Pancreatic cancer (PC) remains one of the leading causes of cancer-associated deaths in the US due to its highly aggressive nature and lack of effective treatments. Pancreatic tumors are characterized by a dense, desmoplastic reaction and poor vasculature leading to reduced oxygen levels within the tumor microenvironment. It is believed that this encounter of pancreatic tumor cells to intratumoral hypoxic condition is a major cause of their persistent survival under a variety of stresses, increased aggressiveness and therapeutic-resistance. However, underlying molecular mechanisms responsible for PC's adaptation to hypoxia (along with enhanced growth and aggressiveness) remain elusive. In this study, we examined the role of exosomes, which are nanoscale biological vesicles with a lipid bilayer membrane, in imparting survival benefit to PC cells. For this, we first examined the effect of conditioned media (CM) from PC cells cultured under hypoxic (0.1% O2, H-CM) or normoxic (21% O2, N-CM) conditions on the growth of fresh PC cells cultured under hypoxic (0.1% O2) conditions. We found that H-CM conferred significant survival benefit to cancer cells under hypoxia as compared to N-CM. Thereafter, we isolated exosomes from N-CM (N-exo) or H-CM (H-exo) and used them to treat pancreatic cancer cells under hypoxic culture conditions. We observed that H-exo imparted a significantly higher survival advantage to cancer cells under hypoxia as compared to N-exo. Interestingly, protein quantification indicated the presence of higher levels of exosomes from cells cultured under hypoxic conditions as compared to those grown in normoxic environment. Western blot analysis with anti-CD9 and anti-CD63 antibodies confirmed enrichment of exosomes. Moreover, Dynamic Light Scattering-based size distribution suggested that H-exo were smaller in size compared to N-exo. Further studies are underway to identify the molecular determinants in exosomes responsible for inducing growth-promoting effects under hypoxia. Overall, our data provides the first evidence that hypoxic PC cells secrete exosomes that enhance survivability under hypoxic conditions.
Citation Format: Mary C. Patton, Haseeb Zubair, Girijesh K. Patel, Seema Singh, Ajay P. Singh. Exosomes from hypoxic pancreatic cancer cells confer resistance to subsequent hypoxia insult. [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 2799.