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Stock Options, Restricted Stock and Stock-Based Compensation (Tables)
3 Months Ended
Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]  
Schedule of Stock Option Activity

Stock option activity is summarized as follows:

 

 

NUMBER OF
STOCK
OPTIONS

 

 

WEIGHTED-
AVERAGE
EXERCISE
PRICE

 

 

WEIGHTED-
AVERAGE
REMAINING
CONTRACTUAL
TERM (IN YEARS)

 

 

AGGREGATE
INTRINSIC
VALUE
(IN THOUSANDS)

 

Outstanding as of December 31, 2023

 

 

5,666,621

 

 

$

2.47

 

 

 

6.61

 

 

 

 

Granted

 

 

67,500

 

 

 

1.59

 

 

 

 

 

 

 

Exercised

 

 

(146,964

)

 

 

1.54

 

 

 

 

 

 

 

Cancelled, forfeited or expired

 

 

(474,484

)

 

 

3.42

 

 

 

 

 

 

 

Outstanding as of March 31, 2024

 

 

5,112,673

 

 

$

2.40

 

 

 

6.66

 

 

$

378

 

Exercisable as of March 31, 2024

 

 

3,500,102

 

 

$

2.41

 

 

 

5.80

 

 

$

133

 

Unvested as of March 31, 2024

 

 

1,612,571

 

 

$

2.37

 

 

 

8.53

 

 

$

245

 

Schedule of Fair Value of Stock Options Granted Was Estimated on Black-Scholes Options

The fair value of stock options granted was estimated on the grant date using the Black-Scholes option pricing model based on the following assumptions:

 

 

THREE MONTHS ENDED
MARCH 31,

 

 

 

2024

 

 

2023

 

Expected option life (years)

 

 

6.08

 

 

 

6.08

 

Risk-free interest rate

 

4.21% - 4.27%

 

 

3.58% - 4.13%

 

Expected volatility

 

99.30% - 99.45%

 

 

91.33% - 92.25%

 

Expected dividend yield

 

 

0

%

 

 

0

%

Summary of Restricted Stock Activity

Restricted stock activity is summarized as follows:

 

 

NUMBER OF
SHARES

 

 

WEIGHTED-
AVERAGE GRANT
DATE FAIR VALUE

 

Unvested at December 31, 2023

 

 

2,526,432

 

 

$

1.06

 

Granted

 

 

 

 

$

 

Vested

 

 

 

 

$

 

Forfeited

 

 

(219,543

)

 

$

1.13

 

Unvested at March 31, 2024

 

 

2,306,889

 

 

$

1.06

 

 

Schedule of Stock-based Compensation Expense

Stock-based compensation expense for the three months ended March 31, 2024 and 2023 was classified in the condensed consolidated statements of operations and comprehensive loss as follows (in thousands):

 

 

 

THREE MONTHS ENDED
MARCH 31,

 

 

 

2024

 

 

2023

 

Research and development

 

$

553

 

 

$

311

 

General and administrative

 

 

490

 

 

 

422

 

Total stock-based compensation expense

 

$

1,043

 

 

$

733