Characterization of monoclonal antibodies raised against the prostatic cancer cell line PC-82

Bone marrow micrometastases and gastrointestinal cancer detection and significance

Accurate staging of cancer is important, as the presence or absence of systemic spread determines treatment. The sensitivity of current imaging and biochemical techniques is suboptimal for the detection of minimal residual disease and latent metastases. This results in understaging and potential undertreatment. To improve detection of disseminated epithelial malignancy, immunohistochemical and molecular methods have been employed that search for epithelial cell-specific proteins in nonepithelial tissue. Bone marrow is mesenchymal tissue (that does not normally express epithelial cell components) and represents an accessible window for detection of micrometastatic carcinoma cells. Detection methods for epithelial cell components (cytokeratins, epithelial membrane antigen, carcinoembryonic antigen) include immunohistochemistry, flow cytometry, reverse transcriptase polymerase chain reaction (rt-PCR), and enzyme linked immunoassay (ELISA). Micrometastatic cells in bone marrow are viable, capable of proliferation, resistant to immune attack, and insensitive to s-phase chemotherapeutic agents. Patients with carcinomas of the lung, breast, prostate, or gastrointestinal tract and in whom bone marrow micrometastases are detected have a foreshortened interval to recurrence and impaired survival. Detection of micrometastases deserves serious consideration in treatment protocols, and standardization of methods is now required.

Micrometastatic bone marrow involvement: detection and prognostic significance

The present review focuses on the methodology and clinical significance of new diagnostic approaches to identify individual cancer cells present in bone marrow, both as a frequent site of metastasis formation and an indicator organ for hematogenous tumor cell dissemination. The steadily increasing number of studies on this issue is characterized by considerable methodological variations of important variables, such as the size of the study population, and the reliability of monoclonal antibodies used for tumor cell detection. Emerging data indicate that this disturbing heterogeneity might be overcome by the use of reliable and specific anti-cytokeratin antibodies (for example, A45-B/B3) as, for the time, standard markers for the detection of micrometastatic tumor cells in bone marrow. Prospective clinical studies have shown that immunoassays based on anti-CK antibodies identify patients' subgroups with a poor clinical prognosis with regard to early metastasis manifestation and reduced overall survival in various epithelial tumor entities, including breast, colon, rectum, stomach, esophagus, prostate, renal, bladder, and non-small cell lung cancer. The immunocytochemical assays may be therefore used to improve tumor staging with potential consequences for adjuvant therapy, because disseminated cells appeared to be dormant, non-cycling (for example Ki-67 antigen-negative) cells, suggesting a resistance to cell-cycle dependent therapy, such as chemotherapy. Therefore, cell-cycle independent antibody-based immunotherapy might be an interesting option to complement chemotherapy. Another promising clinical application is monitoring the response of micrometastatic cells to adjuvant therapies, which, at present, can only be assessed retrospectively after an extended period of clinical follow-up. The outlined current strategies for detection and characterization of cancer micrometastasis might help to design and control new therapeutic strategies for secondary prevention of metastatic relapse in patients with operable primary carcinomas.

Prognostic significance of micrometastatic bone marrow involvement

The present review focuses on the methodology and clinical significance of new diagnostic approaches to identify micrometastatic breast cancer cells present in bone marrow (BM), as a frequent site of overt metastases. Using monoclonal antibodies (mAbs) to epithelial cytokeratins (CK) or tumor-associated cell membrane glycoproteins, individual carcinoma cells can be detected on cytologic BM preparations at frequencies of 10(-5) to 10(-6). Prospective clinical studies have shown that the presence of these immunostained cells is prognostically relevant with regard to relapse-free and overall survival. The current interest in autologous bone marrow transplantation in patients with solid tumors further underlines the need for screening methods that allow the detection of minute numbers of residual tumor cells in the transplant. Although the development of new molecular detection methods based on the amplification of a marker mRNA species by the polymerase chain reaction technique is a very exciting area of research, the clinical significance of this approach needs to be demonstrated in prospective studies. The immunocytochemical assays may be, therefore, used to improve tumor staging with potential consequences for adjuvant therapy. Another promising clinical application is monitoring the response of micrometastatic cells to adjuvant therapies, which, at present, can only be assessed retrospectively after an extended period of clinical follow-up. The extremely low frequency of BM tumor cells greatly hampers approaches to obtain more specific information on their biological properties. The available data indicate that these cells represent a selected population of cancer cells which, however, still express a considerable degree of heterogeneity with regard to the expression of MHC class I antigens, adhesion molecules (EpCAM), growth factor receptors (EGF receptor, erb-B2, transferrin receptor), or proliferation-associated markers (Ki-67, p120). Regardless of the detection technique applied, there is an urgent demand for large multicentre trials, in which standardized methods are related to specified clinical outcomes.

Identification of second malignancies on effusions and fine-needle aspirates using a panel of monoclonal antibodies

The longer survival of neoplastic patients achieved through improvements of therapeutic regimens has increased the relative risk of developing a second primary tumour (SPT). In this context, conventional cytopathology can define tumour histotype only in a small fraction of cases. In this study, we have evaluated whether selected combinations of monoclonal antibodies (MAbs) to tumour-associated antigens (TAAs) can increase the accuracy of conventional morphology in detecting second primary tumours (SPTs) in two particularly difficult areas of cytodiagnosis, namely that of effusions and pulmonary fine-needle aspirates (FNAs). The immunocytochemical (ICC) analysis of 334 cytological specimens demonstrated that the use of our selected panel of MAbs could allow a more efficient identification of SPTs in comparison with conventional morphology. This diagnostic improvement was statistically significant (P < 0.0001). The present findings show that the immunophenotyping of effusions and FNAs, providing a more accurate and objective identification of SPTs, may have significant therapeutic and epidemiological relevance.

Immunocytochemical detection and phenotypic characterization of micrometastatic tumour cells in bone marrow of patients with prostate cancer

Monoclonal antibodies (mAbs) specific for cytokeratins are potent probes for the identification of disseminated individual epithelial tumour cells in mesenchymal organs such as bone marrow. We have used a monoclonal antibody (mAB) against cytokeratin 18 (CK18) for the detection of individual metastatic tumour cells in bone marrow aspirates from 84 patients with carcinoma of the prostate. CK18+ cells were detected in a sensitivity of 1 per 8 x 10(5) marrow cells using the alkaline phosphatase anti-alkaline phosphatase (APAAP) system for staining. We were able to detect CK18+ tumour cells in the marrow of 33% of patients with stage N0M0 prostate cancers. The incidence of CK18+ cells showed a significant correlation with established risk factors, such as local tumour extent, distant metastases and tumour differentiation. For further characterization of such cells in patients with prostate cancer, we developed an immunocytochemical procedure for simultaneous labelling of cytokeratin component no. 18 (CK18) and prostate-specific antigen (PSA). In a first step, cells were incubated with a murine mAb against PSA, followed by gold-conjugated goat anti-mouse antibodies. In a second step, a biotinylated mAb to CK18 was applied as primary antibody and subsequently incubated with complexes of streptavidin-conjugated alkaline phosphatase, which were developed with Newfuchsin substrate. The binding of gold-labelled antibodies was visualized by silver enhancement. CK18+ cells co-expressing PSA were found in bone marrow aspirates from 5 out of 14 patients with carcinomas of the prostate. The specificity of CK18 for epithelial tumour cells in bone marrow was supported by negative staining of 12 control aspirates from patients with benign prostatic hyperplasia (BPH).(ABSTRACT TRUNCATED AT 250 WORDS)

Do neuroendocrine cells in human prostate cancer express androgen receptor?

The presence of androgen receptors (AR) in neuroendocrine cells was investigated in benign tissue of 10 prostatectomy specimens, in 12 prostatic adenocarcinomas with focal neuroendocrine differentiation and in 1 case of a pure neuroendocrine small cell carcinoma of the prostate. Neuroendocrine cells were defined by their reactivity with an antibody to chromogranin A. Monoclonal antibody F39.4 directed against the amino-terminal domain of the AR molecule was used to detect AR. AR and chromogranin A were simultaneously visualized with a double immunofluorescence technique. The results indicate that chromogranin positive cells in both benign and malignant prostatic tissue lack detectable expression of AR. No effect of endocrine therapy was noted. These results are in agreement with the hypothesis that prostatic neuroendocrine tumour cells represent an androgen insensitive cell population, which incidentally may expand to replace the androgen-sensitive tumour cell population during androgen ablation therapy.

Immunocytochemical double staining of cytokeratin and prostate specific antigen in individual prostatic tumour cells

Early dissemination of malignant cells is the main cause for metastatic relapse in patients with solid tumours. By use of monoclonal antibodies (mAbs) specific for cytokeratins, disseminated individual epithelial tumour cells can now be identified in mesenchymal organs such as bone marrow. Further to characterize such cells in patients with prostate cancer, an immunocytochemical procedure was developed for simultaneous labelling of cytokeratin component no. 18 (CK18) and prostate specific antigen (PSA). In a first step, cells were incubated with mAb ER-PR8 against PSA and secondary gold-conjugated goat anti-mouse antibodies. In a second step, biotinylated mAb CK2 to CK18 was applied as primary antibody and subsequently incubated with complexes of streptavidin-conjugated alkaline phosphatase, which were developed with the Newfuchsin substrate. The binding of gold-labelled antibodies was visualized by silver enhancement. The sensitivity and specificity of the technique was demonstrated on cryostat sections of hyperplastic prostatic tissue, and cytological preparations of LNCaP prostatic tumour cells. Double staining was restricted to cells derived from the secretory epithelium of the prostate. Cross-reactivity between both detection systems was excluded by several controls, including the use of unrelated antibodies of the same isotype and the staining of CK18+/PSA- HT29 colon carcinoma cells. CK18+ cells co-expressing PSA were found in bone marrow aspirates from 5 out of 13 patients with carcinomas of the prostate, a finding that is consistent with the relative fraction of double-positive LNCaP cells. The specificity of CK18 for epithelial tumour cells in bone marrow was supported by negative staining of 12 control aspirates from patients with benign prostatic hypertrophy.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the human kallikrein locus

The human kallikrein gene family is composed of three members: tissue kallikrein (KLK1), prostate-specific antigen (PA or APS), and human glandular kallikrein-1 (hGK-1 or KLK2). The three genes have previously been isolated and mapped to chromosome 19q13.2-q13.4. Further analysis of an area of 110 kb surrounding the kallikrein genes by CHEF electrophoresis and chromosome walking showed clustering of the three genes. The KLK1 gene is positioned in the opposite orientation of the APS and KLK2 genes in the order KLK1-APS-KLK2. The APS and KLK2 gene are separated by 12 kb; the distance between KLK1 and APS is 31 kb. A CpG island was detected in the region between KLK1 and APS. Preliminary data indicate that this CpG island is located directly adjacent to a gene that is unrelated to the kallikreins and seems to be ubiquitously expressed.

Androgen receptors in endocrine-therapy-resistant human prostate cancer

Despite the initial androgen-dependent growth of most human prostate cancers, eventually all prostate cancers become androgen-independent at varying intervals after androgen ablation or anti-androgen therapy. In order to gain more insight into the role of the androgen receptor (AR) in this process, AR and prostate-specific antigen (PA) expression was evaluated immunohistochemically in prostatic tumour tissues from patients who developed urinary flow obstruction between 4 and 107 months after onset of treatment. AR expression was evaluated with a monoclonal antibody (MAb) specific for the N-terminal domain of the human AR. To substantiate the progressive tumour growth, proliferative activity was assessed immunohistochemically by staining with MAb Ki-67. Ki-67-defined tumour-growth fractions varied from 0.8-64.7%. In 13 of the 17 examined tumours over 80% of the tumour cells were AR-positive, 3 tumours showed a considerable heterogeneity in AR expression and in 1 tumour almost all tumour cells seemed to be AR-negative. Two-thirds of the examined tumours contained variable proportions of PA-positive tumour areas. These observations contrast with the view that androgen ablation induces a preferential outgrowth of receptor-negative tumour cells.

Variation of prostate-specific antigen expression in different tumour growth patterns present in prostatectomy specimens

A series of 55 randomly chosen radical prostatectomy specimens was analyzed for expression of prostate-specific antigen (PSA) by immunohistochemical techniques. Tissue sections were selected in such a manner that in addition to glandular benign prostatic hyperplasia (BPH), one or more different prostatic tumour growth patterns were present. Four monoclonal antibodies, directed against three different PSA epitopes, and one polyclonal anti-PSA antiserum were used. Expression of PSA was compared with that of prostate-specific acid phosphatase (PAP), recognized by two different polyclonal antisera. A critical dilution aimed at a maximum of staining intensity on BPH tissue sections was chosen for all antibodies. Anti-PSA and anti-PAP antisera stained essentially all BPH samples (over 90%). Irrespective of the nature of the antibodies used, PSA expression was found to be decreased in prostatic carcinoma. A clear cut relationship was found between immunoreactivity for PSA and the degree of differentiation of the tumour area. Under the experimental conditions used the PSA monoclonal antibodies stained only 1 out of 10 undifferentiated carcinomas, whereas 50% to 70% of the well- and moderately-differentiated carcinomas showed immunoreactivity. This correlation was less pronounced with the PAP staining pattern. If the PSA antibody titer was raised the percentage of clearly staining undifferentiated carcinomas could be considerably increased (up to 60%-100%), indicating that PSA expression is not absent, but lowered in most (if not all) undifferentiated carcinomas.

Expression of the gene coding for human prostate-specific antigen and related hGK-1 in benign and malignant tumors of the human prostate

Human glandular kallikrein-1 gene (hGK-1) is closely related to the gene of human prostate-specific antigen (PSA) and both genes are expressed in the human prostate. We have studied PSA and hGK-1 mRNAs in human prostatic tissue samples from patients with benign prostatic hyperplasia (BPH) or adenocarcinoma (CA), using Northern and slot-blot analysis in order to gain insight into the expression of these highly similar genes. Multiple mRNAs were found to originate from both genes. The major mRNA species of 1.6 kb accounted for 57% to 76% of the total coding capacity for PSA in different tissue specimens, but a variant mRNA species of 1.9 kb was also abundant. Most of the BPH samples contained marked amounts of an aberrant 0.9 kb mRNA, and long PSA mRNAs of 6.1 kb, 4.5 kb and 3.1 kb were found in elevated amounts in some of the CA samples. The amount of PSA mRNAs that would produce aberrant PSA proteins if translated into protein varied from 18% to 38% in these tissue samples. The major mRNA species originating from hGK-1 was of 1.6 kb, but other less abundant mRNA species could also be observed. The amount of PSA and hGK-1 mRNAs was determined from slot blots hybridized with specific oligonucleotide probes. No significant differences could be found in the PSA gene expression between BPH and CA samples. The total amount of the PSA mRNAs in all the different BPH specimens was fairly similar, but there was a 3-fold difference between the highest and lowest PSA mRNA levels in the CA samples. The hGK-1 mRNA levels in the BPH specimens studied demonstrated greater variance than the PSA mRNA levels in the same samples. The correlation between PSA gene and hGK-1 expression in the BPH samples was good, suggesting that there are similarities in the regulation of these genes. However, the lack of correlation between the amounts of PSA and hGK-1 mRNAs in the CA samples except in sample C1 indicates that there are also differences in the gene regulation. The observed 3.7- to 6.5-fold excess of PSA mRNAs as compared with the amount of hGK-1 mRNAs present in the same tissue specimen also indicated differences in the cis- or trans-acting regulatory elements of these genes.

The prostate-specific antigen gene and the human glandular kallikrein-1 gene are tandemly located on chromosome 19

Using a prostate-specific antigen cDNA as a hybridization probe, clones containing the kallikrein genes encoding prostate-specific antigen, human glandular kallikrein-1 and pancreas/kidney kallikrein were isolated from a human genomic library. Clones containing the prostate-specific antigen gene and the human glandular kallikrein-1 gene overlap and span a region of about 36 kb. The two genes are aligned in a head to tail orientation at a mutual distance of 12 kb. Southern blot analysis of DNA from a panel of human-hamster hybrid cells with specific probes revealed the genes to be situated on chromosome 19. Assuming that the pancreas/kidney kallikrein gene is located in the same cluster, the distance to the prostate-specific antigen gene and the human glandular kallikrein gene must be at least 15 kb.

Characterization of the prostate-specific antigen gene: a novel human kallikrein-like gene

Using Prostate-specific Antigen cDNA fragments as hybridization probes a clone containing the information for the gene encoding Prostate-specific Antigen was isolated form a human genomic DNA library. The complete gene (about 6 kb) was sequenced and shown to be composed of four introns and five exons. Two major transcription initiation sites were found. The sequence of the promoter region revealed the presence of various well known transcription regulatory elements including a TATA box. A high percentage of homology was found between the Prostate-specific Antigen gene and the hGK-1 gene (82%). This homology extended into the promoter region. Two previously described variant Prostate-specific Antigen cDNAs can now be explained by intron retention and alternative splicing of the primary transcript.

Diagnostic and therapeutic utility of monoclonal antibodies in urologic oncology

Remarkable advances in the treatment of urologic malignancies have recently been made. Monoclonal antibodies selective for a variety of normal and malignant urologic tissues have been useful in defining normal antigens and tumor-associated antigens and have potential as diagnostic and immunotherapeutic agents. In renal cancer, monoclonal antibodies can define serum markers, radiolabel tumor xenografts, and assist in specific tissue diagnosis. Additionally, there is potential for these antibodies either alone or as conjugates to localize and kill tumors. Monoclonal antibodies to bladder cancer associated antigens are able to demonstrate differential antigen expression on superficial versus invasive tumors, to refine urinary cytologic diagnosis of bladder cancer, and to predict invasive recurrence of superficial cancer. Monoclonal antibodies have localized bladder tumor xenografts and can inhibit tumor growth when conjugated to radioisotopes or toxins. In prostate cancer monoclonal antibodies to prostate antigens are not usually tumor specific. Monoclonal antibodies to prostate antigen (PA) and prostatic acid phosphatase (PAP) are able to localize prostate cancer metastases. Chemotherapy-conjugated anti-PAP monoclonal antibodies have demonstrable inhibition on human prostate cancer xenografted tumor growth. Monoclonal antibodies have defined normal and tumor-associated antigens in urologic cancers and are expected to be useful in immunodiagnosis and cancer therapy in the near future.

Molecular cloning and characterization of novel prostate antigen cDNA's

Three different prostate antigen cDNA's were isolated from a PC 82 prostate tumor cDNA library. PA 75 has a size of 1.4 kb and contains the almost complete information for the 35 kD prostate antigen preproprotein. The 1.6 kb PA 525 cDNA lacks about 0.2 kb of the 3'-non coding region and contains an additional internal 0.4 kb fragment as a result of alternative splicing. PA 424 represents a 0.6 kb variant of PA 75. It contains a 0.15 kb internal fragment and a poly(A) tail preceded by an AAGAAA motive at the 3'-end. The predicted protein products of PA 525 and PA 424 will be different from PA 75 at the C-terminal end. In RNA preparations of two human prostate tumors (PC 82 and PC EW) seven different prostate antigen transcripts can be detected ranging in size from 0.5 kb to 5.6 kb. PA 75 cDNA represents the major 1.5 kb mRNA. PA 424 correlates with a 0.9 kb transcript and PA 525 with a 1.9 kb mRNA species.