Redox-triggered USP18 confers cisplatin resistance in ovarian cancer by selectively activating a non-canonical FSP1-dependent ferroptosis escape pathway

Background Cisplatin resistance is a primary cause of treatment failure in ovarian cancer (OC), partly due to enhanced antioxidant defenses that counteract cisplatin-induced DNA damage and reactive oxygen species (ROS). Beyond the classic Glutathione Peroxidase 4 (GPX4) pathway, evidence suggests that non-canonical pathways like those mediated by Ferroptosis Suppressor Protein 1 (FSP1) may drive resistance. This study aims to elucidate how such alternative pathways facilitate resistance under cisplatin-induced ROS stress. Methods Ubiquitin Specific Peptidase 18 (USP18) was identified from a deubiquitination library. Protein/RNA interaction and m 6 A analyses revealed its regulation of downstream effectors Insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2) and FSP1. The combination of cisplatin with the FSP1 inhibitor (iFSP1) was evaluated in vitro and in vivo models. Results Cisplatin-induced ROS upregulates the expression of the USP18 through the transcription factor c-JUN, establishing the ROS-c-JUN-USP18 signaling axis. This axis stabilizes the IGF2BP2 protein via USP18-mediated deubiquitination, which in turn enhances the stability of FSP1 mRNA in an m6A methylation-dependent manner, thereby driving the selective activation of the FSP1-mediated pathway over the canonical GPX4 pathway. The predictive efficacy of models derived from the ROS-c-JUN-USP18-IGF2BP2-FSP1 axis was demonstrated by ROC curves and nomograms, confirming their utility in identifying patients with cisplatin-resistant OC. Importantly, the combination of iFSP1 with cisplatin produces a significant synergistic effect, effectively overcoming drug resistance in USP18-high tumors. Conclusion This study elucidates the mechanism by which the ROS-c-JUN-USP18-IGF2BP2-FSP1 axis regulates cisplatin resistance and proposes a novel iFSP1-cisplatin combination therapy, offering a promising new strategy for OC treatment.