Prosaposin, a novel tumor marker for prostate cancer

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DESCRIPTION (provided by applicant): Identification of tumor markers that are expressed at high amounts only in malignant state and correlate with disease stage and progression are needed to improve the diagnosis and treatment of prostate cancer (PCa). We have cloned prosaposin from the poorly differentiated androgen-independent (Al) PCa cell line, PC-3. Our results to date show: 1) prosaposin expression is higher in metastatic Al than in androgen-dependent (AD) PCa cells, 2) serum levels of prosaposin is higher in hormone-refractory PCa patients than in the normal male population, 3) prosaposin gene is amplified in PCa cells and punch biopsy specimens of prostate cancer xenografts and metastatic lymph nodes, and 4) prosaposin stimulates growth, migration, and invasion and acts as a cell survival and anti-apoptotic factor in both AD and Al PCa cells. These results lead us to propose the hypothesis that prosaposin contributes to prostate carcinogenesis and has the characteristics of a PCa tumor marker. Thus, the goal of this project is to establish the usefulness of this molecule as a tumor marker for prostate cancer. The Specific Aims of this R21 project are: 1. To assess, in proliferating tumor cells from prostate cancer tissues, the relationship between prosaposin expression and patients' Gleason's score and serum-PSA level. We will use immunohistochemical staining and tissue microarray to measure prosaposin expression level in proliferating (Ki-67 positive) tumor cells and its relationship with the two most important current predictive factors, Gleason's score (GS) and PSA. 2. To define the clinical significance of prosaposin expression as a marker of differentiation or disease progression in prostate cancer. Using sensitive quantitative laser capture microdissection, Real-Time PCR, and DELFIA-prosaposin immunoquantification assays, we will: a) in frozen tissue sections of radical prostatectomy specimens, assess the correlation between prosaposin (mRNA and protein) expression and dominant Gleason's pattern (as a measure of glandular differentiation), and b) in sera from patients, evaluate the relationship between prosaposin and metastatic versus non-metastatic PCa, hormone-sensitive versus hormone-refractory, and other prognostic or risk factors (e.g., PSA, GS, age, race) Significance. The results of this exploratory (R21) project will provide the basis for design of future large- scale prospective clinical investigation that will test the validity, reliability, and predictability of prosaposin as a tumor marker in relationship to PCa severity, progression, response to treatment, and outcomes.