Inhibition of both stage I and stage II skin tumor promotion in SENCAR mice by a polyphenolic fraction isolated from green tea: inhibition depends on the duration of polyphenol treatment

The polyphenolic fraction isolated from green tea (GTP) is a potent inhibitor of phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced tumor promotion in mouse skin. In this study, we assessed the effect of GTP on both stage I and stage II skin tumor promotion, and also analyzed the effect of duration of GTP treatment on skin tumor promotion in SENCAR mice. Topical application of GTP (6 mg/animal) concurrently with each application of either TPA (3.2 nmol) or mezerein (3.2 nmol) in stage I or stage II of the murine skin tumor promotion protocol, respectively, resulted in significant protection against skin papilloma formation in terms of both tumor multiplicity (42-50%) and tumor growth (43-54%). More profound and sustained protective effects of GTP were evident when it was applied continuously during both stage I and stage II of the skin tumor promotion protocol concurrently with TPA or mezerein treatments, respectively. Under this treatment regimen, compared to non-GTP-treated positive controls, GTP application showed 71%, 37% and 74% protection in terms of tumor multiplicity, tumor incidence and tumor growth, respectively. These data indicate that GTP inhibits both stage I and stage II of skin tumor promotion and that the inhibition of tumor promotion depends on the duration of GTP treatment.