STUDY OF FREE AND COMPLEXED PROSTATE-SPECIFIC ANTIGEN IN MICE BEARINGHUMAN PROSTATE-CANCER XENOGRAFTS

BACKGROUND. Our objective was to evaluate five preclinical prostate ca ncer (CaP) xenograft models to determine whether (1) prostate-specific antigen (PSA) formed complexes in murine serum, (2) the percentage of free PSA (f-PSA) was characteristic of a given xenograft line, and (3 ) the percentage of f-PSA was similar to that in the patient at time o f tumor harvest. Our fourth objective was to identify which murine ser pin(s) bind(s) to PSA in vivo. METHODS. Xenografts were established fr om metastatic foci. The percentage of F-PSA, and total PSA (t-PSA) in serum of animals bearing Cap xenografts was determined by immunoassay. Size exclusion high-performance Liquid chromatography and Western blo ts were used to evaluate the presence of PSA complexes in murine serum . Edman degradation was used to determine the N-terminal sequence of c omplexed proteins. RESULTS. PSA was detected as both free and complexe d forms in murine serum from all mice bearing the CaP xenografts. Thre e xenografts (related sublines) produced PSA that resulted in low mean percentages of f-PSA (1.9-6.4%). In sera from the other two xenograft s, the mean percentages of f-PSA were high (>25%); patient sera, where available at time of tumor acquisition, were in agreement. Western bl ots showed that murine protease inhibitors formed complexes with PSA. Edman degradation yielded a sequence with 80% homology over 15 amino a cids with that of murine alpha(1)-protease inhibitor (alpha(1)-PI). CO NCLUSIONS. Our data have shown that the majority of PSA secreted by th ese Cap xenografts complexes in murine serum with a protease inhibitor with high homology to murine alpha(1)-PI and that the percentage of f -PSA is a characteristic of each xenograft line tested, which is in ag reement with patient values at time of tumor harvest. These CaP xenogr afts offer opportunities for study of human PSA biology and phenomenol ogy. Prostate 36:194-200, 1998. (C) 1998 Wiley-Liss, Inc.