
	Three Months Ended March 31,
	2022		2021
Service-based awards:

Restricted stock units	$	12	$	104
Stock option awards	200		391
	212		495
Performance-based awards:
Restricted stock awards	(391)		(391)

Stock option awards	—		(340)
	(391)		(731)
Total	$	(179)	$	(236)

A summary of the Company’s restricted stock awards during the three months ended March 31, 2022 is as follows:


	Number of Shares	Weighted Average Grant-Date Fair Value
Unvested at January 1, 2022	7,118	$	62.70
Forfeited	(6,227)	$	62.70
Unvested at March 31, 2022	891	$	62.70

A summary of the Company’s restricted stock awards during the three months ended March 31, 2021 is as follows:


	Number of Shares	Weighted Average Grant-Date Fair Value
Unvested at January 1, 2021	13,345	$	62.70
Forfeited	(6,227)	$	62.70
Unvested at March 31, 2021	7,118	$	62.70

The fair value of restricted stock awards are measured based on their fair value on the date of grant and amortized over the vesting period of 20 months. As of March 31, 2022, unvested restricted stock awards of 891 were related to performance-based awards. The forfeited performance-based restricted stock awards of 6,227 was due to the resignation of the Company's Chief Development Officer on March 25, 2022. These forfeited awards reduced stock-based compensation expense by $0.4 million.

A summary of the Company’s service-based restricted stock units during the three months ended March 31, 2022 is as follows:


	Number of Shares	Weighted Average Grant-Date Fair Value
Unvested at January 1, 2022	29,289	$	12.87


Forfeited	(1,223)	52.91
Unvested at March 31, 2022	28,066	$	11.11

A summary of the Company’s service-based restricted stock units during the three months ended March 31, 2021 is as follows:


	Number of Shares	Weighted Average Grant-Date Fair Value
Unvested at January 1, 2021	24,136	$	28.60
Granted	914	22.99
Vested	(1,042)	52.91
Forfeited	(2,396)	27.50

Unvested at March 31, 2021	21,612	$	27.39

The fair value of service based restricted stock units are measured based on their fair value on the date of grant and amortized over the vesting period. The vesting periods range from 1 to 3 years. Stock-based compensation expense of $12,000 and $104,000 was recognized for the three months ended March 31, 2022 and 2021, respectively. As of March 31, 2022, the unrecognized stock-based compensation expense was $0.1 million, which is expected to be recognized over an estimated weighted average remaining term of less than 1 year.

The fair value of the service-based stock options granted for the three months ended March 31, 2022 were based on the following assumptions:


			March 31, 2022
Exercise price			$4.12
Expected stock price volatility			76.2%
Risk-free interest rate			1.98%
Term (years)			6.5

A summary of the Company’s service-based stock option activity for the three months ended March 31, 2022 is as follows:


	Shares Underlying Options	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value
Outstanding at January 1, 2022	528,591	$	32.01	7.5	$	—
Granted	909	4.07		9.9	—

Forfeited	(14,839)	17.49		—	—
Expired	(3,545)	85.36		—	—
Outstanding at March 31, 2022	511,116	$	32.01	7.0	$	1

Exercisable at March 31, 2022	236,720	$	52.14	5.0	$	—

A summary of the Company’s service-based stock option activity for the three months ended March 31, 2021 is as follows:


	Shares Underlying Options	Weighted Average Exercise Price		Weighted Average Remaining Contractual Term	Aggregate Intrinsic Value
Outstanding at January 1, 2021	519,814	$	50.05	6.6	$	—
Granted	7,672	17.60		6.0	—
Forfeited	(16,721)	27.39		—	—
Expired	(20,530)	84.26		—	—
Outstanding at March 31, 2021	490,235	$	48.95	6.1	$	—

Exercisable at March 31, 2021	251,180	$	73.48	3.2	$	—

The aggregate intrinsic value in the table above is calculated as the difference between the closing price of the Company's common stock and the exercise price of the stock options that had strike prices below the closing price.

During the three months ended March 31, 2022, the Company granted stock options to purchase up to 909 shares of common stock to certain employees. During the three months ended March 31, 2022, 14,839 shares were forfeited and 3,545 shares expired. Forfeitures are recorded in the period of occurrence; compensation expense is adjusted accordingly.

Stock-based compensation expense recognized for service-based stock options was $0.2 million and $0.4 million for the three months ended March 31, 2022 and 2021, respectively. As of March 31, 2022, total stock-based compensation expense related to unvested options not yet recognized totaled approximately $1.0 million, which is expected to be recognized over an estimated weighted average remaining term of 3.1 years.