NS Pharma steals a march on Sarepta with DMD drug

Japan’s Nippon Shinyaku Pharma has filed for approval of its Duchenne muscular dystrophy (DMD) in the US, increasing the pressure on Sarepta whose rival DMD drug was rejected in August.

Like Sarepta’s Vyondys 53 (golodirsen), NS Pharma’s drug – called viltolarsen – is a therapy designed to treat patients with DMD amenable to exon 53 skipping, a group that can currently only be treated with steroid drugs.

The DMD gene is made up of 79 exons, and mutations in that code can result in a deficiency in dystrophin which is responsible for the muscle wasting in DMD. Exon-skipping drugs are used to patch the mutations and allow the gene to produce partially functional dystrophin.

The FDA’s rejection of Vyondys 53 because of safety concerns stripped away a healthy lead for Sarepta in this form of DMD. NS Pharma says its drug now has a chance of beating its rival to the US market, assuming approval by the FDA in mid-2020 – on the proviso it doesn’t also run into any roadblocks at the US regulator. The Japanese drugmaker also submitted viltolarsen for approval in Japan last week.

Sarepta already markets another drug called Exondys 51 (eteplirsen) for DMD associated with mutations in exon 51, which was approved in 2018 amid some controversy as the FDA’s own expert advisers recommended rejecting it because they felt its clinical trials did not clearly demonstrate efficacy.

Exondys 51 has nevertheless seen sales grow healthily to reach $182 million in the first half of this year. It is suitable for treating around 13% of DMD patients, while around 8% of patients would be eligible for treatment with the exon 53 skipping drugs.

NS Pharma’s application is based on a phase 2 study conducted in the US and Canada which showed the drug could increase levels of dystrophin as well as give a preliminary indication of clinical improvement as measured by timed muscle function tests.

Last month, the company started a phase 3 trial that aims to recruit 74 patients and is scheduled to generate results in 2024 that will further explore whether the dystrophin increases equate to improvements in muscle function.

Sarepta is running a phase 3 trial of golodirsen – as well as an exon 45-skipping drug called casimersen – that will also investigate muscle function outcomes and is due to generate results in 2022.

DMD is one of the most common fatal genetic disorders, affecting around one in every 3,500-5,000 male births worldwide.