Immunohistochemical distribution patterns of epidermal growth factor receptor in malignant mesothelioma and non-neoplastic mesothelium

Cyclooxygenase-2, epidermal growth factor receptor, and aromatase signaling in inflammation and mesothelioma

Malignant mesothelioma or mesothelioma is a rare form of cancer that develops from transformed cells originating in the mesothelium, the protective lining that covers many of the internal organs of the body. It is directly linked to asbestos exposure, which acts as a carcinogen by initiating the carcinogenic process. Because of their shape, asbestos fibers can cross the membrane barriers inside the body and cause inflammatory and fibrotic reactions. Such reactions are believed to be the mechanism by which asbestos fibers may trigger malignant mesothelioma in the pleural membrane around the lungs. Carcinogens are known to modulate the transcription factors, antiapoptotic proteins, proapoptotic proteins, protein kinases, cell-cycle proteins, cell adhesion molecules, COX-2, and growth factor signaling pathways. This article reviews recent studies regarding some malignant mesothelioma molecular targets not only for cancer prevention but also for cancer therapy.

Epidermal growth factor receptor overexpression in malignant pleural mesothelioma: prognostic correlations

BACKGROUND

To evaluate epidermal growth factor receptor (EGFR) phenotypic expression and related gene status in malignant pleural mesothelioma (MPM) and to correlate the results with patients' prognosis.

METHOD

Eighty-three cases of MPM specimens were submitted to immunohistochemical (IHC) staining to evaluate the expression of EGFR protein; positive cases were submitted to fluorescence in situ hybridization (FISH) to investigate the gene status. Results were correlated with clinico-pathological characteristics and long-term survival.

RESULTS

Thirty-eight cases (46%) demonstrated a positive IHC reaction [30/57 (52%) epithelial and 8/20 (40%) biphasic whereas sarcomatous MPM were negative]. No association was recorded between EGFR IHC positive staining and age, gender, or asbestos exposure. Three out of 38 (8%) cases submitted to FISH were positive revealing gene amplification or polysomy. Mean follow-up was 15.4  months (range 2-44). Epithelial subtype only was confirmed to affect prognosis (2-years survival rate 40 vs. 18% for non-epithelial subtype, P = 0.042). When epithelial MPM patients were considered, IHC EGFR positive staining was demonstrated to be a negative prognostic factor (2-years survival rate 26 vs. 60% for IHC EGFR negative staining; P = 0.026).

CONCLUSIONS

EGFR overexpression is identified by IHC in 52% of epithelial MPM and is demonstrated to be a factor negatively affecting prognosis. Phenotypic overexpression seems not to be related to gene status alteration.

The extracellular domain of p185(c-neu) induces density-dependent inhibition of cell growth in malignant mesothelioma cells and reduces growth of mesothelioma in vivo

EGFR is involved in the density-dependent inhibition of cell growth, while coexpression of EGFR with erbB2 can render normal cells transformed. In this study, we have examined the effect of a species of p185 that contains the transmembrane domain and the extracellular domain of p185(c-neu), on growth properties of a human malignant mesothelioma cell line that coexpresses EGFR and erbB2. The ectodomain form of p185(c-neu) enhanced density-dependent inhibition of cell growth and we found that p21 induction appeared to be responsible for this inhibitory effect. Previously, the extracellular domain species was shown to suppress the transforming abilities of EGFR and p185(c-neu/erbB2) in a dominant-negative manner. The ability of this subdomain to affect tumor growth is significant, as it reduced in vivo tumor growth. Unexpectedly, we found that the domain did not abrogate all of EGFR functions. We noted that EGFR-induced density-dependent inhibition of cell growth was retained. Tyrosine kinase inhibitors of EGFR did not cause density-dependent inhibition of cell growth of malignant mesothelioma cells. Therefore, simultaneously inhibiting the malignant phenotype and inducing density-dependent inhibition of cell growth in malignant mesothelioma cells by the extracellular domain of p185(c-neu) may represent an important therapeutic advance.

EGFR expression: associations with outcome and clinicopathological variables in malignant pleural mesothelioma

Malignant mesothelioma (MM) is a fatal tumour of increasing incidence which is related to asbestos exposure. This work evaluated expression in MM of Epidermal Growth Factor Receptor (EGFR) by immunohistochemistry in 168 tumour sections and its correlations with clinicopathological and biological factors. The microvessel density (MVD) was derived from CD34 immunostained sections. Hematoxylin and eosin stained sections were examined for intratumoural necrosis. COX-2 protein expression was evaluated with semi-quantitative Western blotting of homogenised tumour supernatants (n=45). EGFR expression was correlated with survival by Kaplan-Meier and log rank analysis. Univariate and multivariate Cox proportional hazards models were used to compare the effects of EGFR with clinicopathological and biological prognostic factors and prognostic scoring systems. EGFR expression was identified in 74 cases (44%) and correlated with epithelioid cell type (p<0.0001), good performance status (p<0.0001), the absence of chest pain (p<0.0001) and the presence of TN (p=0.004), but not MVD or COX-2. EGFR expression was a good prognostic factor in univariate analysis (p=0.01). Independent indicators of poor prognosis in multivariate analysis were non-epithelioid cell type (p=0.0001), weight loss, performance status and WBC>8.3x10(9)L(-1). EGFR status was not an independent prognostic factor. EGFR expression in MM correlates with epithelioid histology and TN. EGFR may be a target for selective therapies in MM.

EGFR overexpression in malignant pleural mesothelioma. An immunohistochemical and molecular study with clinico-pathological correlations

The epidermal growth factor receptor (EGFR) is overexpressed in many epithelial malignancies, against which some antitumoral drugs have been developed. There is a lack of information as to EGFR expression in malignant pleural mesothelioma (MPM), an aggressive and fatal cancer poorly responsive to current oncological treatments. Our aim was to: (a) compare EGFR immunohistochemical expression with mRNA levels measured by real time PCR; (b) assess the relationships between EGFR expression and clinico-pathological data including survival; (c) analyze the EGFR mutations. We developed an immunohistochemical method of EGFR evaluation based on the number of immunoreactive cells and staining intensity in 61 MPMs. EGFR immunoreactivity was documented in 34/61 (55.7%) cases. A significant correlation between EGFR protein and mRNA levels (p = 0.0077) was found, demonstrating the reliability of our quantification method of EGFR membrane expression. Radically resected patients (p = 0.005) and those with epithelial histotype (p = 0.048) showed an increased survival. No statistical correlation between EGFR immunoreactivity and patients survival was observed. No EGFR mutation was documented. This study documents EGFR overexpression in MPM at the protein and the transcriptional levels; it proposes a reliable method for EGFR expression evaluation in MPM. EGFR levels are not associated with clinico-pathological features of patients, including survival.

Defective core-apoptosis signalling in diffuse malignant pleural mesothelioma: opportunities for effective drug development

Because of a lack of effective treatments, survival from diffuse pleural mesothelioma remains poor. Many people do not think that treatments for this disease are effective. The understanding of the biology of mesothelioma relevant to the apoptosis-resistant phenotype has been slow to advance. However, this is now changing, and strategies for rational therapeutic drug development are emerging that have the potential to change the natural history and improve survival in the increasing number of patients that will be diagnosed in the next two decades. This review discusses recent developments in apoptosis biology that are specific to mesothelioma and the therapeutic implications for this aggressive cancer.

Transforming growth factor alpha and epidermal growth factor receptor in reactive and malignant mesothelial proliferations

BACKGROUND

Growth factors such as transforming growth factor alpha (TGF-alpha) and epidermal growth factor receptor (EGFR) play an important role in cell proliferation. The immunohistochemical expression of these factors has been extensively studied in malignant tumors including mesothelioma. However, the comparative expression of these growth factors in mesothelioma and reactive mesothelial proliferations has been less well studied.

OBJECTIVE

To evaluate the possible role of TGF-alpha and EGFR in the clinically important distinction between reactive mesothelial proliferations and malignant mesothelioma.

METHODS

The expression of TGF-alpha and EGFR was studied in 39 cases of mesothelioma and 30 cases of reactive mesothelial proliferations by means of immunohistochemistry.

RESULTS

Fourteen (70%) of 20 reactive mesothelial proliferations tested and 29 (76%) of 38 mesotheliomas tested expressed TGF-alpha. One (3%) of 30 reactive mesothelial proliferations and 17 (45%) of 39 mesotheliomas expressed EGFR.

CONCLUSIONS

These results suggest an up-regulation of EGFR in mesothelioma as compared with reactive mesothelial proliferations. This up-regulation further suggests a possible use of EGFR as an adjunct immunohistochemical test in the differential diagnosis of mesothelioma and reactive mesothelial proliferations.

Increased serum concentrations of growth factor receptors and Neu in workers previously exposed to asbestos

OBJECTIVES

Epidermal growth factor receptor (EGFR) and oncogene Neu belong to a family of growth factor receptors which may play a part in carcinogenesis. Although increased serum concentrations of Neu and EGFR have been shown in several patients with asbestosis who later developed cancer, serum concentrations have not been studied in workers exposed in the past to asbestos but without asbestos related diseases.

METHODS

Serum concentrations of secreted growth factor receptors were studied in 300 workers exposed in the past to asbestos and the results were compared with those of 70 controls.

RESULTS

In the controls 4.3% (3/70) had EGFR values > 912 units/ml, compared with 39% (117/299) of the exposed group (p < 0.001). The difference in high values was even more pronounced for Neu with 4.3% of controls having Neu values > 2580 fmol/ml compared with 72% (216/299) of the exposed workers (p < 0.001). Pleural plaques predicted lower serum concentrations of EGFR but not lower Neu concentrations, and this finding remained significant after adjustment for age, exposure time, smoking, and time from initial exposure.

CONCLUSIONS

Enhanced secretion of EGFR and Neu was found in a large cohort of retired asbestos workers with a wide range of exposure and latency periods. They did not have asbestosis or cancer and their EGFR values were higher in those without plaques. Further studies are needed to confirm our results, to determine the source of the secreted growth factor receptors, and to study their possible value as risk factors in the development of cancer.

Prognostic implications of epidermal growth factor receptor immunoreactivity in squamous cell carcinoma of the oral mucosa

To evaluate the clinical significance of the expression of epidermal growth factor receptor (EGFr) in oral squamous cell carcinoma (SCC), 100 formalin-fixed, paraffin-embedded cases of this tumour and ten samples of normal oral mucosa were immunostained with a monoclonal anti-EGFr antibody using an immunoalkaline phosphatase (APAAP) technique. EGFr immunoreactivity was detected in 36 of 100 tumours and in all samples of normal mucosa. Tumour cells demonstrated distinct membrane staining in 14 cases and predominantly cytoplasmic staining in 22 additional cases. EGFr was exclusively localized on the cell membrane of normal epithelial cells. Kaplan-Meyer survival curves and Cox proportional hazard regression models were used to assess overall survival and disease-free survival. A significant positive correlation was shown between EGFr membranous immunoreactivity and prolonged survival, in both univariate and multivariate analyses. Accordingly, patients with oral SCC showing down-regulated expression of membranous EGFr, who are more likely to suffer recurrence and death, should be strictly followed up and possibly treated with more aggressive therapeutic regimens.

Expression of epidermal growth factor and epidermal growth factor receptor immunoreactivity in the asthmatic human airway

Chronic airway inflammation, one of the pathophysiologic features of bronchial asthma, is suspected to be responsible for irreversible pathological changes of airways, called airway remodeling. To examine the mechanisms of airway remodeling in asthma, we investigated the expression of epidermal growth factor (EGF) and its receptor immunohistochemically in asthmatic human airways. Airway specimens from seven patients with asthma were obtained from autopsied and surgically resected lungs. Control specimens were obtained from lungs of eight subjects without asthma and other pulmonary complications at autopsy. We stained those specimens by the avidin-biotin-peroxidase complex (ABC) method with anti-human polyclonal EGF antibody and monoclonal EGF receptor antibodies. Three different portions of airways-large bronchi (about 1 cm in diameter), small bronchi (about 3 mm in diameter), and peripheral airways (less than 2 mm in diameter)-were examined. The thickness of the bronchial smooth muscle and basement membrane was significantly greater in the asthmatic airways than in controls. Clear immunoreactivities of EGF were widely observed on bronchial epithelium, glands, and smooth muscle in asthmatic airways. In the controls, the bronchial epithelium and the bronchial glands partially expressed faint EGF immunoreactivity. For the EGF receptor, clear immunoreactivities were also observed on bronchial epithelium, glands, smooth muscle, and basement membrane in asthmatic airways. In control airways, only part of the bronchial epithelium and smooth muscle weakly expressed EGF receptor immunoreactivity. These results suggest a possible contribution of EGF to the pathophysiology of bronchial asthma, including airway remodeling.

PKC activation is required by EGF-stimulated Na(+)-H+ exchanger in human pleural mesothelial cells

Epidermal growth factor (EGF) stimulates the Na(+)-H+ exchanger, leading to enhanced cell proliferation. In human pleural mesothelial cells (PMCs), the intracellular signaling mechanism mediating the EGF-induced stimulation of the Na(+)-H+ exchanger has not yet been identified. Using a pH-sensitive fluorescent probe, 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, to measure changes in intracellular pH (pHi), we found that 1) EGF and 12-O-tetradecanoylphorbol 13-acetate (TPA; a phorbol ester) both stimulate the ethylisopropyl amiloride-sensitive Na(+)-H+ exchanger; 2) TPA-induced alkalosis can be blocked by protein kinase C (PKC) inhibitors (chelerythrine and staurosporine) or by PKC down-regulation, indicating that PKC activation is involved in the stimulation of the Na(+)-H+ exchanger. However, TPA-induced alkalosis is not blocked by tyrosine kinase inhibitors; and 3) the stimulatory effect of EGF on the Na(+)-H+ exchanger acts via stimulation of tyrosine kinase-receptor activity because it is inhibited by tyrosine kinase inhibitors (genistein, lavendustin A, and herbimycin A). It also involves PKC activation because EGF-induced alkalosis was blocked by PKC inhibitors. These results suggest that PKC activation is one of the downstream signals for EGF-induced activation of the Na(+)-H+ exchanger in primary cultures of human pleural mesothelial cells.

Growth factor responses and protooncogene expression of murine mesothelial cell lines derived from asbestos-induced mesotheliomas

Repeated intraperitoneal injections of crocidolite asbestos fibers induced diffuse malignant mesotheliomas in mice. A series of mesothelial cell lines was isolated from mice at different stages in the development of these tumors. The cell lines isolated from mice with mesotheliomas recapitulated their growth pattern in vivo and were tumorigenic when reinjected into syngeneic mice. Similar to human mesothelial cells, growth of the murine cell lines was stimulated by epidermal growth factor. Reactive mesothelial cells and mesotheliomas expressed the receptor for this growth factor. Crocidolite asbestos fibers have been reported to induce sustained expression of the c-fos and c-jun protooncogenes in rat pleural mesothelial cells in vitro (Heintz et al, Proc. Natl. Acad. Sci. USA 90: 3299-303, 1993). Human malignant mesotheliomas have been shown to express c-fos in situ (Ramael et al, Histol. Histopathol. 10: 639-643, 1995). Two of the cell lines derived from highly invasive murine mesotheliomas overexpressed c-fos and c-jun. This murine model recapitulates the histopathology, growth factor responses, and protooncogene expression of human malignant mesotheliomas.

WT1 mutation in malignant mesothelioma and WT1 immunoreactivity in relation to p53 and growth factor receptor expression, cell-type transition, and prognosis

The Wilms tumour 1 (WT1) gene is believed to contribute to the growth and differentiation of certain tissues, including mesothelium. This study assessed WT1 gene status by mutational screening in 42 malignant mesotheliomas (MMs) and 3 MM cell lines and detected two tumours with identical heterozygous single nucleotide deletions in intron 7, with no apparent consequence for WT1 function. Furthermore, the expression pattern of the WT1 gene was studied in MMs and related lesions using three anti-WT1 monoclonal antibodies (MAbs). Strong to moderate nuclear immunoreactivity was noted in MM in situ (54/56), cultured mesothelioma cells (4/5), and hyperplastic and normal pleural (non-neoplastic, NNM) specimens. WT1 immunoreactivity was absent in all primary tumours of lung and in pleural metastases from adenocarcinomas of breast and colon; immunoreactivity was present in pleural metastases from renal carcinomas, melanomas, and papillary carcinomas of the ovary. Expression of the WT1 protein in MM was not correlated with survival. Coordinate expression of the WT1 protein and its putative transcriptional target genes was determined by correlating WT1 immunostaining with epidermal growth factor receptor (EGF-R) and insulin-like growth factor 1 receptor (IGF-1R) expression on MM and NNM; no significant correlation was found, irrespective of p53 expression status. Finally, the putative involvement of WT1 in cell-type transition was supported by this study, in that epithelial mesothelioma showed the strongest WT1 immunoreactivity while sarcomatous mesothelioma showed the least.

Detection of numerical chromosomal aberrations in paraffin-embedded malignant pleural mesothelioma by non-isotopic in situ hybridization

An in situ hybridization (ISH) study on paraffin sections of 13 malignant mesotheliomas was performed to detect numerical chromosomal aberrations with biotin-labelled DNA probes specific for the centromeric regions of chromosomes 1, 3, 6, 7, 11, and 17. All chromosomes contributed to numerical changes, which can be summarized as follows: first, a monosomy for chromosome 6 was found in one case; second, in five cases a trisomy for at least one chromosome was detected; and third, in seven cases a pentasomy or a higher polysomy was found for at least one chromosome. Although these data have to be confirmed on a larger group of patients, survival analysis of this group showed no significant difference between the first and second groups taken together and the third group. In this study no specific numerical chromosomal aberrations were identified. Nevertheless, numerical gains appear to be more frequent than has previously been shown by karyotype analysis.

Autocrine stimulation of a human lung mesothelioma cell line is mediated through the transforming growth factor alpha/epidermal growth factor receptor mitogenic pathway

Malignant cells frequently acquire a certain independency of exogenous growth factors via the coexpression of epidermal growth factor receptor (EGFR) and epidermal growth factor (EGF)-related molecules. In the present study we investigate a possible involvement of EGF-related molecules in the growth of human lung mesothelioma. Four well-characterised cell lines are analysed for their responsiveness to exogenous EGF and transforming growth factor alpha (TGF-alpha) as well as for coexpression of EGFR and EGF/TGF-alpha. Both growth factors are able to stimulate DNA synthesis in three cell lines, although the degree of responsiveness is very variable, but neither EGF nor TGF-alpha has an effect on the cell line ZL34. In contrast, no heterogeneity is observed in the expression of EGFR, which is similarly high in all cell lines. Analysis of cell supernatants reveals that, whereas no EGF is detected, TGF-alpha is released by two cell lines. Furthermore, these two cell lines, ZL5 and ZL34, are shown to express the membrane anchored precursor pro-TGF-alpha. Thus, coexpression of EGFR and TGF-alpha is observed on two mesothelioma cell lines. The potential autocrine mitogenic role of TGF-alpha in these two cell lines was tested using neutralising antibodies against TGF-alpha and EGFR. In ZL5 cells DNA synthesis was not affected by the presence of neutralising antibodies, indicating that an external autocrine mitogenic pathway is not active in these cells. In ZL34 cells, however, the potential autocrine loop could be disrupted, as DNA synthesis was significantly reduced in the presence of neutralising antibodies. This result gives strong evidence for an autocrine role of TGF-alpha in the growth of the mesothelioma cell line ZL34.

Expression of epidermal growth factor receptor in bladder cancer as related to established prognostic factors, oncoprotein (c-erbB-2, p53) expression and long-term prognosis

The expression of epidermal growth factor receptor (EGFR) was studied immunohistochemically in 234 cases of transitional cell bladder cancer. EGFR was overexpressed in 35% of cases and distinct nuclear localisation of EGFR positivity was found in 31% of the tumours. Overexpression was related to invasive growth, grade 2-3 histology, non-papillary type, DNA aneuploidy and high proliferation rate of cancer cells. The expressions of p53 and EGFR were interrelated, while expression of c-erbB-2 was independent of EGFR expression. Progression of superficial tumours, recurrence-free survival and survival were independently related to overexpression of EGFR in multivariate analysis. T category, S-phase fraction and non-papillary type included all the available prognostic information when the entire cohort was analysed by multivariate methods. The results show that overexpression of EGFR is related to several malignant features and prognosis in superficial bladder cancer. Moreover, the results suggest that overexpression of EGFR is usually a late event in bladder cancer development related to genetic instability rather than an early event in malignant transformation. Further studies are still needed to establish whether the direct measurement of cell proliferation or analysis of growth factor receptors and other oncoproteins gives more accurate prognostic information in bladder cancer.

Immunohistochemical staining of ras oncogene product in neoplastic and non-neoplastic mesothelial tissues: immunoreactivity for N-ras and lack of immunohistochemical staining for Ha-ras and K-ras

Immunohistochemical staining of 36 malignant mesotheliomas and 45 cases of non-neoplastic mesothelium including 20 specimens with signs of hyperplasia were investigated using murine monoclonal antibodies directed against p21 ras protein, Ha-ras protein, K-ras protein, and N-ras protein. All cases of non-neoplastic mesothelium and the majority of the malignant mesotheliomas (78 per cent) showed cytoplasmic and often submembranous immunoreactivity in more than 50 per cent of the cells with both the pan-ras and N-ras antibody. No immunoreactivity was observed for Ha- and K-ras. There was no statistically significant difference with respect to immunoreactivity between neoplastic and non-neoplastic mesothelium or between the various mesothelioma subtypes.