Abstract
Detection of circulating tumor-specific DNA, RNA or proteins can be difficult due to relative scarcity. Exosomes are extracellular vesicles, 30 - 150 nm in diameter derived from fusion of multivesicular bodies with the plasma membrane. They are composed of a lipid bilayer membrane and contain proteins, mRNA and miRNA. Exosomes are secreted by multiple cell types, including cancer cells. However, there is a relative lack of information concerning the contents of exosomes secreted by various tumor cell types. To examine exosomes in cancer, we collected blood plasma samples from patients with breast, ovarian, prostate, hepatic, gastric, colon, and pancreatic cancers. Exosomes were isolated from plasma and confirmed by AchE assay, transmission electron microscopy and expression of the CD63 exosomal marker. Expression of AFP, CA724, CA153, CEA, CA125, CA199 and PSA antigens were determined using an automated electro-chemiluminescence assay. Expression of the tumor-related chaperone protein, mortalin, was determined by Western blot analysis. Levels of exosome secretion were variable among the different tumor types. Both exosome levels and mortalin expression within tumor cell exosomes were higher than in healthy donors, except in pancreatic carcinoma, where exosomes were elevated but mortalin expression was not significantly different from healthy donors. Exosomes provide unique opportunities for the enrichment of tumor-specific materials and may be useful as biomarkers and possibly as tools of cancer therapies. Mortalin, which has been linked to cell proliferation and induction of epithelial-mesenchymal transition of cancer cells, may be useful as a prognostic bio-marker and as a possible therapeutic target.