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Stock Plans and Stock-Based Compensation
 6 Months Ended
Jun. 30, 2025
Share-Based Payment Arrangement [Abstract]  
Stock Plans and Stock-Based Compensation Stock Plans and Stock-Based Compensation
As of June 30, 2025, the Company had two stockholder-approved, stock-based compensation plans: (i) the Fifth Amended and Restated 2010 Stock Incentive Plan, as amended (“2010 Plan”) and (ii) the Amended and Restated 2010 Employee Stock Purchase Plan (“ESPP”). New employees are generally issued options as an inducement equity award under Nasdaq Listing Rule 5635(c)(4) outside of the 2010 Plan (“Inducement Awards”).
The Fifth Amended and Restated 2010 Stock Incentive Plan
The 2010 Plan permits the granting of incentive and non-qualified stock options and stock awards to employees, officers, directors, and consultants of the Company and its subsidiaries at prices determined by the Company’s board of directors. In May 2025, the Company's stockholders approved an amendment to the 2010 Plan to reserve an additional 1,255,000 shares of common stock for issuance under the 2010 Plan. The Company can issue up to 3,356,600 shares of its common stock pursuant to awards granted under the 2010 Plan. Options vest and become exercisable based on a schedule determined by the board of directors and expire up to ten years from the date of grant. The 2010 Plan uses a “fungible share” concept under which each share of stock subject to awards granted as options and stock appreciation rights (“SARs”) will cause one share per share under the award to be removed from the available share pool, while each share of stock subject to awards granted as restricted stock, restricted stock units, other stock-based awards or performance awards where the price charged for the award is less than 100% of the fair market value of the Company’s common stock will cause 1.3 shares per share under the award to be removed from the available share pool.
As of June 30, 2025, the Company granted options to employees, executive officers, and non-employee directors with an exercise price equal to the closing price of the Company's common stock on the grant date. The Company granted employees restricted stock awards ("RSAs") and restricted stock units ("RSUs") at no cost. As of June 30, 2025, 707,694 shares remained available for grant under the 2010 Plan.
During the six months ended June 30, 2025, the Company’s board of directors granted options to purchase 1,108,400 shares of the Company’s common stock to executive officers and employees of the Company under the 2010 Plan. These options vest and become exercisable as to 25% of the shares underlying the award after the first year and as to an additional
6.25% of the shares underlying the award in each subsequent quarter, based upon continued employment over a four year period.
During the six months ended June 30, 2025, the Company’s board of directors granted 350,600 RSUs to employees of the Company under the 2010 Plan. These RSUs vest and become exercisable as to 25% of the shares underlying the award annually on the date of grant, based upon continued employment over a four year period.
During the six months ended June 30, 2025, the Company’s board of directors granted options to its non-employee directors to purchase 80,000 shares of common stock under the 2010 Plan, which will vest and become exercisable one year from the date of grant.
Inducement Awards
The Company grants Inducement Awards to certain new employees. These options generally vest as to 25% of the shares underlying the option on the first anniversary of the grant date, and as to an additional 6.25% of the shares underlying the option on each successive quarter thereafter. During the six months ended June 30, 2025, the Company’s board of directors granted Inducement Awards to purchase 200,000 shares of common stock. These options were granted at an exercise price that equaled the closing market price of the Company’s common stock on the grant date.
Stock Options
A summary of stock option activity under the 2010 Plan and Inducement Awards are summarized as follows:
Number of
Shares		Weighted
Average
Exercise
Price per
Share		Weighted
Average
Remaining Contractual Life		Aggregate Intrinsic Value
Outstanding, December 31, 20241,160,251 $33.44 7.19$— 
Granted1,388,400 3.04 
Exercised— — 
Canceled/Forfeited(122,121)10.57 
Outstanding, June 30, 2025
2,426,530 $17.30 8.17$— 
Exercisable at June 30, 2025
774,125 $45.01 5.64$— 
Vested and unvested expected to vest at June 30, 2025
2,426,530 $17.30 8.17$— 
The weighted average grant date fair values of the stock options granted during the six months ended June 30, 2025 and 2024 were $2.13 and $9.71, respectively, and were calculated using the following estimated assumptions under the Black-Scholes option pricing model:
Six Months Ended
June 30,
 20252024
Expected term (years) 6.06.0
Risk free interest rate
3.9% - 4.4%
3.9% - 4.3%
Expected volatility
113% - 114%
114% - 116%
Expected dividendsNoneNone
As of June 30, 2025, there was $6.0 million of unrecognized compensation cost related to unvested employee stock option awards outstanding, which is expected to be recognized as expense over a weighted average period of 2.6 years. There were no employee stock options exercised during each of the six months ended June 30, 2025 and 2024.
Restricted Stock Awards
The following table presents a summary of RSAs under the 2010 Plan as of June 30, 2025:
Number of SharesWeighted Average Grant Date Fair Value
Unvested, December 31, 202440,137 $18.20 
Awarded— — 
Vested(39,637)18.20 
Forfeited(500)18.20 
Unvested, June 30, 2025
— $— 
Restricted Stock Units
The following table presents a summary of RSUs under the 2010 Plan as of June 30, 2025:
Number of SharesWeighted Average Grant Date Fair Value
Unvested, December 31, 2024— $— 
Awarded350,600 3.13 
Vested— — 
Forfeited(67,100)3.13 
Unvested, June 30, 2025
283,500 3.13 
As of June 30, 2025, there was $0.8 million of unrecognized compensation costs related to RSUs, which are expected to be recognized as expense over a remaining weighted average period of 3.6 years.
Amended and Restated 2010 Employee Stock Purchase Plan
The Company has reserved 500,000 shares of common stock for issuance under the ESPP. Eligible employees may purchase shares of the Company’s common stock at 85% of the lower closing market price of the common stock at the beginning of the enrollment period or ending date of the purchase period within a two-year enrollment period, as defined. The Company has four six-month purchase periods per each two-year enrollment period. If, within any one of the four purchase periods in an enrollment period, the purchase period ending stock price is lower than the stock price at the beginning of the enrollment period, the two-year enrollment resets at the new lower stock price. During the three and six months ended June 30, 2025, 36,649 shares were issued under the ESPP. During the three and six months ended June 30, 2024, 11,307 shares were issued under the ESPP. As of June 30, 2025, there were 357,814 shares available for future purchase under the ESPP.
Stock-Based Compensation Expense
For the three and six months ended June 30, 2025 and 2024, the Company recorded stock-based compensation expense to the following line items in its costs and expenses section of the Condensed Consolidated Statements of Operations and Comprehensive Loss:
 Three Months Ended
June 30,		Six Months Ended
June 30,
(in thousands)2025202420252024
Research and development$492 $737 $1,084 $1,546 
General and administrative643 967 1,215 1,717 
Total stock-based compensation expense$1,135 $1,704 $2,299 $3,263