Sensitivity of breast cancer stem cells (CD24^-/CD44⁺) to doxorubicin is associated with oxidative stress status

Objective: The aim of this study was to analyze the sensitivity of BCSCs to doxorubicin and its association with oxidative stress. Methods: BCSCs (CD24^-/CD44⁺) were treated with doxorubicin every 2 d for 14 d. The determination of cell viability was performed using a trypan blue exclusion assay. The levels of reactive oxygen species (ROS) were measured using a dihydroethidium (DHE) and a 2’,7’-dichlorofluorescein diacetate (DCFH-DA) probes. Manganese superoxide dismutase (MnSOD) mRNA expression and specific activity were also analyzed. Glutathione (GSH) level was measured using Ellman’s method. Results: The viability of the BCSCs decreased after 2 d of treatment with doxorubicin, but started to increase after 8 d. After 8 d of doxorubicin treatment, the ROS level in the BCSCs decreased, while the MnSOD specific activity increased. In addition, the MnSOD mRNA expression and GSH level were suppressed after 8 d of treatment. Conclusion: Doxorubicin treatment induced cytotoxicity after 2 d by increasing the superoxide levels of the BCSCs. After 8 d of treatment, the sensitivity of BCSCs to doxorubicin decreased due to the suppressed oxidative stress from the enhanced antioxidant activity of the MnSOD.