Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2021

Stock-Based Compensation Expense Related to Common Stock Options, Restricted Common Stock and Common Stock Warrants

Following is the stock-based compensation expense related to common stock options, restricted common stock, common stock warrants and deferred stock units:

	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
	in thousands
Research and development	$	89	$	83	$	156	$	240
General and administrative		492		311		679		584
Total stock-based compensation expense	$	581	$	394	$	835	$	824

Summary of Stock Option Activity

The following table summarizes the stock option activity in the Company’s equity incentive plans, including non-plan grants to Company executives, from December 31, 2020 through June 30, 2021:

	Shares			Weighted Average Exercise Price
Outstanding, December 31, 2020		3,987,575		$	4.29
Granted		2,065,000			2.20
Exercised		(252,500	)		2.19
Options forfeited/cancelled		(880,350	)		5.52
Outstanding, June 30, 2021		4,919,725		$	3.30

Weighted Average Assumptions Used to Determine Fair Value of Options Granted

The fair value of all other options granted is determined using the Black-Scholes option-pricing model. The following weighted average assumptions were used:

	Six Months Ended June 30,			Six Months Ended June 30,
	2021			2020
Risk-free interest rate		0.57	%		1.55	%
Expected life of the options		6 years			6 years
Expected volatility of the underlying stock		91	%		100	%
Expected dividend rate		0	%		0	%