| Abstract: |
Total levels of circulating prostate-specific antigen (tPSA) are strongly associated with prostate cancer (PCa) risk and outcome but benign prostate disease is the most frequent cause of a moderately elevated PSA level. Free PSA (fPSA) forms are independently associated with PCa risk and contribute modest diagnostic enhancements above and beyond tPSA alone. We developed an immunoassay for fPSA subfractions containing internal cleavages at Lys145 or Lys146 (fPSA-N). The assay was based on blocking intact single-chain fPSA (fPSA-I) with antibody 4D4 which does not detect PSA containing internal cleavages at Lys145 or Lys146. We also measured fPSA-N in blood from healthy volunteers and in anti-coagulated plasma from 76 men with or without evidence of PCa at biopsy. The analytical and functional detection limits of this assay were 0.016ng/mL and 0.10ng/mL, respectively. The median recovery of male fPSA-N from female plasma was 95.0%. All 12 female samples (average age 28years) had fPSA-N concentrations at or below the analytical detection limit. The median fPSA-N concentration (0.050ng/mL) in 9 healthy male volunteers (age<40years) was below the functional detection limit, 0.420ng/mL in 27 patients with benign prostate conditions and 0.239ng/mL in 49 patients with PCa. Deming regression analysis of the patient samples showed that the measured fPSA-N concentrations were generally 23% lower than the previously calculated (fPSA minus fPSA-I) concentrations, likely due to differences in the antibody combinations used. In conclusion, we have developed a sensitive, specific and direct immunoassay for fPSA-N which can be used to study the clinical relevance of this PSA isoform. © 2011 Elsevier B.V. |
