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Stock-based Compensation (Tables)
12 Months Ended
Dec. 31, 2023
Weighted-Average Fair Value of Options Granted

    

2023

2022

2021

Expected term

 

6.25 years

6.25 years

6.25 years

Expected volatility

 

78.36%

84.66%

84.19%

Risk-free interest rate

 

3.60%

1.90%

0.78%

Expected dividend yield

 

0%

0%

0%

Stock-Based Compensation Expense

    

    

2023

    

2022

    

2021

Research and development expense

$

909,981

$

1,059,591

$

2,214,848

General and administrative expense

 

2,614,495

 

2,797,989

 

3,872,438

Total stock-based compensation expense

$

3,524,476

$

3,857,580

$

6,087,286

2013 Equity Incentive Plan  
Company's Stock Option Activity

WEIGHTED-

AGGREGATE

 

WEIGHTED-

AVERAGE

INTRINSIC

 

AVERAGE

REMAINING

VALUE

 

OUTSTANDING

EXERCISE

CONTRACTUAL

(IN

 

OPTIONS

    

PRICE

    

TERM (YEARS) 

    

THOUSANDS)

Outstanding as of December 31, 2022

6,774,792

$

6.37

6.1

Options granted

2,496,850

2.52

Options exercised

(100,960)

1.15

Options forfeited

(896,882)

6.16

Outstanding as of December 31, 2023

8,273,800

5.29

6.3

$

2,043

Vested or expected to vest as of December 31, 2023

8,131,900

5.37

6.3

1,865

Exercisable as of December 31, 2023

4,993,061

7.30

4.5

921

Summary of RSU Activity

The following is a summary of RSU activity for the 2013 Plan for the year ended December 31, 2023:

 

Weighted-Average

 

Number of Shares

Grant Date

 

Underlying RSUs

    

Fair Value

 

Unvested at December 31, 2022

204,785

$

3.81

Forfeited

(19,573)

 

3.81

Vested

(68,055)

 

3.81

Unvested at December 31, 2023

117,157

 

3.81

Inducement Plan  
Company's Stock Option Activity

WEIGHTED-

AGGREGATE

 

WEIGHTED-

AVERAGE

INTRINSIC

 

AVERAGE

REMAINING

VALUE

 

OUTSTANDING

EXERCISE

CONTRACTUAL

(IN

 

OPTIONS

    

PRICE

    

TERM (YEARS) 

    

THOUSANDS)

Outstanding as of December 31, 2022

2,333,525

$

1.82

8.7

Options granted

360,000

2.76

Options forfeited

(103,125)

1.34

Outstanding as of December 31, 2023

2,590,400

1.97

8.0

$

1,304

Vested or expected to vest as of December 31, 2023

2,006,200

1.96

8.0

1,077

Exercisable as of December 31, 2023

887,696

1.90

7.7

460