Cancer chemopreventive activity of oleanane-type triterpenoids from the stem bark of Betula ermanii.

In search for cancer chemopreventive agents from natural sources, three oleanane- and four known lupane-type triterpenoids, and sitosterol from the stem bark of Betula ermanii were tested for their inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). Among them, 3beta-acetoxy-12alpha-hydroxyoleanan-13beta,28-olide (1) and 3beta-acetoxy-11alpha,12alpha-epoxyoleanan-13beta,28-olide (2) were investigated for the inhibitory effect in a two-stage carcinogenesis test on mouse skin using 7,12-dimethylbenz[a]anthracene (DMBA) as an initiator and TPA as a promoter. 3beta-Acetoxy-11alpha,12alpha-epoxyoleanan-13beta,28-olide (2) was found to exhibit the potent antitumor promoting activity in the in vivo carcinogenesis test.