DISCRIMINATION OF MEN WITH PROSTATE CANCER FROM THOSE WITH BENIGN DISEASE BY MEASUREMENTS OF HUMAN GLANDULAR KALLIKREIN 2 (HK2) IN SERUM

Biosensors for prostate cancer detection

Prostate cancer (PC) is one of the most common tumors and a leading cause of mortality among men, resulting in ~375 000 deaths annually worldwide. Various analytical methods have been designed for quantitative and rapid detection of PC biomarkers. Electrochemical (EC), optical, and magnetic biosensors have been developed to detect tumor biomarkers in clinical and point-of-care (POC) settings. Although POC biosensors have shown potential for detection of PC biomarkers, some limitations, such as the sample preparation, should be considered. To tackle such shortcomings, new technologies have been utilized for development of more practical biosensors. Here, biosensing platforms for the detection of PC biomarkers such as immunosensors, aptasensors, genosensors, paper-based devices, microfluidic systems, and multiplex high-throughput platforms, are discussed.

Re-evaluating the diagnostic efficacy of PSA as a referral test to detect clinically significant prostate cancer in contemporary MRI-based image-guided biopsy pathways

Introduction

Modern image-guided biopsy pathways at diagnostic centres have greatly refined the investigations of men referred with suspected prostate cancer. However, the referral criteria from primary care are still based on historical prostate-specific antigen (PSA) cut-offs and age-referenced thresholds. Here, we tested whether better contemporary pathways and biopsy methods had improved the predictive utility value of PSA referral thresholds.

Methods

PSA referral thresholds, age-referenced ranges and PSA density (PSAd) were assessed for positive predictive value (PPV) in detection of clinically significant prostate cancer (csPCa - histological ⩾ Grade Group 2). Data were analysed from men referred to three diagnostics centres who used multi-parametric magnetic resonance imaging (mpMRI)-guided prostate biopsies for disease characterisation. Findings were validated in a separate multicentre cohort. Results: Data from 2767 men were included in this study. The median age, PSA and PSAd were 66.4 years, 7.3 ng/mL and 0.1 ng/mL2, respectively. Biopsy detected csPCa was found in 38.7%. The overall area under the curve (AUC) for PSA was 0.68 which is similar to historical performance. A PSA threshold of ⩾ 3 ng/mL had a PPV of 40.3%, but this was age dependent (PPV: 24.8%, 32.7% and 56.8% in men 50-59 years, 60-69 years and ⩾ 70 years, respectively). Different PSA cut-offs and age-reference ranges failed to demonstrate better performance. PSAd demonstrated improved AUC (0.78 vs 0.68, p < 0.0001) and improved PPV compared to PSA. A PSAd of ⩾ 0.10 had a PPV of 48.2% and similar negative predictive value (NPV) to PSA ⩾ 3 ng/mL and out-performed PSA age-reference ranges. This improved performance was recapitulated in a separate multi-centre cohort (n = 541).

Conclusion

The introduction of MRI-based image-guided biopsy pathways does not appear to have altered PSA diagnostic test characteristics to positively detect csPCa. We find no added value to PSA age-referenced ranges, while PSAd offers better PPV and the potential for a single clinically useful threshold (⩾0.10) for all age groups.

Level of evidence

IV.

Biosensors for detection of prostate cancer: a review

Diagnosis of prostate cancer (PC) has posed a challenge worldwide due to the sophisticated and costly diagnostics tools, which include DRE, TRUS, GSU, PET/CT scan, MRI, and biopsy. These diagnostic techniques are very helpful in the detection of PCs; however, all the techniques have their serious limitations. Biosensors are easier to fabricate and do not require any cutting-edge technology as required for other imaging techniques. In this regard, point-of-care (POC) biosensors are important due to their portability, convenience, low cost, and fast procedure. This review explains the various existing diagnostic tools for the detection of PCs and the limitation of these methods. It also focuses on the recent studies on biosensors technologies as an alternative to the conventional diagnostic techniques for the detection of PCs.

Markers of Toxicity and Response to Radiation Therapy in Patients With Prostate Cancer

The main treatment modalities for localized prostate cancer are surgery and radiation. Surgery removes the whole prostate gland, whereas with radiation therapy the irradiated prostate remains within the patient's body. Biomarkers specific to the prostate gland should become undetectable after surgery, but this is not the case when radiation therapy is used, as residual prostate cells may still be metabolically active. Here, we review the role of tumor markers of toxicity and response to radiation therapy in patients with prostate cancer, including prostate specific antigen, human kallikrein 2, osteopontin, prostate cancer associated 3, citrulline, and others.

A Highly Sensitive Porous Silicon (P-Si)-Based Human Kallikrein 2 (hK2) Immunoassay Platform toward Accurate Diagnosis of Prostate Cancer

Levels of total human kallikrein 2 (hK2), a protein involved the pathology of prostate cancer (PCa), could be used as a biomarker to aid in the diagnosis of this disease. In this study, we report on a porous silicon antibody immunoassay platform for the detection of serum levels of total hK2. The surface of porous silicon has a 3-dimensional macro- and nanoporous structure, which offers a large binding capacity for capturing probe molecules. The tailored pore size of the porous silicon also allows efficient immobilization of antibodies by surface adsorption, and does not require chemical immobilization. Monoclonal hK2 capture antibody (6B7) was dispensed onto P-Si chip using a piezoelectric dispenser. In total 13 × 13 arrays (169 spots) were spotted on the chip with its single spot volume of 300 pL. For an optimization of capture antibody condition, we firstly performed an immunoassay of the P-Si microarray under a titration series of hK2 in pure buffer (PBS) at three different antibody densities (75, 100 and 145 µg/mL). The best performance of the microarray platform was seen at 100 µg/mL of the capture antibody concentration (LOD was 100 fg/mL). The platform then was subsequently evaluated for a titration series of serum-spiked hK2 samples. The developed platform utilizes only 15 µL of serum per test and the total assay time is about 3 h, including immobilization of the capture antibody. The detection limit of the hK2 assay was 100 fg/mL in PBS buffer and 1 pg/mL in serum with a dynamic range of 10⁶ (10⁻⁴ to 10² ng/mL).

A functional variant in miR-143 promoter contributes to prostate cancer risk

MicroRNAs are important regulators in numerous cellular processes, including cell differentiation, proliferation, and apoptosis. Recently, miR-143 was identified as a tumor suppressor in prostate cancer (PCa). To explore the mechanism of dysregulation and anti-tumor function of miR-143 in PCa, we first found a single-nucleotide polymorphism rs4705342T>C in the promoter region of miR-143 through bioinformatics tools and then performed a case-control study including 608 PCa patients and 709 controls. Results suggested that subjects with TC/CC genotypes had significantly decreased risk of PCa compared with those with TT genotype (adjusted OR 0.68, 95 % CI 0.55-0.85). Further functional assays showed that the risk-associated T allele increased the protein-binding affinity and reduced the activity of the promoter compared with C allele. In addition, restoration of miR-143 by mimics in PCa cells significantly inhibited cell proliferation and migration and down-regulated the expression level of kallikrein-related peptidase 2 (KLK2) mRNA and protein. The miR-143-KLK2 axis was also confirmed by luciferase reporter assay in vitro. In conclusion, our findings demonstrate that there is the significant association between the functional promoter variant rs4705342T>C in miR-143 and PCa risk and newly describe the miR-143-KLK2 interaction which provided another potential mechanism for miR-143 anti-tumor function.

Identification of plasma protein profiles associated with risk groups of prostate cancer patients

PURPOSE

Early detection of prostate cancer (PC) using prostate-specific antigen (PSA) in blood reduces PC-death among unscreened men. However, due to modest specificity of PSA at commonly used cut-offs, there are urgent needs for additional biomarkers contributing enhanced risk classification among men with modestly elevated PSA.

EXPERIMENTAL DESIGN

Recombinant antibody microarrays were applied for protein expression profiling of 80 plasma samples from routine PSA-measurements, a priori divided into four risk groups, based on levels of total and %free PSA.

RESULTS

The results demonstrated that plasma protein profiles could be identified that pin-pointed PC (a malignant biomarker signature) and most importantly that showed moderate to high correlation with biochemically defined PC risk groups. Notably, the data also implied that the risk group with midrange PSA and low %free PSA, a priori known to be heterogeneous, could be further stratified into two subgroups, more resembling the lowest and highest risk groups, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

In this pilot study, we have shown that plasma protein biomarker signatures, associated with risk groups of PC, could be identified from crude plasma samples using affinity proteomics. This approach could in the longer perspective provide novel opportunities for improved risk classification of PC patients.

The development of nomograms for stratification of men at risk of prostate cancer prior to prostate biopsy

A main limitation of early prostate cancer (PCa) detection due to elevated PSA levels is caused by the low specificity of PSA, which is associated with a high proportion of men detected with nonmalignant findings at first or subsequent prostate biopsy (PBX). Multivariate prediction models, such as nomograms, have been developed, providing a more accurate method to prospectively determine the risk of a positive PBX. Combining established clinical risk factors with novel diagnostic markers of PCa appears promising to further improve predictive accuracy estimates. Ideally, these nomograms should be capable of identifying PCa at PBX without missing men with high-grade PCa, and preventing a significant proportion of men without, or with insignificant, PCa from undergoing PBX. The intention is to reduce disease morbidity and mortality by detecting significant PCa at an early stage, and at the same time to avoid overdiagnosis as well as overintervention.

Prostate-specific antigen and other serum and urine markers in prostate cancer

Prostate-specific antigen (PSA) is one of the most widely used tumor markers, and strongly correlates with the risk of harboring from prostate cancer (PCa). This risk is visible already several years in advance but PSA has severe limitations for PCa detection with its low specificity and low negative predictive value. There is an urgent need for new biomarkers especially to detect clinically significant and aggressive PCa. From all PSA-based markers, the FDA-approved Prostate Health Index (phi) shows improved specificity over percent free and total PSA. Other serum kallikreins or sarcosine in serum or urine show more diverging data. In urine, the FDA-approved prostate cancer gene 3 (PCA3) has also proven its utility in the detection and management of early PCa. However, some aspects on its correlation with aggressiveness and the low sensitivity at very high values have to be re-examined. The detection of a fusion of the androgen regulated TMPRSS2 gene with the ERG oncogene (from the ETS family), which acts as transcription factor gene, in tissue of ~50% of all PCa patients was one milestone in PCa research. When combining the urinary assays for TMPRSS2:ERG and PCA3, an improved accuracy for PCa detection is visible. PCA3 and phi as the best available PCa biomarkers show an equal performance in direct comparisons.

Kallikreins as biomarkers for prostate cancer

The introduction of testing for prostate-specific antigen (PSA), a member of the fifteen-gene family of kallikrein-related peptidases and also known as kallikrein-related peptidase 3 (KLK3), in blood has revolutionized both the detection and management of prostate cancer. Given the similarities between PSA and other KLK gene family members along with limitations of PSA as a biomarker for prostate cancer mainly in reference to diagnostic specificity, the potential roles of other members of this gene family as well as PSA derivatives and isoforms in the management of prostate cancer have been studied extensively. Of these, approaches to measure distinct molecular forms of PSA (free, intact, complexed PSA, and pro-PSA) combined with kallikrein-related peptidase 2 (KLK2), also known as hK2, have been considered holding particular promise in enhancing the diagnosis of prostate cancer. Recently, an integrated approach of applying a panel of four kallikrein markers has been demonstrated to enhance accuracy in predicting the risk of prostate cancer at biopsy. This review presents an overview of kallikreins, starting with the past and current status of PSA, summarizing published data on the evaluations of various KLKs as biomarkers in the diagnosis, prognostication, and monitoring of prostate cancer.

Biomarkers in prostate cancer surveillance and screening: past, present, and future

The use of biomarkers for prostate cancer (PCa) screening, detection, and prognostication have revolutionized the diagnosis and management of the disease. Current clinical practice has been driven largely by the utilization of prostate-specific antigen (PSA). The lack of specificity of PSA for PCa has led to both unnecessary biopsies and overdiagnosis of indolent cancers. The recent controversial recommendation by the United States Preventive Services Task Force against PCa screening has highlighted the need for novel clinically useful biomarkers. We review the literature on PCa biomarkers in serum, urine, and tissue. While these markers show promise, none seems poised to replace PSA, but rather may augment it. Further validation and consideration of how these novel markers improve clinical outcome is necessary. The discovery of new genetic markers shows promise in stratifying men with aggressive PCa.

Circulating microRNAs and kallikreins before and after radical prostatectomy: are they really prostate cancer markers?

The aim of our study was to monitor serum levels of two miRNAs (miR-21 and miR-141) and three KLKs (hK3/PSA, hK11, and hK13) before and 1, 5, and 30 days after radical prostatectomy, in order to characterize their fluctuations after surgery. 38 patients with prostate cancer were included. miR-21 and miR-141 were quantified through real-time PCR, while ELISA assays were used to quantify hK3 (PSA), hK11, and hK13. Both miR-21 and miR-141 showed a significant increase at the 5th postoperative day, after which a gradual return to the preoperative levels was recorded. These findings suggest that miR-21 and miR-141 could be involved in postsurgical inflammatory processes and that radical prostatectomy does not seem to alter their circulating levels. Postoperative serum kallikreins showed a significant decrease, highlighting the potential usefulness of kallikreins apart from PSA as potential prostate cancer markers.

Genome-wide association study identifies genetic determinants of urine PCA3 levels in men

Prostate cancer gene 3 (PCA3) is a non-coding gene specifically overexpressed in prostate cancer (PCa) that has great potential as a clinical biomarker for predicting prostate biopsy outcome. However, genetic determinants of PCA3 expression level remain unknown. To investigate the association between genetic variants and PCA3 mRNA level, a genome-wide association study was conducted in 1371 men of European descent in the REduction by DUtasteride of prostate Cancer Events trial. First-voided urine specimens containing prostate cells were obtained after digital rectal examination. The PROGENSA PCA3 assay was used to determine PCA3 score in the urinary samples. A linear regression model was used to detect the associations between (single nucleotide polymorphisms) SNPs and PCA3 score under an additive genetic model, adjusting for age and population stratification. Two SNPs, rs10993994 in β-microseminoprotein at 10q11.23 and rs10424878 in kallikrein-related peptidase 2 at 19q13.33, were associated with PCA3 score at genome-wide significance level (P = 1.22 x 10(-9) and 1.06 x 10(-8), respectively). Men carrying the rs10993994 "T" allele or rs10424878 "A" allele had higher PCA3 score compared with men carrying rs10993994 "C" allele or rs10424878 "G" allele (β = 1.25 and 1.24, respectively). This is the first comprehensive search for genetic determinants of PCA3 score. The novel loci identified may provide insight into the molecular mechanisms of PCA3 expression as a potential marker of PCa.

Assays for prostate cancer : changing the screening paradigm?

Prostate cancer (PCa) screening and detection have changed dramatically since the introduction of serum prostate-specific antigen (PSA) testing. Despite the resulting improvement in early PCa detection and stage migration, in clinical practice the use of PSA testing may cause overdetection and ultimately overtreatment. As a consequence, novel biomarkers are needed to increase the specificity of PCa detection. The aim of this article is to present an overview of novel blood- and urine-based biomarkers that may optimize PCa detection, with improved identification of patients with significant PCa and avoidance of unnecessary prostate biopsies. A systematic and comprehensive PubMed search was performed using the MeSH search terms 'prostate cancer', 'biomarker', 'marker', and 'detection'. Results were restricted to the English language. Several blood- and urine-based biomarkers have the potential to improve prediction of the presence and/or significance of PCa. Ideally, biomarkers should be used in combination within multivariate models, leading to superior accuracy for prediction of any PCa or clinically significant PCa, compared with the use of a single marker.

Immunotherapy of prostate cancer: should we be targeting stem cells and EMT?

Cancer stem cells have been implicated in a number of solid malignancies including prostate cancer. In the case of localised prostate cancer, patients are often treated with surgery (radical prostatectomy) and/or radiotherapy. However, disease recurrence is an issue in about 30% of patients, who will then go on to receive hormone ablation therapy. Hormone ablation therapy is often palliative in a vast proportion of individuals, and for hormone-refractory patients, there are several immunotherapies targeting a number of prostate tumour antigens which are currently in development. However, clinical responses in this setting are inconsistent, and it is believed that the failure to achieve full and permanent tumour eradication is due to a small, resistant population of cells known as 'cancer stem cells' (CSCs). The stochastic and clonal evolution models are among several models used to describe cancer development. The general consensus is that cancer may arise in any cell as a result of genetic mutations in oncogenes and tumour suppressor genes, which consequently result in uncontrolled cell growth. The cancer stem cell theory, however, challenges previous opinion and proposes that like normal tissues, tumours are hierarchical and only the rare subpopulation of cells at the top of the hierarchy possess the biological properties required to initiate tumourigenesis. Furthermore, where most cancer models infer that every cell within a tumour is equally malignant, i.e. equally capable of reconstituting new tumours, the cancer stem cell theory suggests that only the rare cancer stem cell component possess tumour-initiating capabilities. Hence, according to this model, cancer stem cells are implicated in both tumour initiation and progression. In recent years, the role of epithelial--mesenchymal transition (EMT) in the advancement of prostate cancer has become apparent. Therefore, CSCs and EMT are both likely to play critical roles in prostate cancer tumourigenesis. This review summarises the current immunotherapeutic strategies targeting prostate tumour antigens taking into account the need to consider treatments that target cancer stem cells and cells involved in epithelial--mesenchymal transition.

Tumor markers in prostate cancer I: blood-based markers

The introduction of total prostate specific antigen (total PSA) testing in blood has revolutionized the detection and management of men with prostate cancer (PCa). The objective of this review was to discuss the challenges of PCa biomarker research, definition of the type of PCa biomarkers, the statistical considerations for biomarker discovery and validation, and to review the literature regarding total PSA velocity and novel blood-based biomarkers.

METHODS

An English-language literature review of the Medline database (1990 to August 2010) of published data on blood-based biomarkers and PCa was undertaken.

RESULTS

The inherent biological variability of total PSA levels affects the interpretation of any single result. Men who will eventually develop PCa have increased total PSA levels years or decades before the cancer is diagnosed. Total PSA velocity improves predictiveness of total PSA only marginally, limiting its value for PCa screening and prognostication. The combination of PSA molecular forms and other biomarkers improve PCa detection substantially. Several novel blood-based biomarkers such as human glandular kallikrein 2 (hK2), urokinase plasminogen activator (uPA) and its receptor (uPAR), transforming growth factor-beta 1 (TGF-β1); interleukin-6 (IL-6) and its receptor (IL-6R) may help PCa diagnosis, staging, prognostication, and monitoring. Panels of biomarkers that capture the biologic potential of PCa are in the process of being validated for PCa prognostication.

CONCLUSIONS

PSA is a strong prognostic marker for long-term risk of clinically relevant cancer. However, there is a need for novel biomarkers that aid clinical decision making about biopsy and initial treatment. There is no doubt that progress will continue based on the integrated collaboration of researchers, clinicians and biomedical firms.

Molecular markers in prostate cancer. Part I: predicting lethality

Assessing the lethality of 'early,' potentially organ-confined prostate cancer (PCa) is one of the central controversies in modern-day urological clinical practice. Such cases are often considered for radical 'curative' treatment, although active surveillance may be equally appropriate for many men. Moreover, the balance between judicious intervention and overtreatment can be difficult to judge. The patient's age, comorbidities, family history and philosophy of self-health care can be weighed against clinical features such as the palpability of disease, the number and percentage of biopsy cores involved with the disease, histological grade, presenting prostate-specific antigen (PSA) and possible previous PSA kinetics. For many years, scientists and physicians have sought additional molecular factors that may be predictive for disease stage, progression and lethality. Usually, claims for a 'new' unique marker fall short of true clinical value. More often than not, such molecular markers are useful only in multivariate models. This review summarizes relevant molecular markers and models reported up to and including 2008.

Screening for prostate cancer in 2008 II: the importance of molecular subforms of prostate-specific antigen and tissue kallikreins

CONTEXT

Over the past decades, prostate-specific antigen (PSA), its isoforms, and other members of the tissue kallikrein family have been of continuous interest with regard to early detection and screening for prostate cancer (PCa).

OBJECTIVE

This review strives to give an overview of the possible clinical utilities of these markers, focused on early diagnostics and PCa screening.

EVIDENCE ACQUISITION

Using the Medline database, a literature search was performed on the role of molecular subforms of PSA and other members of the tissue kallikrein family in PCa detection.

EVIDENCE SYNTHESIS

With respect to PSA isoforms, only the combination of the various truncated forms (pPSA) shows additional value over total PSA (tPSA) and free PSA (fPSA) in PCa detection within the range of 2-10 ng/ml tPSA. At a high sensitivity for PCa, the specificity of the ratio of pPSA to fPSA (%pPSA) is, in general, better than that of the ratio of fPSA to tPSA (%fPSA), with a gain of 5-11%. The (-2)pPSA, (-4)pPSA, (-5)pPSA, (-7)pPSA, and benign PSA (BPSA) isoforms generally show no additional value over either pPSA or the existing parameters of tPSA and fPSA. Of the other members of the tissue kallikrein family, most studies on human kallikrein 2 (hK2) show an additional value of the ratio of hK2 to fPSA (%hK2) over %fPSA alone in PCa prediction. Other tissue kallikreins cannot be recommended for diagnosing PCa, due to the lack of additional value over tPSA or fPSA or to insufficient research. Regarding a prognostic role, the value of PSA subforms as well as of other members of the tissue kallikrein family is limited with regard to existing parameters.

CONCLUSIONS

pPSA and hK2 are able to improve PCa diagnosis in the range of 4-10 ng/ml tPSA over the existing variables tPSA and fPSA.

[PSA and hK2 in the diagnosis of prostate cancer]

Serum markers for prostate carcinoma are widely applied for the purpose of early detection of cancer and the differentiation between benign and malignant disease, for the pre-treatment staging of detected prostatic cancers, and for the monitoring of prostate cancer after curative or palliative therapies. Since its discovery in 1979, serum PSA has been the most powerful marker of prostate cancer, but, when used alone, PSA is not sufficiently sensitive or specific to consider it an ideal tool for the early detection or staging of prostate cancer. To optimize the use of PSA, the concepts of PSA velocity, PSA density, and age-related PSA values were developed. Moreover, the molecular forms of PSA, especially the percentage of free PSA, seem to be useful tools for the detection of prostate cancer in men with slightly elevated total PSA. Human kallikrein 2 (hK2), a serine protease closely related to PSA that also is expressed predominantly in the prostate, is a new complementary marker to PSA for early detection of prostate cancer. In this review, we examine PSA testing and its effectiveness in the diagnosis of prostate cancer. Further, we also evaluate recent literature regarding the use of hk2.

Practical approaches to proteomic biomarkers within prostate cancer radiotherapy trials

INTRODUCTION

Proteomic biomarkers may be useful for monitoring therapeutic response and to triage cancer patients to best therapy.

OBJECTIVES

In this review, we highlight the importance of specimen acquisition, preparation and analysis in radiotherapy proteomic studies. We also discuss practical approaches for the design and execution of clinical proteomic studies using our recent experience based on specimens accrued during prostate cancer radiation therapy.

DISCUSSION AND CONCLUSIONS

Numerous proteomic methods are being employed, including high-throughput mass spectrometry and immunoassays, and using solid tissues, blood and urine for analysis. Given the potential complexity of cytokine and other protein responses, there is a need to assess proteomic signatures within serial samples as longitudinal studies during a course of fractionated radiotherapy (RT).

Serum markers for prostate cancer: a rational approach to the literature

INTRODUCTION

Due to its universal applicability for early detection and prediction of cancer stage and disease recurrence, widespread implementation of serum-based prostate-specific antigen (PSA) measurements has a significant influence on current treatment strategies for men with prostate cancer (PCa). However, over-detection and the resultant over-treatment of indolent cancers have been strongly implicated to occur. Using current recommended guidelines, the PSA test suffers from both limited sensitivity and specificity to enable efficacious population-based cancer detection. Therefore, novel biomarkers are much needed to complement PSA by enhancing its diagnostic and prognostic performance.

METHODS

The present literature on serum markers for PCa was reviewed. PSA derivatives, molecular PSA isoforms, and novel molecular targets in blood were summarized and weighted against their potential to improve decision-making of men with PCa.

RESULTS

Current evidence suggests that no single analyte is likely to achieve the desired level of diagnostic and prognostic accuracy for PCa. However, the combination of biomarkers with clinical and demographic data, for example, using established standard nomograms, has produced progress toward the goal of both optimal screening and risk assessment. Furthermore, potential candidate molecular markers for PCa can be derived from high-throughput technologies. Current studies demonstrate that understanding dynamic PSA changes over time may offer diagnostic and prognostic information.

CONCLUSIONS

Bridging the gap between basic science and clinical practice represents the main goal in the near future to enable physicians to tailor risk-adjusted screening and treatment strategies for current patients with PCa.

New circulating biomarkers for prostate cancer

The introduction of prostate-specific antigen (PSA) revolutionized prostate cancer (PCa) screening and ushered the PSA era. However, its use as a screening tool remains controversial and changes in the epidemiology of PCa have strongly limited its prognostic role. Therefore, we need novel approaches to improve our ability to detect PCa and foretell the course of the disease. To improve the specificity of total PSA, several approaches based on PSA derivatives have been investigated such as age-specific values, PSA density (PSAD), PSAD of the transition zone, PSA velocity and assessment of various isoforms of PSA. With recent advances in biotechnology such as high-throughput molecular analyses, many potential blood biomarkers have been identified and are currently under investigation. Given the plethora of candidate PCa biomarkers, we have chosen to discuss a select group of candidate blood-based biomarkers including human glandular kallikrein, early prostate cancer antigens, insulin-like growth factor-I (IGF-I) and its binding proteins (IGFBP-2 and IGFBP-3), urokinase plasminogen activation system, transforming growth factor-beta1, interleukin-6, chromogranin A, prostate secretory protein, prostate-specific membrane antigen, PCa-specific autoantibodies and alpha-methylacyl-CoA racemase. While these and other markers have shown promise in early phase studies, no single biomarker is likely to have the appropriate degree of certainty to dictate treatment decisions. Consequently, the future of cancer prognosis may rely on small panels of markers that can accurately predict PCa presence, stage, metastasis, and serve as prognosticators, targets and/or surrogate end points of disease progression and response to therapy.

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.

PSA and new biomarkers within multivariate models to improve early detection of prostate cancer

This review gives an overview of the use of prostate-specific antigen (PSA) and percent free-PSA (%fPSA)-based artificial neural networks (ANNs) and logistic regression models (LR) to reduce unnecessary prostate biopsies. There is a clear advantage in including clinical data such as age, digital rectal examination and transrectal ultrasound (TRUS) variables like prostate volume and PSA density as additional factors to tPSA and %fPSA within ANNs and LR models. There is also positive impact of tPSA and fPSA assays on the outcome of ANNs. New markers provide additional value within ANNs but to prove their clinical usefulness further testing is necessary.

Circulating biomarkers for prostate cancer

Due to its significant applicability for early detection, risk prediction and follow-up evaluation, prostate specific antigen (PSA) has revolutionized our ability to treat prostate cancer patients. With the prevalent use of PSA for early detection during the last two decades, disease characteristics have been altered towards early detected, localized tumors with a high chance of cure following local therapy. This advantage faces the risk of overdetection and overtreatment. In addition, PSA lacks both, sensitivity and specificity to accurately detect patients at risk of prostate cancer. Therefore, novel biomarkers are urgently needed to improve identification of men at risk of having the disease and to predict the natural behaviour of the tumor. Recent advances in the evaluation of high-throughput technologies have led to the discovery of novel candidate markers for prostate cancer. This article will briefly discuss current PSA-based strategies and review several novel biomarkers for prostate cancer, detectable in blood.

Molecular markers of prostate cancer

Although prostate-specific antigen (PSA) has evolved as a very useful tool for detection of prostate cancer, there remains an urgent need for more accurate biomarkers to diagnose prostate cancer and predict cancer-related outcomes. Recent advances in the study of proteomics and high throughput techniques have led to the discovery of many potential biomarkers for prostate cancer. This article briefly reviews the current status of PSA testing and discusses several candidate protein biomarkers for prostate cancer, as well as highlighting some recent proteomic discoveries with the potential to supplement or even replace PSA for the diagnosis and prognosis of prostate cancer.

Mutant recombinant serpins as highly specific inhibitors of human kallikrein 14

The reactive center loop (RCL) of serpins plays an essential role in the inhibition mechanism acting as a substrate for their target proteases. Changes within the RCL sequence modulate the specificity and reactivity of the serpin molecule. Recently, we reported the construction of alpha1-antichymotrypsin (ACT) variants with high specificity towards human kallikrein 2 (hK2) [Cloutier SM, Kündig C, Felber LM, Fattah OM, Chagas JR, Gygi CM, Jichlinski P, Leisinger HJ & Deperthes D (2004) Eur J Biochem271, 607-613] by changing amino acids surrounding the scissile bond of the RCL and obtained specific inhibitors towards hK2. Based on this approach, we developed highly specific recombinant inhibitors of human kallikrein 14 (hK14), a protease correlated with increased aggressiveness of prostate and breast cancers. In addition to the RCL permutation with hK14 phage display-selected substrates E8 (LQRAI) and G9 (TVDYA) [Felber LM, Borgoño CA, Cloutier SM, Kündig C, Kishi T, Chagas JR, Jichlinski P, Gygi CM, Leisinger HJ, Diamandis EP & Deperthes D (2005) Biol Chem386, 291-298], we studied the importance of the scaffold, serpins alpha1-antitrypsin (AAT) or ACT, to confer inhibitory specificity. All four resulting serpin variants ACT(E8), ACT(G9), AAT(E8) and AAT(G9) showed hK14 inhibitory activity and were able to form covalent complex with hK14. ACT inhibitors formed more stable complexes with hK14 than AAT variants. Whereas E8-based inhibitors demonstrated a rather relaxed specificity reacting with various proteases with trypsin-like activity including several human kallikreins, the two serpins variants containing the G9 sequence showed a very high selectivity for hK14. Such specific inhibitors might prove useful to elucidate the biological role of hK14 and/or its implication in cancer.

Free and total human glandular kallikrein 2 in patients with prostate cancer

OBJECTIVES

The use of prostate-specific antigen (PSA, hK3) results in the overdiagnosis and overtreatment of prostate cancer. Markers are needed that could identify aggressive, fast-growing tumors and help decide which patients would benefit most from aggressive treatment. Human glandular kallikrein 2 (hK2) could be such a marker. The aim of this study was to test how PSA and hK2 could predict the pathologic stage and grade in a set of patients with clinically organ-confined disease.

METHODS

Heparin plasma was collected from 188 patients who had undergone radical prostatectomy at the Turku University Central Hospital. Total and free PSA, as well as total and free hK2, were measured and the results compared with the pathologic TNM stage, tumor World Health Organization grade, and Gleason score.

RESULTS

Free and total hK2 performed similarly to PSA in their ability to separate groups of patients with different stages or grades. Concentrations of both kallikreins were significantly different in patients with World Health Organization grade 1 cancer compared with grade 2. Neither marker could separate patients with different Gleason scores. Although PSA concentrations increased most between patients with Stage pT2b and those with pT3a, the increase in hK2 was most pronounced between those with Stage pT3a and those with pT3b.

CONCLUSIONS

Although hK2 could not predict the cancer stage or grade better than PSA, changes in the hK2 and PSA concentrations occurred at different points in cancer progression. hK2 may have a role in the prognosis of prostate cancer, but additional studies with longer follow-up are required to determine whether hK2 can help when selecting treatment options.

Serum human glandular kallikrein 2 (hK2) for distinguishing stage and grade of prostate cancer

BACKGROUND

Human glandular kallikrein (hK2) has been shown to add important information regarding the early detection and staging of prostate cancer. Preliminary analysis pointed out that hK2 may discriminate between pT2 and pT3 tumors, and that hK2 may predict Gleason grade 4/5 cancer volume, better than prostate-specific antigen (PSA) or percent free PSA (%fPSA). We investigated the role of hK2 serum values for predicting pathological stage, grade and Gleason score.

METHODS

Prostate-specific antigen, free PSA and hK2 were measured on 222 untreated prostate cancer patients who had received radical prostatectomy at the Charité Hospital, Berlin, Germany. Pathological work up revealed pT2-cancer in 111 patients and pT3-cancer in 111 patients. Grade 2 was found in 118 patients whereas grade 3 tumors were found in 104 patients.

RESULTS

For pT2 and pT3 patients, the %fPSA (P=0.006), the ratios hK2/fPSA (P=0.08) and hK2xtPSA/fPSA (P=0.002) were all significant different whereas hK2 (P=0.143) and PSA (P=0.1) did not differ. Between grade 2 and grade 3 tumors, the hK2 alone (P=0.27), the %fPSA (P=0.13), the ratios hK2/fPSA (P=0.94) and hK2xtPSA/fPSA (P=0.12) did not separate, whereas PSA (P=0.039) showed a difference. The same relationships were found between the two groups in Gleason score<7 and >or=7. Neither the hK2 ratio, nor % fPSA was different.

CONCLUSION

Human glandular kallikrein was not different between pT2 and pT3, nor between G2 versus G3 or Gleason scores<7 and >or=7 prostate cancer. Together with %fPSA, hK2 may only help to distinguish preoperatively between pT2 and pT3 prostate cancer but cannot add further information.

Prostate Specific Antigen Isoforms and Human Glandular Kallikrein 2—Which Offers the Best Screening Performance in a Predominantly Black Population?

PURPOSE

Free prostate specific antigen, complexed PSA and human glandular kallikrein 2 have independently been tested against the gold standard of total PSA for prostate cancer screening in largely white populations. With the incidence of prostate cancer much higher in black men, we sought to evaluate these markers simultaneously in a predominantly black population.

MATERIALS AND METHODS

A total of 138 men, of whom 108 were black, underwent ultrasound guided biopsy of the prostate for tPSA levels greater than 2.5 ng/ml or an abnormal digital rectal examination. Sera were drawn before biopsy and analyzed for tPSA, fPSA, cPSA and hK2 concentrations using standard methods (hK2 assay is for research use only, not for use in diagnostic procedures). The areas under the receiver operator characteristic curves were determined for each marker as well as biomarker combinations. Additionally, each parameter's specificity, positive and negative predictive values, and theoretical screening efficiency were assessed at or above the 95% sensitivity level.

RESULTS

A total of 43 (31.1%) men had prostate cancer by biopsy. While the AUC for %fPSA was statistically the highest (0.822, p <0.001), cPSA offered the highest specificity (31.6%) and positive predictive power (31.7%) of any of the tested biomarkers at comparable sensitivity (greater than 95%). The calculated efficiency of cPSA (51.4%) was also higher than the other markers. Nearly 20% of biopsies would be avoided using cPSA vs standard tPSA screening methods.

CONCLUSIONS

Comparing the major PSA isoforms and hK2, cPSA alone appears to offer superior diagnostic discrimination for cancer detection in a predominantly black population.

Prognostic value of serum markers for prostate cancer

The incidence of prostate cancer has increased dramatically during the last 10-15 years and it is now the commonest cancer in males in developed countries. The increase is mainly caused by the increasing use of opportunistic screening or case-finding based on the use of prostate-specific antigen (PSA) testing in serum. With this approach, prostate cancer is detected 5-10 years before giving rise to symptoms and on average 17 years before causing the death of the patient. While this has led to detection of prostate cancer at a potentially curable stage, it has also led to substantial overdiagnosis, i.e. detection of cancers that would not surface clinically in the absence of screening. A major challenge is thus to identify the cases that need to be treated while avoiding diagnosing patients who will not benefit from being diagnosed and who will only suffer from the stigma of being a cancer patient. It would be useful to have prognostic markers that could predict which patients need to be diagnosed and which do not. Ideally, it should be possible to measure these markers using non-invasive techniques, i.e. by means of serum or urine tests. As it is very useful for both early diagnosis and monitoring of prostate cancer, PSA is considered the most valuable marker available for any tumor. Although the prognostic value of PSA is limited, measurement of the proportion of free PSA has improved the identification of patients with aggressive disease. Furthermore, the rate of increase in serum PSA reflects tumor growth rate and prognosis but, due to substantial physiological variation in serum PSA, reliable estimation of the rate of PSA increase requires follow-up for at least 2 years. Algorithms based on the combined use of free and total PSA and prostate volume in logistic regression and neural networks can improve the diagnostic accuracy for prostate cancer, and assays for minor subfractions of PSA and other new markers may provide additional prognostic information. Markers of neuroendocrine differentiation are useful for the monitoring of androgen-independent disease and various bone markers are useful in patients with metastatic disease.

HUMAN KALLIKREIN-2 GENE POLYMORPHISM IS ASSOCIATED WITH THE OCCURRENCE OF PROSTATE CANCER

PURPOSE

Human glandular kallikrein, which is encoded by the human kallikrein-2 (KLK2) gene, is significantly associated with the occurrence of prostate cancer (PCa). We tested the association between a functional C748T polymorphism of the KLK2 gene and the occurrence of PCa.

MATERIALS AND METHODS

Peripheral venous blood samples were obtained from 254 patients with PCa and 168 controls with benign prostatic hyperplasia. All control subjects had normal serum prostate specific antigen and proved to be free from malignancy on pathological examination of resected prostatic tissues. Serum prostate specific antigen, testosterone, Gleason score, clinical and pathological stage, tumor and prostate volume of the patients were investigated. The KLK2 gene polymorphism was determined by the polymerase chain reaction based restriction fragment length polymorphism method.

RESULTS

The PCa group had a younger mean age +/- SEM (73.0 +/- 0.5 vs 74.7 +/- 0.5 years, p = 0.010) and higher C allele frequency (82.1% vs 74.7%, p = 0.010) than the control group. The frequency of the CC, CT and TT genotypes was 65.7%, 32.7% and 1.6% in patients with PCa, and 56.0%, 37.5% and 6.5%, respectively, in controls (p = 0.010). C allele carriers (CC and CT genotypes) were at significantly higher risk for PCa than TT homozygous subjects (p = 0.002). CC homozygous subjects were at significantly higher risk for PCa than T allele carriers (CT and TT genotypes) (p = 0.043). The PCa subgroup of patients with pathologically proved, localized PCa also had a higher frequency of the C allele (87.5% vs 74.7%, p = 0.026) and CC genotypes (78.7% vs 56.0%, p = 0.019) than controls.

CONCLUSIONS

Our results suggest that the C allele of the functional C748T polymorphism of KLK2 may increase the risk of PCa.

The evolution of the glandular kallikrein locus: identification of orthologs and pseudogenes in the cotton-top tamarin

Comparisons of the glandular kallikreins loci in human, mouse and rat revealed remarkable differences. For example, the mouse and the rat lack the genes encoding prostate-specific antigen (PSA) and human glandular kallikrein 2 (hK2). In contrast, the intergenic region between KLK1 and KLK15 is devoid of genes and spans only 1.5 kb in humans, but encompasses 23 KLK1-like genes spanning 290 kb in the mouse. To further elucidate the evolution of glandular kallikrein genes, we investigated the structure and organization of these genes in the cotton-top tamarin (Saguinus oedipus), a New World monkey. We conclude that this species has no PSA gene. Moreover, the ortholog of the hK2 gene is a pseudogene, as it contains several mutations that preclude formation of a functional serine protease. The expression of this gene was probably silenced by a 15-bp deletion observed in an androgen response element in the upstream promoter region. Replacing the deleted base pairs in vitro with nucleotides from the human counterpart dramatically restored the transcriptional activity to a level that even surpassed that of the human ortholog. We also determined the nucleotide sequence of KLK15 and the intergenic region between this gene and KLK1 in the cotton-top tamarin. The region between KLK1 and KLK15 is conserved between the cotton-top tamarin and humans, and there are no signs of the extension seen in the mouse. KLK15 appeared to be functional, thus, we predict that it generates a protease with specificity similar to that of the human ortholog.

Applicability of biomarkers in the early diagnosis of prostate cancer

Early diagnosis of prostate cancer can increase the curative success rate for this disease. Although serum prostate-specific antigen measurement is regarded as the best conventional tumor marker available, there is little doubt that it has great limitations. The threshold above which biopsies are indicated has now decreased to a serum prostate-specific antigen value of 3 ng/ml, which results in a negative biopsy rate of 70-80%. This can readily be explained by the fact that prostate-specific antigen is not specific for prostate cancer. Clinicians need more sensitive tools to help diagnose prostate cancer and monitor progression of the disease. Molecular oncology is playing an increasing role in the fields of diagnosis and therapy for prostate cancer and has already been instrumental in elucidating many of the basic mechanisms underlying the development and progression of this disease. The identification of new prostate cancer-specific genes, such as DD3PCA3, would represent a considerable advance in the improvement of diagnostic tests for prostate cancer. This could subsequently lead to a reduction of the number of unnecessary biopsies.

Development of sensitive immunoassays for free and total human glandular kallikrein 2

BACKGROUND

Free and total human kallikrein 2 (hK2) might improve the discrimination between prostate cancer and benign prostatic hyperplasia. Concentrations of hK2 are 100-fold lower than concentrations of prostate-specific antigen (PSA); therefore, an hK2 assay must have a low detection limit and good specificity.

METHODS

PSA- and hK2-specific monoclonal antibodies were used in solid-phase, two-site immunofluorometric assays to detect free and total hK2. The total hK2 assay used PSA-specific antibodies to block nonspecific signal. The capture antibody of the free hK2 assay did not cross-react with PSA. To determine the hK2 concentrations in the male bloodstream, total hK2 was measured in a control group consisting of 426 noncharacterized serum samples. Free and total hK2 were measured in plasma from 103 patients with confirmed prostate cancer.

RESULTS

All 426 males in the control group had a total hK2 concentration above the detection limit of 0.0008 microg/L. The median total hK2 concentration was 0.022 microg/L (range, 0.0015-0.37 microg/L). hK2 concentrations were 0.1-58% of total PSA (median, 3.6%). hK2 concentrations were similar in men 41-50 and 51-60 years of age. The ratio of hK2 to PSA steadily decreased from 5-30% at PSA <1 microg/L to 1-2% at higher PSA concentrations. In 103 patients with prostate cancer, the median hK2 concentration in plasma was 0.079 microg/L (range, 0.0015-16.2 microg/L). The median free hK2 concentration was 0.070 (range, 0.005-12.2) microg/L. The proportion of free to total hK2 varied from 17% to 131% (mean, 85%).

CONCLUSIONS

The wide variation in the free-to-total hK2 ratio suggests that hK2 in blood plasma is not consistently in the free, noncomplexed form in patients with prostate cancer. The new assay is sufficiently sensitive to be used to study the diagnostic accuracies of free and total hK2 for prostate cancer.

Are multiple markers the future of prostate cancer diagnostics?

Prostate specific antigen (PSA) is the most successful and widely employed cancer serum marker in use today. There is growing evidence that the introduction of wide PSA screening and earlier detection can result in decreased cancer mortality associated with a decline in metastatic disease. PSA circulates in a number of distinct forms. Measurement of these in addition to total PSA significantly increases diagnostic utility. Diagnostic utility is likely to be further increased by adding kallikreins, cytokines, growth factors, receptors and cellular adhesion factors to the biomarker panel. The need for multiple markers reflects the multidimensional nature of prostate disease which ranges from metastatic cancer to indolent cancer to benign hyperplasia and inflammation, all of which require distinct treatments and medical interventions.

Rapid elimination by glomerular filtration of free prostate specific antigen and human kallikrein 2 after renal transplantation

PURPOSE

The low molecular mass and short half-life of free (f) prostate specific antigen (PSA) implies elimination from blood by glomerular filtration. In addition, patients with terminal renal failure have increased fPSA in serum but there have been sparse data reported on the rates and pathways of elimination of PSA complexes and human kallikrein 2 (hK2). We studied glomerular filtration dependent elimination of fPSA and hK2 in patients with renal insufficiency undergoing successful renal transplantation.

MATERIALS AND METHODS

We studied 14 patients with immediate onset of renal function after renal transplantation. Blood samples were obtained before and at regular intervals up to 160 hours after transplanted kidney reperfusion. Measurements of fPSA, total PSA and hK2 were performed with immunofluorometric assays and complexed PSA was determined by a chemiluminiscence assay. Glomerular filtration rates were monitored by analyzing serum creatinine and cystatin C. NONMEM, a multivariate pharmacokinetic approach, was used to determine the elimination rates of fPSA and hK2 after renal transplantation.

RESULTS

Serum fPSA and hK2 but not PSA complexes, decreased rapidly after renal transplantation. Significant reductions in fPSA and hK2 were observed after only 16 and 8 hours, respectively. fPSA and hK2 showed similar elimination patterns, decreasing to 42% and 44% of their original levels compared to cystatin C, which was at 44% after 160 hours. The median half-lives of fPSA and hK2 were 17.4 and 11.5 hours, respectively.

CONCLUSIONS

These results verify the hypothesis that fPSA and hK2 are eliminated from the blood circulation by glomerular filtration and severe renal failure influences the levels of the 2 proteins in serum.

Prostate-specific antigen and related isoforms in the diagnosis and management of prostate cancer

Despite its unparalleled merits for prostate cancer detection and staging, prostate-specific antigen (PSA) is not a marker for prostate cancer only, but also is expressed in benign conditions. For early detection, limitations of PSA are obvious. Its widespread use has led to an extensive amount of expensive and often unnecessary diagnostic procedures associated with significant morbidity. Total PSA derivatives may enhance the accuracy of prostate cancer diagnosis. The ratio of free-to-total PSA improves specificity while maintaining a high sensitivity for prostate cancer detection for men with a total PSA of 2.5 to 10 ng/mL. Human glandular kallikrein also has the potential to be a valuable tool in combination with total and free PSA for early diagnosis of prostate cancer. Complex PSA seems to be a reliable tool to improve specificity at high sensitivity levels in men with suspected prostate cancer (mainly in PSA levels below 4 ng/mL). Newly discovered isoforms of free PSA also may impact early detection of prostate cancer with encouraging preliminary results that warrant further clinical investigation.

Early detection of prostate cancer in African-American men through use of multiple biomarkers: human kallikrein 2 (hK2), prostate-specific antigen (PSA), and free PSA (fPSA)

Recent studies have reported enhanced prostate cancer detection in Caucasians with serum human glandular kallikrein 2 (hK2) in combination with total- (tPSA) and free-prostate-specific antigen (fPSA). The purpose of this study is to validate these findings in an African-American patient cohort. A total of 137 African-American men were found by routine screening to have tPSA levels above 2.5 ng/ml or an abnormal digital rectal examination. Sera were drawn prior to biopsy of the prostate and Hybritech PSA, FPSA and hK2 (for research use only, not for use in diagnostic procedures) concentrations were determined on Beckman Coulter's Access immunoanalyzer. These independent variables and the ratios of percent fPSA (%fPSA), hK2/tPSA, hK2/fPSA, and hK2*tPSA/fPSA were compared between cancer and non-cancer groups. In all, 49 of 137 men had prostate cancer. hK2 and its calculated ratios outperformed tPSA on receiver operator characteristic (ROC) analysis, but %fPSA had statistically the highest area under the curve (AUC) at 0.801. When restricting the analysis to only the tPSA range of 4.0-10 ng/ml, hK2/fPSA yielded the highest AUC (0.721). The ratio of hK2/fPSA was also found to increase the positive predictive value (PPV) of the %fPSA ranges less than 10 and 10-25%. %fPSA offered the best performance and highest specificity in prostate cancer detection in African-American males over the entire range of tPSA. hK2/fPSA may offer modest improvement in the tPSA range of 4.0-10 ng/ml. Furthermore, hK2/fPSA can enhance the PPV of low %fPSA values. Therefore, the use of multiple biomarkers may ultimately increase the specificity of prostate cancer screening in African-American men.

Testing in Serum for Human Glandular Kallikrein 2, and Free and Total Prostate Specific Antigen in Biannual Screening for Prostate Cancer

PURPOSE

We investigated the value of serum measurements for glandular kallikrein 2 (hK2), and free (f) and total (t) prostate specific antigen (PSA) in a second round of biannual screening for prostate cancer.

MATERIALS AND METHODS

In 1995 to 1996, 5,853 of 9,811 randomly selected men in Göteborg, Sweden 50 to 66 years old had PSA measurements. Of 660 men 611 with tPSA 3 ng/ml or greater underwent biopsy and 145 had cancer. All were re-invited 2 years later for PSA testing, and 506 of 596 men with tPSA 3 ng/ml or greater underwent biopsy and 113 cancers were detected. We analyzed hK2, tPSA and fPSA in 423 of 453 (93%) men who underwent biopsy in 1997 to 1998 who were also screened in 1995 to 1996.

RESULTS

The 99 of 423 (23%) men who underwent biopsy diagnosed with prostate cancer in 1997 to 1998 had significantly different tPSA, percent fPSA and hK2 x tPSA/fPSA compared to the men with negative biopsies from 2 years earlier. The largest area under curve was obtained for hK2 x tPSA/fPSA in serum from 1995 to 1996 and from 1997 to 1998, but the difference was not significant compared to tPSA and percent fPSA. In serum from 1997 to 1998 measurements of hK2 x tPSA/fPSA gave significantly higher specificity than tPSA at 85% sensitivity, and significantly higher specificity than tPSA and percent fPSA at 70% to 75% sensitivity. In addition, levels of hK2 and hK2 x tPSA/fPSA manifested a significantly greater 2-year increase in men with cancer compared to those with benign biopsies.

CONCLUSIONS

In men with tPSA levels 3.0 ng/ml or greater who were not diagnosed with cancer during a first round of screening, hK2 measurements enhanced specificity compared to tPSA testing at moderately high sensitivity, and manifested a greater 2-year increase in men with cancer.

Standardization of two immunoassays for human glandular kallikrein 2

BACKGROUND

Measurement of human kallikrein 2 (hK2) has improved early detection and staging of prostate cancer. However, reported concentrations of hK2 among currently used assays have not been standardized in any way. We compared two hK2 assays and five different recombinant hK2 variants (rhK2) and suggest a common calibrator as an important step and putative reference substance in hK2 assay standardization.

METHODS

We measured 146 sera by two hK2 assays, using assay-specific calibrators to assess the difference between the two assays. Serial dilutions of five rhK2 preparations were measured repeatedly, with one preparation assigned as calibrator and the others as unknowns to define which variant provided the closest match between the two assays. This rhK2 variant was used to recalibrate both assays. We measured hK2 concentrations in the same 146 patients to evaluate the change in the difference.

RESULTS

Use of assay-specific calibrators for comparison of the two assays yielded a Deming regression equation of: y = 0.789 (95% confidence interval, 0.674-0.922)x + 0.014 (0.004-0.025) micro g/L; R(2) = 0.667. Analysis of five rhK2 variants revealed that the enterokinase (ek)-rhK2 form provided the best match between both assays. Using the ek-rhK2 as a common calibrator, we observed a change in the slope of the regression curve to: y = 1.106 (0.872-1.340)x + 0.006 (-0.002 to 0.016) micro g/L; R(2) = 0.648, suggesting an increase in the mean estimate of agreement between the two assays.

CONCLUSION

Calibration with a common calibrator substantially increased agreement between the assays. The ek-rhK2 variant provided the best performance of all tested rhK2 variants and should undergo mass spectrometry and amino acid analysis for exact mass determination and value assignment to evaluate its potential as a reference material for immunoassays for hK2.

The role of human glandular kallikrein 2 for prediction of pathologically organ confined prostate cancer

BACKGROUND

In recent studies serum levels of human glandular kallikrein 2 (hK2) demonstrated significant differences in pathologically organ-confined versus non-organ-confined prostate cancer (PCa). In this study we investigated whether hK2 adds independent information when considered together with traditionally used parameters to predict organ confined (pT2a/b) PCa.

METHODS

Serum levels of hK2, total and free prostate-specific antigens (PSA) were obtained one day before radical prostatectomy in 245 consecutive men. These were included with clinical stage and biopsy Gleason grade into univariate analysis and multivariate logistic regression models.

RESULTS

pT2a/b PCa was found in n = 148 patients. In univariate analysis all preoperative parameters demonstrated significant association with the presence of pT2a/b PCa. Using multivariate logistic regression model hK2 (P = 0.022), clinical stage (P < 0.0001), and Gleason grade (P < 0.0001) were independent predictors of pT2a/b PCa whereas PSA (P = 0.3) was not. In bootstrap corrected logistic regression based nomograms the addition of hK2 density marginally enhanced predictive accuracy when PSA, PSA density, clinical stage, and Gleason grade were considered (AUC = 0.879 without hK2 density and 0.883 with hK2 density).

CONCLUSIONS

hK2 and hK2 density could independently predict pT2a/b PCa. However, improvement in predictive accuracy was marginal when nomograms based on traditional variables were complemented with this serum marker.

Serum human glandular kallikrein (hK2) and insulin-like growth factor 1 (IGF-1) improve the discrimination between prostate cancer and benign prostatic hyperplasia in combination with total and %free PSA

BACKGROUND

There is growing evidence describing an association of hK2 and IGFs with cancer. The aim of this study is to investigate the differences in serum levels of hK2 and IGFs in a large group of patients with benign prostatic hyperplasia (BPH) or prostatic carcinoma (CaP) and to examine the value of these variables, as well as their various combinations with PSA, for discriminating between these two clinical entities.

METHODS

Human glandular kallikrein 2 (hK2), insulin-like growth factor-1 (IGF-1), free and total PSA concentrations were measured with non-competitive immunological procedures. Receiver operating characteristic (ROC) analysis as well as univariate and multivariate logistic regression analysis were performed to investigate the potential utility of the various markers and their combinations for discriminating between BPH and CaP.

RESULTS

hK2 and IGF-1 concentrations were increased in CaP patients, in comparison to BPH patients. hK2/free PSA and free/total PSA ratios (area under the curve, AUC = 0.70) were stronger predictors of prostate cancer than the IGF-1/total PSA ratio (AUC = 0.56) in the group of patients with total PSA <4 microg/L. The hK2/free PSA ratio (AUC = 0.74) was found to have significant discriminatory value in patients with total PSA within the "gray zone" (4-10 microg/L). Multivariate logistic regression models confirmed the observed relationships and identified IGF-1/free PSA and hK2/free PSA as independent predictors of CaP.

CONCLUSIONS

hK2/free PSA and IGF-1/free PSA ratios may be useful adjuncts in improving patient selection for prostate biopsy.

Simultaneous Quantification of Prostate-specific Antigen and Human Glandular Kallikrein 2 mRNA in Blood Samples from Patients with Prostate Cancer and Benign Disease

Background: Detection or quantification of circulating cancer cells has been proposed as an aid in detection and monitoring of several solid tumors. We investigated the classification accuracy of prostate-specific antigen (PSA) and human glandular kallikrein 2 (hK2) mRNA copy numbers in blood for the differentiation of patients with prostate cancer (PC) and benign disease.

Methods: PSA and hK2 mRNA expression was studied in blood samples from 51 men with PC and 19 men with benign disease. Among the PC patients, 10 had organ-confined disease (pT1–pT2). We used a multiplexed reverse transcription-PCR assay with two highly target-like mRNA internal standards for the simultaneous quantification of PSA and hK2 mRNA. An external calibration curve covered the range of 102–106 mRNA copies.

Results: PSA and hK2 mRNA were detected in 41 of 51 (median, 1200 copies/0.5 mL of blood) and 43 of 51 (median, 3800 copies/0.5 mL of blood) patients with PC, respectively, whereas only 1 of 19 men with benign disease was positive for both mRNAs (1500 PSA and 3100 hK2 mRNA copies/0.5 mL of blood; P &lt;0.0001, Mann–Whitney U-test). Of the 10 patients with organ-confined PC, only 3 with low Gleason scores (≤5) were negative for both PSA and hK2 (P = 0.02, Mann–Whitney U-test).

Conclusions: The presence of PC cells in the blood circulation is an early event in PC progression, and quantitative assays for PSA and hK2 mRNA discriminate benign from PC cases. Further studies are needed to determine the diagnostic accuracy and prognostic value of the assays.

Separation methods applicable to prostate cancer diagnosis and monitoring therapy

During the last decade, significant research has been conducted using prostate-specific antigen (PSA) in the basic and clinical sciences and many advances have occurred in the clinical use of PSA for detecting and monitoring prostate cancer (PCa). Separation methods including gel-permeation chromatography, isoelectric focusing, lectin-affinity chromatography, polyacrylamide gel electrophoresis and high-performance liquid chromatography have made significant contributions to the discovery and identification of different molecular forms of PSA. Furthermore, the measurement of free and total PSA has improved the ability of PSA to detect early PCa. However, unnecessary biopsies are still needed for men with slightly elevated PSA values. On the other hand, PSA is not adequate for staging newly diagnosed PCa and prognosticating the course in individual cases. The possible application of separation methods in the basic science of prostate cancer may be associated with identification of more cancer-specific forms of PSA and discoveries of other serum proteins useful not only for detecting, but also for staging and prognosticating PCa. Such novel markers might lead to a better understanding of PCa aggressiveness and to developments in the clinical field of treatment.