The U.S. Food and Drug Administration (FDA) is considering whether to conditionally approve zeleciment rostudirsen (z-rostudirsen), an experimental therapy for Duchenne muscular dystrophy (DMD) in patients with mutations that are amenable to exon 51 skipping.
Z-rostudirsen developer Dyne Therapeutics announced that the FDA has agreed to review an application seeking accelerated approval of the investigational treatment. A final decision from the FDA is expected by Jan. 21, 2027. Assuming that the FDA grants approval, Dyne said it expects z-rostudirsen to be commercially available within the first months of 2027.
“With a potential approval in six months, we are continuing our launch preparations with the aim of making z-rostudirsen available as quickly as possible. We are deeply grateful to the entire Duchenne community, whose partnership and support have been essential in developing this potential therapy,” John Cox, president and CEO of Dyne, said in a company press release.
Dystrophin protein lacking in DMD
DMD is a genetic disorder caused by mutations that lead to virtually no production of dystrophin, a protein that’s vital for maintaining muscle health. Many DMD-causing mutations lead the genetic code to fall out of alignment, resulting in a garbled sequence that doesn’t produce any functional dystrophin protein.
Exon-skipping is a strategy that aims to skip over specific parts of the code when it’s read to make protein, allowing the rest of the code to fall back into alignment and facilitating the production of a shortened but functional version of the protein. Z-rostudirsen (formerly known as DYNE-251) is designed to skip over a section of the dystrophin gene called exon 51.
“With z-rostudirsen, we set out to advance the treatment paradigm in DMD by combining a robust increase in near-full length dystrophin with broad delivery to relevant tissues,” Cox said.
Dyne is asking the FDA to grant the therapy accelerated approval, which is a type of conditional approval where the FDA allows a therapy to be sold based on early evidence that it is likely to benefit patients. The FDA has previously granted accelerated approval to several experimental exon-skipping therapies for DMD based on early data showing the treatment increased dystrophin protein levels.
With z-rostudirsen, we set out to advance the treatment paradigm in DMD by combining a robust increase in near-full length dystrophin with broad delivery to relevant tissues.
In this case, Dyne is seeking accelerated approval based mainly on data from a Phase 1/2 clinical trial called DELIVER (NCT05524883), which demonstrated that z-rostudirsen treatment increased dystrophin protein levels and led to trends of improvement across several functional measures in DMD patients with eligible mutations.
Cox said that the FDA’s decision to review Dyne’s application “represents significant progress toward our goal of delivering functional improvement for those living with DMD amenable to exon 51 skipping.”
If the FDA agrees to grant accelerated approval to z-rostudirsen, Dyne will be required to conduct additional testing to prove that the therapy offers clinical benefits for DMD patients, with long-term approval contingent on the results. FORZETTO, a global Phase 3 trial (NCT07608432) now underway, is intended to serve as the confirmatory trial for U.S. approval and to support future applications outside the U.S.
After a period of 72 weeks where z-rostudirsen will be compared to a placebo, a long-term extension period of 96 weeks (almost two years) will further test the therapy’s efficacy and safety. DMD patients ages 4 to 18 with mutations amenable to exon 51 skipping may be eligible to take part. The exon-skipping therapy is being given by into-the-vein infusions every four weeks.
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