Spiroepoxytriazoles Are Fumagillin-like Irreversible Inhibitors of MetAP2 with Potent Cellular Activity

Methionine
aminopeptidases (MetAPs) are responsible for the cotranslational
cleavage of initiator methionines from nascent proteins. The MetAP2
subtype is up-regulated in many cancers, and selective inhibition
of MetAP2 suppresses both vascularization and growth of tumors in
animal models. The natural product fumagillin is a selective and potent
irreversible inhibitor of MetAP2, and semisynthetic derivatives of
fumagillin have shown promise in clinical studies for the treatment
of cancer, and, more recently, for obesity. Further development of
fumagillin derivatives has been complicated, however, by their generally
poor pharmacokinetics. In an attempt to overcome these limitations,
we developed an easily diversifiable synthesis of a novel class of
MetAP2 inhibitors that were designed to mimic fumagillin’s
molecular scaffold but have improved pharmacological profiles. These
substances were found to be potent and selective inhibitors of MetAP2,
as demonstrated in biochemical enzymatic assays against three MetAP
isoforms. Inhibitors with the same relative and absolute stereoconfiguration
as fumagillin displayed significantly higher activity than their diastereomeric
and enantiomeric isomers. X-ray crystallographic analysis revealed
that the inhibitors covalently modify His231 in the MetAP2 active
site via ring-opening of a spiroepoxide. Biochemically active substances
inhibited the growth of endothelial cells and a MetAP2-sensitive cancer
cell line, while closely related inactive isomers had little effect
on the proliferation of either cell type. These effects correlated
with altered N-terminal processing of the protein 14-3-3-γ.
Finally, selected substances were found to have improved stabilities
in mouse plasma and microsomes relative to the clinically investigated
fumagillin derivative beloranib.