The frequency and distribution of thiopurine methyltransferase alleles in Caucasian and Asian populations

Long-term effect of NUDT15 R139C on hematologic indices in inflammatory bowel disease patients treated with thiopurine

BACKGROUND AND AIM

A missense variant of the nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15) gene (R139C) predisposes Asian patients with inflammatory bowel disease (IBD) to thiopurine-induced leukopenia. This study evaluates the long-term effect of NUDT15 R139C heterozygosity on hematological parameters during thiopurine administration.

METHODS

We enrolled 83 Japanese IBD patients who were on anti-tumor necrosis factor-α agents and had used thiopurine. NUDT15 R139C was genotyped by polymerase chain reaction. We retrospectively reviewed patient clinical charts to collect data on white blood cell (WBC) count, mean corpuscular volume (MCV), hemoglobin, and platelet count during the 24 months following thiopurine initiation.

RESULTS

The included patients had either Crohn's disease (54; 65.1%) or ulcerative colitis (29; 34.9%). Genotyping of NUDT15 R139C identified 62 patients (74.7%) of genotype C/C and 21 (25.3%) of genotype C/T. The median dose of thiopurine was lower in the C/T group than in the C/C group after starting thiopurine. At 6 months, the mean WBC count of the C/T group became significantly lower than that of the C/C group (P = 0.008) and remained lower through the 24 months. The C/T group developed grade 2-4 leukopenia by 6 months, which persisted through 12-24 months. The mean MCV in the C/T group became higher than that of the C/C group after 3 months.

CONCLUSIONS

NUDT15 R139C heterozygosity affected the WBC count and MCV for 24 months after thiopurine administration. Our results indicate that careful monitoring of leukopenia and dose adjustment are necessary throughout treatment in IBD patients heterozygous for the NUDT15 R139C.

Thiopurine Therapy in Patients With Inflammatory Bowel Disease: A Focus on Metabolism and Pharmacogenetics

Thiopurines have been widely used for the maintenance of remission or steroid sparing in patients with inflammatory bowel disease. However, potential drug-related adverse events frequently interfere with their use. Indeed, drug withdrawals associated with adverse reactions have been reported in approximately 25% of patients. To balance the efficacy, safety, and tolerability of thiopurines, regular monitoring of biomarkers (complete blood cell count, liver function test, and metabolic profiles), steady dose escalation, and pretreatment thiopurine S-methyltransferase (TPMT) genotype screening have been routinely recommended. However, the complex thiopurine metabolic pathway and individual differences attributed to pharmacogenetic diversity limit the effectiveness of these strategies in the optimization of thiopurine therapy. Recently, in an effort to facilitate more accurate and personalized prediction of thiopurine response or toxicity, novel genetic markers including NUDT15 and FTO genes were discovered. These discoveries are remarkable because TPMT screening has minimal efficacy for predicting myelosuppression especially in Asian populations, despite the fact that thee populations have a higher frequency of myelosuppression than Western populations. This review focuses on the current understanding of the metabolic pathway and the pharmacogenetics of thiopurines and suggests a personalized preventive strategy against potential adverse drug reactions to optimize their therapeutic application.

ITPA, TPMT, and NUDT15 Genetic Polymorphisms Predict 6-Mercaptopurine Toxicity in Middle Eastern Children With Acute Lymphoblastic Leukemia

Background: Acute lymphoblastic leukemia (ALL) is the most common cancer seen in children worldwide and in the Middle East. Although there have been major advances in treatment approaches for childhood ALL, serious toxicities do occur but with significant inter-individual variability. The aim of this study is to measure the frequency of polymorphisms in candidate genes involved in 6-Mercaptopurine (6-MP) disposition in a combined cohort of Middle Eastern Children with ALL, and evaluate whether these polymorphisms predict 6-MP intolerance and toxicity during ALL maintenance therapy.

Methods: The study includes children treated for ALL on two treatment protocols from two cohorts; one from Lebanon (N = 136) and another from Kurdistan province of Iran (N = 74). Genotyping for the following six candidate genetic polymorphisms: ITPA 94C > A (rs1127354) and IVS2+21A > C (rs7270101), TPMT*2 238G > C (rs1800462), TPMT*3B 460G > A (rs1800460) and *3C 719A > G (rs1142345), and NUDT15 415C > T (rs116855232) was performed and analyzed in association with 6-MP dose intensity and toxicity.

Results: As expected, TPMT and NUDT15 variants were uncommon. As for ITPA, both polymorphisms were more common in the Lebanese as compared to the Kurdish cohort with a minor allele frequency of 0.05 for 94C > A and 0.14 for IVS2+21A > C in the Lebanese only (N = 121), and of 0.01 for either ITPA polymorphism in Kurds. The most significant toxic effects were depicted with the NUDT15 polymorphism with a median 6-MP dose intensity of 33.33%, followed by 46.65% for TPMT*3A polymorphism, followed by 65.33% for two ITPA risk allele carriers and 74% for one ITPA risk allele carriers, in comparison to a median of 100% for the homozygous wild type in the combined cohort (P < 0.001). In addition, the onset of febrile neutropenia was significantly higher in variant allele carriers in the combined cohorts.

Conclusions: These data confirm the predictive role of TPMT, NUDT15, and ITPA in 6-MP intolerance in Middle Eastern children with ALL. Given the relatively high frequency of ITPA variants in our study and their significant association with 6-MP dose intensity, we recommend that physicians consider genotyping for ITPA variants in conjunction with TPMT and NUDT15 prior to 6-MP therapy in these children.

Correlation between Thiopurine S-Methyltransferase Genotype and Adverse Events in Inflammatory Bowel Disease Patients

Background and Objectives: In patients with inflammatory bowel diseases (IBD), the use of azathioprine results in adverse events at a rate of 5% to 20%. The aim of the study was to assess a possible correlation between genetic variability of the enzyme thiopurine S-methyltransferase (TPMT) and the development of toxicity to azathioprine. Materials and Methods: A retrospective, single center, blind, case-control study was conducted on 200 IBD patients, of whom 60 cases suspended azathioprine due to toxicity (leukopenia, pancreatitis, hepatitis, and nausea or vomiting), and 140 controls continued treatment with the drug without adverse events. Results: In the entire cohort, only 8 cases of heterozygous mutations of TPMT were observed, corresponding to 4% mutated haplotype rate, much lower than that reported in literature (close to 10%). No homozygous mutation was found. Regarding the TPMT allelic variants, we did not find any statistically significant difference between patients who tolerated azathioprine and those who suffered from adverse events. (OR = 0.77, 95% CI = 0.08-7.72; p = 0.82). Conclusions: According to our study, in IBD patients, the search for TPMT gene mutations before starting treatment with azathioprine is not helpful in predicting the occurrence of adverse events. Importantly, patients with allelic variants should not be denied the therapeutic option of azathioprine, as they may tolerate this drug.

Association between the c.415C > T, c.52G > A, and 36_37insGGAGTC polymorphisms of NUDT 15 and thiopurine-induced leukopenia, thiopurine intolerance, and severe hair loss: an updated meta-analysis

Purpose

As a common immunosuppressive and anticancer drug, thiopurine has achieved remarkable clinical success. However, higher inter-individual dose variability and unpredictable toxicity still challenge its use in clinical practices. Some studies indicate that NUDT 15 polymorphisms are associated with this variation, but specific correlation remains controversial. This meta-analysis assessed the association between three polymorphisms of NUDT 15 and thiopurine-induced toxicities.

Methods

Three databases were electronically searched: PubMed, Embase, and Web of Science. Only case–control studies and cohort studies were eligible. The overall pooled ORs and corresponding 95% CIs were used to represent the results.

Findings

We included 16 studies that focus on NUDT 15 c.415C > T, c.52G > A, and 36_37insGGAGTC polymorphisms in patients treated with thiopurine. Significant associations between NUDT 15 c.415C > T polymorphism and leukopenia were found in all genetic models (TC/TT vs CC, OR: 7.64, 95% CI: (6.19, 9.44), P<0.00001; TT vs CC/TC, OR: 29.66, 95% CI: (12.31, 71.46), P<0.00001; TT vs CC, OR: 45.60, 95% CI: (18.84, 110.37), P<0.00001; TC vs CC, OR: 6.41, 95% CI: (5.19, 7.94), P<0.00001; TT vs TC, OR: 6.38, 95% CI: (2.59, 15.72), P<0.00001), early/late leukopenia (in recessive and co-dominant model), leukopenia (grade 3–4), and severe hair loss in all genetic models. Besides, c.52G > A and 36_37insGGAGTC polymorphisms were also significantly associated with leukopenia. No significant association between NUDT 15 c.415C > T polymorphism and early/late leukopenia in the Chinese population was determined in the co-dominant model (TC vs CC).

Implications

NUDT 15 c.415C > T polymorphism could increase the risk of leukopenia, early/late leukopenia, leukopenia (grade 3–4), and severe hair loss. Meanwhile, c.52G > A and c.36_37insGGAGTC mutations also probably increase the risk of leukopenia. Preemptive tests for NUDT 15 polymorphisms are highly recommended to individualize the treatment of thiopurine for a better outcome with less toxicity.

Pharmacogenetics of thiopurines

Polychemotherapeutic protocols for the treatment of pediatric acute lymphoblastic leukemia (ALL) always include thiopurines. Specific approaches vary in terms of drugs, dosages and combinations. Such therapeutic schemes, including risk-adapted intensity, have been extremely successful for children with ALL who have reached an outstanding 5-year survival of greater than 90% in developed countries. Innovative drugs such as the proteasome inhibitor bortezomib and the bi-specific T cell engager blinatumomab are available to further improve therapeutic outcomes. Nevertheless, daily oral thiopurines remain the backbone maintenance or continuation therapy. Pharmacogenetics allows the personalization of thiopurine therapy in pediatric ALL and clinical guidelines to tailor therapy on the basis of genetic variants in TPMT and NUDT15 genes are already available. Other genes of interest, such as ITPA and PACSIN2, have been implicated in interindividual variability in thiopurines efficacy and adverse effects and need additional research to be implemented in clinical protocols. In this review we will discuss current literature and clinical guidelines available to implement pharmacogenetics for tailoring therapy with thiopurines in pediatric ALL.

Distribution of Genetic Polymorphisms of Genes Implicated in Thiopurine Drugs Metabolism

Thiopurine-S-methyltransferase (TPMT) and inosine triphosphate pyrophosphatase (ITPA) are crucial enzymes involved in the metabolism of thiopurine drugs. Significant interethnic variation in the expression of TPMT and ITPA is caused by single nucleotide polymorphisms of genes encoding these proteins. The aim of this study was to describe the distribution of TPMT and ITPA polymorphisms in healthy Tunisian subjects and to establish the metabolizer status of thiopurine drugs in this population. A total of 309 healthy Tunisian subjects were recruited among blood donors of Fattouma Bourguiba Hospital of Monastir. A written informed consent was obtained from all subjects. Whole blood samples were collected from every subject in ethylenediaminetetraacetic acid tubes. TPMT (c.238 G > C, c.460 G > A and c.719A > G) and ITPA (c.94C > A and IVS2+21A > C) mutations were genotyped using polymerase chain reaction-restriction fragment length polymorphism. The observed frequencies of TPMT*3A and TPMT*3C alleles were both 0.8%. The phenotype distribution of TPMT was bimodal: 96.8% of subjects were extensive metabolizers and 3.2% were intermediate metabolizers. Genotyping of ITPA revealed frequencies of 9% and 3% for IVS2+21A > C and c.94C > A mutations, respectively. Accordingly, a trimodal phenotype distribution was found: 75.4% of the subjects were extensive metabolizers, 23.4% were intermediate metabolizers, and 1.2% wereslow metabolizers. Combination of TPMT and ITPA genotyping has revealed that a quarter of the Tunisian Population carries polymorphisms that reduce the metabolic activities of these enzymes.

NUDT15 Polymorphism Confer Increased Susceptibility to Thiopurine-Induced Leukopenia in Patients With Autoimmune Hepatitis and Related Cirrhosis

The aim of this study was to investigate the influence of NUDT15 R139C and thiopurine S-methyltransferase (TPMT) on azathioprine (AZA) induced leukopenia in patients with autoimmune hepatitis (AIH) and related cirrhosis. A total of 149 Chinese AIH patients with a history of AZA treatment were retrospectively evaluated. The clinical and epidemiological characteristics of the patients were obtained from an electronic database and reviewed. NUDT15 (rs116855232) and TPMT^∗3C (rs1142345) SNPs were genotyped using a PCR method. Twelve patients developed leukopenia, and this adverse drug reaction was significantly associated with the T risk allele in NUDT15 [P < 0.00001, odds ratio = 20.41; 95% confidence interval (CI) (7.84, 53.13)], with the sensitivity and specificity of 91.67 and 89.05%, respectively. The median maintenance dosages for patients with the rs116855232 CC and CT genotypes were 1.23 (0.95, 1.53) mg ⋅ kg⁻¹ ⋅ d⁻¹ and 0.96 (0.83, 1.19) mg ⋅ kg⁻¹ ⋅ d⁻¹, respectively (P = 0.028). In contrast, no significant association was observed for TPMT^∗3C genotypes. Notably, subgroup analysis of the 13 patients with leukopenia before therapy, these white blood cell (WBC) counts did not show further reduction after AZA treatment and maintenance dosage was 1.13 (0.94, 1.60) mg ⋅ kg⁻¹ ⋅ d⁻¹. Therefore, NUDT15 polymorphism is significantly associated with thiopurine-induced leukopenia in Chinese patients with AIH and related cirrhosis. Adjusting the AZA dosage should be considered in patients according to the NUDT15 R139C genotypes.

Development of duplex-crossed allele-specific PCR targeting of TPMT*3B and *3C using crossed allele-specific blockers to eliminate non-specific amplification

Prospective testing for variants in the thiopurine S-methyltransferase (TPMT) is considered a key process in the development of thiopurine therapy. This testing is done to avoid toxicity and side effects in the management of diverse immunological and malignant conditions. Real-time fluorescent PCR techniques using duplex-crossed allele-specific primers in a single tube (DCAS-PCR) were developed in this study to genotype the common loss-of-function TPMT*3B c.460G > A (rs1800460) and TPMT*3C c.719A > G (rs1142345) usually occurring in individuals of Chinese ethnicity. In this method, several integrated strategies were used to completely eliminate the non-specific amplification that is commonly presented in traditional allele-specific (AS) PCR. These strategies include using AS-primers (ASP) that both are artificially mismatched in the penultimate positions and phosphorothioate modifications in the 5'-termini positions. In the assay, an AS-blocker was used, locus-specific TaqMan (LST) probes were used and we used at least two fragments were simultaneously amplified in a single tube which satisfy the thermodynamic characteristics of DNA polymerase to eliminate non-specific amplification. In a group of 200 unselected subjects, the results showed that 8 samples were heterozygous of TPMT*3C, and all samples possessed wild-type TPMT*3B. There was no non-specific amplification, and the genotypes were 100% consistent with Sanger sequencing.

Weekly Azathioprine Pulse versus Betamethasone Oral Mini-Pulse in the Treatment of Moderate-to-Severe Alopecia Areata

Background:

Corticosteroids are the most common agents used in the treatment of alopecia areata (AA), however, their long-term use is associated with severe side effects. Therefore, other immunosuppressive agents have been tried and azathioprine appears to be an effective and promising alternative.

Objective:

The main objective of this study was to compare the efficacy of 300 mg once weekly azathioprine pulse (WAP) and 5 mg betamethasone on 2 consecutive days every week in the management of AA.

Materials and Methods:

In this open-label, randomized comparative study, 50 patients of AA with >10% scalp area involvement were treated with either 300 mg WAP or 5 mg betamethasone on 2 consecutive days every week for 4 months or till complete scalp hair regrowth and followed up for next 5 months. Primary efficacy parameters were average percentage scalp hair regrowth and change in average Severity of Alopecia Tool (SALT) score at 4 months.

Results:

Twenty patients in WAP group and 21 patients in betamethasone group completed the study. The median percent scalp hair regrowth and the median change in SALT score was 44.52 and 9.5 in WAP group compared to 71.43 and 14 in betamethasone group at 4-month, respectively, which were statistically similar in two groups, however, side effects were significantly higher in betamethasone group. On further follow-up at 9 months, 10 (50%) patients in WAP group and 13 (62%) patients in betamethasone group achieved complete hair regrowth. Lack of control group was a limitation of our study.

Conclusion:

WAP and betamethasone therapy, both appear to be effective in the treatment of AA. However, betamethasone caused several side effects; therefore, WAP can be used as a better alternative to corticosteroids in AA.

Pharmacogenetics of treatments for inflammatory bowel disease

Inflammatory bowel disease is a chronic inflammation of the gut whose pathogenesis is still unclear. Although no curative therapy is currently available, a number of drugs are used in induction and maintenance therapy; however, for most of these drugs, a high inter-individual variability in response is observed. Among the factors of this variability, genetics plays an important role. Areas covered: This review summarizes the results of pharmacogenetic studies, considering the most important drugs used and in particular aminosalycilates, glucocorticoids, thiopurines, monoclonal antibodies and thalidomide. Most studies used a candidate gene approach, even if significant breakthroughs have been obtained recently from applying genome-wide studies. When available, also investigations considering epigenetics and pharmacogenetic dosing guidelines have been included. Expert opinion: Only for thiopurines, genetic markers identified as predictors of efficacy or adverse events have allowed the development of dosing guidelines. For the other drugs, encouraging results are available and great expectations rely on the study of epigenetics and integration with pharmacokinetic information, especially useful for biologics. However, to improve therapy of IBD patients with these drugs, for implementation in the clinics of pharmacogenetics, informatic clinical decision support systems and training about pharmacogenetics of health providers are needed.

Thiopurine Methyltransferase Genetic Polymorphisms and Activity and Metabolic Products of Azathioprine in Patients with Inflammatory Bowel Disease

BACKGROUND

Thiopurine S-methyltransferase (TPMT) is a cytoplasmic enzyme that catalyzes thiopurine drugs such as 6-mercaptopurine, 6-thioguanine, and azathioprine. There is a correlation between thiopurine drug metabolism, response, and toxicity and genetic polymorphism of TPMT. The aim of this study is to assess TPMT genetic polymorphisms activity and metabolic products of AZA in patients with IBD.

METHODS

Blood samples were obtained from 50 IBD unrelated patients from a private laboratory. We used polymerase chain reaction-restriction length polymorphism (PCR-RFLP) and allele-specific PCRbased assays to determine the TPMT gene for the different variants. A high-performance liquid chromatography system (HPLC) was carried out to determine the whole blood 6-TGN concentration. Determination of serum TMPT activity was done by ELISA kit.

RESULTS

In IBD patients, 46/50 (92%) subjects were homozygous for the wild-type allele (TPMT*1/*1). Mutant TPMT*1/*2 and TPMT*1/*3C alleles were found in 4/46 (8%) and 3/47 (6%) of IBD patients, respectively. TPMT*1/*3B variant was not detected in any of the IBD patients. TPMT enzyme activity was higher in wild-type than that mutant variants TPMT*1/*2 and TPMT*1/*3C, suggesting that there are statistically significant differences between 6-TG levels and polymorphisms of TMPT enzyme. 6-TG levels significantly increased in IBD patients mutant variants TPMT*1/*2 and TPMT*1/*3C.

CONCLUSIONS

Our results showed that TPMT polymorphisms are associated with 6-TGN levels in patients using AZA. This study suggests that AZA dosage may be determined according to the high or low prevalence of a TPMT genotype. Moreover, the results present the determination of metabolite for assessing possible safe effective dosage of the drug.

Revisiting the Role of Thiopurines in Inflammatory Bowel Disease Through Pharmacogenomics and Use of Novel Methods for Therapeutic Drug Monitoring

Azathioprine and 6-mercaptopurine, often referred to as thiopurine compounds, are commonly used in the management of inflammatory bowel disease. However, patients receiving these drugs are prone to developing adverse drug reactions or therapeutic resistance. Achieving predefined levels of two major thiopurine metabolites, 6-thioguanine nucleotides and 6-methylmercaptopurine, is a long-standing clinical practice in ensuring therapeutic efficacy; however, their correlation with treatment response is sometimes unclear. Various genetic markers have also been used to aid the identification of patients who are thiopurine-sensitive or refractory. The recent discovery of novel Asian-specific DNA variants, namely those in the NUDT15 gene, and their link to thiopurine toxicity, have led clinicians and scientists to revisit the utility of Caucasian biomarkers for Asian individuals with inflammatory bowel disease. In this review, we explore the limitations associated with the current methods used for therapeutic monitoring of thiopurine metabolites and how the recent discovery of ethnicity-specific genetic markers can complement thiopurine metabolites measurement in formulating a strategy for more accurate prediction of thiopurine response. We also discuss the challenges in thiopurine therapy, alongside the current strategies used in patients with reduced thiopurine response. The review is concluded with suggestions for future work aiming at using a more comprehensive approach to optimize the efficacy of thiopurine compounds in inflammatory bowel disease.

NUDT15 R139C Variants Increase the Risk of Azathioprine-Induced Leukopenia in Chinese Autoimmune Patients

The aim of this study was to investigate the influence of NUDT15 R139C, thiopurine S-methyltransferase (TPMT), and 6-TGN on azathioprine (AZA) induced leukopenia in Chinese autoimmune patients. Among 87 enrolled patients, 23 (26.4%) had leukopenia. The NUDT15 R139C variant was associated with leukopenia (p = 1.86 × 10⁻⁷; OR: 7.59; 95% CI: 3.16–18.21). However, TPMT genotype was not shown to be correlated with the incidence of leukopenia (p = 0.95). There was no significant difference of 6-TGN concentration between patients with or without leukopenia (p = 0.15) and no association was found in patients with NUDT15 R139C variants alleles (p = 0.62). Finally, we found that the range of 6-TGN concentrations in autoimmune diseases was much lower than the established 6-TGN monitoring range for inflammatory bowel diseases. Therefore, the variant of NUDT15 R139C is strongly associated with AZA-induced leukopenia in Chinese patients with various autoimmune diseases such as systemic lupus erythematosus, Sjögren's syndrome, etc.

Azathioprine-induced Agranulocytosis and Severe Alopecia After Kidney Transplantation Associated With a NUDT15 Polymorphism: A Case Report

BACKGROUND

Azathioprine (AZA) is the drug recommended for the continuation of immunosuppressive treatment after renal transplant in women during pregnancy.

CASE REPORT

A 37-year-old Japanese female developed agranulocytosis and severe alopecia after initiation of AZA (50 mg), used as an alternative to mycophenolate mofetil (MMF, 1000 mg) therapy in anticipation of a planned pregnancy. Within 4 days of the initiation of AZA therapy, the patient developed a high fever, leucopenia, and cranial alopecia. Genetic testing revealed a homozygous polymorphism of NUDT15 (rs116855232, NM_018283.3:c.415C>T: p.Arg139Cys), which has previously been identified as a risk factor for AZA-related complications in patients with inflammatory bowel disease.

CONCLUSION

Genetic screening for NUDT15 could contribute to the prevention of serious adverse reactions to AZA and provide the opportunity for personalized medicine. Identification of a safe alternative to MMF during pregnancy after a renal transplant is a problem to be resolved in the future.

NUDT15 R139C variation increases the risk of azathioprine-induced toxicity in Chinese subjects: Case report and literature review

INTRODUCTION

Azathioprine (AZA) is widely used as an immunosuppressive agent, and its efficacy has been recommended by many clinical studies. However, leukopenia, the most common toxicity, still restricts its clinical applications. Recent studies found that NUDT15 R139C polymorphism is strongly associated with AZA-induced leukopenia in Koreans. However, the follow-up studies available are all limited to inflammatory bowel disease (IBD). Here, we report a case of a Chinese patient with Sjögren syndrome (SS) with wild-type TPMT*3C who was diagnosed with AZA-induced severe toxicity due to NUDT15 mutation based on clinical and laboratory characteristics.

CASE PRESENTATION

A 22-year-old Chinese woman with SS developed severe leukopenia after AZA administration for 21 days. Detection of 6-thioguanine nucleotides (6-TGN) showed that the erythrocyte concentration had beyond the monitoring range, indicating that severe leukopenia might be caused by AZA. Furthermore, gene sequencing showed that NUDT15 R139C (poor metabolizer) homozygosity might explain this adverse event. Based on the evidence, AZA administration was immediately stopped and supportive treatments provided, and the patient eventually recovered.

CONCLUSION

In this report, we first provide detailed clinical and laboratory characteristics of AZA-induced leukopenia in a patient with SS with a mutant NUDT15 R139C genotype (TT allele) and normal TPMT activity. This case indicates that NUDT15 R139C and TPMT*3C genotypes, and more importantly, 6-TGN levels, should be routinely monitored for those administered with AZA to predict and prevent AZA-induced toxicity.

WITHDRAWN: Association between TPMT*3C and decreased thiopurine S-methyltransferase activity in patients with neuromyelitis optica spectrum disorders in China

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[Usefulness of thiopurine methyltransferase polymorphism study and metabolites measurement for patients treated by azathioprine]

Azathioprine is widely used in internal medicine and frequently implicated in occurrence of adverse events. Among these adverse events the bone marrow suppression, a dose-related one, is the most serious because of is potential morbidity and mortality. Severe myelosuppression, associated with abnormal AZA metabolism, is linked to the thiopurine methyltransferase (TPMT) genetic polymorphism that results in a high variability of its activity with 89% of patients with a normal activity, 11% with an intermediate activity, and 0.3% with very low activity leading to a very high risk of bonne marrow suppression. TPMT status can be assessed prior to AZA treatment by measuring enzyme activity or genotyping techniques to identify patients for which the standard dose is not advisable. Furthermore, azathioprine metabolites monitoring is helpful for the follow up of patients, especially in therapeutic failure, to distinguish non-compliant patients from under-dosed, "shunters" or resistant patients.

Influence of thiopurine methyltransferase gene polymorphism on Egyptian children with acute lymphoblastic leukaemia

Thiopurine methyltransferase (TPMT) gene polymorphism regulates thiopurine therapeutic efficacy and toxicity. The aim of this study was to determine the influence of TPMT gene polymorphism in Egyptian children with acute lymphoblastic leukaemia (ALL). Sixty-four patients with ALL, T lineage (27%) and pre-B phenotype (73%), who were treated with BFM 90 or CCG 1991 standard risk protocol, and who also experiencedmyleosuppresion toxicity and required interruption and/ormodification of thiopurine chemotherapy were recruited over a year period. Thirty-two patients were on maintenance and another 32 completed their chemotherapy. Seventy healthy age-matched and sex-matched children served as controls. They were subjected to clinical assessment, haematological panel investigations and TPMT gene polymorphism for G238C, G460A and A719G alleles assessment using PCRfollowed byRFLP analysis.Although none of the studied patients had themutantTPMTvariant alleles,myelosuppression toxicity in the form of different degree of neutropenia was detected in all patients. As a result of myelosuppression toxicity, most of the patients needed 6-MP dose modification either once (53.1%), twice (15.6%), or ≥ thrice (25.1%) during their maintenance course and 96.9% of the patients required to stop 6-MP for less than a week (62.5%), up to 2 weeks (28.1%), or > 2 weeks (6.3%). Patients also developed infection who mostly (71%) needed hospitalization. None of the studied G238C, G460A and A719G TPMT variant alleles were detected. Infections and febrile neutropenia were common causes of 6-PM dose modification and interruption.

Addition of Allopurinol for Altering Thiopurine Metabolism to Optimize Therapy in Patients with Inflammatory Bowel Disease

Thiopurine drugs, including azathioprine and 6-mercaptopurine, are used commonly in patients with inflammatory bowel disease for maintenance of remission. Although generally well tolerated, adverse effects lead to discontinuation in a significant minority of patients. Pharmacogenomic studies have suggested that metabolic breakdown of azathioprine in an individual is genetically determined. Coupled with the fact that certain thiopurine metabolites, notably 6-thioguanine nucleotide and 6-methylmercaptopurine, are associated with antiinflammatory effects and adverse effects, respectively, some investigators have examined intentionally shunting the metabolism of azathioprine toward increasing 6-thioguanine nucleotide levels by using low doses of the xanthine oxidoreductase inhibitor allopurinol to improve efficacy and decrease toxicity of azathioprine in patients with inflammatory bowel disease. We performed a search of the MEDLINE and Embase databases for basic and clinical research reports of this modality. Pertinent articles were retrieved, reviewed, and assessed by the authors. Case series, cohort studies, and one randomized trial have investigated adding allopurinol to azathioprine therapy in patients with inflammatory bowel disease. Most reports primarily examined metabolite levels in these patients. In general, the literature suggests that this modality was successful at significantly increasing 6-thioguanine nucleotide levels while decreasing 6-methylmercaptopurine levels. Several small reports have suggested that patients with increased 6-thioguanine nucleotide levels had improved symptoms or symptom remission. Adverse effects and discontinuation rates remained similar or were improved in patients who were taking a thiopurine and started allopurinol. In conclusion, the addition of allopurinol may be an option for optimizing thiopurine metabolite production in select patients with low 6-thioguanine nucleotide levels. Appropriate care and monitoring of these patients are mandatory to prevent neutropenia or other adverse effects.

A practical guide to thiopurine prescribing and monitoring in IBD

Thiopurines are often the mainstay of treatment for many patients with inflammatory bowel disease. As such, a general understanding of the evidence behind their use and of their metabolism is extremely useful in clinical practice. This review gives a practical overview of thiopurine metabolism, the importance of thiopurine S-methyltransferase testing prior to the start of therapy and the monitoring of thioguanine nucleotide levels while on treatment, guiding a personalised approach to optimising thiopurine therapy.

Measurements of 6-thioguanine nucleotide levels with TPMT and NUDT15 genotyping in patients with Crohn's disease

The association between the 6-thioguanine nucleotide (6-TGN) level and clinical remission in Crohn's disease (CD) remains controversial. Thiopurine-induced leukopenia is a life-threatening complication of CD in Asians that was recently shown to strongly correlate with NUDT15 genetic variants. This study aimed to determine the relationship between thiopurine metabolite levels and therapeutic response, and to investigate the association of NUDT15, TPMT, and thiopurine metabolites with leukopenia in patients with CD. We enrolled 165 adult patients with CD undergoing thiopurine treatment. Clinical evaluation and laboratory examinations were carried out every 2-3 months. We measured thiopurine metabolites levels and genotyped NUDT15 and TPMT. During the median 12-month observational period, 95 (67.9%) patients exhibited clinical response and 45 (32.1%) did not respond to the treatment. The median 6-TGN level was significantly higher in responders than in non-responders (P < 0.001). The odds ratio of patients with a 6-TGN level ≥230 pmol/8 × 108 red blood cells for showing a clinical response was 4.63 (95% CI 1.62-11.9). NUDT15 variant types were strongly associated with developing leukopenia. Patients with NUDT15 homozygous variant genotype developed severe early leukopenia with an average reduction of 88.2% (range, 84-94%) from the baseline white blood cell count at 4 weeks. Our findings support the role of therapeutic drug monitoring in thiopurine maintenance treatment to optimize thiopurine therapy, especially, for non-responding CD patients. Thiopurine treatment should not be recommended to patients with NUDT15 homozygous variant genotype due to severe early leukopenia.

Association between TPMT*3C and decreased thiopurine S-methyltransferase activity in patients with neuromyelitis optica spectrum disorders in China

AIM OF THE STUDY

Thiopurines are effective drugs in treating neuromyelitis optica spectrum disorders and other diseases. Thiopurines' toxicity is mainly imputed to thiopurine S-methyltransferase activity. In Chinese population, the most common and important variation of thiopurine S-methyltransferase is TPMT*3C (rs1142345). This study aims to reveal the association between thiopurine S-methyltransferase activity and genetic polymorphisms of thiopurine S-methyltransferase in patients with neuromyelitis optica spectrum disorders in China.

MATERIAL AND METHODS

A liquid chromatography tandem mass/mass method was used to evaluate the thiopurine S-methyltransferase activity by using 6-mercapthioprine as the substrate in human erythrocyte haemolysate via 1 h incubation at 37 °C to form its methylated product 6-methylmercaptopurine. The amount of 6-methylmercaptopurine was adjusted by haematocrit and normalized to 8 × 10⁸ erythrocytes. The selected polymorphisms of thiopurine S-methyltransferase were identified using MassARRAY system (Sequenom) and multiple SNaPshot technique.

RESULTS

In 69 patients with neuromyelitis optica spectrum disorders, thiopurine S-methyltransferase activity was 80.29-154.53 (127.51 ± 16.83) pmol/h/8 × 10⁸ erythrocytes. TPMT*3C (rs1142345) was associated with lower thiopurine S-methyltransferase activity (BETA = -25.37, P = 0.011). Other selected variants were not associated with thiopurine S-methyltransferase activity.

CONCLUSIONS

TPMT*3C affects TPMT activity in Chinese patients with neuromyelitis optica spectrum disorders. Further studies are warranted to confirm the results.

ABBREVIATIONS

TPRs = thiopurines; NMOSD = neuromyelitis optica spectrum disorders; TPMT = thiopurine S-methyltransferase; LC-MS/MS = liquid chromatography tandem mass/mass; 6-MMP = 6-methylmercaptopurine; IS = internal standard; SNP = single nucleotide polymorphism; MAF = minor allele frequency; HWE = Hardy-Weinberg equilibrium; BETA = regression coefficients; UTR-3 = untranslated region 3.

LC-MS/MS Analysis of Erythrocyte Thiopurine Nucleotides and Their Association With Genetic Variants in Patients With Neuromyelitis Optica Spectrum Disorders Taking Azathioprine

BACKGROUND

Azathioprine is a first-line drug in treating neuromyelitis optica spectrum disorders (NMOSD). To exhibit its bioactivity, azathioprine needs to be converted to thiopurine nucleotides (TPNs) including 6-thioguanine nucleotides (6-TGNs) and 6-methylmercaptopurine nucleotides (6-MMPNs) that are affected by genetic polymorphisms. This study aims to develop an LC-MS/MS method for the analysis of erythrocyte concentrations of TPNs and to evaluate their associations with variants of various genes (MTHFR, TPMT, HLA, SLC29A1, SLC28A2, SLC28A3, ABCB1, and ABCC4) in patients with NMOSD.

METHODS

Erythrocyte 6-TGNs and 6-MMPNs were converted to their free bases 6-thioguanine and 6-methylmercaptopurine derivative by 1-hour acid hydrolysis at 95°C. An LC-MS/MS method was developed, validated, and used to study 32 patients with NMOSD to determine these free bases. Genetic variants were identified by MassARRAY (Sequenom) and multiple SNaPshot techniques. The associations between genetic variants and the concentrations of TPNs or the 6-MMPNs:6-TGNs ratio were evaluated by PLINK software using linear regression.

RESULTS

Methanol and water were used for separation with a total run time of 6.5 minutes. The lowest limit of quantification was 0.1 μmol/L with an injection volume of 10 μL. rs10868138 (SLC28A3) was associated with a higher erythrocyte concentration of 6-TGNs (P = 0.031), whereas rs12378361 (SLC28A3) was associated with a lower erythrocyte concentration of 6-TGNs (P = 0.0067). rs507964 (SLC29A1) was significantly associated with a lower erythrocyte concentration of 6-MMPNs (P = 0.024) and a lower 6-MMPNs:6-TGNs ratio (P = 0.029).

CONCLUSIONS

An LC-MS/MS method for the analysis of erythrocyte TPNs was developed, validated, and used to study 32 patients with NMOSD. SLC29A1 and SLC28A3 were associated with the erythrocyte concentrations of TPNs and 6-MMPNs:6-TGNs ratio. Further studies are needed to confirm these results.

Prevalence of thiopurine S-methyltransferase gene polymorphisms in patients with inflammatory bowel disease from the island of Crete, Greece

BACKGROUND

There is evidence that genotyping for the thiopurine S-methyltransferase (TPMT) gene variants is useful for the prediction of response to thiopurine analogs (azathioprine and 6-mercaptopurine) in patients with inflammatory bowel disease (IBD). The aim of the present study was to determine the prevalence of TPMT gene polymorphisms in a genetic homogenous population of IBD patients in Crete and to correlate the results with adverse reactions to thiopurine drugs.

PATIENTS AND METHODS

Genotyping for the most common TPMT variants TPMT*2, TPMT*3A, TPMT3*C, and TPMT*3B was performed using the PCR-restriction fragment length polymorphism method in 223 consecutive IBD patients and 119 age-matched and sex-matched healthy controls. The hospital medical records were reviewed for thiopurine use in these patients and related adverse events.

RESULTS

The prevalence of TPMT variants TPMT*2, TPMT*3A, TPMT*3B, and TPMT*3C was 1.8, 2.7, 1.3, and 1.8%, respectively. The G238C mutation was detected in four (1.8%) out of 223 patients, three (1.3%) patients were carriers of the G460A mutation, four (1.8%) of the A719G mutation, and six (2.7%) of both G460A and A719G mutations. In healthy controls, only one (0.8%) carried both the G460A and the A719G mutation, whereas TPMT*2, TPMT*3C, and TPMT*3B were not detected. None of the genotypes was homozygous. A statistically significant correlation between the presence of the G460A mutation and the development of leucopenia after the administration of thiopurines was observed (P=0.048).

CONCLUSION

This study showed a lower frequency of total TPMT variants and a higher frequency of TPMT*3B in Cretan IBD patients compared with other Caucasian populations. The presence of the G460A mutation is associated with the development of leukopenia.

Thiopurine metabolite level and toxicity in Indians with inflammatory bowel disease

Background and Aim

A lower dose requirement and higher toxicity of thiopurine is reported in Asian patients with inflammatory bowel disease (IBD) as compared with Caucasian patients. These reports are based on thiopurine methyltransferase measurement studies rather than metabolite estimation.We studied the utility of thiopurine metabolite estimation in Indian patients with IBD and compared dose and toxicity with Asian and Caucasian patients.

Methods

In this prospective study, 6-thioguanine nucleotide (6-TGN) and 6-methylmercaptopurine levels were determined by HPLC in 76 IBD patients treated with thiopurines. The levels were correlated with dose, disease activity, and toxicity. The dose-related metabolite levels and toxicity were compared with Caucasian and Asian patients reported in literature.

Results

Of the 76 patients (32 women, mean age: 35.9 [SD: 14.54] years, 36 Crohn's disease and 40 ulcerative colitis), 1 non-compliant patient had undetectable level of metabolites. Of the 75 patients, 21(28%) had therapeutic level of 6-TGN, 37(49%) had subtherapeutic level and 17(23%) had supratherapeutic level. The 6-methylmercaptopurine levels ranged up to 4971 pmol/8 × 10⁸ red blood cells. Six (8%) patients showed toxicity. Thiopurine dose was optimized in 20 (26.31%) patients. Dose-based metabolite levels were comparable to Asian and Caucasian patients. The toxicity (8%) observed in our patients was less than that reported (12-39%).

Conclusion

Half of the patients in this study had low and a quarter had high 6-TGN levels. One-fourth of the patients needed dose modification. The dose-based metabolite levels were comparable and the toxicity was less than that reported in Asian and Caucasian patients.

Relationship between Azathioprine metabolites and therapeutic efficacy in Chinese patients with neuromyelitis optica spectrum disorders

BACKGROUND

Neuromyelitis optica spectrum disorders (NMOSD) are demyelinating autoimmune diseases in the central nervous system (CNS) that are characterized by a high relapse rate and the presence of anti-aquaporin 4 antibodies (AQP4-IgG) in the serum. Azathioprine (AZA) is a first-line immunomodulatory drug that is widely used for the treatment of patients with NMOSD. However, the efficacy and safety of AZA vary in different individuals.

METHOD

Thirty-two patients with NMOSD who regularly took AZA were enrolled in the study at Beijing Tiantan Hospital, Capital Medical University. The efficacy of AZA was evaluated using the expanded disability status scale (EDSS) and the annual relapse rate (ARR). The erythrocyte concentrations of AZA metabolites were detected using an LC-MS/MS method.

RESULTS

The erythrocyte concentrations of 6-thioguanine nucleotides (6-TGNs) and 6-methylmercaptopurine nucleotides (6-MMPNs) were 202.03 ± 63.35 pmol/8*10⁸ RBC and 1618.90 ± 1607.06 pmol/8*10⁸ RBC, respectively. After the patients had received AZA therapy for more than one year, the EDSS score decreased from 5.21 ± 0.24 to 2.57 ± 0.33 (p < 0.0001), and the ARR decreased from 1.41 ± 0.23 to 0.36 ± 0.09 (p < 0.0001). The 6-TGN and 6-MMPN levels were significantly different between the non-relapsed and relapsed groups (p < 0.0001, p = 0.006, respectively). A higher ARR was significantly correlated with higher erythrocyte concentrations of 6-TGNs (p < 0.0001) and 6-MMPNs (p = 0.004).

CONCLUSION

AZA can reduce the EDSS score and ARR in NMOSD patients. Additionally, the efficacy of AZA is significantly related to the erythrocyte concentrations of 6-TGNs and 6-MMPNs. Within the safe upper limits, a higher concentration of 6-TGNs is associated with better efficacy of AZA.

TRIAL REGISTRATION NUMBER

ISRCTN16551495 , retrospectively registered on May 22, 2017.

State of Art of Cancer Pharmacogenomics in Latin American Populations

Over the past decades, several studies have shown that tumor-related somatic and germline alterations predicts tumor prognosis, drug response and toxicity. Latin American populations present a vast geno-phenotypic diversity due to the great interethnic and interracial mixing. This genetic flow leads to the appearance of complex characteristics that allow individuals to adapt to endemic environments, such as high altitude or extreme tropical weather. These genetic changes, most of them subtle and unexplored, could establish a mutational profile to develop new pharmacogenomic therapies specific for Latin American populations. In this review, we present the current status of research on somatic and germline alterations in Latin America compared to those found in Caucasian and Asian populations.

Thiopurine S-methyltransferase polymorphisms in acute lymphoblastic leukemia, inflammatory bowel disease and autoimmune disorders: influence on treatment response

The thiopurine S-methyltransferase (TPMT) gene encodes for the TPMT enzyme that plays a crucial role in the metabolism of thiopurine drugs. Genetic polymorphisms in this gene can affect the activity of the TPMT enzyme and have been correlated with variability in response to treatment with thiopurines. Advances in the pharmacogenetics of TPMT allowed the development of dosing recommendations and treatment strategies to optimize and individualize prescribing thiopurine in an attempt to enhance treatment efficacy while minimizing toxicity. The influence of genetic polymorphisms in the TPMT gene on clinical outcome has been well-documented and replicated in many studies. In this review, we provide an overview of the evolution, results, conclusions and recommendations of selected studies that investigated the influence of TPMT pharmacogenetics on thiopurine treatment in acute lymphoblastic leukemia, inflammatory bowel disease and autoimmune disorders. We focus mainly on prospective studies that explored the impact of individualized TPMT-based dosing of thiopurines on clinical response. Together, these studies demonstrate the importance of preemptive TPMT genetic screening and subsequent dose adjustment in mitigating the toxicity associated with thiopurine treatment while maintaining treatment efficacy and favorable long-term outcomes. In addition, we briefly address the cost-effectiveness of this pharmacogenetics approach and its impact on clinical practice as well as the importance of recent breakthrough advances in sequencing and genotyping techniques in refining the TPMT genetic screening process.

Association of NUDT15 c.415C>T allele and thiopurine-induced leukocytopenia in Asians: a systematic review and meta-analysis

BACKGROUND

Thiopurines, commonly used to treat autoimmune conditions and cancer, can be limited by life-threatening leucopenia. However, whether NUDT15 (nucleoside diphosphate-linked moiety X-type motif 15) is associated with thiopurine-induced leucopenia in Asians is controversial.

METHODS

Relevant studies in English that were published until July 10, 2016 were identified through PubMed, EMbase, and other web knowledge databases. Study quality was assessed according to the Newcastle-Ottawa Scale (NOS) criteria. Summary risk ratio (RR) and 95% confidence intervals (CI) were estimated based on a fixed-effects model or a random-effects model, depending on the absence or presence of significant heterogeneity.

RESULTS

Seven studies of 1138 patients met our inclusion criteria. Random-effects model meta-analysis provided evidence that T carriers of NUDT15 c.415C>T were significantly correlated with high incidences of thiopurine-induced leukocytopenia [CT + TT vs. CC: RR = 3.79, 95%CI (2.64 ~ 5.44), P < 0.00001]. This correlation was especially strong in TT patients, where it was found to be significantly increased by 6.54-fold compared with CC patients [TT vs. CC: RR = 6.54, 95%CI (3.34 ~ 12.82), P < 0.00001]. We also found that the NUDT15 c.415C>T variant was common in Asians and Hispanics, but rare in Europeans and Africans; the frequency of the NUDT15 c.415C>T distribution varied substantially by race/ethnicity.

CONCLUSION

The results of this meta-analysis confirm that NUDT15 c.415C>T may be an important predictor of thiopurine-induced leukocytopenia in Asians. Genotype targeting of NUDT15 c.415C>T before initiating thiopurine treatment may be useful to limit leukocytopenia.

Genome-Wide Association Studies of Chemotherapeutic Toxicities: Genomics of Inequality

With an estimated global population of cancer survivors exceeding 32 million and growing, there is a heightened awareness of the long-term toxicities resulting from cancer treatments and their impact on quality of life. Unexplained heterogeneity in the persistence and development of toxicities, as well as an incomplete understanding of their mechanisms, have generated a growing need for the identification of predictive pharmacogenomic markers. Early studies addressing this need used a candidate gene approach; however, over the last decade, unbiased and comprehensive genome-wide association studies (GWAS) have provided markers of phenotypic risk and potential targets to explore the mechanistic and regulatory pathways of biological functions associated with chemotherapeutic toxicity. In this review, we provide the current status of GWAS of chemotherapeutic toxicities with an emphasis on examining the ancestral diversity of the representative cohorts within these studies. Persistent calls to incorporate both ancestrally diverse and/or admixed populations into genomic efforts resulted in a recent rise in the number of studies utilizing cohorts of East Asian descent; however, few pharmacogenomic studies to date include cohorts of African, Indigenous American, Southwest Asian, and admixed populations. Through comprehensively evaluating sample size, composition by ancestry, genome-wide significant variants, and population-specific minor allele frequencies as reported by HapMap/dbSNP using NCBI PubMed and the NHGRI-EBI GWAS Catalog, we illustrate how allele frequencies and effect sizes tend to vary among individuals of differing ancestries. In an era of personalized medicine, the lack of diversity in genome-wide studies of anticancer agent toxicity may contribute to the health disparity gap. Clin Cancer Res; 23(15); 4010-9. ©2017 AACR.

Role of Allopurinol in Optimizing Thiopurine Therapy in Patients with Autoimmune Hepatitis: A Review

Autoimmune hepatitis (AIH) is a chronic immune mediated liver disease characterized by elevated transaminases, hyper gammaglobulinemia, presence of autoantibodies and interface hepatitis in the absence of a known etiology of liver disease. Thiopurines (azathioprine [AZA]/6-mercaptopurine [6MP]) and steroids remain the first line of treatment of AIH in both children and adults. However, a small proportion of AIH patients are either non-responders or develop side effects with AZA. The metabolism of AZA is complex and mediated by multiple enzymes. After absorption and getting converted to 6MP, it is converted to 6-thiouric acid, 6-methyl mercaptopurine (6MMP) and 6-thioguanine (6TG) by different enzymes. Elevated 6MMP levels are associated with hepatotoxicity and also poor efficacy due to simultaneous lower levels of 6TG, which is the active drug metabolite related to both efficacy and myelosuppression. Allopurinol, a xanthine oxidase inhibitor shifts the metabolism of AZA away from 6MMP toward 6TG. This combination of allopurinol with reduced dose of AZA is an alternative to more expensive and toxic second line therapy to induce remission in patients with AIH. This article discusses the mechanism of action of allopurinol in inducing response to AZA, reviews the published literature on this combination therapy and gives guidelines on the use of allopurinol in patients with AIH.

Nucleoside diphosphate-linked moiety X-type motif 15 C415T variant as a predictor for thiopurine-induced toxicity in Indian patients

BACKGROUND AND AIM

Interindividual variation seen in the thiopurine metabolism is attributed to the genetic variant in thiopurine methyltransferase (TPMT) gene leading to myelosuppression. In Asians, the thiopurine-induced toxicity is not completely explained by TPMT variants. Literature indicates that a newer genetic variant in nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15) gene is associated with thiopurine intolerance. We aimed to determine the risk allele frequency of NUDT15 genetic variant and its association with thiopurine-induced toxicity in Indian patients.

METHODS

In this pilot study, 69 patients on thiopurine therapy were analyzed. The frequencies of thiopurine-induced leukopenia were recorded. NUDT15 (C415T) and TPMT (*2, *3A, *3B, and *3C) genotyping was performed using amplification refractory mutation system-polymerase chain reaction and restriction fragment length polymorphism technique. Results were validated by DNA sequencing.

RESULTS

The NUDT15 CC, CT, and TT genotypes were found to be 86.9%, 11.5%, and 1.5%, respectively, whereas TPMT genetic variants were absent. Of 60 patients without NUDT15 variant, none developed leukopenia, whereas of nine patients with NUDT15 variant, six developed leukopenia (P-value < 0.0001). The mean thiopurine dose of 1.01 and 0.73 mg/kg/day for patients with wild and mutant NUDT15 alleles, respectively, was statistically significant (P < 0.01). The sensitivity and specificity for NUDT15 variant were 100% and 95.2%, respectively.

CONCLUSIONS

The NUDT15 risk allele frequency was 7.2%. There are 6/69 (8.7%) patients who developed leukopenia and harbored NUDT15 variant, thus showing a strong association for thiopurine-induced toxicity. Hence, NUDT15 genotyping may be considered before thiopurine therapy in Indian patients.

Comparison of 6-mercaptopurine with 6-thioguanine for the analysis of thiopurine S-methyltransferase activity in human erythrocyte by LC-MS/MS

Thiopurines (TPDs) are first-line drugs in treating neuromyelitis optica spectrum disorders (NMOSD). Evaluation of thiopurine S-methyltransferase activity (TPMT), a major determinant of TPD toxicity, before TPD treatment using 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG) as substrate was suggested. However, the equivalent of the two substrates in TPMT activity evaluation was unknown, and an alternative substrate was required in TPMT activity evaluation in patients who were already taking 6-MP or 6-TG. Before evaluating the agreement of 6-MP and 6-TG in TPMT activity measurement in patients with NMOSD, the affinity of the two substrates for the active center of TPMT should be established. A computer-based simulation indicated that 6-MP and 6-TG had similar affinities for the two active sites of TPMT. According to the guidelines, an LC-MS/MS method was developed and validated to evaluate the TPMT activity in human erythrocyte hemolysate using 6-MP or 6-TG as substrates via 1 h incubation at 37°C. The method was applied in 81 patients with NMOSD. Evaluated by Bland-Altman plot, 6-methylmercaptopurine and 6-methylthioguanine represented TPMT activities were in agreement with each other. Further studies are warranted to confirm the results.

Pharmacogenetics of immunosuppressants: State of the art and clinical implementation - recommendations from the French National Network of Pharmacogenetics (RNPGx)

Therapeutic drug monitoring is already widely used for immunosuppressive drugs due to their narrow therapeutic index. This article summarizes evidence reported in the literature regarding the pharmacogenetics of (i) immunosuppressive drugs used in transplantation and (ii) azathioprine used in chronic inflammatory bowel disease. The conditions of use of currently available major pharmacogenetic tests are detailed and recommendations are provided based on a scale established by the RNPGx scoring tests as "essential", "advisable" and "potentially useful". Other applications for which the level of evidence is still debated are also discussed.

Frequency of thiopurine methyltransferase mutation in patients of Mediterranean area with inflammatory bowel disease and autoimmune disorders

BACKGROUND AND AIMS

Few studies exist on the frequency of thiopurine methyltransferase (TPMT) mutation in patients from Southern Europe. We aimed to evaluate the frequency of TPMT mutation in a homogeneous Sicilian cohort of patients with inflammatory bowel disease (IBD), autoimmune and hematological disorders, the rate of thiopurine-related adverse events, and its association with the TPMT genotype.

RESULTS

Among 105 patients with IBD, 45 with autoimmune disease, and 34 with hematologic diseases, the homozygous TPMT variant genotype was found in one patient only (0.5%), while the heterozygous TPMT genotype was identified in 8 patients (4.3%). In patients with IBD, leukopenia was observed in ten patients: one had the homozygous TPMT genotype, one the heterozygous genotype, and the remaining eight the wild type genotype.

CONCLUSIONS

The frequency of TPMT mutation in a Mediterranean area was low. TPMT genotyping is not a sensitive tool for predicting thiopurine-induced leukopenia.

Influences of XDH genotype by gene-gene interactions with SUCLA2 for thiopurine-induced leukopenia in Korean patients with Crohn's disease

BACKGROUND

The impact of genetic variation in the thiopurine S-methyltransferase (TPMT) gene on thiopurine-induced leukopenia has been well demonstrated. Although xanthine dehydrogenase (XDH) is the second major contributor to azathioprine breakdown, polymorphisms in XDH have rarely been studied in IBD patients. We aim to access association between XDH variants and thiopurine-induced leukopenia by gene-gene interaction in a Crohn's disease (CD) population.

STUDY

A total of 964 CD patients treated with thiopurines were recruited from a tertiary referral center. The association between four XDH variants (p.Gly172Arg, p.Asn1109Thr, p.Arg149Cys, and p.Thr910Lys) and thiopurine-induced leukopenia was analyzed in cases with early leukopenia (n = 66), late leukopenia (n = 264), and in controls without leukopenia (n = 632). Three non-synonymous SNPs, which we previously reported association with thiopurine-induced leukopenia, NUDT15 (p.Arg139Cys), SUCLA2 (p.Ser199Thr), and TPMT *3C were selected for epistasis analysis with the XDH variants.

RESULTS

There was no significant association for two variants of XDH and thiopurine-induced leukopenia. In the epistasis analysis, only XDH (p.Asn1109Thr) * SUCLA2 (p.Ser199Thr) showed a statistically significant association with early leukopenia [odds ratio (OR) = 0.16; p = 0.03]. After genotype stratification, a positive association on the background of SUCLA2 wild-type (199Ser) between the XDH (p.Asn1109Thr) and early leukopenia (OR = 4.39; p = 0.01) was detected.

CONCLUSION

Genes associated with thiopurine-induced leukopenia can act in a complex interactive manner. Further studies are warranted to explore the mechanisms underlying the effects of the combination of XDH (p.Asn1109Thr) and SUCLA2 (199Ser) on thiopurine-induced leukopenia.

NUDT15 polymorphisms are better than thiopurine S-methyltransferase as predictor of risk for thiopurine-induced leukopenia in Chinese patients with Crohn's disease

BACKGROUND

Thiopurine-induced leukopenia is the most common dangerous adverse event in Asians. NUDT15 R139C was recently proposed to be a promising biomarker for leukopenia with thiopurine therapy in Asians, but this has not been replicated in the Chinese population.

AIM

To investigate the influence of NUDT15 R139C, thiopurine S-methyltransferase (TPMT), 6-TGN and 6-MMPR on thiopurine-induced leukopenia in Chinese patients with Crohn's disease.

METHODS

Clinical and epidemiological characteristics were reviewed from medical records. NUDT15 R139C and TPMT were genotyped. 6-TGN/6-MMPR concentrations were measured with high-performance liquid chromatography (HPLC).

RESULTS

A total of 253 patients were included, 65 (25.7%) of whom experienced leukopenia. The median follow-up with thiopurine treatment was 38.0 weeks (range, 1-192 weeks). NUDT15 R139C was strongly associated with the incidence of leukopenia (70.2% mutation vs. 12.8% wild type; P=8.61×10^-19 ; odds ratio, 10.80; 95% CI, 5.89-19.83). However, TPMT genotype was not found to be correlated with the incidence of leukopenia (P = 0.44). In subgroup of NUDT15 wild type, there was significant difference of 6TGN concentration between patients with and without leukopenia (413.0 (174.2-831.4) vs. 279.7 (77.3-666.9) pmol/8 × 10⁸ RBC, P = 0.0055). In contrast, no association was found in patients with NUDT15 R139C variant alleles (P = 0.26). 6-MMPR was not correlated with leukopenia (P = 0.84).

CONCLUSIONS

In Chinese patients, it is strongly recommended to detect NUDT15 genotype rather than TPMT before initiating thiopurine drugs. 6TGN concentration should be routinely monitored in CD patients with NUDT15 wild type. As for CT genotype, starting at low dose and careful monitoring for leukopenia and 6TGN levels is recommended.

Pharmacogenomics in Pediatric Oncology: Review of Gene-Drug Associations for Clinical Use

During the 3rd congress of the European Society of Pharmacogenomics and Personalised Therapy (ESPT) in Budapest in 2015, a preliminary meeting was held aimed at establishing a pediatric individualized treatment in oncology and hematology committees. The main purpose was to facilitate the transfer and harmonization of pharmacogenetic testing from research into clinics, to bring together basic and translational research and to educate health professionals throughout Europe. The objective of this review was to provide the attendees of the meeting as well as the larger scientific community an insight into the compiled evidence regarding current pharmacogenomics knowledge in pediatric oncology. This preliminary evaluation will help steer the committee’s work and should give the reader an idea at which stage researchers and clinicians are, in terms of personalizing medicine for children with cancer. From the evidence presented here, future recommendations to achieve this goal will also be suggested.

[Not Available]

6-mercaptopurine, a key drug for the treatment of acute lymphoblastic leukaemia in children, is a prodrug metabolized into 6-thioguanine (6-TGN) which are the active compounds and into methylated metabolites, primary by thiopurine S-methyltransferase enzyme (TPMT). This enzyme displays important inter subject variability linked to a genetic polymorphism: when treated with standard doses of thiopurine, TPMT-deficient and heterozygous patients are at great risk for developing severe and potentially life-threatening toxicity (hematopoietic, hepatic, mucositis. . . ) but show a better survival rate while patients with high TPMT activity (wild type) present lower peripheral red blood cells 6-TGN concentrations and a higher risk of leukemia relapse. Genotyping remains crucial before 6-MP administration at diagnosis to identify patients with homozygous mutant TPMT genotype and therefore prevent severe and life-threatening toxicity, and to individualize therapy according to TMPT genotype. Follow-up of ALL treatment should preferentially be based on repeated determinations of intracellular active metabolites (6-thioguanine nucleotides) and methylated metabolites in addition to haematological surveillance.

NUDT15 variant is the most common variant associated with thiopurine-induced early leukopenia and alopecia in Korean pediatric patients with Crohn's disease

PURPOSE

Thiopurine-induced leukopenia is a relatively common adverse event related to thiopurine medication in Korean pediatric Crohn's disease. In addition to the mutations of TPMT gene, the NUDT15 c.415C>T variant was recently identified to have a strong association with thiopurine-induced early leukopenia. We conducted this study to define the incidence of azathioprine (AZA)-related leukopenia and to determine the incidence and characteristics of their genetic variants in Korean pediatric Crohn's disease patients.

PATIENTS AND METHODS

Patients diagnosed with pediatric Crohn's disease who had used AZA for more than 3 months were recruited. The dose and duration of medication and data regarding adverse events including leukopenia were collected. TPMT and NUDT15 gene sequencing was performed for patients who had experienced AZA-induced leukopenia.

RESULTS

A total of 81 patients had used AZA as a maintenance therapy of Crohn's disease. The mean dose of AZA was 1.88±0.39 mg/kg/day. Nine patients (11.1%) experienced AZA-induced leukopenia, and eight patients (9.9%) experienced AZA-induced early leukopenia. Among the eight early leukopenia patients, six patients (75.0%) harbored the NUDT15 c.415C>T variant and one patient (12.5%) had the TPMT c.719A>G (TPMT*3C) variant. All the three patients with NUDT15 c.415C>T homozygous variant suffered from alopecia totalis, and two of them experienced severe systemic infection. Three patients with the NUDT15 heterozygous variant are currently treated with AZA at a dose of 0.76 mg/kg/day.

CONCLUSION

Mutations of the NUDT15 and TPMT gene accounted for ∼88% of cases with thiopurine-induced early leukopenia. Extensive hair loss was a recognizable early symptom in patients with the homozygous NUDT15 c.415C>T variant. Sequencing of the NUDT15 genes can guide the clinicians before thiopurine medication. An alternative immunosuppressive medication is recommended for patients with homozygous NUDT15 c.415C>T variant. For those with the heterozygous variant, half the usual dose of AZA can achieve efficacy comparable to that for wild-type patients.

Review article: recent advances in pharmacogenetics and pharmacokinetics for safe and effective thiopurine therapy in inflammatory bowel disease

BACKGROUND

Azathioprine and mercaptopurine have a pivotal role in the treatment of inflammatory bowel disease (IBD). However, because of their complex metabolism and potential toxicities, optimal use of biomarkers to predict adverse effects and therapeutic response is paramount.

AIM

To provide a comprehensive review focused on pharmacogenetics and pharmacokinetics for safe and effective thiopurine therapy in IBD.

METHODS

A literature search up to July 2015 was performed in PubMed using a combination of relevant MeSH terms.

RESULTS

Pre-treatment thiopurine S-methyltransferase typing plus measurement of 6-tioguanine nucleotides and 6-methylmercaptopurine ribonucleotides levels during treatment have emerged with key roles in facilitating safe and effective thiopurine therapy. Optimal use of these tools has been shown to reduce the risk of adverse effects by 3-7%, and to improve efficacy by 15-30%. For the introduction of aldehyde oxidase (AOX) into clinical practice, the association between AOX activity and AZA dose requirements should be positively confirmed. Inosine triphosphatase assessment associated with adverse effects also shows promise. Nucleoside diphosphate-linked moiety X-type motif 15 variants have been shown to predict myelotoxicity on thiopurines in East Asian patients. However, the impact of assessments of xanthine oxidase, glutathione S-transferase, hypoxanthine guanine phosphoribosyltransferase and inosine monophosphate dehydrogenase appears too low to favour incorporation into clinical practice.

CONCLUSIONS

Measurement of thiopurine-related enzymes and metabolites reduces the risk of adverse effects and improves efficacy, and should be considered part of standard management. However, this approach will not predict or avoid all adverse effects, and careful clinical and laboratory monitoring of patients receiving thiopurines remains essential.

Clinical implication of thiopurine methyltransferase polymorphism in children with acute lymphoblastic leukemia: A preliminary Egyptian study

Background:

6-mercaptopurine (6-MP) is an essential component of pediatric acute lymphoblastic leukemia (ALL) maintenance therapy. Individual variability in this drug-related toxicity could be attributed in part to genetic polymorphism thiopurine methyltransferase (TPMT).

Aim:

To investigate the frequency of common TPMT polymorphisms in a cohort of Egyptian children with ALL and the possible relation between these polymorphisms and 6-MP with short-term complications.

Materials and Methods:

This study included 25 children. Data related to 6-MP toxicity during the maintenance phase were collected from the patients’ files. DNA was isolated and genotyping for TPMT G460A, and A719G mutations were performed by polymerase chain reaction-restriction fragment length polymorphism.

Results:

Twenty (80%) of the included 25 patients had a polymorphic TPMT allele. TPMT*3A was the most frequent (14/25, 56%), 8 patients were homozygous and 6 were heterozygous. TPMT*3C mutant allele was found in 4 patients (16%) in the heterozygous state while 2 patients (8%) were found to be heterozygous for TPMT*3B mutant allele. TPMT mutant patients, especially homozygous, were at greater risk of 6-MP hematological toxicity without significant difference regarding hepatic toxicity.

Conclusions:

TPMT polymorphism was common among the studied group and was associated with increased risk of drug toxicity. A population-based multi-center study is required to confirm our results.