Structure-Based Drug Design of Bisubstrate Inhibitors of Phenylethanolamine <i>N</i>‑Methyltransferase Possessing Low Nanomolar Affinity at Both Substrate Binding Domains¹

The
enzyme phenylethanolamine N-methyltransferase
(PNMT, EC 2.1.1.28) catalyzes the final step in the biosynthesis of
epinephrine and is a potential drug target, primarily for the control
of hypertension. Unfortunately, many potent PNMT inhibitors also possess
significant affinity for the a2-adrenoceptor, which complicates
the interpretation of their pharmacology. A bisubstrate analogue approach
offers the potential for development of highly selective inhibitors
of PNMT. This paper documents the design, synthesis, and evaluation
of such analogues, several of which were found to possess human PNMT
(hPNMT) inhibitory potency <5 nM versus AdoMet. Site-directed mutagenesis
studies were consistent with bisubstrate binding. Two of these compounds
(19 and 29) were co-crystallized with hPNMT
and the resulting structures revealed both compounds bound as predicted,
simultaneously occupying both substrate binding domains. This bisubstrate
inhibitor approach has resulted in one of the most potent (20) and selective (vs the a2‑adrenoceptor) inhibitors
of hPNMT yet reported.