Green tea epigallocatechin gallate shows a pronounced growth inhibitory effect on cancerous cells but not on their normal counterparts
Introduction
Epidemiological studies, though inconclusive, suggest a protective effect of tea consumption on certain human cancers 1, 2. Animal studies show that green tea polyphenols inhibit carcinogen-induced skin, lung, forestomach, esophagus, duodenum and colon tumors in rodents and inhibit TPA-induced skin tumor promotion in mice 3, 4, 5, 6. The green tea polyphenols have also been shown to inhibit the proliferation of cultured mammalian cells, including colon carcinoma, lung carcinoma, breast carcinoma, melanoma and leukemic cells 7, 8, 9, 10. Six polyphenol compounds, (+)-gallocatechin (GC), (−)-epicatechin (EC), (−)-epigallocatechin (EGC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin gallate (EGCG) and caffeine, have been isolated and purified from green tea [11]. Of these, the most active is (−)-epigallocatechin-3-gallate (EGCG), the major constituent in green tea extracts. One major goal in developing effective cancer chemotherapy is to search for specific anticancer agents. Previous work 1, 2, 3, 4, 5, 6, 7, 8, 9, 10has suggested that EGCG may have the potential to be developed into a new class of chemotherapeutic agents. In light of this possibility, we have initiated systematic studies to determine whether the effects of EGCG on cell proliferation and gene expression are cancer cell-specific. We report here that EGCG inhibited cell growth, induced apoptosis and modulated gene expression differently in transformed cells as compared to their normal counterparts.
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Materials
Dulbecco's modified Eagle's medium and fetal bovine serum were obtained from GIBCO (Gaithersburg, MD). Other chemicals were from Sigma (St. Louis, MO). [α-32P]dCTP (>3000 Ci/mmol) was purchased from ICN Chemical, Radioisotope Division (Irvine, CA).
Tissue culture
WI38 cells (AG06814, passage number 12) and the SV40 virally transformed WI38VA cells (AG07217) were obtained from the National Institute on Aging Repository, Coriell Institute for Medical Research (Camden, NJ). Colon cancer cells, Caco-2 (ATCC #
Differential effect of EGCG on the growth of WI38 and WI38VA cells
WI38 cells are normal human diploid lung fibroblasts with a finite life-span [14]and the immortalized WI38VA cell line is derived from WI38 cells by SV40 virus transformation [15]. The pair has been used as an in vitro transformed and non-transformed cell model [15]. Fig. 1A shows that the transformed WI38VA cells were more sensitive to the inhibition of growth than the normal WI38 cells. Thus, EGCG at 40 μM completely inhibited the growth of WI38VA cells, but had little effect on the growth of
Discussion
Polyphenols from green tea, particularly EGCG, have been demonstrated to possess anticarcinogenic and chemopreventive effects both in vitro and in vivo 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. Since comparative studies of the effects of EGCG on normal and transformed cells have not been done previously, it is not clear whether these pharmacological effects of EGCG are specific for cancer cells. Our studies showed for the first time that EGCG at an appropriate dosage inhibited the growth of transformed
Acknowledgements
We are grateful to Dr Robert Rosen for providing us with EGCG and other nutraceuticals and to Dr E. White for the Bax probe. We thank Dr Geetha Ghai for many useful discussions. This study was supported by the Commission on Science and Technology, State of New Jersey as a component of the Program in Pioneering Nutraceutical Research.
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