Lumiflavin Enhances the Effects of Ionising Radiation on Ovarian Cancer Stem-Like Cells by Inhibiting Autophagy

Background: The development of cancer stem-like cells (CSCs) is one of the main causes of ovarian cancer tolerance to radiotherapy. Autophagy is an adaptive process by which cells repair damage due to radiation. As a metabolite of riboflavin, lumiflavin can enhance the chemotherapeutic effects of cisplatin on ovarian cancer CSCs. Objective: This study aimed to investigate the synergistic effects of lumiflavin and ionising radiation on ovarian cancer CSCs and explore the association of this metabolite with autophagy. Methods: CSCs of human ovarian cancer cell lines HO8910 were treated with lumiflavin and rapamycin and then subjected to irradiation at a cumulative dose of 8 Gy. Cell proliferation ability, clonal formation ability, apoptosis rate, autophagy changes and autophagy-related protein changes were detected. Results: Lumiflavin and ionising radiation synergistically reduced cell vitality and clone formation and increased the apoptosis of CSCs compared with irradiation alone. In addition, ionising radiation increased autophagy and the expression of associated proteins, whereas lumiflavin reduced those changes in autophagy progression. Moreover, rapamycin, an autophagy inhibitor, was observed to block the synergistic effects of lumiflavin and ionising radiation on CSC apoptosis. Conclusion: Lumiflavin can enhance the effects of ionising radiation on ovarian cancer CSCs. The mechanism by which these effects are exerted is related to blocking the autophagy pathway.