“At the Market” Equity Offering Program

From April 1, 2014 through the date of this free writing prospectus, we have offered and sold 809,214 shares of our common stock pursuant to our At-the-Market Issuance Sales Agreement with MLV & Co. LLC. These sales resulted in net proceeds to us of approximately $2.9 million. Prior to these sales, we had not made any sales under this “at the market” equity offering program, and, as the date of this free writing prospectus, shares of our common stock having an aggregate value of approximately $22.0 million remained available for sale under this offering program.

Based on our current expectations and operating plans, and before giving effect to the receipt of net proceeds from this offering, we believe that our cash, cash equivalents, short-term investments and receivables from our collaboration arrangement with Teva Pharmaceutical Industries Ltd. will be sufficient to fund our current planned operations into the third quarter of 2015.

Borealis 1 Phase 2 Trial

Our Borealis 1 Phase 2 trial in first-line metastatic bladder cancer was fully enrolled in July 2013. As a result of death events occurring more slowly than previously expected, the anticipated timing of the pre-specified number of events is currently projected to occur in the fourth quarter of 2014. These survival results are expected to be announced in first quarter of 2015. No conclusion regarding the possible outcome of the trial can or should be drawn from the fact that death events have occurred more slowly than expected.

20,313,061 shares, which is based on 14,753,195 shares of common stock outstanding as of March 31, 2014 and excludes:

•       809,214 shares of our common stock sold after March 31, 2014 pursuant to our “at the market” equity offering program;

•       1,257,088 shares of common stock issuable upon the exercise of options outstanding as of March 31, 2014, at a weighted average exercise price of $11.47 per share;

•       25,000 shares of common stock issuable upon the exercise of options granted after March 31, 2014, with an exercise price of $3.62 per share;

•       557,149 shares of common stock subject to restricted stock units outstanding as of March 31, 2014;

•       472,000 shares of common stock subject to restricted stock units granted after March 31, 2014;

•       1,587,301 shares of common stock issuable upon the exercise of warrants outstanding as of March 31, 2014, with an exercise price of $20.00 per share;

•       521,311 shares of common stock reserved for future issuance under our 2010 Performance Incentive Plan as of March 31, 2014;

•       750,000 shares of common stock reserved for future issuance under our 2010 Performance Incentive Plan after March 31, 2014;

•       2,779,933 shares of common stock issuable upon exercise of the Series A warrants;

•       1,340,538 shares of common stock issuable upon exercise of the Pre-Funded Series B warrants; and

•       670,269 shares of common stock issuable upon exercise of the Series B warrants.

The underwriter will require all of our directors, executive officers and a consultant to agree not to offer, sell, agree to sell, directly or indirectly, or otherwise dispose of any shares of common stock or any securities convertible into or exchangeable for shares of common stock, subject to certain exceptions, without the prior written consent of Stifel, Nicolaus & Company, Incorporated for a period of 90 days after the date of this prospectus supplement. Notwithstanding the foregoing, if (a) during the last 17 days of this 90-day period, we release or publish financial results or results from operations or announce material news or a material event or (b) prior to the expiration of this 90-day period, we announce that we will release or publish financial results or results from operations during the 15-day period following the last day of the 90-day period, then in each case the above restrictions will be automatically extended until the expiration of the 18-day period beginning on the date of release of the earnings results or the announcement of the material news or material event, as applicable, subject to certain exceptions, unless Stifel, Nicolaus & Company, Incorporated waives, in writing, such extension.

Subject to certain exceptions, we have agreed that for a period of 90 days after the date of this prospectus supplement, subject to extension as described above, we will not, without the prior written consent of Stifel, Nicolaus & Company, Incorporated, offer, sell, contract to sell or otherwise dispose of any shares of common stock, including any sales under our “at the market” equity offering program, or any securities that are substantially similar to the common stock, including any securities that are convertible into or exchangeable for, or that represent the right to receive, shares of common stock or any such substantially similar securities, except for:

•       the securities offered in this offering;

•       the shares of common stock issuable upon conversion or exercise of convertible or exercisable securities outstanding on the date of this prospectus supplement; and

•       the shares of our common stock that are issued under our existing equity incentive plans.