Genetic polymorphisms of NAD(P)H quinone oxidoreductase, CYP1A1 and microsomal epoxide hydrolase and lung cancer risk in Nanjing, China

Genetic polymorphisms in the mEH gene in relation to tobacco smoking: role in lung cancer susceptibility and survival in north Indian patients with lung cancer undergoing platinum-based chemotherapy

Aim: Epoxide hydrolase is involved in oxidative defenses and is responsible for the activation of carcinogens. The relationship between EPHX1 polymorphisms (Tyr¹¹³His and His¹³⁹Arg) and overall survival (OS) and lung cancer (LC) risk was investigated. Methods: The study comprised 550 cases and 550 controls. Genotyping and statistical analysis were applied. Results: The variant genotypes of EPHX1 polymorphisms exhibited no association with LC risk. The Tyr¹¹³His polymorphism exhibited twofold increased odds of lymph node invasion (p = 0.04). The Tyr/His genotype is a risk factor for smokers. Subjects carrying the combined genotype for His¹³⁹Arg showed better median survival time (MST) and the heterozygous genotype revealed better MST in the case of small-cell lung cancer (SCLC; 11.30 vs 6.73 months; log-rank test: p = 0.02). The heterozygous genotype (His139Arg) had longer MST in patients receiving cisplatin/carboplatin and irinotecan (11.30 vs 7.23; log-rank test: p = 0.007) Conclusion: The Tyr¹¹³His polymorphism is associated with LC risk in smokers and is a potential prognostic factor for OS in patients with SCLC after irinotecan.

Polymorphisms in the Microsomal Epoxide Hydrolase Gene: Role in Lung Cancer Susceptibility and Prognosis

Aims and background

The aim of this study was to investigate the relationship between EPHXI exon 3 Tyr113His and exon 4 His139Arg polymorphisms, predicted microsomal epoxide hydrolase (mEH) activity, and lung cancer development. mEH is a protective enzyme involved in oxidative defences against a number of environmental chemicals and pollutants, but it is also responsible for the xenobiotic activation of carcinogens.

Methods

We investigated the two polymorphisms of the mEH gene (EPHX1) in 58 lung cancer patients and 41 controls using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

Results

The exon 3 Tyr113His polymorphism was associated with lung cancer (P <0.001). The frequency of the His113His homozygote genotype in exon 3 was significantly increased in patients compared with controls (P <0.001). In contrast, there was no significant difference in exon 4 polymorphisms between patients and controls. When the exon 3 and 4 polymorphisms were considered together, the combined EPHX1 His113His113/His139His139 genotype (very low predicted enzyme activity) was found to be associated with an increased risk of lung cancer (P = 0.044, OR = 3.063, CI = 0.932–10.069). We observed that patients with T3 + T4 tumors had an approximately 3-fold higher risk of the Tyr113/His113 genotype than patients with T1 + T2 tumors. Lung cancer patients carrying aheterozygote Tyr113/His113 genotype had a 2-fold increased risk of lymph node metastases (P = 0.051).

Conclusion

These findings suggest that the exon 3 Tyr113His and exon 4 His139Arg polymorphisms of EPHXI may be associated with a increased risk of lung cancer and a worse prognosis. Free full text available at www.tumorionline.it

EPHX1 rs2234922 polymorphism and lung cancer susceptibility in Asian populations: a meta-analysis

OBJECTIVE

Polymorphisms of epoxide hydrolase 1 (EPHX1) rs2234922 have been reported to be associated with variations in EPHX1 activity. Many studies have investigated the association between EPHX1 rs2234922 polymorphism and lung cancer risk, but their results have been inconsistent. The purpose of this study was to perform a meta-analysis of all eligible studies to derive a more precise estimation of the associations of EPHX1 rs2234922 polymorphism with lung cancer.

METHODS

The PubMed was searched for case-control studies published up to Oct 01, 2014. Data were extracted and pooled odds ratios (ORs) with 95% confidence interval (CI) were calculated. The pooled ORs for the risk associated with the genotypes of homozygote G/G and G allele carriers (A/G + G/G) with the A/A genotype were calculated. Heterogeneity assumption was checked by the chi-square-based Q-test. A P value greater than 0.10 for the Q-test indicates a lack of heterogeneity among studies, so the pooled OR estimate of the each study was calculated by the fixed-effects model (the Mantel-Haenszel method). Otherwise, the random-effects model (the DerSimonian and Laird method) was used.

RESULTS

In this meta-analysis, we assessed eight published studies involving comprising 1,175 cases and 1,550 controls of the association between EPHX1 rs2234922 polymorphism and lung cancer risk. For the homozygote G/G and G allele carriers (A/G + G/G), the pooled ORs were 1.47 (95% CI: 1.18-1.79, P=0.007 for heterogeneity) and 1.36 (95% CI: 1.14-1.62, P=0.828 for heterogeneity), when compared with the homozygous wild-type genotype (A/A).

CONCLUSIONS

EPHX1 rs2234922 polymorphism contributes to risk of lung cancer among Asian population.

The NQO1 polymorphism C609T (Pro187Ser) and cancer susceptibility: a comprehensive meta-analysis

Background:

Evidence is increasingly emerging about multiple roles for the NAD(P)H quinone oxidoreductase 1 enzyme in cancer. The C609T (rs1800566, Pro187Ser) null polymorphism of the NQO1 gene contributes significantly to the variation in enzymatic activity across different populations. NQO1 C609T polymorphism was thoroughly investigated with respect to cancer susceptibility. The results were inconsistent partly due to low sample sizes. The aim of the present work was to perform a meta-analysis to assess association for all common cancer sites separately and in combination.

Methods:

Our meta-analysis involved 92 studies including 21 178 cases and 25 157 controls. Statistical analysis involved individual cancer sites and the combined cancer risk. Association was tested under different genetic models.

Results:

We found a statistically significant association between the variant T allele and overall cancer risk in the worldwide population (for the TT vs CC model, OR=1.18 (1.07–1.31), P=0.002, I²=36%). Stratified analysis revealed that this association was largely attributed to the Caucasian ethnicity (for the TT vs CC model, OR=1.28 (1.12–1.46), P=0.0002, I²=1%). Stratification by tumour site showed significant association for bladder cancer in the worldwide population (for the TT vs CC model, OR=1.70 (1.17–2.46), P=0.005, I²=0%), and in the Asian population (for the TT vs CC model, 1.48 (1.14–1.93), P=0.003, I²=16%). Positive association was also found for gastric cancer in the worldwide population under the dominant model (OR=1.34 (1.09–1.65), P=0.006, I²=15%).

Conclusion:

Our results indicate that the C609T polymorphism of the NQO1 gene is an important genetic risk factor in cancer.

Association between microsomal epoxide hydrolase 1 T113C polymorphism and susceptibility to lung cancer

Previous case-control studies assessing the association between microsomal epoxide hydrolase 1 (EPHX1) T113C and susceptibility to lung cancer reported conflicting results. Thus, a systemic review and meta-analysis of published studies were performed to assess the possible association. PubMed and Embase databases were searched for all eligible studies. The strength of the association between EPHX1 T113C polymorphism and lung cancer risk was estimated by the pooled odds ratios (ORs) with its 95 % confidence interval. Twenty-four individual case-control studies involving a total of 4,970 lung cancer cases and 8,917 controls were finally included into the meta-analysis. When all 24 studies were included into the meta-analysis, the pooled results suggested that there was no association between EPHX1 T113C polymorphism and lung cancer risk under all four comparison models, and all P values for the pooled ORs were more than 0.05. In the subgroup analysis of Caucasians, the pooled results suggested that EPHX1 T113C polymorphism was associated with decreased risk of lung cancer under all four comparison models, and all P values for the pooled ORs were less than 0.05. However, in the subgroup analysis of Asians, the pooled results suggested that EPHX1 T113C polymorphism was associated with increased risk of lung cancer under three comparison models, and all P values for the pooled ORs were less than 0.05. There was no risk of publication bias. This current meta-analysis suggests that EPHX1 T113C polymorphism is associated with lung cancer risk, and there is an obvious race-specific effect in the association.

Genetic susceptibility to lung cancer--light at the end of the tunnel?

Lung cancer is one of the most common and deadliest cancers in the world. The major socio-environmental risk factor involved in the development of lung cancer is cigarette smoking. Additionally, there are multiple genetic factors, which may also play a role in lung cancer risk. Early work focused on the presence of relatively prevalent but low-penetrance alterations in candidate genes leading to increased risk of lung cancer. Development of new technologies such as genomic profiling and genome-wide association studies has been helpful in the detection of new genetic variants likely involved in lung cancer risk. In this review, we discuss the role of multiple genetic variants and review their putative role in the risk of lung cancer. Identifying genetic biomarkers and patterns of genetic risk may be useful in the earlier detection and treatment of lung cancer patients.

Lack of association between NADPH quinone oxidoreductase 1 (NQO1) gene C609T polymorphism and lung cancer: a case-control study and a meta-analysis

Background

The association between NAD(P)H:quinone oxidoreductase 1 (NQO1) gene C609T polymorphism (rs1800566) and lung cancer has been widely evaluated, and a definitive answer so far is lacking. We first conducted a case-control study to assess this association in northeastern Han Chinese, and then performed a meta-analysis to further address this issue.

Methodology/Principal Findings

This case-control study involved 684 patients clinically diagnosed as lung cancer and 602 age-matched cancer-free controls from Harbin city, Heilongjiang province, China. Genotyping was conducted using the PCR-LDR (ligase detection reactions) method. Meta-analysis was managed by STATA software. Data and study quality were assessed in duplicate. Our case-control association study indicated no significant difference in the genotype and allele distributions of C609T polymorphism between lung cancer patients and controls, consistent with the results of the further meta-analysis involving 7286 patients and 9167 controls under both allelic (odds ratio (OR) = 0.99; 95% confidence interval (CI): 0.92–1.06; P = 0.692) and dominant (OR = 0.98; 95% CI: 0.89–1.08; P = 0.637) models. However, there was moderate evidence of between-study heterogeneity and low probability of publication bias. Further subgroup analyses by ethnicity, source of controls and sample size detected no positive associations in this meta-analysis.

Conclusions

Our study in northeastern Han Chinese, along with the meta-analysis, failed to confirm the association of NQO1 gene C609T polymorphism with lung cancer risk, even across different ethnic populations.

The modifying effect of CYP2E1, GST, and mEH genotypes on the formation of hemoglobin adducts of acrylamide and glycidamide in workers exposed to acrylamide

This study assesses the association of acrylamide (AA) and glycidamide (GA) hemoglobin adducts (AAVal and GAVal) and their ratios with genetic polymorphisms of the metabolic enzymes cytochrome P450 2E1 (CYP2E1), exon 3 and 4 of microsomal epoxide hydrolase (mEH3 and mEH4), glutathione transferase theta (GSTT1), and mu (GSTM1) or/and the combinations of these polymorphisms, involved in the activation and detoxification of AA in humans. Fifty-one AA-exposed workers and 34 controls were recruited and provided a post-shift blood sample. AAVal and GAVal were determined simultaneously using isotope-dilution liquid chromatography-electronspray ionization/tandem mass spectrometry (LC-ESI-MS/MS). Genetic polymorphisms of CYP2E1, mEH3 and 4, GSTT1, and GSTM1 were also analyzed. Our results reveal that the GAVal/AAVal ratio, potentially reflecting the proportion of AA metabolized to GA, ranged from 0.13 to 0.45 with a mean at 0.27. Multivariate regression analysis demonstrates that the joint effect of CYP2E1, GSTM1, and mEH4 genotypes was significantly associated with AAVal and GAVal levels after adjustment for AA exposures. These results suggest that mEH4 and the combined genotypes of CYP2E1, GSTM1 and mEH4 may be associated with the formation of AAVal and GAVal. Further studies may be needed to shed light on the roles that phase I and II enzymes play in AA metabolism.

Genetic polymorphisms in CYP1A1, GSTM1, GSTP1 and GSTT1 metabolic genes and risk of lung cancer in Asturias

BACKGROUND

Metabolic genes have been associated with the function of metabolizing and detoxifying environmental carcinogens. Polymorphisms present in these genes could lead to changes in their metabolizing and detoxifying ability and thus may contribute to individual susceptibility to different types of cancer. We investigated if the individual and/or combined modifying effects of the CYP1A1 MspI T6235C, GSTM1 present/null, GSTT1 present/null and GSTP1 Ile105Val polymorphisms are related to the risk of developing lung cancer in relation to tobacco consumption and occupation in Asturias, Northern Spain.

METHODS

A hospital-based case-control study (CAPUA Study) was designed including 789 lung cancer patients and 789 control subjects matched in ethnicity, age, sex, and hospital. Genotypes were determined by PCR or PCR-RFLP. Individual and combination effects were analysed using an unconditional logistic regression adjusting for age, pack-years, family history of any cancer and occupation.

RESULTS

No statistically significant main effects were observed for the carcinogen metabolism genes in relation to lung cancer risk. In addition, the analysis did not reveal any significant gene-gene, gene-tobacco smoking or gene-occupational exposure interactions relative to lung cancer susceptibility. Lastly, no significant gene-gene combination effects were observed.

CONCLUSIONS

These results suggest that genetic polymorphisms in the CYP1A1, GSTM1, GSTT1 and GSTP1 metabolic genes were not significantly associated with lung cancer risk in the current study. The results of the analysis of gene-gene interactions of CYP1A1 MspI T6235C, GSTM1 present/null, GSTT1 present/null and GSTP1 Ile105Val polymorphisms in lung cancer risk indicate that these genes do not interact in lung cancer development.

NAD(P)H: quinone oxidoreductase 1 deficiency conjoint with marginal vitamin C deficiency causes cigarette smoke induced myelodysplastic syndromes

Background

The etiology of myelodysplastic syndromes (MDS) is largely unknown. Exposure to cigarette smoke (CS) is reported to be associated with MDS risk. There is inconsistent evidence that deficiency of NAD(P)H-quinone: oxidoreductase 1 (NQO1) increases the risk of MDS. Earlier we had shown that CS induces toxicity only in marginal vitamin C-deficient guinea pigs but not in vitamin C-sufficient ones. We therefore considered that NQO1 deficiency along with marginal vitamin C deficiency might produce MDS in CS-exposed guinea pigs.

Methodology and Principal Findings

Here we show that CS exposure for 21 days produces MDS in guinea pigs having deficiency of NQO1 (fed 3 mg dicoumarol/day) conjoint with marginal vitamin C deficiency (fed 0.5 mg vitamin C/day). As evidenced by morphology, histology and cytogenetics, MDS produced in the guinea pigs falls in the category of refractory cytopenia with unilineage dysplasia (RCUD): refractory anemia; refractory thrombocytopenia that is associated with ring sideroblasts, micromegakaryocytes, myeloid hyperplasia and aneuploidy. MDS is accompanied by increased CD34(+) cells and oxidative stress as shown by the formation of protein carbonyls and 8-oxodeoxyguanosine. Apoptosis precedes MDS but disappears later with marked decrease in the p53 protein. MDS produced in the guinea pigs are irreversible. MDS and all the aforesaid pathophysiological events do not occur in vitamin C-sufficient guinea pigs. However, after the onset of MDS vitamin C becomes ineffective.

Conclusions and Significance

CS exposure causes MDS in guinea pigs having deficiency of NQO1 conjoint with marginal vitamin C deficiency. The syndromes are not produced in singular deficiency of NQO1 or marginal vitamin C deficiency. Our results suggest that human smokers having NQO1 deficiency combined with marginal vitamin C deficiency are likely to be at high risk for developing MDS and that intake of a moderately large dose of vitamin C would prevent MDS.

Putative EPHX1 enzyme activity is related with risk of lung and upper aerodigestive tract cancers: a comprehensive meta-analysis

Background

EPHX1 is a key enzyme in metabolizing some exogenous carcinogens such as products of cigarette-smoking. Two functional polymorphisms in the EPHX1 gene, Tyr113His and His139Arg can alter the enzyme activity, suggesting their possible association with carcinogenesis risk, particularly of some tobacco-related cancers.

Methodology/Principal Findings

A comprehensive systematic review and meta-analysis was performed of available studies on these two polymorphisms and cancer risk published up to November 2010, consisting of 84 studies (31144 cases and 42439 controls) for Tyr113His and 77 studies (28496 cases and 38506 controls) for His139Arg primarily focused on lung cancer, upper aerodigestive tract (UADT) cancers (including oral, pharynx, larynx and esophagus cancers), colorectal cancer or adenoma, bladder cancer and breast cancer. Results showed that Y113H low activity allele (H) was significantly associated with decreased risk of lung cancer (OR = 0.88, 95%CI = 0.80–0.96) and UADT cancers (OR = 0.86, 95%CI = 0.77–0.97) and H139R high activity allele (R) with increased risk of lung cancer (OR = 1.18, 95%CI = 1.04–1.33) but not of UADT cancers (OR = 1.05, 95%CI = 0.93–1.17). Pooled analysis of lung and UADT cancers revealed that low EPHX1 enzyme activity, predicted by the combination of Y113H and H139R showed decreased risk of these cancers (OR = 0.83, 95%CI = 0.75–0.93) whereas high EPHX1 activity increased risk of the cancers (OR = 1.20, 95%CI = 0.98–1.46). Furthermore, modest difference for the risk of lung and UADT cancers was found between cigarette smokers and nonsmokers both in single SNP analyses (low activity allele H: OR = 0.77/0.85 for smokers/nonsmokers; high activity allele R: OR = 1.20/1.09 for smokers/nonsmokers) and in combined double SNP analyses (putative low activity: OR = 0.73/0.88 for smokers/nonsmokers; putative high activity: OR = 1.02/0.93 for smokers/ nonsmokers).

Conclusions/Significance

Putative low EPHX1 enzyme activity may have a potential protective effect on tobacco-related carcinogenesis of lung and UADT cancers, whereas putative high EPHX1 activity may have a harmful effect. Moreover, cigarette-smoking status may influence the association of EPHX1 enzyme activity and the related cancer risk.

Genetic polymorphism in metabolism and host defense enzymes: implications for human health risk assessment

Genetic polymorphisms in xenobiotic metabolizing enzymes can have profound influence on enzyme function, with implications for chemical clearance and internal dose. The effects of polymorphisms have been evaluated for certain therapeutic drugs but there has been relatively little investigation with environmental toxicants. Polymorphisms can also affect the function of host defense mechanisms and thus modify the pharmacodynamic response. This review and analysis explores the feasibility of using polymorphism data in human health risk assessment for four enzymes, two involved in conjugation (uridine diphosphoglucuronosyltransferases [UGTs], sulfotransferases [SULTs]), and two involved in detoxification (microsomal epoxide hydrolase [EPHX1], NADPH quinone oxidoreductase I [NQO1]). This set of evaluations complements our previous analyses with oxidative and conjugating enzymes. Of the numerous UGT and SULT enzymes, the greatest likelihood for polymorphism effect on conjugation function are for SULT1A1 (*2 polymorphism), UGT1A1 (*6, *7, *28 polymorphisms), UGT1A7 (*3 polymorphism), UGT2B15 (*2 polymorphism), and UGT2B17 (null polymorphism). The null polymorphism in NQO1 has the potential to impair host defense. These highlighted polymorphisms are of sufficient frequency to be prioritized for consideration in chemical risk assessments. In contrast, SNPs in EPHX1 are not sufficiently influential or defined for inclusion in risk models. The current analysis is an important first step in bringing the highlighted polymorphisms into a physiologically based pharmacokinetic (PBPK) modeling framework.

NAD(P)H:quinone oxidoreductase 1 Pro187Ser polymorphism and the risk of lung cancer: A meta-analysis

BACKGROUND

NAD(P)H:quinine oxidoreductase 1 (NQO1) is a two-electron reductase that catalyzes quinine to hydroquinone. Variant genotypes of NQO1 Pro187Ser may be related to low enzyme activity and thus are suggested as affecting the risk of lung cancer. Our purpose was to study the NQO1 Pro187Ser polymorphism and the risk of lung cancer.

METHODS

We conducted a PubMed search and a China National Knowledge Infrastructure search using "NAD(P)H quinine reductase 1" ,"lung cancer", and " polymorphism" for articles published from January 1997 to March 2010. For each study, we calculated the crude odds ratios (OR) and 95% confidence intervals (CI) for lung cancer. Summary estimates for crude as well as adjusted OR were calculated with the statistical program stata.

RESULTS

The summary OR for carrying one variant allele and the homozygous variant genotype was 1.04 (95%CI, 0.97-1.13). In the Asian population, the summary OR for carrying one variant genotype was 1.09 (95%CI, 0.95-1.25).

CONCLUSIONS

Through our meta-analysis, we found that the Pro/Ser and Ser/Ser genotypes involving NQO1 were non-significantly associated with lung cancer. In the Asian population, the combined genotype was marginally associated with increased risk of lung cancer. When stratified on gender and smoking, the meta-analysis showed that there was no statistically significant difference between men and women, smokers and non-smokers, respectively.

Polymorphisms in genes encoding drugs and xenobiotic metabolizing enzymes in a Brazilian population

Polymorphic variations of several genes associated with drugs and xenobiotic metabolism have been linked to the factors that predispose to the carcinogenesis process. As considerable interindividual and interethnic variation in metabolizing enzyme activity has been associated with polymorphic alleles, we evaluated the frequency of the polymorphisms of CYP2D6, EPHX1 and NQO1 genes in 361 Brazilian individuals separated by ethnicity (European and African ancestry), using the polymerase chain reaction-restriction fragment length (PCR-RFLP) method. The allele frequencies of the variants *3 and *4 for the gene CYP2D6 were 0.04 and 0.14 for white subjects and 0.03 and 0.10 for black individuals, respectively. For the both variants of the gene EPHX1, we found higher allele frequencies among white individuals compared with mulatto subjects (0.62 vs 0.54 and 0.18 vs 0.14, respectively); however, these differences were not statistically significant (p = 0.39 and 0.56, respectively). For the NQO1 gene we observed a higher frequency of the homozygous genotype among black individuals (7.9%) compared with white subjects (6.3%) (p = 0.003). The genotype frequencies were within the Hardy-Weinberg equilibrium. We concluded that the allele frequencies of CYP2D6, EPHX1 and NQO1 gene polymorphisms in this Brazilian population showed ethnic variability when compared with those observed in other populations.

NQO1, MPO, and the risk of lung cancer: a HuGE review

The aim of this study is to summarize the available molecular epidemiologic studies of lung cancer and metabolic genes, such as NAD(P)H quinone reductase 1 (NQO1) and myeloperoxidase (MPO). NQO1 plays a dual role in the detoxification and activation of procarcinogens whereas MPO has Phase I activity by converting lipophilic carcinogens into hydrophilic forms. Variant genotypes of both NQO1 Pro187 Ser and MPO G-463A polymorphisms may be related to low enzyme activity. The Pro/Ser and Ser/Ser genotypes combined of NQO1 was significantly associated with decreased risk of lung cancer in Japanese [random effects odds ratio (OR) = 0.70, 95% confidence interval (CI) = 0.56-0.88] among whom the variant allele is common. The variant genotype of MPO was associated with decreased risk of lung cancer among Caucasians (random effects OR = 0.70, 95% CI = 0.47-1.04). Gene-environment interactions in both polymorphisms may be hampered by inaccurate categorization of tobacco exposure. Evidence on gene-gene interactions is extremely limited. As lung cancer is a multifactorial disease, an improved understanding of such interactions may help identify individuals at risk for developing lung cancer. Such a study should include larger sample size and other polymorphisms in the metabolism of tobacco-derived carcinogens and address interactions with smoking status. The effects of polymorphisms are best represented by their haplotypes. In future studies on lung cancer, the development of haplotype-based approaches will facilitate the evaluation of haplotypic effects, either for selected polymorphisms physically close to each other or for multiple genes within the same drug-metabolism pathway.

CYP1A1 and GSTM1 polymorphisms and lung cancer risk in Chinese populations: a meta-analysis

Genetic polymorphisms of cytochrome p450 (CYP1A1) and glutathione S-transferase M1 (GSTM1) genes are thought to have significant effects on the metabolism of environmental carcinogens and thus on cancer risk, but the reported results are not always consistent. In this meta-analysis, we assessed reported studies of associations between polymorphisms of these two genes and risk of lung cancer in Chinese populations. Through a systematic literature search for publications between 1989 and 2006, we summarized the data from 46 studies on polymorphisms of MspI and exon7-Val of CYP1A1 and GSTM1 and lung cancer risk in Chinese populations, and found that compared with the wild-type homozygous genotype (type A), lung cancer risk for the combined variant genotypes (types B and C) was 1.34-fold (95% confidence interval [CI]=1.08-1.67) (Z=2.64, P=0.008); the risk for the combined variant genotypes (Ile/Val and Val/Val) of CYP1A1 exon7 was 1.61-fold (95% CI=1.24-2.08) (Z=3.62, P<0.001), compared with the Ile/Ile genotype; and that the risk for the GSTM1 null genotype was 1.54-fold (95% CI=1.31-1.80) (Z=5.32, P<0.001), compared with the GSTM1 present genotype. Therefore, in 46 published studies in Chinese populations, we found evidence of an association between the CYP1A1 variant and GSTM1 null genotypes and increased risk of lung cancer.

Polymorphism of selected enzymes involved in detoxification and biotransformation in relation to lung cancer

Available data indicate that there are significant differences in individual susceptibility to lung cancer within the human population. It is believed to be underlie by inherited genetic predispositions related to the genetic polymorphism of several enzymes involved in the detoxification and xenobiotic metabolism. In this review, we collect and discuss the evidence reported up to date on the association between lung cancer and genetic polymorphism of cytochromes P450, N-acetyltransferase, glutathione S-transferases, microsomal epoxide hydrolase, NAD(P)H:quinone oxidoreductase, myeloperoxidase and glutathione peroxidase. All these genes might appear to be candidates for lung cancer susceptibility genes, nevertheless, the present state of the art still offers only a limited explanation of the link between such polymorphisms and increased risk of lung cancer.

NAD(P)H:quinone oxidoreductase 1 (NQO1) Pro187Ser polymorphism and the risk of lung, bladder, and colorectal cancers: a meta-analysis

NAD(P)H:quinone oxidoreductase 1 (NQO1) is a cytosolic enzyme that catalyzes the two-electron reduction of quinoid compounds into hydroquinones, their less toxic form. A sequence variant at position 609 (C --> T) in the NQO1 gene encodes an enzyme with reduced quinone reductase activity in vitro and thus was hypothesized to affect cancer susceptibility. We conducted meta-analyses focusing on three cancer sites (lung, bladder, and colorectum) to summarize the findings from the current literature and to explore sources of heterogeneity.

RESULTS

There is no clear association between the NQO1 Pro187Ser polymorphism and lung cancer risk in the three ethnic groups examined: odds ratio (OR(White)) C/T + T/T versus C/C = 1.04 [95% confidence interval (95% CI), 0.96-1.13], OR(Asian) = 0.99 (95% CI, 0.72-1.34), and OR(Blacks) = 0.95 (95% CI, 0.66-1.36). However, a modestly increased risk was suggested for the variant homozygotes in whites (OR T/T versus C/C, 1.19; 95% CI, 0.94-1.50). Analysis excluding one outlier study suggested the variant allele may be associated with reduced lung cancer risk in Asians. Meta-analyses for bladder and colorectal cancer suggested a statistically significant association with the variant genotypes in whites. In stratified analyses, the NQO1 Pro187Ser variant genotypes were associated with slightly increased lung cancer risk in white ever smokers but not in white never smokers and were mainly associated with a reduced risk of lung adenocarcinoma but not squamous cell carcinoma in Asians.

CONCLUSIONS

Results from our meta-analyses suggest that the variant NQO1 Pro187Ser genotype may affect individual susceptibility to lung, bladder, and colorectal cancer. Such effects of the NQO1 polymorphism seem to be modified by ethnicity and smoking status.

EPHX1 polymorphisms and the risk of lung cancer: a HuGE review

BACKGROUND

Microsomal epoxide hydrolase 1 (EPHX1) plays an important role in both the activation and detoxification of tobacco-derived carcinogens. Polymorphisms at exons 3 and 4 of the EPHX1 gene have been reported to be associated with variations in EPHX1 activity. The aim of this study is to review and summarize the available molecular epidemiologic studies of lung cancer and EPHX1.

METHODS

We searched MEDLINE, Current Contents, and Web of Science databases for studies published before August 2004. We conducted a systematic review and meta-analysis of 13 case-control studies. Summary odds ratios and summary prevalence of the variant allele (genotype) of both polymorphisms in the EPHX1 gene were calculated using the DerSimonian and Laird method.

RESULTS

The low-activity (variant) genotype of EPHX1 polymorphism at exon 3 was associated with decreased risk of lung cancer (odds ratio = 0.65; 95% confidence interval = 0.44-0.96) in lung cancer risk among whites. In white populations, the high-activity (variant) genotype of EPHX1 polymorphism at exon 4 was associated with a modest increase in risk of lung cancer (1.22; 0.79-1.90) and the predicted low activity was associated with a modest decrease in risk (0.72; 0.43-1.22).

CONCLUSIONS

EPHX1 enzyme may act as a phase I enzyme in lung carcinogenesis. The low-activity genotype of EPHX1 gene is associated with decreased risk of lung cancer among whites.

Genetic analysis of microsomal epoxide hydrolase gene and its association with lung cancer risk

The human microsomal epoxide hydrolase (EH) gene contains polymorphic alleles, which may be linked to increased risk for tobacco-related lung cancer. The purpose of this study is to screen new polymorphisms and determine whether these polymorphisms can be used to predict individual susceptibility to lung cancer. The polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis was used to screen for polymorphisms in the coding region of the EH gene. Eleven polymorphisms, including previously reported polymorphisms, were identified and the prevalence of these variants was assessed in at least 50 healthy Caucasians and African-Americans. Among the 11 polymorphisms, the prevalence of the amino acid-changing EH polymorphisms in codons 43, 113 and 139 was examined in 182 Caucasian incident cases with primary lung cancer, as well as in 365 frequency-matched controls to examine the role of EH polymorphisms in lung cancer risk. A significant increase in lung cancer risk was observed for predicted high EH activity genotypes (odds ratio (OR) 2.3, 95% confidence interval (CI) 1.2-4.3) as compared with low EH activity genotypes. This association was more pronounced among patients with lung adenocarcinoma (OR 4.7, 95% CI 1.7-13.1). These results suggest that the EH polymorphism plays an important role in lung cancer risk and is linked to tobacco smoke exposure.

An association between a NQO1 genetic polymorphism and risk of lung cancer

NAD(P)H:quinone oxidoreductase (NQO1) is a detoxification enzyme that protects against the regeneration of reactive oxygen species chemically induced by oxidative stress, cytotoxicity, mutagenicity, and carcinogenicity. The protection conferred by NQO1 protein reduces certain environmental carcinogens, such as nitroaromatic compounds, heterocyclic amines, and possible cigarette smoke condensate. The gene coding for NQO1 has a genetic polymorphism (C-->T) at nucleotide position 609 (i.e. amino acid codon 187) of the NQO1 cDNA. This polymorphism was shown to reduce NQO1 enzyme activity, thereby diminishing the protection provided by NQO1. Therefore, we hypothesized that individuals with the variant NQO1 genotype are at higher risk for lung cancer. Using a case-control study, we genotyped the NQO1 variants successfully by PCR-RFLP in 826 lung cancer patients and 826 healthy control subjects matched for age, sex, ethnicity, and smoking status. The frequency of the NQO1 T-allele was statistically significantly different among three ethnic groups (p<0.001). In further analysis of Caucasians, the variant NQO1 genotypes (CT and TT) were associated with a marginally increased lung cancer risk (OR=1.19; 95% CI: 0.95-1.50). The elevated lung cancer risk was only evident in younger individuals (age <62 years old) (OR=1.46; 95% CI: 1.04-2.05), women (OR=1.89; 95% CI: 1.33-2.68), and never smokers (OR=1.80; 95% CI: 1.03-3.13). Furthermore, we found a statistically significant trend in the development of lung cancer at an early age in women with increasing copies of the variant allele (p=0.03). These results suggest that the NQO1 variant genotype may modulate lung cancer risk, especially in younger individuals (age<62), women, and never smokers.

Effects of Genetic Polymorphisms of Metabolic Enzymes on Cytokinesis-Block Micronucleus in Peripheral Blood Lymphocyte among Coke-Oven Workers

Exploring the associations between genetic polymorphisms of metabolic enzymes and susceptibility to polycyclic aromatic hydrocarbon (PAH)–induced chromosomal damage is of great significance for understanding PAH carcinogenesis. Cytochrome P450, glutathione S-transferase, microsomal epoxide hydrolase, NAD(P)H:quinone oxidoreductase, and N-acetyltransferase are PAH-metabolizing enzymes. In this study, we genotyped for the polymorphisms of these genes and assessed their effects on cytokinesis-block micronucleus (CBMN) frequencies in peripheral blood lymphocytes among 141 coke-oven workers and 66 non–coke-oven worker controls. The geometric means of urinary 1-hydroxypyrene levels in coke-oven workers and the controls were 12.0 and 0.7 μmol/mol creatinine, respectively (P &lt; 0.01). The CBMN frequency (number of micronuclei per 1,000 binucleated lymphocytes) was significantly higher in coke-oven workers (9.5 ± 6.6‰) than in the controls (4.0 ± 3.6‰; P &lt; 0.01). Among the coke-oven workers, age was positively associated with CBMN frequency; the mEH His113 variant genotype exhibited significantly lower CBMN frequency (8.5 ± 6.5‰) than did the Tyr113/Tyr113 genotype (11.3 ± 6.4‰; P &lt; 0.01); the low mEH activity phenotype exhibited a lower CBMN frequency (8.6 ± 6.8‰) than did the high mEH activity phenotype (13.2 ± 6.7‰; P = 0.01); the GSTP1 Val105/Val105 genotype exhibited a higher CBMN frequency (15.0 ± 5.8‰) than did the GSTP1 Ile105/Ile105 or Ile105/Val105 genotypes (9.3 ± 6.5‰; P &lt; 0.01); the joint effect of high mEH activity phenotype and GSTM1 null genotype on CBMN frequencies was also found. Gene-environment interactions between occupational PAH exposure and polymorphisms of mEH and/or GSTM1 were also evident. These results indicate that the mEH, GSTP1, and GSTM1 polymorphisms may play a role in sensitivity or genetic susceptibility to the genotoxic effects of PAH exposure in the coke-oven workers.

DT-diaphorase: a target for new anticancer drugs

DT-diaphorase (DTD) is an obligate two-electron reductase which bioactivates chemotherapeutic quinones. DTD levels are elevated in a number of tumour types, including non-small cell lung carcinoma, colorectal carcinoma, liver cancers and breast carcinomas, when compared to the surrounding normal tissue. The differential in DTD between tumour and normal tissue should allow targeted activation of chemotherapeutic quinones in the tumour whilst minimising normal tissue toxicity. The prototypical bioreductive drug is Mitomycin C (MMC) which is widely used in clinical practice. However, MMC is actually a relatively poor substrate for DTD and its metabolism is pH-dependent. Other bioreductive drugs have failed because of poor solubility and inability to surpass other agents in use. RH1, a novel diaziridinylbenzoquinone, is a more efficient substrate for DTD. It has been demonstrated to have anti-tumour effects both in vitro and in vivo and demonstrates a relationship between DTD expression levels and drug response. RH1 has recently entered a phase I clinical trial in solid tumours under the auspices of Cancer Research UK. Recent work has demonstrated that DTD is present in the nucleus and is associated with both p53 and the heat shock protein, HSP-70. Furthermore, DTD is inducible by several non-toxic compounds and therefore much interest has focussed on increasing the differential in DTD levels between tumour and normal tissues.

Genetic polymorphisms in the Hmong population

BACKGROUND

The Hmong, an isolated, agrarian people from southern China, migrated to the mountainous regions of what are today Vietnam, Cambodia, and Laos. Minnesota has the second largest Hmong population in the United States. The authors compared frequencies of common genetic polymorphisms believed to influence risk of malignancy to determine whether frequencies in the Hmong are different from those in other Asian populations and in white Minnesotans.

METHODS

Genotyping for glutathione S-transferase micro1 (GSTM1), glutathione S-transferase theta1 (GSTT1), myeloperoxidase (MPO) (C(-)463T), nicotinamide adenine dinucleotide phosphate:quinone oxidoreductase (NQO1) (C609T), 5,10-methylenetetrahydrofolate reductase (MTHFR) (C677T), MTHFR (A1298C), methionine synthase reductase (MTRR) (A66G), X-ray repair cross complementing 1 (XRCC1) 194 (Arg194Trp), XRCC1 280 (Arg280His), and XRCC1 399 (Arg399Gln) alleles was performed by TaqMan analysis using DNA isolated from newborn heel-stick spots provided by the Minnesota Department of Health.

RESULTS

The Hmong had significantly higher frequencies of the NQO1 T allele and the XRCC1 Trp polymorphism (Arg194Trp) and had significantly lower frequencies of the G allele in MTRR (A66G) and the T allele in MTHFR (C677T) compared with white Minnesotans. The Hmong also were significantly more likely to lack the GSTM1 and GSTT1 genes compared with whites (82% vs. 54% and 61% vs. 18%, respectively). Genotype frequencies were similar for MTHFR (A1298C), MPO (C(-)463T), and XRCC1 (Arg280His, Arg399Gln). Genotype frequencies at these loci also were compared with those reported for other Asian populations and showed notable differences between the Hmong and Chinese/Taiwanese, Korean, and Japanese populations.

CONCLUSIONS

The genetic differences identified have implications for both cancer etiology and prognosis in this unique population.

Epoxide hydrolase Tyr113His polymorphism is not associated with susceptibility to esophageal squamous cell carcinoma in population of North China

AIM: To investigate the possible association of microsomal epoxide hydrolase (mEH) Tyr113His polymorphism with susceptibility to esophageal squamous cell carcinoma (ESCC) in a population of North China.

METHODS: The mEH Tyr113His genotypes were determined by polymerase-chain reaction (PCR)-restriction fragment length polymorphism (RFLP) analysis in 257 patients with esophageal squamous cell carcinoma (ESCC) and 252 healthy subjects as a control group.

RESULTS: The frequencies for Tyr and His alleles were 44.2%, 55.8% in ESCC patients, and 44.0% and 56.0% in healthy subjects, respectively. No statistic difference in allele distribution was observed between ESCC patients and controls (χ² = 0.008, P = 0.929). The overall genotype distribution difference was not observed between cancer cases and controls (χ² = 2.116, P = 0.347). Compared with Tyr/Tyr genotype, neither His/His genotype nor in combination with Tyr/His genotype significantly modified the risk of the development of ESCC, the adjusted odds ratio was 1.076 (95%CI = 0.850-1.361) and 0.756 (95%CI = 0.493-1.157), respectively. When stratified for sex, age, smoking status and family history of upper gastrointestinal cancer, His/His genotype alone or in combination with Tyr/His genotype also did not show any significant influence on the risk of developing ESCC.

CONCLUSION: MEH Tyr113His polymorphism may not be used as a stratification marker in screening individuals at a high risk of ESCC.

Epoxide hydrolase genotype and orolaryngeal cancer risk: interaction with GSTM1 genotype

The human microsomal epoxide hydrolase (EH) gene contains polymorphic alleles which are associated with altered EH activity and may be linked to increased risk for tobacco-related cancers. The objective was to examine the role of EH polymorphisms in orolaryngeal cancer risk. The prevalence of the EH codons 113 and 139 polymorphisms were examined in 81 African American and 142 Caucasian incident orolaryngeal cancer patients and 335 controls frequency-matched on age, sex, and race. In Caucasians, a significant risk increase was observed for subjects with the EH(113Tyr) variant (OR=2.1, 95% CI=1.1-4.0) and predicted high-activity EH genotypes in heavy-smokers (>or=35 pack-years; OR=3.4, 95% CI=1.2-9.6). A significant association between predicted high EH activity genotypes and orolaryngeal cancer risk was observed in Caucasian subjects with the GSTM1 null (OR=3.5, 95% CI=1.3-9.3) but not GSTM [+] (OR=0.9, 95%CI=0.4-2.1) genotype. These results suggest that EH polymorphisms play an important role in risk for orolaryngeal cancer in Caucasians.

Markers of genetic susceptibility in human environmental hygiene and toxicology: the role of selected CYP, NAT and GST genes

Inherited genetic traits co-determine the susceptibility of an individual to a toxic chemical. Special emphasis has been put on individual responses to environmental and industrial carcinogens, but other chronic diseases are of increasing interest. Polymorphisms of relevant xenobiotic metabolising enzymes may be used as toxicological susceptibility markers. A growing number of genes encoding enzymes involved in biotransformation of toxicants and in cellular defence against toxicant-induced damage to the cells has been identified and cloned, leading to increased knowledge of allelic variants of genes and genetic defects that may result in a differential susceptibility toward environmental toxicants. "Low penetrating" polymorphisms in metabolism genes tend to be much more common in the population than allelic variants of "high penetrating" cancer genes, and are therefore of considerable importance from a public health point of view. Positive associations between cancer and CYP1A1 alleles, in particular the *2C I462V allele, were found for tissues following the aerodigestive tract. Again, in most cases, the effect of the variant CYP1A1 allele becomes apparent or clearer in connection with the GSTM1 null allele. The CYP1B1 codon 432 polymorphism (CYP1B1*3) has been identified as a susceptibility factor in smoking-related head-and-neck squameous cell cancer. The impact of this polymorphic variant of CYP1B1 on cancer risk was also reflected by an association with the frequency of somatic mutations of the p53 gene. Combined genotype analysis of CYP1B1 and the glutathione transferases GSTM1 or GSTT1 has also pointed to interactive effects. Of particular interest for the industrial and environmental field is the isozyme CYP2E1. Several genotypes of this isozyme have been characterised which seem to be associated with different levels of expression of enzyme activity. The acetylator status for NAT2 can be determined by genotyping or by phenotyping. In the pathogenesis of human bladder cancer due to occupational exposure to "classical" aromatic amines (benzidine, 4-aminodiphenyl, 1-naphthylamine) acetylation by NAT2 is regarded as a detoxication step. Interestingly, the underlying European findings of a higher susceptibility of slow acetylators towards aromatic amines are in contrast to findings in Chinese workers occupationally exposed to aromatic amines which points to different mechanisms of susceptibility between European and Chinese populations. Regarding human bladder cancer, the hypothesis has been put forward that genetic polymorphism of GSTM1 might be linked with the occurrence of this tumour type. This supports the hypothesis that exposure to PAH might causally be involved in urothelial cancers. The human polymorphic GST catalysing conjugation of halomethanes, dihalomethanes, ethylene oxide and a number of other industrial compounds could be characterised as a class theta enzyme (GSTT1) by means of molecular biology. "Conjugator" and "non-conjugator" phenotypes are coincident with the presence and absence of the GSTT1 gene. There are wide variations in the frequencies of GSTT1 deletion (GSTT1*0/0) among different ethnicities. Human phenotyping is facilitated by the GST activity towards methyl bromide or ethylene oxide in erythrocytes which is representative of the metabolic GSTT1 competence of the entire organism. Inter-individual variations in xenobiotic metabolism capacities may be due to polymorphisms of the genes coding for the enzymes themselves or of the genes coding for the receptors or transcription factors which regulate the expression of the enzymes. Also, polymorphisms in several regions of genes may cause altered ligand affinity, transactivation activity or expression levels of the receptor subsequently influencing the expression of the downstream target genes. Studies of individual susceptibility to toxicants and gene-environment interaction are now emerging as an important component of molecular epidemiology.

Association of GSTM1, CYP1A1 and CYP2E1 genetic polymorphisms with susceptibility to lung adenocarcinoma: a case-control study in Chinese population

A case-control study of 164 lung adenocarcinoma (AC) patients with 181 age- and gender-matched healthy controls was conducted in order to assess any associations between glutathione-S-transferase M1 (GSTM1), cytochrome P4501A1 (CYP1A1) and cytochrome P4502E1 (CYP2E1) polymorphisms and susceptibility to lung AC in Chinese. The presence of CYP2E1 variant allele was significantly less frequent in cases than in controls, while the distribution of GSTM1 null genotype and variant CYP1A1 Msp1 allele did not vary between cases and controls. After adjustment for age, gender, smoking and all other genotypes, the CYP2E1 Rsa1 variant allele was significantly associated with decreased risk of lung AC [odds ratio 0.534 (95% confidence interval, 0.340-0.837)]. Furthermore, 3.0-fold increased risk was found in individuals with combined GSTM1 null genotype and CYP2E1 Rsa1 wild type versus those with combined GSTM1 non-null type and CYP2E1 variant allele. Our results suggest that CYP2E1 Rsa1 variant allele is associated with a decreased risk of lung AC, and combined GSTM1 null genotype and CYP2E1 Rsa1 wild type has a promoting effect on susceptibility to lung AC.

An association between NQO1 genetic polymorphism and risk of bladder cancer

NAD(P)H:quinone oxidoreductase (NQO1) is a detoxification enzyme that plays a critical role in protecting cells against chemically induced oxidative stress, cytotoxicity, mutagenicity, and carcinogenicity. NQO1 protects cells from oxidative damage by preventing the generation of reactive oxygen species and reducing certain environmental carcinogens, such as nitroaromatic compounds, heterocyclic amines, and possible cigarette smoke condensate. A C-->T single nucleotide polymorphism in exon 6 was shown to reduce NQO1 enzyme activity, which may diminish the protection provided by NQO1. Therefore, we hypothesized that people with the variant allele genotypes of NQO1 are at higher risk for bladder cancer. In an ongoing case-control study, the NQO1 genotypes were successfully identified by polymerase chain reaction restriction fragment length polymorphism in 265 bladder cancer patients and 261 control subjects matched for age, sex, and ethnicity. The frequency of the variant NQO1 allele was 18% for controls and 21% for cases. The variant allele genotypes of NQO1 were associated with a higher risk of bladder cancer in Caucasians (odds ratio (OR)=1.51; 95% confidence interval (CI)=1.01-2.25). Further analysis in Caucasians showed an elevated bladder cancer risk in men (OR=1.75; 95% CI=1.08-2.85) but not in women (OR=1.16; 95% CI=0.57-2.37). In addition, the variant allele genotypes were associated with higher bladder cancer risk in ever smokers (OR=1.78; 95% CI=1.06-3.00), but not in never smokers (OR=1.19; 95% CI=0.65-2.20). These results suggest that the NQO1 genetic polymorphism modulates bladder cancer risk, especially in men and ever smokers.

Advanced presentation of lung cancer in Asian immigrants: a case-control study

STUDY OBJECTIVES

To determine if Asian immigrants to the United States present with more advanced lung cancer compared to non-Asians.

DESIGN

A 5-year retrospective case-control study (January 1, 1992, to December 31, 1996) of patients with lung cancer identified using the New England Medical Center cancer center database. A 2-year follow up was obtained in all subjects.

SETTING

A tertiary level care hospital providing all levels of medical care to the local Asian population in the Boston area.

PATIENTS

Forty-two Asian immigrants with lung cancer diagnosed over the study period were matched for age and sex with 42 non-Asian control subjects.

RESULTS

Asians presented more frequently with advanced stage (stage III or IV) and less frequently with early stage (stage I or II) lung cancer compared with the non-Asian control group (p < 0.05). Asians were more likely to present with hemoptysis or constitutional symptoms (p < 0.01) and had a longer duration of symptoms prior to presentation (p < 0.01) compared with non-Asians. There was no difference in the length of time elapsed between diagnosis and start of treatment (approximation of workup time) between the two groups. The utilization of tests and procedures for clinical disease staging was not significantly different between the two groups. The incidence of large cell carcinoma (p < 0.05) was higher in Asians compared with non-Asians. Asians were more likely to receive radiotherapy and less likely to receive combination therapy compared with non-Asians (p < 0.05). The treatment of stage I and II lung cancer did not differ between the two groups. The median 2-year survival was significantly reduced in Asians compared with non-Asians: Asians, 7 months (95% confidence interval [CI], 3.1 to 10.9); non-Asians, 15 months (95% CI, 12.0 to 17.5) [p < 0.001].

CONCLUSIONS

Asian immigrants with lung cancer appear to present with more advanced stage of disease, have more prolonged symptomatology, and have reduced survival compared with non-Asians. These data suggest that ethnicity may play a role in the presentation and outcome of lung cancer in the Asian immigrant population.

Genetic polymorphisms and lung cancer susceptibility: a review

Lung cancer is a major cause of cancer-related death in the developed countries and the overall survival rate has still an extremely poor. Cigarette smoking is an established risk factor for lung cancer although a possible role for genetic susceptibility in the development of lung cancer has been inferred from familial clustering of the disease and segregation analyzes. Everyone may have a unique combination of polymorphic traits that modify genetic susceptibility and response to drugs, chemicals and carcinogens. Developments in molecular biology have led to growing interest in investigation of biological markers, which may increase predisposition to lung carcinogenesis. Therefore, the high-risk genotype of an individual could be determined easily. As there are the great number of carcinogen-activating and -detoxifying enzymes, the variation in their expression and the complexity of exposures to tobacco carcinogens, the existence of multiple alleles at loci of those enzymes may result in differential susceptibilities of individuals. This review summarize data addressing the relationships of lung cancer to markers of genetic susceptibility genes, including metabolic polymorphisms other than well-investigated cytochrome P450s or glutathione S-transferases, DNA repair genes and the p53 tumor suppressor gene. Among genetic polymorphisms reviewed here, myeloperoxidase gene (a G to A mutation) and microsomal epoxide hydrolase exon 4 polymorphism (substitution of Arg for His) were significantly associated with lung cancer risk. As lung cancer is a multifactorial disease, an improved understanding of the interplay of environmental and genetic polymorphisms at multiple loci may help identify individuals who are at increased risk for lung cancer. Hopefully, in the future we will be able to screen for lung cancer susceptibility by using specific biomarkers.

NAD(P)H:quinone oxidoreductase (NQO1) polymorphism, exposure to benzene, and predisposition to disease: a HuGE review

NAD(P)H:quinone oxidoreductase (NQO1) catalyzes the two- or four-electron reduction of numerous endogenous and environmental quinones (e.g., the vitamin E alpha-tocopherol quinone, menadione, benzene quinones). In laboratory animals treated with various environmental chemicals, inhibition of NQO1 metabolism has long been known to increase the risk of toxicity or cancer. Currently, there are 22 reported single-nucleotide polymorphisms (SNPs) in the NQO1 gene. Compared with the human consensus (reference, "wild-type") NQO1*1 allele coding for normal NQO1 enzyme and activity, the NQO1*2 allele encodes a nonsynonymous mutation (P187S) that has negligible NQO1 activity. The NQO1*2 allelic frequency ranges between 0.22 (Caucasian) and 0.45 (Asian) in various ethnic populations. A large epidemiologic investigation of a benzene-exposed population has shown that NQO1*2 homozygotes exhibit as much as a 7-fold greater risk of bone marrow toxicity, leading to diseases such as aplastic anemia and leukemia. The extent of the contribution of polymorphisms in other genes involved in the metabolism of benzene and related compounds-such as the P450 2E1 (CYP2E1), myeloperoxidase (MPO), glutathione-S-transferase (GSTM1, GSTT1), microsomal epoxide hydrolase (EPHX1), and other genes-should also be considered. However, it now seems clear that a lowered or absent NQO1 activity can increase one's risk of bone marrow toxicity, after environmental exposure to benzene and benzene-like compounds. In cancer patients, the NQO1*2 allele appears to be associated with increased risk of chemotherapy-related myeloid leukemia. Many other epidemiological studies, attempting to find an association between the NQO1 polymorphism and one or another human disease, have now begun to appear in the medical literature.