Objective:To investigate the effects of triptolide (TPL) and BET protein inhibitor JQ1 on proliferation inhibition and apoptosis induction of MLL-rearranged acute myeloid leukemia (AML) cell line MV4-11, and to explore their synergistic mechanisms.Methods:MV4-11 cells in logarithmic growth phase were treated with different concentrations (100, 200, 300, and 400 nmol/L) of JQ1, 4 nmol/L TPL or different concentrations of JQ1 combined with 4 nmol/L TPL for 48 h. Cell proliferation was detected by CCK-8 method, apoptosis was detected by flow cytometry (FCM), mitochondrial membrane potential was detected by JC-1 method, and expressions of mitochondrial apoptosis pathway-related proteins were detected by Western blot.Results:The 50% inhibitory concentration ( IC50) value of MV4-11 cells treated with JQ1 for 48 h was (283.9±10.7) nmol/L. However, 4 nmol/L TPL significantly enhanced the inhibitory effect of JQ1 on proliferation of MV4-11 cells, the IC50 value of MV4-11 cells treated with JQ1 combined with TPL was (148.1±2.6) nmol/L, and the difference was statistically significant ( t = 25.31, P = 0.029). The result of FCM assay showed that compared with the JQ1 alone group [(9.6±2.3)%, (12.6±1.4)%, (19.5±3.3)%, and (22.7±2.1)%], 4 nmol/L TPL combined with different concentrations (100, 200, 300, and 400 nmol/L) of JQ1 acted on MV4-11 cells for 48 h, the proportions of apoptotic cells were (16.4±1.9)%, (27.5±2.1)%, (32.9±3.6)%, and (35.5±3.0)%, respectively, the difference was statistically significant ( F = 9.25, P < 0.01). After treated with 4 nmol/L TPL and JQ1 for 12 h, the level of cell membrane potential in MV4-11 cells was significantly lower than that of JQ1 single agent group, and the difference was statistically significant ( P < 0.05). After treated by 4 nmol/L TPL combined with JQ1 for 24 h, the levels of anti-apoptotic proteins bcl-2 and Mcl-1 decreased, and the level of pro-apoptotic protein bax increased. Conclusion:TPL can significantly enhance the proliferation inhibition and apoptosis induction effects of BET protein inhibitor JQ1 on MLL-rearranged AML cells, and the mechanism may be related to enhancing the mitochondrial apoptosis pathway.