Stockholders’ Equity

Shares Reserved for Future Issuance

The following shares of common stock were reserved for future issuance as of September 30, 2017:



Common stock options outstanding	10,483,174
Common stock available for future grant under 2012 Equity Incentive Plan	1,240,667
Common stock available for future grant under 2015 Inducement Plan	41,948
Employee Stock Purchase Plan	1,675,110
Total common shares reserved for future issuance	13,440,899

The following table summarizes our stock option activity under all equity incentive plans for the nine months ended September 30, 2017 (shares in thousands):



	Number of options		Weighted average exercise price
Options outstanding at December 31, 2016	8,931		$	6.70
Granted	4,523		$	1.41
Exercised	(11	)	$	0.38
Canceled/forfeited/expired	(2,960	)	$	6.03
Options outstanding at September 30, 2017	10,483		$	4.62

Stock-Based Compensation

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 2012 Equity Incentive Plan and 2015 Inducement Plan and the shares purchasable under our Employee Stock Purchase Plan during the periods presented:



	Three months ended September 30,				Nine months ended September 30,
	2017		2016		2017		2016
Stock options
Risk-free interest rate	1.9	%	1.5	%	2.0	%	1.4	%
Volatility	89.5	%	80.0	%	89.4	%	79.9	%
Dividend yield	—		—		—		—
Expected term (years)	6.1		5.7		6.1		5.9
Performance stock options
Risk-free interest rate	—		—		2.1	%	1.4	%
Volatility	—		—		89.9	%	79.3	%
Dividend yield	—		—		—		—
Expected term (years)	0		0		5.6		6.0
Employee stock purchase plan shares
Risk-free interest rate	1.0	%	0.5	%	0.8	%	0.5	%
Volatility	104.5	%	94.5	%	110.7	%	85.4	%
Dividend yield	—		—		—		—
Expected term (years)	0.5		0.5		0.5		0.5

The following table summarizes the allocation of our stock-based compensation expense for all stock awards during the periods presented, including the adjustments to stock-based compensation expense associated with our May 2017 corporate restructuring (in thousands):



	Three months ended September 30,				Nine months ended September 30,
	2017		2016		2017			2016
Research and development	$	653	$	1,199	$	2,411		$	3,931
Research and development-restructuring related adjustments	—		—		(1,399		)	—
General and administrative	631		2,268		2,840			5,522
General and administrative-restructuring related adjustments	—		—		2,679			—
Total	$	1,284	$	3,467	$	6,531		$	9,453

In connection with our May 2017 corporate restructuring we recorded a reversal of stock-based compensation in research and development expenses of $1.4 million as a result of the cancellation of unvested stock options. Additionally, we recorded additional stock-based compensation in general and administrative expenses of $2.7 million as a result of termination provisions within certain employment agreements. These amounts were recorded in the second quarter of 2017.

Public Offering

In July 2017, we completed an underwritten public offering of 50,600,000 shares of common stock at an offering price of $0.91 per share. We received net proceeds from the offering of $43.0 million after deducting underwriting discounts, commissions and other offering expenses payable by us.