Clinical utility of measurements of free and total prostate-specific antigen (PSA): a review

Association of Free-to-Total PSA Ratio and 18F-DCFPyL Prostate-Specific Membrane Antigen PET/CT Findings in Patients with Biochemical Recurrence After Radical Prostatectomy: A Prospective Single-Center Study

In Canada and across the globe, access to PSMA PET/CT is limited and expensive. For patients with biochemical recurrence (BCR) after treatment for prostate cancer, novel strategies are needed to better stratify patients who may or may not benefit from a PSMA PET scan. The role of the free-to-total prostate-specific antigen (PSA) ratio (FPSAR) in posttreatment prostate cancer, specifically in the PSMA PET/CT era, remains unknown. Our aim in this study was to determine the association of FPSAR in patients referred for 18F-DCFPyL PSMA PET/CT in the BCR setting and assess the correlation between FPSAR and 18F-DCFPyL PSMA PET/CT positivity (local recurrence or distant metastases). Methods: This prospective study included 137 patients who were referred for 18F-DCFPyL PSMA PET/CT and had BCR with a total PSA of less than 1 ng/mL after radical prostatectomy (RP) (including adjuvant or salvage radiotherapy). Blood samples were collected on the day of 18F-DCFPyL PSMA PET/CT. FPSAR was categorized as less than 0.10 or as 0.10 or more. A positive 18F-DCFPyL PSMA PET/CT scan was defined by a PROMISE classification lesion score of 2 or 3, irrespective of the site of increased tracer uptake (e.g., prostate, pelvic nodes, bone, or viscera). Results: Overall, 137 blood samples of patients with BCR after RP were analyzed to calculate FPSAR. The median age at 18F-DCFPyL PSMA PET/CT was 68.6 y (interquartile range, 63.0-72.4 y), and the median PSA at 18F-DCFPyL PSMA PET/CT was 0.3 ng/mL (interquartile range, 0.3-0.6 ng/mL). Eighty-six patients (62.8%) had an FPSAR of less than 0.10, whereas 51 patients (37.2%) had an FPSAR of 0.10 or more. An FPSAR of 0.10 or more was identified as an independent predictor of a positive 18F-DCFPyL PSMA PET/CT scan, with an odds ratio of 6.99 (95% CI, 2.96-16.51; P < 0.001). Conclusion: An FPSAR of 0.10 or more after RP independently correlated with increased odds of a positive 18F-DCFPyL PSMA PET/CT scan among BCR post-RP patients. These findings may offer an inexpensive method by which to triage access to 18F-DCFPyL PSMA PET/CT in jurisdictions where availability is not replete.

Elevation of Serum Prostate-Specific Antigen Levels in Males With Pulmonary Embolism

Hypoxemia is a clinical characteristic of pulmonary embolism (PE). Hypoxemia is associated with variations in serum prostate-specific antigen (PSA) levels. Thus, the present study aimed to determine serum PSA levels in patients with PE, which may be helpful in improving clinical evaluation in screening for prostate diseases in those with PE. Clinical data from 61 consecutive male patients with PE and 113 age-matched healthy male controls were retrospectively analyzed. The pulmonary artery obstruction index (PAOI) was used to evaluate the pulmonary embolic burden. Compared with healthy controls, serum total PSA (tPSA) levels were significantly increased (P = .003), and free PSA (fPSA)/tPSA ratio was significantly decreased in patients with PE (P < .001). There was no significantly difference in serum fPSA levels between patients with PE and healthy controls (P = .253). A significant positive association was observed between serum tPSA levels and PAOI in patients with PE (β = .270, P = .036). Multivariable linear regression analysis revealed that serum tPSA levels were independently associated with PAOI in patients with PE (β = .347, P = .003). Serum tPSA levels were higher in male patients with PE than those in healthy controls, but fPSA was not affected. These findings highlight that PE may elevate serum tPSA levels, and that measures of tPSA should be interpreted with caution in screening for prostate diseases in patients with PE.

Endemic statistical paradoxes in epidemiologic studies distort knowledge on prostate cancer: mitigation and caution of fallacies in prostate cancer causal epidemiological studies

PURPOSE OF REVIEW

Many studies on epidemiology of prostate cancer (PCa) are based on a diagnosis of PCa using PSA (prostate-specific antigen) level. However, biases can distort the interpretation of the results, which in turn limits policy and decision making on public health prevention strategies or clinical guidelines. The main confusion is to interpret the posterior probability of the outcome following the exposure as a change in the prevalence of the disease outcome, whereas this change reflects only the predictive values of the PSA test induced by the exposure of interest.

RECENT FINDINGS

Many studies report potential causal factors involved in PCa risk. However, the lack of integration of how physiological changes in PSA values are associated with the exposures being investigated, they explain in part contradictory and controversial results on PCa risk factors in the literature.

SUMMARY

A strategy to perform case--control studies based on PSA stratification is suggested to avoid misinterpretation related to PSA misclassification. Real data are analysed, and we show that we can exploit the mechanism of selection biases using different modalities of controls recruitment based on biomarker stratification to distinguish real from false causal factors.

Can post-treatment free PSA ratio be used to predict adverse outcomes in recurrent prostate cancer?

OBJECTIVES

To assess whether free PSA ratio (FPSAR) at biochemical recurrence (BCR) can predict metastasis, castrate-resistant prostate cancer (CRPC), and cancer-specific survival (CSS), following therapy for localised disease.

PATIENTS AND METHODS

A single-centre retrospective cohort study (NCT03927287) including a discovery cohort composed of patients with an FPSAR after radical prostatectomy (RP) or radiotherapy (RT) between 2000 and 2017. For validation, an independent Biobank cohort of patients with BCR after RP was tested. Using a defined FPSAR cut-off, the metastasis-free-survival (MFS), CRPC-free survival, and CSS were compared. Multivariable Cox models determined the association between post-treatment FPSAR, metastases, and CRPC.

RESULTS

Overall, 822 patients (305 RP- and 363 RT-treated patients and 154 Biobank patients) were analysed. In the RP cohort, a total of 272/305 (89.1%) and 33/305 (10.9%) had a FPSAR test incidentally and reflexively, respectively. In the RT cohort, 155/363 (42.7%) and 208/263 (57.3%) had a FPSAR test incidentally and reflexively, respectively. However, in the prospective Biobank RP cohort, FPSAR testing was done on all samples of patients diagnosed with BCR. A FPSAR cut-off of 0.10 was determined using receiver operating characteristic analyses in both the RP and RT cohorts. A FPSAR of <0.10 resulted in longer median MFS (14.8 vs 9.3 years and 14.8 vs 13 years, respectively), and longer median CRPC-free survival (median not reached vs 9.9 years and 20.7 vs 13.8 years, respectively). Multivariable analyses showed that a FPSAR of ≥0.10 was associated with increased metastasis in the RP cohort (hazard ratio [HR] 1.915, 95% confidence interval [CI] 1.241-2.955) and RT cohort (HR 1.754, 95% CI 1.112-2.769), and increased CRPC in the RP cohort (HR 2.470, 95% CI 1.493-4.088). Findings were validated in the Biobank cohort.

CONCLUSIONS

A post-treatment FPSAR of ≥0.10 is associated with more aggressive disease, suggesting a potentially novel role for this biomarker.

Prostate-specific antigen and its derivatives in young adults occupationally exposed to quarry pollutants in southeastern Nigeria

To evaluate the level of total prostate-specific antigen (PSA) and effect of duration of exposure to pollutants in quarry workers, 5 mls of blood sample was collected from participants: 72 male quarry workers exposed to quarry pollutants and 72 unexposed controls. PSA estimations were done using the principle of ELISA. Mean total PSA, free PSA, and free-total PSA ratio levels of quarry workers did not differ from those of controls and was below the cutoff for the risk of prostate diseases. Higher mean total PSA and free PSA were observed in workers exposed for > 3 years compared to the unexposed control and workers exposed for ≤ 3 years. Age-adjusted linear regression indicated significant association (R = 0.515; p < .001) between the duration of exposure and total PSA level in quarry workers. This study suggests that longer duration of exposure to the quarry pollutants may elevate PSA level if precautions are not taken to minimize dose of exposure.

Stability and accuracy of total and free PSA values in samples stored at room temperature

INTRODUCTION

In 2010, an estimated 476,076 total PSA tests were performed in Ireland, at a cost of €3.6 million with the majority ordered by general practitioners. We aimed to replicate storage conditions at room temperature and see if prolonged storage affected total and free PSA values.

METHODS

Blood samples were taken from 20 male patients in four VACUETTE^® Serum Separator tubes (Greiner-Bio-One, Austria) and stored at room temperature (22 °C) for different time intervals (4, 8, 24, 48 h) before being centrifuged and analyzed. Total PSA (tPSA) and free PSA (fPSA) values were determined using the Tosoh AIA 1800 assay (Tokyo, Japan).

RESULTS

Mean tPSA values were measured at 4, 8, 24 and 48 h with values of 7.9, 8.1, 7.8 and 8.0 μg/L, respectively. Values ranged from -1.26 to +2.53 % compared to the initial 4 h interval reading, indicating tPSA remained consistent at room temperature. The tPSA showed no significance between groups (ANOVA, p = 0.283). Mean fPSA values at 4, 8, 24 and 48 h were 2.05, 2.04, 1.83, 1.82 μg/L, respectively. At 24 and 48 h there was 10.73 and 11.22 % reduction, respectively, in fPSA compared to the 4-h time interval, indicating prolonged storage resulted in reduced fPSA values. After 24 h, there was an 8.8 % reduction in the free/total PSA %. The fPSA showed significant differences between groups (ANOVA, p = 0.024).

CONCLUSIONS

Our recommendation is that samples that have been stored for prolonged amounts of time (greater than 24 h) should not be used for free PSA testing.

Effect of histological inflammation on total and free serum prostate-specific antigen values in patients without clinically detectable prostate cancer

Purpose

We are often confronted with patients in the "gray zone" (prostate-specific antigen [PSA]<10 ng/mL) whose biopsies reveal no malignancy but only inflammation. We investigated the relationship between histological inflammation and total PSA (tPSA), free PSA (fPSA), and percentage of free PSA (f/tPSA) levels in patients without prostate cancer (PC).

Materials and Methods

We studied 106 men with tPSA<10 ng/mL who had undergone biopsy that was negative for PC and who had no clinical prostatitis. Inflammation observed at biopsies was scored for inflammation type in each biopsy core by use of a four-point scale and was then correlated with tPSA, fPSA, and f/tPSA.

Results

Different patterns of inflammation were found in each set of biopsies. Regression factor analysis was used to form two groups according to inflammation type: more chronic and more acute. Median tPSA, fPSA, and f/tPSA levels in the more chronic and more acute inflammation groups were 6.4 ng/mL, 1.09 ng/mL, and 15%, and 7.3 ng/mL, 0.79 ng/mL, and l2%, respectively. A significant difference was found in fPSA (p=0.003) and f/tPSA (p<0.001), whereas the difference in tPSA was not significant (p=0.200). Total PSA correlated with fPSA (r=0.4, p<0.001) but not with inflammation type (r=0.12, p>0.010). A correlation existed between inflammation type and fPSA (r=-0.31, p=0.001) and f/tPSA (r=-0.43, p<0.001) in that the fPSA and f/tPSA were lower in the group with more acute inflammation.

Conclusions

Subclinical inflammation has a significant influence on fPSA in patients with tPSA<10 ng/mL but without PC or clinical prostatitis. Subclinical inflammation is not characterized by elevated tPSA alone but also by a decreased fPSA, a tendency similar to that in PC.

Physiology, pathology and pharmacology of the male reproductive system

The male reproductive system consists of the testes, a ductal system and sex accessory organs. Production of sperm by the testes combined with fluids formed by the sex accessory organs (e.g. seminal vesicles, prostate and bulbourethral glands) produce a secretion that supports the survival of spermatozoa and provides a medium through which they can move through the reproductive ducts (e.g. epididymis, vas deferens, ejaculatory duct and urethra) for ejaculation of viable sperm into the female reproductive tract. Summarized herein are the essentials of normal male reproductive physiology, disorders of male sexual differentiation, pharmacological therapy of common diseases of the male genitourinary tract and the impact of drugs of abuse on the male reproductive system.

Combined immunotherapy with Listeria monocytogenes-based PSA vaccine and radiation therapy leads to a therapeutic response in a murine model of prostate cancer

Radiation therapy (RT) is an integral part of prostate cancer treatment across all stages and risk groups. Immunotherapy using a live, attenuated, Listeria monocytogenes-based vaccines have been shown previously to be highly efficient in stimulating anti-tumor responses to impact on the growth of established tumors in different tumor models. Here, we evaluated the combination of RT and immunotherapy using Listeria monocytogenes-based vaccine (ADXS31-142) in a mouse model of prostate cancer. Mice bearing PSA-expressing TPSA23 tumor were divided to 5 groups receiving no treatment, ADXS31-142, RT (10 Gy), control Listeria vector and combination of ADXS31-142 and RT. Tumor growth curve was generated by measuring the tumor volume biweekly. Tumor tissue, spleen, and sera were harvested from each group for IFN-γ ELISpot, intracellular cytokine assay, tetramer analysis, and immunofluorescence staining. There was a significant tumor growth delay in mice that received combined ADXS31-142 and RT treatment as compared with mice of other cohorts and this combined treatment causes complete regression of their established tumors in 60 % of the mice. ELISpot and immunohistochemistry of CD8+ cytotoxic T Lymphocytes (CTL) showed a significant increase in IFN-γ production in mice with combined treatment. Tetramer analysis showed a fourfold and a greater than 16-fold increase in PSA-specific CTLs in animals receiving ADXS31-142 alone and combination treatment, respectively. A similar increase in infiltration of CTLs was observed in the tumor tissues. Combination therapy with RT and Listeria PSA vaccine causes significant tumor regression by augmenting PSA-specific immune response and it could serve as a potential treatment regimen for prostate cancer.

Nanotechnology for early cancer detection

Vast numbers of studies and developments in the nanotechnology area have been conducted and many nanomaterials have been utilized to detect cancers at early stages. Nanomaterials have unique physical, optical and electrical properties that have proven to be very useful in sensing. Quantum dots, gold nanoparticles, magnetic nanoparticles, carbon nanotubes, gold nanowires and many other materials have been developed over the years, alongside the discovery of a wide range of biomarkers to lower the detection limit of cancer biomarkers. Proteins, antibody fragments, DNA fragments, and RNA fragments are the base of cancer biomarkers and have been used as targets in cancer detection and monitoring. It is highly anticipated that in the near future, we might be able to detect cancer at a very early stage, providing a much higher chance of treatment.

Aggressiveness of Inflammation in Histological Prostatitis – Correlation with Total and Free Prostate Specific Antigen Levels in Men with Biochemical Criteria for Prostate Biopsy

Background and Aims

Although prostatitis can contribute to the lack of prostate specific antigen (tPSA) specificity, there is disagreement concerning the effect of histological inflammation on free PSA (fPSA). We investigated the correlation between aggressiveness of histological inflammation and tPSA, fPSA and f/tPSA in patients without detectable prostate cancer (PC).

Methods

The study included 106 patients with tPSA <10 ng/mL, without clinical prostatitis and with biopsy negative for PC. The inflammation in prostate biopsies was scored for aggressiveness using the four-point scale reported by Irani. The patients were divided into two groups of less aggressive and more aggressive inflammation and compared by use of regression analysis.

Results

The median tPSA, fPSA and f/tPSA levels were 6.39 ng/mL, 1.1 ng/mL and 16% in the less aggressive inflammation group and 7.3 ng/mL, 0.79 ng/mL and 10.7% in the more aggressive inflammation group, respectively. There was no significant between-group difference in tPSA levels (P=0.16), however, statistically significant between-group differences were recorded in fPSA and f/tPSA levels (P<0.001 both). Spearman's analysis yielded a significant negative correlation of inflammation aggressiveness with fPSA (r=-0.34; P<0.001) and f/tPSA (r=-0.45; P<0.001). Free PSA and f/tPSA were lower in the group with more aggressive inflammation.

Conclusions

Histological inflammation has a high prevalence in cancer-free prostate biopsy specimens and exerts similar effects on fPSA and f/tPSA levels as PC. Our study suggests histological prostatitis to be an important cause of decreased fPSA and f/tPSA values; therefore, when it is identified, antibiotic or anti-inflammatory therapy should be introduced to reduce the percentage of men with a continuing indication for prostate biopsy.

Free/Total PSA (F/T ratio) kinetics in patients with clinically localized prostate cancer undergoing radical prostatectomy

BACKGROUND

In this paper we study the Free/Total PSA kinetics in patients with clinically localized prostate cancer undergoing radical prostatectomy.

METHODS

Serum PSA, Free PSA and Free/Total Ratio were determined preoperatively, at the time of prostate removal (0 time) and then at 3, 6, 12, 24, 48, 72 and 168 h, from 9 patients with clinically localized prostate cancer who underwent radical retropubic prostatectomy. The elimination rates and half-lives of Total, Free PSA and F/T Ratio were studied applying one and two compartment models for pharmacokinetic analysis.

RESULTS

Surgical manipulations of the prostate caused a mean 2.16-fold increase of PSA, 12-fold increase of free PSA and 4.2-fold increase of F/T PSA ratio. Removal of the prostate caused a rapid biphasic, biexponential elimination of Free PSA with a mean half-life of 0.8 h for the alpha (a) phase and 32.6 h for the beta (b) phase. PSA was eliminated following a rapid exponential (a) phase with a half-life of 1.15 h and a non-exponential (b) phase with a half-life of 71.96 h. Free/Total PSA followed a biphasic kinetic, with an initial exponential elimination phase and a mean half-life of 2.6 h and a second non-exponential increase phase with a doubling time of 130.8 h. Free/Total PSA reached its nadir very soon, at the first postoperative 24 h.

CONCLUSIONS

Free/Total PSA kinetic after radical prostatectomy reflects the differences of Free and Total PSA elimination kinetics. Free/Total Ratio follows a biphasic kinetic, with an initial rapid exponential elimination phase, which is affected mainly by the rapid exponential (a) phase of Free PSA elimination and a second slow increase, which is affected mainly by the terminal non-exponential (b) phase of PSA elimination.

Gold nanoparticle probes for the detection of nucleic acid targets

BACKGROUND

Advances in nanoscience are having a significant impact on many scientific fields and are resulting in the development of a variety of important technologies. This impact is particularly large in the field of biodiagnostics, where a number of nanoparticle-based assays have been introduced for biomolecular detection, with DNA- or protein-functionalized gold nanoparticles used as the target-specific probes.

METHODS

Assays provide an analysis of the unique biophysical properties displayed by gold nanoparticles and have advantages over conventional detection methods (e.g., molecular fluorophores, real-time polymerase chain reaction, RT-PCR, enzyme linked immunosorbent assays, ELISAs, gel electrophoresis, and microarray technologies).

CONCLUSION

Some of the advantages include the assays' PCR-like sensitivity, their selectivity for target sequences, their capacity for massive multiplexing, their time efficiency, and most importantly, their ability to be performed at the point of care.

The measurement of complexed prostate-specific antigen has a better performance than total prostate-specific antigen

The aim of this study was to compare the diagnostic utility of complexed prostate-specific antigen (cPSA) with total PSA (tPSA) in screening for prostate cancer. Serum concentrations of tPSA and cPSA were measured in 4479 adult men during the prostate cancer screening program in the Saarland region (Germany). The percentage of men with c/tPSA ratio above the cut-off value of 0.75 increased with increasing tPSA intervals: tPSA 0-0.9 microg/l, 4.4%; 1.0-1.9 microg/l, 24.3%; 2.0-2.9 microg/l, 43.9%; 3.0-3.9 microg/l, 50.4%; and 4.0-20 microg/l, 60.2%. The commonly accepted tPSA cut-off value of 3.9 microg/l matched to the 93rd percentile of the overall population (corresponding cPSA value, 2.9 microg/l). A total of 202 men out of 313 with increased cPSA had increased c/tPSA ratio (cut-off > or = 0.75) vs. 186 out of 312 men with increased tPSA. Thus, an additional 16 men at high risk for prostate cancer were selected only if cPSA was utilised as a first line parameter. Our data show that, compared to tPSA, cPSA measurement will always detect more high-risk patients, independent of the cut-off levels utilised for cPSA, tPSA and c/tPSA ratio. cPSA is more effective than tPSA in selecting subjects with an elevated c/tPSA ratio who are at high risk of prostate cancer. Thus, cPSA might be seen as the superior first-line parameter in screening for prostate cancer. Using lower cut-off values for tPSA or cPSA than the commonly accepted values seems reasonable for screening purposes.

Selective recognition of enzymatically active prostate-specific antigen (PSA) by anti-PSA monoclonal antibodies

Prostate-specific antigen (PSA) is widely used as a serum marker for the diagnosis of prostate cancer. To evaluate two anti-free PSA monoclonal antibodies (mAbs) as potential tools in new generations of more relevant PSA assays, we report here their properties towards the recognition of specific forms of free PSA in seminal fluids, LNCaP supernatants, 'non-binding' PSA and sera from cancer patients. PSA from these different origins was immunopurified by the two anti-free PSA mAbs (5D3D11 and 6C8D8) as well as by an anti-total PSA mAb. The composition of the different immunopurified PSA fractions was analysed and their respective enzymatic activities were determined. In seminal fluid, enzymatically active PSA was equally purified with the three mAbs. In LNCaP supernatants and human sera, 5D3D11 immunopurified active PSA mainly, whereas 6C8D8 immunopurified PSA with residual activity. In sera of prostate cancer patients, we identified the presence of a mature inactive PSA form which can be activated into active PSA by use of high saline concentration or capture by an anti-total PSA mAb capable of enhancing PSA activity. According to PSA models built by comparative modelling with the crystal structure of horse prostate kallikrein described previously, we assume that active and activable PSA could correspond to mature intact PSA with open and closed conformations of the kallikrein loop. The specificity of 5D3D11 was restricted to both active and activable PSA, whereas 6C8D8 recognized all free PSA including intact PSA, proforms and internally cleaved PSA.

Comparative evaluation of various prostate specific antigen ratios for the early detection of prostate cancer

OBJECTIVE

To compare the performance of various ratios using total prostate specific antigen (PSA), complexed PSA (cPSA) and free PSA (fPSA) in the early detection of prostate cancer.

PATIENTS AND METHODS

The study included 535 consecutive patients evaluated at a prostate cancer detection clinic between January 1998 and October 1999. Patients had blood samples drawn before transrectal ultrasonography and prostate biopsy to measure PSA, cPSA and fPSA. Receiver operating characteristic (ROC) curves (sensitivity vs 1 - specificity) were used to evaluate the performance of PSA, cPSA, f/tPSA, cPSA/tPSA, fPSA/cPSA, tPSA/prostate volume (PV), fPSA/PV, and cPSA/PV. The areas under the curve (AUC) were calculated for each ratio. The performance of each ratio over all patients or in those with a tPSA of 4-6 or 4-10 ng/mL were evaluated.

RESULTS

Of the 535 patients, 204 (38%) had biopsy-confirmed prostate cancer. The AUC obtained with tPSA alone was 0.64; when measured for all patients the cPSA/PV (0.78), PSA/PV (0.77), f/tPSA (0.76) and fPSA/cPSA (0.75) performed better than tPSA alone. Furthermore, in patients with a tPSA of 4-10 ng/mL, tPSA/PV (0.72), cPSA/PV (0.71), f/tPSA (0.69), fPSA/cPSA (0.69) and cPSA/tPSA (0.62) performed better than tPSA alone (0.52). Finally, in patients with a tPSA of 4-6 ng/mL, PSA/PV and cPSA/PV performed better than the other ratios.

CONCLUSIONS

The use of PSA ratios gives a higher sensitivity and specificity for detecting prostate cancer than the use of tPSA alone.

Separation of enzymatically active and inactive prostate-specific antigen (PSA) by peptide affinity chromatography

BACKGROUND

Prostate-specific antigen (PSA) is a serine protease with highly prostate-specific expression and an important marker for prostate cancer. We have previously identified novel PSA-binding peptides that enhance the enzymatic activity of PSA when produced as fusion proteins.

METHOD

PSA-binding peptides and derivatives with a spacer were chemically synthesized and used to prepare an affinity column, which was used to fractionate PSA in seminal plasma, serum, and LNCap cell culture medium.

RESULTS

Approximately 67% of seminal plasma PSA bound to the peptide affinity column and was eluted under mild conditions. Eluted PSA was intact and enzymatically active while the unbound fraction mainly contained various nicked forms. ProPSA from LNCap cells bound to the peptide column only after activation by trypsin.

CONCLUSIONS

PSA-binding peptides can be used to separate enzymatically active and inactive forms of PSA. Thus the peptides are potentially useful as ligands for development of methods for specific detection of active free PSA.

Prostatic zinc and prostate specific antigen: an experimental evaluation of their combined diagnostic value

PURPOSE

In cancer affected prostate cells lose the ability to concentrate zinc, resulting in a substantial decrease in Zn in the prostate. We investigated the possibility of using prostatic zinc combined with prostate specific antigen (PSA) as a novel tool for the reliable diagnosis of prostate cancer.

MATERIALS AND METHODS

Using the x-ray fluorescence method the Zn concentration was determined in vitro in prostate samples extracted by surgery from 28 patients. Clinical records included age, serum PSA, sextant prostate needle biopsy, previous medical therapy, surgical procedure and histological findings.

RESULTS

A new relationship was found between Zn in prostate tissue and PSA in blood, which allows improved separation between prostate cancer and benign prostate hyperplasia, and might have a significant impact on the reliable diagnosis of prostate cancer.

CONCLUSIONS

Zn concentration is not uniform even in the same anatomical region of the prostate, so that a number of measurements at various locations are required for a diagnostic procedure. The most interesting finding in this study is the relationship between Zn concentration and PSA. A combination of these parameters represents a significant improvement on the diagnostic value of each of them separately and provides a powerful tool for more accurate diagnosis. Although the method may be applied in vitro on biopsy samples, our study underlines the importance of developing a facility for in vivo Zn determination in the prostate.

Determination of non-alpha1-antichymotrypsin-complexed prostate-specific antigen as an indirect measurement of free prostate-specific antigen: analytical performance and diagnostic accuracy

BACKGROUND

A new assay measures prostate-specific antigen (PSA) not complexed to alpha(1)-antichymotrypsin (nACT-PSA) after removing PSA complexed to ACT by use of anti-ACT antibodies. We evaluated nACT-PSA and its ratio to total PSA (tPSA) as alternatives to free PSA (fPSA) and its ratio to tPSA in differentiating prostate cancer (PCa) and benign prostatic hyperplasia (BPH) in patients with tPSA of 2-20 micro g/L.

METHODS

PSA in serum of 183 untreated patients with PCa and 132 patients with BPH was measured retrospectively on the chemiluminescence immunoassay analyzer LIAISON(R) (Byk-Sangtec Diagnostica) with the LIAISON tPSA and LIAISON fPSA assays. The nACT-PSA fraction was determined with a prototype assay measuring the residual PSA after precipitation of ACT-PSA with an ACT-precipitating reagent.

RESULTS

nACT-PSA was higher than fPSA in samples with fPSA concentrations <1 microg/L but lower in samples with >1 microg/L fPSA. The median ratios of fPSA/tPSA and of nACT-PSA/tPSA were significantly different between patients with BPH and PCa (19.4% vs 12.2% and 17.4% vs 13.0%, respectively). Within the tPSA ranges tested (2-20, 2-10, and 4-10 microg/L), areas under the ROC curves for the fPSA/tPSA ratios were significantly larger than those for nACT-PSA/tPSA. In the tPSA ranges <10 microg/L, the areas under the ROC curves for fPSA/tPSA were significantly larger than those for tPSA, whereas the areas for nACT-PSA/tPSA were not. At decision limits for 95% sensitivity and specificity, both ratios significantly increased specificity and sensitivity, respectively, compared with tPSA, but the fPSA/tPSA ratio showed higher values.

CONCLUSIONS

nACT-PSA and its ratio to tPSA provide lower diagnostic sensitivity and specificity than fPSA/tPSA. The fPSA/tPSA ratio represents the state-of-the-art method for differentiating between PCa and BPH.

The new human tissue kallikrein gene family: structure, function, and association to disease

The human tissue kallikrein gene family was, until recently, thought to consist of only three genes. Two of these human kallikreins, prostate-specific antigen and human glandular kallikrein 2, are currently used as valuable biomarkers of prostatic carcinoma. More recently, new kallikrein-like genes have been discovered. It is now clear that the human tissue kallikrein gene family contains at least 15 genes. All genes share important similarities, including mapping at the same chromosomal locus (19q13.4), significant homology at both the nucleotide and protein level, and similar genomic organization. All genes encode for putative serine proteases and most of them are regulated by steroid hormones. Recent data suggest that at least a few of these kallikrein genes are connected to malignancy. In this review, we summarize the recently accumulated knowledge on the human tissue kallikrein gene family, including gene and protein structure, predicted enzymatic activities, tissue expression, hormonal regulation, and alternative splicing. We further describe the reported associations of the human kallikreins with various human diseases and identify future avenues for research.

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

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

Using the free-to-total prostate-specific antigen ratio to detect prostate cancer in men with nonspecific elevations of prostate-specific antigen levels

BACKGROUND

Prostate-specific antigen (PSA) levels between 4.0 to 10.0 ng/ml have poor specificity in prostate cancer screening, leading to unnecessary biopsies.

OBJECTIVE

To determine whether the free-to-total PSA ratio (F/T PSA) improved the diagnostic accuracy of these nonspecific PSA levels.

MEASUREMENTS AND MAIN RESULTS

MEDLINE searchedwas from 1986 to 1997. Additional studies were identified from article bibliographies and by searching urology journals. Two investigators independently identified English-language studies providing F/T PSA ratio test-operating characteristics data on > or = 10 cancer patients with PSA values between 2.0 and 10.0 ng/ml. Twenty-one of 90 retrieved studies met selection criteria. Two investigators independently extracted data on methodology and diagnostic performance. Investigator-selected cut points for the optimal F/T PSA ratio had a median likelihood ratio of 1.76 (interquartile range, 1.40 to 2.11) for a positive test and 0.27 (0.20 to 0.40) for a negative test. Assuming a 25% pretest probability of cancer, the posttest probabilities were 37% following a positive test and 8% following a negative test. The summary receiver operating characteristic curve showed that maintaining test sensitivity above 90% was associated with false positive rates of 60% to 90%. Methodologic problems limited the validity and generalizability of the literature.

CONCLUSIONS

A negative test reduced the posttest probability of cancer to approximately 10%. However, patients may find that this probability is not low enough to avoid undergoing prostate biopsy. The optimal F/T PSA ratio cut point and precise estimates for test specificity still need to be determined.

Clinical value of human glandular kallikrein 2 and free and total prostate-specific antigen in serum from a population of men with prostate-specific antigen levels 3.0 ng/mL or greater

OBJECTIVES

To investigate the clinical value of human glandular kallikrein 2 (hK2) compared with free (f) and total (t) prostate-specific antigen (PSA) in the early detection of prostate cancer (PCa).

METHODS

In PCa screening conducted in 1995 to 1996 in Göteborg, Sweden, 5853 of 9811 randomly selected men (aged 50 to 66 years; median 61) accepted PSA testing; those with tPSA levels of 3. 0 ng/mL or greater were offered digital rectal examination, transrectal ultrasound, and sextant biopsies. Serum from 604 of 611 biopsied men (18% with positive digital rectal examinations, tPSA range 3.0 to 220 ng/mL, 144 men with PCa) was analyzed for hK2 (research assay) and tPSA and fPSA (Prostatus). Sera were stored at -20 degrees C for a maximum of 2 weeks for tPSA and fPSA and 3 years for hK2.

RESULTS

hK2 levels and hK2 x tPSA/fPSA values were significantly elevated in men with PCa. Receiver operating characteristic data revealed that the area under the curve for hK2 x tPSA/fPSA was significantly greater than that for tPSA and greater, but not significantly greater, than that for percent fPSA. Also, the cancer-detecting sensitivity was significantly improved (P <0.05) using hK2 x tPSA/fPSA compared with tPSA and percent fPSA at specificity levels of 75% to 90%. At 75% specificity, a sensitivity of 74% was obtained compared with 64% or 54% using percent fPSA or tPSA; at 90% specificity, the corresponding sensitivity level was 55%, 41%, and 36%, respectively.

CONCLUSIONS

Discrimination of men with and without PCa in a randomly selected population was improved by measuring hK2 in addition to tPSA and fPSA.

Comparison of the percent free prostate-specific antigen levels in the serum of healthy men and in men with recurrent prostate cancer after radical prostatectomy

The percentage of free PSA in serum is currently used to better discriminate between patients with prostate cancer and patients with benign prostatic hyperplasia, in prostate cancer screening programs. We measured using non-competitive immunological techniques, the total PSA and free PSA in post-surgical serum of prostate cancer patients who underwent radical prostatectomy and then relapsed. We compared these data with those of a group of 40 age-matched men with no evidence of prostatic disease. Although in general, patients with prostate cancer had lower percentage of free PSA in serum in comparison to the controls, a subset of these patients (approximately 20%) had percent free PSA significantly higher than the levels considered as exclusive of prostate cancer in screening programs. We also found that percent free PSA does not correlate significantly with most of the standard clinical or pathological indicators of prostate cancer aggressiveness. Only a weak negative association with Gleason Score was observed. The percent free PSA in serum of relapsing prostate cancer patients varies within a relatively wide range and does not correlate significantly with indicators of cancer aggressiveness. The use of percent free PSA for excluding prostate cancer in screening programs must be approached with caution until the mechanism of low percent free PSA in the majority but not all prostate cancer patients is elucidated.

The stability of free and bound prostate-specific antigen

OBJECTIVE

To determine if the assay for free prostate specific antigen (fPSA) and the calculated ratio of fPSA to total PSA (f/tPSA) is stable in conditions likely to be met in routine clinical practice.

MATERIALS AND METHODS

Two blood samples were obtained from 27 patients attending a routine urology clinic. Sample 1 was centrifuged immediately, assayed for fPSA and tPSA, and the f/tPSA calculated. This sample was then stored at 4 degrees C for 24 h, 48 h and 1 week, or at -20 degrees C for 24 h, 1 week and 1 month before the assays for fPSA and tPSA were repeated. The second sample was left at room temperature for 24 h before assay and processing, as for sample 1.

RESULTS

tPSA is a highly stable analyte; if whole blood samples are processed immediately, fPSA is stable for 24 h at 4 degrees C and 1 month at -20 degrees C. There was a significant reduction in the calculated f/tPSA in samples stored for >/=24 h at 4 degrees C (P<0.01); if the sample was stored at -20 degrees C the calculated f/tPSA was stable. After 24 h storage at room temperature, fPSA decreased by 6.3% and f/tPSA by 6.4%. Subsequent storage of serum at 4 degrees C for 1 week resulted in a 25% decrease from the baseline value. After 1 month at -20 degrees C the fPSA value was 13% lower than the baseline value.

CONCLUSION

These results indicate that if there is to be confidence in the accuracy of the f/tPSA value, then blood samples must be handled and processed correctly. Total PSA is sufficiently stable to permit whole blood samples to remain at room temperature for 24 h before serum is separated. If fPSA is to be determined accurately then the whole blood sample must be centrifuged promptly. As the fPSA values in blood samples left at room temperature for 24 h are up to 25% lower than those on immediate assay, and the subsequent f/tPSA 29% lower, then for the optimum use of this test, these samples should also be handled appropriately.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Two-dimensional electrophoresis of prostate-specific antigen in sera of men with prostate cancer or benign prostate hyperplasia

Prostate-specific antigen (PSA), the main marker for prostate cancer (PCa), is released from the prostate into the blood stream at nanogram level and may increase in PCa and nonmalignant disease such as benign prostate hyperplasia (BPH). More recently, advantage was taken of PSA's ability to bind to protease inhibitors in serum in order to improve discrimination between PCa and BPH, using the free PSA to total PSA ratio. The understanding of this phenomenon at molecular level, which is still unknown, may promise new improvements in the field of diagnostics. For this purpose, we determined the pattern of PSA forms in PCa and BPH sera, using the high resolving power of two-dimensional electrophoresis (2-DE) in conjunction with the high sensitivity of chemiluminescence detection. Serum PSA differs drastically from seminal PSA: apart from complexed forms, serum PSA shows few cleaved forms. Moreover, 2-DE patterns from PCa are relatively homogeneous, whereas patterns from BPH may in some cases present a higher proportion of cleaved forms and in other cases present slightly more basic spots. We therefore demonstrated, for the first time, that an increase in the free to total PSA ratio in BPH cases may be due to cleaved PSA forms (which are enzymatically inactive and unable to bind inhibitors), or possibly related to basic free PSA, which may represent the zymogen forms.

Human Kallikrein 2 (hK2) and prostate-specific antigen (PSA): two closely related, but distinct, kallikreins in the prostate

Recent studies on human kallikrein 2 (hK2) have revealed striking similarities and significant differences with the closely related kallikrein PSA. Both PSA and hK2 are primarily localized to the prostate and share close structural similarities. Although both kallikreins are produced by the same secretory epithelial cells in the prostate, hK2 is associated more with prostate tumors than PSA and is highly expressed in poorly differentiated cancer cells. The potent trypsin-like activity of hK2 contrasts with the weak chymotrypsin-like activity of PSA. The inactive precursor form of PSA, proPSA, is converted rapidly to active PSA by hK2, suggesting an important in vivo regulatory function by hK2 on PSA activity. The high homology between hK2 and PSA results in significant cross-reactivity to hK2 by polyclonal and some monoclonal antibodies to PSA. Future studies on both PSA and hK2 need to take into account this potential for cross-reactivity. Specific monoclonal antibodies to hK2 have now demonstrated that serum levels of hK2, like PSA, are correlated with prostate cancer. The production of hK2 protein in active protease form and specific monoclonal antibodies to the hK2 antigen will allow extensive future studies delineating the physiological and clinical utility of this new prostate antigen.

Value of the free to total prostate specific antigen ratio and prostate specific antigen density for detecting prostate cancer in Japanese patients

BACKGROUND

This study evaluated the free to total serum prostate specific antigen (f/t PSA) ratio and prostate specific antigen density (PSAD) in detecting prostate cancer in Japanese males with a PSA level between 2.5 and 20.0 ng/mL in a community-based urology practice.

METHODS

Twenty-six patients with clinically localized prostate cancer and 44 patients with histologically-proven benign prostatic hyperplasia (BPH) were studied. The serum levels of free PSA (fPSA) and total (t) PSA were determined using a chemiluminescent enzyme immunoassay. The f/t PSA ratio was calculated by dividing the fPSA value by the total PSA value and was compared with the PSA and PSAD via the receiver operating characteristic (ROC) curves.

RESULTS

Patients with prostate cancer had a significantly lower f/t PSA ratio than patients with BPH. The PSAD was a superiordiagnostic tool over PSA (P< 0.01) when analyzed by ROC curves. The f/t PSA ratio was also superior to PSA, but lacked significance (P=0.12), and similarly, the PSAD was superior, but not significant, to the f/t PSA ratio. Using a cut-off value of 0.19, the PSAD had a sensitivity of 81% and a specificity of 82%. With a cut-off value of 14.0%, the f/t PSA ratio had a sensitivity of 81% and a specificity of 66%.

CONCLUSION

This study showed that PSAD alone improved cancer detection significantly better than PSA. However, it is still unclear whether the f/t PSA ratio is superior to PSA or PSAD in the discrimination between BPH and prostate cancer in Japanese male patients.

Ratio of free-to-total prostate specific antigen in serum cannot distinguish patients with prostate cancer from those with chronic inflammation of the prostate

PURPOSE

We demonstrate the effect of chronic inflammation of the prostate on the ratio of free-to-total prostate specific antigen (PSA) in serum calculated as a percentage of free PSA and, therefore, that percentage of free PSA is an unspecific means to distinguish among prostate cancer, chronic prostatitis and benign prostatic hyperplasia (BPH).

MATERIALS AND METHODS

Total, free and percentage of free PSA was measured in 66 men with prostate cancer, 119 with BPH and 17 with asymptomatic chronic prostatitis. In all patients the diagnosis was histopathologically confirmed by microscopic examination of prostatic specimens after sextant biopsy, transurethral prostatic resection or prostatectomy.

RESULTS

The median values of total, free and percentage of free PSA were 4.11 microg./l., 0.75 microg./l. and 20.4% in patients with BPH, 10.0 microg./l., 0.84 microg./l. and 8.5% in those with prostate cancer, and 7.60 microg./l., 1.23 microg./l. and 10.6% in those with chronic prostatitis. Patients with prostate cancer and chronic prostatitis had a significantly lower percentage of free PSA than those with BPH. Receiver operating characteristics curve analysis showed that percentage of free PSA as a discriminator between prostate cancer and BPH was not suitable for differentiating between prostate cancer and chronic prostatitis.

CONCLUSIONS

Chronic prostatitis is not characterized by elevated total PSA concentrations alone but also by a decreased percentage of free PSA, a tendency similar to that in prostate cancer. This unspecific change in percentage of free PSA must be considered to interpret the percentage of free PSA correctly.

Development of monoclonal antibodies specific for human glandular kallikrein (hK2): development of a dual antibody immunoassay for hK2 with negligible prostate-specific antigen cross-reactivity

OBJECTIVES

Human glandular kallikrein (hK2) is a protein that is 80% homologous to prostate-specific antigen (PSA), and, like PSA, is localized to the prostate. We developed a specific immunoassay for hK2 that can be used to evaluate its clinical diagnostic utility.

METHODS

We developed monoclonal antibodies (mAbs) specific for hK2 by immunizing with hK2 and screening for clones reactive with hK2 and not PSA. Prototype sandwich assays using these mAbs were tested, and the optimum pair selected. Purified hK2 was used as standard and PSA cross-reactivity was assessed in the assay. Both hK2 and hK2-alpha1-antichymotrypsin (ACT) complexes have been identified in sera of patients with prostate cancer (PCa). Serum samples (n = 671) from healthy volunteers and patients with prostate disease were assayed for hK2 and PSA levels.

RESULTS

The assay had a detection limit of less than 0.12 ng/mL and a less than 0.5% cross-reactivity with PSA. The assay preferentially detected free hK2 with a 3.5-fold higher molar response than with hK2-ACT. The mean serum concentration of hK2 in normal control samples was low (0.33 and 0.37 ng/mL for normal healthy men and women, respectively) but was elevated in patients with prostate disease (0.86 and 6.77 ng/mL for patients with benign prostatic hyperplasia and PCa, respectively). Negligible cross-reactivity to hK2 was measured by Tandem PSA assays (Hybritech).

CONCLUSIONS

Significant concentrations of hK2, relative to PSA, were detected in human serum, especially in patients with prostate disease. Serum hK2 concentrations were not proportional to PSA concentration. Therefore, hK2 has the potential to be an independent and clinically useful marker for PCa.

Factors influencing the ratio of free to total prostate-specific antigen in serum

The ratio of free prostate-specific antigen (f-PSA) to total PSA (t-PSA) in serum, calculated as percent free PSA (f-PSA%), is lower in patients with prostate carcinoma (PCa) than in patients with benign prostate hyperplasia (BPH). This parameter facilitates discrimination between the 2 groups of patients, but there is an overlapping of data. A better understanding of factors influencing this ratio is of practical importance. Therefore, f-PSA% was measured in controls and patients suffering from BPH, PCa and chronic prostatic inflammation with t-PSA concentrations up to 20 microg/l using the IMMULITE assays. The relationships of f-PSA% to clinical situation, age, prostate volume, kind of treatment, and stage and grade of tumor were calculated. Compared with controls or BPH patients, mean f-PSA% values were reduced in PCa patients and in patients with chronic prostatic inflammation. The prostate volume was the most important factor to influence f-PSA%. The difference of f-PSA% between PCa and BPH patients with prostate volumes smaller than 40 cm3 was lost if the prostate volumes exceeded 40 cm3. No relationship of f-PSA% to pTNM stage or grade of tumor was observed. In contrast to t-PSA concentrations, the f-PSA% values were not age-dependent and were not influenced by any kind of treatment in BPH and PCa patients either, which simplifies the use of f-PSA% compared with t-PSA. Thus, for using f-PSA% in clinical practice and for interpreting the data correctly, the advantages shown have to be considered along with the potential limitations of f-PSA%.

Serpin-derived peptide substrates for investigating the substrate specificity of human tissue kallikreins hK1 and hK2

The third human tissue kallikrein to be identified, hK2, could be an alternate or complementary marker to kallikrein hK3 (prostate-specific antigen) for prostate diseases. Most of the hK2 in seminal plasma forms an inactive complex with protein C inhibitor (PCI), a serpin secreted by seminal vesicles. As serpin inhibitors behave as suicide substrates that are cleaved early in the interaction with their target enzyme, and kallikreins have different sensitivities to serpin inhibitors, we prepared a series of substrates with intramolecularly quenched fluorescence based on the sequences of the serpin reactive loops. They were used to compare the substrate specificities of hK1 and hK2, which both have trypsin-like specificity, and thus differ from chymotrypsin-like hK3. The serpin-derived peptides behaved as kallikrein substrates whose sensitivities reflected the specificity of the parent inhibitory proteins. Substrates derived from PCI were the most sensitive for both hK1 and hK2 with specificity constants of about 10(7) M-1. s-1. Those derived from antithrombin III and alpha2-antiplasmin were more specific for hK2 while a kallistatin-derived substrate was specifically cleaved by hK1. hK1 and hK2 substrates of greater specificity were obtained using chimeric peptides based on the sequence of serpin reactive loops. The main difference between specificities of hK1 and hK2 arise because hK2 can accommodate positively charged as well as small residues at P2 and requires an arginyl residue at P1. Thus, unlike hK1, hK2 does not cleave kininogen-derived substrates overlapping the region of N-terminal insertion of bradykinin in human kininogens.

A precursor form of PSA (pPSA) is a component of the free PSA in prostate cancer serum

OBJECTIVES

Prostate-specific antigen (PSA) is a widely used serum marker for human prostate cancer (PCa). The majority of PSA in serum is present as a complex with alpha-1-antichymotrypsin (ACT). In recent years, the ratio of free (uncomplexed) to total PSA has shown improved discrimination of PCa from benign prostatic hyperplasia. This study examines the nature of the free PSA from detected in PCa serum and shows that some of the uncomplexed PSA is an inactive precursor of PSA (pPSA).

METHODS

Western blot analysis was used to detect clipped, fragment forms of PSA in sera and seminal fluid. Hydrophobic interaction chromatography-high performance liquid chromatography (HIC-HPLC) was used to identify forms of PSA present in the free PSA population. Pooled sera was passed over a PSA immunoaffinity column, and the eluted PSA components were further resolved by HIC-HPLC.

RESULTS

Western blot analysis of whole sera showed complexed PSA and the intact, approximately 34 kilodalton free PSA. Only negligible levels of clipped or degraded forms of PSA, as found in seminal fluid, were detected. Column fractions measured for uncomplexed PSA using the Tandem-MP free PSA assay showed that about 25% of the free PSA eluted as pPSA beginning at the [-4]amino acid. Studies with purified recombinant [-4]pPSA showed that this proenzyme form is inactive and does not complex with ACT.

CONCLUSIONS

These results suggest that the uncomplexed PSA in PCa serum is primarily unclipped PSA that contains a significant fraction of pPSA.