Production of milligram concentrations of free prostate specific antigen (fPSA) from LNCaP cell culture: Difference between fPSA from LNCaP cell and seminal plasma

Free PSA forms in prostatic tissue and sera of prostate cancer patients: Analysis by 2-DE and western blotting of immunopurified samples

OBJECTIVE

The isoform pattern of free prostate-specific antigen (fPSA) from sera of patients with prostate cancer (PCa) and no evidence of prostate cancer (NPCa), cancerous and non-cancerous tissues and seminal plasma, have been compared, above all regarding the degree of sialylation, with the aim to show a better discrimination of PCa and NPCa.

DESIGN AND METHODS

The samples have been immunopurified and analyzed by two dimensional gel electrophoresis and western blotting. It was investigated which patterns were obtained when looking for the fPSA and the (-5/-7)proPSA (precursor form) before and after desialylation.

RESULTS

The fPSA sialylation and the proPSA pattern in cancerous and non-cancerous prostate tissues were similar to each other and only slightly different from PCa and NPCa sera. The different fPSA isoforms observed could not be due solely to differences in the degree of sialylation, because different fPSA and (-5/-7)proPSA precursor isoforms were still present after complete desialylation.

CONCLUSIONS

Although slight differences in the fPSA and (-5/-7) proPSA glycosylation and isoform pattern were observed, they were not large enough to be considered to improve PCa diagnosis.

Different glycan structures in prostate-specific antigen from prostate cancer sera in relation to seminal plasma PSA

Prostate-specific antigen (PSA), the tumor marker currently used for prostate cancer (PCa), is not specific enough to distinguish between PCa and benign prostate hyperplasia (BPH). Glycan processing is normally perturbed in tumors, therefore we investigated whether changes in glycosylation of PSA could be useful diagnostic indicators. Previously we determined that the glycosylation of PSA secreted by the tumor prostate cell line LNCaP differs significantly from that of PSA from seminal plasma (normal control). We therefore undertook a detailed glycan analysis of PSA derived from sera from PCa patients and, importantly, established that the glycosylation of the PCa serum PSA was significantly different from the PSA from the LNCaP cell line. In comparison with seminal plasma PSA, the fucose content of PSA from the PCa patient serum was significantly lower and there was a decrease in alpha2,3-linked sialic acid. Differences in the glycosylation of PSA derived from PCa patients' sera, seminal plasma, and LNCaP cells were further established by lectin detection, glycosylation immunosorbent assay, and two-dimensional electrophoresis. We also investigated whether the impact of glycosylation changes initiated by the tumor was reflected in the serum glycome. By comparing the glycans released from the total glycoproteins in PCa patient serum with those of normal serum we found an increase in the proportion of sialyl-Lewis x structures. Further analysis of the glycosylation of PSA from PCa and BPH sera will be required in order to determine the utility of these glycan differences to discriminate specifically between benign and malignant prostate states.

Selective recognition of enzymatically active prostate-specific antigen (PSA) by anti-PSA monoclonal antibodies

Prostate-specific antigen (PSA) is widely used as a serum marker for the diagnosis of prostate cancer. To evaluate two anti-free PSA monoclonal antibodies (mAbs) as potential tools in new generations of more relevant PSA assays, we report here their properties towards the recognition of specific forms of free PSA in seminal fluids, LNCaP supernatants, 'non-binding' PSA and sera from cancer patients. PSA from these different origins was immunopurified by the two anti-free PSA mAbs (5D3D11 and 6C8D8) as well as by an anti-total PSA mAb. The composition of the different immunopurified PSA fractions was analysed and their respective enzymatic activities were determined. In seminal fluid, enzymatically active PSA was equally purified with the three mAbs. In LNCaP supernatants and human sera, 5D3D11 immunopurified active PSA mainly, whereas 6C8D8 immunopurified PSA with residual activity. In sera of prostate cancer patients, we identified the presence of a mature inactive PSA form which can be activated into active PSA by use of high saline concentration or capture by an anti-total PSA mAb capable of enhancing PSA activity. According to PSA models built by comparative modelling with the crystal structure of horse prostate kallikrein described previously, we assume that active and activable PSA could correspond to mature intact PSA with open and closed conformations of the kallikrein loop. The specificity of 5D3D11 was restricted to both active and activable PSA, whereas 6C8D8 recognized all free PSA including intact PSA, proforms and internally cleaved PSA.

Thiophilic interaction chromatography facilitates detection of various molecular complexes of prostate-specific antigen in biological fluids

BACKGROUND

It is known that total PSA values are often greater than the sum total of free-PSA (f-PSA) and PSA-ACT complex. It is primarily because other PSA complexes are present in the patient serum and currently cannot be quantified. Our studies were aimed in developing methodology that will permit recovery of all molecular forms of PSA from various biological fluids.

METHODS

Thiophilic interaction (3S,T-gel) chromatography procedure was used to isolate various PSA molecular forms present in biological fluids. f-PSA and PSA complexes were shown to have strong affinity for T-gel. PSA forms eluted from the column were analyzed by SDS-PAGE/Western blot and were identified by immunostaining with antibody-specific to PSA and to various protease inhibitors. The identity of PSA complexes was also confirmed by Enzyme-linked Immunosorbent-assay (ELISA).

RESULTS

One step affinity chromatography procedure (3S,T-gel) was used to isolate different molecular forms of PSA in seminal plasma, patient sera, and in prostate cancer cell culture medium. Seminal plasma was shown to contain f-PSA, PSA-ACT, PSA-A2M, and PSA-PCI. Sera from prostate cancer patients at different stages of the disease contained f-PSA, PSA-ACT, and PSA-A2M. Besides these PSA forms, some patients at late stage of the disease (T3 and T4) also contained two additional PSA-complexes that have not been identified as of yet. Conditioned medium from LNCaP cells was shown to contain f-PSA, PSA-ACT, and PSA-A2M complexes.

CONCLUSIONS

Thiophilic gel has strong affinity for all known molecular forms of PSA present in any biological material. Visualization of PSA molecular forms in Western-blot analysis was feasible only after patient serum was processed through T-gel. Our procedure can be used to screen hybridoma and antibodies specific to the individual PSA complex. The PSA molecular forms isolated from patient serum after T-gel procedure may provide useful internal calibrators, and thus may significantly enhance the reliability of PSA measurements.

Fatty acid synthase (FAS) expression in human breast cancer cell culture supernatants and in breast cancer patients

Fatty acid synthase (FAS) is selectively expressed in certain human cancers, including carcinoma of the breast, prostate, colon, ovary, and endometrium, compared to normal human tissues and therefore is a putative tumor marker. In this study, we found FAS concentrations were elevated in cell culture supernatants during cell growth in two human breast cancer cell lines but not other cancer cell lines. A quantitative enzyme-linked immunosorbent assay and Western blot analysis were employed in this study. In addition, serum FAS levels were significantly higher in breast cancer patients with different clinical stages (Stage II: 0.59+/-0.09 units/l, Stage III: 0.79+/-0.13 units/l, and Stage IV: 1.39+/-0.35 units/l) compared with healthy subjects (0.27+/-0.02 units/l, P<0.05). Taken together, our data suggest that FAS expression may be a useful tumor marker for breast cancer and play a role in assessing cancer virulence.

Analysis of Free Prostate-specific Antigen (PSA) after Chemical Release from the Complex with α1-Antichymotrypsin (PSA-ACT)

Background: Prostate-specific antigen (PSA), a marker for prostate cancer (CaP), forms a covalent complex with α1-antichymotrypsin (ACT) in human blood. Structural analysis of the PSA-ACT complex is difficult, and complexation may be a reason for biased immunological assays when compared with the analysis of free PSA. We developed a method to cleave the PSA-ACT complex chemically. The liberated PSA was thus available for analysis as free PSA (F-PSA).

Methods: PSA was released from the PSA-ACT complex by cleaving the interprotein ester bond with ethanolamine under alkaline conditions. The release was followed by reversed-phase HPLC and an immunoassay for F-PSA. Released PSA obtained from human blood was further immunopurified and analyzed by matrix-assisted laser desorption-induced time of flight (MALDI-TOF) mass spectrometry.

Results: In vitro-prepared PSA-ACT complex was completely cleaved by treatment with nucleophilic compounds such as ethanolamine at pH 9–10. The released PSA was stable under these conditions and could be measured by reversed-phase HPLC as well as the ENZYMUN® immunoassay for F-PSA. When plasma from a CaP patient [containing 190 μg/L F-PSA and 1890 μg/L total PSA (T-PSA)] was treated under similar conditions, a concentration of ∼1600 μg/L F-PSA was measured at the end of the incubation, indicating that the PSA-ACT complex was completely cleaved. Two benign prostatic hyperplasia and CaP sera panels (12 and 13 sera, respectively) containing 4–45 μg/L T-PSA were similarly treated. The concentrations of F-PSA measured after incubation were, on average, 85% of the T-PSA values of the untreated sera. Finally, the PSA released from the complex of the CaP plasma was isolated by immunosorption, analyzed by MALDI-TOF mass spectrometry, and compared to PSA obtained from semen. The intact PSA as well as the peptides observed after digestion with endoproteinase Lys C did not reveal any structural difference between the PSA from these two sources.

Conclusions: PSA complexed to ACT in plasma of a CaP patient seems to be structurally very similar to the PSA reference material from semen. The release of PSA from the PSA-ACT complex allows F-PSA and T-PSA to be measured by the same immunological assay, thus eliminating any possible bias between two different assays.