Abstract MIP-061: RAC 1 AND CDC42 GTPASES AS REGULATORS OF OVARIAN CANCER PROGRESSION AND NICHE INTERACTIONS

Abstract

Abstract PURPOSE OF THE STUDY: The Ras-homologous (Rho) family GTPases Rac1 and Cdc42 contribute to metastatic dissemination through regulation of actin reorganization, cell motility, cell-cell and cell-extracellular matrix adhesion. The purpose of the study was to investigate the contributions of these GTPases in ovarian cancer progression. EXPERIMENTAL PROCEDURES: GTPase target expression and activity was determined by analysis of The Cancer Genome Atlas (TCGA), immunohistochemistry of ovarian cancer tissues and enzymatic assays of patient samples. The effects Rac1 and Cdc42 expression were investigated by comparing cell behaviors in vitro and in vivo in engineered cell lines and use of inhibitors of Rac1, Cdc42 or dual inhibition by the R-enantiomer of ketorolac. SUMMARY OF THE DATA: Expression of the constitutively active Rac1 splice variant Rac1b and elevation of Cdc42 protein were detected in advanced ovarian cancer specimens thus providing the first evidence for dysregulation of these GTPase targets in ovarian cancer. To confirm the importance of Rac1, RNA-seq gene expression data from 305 Stage III or IV ovarian cancer samples were downloaded from The Cancer Genome Atlas (TCGA) and evaluated for RAC1 gene expression. The samples with the highest Rac1 RNA levels had significantly worse (p=0.039) age adjusted survival than the patients with the lowest Rac1 levels. Additional analyses identified more than 4,000 genes that were differentially expressed (FDR corrected p <0.05) between these patient groups. Gene Ontology analysis revealed several highly enriched biological processes including: extracellular matrix organization (67 genes p=1.60E-25), multicellular organismal catabolic processes (29 genes p=4.30E-22), regulation of epithelial cell proliferation (30 genes p=6.10E-09 and regulation of cell migration (48 genes p=1.50E-08). Relevance of the pathway analyses is illustrated by experimental evidence that increased GTPase expression leads to enhanced homing and engraftment in the omental niche; suggesting that elevated activity detected in patients may contribute to disease progression. Conversely, dual inhibition of Rac1 and Cdc42 activity by R-ketorolac inhibits ovarian patient-derived tumor cell adhesion and invasion, omental homing and tumor implantation in a mouse xenograft model. CONCLUSIONS: These findings indicate that high expression of Rac1 is associated with late stage disease and/or poor patient survival and with genes involved in extracellular matrix, cell proliferation and cell migration. These functions of Rac1 were confirmed in experimental models and inhibition of protein activity provided anti-tumor benefit in vivo. Together, these data suggest that Rac1 and/or Cdc42 function as drivers of ovarian cancer and may represent novel therapeutic targets to improve ovarian cancer outcome. Citation Format: Hudson LG, Kenney SR, Rivera, M., Weisend, J. Luo, L., Ness, S., Gillette, JM, Wandinger-Ness A. RAC 1 AND CDC42 GTPASES AS REGULATORS OF OVARIAN CANCER PROGRESSION AND NICHE INTERACTIONS [abstract]. In: Proceedings of the 11th Biennial Ovarian Cancer Research Symposium; Sep 12-13, 2016; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(11 Suppl):Abstract nr MIP-061.