Unveiling the link between NADPH oxidase 2 activation and mitochondrial superoxide formation in leukemic cell killing...

This study focused on the interplay between NADPH oxidase 2 (NOX 2) activation and mitochondrial superoxide (mitoO₂^.-) formation induced by clinically relevant concentrations of arsenic trioxide (ATO; As₂O₃) in acute promyelocytic leukemia (APL) cells. Carefully controlled inhibitor studies and small interfering RNA mediated downregulation of p47^phox (a component of the NOX 2 complex) expression demonstrated that, in an APL cell line, ATO promotes upstream NOX 2 activation critically connected with the formation of mitoO₂^.- and with the ensuing mitochondrial permeability transition (MPT)-dependent apoptosis. Instead, acute myeloid leukemia (AML) cell lines respond to ATO with low NOX 2 activation, resulting in a state that is non-permissive for mitoO₂^.- formation. Consistently, through rescue experiments, we demonstrate that pharmacological stimulation of NOX 2 overcomes resistance in these cells, thereby initiating the same cascade of downstream events observed in APL cells. As a final note, several lines of evidence, including measurement of glutathione, catalase and glutathione peroxidase levels, indicated that the antioxidant machinery was similar in APL and AML cells. The results regarding nuclear factor erythroid 2 p45-related factor 2-dependent antioxidant responses were instead of more complex interpretation as NB4 cells appeared particularly responsive to ATO. Our findings allow a novel interpretation of the interplay between NOX 2 activation and mitoO₂^.- formation induced by ATO, ultimately steering leukemic cells towards MPT-dependent apoptosis. These mechanistic insights provide a rationale for the disparate responses of APL and AML cells to ATO, offering potential avenues for the development of therapeutic intervention tailored to specific leukemia subtypes.