9. STOCKHOLDERS’ EQUITY

Preferred Stock

We are authorized to issue 10,000,000 shares of preferred stock. As of December 31, 2017 and 2016, there were no issued and outstanding shares of preferred stock. Our board of directors is authorized to fix or alter the designation, powers, preferences and rights of the shares of each series of preferred shares, and the qualifications, limitations or restrictions of any wholly unissued shares, to establish from time to time the number of shares constituting any such series, and to increase or decrease the number of shares, if any.

Controlled Equity Offering

In August 2015, we entered into a Controlled Equity OfferingSM Sales Agreement (Original Sales Agreement) with Cantor Fitzgerald & Co. (Cantor), as sales agent, pursuant to which we may sell, through Cantor, up to an aggregate of $30.0 million in shares of our common stock. As of December 31, 2016, 9,617,875 shares of our common stock had been issued under the Original Sales Agreement with aggregate gross proceeds of $30.0 million. As of December 31, 2016, there are no amounts remaining for future sales under the Original Sales Agreement. In May 2017, we entered into an Amendment No. 1 (Amended Sales Agreement) to the Controlled Equity OfferingSM Sales Agreement pursuant to which we may offer and sell, through Cantor, additional shares of our common stock, up to an aggregate offering price of $40.0 million.  These shares are in addition to the shares of common stock sold under the Original Sales Agreement. During the year ended December 31, 2017, 2,166,093 shares of common stock were sold under the Amended Sales Agreement, with an aggregate net proceeds of $5.7 million. In October 2017, we terminated the Amended Sales Agreement with Cantor.

All sales of our common stock were made pursuant to a shelf registration statement filed by us in May 2015 and declared effective by the Securities and Exchange Commission (SEC) in July 2015. Cantor acted as our sole sales agent for all sales made under the Amended Sales Agreement for a low single-digit commission on gross proceeds. The common stock was sold at prevailing market prices at the time of the sale.

Underwritten Public Offerings

In February 2017, we completed an underwritten public offering in which we sold 23,000,000 shares of our common stock pursuant to an effective registration statement at a price to the public of $2.00 per share. We received proceeds of approximately $43.0 million, net of underwriting discounts and commissions and offering expenses payable by us. In October 2017, we completed another underwritten public offering in which we sold 20,815,000 shares of our common stock pursuant to an effective registration statement at a price to the public of $3.35 per share. We received proceeds of approximately $65.3 million, net of underwriting discounts and commissions and offering expenses payable by us.