Avidity Biosciences Reports Topline Data From Dose Escalation Cohorts Of Del-Brax Phase 1/2 FORTITUDE Program In FSHD; Data Support Planned Accelerated Approval BLA Submission In H2 2026

-- Unprecedented data from FORTITUDE™ dose escalation cohorts for del-brax treated participants, compared to placebo, demonstrate improvement in function, strength and PROs as well as rapid and significant reduction in biomarkers --

-- Data support planned accelerated approval BLA submission in H2 2026 --

-- Data being presented at the 32nd Annual FSHD Society International Research Congress (IRC); Investor and analyst webcast event today, Monday, June 9 at 8:00 a.m. ET --

SAN DIEGO, June 9, 2025 /PRNewswire/ -- Avidity Biosciences, Inc. (NASDAQ:RNA), a biopharmaceutical company committed to delivering a new class of RNA therapeutics called Antibody Oligonucleotide Conjugates (AOCs™) to profoundly improve people's lives, today announced positive topline data from the dose escalation cohorts of the delpacibart braxlosiran (del-brax) Phase 1/2 FORTITUDE™ program in Facioscapulohumeral Muscular Dystrophy (FSHD). These data as well as research supporting KHDC1L as a novel DUX4 regulated circulating biomarker will be presented in oral and poster presentations at the 32nd Annual FSHD Society International Research Congress (IRC), being held June 12-13, 2025, in Amsterdam, the Netherlands.

Del-brax is the first investigational therapy designed to treat the underlying cause of FSHD by directly targeting the disease-causing gene, double homeobox 4 (DUX4). Currently, there are no approved therapies for the treatment of FSHD, a rare, hereditary disorder marked by life-long, relentless loss of muscle strength and function, significant pain, fatigue, and progressive disability. FSHD affects approximately 45,000 to 87,000 people in the United States and Europe.

Avidity today also announced that the accelerated approval regulatory pathway in the U.S. is open for del-brax and that the company has initiated the global, confirmatory Phase 3 FORWARD™ study in FSHD.

Topline Data from the Phase 1/2 FORTITUDE™ Dose Escalation Cohorts

The FORTITUDE™ clinical development program includes a randomized, placebo-controlled, double-blind, Phase 1/2 clinical trial designed to evaluate multiple doses of del-brax in participants with FSHD as well as an open-label extension study. The two dose escalation cohorts evaluated 39 participants on either 2 mg/kg or 4 mg/kg of del-brax versus placebo over a period of 12 months. In these cohorts, del-brax was given every six weeks for the first three months and then every 13 weeks thereafter.

Topline data from these cohorts for del-brax treated participants, compared to placebo, demonstrated:

• Consistent improvement of functional mobility and muscle strength as measured by 10-Meter Walk-Run test (10MWRT), Timed Up and Go (TUG) and quantitative muscle testing (QMT) as compared to placebo;
• Consistent improvement in multiple measures of quality of life as measured by patient reported outcomes and compared to placebo;
• Rapid and significant reductions in levels of KHDC1L and creatine kinase, a biomarker of muscle damage; and
• Favorable long-term safety and tolerability with most adverse events (AEs) mild or moderate, with no related serious or severe adverse events and no discontinuations.

Topline data from the ongoing, fully enrolled del-brax Phase 1/2 FORTITUDE biomarker cohort are anticipated in Q2 2026. The primary endpoint of the FORTITUDE biomarker cohort is reduction of KHDC1L, a novel DUX4-regulated circulating biomarker. Avidity collaborated with Stephen Tapscott, M.D., Ph.D., Professor of Human Biology and Clinical Research at the Fred Hutchinson Cancer Center around the identification of the KHDC1L circulating biomarker in people living with FSHD.