Arsenic Trioxide Selectively Induces Acute Promyelocytic Leukemia Cell Apoptosis Via a Hydrogen Peroxide-Dependent Pathway

Abstract

Low concentrations of As2O3 (≤1 μmol/L) induce long-lasting remission in patients with acute promyelocytic leukemia (APL) without significant myelosuppressive side effects. Several groups, including ours, have shown that 0.5 to 1 μmol/L As2O3 induces apoptosis in APL-derived NB4 cells, whereas other leukemic cells are resistant to As2O3 or undergo apoptosis only in response to greater than 2 μmol/L As2O3. In this report, we show that the ability of As2O3 to induce apoptosis in leukemic cells is dependent on the activity of the enzymes that regulate cellular H2O2 content. Thus, NB4 cells have relatively low levels of glutathione peroxidase (GPx) and catalase and have a constitutively higher H2O2content than U937 monocytic leukemia cells. Glutathione-S-transferase π (GSTπ), which is important for cellular efflux of As2O3, is also low in NB4 cells. Moreover, As2O3 further inhibits GPX activity and increases cellular H2O2 content in NB4 but not in U937 cells. Selenite pretreatment of NB4 cells increases the activity of GPX, lowers cellular H2O2 levels, and renders NB4 cells resistant to 1 μmol/L As2O3. In contrast, concentrations of As2O3 that alone are not capable of inducing apoptosis in NB4 cells induce apoptosis in the presence of the GPx inhibitor mercaptosuccinic acid. Similar effects are observed by modulating the activity of catalase with its inhibitor, aminotriazol. More important from a therapeutic point of view, U937 and HL-60 cells, which require high concentrations of As2O3 to undergo apoptosis, become sensitive to low, clinically acceptable concentrations of As2O3 when cotreated with these GPx and catalase inhibitors. The induction of apoptosis by As2O3 involves an early decrease in cellular mitochondrial membrane potential and increase in H2O2 content, followed by cytochrome c release, caspase 3 activation, DNA fragmentation, and the classic morphologic changes of apoptosis.