Note 9 – Stock-Based Compensation

Stock Options

The 2015 Stock Incentive Plan, as amended, (“2015 Plan”) was approved at the Company’s annual meeting of stockholders in June 2015. Under the 2015 Plan, equity awards may be granted to officers, directors, employees and consultants of and advisors to the Company and any present or future subsidiary.

The 2015 Plan authorizes the issuance of up to 36,000,000 shares of common stock under equity awards granted under the plan. All such shares authorized for issuance under the 2015 Plan have been reserved. The Company will seek approval to increase the number of shares of common stock available for issuance under the 2015 Plan by 20,000,000 shares at its June 2018 annual meeting of stockholders. The 2015 Plan will expire on March 4, 2025.

The Amended and Restated 2005 Stock Incentive Plan (“2005 Plan”) expired in February 2015 and no new awards may be made under such plan, although awards will continue to be outstanding in accordance with their terms.

The 2015 Plan permits and the 2005 Plan permitted the grant of stock options (including incentive stock options), restricted stock, stock appreciation rights and restricted stock units. In addition, under the 2015 Plan, unrestricted stock, stock units and performance awards may be granted. Stock options and stock appreciation rights generally have a maximum term of 10 years and may be or were granted with an exercise price that is no less than 100% of the fair market value of the Company’s common stock at the time of grant. Grants of stock options are generally subject to vesting over periods ranging from six months to four years.

Stock Options Awards

The following is a summary of option activity under the 2015 Plan and 2005 Plan for the three months ended March 31, 2018:

	2015 Plan				2005 Plan
	Stock Options		Weighted- Average Exercise Price		Stock Options		Weighted- Average Exercise Price
Outstanding at January 1, 2018		33,675,720	$	3.61		12,818,929	$	3.26
Granted		140,500	$	1.95		—	$	—
Exercised		(139,645)	$	1.35		(281,020)	$	1.89
Canceled		(744,928)	$	4.47		(343,057)	$	4.08
Outstanding at March 31, 2018		32,931,647	$	3.59		12,194,852	$	3.27
Shares exercisable at March 31, 2018		10,614,915	$	5.86		11,789,727	$	3.22
Shares available for grant at March 31, 2018		2,883,708

The fair value of stock options granted under the 2015 Plan and 2005 Plan was estimated at the date of grant using the Black-Scholes option-pricing model with the following assumptions:

	Three Months Ended March 31,
	2018		2017
Weighted-average Black-Scholes fair value of stock options granted		$1.50		$1.13
Risk-free interest rate		2.26%-2.54%		1.73%-2.34%
Dividend yield		0%		0%
Volatility		113.98%-114.12%		88.91%-109.50%
Expected term (in years)		4.12-4.14		4.19-7.46
Expected forfeiture rate		0%		0%

The total aggregate intrinsic value and weighted-average remaining contractual term of stock options outstanding under the 2015 Plan and 2005 Plan as of March 31, 2018 was $16.9 million and 7.5 years, respectively. The total aggregate intrinsic value and weighted-average remaining contractual term of stock options exercisable under the 2015 Plan and 2005 Plan as of March 31, 2018 was $4.4 million and 6.1 years, respectively. The aggregate intrinsic value represents the total intrinsic value (the difference between the Company’s closing stock price on the last trading day of the period and the exercise price, multiplied by the number of in-the-money options) that would have been received by the option holders had all option holders exercised their options on March 31, 2018. This amount is subject to change based on changes to the closing price of the Company’s common stock. The aggregate intrinsic value of options exercised and vesting of restricted stock awards for the three months ended March 31, 2018 and 2017 was $0.3 million and less than $0.1 million, respectively.

Employee Stock Purchase Plan

In 2013, the Company adopted an Employee Stock Purchase Plan (the “ESPP”), which currently authorizes an aggregate of 3,600,000 shares of common stock to be purchased, and the aggregate amount of shares will continue to increase 5% on each anniversary of its adoption up to a maximum of 4,000,000 shares. The ESPP allows employees to purchase shares of common stock of the Company at each purchase date through payroll deductions of up to a maximum of 15% of their compensation, at 85% of the lesser of the market price of the shares at the time of purchase or the market price on the beginning date of an option period (or, if later, the date during the option period when the employee was first eligible to participate). At March 31, 2018, there were 270,880 shares available for issuance under the ESPP. The Company will seek approval to increase the maximum number of shares of common stock available for issuance under the ESPP by 4,000,000 shares at its June 2018 annual meeting of stockholders.

The ESPP is considered compensatory for financial reporting purposes. As such, the fair value of ESPP shares was estimated at the date of grant using the Black-Scholes option-pricing model with the following assumptions:

	Three Months Ended March 31,
	2018		2017
Range of Black-Scholes fair value of ESPP shares granted		$0.45-$3.53		$1.05-$5.47
Risk-free interest rate		0.66%-1.79%		0.45%-0.70%
Dividend yield		0%		0%
Volatility		59.84%-203.83%		45.98%-267.85%
Expected term (in years)		0.5-2.0		0.5-2.0
Expected forfeiture rate		0%		0%

Restricted Stock Awards

The following is a summary of restricted stock awards activity for the three months ended March 31, 2018:

	Number of Shares		Per Share Weighted- Average Grant-Date Fair Value
Outstanding and Unvested at January 1, 2018		18,750	$	4.99
Restricted stock granted		—	$	—
Restricted stock vested		—	$	—
Restricted stock forfeited		(18,750)	$	4.99
Outstanding and Unvested at March 31, 2018		—	$	—

The Company recorded all stock-based compensation expense in the consolidated statements of operations as follows (in thousands):

	Three Months Ended March 31,
	2018		2017
Research and development	$	3,098	$	2,215
General and administrative		2,147		1,998
Total stock-based compensation expense	$	5,245	$	4,213

As of March 31, 2018, there was approximately $31 million of total unrecognized compensation expense related to unvested stock options and ESPP. This unrecognized non-cash compensation expense is expected to be recognized over a weighted-average period of 1.6 years, and will be allocated between research and development and general and administrative expenses accordingly. This estimate does not include the impact of other possible stock-based awards that may be made during future periods.