Introduction: Prostate cancer (CaP) is the most common malignancy and the second leading cause of cancer-related death in men in the US. The etiology of CaP is currently unclear, making primary prevention unfeasible. Early detection and treatment of prostate tumors that are localized to the prostate significantly improves the clinical outcome of CaP patients. Measuring PSA levels in blood is widely used for early detection of CaP, albeit it suffers from low specificity. There is, therefore, a need for more specific tumor markers for early detection of prostate cancer. Purpose: The objective of this study was to identify and characterize novel proteins identified in the conditioned media (CM) of three CaP cell lines: PC3, LNCaP, and 22Rv1. We hypothesize that the secreted and shed membrane proteins from these cell lines represent candidate biomarkers for CaP. Methods: The cell lines were first cultured in RPMI1640 media with 8% FBS for 48 hours, after which the media was changed to serum-free media for 48 hours. The CM was dialysed O/N, lyophilized, then reduced, alkylated, trypsin digested and fractionated by strong cation exchange (SCX) chromatography. Twenty fractions were collected from each SCX run, each of which were lyophilized and analyzed by reversed phase C-18 LC-MS/MS using an LTQ mass spectrometer. The mass spectra were searched via Mascot database searching. The proteins identified from each cell line were compared as shown in the following figure. After the comparisons were made, overlapping regions (shaded black in the figure) were selected for further study for their potential as CaP biomarkers. Criteria used for selection included: selecting secreted and membrane proteins, novel proteins that had not been previously characterized as a biomarker, proteins associated with CaP or other cancers, proteins expressed differentially in cancer, and proteins showing preferential expression in the prostate. These proteins are candidates for validation as CaP biomarkers. Outlook: Systematic proteomic and bioinformatic analysis of the secreted proteome of CaP cell lines may reveal proteins that could be biomarkers of CaP and other carcinomas.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]