| Abstract
| - Calcitonin gene-related peptide (CGRP) is a 37-residue neuropeptide that can be converted to a CGRP1 receptor antagonist by the truncation of its first seven residues. CGRP(8−37), 1, has a CGRP1 receptor Ki = 3.2 nM but is rapidly degraded in human plasma (t1/2 = 20 min). As part of an effort to identify a prolonged in vivo circulating CGRP peptide antagonist, we found that the substitution of multiple residues in the CGRP peptide increased CGRP1 receptor affinity >50-fold. Ac-Trp-[Arg24,Lys25,Asp31,Pro34,Phe35]CGRP(8−37)-NH2, 5 (Ki = 0.06 nM) had the highest CGRP1 receptor affinity. Using complimentary in vitro and in vivo metabolic studies, we iteratively identified degradation sites and prepared high affinity analogues with significantly improved plasma stability. Ac-Trp-[Cit11,18,hArg24,Lys25,2-Nal27,37,Asp31,Oic29,34,Phe35]CGRP(8−37)-NH2, 32 (Ki = 3.3 nM), had significantly increased (>100-fold) stability over 1 or 5, with a cynomolgus monkey and human in vitro plasma half-life of 38 and 68 h, respectively.
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