Selective Inhibition of EZH2 and EZH1 Enzymatic Activity By a Small Molecule Suppresses MLL rearrangement-Induced Leukemia

Enhancer of Zeste Homolog-2 (EZH2) and Related EZH1 Control Gene Expression and Promote Oncogenesis Via Methylating Histone H3 Lysine 27 (H3K27). These Methyltransferases Are Proposed to be Therapeutic Targets Due to Their Hyperactive Mutations and Overexpression Found in Cancer Including Various Hematological Malignancies. Here, We Characterized a Set of Small Molecules That Allow Pharmacological Manipulation of EZH2 and EZH1, Which Include UNC1999, a Highly Selective Inhibitor of Both Enzymes, and Its Di-Methylated Analog UNC2400, an Inactive Compound Useful to Assess Off-Target Effects. We Show That UNC1999 Suppresses H3K27 Tri- and Di-Methylation Globally and Inhibits Growth of MLL-Rearranged Leukemia Lines. Mechanistically, UNC1999 Preferentially Affects the Regulatory Elements Such As Enhancers and Distal Promoters, Leading to De-Repression of Many Known Polycomb Target Genes. Gene De-Repression Correlates with Decrease in H3K27me3 and Concurrent Gain in H3K27 Acetylation. UNC2400 Does Not Induce These Effects, Demonstrating UNC1999’s on-Target Inhibition. Oral Administration of UNC1999 Significantly Prolongs the Survival of a Well-Defined Murine Leukemia Model Generated By MLL-AF9. Thus, Our Studies Provide Detailed Profiling of a Set of Compounds for Studying EZH2 and EZH1 in Cancer and Establish Specific Inhibition of EZH2 and EZH1 Enzymatic Activities By Small Molecules As a Promising Therapeutics for MLL-Rearranged Leukemia.