| Offering | | Number of Shares Issuable Upon Exercise of Outstanding Warrants | | Exercise Price | | Expiration Date | | |
| | | | | | | | | |
| February 2013 Public Offering (1) | | 11,000,000 | | $ | 0.50 | | February 20, 2018 | |
| February 2013 Public Offering (1) (2) | | 5,500,000 | | $ | 0.50 | | February 20, 2014 | |
| February 2013 Public Offering – Placement Agents | | 770,000 | | $ | 0.625 | | February 4, 2018 | |
| November 2012 Private Placement | | 1,000,000 | | $ | 1.25 | | November 2, 2017 | |
| June 2012 Public Offering | | 2,981,440 | | $ | 1.25 | | June 13, 2017 | |
| December 2011 Underwritten Offering | | 9,248,334 | | $ | 0.60 | | December 6, 2016 | |
| April 2011 Private Placement | | 6,058,811 | | $ | 0.75 | | March 31, 2016 | |
| Legacy warrants (1) | | 27,310 | | $ | 0.50 | | July 27, 2015 | |
| Legacy warrants | | 105,040 | | $ | 16.065 | | July 27, 2015 | |
| Legacy warrants | | 91,524 | | $ | 99.45-100.98 | | December 31, 2015 | |
| | | | | | | | | |
| Total | | 36,782,459 | | | | | | |
| (1) | The exercise prices of these warrants are subject to adjustment for “down-rounds” and the warrants have been accounted for as derivative instruments as described in Note 3. |
| (2) | On February 20, 2014, warrants to purchase 5,500,000 shares of common stock expired unexercised (see Note 17). |