Epizyme Initiates Pediatric MLL-r Proof-of-Concept Study for EPZ-5676

First-in-class DOT1L Inhibitor in Clinical Development as Potential Personalized Therapeutic for Patients with Genetically Defined Acute Leukemias

Cambridge, MA — Epizyme, Inc., a clinical stage biopharmaceutical company creating innovative personalized therapeutics for patients with genetically defined cancers, today announced the initiation of a Phase 1b open-label clinical study of EPZ-5676 in pediatric patients with acute leukemias bearing a rearrangement of the MLL gene (MLL-r). This Phase 1b study is designed to evaluate the safety, pharmacokinetics, and pharmacodynamics of escalating doses of EPZ-5676 in patients between the ages of 3 months and 18 years and to provide a preliminary assessment of efficacy. Including this study, Epizyme now has ongoing assessments of proof-of-concept (POC) in three genetically defined cancer patient groups in the EPZ-5676 clinical program (MLL-r adults, MLL-PTD, and MLL-r pediatrics) with expected data disclosures in the second half of 2014.

“Acute leukemias with MLL-r affect young children and are one of the last remaining forms of childhood leukemia with inadequate treatment options,” said Eric Hedrick, M.D., Chief Medical Officer, Epizyme. “Children who are afflicted with this genetically defined cancer have an extremely poor prognosis, especially in comparison to pediatric leukemias without the MLL rearrangement. This pediatric clinical study of EPZ-5676 is an important complement to our ongoing adult studies and reflects our commitment to developing personalized treatments for patients with genetically defined cancers.”

“While there has been tremendous progress in improving outcomes for pediatric patients with acute leukemia, patients with MLL-r, a genetically defined leukemia, still present a considerable challenge and a significant area of unmet need,” said Lee Greenberger, Ph.D., Chief Scientific Officer, The Leukemia & Lymphoma Society. “We invested in the pre-clinical development of Epizyme’s DOT1L inhibitor and applaud Epizyme’s efforts as they develop targeted therapies to treat leukemia patients of all ages.”

Epizyme is currently enrolling adult MLL-r and MLL-PTD acute leukemia patients in the expansion stage of the adult EPZ-5676 Phase 1 study. In January 2014, Epizyme announced the achievement of a $25 million clinical proof-of-concept milestone in their Celgene collaboration with objective responses observed in two adult MLL-r patients in the fourth cohort of the dose escalation stage of the Phase 1 study, which completed enrollment in December 2013. Epizyme plans to disclose data from the adult Phase 1 dose escalation and expansion stage study for EPZ-5676 in the second half of 2014.

About EPZ-5676 Epizyme is developing EPZ-5676, a small molecule inhibitor of DOT1L created with Epizyme’s proprietary product platform, for the treatment of patients with acute leukemia in which the MLL gene is rearranged due to a chromosomal translocation (MLL-r) or a partial tandem duplication (MLL-PTD). Due to these rearrangements, DOT1L is misregulated, resulting in the increased expression of genes causing leukemia.

Epizyme believes that EPZ-5676 was the first HMT inhibitor to enter human clinical development. Epizyme is currently conducting a two-stage Phase 1 study in adult MLL-r and MLL-PTD patients and in May 2014, initiated a Phase 1b study of EPZ-5676 in pediatric patients with rearrangements of the MLL gene. The adult dose escalation stage has completed enrollment, and the adult MLL-r and MLL-PTD expansion stage is now enrolling patients.

EPZ-5676 has been granted orphan drug designation for the treatment of acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) by the Food and Drug Administration in the U.S. and by the European Commission in Europe.

Epizyme retains all U.S. rights to EPZ-5676 and has granted Celgene an exclusive license to EPZ-5676 outside of the U.S. Epizyme is working with Abbott to develop a companion diagnostic to identify patients with the MLL-r genetic alteration targeted by EPZ-5676.

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