Objective   To investigate the effect of saikosaponin-d (SSd) on the expressions of STAT3 and COX-2 in hepatocellular carcinoma cells

and explore the underlying signal pathway mechanism of its anti-tumor effect.  Methods   MTT assay was used to detect the effect of SSd on the proliferation of cultured human hepatocellular carcinoma SMMC-7721 cells. Then the cells were divided into control

IL-6 group

AG490 group and SSd group

which were treated respectively with IL-6 25 ng/ml

IL-6 25 ng/ml+AG490 50 μmol/L

and IL-6 25 ng/ml+ SSd 5 μg/ml. The protein expressions of STAT3

p-STAT3 and COX-2 were measured by immunocytochemical technique as well as Western blotting. Their relationship was further analyzed.  Results  MTT assay showed SSd had obvious inhibitory effect on the proliferation of SMMC-7721 cells

especially at a dose of 10 μg/ml for 48 h. Immunocytochemical  Results  showed that both p-STAT3 and COX-2 were obviously increased in SMMC-7721 cells after exposure to IL-6 compared with blank group. Compared with IL-6 group

the protein level of COX-2 was decreased by AG490 or SSd

so was the expression of p-STAT3. While

the expression of STAT3 had no difference among these groups. Western blotting further confirmed the above  Results . SMMC-7721 cells had obviously enhanced expressions of p-STAT3 and COX-2 after IL-6 treatment

and AG490 or SSd decreased p-STAT3 expression in a dose-dependent manner. The expression of COX-2 was decreased.  Conclusion  p-STAT3 is involved the regulation of COX-2 in SMMC-7721 cells. SSd may down-regulate the expression of COX-2 through inhibiting STAT3 phosphorylation and thus exert its anti-tumor effect.