Arqule (ARQL) 10-Q 30 Oct 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Oct. 16, 2019
Document and Entity Information [Abstract]
Entity Registrant Name	ARQULE INC
Entity Central Index Key	0001019695
Trading Symbol	arql
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Common Stock, Shares Outstanding		120,733,695
Document Type	10-Q
Document Period End Date	Sep. 30, 2019
Entity Shell Company	false
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Small Business	true
Entity Emerging Growth Company	false

CONDENSED BALANCE SHEETS

CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 42,199	$ 19,236
Marketable securities - short term	83,014	80,322
Contract receivables	874	5,984
Prepaid expenses	1,952	861
Total current assets	128,039	106,403
Marketable securities - long term	48,900
Property and equipment, net	463	69
Operating lease assets	2,691
Other assets	249	204
Total assets	180,342	106,676
Current liabilities:
Accounts payable and accrued expenses	9,933	12,948
Notes payable - current portion	5,000	1,667
Operating lease liability - current portion	546
Total current liabilities	15,479	14,615
Long-term liabilities:
Notes payable - long term	9,582	13,093
Operating lease liability - long term	2,155
Total liabilities	27,216	27,708
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.01 par value; 1,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.01 par value; 200,000,000 shares authorized; 120,661,081 and 109,003,637 shares issued and outstanding at September 30, 2019 and December 31, 2018, respectively	1,207	1,090
Additional paid-in capital	729,910	625,993
Accumulated other comprehensive income (loss)	127	(95)
Accumulated deficit	(578,118)	(548,020)
Total stockholders' equity	153,126	78,968
Total liabilities and stockholders' equity	$ 180,342	$ 106,676

CONDENSED BALANCE SHEETS (Paren

CONDENSED BALANCE SHEETS (Parentheticals) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
CONDENSED BALANCE SHEETS
Preferred Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	1,000,000	1,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	120,661,081	109,003,637
Common stock, shares outstanding	120,661,081	109,003,637

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue:
Research and development revenue	$ 208	$ 4,979	$ 1,834	$ 22,823
Costs and expenses:
Research and development	8,313	7,261	22,091	19,860
General and administrative	3,170	3,429	10,638	8,014
Total costs and expenses	11,483	10,690	32,729	27,874
Loss from operations	(11,275)	(5,711)	(30,895)	(5,051)
Interest income	961	514	2,085	843
Interest expense	(425)	(422)	(1,288)	(1,235)
Other expense				(1,552)
Net loss	(10,739)	(5,619)	(30,098)	(6,995)
Unrealized gain (loss) on marketable securities	47	(10)	222	(16)
Comprehensive loss	$ (10,692)	$ (5,629)	$ (29,876)	$ (7,011)
Basic and diluted net loss per share:
Net loss per share (in dollars per share)	$ (0.09)	$ (0.05)	$ (0.27)	$ (0.07)
Weighted average basic and diluted common shares outstanding (in shares)	120,374	107,445	113,126	95,678

CONDENSED STATEMENTS OF STOCKHO

CONDENSED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	PREFERRED STOCK	Common Stock	ADDITIONAL PAID-IN CAPITAL	ACCUMULATED OTHER COMPREHENSIVE INCOME/(LOSS)	ACCUMULATED DEFICIT	Total
Balance at Dec. 31, 2017	$ 8,843	$ 871	$ 547,364	$ (16)	$ (534,038)	$ 14,181
Balance (in shares) at Dec. 31, 2017	8,370	87,110,202
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises and issuance of common stock			25			25
Stock option exercises and issuance of common stock (in shares)		15,125
Stock based compensation expense			423			423
Warrants issued upon debt extension			120			120
Change in unrealized gain on marketable securities				(25)		(25)
Increase to opening accumulated deficit upon adoption of new accounting standard					1,500	1,500
Net income/loss					(6,532)	(6,532)
Balance at Mar. 31, 2018	$ 8,843	$ 871	547,932	(41)	(539,070)	9,692
Balance (in shares) at Mar. 31, 2018	8,370	87,125,327
Balance at Dec. 31, 2017	$ 8,843	$ 871	547,364	(16)	(534,038)	14,181
Balance (in shares) at Dec. 31, 2017	8,370	87,110,202
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income/loss						(6,995)
Balance at Sep. 30, 2018		$ 1,090	625,572	(32)	(539,533)	87,097
Balance (in shares) at Sep. 30, 2018		108,993,547
Balance at Mar. 31, 2018	$ 8,843	$ 871	547,932	(41)	(539,070)	9,692
Balance (in shares) at Mar. 31, 2018	8,370	87,125,327
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock and warrants due to conversion of preferred stock to common stock and preferred warrants to common warrants	$ (8,843)	$ 84	11,823			11,907
Issuance of common stock and warrants due to conversion of preferred stock to common stock and preferred warrants to common warrants ( in shares)	(8,370)	8,370,000
Stock option exercises and issuance of common stock		$ 3	152			155
Stock option exercises and issuance of common stock (in shares)		337,616
Shares issued from exercise of warrants		$ 3	(2)			1
Shares issued from exercise of warrants (in shares)		269,584
Stock based compensation expense			314			314
Change in unrealized gain on marketable securities				19		19
Net income/loss					5,156	5,156
Balance at Jun. 30, 2018		$ 961	560,219	(22)	(533,914)	27,244
Balance (in shares) at Jun. 30, 2018		96,102,527
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from stock offering, net		$ 127	64,435			64,562
Issuance of common stock from stock offering, net (in shares)		12,650,000
Stock option exercises and issuance of common stock		$ 2	555			557
Stock option exercises and issuance of common stock (in shares)		241,020
Stock based compensation expense			363			363
Change in unrealized gain on marketable securities				(10)		(10)
Net income/loss					(5,619)	(5,619)
Balance at Sep. 30, 2018		$ 1,090	625,572	(32)	(539,533)	87,097
Balance (in shares) at Sep. 30, 2018		108,993,547
Balance at Dec. 31, 2018		$ 1,090	625,993	(95)	(548,020)	$ 78,968
Balance (in shares) at Dec. 31, 2018		109,003,637				109,003,637
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock option exercises and issuance of common stock		$ 1	143	0	0	$ 144
Stock option exercises and issuance of common stock (in shares)		92,122
Stock based compensation expense			2,124			2,124
Change in unrealized gain on marketable securities				117		117
Net income/loss					(10,267)	(10,267)
Balance at Mar. 31, 2019		$ 1,091	628,260	22	(558,287)	71,086
Balance (in shares) at Mar. 31, 2019		109,095,759
Balance at Dec. 31, 2018		$ 1,090	625,993	(95)	(548,020)	$ 78,968
Balance (in shares) at Dec. 31, 2018		109,003,637				109,003,637
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income/loss						$ (30,098)
Balance at Sep. 30, 2019		$ 1,207	729,910	127	(578,118)	$ 153,126
Balance (in shares) at Sep. 30, 2019		120,661,081				120,661,081
Balance at Mar. 31, 2019		$ 1,091	628,260	22	(558,287)	$ 71,086
Balance (in shares) at Mar. 31, 2019		109,095,759
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from stock offering, net		$ 106	97,234			97,340
Issuance of common stock from stock offering, net (in shares)		10,637,500
Stock option exercises and issuance of common stock		$ 6	1,301			1,307
Stock option exercises and issuance of common stock (in shares)		527,126
Stock based compensation expense			917			917
Change in unrealized gain on marketable securities				58		58
Net income/loss					(9,092)	(9,092)
Balance at Jun. 30, 2019		$ 1,203	727,712	80	(567,379)	161,616
Balance (in shares) at Jun. 30, 2019		120,260,385
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from stock offering, net			(13)			(13)
Stock option exercises and issuance of common stock		$ 3	1,004			1,007
Stock option exercises and issuance of common stock (in shares)		286,410
Shares issued from exercise of warrants		$ 1	199			200
Shares issued from exercise of warrants (in shares)		114,286
Stock based compensation expense			1,008			1,008
Change in unrealized gain on marketable securities				47		47
Net income/loss					(10,739)	(10,739)
Balance at Sep. 30, 2019		$ 1,207	$ 729,910	$ 127	$ (578,118)	$ 153,126
Balance (in shares) at Sep. 30, 2019		120,661,081				120,661,081

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income/loss	$ (30,098)	$ (6,995)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	82	35
Amortization of premium on marketable securities	533	387
Amortization of debt discount	239	242
Change in fair value of warrant liability		1,552
Non-cash stock compensation	4,050	1,100
Changes in operating assets and liabilities:
Contract receivables	5,065	(6,401)
Prepaid expenses and others, net	(1,081)	(229)
Accounts payable and accrued expenses	(3,015)	2,513
Net cash used in operating activities	(24,225)	(7,796)
Cash flows from investing activities:
Purchases of marketable securities	(125,645)	(100,285)
Proceeds from sale or maturity of marketable securities	73,742	38,779
Purchases of property and equipment	(476)
Net cash used in investing activities	(52,379)	(61,506)
Cash flows from financing activities:
Costs from notes payable and warrants, net		(48)
Proceeds from stock offering, net of offering costs	97,327	64,561
Proceeds from stock option exercises and employee stock plan purchases	2,458	738
Proceeds from warrant exercises	199
Principal payments on long-term debt	(417)
Net cash provided by financing activities	99,567	65,251
Net increase (decrease) in cash and cash equivalents	22,963	(4,051)
Cash and cash equivalents, beginning of period	19,236	20,229
Cash and cash equivalents, end of period	$ 42,199	$ 16,178

NATURE OF OPERATIONS AND BASIS

NATURE OF OPERATIONS AND BASIS OF PRESENTATION	9 Months Ended
	Sep. 30, 2019
NATURE OF OPERATIONS AND BASIS OF PRESENTATION
NATURE OF OPERATIONS AND BASIS OF PRESENTATION	1. NATURE OF OPERATIONS AND BASIS OF PRESENTATION We are a biopharmaceutical company engaged in the research and development of innovative therapeutics to treat cancers and rare diseases. Our mission is to discover, develop and commercialize novel small molecule drugs in areas of high unmet need that will dramatically extend and improve the lives of our patients. These product candidates target biological pathways implicated in a wide range of cancers and certain non-oncology indications. Our discovery and development efforts are guided, when possible, by an understanding of the role of biomarkers, which are indicators of a particular biological condition or process and may predict the clinical benefit of our compounds in defined patient populations. Our clinical-stage pipeline consists of four product candidates, all of which are in targeted patient populations, making ArQule a leader among companies our size in precision medicine. ArQule has a long history of kinase drug discovery and development, having discovered and introduced ten kinase inhibitors into clinical trials. Our drug discovery efforts have been informed by our historical expertise in chemistry, our work in rational drug design and by our insight into kinase binding and regulation. We have applied this knowledge to produce significant chemical matter for a number of kinase targets and to build an extensive library of proprietary compounds with the potential to target multiple kinases in oncology and other therapeutic areas, such as rare diseases. We may bring further preclinical programs forward and interrogate our library against new targets beyond kinases either directly or with collaborators. Our proprietary pipeline of orally bioavailable product candidates is directed toward molecular targets and biological processes with demonstrated roles in the development of both human cancers and rare, non-oncology diseases. All of these programs are being developed in targeted, biomarker-defined patient populations. By seeking out subgroups of patients that are most likely to respond to our product candidates, we seek to identify small, often orphan, indications that allow for focused and efficient development. At the same time, in addition to pursuing these potentially fast-to-market strategies, we also pursue development in other indications that could allow us to expand the utility of the product candidates if approved. Our clinical pipeline includes the following product candidates: · ARQ 531 is a potent and reversible dual inhibitor of both wild type and C481S-mutant Bruton’s tyrosine kinase (BTK) that is in Phase 1/2 clinical development for B-cell malignancies refractory to other therapeutic options; · Miransertib (ARQ 092) is a potent and selective inhibitor of protein kinase B (AKT), a serine/threonine kinase that is in a registrational clinical trial for the treatment of Proteus syndrome and PIK3CA-Related Overgrowth Syndromes (PROS); · ARQ 751 is a next-generation, highly potent and selective inhibitor of AKT that is in Phase 1 clinical development for solid tumors harboring AKT, phosphoinositide 3‑kinase (PI3K) or phosphatase and tensin homolog (PTEN) loss mutations or that are PTEN null; and · Derazantinib (ARQ 087) is a multi-kinase inhibitor designed to preferentially inhibit the fibroblast growth factor receptor (FGFR) family of kinases that is in a registrational clinical trial in intrahepatic cholangiocarcinoma (iCCA) in patients with FGFR2 fusions. Derazantinib was exclusively licensed to Basilea Pharmaceutica Limited (Basilea) in April 2018 in the United States, European Union, Japan and the rest of the world, excluding the People’s Republic of China, Hong Kong, Macau, and Taiwan (collectively, Greater China) where derazantinib was exclusively licensed to Sinovant Sciences Ltd., a subsidiary of Roivant Sciences Ltd. (Sinovant) in February 2018. Our uses of cash for operating activities have primarily consisted of salaries and wages for our employees, facility and facility-related costs for our offices and laboratories, fees paid in connection with preclinical and clinical studies, laboratory supplies and materials, and professional fees. The sources of our cash flow from operating activities have historically consisted primarily of upfront and other payments received from our collaborators in connection with license agreements. In the nine months ended September 30, 2019 and 2018, our net use of cash was primarily driven by payments for operating expenses which resulted in net cash outflows of $24.2 million and $7.8 million, respectively. Our cash requirements may vary materially from those now planned depending on the results of our drug discovery and development strategies, our ability to enter into additional corporate collaborations and the terms of such collaborations, results of research and development, unanticipated required capital expenditures, competitive and technological advances, acquisitions and other factors. We cannot guarantee that we will be able to develop any of our product candidates into a commercial product. In January 2017, we entered into a loan and security agreement with Oxford Finance, LLC (the “Loan Agreement”) with an initial principal balance of $15 million (see Note 8). The terms of the Loan Agreement, which was amended in February 2018, required only payments of interest on a monthly basis through August 2019 . As of September 2019, we are required to make payments of principal and interest on a monthly basis through the maturity date of the loan on August 1, 2022. In November 2017, we entered into definitive securities purchase agreements with certain institutional investors. In conjunction with this stock offering we raised net proceeds of  $9.5 million through the sale of 8,370 shares of series A convertible preferred stock (Series A Preferred) and warrants to purchase 2,259 shares of Series A Preferred (Warrants). Each share of Series A Preferred converted into 1,000 shares of common stock and each associated Warrant converted into 1,000 common stock warrants in May 2018. In September 2019, holders of the common stock warrants exercised warrants covering 114,286 shares of common stock, resulting in net proceeds of $0.2 million. The remaining common stock warrants have a post-conversion exercise price of  $1.75 per share, are exercisable immediately and expire in May 2022. In February 2018, we entered into a License Agreement with Sinovant pursuant to which we granted Sinovant an exclusive license to develop and commercialize derazantinib in Greater China. The agreement provided for an upfront payment to ArQule of $3 million and a $2.5 million development milestone that was paid in the first quarter of 2019. We are also eligible for up to an additional $12.0 million in regulatory milestone payments and $70.0 million in commercial milestone payments. Upon commercialization, we are entitled to receive double digit royalties in the low teens from Sinovant on net sales of derazantinib in Greater China. Sinovant will be responsible for all costs and expenses of development, manufacture and commercialization in Greater China. In the three and nine months ended September 30, 2019 , we recognized revenue of $0.2 million and $1.6 million, respectively, for providing certain Manufacturing Services (as defined in Note 2) to Sinovant. During the three and nine months ended September 30, 2018, we recognized revenue of $2.9 million and $5.9 million, respectively, related primarily to the transfer of the license to Sinovant and the expected achievement of a development milestone that was ultimately paid in the first quarter of 2019. In April 2018, we entered into a License Agreement with Basilea pursuant to which we granted Basilea an exclusive license to develop and commercialize derazantinib in the United States, European Union, Japan and the rest of the world, excluding Greater China. Under the terms of the agreement, we received an upfront payment of  $10 million and are eligible for up to $63.0 million in development and regulatory milestone payments and up to $262.5 million in commercial milestone payments. Upon commercialization, we are entitled to receive tiered royalties on future net sales of derazantinib ranging from the high-single digits to the mid-teens on direct sales and mid-single digits to low-double digits on indirect sales. Basilea will be responsible for all costs and expenses of development, manufacture and commercialization in its territory. Under certain circumstances, we may have the opportunity to promote derazantinib in the United States directly. In the three and nine months ended September 30, 2019, we recognized revenue of zero and $0.2 million, respectively, for providing R&D Services (as defined in Note 2) to Basilea, recognized as revenue on a “cost-to-cost method". In the three and nine months ended September 30, 2018 we recognized revenue of $2.0 million and $15.7 million, respectively, related to providing R&D Services to Basilea as well as the transfer of the Basilea License. In July 2018, we sold 12,650,000 shares of common stock at $5.50 per share for aggregate net proceeds of approximately $64.6 million after commissions and other offering expenses. In June 2019, we sold 10,637,500 shares of common stock at $9.75 per share for aggregate net proceeds of approximately $97.3 million after commissions and other offering expenses. We anticipate that our cash, cash equivalents and marketable securities on hand at September 30, 2019 will be sufficient to finance our operations for at least 12 months from the issuance date of these financial statements. We expect that we will need to raise additional capital or incur indebtedness to continue to fund our operations in the future. Our ability to raise additional funds will depend on financial, economic and market conditions, and due to global capital and credit market conditions or for other reasons, we may be unable to raise capital when needed, or on terms favorable to us. If necessary funds are not available, we may have to delay, reduce the scope of, or eliminate some of our development programs, potentially delaying the time to market for any of our product candidates.

COLLABORATIONS AND ALLIANCES

COLLABORATIONS AND ALLIANCES	9 Months Ended
	Sep. 30, 2019
COLLABORATIONS AND ALLIANCES
COLLABORATIONS AND ALLIANCES	2. COLLABORATIONS AND ALLIANCES Basilea Agreement In April 2018, we entered into a License Agreement with Basilea (the "Basilea Agreement") pursuant to which we granted Basilea an exclusive license to develop and commercialize derazantinib in the United States, European Union, Japan and the rest of the world, excluding Greater China (the "Basilea Territory"). Under the terms of the Basilea Agreement, we received an upfront payment of $10.0 million . In addition, we are eligible to receive up to $63.0 million in development and regulatory milestone payments across multiple indications in the United States, European Union and Japan, none of which exceed $12.0 million on an individual basis, and up to $262.5 million in commercial milestone payments based upon the attainment of specified calendar year net sales levels for all indications in the Basilea Territory. Upon commercialization, we are entitled to receive tiered royalties on future net sales of derazantinib ranging from the high-single digits to the mid-teens on direct sales in the Basilea Territory and mid-single digits to low-double digits on indirect sales in the Basilea Territory. Basilea is responsible for all costs and expenses of development, manufacture and commercialization in its territory. Under certain circumstances, we may have the opportunity to promote derazantinib in the United States directly. We evaluated the Basilea Agreement in accordance with ASC 606, Revenue from Contracts with Customers . We concluded there were two performance obligations under the Basilea Agreement at contract inception: (1) the grant of the exclusive license (the "Basilea License") to derazantinib in the Basilea Territory and (2) the provision of specified research and development services to Basilea (the "R&D Services"). The total transaction price for the Basilea Agreement at contract inception was determined to be $19.8 million, which was comprised of the $10.0 million upfront payment and an estimated $9.8 million of variable consideration to be received for the R&D Services. As of June 30, 2019, the R&D Services performance obligation was substantially complete. At contract inception, the variable consideration associated with development and regulatory milestone payments was excluded from the transaction price, and as of September 30, 2019 continued to be excluded from the transaction price, as achievement of the milestones is contingent upon future events and is not considered the most-likely outcome. We update our estimates for development and regulatory milestone variable consideration at each reporting date and will recognize revenue associated with a particular milestone when achieving the milestone is considered the most-likely outcome and it is probable that a significant reversal of cumulative revenue under the contract will not occur. The commercial milestone and royalty consideration were excluded from the transaction price because the Basilea License was determined to be the predominant item in the contract. As a result, we will recognize revenue associated with the commercial milestones and royalties at the later of when (i) the related sales occur or (ii) the performance obligation to which some or all of the applicable commercial milestone and/or royalty has been allocated has been satisfied (or partially satisfied). As of September 30, 2019, we have not recognized any commercial milestone or royalty revenue under the Basilea Agreement. The total transaction price was allocated to the two performance obligations based on the relative standalone selling price of each performance obligation at contract inception. The standalone selling price for the Basilea License was determined on a discounted cash flow basis. At contract inception, $10.3 million of the total transaction price was allocated to the Basilea License and was recognized when control of the Basilea License was transferred and the license period began. The standalone selling price for the R&D Services was determined based upon a cost-plus margin approach. At contract inception, $9.5 million of the transaction price was allocated to the R&D Services. Revenue related to the R&D Services is recognized on a “cost-to-cost” percentage of completion basis as the services are performed. For the three and nine months ended September 30, 2019, we recognized revenue of zero and $0.2 million, respectively, under the Basilea Agreement related to R&D Services provided to Basilea. For the three and nine months ended September 30, 2018, we recognized revenue of $2.0 million and $15.7 million, respectively, related to providing R&D Services to Basilea as well as the transfer of the Basilea License. Sinovant Agreement In February 2018, we entered into a License Agreement with Sinovant (the "Sinovant Agreement") pursuant to which we granted Sinovant an exclusive license to develop, manufacture and commercialize derazantinib in Greater China. Under the terms of the Sinovant Agreement, we have received an upfront payment of  $3.0 million and recognized a $2.5 million regulatory milestone payment in the third quarter of 2018. We are also eligible to receive up to an additional $12.0 million in regulatory milestone payments across multiple indications in Greater China and $70.0 million in commercial milestone payments based upon the attainment of specified calendar year net sales levels for all indications in Greater China. Upon commercialization, we are entitled to receive double digit royalties in the low teens from Sinovant on net sales of derazantinib in Greater China. Sinovant will be responsible for all costs and expenses of development, manufacture and commercialization in Greater China. We evaluated the Sinovant Agreement in accordance with ASC 606, Revenue from Contracts with Customers . We concluded that the only performance obligation under the Sinovant Agreement at contract inception was the grant of the exclusive license (the “Sinovant License”) to derazantinib in Greater China. The Sinovant Agreement also contemplated that we might provide certain manufacturing services (the “Manufacturing Services”), which we concluded was not a separate performance obligation at contract inception. The total transaction price for the Sinovant Agreement at contract inception was determined to be $3.0 million, which was equal to the upfront payment under the Sinovant Agreement. The $3.0 million was fully allocable to the Sinovant License and was recognized as revenue when control was transferred and the license period began. Our right to receive regulatory milestone payments is considered variable consideration. At contract inception, the variable consideration associated with regulatory milestone payments was excluded from the transaction price as achievement of the milestones was contingent upon future events and achievement of the milestones is not considered the most-likely outcome. We update our estimates for regulatory milestones at each reporting date and will recognize revenue associated with a particular milestone when we determine that achieving the milestone is the most-likely outcome and it is probable that a significant reversal of cumulative revenue under the contract will not occur. Based on the above analysis, we recognized $2.5 million in revenue associated with a regulatory milestone in the third quarter of 2018. The commercial milestones and royalty consideration were excluded from the transaction price because the Sinovant License is the only performance obligation and therefore considered the predominant item under the contract. As a result, we recognize revenue associated with the commercial milestones and royalties at the later of when (i) the related sales occur or (ii) the performance obligation to which some or all of the applicable commercial milestone and/or royalty has been allocated has been satisfied (or partially satisfied). As of September 30, 2019, we have not recognized any commercial milestone or royalty revenue under the Sinovant Agreement. In December 2018, we entered into a Supply Agreement with Sinovant where we agreed to provide the Manufacturing Services to Sinovant beyond the term contemplated for those services under the Sinovant Agreement. The Manufacturing Services are the only performance obligation under the Supply agreement and revenue related to the Supply Agreement is recognized on a “cost-to-cost” percentage of completion basis as the services are performed. For the three and nine months ended September 30, 2019, we recognized revenue of  $0.2 million and  $1.6 million, respectively, under the Sinovant Agreement related to the Manufacturing Services that we provided. For the three and nine months ended September 30, 2018, we recognized revenue of $2.9 million and $5.9 million, respectively, related primarily to the transfer of the Sinovant License and the achievement of a regulatory milestone discussed above. Other Licensing Agreements In October 2017, we granted a third party a non-exclusive license to certain of our library compounds. The licensed compounds were delivered and were accepted by the third party in 2018. Accordingly, revenue for the three and nine months ended September 30, 2019 was zero. For the three and nine months ended September 30, 2018, we recorded revenue of $0.1 million and $1.3 million, based upon the achievement of the quality and acceptance testing.

MARKETABLE SECURITIES AND FAIR

MARKETABLE SECURITIES AND FAIR VALUE MEASUREMENTS	9 Months Ended
	Sep. 30, 2019
MARKETABLE SECURITIES AND FAIR VALUE MEASUREMENTS
MARKETABLE SECURITIES AND FAIR VALUE MEASUREMENTS	3. MARKETABLE SECURITIES AND FAIR VALUE MEASUREMENTS We generally classify our marketable securities as available-for-sale at the time of purchase and re-evaluate such designation as of each balance sheet date. Since we generally intend to convert them into cash as necessary to meet our liquidity requirements our marketable securities are classified as cash equivalents if the original maturity, from the date of purchase, is ninety days or less and as short-term investments if the original maturity, from the date of purchase, is in excess of ninety days but less than or equal to one year. Our marketable securities are classified as long-term investments if the maturity date is in excess of one year of the balance sheet date. We report available-for-sale debt securities at fair value as of each balance sheet date and include any unrealized gains and, to the extent deemed temporary, unrealized losses in stockholders’ equity. Realized gains and losses are determined using the specific identification method and are included in other income (expense) in the statements of operations and comprehensive loss. We conduct quarterly reviews to determine the fair value of our investment portfolio and to identify and evaluate each investment that has an unrealized loss, in accordance with the meaning of other-than-temporary impairment and its application to certain investments. An unrealized loss exists when the current fair value of an individual security is less than its amortized cost basis. In the event that the cost basis of a security exceeds its fair value, we evaluate, among other factors, the duration of the period that, and extent to which, the fair value is less than cost basis, the financial health of and business outlook for the issuer, including industry and sector performance, and operational and financing cash flow factors, overall market conditions and trends, our intent to sell the investment and if it is more likely than not that we would be required to sell the investment before its anticipated recovery. Unrealized losses on available-for-sale securities that are determined to be temporary, and not related to credit loss, are recorded in accumulated other comprehensive income (loss). For available-for-sale debt securities with unrealized losses, we perform an analysis to assess whether we intend to sell or whether we would more likely than not be required to sell the security before the expected recovery of the amortized cost basis. Where we intend to sell an available-for-sale debt security, or may be required to do so, the security’s decline in fair value is deemed to be other-than-temporary and the full amount of the unrealized loss is reflected in the statements of operations and comprehensive loss as an impairment loss. Regardless of our intent to sell a security, we perform additional analysis on all securities with unrealized losses to evaluate losses associated with the creditworthiness of the security. Credit losses are identified where we do not expect to receive cash flows sufficient to recover the amortized cost basis of a security. We invest our available cash primarily in commercial paper, money market funds, and U.S. Treasury bill funds that have investment grade ratings. The following is a summary of the fair value of available-for-sale marketable securities we held at September 30, 2019 and December 31, 2018 (in thousands): Gross Gross Amortized Unrealized Unrealized Fair September 30, 2019 Cost Gains Losses Value Security type Corporate debt securities-short term $ 82,929 $ 89 $ (4) $ 83,014 Corporate debt securities-long term 48,857 50 (7) 48,900 Total available-for-sale marketable securities $ 131,786 $ 139 $ (11) $ 131,914 Gross Gross Amortized Unrealized Unrealized Fair December 31, 2018 Cost Gains Losses Value Security type Corporate debt securities-short term $ 80,417 $ 2 $ (97) $ 80,322 Total available-for-sale marketable securities $ 80,417 $ 2 $ (97) $ 80,322 None of our available-for-sale marketable securities were in a continuous unrealized loss position for more than 12 months at September 30, 2019 or December 31, 2018. The following tables present information about our assets and liabilities that are measured at fair value on a recurring basis for the periods presented and indicates the fair value hierarchy of the valuation techniques we utilized to determine such fair value. There were no transfers in or out of Level 1 or Level 2 measurements for the periods presented (in thousands): Quoted Significant Prices in Other Significant Active Observable Unobservable September 30, Markets Inputs Inputs 2019 (Level 1) (Level 2) (Level 3) Cash equivalents $ 40,662 $ 40,662 $ — $ — Corporate debt securities-short term 83,014 — 83,014 — Corporate debt securities-long term 48,900 — 48,900 — Total $ 172,576 $ 40,662 $ 131,914 $ — Quoted Significant Prices in Other Significant Active Observable Unobservable December 31, Markets Inputs Inputs 2018 (Level 1) (Level 2) (Level 3) Cash equivalents $ 14,444 $ 14,444 $ — $ — Corporate debt securities-short term 80,322 — 80,322 — Total $ 94,766 $ 14,444 $ 80,322 $ —

ACCOUNTS PAYABLE AND ACCRUED EX

ACCOUNTS PAYABLE AND ACCRUED EXPENSES	9 Months Ended
	Sep. 30, 2019
ACCOUNTS PAYABLE AND ACCRUED EXPENSES
ACCOUNTS PAYABLE AND ACCRUED EXPENSES	4. ACCOUNTS PAYABLE AND ACCRUED EXPENSES Accounts payable and accrued expenses include the following at September 30, 2019 and December 31, 2018 (in thousands): September 30, December 31, 2019 2018 Accrued outsourced preclinical and clinical fees $ 5,748 $ 8,497 Accrued payroll 2,154 1,971 Accrued professional fees 905 666 Accounts payable 801 1,329 Other accrued expenses 325 485 $ 9,933 $ 12,948

NET LOSS PER SHARE

NET LOSS PER SHARE	9 Months Ended
	Sep. 30, 2019
NET LOSS PER SHARE
NET LOSS PER SHARE	5. NET LOSS PER SHARE Net loss per share is computed using the weighted average number of common shares outstanding. Basic and diluted net loss per share amounts are equivalent for the periods presented as the inclusion of potential common shares in the number of shares used for the diluted computation would be anti-dilutive to loss per share. Potential common shares, for the three and nine months ended September 30, 2019, include 12,376,291 shares that would be issued upon the exercise of outstanding employee and Board of Director stock options, 93,168 shares that would be issued upon the exercise of the warrants from our February 2018 amendment to our loan agreement, 3,123,674 shares that would be issued upon the exercise of the warrants from our October 2017 common stock offering and 2,144,714 common shares that would be issued upon the exercise of the warrants from our November 2017 preferred stock offering. Potential common shares, for the three and nine months ended September 30, 2018, include 10,720,022 shares that would be issued upon the exercise of outstanding employee and Board of Director stock options, 93,168 shares that would be issued upon the exercise of the warrants from our February 2018 amendment to our loan agreement, 3,123,674 shares that would be issued upon the exercise of the warrants from our October 2017 common stock offering and 2,259,000 common shares that would be issued upon the exercise of the warrants from our November 2017 preferred stock offering. The preferred shares and warrants from our November 2017 preferred stock offering were converted to common stock and common stock warrants in May 2018.

STOCK-BASED COMPENSATION AND ST

STOCK-BASED COMPENSATION AND STOCK PLANS	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs, Share-Based Payments [Abstract]
STOCK-BASED COMPENSATION AND STOCK PLANS	6. STOCK-BASED COMPENSATION AND STOCK PLANS Our stock-based compensation cost is measured at the grant date, based on the calculated fair value of the award, and is recognized as an expense over the employees’ requisite service period (generally the vesting period of the equity grant). We estimate the fair value of stock options using the Black-Scholes valuation model. Key input assumptions used to estimate the fair value of stock options include the exercise price of the award, expected option term, expected volatility of our stock over the option’s expected term, risk-free interest rate over the option’s expected term, and the expected annual dividend yield. We believe that the valuation technique and approach utilized to develop the underlying assumptions are appropriate in calculating the fair values of our stock options granted in the three and nine months ended September 30, 2019 and 2018. The following table presents stock-based compensation expense included in our condensed statements of operations and comprehensive loss (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Research and development $ 223 $ 84 $ 741 $ 269 General and administrative 785 279 3,308 831 Total stock-based compensation expense $ 1,008 $ 363 $ 4,049 $ 1,100 In the nine months ended September 30, 2019, we recorded stock-based compensation expense of $1.0 million related to the modification of awards to our former Chief Financial Officer in connection with his retirement in March 2019. In the three and nine months ended September 30, 2019 and 2018, no stock-based compensation expense was capitalized and there were no recognized tax benefits associated with the stock-based compensation expense. Option activity under our stock plans for the nine months ended September 30, 2019 was as follows: Weighted Number of Average Stock Options Shares Exercise Price Outstanding as of December 31, 2018 10,748,157 $ 2.90 Granted Exercised Cancelled (157,508) 2.44 Outstanding as of September 30, 2019 $ Exercisable as of September 30, 2019 7,207,088 $ 3.26 The aggregate intrinsic value of options outstanding at September 30, 2019 was $50.1 million, including $28.7 million related to exercisable options. The weighted average fair value of options granted in the nine months ended September 30, 2019 and 2018 was $2.54 and $1.70 per share, respectively. The intrinsic value of options exercised in the nine months ended September 30, 2019 was $3.9 million. Weighted- Average Weighted- Remaining Aggregate Average Contractual Intrinsic Shares Exercise Price Term (in years) Value Vested and unvested expected to vest at September 30, 2019 12,218,754 $ 3.17 $ 49,485 Exercisable at September 30, 2019 7,207,088 $ 3.26 $ 28,730 The total compensation cost not yet recognized as of September 30, 2019 related to non-vested option awards was $7.2 million, which will be recognized over a weighted-average period of 2.6 years. During the nine months ended September 30, 2019, 28,350 shares expired and 129,158 shares were forfeited. The weighted average remaining contractual life for options exercisable at September 30, 2019 was 4.37 years.

COMMON STOCK OFFERINGS

COMMON STOCK OFFERINGS	9 Months Ended
	Sep. 30, 2019
COMMON STOCK OFFERINGS
COMMON STOCK OFFERINGS	7. COMMON STOCK OFFERINGS In June 2019, we sold 10,637,500 shares of common stock at $9.75 per share for aggregate net proceeds of approximately $97.3 million after commissions and other offering expenses. In July 2018, we sold 12,650,000 shares of common stock at $5.50 per share for aggregate net proceeds of approximately $64.6 million after commissions and other offering expenses.

LOAN AGREEMENT

LOAN AGREEMENT	9 Months Ended
	Sep. 30, 2019
LOAN AGREEMENT
LOAN AGREEMENT	8. LOAN AGREEMENT In January 2017, we entered into a loan and security agreement (the “Loan Agreement”) with Oxford Finance LLC, as collateral agent and a lender (the “Lender”), and any additional lenders that may become parties thereto. Pursuant to the terms of the Loan Agreement, the Lender issued us a loan with an initial principal amount of $15.0 million. The loan bears interest at the rate equal to (a) the greater of (i) the 30 day U.S. LIBOR rate reported in the Wall Street Journal on the date occurring on the last business day of the month that immediately precedes the month in which the interest will accrue or (ii) 0.65% (b) plus 6.85%. The applicable interest rate on the loan at September 30, 2019 was 8.94%. The Loan Agreement required interest-only payments through August 2019, followed by an amortization period of monthly principal and interest payments of 36 months. The original maturity date of the loan was August 1, 2021 and in February 2018 we signed an amendment with the Lender which extended the maturity date by one year to August 1, 2022. The expected remaining repayment of the $14.583 million loan principal at September 30, 2019 is as follows (in thousands): 2019 $ 1,250 2020 5,000 2021 5,000 2022 3,333 $ 14,583 Upon prepayment of the loan or on the maturity date, we will pay to the Lender a final payment of 6% of the full principal amount of the loan. We may elect to prepay all amounts owed prior to the maturity date, provided that a prepayment fee also is paid equal to 1% of the outstanding principal balance. Pursuant to the terms of the Loan Agreement, we are bound by certain affirmative covenants setting forth actions that are required during the term of the Loan Agreement, including, without limitation, certain information delivery requirements, obligations to maintain certain insurance, and certain notice requirements. Additionally, we are bound by certain negative covenants setting forth actions that are not permitted to be taken during the term of the Loan Agreement without consent, including, without limitation, incurring certain additional indebtedness, entering into certain mergers, acquisitions or other business combination transactions, or incurring any non-permitted lien or other encumbrance on our assets. We were in compliance with the loan covenants at September 30, 2019. Upon the occurrence of an event of default under the Loan Agreement (subject to cure periods for certain events of default), all amounts owed by us thereunder will begin to bear interest at a rate that is 5% higher than the rate that is otherwise applicable and may be declared immediately due and payable by the Lender. Events of default under the Loan Agreement include, among other things, the following: the occurrence of certain bankruptcy events; the failure to make payments under the Loan Agreement when due; the occurrence of a material adverse change in our business, operations or financial condition; the rendering of certain types of fines or judgments against us; any breach by us of any covenant (subject to cure for certain covenants only) made in the Loan Agreement; and the failure of any representation or warranty made by us in connection with the Loan Agreement to be correct in all material respects when made. We have granted the Lender, a security interest in substantially all of our personal property, rights and assets, other than intellectual property, to secure the payment of all amounts owed to the Lender under the Loan Agreement. We have also agreed not to encumber any of our intellectual property without the Lender’s prior written consent. In February 2018, the Loan Agreement was amended to extend the maturity date and to require payments of interest on a monthly basis through August 2019 and payments of interest and principal from September 2019 to August 2022. In connection with entering into the amendment we issued to the Lender warrants to purchase an aggregate of 93,168 shares of our common stock. The warrants are exercisable immediately, have a per-share exercise price of $1.61 and have a term of ten years. The amendment was determined to be a modification of debt in accordance with ASC 470 Debt. We have recorded the relative fair value of the additional warrants as a discount to the carrying value of the notes payable with a corresponding increase to additional paid in capital.

PREFERRED STOCK AND WARRANT LIA

PREFERRED STOCK AND WARRANT LIABILITY	9 Months Ended
	Sep. 30, 2019
PREFERRED STOCK AND WARRANT LIABILITY
PREFERRED STOCK AND WARRANT LIABILITY	9. PREFERRED STOCK AND WARRANT LIABILITY Our Restated Certificate of Incorporation , as amended, authorizes the issuance of up to 1 million shares of $0.01 par value preferred stock. In November 2017, we entered into definitive securities purchase agreements with certain institutional investors. In conjunction with this stock offering we raised net proceeds of $9.5 million through the sale of 8,370 shares of series A convertible preferred stock (Series A Preferred) and warrants covering 2,259 shares of Series A Preferred (Warrants). Each share of Series A Preferred converted into 1,000 shares of common stock and each associated Warrant converted into 1,000 common stock warrants in May 2018. The terms of the Series A Preferred for which the warrants were exercisable required that the fair value allocated to the warrants at the date of issuance be recorded as a liability on our balance sheet. The warrant liability was marked to market value through the statement of operations and comprehensive loss as a non-cash gain or loss at each reporting period until the conversion of the Series A Preferred to common stock in May 2018. Upon conversion, the warrant liability of $3.1 million was extinguished with an offsetting amount included as additional paid-in capital in stockholders’ equity. Accordingly, at each of December 31, 2018 and September 30, 2019, the warrant liability was zero. In the three and nine months ended September 30, 2018, we recognized a non-cash expense of zero and $1.5 million , respectively, recorded in other expense on the statement of operations and comprehensive loss related to the change in the fair value of the warrant liability.

RECENT ACCOUNTING PRONOUNCEMENT

RECENT ACCOUNTING PRONOUNCEMENTS	9 Months Ended
	Sep. 30, 2019
RECENT ACCOUNTING PRONOUNCEMENTS
RECENT ACCOUNTING PRONOUNCEMENTS	10. RECENT ACCOUNTING PRONOUNCEMENTS Recently Adopted Accounting Pronouncements In February 2016 the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) No. 2016‑02, Leases (Topic 842). This standard established a right-of-use model that requires all lessees to recognize right-of-use assets and liabilities on their balance sheet that arise from leases with terms longer than 12 months as well as provide disclosures with respect to certain qualitative and quantitative information related to their leasing arrangements. This standard became effective for us on January 1, 2019 (“the Effective Date”). The FASB has subsequently issued the following amendments to ASU 2016‑02, which also became effective on January 1, 2019, and which we collectively refer to as the new leasing standards:  ASU No. 2018‑01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842, which permits an entity to elect an optional transition practical expedient to not evaluate under Topic 842 land easements that exist or expired prior to adoption of Topic 842 and that were not previously accounted for as leases under the prior standard, ASC 840, Leases.  ASU No. 2018‑10, Codification Improvements to Topic 842, Leases, which amends certain narrow aspects of the guidance issued in ASU 2016‑02.  ASU No. 2018‑11, Leases (Topic 842): Targeted Improvements, which allows for a transition approach to initially apply ASU 2016‑02 at the adoption date and recognize a cumulative-effect adjustment to the opening balance of accumulated deficit in the period of adoption as well as an additional practical expedient for lessors to not separate non-lease components from the associated lease component.  ASU No. 2018‑20, Narrow-Scope Improvements for Lessors, which contains certain narrow scope improvements to the guidance issued in ASU 2016‑02. We adopted the new lease accounting standard on January 1, 2019, using a modified retrospective transition approach of applying the new standard to all leases existing as of, or entered into after, the Effective Date and with remaining terms of 12 months or more. Our assessment included the lease of our headquarters in Burlington, MA which commenced in May 2015 and , prior to our October 2019 amendment discussed below, was scheduled to expire in July 2020 and our laboratory space in Woburn, MA which commenced in March 2019 and expires in April 2024. The adoption of the new standard on January 1, 2019 resulted in the recording of a right-of-use asset and lease liability of $0.7 million related to the lease of our headquarters in Burlington, MA that existed on the Effective Date. The lease liability is based on the present value of the remaining minimum lease payments, discounted using our secured incremental borrowing rate at the Effective Date. As permitted under ASC 842, we elected several practical expedients and therefore did not reassess at the Effective Date (1) whether any existing contract is or contains a lease, (2) the classification of existing leases, and (3) whether previously capitalized costs continue to qualify as initial indirect costs. We also elected the practical expedient to not separate lease and non-lease components. The application of the practical expedients did not have a significant impact on the measurement of the operating lease liability. In addition, we implemented internal controls to enable the preparation of financial information on adoption. The adoption did not have a material impact on our condensed financial statements related to the existing lease of our headquarters in Burlington, MA for the three and nine months ended September 30, 2019. As a result, there was no cumulative-effect adjustment. For contracts entered into on or after the Effective Date, at the inception of a contract we assess whether the contract is, or contains, a lease. Our assessment is based on: (1) whether the contract involves the use of a distinct identified asset, (2) whether we obtain the right to substantially all the economic benefit from the use of the asset throughout the period, and (3) whether we have the right to direct the use of the asset. At inception of a lease, we allocate the consideration in the contract to each lease component based on its relative stand-alone price to determine the lease payments. Leases are classified as either finance leases or operating leases. A lease is classified as a finance lease if any one of the following criteria are met: (1) the lease transfers ownership of the asset by the end of the lease term, (2) the lease contains an option to purchase the asset that is reasonably certain to be exercised, (3) the lease term is for a major part of the remaining useful life of the asset or (4) the present value of the lease payments equals or exceeds substantially all of the fair value of the asset. A lease is classified as an operating lease if it does not meet any one of these criteria. Our leases are comprised of operating leases related to our headquarters in Burlington, MA and laboratory space in Woburn, MA. For all leases at the lease commencement date, a right-of-use asset and a lease liability are recognized. The right-of-use asset represents the right to use the leased asset for the lease term. The lease liability represents the present value of the lease payments under the lease. The right-of-use asset is initially measured at cost, which primarily comprises the initial amount of the lease liability, plus any initial direct costs incurred, consisting mainly of brokerage commissions, less any lease incentives received. All right-of-use assets are reviewed for impairment. The lease liability is initially measured at the present value of the lease payments, discounted using the interest rate implicit in the lease or, if that rate cannot be readily determined, the secured incremental borrowing rate. For our operating leases, we use our secured incremental borrowing rate if the implicit lease rate cannot be determined. Lease payments included in the measurement of the lease liability comprise the following: the fixed noncancelable lease payments, payments for optional renewal periods where it is reasonably certain the renewal period will be exercised, and payments for early termination options unless it is reasonably certain the lease will not be terminated early. Lease expense for operating leases consists of the lease payments plus any initial direct costs and is recognized on a straight-line basis over the lease term. Certain leases contain rent escalation clauses and variable lease payments that require additional rental payments in later years of the term, including payments based on an index or inflation rate. Payments based on the change in an index or inflation rate, or payments based on a change in our portion of the operating expenses, including real estate taxes and insurance, are not included in the initial lease liability and are recorded as a period expense when incurred. Our operating leases may include an option to renew the lease term for various renewal periods and/or to terminate the leases early. As an option to exercise the renewal or early termination of our operating leases were either non-existent or not reasonably certain as of the ASC 842 Effective Date for our headquarters in Burlington, MA and the lease commencement date of our laboratory space in Woburn, MA, we did not include such options in our initial lease liability. Subsequent to the Effective Date and during the quarter ending September 30, 2019, the option to renew the lease term of our headquarters in Burlington, MA became reasonably certain. This resulted in a $1.98 million increase of our right-of-use asset and lease liability of as of September 30, 2019. As of September 30, 2019, we recognized right-of-use assets related to our headquarters in Burlington, MA and laboratory space in Woburn, MA of $2.7 million and the related net lease liabilities of $2.7 million, which represents the net present value of the remaining lease payments of approximately $3.7 million, discounted using the Company’s incremental borrowing rate of 8.87%. We have included the right-of-use assets and lease liabilities in the condensed balance sheet as of September 30, 2019. The following table summarizes future minimum lease payments for our operating leases as of September 30, 2019 (in thousands): Year Ending December 31, 2019 (three months ending December 31, 2019) $ 152 2020 619 2021 642 2022 657 2023 672 Thereafter 963 Total minimum lease payments $ 3,705 In October 2019, we entered into an amendment to the lease of our headquarters in Burlington, MA that increased the amount of space subject to the lease and extended the term of the lease until July 2025. As previously disclosed in our 2018 Annual Report on Form 10‑K and under the previous lease accounting standard, ASC 840, Leases , the total commitment for our non-cancelable operating lease was $0.8 million as of December 31, 2018 (in thousands): Year Ending December 31, 2019 $ 523 2020 296 Thereafter — Total minimum lease payments $ 819 Recently Issued Accounting Pronouncements In August 2018, the FASB issued ASU 2018‑13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, (“ASU 2018‑13”). The new standard removes certain disclosures, modifies certain disclosures and adds additional disclosures related to fair value measurement. The new standard will be effective beginning January 1, 2020. We are currently evaluating the impact that the adoption of ASU 2018‑13 will have on our consolidated financial statements. In August 2018, the FASB issued ASU 2018‑15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350‑40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, (“ASU 2018‑15”). The amendments in this update align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The accounting for the service element of a hosting arrangement that is a service contract is not affected by the amendments in this update. The new standard will be effective beginning January 1, 2020. The amendments in this update should be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. We are currently evaluating the impact that the adoption of ASU 2018‑15 will have on our consolidated financial statements. In June 2016, the FASB issued ASU No. 2016-13, “ Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” . This ASU will require that credit losses be reported using an expected losses model rather than the incurred losses model that is currently used, and establishes additional disclosures related to credit risks. For available-for-sale debt securities with unrealized losses, this standard will require allowances to be recorded instead of reducing the amortized cost of the investment. ASU 2016-13 will limit the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which the carrying value exceeds the fair value and requires the reversal of previously recognized credit losses if fair value increases. ASU 2016-13 will be effective for fiscal years beginning after December 15, 2019 with early adoption permitted, and requires adoption using a modified retrospective approach, with certain exceptions. Based on the composition of the Company’s investment portfolio, current market conditions and historical credit loss activity, we are currently evaluating the impact of the adoption of this standard on the Company’s financial statements.

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2019
INCOME TAXES
INCOME TAXES	11. INCOME TAXES As of December 31, 2018, we had federal net operating losses (“NOL”), state NOL, and research and development credit carryforwards of approximately $422,045, $240,916 and $28,378 respectively, which expire at various dates through 2037. As of September 30, 2019, and December 31, 2018 we had no unrecognized tax benefits. We do not expect that the total amount of unrecognized tax benefits will significantly increase in the next twelve months. Our policy is to recognize interest and penalties related to uncertain tax positions in income tax expense. As of September 30, 2019, and December 31, 2018, we had no accrued interest or penalties related to uncertain tax positions. Our U.S. federal tax returns for the tax years 2015 through 2018 and our state tax returns for the tax years 2015 through 2018 remain open to examination. Prior tax years remain open to the extent of NOL and tax credit carryforwards. Utilization of NOL and research and development credit carryforwards may be subject to a substantial annual limitation in the event of an ownership change that has occurred previously or could occur in the future pursuant to Section 382 and 383 of the Internal Revenue Code of 1986, as amended, as well as similar state provisions. An ownership change may limit the amount of NOL and research and development credit carryforwards that can be utilized annually to offset future taxable income, and may, in turn, result in the expiration of a portion of those carryforwards before utilization. In general, an ownership change, as defined by Section 382, results from transactions that increase the ownership of certain stockholders or public groups in the stock of a corporation by more than 50 percentage points over a three-year period. We undertook a detailed study of our NOL and research and development credit carryforwards through January 31, 2019, to determine whether such amounts are likely to be limited by Sections 382 or 383. As a result of this analysis, we currently do not believe any Sections 382 or 383 limitations will significantly impact our ability to offset income with available NOL and research and development credit carryforwards. However, future ownership changes under Section 382 may limit our ability to fully utilize these tax benefits.

RECENT ACCOUNTING PRONOUNCEME_2

RECENT ACCOUNTING PRONOUNCEMENTS (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
RECENT ACCOUNTING PRONOUNCEMENTS	Recently Adopted Accounting Pronouncements In February 2016 the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) No. 2016‑02, Leases (Topic 842). This standard established a right-of-use model that requires all lessees to recognize right-of-use assets and liabilities on their balance sheet that arise from leases with terms longer than 12 months as well as provide disclosures with respect to certain qualitative and quantitative information related to their leasing arrangements. This standard became effective for us on January 1, 2019 (“the Effective Date”). The FASB has subsequently issued the following amendments to ASU 2016‑02, which also became effective on January 1, 2019, and which we collectively refer to as the new leasing standards:  ASU No. 2018‑01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842, which permits an entity to elect an optional transition practical expedient to not evaluate under Topic 842 land easements that exist or expired prior to adoption of Topic 842 and that were not previously accounted for as leases under the prior standard, ASC 840, Leases.  ASU No. 2018‑10, Codification Improvements to Topic 842, Leases, which amends certain narrow aspects of the guidance issued in ASU 2016‑02.  ASU No. 2018‑11, Leases (Topic 842): Targeted Improvements, which allows for a transition approach to initially apply ASU 2016‑02 at the adoption date and recognize a cumulative-effect adjustment to the opening balance of accumulated deficit in the period of adoption as well as an additional practical expedient for lessors to not separate non-lease components from the associated lease component.  ASU No. 2018‑20, Narrow-Scope Improvements for Lessors, which contains certain narrow scope improvements to the guidance issued in ASU 2016‑02. We adopted the new lease accounting standard on January 1, 2019, using a modified retrospective transition approach of applying the new standard to all leases existing as of, or entered into after, the Effective Date and with remaining terms of 12 months or more. Our assessment included the lease of our headquarters in Burlington, MA which commenced in May 2015 and , prior to our October 2019 amendment discussed below, was scheduled to expire in July 2020 and our laboratory space in Woburn, MA which commenced in March 2019 and expires in April 2024. The adoption of the new standard on January 1, 2019 resulted in the recording of a right-of-use asset and lease liability of $0.7 million related to the lease of our headquarters in Burlington, MA that existed on the Effective Date. The lease liability is based on the present value of the remaining minimum lease payments, discounted using our secured incremental borrowing rate at the Effective Date. As permitted under ASC 842, we elected several practical expedients and therefore did not reassess at the Effective Date (1) whether any existing contract is or contains a lease, (2) the classification of existing leases, and (3) whether previously capitalized costs continue to qualify as initial indirect costs. We also elected the practical expedient to not separate lease and non-lease components. The application of the practical expedients did not have a significant impact on the measurement of the operating lease liability. In addition, we implemented internal controls to enable the preparation of financial information on adoption. The adoption did not have a material impact on our condensed financial statements related to the existing lease of our headquarters in Burlington, MA for the three and nine months ended September 30, 2019. As a result, there was no cumulative-effect adjustment. For contracts entered into on or after the Effective Date, at the inception of a contract we assess whether the contract is, or contains, a lease. Our assessment is based on: (1) whether the contract involves the use of a distinct identified asset, (2) whether we obtain the right to substantially all the economic benefit from the use of the asset throughout the period, and (3) whether we have the right to direct the use of the asset. At inception of a lease, we allocate the consideration in the contract to each lease component based on its relative stand-alone price to determine the lease payments. Leases are classified as either finance leases or operating leases. A lease is classified as a finance lease if any one of the following criteria are met: (1) the lease transfers ownership of the asset by the end of the lease term, (2) the lease contains an option to purchase the asset that is reasonably certain to be exercised, (3) the lease term is for a major part of the remaining useful life of the asset or (4) the present value of the lease payments equals or exceeds substantially all of the fair value of the asset. A lease is classified as an operating lease if it does not meet any one of these criteria. Our leases are comprised of operating leases related to our headquarters in Burlington, MA and laboratory space in Woburn, MA. For all leases at the lease commencement date, a right-of-use asset and a lease liability are recognized. The right-of-use asset represents the right to use the leased asset for the lease term. The lease liability represents the present value of the lease payments under the lease. The right-of-use asset is initially measured at cost, which primarily comprises the initial amount of the lease liability, plus any initial direct costs incurred, consisting mainly of brokerage commissions, less any lease incentives received. All right-of-use assets are reviewed for impairment. The lease liability is initially measured at the present value of the lease payments, discounted using the interest rate implicit in the lease or, if that rate cannot be readily determined, the secured incremental borrowing rate. For our operating leases, we use our secured incremental borrowing rate if the implicit lease rate cannot be determined. Lease payments included in the measurement of the lease liability comprise the following: the fixed noncancelable lease payments, payments for optional renewal periods where it is reasonably certain the renewal period will be exercised, and payments for early termination options unless it is reasonably certain the lease will not be terminated early. Lease expense for operating leases consists of the lease payments plus any initial direct costs and is recognized on a straight-line basis over the lease term. Certain leases contain rent escalation clauses and variable lease payments that require additional rental payments in later years of the term, including payments based on an index or inflation rate. Payments based on the change in an index or inflation rate, or payments based on a change in our portion of the operating expenses, including real estate taxes and insurance, are not included in the initial lease liability and are recorded as a period expense when incurred. Our operating leases may include an option to renew the lease term for various renewal periods and/or to terminate the leases early. As an option to exercise the renewal or early termination of our operating leases were either non-existent or not reasonably certain as of the ASC 842 Effective Date for our headquarters in Burlington, MA and the lease commencement date of our laboratory space in Woburn, MA, we did not include such options in our initial lease liability. Subsequent to the Effective Date and during the quarter ending September 30, 2019, the option to renew the lease term of our headquarters in Burlington, MA became reasonably certain. This resulted in a $1.98 million increase of our right-of-use asset and lease liability of as of September 30, 2019. As of September 30, 2019, we recognized right-of-use assets related to our headquarters in Burlington, MA and laboratory space in Woburn, MA of $2.7 million and the related net lease liabilities of $2.7 million, which represents the net present value of the remaining lease payments of approximately $3.7 million, discounted using the Company’s incremental borrowing rate of 8.87%. We have included the right-of-use assets and lease liabilities in the condensed balance sheet as of September 30, 2019. The following table summarizes future minimum lease payments for our operating leases as of September 30, 2019 (in thousands): Year Ending December 31, 2019 (three months ending December 31, 2019) $ 152 2020 619 2021 642 2022 657 2023 672 Thereafter 963 Total minimum lease payments $ 3,705 In October 2019, we entered into an amendment to the lease of our headquarters in Burlington, MA that increased the amount of space subject to the lease and extended the term of the lease until July 2025. As previously disclosed in our 2018 Annual Report on Form 10‑K and under the previous lease accounting standard, ASC 840, Leases , the total commitment for our non-cancelable operating lease was $0.8 million as of December 31, 2018 (in thousands): Year Ending December 31, 2019 $ 523 2020 296 Thereafter — Total minimum lease payments $ 819 Recently Issued Accounting Pronouncements In August 2018, the FASB issued ASU 2018‑13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement, (“ASU 2018‑13”). The new standard removes certain disclosures, modifies certain disclosures and adds additional disclosures related to fair value measurement. The new standard will be effective beginning January 1, 2020. We are currently evaluating the impact that the adoption of ASU 2018‑13 will have on our consolidated financial statements. In August 2018, the FASB issued ASU 2018‑15, Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350‑40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, (“ASU 2018‑15”). The amendments in this update align the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software (and hosting arrangements that include an internal-use software license). The accounting for the service element of a hosting arrangement that is a service contract is not affected by the amendments in this update. The new standard will be effective beginning January 1, 2020. The amendments in this update should be applied either retrospectively or prospectively to all implementation costs incurred after the date of adoption. We are currently evaluating the impact that the adoption of ASU 2018‑15 will have on our consolidated financial statements.

MARKETABLE SECURITIES AND FAI_2

MARKETABLE SECURITIES AND FAIR VALUE MEASUREMENTS (Tables)	9 Months Ended
	Sep. 30, 2019
MARKETABLE SECURITIES AND FAIR VALUE MEASUREMENTS
Schedule of fair value of available-for-sale marketable securities	Gross Gross Amortized Unrealized Unrealized Fair September 30, 2019 Cost Gains Losses Value Security type Corporate debt securities-short term $ 82,929 $ 89 $ (4) $ 83,014 Corporate debt securities-long term 48,857 50 (7) 48,900 Total available-for-sale marketable securities $ 131,786 $ 139 $ (11) $ 131,914 Gross Gross Amortized Unrealized Unrealized Fair December 31, 2018 Cost Gains Losses Value Security type Corporate debt securities-short term $ 80,417 $ 2 $ (97) $ 80,322 Total available-for-sale marketable securities $ 80,417 $ 2 $ (97) $ 80,322
Schedule of assets and liabilities that are measured at fair value on recurring basis	Quoted Significant Prices in Other Significant Active Observable Unobservable September 30, Markets Inputs Inputs 2019 (Level 1) (Level 2) (Level 3) Cash equivalents $ 40,662 $ 40,662 $ — $ — Corporate debt securities-short term 83,014 — 83,014 — Corporate debt securities-long term 48,900 — 48,900 — Total $ 172,576 $ 40,662 $ 131,914 $ — Quoted Significant Prices in Other Significant Active Observable Unobservable December 31, Markets Inputs Inputs 2018 (Level 1) (Level 2) (Level 3) Cash equivalents $ 14,444 $ 14,444 $ — $ — Corporate debt securities-short term 80,322 — 80,322 — Total $ 94,766 $ 14,444 $ 80,322 $ —

ACCOUNTS PAYABLE AND ACCRUED _2

ACCOUNTS PAYABLE AND ACCRUED EXPENSES (Tables)	9 Months Ended
	Sep. 30, 2019
ACCOUNTS PAYABLE AND ACCRUED EXPENSES
Schedule of accounts payable and accrued expenses	September 30, December 31, 2019 2018 Accrued outsourced preclinical and clinical fees $ 5,748 $ 8,497 Accrued payroll 2,154 1,971 Accrued professional fees 905 666 Accounts payable 801 1,329 Other accrued expenses 325 485 $ 9,933 $ 12,948

STOCK-BASED COMPENSATION AND _2

STOCK-BASED COMPENSATION AND STOCK PLANS (Tables)	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs, Share-Based Payments [Abstract]
Schedule of stock-based compensation expense	Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Research and development $ 223 $ 84 $ 741 $ 269 General and administrative 785 279 3,308 831 Total stock-based compensation expense $ 1,008 $ 363 $ 4,049 $ 1,100
Schedule of stock option activity	Weighted Number of Average Stock Options Shares Exercise Price Outstanding as of December 31, 2018 10,748,157 $ 2.90 Granted Exercised Cancelled (157,508) 2.44 Outstanding as of September 30, 2019 $ Exercisable as of September 30, 2019 7,207,088 $ 3.26
Schedule of options vested, expected to vest and exercisable	Weighted- Average Weighted- Remaining Aggregate Average Contractual Intrinsic Shares Exercise Price Term (in years) Value Vested and unvested expected to vest at September 30, 2019 12,218,754 $ 3.17 $ 49,485 Exercisable at September 30, 2019 7,207,088 $ 3.26 $ 28,730

LOAN AGREEMENT (Tables)

LOAN AGREEMENT (Tables)	9 Months Ended
	Sep. 30, 2019
LOAN AGREEMENT
Schedule of expected remaining repayment	2019 $ 1,250 2020 5,000 2021 5,000 2022 3,333 $ 14,583

RECENT ACCOUNTING PRONOUNCEME_3

RECENT ACCOUNTING PRONOUNCEMENTS (Tables)	9 Months Ended
	Sep. 30, 2019
RECENT ACCOUNTING PRONOUNCEMENTS
Schedule of future minimum operating leases	Year Ending December 31, 2019 (three months ending December 31, 2019) $ 152 2020 619 2021 642 2022 657 2023 672 Thereafter 963 Total minimum lease payments $ 3,705 Year Ending December 31, 2019 $ 523 2020 296 Thereafter — Total minimum lease payments $ 819

NATURE OF OPERATIONS AND BASI_2

NATURE OF OPERATIONS AND BASIS OF PRESENTATION (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended					3 Months Ended		6 Months Ended	9 Months Ended
	Jun. 30, 2019	Jul. 31, 2018	Apr. 30, 2018	Feb. 28, 2018	Nov. 30, 2017	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Organization And Nature Of Operations [Line Items]
Net cash outflows driven by payments for operating expenses									$ 24,225	$ 7,796
Common Stock, Shares, Issued	10,637,500	12,650,000				120,661,081		10,637,500	120,661,081		109,003,637
Share price	$ 9.75	$ 5.50						$ 9.75
Aggregate net proceeds from common stock issued	$ 97,300	$ 64,600						$ 97,300
Proceeds from stock offering									$ 97,327	64,561
Definitive stock purchase agreements | Series A convertible preferred stock and warrants
Organization And Nature Of Operations [Line Items]
Proceeds from stock offering					$ 9,500
Definitive stock purchase agreements | Series A convertible preferred stock
Organization And Nature Of Operations [Line Items]
Number of stock issued under agreement					8,370
Number of common stock issued upon conversion					1,000
Definitive stock purchase agreements | Series A Preferred Warrants
Organization And Nature Of Operations [Line Items]
Number of stock issued under agreement					2,259
Number of common stock issued upon conversion					1,000
Post-conversion price of common stock					$ 1.75
Common stock warrants exercised									114,286
Net proceeds from common stock warrants									$ 200
Roivant Sciences Licensing Agreement | Roivant Sciences Ltd. (Sinovant)
Organization And Nature Of Operations [Line Items]
Revenue for completing performance obligation						$ 200	$ 2,900		1,600	5,900
Regulatory and sales commercial milestones				$ 70,000
Upfront payment				3,000
Additional development milestone				2,500
Regulatory and sales milestones				$ 12,000
Basilea Licensing Agreement | Basilea Pharmaceutical International Limited
Organization And Nature Of Operations [Line Items]
Revenue for completing performance obligation						0	$ 2,000		200	$ 15,700
Regulatory and sales commercial milestones			$ 262,500
Upfront payment			10,000
Regulatory and sales milestones			63,000
Basilea Licensing Agreement | Basilea Pharmaceutica Limited (Basilea)
Organization And Nature Of Operations [Line Items]
Regulatory and sales commercial milestones			$ 262,500
Loan and security agreement | Oxford Finance, LLC (the "Loan Agreement")
Organization And Nature Of Operations [Line Items]
Loan principal amount						$ 15,000			$ 15,000

COLLABORATIONS AND ALLIANCES (D

COLLABORATIONS AND ALLIANCES (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	Apr. 30, 2018	Feb. 28, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development revenue			$ 208	$ 4,979	$ 1,834	$ 22,823
Basilea Pharmaceutical International Limited | Research and development service
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Research and development revenue	$ 9,800
Revenue for completing performance obligation	10,300
Total transaction price	9,500
Basilea Licensing Agreement | Basilea Pharmaceutical International Limited
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Regulatory and sales milestones	63,000
Revenue Recognition Commercial Milestone Method Revenue Expected	262,500
Upfront payment	10,000
Revenue for completing performance obligation			0	2,000	200	15,700
Total transaction price	$ 19,800
Roivant Sciences Licensing Agreement | Roivant Sciences Ltd. (Sinovant)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Regulatory and sales milestones		$ 12,000
Revenue Recognition Commercial Milestone Method Revenue Expected		70,000
Upfront payment		3,000
Additional development milestone		$ 2,500
Revenue for completing performance obligation			200	2,900	1,600	5,900
Other Licensing Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue for completing performance obligation			$ 0	$ 100	$ 0	$ 1,300

MARKETABLE SECURITIES AND FAI_3

MARKETABLE SECURITIES AND FAIR VALUE MEASUREMENTS - Summary of fair value of available-for-sale securities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 131,786	$ 80,417
Gross Unrealized Gains	139	2
Gross Unrealized Losses	(11)	(97)
Fair Value	131,914	80,322
Corporate debt securities-short term
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	82,929	80,417
Gross Unrealized Gains	89	2
Gross Unrealized Losses	(4)	(97)
Fair Value	83,014	$ 80,322
Corporate debt securities-long term
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	48,857
Gross Unrealized Gains	50
Gross Unrealized Losses	(7)
Fair Value	$ 48,900

MARKETABLE SECURITIES AND FAI_4

MARKETABLE SECURITIES AND FAIR VALUE MEASUREMENTS - Assets measured at fair value on a recurring basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 40,662	$ 14,444
Total	172,576	94,766
Corporate debt securities-short term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	83,014	80,322
Corporate debt securities-long term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	48,900
Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	40,662	14,444
Total	40,662	14,444
Quoted Prices in Active Markets (Level 1) | Corporate debt securities-short term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	0	0
Quoted Prices in Active Markets (Level 1) | Corporate debt securities-long term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Total	131,914	80,322
Significant Other Observable Inputs (Level 2) | Corporate debt securities-short term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	83,014	80,322
Significant Other Observable Inputs (Level 2) | Corporate debt securities-long term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	48,900
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Total	0	0
Significant Unobservable Inputs (Level 3) | Corporate debt securities-short term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	0	$ 0
Significant Unobservable Inputs (Level 3) | Corporate debt securities-long term
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Corporate debt securities	$ 0

ACCOUNTS PAYABLE AND ACCRUED _3

ACCOUNTS PAYABLE AND ACCRUED EXPENSES - Summary of accounts payable and accrued expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
ACCOUNTS PAYABLE AND ACCRUED EXPENSES
Accrued outsourced preclinical and clinical fees	$ 5,748	$ 8,497
Accrued payroll	2,154	1,971
Accrued professional fees	905	666
Accounts payable	801	1,329
Other accrued expenses	325	485
Accounts payable and accrued expenses, Total	$ 9,933	$ 12,948

NET LOSS PER SHARE (Details)

NET LOSS PER SHARE (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Exercise of outstanding employee and Board of Director stock options
Net Income Loss Per Share [Line Items]
Potential common shares in number of shares used for diluted computation	12,376,291	10,720,022	12,376,291	10,720,022
Exercise of options from February 2018 loan agreement
Net Income Loss Per Share [Line Items]
Potential common shares in number of shares used for diluted computation	93,168	93,168	93,168	93,168
Exercise of warrants from October 2017 common stock offering
Net Income Loss Per Share [Line Items]
Potential common shares in number of shares used for diluted computation	3,123,674	3,123,674	3,123,674	3,123,674
Exercise of warrants from November 2017 preferred stock offering
Net Income Loss Per Share [Line Items]
Potential common shares in number of shares used for diluted computation	2,144,714	2,259,000	2,144,714	2,259,000

STOCK-BASED COMPENSATION AND _3

STOCK-BASED COMPENSATION AND STOCK PLANS - Stock-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,008	$ 363	$ 4,049	$ 1,100
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	223	84	741	269
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 785	$ 279	$ 3,308	$ 831

STOCK-BASED COMPENSATION AND _4

STOCK-BASED COMPENSATION AND STOCK PLANS - Option activity (Details) - Stock Options	9 Months Ended
	Sep. 30, 2019$ / sharesshares
Number of Shares
Outstanding as of December 31, 2018 | shares	10,748,157
Granted | shares	2,666,510
Exercised | shares	(880,868)
Cancelled | shares	(157,508)
Outstanding as of March 31, 2019 | shares	12,376,291
Exercisable as of March 31, 2019 | shares	7,207,088
Weighted Average Exercise Price
Outstanding as of December 31, 2018 | $ / shares	$ 2.90
Granted | $ / shares	4.07
Exercised | $ / shares	2.70
Cancelled | $ / shares	2.44
Outstanding as of March 31, 2019 | $ / shares	3.17
Exercisable as of March 31, 2019 | $ / shares	$ 3.26

STOCK-BASED COMPENSATION AND _5

STOCK-BASED COMPENSATION AND STOCK PLANS - Shares vested, expected to vest and exercisable (Details) - Stock Options $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2019USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested and unvested expected to vest, Options | shares	12,218,754
Vested and unvested expected to vest, weighted-average exercise price | $ / shares	$ 3.17
Vested and unvested expected to vest, weighted-average remaining contractual term (in years)	6 years 1 month 6 days
Vested and unvested expected to vest, aggregate intrinsic value | $	$ 49,485
Exercisable, Options | shares	7,207,088
Exercisable, weighted-average exercise price | $ / shares	$ 3.26
Exercisable, weighted-average remaining contractual term (in years)	4 years 4 months 24 days
Exercisable, aggregate intrinsic value | $	$ 28,730

STOCK-BASED COMPENSATION AND _6

STOCK-BASED COMPENSATION AND STOCK PLANS - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-Based Compensation			$ 4,050	$ 1,100
Share-based compensation expense	$ 1,008	$ 363	4,049	$ 1,100
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of options outstanding	50,100		50,100
Intrinsic value of options exercisable	28,700		$ 28,700
Weighted average grant date fair value of options granted (in dollars per share)			$ 2.54	$ 1.70
Intrinsic value of options exercised			$ 3,900
Compensation cost not yet recognized related to non-vested option awards	$ 7,200		$ 7,200
Weighted-average recognition period related to non-vested option awards			2 years 7 months 6 days
Number of shares expired during the period			28,350
Number of shares forfeited during the period			129,158
Weighted average remaining contractual life for options exercisable			4 years 4 months 13 days
Share-Based Compensation			$ 1,000

COMMON STOCK OFFERINGS (Details

COMMON STOCK OFFERINGS (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		6 Months Ended
	Jun. 30, 2019	Jul. 31, 2018	Jun. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
COMMON STOCK OFFERINGS
Common Stock, Shares, Issued	10,637,500	12,650,000	10,637,500	120,661,081	109,003,637
Share price	$ 9.75	$ 5.50	$ 9.75
Aggregate net proceeds from common stock issued	$ 97.3	$ 64.6	$ 97.3

LOAN AGREEMENT - Expected remai

LOAN AGREEMENT - Expected remaining repayment (Details) $ in Thousands	Sep. 30, 2019USD ($)
LOAN AGREEMENT
2019	$ 1,250
2020	5,000
2021	5,000
2022	3,333
Loan principal amount	$ 14,583

LOAN AGREEMENT (Details)

LOAN AGREEMENT (Details) - Oxford Finance, LLC (the "Loan Agreement") - Loan and security agreement - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		9 Months Ended
	Feb. 28, 2018	Jan. 31, 2017	Sep. 30, 2019
Debt Instrument [Line Items]
Loan principal amount			$ 15
Interest rate description		(a) the greater of (i) the 30 day U.S. LIBOR rate reported in the Wall Street Journal on the date occurring on the last business day of the month that immediately precedes the month in which the interest will accrue or (ii) 0.65% (b) plus 6.85%.
Interest rate		0.65%
Basis spread interest rate		0.85%
Applicable interest rate			8.94%
Amortization period		36 months
Maturity date	Aug. 1, 2022	Aug. 1, 2021
Percentage of final principal payment		6.00%
Term of payment of interest and principal after amendment		September 2019 to August 2022
Additional interest rate after default		5.00%
Percentage of prepayment fee if payment made before maturity		1.00%
Term of payment of interest after amendment	Monthly basis through August 2019
Common Stock
Debt Instrument [Line Items]
Number of warrants issued to purchase common stock	93,168
Pre-share exercise price of warrants or rights	$ 1.61
Exercise term of warrants or rights	10 years

PREFERRED STOCK AND WARRANT L_2

PREFERRED STOCK AND WARRANT LIABILITY (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended	9 Months Ended
	Nov. 30, 2017	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Preferred Stock And Warrant Liability [Line Items]
Series A Preferred stock, shares authorized			1,000,000
Series A Preferred stock, par value (in dollars per share)			$ 0.01
Proceeds from stock offering			$ 97,327	$ 64,561
Change in fair value of warrant liability				1,552
Warrant liability extinguished			3,100
Warrant Liability			$ 0		$ 0
Warrant non cash expense		$ 0		$ 1,500
Definitive stock purchase agreements | Series A convertible preferred stock and warrants
Preferred Stock And Warrant Liability [Line Items]
Proceeds from stock offering	$ 9,500
Definitive stock purchase agreements | Series A convertible preferred stock
Preferred Stock And Warrant Liability [Line Items]
Number of stock issued under agreement	8,370
Number of common stock issued upon conversion	1,000
Definitive stock purchase agreements | Series A Preferred Warrants
Preferred Stock And Warrant Liability [Line Items]
Number of stock issued under agreement	2,259
Number of common stock issued upon conversion	1,000
Post-conversion price of common stock	$ 1.75

RECENT ACCOUNTING PRONOUNCEME_4

RECENT ACCOUNTING PRONOUNCEMENTS - Total minimum lease payments (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
RECENT ACCOUNTING PRONOUNCEMENTS
2019 (three months ending December 31, 2019)	$ 152
2019		$ 523
2020		296
2020	619
2021	642
2022	657
2023	672
Thereafter	963
Total minimum lease payments	$ 3,705	$ 819

RECENT ACCOUNTING PRONOUNCEME_5

RECENT ACCOUNTING PRONOUNCEMENTS - Additional information (Details) - USD ($) $ in Thousands	Jan. 01, 2019	Sep. 30, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Present value of the remaining lease payments		$ 3,705	$ 819
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative impact for accounting changes to recognize a lease liability		700
Increase in right-of-use asset		1,980
Increase in lease liability		1,980
Right-of-use asset		2,700
Net lease liabilities		2,700
Present value of the remaining lease payments		$ 3,700
Incremental borrowing rate		8.87%
Lease, Practical Expedient, Land Easement [true false]	false

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Increase in ownership percentage of certain stockholders or public groups	more than 50 percentage points
Ownership change, increase in ownership percentage, term	3 years
Federal income tax
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		$ 422,045
State income tax
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		240,916
Research and development credit carryforwards
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards		$ 28,378