Antileukemia Activity Of The Combination Of Valproic Acid And Decitabine

Epigenetic mechanisms including aberrant methylation of CpG islands in promoter and abnormal modifications of histone are implicated in carcinogenesis and development of a variety of tumors. As epigenetic alteration is reversible, epigenetic modification agents like DNMTs inhibitors and HDACs inhibitors have been found to be alternative cancer treatment. In recent years, these agents have been reported to exert antileukemia effects and the combination of HDACs inhibitor valproic acid (VPA) and DNMTs inhibitor 5-aza-2'-dexoycytidine (DAC) shows promise for the treatment of patients with leukemia. However, the mechanisms underlying the combined effects on leukemia cells are not fully understood, which limits this combination as a well-accepted strategy for targeted therapy in leukemia. In this study, we investigated the growth-inhibition of VPA plus DAC on several leukemia cell lines and the apoptosis induction by this combination in K562 cells. In addition, we explored the effects of the combination on mRNA levels of DNMT1/3b genes and Polycomb Group (PcG) genes including YY1, EZH2, and Bmi-1 in K562 cells.Methods:Part I1. MTT assay was used to measure the effects of VPA combined with DAC on growth-inhibition in leukemia cells.2. Western blot was performed to detect PARP cleavage in K562 cells exposed to VPA combined with DAC for 4 days.Part II1. RT-PCR was performed to measure mRNA levels of Polycomb Group (PcG) genes including YY1, EZH2, and Bmi-1 in K562 cells in exposure to VPA combined with DAC for 4 days.2. RT-PCR was performed to measure mRNA levels of DNMT1/3b genes in K562 cells in exposure to VPA combined with DAC for 4 days.Results:Part I1. Synergistic effects of VPA plus DAC on growth-inhibition were observed in K562 and HL-60 but not in U937.2. PARP cleavage was detected in K562 cells exposed to VPA combined with DAC for 4 days. Part II 1. mRNA levels of YY1, EZH2, and Bmi-1 were down-regulated in K562 cells exposed to DAC and VPA, alone or in combination. No synergistic effect of the combination was observed.2. mRNA levels of DNMT1/3b were down-regulated in K562 cells exposed to DAC and VPA, alone or in combination. No synergistic effect of the combination was observed.Conclusions:1. The combination of VPA and DAC exerts synergistic effects on growth-inhibition in leukemia cells and induces apoptosis in K562 cells.2. It seems that there is no synergistic effect of VPA plus DAC on down-regulation of mRNA levels of YY1, EZH2, Bmi-1, and DNMT1/3b in K562 cells.