Discovery of Selective Pituitary Adenylate Cyclase 1 Receptor (PAC1R) Antagonist Peptides Potent in a Maxadilan/PACAP38-Induced Increase in Blood Flow Pharmacodynamic Model

Abstract

Inhibition of the pituitary adenylate cyclase 1 receptor (PAC1R) is a novel mechanism that could be used for abortive treatment of acute migraine. Our research began with comparative analysis of known PAC1R ligand scaffolds, PACAP38 and Maxadilan, which resulted in the selection of des(24-42) Maxadilan, <b>6</b>, as a starting point. C-terminal modifications of <b>6</b> improved the peptide metabolic stability <i>in vitro</i> and <i>in vivo</i>. SAR investigations identified synergistic combinations of amino acid replacements that significantly increased the <i>in vitro</i> PAC1R inhibitory activity of the analogs to the pM IC₉₀ range. Our modifications further enabled deletion of up to six residues without impacting potency, thus improving peptide ligand binding efficiency. Analogs <b>17</b> and <b>18</b> exhibited robust <i>in vivo</i> efficacy in the rat Maxadilan-induced increase in blood flow (MIIBF) pharmacodynamic model at 0.3 mg/kg subcutaneous dosing. The first cocrystal structure of a PAC1R antagonist peptide (<b>18</b>) with PAC1R extracellular domain is reported.