Total share-based compensation related to stock options, common stock awards, and non-financing warrants was $1,731,803 and $89,970 for the three months ended June 30, 2016 and 2015, respectively, and $2,018,263 and $237,198 for the six months ended June 30, 2016 and 2015, respectively.

Share-based compensation expense is classified in the condensed consolidated statements of comprehensive loss as follows:

Employee Stock Options

During the six months ended June 30, 2016 and 2015, the Company granted 12,122 employee stock options. The key valuation assumptions used consisted of the Company’s stock price, a risk free rate of 0.54% and an expected volatility of 123%. There were no employee stock options granted during the same period in 2015. During the six months ended June 30, 2016, the Company extended the exercise expiration date of certain former employee stock option awards resulting in a change in incremental value of approximately $24,000 which was charged to administrative expense. The Company recognized compensation expense related to employee stock options of $310,469 and $20,668 during the three months ended June 30, 2016 and 2015, respectively, and $765,026 and $84,303 during the six months ended June 30, 2016 and 2015, respectively.

Non-Employee Stock Options

No non-employee stock options were granted during the six months ended June 30, 2016 or 2015 and no non-employee stock options were exercised during the six months ended June 30, 2016 or 2015. The Company recognized compensation expense related to non-employee stock options of $3,474 and $4,755 during the three months ended June 30, 2016 and 2015, respectively, and $2,503 and $9,193 during the six months ended June 30, 2016 and 2015, respectively.

Common stock awards

The Company granted 9,581 and 925 common stock awards during the three months ended June 30, 2016 and 2015, respectively, and 11,939 and 2,043 common stock awards during the six months ended June 30, 2016 and 2015, respectively, based on the value of the services provided and the average stock price during each respective period. The Company recognized compensation expense related to common stock awards of $50,000 and $25,500 during the three months ended June 30, 2016 and 2015, respectively, and $107,790 and $51,000 during the six months ended June 30, 2016 and 2015, respectively.

Warrants

In connection with certain of the Company’s collaboration agreements and consulting arrangements, the Company has issued warrants to purchase shares of common stock. On May 16, 2016, the Company modified the exercise price of 150,307 performance-based warrants held by Serum and individuals related to Serum from $25.41 to $7.92 and resulted in an incremental value expense of $204,000. Additionally, the Company issued 212,122 warrants to purchase shares of common stock to Serum with an exercise price of $7.92. The new warrants were fully vested and the Company recognized $1.37 million of expense related to the grant.

As of June 30, 2016, and December 31, 2015, warrants to purchase 758,347 shares of common stock were outstanding. These warrants were fair valued at each issuance date using the Black-Scholes option pricing model. Warrants for which a measurement has not been reached are subject to re-measurement at each reporting period until the measurement date is reached. Expense is recognized on a straight-line basis over the expected service period or at the date of issuance, if there is not a service period. Expense for the six months ended June 30, 2016, was $1.1 million including the incremental value recognized for the warrant modification. The Company issued no warrants in connection with collaboration agreements and consulting services during the three and six months ended June 30, 2015.