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The complement system is a sophisticated part of the immune system that enhances the ability of antibodies and phagocytic cells to clear microbes and damaged cells, promotes inflammation, and attacks the pathogen's cell membrane. This system is named for its capacity to "complement" the killing of pathogens by antibodies.
Comprising over 30 small proteins produced by the liver, the complement system circulates in the blood serum and within tissues throughout the body. These proteins are normally inactive but become sequentially activated in response to a pathogen. Activation can occur via three pathways: the classical pathway, which is triggered by antibodies bound to a pathogen; the lectin pathway, which is activated by mannose-binding lectin attaching to the pathogen surface; and the alternative pathway, which can be initiated directly by pathogen surfaces.
Each pathway leads to the cleavage of the protein C3, generating C3a and C3b fragments. C3b binds to the pathogen surface and can lead to direct opsonization—tagging the pathogen for destruction by phagocytes. C3a, along with other small fragments released during complement activation, acts as a chemoattractant to recruit immune cells to the site of infection and promote inflammation.
The final common step of the complement activation pathways is the assembly of the membrane attack complex (MAC). This complex forms a pore in the membrane of the target cell, leading to cell lysis and death. The MAC is particularly effective against gram-negative bacteria.
Regulation of the complement system is crucial, as overactivation can damage host cells. Regulators are present in blood plasma and on cell surfaces, ensuring the system is directed only at pathogens or damaged cells.
The complement system plays a crucial role not only in innate immunity but also as a bridge to adaptive immunity. It assists in clearing immune complexes and apoptotic cells, and in enhancing the humoral response and immune memory.
Understanding and manipulating the complement system has therapeutic potential for numerous diseases, including those that involve excessive or inappropriate activation of the complement pathways.
Synonyms: LNP 023
LNP023 is a highly potent factor B (FB) inhibitor with an IC50 value of 10 nM. LNP023 shows direct, reversible, and high-affinity binding to human FB (KD=7.9 nM).
FD-IN-1 (Compound 12) is a factor D (FD) inhibitor with an IC50 of 12 nM.
Synonyms: ACH-4471
Danicopan (ACH-4471), a selective and orally active small-molecule factor D inhibitor, shows high binding affinity to human Factor D with Kd value of 0.54 nM.
Complement C5-IN-1 (Compound 7) is a small-molecule inhibitor of complement component 5 protein (C5).
Complement factor D-IN-1 is a potent and selective small-molecule reversible factor d inhibitor, with IC50s of 0.006 and 0.05 μM in FD Thioesterolytic Fluorescent Assay and a MAC Deposition Assay, respectively.
Compstatin, a 13-residue cyclic peptide, is a potent inhibitor of the complement system C3 with species specificity. Compstatin binds to baboon C3 and is resistant to proteolytic cleavage in baboon blood (similar to humans). Compstatin inhibits only the activation of primates' complement system. Compstatin exhibits IC50 values of 63 μM and 12 μM for classical and alterative complement pathway, respectively.
Synonyms: Cp40 TFA
AMY-101 TFA (Cp40 TFA), a peptidic inhibitor of the central complement component C3 (KD = 0.5 nM), inhibits naturally occurring periodontitis in non-human primates (NHPs). AMY-101 (Cp40) exhibits a favorable anti-inflammatory activity in models with COVID-19 severe pneumonia with systemic hyper inflammation.
Synonyms: AL-78898A
POT-4 (AL-78898A), a Compstatin derivative, is a potent inhibitor of complement factor C3 activation. POT-4 can be used for age-related macular degeneration research
CP-289,503 is an inhibitor of the complement C5a receptor, with an IC₅₀ of 1 μM. The C5a receptor mediates pro-inflammatory signaling by binding to C5a, a complement activation product that stimulates leukocyte and phagocyte activation, upregulates integrins, and induces degranulation of inflammatory cells, contributing to endothelial damage. By blocking C5a signaling, CP-289,503 may be useful in the treatment of various inflammatory diseases.
Lanoracopan is a potent inhibitor of complement factor B, with an IC₅₀ of 1.2 μM. It is suitable for research in inflammation- and immunity-related diseases.
Tarvicopan is an inhibitor for complement factor D.
PIC1 PA is a 15-amino-acid peptide and a potent analog of PIC1 that inhibits classical pathway–mediated complement activation. It functions by disrupting the interaction between C1s-C1r-C1r-C1s/MASPs and the collagen-like region (CLR) of C1q or MBL. PIC1 PA specifically binds to the CLR of C1q, with a mean equilibrium dissociation constant (K\_D) of 33.3 nM for purified C1q.
Zoracopan is a selective inhibitor of complement factor D (CFD). Upon systemic administration (oral or intravenous), it preferentially accumulates in ocular tissues and is released in a sustained manner, primarily targeting the choroid–retinal pigment epithelium (C-RPE) and/or iridociliary body (I-CB).
Synonyms: BCX9930
Pelecopan (BCX9930) is a potent, selective, and orally active inhibitor of complement factor D, with an IC₅₀ value of 14.3 nM. It targets factor D to prevent both intravascular and extravascular hemolysis in paroxysmal nocturnal hemoglobinuria (PNH) and is also applicable to other diseases mediated by the alternative complement pathway.
NDT 9513727 is a potent, selective, orally active, and competitive inverse agonist of the human C5a receptor (C5aR), with an IC₅₀ of 11.6 nM. It is suitable for research in human inflammatory diseases.
Synonyms: ACH 0145228; ACH-5228; ALXN2050
Vemircopan (ALXN2050) is an orally active inhibitor of complement factor D (FD). It is being investigated for the treatment of complement-mediated diseases, including myasthenia gravis, lupus nephritis, IgA nephropathy, and paroxysmal nocturnal hemoglobinuria (PNH).
Perforin-IN-2 (Compound 1) is a perforin inhibitor that blocks perforin-mediated cell lysis. It has potential to reduce graft rejection in the context of allogeneic bone marrow or stem cell transplantation.
EG01377 dihydrochloride is a potent, bioavailable, and selective inhibitor of neuropilin-1 (NRP1), with a Kd of 1.32 μM and IC₅₀ values of 609 nM for both NRP1-a1 and NRP1-b1 domains. It exhibits antiangiogenic, antimigratory, and antitumor activities.
Synonyms: DSS (MW 5000); DXS (MW 5000)
Dextran sulfate sodium salt (DSS, MW 5000) primarily functions as a complement inhibitor, derived from a polymer of dehydrated glucose. This compound exhibits significant biological activities, including anticoagulation, antiviral properties, and anti-lipemic effects. Its mechanisms involve blocking HIV-1 adsorption to host cells, preventing natural killer (NK) cell-mediated cytotoxicity, and inhibiting instant blood-mediated inflammatory reactions (IBMIR). Dextran sulfate sodium salt (MW 5000) is valuable in research related to immunology, virology, and cardiovascular studies.
Synonyms: LNP023 TFA
Iptacopan TFA is a selective inhibitor of Factor B, demonstrating an IC50 value of 10 nM and a KD of 7.9 nM. This compound modulates the complement cascade, effectively preventing hemolysis of red blood cells in paroxysmal nocturnal hemoglobinuria (PNH) and protecting renal cells in primary immunoglobulin A nephropathy (IgAN) and complement 3 glomerulopathy (C3G). Iptacopan TFA is applicable for research into complement-mediated diseases, providing insights into therapeutic strategies for conditions associated with dysregulated complement activity.
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Synonyms: LNP023 hydrochloride
Iptacopan hydrochloride is a highly selective inhibitor of Factor B, exhibiting an IC50 of 10 nM and a KD of 7.9 nM. This compound disrupts the complement cascade, thereby preventing hemolysis in paroxysmal nocturnal hemoglobinuria (PNH) and protecting renal cells in primary immunoglobulin A nephropathy (IgAN) and complement 3 glomerulopathy (C3G). Iptacopan hydrochloride is valuable for research on complement-mediated diseases, facilitating the exploration of therapeutic strategies in these conditions.
Synonyms: IONIS-FB-LRx sodium; RG6299 sodium; ISIS 696844 sodium
Sefaxersen sodium is a specific antisense oligonucleotide (ASO) that targets complement factor B (CFB). It effectively reduces circulating levels of CFB, making it a valuable tool for research into geographic atrophy (GA). This compound facilitates the exploration of therapeutic strategies aimed at modulating the complement pathway in ocular diseases.
Factor D Inhibitor 6 is a selective inhibitor of Factor D, exhibiting a potent inhibitory activity with an IC50 of 30 nM and a Kd of 6 nM. It demonstrates high specificity, being inactive against Factor B and not affecting classical or lectin complement pathway activation, as well as a range of receptors, ion channels, kinases, and proteases. This compound is useful in research involving the complement system and its associated pathways, providing significant potential for therapeutic application in diseases influenced by aberrant complement activation.
C1s-IN-1 trihydrochloride is a selective inhibitor of the C1s protease with a Ki of 5.8 μM. It effectively inhibits the cleavage of C2 by C1s with an IC50 of 85 μM and disrupts the activation of the classical pathway at an IC50 of 22 μM. Additionally, this compound acts as a competitive inhibitor for thrombin with a Ki of 51.2 μM, making it a valuable tool for research into complement system regulation and thrombin-related pathways.
Synonyms: m-Phenoxybenzaldehyde
3-Phenoxybenzaldehyde is a compound identified as a complement inhibitor, exhibiting weak inhibition of the classical pathway of the complement system. This compound demonstrates hemolytic activity, making it relevant for studies related to immune response modulation and complement pathway research. Its applications extend to investigations in autoimmune diseases and therapies targeting complement-mediated cytotoxicity.
