Green tea polyphenol epigallocatechin-3-gallate inhibits the endothelin axis and downstream signaling pathways in ovarian carcinoma

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Abstract
The polyphenol epigallocatechin-3-gallate (EGCG), the principal mediator of the green tea, has been known to possess antitumor effect. The endothelin A receptor (ETAR)/endothelin-1 (ET-1) axis is overexpressed in ovarian carcinoma representing a novel therapeutic target. In this study, we examined the green tea and EGCG effects on two ovarian carcinoma cell lines, HEY and OVCA 433. EGCG inhibited ovarian cancer cell growth and induced apoptosis that was associated with a decrease in Bcl-XL expression and activation of caspase-3. Treatment with green tea or EGCG inhibited ETAR and ET-1 expression and reduced the basal and ET-1-induced cell proliferation and invasion. The EGCG-induced inhibitory effects were associated with a decrease of ETAR-dependent activation of the p42/p44 and p38 mitogen-activated protein kinases and phosphatidylinositol 3-kinase pathway. Remarkably, EGCG treatment resulted in a lowering of basal and ET-1-induced angiogenesis and invasiveness mediators, such as vascular endothelial growth factor and tumor proteinase activation. Finally, in HEY ovarian carcinoma xenografts, tumor growth was significantly inhibited by oral administration of green tea. This effect was associated with a reduction in ET-1, ETAR, and vascular endothelial growth factor expression, microvessel density, and proliferation index. These results provide a novel insight into the mechanism by which EGCG, affecting multiple ETAR-dependent pathways, may inhibit ovarian carcinoma growth, suggesting that EGCG may be useful in preventing and treating ovarian carcinoma in which ETAR activation by ET-1 plays a critical role in tumor growth and progression. [Mol Cancer Ther 2006;5(6):1483–92]