AML-250 Mitochondrial Respiration Regulates GPX4 Inhibition-Induced Ferroptosis in Acute Myeloid Leukemia

Context: Ferroptosis, a form of non-apoptotic cell death regulated by iron-dependent lipid peroxidation, has drawn extensive attention as a potential anti-cancer strategy. However, it remains to be explored in hematologic malignancies. We here investigate the molecular mechanisms of ferroptosis in acute myeloid leukemia (AML) and its therapeutic potential of co-targeting mitochondrial respiration. Results: Analyses of publicly available databases (TCGA, DepMap) showed that AML patients with higher mRNA expression of major anti-ferroptotic genes had significantly shorter survival and that leukemia cells are one of the cell types that are highly dependent on GPX4 among other cancers. This suggests the potential prognostic impact and relevance in therapeutics of this pathway in AML. Indeed, pharmacological inhibition or genetic knockdown of a well-established anti-ferroptosis regulator GPX4 induced profound ferroptosis, evidenced by dependency on iron and lipid peroxidation. Importantly, the induced cell death was agonistic of TP53 mutational status. As a potentially AML-specific mechanism that is unusual in solid tumor models, we found that GPX4 inhibition-induced ferroptosis was efficiently blocked by the mitochondria-targeted ubiquinone MitoQ in AML cells. Ubiquinone is an endogenous antioxidant protecting cells from lipid peroxidation, and in the mitochondria, the respiratory chain is essential for the recycling of ubiquinone. Thus, we hypothesized that mitochondria protect AML cells from ferroptosis by activating the ubiquinone cycle. Consistently, mitochondrial DNA-depleted HL60 Rho0 cells, which lack mitochondrial respiration, were more sensitive to ML210 compared to the parental cells. To translate this finding to a pharmacological approach, we utilized the imipridone ONC201, which hyperactivates mitochondrial protease ClpP to degrade mitochondrial proteins, including the respiratory chain complex, and exerts cancer-selective lethality (Ishizawa et al. Cancer Cell 2019). Indeed, the combination of ONC201 and ML210 resulted in synergistic anti-leukemia effects in primary AML cells. The combinatorial effect was also validated by utilizing genetically engineered AML cells (genetic knockdown of GPX4 or overexpression of hyperactivated mutant ClpP). Conclusions: GPX4 inhibition induces ferroptosis involving mitochondrial redox machinery in AML. Combinatorial targeting of mitochondrial respiration with GPX4 inhibition exerts synergistic anti-leukemia effects. Further studies are in progress to assess the molecular mechanisms and the in-vivo efficacy of the combinatorial treatments.