Abstract A22: Functional analysis of PGE2 pathway members EP4 and MRP4 in ovarian cancer
Authors: Ching Mc Millan , Fan Cong , Roque Dana , Rao Gautam , Staats Paul , Fulton Amy , Reader Jocelyn 
Published: August 2018

Abstract
Ovarian cancer is the leading cause of death from gynecologic malignancy in the United States. Most cases of ovarian cancer present in late stages, leading to recurrent disease that is incurable and often fatal due to innate or acquired chemoresistance; therefore, new therapies are desperately needed. Cyclo-oygenases, COX-1 and COX-2, are enzymes that catalyze the production of the prostaglandin E2 (PGE2), a lipid mediator that is functionally linked to progression of many cancers including breast and ovarian cancer. PGE2 is exported from the cell via multidrug resistance-associated protein 4 (MRP4) where it acts in a paracrine and autocrine manner by activating a family of four G-protein coupled receptors (EP1-4) that are linked to different intracellular signaling pathways. EP2 and EP4 can activate PKA/cAMP, PI3K, and ERK pathways. COX-1 and COX-2 have been shown to be overexpressed in primary ovarian cancer as well as in many ovarian cancer cell lines. We hypothesized that the EP4 receptor is overexpressed in ovarian cancer; that binding of its cognate ligand, PGE2, will drive ovarian cancer progression; and that inhibition of the EP4-mediated signaling will lead to inhibition of ovarian cancer growth and metastasis.
In order to test this hypothesis, we analyzed the expression of the EP4 receptor in a human ovarian cancer tissue microarray (TMA) as well as human ovarian cancer cell lines. Immunohistochemical analysis of EP4 on the TMA composed of varying histologies, including serous, endometrioid, and clear cell, as well as normal ovarian tissue revealed that EP4 was expressed in 38.7% of ovarian cancer patients, whereas EP4 was not expressed in the 10 normal ovarian tissue samples. Additionally, in comparison to immortalized human ovarian surface epithelial (HOSE) cells, EP4 is overexpressed in many of the cell lines analyzed, including OVCAR-3, COAV-3, SKOV3, and Kuramochi cells. Blockade of the EP4 receptor via antagonist or siRNA results in a decrease in proliferation, migration, and invasion in ovarian cancer cell lines.
In addition to overexpression of EP4, MRP4 was also found to be overexpressed in ovarian cancer cell lines when compared to HOSE cells. Given the role of MRP4 in exporting PGE2 and affecting drug resistance/ sensitivity in breast cancer cell lines, we hypothesize that MRP4 will similarly play a role in modulating the amount of PGE2 in the microenvironment in ovarian cancer, thereby affecting signaling via of EP4 receptor. Functional testing of dual EP4/ MRP4 inhibition may provide much-needed new therapies for the treatment of ovarian cancer.
Citation Format: Mc Millan Ching, Cong Fan, Dana Roque, Gautam Rao, Paul Staats, Amy Fulton, Jocelyn Reader. Functional analysis of PGE2 pathway members EP4 and MRP4 in ovarian cancer. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A22.