Abstract： Objective To study the effects of siltuximab on the interleukin-6 (IL-6)/signal transducer and activator of transcription 3 (Stat3) signaling pathway in ovarian epithelial carcinoma.Methods (1) Expressions of IL-6 in ovarian cancer patient specimens were assessed by immunohistochemistry.(2) Expression of phosphorylation Stat3 (pStat3) protein in siltuximab and IL-6 treated SKOV3 cell lines was determined by western blot, and expression levels of Stat3-induced bcl-XL,MCL-1, survivin, in siltuximab treated SKOV3/TR and CAOV3/TR cells lines were also determined by western blot.(3) Real-time image analysis was used to study the nuclear translocation of pEGFP-Stat3 fusion protein in ovarian cancer cell line SKOV3-pEGFP-Stat3 treated with siltuximab and IL-6.(4)Paclitaxel sensitivity in siltuximab treated SKOV3/TR and CAOV3/TR cell lines were assessed using the methyl thiazolyl tetrazolium (MTT).The 50% inhibiting concentration ( IC50 ) was defined as the paclitaxel concentration required to decrease the A490 value to 50%.Results ( 1 ) There were significantly difference in IL-6 staining density and the positive rate of IL-6 protein stained among the metastatic, and drug-resistant recurrent tumors,and matched primary tumors [69%(18/26)] vs.77% (20/26)vs.23% (6/26), P＜0.05].(2)A clear increase in Stat3 phosphorylation levels was observed in the IL-6-treated SKOV3 cell lines as compared to the SKOV3 cell lines.When the IL-6-treated SKOV3 cells were incubated with siltuximab with a range of concentrations of 0.001,0.01,0.1, 1.0 and 10 μg/ml, there were trends toward reduced pStat3 expression in the treated cell lines.Compared without treatment with siltuximab, the expression of the anti-apoptotic proteins MCL-1, bcl-XL and survivin in SKOV3/TR and CAOV3/TR cell lines were significantly decreased after treated with siltuximab.(3) In resting cells, the majority of pEGFPStat3 was cytoplasmic until the addition of human IL-6, which promptly induced the translocation of fluorescent Stat3 molecules to the nucleus.Exposure of cells to siltuximab with a range of concentrations of 0.001, 0.01,0.1, 1.0 and 10 μg/ml, followed by an incubation in IL-6 significantly reduced pEGFP-Stat3 nucleocytoplasmic translocation.(4) MTT cytotoxicity assay demonstrated that siltuximab increased paclitaxel-induced cell death and partially overcame paclitaxel resistance.Treated with siltuximab ( 1 and 10 μg/ml) ,the paclitaxel IC50 value of siltuximab in SKOV3/TR (0.49, 0.19 μg/ml) and CAOV3/TR (0.0010, 0.0008 μg/ml) cells were significantly lower than those in untreated cells (0.71,0.0021 μg/ml;all P ＜ 0.05).Conclusions These results demonstrated that siltuximab effectively block the IL-6 signaling pathways, which .Blockage of IL-6 signaling may provide benefits for the treatment of ovarian cancer.