Novartis’ $12bn Avidity Biosciences buyout is looking increasingly well positioned, as one of the latter company’s lead assets, delpacibart braxlosiran (del-brax), has posted a mid-stage win in the rare muscle wasting disease facioscapulohumeral muscular dystrophy (FSHD).
In the Phase I/II FORTITUDE study (NCT05747924), Avidity investigated the safety, pharmacokinetics (PK) and pharmacodynamics (PD), as well as the exploratory efficacy of del-brax, an antibody-oligonucleotide conjugate, in 90 patients with FSHD.
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Within the biomarker cohort of FORTITUDE, del-brax triggered a significant drop in creatine kinase and KDHC1L levels – replicating the results observed in an earlier dose escalation cohort of the trial and meeting the primary endpoint. Both proteins act as key biomarkers of disease activity in FSHD and Novartis says their reduction highlights del-brax’s “strong target engagement”, as well as its ability to reduce FSHD-linked muscle damage.
Del-brax touts first-in-disease potential
According to Novartis global head of neuroscience and gene therapy development, Nazem Atassi, the updated FORTITUDE results also “validate the dosing regimen” used in the Phase III FORTITUDE-3 trial (NCT07038200), which is currently recruiting. Avidity estimates the multinational study will enrol 200 patients, with data expected in Q3, 2028.
Novartis originally absorbed the rights to del-brax, as well as two other clinical-stage neuromuscular disease therapies, through its $12bn Avidity Biosciences buyout, which aligned with the company’s goal to pursue value-creating, bolt-on deals to strengthen its pipeline growth.
If del-brax is successful in late-stage trials, it could become the first approved therapy to reach patients with FSHD, who currently rely on pain management, physical therapy and supportive care as their main treatment options. While researchers class FSHD as a rare disease, it is currently the most common form of muscular dystrophy. FSHD is estimated to impact between 45,000 and 87,000 people in the US and EU combined.
By suppressing Double Homeobox 4 (DUX4), a gene at the root of FSHD, in a patient’s muscle cells, del-brax could offer a therapy with the potential to modify the course of disease, and improve outcomes and general quality of life.
Race to the FSHD market
While Novartis currently holds the most advanced clinical FSHD candidate, the Swiss pharma giant is not alone in its mission to secure a place on the market, as Scholar Rock is also looking into the potential of its muscle growth promoter, apitegromab, in FSHD in a Phase II study (NCT07435129).
The US Food and Drug Administration (FDA) recently accepted the drug, which acts as a selective myostatin inhibitor, for US regulatory review for the treatment of spinal muscular atrophy (SMA), after the agency previously refused to approve the drug based on its concerns around third-party manufacturing. The regulator’s new target action date for apitegromab in SMA is 30 September 2026.
Satellos Bioscience is also planning to initiate a Phase II trial on its adaptor-associated kinase 1 (AAK1) inhibitor, SAT-3247, for the treatment of FSHD later on in the year, according to a March 2026 company presentation.
