Liabilities, Convertible Preferred Stock and Stockholders' (Deficit) Equity (Tables)

9 Months Ended

Sep. 30, 2023

Share-Based Payment Arrangement [Abstract]

Pre-funded Warrants for Common Stock Issued and Outstanding

As of September 30, 2023, the following pre-funded warrants for common stock were issued and outstanding:

Issue Date	Expiration Date	Exercise Price		Number of Warrants Outstanding
February 8, 2019	None	$	0.0025	—
April 30, 2020	None	$	0.0025	—
May 20, 2022	None	$	0.0025	250,000
Total pre-funded warrants				250,000

Stock Awards Granted

The following table summarizes the Company’s stock awards granted under all plans for each of the periods indicated:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2023			2022			2023			2022
	Grants	Weighted Average Grant Date Fair Value		Grants	Weighted Average Grant Date Fair Value		Grants	Weighted Average Grant Date Fair Value		Grants	Weighted Average Grant Date Fair Value
Stock options	1,044,667	$	14.50	50,806	$	16.75	3,867,366	$	9.65	153,686	$	52.50

Stock-Based Compensation Expense

Total stock-based compensation expense related to all plans was as follows (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2023		2022		2023		2022
Research and development (1)	$	2,965	$	639	$	4,136	$	2,031
General and administrative	1,820		926		4,269		3,653
Total stock-based compensation expense	$	4,785	$	1,565	$	8,405	$	5,684
(1) For the three and nine months ended September 30, 2023, $2.7 million and $2.9 million, respectively, was recognized as stock compensation expense related to the Parapyre Option Obligation. There were no such expenses for the three and nine months ended September 30, 2022.

Assumptions used to Estimate the Fair Value of Stock Options Granted

The following table summarizes the weighted-average Black-Scholes option pricing model assumptions used to estimate the fair value of stock options granted under the Company’s 2016 Plan, and the shares purchasable under the 2016 ESPP during the periods presented:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2023	2022	2023	2022
2016 Plan
Expected term (in years)	6.08	6.02	6.04	5.96
Expected volatility	101%	85%	111%	83%
Risk-free interest	4.28%	3.16%	4.07%	2.43%
Dividend yield	—	—	—	—
2016 ESPP
Expected term (in years)	0.50	0.50	0.49	0.49
Expected volatility	222%	95%	181%	84%
Risk-free interest	5.29	3.26	4.99%	1.95%
Dividend yield	—	—	—	—