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

Plasma enabled devices for the selective capture and photodynamic identification of prostate cancer cells

Prostate cancer is the second most common cancer in men and the second leading cause of male cancer deaths. The current blood test for detecting prostate cancers measures prostate-specific antigen. It has many limitations including a very high rate of false positives. Herein, prostate-specific membrane antigen (PSMA) based immunocapture and hexaminolevulinate (HAL) based photodetection are integrated into a new diagnostic device designed to selectively identify whole prostate cancer cells from voided urine with the aim of providing an accurate noninvasive alternative to current diagnosis methods. Prestained, prostate cancer cells spiked in urine samples at concentrations ranging from 1500 to 2000 cells/ml were captured with 89% sensitivity and 95% specificity. HAL, a cancer specific photosensitizer, was then used to circumvent the need for prestaining. Optimum HAL incubation conditions were identified (50 μM at 37 °C for 2 h) where the mean HAL-induced fluorescence intensity of LNCaP cells was three times that of healthy PNT2 cells, thus providing an independent way to discriminate captured cancer cells from background metabolites. Combining anti-PSMA immunocapture with HAL-induced fluorescent detection, 86% sensitivity and 88% selectivity were achieved, thereby proving the validity of the dual-method for the selective photospecific detection of prostate cancer cells.

Comparative analysis of monoclonal antibodies against prostate-specific membrane antigen (PSMA)

BACKGROUND

Prostate-specific membrane antigen (PSMA), also known as glutamate carboxypeptidase II (GCPII), is generally recognized as a diagnostic and therapeutic cancer antigen and a molecular address for targeted imaging and drug delivery studies. Due to its significance in cancer research, numerous monoclonal antibodies (mAbs) against GCPII have been described and marketed in the past decades. Unfortunately, some of these mAbs are poorly characterized, which might lead to their inappropriate use and misinterpretation of the acquired results.

METHODS

We collected the 13 most frequently used mAbs against GCPII and quantitatively characterized their binding to GCPII by enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR). Using a peptide library, we mapped epitopes recognized by a given mAb. Finally, we assessed the applicability of these mAbs to routine experimental setups, including Western blotting, immunohistochemistry, and flow cytometry.

RESULTS

ELISA and SPR analyses revealed that mAbs J591, J415, D2B, 107-1A4, GCP-05, and 2G7 bind preferentially to GCPII in native form, while mAbs YPSMA-1, YPSMA-2, GCP-02, GCP-04, and 3E6 bind solely to denatured GCPII. mAbs 24.4E6 and 7E11-C5.3 recognize both forms of GCPII. Additionally, we determined that GCP-02 and 3E6 cross-react with mouse GCPII, while GCP-04 recognizes GCPII and GCPIII proteins from both human and mouse.

CONCLUSION

This comparative analysis provides the first detailed quantitative characterization of the most commonly used mAbs against GCPII and can serve as a guideline for the scientific community to use them in a proper and efficient way.

Targeting the prostate-specific membrane antigen for prostate cancer therapy

Prostate cancer remains a leading cause of death for men in Western civilization. Despite the effectiveness of surgical prostatectomy, radiotherapy and hormonal therapy, a significant proportion of patients progress to advanced metastatic disease for which there are currently no curative treatment options. Therefore, new therapeutic approaches need to be considered. The prostate-specific membrane antigen is a cell-surface glycoprotein that is highly and specifically expressed on prostate epithelial cells and strongly upregulated in prostate cancer at all stages. These characteristics make it an attractive target for antibody-based imaging and therapies and the first anti-prostate-specific membrane antigen agents have already entered clinical trials. The proposed strategies include targeted toxins and radiotherapeutics as well as immunotherapeutic agents and vaccines.

A bispecific diabody directed against prostate-specific membrane antigen and CD3 induces T-cell mediated lysis of prostate cancer cells

Background

Although cancer of the prostate is one of the most commonly diagnosed cancers in men, no curative treatment currently exists after its progression beyond resectable boundaries. Therefore, new agents for targeted treatment strategies are needed. Cross-linking of tumor antigens with T-cell associated antigens by bispecific monoclonal antibodies have been shown to increase antigen-specific cytotoxicity in T-cells. Since the prostate-specific membrane antigen (PSMA) represents an excellent tumor target, immunotherapy with bispecific diabodies could be a promising novel treatment option for prostate cancer.

Methods

A heterodimeric diabody specific for human PSMA and the T-cell antigen CD3 was constructed from the DNA of anti-CD3 and anti-PSMA single chain Fv fragments (scFv). It was expressed in E. coli using a vector containing a bicistronic operon for co-secretion of the hybrid scFv V_HCD3-V_LPSMA and V_HPSMA-V_LCD3. The resulting PSMAxCD3 diabody was purified from the periplasmic extract by immobilized metal affinity chromatography (IMAC). The binding properties were tested on PSMA-expressing prostate cancer cells and PSMA-negative cell lines as well as on Jurkat cells by flow cytometry. For in vitro functional analysis, a cell viability test (WST) was used. For in vivo evaluation the diabody was applied together with human peripheral blood lymphocytes (PBL) in a C4-2 xenograft-SCID mouse model.

Results

By Blue Native gel electrophoresis, it could be shown that the PSMAxCD3 diabody is mainly a tetramer. Specific binding both to CD3-expressing Jurkat cells and PSMA-expressing C4-2 cells was shown by flow cytometry. In vitro, the diabody proved to be a potent agent for retargeting PBL to lyze C4-2 prostate cancer cells. Treatment of SCID mice inoculated with C4-2 tumor xenografts with the diabody and PBL efficiently inhibited tumor growth.

Conclusions

The PSMAxCD3 diabody bears the potential for facilitating immunotherapy of prostate cancer and for the elimination of minimal residual disease.

Development of a novel fragments absorbed immunocapture enzyme assay system for tartrate-resistant acid phosphatase 5b

BACKGROUND

Osteoclastic activity is mainly assessed by measuring urinary markers. To correct for differences in renal clearance, the levels of urinary markers are usually corrected by the urine creatinine concentration. Therefore, alternative serum markers to evaluate osteoclastic activity are required. We developed a novel system for the determination of serum tartrate-resistant acid phosphatase 5b (TRACP5b) activity to evaluate osteoclastic activity.

METHODS

Two unique monoclonal antibodies were generated and the specificity was tested using a surface enhanced laser desorption/ionization time-of-flight mass spectroscopy (SELDI TOF-MS). A novel fragments absorbed immunocapture enzymatic assay (FAICEA) method was developed using 2 monoclonal antibodies.

RESULTS

FAICEA gave a sensitivity 0.1 U/l, linearity of 0.1-28 U/l, recovery 92-103%, inter-assay CV 2.95% and intra-assay CV 2.15%. Unlike other TRACP5b assay systems, FAICEA avoided interference from TRACP 5a.

CONCLUSIONS

According to the FAICEA, postmenopausal women had higher TRACP5b concentrations than younger women. The results show that TRACP5b is a novel bone resorption marker in serum.

A recombinant PSMA-specific single-chain immunotoxin has potent and selective toxicity against prostate cancer cells

Prostate cancer is the most commonly diagnosed form of cancer and the second leading cancer-related death among men in the Western civilization. Since no effective therapy exists for this tumor after progression beyond resectable boundaries, there is an urgent need for new treatment strategies. Prostate specific membrane antigen (PSMA) represents an excellent target on prostate cancer cells, and therefore specific immunotherapy may be a novel therapeutic option for the management of this tumor. We constructed a fully recombinant immunotoxin (A5-PE40) from a single-chain antibody fragment (scFv) against cell-adherent PSMA and a truncated form of Pseudomonas exotoxin A (PE40) lacking its natural binding domain Ia. The scFv A5 was obtained from a mAb elicited with native PSMA by phage display technology and direct selection on cells carrying the antigen. The bacterially expressed and purified immunotoxin A5-PE40 specifically binds to PSMA-positive prostate cancer cells and induces a 50% reduction of viability (IC50) at a concentration of 20 pM, while PSMA-negative cells remain unaffected. Due to its high and specific toxicity this recombinant immunotoxin is a promising candidate for therapeutic applications in patients with prostate cancer.

A new generation of monoclonal and recombinant antibodies against cell-adherent prostate specific membrane antigen for diagnostic and therapeutic targeting of prostate cancer

BACKGROUND

Prostate-specific membrane antigen (PSMA) is an excellent candidate for targeting prostate cancer by virtue of its restricted expression on prostatic epithelial cells and its upregulation on prostatic carcinoma cells. PSMA is expressed on the cell surface displaying a specific three-dimensional structure. Therefore, only antibodies with a high cell binding activity will have an important impact on antibody-based imaging and therapy.

METHODS

Monoclonal antibodies (mAbs) and single chain antibody fragments (scFvs) were prepared from spleen cells of mice that had been immunized either with purified PSMA or a cell lysate of prostate cancer LNCaP cells containing native PSMA. mAbs and scFvs were screened for reactivity with purified PSMA and binding to PSMA-expressing LNCaP cells.

RESULTS

From mice immunized with purified PSMA, we obtained three mAbs (K7, K12, D20) and four scFvs (G0, G1, G2, G4), which were highly reactive with the isolated antigen, but showed weak or no reaction with viable LNCaP cells. From mice immunized with unpurified LNCaP lysate, we obtained three mAbs (3/E7, 3/F11, 3/A12), and one scFv (A5), which were reactive with purified PSMA, also showing a strong and specific binding to viable LNCaP cells and PSMA-transfected cells.

CONCLUSIONS

Our results suggest that only the mAbs and scFvs, that were elicited with unpurified LNCaP lysate and not with purified PSMA will be useful agents for diagnostic imaging and therapeutic applications of prostate cancer.

Proteomic patterns: their potential for disease diagnosis

Alterations in proteins abundance, structure, or function, act as useful indicators of pathological abnormalities prior to development of clinical symptoms and as such are often useful diagnostic and prognostic biomarkers. The underlying mechanism of diseases such as cancer are, however, quite complicated in that often multiple dysregulated proteins are involved. It is for this reason that recent hypotheses suggest that detection of panels of biomarkers may provide higher sensitivities and specificities for disease diagnosis than is afforded with single markers. Recently, a novel approach based on the analysis of protein patterns has emerged that may provide a more effective means to diagnose diseases, such as ovarian and prostate cancer. The method is based on the use of surface-enhanced laser desorption/ionization (SELDI) time-of-flight mass spectrometry (TOF-MS) to detect differentially captured proteins from clinical samples, such as serum and plasma. This analysis results in the detection of "proteomic" patterns that have been shown in recent investigations to distinguish diseased and unaffected subjects to varying degrees. This review will discuss the basics of SELDI protein chip technology and highlight its recent applications in disease biomarker discovery with emphasis on cancer diagnosis.

Prostate carcinoma tissue proteomics for biomarker discovery

BACKGROUND

The advent of the prostate-specific antigen (PSA) test has had a profound impact on the diagnosis and treatment of prostate carcinoma. However, the use of PSA levels alone for screening for prostate carcinoma was compromised by the variations in the amount of PSA produced by the benign prostatic tissue specimens. Proteins were involved in various pathways that determine the behavior of a cell. Therefore, information regarding proteins may reveal drug targets and/or markers for early detection.

METHODS

The authors used surface-enhanced laser desorption/ionization time-of-flight mass spectrometry to determine the protein profiles from fresh tissues of the prostate. Laser capture microdissection was performed to isolate pure populations of cells.

RESULTS

The authors identified a protein with an average m/Z of 24,782.56 +/- 107.27 that was correlated with the presence of prostate carcinoma. Furthermore, using laser capture microdissection, they demonstrated that the origin of this protein, which the authors designated PCa-24, was derived from the epithelial cells of the prostate. PCa-24 expression was detected in 16 of 17 (94%) prostate carcinoma specimens but not in paired normal cells. In addition, this protein was not expressed in any of the 12 benign prostatic hyperplasia specimens that were assayed.

CONCLUSIONS

PCa-24 may be useful a marker for prostate carcinoma.

Putative protein markers in the sera of men with prostatic neoplasms

OBJECTIVE

To describe the preliminary identification of serum proteins that may be diagnostic markers in prostate cancer.

PATIENTS AND METHODS

The study included 11 men referred for treatment of localized prostate cancer, 12 with benign prostatic hyperplasia (BPH) and 12 disease-free controls. For serum protein analysis, the protein-chip array surface-enhanced laser desorption/ionization (SELDI) technique was used (Ciphergen Biosystems, Fremont, CA). SELDI combines protein-chip technology with time-of-flight mass spectrometry, and offers the advantages of speed, simplicity and sensitivity.

RESULTS

Three protein peaks were identified in the serum of men with prostate cancer and BPH, but not in controls, with relative molecular masses of 15.2, 15.9 and 17.5 kDa. These three proteins were significantly associated with BPH and prostate cancer when compared with controls (P = 0.001, 0.004, and 0.011, respectively, Kruskal-Wallis test). Interestingly, the 17.5 kDa protein was more abundant in five men with stage T1 prostate cancer than in eight with stage T2 (P = 0.016, two tailed Mann-Whitney U-test corrected for ties).

CONCLUSIONS

These proteins, particularly the 15.9 kDa one, may be used for the diagnosis or monitoring of prostate cancer and differentiation from BPH, and have the potential for antibody-based chip SELDI-TOF technology. Identified proteins may be targets for immunotherapy.

Further investigation of the epitope recognized by the new monoclonal antibody 2C9

OBJECTIVE

We established a new monoclonal antibody (2C9) that reacted with prostate tissue. The immunohistochemical reactivity of this antibody is similar to anti-prostate-specific membrane antigen (PSMA). Herein, we report the antigenic determinant of 2C9 antibody.

METHODS

The reactivity of the antibody was characterized by immunohistochemical staining and the antigen target was characterized by amino acid sequencing after immuno-affinity purification from an LNCaP cell lysate and cloning of a cDNA using a mammalian expression cDNA cloning system.

RESULTS

The amino acid and nucleotide sequences for the antigen molecule recognized with 2C9 monoclonal antibody demonstrated identity with PSMA.

CONCLUSION

The target molecule of the 2C9 monoclonal antibody is PSMA, pointing to future diagnostic and therapeutic applications.

Prostate targeting ligands based on N-acetylated alpha-linked acidic dipeptidase

To identify inhibitors of the intrinsic N-acetylated alpha-linked acidic dipeptidase (NAALADase) activity of prostate specific membrane antigen (PSMA) that may be useful for targeting imaging agents or chemotherapeutic drugs to disseminated prostate cancer, analogs of the tetrahedral transition state for hydrolysis of the natural substrate, N-acetylaspartylglutamate (NAAG), were synthesized. These compounds were assayed for their ability to inhibit the membrane-associated enzyme isolated from LNCaP prostate cancer cells. Active inhibitors were further assayed for their cytotoxicity and membrane binding. We have identified nine compounds, including fluorescent and iodine-labeled conjugates, which inhibit NAALADase enzyme activity with IC(50)s at, or below, 120nM. The binding of these compounds to the cell surface of viable LNCaP prostate tumor cells appears to be specific and saturable, and none of the compounds alter the cell cycle kinetics or induce apoptosis in LNCaP cells, suggesting that they are relatively innocuous and are suitable for targeting imaging agents or cytotoxic drugs to disseminated prostate cancer.

The proteome: anno Domini 2002

We present some current definitions related to functional and structural proteomics and the human proteome, and we review the following aspects of proteome analysis: Classical 2-D map analysis (isoelectric focusing (IEF) followed by SDS-PAGE); Quantitative proteomics (isotope-coded affinity tag (ICAT), fluorescent stains) and their use in e.g., tumor analysis and identification of new target proteins for drug development; Electrophoretic pre-fractionation (how to see the hidden proteome!); Multidimensional separations, such as: (a) coupled size-exclusion and reverse-phase (RP)-HPLC; (b) coupled ion-exchange and RP-HPLC; (c) coupled RP-HPLC and RP-HPLC at 25/60 degrees C; (d) coupled RP-HPLC and capillary electrophoresis (CE); (e) metal affinity chromatography coupled with CE; Protein chips. Some general conclusions are drawn on proteome analysis and we end this review by trying to decode the glass ball of the aruspex and answer the question: "Quo vadis, proteome"?

High affinity capture surface for matrix-assisted laser desorption/ionisation compatible protein microarrays

A surface for the capture of biotin-tagged proteins on matrix-assisted laser desorption/ionisation (MALDI) targets has been investigated. Binding of a poly-L-lysine poly(ethylene glycol)-biotin polymer to glass and gold surfaces has been demonstrated using dual wavelength interferometry. Biotinylated proteins were captured onto this surface using tetrameric neutravidin as a multivalent bridging molecule. Biotin tagging of proteins was achieved by chemical biotinylation or by expressing a protein with a biotinylation consensus sequence in E. coli. The specificity of the surface for biotin-tagged proteins allowed the purification of biotin-tagged glutathione-S-transferase from a bacterial lysate directly onto a MALDI target. Subsequently, the protein was digested on the MALDI target and a protein fingerprint analysis confirmed its presence directly, but no E. coli proteins were detected. Therefore, we conclude that this surface is highly specific for the capture of biotin-labelled proteins and has low non-specific binding properties for non-biotinylated proteins. Furthermore, protein-protein interactions using biotinylated lectins were investigated, and the selective capture of the glycoprotein fetuin with wheat germ agglutinin was demonstrated. Also, immobilised Arachis hypogea agglutinin recognised a minor asialo component of this glycoprotein on the array. The high affinity immobilisation of proteins onto this surface allowed effective desalting procedures to be used which improved the desorption of high molecular weight proteins. Another aspect of this surface is that a highly ordered coupling of the analyte can be achieved which eliminates the search for the sweet spot and allows the creation of densely packed protein microarrays for use in mass spectrometry.

Surface-enhanced laser desorption-ionization retentate chromatography mass spectrometry (SELDI-RC-MS): a new method for rapid development of process chromatography conditions

Protein biochip arrays carrying functional groups typical of those employed for chromatographic sorbents have been developed. When components of a protein mixture are deposited upon an array's functionalized surface, an interaction occurs between the array's surface and solubilized proteins, resulting in adsorption of certain species. The application of gradient wash conditions to the surface of these arrays produces a step-wise elution of retained compounds akin to that accomplished while utilizing columns for liquid chromatography (LC) separations. In retentate chromatography-mass spectrometry (RC-MS), the "retentate" components that remain following a wash are desorbed and ionized when a nitrogen laser is fired at discrete spots on the array after treatment with a laser energy-absorbing matrix solution. Ionized components are analyzed using a time-of-flight mass spectrometer (TOF MS). The present study demonstrates that protein biochips can be used to identify conditions of pH and ionic strength that support selective retention-elution of target proteins and impurity components from ion-exchange surfaces. Such conditions give corresponding behavior when using process-compatible chromatographic sorbents under elution chromatography conditions. The RC-MS principle was applied to the separation of an Fab antibody fragment expressed in Escherichia coli as well as to the separation of recombinant endostatin as expressed in supernatant of Pichia pastoris cultures. Determined optimal array binding and elution conditions in terms of ionic strength and pH were directly applied to regular chromatographic columns in step-wise elution mode. Analysis of collected LC fractions showed favorable correlation to results predicted by the RC-MS method.

Current achievements using ProteinChip Array technology

Because of its inherent flexibility, the ProteinChip Array platform has demonstrated utility into basic research as well as clinical research. In the domain of basic research, it has been used to examine protein modifications, characterize protein-protein interactions and study signal transduction and enzymatic pathways. In clinical research, it has been used to elucidate and identify biomarkers of disease, and as a platform for predictive medicine.

Profiling of acyl-CoA oxidase-deficient and peroxisome proliferator Wy14,643-treated mouse liver protein by surface-enhanced laser desorption/ionization ProteinChip Biology System

Peroxisome proliferators induce hepatic peroxisome proliferation and hepatocellular carcinomas in rodents. These chemicals increase the expression of the peroxisomal beta-oxidation pathway and the cytochrome P-450 4A family, which metabolizes lipids, including fatty acids. Mice lacking fatty acyl-CoA oxidase (AOX-/-), the first enzyme of the peroxisomal beta-oxidation system, exhibit extensive microvesicular steatohepatitis, leading to hepatocellular regeneration and massive peroxisome proliferation. To investigate proteins involved in peroxisome proliferation, we adopted a novel surface-enhanced laser desorption/ionization (SELDI) ProteinChip technology to compare the protein profiles of control (wild-type), AOX-/-, and wild-type mice treated with peroxisome proliferator, Wy-14,643. The results indicated that the protein profiles of AOX-/- mice were similar to the wild-type mice treated with Wy14,643, but significantly different from the nontreated wild-type mice. Using four different ProteinChip Arrays, a total of 40 protein peaks showed more than twofold changes. Among these differentially expressed peaks, a downregulated peak was identified as the major urinary protein in both AOX-/- and Wyl4,643-treated mice by SELDI. The identification of MUP was further confirmed by two-dimensional electrophoresis and liquid chromatography coupled tandem mass spectrometry (LC-MS-MS). This SELDI method offers several technical advantages for detection of differentially expressed proteins, including ease and speed of screening, no need for chromatographic processing, and small sample size.