Abstract
In recent years, ferric iron divalent iron-mediated lipid oxidation-dependent cell death ferroptosis induced by anticancer drugs such as erastin, that decrease intracellular glutathione and RSL3, that inhibit GPx4 activity, has attracted much attention, and its regulating factors have been identified in rapid succession. On the other hand, we found that disruption of the GPx4 genome gene by addition of Tam causes slowly progressive cell death, lipoxytosis mediated by lipid oxidation without iron, and that the Lipo-1 gene, which is involved in lipid oxidation, and the Lipo-2-6 gene, which functions downstream of lipid oxidation, were identified as the execution factors for the slowly progressive cell death, lipoxytosis by disruption of the GPx4 gene by Tam, using whole genome-wide shRNA library screening. Knockdown cells of these Lipo genes inhibit lipoxytosis but not ferroptosis. We screened the Omura Memorial Natural Products Library for lipoxytosis inducers that inhibit cell death in Lipo knockdown cells and induce cell death in WT cells. In addition, compounds that could be inhibited by lipoxytosis inhibitors were selected, yielding six compounds. Cell death by these compounds was inhibited by the vitamin E derivative Trolox, suggesting that cell death is induced via lipid oxidation. Therefore, we investigated lipid oxidation using NBD-PEN, which can detect lipid radicals. We found that lipid oxidation induced by 2D3, a lipoxytosis inducer, could not be inhibited by iron chelators, but could be inhibited by Trolox. We also found that 2D3-induced lipid oxidation was inhibited by knockdown of the lipoxytosis execution factor Lipo-1, and cell death was also suppressed by Trolox. Thus, cell death by the lipoxytosis inducer 2D3 is an iron-independent cell death mediated by Lipo-1 and different from ferroptosis.
