Stockholders' equity (Tables)

12 Months Ended

Dec. 31, 2022

Equity [Abstract]

Schedule of Stock Option Activity

A summary of the Company's stock option activity and related information for the year ended December 31, 2022 is as follows:

	Number of Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (In Years)	Aggregate Intrinsic Value (In Thousands)
Outstanding at December 31, 2021	8,963,945	$	7.20	8.32	$	6,912
Options granted	3,431,050	$	1.32
Options exercised	(36,500)	$	3.67
Options cancelled/forfeited	(3,844,114)	$	7.10
Outstanding at December 31, 2022	8,514,381	$	4.89	8.32	$	—
Exercisable as of December 31, 2022	3,890,924	$	6.01	7.18	$	—

Schedule of Weighted Average Assumptions

The fair value of stock options granted is estimated using the Black-Scholes option pricing model with the following weighted average assumptions:

	December 31,
	2022		2021
Expected volatility	84	%	89	%
Expected dividends	0	%	0	%
Expected terms (years)	6.04		6.03
Risk free rate	2.66	%	0.93	%

Schedule of RSU Activity

A summary of the Company's restricted stock unit activity and related information for the year ended December 31, 2022 is as follows:

	Number of Shares	Weighted Average Grant Date Fair Value
Non-vested at December 31, 2021	132,000	$	9.97
Restricted stock units granted	700,000	$	3.69
Restricted stock units vested	(24,750)	$	12.20
Restricted stock units forfeited	(428,750)	$	4.66
Non-vested at December 31, 2022	378,500	$	4.22

Summary of Stock-based Compensation Expense

Stock-based compensation expense is classified in the statements of operations as follows (in thousands):

	December 31,
	2022		2021
Research and development expenses	$	4,342	$	5,095
General and administrative expenses	4,487		6,462
Total stock-based compensation expense	$	8,829	$	11,557