Merrimack Initiates Phase 1 Clinical Study of MM-398 in Combination With Cyclophosphamide for Pediatric Solid Tumors

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CAMBRIDGE, Mass., Jan. 23, 2014 (GLOBE NEWSWIRE) -- Merrimack Pharmaceuticals, Inc. (Nasdaq:MACK) today announced enrollment of its first patient in a Phase 1 dose-escalating clinical study of MM-398 in conjunction with cyclophosphamide for the treatment of pediatric solid tumors. MM-398 is a stable nanoliposomal irinotecan that is designed to exploit leaky tumor vasculature for enhanced drug delivery to tumors.

"Our preclinical research suggests that MM-398 accumulates particularly well in Ewing's sarcoma tumors," said Jonathan Fitzgerald, PhD, MM-398 Senior Director at Merrimack.

Preclinical research indicates that MM-398 administration results in delivery to the tumor of larger quantities of chemotherapy that are sustained for longer time periods compared with conventional chemotherapy administration. These effects may be applicable across other types of pediatric solid tumors. The most common forms of pediatric solid tumors include Ewing's sarcoma, rhabdomyosarcoma, neuroblastoma, and osteosarcoma.

"We are encouraged by the sensitivity of Ewing's sarcoma tumors to MM-398 that has been demonstrated in the laboratory setting. We are hopeful that the clinical results will mirror what we have seen in the preclinical studies," said C Patrick Reynolds, MD, PhD, Director of the Texas Tech University Health Sciences Center School of Medicine Cancer Center and of the South Plains Oncology Consortium.

This Phase 1 study will assess the safety of MM-398 in combination with cyclophosphamide in patients with recurrent or refractory pediatric solid tumors and will seek to determine the recommended Phase 2 dose. The trial will be sponsored by the South Plains Oncology Consortium and will be executed by participating institutions. Approximately 40 patients from 1 to 21 years old are expected to be enrolled. The first patient was dosed at the University of Texas Southwestern Medical Center.

About Ewing's Sarcoma

Ewing's sarcoma is an aggressive bone cancer primarily affecting children and adolescents, and is caused by the activation of the EWS gene due to a translocation between chromosomes 11 and 22.1 There is currently no known risk factor or prevention for this disease.2 Treatment includes multidrug chemotherapy and surgical resection, with radiation when necessary.3 Metastatic Ewing's sarcoma is often seen at the time of diagnosis, and occurs in approximately 25% of patients.4 While the outlook for patients with localized tumors is encouraging, with a five-year survival rate of approximately 60%-70%, outcomes for patients with metastatic tumors remain poor, with a five-year survival rate of approximately 20-30%.5

About MM-398

MM-398 is a stable nanoliposomal irinotecan, designed to optimize the delivery of irinotecan by extending the duration of circulation in the body and preferentially activating the drug within the tumor to achieve higher levels of the active cytotoxic, SN-38. MM-398 is being evaluated in several clinical trials including a Phase 3 study in metastatic pancreatic cancer, a Phase 2 study in patients with metastatic colorectal cancer and a Phase 1 cross indication translational study. MM-398 is not approved for any indication by the FDA or any other regulatory agency. Under a 2011 agreement with PharmaEngine, Inc. (Taipei, Taiwan), Merrimack consolidated the worldwide development and commercialization rights to MM-398, with the exception of commercialization rights in Taiwan which are held by PharmaEngine, Inc.

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 applies its systems biology-based approach to biomedical research throughout the research and development process. Merrimack currently has six oncology therapeutics in clinical development. For more information, please visit Merrimack's website at

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 for MM-398 to provide clinical benefit, the timing for enrollment of clinical studies, and the likelihood of conducting follow-on clinical studies. 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 8, 2013 and other reports Merrimack files with the SEC.

1 Sorensen et al. A second Ewing's sarcoma translocation, t(21;22), fuses the EWS gene to another ETS-family transcription factor, ERG. Nat Genet. 1994 Feb;6(2):146-51.

2 "Childhood Ewing Sarcoma." Dana-Farber Cancer Institute. Web.

3 "Ewing Sarcoma Treatment - Treatment Option Overview." National Cancer Institute. National Institutes of Health, 18 October 2013. Web.

4 Esiashvili et al. Changes in incidence and survival of Ewing sarcoma patients over the past 3 decades: Surveillance Epidemiology and End Results data. J Pediatr Hematol Oncol 30 (6): 425-30, 2008.

5 Elomaa et al. Five-year results in Ewing's sarcoma. The Scandinavian Group experience with the SSG IX protocol. Eur J Cancer. 2000 May;36(7):875-80.

CONTACT: Media Contacts: Dana Robie, Merrimack 617-441-7408 Heather Gitlitz, Spectrum 202-955-6222

Source:Merrimack Pharmaceuticals