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(5_Suppl_2):Abstract nr B032.