Epigenetic Multiple Ligands: Mixed Histone/Protein Methyltransferase, Acetyltransferase, and Class III Deacetylase (Sirtuin) Inhibitors

A number of new compounds bearing two ortho-bromo- and ortho,ortho-dibromophenol moieties linked through a saturated/unsaturated, linear/(poly)cyclic spacer (compounds 1–9) were prepared as simplified analogues of AMI-5 (eosin), a recently reported inhibitor of both protein arginine and histone lysine methyltransferases (PRMTs and HKMTs). Such compounds were tested against a panel of PRMTs (RmtA, PRMT1, and CARM1) and against human SET7 (a HKMT), using histone and nonhistone proteins as a substrate. They were also screened against HAT and SIRTs, because they are structurally related to some HAT and/or SIRT modulators. From the inhibitory data, some of tested compounds (1b, 1c, 4b, 4f, 4j, 4l, 7b, and 7f) were able to inhibit PRMTs, HKMT, HAT, and SIRTs with similar potency, thus behaving as multiple ligands for these epigenetic targets (epi-MLs). When tested on the human leukemia U937 cell line, the epi-MLs induced high apoptosis levels [i.e., 40.7% (4l) and 42.6% (7b)] and/or massive, dose-dependent cytodifferentiation [i.e., 95.2% (1c) and 96.1% (4j)], whereas the single-target inhibitors eosin, curcumin, and sirtinol were ineffective or showed a weak effect.