CAMBRIDGE, Mass., Dec. 13, 2013 (GLOBE NEWSWIRE) -- Merrimack Pharmaceuticals, Inc. (Nasdaq:MACK) today announced Phase 1 clinical trial results for MM-302, a novel HER2-targeted liposomal doxorubicin for the treatment of advanced HER2-positive breast cancer. Primary objectives for the trial are to assess the safety of MM-302 as a monotherapy and in combination with trastuzumab, as well as to determine the Phase 2 dose for MM-302. Data were presented at the 2013 San Antonio Breast Cancer Symposium, Dec. 10-14, 2013 in San Antonio, Texas. Anthracyclines, particularly doxorubicin, have been an effective component of breast cancer treatment for decades, though their use is ultimately limited by cardiac toxicity. These cardiotoxic effects limit the use of traditional anthracyclines in combination with targeted therapies, such as trastuzumab, for treatment of HER2-positive breast cancer. MM-302 is specifically designed to address this issue by delivering doxorubicin to tumor cells overexpressing HER2, while minimizing uptake into normal cells, including those of the heart. In this ongoing Phase 1 study, patients treated with MM-302 showed no signs of clinical decline in cardiac function. The most common adverse events were fatigue, nausea and decreased appetite; the rates of these events were consistent across MM-302 as a monotherapy and in combination with trastuzumab. Results from the trial also showed that patients treated with MM-302 as a monotherapy at doses of 30, 40 and 50 mg/m 2 had an estimated progression free survival (PFS) of 5.6 months (95% CI: 2.8-10.9 months) and a clinical benefit response rate of 37%. Of note, 5 of 9 patients who had not been previously treated with anthracyclines had a PFS of greater than 9 months. "We are pleased with the data for this trial and the preliminary safety profile for MM-302, particularly in regards to cardiac toxicity," said Ulrik Nielsen, Chief Scientific Officer at Merrimack. "These results are encouraging for the development of our nanoliposomal technology platform, and an important step towards successfully establishing the safety and activity profile of MM-302 in the HER2-positive breast cancer population."