GPX4 and fibrosarcoma: GPX4 was subsequently identified as the primary target of RSL3 using an unbiased, affinity-based chemoproteomics approach.13 Moreover, genetically knocking down and overexpressing GPX4 were shown to cause sensitization and resistance to RSL3, respectively, providing further evidence that GPX4 is the target of RSL3.13 Since these previous studies, RSL3 has been widely used as a ferroptosis agonist in vitro in a wide range of cancer cell types, including pancreatic cancer, adrenocortical carcinoma, fibrosarcoma,201 and breast cancer15 cells.