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Merrimack Pharmaceuticals Announces Initiation of a Phase 2 Biomarker-Selected Clinical Trial of MM-121 in Patients with Heregulin Positive Non-Small Cell Lung Cancer

Trial is recruiting biomarker-selected patients previously treated with two lines of therapy for locally advanced or metastatic disease

Merrimack's first study to prospectively select patients based on heregulin status

CAMBRIDGE, Mass., Feb. 19, 2015 (GLOBE NEWSWIRE) -- Merrimack Pharmaceuticals, Inc. (Nasdaq:MACK) today announced the initiation of a global, open-label, biomarker-selected, randomized Phase 2 clinical trial of MM-121, a fully human monoclonal antibody targeting ErbB3, in combination with docetaxel or pemetrexed versus docetaxel or pemetrexed alone in patients with heregulin positive, locally advanced or metastatic non-small cell lung cancer.

"This marks the first MM-121 trial we've initiated where only patients with a high heregulin biomarker profile will be enrolled into the study. It builds on our learnings from the previous MM-121 Phase 2 clinical trials we completed across lung, ovarian and breast cancers where we saw a clear trend of patients in those studies with this biomarker profile benefitting from combining MM-121 with standard therapies," said Akos Czibere, MD, PhD, MM-121 Global Development Lead at Merrimack. "This study is a significant step toward preparing a registration trial of MM-121 in non-small cell lung cancer, and further supports Merrimack's systems biology approach and its impact on drug discovery and development. We look forward to applying our clinical biomarker findings to future studies with MM-121 and ultimately improving outcomes in patients who no longer respond to standard-of-care therapies."

MM-121 is Merrimack's wholly owned, fully human monoclonal antibody that targets ErbB3, a cell surface receptor that is activated by the ligand heregulin. Heregulin-driven ErbB3 signaling has been implicated as a mechanism of tumor growth and resistance to targeted, cytotoxic and anti-endocrine therapies. When used in the combination setting, MM-121 is designed to block ErbB3 signaling in order to enhance the anti-tumor effect of a combination therapy partner. Merrimack is pursuing this study based on encouraging results from a broad MM-121 Phase 2 program which identified high heregulin levels as a potential prognostic factor of poor response to standard-of-care therapy across multiple cancers. The results also showed that patients with heregulin-high tumors experienced a longer time to progression when they received a combination of MM-121 with their standard-of-care therapy as compared to patients who received the standard therapy alone. Across the three different standard-of-care combination regimens, a consistent safety profile demonstrated a modest yet tolerable increase in adverse events.

As part of this trial, Merrimack expects to enroll approximately 120 heregulin positive patients that will be randomized (2:1) to receive either 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 trial must have failed prior treatment with no more than two lines of therapy for locally advanced or metastatic disease. The primary endpoint of the trial is progression free survival (PFS). Secondary endpoints include overall survival, objective response rate, safety and tolerability. Merrimack plans to conduct the trial at sites in the United States, Canada and Europe. Initial trial sites located at the Horizon Oncology Center in Lafayette, Indiana and Northwestern Medicine Developmental Therapeutics Institute in Chicago, Illinois are now open to screen patients in the United States. For more information on this trial, please visit www.clinicaltrials.gov.

Merrimack regained worldwide rights to MM-121 in 2014 and is pursuing a partnership to accelerate the development of the program.

About MM-121

MM-121 is a fully human monoclonal antibody that targets ErbB3, a cell surface receptor that is activated by the ligand heregulin. Heregulin-driven ErbB3 signaling has been implicated as a mechanism of tumor growth and resistance to targeted, cytotoxic and anti-endocrine therapies. When used in the combination setting, MM-121 is designed to block ErbB3 signaling in order to restore or enhance the anti-tumor effect of a combination therapy partner.

MM-121 has been investigated in four Phase 2 and six Phase 1 clinical trials covering a broad spectrum of patient populations and drug combinations. An extensive translational component of the MM-121 clinical program was designed to establish clinically meaningful biomarkers that were initially identified using Merrimack's systems biology approach and confirmed in preclinical studies.

About Merrimack

Merrimack is a biopharmaceutical company discovering, developing and preparing to commercialize innovative medicines paired with companion diagnostics for the treatment of cancer. Merrimack seeks to gain a deeper understanding of underlying cancer biology through its systems biology-based approach and develop new insights, therapeutics and diagnostics to improve outcomes for cancer patients. Merrimack currently has six oncology therapeutics in clinical development and three additional candidates in late stage preclinical development. Merrimack's lead product candidate, MM-398, recently completed a Phase 3 clinical trial in post-gemcitabine pancreatic cancer. Based on the results of this clinical trial, Merrimack is currently preparing a New Drug Application for MM-398. For more information, please visit Merrimack's website at www.merrimackpharma.com or connect on Twitter at @MerrimackPharma.

Forward-Looking Statements

To the extent that statements contained in this press release are not descriptions of historical facts, they are forward-looking statements reflecting the current beliefs and expectations of management made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995, as amended. Forward-looking statements include any statements about Merrimack's strategy, future operations, future financial position and future expectations and plans and prospects for Merrimack, and any other statements containing the words "anticipate," "believe," "estimate," "expect," "intend," "may," "plan," "predict," "project," "target," "potential," "will," "would," "could," "should," "continue," "hope" and similar expressions. In this press release, Merrimack's forward-looking statements include statements about the potential effectiveness and safety profile of MM-121 in certain patient populations or subpopulations, its ability to use heregulin as a predictive diagnostic, the initiation of future clinical trials and its ability to translate clinical data into future clinical success. Such forward-looking statements involve substantial risks and uncertainties that could cause Merrimack's clinical development programs, future results, performance or achievements to differ significantly from those expressed or implied by the forward-looking statements. Such risks and uncertainties include, among others, availability of data from ongoing clinical trials, expectations for regulatory approvals, development progress of Merrimack's companion diagnostics and other matters that could affect the availability or commercial potential of Merrimack's drug candidates or companion diagnostics. Merrimack undertakes no obligation to update or revise any forward-looking statements. Forward-looking statements should not be relied upon as representing Merrimack's views as of any date subsequent to the date hereof. For a further description of the risks and uncertainties that could cause actual results to differ from those expressed in these forward-looking statements, as well as risks relating to Merrimack's business in general, see the "Risk Factors" section of Merrimack's Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission (SEC) on November 10, 2014 and other reports Merrimack files with the SEC.

CONTACT: Media Contacts: Dana Robie Merrimack 617-441-7408 drobie@merrimackpharma.com Liz Bryan Spectrum 202-955-6222 lbryan@spectrumscience.com Investor Contact: Geoffrey Grande, CFA Merrimack 617-441-7602 ggrande@merrimackpharma.com

Source:Merrimack Pharmaceuticals