iFSP1, a potent, selective, and glutathione-independent ferroptosis suppressor protein 1 (FSP1) (AIFM2) inhibitor with an EC50 of 103 nM, sensitizes diverse human cancer cell lines to ferroptosis inducers like (1S,3R)-RSL3. It uniquely triggers ferroptosis in GPX4-knockout cells overexpressing FSP1.

iFSP1 (0.001-1 μM; 24 hours) is less efficient than genetic deletion of FSP1, whereas iFSP1 treatment in the FSP1-knockout background had no additive effect to RSL3-induced ferroptosis.iFSP1 (3 μM; 24 hours) treatment results in an obvious toxicity of RSL3 in a panel of genetically engineered (FSP1-knockout) human cancer cell lines.AIFM2: the flavoprotein apoptosis-inducing factor mitochondria-associated 2 is a previously unrecognized anti-ferroptotic gene. AIFM2, which is renamed ferroptosis suppressor protein 1 (FSP1).iFSP1 (0.001-1 μM; 24 hours) inhibits the Gpx4-knockout cell growth as a dose-dependent manner, but does not inhibit the wild type cell growth. Treatment with the ferroptosis inhibitor Lip-1 protects GPX4- knockout cells from iFSP1-induced ferroptosis.