Regenxbio Prepares to Compete with Sarepta in DMD as Gene Therapy Progresses to Key Pivotal Trials
On Monday, Regenxbio disclosed that it has successfully reached an agreement with the FDA regarding a development strategy and accelerated approval pathway for its prospective gene therapy, RGX-202, which is intended as a one-time treatment option for Duchenne muscular dystrophy.
Following their End of Phase II meeting with FDA officials, Regenxbio is targeting a Biologics License Application submission for RGX-202 by 2026. The FDA has also approved the expansion of the ongoing Phase I/II AFFINITY DUCHENNE trial into a multicenter, open-label pivotal Phase I/II/III study. This study will administer a dose of 2×1014 GC/kg of the therapy to approximately 30 ambulatory patients aged 1 and older.
The initial patient has already been dosed in this pivotal study on Monday.
The development of RGX-202 is based on positive early-stage results that show “evidence of improving outcomes for boys with Duchenne and altering the trajectory of this devastating disease,” as noted by CEO Curran Simpson. For example, data from a 12-month period released on Monday indicated consistent or enhanced function scores among all five treated subjects, assessed using the North Star Ambulatory Assessment, a recognized tool for evaluating motor capabilities in ambulant Duchenne patients.
Regenxbio compared its results with those from historical controls that were matched for age and initial performance, revealing superior outcomes in patients receiving the pivotal dose of RGX-202.
From a safety perspective, RGX-202 was well-tolerated, with no serious adverse reactions reported. Typical side effects included nausea, vomiting, and fatigue, which are common among gene therapies and were promptly resolved.
Simpson emphasized that the findings suggest “consistent, robust expression of our innovative microdystrophin translating into substantial clinical benefits.”
Following the demise of Pfizer’s gene therapy fordadistrogene movaparvovec, which failed in the Phase III CIFFREO study in June 2024, Regenxbio is positioned as a significant competitor to Sarepta Therapeutics, which has gained prominence with its FDA-approved Elevidys (delandistrogene moxeparvovec-rokl). In its latest earnings report, Sarepta announced impressive worldwide sales of 0.5 million for Elevidys, marking a 49% increase compared to the previous year.
Nevertheless, experts seem to be dissatisfied with the data shared by Sarepta for Elevidys thus far. During the World Muscle Society meeting last month, the biotech presented five-year results from the first four patients treated with the therapy—findings that many experts considered insufficient, particularly since they were derived from “a small open-label trial” not designed to assess the therapeutic impact on disease progression, as noted by Michael Kelly, chief scientific officer at CureDuchenne, to BioSpace.
Despite this backdrop, analysts do not seem overly concerned about Regenxbio’s competition. Jefferies’ Andrew Tsai remarked in a recent note that Regenxbio is several years behind Sarepta and that its data originate from a limited patient pool.
BMO Capital Markets’ Kostas Biliouris acknowledged that, while RGX-202’s results appear “promising,” there remains a necessity for “richer datasets before making conclusions.” Even if Regenxbio’s gene therapy sustains its favorable profile, he suggested that “the pivotal design may lead to a narrow label that might allow RGX-202 to capture some market share without threatening Elevidys’ position.”