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

Fifty Years of Diazeniumdiolate Research: A Tribute to Dr. Larry K. Keefer

The pioneering studies of Dr. Larry Keefer and colleagues with diazeniumdiolates or NONOates as a platform have unraveled the chemical biology of many nitric oxides and have led to the design of a variety of promising therapeutic agents in oncology, gastroenterology, antimicrobials, wound healing, and the like. This dedication to Dr. Larry Keefer briefly highlights some of his studies using the diazeniumdiolate platform in the cancer arena.

Glutathione S-transferase genes variants and glioma risk: A case-control and meta-analysis study

Background: The glutathione S-transferase (GST) genes encode enzymes that metabolize carcinogenic compounds, and their variants, GSTP1 (Ile105Val and Ala114Val), GSTT1 (null/present), and GSTM1 (null/present), reduce enzyme activity that may affect the risk of developing cerebral glioma. This study undertook a case-control study and a meta-analysis to evaluate associations between these GST gene variants and the risk of glioma. Methods: The study enrolled 384 glioma patients (194 men and 190 women; mean age, 48.3 ± 9.2 years) and 340 healthy controls (174 men and 166 women; mean age, 46.5 ± 9.8 years). The amplification refractory mutation system assay was performed to identify GST gene variants of all 724 subjects. A meta-analysis enrolled 15 studies (including our case-control results) was performed. Results: Our case-control study found that the frequency of GSTP1 Ile105Val Val/Val genotype was significantly higher in the glioma group than that in the healthy controls (11.7% vs. 6.4%) (OR=1.50; 95% CI=1.05-2.04; P=0.01); the frequency of the Val/Ile + Ile/Ile genotypes was different from glioma patients and controls (88.3% vs. 93.6%) (OR=1.47(1.04-2.10); P=0.015); there were no associations between GSTP1 Ala114Val, GSTT1 (null/present) and GSTM1 (null/present) variants and glioma risk. Our meta-analysis confirmed that the GSTP1 Ile105Val variant was associated with an overall increased glioma risk. Moreover, our meta-analysis also confirmed the GSTP1 Ala114Val and GSTT1 null/present variants were associated with an increased glioma risk in the Caucasian population, rather than the Asian population. Conclusions: This study showed that GST gene variants were associated with an increased risk of glioma with ethnic differences. Future large-scale, multi center, controlled, prospective studies are required to support these findings and to determine how these GST gene variants may affect the pathogenesis of glioma.

Comprehensive Analysis of the Association Between the rs1138272 Polymorphism of the GSTP1 Gene and Cancer Susceptibility

Background: We obtained conflicting results regarding the relationship between the genetic role of the rs1138272 C/T polymorphism of the GSTP1 (Glutathione S-Transferase pi) gene and the risk of various cancers.

Methods: Using the presently available data, a meta-analysis was conducted to comprehensively evaluate the genetic relationship between the GSTP1 rs1138272 polymorphism and cancer susceptibility.

Results: A total of 43 studies including 15,688 cases and 17,143 controls were recruited into our quantitative synthesis. In the overall population, we observed an increased risk of overall cancer cases, compared with unrelated controls, in the genetic models of allele T vs. allele C (P-association = 0.007, OR = 1.17), carrier T vs. carrier C (P-association = 0.035, OR = 1.11), TT vs. CC (P-association = 0.002, OR = 1.45), TT vs. CC+CT (P-association = 0.009, OR = 1.42), and CT+TT vs. CC (P-association = 0.027, OR = 1.13). We detected similar positive results within the Asian population. Additionally, there was a significant increase in the incidence of cancer for Africans under all genetic models (all P-association < 0.05, OR > 1). When targeting the Caucasian population, we detected a positive association with the TT vs. CC and TT vs. CC+CT models in the “Colorectal cancer” (P-association < 0.05, OR < 1) and “Head and neck cancer” (P-association < 0.05, OR > 1) subgroups. For the “Lung cancer” subgroup, we observed a slightly increased risk in Caucasians under the models of allele T vs. allele C, carrier T vs. carrier C, CT vs. CC, and CT+TT vs. CC (P-association < 0.05, OR > 1).

Conclusion: The TT genotype of the GSTP1 rs1138272 polymorphism is likely related to the susceptibility to overall cancer in the Asian and African populations and, specifically, “Colorectal” and “Head and neck” cancers in the Caucasian population. In addition, the CT genotype of the GSTP1 rs1138272 polymorphism may be linked to the risk of lung cancer in Caucasians. Additional evidence is required to confirm this conclusion.

Genetic Contribution of Polymorphisms in Glutathione S-Transferases to Brain Tumor Risk

Existing data have shown a major effect of glutathione S-transferase (GST) single-nucleotide polymorphisms on activities of detoxification-related enzymes, and it is the functional importance that leads to extensive research on the association of GST polymorphisms with the risk of developing brain tumor. Previously reported associations, nevertheless, remain inconsistent. This study aimed to reevaluate the association with new information from recent research articles. We weekly searched multiple databases, aiming to cover all studies looking at the associations being examined in this work. Eligibility of studies was evaluated based on predesigned inclusion criteria. To assess the association of GST polymorphisms with brain tumor risk, we calculated genotypic ORs by comparing the number of genotypes between cases and controls. We also detected interstudy heterogeneity, publication bias, and single studies' influence. A total of 13 research articles were identified through databases and hand search. We found significantly elevated risk of brain tumor associated with GSTT1 null status in individuals of European ethnicity (OR 1.46, 95% CI 1.12-1.92). In the analysis of GSTP1 I105V, we observed that Val/Val genotype compared to the Ile/Ile genotype was more prone to a reduced brain tumor risk (OR 0.77, 95% CI 0.64-0.93). Such major effects were similarly seen for GSTP1 A114V (OR 1.14, 95% CI 1.01-1.29 for Val/Val + Ala/Val vs. Ala/Ala). When data were limited to glioma, we found a significant elevation associated with the combination of Val/Val and Ala/Val genotypes (OR 1.18, 95% CI 1.01-1.37). However, no clear association was detected between other polymorphisms investigated and glioma. These statistical data suggest that some of the polymorphisms at GST loci are possibly associated with the genetic risk of brain tumor.

Association between glutathione S-transferase T1 null genotype and glioma susceptibility: a meta-analysis

The relationship between genetic polymorphisms of glutathione S-transferase (GST) and the development of glioma has been investigated in several epidemiologic studies. However, these studies report inconsistent results. In order to get this precise result, a meta-analysis was conducted by calculating the pooled odds ratios (OR) and the 95% confidence intervals (95 % CI). Eleven case-control research studies with a total of 2,416 glioma cases and 4,850 controls were included into this meta-analysis. The combined results based on all studies showed that there was no significant association between the GSTT1 null allele and glioma risk (OR = 1.188, 95% CI = 0.929–1.520, P(heterogeneity) = 0.003, P = 0.170). In the subgroup analysis, the same results were found in our work. There was no risk of publication bias in this meta-analysis. Our results suggest that GSTT1 null genotype was not associated with the increased risk of glioma.

Discovering gene-environment interactions in glioblastoma through a comprehensive data integration bioinformatics method

Glioblastoma multiforme (GBM) is the most common and aggressive type of human brain tumor. Although considerable efforts to delineate the underlying pathophysiological pathways have been made during the last decades, only very limited progress on treatment have been achieved because molecular pathways that drive the aggressive nature of GBM are largely unknown. Recent studies have emphasized the importance of environmental factors and the role of gene-environment interactions (GEI) in the development of GBM. Factors such as small sample sizes and study costs have limited the conduct of GEI studies in brain tumors however. Additionally, advances in high-throughput microarrays have produced a wealth of information concerning molecular biology of glioma. In particular, microarrays have been used to obtain genetic and epigenetic changes between normal non-tumor tissue and glioma tissue. Due to the relative rarity of gliomas, microarray data for these tumors is often the product of small studies, and thus pooling this data becomes desirable. To address the challenge of small sample sizes and GEI study difficulties, we introduce a comprehensive bioinformatics method using genetic variations (copy number variations and small-scale variations) and environmental data integration that links with glioblastoma (GEG) to identify: (1) genes that interact with chemicals and have genetic variants linked to the development of GBM, (2) important pathways that may be influenced by environmental exposures (or endogenous chemicals), and (3) genes with variants in GBM that have been understudied in relation to GBM development. The first step in our GEG method identified genes responsive to environmental exposures using the Environmental Genome Project, Comparative Toxicology, and Seattle SNPs databases. These environmentally responsive genes were then compared to a curated list of genes containing copy number variation and/or mutations in GBM. This comparison produced a list of genes responsive to the environment and important to GBM that was then further analyzed using gene networking tools such as RSpider, Cytoscape, and DAVID. Using this GEG bioinformatics method we were able to identify 173 genes with the potential to be involved in GEI that may be important to the development of GBM. Sixty five of these environmentally responsive genes have not been reported as important to GBM development, despite several of them having substantial potential for response to chemicals and subsequent disease related actions. The main biological functions of these 173 genes include signaling by nerve growth factor, DNA repair, integrin cell surface interactions, biological oxidations, apoptosis, synaptic transmission, cell cycle checkpoints, and arachidonic acid metabolism. Importantly, some of these functions have been implicated in the development of several cancers, including glioma. In summary, our GEG bioinformatics approach revealed potential gene-environment interactions, and generated new data for hypothesis generation, in GBM.

Glutathione S-transferase M1, T1, and P1 polymorphisms and risk of glioma: a meta-analysis

The relationship between genetic polymorphisms of glutathione S-transferase (GST) and the development of glioma has been investigated in several epidemiologic studies. However these studies report inconsistent results. In order to quantitatively summarise the evidence for such a relationship, a meta-analysis is conducted. The PubMed database was searched from inception to January 2012 to identify relevant studies that met pre-stated inclusion criteria. We also reviewed reference lists from retrieved articles. Two researchers evaluated study eligibility and extracted the data independently, and disagreements were resolved by discussion. The principal outcome measure was the odds ratio (OR) with 95 % confidence interval (CI) for the risk of glioma associated with GSTM1, GSTT1, GSTP1 I105V or GSTP1 A114V. This meta-analysis included 11 case-control studies, which included 2,404 glioma cases and 6,379 controls. The combined results based on all studies showed that there was no association between any of the GST variants and the risk of glioma (for GSTM1: pooled OR = 1.03; 95 % CI, 0.92-1.15; for GSTT1: pooled OR = 1.12; 95 % CI, 0.90-1.40; for GSTP1 I105V: pooled OR = 0.92; 95 % CI, 0.64-1.31 and for GSTP1 A114V: pooled OR = 1.14; 95 % CI, 0.97-1.34). Subgroup analyses showed that GSTP1 A114V genotype was associated with an increased risk of other histopathologic glioma except glioblastoma multiforme (GBM) (pooled OR = 1.30; 95 % CI = 1.06-1.60); no relationship was found between other GST variants and histopathologic groups. In conclusion, our meta-analysis suggests no association between GST variants and the risk of glioma. However, the significant risk elevation is present between GSTP1 A114V genotype and other histopathologic glioma except GBM.

Lack of association between GSTM1 and GSTT1 polymorphisms and brain tumour risk

OBJECTIVE

Glutathione S-transferases (GSTs) are important enzymes that are involved in detoxification of environmental carcinogens. Molecular epidemiological studies have been conducted to investigate the association between GSTM1 and GSTT1 homozygous deletion polymorphisms and brain tumours but results have been conflicting. The aim of this study was to clarify this problem using a meta-analysis.

METHODS

A total of 9 records were identified by searching the PubMed and Embase databases. Fixed- and random-effects models were performed to estimate the pooled odds ratios.

RESULTS

No significant association was found between the GSTM1 and GSTT1 homozygous deletion polymorphisms and risk of brain tumours, including glioma and meningioma. Similar negative results were also observed in both population-based and hospital-based studies.

CONCLUSION

These findings indicate that the GSTM1 and GSTT1 polymorphisms may not be related to the development of brain tumours.

JS-K, a glutathione S-transferase-activated nitric oxide donor with antineoplastic activity in malignant gliomas

BACKGROUND

Glutathione S-transferases (GSTs) control multidrug resistance and are upregulated in many cancers, including malignant gliomas. The diazeniumdiolate JS-K generates nitric oxide (NO) on enzymatic activation by glutathione and GST, showing promising NO-based anticancer efficacy.

OBJECTIVE

To evaluate the role of NO-based antitumor therapy with JS-K in U87 gliomas in vitro and in vivo.

METHODS

U87 glioma cells and primary glioblastoma cell lines were exposed to JS-K and a variety of inhibitors to study cell death by necrosis, apoptosis, and other mechanisms. GST expression was evaluated by immunocytochemistry, polymerase chain reaction, and Western blot, and NO release from JS-K was studied with a NO assay. The growth-inhibitory effect of JS-K was studied in a U87 xenograft model in vivo.

RESULTS

Dose-dependent inhibition of cell proliferation was observed in human U87 glioma cells and primary glioblastoma cells in vitro. Cell death was partially induced by caspase-dependent apoptosis, which could be blocked by Z-VAD-FMK and Q-VD-OPH. Inhibition of GST by sulfasalazine, cGMP inhibition by ODQ, and MEK1/2 inhibition by UO126 attenuated the antiproliferative effect of JS-K, suggesting the involvement of various intracellular death signaling pathways. Response to JS-K correlated with mRNA and protein expression of GST and the amount of NO released by the glioma cells. Growth of U87 xenografts was reduced significantly, with immunohistochemical evidence for increased necrosis and apoptosis and reduced proliferation.

CONCLUSION

Our data show for the first time the potent antiproliferative effect of JS-K in gliomas in vitro and in vivo. These findings warrant further investigation of this novel NO-releasing prodrug in gliomas.

Childhood brain tumors and maternal cured meat consumption in pregnancy: differential effect by glutathione S-transferases

BACKGROUND

Some epidemiologic studies suggest that maternal consumption of cured meat during pregnancy may increase risk of brain tumors in offspring. We explored whether this possible association was modified by fetal genetic polymorphisms in genes coding for glutathione S-transferases (GSTs) that may inactivate nitroso compounds.

METHODS

We assessed six GST variants: GSTM1 null, GSTT1 null, GSTP1(I105V) (rs1695), GSTP1(A114V) (rs1138272), GSTM3*B (3-bp deletion), and GSTM3(A-63C) (rs1332018) within a population-based case-control study with data on maternal prenatal cured meat consumption (202 cases and 286 controls born in California or Washington, 1978-1990).

RESULTS

Risk of childhood brain tumor increased with increasing cured meat intake by the mother during pregnancy among children without GSTT1 [OR = 1.29; 95% confidence interval (95% CI), 1.07-1.57 for each increase in the frequency of consumption per week] or with potentially reduced GSTM3 (any -63C allele; OR = 1.14; 95% CI, 1.03-1.26), whereas no increased risk was observed among those with GSTT1 or presumably normal GSTM3 levels (interaction P = 0.01 for each).

CONCLUSIONS

Fetal ability to deactivate nitrosoureas may modify the association between childhood brain tumors and maternal prenatal consumption of cured meats.

IMPACT

These results support the hypothesis that maternal avoidance during pregnancy of sources of some nitroso compounds or their precursors may reduce risk of brain tumors in some children.

GSTP1 Ile105Val polymorphism in astrocytomas and glioblastomas

Glutathione S-transferases (GSTs) constitute a superfamily of ubiquitous multifunctional enzymes that are involved in the cellular detoxification of a large number of endogenous and exogenous chemical agents that have electrophilic functional groups. People who have deficiencies in this family of genes are at increased risk of developing some types of tumors. We examined GSTP1 Ile105Val polymorphism using PCR-RFLP in 80 astrocytoma and glioblastoma samples. Patients who had the Val allele of the GSTP1 Ile105Val polymorphism had an increased risk of tumor development (odds ratio = 8.60; 95% confidence interval = 4.74-17.87; P < 0.001). Overall survival of patients did not differ significantly. We suggest that GSTP1 Ile105Val polymorphisms are involved in susceptibility to developing astrocytomas and glioblastomas.

Advances in the genetics of glioblastoma: are we reaching critical mass?

Glioblastoma is the most common and highest-grade brain tumor, causing over 10,000 deaths each year in the US alone. Given the resistance of this tumor to standard surgery, radiation and chemotherapy, an understanding of the underlying genetic lesions is vital. Recent efforts to comprehensively profile glioblastomas using the latest technologies, both by The Cancer Genome Atlas (TCGA) project and by other groups, are addressing this need. Some genetic aberrations in glioblastoma have been known for decades, but early output from the new profiling initiatives has further illuminated the relevant genetics in this disease. Some genetic lesions, such as TP53 mutation, NF1 deletion or mutation, and ERBB2 amplification, have been found to be more common than was previously reported. New and unexpected discoveries have also been made, such as frequent mutations of the IDH1 and IDH2 genes in secondary glioblastoma. We might be tempted to speculate that we are approaching a comprehensive knowledge of the genetic lesions involved in glioblastoma, although other major discoveries doubtless remain to be made. In addition, the complex task of incorporating our updated knowledge into new--and possibly personalized--therapies for patients with glioblastoma still lies ahead.

Molecular epidemiology of primary brain tumors

Although primary brain tumors (PBTs) are generally considered to be a multifactorial disorder, understanding the genetic basis and etiology of the disease is essential for PBT risk assessment. Understanding of the genetic susceptibility for PBT has come from studies of rare genetic syndromes, linkage analysis, family aggregation, early-onset pediatric cases, and mutagen sensitivity. There are currently no effective markers to assess biological dose of exposures and genetic heterogeneity. The priorities recently recommended by the Brain Tumor Epidemiology Consortium emphasized the need for expanding research in genetics and molecular epidemiology. In this article, we review the literature to identify molecular epidemiologic case-control studies of PBTs that were hypothesis-driven and focused on four hypothesized candidate pathways: DNA repair, cell cycle, metabolism, and inflammation. We summarize the results in terms of genetic associations of single nucleotide polymorphisms of these pathways. We also discuss future research directions based on available evidence and technologies, and conclude that high resolution whole genome approach with significantly large sample size could rapidly advance our understanding of the genetic etiology of PBTs. Literature searches were done on PubMed in March 2009 with the terms glioma, glioblastoma, brain tumor, association, and polymorphism, and we only reviewed English language publications.

Acquisition of inverted GSTM exons by an intron of primate GSTM5 gene

The human GSTM gene family is composed of five gene members, GSTM1-5, and plays an important role in detoxification. In this study, the human GSTM5 gene was found to have a long inverted repeat (LIR) in intron 5. The LIR is able to form a stem-loop structure with a 31-bp stem and a 9-nt loop. The intronic LIR was also identified in other primates but not in non-primates. The human and chimpanzee LIRs had undergone compensating mutations that make the stem loop more stable, suggesting a functional role for the LIR. Sequence homology showed that the LIR was actually a part of inverted exons acquired by the intron. Results of phylogenetic analysis indicate that the inverted exons were derived from exon 5 of GSTM4 and exon 5 of GSTM1. The intronic LIR and inverted GSTM exons can probably introduce complexity in the expression of GSTM gene family.

Epidemiology of brain tumors

Gliomas account for more than 70% of all brain tumors, and of these, glioblastoma is the most frequent and malignant histologic type (World Health Organization [WHO] grade IV). There is a tendency toward a higher incidence of gliomas in highly developed, industrialized countries. Some reports indicate that Caucasians have a higher incidence than African or Asian populations. With the exception of pilocytic astrocytomas (WHO grade I), the prognosis of glioma patients is still poor. Fewer than 3% of glioblastoma patients are still alive at 5 years after diagnosis, older age being the most significant and consistent prognostic factor of poorer outcome. Gliomas are components of several inherited tumor syndromes, but the prevalence of these syndromes is very low. Many environmental and lifestyle factors including several occupations, environmental carcinogens, and diet have been reported to be associated with an elevated glioma risk, but the only factor unequivocally associated with an increased risk is therapeutic X-irradiation. In particular, children treated with X-irradiation for acute lymphoblastic leukemia show a significantly elevated risk of developing gliomas and primitive neuroectodermal tumors, often within 10 years after therapy. Significant correlation between G:C --> A:T transitions in the TP53 gene and promoter methylation of the O6 -methylguanine-DNA methyltransferase (MGMT) gene in glio-mas have been reported in several studies, suggesting the possible involvement of O6-methylguanine DNA adducts, which may be produced by exogenous or endogenous alkylating agents in the development of gliomas.

Polymorphisms in genes encoding drug metabolizing enzymes and their influence on the outcome of children with neuroblastoma

BACKGROUND

Although several studies have shown that drug metabolizing enzyme gene polymorphisms may influence the impact of therapy in childhood leukemia, no comprehensive investigations have been carried out in children with neuroblastoma. The aim of this study was to identify polymorphisms in the genes encoding phase I and II drug metabolizing enzymes associated with the risk of relapse or death in a cohort of 209 children with neuroblastoma.

METHODS

Real-time PCR allelic discrimination was used to characterize the presence of polymorphisms in DNA from children with neuroblastoma. Three broad gene categories were examined: cytochrome P450, glutathione-S-transferase and N-acetyltransferase. Cumulative event-free survival was computed by the Kaplan-Meier method. The influence of selected factors on event-free survival was tested using the Cox proportional hazards model.

RESULTS

As previously reported, amplification of MYCN (hazards ratio=4.25, 95% confidence interval=2.76-6.56, P<0.001), unfavorable stage (hazard ratio=4.14, 95% confidence interval=2.3-7.47, P<0.001) or age more than 1 year at diagnosis (hazard ratio=1.86, 95% confidence interval=1.19-2.92, P=0.007) were all associated with an increased risk of relapse or death. Carriers of a NAT1*11 allele variant were significantly less likely to relapse or die compared with those with NAT1*10 or other NAT1 allele variants (P<0.001). In multivariate analysis, children who were GSTM1 null were more likely to relapse or die during follow-up after adjusting for MYCN amplification, stage and age at diagnosis (hazard ratio=1.6, 95% confidence interval=1.02-2.9, P=0.04).

CONCLUSIONS

These observations suggest that the NAT1*11 variant and the GSTM1 wild-type genotype contribute to a more favorable outcome in patients treated for neuroblastoma and are the first to demonstrate a relationship between NAT1 and GSTM1 genotypes in childhood neuroblastoma.

Proteomic analysis of protein expression changes in a model of gliomagenesis

Loss of p53 function is a common event in a variety of human cancers including tumors of glial origin. Using an in vitro mouse model of malignant astrocyte transformation, three cleavable isotope coded affinity tag (cICAT) experiments were performed comparing cultured wild-type astrocytes and two p53(-/-) astrocyte cultures before and after malignant transformation. We identified and quantitated an average of 1366 proteins per experiment and demonstrated that the protein quantitation ratios in each individual cICAT experiment correlated well to ratios determined in the other two studies. These data were further supported by microarray analysis which also correlated to changes in protein expression. The results showed significant changes in protein expression in association with malignant transformation. Proteins overexpressed in malignant astrocytes were typically involved in ribosome biogenesis/protein synthesis and DNA replication, while underexpressed proteins were generally associated with the regulation of cell cycle checkpoint control, tumor suppression, and apoptosis. Among the significantly up-regulated proteins and transcripts in malignant mouse astrocytes were members of the minichromosome maintenance (MCM) family. Western blot analysis verified increased expression of MCM proteins in malignant human astrocytoma cell lines, which had not previously been described. These results demonstrate the usefulness of the cICAT approach for comparing differences in protein expression profiles between normal and malignant cells.

Genetic polymorphism and function of glutathione S-transferases in tumor drug resistance

The human glutathione S-transferase, GSTs, possess both enzymatic and non-enzymatic functions and are involved in many important cellular processes, such as, phase II metabolism, stress response, cell proliferation, apoptosis, oncogenesis, tumor progression and drug resistance. The non-enzymatic functions of GSTs involve their interactions with cellular proteins, such as, JNK, TRAF, ASK, PKC, and TGM2, during which, either the interacting protein partner undergoes functional alteration or the GST protein itself is post-translationally modified and/or functionally altered. The majority of GST genes harbor polymorphisms that influence their transcription and/or function of their encoded proteins. This overview focuses on recent insights into the biology and pharmacogenetics of GSTs as a determinant of cancer drug resistance and response of cancer patients to therapy.

Genetic polymorphisms of GSTs and their association with primary brain tumor incidence

Glutathione S-transferases GSTM1, GSTT1, and GSTP1 are phase II biotransformation enzymes that function on detoxification of a wide range of exogenous agents including carcinogens. It has been shown that genetic variations in these genes play an important role in determining the response of an individual to environmental carcinogens. Some studies revealed a statistically significant association between the polymorphisms in the genes encoding GST enzymes and some cancers, although contrary reports exist. In this study, the association between polymorphisms in these genes and primary brain tumor incidence was investigated in 228 Turkish individuals (75 patients with primary brain tumor and 153 controls). The prevalence of GSTM1 null genotype in the case group was 43%, compared to 24% in the control group, giving an odds ratio (OR) of 2.33 (95% confidence interval CI=1.24-4.39). No association was observed between the GSTT1 or GSTP1 Ile105Val polymorphism and brain tumor incidence. Polymorphisms in GSTM1, GSTT1, and GSTP1 did not show association with histopathologic type of brain tumor (glioma or meningioma). Analysis of the polymorphisms in the studied genes and smoking status of the brain tumor patients revealed no statistically significant association. The presented data clearly suggest a relation between brain tumor incidence with GSTM1 null genotype but not with GSTT1 or GSTP1 gene variants.

Possible association of p53 codon 72 polymorphism with susceptibility to adult and pediatric high-grade astrocytomas

Polymorphisms in codon 72 of the p53 tumor suppressor gene have been associated with susceptibility to human cancer. We wished to evaluate whether variant allelic forms of the p53 protein were associated with brain tumors. In this study, we scored 135 brain tumor samples (92 adult and 43 pediatric cases consisting of 64 high-grade astrocytomas and 71 non-astrocytomas) for the P53 Arg72Pro polymorphisms. Our data show that the genotype frequencies of P53 Arg72Pro vary not only between patients with brain tumors and controls, but also between different histological subtypes of brain tumors. Specifically, we found (i) that the genotype distributions of the P53 Arg72Pro between all brain tumors and controls were statistically significant (P < 0.001) as well as their variant allele frequencies between cases and controls (P < 0.001); (ii) that there was a significant increase in the Arg/Pro heterozygous genotype among high-grade astrocytomas compared with non-astrocytomas (P = 0.002); and (iii) that there was a significant increase in the Arg/Pro heterozygous genotype among high-grade astrocytomas containing transdominant as well as recessive p53 mutations compared with controls (P = 0.002). Our results suggest a possible association between P53 Arg72Pro polymorphisms and susceptibility to brain tumors, particularly high-grade astrocytomas.

Epidemiology and etiology of gliomas

Gliomas of astrocytic, oligodendroglial and ependymal origin account for more than 70% of all brain tumors. The most frequent (65%) and most malignant histological type is the glioblastoma. Since the introduction of computerized tomography and magnetic resonance imaging, the incidence rates of brain tumors have been rather stable, with a tendency of higher rates in highly developed, industrialized countries. Some reports indicate that Caucasians have higher incidence than black or Asian populations, but to some extent, this may reflect socio-economic differences and under-ascertainment in some regions, rather than a significant difference in genetic susceptibility. With the exception of pilocytic astrocytomas, the prognosis of glioma patients is still poor. Less than 3% of glioblastoma patients are still alive at 5 years after diagnosis, higher age being the most significant predictor of poor outcome. Brain tumors are a component of several inherited tumor syndromes, but the prevalence of these syndromes is very low. Several occupations, environmental carcinogens, and diet (N-nitroso compounds) have been reported to be associated with an elevated glioma risk, but the only environmental factor unequivocally associated with an increased risk of brain tumors, including gliomas, is therapeutic X-irradiation. In particular, children treated with X-irradiation for acute lymphoblastic leukemia show a significantly elevated risk of developing gliomas and primitive neuroectodermal tumor (PNET), often within 10 years after therapy. TP53 mutations are frequent in low-grade gliomas and secondary glioblastomas derived therefrom. Approximately 60% of mutations are located in the hot spot codons 248 and 273, and the majority of these are G:C-->A:T transitions at CpG sites. TP53 mutations are significantly more frequent in low-grade astrocytomas with promoter methylation of the O(6)-methylguanine-DNA methyltransferase repair gene, suggesting that, in addition to deamination of 5-methylcytosine, exogenous or endogenous alkylation in the O(6) position of guanine may contribute to the formation of these mutations.

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.