162 - GPX3 supports ovarian cancer progression by manipulating the extracellular redox environment

Abstract

Ovarian cancer is the most lethal gynecologic malignancy, as most cases remain undiagnosed until considerable metastasis has occurred throughout the peritoneal cavity, resulting in 5-year overall survival rates of less than 29%. Ascites accumulation in the abdominal cavity provides a tumor-supporting medium in which metastatic ovarian cancer cells gain access to nutrients, growth factors, and cytokines that promote survival and proliferation. However, little is known about the redox status of ascites, or whether antioxidant enzymes are required to maintain an optimal redox homeostasis of this medium to support ovarian cancer survival during transcoelomic metastasis. Using gene expression cluster analysis of the major antioxidant enzymes, we identified two distinct populations of high grade serous ovarian tumors (The Cancer Genome Atlas, TCGA) that specifically clustered into high and low GPX3 expression, an extracellular glutathione peroxidase previously reported to be highly expressed in clear cell ovarian cancer and in ascites of advanced serous ovarian cancer patients. Interestingly, high GPX3 expression was associated with poorer overall patient survival. To assess whether cell survival advantages are associated with high GPX3 expression, we generated stable OVCAR3 GPX3 knockdown cell lines using lentiviral shRNA constructs. Decreased GPX3 expression inhibited clonogenicity and cell viability of OVCAR3 cells in response to treatment with H2O2 and high-dose ascorbate. GPX3 depletion resulted in increased extracellular H2O2 accumulation following ascorbate treatment, as measured by Amplex Red. Investigating the iron and oxidation reduction potential (ORP) of a cohort of 11 ovarian cancer patient ascites samples revealed heterogeneity in ascites ORP between patients and a positive correlation between iron content and ORP. GPX3 was necessary for overall cell survival in ascites. However, this did not correlate with ascites iron content or ORP. Collectively, our data suggest that GPX3 is a necessary antioxidant responsible for protection of ovarian cancer cells during metastatic spread in the peritoneal cavity.