How sensitive is a prostate-specific antigen measurement? How sensitive does it need to be?

Application of Single-Domain Antibodies ("Nanobodies") to Laboratory Diagnosis

Antibodies have proven to be central in the development of diagnostic methods over decades, moving from polyclonal antibodies to the milestone development of monoclonal antibodies. Although monoclonal antibodies play a valuable role in diagnosis, their production is technically demanding and can be expensive. The large size of monoclonal antibodies (150 kDa) makes their re-engineering using recombinant methods a challenge. Single-domain antibodies, such as “nanobodies,” are a relatively new class of diagnostic probes that originated serendipitously during the assay of camel serum. The immune system of the camelid family (camels, llamas, and alpacas) has evolved uniquely to produce heavy-chain antibodies that contain a single monomeric variable antibody domain in a smaller functional unit of 12–15 kDa. Interestingly, the same biological phenomenon is observed in sharks. Since a single-domain antibody molecule is smaller than a conventional mammalian antibody, recombinant engineering and protein expression in vitro using bacterial production systems are much simpler. The entire gene encoding such an antibody can be cloned and expressed in vitro. Single-domain antibodies are very stable and heat-resistant, and hence do not require cold storage, especially when incorporated into a diagnostic kit. Their simple genetic structure allows easy re-engineering of the protein to introduce new antigen-binding characteristics or attach labels. Here, we review the applications of single-domain antibodies in laboratory diagnosis and discuss the future potential in this area.

Microfluidic Device Directly Fabricated on Screen-Printed Electrodes for Ultrasensitive Electrochemical Sensing of PSA

How to fabricate scale low-cost microfluidic device for detection of biomarkers owns a great requirement. Herein, it is for the first time reported that a new microfluidic device based on bonding polydimethylsiloxane microfluidic channels onto the substrate of a screen-printed electrode with coating glass solution was fabricated for electrochemical sensing of prostate-specific antigen (PSA). Compared to traditional microfabrication processes, this method is simple, fast, low cost, and also suitable for mass production. The prepared screen-printed electrode-based microfluidic device (CASPE-MFD) was used for the detection of the PSA in human serum. The prepared CASPE-MFD had a detection limit of 0.84 pg/mL (25.8 fM) and a good linearity with PSA concentration ranging from 0.001 to 10 ng/mL, which showed a great promise platform toward the development of miniaturized, low-cost electrochemical microfluidic device for use in human health, environmental monitoring, and other applications.

A Joint Model for the Kinetics of CTC Count and PSA Concentration During Treatment in Metastatic Castration-Resistant Prostate Cancer

Assessment of treatment efficacy in metastatic castration-resistant prostate cancer (mCRPC) is limited by frequent nonmeasurable bone metastases. The count of circulating tumor cells (CTCs) is a promising surrogate marker that may replace the widely used prostate-specific antigen (PSA). The purpose of this study was to quantify the dynamic relationships between the longitudinal kinetics of these markers during treatment in patients with mCRPC. Data from 223 patients with mCRPC treated by chemotherapy and/or hormonotherapy were analyzed for up to 6 months of treatment. A semimechanistic model was built, combining the following several pharmacometric advanced features: (1) Kinetic-Pharmacodynamic (K-PD) compartments for treatments (chemotherapy and hormonotherapy); (2) a latent variable linking both marker kinetics; (3) modeling of CTC kinetics with a cell lifespan model; and (4) a negative binomial distribution for the CTC random sampling. Linked with survival, this model would potentially be useful for predicting treatment efficacy during drug development or for therapeutic adjustment in treated patients.

Fifth-generation digital immunoassay for prostate-specific antigen by single molecule array technology

BACKGROUND

Measurement of prostate-specific antigen (PSA) in prostate cancer patients following radical prostatectomy (RP) has been hindered by the limit of quantification of available assays. Because radical prostatectomy removes the tissue responsible for PSA production, postsurgical PSA is typically undetectable with current assay methods. Evidence suggests, however, that more sensitive determination of PSA status following RP could improve assessment of patient prognosis and response to treatment and better target secondary therapy for those who may benefit most. We developed an investigational digital immunoassay with a limit of quantification 2 logs lower than current ultrasensitive third-generation PSA assays.

METHODS

We developed reagents for a bead-based ELISA for use with high-density arrays of femtoliter-volume wells. Anti-PSA capture beads with immunocomplexes and associated enzyme labels were singulated within the wells of the arrays and interrogated for the presence of enzymatic product. We characterized analytical performance, compared its accuracy with a commercially available test, and analyzed longitudinal serum samples from a pilot study of 33 RP patients.

RESULTS

The assay exhibited a functional sensitivity (20% interassay CV) <0.05 pg/mL, total imprecision <10% from 1 to 50 pg/mL, and excellent agreement with the comparator method. All RP samples were well within the assay measurement capability. PSA concentrations following surgery were found to be predictive of prostate cancer recurrence risk over 5 years.

CONCLUSIONS

The robust 2-log improvement in limit of quantification relative to current ultrasensitive assays and the validated analytical performance of the assay allow for accurate assessment of PSA status after RP.

Clinical evaluation of a novel method for the measurement of prostate-specific antigen, AccuPSA(TM) , as a predictor of 5-year biochemical recurrence-free survival after radical prostatectomy: results of a pilot study

Study Type - Diagnostic (validating cohort) Level of Evidence 1b What's known on the subject? and What does the study add? Nadir Ultrasensitive PSA levels has some value for predicting BCR following RD. AccuPSA assays lower limit of PSA quantification of <0.01 pg/ml greatly enhances sensitivity and specificity of nadir PSA to predict BCR following RP. Our pilot study shows an AccuPSA of 3 pg/ml has a sensitory and specificity of 100% and 75% respectively for predicting 5 year BCR following RP. OBJECTIVES • To conduct a proof of concept study to evaluate a novel digital single molecule immunoassay (AccuPSA(TM) ) that detects prostate-specific antigen (PSA) a thousandfold more sensitively than current PSA detection methods. • To determine the ability of the AccuPSA(TM) assay to predict 5-year biochemical recurrence (BCR)-free survival after radical prostatectomy (RP). PATIENTS AND METHODS • A total of 31 frozen serum specimens were obtained from specimen logs maintained at New York University Langone Medical Center and the Johns Hopkins University School of Medicine on men who had undergone RP. Those men without evidence of BCR had a minimum of 5 years' PSA follow-up. • In all cases, preoperative and pathological information were available, as was a serum specimen 3-6 months after RP, with a PSA level of <0.1 ng/mL measured by conventional PSA methods at the time of serum collection. • Specimens were tested using the AccuPSA(TM) method. • A Cox proportional hazard model and Kaplan-Meier analysis were used to determine whether AccuPSA(TM) predicted the risk of BCR. RESULTS • Overall, 11/31 (35.5%) men developed BCR. • Mean AccuPSA(TM) nadir levels were significantly different (P < 0.001) between the non-BCR group (2.27 pg/mL) and the BCR group (46.99 pg/mL). • Using a multivariate Cox proportional hazard model, AccuPSA(TM) nadir level was a significant predictor of BCR-free survival (P < 0.01). • Kaplan-Meier analysis of up to 5 years follow-up showed that 100% of men with AccuPSA(TM) nadir values <3 pg/mL did not develop BCR, whereas 62.5% of men with values >3 pg/mL developed BCR (P= 0.00024). • The sensitivity, specificity, positive predictive value and negative predictive value of the AccuPSA(TM) method was 100%, 75%, 69% and 100%, respectively. CONCLUSIONS • AccuPSA(TM) assay predicts 5-year BCR- free survival after RP. • Identifying a reliable predictor of BCR soon after RP has important implications for frequency of PSA testing, selection of candidates for adjuvant therapy, and reassuring a large subset of men that they are not at risk of recurrence. • Larger studies are needed to validate these findings.

Role of glutathione-S-transferase P1 hypermethylation in molecular detection of prostate cancer

AIM

The aim of this study was to evaluate the diagnostic potential of the quantification of glutathione-S-transferase P1 (GSTP1) gene hypermethylation in molecular detection of prostate cancer in tissue biopsies.

METHODS

One hundred fourteen male patients were enrolled in the study; 44 patients with histopathologically confirmed prostate adenocarcinoma, 20 patients with variable degrees of prostate intraepithelial neoplasia, and 50 with benign prostatic hyperplasia, who served as a control group. Real-time quantitative methylation-specific polymerase chain reaction was used for assessment of methylation of the promoter region of the GSTP1 gene.

RESULTS

Methylation of the GSTP1 promotor was detected in 24% of patients with benign prostatic hyperplasia, 60% of patients with prostate intraepithelial neoplasia, and in 86.3% of prostate adenocarcinoma patients. A statistically significant difference in the GSTP1/MYOD1 (myogenic differentiation 1gene) methylation ratios among the three groups was observed (p=0.0001). At the cutoff value of 9, GSTP1/MYOD1 methylation ratios showed sensitivity in the detection of prostate adenocarcinoma of 71.8% and specificity of 96%.

CONCLUSIONS

Methylation of the GSTP1 promotor is a common molecular alteration in prostate cancer that may be a useful adjunct to serum screening tests and digital rectal examination findings and the use of quantitative real-time methylation-specific polymerase chain reaction is a promising technique that often distinguishes malignant from nonmalignant prostate disease.

Single-molecule enzyme-linked immunosorbent assay detects serum proteins at subfemtomolar concentrations

The ability to detect single protein molecules in blood could accelerate the discovery and use of more sensitive diagnostic biomarkers. To detect low-abundance proteins in blood, we captured them on microscopic beads decorated with specific antibodies and then labeled the immunocomplexes (one or zero labeled target protein molecules per bead) with an enzymatic reporter capable of generating a fluorescent product. After isolating the beads in 50-fl reaction chambers designed to hold only a single bead, we used fluorescence imaging to detect single protein molecules. Our single-molecule enzyme-linked immunosorbent assay (digital ELISA) approach detected as few as approximately 10-20 enzyme-labeled complexes in 100 microl of sample (approximately 10(-19) M) and routinely allowed detection of clinically relevant proteins in serum at concentrations (<10(-15) M) much lower than conventional ELISA. Digital ELISA detected prostate-specific antigen (PSA) in sera from patients who had undergone radical prostatectomy at concentrations as low as 14 fg/ml (0.4 fM).

Nanoparticle-based bio-barcode assay redefines "undetectable" PSA and biochemical recurrence after radical prostatectomy

We report the development of a previously undescribed gold nanoparticle bio-barcode assay probe for the detection of prostate specific antigen (PSA) at 330 fg/mL, automation of the assay, and the results of a clinical pilot study designed to assess the ability of the assay to detect PSA in the serum of 18 men who have undergone radical prostatectomy for prostate cancer. Due to a lack of sensitivity, available PSA immunoassays are often not capable of detecting PSA in the serum of men after radical prostatectomy. This new bio-barcode PSA assay is approximately 300 times more sensitive than commercial immunoassays. Significantly, with the barcode assay, every patient in this cohort had a measurable serum PSA level after radical prostatectomy. Patients were separated into categories based on PSA levels as a function of time. One group of patients showed low levels of PSA with no significant increase with time and did not recur. Others showed, at some point postprostatectomy, rising PSA levels. The majority recurred. Therefore, this new ultrasensitive assay points to significant possible outcomes: (i) The ability to tell patients, who have undetectable PSA levels with conventional assays, but detectable and nonrising levels with the barcode assay, that their cancer will not recur. (ii) The ability to assign recurrence earlier because of the ability to measure increasing levels of PSA before conventional tools can make such assignments. (iii) The ability to use PSA levels that are not detectable with conventional assays to follow the response of patients to adjuvant or salvage therapies.

Dynamic contrast-enhanced MR imaging in the evaluation of patients with prostate cancer

Prostate cancer is a common tumor among men, with increasing diagnosis at an earlier stage and a lower volume of disease because of screening with prostate-specific antigen (PSA). The need for imaging of the prostate stems from a desire to optimize treatment strategy on a patient and tumor-specific level. The major goals of prostate imaging are (1) staging of known cancer, (2) determination of tumor aggressiveness, (3) diagnosis of cancer in patients who have elevated PSA but a negative biopsy, (4) treatment planning, and (5) the evaluation of therapy response. This article concentrates on the role of dynamic contrast-enhanced MR imaging in the evaluation of patients who have prostate cancer and how it might be used to help achieve the above goals. Various dynamic contrast enhancement approaches (quantitative/semiquantitative/qualitative, high temporal versus high spatial resolution) are summarized with reference to the relevant strengths and compromises of each approach.

Multimarker circulating DNA assay for assessing blood of prostate cancer patients

BACKGROUND

Prostate cancer (PCa) detection using serum-based prostate specific antigen (PSA) is limited by frequent false-positive and -negative results. Genetic aberrations such as allelic imbalance (AI) and epigenetic changes such as promoter hypermethylation have been detected in circulating DNA of cancer patients. We hypothesized that circulating multimarker DNA assays detecting both genetic and epigenetic markers in serum would be useful in assessing PCa patients.

METHODS

We assayed blood from healthy male donors (n = 40) and 83 patients with American Joint Cancer Committee (AJCC) stage I-IV PCa. DNA was assayed for AI of 6 genome microsatellites. We assessed methylation of RASSF1, RARB2, and GSTP1 using a methylation-specific PCR assay and analyzed the sensitivity of each assay for the detection of genetic or epigenetic changes in circulating DNA. The relation between circulating tumor-related DNA detection and prognostic factors was investigated.

RESULTS

The proportion of patients demonstrating AI for > or =1 marker was 47% (38 of 81 patients). Methylation biomarkers were detected in 24 of 83 patients (28%). By combining 2 DNA assays, the number of PCa patients positive for > or =1 methylated or LOH marker increased (52 of 83; 63%). The combined assays detected PCa in 15 of 24 patients (63%) with normal PSA concentrations. The combination of the DNA assays detected the presence of PCa regardless of AJCC stage or PSA concentration. Combination of the DNA and PSA assays gave 89% sensitivity.

CONCLUSIONS

This pilot study demonstrates that the combined circulating DNA multimarker assay identifies patients with PCa and may yield information independent of AJCC stage or PSA concentration.

Major inter-laboratory variations in PSA testing practices: results from national surveys in Ireland in 2006 and 2007

BACKGROUND

Ireland had the highest prostate cancer incidence in Europe in 2006. In that year, the National Cancer Forum (NCF) recommended against prostate specific antigen (PSA) testing for population-based screening.

AIMS

To investigate (1) PSA services and (2) impact of the NCF recommendation.

METHODS

Questionnaires were dispatched to biochemistry laboratories nationwide in 2006 and 2007.

RESULTS

All 55 laboratories responded in 2006; 33/36 (89%) responded in 2007. 36 laboratories measured total PSA (tPSA); 14 measured free PSA (fPSA). Laboratories with higher tPSA workload were more likely to measure fPSA (P = 0.024). A total of 15 laboratories used age-specific PSA ranges. In 2006, there were [382,000 tPSA and [48,000 fPSA tests costing an estimated euro 4,900,000. During 2006-2007 tPSA tests increased by 11%; fPSA tests decreased by 36%.

CONCLUSIONS

There is considerable inter-laboratory variation in PSA testing practices. Because of the potential clinical consequences, standardisation should be considered. Testing practice was unaffected by the NCF recommendation.