Stockholders' equity (Tables)

6 Months Ended

12 Months Ended

Jun. 30, 2023

Dec. 31, 2022

Equity [Abstract]

Schedule of Stock Option Activity

A summary of the Company’s stock option activity and related information for the six months ended June 30, 2023 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, 2022		8,514,381		$	4.89		8.32	$	—
Options granted		260,500		$	0.70
Options exercised		—		$	—
Options cancelled/forfeited		(4,138,321	)	$	5.07
Outstanding at June 30, 2023		4,636,560		$	3.96		4.41	$	11
Exercisable as of June 30, 2023		3,534,712		$	4.51		3.01	$	—

Stock options

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 values of stock options granted are estimated using the Black-Scholes option pricing model with the following weighted average assumptions:

	Three Months Ended June 30,						Six Months Ended June 30,
	2023			2022			2023			2022
Expected volatility		87.37	%		82.68	%		86.77	%		83.01	%
Expected dividends		0	%		0	%		0	%		0	%
Expected terms (years)		5.27			5.73			5.60			5.96
Risk free rate		3.82	%		2.77	%		3.67	%		2.22	%

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

Restricted stock units

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 condensed statements of operations and comprehensive income (loss) as follows:

(in thousands)	Three Months Ended June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
Research and development expenses	$	—	$	1,051	$	255	$	2,315
General and administrative expenses		331		1,261		1,267		2,443
Total stock-based compensation expense	$	331	$	2,312	$	1,522	$	4,758

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

Schedule of Unvested Restricted Stock Units Roll Forward

(d) Restricted stock units

A summary of the Company’s RSU activity and related information for the six months ended June 30, 2023 is as follows:

	Number of Shares			Weighted Average Grant Date Fair Value
Non-vested at December 31, 2022		378,500		$	4.22
Restricted stock units granted		—		$	—
Restricted stock units vested		(180,000	)	$	4.18
Restricted stock units forfeited		(152,250	)	$	4.15
Non-vested at June 30, 2023		46,250		$	4.59