Abstract B67: Analysis of function and inhibition of PGE2 pathway members MRP4 and EP4 in treatment of ovarian cancer

Ovarian cancer has the highest mortality incidence of all gynecologic malignancies in the United States. The majority of ovarian cancer cases lead to recurrent disease that is often incurable and fatal due to innate or acquired chemoresistance; therefore, novel therapeutic interventions are desperately needed. Cyclooxygenases–COX-1 and COX-2–are enzymes that catalyze the production of prostaglandin E2 (PGE2), an important inflammatory 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. We hypothesize that the EP4 receptor has increased expression in ovarian cancer and that binding of its cognate ligand, PGE2, will drive ovarian cancer progression. We also hypothesize that alternation of the tumor microenvironment via MRP4 will also lead to inhibition of EP4-mediated signaling and affect phenotypes associated with ovarian cancer progression. In order to test this hypothesis, we analyzed the expression of the EP4 and MRP4 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 tissues, whereas EP4 had no or low expression in 10 normal ovarian tissue samples. Immunohistochemistry of MRP4 also revealed increased expression in ovarian cancer histologies compared to normal ovarian tissue. Serous, endometrioid, and clear-cell subtypes presented with a majority of 4+ and 3+ staining intensities compared to normal ovarian tissue, which presented with mostly 2+ and 1+ staining, and none of the normal ovarian tissue presented with 4+ intensity. EP4 and MRP4 also has increased expression in multiple ovarian cancer cells lines including those representing low-grade serous, clear-cell, and high-grade serous ovarian cancer. Treatment of these cell lines with an EP4 antagonist resulted in decreased proliferation and migration compared to vehicle control. Consistent with the pharmacologic data, treatment of ovarian cancer cell lines with siRNA