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Stockholders' Equity (Tables)
12 Months Ended
Dec. 31, 2022
Equity [Abstract]  
Summary of Stock Option Activity

The following summarizes stock option activity for the year ended December 31, 2022:

 

 

 

Outstanding Options

 

 

Weighted-
Average
Exercise Price
Per Share

 

 

Weighted
Average
Remaining
Contractual
Term
(in years)

 

 

Aggregate
Intrinsic Value
(in thousands)
(a)

 

Balances as of December 31, 2021

 

 

3,947,025

 

 

$

4.58

 

 

 

 

 

 

 

Granted

 

 

2,169,800

 

 

$

3.63

 

 

 

 

 

 

 

Exercised

 

 

-

 

 

$

-

 

 

 

 

 

 

 

Forfeitures and cancellations

 

 

(1,014,324

)

 

$

4.90

 

 

 

 

 

 

 

Balances as of December 31, 2022

 

 

5,102,501

 

 

$

4.11

 

 

 

7.71

 

 

$

-

 

Options exercisable as of December 31, 2022

 

 

2,483,222

 

 

$

4.23

 

 

 

6.75

 

 

$

-

 

(a)
Aggregate intrinsic value in this table was calculated as the positive difference, if any, between the closing price per share of the Company’s common stock on December 31, 2022 of $1.06 and the price of the underlying options.
Summary of Non-cash Stock-based Compensation Expense

Total non-cash stock-based compensation expense for all stock awards and purchase rights, net of forfeitures recognized as they occur, that was recognized in the consolidated statement of operations is as follows (in thousands):

 

 

 

Year Ended
December 31,

 

 

 

2022

 

 

2021

 

Research and development

 

$

1,799

 

 

$

1,976

 

General and administrative

 

 

3,042

 

 

 

2,434

 

Total

 

$

4,841

 

 

$

4,410

 

Summary of Weighted-Average Assumptions Used to Determine Fair Value of Stock Option Grants

The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee and nonemployee stock option grants were as follows:

 

 

 

Year Ended
December 31,

 

 

2022

 

2021

Risk-free interest rate

 

1.93%

 

0.68%

Expected volatility

 

81.60%

 

88.55%

Expected term (in years)

 

5.84

 

6.01

Expected dividend yield

 

0%

 

0%

Summary of Reserved Shares of Common Stock for Future Issuance

Common stock reserved for future issuance consists of the following as of December 31, 2022 and 2021:

 

 

 

December 31,

 

 

 

2022

 

 

2021

 

Stock options issued and outstanding

 

 

5,102,501

 

 

 

3,947,025

 

Warrants for common stock

 

 

1,366,141

 

 

 

1,366,141

 

Awards available under the 2018 Equity Incentive Plan

 

 

784,331

 

 

 

467,024

 

Employee stock purchase plan

 

 

925,963

 

 

 

769,658

 

Total

 

 

8,178,936

 

 

 

6,549,848