CCX168 was prepared by the Medicinal Chemistry Department at ChemoCentryx21 and formulated in polyethylene glycol 400/Solutol (70/30). blockade of C5aR/CD88 might have therapeutic benefit in patients with ANCA-associated vasculitis and GN. Necrotizing and crescentic GN (NCGN) and vasculitis are associated with ANCA.1,2 ANCAs are specific for myeloperoxidase (MPO) and proteinase 3 (PR3).1 Experimental data indicate that this pathogenesis of ANCA-associated vasculitis (AAV) involves activation of neutrophils by ANCA.1,2 Injection of anti-MPO antibodies into mice causes NCGN and vasculitis, closely mimicking human AAV.3 Alternative match pathway activation is pivotal in the pathogenesis of anti-MPO NCGN in mice.4C6 The relevance of alternative match pathway activation to human AAV is supported by immunohistochemical demonstration of alternative match pathway components at sites of AAV7,8 and by correlation of plasma alternative match pathway activation fragments with AAV disease activity.9 The complement anaphylatoxin C5a is a potent inflammatory mediator.10,11 The alternative vintage and lectin pathways converge at the activation of C5, releasing C5a and C5b. C5a is a powerful chemoattractant Elacridar hydrochloride for neutrophils, and ligation by C5a of C5aR/CD88 activates neutrophils. Blockade of C5a or C5a receptor (C5aR/CD88) ameliorates anti-MPO NCGN in mice.5,6 ANCA-activated neutrophils activate the alternative match pathway.4,6,12 Neutrophil priming results in increased availability of ANCA antigens at the surface where they interact with ANCA to activate neutrophils. Human neutrophils activated by human ANCA release factors that activate the alternative match pathway.4,6,12 In turn, C5a primes neutrophils and increase ANCA antigen expression.6,12 Cleavage of C5 also releases C5b, which joins with C6 to initiate the membrane attack complex (MAC).11 Here we confirm the importance of C5aR/CD88 in mediating anti-MPO NCGN and statement that Elacridar hydrochloride C6 is not required. We also demonstrate that deficiency of another receptor for C5a, C5L2 (C5a-like receptor 2),10 results in more severe disease. This is in accord with Elacridar hydrochloride earlier studies that have shown an anti-inflammatory effect of C5L2 engagement.10,13,14 Therapeutic implications were investigated using CCX168, an antagonist of human C5aR/CD88 that is undergoing phase 2 evaluation in patients with AAV (EU Clinical Trials Register ID: EUCTR2011C001222C15-GB). Oral administration of CCX168 to humanized mice with knocked-in human C5aR/CD88 ameliorated anti-MPO NCGN. Results C5aR/CD88 Deficiency Ameliorates, C5L2 Deficiency Exacerbates, and C6 Deficiency Has No Effect on Anti-MPOCInduced NCGN Injection of 50 g/g mouse antimouse MPO IgG into wild-type (WT) B6 mice resulted in NCGN (Physique 1A) in all mice (test; **human C5aR. (A) Mouse and human C5aR expression in isolated leukocytes from hC5aR knock-in mice. Circulation cytometric leukocyte staining with antibodies specific for mouse or human C5aR is shown in blue with Elacridar hydrochloride isotype controls (green collection) shown for comparison. (B) Chemotaxis of hC5aR knock-in cells in response to a dose range of human C5a in the absence (square) or presence (circle) of CCX168 (100 nM) showing inhibition of chemotaxis by CCX168. Migration transmission is a measure of cell figures migrating between ChemoTX chambers based on intensity of fluorescence of a DNA-binding fluorescent marker. (C) Effects of oral pretreatment with vehicle or a single dose of CCX168 on cell count in the peritoneal lavage 24 hours after intraperitoneal thioglycollate injection. (D) Schematic of the C5a-induced leukopenia study in hC5aR knock-in mice. One hour after oral administration of CCX168, blood was drawn 1 minute before and 1 minute after intravenous (IV) administration of C5a (20 g/kg); leukocyte concentrations were decided in these blood samples. (E) Following the study outline shown in panel D (test. A Small Molecule Inhibitor of hC5aR/CD88 MKK6 (CCX168) in Mice with hC5aR/CD88 Ameliorates Anti-MPOCInduced NCGN Oral CCX168, 30 mg/kg daily, reduced the severity of anti-MPO NCGN in hC5aR mice. Glomerular crescents were reduced from 30.4% to 3.3% with CCX168 (detected factor B, properdin, MAC, and C3d in glomeruli and small blood vessels with active AAV, which suggested alternative pathway activation.7 Gigante also detected match components in AAV lesions and observed that this extent of lesional.