5-Aza-2-deoxycytidine Enhances the Sensitivity of 5-Fluorouracil by Demethylation of the Thymidine Phosphorylase Promoter

Abstract

Background/aim: 5-Aza-2-deoxycytidine (5-Aza-CdR) enhances the sensitivity to 5-fluorouracil (5-FU), but the molecular mechanism is not fully understood. The aim of this study was to investigate the molecular mechanism that enhances the sensitivity to 5-FU treated with 5-Aza-CdR via thymidine phosphorylase (TP).

Materials and methods: The sensitivity to drugs was determined on several cancer cell lines by the MTT assay. Protein and mRNA levels were examined by immunoblot and RT-PCR, respectively. Gene silencing, binding of Sp1 to DNA and methylation of DNA was performed by siRNA, ChIP assay and sodium bisulfate genomic sequencing, respectively.

Results: Sp1-binding sites in the TP promoter were methylated in epidermoid carcinoma. 5-Aza-CdR demethylated Sp1-binding sites and enhanced sensitivity to 5-FU.

Conclusion: Demethylation of Sp1-binding sites by 5-Aza-CdR was a key factor enhancing 5-FU sensitivity, which may enable more effective treatments for cancer patients with the combination of 5-Aza-CdR and 5-FU.

Keywords: 5-aza-2-deoxycytidine; 5-fluorouracil; methylation; thymidine phosphorylase.