Ononin synergistically enhances the cytotoxic effect of doxorubicin in MDA-MB-231 triple-negative breast cancer cell line

Background : Triple-negative breast cancer (TNBC) represents approximately 15% of breast cancer cases worldwide. This subtype is characterized by aggressive behavior, poor prognosis, and a high recurrence rate. The lack of estrogen receptor alpha (ERα) renders hormonal therapies ineffective, leaving chemotherapy as the mainstay of treatment. However, chemotherapy often causes severe side effects. This study investigates the cytotoxic activity of ononin against TNBC in vitro and evaluates its potential to enhance the chemosensitivity of doxorubicin (DOX) in MDA-MB-231 cells. Materials and methods : The effects of ononin and the ononin–DOX combination on cytotoxicity, migration, colony formation, and apoptosis were investigated. Results : Ononin exhibited a cytotoxic effect against MDA-MB-231 cells, with an IC 50 of 50 µM, while DOX had an IC 50 of 1.8 µM. The CompuSyn-calculated combination index (CI) values indicated synergistic interactions, ranging from 0.23 to 0.08 at a constant DOX concentration of 1.8 µM. Analysis of the dose-reduction index (DRI) revealed 6.98-, 16.22-, and 66.86-fold reductions in the effective doses of DOX at ED 50 , ED 75 , and ED 95 , respectively, when combined with a 10-fold concentration of ononin. Combining 0.45 µM DOX with 6 µM ononin resulted in a significant decrease in colony formation compared with 0.45 µM DOX alone (p < 0.0001). Ononin also exhibited anti-migratory activity, and its combination with DOX further reduced cell migration compared with DOX alone after 72 hours (p < 0.05). However, ononin (25 µM) had no significant effect on caspase-3 gene expression. Conclusion : This study is the first to demonstrate that ononin alone inhibits viability, migration, and colony formation in MDA-MB-231 cells and synergistically enhances the cytotoxic activity of DOX. These findings suggest that ononin may serve as a promising adjuvant agent to improve DOX efficacy in TNBC therapy.