Effects of DNA methyltransferase inhibitors (DNMTIs) on MDS-derived cell lines.

DNA methyltransferase inhibitors (DNMTIs), including decitabine (DAC) and azacitidine (AZA), have recently been highlighted for the treatment of high-risk myelodysplastic syndrome (MDS); however, their action mechanisms have not been clearly defined. Therefore, we investigated the effects of DNMTIs on MDS-derived cell lines in vitro. An MDS-derived cell line MDS92 and its blastic subline MDS-L and HL-60 were used. All three cell lines were sensitive to DNMTIs, but MDS-L was the most susceptible. DAC-induced cell death in MDS-L was preceded by DNA damage-induced G2 arrest via a p53-independent pathway. AZA did not influence the pattern of cell cycle, although it induced DNA damage response. The IC(50) of DAC or AZA on MDS-L cells was associated with the dose inducing the maximal hypomethylation in long interspersed nuclear elements-1 (LINE-1) methylation assay. AZA suppressed the level of methylation in a time-dependent manner (days 4, 7, and 10), whereas DAC maintained the level of methylation from day 4 to 11. The protein expression of DNMT1 and DNMT3a decreased with the suppression of growth and methylation. We conclude that this study provides in vitro models for understanding the effects of DNMTIs on cell growth and gene regulation, including differences in the possible action mechanism of DAC and AZA.