Variantes genéticas de la tiopurina metiltransferasa e incidencia de eventos adversos en pacientes con indicación de azatioprina / Genetic polymorphisms of thiopurine methyltransferase and incidence of adverse events in patients with medical indication of azathioprine

La azatioprina es una tiopurina que presenta rango terapéutico estrecho y marcada toxicidad hematológica y hepática. La tiopurina S-metiltransferasa es una enzima que metaboliza ese grupo de drogas. Mutaciones en el gen que codifica dicha enzima aumentan el riesgo de presentar eventos adversos, por lo que su estudio farmacogenético permite contar con información para el diseño de la estrategia terapéutica. Sin embargo, su utilidad en el medio local no está completamente establecida. Fueron incluidos 45 sujetos (13 hombres) con indicación de azatioprina. Se determinó la presencia de las mutaciones *2, *3A, *3B y *3C de TMPT por PCR-RFLP y se analizó la relación entre el genotipo y la incidencia de eventos adversos relacionados al fármaco. Nueve portaban al menos un alelo no funcional, uno de ellos con genotipo *3A/*3A. Se detectó toxicidad en 3 de los 18 que iniciaron tratamiento con azatioprina: 2 pacientes con genotipo normal presentaron eventos adversos leves, y el único evento adverso de gravedad (aplasia medular) ocurrió en el sujeto con genotipo homocigota mutado. El único que presentó genotipo homocigota mutado desarrolló el más grave de los eventos adversos registrados, a pesar de estar en tratamiento con dosis bajas de azatioprina. Por este motivo, la determinación del genotipo de la tiopurina metiltransferasa pareciera ser de utilidad, pero no reemplaza la necesidad de seguimiento clínico y bioquímico en pacientes en tratamiento con tiopurinas.

Azathioprine is a thiopurine which has a narrow therapeutic index and marked hematological and hepatic toxicity. Thiopurine s-methyltransferase is an enzyme involved in the metabolism of thiopurines. Mutations in the gene that encodes the enzyme may augment the risk of adverse events. For that reason, pharmacogenetic determinations prior to the initiation of therapy can provide useful information for the future therapeutic strategy. Nevertheless, its utility in the local environment is not completely established. Forty-five subjects (13 men) who had been prescribed azathioprine were included. The presence of *2, *3A, *3B and *3C mutations were determined by PCR-RFLP, and the relationship between genotype and incidence of adverse events related to the drug was analyzed. Nine carried at least one non-functional allele, one of them with *3A/*3A genotype. Among the eighteen patients who initiated treatment with azathioprine, toxicity was detected in 3 cases: 2 mild events were observed in patients with normal genotype, and the only serious event (bone marrow suppression) occurred in the individual with homozygous mutant genotype. The only homozygous mutant patient developed the most severe of the registered events, in spite of being under treatment with low doses of azathioprine. This is the reason why enzymatic determination could be of utility, even though it does not replace clinical and biochemical follow-up in patients under thiopurine treatment.

Successful Azathioprine Treatment with Metabolite Monitoring in a Pediatric Inflammatory Bowel Disease Patient Homozygous for TPMT*3C

Thiopurine S-methyltransferase (TPMT) methylates purine analogues, showing TPMT activity in inverse relation to concentrations of active metabolites such as 6-thioguanine nucleotide (6-TGN). With conventional dosing of thiopurines, patients with homozygous variant TPMT alleles consistently suffer from severe myelosuppression. Here, we report a patient with TPMT*3C/*3C who managed successfully with monitoring of thiopurine metabolites. The patient was an 18-year-old male diagnosed with Crohn's disease. The standard dose of azathioprine (AZA) (1.8 mg/kg/day) with mesalazine (55.6 mg/kg/day) was prescribed. Two weeks after starting AZA treatment, the patient developed leukopenia. The DNA sequence analysis of TPMT identified a homozygous missense variation (NM_000367.2: c.719A>G; p.Tyr240Cys), TPMT*3C/*3C. He was treated with adjusted doses of azathioprine (0.1-0.2 mg/kg/day) and his metabolites were closely monitored. Leukopenia did not reoccur during the follow-up period of 24 months. To our knowledge, this is the first case of a patient homozygous for TPMT*3C successfully treated with azathioprine in Korea. While a TPMT genotyping test may be helpful to determine a safe starting dose, it may not completely prevent myelosuppression. Monitoring metabolites as well as routine laboratory tests can contribute to assessing drug metabolism and optimizing drug dosing with minimized drug-induced toxicity.

6-Thioguanine-Induced Hepatic Sinusoidal Obstruction Syndrome in a Leukemic Child with TPMT Heterozygote / 임상소아혈액종양

Hepatic sinusoidal obstruction syndrome (hSOS) can be developed as a common complication after hematopoietic stem cell transplantation (HSCT), and rarely after 6-thioguanine-based chemotherapy without HSCT. A four-year-old boy with heterozygotic polymorphism for thiopurine methyltransferase (TPMT) developed hSOS after he received chemotherapy with cytarabine, cyclophosphamide, intrathecal methotrexate and 6-thioguanine (6-TG) as reconsolidation chemotherapy of acute lymphoblastic leukemia (ALL). He was treated with defibrotide, N-acetylcysteine, urusodeoxycholic acid, glutathione, and supportive care. He recovered completely in nine days without long-term complication, and completed chemotherapy with 6-mercaptopurine without severe complication. We report a case of hSOS developed in an ALL patient with TPMT heterozygote after 6-TG based reconsolidation chemotherapy.

6-Thioguanine-Induced Hepatic Sinusoidal Obstruction Syndrome in a Leukemic Child with TPMT Heterozygote / 임상소아혈액종양

Hepatic sinusoidal obstruction syndrome (hSOS) can be developed as a common complication after hematopoietic stem cell transplantation (HSCT), and rarely after 6-thioguanine-based chemotherapy without HSCT. A four-year-old boy with heterozygotic polymorphism for thiopurine methyltransferase (TPMT) developed hSOS after he received chemotherapy with cytarabine, cyclophosphamide, intrathecal methotrexate and 6-thioguanine (6-TG) as reconsolidation chemotherapy of acute lymphoblastic leukemia (ALL). He was treated with defibrotide, N-acetylcysteine, urusodeoxycholic acid, glutathione, and supportive care. He recovered completely in nine days without long-term complication, and completed chemotherapy with 6-mercaptopurine without severe complication. We report a case of hSOS developed in an ALL patient with TPMT heterozygote after 6-TG based reconsolidation chemotherapy.

Evaluation of thiopurine methyltransferase genotyping and enzyme activity detection in treatment of patients with inflammatory bowel disease / 中华消化杂志

Objective To assess the predictive value of thiopurine methyltransferase genotyping and enzyme activity in relation to side effects in patients with inflammatory bowel disease (IBD) who were treated with azathioprine (AZA). Methods One hundred and eleven IBD patients (26 with ulcerative colitis and 86 with Cronh's disease) with indication of AZA administration between April 2004 and Dec. 2009 were enrolled. All patients received 2 mg/kg of AZA daily. Polymerase chain reaction and high performance liquid chromatography were used to genotype the TPMT * 2, * 3A, * 3B, * 3C and to detect TPMT activity, respectively. The association of TPMT genotype and activity with side effects was analyzed in patients treated with AZA for 24 weeks or more, or in those discontinued AZA because of adverse effects. Results Adverse effects were reported in 38(33. 9%) patients, the most frequent being myelosuppression (20. 5%). The frequency of TPMT * 3C heterozygous mutation was 0. 9% (1/112). The TPMT activity was (12. 9±4. 8) U/ml RBC with unimodal distribution. One patient with TPMT * 3C heterozygous mutation developed myelosuppression at the 4th week after AZA treatment. The TPMP genotype myelosuppression patients. Conclusions TPMT genotype mutation and low enzyme activity can be used to predict myelosuppression with high specifically and low sensitivity. In patients treated with AZA, co-administration of 5-ASA results in a high frequency of myelosuppression with no effect on TPMT activity.

Thiopurine S-methyltransferase Polymorphisms and the Relationship between the Mutant Alleles and the Adverse Effects in Systemic Lupus Erythematosus Patients Taking Azathioprine / 대한류마티스학회지

OBJECTIVES: To elucidate the genetic basis for Thiopurine methyltransferase (TPMT) polymorphism and investigate the relationship between TPMT mutant and the adverse effect in patients with systemic lupus erythematosis (SLE) taking azathioprine (AZA) in Korea. METHODS: The TPMT genotype was determined in two hundred healthy adults and 342 patients with SLE by MALDI-TOF and correlated with the effects of clinical exposure to AZA. RESUTLS: TPMT polymorphism were detected in 2/200 healthy adults (1%), which were heterozygotes with TPMT*3C and TPMT*6 allele, respectively, and 17/342 (4.97%), which were 12 heterozygotes with TPMT*3C and 5 heterozygotes with TPMT*6 allele, respectively, which had a higher frequency of TPMT mutant alleles compared to the healthy controls (p=0.015). Severe nausea occurred in 4 patient with TPMT*3C allele, and severe bone marrow toxicity in a patient with TPMT*6 allele taking AZA. Twenty three in 94 (24.47%) SLE patients taking AZA were suspicious of the adverse effects such as leucopenia (n=17), nausea (n=4) and abnormal liver function test (n=1). AZA was relatively well tolerated among the rest of them. CONCLUSION: The heterozygote with TPMT*3C and *6 were frequently detected in the patient with SLE compared to healthy adults and there was no statistical correlation between TPMT genotype and AZA toxicity. TMPT genotyping cannot replace regular blood monitoring in SLE patients on AZA treatment.

Effects of five drugs including ciclosporin and nifedipine which were usually used in patients with kidney transplantation on erythrocyte thiopurine methyltransferase activity / 中国临床药理学与治疗学

AIM:To investigate the effects of five drugs which were usually used simultaneously with aza- thioprine(AZA)in patients with kidney transplantation: ciclosporin,hydrocortisone,nifedipine,captopril and al- lopurinol on erythrocyte thiopurine methyltransferase (TPMT)activity.METHODS:The erythrocyte TPMT activity of healthy volunteers was measured by high-per- formance liquid chromatography(HPLC).Sixteen volun- teers were chosen,in which 8 cases with intermediate TPMT activity and others with normal TPMT activity.The mean inhibition ratio of each drug concentration and the mean IC_(50)values of the inhibitors were determined.RE- SULTS:Ciclosporin,hydrocortisone,captopril and allo- purinol had nearly no impacts on TPMT activity.Nifedip- ine highly inhibited TPMT activity in vitro,the mean IC_(50)value in intermediate TPMT activity group was(24?17)?g/mL and in normal TPMT activity group was(12?10)?g/mL.CONCLUSION:The co-administration of nifedipine and thiopurines may lead to drug interactions.