The histone deacetylase inhibitor sodium butyrate induces breast cancer cell apoptosis through diverse cytotoxic actions including glutathione depletion and oxidative stress

Sodium butyrate (NaBu), a potent histone deacetylase inhibitor, modulates the expression of a large number of genes. The purpose of this study was to determine whether this dietary agent could induce apoptosis in MCF-7 cells, a breast cancer cell line that lacks caspase-3 activity, and to identify the mechanisms that underlie NaBu toxicity in these cells. Cell viability assessed by the activity of mitochondrial succinate dehydrogenase (MTT assay) revealed a dose-dependent reduction of MCF-7 cellular growth in response to NaBu treatment. Restoring caspase-3 function by transfection did not modify NaBu toxicity in these cells. Following a 24-h exposure, NaBu-induced cell growth arrest in G2/M phase in a dose-dependent fashion in association with stable expression of CDC25A, a G1-specific regulator of the cell cycle. The anti-proliferative effects of NaBu were accompanied by diminished expression of p53. Similarly, mRNA encoding c-Myc, a well-known regulator of p53, was decreased in NaBu-treated cells, while p21(Waf1/Cip1) mRNA was increased. Furthermore, bax mRNA level was up-regulated whereas a decline in Bcl-2 both protein and mRNA levels were detected in NaBu-treated cells. Apoptosis was observed following a treatment with 2 mM NaBu, reflected by Annexin-V staining and by the cleavage of poly(ADP-ribose) polymerase, whereas DNA laddering was absent. Apoptosis was associated with a pronounced depletion of intracellular glutathione levels. Finally, NaBu treatment significantly increased the activities of several antioxidant enzymes, including glutathione reductase, glutathione peroxidase, and catalase. Together, these data suggest that the pro-apoptotic effects of NaBu observed in MCF-7 cells are associated with oxidative stress.