Histone deacetylase inhibitors induce thymidine phosphorylase expression in cultured breast cancer cell lines.

Thymidine phosphorylase (TP) is an enzyme involved in thymidine synthesis and degradation. The expression of this enzyme has been proposed as a predictive factor for the therapeutic benefit of capecitabine, which is a precursor of the drug 5'-fluorouracil. In fact, TP is the rate-limiting enzyme in the activation of capecitabine. Therefore, higher levels of TP are expected to sensitize cancer cells to capecitabine treatment. In the present study, using breast cancer cell lines, we found a correlation between TP mRNA and protein levels, suggesting that compounds able to increase TP gene expression also increase protein levels. Accordingly, we demonstrated that treatment of breast cancer MCF7 and MDA231 cell lines with histone deacetylase inhibitors, tricostatin A and suberoylanilide hydroxamic acid, increased TP both at the mRNA and protein level. The effects of histone deacetylase inhibitors were not found to occur via the cytokine TNFα, a known inducer of TP expression. Our findings suggest a strategy to sensitize breast cancer cells to capecitabine treatment.