Enhancing Stability and Bioavailability of Peptidylglycine Alpha-Amidating Monooxygenase in Circulation for Clinical Use

Peptidylglycine alpha-amidating monooxygenase (PAM) is the only enzyme known to catalyze C-terminal amidation, a final post-translational modification step essential for the biological activity of over 70 bioactive peptides, including adrenomedullin (ADM), calcitonin gene-related peptide (CGRP), amylin, neuropeptide Y (NPY), and others. Bioactive (amidated) peptide hormones play crucial roles in various physiological processes and have been extensively explored as therapeutic compounds in clinical and preclinical research. However, their therapeutic viability is limited due to their short half-life and, in most cases, the need for prolonged infusion to maintain effective concentrations. PAM itself has also been considered as a therapeutic compound aiming to increase the level of amidated peptide hormones; however, similarly to peptide hormones, PAM's rapid degradation limits its utility. Here, we present a strategy to enhance PAM stability and bioavailability through PEGylation, significantly extending the enzyme's half-life in circulation assessed in healthy rats. Furthermore, single subcutaneous (s.c.), intramuscular (i.m.), or intraperitoneal (i.p.) administration of PEGylated PAM resulted in a sustained increase in circulating amidating activity, with peak activity observed at 12-24 h post-bolus administration. Notably, amidating activity remained significantly elevated above baseline levels for up to seven days post-administration, with no observable adverse effects. These findings highlight PEGylated PAM's potential as a viable therapeutic compound.