Aceragen (ACGN) 10-Q 9 Aug 21 2021 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Aug. 06, 2021
Document and Entity Information
Document Type	10-Q
Document Period End Date	Jun. 30, 2021
Document Quarterly Report	true
Document Transition Report	false
Entity File Number	001-31918
Entity Registrant Name	IDERA PHARMACEUTICALS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-3072298
Entity Address, Address Line One	505 Eagleview Blvd., Suite 212
Entity Address, City or Town	Exton
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19341
City Area Code	484
Local Phone Number	348-1600
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	IDRA
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		52,762,048
Entity Central Index Key	0000861838
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Amendment Flag	false

CONDENSED BALANCE SHEETS

CONDENSED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 40,590	$ 33,229
Short-term investments		4,499
Prepaid expenses and other current assets	2,885	3,627
Total current assets	43,475	41,355
Property and equipment, net	33	44
Operating lease right-of-use assets	833	930
Other assets	70	70
Total assets	44,411	42,399
Current liabilities:
Accounts payable	184	329
Accrued expenses	5,645	6,072
Operating lease liability	200	191
Other current liability		435
Total current liabilities	6,029	7,027
Warrant liability, long-term		6,983
Future tranche right liability, long-term		118,803
Operating lease liability, net of current portion	656	758
Total liabilities	6,685	133,571
Commitments and contingencies (Note 13)
Stockholders' equity (deficit):
Common stock, $0.001 par value, Authorized - 140,000 shares; Issued and outstanding - 52,115 and 38,291 at June 30, 2021 and December 31, 2020, respectively	52	38
Additional paid-in capital	763,051	742,342
Accumulated deficit	(725,377)	(833,552)
Total stockholders' equity (deficit)	37,726	(91,172)
Total liabilities and stockholders' equity (deficit)	44,411	42,399
Series B1 Redeemable Convertible Preferred Stock
Stockholders' equity (deficit):
Preferred stock
Series A Convertible Preferred Stock
Stockholders' equity (deficit):
Preferred stock

CONDENSED BALANCE SHEETS (Paren

CONDENSED BALANCE SHEETS (Parenthetical) - $ / shares	Jun. 30, 2021	Dec. 31, 2020
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	140,000,000	140,000,000
Common stock, shares issued	52,115,000	38,291,000
Common stock, shares outstanding	52,115,000	38,291,000
Series B1 Redeemable Convertible Preferred Stock
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares designated	278,000	278,000
Preferred stock, shares issued	0	24,000
Preferred stock, shares outstanding	0	24,000
Common stock, shares outstanding		24,000
Series A Convertible Preferred Stock
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares designated	1,500,000	1,500,000
Preferred stock, shares issued	1,000	1,000
Preferred stock, shares outstanding	1,000	1,000

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating expenses:
Research and development	$ 3,893	$ 5,379	$ 10,764	$ 14,889
General and administrative	2,472	2,632	5,628	6,274
Restructuring costs	1,192		1,192
Total operating expenses	7,557	8,011	17,584	21,163
Loss from operations	(7,557)	(8,011)	(17,584)	(21,163)
Other income (expense):
Interest income	2	27	5	152
Interest expense	(4)		(7)
Warrant revaluation gain		(913)	6,983	188
Future tranche right revaluation gain		(15,349)	118,803	5,362
Foreign currency exchange (loss) gain	(4)	20	(25)	52
Net income / (loss)	(7,563)	(24,226)	108,175	(15,409)
Net income (loss) applicable to common stockholders (Note 12)
Basic	(7,563)	(24,226)	105,450	(15,409)
Diluted	$ (7,563)	$ (24,226)	$ (17,611)	$ (17,693)
Net income (loss) per share applicable to common stockholders (Note 12)
Basic	$ (0.15)	$ (0.72)	$ 2.31	$ (0.48)
Diluted	$ (0.15)	$ (0.72)	$ (0.32)	$ (0.52)
Weighted-average number of common shares used in computing net income (loss) per share applicable to common stockholders
Basic	49,909	33,583	45,575	31,941
Diluted	49,909	33,583	54,937	34,123

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash Flows from Operating Activities:
Net income (loss)	$ 108,175	$ (15,409)
Adjustments to reconcile net income (loss) to net cash used in operating activities:
Stock-based compensation	1,515	1,504
Warrant liability revaluation gain	(6,983)	(188)
Future tranche right liability revaluation gain	(118,803)	(5,362)
Issuance of common stock for services rendered	130	98
Accretion of discounts on short-term investments	(1)	(36)
Depreciation and amortization expense	11	41
Changes in operating assets and liabilities:
Prepaid expenses and other assets	742	819
Accounts payable, accrued expenses, and other liabilities	(640)	(575)
Other	4	8
Net cash used in operating activities	(15,850)	(19,100)
Cash Flows from Investing Activities:
Purchases of available-for-sale securities		(5,535)
Proceeds from maturity of available-for-sale securities	4,500	5,149
Purchases of property and equipment		(7)
Net cash provided by (used in) investing activities	4,500	(393)
Cash Flows from Financing Activities:
Proceeds from common stock financings, net	18,841	7,230
Proceeds from employee stock purchases	34	54
Proceeds from exercise of common stock options and warrants	271
Payments on seller-financed purchases	(435)
Net cash provided by financing activities	18,711	7,284
Net increase (decrease) in cash and cash equivalents	7,361	(12,209)
Cash and cash equivalent, beginning of period	33,229	40,019
Cash and cash equivalents, end of period	40,590	27,810
Supplemental disclosure of cash flow information:
Cash paid for interest	5
Supplemental disclosure of non-cash financing and investing activities:
Offering costs in accounts payable and accrued expenses	$ 68	$ 25

CONDENSED STATEMENTS OF REDEEMA

CONDENSED STATEMENTS OF REDEEMABLE PREFERRED STOCK AND STOCKHOLDERS' DEFICIT - USD ($) $ in Thousands	Common StockSeries B1 Redeemable Convertible Preferred Stock	Common Stock	Additional Paid-in CapitalSeries B1 Redeemable Convertible Preferred Stock	Additional Paid-in Capital	Accumulated Deficit	Series B1 Redeemable Convertible Preferred Stock	Total
Beginning balance at Dec. 31, 2019		$ 30		$ 709,692	$ (720,890)	$ 24	$ (11,168)
Beginning balance (in shares) at Dec. 31, 2019		29,672,000
Sale of common stock, net of issuance costs		$ 1		1,405			1,406
Sale of common stock, net of issuance costs (in shares)		854,000
Issuance of common stock under equity incentive plan (vesting of restricted stock units (in shares)		48,000
Issuance of common stock under employee stock purchase plan				25			25
Issuance of common stock under employee stock purchase plan (in shares)		19,000
Issuance of common stock for services rendered				26			26
Issuance of common stock for services rendered (in shares)		14,000
Stock-based compensation expense				750			750
Net income					8,817		8,817
Ending balance at Mar. 31, 2020		$ 31		711,898	(712,073)	24	(144)
Ending balance (in shares) at Mar. 31, 2020		30,607,000
Beginning balance at Dec. 31, 2019		$ 30		709,692	(720,890)	$ 24	(11,168)
Beginning balance (in shares) at Dec. 31, 2019		29,672,000
Net income							(15,409)
Ending balance at Jun. 30, 2020		$ 34		718,574	(736,299)		(17,691)
Ending balance (in shares) at Jun. 30, 2020		34,291,000				24,000
Beginning balance at Mar. 31, 2020		$ 31		711,898	(712,073)	$ 24	(144)
Beginning balance (in shares) at Mar. 31, 2020		30,607,000
Sale of common stock, net of issuance costs		$ 3		5,821			5,824
Sale of common stock, net of issuance costs (in shares)		3,607,000
Issuance of common stock under employee stock purchase plan				29			29
Issuance of common stock under employee stock purchase plan (in shares)		21,000
Issuance of common stock for services rendered				72			72
Issuance of common stock for services rendered (in shares)		56,000
Stock-based compensation expense				754			754
Net income					(24,226)		(24,226)
Ending balance at Jun. 30, 2020		$ 34		718,574	(736,299)		(17,691)
Ending balance (in shares) at Jun. 30, 2020		34,291,000				24,000
Beginning balance at Dec. 31, 2020		$ 38		742,342	(833,552)		$ (91,172)
Beginning balance (in shares) at Dec. 31, 2020		38,291,000				24,000	38,291,000
Sale of common stock, net of issuance costs		$ 3		16,258			$ 16,261
Sale of common stock, net of issuance costs (in shares)		3,195,000
Issuance of common stock under equity incentive plan (vesting of restricted stock units (in shares)		237,000
Issuance of common stock under employee stock purchase plan				28			28
Issuance of common stock under employee stock purchase plan (in shares)		8,000
Issuance of common stock upon exercise of common stock options and warrants		$ 4		267			271
Issuance of common stock upon exercise of common stock options and warrants (in shares)		3,375,000
Issuance of common stock for services rendered				67			67
Issuance of common stock for services rendered (in shares)		16,000
Stock-based compensation expense				1,111			1,111
Conversion of preferred stock to common	$ 1		$ (1)
Conversion of preferred stock to common (in shares)	1,415,000					(14,000)
Net income					115,738		115,738
Ending balance at Mar. 31, 2021		$ 46		760,072	(717,814)		42,304
Ending balance (in shares) at Mar. 31, 2021		46,537,000				10,000
Beginning balance at Dec. 31, 2020		$ 38		742,342	(833,552)		$ (91,172)
Beginning balance (in shares) at Dec. 31, 2020		38,291,000				24,000	38,291,000
Conversion of preferred stock to common (in shares)						(23,684)
Net income							$ 108,175
Ending balance at Jun. 30, 2021		$ 52		763,051	(725,377)		$ 37,726
Ending balance (in shares) at Jun. 30, 2021		52,115,000					52,115,000
Beginning balance at Mar. 31, 2021		$ 46		760,072	(717,814)		$ 42,304
Beginning balance (in shares) at Mar. 31, 2021		46,537,000				10,000
Sale of common stock, net of issuance costs		$ 2		2,510			2,512
Sale of common stock, net of issuance costs (in shares)		2,076,000
Issuance of common stock under employee stock purchase plan				6			6
Issuance of common stock under employee stock purchase plan (in shares)		6,000
Issuance of common stock upon exercise of common stock options and warrants		$ 3		(3)
Issuance of common stock upon exercise of common stock options and warrants (in shares)		2,496,000
Issuance of common stock for services rendered				63			63
Issuance of common stock for services rendered (in shares)		47,000
Stock-based compensation expense				404			404
Conversion of preferred stock to common		$ 1		(1)
Conversion of preferred stock to common (in shares)		953,000				(10,000)
Net income					(7,563)		(7,563)
Ending balance at Jun. 30, 2021		$ 52		$ 763,051	$ (725,377)		$ 37,726
Ending balance (in shares) at Jun. 30, 2021		52,115,000					52,115,000

Business and Organization

Business and Organization	6 Months Ended
	Jun. 30, 2021
Business and Organization
Business and Organization	Note 1. Business and Organization ​ Business Overview ​ Idera Pharmaceuticals, Inc. (“Idera” or the “Company”), a Delaware corporation, is a clinical-stage biopharmaceutical company with a business strategy focused on the clinical development, and ultimately the commercialization , of drug candidates for rare disease indications characterized by small, well-defined patient populations with serious unmet medical needs. The Company’s current focus is on its Toll-like receptor (“TLR”) agonist, tilsotolimod (IMO-2125), for oncology, as well as identifying and potentially acquiring rights to novel development or commercial stage rare disease programs. The Company believes it can develop and commercialize targeted therapies on its own. To the extent the Company seeks to develop drug candidates for other disease indications, it has entered into and may explore additional collaborative alliances to support development and commercialization. ​ Reduction-in-Force ​ In April 2021, following the announcement that the Company’s ILLUMINATE-301 trial did not meet its primary endpoint of objective response rate (ORR), the Company implemented a reduction in force which affected approximately 50% of its workforce through June 30, 2021. 16 positions were eliminated, primarily in the area of research and development. The decision was made in order to align the Company’s workforce with its needs in light of the outcome of ILLUMINATE-301’s ORR endpoint, its ongoing ILLUMINATE development program and other business development activities focused on identifying new portfolio opportunities. In connection with these actions, the Company incurred and paid one-time termination costs for the reduction in workforce, which includes severance, benefits and related costs, of approximately $1.2 million during the second quarter of 2021. ​ Liquidity and Financial Condition ​ As of June 30, 2021, the Company had an accumulated deficit of $725.4 million and a cash and cash equivalents balance of $40.6 million. The Company expects to incur substantial operating losses in future periods and will require additional capital as it seeks to advance tilsotolimod and/or acquire and advance any new drug candidates through development to commercialization. The Company does not expect to generate product revenue, sales-based milestones, or royalties until the Company successfully completes development of and obtains marketing approval for tilsotolimod or any other future drug candidates, either alone or in collaboration with third parties, which the Company expects will take a number of years, if at all. To commercialize tilsotolimod and any other future drug candidates, the Company needs to complete clinical development and comply with comprehensive regulatory requirements. The Company is subject to a number of risks and uncertainties similar to those of other companies of the same size within the biotechnology industry, such as uncertainty of clinical trial outcomes, uncertainty of additional funding, and history of operating losses. ​ The Company follows the provisions of Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) 205-40, Presentation of Financial Statements—Going Concern

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2021
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	Note 2. Summary of Significant Accounting Policies ​ Basis of Presentation ​ The accompanying unaudited financial statements included herein have been prepared by the Company in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and pursuant to the rules and regulations of the SEC. Accordingly, certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. In the opinion of management, all adjustments, consisting of normal recurring adjustments, and disclosures considered necessary for a fair presentation of interim period results have been included. Interim results for the three and six months ended June 30, 2021 are not necessarily indicative of results that may be expected for the year ending December 31, 2021. For further information, refer to the financial statements and footnotes thereto included in the Company’s 2020 Form 10-K. ​ Cash and Cash Equivalents ​ The Company considers all highly liquid investments with maturities of 90 days or less when purchased to be “cash equivalents.” Cash and cash equivalents at June 30, 2021 consisted of cash and money market funds. Cash and cash equivalents at December 31, 2020 consisted of cash and cash equivalents and short-term investments. ​ Financial Instruments ​ The fair value of the Company’s financial instruments is determined and disclosed in accordance with the three-tier fair value hierarchy specified in Note 3. The Company is required to disclose the estimated fair values of its financial instruments. As of June 30, 2021, the Company’s financial instruments consisted of cash and cash equivalents. As of December 31, 2020, the Company’s financial instruments consisted of cash, cash equivalents, short-term investments, receivables and warrant and future tranche right liabilities. The estimated fair values of these financial instruments approximate their carrying values. As of June 30, 2021, the Company did not have any derivatives, hedging instruments or other similar financial instruments. ​ Concentration of Credit Risk ​ Financial instruments that subject the Company to credit risk primarily consist of cash, cash equivalents, and short-term investments. The Company’s credit risk is managed by investing in highly rated money market instruments, U.S. treasury bills, corporate bonds, commercial paper and/or other debt securities. Due to these factors, no significant additional credit risk is believed by management to be inherent in the Company’s assets. As of June 30, 2021, all the Company’s cash and cash equivalents were held at two financial institutions. ​ Operating Lease Right-of-use Assets and Lease Liability ​ The Company accounts for leases under ASC Topic 842, Leases Property, Plant, and Equipment ​ As of June 30, 2021 and December 31, 2020, the Company’s operating lease ROU assets and corresponding short-term and long-term lease liabilities primarily relate to its existing Exton, PA facility operating lease which expires on May 31, 2025. ​ Note 2. Summary of Significant Accounting Policies (Continued) ​ Warrant Liability ​ The Company accounts for stock warrants as either equity instruments, liabilities or derivative liabilities in accordance with ASC Topic 480, Distinguishing Liabilities from Equity Derivatives and Hedging ​ Future Tranche Right Liability ​ On December 23, 2019, the Company entered into a Securities Purchase Agreement (the “December 2019 Securities Purchase Agreement”) with institutional investors affiliated with Baker Brothers (as defined below), an existing stockholder (see Note 11). As more fully described in Note 7, the December 2019 Securities Purchase Agreement contained call options on redeemable preferred shares with warrants (conditionally exercisable for shares that are puttable). The Company determined that these call options represented freestanding financial instruments and accounted for the options as liabilities (“Future Tranche Right Liability”) under ASC 480, which requires the measurement and recognition of the fair value of the liability at the time of issuance and at each reporting period. Any change in fair value is recognized in Future Tranche Right Liability Revaluation Gain (Loss) in the Company’s condensed statements of operations. During the three months ended March 31, 2021, the liability-classified call options provided for under the December 2019 Securities Purchase Agreement terminated and, accordingly, the liability balance was derecognized ​ Preferred Stock ​ The Company applies ASC 480 when determining the classification and measurement of its preferred stock. Preferred shares subject to mandatory redemption are classified as liability instruments and are measured at fair value. Conditionally redeemable preferred shares (including preferred shares that feature redemption rights that are either within the control of the holder or subject to redemption upon the occurrence of uncertain events not solely within the Company’s control) are classified as temporary equity. At all other times, preferred shares are classified as stockholders’ equity. ​ Accretion of redeemable convertible preferred stock includes the accretion of the Company's Series B redeemable convertible preferred stock to its stated value. The carrying value of the Series B redeemable convertible preferred stock is accreted to redemption value using the effective interest method, from the date of issuance to the earliest date the holders can demand redemption or until the redeemable convertible preferred stock cease to be outstanding. ​ Income Taxes ​ In accordance with ASC Topic 270, Interim Reporting Income Taxes Note 2. Summary of Significant Accounting Policies (Continued) ​ New Accounting Pronouncements ​ From time to time, new accounting pronouncements are issued by the FASB and rules are issued by the SEC that the Company has or will adopt as of a specified date. Unless otherwise noted, management does not believe that any other recently issued accounting pronouncements issued by the FASB or guidance issued by the SEC had, or is expected to have, a material impact on the Company’s present or future financial statements. ​ Recently Adopted Accounting Pronouncements ​ In August 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU 2020-06”), which simplifies the guidance on an issuer’s accounting for convertible instruments and contracts in its own equity. The Company adopted ASU 2020-06 in the first quarter of 2021. The adoption of this ASU did not have a material effect on the Company’s financial statements. ​ COVID-19 While the Company is not aware of a material impact from the continuation of the coronavirus ("COVID-19") pandemic through June 30, 2021, the full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations, and financial condition, including expenses and manufacturing, clinical trials, and research and development costs, depends on future developments that are highly uncertain at this time.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2021
Fair Value Measurements
Fair Value Measurements	Note 3. Fair Value Measurements ​ Assets and Liabilities Measured at Fair Value on a Recurring Basis ​ The Company applies the guidance in ASC Topic 820, Fair Value Measurement ​ The Company uses a fair value hierarchy, which distinguishes between assumptions based on market data (observable inputs) and an entity's own assumptions (unobservable inputs). The guidance requires that fair value measurements be classified and disclosed in one of the following three categories: ● Level 1: Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities; ● Level 2: Quoted prices in markets that are not active or inputs which are observable, either directly or indirectly, for substantially the full term of the asset or liability, or ● Level 3: Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity). ​ Determining which category an asset or liability falls within the hierarchy requires significant judgment. The Company evaluates its hierarchy disclosures each reporting period. There were no transfers between Level 1 , 2 , and 3 during the six months ended June 30, 2021. ​ ​ Note 3. Fair Value Measurements (Continued) ​ The table below presents the assets and liabilities measured and recorded in the financial statements at fair value on a recurring basis at June 30, 2021 and December 31, 2020 categorized by the level of inputs used in the valuation of each asset and liability. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2021 (In thousands) ​ Total ​ Level 1 ​ Level 2 ​ Level 3 Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash ​ $ 250 ​ $ 250 ​ $ — ​ $ — ​ Cash equivalents – money market funds ​ ​ 40,340 ​ ​ 40,340 ​ ​ — ​ ​ — ​ Total assets ​ $ 40,590 ​ $ 40,590 ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ (In thousands) ​ Total ​ Level 1 ​ Level 2 ​ Level 3 ​ Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash ​ $ 250 ​ $ 250 ​ $ — ​ $ — ​ Cash equivalents – money market funds ​ ​ 32,979 ​ ​ 32,979 ​ ​ — ​ ​ — ​ Short-term investments – commercial paper ​ ​ 3,499 ​ ​ — ​ 3,499 ​ — ​ Short-term investments – US treasury bills ​ 1,000 ​ — ​ 1,000 ​ — ​ Total assets ​ $ 37,728 ​ $ 33,229 ​ $ 4,499 ​ $ — ​ Liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Warrant liability ​ $ 6,983 ​ $ — ​ $ — ​ $ 6,983 ​ Future tranche right liability ​ ​ 118,803 ​ ​ — ​ ​ — ​ ​ 118,803 ​ Total liabilities ​ $ 125,786 ​ $ — ​ $ — ​ $ 125,786 ​ ​ The Level 1 assets consist of money market funds, which are actively traded daily. The Level 2 assets consist of commercial paper and U.S. treasury bills whose fair value may not represent actual transactions of identical securities. The fair value of commercial paper is generally determined based on the relationship between the investment’s discount rate and the discount rates of the same issuer’s commercial paper available in the market which may not be actively traded daily. Since these fair values may not be based upon actual transactions of identical securities, they are classified as Level 2. ​ Changes in Level 3 Liabilities Measured at Fair Value on a Recurring Basis ​ Warrant Liability and Future Tranche Right Liability ​ The reconciliation of the Company's warrant and future tranche right liability measured at fair value on a recurring basis using unobservable inputs (Level 3) is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Future ​ ​ Warrant ​ Tranche Right (In thousands) ​ Liability ​ Liability Balance, December 31, 2020 $ 6,983 ​ $ 118,803 Change in the fair value of liability (1) (6,983) ​ (118,803) Balance, June 30, 2021 $ — ​ $ — (1) During the six months ended June 30, 2021, the Company’s liability-classified warrants and future tranche rights terminated, and accordingly, the liabilities were derecognized.

Investments

Investments	6 Months Ended
	Jun. 30, 2021
Investments
Investments	Note 4. Investments ​ The Company’s available-for-sale investments at fair value consisted of the following as of December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ ​ ​ ​ ​ Unrealized ​ Unrealized ​ Fair (In thousands) Cost (Losses) Gains Value Short-term investments – commercial paper ​ $ 3,499 ​ $ — ​ $ — ​ $ 3,499 ​ Short-term investments – US treasury bills ​ 1,000 ​ — ​ — ​ 1,000 ​ Total short-term investments ​ $ 4,499 ​ $ — ​ $ — ​ $ 4,499 ​ ​ The Company had no realized gains or losses from the sale of investments in available-for-sale securities during each of the six months ended June 30, 2021 and 2020. In accordance with ASU 2016-13, if the fair value of the Company’s investments in available-for-sale debt securities is less than the amortized cost, the Company records (i) an allowance for credit losses with a corresponding charge to net income (loss) for any credit-related impairment, with subsequent improvements in expected credit losses recognized as a reversal of the allowance, and/or (ii) any non-credit impairment loss to other comprehensive income (loss). ​ As of December 31, 2020, the Company had no allowance for credit losses pertaining to the Company’s investments in available-for-sale debt securities. Additionally, there were no impairment charges or recoveries recorded during each of the six months ended June 30, 2021 and 2020.

Property and Equipment

Property and Equipment	6 Months Ended
	Jun. 30, 2021
Property and Equipment
Property and Equipment	Note 5. Property and Equipment ​ At June 30, 2021 and December 31, 2020, property and equipment, net, consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, ​ December 31, ​ (In thousands) 2021 2020 Leasehold improvements ​ $ 107 ​ $ 107 ​ Equipment and other ​ 712 ​ 770 ​ Total property and equipment, at cost ​ $ 819 ​ $ 877 ​ Less: Accumulated depreciation and amortization ​ 786 ​ 833 ​ Property and equipment, net ​ $ 33 ​ $ 44 ​ ​ ​ Depreciation and amortization expense on property and equipment was less than $0.1 million for each of the three and six months ended June 30, 2021 and 2020. Additionally, there were

Accrued Expenses

Accrued Expenses	6 Months Ended
	Jun. 30, 2021
Accrued Expenses
Accrued Expenses	Note 6. Accrued Expenses ​ At June 30, 2021 and December 31, 2020, accrued expenses consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, ​ December 31, (In thousands) ​ 2021 2020 Payroll and related costs ​ $ 909 ​ $ 2,133 ​ Clinical and nonclinical trial expenses ​ 3,890 ​ 3,229 ​ Professional and consulting fees ​ 733 ​ 584 ​ Other ​ 113 ​ 126 ​ Total accrued expenses ​ $ 5,645 ​ $ 6,072 ​ ​

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	6 Months Ended
	Jun. 30, 2021
Redeemable Convertible Preferred Stock
Redeemable Convertible Preferred Stock	Note 7. Redeemable Convertible Preferred Stock ​ December 2019 Private Placement ​ On December 23, 2019, the Company entered into the December 2019 Securities Purchase Agreement, under which the Company sold 23,684 shares of Series B1 convertible preferred stock (“Series B1 Preferred Stock”) and warrants to purchase 2,368,400 shares of the Company’s common stock at an exercise price of $1.52 per share (or, if the holder elected to exercise the warrants for shares of Series B1 Preferred Stock, 23,684 shares of Series B1 Preferred Stock at an exercise price of $152 per share) for aggregate gross proceeds of $3.9 million (the “Initial Closing”). ​ In addition, the Company agreed to sell to the purchasers, at their option and subject to certain conditions, (i) 98,685 shares of Series B2 convertible preferred stock (“Series B2 Preferred Stock”) and 9,868,500 warrants to purchase common stock at an exercise price of $1.52 per share (or, at the election of the holder, 98,685 shares of Series B2 Preferred Stock at an price of $152 per share), for aggregate gross proceeds of $15 million (the “Series B2 Tranche”), (ii) 82,418 shares of Series B3 convertible preferred stock (“Series B3 Preferred Stock”) and 6,593,440 warrants to purchase common stock at an exercise price of $1.82 per share (or, at the election of the holder, 65,934 shares of Series B3 Preferred Stock at a price of $182 per share), for aggregate gross proceeds of $15 million (the “Series B3 Tranche”), and (iii) 82,418 shares of Series B4 convertible preferred stock (“Series B4 Preferred Stock”) and 6,593,440 warrants to purchase common stock at an exercise price of $1.82 per share (or, at the election of the holder, 65,934 shares of Series B3 Preferred Stock at a price of $182 per share), for aggregate gross proceeds of $15 million (the “Series B4 Tranche”) over a period of up to 21 months following the Company’s 2020 Annual Meeting of Stockholders held on May 12, 2020, where stockholders of the Company voted to approve an amendment to the Company’s Restated Certificate of Incorporation to increase the authorized number of shares of the Company’s common stock to 140,000,000 . As consideration for the future tranche rights, the Company received aggregate gross proceeds of $6.2 million in December 2019. ​ The purchase and sale of the securities issuable under the Series B2, B3, and B4 tranches described above were subject to three separate closings, each to be conducted at the purchasers’ discretion. The right of the purchasers to purchase Series B2, Series B3 and Series B4 Preferred Stock was set to expire on the 10 th business day following the Company’s ORR Data Announcement, as defined in the December 2019 Securities Purchase Agreement, for its ILLUMINATE-301 study. As a result of the purchasers not exercising the Series B2 Tranche prior to expiration, all future tranche rights and outstanding warrants previously issued pursuant to the December 2019 Securities Purchase Agreement were terminated during the three months ended March 31, 2021. Accordingly, the Company is no longer eligible to receive additional proceeds pursuant to the December 2019 Securities Purchase Agreement and the related warrant liability and future tranche right liability were derecognized during the three months ended March 31, 2021. ​ Accounting Considerations ​ The Company determined that the Series B1 Preferred Stock, the accompanying Series B1 warrants, and each of the future tranche rights represent freestanding financial instruments. The Series B1 warrants and the future tranche rights were classified as liabilities until their termination in March 2021 as the underlying shares were potentially redeemable and such redemption was deemed to be outside of the Company’s control. ​ Due to the redeemable nature of the Series B1 Preferred Stock, the Series B1 Preferred Stock was classified as temporary equity and the carrying value was being accreted to its redemption value as of December 31, 2020 and while the Series B1 Preferred Stock was outstanding during 2021. During the six months ended June 30, 2021, all the Company’s 23,684 shares of Series B1 Preferred Stock outstanding were converted into shares of the Company’s common stock. See Note 11 for details. For the three and six months ended June 30, 2021 and 2020, accretion was de minimis.

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Jun. 30, 2021
Stockholders' Equity
Stockholders' Equity	Note 8. Stockholders’ Equity ​ Equity Financings ​ Common Stock Purchase Agreement ​ On March 4, 2019, the Company entered into a Purchase Agreement with Lincoln Park Capital Fund, LLC (“Lincoln Park”), which was amended on September 2, 2020 (as amended to date, the “LPC Purchase Agreement”), pursuant to which, upon the terms and subject to the conditions and limitations set forth therein, Lincoln Park has committed to purchase an aggregate of $35.0 million of shares of Company common stock from time to time at the Company’s sole discretion over a 36-month period. As consideration for entering into the LPC Purchase Agreement, the Company issued 269,749 shares of its common stock to Lincoln Park as a commitment fee (the “Commitment Shares”). The closing price of the Company’s common stock on March 4, 2019 was $2.84 and the Company did not receive any cash proceeds from the issuance of the Commitment Shares. ​ During the six months ended June 30, 2021 and 2020, the Company sold 800,000 and 600,000 shares, respectively, pursuant to the LPC Purchase Agreement, resulting in net proceeds of $4.2 million and $1.1 million, respectively. As of June 30, 2021, the Company may sell up to an additional $25.3 million of shares under the LPC Purchase Agreement, subject to certain limitations. ​ "At-The-Market" Equity Program ​ In November 2018, the Company entered into an Equity Distribution Agreement (the “ATM Agreement”) with JMP Securities LLC (“JMP”) pursuant to which the Company may issue and sell shares of its common stock having an aggregate offering price of up to $50.0 million (the “ATM Shares”) through JMP as its agent. Subject to the terms and conditions of the ATM Agreement, JMP will use its commercially reasonable efforts to sell the ATM Shares from time to time, based upon the Company’s instructions, by methods deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act, or if specified by the Company, by any other method permitted by law, including but not limited to in negotiated transactions. The Company has no obligation to sell any of the ATM Shares, and the Company or JMP may at any time suspend sales under the ATM Agreement or terminate the ATM Agreement. JMP is entitled to a fixed commission of 3.0% of the gross proceeds from ATM Shares sold. ​ During the six months ended June 30, 2021 and 2020, the Company sold 4,470,593 and 821,018 shares, respectively, pursuant to the ATM Agreement, resulting in net proceeds, after deduction of commissions and other offering expenses, of $14.6 million and $1.4 million, respectively. In addition, from July 1, 2021 through July 7, 2021, the Company sold an additional 646,764 shares for $0.7 million in net proceeds under the ATM Agreement. The Company may sell up to an additional ​ April 2020 Private Placement ​ On April 7, 2020, the Company entered into a Securities Purchase Agreement with Pillar Partners Foundation, L.P. (“Pillar Partners”), a related party as more fully described in Note 11, which was amended on December 11, 2020 (as amended to date, the “April 2020 Securities Purchase Agreement”), under which the Company sold 3,039,514 shares of common stock and accompanying warrants to purchase 3,039,514 shares of the Company’s common stock with an exercise price of $2.28 per share, for aggregate gross proceeds of $5.0 million. Each share and the accompanying common warrant had a combined purchase price of $1.645, which included $0.125 for each share of common stock underlying each warrant. The April 2020 Securities Purchase Agreement also provided for the option for Pillar Partners to purchase 2,747,252 shares of the Company’s common stock (or pre-funded warrants to purchase shares of the Company’s common stock at an exercise price of $0.01 in lieu of certain shares to the extent that purchasing such shares will cause Pillar Investment Entities (as defined below) to beneficially own in excess of 19.99% of the total number of shares of common stock outstanding post transaction) and warrants to purchase up to 1,373,626 shares of the Company’s common stock (with an exercise price of $2.71), for aggregate gross proceeds of $5.0 million (the “April 2020 Private Placement Second Closing”). Subsequently, in December 2020, the April 2020 Private Placement Second Closing was consummated. Total net proceeds received pursuant to the April 2020 Securities Purchase Agreement, after deduction of offering expenses, was $9.8 million. ​ ​ Note 8. Stockholders’ Equity (Continued) ​ July 2020 Private Placement On July 13, 2020, the Company entered into a Securities Purchase Agreement (the “July 2020 Securities Purchase Agreement”) with Pillar Partners, Pillar Pharmaceuticals 6 L.P. (“Pillar 6”), and Pillar Pharmaceuticals 7 L.P. (“Pillar 7” and, together with Pillar Partners and Pillar 6, the “July 2020 Purchasers”), each a related party as more fully described in Note 11, pursuant to which, among other things, provided the July 2020 Purchasers the option to purchase, at their sole discretion, pre-funded warrants to purchase up to 784,615 shares of the Company’s common stock, at an exercise price of $0.01 per share, and warrants to purchase up to 274,615 shares of the Company’s common stock, at an exercise price of $9.75 , for aggregate gross proceeds of $5.1 million (the “July 2020 Private Placement Second Closing”). ​ Common Stock Warrants ​ In connection with various financing transactions, the Company has issued warrants to purchase shares of the Company’s common and preferred stock. The Company accounts for common and preferred stock warrants as equity instruments or liabilities, depending on the specific terms of the warrant agreement. ​ The following table summarizes outstanding warrants to purchase shares of the Company’s common and preferred stock as of June 30, 2021 and December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of Shares ​ ​ ​ ​ ​ ​ ​ June 30, ​ December 31, ​ Weighted-Average ​ ​ ​ Description ​ 2021 ​ 2020 ​ Exercise Price ​ Expiration Date Liability-classified Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 2019 Series B1 warrants (1) ​ — ​ 2,368,400 ​ ​ $ 1.52 ​ Dec 2026 ​ ​ ​ — ​ 2,368,400 ​ ​ ​ ​ ​ ​ Equity-classified Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ May 2013 warrants 15,437 ​ 1,949,754 ​ ​ $ 0.08 ​ None ​ September 2013 warrants 4,096 ​ 514,756 ​ ​ $ 0.08 ​ None ​ February 2014 warrants 2,171 ​ 266,006 ​ ​ $ 0.08 ​ None ​ April 2020 Private Placement first closing warrants ​ 3,039,514 ​ 3,039,514 ​ ​ $ 2.28 ​ Apr 2023 ​ April 2020 Private Placement second closing warrants ​ 1,373,626 ​ 1,373,626 ​ ​ $ 2.71 ​ Dec 2023 ​ April 2020 Private Placement second closing warrants ​ 1,143,428 ​ 2,677,311 ​ ​ $ 0.01 ​ None ​ July 2020 Private Placement first closing warrants ​ 389,731 ​ 2,014,234 ​ ​ $ 0.01 ​ None ​ July 2020 Private Placement first closing warrants ​ 2,764,227 ​ 2,764,227 ​ ​ $ 2.58 ​ Jul 2023 ​ ​ ​ 8,732,230 ​ 14,599,428 ​ ​ ​ ​ ​ ​ Total outstanding 8,732,230 ​ 16,967,828 ​ ​ ​ ​ ​ ​ (1) The Series B1 warrants were exercisable for either common stock (exercise price of $1.52 ) or Series B1 Convertible Preferred Stock (exercise price of $152 ) at the discretion of the warrant holder. However, as more fully disclosed in Note 7, the December 2019 Series B1 warrants were terminated during the three months ended March 31, 2021 contemporaneously with the termination of the future tranche rights. ​ Note 8. Stockholders’ Equity (Continued) ​ The table below is a summary of the Company’s warrant activity for the six months ended June 30, 2021. ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Weighted-Average ​ ​ Warrants ​ Exercise Price Outstanding at December 31, 2020 16,967,828 ​ $ 1.28 Issued — ​ — Exercised (1) (5,867,198) ​ 0.04 Expired (2,368,400) ​ 1.52 Outstanding at June 30, 2021 8,732,230 ​ $ 2.04 (1) During the six months ended June 30, 2021, certain related parties exercised warrants as more fully described in Note 11.

Collaboration and License Agree

Collaboration and License Agreements	6 Months Ended
	Jun. 30, 2021
Collaboration and License Agreements
Collaboration and License Agreements	Note 9. Collaboration and License Agreements ​ Scriptr Collaboration and Option Agreement ​ In February 2021, the Company entered into a collaboration and option agreement with Scriptr Global, Inc. (“Scriptr”), pursuant to which (i) the Company and Scriptr will conduct a research collaboration utilizing Scriptr Platform Technology (“SPT”) to identify, research and develop gene therapy candidates (each, a “Collaboration Candidate”) for the treatment, palliation, diagnosis or prevention of (a) myotonic dystrophy type 1 (“DM1 Field”) and (b) Friedreich’s Ataxia (“FA Field”) on a Research Program-by-Research Program basis, as applicable, and (ii) the Company was granted an exclusive option, in its sole discretion, to make effective the Scriptr License Agreement, as defined below, for a given Research Program, as defined below, to make use of Collaboration Candidates and related intellectual property (collectively, the “Scriptr Agreement”). ​ Pursuant to the Scriptr Agreement, Scriptr will use commercially reasonable efforts to carry out research activities set forth in accordance with the applicable DM1 Field and FA Field research plans, including certain pre-clinical proof of concept studies, to identify research Collaboration Candidates utilizing SPT (each, a “Research Program”). Following the completion of activities under a given Research Program, Scriptr will prepare and submit to Idera a comprehensive data package (each, a “Data Package”) that summarizes, on a Program-by-Program basis, any Collaboration Candidates researched under the Research Program, including any data and results. Upon receipt of a Data Package, the Company has, in its sole discretion, up to two-hundred seventy (270) calendar days to make effective the exclusive license agreement entered into by and between the Company and Scriptr, pursuant to which, among other things, grants Idera exclusive rights and licenses with respect to the development, manufacture and commercialization of licensed candidates and products, subject to certain conditions and limitations (the “Scriptr License Agreement”), for a given Research Program (each licensed Research Program, a “Licensed Program”). The Scriptr License Agreement provides for customary development milestones on candidates developed under a Licensed Program and royalties on licensed products, if any. ​ In partial consideration of the rights granted by Scriptr to the Company under the Scriptr Agreement, the Company made a one-time, non-creditable and non-refundable payment to Scriptr during the first quarter of 2021. In order to fund conduct of the Research Programs, the Company shall reimburse Scriptr for costs incurred by or on behalf of Scriptr in connection with the conduct of each Research Program during the Research Term in accordance with the applicable Research Program budget and payment schedule. The Company incurred approximately ​

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2021
Stock-Based Compensation
Stock-Based Compensation	Note 10. Stock-Based Compensation ​ As of June 30, 2021, the only equity compensation plans from which the Company may currently issue new awards are the Company’s 2013 Stock Incentive Plan (as amended to date, the “2013 Plan”) and 2017 Employee Stock Purchase Plan (as amended to date, the “2017 ESPP”), each as more fully described below. ​ Equity Incentive and Employee Stock Purchase Plans ​ 2013 Stock Incentive Plan ​ The 2013 Plan allows for the issuance of incentive stock options intended to qualify under Section 422 of the Internal Revenue Code, non-statutory stock options, stock appreciation rights, restricted stock awards, restricted stock units (“RSUs”), other stock-based awards and performance awards. The total number of shares of common stock authorized for issuance under the 2013 Plan is 5,653,057 shares of the Company’s common stock, plus such additional number of shares of common stock (up to 868,372 shares) as is equal to the number of shares of common stock subject to awards granted under the Company’s 2005 Stock Incentive Plan or 2008 Stock Incentive Plan (the “2008 Plan”), to the extent such awards expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right. ​ As of June 30, 2021, options to purchase a total of 4,355,465 shares of common stock and 594,292 RSUs were outstanding and up to 516,146 shares of common stock remained available for grant under the 2013 Plan. ​ Other Awards and Inducement Grants ​ The Company has not made any awards pursuant to other equity incentive plans, including the 2008 Plan, since the Company’s stockholders approved the 2013 Plan. As of June 30, 2021, options to purchase a total of 207,908 shares of common stock were outstanding under the 2008 Plan. In addition, as of June 30, 2021, non-statutory stock options to purchase an aggregate of 325,000 shares of common stock were outstanding. These options were issued outside of the 2013 Plan to certain newly-hired employees in 2015 and 2014 pursuant to the Nasdaq inducement grant exception as a material component of such new hires’ employment compensation. ​ 2017 Employee Stock Purchase Plan ​ The 2017 ESPP is intended to qualify as an "employee stock purchase plan" as defined in Section 423 of the Internal Revenue Code. The total number of shares of common stock authorized for issuance under the 2017 ESPP is 412,500 shares of common stock, subject to adjustment as described in the 2017 ESPP. As of June 30, 2021, 231,344 shares remained available for issuance under the 2017 ESPP. ​ For the six months ended June 30, 2021 and 2020, the Company issued 13,998 and 40,024 shares of common stock, respectively, under the 2017 ESPP and received proceeds of less than $0.1 million during each period, as a result of employee stock purchases. ​ ​ Note 10. Stock-Based Compensation (Continued) ​ Accounting for Stock-based Compensation ​ The Company recognizes non-cash compensation expense for stock-based awards under the Company’s equity incentive plans and employee stock purchases under the Company’s 2017 ESPP as follows: ● Stock Options : Compensation cost is recognized over an award’s requisite service period, or vesting period, using the straight-line attribution method, based on the grant date fair value determined using the Black-Scholes option-pricing model. ● RSUs : Compensation cost for time-based RSUs, which vest over time based only on continued service, is recognized on a straight-line basis over the requisite service period based on the fair value of the Company’s common stock on the date of grant. Compensation cost for awards that are subject to market considerations is recognized on a straight-line basis over the implied requisite service period, based on the grant date fair value estimated using a Monte Carlo simulation. Compensation cost for awards that are subject to performance conditions is recognized over the period of time commencing when the performance condition is deemed probable of achievement based on the fair value of the Company’s common stock on the date of grant. ● Employee Stock Purchases : Compensation cost is recognized over each plan period based on the fair value of the look-back provision, calculated using the Black-Scholes option-pricing model, considering the 15% discount on shares purchased. ​ Total stock-based compensation expense attributable to stock-based awards made to employees and directors and employee stock purchases included in operating expenses in the Company's condensed statements of operations for the three and six months ended June 30, 2021 and 2020 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ June 30, ​ June 30, (in thousands) ​ 2021 2020 ​ 2021 2020 Stock-based compensation: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Research and development ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Employee Stock Purchase Plan ​ $ 3 $ 15 ​ $ 15 $ 26 Equity Incentive Plan ​ ​ 50 ​ 192 ​ ​ 418 ​ 385 ​ ​ $ 53 $ 207 ​ $ 433 $ 411 General and administrative ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Employee Stock Purchase Plan ​ $ 1 $ 1 ​ $ 3 $ 2 Equity Incentive Plan ​ ​ 350 ​ 546 ​ ​ 1,079 ​ 1,091 ​ ​ $ 351 $ 547 ​ $ 1,082 $ 1,093 Total stock-based compensation expense ​ $ 404 $ 754 ​ $ 1,515 $ 1,504 ​ During the six months ended June 30, 2021 and 2020, the weighted average fair market value of stock options granted was $2.02 and $1.09, respectively. ​ The following weighted average assumptions apply to the options to purchase 833,500 and 727,129 shares of common stock granted to employees and directors during the six months ended June 30, 2021 and 2020, respectively: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2021 2020 Average risk-free interest rate ​ 0.4% ​ ​ 1.0% ​ Expected dividend yield ​ — ​ ​ — ​ Expected lives (years) ​ 3.6 ​ ​ 3.9 ​ Expected volatility ​ 87% ​ ​ 84% ​ Weighted average exercise price (per share) ​ $ 3.66 ​ $ 2.08 ​ ​ All options granted during the six months ended June 30, 2021 and 2020 were granted at exercise prices equal to the fair market value of the common stock on the dates of grant . ​ Note 10. Stock-Based Compensation (Continued) ​ Stock Option Activity ​ The following table summarizes stock option activity for the nine months ended June 30, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ($ in thousands, except per share data) ​ Stock ​ Weighted-Average ​ Weighted-Average ​ Aggregate Intrinsic Value Outstanding at December 31, 2020 4,614,323 ​ $ 9.78 6.8 ​ $ 2,949 ​ Granted 833,500 ​ ​ 3.66 ​ ​ ​ ​ ​ ​ Exercised (22,500) ​ ​ 2.11 ​ ​ ​ ​ ​ ​ Forfeited (236,394) ​ ​ 4.47 ​ ​ ​ ​ ​ ​ Expired (300,556) ​ ​ 11.91 ​ ​ ​ ​ ​ ​ Outstanding at June 30, 2021 (1) 4,888,373 ​ $ 8.89 ​ 6.6 ​ $ — ​ Exercisable at June 30, 2021 4,113,264 ​ $ 9.83 ​ 6.2 ​ $ — ​ (1) Includes both vested stock options as well as unvested stock options for which the requisite service period has not been rendered but that are expected to vest based on achievement of a service condition. ​ During the three months ended March 31, 2021, the Company accelerated the vesting of 1,535,578 options, which were previously granted from 2019 through 2021. As of June 30, 2021, there was $1.5 million of unrecognized compensation cost related to unvested options, which the Company expects to recognize over a weighted average period of 1.7 years. ​ Restricted Stock Activity ​ The following table summarizes restricted stock activity for the six months ended June 30, 2021: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Time-based Awards ​ Market/Performance-based Awards ($ in thousands, except per share data) ​ Number of Shares ​ Weighted-Average Grant Date Fair Value ​ Number of Shares ​ Weighted-Average Grant Date Fair Value Nonvested shares at December 31, 2020 354,003 ​ $ 2.27 ​ 549,318 ​ $ 1.54 Granted — ​ — ​ — ​ — Forfeited (48,563) ​ 2.31 ​ (23,701) ​ 1.54 Vested (236,765) ​ 2.25 ​ — ​ — Nonvested shares at June 30, 2021 68,675 ​ $ 2.30 ​ 525,617 ​ $ 1.54 ​ Time-based Restricted Stock Units ​ During the three months ended March 31, 2021, the Company accelerated the vesting of 137,872 unvested time-based restricted stock units which were previously granted in 2019 and 2020. As of June 30, 2021, there was $0.1 million of unrecognized compensation expense related to the Company’s time-based RSUs, which is expected to be recognized over a weighted-average period of 2.0 years. ​ Market/Performance-based Restricted Stock Units ​ In July 2020, the Company granted RSUs to certain employees, including executive officers, under the 2013 Plan, with vesting that may occur upon a combination of specific performance and/or market conditions. Accordingly, the Company views these RSUs as two separate awards: (i) an award that vests if the market condition is achieved, and (ii) an award that vests whether or not the market condition is achieved, so long as the performance condition is achieved. The Company is currently recognizing compensation expense for these awards over the estimated requisite service period of 2.36 years based on the estimated fair value when considering the market condition of the award, which was determined using a Monte Carlo simulation. During the six months ended June 30, 2021, the Company recognized $0.1 million of compensation expense related to these awards. As of June 30, 2021, the remaining unrecognized compensation cost for the market-based component of these awards, which is expected to be recognized over a weighted-average period of 1.4 years, is $0.5 million. In addition, should the performance condition be achieved, the Company would recognize an additional $0.3 million of compensation expense.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2021
Related Party Transactions
Related Party Transactions	Note 11. Related Party Transactions ​ Baker Brothers ​ Julian C. Baker, previously a member of the Company’s Board of Directors (the “Board”) until his resignation in September 2018, is a principal of Baker Bros. Advisors, LP. Additionally, Kelvin M. Neu, previously a member of Company’s Board until his resignation in June 2019, was an employee of Baker Bros. Advisors, LP. At December 31, 2020, Baker Bros. Advisors, LP and certain of its affiliated funds (collectively, “Baker Brothers”) held sole voting power with respect to an aggregate of 4,608,786 shares of the Company’s common stock, representing approximately 12% of the Company's outstanding common stock. ​ During the six months ended June 30, 2021, Baker Brothers exercised warrants to purchase 2,708,812 shares of the Company’s common stock at an exercise price of $0.08 per share for a total exercise price of approximately $0.2 million. Additionally, during the six ​ Pillar Investment Entities ​ Youssef El Zein, previously a member of the Company’s Board until his resignation in October 2017, is a director and controlling stockholder of Pillar Invest Corporation, which is the general partner of Pillar Pharmaceuticals I, L.P. (“Pillar I”), Pillar Pharmaceuticals II, L.P. (“Pillar II”), Pillar Pharmaceuticals III, L.P. (“Pillar III”), Pillar Pharmaceuticals IV, L.P. (“Pillar IV”), Pillar Pharmaceuticals V, L.P. (“Pillar V”), Pillar 6, Pillar 7, and Pillar Partners (collectively, the “Pillar Investment Entities”). As of June 30, 2021, the Pillar Investment Entities owned approximately 19.9% of the Company's common stock. ​ During the six months ended June 30, 2021, certain of the Pillar Investment Entities exercised warrants to purchase 3,158,386 shares of the Company’s common stock at an exercise price of $0.01 per share for a total exercise price of less than $0.1 million. 19,052 shares were used as cashless shares for the exercise costs. ​ As of June 30, 2021, the Pillar Investment Entities held (i) prefunded warrants to purchase up to 1,533,159 shares of the Company’s common stock at an exercise price of $0.01 per share, (ii) warrants to purchase up to 3,039,514 shares of the Company’s common stock at an exercise price of $2.28 per share, (iii) warrants to purchase up to 2,764,227 shares of the Company’s common stock at an exercise price of $2.58 per share, and (iv) warrants to purchase up to 1,373,626 shares of the Company’s common stock at an exercise price of $2.71 per share. ​ Board Fees Paid in Stock ​ Pursuant to the Company’s director compensation program, in lieu of director board and committee fees of $0.1 million during each of the six months ended June 30, 2021 and 2020, the Company issued 47,400 and 96,551 shares of common stock, respectively, to certain of its directors. Director board and committee fees are paid in arrears and the number of shares issued was calculated based on the market closing price of the Company’s common stock on the issuance date.

Net Income (Loss) per Common Sh

Net Income (Loss) per Common Share	6 Months Ended
	Jun. 30, 2021
Net Income (Loss) per Common Share
Net Income (Loss) per Common Share	Note 12. Net Income (Loss) per Common Share ​ The Company uses the two-class method to compute net income per common share during periods the Company realizes net income and has securities outstanding (redeemable convertible preferred stock) that entitle the holder to participate in dividends and earnings of the Company. In addition, the Company analyzes the potential dilutive effect of outstanding redeemable convertible preferred stock under the "if-converted" method when calculating diluted earnings per share and reports the more dilutive of the approaches (two class or "if-converted"). The two-class method is not applicable during periods with a net loss, as the holders of the redeemable convertible preferred stock have no obligation to fund losses. ​ The Company also analyzes the potential dilutive effect of stock options, restricted stock units, warrants and shares underlying future tranche rights under the treasury stock method (as applicable), during periods of income, or during periods in which income is recognized related to changes in fair value of its liability-classified securities. ​ For the six months ended June 30, 2021 and 2020, the Company used the two-class method to compute net income per common share. Under this method, net income is reduced by the amount of any dividends earned and the accretion of redeemable convertible preferred stock to its redemption value, if any, during the period. The remaining earnings (undistributed earnings) are allocated to common stock and each series of redeemable convertible preferred stock to the extent that each preferred security may share in earnings as if all the earnings for the period had been distributed. The total earnings allocated to common stock is then divided by the number of outstanding shares to which the earnings are allocated to determine the earnings per share. ​ Details in the computation of basic and diluted net income (loss) per common share were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ($ in thousands except per share data) ​ ​ 2021 ​ ​ 2020 ​ ​ 2021 ​ ​ 2020 Net (loss) income per share — Basic: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net (loss) income ​ $ (7,563) ​ $ (24,226) ​ $ 108,175 ​ $ (15,409) Less: Undistributed earnings to preferred stockholders ​ ​ — ​ ​ — ​ ​ (2,725) ​ ​ — Net (loss) income attributable to common stockholders ​ $ (7,563) ​ $ (24,226) ​ $ 105,450 ​ $ (15,409) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net (loss) income attributable to common stockholders ​ $ (7,563) ​ $ (24,226) ​ $ 105,450 ​ $ (15,409) Denominator for basic net (loss) income per share ​ ​ 49,909 ​ ​ 33,583 ​ ​ 45,575 ​ ​ 31,941 Basic net (loss) income per common share ​ $ (0.15) ​ $ (0.72) ​ $ 2.31 ​ $ (0.48) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net (loss) income per share — Diluted: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net (loss) income ​ $ (7,563) ​ $ (24,226) ​ $ 108,175 ​ $ (15,409) Less: Warrant revaluation gain applicable to dilutive warrants ​ ​ — ​ ​ — ​ ​ (6,983) ​ ​ — Less: Future tranche right revaluation gain applicable to dilutive future tranche rights ​ ​ — ​ ​ — ​ ​ (118,803) ​ ​ (2,284) Less: Undistributed earnings to preferred stockholders ​ ​ — ​ ​ — ​ ​ — ​ ​ — Numerator for diluted net (loss) income per share ​ $ (7,563) ​ $ (24,226) ​ $ (17,611) ​ $ (17,693) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Denominator for basic net income per share ​ ​ 49,909 ​ ​ 33,583 ​ ​ 45,575 ​ ​ 31,941 Plus: Incremental shares underlying “in the money” warrants outstanding ​ ​ — ​ ​ — ​ ​ 496 ​ ​ — Plus: Incremental shares underlying “in the money” future tranche rights outstanding ​ ​ — ​ ​ — ​ ​ 8,866 ​ ​ 2,182 Denominator for diluted net (loss) income per share ​ ​ 49,909 ​ ​ 33,583 ​ ​ 54,937 ​ ​ 34,123 Diluted net (loss) income per common share ​ $ (0.15) ​ $ (0.72) ​ $ (0.32) ​ $ (0.52) ​ ​ ​ Note 12. Net Income (Loss) per Common Share (Continued) ​ Total antidilutive securities excluded from the calculation of diluted net loss per share for the three and six months ended June 30, 2021 and 2020 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, (in thousands) ​ ​ 2021 ​ ​ 2020 ​ ​ 2021 ​ ​ 2020 Stock options ​ ​ 4,888 ​ ​ 4,756 ​ ​ 4,888 ​ ​ 4,756 Restricted stock units ​ ​ 594 ​ ​ 376 ​ ​ 594 ​ ​ 376 Common stock warrants ​ ​ 8,732 ​ ​ 8,138 ​ ​ 8,732 ​ ​ 8,138 Convertible preferred stock ​ ​ — ​ ​ 2,369 ​ ​ — ​ ​ 2,369 Future tranche rights ​ ​ — ​ ​ 53,528 ​ ​ — ​ ​ 33,791 Total ​ ​ 14,214 ​ ​ 69,167 ​ ​ 14,214 ​ ​ 49,430 ​

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2021
Subsequent Events
Subsequent Events	Note 13. Subsequent Events ​ The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the financial statements to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. ​ ​

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2021
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation ​ The accompanying unaudited financial statements included herein have been prepared by the Company in accordance with U.S. generally accepted accounting principles (“GAAP”) for interim financial information and pursuant to the rules and regulations of the SEC. Accordingly, certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. In the opinion of management, all adjustments, consisting of normal recurring adjustments, and disclosures considered necessary for a fair presentation of interim period results have been included. Interim results for the three and six months ended June 30, 2021 are not necessarily indicative of results that may be expected for the year ending December 31, 2021. For further information, refer to the financial statements and footnotes thereto included in the Company’s 2020 Form 10-K. ​
Cash and Cash Equivalents	Cash and Cash Equivalents ​ The Company considers all highly liquid investments with maturities of 90 days or less when purchased to be “cash equivalents.” Cash and cash equivalents at June 30, 2021 consisted of cash and money market funds. Cash and cash equivalents at December 31, 2020 consisted of cash and cash equivalents and short-term investments.
Financial Instruments	Financial Instruments ​ The fair value of the Company’s financial instruments is determined and disclosed in accordance with the three-tier fair value hierarchy specified in Note 3. The Company is required to disclose the estimated fair values of its financial instruments. As of June 30, 2021, the Company’s financial instruments consisted of cash and cash equivalents. As of December 31, 2020, the Company’s financial instruments consisted of cash, cash equivalents, short-term investments, receivables and warrant and future tranche right liabilities. The estimated fair values of these financial instruments approximate their carrying values. As of June 30, 2021, the Company did not have any derivatives, hedging instruments or other similar financial instruments.
Concentration of Credit Risk	Concentration of Credit Risk ​ Financial instruments that subject the Company to credit risk primarily consist of cash, cash equivalents, and short-term investments. The Company’s credit risk is managed by investing in highly rated money market instruments, U.S. treasury bills, corporate bonds, commercial paper and/or other debt securities. Due to these factors, no significant additional credit risk is believed by management to be inherent in the Company’s assets. As of June 30, 2021, all the Company’s cash and cash equivalents were held at two financial institutions.
Operating Lease Right-of-use Asset and Lease Liability	Operating Lease Right-of-use Assets and Lease Liability ​ The Company accounts for leases under ASC Topic 842, Leases Property, Plant, and Equipment ​ As of June 30, 2021 and December 31, 2020, the Company’s operating lease ROU assets and corresponding short-term and long-term lease liabilities primarily relate to its existing Exton, PA facility operating lease which expires on May 31, 2025.
Warrant Liability	Warrant Liability ​ The Company accounts for stock warrants as either equity instruments, liabilities or derivative liabilities in accordance with ASC Topic 480, Distinguishing Liabilities from Equity Derivatives and Hedging
Future Tranche Right Liability	Future Tranche Right Liability ​ On December 23, 2019, the Company entered into a Securities Purchase Agreement (the “December 2019 Securities Purchase Agreement”) with institutional investors affiliated with Baker Brothers (as defined below), an existing stockholder (see Note 11). As more fully described in Note 7, the December 2019 Securities Purchase Agreement contained call options on redeemable preferred shares with warrants (conditionally exercisable for shares that are puttable). The Company determined that these call options represented freestanding financial instruments and accounted for the options as liabilities (“Future Tranche Right Liability”) under ASC 480, which requires the measurement and recognition of the fair value of the liability at the time of issuance and at each reporting period. Any change in fair value is recognized in Future Tranche Right Liability Revaluation Gain (Loss) in the Company’s condensed statements of operations. During the three months ended March 31, 2021, the liability-classified call options provided for under the December 2019 Securities Purchase Agreement terminated and, accordingly, the liability balance was derecognized
Preferred Stock	Preferred Stock ​ The Company applies ASC 480 when determining the classification and measurement of its preferred stock. Preferred shares subject to mandatory redemption are classified as liability instruments and are measured at fair value. Conditionally redeemable preferred shares (including preferred shares that feature redemption rights that are either within the control of the holder or subject to redemption upon the occurrence of uncertain events not solely within the Company’s control) are classified as temporary equity. At all other times, preferred shares are classified as stockholders’ equity. ​ Accretion of redeemable convertible preferred stock includes the accretion of the Company's Series B redeemable convertible preferred stock to its stated value. The carrying value of the Series B redeemable convertible preferred stock is accreted to redemption value using the effective interest method, from the date of issuance to the earliest date the holders can demand redemption or until the redeemable convertible preferred stock cease to be outstanding.
Income Taxes	Income Taxes ​ In accordance with ASC Topic 270, Interim Reporting Income Taxes
New Accounting Pronouncements	New Accounting Pronouncements ​ From time to time, new accounting pronouncements are issued by the FASB and rules are issued by the SEC that the Company has or will adopt as of a specified date. Unless otherwise noted, management does not believe that any other recently issued accounting pronouncements issued by the FASB or guidance issued by the SEC had, or is expected to have, a material impact on the Company’s present or future financial statements. ​ Recently Adopted Accounting Pronouncements ​ In August 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU 2020-06”), which simplifies the guidance on an issuer’s accounting for convertible instruments and contracts in its own equity. The Company adopted ASU 2020-06 in the first quarter of 2021. The adoption of this ASU did not have a material effect on the Company’s financial statements.
COVID-19	COVID-19 While the Company is not aware of a material impact from the continuation of the coronavirus ("COVID-19") pandemic through June 30, 2021, the full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations, and financial condition, including expenses and manufacturing, clinical trials, and research and development costs, depends on future developments that are highly uncertain at this time.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2021
Fair Value Measurements
Schedule of assets and liabilities measured and recorded in financial statements at fair value on a recurring basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, 2021 (In thousands) ​ Total ​ Level 1 ​ Level 2 ​ Level 3 Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash ​ $ 250 ​ $ 250 ​ $ — ​ $ — ​ Cash equivalents – money market funds ​ ​ 40,340 ​ ​ 40,340 ​ ​ — ​ ​ — ​ Total assets ​ $ 40,590 ​ $ 40,590 ​ $ — ​ $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ (In thousands) ​ Total ​ Level 1 ​ Level 2 ​ Level 3 ​ Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash ​ $ 250 ​ $ 250 ​ $ — ​ $ — ​ Cash equivalents – money market funds ​ ​ 32,979 ​ ​ 32,979 ​ ​ — ​ ​ — ​ Short-term investments – commercial paper ​ ​ 3,499 ​ ​ — ​ 3,499 ​ — ​ Short-term investments – US treasury bills ​ 1,000 ​ — ​ 1,000 ​ — ​ Total assets ​ $ 37,728 ​ $ 33,229 ​ $ 4,499 ​ $ — ​ Liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Warrant liability ​ $ 6,983 ​ $ — ​ $ — ​ $ 6,983 ​ Future tranche right liability ​ ​ 118,803 ​ ​ — ​ ​ — ​ ​ 118,803 ​ Total liabilities ​ $ 125,786 ​ $ — ​ $ — ​ $ 125,786 ​
Schedule of reconciliation measured at fair value on a recurring basis using unobservable inputs	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Future ​ ​ Warrant ​ Tranche Right (In thousands) ​ Liability ​ Liability Balance, December 31, 2020 $ 6,983 ​ $ 118,803 Change in the fair value of liability (1) (6,983) ​ (118,803) Balance, June 30, 2021 $ — ​ $ — (1) During the six months ended June 30, 2021, the Company’s liability-classified warrants and future tranche rights terminated, and accordingly, the liabilities were derecognized.

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 2021
Investments
Schedule of available-for-sale investments at fair value	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ ​ ​ ​ ​ Unrealized ​ Unrealized ​ Fair (In thousands) Cost (Losses) Gains Value Short-term investments – commercial paper ​ $ 3,499 ​ $ — ​ $ — ​ $ 3,499 ​ Short-term investments – US treasury bills ​ 1,000 ​ — ​ — ​ 1,000 ​ Total short-term investments ​ $ 4,499 ​ $ — ​ $ — ​ $ 4,499 ​

Property and Equipment (Tables)

Property and Equipment (Tables)	6 Months Ended
	Jun. 30, 2021
Property and Equipment
Schedule of net property and equipment at cost	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, ​ December 31, ​ (In thousands) 2021 2020 Leasehold improvements ​ $ 107 ​ $ 107 ​ Equipment and other ​ 712 ​ 770 ​ Total property and equipment, at cost ​ $ 819 ​ $ 877 ​ Less: Accumulated depreciation and amortization ​ 786 ​ 833 ​ Property and equipment, net ​ $ 33 ​ $ 44 ​ ​ ​

Accrued Expenses (Tables)

Accrued Expenses (Tables)	6 Months Ended
	Jun. 30, 2021
Accrued Expenses
Schedule of accrued expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ June 30, ​ December 31, (In thousands) ​ 2021 2020 Payroll and related costs ​ $ 909 ​ $ 2,133 ​ Clinical and nonclinical trial expenses ​ 3,890 ​ 3,229 ​ Professional and consulting fees ​ 733 ​ 584 ​ Other ​ 113 ​ 126 ​ Total accrued expenses ​ $ 5,645 ​ $ 6,072 ​

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	6 Months Ended
	Jun. 30, 2021
Stockholders' Equity
Schedule of warrants outstanding and exercisable for purchase of common stock	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of Shares ​ ​ ​ ​ ​ ​ ​ June 30, ​ December 31, ​ Weighted-Average ​ ​ ​ Description ​ 2021 ​ 2020 ​ Exercise Price ​ Expiration Date Liability-classified Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 2019 Series B1 warrants (1) ​ — ​ 2,368,400 ​ ​ $ 1.52 ​ Dec 2026 ​ ​ ​ — ​ 2,368,400 ​ ​ ​ ​ ​ ​ Equity-classified Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ May 2013 warrants 15,437 ​ 1,949,754 ​ ​ $ 0.08 ​ None ​ September 2013 warrants 4,096 ​ 514,756 ​ ​ $ 0.08 ​ None ​ February 2014 warrants 2,171 ​ 266,006 ​ ​ $ 0.08 ​ None ​ April 2020 Private Placement first closing warrants ​ 3,039,514 ​ 3,039,514 ​ ​ $ 2.28 ​ Apr 2023 ​ April 2020 Private Placement second closing warrants ​ 1,373,626 ​ 1,373,626 ​ ​ $ 2.71 ​ Dec 2023 ​ April 2020 Private Placement second closing warrants ​ 1,143,428 ​ 2,677,311 ​ ​ $ 0.01 ​ None ​ July 2020 Private Placement first closing warrants ​ 389,731 ​ 2,014,234 ​ ​ $ 0.01 ​ None ​ July 2020 Private Placement first closing warrants ​ 2,764,227 ​ 2,764,227 ​ ​ $ 2.58 ​ Jul 2023 ​ ​ ​ 8,732,230 ​ 14,599,428 ​ ​ ​ ​ ​ ​ Total outstanding 8,732,230 ​ 16,967,828 ​ ​ ​ ​ ​ ​ (1) The Series B1 warrants were exercisable for either common stock (exercise price of $1.52 ) or Series B1 Convertible Preferred Stock (exercise price of $152 ) at the discretion of the warrant holder. However, as more fully disclosed in Note 7, the December 2019 Series B1 warrants were terminated during the three months ended March 31, 2021 contemporaneously with the termination of the future tranche rights.
Summary of warrant activity	​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Weighted-Average ​ ​ Warrants ​ Exercise Price Outstanding at December 31, 2020 16,967,828 ​ $ 1.28 Issued — ​ — Exercised (1) (5,867,198) ​ 0.04 Expired (2,368,400) ​ 1.52 Outstanding at June 30, 2021 8,732,230 ​ $ 2.04 (1) During the six months ended June 30, 2021, certain related parties exercised warrants as more fully described in Note 11.

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2021
Stock-Based Compensation
Schedule of stock-based compensation expense attributable to share-based payments made to employees and directors and included in operating expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ June 30, ​ June 30, (in thousands) ​ 2021 2020 ​ 2021 2020 Stock-based compensation: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Research and development ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Employee Stock Purchase Plan ​ $ 3 $ 15 ​ $ 15 $ 26 Equity Incentive Plan ​ ​ 50 ​ 192 ​ ​ 418 ​ 385 ​ ​ $ 53 $ 207 ​ $ 433 $ 411 General and administrative ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Employee Stock Purchase Plan ​ $ 1 $ 1 ​ $ 3 $ 2 Equity Incentive Plan ​ ​ 350 ​ 546 ​ ​ 1,079 ​ 1,091 ​ ​ $ 351 $ 547 ​ $ 1,082 $ 1,093 Total stock-based compensation expense ​ $ 404 $ 754 ​ $ 1,515 $ 1,504
Schedule of weighted average assumptions applied to options	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2021 2020 Average risk-free interest rate ​ 0.4% ​ ​ 1.0% ​ Expected dividend yield ​ — ​ ​ — ​ Expected lives (years) ​ 3.6 ​ ​ 3.9 ​ Expected volatility ​ 87% ​ ​ 84% ​ Weighted average exercise price (per share) ​ $ 3.66 ​ $ 2.08 ​
Schedule of information related to outstanding and exercisable options	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ($ in thousands, except per share data) ​ Stock ​ Weighted-Average ​ Weighted-Average ​ Aggregate Intrinsic Value Outstanding at December 31, 2020 4,614,323 ​ $ 9.78 6.8 ​ $ 2,949 ​ Granted 833,500 ​ ​ 3.66 ​ ​ ​ ​ ​ ​ Exercised (22,500) ​ ​ 2.11 ​ ​ ​ ​ ​ ​ Forfeited (236,394) ​ ​ 4.47 ​ ​ ​ ​ ​ ​ Expired (300,556) ​ ​ 11.91 ​ ​ ​ ​ ​ ​ Outstanding at June 30, 2021 (1) 4,888,373 ​ $ 8.89 ​ 6.6 ​ $ — ​ Exercisable at June 30, 2021 4,113,264 ​ $ 9.83 ​ 6.2 ​ $ — ​ (1) Includes both vested stock options as well as unvested stock options for which the requisite service period has not been rendered but that are expected to vest based on achievement of a service condition.
Schedule of information related to restricted stock activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Time-based Awards ​ Market/Performance-based Awards ($ in thousands, except per share data) ​ Number of Shares ​ Weighted-Average Grant Date Fair Value ​ Number of Shares ​ Weighted-Average Grant Date Fair Value Nonvested shares at December 31, 2020 354,003 ​ $ 2.27 ​ 549,318 ​ $ 1.54 Granted — ​ — ​ — ​ — Forfeited (48,563) ​ 2.31 ​ (23,701) ​ 1.54 Vested (236,765) ​ 2.25 ​ — ​ — Nonvested shares at June 30, 2021 68,675 ​ $ 2.30 ​ 525,617 ​ $ 1.54

Net Income (Loss) per Common _2

Net Income (Loss) per Common Share (Tables)	6 Months Ended
	Jun. 30, 2021
Net Income (Loss) per Common Share
Computation of basic and diluted net income (loss) per share	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ($ in thousands except per share data) ​ ​ 2021 ​ ​ 2020 ​ ​ 2021 ​ ​ 2020 Net (loss) income per share — Basic: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net (loss) income ​ $ (7,563) ​ $ (24,226) ​ $ 108,175 ​ $ (15,409) Less: Undistributed earnings to preferred stockholders ​ ​ — ​ ​ — ​ ​ (2,725) ​ ​ — Net (loss) income attributable to common stockholders ​ $ (7,563) ​ $ (24,226) ​ $ 105,450 ​ $ (15,409) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net (loss) income attributable to common stockholders ​ $ (7,563) ​ $ (24,226) ​ $ 105,450 ​ $ (15,409) Denominator for basic net (loss) income per share ​ ​ 49,909 ​ ​ 33,583 ​ ​ 45,575 ​ ​ 31,941 Basic net (loss) income per common share ​ $ (0.15) ​ $ (0.72) ​ $ 2.31 ​ $ (0.48) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net (loss) income per share — Diluted: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net (loss) income ​ $ (7,563) ​ $ (24,226) ​ $ 108,175 ​ $ (15,409) Less: Warrant revaluation gain applicable to dilutive warrants ​ ​ — ​ ​ — ​ ​ (6,983) ​ ​ — Less: Future tranche right revaluation gain applicable to dilutive future tranche rights ​ ​ — ​ ​ — ​ ​ (118,803) ​ ​ (2,284) Less: Undistributed earnings to preferred stockholders ​ ​ — ​ ​ — ​ ​ — ​ ​ — Numerator for diluted net (loss) income per share ​ $ (7,563) ​ $ (24,226) ​ $ (17,611) ​ $ (17,693) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Denominator for basic net income per share ​ ​ 49,909 ​ ​ 33,583 ​ ​ 45,575 ​ ​ 31,941 Plus: Incremental shares underlying “in the money” warrants outstanding ​ ​ — ​ ​ — ​ ​ 496 ​ ​ — Plus: Incremental shares underlying “in the money” future tranche rights outstanding ​ ​ — ​ ​ — ​ ​ 8,866 ​ ​ 2,182 Denominator for diluted net (loss) income per share ​ ​ 49,909 ​ ​ 33,583 ​ ​ 54,937 ​ ​ 34,123 Diluted net (loss) income per common share ​ $ (0.15) ​ $ (0.72) ​ $ (0.32) ​ $ (0.52)
Schedule of potentially dilutive securities excluded from diluted net income (loss) per common share	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, (in thousands) ​ ​ 2021 ​ ​ 2020 ​ ​ 2021 ​ ​ 2020 Stock options ​ ​ 4,888 ​ ​ 4,756 ​ ​ 4,888 ​ ​ 4,756 Restricted stock units ​ ​ 594 ​ ​ 376 ​ ​ 594 ​ ​ 376 Common stock warrants ​ ​ 8,732 ​ ​ 8,138 ​ ​ 8,732 ​ ​ 8,138 Convertible preferred stock ​ ​ — ​ ​ 2,369 ​ ​ — ​ ​ 2,369 Future tranche rights ​ ​ — ​ ​ 53,528 ​ ​ — ​ ​ 33,791 Total ​ ​ 14,214 ​ ​ 69,167 ​ ​ 14,214 ​ ​ 49,430

Business and Organization (Deta

Business and Organization (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2021USD ($)employee	Jun. 30, 2021USD ($)	Dec. 31, 2020USD ($)
Business and Organization
Percentage of positions eliminated	50.00%
Restructuring and Related Cost, Number of Positions Eliminated | employee	16
Restructuring costs	$ 1,192	$ 1,192
Accumulated deficit	725,377	725,377	$ 833,552
Cash, cash equivalents and investments	$ 40,600	$ 40,600

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2021USD ($)Institution	Jun. 30, 2020USD ($)	Dec. 31, 2020USD ($)
Summary of Significant Accounting Policies
Number of financial institutions | Institution			2
Other current liability					$ 435
Uncertain tax positions	$ 0		$ 0		$ 0
Tax expense (benefit)	$ 0	$ 0	$ 0	$ 0

Fair Value Measurements - Trans

Fair Value Measurements - Transfers Between Levels (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2021USD ($)
Fair Value Measurements
Fair value of assets transfers from level 1 to level 2	$ 0
Fair value of assets transfers from level 2 to level 1	0
Fair value of liabilities transfers from level 1 to level 2	0
Fair value of liabilities transfers from level 2 to level 1	0
Fair value of assets transfers into level 3	0
Fair value of assets transfers out of level 3	0
Fair value of liabilities transfers into level 3	0
Fair value of liabilities transfers out of level 3	$ 0

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments		$ 4,499
Fair value on a recurring basis
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Assets	$ 40,590	37,728
Total Liabilities		125,786
Fair value on a recurring basis | Warrant liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities		6,983
Fair value on a recurring basis | Future tranche right liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities		118,803
Fair value on a recurring basis | Cash
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash and Money market funds	250	250
Fair value on a recurring basis | Money market funds
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash and Money market funds	40,340	32,979
Fair value on a recurring basis | Short-term investments - commercial paper
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments		3,499
Fair value on a recurring basis | Short-term investments - U.S. treasury bills
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments		1,000
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) | Fair value on a recurring basis
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Assets	40,590	33,229
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) | Fair value on a recurring basis | Cash
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash and Money market funds	250	250
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) | Fair value on a recurring basis | Money market funds
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash and Money market funds	$ 40,340	32,979
Significant Other Observable Inputs (Level 2) | Fair value on a recurring basis
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Assets		4,499
Significant Other Observable Inputs (Level 2) | Fair value on a recurring basis | Short-term investments - commercial paper
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments		3,499
Significant Other Observable Inputs (Level 2) | Fair value on a recurring basis | Short-term investments - U.S. treasury bills
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments		1,000
Significant Other Unobservable Inputs (Level 3) | Fair value on a recurring basis
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities		125,786
Significant Other Unobservable Inputs (Level 3) | Fair value on a recurring basis | Warrant liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities		6,983
Significant Other Unobservable Inputs (Level 3) | Fair value on a recurring basis | Future tranche right liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities		$ 118,803

Fair Value Measurements - Ass_2

Fair Value Measurements - Assets and Liabilities at Fair Value Changes in Level 3 Liabilities (Details) - Fair value on a recurring basis $ in Thousands	6 Months Ended
	Jun. 30, 2021USD ($)
Warrant liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Beginning balance	$ 6,983
Change in the fair value of liability	(6,983)
Future tranche right liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Beginning balance	118,803
Change in the fair value of liability	$ (118,803)

Investments - Summary of Availa

Investments - Summary of Available-for-Sale Investments at Fair Value (Details) $ in Thousands	Dec. 31, 2020USD ($)
Short-term investments
Schedule of Available-for-sale Securities
Cost	$ 4,499
Estimated Fair Value	4,499
Short-term investments - commercial paper
Schedule of Available-for-sale Securities
Cost	3,499
Estimated Fair Value	3,499
Short-term investments - U.S. treasury bills
Schedule of Available-for-sale Securities
Cost	1,000
Estimated Fair Value	$ 1,000

Investments (Details)

Investments (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Investments
Realized gains or losses	$ 0	$ 0
Allowance for credit losses on available-for-sale debt securities			$ 0
Losses or other-than-temporary declines	$ 0	$ 0

Property and Equipment - Net Pr

Property and Equipment - Net Property and Equipment at Cost (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment
Total property and equipment, at cost	$ 819	$ 877
Less: Accumulated depreciation and amortization	786	833
Property and equipment, net	33	44
Leasehold improvements
Property, Plant and Equipment
Total property and equipment, at cost	107	107
Equipment and other
Property, Plant and Equipment
Total property and equipment, at cost	$ 712	$ 770

Property and Equipment - Deprec

Property and Equipment - Depreciation and Amortization Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Property, Plant and Equipment
Non-cash property additions	$ 0	$ 0	$ 0	$ 0
Maximum
Property, Plant and Equipment
Depreciation and amortization expense on property and equipment	$ 100	$ 100	$ 100	$ 100

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Accrued Expenses
Payroll and related costs	$ 909	$ 2,133
Clinical and nonclinical trial expenses	3,890	3,229
Professional and consulting fees	733	584
Other	113	126
Total accrued expenses	$ 5,645	$ 6,072

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 23, 2019	Dec. 31, 2019	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Temporary Equity
Warrant exercised price (per share)			$ 2.04		$ 2.04	$ 1.28
Aggregate gross proceeds	$ 3.9
Gross proceeds		$ 6.2
Common Stock, Shares Authorized		140,000,000	140,000,000		140,000,000	140,000,000
Baker Bros. Advisors LP
Temporary Equity
Warrant exercised price (per share)			$ 0.08		$ 0.08
Conversion of preferred stock to common, shares					2,368,400
Series B1 Redeemable Convertible Preferred Stock
Temporary Equity
Sale of redeemable convertible preferred stock	23,684
Conversion of preferred stock to common, shares			10,000	14,000	23,684
Series B1 Redeemable Convertible Preferred Stock | Baker Bros. Advisors LP
Temporary Equity
Conversion of preferred stock to common, shares					23,684
Series B1 Redeemable Convertible Preferred Stock | Common Stock Warrants
Temporary Equity
Warrant to purchase stock	2,368,400
Warrant exercised price (per share)	$ 1.52
Series B1 Redeemable Convertible Preferred Stock | Preferred Stock Warrant
Temporary Equity
Warrant to purchase stock	23,684
Warrant exercised price (per share)	$ 152
Series B2 Redeemable Convertible Preferred Stock
Temporary Equity
Aggregate gross proceeds	$ 15
Preferred Shares	98,685
Series B2 Redeemable Convertible Preferred Stock | Common Stock Warrants
Temporary Equity
Warrant to purchase stock	9,868,500
Warrant exercised price (per share)	$ 1.52
Series B2 Redeemable Convertible Preferred Stock | Preferred Stock Warrant
Temporary Equity
Warrant to purchase stock	98,685
Warrant exercised price (per share)	$ 152
Series B3 Redeemable Convertible Preferred Stock
Temporary Equity
Aggregate gross proceeds	$ 15
Preferred Shares	82,418
Series B3 Redeemable Convertible Preferred Stock | Common Stock Warrants
Temporary Equity
Warrant to purchase stock	6,593,440
Warrant exercised price (per share)	$ 1.82
Series B3 Redeemable Convertible Preferred Stock | Preferred Stock Warrant
Temporary Equity
Warrant to purchase stock	65,934
Warrant exercised price (per share)	$ 182
Series B4 Redeemable Convertible Preferred Stock
Temporary Equity
Aggregate gross proceeds	$ 15
Preferred Shares	82,418
Expiration period	21 months
Series B4 Redeemable Convertible Preferred Stock | Common Stock Warrants
Temporary Equity
Warrant to purchase stock	6,593,440
Warrant exercised price (per share)	$ 1.82
Series B4 Redeemable Convertible Preferred Stock | Preferred Stock Warrant
Temporary Equity
Warrant to purchase stock	65,934
Warrant exercised price (per share)	$ 182

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock (Details) - USD ($) $ / shares in Units, $ in Millions	Jul. 07, 2021	Jul. 13, 2020	Apr. 07, 2020	Dec. 23, 2019	Mar. 04, 2019	Nov. 30, 2018	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Dec. 31, 2020
Class of Stock
Stock issued (per share)					$ 2.84
Par value (per share)							$ 0.001		$ 0.001	$ 0.001
Proceeds from issuance				$ 3.9
Warrant exercised price (per share)							$ 2.04		$ 2.04	$ 1.28
"At-The-Market" Equity Program
Class of Stock
Value of shares which may be sold							$ 19.5		$ 19.5
Stock issued (in shares)	646,764						4,470,593	821,018
Net proceeds from offering of common stock	$ 0.7						$ 14.6	$ 1.4
Percentage of fixed commission expense of gross proceeds of shares sold in ATM agreement						3.00%
Lincoln Park Capital Fund, LLC ("Investor")
Class of Stock
Value of shares which may be sold					$ 35		$ 25.3		25.3
Duration over which common stock purchase agreement may be sold					36 months
Stock issued (in shares)					269,749		800,000	600,000
Net proceeds from offering of common stock							$ 4.2	$ 1.1
Common Stock | "At-The-Market" Equity Program
Class of Stock
Net proceeds from offering of common stock						$ 50
April 2020 Private Placement
Class of Stock
Stock issued (in shares)			3,039,514
Shares of common stock that may be purchased upon exercise of warrants			3,039,514
Warrant exercised price (per share)			$ 2.28
Gross proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any			$ 5
Combined purchase price (per share)			$ 1.645
Stock price underlying warrants (per share)			$ 0.125
April 2020 Private Placement Second Closing
Class of Stock
Stock issued (in shares)			2,747,252
Ownership percentage			19.99%
Shares of common stock that may be purchased upon exercise of warrants			1,373,626
Warrant exercised price (per share)			$ 2.71
Gross proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any			$ 5
Stock price (in dollars per share)			$ 0.01
April 2020 Private Placement and April 2020 Private Placement Second Closing in Aggregate
Class of Stock
Net proceeds from offering of common stock									$ 9.8
July 2020 Private Placement Second Closing
Class of Stock
Proceeds from issuance		$ 5.1
July 2020 Private Placement Second Closing | Pre-funded Warrants
Class of Stock
Shares of common stock that may be purchased upon exercise of warrants		784,615
Stock price (in dollars per share)		$ 0.01
July 2020 Private Placement Second Closing | Warrants
Class of Stock
Shares of common stock that may be purchased upon exercise of warrants		274,615
Stock price (in dollars per share)		$ 9.75

Stockholders' Equity - Common_2

Stockholders' Equity - Common Stock Warrants (Details) - $ / shares	Jun. 30, 2021	Dec. 31, 2020
Class of Warrant or Right
Number of Shares	8,732,230	16,967,828
Weighted-Average Exercise Price	$ 2.04	$ 1.28
Warrants
Class of Warrant or Right
Weighted-Average Exercise Price		1.52
Preferred stock
Class of Warrant or Right
Weighted-Average Exercise Price		$ 152
Liability Classified Warrants
Class of Warrant or Right
Number of Shares		2,368,400
December 2019 Series B1 warrants
Class of Warrant or Right
Number of Shares		2,368,400
Weighted-Average Exercise Price		$ 1.52
Equity Classified Warrants
Class of Warrant or Right
Number of Shares	8,732,230	14,599,428
May 2013 Warrants
Class of Warrant or Right
Number of Shares	15,437	1,949,754
Weighted-Average Exercise Price	$ 0.08
September 2013 Warrants
Class of Warrant or Right
Number of Shares	4,096	514,756
Weighted-Average Exercise Price	$ 0.08
February 2014 Warrants
Class of Warrant or Right
Number of Shares	2,171	266,006
Weighted-Average Exercise Price	$ 0.08
April 2020 Private Placement first closing warrants
Class of Warrant or Right
Number of Shares	3,039,514	3,039,514
Weighted-Average Exercise Price	$ 2.28
April 2020 Private Placement second closing warrants
Class of Warrant or Right
Number of Shares	1,373,626	1,373,626
Weighted-Average Exercise Price	$ 2.71
April 2020 Private Placement second closing warrants
Class of Warrant or Right
Number of Shares	1,143,428	2,677,311
Weighted-Average Exercise Price	$ 0.01
July 2020 Private Placement first closing warrants
Class of Warrant or Right
Number of Shares	389,731	2,014,234
Weighted-Average Exercise Price	$ 0.01
July 2020 Private Placement first closing warrants
Class of Warrant or Right
Number of Shares	2,764,227	2,764,227
Weighted-Average Exercise Price	$ 2.58

Stockholders' Equity - Common_3

Stockholders' Equity - Common Stock Warrant Activity (Details)	6 Months Ended
	Jun. 30, 2021$ / sharesshares
Stockholders' Equity
Outstanding warrants, beginning of period | shares	16,967,828
Exercised | shares	(5,867,198)
Expired | shares	(2,368,400)
Outstanding warrants, end of period | shares	8,732,230
Warrant exercise price per share, beginning of period | $ / shares	$ 1.28
Exercised | $ / shares	$ 0.04
Warrant exercise price per share, expired | $ / shares	1.52
Warrants exercise price per share, end of period | $ / shares	$ 2.04

Collaboration and License Agr_2

Collaboration and License Agreements (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Feb. 28, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Research and development		$ 3,893	$ 5,379	$ 10,764	$ 14,889
Scriptr Global, Inc. | Research and Development Plans and Designation of Development Candidates
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Research and development		$ 600		$ 1,300
Scriptr Global, Inc. | Maximum | Research and Development Plans and Designation of Development Candidates
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Deferred revenue recognition period	270 days

Stock-Based Compensation - Equi

Stock-Based Compensation - Equity Incentive Plans (Details) - shares	1 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2021	Dec. 31, 2020
Class of Stock
Common stock options outstanding		4,888,373	4,614,323
Options outstanding under earlier plans		207,908
Grant of inducement stock option		325,000
2013 Stock Incentive Plan
Class of Stock
Common stock, shares reserved for future issuance	5,653,057
Common shares available for grant		516,146
Maximum number of additional common shares	868,372
Common stock options outstanding		4,355,465
Restricted stock units outstanding		594,292

Stock-Based Compensation - Empl

Stock-Based Compensation - Employee Stock Purchase Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 07, 2017
Class of Stock
Proceeds from employee stock purchases	$ 34	$ 54
Percentage of share-based compensation expense	15.00%
Weighted average grant date fair value of options granted during the period (per share)	$ 2.02	$ 1.09
2017 Employee Stock Purchase Plan
Class of Stock
Common stock shares authorized for issuance under stock purchase plan			412,500
Common shares available for grant	231,344
Common stock share issued	13,998	40,024
Maximum | 2017 Employee Stock Purchase Plan
Class of Stock
Proceeds from employee stock purchases	$ 100	$ 100

Stock-Based Compensation - Acco

Stock-Based Compensation - Accounting for Stock-based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	$ 404	$ 754	$ 1,515	$ 1,504
Research and development
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	53	207	433	411
Research and development | Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	3	15	15	26
Research and development | Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	50	192	418	385
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	351	547	1,082	1,093
General and administrative | Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	1	1	3	2
General and administrative | Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	$ 350	$ 546	$ 1,079	$ 1,091

Stock-Based Compensation - Assu

Stock-Based Compensation - Assumptions Used in Determining Fair Value of Stock Options (Details) - $ / shares	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Stock-Based Compensation
Options to purchase common stock granted to employees and directors	833,500	727,129
Average risk free interest rate	0.40%	1.00%
Dividend rate	0.00%	0.00%
Expected lives (years)	3 years 7 months 6 days	3 years 10 months 24 days
Expected volatility	87.00%	84.00%
Weighted average exercise price of options granted during the period (per share)	$ 3.66	$ 2.08

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended		12 Months Ended
	Mar. 31, 2021	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, Outstanding, Beginning Balance	4,614,323	4,614,323
Granted		833,500
Exercised		(22,500)
Forfeited		(236,394)
Expired		(300,556)
Options, Outstanding, Ending Balance		4,888,373		4,614,323
Exercisable, Ending Balance		4,113,264
Weighted Average Exercise Price, Beginning Balance	$ 9.78	$ 9.78
Granted, Weighted Average Exercise Price		3.66	$ 2.08
Exercised, Weighted Average Exercise Price		2.11
Forfeited, Weighted Average Exercise Price		4.47
Expired, Weighted Average Exercise Price		11.91
Weighted Average Exercise Price, Ending Balance		8.89		$ 9.78
Exercisable, Weighted Average Exercise Price		$ 9.83
Outstanding, Ending balance, Weighted Average Remaining Contractual Term		6 years 7 months 6 days		6 years 9 months 18 days
Exercisable Ending Balance, Weighted Average Remaining Contractual Term		6 years 2 months 12 days
Outstanding, Intrinsic Value, Ending Balance				$ 2,949
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Accelerated vesting, number of shares	1,535,578
Unrecognized compensation cost related to nonvested stock-based compensation		$ 1,500
Weighted average remaining period over which unrecognized compensation expense will be recognized		1 year 8 months 12 days

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended			6 Months Ended
	Jul. 31, 2020	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Restricted Stock Activity, Weighted-Average Grant Date Fair Value
Share-based compensation		$ 404		$ 754	$ 1,515	$ 1,504
2013 Stock Incentive Plan
Restricted Stock Activity, Number of Shares
Nonvested shares, Ending Balance		594,292			594,292
Restricted Stock Activity, Weighted-Average Grant Date Fair Value
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		516,146			516,146
Restricted stock units
Restricted Stock Activity, Number of Shares
Nonvested shares, Beginning Balance			354,003		354,003
Cancelled					(48,563)
Vested					(236,765)
Nonvested shares, Ending Balance		68,675			68,675
Restricted Stock Activity, Weighted-Average Grant Date Fair Value
Nonvested shares, Weighted Average Grant Date Fair Value, Beginning Balance			$ 2.27		$ 2.27
Cancelled, Weighted-Average Grant Date Fair Value					2.31
Vested, Weighted-Average Grant Date Fair Value					2.25
Nonvested shares, Weighted Average Grant Date Fair Value, Ending Balance		$ 2.30			$ 2.30
Accelerated vesting, number of shares			137,872
Unrecognized compensation expense		$ 100			$ 100
Weighted average remaining period over which unrecognized compensation expense will be recognized					2 years
Market/Performance-based Awards
Restricted Stock Activity, Number of Shares
Nonvested shares, Beginning Balance			549,318		549,318
Cancelled					(23,701)
Nonvested shares, Ending Balance		525,617			525,617
Restricted Stock Activity, Weighted-Average Grant Date Fair Value
Nonvested shares, Weighted Average Grant Date Fair Value, Beginning Balance			$ 1.54		$ 1.54
Cancelled, Weighted-Average Grant Date Fair Value					1.54
Nonvested shares, Weighted Average Grant Date Fair Value, Ending Balance		$ 1.54			$ 1.54
Weighted average remaining period over which unrecognized compensation expense will be recognized					1 year 4 months 24 days
Requisite service period (in years)	2 years 4 months 9 days
Share-based compensation					$ 100
Unrecognized compensation expense related to the restricted stock units		$ 500			500
Additional compensation expense as a result of meeting certain achievements					$ 300

Related Party Transactions - Ov

Related Party Transactions - Overview of Related Parties (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Related Party Transactions
Exercise price of warrants	$ 2.04		$ 2.04		$ 1.28
Number of Shares	8,732,230		8,732,230		16,967,828
Board fees paid in stock in lieu of director board and committee fees			$ 0.1	$ 0.1
Common stock issued in lieu of board fees			47,400	96,551
Series B1 Redeemable Convertible Preferred Stock
Related Party Transactions
Conversion of preferred stock to common, shares	10,000	14,000	23,684
Baker Bros. Advisors LP
Related Party Transactions
Ownership percentage	4.00%		4.00%		12.00%
Issuance of common stock upon exercise of warrants (in shares)			2,708,812
Exercise price of warrants	$ 0.08		$ 0.08
Proceeds from exercise of warrants			$ 0.2
Aggregate common shares					4,608,786
Conversion of preferred stock to common, shares			2,368,400
Baker Bros. Advisors LP | Series B1 Redeemable Convertible Preferred Stock
Related Party Transactions
Conversion of preferred stock to common, shares			23,684
Pillar Investment Entities
Related Party Transactions
Ownership percentage	19.90%		19.90%
Issuance of common stock upon exercise of warrants (in shares)			3,158,386
Exercise price of warrants	$ 0.01		$ 0.01
Proceeds from exercise of warrants			$ 0.1
Cashless shares	19,052		19,052
Pillar Investment Entities | Pre-funded Warrants
Related Party Transactions
Exercise price of warrants	$ 0.01		$ 0.01
Number of Shares	1,533,159		1,533,159
Pillar Investment Entities | Warrant, Tranche One
Related Party Transactions
Exercise price of warrants	$ 2.28		$ 2.28
Number of Shares	3,039,514		3,039,514
Pillar Investment Entities | Warrant, Tranche Two
Related Party Transactions
Exercise price of warrants	$ 2.58		$ 2.58
Number of Shares	2,764,227		2,764,227
Pillar Investment Entities | Warrant, Tranche Three
Related Party Transactions
Exercise price of warrants	$ 2.71		$ 2.71
Number of Shares	1,373,626		1,373,626

Net Income (Loss) per Common _3

Net Income (Loss) per Common Share -Computation of basic and diluted net income per common share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Basic- net (loss) income per share
Net income (loss)	$ (7,563)	$ 115,738	$ (24,226)	$ 8,817	$ 108,175	$ (15,409)
Less: Undistributed earnings to preferred stockholders					(2,725)
Net (loss) income attributable to common stockholders	$ (7,563)		$ (24,226)		$ 105,450	$ (15,409)
Denominator for basic net (loss) income per share	49,909		33,583		45,575	31,941
Basic net (loss) income per common share	$ (0.15)		$ (0.72)		$ 2.31	$ (0.48)
Diluted- net (loss) income per share
Net income (loss)	$ (7,563)	$ 115,738	$ (24,226)	$ 8,817	$ 108,175	$ (15,409)
Less: Warrant revaluation gain applicable to dilutive warrants					(6,983)
Less: Future tranche right revaluation gain applicable to dilutive future tranche rights					(118,803)	(2,284)
Numerator for diluted net (loss) income per share	$ (7,563)		$ (24,226)		$ (17,611)	$ (17,693)
Denominator for basic net (loss) income per share	49,909		33,583		45,575	31,941
Plus: Incremental shares underlying "in the money" warrants outstanding					496
Plus: Incremental shares underlying "in the money" future tranche rights outstanding					8,866	2,182
Denominator for diluted net (loss) income per share	49,909		33,583		54,937	34,123

Net Income (Loss) per Common _4

Net Income (Loss) per Common Share - Antidilutive securities (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Antidilutive securities
Total antidilutive securities	14,214	69,167	14,214	49,430
Stock options
Antidilutive securities
Total antidilutive securities	4,888	4,756	4,888	4,756
Restricted stock units
Antidilutive securities
Total antidilutive securities	594	376	594	376
Common Stock Warrants
Antidilutive securities
Total antidilutive securities	8,732	8,138	8,732	8,138
Convertible preferred stock
Antidilutive securities
Total antidilutive securities		2,369		2,369
Future tranche right liability
Antidilutive securities
Total antidilutive securities		53,528		33,791