Enzyme immunoassay for prostate-specific antigen and its diagnostic application in prostate cancer

The purpose of this study was to develop a reliable screening test for prostate cancer. Monoclonal antibodies specific to the prostate-specific antigen (PSA) were generated with an improved hybridoma technique. The hybrid cells were initially cultured in a semisolid medium containing methylcellulose and later transferred to a liquid medium for further subculture. Thirty-six out of a total 1,250 recovered colonies were shown to exhibit a high affinity to PSA by radioimmunobinding assay. Eight hybrid cell lines which secreted either IgG1 or IgG2a antibodies of a high affinity and specificity were established for evaluation. The association constants between PSA and these monoclonal antibodies were shown to range from 1 x 10(9) to 5 x 10(9) M-1. From the results of a matrix cross-matching procedure, pairs of monoclonal antibodies were identified and the corresponding epitopes assigned, and most of them could also be paired with rabbit anti-PSA in a typical sandwich enzyme immunoassay. The designated EIA procedure was performed over 90 minutes at room temperature in a two-stage incubation protocol with a sensitivity of 0.4 ng/mL. The EIA kit was shown to have little cross-reactivity with thyroid stimulating hormone, alpha-fetoprotein, carcinoembryonic antigen and prostate acid phosphatase. Preliminary evaluations with clinically defined patients' sera revealed that proper selections of antibody pairs in sandwich immunoassays are crucial to the adequate performance of the EIA kits.