Pancreatic Cancer-Derived Exosomes Cause Paraneoplastic β-cell Dysfunction

Purpose: Pancreatic cancer frequently causes diabetes. We recently proposed adrenomedullin as a candidate mediator of pancreatic beta-cell dysfunction in pancreatic cancer. How pancreatic cancer-derived adrenomedullin reaches beta cells remote from the cancer to induce beta-cell dysfunction is unknown. We tested a novel hypothesis that pancreatic cancer sheds adrenomedullin-containing exosomes into circulation, which are transported to beta cells and impair insulin secretion. Experimental Methods: We characterized exosomes from conditioned media of pancreatic cancer cell lines (n = 5) and portal/peripheral venous blood of patients with pancreatic cancer (n = 20). Western blot analysis showed the presence of adrenomedullin in pancreatic cancer-exosomes. We determined the effect of adrenomedullin-containing pancreatic cancer exosomes on insulin secretion from INS-1 beta cells and human islets, and demonstrated the mechanism of exosome internalization into beta cells. We studied the interaction between beta-cell adrenomedullin receptors and adrenomedullin present in pancreatic cancer-exosomes. In addition, the effect of adrenomedullin on endoplasmic reticulum (ER) stress response genes and reactive oxygen/nitrogen species generation in beta cells was shown. Results: Exosomes were found to be the predominant extracellular vesicles secreted by pancreatic cancer into culture media and patient plasma. Pancreatic cancer-exosomes contained adrenomedullin and CA19-9, readily entered beta cells through caveolin-mediated endocytosis or macropinocytosis, and inhibited insulin secretion. Adrenomedullin in pancreatic cancer exosomes interacted with its receptor on beta cells. Adrenomedullin receptor blockade abrogated the inhibitory effect of exosomes on insulin secretion. beta cells exposed to adrenomedullin or pancreatic cancer exosomes showed upregulation of ER stress genes and increased reactive oxygen/nitrogen species. Conclusions: Pancreatic cancer causes paraneoplastic beta-cell dysfunction by shedding adrenomedullin(+)/CA19-9(+) exosomes into circulation that inhibit insulin secretion, likely through adrenomedullin-induced ER stress and failure of the unfolded protein response. (C) 2014 AACR.