The male prostate gland is a walnut-sized structure responsible for controlling the flow of urine and adding fluid to contribute to the total volume of semen produced. Prostate cancer is the second leading cause of death among men, with 1 in 7 men being diagnosed in his lifetime. Prostate cancer can be detected currently by measuring the PSA (prostate specific antigen) levels in the blood; however this is not a reliable and specific test and can lead to over-diagnosis and treatment. The search for a non-invasive, reliable biomarker is therefore of great importance.
Exosomes are quickly emerging as a rich source of tumor-specific proteins and could provide the answer for a prognostic and diagnostic tool for prostatic cancer. This is because when exosomes are released, they contain a specific set of molecules from their site of origin. The exosomes secreted by the prostate can be isolated from the patients serum or urine to allow further exosomal protein analysis to take place. Protein levels identified can then be used to determine tumor characteristics and help devise an appropriate treatment plan.
Recently, Duijvesz and colleagues (2013) carried out research to identify which exosomal proteins can be used as diagnostic biomarkers for prostate cancer . Exosomal proteins were compared from exosomes derived from non-cancerous prostate cells and normal control cells to measure their presence and significance. The exosomes were identified using electron microscopy, before fixation and staining. Mass spectrometry analysis was then carried out on each exosome to determine the protein composition.
Analysis revealed 4 candidate protein biomarkers, which had a different abundance between the two exosome populations, for prostate cancer (PDCD6IP, FASN, XPO1 and ENO1). These results provide hope for the emergence of exosomal protein profiling as a non-invasive and specific diagnostic tool of the future for prostate cancer.
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 Duijvesz, D. et al. Proteomic Profiling of Exosomes Leads to the Identification of Novel Biomarkers for Prostate Cancer. Dec 2013. PLoS ONE. 8: e82589. doi:10.1371/journal.pone.0082589.