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Regenxbio Advances Phase I/II Trial for DMD Gene Therapy

NEW YORK – Regenxbio on Wednesday said that a patient with Duchenne muscular dystrophy (DMD) has received its investigational gene therapy RGX-202 at the second dose level within a Phase I/II trial.

DMD is caused by mutations in the eponymous gene that hinder production of dystrophin, a protein necessary to maintain muscle structure. Without it, DMD patients' muscles become weak, and they eventually lose the ability to move and breath independently. RGX-202 uses an adeno-associated virus serotype 8 to deliver a transgene for a novel microdystrophin that has functional elements of the C-terminal domain found in naturally occurring dystrophin.

Regenxbio is evaluating the safety, tolerability, and efficacy of RGX-202 in the ongoing Phase I/II AFFINITY DUCHENNE trial. In the dose-evaluation portion of the study, the company will enroll four ambulatory pediatric patients between 4 and 11 years old and give them the gene therapy at one of two dose levels.

Two patients who received RGX-202 at the first dose level and completed a three-month assessment had "robust" microdystrophin expression in the muscle cell membrane. Now, the first of two patients has received RGX-202 at the second dose level. Preclinical data suggests that RGX-202 at the second dose level should improve patients' functional performance better than at the first dose level.

After two patients receive the gene therapy at the second dose level, there will be an independent safety data review, and the trial will proceed to a dose-expansion phase and enroll more patients. Regenxbio said in a statement that it will share initial strength and functional assessment data for patients receiving RGX-202 at both dose levels and determine a pivotal dose by next year.

The Rockville, Maryland-based firm said it also plans to start a pivotal trial for the gene therapy in 2024, in which it will track the drug's impact on microdystrophin expression as a surrogate endpoint. Based on data from this trial, Regenxbio may submit a biologics license application (BLA) to the US Food and Drug Administration for RGX-202 and seek accelerated approval.

The FDA earlier this year granted accelerated approval to Sarepta Therapeutics' DMD gene therapy Elevidys (delandistrogene moxeparvovec) for patients between 4 and 5 years old based on the treatments ability to increase microdystrophin expression.