Objective To detect the curative effectiveness and its possible mechanisms of triptolide (TPL) on prostate cancer DU145 cells.Methods After DU145 cells were treated with 0,5,25,50,and 100 mmol/L TPL for 24 and 48 h,methyl thiazol tetrazolium (MTT) assay was used to observe the proliferation inhibition.Apoptosis was evaluated by Annexin V-fluoresceine isothiocyanate (FITC)/propidirum iodide (PI) double staining with flow cytometry and visualized using PI staining of apoptotic nuclei.Protein histone H3 containing the trimethylated lysine 27 (H3K27me3) and enhancer of zeste homolog 2 (EZH2) expression levels were detected by Western blotting,and EZH2 gene expression by real-time quantitative polymerase chain reaction (FQ-PCR).Results Treatment with TPL for 24 h or 48 h inhibited proliferation of DU145 cells with 50％ inhibitory dose (IC50) being (68.71 ±0.15) and (36.87 ±5.80)nmol/L respectively,with the difference being statistically significant in comparison to the normal control group (P ＜ 0.05).As compared with the normal control group,with the increases of TPL concentrations (25,50 and 100 nmol/L),the apoptosis rate was gradually increased,and the early apoptosis rate was (10.9 ± 1.3) ％,(22.4 ± 1.3) ％ and (31.3 ± 2.4) ％,respectively.There was statistically significant difference between each two groups (P ＜ 0.05).PI staining results showed typical apoptotic characteristics.After DU145 cells were treated with TPL at different concentrations for 24 h,Western blotting showed the expression levels of trimethylated H3K27me3 and EZH2 were significantly reduced (P ＜ 0.05).Using FQ-PCR,we verified that EZH2 mRNA was decreased by TPL in a concentration-dependent manner (P ＜0.05).Conclusion TPL inhibited the proliferation of DU145 cells in a concentration-and time-dependent manner and induced epigenetic alterations probably by regulating histone methylation.