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Combination of DNA methylation inhibitor 5‐azacytidine and arsenic trioxide has synergistic activity in myeloma

XAF1 is a newly identified candidate tumour‐suppressor gene that can antagonise XIAP and sensitise cells to cell death triggers. This study was undertaken to study the effect of 5‐azacytidine (AZA) on XAF1 expression in myeloma cells and efficacy of 5‐AZA and arsenic trioxide (ATO) combination treatment in myeloma in vivo and in vitro. XAF1 expression was analysed by semi‐quantitative PCR and western blotting. Methylation specific PCR was used to detect methylation status of XAF1 promoter CpG islands. RPMI 8226 and XG‐7 cells were treated with various concentrations of 5‐AZA and ATO. 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 transcript after treated with 2.5 μmol/L 5‐AZA for 72 h. Our studies demonstrated that 5‐AZA exhibits anti‐myeloma synergy with ATO. In addition, ATO alone, 5‐AZA alone, or combination of 5‐AZA and ATO was effective in slowing myeloma growth and prolonging survival of myeloma‐loaded nude mice. The findings suggested that 5‐AZA and ATO may be an effective combination in the therapy of myeloma patients.