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Avidity Biosciences Expediting Development of AOC for Rare Muscular Dystrophy Therapy

NEW YORK – Avidity Biosciences wants to quickly advance its investigational antibody oligonucleotide conjugate (AOC) therapy for facioscapulohumeral muscular dystrophy (FSHD) into registrational cohorts after patients who received the treatment in an ongoing Phase I/II trial experienced functional improvements and increased muscle strength.

FSHD is a rare disease caused by abnormal expression of the DUX4 gene, which causes the loss of muscle function, chronic pain, fatigue, and progressive disability. The disorder currently lacks any approved targeted therapy.

Delpacibart braxlosiran (del-brax), also known as AOC 1020, is designed to reduce DUX4 expression in FSHD patients. AOC therapies combine antibody-mediated cell specificity with the genetic sequence-targeting precision of antisense oligonucleotides.

Avidity is testing the activity of del-brax in the randomized, placebo-controlled Phase I/II FORTITUDE trial. The San Diego-based company this week reported data from 12 adult participants given a single 1 mg/kg dose of the treatment followed by two 2 mg/kg doses. Four months after treatment, patients on del-brax had functional improvements such as increased upper and lower limb muscle strength and better muscle function compared to those on placebo and to outcomes seen in the ReSolve natural history study.

At the annual FSHD Society International Research Congress in Denver this week, Avidity reported that the 12 participants on del-brax also experienced greater than 20 percent reductions in DUX4-regulated genes and greater than 50 percent mean reductions in muscle-specific DUX4 regulated genes. Additionally, on average, patients saw at least a 25 percent reduction in novel circulating biomarkers and in creatine kinase, as well as other improvements in both patient- and clinician-reported outcomes. Patients appeared to tolerate del-brax well and experienced only mild-to-moderate adverse events. None of the patients discontinued treatment.

Based on these data, Avidity said it will accelerate initiation of registrational cohorts in the FORTITUDE study.

"With the unprecedented del-brax data from the FORTITUDE trial, we are now focused on accelerating our registrational plans as we understand the urgency to develop a treatment for people living with FSHD who have no treatment options," Avidity President and CEO Sarah Boyce said in a statement. "By directly targeting the root cause of FSHD, we believe that del-brax has the potential to be a first-in-class, best-in-class therapy for people living with FSHD."

Boyce added that this is Avidity's third rare muscle disease program that has shown it can be delivered to the muscle and engage targets and the second therapy to show signs of functional improvement in patients with rare neuromuscular diseases. San Diego-based Avidity is also testing AOC therapies for myotonic dystrophy type 1 and Duchenne muscular dystrophy.