Resistance of Ovarian Cancer Cells to Platinum Requires Exogenous Cholesterol, Scavenger Receptor Class B Type 1, and Glutathione Peroxidase 4
Essentially, all patients diagnosed with ovarian cancer (OC) are treated with platinum (Pt); however, Pt resistance (Pt-R) rapidly develops. We show OC cells resistant to Pt increase intracellular cholesterol by increasing expression of the high-density lipoprotein (HDL) receptor, scavenger receptor class B type 1 (SR-B1). Expression of SR-B1 was associated with chemoresistance in OC cells and tumors. SR-B1 blockade using synthetic cholesterol-poor HDL-like nanoparticles (HDL NPs) diminished cholesterol uptake leading to cell death of Pt-R OC cells in vitro and suppressed Pt-R OC tumor growth in vivo. Reduced cholesterol accumulation in Pt-R OC cells induced lipid oxidative stress through reduction of glutathione peroxidase 4 (GPx4) expression leading to ferroptosis. Reduction of GPx4 expression in OC cells re-sensitized Pt-R cells to Pt by reducing cholesterol uptake and enhancing the accumulation of lipid reactive oxygen species (L-ROS). Mechanistically, GPx4 knockdown in OC cells was associated with reduced expression of the histone acetyltransferase EP300, leading to reduced H3K27 acetylation around the SREBP2 promoter suppressing its expression. As SREBP2 regulates SR-B1 transcription, these data demonstrate chemoresistance and cancer cell survival under high ROS burden obligates high GPx4 and SR-B1 expression through SREBP2. Targeting SR-B1 to modulate cholesterol uptake inhibits this axis and causes ferroptosis in vitro and in vivo in Pt-R OC. Overall design: To study the role of GPX4 in regulating chemoresistance of ovarian cancer, RNA sequencing was conducted on platinum resistant OVCAR5 (pt-R) ovarian cancer cells transfected with shRNA targeting GPX4 and sh control RNA (shctrl). Transcriptome of OVCAR5 Pt-R cells with GPX4 knocking-down was compared with control cells.