The DNA methyl transferase inhibitor, 5'-aza-2-deoxycitidine, enhances the apoptotic effect of Mevastatin in human leukemia HL-60 cells.

Statins induce antiproliferative effects and apoptotic response in various cancer cell types. Moreover, they also sensitize tumor cell lines from different origins to many agents. We aimed to investigate possible effects of Mevastatin (Mev) alone and sequential treatment of 5'-aza-2-deoxycitidine (DAC) and Mev on HL-60 cell line using XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide) assay, lactate dehydrogenase release assay, flourescence microscopy, DNA fragmentation analysis, determination of DNA synthesis rate, and active caspase-3 assay. Messenger RNA (mRNA) expression of apoptotic and antiapoptotic genes were also evaluated by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) for BAX, BCL2, and XIAP genes and quantitative Real-time PCR for CASP3, CASP8, and CASP9 genes. We showed that treatment with Mev alone and DAC followed by Mev resulted in apoptotic response in a time- and dose-dependent manner. We also found that pretreatment with DAC sensitized HL-60 cells to Mev and caused more apoptotic cell death than Mev-alone treatment via caspase-3 activation and DNA fragmentation. Moreover, sequential addition of Mev after DAC diminished DNA synthesis rate more effectively than Mev-alone treatment. Furthermore, DAC pretreatment significantly increased CASP3 and CASP9 mRNA expression even with lower doses of Mev. BAX, BCL2, and XIAP gene mRNA levels were also found to be changed in the presence of DAC and Mev. Determination of the exact molecular effects of statins and DAC would allow us to identify new molecular targets to develop more effective treatment regimens for cancer.