Merrimack Pharmaceuticals to Regain Worldwide Rights to Develop and Commercialize MM-121

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| Source: Merrimack Pharmaceuticals

Merrimack to Pursue Registration Path for MM-121 and Partnership Opportunities

Top Line Results Released From Final Phase 2 Study in the Collaboration

CAMBRIDGE, Mass., June 19, 2014 (GLOBE NEWSWIRE) -- Merrimack Pharmaceuticals, Inc. (Nasdaq:MACK) today announced that it has reached an agreement with Sanofi to regain worldwide rights to develop and commercialize MM-121, a monoclonal antibody designed to block ErbB3 (HER3) activation in patients with heregulin-positive tumors and improve response to standard of care treatments.

In partnership with Sanofi, Merrimack completed an extensive Phase 2 program for MM-121 which was designed to assess the role of ErbB3 in a number of cancer indications in both the metastatic and neoadjuvant settings. In advanced settings of ovarian cancer, ER/PR+ HER2 negative breast cancer and non-small cell lung cancer, Merrimack was able to identify that heregulin, the principal ligand that binds to and activates the ErbB3 receptor, is associated with poor response to standard of care therapy and that adding MM-121 may restore sensitivity in these most at-risk patients. Consistent across three metastatic cancer indications with three different standard of care therapies, patients in these trials with heregulin-positive tumors experienced a statistically significant reduction in their risk of progression when they received a combination with MM-121. Heregulin-driven drug resistance pathways were found to be active in approximately 30-50 percent of patients tested. Data from these studies were recently presented at the 2014 American Society of Clinical Oncology (ASCO) Annual Meeting. To view the clinical posters presented at ASCO 2014, click here.

"We are grateful for Sanofi's support over the last five years and believe that the data generated through this partnership validate the potential for MM-121 to help patients most at risk for progression on current therapies. Regaining MM-121 is an opportunity to capitalize on our leadership position among the other oncology companies that are pursuing ErbB3," said Robert Mulroy, President and CEO at Merrimack. "With these data and the feedback we've received from our committed investigators, we believe MM-121 has the potential to be a foundational therapy for use across multiple solid tumor types and we plan to continue its development through subsequent strategic partnerships. Our next step is to discuss our Phase 2 data and potential registration paths with the FDA."

Sanofi will continue to fund the existing MM-121 Phase 2 program for the next six months. The neoadjuvant cohort of a Phase 2 study testing MM-121 in combination with paclitaxel in patients with triple negative breast cancer is the final study to be completed through this collaboration. Top line results of that study are below.

Results from the Second Cohort of a Phase 2 Study of MM-121 in Combination with Paclitaxel in Neoadjuvant Breast Cancer

Merrimack and Sanofi completed a randomized (2:1), exploratory Phase 2 study testing MM-121 in combination with paclitaxel followed by doxorubicin and cyclophosphamide. The study was conducted in two populations of patients with either ER/PR positive (ER/PR+) HER2 negative breast cancer (n=101) or triple negative breast cancer (TNBC) (n=99). There was no formal quantitative endpoint specified for this study.

In November 2013, Merrimack released initial top line results from the ER/PR+ HER2 negative cohort. Those results demonstrated that patients who received the combination of MM-121 and paclitaxel achieved a pCR rate of 10.6% (95% CI [5.2; 20.3]) compared to 3.3% (95% CI [0.6; 16.7]) for the control arm.   Top line results from this second cohort of patients with TNBC showed that patients who received the combination of MM-121 and paclitaxel achieved a pCR rate of 42.9% (95% CI 30.8; 55.9) compared to 51.7 (95% CI 34.4; 68.6) for the control arm.  Translational analysis is ongoing for both cohorts and the full data set will be reported at a future medical conference. Preliminary analysis of approximately 50 percent of the pretreatment biopsies suggests a link between heregulin levels and pCR rates.

For the TNBC cohort, rates for serious adverse events were 28.1% vs. 15.6%, and rates for grade 3 or higher adverse events were 50.0% vs. 31.3% between the treatment and control arms, respectively.  As reported previously, in the ER/PR+ HER2 negative cohort, similar frequencies were reported for adverse events of any grade between the treatment and control arms, with no unexpected toxicities experienced and no increase in serious adverse events. Grade 3 or worse adverse events in the ER/PR+ HER2 negative cohort were 55.2% on treatment arm versus 53.1% on control arm.

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 studies 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 useful 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 program, MM-398, recently completed a Phase 3 trial in post-gemcitabine pancreatic cancer. Based on the results of this study, Merrimack intends to file a New Drug Application for MM-398 in 2014. For more information, please visit Merrimack's website at www.merrimackpharma.com.

Forward-Looking Statement

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 tolerability of MM-121 and its other therapeutics in certain patient populations or subpopulations, its ability to develop a predictive diagnostic, the initiation of future clinical studies, its ability to translate clinical data into future clinical success, discussions with and applications to regulatory authorities, and its ability to establish and maintain additional collaborations. 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 May 6, 2014 and other reports Merrimack files with the SEC.

Investor Contact:
Geoffrey Grande, CFA
Merrimack Pharmaceuticals
617-441-7602


Media Contacts:
Kathleen Gallagher
Merrimack Pharmaceuticals
617-441-1043


Heather Bonsiero
Spectrum
202-955-6222