Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.1.1.67 (thiopurine methyltransferase)
 551 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have expressed the human thiopurine methyltransferase cDNA in a baculovirus vector in Sf21 (Spodoptera frugiperda) cells. This system expresses the enzyme at levels such that the thiopurine methyltransferase enzyme may be readily visualised by Coomassie blue stained sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The expressed enzyme catalysed the methylation of 6-mercaptopurine with an apparent Km of 892 microM, similar to that observed in human liver cytosol ie. 657 microM however, the Vmax was 13,500 pmole/mg/min, which is approximately 400 times higher than the Vmax observed in human liver cytosol ie. 33 pmole/mg/min. The thiopurine methyltransferase inhibitors 6-thioxanthine, p-methoxybenzoic acid and 3,5-dimethoxy benzoic acid were found to be potent inhibitors of the expressed enzyme.
Biochem Mol Biol Int 1996 Feb
PMID:Baculovirus-mediated high level expression of a human thiopurine methyl transferase. 885 May 31

Pharmacogenetics has emerged as a novel and challenging area of interest in oncology. Cancer chemotherapy is characterized by major intersubject variability in tumor responses and host toxicity. This variation may be caused by genetic differences in the enzymes involved in the metabolism of anticancer agents. Anticancer agents, such as 6-mercaptopurine, 5-fluorouracil, and irinotecan, have a narrow therapeutic index that can sometimes result in severe life-threatening toxicities. The impact of polymorphisms in metabolizing enzymes (thiopurine S-methyltransferase, dihydropyrimidine dehydrogenase, and uridine diphosphate glucuronosyltransferase) that participate significantly in the disposition of these anticancer agents is discussed.
Mol Diagn 1999 Dec
PMID:Inherited variations in drug-metabolizing enzymes: significance in clinical oncology. 1067 43

Although the thiopurine drugs 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG) are well established agents for the treatment of leukemia, controversies remain regarding their main mode of action. Previous evidence has suggested that although 6-TG exerts a cytotoxic effect through incorporation of 6-thioguanine nucleotides into newly synthesized DNA (DNA-TGN), an important component of the mode of action of 6-MP is inhibition of purine de novo synthesis (PDNS) through the production of S-methyl-thioinosine 5'-monophosphate (MeTIMP), not formed in cells exposed to 6-TG. We have shown that thiopurine methyltransferase (TPMT) modulates this effect. By transfection of the human TPMT gene using an inducible system to produce a 3.8-fold increase in TPMT activity in the ecdysone receptor 293 embryonic kidney cell line, we demonstrated a 4.4-fold increase in sensitivity to 6-MP. This was associated with a rise in intracellular levels of MeTIMP but a decrease in levels of DNA-TGN. In contrast, induction of TPMT produced a 1.6-fold decrease in sensitivity to 6-TG, a decrease in levels of DNA-TGN, and an increase in levels of methylated thioguanosine monophosphate. Exposure of cells to equitoxic doses of drug showed similar incorporation of DNA-TGN for 6-TG but for 6-MP significantly reduced DNA-TGN in TPMT-induced compared with uninduced cells. For equitoxic doses of 6-MP, equivalent levels of MeTIMP correlated with equivalent amounts of PDNS. These observations suggest that intracellular TGN levels do not give an accurate reflection of cytotoxic potential in patients treated with 6-MP, because different levels of DNA-TGN may be associated with equitoxic effects.
Mol Pharmacol 2002 Jul
PMID:The effect of thiopurine methyltransferase expression on sensitivity to thiopurine drugs. 1206 60

In humans, the enzyme thiopurine methyltransferase (TPMT) metabolizes 6-thiopurine (6-TP) medications, including 6-thioguanine, 6-mercaptopurine and azathioprine, commonly used for immune suppression and for the treatment of hematopoietic malignancies. S-Methylation by TPMT prevents the intracellular conversion of these drugs into active 6-thioguanine nucleotides (6-TGNs). Genetic polymorphisms in the TPMT protein sequence have been associated with decreased tissue enzymatic activities and an increased risk of life-threatening myelo-suppression from standard doses of 6-TP medications. Biochemical studies have demonstrated that TPMT deficiency is primarily associated with increased degradation of the polymorphic proteins through an ubiquitylation and proteasomal-dependent pathway. We have now determined the tertiary structure of the bacterial orthologue of TPMT from Pseudomonas syringae using NMR spectroscopy. Bacterial TPMT similarly catalyzes the S-adenosylmethionine (SAM)-dependent transmethylation of 6-TPs and shares 45% similarity (33% identity) with the human enzyme. Initial studies revealed an unstructured N terminus, which was removed for structural studies and subsequently determined to be required for enzymatic activity. Despite lacking sequence similarity to any protein of known three-dimensional structure, the tertiary structure of bacterial TPMT reveals a classical SAM-dependent methyltransferase topology, consisting of a seven-stranded beta-sheet flanked by alpha-helices on both sides. However, some deviations from the consensus topology, along with multiple insertions of structural elements, are evident. A review of the many experimentally determined tertiary structures of SAM-dependent methyltransferases demonstrates that such structural deviations from the consensus topology are common and often functionally important.
J Mol Biol 2003 Oct 24
PMID:Tertiary structure of thiopurine methyltransferase from Pseudomonas syringae, a bacterial orthologue of a polymorphic, drug-metabolizing enzyme. 1455 46

1. Pharmacogenomics is the study of the role of inheritance in variation in the drug response phenotype-a phenotype that can vary from adverse drug reactions at one end of the spectrum to lack of therapeutic efficacy at the other. 2. The thiopurine S-methyltransferase (TPMT) genetic polymorphism represents one of the best characterized and most clinically relevant examples of pharmacogenomics. This polymorphism has also served as a valuable "model system" for studies of the ways in which variation in DNA sequence might influence function. 3. The discovery and characterization of the TPMT polymorphism grew directly out of pharmacogenomic studies of catechol O-methyltransferase (COMT), an enzyme discovered by Julius (Julie) Axelrod and his coworkers. 4. This review will outline the process by which common, functionally significant genetic polymorphisms for both COMT and TPMT were discovered and will use these two methyltransferase enzymes to illustrate general principles of pharmacogenomic research-both basic mechanistic and clinical translational research-principles that have been applied to a series of genes encoding methyltransferase enzymes.
Cell Mol Neurobiol
PMID:Pharmacogenomics: catechol O-methyltransferase to thiopurine S-methyltransferase. 1680 86

Multiple drug strategies for many cancer types are now readily available and there is a clear need for tools to inform decision making on therapy selection. Although there is still a long way to go before pharmacogenomics achieves the goal of individualized selection of cancer treatment, promising progress is being made. Genetic testing for thiopurine methyltransferase (TPMT) variant alleles in patients prior to mercaptopurine administration, and for UGT1A1*28 in patients prior to administration of irinotecan therapy, along with the instigation of genotype-guided clinical trials (e.g. TYMS) are important advances in cancer pharmacogenomics. Markers for the toxicity and efficacy of many oncology drugs remain unknown; however, the examples highlighted here suggest progress is being made towards the incorporation of pharmacogenomics into clinical practice in oncology.
Mol Diagn Ther 2007
PMID:Impact of pharmacogenomics on clinical practice in oncology. 1739 43

Prospective clinical pharmacogenetic testing of the thiopurine S-methyltransferase gene remains to be realized despite the large body of evidence demonstrating clinical benefit for the patient and cost effectiveness for health care systems. We describe an entirely microchip-based method to genotype for common single nucleotide polymorphisms in the thiopurine S-methyltransferase gene that lead to serious adverse drug reactions for patients undergoing thiopurine therapy. Restriction fragment length polymorphism and allele-specific polymerase chain reaction have been adapted to a microfluidic chip-based polymerase chain reaction and capillary electrophoresis platform to genotype the common *2, *3A, and *3C functional alleles. In total, 80 patients being treated with thiopurines were genotyped, with 100% concordance between microchip and conventional methods. This is the first report of single nucleotide polymorphism detection using portable instrumentation and represents a significant step toward miniaturized for personalized treatment and automated point-of-care testing.
J Mol Diagn 2007 09
PMID:Microfluidic platform for single nucleotide polymorphism genotyping of the thiopurine S-methyltransferase gene to evaluate risk for adverse drug events. 2843 80

Environmental chemicals may be involved in the etiology of breast cancer. Among them, organophosphorous compounds are the most widely used pesticides because of their extensive use in agriculture, medicine and industry. The risk of breast cancer is associated with prolonged exposure to female hormones and is attributed to estrogen since prolonged stimulation by steroid hormones may increase cell division. The aim of the present study was to identify the differentially expressed genes encoding enzymes that are important to drug transport and metabolism in parathion- and estrogen-treated human breast epithelial cell lines using cDNA microarrays. MCF-l0F, an immortalized human breast epithelial cell line was treated with parathion and estrogen, either alone or in combination, and malignant cells were developed through a series of sequential steps. Differential expression from the drug metabolism gene array showed that 17 genes were found to be altered either by parathion or estrogen alone, or the combination of both. Among the genes altered by parathion in comparison to the control were CHST5, CHST6 and CHST7 (sulfotransferases); CYP2F1, CYP3A7 and CYP4F3 (CYPs); GSTP1, GSTT2 and MGST1 (GSTs); MT1X (metallothionein); TPMT (methyltransferase); UGT1A1 and UGT2B (UDP glycosyltransferases). The same genes were down-regulated in estrogen alone including several metallothioneins (MT1A, MT1E, MT1H, MT1L and MT2A). The combination of parathion and estrogen induced down-regulation of three sulfotransferases, CYP2F1 and CYP4F3, MGST1, all metallothioneins and TPMT genes. There was no change in CYP3A7, GSTP1, GSTT2, UGT1A1 and UGT2B genes in the presence of both substances. It can be concluded from this study that organophosphorous pesticides such as parathion in the presence of estradiol induced changes in human drug metabolism gene expression in breast cells.
Int J Mol Med 2007 Dec
PMID:Human drug metabolism genes in parathion-and estrogen-treated breast cells. 1798 97

There is wide variability in the response of individuals to standard doses of drug therapy. This is an important problem in clinical practice, where it can lead to therapeutic failures or adverse drug events. Polymorphisms in genes coding for metabolizing enzymes and drug transporters can affect drug efficacy and toxicity. Pharmacogenomics aims to identify individuals predisposed to high risk of toxicity and low response from standard doses of anticancer drugs. This chapter focuses on the clinical significance of polymorphisms in drug-metabolizing enzymes and drug transporters in influencing efficacy and toxicity of anticancer therapy. The most important examples to demonstrate the influence of pharmacogenomics on anticancer therapy are thiopurine methyltransferase (TPMT), UGT (uridine diphosphate glucuronosyltransferase) 1A1*28, and DPD (dihydropyrimidine dehydrogenase) *2A, respectively, for 6-mercaptopurine, irinotecan, and 5-fluorouracil therapy. However, in most other anticancer therapies no clear association has been found for polymorphisms in drug-metabolizing enzymes and drug transporters and pharmacokinetics or pharmacodynamics of anticancer drugs. Evaluation of different regimens and tumor types showed that polymorphisms can have different, sometimes even contradictory, pharmacokinetic and pharmacodynamic effects in different tumors in response to different drugs. The clinical application of pharmacogenomics in cancer treatment therefore requires more detailed information regarding the different polymorphisms in drug-metabolizing enzymes and drug transporters. A greater understanding of complexities in pharmacogenomics is needed before individualized therapy can be applied on a routine basis.
Methods Mol Biol 2008
PMID:Pharmacogenomics of drug-metabolizing enzymes and drug transporters in chemotherapy. 1837 Feb 31

Genetic polymorphism among patients with acute lymphoblastic leukemia (ALL) is an important factor in the effectiveness and toxicity of anti-leukemic drugs. Genotyping of various polymorphisms that impact the outcome of anti-leukemic drug therapy (pharmacogenetics) presents an attractive approach for developing individualized therapy. We developed an easy and accurate method of analyzing multiple genes using a small amount of DNA, which we termed TotalPlex amplification. We used 16 pairs of specific bulging specific primers (SBS primers) for simultaneous amplification of 16 loci in a single PCR tube. Sixteen single nucleotide polymorphisms (SNPs) (CYP3A4*1B A>G, CYP3A5*3 G>A, GSTP1 313 A>G, GSTM1 deletion, GSTT1 deletion, MDR1 exon 21 G>T/A, MDR1 exon 26 C>T, MTHFR 677 C>T, MTHFR 1298 A>C, NR3C1 1088 A>G, RFC 80 G>A, TPMT 238 G>C, TPMT 460 G>A, TPMT 719 A>G, VDR intron 8 G>A, VDR FokI T>C) that have been implicated in the pharmacogenetics of ALL therapy were analyzed by TotalPlex amplification and SNP genotyping. We successfully amplified specific gene fragments using 16 pairs of primers in one PCR reaction tube with minimal spurious amplification products using TotalPlex amplification coupled to a multiplexed bead array detection system. The genotypes of 16 loci from 34 different genomic DNA (gDNA) samples derived using the TotalPlex system were consistent with the results of several standard genotyping methods, including automatic sequencing, PCR restriction fragment length polymorphism (RFLP) analysis, PCR, and allele-specific PCR (AS-PCR). Thus, the TotalPlex system represents a useful method of amplification that can improve the time, cost, and sample size required for high-throughput pharmacogenetic analysis of SNPs.
Mol Cell Probes 2008 Jun
PMID:TotalPlex gene amplification using bulging primers for pharmacogenetic analysis of acute lymphoblastic leukemia. 1838 10


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