The Impact of 6-Thioguanine on Epigenetics of Acute Myeloid Leukemia

The drug 6-thioguanine (6-TG) is one of the thiopurines successfully used in oncology, especially for acute myeloid leukemia (AML). It is proposed to act as an epigenetic drug affecting DNA methylation. The aim of this study was to clarify the effect of 6-TG on the proliferation, viability and expression of genes coding for the enzymes DNA methyltransferase 3A and DNA methyltransferase 3B (DNMTs) as well as histone deacetylase 3 (HDAC3) and histone deacetylase 7 (HDAC7) in the human promyelocytic AML cell line HL60. In this experimental study, HL60 cells and also normal peripheral blood mononuclear cells (PBMCs) were grown in RPMI 1640 medium containing 10% fetal bovine serum. They were then treated with 6-TG at their exponential growth phase. Cell viability was monitored using the Cell Counting Kit-8 assay with an enzyme-linked immunosorbent assay (ELISA) reader. The expressions of the above mentioned 4 genes were quantified using real-time PCR. 6-TG could inhibit the proliferation of HL60 cells and decrease their viability. In HL60 cells, as compared to normal PBMCs, 6-TG significantly decreased HDAC3 (p = 0.0034) as well as DNMT3B (p = 0.03) and HDAC7 (p = 0.0031) gene expressions, but increased the expression of DNMT3A gene (p = 0.16) after normalization to GAPDH as the housekeeping gene.These findings suggest that the altered expression of DNMT3A , DNMT3B , HDAC3 and HDAC7 genes is responsible for at least part of the antitumor properties of 6-TG, providing an insight into the mechanism of its action as an epigenetic drug.