Goodmanson, Marcia K.

AbstractBackground: Human kallikrein 2 (hK2) shares 80% sequence identity with prostate-specific antigen (PSA). Because both hK2 and hK2-α1-antichymotrypsin (hK2-ACT) complexes have been identified in patient sera, we devised an immunoassay for total hK2 [(thK2); hK2 and hK2-ACT] and evaluated it in healthy subjects and patients with prostate disease.Methods: We developed monoclonal antibodies (mAbs) with high specificity for hK2 and hK2-ACT and minimal cross-reactivity to PSA. Using these mAbs, a sandwich assay was developed and its specificity for forms of hK2 was assessed. Serum samples (n = 1035) from healthy volunteers, patients with increased PSA, and men who had undergone radical prostatectomy were assayed for thK2. We also measured thK2 in samples before and after storage under common laboratory conditions.Results: The minimum detectable concentration in the thK2 assay was 0.008 μg/L, and PSA cross-reactivity was <0.001%. The assay detected prohK2 and three different hK2–serum protease complexes. The median serum concentration of thK2 in control samples (0.013 μg/L) was significantly lower than the median in samples from patients with increased PSA concentrations (0.085 μg/L). Immunoreactive hK2 changed little in samples stored for up to 1 month at −70 °C.Conclusions: The thK2 assay recognizes all forms of hK2 that have been found in bodily fluids to date.

AbstractBackground: Human glandular kallikrein (hK2) is a serine protease that has 79% amino acid identity with prostate-specific antigen (PSA). Both free hK2 and hK2 complexed to α1-antichymotrypsin (ACT) are present in the blood in low concentrations. We wished to measure hK2 in serum with limited contribution from hK2-ACT for the results.Methods: We developed an automated assay for hK2 with use of a select pair of monoclonal antibodies. The prototype assay was implemented on a Beckman Coulter ACCESS® analyzer.Results: The detection limit of the assay was 1.5 ng/L, the “functional sensitivity” (day-to-day CV <15%) was <4 ng/L, cross-reactivity with PSA and PSA-ACT was negligible, and cross-reactivity with hK2-ACT was 2%. After surgical removal of prostate glands, serum hK2 was <7 ng/L and was <15 ng/L in most healthy women. The median serum concentration of hK2 in healthy men without prostate cancer was 26 ng/L. The median concentration of hK2 was 72 ng/L for men having prostate cancer with lower Gleason scores compared with 116 ng/L for men with more advanced cancer. The concentration of hK2 correlated weakly with PSA, with the mean hK2 concentrations generally 30- to 80-fold lower than PSA concentrations.Conclusion: The availability of a robust, high sensitivity automated assay for hK2 should facilitate further investigations of the role of hK2 measurements in the management of patients with prostate disease.

Context.— Prostate-specific antigen (PSA) is a 34-kDa glycoprotein with chymotrypsin-like enzyme activity that circulates both in free forms and complexed to various enzyme inhibitors including antichymotrypsin and α 2 -macroglobulin. Prostate-specific antigen bound to α 2 -macroglobulin is not detected by commercial PSA immunoassays. Objective.— To develop a mass spectrometry assay that detects the same forms of PSA as the immunoassays, which could serve as a reference for harmonizing PSA immunoassays. Design.— Prostate-specific antigen was immune extracted from serum, trypsin was digested, and the LSEPAELTDAVK peptide was quantitated on an API 5000 spectrometer. Calibrators were made by adding 10% free and 90% antichymotrypsin-bound PSA to female sera. The assay was standardized to the World Health Organization 96/670 reference standard. Validation of clinical utility and comparisons with 2 immunoassays (Roche cobas and Beckman Access) were performed using frozen sera aliquots from 100 men undergoing prostate biopsy (50 negative, 50 with cancer) and 5 serial samples collected over time from 5 men with advanced prostate cancer. Results.— The antibody extraction efficiency was greater than 99%. The assay has an analytic range from 1.2 to 76 ng/mL, with precision ranging from 8.6% at 1.5 ng/mL to 5.4% at 27 ng/mL. The mass spectrometry assay correlated well with 2 immunoassays. All 3 assays showed statistically equivalent separation of prostate cancer from benign disease using receiver operating characteristic curve analysis. Conclusions.— This mass spectrometry assay can reliably measure PSA concentrations in human serum and could serve as a reference standard for harmonizing PSA immunoassays.

Abstract BACKGROUND Improved tests are needed for detection and management of prostate cancer. We hypothesized that differential gene expression in prostate tissue could help identify candidate blood biomarkers for prostate cancer and that blood from men with advanced prostate disease could be used to verify the biomarkers presence in circulation. METHODS We identified candidate markers using mRNA expression patterns from laser-capture microdissected prostate tissue and confirmed tissue expression using immunohistochemistry (IHC) for the subset of candidates having commercial antisera. We analyzed tissue extracts with tandem mass spectrometry (MS/MS) and measured blood concentrations using immunoassays and MS/MS of trypsin-digested, immunoextracted peptides. RESULTS We selected 35 novel candidate prostate adenocarcinoma biomarkers. For all 13 markers having commercial antisera for IHC, tissue expression was confirmed; 6 showed statistical discrimination between nondiseased and malignant tissue, and only 5 were detected in tissue extracts by MS/MS. Sixteen of the 35 candidate markers were successfully assayed in blood. Four of 8 biomarkers measured by ELISA and 3 of 10 measured by targeted MS showed statistically significant increases in blood concentrations of advanced prostate cancer cases, compared with controls. CONCLUSIONS Seven novel biomarkers identified by gene expression profiles in prostate tissue were shown to have statistically significant increased concentrations in blood from men with advanced prostate adenocarcinoma compared with controls: apolipoprotein C1, asporin, cartilage oligomeric matrix protein, chemokine (C-X-C motif) ligand 11 (CXCL11), CXCL9, coagulation factor V, and proprotein convertase subtilisin/kexin 6.