Dimension Therapeutics Commences Patient Dosing in Global, Multi-Center Phase 1/2 Clinical Trial of DTX301 in Ornithine Transcarbamylase (OTC) Deficiency

Twelve trial sites recruiting patients with OTC deficiency in the United States, United Kingdom, Spain, and Canada

Initial data from the company’s Phase 1/2 study anticipated by late 2017

CAMBRIDGE, MA, USA I August 31, 2017 I Dimension Therapeutics, Inc. (NASDAQ:DMTX), a biopharmaceutical company advancing novel, adeno-associated virus (AAV) gene therapies targeting the liver, a key organ for human metabolism, today announced the initiation of patient dosing in the company’s global, multi-center Phase 1/2 clinical trial to evaluate DTX301, the only AAV gene therapy in clinical testing for the treatment of patients with Ornithine Transcarbamylase (OTC) Deficiency. DTX301 is designed to deliver stable expression and activity of OTC following a single intravenous infusion and has been shown in academic preclinical studies in relevant mouse models to normalize levels of urinary orotic acid, a marker of ammonia metabolism. In the late onset form of the disease, elevated ammonia can lead to significant medical issues for patients who are in need of better disease-modifying therapies.

“OTC deficiency is an inherited metabolic disease (IMD) for which approved therapies are unable to eliminate the risk of metabolic crises from elevated ammonia. We believe that DTX301, based on our differentiated AAV8 platform in IMD, holds great promise for addressing the unmet need among patients, and we look forward to the continued advancement of the trial,” said Annalisa Jenkins, MBBS, FRCP, Chief Executive Officer of Dimension. Based on the current progress, Dimension anticipates reporting initial clinical data from the Phase 1/2 DTX301 clinical trial by late this year.

Dimension’s phase 1/2 clinical trial is an open-label, dose-finding safety study of single ascending doses of DTX301 in adults with late-onset OTC Deficiency. To evaluate therapeutic response of DTX301, the trial plans to measure ammonia levels and other biomarkers, including 13C-acetate, which are established measures of OTC deficiency disease status and hepatocyte (liver) ureagenesis capacity, respectively. Additional information about Dimension’s Phase 1/2 study of DTX301 may be found at ClinicalTrials.gov, using Identifier NCT: NCT02991144.

“Inherited metabolic diseases can have severe effects on patient health and quality of life, and in many of these urea cycle diseases, including OTC deficiency, the only curative option is liver transplantation, which is often associated with significant morbidity and mortality,” stated Mark L. Batshaw, M.D., Executive Vice President, Physician-in-Chief & Chief Academic Officer of Children’s National Medical Center and head of Dimension’s Clinical Advisory Board (CAB) for urea cycle disorders.

About DTX301

Dimension is developing its AAV gene therapy product DTX301 for the treatment of individuals with OTC deficiency. DTX301 is designed to deliver ornithine transcarbamylase gene expression in a durable fashion, preventing or reducing the occurrence of complications associated with OTC deficiency. Preclinical studies completed to date indicate DTX301 has the potential to be a well-tolerated, effective therapy for OTC deficiency. DTX301 was granted Orphan Drug Designation in the United States and Europe in January and March 2016, respectively.

Background on OTC Deficiency

OTC deficiency, the most common urea cycle disorder, is caused by a genetic defect in a liver enzyme responsible for detoxification of ammonia. Individuals with OTC deficiency can build up excessive levels of ammonia in their blood, potentially resulting in neurological deficits and other toxicities. It is estimated that more than 10,000 patients are affected by OTC deficiency worldwide, of which approximately 80% are classified as late-onset, Dimension’s target population. The greatest percentage of patients, including males and females, experience late-onset disease, representing a clinical spectrum of disease severity. Neonatal onset disease occurs in males, presents as severe disease, and can be fatal at an early age. Approved therapies, which must be taken multiple times a day for the patient's entire life, do not eliminate the risk of future metabolic crises. Currently, the only curative approach is liver transplantation.

About Dimension Therapeutics, Inc.

Dimension Therapeutics, Inc. (NASDAQ:DMTX) is a leader in discovering and developing new therapeutic products for people living with devastating rare and metabolic 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, and a collaboration with Bayer in hemophilia A. Dimension has initiated a phase 1/2 clinical trial with DTX301 for the treatment of OTC deficiency. 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.

SOURCE: Dimension Therapeutics

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