Selective death of cancer cells by preferential induction of reactive oxygen species in response to (-)-epigallocatechin-3-gallate.

(-)-Epigallocatechin-3-gallate (EGCG) induces apoptosis in cancer cells without adversely affecting normal cells. Understanding the cancer-specific cytotoxic activity of EGCG is very important in defining the mechanism of tumorigenesis and identifying superb chemotherapeutic agents against cancer. We comparatively assayed human telomerase reverse transcriptase (hTERT)-mediated apoptosis by EGCG-induced reactive oxygen species (ROS) in normal cells and cancer cells. EGCG showed differential levels of ROS induction between the cell types; ROS, especially hydrogen peroxide, was highly induced in cancer cells, while it was not in normal cells. In addition, the higher level of ROS down-regulated hTERT via binding of CCCTC binding factor (CTCF) to the core promoter region of hTERT, which repressed hTERT expression. CTCF binding was epigenetically controlled by the demethylation of the previously hypermethylated site for CTCF, which was induced by down-regulation of DNA methyltransferase 1 (DNMT1). In contrast, hTERT down-regulation was not observed in normal cells. These results suggest that preferential death of cancer cells by EGCG could be caused by the cancer-specific induction of ROS and epigenetic modulation of expression of apoptosis-related genes, such as hTERT.