Abstract 2824: Physiologic regulation of lipid oxidation and ferroptosis by vitamin E, high-density lipoprotein and scavenger receptor class B type 1

Abstract Introduction: Ferroptosis is a form of cell death caused by oxidative (-OOH) damage to phospholipids (PL) in the cell membrane. Understanding mechanisms of ferroptosis is important because of the role it plays in cancer. Previous work has focused on the intracellular antioxidant enzyme glutathione peroxidase 4 (GPx4), which detoxifies PL-peroxides (PL-OOH) and prevents ferroptosis. Studies show that alpha-tocopherol (α-toc), the active form of Vitamin E, is an exogenous lipophilic antioxidant that inhibits ferroptosis in cancer cells in vitro. The mechanisms by which α-toc engages cells to manipulate PL redox balance and ferroptosis are unknown. Lipoproteins, like high- and low-density lipoproteins (HDL and LDL), carry α-toc in the circulation. Using diffuse large B cell lymphoma (DLBCL) and clear cell renal cell carcinoma (ccRCC) models, two malignancies sensitive to ferroptosis, we show that lipoproteins, particularly HDL, deliver α-toc by binding the cell membrane receptor scavenger receptor class B type 1 (SR-B1) to prevent ferroptosis. Methods: Ramos (lymphoma), SUDHL4 (lymphoma) and 786-O (ccRCC) cell lines were used in these experiments. Ferroptosis was induced using ML210 and erastin. α-toc loading of native HDL and LDL was increased by incubation with free α-toc and spin filter purification. To isolate α-toc as the component responsible for modulating ferroptosis, we developed synthetic α-toc-loaded HDLs (sHDL). siRNAs were used to reduce SR-B1 and LDL Receptor (LDLR) expression. Blocker of lipid transport-1 (BLT-1) was used to inhibit uptake of lipoprotein cargo via SR-B1. Cell viability was measured by MTS assay and lipid peroxidation was measured by C11-BODIPY. Results: The α-toc level was higher in LDLs compared to HDLs (6.0 ± 0.1 α-toc/ apoB-100 vs. 1.0 ± 0.1 α-toc/ apoA-I) and increased in both HDL and LDL following incubation with free α-toc (α-toc LDL, 10.1 ± 0.1; α-toc HDL, 1.6 ± 0.3). HDL, α-toc HDL and α-toc LDL, but not LDL, rescued DLBCL and ccRCC cells from ferroptosis induced by the addition of ML210 and erastin, with a corresponding decrease in PL-OOH accumulation. Similarly, α-toc sHDLs, but not empty sHDLs, prevented ferroptosis in DLBCL and ccRCC. Knockdown of SR-B1 resulted in down-regulation of GPx4 expression and ferroptosis in ccRCC cells, requiring the use of BLT-1 to investigate SR-B1’s role in α-toc delivery. Addition of BLT-1 prevented α-toc lipoprotein rescue from ferroptosis. Knockdown of LDLR expression did not alter the ability of HDL and α-toc HDL to prevent ferroptosis and enhanced the ability of α-toc LDL to prevent ferroptosis. Conclusion: We reveal a tunable cellular redox axis whereby HDLs containing α-toc target SR-B1 to reduce PL-OOH and prevent ferroptosis. Accordingly, this work reveals that the α-toc / HDL/ SR-B1 axis of ferroptosis prevention must be accounted for when targeting ferroptosis in vivo. Citation Format: Jonathan S. Rink, Andrea E. Calvert, Adam Y. Lin, SonBihn T. Nguyen, Leo I. Gordon, C Shad Thaxton. Physiologic regulation of lipid oxidation and ferroptosis by vitamin E, high-density lipoprotein and scavenger receptor class B type 1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2824.