Phase 3 trial of experimental DM1 treatment fails to hit main goal

A Phase 3 clinical trial testing delpacibart etedesiran (del-desiran), an experimental treatment for myotonic dystrophy type 1 (DM1), failed to hit its main goal.

The Phase 3 HARBOR trial (NCT06411288) enrolled nearly 160 people with DM1, ages 16 to 65. Participants received seven infusions of either del-desiran or a placebo over the course of about a year. The study’s main goal was to see if del-desiran would significantly improve video Hand Opening Time (vHOT), a measure of myotonia — the hallmark symptom of DM1, in which muscles can’t relax after contracting. Secondary outcomes included measures of grip strength, walking ability, and self-reported activity participation.

Novartis, which is developing del-desiran after acquiring previous developer Avidity Biosciences, said trial results showed no significant difference in vHOT between patients given del-desiran or the placebo. There was “evidence of clinical activity in secondary endpoints,” and del-desiran’s safety profile was “generally consistent with previously reported data,” Novartis said in a company press release It didn’t provide further details on the study’s outcomes.

“Despite decades of research, there are still no approved treatment options for DM1, and patients and caregivers continue to face a significant daily burden,” said Shreeram Aradhye, MD, president of development and chief medical officer at Novartis. “Developing therapies for a complex disease like DM1 remains challenging, and setbacks are part of scientific progress.”

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Data evaluation continues

DM1 is caused by mutations in the DMPK gene that result in the production of an abnormally long messenger RNA (mRNA). mRNA is normally used as an intermediate template during protein production, but the extra-long mRNA in DM1 forms toxic clumps that damage muscle cells. Del-desiran is designed to reduce levels of the toxic mRNA.

Novartis said it continues to evaluate all data from the HARBOR trial and plans to engage with regulatory authorities on the best path forward for del-desiran. In the meantime, the company is continuing work to develop experimental treatments targeting other forms of muscular dystrophy.

“As we continue to evaluate the full HARBOR dataset, we remain committed to identifying the most appropriate development path for the del-desiran program and advancing innovative approaches for people living with DM1 and other serious neuromuscular diseases,” Aradhye said.

Novartis has asked the U.S. Food and Drug Administration (FDA) to grant conditional approval to delpacibart zotadirsen (del-zota), an experimental therapy for Duchenne muscular dystrophy (DMD) caused by mutations amenable to exon 44 skipping. The company is asking the FDA to conditionally authorize del-zota based on early clinical trial data showing the therapy can boost levels of dystrophin, the protein whose deficit causes DMD. A global Phase 3 trial, SAFARI4, aims to further evaluate del-zota’s long-term safety and confirm its clinical benefit. That study will be conducted outside the U.S.

The FDA recently granted priority review to the application,  which will be assessed under the agency’s accelerated approval pathway.

Novartis is also developing delpacibart braxlosiran (del-brax), an experimental therapy for facioscapulohumeral muscular dystrophy (FSHD) that has shown promise in early clinical testing. Novartis said it plans to meet with the FDA to discuss next steps for the development of del-brax. Like del-desiran, del-brax and del-zota were being developed by Avidity before Novartis acquired the company.