Avidity's Muscular Dystrophy Drug Shows Promise, FDA Endorses Accelerated Approval Pathway

Avidity Biosciences has made significant strides in the treatment of facioscapulohumeral muscular dystrophy (FSHD), with its novel antibody-oligonucleotide conjugate demonstrating improved mobility and muscle strength in early-stage trials. The San Diego-based biotech company announced on Monday that the FDA has opened the door for an accelerated approval application for delpacibart braxlosiran, potentially paving the way for the first disease-modifying treatment for FSHD.

Promising Clinical Results and FDA Endorsement

Topline data from the Phase I/II FORTITUDE study revealed that patients receiving delpacibart braxlosiran experienced improvements across multiple mobility and strength tests compared to those on placebo. These tests included the 10-meter walk-run test, timed up and go, and quantitative muscle testing. Additionally, treated patients showed reduced levels of KHDC1L and creatine kinase, both biomarkers of muscle damage.

The FDA's endorsement of an accelerated approval pathway for delpacibart braxlosiran marks a significant milestone for Avidity. BMO Capital Markets analysts described this development as "significantly positive" and "a big win" for the company. Avidity plans to submit a biologics license application for the drug in the second half of 2026, supported by an ongoing registrational study and a planned global confirmatory Phase III study called FORWARD.

Innovative Mechanism of Action

Delpacibart braxlosiran represents a novel approach to treating FSHD, a condition caused by abnormal expression of the DUX4 protein. The drug utilizes an antibody to target a transferrin receptor, delivering an siRNA molecule that destroys DUX4 mRNA. This mechanism makes delpacibart braxlosiran the first therapy designed to address the underlying cause of FSHD.

Avidity's Expanding Muscular Dystrophy Portfolio

While the FSHD treatment breakthrough is noteworthy, it's just one part of Avidity's growing muscular dystrophy pipeline. The company has also made progress with delpacibart zotadirsen, an exon-skipper for Duchenne muscular dystrophy, which demonstrated a 25% increase in dystrophin production in a Phase I/II trial in August 2024. Furthermore, Avidity's myotonic dystrophy type I treatment received FDA breakthrough status last year.

The company's innovative antibody-oligonucleotide technology has attracted significant industry attention, with Bristol Myers Squibb investing up to $2.3 billion in 2023 to apply this approach to five different cardiovascular targets.

Despite these positive developments, Avidity's shares experienced an 11% decline following the announcement, trading at $32.14 as of 11:17 a.m. ET on Monday. The company plans to present more detailed results from the FORTITUDE study at the 32nd Annual FSHD Society International Research Congress in Amsterdam on June 12-13.