113 - Low-Density Lipoprotein Docosahexaenoic Acid Nanoparticles Kill Liver Cancer Cells by Ferroptosis

Abstract

Low-density lipoprotein nanoparticles reconstituted with the natural omega-3 fatty acid, docosahexaenoic acid (LDL-DHA), is a novel experimental therapeutic that has been reported to selectively kill malignant hepatoma cells over normal hepatocytes and effectively treat orthotopic liver tumors in the rat. To date, little is known about the cell death pathways by which LDL-DHA nanoparticles kill tumor cells. Here we show that the LDL-DHA nanoparticles are cytotoxic to both rat and human hepatocellular carcinoma (HCC) cell lines. Following LDL-DHA treatment both rat and human HCC cells experience pronounced lipid peroxidation, depletion of glutathione and inactivation of the lipid antioxidant glutathione peroxidase-4 (GPX4) . Inhibitor studies revealed that treated HCC cells die independent of apoptotic, necroptotic or autophagic pathways, but require the presence of cellular iron. These hallmark features are consistent and were later confirmed to reflect ferroptosis, a novel form of nonapoptotic iron-dependent cell death. In keeping with the mechanisms of ferroptosis cell death, GPX4 was also found to be a central regulator of LDL-DHA induced cytotoxicity. We also investigated the effects of LDL-DHA treatments in mice bearing human HCC tumor xenografts. In vivo treatments of LDL-DHA were extremely cytotoxic to the HCC tumors and severely inhibited their growth long term. Consistent with our in vitro findings, the LDL-DHA treated HCC tumors experienced ferroptotic cell death characterized by increased levels of lipid hydroperoxides and suppression of GPX4 expression. Supplementary studies with specific ferrrpotosis inhibitors also confirmed this mechanism of tumor killing by LDL-DHA. Conclusion LDL-DHA induces cell death in HCC cells through the ferroptosis pathway, this represents a novel molecular mechanism of anticancer activity for LDL-DHA nanoparticles.