Epigenetic Priming with Decitabine Augments the Therapeutic Effect of Cisplatin on Triple-Negative Breast Cancer Cells through Induction of Proapoptotic Factor NOXA

Simple Summary Triple-negative breast cancer is a subset of breast cancer that occurs frequently in young women and tends to exhibit aggressive, metastatic behavior. The therapeutic molecular targets found in other types of breast cancer are absent; therefore, this type of cancer has a poorer prognosis. To search for effective treatments for this type of cancer, we analyzed the effect of the DNA-demethylating agent, decitabine, which is commonly used in patients with myelodysplastic syndrome. We found that in triple-negative breast cancer cell subtypes, inhibition of cell death and cell growth in response to cisplatin, which is used to treat metastatic breast cancer, is enhanced when used in combination with decitabine. We also found that in decitabine-refractory cell subtypes, cisplatin alone is effective at inducing cell death. These results indicate the possibility of effective new combination therapies in triple-negative breast cancers. Epigenetic alterations caused by aberrant DNA methylation have a crucial role in cancer development, and the DNA-demethylating agent decitabine, is used to treat hematopoietic malignancy. Triple-negative breast cancers (TNBCs) have shown sensitivity to decitabine; however, the underlying mechanism of its anticancer effect and its effectiveness in treating TNBCs are not fully understood. We analyzed the effects of decitabine on nine TNBC cell lines and examined genes associated with its cytotoxic effects. According to the effect of decitabine, we classified the cell lines into cell death (D)-type, growth inhibition (G)-type, and resistant (R)-type. In D-type cells, decitabine induced the expression of apoptotic regulators and, among them, NOXA was functionally involved in decitabine-induced apoptosis. In G-type cells, induction of the cyclin-dependent kinase inhibitor, p21, and cell cycle arrest were observed. Furthermore, decitabine enhanced the cytotoxic effect of cisplatin mediated by NOXA in D-type and G-type cells. In contrast, the sensitivity to cisplatin was high in R-type cells, and no enhancing effect by decitabine was observed. These results indicate that decitabine enhances the proapoptotic effect of cisplatin on TNBC cell lines that are less sensitive to cisplatin, indicating the potential for combination therapy in TNBC.