CAMBRIDGE, Mass., June 4, 2013 /PRNewswire-USNewswire/ -- Merrimack Pharmaceuticals, Inc. (NASDAQ: MACK) today announced results from a Phase 1 clinical study that indicate the novel antibody MM-121 can be combined with standard doses of certain cytotoxic agents for investigation as treatment for patients with advanced solid tumors. The research was presented at the 2013 American Society of Clinical Oncology Annual Meeting in Chicago, IL, May 31 – June 4, 2013. The Phase 1 study of 43 patients with advanced solid tumors established that MM-121 can be combined at its recommended single agent dose with gemcitabine, pemetrexed, cabazitaxel or carboplatin. MM-121 is a fully human monoclonal antibody that targets ErbB3, a cell surface receptor implicated in tumor growth and survival across multiple malignancies. Preclinical research in several model systems has shown that by inhibiting ErbB3 signaling, MM-121 may restore sensitivity, delay resistance and enhance the effect of certain cytotoxic agents as a combination therapy. "These data serve as the foundation for moving MM-121 into potential Phase 2 studies in combination with these chemotherapy agents in certain tumor types," said Akos Czibere, MD, Ph.D., Senior Medical Director of the MM-121 program at Merrimack. "MM-121 has the potential to complement the impact of several existing standard-of-care therapies and we look forward to further exploring its promise." Sanofi and Merrimack entered into an exclusive, global license and collaboration agreement for MM-121 in 2009. Study Methodology & ResultsAbstract Number: 2609 Abstract Title: A phase I study of MM-121 in combination with multiple anticancer therapies in patients with advanced solid tumors. Session Title: General Poster Session: Developmental Therapeutics - Clinical Pharmacology and Experimental Therapeutics Presenter: Monica Arnedos, MD, Institut Gustave Roussy, Paris, France In studying the safety of MM-121 in combination with gemcitabine (Arm A), carboplatin (Arm B), pemetrexed (Arm C) and cabazitaxel (Arm D) for subjects with advanced cancer, patients were treated in a dose escalation "3+3" design. MM-121 was administered weekly in combination with these cytotoxic agents to assess the safety, tolerability and pharmacokinetics of the antibody. Doses were escalated until the maximum tolerated dose (MTD) was identified and/or the combination was shown to be tolerable at the highest planned doses. Secondary objectives included determining the objective response rate, clinical benefit rate, pharmacokinetics and immunogenicity of MM-121. No MTD was identified for the combination of MM-121 and standard doses of gemcitabine, pemetrexed and cabazitaxel; a MTD of carboplatin (AUC 5) was identified in combination with the recommended dose of MM-121 (40 mg/kg loading, followed by 20 mg/kg weekly maintenance). The two dose limiting toxicities observed in combination with carboplatin were one grade 3-4 prolonged thrombocytopenia and one grade 3 maculopapular rash.