Debt”). During the year ended December 31, 2020, transactions related to warrants were as follows: Shares Weighted average exercise price Weighted average remaining contractual life (years) Warrants outstanding at December 31, 2019 323,894 $ 4.32 3.74 Granted - Exercised - Forfeited (2 ) 520.00 Warrants outstanding at December 31, 2020 323,892 $ 4.31 2.74 Warrants exercisable at December 31, 2020 323,892 $ 4.31 2.74

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Transactions Related to Grant of Stock Options to Employees and Directors	Transactions during the year ended December 31, 2020 related to stock options granted to employees and directors were as follows: Shares Weighted average exercise price per Share Weighted average remaining contractual life (years) Aggregate intrinsic value Options outstanding as of December 31, 2019 4,737,670 $ 11.17 8.54 $ 3,629,073 Granted 1,400,010 3.52 Exercised (17,210 ) 4.08 Forfeited (2,317,409 ) (9.86 ) Options outstanding as of December 31, 2020 3,803,061 $ 10.16 8.20 $ 1,936,183 Options exercisable at December 31, 2020 1,766,009 $ 13.80 7.29 $ 1,266,440
Assumptions Used to Estimate Fair Values of Stock Options Granted	The following table presents the assumptions used to estimate the fair values of stock options granted in the periods presented: Year ended December 31, 2020 2019 2018 Dividend yield 0% 0% 0% Volatility 72%-80% 76%-92% 90%-92% Risk-free interest rate 0.36%-1.63% 1.51%-2.62% 2.55%-3.20% Expected term (years) 5.5-6.0 5.5-6.0 — Contractual term (years) 10 10 10 Forfeiture rate post-vesting — — 10% Suboptimal exercise — — 2.3
Transactions Related to Grant of Restricted Stock Units to Employees	Transactions during the year ended December 31, 2020 related to RSUs granted to employees were as follows: Shares Weighted average grant date fair value per share Unvested at December 31, 2019 463,945 $ 9.45 Granted 300,000 3.59 Vested (147,243 ) 10.32 Forfeited (266,977 ) 8.65 Unvested at December 31, 2020 349,725 $ 4.67
Summary of Allocated Stock-based Compensation Expense	The total equity-based compensation expense related to all of the Company’s equity-based awards was recognized as follows (in thousands): Year ended December 31, 2020 2019 2018 Research and development $ 979 $ 2,458 $ 1,745 General and administrative 5,563 8,878 11,625 Restructuring charges 2,124 — — Total stock-based compensation expense $ 8,666 $ 11,336 $ 13,370

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Components of Income (Loss) Before Taxes	The components of income (loss) before taxes on income are as follows (in thousands): Year ended December 31, 2020 2019 2018 U.S. $ (18,582 ) $ (22,242 ) $ (24,439 ) Israel (15,995 ) (28,632 ) (22,624 ) Loss before taxes on income $ (34,577 ) $ (50,874 ) $ (47,063 )
Current Income Tax Provision	There were no taxes on income during the year ended December 31, 2020 or 2019. Taxes on income during the year ended December 31, 2018 resulted primarily from subsidiary income as a result of the implementation of an intercompany cost-plus arrangement. The current income tax provision consisted of the following (in thousands): Year ended December 31, 2020 2019 2018 Federal $ — $ — $ 94 State and local — — 28 Foreign — — — Income tax provision $ — $ — $ 122
Significant Components of Deferred Tax Assets	The significant components of the Company’s deferred tax assets were comprised of the following (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 43,759 $ 38,357 Stock-based compensation 2,200 2,801 Reserves and allowances 431 615 U.S. tax credits and other credits 3,624 2,980 Research and development credits 2,511 1,831 Operating lease right-of-use assets (98 ) (169 ) Operating lease liabilities 98 169 Other 59 98 Total deferred tax assets 52,584 46,682 Valuation allowance (52,584 ) (46,682 ) Net deferred tax assets $ — $ —
Reconciliation of Expected Tax Expense with Actual Tax Expense	For the years ended December 31, 2020, 2019 and 2018 the expected tax expense based on the federal statutory rate is reconciled with the actual tax expense as follows: Year ended December 31, 2020 2019 2018 U.S. federal statutory rate 21.0 % 21.0 % 21.0 % State tax rate, net of federal benefit 1.0 0.9 2.4 Permanent differences (2.0 ) (1.5 ) (3.0 ) Adjustment to deferred taxes — — (1.8 ) Tax credits 2.9 — — Effect of rate differences from statutory 0.9 1.1 0.8 Tax reform - federal tax rate change — — 0.1 Tax reform - change in valuation allowance — — (0.1 ) Change in valuation allowance (23.8 ) (21.5 ) (19.5 ) Other — — (0.2 ) Income tax provision 0.0 % 0.0 % -0.3 %

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Schedule of Loss and Weighted Average Number of Shares Used in Computing Basic and Diluted Net Loss Per Share	The loss and the weighted average number of shares used in computing basic and diluted net loss per share for the years ended December 31, 2020, 2019, and 2018, are as follows (in thousands, except share and per share data): Year ended December 31, 2020 2019 2018 Numerator: Net loss $ (34,577 ) $ (50,874 ) $ (47,185 ) Denominator: Weighted average number of shares of common stock used in computing net loss per share, basic and diluted 40,124,953 38,063,173 32,436,506 Net loss per share, basic and diluted $ (0.86 ) $ (1.34 ) $ (1.45 )

Other Expense (Income), net (Ta

Other Expense (Income), net (Tables)	12 Months Ended
	Dec. 31, 2020
Other Income And Expenses [Abstract]
Schedule of Other Expense (Income)	Other Expense (income) consisted of the following (in thousands): Year ended December 31, 2020 2019 2018 Interest and other income $ (337 ) $ (1,072 ) $ (601 ) Foreign currency exchange losses (gains), net 35 76 92 Investment income, net 15 (301 ) — Interest and other expense 1,409 1,616 7 Total other expense (income), net $ 1,122 $ 319 $ (502 )

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2020
Investments Debt And Equity Securities [Abstract]
Summary of Cash, Cash Equivalents and Marketable Securities	Below is a summary of cash, cash equivalents and marketable securities at December 31, 2020 (in thousands): Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents $ 24,668 $ — $ — $ 24,668 Marketable securities - U.S. treasuries — — — — Total cash, cash equivalents and marketable securities $ 24,668 $ — $ — $ 24,668 Below is a summary of cash, cash equivalents and marketable securities at December 31, 2019 (in thousands): Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents $ 22,493 $ — $ — $ 22,493 Marketable securities - U.S. treasuries 33,765 19 (1 ) 33,783 Total cash, cash equivalents and marketable securities $ 56,258 $ 19 $ (1 ) $ 56,276

Restructuring (Tables)

Restructuring (Tables)	12 Months Ended
	Dec. 31, 2020
Restructuring And Related Activities [Abstract]
Summary of Accrued Charges and Associated Payments	The accrued charges and associated payments that occurred for the year ended December 31, 2020, are as follows (amounts in thousands): Beginning Balance Additions Deductions Ending Balance Severance and related costs $ — $ 1,729 $ (1,471 ) $ 258 Contract termination costs — 165 (165 ) — Total restructuring charges $ — $ 1,894 $ (1,636 ) $ 258

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)Disease	Dec. 31, 2019USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of rare diseases | Disease	1,800
Accumulated deficit	$ (171,596)	$ (137,019)
Cash, cash equivalents and marketable securities	$ 24,668	$ 56,276

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Line Items]
Research and development	$ 14,590,000	$ 26,349,000	$ 20,489,000
General and administrative	14,847,000	24,206,000	26,482,000
Cash equivalents	24,668,000	22,493,000	$ 48,606,000
Realized gains or losses on the sale of securities	0
Impairment of long-lived assets	0
Asset Impairment	0
Assets, transfer from level 2 to level 3	0	0
Liability for unrecognized tax benefits	0	0
Interest or penalties related to uncertain tax positions	$ 0	0
ASU No. 2016-13 [Member]
Accounting Policies [Line Items]
Change In Accounting Principle Accounting Standards Update Adopted	true
Change In Accounting Principle Accounting Standards Update Adoption Date	Jan. 1, 2020
Change In Accounting Principle Accounting Standards Update Immaterial Effect	true
ASU No. 2018-13 [Member]
Accounting Policies [Line Items]
Change In Accounting Principle Accounting Standards Update Adopted	true
Change In Accounting Principle Accounting Standards Update Adoption Date	Jan. 1, 2020
Change In Accounting Principle Accounting Standards Update Immaterial Effect	true
Revision of Prior Period, Reclassification, Adjustment [Member]
Accounting Policies [Line Items]
Research and development		500,000
Previously Reported [Member]
Accounting Policies [Line Items]
Research and development		25,800,000
General and administrative		$ 24,700,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Useful Lives of Principal Classes of Assets (Detail)	12 Months Ended
	Dec. 31, 2020
Computers and software [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of asset	3 years
Office furniture and equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of asset	5 years
Office furniture and equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of asset	12 years
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of asset	5 years
Leasehold improvement [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life of asset, description	Over the shorter of the expected remaining lease term or estimated useful life

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Schedule of Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Research and development	$ 631	$ 448
Insurance	170	217
VAT receivables		26
Other	368	699
Totals	$ 1,169	$ 1,390

Property and Equipment, net - P

Property and Equipment, net - Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	$ 446	$ 488
Less: Accumulated depreciation	(313)	(287)
Property and equipment, net	133	201
Computers and software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	124	166
Office furniture and equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	164	164
Leasehold improvement [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, at cost	$ 158	$ 158

Property and Equipment, net - A

Property and Equipment, net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Abstract]
Depreciation expenses	$ 68	$ 87	$ 216

Accrued Expenses - Accrued Expe

Accrued Expenses - Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Payables And Accruals [Abstract]
Research and development	$ 802	$ 1,560
Payroll, bonus and other employee-related expenses	1,315	2,200
Restructuring	258
Professional services	415	664
Other	39	137
Interest on debt	57	94
Total	$ 2,886	$ 4,655

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Operating lease cost	$ 0.6	$ 0.5
Operating lease weighted average incremental borrowing rate	8.00%
Weighted average remaining lease term	10 months 9 days

Leases - Summary of Maturities

Leases - Summary of Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
2021	$ 404
2022	32
Total lease payments	436
Less: present value discount	(14)
Total operating lease liabilities	422
Less: current portion	(389)	$ (499)
Operating lease liability	$ 33	$ 425

Debt - Additional Information (

Debt - Additional Information (Detail) $ / shares in Units, $ in Thousands	Jan. 30, 2019USD ($)Installment$ / sharesshares	Apr. 30, 2020USD ($)	Dec. 31, 2020USD ($)$ / shares	Dec. 31, 2019USD ($)$ / shares
Debt Instrument [Line Items]
Aggregate principal amount of initial loan advance			$ 10,715
Warrant exercise price | $ / shares			$ 4.31	$ 4.32
Loan, principal outstanding			$ 11,213
Loan, unamortized debt discount			498
Loan, final maturity payment			$ 900
Loan Agreement [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate terms	Outstanding principal on the loan accrues interest at a floating rate equal to the greater of (i) 5.25% per annum and (ii) the sum of 2.5% plus the prime rate, as published in the Wall Street Journal. Interest payments are payable monthly following the funding of the loan.
Debt instrument, payment terms	The Company commenced making payments on the outstanding principal balance of the loan on February 1, 2020, which is payable in 36 equal monthly installments.
Loan, floating interest rate	5.25%
Loan, interest rate			5.75%
Loan, frequency of periodic payment	monthly
Loan, number of repayment installments | Installment	36
Loan, periodic principal and interest payment commencement date	Feb. 1, 2020
Loan, maturity date	Jan. 1, 2023
Warrant exercise price | $ / shares	$ 11.02
Common stock average closing bid price number of trading days	10 days
Loan, prepayment fee percentage	6.00%
Loan, principal outstanding			$ 10,400
Loan, unamortized debt discount			500
Loan, interest expense			$ 1,300	$ 1,600
Loan, effective interest rate			10.85%
Loan, final maturity payment			$ 900
Loan Agreement [Member] | Minimum [Member]
Debt Instrument [Line Items]
Loan, prepayment fee percentage	1.00%
Loan Agreement [Member] | Maximum [Member]
Debt Instrument [Line Items]
Loan, prepayment fee percentage	3.00%
Loan Agreement [Member] | Prime Rate [Member]
Debt Instrument [Line Items]
Loan, floating interest rate	2.50%
Loan Agreement [Member] | Initial Loan [Member]
Debt Instrument [Line Items]
Aggregate principal amount of initial loan advance	$ 15,000
Warrants issued to purchase shares of common stock | shares	40,834
Loan Agreement [Member] | PPP Loan [Member]
Debt Instrument [Line Items]
Loan, periodic principal and interest payment commencement date		Sep. 21, 2021
Loan, maturity date		Apr. 21, 2022
PPP Loan proceeds received		$ 800
Promissory note interest rate		1.00%

Debt - Schedule of Future Princ

Debt - Schedule of Future Principal Payments for Long-Term Debt (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Disclosure [Abstract]
2021	$ 5,398
2022	5,398
2023	417
Total future principal payments	11,213
Less: unamortized discount	(498)
Carrying value of long-term debt	10,715
Less: current portion	(5,239)	$ (4,336)
Add: final Term Loan fee due at maturity in 2023	900
Long-term portion	$ 6,376	$ 10,502

Related Parties - Additional In

Related Parties - Additional Information (Detail) - USD ($) $ in Thousands	Aug. 29, 2013	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Related Party Transaction Details [Line Items]
Research and development expense		$ 14,590	$ 26,349	$ 20,489
Accrued expenses		2,886	4,655
Technion Research and Development Foundation Ltd [Member]
Schedule Of Related Party Transaction Details [Line Items]
Aggregate milestone payment		100
Technion Agreement [Member] | Technion Research and Development Foundation Ltd [Member]
Schedule Of Related Party Transaction Details [Line Items]
Research and development expense	$ 100	0	200	$ 100
Accrued expenses		0	$ 100
Aggregate milestone payment		$ 6,100

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended			48 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2018
Legal And Other Contingencies [Line Items]
Advances from collaboration partners		$ 805,000	$ 403,000
Subsequent Event [Member]
Legal And Other Contingencies [Line Items]
Additional payments received from collaboration partners	$ 2,600,000
Additional payments were received	$ 3,400,000
Maximum [Member]
Legal And Other Contingencies [Line Items]
Related party transaction percentage of expenses		5.00%
Research and Development Agreements [Member]
Legal And Other Contingencies [Line Items]
R&D grants received		$ 0	$ 0	$ 0	$ 2,600,000
Royalty payment as percentage of net sales		3.00%
Repayment percentage of grants received		100.00%
Royalty received including accrued LIBOR interest		$ 2,700,000

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	Jun. 24, 2019	Apr. 30, 2018	Jan. 31, 2019	Nov. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Nov. 16, 2018	Apr. 20, 2018	Dec. 31, 2017
Common stock, shares authorized					500,000,000		500,000,000
Common stock, par value					$ 0.01		$ 0.01
Common stock, shares outstanding					40,030,763		40,157,187
Preferred Stock, shares authorized					5,000,000		5,000,000
Preferred stock, par value					$ 0.01		$ 0.01
Preferred stock, shares issued					0		0
Preferred Stock, shares outstanding					0		0
Net proceeds from common stock shares issued at public offering					$ 710,000	$ 2,165,000
Equity Sales Agreement [Member]
Issuance of shares upon public offering, shares			35,362			201,100
Net proceeds from common stock shares issued at public offering			$ 700,000			$ 2,200,000
Legal,accounting and other fees				$ 300,000
Common Stock [Member]
Common stock, shares outstanding					40,030,763	35,860,114	40,157,187			27,527,738
Maximum [Member]
Shelf registration statement securities value								$ 200,000,000	$ 125,000,000
Maximum [Member] | Equity Sales Agreement [Member] | Citigroup Global Markets Inc. and Cantor Fitzgerald & Co. [Member]
Aggregate offering price				$ 50,000,000
Percentage of sales agents commission				3.00%
Underwritten Public Offering [Member]
Underwriting discounts and commissions and offering expenses		$ 3,900,000
Net proceeds from common stock shares issued at public offering					$ 32,172,000	$ 53,573,000
Underwritten Public Offering [Member] | Common Stock [Member]
Issuance of shares upon public offering, shares	3,833,334	5,899,500
Common stock public offering price	$ 9	$ 9.75
Gross proceeds from common stock shares issued at public offering		$ 57,500,000
Net proceeds from common stock shares issued at public offering	$ 32,200,000
Underwriting discounts and commissions	2,100,000
Offering expenses	$ 200,000
Over-Allotment Option [Member]
Common stock, shares issued		769,500

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Transaction Related to Warrants to Purchase Common Stock (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Stockholders Equity [Abstract]
Warrants outstanding beginning balance, Shares	323,894
Warrants forfeited, Shares	(2)
Warrants outstanding ending balance, Shares	323,892	323,894
Warrants exercisable, Shares	323,892
Warrants outstanding beginning balance, Weighted average exercise price	$ 4.32
Warrants forfeited, Weighted average exercise price	520
Warrants outstanding ending balance,Weighted average exercise price	4.31	$ 4.32
Warrants exercisable, Weighted average exercise price	$ 4.31
Warrants outstanding and exercisable Weighted average remaining contractual life	2 years 8 months 26 days	3 years 8 months 26 days
Warrants exercisable, Weighted average remaining contractual life	2 years 8 months 26 days

Stock-based Compensation - Addi

Stock-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Apr. 20, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options to purchase common stock granted	1,400,010
Exercise price per share	$ 3.52
Unrecognized compensation cost related to outstanding options	$ 7.6
Unrecognized compensation cost expected to be recognized over a weighted-average period	2 years 4 months 24 days
Weighted average grant date fair value of options granted	$ 2.29	$ 6.28	$ 18.06
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted stock unit	300,000
Unrecognized compensation cost expected to be recognized over a weighted-average period	3 years 3 days
Unrecognized compensation cost related to outstanding other than options	$ 1.4
Chief Executive Officer [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options to purchase common stock granted				663,212
Exercise price per share				$ 8
Restricted stock unit				663,212
2018 Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance					5,000,000
Contractual life of stock options granted	10 years
2018 Plan [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercisable period of vested options	1 month
2018 Plan [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercisable period of vested options	3 months

Stock-based Compensation - Tran

Stock-based Compensation - Transactions Related to Grant of Stock Options to Employees and Directors (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Amount
Options outstanding as of December 31, 2019	4,737,670
Granted	1,400,010
Exercised	(17,210)
Forfeited	(2,317,409)
Options outstanding as of December 31, 2020	3,803,061	4,737,670
Options exercisable at December 31, 2020	1,766,009
Weighted average exercise price per Share
Options outstanding as of December 31, 2019	$ 11.17
Granted	3.52
Exercised	4.08
Forfeited	(9.86)
Options outstanding as of December 31, 2020	10.16	$ 11.17
Options exercisable at December 31, 2020	$ 13.80
Weighted average remaining contractual life
Options outstanding	8 years 2 months 12 days	8 years 6 months 14 days
Options exercisable	7 years 3 months 14 days
Aggregate intrinsic value
Options outstanding	$ 1,936,183	$ 3,629,073
Options exercisable	$ 1,266,440

Stock-based Compensation - Assu

Stock-based Compensation - Assumptions Used to Estimate Fair Values of Stock Options Granted (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield	0.00%	0.00%	0.00%
Volatility, minimum	72.00%	76.00%	90.00%
Volatility, maximum	80.00%	92.00%	92.00%
Risk free interest rate, minimum	0.36%	1.51%	2.55%
Risk free interest rate, maximum	1.63%	2.62%	3.20%
Contractual term (years)	10 years	10 years	10 years
Forfeiture rate post-vesting			10.00%
Suboptimal exercise			$ 2.3
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 6 months	5 years 6 months
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years	6 years

Stock-based Compensation - Tr_2

Stock-based Compensation - Transactions Related to Grant of Restricted Stock Units to Employees (Detail) - Restricted Stock Units [Member]	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Amount
Unvested at December 31, 2019 | shares	463,945
Granted | shares	300,000
Vested | shares	(147,243)
Forfeited | shares	(266,977)
Unvested at December 31, 2020 | shares	349,725
Weighted average grant date fair value price
Unvested at December 31, 2019 | $ / shares	$ 9.45
Granted | $ / shares	3.59
Vested | $ / shares	10.32
Forfeited | $ / shares	8.65
Unvested at December 31, 2020 | $ / shares	$ 4.67

Stock-based Compensation - Summ

Stock-based Compensation - Summary of Allocated Stock-based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 8,666	$ 11,336	$ 13,370
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	979	2,458	1,745
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	5,563	$ 8,878	$ 11,625
Restructuring Charges [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 2,124

Income Taxes - Components of In

Income Taxes - Components of Income (Loss) Before Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
U.S.	$ (18,582)	$ (22,242)	$ (24,439)
Israel	(15,995)	(28,632)	(22,624)
Loss before taxes on income	$ (34,577)	$ (50,874)	$ (47,063)

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 23, 2017	Dec. 19, 2017
Income Tax Disclosure [Line Items]
Taxes on income	$ 0	$ 0	$ 122,000
Deferred tax assets, valuation allowance	52,584,000	46,682,000
Net deferred tax asset	0	0
Change in valuation allowance	5,900,000	10,800,000
Federal research tax credit carryforwards	$ 3,600,000	$ 3,000,000				$ 700,000
U.S. federal corporate income tax rate	21.00%	21.00%	21.00%	35.00%
Provisional estimate of deferred tax expense				$ 10,200,000
Income tax examination, description	The Company is subject to income taxes in the United States and Israel. The Company files income tax returns in the U.S. and in several states. The federal and state tax returns are generally subject to tax examination by taxing authorities for tax years beginning in June 30, 2015 to present. To the extent the Company has tax attribute carryforwards, the tax years in which the attribute was generated may still be adjusted upon examination by the Internal Revenue Service or state tax authorities to the extent utilized in a future period. The Israeli income tax returns remain open to examination beginning in 2013 to present. If and when the Company claims NOL carryforwards from any prior years against future taxable income, those losses may be examined by the taxing authorities.
Earliest Tax Year [Member]
Income Tax Disclosure [Line Items]
Federal research tax credit expiry, beginning period	2026
Latest Tax Year [Member]
Income Tax Disclosure [Line Items]
Federal research tax credit expiry, beginning period	2040
Federal [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 108,900,000	$ 99,400,000				$ 77,200,000
U.S. federal NOL carryforwards, not subject to expiration					$ 34,900,000
Net operating loss carryforwards eligible to offset taxable income, maximum	80.00%
Federal [Member] | Earliest Tax Year [Member]
Income Tax Disclosure [Line Items]
U.S. net operating loss expiry, beginning period	2021
Federal [Member] | Latest Tax Year [Member]
Income Tax Disclosure [Line Items]
U.S. net operating loss expiry, beginning period	2037
State [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 13,700,000	31,900,000
Israel Tax Authority [Member]
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 86,900,000	$ 73,700,000

Income Taxes - Current Income T

Income Taxes - Current Income Tax Provision (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Federal			$ 94,000
State and local			28,000
Income tax provision	$ 0	$ 0	$ 122,000

Income Taxes - Significant Comp

Income Taxes - Significant Components of Deferred Tax Assets (Detail) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryforwards	$ 43,759,000	$ 38,357,000
Stock-based compensation	2,200,000	2,801,000
Reserves and allowances	431,000	615,000
U.S. tax credits and other credits	3,624,000	2,980,000
Research and development credits	2,511,000	1,831,000
Operating lease right-of-use assets	(98,000)	(169,000)
Operating lease liabilities	98,000	169,000
Other	59,000	98,000
Total deferred tax assets	52,584,000	46,682,000
Valuation allowance	(52,584,000)	(46,682,000)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Expected Tax Expense with Actual Tax Expense (Detail)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
U.S. federal statutory rate	21.00%	21.00%	21.00%	35.00%
State tax rate, net of federal benefit	1.00%	0.90%	2.40%
Permanent differences	(2.00%)	(1.50%)	(3.00%)
Adjustment to deferred taxes			(1.80%)
Tax credits	2.90%
Effect of rate differences from statutory	0.90%	1.10%	0.80%
Tax reform - federal tax rate change			0.10%
Tax reform - change in valuation allowance			(0.10%)
Change in valuation allowance	(23.80%)	(21.50%)	(19.50%)
Other			(0.20%)
Income tax provision	0.00%	0.00%	(0.30%)

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Loss and Weighted Average Number of Shares Used in Computing Basic and Diluted Net Loss Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss	$ (34,577)	$ (50,874)	$ (47,185)
Denominator:
Weighted average number of shares of common stock used in computing net loss per share, basic and diluted	40,124,953	38,063,173	32,436,506
Net loss per share, basic and diluted	$ (0.86)	$ (1.34)	$ (1.45)

Net Loss Per Share - Additional

Net Loss Per Share - Additional Information (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Shares excluded from the calculation of the diluted net loss per share	4,476,678	5,525,509	4,163,107

Other Expense (Income), net - S

Other Expense (Income), net - Schedule of Other Expense (Income) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Income And Expenses [Abstract]
Interest and other income	$ (337)	$ (1,072)	$ (601)
Foreign currency exchange losses (gains), net	35	76	92
Investment income, net	15	(301)
Interest and other expense	1,409	1,616	7
Total other expense (income), net	$ 1,122	$ 319	$ (502)

Segment and Geographic Inform_2

Segment and Geographic Information - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2020SegmentRegion
Segment Reporting [Abstract]
Number of operating segment | Segment	1
Number of geographic regions | Region	2

Marketable Securities - Summary

Marketable Securities - Summary of Cash, Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Cash and cash equivalents	$ 24,668	$ 22,493	$ 48,606
Cash and cash equivalents, Fair Value	24,668	22,493
Total cash, cash equivalents and marketable securities, Amortized Cost	24,668	56,258
Total cash, cash equivalents and marketable securities, Unrealized Gains		19
Total cash, cash equivalents and marketable securities, Unrealized Losses		(1)
Total cash, cash equivalents and marketable securities, Fair Value	$ 24,668	56,276
U.S. treasuries [Member]
Schedule Of Available For Sale Securities [Line Items]
Marketable securities, Amortized Cost		33,765
Marketable securities, Unrealized Gains		19
Marketable securities, Unrealized Losses		(1)
Marketable securities, Fair Value		$ 33,783

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Credit losses related to the cash equivalents or marketable securities	$ 0	$ 0

Restructuring - Additional Info

Restructuring - Additional Information (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2020USD ($)Employee
Restructuring And Related Activities [Abstract]
Elimination of managerial full time positions | Employee	13
Severance costs, one-time charge	$ 4
Severance costs, stock-based compensation expense	$ 2.1
Restructuring and related costs, severance cost payment period	1 year

Restructuring - Summary of Accr

Restructuring - Summary of Accrued Charges and Associated Payments (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Restructuring Cost And Reserve [Line Items]
Additions	$ 1,894
Deductions	(1,636)
Ending Balance	258
Severance and Related Costs [Member]
Restructuring Cost And Reserve [Line Items]
Additions	1,729
Deductions	(1,471)
Ending Balance	258
Contract Termination Costs [Member]
Restructuring Cost And Reserve [Line Items]
Additions	165
Deductions	$ (165)