Discovery of Novel Substrate-Competitive Lysine Methyltransferase G9a Inhibitors as Anticancer Agents

Identification of structurally novel
inhibitors of lysine methyltransferase
G9a has been a subject of intense research in cancer epigenetics.
Starting with the high-throughput screening (HTS) hit rac-10a obtained from the chemical library of the University
of Tokyo Drug Discovery Initiative, the structure–activity
relationship of the unique substrate-competitive inhibitors was established
with the help of X-ray crystallography and fragment molecular orbital
(FMO) calculations for the ligand–protein interaction. Further
optimization of the in vitro characteristics and
drug metabolism and pharmacokinetics (DMPK) properties led to the
identification of 26j (RK-701), which is a structurally
distinct potent inhibitor of G9a/GLP (IC50 = 27/53 nM).
Compound 26j exhibited remarkable selectivity against
other related methyltransferases, dose-dependent attenuation of cellular
H3K9me2 levels, and tumor growth inhibition in MOLT-4 cells in vitro. Moreover, compound 26j showed inhibition
of tumor initiation and growth in a carcinogen-induced hepatocellular
carcinoma (HCC) in vivo mouse model without overt
acute toxicity.