Discovery of the First-in-Class G9a/GLP Covalent Inhibitors

The highly homologous protein lysine methyltransferases
G9a and
GLP, which catalyze mono- and dimethylation of histone H3 lysine 9
(H3K9), have been implicated in various human diseases. To investigate
functions of G9a and GLP in human diseases, we and others reported
several noncovalent reversible small-molecule inhibitors of G9a and
GLP. Here, we report the discovery of the first-in-class G9a/GLP covalent
irreversible inhibitors, 1 and 8 (MS8511),
by targeting a cysteine residue at the substrate binding site. We
characterized these covalent inhibitors in enzymatic, mass spectrometry
based and cellular assays and using X-ray crystallography. Compared
to the noncovalent G9a/GLP inhibitor UNC0642, covalent inhibitor 8 displayed improved potency in enzymatic and cellular assays.
Interestingly, compound 8 also displayed potential kinetic
preference for covalently modifying G9a over GLP. Collectively, compound 8 could be a useful chemical tool for studying the functional
roles of G9a and GLP by covalently modifying and inhibiting these
methyltransferases.