Real-world experience with eculizumab and switching to ravulizumab for generalized myasthenia gravis.

OBJECTIVE: Eculizumab and ravulizumab are complement protein C5 inhibitors, showing efficacy and tolerability for patients with anti-acetylcholine receptor-positive (AChR+) generalized myasthenia gravis (gMG) in phase 3 clinical trials and subsequent analyses. The purpose of the present study was to evaluate the clinical significance of eculizumab and switching to ravulizumab for refractory AChR+ gMG patients in the real-world experience. METHODS: Among the database of Japan MG registry survey 2021, we studied AChR+ gMG patients who received eculizumab. We also evaluated these patients who switched from eculizumab to ravulizumab. Responder was defined as an improvement of at least 3 points in MG-ADL. We performed a questionnaire of preference between eculizumab and ravulizumab. RESULTS: Among 1,106 patients with AChR+ gMG, 36 patients (3%) received eculizumab (female 78%, mean age 56.0 years). Eculizumab was preferentially used in severe and refractory MG patients. The duration of eculizumab treatment was 35 months on average. MG-ADL improved from 9.4 ± 4.9 to 5.9 ± 5.1, and 25 (70%) of the 36 gMG patients were responders. Postintervention status was markedly improved after the eculizumab treatment. Of 13 patients who did not continue eculizumab, 6 showed insufficiencies. Early onset MG was most effective. However, 15 patients switching from eculizumab to ravulizumab kept favorable response and tolerability. Questionnaire surveys showed preference for ravulizumab over eculizumab. INTERPRETATION: Eculizumab and switching to ravulizumab showed to be effective for refractory AChR+ gMG patients in clinical settings.

Design and Biological Evaluation of the Long-Acting C5-Inhibited Ornithodoros moubata Complement Inhibitor (OmCI) Modified with Fatty Acid.

Disorder of complement response is a significant pathogenic factor causing some autoimmune and inflammation diseases. The Ornithodoros moubata Complement Inhibitor (OmCI), a small 17 kDa natural protein, was initially extracted from soft tick salivary glands. The protein was found binding to complement C5 specifically, inhibiting the activation of the complement pathway, which is a successful therapeutic basis of complement-mediated diseases. However, a short half-life due to rapid renal clearance is a common limitation of small proteins for clinical application. In this study, we extended the half-life of OmCI by modifying it with fatty acid, which was a method used to improve the pharmacokinetics of native peptides and proteins. Five OmCI mutants were initially designed, and single-site cysteine mutation was introduced to each of them. After purification, four OmCI mutants were obtained that showed similar in vitro biological activities. Three mutants of them were subsequently coupled with different fatty acids by nucleophilic substitution. In total, 15 modified derivatives were screened and tested for anticomplement activity in vitro. The results showed that coupling with fatty acid would not significantly affect their complement-inhibitory activity (CH50 and AH50). OmCIT90C-CM02 and OmCIT90C-CM05 were validated as the applicable OmCI bioconjugates for further pharmacokinetic assessments, and both showed improved plasma half-life in mice compared with unmodified OmCI (15.86, 17.96 vs 2.57 h). In summary, our data demonstrated that OmCI conjugated with fatty acid could be developed as the potential long-acting C5 complement inhibitor in the clinic.

Promising therapies for the treatment of myasthenia gravis.

INTRODUCTION: Myasthenia gravis (MG) is an autoimmune condition targeting the neuromuscular junction, which manifests with neuromuscular symptoms of varying severity and significant morbidity. The mainstay of treatment in MG is mitigation of the immune cascade with steroids and non-steroidal immunosuppressive therapies. The therapeutic strategies in MG are transitioning from broad and indiscriminate immunosuppression to novel agents targeting key steps in MG pathogenesis, including T cell activation, B cell proliferation, complement activation, maintenance of pathogenic antibody production, and proinflammatory cytokine production. AREAS COVERED: In this review, an overview of the pathogenesis of MG and traditional MG therapies is presented, followed by a discussion of the novel MG drugs that have been evaluated in phase 3 clinical trials with an emphasis on those which have received regulatory approval. EXPERT OPINION: Novel MG therapeutics belonging to the classes of complement inhibitors, neonatal Fc receptor (FcRn) inhibitors and B cell depletors, as well as the other emerging MG drugs in the pipeline constitute promising treatment strategies with potentially better efficacy and safety compared to the conventional MG treatments. However, further long-term research is needed in order to optimize the implementation of these new treatment options for the appropriate patient populations.

Triple-fusion protein (TriFu): A potent, targeted, enzyme-like inhibitor of all three complement activation pathways.

The introduction of a therapeutic anti-C5 antibody into clinical practice in 2007 inspired a surge into the development of complement-targeted therapies. This has led to the recent approval of a C3 inhibitory peptide, an antibody directed against C1s and a full pipeline of several complement inhibitors in preclinical and clinical development. However, no inhibitor is available that efficiently inhibits all three complement initiation pathways and targets host cell surface markers as well as complement opsonins. To overcome this, we engineered a novel fusion protein combining selected domains of the three natural complement regulatory proteins decay accelerating factor, factor H and complement receptor 1. Such a triple fusion complement inhibitor (TriFu) was recombinantly expressed and purified alongside multiple variants and its building blocks. We analyzed these proteins for ligand binding affinity and decay acceleration activity by surface plasmon resonance. Additionally, we tested complement inhibition in several in vitro/ex vivo assays using standard classical and alternative pathway restricted hemolysis assays next to hemolysis assays with paroxysmal nocturnal hemoglobinuria erythrocytes. A novel in vitro model of the alternative pathway disease C3 glomerulopathy was established to evaluate the potential of the inhibitors to stop C3 deposition on endothelial cells. Next to the novel engineered triple fusion variants which inactivate complement convertases in an enzyme-like fashion, stoichiometric complement inhibitors targeting C3, C5, factor B, and factor D were tested as comparators. The triple fusion approach yielded a potent complement inhibitor that efficiently inhibits all three complement initiation pathways while targeting to surface markers.

Complement inhibitors in pediatric kidney diseases: new therapeutic opportunities.

Historically, the complement system (classical, lectin, alternative, and terminal pathways) is known to play a crucial role in the etiopathogenesis of many kidney diseases. Direct or indirect activation in these settings is revealed by consumption of complement proteins at the serum level and kidney tissue deposition seen by immunofluorescence and electron microscopy. The advent of eculizumab has shown that complement inhibitors may improve the natural history of certain kidney diseases. Since then, the number of available therapeutic molecules and experimental studies on complement inhibition has increased exponentially. In our narrative review, we give a summary of the main complement inhibitors that have completed phase II and phase III studies or are currently used in adult and pediatric nephrology. The relevant full-text works, abstracts, and ongoing trials (clinicaltrials.gov site) are discussed. Data and key clinical features are reported for eculizumab, ravulizumab, crovalimab, avacopan, danicopan, iptacopan, pegcetacoplan, and narsoplimab. Many of these molecules have been shown to be effective in reducing proteinuria and stabilizing kidney function in different complement-mediated kidney diseases. Thanks to their efficacy and target specificity, these novel drugs may radically improve the outcome of complement-mediated kidney diseases, contributing to an improvement in our understanding of their underlying pathophysiology.

Complement in human disease: approved and up-and-coming therapeutics.

The complement system is recognised as a protector against blood-borne pathogens and a controller of immune system and tissue homoeostasis. However, dysregulated complement activity is associated with unwanted or non-resolving immune responses and inflammation, which induce or exacerbate the pathogenesis of a broad range of inflammatory and autoimmune diseases. Although the merit of targeting complement clinically has long been acknowledged, the overall complement drug approval rate has been modest. However, the success of the humanised anti-C5 antibody eculizumab in effectively treating paroxysmal nocturnal haemoglobinuria and atypical haemolytic syndrome has revitalised efforts to target complement therapeutically. Increased understanding of complement biology has led to the identification of novel targets for drug development that, in combination with advances in drug discovery and development technologies, has resulted in a surge of interest in bringing new complement therapeutics into clinical use. The rising number of approved drugs still almost exclusively target rare diseases, but the substantial pipeline of up-and-coming treatment options will possibly provide opportunities to also expand the clinical targeting of complement to common diseases.

Complement System Inhibitory Drugs in a Zebrafish (Danio rerio) Model: Computational Modeling.

The dysregulation of complement system activation usually results in acute or chronic inflammation and can contribute to the development of various diseases. Although the activation of complement pathways is essential for innate defense, exacerbated activity of this system may be harmful to the host. Thus, drugs with the potential to inhibit the activation of the complement system may be important tools in therapy for diseases associated with complement system activation. The synthetic peptides Cp40 and PMX205 can be highlighted in this regard, given that they selectively inhibit the C3 and block the C5a receptor (C5aR1), respectively. The zebrafish (Danio rerio) is a robust model for studying the complement system. The aim of the present study was to use in silico computational modeling to investigate the hypothesis that these complement system inhibitor peptides interact with their target molecules in zebrafish, for subsequent in vivo validation. For this, we analyzed molecular docking interactions between peptides and target molecules. Our study demonstrated that Cp40 and the cyclic peptide PMX205 have positive interactions with their respective zebrafish targets, thus suggesting that zebrafish can be used as an animal model for therapeutic studies on these inhibitors.

Implications of Complement Imbalance in COVID-19: A Molecular Mechanistic Discussion on the Importance of Complement Balance.

Two central questions in COVID-19 treatment which should be considered are: "How does the imbalance of the complement system affect the therapeutic approaches?" and "Do we consider complement inhibitors in therapeutic protocols?". The complement system is a double-edged sword since it may either promote immune responses against COVID-19 or contribute to destructive inflammation in the host. Therefore, it is crucial to regulate this system with complement inhibitors. In this manuscript, we discuss the molecular mechanisms of complement and complement inhibitors in COVID-19 patients. We searched the terms "COVID-19", "Complement", "Complement inhibitor", "SARS-CoV-2", and all complement fragments and inhibitors from 2000 to 2022 in PubMed and google scholar and checked the pathways in "KEGG pathway database". Complement is not well-appreciated in the treatment protocols despite its multiple roles in the disease, and most of the preventive anti-inflammatory therapeutic approaches did not include a complement inhibitor in COVID-19 therapeutic protocols. In this review article, we discussed the most recent studies regarding complement components mediated interventions and the mechanism of these interventions in COVID-19 patients. Since the control of the complement system overactivation is associated with a better prognosis in the initial stages of COVID-19, heparin, anti-thrombin, C1-inhibitor, montelukast, and hydralazine can be effective in the initial stages of this viral infection. Recombinant complement activation (RCA) proteins are more effective in regulating complement compared to terminal pathway therapeutic approaches such as the C3a and C5a inhibitors.

Complement inhibitors for kidney disease.

A refined understanding of the role of complement in the pathogenesis of glomerular and other kidney diseases has, over the past two decades, been matched by the development of novel, complement-targeting therapies. As we increasingly recognize the important role that complement activation across all three pathways-classical, lectin and alternative-plays in glomerular lesions both rare (e.g. C3 glomerulopathy) and common (e.g. immunoglobulin A nephropathy), we can identify avenues for precise, targeted approaches to modifying the natural history of these kidney diseases. In this review, we survey the evidence on using complement inhibition from the earliest, small-scale studies focusing on C5-targeting agents to more recent, large, multicenter, randomized trials utilizing complement blockade higher up in the complement pathway at the level of C3. We conclude by examining where the field of complement targeting therapy may be headed in light of these studies.

Complement-targeted therapeutics: An emerging field enabled by academic drug discovery.

Within a short few years, the number of complement inhibitors that are either approved for therapeutic application or evaluated in late-stage clinical trials has expanded remarkably. The sudden emergence of this target area in the pipelines of many biotech start-ups and even large pharmaceutical companies appears even more surprising when considering that the involvement of the complement system in various clinical conditions had long been recognized. In many aspects, however, the complement system is far from being a traditional drug target, which may explain the delayed breakthrough of this therapeutic strategy. While complement modulation is now considered an attractive "platform technology" with applications in a wide spectrum of disorders, the broad yet heterogeneous disease involvement of the complement system has long restricted its placement in traditional drug discovery programs. Concerns about the safety of complement-targeted interventions, the large number and high plasma concentrations of target proteins, and the complexity of the complement system's engagement in biological processes are among other factors that kept complement off the drug discovery radar for decades. Alongside technical advances and financial incentives, the innovation and persistence of academic and clinical researchers have been the critical driving force to navigate complement therapeutics out of the shadow into the spotlight. In this commentary, we document this remarkable development using select examples and aim to venture some predictions where this promising field may be headed to.

Biomarkers and laboratory assessments for monitoring the treatment of patients with paroxysmal nocturnal hemoglobinuria: Differences between terminal and proximal complement inhibition.

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, life-threatening, acquired disease in which blood cells lacking complement regulatory proteins are destroyed because of uncontrolled complement activity. Since 2007, terminal complement inhibitors have revolutionized the treatment of this disease. However, patients treated with these inhibitors can still experience anemia because of C3-mediated extravascular hemolysis and clinically relevant levels of breakthrough or residual intravascular hemolysis. Proximal complement inhibitors, which are only just beginning to emerge, have the potential to address this problem by targeting components of the pathway upstream of C5, thereby protecting patients against both intra- and extravascular hemolysis. In this review, we describe different biomarkers that can be used to monitor complement pathway blockade and discuss key laboratory assessments for evaluating treatment efficacy. We also consider how these assessments are affected by each class of inhibitor and highlight how evolving treatment goals may influence the relative importance of these assessments.

Paroxysmal nocturnal hemoglobinuria: Where we stand.

For the last 20 years, therapy of paroxysmal nocturnal hemoglobinuria (PNH) relied-up until recently-on antibody based terminal complement inhibitionon. PNH pathophysiology-a mutational defect leading to partial or complete absence of complement-regulatory proteins on blood cells-leads to intravascular hemolysis and consequences such as thrombosis and other sequelae. A plethora of new drugs interfering with the proximal and terminal complement cascade are under recent development and the first "proof-of-pinciple" proximal complement inhibitor targeting C3 has been approved in 2021. "PNH: where we stand" will try to give a brief account on where we came from and where we stand focusing on approved therapeutic options. The associated improvements as well as potential consequences of actual and future treatments as well as their impact on the disease will continue to necessitate academic and scientific focus on improving treatment options as well as on side effects and outcomes relevant to individual patient lives and circumstances in order to develop effective, safe, and available treatment for all hemolytic PNH patients globally.

Protein therapeutics and their lessons: Expect the unexpected when inhibiting the multi-protein cascade of the complement system.

Over a century after the discovery of the complement system, the first complement therapeutic was approved for the treatment of paroxysmal nocturnal hemoglobinuria (PNH). It was a long-acting monoclonal antibody (aka 5G1-1, 5G1.1, h5G1.1, and now known as eculizumab) that targets C5, specifically preventing the generation of C5a, a potent anaphylatoxin, and C5b, the first step in the eventual formation of membrane attack complex. The enormous clinical and financial success of eculizumab across four diseases (PNH, atypical hemolytic uremic syndrome (aHUS), myasthenia gravis (MG), and anti-aquaporin-4 (AQP4) antibody-positive neuromyelitis optica spectrum disorder (NMOSD)) has fueled a surge in complement therapeutics, especially targeting diseases with an underlying complement pathophysiology for which anti-C5 therapy is ineffective. Intensive research has also uncovered challenges that arise from C5 blockade. For example, PNH patients can still face extravascular hemolysis or pharmacodynamic breakthrough of complement suppression during complement-amplifying conditions. These "side" effects of a stoichiometric inhibitor like eculizumab were unexpected and are incompatible with some of our accepted knowledge of the complement cascade. And they are not unique to C5 inhibition. Indeed, "exceptions" to the rules of complement biology abound and have led to unprecedented and surprising insights. In this review, we will describe initial, present and future aspects of protein inhibitors of the complement cascade, highlighting unexpected findings that are redefining some of the mechanistic foundations upon which the complement cascade is organized.

Management of infection in PNH patients treated with eculizumab or other complement inhibitors: Unmet clinical needs.

This article presents the results of group discussion among an ad hoc constituted panel of experts aimed at identifying and addressing unmet clinical needs (UCNs) in the management of infectious risk associated with eculizumab or new terminal complement inhibitors (CIs) in paroxysmal nocturnal hemoglobinuria (PNH). With the Delphi technique, the most clinically relevant UCNs in PNH patients candidate to or on terminal CI were selected. They resulted to be: optimizing the infection prevention measures; developing non pharmacological infectious risk-mitigation strategies; improving the management of disease exacerbation during infectious complications. For each of these issues consensus opinions were provided and, when appropriate, proposals for advancement in clinical practice were addressed. The hope is that this comprehensive overview will serve to improve the practice of CIs therapy and inform the design and implementation of new studies in the field.

With complements: C3 inhibition in the clinic.

C3 is a key complement protein, located at the nexus of all complement activation pathways. Extracellular, tissue, cell-derived, and intracellular C3 plays critical roles in the immune response that is dysregulated in many diseases, making it an attractive therapeutic target. However, challenges such as very high concentration in blood, increased acute expression, and the elevated risk of infections have historically posed significant challenges in the development of C3-targeted therapeutics. This is further complicated because C3 activation fragments and their receptors trigger a complex network of downstream effects; therefore, a clear understanding of these is needed to provide context for a better understanding of the mechanism of action (MoA) of C3 inhibitors, such as pegcetacoplan. Because of C3's differential upstream position to C5 in the complement cascade, there are mechanistic differences between pegcetacoplan and eculizumab that determine their efficacy in patients with paroxysmal nocturnal hemoglobinuria. In this review, we compare the MoA of pegcetacoplan and eculizumab in paroxysmal nocturnal hemoglobinuria and discuss the complement-mediated disease that might be amenable to C3 inhibition. We further discuss the current state and outlook for C3-targeted therapeutics and provide our perspective on which diseases might be the next success stories in the C3 therapeutics journey.

Pegcetacoplan: A Review in Paroxysmal Nocturnal Haemoglobinuria.

Subcutaneous pegcetacoplan (EMPAVELI® in the USA and ASPAVELI® in the EU) is the first complement component 3 (C3) inhibitor approved for the treatment of adults with paroxysmal nocturnal haemoglobinuria (PNH) in the USA, and in adults with PNH who are anaemic after ≥ 3 months of treatment with a C5 inhibitor in the EU. In the phase III PRINCE trial in adults with PNH who were anaemic and naïve to a complement inhibitor therapy, pegcetacoplan was superior to the control group (supportive care, excluding complement inhibitors) in achieving haemoglobin stabilization and reducing lactate dehydrogenase levels. Similarly, in the phase III PEGASUS trial in adults with PNH who had a haemoglobin level < 10.5 g/dL despite eculizumab therapy, pegcetacoplan was superior to eculizumab in improving haemoglobin levels. In both trials, pegcetacoplan also improved other clinical and haematological parameters of haemolysis, as well as quality of life (QOL) outcomes. Clinical benefits of pegcetacoplan were sustained for up to 48 weeks of treatment. Pegcetacoplan was generally well tolerated in patients with PNH, with its tolerability profile being similar in patients previously treated with eculizumab and in complement inhibitor-naïve patients. Long-term data would be beneficial to further support the safety profile of pegcetacoplan. Current evidence indicates that pegcetacoplan is a valuable treatment option for adults with PNH.

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare haematological disorder that is characterized by complement-mediated haemolysis, fatigue and thrombotic events. Complement component 5 (C5) inhibitors eculizumab and ravulizumab have demonstrated substantial efficacy in reducing intravascular haemolysis and improving quality of life (QOL) in patients with PNH; however, many patients continue to exhibit anaemia and require transfusions because of uncontrolled extravascular haemolysis. Subcutaneous pegcetacoplan (EMPAVELI^® in the USA and ASPAVELI^® in the EU) is the first C3 inhibitor approved in the USA and EU for the treatment of PNH. Pegcetacoplan targets C3 in the complement cascade, upstream of C5, thereby providing control over both intravascular and extravascular haemolysis. Pegcetacoplan was superior to supportive care in improving clinical and haematological outcomes in patients with PNH who were naïve to a complement inhibitor therapy. Similarly, pegcetacoplan was superior to eculizumab in improving clinical and haematological outcomes in patients with uncontrolled PNH despite eculizumab therapy. Pegcetacoplan also improved QOL and fatigue symptoms. Pegcetacoplan was generally well tolerated, with most adverse events being mild to moderate in severity. Current evidence indicates that pegcetacoplan is a valuable treatment option for adults with PNH.

[Complement inhibitors: A global point of view]. / Les inhibiteurs du complément : une vue d'ensemble.

Innate immunity, and more specifically the complement system, has arised renewed interest in the medical field in recent years. Many innovative complement-inhibiting drugs have appeared, acting at various levels of the complement cascade. These drugs have made it possible to transform poor prognosis of certain diseases. Many of them are currently being tested in clinical trials for various indications. Many questions appear about their optimal use and their future indications. This article recalls the fundamental role of the complement system in the human organism. It then discusses the diseases in which the complement is involved on the pathophysiological level. The third part details the different classes of complement inhibitors and briefly recalls the indications for which these treatments seem the most promising. Finally, we end with a discussion that highlights the different aspects and questions induced by these new treatments.

Insight into mode-of-action and structural determinants of the compstatin family of clinical complement inhibitors.

With the addition of the compstatin-based complement C3 inhibitor pegcetacoplan, another class of complement targeted therapeutics have recently been approved. Moreover, compstatin derivatives with enhanced pharmacodynamic and pharmacokinetic profiles are in clinical development (e.g., Cp40/AMY-101). Despite this progress, the target binding and inhibitory modes of the compstatin family remain incompletely described. Here, we present the crystal structure of Cp40 complexed with its target C3b at 2.0-Å resolution. Structure-activity-relationship studies rationalize the picomolar affinity and long target residence achieved by lead optimization, and reveal a role for structural water in inhibitor binding. We provide explanations for the narrow species specificity of this drug class and demonstrate distinct target selection modes between clinical compstatin derivatives. Functional studies provide further insight into physiological complement activation and corroborate the mechanism of its compstatin-mediated inhibition. Our study may thereby guide the application of existing and development of next-generation compstatin analogs.