Introduction: In B-cell lymphomas, disparate molecular aberrations often produce common onco-metabolic phenotypes, including a dependency upon cholesterol uptake from serum lipoproteins rather than de novo synthesis. Recent reports have linked cancer cell cholesterol to ferroptosis, a newly appreciated form of programmed cell death characterized by the accumulation of oxidized membrane polyunsaturated fatty acids (PUFAs), facilitated by reduced glutathione peroxidase 4 (GPX4) activity. Diffuse large B-cell lymphoma (DLBCL) and anaplastic large T-cell lymphoma (ALCL) were identified as potentially sensitive to ferroptosis. We have developed high-density biomimetic lipoprotein nanoparticles (HDL NPs), a first-in-class platform that specifically targets scavenger receptor type B1 (SCARB1) and inhibits cholesterol uptake. In DLBCL, HDL NPs potently induces cell death. Accordingly, we hypothesized that HDL NPs induce ferroptosis in DLBCL and would be potent therapy for other cholesterol-addicted malignancies.
Methods: Burkitt's lymphoma (Ramos), DLBCL (SUDHL4), ALCL (SR-786, SUDHL1), and histiocytic lymphoma (U937) cell lines were used. RNA, protein, and cholesterol were isolated from cells treated with HDL NPs and analyzed using RT-qPCR, Western blot, and total cholesterol assays, respectively. Oxidized PUFA accumulation was quantified using the C11-BODIPY dye and flow cytometry. The lipophilic antioxidant ferrostatin-1 (Fer-1) and iron chelator deferoxamine (DFO) were used to inhibit ferroptosis. Following informed consent, primary B-cell lymphoma samples were isolated from patients and assayed for SCARB1 expression and viability following HDL NP treatment.
Results: HDL NPs reduced cholesterol levels in Ramos and SUDHL4 cells, leading to upregulation of cholesterol biosynthesis genes and downregulation of GPX4. This correlated with an increase in accumulation of oxidized PUFAs, and eventually cell death by ferroptosis. Fer-1 and DFO rescued Ramos and SUDHL4 cells from HDL NP-induced cell death. Oxidized PUFA accumulation and GPX4 downregulation were confirmed in vivo using HDL NP-treated SUDHL4 xenografts, which resulted in reduced tumor burden compared with controls. These results were replicated in other ferroptosis-sensitive malignancies, including SCARB1+ ALCL (SUDHL1, SR-786) and histiocytic lymphoma (U937) cell lines. Finally, primary B-cell lymphoma cells isolated from patients with follicular lymphoma (n=4) and DLBCL (n=2) demonstrated SCARB1 expression and were sensitive to HDL NP-induced cell death.
Conclusion: HDL NP binding to SCARB1 results in inhibition of cholesterol uptake and triggers a metabolic compensatory response, namely upregulation of cholesterol biosynthesis genes and downregulation of GPX4, obligating cells to ferroptosis. As this onco-metabolic profile is observed across a range of cancers, HDL NPs represent a unique platform for metabolic therapy for cholesterol- and GPX4-dependent malignancies.
Citation Format: Jonathan S. Rink, Adam Lin, Kaylin M. McMahon, Andrea E. Calvert, Shuo Yang, Amir Behdad, Reem Karmali, Colby S. Thaxton, Leo I. Gordon. Targeting scavenger receptor type B1 in cholesterol-addicted lymphomas abolishes glutathione peroxidase 4 expression and results in ferroptosis [abstract]. In: Proceedings of the AACR Virtual Meeting: Advances in Malignant Lymphoma; 2020 Aug 17-19. Philadelphia (PA): AACR; Blood Cancer Discov 2020;1(3_Suppl):Abstract nr PO-11.