Inhibition of mouse skin tumor‐initiating activity of DMBA by chronic oral feeding of glycyrrhizin in drinking water

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Abstract
Licorice (Glycyrrhiza glabra), a Mediterranean plant, has been used as an antidote, demulcent, and elixir folk medicine for generations in China. The main water‐soluble constituent of licorice is glycyrrhizin (GL), which has been shown to possess several pharmacological properties. In this study, we show that oral feeding of GL to Sencar mice resulted in substantial protection against skin tumorigenesis caused by 7,12‐dimethyl‐benz[a]anthracene (DMBA) initiation and 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) promotion. The latent period prior to the onset of tumor development was considerably prolonged in GL‐fed animals compared with animals not fed GL and resulted in significant decrease in the number of tumors per mouse, during and at the termination of the experiment. Oral feeding of GL in drinking water also resulted in inhibition in the binding of topically applied [3H]benzo[a]pryene and [3H]DMBA to epidermal DNA. The possible mechanism(s) of the antitumor‐initiating activity may be due to the involvement of GL as inhibitor of the carcinogen metabolism followed by DNA adduct formation. Our results suggest that GL possesses considerable antitumorigenic activity and could prove useful in protecting some forms of human cancer.