Equivalent recognition of free and ACT-complexed PSA in a monoclonal-polyclonal sandwich assay is conferred by binding specificity of the monoclonal antibody

Multicenter Evaluation of the Performance and Clinical Utility in Longitudinal Monitoring of the Bayer Immuno 1™ Complexed PSA Assay

We conducted a multicenter evaluation of the analytical and clinical performance of the automated Bayer Immuno 1™ complexed PSA (cPSA) assay, and compared assay performance to the Bayer Immuno 1™ PSA assay. We sought to determine whether measurements of cPSA could be of clinical utility in the management of patients with prostate cancer. Results of the 10–day imprecision across three evaluation sites produced total CV < 2.50% and an analytical sensitivity of 0.02μg/L. There was an increased trend in clinical sensitivity for prostate cancer with increasing stage of disease (71–86%). Clinical specificity for patients with benign urogenital disease was 74.8%, and for other nonprostate diseases ranged from 91.1–100%. Retrospective serial monitoring of 155 patients with prostate cancer demonstrated concordance of cPSA measurements to clinical status for 97% of the patients analyzed. Results from the clinical studies using the Bayer Immuno 1 cPSA assay were comparable to results obtained with the Bayer Immuno 1 PSA assay. The Bayer Immuno 1 cPSA assay demonstrates analytical performance and clinical effectiveness in the management of prostate cancer patients during the course of disease and therapy.

Three immunoassays based on monoclonal antibodies specific for prostate specific antigen (PSA), alpha-1-antichymotrypsin (ACT), and the PSA-ACT complex

BACKGROUND

Prostate specific antigen (PSA) has been widely used as a biomarker for the screening and diagnosis of prostate cancer. PSA in serum predominantly exists as a complex with alpha-1-antichymotrypsin (ACT), and measurement of free PSA and the PSA-ACT complex may improve the utility of the serum PSA assay for differential diagnosis of prostate cancer and non-malignant prostate diseases, such as benign prostatic hyperplasia (BPH).

METHODS

Monoclonal antibodies (MAbs) against PSA, ACT, and the PSA-ACT complex were produced by immunizing mice with an incubated mixture of PSA and ACT, and characterized by Western blot analyses and several enzyme-linked immunosorbant assay (ELISA) methods.

RESULTS

The MAbs produced in this study are capable of distinguishing the PSA-ACT complex from free PSA and ACT. Four MAbs have been selected and utilized to construct three ELISA systems for the separate measurements of free PSA, the PSA-ACT complex, and total PSA.

CONCLUSIONS

The three PSA assay systems developed in this study can specifically measure free PSA, total PSA, and the PSA-ACT complex with equal molar sensitivity. It is expected that these PSA assay systems could be useful in the diagnosis of prostate cancer.

Evaluation of the clinical performance of equimolar- and skewed-response total prostate-specific antigen assays versus complexed and free PSA assays and their ratios in discriminating between benign prostatic hyperplasia and prostate cancer

BACKGROUND

Prostate-specific antigen (PSA) exists in human serum in two principal forms, free PSA (fPSA) and protein-complexed PSA, predominantly PSA-ACT (alpha(1)-antichymotrypsin). Equimolar response (EMR) total PSA (tPSA) immunoassays measure each of these forms equally while skewed-response (SKR) assays overestimate or underestimate the tPSA concentration. The advantages of EMR over SKR tPSA assays are controversial.

METHODS

We used five nonhuman serum-based samples each containing a different proportion of fSPA:PSA-ACT (0:100 to 100:0, %:%) and patients' serum samples from men with histologically confirmed benign prostatic hyperplasia (BPH) (n=94) or PCA (n=30) and a wide range of fPSA concentrations to investigate the molar response status of six tPSA assays. Receiver-operator characteristic (ROC) curve analysis was used to compare the discriminatory power of these assays in distinguishing men with BPH from those with PCA.

RESULTS

The Bayer Immuno-1 tPSA (BtPSA) assay demonstrated EMR characteristics and diagnostic accuracy similar to the Hybritech Tandem-E and Tandem-R tPSA assays. At 90% sensitivity, EMR tPSA assays had higher specificity than SKR tPSA assays.

CONCLUSIONS

The BtPSA assay is an EMR tPSA assay and EMR assays provide improved diagnostic specificity over SKR tPSA assays.

Complexed prostate-specific antigen, complexed prostate-specific antigen density of total and transition zone, complexed/total prostate-specific antigen ratio, free-to-total prostate-specific antigen ratio, density of total and transition zone prostate-specific antigen: results of the prospective multicenter European trial

This prospective, multicenter European Prostate Cancer Detection study evaluated the value and performance of the molecular forms of prostate-specific antigen (PSA) and their derivatives in combination with prostate gland and transition zone volumes in early detection of prostate cancer in patients with PSA levels between 4 and 10 ng/mL. Of 750 men enrolled at 7 different European urology centers into the study between November 2001 and March 2002, 340 (45.3%) had a total PSA (tPSA) between 4 and 10 ng/mL (age range, 46 to 87 years). In all patients, the ratio of complexed PSA (cPSA) to tPSA (c/tPSA), cPSA density (cPSAD), cPSAD of the transition zone, PSA, free PSA (fPSA), ratio of fPSA to tPSA (f/tPSA), tPSA density (PSAD), and PSAD of the transition zone were measured and collected 5 to 10 minutes before the sextant biopsy with 2 additional transition zone cores. Measurements of tPSA and fPSA were done with the AxSYM test, whereas cPSA was measured with the ACS 180 cPSA assay. All patients had a transrectal ultrasound-guided sextant prostate biopsy, and 2 additional transition zone biopsies and total and transition zone volumes were measured at the time of biopsy. Histopathologic findings revealed benign histology in 237 patients and prostate cancer in 103 patients (69.7% and 30.3%, respectively). Statistically significant differences included larger total volumes, larger transition zone volumes, and f/tPSA in patients with benign disease (P = 0.0009, P <0.0001, P <0.0001, respectively). At 90% and 95% sensitivity, specificity of cPSA was significantly greater than that for PSA (P <0.0001). At sensitivity levels of 90% and 95%, the specificity of the cPSA assay using cutoff values of 3.06 and 2.52 ng/mL was 20.3% and 9.1%, respectively. A cPSA cutoff value of 6.95 ng/mL and 7.57 ng/mL afforded 90% and 95% specificity for detecting prostate cancer. The area under the curve (AUC) in the receiver operating characteristics curve of cPSA was statistically significantly higher compared with tPSA (60.8 vs 56.9, P = 0.032). AUC for volume-related parameters PSAD, cPSAD, PSAD of the transition zone, and cPSAD of the transition zone were 62.8%, 63.1%, 63.0%, and 63.6%, respectively. cPSA performs better than tPSA in the differentiation between benign disease and prostate cancer and provides similar information to the f/tPSA ratio. In addition, cPSA and cPSA volume-related parameters (cPSAD, cPSAD of the transition zone) further improved the specificity of PSA in early detection of prostate cancer.

Amperometric biosensors for detection of the prostate cancer marker (PSA)

Prostate specific antigen (PSA) has been identified as the most reliable clinical tool for diagnosing and monitoring prostate cancer (CAP). Since, there is no curative therapy available for prostate cancer, detecting the disease at the early stage is the best hope of increasing mortality rate. There are some procedures available for the detection of prostate cancer e.g. Tandem-R PSA, Hybritech Inc. (USA), IMx-PSA Abbott Laboratories (USA). However, these are time consuming and costly. We have developed a very simple and cost effective technique for identification and monitoring of prostate cancer using amperometric immunosensor. PSA is a glycoprotein with 93% peptide and 7% sugar content and isoelectric pH of 6.9. It may exist in the human serum as free (f-PSA) and complex (PSA-ACT) forms. Normally if the total PSA (t-PSA) level is more than 10 ng/ml, CAP is suspected. This paper presents an amperometric detection procedure for t-PSA using three electrode system in which working electrode (WE) is made of hydroxyethyl cellulose (HEC) and rhodinised carbon. The method used is rapid, very easy to use and involves low cost compared with other procedures. The electrochemical response was directly observed due to enzymatic reaction via a sandwich immunoassay on the WE. Monoclonal capture antibody (Mab) to PSA was immobilised on the WE and the other Mab labelled by the enzyme marker, horseradish peroxidase (HRP), was used as a tracer antibody.

Free and complexed prostate-specific antigen (PSA) in the early detection of prostate cancer

We evaluated the analytical performance and diagnostic utility of complexed prostate-specific antigen (CPSA) and their ratios, complexed-to-total PSA (C/T PSA) and free-to-complexed PSA (F/C PSA), in comparison with the total PSA (TPSA) and free-to-total PSA ratio (F/T PSA) as means of diagnosing prostate cancer (PC). Samples (n=101) were drawn from men with no evidence of malignancy (n=80) and from men with PC (n=21) at biopsy. For determination of the F/T PSA ratio, the DPC Immulite-2000 method was used; and the Bayer Immuno-1 CPSA and TPSA assays were used to determine the C/T PSA ratio. The Bayer Immuno-1 CPSA assay provides accurate and precise CPSA values in human serum. The performance of the different forms and ratios was compared using receiver operating characteristic curve analysis. CPSA had the greatest area under the curve (AUC, 0.689) although it was not statistically different from the other parameters. A cut-off value of 4.66 ng/ml for CPSA provided a specificity of 38% and a sensitivity of 93%. The F/C PSA ratio maintained a sensitivity of 93% and had an increased specificity of 41%. The measurement of CPSA provides a slight increase in specificity compared with the use of the TPSA in the early detection of prostate cancer.

Ratio of Free or Complexed Prostate-specific Antigen (PSA) to Total PSA: Which Ratio Improves Differentiation between Benign Prostatic Hyperplasia and Prostate Cancer?

Background: The aim of this study was to compare the diagnostic utility of a new assay that measures all forms of prostate-specific antigen complexed (cPSA) to serum proteins except α2-macroglobulin with the assay of free PSA (fPSA) and the corresponding ratios to total PSA (tPSA) to improve the differentiation between benign prostatic hyperplasia (BPH) and prostate cancer (PCa).

Methods: Serum samples were collected from 91 men without prostate disease and with normal digital rectal examination (controls), 144 untreated patients with PCa, and 89 patients with BPH. tPSA and cPSA were measured using the Bayer Immuno 1 system; fPSA and the additional tPSA were measured with the Roche Elecsys system.

Results: The median cPSA/tPSA, fPSA/tPSA, and fPSA/cPSA ratios were significantly different between patients with BPH and PCa (78.7% vs 90.7%, 25.5% vs 12.1%, and 36.8% vs 14.3%, respectively; P &lt;0.001). No correlations of cPSA and its ratios to tumor stage and grade were found. ROC analysis showed that cPSA was not different from tPSA (areas under the curve, 0.632 vs 0.568), whereas the cPSA/tPSA ratio was similar to the fPSA/tPSA ratio in increasing discrimination between BPH and PCa patients with tPSA concentrations in the tPSA gray zone between 2 and 10 μg/L (areas under the curve, 0.851 vs 0.838).

Conclusions: Compared with tPSA, the fPSA/tPSA and cPSA/tPSA ratios both improve the differentiation between BPH and PCa comparably and are similarly effective in reducing the rate of unnecessary biopsies, whereas cPSA alone does not have any effect.