Objective Cucurbitacins are the highly oxygenated tetracyclic triterpenes,which are predominantly found in the Cucurbitaceae family but are also present in several other families of the plant kingdom.A number of compounds of this group have been investigated for their cytotoxic,hepatoprotective,anti-inflammatory,cardiovascular and anti-diabetic activities.In China,the cucurbitacin preparation,which contains mostly cucurbitacin B and cucurbitacin E,has been clinically used for the treatment of the primary liver carcinoma.It has been previously reported that cucurbitacin E could produce cytotoxicity against a variety of cancer cells,and various mechanisms were implicated in its cytotoxic effect.The present study is to investigate the effect of cucurbitacin E on hepatoma cells in vitro and in vivo and to study their potential mechanisms of action.Methods The MTT assay was used to assess the viability of human HepG2 and BEL7402 hepatoma cells in vitro after treatment with different concentrations of cucurbitacin E.The cell cycle distribution was determined by flowcytometric analysis after propidium iodide(PI)staining.The cell cycle-related proteins were detected using western blotting analysis.Implanted mouse hepatoma H22 model was built to evaluate the growth inhibitory effect of cucurbitacin E in vivo in mice.Results Our studies found that cucurbitacin E(10-300 nM)produced anti-proliferative effect on human HepG2 and BEL7402 hepatoma cells in vitro without cytotoxicity.According to flowcytometric analysis,cucurbitacin E arrested the cell cycle at G2/M phase in both HepG2 and BEL7402 hepatoma cells after 24 h treatment.Cucurbitacin E induced the decrease in the level of CDK1 protein and the increase in the level of p21 protein,but had no effect on the levels of cyclin A,cyclin B1 and Cdc25C protein.In in vivo anti-tumor experiment,cucurbitacin E had significant inhibitory effects on the growth of mouse H22 hepatoma cells.Conclusions Cucurbitacin E inhibited the proliferation of hepatoma cells in vitro and in vivo,at least in part,through induction of cell cycle arrest at G2/M phase,which was mediated by concomitant upregulation of p21 and downregulation of CDK1.We consider that cucurbitacin E may be useful in the treatment of liver cancer. Objective Cucurbitacins are the highly oxygenated tetracyclic triterpenes, which are predominantly found in the Cucurbitaceae family but also present in several other families of the plant kingdom. A number of compounds of this group have been investigated for their cytotoxicity, hepatoprotective, anti-inflammatory, cardiovascular and anti-diabetic activities. In China, the cucurbitacin preparation, which contains mostly cucurbitacin B and cucurbitacin E, has been clinically used for the treatment of the primary liver carcinoma. It has been previously reported that cucurbitacin E could produce cytotoxicity against a variety of cancer cells, and various mechanisms were implicated in its cytotoxic effect. The present study is to investigate the effect of cucurbitacin E on hepatoma cells in vitro and in vivo and to study their potential mechanisms of action. Methods The MTT assay was used to assess the viability of human HepG2 and BEL7402 hepatoma cells in vitro after treatment with different concent The cell cycle-related proteins were detected using western blotting analysis. Implanted mouse hepatoma H22 model was built to evaluate the growth inhibitory effect of cucurbitacin E in vivo in mice. Results Our Studies found that cucurbitacin E (10-300 nM) produced anti-proliferative effect on human HepG2 and BEL7402 hepatoma cells in vitro without cytotoxicity. Based on flow cytometric analysis, cucurbitacin E arrested the cell cycle at G2 / M phase in both HepG2 and BEL7402 hepatoma cells after 24 h treatment. Cucurbitacin E induced the decrease in the level of CDK1 protein and the increase in the level of p21 protein, but had no effect on the levels of cyclin A, cyclin B1 and Cdc25C protein.In in vivo anti-tumor experiment, cucurbitacin E had significant inhibitory effects on the growth of mouse H22 hepatoma cells. Confccussion Cucurbitacin E inhibited the proliferativeration of hepatoma cells in vitro and in vivo, at least in part, through induction of cell cycle arrest at G2 / M phase, which was mediated by concomitant upregulation of p21 and downregulation of CDK1.We consider that cucurbitacin E may be useful in the treatment of liver cancer.