Zeleciment rostudirsen

Duchenne is caused by mutations in the dystrophin gene that scramble its instructions, so muscle cells make almost no dystrophin, the protein that keeps muscle fibers from tearing. In boys whose mutation is amenable to exon 51 skipping, skipping 1 extra piece of the gene, exon 51, puts the instructions back in order so the cell can make a shorter dystrophin that still works partly, similar to the protein in the milder Becker muscular dystrophy.

Zeleciment rostudirsen carries the same kind of exon 51 skipping strand used in Exondys 51, a phosphorodiamidate morpholino oligomer, but attaches it to a piece of an antibody (a Fab) that grips transferrin receptor 1, a protein muscle cells use to take in iron. The muscle cell pulls in the receptor and the drug with it, which Dyne designed to get more of the strand into muscle, the heart and the central nervous system.

DELIVER (NCT05524883) is a Phase 1/2 placebo-controlled trial in boys aged 4 to 16 with exon 51 amenable Duchenne that enrolled 86 participants at 30 sites, 11 of them in the US, and continues as an open-label extension; ClinicalTrials.gov lists it as active, not recruiting^[8].

Its registrational expansion cohort randomized 32 boys, 24 to 20mg/kg every 4 weeks and 8 to placebo, and met its main goal: mean dystrophin measured by Western blot reached 5.46% of normal at 6 months adjusted for muscle content (p<0.0001), and 2.87% of normal without that adjustment^[2].

Compared with pooled placebo, time to rise from the floor and 10-meter walk/run speed improved with nominal p<0.05 in a post hoc analysis; the study was not designed to test function formally, and the North Star Ambulatory Assessment, stride velocity and upper limb scores also moved in the drug's favor without formal testing^[2].

In March 2026 Dyne reported that lung function and 2 heart measures improved from baseline through 24 months in boys first assigned to the drug, compared with the decline expected from natural history data; most of those boys started at doses well below 20mg/kg^[5]. FORZETTO (NCT07608432), the confirmatory Phase 3 trial, began in May 2026 and plans to enroll about 90 boys aged 4 to 18 who can walk, randomized to 20mg/kg or placebo every 4 weeks for 72 weeks; its main goal is rise-from-floor speed at week 73^[4][9].

Dyne's safety data cover 86 boys in DELIVER followed for up to 36 months, as of August 19, 2025, with about 1,441 doses given, 1,062 of them at the 20mg/kg dose, and 113 patient-years of follow-up. Most treatment-related adverse events were mild or moderate, and the most common were fever and headache. No treatment-related serious adverse events occurred in the 32-boy registrational cohort.

In the open-label extension, 2 boys had treatment-related serious adverse events of malaise, fever or both, and both recovered and kept receiving the drug^[2]. Dyne has not published a full list of adverse event rates, and there is no US label yet.

Dyne built zeleciment rostudirsen on its FORCE platform, which links an oligonucleotide to a transferrin receptor antibody fragment. The FDA granted Breakthrough Therapy, Fast Track, Rare Pediatric Disease and Orphan Drug designations, and the drug also holds orphan designation from the European Medicines Agency and Japan's health ministry^[1].

DELIVER started in August 2022^[8]. Dyne reported topline registrational cohort results on December 8, 2025^[2], started FORZETTO in May 2026^[4] and announced the BLA submission on May 26, 2026^[3]. On July 20, 2026 Dyne announced that the FDA had accepted the application with Priority Review and a January 21, 2027 goal date^[1]. BioSpace reported on July 21, 2026 that Dyne said the FDA does not plan an advisory committee meeting^[7].

Dyne's November 5, 2026 quarterly release says the application is still under Priority Review and that Dyne expects a possible US launch in the first quarter of 2027 if approval comes on time^[6].