Concentration of enzymatically active prostate-specific antigen (PSA) in the extracellular fluid of primary human prostate cancers and human prostatecancer xenograft models

BACKGROUND. Prostate-specific antigen (PSA) targeted prodrugs are under dev elopment in our laboratory. Concentrations of total PSA and enzymatically a ctive PSA produced by various human prostate cancer xenograft models have n ot been well characterized. METHOD. The concentration of PSA secreted into the extracellular fluid (ECF ) in normal human prostate tissue, primary prostate cancers obtained direct ly from patients, and serially passageable human prostate cancer xenografts (PC-82, LNCaP, LAPC-4) were determined using Tandem assays. Percent enzyma tically active PSA in the ECF and in conditioned media was also determined using a previously validated assay employing a monoclonal antibody to the P SA catalytic site. In addition, the concentration and activity of PSA withi n sera from men with and without prostate cancer, as well as from tumor-bea ring animals, was likewise assayed. RESULTS. Normal human prostate tissue and primary human prostate cancers ha ve high concentrations of PSA in the ECF (i.e., 1600-2100 nM). The majority of this PSA is enzymatically active (i.e., 80-90%). Human PC-82 prostate c ancer xenografts also have high concentrations of PSA in the ECF (624 +/- 3 60 nM), and the majority of this PSA is also enzymatically active (i.e., 66 +/- 4%). In contrast, much lower concentrations of PSA are found in the EC F from LNCaP (45 +/- 9 nM) and LAPC-4 (7.3 +/- 0.6 nM). Only a small portio n of the total PSA isolated from DHT-containing, serum-free, conditioned me dia from these cell lines is enzymatically active (i.e., similar to 18%). W hile PSA was detected in all serum samples regardless of the type of host, no enzymatically active PSA was detected in any of these serum samples. CONCLUSIONS. Prostate cancers obtained directly from patients produce and s ecrete large amounts of PSA, the majority of which is highly enzymatically active. In contrast, while PSA was detected in the sera, none of this PSA w as enzymatically active. This is also the case for the human PC-82 prostate cancer xenografts. In contrast, LNCaP and LAPC-4 human prostate cancer xen ograft models secrete similar to 70-300-fold less PSA in the ECF than prost ate cancers from patients and the majority of this PSA is enzymatically ina ctive. Also, the serum from these animals had detectable PSA, but none of t his PSA was enzymatically active. Thus, these latter two prostate cancer mo dels define the least and the PC-82, the most, optimized xenograft model fo r screening PSA targeted prodrugs. Prostate 48:1-6, 2001.. (C) 2001 Wiley-L iss, Inc.