Discovery of 2-tetrahydroisoquinoline substituted quinazoline derivatives as lysine methyltransferase G9a inhibitors with in vivo antitumor efficacy.

Overexpression of protein lysine methyltransferase G9a, which catalyzes mono- and di-methylation of histone H3K9 and non-histone proteins, is closely associated with poor prognosis and metastasis of various cancers. Here, we designed and synthesized a series of novel G9a inhibitors bearing 2-tetrahydroisoquinoline substituted quinazoline scaffold. Among them, compound 31 with 2-dioxole fused tetrahydroisoquinoline exhibited the most potent inhibitory effects against G9a with an IC50 value of 0.032 μM and high selectivity against the other tested lysine/arginine methyltransferases. Molecular docking showed that the bulky tricyclic moiety of compound 31 enhanced its interaction with the active sites of G9a through additional van der Waals forces. Compared to the reference compound UNC0642, compound 31 exhibited much improved enzymatic activity against G9a and more potent antiproliferative effects against all tested cancer cells. In CT26 colon cells, this compound not only significantly suppressed the H3K9me2 level, but also triggered autophagy by inducing the production of ROS, thus leading to cell apoptosis and cell cycle arrest at G0/G1. It also possessed good microsomal metabolic stability and acceptable in vivo pharmacokinetic properties. More importantly, in the CT26 tumor mouse model, compound 31 demonstrated in vivo antitumor efficacy with a TGI rate of 45.10 % without significant body weight loss and visible toxicity, indicating a superior safety profile compared to UNC0642. Overall, compound 31 with 2-tetrahydroisoquinoline substituted quinazoline scaffold could be used as a promising lead compound for the development of novel G9a inhibitors.