Merrimack to discontinue development of MM-310

Merrimack announced the company is discontinuing development of MM-310, its antibody-directed nanotherapeutic for the treatment of solid tumors. This decision was the result of a comprehensive review of available safety data from its Phase 1 study. Based on emerging data since the recent amendment of the clinical protocol, the company has concluded that the study would not be able to reach an optimal therapeutic index for MM-310. Merrimack has terminated the study and expects to initiate a workforce reduction as it closes out clinical activities, reflective of its narrowed preclinical pipeline and in line with prior cost-cutting measures. “We are disappointed that amending the trial protocol does not appear to have solved the cumulative toxicity observed in patients treated with MM-310,” said Sergio Santillana, M.D., M.Sc., Chief Medical Officer of Merrimack. “However, we are grateful to our investigators and patients for their commitment to cancer research, and to our team for all their efforts in supporting the development and clinical evaluation of MM-310.” “Due to our ongoing exploration of strategic alternatives and given these unfortunate challenges in identifying a clinically meaningful safety profile for MM-310, we have decided to halt further development of the program,” said Richard Peters, M.D., Ph.D., President & Chief Executive Officer of Merrimack. “Additionally, as we have narrowed the scope of our pipeline to our two most promising preclinical programs, MM-401 and MM-201, we are initiating steps to close out remaining clinical activities in order to further preserve our resources. We continue to prudently advance these programs as we work expeditiously to bring our ongoing strategic process to conclusion.” In November, Merrimack announced the observation of emerging cumulative grade 3 peripheral neuropathy in three solid tumor patients following multiple cycles of treatment with MM-310 and amended the clinical protocol to extend the dosing schedule from an every three week to an every four week regimen, tightened inclusion and exclusion criteria and implemented proactive dose-reduction rules at the first signs of peripheral neuropathy. Despite the amended protocol, emerging data show MM-310 administered every four weeks continues to result in significant cumulative peripheral neuropathy, which precludes the study from reaching an optimal therapeutic index for MM-310. Merrimack plans to work swiftly to close out clinical activities and carry out associated cost-cutting measures and expects to provide an update on these efforts with its first quarter 2019 financial results. Additionally, in light of its ongoing strategic process, the Company continues to prudently advance its preclinical immuno-oncology pipeline: MM-401, an agonistic antibody targeting a novel immuno-oncology target, TNFR2; and MM-201, a highly stabilized agonist-Fc fusion protein targeting death receptors 4 and 5. Encouraging data from both programs were presented at the American Association for Cancer Research Annual Meeting held March 29 – April 3 in Atlanta, GA.
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