After seeing improved muscle function in phase 1/2 trial, Regenxbio launches pivotal DMD study

Regenxbio’s investigational gene therapy improved muscle function for patients with Duchenne muscular dystrophy (DMD) in a phase 1/2 study. After discussions with the FDA, the biotech has launched a pivotal study and plans on filing for accelerated approval in 2026.

The new data include results from five boys enrolled in Regenxbio’s ongoing trial, called Affinity Duchenne. A 12-month snapshot was taken for three patients—ages 4 to 11 years—who received the initial dose level, while nine-month data was taken for two patients—ages 8 and 12 years—who received a second dose level.

All five participants receiving RGX-202—an adeno-associated virus (AAV) gene therapy—demonstrated stable or improved function, as measured by timed tests and a 17-item rating scale called the North Star Ambulatory Assessment (NSAA), according to Regenxbio’s Nov. 18 release.

The results were measured against external natural history controls matched by age and baseline function and demonstrate evidence of RGX-202 improving disease trajectory, according to Regenxbio.

The one-time administration of RGX-202 was well-tolerated, with no serious adverse events (AEs) or AEs of special interests reported as of Nov. 1, the biotech said. Common drug-related AEs included nausea, vomiting and fatigue.

The biotech has also said it achieved “alignment” with the FDA on expanding the Affinity Duchenne trial into a phase 1/2/3 pivotal study, plus on a pathway for potential accelerated approval.

Regenxbio’s open-label, pivotal trial has already dosed its first patient and is testing RGX-202’s efficacy at the second dose level in 30 ambulatory patients ages one year and older. The trial isn’t expected to include a placebo cohort. Regenxbio expects to file for accelerated approval with the FDA in 2026, according to the company release.

Currently, the only approved gene therapy for DMD is Sarepta Therapeutics’ Elevidys, which gained accelerated approval for ambulatory boys ages 4 or 5 years in 2023. Then, this summer, the FDA expanded the label to include all patients 4 years and older.

Though Elevidys failed to meet the main goal of a pivotal trial, coming up short of statistical significance in the NSAA, Sarepta’s study did score statistically significant results on all key prespecified secondary endpoints, including time to rise and 10-meter walk test.

Currently, no marketed gene therapy exists for DMD patients younger than 4 years, and Regenxbio is the only gene therapy sponsor enrolling patients younger than 4 in the U.S., according to the biotech. The company didn’t indicate which patient group its accelerated approval filing might cover.

The FDA has also granted RGX-202 orphan, rare pediatric and fast track tags.

DMD is an inherited disease caused by mutations in a gene that encodes for dystrophin, a protein involved in muscle structure and function. Regenxbio’s gene therapy is designed to help produce microdystrophin—a shortened form of dystrophin—in muscle cells to preserve function and protect against damage.

Biomarker data showed consistent expression of differentiated RGX-202 microdystrophin in the muscle, according to the biotech. The results in ambulatory patients ages 8 and older are the highest reported microdystrophin levels across approved or investigational gene therapies, Regenxbio said.

The biomarker data cut included more than the five aforementioned patients, with five patients between the ages of 8 to 11 receiving the second dose level seeing a range of microdystrophin expression between 20.8% up to 75.7%, as measured by a Western Blot test.

The primary endpoint of Regenxbio’s pivotal trial will be the proportion of participants whose RGX-202 microdystrophin expression is higher than 10% at week 12.

Since market close last Friday, Regenxbio’s stock has risen 6%, up from $9.63 Friday to $10.24 as of midday Nov. 18.

The Regenxbio data release comes five months after Pfizer shared that its phase 3 gene therapy trial failed to demonstrate significant improvement in motor function for boys with DMD, as measured by NSAA. Key secondary endpoints, such as 10-meter run/walk velocity and time to rise, also failed to demonstrate a significant difference between treatment and placebo. Earlier results had shown sustained levels of mini-dystrophin expression tied to Pfizer’s treatment.

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