Quantification of deoxythioguanosine in human DNA with LC-MS/MS, a marker for thiopurine therapy optimisation.

In the treatment of diseases such as acute childhood leukaemia (ALL) and inflammatory bowel disease (IBD), the thiopurines azathioprine, 6-mercaptopurine, and 6-thioguanine are used. Thiopurines are antimetabolites and immunomodulators used to maintain remission in patients. They are all prodrugs and must be converted into the competing antimetabolites thioguanosine triphosphate and deoxythioguanosine triphosphate for final incorporation into RNA or DNA.

No association between relapse hazard and thiopurine methyltransferase geno- or phenotypes in non-high risk acute lymphoblastic leukemia: a NOPHO ALL2008 sub-study.

Purpose: 6-mercaptopurine(6MP)/methotrexate maintenance therapy is essential to reduce relapse of childhood acute lymphoblastic leukemia (ALL). Common germline variants in TPMT cause low activity of thiopurine methyltransferase (TPMT) and higher 6MP metabolite (TGN) levels. Higher levels of TGNs incorporated into DNA (DNA-TG) and low TPMT activity have previously been associated with a lower relapse risk.

Pharmacogenetic studies of thiopurine methyltransferase genotype-phenotype concordance and effect of methotrexate on thiopurine metabolism.

The discovery and implementation of thiopurine methyltransferase (TPMT) pharmacogenetics has been a success story and has reduced the suffering from serious adverse reactions during thiopurine treatment of childhood leukaemia and inflammatory bowel disease. This MiniReview summarizes four studies included in Dr Zimdahl Kahlin's doctoral thesis as well as the current knowledge on this field of research. The genotype-phenotype concordance of TPMT in a cohort of 12 663 individuals with clinically analysed TPMT status is described.

The Role of TPMT, ITPA, and NUDT15 Variants during Mercaptopurine Treatment of Swedish Pediatric Patients with Acute Lymphoblastic Leukemia.

Objective: To evaluate the roles of thiopurine methyltransferase (TPMT), inosine triphosphatase (ITPA), and Nudix hydrolase 15 (NUDT15) in 6-mercaptopurine (6-MP) sensitivity during treatment of pediatric patients with acute lymphoblastic leukemia (ALL).

Study Design: The study included 102 pediatric patients with ALL subject to the Nordic society Of Paediatric Haematology and Oncology (NOPHO) ALL-2000 and ALL-2008 protocols. Episodes of neutropenia and febrile neutropenia, TPMT sequence variants, as well as 6-MP end doses, were collected retrospectively from medical records.

Comprehensive study of thiopurine methyltransferase genotype, phenotype, and genotype-phenotype discrepancies in Sweden.

Thiopurines are widely used in the treatment of leukemia and inflammatory bowel diseases. Thiopurine metabolism varies among individuals because of differences in the polymorphic enzyme thiopurine methyltransferase (TPMT, EC 2.1.

Role of TPMT and ITPA variants in mercaptopurine disposition.

Purpose: To explore the levels of thioguanine incorporated into DNA (DNA-TG), and erythrocyte levels of 6-thioguanine nucleotides (Ery-TGN) and methylated metabolites (Ery-MeMP) during 6-mercaptopurine (6MP)/Methotrexate (MTX) therapy of childhood acute lymphoblastic leukemia (ALL) and the relation to inosine triphosphatase (ITPA) and thiopurine methyltransferase (TPMT) gene variants.

Methods: Blood samples were drawn during 6MP/MTX maintenance therapy from 132 children treated for ALL at Rigshospitalet, Copenhagen. The samples were analysed for thiopurine metabolites and compared to TPMT (rs1800460 and rs1142345) and ITPA (rs1127354) genotypes.

One amino acid makes a difference-Characterization of a new TPMT allele and the influence of SAM on TPMT stability.

Thiopurine induced toxicity is associated with defects in the thiopurine methyltransferase (TPMT) gene. TPMT is a polymorphic enzyme, with most of the single nucleotide polymorphisms (SNPs) causing an amino acid change, altering the enzymatic activity of the TPMT protein. In this study, we characterize a novel patient allele c.

Interconnections between apoptotic and autophagic pathways during thiopurine-induced toxicity in cancer cells: the role of reactive oxygen species.

Thiopurines (azathioprine, 6-mercaptopurine and 6-thioguanine) are a class of genotoxic drugs extensively used in the treatment of various illnesses including leukemia. Their underlying molecular mechanism of action involves the activation of apoptosis and autophagy but remains widely unclear. Here we present evidence that autophagy induction by thiopurines is a survival mechanism that antagonizes apoptosis and is involved in degrading damaged mitochondria through mitophagy.

Pharmacogenetically based dosing of thiopurines in childhood acute lymphoblastic leukemia: influence on cure rates and risk of second cancer.

Background: Previous studies have indicated that patients with thiopurine methyltransferase (TPMT) low activity (TPMT(LA)) have reduced risk of relapse but increased risk of second malignant neoplasm (SMN) compared to patients with TPMT wild-type (TPMT(WT)) when treated with 6 MP maintenance therapy starting doses of 75 mg/m(2)/day. To reduce SMN risk, 6MP starting doses were reduced to 50 mg/m(2)/day for patients with TPMT heterozygosity in the Nordic Society of Paediatric Haematology and Oncology (NOPHO) ALL2000 protocol.

Procedure: We explored the pattern of SMN and relapse in the NOPHO ALL2000 protocol (n = 674) and NOPHO ALL92 protocol (n = 601) in relation to TPMT pheno- and/or genotype.

Comparison of three methods for measuring thiopurine methyltransferase activity in red blood cells and human leukemia cells.

Thiopurine efficacy is partly reflected by the genetic polymorphism of the thiopurine methyltransferase (TPMT) enzyme, which is responsible for variation in the metabolism, toxicity and therapeutic efficacy of the thiopurines azathioprine (AZA), 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG). Determination of TPMT activity before administration of thiopurines is thus crucial for individualized dosing in order to prevent toxicity in TPMT deficient individuals. These individuals must be treated with markedly lower (eg, 5-10% of the standard) doses of the prescribed medications.

Methotrexate binds to recombinant thiopurine S-methyltransferase and inhibits enzyme activity after high-dose infusions in childhood leukaemia.

Purpose: Important drugs in the treatment of childhood acute lymphoblastic leukaemia (ALL) are 6-mercaptopurine (6-MP) and methotrexate (MTX). Thiopurine methyltransferase (TPMT) is a polymorphic enzyme causing variability in 6-MP response and toxicity. The aim of this study was to investigate the fluctuation in TPMT enzyme activity over time and the effect of high-dose MTX infusions on TPMT enzyme activity and 6-MP metabolites in paediatric ALL patients.

Nomenclature for alleles of the thiopurine methyltransferase gene.

The drug-metabolizing enzyme thiopurine methyltransferase (TPMT) has become one of the best examples of pharmacogenomics to be translated into routine clinical practice. TPMT metabolizes the thiopurines 6-mercaptopurine, 6-thioguanine, and azathioprine, drugs that are widely used for treatment of acute leukemias, inflammatory bowel diseases, and other disorders of immune regulation. Since the discovery of genetic polymorphisms in the TPMT gene, many sequence variants that cause a decreased enzyme activity have been identified and characterized.

A skewed thiopurine metabolism is a common clinical phenomenon that can be successfully managed with a combination of low-dose azathioprine and allopurinol.

Background And Aims: A skewed thiopurine metabolism is a phenomenon associated with both poor treatment response and toxicity. Our aim was to evaluate the frequency of this phenomenon and the relationship to thiopurine methyltransferase (TPMT) function.

Methods: All thiopurine metabolite measurements in adult patients (n=4033) between January 2006 and April 2012 were assessed to evaluate the occurrence of a skewed metabolism and the relationship to TPMT genotype and activity.

Structural characteristics determine the cause of the low enzyme activity of two thiopurine S-methyltransferase allelic variants: a biophysical characterization of TPMT*2 and TPMT*5.

The enzyme thiopurine S-methyltransferase (TPMT) is involved in the metabolism of thiopurine drugs used to treat acute lymphoblastic leukemia and inflammatory bowel disease. Thus far, at least 29 variants of the TPMT gene have been described, many of which encode proteins that have low enzyme activity and in some cases become more prone to aggregation and degradation. Here, the two naturally occurring variants, TPMT*2 (Ala80 → Pro) and TPMT*5 (Leu49 → Ser), were cloned and expressed in Escherichia coli.

Genotyping should be considered the primary choice for pre-treatment evaluation of thiopurine methyltransferase function.

Background And Aims: A pre-treatment determination of the thiopurine S-methyltransferase (TPMT) genotype or phenotype can identify patients at risk of developing severe adverse reactions from thiopurine treatment. The risk of misclassifying a patient might be dependent on the method used. The aim of this study was to investigate the concordance between TPMT genotyping and phenotyping.

Characterization of a novel sequence variant, TPMT*28, in the human thiopurine methyltransferase gene.

Background: The activity of the human enzyme thiopurine methyltransferase (TPMT) varies greatly between individuals because of genetic polymorphism. TPMT is involved in the detoxification and activation of thiopurines such as 6-mercaptopurine, 6-thioguanine, and azathioprine. These drugs are used in the treatment of acute lymphoblastic leukemia and inflammatory bowel disease.