Stockholders' equity (Tables)

6 Months Ended

12 Months Ended

Jun. 30, 2023

Dec. 31, 2022

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		1,702,876		$	24.45		8.32	$	—
Options granted		52,100		$	3.50
Options exercised		—		$	—
Options cancelled/forfeited		(827,664	)	$	25.35

Outstanding at June 30, 2023		927,312		$	19.80		4.41	$	11

Exercisable as of June 30, 2023		706,942		$	22.55		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		1,792,789		$	36.00		8.32	$	6,912
Options granted		686,210		$	6.60
Options exercised		(7,300	)	$	18.35
Options cancelled/forfeited		(768,822	)	$	35.50

Outstanding at December 31, 2022		1,702,877		$	24.45		8.32	$	—

Exercisable as of December 31, 2022		778,184		$	30.05		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 r

tricted stock unit activity and related informatio

for the year ended December 31, 2022, after giving effect to the 1-for-5 reverse stock split of the Company’s common stock that was effected on September 25, 2023, is as follows:


	Number of Shares			Weighted Average Grant Date Fair Value


Non-vested at December 31, 2021		26,400		$	49.85
Restricted stock units granted		140,000		$	18.45
Restricted stock units vested		(4,950	)	$	61.00
Restricted stock units forfeited		(85,750	)	$	23.30

Non-vested at December 31, 2022		75,700		$	21.10

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, giving effect to the 1-for-5 reverse stock split of the Company’s common stock that was effected on September 25, 2023:


	Number of Shares			Weighted Average Grant Date Fair Value
Non-vested at December 31, 2022		75,700		$	21.10
Restricted stock units granted		—		$	—
Restricted stock units vested		(36,000	)	$	20.90
Restricted stock units forfeited		(30,450	)	$	20.75

Non-vested at June 30, 2023		9,250		$	22.95