Serum oncoproteins and growth factors in asbestosis and silicosis patients

Role of p53 in Regulating Radiation Responses

p53 is known as the guardian of the genome and plays various roles in DNA damage and cancer suppression. The p53 gene was found to express multiple p53 splice variants (isoforms) in a physiological, tissue-dependent manner. The various genes that up- and down-regulated p53 are involved in cell viability, senescence, inflammation, and carcinogenesis. Moreover, p53 affects the radioadaptive response. Given that several studies have already been published on p53, this review presents its role in the response to gamma irradiation by interacting with MDM2, NF-κB, and miRNA, as well as in the inflammation processes, senescence, carcinogenesis, and radiation adaptive responses. Finally, the potential of p53 as a biomarker is discussed.

Expression of p21ras-related protein in the plasma and tissue of patients with adenomas and carcinomas of the colon

Abstract Over-expression of p21 ras-related protein was determined in the plasma by immunoblotting and in the tissue by immuno-histochemistry in a cohort of patients undergoing colonoscopy. In the plasma samples, p21 ras over-expression was detected in: 9% (4/47) of normal controls; 21% (13/61) of individuals with normal colonoscopies but with a prior history of colonic neoplasia; 12% (4/33) of small adenoma patients, 29% (6/21) of large adenoma patients; 63% (5/8) of carcinoma-in-adenoma patients; 50% (2/4) of Dukes' A carcinoma patients; and 20% (2/10) of Dukes' B-D carcinoma patients. In the tissue samples, p21 ras over-expression was detected in: 25% (2/8) of small adenoma patients; 44% (4/9) of large adenoma patients; 100% (4/4) of carcinoma-in-adenoma patients; and 33% (1/3) of Dukes' B-C carcinoma patients. For matched plasma-tissue pairs, there was a statistically significant correlation for p21 ras over-expression (R = 0.47, p = 0.02).

Differences in gene expression and cytokine production by crystalline vs. amorphous silica in human lung epithelial cells

Background

Exposure to respirable crystalline silica particles, as opposed to amorphous silica, is associated with lung inflammation, pulmonary fibrosis (silicosis), and potentially with lung cancer. We used Affymetrix/GeneSifter microarray analysis to determine whether gene expression profiles differed in a human bronchial epithelial cell line (BEAS 2B) exposed to cristobalite vs. amorphous silica particles at non-toxic and equal surface areas (75 and 150 × 10⁶μm²/cm²). Bio-Plex analysis was also used to determine profiles of secreted cytokines and chemokines in response to both particles. Finally, primary human bronchial epithelial cells (NHBE) were used to comparatively assess silica particle-induced alterations in gene expression.

Results

Microarray analysis at 24 hours in BEAS 2B revealed 333 and 631 significant alterations in gene expression induced by cristobalite at low (75) and high (150 × 10⁶μm²/cm²) amounts, respectively (p < 0.05/cut off ≥ 2.0-fold change). Exposure to amorphous silica micro-particles at high amounts (150 × 10⁶μm²/cm²) induced 108 significant gene changes. Bio-Plex analysis of 27 human cytokines and chemokines revealed 9 secreted mediators (p < 0.05) induced by crystalline silica, but none were induced by amorphous silica. QRT-PCR revealed that cristobalite selectively up-regulated stress-related genes and cytokines (FOS, ATF3, IL6 and IL8) early and over time (2, 4, 8, and 24 h). Patterns of gene expression in NHBE cells were similar overall to BEAS 2B cells. At 75 × 10⁶μm²/cm², there were 339 significant alterations in gene expression induced by cristobalite and 42 by amorphous silica. Comparison of genes in response to cristobalite (75 × 10⁶μm²/cm²) revealed 60 common, significant gene alterations in NHBE and BEAS 2B cells.

Conclusions

Cristobalite silica, as compared to synthetic amorphous silica particles at equal surface area concentrations, had comparable effects on the viability of human bronchial epithelial cells. However, effects on gene expression, as well as secretion of cytokines and chemokines, drastically differed, as the crystalline silica induced more intense responses. Our studies indicate that toxicological testing of particulates by surveying viability and/or metabolic activity is insufficient to predict their pathogenicity. Moreover, they show that acute responses of the lung epithelium, including up-regulation of genes linked to inflammation, oxidative stress, and proliferation, as well as secretion of inflammatory and proliferative mediators, can be indicative of pathologic potential using either immortalized lines (BEAS 2B) or primary cells (NHBE). Assessment of the degree and magnitude of these responses in vitro are suggested as predictive in determining the pathogenicity of potentially harmful particulates.

Serum growth factors in asbestosis patients

Various growth factors, including platelet-derived growth factor (PDGF) and transforming growth factor (TGF)-beta, have been implicated in the pathogenesis of asbestos-induced disease. PDGF and TGF-beta levels were determined by enzyme-linked immunosorbent assays in the banked serum samples of a cohort of workers with asbestosis, and the relationships of the growth factor levels to the subsequent development of cancer and to the radiographic severity and progression of asbestosis in the cohort were examined. Serum levels of PDGF and TGF-beta were found to be unrelated to the development of cancer, and serum levels of PDGF were found to be unrelated to the severity and progression of asbestosis. However, serum levels of TGF-beta were found to be statistically significantly related to disease severity (p = 0.01), increasing approximately 2.4-fold from ILO radiographic category 0 to category 3, and they were marginally related to disease progression (p = 0.07), in multivariate analysis controlling for other contributory factors including cumulative asbestos exposure. This suggests that serum TGF-beta may be a useful biomarker for asbestos-induced fibrotic disease.

Oncogene and tumor-suppressor gene products as serum biomarkers in occupational-derived lung cancer

Since lung cancer is the most frequent occupational cancer and one of the leading causes of cancer mortality in the world, it is one of the biggest challenges for research. In the literature, there are inconsistent results regarding the utility of the serum biomarkers p53, anti-p53 antibodies, EGF receptor or Ras. Based on the published results, routine use of these biomarkers for detection of occupationally derived lung carcinomas is not currently recommended. In this review, we summarize the literature and discuss the relevance of these oncogene and tumor-suppressor gene products as serum biomarkers in occupational-derived lung cancer.

Mechanistically identified suitable biomarkers of exposure, effect, and susceptibility for silicosis and coal-worker's pneumoconiosis: a comprehensive review

Clinical detection of silicosis is currently dependent on radiological and lung function abnormalities, both late manifestations of disease. Markers of prediction and early detection of pneumoconiosis are imperative for the implementation of timely intervention strategies. Understanding the underlying mechanisms of the etiology of coal workers pneumoconiosis (CWP) and silicosis was essential in proposing numerous biomarkers that have been evaluated to assess effects following exposure to crystalline silica and/or coal mine dust. Human validation studies have substantiated some of these proposed biomarkers and argued in favor of their use as biomarkers for crystalline silica- and CWP-induced pneumoconiosis. A number of "ideal" biological markers of effect were identified, namely, Clara cell protein-16 (CC16) (serum), tumor necrosis factor-alpha (TNF-alpha) (monocyte release), interleukin-8 (IL-8) (monocyte release), reactive oxygen species (ROS) measurement by chemiluminescence (neutrophil release), 8-isoprostanes (serum), total antioxidant levels measured by total equivalent antioxidant capacity (TEAC), glutathione, glutathione peroxidase activity, glutathione S-transferase activity, and platelet-derived growth factor (PDGF) (serum). TNF-alpha polymorphism (blood cellular DNA) was identified as a biomarker of susceptibility. Further studies are planned to test the validity and feasibility of these biomarkers to detect either high exposure to crystalline silica and early silicosis or susceptibility to silicosis in gold miners in South Africa.

Plasma Mutant-p53 Protein and Anti-p53 Antibody as a Marker: An Experience in Vinyl Chloride Workers in Italy

OBJECTIVE

The objective of this study was to examine the presence of mutant-p53 protein (p53Ag) and antibodies to p53 protein (p53Ab) in a population of workers exposed to vinyl chloride (VC).

METHOD

We have investigated the presence of two cancer markers in the plasma of 151 subjects exposed to varying concentrations of VC (4-2823 ppm). The investigation took place in two sessions: in 1999, the analysis was limited to p53Ab, and in 2000, the analysis was repeated and extended to include also the mutant-p53Ag. The available information on the subjects in this study includes age, total years of employment in the VC polymerization industry, exposure concentration, results of abdominal ultrasonogram, hepatitis status, smoking and alcohol drinking status, and clinical records. Logistic regression analyses were performed to calculate the association between prevalence of positivity for p53Ab or mutant-p53Ag and cumulative VC exposure concentration after adjustment for confounding factors. t test and chi analyses were performed to test significant differences among groups.

RESULTS

Three (1.9%) of the 151 workers exposed to VC resulted seropositive for the mutant-p53Ag and five (3.3%) for the p53Ab. All seropositive subjects are distributed in the highest exposure classes (>1000 ppm). No seropositivity was found among controls. The stratified relationship between seropositivity and exposure appeared statistically significant (chi = 23.65 for mutant-p53Ag and 30.35 for p53Ab).

CONCLUSIONS

revealing its presence in subjects having a history of VC exposure greater than 1000 ppm. On the basis of this study, and the clinical experience of the authors, the presence of a minimum threshold for the carcinogenic effects of VC is hypothesized.

Serum PDGF-AB in pleural mesothelioma

Overexpression of platelet-derived growth factor (PDGF) has been observed in lung and pleural tumors. The aim of this study was to evaluate the diagnostic and prognostic role of serum PDGF in pleural mesothelioma (PM). Four groups of subjects were studied: 93 malignant PM patients, 33 primary non small cell lung cancer patients, 51 subjects exposed to asbestos, defined as high-risk controls, and 24 healthy controls. PDGF-AB mean concentration was higher in PM patients (45.8 ng/ml) than in high-risk controls (33.1 ng/ml) and healthy controls (26.8 ng/ml). Using the cut-off level of 49.8 ng/ml, corresponding to the mean+2SD of PDGF-AB in healthy controls, 43% of PM patients showed positive PDGF-AB levels. Survival was evaluated in 82 PM patients. At the end of the follow-up (median 9.8 months) 80.5% of patients had died. Median survival was 13.1 and 7.9 months for patients with PDGF-AB lower and higher than the cut-off, respectively. Adjusting for age, sex, histology and platelet count, positive PDGF-AB levels were associated with lower survival (OR=1.2, 95%CI: 0.9-1.6), even if not significantly so. In conclusion, serum PDGF may represent a useful additional parameter to prognostic factors already available for PM.

p53 autoantibodies predict subsequent development of cancer

Because TP53 mutations can induce an immune response and can occur early in the carcinogenic process for some tumors, p53 autoantibodies may be useful biomarkers for risk of development of cancer. Using banked serum samples from an asbestosis cohort at high risk for cancer, we demonstrate for the first time a statistically significant relationship between p53 autoantibodies and the subsequent development of malignancy (hazard ratio [HR] = 5.5, 95% confidence interval [CI] = 2.8-10.9) with a positive predictive value of 0.76 and an average lead time to diagnosis of 3.5 years. p53 autoantibodies were also significantly associated with p53 alterations in the resultant tumors (kappa = 0.78, p = 0.01).

Molecular epidemiology of plasma oncoproteins in vinyl chloride monomer workers in Taiwan

AIMS

To determine the presence of Asp13-p21-ki-ras oncoprotein and p53 oncoprotein in the plasma of vinyl chloride monomer (VCM)-workers in Taiwan.

METHODS

We used enhanced chemiluminescence (ECL) western blotting to detect Asp13-p21-ki-ras and ELISA to detect mutant p53 protein (p53-Ag) and anti-p53 antibodies (p53-Ab) in the plasma of VCM-exposed workers.

RESULTS

Twenty-five out of 251 (10%) VCM-workers were positive for Asp13-p21-ki-ras in plasma, but 0 out of 36 controls were positive. There were 15 out of 95 (15.8%) plasma-positives among the more highly exposed (> 480 ppm-month) workers and 10 out of 156 (6.4%) plasma-positives among the lesser exposed (< or = 480 ppm-month). Compared to the unexposed controls, age and drinking adjusted odds ratios (95% CI) were 1.2 (0.1, 9.8) in the lower exposed workers, and 4.8 (0.8, 28) in the higher exposed workers, and there was a significant linear trend between exposure and plasma positivity (P=0.001). Thirty-three out of 251 (13.2%) VCM-workers were positive for the p53 over-expression (10% with positive p53-Ag and 2.8% with positive p53-Ab). There was a significant association between cumulative VCM exposure concentration and positive p53 expression (P=0.032) among VCM-workers after adjusting for age, hepatitis, drinking and smoking status.

CONCLUSIONS

Asp13-p21-ki-ras oncoprotein and p53 over-expression (p53-Ag or p53-Ab) can be found in the plasma of VCM-workers in Taiwan, and a significant dose-response relationship exists between plasma oncoproteins expression and VCM exposure.

Association between the ras p21 oncoprotein in blood samples and breast cancer

To assess the potential of using oncoprotein levels in blood as a marker of breast cancer status, we measured ras p21 in blood samples taken from 34 breast cancer cases and 60 non-cancer controls including 26 women with benign breast disease (BBD) and 34 healthy women. Plasma samples drawn before surgery or at routine office visit were analyzed for ras p21 by Western blot with computer aided image analysis to measure staining intensity in integrated pixel units (IPU). We found detectable levels of ras p21 in 53% of the blood samples of cases, in 27% of the BBD controls and 26% of the healthy controls. Comparing cases to the combined control group (n=60) and controlling for known breast cancer risk factors, ras p21 was associated with breast cancer status (odds ratio=5.22, 95% CI=1.58-17.23). The median levels of ras p21 staining were higher in cases (7.04 IPU, P=0.03) compared to BBD controls (0.00 IPU) or healthy controls (0.00 IPU). The sensitivity of the assay for detecting breast cancer was 50% which compares favorably with that seen for erbB-2 ( approximately 10%), a more extensively studied blood-borne tumor marker. Ras p21 may be useful in the early detection of breast tumors and in post-surgical follow-up of patients, giving patients and physicians new tools for managing breast cancer.

Use of biomarkers in risk assessment

The systematic development and application of biomarkers in environmental health risk assessment is a relatively new field. At first, the major interest was in biomarkers of exposure, borrowing concepts from pharmacology, then it moved from the external estimates of exposure to internal measures of dose, and ultimately, to markers of target dose. While these markers provide evidence of exposures, they do not provide evidence of that toxicological damage has occurred. For this reason, measurements of DNA adducts and protein adducts are of interest, since they may provide bridges between exposures and disease end-points. In parallel, more quantitative and more sensitive end-points for diseases have been sought. Again, with advancing techniques in cytogenetics, extensive studies were conducted on such markers as chromosomal aberrations, micronuclei and other changes deemed to represent genomic damage. However, these types of end-points are quite unspecific for application to new hazards of uncertain human toxic (carcinogenic) potential. Recent work focusing on more specific early-effect markers such as certain oncogenes and tumour-suppressor genes have substantial promise as shown by work with aflatoxins and vinyl chloride. Such studies have also enhanced mechanistic insight. The advances in molecular genetics have led to an upsurge in interest in most susceptibility factors, and identification of polymorphisms of various enzymes has become possible. Ongoing search for "ultra-high risk" individuals may be fruitful, but probably only relevant to a small segment of potentially exposed populations. Factors associated with a small differential risk, however theoretically or mechanistically important, offer only little practical use.

Serum ras (p21) as a marker for occupationally derived lung cancer?

Certain subsets of the population are especially sensitive to carcinogens, and this can be determined using molecular biological methods. In the literature there has been evidence presented for the use of p21ras (ras) as a tumor marker for human carcinogenic substances such as asbestos, polycyclic aromatic hydrocarbons, and vinyl chloride in the workplace. In this study we have examined whether serum ras could serve as a biomarker for the early detection of occupationally derived lung cancer, with an emphasis on Schneeberger (radon-induced) lung cancer. Sera were taken from 65 male tumor patients. Fifty-nine patients suffered from primary lung cancer (including 18 patients with Schneeberger lung cancer and 12 patients with asbestos-related lung cancer). Additionally, 29 patients with non-malignant lung disease, and a healthy control group (44) including 32 former uranium miners of SDAG Wismut exposed to ionizing radiation (radon and its decay products) were examined. Ras protein was determined via three different methods: 1) immunoprecipitation followed by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting; 2) SDS-PAGE using 5-17% gradient gels followed by Western blotting; 3) pre-incubation with Blue Sepharose, SDS-PAGE on 5-17% gradient gels, and Western blotting. The results show that 1 ng ras protein was measurable in serum standards. This protein could not be detected in patient sera or in sera from any of the study groups. Thus, ras cannot be considered useful as a marker for the early detection of asbestos-induced or Schneeberger lung cancer.

Serum levels of pantropic p53 protein and EGF-receptor, and detection of anti-p53 antibodies in former uranium miners (SDAG Wismut)

BACKGROUND

The oncogene product EGF-receptor (EGF-R), the tumor suppressor gene product p53, and anti-p53 antibodies are detectable in serum of certain cancer patients. Increased levels of some of these products were reported in lung cancer patients after occupational asbestos exposure, after exposure to polycyclic aromatic hydrocarbons or vinyl chloride. This molecular epidemiological study investigated the use of serum EGF-R, p53-protein, and anti-p53 antibodies as biomarkers for detection of effects of radon and its decay products.

METHODS

Serum EGF-R, p53-protein, and anti-53 antibodies were measured using ELISA in former uranium miners of SDAG Wismut without lung disease (n=106) and miners with Schneeberg lung cancer (n=22). They were compared with healthy subjects (n=23), patients with lung cancer not due to ionizing radiation (n=88), and patients with non-malignant lung or pleural diseases (n=50).

RESULTS

No significantly elevated or decreased serum values for p53 protein, EGF-R, or anti-p53 antibodies could be found. There was no correlation of these with Working Level Months (WLM).

CONCLUSIONS

p53 protein, EGF-R, or anti-p53 antibodies in serum are not useful as biomarkers for detection of lung cancer related to ionizing radiation (i.e., Schneeberg lung cancer).

Examination of ras oncoproteins in human plasma from healthy controls and workers exposed to petroleum emissions, including benzene-related compounds

Ras oncoproteins in blood plasma from workers exposed to petroleum emissions and unexposed controls were examined from Polish and Estonian samples. Twenty-four workers and 35 unexposed controls were examined from Poland and 97 exposed and 40 unexposed controls from Estonia. Of the Estonian workers, 50 were exposed to benzene in a benzene production plant and 47 to polyaromatic hydrocarbons and benzene in a cokery. Blood plasma proteins were separated by gel electrophoresis, transferred to a nitrocellulose membrane by Western blotting and detected by chemiluminescence using a monoclonal antibody as the primary antibody. There were no statistically significant differences between the exposed and the control groups in either the Polish or the Estonian samples.

p53 protein, EGF receptor, and anti-p53 antibodies in serum from patients with occupationally derived lung cancer

The oncogene product epidermal growth factor receptor (EGF-R), the tumour suppressor gene product p53 and anti-p53 antibodies are detectable in the serum of certain cancer patients. Increased levels of some of these products were reported in lung cancer patients after occupational asbestos exposure and after exposure to polycyclic aromatic hydrocarbons or vinylchloride. In the first step, this study investigated the possible diagnostic value of serum EGF-R, p53-protein and anti-p53 antibodies, measured by an enzyme-linked immunosorbent assay, in lung tumour patients. In addition to being investigated on a molecular epidemiological basis, these parameters were examined as biomarkers of carcinogenesis, especially with regard to asbestos incorporation effects or of radon-induced lung cancers. Also, a possible effect of cigarette smoking and age dependence were studied. A total of 116 male patients with lung or pleural tumours were examined. The histological classification was four small-cell cancers, six large-cell cancers, 32 adenocarcinomas, 47 squamous carcinomas, 12 mixed lung carcinomas, five diffuse malignant mesotheliomas and ten lung metastasis of extrapulmonary tumours. Twenty-two lung cancers and all mesotheliomas were related to asbestos, 22 lung cancers were related to ionizing radiation and 61 patients had cigarette smoke-related lung cancer. Besides these patients 50 male patients with non-malignant lung or pleural diseases were included; of the latter eight subjects suffered from asbestosis. Controls were 129 male subjects without any lung disease. No significantly elevated or decreased serum values for p53 protein, EGF-R, or anti-p53 antibodies as a function of histological tumour type, age, or degree and type of exposure (asbestos, smoking, ionizing radiation) could be found. The utility of p53-protein, EGF-R and anti-p53 antibodies as routine biomarkers for screening occupationally derived lung cancers is limited.

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.

Use of biomarkers--new frontiers in occupational toxicology and epidemiology

The incorporation of biomarkers into occupational toxicology and epidemiology some 25 years ago marked a turning-point for the discipline. The advances in molecular biology have provided new tools. At first, the major interest was in biomarkers of exposure, borrowing concepts from pharmacology, then it moved from the external estimates of exposure to internal measures of dose, and ultimately, to markers of target dose. Concerted efforts to measure carcinogens at the molecular level, e.g. DNA adducts, occupied a substantial fraction of the biomarkers work. In parallel, more quantitative and more sensitive end-points for etiological studies were sought earlier. Again, with advancing techniques in cytogenetics, extensive studies were conducted on such markers as sister chromatid exchanges (SCEs), micronuclei and other changes deemed to represent genomic damage. However, these types of end-points were quite unspecific for application to new hazards of uncertain human carcinogenic potential. Recent work focusing on more specific early-effect markers such as certain oncogenes and tumour-suppressor genes have substantial promise as shown by work with aflatoxins and vinyl chloride. Such studies have also enhanced mechanistic insight. The advances in molecular genetics have led to an upsurge in interest in most susceptibility factors, and identification of polymorphisms of various enzymes has become possible. Ongoing search for 'ultra-high risk' individuals may be fruitful, but probably only relevant to a small segment of potentially exposed populations. Factors associated with a small differential risk, however theoretically or mechanistically important, offer only little practical use.

Molecular markers of carcinogenesis

The protein products of oncogenes and tumor suppressor genes play critical roles in the development of many cancers. The expression of a number of these proteins can be detected in extracellular fluids such as blood. This article reviews the literature on the application of methods for the detection of the proteins of oncogenes and tumor suppressor genes in the blood of humans with cancer or at risk for the development of cancer. The detection of these proteins in blood may be useful molecular markers of carcinogenesis that could play an important part in cancer diagnosis, prognosis, and prevention.

Examination of ras (P21) proteins in plasma from workers exposed to benzene emissions from petrochemical plants and healthy controls

Exposure of workers to benzene and polyaromatic hydrocarbons has been documented to be at relatively high levels in the production of benzene and in the coking process at a petrochemical plant in the oil shale area in Estonia. Altogether 97 plasma samples from workers and 40 from unexposed matched referents from two samplings in different seasons were analyzed for the presence of ras (P21) proteins; of the workers 50 were exposed to benzene in the benzene production plant and 47 to polyaromatic hydrocarbons and benzene in a cokery. Proteins were separated by gel electrophoresis, transferred to a nitrocellulose membrane by Western blotting and detected by chemiluminescence, using a monoclonal antibody as the primary antibody. There were no statistically significant differences between the exposed and the referent groups. The results are thus in keeping with the lack of exposure related cytogenetic effects for this same workforce.

Molecular epidemiology: cancer risk assessment using biomarkers for detecting early health effects in individuals exposed to occupational and environmental carcinogens

Detecting changes that precede the overt symptoms of cancer and identifying measurable indices of such changes in persons exposed to occupational and environmental carcinogens constitutes one of the primary objectives of molecular epidemiology research. Biomarkers represent a valuable research tool that makes it possible to attain that objective. Suitably selected biomarker sets may provide information on the extent of exposure to carcinogenic agents (internal dose, biologically effective dose), detect early changes caused by those agents in the exposed organism, and identify individuals with a particularly high risk of cancer development. The tremendous progress in research on the mechanisms of cancer initiation and promotion has enabled the assessment of cancer risk in healthy individuals by examining specific results from determinations of suitably selected biomarkers. The finding that gene defects (gene mutations and changes of their expression) constitute the background of carcinogenesis has resulted in molecular biology becoming focused on detecting defective genes or proteins synthesized under control of the defective genes.

Selective hyperexpression of c-jun oncoprotein by glass fiber- and silica-transformed BALB/c-3T3 cells

Mining and mineral processing are important industries in the United States. A large number of workers are potentially exposed to silica during mining and to glass fibers during manufacturing. There is a concern regarding lung cancer risk among workers exposed to silica and glass fibers. Our previous studies showed that both glass fibers and silica induced transformation of BALB/c-3T3 cells. In order to explore the relationship between silica and glass fiber-induced cell transformation and oncoprotein expression, the protein products of seven proto-oncogenes (c-K-ras, c-H-ras, c-sis, c-myc, c-myb, c-erb B1 and c-jun) and one tumor suppressor gene (p53) were examined in BALB/c-3T3 cells transformed by glass fibers or silica using immunoblotting with specific monoclonal or polyclonal antibodies. The results showed that all transformants, including eight induced by glass fibers and eight by silica (Min-U-Sil 5), were positive for c-jun protein expression; the level of c-jun protein was elevated 8-21-fold in these transformants. Other protooncogene proteins in transformed cells were either not detectable or not different from non-transformed cells. These results suggest that the overexpression of c-jun is common in BALB/c-3T3 transformed cells induced by glass fibers or silica. It seems, therefore, that the expression of c-jun may play an important role in the transformation process.

Mutations, tissue accumulations, and serum levels of p53 in patients with occupational cancers from asbestos and silica exposure

In order to determine the relationship between mutations, tissue accumulations, and serum levels of p53 in occupational cancers, we used denaturing gradient gel electrophoresis and DNA sequencing of exons 5-9 of the p53 gene, immunohistochemical analysis for tissue identification of mutant p53 protein, and enzyme-linked immunosorbent assay for serum levels of mutant p53 protein to examine for such alteration in a cohort of individuals with workplace exposure to asbestos or silica, and resultant lung cancers or mesotheliomas. DNA analysis detected mutations in 5 of 18 (28%) tumors, and tissue accumulations of protein were detected in 7 of 20 (35%) tumors; the agreement between mutational and immunohistochemical analyses was significant (kappa = 0.62, P = 0.002). Serum elevations of protein were detected in 4 of 11 (36%) cases with available serum samples; the agreement between tissue alterations and serum elevations was also significant (kappa = 0.71, P = 0.017). In addition, based on the analysis of banked samples, serum results tended to be consistent over time prior to the diagnosis of disease (positive predictive value = 0.67, negative predictive value = 0.83). These results suggest that serum levels of p53 are reasonably accurate in reflecting tissue alterations in p53 at the gene and/ or protein level and may be early biomarkers of disease risk.

Biology of lung cancer

OBJECTIVES

To provide a review of the biology of lung tumor development and progression, and advances in gene and antimetastatic therapies.

DATA SOURCES

Review articles, research studies, and book chapters pertaining to the biology of lung cancer.

CONCLUSION

Advances in understanding the molecular basis of lung cancer initiation, promotion, and progression will provide more effective methods of early detection and treatment of this disease. Promising new treatment methods based on tumor biology include gene therapies, antibodies against growth factors, and agents that prevent angiogenesis and tissue invasion.

IMPLICATIONS FOR NURSING PRACTICE

An understanding of the biology of cancer assists nurses with the development of protocols for the assessment and monitoring of patients receiving treatments based on cancer biology. Oncology nurses will assume important counseling roles with the development of genetic testing and prognostic markers.

Laboratory probing of oncogenes from human liquid and solid specimens as markers of exposure to toxicants

Recent discoveries regarding the mechanistic role of oncogenes and tumor suppressor genes in cancer development have opened a new era of molecular diagnosis. It has been observed repeatedly that genetic lesions serve as tumor markers in a broad variety of human cancers. The ras gene family, consisting of three related genes, H-ras, K-ras, and N-ras, acquires transforming activity through amplification or mutation in many tissues. If not all, then most types of human malignancies have been found to contain an altered ras gene. Because the ras oncogenes actively participate in both early and intermediate stages of cancer, several highly specific and sensitive approaches have been introduced to detect these genetic alterations as biomarkers of exposure to carcinogens. There is also mounting evidence that implicate chemical-specific alterations of the p53 tumor suppressor gene detected in most human tumors. Therefore, it seems a reliable laboratory approach to identify both altered p53 and ras genes as biomarkers of human chronic or intermittent exposure to toxicants in a variety of occupational settings.

Levels of ras oncoproteins in human plasma from 1,3-butadiene-exposed workers and controls

In a Czech plant near Prague, 10 samples from male workers occupationally exposed to 1,3-butadiene and 13 exposed to 1,3-butadiene/styrene were compared with unexposed male negative controls, matched for age and smoking habits, for the presence of ras oncoproteins in their plasma. Proteins were separated by gel electrophoresis, transferred to a nitrocellulose membrane by Western blotting and detected by chemiluminescence, using monoclonal ras antibody as the primary antibody. There were no statistically significant differences between the 3 groups (pooled two-sample t-test, untransformed and non-parametric Mann-Whitney test). These results are in keeping with the lack of exposure-related effects for 3 cytogenetic endpoints (chromosome aberrations, sister chromatid exchanges and micronuclei) already reported (Sorsa et al., 1994 Mutation Res., 309, 321-326) for this work-force exposed to low (below 3 ppm) exposure levels.

Mutant c-Ki-ras p21 protein in chemical carcinogenesis in humans exposed to vinyl chloride

Mutations in ras oncogenes and expression of their encoded p21 protein products are believed to play an important role in carcinogenesis in humans. Detection of mutant p21 proteins in serum may be a useful molecular epidemiologic biomarker with which to study this process, and workers with heavy exposure to vinyl chloride (VC) represent a model population for such study. We studied the occurrence of a specific ras mutation (Asp 13 c-Ki-ras) by oligonucleotide hybridization and the expression of the corresponding p21 protein in tumor tissue and serum by immunohistochemistry and immunoblotting with monoclonal antibodies in five individuals with heavy exposure to VC and resultant angiosarcomas of the liver (ASL). Four of five (80 percent) of the cases of ASL were found to contain the mutation and to express the corresponding mutant protein in their tumor tissue and serum. Serum expression of the mutant protein also was examined in nine VC-exposed workers with liver angiomas and 45 VC-exposed workers with no evidence of liver neoplasia; eight of nine (89 percent) of the former and 22 of 45 (49 percent) of the latter were also positive for the mutant p21 in their serum. However, serum immunoblotting results for 28 age-gender-race matched, unexposed controls were all negative. Stratification by years of VC exposure showed a significant linear trend (P < 10(-5)) for the occurrence of the serum mutant p21 protein with increasing duration of exposure. These results suggest that detection of serum mutant p21 protein can be a valid surrogate for ras gene expression at the tissue level.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of increased amounts of the extracellular domain of the c-erbB-2 oncoprotein in serum during pulmonary carcinogenesis in humans

Over-expression of the c-erbB-2 oncogene-encoded p185 protein product has been implicated in the pathogenesis of a wide variety of human malignancies, including lung cancer. Over-expression of p185 can be detected immunologically by quantification of the extracellular domain of p185 (c-erbB-2 oncopeptide) in extracellular fluid in vitro and in serum in vivo. An enzyme-linked immunosorbent assay (ELISA) for the c-erbB-2 oncopeptide was used to examine banked serum samples of 11 pneumoconiosis patients who subsequently developed lung cancer and serum samples from 11 hospital controls matched for age, sex, ethnic group and smoking as well as 55 unmatched general population controls. The mean serum level for the c-erbB-2 oncopeptide in human neu units/ml in the lung cancer cases (1,756 +/- 549 HNU/ml) was statistically significantly elevated (p < 0.001) in comparison to the mean level in the matched controls (976 +/- 488 HNU/ml) or the general population controls (888 +/- 655 HNU/ml). Defining a positive elevation of the serum c-erbB-2 oncopeptide as any value more than 2 standard deviations above the mean of the matched controls, 64% (7 of 11) of the lung cancer cases were positive compared to 0% (0 of 11) matched controls and 5% (3 of 55) of the unmatched controls. In addition, 4 of the 7 c-erbB-2 oncopeptide-positive cancer cases had positive serum samples prior to the time of disease diagnosis (average = 35 months). These results suggest that serum c-erbB-2 oncopeptide may be elevated at an early stage of pulmonary carcinogenesis and that further prospective study of the utility of this biomarker is warranted.

K-ras mutations in human adenocarcinoma of the lung: association with smoking and occupational exposure to asbestos

We investigated point mutational activation of the ras genes (K-ras codons 12, 13 and 61; N-ras codons 12, 13 and 61; H-ras codons 12 and 61) in primary, resected lung cancer by dot blotting and oligonucleotide hybridization. K-ras mutations were found in 14 (29%) of the 48 lung tumour specimens examined, but no N-ras or H-ras mutations were found. The highest frequency of K-ras mutation was observed in adenocarcinoma: 12 of the 21 samples studied (57%) had a mutation, which is one of the highest frequencies reported for lung adenocarcinoma. The commonest type of mutation in these lung tumour samples consisted of transversions: we observed 11, of which 8 (57% of all mutations) were G to T transversions. Most of the 48 patients studied had a history of heavy smoking, either with or without evidence of occupational exposure to asbestos. Statistical analysis revealed--in addition to the highly significant association between the adenocarcinoma type of lung cancer and K-ras mutation--a clear association of K-ras mutations with heavy life-time smoking (> or = 50 pack-years of cigarette smoking; odds ratio (OR) 4.9, 90% CI 1.2-19.5, multivariate analysis). In addition, occupational asbestos exposure showed an elevated, but non-significant, OR of 2.2 (90% CI 0.6-8.7) with the presence of K-ras mutation. We conclude that the occurrence of K-ras mutations in adenocarcinoma of the lung is frequent, and that such mutations are associated with heavy life-time exposure to tobacco smoke, possibly in combination with occupational exposure to asbestos fibres.

Molecular biology approaches to biological monitoring of genotoxic substances

Genetic testing is subdivided into genetic monitoring (evaluation over time of induced genetic changes) and genetic screening (detection of inherited traits). Genetic factors in relation to susceptibility to environmental agents are briefly examined, as well as mutation assays suitable for use in genetic monitoring, techniques for identifying specific DNA lesions, and oncogene products as biomarkers. In vitro studies with AS52 Chinese hamster ovary cells indicate that the distribution of lesions (e.g., point mutations or segment deletions) at the xanthine-guanine phosphoribosyl transferase (gpt) gene in mutants generated by exposure to nickel compounds show some substance specificity. This ability is viewed as a promising development for the molecular epidemiology of occupational and environmental cancers. It is concluded that technical limitations pertaining to specificity and sensitivity, as well as ethical and legal implications, need to be resolved before routine application of genetic monitoring and screening is feasible.