Activities for the Company’s stock option plans for the three months ended March 31, 2023 were as follows:


	Options Outstanding
	Number of Options			Weighted- Average Exercise Price Per Share
Balance at December 31, 2022		13,289,838		$	7.67
Options granted		1,151,023			2.59
Options exercised		-			-
Option forfeited/expired		(307,176	)		5.89
Balance at March 31, 2023		14,133,685		$	7.30

The Company recorded $1.9 million and $2.9 million of stock-based compensation expense related to the stock option plans for the three months end March 31, 2023 and 2022, respectively.

Activities for the Company’s TRSUs for the three months ended March 31, 2023 were as follows:


	Number of Shares			Weighted Average Grant Date Fair Value Per Share

Balance at December 31, 2022		1,212,884		$	2.81
RSU's awarded		597,767			2.50
RSU's vested		(110,892	)		3.86
RSU's cancelled		(6,941	)		3.58
Balance at March 31, 2023		1,692,818		$	2.63

The Company recorded $0.4 million and $0.3 million of stock-based compensation expense related to the TRSUs for the three months end March 31, 2023 and 2022, respectively.

In October 2021, the Company granted 435,000 PSUs to executive employees with an aggregated grant date fair value of $2.3 million. Vesting for 50% of the PSUs granted will occur within one year of the grant date upon achievement of certain specific milestones ("2021-Tranche 1") and the remaining 50% will vest within two years of the grant date upon achievement of additional company objectives ("2021-Tranche 2").

In July 2022, the Company determined that the performance condition for 2021-Tranche 1 was met and recorded $1.0 million of stock-based compensation expense for the year ended December 31, 2022. As the achievement of the milestones for Tranche 2 was not considered probable, no compensation cost was recorded for 2021-Tranche 2 of these awards through March 31, 2023.

In August 2022, the Company granted 250,000 PSUs to executive employees with an aggregated grant date fair value of approximately $0.4 million. Vesting for 50% of the PSUs granted will occur upon attaining certain specific milestones by December 2023 (“2022-Tranche 1”), and the remaining 50% will vest upon attaining certain specific milestones by December 2024 (“2022-Tranche 2”). As of December 31, 2022, and March 31, 2023, the Company determined that it is probable that the performance conditions for 2022-Tranche 1 will be satisfied and hence recorded $55,000 and $29,000 compensation cost, respectively, for those awards for the year ended December 31, 2022 and for the three months ended March 31, 2023. As of December 31, 2022 and March 31, 2023, the Company determined that it is not probable that the performance conditions for 2022-Tranche 2 will be satisfied and hence recorded no compensation cost for those awards through March 31, 2023.

In February 2023, the Company granted 710,000 PSUs to executive employees with an aggregated grant date fair value of approximately $1.8 million. Vesting for 50% of the PSUs granted will occur upon attaining certain specific milestones by December 2024 (“2023-Tranche 1”), and the remaining 50% will vest upon attaining certain specific milestones by December 2025 (“2023-Tranche 2”). The Company determined that it is not probable that the performance conditions will be satisfied for each of these tranches and hence no compensation cost was recorded for these awards through March 31, 2023.

Activities for the Company’s PSUs for the three months ended March 31, 2023 were as follows:


	Number of Shares			Weighted Average Grant Date Fair Value Per Share

Balance at December 31, 2022		383,750		$	2.96
PSU's awarded		710,000			2.59
PSU's vested		—			-
PSU's cancelled		(13,750	)		1.59
Balance at March 31, 2023		1,080,000		$	2.73

Total stock-based compensation recorded was as follows:


	Three Months Ended
	March 31,
	2023		2022
	(in thousands)
Stock-based compensation expense:
Research and development	$	961	$	1,605
General and administrative		1,448		1,765
Total stock-based compensation expense	$	2,409	$	3,370