Inhibitory Effects of Tea on Carcinogenesis: Evidence from Cell Transformation Assays

Carcinogenesis, the development of cancer, is a complex multistep process that involves the interaction between genetic and environmental factors. Several studies have shown that exposure to carcinogens and promoters can cause DNA damage and mutations, leading to the development of cancer. Antipromoters in natural edible products, such as tea, have been found to have preventive effects on human cancers. In this article, we will discuss the inhibitory effects of tea on carcinogenesis, specifically evidence from cell transformation assays.

Cell transformation assays are widely used to study the effects of chemical and physical agents on cells’ ability to grow and divide uncontrollably, a hallmark of cancer cells. In these assays, cells are treated with carcinogens and promoters, and the number of transformed cells is measured to assess the effects of different agents on carcinogenesis.

Green tea, one of the most widely consumed beverages in the world, has been found to have potent inhibitory effects on carcinogenesis. Green tea contains several polyphenols, including epigallocatechin-3-gallate (EGCG), epigallocatechin, epicatechin-3-gallate, and epicatechin. Several studies have shown that these polyphenols have potent antioxidant and anticancer properties, making green tea a potential chemopreventive agent.

In a cell transformation assay using BALB/3T3 cells, a type of mouse fibroblast cell, treated with the carcinogen 3-methylcholanthrene (MCA) and the promoter 12-o-tetradecanoylphorbol-13-acetate (TPA), green tea extract (GTE) significantly inhibited the transformation frequency of cells. The frequency of transformed cells was reduced from 63.2/105 survivors to 5.6-8.6/105 survivors when treated with GTE, demonstrating the inhibitory effects of green tea extract on both initiation and promotion of carcinogenesis. EGCG, the main component of green tea polyphenols, was also found to have the same inhibitory effects on cell transformation as GTE.

Another study using mouse epidermal JB6 cells found that hot water extracts of green tea, black tea, Puerh tea, and Oolong tea all showed antitumor promoting effects, with green tea extract containing catechins, such as EGCG, having the highest activity. The green tea extract was found to decrease the TPA-induced anchorage independent colony induction by 70%. These results suggest that green tea polyphenols may have potential as chemopreventive agents.

In a mouse skin test, the topical application of GTE or EGCG was found to significantly inhibit both edema and hyperplasia induced by TPA, further demonstrating the inhibitory effects of green tea on cancer promotion. It has also been reported that topical application of green tea polyphenols or green tea in drinking water inhibited both initiation and promotion of mouse skin carcinogenesis.

In an X-ray-induced BALB/3T3 cell transformation assay, GTE was found to significantly inhibit the transformation of cells, providing further evidence of the inhibitory effects of green tea on carcinogenesis.

In conclusion, several cell transformation assays have demonstrated the inhibitory effects of green tea and its polyphenols, such as EGCG, on carcinogenesis. These findings suggest that green tea may have potential as a chemopreventive agent for human cancers. However, further research is needed to determine the optimal dosage and duration of green tea consumption to achieve maximum chemopreventive effects.