"BPSA," a specific molecular form of free prostate-specific antigen, is found predominantly in the transition zone of patients with nodular benign prostatic hyperplasia

Ejaculation physiology and dysfunction after BPH surgery: the role of the new MISTs

BACKGROUND

Human ejaculation can be defined as a complex and still largely unknown function. Since decades, Benign Prostatic Hyperplasia (BPH) surgery-associated loss of antegrade ejaculation has been reported as a bother by many patients. New technologies and modified surgical techniques were developed, to reduce the impact of ejaculatory dysfunction on patients' perceived quality of life. Recently, the emerging of the new Minimally Invasive Surgical Techniques (MISTs) empowered the urological surgeons with the technological means to introduce the ejaculation-sparing principles into everyday clinical practice.

METHODS

Our paper was conceived as a state-of-the-art analysis about the anatomical and physiological premises of the human ejaculation and their clinical application in the field of ejaculation-sparing surgery for the treatment of Lower Urinary Tract Symptoms (LUTS). Moreover, we proposed an innovative physiological model for antegrade ejaculation.

RESULTS

We analysed the elements of the "ejaculatory apparatus" from an anatomical point of view. We investigated the physio-pathological models of the human ejaculation, from the classical "combustion chamber" paradigm to the new evidences by which it could be overcome. Finally, we provided a synthetic literature review about the ejaculation-sparing techniques for BPH surgery. Particularly, we distinguished them between classical techniques, modified for ejaculation-preserving purposes, and the new MISTs, characterized by the introduction of new technologies and different treatment modalities.

CONCLUSIONS

Modified surgical techniques and new technologies opened new perspectives about human ejaculation. Previously established functional paradigms were questioned and overcome by recent clinical evidence. The new MISTs gained a prominent role in the process, opening a whole new era for BPH surgery.

Software-Assisted Data Processing Workflow for Intact Glycoprotein Mass Spectrometry

Intact protein analysis by mass spectrometry is important for several applications such as assessing post-translational modifications and biotransformation. In particular, intact protein analysis allows the detection of proteoforms that are commonly missed by other approaches such as proteolytic digestion followed by bottom-up analysis. Two quantification methods are mainly used for intact protein data quantification, namely the extracted ion and deconvolution approaches. However, a consensus with regard to a single best practice for intact protein data processing is lacking. Furthermore, many data processing tools are not fit-for-purpose and, as a result, the analysis of intact proteins is laborious and lacks the throughput required to be implemented for the analysis of clinical cohorts. Therefore, in this study, we investigated the application of a software-assisted data analysis and processing workflow in order to streamline intact protein integration, annotation, and quantification via deconvolution. In addition, the assessment of orthogonal data sets generated via middle-up and bottom-up analysis enabled the cross-validation of cleavage proteoform assignments present in seminal prostate-specific antigen (PSA). Furthermore, deconvolution quantification of PSA from patients' urine revealed results that were comparable with manually performed quantification based on extracted ion electropherograms. Overall, the presented workflow allows fast and efficient processing of intact protein data. The raw data is available on MassIVE using the identifier MSV000086699.

Profiling the proteoforms of urinary prostate-specific antigen by capillary electrophoresis - mass spectrometry

Early detection of prostate cancer may lead to the overdiagnosis and overtreatment of patients as well as missing significant cancers. The current diagnostic approach uses elevated serum concentrations of prostate-specific antigen (PSA) as an indicator of risk. However, this test has been widely criticized as it shows poor specificity and sensitivity. In order to improve early detection and diagnosis, several studies have investigated whether different PSA proteoforms are correlated to prostate cancer. Until now, studies and methodologies for the comprehensive characterization of PSA proteoforms from biofluids are scarce. For this purpose, we developed an intact protein assay to analyze PSA by capillary electrophoresis-electrospray ionization-mass spectrometry after affinity purification from patients' urine. Here, we determined six proteolytic cleavage variants. In regard to glycosylation, tri-, di-, mono- and non-sialylated complex-type N-glycans were found on non-cleaved PSA, as well as the non-glycosylated variant. The performance of the intact protein assay was assessed using a pooled sample, obtaining an inter-day variability of 15%. Furthermore, urinary patient samples were analyzed by intact protein analysis and a bottom-up approach (glycopeptide analysis). This combined approach revealed complimentary information on both levels, demonstrating the benefit of using two orthogonal techniques to provide a thorough profile of urinary PSA. SIGNIFICANCE: The detection of clinically relevant prostate cancer requires a more specific and sensitive biomarker and, in this case, several PSA proteoforms may be able to aid or improve the current PSA test. However, a comprehensive analysis of the intact PSA proteoform profile is still lacking. This study investigated the PSA proteoforms present in urine and, in particular, determined the relative contribution of cleaved PSA and non-cleaved PSA forms to the total glycosylation profile. Importantly, intact protein analysis did not require further sample treatment before being measured by CE-ESI-MS. Furthermore, its glycosylation was also assessed in a bottom-up approach to provide complementary information. Overall, these results represent an important basis for future characterization and biomarker studies.

Towards the differential diagnosis of prostate cancer by the pre-treatment of human urine using ionic liquids

Prostate specific antigen (PSA) is the most widely used clinical biomarker for the diagnosis and monitoring of prostate cancer. Most available techniques for PSA quantification in human fluids require extensive sample processing and expensive immunoassays that are often unavailable in developing countries. The quantification of PSA in serum is the most common practice; however, PSA is also present in human urine, although less used in diagnosis. Herein we demonstrate the use of ionic-liquid-based aqueous biphasic systems (IL-based ABS) as effective pre-treatment strategies of human urine, allowing the PSA detection and quantification by more expedite equipment in a non-invasive matrix. If properly designed, IL-based ABS afford the simultaneous extraction and concentration of PSA (at least up to 250-fold) in the IL-rich phase. The best ABS not only allow to concentrate PSA but also other forms of PSA, which can be additionally quantified, paving the way to their use in differential prostate cancer diagnosis.

Mesenchymal stem cells and the embryonic reawakening theory of BPH

The prostate is the only organ in a man that continues to grow with age. John McNeal proposed, 40 years ago, that this BPH is characterized by an age-related reinitiation of benign neoplastic growth selectively in developmentally abortive distal ducts within the prostate transition-periurethral zone (TPZ), owing to a reawakening of inductive stroma selectively within these zones. An innovative variant of this hypothesis is that, owing to its location, the TPZ is continuously exposed to urinary components and/or autoantigens, which produces an inflammatory TPZ microenvironment that promotes recruitment of bone marrow-derived mesenchymal stem cells (MSCs) and generates a paracrine-inductive stroma that reinitiates benign neoplastic nodular growth. In support of this hypothesis, MSCs infiltrate human BPH tissue and have the ability to stimulate epithelial stem cell growth. These results provide a framework for defining both the aetiology of BPH in ageing men and insights into new therapeutic approaches.

Human Serum Low Molecular Mass Prostate-specific Antigen As Biomarker

Background

Prostate-specific antigen (PSA) is a glycoprotein tumor marker known to exist as numerous glycospecies. Investigations on its glycobiochemical properties aimed at their use in the preparation of adjuncts in determining PSA concentration for clinical purposes have accumulated a lot of data on its structural properties. In this study, we reconsidered unexplored ubiquitously present low molecular mass species of PSA regarding to molecular mass, origin and pathophysiological source specificity in order to evaluate them as biomarkers.

Methods

Data on low molecular mass PSA-immunoreactive species from sera of subjects with prostate cancer (PCa), benign prostatic hyperplasia (BPH), breast cancer (BCa), and urine of healthy males obtained by on-chip immunoaffinity chromatography combined with mass spectrometry were analyzed.

Results

The results obtained indicated PSA species common to BCa, PCa, and BPH at 12-13 kDa, 17-19 kDa and 21-24 kDa. The striking difference in predominant frequencies made the profile characteristic in each examined pathophysiological condition. On the other hand, paired groups of prostatic and extraprostatic PSA contained rare species with small differences among groups concerning individual species. Low molecular mass PSA also included rare species unique for each group of samples.

Conclusion

The results obtained revealed that uniformity of low molecular mass PSA-immunoreactive species in sera prevails over diversity related to cancer and non-cancer conditions, but at the same time some of them are molecules with biomarker potential for BPH detection.

Mutational Analysis of Prostate-Specific Antigen Defines the Intrinsic Proteolytic Activity of the proPSA Zymogen

BACKGROUND

Prostate-specific antigen (PSA) is an important prostate cancer biomarker. It is also a protease expressed at high concentrations by the normal and malignant prostate. PSA is secreted as a zymogen (proPSA) with an inhibitory prodomain that must be removed for full activity. ProPSA variants, assumed to be inactive, are found in the blood of prostate cancer patients, and are indicative of poor clinical outcome. Despite the abundance of clinical reports, our understanding of PSA's enzymology is limited, in part due to a lack of appropriate experimental systems. We sought to develop a series of PSA-derived mutants that would help to enhance our understanding of the gene.

METHODS

Sixteen rPSA variants were generated and characterized by a variety of biochemical methods.

RESULTS

The wildtype cDNA (WT) provided the template for generating a panel of recombinants. These included variants that abolished removal of the prodomain (R24A), disabled its enzymatic activity (S213A), and/or facilitated a cell-based conversion to the active conformation (FR). The purified variants' proteolytic activity was examined using a fluorogenic substrate, known PSA-cleavable proteins, and physiologically relevant inhibitors. Upon demonstrating our successful generation and purification of the PSA variants, we characterized proPSA activity, describing cleavage of synthetic and biologic substrates, but not serum protease inhibitors. This finding was exploited in the development of a self-activating mutant (PSA_QY) that exhibited the greatest enzymatic activity of all the variants.

CONCLUSIONS

The system described herein will prove useful for varied applications. ProPSA is partially functional with relatively high activity compared to the mature enzyme. In demonstrating the zymogen's intrinsic activity, we suggest that the proPSA in prostate cancer patient serum is not inert. This may have implications for our understanding of the disease. Prostate 76:1203-1217, 2016. © 2016 Wiley Periodicals, Inc.

A Single Glycan at the 99-Loop of Human Kallikrein-related Peptidase 2 Regulates Activation and Enzymatic Activity

Human kallikrein-related peptidase 2 (KLK2) is a key serine protease in semen liquefaction and prostate cancer together with KLK3/prostate-specific antigen. In order to decipher the function of its potential N-glycosylation site, we produced pro-KLK2 in Leishmania tarentolae cells and compared it with its non-glycosylated counterpart from Escherichia coli expression. Mass spectrometry revealed that Asn-95 carries a core glycan, consisting of two GlcNAc and three hexoses. Autocatalytic activation was retarded in glyco-pro-KLK2, whereas the activated glyco-form exhibited an increased proteolytic resistance. The specificity patterns obtained by the PICS (proteomic identification of protease cleavage sites) method are similar for both KLK2 variants, with a major preference for P1-Arg. However, glycosylation changes the enzymatic activity of KLK2 in a drastically substrate-dependent manner. Although glyco-KLK2 has a considerably lower catalytic efficiency than glycan-free KLK2 toward peptidic substrates with P2-Phe, the situation was reverted toward protein substrates, such as glyco-pro-KLK2 itself. These findings can be rationalized by the glycan-carrying 99-loop that prefers to cover the active site like a lid. By contrast, the non-glycosylated 99-loop seems to favor a wide open conformation, which mostly increases the apparent affinity for the substrates (i.e. by a reduction of K_m). Also, the cleavage pattern and kinetics in autolytic inactivation of both KLK2 variants can be explained by a shift of the target sites due to the presence of the glycan. These striking effects of glycosylation pave the way to a deeper understanding of kallikrein-related peptidase biology and pathology.

Prostate Specific Antigen as a Tumor Marker in Prostate Cancer: Biochemical and Clinical Aspects

In this chapter the use of prostate specific antigen (PSA) as a tumor marker for prostate cancer is discussed. The chapter provides an overview of biological and clinical aspects of PSA. The main drawback of total PSA (tPSA) is its lack of specificity for prostate cancer which leads to unnecessary biopsies. Moreover, PSA-testing poses a risk of overdiagnosis and subsequent overtreatment. Many PSA-based markers have been developed to improve the performance characteristics of tPSA. As well as different molecular subforms of tPSA, such as proPSA (pPSA) and free PSA (fPSA), and PSA derived kinetics as PSA-velocity (PSAV) and PSA-doubling time (PSADT). The prostate health index (phi), PSA-density (PSAD) and the contribution of non PSA-based markers such as the urinary transcripts of PCA3 and TMPRSS-ERG fusion are also discussed. To enable further risk stratification tumor markers are often combined with clinical data (e.g. outcome of DRE) in so-called nomograms. Currently the role of magnetic resonance imaging (MRI) in the detection and staging of prostate cancer is being explored.

Implementation of PSA-based active surveillance in prostate cancer

Prostate cancer screening had led to the diagnosis of a large proportion of localized and low-risk disease. Many of these cancer cases are believed to be indolent and would not be clinically perceived in the absence of screening. In addition to that, the wide use of active treatment has exposed these patients to treatment-related quality-of-life impact. In this setting active surveillance as a way of deferring active treatment and reserving such treatment to cases of disease progression only has gained interest. PSA has been widely used to identify patients eligible for active surveillance and also for disease monitoring. The goal of this review was to describe the place of PSA in the monitoring of patients under active surveillance based on the existing studies and to discuss the importance of PSA in light of other existing or emerging tools to monitor prostate cancer in active surveillance.

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.

Prostate cancer biomarkers: an update

Many aspects of prostate cancer diagnosis and treatment could be greatly advanced with new, effective biomarkers. Prostate-specific antigen (PSA) has multiple weaknesses as a biomarker, such as not distinguishing well between cancer and benign prostatic hyperplasia or between indolent and aggressive cancers, thus leading to overtreatment, especially unnecessary biopsies. PSA also often fails to indicate accurately which patients are responding to a given treatment. Yet PSA is the only prostate cancer biomarker routinely used by urologists. Here, we provide updated information on the most relevant of the other biomarkers currently in use or in development for prostate cancer. Recent research shows improvement over using PSA alone by comparing total PSA (tPSA) or free PSA (fPSA) with new, related markers, such as prostate cancer antigen (PCA) 3, the individual molecular forms of PSA (proPSA, benign PSA, and intact PSA), and kallikreins other than PSA. Promising results have also been seen with the use of the fusion gene TMPRSS2:ERG and with various forms of the urokinase plasminogen activation receptor. Initially, there were high hopes for early PCA, but those data were not reproducible and thus research on early PCA has been abandoned. Much work remains to be done before any of these biomarkers are fully validated and accepted. Currently, the only markers discussed in this paper with Food and Drug Administration-approved tests are PCA 3 and an isoform of proPSA, [-2]proPSA. Assays are in development for most of the other biomarkers described in this paper. While the biomarker validation process can be long and filled with obstacles, the rewards will be great-in terms of both patient care and costs to the health care system.

Evaluation of molecular species of prostate-specific antigen complexed with immunoglobulin M in prostate cancer and benign prostatic hyperplasia

This study was aimed at defining molecular species of prostate-specific antigen (PSA) in immune complexes with immunoglobulin M (IgM). Having in mind the oligoreactivity of IgM and its preference for carbohydrate antigens, there is the possibility that it can selectively recognize known PSA glycoisoforms. PSA-IgM complexes and free PSA fractions were separated from the sera of subjects with prostate cancer (PCa) and benign prostatic hyperplasia (BPH) by gel filtration and subjected to on-chip immunoaffinity and ion-exchange chromatography. PSA-immunoreactive species were detected using surface-enhanced laser desorption/ionization time of flight mass spectrometry. The obtained spectra were analyzed for protein and glycan composition. The general pattern of the molecular species of PCa PSA and BPH PSA found in complexes with IgM was similar. It comprised major peaks at 17 kDa and minor peaks at 28 kDa, corresponding to the entire mature glycosylated PSA. The main difference was the presence of incompletely glycosylated 26.8 kDa species, having putative paucimannosidic structures, observed in PCa PSA-IgM, but not in BPH PSA-IgM. Characteristic PCa PSA-IgM glycoforms pose the question of the possible role of glycosylation as a framework for immune surveillance and may be of interest in light of recent data indicating mannose-containing glycans as cancer biomarker.

On-chip screening for prostate cancer: an EIS microfluidic platform for contemporary detection of free and total PSA

Prostate cancer affects a large part of the western male population. The need for an early and accurate detection is thus a great challenge in common clinical practice, but the lack of specificity of the serum marker PSA (Prostate Specific Antigen) is a serious problem since its increased concentration can be related to several abnormalities. PSA, however, is found in serum in both a free and a complexed form with other proteins and the percentage amount of unbound PSA (the free-to-total PSA ratio) can be employed to distinguish prostate cancer from benign prostatic conditions, and also to predict the future risk of prostate cancer. To improve the operating characteristics of current PSA tests and to provide a clinical tool able to run label-free and sensitive analysis, we thus developed a biosensing platform based on Electrochemical Impedance Spectroscopy (EIS), which allows the contemporary detection of free and total PSA on a single biochip, enabling a quick screening for the risk of prostate cancer thanks to the presence of two different immobilized antibodies specific for the different antigens researched.

Aberrant PSA glycosylation--a sweet predictor of prostate cancer

Prostate cancer--the most commonly diagnosed cancer in men worldwide--can have a substantial effect on quality of life, regardless of the route the cancer takes. The serum PSA assay is the current gold standard option for diagnosing prostate cancer. However, a growing body of evidence suggests that PSA screening for prostate cancer results in extensive overdiagnosis and overtreatment. It is increasingly evident that the potential harm from overdiagnosis (in terms of unnecessary biopsies) must be weighed against the benefit derived from the early detection and treatment of potentially fatal prostate cancers. Rapid screening methods have been used to analyse glycosylation patterns on glycoproteins in large cohorts of patients, enabling the identification of a new generation of disease biomarkers. Changes to the expression status of certain glycan structures are now widely thought to be common features of tumour progression. In light of this development, much research has focused on the potential role of altered PSA glycosylation patterns in discriminating between significant and insignificant prostate cancers, with the aim of developing a more reliable diagnostic tool than the current serum PSA test.

PSA forms complexes with α1-antichymotrypsin in prostate

BACKGROUND

PSA is the most useful prostate cancer marker. However, its levels are increased also in some non-malignant conditions. In circulation, the majority of PSA is complexed with protease inhibitors, including α(1) -antichymotrypsin (ACT). The proportion of the PSA-ACT complex is higher in patients with prostate cancer than in controls without cancer. The expression of ACT has been shown to be higher in prostate cancer than in benign prostatic hyperplasia. However, results regarding the extent which PSA forms complexes within the prostate and whether there are differences in complex formation between normal and malignant prostatic tissue are inconsistent and limited.

METHODS

We studied complex formation of PSA secreted by cultured human prostate tissues and in the tissue by in situ proximity ligation assay (PLA). Free, total and active PSA, and the PSA-ACT complex were determined in tissue culture media by immunoassays, immunoblotting, and chromatographic methods.

RESULTS

The majority of PSA in tissue culture medium was free and enzymatically active. However, a significant proportion (1.6 ± 0.5%) of immunoreactive PSA was found to be complexed with ACT. Complex formation was confirmed by in situ PLA, which showed more intense staining of PSA-ACT in cancers with Gleason grade 3 than in adjacent benign tissues from the same patients.

CONCLUSIONS

These results show that PSA forms complexes already within the prostate and that PSA-ACT levels are increased in moderately differentiated prostate cancer tissue. This may explain, at least partially, why the ratio of serum PSA-ACT to total PSA is increased in prostate cancer.

From prostate-specific antigen (PSA) to precursor PSA (proPSA) isoforms: a review of the emerging role of proPSAs in the detection and management of early prostate cancer

Despite the popularity of PSA blood testing for prostate cancer, there are a number of important limitations of this popular serum marker including the limited ability to accurately distinguish patients with and without prostate cancer and those who harbour an aggressive form of the disease. This is especially true when the total PSA is <10 ng/mL. Thus, significant efforts have been placed to find new serum markers that can help overcome these limitations. In this review article, we discuss the emerging role of the various precursor forms of PSA (proPSAs), with a special emphasis on [-2]proPSA in the detecion and management of early prostate cancer. The clinical utility of Prostate Health Index (phi) is also discussed. Despite the overall success of prostate-specific antigen (PSA) blood test, its use as a serum marker for prostate cancer has been limited due to the lack of specificity, especially in men presenting with a total PSA (tPSA) level of <10 ng/mL. PSA testing has also resulted in an increase in the number of patients being diagnosed with low-grade, potentially clinically insignificant prostate cancer. There is therefore an urgent need for new markers that can accurately detect as well as differentiate patients with aggressive vs unaggressive prostate cancer. In this review, we discuss the emerging role of precursor forms of PSA (proPSAs) and the Prostate Health Index (phi) measurement in the detection and management of early stage prostate cancer. A literature search was conducted using PubMed® to identify key studies. Studies to date suggest that [-2]proPSA, a truncated form of proPSA is the most cancer-specific form of all, being preferentially expressed in cancerous prostatic epithelium and being significantly elevated in serum of men with prostate cancer. There is evidence to suggest that %[-2]proPSA measurement ([-2]proPSA/free PSA [fPSA] × 100) improves the specificity of both tPSA and fPSA in detecting prostate cancer. phi incorporating [-2]proPSA, fPSA and tPSA measurements has also yielded promising results and appears superior to tPSA and fPSA in predicting those patients with prostate cancer. Increased phi levels also seem to preferentially detect patients harbouring more aggressive disease. Further studies in the form of large, multicentre, prospective trials with detailed health economic analyses are required to evaluate the true clinical applicability of these novel markers.

Glycosylation of prostate specific antigen and its potential diagnostic applications

Prostate specific antigen (PSA) assays are widely used for early detection of prostate cancer. However, those analyses are associated with considerable sensitivity and specificity problems. Several approaches have been developed to tackle this issue. PSA is a glycoprotein, which is primarily produced by the prostatic epithelial cells. Aberrant glycosylation modification of proteins is a fundamental characteristic of tumorigenesis. Study of PSA glycoforms offers interesting diagnostic perspectives. Modern technology allows us to analyze PSA glycoforms in a variety of clinical samples (serum or plasma, urine, seminal fluid, tissue). A number of novel techniques, such as lectin-based detection methods, mass spectrometry, 2-dimensional electrophoresis and capillary electrophoresis have been developed to analyze PSA glycosylation. This article reviews the technical and diagnostic aspects of PSA glycoforms.

Longitudinal changes of benign prostate-specific antigen and [-2]proprostate-specific antigen in seven years in a community-based sample of men

OBJECTIVE

To determine the longitudinal changes of benign prostate-specific antigen (BPSA) and [-2]proPSA and how these changes relate to the outcomes. These markers have been shown to be predictive of prostate cancer (CaP) and benign prostatic hyperplasia treatment; however, little is known about longitudinal changes in these markers.

METHODS

In 1990, a 25% subsample from a cohort of white men aged 40-79 years, who were randomly selected from Olmsted County, Minnesota residents, completed a detailed clinical examination. BPSA and [-2]proPSA were measured from frozen sera. The men were evaluated biennially (median follow-up 7 years; range 0-8.8). Mixed-effects regression models were used to estimate the longitudinal changes in the BPSA and [-2]proPSA levels overall and by outcomes. Spearman correlations were used to compare these changes with the baseline levels and the annualized changes in urologic measures.

RESULTS

The median and 25th and 75th percentiles annualized percent change for [-2]proPSA and BPSA was 3.7%, 2.5% and 5.2% and 7.3%, 6.8%, and 7.7%, respectively. The annualized percent change for both markers correlated with the baseline and annualized changes in PSA and prostate volume. The annualized percent change increased with increasing age decade for [-2]proPSA but not for BPSA. The rate of increase in [-2]proPSA was significantly greater for men who developed enlarged prostates (median 3.5%, 25th and 75th percentile 2.6% and 4.4%, respectively) or CaP (median 8.1%, 25th and 75th percentile 6.6% and 9.8%, respectively) compared with those who did not develop enlarged prostates (median 1.9%, 25th and 75th percentile 0.9% and 3.0%, respectively) or CaP (median 3.5%, 25th and 75th percentile 2.3% and 4.8%, respectively).

CONCLUSION

BPSA and [-2]proPSA levels increase over time. The annualized percent change in [-2]proPSA increases with age and might be a useful predictor of CaP development.

Molecular microheterogeneity of prostate specific antigen in seminal fluid by mass spectrometry

OBJECTIVES

Prostate specific antigen (PSA) is a widely used and clinically valuable marker for prostate disease. In order to enable the development of new PSA assays and progress the understanding of the biology of PSA we have analyzed PSA in seminal plasma.

DESIGN AND METHODS

PSA in seminal plasma from men attending a fertility clinic and healthy controls was analyzed using SDS-PAGE, Western blotting and mass spectrometry.

RESULTS

Using mass spectrometry, different forms of PSA could be identified in 1-9 bands seen on SDS-PAGE analysis of the respective sample. However, a majority of these molecular forms of PSA were not observed on Western blots. Enzymatic activity of PSA isoforms was demonstrated by sequencing data in zymogram gels. Multivariate analysis of clinical data revealed well-separated patient groups.

CONCLUSIONS

We demonstrated that PSA in seminal plasma occurs in several isoforms, yet not all were detectable using an antibody based clinical routine method. The heterogeneity of PSA expression might be of clinical significance, by an improved patient phenotyping.

Benign prostate specific antigen distribution and associations with urological outcomes in community dwelling black and white men

PURPOSE

We describe cross-sectional associations of benign prostate specific antigen with clinical urological measures and examined the risk of future urological outcomes in 2 population based cohorts of black and white men, respectively.

MATERIALS AND METHODS

Two population based cohort studies were established to characterize the natural history of and risk factors for prostate disease progression in white and black male residents of Olmsted County, Minnesota, and Genesee County, Michigan, respectively.

RESULTS

The benign prostate specific antigen distribution was similar in black men at a median of 32.9 pg/ml (25th, 75th percentiles 17.3, 68.0) and white men at a median of 32.2 pg/ml (25th, 75th percentiles 16.6, 68.9, respectively). However, it was much lower than in previous reports. For Olmsted County men in the upper quartile of benign prostate specific antigen there was a fifteenfold increased risk of prostate cancer (HR 14.6, 95% CI 3.1-68.6) and a twofold higher risk of treatment for benign prostatic hyperplasia (HR 2.2, 95% CI 1.2-4.2) after adjusting for age. After additional adjustment for baseline prostate specific antigen the association between benign prostate specific antigen and prostate cancer risk was attenuated but remained almost ninefold higher for men in the upper quartile of benign prostate specific antigen (HR 8.7, 95% CI 1.8-42.4). The twofold higher risk of treatment for benign prostatic hyperplasia also remained after adjusting for baseline prostate specific antigen for men in the upper benign prostate specific antigen quartile (HR 1.9, 95% CI 0.9-4.0).

CONCLUSIONS

Results suggest that increased benign prostate specific antigen may help identify men with prostate cancer and those at risk for benign prostatic hyperplasia treatment.

Bioinformatic strategies for unambiguous identification of prostate specific antigen in clinical samples

Prostate specific antigen (PSA), as a widely used clinical biomarker in prostate cancer diagnostics, exists in multiple molecular forms. However, all of these forms might not be recognized in a given sample by the standard immunoassays. Therefore, we have investigated PSA isoforms, separated by size, using mass spectrometric analyses. The objective of these developments was to identify and specify the various forms of PSA. To optimize successful identification of different PSA forms, we have developed a bioinformatic strategy, consisting of high resolution MALDI-MS PMF and sequencing MS/MS data searches. To improve sequence-based identification, the recently introduced Proteios software environment was employed, allowing the combination of multiple database search engines in an automated manner. We could unambiguously identify PSA in clinical samples by all detectable tryptic peptides, which were found to be common in several isoforms.

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.

Immunoassay for the discrimination of free prostate-specific antigen (fPSA) forms with internal cleavages at Lys(₁₄₅) or Lys(₁₄₆) from fPSA without internal cleavages at Lys(₁₄₅) or Lys(₁₄₆)

Total levels of circulating prostate-specific antigen (tPSA) are strongly associated with prostate cancer (PCa) risk and outcome but benign prostate disease is the most frequent cause of a moderately elevated PSA level. Free PSA (fPSA) forms are independently associated with PCa risk and contribute modest diagnostic enhancements above and beyond tPSA alone. We developed an immunoassay for fPSA subfractions containing internal cleavages at Lys(145) or Lys(146) (fPSA-N). The assay was based on blocking intact single-chain fPSA (fPSA-I) with antibody 4D4 which does not detect PSA containing internal cleavages at Lys(145) or Lys(146). We also measured fPSA-N in blood from healthy volunteers and in anti-coagulated plasma from 76 men with or without evidence of PCa at biopsy. The analytical and functional detection limits of this assay were 0.016 ng/mL and 0.10 ng/mL, respectively. The median recovery of male fPSA-N from female plasma was 95.0%. All 12 female samples (average age 28 years) had fPSA-N concentrations at or below the analytical detection limit. The median fPSA-N concentration (0.050 ng/mL) in 9 healthy male volunteers (age<40 years) was below the functional detection limit, 0.420 ng/mL in 27 patients with benign prostate conditions and 0.239 ng/mL in 49 patients with PCa. Deming regression analysis of the patient samples showed that the measured fPSA-N concentrations were generally 23% lower than the previously calculated (fPSA minus fPSA-I) concentrations, likely due to differences in the antibody combinations used. In conclusion, we have developed a sensitive, specific and direct immunoassay for fPSA-N which can be used to study the clinical relevance of this PSA isoform.

[-2]Proenzyme prostate specific antigen is more accurate than total and free prostate specific antigen in differentiating prostate cancer from benign disease in a prospective prostate cancer screening study

PURPOSE

Due to the limited specificity of prostate specific antigen for prostate cancer screening, there is an ongoing search for adjunctive biomarkers. Retrospective studies have suggested that an isoform of proenzyme prostate specific antigen called [-2]proenzyme prostate specific antigen may enhance the specificity of prostate specific antigen based screening. We examined the usefulness of this isoform in a prospective prostate cancer screening study.

MATERIALS AND METHODS

From a population of 2,034 men undergoing prostate cancer screening we examined the relationship between the measurement of the [-2]isoform of proenzyme prostate specific antigen (p2PSA) and prostate cancer detection. Specifically we compared the usefulness of total prostate specific antigen, the ratio of free-to-total prostate specific antigen, the ratio of p2PSA-to-free prostate specific antigen, and a formula combining prostate specific antigen, free prostate specific antigen and p2PSA (the Beckman Coulter prostate health index or phi) to predict prostate cancer in men from the study undergoing prostate biopsy with a prostate specific antigen of 2.5 to 10 ng/ml and nonsuspicious digital rectal examination.

RESULTS

Despite similar total prostate specific antigen (p = 0.88), percent free prostate specific antigen (p = 0.02) and %p2PSA (p = 0.0006) distinguished between positive and negative biopsy results. On ROC analysis %p2PSA (AUC 0.76) outperformed prostate specific antigen (AUC 0.50) and percent free prostate specific antigen (AUC 0.68) for differentiating between prostate cancer and benign disease. Setting the sensitivity at 88.5%, p2PSA led to a substantial improvement in specificity as well as positive and negative predictive values. The Beckman Coulter prostate health index (AUC 0.77) had the best overall performance characteristics.

CONCLUSIONS

This is the first prospective study to our knowledge to demonstrate that p2PSA provides improved discrimination between prostate cancer and benign disease in screened men with a prostate specific antigen of 2.5 to 10 ng/ml and a negative digital rectal examination.

Prostate-specific antigen (PSA) isoform p2PSA in combination with total PSA and free PSA improves diagnostic accuracy in prostate cancer detection

BACKGROUND

Novel markers for prostate cancer (PCa) detection are needed. Total prostate-specific antigen (tPSA) and percent free prostate-specific antigen (%fPSA=tPSA/fPSA) lack diagnostic specificity.

OBJECTIVE

To evaluate the use of prostate-specific antigen (PSA) isoforms p2PSA and benign prostatic hyperplasia-associated PSA (BPHA).

DESIGN, SETTING, AND PARTICIPANTS

Our study included 405 serum samples from the Rotterdam arm of the European Randomised Study of Screening for Prostate Cancer and 351 samples from the Urology Department of Innsbruck Medical University.

MEASUREMENTS

BPHA, tPSA, fPSA, and p2PSA levels were measured by Beckman-Coulter Access Immunoassay. In addition, the Beckman Coulter Prostate Health Index was calculated: phi=(p2PSA/fPSA)×√(tPSA).

RESULTS AND LIMITATIONS

The p2PSA and phi levels differed significantly between men with and without PCa. No difference in BPHA levels was observed. The highest PCa predictive value in both cohorts was achieved by phi with areas under the curve (AUCs) of 0.750 and 0.709, a significant increase compared to tPSA (AUC: 0.585 and 0.534) and %fPSA (AUC: 0.675 and 0.576). Also, %p2PSA (p2PSA/fPSA) showed significantly higher AUCs compared to tPSA and %fPSA (AUC: 0.716 and 0.695, respectively). At 95% and 90% sensitivity, the specificities of phi were 23% and 31% compared to 10% and 8% for tPSA, respectively. In both cohorts, multivariate analysis showed a significant increase in PCa predictive value after addition of p2PSA to a model consisting of tPSA and fPSA (increase in AUC from 0.675 to 0.755 and from 0.581 to 0.697, respectively). Additionally, the specificity at 95% sensitivity increased from 8% to 24% and 7% to 23%, respectively. Furthermore, %p2PSA, phi, and the model consisting of tPSA and fPSA with or without the addition of p2PSA missed the least of the tumours with a biopsy or pathologic Gleason score ≥7 at 95% and 90% sensitivity.

CONCLUSIONS

This study shows significant increases in PCa predictive value and specificity of phi and %p2PSA compared to tPSA and %fPSA. p2PSA has limited additional value in identifying aggressive PCa (Gleason score ≥7).

Benign prostatic hyperplasia-associated free prostate-specific antigen improves detection of prostate cancer in an artificial neural network

OBJECTIVES

To show discriminative power between patients with prostate cancer (PCa) and those with "no evidence of malignancy" using "benign" prostate-specific antigen (bPSA) and the new automated Access benign prostatic hyperplasia-associated (BPHA) research assay within a percent free PSA (%fPSA)-based artificial neural network (ANN) model.

METHODS

The sera from 287 patients with PCa and 254 patients with no evidence of malignancy were measured using the BPHA, total PSA (tPSA), and fPSA assays with Access immunoassay technology, with a 0-10 ng/mL tPSA range. Two ANN models with Bayesian regularization and leave-one-out validation using the 4 input parameters of tPSA, %fPSA, age, and prostate volume and 1 containing BPHA/tPSA were constructed and compared by receiver operating characteristic curve analysis.

RESULTS

The BPHA/tPSA-based ANN reached the significant greatest area under the receiver operating characteristic curve (AUC 0.81; P = .0004 and P = .0024) and best specificity (53.9% and 44.5%) compared with the ANN without BPHA/tPSA (AUC 0.77; specificity 50% and 40.6%) and %fPSA (AUC 0.77; specificity 40.9% and 27.2%) at 90% and 95% sensitivity, respectively. The AUCs for tPSA (0.58), BPHA (0.55), BPHA/fPSA (0.51), prostate volume (0.69), and BPHA/tPSA (0.69) were significantly lower.

CONCLUSIONS

Although BPHA as single marker or ratio to tPSA did not improve the diagnostic performance of %fPSA or tPSA, the incorporation of BPHA/tPSA into an ANN model increased the specificity compared with %fPSA by 13% and 17% at 90% and 95% sensitivity, respectively. Thus, the automated BPHA research assay might improve PCa detection when incorporating this new marker into an ANN.

Critical appraisal of prostate-specific antigen in prostate cancer screening: 20 years later

Prostate-specific antigen (PSA) is secreted by all types of prostate epithelial cells and has been used for 2 decades as a biologic marker for prostate cancer (PCa). Since the implementation of PSA screening in the United States, the detection of PCa has increased, accompanied by a decrease in the incidence of high-grade cancer and PCa-specific mortality rates. It has been suggested that these decreases have resulted from the enhanced detection of PCa while still curable. These data have been the impetus for early detection programs, which have recommended the initiation of screening as early as 40 years of age. Despite widespread use, PSA screening remains controversial, principally because of the lack of evidence from randomized controlled trials demonstrating a mortality benefit that could outweigh the concerns of the costs of overdiagnosis and overtreatment. Two ongoing, randomized controlled trials are examining whether screening reduces the risk of PCa-related mortality, and the results of these studies are expected soon. Although it has its limitations, PSA still remains the best-studied marker for the detection of PCa.

Biomarkers for benign prostatic hyperplasia progression

Despite the fact that almost all men will develop symptoms associated with benign prostatic hyperplasia within their lifetimes, no molecular markers for the disease or its likelihood to progress have been established. A marker of this type could be used to stratify patients into subpopulations as well as to identify individuals whose disease is most likely to progress. Several molecular biomarkers have high potential to fulfill these needs, although none is currently approved for the clinical setting. The future does look promising as research to find novel biologic biomarkers is progressing while existing markers are optimized and validated for clinical use.

High-speed spinning-disk interferometry on the BioCD for human diagnostic applications

The BioCD is an optical biosensor that uses high-speed spinning-disk interferometry for direct detection of antigen binding in multiplexed immunoassay protein arrays. The high-frequency sampling suppresses the noise floor and enables a metrology-limited height resolution of 1 picometer for measuring surface-bound protein. In assay protocols there is a direct trade-off between multiplex degree and limit of detection. In this paper, we demonstrate quantitative assays and the scaling properties of direct detection on the BioCD in assays of clinical relevance for human diagnostics, including haptoglobin assays and prostate-specific antigen assays in human patient sera.

Prostate cancer: diagnosis and staging

Prostate cancer represents an increasing health burden. The past 20 years, with the introduction of prostate-specific antigen (PSA), has seen prostate cancer move increasingly from a condition that presented with locally advanced disease or metastases to one that is found upon screening. More is also known about the pathology of pre-malignant lesions. Diagnosis relies on trans-rectal ultrasound (TRUS) to obtain biopsies from throughout the prostate, but TRUS is not useful for staging. Imaging for staging, such as magnetic resonance imaging or computed tomography, still has a low accuracy compared with pathological specimens. Current techniques are also inaccurate in identifying lymph node and bony metastases. Nomograms have been developed from the PSA, Gleason score and clinical grading to help quantify the risk of extra-capsular extension in radical prostatectomy specimens. Improved clinical staging modalities are required for more reliable prediction of pathological stage and for monitoring of response to treatments.

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.

The Tissue Kallikrein Family of Serine Proteases: Functional Roles in Human Disease and Potential as Clinical Biomarkers

Prostate specific antigen (PSA) or human kallikrein 3 (hK3) has long been an effective biomarker for prostate cancer. Now, other members of the tissue kallikrein (KLK) gene family are fast becoming of clinical interest due to their potential as prognostic biomarkers. particularly for hormone dependent cancers. The tissue kallikreins are serine proteases that are encoded by highly conserved multi-gene family clusters in rodents and humans. The rat and mouse loci contain 10 and 25 functional genes, respectively, while the human locus at 19q 13.4 contains 15 genes. The structural organization and size of these genes are similar across species; all genes have 5 coding exons that encode a prepro-enzyme. Although the physiological activators of these zymogens have not been described, in vitro biochemical studies show that some kallikreins can auto-activate and others can activate each other, suggesting that the kallikreins may participate in an enzymatic cascade similar to that of the coagulation cascade. These genes are expressed, to varying degrees, in a wide range of tissues suggesting a functional involvement in a diverse range of physiological and pathophysiological processes. These include roles in normal skin desquamation and psoriatic lesions, tooth development, neural plasticity, and Alzheimer's disease (AD). Of particular interest is the expression of many kallikreins in prostate, ovarian, and breast cancers where they are emerging as useful prognostic indicators of disease progression.

[-2]proenzyme prostate specific antigen for prostate cancer detection: a national cancer institute early detection research network validation study

PURPOSE

This study evaluated the [-2]proenzyme prostate specific antigen serum marker using a blinded reference specimen set from 3 National Cancer Institute Early Detection Research Network centers from men with an indication for prostate biopsy.

MATERIALS AND METHODS

Serum was collected before biopsy from 123 men with no prior biopsy or prostate cancer history. Specimens (cancer cases 51%, noncancer controls 49%) were selected equally from the 3 sites, and analyzed for prostate specific antigen, free prostate specific antigen, [-2]proenzyme prostate specific antigen, benign prostate specific antigen and testosterone (Beckman Coulter ACCESS(R) analyzer).

RESULTS

There was no difference in total prostate specific antigen concentrations (noncancer 6.80 +/- 5.20 ng/ml, cancer 6.94 +/- 5.12 ng/ml) among the groups. Overall %[-2]proenzyme prostate specific antigen had the greatest area under the curve (AUC 0.69) followed by percent free prostate specific antigen (AUC 0.61). For %[-2]proenzyme prostate specific antigen maximal sensitivity was 60% and specificity was 70%. A logistic regression model combining prostate specific antigen, benign prostate specific antigen, percent free prostate specific antigen, %[-2]proenzyme prostate specific antigen, [-2]proenzyme prostate specific antigen/benign prostate specific antigen and testosterone had an AUC of 0.73. In the 2 to 10 ng/ml prostate specific antigen range %[-2]proenzyme prostate specific antigen and the model had the largest AUC (0.73). The AUC for percent free prostate specific antigen was 0.53. Specificities for %[-2]proenzyme prostate specific antigen, the logistic regression model and percent free prostate specific antigen at 90% sensitivity were 41%, 32% and 18%, and at 95% sensitivity were 31%, 26% and 16%, respectively.

CONCLUSIONS

%[-2]proenzyme prostate specific antigen was the best predictor of prostate cancer detection compared to percent free prostate specific antigen, particularly in the 2 to 10 ng/ml total prostate specific antigen range. These findings provide a rationale for broader validation studies to determine whether %[-2]proenzyme prostate specific antigen alone can replace other molecular prostate specific antigen assays (such as percent free prostate specific antigen) for improving the accuracy of prostate cancer early detection. These findings also support the usefulness of well characterized, carefully collected reference sets to evaluate new biomarkers.

Blood biomarkers for prostate cancer detection and prognosis

Prostate cancer is the most non-cutaneous malignancy diagnosed in men in the USA. The discovery of prostate-specific antigen (PSA) revolutionized prostate cancer diagnosis and management in the 1990s. Despite its remarkable performance as a marker for prostate cancer, PSA is not prostate cancer specific. PSA can be released by normal as well as hyperplastic prostate cells, which undermines the specificity of PSA for prostate cancer diagnosis. Hence, there is a need for new biomarkers that can detect prostate cancer and, in addition, distinguish indolent from biologically aggressive cancers. Moreover, the emergence of new therapeutic approaches for prostate cancer cannot flourish without a more reliable set of markers to serve as prognosticators, targets and surrogate end points of disease progression and response to treatment. As the most useful clinical biomarkers are likely to be those assayed from blood, there is an increasing interest in profiling blood proteins. With recent advances in biotechnology such as high-throughput molecular analyses, many potential blood biomarkers have been identified and are currently under investigation.