The polymorphic human glutathione transferase T1-1, the most efficient glutathione transferase in the denitrosation and inactivation of the anticancer drug 1,3-bis(2-chloroethyl)-1-nitrosourea

Low-molecular-weight thiol transferases in redox regulation and antioxidant defence

Low-molecular-weight (LMW) thiols are produced in all living cells in different forms and concentrations. Glutathione (GSH), coenzyme A (CoA), bacillithiol (BSH), mycothiol (MSH), ergothioneine (ET) and trypanothione T(SH)2 are the main LMW thiols in eukaryotes and prokaryotes. LMW thiols serve as electron donors for thiol-dependent enzymes in redox-mediated metabolic and signaling processes, protect cellular macromolecules from oxidative and xenobiotic stress, and participate in the reduction of oxidative modifications. The level and function of LMW thiols, their oxidized disulfides and mixed disulfide conjugates in cells and tissues is tightly controlled by dedicated oxidoreductases, such as peroxiredoxins, glutaredoxins, disulfide reductases and LMW thiol transferases. This review provides the first summary of the current knowledge of structural and functional diversity of transferases for LMW thiols, including GSH, BSH, MSH and T(SH)2. Their role in maintaining redox homeostasis in single-cell and multicellular organisms is discussed, focusing in particular on the conjugation of specific thiols to exogenous and endogenous electrophiles, or oxidized protein substrates. Advances in the development of new research tools, analytical methodologies, and genetic models for the analysis of known LMW thiol transferases will expand our knowledge and understanding of their function in cell growth and survival under oxidative stress, nutrient deprivation, and during the detoxification of xenobiotics and harmful metabolites. The antioxidant function of CoA has been recently discovered and the breakthrough in defining the identity and functional characteristics of CoA S-transferase(s) is soon expected.

Echinodorus macrophyllus: Acute toxicological evaluation of hydroxycinnamoyl derivatives from SF1 subfractions

ETHNOPHARMACOLOGICAL RELEVANCE

Echinodorus macrophyllus (Kunth.) Micheli (Alismataceae), known as chapéu-de-couro in Brazil, is popularly used to treat inflammatory diseases. We have previously demonstrated a significant reduction in the acute inflammation for the aqueous extract of E. macrophyllus (AEEm) and its ethanolic fraction (Fr20) and described that hydroxycinnamoyl derivatives present in SF1 (Fr20 subfraction) showed higher anti-inflammatory properties by mechanisms that include a reduction of TNF-α, IL-1β, CKCL1/KC, LTB4, and PGE2 levels in exudate.

AIM OF THE STUDY

This work describes the acute toxicological effect of SF1 subfraction on SW mice treated orally for five days in the air pouch model by evaluating the hematological and biochemical determinations on the blood samples; the relative organ weight and its histopathological analysis; the liver genotoxicity assessment and the activity of liver enzymes from xenobiotic metabolism.

MATERIALS AND METHODS

Fr20 was earlier fractionated on the Sephadex LH-20 column, yielding mainly four subfractions, including SF1. The SF1 toxicity was evaluated in mice challenged with carrageenan on the air pouch inflammation model and orally treated for five days. The body weight was monitored daily, and the organs were weighed after the euthanasia. Hematological and biochemical determinations were carried out using specific commercial kits and following the protocols provided by the manufacturers. The organs were fixed, sectioned, processed for hematoxylin and eosin staining, and analyzed by light microscopy. Genotoxicity assessment was performed by the alkaline single-cell gel electrophoresis. Livers were processed for ethoxyresorufin-O-deethylase (EROD) and Glutathione S-transferase (GST) assays.

RESULTS

SF1 exhibited low toxicity, as no significant discrepancy was observed in the relative weight of the body organs of mice. Moreover, the daily treatment with SF1 did not alter the number and percentage of red blood cells or hemoglobin concentration in the blood. The treatment with SF1 did not affect the creatinine concentration, but the 25 mg/kg dose reduced the plasma urea level and uric acid, suggesting its use in treating acute renal failure. The parameters analyzed did not present biochemical alterations indicative of liver disease. Regarding serum triglyceride and cholesterol levels, a significant decrease was detected in both parameters in mice treated with SF1. In addition, the histopathological analysis showed that inflammatory focus in the livers seemed more relevant in the control groups than in those treated. There were no significant changes in the renal or splenic tissues of animals treated with SF1. Treatment with SF1 also does not have a genotoxic effect on liver cells.

CONCLUSION

Treatment with SF1 showed no toxicity in mice at doses equivalent to those recommended for humans, which provides evidence of the safety of the therapeutic use of this subfraction.

GSTM1 and GSTT1 polymorphisms in healthy volunteers - a worldwide systematic review

The GSTM1 and GSTT1 genes encode homonymous enzymes, which are responsible for the detoxification of several substances potentially harmful to the human body, such as air pollution, drugs, pesticides, and tobacco. However, some individuals may present a complete deletion of these genes and, consequently, an enzyme deficiency leading to an inadequate metabolism and, therefore, a higher susceptibility to some clinical conditions. Interethnic variations have also been described for both genes, making necessary the study of the deletion frequencies of GSTM1 and GSTT1 in different populations around the world. So, the aim of this study was to enable the synthesis and discussion of the main population differences of GSTM1 and GSTT1 polymorphisms in healthy volunteers. Searches were performed in the PubMed database, including 533 articles and 178,566 individuals in the analyses. We found an overrepresentation of European individuals and studies, and an underrepresentation of non-European ethnicities. Moreover, there are significant frequency differences among distinct ethnic groups: East Asians present the highest frequencies worldwide for GSTM1 and GSTT1 deletions, which could suggest higher disorders risk for this population; in contrast, Sub-Saharan Africans presented the lowest frequency of GSTM1 worldwide, corroborating evolution inferences performed previously for other genes codifying metabolism enzymes. Also, admixture is a relevant component when analyzing frequency values for both genes, but further studies focusing on this subject are warranted.

Hybrid Drugs-A Strategy for Overcoming Anticancer Drug Resistance?

Despite enormous progress in the treatment of many malignancies, the development of cancer resistance is still an important reason for cancer chemotherapy failure. Increasing knowledge of cancers' molecular complexity and mechanisms of their resistance to anticancer drugs, as well as extensive clinical experience, indicate that an effective fight against cancer requires a multidimensional approach. Multi-target chemotherapy may be achieved using drugs combination, co-delivery of medicines, or designing hybrid drugs. Hybrid drugs simultaneously targeting many points of signaling networks and various structures within a cancer cell have been extensively explored in recent years. The single hybrid agent can modulate multiple targets involved in cancer cell proliferation, possesses a simpler pharmacokinetic profile to reduce the possibility of drug interactions occurrence, and facilitates the process of drug development. Moreover, a single medication is expected to enhance patient compliance due to a less complicated treatment regimen, as well as a diminished number of adverse reactions and toxicity in comparison to a combination of drugs. As a consequence, many efforts have been made to design hybrid molecules of different chemical structures and functions as a means to circumvent drug resistance. The enormous number of studies in this field encouraged us to review the available literature and present selected research results highlighting the possible role of hybrid drugs in overcoming cancer drug resistance.

Functional diversification of three delta-class glutathione S-transferases involved in development and detoxification in Tribolium castaneum

Glutathione S-transferases (GSTs) are members of a multifunctional enzyme superfamily. Forty-one GSTs have been identified in Tribolium castaneum; however, none of the 41 GSTs has been functionally characterized. Here, three delta-class GSTs, TcGSTd1, TcGSTd2 and TcGSTd3, of T. castaneum were successfully cloned and expressed in Escherichia coli. All of the studied GSTs catalysed the conjugation of reduced glutathione with 1-chloro-2,4-dinitrobenzene. Insecticide treatment showed that the expression levels of TcGSTd3 and TcGSTd2 were significantly increased after exposure to phoxim and lambda-cyhalothrin, whereas TcGSTd1 was slightly upregulated only in response to phoxim. A disc diffusion assay showed that overexpression of TcGSTD3, but not TcGSTD1 or TcGSTD2, in E. coli increased resistance to paraquat-induced oxidative stress. RNA interference knockdown of TcGSTd1 caused metamorphosis deficiencies and reduced fecundity by regulating insulin/target-of-rapamycin signalling pathway-mediated ecdysteroid biosynthesis, and knockdown of TcGSTd3 led to reduced fertility and a decreased hatch rate of the offspring, probably caused by the reduced antioxidative activity in the reproductive organs. These results indicate that TcGSTd3 and TcGSTd2 may play vital roles in cellular detoxification, whereas TcGSTd1 may play essential roles in normal development of T. castaneum. These delta-class GSTs in T. castaneum have obtained different functions during the evolution.

The mercapturic acid pathway

The mercapturic acid pathway is a major route for the biotransformation of xenobiotic and endobiotic electrophilic compounds and their metabolites. Mercapturic acids (N-acetyl-l-cysteine S-conjugates) are formed by the sequential action of the glutathione transferases, γ-glutamyltransferases, dipeptidases, and cysteine S-conjugate N-acetyltransferase to yield glutathione S-conjugates, l-cysteinylglycine S-conjugates, l-cysteine S-conjugates, and mercapturic acids; these metabolites constitute a "mercapturomic" profile. Aminoacylases catalyze the hydrolysis of mercapturic acids to form cysteine S-conjugates. Several renal transport systems facilitate the urinary elimination of mercapturic acids; urinary mercapturic acids may serve as biomarkers for exposure to chemicals. Although mercapturic acid formation and elimination is a detoxication reaction, l-cysteine S-conjugates may undergo bioactivation by cysteine S-conjugate β-lyase. Moreover, some l-cysteine S-conjugates, particularly l-cysteinyl-leukotrienes, exert significant pathophysiological effects. Finally, some enzymes of the mercapturic acid pathway are described as the so-called "moonlighting proteins," catalytic proteins that exert multiple biochemical or biophysical functions apart from catalysis.

Role of pharmacogenetics of drug-metabolizing enzymes in treating osteosarcoma

INTRODUCTION

Drug-metabolizing enzymes (DMEs) biotransform several toxins and xenobiotics in both tumor and normal cells, resulting in either their detoxification or their activation. Since DMEs also metabolize several chemotherapeutic drugs, they can significantly influence tumor response to chemotherapy and susceptibility of normal tissues to collateral toxicity of anticancer treatments.

AREAS COVERED

This review discusses the pharmacogenetics of DMEs involved in the metabolism of drugs which constitute the backbone of osteosarcoma (OS) chemotherapy, highlighting what is presently known for this tumor and their possible impact on the modulation of future treatment approaches.

EXPERT OPINION

Achieving further insight into pharmacogenetic markers and biological determinants related to treatment response in OS may ultimately lead to individualized treatment regimens, based on a combination of genotype and tumor characteristics of each patient.

Antitumor sulfonylhydrazines: design, structure-activity relationships, resistance mechanisms, and strategies for improving therapeutic utility

1,2-Bis(sulfonyl)-1-alkylhydrazines (BSHs) were conceived as more specific DNA guanine O-6 methylating and chloroethylating agents lacking many of the undesirable toxicophores contained in antitumor nitrosoureas. O(6)-Alkylguanine-DNA alkyltransferase (MGMT) is the sole repair protein for O(6)-alkylguanine lesions in DNA and has been reported to be absent in 5-20% of most tumor types. Many BSHs exhibit highly selective cytotoxicity toward cells deficient in MGMT activity. The development of clinically useful MGMT assays should permit the identification of tumors with this vulnerability and allow for the preselection of patient subpopulations with a high probability of responding. The BSH system is highly versatile, permitting the synthesis of many prodrug types with the ability to incorporate an additional level of tumor-targeting due to preferential activation by tumor cells. Furthermore, it may be possible to expand the spectrum of activity of these agents to include tumors with MGMT activity by combining them with tumor-targeted MGMT inhibitors.

Optimization of storage and stability of camel liver glutathione S-transferase

Glutathione S-transferases (GSTs) are multifunctional enzymes and play an important role in cellular detoxification. Besides this, GSTs act as cytosolic carrier proteins that bind hydrophobic compounds such as heme, bilirubin, steroids, and polycyclic hydrocarbons. GST has great importance in biotechnology, as it is a target for vaccine and drug development and biosensors development for xenobiotics. Moreover, the GST tag has been extensively used for protein expression and purification. Until now, biophysical properties of camel liver GST have not been characterized. In the present study we have purified camel (Camelus dromedarius) liver GST to homogeneity in a single step by affinity chromatography with 23.4-fold purification and 60.6% yield. Our results showed that maximal activity of GST was at pH 6.5 and it was stable in the pH range of 5 to 10. The optimum temperature was 55°C and the Tm was 57°C. The chemical chaperone glycerol (3.3 M) was able to protect GST activity and aggregation against thermal denaturation by stabilizing the protein structure at 50 and 57°C, respectively. However, L-arginine (125 mM) did not protect GST against thermal stress. Far-ultraviolet circular dichroism (CD) spectra showed that glycerol protected the secondary structure of GST while L-arginine induced conformational changes under thermal stress. In conclusion, our studies on the GST stability suggest that glycerol works as a stabilizer and L-arginine acts as a destabilizer.

Influence of glutathione and glutathione S-transferases on DNA interstrand cross-link formation by 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine, the active anticancer moiety generated by laromustine

Prodrugs of 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine (90CE) are promising anticancer agents. The 90CE moiety is a readily latentiated, short-lived (t_1/2 ∼ 30 s) chloroethylating agent that can generate high yields of oxophilic electrophiles responsible for the chloroethylation of the O-6 position of guanine in DNA. These guanine O-6 alkylations are believed to be responsible for the therapeutic effects of 90CE and its prodrugs. Thus, 90CE demonstrates high selectivity toward tumors with diminished levels of O⁶-alkylguanine-DNA alkyltransferase (MGMT), the resistance protein responsible for O⁶-alkylguanine repair. The formation of O⁶-(2-chloroethyl)guanine lesions ultimately leads to the generation of highly cytotoxic 1-(N³-cytosinyl),-2-(N¹-guaninyl)ethane DNA interstrand cross-links via N¹,O⁶-ethanoguanine intermediates. The anticancer activity arising from this sequence of reactions is thus identical to this component of the anticancer activity of the clinically used chloroethylnitrosoureas. Herein, we evaluate the ability of glutathione (GSH) and other low molecular weight thiols, as well as GSH coupled with various glutathione S-transferase enzymes (GSTs) to attenuate the final yields of cross-links generated by 90CE when added prior to or immediately following the initial chloroethylation step to determine the major point(s) of interaction. In contrast to studies utilizing BCNU as a chloroethylating agent by others, GSH (or GSH/GST) did not appreciably quench DNA interstrand cross-link precursors. While thiols alone offered little protection at either alkylation step, the GSH/GST couple was able to diminish the initial yields of cross-link precursors. 90CE exhibited a very different GST isoenzyme susceptibility to that reported for BCNU, this could have important implications in the relative resistance of tumor cells to these agents. The protection afforded by GSH/GST was compared to that produced by MGMT.

Enzymatic GST levels and overall health of mullets from contaminated Brazilian Lagoons

Glutathione S-transferase (GST) assays in non-mammalian organisms are usually conducted inappropriately, since no previous standardization of the optimal concentrations of proteins and substrates and adequate pH is conducted. Standardization is a key task to adjust enzyme assays at their kinetically correct maximal initial velocities, if one wants these velocities to indicate the amount of enzyme in a sample. In this paper GST assays were standardized in liver cytosol to compare seasonal GST levels in liver of mullet from two contaminated lagoons in the Rio de Janeiro to those from a reference bay. GST potential as a biomarker of sublethal intoxication in this species was also evaluated. Mullet liver GST levels assayed with substrates that corresponded to three different GST isoenzymes varied throughout the year. The differences indicated that mullets are suffering from sublethal intoxication from contaminants in these lagoons. Seasonal variations of activity were relevant, since these could indicate differences in xenobiotic input into the areas. An analysis of overall mullet health condition using a morphological index (the Fulton Condition Factor) and macroscopic abnormalities corroborated the differences in GST levels, with fish from one of the sites in worse overall health condition showing lower and significantly different FCF when compared to the reference site. Therefore, GST standardized activity levels are useful biomarkers of environmental contamination for mullet.

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.

Functional studies of single-nucleotide polymorphic variants of human glutathione transferase T1-1 involving residues in the dimer interface

Glutathione transferase T1-1 catalyses detoxication and bioactivation processes in which glutathione conjugates are formed from endogenous and xenobiotic substrates, including alkylating agents and halogenated alkanes. Although the common null polymorphism of the human GSTT1 gene has been studied extensively, little is known about the consequences of GSTT1 single-nucleotide polymorphisms (SNPs). Here, we have examined the effects of two SNPs that alter amino acid residues in the dimer interface of the GST T1-1 protein and one that causes a conservative substitution in the core of the subunit. Variant proteins were expressed in an Escherichia coli strain in which the metabolism of ethylene dibromide to a glutathione conjugate leads to lacZ reversion mutations. We measured the kinetic properties of the enzymes with the characteristic substrate 1,2-epoxy-3-(p-nitrophenoxy)propane (EPNP) and determined the specific activities with several other substrates. Circular dichroism spectroscopy was used to measure protein thermal denaturation profiles. Variant T104P, which has been reported as inactive, showed weak but detectable activity with each substrate. Variant R76S was expressed at lower levels and showed much-reduced thermal stability. The results are interpreted in the context of the three-dimensional structure of human GST T1-1.

GSTT1: a marker of the aggressiveness of bladder cancer

INTRODUCTION

Glutathione S-transferases have been implicated in the development of bladder cancer (BC). We investigated the genotype and expression of glutathione S-transferase-mu (GSTM1) and glutathione S-transferase-theta (GSTT1) in BC tissue specimens.

MATERIALS AND METHODS

Tumor samples and matched normal mucosae were obtained from 34 patients. Genomic DNA was used to analyze GSTM1 and GSTT1 genotypes using multiplex polymerase chain reaction. GSTM1 and GSTT1 mRNA levels were measured using real-time reverse transcriptase polymerase chain reaction.

RESULTS

GSTM1 mRNA expression was lower in tumor tissues than in matched normal bladder mucosae, whereas GSTT1 mRNA expression was significantly higher. GSTT1 mRNA expression was higher in muscle-invasive BC and high-grade cancers than in non-muscle-invasive BC and lower-grade tumors.

CONCLUSIONS

GSTT1 is correlated with characteristics of aggressive BC. GSTT1 may play an important role in tumorigenesis and disease progression in patients with BC.

A high-throughput 1,536-well luminescence assay for glutathione S-transferase activity

Glutathione S-transferases (GSTs) constitute a family of detoxification enzymes that catalyze the conjugation of glutathione with a variety of hydrophobic compounds, including drugs and their metabolites, to yield water-soluble derivatives that are excreted in urine or bile. Profiling the effect of small molecules on GST activity is an important component in the characterization of drug candidates and compound libraries. Additionally, specific GST isozymes have been implicated in drug resistance, especially in cancer, and thus represent potential targets for intervention. To date, there are no sensitive miniaturized high-throughput assays available for GST activity detection. A series of GST substrates containing a masked luciferin moiety have been described recently, offering the potential for configuring a sensitive screening assay via coupled luciferase reaction and standard luminescence detection. We report on the optimization and miniaturization of this homogeneous method to 1,536-well format using GSTs from 3 different species: mouse isozyme A4-4, human isozymes A1-1, M1-1, and P1-1, and the major GST from the parasitic worm Schistosoma japonicum.

Genetic variations in human glutathione transferase enzymes: significance for pharmacology and toxicology

Glutathione transferase enzymes (GSTs) catalyze reactions in which electrophiles are conjugated to the tripeptide thiol glutathione. While many GST-catalyzed transformations result in the detoxication of xenobiotics, a few substrates, such as dihaloalkanes, undergo bioactivation to reactive intermediates. Many molecular epidemiological studies have tested associations between polymorphisms (especially, deletions) of human GST genes and disease susceptibility or response to therapy. This review presents a discussion of the biochemistry of GSTs, the sources-both genetic and environmental-of interindividual variation in GST activities, and their implications for pharmaco- and toxicogenetics; particular attention is paid to the Theta class GSTs.

Clinical pharmacokinetics of amifostine and WR1065 in pediatric patients with medulloblastoma

PURPOSE

We evaluated the pharmacokinetics of amifostine and WR1065 in pediatric patients with newly diagnosed medulloblastoma to assess the influence of patient covariates, including demographics, clinical characteristics, and genetic polymorphisms, on amifostine and WR1065 pharmacokinetic parameters.

EXPERIMENTAL DESIGN

We assessed the pharmacokinetics of amifostine and WR1065 in 33 children who received amifostine (1-minute infusion, 600 mg/m(2)) just before the start of and 3 hours into a 6-hour cisplatin infusion. Serial blood samples were collected after doses 1 (0 hour) and 2 (3 hours) of course 1. Amifostine and WR1065 were quantitated by high performance liquid chromatography with electrochemical detection. A pharmacokinetic model was simultaneously fit to amifostine and WR1065 plasma or whole blood concentration-versus-time data. The influence of demographic, biochemical, and pharmacogenetic covariates on amifostine and WR1065 disposition was evaluated.

RESULTS

Body surface area was the primary size-based covariate for amifostine pharmacokinetics explaining 53% and 56% of interindividual variability in plasma and whole-blood amifostine clearance, respectively. The population-predicted values for amifostine clearance, volume, and apparent WR1065 clearance from the plasma data were 107 L/h/m(2), 5.53 L/m(2), and 30.6 L/h/m(2). The population-predicted values for amifostine clearance, volume, and apparent WR1065 clearance from whole blood data were 136 L/h/m(2), 7.23 L/m(2), and 12.5 L/h/m(2).

CONCLUSIONS

These results support using body surface area for calculating doses of amifostine in children. Similar to data in adults, amifostine and WR1065 are rapidly cleared from plasma and whole blood in children.

Minor modifications of the C-terminal helix reschedule the favored chemical reactions catalyzed by theta class glutathione transferase T1-1

Adaptive responses to novel toxic challenges provide selective advantages to organisms in evolution. Glutathione transferases (GSTs) play a pivotal role in the cellular defense because they are main contributors to the inactivation of genotoxic compounds of exogenous as well as of endogenous origins. GSTs are promiscuous enzymes catalyzing a variety of chemical reactions with numerous alternative substrates. Despite broad substrate acceptance, individual GSTs display pronounced selectivities such that only a limited number of substrates are transformed with high catalytic efficiency. The present study shows that minor structural changes in the C-terminal helix of mouse GST T1-1 induce major changes in the substrate-activity profile of the enzyme to favor novel chemical reactions and to suppress other reactions catalyzed by the parental enzyme.

Glutathione S-transferase T1 and M1: gene sequence variation and functional genomics

PURPOSE

The glutathione S-transferases (GSTs) catalyze the glutathione conjugation of reactive electrophiles, including carcinogens and many antineoplastic drugs. GSTT1 and GSTM1 are polymorphically deleted, but the full range of genetic variation in these two genes has not yet been explored. We set out to systematically identify common polymorphisms in GSTT1 and GSTM1, followed by functional genomic studies.

EXPERIMENTAL DESIGN

First, multiplex PCR was used to determine GSTT1 and GSTM1 copy number in 400 DNA samples (100 each from 4 ethnic groups). Exons, splice junctions, and 5'-flanking regions (5'-FR) were then resequenced using DNA samples that contained at least one copy of GSTT1 or GSTM1.

RESULTS

Gene deletion frequencies among ethnic groups were from 33.5% to 73.5% for GSTT1 and from 50.5% to 78.0% for GSTM1. GSTT1 deletion data correlated with the results of mRNA microarray expression studies. The 18 single nucleotide polymorphisms (SNP) observed in GSTT1 included three nonsynonymous coding SNPs (cSNPs) and one single-nucleotide deletion, whereas the 51 GSTM1 SNPs included two nonsynonymous cSNPs. Two of the GSTT1 nonsynonymous cSNPs resulted in decreases in levels of immunoreactive protein to 56% and 12% of wild type (WT), whereas those in GSTM1 resulted in modest increases in protein levels. Reporter gene assays showed that one GSTT1 5'-FR haplotype, with a frequency of 32% in African-American subjects, resulted in an increase in transcription in JEG-3 cells to 351% of that for the WT sequence, and one GSTM1 5'-FR haplotype resulted in an increase in transcription in JEG-3 cells to 129% of WT.

CONCLUSIONS

These observations suggest that functionally significant pharmacogenomic variation beyond GSTT1 and GSTM1 gene deletion may contribute to carcinogenesis or individual variation in antineoplastic drug therapy response.

Generation and functional characterization of mice with a disrupted glutathione S-transferase, theta 1 gene

Glutathione S-transferase (GST) theta 1 (GSTT1) has been regarded as one of the key enzymes involved in phase II reactions because of its unique substrate specificity. In this study, we generated mice with the disrupted Gstt1 gene (Gstt1-null mice) by gene targeting and analyzed the metabolic properties in cytosolic and in vivo studies. The resulting Gstt1-null mice failed to express the Gstt1 mRNA and GSTT1 protein by reverse transcriptase-polymerase chain reaction analysis and two-dimensional fluorescence difference gel electrophoresis/mass spectrometry analysis, respectively. However, the Gstt1-null mice appeared to be normal and were fertile. In an enzymatic study using cytosolic samples from the liver and kidney, GST activity toward 1,2-epoxy-3-(p-nitrophenoxy)propane (EPNP), dichloromethane (DCM), and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) was markedly lower in Gstt1-null mice than in the wild-type controls, despite there being no difference in GST activity toward 1-choloro-2,4-dinitrobenzene between Gstt1-null mice and the wild-type controls. Gstt1-null mice had GST activity of only 8.7 to 42.1% of the wild-type controls to EPNP, less than 2.2% of the wild-type controls to DCM, and 13.2 to 23.9% of the wild-type controls to BCNU. Plasma BCNU concentrations after a single i.p. administration of BCNU to Gstt1-null mice were significantly higher, and there was a larger area under the curve(5-60) min (male, 2.30 times; female, 2.28 times, versus the wild-type controls) based on the results. In conclusion, Gstt1-null mice would be useful as an animal model of humans with the GSTT1-null genotype.

Autotransplant conditioning regimens for aggressive lymphoma: are we on the right road?

High-dose chemotherapy and autologous stem cell transplant (ASCT) is the standard approach for chemosensitive, relapsed aggressive non-Hodgkin's lymphoma (NHL). Various conditioning regimens have been used as treatment before ASCT and disease-free (DFS) and overall survival (OS) rates range from 34 to 60% and 26 to 46%, respectively. To date, few comparative randomized trials have been performed and no regimen has demonstrated superiority to another. Reduction of disease relapse remains the major hurdle for improving patient outcome and in vitro and in vivo purging of lymphoma cells has not necessarily enhanced results. Rituximab pre-mobilization and post-transplant appear to provide better response rates with OS approaching 87-91% at 2-3 years. Newer approaches with radioimmunotherapy may raise DFS to 78% and OS to 93%, albeit with short follow-up. Advances in the conditioning regimens and supportive care have reduced transplant-related mortality to less than 10%. In this review we discuss commonly utilized conditioning regimens, describe their pros and cons and address purging and present conditioning strategies. Owing to the poor outcome with conventional chemotherapy in mantle cell, Burkitt's and T-cell lymphoma, we propose the standard approach of front-line ASCT for these high-risk lymphoma patients. Finally, we will present novel strategies, which can enhance the anti-lymphoma effect, at the same time reducing toxicity, to improve the outcome of ASCT in NHL patients.

Human glutathione transferases catalyzing the bioactivation of anticancer thiopurine prodrugs

cis-6-(2-Acetylvinylthio)purine (cAVTP) and trans-6-(2-acetylvinylthio)guanine (tAVTG) are thiopurine prodrugs provisionally inactivated by an alpha,beta-unsaturated substituent on the sulfur of the parental thiopurines 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG). The active thiopurines are liberated intracellularly by glutathione (GSH) in reactions catalyzed by glutathione transferases (GSTs) (EC 2.5.1.18). Catalytic activities of 13 human GSTs representing seven distinct classes of soluble GSTs have been determined. The bioactivation of cAVTP and tAVTG occurs via a transient addition of GSH to the activated double bond of the S-substituent of the prodrug, followed by elimination of the thiopurine. The first of these consecutive reactions is rate-limiting for thiopurine release, but GST-activation of this first addition is shifting the rate limitation to the subsequent elimination. Highly active GSTs reveal the transient intermediate, which is detectable by UV spectroscopy and HPLC analysis. LC/MS analysis of the reaction products demonstrates that the primary GSH conjugate, 4-glutathionylbuten-2-one, can react with a second GSH molecule to form the 4-(bis-glutathionyl)butan-2-one. GST M1-1 and GST A4-4 were the most efficient enzymes with tAVTG, and GST M1-1 and GST M2-2 had highest activity with cAVTP. The highly efficient GST M1-1 is polymorphic and is absent in approximately half of the human population. GST P1-1, which is overexpressed in many cancer cells, had no detectable activity with cAVTP and only minor activity with tAVTG. Other GST-activated prodrugs have targeted GST P1-1-expressing cancer cells. Tumors expressing high levels of GST M1-1 or GST A4-4 can be predicted to be particularly vulnerable to chemotherapy with cAVTP or tAVTG.

Inhibition of cytosolic glutathione S-transferase activity from rat liver by copper

H(2)O(2) inactivation of particular GST isoforms has been reported, with no information regarding the overall effect of other ROS on cytosolic GST activity. The present work describes the inactivation of total cytosolic GST activity from liver rats by the oxygen radical-generating system Cu(2+)/ascorbate. We have previously shown that this system may change some enzymatic activities of thiol proteins through two mechanisms: ROS-induced oxidation and non-specific Cu(2+) binding to protein thiol groups. In the present study, we show that nanomolar Cu(2+) in the absence of ascorbate did not modify total cytosolic GST activity; the same concentrations of Cu(2+) in the presence of ascorbate, however, inhibited this activity. Micromolar Cu(2+) in either the absence or presence of ascorbate inhibited cytosolic GST activity. Kinetic studies show that GSH but no 1-chloro-2,4-dinitrobenzene prevent the inhibition on cytosolic GST induced by micromolar Cu(2+) either in the absence or presence of ascorbate. On the other hand, NEM and mersalyl acid, both thiol-alkylating agents, inhibited GST activity with differential reactivity in a dose-dependent manner. Taken together, these results suggest that an inhibitory Cu(2+)-binding effect is likely to be negligible on the overall inhibition of cytosolic GST activity observed by the Cu(2+)/ascorbate system. We discuss how modification of GST-thiol groups is related to the inhibition of cytosolic GST activity.

Cloning and characterization of a theta class glutathione transferase from the potato pathogen Phytophthora infestans

A glutathione transferase (GST) related to the theta (T) class of enzymes found in plants and animals has been cloned from the potato pathogen Phytophthora infestans. The cDNA encoded a 25kDa polypeptide termed PiGSTT1 which was expressed in E. coli as the native protein. The purified recombinant enzyme behaved as a dimer (PiGSTT1-1) and while being unable to catalyse the glutathione conjugation of 1-chloro-2,4-dintrobenzene, was highly active as a glutathione peroxidase with organic hydroperoxide substrates. In addition to reducing the synthetic substrate cumene hydroperoxide, PiGSTT1-1 was shown to be highly active toward 9(S)-hydroperoxy-(10E,12Z,15Z)-octadecatrienoic acid=9(S)-HPOT, which is formed in potato plants during infection by P. infestans as a precursor of the antifungal oxylipin colnelenic acid. An antiserum was raised to PiGSTT1-1 and used to demonstrate that the respective enzyme was abundantly expressed in P. infestans both cultured on pea agar and during the infection of potato plants.

Divergent activities of human glutathione transferases in the bioactivation of azathioprine

Azathioprine is a thiopurine prodrug clinically used for immunosuppression in the treatment of inflammatory diseases and in pharmacological regimens of organ transplantations. Its pharmacological action is based on the release of 6-mercaptopurine, but the biochemical processes underlying this biotransformation have remained obscure. In this investigation, human glutathione transferases (GSTs) from seven distinct classes were assayed with azathioprine. GSTs A1-1, A2-2, and M1-1, all abundantly expressed in human liver, displayed the highest activity among the 14 GSTs tested. The uncatalyzed reaction of azathioprine with glutathione was estimated to be less than 1% of the GST-catalyzed biotransformation. GST M1-1 is polymorphic with a frequently occurring null allele, and GSTs A1-1 and A2-2 show variable expression levels in human subjects, implying significant differences in the rate of 6-mercaptopurine release from azathioprine. Individuals expressing high GST activity are apparently predisposed for adverse reactions to azathioprine treatment, both by promoting excessively high concentrations of free 6-mercaptopurine and its toxic metabolites and by depleting cellular glutathione. These novel aspects of GST-dependent azathioprine biotransformation have not been considered previously.

Microarray analysis of altered gene expression in murine fibroblasts transformed by nickel(II) to nickel(II)-resistant malignant phenotype

B200 cells are Ni(II)-transformed mouse BALB/c-3T3 fibroblasts displaying a malignant phenotype and increased resistance to Ni(II) toxicity. In an attempt to find genes whose expression has been altered by the transformation, the Atlas Mouse Stress/Toxicology cDNA Expression Array (Clontech Laboratories, Inc., Palo Alto, CA) was used to analyze the levels of gene expression in both parental and Ni(II)-transformed cells. Comparison of the results revealed a significant up- or downregulation of the expression of 62 of the 588 genes present in the array (approximately 10.5%) in B200 cells. These genes were assigned to different functional groups, including transcription factors and oncogenes (9/14; fractions in parentheses denote the number of up-regulated versus the total number of genes assigned to this group), stress and DNA damage response genes (11/12), growth factors and hormone receptors (6/9), metabolism (7/7), cell adhesion (2/7), cell cycle (3/6), apoptosis (3/4), and cell proliferation (2/3). Among those genes, overexpression of beta-catenin and its downstream targets c-myc and cyclin D1, together with upregulated cyclin G, points at the malignant character of B200 cells. While the increased expression of glutathione (GSH) synthetase, glutathione-S-transferase A4 (GSTA4), and glutathione-S-transferase theta (GSTT), together with high level of several genes responding to oxidative stress, suggests the enforcement of antioxidant defenses in Ni-transformed cells.

Glutathione transferases

This review describes the three mammalian glutathione transferase (GST) families, namely cytosolic, mitochondrial, and microsomal GST, the latter now designated MAPEG. Besides detoxifying electrophilic xenobiotics, such as chemical carcinogens, environmental pollutants, and antitumor agents, these transferases inactivate endogenous alpha,beta-unsaturated aldehydes, quinones, epoxides, and hydroperoxides formed as secondary metabolites during oxidative stress. These enzymes are also intimately involved in the biosynthesis of leukotrienes, prostaglandins, testosterone, and progesterone, as well as the degradation of tyrosine. Among their substrates, GSTs conjugate the signaling molecules 15-deoxy-delta(12,14)-prostaglandin J2 (15d-PGJ2) and 4-hydroxynonenal with glutathione, and consequently they antagonize expression of genes trans-activated by the peroxisome proliferator-activated receptor gamma (PPARgamma) and nuclear factor-erythroid 2 p45-related factor 2 (Nrf2). Through metabolism of 15d-PGJ2, GST may enhance gene expression driven by nuclear factor-kappaB (NF-kappaB). Cytosolic human GST exhibit genetic polymorphisms and this variation can increase susceptibility to carcinogenesis and inflammatory disease. Polymorphisms in human MAPEG are associated with alterations in lung function and increased risk of myocardial infarction and stroke. Targeted disruption of murine genes has demonstrated that cytosolic GST isoenzymes are broadly cytoprotective, whereas MAPEG proteins have proinflammatory activities. Furthermore, knockout of mouse GSTA4 and GSTZ1 leads to overexpression of transferases in the Alpha, Mu, and Pi classes, an observation suggesting they are part of an adaptive mechanism that responds to endogenous chemical cues such as 4-hydroxynonenal and tyrosine degradation products. Consistent with this hypothesis, the promoters of cytosolic GST and MAPEG genes contain antioxidant response elements through which they are transcriptionally activated during exposure to Michael reaction acceptors and oxidative stress.

Glutathione S-transferase T1-1 activity upregulated in transitional cell carcinoma of urinary bladder

OBJECTIVES

To perform a systematic functional investigation of different glutathione S-transferase (GST) classes, including GST class Theta (GSTT) member GSTT1-1, in transitional cell carcinoma (TCC) and the surrounding normal uroepithelium of the same individuals. Recently, it was suggested that GSTT1-1 might be an important risk modulator for TCC.

METHODS

Tumor samples and surrounding normal uroepithelium were obtained from 24 patients with TCC of urinary bladder. The following substrates with differential specificities were used: 1-chloro-2,4-dinitrobenzene for overall GST activity; 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole for GST Alpha; 1,2-dichloro-4-nitro-benzene for GST Mu; 4-vinylpyridine for GST Pi 1-1(GSTP1-1); and 1,2-epoxy-3-(p-nitrophenoxy)propane for GSTT1-1.

RESULTS

GSTP1-1 and GSTT1-1 activities were demonstrated in all uroepithelial and TCC samples, and GST Mu activity was detectable in 11 of 24 patients. In the tumor specimens, significant upregulation of all expressed GST subtypes was observed. The mean GSTP1-1 and GSTT1-1 level in TCC was increased 2-fold and 3.6-fold, respectively, compared with the mean level in the normal uroepithelium (P <0.001). Tumor GSTT1-1 activities correlated statistically significantly with the tumor stage (P <0.05).

CONCLUSIONS

In tumors and adjacent normal uroepithelium of patients with TCC, three major cytosolic GST classes, Mu, Pi, and Theta, were expressed. Although the GST isoenzyme pattern in TCC was similar to that of the corresponding normal uroepithelium, during cancer progression a clear tendency toward an increase in all the GST subtypes expressed was noted. For the first time, distinct GSTT1-1 activity levels were demonstrated in human uroepithelium, as well as its pronounced upregulation in TCC.

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.

Inhibition of glutathione S-transferases by thonningianin A, isolated from the African medicinal herb, Thonningia sanguinea, in vitro

There is evidence that increased expression of glutathione S-transferase (EC: 2.5.1.18, GST) is involved in resistance of tumor cells against chemotherapeutic agents. In this study we investigated the inhibitory effects of thonningianin A (Th A), a novel antioxidant isolated from the medicinal herb, Thonningia sanguinea on uncharacterized rat liver GST and human GST P1-1. Using 1-chloro-2,4-dinitrobenzene (CDNB) as substrate, rat liver cytosolic GST activity was inhibited by Th A in a concentration dependent manner with 50% inhibition concentration (IC50) of 1.1 microM. When Th A was compared with known potent GST inhibitors the order of inhibition was tannic acid>cibacron blue>hematin>Th A>ethacrynic acid with CDNB as substrate. Th A also exhibited non-competitive inhibition towards both CDNB and glutathione. Furthermore, using 1,2-dichloro-4-nitrobenzene, ethacrynic acid and 1,2-epoxy-3-(p-nitrophenoxy) propane as substrates Th A at 1.0 microM inhibited cytosolic GST by 2%, 12% and 36% respectively. Human GST P1-1 was also inhibited by Th A with an IC50 of 3.6 microM. While Th A showed competitive inhibition towards CDNB it exhibited non-competitive inhibition towards GSH of the human GST P1-1. These results suggest that Th A represents a new potent GST in vitro inhibitor.