Glutathione S transferase theta 1 gene defects in myelodysplastic syndromes and their correlation with karyotype and exposure to potential carcinogens

Association between glutathione S-transferase T1 null genotype and risk of myelodysplastic syndromes: a comprehensive meta-analysis

Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal hematologic neoplasms, and the pathophysiology of these disorders is still unclear. Previous studies investigating the association between glutathione S-transferase Tl (GSTT1) null genotype and risk of MDS reported controversial results. We performed a comprehensive meta-analysis to clarify the effect of GSTT1 null genotype on risk of MDS. The strength of the association was measured by odds ratio (OR) with 95 % confidence interval (CI). Fifteen studies were finally included, involving a total of 1,796 cases and 2,502 controls. Subgroup analysis was performed by race. Meta-analysis of all 15 studies showed that the GSTT1 null genotype was significantly associated with an increased risk of MDS (OR = 1.47, 95 % CI 1.16-1.88, P OR = 0.002; I (2) = 54.4 %). Besides, an obvious association was also observed after adjusting the heterogeneity (OR = 1.32, 95 % CI 1.13-1.54, P OR = 0.001; I (2) = 9.0 %). Subgroup analysis by race suggested that this association existed in both Caucasians (OR = 1.40, 95 % CI 1.04-1.89, P OR = 0.027) and Asians (OR = 1.68, 95 % CI 1.00-2.81, P OR = 0.049). This meta-analysis suggests the GSTT1 null genotype is significantly associated with an increased risk of MDS in both Caucasians and Asians.

Variations in glutathione-S-transferase genes influence risk of chronic myeloid leukemia

Glutathione S-transferases (GSTs) are phase II enzymes that detoxify hazardous xenobiotics including carcinogens. Inter-individual variations in GSTM1 and GSTT1 loci have been associated with several types of cancer, including leukemias. In this study, we investigated the possible association between GSTM1 and GSTT1 polymorphisms and susceptibility to chronic myeloid leukemia (CML) in a Turkish population. In a case-control study, 106 CML patients and 190 healthy controls were evaluated for GSTM1 and GSTT1 polymorphisms. GSTM1 null (GSTM1(-)) genotype frequencies in CML cases and controls were 45.3% and 42.6%, respectively. GSTT1 null (GSTT1(-)) genotype frequencies were 44.3% and 18.4%, respectively. The frequency of the GSTT1(-) genotype among CML patients was significantly higher than in controls [odds ratio (OR) 3.53, 95% confidence interval (CI) 2.08-6.00; P < 0.0001]. Individuals with the GSTM1(-) genotype did not have increased risk of CML [OR: 1.11; 95% CI: 0.69-1.80; P = 0.714]. The combined GSTM1(-)/GSTT1(-) genotype was significantly associated with risk of CML compared to the GSTM1(+) /GSTT1(+) genotype which was most frequent in both cases and controls [OR: 9.47; 95% CI: 3.61-24.87]. Similar findings have only been obtained in Turkish and Indian populations but not elsewhere. The GSTM1(+) /GSTT1(-) genotype was associated with a 2.5-fold increased risk compared with the GSTM1(-)/GSTT1(+) genotype, the second most frequent genotype (OR; 2.46; 95% CI: 1.17, 5.20), suggesting a complex interaction between GSTM1 and GSTT1. Our results indicate an association between the GSTT1(-) genotype, either alone or in combination with GSTM1(-) genotype, and risk of CML, suggesting a possible interaction between GSTM1 and GSTT1. These findings, which are possibly restricted to Turkey and India, warrant further research.

Detoxification and DNA repair genes polymorphisms and susceptibility of primary myelodysplastic syndromes in Chinese population

Molecular epidemiological studies have found new insights into the etiology of myelodysplastic syndromes (MDS). We analyzed the polymorphisms of 5 genes in 275 patients with primary MDS and 354 healthy controls in an attempt to identify candidate genetic risk factors for primary MDS in Chinese Han population. There was no difference in polymorphic variants of GSTM1, NQO1-C609T and XRCC3-C241T between the patients and controls. The homozygous variant C/C of RAD51-G135C was found to increase the susceptibility to MDS (OR, 4.13; p=0.001) and the risk of MDS association with structural abnormal karyotype (OR, 7.67; p=0.001). In addition, the null genotype of GSTT1 was correlated MDS patients with complex aberrant karyotype (OR, 3.25; p=0.012). These potential genetic predisposition suggested their possible involvement in the multistep pathogenesis of MDS.

GSTT1 and GSTM1 polymorphisms and myelodysplastic syndrome risk: a systematic review and meta-analysis

Glutathione-S-transferace polymorphisms may make hematopoietic lineage cells susceptible to genotoxicity following exposure to heavy metals or benzene. We conducted a systematic review and meta-analysis to define the effect of GSTM1 and GSTT1 null polymorphisms on MDS risk. We searched the PubMed and SCOPUS databases to identify peer-reviewed published case-control studies investigating the association between GSTT1 and/or GSTM1 null genotypes and development of MDS. Between-study heterogeneity was assessed using Cochran's Q statistic and the I(2) statistic. Odds ratios from individual studies were pooled using fixed and random effects models. Thirteen studies were considered eligible for the GSTT1 meta-analysis (1471 cases, 1907 controls) and 10 were considered eligible for the GSTM1 meta-analysis (1161 cases, 1668 controls). For the GSTT1 polymorphism, there was moderate between study heterogeneity (p(Q) = 0.01; I(2) = 52.3%) and the null genotype was significantly associated with increased risk of MDS development, random effects OR = 1.43 (95% CI, 1.09-1.89); p = 0.01. For the GSTM1 polymorphisms there was moderate between-study heterogeneity (p = 0.07; I(2) = 43.1%) and the random effects OR = 1.02 (95% CI, 0.82-1.28) was non-significant (p = 0.85). The GSTT1 null genotype is a significant risk factor for MDS development. Gene-environment interactions need to be further explored.

Diagnostic challenges in the myelodysplastic syndromes: the current and future role of genetic and immunophenotypic studies

Myelodysplastic syndromes (MDS) comprise a clinically and pathologically diverse collection of hematopoietic neoplasms, most commonly presenting with peripheral cytopenias typically in the context of bone marrow hypercellularity. Mechanistically, at least in the early phases of the disease, this apparently paradoxical picture is primarily due to ineffective hematopoiesis, which is accompanied by a variety of morphologic abnormalities in hematopoietic cells. The identification of recurrent, clinically relevant cytogenetic defects in MDS has spurred the research of molecular mechanisms that contribute to its inception as well as to the development of heterogeneous subtypes. Although conventional cytogenetic analyses remain a diagnostic mainstay in MDS, the application of contemporary techniques including molecular cytogenetics, microarray technologies and multiparametric flow cytometry may ultimately reveal new diagnostic parameters that are theoretically more objective and sensitive than current morphologic approaches. This review aims to outline the role of genetic and immunophenotypic studies in the evaluation of MDS, including findings that may potentially influence future diagnostic classifications, which could refine prognostication and ultimately facilitate the growth of targeted therapies.

Epidemiology of myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are one of the most common hematological conditions among the elderly. Differences in disease classification and diagnosis have made population-based studies an arduous endeavor. A variety of risk factors have been linked with increased risk (smoking and exposure to solvents and agrochemicals) or decreased risk of MDS (wine drinking), but the majority of cases remain unexplained. One area that has not been explored is the influence of diet in MDS development. Much still needs to be learned about what causes MDS and the genetic factors that increase susceptibility. Multi-institutional studies with a molecular-epidemiologic approach are necessary to develop a MDS risk predictive model.

Influence of genetic polymorphisms on the risk of developing leukemia and on disease progression

BACKGROUND

Recent studies have provided evidence that common genetic variations with low penetrance could account for a proportion of leukemia and could also influence disease outcome, although the results obtained are still controversial.

MATERIAL AND METHODS

We reviewed 54 recent reports focused on the contribution of genetic polymorphisms to the risk of developing leukemia and to disease progression. The polymorphisms of genes encoding drug-metabolising enzymes (CYP family, NQO1, GSTT1, GSTM1, GSTP1), enzymes involved in folate metabolism (MTHFR, TYMS, SHMT1, MTRR), and DNA repair enzymes (XPD, XPG, RAD51, XRCC1, XRCC3, CHEK2, ATM) were considered in the review.

RESULTS

There was a good agreement on the influence of NQO1*2 polymorphism and those of the enzymes involved in DNA repair with the increased risk of therapy-related leukemia/myelodysplastic syndrome. Most studies found a strong association between the polymorphisms MTHFR, C677T or A1298C, and NQO1*2 or *3 and the risk of acute lymphoblastic leukemia (ALL). In addition, most of the studies reported an association between GSTT1 deletions and an increased risk of de novo acute myeloid leukemia. In ALL, polymorphisms in the genes of folate metabolism are associated with poor prognosis, and the 3R3R TYMS polymorphism in particular is associated with methotrexate resistance.

CONCLUSION

The reports reviewed support the hypothesis that several low-penetrance genes with multiplicative effects together with dietary effects, ambient exposition, and individual immune system responses, may account for the risk of leukaemia.

Glutathione S transferase theta 1 gene (GSTT1) null genotype is associated with an increased risk for acquired aplastic anemia in children

Two main factors have been implicated in the mechanism underlying the pathogenesis of acquired aplastic anemia: environmental factors and genetic susceptibility. Individuals vary in their ability to metabolize several DNA-damaging agents due to polymorphisms of biotransforming enzymes. Genetically determined differences in the expression of these enzymes could explain interindividual risks in developing acquired aplastic anemia. The aim of the study was to characterize the genetic polymorphism of biotransforming phase I (p450-cyp2E1) and phase II [microsomal epoxide hydrolase (mEh), glutathione S-transferase (GST)] enzymes in pediatric patients with acquired aplastic anemia. The GSTT1 null genotype (absence of both alleles) was associated with a significantly increased risk for acquired aplastic anemia (odds ratio, 2.8; 95% confidence interval, 0.15-5.7). In contrast, the GSTM1 null genotype or polymorphisms within the p450-cyp2E1 and mEh genes was not significantly different in patients and controls. Multivariate analysis was performed to assess whether the enzymes together or with other variables as age, gender, or response to therapy may have any significant association with the tested genotypes. In no combinations of the mentioned parameters was an association found with acquired aplastic anemia. GST are mainly involved in metabolizing hematotoxic and mutagenic substrates such as benzene derivatives. The GSTT1 null genotype may modulate the metabolism of exogenous pollutants or toxic intermediates. The absence of the GSTT1 enzyme, leading to genetic susceptibility toward certain pollutants, might determine the individual risk for development of acquired aplastic anemia in children.

Increased risk for aplastic anemia and myelodysplastic syndrome in individuals lacking glutathione S-transferase genes

BACKGROUND

Aplastic anemia (AA) and myelodysplastic syndrome (MDS) are marrow failure states that may be associated with chromosomal instability. An absence of the glutathione S-transferase (GST) enzyme may genetically predispose individuals to AA or MDS.

PROCEDURE AND RESULTS

To test this hypothesis, we determined the GSTM1 and GSTT1 genotypes in a total of 196 patients using multiplex PCR. The GSTT1 null genotype was found to be overrepresented in Caucasian, Asian, and Hispanic patients with either AA or MDS. We confirmed a difference in the expected frequency of the GSTM1 null genotype in Caucasian MDS patients. The double null GSTM1/GSTT1 genotype was also overrepresented in Caucasian AA and MDS patients. In our population, 26% of AA patients and 40% of MDS patients had a chromosomal abnormality identified by karyotype or FISH analyses for chromosomes 7 and 8. Patients with AA and the GSTT1 null genotype had an increased frequency of chromosomal abnormalities (P = 0.003).

CONCLUSION

There seems to be an increased risk for AA and MDS in individuals lacking GSTT1 or both GSTM1/GSTT1.

Mutant type glutathione S-transferase theta 1 gene homologue to mTOR in myelodysplastic syndrome: possible clinical application of rapamycin

In this study, we observed the expression of the GSTT-1 gene in patients with myelodysplastic syndrome (MDS) at the messenger RNA level. Reverse transcription-polymerase chain reaction (RT-PCR) for GSTT-1 was performed with a pair of primers complementary to the 5' coding section and the 3' coding section of the GSTT-1 cDNA for amplifying the 623-bp band. Among 20 patients with MDS, 8 patients showed the expected 623-bp band on RT-PCR, and 12 patients showed a 500-bp band on RT-PCR, indicating that a 123-bp sequence was deleted as a mutant of the GSTT-1 gene. Furthermore, a BLAST DNA search showed that the deletion of a 123 bp sequence creates a sequence that is 63% homologous to human FKBP-rapamycin associated protein (FRAP); this protein has been termed a mammalian target of rapamycin (mTOR). We respectively transfected the wild type and the mutant type GSTT-1 gene in an expression vector to two cell lines (K562 and HL-60). The stable transformants for the wild type and the mutant type GSTT-1 genes were made by G418 selection. Interestingly, rapamycin could induce significant growth inhibition of the stable transformants for mutant type GSTT-1, which was indicative of apoptosis, but not that of those for wild type GSTT-1. These results suggest that rapamycin could be included in the therapeutic modality for the patients with MDS who have the mTOR sequences in GSTT-1 gene.

Polymorphisms of drug metabolizing enzymes and markers of genotoxicity to identify patients with Hodgkin's lymphoma at risk of treatment-related complications

Survivors of childhood Hodgkin's lymphoma (HL) have an increased risk of developing treatment-related complications, especially second malignant neoplasms, as a result of treatment regimens incorporating chemotherapy and radiation therapy. Second cancers include leukemias that generally occur in the first two decades after therapy, and adult-type solid tumors that generally exhibit continued increasing incidence throughout subsequent follow-up. Identified clinical risk factors for second cancers include age at the time of treatment and intensity and type of therapy, with particularly strong associations between the use of radiotherapy and subsequent breast cancer, and alkylator chemotherapy dose-intensity and risk of secondary leukemia. However, second cancers affect a minority of patients, and there is probably great variability in individual susceptibility for this complication. Common genetic polymorphisms in drug-metabolizing enzymes that result in impaired detoxification of chemotherapy or inefficient repair of drug- or radiation-induced genetic damage may lead to increased risk of a second cancer. Studies of the potential role of polymorphisms in the genes encoding the glutathione S-transferases, cytochrome P450 3A4, NAD(P)H:quinone oxidoreductase and myeloperoxidase in the etiology of treatment-related complications are reviewed. Biological markers of drug- and radiation-induced genetic damage may also identify patients at higher risk of immediate and delayed side effects of therapy. The Children's Oncology Group (COG) is examining the roles of polymorphisms in drug metabolizing enzymes and biological markers of genotoxicity in predicting the treatment-related outcomes of patients with HL. These investigations may ultimately allow the use of pharmacogenetically guided therapy to improve the outcome of HL therapy and reduce the risk of therapy-related complications, especially secondary malignancies.

Negative prognostic value of glutathione S-transferase (GSTM1 and GSTT1) deletions in adult acute myeloid leukemia

Glutathione S-transferases (GSTs) are enzymes involved in the detoxification of several environmental mutagens, carcinogens, and anticancer drugs. GST polymorphisms resulting in decreased enzymatic activity have been associated with several types of solid tumors. We determined the prognostic significance of the deletion of 2 GST subfamilies genes, M1 and T1, in patients with acute myeloid leukemia (AML). Using polymerase chain reactions, we analyzed the GSTM1 and GSTT1 genotype in 106 patients with AML (median age, 60.5 years; range, 19-76 years). The relevance of GSTM1 and GSTT1 homozygous deletions was studied with respect to patient characteristics, response to therapy, and survival. Homozygous deletions resulting in null genotypes at the GSTM1 and GSTT1 loci were detected in 45 (42%) and 30 (28%) patients, respectively. The double-null genotype was present in 19 patients (18%). GST deletions predicted poor response to chemotherapy (P =.04) and shorter survival (P =.04). The presence of at least one GST deletion proved to be an independent prognostic risk factor for response to induction treatment and overall survival in a multivariate analysis including age and karyotype (P =.02). GST genotyping was of particular prognostic value in the cytogenetically defined intermediate-risk group (P =.003). In conclusion, individuals with GSTM1 or GSTT1 deletions (or deletions of both) may have an enhanced resistance to chemotherapy and a shorter survival.

Molecular, cytogenetic and genetic abnormalities in MDS and secondary AML

Myelodysplasia (MDS) is a clonal disease, which increases with age, suggesting that multiple steps are required for the evolution of the condition. Approximately 30% of MDS evolve into acute myelogenous leukemia (AML). In this review, we intend to delineate the genetic events, which may drive this sequence and therefore we will focus primarily on cytogenetic abnormalities where the genes have been identified and oncogenes and suppressor genes that have been implicated. In terms of the biological mechanisms, which characterise this process, it is generally thought that the MDS cell has impaired differentiation, and has increased apoptosis. As the disease progresses in addition, the cells have increased proliferation. As the disease evolves, the population of cells, which predominate remain immature, have decreased apoptosis and in many cases, upregulate anti-apoptotic genes and have deregulated proliferation as the number of blast cells increase. Etiological factors, which contribute to the development of leukemia, include therapeutic agents administered for a primary malignancy. The cytogenetic abnormalities, predisposition factors and genes involved in secondary leukemia will also be reviewed.

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

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

Thalidomide in myelodysplastic syndromes

The myelodysplastic syndromes are a heterogeneous group of clonal diseases of haemopoiesis, which are a challenge for both biologists and clinicians. In this paper the current classification and the recent advances in the understanding the disease mechanisms are reviewed. The recent therapeutic advances are also indicated, such as intensive and low-dose chemotherapy, new drugs, erythropoietin and colony-stimulating factors. However, the work has been focused on thalidomide, its therapeutic potential, its modes of actions, side effects, indications and future applications.

Prognostic significance of the null genotype of glutathione S-transferase-T1 in patients with acute myeloid leukemia: increased early death after chemotherapy

We investigated the prognostic significance of genetic polymorphism in glutathione-S transferase mu 1 (GSTM1), glutathione-S transferase theta 1 (GSTT1), NAD(P)H:quinone oxidoreductase (NQO1) and myeloperoxidase (MPO), the products of which are associated with drug metabolism as well as with detoxication, in 193 patients with de novo acute myeloid leukemia (AML) other than M3. Of the patients, 64.2% were either homozygous or heterozygous for GSTT1 (GSTT1(+)), while 35.8% showed homozygous deletions of GSTT1 (GSTT1(-)). The GSTT1(-) group had a worse prognosis than the GSTT1(+) group (P = 0.04), whereas other genotypes did not affect the outcome. Multivariate analysis revealed that GSTT1(-) was an independent prognostic factor for overall survival (relative risk: 1.53; P = 0.026) but not for disease-free survival of 140 patients who achieved complete remission (CR). The rate of early death after the initiation of chemotherapy was higher in the GSTT1(-) group than the GSTT1(+) group (within 45 days after initial chemotherapy, P = 0.073; within 120 days, P = 0.028), whereas CR rates and relapse frequencies were similar. The null genotype of GSTT1 might be associated with increased toxicity after chemotherapy.

Increased risk for acute myeloid leukaemia in individuals with glutathione S-transferase mu 1 (GSTM1) and theta 1 (GSTT1) gene defects

OBJECTIVES

Glutathione S-transferases (GST) modulate the effects of exposure to various cytotoxic and genotoxic agents, including those associated with increased risks of the myelodysplastic syndrome (MDS), acute myeloid leukaemia (AML) and aplastic anemia (AA). Both the GST mu 1 (GSTM1) and GST theta 1 (GSTT1) genes have a null variant allele in which the entire gene is absent. In this study, we tested whether null genotypes for the GSTM1 and GSTT1 genes altered the risks for MDS, AML and AA.

METHODS

Genomic DNA from 49 MDS, 38 AML and 37 AA patients and 276 controls was analysed using the polymerase chain reaction (PCR).

RESULTS

The frequencies of GSTM1 (73.6%) and GSTT1 (34.2%) null genotypes were significantly higher in AML patients than in the controls (36.9 and 18.1%, respectively). A higher frequency of the combined null genotype for both genes was also observed in patients with AML (26.3% compared with 5.0% in the controls). In contrast, no differences in the frequencies of the null genotypes were found among MDS patients, AA patients and the controls.

CONCLUSION

Our observation of a 4.7-fold (95% CI: 2.1-11.0) and 2.3-fold (95% CI: 1.0-5.2) increased risk associated with the GSTM1 and GSTT1 null genotypes, respectively, and a 6.6-fold (95% CI: 2.4-7.9) increased risk associated with the combined null genotype presents preliminary evidence that the inherited absence of this carcinogen detoxification pathway may be an important determinant of AML.

Chromosome and molecular abnormalities in myelodysplastic syndromes

Cytogenetic abnormalities are seen in approximately 50% of cases of myelodysplastic syndrome (MDS) and 80% of cases of secondary MDS (following chemotherapy or radiotherapy). These abnormalities generally consist of partial or complete chromosome deletion or addition (del5q, -7, +8, -Y, del20q), whereas balanced or unbalanced translocations are rarely found in MDS. Fluorescence hybridization techniques (fluorescence in situ hybridization [FISH], multiplex FISH, and spectral karyotyping) are useful in detecting chromosomal anomalies in cases in which few mitoses are obtained or rearrangements are complex. Ras mutations are the molecular abnormalities most frequently found in MDS, followed by p15 gene hypermethylation, FLT3 duplications, and p53 mutations, but none of these abnormalities are specific for MDS. The rare cases of balanced translocations in MDS have allowed the identification of genes whose rearrangements appear to play a role in the pathogenesis of some cases of MDS. These genes include MDS1-EVI1 in t(3;3) or t(3;21) translocations, TEL in t(5;12), HIP1 in t(5;7), MLF1 in t(3;5), and MEL1 in t(1;3). Genes more frequently implicated in the pathogenesis of MDS cases, such as those involving del5q, remain unknown, although some candidate genes are currently being studied. Cytogenetic and known molecular abnormalities generally carry a poor prognosis in MDS and can be incorporated into prognostic scoring systems such as the International Prognostic Scoring System.

Genetic predisposition and treatment-related leukemia

Treatment-related leukemias are one of the most devastating late complications of cancer therapy. Patients with rare cancer predisposition syndromes including neurofibromatosis type 1 and inherited p53 mutations are at an increased risk for this complication. Other patients may have increased susceptibility because they possess common genetic polymorphisms in drug-metabolizing enzymes that result in impaired detoxification of chemotherapy or inefficient repair of drug-induced genetic damage. We review studies that have identified a potential role for polymorphisms in the genes encoding the glutathione-S-transferases (GSTs), NAD(P) H: quinone oxidoreductase, myeloperoxidase, N-acetyltransferase (NATs), cytochrome P450 (CYP) 1A1 and 3A4, methylenetetrahydrofolate reductase (MTHFR), cystathionine-beta-synthase (CBS), and others in the etiology of primary or secondary acute leukemias, and therapy-related complications. The identification of high risk polymorphisms and use of pharmacogenetically-guided therapies holds promise to improve the outcome of cancer therapy and reduce the risk of treatment-related leukemias.

Mammalian class theta GST and differential susceptibility to carcinogens: a review

Glutathione S-transferases (GSTs) are an important part of the cellular detoxification system and, perhaps, evolved to protect cells against reactive oxygen metabolites. Theta is considered the most ancient among the GSTs and theta-like GSTs are found in mammals, fish, insects, plants, unicellular algae, and bacteria. It is thought that an ancestral theta-gene underwent an early duplication before the divergence of fungi and animals and further duplications generated the variety of the other classes of GSTs (alpha, mu, phi, etc.). The comparison of the aminoacidic homologies among mammals suggests that a duplication of an ancient GST theta occurred before the speciation of mammals and resulted in the subunits GSTT1 and GSTT2. The ancestral GST theta has a dehalogenase activity towards several halogenated compounds, such as the dichloromethane. In fact, some aerobic and anaerobic methylotrophic bacteria can use these molecules as the sole carbon and energy source. The mammalian GST theta cannot sustain the growth of bacteria but still retains the dehalogenating activity. Therefore, although mammalian GST theta behaves as a scavenger towards electrophiles, such as epoxides, it acts also as metabolic activator for halogenated compounds, producing a variety of intermediates potentially dangerous for DNA and cells. For example, mice exposed to dichloromethane show a dose-dependent incidence of cancer via the GSTT1-1 pathway. Because GSTT1-1 is polymorphic in humans, with about 20% of Caucasians and 80% of Asians lacking the enzyme, the relationship between the phenotype and the incidence of cancer has been investigated extensively in order to detect GSTT1-1-associated differential susceptibility towards endogenous or exogenous carcinogens. The lack of the enzyme is related to a slightly increased risk of cancer of the bladder, gastro-intestinal tract, and for tobacco-related tumors (lung or oral cavity). More pronounced risks were found in males with the GSTT1-null genotype for brain diseases and skin basal cell carcinomas not related to sunlight exposures. Moreover, there was an increased risk of kidney and liver tumors in humans with the GSTT1-1 positive genotype following exposures to halogenated solvents. Interestingly, the liver and kidney are two organs that express the highest level of GST theta in the human body. Thus, the GSTT1-1 genotype is suspected to confer decreased or increased risk of cancer in relation to the source of exposure; in vitro studies, mostly conducted on metabolites of butadiene, confirm the protective action of GSTT1-1, whereas, thus far, experimental studies prove that the increasing risk is limited.

Achievements in Understanding and Treatment of Myelodysplastic Syndromes

The myelodysplastic syndromes (MDS) constitute a challenge for the biologist as well as for the treating physician. In Section I, Dr. Willman reviews the current classifications and disease mechanisms involved in this heterogeneous clonal hematopoietic stem cell disorder. A stepwise genetic progression model is proposed in which inherited or acquired genetic lesions promote the acquisition of “secondary” genetic events mainly characterized by gains and losses of specific chromosome regions. The genetic risk to develop MDS is likely multifactorial and dependent on various constellations of risk-producing and -protecting alleles. In Section II Dr. Barrett with Dr. Saunthararajah addresses the immunologic factors that may act as important secondary events in the development of severe pancytopenia. T cells from patients with MDS may suppress autologous erythroid and granulocytic growth in vitro, and T cell suppression by antithymocyte globulin or cyclosporine may significantly improve cytopenia, especially in refractory anemia. Recent studies have also demonstrated an increased vessel density in MDS bone marrow, and a phase II trial of thalidomide showed responses in a subgroup of MDS patients especially in those with low blast counts. In Section III Dr. Hellström-Lindberg presents results of allogeneic and autologous stem cell transplantation (SCT), intensive and low-dose chemotherapy. The results of allogeneic SCT in MDS are slowly improving but are still poor for patients with unfavorable cytogenetics and/or a high score according to the International Prognostic Scoring System. A recently published study of patients between 55-65 years old showed a disease-free survival (DFS) at 3 years of 39%. Consolidation treatment with autologous SCT after intensive chemotherapy may result in long-term DFS in a proportion of patients with high-risk MDS. Low-dose treatment with 5-azacytidine has been shown to significantly prolong the time to leukemic transformation or death in patients with high-risk MSA. Erythropoietin and granulocyte colony-stimulating factor may synergistically improve hemoglobin levels, particularly in sideroblastic anemia. Recent therapeutic advances have made it clear that new biological information may lead to new treatment modalities and, in combination with statistically developed predictive models, help select patients for different therapeutic options.

Achievements in Understanding and Treatment of Myelodysplastic Syndromes

The myelodysplastic syndromes (MDS) constitute a challenge for the biologist as well as for the treating physician. In Section I, Dr. Willman reviews the current classifications and disease mechanisms involved in this heterogeneous clonal hematopoietic stem cell disorder. A stepwise genetic progression model is proposed in which inherited or acquired genetic lesions promote the acquisition of “secondary” genetic events mainly characterized by gains and losses of specific chromosome regions. The genetic risk to develop MDS is likely multifactorial and dependent on various constellations of risk-producing and -protecting alleles. In Section II Dr. Barrett with Dr. Saunthararajah addresses the immunologic factors that may act as important secondary events in the development of severe pancytopenia. T cells from patients with MDS may suppress autologous erythroid and granulocytic growth in vitro, and T cell suppression by antithymocyte globulin or cyclosporine may significantly improve cytopenia, especially in refractory anemia. Recent studies have also demonstrated an increased vessel density in MDS bone marrow, and a phase II trial of thalidomide showed responses in a subgroup of MDS patients especially in those with low blast counts. In Section III Dr. Hellström-Lindberg presents results of allogeneic and autologous stem cell transplantation (SCT), intensive and low-dose chemotherapy. The results of allogeneic SCT in MDS are slowly improving but are still poor for patients with unfavorable cytogenetics and/or a high score according to the International Prognostic Scoring System. A recently published study of patients between 55-65 years old showed a disease-free survival (DFS) at 3 years of 39%. Consolidation treatment with autologous SCT after intensive chemotherapy may result in long-term DFS in a proportion of patients with high-risk MDS. Low-dose treatment with 5-azacytidine has been shown to significantly prolong the time to leukemic transformation or death in patients with high-risk MSA. Erythropoietin and granulocyte colony-stimulating factor may synergistically improve hemoglobin levels, particularly in sideroblastic anemia. Recent therapeutic advances have made it clear that new biological information may lead to new treatment modalities and, in combination with statistically developed predictive models, help select patients for different therapeutic options.

A patient with genetic deletion of glutathione-S-transferase T1 and M1 who developed non-small-cell lung cancer and myelodysplastic syndromes

Glutathione S-transferase (GST) M1 polymorphism is a marker for susceptibility to smoking-related neoplasms, such as lung and bladder cancer. Recently, a genetic deletion of GSTT1, an isoenzyme of GST, has been reported to be associated with myelodysplastic syndromes (MDS). A 59-year-old man with a long-term smoking habit was treated successfully for non-small-cell lung cancer. Four years after the surgical removal of his lung cancer, he developed MDS and died. Using a polymerase chain reaction-based genotyping method, he was found to have a deletion of both the GSTM1 and GSTT1 genes. Screening for the deletion of the GSTM1 and GSTT1 genes may be useful for assessing individual genetic susceptibility to smoking-related lung cancer and MDS.

Genotype of glutathione S-transferase and other genetic configurations in myelodysplasia

We examined polymorphisms of glutathione S-transferase (GST) genes in 159 Japanese patients with myelodysplasia and compared the incidence with that in 43 normal individuals to clarify their pathogenetic significance in myelodysplasia. In individuals with the GSTT1 null genotype, the odds ratios for disease risk were elevated to 2.65 (95%CI; 1.27-5.52) in de novo MDS, 4.62 (1.48-14.4) in therapy-related AML, and 2.94 (1.07-8.07) in AML with triliniage dysplasia. Other representative polymorphisms of GSTs had a similar incidence among patients with myelodysplasia, and those of the controls and other hematological disorders. To further investigate the genetic pathway of myelodysplasia, the association between GST genotype and karyotype or configurations of TP53 and NRAS was evaluated, but no relationship was noted. These results suggest that the GSTT1 null genotype may play a role in an increased risk of myelodysplasia unrelated to other mechanisms of myelodysplasia, such as chromosomal alterations or mutation of TP53 or NRAS.

Polymorphisms of N-acetyltransferases, glutathione S-transferases, microsomal epoxide hydrolase and sulfotransferases: influence on cancer susceptibility

It has become clear that several polymorphisms of human drug-metabolizing enzymes influence an individual's susceptibility for chemical carcinogenesis. This review gives an overview on relevant polymorphisms of four families of drug-metabolizing enzymes. Rapid acetylators (with respect to N-acetyltransferase NAT2) were shown to have an increased risk of colon cancer, but a decreased risk of bladder cancer. In addition an association between a NAT1 variant allele (NAT*10, due to mutations in the polyadenylation site causing approximately two fold higher activity) and colorectal cancer among NAT2 rapid acetylators was observed, suggesting a possible interaction between NAT1 and NAT2. Glutathione S-transferases M1 and T1 (GSTM1 and GSTT1) are polymorphic due to large deletions in the structural gene. Meta-analysis of 12 case-control studies demonstrated a significant association between the homozygous deletion of GSTM1 (GSTM1-0) and lung cancer (odds ratio: 1.41; 95% CI: 1.23-1.61). Combination of GSTM1-0 with two allelic variants of cytochrome P4501A1 (CYP1A1), CYP1A1 m2/m2 and CYP1A1 Val/Val further increases the risk for lung cancer. Indirect mechanisms by which deletion of GSTM1 increases risk for lung cancer may include GSTM1-0 associated decreased expression of GST M3 and increased activity of CYP1A1 and 1A2. Combination of GST M1-0 and NAT2 slow acetylation was associated with markedly increased risk for lung cancer (odds ratio: 7.8; 95% CI: 1.4-78.7). In addition GSTM1-0 is clearly associated with bladder cancer and possibly also with colorectal, hepatocellular, gastric, esophageal (interaction with CYP1A1), head and neck as well as cutaneous cancer. In individuals with the GSTT1-0 genotype more chromosomal aberrations and sister chromatid exchanges (SCEs) were observed after exposure to 1,3-butadiene or various haloalkanes or haloalkenes. Evidence for an association between GSTT1-0 and myelodysplastic syndrome and acute lymphoblastic leukemia has been presented. A polymorphic site of GSTP1 (valine to isoleucine at codon 104) decreases activity to several carcinogenic diol epoxides and was associated with testicular, bladder and lung cancer. Microsomal expoxide hydrolase (mEH) is polymorphic due to amino acid variation at residues 113 and 139. Polymorphic variants of mEH were associated with hepatocellular cancer (His-113 allele), ovarian cancer (Tyr-113 allele) and chronic obstructive pulmonary disease (His-113 allele). Three human sulfotransferases (STs) are regulated by genetic polymorphisms (hDHEAST, hM-PST, TS PST). Since a large number of environmental mutagens are activated by STs an association with human cancer risk might be expected.

Glutathione S-transferase T1 and M1 gene defects in ovarian carcinoma

Glutathione S-transferases (GSTs) M1 and T1 are known to be polymorphic in humans. Both polymorphisms are due to gene deletions, which are responsible for the existence of null genotypes. The gene defect of GSTT1 has been reported to be associated with an increased risk of myelodysplastic syndromes, astrocytoma and meningioma. A lack of GSTM1 was associated with tobacco smoke-induced lung and bladder cancer. In this study we examined whether the GSTT1 and/or GSTM1 homozygous null genotypes were associated with an increased risk of ovarian cancer using a multiplex polymerase chain reaction protocol. The GSTT1 null genotype was observed in 14% of the control subjects that had never suffered from neoplastic disease (n = 115) and in 16% of the patients affected with ovarian cancer (n = 103, OR 0.87, 95% CI 0.39-1.92, P = 0.73). A lack of GSTM1 was observed in 38% of the control subjects and in 46% of the patients (OR 0.77, 95% CI 0.44-1.32). This difference was not significant (P = 0.34). Similarly, no significant differences were obtained if GSTT1 and/or GSTM1 null genotypes were analyzed in subgroups of control subjects and ovarian cancer patients between the ages of 20-40, 41-70 and 71-90 years and in individuals with a positive family history of neoplastic disease. GSTT1 and/or GSTM1 null genotypes were not significantly associated with the histologic type and grade or FIGO (International Federation of Gynecology and Obstetrics) stages of the ovarian carcinomas. In conclusion, GSTT1 and/or GSTM1 null genotypes are not markers for an increased risk of ovarian cancer.

The myelodysplastic syndromes: towards a functional classification

The French-American-British classification of myelodysplastic syndromes (MDS) has contributed greatly to better communication and conduct of clinical trials. However, the advent of novel cytogenetic, immunological and molecular techniques in recent years warrant some alterations to this purely morphological classification. This review aims at highlighting the advances which reflect more closely the unique biological and clinical features of various subtypes of MDS. We propose a comprehensive classification of MDS, to include the newly defined categories, as well as those not included in previous classifications, such as the therapy-induced and hereditary MDS. We hope that this classification will help in focusing attention on the biological features of MDS, the understanding of which will be crucial to combat this disease.