Abstract B030: PAX8 modulates the tumor microenvironment of high grade serous ovarian cancer through changes in the secretome
Authors: Salvi Amrita , Hardy Laura R. , Heath Kimberly N. , Watry Samantha , Pergande Melissa R. , Cologna Stephanie M. , Burdette Joanna E. 
Published: January 2023

Abstract
High grade serous ovarian cancer (HGSC), the most common and lethal form of ovarian cancer, is a highly heterogeneous disease. HGSC is rarely detected early, and likely arises from the fimbriated end of the fallopian tube epithelium (FTE), and in some cases, the ovarian surface epithelium (OSE). PAX8 is a commonly used biomarker for ovarian serous tumors and is expressed in ~90% of HGSC. Although the OSE does not express PAX8, murine models of HGSC derived from the OSE acquire PAX8, suggesting that it is not only a marker of Müllerian origin, but also an essential part of cancer progression, potentially from both the OSE and FTE. Our data shows that PAX8 loss by CRISPR and shRNA in HGSC cell lines causes tumor cell death and reduces cell migration and invasion. Additionally, loss of PAX8 significantly reduced tumor burden in a xenograft model of HGSC. Herein, secretome analysis was performed on PAX8 deleted cells, and we identified a reduction of the extracellular matrix (ECM) components, collagen and fibronectin. Immunoblotting and immunofluorescence in PAX8 deleted OVCAR8 HGSC cells further validated the results from the secretome analysis. PAX8 loss reduced the amount of secreted TGFbeta, a cytokine that plays a crucial role in remodeling of the tumor microenvironment. Furthermore, PAX8 loss reduced the integrity of 3D spheroids and caused a reduction of ECM proteins in 3D cultures: fibronectin and collagen. Due to the ubiquitous expression of PAX8 in HGSC, regardless of cell origin, and evidence that reducing PAX8 protein levels inhibits tumor growth, a PAX8 inhibitor could be a promising drug lead against HGSC. To accomplish this, we generated a murine oviductal epithelial (MOE) cell line stably expressing the PAX8 promoter driving luciferase reporter protein. Using this cell line, we performed a screening assay with a library of FDA-approved drugs (Prestwick Library) and quantitatively assessed these compounds for their inhibition of PAX8-luciferase. We identified two hits: losartan and captropril, both inhibitors of the renin-angiotensin pathway that inhibit PAX8 expression and function. We are currently working to monitor if these compounds reduce tumor burden via PAX8 reduction. Further, if PAX8 reduction in vivo diminishes collagen and fibronectin, this may impact immune cell infiltration via changes in the tumor microenvironment. Overall, this study validates PAX8 as a regulator of ECM deposition in the tumor microenvironment.
Citation Format: Amrita Salvi, Laura R. Hardy, Kimberly N. Heath, Samantha Watry, Melissa R. Pergande, Stephanie M. Cologna, Joanna E. Burdette. PAX8 modulates the tumor microenvironment of high grade serous ovarian cancer through changes in the secretome [abstract]. In: Proceedings of the AACR Special Conference: Cancer Metastasis; 2022 Nov 14-17; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;83(2 Suppl_2):Abstract nr B030.