Multicenter Evaluation of the Performance and Clinical Utility in Longitudinal Monitoring of the Bayer Immuno 1™ Complexed PSA Assay

We conducted a multicenter evaluation of the analytical and clinical performance of the automated Bayer Immuno 1™ complexed PSA (cPSA) assay, and compared assay performance to the Bayer Immuno 1™ PSA assay. We sought to determine whether measurements of cPSA could be of clinical utility in the management of patients with prostate cancer. Results of the 10–day imprecision across three evaluation sites produced total CV < 2.50% and an analytical sensitivity of 0.02μg/L. There was an increased trend in clinical sensitivity for prostate cancer with increasing stage of disease (71–86%). Clinical specificity for patients with benign urogenital disease was 74.8%, and for other nonprostate diseases ranged from 91.1–100%. Retrospective serial monitoring of 155 patients with prostate cancer demonstrated concordance of cPSA measurements to clinical status for 97% of the patients analyzed. Results from the clinical studies using the Bayer Immuno 1 cPSA assay were comparable to results obtained with the Bayer Immuno 1 PSA assay. The Bayer Immuno 1 cPSA assay demonstrates analytical performance and clinical effectiveness in the management of prostate cancer patients during the course of disease and therapy.

Restoration of tumor suppression in prostate cancer by targeting the E3 ligase E6AP

Restoration of tumor suppression is an attractive onco-therapeutic approach. It is particularly relevant when a tumor suppressor is excessively degraded by an overactive oncogenic E3 ligase. We previously discovered that the E6-associated protein (E6AP; as classified in the human papilloma virus context) is an E3 ligase that has an important role in the cellular stress response, and it directly targets the tumor-suppressor promyelocytic leukemia protein (PML) for proteasomal degradation. In this study, we have examined the role of the E6AP-PML axis in prostate cancer (PC). We show that knockdown (KD) of E6AP expression attenuates growth of PC cell lines in vitro. We validated this finding in vivo using cell line xenografts, patient-derived xenografts and mouse genetics. We found that KD of E6AP attenuates cancer cell growth by promoting cellular senescence in vivo, which correlates with restoration of tumor suppression by PML. In addition, we show that KD of E6AP sensitizes cells to radiation-induced death. Overall, our findings demonstrate a role for E6AP in the promotion of PC and support E6AP targeting as a novel approach for PC treatment, either alone or in combination with radiation.

Overexpression and gene amplification of BAG-1L in hormone-refractory prostate cancer

BAG-1L (Bcl-2-associated anthanogene 1) has been found to interact with androgen receptor (AR), and has been suggested to be involved in the development of prostate cancer. In order to determine the presence of genetic and/or expression alterations of BAG-1L in prostate cancer, we analysed human prostate cancer cell lines and xenografts as well as patient samples of untreated, hormone-naïve, and hormone-refractory prostate carcinomas for sequence variations using denaturing high-performance liquid chromatography (DHPLC), for gene copy number using fluorescence in situ hybridization (FISH), and for expression using both quantitative RT-PCR and immunostaining. Only one sequence variation was found in all 37 cell lines and xenografts analysed. BAG-1 gene amplification was detected in two xenografts. In addition, gene amplification was found in 6 of 81 (7.4%) hormone-refractory clinical tumours, whereas no amplification was found in any of the 130 untreated tumours analysed. Additionally, gain of the BAG-1 gene was observed in 27.2% of the hormone-refractory tumours and in 18.5% of the untreated carcinomas. In a set of 263 patient samples, BAG-1L protein expression was significantly higher in hormone-refractory tumours than in primary tumours (p = 0.002). Altogether, these data suggest that amplification and overexpression of BAG-1L may be involved in the progression of prostate cancer.

Ubiquitin E3 ligase WWP1 as an oncogenic factor in human prostate cancer

The gene for E3 ubiquitin ligase WWP1 is located at 8q21, a region frequently amplified in human cancers, including prostate cancer. Recent studies have shown that WWP1 negatively regulates the TGFbeta tumor suppressor pathway by inactivating its molecular components, including Smad2, Smad4 and TbetaR1. These findings suggest an oncogenic role of WWP1 in carcinogenesis, but direct supporting evidence has been lacking. In this study, we examined WWP1 for gene dosage, mRNA expression, mutation and functions in a number of human prostate cancer samples. We found that the WWP1 gene had copy number gain in 15 of 34 (44%) xenografts and cell lines from prostate cancer and 15 of 49 (31%) clinical prostate cancer samples. Consistently, WWP1 was overexpressed in 60% of xenografts and cell lines from prostate cancer. Mutation of WWP1 occurred infrequently in prostate cancer. Functionally, WWP1 overexpression promoted colony formation in the 22Rv1 prostate cancer cell line. In PC-3 prostate cancer cells, WWP1 knockdown significantly suppressed cell proliferation and enhanced TGFbeta-mediated growth inhibition. These findings suggest that WWP1 is an oncogene that undergoes genomic amplification at 8q21 in human prostate cancer, and WWP1 overexpression is a common mechanism involved in the inactivation of TGFbeta function in human cancer.

Comparison of Fc-osteoprotegerin and zoledronic acid activities suggests that zoledronic acid inhibits prostate cancer in bone by indirect mechanisms

Zoledronic acid (ZA) has been shown to inhibit prostate tumor growth in vitro and have beneficial effects in patients with advanced prostate cancer (CaP). The aim of this study was to determine whether ZA exhibits direct anti-tumor effects on CaP cells in vivo. To distinguish the effects of inhibition of osteolysis and direct anti-tumor activity of ZA in vivo, we compared the results of treatment with ZA and osteoprotegerin (Fc-OPG), which inhibits osteolysis, but without significant direct anti-tumor effects. In vitro Fc-OPG had no significant effects on C4-2 proliferation, whereas ZA decreased proliferation. However, both agents decreased tumor growth in bone. Moreover, both increased bone volume and prevented the overall decreases in BMD associated with growth of C4-2 cells in bone. Our study provides novel and significant observations that the in vivo effects of ZA are consistent with indirect effects mediated by osteoclasts.

The effect of osteoprotegerin administration on the intra-tibial growth of the osteoblastic LuCaP 23.1 prostate cancer xenograft

Osteoprotegerin (OPG) plays a central role in controlling bone resorption. Exogenous administration of OPG has been shown to be effective in preventing osteolysis and limiting the growth of osteolytic metastasis. The objective of this study was to investigate the effects of OPG on osteoblastic prostate cancer (CaP) metastases in an animal model. LuCaP 23.1 cells were injected intra-tibially and Fc-OPG (6.0 mg/kg) was administered subcutaneously three times a week starting either 24 hours prior to cell injection (prevention regimen) or at 4 weeks post-injection (treatment regimen). Changes in bone mineral density at the tumor site were determined by dual x-ray absorptiometry. Tumor growth was monitored by evaluating serum prostate specific antigen (PSA). Fc-OPG did not inhibit establishment of osteoblastic bone lesions of LuCaP 23.1, but it decreased growth of the tumor cells, as determined by decreases in serum PSA levels of 73.0 +/- 44.3% (P < 0.001) and 78.3 +/- 25.3% (P < 0.001) under the treatment and prevention regimens, respectively, compared to the untreated tumor-bearing animals. Administration of Fc-OPG decreased the proliferative index by 35.0% (P = 0.1838) in the treatment group, and 75.2% (P = 0.0358) in the prevention group. The results of this study suggest a potential role for OPG in the treatment of established osteoblastic CaP bone metastases.

Metastatic conventional prostatic adenocarcinoma with diffuse chromogranin A and androgen receptor positivity

Conventional prostate adenocarcinomas consist mainly of tumour cells of luminal immunophenotype with scattered neuroendocrine (NE) cells. NE cells are defined by chromogranin A (CGA) immunoreactivity. Unlike luminal cells, NE cells lack androgen receptor (AR) and prostate specific antigen (PSA) immunoreactivity. This report describes the first case of conventional prostate adenocarcinoma expressing CGA, PSA, and AR as determined by immunohistochemistry. A 64 year old man was diagnosed with conventional prostate adenocarcinoma in 1993; he underwent cystoprostatectomy in 1994; he developed an iliac bone metastasis in 1997 and mediastinal lymph node metastases in 1999. All specimens obtained during the progression of the disease consisted primarily of luminal cells with only scattered NE cells. In contrast, in samples of non-osseous and osseous metastases obtained at necropsy in 2001, greater than 80% of tumour cells were shown to express PSA, AR, and CGA. This suggests that during tumour progression, conventional prostate adenocarcinomas may evolve into an NE cell phenotype.

Bone histology at autopsy and matched bone scintigraphy findings in patients with hormone refractory prostate cancer: the effect of bisphosphonate therapy on bone scintigraphy results

Bisphosphonates (BisP) are non-metabolized compounds with high bone affinity used in bone metastasis diagnosis and treatment. Currently, BisP are used to treat hypercalcemia of malignancy as well as to prevent, minimize, or delay skeletal morbidity. These compounds have a long half-life in bone. Thus long-term BisP treatment might saturate bone and interfere with a single-dose scanning agent used for bone scintigraphy when visualizing bone metastases. In an effort to answer this question, this study evaluated the concordance of histology and Technetium99 methylene diophosphonate (Tc99 MDP) bone scintigraphy in the diagnosis of bone metastases in prostate cancer patients. We assessed the concordance of findings between bone scintigraphy and histology using 188 bone biopsies from 11 autopsied patients who died with metastatic prostate cancer, 5 of whom were treated with pamidronate for 2 to 13 months before death. Overall agreement between histology and bone scintigraphy was 84%, 86% in non-pamidronate-treated patients and 82% in pamidronate-treated patients. Scintigraphic bone metastases without histological metastasis (false negatives = 12.7%) were observed in 24 anatomic locations; half of these were in one patient who had been treated with pamidronate and had no histological bone response to the carcinoma. There were only 4 sites where a positive bone scan was not associated with histologic metastasis (false positives = 2.21%). There was no statistical difference between the treated and non-treated group for concordance, specificity, sensitivity, positive and negative predictive values of bone scintigraphy and prevalence of histological abnormality. Long-term pamidronate treatment of prostate cancer bone metastases does not generally affect the ability to detect bone metastases with Tc99 MDP bone scintigraphy.

Cathepsin K mRNA and protein expression in prostate cancer progression

Prostate cancer (CaP) is the most commonly diagnosed malignancy in men and is often associated with bone metastases, which cause much of the morbidity associated with CaP. Lesions associated with CaP generally exhibit increased bone formation and resorption. Increased bone resorption may release factors from the extracellular matrix that contribute to tumor growth. Cathepsin K (cat K) is a cysteine protease that exhibits strong degradative activity against the extracellular matrix and is involved in osteoclast-mediated bone destruction. In this study, we analyzed the expression of cat K in CaP cell lines and patient samples. Cat K message was detected in CaP cell lines by reverse transcription-polymerase chain reaction (RT-PCR) and in primary CaP and metastases by in situ hybridization. Immunohistochemistry revealed variable expression of cat K in primary CaP samples, as well as nonosseous metastases, whereas expression in bone metastases was significantly higher than in primary CaP, and normal prostate tissues were negative. Cat K protein was detected in CaP cell lines by Western blotting after immunoprecipitation. Cat K enzymatic activity was also detected in CaP cell lines by a fluorogenic assay and by an assay for degradation of collagen type I. Increased levels of NTx, a marker of bone matrix degradation mediated primarily by cat K, were also detected in sera of patients with CaP bone metastases. We hypothesize that CaP-expressed cat K may contribute to the invasive potential of CaP, while increased expression in bone metastases is consistent with a role in matrix degradation.

Bone morphogenetic protein signaling in prostate cancer cell lines

Prostate cancer is the most commonly diagnosed malignancy in men and is often associated with bone metastases. Prostate cancer bone lesions can be lytic or schlerotic, with the latter predominating. Bone morphogenetic proteins (BMPs) are a family of growth factors, which may play a role in the formation of prostate cancer osteoblastic bone metastases. This study evaluated the effects of BMPs on prostate cancer cell lines. We observed growth inhibitory effects of BMP-2 and -4 on LNCaP, while PC-3 was unaffected. Flow cytometric analysis determined that LNCaP cell growth was arrested in G(1) after bone morphogenetic protein-2 treatment. Treatment of LNCaP and PC-3 with BMP-2 and -4 activated downstream signaling pathways involving SMAD-1, up-regulation of p21(CIP1/WAF1) and changes in retinoblastoma (Rb) phosphorylation. Interestingly, bone morphogenetic protein-2 treatment stimulated a 2.7-fold increase in osteoprotegerin (OPG), a molecule, which inhibits osteoclastogenesis, production in PC-3.

Serum osteoprotegerin levels are increased in patients with advanced prostate cancer

PURPOSE

Osteoprotegerin (OPG) is a soluble osteoclastogenesis inhibitor that regulates bone turnover. We reported recently that OPG protein expression is significantly increased in prostate cancer (CaP) cells present in bone metastases. The aim of this study was to determine serum OPG levels in patients at different stages of CaP and correlate the results with disease status.

EXPERIMENTAL DESIGN

OPG levels were examined in patients with benign prostatic hyperplasia, clinically localized CaP, early recurrence of CaP, and advanced CaP and evidence of bone metastases. Serum OPG levels were measured by sandwich ELISA assays. The serum Crosslaps (sCTX) assay was used to quantify bone resorption in the advanced CaP group.

RESULTS

Serum OPG levels were increased significantly in the advanced CaP group versus all other groups. There was no significant correlation between serum OPG levels and PSA levels either in the advanced CaP group or within any of three treatment subclasses of this group: no Tx, those not treated; Tx, those treated; and R, those treated with resorption blockers. Levels of OPG were negatively correlated with sCTX levels only in the advanced CaP Tx group. sCTX levels correlated with prostate-specific antigen levels in the advanced CaP Tx and R groups but not in the no-Tx group.

CONCLUSIONS

Our data show that serum OPG levels are increased with advanced CaP. We hypothesize that OPG levels are related to CaP progression and suggest that further studies of the biological effects of OPG on CaP metastases are warranted.

The percentage of free prostate-specific antigen does not predict extracapsular disease in patients with clinically localized prostate cancer before radical prostatectomy

OBJECTIVE

To determine whether the percentage of free/total prostate-specific antigen (f/tPSA) can predict the pathological features in patients with clinically localized prostate cancer before radical prostatectomy.

PATIENTS AND METHODS

Univariate and multivariate logistic regression was used to analyse data from 171 untreated patients who underwent radical prostatectomy. Variables included the total PSA (tPSA), fPSA, f/tPSA, biopsy Gleason score, clinical stage and patient age.

RESULTS

In 115 patients with pathologically organ-confined tumours ( pT2N0) the mean (SD) tPSA value was 6.9 (5.6) ng/mL; in 56 patients with extracapsular disease ( pT3pN0/N+) it was 10.2 (7.6) ng/mL; the respective f/tPSA values were 14.9 (8.1)% and 14.2 (12.9)%. In the univariate and multivariate analysis, tPSA and biopsy Gleason score were highly significant in predicting extracapsular disease (P < 0.001 and 0.002) but the f/tPSA was not (P = 0.18). There was no significant difference between the mean f/tPSA and final Gleason scores.

CONCLUSION

The f/tPSA does not predict extracapsular disease in patients with clinically localized prostate cancer before radical prostatectomy. Knowing the f/tPSA provides no significant additional information in predicting extracapsular disease when the biopsy Gleason score and tPSA are known.

Identification of the target of monoclonal antibody A6H as dipeptidyl peptidase IV/CD26 by LC MS\MS

The monoclonal antibody (MAb) A6H, originally developed to fetal renal tissues, was found to be highly reactive to renal cell carcinoma and was subsequently demonstrated to co-stimulate a subpopulation of T cells. The A6H antigen had not been identified heretofore. Antigen from detergent extracts of renal cell carcinoma cells (7860) was immunoabsorbed with A6H-agarose, and the resin-bound proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The antigen had a molecular weight of approximately 120 kDa as determined by Western blots. The 120-kDa protein band was excised and subjected to in-gel tryptic digestion, and the resulting peptides were separated and analyzed by liquid chromatography tandem mass spectrometry (LC MS\MS). The tandem mass spectra of the eluting peptides were used in combination with the SEQUEST computer program to search a human National Cancer Institute (NCI) protein database for the identity of the protein. The target antigen was shown to be dipeptidyl peptidase IV (DPP IV), which is also known as the cluster differentiation antigen CD26. Flow analysis of the expression of the A6H antigen and of CD26 on 7860 cells and on peripheral blood lymphocytes supported the identification of the A6H antigen as DPP IV. Recognition that the A6H antigen is DPP IV/CD26 afforded the opportunity to compare previous studies on A6H with those on other anti-CD26 antibodies in terms of expression in cancer cell lines and various tissues and as co-stimulators of T-cell activation.

Serial prostate specific antigen, free-to-total prostate specific antigen ratio and complexed prostate specific antigen for the diagnosis of prostate cancer

PURPOSE

The free-to-total prostate specific antigen (PSA) ratio and complexed PSA have been introduced as adjuncts to total PSA for prostate cancer screening. Little data exist on the use of these tests for serial PSA screening. We compared serial total PSA, the free-to-total PSA ratio and calculated complexed PSA in men diagnosed with prostate cancer and matched controls in a population based study.

MATERIALS AND METHODS

We identified 90 men diagnosed with prostate cancer between 1988 and 1996 with at least 3 serial serum samples obtained at 2-year intervals who were participants in the beta-Carotene and Retinol Efficacy Trial for the prevention of lung cancer. Samples were available up to 10 years before diagnosis. A total of 90 age matched men from the same cohort without prostate carcinoma were identified as controls. Free and total PSA was measured by the Abbott AxSYM system.

RESULTS

Baseline demographics of cases and controls were similar. At baseline and diagnosis the men with prostate cancer had higher total and complexed PSA, and a lower free-to-total PSA ratio than controls. Mean followup was 5.2 years in cases and 5.5 in controls. The yearly change in PSA parameters in cases versus controls was 20.7% versus 3.5% for total, -3.4% versus 0.2% for free-to-total and 21.5% versus 3.4% for complexed PSA (p <0.0001). At diagnosis PSA alone was estimated to perform with more than 90% specificity in our model.

CONCLUSIONS

In this population based study total PSA was superior to the free-to-total PSA ratio for predicting the development of prostate cancer. While serial changes in free-to-total PSA ratios with time were statistically significantly different in men diagnosed with prostate cancer and controls, the magnitude of these serial changes were slight enough to render them clinically insignificant.

Placental bone morphogenetic protein (PLAB) gene expression in normal, pre-malignant and malignant human prostate: relation to tumor development and progression

The second most common target of prostate-cancer metastasis is bone, and the phenomenon of skeletal metastasis represents the incurable stage of disease. Histologically, skeletal metastasis from prostate cancer is distinctive due to its osteoblastic nature. The osteoblastic bone metastasis shows extensive new bone formation, with possible involvement of the soluble growth factors secreted by tumor cells, such as bone morphogenetic proteins (BMPs). In the present study, we analyzed the gene expression of one of the new members of the BMP family, placental bone morphogenetic protein (PLAB). In situ hybridization studies showed high levels of this gene in normal prostate. However, the gene is down-regulated during the progression of cancer at the primary site. The most significant finding was re-expression of the PLAB gene in osseous metastatic lesions. Our results demonstrate that tumor cells, when released from the primary site and after re-growth elsewhere, are capable of re-expressing specific genes that may play a different role at metastatic sites than at the primary site.

Amplification and overexpression of androgen receptor gene in hormone-refractory prostate cancer

The expression level of the androgen receptor (AR) gene in androgen-dependent and -independent prostate cancer was determined by using real-time quantitative reverse transcription-PCR assay. Eight benign prostate hyperplasias, 33 untreated and 13 hormone-refractory locally recurrent carcinomas, as well as 10 prostate cancer xenografts, were analyzed. All hormone-refractory tumors expressed AR and showed, on average, 6-fold higher expression than androgen-dependent tumors or benign prostate hyperplasias (P < 0.001). Four of 13 (31%) hormone-refractory tumors contained AR gene amplification detected by fluorescence in situ hybridization. Androgen-independent tumors with gene amplification expressed, on average, a 2-fold higher level of AR than the refractory tumors without the gene amplification. Two xenografts (LuCaP 35 and 69) showed amplification and high-level expression of the AR gene. These xenografts are the first prostate cancer model systems containing the gene amplification. The findings demonstrate that AR is highly expressed in androgen-independent prostate cancer, suggesting that the AR signaling pathway is important in the progression of prostate cancer during endocrine treatment. The two xenografts with the AR gene amplification will enable studies evaluating the functional significance of the amplification and development of new treatment strategies based on high-level expression of AR.

Osteoprotegerin and rank ligand expression in prostate cancer

OBJECTIVES

To investigate the expression of osteoprotegerin (OPG) and RANK ligand (RANKL) in human prostatic tissues. The factors regulating the increased turnover associated with prostate cancer (CaP) bone metastasis are unknown. OPG and RANKL are recently identified regulators of bone resorption and bone remodeling.

METHODS

Tissues from 28 patients with CaP and from 4 normal organ donors were analyzed by reverse transcriptase-polymerase chain reaction and immunohistochemistry for the expression of OPG and RANKL.

RESULTS

OPG and RANKL messages were detected in both normal and cancerous prostate samples. In the normal prostate, OPG protein was detected in luminal epithelial and stromal cells (5% to 65% and 15% to 70%, respectively) and RANKL immunoreactivity was observed in 15% to 50% of basal epithelial cells, 40% to 90% of luminal epithelial cells, and 70% to 100% of stromal cells. OPG was not detected in 8 of 10 primary CaP specimens; RANKL was heterogeneously expressed in 10 of 11 CaP specimens. The percentage of tumor cells expressing OPG and RANKL was significantly increased in all CaP bone metastases compared with nonosseous metastases or primary CaP.

CONCLUSIONS

CaP bone metastases were consistently immunoreactive for both OPG and RANKL compared with nonosseous metastases or primary CaP. The presence of these crucial bone resorption regulators in CaP bone metastases suggests a mechanism whereby CaP cells may modulate bone turnover and has profound implications for the establishment and development of CaP bone metastases in advanced disease.

Identification of prostate specific membrane antigen (PSMA) as the target of monoclonal antibody 107-1A4 by proteinchip�; array, surface-enhanced laser desorption/ionization (seldi) technology

Recently we described the generation of the prostate tissue-specific monoclonal antibody (MAb) 107-1A4, its expression pattern and preliminary targeting of human prostate cancer xenografts. In this report we demonstrate that the target antigen for MAb 107-1A4 is prostate-specific membrane antigen (PSMA) using immunoaffinity absorption followed by SDS-PAGE and mass spectrometric analysis of peptides produced by in-gel tryptic digestion. The identity of the antigen has been confirmed by Western blots using MAbs of known specificity. MAb 107-1A4 is not reactive on Western blots. The conformational epitope for 107-1A4 is on the extracellular domain of PSMA. In competition studies, the binding of MAb 107-1A4 to LNCaP cells is inhibited by itself but not by any other of several other anti-PSMA MAbs, suggesting that the epitope may be unique. These results suggest that 107-1A4 is reactive to a conformational epitope in the external domain of PSMA that is unique among the panel of anti-PSMA MAbs in this study. Furthermore this work demonstrates the ability of mass spectroscopy to elucidate antibody-ligand interaction.

Increased AKT activity contributes to prostate cancer progression by dramatically accelerating prostate tumor growth and diminishing p27Kip1 expression

The PTEN tumor suppressor gene is frequently inactivated in human prostate cancers, particularly in more advanced cancers, suggesting that the AKT/protein kinase B (PKB) kinase, which is negatively regulated by PTEN, may be involved in human prostate cancer progression. We now show that AKT activation and activity are markedly increased in androgen-independent, prostate-specific antigen-positive prostate cancer cells (LNAI cells) established from xenograft tumors of the androgen-dependent LNCaP cell line. These LNAI cells show increased expression of integrin-linked kinase, which is putatively responsible for AKT activation/Ser-473 phosphorylation, as well as for increased phosphorylation of the AKT target protein, BAD. Furthermore, expression of the p27(Kip1) cell cycle regulator was diminished in LNAI cells, consistent with the notion that AKT directly inhibits AFX/Forkhead-mediated transcription of p27(Kip1). To assess directly the impact of increased AKT activity on prostate cancer progression, an activated hAKT1 mutant was overexpressed in LNCaP cells, resulting in a 6-fold increase in xenograft tumor growth. Like LNAI cells, these transfectants showed dramatically reduced p27(Kip1) expression. Together, these data implicate increased AKT activity in prostate tumor progression and androgen independence and suggest that diminished p27(Kip1) expression, which has been repeatedly associated with prostate cancer progression, may be a consequence of increased AKT activity.

Probability of prostate cancer detection based on results of a multicenter study using the AxSYM free PSA and total PSA assays

OBJECTIVES

The determination of the percentage of free prostate-specific antigen (%fPSA) enhances the specificity of prostate cancer (CaP) detection. This study was undertaken to assess the performance of %fPSA in differentiating benign prostate disease from CaP and to determine the CaP probability estimates using the AxSYM Free PSA and AxSYM Total PSA assays.

METHODS

In this prospective study, 297 men, 50 years old or older, with a total PSA level between 4 and 10 ng/mL and a nonsuspicious digital rectal examination were enrolled at 10 clinical sites. All subjects underwent at least sextant prostate biopsies to establish the diagnosis. fPSA and total PSA (tPSA) levels were determined using the AxSYM Free PSA and AxSYM Total PSA assays. Percent fPSA values were compared with tPSA values to determine the appropriate cutoffs for prostate biopsy and to calculate the CaP probability estimates.

RESULTS

The strongest predictor of CaP in a logistic regression model was %fPSA (odds ratio 2.29), which contributed significantly more than age or tPSA to the predictive model. In this study population, a %fPSA cutoff of 26.4% would have detected 96% of subjects with CaP (sensitivity) and would have eliminated 27.4% of unnecessary biopsies (specificity). CaP probability estimates ranged from 9% to 69% and increased as the %fPSA value decreased. Men with a %fPSA level of 10% or lower had a 69% probability of CaP, and men with a %fPSA level of greater than 26% had a 9% probability of CaP.

CONCLUSIONS

Percent fPSA values can help differentiate CaP from benign prostate disease and reduce unnecessary biopsies in 27% of men 50 years old or older whose digital rectal examination was normal and whose tPSA level was between 4 and 10 ng/mL. A %fPSA result can assist the physician and patient in determining the probability of CaP and assessing the need for prostate biopsy.

Mechanistic studies of the effects of anti-factor H antibodies on complement-mediated lysis

We have recently reported that complement factor H, a negative regulator of complement-mediated cytotoxicity, is produced and secreted by most bladder cancers. This observation was exploited in the development of the BTA stat and BTA TRAK diagnostic assays, both of which make use of two factor H-specific monoclonal antibodies in sandwich format. Here we show that both antibodies exert interesting effects on the biochemistry of complement activation in in vitro systems. Antibody X13.2 competes with C3b for association with factor H and strongly inhibits factor H/factor I-mediated cleavage of C3b, thereby evidently inactivating a negative regulator of complement; yet, the antibody strongly inhibits complement-mediated lysis as well. Conversely, antibody X52. 1, which does not compete with C3b and has no effect on solution-phase cleavage of C3b, is capable of enhancing complement-mediated lysis of various cell types, including cancer cells, by over 10-fold. Our observations indicate that it is possible to deconvolute the biochemical roles of factor H in complement by means of appropriate inhibitors, a finding with potentially valuable implications for both basic research and cancer therapy.

Intermittent androgen suppression in the LuCaP 23.12 prostate cancer xenograft model

BACKGROUND

Intermittent androgen suppression (IAS) has been proposed as a method of delaying the onset of androgen-independent growth in prostate cancer. While several pilot studies have demonstrated the feasibility of such a treatment, no study to date has defined the effect of IAS on survival.

METHODS

We developed an IAS protocol for mice bearing the LuCaP 23.12 human prostate cancer xenograft, with each cycle consisting of 1 week of androgen replacement with a testosterone pellet followed by 3 weeks of androgen withdrawal. Mice that responded to castration with a 40% or greater decrease in serum prostate-specific antigen (PSA) were randomized to treatment with either continuous androgen suppression (CAS) or IAS. Serum PSA, tumor volume, and overall survival were monitored.

RESULTS

A total of 75 mice met the randomization criteria. There was no significant difference of survival between animals treated with CAS or IAS (185 vs. 239 days, P = 0.1835). Serum PSA showed evidence of cycling with hormonal manipulation. No cycling was noted in tumor volume.

CONCLUSIONS

IAS is not associated with a decrease in survival compared to CAS, yet in patients may offer quality-of-life improvements. Further studies of IAS in the setting of Institutional Review Board (IRB) approved clinical trials should be encouraged. Prostate 43:63-70, 2000. Published 2000 Wiley-Liss, Inc.

Differential expression of osteonectin/SPARC during human prostate cancer progression

The precise mechanism(s) involved in invasion and metastasis of prostate cancer (CaP) is poorly understood. Osteonectin [ON (also known as SPARC or BM-40)] is an antiadhesive protein known to be involved in cell-matrix interactions, migration, and angiogenesis. In this report, we studied the expression of ON in human prostate cell lines, primary tumors, and metastatic foci of CaP. Reverse transcription-PCR and nonradioactive in situ hybridization (ISH) techniques were used to determine ON gene expression. Immunohistochemistry was carried out using the polyclonal antibody LF37 and/or the monoclonal antibody ON-mAb. Low to moderate levels of ON mRNA and protein were observed in glandular epithelial cells of normal tissue as well as a few primary CaPs. However, high levels of ON mRNA and protein were observed in most of the CaP metastatic foci, both osseous and nonosseous. This correlated well with our findings that multiple different CaP cell lines including four CaP cell lines derived from metastases show high levels of ON gene expression. Furthermore, ISH analyses and cell-specific reverse transcription-PCR evaluation showed that both the luminal and basal cells express the ON gene. We conclude that the differential pattern of ON expression suggests that it may play an important role in the progression of CaP.

Development of new biotin/streptavidin reagents for pretargeting

The high affinity of biotin for streptavidin has made this pair of molecules very useful for in vivo applications. To optimize reagents for one potential in vivo application, antibody-based pretargeting of cancer, we have prepared a number of new biotin and streptavidin derivatives. The derivatives developed include new radiolabeled biotin reagents, new protein biotinylation reagents, and new biotin multimers for cross-linking and/or polymerization of streptavidin. We have also modified streptavidin by site-directed mutation and chemical modification to improve its in vivo characteristics, and have developed new reagents for cross-linking antibody fragments with streptavidin. A brief overview of these new reagents is provided.

Mechanisms, hypotheses and questions regarding prostate cancer micrometastases to bone

The morbidity and mortality associated with prostate cancer can almost universally be attributed to the consequences of metastases to the bone. While clinically there have been descriptive reports of these lesions and their detection by bone scan, there is an embrrassing paucity of reports as to the mechanisms of prostate cancer cell trafficking to the bone, adaptation to the bone environment, pertubation of the normal bone reformation process and the events leading to cachexia and death. In recent years, there have been numerous in vitro studies suggesting that PSA and hK2 may play a significant biological role in these events. Also, recent data generated form reverse transcription polymerase chain reaction assays reveal that metastasis to the bone may be an early event which further underscores the need to better understand this complex and critically important process. This commentary highlights several general concepts and a few specific issues related to CaP bone metastasis with the intent of revealing numerous opportunities for further investigation and inquiry.

Analysis and sorting of prostate cancer cell types by flow cytometry

BACKGROUND

Prostate tumor heterogeneity as manifested by differential expression of markers can be attributed to multiple types of cancer cells populating a tumor. Does the composition differ between primary tumor and metastasis? How can one isolate the different cancer cell types to study? What is the relationship among cancer cell types?

METHODS

Flow cytometry keying on the prostate epithelial cell surface markers CD57 and CD44 was applied to analyze and sort single cells prepared from tumor tissue samples by collagenase digestion. In normal tissue, CD57 is found on luminal cells and CD44 on basal cells.

RESULTS

CD57(+) and CD44(+) cells were sorted from various prostate tumor tissue specimens. The CD57(+) cancer cell type was found to predominate in primary tumors, while the CD44(+) cancer cell type was found to predominate in two visceral metastases. All tumors could be characterized by a ratio of CD57(+) and CD44(+) cancer cells.

CONCLUSIONS

Two types of prostate cancer cells, CD57(+) and CD44(+), were identified. The finding that most primary tumors contain a predominantly CD57(+) cancer cell population agrees with the argument that cancer cells arise from the transformation of CD57(+) luminal cells. However, CD44(+) cancer cells are also present in some primary tumors; and in some metastases, they, and not CD57(+) cells, constitute a predominant population.

High prevalence of antibodies against HERV-K10 in patients with testicular cancer but not with AIDS

Human endogenous retrovirus K10 (HERV-K10) env and gag expression has been detected in placenta, embryonic tissue, and cell lines. By transfection, these sequences have been expressed in insect cells and developed into serological assays, revealing HERV-K10 antibodies in patients with testicular cancer. Patients with AIDS are at an increased risk for testicular cancer and frequently reactivate latent infections. We postulated that HERV-K10 seroprevalence might be increased with HIV infection or AIDS. Stored, frozen serum samples from 52 patients with testicular cancer (8 patients with HIV and 30 patients with samples near the time of diagnosis) and 84 controls (40 patients with HIV) were diluted 1:40 and tested by immunofluorescence against SF158 cells transfected with HERV-K10 env [ENV1.9(+)] or gag (pACGAG). Seroprevalence rates were compared cross-sectionally in cases and controls, excluding those with indeterminate results (3 of 30 cases and 7 of 84 controls), and also were examined longitudinally in the cases before or after diagnosis of testicular cancer. Seroprevalence to HERV-K10 Env or Gag was 17 of 27 testicular cancer patients (63%) around the time of diagnosis, compared to 4 of 77 controls (5%; P < 0.0001). Seroprevalence was similar (50% to 60%) with seminoma, teratocarcinoma, or embryonal carcinoma, and it was not increased with HIV infection in either cases (33%) or controls (3%). HERV-K10 antibodies were detected in 12 of 19 cases (63%) more than 6 months before seminoma diagnosis, as well as in four cases with residual or recurrent malignancy more than 1 month after initial diagnosis. Thus, HERV-K10 antibodies are detected frequently with testicular cancer and seem to resolve rapidly with effective therapy of the malignancy. Antibody reactivity also occurs in approximately 5% of controls, perhaps because of nonspecific or cross-reactive epitopes. HIV and AIDS were not associated with HERV-K10 antibodies, thus, leaving their higher risk of testicular cancer unexplained.

Effects of phenylbutyrate on proliferation and apoptosis in human prostate cancer cells in vitro and in vivo

Phenylbutyrate (PB) is a potent differentiating agent and currently under investigation for the treatment of prostate cancer (CaP) and other malignancies. We have studied the impact of PB in vitro and in vivo on differentiation, proliferation and apoptosis in the LNCaP and LuCaP 23.1 prostate cancer xenograft models. In vitro we found that i) PB increased PSA secretion/cell, ii) inhibited cell proliferation in a time- and dose-dependent manner resulting in a cell cycle arrest in G1-phase and iii) induced apoptosis at concentrations of 2.5 mM after 3 days of treatment. In PB treated animals tumor growth stabilized or regressed. Combination of castration and PB treatment had a synergistic antiproliferative effect. The growth-inhibitory and differentiating properties and a low toxicity profile of PB provide rationale for further clinical studies in patients with CaP.

Interleukin-8 serum levels in patients with benign prostatic hyperplasia and prostate cancer

OBJECTIVES

Using arbitrarily primed polymerase chain reaction (AP-PCR) ribonucleic acid (RNA) fingerprinting, we discovered a messenger RNA (mRNA) that encoded the cytokine interleukin-8 (IL-8) that was up-regulated in the peripheral blood leukocytes (PBLs) of patients with metastatic prostate cancer (CaP) compared with similar cells from healthy individuals. We compared the total prostate-specific antigen (PSA) levels, the free/total (f/t) PSA ratios, and the immunoreactive IL-8 serum concentrations in patients with either biopsy-confirmed benign prostatic hyperplasia (BPH) or CaP.

METHODS

The sera from 35 apparently healthy normal volunteers and 146 patients with biopsy-confirmed BPH and CaP obtained from two academic centers were retrospectively examined to determine the serum levels of IL-8, total PSA (tPSA), and the f/t PSA ratio. Logistic regression and trend analysis statistical methods were used to assess the results.

RESULTS

Normals (n = 35), BPH patients (n = 53), patients with clinical Stages A to C CaP (n = 81), and patients with metastatic CaP (n = 1 2) had mean levels of IL-8 of 6.8, 6.5, 15.6, and 27.8 pg/mL, respectively. The IL-8 serum concentrations correlated with increasing CaP stage and also differentiated BPH from clinical Stages A, B, C, or D CaP better than tPSA and performed similarly to the f/t PSA ratio. The combination of the IL-8 levels and f/t PSA ratios using multivariate logistic regression analysis distinguished BPH from Stages A, B, C, or D CaP or only Stages A and B with a receiver operating characteristic area under the curve of 89.8% and 87.5%, respectively (P <0.0001).

CONCLUSIONS

The IL-8 serum concentration in our clinically well-defined patient sample was independent of the f/t PSA ratio as a predictor of CaP. When test samples are controlled for extraneous clinical origin of inflammation or infection, the combination of the IL-8 and f/t PSA assay results may offer an improved approach for distinguishing BPH from CaP.

Bayer Immuno 1 PSA Assay: an automated, ultrasensitive method to quantitate total PSA in serum

The Bayer Immuno 1 PSA Assay measures total PSA in human serum and demonstrates excellent performance with an interassay CV < or = 3.4% and a biological detection limit of 0.03 microgram/L. No significant interference from common hormonal and chemotherapeutic drugs, kallikrein, prostatic acid phosphatase, and trypsin, or elevated levels of total bilirubin, hemoglobin, triglycerides, and IgG was observed. The 95th percentile values for healthy individuals increased with age from 3.0 micrograms/L for males 50-59 years and 3.3 micrograms/L for males 60-69 years, to 4.6 micrograms/L for males > or = 70 years. Clinical studies with retrospective samples demonstrated correspondence between serial measurements of PSA and clinical outcome for 98% of 159 prostate cancer patients. Clinical sensitivity for patients with clinical evidence of disease, untreated at the time of specimen draw, increased with increasing stage from 77.5-100%. Specificity of 60-70% for BPH and other benign urogenital diseases was consistent with previous findings. Bayer Immuno 1 PSA Assay values for 2131 specimens from healthy subjects and patients with prostate cancer, BPH, and other malignant and nonmalignant diseases correlated well with the Abbott IMx PSA Assay over the range 0.0-6,238 micrograms/L (Y = 1.10 x + 0.02). The Bayer Immuno 1 PSA Assay provides automated ultrasensitive, precise, and equimolar measurement of total PSA in human serum.

Biotin reagents for antibody pretargeting. 3. Synthesis, radioiodination, and evaluation of biotinylated starburst dendrimers

We are investigating the hypothesis that biotin multimers can be used with streptavidin and monoclonal antibody conjugates in cancer pretargeting protocols to provide a method of increasing the amount of radioactivity bound on cancer cells in patients. As part of that investigation, a series of biotinylated Starburst dendrimers (BSBDs) have been prepared and evaluated in vitro and in vivo. In this study, a new biotinidase-stabilized, water-solubilizing biotinylation reagent was prepared and reacted with Starburst (PAMAM) dendrimers, generations 0, 1, 2, 3, and 4. The reaction conditions employed resulted in perbiotinylation of generation 0 (four biotin moieties conjugated), generation 1 (eight biotin moieties conjugated), generation 2 (16 biotin moieties conjugated), and generation 3 (32 biotin moieties conjugated). With generation 4, incomplete biotinylation was achieved resulting in the largest portion of that BSBD having 51 biotin moieties (of 64 possible) conjugated. The ability of each BSBD to cross-link streptavidin (SAv) was examined in an in vitro assay. In that assay, an assessment was made of the quantity of [125I]SAv bound with polystyrene-bound SAv after treatment with the synthesized BSBDs. All BSBDs cross-linked the polystyrene-bound SAv with [125I]SAv; however, the amount of [125I]SAv bound varied with the different BSBDs. Roughly 1 equiv of [125I]SAv was bound when Starburst dendrimers containing three or four biotin moieties (generation 0) were used. Two equivalents were bound with BSBD generation 1, and 4 equiv were bound with BSBDs generations 2, 3, and 4. To assess the distribution of BSBDs generations 0, 1, and 2 in mice (at 4 h postinjection), a method was developed for radioiodinating them using the NHS ester of p-[125I]iodobenzoate ([125I]PIB). It was found that the radioiodinated BSBDs had low blood concentrations (i.e., 0.13-0.20% ID/g) at the 4 h time point. In fact, most tissues examined had low concentrations of biotinylated dendrimers, except kidney and liver. Kidney had the highest concentration of [125I]-labeled BSBDs, and its concentration increased with increasing size and charge of dendrimer (e.g., 8-48% ID/g). On the basis of the increased radioactivity observed in the in vitro assay and the rapid clearance from blood in mice, additional in vivo studies with perbiotinylated Starburst dendrimer, generation 2, are planned.

Engineering the isoelectric point of a renal cell carcinoma targeting antibody greatly enhances scFv solubility

BACKGROUND

The murine A6H monoclonal antibody targets a cell surface antigen associated with renal cell carcinoma with high specificity and excellent biodistribution properties. Tumor to blood ratios of > 40:1 have been achieved in clinical studies.

OBJECTIVES

In order to generate an antibody engineering system that would allow the construction of improved derivatives for diagnostics and therapeutics, a single-chain Fv antibody (scFv) derived from A6H was constructed. The initial single-chain Fv, constructed with a cysteine residue and hexa-histidine sequence at the C-terminus, displayed a limited solubility of 100 microg/ml at pH 7.4. The low solubility and refolding yield of the original single-chain Fv required that a more soluble variant be designed and constructed.

STUDY DESIGN

We hypothesized that lowering the pI of the scFv antibody away from the physiological range would yield a more soluble antibody. A derivative was thus subsequently engineered with five glutamic acid residues followed by the cysteine and hexa-histidine residues. The cysteine was included to provide a conjugation site for future radiolabeling studies.

RESULTS

The redesigned A6H single-chain Fv has a predicted pI of 6.1, relative to 7.5 for the native scFv. The redesigned A6H scFv displayed a greatly enhanced solubility of > 15 mg/ml at pH 7.4. Both the original scFv and the redesigned single-chain Fv exhibited a strong tendency to form dimers and soluble high molecular weight aggregates. The monomer and disulfide bonded dimer were separated from the aggregates and complete cell binding isotherms were obtained, demonstrating that the purified A6H scFv retains much of the activity of the parent monoclonal.

CONCLUSION

The addition of glutamic acid to the C-terminus of poorly soluble scFv antibodies could provide a straightforward avenue for improving their solubility properties. The increased solubility of the A6H scFv allowed the purification of the monomeric and dimeric species from the soluble aggregated species.

Serum percent free prostate-specific antigen in metastatic prostate cancer

OBJECTIVES

To define the serum prostate-specific antigen (PSA) isoform profile in patients who have prostate cancer but do not have a prostate gland, that is, men who have had a previous radical prostatectomy (RP) and subsequently persistent disease as evidenced by elevated PSA. PSA can be reliably measured in the serum in two major isoforms: PSA complexed to alpha1-antichymotrypsin and uncomplexed free PSA (fPSA). Multiple investigations have illustrated the usefulness of the free/total PSA proportion (percent fPSA) in differentiating prostate cancer from benign prostate disease in patients who still have their prostate gland in situ.

METHODS

Sera were evaluated from 52 men who underwent RP and postoperatively had increased PSA. fPSA and total PSA (tPSA) concentrations were determined using the Abbott AxSYM PSA assays. Percent fPSA was calculated for all patients.

RESULTS

Median tPSA was 5.45 ng/mL (range 0.93 to 214.99). Median fPSA was 0.69 ng/mL (range 0.11 to 54.93); the median percent fPSA was 13.3% (range 3.9% to 62.9%). There were 27 (52%) patients with percent fPSA less than 15%, 25 (48%) patients with greater than 15%, and 7 (13%) with greater than 30%. No significant relationship was found between percent fPSA and grade, stage, and severity of disease. Percent fPSA was significantly increased in patients who received hormonal, radiation, or combination treatment versus those who received no treatment (P = 0.02 to 0.0007).

CONCLUSIONS

Serum percent fPSA in men after RP with persistent prostate cancer encompasses a wide range of values with no clear stratifying factor or factors. These observations and further serial studies in patients with progressive metastatic disease may be important in determining the mechanism(s) for lower percent fPSA in men with newly diagnosed prostate cancer.

Study of free and complexed prostate-specific antigen in mice bearing human prostate cancer xenografts

BACKGROUND

Our objective was to evaluate five preclinical prostate cancer (CaP) xenograft models to determine whether (1) prostate-specific antigen (PSA) formed complexes in murine serum, (2) the percentage of free PSA (f-PSA) was characteristic of a given xenograft line, and (3) the percentage of f-PSA was similar to that in the patient at time of tumor harvest. Our fourth objective was to identify which murine serpin(s) bind(s) to PSA in vivo.

METHODS

Xenografts were established from metastatic foci. The percentage of f-PSA, and total PSA (t-PSA) in serum of animals bearing CaP xenografts was determined by immunoassay. Size exclusion high-performance liquid chromatography and Western blots were used to evaluate the presence of PSA complexes in murine serum. Edman degradation was used to determine the N-terminal sequence of complexed proteins.

RESULTS

PSA was detected as both free and complexed forms in murine serum from all mice bearing the CaP xenografts. Three xenografts (related sublines) produced PSA that resulted in low mean percentages of f-PSA (1.9-6.4%). In sera from the other two xenografts, the mean percentages of f-PSA were high (>25%); patient sera, where available at time of tumor acquisition, were in agreement. Western blots showed that murine protease inhibitors formed complexes with PSA. Edman degradation yielded a sequence with 80% homology over 15 amino acids with that of murine alpha1-protease inhibitor (alpha1-PI).

CONCLUSIONS

Our data have shown that the majority of PSA secreted by these CaP xenografts complexes in murine serum with a protease inhibitor with high homology to murine alpha1-PI and that the percentage of f-PSA is a characteristic of each xenograft line tested, which is in agreement with patient values at time of tumor harvest. These CaP xenografts offer opportunities for study of human PSA biology and phenomenology.

A novel monoclonal antibody 107-1A4 with high prostate specificity: generation, characterization of antigen expression, and targeting of human prostate cancer xenografts

Monoclonal antibodies with high specificity for prostate tissue are of interest for prostate cancer research and treatment. Reactivity and specificity of a new murine monoclonal antibody, 107-1A4, was assessed by immunohistochemistry, ELISA and indirect immunofluorescence (IDIF). 107-1A4 stained all normal and malignant prostate tissue specimens while reactivity to non-prostate tissue was limited to the tubules of the normal kidney and renal cell carcinoma. Twenty two human cell lines were included in the reactivity survey; only the immunogen prostate cancer line LNCaP reacted with 107-1A4. Seminal plasma proteins PSA, PAP, PSMA, and PSP-94 were determined not to be the 107-1A4 antigen.

LNCaP produces both putative zymogen and inactive, free form of prostate-specific antigen

BACKGROUND

Our objective was to investigate the presence of prostate specific antigen (PSA) and alpha-1-antichymotrypsin (ACT) mRNA and protein in prostate cancer cell lines, and the complexing characteristics of expressed PSA.

METHODS

RT-PCR, immunohistochemistry, and Western blots were employed. Trypsin treatment of PSA was performed to establish the possible presence of an activatable form of PSA.

RESULTS

ACT mRNA and protein were detected in LNCaP, PC-3, and DU 145 by RT-PCR and by immunohistochemistry, respectively. Only LNCaP cells were positive for PSA mRNA and protein. LNCaP expressed approximately 30% active PSA, approximately 40% putative zymogen form of PSA, and approximately 30% stably inactive PSA.

CONCLUSIONS

We have shown that the majority of PSA expressed by LNCaP cells is present in free, noncomplexed forms in the conditioned media. A portion (40%) can be activated by trypsin, while the rest is stably inactive PSA. LNCaP cells may serve as a source of the "unreactive" PSA present in prostate cancer patients' serum.

Streptavidin in antibody pretargeting. 2. Evaluation Of methods for decreasing localization of streptavidin to kidney while retaining its tumor binding capacity

An investigation has been conducted to determine if the kidney localization of recombinant streptavidin can be decreased to improve its characteristics in pretargeting protocols. Three different methods of accomplishing this were evaluated. The first method, blocking kidney uptake with a preadministration of recombinant streptavidin in which biotin occupied all of the binding sites, was unsuccessful. In a second method, l-lysine administration was used to block kidney localization. This method worked well, decreasing the concentration to 29% of the unmodified amount at 8 h postinjection. However, this method suffered from a requirement for constant infusion of lysine during the period of observation. A third method, use of succinylated recombinant streptavidin, was found to be the best approach. Succinylation of streptavidin was readily accomplished with very good protein recovery. With the succinylated streptavidin, the kidney concentration was only 14% of that of nonmodified streptavidin at 4 h postinjection. While these results demonstrated that the concentration of streptavidin could be decreased in the kidney, it was important to assess whether the tumor colocalization of streptavidin with biotinylated antibody was affected under those conditions. As part of our continuing investigation of pretargeting, a new water-solubilized biotinidase-stabilized biotinylation reagent was prepared. Using that reagent in a pretargeting experiment, an equivalent quantity of succinylated recombinant streptavidin as biotinylated antibody Fab' was localized in a tumor xenograft model. In that experiment, the kidney concentration was decreased to less than 10% of that obtained with unmodified recombinant streptavidin at 24 h postinjection. The results of our investigation have demonstrated that succinylation of streptavidin improves its distribution characteristics for pretargeting applications. The fact that succinylated streptavidin has no specific tissue localization should allow its use as a carrier of radioactivity in "two-step" pretargeting protocols.

Inactivation of the tumor suppressor PTEN/MMAC1 in advanced human prostate cancer through loss of expression

The recently identified PTEN/MMAC1 gene is a candidate tumor suppressor implicated in multiple tumor types based on mutations or homozygous deletions of the gene in certain human cancers. No studies of PTEN/MMAC1 mRNA or protein expression in cancer cells have been reported, primarily because of significant numbers of normal cells contaminating most tumor samples and because of the lack of antibody reagents. We examined PTEN/MMAC1 in advanced prostate cancer for gene mutations or abnormalities in expression by using a series of recently derived xenografts free of normal human cells and a PTEN/MMAC1-specific antibody. Only 1 of 10 tumors contained a homozygous deletion of PTEN/MMAC1, and no mutations were detected in the entire coding region of the remaining nine xenografts. However, five of these showed reduced or absent PTEN/MMAC1 expression by Northern analysis and reverse transcription-PCR of mRNA. PTEN/MMAC1 mRNA expression was restored in nonexpressing prostate cancer cells by in vitro treatment with the demethylating agent 5-azadeoxycytidine. Alterations in PTEN/MMAC1 expression were confirmed at the protein level by immunoblot analysis, and immunohistochemical studies show that the endogenous wild-type PTEN/MMAC1 protein is localized exclusively in the cytoplasm. These results demonstrate that loss of PTEN/MMAC1 expression occurs frequently in advanced prostate cancer.

The value of a reverse transcriptase polymerase chain reaction assay in preoperative staging and followup of patients with prostate cancer

PURPOSE

The reverse transcriptase polymerase chain reaction (RT-PCR) assay is an extremely sensitive technique of detecting cells expressing prostate specific antigen (PSA). Controversy exists regarding the ability of peripheral blood PSA RT-PCR testing to reflect pathological staging or treatment outcome. We examine the phenomenology of RT-PCR results in patients with prostate cancer, with particular emphasis on the RT-PCR test before and after radical prostatectomy, and correlations with pathological staging and treatment outcome.

MATERIALS AND METHODS

Peripheral blood was obtained from a wide variety of patients with and without prostate cancer, including before and after radical prostatectomy. After ribonucleic acid isolation, complementary deoxyribonucleic acid was generated and amplified with a hot-start technique. RT-PCR results were compared with pathological stage, Gleason score, tumor volume and disease-free status. Correlations between preoperative and postoperative RT-PCR tests were also made.

RESULTS

The RT-PCR test was positive in 1 of 56 controls (1.8%) without suspicion of prostate cancer. A positive test was obtained in 12 of 65 men (18.5%) with a suspicion of prostate cancer but a negative biopsy. Before radical prostatectomy a positive test was obtained in 13 of 75 men (17.3%) with pT2 disease versus 10 of 46 (21.7%) with pT3 disease. There was no significant difference in serum PSA, Gleason score or tumor volume between the men with positive or negative results. With repetitive testing an increasing percentage of men had at least 1 positive test preoperatively. With a median followup of 8 months 6 of the 7 patients in whom radical prostatectomy failed had had negative RT-PCR before treatment. Of patients with known metastatic disease or failed primary treatment a positive test was obtained in 32 to 75%. Radical prostatectomy and prostate needle biopsy appeared to have a negligible effect on RT-PCR tests immediately following these procedures. Following radical prostatectomy results were variable but many men who are RT-PCR positive preoperatively become RT-PCR negative postoperatively.

CONCLUSIONS

The PSA RT-PCR test in our laboratory cannot be used preoperatively to predict pathological stage of prostate cancer or treatment failure. Most cases that are positive preoperatively become negative postoperatively. While increasing tumor burden increases the likelihood of positive tests, there appears to be significant sampling error associated with the use of this test in the peripheral blood.

Streptavidin in antibody pretargeting. Comparison of a recombinant streptavidin with two streptavidin mutant proteins and two commercially available streptavidin proteins

In this investigation, a comparison of wild type recombinant streptavidin (r-SAv) with two genetically engineered mutant r-SAv proteins was undertaken. The investigation also included a comparison of the r-SAv with two streptavidin (SAv) proteins from commercial sources. In vitro characterization of the SAv proteins was conducted by HPLC, SDS-PAGE, IEF, and electrospray mass spectral analyses. All SAv proteins studied appeared to be a single species by size exclusion chromatography (HPLC) and SDS-PAGE analyses, but multiple species were noted in the IEF and MS analyses. In vivo comparisons of the SAv proteins were accomplished with dual isotope-labeled SAv in athymic mice. In an initial experiment, tissue localization of r-[131I]SAv directly radiolabeled using chloramine-T was compared with r-SAv radiolabeled with the N-hydroxysuccinimidyl p-iodobenzoate conjugate ([125I]-PIB), a radioiodination reagent that has been shown to result in iodine-labeled proteins which are stable to in vivo deiodination. The data obtained indicated that there is little difference in the distribution (except kidney localization) when r-SAv labeled by the two methods. Data obtained from comparison of r-[131I]SAv with a disulfide-stabilized r-SAv mutant (r-SAv-H127C), a C-terminal cysteine-containing r-SAv mutant (r-[125I]SAv-S139C), and two 125I-labeled SAv proteins obtained from commercial sources indicated that their distributions were quite similar, except the kidney concentrations were generally lower than that of r-[131I]SAv. On the basis of the similar distributions of the SAv proteins studied, it appears that the r-SAv mutants may be interchanged for the (wild type) r-SAv in pretargeting studies. Further, the similarity of distributions with two commercially available SAv proteins suggests that the results obtained in our studies and those of other groups may be directly compared (with consideration of animal model, sacrifice time, etc.).

Cross-reactivity of ten anti-prostate-specific antigen monoclonal antibodies with human glandular kallikrein

OBJECTIVES

Prostate-specific antigen (PSA) is commonly used as a marker for prostate disease. Prostate epithelium expresses both PSA and human glandular kallikrein (hK2) proteins, which share 80% sequence homology. The immunologic cross-reactivity of these two proteins could potentially interfere with determination of PSA levels in diagnoses of prostate cancer. We set out to determine the extent of this cross-reactivity for a panel of 10 anti-PSA monoclonal antibodies (mAbs).

METHODS

Enzyme-linked immunosorbent assay (ELISA), sandwich assays, and western transfer techniques were used to assess the PSA/hK2 cross-reactivity of the anti-PSA mAbs.

RESULTS

We did not detect the hK2 protein with any of the 10 anti-PSA mAbs under western transfer conditions. In ELISA experiments, 8 of 10 mAbs exhibited hK2 cross-reactivity under certain conditions. However, no combination of mAbs tested in sandwich assays exhibited a signal in hK2 cross-reactivity experiments greater than 0.1% of the PSA signal.

CONCLUSIONS

We have evaluated 10 anti-PSA mAbs and determined that despite the 80% homology between PSA and hK2 proteins, cross-reactivity with hK2 by these antibodies would not significantly affect the determination of PSA levels by means of sandwich assays.

Early detection of recurrent prostate cancer with an ultrasensitive chemiluminescent prostate-specific antigen assay

OBJECTIVES

Treatment failure after radical prostatectomy is most commonly heralded by an increase in serum prostate-specific antigen (PSA) to detectable levels. We evaluated the clinical utility of an ultrasensitive chemiluminescent PSA assay.

METHODS

We evaluated the assay in banked sera obtained from 170 men after radical prostatectomy. Controls consisted of 142 females, 29 men who had undergone cystoprostatectomy without evidence of prostate cancer, and 25 men without evidence of recurrent disease at least 5 years after prostatectomy for organ-confined disease. Lead time to diagnosis of recurrence was based on comparisons with the IMx or Tandem E assays using a cutoff of 0.1 ng/mL (100 pg/mL).

RESULTS

The biologic level of detection of this assay is 8 pg/mL. Serum PSA levels were undetectable in 82.4% of females, 86.2% of the cystoprostatectomy patients, and 96% of the radical prostatectomy controls. After radical prostatectomy, PSA levels were undetectable at last check in 104 of 168 (61.9%) men. In the 24 men with prostate cancer recurrence, the enhanced sensitivity of 8 pg/mL provided a mean lead time based on conservative calculations of 12.7 to 22.5 months over conventional assays. Thirty-four of the 41 men with detectable PSA levels and no evidence of disease recurrence had PSA levels of 30 pg/mL or less.

CONCLUSIONS

PSA levels are undetectable in most men who do not have recurrence of disease after radical prostatectomy. Low but detectable serum PSA levels less than or equal to 30 pg/mL can be produced by nonmalignant sources of PSA. PSA assays with enhanced sensitivity can detect recurrent prostate cancer with significant lead time over conventional assays.

Cell-cell interaction in prostate gene regulation and cytodifferentiation

To examine the role of intercellular interaction on cell differentiation and gene expression in human prostate, we separated the two major epithelial cell populations and studied them in isolation and in combination with stromal cells. The epithelial cells were separated by flow cytometry using antibodies against differentially expressed cell-surface markers CD44 and CD57. Basal epithelial cells express CD44, and luminal epithelial cells express CD57. The CD57+ luminal cells are the terminally differentiated secretory cells of the gland that synthesize prostate-specific antigen (PSA). Expression of PSA is regulated by androgen, and PSA mRNA is one of the abundant messages in these cells. We show that PSA expression by the CD57+ cells is abolished after prostate tissue is dispersed by collagenase into single cells. Expression is restored when CD57+ cells are reconstituted with stromal cells. The CD44+ basal cells possess characteristics of stem cells and are the candidate progenitors of luminal cells. Differentiation, as reflected by PSA production, can be detected when CD44+ cells are cocultured with stromal cells. Our studies show that cell-cell interaction plays an important role in prostatic cytodifferentiation and the maintenance of the differentiated state.

A very sensitive coupled luminescent assay for cytotoxicity and complement-mediated lysis

The demand for convenient and sensitive means of measuring cytotoxicity and complement-mediated killing is likely to be increased by the recent identification of Complement Factor H, an important regulatory protein of both the classical and alternate pathways of complement, as a tumor-associated antigen. Here we describe a simple luminometric assay capable of detecting the death of approximately 0.03 nucleated human-cell equivalent or approximately 1 rabbit-erythrocyte equivalent. The assay measures the release of glyceraldehyde-3-phosphate dehydrogenase (G3PDH) from dead or damaged cells by coupling its enzymatic activity to production of ATP, which in turn is measured by well-known methods involving firefly luciferase. This is accomplished by means of a reaction series in which the activity of G3PDH is coupled with that of phosphoglycerate kinase, the next enzyme in the glycolytic pathway. As described, the assay uses inexpensive, commercially available reagents. This coupled assay was used to demonstrate that an anti-factor-H antibody is capable of enhancing complement-mediated killing of the Raji cancer cell line by > 1000%.

Detection of circulating prostate cells by reverse transcriptase-polymerase chain reaction of human glandular kallikrein (hK2) and prostate-specific antigen (PSA) messages

OBJECTIVES

To investigate the clinical value of human glandular kallikrein (hK2) reverse transcriptase-polymerase chain reaction (RT-PCR) for detection of prostate cells in circulation and to compare the results with those obtained from prostate-specific antigen (PSA) RT-PCR.

METHODS

We examined peripheral blood (PB) and bone marrow (BM) samples of 13 patients with advanced-stage prostate cancer and 63 patients with clinically localized disease for the presence of circulating prostate cells. An RT-PCR protocol with a two-step amplification cycle and hot-start conditions was used.

RESULTS

The limit of detection of the PCR portion is similar for PSA and hK2 (5 to 10 copies of the plasmid containing the cDNA). The RT-PCR limit of detection is one LNCaP cell in 10(8) peripheral blood mononuclear cells (PMBC) for PSA, and one LNCaP cell in 10(7) PMBC for hK2. Of the BM samples obtained prior to radical prostatectomy, 71.4% were positive for PSA mRNA and 41.3% were positive for hK2 mRNA. In PB, the PSA positivity was 19% and hK2 positivity 12.7%. In advanced-stage patients, there were 76.9% PSA-positive samples in BM versus 38.5% hK2-positive samples; 46.2% of patients were positive in PB for PSA versus 30.8% for hK2.

CONCLUSIONS

We have developed a sensitive RT-PCR protocol for detection of hK2 mRNA and evaluated the suitability of hK2 mRNA in comparison with PSA mRNA as an additional marker for detection of prostate cells in circulation. Combining results of these two tests increased the sensitivity of detection.

Characterization of 10 new monoclonal antibodies against prostate-specific antigen by analysis of affinity, specificity and function in sandwich assays

While prostate-specific antigen (PSA) is already an invaluable marker for prostate cancer, there is continuing demand for new anti-PSA antibodies with specific characteristics, e.g., high sensitivity and specificity and equimolar binding to free PSA (f-PSA) and the PSA-alpha-1-antichymotrypsin complex (PSA-ACT), as well as the ability to distinguish between these 2 immunoreactive forms of PSA. We have therefore generated and characterized 10 anti-PSA monoclonal antibodies (MAbs). Apparent dissociation constants (Kd) of MAbs were determined by direct ELISA yielding Kd-0.2-164.0 nM. Western blots suggested that 3 of the MAbs (60-1A2, 60-8A2 and 17-1A2) bind to linear epitopes. Sandwich assays identified 5 major antigenic regions as binding targets of the MAbs. Three combinations of MAbs recognize f-PSA and PSA-ACT in equimolar fashion with high sensitivity. Two of the MAb combinations are specific for f-PSA. Physical analysis of the new antibodies has allowed us to assign the MAbs to binding classes (based on their sandwiching capabilities) and to determine accurate apparent dissociation constants.

[In vitro and in vivo models developed from human prostatic cancer]

The possibility of maintaining and studying human prostatic cancers in an in vitro and in vivo environment has allowed the development of rare but essential tools to study many aspects of the biology of these cancers. Although none of the available models is perfect, the sum of the studies conducted with these models over more than 20 years constitutes the basis for major progress in our understanding of this disease. The most widely used cell lines (cultured in vitro) are PC-3, DU-145 and LNCaP. They are limited by the fact that they are essentially androgen-independent cell lines, derived from metastatic sites. Due to the slow growth of prostatic cancers, it is very difficult to obtain cancer cell lines which can be transplanted in immunodeficient animals (such as athymic mice) and only a few xenografts are currently available, some of which, like PCV-82, LuCaP 23, CWR-22, are androgen-dependent or sensitive. These models can be used to study host-tumour interactions as well as endocrinological interactions, stroma-tumour cell interactions, and to analyse molecular phenomena related to stages of hormone dependence and hormone resistance. In vitro and in vivo models of metastatic prostatic cancer have also been developed and appear to have a crucial impact on the understanding of metastatic mechanisms and new therapeutic approaches. This paper describes the main experimental models developed from human prostatic cancers, their main characteristics, their value compared to clinical cancers and some of the major studies conducted with these models. Due to the exponential progress in molecular biology techniques and oncogenetics, it appears essential to increase the number and diversity of experimental models of prostatic cancer in order to advance research concerning the crucial phenomena occurring during the course of this disease, from oncogenesis to currently incurable metastatic stages.

Issues in the assessment of prostate-specific antigen immunoassays. An update

Prostate-specific antigen (PSA) immunoassays continue to provide unique and valuable information in the early diagnosis and clinical management of prostate cancer. During the past few years there has been considerable progress in the standardization of routine PSA assays and an emergence of PSA assays with novel applications. The authors discuss these developments and provide some insight when assessing the nuances of assay performance and clinical value.

Prostate-specific antigen: characterization of epitopes by synthetic peptide mapping and inhibition studies

To improve our understanding of the prostate-specific antigen (PSA) antigenic regions, we studied the association targets of one anti-PSA polyclonal antibody and 10 anti-PSA monoclonal antibodies (mAbs). We also examined the ability of the mAbs to inhibit PSA enzymatic activity and block the association of PSA with alpha 1-antichymotrypsin (ACT). Linear epitope mapping with a polyclonal antibody indicated the presence of six major antigenic regions in PSA. Examination of the panel of mAbs established that three of them bind to linear epitopes. Five of the mAbs inhibited > 90% of PSA enzymatic activity. However, inhibition of PSA enzymatic activity and hindrance of PSA-ACT association by mAbs cannot be used to predict whether the mAbs bind to free PSA, the PSA-ACT complex, or both. Some of the mAbs may block PSA-ACT association through peripheral occlusion of the binding site, or through induction of conformational changes in PSA.