The US Food and Drug Administration (FDA) approved Scholar Rock’s rare neuromuscular disease therapy, Isemblyd (apitegromab), making it the first muscle-targeted treatment to reach the market in spinal muscular atrophy (SMA).
This means that Isemblyd, a selective myostatin inhibitor, is now indicated for patients aged two years and older with SMA—specifically if they are already receiving treatment with a standard of care (SoC) survival motor neuron 2 (SMN2) therapy. This could be one of the four targeted drugs of this class approved by US regulators, including medicines such as Biogen and Ionis Pharmaceuticals’ Spinraza (nusinersen) and Novartis’ Zolgensma (onasemnogene abeparvovec-xioi).
The FDA gave Isemblyd the green light based on the outcome of the Phase III SAPPHIRE study (NCT05156320), in which the drug plus SMN2-directed treatment triggered a significant improvement in motor function and physical abilities compared with SMN2-targeted treatment alone at the one-year mark.
Isemblyd nets an indication first
Isemblyd’s approval marks the first time a muscle-targeted treatment has made it to market in SMA. Currently, the SMN2-targeting treatments, which focus on enhancing levels of a protein that protects motor neurons, dominate the therapeutic landscape. Isemblyd, meanwhile, offers a disease-modifying impact in SMA by inhibiting the conversion of the muscle protein, myostatin, into its active form, which naturally limits skeletal muscle growth.
Isemblyd’s approval comes after the FDA’s prior refusal to approve the drug last year, after the agency raised concerns following a routine general site inspection at a third-party, Catalent-owned fill-finish facility that was producing Isemblyd. These observations were not related to Isemblyd itself, and the FDA did not raise any concerns about the drug’s safety or efficacy.
With an approval now secured, Scholar Rock has set up a programme to ensure there is widespread access to Isemblyd. This means that patients can now gain personalised support in securing financial assistance and insurance coverage, education about the disease and its treatment, and navigating site of care options. The company is also working with payers to establish Isemblyd’s broad patient availability across the US.
Scholar claims that Isemblyd will be ready for shipping “in the coming days” and can be administered in both the home and infusion centre settings.
According to a recent report from GlobalData, the parent company of Pharmaceutical Technology, the potential launch of three myostatin inhibitors, including Isemblyd, will act as key future growth drivers for the SMA market. Analysts forecast this drug class will contribute $253m of the $3bn estimated total indication sales in 2033.
