Prostate cancer is a slow growing disease that is regulated by androgen dependent gene pathways and its progression can be influenced by the treatment to which patients are exposed. Currently, patients who fail the first line treatments of surgery or radiation usually undergo androgen deprivation therapy (ADT). Among these, 25-40% of cases develop castrate resistance prostate cancer (CRPC) with a rise in serum levels of prostate specific antigen (PSA), used as a marker of tumour growth, and continue to progress with metastatic disease.
Exosomes are vesicles constitutively secreted by cells, which range from 30-100 nm in diameter. Their size and content vary depending on their cell type of origin. Exosomes contain mRNA and small functional RNA, the microRNA (miRNA), and multivesicular bodies (MVB) associated proteins e.g. heat shock proteins, signal transduction intermediates and metabolic enzymes, and transmembrane proteins such as the integrins, tetraspanins, cytoskeletal proteins, MHC class I and II. In addition to shared common proteins, these tumour-derived exosomes express an array of antigens that reflect the originating tumour cells. Exosomes secreted by a tumour can trigger an immune response in the tumour microenvironment and have been shown to support tumour escape and growth. This support the notion that exosomes are involved in cell to cell communication and membrane exchange between cells. There is currently much interest in tumour derived exosomes, as their protein and RNA content may provide potential biomarkers and indicate prognosis for patients with prostate cancer.
