EPZ005687 is a potent inhibitor of EZH2, an enzymatic subunit of polycomb repressive complex 2 (PRC2) catalyzing the methylation of histone H3 lysine 27 (H3K27), that inhibits EZH2 with Ki of 24 nM, which is 500-fold and 50-fold greater in selectivity than 15 other protein methyltransferases and closely related EZH1 respectively. EPZ005687 concentration-dependently inhibits the enzymatic activity of PRC2 with IC50 of 54 nM through binding to the S-adenosylmethionine (SAM) pocket of the EZH2 SET domain. Study results have shown that EPZ005687 reduces H3K27 methylation in a variety of lymphoma cells and induces apoptotic cell killing in heterozygous Tyr641 or Ala677 mutant cells.