Development of novel peptide ligands modulating the enzyme activity of prostate-specific antigen

Prostate-specific antigen (PSA) is a serine proteinase produced mainly by epithelial cells of the prostate. Measurement of PSA in serum is widely used for diagnosis and monitoring of prostate cancer. The major problem of the PSA determination in early diagnosis is the high false positive rate due to benign prostatic hyperplasia, but the clinical accuracy can be improved by determining the proportions of various molecular forms of PSA. The main biological function of PSA is liquefaction of the seminal gel formed after ejaculation, but PSA has also been suggested to regulate invasiveness and metastatic potential of prostatic tumors. Thus, agents binding to and affecting the function of PSA have the potential to be used for diagnosis and therapy of prostate cancer. We have developed peptides specific for PSA by using cyclic phage display peptide libraries. After deducing the amino acid sequence of the peptides by sequencing the relevant part of phage genome, the peptides were expressed as glutathione-S-transferase (GST) fusion proteins or produced by chemical synthesis. The peptides were shown to bind to PSA specifically as indicated by lack of binding to other related serine proteinases. The binding of the peptides with PSA was strongly inhibited by monoclonal antibodies specific for free PSA and they did not bind to PSA-inhibitor complexes indicating that they bind close to the active site of the enzyme. Most of the peptides enhanced the enzyme activity of PSA against a chromogenic substrate. The affinity of the peptides could be increased by including Zn2+ in the reaction mixture. These results show that peptides that bind to PSA and modulate its enzyme activity can be developed by phage display techniques. These peptides have the potential to be used for targeting of prostatic tumors and diagnostics of prostate cancer.

The levels of trypsinogen isoenzymes in ovarian tumour cyst fluids are associated with promatrix metalloproteinase-9 but not promatrix metalloproteinase-2 activation

Proteolysis mediated by matrix metalloproteinases (MMPs) and serine proteinases is associated with cancer invasion and metastasis. Activation of latent proMMPs, and especially the proforms of the type IV collagen degrading gelatinases A and B (proMMP-2 and proMMP-9), is thought to be a critical step in this process. We have recently found that human tumour-associated trypsin-2 is a potent activator of proMMP-9 and it also activates proMMP-2 in vitro. Trypsinogen, MMP-2, and MMP-9 are expressed in ovarian cancer. To elucidate the function of trypsin in vivo, we studied whether high concentrations of trypsinogen-1, trypsinogen-2, their alpha(1)-proteinase inhibitor (API) complexes, and tumour-associated trypsin inhibitor (TATI) are associated with proMMP-2 and proMMP-9 activation in ovarian tumour cyst fluids. Zymography and immunofluorometric analysis of 61 cyst fluids showed a significant association between high trypsin concentrations and the activation of MMP-9 (P = 0.003-0.05). In contrast, the trypsin concentrations were inversely associated with the activation of MMP-2 (P = 0.01-0.02). Immunohistochemical analysis of ovarian tumour tissue demonstrated expression of trypsinogen-2 and TATI in the secretory epithelium. MMP-2 was detected both in stromal and epithelial cells whereas MMP-9 was detected in neutrophils and macrophage-like cells in stromal and epithelial areas. These results suggest that trypsin may play a role in the regulation of the MMP-dependent proteolysis associated with invasion and metastasis of ovarian cancer.

Plasma prolactin and prostate cancer risk: A prospective study

Prolactin, a pituitary peptide hormone with multiple effects, stimulates prostate growth in experimental models. In humans, prolactin receptors are present in the prostate and are particularly abundant in pre-cancerous lesions. This suggests that prolactin could also be involved in the development of prostate cancer. In this study, we tested the hypothesis that elevated levels of circulating prolactin are associated with an increase in prostate cancer risk. We conducted a case-control study nested within the Northern Sweden Health and Disease Cohort using plasma samples collected from 29,560 men at a health survey. We measured prolactin in plasma from 144 men who had a diagnosis of prostate cancer after a median follow-up time of 4 years after health survey and from 289 controls matched for age and date of recruitment. Risk was not associated with plasma prolactin levels in univariate regression analysis. Odds ratios of prostate cancer for increasing quartiles of prolactin were 1.0, 0.92 (95% CI 0.51-1.65), 0.82 (0.45-1.51) and 0.85 (0.49-1.47). Relative risk estimates remained unchanged after adjustments for height and weight or for plasma levels of testosterone, sex hormone-binding globulin, IGF-I and IGF-binding protein-3. Elevated circulating levels of prolactin were not related to an increase in prostate cancer risk, indicating that high circulating prolactin is not associated with development of prostate cancer.

Predictors of biological aggressiveness of prostate specific antigen screening detected prostate cancer

PURPOSE

It is not known whether screening of asymptomatic men with prostate specific antigen (PSA) decreases the mortality of prostate cancer. We evaluated the extent to which PSA screening identifies clinically significant prostate cancer by analyzing markers of biological aggressiveness.

MATERIALS AND METHODS

We compared prostate cancer in 56 patients in the screening and 21 in the randomized control arm of a population based cohort of 8,975 men 55 to 67 years old participating in the Finnish arm of the European Randomized Study of Screening for Prostate Cancer to 47 clinically detected organ confined, 30 clinically detected metastatic and 16 latent prostate tumors identified at autopsy in 46 consecutive subjects. Biological aggressiveness was determined by histological grading using the Gleason and Mostofi scales, tumor proliferation rate by Ki-67 immunostaining, p53 over expression by immunostaining and aneuploidy by fluorescence in situ hybridization using formalin fixed, paraffin embedded tumor specimens.

RESULTS

A total of 56 neoplasms were detected in 2,781 men (2%) who participated in PSA screening and 21 were detected in 5,975 nonscreened controls (0.35%) during the study period. Disease in nonscreened controls more often involved a high tumor proliferation rate (p = 0.004) and p53 over expression (p = 0.015) than screening detected disease. At least 1 feature of biological aggressiveness was present in 19% of latent, 34% of screening detected, 51% of clinically detected and organ confined, 62% of randomized control and 87% of metastasis cases. Of the screening detected tumors defined as biologically aggressive 74% were identified at organ confined stages pT1-2N0M0.

CONCLUSIONS

PSA screening detects a significant number of biologically aggressive cancers at an early clinical stage, implying that screening may decrease mortality.

Specific staining of human chorionic gonadotropin beta in benign and malignant gastrointestinal tissues with monoclonal antibodies

AIMS

Human chorionic gonadotropin (hCG) beta in serum is a promising tumour marker for gastrointestinal malignancies. Our aim was to investigate the expression of hCGbeta by immunohistochemistry in various gastrointestinal cancers and benign tissues.

METHODS AND RESULTS

A monoclonal antibody (MAb) specific for free hCGbeta was used to stain 107 tissue samples from various gastrointestinal malignancies and 36 benign or normal tissue samples. The specificity of the staining was verified and the results compared with those obtained with a widely used commercial polyclonal antibody (PAb) which reacts with both free hCGbeta and intact hCG, as well as with luteinizing hormone beta. With the MAb, we observed positive immunohistochemical staining in 24% of the malignant gastrointestinal tumours. Gastric (60%) and pancreatic (56%) carcinomas, as well as extrahepatic cholangiocarcinomas (36%), were positive most frequently. We also discovered immunoreactivity in half of the non-malignant samples from pancreatic and biliary tissues. With the PAb, hCG immunoreactivity was evident more frequently in some cancers, but the staining was diffuse and occasionally polymorphonuclear leucocytes were strongly stained.

CONCLUSIONS

This study shows that our MAbs specific for hCGbeta are well suited for immunohistochemistry. Our results confirm previous findings on gastrointestinal cancers and, furthermore, we demonstrate hCGbeta tissue expression in pancreatic adenocarcinoma. The results support reports on hCGbeta as a serum tumour marker for digestive tract diseases.

Leptin is associated with increased prostate cancer risk: a nested case-referent study

A Western lifestyle has been implicated in the pathogenesis of prostate cancer. However, no clear association between obesity and prostate cancer has been shown. Leptin may stimulate prostate growth and angiogenesis, and receptors for leptin are present in the prostate. Leptin may, thus, be associated with increased risk of prostate cancer. One hundred forty-nine men with prostate cancer were identified (together with 298 matched referents) who, before diagnosis, had participated in population-based health surveys in Northern Sweden. Blood pressure, body mass index, and use of tobacco were recorded. Leptin, insulin, insulin-like growth factor I (IGF-I), IGF-I-binding proteins 1-3, testosterone, and sex hormone-binding globulin were analyzed in stored samples. Their influences on prostate cancer were estimated by conditional logistic regression analysis. Prostate cancer specimens were investigated for immunoreactivity for the leptin receptor. Relative risk (95% confidence intervals) estimates of prostate cancer over the quintiles of leptin were 1.0, 2.1 (1.1-4.1), 2.6 (1.4-4.8), 1.4 (0.7-2.7), and 1.6 (0.8-3.2). Adjustments for metabolic variables, testosterone, and IGF-I and its binding proteins did not attenuate this increased risk. Immunoreactivity for the leptin receptor was detected in normal, high-grade prostatic intraepithelial neoplasia lesions and malignant prostatic epithelium. Moderately elevated plasma leptin concentrations are associated with later development of prostate cancer. This may be due to direct effects of leptin on prostatic intraepithelial neoplasia lesions, or to indirect actions through other mechanisms. A critical fat mass related to an interior milieu favorable for prostate cancer development seems to exist, because intermediate but not high leptin levels are related to prostate cancer risk.

Tumor associated trypsin inhibitor as a prognostic factor in renal cell carcinoma

PURPOSE

We analyzed the prognostic significance of pretreatment serum tumor associated trypsin inhibitor in renal cell carcinoma.

MATERIALS AND METHODS

Serum samples were obtained before surgery from 188 patients who underwent radical nephrectomy for renal cell carcinoma. Median followup of living patients was 8.5 years. Serum tumor associated trypsin inhibitor was measured by a time resolved immunofluorometric assay. Statistical analysis was performed using the Kaplan-Meier method, log rank and stratified log rank tests.

RESULTS

Preoperatively serum tumor associated trypsin inhibitor was elevated with a cutoff 16 microg/l in 48% of the patients with normal serum creatinine. The concentration in patients with cancer was significantly higher than in controls (p <0.0001). The serum level correlated with clinical stage and nuclear grade. Patients with an elevated level had significantly shorter survival time than those with a normal level (p = 0.005). Stratified log rank test demonstrated that tumor associated trypsin inhibitor was a prognostic factor independent of stage and grade in all patients as well as in those with nonmetastatic disease.

CONCLUSIONS

Increased preoperative serum tumor associated trypsin inhibitor was associated with poor survival in renal cell carcinoma. The serum level was an independent prognostic variable. Preoperative serum tumor associated trypsin inhibitor appears to be a useful predictive factor that may be used to identify patients at increased risk of aggressive disease.

A comparison of serum trypsinogen-2 and trypsin-2-alpha1-antitrypsin complex with lipase and amylase in the diagnosis and assessment of severity in the early phase of acute pancreatitis

OBJECTIVE

The aim of the study was to compare the recently introduced laboratory markers trypsinogen-2 and trypsin-2-alpha1 antitrypsin complex (trypsin-2-AAT) in serum with lipase and amylase in the diagnostic and prognostic evaluation of patients with acute pancreatitis (AP).

METHODS

The analytes were measured on admission in 64 consecutive patients with AP and in 30 controls with acute abdominal disease of extrapancreatic origin. Twenty-one patients had severe and 43 mild AP. As reference methods we used serum amylase and C-reactive protein.

RESULTS

In subjects with AP, elevated trypsinogen-2 values (> or = 90 microg/L) were observed in 63 patients (98%), trypsin-2-AAT values (> or = 12 microg/L) in 64 patients (100%), lipase values (> or = 200 U/L) in 64 patients (100%), and amylase values (> or = 300 IU/L) in 62 patients (97%). The diagnostic accuracy of the markers was evaluated by receiver operating characteristic (ROC) analysis. On admission, trypsinogen-2, trypsin-2-AAT, lipase, and amylase differentiated patients with AP from controls with high accuracy and ROC analyses showed similar areas under the ROC curves (AUC) for trypsinogen-2 (AUC 0.960), trypsin-2-AAT (0.948), lipase (AUC 0.947), and amylase (AUC 0.930). For differentiation between severe and mild AP, trypsin-2-AAT (AUC 0.805) was slightly better than trypsinogen-2 (AUC 0.792), and they were both clearly better than lipase (AUC 0.583), C-reactive protein (AUC 0.519), or amylase (AUC 0.632) (p < 0.05).

CONCLUSIONS

All the markers studied showed high accuracy for differentiating between AP and extrapancreatic diseases. However, trypsinogen-2 and trypsin-2-AAT displayed the best accuracy for predicting a severe AP already at admission, which makes these markers superior for clinical purposes.

The ratio of trypsin-2-alpha(1)-antitrypsin to trypsinogen-1 discriminates biliary and alcohol-induced acute pancreatitis

BACKGROUND

Rapid determination of the etiology of acute pancreatitis (AP) enables institution of appropriate treatment. We evaluated the ability of trypsinogen-1, trypsinogen-2, trypsin-1-alpha(1)-antitrypsin (AAT), and trypsin-2-AAT in serum to identify the etiology of AP.

METHODS

The study consisted of 67 consecutive patients with AP admitted to Helsinki University Central Hospital. Forty-two had alcohol-induced AP, 16 had biliary AP, and 9 had unexplained etiology. Serum samples were drawn within 12 h after admission. Trypsinogen-1, trypsinogen-2, trypsin-1-AAT, and trypsin-2-AAT were determined by time-resolved immunofluorometric assays. Logistic regression was used to estimate the ability of the serum analytes to discriminate between alcohol-induced and biliary AP. The validity of the tests was evaluated by ROC curve analysis.

RESULTS

Patients with alcohol-induced AP had higher median values of trypsin-1-AAT (P = 0.065), trypsinogen-2 (P = 0.034), and trypsin-2-AAT (P <0.001) than those with biliary AP, who had higher values of amylase (P = 0.002), lipase (P = 0.012), and alanine aminotransferase (P = 0.036). The ratios of trypsin-2-AAT to trypsinogen-1, lipase, or amylase efficiently discriminated between biliary and alcohol-induced AP (areas under ROC curves, 0.92-0.96).

CONCLUSIONS

Trypsinogen-2 and trypsin-2-AAT are markedly increased in AP of all etiologies, whereas trypsinogen-1 is increased preferentially in biliary AP. The trypsin-2-AAT/trypsinogen-1 ratio is a promising new marker for discrimination between biliary and alcohol-induced AP.

Tissue expression of human chorionic gonadotropin beta predicts outcome in colorectal cancer: a comparison with serum expression

Production of the glycoprotein hormone human chorionic gonadotropin beta (hCGbeta) has been associated with more aggressive behavior in non-trophoblastic tumors. In this study, the prognostic value of immunohistochemical hCGbeta expression was evaluated in 239 patients with colorectal cancer. Paraffin-embedded, formalin-fixed specimens were stained with hCGbeta-specific monoclonal antibody, and the results were compared with serum levels determined with an assay based on the same antibody. hCGbeta immunoreactivity was seen in 52 of 239 tumors (22%). The difference in survival time between patients with histologically hCGbeta-negative (median survival 94 months) and -positive (median survival 27 months) tumors was statistically significant (p = 0.014). The risk ratio during follow-up for patients with positive hCGbeta tissue expression was 1.65 (95% CI 1.11-2.46). In a Cox multivariate analysis, Dukes' stage, hCGbeta and age remained independent prognostic factors. There was moderate agreement between immunohistochemical and serum expression levels of hCGbeta (kappa = 0.30). Using a combination of histological and serum levels of hCGbeta, the difference between survival rates was highly significant (p < 0.001). The accuracy when predicting 5-year survival status with the combined results of serum and tissue expression was 1.3% higher compared to hCGbeta tissue expression alone. Our results show that hCGbeta expression in both tumor tissue and serum has prognostic significance independent of other clinicopathological variables. Positive tumor staining does not always occur together with elevated serum levels, and the prognostic accuracy can slightly be increased by combining the results.

Plasma insulin-like growth factor-I, insulin-like growth factor-binding proteins, and prostate cancer risk: a prospective study

BACKGROUND

Recent studies have suggested that men with elevated plasma levels of insulin-like growth factor-I (IGF-I) may have an increased risk of prostate cancer. Furthermore, IGF-binding proteins (IGFBPs) and insulin can modulate the activity of IGF-I. In this study, we sought to determine the role of IGF-I as well as IGFBPs-1, -2, and -3 and insulin as possible etiologic factors for prostate cancer.

METHODS

We conducted a nested case-control study within the Northern Sweden Health and Disease Cohort Study. We measured levels of IGF-I, IGFBP-1, IGFBP-2, IGFBP-3, and insulin in plasma samples from 149 men who had a diagnosis of prostate cancer between 1 month and 10 years after blood collection and among 298 control men. All statistical tests are two-sided.

RESULTS

Case subjects had statistically significantly higher mean levels of IGF-I than control subjects (229 ng/mL; 95% confidence interval [CI] = 218-240 ng/mL] versus 214 ng/mL [95% CI = 208-221 ng/mL]; P =.02) and IGFBP-3 (2611 ng/mL [95% CI = 2518-2704 ng/mL] versus 2498 ng/mL [95% CI = 2437-2560 ng/mL]; P =.04). Conditional logistic regression analyses showed increases in prostate cancer risk with rising levels of IGF-I (P:(for trend) =.02) and IGFBP-3 (P(for trend) =.03). In case subjects younger than 59 years at the time of blood collection, the risk associated with increased IGF-I was higher (P:(for trend) =.01), whereas the risk associated with increased IGFBP-3 was lower (P(for trend) =.44) than the corresponding risks in the full cohort. Prostate cancer risk was not associated with levels of IGFBP-1, IGFBP-2, or insulin.

CONCLUSIONS

Prostate cancer risk is increased in men with elevated plasma IGF-I. This association was particularly strong in younger men in this study, suggesting that circulating IGF-I may be specifically involved in the early pathogenesis of prostate cancer.

Expression and characterization of trypsinogen produced in the human male genital tract

Trypsinogen is a serine proteinase produced mainly by the pancreas, but it has recently been found to be expressed also in several cancers such as ovarian and colon cancer and in vascular endothelial cells. In this study, we found that trypsinogen-1 and -2 are present at high concentrations (median levels, 0.4 and 0.5 mg/L, respectively) in human seminal fluid and purified them to homogeneity by immunoaffinity and anion exchange chromatography. Purified trypsinogen isoenzymes displayed a M(r) of 25 to 28 kd in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting. Most of the trypsinogen-1 purified from seminal fluid was enzymatically active whereas trypsinogen-2 occurred as the proform, which could be activated by enteropeptidase in vitro. Immunohistochemically, trypsinogen protein was detected in the human prostate, urethra, utriculus, ejaculatory duct, seminal vesicles, deferent duct, epididymal glands, and testis. Expression of trypsinogen mRNA in the same organs was demonstrated by in situ hybridization. Trypsinogen mRNA was also detected in the prostate and seminal vesicles by reverse transcriptase-polymerase chain reaction and Northern blotting. Isolated trypsin was shown to activate the proenzyme form of prostate-specific antigen. These results suggest that trypsinogen isoenzymes found in seminal fluid are produced locally in the male genital tract and that they may play a physiological role in the semen.

Use of the complex between prostate specific antigen and alpha 1-protease inhibitor for screening prostate cancer

PURPOSE

We assess whether the complex between prostate specific antigen (PSA) and alpha1-protease inhibitor in serum can be used to reduce further the number of false-positive PSA screen results independent of total and free PSA.

MATERIALS AND METHODS

Sera from 304 consecutive screen positive subjects, including 78 with and 226 without prostate cancer, and serum PSA of 4 to 10 microg./l. or higher in the Finnish, randomized, population based prostate cancer screening trial were analyzed for PSA-alpha-protease inhibitor, and total and free PSA. Main outcome measures were specificity, sensitivity and area under receiver operating characteristics curve for proportions of free PSA and PSA-alpha 1-protease inhibitor, and for a combination of these among screen positive cases.

RESULTS

The proportion of serum PSA-alpha 1-protease inhibitor of total PSA was lower in cancer cases than in controls (0.9% versus 1.6%, p <0.001). Logistic regression analysis of total PSA, free PSA and PSA-alpha 1-protease inhibitor showed that PSA-alpha 1-protease inhibitor in serum was an independent variable for discrimination between subjects with and without prostate cancer (p = 0.006) in the PSA range of 4 to 10 microg./l. The proportion of PSA-alpha 1-protease inhibitor alone improved specificity less than the proportion of free PSA but when these were combined by logistic regression they performed better than the proportion of free PSA alone at sensitivities of 85% to 95% (p <0.001).

CONCLUSIONS

Serum PSA-alpha 1-protease inhibitor improves the specificity of total and free PSA in a screening population with total PSA 4 to 10 microg./l.

A comparison of serum and tissue hCG beta as prognostic markers in colorectal cancer

BACKGROUND

Production of the glycoprotein hormone hCG beta has been associated with aggressive behavior in nontrophoblastic tumors. In this study the prognostic value of serum level and tissue expression of hCG beta were compared in 232 patients with colorectal cancer.

MATERIALS AND METHODS

Serum levels were measured with a hCG beta specific immunofluorometric assay. Tissue specimens were stained with the same monoclonal antibody as in the serum assay.

RESULTS

The proportion of patients with a positive immunohistochemical expression of hCG beta was higher (22%) than the proportion with elevated serum levels (17%). The correlation between serum and tissue expression was moderate (kappa 0.298). Both serum and tissue expression of hCG beta were independent prognostic factors. hCG beta serum level was a stronger prognostic factor than tissue expression both in uni- and in multivariate analysis. The accuracy when predicting 5-year survival status of the patients was highest (63%) when using the combined results of serum and tissue expression.

CONCLUSIONS

There is a moderate correlation between hCG beta expression in serum and in tissue. The predictive accuracy of serum hCG beta was higher than the predictive accuracy of tissue expression, and the prognostic accuracy was further slightly increased when using a combination of tissue and serum expression.

Time course profile of serum trypsinogen-2 and trypsin-2-alpha1-antitrypsin in patients with acute pancreatitis

BACKGROUND

Trypsinogen-2 and the trypsin-2-alpha1-antitrypsin complex are recently introduced new laboratory markers for acute pancreatitis. They show high sensitivity and specificity for acute pancreatitis on admission, but little is known on their time course profiles.

METHODS

The serum concentrations of trypsinogen-2 and trypsin-2-alpha1-antitrypsin were monitored in 92 patients with verified acute pancreatitis. The follow-up period was 42 days in patients with severe acute pancreatitis (N = 73) and 9 days in mild disease (N = 19).

RESULTS

On admission the mean serum concentration of trypsinogen-2 was 2880 microg/l in severe and 920 microg/l in mild acute pancreatitis. These values were 32- and 10-fold the upper reference limit, respectively. Trypsin-2-alpha1-antitrypsin concentrations were 1250 microg/l (100-fold the upper reference limit) and 635 microg/l (52-fold), respectively. The differences were statistically significant (P = 0.026-0.001). The concentrations of trypsinogen-2 and trypsin-2-alpha1-antitrypsin decreased gradually during the follow-up period, but they remained elevated for the entire study period in patients with severe and mild disease.

CONCLUSIONS

The time course profile of trypsinogen-2 and trypsin-2-alpha1-antitrypsin is favorable for diagnosing acute pancreatitis. The elevation starts within hours after the onset of the disease and it is very steep. Both markers remain elevated longer than amylase and the magnitude of the elevation correlates with the severity of the disease. This is further evidence to support the use of trypsinogen-2 and trypsin-2-alpha1-antitrypsin for the evaluation of patients suspected of having acute pancreatitis.

Summary report of the TD-3 workshop: characterization of 83 antibodies against prostate-specific antigen

Twelve research groups participated in the ISOBM TD-3 Workshop in which the reactivity and specificity of 83 antibodies against prostate-specific antigen (PSA) were investigated. Using a variety of techniques including cross-inhibition assays, Western blotting, BIAcore, immunoradiometric assays and immunohistochemistry, the antibodies were categorized into six major groups which formed the basis for mapping onto two- and three-dimensional (2-D and 3-D) models of PSA. The overall findings of the TD-3 Workshop are summarized in this report. In agreement with all participating groups, three main antigenic domains were identified: free PSA-specific epitopes located in or close to amino acids 86-91; discontinuous epitopes specific for PSA without human kallikrein (hK2) cross-reactivity located at or close to amino acids 158-163; and continuous or linear epitopes shared between PSA and hK2 located close to amino acids 3-11. In addition, several minor and partly overlapping domains were also identified. Clearly, the characterization of antibodies from this workshop and the location of their epitopes on the 3-D model of PSA illustrate the importance of selecting appropriate antibody pairs for use in immunoassays. It is hoped that these findings and the epitope nomenclature described in this TD-3 Workshop are used as a standard for future evaluation of anti-PSA antibodies.