[Advance on quality control of toad venom and its key influence factors].

Toad venom (Chansu) is prepared from the dried secretion of Bufo bufo gargarizans or B. melanostictus. It is not only one of the famous and expensive traditional Chinese medicines(TCMs) from animal origin, but also one of 28 kinds of toxic TCMs to be required for special management issued by the State Council of the People's Republic of China. Chansu contains the rich bufadienolides and indole alkaloids, and displays various bioactivity including cardiotonic, anti-tumor, analgesia, and local anesthesia. Based on the published references in the recent years, the advance on the identification of adulterants and quality evaluation as well as the influence factors on the quality of toad venom was summarized to improve the quality standards and promote the level of quality control of toad venom and its preparations.

[Research on therapeutic effects of bufonis venenum on L7212 leukemia and its mechanism].

OBJECTIVE: To study the therapeutic effects of Bufonis Venenum on L7212 leukemia and the potential mechanism. METHODS: L7212 leukemia model mice were randomly divided into four groups: model group, low and high dose Bufonis Venenum groups and chemotherapy group. Normal mice were treated as control group. Mice were injected intraperitoneally for 10 days continually. The body weight, survival time, peripheral blood leukocyte, hepatic and splenic indexes, bone marrow leukocyte and T lymphocyte were observed and determined. RESULTS: Body weight of L7212 leukemia model group mice were decreased significantly. Compared with other groups, high dose Bufonis Venenum group's weight loss was the least. Bufonis Venenum groups survived longer than L7212 model group. Compared with model group, high dose Bufonis Venenum group's liver index was higher (P < 0.05). After inoculation for 1 day, leukocyte count as well as percentage of leukemic cells within five groups had no significant difference (P > 0.05). Compared with the model group, after inoculation for 10 days, leukocyte count in Bufonis Venenum groups and the chemotherapy group were significantly reduced (P < 0.05). Percentage of leukemia cells in blood and bone marrow in high dose Bufonis Venenum group was significantly decreased (P < 0.05). Compared with model group, CD3+ and CD4+ in Bufonis Venenum groups and the chemotherapy group were increased, CD8+ was decreased, but had no significant difference (P > 0.05). CONCLUSION: Bufonis Venenum has therapeutic effects on the L7212 leukemia by inducing apoptosis and improving immune system.

Bufalin inhibits platelet-derived growth factor-BB-induced mesangial cell proliferation through mediating cell cycle progression.

Bufalin, a traditional Chinese medicine, has been reported as a protective factor in many tumors. We therefore investigated the effect of bufalin on platelet-derived growth factor (PDGF)-BB-induced proliferation of cultured rat mesangial cells. The effect of bufalin on cell proliferation and its underlying mechanisms were investigated in cultured rat mesangial cells (MCs) by the methylthiazoletetrazolium (MTT) assay, flow cytometry, reverse transcription-polymerase chain reaction (RT-PCR), Western blotting, and cyclin-dependent kinases (CDK)2 and CDK4 kinase assays. Bufalin inhibited 20 ng/ml PDGF-BB-induced MC proliferation in a dose-dependent manner. Similar results were observed in different concentrations of bufalin, which blocked PDGF-BB-induced progression through G0/G1 to S phase of the cell cycle. Furthermore, bufalin not only inhibited upregulation of cyclin D1 and CDK4, but also downregulation of p21 in both mRNA and protein levels. Although bufalin did not affect p27 and CDK2 mRNA expression, it reversed downregulation of p27 and upregulation of CDK2 in protein level. Activity of CDK2 and CDK4 was also inhibited by bufalin. However, both bufalin and PDGF-BB did not affect cyclin E mRNA or protein expression. These results suggest that bufalin could inhibit MC proliferation by modulating cell cycle progress, indicating that bufalin could be a potential therapeutic agent for the prevention of mesangial proliferative glomerulonephritis.

[Effect of cinobufotalin on growth of xenograft of endometrial carcinoma cell line ishikawa in nude mouse and its impact on RRM2 expression].

OBJECTIVE: To investigate the inhibitory effect of cinobufotalin (CBT) on the growth of xenograft endometrial carcinoma cell line ishikawa in nude mice, and its impact on the expression of ribonucleotide reductase subunit M2 (RRM2). METHODS: Eleven nude mice with xenograft were randomly divided into two groups, the CBT group and the control group, which received intra-tumor injection of CBT and saline respectively for one week. The sizes of xenografts were measured before and after the treatment to calculate the inhibition ratio of tumor proliferation; the RRM2-mRNA and protein expressions in tumor tissue were measured by RT-PCR and Western blot respectively. RESULTS: After treatment, the size of xenografts in the CBT group was (0.1314 +/- 0.0304) cm3, which was significantly lower than that in the control group (0.360 0 +/- 0.1145) cm3, (P < 0.05), the tumor proliferation inhibition ratio being 43.46%. The differences of RRM2 mRNA and protein expression levels between the two group were significant (P = 0.019 and P = 0.001). CONCLUSION: CBT significantly inhibits the growth of the xenografts of endometrial carcinoma Ishikawa in nude mice, and the action mechanism is possibly associated with the inhibition on RRM2 expression.

[Pilot study on the mechanisms of growth inhibitory effect of cinobufagin on HeLa cells].

OBJECTIVE: To study the effect of cinobufagin (CBG) on HeLa cell proliferation, and to analyze its mechanism. METHODS: Proliferation inhibition in vitro was evaluated by MTT and Sulforhodamine B (SRB) assays in several human tumor cell lines, including Bel-7402, HeLa, MCF-7, BGC-823 and HL60. The cycle of HeLa cells was analyzed by flow cytometry. Two-dimensional electrophoresis was applied to analyze the influence of CBG on HeLa cell proteomics. RESULTS: CBG had inhibitory effects on proliferation of five human cancer cell lines, and the IC(50) values were 0.011 micromol/L (Bel-7402), 0.019 micromol/L (HeLa), 0.116 micromol/L (MCF-7), 0.149 micromol/L (BGC-823) and 1.369 micromol/L (HL60), respectively. HeLa and Bel-7402 cells were among the most sensitive. Flow cytometry assay indicated that the treatment of HeLa cells with various concentrations of CBG for 72 h was able to increase the cell number at G(2)/M phase, from 17.3% up to 35.6%. The results of two-dimensional electrophoresis showed that treatment of HeLa cells with 0.02 micromol/L CBG for 48 h resulted in apparent changes of certain small molecular weight (30,000 - 90,000) acidic proteins (pH 4 - 6). CONCLUSION: Cinobufagin has significant inhibitory effect on growth of five human cancer cells in vitro. It may lead to cell cycle arrest of HeLa cells at G(2)/M phase. It can also change the expression of some small molecular acidic proteins in HeLa cells.

Chronic blood pressure effects of bufalin, a sodium-potassium ATPase inhibitor, in rats.

Endogenous Na+,K(+)-ATPase inhibitors may have a role in the mechanism of low-renin hypertension. Two such compounds have been characterized: ouabain from human plasma and resibufogenin from toad plasma. Previously, we examined the acute effects of ouabain and bufalin (which has the same structure as resibufogenin except for one H+) in normal rats. Bufalin raised blood pressure, but ouabain had little effect. In contrast, given chronically, ouabain substantially increased blood pressure in normal rats and 70% reduced renal mass rats on a salt-free diet. We have now examined the chronic effects of bufalin in rats. Normal rats received 14.8 micrograms/kg per day bufalin or an equimolar dose of ouabain intraperitoneally for 6 weeks; 70% reduced renal mass rats also received 14.8 micrograms/kg per day bufalin. Another group of normal rats received 29.6 micrograms/kg per day bufalin intraperitoneally for 6 weeks. Respective control animals received vehicle. In contrast to ouabain, blood pressure did not increase in normal rats receiving the 14.8 micrograms dose of bufalin. However, normal rats receiving 29.6 micrograms bufalin and 70% reduced renal mass rats receiving 14.8 micrograms bufalin developed significant increases in blood pressure. Increases in blood pressure were associated with decreases in myocardial Na+,K(+)-ATPase activity and correlated with increased plasma Na+,K(+)-ATPase inhibitory activity. Thus, although bufalin is a more potent pressor agent than ouabain when both agents are given acutely, ouabain is at least as potent a vasopressor agent as bufalin when given chronically. Thus, both are pressor agents, more so in the presence of reduced renal mass, when given chronically in the rat.

Cell cycle arrest and protein kinase modulating effect of bufalin on human leukemia ML1 cells.

Bufalin, an active principle of the traditional Chinese medicine chan'su, has been proved to be a potent differentiation inducer in human leukemia cells. To study the mechanism of the differentiation of human leukemia ML1 cells induced by bufalin, we measured the effect of 10 nM bufalin on cell growth, activities of various protein kinases, and cell cycle. The ML1 cell growth was inhibited significantly at 24 hr and the inhibiting effect persisted for 6 days. Activities of PKC, PKA, cdc2 kinase and CK II in ML1 cells were changed early by bufalin; PKA and PKC activities were inhibited, and cdc2 kinase and CK II activities were increased. These results suggest that bufalin induces differentiation of ML1 cells by modulating several protein kinase activities in a distinct way from RA and 1 alpha, 25(OH) 2D3. Cell cycle changes, measured by flow cytometry, became evident at 12 hr after treatment of ML1 cells with bufalin and the cells were preferentially arrested in the G2/M phase. This effect of bufalin on the cell cycle of leukemia cells is similar to that of topoisomerase inhibitors. Indeed, the activity of topoisomerase II but not topoisomerase I of ML1 cells was inhibited remarkably by the treatment of the cells with 10 nM bufalin.

Differentiation of promyelocytic leukemia cells HL-60 induced by daidzein in vitro and in vivo.

We have screened more than one thousand synthetic and natural chemicals to explore differentiation inducers and found that daidzein has potent differentiation-inducing activity for human leukemia HL-60 cells, both in vitro and in vivo. In vitro study showed that daidzein at concentrations exceeding 10 micrograms/ml caused inhibition of HL-60 cells; and it induced differentiation of the cells into granulocytic lineage as judged by NBT reduction activity, phagocytic ability and morphological characteristics. Flow cytometry study indicated that daidzein arrested HL-60 cells in the G1 phase. The growth of HL-60 cells in the subrenal capsules of mice and in diffusion chambers implanted into the peritoneal cavities of mice was inhibited by 50 mg/kg daidzein. HL-60 cells treated with daidzein in vivo also exhibited characteristic morphological changes of matured cells. Moreover, the colony forming efficiency of HL-60 cells in diffusion chambers in mice was markedly inhibited by the administration of daidzein.

Effects of intraduodenal administration of "kyushin," a senso (toad venom)-containing drug, on systemic hemodynamics, cardiacfunction and myocardial oxygen consumption in anesthetized dogs.

The effects of "Kyushin" (KY), a Senso (toad venom)-containing drug, on the cardiovascular system were examined by intraduodenal administration of KY in anesthetized open-chest dogs. KY (3 or 10 mg/kg) dose-dependently increased the peak positive first derivative of left ventricular pressure ((+)LVdP/dt) and mean aortic pressure, and decreased the left ventricular end-diastolic pressure (LVEDP). Myocardial oxygen consumption (MVO2) and heart rate (HR) were not significantly influenced by KY. KY produced a cardiotonic effect without any increase in MVO2, because the increase in MVO2 due to the cardiotonic effect of KY may have been cancelled by a decrease in MVO2 due to reduction of preload and the lack of increase in HR. In order to clarify the relationship between the cardiovascular effects of KY and the drug concentration in plasma, the concentration of anti-bufalin IgG reactive substance (BRS) in plasma was measured by enzyme immunoassay. The maximum BRS concentrations 20 min after administration of 3 and 10 mg/kg KY were dose-dependent. From the relationship between changes in (+)LVdP/dt and changes in BRS concentration after administration of KY, it is inferred that the effective concentration of BRS in plasma at which KY produces a cardiotonic effect in dogs is approximately 2-3 ng/ml.

Pharmacological actions of "kyushin," a drug containing toad venom(2): effects on urinary volume and electrolyte excretion.

A study was conducted on the pharmacological actions of the toad venom-containing drug "Kyushin" (KY-2 and KY-R) on urinary volume and electrolytes excretion, regional blood flow, renal artery blood flow and carrageenin-induced hind-paw edema. In rabbits, KY-2 and KY-R significantly increased urinary volume after intravenous administration of 8 mg/kg. In guinea pigs, KY-2 and KY-R produced a significant increase in urinary volume after intraduodenal administration (i.d.) of 80 mg/kg. In guinea pigs treated with propranolol, KY-2 at 20 and 40 mg/kg p.o. and KY-R at 40 mg/kg p.o. increased urinary volume. At 40 mg/kg i.d. both KY-2 and KY-R produced an increase in regional blood flow, as determined by the hydrogen gas clearance method, of the brain areas including the amygdaloid nucleus, but did not affect regional blood flow in liver, kidney and skeletal muscle, or renal artery blood flow. In rats, carrageenin-induced hind-paw edema was inhibited by KY-2 or KY-R at 600 mg/kg p.o.

[Effect of cinobufagin on the guinea pig vas deferens and its mechanism of action].

Cinobufagin, one of the active principles extracted from toad venom, was studied on the isolated vas deferens of the guinea pig. The preparation was suspended in a bath containing 10 ml Krebs solution. Isometric tension of vas deferens was recorded on polygraph with a force displacement transducer. Cinobufagin caused a long lasting contraction of the vas deferens of the guinea pig at concentrations of 15-50 mumol/L. The contraction was inhibited following reserpinization and cold storage treatment. The cinobufagin induced contraction was partly blocked by pretreatment with phentolamine and verapamil. These results suggest that the cinobufagin induced contraction of vas deferens might be related to an action which promotes release of NA from the adrenergic nerve terminals.

[Inhibitory effects of co-cinobufotalin oral liquor on hepatitis B in vitro].

Co-Cinobufotalin Oral Liquor (CCOL) was studied for its ability to inhibit hepatitis B virus DNA replication, HBsAg and HBeAg expression in a HBV-transfected cell line (2.2.15 cell). The result showed that ID50 (the drug concentration that inhibits HBsAg or HBeAg secretion by 50%) was 0.08 mg/ml and 0.07 mg/ml on HBsAg and HBeAg respectively. CD50 (the drug concentration that reduces cell growth by 50%) was 2.5 mg/ml. TI (therapeutic index) was 31.3 and 35.7 respectively. The present data suggest that CCOL could exert a potent antiviral activity against HBV in vitro. Southern blot showed that CCOL inhibited HBV-DNA repication in a dose-dependent manner.

[Preliminary study on apoptosis of human leukemic cells induced by bufalin].

OBJECTIVE: To study the mechanism of inhibiting actions of bufalin on human leukemic cells (HL60). METHODS: HL60 cells were incubated with bufalin at different concentrations and growth inhibition was analyzed by trypan-blue staining. Cell apoptosis was evaluated by phase contrast microscopy, transmission eletron microscopy and agarose gel electrophoresis. RESULTS: Bufalin remarkably inhibited the growth of HL60 cells. Apoptosis of HL60 cells could be effectively induced by bufalin at concentration of 0.01 mumol.L-1 or higher, showing the apoptotic changes in morphology, including cell shrinkage, chromatin agglutination and formation of apoptotic corpuscula; DNA cleavage was observed with agarose gel electrophoresis. CONCLUSION: Bufalin can effectively induce apoptosis of HL60 cells, which is possibly one of the mechanisms for anti-cancer of bufalin.

[Effects of cinobufagin on apoptosis in U-2OS osteosarcomas cells].

OBJECTIVE: To investigate the effects of cinobufagin on the apoptosis in U-2OS osteosarcomas cells (U-2OS cells) and explore its potential mechanism. METHODS: The cytostatic effects of cinobufagin (10, 20, 50, 100, 200, and 400 nmol/L) on U-2OS cells were evaluated by MTT assay at 24, 48, and 72 hours after culture; simple U-2OS cells served as control group. The impact of cinobufagin (100 nmol/L) on the apoptosis in U-2OS cells was determined by flow cytometry at 48 hours after culture, which were treated with cinobufagin (experimental group) or with cinobufagin plus Z-VAD-FMK (control group), and simple U-2OS cells served as blank control group. The Caspase-3 activity was measured by Caspase-3 activity assay kit at 48 hours after culture, which were treated with cinobufagin (20, 50, and 100 nmol/L), and simple U-2OS cells served as control group. The expression of apoptosis signal pathway related proteins in U-2OS cells treated with cinobufagin were detected by Western blot at 48 hours after culture, which were treated with cinobufagin (20, 50, and 100 nmol/L), and simple U-2OS cells served as control group. RESULTS: The results of MTT assay showed that cinobufagin inhibited the proliferation of U-2OS cells in a dose- and time-dependent manners. At each time point, the growth rate of U-2OS cells was significantly reduced with the increasing cinobufagin concentration, and as time prolonged, the growth rate of U-2OS cells behaved the same way in the same group. There were significant differences among different time points and groups (P < 0.05). The apoptotic rate of experimental group (46.87% +/- 11.23%) was significantly higher than that of the control group (2.34% +/- 0.98%) and blank control group (1.04% +/- 0.25%) (P < 0.05). The Caspase-3 activity in 20, 50, and 100 nmol/L groups were 1.14 +/- 0.32, 1.31 +/- 0.41, and 1.92 +/- 0.54, respectively, which were significantly higher than that in control group (P < 0.05). Compared with 20and 50 nmol/L groups, 100 nmol/L group significantly increased the Caspase-3 activity in U-2OS cells (P < 0.05). Compared with the control group, the expressions of cleaved Caspase-3, cleaved Caspase-9, and Bax were obviously up-regulated; the Bcl-2 expression was down-regulated; and the ratio of Bax/Bcl-2 was increased in different cinobufagin-treated groups (P < 0.05). The same tendency was seen in different cinobufagin-treated goups, showing significant differences among groups (P < 0.05). CONCLUSION: Cinobufagin can inhibite the proliferation of U-2OS cells, and induce cell apoptosis. The potential mechanism of cinobufagin-induced apoptosis may be related to the mitochondria-mediated pathway.

[Effect of cinobufagin on nuclear factor-kappaB pathway in HepG2 cells].

OBJECTIVE: To investigate the effect of cinobufagin on nuclear factor-kappaB (NF-kappaB) pathway of liver cancer cell line HepG2. METHODS: Dual-luciferase cis-reporting system was used to detect the relative value of pNF-kappaB-TA-luc upon tumor necrosis factor-alpha (TNF-alpha) stimulation of NF-kappaB pathway. Western blotting was used to detect the protein level of NF-kappaB p65, and RT-PCR was used to detect the gene transcription level of intercellular adhesion molecule-1 (ICAM-1), a target downstream gene of NF-kappaB. RESULTS: At the concentration of 0.25 and 0.5 microg/ml, cinobufagin significantly lowered the relative value of luciferase (P<0.05). The results of Western blotting showed that cinobufagin significantly suppressed the protein expression of NF-kappaB p65. The transcription level of ICAM-1 was reduced by different doses of cinobufagin. CONCLUSION: The anti-cancer effect of cinobufagin may be related to its activity in inhibiting the activation of NF-kappaB pathway.

[Effect of bufalin-inducing apoptosis on Bcl-2 and PKC in HL-60 cells].

Previous study revealed that bufalin can inhibit proliferation, and induce apoptosis in some human cancer cell lines. However, the mechanism of its anticancer effect has not been fully understood. The present study was designed to investigate the effects of bufalin-induced apoptosis on Bcl-2 and PKC in human leukemic HL-60 cells. The cell viability was determined by trypan blue dye exclusion. The apoptosis was detected by morphology, flow cytometry and DNA agarose gel electrophoresis. The expressions of Bcl-2 and PKC were analyzed by Western blot, and activity of PKC was assayed by [gamma-(32)P] isotope incorporation method. The results showed as follows: (1) proliferation of HL-60 cells was inhibited by bufalin and the IC(50) at 24, 48, 72 hours were (25.8 +/- 2.1), (8.0 +/- 1.2) and (2.3 +/- 0.3) nmol/L, respectively. (2) apoptosis of HL-60 cells was induced when the cells were treated with bufalin at concentration of 50 nmol/L for 24 hours. (3) compared with control, treatment with bufalin at concentration of 50 nmol/L for 6 - 24 hours resulted in downregulation of protein expression, decrease of phosphorylation, and cleavage of Bcl-2, simultaneously. (4) the activity of total PKC was unchanged when HL-60 cells were exposed to 1 - 100 nmol/L bufalin for 30 minutes, but PKCbetaII underwent translocation from cytosol to membrane. It is concluded that apoptosis induced by bufalin is associated with downregulation of protein expression, dephosphorylation, and cleavage of Bcl-2 in HL-60 cells.

Interactions between drugs and Asian medicine: displacement of digitoxin from protein binding site by bufalin, the constituent of Chinese medicines Chan Su and Lu-Shen-Wan.

Asian medicines are widely used as alternative medicine. However, interactions between drugs and Asian medicines have been poorly studied. Chan Su and Lu-Shen-Wan are Asian medicines that contain the cardiaoactive compound bufalin. Bufalin is structurally similar to digitoxin and is also strongly bound to serum albumin. The authors studied possible displacement of digitoxin from the protein binding site by bufalin. The authors prepared three serum pools from patients taking digitoxin and supplemented aliquots of each serum pool with no bufalin (control) and 25 ng/mL, 50 ng/mL, 100 ng/mL, 250 ng/mL, 500 ng/mL, and 1000 ng/mL bufalin. The authors observed significant displacement of digitoxin by bufalin as evidenced by increased free digitoxin concentrations. For example, the concentration of free digitoxin increased from a control value of 1.6 ng/mL to 2.5 ng/mL in the presence of 1000 ng/mL bufalin (total digitoxin: 36.3 ng/mL) in the serum pool 1. The authors observed similar increases in free digitoxin concentrations in other serum pools in the presence of various concentrations of bufalin. The authors used a chemiluminescent assay and ACS:180 analyzer to measure both total (in the original serum) and free (in the protein-free ultrafiltrate) digitoxin concentrations because the chemiluminescent assay does not cross-react with bufalin. When an acetone/water (1:1 by volume) extract of Chan Su was added to a serum pool containing digitoxin, the authors observed a significantly increased free digitoxin concentration, indicating that Chan Su can displace digitoxin from the protein binding site in vitro. The authors conclude that bufalin and acetone/water extract of Chan Su can cause significant displacement of digitoxin from the protein binding site.

Bufalin as a potent inducer of differentiation of human myeloid leukemia cells.

Bufalin was found to be a potent inducer of differentiation in human erythroleukemia K562 cells by examination of various differentiation markers (as assessed by the morphology, histochemistry, and the abilities to phagocytose latex particles, to reduce nitro-blue tetrazolium and to develop Fc receptors). Bufalin, at a concentration as low as 10 nM, also produced a strong differentiation-inducing activity in three other human leukemia-derived cell lines (human promyelocytic HL60, monoblastic U937 and myeloblastic ML1). Treatment of K562 cells with other cardiotonic steroids, such as cinobufagin, ouabain and digitoxigenin, at the concentration of 10 nM for four days resulted in weak or no effect on the cells. These findings suggest that bufalin might have potentiality as a new agent in the differentiation therapy for human myelogenous leukemia.

Effects of bufalin and cinobufagin on the proliferation of androgen dependent and independent prostate cancer cells.

BACKGROUND: Cardiac glycosides may induce oncolytic effects in cancers. This study was to evaluate bufalin and cinobufagin effects on the proliferation of prostate cancer cell lines named LNCaP, DU145, and PC3. METHODS: Cell proliferation was measured by MTT assay. The cytotoxic effects were determined by lactate dehydrogenase measurements. The intracellular calcium concentration ([Ca(2+)](i)) was measured by a dual-wavelength spectrometer system. TUNEL assay and flow cytometry were performed to measure percentage of apoptotic cells. A colorimetric assay was to measure caspases activities. RESULTS: Bufalin and cinobufagin inhibited proliferation of cancer cells at doses of 0.1, 1, or 10 microM after 2-4 days of culture. Cytotoxicity of bufalin and cinobufagin on the DU145 and LNCaP cells was dose-dependent. Bufalin or cinobufagin increased [Ca(2+)](i) and apoptosis in cancer cells after a 24-hr culture as well as caspase 3 activities in DU145 and PC3 cells and caspase 9 activities in LNCaP cells. CONCLUSIONS: Bufalin and cinobufagin may inhibit the proliferation of prostate cancer cell lines associated with sustained elevation of the [Ca(2+)](i) and that of apoptosis.

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.