Development of an immunoassay specific for the PSA-ACT complex without the problem of high background

Characterisation of the main PSA glycoforms in aggressive prostate cancer

Serum levels of prostate specific antigen (PSA) are commonly used for prostate cancer (PCa) detection. However, their lack of specificity to distinguish benign prostate pathologies from PCa, or indolent from aggressive PCa have prompted the study of new non-invasive PCa biomarkers. Aberrant glycosylation is involved in neoplastic progression and specific changes in PSA glycosylation pattern, as the reduction in the percentage of α2,6-sialic acid (SA) are associated with PCa aggressiveness. In this study, we have characterised the main sialylated PSA glycoforms from blood serum of aggressive PCa patients and have compared with those of standard PSA from healthy individuals’ seminal plasma. PSA was immunoprecipitated and α2,6-SA were separated from α2,3-SA glycoforms using SNA affinity chromatography. PSA N-glycans were released, labelled and analysed by hydrophilic interaction liquid chromatography combined with exoglycosidase digestions. The results showed that blood serum PSA sialylated glycoforms containing GalNAc residues were largely increased in aggressive PCa patients, whereas the disialylated core fucosylated biantennary structures with α2,6-SA, which are the major PSA glycoforms in standard PSA from healthy individuals, were markedly reduced in aggressive PCa. The identification of these main PSA glycoforms altered in aggressive PCa opens the way to design specific strategies to target them, which will be useful to improve PCa risk stratification.

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.

Combining electrochemical sensors with miniaturized sample preparation for rapid detection in clinical samples

Clinical analyses benefit world-wide from rapid and reliable diagnostics tests. New tests are sought with greatest demand not only for new analytes, but also to reduce costs, complexity and lengthy analysis times of current techniques. Among the myriad of possibilities available today to develop new test systems, amperometric biosensors are prominent players-best represented by the ubiquitous amperometric-based glucose sensors. Electrochemical approaches in general require little and often enough only simple hardware components, are rugged and yet provide low limits of detection. They thus offer many of the desirable attributes for point-of-care/point-of-need tests. This review focuses on investigating the important integration of sample preparation with (primarily electrochemical) biosensors. Sample clean up requirements, miniaturized sample preparation strategies, and their potential integration with sensors will be discussed, focusing on clinical sample analyses.

PSA and other tissue kallikreins for prostate cancer detection

Prostate cancer is the most common neoplasia of middle-aged men. Prostate specific antigen (PSA) is the first FDA-approved tumour marker for early detection of cancer and it is now in widespread clinical use. The discovery of different PSA molecular forms in serum (free PSA, PSA complexed with various protease inhibitors) in the early 1990s renewed clinical research to enhance the specificity of PSA. Also, the use of a homologous prostate-localised antigen, human glandular kallikrein 2 (KLK2) may further reduce the number of unnecessary prostate biopsies. More recently, promising data is emerging regarding molecular forms of free PSA (proPSA, BPSA, 'intact' PSA) and other members of the expanded human kallikrein family. These new findings may add substantial clinical information for early detection of prostate cancer.

Protein detection using biobarcodes

Over the past 50 years the development of assays for the detection of protein analytes has been driven by continuing demands for higher levels of sensitivity and multiplexing. The result has been a progression of sandwich-type immunoassays, starting with simple radioisotopic, colorimetric, or fluorescent labeling systems to include various enzymatic or nanostructure-based signal amplification schemes, with a concomitant sensitivity increase of over 1 million fold. Multiplexing of samples and tests has been enabled by microplate and microarray platforms, respectively, or lately by various molecular barcoding systems. Two different platforms have emerged as the current front-runners by combining a nucleic acid amplification step with the standard two-sided immunoassay. In both, the captured protein analyte is replaced by a multiplicity of oligonucleotides that serve as surrogate targets. One of these platforms employs DNA or RNA polymerases for the amplification step, while detection is by fluorescence. The other is based on gold nanoparticles for both amplification as well as detection. The latter technology, now termed Biobarcode, is completely enzyme-free and offers potentially much higher multiplexing power.

PSA markers in prostate cancer detection

The PSA revolution that has occurred over the previous 2 decades has positively impacted the detection and treatment of men with prostate cancer. Although methods to improve specificity have shown promise (eg, PSAD, age-specific PSA, and PSA velocity), meaningful interpretation has yet to be uniformly accepted within clinical practice. The identification of other molecular forms of PSA within serum has led to a new era in PSA markers. Initial application employing %fPSA has provided improved discrimination between benign and malignant prostatic disease; however, questions remain regarding the ultimate threshold value. The discovery of various free forms of PSA--such as proPSA, BPSA, and iPSA--also have introduced the potential for improved specificity in detection. Although early results are encouraging, further evaluation is anticipated. The development of improved methods to detect and measure cPSA has demonstrated provocative results, and exhibits the potential to replace PSA as a standard diagnostic test in cancer screening.

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.

Dual-label immunoassay for simultaneous measurement of prostate-specific antigen (PSA)-alpha1-antichymotrypsin complex together with free or total PSA

BACKGROUND

A major portion of prostate-specific antigen exists in circulation as a complex with alpha(1)-antichymotrypsin (PSA-ACT), whereas a minor part is free (fPSA). The proportion of PSA-ACT is increased in prostate cancer (PCa), but immunologic determination of PSA-ACT is hampered by a background produced by nonspecific adsorption of ACT to the solid phase. To reduce the nonspecific interference, we produced an antibody specific for complexed ACT and developed immunofluorometric assays (IFMAs) for simultaneous measurement of fPSA + PSA-ACT (fPSA/PSA-ACT) and PSA-ACT + total PSA (tPSA, PSA-ACT/tPSA).

METHODS

Monoclonal antibodies (MAbs) were produced by immunization with PSA-ACT. The dual-label time-resolved IFMAs for fPSA/PSA-ACT and PSA-ACT/tPSA used a capture MAb to tPSA, an Eu(3+)-labeled MAb to fPSA or complexed ACT, and an Sm(3+)-labeled MAb to complexed ACT or to tPSA as tracer antibodies. The clinical utility was evaluated using serum samples from individuals with or without PCa with PSA concentrations of 2.0-20.0 micro g/L.

RESULTS

One MAb (1D10) showed low cross-reactivity with free ACT and cathepsin G-ACT. A sandwich assay for PSA-ACT with 1D10 as tracer had a detection limit of 0.05 micro g/L, and with this assay, PSA-ACT was undetectable in female sera. The detection limit for fPSA was 0.004 micro g/L. Determinations of the ratio of fPSA to PSA-ACT and the proportions of fPSA/tPSA and PSA-ACT/tPSA provided the same clinical specificity for PCa and provided significantly better clinical specificity than did tPSA.

CONCLUSIONS

Background problems observed in earlier PSA-ACT assays are eliminated by the use of a MAb specific for complexed ACT as a tracer. The same clinical validity can be obtained by determination of fPSA or PSA-ACT together or in combination with tPSA.

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.

Complexed prostate-specific antigen improvement in detecting prostate cancer

This article presents the current reports of complexed prostate-specific antigen (PSA) aimed for the enhancement of prostate cancer detection. Further studies are needed to ascertain the variability of complexed PSA. Comparisons of percent free PSA, potential additive value of alpha(1)-antichymotripsin-bound PSA (PSA-ACT) and Bayer complexed PSA (cPSA) remains controversial in men with intermediate elevated total PSA concentration. Volume-referenced complexed PSA (PSA-ACT and cPSA) can enhance prostate cancer detection. Preliminary results show that PSA-alpha(2)-macrobloblin (PSA-a(2)M) and PSA-alpha(1)-protease inhibitor (PSA-API) are promising assays for improving cancer detection.

Different stability of free and complexed prostate-specific antigen in serum in relation to specimen handling and storage conditions

The effect of sample collection, storage conditions (time and temperature), and freeze-thaw cycles on the stability of free prostate-specific antigen (fPSA), PSA complexed with alpha1-antichymotrypsin (ACT-PSA), and total PSA (tPSA) in serum was studied. The analytes were quantified using immunoassays for tPSA and fPSA on the Elecsys system 2010 and a research assay for ACT-PSA on the ES system (Roche Diagnostics). The stability of the analytes was calculated as percentages of the values measured in samples 1 h after blood collection. When the samples were stored at 37 degrees C, at room temperature or at 4 degrees C, the stability of ACT-PSA was less impaired than that of fPSA. To avoid erroneous results in the determination of PSA isoforms and their corresponding ratios, serum samples should be preserved at 4 degrees C when the analysis is performed within 8 h after blood collection, or they should be stored at -80 degrees C if the analysis is not feasible during that period.

Prostate specific antigen adjusted for transition zone volume: the most powerful method for detecting prostate carcinoma

BACKGROUND

Several methods for the identification of patients with prostate carcinoma have been proposed to enhance the clinical usefulness of prostate specific antigen (PSA). However, it remains unclear which method is superior in practical use. The authors attempted prospectively to identify the most powerful method with which to detect prostate carcinoma, especially among patients with intermediate PSA levels.

METHODS

Between October 1997 and August 1999, systematic sextant biopsies were performed on 281 patients, including 147 with PSA levels between 4.1 ng/mL and 10.0 ng/mL. The clinical values of PSA, the free PSA to total PSA ratio (free/total PSA ratio), alpha-1-antichymotrypsin-PSA complex (PSA-ACT), the calculated derivatives, PSA density (PSAD), and PSA density of the transition zone (PSATZD) for the detection of prostate carcinoma were compared by using receiver operating characteristic (ROC) curves and logistic regression analyses.

RESULTS

According to ROC curve analysis, PSATZD had the greatest area under the curve in the overall patient population and in patients with intermediate PSA levels. In patients with intermediate PSA levels, at the sensitivity of 90%, PSATZD would have prevented unnecessary biopsies in 68 of 117 patients who were without prostate carcinoma, whereas PSA, free/total PSA ratio, and PSA-ACT would have prevented unnecessary biopsies in 25, 28, and 25 patients, respectively. Stepwise logistic regression analysis showed that PSATZD and findings on digital rectal examination were significant independent predictors.

CONCLUSIONS

PSATZD had the most useful validity in the differentiation between prostate carcinoma and benign prostatic enlargement in the overall patient population and in patients with intermediate PSA levels.

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.

Determination of alpha1-antichymotrypsin-PSA complex in serum does not improve the differentiation between benign prostatic hyperplasia and prostate cancer compared with total PSA and percent free PSA

OBJECTIVES

To evaluate the analytical performance and diagnostic utility of alpha1-antichymotrypsin (ACT)-prostate-specific antigen (PSA) complex in serum to improve the differentiation between benign prostatic hyperplasia (BPH) and prostate cancer (PCa).

METHODS

Serum concentrations of total PSA (tPSA), free PSA (fPSA), and ACT-PSA were measured in 112 untreated patients with PCa (median age 65 years), 34 patients with BPH (median age 66 years) with histologic confirmation, and 33 men without prostate disease and with a normal digital rectal examination considered as controls (median age 54 years). Sera were frozen at -80 degrees C within 2 hours after collection and then analyzed during a 12-week period. Determinations were made with the Enzymun-Test for tPSA and fPSA and with a prototype assay for ACT-PSA on the ES system (Roche Diagnostics, Boehringer Mannheim).

RESULTS

The new ACT-PSA assay showed reliable data of analytical performance. The lower detection limit amounted to 0.068 microg/L. The assay was linear to 50 microg/L. Spiking experiments showed a mean recovery rate of 98.2%. No interferences of the assay were observed in patients with acute inflammation and highly increased ACT concentrations. The values of intra- and interassay imprecision ranged from 1.51% to 3.48% and 2.1% to 6.3%, respectively. The median value of ACT-PSA concentrations were significantly different (P <0.001) between controls and patients with BPH and PCa (0.40, 3.86, 5.26 microg/L, respectively). The median fPSA/tPSA and fPSA/ACT-PSA ratios were significantly different between BPH and PCa (24.3% versus 12.2%, P <0.001 and 32.9% versus 15.0%, P <0.001, respectively), but no difference of the ACT-PSA/tPSA ratio was observed (78.2% versus 78.7%, P = 0.696). Receiver operating characteristics of ACT-PSA (area under the curve = 0.630) and all the derivative ratios of fPSA/ACT-PSA (area = 0.737) and ACT-PSA/tPSA (area = 0.528) were not different from that of tPSA (area = 0.619), but showed a lower discrimination power between BPH and PCa than the fPSA/tPSA ratio (area = 0.790).

CONCLUSIONS

Using this prototype assay to quantify ACT-PSA in serum, we have demonstrated that ACT-PSA and the calculated derivatives are not superior in the differentiation between BPH and PCa compared with tPSA and the ratio of fPSA to tPSA.