Novel stable PACAP analogs with potent activity towards the PAC1 receptor

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38- or 27-amino acid neuropeptide with promising therapeutic applications for the treatment of several pathophysiological states related to neurodegenerative diseases. However, its use for therapeutic applications is actually limited by its restricted bioavailability and rapid degradation. Therefore, metabolically stable PACAP analogs represent promising tools to further investigate the physiological roles of PACAP and ascertain its usefulness in some clinical conditions. In this study, derivatives of PACAP27 and PACAP38 have been rationally designed to develop PAC1 receptor agonists resistant to peptidase action. Results showed that N-terminal modifications confer resistance to dipeptidyl peptidase IV, a major proteolytic process involved in PACAP degradation. Moreover, in vitro incubation of both PACAP isoforms in human plasma revealed that PACAP38 is rapidly metabolized, with a half-life of less than 5 min, while PACAP27 was stable in these experimental conditions. Hence, following the elucidation of its plasmatic metabolites, PACAP38 was modified at its putative endopeptidase and carboxypeptidase sites of cleavage. All peptide analogs were tested for their ability to bind the PAC1 receptor, as well as for their potency to induce calcium mobilization and inhibit PC12 cell proliferation through the PAC1 receptor. This approach revealed two leading compounds, i.e. acetyl-[Ala15, Ala20]PACAP38-propylamide and acetyl-PACAP27-propylamide, which exhibited improved metabolic stability and potent biological activity. This study describes innovative data related to PACAP metabolism in human plasma and depicts the development of a metabolically stable PACAP38 analog, acetyl-[Ala15, Ala20]PACAP38-propylamide, which behaves as a super-agonist towards the PAC1 receptor.