Inhibition of tumor promoter-induced ornithine decarboxylase activity by tannic acid and other polyphenols in mouse epidermis in vivo.

Naturally occurring plant phenols with antimutagenic and anticarcinogenic activities were tested for their abilities to inhibit the ornithine decarboxylase (ODC) response linked to skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate (TPA). Topical applications of tannic acid (TA) inhibit remarkably and in a dose-dependent manner TPA-induced ODC activity in mouse epidermis in vivo. This inhibitory effect of TA is dependent on the time of its administration relative to TPA. The induction of epidermal ODC activity by 8.5 nmol of TPA is inhibited maximally when 20 mumol of TA are applied topically to the skin 20 min before the tumor promoter. Gallic acid and several of its derivatives inhibit the ODC response to TPA to a lesser degree than TA. Ellagic acid is the least effective inhibitor tested. TA also inhibits the ODC-inducing activities of several structurally different tumor promoters and the greater ODC responses produced by repeated TPA treatments. The ability of TA to inhibit by 85% the ODC marker of skin tumor promotion suggests that TA and other polyphenols may be effective not only against tumor initiation and complete carcinogenesis but also against the promotion phase of tumorigenesis.