Potential anti-tumor promoting activity of lupane-type triterpenoids from the stem bark of Glochidion zeylanicum and Phyllanthus flexuosus.

Four known lupane-type triterpenoids, glochidonol (1), glochidiol (2), lup-20(29)-ene-1beta,3beta-diol (3) and glochidone (3) were isolated from the stem bark of Glochidion zeylanicum. Previously, lupeol (5), lup-20(29)-ene-3beta,24-diol (6) and betulin (7) were isolated from the stem bark of Phyllanthus flexuosus. This study reports the assays of these lupane-type triterpenoids: all isolates 1-7 and synthetic analogues, glochidonyl acetate (1a), lup-20(29)-ene-1,3-dione (1b) and lup-20(29)-ene 3beta,24-diacetate (6a) 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, the effects of compounds 2 (IC50 = 290 mol ratio/32 pmol TPA) and 3 (IC50 = 300) were stronger than the others. In addition, compound 2 exhibited a strong inhibitory effect on mouse skin tumor promotion in an in vivo mouse two-stage carcinogenesis test.