Characterization of monoclonal antibodies for prostate-specific antigen and development of highly sensitive free prostate-specific antigen assays

BACKGROUND: The recent elucidation of the importance of serological free prostate-specific antigen (PSA) in the diagnosis of prostate cancer has created a demand for immunoassays specific for free PSA. METHODS: We developed and characterized 11 monoclonal antibodies with high affinities for PSA (Ka values from 1.1 x 10(8) to 1.8 x 10(10)L/mol), only 3 of which cross-react with human glandular kallikrein (hK2). Using these antibodies and PSA antibodies developed by others, in conjunction with time-resolved fluorometry, we developed ultrasensitive sandwich immunoassays specific for the free form of PSA. RESULTS: The analytical detection limit of these immunoassays is 0.001 microg/L. To our knowledge, this is the most sensitive free PSA assay reported to date. The free PSA immunoassays exhibit <1% cross-reactivity with PSA-alpha1-antichymotrypsin, show no cross-reactivity with hK2, and correlate well with established free PSA kits. The 11 antibodies developed by our group, in conjunction with 4 commercially available antibodies, were used to generate a putative epitope map of the PSA molecule. CONCLUSION: The highly sensitive free PSA immunoassays may be used for measuring PSA subfractions in female serum, an application currently impossible with other reported free PSA immunoassays.