A selective EZH2 inhibitor (IC50s = 0.5 and 2.5 nM for wild-type EZH2 and Y641N mutant EZH2, respectively); decreases cellular levels of H3K27me3 and H3K27me2 (EC50s = 56 and 65 nM, respectively), triggering cell cycle arrest and ultimately resulting in apoptosis in a large panel of NHL cell lines.