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Dimension Therapeutics Announces Recombinant DNA Advisory Committee’s Unanimous Approval of Phase 1/2 Study Protocol for DTX301, Lead Inherited Metabolic Disease (IMD) Product Candidate to Treat OTC Deficiency

CAMBRIDGE, Mass., June 22, 2016 (GLOBE NEWSWIRE) -- 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 unanimous approval by the National Institutes of Health's Recombinant DNA Advisory Committee (RAC) of a Phase 1/2 study protocol for DTX301 for the treatment of Ornithine Transcarbamylase (OTC) Deficiency. The RAC also issued recommendations on certain design elements of the research and clinical development program that will be communicated to participating sites in the United States.

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. Based upon the RAC vote, Dimension plans to continue moving forward to complete its IND-enabling studies to support global regulatory submissions in the second half of 2016.

“The RAC’s unanimous approval is an important milestone for Dimension and the patient community, and represents a key step in advancing our lead IMD candidate towards the clinic,” said Dr. Annalisa Jenkins, MBBS, FRCP, Chief Executive Officer of Dimension. “We appreciate the approval from the RAC’s members for our DTX301 clinical trial protocol. Regarding comments addressing the relevant species for preclinical testing, following consultation in the last 12 months with relevant experts in the field and key regulatory agencies, we believe our current approach is scientifically valid and will meet the standards required to support our primary concern, namely, ensuring the safety of patients with OTC deficiency. We will carefully consider the RAC’s recommendations in the context of the ongoing IND-enabling studies for DTX301 and through continued regulatory consultation. We are encouraged by the evolving preclinical and clinical database supporting the safety profile of the AAV vector class that has taken the field well beyond the unfortunate events nearly 20 years ago when it was confirmed that an adenovirus vector was not a viable approach that could be safely administered to humans."

Cary O. Harding, M.D., Professor, Department of Molecular and Medical Genetics at Oregon Health & Science University, stated, “Inherited metabolic diseases, like OTC deficiency, represent an area of compelling unmet medical need. Unfortunately, for many of these patients, there are few or no effective treatment options other than liver transplantation. Gene therapy utilizing liver-directed AAV technology holds great promise in offering potentially long-term replacement of the missing gene. I look forward to the continued advancement of this program.”

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 the 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.

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

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, GSDIa, citrullinemia type 1, PKU, Wilson disease, 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.

About the RAC Review Process

The outcome of RAC review is a series of recommendations and advice from experts in the field. RAC review does not entail a formal approval of a proposed protocol. The recommendations will be captured in a summary letter, which will be sent to the institutional review boards (IRBs) reviewing the protocol in the United States, as well as the U.S. Food & Drug Administration. The recommendations are non-binding.

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 progress of Dimension's portfolio and lead programs, including DTX301, the timing, scope or likelihood of regulatory filings and approvals, the progress and results of preclinical studies, and our ability to develop and advance product candidates into, and successfully complete, clinical studies. 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 DTX301, will not successfully be developed or commercialized in the times indicated or at all; and the risks described under the caption "Risk Factors" in Dimension Therapeutics’ Quarterly Report on Form 10-Q for the quarter ended March 31, 2016, 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

Source:Dimension Therapeutics