Abstract B032: Role of FSP1 in ferroptosis resistance of chromophobe renal cell carcinoma

Abstract Background: High basal glutathione is a hallmark of Chromophobe renal cell carcinoma (ChRCC). ChRCC cells are sensitive to ferroptosis, a form of regulated cell death induced by lipid peroxidation. Imidazole Ketone Erastin (IKE) blocks the SCL7A11 cystine/glutamate antiporter, limiting glutathione synthesis and thereby inducing ferroptosis. In other cancers, ferroptosis resistance can promote metastasis by enabling adaptation to lipid peroxidation. Methods: IKE-resistant ChRCC cell lines were created through long-term culture of UOK276 and RCJ-T2 cells in fixed concentrations of IKE (1 μM for UOK276, 5 μM for RCJ-T2). The cells cultured with IKE started forming colonies after 25 days and were exhibiting proliferation rates similar to the cells in culture without IKE after 45 days. Results: IKE-resistant ChRCC cell lines have a 10-fold increase in SLC7A11 mRNA expression, which was confirmed at the protein level. Surprisingly, under IKE-induced lipid peroxidation, IKE-resistant cells showed no change in GSH (reduced glutathione), while in the sensitive cells, GSH levels dropped significantly (6-fold in UOK276, 2. 3-fold in RCJ-T2). Similarly, the GSH/GSSG (reduced/oxidized glutathione) ratio was decreased in sensitive cells while maintaining steady levels in the resistant cell lines, indicating a stable high reducing environment under oxidative stress. Surprisingly, IKE-resistant cells exhibited cross-resistance with RSL3, which induces ferroptosis by inhibiting glutathione peroxidase 4 (GPX4), with the IC50 shifting from 8. 2 nM in sensitive cells to 19. 7 nM in IKE-resistant RCJ-T2, and from 3. 4 nM in sensitive to 36. 9 nM in IKE-resistant UOK276 cells. Transcriptomic analysis revealed significant upregulation of FSP1 (ferroptosis suppressor protein 1) in IKE-resistant cell lines compared to sensitive cells (5-fold in UOK276, 17-fold in RCJ-T2), which was confirmed at the protein level. Treatment of IKE-resistant cells with IKE or RSL3 in combination with FSP1 inhibitors (FSEN-1 or icFSP1) restored sensitivity to both IKE and RSL3-induced ferroptosis. Conclusion: IKE-resistant ChRCC-derived cells upregulate ferroptosis suppressor protein 1 (FSP1), and FSP1 inhibitors reverse ferroptosis resistance. FSP1 may represent a therapeutic target in ChRCC, as higher levels of FSP1 are associated with poorer overall survival in ChRCC TCGA data. Citation Format: Steven Safi, Joelle Chami, Samer Salem, Tiegang Han, Wafaa Bzeih, Jessalyn M. Ubellacker, Carmen Priolo, Elizabeth P. Henske. Role of FSP1 in ferroptosis resistance of chromophobe renal cell carcinoma abstract. In: Proceedings of the AACR Special Conference in Cancer Research: Innovations in Kidney Cancer Research: From Molecular Insights to Therapeutic Breakthroughs; 2026 Mar 13-16; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2026;86 (5Suppl₂): Abstract nr B032.