Targeting SQLE-Mediated Cholesterol Metabolism to Promote Oxidative Stress and Attenuate Drug Resistance in Osteosarcoma.

High-grade osteosarcoma presents a significant clinical challenge due to unpredictable therapeutic responses and aggressive progression. This study aimed to identify the critical molecular pathways driving chemotherapy resistance and aggressive phenotypes in osteosarcoma patients. Through transcriptomic and bioinformatic analyses, we identified cholesterol biosynthesis as a key upregulated metabolic pathway in poor chemotherapy responders, where squalene epoxidase (SQLE) emerged as an exploratory candidate hub gene whose elevated expression significantly correlates with shortened survival in the TCGA cohort. We validated these findings by administering terbinafine, a known SQLE inhibitor. In highly chemoresistant SaOS-2 cells exhibiting the highest baseline SQLE expression, terbinafine synergistically sensitized cells to doxorubicin by driving cell death partly through apoptosis, as confirmed by caspase inhibition. The combination also promoted ferroptosis, indicated by elevated ROS and MDA along with decreased FSP1 and GPX4 expression. Furthermore, the co-treatment effectively suppressed clonogenic potential, induced G2/M phase cell cycle arrest, and inhibited metastatic progression. These effects were mediated by the modulation of cell proliferation, metastasis, and survival genes through the coordinated regulation of the PI3K/AKT/mTOR, ERK, and JNK signaling cascades. Together, these results highlight the therapeutic potential of targeting the SQLE pathway to overcome doxorubicin resistance and suppress aggressive progression in high-grade osteosarcoma.