Structure-activity study of hCGRP sub(8-37), a calcitonin gene-related peptide receptor antagonist

• Published in: Journal of medicinal chemistry 1992-01, Vol.35 (12), p.2163-2168
• Main Authors: Mimeault, M, Quirion, R, Dumont, Y, St-Pierre, S, Fournier, A
• Format: Article
• Language: English
• ISSN: 0022-2623

A structure-activity study was carried out to determine the importance of the N-terminal amino acids of hCGRP sub(8-37) in binding and antagonistic activity to CGRP receptors. Therefore, fragments of hCGRP sub(8-37) as well as analogs obtained by the replacement of residues 9-12 by L-alanine were synthesized by solid-phase peptide synthesis, using BOP as a coupling reagent. The affinities of the peptides to CGRP receptors were evaluated in the rat brain, guinea pig atrium, and guinea pig vas deferens membrane preparations. Their antagonistic activities were measured in the guinea pig atria and rat vas deferens bioassays. The pharmacological characterization showed that arginine-11 and leucine-12 play a crucial role for the affinity of hCGRP sub(8-37). Interestingly, it was observed that [Ala super(11)]hCGRP sub(8-37) was able to potentiate the twitch response of the electrically stimulated rat vas deferens. On the other hand, the substantial antagonistic potencies of analogs [Ala super(9)]-, [Ala super(10)]-, and [Ala super(12)]hCGRP sub(8-37), as compared to those of the fragments hCGRP sub(10-37), hCGRP sub(11-37), and hCGRP sub(12-37), suggest that the side chains of Thr-9, His-10, and Leu-12 assume mainly a structural role. Accordingly, the conformational characterization of these peptides by circular dichroism spectroscopy revealed that the residues 9-12 are important for the integrity of the amphiphilic alpha -helix of hCGRP sub(8-37).