Pre-funded warrants to purchase up to 15,816,327 shares of our common stock. Each pre-funded warrant will have an exercise price of $0.01 per share, will be exercisable upon issuance and will expire seven years from the date of issuance. In addition, at any time after the second anniversary of the original date of issuance, we may redeem the pre-funded warrants for $0.01 per share of common stock issuable on exercise of the pre-funded warrants following notice to the holder thereof if the closing price of our common stock for 20 or more trading days in a period of 30 consecutive trading days is greater than or equal to $2.80 (subject to adjustment).

Pre-funded warrants are being offered to those purchasers, whose purchase of shares of common stock in this offering would result in the purchaser, together with its affiliates and certain related parties, beneficially owning more than 9.9% of our outstanding common stock following the consummation of this offering. In lieu of the shares of our common stock that would result in ownership in excess of 9.9%, such purchasers are purchasing warrants to purchase such excess shares of our common stock.

45,142,969 shares of common stock, which is based on 27,642,969 shares outstanding as of December 31, 2012, and excludes:

•     5,657,256 shares of common stock issuable upon exercise of stock options outstanding as of December 31, 2012, at a weighted-average exercise price of $4.96 per share;

•     2,413,469 shares of common stock reserved as of December 31, 2012 for future issuance under our equity incentive plans;

•     1,926 shares of common stock reserved as of December 31, 2012 for issuance upon any conversion of our outstanding Series A convertible preferred stock, or Series A preferred stock;

•     6,266,175 shares of common stock reserved as of December 31, 2012 for issuance upon any conversion of our outstanding Series D redeemable convertible preferred stock, or Series D preferred stock;

•     8,484,840 shares of common stock reserved as of December 31, 2012 for issuance upon any conversion of our outstanding Series E convertible preferred stock, or Series E preferred stock; and

•     12,923,892 shares of common stock issuable upon exercise of warrants outstanding as of December 31, 2012, at a weighted average exercise price of $1.24 per share.