We reported previously that white tea, the least processed form of tea, was an inhibitor of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced colonic aberrant crypt foci (ACF) in the rat when administered before, during and after the carcinogen. To distinguish blocking from suppressing effects, rats were given white tea (2% wt/vol) either before and during PhIP treatment or after the carcinogen. Additional groups received green tea (2% wt/vol) or corresponding doses of epigallocatechin-3-gallate (EGCG) or caffeine in the drinking water. In the blocking study, white tea was more potent than green tea at inducing hepatic cytochromes P4501A1 and 1A2, glutathione S-transferase, and UDP-glucuronosyltransferase, based on enzyme assays and/or immunoblotting; however, white tea and green tea were equally effective as blocking agents against PhIP-induced ACF. In the suppression study, white tea, caffeine and EGCG inhibited PhIP-induced ACF, whereas green tea had no significant effect. Interestingly, the most potent suppression was seen in rats given EGCG (**P<0.01). Immunohistochemical analyses performed on longitudinal sections of colonic crypts showed that EGCG inhibited the bromodeoxyuridine labeling index and caused an increase in apoptosis, based on apopTag in situ labeling. In the latter assay, EGCG was significantly more effective than tea or caffeine alone. These results provide further evidence for the chemoprotective effects of tea and EGCG against PhIP-induced ACF, and a 1 year bioassay is in progress to compare white tea, EGCG and caffeine as suppressing agents of PhIP-induced colon tumors in the rat. Studies supported by NIH grants CA90890, CA65525 and CA80176.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]