Systematic optimization of a lead-structure identities for a selective short peptide agonist for the human orphan receptor BRS-3

The orphan receptor human bombesin receptor subtype 3 (BRS 3) was assigned to the G protein coupled bombesin receptor family because of its high sequence homology with the neuromedin B receptor (NMB R) and gastrin releasing peptide receptor (GRP R) Since its pharmacology is still unknown new highly potent and selective tool substances are needed that may be able to elucidate its possible role in obesity and cancer We have performed structure activity relationship studies on the high affinity peptide agonists [D Phe(6) beta Ala(11) Phe(13) Nle(14) ]Bn(6-14) and [D Phe(6) Phe(13)]Bn(6-13)propylamide using their ability to mobilize intracellular calcium in BRS 3 transfected CHOGalpha 16 cells combined with receptor binding studies It was demonstrated that for [D Phe(6) beta Ala(11) Phe(13) Nle(14)]Bn(6-14) the side chains of the residues Trp(8) and Phe(13) and to a smaller extent beta Ala(11) are the important amino acid side chains for receptor activation and binding however for [D Phe(6) Phe(13)]Bn(6-13) propylamide His(12) seems to be more important than Phe(13) C and N terminal deletions and amino acid substitutions allowed further understanding It was demonstrated that substitution of His(12) by Tyr leads to a high selectivity towards GRP R Using the acquired information a small tetrapeptide library was designed with compounds presenting Trp, and Phe at varying stereochemistry and distances which led to the discovery of the lead structure H D Phe Gln D Trp Phe NH2 Systematic SAR revealed the important structural features of this peptide C terminal optimization resulted in the highly active and selective BRS, 3 agonist H D Phe Gln. D Trp, 1 (2 phenylethyl)amide In summary the size of the peptide was reduced from 8 or 9 amino acids to a tripeptide for BRS 3 Copyright (C) 2002 European Peptide Society and John Wiley Sons Ltd.