Anti-tumor promoting activity of bufadienolides from Kalanchoe pinnata andK. daigremontiana X tubiflora

Five bafadienolides (1-5) isolated from the leaves of Kalanchoe pinnata and K. daigremontiana x tubiflora (Crassulaceae) mere examined for their inhib itory effects on Epstein-Barr virus early antigen (EBV-EA) activation in Ra ji cells induced by the tumor promoter, 12-O-tetradecanoylphorbol-13-acetat e. All bufadienolides showed inhibitory activity, and bryophyllin A (1) exh ibited the most marked inhibition (IC50 = 0.4 mum) among the tested compoun ds. Bryophyllin C (2), a reduction analogue of 1, and bersaldegenin-3-aceta te (3) lacking tile orthoacetate moiety mere less active. These results str ongly suggest that bufadienolides are potential cancer chemopreventive agen ts.