The flavonoid GL-V9 induces oxidative stress mediated apoptosis in small cell lung cancer by promoting STEAP3 degradation.

Small cell lung cancer (SCLC) is an aggressive malignancy characterized by limited therapeutic options. In this study, we identified GL-V9 as a potent anti-SCLC agent that induces apoptosis through oxidative stress. GL-V9 significantly reduced SCLC cell viability in a dose-dependent manner and triggered apoptosis both in vitro and in xenograft models. Mechanistically, GL-V9 increased reactive oxygen species (ROS) levels and lipid peroxidation while impairing mitochondrial function, suggesting that its cytotoxic effects are mediated by oxidative stress. Drug-target interaction analyses revealed that GL-V9 directly binds to STEAP3, a key regulator of iron metabolism, and promotes its degradation via the ubiquitin-proteasome pathway. The loss of STEAP3 disrupted iron homeostasis and exacerbated oxidative stress. In contrast, STEAP3 overexpression attenuated ROS accumulation, mitochondrial damage, and apoptosis both in vitro and in vivo. Further investigation demonstrated that STEAP3 degradation decreased the stability of CISD2, a [2Fe-2S] cluster-containing mitochondrial protein essential for redox balance. GL-V9 downregulated CISD2 in a STEAP3-dependent manner, and restoring CISD2 expression significantly rescued cells from GL-V9-induced oxidative stress and apoptosis. Clinically, both STEAP3 and CISD2 are upregulated in SCLC tumors, and their elevated expression correlates with poor patient survival. Co-expression analysis associated these proteins with pathways involved in oxidative stress and mitochondrial dysfunction. Overall, these findings suggest that GL-V9 induces apoptosis in SCLC by targeting STEAP3 for proteasomal degradation, thereby disrupting the STEAP3-CISD2 axis and promoting oxidative stress-driven cell death. This study identifies a previously unrecognized redox regulatory pathway in SCLC and proposes a potential therapeutic strategy centered on selective induction of oxidative stress.