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

The thiopurine drugs, 6-mercaptopurine (6-MP), 6-thioguanine (6-TG) are commonly used cytotoxic agents. A derivative of 6-MP, azathioprine, is commonly used as an immunosuppressant. A prominent route for the metabolism of these agents is mediated by the enzyme thiopurine methyltransferase (TPMT). This enzyme exhibits considerable inter-individual variation in activity, partly due to the presence of common genetic polymorphisms, which influence cytotoxicity of the thiopurine drugs. Variations in the number of tandem repeats in the 5' promoter region have also been shown to influence TPMT expression in vitro. In this article, we review the impact of variations in TPMT activity on sensitivity to the thiopurine drugs in vitro and also in vivo in terms of their clinical efficacy and toxicity. A possible relationship between TPMT and secondary malignancies is also reviewed.
Invest New Drugs 2005 Dec
PMID:The thiopurines: an update. 1626 26

Azathioprine is a frequently used immunosuppressant for managing inflammatory bowel disease (IBD). In recent years the hepatotoxic profile of thiopurines has been recognised. We report the case of a 40-year-old man with Crohn's disease treated with azathioprine. After taking azathioprine (2.2 mg/kg daily) for two years, his liver function tests were found to be elevated. Moreover, a myelodepression was established as platelet and leucocytes counts were lowered. The 6-thioguaninenucleotide level was 738 picomoles/8 x 10(8) per red blood cell, which is well above the proposed upper limit of efficacy and associated with an increased risk of developing a myelodepression. Genotyping of the enzyme thiopurine methyltransferase revealed no mutant alleles. The ultrasonography and CT scan showed signs of portal hypertension (spleen 17 cm and widened splenic vein). A liver biopsy was performed and an incomplete septal liver cirrhosis was found. An upper endoscopy revealed oesophageal varices (grade 2 to 3). Autoimmune and viral liver diseases were ruled out by laboratory parameters. After cessation of therapy, all laboratory parameters normalised. Therefore, azathioprine is believed to be the causative factor for inducing the liver cirrhosis. Continuous monitoring of patients taking thiopurines is mandatory. The role of 6-thioguaninenucleotide levels in inducing myelotoxicity and hepatotoxicity is discussed.
Neth J Med 2005 Dec
PMID:Myelotoxicity and hepatotoxicity during azathioprine therapy. 1639 13

There is great heterogeneity in the way humans respond to medications, often requiring empirical strategies to define the appropriate drug therapy for each patient. Genetic polymorphisms in drug metabolizing enzymes, transporters, receptors, and other drug targets provide putative markers for predicting which patients will experience extreme toxicity and treatment failure. Both quantitative (allele frequency) and qualitative (specific allele) differences for polymorphic genes have been observed between different population groups. For example, the frequency of mutations in thiopurine methyltransferase is lower in Chinese than Caucasian populations. In addition, the predominant mutation responsible for deficient enzyme activity differs between the two populations (TPMT*l3C versus TPMT*3A). Understanding the influence of ethnicity on pharmacogenomics will allow for comprehensive strategies for using the genome to optimize therapy for patients throughout the world.
Curr Drug Targets 2006 Dec
PMID:Ethnic differences in pharmacogenetically relevant genes. 1716 39

Pharmacoeconomics and pharmacogenetics are two fields converging together as it is increasingly recognized that genetic markers predicting efficacy and toxicity to drugs can cost-effectively improve patient care. While pharmacogenetics aims at identifying genetic markers underlying the response to drugs, pharmacoeconomics aims at delivering healthcare cost-effectively. Several studies have investigated the potential cost-effectiveness of pharmacogenetic-based approaches. Recent evidences include screening for thiopurine methyltransferase gene polymorphisms to prevent azathioprine-induced myelosuppression, or screening for human leukocyte antigen (HLA)B5701 to prevent hypersensitivity reactions to abacavir therapy. Furthermore, examples suggesting a cost-effectiveness of markers predicting drug efficacy include screening the angiotensin-converting enzyme gene polymorphisms for statins therapy, the alpha-adducin gene variant for diuretic therapy and the assessment of human epidermal growth factor receptor (HER2) expression for trastuzumab therapy. However, thus far, all these pharmacoeconomic analyses are exploratory and validations in prospective randomized clinical trials are warranted.
Pharmacogenomics 2006 Dec
PMID:Overview of the pharmacoeconomics of pharmacogenetics. 1718 5

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

Azathioprine undergoes extensive metabolism in vivo. Most of its immunosuppressive and myelotoxic effects are exerted by the intracellular metabolites 6-thioguanine nucleotides (6-TGN). There is large individual variability in thiopurine pharmacokinetics. When transplant recipients are started on the standard azathioprine dosage, low and probably subtherapeutic 6-TGN concentrations [<100 pmol/8 x 10(8) red blood cells (RBC)] are measured in the majority of patients with normal kidney function. When renal function is severely impaired, 6-TGN concentrations rise 8- to 10-fold or higher. Due to genetic polymorphism, the activity of the enzyme thiopurine methyltransferase (TPMT) is intermediate to undetectable in approximately 11% of the population. With low TPMT activity, transmethylation is reduced and more intermediate metabolites are left for alternative pathways such as 6-TGN formation. High 6-TGN concentrations are associated with increased frequency and severity of leucopenia. It has been suggested that active monitoring of azathioprine to keep 6-TGN concentrations between 100 and 200 pmol/8 x 10(8) RBC may contribute to more effective treatment by reducing the incidence of rejection episodes and leucopenia. Such monitoring is currently being evaluated in a controlled, prospective study of renal allograft recipients.
BioDrugs 1997 Dec
PMID:Optimisation of azathioprine immunosuppression after organ transplantation by pharmacological measurements. 1803 Nov 7

Thiopurines are frequently used for the treatment of IBD. The complex pharmacology, metabolism, mechanism of action and toxicity profile of these immunosuppressive drugs have now been partly elucidated. The activity of thiopurines is partly mediated by the metabolite 6-thioguanosine 5'-triphosphate, which inhibits the function of the small GTPase Rac1, leading to apoptosis of activated T cells, and influences the conjugation of T cells with antigen-presenting cells. The activity of the enzyme thiopurine S-methyltransferase has a major influence on the bioavailability and toxicity of thiopurines, and several thiopurine metabolites might have adverse effects in patients. Myelotoxicity can be caused by grossly elevated levels of 6-thioguanine nucleotides, and elevated levels of 6-methylmercaptopurine ribonucleotides have been associated with hepatotoxicity. The sensitivity and specificity of these methylated metabolites for predicting thiopurine-induced liver enzyme abnormalities are, however, poor. 6-Thioguanine has been suggested as an alternative to the classical thiopurines azathioprine and 6-mercaptopurine for the treatment of IBD, but there are concerns about its toxicity profile, especially with regard to the induction of nodular regenerative hyperplasia of the liver. Data now suggest that the induction of nodular regenerative hyperplasia of the liver during 6-thioguanine therapy might be dose-dependent or dependent on the level of 6-thioguanine nucleotides.
Nat Clin Pract Gastroenterol Hepatol 2007 Dec
PMID:Drug Insight: pharmacology and toxicity of thiopurine therapy in patients with IBD. 1804 78

Recently, conventional therapies for inflammatory bowel disease (IBD) have not received the same amount of attention as biologic therapies, yet they remain the backbone of therapy for IBD because of their efficacy, safety, and relatively low cost. Advances in efficacy and safety continue because of modifications in drug dosing and monitoring. Higher doses of mesalamine per pill, together with once-daily dosing, may help to optimize drug delivery and patient compliance. Budesonide, an effective agent for both induction and short-term remission maintenance in Crohn's disease, is devoid of many of the toxicities common to corticosteroids. Assessments of thiopurine methyltransferase and metabolite levels are helping to fine-tune dose optimization for the thiopurines azathioprine and 6-mercaptopurine. The oral calcineurin inhibitors tacrolimus and cyclosporine have been shown to have expanded roles in IBD, and methotrexate may be useful in some patients with refractory ulcerative colitis. Probiotics are showing promise for maintenance of remission in Crohn's disease, ulcerative colitis, and pouchitis.
Curr Gastroenterol Rep 2008 Dec
PMID:Optimizing conventional therapy for inflammatory bowel disease. 1900 15

The frequency of allele variants of gene TPMT*2, *3A, *3B, and *3C was estimated in a population of 116 Brazilian children with acute lymphoblastic leukemia. The association between genotype and clinical and laboratory data obtained during chemotherapy maintenance phase and the correlation of intraerythrocyte concentration of 6-mercaptopurine metabolites (6-tioguanine nucleotide nucleotides and methylmercaptopurine) were analyzed. A multiplex amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) was used in DNA amplification. Twelve patients presented TPMT gene mutation, all in heterozygous form. The most frequent allele variation was TPMT*3A (3.9%), followed by *3C (0.9%), *2 (0.4%), and *3B (0%). There was no significant association between clinical and laboratory data and the presence of mutation in TPMT gene. Of the 36 patients who were monitored for 6-mercaptopurine metabolite levels, only 1 had the mutation. In this patient, high 6-tioguanine nucleotide and low methylmercaptopurine concentrations were found. Event-free survival (EFS) for the whole group was 73.4%. There was no significant difference in event-free survival in the comparison between the groups with and without mutation (P = 0.06).
Ther Drug Monit 2008 Dec
PMID:Thiopurine S-methyltransferase (TPMT) gene polymorphism in Brazilian children with acute lymphoblastic leukemia: association with clinical and laboratory data. 1905 72

Cisplatin is a widely used and effective chemotherapeutic agent, although its use is restricted by the high incidence of irreversible ototoxicity associated with it. In children, cisplatin ototoxicity is a serious and pervasive problem, affecting more than 60% of those receiving cisplatin and compromising language and cognitive development. Candidate gene studies have previously reported associations of cisplatin ototoxicity with genetic variants in the genes encoding glutathione S-transferases and megalin. We report association analyses for 220 drug-metabolism genes in genetic susceptibility to cisplatin-induced hearing loss in children. We genotyped 1,949 SNPs in these candidate genes in an initial cohort of 54 children treated in pediatric oncology units, with replication in a second cohort of 112 children recruited through a national surveillance network for adverse drug reactions in Canada. We identified genetic variants in TPMT (rs12201199, P value = 0.00022, OR = 17.0, 95% CI 2.3-125.9) and COMT (rs9332377, P value = 0.00018, OR = 5.5, 95% CI 1.9-15.9) associated with cisplatin-induced hearing loss in children.
Nat Genet 2009 Dec
PMID:Genetic variants in TPMT and COMT are associated with hearing loss in children receiving cisplatin chemotherapy. 2424 39


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