Abstract DPOC-001: CANCER STEM CELLS: THE SEEDS FOR RECURRENT OVARIAN CANCER

PURPOSE: The treatment of ovarian cancer (OC) with chemotherapy leaves resistant cancer cells which in a short time re–grow as recurrent cancer. A diverse array of resistance mechanisms for chemotherapy in tumor cells has been described but none has proven to be a viable target in a clinical setting. Cancer stem cells (CSCs) are increasingly accepted as the putative mediators of chemoresistance and relapse of cancer. This study aimed to understand the molecular mechanisms involved with chemoresistance and recurrence by investigating the roles of CSCs and their associated pathways in OC cell lines and tumor cells isolated from the ascites of OC patients. METHODS: Tumor cells were collected from chemonaive (CN) and recurrent (CR) OC patients diagnosed with advanced–stage serous OC using a novel in vitro method to obtain a distinct population of epithelial tumor cells. Flow cytometry and immunofluorescence were used to characterize the tumor population. High–resolution label–free quantitative proteomic profiling was used to define significantly differentially expressed proteins between CN and CR tumor cells. KEGG and DAVID software9s were used to determine pathways associated with CR cells. The mechanisms of survival of in vitro cisplatin or paclitaxel treated ascites–derived tumor cells as well as cultured OC cell lines were determined by in vitro assays and in mouse xenografts. In another approach, the expression of embryonic stem cell factor Oct4A was determined in primary ovarian tumors and its functional role was investigated using in vitro assays and in vivo mouse models with stable knockdown (shRNA) of Oct4A in OC cell lines. RESULTS: Proteomic profiling of CN and CR tumor cells showed significant differences in proteins encoding for immune surveillance, DNA repair mechanisms, cytoskeleton rearrangement, cell–cell adhesion, cell cycle pathways, cellular transport, and proteins involved with glycine/proline/arginine synthesis in tumor cells isolated from CR relative to CN patients. Pathway analyses revealed enrichment of metabolic pathways, DNA repair mechanisms and energy metabolism in CR tumor cells. The treatment of ascites–derived OC cells with chemotherapy in vitro resulted in a CSC–like residual population with increased activation of JAK2/STAT3 pathway. Both JAK2/STAT3 activation and CSC–like characteristics were suppressed by a low dose JAK2 specific inhibitor, Momelotinib, in vitro and in vivo. This also resulted in a significantly reduced tumor burden and increased disease–free survival periods in mice in vivo. In another approach, stable knockdown of Oct4A resulted in the decreased expression of CSCs in OC cells and was consistent with decreased cell proliferation, migration and chemoresistance in vitro. In vivo Oct4A knockdown cells produced a significantly reduced tumor burden in mice resulting in a significantly increased disease–free survival periods compared to vector control cells. CONCLUSION: The above studies suggest that targeting the CSCs may prove a therapeutic option for advanced–stage OC patients. Citation Format: Nuzhat Ahmed, Emily Chan, Chantel Samardzija, Khalid Abubaker, Ardian Latifi, George Kannourakis & Jock Findlay. CANCER STEM CELLS: THE SEEDS FOR RECURRENT OVARIAN CANCER [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 DPOC-001.