Antitumour Activity And Action Mechanism Of Escin

Escin is a natural mixture of triterpene saponins.As a kind of non-steroidal anti-inflammatory drug,the sodium salt of escin is widely used in clinical.It can reduce swelling,inhibit exudation and inflammation,promote gastrointestinal transit to attenuate formation of postoperative adhesions,and retrieve the normal permeability of micrangium. Studies have shown that many non-steroidal anti-inflammatory drugs have anti-tumour activities,and escin has gained attention in the field of cancer research as an anticancer agent. However,despite of its therapeutic potential,the mechanism by which escin elicits its chemopreventive effects remains largely unknown.In the present study,the antitumour activity of escin was studied in vivo and in vitro,and the possible action mechanism was investigated.The results are summarized as follows:1 In vitro study of eight kinds of human tumour cellsHuman tumour cell lines,hepatoma SMMC7721 and HepG2,cervical carcinoma Hela, lung adenocarcinoma A549,acute leukemia HL-60,laryngeal squamous cell carcinoma Hep-2,gastric carcinoma SGC-7901 and BGC-82,were used to investigate the antitumour activity of escin.Growth of the 8 kinds of tumour cell lines was suppressed significantly in a concentration-and time-dependent way and the IC₅₀ values ranged within 37.33～50.24μg/mL. In hepatoma SMMC7721 and HepG2 cell lines,combination of escin with CDDP/ ADM/MMC dropped the IC₅₀ values of the chemotherapeutic drugs.The synergistic effect of escin on lowe-concentration chemotherapeutic drugs was especially significant.2 In vivo study of tumour-bearing miceIn solid tumour mice model,treatment(ip.) of 1.4 mg/kg and 2.8 mg/kg escin showed significant inhibition on the growth of mouse hepatoma H22,sarcoma S180 and cervical carcinoma U₁₄.In ascitic tumour mice model,the survival times of all the escin-treated groups were prolonged except the 0.7 mg/kg escin group in S180 model.In solid hepatoma H22 model,the combinations of 1.4 mg/kg and 2.8 mg/kg escin with ADM led to 47.9%and 55.3%tumour inhibition rates,respectively;and in ascitic hepatoma H22 model,the combinations obtained 50.0%and 54.2%life prolonging rates,respectively,in both of which the drug interaction appeared to be synergistic effect.For 0.7 mg/kg escin,combination with ADM caused 27.7%of tumour inhibition rate and 33.3%of life prolonging rate,respectively, and the drug interaction appeared to be additive effect.The immunity indices were not influenced by escin treatment in tumour-bearing mice,suggesting that escin neither elicted the antitumour effect via immune enhancement,nor induced immunosuppression. 3 Molecular mechanism of the antitumour activity(1) Disruption of cell cycle control.G₁/S cell cycle blockage was observed in escin-treated HepG2 cells and the effect of cell cycle arrest was concentration-dependent. Escin caused a reduction in Cyclin E/Cdk2 expression,at the same time resulted in 35%to 57%suppression of the phosphorylated Rb(pRb) expression.In addition,a more pronounced decrease in the expression of E2F was also detected in the escin-treated cells, suggesting that these changes collectively contributed to the decrease in S phase cell population caused by escin.(2) Induction of Caspase-independent apoptosis.Pulse-field gel electrophoresis showed the addition of escin to cultures led to the generation of high m.w.fragments(～50 kb) that did not progress to the formation of internucleosomal DNA laddering,suggesting a Caspase-independent apoptosis.PARP-1 cleavage didn't occur in escin-treated HepG2 cells, permitting PARP-1 induced the release of AIF and Cyt C from mitochondria into the nucleus. AIF translocated from the mitochondria to the nucleus where it mediated chromatin condensation and large-scale fragmentation of DNA.Western blot analysis clearly showed a concentration-dependent suppression of Bcl-2 expression,accompanied by concomitant increase of Bax,in escin-treated cells compared to control cells.The increased Bax-to-Bcl-2 expression ratio could induce the release of Cyt C from mitochondria.These results support the ability of escin to activate the PARP-1/AIF-mediated apoptotic cascade.(3) Synergistic effect of escin on low-concentration chemotherapeutic drugs.After trentment by 5 or 10μg/mL escin,the cell membrane permeability was enhanced and more chemotherapeutic drug moleculars entered in cells,by which escin showed synergistic effect on the antitumour activity of chemotherapeutic drugs.