Prevention of Anti-HMGCR Immune-Mediated Necrotising Myopathy by C5 Complement Inhibition in a Humanised Mouse Model

Introduction: immune-mediated necrotising myopathy (IMNM) is associated with pathogenic anti-signal recognition particle (SRP) or 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) antibodies, at least partly through activation of the classical pathway of the complement. We evaluated zilucoplan, an investigational drug, and a macrocyclic peptide inhibitor of complement component 5 (C5), in humanized mouse models of IMNM. Methods: purified immunoglobulin G (IgG) from an anti-HMGCR(+) IMNM patient was co-injected intraperitoneally with human complement in C57BL/6, C5-deficient B10 (C5(def)) and Rag2 deficient (Rag2(-/-)) mice. Zilucoplan was administered subcutaneously in a preventive or interventional paradigm, either injected daily throughout the duration of the experiment in C57BL/6 and C5(def) mice or 8 days after disease induction in Rag2(-/-) mice. Results: prophylactic administration of zilucoplan prevented muscle strength loss in C5(def) mice (anti-HMGCR(+) vs. anti-HMGCR(+) + zilucoplan: p = 0.0289; control vs. anti-HMGCR(+) + zilucoplan: p = 0.4634) and wild-type C57BL/6 (anti-HMGCR(+) vs. anti-HMGCR(+) + zilucoplan: p = 0.0002; control vs. anti-HMGCR(+) + zilucoplan: p = 0.0939) with corresponding reduction in C5b-9 deposits on myofibres and number of regenerated myofibres. Interventional treatment of zilucoplan after disease induction reduced the complement deposits and number of regenerated myofibres in muscles of Rag2(-/-) mice, although to a lesser extent. In this latter setting, C5 inhibition did not significantly ameliorate muscle strength. Conclusion: Early administration of zilucoplan prevents the onset of myopathy at the clinical and histological level in a humanized mouse model of IMNM.