Objectives: We investigated the effect of 5-aza-2'-deoxycytidine (DAC), a DNA methyltransferase inhibitor, on transitional cell carcinoma (TCC) cell lines, and examined the synergistic suppression of TCC growth by DAC and five chemotherapeutic agents.
Methods: We measured the cytotoxicity of DAC and chemotherapeutic agents against five TCC cell lines using the WST-1 assay, and analyzed the synergy of DAC and these agents by isobolographic analysis. The effects of each single agent or the combined treatment on apoptosis induction and cell cycle arrest were analyzed by flow cytometric analysis. We also investigated caspase activity and PCNA expression to clarify the mechanism of the synergistic actions of DAC and chemotherapeutic agents against TCC.
Results: We demonstrated that DAC could significantly increase the susceptibility of TCC cells to cisplatin (CDDP). Synergistic growth suppression by DAC and CDDP was confirmed in all TCC cell lines tested, but not by DAC combined with other chemotherapeutic agents. DAC inhibited proliferation via inducing G2/M cell cycle arrest, whereas CDDP inhibited proliferation via inducing both apoptosis and G2/M arrest. DAC enhanced the CDDP-induced upregulation of caspase activity and antiproliferative effect, resulting in an increase of cells in subG1 and G2/M phases. In addition, the synergy of DAC and CDDP was independent of p53 status in TCC.
Conclusions: The synergy of DAC and CDDP against TCC suggested that combination chemotherapy with these two agents might be a new strategy to improve the clinical response rate of this malignancy, regardless of p53 mutation.