Study of the combined effect of X-irradiation and epigallocatechin-gallate (a tea component) on the growth inhibition and induction of apoptosis in human cancer cell lines.

Over the past 15 years, some potential anticarcinogenic and anti-inflammatory effects of antioxidants have been defined. Antioxidants are known to act as powerful free-radical scavengers. Free radicals are able to induce DNA strand breaks and oxidative modifications of DNA bases and are not only produced naturally in the cell following a stress or respiration but also following ionizing radiation. The present study was undertaken in order to explore whether some antioxidants naturally present in the food or in the beverages could enhance apoptosis in cancerous cells submitted to X-irradiation. Epigallocatechin gallate (EGCG), a potent antioxidant present in tea was tested on three human cancerous cell lines: HeLa (derived from cervix carcinoma), K-562 (derived from chronic myelogenous leukaemia) and IM-9 (derived from multiple myeloma). The parameters investigated were cell proliferation, morphological changes, cell cycle effects and apoptosis. When given alone, irradiation induced a decrease of cell proliferation and an increase of apoptosis as well as the appearance of polyploid cells in the three cell lines. All these effects were dose-dependent. Taking into account the various parameters, IM-9 cells appeared as the most radiation sensitive and HeLa cells as the least radiation sensitive, while K-562 cells exhibited an intermediary radiation sensitivity. EGCG had no effect on cell proliferation, while it induced a dose-dependent increase of apoptosis in the three cell lines. IM-9 cells were again most sensitive to this effect, while HeLa and K-562 cells were slightly less sensitive. A combined treatment by X-irradiation and EGCG resulted in a significant enhancement of apoptosis correlated with a decrease of proliferation in IM-9 and K-562 cells and at a lesser extent, in HeLa cells, compared to treatments by either EGCG or ionising radiation alone. In conclusion, these preliminary results show that depending on the concentration and on the cell line, EGCG could act as a radiation enhancer on cancerous cell lines.