Common Stock Warrants

On November 25, 2014, the Company issued the Warrants to purchase a total of 27,500 shares of common stock to SVB and Life Science Loans, LLC at an exercise price of $11.04 per share in connection with the Second Loan Modification Agreement (See Note 8). In connection with the Company's drawdown of an additional $5.0 million pursuant to the Loan Agreement in May 2015, the Warrants automatically became exercisable for the purchase of an additional 27,500 shares of common stock at a per share exercise price of $11.83. The Warrants are exercisable immediately and have a ten-year life. The Warrants were initially valued at $0.3 million each using the Black-Scholes option-pricing model. As of December 31, 2018, all 55,000 warrants remain un-exercised.

On December 2, 2014, the Company issued warrants to purchase 871,840 shares of common stock at an exercise price of $15.00 per share in connection with a private placement of common stock (the "PIPE Warrants"). The PIPE Warrants were exercisable immediately and had a three-year life. Upon certain events, the Company was required to settle the PIPE Warrants for cash. As a result, the Company had classified the PIPE Warrants as a liability. The PIPE Warrants expired un-exercised in December 2017.

The Company allocated $3.0 million to the PIPE Warrants with the residual proceeds allocated to the common stock. The fair value of the PIPE Warrants was determined using the Black-Scholes option pricing model. The fair value of the PIPE Warrants was re-measured at each reporting date using then-current assumptions with changes in fair value charged to other income (expense) on the statements of operations and comprehensive (loss) income. The following assumptions were used in valuing the PIPE Warrants:



	December 31, 2016
Risk-free interest rate	0.85	%
Expected dividend yield	—	%
Expected term (in years)	0.92
Expected volatility	83.39	%

On November 1, 2017, the Company issued warrants (the "November 2017 Warrants") to purchase a total of 10,000,000 shares of common stock at an exercise price of $0.80 per share. Each of the November 2017 Warrants is exercisable immediately and will expire five years from the date of issuance. The warrants were concluded to be equity classified and recorded to Additional Paid-in Capital. As of December 31, 2018, a total of 1,991,687 warrants remain un-exercised.

On March 23, 2018, the Company issued warrants to purchase a total of 7,968,128 shares of common stock at an exercise price of $1.20 per share. Each of the March 2018 Warrants were purchased at a price of $0.125 per warrant and, subject to certain ownership limitations, the common stock purchase warrants issued were exercisable immediately upon issuance at an exercise price of $1.20 per share of common stock. The warrants were concluded to be equity classified and recorded to Additional Paid-in Capital. The common stock warrants are exercisable for five years from March 23, 2018. As of December 31, 2018, a total of 7,210,945 remain un-exercised.