Avidity’s Delpacibart Gets Japan Orphan Drug Status for DM1

Avidity Biosciences, Inc, a biopharmaceutical company committed to delivering a new class of RNA therapeutics called antibody oligonucleotide conjugates (AOCs), announced that the Japan Ministry of Health, Labour and Welfare (MHLW) has granted orphan drug designation (ODD) to delpacibart etedesiran (del-desiran) for the treatment of myotonic dystrophy type 1 (DM1), an investigational treatment designed to address the root cause of DM1, an underrecognized, progressive and often fatal neuromuscular disease with no approved therapies.

Del-desiran is the first investigational treatment for DM1 to receive Orphan Drug designation in Japan. Del-desiran has also received breakthrough therapy, orphan drug and fast track designations by the US FDA and orphan designation by the EMA.

“This decision by Japan MHLW further reinforces the significant potential of del-desiran to address the root cause of DM1 and the urgent need to bring an approved therapy to the many people impacted by this devastating rare disease in Japan and around the world,” said Steve Hughes,  chief medical officer at Avidity. “We are very encouraged by del-desiran data reported from the MARINA and MARINA-OLE studies thus far, demonstrating favorable long-term safety and tolerability, reversal of disease progression, and consistent and durable improvements in multiple clinical endpoints. Looking ahead, there are multiple key milestones this year as we complete enrollment in the phase 3 HARBOR trial and continue to advance our global commercialization preparations to potentially deliver the first globally approved drug for people living with DM1.”

Avidity has aligned with global regulators on the registrational path for del-desiran for the treatment of DM1, which informed the design of the ongoing phase 3 HARBOR study. Avidity expects to complete participant enrollment in the phase 3 HARBOR study in mid-2025 and submit marketing applications starting 2026 in the US, European Union and Japan.

Japan’s MHLW grants Orphan Drug designation to drugs in development for the treatment of diseases that affect fewer than 50,000 patients in Japan and for which there is a high unmet medical need. An investigational therapy is eligible to qualify for Orphan Drug designation if there is no approved alternative treatment option or if there is high efficacy or safety expected compared to existing treatment options. Orphan Drug designation provides certain benefits, including prioritized consultation regarding clinical development, reduced consultation fees, tax incentives, priority review of applications, reduced application fees, and extended registration validity period.

The global phase 3 HARBOR trial is a randomized, placebo-controlled, double blind pivotal study designed to evaluate del-desiran in approximately 150 people (age 16 and older) living with DM1. The trial will be conducted at approximately 40 sites globally. Patients will be administered either del-desiran or placebo (1:1) every eight weeks. HARBOR is designed to assess multiple key functional aspects of DM1. The primary endpoint is video hand opening time (vHOT), a measurement of myotonia, which is a hallmark symptom of DM1. Key secondary endpoints include muscle strength as measured by hand grip strength and quantitative muscle testing (QMT) total score, and activities of daily living as measured by DM1-Activ. All study participants, regardless of whether they receive active treatment or placebo, will have the option to enroll into an open-label extension trial.

Phase 2 MARINA-OLE study is an open-label, multi-center trial designed to evaluate the long-term safety and tolerability of del-desiran in participants with DM1 who were previously enrolled in the MARINA phase 1/2 trial. This trial will continue to evaluate the safety, tolerability, PK, PD, and efficacy of del-desiran in participants enrolled in the randomized, placebo-controlled, Phase 1/2 MARINA clinical trial. Participants enrolled in the MARINA-OLE study receive quarterly doses of del-desiran regardless of whether they received active treatment or placebo in the MARINA study. The total duration of active treatment with del-desiran in the MARINA-OLE study is approximately 24 months. Once patients have completed active treatment, there will be a nine-month safety follow-up period. Avidity may extend active treatment beyond 24 months at a future timepoint.

Del-desiran, Avidity’s lead product candidate utilizing its AOC platform, is designed to address the root cause of DM1 by reducing levels of a disease-related mRNA called DMPK. Del-desiran consists of a proprietary monoclonal antibody that binds to the transferrin receptor 1 (TfR1) conjugated with a siRNA targeting DMPK mRNA. Del-desiran is currently being assessed in the global Phase 3 HARBOR™ trial and in the ongoing MARINA-OLE trial in people with DM1. Long-term data from the MARINA-OLE trial showed reversal of disease progression in people living with DM1 across multiple endpoints including video hand opening time (vHOT) as a measure of hand function and myotonia, muscle strength and activities of daily living when compared to END-DM1 natural history data.

Myotonic dystrophy type 1 is an underrecognized, autosomal dominantly inherited, progressive and often fatal disease caused by a triplet-repeat in the DMPK gene, resulting in a toxic gain of function mRNA. The disease is highly variable with respect to severity, presentation and age of onset, however all forms of DM1 are associated with high levels of disease burden and may cause premature mortality. DM1 primarily affects skeletal and cardiac muscle, however patients can suffer from a constellation of manifestations including myotonia and muscle weakness, respiratory problems, fatigue, hypersomnia, cardiac abnormalities, severe gastrointestinal complications, and cognitive and behavioral impairment. Currently, there are no approved treatments for people living with DM1.

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