Oncogenes in prostate cancer. An update

Statins and prostate cancer: molecular and clinical aspects

The field of the potential applications of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) beyond their unambiguous cardiovascular beneficial effects is steadily increasing. In this regard, statins have also been shown to possess anti-inflammatory, immunomodulatory, antioxidant and growth inhibitory properties. Regarding their role in carcinogenesis, both preclinical and clinical studies report conflicting results. Intriguingly, accumulating evidence suggests that statins may relate to decreased prostate cancer incidence and recurrence risk. However, data from clinical studies seem to be still weak and are confounded by several factors. Nonetheless, preclinical data suggest that statins might exert a chemopreventive role against prostate cancer by inhibiting the proliferation and inducing apoptosis of prostate cancer cells and also inhibiting angiogenesis, inflammation and metastasis. Cholesterol lowering as well as statin pleiotropy through inhibition of the synthesis of isoprenoids have both been implicated in their anticancer properties. In this review, we discuss the preclinical and clinical evidence supporting the preventive or potentially harmful effects of statins on prostate tumourigenesis and conclude that statins should not be recommended for the prevention of prostate cancer development or progression based on the current data.

Targeting prostate cancer based on signal transduction and cell cycle pathways

Prostate cancer remains a leading cause of death in men despite increased capacity to diagnose at earlier stages. After prostate cancer has become hormone independent, which often occurs after hormonal ablation therapies, it is difficult to effectively treat. Prostate cancer may arise from mutations and dysregulation of various genes involved in regulation signal transduction (e.g., PTEN, Akt, etc.,) and the cell cycle (e.g., p53, p21(Cip1), p27(Kip1), Rb, etc.,). This review focuses on the aberrant interactions of signal transduction and cell cycle genes products and how they can contribute to prostate cancer and alter therapeutic effectiveness.

Down-regulation of c-Myc following MEK/ERK inhibition halts the expression of malignant phenotype in rhabdomyosarcoma and in non muscle-derived human tumors

Background

Expression of c-myc proto-oncogene is inappropriate in a wide range of human tumors, and is a downstream target of Ras/Raf/ERK pathway, which promotes c-Myc stability by enhancing c-Myc expression and activity.

The aim of this study was to investigate whether the oncogenic phenotype in the human muscle-derived Rhabdomyosarcoma (RD) cell line and in non muscle-derived human tumor cell lines (SW403, IGR39 and PC3) can be blocked by disrupting the c-Myc pathway either by means of pharmacological MEK/ERK inhibition or by direct inactivation of the c-Myc protein.

Results

We demonstrate that, in all the tumor cell lines used, the MEK/ERK inhibitor U0126 rapidly induces c-Myc de-phosphorylation, which is followed by a marked reduction in its expression level, by inhibition of proliferation and by reversion of anchorage-independent growth. These data suggest that the targeting of pathways controlling c-Myc expression or stability reverses deregulated growth of different tumor-derived cell lines. Indeed, in RD cells, we found a marked down-regulation of cyclins E2, A and B and CDK2, all of which are known to be targets of c-Myc. Moreover, ectopic MadMyc chimera, a c-Myc function antagonist, causes dramatic growth arrest, CDK and cyclin modulation as well as inhibition of anchorage-independent growth in RD cells, as occurs in U0126-treated cells. In particular, we found that the mere inhibition of c-Myc by MadMyc chimera rescues the myogenic program, MHC expression and the acquisition of the myogenic-like phenotype in RD cells.

Conclusion

Our data provide evidence of the key role played by the MEK/ERK pathway in the growth arrest and transformation phenotype of Rhabdomyosarcoma and of non muscle-derived tumor cell lines. In fact, MEK/ERK inhibitor, U0126, induces growth arrest, anchorage-dependent growth of these cell lines. In addition, the results of this study demonstrate that the direct inactivation of c-Myc by Mad/Myc chimera rescues myogenic program and leads to the reversal of the Rhabdomyosarcoma phenotype. In conclusion these data strongly suggest that the targeting of c-Myc by means of the MEK inhibitor can be tested as a promising strategy in anti-cancer therapy.

U94 alters FN1 and ANGPTL4 gene expression and inhibits tumorigenesis of prostate cancer cell line PC3

Background

Insensitivity of advanced-stage prostate cancer to androgen ablation therapy is a serious problem in clinical practice because it is associated with aggressive progression and poor prognosis. Targeted therapeutic drug discovery efforts are thwarted by lack of adequate knowledge of gene(s) associated with prostate tumorigenesis. Therefore there is the need for studies to provide leads to targeted intervention measures. Here we propose that stable expression of U94, a tumor suppressor gene encoded by human herpesvirus 6A (HHV-6A), could alter gene expression and thereby inhibit the tumorigenicity of PC3 cell line. Microarray gene expression profiling on U94 recombinant PC3 cell line could reveal genes that would elucidate prostate cancer biology, and hopefully identify potential therapeutic targets.

Results

We have shown that stable expression of U94 gene in PC3 cell line inhibited its focus formation in culture, and tumorigenesis in nude mice. Moreover gene expression profiling revealed dramatic upregulation of FN 1 (fibronectin, 91 ± 16-fold), and profound downregulation of ANGPTL 4 (angiopoietin-like-4, 20 ± 4-fold) in U94 recombinant PC3 cell line. Quantitative real-time polymerase chain reaction (QRT-PCR) analysis showed that the pattern of expression of FN 1 and ANGPTL 4 mRNA were consistent with the microarray data. Based on previous reports, the findings in this study implicate upregulation of FN 1 and downregulation of ANGPTL 4 in the anti tumor activity of U94. Genes with cancer inhibitory activities that were also upregulated include SERPINE 2 (serine/cysteine protease inhibitor 2, 7 ± 1-fold increase) and ADAMTS 1 (a disintegrin-like and metalloprotease with thrombospondin type 1 motif, 7 ± 2-fold increase). Additionally, SPUVE 23 (serine protease 23) that is pro-tumorigenic was significantly downregulated (10 ± 1-fold).

Conclusion

The dramatic upregulation of FN 1 and downregulation of ANGPTL 4 genes in PC3 cell line stably expressing U94 implicate up-regulation of FN 1 and downregulation of ANGPTL 4 in anti tumor activity of U94. Further studies are necessary to determine functional roles of differentially expressed genes in U94 recombinant PC3 cell line, and hopefully provide leads to potential therapeutic targets in prostate cancer.

Molecular biology of prostate cancer

Development of any cancer reflects a progressive accumulation of alterations in various genes. Oncogenes, tumour suppressor genes, DNA repair genes and metastasis suppressor genes have been investigated in prostate cancer. Here, we review current understanding of the molecular biology of prostate cancer. Detailed understanding of the molecular basis of prostate cancer will provide insights into the aetiology and prognosis of the disease, and suggest avenues for therapeutic intervention in the future.

Prognostic markers in prostate cancer

In this review, a series of relatively well-documented ancillary biomarkers and emerging molecular assays are evaluated for their relative ability to predict prognosis in prostate cancer. Prognostic factors that have achieved widespread use and classified as Category I by the College of American Pathologists Solid Tumor Prognostic Factor Consensus Conference are compared with newer tests that are beginning to be used in clinical practice (Category II) and emerging molecular-based assays that have yet to be widely validated in the published literature or clinical trials (Category III).

Morphologic and molecular prognostic markers in prostate cancer

In this review, a series of traditional morphology-based measurements, relatively well-documented ancillary biomarkers, and emerging molecular assays are evaluated for their relative ability to predict prognosis in prostate cancer. Prognostic factors that have achieved widespread use and are classified as category I by the College of American Pathologists' Solid Tumor Prognostic Factor Consensus Conference are compared with newer tests that are beginning to be used in clinical practice (category II) and emerging molecular-based assays that have yet to be widely validated in the published literature or in clinical trials (category III).

Angiogenesis as a potential biomarker in prostate cancer chemoprevention trials

Prostate cancer is a multistep process in which progression rather than initiation may be the rate-limiting step. A strong possibility is that prostatic intraepithelial neoplasia lesions that switch to angiogenic phenotype eventually progress to cancer. However, it is a challenging task to quantitate angiogenesis in preneoplastic lesions. A promising approach to measuring angiogenesis involves real-time TaqMan polymerase chain reaction to quantitate mRNAs encoding a panel of angiogenesis markers. This highly sensitive molecular technique has potential for quantitating angiogenesis in clinical settings and can be used as a high-throughput screening procedure in prostate cancer clinical trials.

Prognostic value of immunohistochemical expression of the c-erbB-2 oncoprotein in metastasic prostate cancer

It is well established that the activation of proto-oncogenes could trigger uncontrolled cell growth and cancer development. Although this correlation has already been evidenced in several human tumors, no conclusive studies have related oncogene activation with the development of prostatic neoplasia. Nevertheless, some reports suggest that c-erbB-2, which is a prognostic marker in breast cancer, could be implicated in the development of prostatic adenocarcinoma. We have studied the expression of the c-erbB-2 oncoprotein in primary prostatic tissue in a series of 70 patients with metastasic disease, by means of immunohistochemistry. The NCL-B 11 anti-c-erbB-2 monoclonal antibody was used, and the immunoreactivity was quantified by image analysis. The overall rate of prostatic-tissue sections presenting positive c-erbB-2 immunostaining was 64.3%. No significant relation was observed between histological grade and c-erbB-2 over-expression or severity of the disease, based on the extent of metastases. The average specific survival in patients with c-erbB-2 over-expression was 33 months, while it was 54 in patients with c-erbB-2 negativity; p < 0. 034. These results, as well as the logistic-regression analysis, suggest that expression of c-erbB-2 oncoprotein would be considered as an independent prognostic factor of metastatic prostate cancer. Moreover, it could discriminate between the prognosis of patients with Gleason score 2 to 7 and those with score 8 to 10. Our results suggest that the expression of c-erbB-2 oncoprotein in primary prostatic tissue could have a prognostic value in patients with metastatic prostate cancer. Int. J. Cancer (Pred. Oncol.) 84:421-425, 1999.

Loss of heterozygosity (LOH), malignancy grade and clonality in microdissected prostate cancer

The aim of the present study was to find out whether increasing malignancy of prostate carcinoma correlates with an overall increase of loss of heterozygosity (LOH), and whether LOH typing of microdissected tumour areas can help to distinguish between multifocal or clonal tumour development. In 47 carcinomas analysed at 25 chromosomal loci, the overall LOH rate was found to be significantly lower in grade 1 areas (2.2%) compared with grade 2 (9.4%) and grade 3 areas (8.3%, P = 0.007). A similar tendency was found for the mean fractional allele loss (FAL, 0.043 for grade 1, 0.2 for grade 2 and 0.23 for grade 3, P = 0.0004). Of 20 tumours (65%) with LOH in several microdissected areas, 13 had identical losses at 1-4 loci within two or three areas, suggesting clonal development of these areas. Markers near RB, DCC, BBC1, TP53 and at D13S325 (13q21-22) showed higher loss rates in grades 2 and 3 (between 25% and 44.4%) compared with grade 1 (0-6.6%). Tumour-suppressor genes (TSGs) near these loci might, thus, be important for tumour progression. TP53 mutations were detected in 27%, but BBC1 mutations in only 7%, of samples with LOH. Evaluation of all 25 loci in every tumour made evident that each prostate cancer has its own pattern of allelic losses.

Molecular biology of prostate development and prostate cancer

The molecular mechanisms that control prostate development have been intensely studied in recent years due to the emergence of prostatic cancer as a major health concern. Several recent studies have led to the identification of numerous genes that are required for prostate organogenesis, many of which also contribute to prostate carcinogenesis. These genes fall into several categories, including proto-oncogenes, transcription factors, homeobox genes, growth factors and cell adhesion molecules. This review focuses on those genes which have been implicated in prostate growth and development, and which exhibit deregulated expression in prostate cancer.

Antisense c-myc retroviral vector suppresses established human prostate cancer

Prostate cancer eventually becomes androgen resistant, resumes growth, and kills the patient. Characterization of genetic events that lead to androgen refractory prostatic neoplasia has revealed the frequent overexpression of c-myc and uncontrolled prostate cancer proliferation. A novel strategy to combat advanced prostate cancer utilized a replication incompetent retrovirus that contained the mouse mammary tumor virus (MMTV) promoter within the retroviral vector to allow transcription of antisense c-myc gene within target prostate tumor cells. The transduction of cultured DU145 cells by XM6:MMTV-antisense c-myc RNA retrovirus did not affect cell proliferation in culture, yet a single direct injection of MMTV-antisense c-myc viral media into established DU145 tumors in nude mice produced a 94.5% reduction in tumor size compared to tumors treated with control virus MTMV sense fos and untreated tumor by 70 days. Two animals in the antisense c-myc-treated group had complete regression of their tumors. Histopathological examination of the tumors revealed that MMTV-antisense c-myc-transduced DU145 tumors had increased tumor cell differentiation, decreased invasion, and a marked stromal response. The mechanism for the antitumor effect of MMTV-antisense c-myc retrovirus appears to be suppression of c-myc mRNA and protein, and decreased bcl-2 protein. The in vivo transduction of prostate cancer cells with MMTV-antisense c-myc retroviruses reduced tumor growth by suppressing c-myc, resulting in the down-regulation of bcl-2 protein. Consequently, the MMTV-antisense c-myc retrovirus may be useful for gene therapy against advanced, hormone-refractory prostate cancer.

Antiproliferative effects of c-myc antisense oligonucleotide in prostate cancer cells: a novel therapy in prostate cancer

OBJECTIVES

To explore the possibility of using antisense oligonucleotide therapy for prostate cancer, we investigated the effect of c-myc-antisense-oligonucleotide (c-myc-As-ODN) in human prostate cancer cell lines such as LNCaP, PC3, and DU145.

METHODS

LNCaP, PC3, and DU145 cells were incubated in the presence of c-myc-As-ODN. Dose (0 to 10 microM) and time dependent (1 to 6 days) effects on proliferation and viability were examined by [3H]thymidine incorporation and MTT assay, respectively. Flow cytometry analysis was carried out to analyze cell cycle status by determining the DNA content in LNCaP cells. Control cultures received either c-myc-sense-ODN or scrambled (nonsense) nucleotides.

RESULTS

Time- and dose-dependent decreases in DNA synthesis and cell viability were noted for all three prostate cancer cell lines after c-myc-As-ODN treatment. Further studies using LNCaP cells indicated that these changes were accompanied by an increase in the percentage of cells with less than 2N DNA content after c-myc-As-ODN treatment. The results suggest that c-myc-As-ODN induces cell death. Comparison of a c-myc-As-ODN-treated group with a group subjected to isoleucine deprivation revealed that thymidine incorporation was almost the same in c-myc-As-ODN-treated LNCaP cells and in LNCaP cells at early S phase.

CONCLUSIONS

These results suggest that c-myc-As-ODN inhibits prostate cancer cell growth and proliferation mainly by decreasing cell viability.

Genetic changes in prostate cancer

Recent advances in molecular biology have allowed us to understand that it is the accumulation of genetic alterations which leads to each step of tumorigenesis. What the specific alterations may be, however, often varies with each neoplasm. Prostate cancer is somewhat unique in its presentation to the pathologist of a bewildering array of histologies difficult to assign to diagnostic categories and contributing to misinterpretations of underlying molecular events. As with any malignancy, it is of utmost importance to thoroughly analyze and record the genetic aberrations found in prostate cancer with the objective of correlation to the pathology and natural history of the disease. Multiple oncogenes and tumor suppressor genes have been investigated in both clinical and latent cancer using conventional mutational analyses. To probe deeper into these genes and to uncover novel molecular events, genomic tumor DNA were examined using restriction landmark genomic scanning (RLGS), a method which allows the identification and comparison of specific genetic alterations within large segments and multiple samples of DNA at a time. This article reviews what has been identified based on numerous molecular studies, focusing on the genetic alterations peculiar to human prostate cancer.

Epidermal growth factor-related peptides in human prostatic fluid: sources of variability in assay results

BACKGROUND

Prostatic fluid (PF) provides a unique medium for noninvasive evaluation of critical growth and differentiation signals in the prostatic microenvironment. The purpose of this study was to establish the feasibility of measuring two prostatic mitogens, epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) in PF, and specifically to quantify extraneous variability attributable to the assay itself, sample handling, or biological variation within an individual over time.

METHODS

PF was collected by transrectal massage from consecutive patients attending a urology clinic. Pooled PF and individual samples from 25 men with stable benign prostatic hyperplasia (BPH) were analyzed for EGF and TGF-alpha by radioimmunoassay and for total protein.

RESULTS

Reproducibility was adequate at dilutions as low as 1:50 (2-microliter pooled sample) and 1:5 (20 microliters) for EGF and TGF-alpha, respectively. Results were not affected by freeze-thaw cycles, time in storage, or protease inhibition in fresh PF. EGF and TGF-alpha were detectable in 100% and 92% of individual men, with respective means of 152 and 0.2 ng/ml. Correlations between two samples obtained from the same man within 12 months were highly significant (EGF r = 0.89, TGF-alpha r = 0.71). Protein concentrations were consistent over time; expression of either peptide per weight of protein rather than per volume did not improve within-man correlation. Between-man variability far exceeded within-man variability for both peptides, and was estimated to account for 84% and 61% of the total variability in EGF and TGF-alpha, respectively. There was no correlation between EGF and TGF-alpha in the same samples.

CONCLUSIONS

We conclude that men with BPH secrete consistent and distinct levels of EGF-related peptides in PF, and that these levels can be detected with acceptable sensitivity and precision by radioimmunoassay (RIA). Measurement of TGF-alpha, which has not been reported previously, requires a relatively larger sample.

Comparison of ras activation in prostate carcinoma in Japanese and American men

BACKGROUND

Comparative studies of point mutations in K-, N-, and H-ras oncogenes were performed on prostate carcinoma from Japanese and American patients to clarify the racial difference.

METHODS

We probed for mutations in 70 Japanese and 31 American specimens using polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) analysis and immunohistochemistry for ras p21.

RESULTS

Within the 70 Japanese specimens, eight mutations in codon 12 of K-ras (five GGT-->GTT transversions and three CGT-->GAT transitions) and one mutation in codon 12 of the N-ras gene (a GGT-->GTT transversion) were confirmed, whereas the American samples yielded only one definable mutation, a GGT-->GAT transition, in codon 12 of K-ras.

CONCLUSIONS

The frequency of ras gene mutations in clinical carcinoma in Japanese men was higher than that in American men. It is suggested that there may be fundamental differences in the etiology of prostate carcinoma in Japan and the United States, perhaps based on genetics and/or environmental factors.

P53 tumour-suppressor gene mutations are mainly localised on exon 7 in human primary and metastatic prostate cancer

Mutations in the p53 tumour-suppressor gene are among the most common genetic alterations in human cancers. In the present study we analysed the mutations in the p53 tumor-suppressor gene in 25 primary and 20 metastatic human prostate cancer specimens. DNA extracted from the paraffin-embedded sections was amplified by hot-start polymerase chain reaction, and p53 gene mutations in the conserved mid-region (exons 4-9) were examined using single-strand conformation polymorphism (SSCP) analysis and immunohistochemistry. In the present study, we used a novel hot-start PCR-SSCP technique using DNA Taq polymerase antibody, which eliminates primer-dimers and non-specific products. Because of this new technique, the results of PCR-SSCP showed very high resolution. Polymerase chain reaction products were sequenced directly for point mutations for the p53 gene. Mutations were found in 2 out of 25 primary prostate cancers (8%) and 4 out of 20 metastatic cancers (20%). Mutations were observed exclusively in exon 7 and not in exons 4, 5, 6, 8 or 9. Nuclear accumulation of p53 protein, determined by immunohistochemistry, correlated with the degree of metastasis in prostatic cancer.

Mitotic activity and prognosis in prostatic adenocarcinoma

Mitotic figures were quantitated by two different methods (number of mitotic figures in 10 high power fields, MI; number of mitotic figures/mm2 of neoplastic epithelium, M/V) in a series of 303 prostatic adenocarcinomas, and the results were related to clinical and histological features as well as to prognosis. Gleason score and mitotic indices were significantly interrelated. Invasive T3-4 tumors showed higher mitosis counts than did the local ones, and metastasis at the time of diagnosis was related to mitotic indices as well. Progression and progression-free survival were related significantly to Gleason score and mitotic indices. In univariate survival analysis, T-category, M-category, Gleason score, MI, and M/V were significant prognostic factors. In multivariate analysis, independent predictors of survival were M-category, T-category, Gleason score, patient age, and the M/V index. If the Gleason score was not included, M/V included all the available prognostic information in T1-2M0 carcinomas. The results show that, in addition to the conventional Gleason grading system, mitotic indices are useful prognostic parameters while evaluating the long-term prognosis in prostatic adenocarcinoma.

Analysis of prostatic fluid: evidence for the presence of a prospective marker for prostatic cancer

In an endeavor to identify marker(s) for prostatic cancer, proteins in prostatic fluids were analyzed by two-dimensional (2-D) gel electrophoresis. The fluids were obtained from five males who had no prostate lesions and five patients each with benign prostatic hyperplasia (BPH) and prostatic carcinoma (PCA). The specimens were collected directly over a mixture of protease inhibitors and centrifuged, and the supernatants were lyophilized and solubilized in sodium dodecyl sulfate mix. Identical amounts of proteins were pooled according to donors' prostate disease and the resulting samples were subjected to 2-D gel analysis employing the ISO-DALT system. The electrophoretograms were developed by silver or double stain. The samples of each group exhibited distinctive profiles with the exception of similar relative positions of major protein spots. A predominant protein occurring as several charge variants was consistently present in prostatic fluids of patients with PCA. This protein appeared to be a previously unknown constituent that we have called protein D (molecular weight approximately 22 kDa and isoelectric point approximately 4), and was undetectable in the fluids of "normal" men and patients with BPH. An analysis of pooled, unprocessed urine from PCA patients revealed that perhaps this protein is excreted in urine in very low quantities. These results strongly suggest that the potential of this protein as a marker for prostatic cancer should be further explored.

Prediction of pathologic stage and postprostatectomy disease recurrence by DNA ploidy analysis of initial needle biopsy specimens of prostate cancer

BACKGROUND

DNA ploidy determination of carcinomas in radical prostatectomy specimens has shown significant correlation with patient outcome, but the predictive value of ploidy status of cancers obtained by transrectal ultrasound-guided needle biopsies has not been studied extensively.

METHODS

Eighty-nine paired needle biopsy specimens (NBX) and radical prostatectomy (RPX) specimens from patients with early clinical stage (A2-B2) prostate cancer were evaluated for DNA content by image analysis of Feulgen stained tissue sections. Findings were compared with Gleason grading on the same specimens by univariate and multivariate analyses for prediction of local tumor invasion, metastasis, disease recurrence, and serum prostate specific antigen concentration during a 0.9-6.0 year clinical follow-up period.

RESULTS

There was excellent correlation of ploidy status between NBX and RPX specimens (P < 0.0001); NBX and RPX grades did not correlate. On RPX specimens, aneuploid status correlated with high tumor grade (P < 0.0005). Aneuploidy in NBX specimens was associated with a twofold higher rate of extracapsular spread (ECS) (P = 0.04). Aneuploid NBX tumors featured a tenfold greater frequency of metastasis than did diploid NBX tumors (P < 0.005). Radical prostatectomy grade correlated with ECS (P < 0.001) and presence of metastatic disease (P = 0.04). On multivariate logistic regression analysis, aneuploidy in both NBX and RPX specimens was the most significant variable and independently predicted the presence of metastasis (P = 0.006 for NBX; P = 0.028 for RPX). Tumor grade of NBX and RPX specimens did not independently predict metastatic disease or disease recurrence, but RPX grade was associated independently with ECS (P = 0.005). Aneuploid NBX tumors recurred after RPX three times more often than did diploid cases, which was significant on univariate (P < 0.001) and multivariate (P = 0.018) analyses using the Cox proportional hazards model. There was no correlation with NBX or RPX Gleason score and disease recurrence. Preoperative serum PSA concentration did not correlate with tumor grade or ploidy status, but on multivariate analysis, when paired with ploidy status, independently contributed to the propensity for ECS, metastasis, and disease recurrence.

CONCLUSIONS

DNA content analysis of early clinical stage prostate carcinoma needle biopsy specimens by image analysis directly correlates with radical prostatectomy specimen ploidy status and is associated independently, with the presence of metastasis, postprostatectomy disease recurrence, and ECS. Needle biopsy tumor grading did not correlate with prostatectomy grade and did not predict disease outcome accurately.

Tumorigenicity of SV40 T antigen immortalized human prostate epithelial cells: association with decreased epidermal growth factor receptor (EGFR) expression

Our primary objectives were to: 1) develop a system for the study of prostatic tumor evolution; and 2) examine the role of the epidermal growth factor/epidermal growth factor receptor (EGF/EGFR) pathway in prostate tumor progression. Adult human prostate epithelial cells previously immortalized by transfection with the SV40 T antigen gene (P69SV40T) produced tumors in only 2/18 mice with a 6 month latency period. Reinjection of cells recovered from these tumors after 1 or 2 cycles of growth in nude mice produced tumors in 2/4 and 2/3 mice with markedly decreased latent intervals of 12, 25, 25 and 25 days each. The chromosomal complement of each tumor was human, consistently pseudodiploid, and retained the Y chromosome. In both anchorage-independent and adherent cell growth assays, EGF stimulated proliferation by approximately 2-fold in both the parental P69SV40T line and the tumor sublines. The tumor sublines expressed less EGFR protein than the parental line, as assessed by Western immunoblotting and flow cytometric analysis. Immunoprecipitation revealed increased production of the 18 and 25 kDa TGF-alpha precursors parallel to decreases in detectable EGFR. The growth of both the parental P69SV40T line and the tumor sublines was inhibited by a neutralizing antibody to TGF-alpha under serum-free defined conditions. Inclusion of the TGF-alpha neutralizing antibody consistently inhibited the proliferation of the tumor sublines more than P69SV40T in both proliferation and [3H]thymidine incorporation assays. This finding suggests that the increased tumorigenicity and decreased latent interval observed among the human prostate tumor cells is partially due to activation of the TGF-alpha/EGFR autocrine network.

Proliferating cell nuclear antigen and p53 expression as prognostic factors in T1-2M0 prostatic adenocarcinoma

The expression of proliferating cell nuclear antigen and p53 protein was analysed by immunocytochemical methods (PC10, CM1 antisera) in 139 patients with T1-2M0 prostatic adenocarcinomas followed-up for > 12 years. p53 protein was expressed in 21 (15%) tumours (15%), the fraction of positive nuclei being very low (mean SE, 1% +/- 0.7%). Accumulation of p53 protein in epithelial cells was independent of tumour stage and Gleason score, and had no effect on prognosis. In 4 cases, p53 protein was expressed only in stromal cells. The fraction of PCNA-positive nuclei (evaluable in 116 cases) was higher in T2 than in T1 tumours (p < 0.001); furthermore, high Gleason score was positively correlated with PCNA positivity (p < 0.001). A finding of over 5% of PCNA-positive nuclei predicted progression in T and M categories and were a sign of poor outcome. The fraction of PCNA-positive stromal-cell nuclei was related to T-category with a borderline significance (p = 0.06). In a multivariate analysis of the prognostic factors, independent predictors of survival included Gleason score (p < 0.001), fraction of PCNA-positive nuclei (p = 0.013), observation before therapy (p = 0.05), and T-category (p = 0.07) in that order of significance. The results suggest that overexpression of p53 protein is of marginal prognostic value in local prostatic adenocarcinomas, whereas direct measurement of cell proliferation by PCNA immunolabelling provides important prognostic information in T1-2M0 tumours, in addition to the Gleason score.

Frequency and characterization of p53 mutations in primary and metastatic human prostate cancer

We have studied the frequency of mutations in the p53 gene in human prostate cancer. The investigated material consisted of 20 primary-tumor tissue specimens, obtained by transurethral resection and tissue specimens of 15 lymph-node metastases, obtained at total prostatectomy. The applied methods encompassed immunohistochemistry on frozen sections, using the monoclonal antibody PAb 1801, and single-strand conformation polymorphism (SSCP) analysis, after amplification of single exon sequences by PCR, on exons 5 to 8 of the p53 gene. The mutations, leading to aberrantly migrating bands in the PCR-SSCP analysis, were identified by direct sequencing of the PCR product. Immunohistochemical and PCR-SSCP analysis were completely confirmative. In the primary tumors, mutations were found in 10% of the specimens (codons 232 and 273), and in lymph-node metastases in 15% of the specimens (codons 248 and 273). In one case (codon 273), the same mutation was found both in the primary tumor and in the lymph-node metastasis. Our results show that p53 mutations are infrequent in both primary and metastatic prostate tumors. In addition, they indicate that there is no strict correlation between p53 mutation and tumor metastasis.