Discovery of Selective Nanomolar Inhibitors for Insulin-Regulated Aminopeptidase Based on α‑Hydroxy-β-amino Acid Derivatives of Bestatin

The oxytocinase subfamily of M1 zinc aminopeptidases
comprises
emerging drug targets, including the ER-resident aminopeptidases 1
and 2 (ERAP1 and ERAP2) and insulin-regulated aminopeptidase (IRAP);
however, reports on clinically relevant inhibitors are limited. Here
we report a new synthetic approach of high diastereo- and regioselectivity
for functionalization of the α-hydroxy-β-amino acid scaffold
of bestatin. Stereochemistry and mechanism of inhibition were investigated
by a high-resolution X-ray crystal structure of ERAP1 in complex with
a micromolar inhibitor. By exploring the P1 side-chain functionalities,
we achieve significant potency and selectivity, and we report a cell-active,
low-nanomolar inhibitor of IRAP with >120-fold selectivity over
homologous
enzymes. X-ray crystallographic analysis of IRAP in complex with this
inhibitor suggest that interactions with the GAMEN loop is an unappreciated
key determinant for potency and selectivity. Overall, our results
suggest that α-hydroxy-β-amino acid derivatives may constitute
useful chemical tools and drug leads for this group of aminopeptidases.