Phase 2 Study Evaluating Apitegromab for the Treatment of FSHD

This Phase 2, randomized, double-blind, placebo-controlled, multicenter study is designed to evaluate the efficacy, safety, and tolerability of apitegromab in participants with facioscapulohumeral muscular dystrophy (FSHD)

• Apitegromab (Drug), also known as SRK-015: Apitegromab (SRK-015) is a fully human anti-promyostatin monoclonal antibody (mAb) that specifically binds to human pro/latent myostatin, inhibiting myostatin activation. Apitegromab will be administered every 4 weeks by intravenous (IV) infusion.
• Placebo (Drug): Placebo is administered every 4 weeks by intravenous (IV) infusion and does not contain the active ingredient.

Primary outcomes

• Assess the efficacy of apitegromab compared with placebo in participants with FSHD [52 Weeks]: Percent change from baseline in total lean muscle volume (LMV) as measured by full body magnetic resonance imaging (MRI) at week 52

Secondary outcomes

• Further assess the efficacy of apitegromab compared with placebo in participants with FSHD [24 Weeks]: Percent change from baseline in total LMV as measured by full body MRI at week 24
• Further assess the efficacy of apitegromab compared with placebo in participants with FSHD [24 Weeks and 52 Weeks]: Change from baseline in additional muscle parameters, such as muscle fat fraction at week 24 and week 52
• Further assess the efficacy of apitegromab compared with placebo in participants with FSHD [24 Weeks and 52 Weeks]: Change from baseline in additional muscle parameters, such as muscle fat infiltration, at week 24 and week 52
• Evaluate the pharmacokinetics of apitegromab in participants with FSHD [52 Weeks]: Serum concentrations of apitegromab
• Evaluate the pharmacodynamics of apitegromab in participants with FSHD [52 Weeks]: Serum concentrations of total latent myostatin
• Evaluate the safety and tolerability of apitegromab in participants with FSHD [52 Weeks]: Incidence of anti-drug antibodies against apitegromab in serum
• Evaluate the safety and tolerability of apitegromab in FSHD participants [52 Weeks]: Incidence of adverse events and serious adverse events

Other outcomes

• Evaluate improvement(s) over time in motor function in participants with FSHD receiving apitegromab [52 Weeks]: Change from baseline in quantitative muscle testing in kilogram-force. Higher score indicates greater function.
• Evaluate improvement(s) over time in motor function in participants with FSHD receiving apitegromab [52 Weeks]: Change from baseline in relative surface area as assessed by reachable workspace. Higher score indicates greater function.
• Evaluate improvement(s) over time in motor function in participants with FSHD receiving apitegromab [52 Weeks]: Change from baseline in FSHD composite outcome measure (FSHD-COM) total score (0 - 72 scale; Higher score indicates greater impairment)

Sex: All, ages: 18 Years to 60 Years

Inclusion Criteria:

1. Male or female participants, 18 to 60 years of age at the time of informed consent.
2. Genetic diagnosis of FSHD Type 1 or FSHD Type 2, confirmed with the appropriate documentation from an accredited laboratory
3. Clinical severity score of 1.5 to 3.0 (Ricci score; range 0 to 5), inclusive, at screening
4. Baseline 10-meter walk/run test time ≤5 seconds

Exclusion Criteria:

1. Prior history of a hypersensitivity reaction to a mAb or recombinant protein bearing an Fc domain (eg, a soluble receptor-Fc fusion protein), apitegromab, or excipients of apitegromab
2. Treatment with other investigational drugs in a clinical trial within 3 months or 5 half-lives, whichever is longer, before screening
3. Previous treatment with apitegromab, or with other anti-myostatin therapies, including activin receptor antagonists
4. Current or prior use of anabolic steroids, growth hormones, glucagon-like peptide-1 receptor agonist or other substances with known effects on muscle.
5. Use of therapies with potentially significant muscle effects (eg, androgens, insulin-like growth factor, growth hormone, systemic beta-agonist, botulinum toxin, or muscle relaxants or muscle-enhancing supplements) or potentially significant neuromuscular effects (eg, acetylcholinesterase inhibitors) within 60 days before screening
6. Use of systemic or corticosteroids within 60 days prior to screening. Inhaled or topical steroids are allowed.
7. Pregnant or breastfeeding.
8. Contraindications for MRI that may include, but are not limited to, certain implanted electronic devices, cochlear implants, metallic foreign bodies, vascular clips, and metallic implants; or claustrophobia, contrast agent allergies, inability to lie still, or external medical devices that may not be removed.
9. History of alcoholism, or illicit drug use (drugs that are illegal and have not been prescribed).
10. Taking medications that impede coagulation or platelet aggregation or has a history or active coagulopathy disorder.
11. Any acute or comorbid condition interfering with the well-being of the participant within 7 days prior to screening, including active systemic infection, the need for acute treatment, or inpatient observation due to any reason