Synergistic effects of valproic acid and arsenic trioxide on RPMI8226 cells in vitro and the possible underlying mechanisms.

The aim of the present study was to investigate the synergistic effects of valproic acid (VPA) and arsenic trioxide (ATO) on the proliferation of RPMI8226 cells and the possible underlying mechanisms. Cell apoptosis was assessed by flow cytometry. The mRNA expression levels were analyzed by semi-quantitative polymerase chain reaction, and the protein expression levels were analyzed by western blotting. The histone acetylation and methylation states of the gene promoters were detected using a chromatin immunoprecipitation technique. The apoptotic rates of the RPMI8226 cells in the combined drug groups were significantly increased compared with those of the single drug groups (P<0.05). The mRNA and protein expression levels of Bcl-2 and the expression levels of HDAC1 mRNA and H3K9me2 protein decreased significantly in the combined groups compared with the single drug groups. The mRNA and protein expression levels of Bax, Caspase 8, Caspase 9 and LSD1, and the protein expression of acetylated H3 increased significantly in the combination groups compared with the single drug groups. Histone methylation and acetylation of the Bcl-2 and bax gene promoters were increased in the combination groups compared with the single drug groups. VPA and ATO had synergistic effects on the proliferation of RPMI8226 cells, which may have been associated with the decreased expression of Bcl-2 and the increased expression levels of Bcl-2-associated X protein, Caspase 8 and Caspase 9. Therefore, the expression levels of the Bcl-2 gene family may have been regulated by the levels of gene promoter methylation and acetylation.