Potent Cyclic Antagonists of the Complement C5a Receptor on Human Polymorphonuclear Leukocytes. Relationships between Structures and Activity

Abstract

Human C5a is a plasma protein with potent chemoattractant and pro-inflammatory properties, and its overexpression correlates with severity of inflammatory diseases. C5a binds to its G protein-coupled receptor (C5aR) on polymorphonuclear leukocytes (PMNLs) through a high-affinity helical bundle and a low-affinity C terminus, the latter being solely responsible for receptor activation. Potent and selective C5a antagonists are predicted to be effective anti-inflammatory drugs, but no pharmacophore for small molecule antagonists has yet been developed, and it would significantly aid drug design. We have hypothesized that a turn conformation is important for activity of the C terminus of C5a and herein report small cyclic peptides that are stable turn mimics with potent antagonism at C5aR on human PMNLs. A comparison of solution structures for the C terminus of C5a, small acyclic peptide ligands, and cyclic antagonists supports the importance of a turn for receptor binding. Competition between a cyclic antagonist and either C5a or an acyclic agonist for C5aR on PMNLs supports a common or overlapping binding site on the C5aR. Structure-activity relationships for 60 cyclic analogs were evaluated by competitive radioligand binding with C5a (affinity) and myeloperoxidase release (antagonist potency) from human PMNLs, with 20 compounds having high antagonist potencies (IC 50 , 20 nM-1 M). Computer modeling comparisons reveal that potent antagonists share a common cyclic backbone shape, with affinitydetermining side chains of defined volume projecting from the cyclic scaffold. These results define a new pharmacophore for C5a antagonist development and advance our understanding of ligand recognition and receptor activation of this G proteincoupled receptor.

PMX-53 as a Dual CD88 Antagonist and an Agonist for Mas-Related Gene 2 (MrgX2) in Human Mast Cells

“…PMX-53 is a potent CD88 antagonist and inhibits C5a-induced neutrophil myeloperoxidase release and chemotaxis with IC 50 values of 22 and 75 nM, respectively (Haynes et al, 2000;March et al, 2004). We therefore sought to determine whether the PMX-53 used in the present study displayed CD88 inhibitory activity.…”

Complement Induction in Spinal Cord Microglia Results in Anaphylatoxin C5a-Mediated Pain Hypersensitivity

“…approximately 10 times the peptide ED 50 concentration (March et al, 2004)]. Control catheters contained PBS alone.…”

The Complement C3a Receptor Contributes to Melanoma Tumorigenesis by Inhibiting Neutrophil and CD4+ T Cell Responses

“…For some experiments, mice received daily injections of either a nonpeptide C3aR antagonist (SB290157; VDM Biochemicals, Bedford Heights, OH; 1 mg/kg/d i.p. ), the cyclic hexapeptide C5aR1 antagonist (PMX53; produced in-house; 1 mg/kg/d) (16), or vehicle only (0.9% saline or 5% glucose solution) control, commencing once tumors became palpable (approximately day 7 after tumor cell injection). Mice were euthanized at day 14 (or once the largest tumor reached ∼150 mm 2 ), blood was collected by cardiac puncture, tumors, spleen, draining lymph nodes (inguinal, axillary, and brachial), and femurs were excised, and tumors were weighed.…”