Epizyme Earns $6 Million Milestone Payment from GlaxoSmithKline for Initiation of Clinical Development with First-in-Class PRMT5 Inhibitor

CAMBRIDGE, Mass., Sept. 15, 2016 -- Epizyme, Inc. (NASDAQ:EPZM), a clinical-stage biopharmaceutical company creating novel epigenetic therapeutics, today announced it has earned a $6 million milestone payment from GlaxoSmithKline (GSK). The milestone payment follows GSK’s initiation of patient dosing in a Phase 1 clinical trial of GSK3326595 (formerly EPZ015938), a first-in-class protein arginine methyltransferase-5 (PRMT5) inhibitor discovered by Epizyme and licensed to GSK. PRMT5 is a protein methyltransferase that is associated with a number of human cancers.

“Epizyme has pioneered the discovery and development of epigenetic therapies for the treatment of cancer, with three agents discovered by Epizyme now in clinical development,” said Robert Bazemore, President and Chief Executive Officer, Epizyme. “Our collaboration with GSK represents an important part of our strategy of partnering with industry leaders to extend the breadth of our epigenetic therapies while providing resources to help us accelerate our portfolio of assets. We look forward to GSK’s continued progress with this program.”

GSK has initiated a Phase 1, dose-escalation study to investigate the safety, pharmacokinetics, pharmacodynamics and clinical activity of GSK3326595 in patients with solid tumors and non-Hodgkin lymphoma.

“The introduction of this PRMT5 inhibitor into the clinic by GSK is an exciting scientific achievement for Epizyme,” said Robert A. Copeland, Ph.D., President of Research and Chief Scientific Officer, Epizyme. “This milestone reinforces the strength of our scientific capabilities, which have enabled us to expand our platform into new epigenetic target classes of potentially high importance in oncology. Through our collaborations with GSK and other biopharmaceutical companies, as well as our in-house research efforts, we have developed a number of novel epigenetic programs that we believe hold tremendous potential, including this first-in-class PRMT5 inhibitor.”

About the Epizyme-GSK Collaboration
Under the terms of its collaboration and license agreement with GSK, Epizyme granted GSK exclusive worldwide license rights to methyltransferase inhibitors directed to three targets. During the research term of the collaboration, Epizyme was primarily responsible for pre-clinical research, and now GSK is responsible for subsequent research, development and commercialization of the three programs. Using its proprietary drug discovery platform, Epizyme discovered and optimized compounds targeting three methyltransferases, including PRMT5. GSK3326595 is the first of these to enter the clinic. GSK holds worldwide rights to all three programs. Epizyme has earned $59 million in up-front, research, and milestone payments to date, and may receive up to an additional $617 million from GSK if all milestones are met for all three programs. Epizyme is eligible to receive up to double-digit royalties on worldwide net sales of collaboration products.

About PRMT5 and GSK3326595
PRMT5 is a protein arginine methyltransferase (PRMT) that is reported to have a role in diverse cellular processes, including tumorigenesis. PRMT5 overexpression is observed in cell lines and primary patient samples derived from a number of cancers, including lymphomas, lung cancer, breast cancer and colorectal cancer. GSK3326595 (formerly EPZ015938), a highly selective and orally bioavailable small molecule, is the first PRMT5 inhibitor and the third epigenetic investigational therapy derived from Epizyme’s proprietary discovery platform to enter the clinic.

About Epizyme, Inc.
Epizyme, Inc. is a clinical-stage biopharmaceutical company creating novel epigenetic therapeutics for people with cancer. Epizyme has built a proprietary product platform to create small molecule inhibitors of chromatin modifying proteins (CMPs), such as histone methyltransferases (HMTs). CMPs are part of the system of gene regulation, referred to as epigenetics, that controls gene expression. Genetic alterations can result in changes to the activity of CMPs, making them oncogenic (cancer-causing). By focusing on the genetic drivers of cancers, Epizyme's targeted science seeks to match the right medicines with the right patients. For more information, visit www.epizyme.com.

Cautionary Note on Forward-Looking Statements
Any statements in this press release about future expectations, plans and prospects for Epizyme, Inc. and other statements containing the words "anticipate," "believe," "estimate," "expect," "intend," "may," "plans," "predict," "project," "target," "potential," "will," "would," "could," "should," "continue," and similar expressions, constitute forward-looking statements within the meaning of The Private Securities Litigation Reform Act of 1995. Actual results may differ materially from those indicated by such forward-looking statements as a result of various important factors, including: uncertainties inherent in the initiation of future clinical studies, whether the Company’s collaborations such as its collaboration with GlaxoSmithKline will be successful, availability of funding sufficient for the Company’s foreseeable and unforeseeable operating expenses and capital expenditure requirements, other matters that could affect the availability or commercial potential of the Company’s therapeutic candidates or companion diagnostics and other factors discussed in the "Risk Factors" section of our Form 10-Q most recently filed with the SEC, and in our other filings from time to time with the SEC. In addition, the forward-looking statements included in this press release represent the Company's views as of the date hereof. The Company anticipates that subsequent events and developments will cause the Company's views to change. However, while the Company may elect to update these forward-looking statements at some point in the future, the Company specifically disclaims any obligation to do so. These forward-looking statements should not be relied upon as representing the Company's views as of any date subsequent to the date hereof.

Investors and Media Contact:
Julie DiCarlo
Epizyme, Inc. 
[email protected] 
(617) 401-0721