Human glutathione S-transferase P1 polymorphisms: relationship to lung tissue enzyme activity and population frequency distribution

Tumoral drug metabolism: overview and its implications for cancer therapy

Drug-metabolizing enzymes (DME) in tumors are capable of biotransforming a variety of xenobiotics, including antineoplastics, resulting in either their activation or detoxification. Many studies have reported the presence of DME in tumors; however, heterogeneous detection methodology and patient cohorts have not generated consistent, firm data. Nevertheless, various gene therapy approaches and oral prodrugs have been devised, taking advantage of tumoral DME. With the need to target and individualize anticancer therapies, tumoral processes such as drug metabolism must be considered as both a potential mechanism of resistance to therapy and a potential means of achieving optimal therapy. This review discusses cytotoxic drug metabolism by tumors, through addressing the classes of the individual DME, their relevant substrates, and their distribution in specific malignancies. The limitations of preclinical models relative to the clinical setting and lack of data on the changes of DME with disease progression and host response will be discussed. The therapeutic implications of tumoral drug metabolism will be addressed-in particular, the role of DME in predicting therapeutic response, the activation of prodrugs, and the potential for modulation of their activity for gain are considered, with relevant clinical examples. The contribution of tumoral drug metabolism to cancer therapy can only be truly ascertained through large-scale prospective studies and supported by new technologies for tumor sampling and genetic analysis such as microarrays. Only then can efforts be concentrated in the design of better prodrugs or combination therapy to improve drug efficacy and individualize therapy.

Pharmacogenomics in colorectal carcinomas: Future perspectives in personalized therapy

The recent introduction of new drugs such as capecitabine, irinotecan, and oxaliplatinum has greatly improved the clinical outcome of patients with advanced/metastatic colorectal cancer. Nevertheless, some patients may suffer from the adverse drug reactions which will probably be the main cause of chemotherapy failure. The goal of pharmacogenomics is to find correlations between therapeutic responses to drugs and the genetic profiles of patients; the different responses to a particular drug are due, in fact, not only to the specific clinico-pathological features of the patient or to environmental factors, but also to the ethnic origins and the particular individual's genetic profile. Genes which codify for the metabolism enzymes, receptor proteins, or protein targets of chemotherapy agents often present various genetic polymorphisms. The main aim of this review is to provide an overview of the known polymorphisms present in the genes which codify for factors (thymidylate synthase dihydropyrimidine dehydrogenase, uridine diphosphate (UDP)-glucuronosyl-transferase 1A1, enzymes implicated in DNA repair) involved in the action mechanisms of the drugs now utilized in chemotherapeutic treatment of colorectal carcinoma, such as fluoropyrimidines, irinotecan, and platinum agents.

Molecular epidemiology of lung cancer in female passive smokers

To clarify etiology of lung cancer in nonsmoker females, various studies have been done. Particularly, host factors and environmental tobacco smoking (ETS) of females have been emphasized. However, traditional epidemiological data showed controversial results of sex or gender differences in lung cancer susceptibility and suggest presence of some confounders. One of them is that most of epidemiology studies are based on self-reports for ETS. To prevent misestimate effects of ETS via the self-report, exposure monitoring of ETS is required. On the other hand, focusing on genetic polymorphisms in metabolic enzymes and DNA repair, molecular epidemiological studies have been done in nonsmoker females. Therefore, this review considered: 1. gender differences in lung cancer; 2. effects of passive smoking on lung cancer; 3. exposure monitoring of ETS including genetic risks of lung cancer to clarify etiology of lung cancer in the nonsmoker females with molecular epidemiological discussion.

Human glutathione S-transferase A1, T1, M1, and P1 polymorphisms and susceptibility to prostate cancer in the Japanese population

PURPOSE

The incidence of prostate cancer is increasing in low-risk populations such as Japanese. One of the causes of this increase is considered to be associated with the Western diet, especially the high intake of red meat and fat. Glutathione S-transferase (GST) A1, T1, M1, and P1 are phase II enzymes that are important for activation and detoxification of chemical carcinogens.

METHODS

In this study, 190 Japanese male patients with prostate cancer and 294 healthy controls, frequency-matched for age, were compared for frequencies of GSTA1, GSTT1, GSTM1, and GSTP1 genotypes.

RESULTS

Among smokers, the frequency of the GSTA1*A/*B or *B/*B genotype in patients with prostate cancer (27.8%) showed a statistically significant increase compared with the control group frequency (18.2%; odds ratio [OR] =1.72; 95% CI, 1.01-2.94). In addition, the frequency of GSTT1 nondeletion genotype was associated with prostate cancer among smokers (OR =1.68; 95% CI, 1.06-2.68). The OR of carrying the combined genotyping of GSTA1*A/*B or *B/*B and GSTT1 nondeletion was 2.08 (95% CI, 1.14-3.80) with the combined genotyping of GSTA1*A/*A and GSTT1 null as a reference. On the other hand, no significant associations were observed for genotypes of GSTM1 and GSTP1 I105V.

CONCLUSIONS

These findings suggest that the GSTA1 and GSTT1 polymorphisms are associated with prostate cancer susceptibility, especially among smokers.

Oligogenic combinations associated with breast cancer risk in women under 53 years of age

Common, but weakly penetrant, functional polymorphisms probably account for most of the genetic risk for breast cancer in the general population. Current polygenic risk models assume that component genes act independently. To test for potential gene-gene interactions, single nucleotide polymorphisms in ten genes with known or predicted roles in breast carcinogenesis were examined in a case-control study of 631 Caucasian women diagnosed with breast cancer under the age of 53 years and 1,504 controls under the age of 53 years. Association of breast cancer risk with individual genes and with two- and three-gene combinations was analyzed. Sixty-nine oligogenotypes from 37 distinct two- and three-gene combinations met stringent criteria for significance. Significant odds ratios (ORs) covered a 12-fold range: 0.5-5.9. Of the observed ORs, 17% differed significantly from the ORs predicted by a model of independent gene action, suggesting epistasis, i.e., that these genes interact to affect breast cancer risk in a manner not predictable from single gene effects. Exploration of the biological basis for these oligogenic interactions might reveal etiologic or therapeutic insights into breast cancer and other cancers.

Glutathione S-transferase polymorphisms and survival in primary malignant glioma

PURPOSE

The purpose of this research was to investigate the relationship between glutathione S-transferase (GST) polymorphisms and survival, and chemotherapy-related toxicity in 278 glioma patients.

EXPERIMENTAL DESIGN

We determined genetic variants for GSTM1, GSTT1, and GSTP1 enzymes by PCR and restriction fragment length polymorphisms. We conducted Kaplan-Meier and Cox-proportional hazard analyses to examine whether the GST polymorphisms are related to overall survival, and logistic regression analysis to explore whether the GST polymorphisms are associated with toxicity.

RESULTS

For patients with anaplastic astrocytoma, anaplastic oligodendroglioma, anaplastic oligoastrocytoma, and anaplastic ependymoma (n = 78), patients with GSTP1*A/*A-M1 null genotype survived longer than did the rest of the group (median survival "not achieved," and 41 months, respectively; P = 0.06). Among patients treated with nitrosoureas (n = 108), those with GSTP1*A/*A and GSTM1 null genotype were 5.7 times (95% confidence interval, 0.9-37.4) more likely to experience an adverse event secondary to chemotherapy, compared with the others.

CONCLUSIONS

In patients with anaplastic astrocytoma, anaplastic oligodendroglioma, and anaplastic oligoastrocytoma, combination of germ-line GSTP1*A/*A and GSTM1 null genotype confers a survival advantage. Patients with this genotype also have an increased risk of adverse events secondary to chemotherapy that primarily comprised nitrosourea alkylating agents.

May glutathione S-transferase M1 positive genotype afford protection against primary open-angle glaucoma?

PURPOSE

To find out whether the polymorphism at GSTM1, GSTT1 and GSTP1 loci is associated with increased susceptibility to glaucoma.

METHODS

We genotyped 153 primary open angle patients and 159 healthy controls. Genomic DNA from peripheral blood was examined using polymerase chain reaction and defined for the genetic polymorphisms of glutathione S-transferase.

RESULTS

The frequency of the GSTM1 null genotype individuals among the glaucoma patients was significanlty higher than in controls (54.9 vs 40.9%) with odds ratio of 1.64 (95% CI: 1.10-2.59). The frequency of the GSTT1 and GSTP1 in both groups were not statistically different.

CONCLUSION

The present study suggests that the GSTM1 null genotype may be a genetic risk factor for development of primary open angle glaucoma. Further associations studies in other polymorphic genes for xenobiotic-metabolizing enzymes are needed to elucidate the environmental-genetic interaction in the underlying cause of primary open angle glaucoma.

Glutathione-S-transferase gene polymorphisms (GSTT1, GSTM1, GSTP1) as increased risk factors for asthma

OBJECTIVES

Asthma is a complex multifactorial disease with an obvious genetic predisposition, immunological aberration, and involvement of noxious environmental factors. Polymorphisms of the glutathione-S-transferase (GST) genes are known risk factors for some environmentally-related diseases. In the present study, the hypothesis that polymorphisms in the GSTT1, GSTM1 and GSTP1 genes are associated with atopic and nonatopic asthma was examined.

METHODOLOGY

The study population consisted of 103 unrelated healthy individuals and 101 patients with bronchial asthma (64 atopic, 37 nonatopic). Asthma was diagnosed according to the American Thoracic Society statement. Genotyping of polymorphisms in the GSTT1, GSTM1 and GSTP1 genes was performed using real time polymerase chain reaction with a Light Cycler instrument and hybridization probes in combination with the Light Cycler DNA master hybridization probes kit.

RESULTS

Patients with atopic asthma (34.4%) had a higher prevalence of the GSTT1 null genotype than the nonatopic asthma patients (13.5%; OR = 3.83; 95% CI, 1.24-11.78). Asthma patients (63.4%) had a higher prevalence of the GSTM1 null genotype than the control group (40.8%; OR = 2.34; 95% CI, 1.31-4.20). Subjects with the GSTP1 homozygous Val/Val genotype had a 3.55-fold increased risk of having atopic asthma compared to nonatopic asthma (OR = 3.55; 95% CI, 1.10-12.56).

CONCLUSIONS

These results suggest that the GSTT1 and GSTM1 null genotypes and the GSTP1 Val/Val polymorphism may play important roles in asthma pathogenesis. It is possible that intermediate electrophilic metabolites, arising in the first phase of detoxification, are not metabolized by GST enzymes in asthmatic patients and are not excreted. These intermediate metabolites may damage cells and generate oxidative stress, and so contribute to the pathogenesis of asthma.

Individual susceptibility to carcinogens

The contribution of polymorphisms in carcinogen metabolizing genes to overall cancer rates may vary widely between groups with differing allele frequencies and with varying levels of carcinogenic exposure. Their effects are modified by interactions with each other and with other genes, particularly those involved in DNA repair. Studies on the combined effects of particular polymorphisms on colorectal and other cancers, and also on intermediate markers such as DNA adduct formation, are discussed. Such susceptibility genes are of considerable scientific interest, but do not confer high enough risks to be clinically relevant.

Genetic susceptibility to tobacco-related cancer

Although cigarette smoking is the dominant risk factor for several epithelial cancers, only a small fraction of individuals with tobacco exposure develop cancer. The underlying hypothesis is that genetic factors may render certain smokers more susceptible to cancer than others. Genetic alterations in critical regulatory pathways may predispose cells to carcinogenesis. These pathways include regulation of xenobiotic metabolism; control of genomic stability, including DNA repair mechanisms, cell-cycle checkpoints, apoptosis and telomere length; and control of microenvironmental factors, such as matrix metalloproteinases, inflammation and growth factors. In addition, epigenetic events, such as promoter hypermethylation and loss of imprinting, are also involved in carcinogenesis. In this review, we will summarize recent advances in genetic susceptibility to tobacco-related cancer. Emphasizing on risk assessment, we will describe how genetic variations in the above-mentioned genetic pathways modify the tobacco-related cancer risk. In addition, we will discuss how genetic variations may assist in predicting clinical outcome, such as the natural history of cancer and treatment response. The measurements of genetic susceptibility by both genotypic and phenotypic assays are covered in the text. Finally, we present a number of current concerns that need to be addressed as the exciting field of molecular cancer epidemiology advances rapidly.

A multivariate analysis of genomic polymorphisms: prediction of clinical outcome to 5-FU/oxaliplatin combination chemotherapy in refractory colorectal cancer

In this marker evaluation study, we tested whether distinct patterns of functional genomic polymorphisms in genes involved in drug metabolic pathways and DNA repair that predict clinical outcome to 5-fluorouracil (5-FU)/oxaliplatin chemotherapy in patients with advanced colorectal cancer could be identified. Functional polymorphisms in DNA-repair genes XPD, ERCC1, XRCC1, XPA, and metabolising genes glutathione S-transferase GSTP1, GSTT1, GSTM1, and thymidylate synthase (TS) were assessed retrospectively in 106 patients with refractory stage IV disease who received 5-FU/oxaliplatin combination chemotherapy, using a polymerase chain reaction-based RFLP technique. Favourable genotypes from polymorphisms in XPD-751, ERCC1-118, GSTP1-105, and TS-3′-untranslated region (3′UTR) that are associated with overall survival were identified. After adjustment for performance status, the relative risks of dying for patients who possessed the unfavourable genotype were: 3.33 for XPD-751 (P=0.037), 3.25 for GSTP1-105 (P=0.072), 2.05 for ERCC1-118 (P=0.037), and 1.65 for TS-3′UTR (P=0.091) when compared to their respective beneficial genomic variants. Combination analysis with all four polymorphisms revealed that patients possessing ⩾2 favourable genotypes survived a median of 17.4 months (95% confidence interval (CI): 9.4, 26.5) compared to 5.4 months (95% CI: 4.3, 6.0) in patients with no favourable genotype. Patients who carried one favourable genotype demonstrated intermediate survival of 10.2 months (95% CI: 6.8, 15.3; P<0.001). Polymorphisms in the TS-3′UTR and GSTP1-105 gene were also associated with time to progression. After adjustment for performance status, patients with an unfavourable TS-3′UTR genotype had a relative risk of disease progression of 1.76 (P=0.020) and those with the unfavourable GSTP1-105 genotype showed a relative risk of progression of 2.00 (P=0.018). The genomic polymorphisms XPD-751, ERCC1-118, GSTP1-105, and TS-3′UTR may be useful in predicting overall survival and time to progression of colorectal cancer in patients who receive 5-FU/oxaliplatin chemotherapy. These findings require independent prospective confirmation.

GST profiling may be useful in the screening for thyroid nodule malignancy

Screening tools are of utmost necessity in order to identify individuals at risk for thyroid nodule cancer. The polymorphic inheritance of human drug-metabolizing enzymes, such as those encoded by the Glutathione-S-Transferase (GST) system, plays an important role in the development of most human cancers. GSTP1 enzyme is the most important detoxification enzyme in human head and neck tissues. An aminoacid substitution (1105V) in the GSTP1 gene result in two genotypes, GSTP1AB and GSTP1BB. Those produce a variant enzyme with lower activity and less capability of effective detoxification of carcinogens than the wild type GSTP1AA. In order to look for the influence of GSTP1 enzymes inheritance pattern on thyroid cancer risk we used a PCR-SSCP-sequencing approach to compare the genotypes of 98 malignant nodules, including 77 papillary carcinomas (PC) and 21 follicular carcinomas (FC), to 44 benign nodules and to 157 healthy control individuals. Individuals with history of previous thyroid disease, exposure to radiation and antecedents of malignancy were excluded. Patients with PC and FC showed a significant over-representation of the variants of GSTP1 allele compared to the control population (p < 0.0001 The risk for thyroid cancer in individuals with the variant GSTP1 enzymes, after adjusting for gender, age, tobacco and drugs use, increased 7,092 (CI: 2,307-21,802) and 9,625 (CI: 2.484-37.291) times for PC and FC, respectively. We suggest that GST genotype may be associated with an increased susceptibility to thyroid cancer. GSTP1 profiling from peripheral blood may be a simple and useful tool in the screening for thyroid nodule malignancy. Glutathione-S-Transferase system; GSTP; Thyroid cancer; Screening.

Bilirubin UDP-glucuronosyltransferase 1A1 (UGT1A1) gene promoter polymorphisms and HPRT, glycophorin A, and micronuclei mutant frequencies in human blood

A dinucleotide repeat polymorphism (5-, 6-, 7-, or 8-TA units) has been identified within the promoter region of UDP-glucuronosyltransferase 1A1 (UGT1A1) gene. The 7-TA repeat allele has been associated with elevated serum bilirubin levels that cause a mild hyperbilirubinemia (Gilbert's syndrome). Studies suggest that promoter transcriptional activity of UGT1A1 is inversely related to the number of TA repeats, and that unconjugated bilirubin concentration increases directly with the number of TA repeat elements. Because bilirubin is a known antioxidant, we hypothesized that UGT1A1 repeats associated with higher bilirubin may be protective against oxidative damage. We examined the effect of UGT1A1 genotype on somatic mutant frequency in the hypoxanthine-guanine phosphoribosyl-transferase (HPRT) gene in human lymphocytes and the glycophorin A (GPA) gene of red blood cells (both N0, NN mutants), and the frequency of lymphocyte micronuclei (both kinetochore (K)-positive or micronuclei K-negative) in 101 healthy smoking and nonsmoking individuals. As hypothesized, genotypes containing 7- and 8-TA displayed marginally lower GPA_NN mutant frequency relative to 5/5, 5/6, 6/6 genotypes ( [Formula: see text] ). In contrast, our analysis showed that lower expressing UGT1A1 alleles (7- and 8-TA) were associated with modestly increased HPRT mutation frequency ( [Formula: see text] ), while the same low-expression genotypes were not significantly associated with micronuclei frequencies (K-positive or K-negative) when compared to high-expression genotypes (5- and 6-TA). We found weak evidence that UGT1A1 genotypes containing 7- and 8-TA were associated with increased GPA_NØ mutant frequency relative to 5/5, 5/6, 6/6 genotypes ( [Formula: see text] ). These data suggest that UGT1A1 genotype may modulate somatic mutation of some types, in some cell lineages, by a mechanism not involving bilirubin antioxidant activity. More detailed studies examining UGT1A1 promoter variation, oxidant/antioxidant balance and genetic damage will be needed.

Glutathione S-transferase variants and their interaction with smoking on lung function

We studied glutathione S-transferase (GST) polymorphisms in 1,098 whites with the lowest (n = 544, FEV(1) % predicted mean +/- SEM = 62.6 +/- 0.1) and the highest (n = 554, FEV(1) % predicted mean +/- SEM = 91.8 +/- 0.1) lung function at the beginning of the Lung Health Study. Homozygosity for GSTP1 105Val was significantly more frequent in the low- than in the high-function group (13.2 vs. 9.3%) (odds ratio = 1.69, 95% confidence interval [CI] = 1.11-2.61, p = 0.016), after adjustment for confounding variables. Subjects with 105Val homozygotes had higher rates of lung function decline in the high-function group (p = 0.017). The frequencies of GSTM1, GSTT1 null genotypes were similar between the high- and low-function groups, but subjects with the GSTT1 null genotype had a faster decline of lung function in the low-function group (p = 0.032). In addition, there was a significant interaction of GSTT1 genotype and pack-years on lung function. When comparing individuals with GSTT1 null genotype with wild type, the adjusted odds ratio was 3.49 (95% CI, 1.48-8.39, p = 0.005) in mild smokers (< or = 25 pack years). We conclude that GST genotypes are risk factors for rapid decline or low lung function in smokers with mild to moderate airflow obstruction.

Oxygen free radical scavenger enzyme polymorphisms in systemic sclerosis

We performed a case-control study of polymorphisms of glutathione S-transferase (GST) isoenzymes and manganese superoxide dismutase (MnSOD) in black South Africans with systemic sclerosis (SSc). The frequency of the GSTM1*B phenotype was significantly decreased in the overall SSc group compared with controls (OR=0.19, p(corr)<.05), implying a possible protective effect against development of the disease. There was also a trend toward increased MnSODAla allele and phenotype frequencies in the diffuse cutaneous SSc subset compared with controls (OR=2.11 and 3.15, respectively, p(corr)<.1). Our findings provide new data on the distribution of GST and MnSOD polymorphisms in healthy Africans and further evidence that genetic factors may have a contributory role to play in predisposing to oxidative stress in SSc.

Polymorphic metabolic susceptibility genes and longevity: a study in octogonarians

In order to investigate possible associations of genetic variants in genes of xenobiotic metabolism with longevity, we compared allele frequencies and genotype distributions of polymorphic genes between 205 octogenarians and a non-cancer reference group of 294 persons aged less than 80 years. We analyzed common sequence variations in the cytochrome P-450 genes CYP1A1 T461N, 3801 T > C and CYP1B1 V432L, and in the glutathione S-transferase genes GSTM1 (deletion), GSTT1 (deletion), and GSTP1 (I105V). In octogenarians, the CYP1B1 432L allele was less prevalent than in the reference group (allele frequency 0.49 versus 0.60; odds ratio, OR, 0.63, 95% confidence limits (CI) 0.40-1.00). Octogenarians turned out to have marginally significant more GSTM1 negatives (frequency 0.56 versus 0.48; OR 1.41, 95% CI 0.97-2.05), but less GSTT1 deficient genotypes (frequency 0.14 versus 0.21; OR 0.64; 95% CI 0.38-1.06). In octogenarians without cancer, GSTT1 negative carriers were less prevalent than in the aged with cancer (frequency 0.12 versus 0.27; OR 2.81; 95% CI 1.00-7.38). Polymorphic metabolic susceptibility genes could become relevant for processes of aging when toxic defense mechanisms decline.

High-throughput detection of glutathione s-transferase polymorphic alleles in a pediatric cancer population

Polymorphisms of glutathione S-transferase (GST) enzymes have been correlated with altered risk of several cancers, as well as altered response and toxicity from cancer chemotherapy. We report a low cost, highly reproducible and specific PCR-based high-throughput assay for genotyping different GSTs designed for use in large clinical trials. In comparison to an alternative genotyping method (single nucleotide extension), the sensitivity and specificity of the high throughput assay was shown to be 92 and 97%, respectively, depending on the source of genomic DNA. Using the high-throughput assay, we demonstrate by multivariate analysis an increased risk of acute lymphoblastic leukemia, glial brain tumors, and osteosarcoma for patients carrying nonnull alleles of GSTM1 and/or GSTT1.

Protective role of glutathione S-transferase P1 (GSTP1) Val105Val genotype in patients with bronchial asthma

BACKGROUND

Glutathione S-transferase P1 (GSTP1), the abundant isoform of glutathione S-transferases (GSTs) in lung epithelium, plays an important role in cellular protection against oxidative stress and toxic foreign chemicals. It has been suggested that polymorphisms in the GSTP1 gene are associated with asthma and related phenotypes. As significant interindividual and interethnic differences exist in the distribution of xenobiotic-metabolizing enzymes, we have studied the GSTP1 Ile105Val polymorphism in patients with asthma in a Turkish sample.

METHODS

GSTP1 Ile105Val polymorphism in exon 5 was determined in 210 patients with asthma (112 extrinsic and 108 intrinsic) and 265 control individuals without lung diseases and without history of allergy or atopy, using polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) techniques.

RESULTS

The proportion of GSTP1 Val105 homozygotes was significantly lower in the patients with asthma than in the control individuals (3.8% vs 12.1%). The odds ratio for GSTP1 Val105 homozygotes vs all other genotypes was 0.29 (95%CL 0.13-0.64, p = 0.01) for asthmatics. The distribution of GSTP1 Ile105Val genotypes and the frequency of GSTP1 Val105Val homozygotes (3.7% vs 3.9%) was not significantly different between extrinsic and intrinsic asthmatics.

CONCLUSION

These results suggest a significant association between GSTP1 Ile105Val polymorphism and susceptibility to asthma and that the GSTP1 Val105Val genotype may be protective against developing this disease.

Locus-specific genetic diversity between human populations: an analysis of the literature

The debate over classification of the human species according to racial or continental lines has involved reports on genetic differences in allele frequencies of a number of loci with important biomedical functions. Such differences are in contrast with the fact that, for human beings, intrapopulation genetic diversity is larger than that seen between populations. In an attempt to address the hypothesis that certain genes show high interpopulation diversity due to selective pressure, the literature was surveyed to quantify such diversity using Wrights Fst statistic. The gene-specific Fst values were then compared to pairwise population values of Fst taken over a large number of genes, which presumably reflect mostly neutral mechanisms of genetic diversity such as drift. The results showed that the majority of pairwise population values of Fst for over 30 genes of biomedical significance were either below or within the expected limits of Fst based on published values. These results do not support the idea that positive or diversifying natural selection plays an important role in increasing genetic diversity, even in genes that might be expected to be subject to selection pressure. Balancing selection, whereby the degree of genetic diversity is actually lower than that expected, appears to occur more frequently for these genes. The fact that allele frequency differences between populations might be "statistically significant" does not therefore necessarily imply a degree of genetic diversity greater than would be expected due to nonselective mechanisms.

Cancer pharmacogenetics

The large number of active combination chemotherapy regimens for most cancers has led to the need for better information to guide the ‘standard’ treatment for each patient. In an attempt to individualise therapy, pharmacogenetics and pharmacogenomics (a polygenic approach to pharmacogenetic studies) encompass the search for answers to the hereditary basis for interindividual differences in drug response. This review will focus on the results of studies assessing the effects of polymorphisms in drug-metabolising enzymes and drug targets on the toxicity and response to commonly used chemotherapy drugs. In addition, the need for polygenic pharmacogenomic strategies to identify patients at risk for adverse drug reactions will be highlighted.

The association of maternal but not paternal genetic variation in GSTP1 with asthma phenotypes in children

Maternal factors including atopy and smoking during pregnancy are associated with asthma risk during childhood. Suggested mechanisms include transmission of specific maternal alleles and maternal influences on the intrauterine environment. We have previously shown that polymorphism in glutathione S-transferase, GSTP1 is associated with airway hyperresponsiveness (AHR) and atopy in adults. We now hypothesise that GSTP1 genotypes in the mother and child, but not the father, mediate asthma phenotypes in the child. One hundred and forty-five Caucasian families were recruited via an asthmatic proband aged 7-18 years. Atopy and asthma were assessed using a questionnaire, skin prick testing, serum IgE, spirometry and methacholine challenge (PC20, dose-response slope--DRS). GSTP1 genotyping was determined using PCR. GSTP1 Val105/Val105 genotype in the child was associated with a reduced risk of atopy (P = 0.038) and AHR (PC20, P = 0.046; DRS, P = 0.032). In mothers (P = 0.014) but not fathers (P = 0.623), Val105/Val105 was associated with a reduced risk of AHR in the child. We have identified, for the first time, an association between maternal genotype and the child's asthma phenotype that appears not to be due to transmission of specific maternal alleles. This preliminary data supports the view of in utero effects of maternal genotype and adds new insights into the possible mechanisms by which maternal factors may influence development of childhood asthma.

Associations between genetic polymorphisms of Phase I and II metabolizing enzymes, p53 and susceptibility to esophageal adenocarcinoma

The objectives of this exploratory case-control study were to evaluate whether genetic polymorphisms of selected Phase I and II metabolizing enzymes are associated with the risk of developing primary esophageal adenocarcinoma, and to investigate potential associations between genotypes and p53 tumor suppressor gene alterations. Cases comprised 45 patients with surgically resected esophageal adenocarcinomas, defined according to strict clinico-pathologic criteria. PCR-based assays (RFLP/SSCP) were used to genotype cytochrome P450 (CYP) 1A1 [MspI; Ile:Val], microsomal epoxide hydroxylase (mEH) (fast and slow alleles), and glutathione S-transferase (GST) T1, M1 and P1. Healthy controls (n=45) from the same geographic region were matched for age, gender and smoking history. For GSTP1, the Ile/Val (a/b) and Val/Val (b/b) variants were seen at increased frequency in cases compared to controls (49% versus 27% and 15% versus 9%, respectively), although these differences achieved only borderline statistical significance (P=0.09). For mEH (exon 3), the presence of the Tyr polymorphism (slow allele) was reduced in cases (42%) compared to controls (53%; P=0.05). Predicted high mEH activity was seen more frequently in cases than controls (OR, 2.2; 95% CI, 0.7-7.3). Polymorphism frequencies for GSTT1, GSTM1, and CYP1A1 were not statistically different between cases and controls. Cases with the GSTT1 null genotype had tumors with altered p53 more frequently than did cases with the common form of GSTT1 (25 versus 6%, respectively; P=0.08). We conclude that polymorphisms of GSTP1 and mEH may be implicated in individual susceptibility to esophageal adenocarcinoma, possibly as a result of increased Phase I activation (mEH) and impaired Phase II detoxification (GSTP1). GSTT1 may also play a role in esophageal tumorigenesis through a pathway that involves abnormalities in the p53 tumor suppressor gene.

GST genetic polymorphisms and lung adenocarcinoma susceptibility in a Chinese population

Lung adenocarcinoma (AC) has been increasing over the last several decades in many countries, including China. Some of the glutathione S-transferases (GSTs) demonstrate polymorphisms which may play a role in lung AC susceptibility. Our previous study of a Chinese population found the GSTM1 null genotype to be associated with an increased risk of lung AC, and the combination of GSTM1 null genotype and CYP2E1 wild type conferred a significantly elevated risk. Here, we extended the study to investigate the potential role of GSTT1 and GSTP1 polymorphisms in likelihood of development of lung AC, either separately or in combination. This case-control study encompassed 112 cases with lung ACs and 119 age- and gender-matched cancer-free controls from Beijing. The frequencies for the GSTM1 null genotype were 61.6 and 50.4% among cases and controls, and for the GSTT1 null genotype 47.3 and 45.4%, respectively. The distribution of the GSTP1 Ile/Ile, Ile/Val and Val/Val genotypes was 59.8, 39.3 and 0.9% in cases, and 70.6, 28.6 and 0.8% in controls, respectively. No relationship between lung AC and the GSTT1 genotype was observed in the present study, either separately or in combination with the GSTM1 or GSTP1 genotypes. Although separate GSTM1 and GSTP1 polymorphisms were not statistically related to lung AC, the combination of GSTM1 null and GSTP1 Val was significantly associated with an elevated lung AC risk (OR=2.4, 95% CI 1.1-5.1).

Effects of prednisone and genetic polymorphisms on etoposide disposition in children with acute lymphoblastic leukemia

Etoposide is a substrate for P-glycoprotein, CYP3A4, CYP3A5, and UGT1A1. Glucocorticoids modulate CYP3A and P-glycoprotein in preclinical models, but their effect on clinical etoposide disposition is unknown. We studied the pharmacokinetics of etoposide and its catechol metabolite in children with acute lymphoblastic leukemia, along with polymorphisms in CYP3A4, CYP3A5, MDR1, GSTP1, UGT1A1, and VDR. Plasma pharmacokinetics were assessed at day 29, after 1 month of prednisone (n = 102), and at week 54, without prednisone (n = 44). On day 29, etoposide clearance was higher (47.4 versus 29.2 mL/min/m2, P <.0001) than at week 54. The day 29 etoposide or catechol area under the curve (AUC) was correlated with neutropenia (P =.027 and P =.0008, respectively). The relationship between genotype and etoposide disposition differed by race and by prednisone use. The MDR1 exon 26 CC genotype predicted higher day 29 etoposide clearance (P =.002) for all patients, and the CYP3A5 AA and GSTP1 AA genotypes predicted lower clearance in blacks (P =.02 and.03, respectively). The UGT1A1 6/6, VDR intron 8 GG, and VDR Fok 1 CC genotypes predicted higher week 54 clearance in blacks (P =.039,.036, and.052, respectively). The UGT1A1 6/6 genotype predicted lower catechol AUC. Prednisone strongly induces etoposide clearance, genetic polymorphisms may predict the constitutive and induced clearance of etoposide, and the relationship between genotype and phenotype differs by race.

Genetic polymorphisms and susceptibility to childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most common form of pediatric cancer. Although exposure to environmental agents appears to predispose individuals to this disease, little attention has been paid to the role of genetic susceptibility to environmental exposures in the etiology of childhood ALL. The enzymes GSTM1, GSTT1, GSTP1, CYP1A1, and CYP2E1 are involved in the bioactivation and detoxification of a variety of xenobiotics present in food, organic solvents, tobacco smoke, drugs, alcoholic drinks, pesticides, and environmental pollutants. Polymorphisms in the genes coding for these enzymes have been associated with increased susceptibility to different cancers, including hematologic malignancies. To investigate whether these polymorphisms represent risk-modifying factors for childhood ALL, a study was conducted involving 113 Brazilian patients of childhood ALL and 221 controls with similar ethnic backgrounds. The data revealed that carriers of the rare GSTP1 Val allele were at higher risk of ALL (odds ratio [OR] = 2.7; 95% confidence interval [CI] = 1.1-6.8; P = 0.04). No difference was found in the prevalence of the GSTM1 and GSTT1 null genotypes between ALL patients and the controls, and no association was found between CYP1A1*2 and CYP2E1*3 variants and ALL. However, when the mutant CYP1A1 and CYP2E1 alleles were considered together with the GSTM1 and GSTP1 risk-elevating genotypes, the risk of ALL was increased further (OR = 10.3; 95% CI = 1.0-111.8; P = 0.05), suggesting a combined effect. These results imply that genetic variants of xenobiotic metabolizing genes influence the risk of developing childhood ALL.

GlutathioneS-transferaseM3 (A/A) genotype as a risk factor for oral cancer and leukoplakia among Indian tobacco smokers

Polymorphism in glutathione S-transferase (GST) genes, causing variations in enzyme activities, may influence susceptibility to oral cancer and leukoplakia in smokers and/or smokeless tobacco users. In this case-control study consisting of 109 leukoplakia and 256 oral cancer patients and 259 controls, genotype frequencies at GSTM1, GSTT1, GSTM3 and GSTP1 loci were determined by polymerase chain reaction-restriction fragment length polymorphism methods and analyzed by multiple logistic regression to determine the risks of the diseases. There were no significant differences in the distributions of GSTM1, GSTM3 and GSTT1 genotypes in patients and controls when all individuals were compared. In contrast, frequencies of ile/ile genotype at codon 105 and variant val-ala haplotype of GSTP1 was significantly higher (OR = 1.5; 95% CI = 1.0-2.0) and lower (OR = 1.4; 95% CI = 1.0-1.9) in oral cancer patients compare to controls, respectively. The impacts of all genotypes on risks of oral cancer and leukoplakia were also analyzed in patients with different tobacco habits and doses. Increased risks of cancer and leukoplakia were observed in tobacco smokers with GSTM3 (A/A) genotype (OR = 2.0, 95% CI = 1.0-4.0; OR = 2.0, 95% CI = 1.0-4.4, respectively). So, GSTM3 (A/A) genotype could become one of the markers to know which of the leukoplakia would be transformed into cancer. Heavy tobacco chewing (> 124 chewing-year) increased the risk of cancer in individuals with GSTT1 homozygous null genotype (OR = 3.0; 95% CI = 1.0-9.8). Furthermore, increased lifetime exposure to tobacco smoking (> 11.5 pack-year) increased the risk of leukoplakia in individuals with GSTM1 homozygous null genotype (OR = 2.4; 95% CI = 1.0-5.7). It may be suggested that polymorphisms in GSTP1, GSTM1, GSTM3 and GSTT1 genes regulate risk of cancer and leukoplakia differentially among different tobacco habituals.

Association studies for asthma and atopic diseases: a comprehensive review of the literature

Hundreds of genetic association studies on asthma-related phenotypes have been conducted in different populations. To date, variants in 64 genes have been reported to be associated with asthma or related traits in at least one study. Of these, 33 associations were replicated in a second study, 9 associations were not replicated either in a second study or a second sample in the same study, and 22 associations were reported in just a single published study. These results suggest the potential for a great amount of heterogeneity underlying asthma. However, many of these studies are methodologically limited and their interpretation hampered by small sample sizes.

Smoking and the Risk of Lung Cancer

BACKGROUND

GSTP1 is a gene that helps detoxify foreign substances in the body. Functional polymorphisms of GSTP1 have been studied as risk factors for lung cancer. Past studies have compared the effect of the "at risk" polymorphism in two strata of smoking pack-years (usually defined by the median among controls). We examined the interaction between GSTP1 polymorphisms and cumulative exposure to smoking and their association with lung cancer risk.

METHODS

Data are from a large hospital-based case-control study of persons treated for primary lung cancer at the Massachusetts General Hospital since 1992. Controls were drawn from friends and nonrelated family members. We genotyped 1,042 cases and 1,161 controls for GSTP1 using polymerase chain reaction-restriction fragment length polymorphism techniques.

FINDINGS

The GSTP1 GG genotype approximately doubled the lung cancer risk associated with pack-years. This interaction was stronger among current smokers. At 26 pack-years (median among controls with a smoking history), the adjusted odds ratio for the association between pack-years and lung cancer risk was 13 (95% confidence interval = 6.5-25) among current smokers with the GSTP1 GG genotype compared with 6.1 (95% confidence interval = 4.9-7.5) among those with the GSTP1 AA genotype.

CONCLUSIONS

GSTP1 GG increases the lung cancer risk associated with pack-years of smoking.

Implications of genetic testing in the management of colorectal cancer

The prognosis of patients with colorectal cancer is impacted by various factors at the time of diagnosis, including location of the tumor, gender, age and overall performance status of the patient. Optimal postoperative management of patients who have undergone successful tumor resection involves the utilization of reliable determninants of prognosis to help select patients who would benefit from adjuvant treatment, while sparing others from drug-related adverse effects. Tailoring chemotherapy for patients with disseminated cancer, or for patients who receive adjuvant chemotherapy, is also critical. Interpatient differences in tumor response and drug toxicity are common during chemotherapy. Genomic variability of key metabolic enzyme complexes, drug targets, and drug transport molecules is an important contributing factor. The identification of genetic markers of response and prognosis will aid in the development of more individualized chemotherapuetic strategies for cancer patients. Potential prognostic indicators in colorectal cancer include oncogenes, tumor suppressor genes, genes involved in angiogenic and apoptotic pathways and cell proliferation, and those encoding targets of chemotherapy. Specifically, molecular markers such as deletion of 18q (DCC), p27 and microsatellite instability are promising as indicators of good or poor prognosis. Molecular determinants of efficacy and host toxicity of the most commonly used drugs in colorectal cancer, fluoracil, irinotecan and oxaliplatin, are being investigated. Alterations in gene expression, protein expression and polymorphic variants in genes encoding thymidylate synthase, dihydropyrimidine dehydrogenase, dUTP nucleotidehydrolase and thymidine phosphorylase (for fluoropyrimidine-based chemotherapy), uridine diphosphate glucosyltransferase (UGT) 1A1 and carboxylesterase (for irinotecan therapy), and excision repair cross-complementing genes (ERCC1 and ERCC2) and glutathione-S-transferase P1 (for oxalilplatin-based regimens) may be useful as markers for clinical drug response, survival and host toxicity.

Nucleotide excision repair pathways involved in Cisplatin resistance in non-small-cell lung cancer

BACKGROUND

In spite of the growing list of genetic abnormalities identified as being involved in DNA repair pathways that alter chemosensitivity in non-small-cell lung cancer (NSCLC) patients, translational assays have not yet been developed for use in individualized chemotherapy.

METHODS

In metastatic NSCLC, no single cisplatin-based chemotherapy regimen has been shown to be superior to any other. Although these studies show a small survival tail at 3 years, the majority of patients had a median survival of 8 to 10 months. We review the principal mechanisms of cisplatin resistance, particularly those involved in the nucleotide excision repair (NER) pathways (transcription-coupled repair and global genomic repair).

RESULTS

ERCC1 is a single-stranded DNA endonuclease that forms a tight heterodimer with xeroderma pigmentosum complementation group F. It incises DNA on the 5' side of a lesion such as cisplatin-DNA adduct. Therefore, overexpression of ERCC1 and other NER enzymes during ovarian cancer chemotherapy with cisplatin appears to be implicated in the formation of cellular and clinical drug resistance. Recently, baseline ERCC1 mRNA overexpression has been related to poor response and survival in cisplatin-treated NSCLC patients.

CONCLUSIONS

The level of evidence for many assays is limited, and only ERCC1 mRNA levels have been analyzed extensively. The impact of ERCC1 should be fully validated in prospective clinical trials.

Glutathione S-transferase Mu null genotype affords protection against alcohol induced chronic pancreatitis

Glutathione S-transferases (GSTs) play critical roles in providing protection against electrophiles and products of oxidative stress, by catalysing the formation of glutathione conjugates and by eliminating peroxides. Most extensively studied are four main families of human cytosolic GST: GSTAlpha(A), GSTMu(M), GSTPi(P) and GSTTheta(T). Absence of GSTM1 or GSTT1 can be attributed to absence of the GSTM1 or GSTT1 gene products (null genotype) in approximately 50% and 20% of the Caucasian population, respectively. We investigated whether polymorphisms in the GSTM1, GSTT1 and GSTP1 genes modified the risk for chronic pancreatitis (CP). DNA samples were obtained from 142 adult CP patients with alcoholic (n = 79), hereditary (n = 21) or idiopathic (n = 42) origin. DNA from 204 healthy controls and from 57 alcoholic controls was analysed for comparison. Patients and controls were all of Caucasian origin. Genetic polymorphisms in GSTs were determined by PCR, eventually followed by restriction-fragment-length-polymorphism analyses in all subjects. The rates of GSTT1 and GSTP1 genotypes did not differ between CP patients and healthy controls. However, GSTM1 null genotypes were significantly less common in alcoholic CP patients (OR = 0.56, 95% CI: 0.33-0.95) as compared to healthy controls and to alcoholic controls (OR = 0.52, 95% CI: 0.26-1.04). Age- and sex-adjustment bolstered our finding (adjusted OR = 0.48, 95% CI: 0.26-0.89). The frequency of the GSTM1 null genotype is significantly lower in alcoholic CP patients, especially young female. This suggests that GSTM1 null alcohol users, particularly young female, are less susceptible to CP.

Characterization of MTHFR, GSTM1, GSTT1, GSTP1, and CYP1A1 genotypes in childhood acute leukemia

The role of methylenetetrahydrofolate reductase (MTHFR C677T), glutathione S-transferases (GSTM1 and GSTT1 null, GSTP1 Ile105Val), and cytochromes p450 (CYP1A1*2A) genotypes in the etiology of childhood leukemia was simultaneously investigated. 144 Turkish children with acute lymphoblastic leukemia (ALL) and 33 with acute nonlymphoblastic leukemia (ANLL) were studied and compared with 185 healthy pediatric controls. The frequency of MTHFR genotype was insignificantly higher in ALL (7.7%) and ANLL (6.3%) than in controls (4.4%). Equal distribution of the GSTM1 null genotype was detected between ALL patients and controls (55%), while its incidence was slightly higher in ANLL patients (61.3%). Although GSTT1 null genotype was insignificantly lower in ALL patients (20.9%) than controls (22.7%), it was significantly underrepresented in ANLL patients (6.5%) (P = 0.05, OR 0.24, 95% CI 0.05-1.03). The homozygous frequency of GSTP1 genotype did not differ significantly between groups of ALL (3.7%), ANLL patients (9.1%) and controls (4.9%). Homozygous CYP1A1*2A genotype was underrepresented in ALL patients (1%) as compared to control (4.8%) but the differences did not reach to statistical significance (OR 0.21; 95% CI 0.03-1.72). Homozygosity for this genotype was not detected in ANLL patients. No particular association was noted between different combinations of combined genotypes and risk of development of childhood ALL and ANLL. These results suggested that there are no significant associations between the studied genotypes and the risk of developing either form of acute leukemia except GSTT1 null and homozygosity for CYP1A1 genotypes that may play protective roles in the development of ANLL in Turkish children.

Naturally occurring Phe151Leu substitution near a conserved folding module lowers stability of glutathione transferase P1-1

Glutathione transferases (GSTs) are a family of enzymes that detoxify electrophilic compounds, such as carcinogens or drugs, by conjugating them to glutathione. The enzymes have contributed to the understanding of protein structure, due to large differences in amino acid sequence within the family, yet similar architecture and folding. Our objective was to conduct a systematic survey of GSTP1 polymorphisms and their function. Nearly all variants detected were known polymorphisms: IVS4+13C>A; Ile105Val; Ala114Val; and g.2596T>C (Ser185Ser). However, we also found a novel Phe151Leu substitution in an African-American subject (1 out of 111). Kinetic parameters for the conjugation reaction with 1-chloro-2,4-dinitrobenzene (CDNB) were determined for the novel variant enzyme purified via heterologous expression in Escherichia coli. Five substrates were used for measurement of specific activities, including isothiocyanate compounds that occur in cruciferous vegetables (benzylisothiocyanate, phenethylisothiocyanate, and sulforaphane). Such isothiocyanate substrates are potential cancer chemopreventive agents that are conjugated by GSTs. No major change in kinetic parameters was observed. However, the half-life at 50 degrees C of the Leu 151 enzyme was reduced to 12 min, as compared to 28 min for the Phe 151 enzyme. Residue 151 is located at the N-terminus of helix alpha6 in GST motif II, surrounded by hydrophobic residues, and near the conserved "hydrophobic staple" and N-capping box motifs. These local structural elements aid in formation of helix alpha6 and promote proper folding and protein stability. Analysis of the three-dimensional structure showed that substitution of Phe 151 with Leu produces a hydrophobic cavity in the GSTP1 core, thereby destabilizing its structure. Phe151Leu represents one of the first-described allelic variations in a protein folding motif.

Glutathione S-transferase GSTP1 genotypes are associated with response to androgen ablation therapy in advanced prostate cancer

We determined whether the glutathione S-transferase GSTP1 Ile105 --> Val105 substitution is associated with response to androgen ablation therapy in patients with advanced prostate cancer. As response may be associated with tumor grade, Gleason score, clinical T stage and presence of metastases we also determined if GSTP1 genotypes were associated with these prognostic parameters. We speculated that GSTP1 Ile105/Ile105 would be linked with good response to androgen ablation therapy and, low/moderate tumor grade, 1/2 clinical T-stage, Gleason score < 6 and, no metastases. Genotype frequencies in cases and controls were not significantly different (P = 0.70) indicating that allelism in GSTP1 is not associated with susceptibility. There was no association between GSTP1 (Ile105/Ile105 versus Ile105/Val105 and Val105/Val105) and grade (P = 0.28, OR = 0.92), Gleason score (P = 0.84, OR = 0.94) or metastatic state (P = 0.68, OR = 0.88) though the frequency of GSTP1 Ile105/Ile105 was higher in cases with stage 1/2 tumors than those with stage 3/4 tumors (P = 0.03, OR = 1.89). GSTP1 Val105/Val105 was also associated with response to hormone ablation therapy. Thus, the GSTP1 Ile105/Ile105 frequency was significantly higher in 86/118 patients who demonstrated a good response than in those with poor response (P = 0.03, OR = 2.70). We speculate that the association of GSTP1 with response results from an effect of the gene product early in carcinogenesis.

Genetic polymorphisms of tobacco- and alcohol-related metabolizing enzymes and the risk of hepatocellular carcinoma

The effect of genetic polymorphisms for glutathione S-transferase ( GST) M1, GSTT1, GSTP1-1( GSTP1), cytochrome P450 2E1 ( CYP2E1) and aldehyde dehydrogenase 2 ( ALDH2) on the risk of hepatocellular carcinoma (HCC) was observed in 78 Japanese patients with HCC and 138 non-cancer hospital controls. We found a positive association between cumulative amounts of alcohol consumption (>/=600,000 ml in a lifetime) and the risk of HCC (OR=4.52, 95% CI 2.39-8.55). However, cigarette smoking was not significantly related to the risk of HCC (OR=1.23, 95% CI 0.57-2.68). The allelic frequencies of GSTM1, GSTT1, GSTP1, CYP2E1and ALDH2of HCC patients were not significantly different from those of controls when odds ratios were only adjusted for age and gender except for any 2 alleles of ALDH2in drinkers (OR=2.53, 95% CI 1.21-5.31). However, the frequency of any C2 alleles of CYP2E1and any 2 alleles of ALDH2were significantly higher than those of controls (OR=5.77, 95% CI 1.24-27.39, OR=9.77, 95% CI 1.63-58.60) when covariates including viremia were selected by using stepwise logistic regression analysis. We conclude that habitual alcohol drinking is likely to lead to an increased risk of HCC, and any C2alleles of CYP2E1as well as any two alleles of ALDH2were also associated with an increased risk of HCC.

Correction of bronchial challenge data for age and size may affect the results of genetic association studies in children

Meaningful studies of asthma genetics require careful definition of airway hyperresponsiveness (AHR). In children, several studies have emphasized the need for correction of bronchial challenge data for baseline parameters, such as age, gender, lung function and atopic status, when undertaking airway responsiveness measurements. However, few studies have suggested how this should be performed in practice. This study describes a method for the correction of dose-response slopes (DRS) and PC20 values for baseline parameters in children, and illustrates the effect of such corrections on the association of AHR with the glutathione S-transferase GSTP1 Ile105Val polymorphism in children. Skin prick and methacholine challenge testing, measurement of total serum IgE concentration and GSTP1 genotyping were performed in 145 unrelated British children aged 7-18 years. Correction of bronchial challenge results, expressed as both DRS and PC20 values, for age, gender, baseline lung function and atopic status was performed using linear regression and discriminant analysis, respectively. Adjusting bronchial challenge results for the age and size of the child altered AHR status, defined as a PC20 methacholine <8 mg/ml, in 37% of children. Correction for baseline parameters also resulted in a significant reduction in mean DRS (original uncorrected DRS 83.6, corrected DRSc 27.4). This had a marked effect on the results of the association study, unmasking a previously unidentified association between the GSTP1 genotype and AHR in children. Age and size adjustment of bronchial challenge data has a significant effect on AHR status and may influence the results of genetic association studies in children.

Association between self-reported environmental tobacco smoke exposure and lung cancer: modification by GSTP1 polymorphism

Environmental Tobacco Smoke (ETS) exposure has been associated with lung cancer risk. ETS is composed of emissions from cigarette smoke and contains a higher concentration of tobacco smoke carcinogens than mainstream smoke. Polymorphisms in genes that metabolize tobacco smoke carcinogens have been studied as effect modifiers of the association between active smoking and lung cancer risk. GSTP1 is a polymorphic gene that encodes for GST pi, a detoxification enzyme and has a high expression in the lung. We investigated the association between ETS and lung cancer risk and the modification of this association by the GSTP1 polymorphism. Using a case-control design, individuals were genotyped for GSTP1 using PCR-RFLP techniques. All analyses were carried out using multiple logistic regression. The association between ETS exposure and lung cancer risk was evaluated in different strata based on smoking habits to evaluate the consistency of results. The effect of the GSTP1 polymorphisms on lung cancer risk was evaluated by considering the joint effect of having both an ETS exposure and the GSTP1 GG genotype compared to the absence of ETS exposure and the GSTP1 AA genotype as a reference group as well as doing stratified analysis by genotype. ETS exposure was associated consistently with higher lung cancer risk in all the strata considered. The adjusted odds ratios (AOR) evaluating the association between ETS and lung cancer risk for the different strata were: nonsmokers (Cases/Controls 66/413; AOR = 1.38; 95% CI = 0.78-2.43), ex-smokers (Cases/Controls 560/527; AOR = 1.66; 95% CI = 1.22-2.25), current smokers (Cases/Controls 415/219; AOR = 1.56; 95% CI = 1.00-2.41). The AORs for ex-smokers and light smoking subgroups were: ex-smokers who quit for 19 years or more (Cases/Controls 144/244; AOR = 2.64; 95% CI = 1.55-4.50), ex-smokers who quit for 10-19 years (Cases/Controls 141/128; AOR = 1.16; 95% CI = 0.66-2.04), ex-smokers who quit for 10 years or less (Cases/Controls 247/122; AOR = 1.45; 95% CI = 0.83-2.55) and participants who had <15 packyears and nonsmokers combined (Cases/Controls 143/640; AOR = 1.52; 95% CI = 1.02-2.28). Among those with the GSTP1 GG genotype the ETS-lung cancer risk association was greater than those with the GSTP1 AA genotype: nonsmokers (GSTP1 GG AOR = 7.84; 95% CI = 0.80-76.68; GSTP1 AA AOR = 1.15; 95% CI = 0.46-2.90), ex-smokers (GSTP1 GG AOR = 2.32; 95% CI = 0.90-5.96; GSTP1 AA AOR = 2.15; 95% CI = 1.34-3.44), current smokers (GSTP1 GG AOR = 1.75; 95% CI = 0.42-7.32; GSTP1 AA AOR = 1.32; 95% CI = 0.67-2.58) and participants who had <15 packyears and nonsmokers (GSTP1 GG AOR = 1.93; 95% CI = 0.54-6.97; GSTP1 AA AOR = 1.58; 95% CI = 0.83-3.01). We found that ETS exposure is associated with higher lung cancer risk. Furthermore, the presence of the GSTP1 GG genotype appears to enhance the magnitude of the association between ETS exposure and lung cancer. Larger studies will be needed to confirm these preliminary findings.

Allele frequencies for glutathione S-transferase and N-acetyltransferase 2 differ in African population groups and may be associated with oesophageal cancer or tuberculosis incidence

Glutathione S-transferase (GST) and arylamine N-acetyltransferase 2 (NAT2) metabolise many environmental and chemotherapeutic agents, which influence susceptibility to disease. Polymorphisms in these enzymes result in different host phenotypes and contribute to different disease profiles or responses to toxic or chemotherapeutic agents, depending on their frequency in different populations. GST and NAT2 polymorphisms were investigated in different population groups, including African populations, and a range of allelic frequencies have been observed. The GSTM1 null genotype frequency, reported in this paper in two South African ethnic groups, is the lowest reported (0.19-0.21). In contrast, these same groups have a high GSTT1 null frequency (0.41-0.54), which is considerably higher than in African-Americans, or other Africans. The GSTT1 null frequency is comparable to the Chinese, a population with a very high oesophageal cancer incidence, similar to that in the African group. The frequency of the GSTPi Val105 variant in the South African Xhosas was also high (0.53), differing significantly from the low frequency in other Africans. These variants could therefore be associated with high cancer susceptibility. In addition, the high proportion of NAT2 "fast" alleles may partially explain the high tuberculosis prevalence in South Africans, due to reduced isoniazid efficacy in the presence of rapid acetylation.

Association between glutathione S-transferase p1 polymorphisms and lung cancer risk in Caucasians: a case-control study

Glutathione transferases (GSTs), a multiple gene family of phase II enzymes, catalyze detoxifying endogenous reactions with glutathione and protect cellular macromolecules from damage caused by cytotoxic and carcinogenic agents. Glutathione S-transferase p1 (GSTP1), the most abundant GST isoform in the lung, metabolizes numerous carcinogenic compounds including benzo[a]pyrene, a tobacco carcinogen. Previous studies suggest that genetic polymorphisms of GSTP1 exon 5 (Ile105Val) and exon 6 (Ala114Val) have functional effects on the GST gene product resulting in reduced enzyme activity. Individuals with reduced GST enzymatic activity may be at a greater risk for cancer due to decreased detoxification of carcinogenic and mutagenic compounds. Utilizing a hospital-based case-control study, we investigated the association between GSTP1 polymorphisms at exons 5 and 6 with lung cancer risk. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay was used to successfully genotype the GSTP1 exons 5 and 6 polymorphism in 582 Caucasian lung cancer cases and 600 frequency matched Caucasian controls. There was no association between the exon 5 variant genotypes (A/G+G/G) and overall lung cancer risk (OR=1.09; 95% CI 0.82-1.45) nor when stratified by age, gender, and smoking status. However, the exon 6 variant genotypes (C/T+T/T) were associated with a statistically significant elevated lung cancer risk (OR=1.40; 95% CI 1.06-1.92). Additionally, there was an increase in lung cancer risk for the exon 6 variant genotypes in younger individuals (<62 years) (OR=1.63; 95% C.I. 1.07-2.49) but no effect in older individuals (OR=1.14; 95% CI 0.72-1.81). A statistically significant increased risk of lung cancer was also observed for the exon 6 variant genotypes among men (OR=2.17; 95% CI 1.41-3.33), but not among women (OR=0.80; 95% CI 0.51-1.28). Among ever smokers, the exon 6 variant genotypes were associated with an elevated lung cancer risk (OR=1.58; 95% CI 1.14-2.19), which was not evident for never smokers (OR=0.53; 95% CI 0.21-1.33). These data demonstrate that the GSTP1 exon 6 polymorphism, but not the exon 5 polymorphism, is associated with lung cancer risk that is especially evident in men, younger individuals, and ever smokers.

Identification of glutathione S-transferase (GST) polymorphisms in brain tumors and association with susceptibility to pediatric astrocytomas

Polymorphisms in the glutathione S-transferase (GST) genes, a superfamily that plays a key role in carcinogen metabolism, have been associated with an increased susceptibility to several types of cancer. We wished to evaluate whether variant allelic forms of GST isoenzymes were associated with an increased susceptibility for brain tumors and age of tumor onset. Here, we examined 394 brain tumors (221 adult and 173 pediatric cases consisting of 197 astrocytic and 197 non-astrocytic tumors) to determine the frequency of polymorphisms in the GSTM1, GSTT1, and GSTP1 genes compared to a healthy control population. Our data shows that the frequency of GST polymorphisms varies not only between adult and pediatric patients with brain tumors and healthy controls, but also between different histological subtypes of brain tumors occurring in pediatric patients. We found (i) a statistically significant increase in the frequency of the functional GSTM1 allele in high-grade pediatric astrocytomas (p < 0.002), (ii) a significant increase in the frequency of the rare GSTP1 variant Val114/Val114 in pediatric astrocytomas (p < 0.002), and (iii) a significant increase in the frequency of the rare GSTP1 Val114/Val114 genotype among pediatric tumors showing microsatellite instability (MSI) due to defects in mismatch repair (MMR) proteins (p = 0.003). Our results suggest that GSTM1 and GSTP1 polymorphisms may play a role in brain tumor susceptibility by histological subtype, particularly high-grade pediatric astrocytomas. Moreover, the presence of the genetic modifier GSTP1 Val114/Val14 genotype may begin to define a high-risk genotype for cancer susceptibility in the pediatric population.

Cancer pharmacogenomics: current and future applications

Heterogeneity in patient response to chemotherapy is consistently observed across patient populations. Pharmacogenomics is the study of inherited differences in interindividual drug disposition and effects, with the goal of selecting the optimal drug therapy and dosage for each patient. Pharmacogenomics is especially important for oncology, as severe systemic toxicity and unpredictable efficacy are hallmarks of cancer therapies. In addition, genetic polymorphisms in drug metabolizing enzymes and other molecules are responsible for much of the interindividual differences in the efficacy and toxicity of many chemotherapy agents. This review will discuss clinically relevant examples of gene polymorphisms that influence the outcome of cancer therapy, and whole-genome expression studies using microarray technology that have shown tremendous potential for benefiting cancer pharmacogenomics. The power and utility of the mouse as an experimental system for pharmacogenomic discovery will also be discussed in the context of cancer therapy.

Lung cancer andCYP1A1 orGSTM1 polymorphisms

Most chemical carcinogens are metabolized and activated in vivo by phase I enzymes including the microsomal cytochromes P450 and epoxide hydroxylases. The carcinogens and their metabolites are detoxified by phase II enzymes that in clude various transferases such as glutathion-S-transferases (GST). Increasing numbers of studies have demonstrated the association of the polymorphisms inGSTM1 (a member of GST) andCYP1A1 genes with the susceptibility to lung cancer. Subsequently, the polymorphisms appear to be important biomarkers that provide information for assessment of exposure and total burden of environmental carcinogens. Therefore, the investigation of the polymorphisms in these genes will provide information not only for the prediction of individual cancer risk but also for the prevention of cancer. In this review, we will summarize the polymorphisms in theGSTM1 andCYP1A1 genes and their relation to lung cancer susceptibility.

The importance of glutathione in human disease

Reduced glutathione (GSH) is the most prevalent non-protein thiol in animal cells. Its de novo and salvage synthesis serves to maintain a reduced cellular environment and the tripeptide is a co-factor for many cytoplasmic enzymes and may also act as an important post-translational modification in a number of cellular proteins. The cysteine thiol acts as a nucleophile in reactions with both exogenous and endogenous electrophilic species. As a consequence, reactive oxygen species (ROS) are frequently targeted by GSH in both spontaneous and catalytic reactions. Since ROS have defined roles in cell signaling events as well as in human disease pathologies, an imbalance in expression of GSH and associated enzymes has been implicated in a variety of circumstances. Cause and effect links between GSH metabolism and diseases such as cancer, neurodegenerative diseases, cystic fibrosis (CF), HIV, and aging have been shown. Polymorphic expression of enzymes involved in GSH homeostasis influences susceptibility and progression of these conditions. This review provides an overview of the biological importance of GSH at the level of the cell and organism.

Polymorphisms of the glutathione S-transferase P1 gene and head and neck cancer susceptibility

BACKGROUND

Factors determining the individual susceptibility to head and neck squamous cell carcinoma (HNSCC) are still largely unknown. An imbalance between enzymes involved in the toxification and detoxification of (pre)-carcinogens closely related to HNSCC, which may appear during smoking and alcohol consumption, may play a role. Genetic polymorphisms in glutathione S-transferases (GSTs) often result in altered detoxification, which may contribute to individual susceptibility to HNSCC.

METHODS

We studied the frequencies of polymorphic variants in the GSTP1 gene in 235 patients with HNSCC and 285 healthy controls. In addition, data on exposure to alcohol and tobacco consumption were recorded. DNA was extracted from whole blood, and polymerase chain reaction-based methods were used to detect genetic polymorphisms.

RESULTS

In patients with HNSCC and control groups, the homozygous GSTP1 BB genotype was observed in 12.3% and 13.6%, respectively. No statistical differences were found for the GSTP1 AA and GSTP1 AB/GSTP1BB genotypes.

CONCLUSIONS

Our study showed that genetic polymorphisms of GSTP1 are not associated with altered susceptibility to HNSCC.

The GSTM1 null genotype confers an increased risk for solar keratosis development in an Australian Caucasian population

Solar keratoses affect approximately 50% of Australian Caucasians aged over 40 y. Solar keratoses can undergo malignant transformation into squamous cell carcinoma followed by possible metastasis and are risk factors for basal cell carcinoma, melanoma, and squamous cell carcinoma. The glutathione-S-transferase genes play a part in detoxification of carcinogens and mutagens, including some produced by ultraviolet radiation. This study examined the role of glutathione-S-transferase M1, T1, P1, and Z1 gene polymorphisms in susceptibility to solar keratoses development. Using DNA samples from volunteers involved in the Nambour Skin Cancer Prevention Trial, allele and genotype frequencies were determined using polymerase chain reaction and restriction enzyme digestion. No significant differences were detected in glutathione-S-transferase P1 and glutathione-S-transferase Z1 allele or genotype frequencies; however, a significant association between glutathione-S-transferase M1 genotypes and solar keratoses development was detected (p=0.003) with null individuals having an approximate 2-fold increase in risk for solar keratoses development (odds ratio: 2.1; confidence interval: 1.3-3.5) and a significantly higher increase in risk in conjunction with high outdoor exposure (odds ratio: 3.4; confidence interval: 1.9-6.3). Also, a difference in glutathione-S-transferase T1 genotype frequencies was detected (p=0.039), although considering that multiple testing was undertaken, this was found not to be significant. Fair skin and inability to tan were found to be highly significant risk factors for solar keratoses development with odds ratios of 18.5 (confidence interval: 5.7-59.9) and 7.4 (confidence interval: 2.6-21.0), respectively. Overall, glutathione-S-transferase M1 conferred a significant increase in risk of solar keratoses development, particularly in the presence of high outdoor exposure and synergistically with known phenotypic risk factors of fair skin and inability to tan.

Glutathione S-transferase P1 genetic polymorphisms and susceptibility to childhood acute lymphoblastic leukaemia

Glutathione S-transferase pi (GSTP1) is involved in the metabolism of carcinogens. We assessed the association of GSTP1 genetic polymorphisms and the susceptibility to childhood acute lymphoblastic leukaemia (ALL) by conducting a case-control study on 278 ALL patients and 303 healthy controls, both of French-Canadian origin. The carriers of the GSTP1*B variant (only the Val105 substitution) were found to be associated with an increased risk of ALL [odds ratio (OR) = 1.5, 95% confidence interval (CI) 1.1-2.0], whereas the GSTP1*C variant (both Val105 and Val114) was underrepresented in cases. Thus, genetic variants of GSTP1 that are expressed at the protein level appear to contribute differently to the risk of ALL, probably because of distinct substrate specificities. When combined with other GST genotypes, we found that the combination of GSTP1*B and GSTM1 null genotypes further increased the risk of ALL (OR = 2.1; 95% CI-1.3-3.4). These findings suggest that GSTP1 variants (alone or combined with other GSTs) represent significant genetic determinants of childhood ALL.

DNA adduct burden and tobacco carcinogenesis

DNA adducts associated with tobacco smoking could provide a marker of biologically effective dose of tobacco carcinogens and improve individual cancer risk prediction. A significant number of clinical and epidemiologic studies have reported associations of increased DNA adduct levels with the occurrence of the prevalent tobacco related cancers including cancer of the lung, head and neck, and bladder. The inducibility of DNA adducts following in vitro treatments using blood lymphocytes also appears to be a risk factor in the development of lung and head and neck cancer. Corroborative evidence pointing to the importance of DNA adducts in tobacco carcinogenesis include numerous studies showing associations of tobacco smoke exposure with the induction of DNA adducts in humans in vivo. Further effort is necessary, however, to more fully characterize the dose-response relationship between smoking and DNA adducts in exposed target and surrogate tissues. The relationship between gene polymorphisms thought to modify tobacco-related cancer risk and DNA adduct levels is complex. Results of some DNA adduct studies (both in vitro and in vivo) appear inconsistent with the epidemiologic findings. This is evident for polymorphisms involving both carcinogen metabolism (e.g. GSTP1) and DNA repair (e.g. XRCC1). Molecular studies of human tumors suggest associations of p53 mutation with DNA adducts and have revealed correlations of DNA adduct levels with somatic alterations (e.g. 3p21 LOH) that are thought to occur at the very earliest stages of tobacco carcinogenesis. More research is needed to assess the relationship between endogenous sources of DNA adducts and tobacco smoke exposure and the relative oncogenic effects of chemically stable versus unstable DNA adducts. Many potentially fruitful new avenues of cancer research are emerging that integrate DNA adduct analyses with assessments of smoking, genetics, diet and ambient air quality. These investigations aim to understand the multifactorial nature of interindividual variability in response to tobacco carcinogens. As these trends continue a variety of innovative study designs and approaches will become important in human populations.

Effects of the ADH3, CYP2E1, and GSTP1 genetic polymorphisms on their expressions in Caucasian lung tissue

Individual differences in lung cancer susceptibility should be considered for effective lung cancer prevention. We investigated the CYP2E1, ADH3, and GSTP1 genetic polymorphisms that biotransform xenobiotic carcinogens, and variations of their enzyme activity in Caucasian lung tissues (N=28), and found a variant distribution in pulmonary ADH and CYP2E1 activity. The ADH3*1/*1 subjects (N=8) showed significantly higher ADH activity than ADH3*2/*2 (N=3) subjects (P<0.01). On the other hand, we found a 5-fold variation in the pulmonary CYP2E1 activity using a sensitive HLPC/EC based technique. A subject with the CYP2E1-c/t allele showed 2-fold higher CYP2E1 activity than subjects with the c/c allele (N=14). GSTP1 expression comprised 83% of the total pulmonary GSTs. However, neither the GSTP1 polymorphism, nor other lifestyle factors, such as age, gender, smoking status, were found to be associated with pulmonary GST expression. In conclusion, subjects with the ADH3*1 allele showed higher ADH activity and acetaldehyde-DNA adducts in lung than other subjects; thus, the ADH3*1 allele could be considered a risk factor for lung cancer.

Genetic polymorphism of cytochrome P450 1A1 (Cyp1A1) and glutathione transferases (M1, T1 and P1) among Africans

The co-ordinate expression and regulation of the drug metabolising enzymes, cytochrome P4501A1 (CYPlAl) and glutathione transferases (GSTM1, GSTT1 and GSTP1), and their metabolic balance in the cells of target organs may determine whether exposure to carcinogens results in cancer. Besides showing variability in activity due to induction and inhibition, these enzymes also exhibit genetic polymorphism that alter enzyme levels and activity. We determined frequencies of common allelic variants of CYP1A1 and glutathione (M1, T1 and P1) among Tanzanians, South African Venda and Zimbabweans using PCR/restriction fragment length polymorphism techniques. The CYP1A1 Val462 mutant variant was found at a frequency of 1.3% among 114 subjects. The GSTM1*0 genotype was found at a frequency of 29% and 33% among Tanzanian psychiatric patients and healthy volunteers, respectively. Similarly, the GSTT1*0 polymorphism was present with a frequency of 25% in both the psychiatric patients and healthy controls. The frequency of GSTP1 Val105 variant was 16%, 12% and 21% among Tanzanians, South African Venda and Zimbabweans, respectively. We conclude here that CYP1A1 Val462 polymorphism is very rare among Africans. This is the first report of the GSTP1 Val105 variant frequency in African populations. We show here that there are no differences in frequencies of the variant alleles for CYP1A1, GSTM1, GSTT1 and GSTP1 in the three African populations.