v3.22.2.2
Stockholders' Equity (Tables)
 9 Months Ended
Sep. 30, 2022
Equity [Abstract]  
Summary of Activity of Shares Warrant Exercise
The following table summarizes preferred stock conversions and warrant exercises (and the related impact on common stock) for the three and nine months ended September 30, 2022 and 2021 (in thousands):
Class A-1 Convertible Preferred StockClass A-2 Convertible Preferred StockClass A-3 Convertible Preferred StockClass A-4 Convertible Preferred StockCommon Stock WarrantsCommon Stock
Balance at December 31, 2021257 1,331 259 3,726 6,187 
Conversions/Exercises— — — — — — 
Balance at March 31, 2022257 1,331 259 3,726 6,187 
Conversions/Exercises— — — — — — 
Balance at June 30, 2022257 1,331 259 3,726 6,187 
Conversions/Exercises— — — — — — 
Balance at September 30, 2022257 1,331 259 3,726 6,187 
Balance at December 31, 2020257 1,416 259 — 6,604 
Conversions/Exercises— (78)— — (392)320 
Balance at March 31, 2021257 1,338 259 — 6,212 
Conversions/Exercises— (7)— — (25)32 
Balance at June 30, 2021257 1,331 259 — 6,187 
Conversions/Exercises— — — — — — 
Balance at September 30, 2021257 1,331 259 — 6,187 
Common Stock Reserved for Future Issuance
The following shares of common stock were reserved for future issuance as of September 30, 2022 (in thousands):
 
Class A-1 convertible preferred stock outstanding (as-converted)257 
Class A-2 convertible preferred stock outstanding (as-converted)1,331 
Class A-3 convertible preferred stock outstanding (as-converted)259 
Class A-4 convertible preferred stock outstanding (as-converted)3,726 
2019 PIPE Initial Closing warrants1,278 
2019 PIPE Milestone Closing warrants3,059 
2020 PIPE warrants1,849 
Common stock options outstanding1,386 
RSUs outstanding85 
Common stock available for future grant under the 2019 Equity Incentive Plan365 
Common stock available for future grant under the 2021 Inducement Plan160 
2022 Employee Stock Purchase Plan129 
Total common shares reserved for future issuance13,884 
Summary of Stock Option Activity RSU
The following table summarizes our stock option and RSU (together Stock Awards) activity under all equity incentive plans for the nine months ended September 30, 2022 (shares in thousands): 
Number of
options		Weighted
average
exercise
price		Number of
RSUs		Weighted average grant date fair value
Stock Awards outstanding at December 31, 2021866 $11.72 40 $9.50 
Granted562 $2.60 85 $2.57 
Exercised (options) or Vested (RSUs)— $— (36)$9.50 
Canceled/forfeited/expired(42)$26.10 (4)$9.50 
Stock Awards outstanding at September 30, 20221,386 $7.58 85 $2.57 
Summary of Assumptions Used to Estimate Fair Value of Stock Options and Performance Stock and Employee Stock Purchase Plan
The following table summarizes the weighted average assumptions used to estimate the fair value of stock options and performance stock awards granted to employees under our 2019 Equity Incentive Plan, 2021 Inducement Plan and the shares purchasable under our Employee Stock Purchase Plans during the periods presented:
 
 Three months ended
September 30,		Nine months ended
September 30,
 2022202120222021
Stock options
    Risk-free interest rate3.1 %0.9 %2.0 %1.0 %
    Volatility97.5 %96.0 %96.1 %95.8 %
    Dividend yield — — — — 
    Expected term (years)6.16.16.16.1
Performance stock options
    Risk-free interest rate— — — 1.0 %
    Volatility— — — 95.7 %
    Dividend yield— — — — 
    Expected term (years)0006.1
Employee stock purchase plan shares
    Risk-free interest rate1.7 %0.1 %0.9 %0.1 %
    Volatility105.9 %103.1 %99.3 %104.4 %
    Dividend yield— — — — 
    Expected term (years)0.50.50.50.5
Summary of Stock-Based Compensation
The following table summarizes the allocation of our stock-based compensation expense for all stock awards during the periods presented (in thousands): 
 Three months ended
September 30,		Nine months ended
September 30,
 2022202120222021
Research and development$56 $277 $425 $687 
General and administrative304 530 1,355 1,565 
Total$360 $807 $1,780 $2,252