Benign prostatic hyperplasia-associated prostate-specific antigen (BPSA) shows unique immunoreactivity with anti-PSA monoclonal antibodies

The emerging landscape of tumor marker panels for the identification of aggressive prostate cancer: the perspective through bibliometric analysis of an Italian translational working group in uro-oncology

Molecular heterogeneity and availability of different therapeutic strategies are relevant clinical features of prostate cancer. On this basis, there is an urgent need to identify prognostic and predictive biomarkers for an individualized therapeutic approach. In this context, researchers focused their attention on biomarkers able to discriminate potential life-threatening from organ-confined disease. Such biomarker could provide aid in clinical decision making, helping to choose the treatment which ensures the best results in terms of patient survival and quality of life. To address this need, many new laboratory tests have been proposed, with a clear tendency to use panels of combined biomarkers. In this review we evaluate current data on the application in clinical practice of the most promising laboratory tests: Phi, 4K score and Stockholm 3 as circulating biomarkers, Mi-prostate score, Exo DX Prostate and Select MD-X as urinary biomarkers, Confirm MDx, Oncotype Dx, Prolaris and Decipher as tissue biomarkers. In particular, the ability of these tests in the identification of clinically significant PCa and their potential use for precision medicine have been explored in this review.

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.

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.

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.

Glycans as a Target in the Detection of Reproductive Tract Cancers

The significance of changes in glycosylation for the beginning, progress and outcome of different human diseases is highly recognized. In this review we summarized literature data on the alteration of glycans in cancer, especially glycoforms of tumor markers of reproductive tract cancers: prostate-specific antigen (PSA) and cancer antigen 125 (CA125). We aimed to highlight the diagnostic potential and relevance of glycan microheterogeneity and to present some novel methods for cancer detection. A computerized search of articles published up to 2007 was performed through the PubMed database. Search terms utilized included prostate/ovarian cancer glycosylation, prostate/ovarian cancer detection, PSA/CA125 glycosylation. Additional sources were identified through cross-referencing and researching in available biomedical books. The comparative studies of sugar chain structures of the PSA and CA125 indicated specific structural alterations associated with malignant transformation, in relation to glycan branching, sialylation and fucosylation. These glycan modifications should be better in distinguishing between benign and malignant conditions than the measurement of marker concentrations alone, which is widely used in practice. Cancer-associated changes in the glycosylation could yield more sensitive and discriminative diagnostic tests for reproductive tract cancer detection, i.e. for improvement of the clinical utility of known tumor markers or the discovery of new ones.

Immunohistochemical Staining of Precursor Forms of Prostate-specific Antigen (proPSA) in Metastatic Prostate Cancer

Precursors of prostate-specific antigen (proPSA) have been previously shown to be more concentrated in prostate cancer tissue. This study characterizes the immunohistochemical staining (IHS) of proPSA forms in metastatic prostate cancer compared with prostate specific antigen (PSA) and prostatic acid phosphatase (PAP). A tissue microarray, consisting of 74 cases of metastatic prostate carcinoma and control tissues, was used. IHS, using monoclonal antibodies against proPSA with a truncated proleader peptide containing 2 amino acids ([-2]pPSA), native ([-5/-7]pPSA), PSA, and PAP, was analyzed. The monoclonal antibodies were specific for both benign and malignant prostatic glandular tissue. IHS with [-5/-7]pPSA showed the least number of cases with negative staining (3%), and the most number of cases with moderate or strong staining (76%). In the 60 cases where all 4 stains could be evaluated, none of them were negative for proPSA and positive for PSA or PAP, and all 7 cases that were negative for both PSA and PAP showed IHS to proPSA. [-5/-7]pPSA (native proPSA) may be a better marker than PSA and PAP in characterizing metastatic prostate adenocarcinoma, with most of the cases showing positivity for the marker. Even cases that were negative for PSA and PAP, were reactive for proPSA. Such enhanced detection is particularly important in poorly differentiated carcinomas involving metastatic sites where prostate carcinoma is a consideration. A panel of markers, including proPSA, should be performed when metastatic prostate carcinoma is in the differential diagnosis.

Evidence of a novel biomarker, αs1-Casein, a milk protein, in benign prostate hyperplasia

Benign prostate hyperplasia (BPH) is a common disease in elderly men. Although it is a non-malignant disease, it has a significant detrimental impact on the quality of life in patients with late-stage disease. Owing to the lack of specific markers, diagnosis of early-stage BPH has been proven unsuccessful. Recently, using two-dimensional electrophoresis, we identified a group of prostatic secretory proteins that are specifically produced by BPH cells (Xu et al., Electrophoresis 2003; 24: 1311). In this study, we investigated the potential diagnostic value of one of the secretory proteins, alphas1-Casein, in BPH by inmmunohistological staining of normal, BPH and prostate cancer tissues. We found that 90% (20 out of 22) of BPH tissues showed moderate to strong alphas1-Casein protein expression whereas none of the normal tissues (0 out of 10) and less than 10% of the prostate cancer tissues (3 out of 30) showed similar staining intensity. Our results suggest that alphas1-Casein may be a potential biomarker for early identification of BPH patients.

Glycosylation of urinary prostate-specific antigen in benign hyperplasia and cancer: assessment by lectin-binding patterns

OBJECTIVES

In the present study, we examined the glycosylation of urinary prostate-specific antigen (PSA) from benign prostatic hyperplasia (BPH) and prostate cancer (PCa) subjects, specifically looking at alterations in its oligosaccharide chain as a potential biomarker of these pathophysiological conditions.

DESIGN AND METHODS

First morning urine voids were collected from subjects with PCa and BPH before initiation of any treatment. Urinary PSA was characterized by ion-exchange chromatography, followed by lectin affinity chromatography on the columns using immobilized plant lectins.

RESULTS

Four isoforms of urinary PSA from both BPH and PCa samples were separated by ion-exchange chromatography. The elution profiles from lectin-affinity columns reflected molecular heterogeneity of PSA isoforms and the main differences observed were in the reactivity to Ulex europaeus agglutinin, Aleuria aurantia agglutinin, Phaseolus vulgaris erythroagglutinin and Phaseolus vulgaris leukoagglutinin.

CONCLUSIONS

The observed differences in the lectin reactivities between BPH PSA and PCa PSA may be of clinical importance in the evaluation of prostate health.

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.

Serum BPSA outperforms both total PSA and free PSA as a predictor of prostatic enlargement in men without prostate cancer

OBJECTIVES

To determine whether the serum concentration of BPSA, a distinct form of free prostate-specific antigen (PSA) enriched in the nodular transition zone (TZ) tissue of benign prostatic hyperplasia (BPH), can predict TZ volume and diagnose BPH-associated prostatic enlargement in patients without prostate cancer.

METHODS

We studied 91 consecutive patients without prostate cancer who underwent a 10-core or greater biopsy of the prostate. The associations between prostate volume, age, International Prostate Symptom Score, and serum concentrations of PSA, free PSA, and BPSA were evaluated by receiver operating characteristic curve and linear and binary logistic regression analyses.

RESULTS

BPSA and free PSA showed stronger correlations with both age (BPSA = 0.38, free PSA = 0.40, PSA = 0.24) and TZ volume (BPSA = 0.67, free PSA = 0.64, PSA = 0.55) than did PSA. The percent free PSA had no statistically significant correlation with TZ volume (P = 0.08). Subtraction of BPSA from free PSA reduced its correlation with TZ volume to below that of PSA (from 0.64 to 0.48). Linear regression analyses showed that, unlike PSA, both BPSA and free PSA displayed an age-independent relationship to TZ volume. The receiver operating characteristic curve (for TZ greater than 30 cm3) and binary logistic regression analyses showed that BPSA (area under the curve = 0.844) outperformed both free PSA (area under the curve = 0.799) and PSA (area under the curve = 0.749) in its ability to predict clinically significant TZ enlargement.

CONCLUSIONS

In patients without prostate cancer, the serum concentration of BPSA displayed an age-independent, log-linear relationship to TZ volume and was a better predictor of prostatic enlargement than either PSA or free PSA. BPSA may also predict clinical parameters of BPH and is under evaluation as a marker of BPH progression and response to therapy.

Molecular diagnosis of prostate cancer

The diagnosis, staging, and management of prostate cancer as we know it today is greatly dependent on our ability to measure serum prostate-specific antigen (PSA) concentration. Nevertheless, because serum PSA concentration, particularly when less than 10 ng/mL, reflects the presence of benign prostatic hyperplasia more often than cancer, there is a clear need for more specific prostate cancer markers. The most promising new markers for prostate cancer are the various molecular forms of free PSA. Mass spectrometry also is emerging as a potential tool in prostate cancer screening. Because it is unlikely that any one marker will have 100% sensitivity and specificity, as new serum markers are tested, nomograms that incorporate multiple independently predictive parameters for the detection of prostate cancer will become indispensable in our efforts to improve prostate cancer screening.

Volume-based evaluation of serum assays for new prostate-specific antigen isoforms in the detection of prostate cancer

OBJECTIVES

Recently, disease-specific isoforms of the prostate-specific antigen (PSA) have been identified. We evaluated the efficacy of precursor isoforms of PSA (pPSA) and an internally cleaved form of PSA referred to as the benign prostatic hyperplasia-associated PSA (BPSA) for the detection of prostate cancer.

METHODS

Serum concentrations of [-2], [-4], and [-7]pPSA, sum pPSA ([-2] + [-4] + [-7]pPSA), and BPSA were retrospectively measured in 43 selected men. The median total PSA levels in men with and without cancer were 6.5 microg/L (range 0.4 to 12.1 microg/L) and 6.1 microg/L (range 3.7 to 21.5 microg/L), respectively. Of the 43 men, 15 had clinical T2 prostate cancer with an ultrasound-estimated prostate volume (PV) of greater than 50 mL, 13 had clinical T2 prostate cancer with PV less than 25 mL, and 15 were prostate cancer free with PV greater than 50 mL.

RESULTS

The median values for BPSA, free-to-total PSA ratio (f/tPSA), and benign-to-total PSA ratio (B/tPSA) differed statistically between men with cancer and a PV less than 25 mL and men with cancer and a PV greater than 50 mL (P <0.05) and between the men with cancer and a PV less than 25 mL and men without cancer and a PV greater than 50 mL (P <0.005). All evaluated variables had no correlation with tumor volume in 15 men who had undergone radical prostatectomy.

CONCLUSIONS

In this preliminary study, the level of [-2], [-4], sum pPSA, and BPSA seemed to be PV related, but only BPSA and B/tPSA and f/tPSA were significantly associated with PV. Therefore, pPSA did not aid in better discriminating cancer from noncancer.

Biology of prostate-specific antigen

Prostate-specific antigen (PSA) is an androgen-regulated serine protease produced by both prostate epithelial cells and prostate cancer (PCa) and is the most commonly used serum marker for cancer. It is a member of the tissue kallikrein family, some of the members of which are also prostate specific. PSA is a major protein in semen, where its function is to cleave semenogelins in the seminal coagulum. PSA is secreted into prostatic ducts as an inactive 244-amino acid proenzyme (proPSA) that is activated by cleavage of seven N-terminal amino acids. PSA that enters the circulation intact is rapidly bound by protease inhibitors, primarily alpha1-antichymotrypsin, although a fraction is inactivated in the lumen by proteolysis and circulates as free PSA. This proteolytic inactivation, as well as the cleavage of proPSA to PSA, is less efficient in PCa. Serum total PSA levels are increased in PCa, and PSA screening has dramatically altered PCa presentation and management. Unfortunately, although high PSA levels are predictive of advanced PCa, a large fraction of organ-confined cancers present with much lower total PSA values that overlap those levels found in men without PCa. Measurement of free versus total PSA can increase specificity for PCa, and tests under development to measure forms of proPSA may further enhance the ability to detect early-stage PCa. PSA is also widely used to monitor responses to therapy and is under investigation as a therapeutic target. Finally, recent data indicate that there may be additional roles for PSA in the pathogenesis of PCa.

Early management of prostate cancer: how to respond to an elevated PSA?

Support for prostate cancer screening efforts is provided by observational studies reporting decreases in prostate cancer-specific mortality in areas where screening is performed with digital rectal exam (DRE) and measurement of serum prostate-specific antigen (PSA) levels. The combination of PSA and DRE is an excellent cancer-screening tool with sensitivity and positive predictive value superior to that of mammography and breast exam. Use of percent free PSA further improves the specificity of PSA testing, particularly in the range of 4-10 ng/ml, at which most false positive PSA tests occur. Men older than 50 with a >10-year life expectancy should be considered for prostate cancer screening. Those with an abnormal DRE or a PSA above 4 ng/ml should be referred to a urologist for further discussion of the risks and benefits of a prostate biopsy. Furthermore, those with a significant change in either DRE or PSA results, or those at higher risk for prostate cancer with a PSA level above 2.5 ng/ml, should also be referred for evaluation.

Natural history of benign prostatic hyperplasia

Studies in varied settings have provided estimates of the prevalence of surrogate markers of benign prostatic hyperplasia (BPH). In population-based studies, the prevalence of moderate-to-severe lower urinary tract symptoms and depressed peak urinary flow rates increases across successively older age groups. Prostatic volume follows a similar pattern. Unlike clinic-based studies in which correlations are almost nonexistent, the population-based studies demonstrate a modest correlation among lower urinary tract symptoms, peak urinary flow rates, and prostatic volume. These cross-sectional observations extend to serum prostate-specific antigen levels and postvoid residual urine volumes. Data collected during the longitudinal follow-up study of men participating in the Olmsted County Study of Urinary Symptoms and Health Status Among Men provide a more detailed description of the natural history of changes in these surrogate markers of BPH. They also provide insights into their relation with each other and with long-term outcomes of BPH, such as acute urinary retention and treatment of BPH. These data demonstrate the progressive nature of BPH and are useful for the design and interpretation of clinical trials. Furthermore, they suggest that observational studies of etiology and prognosis should take advantage of the spectrum of disease reflected by the full range of values of these quantitative traits, rather than an arbitrary dichotomized outcome.

Characterization of PSA-RP2, a protein related to prostate-specific antigen and encoded by alternative hKLK3 transcripts

Despite the wide use of prostate-specific antigen (PSA) as a marker of prostate cancer, analysis of its gene products has not yet been completed. The structure of two alternative mRNAs (0.9 and 1.65 kb) of the hKLK3 gene that retain the third intron is reported here. These partially spliced transcripts were detected by hybridization or RT-PCR in normal prostate tissue, benign prostate hyperplasia (BPH) and cancerous prostate tissues, and also in the prostate LNCaP cell line. Insertion of the unspliced intron creates an in-frame stop codon and results in a truncated prepro PSA variant of 180 amino-acid residues. This novel variant, designated PSA-RP2, has an alternate C-terminal tail and lacks the serine residue essential for the catalytic activity of PSA. Prepro PSA-RP2 was transiently produced in COS-7 cells and detected in the spent medium using an anti-PSA serum. Secreted PSA-RP2 was glycosylated with an apparent molecular mass of 25 kDa. Our findings suggest that PSA-RP2 contributes to the molecular heterogeneity of free-PSA in the serum of patients with benign or malignant prostate tumors.

Seminal plasma contains "BPSA," a molecular form of prostate-specific antigen that is associated with benign prostatic hyperplasia

BACKGROUND

We previously reported that levels of BPSA, a modified form of prostate-specific antigen (PSA), are significantly elevated in prostate transition-zone tissue exhibiting nodular hyperplastic changes associated with the presence of benign prostatic hyperplasia (BPH). BPSA was purified and found to contain a characteristic clip between Lys182 and Ser183. We now describe the identification of BPSA in seminal plasma.

METHODS

PSA was purified from seminal plasma by immunoaffinity chromatography. The purified PSA was further resolved by hydrophobic interaction chromatography, and the individual PSA forms were analyzed by gel electrophoresis and N-terminal amino-acid sequencing.

RESULTS

BPSA comprised about 8% of the PSA in pooled seminal plasma, and was identical to BPSA purified from prostate tissues. BPSA was cleanly resolved from all active and inactive forms of PSA. Other inactive forms of PSA in seminal plasma consisted largely of PSA clipped at Lys145, though about 30% of the inactive seminal plasma PSA was intact, mature PSA.

CONCLUSIONS

BPSA represents a distinct form of inactive PSA in the seminal plasma that may represent a specific marker for the biochemical changes associated with nodular development in the prostate transition zone found in patients with BPH.