Merrimack Amends MM-121 Phase 2 Clinical Study in Heregulin-Positive Non-Small Cell Lung Cancer to Support Potential Registration

Merrimack Pharmaceuticals, Inc.

today announced it filed an amendment to its ongoing Phase 2 clinical study of MM-121 (seribantumab) in patients with heregulin-positive non-small cell lung cancer (NSCLC) with the U.S. Food and Drug Administration (FDA). The amendment includes a change in primary endpoint to overall survival to enable a potential registration opportunity for MM-121. "We believe MM-121 has the potential to address the pervasive clinical problem of resistance in cancer. This amendment is intended to accelerate development of this new treatment option for heregulin-positive non-small cell lung cancer patients who are resistant to standard-of-care therapies," said Robert Mulroy, Merrimack's President and CEO. "The financing we announced today will allow us to independently advance and retain sole ownership of MM-121. In light of this amendment, we are focusing the development of MM-121 on this indication." MM-121 is a fully human monoclonal antibody targeting ErbB3. The ongoing clinical study in NSCLC is an open-label, biomarker–selected randomized study of MM-121 in combination with docetaxel or pemetrexed compared to docetaxel or pemetrexed alone, in patients with heregulin-positive, locally advanced or metastatic NSCLC. Three prior Phase 2 clinical studies demonstrated that a subset of biomarker positive patients treated with MM-121 had a statically significant reduction in the risk of progression, with hazard ratios in a range of 0.26 – 0.37. "We are pleased with investigator enthusiasm for the trial, which highlights the high unmet medical need in metastatic non-small cell lung cancer. Consistent with our previous Phase 2 study, more than half of the patients screened to date have been biomarker positive," said Akos Czibere, M.D., Ph.D., MM-121 Global Development Lead at Merrimack. "Amending this study design is a significant step forward in the development path for MM-121 in non-small cell lung cancer, where there is an urgent need for novel, biomarker-directed therapies to help patients battle drug resistance. We look forward to advancing this therapy and providing a potential new treatment option for this patient population." Under the filed amendment, Merrimack expects to enroll approximately 280 heregulin-positive patients who will be randomized (2:1) to receive MM-121 plus the investigator's choice of docetaxel or pemetrexed, or the investigator's choice of docetaxel or pemetrexed alone. Eligible patients for the study must have failed prior treatment with no more than three lines of therapy for locally advanced or metastatic disease and, where applicable, prior PDL1 therapy. The amended primary endpoint of the study will be overall survival. Secondary endpoints include progression free survival, objective response rate, safety and quality of life measures. Merrimack continues to open study sites in the United States, Canada, Asia and Europe. With this updated study design, Merrimack expects survival data in 2018.