Exosomes: Novel Biomarkers or Therapeutic Targets?

Prostate cancer (PCa) is the leading type of cancer diagnosed in men. In 2010, approximately 217,730 new cases of prostate cancer were reported in the USA. Prompt diagnosis of the disease can substantially improve its clinical outcome. Improving capability for early detection, as well as developing new therapeutic targets in advanced disease are research priorities that will ultimately lead to better patient survival. Exosomes are extracellular membrane vesicles which are formed in the endosomal compartment of cells and secreted upon fusion of multivesicular bodies with the plasma membrane. They have been shown to be derived from a multitude of cell types and, while it is postulated that they are important for membrane trafficking as communication vesicles, their relevance in PCa initiation and specifically prostate tumor growth and progression has yet to be determined. Studies on tumor-related microvesicles suggest that exosomes play a significant role in cell communication thus potentially influencing cancer progression via different mechanisms. The presence of distinct exosomal protein markers for cancer progression combined with the presence of exosomes in accessible biological fluids also suggests a potential role of exosomes as clinical biomarkers for PCa at diagnosis and progression. In this study, we hypothesize that exosomes have a pivotal role in cell-cell communication in the local tumour microenvironment, conferring activation of numerous survival mechanisms during PCa progression and development of therapeutic resistance.Therefore, the specific aims of this study are: i) To characterize exosomes derived from +/- AR PCa cells in comparison with a benign prostate cell line. ii) To delineate the role of specific proteins/lipids present within exosomes which are involved in PCa progression. In this research exosomes were purified from culture media of all six different prostate cell lines using different centrifugation steps followed by a final ultracentrifugation step in sucrose cushion. Purified exosomes were further analyzed using Transmission Electron Microscopy (TEM) in addition to Western Blot analysis (WBA). Furthermore, the protein and lipid profile of exosomes were characterized using liquid chromatography-Mass spectrometry. In this study, we confirmed that exosomes are released from a range of androgen sensitive/insensitive PCa cell lines. Using WBA alongside TEM imaging, we confirmed these secreted vesicles are in fact exosomes. Proteomic and lipid analysis of exosomes derived from PCa cells has been conducted. Proteomic analysis of exosomes derived from these different PCa cells lines versus normal epithelial prostate cell reveals insightful information about protein present in the different PCa and benign prostate cells for potential biomarker elucidation. In conclusion we believe that this comprehensive proteomic and lipidomic analysis of prostate derived exosomes can form a platform for future validation of novel biomarkers and therapeutic targets in PCa.