Chasing Pfizer and Roche, Regenxbio benefits from FDA boost for DMD gene therapy

The FDA has boosted Regenxbio’s attempt to move five adeno-associated virus (AAV) drugs into pivotal trials or onto the market by 2025. The agency has given the company a fast-track designation that could accelerate its bid to muscle in on the Duchenne muscular dystrophy (DMD) sector.

Regenxbio secured the regulatory privilege for RGX-202, an AAV therapy designed to deliver a transgene for a novel microdystrophin to correct the muscle degeneration that drives DMD. The FDA previously gave orphan-drug and rare pediatric disease designations to the candidate, and cleared Regenxbio to run a phase 1/2 trial that is on course to deliver initial data in the second half of the year.

Securing the fast-track status positions Regenxbio to benefit from more frequent interactions with the FDA as it works to bring the one-time DMD treatment to market, plus potentially a priority review if the candidate makes it as far as a filing for approval.

Regenxbio is trailing the leaders in the DMD gene therapy space. Pfizer has a candidate, PF-06939926, in phase 3, as does the Roche-partnered Sarepta Therapeutics. The leading pair are pursued by a pack of would-be rivals with earlier-stage programs that includes Solid Biosciences, Ultragenyx and Vertex.

Faced with that level of competition, Regenxbio sees its use of functional elements of the C-Terminal domain found in naturally occurring dystrophin as evidence that it can carve out a slice of the market. In preclinical tests, the inclusion of the domain was associated with the recruitment of key proteins to the muscle cell membrane and with improved muscle resistance to contraction-induced damage.

Regenxbio recently began enrolling patients to test whether the benefits seen in mice translate into humans. The study tests two doses of the therapy in boys aged 4 to 11 years. Initially, the cohorts will enroll three participants each, but Regenxbio has the option to add up to six additional patients at each dose level. Investigators are tracking endpoints such as muscle strength and function.