Green tea consumption has been linked to lower incidence of some cancers in humans and animals. Epidemiological studies, however, have not provided consistent evidence about the anti-tumorigenic effect of green tea in humans.
For a better understanding of the ability of green tea to control different forms of prostate tumors, we produced tumors in athymic mice by subcutaneously inoculating athymic mice with AR positive and A-dependent LNCaP 104-S cells, AR positive LNCaP 104-R2,104-R1 or CDXR cells whose growth is repressed by A, or AR negative PC-3 or IS cells whose growth is neither stimulated or repressed by A. We found that green tea EGCG (>98% pure, 1 mg/20g body weight daily), injected intraperitoneally (ip), significantly inhibited the growth and rapidly (in 1-2 week) reduced the size of all types of human prostate tumors in athymic mice. Structurally-related catechins, such as epicatechin gallate (ECG) that lacks only one of the eight hydroxyl groups in EGCG, were inactive. Epicatechin (EC) and epigallocatechin (EGC) were also inactive (25).
Since both A-dependent and A-independent prostate tumors respond to tumor suppression by EGCG. EGCG action was not related to modulation of A activity or due to 5a-reductase inhibition. In addition, the growth of human breast tumors in athymic mice produced by human breast cancer MCF-7 cells, were also clearly inhibited by ip injection of EGCG.
It is possible that the low clinical incidence of prostate and breast cancer in some Asian countries is, in part, related to high green tea consumption. The frequency of the latent, localized PCA does not vary significantly among geographically different populations, but the clinical incidence ofmetastatic PCAr varies considerably among countries (low in Japan and high in the USA). If consumption of green tea beverage is related to this difference, EGCG may play an important role in preventing the progression or metastasis of PCA cells.
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