Combination of DNA Methylation Inhibitor 5-Azacytidine and Arsenic Trioxide Has Synergistic Activity in Multiple Myeloma

This study was undertaken to study the effect of 5-azacytidine on XAF1 expression in myeloma cells and efficacy of 5-azacytidine and arsenic trioxide combination treatment in myeloma in vivo and in vitro. XAF1 expression was analyzed by semi-quantitative PCR and Western blotting. Methylation specific PCR (MSP) was used to detect methylation status of XAF1 promoter CpG islands. RPMI 8226 and XG-7 cells were treated with various concentrations of arsenic trioxide and 5-azacytidine. Expression of XAF1 mRNA variants were confirmed by gel electrophoresis and sequencing. Untreated RPMI 8226 cell expresses two variants of XAF1 mRNA. Untreated XG-7 cell has no expression of XAF1. Hypermethylation of XAF1 promoter CpG islands was detected in both cell lines. Both cell lines express full-length XAF1 mRNA transcript after treated with 2.5 μmol/L 5-azacytidine for 72 h. Our studies demonstrated that 5-azacytidine exhibits antimyeloma synergy with arsenic trioxide. 5-azacytidine treatment reversed XAF1 promoter region hypermethylation status, leading to expression of full-length XAF1 transcript. In addition, combination of 5-azacytidine and arsenic trioxide was effective in slowing myeloma growth and prolonging survival of myeloma-loaded nude mice. The findings suggested that 5-azacytidine and arsenic trioxide may be an effective combination in the therapy of myeloma patients.