Abstract 2116: Chemotherapy-induced exosomal secretion promotes chemoresistance in pancreatic cancer cells

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of death from cancer in the United States, with a dismal median survival rate of 2-8 months after diagnosis and a 5-year overall survival rate of ∼7%. It carries a notoriously poor prognosis due to advanced stage at presentation for most patients, lack of very effective therapy and development of resistance to available chemotherapy. Intercellular communication between tumor-tumor and tumor-nontumor cells is critical for tumor growth and progression. Extracellular vesicles (EVs) comprising of exosomes, microvesicles and apoptotic bodies are considered important mediators of intercellular communication and play pivotal roles in different physiological and pathological processes. However, role of EVs in the development of acquired resistance to chemotherapy in PDAC cells is largely unexplored. Here, we examined the role of EVs in chemotherapeutic resistance of PDAC cells. Methods: Conditioned media from vehicle-treated and (V-CM) gemcitabine-treated PDAC cells (Gem-CM) were collected and fractionated into soluble (Gem-Sol) and vesicular (GEM-EV) factions. PDAC cells were pre-treated with Gem-CM, Gem-Sol and Gem-EV followed by treatment with various doses (0-20 μM) of gemcitabine for different time intervals (48 and 72 h). EVs were then separated by differential ultracentrifugation, size was determined using Dynamic Light Scattering (DLS) and assessed for their chemoresistance conferring activity in PDAC cells. Immunoblotting was performed to examine the specific markers associated with EVs. Results: Both Gem-CM and Gem-EV provided significant protection to gemcitabine-treated cells, while Gem-Sol had only negligible effect. DLS based-size distribution analysis identified EVs of three different size viz. large (> 1500 nm), medium (500-1500 nm) and small (100-300 nm). Treatment of large and medium sized Gem-EVs did not show any chemoprotective effect in PDAC cells, while smaller Gem-EVs provided remarkable survival benefits to PDAC cells against gemcitabine treatment. Immunoblot data revealed that these active EVs are enriched with CD9 and CD63, specific markers of exosomes. Interestingly, we observed that exosomes of gemcitabine-treated PDAC cells were larger than those secreted by vehicle treated cells. Moreover, the amount of exosomes in Gem-CM was significantly higher as comparison to the CM of vehicle-treated cells. Studies are being conducted to identify the cargo encapsulated by exosomes responsible for exosomes-mediated chemoresistance in PDAC cells. Conclusion: Our findings suggest that chemotherapy induces secretion of exosomes in PDAC cells that enhances chemoresistance by spreading the molecular signals. Citation Format: Girijesh K. Patel, Arun Bhardwaj, Sanjeev K. Srivastava, Mohammad Aslam Khan, Seema Singh, Moh’d Khushman, Ajay P. Singh. Chemotherapy-induced exosomal secretion promotes chemoresistance in pancreatic cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2116.