Pharmacological inhibition of cystine-glutamate exchange induces endoplasmic reticulum stress and ferroptosis Scott J Dixon, Darpan N Patel, Matthew Welsch, Rachid Skouta, Eric D Lee, Miki Hayano, Ajit G Thomas, Caroline E Gleason, Nicholas P Tatonetti, Barbara S Slusher, Brent R Stockwell Abstract: The antiporter system x_c^- is involved in various pathologies. The small molecule erastin is a potent and selective inhibitor of system x_c^-. RNA sequencing revealed that inhibition of cystine-glutamate exchange leads to activation of an ER stress response and upregulation of CHAC1, providing a pharmacodynamic marker for system x_c^- inhibition. The clinically approved anti-cancer drug sorafenib, but not other kinase inhibitors, inhibits system x_c^- function and can trigger ER stress and ferroptosis. Analysis of hospital records and adverse event reports found that patients treated with sorafenib exhibited unique metabolic and phenotypic alterations compared to patients treated with other kinase-inhibiting drugs. Using a genetic approach, new genes dramatically upregulated in cells resistant to ferroptosis were identified. Introduction: Transporters for small molecule nutrients, including sugars, nucleotides, and amino acids, are essential for cellular metabolism and represent potential targets for drug development. System x_c^- is a cell-surface Na+-independent cystine-glutamate antiporter composed of the 12-pass transmembrane transporter protein SLC7A11 (xCT) linked via a disulfide bridge to the single-pass transmembrane regulatory subunit SLC3A2 (4F2hc). System x_c^- is required for normal mammalian blood plasma redox homeostasis, skin pigmentation, immune system function, and memory formation. Aberrant system x_c^- function is implicated in tumor growth and survival, cancer stem cell maintenance, drug resistance, and neurological dysfunction. Inhibition of system x_c^- may prove useful in a number of therapeutic contexts. Efforts to treat gliomas and lymphomas in human patients by modulating system x_c^- activity with the low potency, metabolically unstable small molecule, sulfasalazine (SAS) were unsuccessful. While some progress has been made toward developing more potent compounds based on the SAS scaffold, the identification of system x_c^- inhibitors based on alternative scaffolds remains a pressing need. We previously demonstrated that the small molecule erastin prevents Na+-independent cystine uptake, suggesting that erastin may inhibit system x_c^- function and represent a novel scaffold targeting this transport system. Intriguingly, treatment of some cell lines with erastin or SAS triggers an iron-dependent, non-apoptotic form of cell death, termed ferroptosis. Ferroptosis is characterized by the accumulation of intracellular soluble and lipid reactivePharmacological inhibition of cystine-glutamate exchange induces endoplasmic reticulum stress and ferroptosis Scott J Dixon, Darpan N Patel, Matthew Welsch, Rachid Skouta, Eric D Lee, Miki Hayano, Ajit G Thomas, Caroline E Gleason, Nicholas P Tatonetti, Barbara S Slusher, Brent R Stockwell Abstract: The antiporter system x_c^- is involved in various pathologies. The small molecule erastin is a potent and selective inhibitor of system x_c^-. RNA sequencing revealed that inhibition of cystine-glutamate exchange leads to activation of an ER stress response and upregulation of CHAC1, providing a pharmacodynamic marker for system x_c^- inhibition. The clinically approved anti-cancer drug sorafenib, but not other kinase inhibitors, inhibits system x_c^- function and can trigger ER stress and ferroptosis. Analysis of hospital records and adverse event reports found that patients treated with sorafenib exhibited unique metabolic and phenotypic alterations compared to patients treated with other kinase-inhibiting drugs. Using a genetic approach, new genes dramatically upregulated in cells resistant to ferroptosis were identified. Introduction: Transporters for small molecule nutrients, including sugars, nucleotides, and amino acids, are essential for cellular metabolism and represent potential targets for drug development. System x_c^- is a cell-surface Na+-independent cystine-glutamate antiporter composed of the 12-pass transmembrane transporter protein SLC7A11 (xCT) linked via a disulfide bridge to the single-pass transmembrane regulatory subunit SLC3A2 (4F2hc). System x_c^- is required for normal mammalian blood plasma redox homeostasis, skin pigmentation, immune system function, and memory formation. Aberrant system x_c^- function is implicated in tumor growth and survival, cancer stem cell maintenance, drug resistance, and neurological dysfunction. Inhibition of system x_c^- may prove useful in a number of therapeutic contexts. Efforts to treat gliomas and lymphomas in human patients by modulating system x_c^- activity with the low potency, metabolically unstable small molecule, sulfasalazine (SAS) were unsuccessful. While some progress has been made toward developing more potent compounds based on the SAS scaffold, the identification of system x_c^- inhibitors based on alternative scaffolds remains a pressing need. We previously demonstrated that the small molecule erastin prevents Na+-independent cystine uptake, suggesting that erastin may inhibit system x_c^- function and represent a novel scaffold targeting this transport system. Intriguingly, treatment of some cell lines with erastin or SAS triggers an iron-dependent, non-apoptotic form of cell death, termed ferroptosis. Ferroptosis is characterized by the accumulation of intracellular soluble and lipid reactive