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Prostate cancer (CaP) is the most common malignancy and the second leading cause of cancer-related death in men in the United States. The etiology of CaP is currently unclear, making primary prevention unfeasible. Therapies for advanced stages of CaP are elusive. However, early detection and treatment of prostate tumors that are localized to the prostate significantly improves the clinical outcome of CaP patients. Prostate specific antigen (PSA) is widely used for early detection of CaP, albeit it suffers from low specificity since it is more indicative of the size of the prostate, which may be due to benign prostate hyperplasia, rather than of the cancer itself. There is therefore a need for more specific tumor markers for early detection of prostate cancer. In this study, our objective was to perform comparative proteomic analysis of conditioned media from normal and prostate cancer cell lines. We hypothesize that the differentially expressed and secreted proteins may represent candidate biomarkers for prostate cancer. The prostate cancer cell lines PC3(AR)6, LNCaP and DU-145 as well as a non-malignant primary prostate cell line, PrEC were cultured in large volumes (200mL) of chemically defined serum-free media for 14 days. The conditioned media were then collected and dialysed at high pH. The dialysed media were fractionated by anion-exchange chromatography and the collected fractions were lyophilized and trypsinized. The tryptic peptides were further fractionated by reversed phase chromatography before being analyzed by electrospray ionization tandem mass spectrometery. The identified proteins from these cell lines were organized into subgroups based on their genome ontology classification of cellular location. An example for the cell line PC3(AR)6 is shown in the following figure. A total of 124 proteins were classified according to cellular location and the sample was found to contain a significant proportion of secreted or soluble proteins. The secreted and membrane-bound proteins are currently examined by ELISA as serological markers of prostatic carcinoma. In conclusion, systematic proteomic analysis of the secreted proteome of cell lines may reveal proteins which could be biomarkers of prostatic and other carcinomas.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]