Abstract LB-036: Elevated STAT3 expression in ovarian tumor ascites regulates invasion and metastasis: a promising therapeutic target

Abstract

Abstract Objectives: Although, the ovarian cancer patient ascites is a recognized source of metastasis, the expression of oncogenic proteins in ascites and their effects on the tumor metastatic microenvironment still remain poorly understood. In this study, we investigate the role of STAT3 in primary ovarian cancer ascites and STAT3 as a potential target for ovarian tumor therapy in a preclinical animal model using our novel and safe STAT3 inhibitor of HO-3867. Methods: We start with culturing the primary cancer cell lines from various human ascites and confirming the status of STAT3 signaling. The exact role that STAT3 plays in ovarian cancer was addressed using STAT3 knocked down and STAT3 overexpression cell lines. These were further used to develop an orthotopic mouse model of ovarian cancer. In vivo antitumor activity of STAT3 inhibitor of HO-3867 assessment was done by oral administration of HO-3867 in orthotopic tumor mice. using histopathological analysis, RPPA, TUNEL and angiogenesis assays. In vivo bio-absorption of HO-3867 compounds in tumors by EPR and LCMS analysis. Results: We have found that pSTAT3 Tyr705 is constitutively expressed in the patient ascites derived cancer cells (ADCCs) and the range of expression could be very high to low. Subsequent in vivo transplantation of ADCCs with higher pSTAT3 expression injected into mice resulted in a large primary tumor and widespread metastases; while the mice with cells with STAT3 Knocked out had a smaller tumor and no metastases. We further demonstrate that the cytokines secreted into the culture medium can activate the JAK/STAT pathway in the STAT3 Ko cells thereby making up for the absence of inherent STAT3 in the cells. Once we proved the importance of STAT3 in ovarian cancer progression and metastases, we moved on to targeting STAT3 using our novel STAT3 inhibitor and pre-clinical orthotopic tumor model. Treatment with HO-3867 (100 ppm) significantly suppressed ovarian tumor growth and metastasis. A substantial amount of HO-3867 was detected in the ovarian tumor tissues. Suppression of STAT3 and its downstream target proteins were confirmed with reverse phase protein array. In vivo Matrigel assay showed that HO-3867 treated samples had significantly reduced vessel formation (∼4 times) when compared to untreated control. HO-3867 was also found to have cytotoxic effects in ex vivo culture of freshly collected human tumor samples, including patients with chemotherapy-resistant disease. Conclusions: Our study has concluded that constitutive expression of STAT3 in patient ascites is a significant contributor in ovarian tumor invasion and metastasis. STAT3-selective targeting agent HO-3867 in orthotopic ovarian tumor and ex vivo tumor tissue culture, results in inhibition of tumor growth and induction of apoptosis both in vivo and ex vivo, suggesting that HO-3867 is an exciting new cytotoxic agent acting through targeting STAT3; which could have a considerable role in the future treatment of ovarian cancer. Citation Format: Uksha Saini, Shan Naidu, Adam C. ElNaggar, Hemant K. Bid, John Wallbillich, Ross Wanner, Kristin Bixel, Maria Riley, Chelsea Bolyard, Adrian A. Suarez, Balveen Kaur, Periannan Kuppusamy, John Hays, Paul Goodfellow, David E. Cohn, Karuppaiyah Selvendiran. Elevated STAT3 expression in ovarian tumor ascites regulates invasion and metastasis: a promising therapeutic target. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-036.