High-grade serous ovarian cancer remains deadly for the majority of woman who are diagnosed every year. The high mortality rate necessitates new treatment options for physicians and patients to consider. To produce new therapies, different signaling pathways that are activated in ovarian cancer need to be identified. In order to mimic the growth of ovarian cancer in the body, 3D culturing systems were used to grow clusters of ovarian cells (spheroids). Comparing gene expression from cells grown in 2D and 3D, we identified the STAT3 signaling pathway as being highly enriched in ovarian spheroids. STAT3 is a transcription factor that is activated by tyrosine phosphorylation. Once phosphorylated, STAT3 dimerizes, translocates to the nucleus, and regulates the expression of many genes involved in cell survival and migration. To determine if STAT3 was activated in 3D growing cells, we analyzed protein from cells grown in 2D and 3D and determined that STAT3 was tyrosine phosphorylated in cells grown in 3D We have found that the increase in STAT3 phosphorylation in 3D grown cells was associated with increased expression of STAT3 target genes. Consistent with this, we found enhanced STAT3 DNA binding to regulatory regions of STAT3 target genes. Recognizing that STAT3 activation is upregulated in 3D, we wanted to know if STAT3 is necessary for growth in 3D. By using siRNA to reduce the expression of STAT3, we were able to hinder the ability for ovarian cancer to grow in 3D. Moreover, reducing the expression of various components in the STAT3 signaling pathway also reduced the growth of ovarian spheroids. One of the major steps in ovarian cancer metastasis is the clearance of mesothelial cells by the cancer cells. To assess the effects of enhanced STAT3 activity in spheroids, we performed a mesothelial clearance assay with spheroids containing and lacking STAT3 expression. We found that ovarian spheroids with reduced STAT3 expression had a decreased ability to metastasize. This suggests that the STAT3 signaling pathway is a critical pathway involved in the growth and metastasis of ovarian cancer spheroids. This raises the possibility of using STAT3 inhibitors by themselves or in conjunction with standard-of-care therapeutics in the treatment of advanced ovarian cancer. Thus, targeting signaling pathways important in 3D growth may be beneficial for the treatment of ovarian cancer.
Citation Format: David F. Walker, Sarah J. Lacroix, Zachary T. Giaccone, David A. Frank, Sarah R. Walker. STAT3 promotes ovarian cancer spheroid growth and metastasis [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr B16.