Avidity has been given the go-ahead by the FDA to request accelerated approval of delpacibart braxlosiran—potentially the first disease-modifying treatment for facioscapulohumeral muscular dystrophy—with an application in the second half of 2026.
Avidity Biosciences’ antibody-oligonucleotide conjugate improved mobility and muscle strength in a type of muscular dystrophy in an early-stage trial, and the FDA is open to receiving an application for accelerated approval of the drug, the San Diego–based biotech revealed Monday.
“Today’s updates are significantly positive for [Avidity],” BMO Capital Markets analysts wrote in a note Monday, adding that the “FDA’s “endorsement of [delpacibart braxlosiran] AA pathway is a big win.”
Nevertheless, Avidity’s shares declined more than 11% to $32.14 as of 11:17 a.m. ET.
Avidity plans to launch a global confirmatory Phase III study called FORWARD for facioscapulohumeral muscular dystrophy (FSHD) to support the submission, according to a separate announcement on Monday. This is on top of an ongoing registrational study to obtain more biomarker data.
The company plans to file a biologics license application for delpacibart braxlosiran in FSHD in the second half of 2026.
Monday’s topline data come from the Phase I/II FORTITUDE study of patients with FSHD, a variant of muscular dystrophy that primarily weakens muscles in the face and upper body but can spread to the rest of the body. Patients who received delpacibart braxlosiran saw improvements in mobility and muscle strength across a number of tests, including the 10-meter walk-run test, timed up and go and quantitative muscle testing, compared to patients who received placebo.
Patients who received delpacibart braxlosiran also had reduced levels of KHDC1L and creatine kinase, biomarkers of muscle damage. The trial had no discontinuations and no serious or severe adverse effects were reported.
The company will present more details at the 32nd Annual FSHD Society International Research Congress, June 12-13 in Amsterdam.
FSHD is caused by abnormal expression of a protein called DUX4. Using similar concepts to an antibody-drug conjugate, Delpacibart braxlosiran uses an antibody to target a transferrin receptor that delivers an siRNA molecule that targets and destroys DUX4 mRNA. Delpacibart braxlosiran is the first therapy designed to treat this underlying cause of FSHD, according to Avidity.
A much-watched company in the muscular dystrophy space, Avidity’s pipeline also includes an exon-skipper, delpacibart zotadirsen, for Duchenne muscular dystrophy, which in August 2024 boosted dystrophin production by an “unprecedented” 25% in a Phase I/II trial. Also last year, the FDA granted breakthrough status to its myotonic dystrophy type I treatment, and in 2023 Bristol Myers Squibb bet up to $2.3 billion that Avidity’s antibody-oligonucleotide technology could be applied to five different cardiovascular targets.
