EPZ005687 is a potent and selective inhibitor of EZH2 with Ki of 24 nM in a cell-free assay, 50-fold selectivity against EZH1 and 500-fold selectivity against 15 other protein methyltransferases.
EPZ005687 shows concentration-dependent inhibition of PRC2 enzymatic activity with an IC50 value of 54 nM. It is a direct inhibitor of PRC2 enzymatic activity and does not function by disrupting the protein-protein interactions among the PRC2 subunits. EPZ005687 binds in the SAM pocket of the EZH2 SET domain and is a SAM-competitive inhibitor of EZH2 enzyme activity. The affinity of EPZ005687 is similar (within a two-fold range) for PRC2 complexes containing wild-type and Tyr641 mutant EZH2, but significantly greater affinity for the A677G mutant enzyme (5.4-fold). EPZ005687 reduces H3K27 methylation in various lymphoma cells. It shows robust cell killing in heterozygous Tyr641 or Ala677 mutant cells, with minimal effects on the proliferation of wild-type cells. EPZ005687 increases G1 phase of the cell cycle with correlative decreases in the S as well as the G2/M phases. In a Tyr641 mutant lymphoma cell line, EPZ005687 can lead to derepression of known EZH2 target genes and affect genes specifically repressed by the EZH2 Tyr641 mutant. [1]
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