Glycyrrhetic acid inhibits tumor-promoting activity of teleocidin and 12-O-tetradecanoylphorbol-13-acetate in two-stage mouse skin carcinogenesis.

Glycyrrhetic acid suppressed tumor promoter-induced effects in vitro, such as stimulation of 32Pi-incorporation into phospholipids of cultured cells and down-regulation of the epidermal growth factor receptor. Glycyrrhetic acid inhibited the promoting activity of both 12-O-tetradecanoylphorbol-13-acetate (TPA) and teleocidin on skin tumor formation in mice initiated with 7,12-dimethylbenz[a]anthracene (DMBA). The percentage of tumor-bearing mice in the group treated with DMBA plus teleocidin was 88% at week 18, whereas that in the group treated with DMBA plus teleocidin and glycyrrhetic acid (10 mumol/painting) was 6%. Similarly, the percentage of tumor-bearing mice of the group treated with DMBA plus TPA was 97% at week 20, whereas that of the group treated with DMBA plus TPA and glycyrrhetic acid was 40%. Therefore, glycyrrhetic acid was proved to inhibit the activity of two different tumor promoters, teleocidin and TPA, in mouse skin.