Viltepso Reduces DMD Motor Function Decline: Phase 2 Data

Increases in standing, walking, climbing times were lower for Viltepso-treated boys

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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Treatment with Viltepso (viltolarsen) helps preserve motor function in boys with Duchenne muscular dystrophy (DMD) amenable to exon 53 skipping, according to four-year data from an open-label extension study.

“These data represent the longest clinical experience of an exon 53 skipping therapy for the treatment of Duchenne muscular dystrophy,” Leslie Magnus, MD, vice president of medical affairs at Viltepso’s developer NS Pharma (a subsidiary of Nippon Shinyaku), said in a press release.

DMD is caused by mutations in the gene that provides instructions for making the protein dystrophin. Viltepso prompts a cell’s molecular machinery to skip this region when the gene is “read,” allowing a shortened but functional version of dystrophin to be produced. In about 8% to 10% of cases, the disease-causing mutation is amenable to skipping 53.

The therapy was granted conditional approval in the U.S. in 2020 based on data from a Phase  2 clinical trial (NCT02740972) that included 16 boys with DMD, ages 4 to 9 at the start of the study.

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Participants were given either a a low dose (40 mg/kg) or a high dose (80 mg/kg) of Viltepso once weekly for about six months and results showed it could increase dystrophin protein levels. At the end of the trial, all participants continued to an open-label extension (NCT03167255) and received Viltepso.

Long-term results to 216 weeks (more than four years) were presented at the 27th International Hybrid Annual Congress of the World Muscle Society (WMS 2022), Halifax, Nova Scotia, Canada.

To assess its effectiveness, outcomes for the boys treated with Viltepso were compared with outcomes from a group of clinically similar boys in the Cooperative International Neuromuscular Research Group Duchenne Natural History Study (CINRG DNHS; NCT00468832). All were treated with steroids according to standard guidelines.

Over four years, the mean time it took boys to stand increased by 8.3 seconds in the control group, compared to 2.7 seconds for the Viltepso-treated boys — a significant difference favoring the exon-skipping therapy.

The mean time to run or walk 10 meters (just over 30 feet) increased by 2 seconds among boys given Viltepso, compared to 6 seconds in the control group. The time to climb four stairs also showed significant improvements compared to the control group.

“In this four-year study, Viltepso-treated patients maintained motor function over the first two years of treatment and experienced significant delay of disease progression over the following two years, compared with the CINRG DNHS control group which declined over this same time period,” Magnus said.

The safety profile of Viltepso during the extension trial was similar to what has been previously reported. There were no serious treatment-related side effects, nor did any patients stop treatment due to side effects. The most common side effects reported included cough, the common cold, rash, fever, and vomiting.

“This long-term study gives physicians who treat patients with DMD important information about the long-term impact of Viltepso on ameliorating the disease course,” Paula Clemens, MD, from the University of Pittsburgh School of Medicine, said.

NS Pharma is sponsoring a Phase 3 trial called RACER53 (NCT04060199) to further evaluate Viltepso’s safety and effectiveness in boys with DMD amenable to exon 53 skipping. The study is recruiting boys, ages 4 to 7, at locations around the world.

“These [long-term Phase 2] data are encouraging as NS Pharma continues to evaluate the effect of Viltepso on improving or stabilizing motor function in a Phase 3 study,” Magnus said.

“Further study is ongoing, but these four-year data give confidence that Viltepso can be considered an important part of the treatment strategy for patients with DMD whose dystrophin mutations are amenable to exon 53 skipping therapy,” Clemens said.