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 (εAhx) linker, AVP(1-9)-εAhx-BK(1-9), bind with relatively high affinity to the bovine kidney medulla B(2a) bradykinin receptor (B(2a) 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 V(1a) vasopressin receptor (V(1a) VPR) and the B(2a) 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 V(1a)-selective antagonist represent the first examples of new classes of B₂ BKR and V(1a) 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.