Merrimack initiates dosing in MM-111 combination Phase 1 study in advanced HER2 positive patients

Merrimack Pharmaceuticals, Inc. announced today that five patients have received therapy in a Phase I clinical study combining MM-111 with multiple standard treatment regimens for patients with advanced HER2 positive (HER2+) solid tumors.

MM-111 is a bi-specific antibody that targets tumor cells over-expressing ErbB2/HER2. MM-111 is designed to inhibit the signaling between ErbB2/HER2 and ErbB3/HER3 thus disabling downstream signaling, including the phosphatidylinositol 3-kinase (PI3K) pathway, and preventing tumor proliferation. In this study, Merrimack is evaluating whether MM-111 could be safely added to standard therapies used to treat HER2 positive cancers. The study could also provide preliminary evidence of activity in patients with advanced/metastatic HER2 positive disease, an area of high unmet medical need for which there are limited treatment options.

"HER2 positive cancers are historically more aggressive and carry a poorer prognosis than other types of solid tumors," says Clet Niyikiza, Ph.D., Executive Vice President of Development, Merrimack Pharmaceuticals. "Patients with HER2 positive metastatic cancer eventually progress or are intolerant of current approved regimens. Close to half of the patients treated with such regimens fail to respond."

The Phase 1 study will evaluate the human safety and pharmacokinetics of MM-111 when administered in combination with either 1) cisplatin, capecitabine, and trastuzumab; 2) lapatinib and trastuzumab; or 3) paclitaxel and trastuzumab in patients with HER2 positive solid tumors. The study is being run in collaboration with US Oncology, a leading integrated oncology company that is affiliated with more than 1,400 physicians nationwide.

"Because ErbB3 activation has been indicated as a cause of resistance to current HER2 targeted treatments and chemotherapies, we plan to investigate MM-111 as a backbone combination therapy for patients with HER2 positive tumors," said Victor Moyo, M.D., Vice President of Clinical Investigations, Merrimack Pharmaceuticals.