Selective Inhibitory Effect of Bufalin on Growth of Human Tumor Cells in vitro: Association with the Induction of Apoptosis in Leukemia HL‐60 Cells

We found that bufalin, an active principle of the Chinese medicine chan'su, has selective inhibitory effects on the growth of various human cancer cells. In order to examine whether the growth‐inhibitory effect of bufalin on human cancer cells is associated with apoptosis, human leukemia cells were treated with bufalin. HL‐60, ML1, and U937 leukemia cells treated with bufalin at 10(−8)M and above had condensed and fragmented nuclei. Flow cytometric analysis of these cells treated with bufalin showed fragmented DNA smaller than that of the G1 phase. DNA of HL‐60 cells treated with bufalin showed a ladder pattern characteristic of apoptosis, as analyzed by agarose gel electrophoretic analysis. DNA synthesis and topoisomerase II activity of HL‐60 cells were markedly inhibited as the concentration of bufalin was increased. The concentration needed for inducing apoptosis of HL‐60 cells was 10(−8)M, which is comparable to that of camptothecin, but lower than those of other antitumor drugs such as cisplatin, VP16 and all‐trans retinoic acid. Apoptosis was not observed when human mononuclear and polymorphonuclear cells were treated with 10(−6)M bufalin for 24 h. These results indicate the association of the growth‐inhibitory effect of bufalin with the induction of apoptosis, at least in HL‐60 cells, and suggest the usefulness of bufalin for differentiation‐apoptosis‐inducing therapy for cancer.