Active Motif's UNC1999 is an orally active, highly selective inhibitor of both wild-type and mutant EZH1 and EZH2 lysine methyltransferases (IC50 = 45 nM and 2 nM respectively). Inhibition of EZH2 with UNC1999 enhanced the efficacy of gefitinib in suppressing the proliferation of colon cancer cells. UNC1999 suppresses global H3K27 trimethylation/demethylation and inhibits the growth of mixed lineage leukemia (MLL)-rearranged leukemia cells.