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Stock-Based Compensation
9 Months Ended
Sep. 30, 2018
Stock-Based Compensation

4. Stock-Based Compensation

Following is the stock-based compensation expense related to common stock options, common stock, restricted common stock and common stock warrants:

 

     Three Months Ended
September 30,
     Nine Months Ended
September 30,
 
     2018      2017      2018      2017  

Research and development

   $ 252      $ 109      $ 1,413      $ 407  

General and administrative

     411        121        1,880        422  
  

 

 

    

 

 

    

 

 

    

 

 

 

Total stock-based compensation expense

   $ 663      $ 230      $ 3,293      $ 829  
  

 

 

    

 

 

    

 

 

    

 

 

 

The following table summarizes the stock option activity in the Company’s equity incentive plans, including non-plan grants to Company executives, from December 31, 2017 through September 30, 2018:

 

     Shares      Weighted Average
Exercise Price
 

Outstanding, December 31, 2017

     5,155,263      $ 4.11  

Granted

     1,011,875        5.02  

Exercised

     (2,193,366      1.99  

Options forfeited/cancelled

     (209,124      4.74  
  

 

 

    

Outstanding, September 30, 2018

     3,764,648      $ 5.55  
  

 

 

    

As of September 30, 2018, there was $1,166,000 of unrecognized compensation related to 846,893 unvested options, which is expected to be recognized over a weighted–average period of approximately 0.25 years. The weighted-average grant date fair value for options granted during the nine months ended September 30, 2018 was $3.98. The Company granted 460,000 stock options in January 2018, of which 115,000 options vested upon grant with the remaining 345,000 options vesting over the remainder of 2018. Approximately $526,000 of non-cash, stock-based compensation expense was recorded during the three months ended March 31, 2018 related to the options granted in January 2018 that vested upon the grant date. Additionally, Company granted 506,875 stock options during May 2018, of which 115,000 options vested upon grant with the remaining 391,875 options vesting over the remainder of 2018. Approximately $433,000 of non-cash, stock-based compensation expense was recorded during the three months ended June 30, 2018 related to the options granted in May 2018 that vested upon the grant date.

The fair value of all other options granted is determined using the Black-Scholes option-pricing model. The following weighted average assumptions were used:

 

     Nine
Months Ended
September 30,
2018
    Nine
Months Ended
September 30,
2017
 

Risk-free interest rate

     2.47     —    

Expected life of the options

     5.7 years       —    

Expected volatility of the underlying stock

     104     —    

Expected dividend rate

     0     —