9. STOCKHOLDERS’ EQUITY

Preferred Stock

We are authorized to issue 10,000,000 shares of preferred stock. As of December 31, 2015 and 2014, 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.

Warrants

In conjunction with the facilities lease entered into in May 2001, we issued a warrant to the lessor to purchase 16,666 shares of our common stock at an exercise price of $80.21 per share, a 15% premium to market at the time of issuance. This warrant expired unexercised in May 2006. The fair market value of this warrant, as determined using the Black‑Scholes valuation model, was approximately $683,000. This amount has been capitalized in other long‑term assets and is being amortized into expense over the life of the lease. As of December 31, 2015, approximately $58,000 remained to be amortized over the remaining term of the lease.

In conjunction with the facilities lease amendment in October 2002, we issued a warrant to the lessor to purchase 55,555 shares of our common stock at an exercise price of $17.73 per share. The warrant expired unexercised in October 2007. The fair value of this warrant, as determined using the Black‑Scholes valuation model, was approximately $565,000. This amount has been capitalized in other long‑term assets and is being amortized into expense over the life of the lease. As of December 31, 2015, approximately $48,000 remained to be amortized over the term of the lease.

In conjunction with the facilities lease amendment in July 2006, we issued a warrant to the lessor to purchase 100,000 shares of our common stock at an exercise price of $10.57 per share. The fair value of this warrant, as determined using the Black‑Scholes valuation model, was approximately $801,000. This amount has been included in other long‑term assets and is being amortized into expense over the term of the lease. As of December 31, 2015, approximately $88,000 remained to be amortized over the term of the lease. The lease agreement was further amended in March 2009. The lease amendment provided for the cancellation of the abovementioned warrant to purchase 100,000 shares of common stock and the issuance of a new warrant granting our landlord the right to purchase 200,000 shares of common stock. The exercise price per share of the new warrant is $6.61. The new warrant is outstanding as of December 31, 2015 and remains exercisable at any time up to February 2016. We applied modification accounting in 2009 and determined the fair value of this warrant using the Black‑Scholes valuation model. The incremental fair value of the new warrant as a result of the modification is $616,000. This amount has been included in other long‑term assets and is being amortized into expense over the term of the lease. As of December 31, 2015, approximately $89,000 remained to be amortized over the term of the lease.

As discussed in Note 8, as a result of the sublease agreement that we entered into in December 2014, we included approximately $265,000 representing the unamortized portion of the above fair value of warrants attributable to the sublet space in the determination of our loss on sublease during the year ended December 31, 2014.

Controlled Equity Offering

In August 2015, we entered into a Controlled Equity OfferingSM Sales Agreement with 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. All sales of our common stock will be made pursuant to a shelf registration statement that was declared effective by the Securities and Exchange Commission (SEC) on July 13, 2015. Cantor is acting as our sole sales agent for any sales made under the Sales Agreement for a low single-digit commission on gross proceeds. The common stock is being sold at prevailing market prices at the time of the sale. Unless otherwise terminated earlier, the Controlled Equity OfferingSM Sales Agreement continues until all shares available under the agreement have been sold. During the year ended December 31, 2015, approximately, 1,722,312 shares of our common stock were sold under the Sales Agreement with aggregate net proceeds of $5.5 million. At December 31, 2015, we had approximately $24.3 million in shares of our common stock registered for sale under the Sales Agreement.