Standardization of two immunoassays for human glandular kallikrein 2

Clinical Perspective of Prostate Cancer

Prostate cancer is the most common noncutaneous cancer affecting men today. It largely affects men in the fifth and sixth decade of life. Screening for prostate cancer, though controversial, is still the only way to detect early prostate cancer. Multiple newer options such as blood tests and genetic markers are being used in the clinical domain today to improve cancer detection and avoid unnecessary biopsies. To date, biopsy of the prostate remains the only modality to stratify the grade of cancer. Significant improvements in the imaging technology have improved localizing and detecting the disease. Treatment of prostate cancer is stratified on the basis of the grade and volume of the disease. There are multiple treatment options involved in the management of prostate cancer. Treatment of localized prostate cancer still continues to have very high cure rates and long-term cancer-specific survival rates.

Molecular diagnosis of prostate cancer: are we up to age?

Prostate cancer (PCa), a highly heterogeneous disease, is the one of the leading cause of morbidity and mortality in the developed countries. Historically used biomarkers such as prostatic acid phosphatase (PAP), serum prostate-specific antigen (PSA), and its precursor have not stood the challenge of sensitivity and specificity. At present, there is need to re-evaluate the approach to diagnose and monitor PCa. To this end, molecular markers that can accurately identify men with PCa at an early stage, and those who would benefit from early therapeutic intervention, are the need of the hour. There has been unprecedented progress in the development of new PCa biomarkers through advancements in proteomics, tissue DNA and protein/RNA microarray, identification of microRNA, isolation of circulating tumor cells, and tumor immunohistochemistry. This review will examine the current status of prostate cancer biomarkers with emphasis on emerging biomarkers by evaluating their diagnostic and prognostic potentials.

Serological proteome analysis to identify systemic candidiasis patients in the intensive care unit: Analytical, diagnostic and prognostic validation of anti-Candida enolase antibodies on quantitative clinical platforms

Systemic candidiasis (SC) is associated with high morbidity and mortality, because it generally affects patients with severe underlying diseases and its diagnosis is difficult and often delayed, resulting in delayed therapy. We used serological proteome analysis to screen serum anti-Candida IgG antibody-reactivity profiles in 24 patients under intensive care, 12 of which had confirmed SC (fungal cultures), and in 12 healthy subjects. A total of 15 immunogenic proteins from Candida albicans protoplast lysates were differentially immunorecognized by serum IgG antibodies from SC patients compared to controls. Two-way hierarchical clustering and principal-component analyses of these antibody-reactivity patterns accurately differentiated SC patients from controls. Anti-Eno1p IgG antibodies were found to be present at high abundance in SC patients and be an important molecular fingerprint in serum for SC diagnosis. Differential anti-Eno1p IgG antibody reactivity was further validated by a tag capture ELISA and a Western blot assay in 45 SC patients and 118 non-SC subjects. Both quantitative assays provided comparable analytical, diagnostic and prognostic performances, and verified initial proteomic-profiling results. If confirmed in prospective cohort studies, these anti-Eno1p IgG antibodies might be useful for SC diagnosis. However, these, at least as measured by these clinical platforms, appear to have limited prognostic value in SC patients.

A panel of kallikrein markers can reduce unnecessary biopsy for prostate cancer: data from the European Randomized Study of Prostate Cancer Screening in Göteborg, Sweden

BACKGROUND

Prostate-specific antigen (PSA) is widely used to detect prostate cancer. The low positive predictive value of elevated PSA results in large numbers of unnecessary prostate biopsies. We set out to determine whether a multivariable model including four kallikrein forms (total, free, and intact PSA, and human kallikrein 2 (hK2)) could predict prostate biopsy outcome in previously unscreened men with elevated total PSA.

METHODS

The study cohort comprised 740 men in Göteborg, Sweden, undergoing biopsy during the first round of the European Randomized study of Screening for Prostate Cancer. We calculated the area-under-the-curve (AUC) for predicting prostate cancer at biopsy. AUCs for a model including age and PSA (the 'laboratory' model) and age, PSA and digital rectal exam (the 'clinical' model) were compared with those for models that also included additional kallikreins.

RESULTS

Addition of free and intact PSA and hK2 improved AUC from 0.68 to 0.83 and from 0.72 to 0.84, for the laboratory and clinical models respectively. Using a 20% risk of prostate cancer as the threshold for biopsy would have reduced the number of biopsies by 424 (57%) and missed only 31 out of 152 low-grade and 3 out of 40 high-grade cancers.

CONCLUSION

Multiple kallikrein forms measured in blood can predict the result of biopsy in previously unscreened men with elevated PSA. A multivariable model can determine which men should be advised to undergo biopsy and which might be advised to continue screening, but defer biopsy until there was stronger evidence of malignancy.

Reliability of antibodies to Candida methionine synthase for diagnosis, prognosis and risk stratification in systemic candidiasis: A generic strategy for the prototype development phase of proteomic markers

To be able to diagnose systemic candidiasis (SC) and to predict outcomes in SC patients are still challenging tasks for physicians. Previous proteomic studies suggest that anti-Candida methionine synthase (Met6p) IgG antibodies may be a candidate marker for SC. To evaluate their reliability for diagnosis, prognosis and risk stratification in SC, we developed a generic prototype strategy for their measurement in SC. Receiver-operating-characteristic curve analyses revealed a high diagnostic accuracy for this prototype format, which was slightly better to that for the widely used Western blot assays. Multivariate logistic-regression models showed a positive association between serum anti-Met6p IgG antibody levels and SC risk that was independent from established SC risk factors and other baseline variables. After adjusting for and stratifying according to known prognostic factors, a significant trend toward a lower two-month mortality risk with increasing levels was evidenced in SC patients at presentation. We conclude that these antibodies may be useful in discriminating SC from non-SC patients and determining risk stratification in SC. These may also confer protection against SC and be valuable for the design of future immunotherapies. Furthermore, our prototype format has the potential to make impact on other infectious diseases, cancers, allergies or autoimmune disorders.

Intact free prostate-specific antigen and free and total human glandular kallikrein 2. Elimination of assay interference by enzymatic digestion of antibodies to F(ab')2 fragments

Various blood constituents can interfere with immunoassays, usually by binding the Fc portion of antibodies. Our previously developed assays for intact free prostate-specific antigen (PSA), free human kallikrein 2 (hK2), and total hK2 frequently yielded falsely high results despite including an excess of scavenger antibodies. We investigated whether this interference could be eliminated by replacing monoclonal capture or tracer antibodies with F(ab')2 or recombinant Fab fragments. Female heparin plasma samples (n = 1092), which should have negligible PSA and hK2, and male samples (n = 957) were analyzed to identify samples manifesting interference, which then were used to optimize protocols for the immunoassays. We compared original assays (monoclonal antibodies) versus optimized assays (F(ab')2 fragments: denatured mouse IgG added as scavenger) using another set of EDTA plasma (n = 113), heparin plasma (n = 160), and serum samples (n = 171). With the original assays, the frequency of falsely elevated hK2 and intact free PSA was 15 and 13%, respectively. The optimized assays eliminated 70-85% of these falsely elevated results and importantly reduced the magnitude in the remainder. F(ab')2 fragmentation was the most important factor in reducing interference. The optimized intact free PSA, free hK2, and total hK2 assays manifested high accuracy close to the lower limit of detection.

Serum human glandular kallikrein 2 (hK2) for distinguishing stage and grade of prostate cancer

BACKGROUND

Human glandular kallikrein (hK2) has been shown to add important information regarding the early detection and staging of prostate cancer. Preliminary analysis pointed out that hK2 may discriminate between pT2 and pT3 tumors, and that hK2 may predict Gleason grade 4/5 cancer volume, better than prostate-specific antigen (PSA) or percent free PSA (%fPSA). We investigated the role of hK2 serum values for predicting pathological stage, grade and Gleason score.

METHODS

Prostate-specific antigen, free PSA and hK2 were measured on 222 untreated prostate cancer patients who had received radical prostatectomy at the Charité Hospital, Berlin, Germany. Pathological work up revealed pT2-cancer in 111 patients and pT3-cancer in 111 patients. Grade 2 was found in 118 patients whereas grade 3 tumors were found in 104 patients.

RESULTS

For pT2 and pT3 patients, the %fPSA (P=0.006), the ratios hK2/fPSA (P=0.08) and hK2xtPSA/fPSA (P=0.002) were all significant different whereas hK2 (P=0.143) and PSA (P=0.1) did not differ. Between grade 2 and grade 3 tumors, the hK2 alone (P=0.27), the %fPSA (P=0.13), the ratios hK2/fPSA (P=0.94) and hK2xtPSA/fPSA (P=0.12) did not separate, whereas PSA (P=0.039) showed a difference. The same relationships were found between the two groups in Gleason score<7 and >or=7. Neither the hK2 ratio, nor % fPSA was different.

CONCLUSION

Human glandular kallikrein was not different between pT2 and pT3, nor between G2 versus G3 or Gleason scores<7 and >or=7 prostate cancer. Together with %fPSA, hK2 may only help to distinguish preoperatively between pT2 and pT3 prostate cancer but cannot add further information.

Prognostic value of serum markers for prostate cancer

The incidence of prostate cancer has increased dramatically during the last 10-15 years and it is now the commonest cancer in males in developed countries. The increase is mainly caused by the increasing use of opportunistic screening or case-finding based on the use of prostate-specific antigen (PSA) testing in serum. With this approach, prostate cancer is detected 5-10 years before giving rise to symptoms and on average 17 years before causing the death of the patient. While this has led to detection of prostate cancer at a potentially curable stage, it has also led to substantial overdiagnosis, i.e. detection of cancers that would not surface clinically in the absence of screening. A major challenge is thus to identify the cases that need to be treated while avoiding diagnosing patients who will not benefit from being diagnosed and who will only suffer from the stigma of being a cancer patient. It would be useful to have prognostic markers that could predict which patients need to be diagnosed and which do not. Ideally, it should be possible to measure these markers using non-invasive techniques, i.e. by means of serum or urine tests. As it is very useful for both early diagnosis and monitoring of prostate cancer, PSA is considered the most valuable marker available for any tumor. Although the prognostic value of PSA is limited, measurement of the proportion of free PSA has improved the identification of patients with aggressive disease. Furthermore, the rate of increase in serum PSA reflects tumor growth rate and prognosis but, due to substantial physiological variation in serum PSA, reliable estimation of the rate of PSA increase requires follow-up for at least 2 years. Algorithms based on the combined use of free and total PSA and prostate volume in logistic regression and neural networks can improve the diagnostic accuracy for prostate cancer, and assays for minor subfractions of PSA and other new markers may provide additional prognostic information. Markers of neuroendocrine differentiation are useful for the monitoring of androgen-independent disease and various bone markers are useful in patients with metastatic disease.

Clinical utility of human glandular kallikrein 2 within a neural network for prostate cancer detection

OBJECTIVE

To assess, using artificial neural networks (ANNs), human glandular kallikrein 2 (hK2), prostate-specific antigen (PSA), and percentage free/total PSA (f/tPSA), for discriminating between prostate cancer and benign prostatic hyperplasia (BPH).

MATERIAL AND METHODS

Serum samples from 475 patients with prostate cancer (n = 347) or BPH (n = 128) within the PSA range of 1-20 ng/mL were analysed for tPSA, fPSA and hK2 (research assay, Toronto, Canada). Data were analysed in the ranges of 1-4, 2-4, 4-10, and 2-20 ng/mL tPSA. Back-propagation ANN models with the variables PSA, f/tPSA, and hK2, hK2/fPSA and hK2/(f/tPSA) were constructed. The diagnostic validity was evaluated by receiver-operating characteristic (ROC) curve analysis.

RESULTS

Whereas the median concentration of hK2 was not significantly different between patients with BPH or prostate cancer in any of the tPSA ranges, the f/tPSA, hK2/fPSA and hK2/(f/tPSA), and the hK2-based ANN outputs were always significantly different between patients with prostate cancer or BPH. Using ROC curve comparison, all variables were significantly better than hK2 in all ranges. The hK2-based ANN performed better than f/tPSA except in the 4-10 ng/mL tPSA range. At 90% and 95% sensitivity, the hK2-based ANN was also significantly better than f/tPSA in the 1-4 ng/mL tPSA range. hK2/(f/tPSA) achieved equal results to the hK2-based ANN except in the range 2-20 ng/mL tPSA.

CONCLUSIONS

The hK2-based ANN improves the outcome of f/tPSA but not hK2/(f/tPSA) in almost all analysed subgroups. When comparing the results at 90% and 95% sensitivity the hK2-based ANN only performed significantly better than f/tPSA in the lowest tPSA range. Only in lower tPSA ranges do hK2-based ANNs show an advantage for further improving prostate cancer detection.

Progress in Lanthanides as Luminescent Probes

Lanthanides have recently found applications in different fields of biomolecular and medical research. Luminescent lanthanide chelates have created interest mainly due to their unique luminescent properties, such as their long Stokes' shift and exceptional decay times allowing efficient temporal discrimination of background interferences in the assays, such as immunoassays. Recently, new organometallic complexes have been developed giving opportunities to novel applications, in heterogeneous and homogeneous immunoassays, DNA hybridization assays, high-throughput screening as well as in imaging. In addition, encapsulating the chelates into suitable matrix in beads enables the use of new members of lanthanides extending the emission wavelength to micrometer range and decays from a few microseconds to milliseconds. As the luminescence is derived from complicated intra-chelate energy transfer, it also gives novel opportunities to exploit these levels in different types of energy transfer based applications. This review gives a short overview of recent development of lanthanide chelate-labels and discusses in more details of energy levels and their exploitation in new assay formats.

Development of sensitive immunoassays for free and total human glandular kallikrein 2

BACKGROUND

Free and total human kallikrein 2 (hK2) might improve the discrimination between prostate cancer and benign prostatic hyperplasia. Concentrations of hK2 are 100-fold lower than concentrations of prostate-specific antigen (PSA); therefore, an hK2 assay must have a low detection limit and good specificity.

METHODS

PSA- and hK2-specific monoclonal antibodies were used in solid-phase, two-site immunofluorometric assays to detect free and total hK2. The total hK2 assay used PSA-specific antibodies to block nonspecific signal. The capture antibody of the free hK2 assay did not cross-react with PSA. To determine the hK2 concentrations in the male bloodstream, total hK2 was measured in a control group consisting of 426 noncharacterized serum samples. Free and total hK2 were measured in plasma from 103 patients with confirmed prostate cancer.

RESULTS

All 426 males in the control group had a total hK2 concentration above the detection limit of 0.0008 microg/L. The median total hK2 concentration was 0.022 microg/L (range, 0.0015-0.37 microg/L). hK2 concentrations were 0.1-58% of total PSA (median, 3.6%). hK2 concentrations were similar in men 41-50 and 51-60 years of age. The ratio of hK2 to PSA steadily decreased from 5-30% at PSA <1 microg/L to 1-2% at higher PSA concentrations. In 103 patients with prostate cancer, the median hK2 concentration in plasma was 0.079 microg/L (range, 0.0015-16.2 microg/L). The median free hK2 concentration was 0.070 (range, 0.005-12.2) microg/L. The proportion of free to total hK2 varied from 17% to 131% (mean, 85%).

CONCLUSIONS

The wide variation in the free-to-total hK2 ratio suggests that hK2 in blood plasma is not consistently in the free, noncomplexed form in patients with prostate cancer. The new assay is sufficiently sensitive to be used to study the diagnostic accuracies of free and total hK2 for prostate cancer.

Total and Gleason grade 4/5 cancer volumes are major contributors of human kallikrein 2, whereas free prostate specific antigen is largely contributed by benign gland volume in serum from patients with prostate cancer or benign prostatic biopsies

PURPOSE

We measured concentrations of human glandular kallikrein 2 (hK2), total prostate specific antigen (tPSA), free PSA (fPSA) and percent fPSA to evaluate their relationship to total prostate gland volume, benign prostatic hyperplasia (BPH) volume, total prostate cancer (PCa) volume (CaVol) and the volume of Gleason grades 4/5 cancer (CaVolGl4) in the serum of 256 patients with PCa undergoing radical retropubic prostatectomy and 185 with negative systematic sextant biopsies.

MATERIALS AND METHODS

Free and total PSA was measured using the Delfia Prostatus (Perkin-Elmer, Turku, Finland) total/free PSA assay and hK2 was measured using a research immunofluorometric assay. Transrectal ultrasound was used to determine total prostate and BPH volume. Total CaVol and CaVolGl4/5 were calculated using a volumetric program in specimens from 158 men with pT2a/b and 98 with pT3a or greater PCa. The Pearson correlation was performed after logarithmic conversion of PSA and hK2 levels. Benign gland, and pT2a/b and pT3a or greater PCa cases were subdivided into small vs large prostate gland volumes (42 cc or less vs greater than 42 cc).

RESULTS

Total prostate and BPH volumes correlated closely with free PSA (r = 0.64 to 0.65, p <0.0001) in 143 patients with negative biopsy and a prostate of greater than 42 cc. Correlations of hK2 and tPSA with total prostate and BPH volumes were weaker (r = 0.35 to 0.36 and 0.45 to 0.46, respectively). In pT2a/b and pT3a or greater PCa cases hK2 most closely correlated with CaVol (range 0.31 to 0.62, p = 0.0072 and <0.0001) and with CaVolGl4/5 (range 0.26 to 0.56, p = 0.021 and <0.0001, respectively). The tPSA level correlated significantly with CaVol and CaVolGl4/5 except in glands 42 cc or greater harboring pT2a/b PCa (p = 0.08). Free PSA correlated significantly with CaVolGl4/5 only in pT3a or greater PCa (p <0.05), and with CaVol in pT3a or greater PCa and in small prostates harboring pT2a/b PCa.

CONCLUSIONS

Large benign prostate gland volume affects fPSA more than tPSA in serum. In PCa hK2 more closely correlates with total cancer volume and high grade PCa volume compared with tPSA or fPSA.

Biology of prostate-specific antigen

The human kallikrein (hk) family, located on chromosome 19, encodes prostate-specific antigen (PSA [or hK3]), hK2, hK4, and hK15 (prostin), as well as other serine proteases. Although PSA has been used in the detection of prostate cancer for several years, much remains unknown about its function and forms. The regulatory mechanisms of PSA are vital to its understanding. A particular mechanism by which PSA forms complexes with either alpha1-antichymotrypsin or alpha2-macroglobulin may provide important information for disease detection and progression. Data are emerging that show that active hK2, hK4, and hK15 may be important to convert pro-PSA to the active PSA enzyme. This information, along with insights into the precise mechanisms of PSA expression, may be used to suggest that PSA and, perhaps, other members of the hK family contribute critical control mechanisms to tumor invasion or progression. Although much remains to be revealed on the role of these gene products in the detection and progression of prostate cancer, findings from studies that show sensitive signaling of the disease > or =20 years before the diagnosis of clinically significant prostate cancer may alter screening procedures and improve treatment options.