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Null Results in Brief |
1 Department of Environmental Health Sciences, Columbia Center for Children's Environmental Health, Mailman School of Public Health of Columbia University, New York, New York and 2 National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina
Requests for reprints: Frederica P. Perera, Department of Environmental Health Sciences and Columbia Center for Children's Environmental Health, Mailman School of Public Health of Columbia University, 100 Haven Avenue, Tower III, #25F, New York, NY 10032. Phone: 212-304-7280; Fax: 212-544-1943. E-mail: fpp1{at}columbia.edu
| Introduction |
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There was a priori evidence that PAH-albumin adducts and ras p21 of the biomarkers were biologically relevant, but their predictive ability had not been evaluated in a prospective design. For example, studies have shown that certain protein adducts, including PAH-albumin adducts, are correlated with the corresponding DNA adducts and might serve as feasible surrogates (2). However, the half-lives of the two biomarkers vary, and, unlike DNA adducts, protein adducts do not reflect interindividual variability in DNA repair. The ras oncogene has been shown to be activated by mutagens and clastogens. Moreover, ras mutation and/or overexpression has been directly implicated in the development of lung tumors (3-9). We also examined the contribution of polymorphisms in genes controlling metabolic activation and detoxification pathways for carcinogens that mediate the initial steps in environmental carcinogenesis (10). Genetic polymorphisms in the selected genes have been previously implicated in at least one study of lung cancer, although results have not been consistent (11-13).
In this nested case-control study, our prior analysis showed that PAH/aromatic-DNA adducts were significant predictors of lung cancer among smokers but not former or non smokers, and the combined GSTM1 null/GSTP1 Val genotype was significantly associated with lung cancer before and after adjusting for PAH-DNA adducts (1, 14). Here, we report on the relationship between lung cancer risk and PAH-albumin adducts, the ras p21 oncoprotein, and polymorphisms in the CYP1A1, CYP2D6, NAT1, and NAT2 genes. Although not part of our original hypotheses, we also report on the association between the polymorphisms and the other biomarkers (PAH-albumin adducts and the ras p21 oncoprotein).
| Materials and Methods |
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40 cigarettes per day), and pipe and cigar smoker (current or past). PAH-albumin adducts were analyzed using a monoclonal antibody (8E11) as described (16). Overexpression and mutations of the ras p21 oncoprotein in plasma were analyzed by Western blotting as described (17). Study samples were scored as having detectable levels of ras if a peak seemed at the same relative position as either the normal ras p21 protein or the val 12 mutant protein standards in the control lanes. Although the primary emphasis in the analysis was on the prevalence of detectable ras, semiquantitative data on the intensity with which the bands were stained were also collected. The intensities of the pixels under the peaks were summed and reported as a score in integrated pixel units (17). DNA was extracted from blood leukocytes, and individual genotypes were analyzed by PCR-RFLP. The individual genotypes included CYP1A1 ("MspI," T3801C, "M1"; A2455G, "M2," or Ile462Val; ref. 18), CYP2D6 (A2549del, "A"; G1846A, "B" allele; ref. 19), NAT1 (1065del9, "NAT1*11"; T1088A, "NAT1*10"; C1095A; ref. 20), and NAT2 [NAT2*4 (WT), NAT2*5 (T341C, C481T, and A803G), NAT2*6 (G590A), NAT2*7 (G857A), and NAT2*14 (G191A); ref. 21].
In statistical analysis, PAH-albumin adducts (fmol/µg) and overexpression of ras oncoprotein (integrated pixel units) were treated as continuous variables or as binary variables (detectable/nondetectable and positive/negative). Polymorphisms in CYP1A1, CYP2D6, NAT1, and NAT2 were treated in conditional logistic regression models as binary variables (present versus absent). Because the biomarkers were analyzed in baseline blood samples, they could not have been confounded by treatment. However, as in our prior reports (1, 14), to be conservative, we analyzed biomarker-lung cancer relationships with and without including treatment in the models. Analyses also distinguished between the major histologic groups of lung cancer (small cell lung carcinoma and nonsmall cell lung carcinoma). Our a priori power to detect hypothesized differences between cases and controls in albumin adducts and ras oncoproteins was >90%. Due to our small sample size, our power was limited to detect associations between genotypes and lung cancer. For example, the estimates of power of this study to detect odds ratios of 2.0 or 2.5 for CYP1A1 MspI were 34% and 45%, respectively. The corresponding power estimates for CYP2D6B were 70% and >80%; for NATI, were 65% and >80%; and for NAT2, were 62% and >80%, respectively.
In secondary analyses, not part of our original hypotheses, we tested the effect of genotypes on adducts and ras p21. For PAH-albumin adducts, we selected CYP1A1 because it is known to be involved in PAH metabolism. For ras p21, we tested all of the genotypes because ras is a nonchemical-specific biomarker.
| Results and Discussion |
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We note that tissue blocks are available through the hospitals where surgery was done.
Several investigators have recently reported associations between certain of these genotypes and risk of developing lung cancer, whereas others have not (12, 13, 22). Results have varied by ethnicity, gender, smoking status, age of onset, of lung cancer, histologic type, and sample size. The finding that PAH-albumin adducts were not predictive, unlike PAH-DNA adducts (1, 23), is biologically plausible, given that DNA, not protein, is the critical target in carcinogenicity of PAHs. No other studies have linked ras p21 overexpression to lung cancer risk. However, a relationship between ras p21 overexpression and survival has been seen for nonsmall cell lung carcinoma (24). In summary, this nested case-control study suggests that PAH-DNA albumin adducts and ras p21 overexpression in blood are not predictive of lung cancer in male Caucasians.
| Acknowledgments |
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| Footnotes |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
Received 9/ 8/05; revised 4/ 3/06; accepted 5/17/06.
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