New analogs of the clinical complement inhibitor compstatin with subnanomolar affinity and enhanced pharmacokinetic properties

The renaissance of complement therapeutics

The increasing number of clinical conditions that involve a pathological contribution from the complement system - many of which affect the kidneys - has spurred a regained interest in therapeutic options to modulate this host defence pathway. Molecular insight, technological advances, and the first decade of clinical experience with the complement-specific drug eculizumab, have contributed to a growing confidence in therapeutic complement inhibition. More than 20 candidate drugs that target various stages of the complement cascade are currently being evaluated in clinical trials, and additional agents are in preclinical development. Such diversity is clearly needed in view of the complex and distinct involvement of complement in a wide range of clinical conditions, including rare kidney disorders, transplant rejection and haemodialysis-induced inflammation. The existing drugs cannot be applied to all complement-driven diseases, and each indication has to be assessed individually. Alongside considerations concerning optimal points of intervention and economic factors, patient stratification will become essential to identify the best complement-specific therapy for each individual patient. This Review provides an overview of the therapeutic concepts, targets and candidate drugs, summarizes insights from clinical trials, and reflects on existing challenges for the development of complement therapeutics for kidney diseases and beyond.

Factor H-IgG Chimeric Proteins as a Therapeutic Approach against the Gram-Positive Bacterial Pathogen Streptococcus pyogenes

Bacteria can cause life-threatening infections, such as pneumonia, meningitis, or sepsis. Antibiotic therapy is a mainstay of treatment, although antimicrobial resistance has drastically increased over the years. Unfortunately, safe and effective vaccines against most pathogens have not yet been approved, and thus developing alternative treatments is important. We analyzed the efficiency of factor H (FH)6-7/Fc, a novel antibacterial immunotherapeutic protein against the Gram-positive bacterium Streptococcus pyogenes This protein is composed of two domains of complement inhibitor human FH (FH complement control protein modules 6 and 7) that bind to S. pyogenes, linked to the Fc region of IgG (FH6-7/Fc). FH6-7/Fc has previously been shown to enhance complement-dependent killing of, and facilitate bacterial clearance in, animal models of the Gram-negative pathogens Haemophilus influenzae and Neisseria meningitidis We hypothesized that activation of complement by FH6-7/Fc on the surface of Gram-positive bacteria such as S. pyogenes will enable professional phagocytes to eliminate the pathogen. We found that FH6-7/Fc alleviated S. pyogenes-induced sepsis in a transgenic mouse model expressing human FH (S. pyogenes binds FH in a human-specific manner). Furthermore, FH6-7/Fc, which binds to protein H and selected M proteins, displaced FH from the bacterial surface, enhanced alternative pathway activation, and reduced bacterial blood burden by opsonophagocytosis in a C3-dependent manner in an ex vivo human whole-blood model. In conclusion, FH-Fc chimeric proteins could serve as adjunctive treatments against multidrug-resistant bacterial infections.

Targeted Delivery of Neutralizing Anti-C5 Antibody to Renal Endothelium Prevents Complement-Dependent Tissue Damage

Complement activation is largely implicated in the pathogenesis of several clinical conditions and its therapeutic neutralization has proven effective in preventing tissue and organ damage. A problem that still needs to be solved in the therapeutic control of complement-mediated diseases is how to avoid side effects associated with chronic neutralization of the complement system, in particular, the increased risk of infections. We addressed this issue developing a strategy based on the preferential delivery of a C5 complement inhibitor to the organ involved in the pathologic process. To this end, we generated Ergidina, a neutralizing recombinant anti-C5 human antibody coupled with a cyclic-RGD peptide, with a distinctive homing property for ischemic endothelial cells and effective in controlling tissue damage in a rat model of renal ischemia/reperfusion injury (IRI). As a result of its preferential localization on renal endothelium, the molecule induced complete inhibition of complement activation at tissue level, and local protection from complement-mediated tissue damage without affecting circulating C5. The ex vivo binding of Ergidina to surgically removed kidney exposed to cold ischemia supports its therapeutic use to prevent posttransplant IRI leading to delay of graft function. Moreover, the finding that the ex vivo binding of Ergidina was not restricted to the kidney, but was also seen on ischemic heart, suggests that this RGD-targeted anti-C5 antibody may represent a useful tool to treat organs prior to transplantation. Based on this evidence, we propose preliminary data showing that Ergidina is a novel targeted drug to prevent complement activation on the endothelium of ischemic kidney.

Safety and Efficacy of the Complement Inhibitor AMY-101 in a Natural Model of Periodontitis in Non-human Primates

Periodontitis is a chronic inflammatory disease associated with overactivation of the complement system. Recent preclinical studies suggest that host-modulation therapies may contribute to effective treatment of human periodontitis, which may lead to loss of teeth and function if untreated. We previously showed that locally administered AMY-101 (Cp40), a peptidic inhibitor of the central complement component C3, can inhibit naturally occurring periodontitis in non-human primates (NHPs) when given once a week. This study was undertaken to determine the local safety of increasing doses of the drug as well as its efficacy when given at a reduced frequency or after systemic administration. Our findings have determined a local dose of AMY-101 (0.1 mg/site) that is free of local irritation and effective when given once every 3 weeks. Moreover, a daily subcutaneous dose of AMY-101 (4 mg/kg bodyweight) was protective against NHP periodontitis, suggesting that patients treated for systemic disorders (e.g., paroxysmal nocturnal hemoglobinuria) can additionally benefit in terms of improved periodontal condition. In summary, AMY-101 appears to be a promising candidate drug for the adjunctive treatment of human periodontitis, a notion that merits investigation in human clinical trials.

Alginate microbeads are coagulation compatible, while alginate microcapsules activate coagulation secondary to complement or directly through FXII

Alginate microspheres are presently under evaluation for future cell-based therapy. Their ability to induce harmful host reactions needs to be identified for developing the most suitable devices and efficient prevention strategies. We used a lepirudin based human whole blood model to investigate the coagulation potentials of alginate-based microspheres: alginate microbeads (Ca/Ba Beads), alginate poly-l-lysine microcapsules (APA and AP microcapsules) and sodium alginate-sodium cellulose sulfate-poly(methylene-co-cyanoguanidine) microcapsules (PMCG microcapsules). Coagulation activation measured by prothrombin fragments 1+2 (PTF1.2) was rapidly and markedly induced by the PMCG microcapsules, delayed and lower induced by the APA and AP microcapsules, and not induced by the Ca/Ba Beads. Monocytes tissue factor (TF) expression was similarly activated by the microcapsules, whereas not by the Ca/Ba Beads. PMCG microcapsules-induced PTF1.2 was abolished by FXII inhibition (corn trypsin inhibitor), thus pointing to activation through the contact pathway. PTF1.2 induced by the AP and APA microcapsules was inhibited by anti-TF antibody, pointing to a TF driven coagulation. The TF induced coagulation was inhibited by the complement inhibitors compstatin (C3 inhibition) and eculizumab (C5 inhibition), revealing a complement-coagulation cross-talk. This is the first study on the coagulation potentials of alginate microspheres, and identifies differences in activation potential, pathways and possible intervention points.

STATEMENT OF SIGNIFICANCE

Alginate microcapsules are prospective candidate materials for cell encapsulation therapy. The material surface must be free of host cell adhesion to ensure free diffusion of nutrition and oxygen to the encapsulated cells. Coagulation activation is one gateway to cellular overgrowth through deposition of fibrin. Herein we used a physiologically relevant whole blood model to investigate the coagulation potential of alginate microcapsules and microbeads. The coagulation potentials and the pathways of activation were depending on the surface properties of the materials. Activation of the complement system could also be involved, thus emphasizing a complement-coagulation cross-talk. Our findings points to complement and coagulation inhibition as intervention point for preventing host reactions, and enhance functional cell-encapsulation devices.

Pig-to-Primate Islet Xenotransplantation: Past, Present, and Future

Islet allotransplantation results in increasing success in treating type 1 diabetes, but the shortage of deceased human donor pancreata limits progress. Islet xenotransplantation, using pigs as a source of islets, is a promising approach to overcome this limitation. The greatest obstacle is the primate immune/inflammatory response to the porcine (pig) islets, which may take the form of rapid early graft rejection (the instant blood-mediated inflammatory reaction) or T-cell-mediated rejection. These problems are being resolved by the genetic engineering of the source pigs combined with improved immunosuppressive therapy. The results of pig-to-diabetic nonhuman primate islet xenotransplantation are steadily improving, with insulin independence being achieved for periods >1 year. An alternative approach is to isolate islets within a micro- or macroencapsulation device aimed at protecting them from the human recipient's immune response. Clinical trials using this approach are currently underway. This review focuses on the major aspects of pig-to-primate islet xenotransplantation and its potential for treatment of type 1 diabetes.

Local endothelial complement activation reverses endothelial quiescence, enabling t-cell homing, and tumor control during t-cell immunotherapy

Cancer immunotherapy relies upon the ability of T cells to infiltrate tumors. The endothelium constitutes a barrier between the tumor and effector T cells, and the ability to manipulate local vascular permeability could be translated into effective immunotherapy. Here, we show that in the context of adoptive T cell therapy, antitumor T cells, delivered at high enough doses, can overcome the endothelial barrier and infiltrate tumors, a process that requires local production of C3, complement activation on tumor endothelium and release of C5a. C5a, in turn, acts on endothelial cells promoting the upregulation of adhesion molecules and T-cell homing. Genetic deletion of C3 or the C5a receptor 1 (C5aR1), and pharmacological blockade of C5aR1, impaired the ability of T cells to overcome the endothelial barrier, infiltrate tumors, and control tumor progression in vivo, while genetic chimera mice demonstrated that C3 and C5aR1 expression by tumor stroma, and not leukocytes, governs T cell homing, acting on the local endothelium. In vitro, endothelial C3 and C5a expressions were required for endothelial activation by type 1 cytokines. Our data indicate that effective immunotherapy is a consequence of successful homing of T cells in response to local complement activation, which disrupts the tumor endothelial barrier.

Complement C3-Targeted Therapy: Replacing Long-Held Assertions with Evidence-Based Discovery

Complement dysregulation underlies several inflammatory disorders, and terminal complement inhibition has thus far afforded significant clinical gains. Nonetheless, emerging pathologies, fueled by complement imbalance and therapy-skewing genetic variance, underscore the need for more comprehensive, disease-tailored interventions. Modulation at the level of C3, a multifaceted orchestrator of the complement cascade, opens up prospects for broader therapeutic efficacy by targeting multiple pathogenic pathways modulated by C3-triggered proinflammatory crosstalk. Notably, C3 intervention is emerging as a viable therapeutic strategy for renal disorders with predominantly complement-driven etiology, such as C3 glomerulopathy (C3G). Using C3G as a paradigm, we argue that concerns about the feasibility of long-term C3 intervention need to be placed into perspective and weighed against actual therapeutic outcomes in prospective clinical trials.

Identification of C3b-Binding Small-Molecule Complement Inhibitors Using Cheminformatics

The complement system is an elegantly regulated biochemical cascade formed by the collective molecular recognition properties and proteolytic activities of more than two dozen membrane-bound or serum proteins. Complement plays diverse roles in human physiology, such as acting as a sentry against invading microorganisms, priming of the adaptive immune response, and removal of immune complexes. However, dysregulation of complement can serve as a trigger for a wide range of human diseases, which include autoimmune, inflammatory, and degenerative conditions. Despite several potential advantages of modulating complement with small-molecule inhibitors, small-molecule drugs are highly underrepresented in the current complement-directed therapeutics pipeline. In this study, we have employed a cheminformatics drug discovery approach based on the extensive structural and functional knowledge available for the central proteolytic fragment of the cascade, C3b. Using parallel in silico screening methodologies, we identified 45 small molecules that putatively bind C3b near ligand-guided functional hot spots. Surface plasmon resonance experiments resulted in the validation of seven dose-dependent C3b-binding compounds. Competition-based biochemical assays demonstrated the ability of several C3b-binding compounds to interfere with binding of the original C3b ligand that guided their discovery. In vitro assays of complement function identified a single complement inhibitory compound, termed cmp-5, and mechanistic studies of the cmp-5 inhibitory mode revealed it acts at the level of C5 activation. This study has led to the identification of a promising new class of C3b-binding small-molecule complement inhibitors and, to our knowledge, provides the first demonstration of cheminformatics-based, complement-directed drug discovery.

Complement C3 inhibitor Cp40 attenuates xenoreactions in pig hearts perfused with human blood

BACKGROUND

The complement system plays a crucial role in acute xenogeneic reactions after cardiac transplantation. We used an ex vivo perfusion model to investigate the effect of Cp40, a compstatin analog and potent inhibitor of complement at the level of C3.

METHODS

Fifteen wild-type pig hearts were explanted, cardiopleged, and reperfused ex vivo after 150 minutes of cold ischemia. Hearts were challenged in a biventricular working heart mode to evaluate cardiac perfusion and function. In the treatment group (n=5), the complement cascade was blocked at the level of C3 using Cp40, using diluted human blood. Untreated human and porcine blood was used for controls.

RESULTS

Throughout the perfusion, C3 activation was inhibited when Cp40 was used (mean of all time points: 1.11 ± 0.34% vs 3.12 ± 0.48% control activation; P<.01). Compared to xenoperfused controls, the cardiac index improved significantly in the treated group (6.5 ± 4.2 vs 3.5 ± 4.8 mL/min/g; P=.03, 180 minutes perfusion), while the concentration of lactate dehydrogenase as a maker for cell degradation was reduced in the perfusate (583 ± 187 U/mL vs 2108 ± 1145 U/mL, P=.02). Histological examination revealed less hemorrhage and edema, and immunohistochemistry confirmed less complement fragment deposition than in untreated xenoperfused controls.

CONCLUSIONS

Cp40 efficiently prevents C3 activation of the complement system, resulting in reduced cell damage and preserved function in wild-type porcine hearts xenoperfused ex vivo. We suggest that this compstatin analog, which blocks all main pathways of complement activation, could be a beneficial perioperative treatment in preclinical and in future clinical xenotransplantation.

Method development and validation for the quantitation of the complement inhibitor Cp40 in human and cynomolgus monkey plasma by UPLC-ESI-MS

Cp40 is a 14-amino acid cyclic analog of the peptidic complement inhibitor compstatin that binds with sub-nanomolar affinity to complement component C3 and has already shown promise in various models of complement-related diseases. The preclinical and clinical development of this compound requires a robust, accurate, and sensitive method for quantitatively monitoring Cp40 in biological samples. In this study, we describe the development and validation of an ultra-high performance liquid chromatography electrospray mass spectrometry method for the quantitation of Cp40 in human and non-human primate (NHP) plasma. Isotope-labeled Cp40 was used as an internal standard, allowing for the accurate and absolute quantitation of Cp40. Labeled and non-labeled Cp40 were extracted from plasma using reversed phase-solid phase extraction, with recovery rates exceeding 80%, indicating minor matrix effects. The triply charged states of Cp40 and isotope-labeled Cp40 were detected at m/z 596.60 and 600.34, respectively, via a Q-TOF mass spectrometer and were used for quantitation. The method was linear in the range of 0.18-3.58μg/mL (r²≥0.99), with precision values below 0.71% in NHP and 0.77% in human plasma. The accuracy of the method ranged from -2.17% to 17.99% in NHP and from -0.26% to 15.75% in human plasma. The method was successfully applied to the quantitation of Cp40 in cynomolgus monkey plasma after an initial intravenous bolus of 2mg/kg followed by repetitive subcutaneous administration at 1mg/kg. The high reproducibility, accuracy, and robustness of the method developed here render it suitable for drug monitoring of Cp40, and potentially other compstatin analogs, in both human and NHP plasma samples during pharmacokinetic and pharmacodynamic studies.

Complement inhibition enables tumor delivery of LCMV glycoprotein pseudotyped viruses in the presence of antiviral antibodies

The systemic delivery of therapeutic viruses, such as oncolytic viruses or vaccines, is limited by the generation of neutralizing antibodies. While pseudotyping of rhabdoviruses with the lymphocytic choriomeningitis virus glycoprotein has previously allowed for multiple rounds of delivery in mice, this strategy has not translated to other animal models. For the first time, we provide experimental evidence that antibodies generated against the lymphocytic choriomeningitis virus glycoprotein mediate robust complement-dependent viral neutralization via activation of the classical pathway. We show that this phenotype can be capitalized upon to deliver maraba virus pseudotyped with the lymphocytic choriomeningitis virus glycoprotein in a Fischer rat model in the face of neutralizing antibody through the use of complement modulators. This finding changes the understanding of the humoral immune response to arenaviruses, and also describes methodology to deliver viral vectors to their therapeutic sites of action without the interference of neutralizing antibody.

Complement component C3 - The "Swiss Army Knife" of innate immunity and host defense

As a preformed defense system, complement faces a delicate challenge in providing an immediate, forceful response to pathogens even at first encounter, while sparing host cells in the process. For this purpose, it engages a tightly regulated network of plasma proteins, cell surface receptors, and regulators. Complement component C3 plays a particularly versatile role in this process by keeping the cascade alert, acting as a point of convergence of activation pathways, fueling the amplification of the complement response, exerting direct effector functions, and helping to coordinate downstream immune responses. In recent years, it has become evident that nature engages the power of C3 not only to clear pathogens but also for a variety of homeostatic processes ranging from tissue regeneration and synapse pruning to clearing debris and controlling tumor cell progression. At the same time, its central position in immune surveillance makes C3 a target for microbial immune evasion and, if improperly engaged, a trigger point for various clinical conditions. In our review, we look at the versatile roles and evolutionary journey of C3, discuss new insights into the molecular basis for C3 function, provide examples of disease involvement, and summarize the emerging potential of C3 as a therapeutic target.

Compstatin Cp40 blocks hematin-mediated deposition of C3b fragments on erythrocytes: Implications for treatment of malarial anemia

During malarial anemia, 20 uninfected red blood cells (RBCs) are destroyed for every RBC infected by Plasmodium falciparum (Pf). Increasing evidence indicates an important role for complement in destruction of uninfected RBCs. Products of RBC lysis induced by Pf, including the digestive vacuole and hematin, activate complement and promote C3 fragment deposition on uninfected RBCs. C3-opsonized cells are then subject to extravascular destruction mediated by fixed tissue macrophages which express receptors for C3 fragments. The Compstatin family of cyclic peptides blocks complement activation at the C3 cleavage step, and is under investigation for treatment of complement-mediated diseases. We demonstrate, that under a variety of stringent conditions, second-generation Compstatin analogue Cp40 completely blocks hematin-mediated deposition of C3 fragments on naïve RBCs. Our findings indicate that prophylactic provision of Compstatin for malaria-infected individuals at increased risk for anemia may provide a safe and inexpensive treatment to prevent or substantially reduce malarial anemia.

Therapeutic complement inhibition in complement-mediated hemolytic anemias: Past, present and future

The introduction in the clinic of anti-complement agents represented a major achievement which gave to physicians a novel etiologic treatment for different human diseases. Indeed, the first anti-complement agent eculizumab has changed the treatment paradigm of paroxysmal nocturnal hemoglobinuria (PNH), dramatically impacting its severe clinical course. In addition, eculizumab is the first agent approved for atypical Hemolytic Uremic Syndrome (aHUS), a life-threatening inherited thrombotic microangiopathy. Nevertheless, such remarkable milestone in medicine has brought to the fore additional challenges for the scientific community. Indeed, the list of complement-mediated anemias is not limited to PNH and aHUS, and other human diseases can be considered for anti-complement treatment. They include other thrombotic microangiopathies, as well as some antibody-mediated hemolytic anemias. Furthermore, more than ten years of experience with eculizumab led to a better understanding of the individual steps of the complement cascade involved in the pathophysiology of different human diseases. Based on this, new unmet clinical needs are emerging; a number of different strategies are currently under development to improve current anti-complement treatment, trying to address these specific clinical needs. They include: (i) alternative anti-C5 agents, which may improve the heaviness of eculizumab treatment; (ii) broad-spectrum anti-C3 agents, which may improve the efficacy of anti-C5 treatment by intercepting the complement cascade upstream (i.e., preventing C3-mediated extravascular hemolysis in PNH); (iii) targeted inhibitors of selective complement activating pathways, which may prevent early pathogenic events of specific human diseases (e.g., anti-classical pathway for antibody-mediated anemias, or anti-alternative pathway for PNH and aHUS). Here we briefly summarize the status of art of current and future complement inhibition for different complement-mediated anemias, trying to identify the most promising approaches for each individual disease.

Targeting the complement cascade: novel treatments coming down the pike

The complement cascade is a vital component of both the innate and adaptive immune systems. Complement activation also contributes to the pathogenesis of many diseases, however, and the kidney is particularly susceptible to complement-mediated injury. Drugs that block complement activation can rapidly reduce tissue inflammation and also attenuate the adaptive immune response to foreign and tissue antigens. Eculizumab is a monoclonal antibody that prevents the cleavage of C5. It has been approved for the treatment of atypical hemolytic uremic syndrome, and it has been used in selected patients with other kidney diseases. Many additional drugs are also in development for blocking the complement cascade, including new monoclonal antibodies, recombinant proteins, small molecules, and small interfering RNA agents. Validation of these new drugs as effective treatments for kidney diseases faces several challenges. Many complement-mediated kidney diseases are rare, so it is not feasible to test all of the new drugs in numerous different rare diseases. The onset and course of the diseases are heterogeneous; many of these diseases also carry a lifelong risk of recurrence, and it is not clear how long complement inhibition must be maintained. In spite of these challenges, new therapeutic options for targeting the complement system will likely become available in the near future and may prove useful for treating patients with kidney disease.

From orphan drugs to adopted therapies: Advancing C3-targeted intervention to the clinical stage

Complement dysregulation is increasingly recognized as an important pathogenic driver in a number of clinical disorders. Complement-triggered pathways intertwine with key inflammatory and tissue destructive processes that can either increase the risk of disease or exacerbate pathology in acute or chronic conditions. The launch of the first complement-targeted drugs in the clinic has undeniably stirred the field of complement therapeutic design, providing new insights into complement's contribution to disease pathogenesis and also helping to leverage a more personalized, comprehensive approach to patient management. In this regard, a rapidly expanding toolbox of complement therapeutics is being developed to address unmet clinical needs in several immune-mediated and inflammatory diseases. Elegant approaches employing both surface-directed and fluid-phase inhibitors have exploited diverse components of the complement cascade as putative points of therapeutic intervention. Targeting C3, the central hub of the system, has proven to be a promising strategy for developing biologics as well as small-molecule inhibitors with clinical potential. Complement modulation at the level of C3 has recently shown promise in preclinical primate models, opening up new avenues for therapeutic intervention in both acute and chronic indications fueled by uncontrolled C3 turnover. This review highlights recent developments in the field of complement therapeutics, focusing on C3-directed inhibitors and alternative pathway (AP) regulator-based approaches. Translational perspectives and considerations are discussed, particularly with regard to the structure-guided drug optimization and clinical advancement of a new generation of C3-targeted peptidic inhibitors.

New milestones ahead in complement-targeted therapy

The complement system is a powerful effector arm of innate immunity that typically confers protection from microbial intruders and accumulating debris. In many clinical situations, however, the defensive functions of complement can turn against host cells and induce or exacerbate immune, inflammatory, and degenerative conditions. Although the value of inhibiting complement in a therapeutic context has long been recognized, bringing complement-targeted drugs into clinical use has proved challenging. This important milestone was finally reached a decade ago, yet the clinical availability of complement inhibitors has remained limited. Still, the positive long-term experience with complement drugs and their proven effectiveness in various diseases has reinvigorated interest and confidence in this approach. Indeed, a broad variety of clinical candidates that act at almost any level of the complement activation cascade are currently in clinical development, with several of them being evaluated in phase 2 and phase 3 trials. With antibody-related drugs dominating the panel of clinical candidates, the emergence of novel small-molecule, peptide, protein, and oligonucleotide-based inhibitors offers new options for drug targeting and administration. Whereas all the currently approved and many of the proposed indications for complement-targeted inhibitors belong to the rare disease spectrum, these drugs are increasingly being evaluated for more prevalent conditions. Fortunately, the growing experience from preclinical and clinical use of therapeutic complement inhibitors has enabled a more evidence-based assessment of suitable targets and rewarding indications as well as related technical and safety considerations. This review highlights recent concepts and developments in complement-targeted drug discovery, provides an overview of current and emerging treatment options, and discusses the new milestones ahead on the way to the next generation of clinically available complement therapeutics.

Therapeutic control of complement activation at the level of the central component C3

The increasing recognition of the complement system's association with diseases of the inflammatory spectrum and with biomaterial and transplant-related complications has generated growing interest in the therapeutic modulation of this innate immune cascade. As a central functional hub that largely drives the activation, amplification, and effector generation of the complement response, the plasma protein C3 has long been recognized as an attractive target. While pharmacological modulation of C3 activation may offer a powerful opportunity to interfere with or even prevent complement-driven pathologies, the development of C3 inhibitors has often been accompanied by concerns regarding the safety and feasibility of this approach. Although no C3-targeted inhibitors have thus far been approved for clinical use, several promising concepts and candidates have emerged in recent years. At the same time, experiences from preclinical development and clinical trials are slowly providing a more detailed picture of therapeutic complement inhibition at the level of C3. This review highlights the current therapeutic strategies to control C3 activation and discusses the possibilities and challenges on the road to bringing C3-targeted therapeutics to the clinic.

Rickettsia conorii is a potent complement activator in vivo and combined inhibition of complement and CD14 is required for attenuation of the cytokine response ex vivo

Mediterranean spotted fever caused by Rickettsia conorii is a potentially lethal disease characterized by vascular inflammation affecting multiple organs. Studies of R. conorii so far have focused on activation of inflammatory cells and their release of inflammatory cytokines, but complement activation has not been investigated in R. conorii-infected patients. Here, we performed a comprehensive analysis of complement activation markers and the soluble cross-talking co-receptor CD14 (sCD14) in plasma from R. conorii-infected patients. The clinical data were supplemented with ex vivo experiments where the cytokine response was characterized in human whole blood stimulated with R. conorii. Complement activation markers at the level of C3 (C3bc, C3bBbP) and terminal pathway activation (sC5b-9), as well as sCD14, were markedly elevated (p <0.01 for all), and closely correlated (p <0.05 for all), in patients at admission compared with healthy matched controls. All tested markers were significantly reduced to baseline values at time of follow up. Rickettsia conorii incubated in human whole blood was shown to trigger complement activation accompanied by release of the inflammatory cytokines interleukin-1β (IL-1β), IL-6, IL-8 and tumour necrosis factor. Whereas inhibition of either C3 or CD14 had only a minor effect on released cytokines, combined inhibition of C3 and CD14 resulted in significant reduction, virtually to baseline levels, of the four cytokines (p <0.05 for all). Our data show that complement is markedly activated upon R. conorii infection and complement activation is, together with CD14, responsible for a major part of the cytokine response induced by R. conorii in human whole blood.

Complement inhibition in pre-clinical models of periodontitis and prospects for clinical application

Periodontitis is a dysbiotic inflammatory disease leading to the destruction of the tooth-supporting tissues. Current therapies are not always effective and this prevalent oral disease continues to be a significant health and economic burden. Early clinical studies have associated periodontitis with elevated complement activity. Consistently, subsequent genetic and pharmacological studies in rodents have implicated the central complement component C3 and downstream signaling pathways in periodontal host-microbe interactions that promote dysbiosis and inflammatory bone loss. This review discusses these mechanistic advances and moreover focuses on the compstatin family of C3 inhibitors as a novel approach to treat periodontitis. In this regard, local application of the current lead analog Cp40 was recently shown to block both inducible and naturally occurring periodontitis in non-human primates. These promising results from non-human primate studies and the parallel development of Cp40 for clinical use highlight the feasibility for developing an adjunctive, C3-targeted therapy for human periodontitis.

Combined Inhibition of Complement and CD14 Attenuates Bacteria-Induced Inflammation in Human Whole Blood More Efficiently Than Antagonizing the Toll-like Receptor 4-MD2 Complex

Background. Single inhibition of the Toll-like receptor 4 (TLR4)–MD2 complex failed in treatment of sepsis. CD14 is a coreceptor for several TLRs, including TLR4 and TLR2. The aim of this study was to investigate the effect of single TLR4-MD2 inhibition by using eritoran, compared with the effect of CD14 inhibition alone and combined with the C3 complement inhibitor compstatin (Cp40), on the bacteria-induced inflammatory response in human whole blood.

Methods. Cytokines were measured by multiplex technology, and leukocyte activation markers CD11b and CD35 were measured by flow cytometry.

Results. Lipopolysaccharide (LPS)–induced inflammatory markers were efficiently abolished by both anti-CD14 and eritoran. Anti-CD14 was significantly more effective than eritoran in inhibiting LPS-binding to HEK-293E cells transfected with CD14 and Escherichia coli–induced upregulation of monocyte activation markers (P < .01). Combining Cp40 with anti-CD14 was significantly more effective than combining Cp40 with eritoran in reducing E. coli–induced interleukin 6 (P < .05) and monocyte activation markers induced by both E. coli (P < .001) and Staphylococcus aureus (P < .01). Combining CP40 with anti-CD14 was more efficient than eritoran alone for 18 of 20 bacteria-induced inflammatory responses (mean P < .0001).

Conclusions. Whole bacteria–induced inflammation was inhibited more efficiently by anti-CD14 than by eritoran, particularly when combined with complement inhibition. Combined CD14 and complement inhibition may prove a promising treatment strategy for bacterial sepsis.

Inhibition of pre-existing natural periodontitis in non-human primates by a locally administered peptide inhibitor of complement C3

AIM

Human periodontitis is associated with overactivation of complement, which is triggered by different mechanisms converging on C3, the central hub of the system. We assessed whether the C3 inhibitor Cp40 inhibits naturally occurring periodontitis in non-human primates (NHPs).

MATERIALS AND METHODS

Non-human primates with chronic periodontitis were intra-gingivally injected with Cp40 either once (5 animals) or three times (10 animals) weekly for 6 weeks followed by a 6-week follow-up period. Clinical periodontal examinations and collection of gingival crevicular fluid and biopsies of gingiva and bone were performed at baseline and during the study. A one-way repeated-measures anova was used for data analysis.

RESULTS

Whether administered once or three times weekly, Cp40 caused a significant reduction in clinical indices that measure periodontal inflammation (gingival index and bleeding on probing), tissue destruction (probing pocket depth and clinical attachment level) or tooth mobility. These clinical changes were associated with significantly reduced levels of pro-inflammatory mediators and decreased numbers of osteoclasts in bone biopsies. The protective effects of Cp40 persisted, albeit at reduced efficacy, for at least 6 weeks following drug discontinuation.

CONCLUSION

Cp40 inhibits pre-existing chronic periodontal inflammation and osteoclastogenesis in NHPs, suggesting a novel adjunctive anti-inflammatory therapy for treating human periodontitis.

Using an in vitro xenoantibody-mediated complement-dependent cytotoxicity model to evaluate the complement inhibitory activity of the peptidic C3 inhibitor Cp40

Simple and reliable methods for evaluating the inhibitory effects of drug candidates on complement activation are essential for preclinical development. Here, using an immortalized porcine aortic endothelial cell line (iPEC) as target, we evaluated the feasibility and effectiveness of an in vitro xenoantibody-mediated complement-dependent cytotoxicity (CDC) model for evaluating the complement inhibitory activity of Cp40, a potent analog of the peptidic C3 inhibitor compstatin. The binding of human xenoantibodies to iPECs led to serum dilution-dependent cell death. Pretreatment of the human serum with Cp40 almost completely inhibited the deposition of C3 fragments and C5b-9 on the cells, resulting in a dose-dependent inhibition of CDC against the iPECs. Using the same method to compare the effects of Cp40 on complement activation in humans, rhesus and cynomolgus monkeys, we found that the inhibitory patterns were similar overall. Thus, the in vitro xenoantibody-mediated CDC assay may have considerable potential for future clinical use.

Complement, a target for therapy in inflammatory and degenerative diseases

Complement is a key component of immunity with crucial inflammatory and opsonic properties; inappropriate activation of complement triggers or exacerbates inflammatory disease.

Complement dysregulation is a core feature of some diseases and contributes to pathology in many others.

Approved agents have been developed for and are highly effective in some orphan applications, but their progress to use in more common diseases has been slow.

Numerous challenges, such as target concentration or high turnover, limit the efficacy of these agents in humans.

Numerous novel agents targeting different parts of the complement system in different ways are now emerging from pre-clinical studies and are entering Phase I/II trials; these agents bring the potential for more-effective and more-specific anti-complement therapies in disease.

Other agents, both biologic and small molecule, are in Phase II or III trials for both rare and common diseases — administration routes include localized (for example, intravitreal) and systemic routes.

There is an urgent need to develop biomarkers and imaging methods that enable monitoring of the effects and efficacy of anti-complement agents.

The complement cascade, a key regulator of innate immunity, is a rich source of potential therapeutic targets for diseases including autoimmune, inflammatory and degenerative disorders. Morgan and Harris discuss the progress made in modulating the complement system and the existing challenges, including dosing, localization of the drug to the target and how to interfere with protein–protein interactions.

The complement system is a key innate immune defence against infection and an important driver of inflammation; however, these very properties can also cause harm. Inappropriate or uncontrolled activation of complement can cause local and/or systemic inflammation, tissue damage and disease. Complement provides numerous options for drug development as it is a proteolytic cascade that involves nine specific proteases, unique multimolecular activation and lytic complexes, an arsenal of natural inhibitors, and numerous receptors that bind to activation fragments. Drug design is facilitated by the increasingly detailed structural understanding of the molecules involved in the complement system. Only two anti-complement drugs are currently on the market, but many more are being developed for diseases that include infectious, inflammatory, degenerative, traumatic and neoplastic disorders. In this Review, we describe the history, current landscape and future directions for anti-complement therapies.

Complement therapeutics in inflammatory diseases: promising drug candidates for C3-targeted intervention

There is increasing appreciation that complement dysregulation lies at the heart of numerous immune-mediated and inflammatory disorders. Complement inhibitors are therefore being evaluated as new therapeutic options in various clinical translation programs and the first clinically approved complement-targeted drugs have profoundly impacted the management of certain complement-mediated diseases. Among the many members of the intricate protein network of complement, the central component C3 represents a 'hot-spot' for complement-targeted therapeutic intervention. C3 modulates both innate and adaptive immune responses and is linked to diverse immunomodulatory systems and biological processes that affect human pathophysiology. Compelling evidence from preclinical disease models has shown that C3 interception may offer multiple benefits over existing therapies or even reveal novel therapeutic avenues in disorders that are not commonly regarded as complement-driven, such as periodontal disease. Using the clinically developed compstatin family of C3 inhibitors and periodontitis as illustrative examples, this review highlights emerging therapeutic concepts and developments in the design of C3-targeted drug candidates as novel immunotherapeutics for oral and systemic inflammatory diseases.

Applying complement therapeutics to rare diseases

Around 350 million people worldwide suffer from rare diseases. These may have a genetic, infectious, or autoimmune basis, and several include an inflammatory component. Launching of effective treatments can be very challenging when there is a low disease prevalence and limited scientific insights into the disease mechanisms. As a key trigger of inflammatory processes, complement has been associated with a variety of diseases and has become an attractive therapeutic target for conditions involving inflammation. In view of the clinical experience acquired with drugs licensed for the treatment of rare diseases such as hereditary angioedema and paroxysmal nocturnal hemoglobinuria, growing evidence supports the safety and efficacy of complement therapeutics in restoring immune balance and preventing aggravation of clinical outcomes. This review provides an overview of the candidates currently in the pharmaceutical pipeline with potential to treat orphan diseases and discusses the molecular mechanisms triggered by complement involved with the disease pathogenesis.

The anti-inflammatory effect of combined complement and CD14 inhibition is preserved during escalating bacterial load

Combined inhibition of complement and CD14 is known to attenuate bacterial-induced inflammation, but the dependency of the bacterial load on this effect is unknown. Thus, we investigated whether the effect of such combined inhibition on Escherichia coli- and Staphylococcus aureus-induced inflammation was preserved during increasing bacterial concentrations. Human whole blood was preincubated with anti-CD14, eculizumab (C5-inhibitor) or compstatin (C3-inhibitor), or combinations thereof. Then heat-inactivated bacteria were added at final concentrations of 5 × 10(4) -1 × 10(8) /ml (E. coli) or 5 × 10(7) -4 × 10(8) /ml (S. aureus). Inflammatory markers were measured using enzyme-linked immunosorbent assay (ELISA), multiplex technology and flow cytometry. Combined inhibition of complement and CD14 significantly (P < 0.05) reduced E. coli-induced interleukin (IL)-6 by 40-92% at all bacterial concentrations. IL-1β, IL-8 and macrophage inflammatory protein (MIP)-1α were significantly (P < 0.05) inhibited by 53-100%, and the effect was lost only at the highest bacterial concentration. Tumour necrosis factor (TNF) and MIP-1β were significantly (P < 0.05) reduced by 80-97% at the lowest bacterial concentration. Monocyte and granulocyte CD11b were significantly (P < 0.05) reduced by 63-91% at all bacterial doses. Lactoferrin was significantly (P < 0.05) attenuated to the level of background activity at the lowest bacterial concentration. Similar effects were observed for S. aureus, but the attenuation was, in general, less pronounced. Compared to E. coli, much higher concentrations of S. aureus were required to induce the same cytokine responses. This study demonstrates generally preserved effects of combined complement and CD14 inhibition on Gram-negative and Gram-positive bacterial-induced inflammation during escalating bacterial load. The implications of these findings for future therapy of sepsis are discussed.

Compstatin analog Cp40 inhibits complement dysregulation in vitro in C3 glomerulopathy

C3 glomerulopathy (C3G) defines a group of untreatable ultra-rare renal diseases caused by uncontrolled activation of the alternative complement pathway. Nearly half of patients progress to end stage renal failure within 10 years. Cp40, a second-generation compstatin analog in clinical development, is a 14 amino-acid cyclic peptide that selectively inhibits complement activation in humans and non-human primates by binding to C3 and C3b. We hypothesized that by targeting C3 Cp40 would provide an effective treatment for C3G. By investigating its effects in vitro using multiple assays of complement activity, we show that Cp40 prevents complement-mediated lysis of sheep erythrocytes in sera from C3G patients, prevents complement dysregulation in the presence of patient-derived autoantibodies to the C3 and C5 convertases, and prevents complement dysregulation associated with disease-causing genetic mutations. In aggregate, these data suggest that Cp40 may offer a novel and promising therapeutic option to C3G patients as a disease-specific, targeted therapy. As such, Cp40 could represent a major advance in the treatment of this disease.

Compstatin: a C3-targeted complement inhibitor reaching its prime for bedside intervention

There is a growing awareness that complement plays an integral role in human physiology and disease, transcending its traditional perception as an accessory system for pathogen clearance and opsonic cell killing. As the list of pathologies linked to dysregulated complement activation grows longer, it has become clear that targeted modulation of this innate immune system opens new windows of therapeutic opportunity for anti-inflammatory drug design. Indeed, the introduction of the first complement-targeting drugs has reignited a vibrant interest in the clinical translation of complement-based inhibitors. Compstatin was discovered as a cyclic peptide that inhibits complement activation by binding C3 and interfering with convertase formation and C3 cleavage. As the convergence point of all activation pathways and a molecular hub for crosstalk with multiple pathogenic pathways, C3 represents an attractive target for therapeutic modulation of the complement cascade. A multidisciplinary drug optimization effort encompassing rational 'wet' and in silico synthetic approaches and an array of biophysical, structural and analytical tools has culminated in an impressive structure-function refinement of compstatin, yielding a series of analogues that show promise for a wide spectrum of clinical applications. These new derivatives have improved inhibitory potency and pharmacokinetic profiles and show efficacy in clinically relevant primate models of disease. This review provides an up-to-date survey of the drug design effort placed on the compstatin family of C3 inhibitors, highlighting the most promising drug candidates. It also discusses translational challenges in complement drug discovery and peptide drug development and reviews concerns related to systemic C3 interception.

Complement inhibition prevents oncolytic vaccinia virus neutralization in immune humans and cynomolgus macaques

Oncolytic viruses (OVs) have shown promising clinical activity when administered by direct intratumoral injection. However, natural barriers in the blood, including antibodies and complement, are likely to limit the ability to repeatedly administer OVs by the intravenous route. We demonstrate here that for a prototype of the clinical vaccinia virus based product Pexa-Vec, the neutralizing activity of antibodies elicited by smallpox vaccination, as well as the anamnestic response in hyperimmune virus treated cancer patients, is strictly dependent on the activation of complement. In immunized rats, complement depletion stabilized vaccinia virus in the blood and led to improved delivery to tumors. Complement depletion also enhanced tumor infection when virus was directly injected into tumors in immunized animals. The feasibility and safety of using a complement inhibitor, CP40, in combination with vaccinia virus was tested in cynomolgus macaques. CP40 pretreatment elicited an average 10-fold increase in infectious titer in the blood early after the infusion and prolonged the time during which infectious virus was detectable in the blood of animals with preexisting immunity. Capitalizing on the complement dependence of antivaccinia antibody with adjunct complement inhibitors may increase the infectious dose of oncolytic vaccinia virus delivered to tumors in virus in immune hosts.

Inflammaging in skin and other tissues - the roles of complement system and macrophage

Inflammaging refers to a continuous, low-grade inflammation associated with aging. Such chronic inflammatory response could build up with time and gradually causes tissue damage. It is considered as one of the driving forces for many age-related diseases such as diabetes, atherosclerosis, age-related macular degeneration (AMD), and skin aging. There is mounting evidence that indicates aging is driven by the pro-inflammatory cytokines and substances produced by our body’s innate immune system. The macrophage and complement system, two important components of innate immune system, have attracted more and more attention since they appear to be involved in the pathogenesis of several inflammaging-associated diseases, such as AMD and atherosclerosis. This paper will review what we know about these two innate immune systems in the pathogenesis of AMD, atherosclerosis and skin aging.

New compstatin peptides containing N-terminal extensions and non-natural amino acids exhibit potent complement inhibition and improved solubility characteristics

Compstatin peptides are complement inhibitors that bind and inhibit cleavage of complement C3. Peptide binding is enhanced by hydrophobic interactions; however, poor solubility promotes aggregation in aqueous environments. We have designed new compstatin peptides derived from the W4A9 sequence (Ac-ICVWQDWGAHRCT-NH2, cyclized between C2 and C12), based on structural, computational, and experimental studies. Furthermore, we developed and utilized a computational framework for the design of peptides containing non-natural amino acids. These new compstatin peptides contain polar N-terminal extensions and non-natural amino acid substitutions at positions 4 and 9. Peptides with α-modified non-natural alanine analogs at position 9, as well as peptides containing only N-terminal polar extensions, exhibited similar activity compared to W4A9, as quantified via ELISA, hemolytic, and cell-based assays, and showed improved solubility, as measured by UV absorbance and reverse-phase HPLC experiments. Because of their potency and solubility, these peptides are promising candidates for therapeutic development in numerous complement-mediated diseases.

Complement Involvement in Periodontitis: Molecular Mechanisms and Rational Therapeutic Approaches

The complement system is a network of interacting fluid-phase and cell surface-associated molecules that trigger, amplify, and regulate immune and inflammatory signaling pathways. Dysregulation of this finely balanced network can destabilize host-microbe homeostasis and cause inflammatory tissue damage. Evidence from clinical and animal model-based studies suggests that complement is implicated in the pathogenesis of periodontitis, a polymicrobial community-induced chronic inflammatory disease that destroys the tooth-supporting tissues. This review discusses molecular mechanisms of complement involvement in the dysbiotic transformation of the periodontal microbiome and the resulting destructive inflammation, culminating in loss of periodontal bone support. These mechanistic studies have additionally identified potential therapeutic targets. In this regard, interventional studies in preclinical models have provided proof-of-concept for using complement inhibitors for the treatment of human periodontitis.

Complement Interception Across Humoral Incompatibility in Solid Organ Transplantation: A Clinical Perspective

The humoral barrier in transplant biology is the result of preformed donor-specific antibodies (DSAs), directed either against human leukocyte antigens (HLA) or non-HLA antigens such as blood group (ABO) molecules. The term "sensitization" applies to patients carrying these antibodies. Transplantation is widely accepted as a life-saving opportunity for patients with terminal end-organ disease. However, in sensitized patients, transplant outcome is hampered by antibody-mediated rejection (AMR) as a consequence of DSA exposure. Furthermore, sensitized patients have limited access to "matched" organs from the both living and deceased donor pool.Considering the crucial role of the complement system in the pathophysiology of AMR and the availability of complement intervention therapeutics, there is a growing interest in complement-targeting strategies. This review highlights the emerging importance of monitoring and modulation of the complement system in the context of enabling transplantation across humoral incompatibility in sensitized recipients with preformed anti-HLA or natural anti-ABO antibodies. It also discusses the significance of the complement system in the induction of accommodation and further emphasizes current and future perspectives of novel complement therapeutics.

Complement inhibition in a xenogeneic model of interactions between human whole blood and porcine endothelium

Xenotransplantation (xeno-Tx) is considered as an alternative solution to overcome the shortage of human donor organs. However, the success of xeno-Tx is hindered by immune reactions against xenogeneic cells (e. g. of porcine origin). More specifically, activation of innate immune mechanisms such as complement and triggering of the coagulation cascade occur shortly after xeno-Tx, and adhesion of human leukocytes to porcine endothelium is another early critical step mediating the immune attack. To investigate the therapeutic potential of complement inhibition in the context of xenogeneic interactions, we have employed a whole-blood model in the present study. Incubation of human blood with porcine endothelial cells (PAECs) led to activation of complement and coagulation as well as to increased leukocyte adhesion. The observed responses can be attributed to the pig-to-human xenogeneicity, since the presence of human endothelium induced a minor cellular and plasmatic inflammatory response. Importantly, complement inhibition using a potent complement C3 inhibitor, compstatin analogue Cp40, abrogated the adhesion of leukocytes and, more specifically, the attachment of neutrophils to porcine endothelium. Moreover, Cp40 inhibited the activation of PAECs and leukocytes, since the levels of the adhesion molecules E-selectin, ICAM-1, ICAM-2, and VCAM-1 on PAECs and the surface expression of integrin CD11b on neutrophils were significantly decreased. Along the same line, inhibition of CD11b resulted in decreased leukocyte adhesion. Taken together, our findings provide a better understanding of the mechanisms regulating the acute innate immune complications in the context of xeno-Tx and could pave the way for complement-targeting therapeutic interventions.

Therapeutic C3 inhibitor Cp40 abrogates complement activation induced by modern hemodialysis filters

Approximately 350,000 individuals in the United States rely on maintenance hemodialysis treatment because of end-stage renal disease. Despite improvements in dialysis technology, the mortality rate for patients treated with maintenance dialysis is still exceptionally high, with a 5-year survival rate of only 35%. Many patients succumb to conditions resulting at least in part from the chronic induction of inflammation. Among the triggers of inflammation, the complement system is of particular importance, being a well-appreciated mediator of inflammatory processes that is involved in many pathologic states. Here we used a refined pre-clinical model of hemodialysis in cynomolgus monkeys to confirm that even modern, polymer-based hemodialysis filters activate complement and to evaluate the potential of Cp40, a peptidic C3 inhibitor, to attenuate hemodialysis-induced complement activation. Our data show marked induction of complement activation even after only a single session of hemodialysis. Importantly, complete inhibition of complement activation was achieved in response to two distinct Cp40 treatment regimens. Further, we show that application of Cp40 during hemodialysis resulted in increased levels of the anti-inflammatory cytokine IL-10, indicating that Cp40 may be a potent and cost-effective treatment option for attenuating chronic inflammatory conditions in dialysis-dependent patients.

Complement in paroxysmal nocturnal hemoglobinuria: exploiting our current knowledge to improve the treatment landscape

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare hematological disorder associated with an acquired deficiency in glycophosphatidylinositol-anchor biosynthesis that renders erythrocytes susceptible to complement attack. Intravascular hemolysis via the membrane attack complex is a clinical hallmark of the disease, and C5 blockade is currently the only approved treatment for PNH. However, residual anemia is an emerging observation for many PNH patients receiving anti-C5 treatment. A range of complement-targeted therapeutic approaches, encompassing surface-directed inhibition of C3 convertases, blockade of membrane attack complex assembly or C3 interception using peptidic inhibitors, has yielded promising results and offers leverage for even more effective treatment of PNH. This article discusses recent advances in this rapidly evolving field, integrating critical perspectives from preclinical PNH models and diverse complement modulation strategies with genetic insights and therapy response profiles. It also evaluates the relative efficacy, limitations and benefits afforded by C3 or C5 inhibition in the context of PNH therapeutics.

The complement system in inflammatory bowel disease

Complement is well appreciated to be a potent innate immune defense against microbes and is important in the housekeeping act of removal of apoptotic and effete cells. It is also understood that hyperactivation of complement, or the lack of regulators, may underlie chronic inflammatory diseases. A pipeline of products to intervene in complement activation, some already in clinical use, is being studied in various chronic inflammatory diseases. To date, the role of complement in inflammatory bowel disease has not received a lot of research interest. Novel genetically modified laboratory animals and experiments using antagonists to complement effector molecules have kindled important research observations implicating the complement system in inflammatory bowel disease pathogenesis. We review the evidence base for the role and potential therapeutic manipulation of the complement cascade in inflammatory bowel disease.

Conjugation to albumin-binding molecule tags as a strategy to improve both efficacy and pharmacokinetic properties of the complement inhibitor compstatin

The compstatin family of complement inhibitors has shown promise in various immuno-inflammatory disorders. Although recent analogues show beneficial pharmacokinetics, further extension of the plasma half-life is expected to benefit systemic application of these peptidic inhibitors. We therefore synthesized conjugates of compstatin analogues and albumin-binding molecules (ABM) to increase circulatory residence. Equilibrium dialysis in complement-depleted serum showed a marked increase in plasma protein binding from <8 % to >99 % for a resulting chimera (ABM2-Cp20). Further analysis confirmed interaction with albumin from different species, primarily via site II. Importantly, ABM2-Cp20 bound 20-fold stronger to its target protein C3b (KD =150 pM) than the parent peptide. Kinetic and in silico analysis suggested that ABM2 occupies a secondary site on C3b and improves the dissociation rate via additional contacts. Addition of an ABM modifier thereby not only improved plasma protein binding but also produced the most potent compstatin analogue to date with potential implications for the treatment of systemic complement-related diseases.

Cholesterol crystal-induced endothelial cell activation is complement-dependent and mediated by TNF

Cholesterol crystals are known to be a hallmark of atherosclerosis with recent studies demonstrating deposition of these crystals in early fatty streak formation as well as penetrating the intima following plaque rupture. Inflammation has also become a central focus in atheroma development and endothelial cell activation is recognized as necessary for the recruitment of inflammatory cells to the plaque. However, the extent to which cholesterol crystals can induce inflammation and activate endothelial cells is not known. To investigate this, we developed a novel model activating human umbilical vein endothelial cells using lepirudin anticoagulated human whole blood. We found that cholesterol crystals caused a marked and dose-dependent increase in the adhesion molecules E-selectin and ICAM-1 on the surface of the endothelial cells after incubation with whole blood. There was no activation of the cells when the crystals were incubated in medium alone, or in human serum, despite substantial crystal-induced complement activation in serum. Complement inhibitors at the C3 and C5 levels reduced the whole blood induced endothelial cell activation by up to 89% (p<0.05) and abolished TNF release (p<0.01). Finally, the TNF inhibitor infliximab reduced endothelial activation to background levels (p<0.05). In conclusion, these data demonstrate that endothelial activation by cholesterol crystals is mediated by complement-dependent TNF release, and suggests that complement-inhibition might have a role in alleviating atherosclerosis-induced inflammation.

Genetic and intervention studies implicating complement C3 as a major target for the treatment of periodontitis

Chronic periodontitis is induced by a dysbiotic microbiota and leads to inflammatory destruction of tooth-supporting connective tissue and bone. The third component of complement, C3, is a point of convergence of distinct complement activation mechanisms, but its involvement in periodontitis was not previously addressed. We investigated this question using two animal species models, namely, C3-deficient or wild-type mice and nonhuman primates (NHPs) locally treated with a potent C3 inhibitor (the compstatin analog Cp40) or an inactive peptide control. In mice, C3 was required for maximal periodontal inflammation and bone loss, and for the sustenance of the dysbiotic microbiota. The effect of C3 on the microbiota was therefore different from that reported for the C5a receptor, which is required for the initial induction of dysbiosis. C3-dependent bone loss was demonstrated in distinct models, including Porphyromonas gingivalis-induced periodontitis, ligature-induced periodontitis, and aging-associated periodontitis. Importantly, local treatment of NHPs with Cp40 inhibited ligature-induced periodontal inflammation and bone loss, which correlated with lower gingival crevicular fluid levels of proinflammatory mediators (e.g., IL-17 and RANKL) and decreased osteoclastogenesis in bone biopsy specimens, as compared with control treatment. To our knowledge, this is the first time, for any disease, that complement inhibition in NHPs was shown to inhibit inflammatory processes that lead to osteoclastogenesis and bone loss. These data strongly support the feasibility of C3-targeted intervention for the treatment of human periodontitis.

Cholesterol crystals induce complement-dependent inflammasome activation and cytokine release

Inflammation is associated with development of atherosclerosis, and cholesterol crystals (CC) have long been recognized as a hallmark of atherosclerotic lesions. CC appear early in the atheroma development and trigger inflammation by NLRP3 inflammasome activation. In this study we hypothesized whether CC employ the complement system to activate inflammasome/caspase-1, leading to release of mature IL-1β, and whether complement activation regulates CC-induced cytokine production. In this study we describe that CC activated both the classical and alternative complement pathways, and C1q was found to be crucial for the activation. CC employed C5a in the release of a number of cytokines in whole blood, including IL-1β and TNF. CC induced minimal amounts of cytokines in C5-deficient whole blood, until reconstituted with C5. Furthermore, C5a and TNF in combination acted as a potent primer for CC-induced IL-1β release by increasing IL-1β transcripts. CC-induced complement activation resulted in upregulation of complement receptor 3 (CD11b/CD18), leading to phagocytosis of CC. Also, CC mounted a complement-dependent production of reactive oxygen species and active caspase-1. We conclude that CC employ the complement system to induce cytokines and activate the inflammasome/caspase-1 by regulating several cellular responses in human monocytes. In light of this, complement inhibition might be an interesting therapeutic approach for treatment of atherosclerosis.

Combined inhibition of complement and CD14 efficiently attenuated the inflammatory response induced by Staphylococcus aureus in a human whole blood model

The complement and TLR systems are activated in sepsis, contributing to an unfavorable inflammatory "storm." Combined inhibition of these systems has been documented to efficiently attenuate the inflammatory responses induced by Gram-negative bacteria. In this study, we hypothesized that the combined inhibition would attenuate the inflammatory responses induced by Gram-positive bacteria. Staphylococcus aureus bacteria (strains Cowan and Wood), as well as S. aureus cell wall lipoteichoic acid (LTA), were incubated in thrombin-inhibited human whole blood. Complement was inhibited at the level of C3 and C5, and the TLRs by inhibiting CD14 and TLR2. Thirty-four inflammatory markers were measured by multiplex technology and flow cytometry. Thirteen markers increased significantly in response to Cowan and Wood, and 12 in response to LTA. Combined inhibition with the C3 inhibitor compstatin and the anti-CD14 Ab 18D11 significantly reduced 92 (Cowan, LTA) and 85% (Wood) of these markers. Compstatin alone significantly reduced 54 (Cowan), 38 (Wood), and 83% (LTA), whereas anti-CD14 alone significantly reduced 23, 15, and 67%, respectively. Further experiments showed that the effects of complement inhibition were mainly due to inhibition of C5a interaction with the C5a receptor. The effects on inhibiting CD14 and TLR2 were similar. The combined regimen was more efficient toward the bacterial effects than either complement or anti-CD14 inhibition alone. Complement was responsible for activation of and phagocytosis by both granulocytes and monocytes. Disrupting upstream recognition by inhibiting complement and CD14 efficiently attenuated S. aureus-induced inflammation and might be a promising treatment in both Gram-negative and Gram-positive sepsis.