Oncogene proteins as biomarkers in the molecular epidemiology of occupational carcinogenesis. The example of the ras oncogene-encoded p21 protein

Elevated serum RAS p21 is an independent prognostic factor in metastatic breast cancer

Background

An important component of the RAS signalling pathway, the RAS p21 oncogene, is frequently hyperactivated in breast cancer. Its expression in tumor tissue has been linked to poor clinical outcome. This study was designed to evaluate the clinical relevance of RAS p21 levels in peripheral blood in a large cohort of metastatic breast cancer patients.

Methods

Two hundred fifty-one patients with metastatic breast cancer were enrolled in this prospective, multicentre, open-label, non-randomized study. Blood samples were collected before start of first-line or later-line treatment. RAS p21 was determined using a sandwich-type ELISA immunoassay. For the determination of the cutoff, blood samples from age-matched healthy controls were analyzed. A value above 452 pg/ml was regarded as elevated (mean + 2 x SD). In the univariate survival analysis, two other cutoffs were considered as well (50th and 75th percentile of patients, i.e. 229 pg/ml and 320 pg/ml). Circulating tumor cells (CTCs) were detected using the CellSearch system.

Results

29 of 251 (12%) patients had RAS p21 levels above the cut-off level of 452 pg/ml. Clinical-pathological parameters, such as hormone receptor and HER2 status, line of therapy and CTC status, did not correlate with RAS p21 levels. Elevated RAS p21 was significantly associated with shorter progression-free and overall survival in the univariate analysis (median PFS: 3.9 months [95%-CI: 1.8–6.0] for patients with elevated RAS p21 levels versus 8.5 months [95%-CI: 7.4–9.5] with non-elevated levels [p = 0.01]; median OS: 7.1 months [95%-CI: 0.3–14.2] versus not reached [p = 0.002], respectively). When RAS p21 cutoffs other than 452 pg/ml were considered, elevated RAS p21 was significantly associated with OS but not with PFS. Classical clinical-pathological factors were included into a multivariate Cox regression analysis. In addition, factors previously shown to influence survival in a univariate analysis, such as serum HER2, CAIX and TIMP1, were included as well. In the multivariate analysis, RAS p21, presence of ≥5 CTCs per 7.5 ml blood, higher grading and higher line of therapy remained independent predictors of shorter OS.

Conclusions

Metastatic breast cancer patients with elevated levels of circulating RAS p21 have significantly worse clinical outcome. Hypothetically, these patients might benefit from therapeutic strategies targeting RAS pathway.

Trial registration

Current Controlled Trials ISRCTN59722891 (DETECT); trial registration date: April, 17th 2010; the trial was registered retrospectively.

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).

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.

Applications of new technology in molecular epidemiology and their relevance to occupational medicine

Technological advances in molecular biology over the past 2 decades have offered more complex techniques that can be used to study the role of specific exogenous agents and host variables that cause ill health. Increasingly, studies in human populations use this new technology, combined with epidemiological methods, to shed light on the understanding of the biological processes associated with development of disease. This approach has many potential applications in occupational and environmental medicine (OEM), and some aspects of the work in this growing field are reviewed. An understanding of biochemistry and genetics at the molecular level, specific knowledge on metabolism and mechanisms of action, and epidemiology have become increasingly important for the OEM practitioner. This is necessary to consider the major question of validation and relevance of these molecular biomarkers. As end users, OEM practitioners should also consider the impact of these advances on their practices. For example, the availability of genetic tests to identify susceptible workers raises issues of ethics, individual privacy, right to work, and the relevance of such tests. Several studies have presented data on the association of environmental measurements and various biomarkers for internal and biologically effective dose, genetic polymorphisms, and early response markers. Given the limitations of individual molecular biomarkers in assessing risk to health, and the multifactorial nature of environmental disease, it is likely that such an approach will increase our understanding of the complex issue of mechanisms of disease and further refine the process of risk assessment.

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.

[Cancer mortality among electricity utility workers in a the state of Sao Paulo, Brazil]

A number of epidemiologic studies have observed an association between exposure to 50-60 Hz electromagnetic fields and the development of specific types of cancer. In Brazil, a preliminary report from a study of electricity facility workers in Rio de Janeiro (RJ) has mentioned relatively similar results. An exploratory analysis of death certificates obtained from a sample of electricity workers in S. Paulo was made. Data was analysed by using the Proportional Mortality Ratio (PMR) and the Proportional Cancer Mortality Ratio (PCMR). A slightly elevated all-sites cancer mortality was observed among these workers (PMR 1.11; 95% CI 0.91-1.35). Site specific analysis has shown a statistically significant higher mortality of laryngeal cancer (PCMR 2.04; 95% CI 1.05-4.20). An excess of deaths was also seen for cancers of the buccal cavity/pharynx, prostate, bladder, brain and Hodgkin's disease, although the results lacked statistical significance. When analysed by categories of estimated exposure to magnetic fields, an excess of deaths from bladder cancer (PCMR 4.17; 95% CI 1.35-9.72), neoplasms of the brain (PCMR 7.7; 95% CI 1.02-9.65) and Hodgkin's disease (PCMR 5.55; 95% CI 1.14-16.21) was observed in the group with probably higher exposure to EMF. A comparison of cancer mortality between these workers and petrochemical employees has shown a higher PCMR for larynx tumours (PCMR 3.51; 95% CI 3.02-15.51) and bladder cancer (PCMR 7.53; 95% CI 3.02-15.51). For brain tumours, however, a PCMR of 0.74 (95% CI 0.27-1.61) was noted. Although restrictions related to sample size in the study and the lack of information about known confounders must be considered, the results of this study do not fully disagree with others previously mentioned in the literature.

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)

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.

Molecular epidemiology in cancer risk assessment and prevention: recent progress and avenues for future research

Molecular epidemiology is increasingly being applied in studies of cancer risks derived from exposure to environmental carcinogens of both endogenous and exogenous origins. Analytical methods have been developed that are capable of detecting and quantifying levels of covalent adducts of several important classes of carcinogens with cellular DNA and blood proteins. Methods of sufficient sensitivity and specificity to detect ambient levels of exposure are in current use. These are being used in studies related to tobacco use (polycyclic aromatic hydrocarbons, aromatic amines, tobacco-specific nitrosamines); dietary exposures (aflatoxins, N-nitrosamines, heterocyclic amines); medicinal exposures (cisplatin, alkylating agents, 8-methoxypsoralen, ultraviolet photoproducts); occupational exposures (aromatic amines, polycyclic aromatic hydrocarbons, oxides of ethylene and styrene, and vinyl chloride); and oxidative damage (8-hydroxyguanine, thymine glycol). Methodologic improvements together with their expanded use in feasibility studies continue to produce results that support the validity of this approach for detecting and quantifying exposure to carcinogens. Genetic markers are also being used to detect early biological responses in efforts to link carcinogen exposure to initiating events in the carcinogenesis process. These include, in addition to traditional cytogenetic markers (e.g., chromosomal aberrations, sister chromatid exchange, micronuclei), other alterations in chromosomal structure such as restriction fragment length polymorphisms, loss of heterozygosity, and translocation markers. Specific genetic changes have recently been identified as critical molecular events in the initiation and development of many cancers. Important among these are activation of oncogenes, especially those of the ras family, and inactivation of tumor-suppressor genes (e.g., p53 and Rb) by point mutations and/or chromosomal deletions and other structural changes. Although some of these changes are known to occur in chemically induced tumors of experimental animals, the possible role of chemical carcinogens in the induction of genetic abnormalities in human cancers has yet to be determined. Continuing investigations employing the methods of molecular epidemiology promise to provide further evidence concerning these relationships. Future investigations employing newly developed molecular biological methods, in particular those based on polymerase chain reaction amplification of DNA, to identify alterations in DNA and chromosomal structure, combined with methods for characterizing exposure to carcinogens and early effects, have great potential for further elucidating the role of genotoxic agents in the etiology of human cancers and also for the development of strategies for their prevention.

Serum oncoproteins and growth factors in asbestosis and silicosis patients

Levels of 9 different oncoproteins and growth factors were assayed by immunoblotting with monoclonal antibodies in 91 serum samples collected between March 1983 and August 1987 from 46 pneumoconiosis patients (36 asbestosis, 10 silicosis) at high risk for the development of cancer. Follow-up of these patients through June 1991 showed that 18 had developed cancer (11 lung, 2 pleural mesothelioma, 2 transitional-cell carcinomas of the urinary bladder, 1 osteosarcoma, 1 non-Hodgkin's lymphoma, 1 adenocarcinoma of the gallbladder). Increased serum levels of ras oncogene-related protein (p21) were found in 7 of the 18 patients who developed cancer (5 lung, 2 pleural mesothelioma) versus 2 of the 28 patients without cancer, a statistically significant difference (p = 0.012). In addition, 6 of the 7 p21-positive cancer cases had positive serum samples prior to clinical diagnosis of disease (average = 16.3 months, range = 3-26 months prior to diagnosis), suggesting that elevated serum p21 levels may be a useful marker for earlier detection in a significant percentage of respiratory malignancies. Finally, elevated serum levels of PDGF-related protein were detected significantly more frequently in advanced pneumoconiosis cases (ILO radiographic classification of 2/1 or greater) than in less advanced cases (80% vs. 41.9%; p = 0.016), and there was a tendency for these PDGF-positive patients to have progression of their disease (68.2% vs. 41.7%; p = 0.065), suggesting that elevated serum PDGF levels may be a marker for the development of severe and progressive pneumoconioses.

Biological monitoring of three 60Co radiation incident victims

Radiation-induced structural chromosomal aberrations were the only adverse effects found in three workers overexposed to 60Co gamma-radiation. Chromosomal analyses were performed on the 5th and 75th days after exposure. Hematologic follow-up was carried out on the 5th, 12th, 16th, and 75th days after exposure. Hematologic findings did not differ over time in any of the three exposed workers. In two workers, we found dicentric chromosomes, which are conventional indicators for exposure to ionizing radiation.

Intermediate endpoint biomarkers for chemoprevention

The understanding of intermediate endpoint biomarker expression in relation to the sequential events in bladder tumorigenesis establishes a useful approach for evaluating chemopreventive agents. Biomarkers may be genotypic or phenotypic and function as biomarkers of susceptibility, exposure, effect, or disease. This paper reviews several years of research on biomarkers and their use in monitoring chemoprevention therapy. In initial animal experiments, mice were dosed with N-butyl-N-(4-hydroxybutyl)nitrosamine (OH-BBN) while co-administering N-(4-hydroxyphenyl)retinamide (4-HPR). 4-HPR did not statistically reduce tumor incidence, but did affect tumor differentiation and, consequently, nuclear size and DNA ploidy. These results suggest that nuclear size and ploidy may function as intermediate endpoint biomarkers of effect for oncogenesis and that epigenetic as well as genetic mechanisms may be primary in the oncogenic process. Early biomarkers of effect which occur prior to genetic effects or chromosome aberration may portend a higher probability of being modulated by differentiating agents such as retinoids. In vitro studies demonstrated that RPMI-7666 cells cultured with a phorbol ester tumor promoter (12-O-tetradecanoyl-phorbol-13-acetate) could be redifferentiated with 13-cis-retinoic acid and dimethyl sulfoxide (DMSO). F-actin, a cytoskeletal biomarker with a presumed function in the epigenetic mechanisms of carcinogenesis, could also be normalized in HL-60 cells treated with 4-HPR or DMSO. A clinical evaluation of F-actin in patients with varying degrees of risk confirmed the value of F-actin as a differentiating biomarker useful for bladder cancer risk assessment. The clarification of when the phenotypic changes of F-actin occur in the oncogenic process was achieved when a variety of biochemical changes were mapped in the patients with bladder cancer. These studies confirmed that G-actin, a reciprocal form of F-actin, is increased relatively early in bladder cancer oncogenesis when multiple biomarkers are quantitated in the field, adjacent area, and the tumor. Comparison of each individual biomarker's expression from field, adjacent to tumor, and tumor, and subsequent cluster analysis of these biomarkers, indicated that the possible sequence of phenotypic expression of biomarkers in bladder cancer oncogenesis is from G-actin, to p300 antigen, to epidermal growth factor receptor (EGFR), to p185 (neu oncogene product), to DNA aneuploidy and, finally, to visual morphology.(ABSTRACT TRUNCATED AT 400 WORDS)