Extracellular Vesicles as Biomarkers for Prostate Cancer

Since current molecular biomarkers lack specificity or sensitivity for PCa diagnostics, new and better markers need to be identified. The main objective of this thesis is the identification of novel candidate biomarkers for PCa by profiling extracellular vesicles.
Chapter 2 provides an overview of known and (clinically) used PCa markers. It de- scribes the clinical use of PSA, its isoforms and a range of other markers. Because the search for new and better biomarkers is hampered by the dynamic range problem, sev- eral techniques can be applied for selection and enrichment. One of those techniques is the isolation of extracellular vesicles. These vesicles contain a selection of proteins and/or RNAs that reflect cellular conditions from the cell they were shed. Chapter 3 introduces extracellular vesicles and explains it potential as a biomarker ‘treasure chest’. It also gives an update on the work that has already been performed regarding these vesicles within the field of Urology when this thesis was initiated.
In chapter 4 we address the discovery phase of biomarker detection by proteome profiling of extracellular vesicles. In collaboration with the Environmental Molecular Sci- ence Laboratory (EMSL), Richland, WA, USA, we aimed to identify proteins from vesicles released by prostate cancer cells and immortal normal prostate cells. Using mass spec- trometry and various techniques to verify our findings, we identified a series of proteins that were more abundant in vesicles from cancer cells as compared to normal prostate epithelial cells.
Our second objective was the validation of novel candidate biomarkers for prostate cancer on patient tissue samples. In chapter 5 and chapter 6 we describe the use of tissue mass spectrometry and an extensive tissue microarray to validate a few markers of interest. With these techniques we explored the diagnostic and prognostic potential of selected candidate biomarkers for PCa.
Unfortunately, current techniques for isolation and characterization of extracellular vesicles are labor intensive and unsuitable for daily clinical practice. Therefore, our third objective compromises the development of a clinically usable (high-throughput) assay to analyze extracellular vesicles from patient samples (urine or serum). In chapter 7 we describe the results of our collaboration with the department of Biotechnology of the University of Turku, Finland. Together we developed a fast, highly sensitive and reliable immunoassay (TR-FIA) that can be used for clinical implementation.
Finally, in part 3 all findings are summarized, a general discussion is provided and future perspectives recited.