Exon-skipping therapy for DMD wins rare pediatric disease status

FDA recently cleared a Phase 2 clinical trial to evaluate NS-089/NCNP-02

Patricia Inácio, PhD avatar

by Patricia Inácio, PhD |

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The U.S. Food and Drug Administration has granted rare pediatric disease status to NS Pharma‘s NS-089/NCNP-02, an investigational exon 44-skipping therapy for Duchenne muscular dystrophy (DMD), the company announced.

The designation is intended to spur treatments for any rare disease (those affecting fewer than 200,000 people in the U.S.) that affects children and can be serious or life-threatening. With this designation, developers can request a voucher when applying for regulatory approval that can be used for a faster review of a future application of another treatment or transferred to another company.

The designation follows the recent FDA clearance of a Phase 2 clinical trial to evaluate the treatment candidate’s effectiveness with DMD.

Its goal is to assess changes in the levels of dystrophin — a key protein for muscle health — and motor function. Details will be available once enrollment is about to start, according to NS Pharma.

DMD is a type of muscular dystrophy caused by mutations in the DMD gene, which has the instructions for producing dystrophin.

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How does exon-skipping therapy work in DMD?

In DNA, sections that code for a protein, called exons, are interspersed with noncoding regions called introns. With DMD, most mutations lead to the deletion of one or more exons. As a result, cells produce a shorter protein that’s rapidly degraded.

To restore dystrophin production, scientists have developed a strategy that skips certain exons. NS-089/NCNP-02 belongs to this exon-skipping therapy strategy and skips exon 44 of the DMD gene, allowing  a shorter than normal, yet functional version of dystrophin to be produced.

The therapy is expected to help 7% to 11% of DMD patients amenable to exon 44 skipping.

In a Phase 1/2 trial (NCT04129294), six boys received weekly infusions, either a low dose (40 mg/kg) or a high dose (80 mg/kg) for 24 weeks, or around six months.

An average increase to 10.27% of normal dystrophin levels was reported with the low dose, while the high dose showed an increase to 15.79%.

Motor function, assessed with the North Star Ambulatory Assessment score, was maintained or showed a tendency to improve. No side effects leading to discontinuing treatment were reported.

All the boys took part in the study’s extension Phase 2 (NCT05135663) that’s evaluating the same two doses, given weekly over 216 weeks. It’s scheduled to be completed in July 2026.

NS Pharma‘s Viltepso (viltolarsen) is conditionally approved in the U.S. for people with DMD amenable to exon 53 skipping. Nippon Shinyaku, NS Pharma’s parent company, is developing additional exon-skipping therapies.