Share-based compensation (Tables)

6 Months Ended

Jun. 30, 2023

Share-based compensation

Schedule of stock-based compensation expense

	Three Months Ended June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
Research and development	$	427	$	462	$	857	$	907
General and administrative		606		865		1,400		1,730
	$	1,033	$	1,327	$	2,257	$	2,637

Weighted average assumptions used in option-pricing

The weighted average assumptions used in the Black-Scholes option-pricing model for stock options granted were:

	Six Months Ended June 30,
	2023			2022
Expected volatility		88.5	%		85.6	%
Risk-free interest rate		3.8	%		2.7	%
Expected term (in years)		6.03			5.97
Expected dividend yield		—			—
Fair value of common stock	$	4.87		$	3.64

Summary of option activity

A summary of option activity under the 2020 Plan and prior Plans during the six months ended June 30, 2023 was as follows:

				Weighted
		Weighted		average
		average		remaining
	Number of	exercise price		contractual
	shares	per share		term (years)
Outstanding at January 1, 2023	2,519,405		9.60	7.90
Granted	658,900		4.87	9.70
Forfeited	(98,216)		11.56	—
Expired	(42,009)		16.25	—
Exercised	—		—	—
Outstanding at June 30, 2023	3,038,080		8.42	7.88
Exercisable at June 30, 2023	1,563,646		8.66	7.02