Fisetin Promotes Autophagy in Osteosarcoma by Activating the ROS/FOXO3 Axis via Oxidative Stress.

Osteosarcoma is a malignant bone tumor that occurs in adolescents and for which surgical resection and chemotherapy are the treatments of first choice. However, tumor cell metastasis and the toxic effects of chemotherapeutic agents bring great challenges to the treatment of osteosarcoma. Fisetin, a dietary flavonoid derived from vegetables and fruits, plays a therapeutic role in many cancers, but its role and underlying mechanism on osteosarcoma remain unrevealed. This study found that fisetin significantly inhibited the proliferation of osteosarcoma cells and organoids. RNA sequencing revealed that forkhead box O3 (FOXO3) may be a key target of fisetin in its anti-osteosarcoma activity, which was also verified by immunofluorescence. siFOXO3 reversed the effects of fisetin on proliferation, apoptosis, and migration of osteosarcoma cells. Fisetin exerts its effects by targeting the ROS/FOXO3 pathway to promote the binding of FOXO3 to the microtubule-associated protein light chain 3 (LC3) promoter, thereby upregulating LC3 levels and inducing autophagy. Subsequently, activated autophagy further triggers ferroptosis, while silencing LC3 reversed fisetin-induced ferroptosis. In vivo, fisetin inhibited tumor growth while promoting FOXO3 and LC3, and inhibiting SLC7A11 protein expression. Therefore, fisetin-induced autophagy in osteosarcoma cells may be associated with the reactive oxygen species (ROS)/FOXO3 axis, thereby promoting ferroptosis. These findings highlight fisetin's potential as a unique therapy for osteosarcoma.