Biological significance of myeloperoxidase (MPO) on green tea component, (−)-epigallocatechin-3-gallate (EGCG)-induced apoptosis: its therapeutic potential for myeloid leukemia

The therapeutic approach to acute myeloid leukemia (AML) is usually chemotherapy, but severe side effects and complications induced by the anticancer drugs are sometimes fatal and are major problems in the clinical setting. Recently, more specifically targeted agents have been developed for the treatment of AML; however, most candidate agents for targeted therapy have yet to be translated into clinical application. Natural compounds appear to be safer than the current chemotherapeutic agents. Recently, it has been reported that reactive oxygen species (ROS) produced by natural compounds such as (−)-epigallocatechin-3-gallate (EGCG) induce apoptosis in myeloid leukemic cells. EGCG markedly induced apoptosis of myeloperoxidase (MPO)-positive myeloid leukemic cells. Treatment with EGCG caused a significant ROS production in MPO-positive leukemic cells. ROS are now thought of as signaling molecules in response to various extracellular stimuli. On the other hand, ROS may be the direct mediator of EGCG-induced apoptosis in myeloid leukemic cells. In particular, highly toxic ROS such as hydroxyl radical (·OH) generated via the H₂O₂/MPO halide system may directly mediate oxidative stress-induced apoptosis in myeloid leukemic cells.