hCXCR1 and hCXCR2 antagonists derived from combinatorial peptide libraries.

The human CXCL8 plays important roles in inflammation by activation of neutrophils through the hCXCR1 and hCXCR2 receptors. The role of hCXCR1 and hCXCR2 in the pathogenesis of inflammatory responses has encouraged the development of antagonists of these receptors. In this study, we used phage display peptide libraries to identify peptides antagonists that block the interactions between hCXCL8 and hCXCR1/2. Two linear hexapeptides (MSRAKE and CAKELR) and two disulfide-constrained hexapeptides (CLRSGRFC and CLPWKENC) were recovered by panning phage libraries on hCXCR1- and hCXCR2-transfected murine pre-B cells after specific elution with hCXCL8. Sequence analysis revealed homology between the linear hexapeptides and the N-terminal domain (1-SAKELR-6), whereas the constrained peptides are composed of non-contiguous amino acids mimicking spatial structure on the surface of folded C-terminal portion of hCXCL8 (50-CLDPKENWVQRVVEKFLKRAENS-72). The synthetic linear and structurally constrained peptides competed for (125)I-hCXCL8 binding to hCXCR1 and hCXCR2 (IC(50) comprised between 10 and 100μM). Furthermore, they inhibited the intracellular calcium flux and the migration of hCXCR1/hCXCR2 transfectants; and desensitized hCXCR1 and hCXCR2 receptors on neutrophils, reducing their chemotactic responses induced by ELR-CXC chemokines (hCXCL8, hCXCL1, hCXCL2, hCXCL3, and hCXCL5). To better characterize the residues required for hCXCL8 binding, we identified three linear peptides MLRQTR, HASILP and KKEPWI specific to hCXCL8. These peptides similarly displaced the binding of (125)I-hCXCL8 to hCXCR1 (IC(50) ranging from 8.5 to 10μM) in a dose-dependent manner, inhibited hCXCL8 induced increases in the intracellular calcium, and migration of hCXCR1- and hCXCR2-transfected cells. The identified peptides could be used as antagonists of hCXCL8-induced activities related to its interaction with hCXCR1 and hCXCR2 receptors and may help in the design of new anti-inflammatory therapeutic molecules.