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[Study on synergistic effect of sodium cantharidinate combined with chemotherapeutic drugs on hepatic carcinoma and its effective mechanism].

OBJECTIVE
To study the synergistic effect on hepatoma cell(SMMC-7721) and the reduction killing effect on normal liver cells(LO-2) treated with sodium cantharidinate (SCA) in combination with fluorouracil(5-FU) or cisplatin(DDP) as well as the related mechanism.


METHODS
MTT assay was used to select the best ratio of SCA with 5-FU or SCA with DDP which had less toxicity on LO-2 cell line and had synergistic effect on SMMC-7721 cell line; Flow cytometry assay was used to analyze the apoptosis-induction of the different ratio of drugs on both cell lines; Hoechst-33258 fluorescent staining assay was used to observe the nuclear morphological changes of cells; Immunoblotting assay was used to analyze the Ras/Raf/ERK1/2 signaling pathway and the apoptosis related signaling pathway in both cell lines.


RESULTS
MTI assay indicated that the proliferation inhibition of SCA,5-FU and DDP on SMMC-7721 cell line was in a time-and dose-dependent manner respectively. Among them, SCA had a more significant inhibition on SMMC-7721 cell line than on LO-2 after 12 h or 24 h treatment (P <0. 01). Moreover, after a treatment of 48 h,the ratio of 2. 5 µg/mL SCA and 2 µg/mL DDP showed a more significant inhibition on SMMC-7721 cell line than on LO-2 cell line,which was then be considered as the optimal concentration ratio for the following experiment. Co-treatment of SCA (2. 5 µg/mL) with DDP (2 µg/mL) induced a more significant apoptosis on SMMC-7721 cell line compared with single treatment with SCA (2. 5 µg/mL) or DDP (2 µg/mL) respectively (P < 0. 01). After a 48 h treatment of the optimal ratio of drugs, the significant morphological apoptotic characteristics were observed both under inverted microscope and by Hoechst-33258 fluorescent staining assay in both cell lines. The results of Western blot assay showed that this ratio of drugs could significantly increase the protein expression of Bax,P53 and P21 and decreased the expression of BCL-2, Casepase-3, p-Erk, p-Ras and p-c-Raf in SMMC-7721 cells. Meanwhile,the effect on the proteins mentioned above was lesser in LO-2 cells.


CONCLUSION
These results indicates that 2. 5 µg/mL SCA + 2 µg/mL DDP showed a higher inhibition on the hepatic carcinoma cells and a relatively lower cytotoxicity on normal liver cells. The major anti-cancer mechanism is related with the inhibition on Erk signaling pathway and the induction of apoptosis through the mitochondrial pathway.