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Stock Incentive Plans | 12 Months Ended
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Dec. 31, 2023
Stock Incentive Plans |
Stock Incentive Plans | 8. Stock Incentive Plans ​ Prior to the Company’s initial public offering in June 2015 (the “IPO”), the Company granted awards to eligible participants under its 2008 Equity Incentive Plan. In May 2015, the Company’s board of directors adopted and, in June 2015, the Company’s stockholders approved the 2015 Stock Incentive Plan, as amended and amended and restated since the IPO (“2015 Plan”), which became effective immediately prior to the effectiveness of the IPO. Subsequent to the IPO, no option grants have been awarded to eligible participants under the 2008 Equity Incentive Plan. ​ The 2015 Plan provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock units, stock appreciation rights and other stock-based awards. The Company’s employees, officers, directors and consultants and advisors are eligible to receive awards under the 2015 Plan. ​ Terms of stock option agreements, including vesting requirements, are determined by the Company’s board of directors, subject to the provisions of the applicable stock incentive plan. Options granted by the Company generally vest ratably over four years, with a one-year cliff, and options are exercisable from the date of grant for a period of ten years. ​ On February 1, 2023, the Company issued stock options exercisable for 855,000 shares of common stock to certain officers of the Company subject to stockholder approval of the authorization of additional shares of common stock for issuance under the 2015 Plan on or before January 31, 2024. On June 2, 2023, the Company’s stockholders approved the addition of 4,300,000 shares of common stock to the shares of common stock authorized for issuance under the 2015 Plan, which satisfied the grant condition on such officer grants. As of December 31, 2023, 755,000 of these options remain outstanding. On February 17, 2022, the Company’s Board of Directors adopted the 2022 Inducement Stock Incentive Plan (the “Inducement Plan”). The Inducement Plan provides for the grant of nonstatutory stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards with respect to an aggregate of 300,000 shares of the Company’s common stock. On January 31, 2023, the Company’s Board of Directors approved an amendment to the Inducement Plan to increase the number of shares of common stock authorized for issuance thereunder from 300,000 shares of common stock to 700,000 shares of common stock. On December 14, 2023, the Company’s Board of Directors approved an additional amendment to the Inducement Plan to increase the number of shares of common stock authorized for issuance thereunder from 700,000 shares of common stock to 1,700,000 shares of common stock. Awards under the Inducement Plan may only be granted to persons who (a) were not previously an employee or director of the Company or (b) are commencing employment with the Company following a bona fide period of non-employment, in either case as an inducement material to the individual’s entering into employment with the Company and in accordance with the requirements of Nasdaq Stock Market Rule 5635(c)(4). As of December 31, 2023, options to purchase 687,900 shares of common stock have been granted under the Inducement Plan, which are included in the table above. ​ A summary of the Company’s stock option activity and related information for employees and non-employees follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | Weighted | ​ | ​ | ​
​ | ​ | ​ | ​ | Weighted- | ​ | Average | ​ | Aggregate
​ | ​ | ​ | ​ | Average | ​ | Remaining | ​ | Intrinsic
​ | ​ | ​ | ​ | Exercise | ​ | Contractual | ​ | Value
​ |  | Shares |  | Price |  | Term (years) |  | (in thousands)
Outstanding at December 31, 2022 | ​ | 2,253,431 | ​ | $ | 15.43 | ​ | 8.57 | ​ | $ | 9,733
Granted |  | 1,906,050 | ​ | $ | 12.01 | ​ | ​ | ​ | ​ | ​
Exercised | ​ | (78,050) | ​ | $ | 5.37 | ​ | ​ | ​ | ​ | ​
Cancelled or forfeited |  | (526,939) | ​ | $ | 16.80 | ​ | ​ | ​ | ​ | ​
Expired | ​ | (523) | ​ | $ | 138.60 | ​ | ​ | ​ | ​ | ​
Outstanding at December 31, 2023 |  | 3,553,969 | ​ | $ | 13.59 |  | 8.39 | ​ | $ | 1,912
Vested and exercisable at December 31, 2023 |  | 1,107,936 | ​ | $ | 18.62 |  | 7.42 | ​ | $ | 821
Vested and expected to vest at December 31, 2023 | ​ | 3,553,969 | ​ | $ | 13.59 | ​ | 8.39 | ​ | $ | 1,912
​ The total intrinsic value of options exercised in the years ended December 31, 2023 and 2022 was $0.5 million and $0.2 million respectively. The total grant date fair value of stock options vested for the year ended December 31, 2023 and 2022 was $4.4 million and $5.6 million, respectively. The weighted-average grant date fair value of options granted to employees and non-employees for the years ended December 31, 2023 and 2022 was $7.20 and $3.82, respectively. ​ At December 31, 2023, the total unrecognized compensation expense related to unvested stock option awards was $13.8 million. The Company expects to recognize that cost over a weighted-average period of approximately 2.5 years. ​ Stock-Based Compensation Expense ​ The fair value of stock options granted to employees and non-employees was estimated using the Black-Scholes option-pricing model based on the following assumptions: ​
​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended December 31,
​ |  | 2023 |  | 2022
Weighted-average expected volatility |  | 65.86%-73.68% | ​ | 65.60-70.22%
Expected term (in years) |  | 5.5-6.25 | ​ | 5-6.25
Risk-free interest rate |  | 3.42%-4.67% | ​ | 1.48-4.17%
Expected dividend yield |  | 0% | ​ | 0%
​ Volatility ​ Due to the lack of company-specific historical and implied volatility data of its common stock, the Company does not have sufficient relevant historical data to support its expected volatility. As such, the Company has used a weighted average of expected volatility based on a combination of the Company’s own historical volatility and volatilities of a representative group of publicly traded biopharmaceutical companies. For purposes of identifying representative companies, the Company considered characteristics such as number of product candidates in early stages of product development, area of therapeutic focus, and length of trading history. The expected volatility was determined using the weighted average of the Company’s own historical volatility and an average of the historical volatilities of the representative group of companies for a period equal to the expected term of the option grant. The Company intends to continue to consistently apply this process using the same representative companies until sufficient historical information regarding the volatility of the Company’s own share price becomes available or until circumstances change, such that the identified entities are no longer representative companies. In the latter case, more suitable, similar entities whose share prices are publicly available would be utilized in the calculation. ​ Expected Term ​ The Company uses the “simplified method” to estimate the expected term of stock option grants. Under this approach, the weighted-average expected life is presumed to be the average of the contractual term (ten years) and the vesting term (generally four years) of the Company’s stock options, taking into consideration multiple vesting tranches. The Company utilizes this method due to lack of historical exercise data and the plain-vanilla nature of the Company’s share-based awards. ​ Risk-Free Rate ​ The risk-free rate was based on the yield curve of United States Treasury securities with periods commensurate with the expected term of the options being valued.

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