Dimension Therapeutics Announces Preclinical Data Supporting Ongoing DTX101 Phase 1/2 Clinical Trial at American Society for Gene and Cell Therapy (ASGCT) Annual Meeting

Findings Demonstrated Dose-Dependent Durable Gene Expression, and No Apparent Safety Issues Across the Dose Range Tested

Topline Data from First Cohort in Phase 1/2 Trial of DTX101 Expected in the Second Half of 2016

CAMBRIDGE, Mass., May 05, 2016 (GLOBE NEWSWIRE) — Dimension Therapeutics, Inc. (NASDAQ:DMTX), a biopharmaceutical company advancing novel, adeno-associated virus (AAV) gene therapies targeting the liver, a central organ for devastating rare diseases, today announced positive preclinical results supporting Dimension’s ongoing Phase 1/2 clinical trial of lead candidate DTX101, which commenced in January 2016. DTX101 is designed to deliver Factor IX, or FIX, gene expression, in adult patients with moderate/severe to severe hemophilia B. Preclinical research conducted with Dimension’s collaborators at the University of Pennsylvania (PENN) demonstrated dose-dependent expression of FIX levels and stability of FIX expression after single dose administration across the majority of doses during the 90-day study period. The study also found there were no apparent safety concerns related to the anticipated clinical dosing. These findings were highlighted in a poster, titled “A Dose-Escalating Preclinical Study to Determine the Efficacy, MED, and Safety of a Clinical Candidate Vector in a Mouse Model of Hemophilia B” (Abstract No. 227), presented at the 19th ASGCT Annual Meeting, which is taking place in Washington, DC, May 4-7, 2016.
“In DTX101, we have pre-clinically developed a potent AAVrh10 vector containing a wild-type FIX gene with the goal of achieving approximately 10 percent of normal FIX levels, which we hope will ultimately lead to the achievement of clinically meaningful benefits for patients via gene delivery,” said James M. Wilson, MD, PhD, a professor of Medicine and Pediatrics, and director of the Orphan Disease Center at the Perelman School of Medicine at the University of Pennsylvania. “Our preclinical data provides supporting evidence for this, both in terms of durability and consistent, dose-dependent activity of DTX101, as well as promising initial safety findings. We look forward to the continued progress of the clinical program, which is expected to report interim topline data later this year.” Lili Wang, PhD, a research associate professor in the Wilson lab, is first author on this poster presentation. Dimension’s phase 1/2 clinical trial of DTX101 is a single arm, open-label, multi-center study, designed to evaluate the safety, dose and early efficacy of DTX101 in adult patients with moderate/severe to severe hemophilia B. Additional information about Dimension’s Phase 1/2 study of DTX101 may be found at ClinicalTrials.gov, using Identifier NCT: NCT02618915.
“Dimension’s presentations at this week’s ASGCT conference, as well as at other important medical and scientific conferences throughout this year, demonstrate our commitment to generating and communicating important data that enables the translation of gene therapy science into the clinic,” said Annalisa Jenkins, MBBS, MRCP, Chief Executive Officer of Dimension. “Based on breakthrough AAV technology and key collaborations, as with PENN, we continue to advance our leading portfolio in liver-associated diseases –hemophilia and inherited metabolic diseases – to meet compelling needs for patients.”
PENN and Wilson are each holders of Dimension stock and Wilson also holds stock in REGENXBIO, Inc.  Dimension holds exclusive sublicenses from REGENXBIO, Inc. for certain PENN-owned AAV technologies related to this development program.
About DTX101
Dimension is developing its lead gene therapy product DTX101 for the treatment of moderate/severe to severe hemophilia B. DTX101 is designed to deliver Factor IX, or FIX, gene expression in a durable fashion, preventing the long-term complications of hemophilia B. Preclinical studies completed to date indicate DTX101 has the potential to be a well-tolerated, effective therapy for hemophilia B. A Phase 1/2 study commenced in January 2016, and the company anticipates reporting interim clinical data in the second half of 2016.
About Dimension Therapeutics, Inc.
Dimension Therapeutics, Inc. (NASDAQ:DMTX) is the leader in discovering and developing new therapeutic products for people living with devastating rare diseases associated with the liver, based on the most advanced, mammalian adeno-associated virus (AAV) gene delivery technology. Dimension is actively progressing its broad pipeline, which features programs addressing unmet needs for patients suffering from inherited metabolic diseases, including OTC deficiency and GSDIa, a collaboration with Bayer in hemophilia A, and a wholly owned clinical program in hemophilia B. The company targets diseases with readily identifiable patient populations, highly predictive preclinical models, and well-described, and often clinically validated, biomarkers. Founded in 2013, Dimension maintains headquarters in Cambridge, Massachusetts.
For more information, please visit www.dimensiontx.com.
Cautionary Note Regarding Forward-Looking Statements
This press release contains “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995, including, but not limited to, statements regarding the timing and progress of Dimension’s preclinical studies and clinical trials for our portfolio and lead programs in hemophilia, the applicability of preclinical data in hemophilia B to the potential success of the clinical program for DTX101, and the potential benefits of Dimension’s products, if approved. All such forward-looking statements are based on management’s current expectations of future events and are subject to a number of risks and uncertainties that could cause actual results to differ materially and adversely from those set forth in or implied by such forward-looking statements. These risks and uncertainties include the risks that Dimension’s product candidates, including its lead candidate, DTX101, will not successfully be developed or commercialized; and the risks described under the caption “Risk Factors” in Dimension Therapeutics’ Annual Report on Form 10-K for the year ended December 31, 2015, which is on file with the Securities and Exchange Commission, as well as other risks detailed in Dimension Therapeutics’ additional filings with the Securities and Exchange Commission. All information in this press release is as of the date of the release, and Dimension Therapeutics undertakes no duty to update this information unless required by law.

CONTACT:
Jean Franchi
Chief Financial Officer
Dimension Therapeutics
617-714-0709
jean.franchi@dimensiontx.com
Burns McClellan, on behalf of Dimension Therapeutics
Media: Justin Jackson
212-213-0006, ext.327
jjackson@burnsmc.com