PT  - JOURNAL ARTICLE
AU  - Darren R. March
AU  - Lavinia M. Proctor
AU  - Martin J. Stoermer
AU  - Robert Sbaglia
AU  - Giovanni Abbenante
AU  - Robert C. Reid
AU  - Trent M. Woodruff
AU  - Khemar Wadi
AU  - Natalii Paczkowski
AU  - Joel D. A. Tyndall
AU  - Stephen M. Taylor
AU  - David P. Fairlie
TI  - Potent Cyclic Antagonists of the Complement C5a Receptor on Human Polymorphonuclear Leukocytes. Relationships between Structures and Activity
AID  - 10.1124/mol.65.4.868
DP  - 2004 Apr 01
TA  - Molecular Pharmacology
PG  - 868--879
VI  - 65
IP  - 4
4099  - http://molpharm.aspetjournals.org/content/65/4/868.short
4100  - http://molpharm.aspetjournals.org/content/65/4/868.full
SO  - Mol Pharmacol2004 Apr 01; 65
AB  - 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 (IC50, 20 nM-1 μM). Computer modeling comparisons reveal that potent antagonists share a common cyclic backbone shape, with affinity-determining 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 protein-coupled receptor.