Recent studies demonstrate that aberrant Stat3 activation promotes tumor growth and survival in several human cancers. We conducted an analysis of Stat3 expression and activation in drug sensitive and resistant ovarian cancer cell lines and matched tumor samples from women with epithelial ovarian cancer. Our results demonstrate that total Stat3 and activated phosphorylated Stat3 (p-Stat3) are over expressed in a subset of paclitaxel resistant ovarian cancer cell lines as compared to their expression in the corresponding paclitaxel sensitive cell lines. Northern blot analysis determined that Stat3 mRNA was overexpressed in 4 of 8 (50%) resistant cell lines. The p-Stat3 protein (Tyr705) was found to be overexpressed in 5 of 8 (63%) resistant cell lines as evaluated by Western blot analysis. Increased Stat3 DNA binding activity was also detected in the paclitaxel resistant cell lines by EMSA. We also evaluated Stat3 expression and activation in a tumor microarray generated from matched tumor specimens from 26 individual epithelial ovarian cancer patients. Each patient sample set comprises a primary ovarian tumor and a separate metastasis obtained at the time of initial debulking surgery along with a recurrent tumor collected at a later operation (post chemotherapy). Immunohistochemical analyses determined that all tumors present on the microarray have moderate to strong staining for total Stat3 and more than 60% of ovarian tumors have strong p-Stat3 staining. Seven of the 26 (27%) matched sample sets have similarly activated levels of p-Stat3 in primary, metastatic and recurrent tumors whereas p-Stat3 levels were elevated in metastatic tumors as compared to the levels detected in primary tumors in 11 of the 26 (42%) sample sets. Finally, 9 of the 26 (35%) sample sets showed increased p-Stat3 nuclear staining in the recurrent tumor as compared to its matched primary or metastatic tumors. High p-Stat3 staining was associated with inflammatory cell infiltrates in the tumor tissues. The relative levels of p-Stat3 nuclear staining in the 26 individual tumor sample sets were scored from no detectable nuclear p-Stat3 staining (0+) to greater than 75% of tumor nuclei positive for p-Stat3 (5+) and compared to the relative levels of inflammatory infiltrates in each sample. Only those tumors that scored as 3+, 4+, or 5+ for p-Stat3 nuclear staining demonstrated significant levels of inflammatory infiltration (14%, 26%, and 36% respectively). Our current in vitro and clinical data suggests that the IL-6-Stat3 pathway is frequently activated in ovarian cancer and that such activation is often associated with the acquisition of drug resistance. In tumors, Stat3 activation is often but not exclusively seen in the setting of inflammatory infiltrates within the tumor supporting the hypothesis that activation of the IL-6-Stat3 pathway in ovarian tumors may be via paracrine or autocrine mechanisms.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]