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

Inflammatory myopathies in 2024: Better classify them to better treat them

The discovery, over the last forty years or so, of specific myositis auto-antibodies (easily dosed in routine nowadays) and the fine clinically and pathologically phenotypic descriptions of affected patients have made it possible to review the classification of inflammatory myopathies. The arrival of "omic" techniques has also led to the discovery of different pathophysiological mechanisms among these different subgroups of myositis. Naturally, therapeutic approaches specifically targeting the representative abnormal pathways of each subgroup are being evaluated. This modern approach to myositis, which is clinical, pathophysiological, and therapeutic in the making, is presented in this review article.

Recent Updates on the Pathogenesis of Inflammatory Myopathies

PURPOSE OF REVIEW

This review aims to provide a comprehensive and updated overview of autoimmune myopathies, with a special focus on the latest advancements in understanding the role of autoantibodies. We will begin by examining the risk factors and triggers associated with myositis. Next, we will delve into recent research on how autoantibodies contribute to disease pathogenesis. Finally, we will explore the latest innovations in treatment strategies and their implications for our understanding of myositis pathogenesis.

RECENT FINDINGS

Recent research has revealed that myositis-specific autoantibodies can infiltrate muscle cells and disrupt the function of their target autoantigens, playing a crucial role in disease pathogenesis. Significant advances in treatment include CD19 CAR-T cell therapy, JAK-STAT inhibitors, and novel strategies targeting the type 1 interferon pathway in dermatomyositis. Additionally, the ineffectiveness of complement inhibitors in treating immune-mediated necrotizing myositis has challenged established views on disease mechanisms. Autoimmune myopathies are a collection of disorders significantly influenced by specific autoantibodies that drive disease pathogenesis. This review highlights the critical role of autoantibody research in deepening our understanding of these conditions and discusses recent therapeutic advancements targeting key pathogenic pathways.

Immune-mediated necrotizing myopathy: A comprehensive review of the pathogenesis, clinical features, and treatments

Immune-mediated necrotizing myopathy (IMNM) is a rare and newly recognized autoimmune disease within the spectrum of idiopathic inflammatory myopathies. It is characterized by myositis-specific autoantibodies, elevated serum creatine kinase levels, inflammatory infiltrate, and weakness. IMNM can be classified into three subtypes based on the presence or absence of specific autoantibodies: anti-signal recognition particle myositis, anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase myositis, and seronegative IMNM. In recent years, IMNM has gained increasing attention and emerged as a research hotspot. Recent studies have suggested that the pathogenesis of IMNM is linked to aberrant activation of immune system, including immune responses mediated by antibodies, complement, and immune cells, particularly macrophages, as well as abnormal release of inflammatory factors. Non-immune mechanisms such as autophagy and endoplasmic reticulum stress also participate in this process. Additionally, genetic variations associated with IMNM have been identified, providing new insights into the genetic mechanisms of the disease. Progress has also been made in IMNM treatment research, including the use of immunosuppressants and the development of biologics. Despite the challenges in understanding the etiology and treatment of IMNM, the latest research findings offer important guidance and insights for delving deeper into the disease's pathogenic mechanisms and identifying new therapeutic strategies.

Immune-Mediated Necrotizing Myopathy (IMNM): A Story of Antibodies

Immune-mediated necrotizing myopathy (IMNM) is a rare and severe disease that corresponds to a specific entity of idiopathic inflammatory myopathy. Patients with IMNM suffer from proximal muscle weakness, and present high levels of creatine kinase and necrotic myofibers. Anti-Signal Recognition Particle (SRP) and anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase autoantibodies (HMGCR) have recently been identified in two thirds of patients with IMNM and are used as a hallmark of the disease. In this review, we provide a detailed description of these antibodies and the tests used to detect them in the serum of patients. Based on in vitro studies and mouse models of IMNM, we discuss the role of autoantibodies in the pathogenesis of the disease. Finally, in the light of the latest knowledge, we conclude with a review of recent therapeutic approaches in IMNM.

Myasthenia Gravis Treatment: From Old Drugs to Innovative Therapies with a Glimpse into the Future

Myasthenia gravis (MG) is a rare autoimmune disease that causes debilitating muscle weakness due to impaired neuromuscular transmission. Since most (about 80-90%) MG patients present autoantibodies against the acetylcholine receptor, standard medical therapy consists of symptomatic treatment with acetylcholinesterase inhibitors (e.g., pyridostigmine). In addition, considering the autoimmune basis of MG, standard therapy includes immunomodulating agents, such as corticosteroids, azathioprine, cyclosporine A, and cyclophosphamide. New strategies have been proposed for the treatment of MG and include complement blockade (i.e., eculizumab, ravulizumab, and zilucoplan) and neonatal Fc receptor antagonism (i.e., efgartigimod and rozanolixizumab). The aim of this review is to provide a detailed overview of the pre- and post-marketing evidence on the five pharmacological treatments most recently approved for the treatment of MG, by identifying both preclinical and clinical studies registered in clinicaltrials.gov. A description of the molecules currently under evaluation for the treatment of MG is also provided.

Contribution of Complement, Microangiopathy and Inflammation in Idiopathic Inflammatory Myopathies

PURPOSE OF REVIEW

Idiopathic inflammatory myopathies (IIMs) are a heterogeneous group characterized by muscle weakness and skin symptoms and are categorized into six subtypes: dermatomyositis (DM), polymyositis (PM), anti-synthetase syndrome (ASS), immune-mediated myopathy (IMNM), inclusion body myopathy (IBM), and overlap myositis. Myositis-specific autoantibodies were detected for the diagnosis and classification of IIM. This review highlights the pathogenic contributions of the complement system, microangiopathy, and inflammation in IIM.

RECENT FINDINGS

Deposition of complement around capillaries and/or the sarcolemma was observed in muscle biopsy specimens from patients with DM, ASS, and IMNM, suggesting the pathomechanism of complement-dependent muscle and endothelial cell injury. A recent study using human muscle microvascular endothelial cells showed that Jo-1 antibodies from ASS induce complement-dependent cellular cytotoxicity in vitro. Based on both clinical and pathological observations, antibody- and complement-mediated microangiopathy may contribute to the development of DM and anti-Jo-1 ASS. Juvenile DM is characterized by the loss of capillaries, perivascular inflammation, and small-vessel angiopathies, which may be related to microinfarction and perifascicular atrophy. Several serum biomarkers that reflect the IFN1 signature and microangiopathy are elevated in patients with DM. The pathological observation of myxovirus resistance protein A (MxA), which suggests a type 1 interferon (IFN1) signature in DM, supports the diagnosis and further understanding of the pathomechanism of IIM. A recent report showed that an increase in triggering receptor expressed on myeloid cells (TREM-1) around perimysial blood vessels and muscles in patients with IIM plays a role in triggering inflammation and promoting the migration of inflammatory cells by secreting proinflammatory cytokines, such as tumor necrosis factor α.

SUMMARY

The deposition of complement in muscles and capillaries is a characteristic feature of DM, ASS, and IMNM. Microangiopathy plays a pathogenic role in DM, possibly resulting in perifascicular atrophy. Further understanding of the detailed pathomechanism regarding complement, microangiopathy, and inflammation may lead to novel therapeutic approaches for IIM.

Efgartigimod restores muscle function in a humanized mouse model of immune-mediated necrotizing myopathy

OBJECTIVE

Immune-mediated necrotizing myopathies (IMNMs) are severe forms of myositis often associated with pathogenic anti-3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) autoantibodies (aAbs). Efgartigimod is an engineered human IgG1 Fc fragment that antagonizes the neonatal Fc receptor (FcRn), thereby preventing recycling and promoting lysosomal degradation of IgG, including aAbs. We evaluated the therapeutic effects of IgG reduction by efgartigimod in a humanized murine model of IMNM.

METHODS

Disease was induced in C5-deficient (C5def) or Rag2-deficient (Rag2-/-) mice receiving co-injections of anti-HMGCR+ IgG from an IMNM patient and human complement. C5def mice were treated in a preventive setting with s.c. injections of efgartigimod and Rag2-/- mice in a curative setting after disease was induced by anti-HMGCR+ IgG injections. Anti-HMGCR aAbs levels were monitored in mouse serum and muscle tissue. Histological analysis was performed on muscle sections. Muscle force was assessed by grip test or measurement of gastrocnemius strength upon electrostimulation.

RESULTS

Administration of efgartigimod rapidly reduced total IgG levels, including the level of pathogenic anti-HMGCR aAbs, in both serum (P < 0.0001) and muscle (P < 0.001). In the preventive setting, efgartigimod prevented myofibre necrosis (P < 0.05), thus precluding loss of muscle strength (P < 0.05). In the therapeutic setting, efgartigimod prevented further necrosis and allowed muscle fibre regeneration (P < 0.05). Hence, muscle strength returned to normal (P < 0.01).

CONCLUSION

Efgartigimod reduces circulating IgG levels, including pathogenic anti-HMGCR+ IgG aAbs, in a humanized mouse model of IMNM, preventing further necrosis and allowing muscle fibre regeneration. These results support investigating the therapeutic efficacy of efgartigimod through a clinical trial in IMNM patients.

Stromal vascular fraction in the treatment of myositis

Muscle regeneration is a physiological process that converts satellite cells into mature myotubes under the influence of an inflammatory environment progressively replaced by an anti-inflammatory environment, with precise crosstalk between immune and muscular cells. If the succession of these phases is disturbed, the immune system can sometimes become auto-reactive, leading to chronic muscular inflammatory diseases, such as myositis. The triggers of these autoimmune myopathies remain mostly unknown, but the main mechanisms of pathogenesis are partially understood. They involve chronic inflammation, which could be associated with an auto-reactive immune response, and gradually with a decrease in the regenerative capacities of the muscle, leading to its degeneration, fibrosis and vascular architecture deterioration. Immunosuppressive treatments can block the first part of the process, but sometimes muscle remains weakened, or even still deteriorates, due to the exhaustion of its capacities. For patients refractory to immunosuppressive therapies, mesenchymal stem cells have shown interesting effects but their use is limited by their availability. Stromal vascular fraction, which can easily be extracted from adipose tissue, has shown good tolerance and possible therapeutic benefits in several degenerative and autoimmune diseases. However, despite the increasing use of stromal vascular fraction, the therapeutically active components within this heterogeneous cellular product are ill-defined and the mechanisms by which this therapy might be active remain insufficiently understood. We review herein the current knowledge on the mechanisms of action of stromal vascular fraction and hypothesise on how it could potentially respond to some of the unmet treatment needs of refractory myositis.

Zilucoplan in immune-mediated necrotising myopathy: a phase 2, randomised, double-blind, placebo-controlled, multicentre trial

Background

Immune-mediated necrotizing myopathy (IMNM) is an autoimmune myopathy characterised by proximal muscle weakness, high creatine kinase (CK) values, and autoantibodies recognizing 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) or the signal recognition particle (SRP). There are currently no approved therapies for IMNM and many patients experience active disease despite off-label treatment with intravenous immunoglobulin, glucocorticoids, and immunosuppressants. Detection of complement-activating anti-HMGCR and anti-SRP autoantibodies and the presence of complement deposition on the sarcolemma of non-necrotic myofibers led to the hypothesis that complement activation may be pathogenic in IMNM, therefore zilucoplan, a complement component 5 (C5) inhibitor, could be a potential therapy.

Methods

IMNM01, a phase 2, multicenter, randomised, double-blind, placebo-controlled study (NCT04025632) at 15 sites (four countries) evaluated efficacy, safety, and tolerability of zilucoplan in adult participants with anti-HMGCR or anti-SRP autoantibody-positive IMNM. Participants were randomised 1:1 to receive daily subcutaneous zilucoplan (0·3mg/kg) or placebo for eight weeks; with optional enrolment in the study open-label extension. Primary efficacy endpoint was percent change from baseline to Week 8 in CK levels. Secondary endpoints included safety.

Findings

Between 07 November 2019 and 07 January 2021, 27 participants (13 female and 14 male) received zilucoplan (n=12) or placebo (n=15) and completed the 8-week main study. At Week 8 there were no clinically relevant or statistically significant differences, despite target engagement based on mode of action, between treatment arms in mean percent change (standard deviation) of CK levels versus baseline (-9·86% [26·06] versus -20·72% [31·22] in zilucoplan [n=10] and placebo arms [n=14], p=0·46, respectively) and no clinically relevant improvement over time within the treatment arm. There were no unexpected adverse safety or tolerability findings. Treatment emergent adverse events (TEAEs) and serious TEAEs were reported in n=9 (75·0%) vs n=13 (86·7%) and n=0 (0%) and n=3 (20·0%) participants, respectively. The most frequent TEAEs were headache (n=4 in both groups [33·3% and 26·7%, respectively]) and nausea (n=3 in both groups [25·0% and 20·0%, respectively]).

Interpretation

C5 inhibition does not appear to be an effective treatment modality for IMNM. Rather than driving myofiber necrosis, complement activation may be secondary to muscle injury.

Funding

Study funded by Ra Pharmaceuticals (now part of UCB Pharma).