Combination of Histone Deacetylase Inhibitor with Cu(II) 5,5-diethylbarbiturate Complex Induces Apoptosis in Breast Cancer Stem Cells: A Promising Novel Approach

Background: Cancer Stem Cells (CSCs) are a subpopulation within the tumor that play a role in the initiation, progression, recurrence, resistance to drugs and metastasis of cancer. It is well known that epigenetic changes lead to tumor formation in cancer stem cells and show drug resistance. Epigenetic modulators and /or their combination with different agents have been used in cancer therapy. Objective: In our study, we scope out the effects of a combination of a histone deacetylases inhibitor, Valproic Acid (VPA), and Cu(II) complex [Cu(barb-ΚN)(barb-Κ2N,O)(phen-ΚN,N’)]·H2O] on cytotoxicity/apoptosis in a stem-cell enriched population (MCF-7s) obtained from parental breast cancer cell line (MCF-7). Methods: The viability of the cells was measured by the ATP assay. Apoptosis was elucidated via the assessment of caspase-cleaved cytokeratin 18 (M30 ELISA) and a group of flow cytometry analysis (caspase 3/7 activity, phosphatidylserine translocation by annexin V-FITC assay, DNA damage and oxidative stress) and 2#136;,7#136;– dichlorofluorescein diacetate staining. Results: The VPA combined with Cu(II) complex showed anti-proliferative activity on MCF-7s cells in a doseand time-dependent manner. Treatment with a combination of 2.5 mM VPA and 3.12 μM Cu(II) complex induced oxidative stress in a time-dependent manner, as well as apoptosis evidenced by the increase in caspase 3/7 activity, positive annexin-V-FITC, and increase in M30 levels. Conclusion: The results suggest that the combination therapy induces apoptosis following increased oxidative stress, thereby making it a possible promising therapeutic strategy for which further analysis is required.