STAT3 is a potential therapeutic target in cervical cancer (257)

Abstract

<b>Objectives:</b> STAT3 is known to be hyperactivated in most human cancers and is associated with poor prognoses. The STAT3 activation pathway within human papillomavirus (HPV)-positive cervical cancer cells is known to be essential for cervical cancer cell proliferation and survival. However, whether STAT3 activity is elevated in cervical cancer patient tumors remains to be determined. We sought to assess whether activated STAT3 (p-STAT3) was more highly expressed in cervical squamous cell carcinoma tissue microarrays compared to benign adjacent cervix tissue. We also assessed the ability of a small molecule inhibitor of STAT3 that has been used in the clinic to attenuate the STAT3 activation pathway and induce tumor cell death of HPV-associated human squamous cell carcinoma cells <i>in vitro</i>. <b>Methods:</b> Tumor microarrays from 12 patients with cervical squamous cell carcinoma with adjacent, benign cervix tissue were first probed with an anti-p-STAT3 antibody and detected with a fluorophore-conjugated secondary antibody for p-STAT3. Confocal imaging of immunofluorescence was performed, and fluorescence quantification was performed by ZEN 2.3 lite software and plotted in GraphPad Prism 8 software. The CaSki HPV16 infected cervical squamous cell carcinoma cell line was used for <i>in vitro</i> experiments. CaSki cells were treated with BBI608 (a small molecule inhibitor of STAT3) and assessed for changes in the STAT3 activation axis using Western Blot. Cell viability was analyzed using CellTiter-Glo® Luminescent Cell Viability Assay. <b>Results:</b> Quantification of p-STAT3 immunofluorescence from confocal imaging showed significantly higher expression of p-STAT3 in cervical squamous cell carcinoma tissue microarrays compared to adjacent, benign cervix tissue with mean expression levels of 37.7 relative units (RU) vs 29.1 RU, respectively (p=0.006). On Western Blot, BBI608 (3uM and 4uM) was found to attenuate the STAT3 activation axis in a dose-dependent fashion, including a significant decrease in p-JAK1 and p-STAT3 protein expressions. Furthermore, the protein expression of <i>HIF1A</i>, a known downstream STAT3 target gene and associated with poor survival and treatment resistance in cervical cancer, was also decreased by BBI608 (3uM and 4uM) in a similar fashion. On analysis of cell viability, BBI608 was found capable of inducing cell death in CaSki cells with an IC50 of 2.6uM after a 48-hour incubation period. <b>Conclusions:</b> The STAT3 activation pathway is a logical and promising target for therapeutic intervention in cervical cancer. On review of HPV-associated cervical cancer tumor arrays, we found a significantly higher expression of pSTAT3 in cervical tumor cells and tumor-infiltrating lymphocytes compared to adjacent, benign tissue. Furthermore, we found that BBI608 was able to attenuate the STAT3 activation axis and induce cell death in the CaSki cervical squamous cell carcinoma cell line.Fig. 1