| Summary of stock option activity |
| | | | | | | | | | | | | | | | | | | | | | | | Options Outstanding and Exercisable | | | | | | | | Weighted | | | | | | | | Weighted | | Average | | Aggregate | | | | | Average | | Remaining | | Intrinsic | | | Number of | | Exercise | | Contractual | | Value(1) | | | Shares | | Price | | Life (Years) | | (in thousands) | Outstanding as of December 31, 2025 | | 848,966 | | $ | 73.76 | | 6.5 | | $ | — | Granted | | 174,500 | | $ | 9.92 | | — | | | — | Exercised | | (2,488) | | $ | 5.76 | | — | | | — | Forfeitures | | (5,960) | | $ | 21.90 | | — | | | — | Outstanding as of June 30, 2026 | | 1,015,018 | | $ | 63.26 | | 6.6 | | | — | Exercisable as of June 30, 2026 | | 709,995 | | $ | 85.67 | | 5.6 | | $ | — |
| (1) | The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the estimated fair value of the common stock for the options that were in the money at December 31, 2025 and June 30, 2026. |
|
A summary of stock option activity for awards under the Plans is presented below: | | | | | | | | | | | | | | | | | | | | | | | | Options Outstanding and Exercisable | | | | | | | | Weighted | | | | | | | | Weighted | | Average | | Aggregate | | | | | Average | | Remaining | | Intrinsic | | | Number of | | Exercise | | Contractual | | Value(1) | | | Shares | | Price | | Life (Years) | | (in thousands) | Outstanding as of January 1, 2024 | | 567,995 | | $ | 105.96 | | 7.3 | | $ | 52 | Granted | | 248,609 | | $ | 19.80 | | — | | | — | Exercised | | (1,214) | | $ | 18.60 | | — | | | — | Forfeitures | | (77,495) | | $ | 41.76 | | — | | | — | Outstanding as of December 31, 2024 | | 737,895 | | $ | 83.84 | | 7.1 | | $ | 22 | Granted | | 120,748 | | $ | 9.33 | | — | | | — | Exercised | | — | | $ | — | | — | | | — | Forfeitures | | (9,677) | | $ | 37.74 | | — | | | — | Outstanding as of December 31, 2025 | | 848,966 | | $ | 73.76 | | 6.5 | | | — | Exercisable as of December 31, 2025 | | 636,486 | | $ | 94.11 | | 5.8 | | $ | 55 |
(1) | The aggregate intrinsic value is calculated as the difference between the exercise price of the underlying options and the fair value of the common stock for the options that were in the money at December 31, 2025 and 2024. |
|
| Summary of stock based compensation expense recorded |
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Three Months Ended | | Six Months Ended | | | | June 30, | | June 30, | | (in thousands) | | 2026 | | 2025 | | 2026 | | 2025 | | Research and development | | $ | 112 | | $ | 285 | | $ | 236 | | $ | 865 | | General and administrative | | | 192 | | | 302 | | | 412 | | | 1,086 | | Total stock-based compensation expense | | $ | 304 | | $ | 587 | | $ | 648 | | $ | 1,951 | |
|
| | | | | | | | | | | | | | | | December 31, | (in thousands) | | 2025 | | 2024 | Research and development | | $ | 1,345 | | $ | 2,756 | General and administrative | | | 1,641 | | | 3,579 | Total stock-based compensation expense | | $ | 2,986 | | $ | 6,335 |
|
| Summary of assumptions used in the Black Scholes option pricing model for stock options granted |
| | | | | | | | | | | | | | | | | | Six Months Ended | | | | June 30, | | | | 2026 | | 2025 | | Expected term | | 6.0 | years | | 6.0 | years | | Expected volatility | | 91.0 | % | | 90.5 | % | | Risk free interest rate | | 3.9 | % | | 4.4 | % | | Expected dividend yield | | — | % | | — | % | |
|
The assumptions used in the Black-Scholes option-pricing model for stock options granted were as follows: | | | | | | | | | | | | | | | | Year Ended | | | December 31, | | | 2025 | | 2024 | Expected term | | 6.0 | years | | 5.8 | years | Expected volatility | | 90.5 | % | | 83.3 | % | Risk free interest rate | | 4.4 | % | | 3.6 - 4.7 | % | Expected dividend yield | | — | % | | — | % |
|