Mechanisms of Increased Reactive Oxygen Species (ROS) Generation Induced by Organic Arsenic Derivative S-Dimethylarsino-Glutathione (SGLU; ZIO-101).

ZIO-101 is organic arsenic with similar anti-leukemia activity to arsenic trioxide (ATO) but much less toxicity. Consequently, ZIO-101 can be given at substantially higher doses than ATO and may be active in more diverse cancers than ATO. The precise anti-cancer mechanism of ZIO-101 is unknown: ZIO-101 increases intracellular production of reactive oxygen species (ROS) in dose dependent manner, resulting in apoptosis of leukemic cells. Modifying intracellular ROS levels alters the ability of ZIO-101 to induce apoptosis. We focused on the 2 most important intracellular ROS generators, mitochondria and NADPH oxidase. Cells were treated with ZIO-101 and NADPH oxidase expression levels, membrane translocation and interactions of subunits were studied. Effects of modified NADPH oxidase levels on ZIO-101-induced ROS production were studied (diphenyleneiodonium [DPI], a specific inhibitor of NADPH oxidase, and SiRNA technique were used to inhibit enzyme function, while bryostatin-1, a specific activator of NADPH oxidase, was used to increase enzyme function). Mitochondrial DNA-depleted HL60 Rho-0 cells were also used to evaluate mitochondrial input to ROS-generation. Our data show that ZIO-101 activates NADPH oxidase. A low concentration of ZIO-101 (1uM) requires 14 h to significantly increase intracellular ROS levels and kill leukemic cell. This effect is strongly inhibited by DPI-pretreatment and is also seen in P47-SiRNA transfected HL60 cells. On the other hand, this A higher dose of ZIO-101 (4uM) increases ROS levels more rapidly (2–6 h). This early increase is not inhibited by DPI-pretreatment or SiRNA transfection. A 14 h but not 2–6 h increase in ROS is detectable in Rho-0 HL60 cells. These data indicate dose-dependent mechanisms of ZIO-101 induction of ROS:

1. 1uM ZIO-101 induces NADPH oxidase activity which results in ROS production detectable at 14 h; there is no mitochondrial component;

2. 4uM ZIO-101 disrupts mitochondrial function resulting in an earlier increase in ROS levels and subsequent apoptosis. effect is significantly enhanced in cells that have increased enzyme function. ROS-production in Rho-0 HL60 cells is unaffected by these interventions.