Soluble urokinase plasminogen activator receptor as a prognostic marker in men participating in prostate cancer screening.

BACKGROUND: The urokinase plasminogen activator (uPA) system is involved in tissue remodelling processes and is up-regulated in many types of malignancies. We investigated whether serum levels of different forms of soluble uPA receptor (suPAR) are associated with survival and in particular with prostate cancer and cardiovascular disease mortality. METHODS: Using time-resolved fluorescence immunoassays, we measured intact suPAR [suPAR(I-III)] and intact plus cleaved suPAR [suPAR(I-III) + suPAR(II-III)] and thus calculated the amount of suPAR(II-III) in serum samples from 375 men participating in a prostate cancer screening trial. A total of 312 men were free of prostate cancer and 63 men had prostate cancer diagnosed at the time of screening. The cohort was followed for 15 years. We assessed survival using Kaplan-Meier estimation and Cox proportional hazards regression. RESULTS: The mean age at blood sampling was 64 years. In total, 152 men died during follow-up. SuPAR(I-III) and suPAR(II-III) were significantly positively associated with mortality (P = 0.001 and P < 0.0001, respectively). In a Cox regression model adjusting for age and prostate cancer status, an increase in suPAR(I-III) and suPAR(II-III) by 1-unit (ln-scale) was associated with a hazard ratio (HR) of 2.26 [95% confidence interval (CI) 1.17-4.35] and 2.53 (95% CI 1.56-4.10), respectively. There was a trend towards an increased risk of death from prostate cancer in screening-detected prostate cancer patients with increased values of either suPAR form. However, this difference was not significant and the association disappeared after adjusting for age, tumour stage, tumour grade and prostate-specific antigen. Being in the highest quartile of any of the suPAR forms was associated with a highly significant increased risk of cardiovascular death, with HR adjusted for age of 3.27 (95% CI 1.38-7.73) for suPAR(I-III) quartile 4 versus quartile 1. Conclusions. High concentrations of serum suPAR(I-III) and suPAR(II-III) were associated with poor overall survival. The association was particularly strong for death from cardiovascular disease. No similar association was found for prostate cancer after adjustment for other prognostic factors.

Reduced release of intact and cleaved urokinase receptor in stimulated whole-blood cultures from human immunodeficiency virus-1-infected patients.

The blood levels of the soluble forms of the urokinase receptor (suPAR) are increased in human immunodeficiency virus (HIV)-1-infected patients. This study investigated whether the release of urokinase-type plasminogen activator receptor (uPAR) in whole-blood cultures was affected by HIV infection. The release of different uPAR forms in whole-blood cultures incubated 24 h with or without phytohemagglutinin and lipopolysaccharide was analysed in 47 HIV patients and 19 controls. suPAR was measured by enzyme-linked immunosorbent assay (ELISA) (bulk-suPAR) and three different time-resolved fluorescence immunoassays measuring three-domain suPAR [suPAR(I-III)], three- and two-domain suPAR [suPAR(I-III) + suPAR(II-III)] and one-domain suPAR [suPAR(I)]. The uPAR release was correlated to leucocyte subpopulations and plasma levels of suPAR. The stimulated net whole-blood culture release of bulk-uPAR, uPAR(I-III), uPAR(II-III) and uPAR(I) was reduced in HIV patients (all P < 0.01), whereas the spontaneous bulk-uPAR and uPAR(I-III) release was increased in HIV patients (both P < 0.05). The stimulated uPAR release in whole-blood cultures correlated well to leucocytes and circulating suPAR levels in controls, whereas the correlation was weaker to leucocytes and nonexisting to circulating suPAR levels in HIV patients. These findings demonstrate that HIV infection affects stimulated and spontaneous uPAR release in whole-blood cultures. Given that high blood levels of suPAR in HIV patients are linked to immune activation, the perturbations in uPAR release in whole-blood cultures from HIV patients may also reflect immune activation.

Human glandular kallikrein 2 levels in serum for discrimination of pathologically organ-confined from locally-advanced prostate cancer in total PSA-levels below 10 ng/ml.

BACKGROUND: We measured serum levels of human glandular kallikrein 2 (hK2) in patients treated with radical retropubic prostatectomy (rrP) for clinically localized prostate cancer (PCa) with a total PSA (tPSA)-level below 10 ng/ml to investigate whether hK2 can be applied to preoperatively distinguish organ-confined (pT2a/b) from nonorgan-confined (> or = pT3a)-PCa more accurately than total PSA. Further, we evaluated hK2, free- and tPSA-concentrations in all pathologic stages of PCa. METHODS: 161 serum samples from men scheduled for rrP were collected 1 day before surgery prior to any prostatic manipulation. Pathologic work-up revealed > or = pT3a-PCa in 48 and pT2a/b-PCa in 113 patients. HK2-levels in serum were measured using an immunofluorometric assay with an analytical sensitivity of 0.5 pg/ml, a functional sensitivity of 5 pg/ml and insignificant cross-reactivity with PSA (< 0.005%). Total (tPSA) and free PSA (fPSA) levels were measured using a commercially available assay from which we calculated %fPSA and an algorithm that combined hK2 and PSA-levels [hK2] x [tPSA/fPSA]. Means, medians, and ranges were calculated for pT2a/b vs. >/= pT3a-PCa and for all pathologic stages. Statistical significance of differences was calculated using Mann-Whitney-U and Kruskal-Wallis tests. Calculation of receiver-operator-characteristic (ROC) curves were performed for hK2, [hK2] x [tPSA/fPSA] and tPSA to compare diagnostic performance. RESULTS: A mean tPSA level in serum of 6.12 ng/ml in > or = pT3a-PCa was not significantly different (P = 0.366) from 5.78 ng/ml in pT2a/b-PCa. Also, there were no statistically significantly different levels of fPSA (P = 0.947) or %fPSA (0.292) for these two groups. By contrast, mean hK2-level in pT2a/b-PCa of 80 pg/ml was significantly different (P = 0.004) from a mean hK2 level of 120 pg/ml in > or = pT3a-PCa as shown by Mann-Whitney-analysis Moreover, the algorithm of [hK2] x [tPSA/fPSA] was significantly lower (P = 0.0004) in pT2a/b-PCa vs. > or = pT3a-PCa. Calculation of areas under curve (AUC) by receiver-operator-characteristics (ROC) demonstrated that the AUC for hK2 (0.64) was larger and the AUC for [hK2] x [tPSA/fPSA] (=0.68) significantly larger (P = 0.007) compared to the AUC of tPSA (0.55). Furthermore, Kruskal-Wallis Test revealed a highly significant correlation to pathologic stage using hK2 (P = 0.008) and [hK2] x [tPSA/fPSA] (P = 0.0015) compared to no significant differences in serum concentration of tPSA (P = 0.296). Also at tPSA-levels from 10-20 ng/ml, the hK2-levels in pT2a/b-PCa were close to significantly different (P = 0.051) from those in men with >/= pT3a-PCa, while the algorithm of [hK2] x [tPSA/fPSA] in that tPSA-range was significantly lower (P = 0.002) in pT2a/b-PCa compared to > or = pT3a0-PCa. CONCLUSIONS: Highly significant differences in serum concentration enable hK2 to be a powerful predictor of organ-confined disease and pathologic stage of clinically localized prostate cancer, especially in the PSA-range below 10 ng/ml. As such, there are important clinical consequences for the application of hK2 for the adequate treatment of prostate cancer patients, i.e., the option of nerve-sparing surgery. (c) 2001 Wiley-Liss, Inc.

Discrimination of prostate cancer from benign disease by plasma measurement of intact, free prostate-specific antigen lacking an internal cleavage site at Lys145-Lys146.

BACKGROUND: The proportion of free prostate-specific antigen (PSA) is higher in the sera of patients with benign prostatic hyperplasia compared with patients with prostate cancer (PCa). We developed an immunoassay that measures intact, free PSA forms (fPSA-I), but does not detect free PSA that has been internally cleaved at Lys145-Lys146 (fPSA-N), and investigated whether this form could discriminate patients with PCa from those without PCa. METHODS: The assay for fPSA-I uses a novel monoclonal antibody (MAb) that does not detect PSA that has been internally cleaved at Lys145-Lys146. A MAb specific for free PSA was used as a capture antibody, and purified recombinant proPSA was used as a calibrator. The concentrations of fPSA-I, free PSA (PSA-F), and total PSA (PSA-T) were analyzed in EDTA-plasma samples (n = 276) from patients who participated in a screening program for PCa (PSA-T, 0.83-76.3 microg/L). RESULTS: The detection limit of the fPSA-I assay was 0.035 microg/L. Both the measured concentrations of fPSA-I and the concentrations of fPSA-N (calculated as PSA-F - fPSA-I) provided statistically significant discrimination of the two clinical groups. By contrast, PSA-F did not discriminate between these groups. Each of the ratios fPSA-I/PSA-F, fPSA-N/PSA-T, and PSA-F/PSA-T separated cancer samples from noncancer samples in a statistically significant manner (P <0.0001). The ratio fPSA-I/PSA-F was significantly higher in cancer (median, 59%) compared with noncancer samples (47%). CONCLUSIONS: The ratio fPSA-I/PSA-F is significantly higher in cancer compared with noncancer. The percentages of both fPSA-N/PSA-T and fPSA-I/PSA-F may provide interesting diagnostic enhancements alone or in combination with other markers and require further studies.

Measurement of circulating forms of prostate-specific antigen in whole blood immediately after venipuncture: implications for point-of-care testing.

BACKGROUND: The purpose of this study was to validate the use of whole-blood samples in the determination of circulating forms of prostate-specific antigen (PSA). METHODS: Blood samples of hospitalized prostate cancer and benign prostatic hyperplasia patients were collected and processed to generate whole-blood and serum samples. Three different rapid two-site immunoassays were developed to measure the concentrations of total PSA (PSA-T), free PSA (PSA-F), and PSA-alpha(1)-antichymotrypsin complex (PSA-ACT) to detect in vitro changes in whole-blood samples immediately after venipuncture. The possible influence of muscle movement on the release of PSA from prostate gland was studied in healthy men by measuring the rapid in vitro whole-blood kinetics of PSA forms before and after 15 min of physical exercise on a stationary bicycle. RESULTS: Rapid PSA-T, PSA-F, and PSA-ACT assays were designed using a 10-min sample incubation. No significant changes were detected in the concentrations of PSA-T, PSA-F, and PSA-ACT from the earliest time point of 12-16 min compared with measurements performed up to 4 h after venipuncture. Physical exercise did not influence the concentrations of the circulating forms of PSA. Hematocrit-corrected whole-blood values of PSA-T and PSA-F forms were comparable to the respective serum values. Calculation of the percentage of PSA-F (PSA F/T ratio x 100) was similar irrespective of the sample format used, i.e., whole blood or serum. CONCLUSIONS: We found that immunodetectable PSA forms are likely at steady state immediately after venipuncture, thus enabling the use of anticoagulated whole-blood samples in near-patient settings for point-of-care testing, whereas determinations of PSA (e.g., PSA-T, PSA-F, or PSA-ACT) performed within the time frame of the office visit would provide results equivalent to conventional analyses performed in serum.

Time-resolved fluorescence imaging for specific and quantitative immunodetection of human kallikrein 2 and prostate-specific antigen in prostatic tissue sections.

OBJECTIVES: To design protocols for specific and quantitative immunohistochemical detection of human kallikrein 2 (hK2) using lanthanide chelate-labeled monoclonal antibodies (Mabs) and time-resolved fluorescence imaging. METHODS: Anti-prostate-specific antigen (PSA) Mabs were tested in microtiterplate assays for their ability to prevent PSA from cross-reacting with the anti-hK2 Mab 6H10. Europium-labeled 6H10 and terbium-labeled anti-PSA Mab 2E9, selected as the best blocker antibody, were used for dual-label immunodetection in routinely fixed benign (n = 7) and malignant (n = 5) prostate specimens. The amounts of IgG bound in tissue were calculated from drops containing known Mab concentrations. RESULTS: The use of anti-PSA Mab 2E9 for blocking diminished the cross-reaction from 5% to 0.3%. In the analyzed tissues, there was considerable variation in staining intensity for both proteins; PSA signals varied from 0.1 to 36.6 times that of hK2, with on average 10-fold more bound anti-PSA Mab than anti-hK2 Mab. In malignant tissue, the amounts of bound IgGs were lower and more variable than in benign tissue using both the anti-PSA Mab and the anti-hK2 Mab. The variation in signal intensities for PSA and hK2 correlated significantly in benign tissue (P >0.05), but not in benign hyperplastic and malignant specimens (P <0.05). CONCLUSIONS: Quantification of two lanthanide chelate-labeled antibodies bound in the same tissue section enabled comparison of PSA and hK2 content in individual cells. The average cellular content of hK2 relative to that of PSA was consistent with previous mRNA studies. The time-resolved fluorescence imaging-based quantification method has universal applicability in fixed tissue specimens.

Production and characterization of novel anti-prostate-specific antigen (PSA) monoclonal antibodies that do not detect internally cleaved Lys145-Lys146 inactive PSA.

BACKGROUND: The nature of free, uncomplexed prostate-specific antigen (PSA) in the circulation is still unknown. In this study, we developed novel anti-PSA antibodies using PSA produced by a metastasized cancer cell line, LNCaP, as an immunogen. METHODS: Hybridoma cell lines were screened with different methods that aimed at finding antibodies specific for the forms of free PSA produced by LNCaP cell line. Obtained antibodies were further studied for their characteristics related to previously characterized monoclonal antibodies. RESULTS: Numerous anti-PSA antibodies were obtained, of which four represented unique epitopes previously unrecognized by us. One free-PSA-specific antibody was bound to PSA on two distinct epitopes, and one antibody was bound to the carboxyl-terminal peptide of PSA. Two antibodies were found to bind to the peptide sequence adjacent to the internal cleavage site Lys145-Lys146. These antibodies failed to recognize internally cleaved PSA at Lys145-Lys146. We could not find anti-proPSA antibodies despite the fact that LNCaP PSA contained more than one-half of the zymogen form of PSA. CONCLUSIONS: We report, for the first time, novel anti-PSA antibodies that do not recognize internally cleaved PSA at Lys145-Lys146 and thus are specific for intact, unclipped PSA.

Clinical value of human glandular kallikrein 2 and free and total prostate-specific antigen in serum from a population of men with prostate-specific antigen levels 3.0 ng/mL or greater.

OBJECTIVES: To investigate the clinical value of human glandular kallikrein 2 (hK2) compared with free (f) and total (t) prostate-specific antigen (PSA) in the early detection of prostate cancer (PCa). METHODS: In PCa screening conducted in 1995 to 1996 in Göteborg, Sweden, 5853 of 9811 randomly selected men (aged 50 to 66 years; median 61) accepted PSA testing; those with tPSA levels of 3. 0 ng/mL or greater were offered digital rectal examination, transrectal ultrasound, and sextant biopsies. Serum from 604 of 611 biopsied men (18% with positive digital rectal examinations, tPSA range 3.0 to 220 ng/mL, 144 men with PCa) was analyzed for hK2 (research assay) and tPSA and fPSA (Prostatus). Sera were stored at -20 degrees C for a maximum of 2 weeks for tPSA and fPSA and 3 years for hK2. RESULTS: hK2 levels and hK2 x tPSA/fPSA values were significantly elevated in men with PCa. Receiver operating characteristic data revealed that the area under the curve for hK2 x tPSA/fPSA was significantly greater than that for tPSA and greater, but not significantly greater, than that for percent fPSA. Also, the cancer-detecting sensitivity was significantly improved (P <0.05) using hK2 x tPSA/fPSA compared with tPSA and percent fPSA at specificity levels of 75% to 90%. At 75% specificity, a sensitivity of 74% was obtained compared with 64% or 54% using percent fPSA or tPSA; at 90% specificity, the corresponding sensitivity level was 55%, 41%, and 36%, respectively. CONCLUSIONS: Discrimination of men with and without PCa in a randomly selected population was improved by measuring hK2 in addition to tPSA and fPSA.

Human glandular kallikrein as a tool to improve discrimination of poorly differentiated and non-organ-confined prostate cancer compared with prostate-specific antigen.

OBJECTIVES: Human glandular kallikrein (hK2) possesses 80% structure identity with prostate-specific antigen (PSA) and is secreted by identical prostate epithelial cells. Although increasing with pathologic stage, PSA is not clinically sufficient to predict histologic grade and pathologic stage of prostate cancer (PCa) in individual cases. To address this issue, serum hK2 in various PCa grades was investigated. METHODS: Sera from 122 consecutive patients with PCa, graded as well-differentiated (G1, n = 35); moderately differentiated (G2, n = 61), and poorly differentiated (G3, n = 26) PCa, was studied. In patients who underwent radical prostatectomy (n = 42), 24 had organ-confined (pT2a-b) and 18 extracapsular (pT3a or greater) disease. hK2 was measured by an indirect immunofluorometric assay with a functional sensitivity of 0.03 ng/mL. Total PSA (tPSA), free PSA (fPSA), and PSA bound to alpha(1)-antichymotrypsin (PSA-ACT) were also measured. Multivariate logistic regression analysis was used for evaluation of the best combinations of tumor markers. RESULTS: Median hK2 and tPSA increased twofold from G1 to G2 tumors (hK2 0.07 versus 0.14 ng/mL, P <0.002; tPSA 6.1 versus 12.1 ng/mL, P <0.0002). Between G2 and G3 tumors, hK2 increased threefold (0.14 versus 0.43 ng/mL, P <0.02), and tPSA showed no significant increase (12.1 versus 26.5 ng/mL, P <0.18). The f/t PSA ratio decreased between G1 and G2 cancers (0.15 vs. 010, P <0.001); no difference was found between G2 and G3 tumors (0.10 versus 0.11, P = 0.93). However, the hK2/fPSA ratio distinguished between G1 and G3 tumors and G2 and G3 tumors (0.085 [G1] and 0.11 [G2] versus 0.22 [G3], P <0.0002 and P <0.002, respectively). Using multivariate regression analysis, the fPSA/(tPSA x hK2) ratio differentiated G2 and G3 tumors (P <0.01). In the tPSA range of 3 to 15 ng/mL, hK2, the hK2/fPSA ratio, and the fPSA/(tPSA x hK2) ratio differentiated between the G1/G2 and G3 tumors, and tPSA, the f/t PSA ratio, and PSA-ACT did not. In radical prostatectomy cases, hK2 (0.06 versus 0. 156, P <0.005) and the fPSA/(tPSA x hK2) ratio (2.104 versus 0.828, P <0.005) discriminated between pT2a-b and pT3a or greater PCa. CONCLUSIONS: hK2 significantly improved the identification of poorly differentiated (G3) tumors compared with PSA. By multivariate logistic regression analysis, the hK2/fPSA and fPSA/(tPSA x hK2) ratios further improved the detection of PCa grade. This improvement was also seen with the intermediate range of tPSA. hK2 was also helpful in the prediction of organ-confined disease. Thus, hK2 may be a useful tool for more accurate prediction of tumor grade or stage and allow better clinical decision-making.

Sensitive and specific immunodetection of human glandular kallikrein 2 in serum.

BACKGROUND: Human glandular kallikrein 2 (hK2) is expressed in the prostate and is present in serum from men with prostate cancer. Specific detection in serum is difficult mainly because of low concentrations and immunological cross-reactivity with prostate-specific antigen (PSA). Our objectives were to design an assay with improved analytical detection and functional sensitivity and nonsignificant cross-reactivity with PSA, and to characterize different immunoreactive forms of hK2. METHODS: In the assay, critical PSA epitopes were blocked with four monoclonal antibodies (MAbs) specific for PSA. Subsequently, hK2 was captured using a MAb against hK2 (5% cross-reactivity with PSA), and after washing, hK2 was detected by a europium-labeled MAb with identical affinity for hK2 and PSA. RESULTS: The analytical detection limit was <10 ng/L, and functional sensitivity was 30 ng/L. Cross-reaction with PSA was <0.01%. Between-assay imprecision was 3.1% for 1600 ng/L hK2 and 4. 8% for 160 ng/L hK2; corresponding values for within-assay precision were 1.9% and 4.5%, respectively. Complexes of hK2-alpha(1)-antichymotrypsin (ACT) were detected in vitro with -6% bias compared with the free form of hK2. Gel filtration of patient samples showed that hK2 correlated in size mainly with free hK2; only 4-19% corresponded to hK2 possibly complexed with ACT or protein C inhibitor. CONCLUSIONS: Our assay had extremely low cross-reactivity with PSA, provided a very low detection limit, and allowed close to equimolar detection of the free and complexed forms of hK2. Moreover, we found that free hK2 is the predominant immunoreactive form of hK2 in serum.

Discrimination of men with prostate cancer from those with benign disease by measurements of human glandular kallikrein 2 (HK2) in serum.

PURPOSE: To investigate the clinical value of measuring human glandular kallikrein 2 (hK2) compared with free and total prostate specific antigen (PSA-F and PSA-T) in serum from patients with prostate disease. MATERIALS AND METHODS: Serum from healthy controls, from men with benign prostate hyperplasia (BPH), clinically localized prostate cancer (PCa), and advanced PCa were analyzed for hK2 (using an in-house-research assay with detection limit of 0.05 ng./mL and <0.1% cross-reaction with PSA) and for PSA-F and PSA-T (using the Dual Prostatus assay from EG&G Wallac). RESULTS: HK2 concentrations were <0.05 ng./mL in 50/50 healthy volunteers but significantly higher (p <0.0001) and > or =0.05 ng./mL in 28/54 (52%) patients with BPH. In comparison to these men, the hK2 levels were significantly higher (p <0.0001, median 0.085 ng./mL) and > or =0.05 ng./mL in 100/136 (74%) men with clinically localized PCa. Compared with localized PCa, the hK2 levels were significantly higher (p <0.0001, median 0.57 ng./mL) and > or =0.05 ng./mL in 55/57 (96%) patients with advanced PCa. The median hK2 levels ranged from 1.3 to 1.6% of those of PSA-T in all three patient groups, whereas percent hK2/PSA-F and hK2 x PSA-T/PSA-F levels were significantly higher in cancer patients compared with those with BPH. In the discrimination of clinically localized PCa from BPH, hK2 x PSA-T/PSA-F gave the largest area under the receiver operating curve (AUC = 0.81) and significantly (p = 0.025) larger AUC than PSA-T alone (0.70). Further, at 95% sensitivity there was significant gain in specificity, and at specificity levels of 90 to 95% there was significant gain in sensitivity using the measurements of PSA-T+PSA-F+hK2 compared with analysis of PSA-T and/or percent free PSA. CONCLUSIONS: Discrimination of patients with benign prostate disease from those with prostate cancer was significantly enhanced using measurements of hK2 in addition to those of PSA-T and PSA-F. Percent hK2/PSA-F was higher in PCa than in BPH, a phenomena not yet understood.

Significance and metabolism of complexed and noncomplexed prostate specific antigen forms, and human glandular kallikrein 2 in clinically localized prostate cancer before and after radical prostatectomy.

PURPOSE: We studied plasma concentrations and elimination rates of prostate specific antigen (PSA) complexed to alpha1-antichymotrypsin and alpha2-macroglobulin, free PSA, total PSA (free PSA plus PSA alpha1-antichymotrypsin) and human glandular kallikrein 2 before, during and after radical retropubic prostatectomy for clinically localized prostate cancer. MATERIALS AND METHODS: Plasma was collected and frozen within 10 minutes after sampling from 18 patients undergoing radical retropubic prostatectomy for prostate cancer. One sample was drawn preoperatively. Subsequent sampling intervals were 5 to 20 minutes perioperatively, 2 to 4 hours during the first 12 postoperative hours and 24 to 48 hours until postoperative day 14. Free PSA, PSA alpha1-antichymotrypsin, total PSA, PSA alpha2-macroglobulin and human glandular kallikrein 2 were measured with time resolved immunofluorometric assays. RESULTS: Preoperatively PSA alpha2-macroglobulin was undetectable (less than 2 ng./ml.) in 17 of 18 patients. Human glandular kallikrein 2, free PSA and total PSA but not PSA alpha1-antichymotrypsin were significantly higher in patients with extraprostatic cancer (pT3a-pT4a, pN1) compared to those with organ confined cancer (pT2a/b). Surgical manipulation of the prostate caused no detectable elevation of human glandular kallikrein 2, PSA alpha1-antichymotrypsin or PSA alpha2-macroglobulin. In contrast, a mean 9.6-fold increase (range 3.4 to 22) in free PSA was noted 5 minutes after prostatectomy. Free PSA was eliminated from plasma in a biphasic exponential pattern with an early plasma half-life of 55 minutes and a late plasma half-life of 18 hours. PSA alpha1-antichymotrypsin decreased slowly, whereas human glandular kallikrein 2 was detectable only 12 hours after prostatectomy. PSA alpha2-macroglobulin remained at insignificant, nondetectable concentrations during the entire perioperative and postoperative period. CONCLUSIONS: Release of free PSA contributes to the elevation of plasma total PSA after prostatectomy. Free PSA is enzymatically inactive as the release does not result in subsequent elevation of PSA alpha1-antichymotrypsin or PSA alpha2-macroglobulin. Biphasic exponential elimination of free PSA may be explained by rapid extracellular redistribution (early half-life) and glomerular filtration in the kidneys (late half-life). Our data suggest rapid metabolism of human glandular kallikrein 2 but do not support suggestions of the significance in vivo of complex formations with alpha2-macroglobulin as a major means to eliminate PSA from plasma in patients with clinically localized prostate cancer.

Reactivity of anti-PSA monoclonal antibodies with recombinant human kallikrein-2.

Seventy-nine monoclonal antibodies submitted to the ISOBM TD-3 PSA Workshop were tested for their reactivity with recombinant human kallikrein-2 (rhK2). A sandwich immunofluorometric assay using polyclonal anti-prostate-specific antigen (PSA) antiserum-coated plates was used to capture rhK2 and subsequently the test antibody. The response of each test antibody was compared with 3 reference antibodies (H50, H117 and 5E4) known to react with hK2. Nine antibodies from the workshop panel failed to react with purified PSA and rhK2 in this assay and were subsequently excluded. From the remaining panel of antibodies, 11/70 showed strong reactivity with rhK2, 9/70 showed weak reactivity with rhK2, while 50/70 antibodies did not react with rhK2 in this assay format. All antibodies binding to rhK2 recognized both free and complexed PSA.

Characterization and processing of prostate specific antigen (hK3) and human glandular kallikrein (hK2) secreted by LNCaP cells.

Prostate specific antigen (PSA, hK3) in serum is predominantly complexed to alpha-1-antichymotrypsin (ACT), but a minor fraction remains in a free form despite the very large excess of serine protease inhibitors and alpha-2-macroglobulin. The fraction of free to total PSA is significantly lower in prostate cancer (CaP) compared to benign prostatic hyperplasia (BPH) which provides improved discrimination of these conditions. The molecular nature of free PSA in the circulation and the reason for its varying concentration in malignant and benign conditions is currently not known. The objective of the present investigation was to study the secretion of PSA and human glandular kallikrein 2 (hK2) by the LNCaP prostate cancer cell line, and to purify and characterize both proteins. LNCaP PSA was thoroughly characterized by immunological characterization, SDS-PAGE, isoelectric focusing, gel filtration, aminoterminal sequencing, reverse-phase chromatography, mass spectrometry and enzymatic activity measurements. LNCAP cells produced approximately equal amounts of zymogen (proPSA) and the one-chain mature form of PSA, whereas there was no evidence for the secretion of any internally cleaved forms. LNCaP cells secreted hK2 into the growth medium at about 3-5% of the amount of PSA. One-chain, mature PSA and hK2 obtained when LNCaP cells were grown in the presence of fetal bovine serum, had no enzymatic activity, but were active when the cells were grown in the absence of serum. Using enzymatically active recombinant hK2, it was possible to activate proPSA secreted by LNCaP cells. ProPSA formed two bands with high isoelectric points (8.2 and 8.4), which disappeared when proPSA was converted to mature PSA with hK2. Cancerous cells produce the zymogen forms of PSA, which by their isoelectric pI points seem to be found in serum of prostate cancer patients, but not BPH patients. Mature, one-chain PSA is inactive in the presence of serum. These findings may be highly relevant for the understanding of the generation of free and complexed PSA in the circulation.

Enhanced expression of prostate-specific antigen in the transition zone of the prostate. A characterization following prostatectomy for benign hyperplasia.

OBJECTIVE: To determine whether the serum levels of total prostate-specific antigen (t-PSA), free PSA (f-PSA) and PSA complexed to alpha 1-antichymotrypsin (PSA-ACT) result from different expressions in various prostatic zones. METHODS: In a series of 127 consecutive men undergoing transurethral resection of the prostate (TURP) for BPH between May 1995 and February 1996, t-PSA, f-PSA (ProStatus, Wallac) and PSA-ACT were measured before and 3-4 months after surgery. Pre- and postoperative prostate volumes were measured by TRUS. Resected tissue was assumed to be the transition zone (TZ) while postoperative volume was defined as peripheral zone (including the central one) (CPZ). Pre- and postoperative serum PSA was related to pre- and postoperative volume and resected tissue to the difference between pre- and postoperative serum PSA, respectively. The serum PSA per 1 g tissue was calculated. Group I consisted of 96 historically proven BPH with no signs of inflammation, group II of 19 BPH patients with transurethral catheters inserted sometime prior to surgery to relieve urinary retention, and group III of 12 patients with incidental carcinomas. RESULTS: In patients undergoing TURP without prior catheterization (group I) t-PSA (group I) declined from median 3.43 to 0.96 ng/ml after TURP by 72%, even though the prostate volume did so only by 44%, whereas the ratio free-to-total (f/t) PSA remained stable (median 24.9% pre- vs. 26.6% postoperatively). The TZ expressed approximately 2.7-fold more t-PSA than the remaining CPZ: median 0.14 vs. 0.052 ng/ml/g, respectively, and as to f-PSA it did so likewise: median 0.032 vs. 0.012 ng/ml/g, respectively. With transurethral catheterization prior to surgery (group II) the t-PSA density within whole prostate increased 1.4-fold as compared to this density without such catheterization: from median 0.089 (group I) to 0.13 ng/ml/g tissue, respectively (p < 0.007), and within the TZ alone 1.6-fold elevation from median 0.14 to 0.23 ng/ml/g, respectively (p < 0.02) was observed. In incidental carcinoma (group III) a reduced ratio of f/t PSA of 11.7% in the TZ as compared to 22.1% in the CPZ (22.1%) was observed. CONCLUSIONS: In BPH both t-PSA and f-PSA are predominantly expressed within the TZ, which could help to improve the specificity of the PSA density in cancer detection by using the sum of the t-PSA densities of the TZ and CPZ: (0.14 ng/ml/g x TZ) + (0.052 ng/ml/g x CPZ). It is the first time that the supposed origin of the incidental carcinoma (from the TZ) is confirmed biochemically by a f/t PSA ratio exclusively reduced in the TZ but not in the CPZ. The post-TURP unchanged free-to-total ratio (26.6%) may be useful for the early detection of cancer in patients followed up after TURP.

In prostatism patients the ratio of human glandular kallikrein to free PSA improves the discrimination between prostate cancer and benign hyperplasia within the diagnostic "gray zone" of total PSA 4 to 10 ng/mL.

OBJECTIVES: Human glandular kallikrein (hK2) possesses approximately 80% structure identity with prostate-specific antigen (PSA). Moreover, messenger ribonucleic acid for hK2 and for PSA is expressed in both benign and malignant prostatic tissue. We investigated whether the hK2 serum measurement may improve the detection of prostate cancer (PCa) in patients with total PSA of 4 to 10 ng/mL (diagnostic "gray zone"). METHODS: Blood samples were obtained from 90 consecutive male patients with lower urinary tract symptoms and total PSA values of 4 to 10 ng/mL. Eighty-one patients underwent transurethral resection of the prostate and 6 radical prostatectomy. The patients were divided into two groups: I, patients with PCa (n = 20) and II, patients with benign prostatic hyperplasia (BPH) (n = 70). An "in-house" immunofluorometric assay with analytical sensitivity of 0.01 ng/mL and the functional sensitivity of 0.05 ng/mL (at this level the mean coefficient of variation, calculated from the precision profile based on the assays of serum samples, was less than 20%) was used to determine serum hK2 concentrations. Total PSA, free PSA (ProStatus), and PSA complexed to alpha1-antichymotrypsin (PSA-ACT) were also measured. Free/total PSA, hK2/total PSA, and hK2/free PSA ratios were calculated. RESULTS: The serum hK2 could be detected in all samples and in 76 (84.4%) of 90 samples (PCa, n = 18; BPH, n = 58) at given functional sensitivity level. For these cases the median concentration of hK2 was 0.135 ng/mL in PCa and 0.09 ng/mL in BPH (P < 0.1). The median hK2/total PSA ratio was 2% for PCa and 1.6% for BPH (P < 0.2). The median free/total PSA ratio was 0.122 for PCa and 0.215 for BPH (P < 0.0008) and the hK2/free PSA ratio was 0.139 for PCa and 0.075 for BPH (P < 0.000003). At a 7.2% cutoff, the specificity of hK2/free PSA ratio was 48.2% at 100% sensitivity and increased to 60.3% at 94.4% sensitivity level (the area under the receiver operating characteristic curve was 0.86). In comparison, the free/total PSA ratio at a 25.2% cutoff had a sensitivity of 94.4% and a specificity of 27.6% (area under the curve = 0.76). CONCLUSIONS: hK2 was detected in all sera with total PSA values of 4 to 10 ng/mL. Of particular clinical interest is the finding that the hK2/free PSA ratio had a better specificity without loss of sensitivity for PCa than total PSA or the PSA free/total ratio within the range of 4 to 10 ng/mL total PSA. hK2 in combination with free PSA may offer a new diagnostic means for PCa detection.

Free-to-total prostate-specific antigen (PSA) ratio improves the specificity for detecting prostate cancer in patients with prostatism and intermediate PSA levels.

OBJECTIVE: To investigate the clinical significance of the free-to-total prostate-specific antigen (PSA) ratio in improving the specificity of PSA measurement for detecting prostate cancer within the diagnostic intermediate range (4-10 ng/mL total PSA) in patients referred for the treatment of urinary symptoms. PATIENTS AND METHODS: Serum samples were obtained from 333 consecutive patients with obstructive and irritative urinary symptoms. Of these men, 114 had total PSA levels of 4-10 ng/mL; 22 had prostate cancer (group 1) and 71 had benign prostatic hyperplasia (BPH, group 2). Group 3 consisted of 21 patients with BPH and a chronic indwelling catheter. The concentrations of free and total PSA (ProStatus, Wallac Oy, Turku, Finland) and PSA complexed to alpha-1-antichymotrypsin were measured and the free-to-total PSA ratio calculated. All patients under 70 years of age or with suspicious findings on digital rectal examination or transrectal ultrasonography underwent ultrasound-guided sextant prostate biopsies. Of the 114 patients, 105 (92%) underwent transurethral resection of the prostate and six (5%) radical retropubic prostatectomy. RESULTS: Patients in group 1 had significantly lower median free PSA concentrations (0.78 ng/mL vs 1.13 ng/mL, P < 0.001) and a lower free-to-total PSA ratio (12.1% vs 19.9%, P < 0.001) than those in group 2. The differences were similar between group 1 and group 3 (median free PSA in group 3, 1.06 ng/mL, P = 0.03, and free-to-total PSA ratio 18.7%, P = 0.007). There were no significant differences between patients in groups 2 and 3. The free-to-total PSA ratio had a higher specificity than total PSA at all sensitivity levels, e.g. a threshold free-to-total PSA ratio of 0.20 detected 91% of cancers and spared 48% (group 2) or 46% (group 3) from unnecessary biopsies. The area under the receiver operating characteristic curve for group 1 vs group 2 was 0.56 (total PSA) and 0.78 (free-to-total PSA ratio) and for group 1 vs group 3 was 0.56 (total PSA) and 0.81 (free-to-total PSA ratio). CONCLUSION: In those patients with extensive symptoms from BPH and requiring surgical treatment, the free-to-total PSA ratio improves the specificity for detecting prostate cancer in the diagnostic 'grey zone' of 4-10 ng/mL total PSA. This improvement occurred in patients with or without a chronic indwelling catheter for urinary retention.

Determination and analysis of antigenic epitopes of prostate specific antigen (PSA) and human glandular kallikrein 2 (hK2) using synthetic peptides and computer modeling.

Prostate specific antigen (PSA) and human glandular kallikrein 2 (hK2), produced essentially by the prostate gland, are 237-amino acid monomeric proteins, with 79% identity in primary structure. Twenty-five anti-PSA monoclonal antibodies (Mabs) were studied for binding to a large array of synthetic linear peptides selected from computer models of PSA and hK2, as well as to biotinylated peptides covering the entire PSA sequence. Sixteen of the Mabs were bound to linear peptides forming four independent binding regions (I-IV). Binding region I was localized to amino acid residues 1-13 (identical sequence for PSA and hK2), II (a and b) was localized to residues 53-64, III (a and b) was localized to residues 80-91 (= kallikrein loop), and IV was localized to residues 151-164. Mabs binding to regions I and IIa were reactive with free PSA, PSA-ACT complex, and with hK2; Mabs binding to regions IIb, IIIa, and IV were reactive with free PSA and PSA-ACT complex, but unreactive with hK2; Mabs binding to region IIIb detected free PSA only. All Mabs tested (n = 7) specific for free PSA reacted with kallikrein loop (binding region IIIb). The presence of Mabs interacting with binding region I did not inhibit the catalytic activity of PSA, whereas Mabs interacting with other binding regions inhibited the catalysis. Theoretical model structures of PSA, hK2, and the PSA-ACT complex were combined with the presented data to suggest an overall orientation of PSA with regard to ACT.

Rapid exponential elimination of free prostate-specific antigen contrasts the slow, capacity-limited elimination of PSA complexed to alpha 1-antichymotrypsin from serum.

OBJECTIVES: To study the rates of elimination of total prostate-specific antigen (PSA-T), free PSA (PSA-F), and PSA complexed to alpha 1-antichymotrypsin (PSA-ACT) from blood after radical retropubic prostatectomy (RRP). METHODS: We obtained venous blood from 10 patients with prostate cancer who were undergoing RRP. We analyzed PSA-F and PSA-ACT and equimolar detection of both of these forms together (PSA-T) by using immunofluorometric assays. An attempt was made to fit the serum concentrations of PSA-F, PSA-ACT, and PSA-T for each patient to exponential curves by applying one- and two-compartment models for pharmacokinetic analysis. RESULTS: Manipulation of the prostate during RRP resulted in a 3- to 28-fold increase in PSA-F concentrations in serum. Removal of the prostate resulted in a rapid, biexponential elimination of PSA-F from serum, corresponding to a mean initial (alpha) half-life of 0.81 hours and a mean terminal (beta) half-life of 13.9 hours. Serum PSA-ACT concentrations decreased by 20% to 40% immediately after removal of the gland; the elimination after surgery was slow and nonexponential, corresponding to a mean rate of 0.8 ng/mL/day. The elimination of PSA-T reflects a combination of the elimination patterns for PSA-F and PSA-ACT. CONCLUSIONS: The main proportion of PSA-F is rapidly eliminated from serum, possibly by glomerular filtration. PSA-F released during surgery did not form complexes with ACT, as suggested by the lack of PSA-ACT elevation in serum. The size (approximately 90 kDa) and the extensive in vitro stability of the PSA-ACT complex prevents renal clearance. The nonexponential elimination of the PSA-ACT complex is evidence of a capacity-limited process (e.g., metabolic transformation).