The lipid peroxidase GPX4 is critical for the survival of therapy-resistant ZEB1+ cancer cells.
Major finding: The lipid peroxidase GPX4 is critical for the survival of therapy-resistant ZEB1+ cancer cells.
Concept: GPX4 protects mesenchymal and highly mesenchymal epithelial tumor cells from ferroptotic cell death.
Impact: Integrated analyses find a druggable vulnerability underlying therapy resistance.
The epithelial-to-mesenchymal transition in a cancer cell is characterized by the loss of epithelial markers and the expression of mesenchymal markers, resulting in a therapy-resistant state. Recent evidence shows that cell-to-cell differences in levels of proteins driving resistance may give rise to rare therapy-resistant cancer cells which do not harbor secondary resistance mutations. To identify targetable vulnerabilities of highly mesenchymal cancer cells, Viswanathan and colleagues generated a mesenchymal score based on the transcriptional signatures of highly mesenchymal cancer cell lines that were associated with therapy resistance. Correlation of cancer cell line drug sensitivity results with corresponding mesenchymal scores revealed that compounds that induce ferroptosis and statins, which inhibit HMGCR and selenocysteine biosynthesis, were the most efficacious against epithelial cancer cell lines with high mesenchymal scores and cancer cell lines of mesenchymal origin. Interrogation of publicly available RNAi sensitivity data for cancer cell lines showed that knockdown of the glutathione peroxidase GPX4, which contains a selenocysteine residue, was most correlated with pro-ferroptotic compound activity. Consistent with these findings, fluvastatin treatment reduced GPX4 levels and synergized with the GPX4 inhibitor RSL3 to increase the accumulation of lipid hydroperoxides, the substrate of GPX4. RSL3 treatment of isogenic cancer cell lines harboring the EMT drivers SNAIL1, TWIST1, or ZEB1 was highly efficacious against ZEB1-expressing, but not SNAIL1- or TWIST1-expressing, cells, and was also efficacious against epithelial cancer cells which had acquired a highly mesenchymal state post–targeted therapy treatment. Treatment with a ferroptosis inhibitor blocked GPX4 knockout–mediated ferroptosis of mesenchymal state cancer cells in vitro and in vivo, promoting tumor regression. Together, these results identify and characterize a lipid peroxidase–dependent pathway that is essential for survival of drug tolerance of highly mesenchymal cancer cells and suggest potential approaches to elucidate the mechanisms driving non–genetic-driven therapy resistance of cancer cells.