Del-desiran for DM1 wins FDA’s breakthrough therapy designation

Phase 3 HARBOR trial planned to assess treatment's safety, effectiveness

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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The U.S. Food and Drug Administration (FDA) has granted breakthrough therapy designation to delpacibart etedesiran (del-desiran, previously called AOC 1001), an investigational treatment for myotonic dystrophy type 1 (DM1) that’s about to enter Phase 3 clinical testing.

The FDA gives the designation to experimental therapies that have the potential to fill unmet medical needs in treating serious conditions. The designation gives del-desiran’s developer Avidity Biosciences access to perks like more frequent communications with the FDA, with the goal of bringing a needed therapy to market faster.

“We are pleased that the FDA has granted breakthrough therapy designation to del-desiran for myotonic dystrophy type 1, underscoring the potential of del-desiran to be an effective treatment and the urgency of bringing this treatment to people living with DM1,” Sarah Boyce, president and CEO of Avidity, said in a company press release.

DM1 is caused by mutations in the DMPK gene and results in an abnormally long messenger RNA (mRNA, an intermediary molecule produced when the gene is “read” to make protein) being produced. The extra-long mRNA forms toxic clumps in cells, causing muscle damage that leads to myotonia, that is, when muscles are unable to relax after a contraction, and other disease symptoms.

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How does del-desiran affect DM1?

Del-desiran is an RNA-based therapy that’s designed to bind to and destroy the toxic DMPK mRNA. It’s given by infusion into the bloodstream. Recently announced one-year data from MARINA-OLE (NCT05479981), an extension study of a Phase 1/2 clinical trial called MARINA (NCT05027269), indicated del-desiran led to long-term reductions in myotonia severity and improvements in muscle strength.

Avidity is planning a Phase 3 clinical trial dubbed HARBOR (NCT06411288) to further assess the safety and effectiveness of del-desiran in DM1 patients. The study plans to enroll about 150 patients, ages 16-65. The participants will be randomly assigned to receive seven infusions of del-desiran or a placebo over 30 weeks, or about seven months. The study’s main goal will be to measure the impact of treatment on video hand opening time, an assessment of myotonia. The trial also will evaluate measures of muscle strength and patient-reported outcomes.

The HARBOR trial is expected to be up and running before the end of June, according to Avidity.

“Initiation is underway for our global Phase 3 HARBOR study as we focus on rapidly advancing del-desiran for people living with DM1, who currently have no treatment options,” Boyce said.