Overexpression of prostate specific membrane antigen by canine hemangiosarcoma cells provides opportunity for the molecular detection of disease burdens within hemorrhagic body cavity effusions

Background

Canine hemangiosarcoma (cHSA) is a highly metastatic mesenchymal cancer that disseminates by hematogenous and direct implantation routes. Therapies for cHSA are generally ineffective, in part due to advanced clinical disease stage at the time of diagnosis. The validation of conventional molecular methods for detecting novel biomarkers preferentially expressed by cHSA could lead to more timely diagnosis, earlier therapeutic interventions, and improved outcomes. In humans, prostate-specific membrane antigen (PSMA) is a transmembrane protein overexpressed by prostate carcinoma and tumor-associated endothelium of various solid cancer histologies. Importantly, the preferential overexpression of PSMA by certain cancers has been leveraged for the development of diagnostic molecular imaging reagents and targeted therapeutics. Recently, PSMA has been qualitatively demonstrated to be expressed in cHSA cell lines, however, quantitative PSMA expressions and the potential utility of PSMA transcript identification in biologic fluids to support the presence of microscopic cHSA burden has not been reported. Therefore, this study sought to characterize the differential quantitative expressions of PSMA between cHSA and non-malignant tissues, and to determine the potential diagnostic utility of PCR-generated PSMA amplicons as a surrogate of rare cHSA cells dwelling within peritoneal and pericardial cavities.

Methods

Quantitative gene and protein expressions for PSMA were compared between one normal endothelial and six cHSA cell lines by RT-PCR, western blot analysis, and fluorescent microscopy. Additionally, gene and protein expressions of PSMA in normal canine tissues were characterized. Graded expressions of PSMA were determined in spontaneously-arising cHSA tumor samples and the feasibility of qualitative PCR as a molecular diagnostic to detect PSMA transcripts in whole blood from healthy dogs and hemorrhagic effusions from cHSA-bearing dogs were evaluated.

Results

PSMA gene and protein expressions were elevated (up to 6-fold) in cHSA cells compared with non-malignant endothelium. By immunohistochemistry, protein expressions of PSMA were detectable in all cHSA tissue samples evaluated. As predicted by human protein atlas data, PSMA’s expression was comparably identified at substantial levels in select normal canine tissues including kidney, liver, and intestine. In young healthy pet dogs, PSMA amplicons could not be identified in circulating whole blood yet were detectable in hemorrhagic effusions collected from pet dogs with confirmed cHSA or PSMA-expressing cancer.

Conclusions

PSMA is quantitatively overexpressed in cHSA compared to normal endothelium, but its protein expression is not restricted to only cHSA tumor tissues, as specific visceral organs also substantively express PSMA. Optimized qualitative PCR methods failed to amplify PSMA amplicons sufficiently for visible detection in circulating whole blood derived from healthy young dogs, yet PSMA transcripts were readily identifiable in hemorrhagic effusions collected from pet dogs with histologically confirmed cHSA or PSMA-expressing cancer. While preliminary, findings derived from a limited cohort of normal and diseased pet dogs provocatively raise the potential value of PSMA amplicon detection as an ancillary molecular diagnostic test for supporting the presence of microscopic cHSA disease burden within hemorrhagic body cavity effusions.

Detection of α-Methylacyl-Coenzyme-A Racemase Transcripts in Blood and Urine Samples of Prostate Cancer Patients

BACKGROUND

Alpha-methylacyl-coenzyme-A racemase (AMACR) has been shown to be a highly specific marker for prostate cancer cells, even in the earliest stages of malignant progression. It is expressed at much higher levels than prostate-specific antigen (PSA) in malignant tissues, and is not expressed at appreciable levels in normal prostatic epithelium. In this study, we demonstrate the quantitative detection of AMACR transcripts in peripheral blood of prostate cancer patients using real-time RT-PCR. In addition, we have undertaken a pilot study to demonstrate the potential application of this technique for the detection of prostate tumor cells in urine samples from patients with prostate cancer.

METHODS

A real-time RT-PCR assay was developed for detection of the expression of AMACR in prostate cancer patients. Blood samples from 163 patients were tested at various stages of disease progression, with or without therapy. Blood specimens from patients with benign prostate disorders and other types of cancer were also evaluated.

RESULTS

In 28 of 58 samples from patients with known metastatic disease who were undergoing treatment, an AMACR expression signal above the cut-off value was detected, consistent with the presence of circulating tumor cells. In 39 of 88 patients with presumptive organ-confined disease, there was evidence of low levels of circulating tumor cells. Comparison of AMACR RT-PCR with known serum PSA values indicated that a combination of these parameters significantly increased the sensitivity for detection of progressive disease. In a pilot study analyzing urine samples from seven prostate cancer patients, elevated AMACR expression levels were detected in the urine sediments of four of six stage-T1 prostate cancer patients and in the one patient with stage-T2 prostate cancer.

CONCLUSION

The data presented in this study indicates that AMACR real-time RT-PCR may aid in the detection and staging of prostate cancer.

Prostate-specific membrane antigen: a new potential prognostic marker of osteosarcoma

Previous studies have demonstrated that the expression of prostate-specific membrane antigen (PSMA) is restricted to endothelium from tumor-associated neovasculature. But the expression of PSMA in osteosarcoma and its clinical significance are unknown. Using immunohistochemical analysis and quantum dot probes, we found that 46.7% (21/45) of the osteosarcoma showed positive staining for PSMA while no PSMA staining in osteofibrous dysplasia. The expression and localization of PSMA was confirmed by CD34 staining. More importantly, the expression of PSMA is correlated with tumor size, pulmonary metastasis and worse survival (survival rate 63.2% in the PSMA-negative group versus 36.6% in the PSMA-positive group). Thus, PSMA could be used as an independent prognostic marker for the osteosarcoma patients, and PSMA staining in tumor-associated neovasculature may be a potential target for antineovasculature-based therapy in osteosarcoma.

Circulating tumor cells in prostate cancer: a potential surrogate marker of survival

Prostate-specific antigen (PSA) levels in blood are widely used in prostate cancer (PCa) for the management of this disease at every stage of progression. Currently, PSA levels combined with clinical stage and Gleason score provide the best predictor of survival and the main element to monitor treatment efficiency. However, these areas could be improved by utilizing emerging biomarkers. Recently, circulating tumor cells (CTCs) and disseminating tumor cells (DTCs) have been detected in PCa and may be a new surrogate candidate. Here we provide a systematic review of the literature in order to describe the current evidence of CTC/DTC surrogacy regarding outcome of prostate cancer patients. We also discuss several markers that could be used to increase the sensitivity and specificity of CTC/DTC detection. CTC/DTC detection is performed using a wide variety of techniques. Initially, reverse transcriptase polymerase chain reaction (RT-PCR) based methods were utilized with weak correlation between their positive detection and patients' outcome. More recent immunological techniques have indicated a reproducible correlation with outcome. Such surrogate markers may enable clinicians to provide early detection for inefficient treatments and patients with poor prognosis that are candidates for treatment intensification. Dissecting the micrometastasis phenomenon in CTCs/DTCs is a key point to increase surrogacy of this biomarker.

Prostate specific membrane antigen mRNA in blood as a potential predictor of biochemical recurrence after radical prostatectomy

We investigated whether the detection of prostate specific membrane antigen (PSMA) in blood preoperatively has predictive value for biochemical recurrence (BCR) after radical prostatectomy in patients with prostate cancer. All 134 patients scheduled to receive radical prostatectomy for prostate cancer were prospectively enrolled. The authors used nested reverse transcriptase-polymerase chain reaction (RT-PCR) assay to detect PSMA mRNA-bearing cells in peripheral blood, and analyzed the ability of PSMA mRNA positivity to predict BCR after surgery. PSMA-mRNA was detected in 24 (17.9%) patients by RT-PCR. Over a median follow-up of 20 months (range, 3 to 46 months), BCR developed in 15 patients (11.2%) and median time to BCR was 7 months (range, 3 to 25 months). Kaplan-Meier analysis revealed a significant difference between those positive or negative for PSMA in terms of recurrence-free actuarial probability (log rank P=0.0039). Multivariate analysis showed that positivity for PSMA mRNA (HR: 3.697, 95% CI 1.285-10.634, P=0.015) and a biopsy Gleason score of >or=7 (HR: 4.500, 95% CI 1.419-14.274, P=0.011) were independent preoperative predictors of BCR. The presence of PSMA mRNA in peripheral blood can be used to predict BCR after radical prostatectomy.

Detection of circulating tumor cells in prostate cancer patients: methodological pitfalls and clinical relevance

Disseminated malignancy is the major cause of prostate cancer-related mortality. Circulating tumor cells (CTCs) are essential for the establishment of metastasis. Various contemporary and molecular methods using prostate-specific biomarkers have been applied to detect extraprostatic disease that is undetectable by conventional imaging techniques, assessing the risk for disease recurrence after therapy of curative intent. However, the clinical relevance of CTC detection is still controversial. We review current literature regarding molecular methods used for the detection of CTCs in the peripheral blood and bone marrow biopsies of patients with prostate cancer, and we discuss the methodological pitfalls that influence the clinical significance of molecular staging.

Mechanisms of bone metastasis in prostate cancer: clinical implications

Prostate cancer shows a strong predilection to spread to the bones. Once prostate tumour cells are engrafted in the skeleton, curative therapy is no longer possible and palliative treatment becomes the only option. Herein, we review the multifactorial mechanisms and complex cellular interactions that take place inside the bone metastatic microenvironment. Emphasis is given to the detection and treatment of the micrometastatic stage of prostate cancer, as well as our recent attempts to target the bone metastasis microenvironment-related survival factors using an anti-survival factor manipulation which can increase the efficacy of anticancer therapies such as androgen ablation therapy and chemotherapy in advanced prostate cancer.

Synergistic Value of Single-Photon Emission Computed Tomography/Computed Tomography Fusion to Radioimmunoscintigraphic Imaging of Prostate Cancer

The rationale on which positron emission tomography/computed tomography (PET/CT) imaging is based, combining the functional features of PET with the anatomic detail of CT, provides many advantages that are easily transferable to single-photon emission computed tomography (SPECT)/CT imaging. Our efforts have focused on applying fused SPECT/CT imaging to identify prostate cancer and its metastasis and recurrence through radioimmunoscintigraphy (RIS). This application of RIS to imaging prostate cancer requires 2 key components: (1) a well-defined target associated with the cancer and (2) a "magic bullet" to seek that target. A well-characterized RIS target for prostate cancer is prostate-specific membrane antigen, or PSMA, and finding the bullet to seek this target with high sensitivity and specificity has been the focus of intensive study for nearly two decades. One of the candidate bullets developed is capromab pendetide, which is a monoclonal antibody that seeks PSMA. This antibody is commercially available as ProstaScint, which can be labeled with indium-111 to localize prostate cancer via SPECT imaging. In the course of applying fused SPECT/CT ProstaScint imaging to more than 800 prostate cancer cases, numerous refinements to our protocol have evolved that are aimed at staging the cancer with utmost accuracy. In addition to optimizing the localization of prostate cancer and its metastasis, these refinements also have been extended toward guiding both the implantation of radioactive seeds in brachytherapy and in other types of radiation therapy which is illustrated through 5 case reports. Progress in the therapeutic targeting of PSMA is also being actively explored, which has more universal ramifications because PSMA is found in the neovasculature of other types of cancers.

Real-time PCR detection of Biscogniauxia mediterranea in symptomless oak tissue

AIMS

Real-time PCR, based on TaqMan chemistry, was used to detect Biscogniauxia mediterranea, a fungal pathogen that after a long endophytic phase may cause charcoal disease in oak trees.

METHODS AND RESULTS

Specific primers and probe were designed and tested on axenic cultures of B. mediterranea and other fungi commonly colonizing oaks. Twig samples were collected in Tuscany from apparently healthy oaks (Quercus cerris, Quercus ilex and Quercus pubescens) growing near trees infected with the fungus. Twigs were divided into two groups: one for isolation in agar plates, and one for real-time PCR after DNA extraction. The detection limit of the assay was 0.01 pg/DNA, whereas the amounts of fungal DNA detected in asymptomatic tissue were >0.5 pg microg(-1) total DNA extracted. In the apparently healthy twigs the frequency of isolation found on agar was 25.0%, much lower than that with real-time PCR (96.4%).

CONCLUSIONS

Real-time PCR is a sensitive and fast technique able to specifically detect and quantify the DNA of B. mediterranea in oak tissue.

SIGNIFICANCE AND IMPACT OF THE STUDY

This diagnostic method is a precise tool to localize fungi in symptomless plant tissues and promises to advance our understanding of fungal infection during their latent phase.

Vaccination of prostatectomized prostate cancer patients in biochemical relapse, with autologous dendritic cells pulsed with recombinant human PSA

This study was conducted in prostate cancer patients in biochemical relapse after radical prostatectomy, to assess the feasibility, safety, and immunogenicity of therapeutic vaccination with autologous dendritic cells (DCs) pulsed with human recombinant prostate-specific antigen (PSA) (Dendritophage-rPSA). Twenty-four patients with histologically proven prostate carcinoma and an isolated postoperative rise of serum PSA (>1 ng/ml to 10 ng/ml) after radical prostatectomy were included. The patients received nine administrations of PSA-loaded DCs by combined intravenous, subcutaneous, and intradermal routes over 21 weeks. Postbaseline blood tests were performed at months 1, 3, 6, 9, and 12 (PSA levels), at months 6 and 12 (circulating prostate cancer cells), at month 6 (anti-PSA IgG and IgM antibodies), and at up to eight time points before, during, and after immunization (PSA-specific T cells). Circulating prostate cancer cells detected in six patients at baseline were undetectable at 6 months and remained undetectable at 12 months. Eleven patients had a postbaseline transient PSA decrease on one to three occasions, predominantly occurring at month 1 (7 patients) or month 3 (2 patients). Maximum PSA decrease ranged from 6% to 39%. PSA decrease on at least one occasion was more frequent in patients with low Gleason score ( p=0.016) at prostatectomy and with positive skin tests at study baseline ( p=0.04). PSA-specific T cells were detected ex vivo by ELISpot for IFN-gamma in 7 patients before vaccination and in 11 patients after vaccination. Of the latter 11 patients, 5 had detectable T cells both before and during the vaccination period, 4 only during the vaccination period, while 2 patients could for technical reasons not be assessed prevaccination. No induction of anti-PSA IgG or IgM antibodies was detected. There were no serious adverse events or otherwise severe toxicities observed during the trial. Immunization with Dendritophage-rPSA was feasible and safe in this cohort of patients. An immune response specific for PSA could be detected in some patients. A notable effect was the disappearance of circulating prostate cells in all patients who were RT-PCR positive before vaccination.

Prognostic value of circulating prostate cells in patients with a rising PSA after radical prostatectomy

BACKGROUND

To predict poor outcome in patients with a biochemical recurrence (rising PSA) after radical prostatectomy (RP), urologists rely primarily on Gleason score, PSA doubling time, and time from surgery to biochemical (i.e., PSA) recurrence. In the present study, we assess the value of RT-PCR detection circulating prostate cells in blood of patients with a rising PSA.

METHODS

RNA from blood samples was obtained from 55 patients with a rising PSA and from 45 patients without evidence of biochemical failure (PSA < 0.1 ng/ml). Both groups were matched for age, Gleason score, pT stage, and interval between radical prostatectomy and PCR testing.

RESULTS

PSA positive cells were detected in 1/45 (2%) patients without a PSA recurrence and 19/55 (34%) patients with a PSA recurrence. In the rising PSA group, mean PSA doubling time was significantly shorter in patients with positive RT-PCR (5 months) than in patients with negative RT-PCR (16 months; P = 0.001). An earlier onset of recurrence was also detected in patients with a positive RT-PCR (31 months for positive RT-PCR vs. 50 months for negative RT-PCR) but this result did not achieve statistical significance (P = 0.102). Salvage radiation therapy was administered in 15 patients. Three of the five patients with a positive RT-PCR progressed during radiotherapy whereas 7 of the 10 patients with a negative RT-PCR obtained a complete response and none have progressed.

CONCLUSIONS

These preliminary results suggest that RT-PCR detection of prostate cells in blood of patients after RP correlates with rapidly progressing biochemical failure after RP.

Preoperative combined nested reverse transcriptase polymerase chain reaction for prostate-specific antigen and prostate-specific membrane antigen does not correlate with pathologic stage or biochemical failure in patients with localized prostate cancer undergoing radical prostatectomy

PURPOSE

We report a prospective study examining the ability of preoperative nested reverse transcriptase polymerase chain reaction (RT-PCR) for prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSM) to predict pathologic stage and biochemical recurrence in patients with clinically localized prostate cancer treated with radical prostatectomy.

PATIENTS AND METHODS

One hundred forty-one patients were entered onto the study. Preoperative evaluation included clinical T stage, serum PSA, biopsy Gleason score, and serum RT-PCR for PSA/PSM. Univariate and multivariate logistic regression models, Kaplan-Meier estimates, and Cox proportional hazards modeling were used to identify predictors of pathologic stage and biochemical failure.

RESULTS

Seventy-three patients (51.8%) were RT-PCR positive for PSA, PSM, or both. In the multivariate logistic regression model, only initial PSA was an independent predictor of pathologic stage as defined by organ-confined disease (odds ratio [OR], 1.06; 95% confidence interval [CI], 1.00 to 1.13; P =.026) or organ-/specimen-confined disease (OR, 1.09; 95% CI, 1.02 to 1.16; P =.009). Overall Kaplan-Meier biochemical relapse-free survival (bRFS) was 85% at 59 months. Multivariate analysis of predictors for bRFS with the Cox proportional hazards model indicated that only initial PSA (OR, 1.05; 95% CI, 1.02 to 1.09; P =.004) and biopsy Gleason score (OR, 3.57; 95% CI, 1.37 to 9.58; P =.009) were independent predictors of biochemical failure. RT-PCR status did not predict pathologic stage or biochemical failure. Repeat analysis excluding 27 patients who received preoperative androgen-deprivation therapy did not change the results.

CONCLUSION

Combined nested RT-PCR for PSA and PSM is not an independent predictor of pathologic stage or biochemical failure in patients with localized prostate cancer undergoing radical prostatectomy. This assay has no clinical utility in this patient population.

The clinical utility of the prostate specific membrane antigen reverse-transcription/polymerase chain reaction to detect circulating prostate cells: an analysis in healthy men and women

OBJECTIVE

To evaluate the overall specificity of nested reverse transcriptase-polymerase chain reaction (RT-PCR) to detect prostate-specific membrane antigen (PSM) mRNA in peripheral blood samples of healthy donors.

SUBJECTS AND METHODS

Peripheral blood samples were taken from 60 healthy blood-donors (30 men and 30 women aged < 50 years) and analysed for PSM-mRNA using nested RT-PCR (in 'hot-start' conditions and confirmed using nested EcoRI restriction enzyme). Intron-spanning primer pairs specific for human PSM were deduced from the GenBank sequence (M99487) using gene software. The outer primer pair for PSM was: fwd: 1368 5'-TCACCGGGACTCATGGGTGT-3'; reverse: 1860 5'-GCCTGAAGCAATTCCAAGTCGG-3'. Inner primer pair for PSM was: fwd: 1480 5'-AAGGAAGGGTGGAGACCTAG-3'; reverse: 5-ACTGAACTCTGGGGAAGGAC-3'. The integrity of cDNAs was checked using primer pairs specific for the housekeeping gene beta-actin. The specificity and false-positive rate were calculated assuming that the underlying prostate cancer incidence was nil.

RESULTS

The first PCR was negative for all samples (100% specificity; 0% false-positive rate). The nested PCR detected 23 positive samples (23/60, 38%) with an overall specificity of 62% (false positive rate, 38%).

CONCLUSION

Nested RT-PCR of PSM-mRNA in peripheral blood is highly unspecific. Its clinical utility in the management of prostate cancer must be low. Further development is needed of quantitative RT-PCR, primers that identify prostatic PSM or another prostate-specific marker gene to differentiate PSM mRNA from circulating prostate cells and from non-prostatic tissues.

Abnormal E-cadherin expression and prostate cell blood dissemination as markers of biological recurrence in cancer

Until now, no molecular parameter has been available for predicting the metastatic potential of prostate tumours, which leaves their outcome uncertain despite an apparent benign histology or early stage. Abnormal expression of adhesion molecules, such as E-cadherin, can be contributing factors for increased invasiveness and metastatic potential. Histological analysis for E-cadherin expression was carried out on paraffin-embedded tumour tissues. Tumour metastatic potential was indirectly evaluated by detecting circulating prostate cells (CPC), using reverse transciptase-polymerase chain reaction (RT-PCR) and prostate-specific membrane antigen (PSMA) as a target. Patients were followed-up for a median of 14 months (range 10--19 months) after surgery with serum prostate-specific antigen (PSA) level measurement. Interestingly, 23 of 44 localised tumours exhibited aberrant E-cadherin expression. Prior to primary surgery, PSMA RT-PCR detected the spread of prostate cells to the blood in 24 patients. Statistical analysis showed that abnormal E-cadherin expression in the tumours was the only variable that was independently correlated with prostate cell dissemination in the blood (P<0.0001). In logistic regression analysis, abnormal E-cadherin expression was a significant independent predictor for a later biological relapse. This impaired adhesion status was clearly correlated with a haematogenous spread of the primary tumour cells. It could therefore be an objective way to restrict the indications for radical surgery to patients not presenting with this feature.

Carcinoembryonic gene member 2 mRNA expression as a marker to detect circulating enterocytes in the blood of colorectal cancer patients

BACKGROUND

The aim of this study was to report our experience with a new molecular tool to detect circulating enterocytes in the blood of patients with colorectal cancer.

METHODS

The study included 193 individuals: 78 patients with colorectal cancer and 115 controls composed of patients with benign colorectal diseases (n = 16), patients with noncolorectal cancer (n = 31), healthy individuals (n = 62), and healthy bone marrow transplantation donors (n = 6). A nested reverse transcriptase-polymerase chain reaction with specific primers for the carcinoembryonic gene member 2 (CGM2) was used to detect circulating enterocytes in the peripheral blood of 78 patients with colorectal cancer. The blood (n = 109) or the bone marrow (n = 6) of the 115 controls was studied to test the absence of CGM2 illegitimate transcription in nucleated blood cells and nucleated blood cell progenitors. The assay sensitivity was effective in detecting 1 CGM2-positive cell per 10(6) nucleated blood cells.

RESULTS

Fifty-nine percent (46/78) of patients with colorectal cancer were found positive whereas all negative controls remained negative. Positivity rates were 38% (3/8) in Dukes' A classification, 43% (9/21) in Dukes' B, 77% (23/30) in Dukes' C, and 58% (11/19) in Dukes' D.

CONCLUSIONS

The clinical significance of enterocyte detection in the blood of colorectal cancer patients by means of this CGM2 messenger RNA assay needs further evaluation.

Blood-based RT-PCR assays of MN/CA9 or PSMA: clinical application in renal cancer patients

OBJECTIVES

To report a survey of blood-based RNAs obtained from common groups of control and renal cancer patients for expression of both MN/CA9 and prostate-specific membrane antigen (PSMA) messenger RNAs.

METHODS

Reverse transcription polymerase chain reaction (RT-PCR) assays for MN/CA9 and PSMA were performed on RNAs extracted from 81 blood samples (59 patients with renal cancer, 7 with benign tumors, and 15 control volunteers). The results of these assays were statistically analyzed to determine whether a positive result (individually or combined) correlates with any tumor characteristics.

RESULTS

Neither MN/CA9 nor PSMA amplification products were detected in the RNAs from peripheral blood samples of the 15 control volunteers and from the 7 patients with benign renal tumor (sensitivity 100%). MN/CA9 alone was detected in 11 (19%) of 59 samples and PSMA alone in 12 (20%) of 59 samples from patients with renal cancer. PSMA positivity was significantly correlated with vascular invasion of the primary tumor. Expression of one or both of these molecular tumor markers was detected in 21 (36%) of 59 renal cancer patients. When combined, the results of the MN/CA9 and PSMA RT-PCR tests were found to be highly associated with vascular invasion in nephrectomy specimens (sensitivity 67%, specificity 77%, odds ratio = 6.89, P = 0.002).

CONCLUSIONS

Combination of RT-PCR assays for MN/CA9 and PSMA provides a sensitive blood test for molecular detection of clear cell carcinoma of the kidney and its potential for vascular invasion. Further testing of this assay will be required to evaluate its efficacy in the diagnosis, screening, and follow-up of patients with kidney cancer.

Molecular detection and characterisation of circulating tumour cells and micrometastases in solid tumours

The detection and molecular characterisation of circulating tumour cells (CTC) and micrometastases may have important prognostic and therapeutic implications. Because their numbers are very small, these tumour cells are not easily detected using conventional methods. In the last decade, numerous groups have attempted to detect occult tumour cells in solid malignancies using the highly sensitive reverse transcriptase polymerase chain reaction (RT-PCR). These assays were in the vast majority directed against tissue-specific markers. PCR was shown to be superior to conventional techniques in detecting occult tumour cells allowing the identification of one malignant cell mixed with 1-10 million normal cells. In some tumours like melanoma and prostatic carcinoma, tissue-specific transcripts were detected with high specificity in the blood of patients with localised and advanced disease. In some reports, PCR was shown to be a strong predictor of poorer outcome. However, due to the many limitations of PCR (e.g false-positives), many groups are developing new approaches for the detection of occult tumour cells. The most attractive technique involves immunomagnetic isolation of CTC and micrometastases prior to downstream analysis. The tumour-rich magnetic fraction can be subjected to RT-PCR, immunocytochemistry and in situ hybridisation. This will lead to better quantification and molecular characterisation of these tumour cells. In conclusion, the molecular detection and characterisation of occult tumour cells offer a great opportunity for better stratifying patients with solid tumours and for developing new prognostic markers and targeted therapies.

Total PSA, free PSA/total PSA ratio, and molecular PSA detection in prostate cancer: which is clinically effective and when?

OBJECTIVES

To ascertain when the serum determination of the free prostate-specific antigen (PSA)/total PSA (fPSA/tPSA) ratio is clinically useful, and whether the identification of PSA or prostate-specific membrane antigen (PSM) mRNA in circulating cells has diagnostic advantages over the determination of their protein product.

METHODS

fPSA, tPSA, and the fPSA/tPSA ratio were determined in the sera of 50 men with benign nonprostatic urologic diseases (EPD), 112 patients with prostate cancer (PCa), and 218 with benign prostatic hyperplasia (BPH). mRNA was extracted from the circulating mononuclear cells of 13 EPD samples, 25 PCa samples, and 38 BPH samples. PSA and PSM mRNA signals were identified in these samples by means of reverse transcriptase-polymerase chain reaction.

RESULTS

Overall, at a fixed specificity of 95%, the sensitivity of tPSA was 19% and that of the fPSA/tPSA ratio was 40% in distinguishing PCa from BPH. The fPSA/tPSA ratio allowed the discrimination of PCa from BPH with satisfactory sensitivity and specificity when considering patients less than 60 years of age (100% and 95%, respectively). PSA and PSM mRNA were positive in 1 and 7 of 13 EPD samples, 6 and 13 of 25 PCa samples, and 6 and 17 of 38 BPH samples. The Gleason score did not correlate with tPSA, the fPSA/tPSA ratio, PSA mRNA, or PSM mRNA.

CONCLUSIONS

The serum determination of the fPSA/tPSA ratio is an excellent index of PCa for subjects younger than 60 years of age; the clinical utility of PSA mRNA identification in circulating cells needs to be validated by large follow-up studies, and the analysis of PSM mRNA seems to be of no clinical interest.

Detection of extraprostatic prostate cells utilizing reverse transcription-polymerase chain reaction

This article reviews the utility of reverse transcription-polymerase chain reaction (RT-PCR) in prostate cancer. RT-PCR aims to detect occult micrometastases in non-prostatic sites. Due to its exquisite analytical sensitivity, RT-PCR is able to amplify and detect even low-level, prostate-specific messages present at these extraprostatic sites. In recent years, a fair amount of data on the clinical utility of the technique had been reported. The target tissues under investigation are peripheral blood, bone marrow aspirate, and lymph nodes. Favorite markers of choice are prostate-specific antigen (PSA), prostate-specific membrane antigen (PSMA), and human glandular kallikrein-2 (hK2). False positives among negative controls are low. For the most part, RT-PCR is inadequate in detecting tumor cells in the peripheral blood from patients who are known to have metastatic prostate cancer. All studies showed that RT-PCR could detect PSA, PSMA or hK2 mRNAs in the circulation of patients who have organ-confined or extraprostatic disease. Most studies showed that RT-PCR utilizing current markers could not be used as a prospective test to diagnose prostate cancer. However, a few studies also showed that the detection rate could be predictive and sensitive enough to differentiate patients with organ-confined disease from those with extraprostatic disease. Data from PSA- or PSMA-RT-PCR using lymph nodes as the tissue source is more encouraging. RT-PCR was able to detect PSA and/or PSMA positive samples that have not been detected by conventional pathology.

Prostate-specific membrane antigen (PSMA): current benefits and future value

We will review the evolution, benefits, and limitations of PSMA testing in the past, as well as its current and future value. Prostate cancer has been the most frequently diagnosed cancer and the second leading cause of cancer death in men in the United States. It has a wide spectrum of biological behavior between latent (indolent) and progressive (aggressive). Further identification of prostate-specific membrane antigen (PSMA) as a prognostic proliferation marker may enhance our understanding of the types of prostate cancer. A review of PSMA testing in the past as well as currently was conducted. Studies were reviewed that deal with detection of PSMA in serum and seminal fluid, reverse transcriptase-polymerase chain reaction (RT-PCR), immunoscintigraphy, and immunohistochemical assays. PSMA is expressed primarily in benign and cancerous prostatic epithelial cells. It is up-regulated in hormone resistant states, and in metastatic situations or other clinical situations where there is tumor recurrence or extension. Based on current results, PSMA detected in the serum by western blotting can assist in the identification, staging, and monitoring of metastatic prostate cancer. In addition, PSMA shows a promising role in directed imaging and therapy of recurrent or metastatic disease.

The detection of prostate cells by the reverse transcription-polymerase chain reaction in the circulation of patients undergoing transurethral resection of the prostate

OBJECTIVE

To determine whether prostate cells are disseminated into the circulation of patients after transurethral resection of the prostate (TURP), as assessed by a reverse transcription-polymerase chain reaction (RT-PCR) assay for prostate specific antigen (PSA) mRNA.

PATIENTS AND METHODS

Fifty-one patients, comprising 34 with benign prostatic hyperplasia (BPH) and 17 with prostate cancer who were undergoing routine TURP, had blood samples taken before and 30 min after surgery. The blood mononuclear cell layer was isolated by density-gradient centrifugation and total RNA extracted. Complementary DNA was synthesized by RT of the RNA. The target PSA sequence was amplified by PCR with specific PSA primers and the product detected on agarose-gel electrophoresis with ethidium bromide staining.

RESULTS

Five patients (all with prostate cancer) were positive on PSA RT-PCR before surgery and remained positive after TURP. Of the remaining 46 patients, five (11%; three with BPH and two with cancer) changed from a negative to a positive result after TURP.

CONCLUSION

In a proportion of patients TURP causes the dissemination of prostate cells into the circulation which are then detectable by RT-PCR of PSA mRNA.

Blood-based reverse transcriptase polymerase chain reaction assays for prostatic specific antigen: long term follow-up confirms the potential utility of this assay in identifying patients more likely to have biochemical recurrence (rising PSA) following radical prostatectomy

Reverse transcriptase polymerase chain reaction (RT-PCR) assay is a sensitive technique to detect circulating cells expressing prostate-specific antigen (PSA) in blood or bone marrow from patients with prostate cancer. When applied to prostate cancer patients at our institution, this technique identifies those patients with a greater likelihood of extra-prostatic disease. We evaluated RT-PCR PSA as a predictor of PSA recurrence and compared it with pre-operative (serum PSA, digital rectal examination, Gleason score on biopsy) and post-operative parameters (pathological findings). Three hundred nineteen men scheduled for radical prostatectomy had an enhanced RT-PCR PSA assay before surgery. The enhanced RT-PCR PSA protocol has been previously described. PSA recurrence was defined as any serum PSA value above 0.2 microgram/l. Forty-six patients had PSA recurrence. The mean follow-up was 25.4 months. Recurrence free survival was 53% for patients with positive RT-PCR PSA vs. 84% if RT-PCR PSA was negative. By using multivariate analyses, RT-PCR PSA status was not an independent predictor of PSA recurrence compared to pathological stage pT3, Gleason score on prostate specimen and serum PSA. If only pre-operative parameters were studied, serum PSA and RT-PCR PSA status were 2 independent pre-operative predictors of PSA recurrence compared with Gleason score on biopsy and digital rectal examination. Int. J. Cancer (Pred. Oncol.) 84:360-364, 1999.

Preoperative nested reverse transcription-polymerase chain reaction for prostate specific membrane antigen predicts biochemical recurrence after radical prostatectomy

OBJECTIVE

To assess the utility of the nested reverse transcription-polymerase chain reaction (RT-PCR) method for measuring prostate specific membrane antigen (PSM) and prostate specific antigen (PSA) in predicting serum PSA recurrence after radical prostatectomy.

PATIENTS AND METHODS

Nested RT-PCRs for PSM and PSA were used in 40 patients who subsequently underwent radical prostatectomy. The accuracy of the RT-PCR assays in predicting PSA failure was compared with those for the preoperative serum PSA level, Gleason score and final pathological staging. The patients were monitored using a PSA assay (Tandem-R, Hybritech, San Diego, CA) at 3 weeks after radical prostatectomy and every 2 months thereafter. Biochemical recurrence was defined as a serum PSA level of >/=0.4 ng/mL.

RESULTS

Statistical analysis indicated that the nested RT-PCR assay for PSM was the most accurate preoperative predictor of potential surgical failure (PCR-PSM, P<0.001; PCR-PSA, P=0.018; serum PSA level, P=0.149; Gleason score P=0.388, by Fisher's exact probability test). Biochemical recurrence was evaluated in relation to these methods during a mean (range) follow-up of 16.7 (6-35) months. Of the 40 patients, eight (20%, one with organ-confined cancer and seven with extraprostatic extension of cancer) developed biochemical recurrence. The Kaplan-Meier recurrence-free actuarial probability curves differed significantly between patients with positive and those with negative results for the preoperative nested RT-PCR for PSM (P<0.01, generalized Wilcoxon's test). The nested RT-PCR for PSA, preoperative serum PSA value and Gleason score were not significant predictors of biochemical recurrence (P=0.16, 0.12 and 0.24, respectively).

CONCLUSIONS

The nested RT-PCR for PSM was the best preoperative predictor of biochemical recurrence among the factors examined.

Characterization of the enzymatic activity of PSM: comparison with brain NAALADase

BACKGROUND

The prostate cancer marker prostate-specific membrane antigen (PSM) is highly homologous to the brain enzyme N-acetylated alpha-linked acidic dipeptidase (NAALADase). NAALADase is known to cleave terminal carboxy glutamates from both the neuronal peptide N-acetylaspartylglutamate (NAAG) and folate polyglutamate. In this report, we compare the NAAG hydrolyzing activity of NAALADase and the prostate enzyme PSM.

METHODS

Using a NAAG hydrolytic radioenzymatic assay, we compared the pharmacological and kinetic properties of the brain and prostate enzymes.

RESULTS

Eight normal prostate tissues from different species exhibited NAAG hydrolyzing activity. Among 14 cancer cell lines examined, activity was observed in human LNCaP, PC-82, and rat Dunning G and AT-1 cells. Brain exhibited membrane-localized activity exclusively, while the prostate enzyme had activity in both membrane and cytosolic fractions. The only observed pharmacological difference was the sensitivity to their putative substrates, folate polyglutamate and NAAG. Kinetically, the soluble form of the prostate enzyme had two catalytic sites, while the membrane-bound form exhibited single site kinetics with a lower Vmax than the brain enzyme, which may suggest a less active hydrolase in the prostate.

CONCLUSIONS

The brain enzyme NAALADase and the prostate enzyme PSM are remarkably similar. The importance of the differences in substrate specificities and kinetic parameters remains to be elucidated.

Molecular expression of PSMA mRNA and protein in primary renal tumors

Human prostate-specific membrane antigen (PSMA), a 100-kDa integral transmembrane glycoprotein, is considered to be a highly specific marker of the prostate gland, and has successfully been used as a marker of circulating prostatic epithelial cells. Extended PSMA homology has been demonstrated with a cDNA found in rat cerebral and renal tissues. In this study, we aimed to evaluate the expression of PSMA mRNA in a variety of human renal cancer tissues (n = 20) and cell lines (n = 12). Using reverse transcriptase-polymerase chain reaction, DNA sequencing, blottings, and specific anti-PSMA labelling with CYT 351 antibody, we identified PSMA mRNA and protein in normal and in neoplastic renal tissue. The sequence of the polymerase-chain-reaction products is identical to that of PSMA cDNA derived from prostate tissue. Immunological staining with the CYT 351 reveals that PSMA is expressed mainly in tubular cells. Since PSMA does not appear to be restricted to prostatic tissue, this novel biomarker may prove useful in the staging of renal cancer and in the search for the hematogenous spread of renal cells.

Prostate-specific membrane antigen-derived primers in a nested reverse transcription polymerase chain reaction for detecting prostatic cancer cells

The detection of prostate-specific membrane antigen (PSM) mRNA in the peripheral blood of prostate cancer patients by a nested reverse transcriptase-polymerase chain reaction (RT-PCR) assay is a useful and sensitive method for the identification of small foci of metastatic lesions. In this study, a nested RT-PCR assay was performed using the two different PSM-derived oligonucleotide primer sets reported by Israeli et al. and Loric et al. (termed PSM primers-1 and primers-2, respectively, in this report), and the differences in the specificity and sensitivity of these primer sets for detecting prostate cancer cells in the blood are discussed. The PCR assay using PSM primers-1 showed DNA bands for 4 of 7 cases of metastatic prostate cancer and amplified the untreated genomic DNA, while that using PSM primers-2 showed 6 bands without the amplification of the genomic DNA. In conclusion, PSM primers-2 is superior to PSM primers-1 for the detection of PSM mRNA in the peripheral blood of prostate cancer patients.

The use of nested RT-PCR of prostate-specific membrane antigen in blood cells: implications for the detection of haematogenous neoplastic cells in patients with prostate adenocarcinoma

The aim of this study was to determine the presence of haematogenous neoplastic cells in patients with prostate cancer. Circulating prostate cells can be detected in cancer patients by using a nested-reverse transcriptase-polymerase chain reaction assay (RT-PCR), for prostate-specific membrane (PSM) antigen mRNA. This sensitive nested RT-PCR assay may play a crucial role in the administration of adjuvant therapy of patients with prostate adenocarcinoma.

De novo expression of CD44 in prostate carcinoma is correlated with systemic dissemination of prostate cancer

AIMS

To evaluate the role of CD44 in early steps in the development of prostate cancer, and to assess the biological significance of preneoplastic lesions in prostate cancer.

METHODS

38 patients with clinically localised prostate cancer were studied. The standard form of CD44 (CD44H) and v6 isoform expressions were semiquantitatively evaluated on paraffin embedded tumour tissue by immunohistochemistry. Disseminated prostatic cells were detected by prostate specific membrane antigen reverse transcriptase polymerase chain reaction in the blood of each patient before radical prostatectomy.

RESULTS

In normal or benign prostate glands, only basal cells showed CD44H and v6 labelling. Fourteen of the 38 prostate cancers (37%) had CD44H membranous staining of prostatic tumour cells. In 18 patients (47%), circulating prostatic cells were detected in blood before surgery. Although no correlation between the expression of CD44 and the Gleason score or staging was observed, a significant correlation was found between the expression of CD44H by tumour cells and prostatic cell blood dissemination (p = 0.04). In 28 cases, foci of prostatic intraepithelial neoplasia were observed, and nine had CD44H immunostaining.

CONCLUSIONS

De novo expression of CD44 by prostatic tumour cells is associated with systemic dissemination of prostate cells independently of pathological criteria.

Detection and clearance of prostate cells subsequent to ultrasound-guided needle biopsy as determined by multiplex nested reverse transcription polymerase chain reaction assay

OBJECTIVES

To determine if circulating prostate cells are detectable subsequent to transrectal ultrasound (TRUS)-guided biopsy, and if so, whether cells remain in circulation for up to 4 weeks.

METHODS

Blood samples were drawn from 90 patients with elevated serum prostate-specific antigen (PSA) levels and/or abnormal digital rectal examination. Two samples were drawn from all patients immediately prior to TRUS and 30 minutes postbiopsy. Blood samples were also obtained 1 week postbiopsy from 83 patients, and 1 month postbiopsy from 61 patients. Multiplex nested reverse transcription polymerase chain reaction assay (RT-PCR) for PSA and prostate-specific membrane antigen (PSM) was performed on total ribonucleic acid (RNA) from each sample. Results were reported as positive if at least one of the targets was detected.

RESULTS

Of 45 patients with biopsy-proven adenocarcinoma, 22 were RT-PCR positive prebiopsy and all remained positive 30 minutes postbiopsy. Of 23 patients with adenocarcinoma who were RT-PCR negative prebiopsy, 5 (22%) converted to positive 30 minutes postbiopsy (P < 0.001). Four of these 5 patients returned to negative after 1 week or 1 month. Of 45 patients without cancer at biopsy, 32 were RT-PCR negative prebiopsy and 6 (19%) converted to positive 30 minutes postbiopsy (P < 0.001). Although four of six available samples were still positive at 1 week, all four samples available 1 month postbiopsy were negative.

CONCLUSIONS

Detection of circulating prostate cells subsequent to biopsy occurred in 11 of 55 (20%) previously RT-PCR negative patients, a proportion twice that reported in the literature. We attribute this higher proportion to the simultaneous detection of PSA and PSM mRNA in our multiplex assay. Conversion rates were similar in patients regardless of biopsy result. Testing of serial postbiopsy blood demonstrates clearing of these cells by 4 weeks in most patients.

Molecular staging of prostate cancer: comparison of nested reverse transcription polymerase chain reaction assay using prostate specific antigen versus prostate specific membrane antigen as primer

BACKGROUND

We examined the utility for prostate cancer staging of nested reverse transcription polymerase chain reaction (RT-PCR) using either prostate specific antigen (PSA) or prostate specific membrane antigen (PSM) as primer.

METHODS

LNCaP cells were used for the in vitro quantification of RT-PCR. RT-PCR was performed on the peripheral blood of 105 control subjects and 63 patients with prostate cancer (32 who eventually underwent radical prostatectomy and 31 with clinical stage D2 cancer).

RESULTS

The nested RT-PCR for the PSA and PSM primers was able to detect 1 LNCaP cell per 10(6) leukemia (K562) cells. None of the control subjects was found positive for the presence of prostate cancer cells by nested RT-PCR. In the 32-patient surgery group, the results of nested RT-PCR were significantly correlated with the pathologic stage of the cancer when using PSM primers (P=2.00 x 10(-3) by Kendall's correlation test) but not when using PSA primers (P=0.06). Extraprostatic extension was significantly more closely correlated with positive PSM nested RT-PCR results (P=0.012 by Fisher's exact probability test) than with positive results of PSA, nested RT-PCR, digital rectal examination, CT imaging, level of serum PSA or Gleason score. In the untreated stage D2 patients, the positive result rate of PSM nested RT-PCR was significantly higher than that of PSA nested RT-PCR (P=0.025 by McNemar test).

CONCLUSION

Nested RT-PCR using PSM primers appears to predict the prostate cancer stage more accurately than does nested RT-PCR using PSA primers or conventional clinical staging modalities.

Utilization of polymerase chain reaction technology in the detection of solid tumors

BACKGROUND

Most cancer detection tests currently performed are based on either antibody assays to a marker protein with altered expression in cancer patients or on imaging studies to identify characteristic lesions. Generally, for a positive result, these detection assays require that a tumor have a significant volume of cancer cells. Advances in diagnostic techniques and technology may allow for cancer detection at earlier stages, when the tumor burden is smaller and potentially more curable. The molecular techniques of polymerase chain reaction (PCR) and reverse transcriptase PCR (RT-PCR) are highly sensitive methods for detecting a small number of cancer cells. Over the past few years, numerous clinical studies have used PCR techniques to detect physical alterations of genes, such as mutations, deletions, translocations and amplification, the presence of oncogenic viruses, and the expression of genes specific to tissue, cancer, and metastasis. The current status of PCR as a method for detecting marker genes in the management of solid tumors is reviewed.

METHODS

A review of the literature on the clinical utility of PCR and RT-PCR in the detection of solid tumor micrometastasis was conducted.

RESULTS

Amplification by PCR is a highly sensitive method to determine gene expression. A single cell expressing a tumor marker among 10-100 million lymphocytes can be detected by the PCR assay. This approach has been used to detect tumor cells in approximately 18 different solid tumor types, with melanoma and carcinoma of the breast and prostate the most widely investigated to date. PCR-based assays have been used to detect cancer cells in biopsies of solid tissue, lymph nodes, bone marrow, peripheral blood, and other body fluids. Several studies have reported a high specificity and sensitivity of tumor marker detection and a high correlation between PCR results and the presence of metastatic disease. However, in a few studies, PCR assays have not consistently demonstrated a higher sensitivity and specificity of detection than traditional modalities for many types of cancer. There has been a wide range in sensitivity and specificity among the studies, which may be partly attributed to the lack of uniformity among the PCR protocols used in different studies.

CONCLUSIONS

PCR can detect tumor marker-expressing cells that are otherwise undetectable by other means in patients with localized or metastatic cancer. Reports from various study groups have lacked uniformity in their protocols, and this has prevented adequate comparison. The clinical utility of this assay as a tool for the prognosis and management of cancer patients remains and area of active investigation. PCR is a powerful tool in the study of the biology of cancer metastasis and will likely serve as a useful adjunct to clinical decision-making in the future.

Utilization of polymerase chain reaction technology in the detection of solid tumors

BACKGROUND

Most cancer detection tests currently performed are based on either antibody assays to a marker protein with altered expression in cancer patients or on imaging studies to identify characteristic lesions. Generally, for a positive result, these detection assays require that a tumor have a significant volume of cancer cells. Advances in diagnostic techniques and technology may allow for cancer detection at earlier stages, when the tumor burden is smaller and potentially more curable. The molecular techniques of polymerase chain reaction (PCR) and reverse transcriptase PCR (RT-PCR) are highly sensitive methods for detecting a small number of cancer cells. Over the past few years, numerous clinical studies have used PCR techniques to detect physical alterations of genes, such as mutations, deletions, translocations and amplification, the presence of oncogenic viruses, and the expression of genes specific to tissue, cancer, and metastasis. The current status of PCR as a method for detecting marker genes in the management of solid tumors is reviewed.

METHODS

A review of the literature on the clinical utility of PCR and RT-PCR in the detection of solid tumor micrometastasis was conducted.

RESULTS

Amplification by PCR is a highly sensitive method to determine gene expression. A single cell expressing a tumor marker among 10-100 million lymphocytes can be detected by the PCR assay. This approach has been used to detect tumor cells in approximately 18 different solid tumor types, with melanoma and carcinoma of the breast and prostate the most widely investigated to date. PCR-based assays have been used to detect cancer cells in biopsies of solid tissue, lymph nodes, bone marrow, peripheral blood, and other body fluids. Several studies have reported a high specificity and sensitivity of tumor marker detection and a high correlation between PCR results and the presence of metastatic disease. However, in a few studies, PCR assays have not consistently demonstrated a higher sensitivity and specificity of detection than traditional modalities for many types of cancer. There has been a wide range in sensitivity and specificity among the studies, which may be partly attributed to the lack of uniformity among the PCR protocols used in different studies.

CONCLUSIONS

PCR can detect tumor marker-expressing cells that are otherwise undetectable by other means in patients with localized or metastatic cancer. Reports from various study groups have lacked uniformity in their protocols, and this has prevented adequate comparison. The clinical utility of this assay as a tool for the prognosis and management of cancer patients remains and area of active investigation. PCR is a powerful tool in the study of the biology of cancer metastasis and will likely serve as a useful adjunct to clinical decision-making in the future.

Clinical usefulness of RT-PCR detection of hematogenous prostate cancer spread

Understaging is commonly associated with therapeutic failure of surgical intervention in apparently localized prostate cancers. Methods that specifically detect prostate cancer cells in the circulation may be able to identify metastatic cancers and thus aid in the selection of the most adequate therapy. The high sensitivity and specificity of the reverse transcriptase-polymerase chain reaction (RT-PCR) encouraged various groups to investigate the mRNA expression of prostate-specific markers in the peripheral blood of patients with prostate cancer. However, probably due to methodological differences, many contradictory results have been obtained with the markers studied so far: prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSM). For this reason, clinical decisions should not be based yet on RT-PCR results. Future research and long-term follow-up on the patients may point out whether RT-PCR assays, following appropriate standardization, will have an additive value in prostate cancer staging and in prediction of tumor progression.

Quantitative reverse transcriptase-polymerase chain reaction for prostate-specific antigen mRNA

OBJECTIVE

To develop a quantitative reverse transcriptase-polymerase chain reaction assay for monitoring the prostate-specific antigen (PSA) mRNA.

METHODS

PSA mRNA is amplified, in parallel, with the mRNA of beta-actin, a housekeeping gene. The ratio of the amplification products obtained reflects the relative amount of PSA mRNA with respect to actin mRNA. During PCR, digoxigenin-dUTP is incorporated in the amplified sequences. The PCR products are analyzed separately by time-resolved immunofluorometric hybridization assays, using specific probes immobilized in microtiter wells. The hybrids are reacted with alkaline phosphatase-labeled anti-digoxigenin antibody. The phosphate ester of fluorosalicylate is used as a substrate. The fluorosalicylate produced forms a fluorescent complex with Tb(3+)-EDTA which is measured by time-resolved fluorometry.

RESULTS

The hybridization assays for both PSA and actin amplification products show linearity in the range of 1.4-110 pmol/L. The exponential phase of PCR amplification extends up to 200,000 and 100,000 PSA and actin cDNA molecules, respectively. We prepared mixtures containing various numbers of LNCaP cells in one million cells that do not express PSA and used them as samples in the proposed assay. The ratio of the fluorescence values obtained after analysis of PSA and actin amplification products is linearly related to the number of LNCaP cells in the range of 20 to 3000 cells. Reproducibility studies demonstrate %CVs for the fluorescence ratios of 14.7, 11.8, and 12.2 when samples containing 150, 300 and 1600 LNCaP cells were analyzed (n = 4).

CONCLUSIONS

A quantitative analytical methodology is provided for monitoring PSA mRNA. The assay is expected to be beneficial in the study of prostate cancer spread.