Hypoxia induced lipid droplet accumulation promotes resistance to ferroptosis in prostate cancer

Abstract

Ferroptosis is a mode of cell death that relies on iron metabolism and lipid peroxidation. Preclinical and clinical studies indicate that ferroptosis suppresses tumor growth, and dysregulation of ferroptosis promotes treatment resistance in cancer. Hypoxia is a universal feature of solid tumors that is particularly relevant to prostate cancer (PCa), which arises in the hypoxic peripheral zone of the organ. Hypoxia has been implicated in resistance to ferroptosis and other forms of cell death, but how hypoxia impacts the sensitivity of PCa to ferroptosis inducing agents (FINs) has not been well studied. Here, we show that hypoxia dramatically reduces the sensitivity of PCa cell lines to mechanistically distinct FINs, Erastin (xCT inhibitor) and RLS3 (GPX4 inhibitor) by inducing lipid droplet (LD) accumulation. Transcriptomic analysis revealed that hypoxia significantly reduced the expression of genes related to incorporating polyunsaturated fatty acids into phospholipids (ACSL4, LPCAT3), and parallel lipidomic analysis demonstrated that hypoxia significantly decreased the levels of the ferroptosis-prone lipid class, phosphatidylethanolamine (PE) and increased production of neutral lipid species, cholesteryl ester (ChE (22:5)) and triglycerides (TG(48:1), TG:(50:4), and TG(58:4)). Targeting LD biogenesis and de novo lipogenesis did not alter sensitivity to RSL3 under hypoxia. These findings suggest that hypoxia promotes ferroptosis resistance in PCa by altering lipid metabolism at the transcriptional level, by producing lipids that are less susceptible to peroxidation, and at the cellular level, by increasing storage in LDs. Thus, manipulating LD dynamics represents a promising strategy to overcome hypoxia-induced resistance to ferroptosis and improve the success of PCa treatment.