Chimeric strategies for the rational design of bioactive analogs of small peptide hormones

The aim of this study was to evaluate a variety of synthetic strategies pertinent to the development of chimeric analogs of the structurally divergent nonapeptide hormones arginine vasopressin (AVP) and bradykinin (BK). Single-chain peptides combining AVP and BK directly, AVP(1-9)-BK(1-9) or via a flexible aminohexanoic acid (epsilonAhx) linker, AVP(1-9)-epsilonAhx-BK(1-9), bind with relatively high affinity to the bovine kidney medulla B2a bradykinin receptor (B2a BKR). Significantly, amino-terminal extended chimeric analogs of BK, including AVP(1-9)-BK(1-9) and galanin(1-13)-BK(1-9), are functional B2 BKR agonists. These findings illustrate that chimeric peptides can activate G-protein-coupled receptors (GPCRs) in a manner analogous to that of endogenous monomeric agonists. Further development, combining the sequences of receptor subtype-selective antagonists, produced high-affinity chimeric antagonists of the V1a vasopressin receptor (V1a VPR) and the B2a BKR. We also determined the pharmacological characteristics of high-affinity chimeric hormone analogs derivatized with the membrane targeting function of mastoparan. Homodimers of an amino-terminal extended BK analog and a V1a-selective antagonist represent the first examples of new classes of B2 BKR and V1a VPR antagonists, respectively. These findings are discussed in relation to the GPCR binding site for small peptides and the development of novel biological probes and therapeutic agents.