Genotype-based Treatment With Thiopurine Reduces Incidence of Myelosuppression in Patients With Inflammatory Bowel Diseases

Therapeutic Drug Monitoring in Patients with Systemic Lupus Erythematosus: Utility and Gaps

Despite advances in the treatment of patients with systemic lupus erythematous (SLE), outcomes have remained suboptimal. Persistent disease activity, patient comorbidities and drug toxicities contribute to the accrual of progressive irreversible damage and high rates of morbidity and mortality. Currently, similar drug doses and regimens are promulgated in the treatment guidelines for all SLE patients, despite the vast differences in patient and environmental factors that affect the drugs' metabolism and blood concentrations. This causes a disconnect between drug dosing and drug blood concentrations, which can then result in unpredictability in drug toxicities and therapeutic effects. In this review, we discuss commonly used oral immunosuppressive medications in SLE, their pharmacogenomics, and factors affecting their metabolism and blood concentrations. Further, we highlight the role of therapeutic drug monitoring in SLE, which is the first accessible step to individualising therapy.

Prevalence of NUDT15 Genetic Variants and Incidence of Thiopurine-induced Leukopenia in Inflammatory Bowel Disease: A Systematic Review and Meta-analysis

BACKGROUND AND AIMS

Nudix hydrolase 15 [NUDT15] genetic variants confer an increased risk of thiopurine-induced leukopenia [TIL]; however, their global prevalence in inflammatory bowel disease [IBD] patients is unknown. We aimed to evaluate the global prevalence of NUDT15 variants in IBD patients and incidence of TIL in these patients.

METHODS

Six databases were searched from inception until July 2022. Studies reporting the frequency of any NUDT15 variant and/or frequency of leukopenia in adult IBD patients with these variants were included. A random effects model was performed to estimate the pooled prevalence of variants, incidence of early [≤8 weeks] and late [>8 weeks] leukopenia, and relative risk of developing leukopenia.

RESULTS

Twenty studies comprising 5232 patients were included. The pooled prevalence of the *1/*3 c.415C > T C/T diplotype was 13% (95% confidence interval [CI]: 10-18%), *3/*3 c.415C > T T/T diplotype was 2% [95% CI: 1-2%], *1/*5 c.52G > A G/A diplotype was 2% [95% CI: 1-3%], and *1/*6 c.36_37insGGAGTC ins/- diplotype was 7% [95% CI: 4-12%]. The pooled prevalence of *1/*3 was high in Japanese [20%, 95% CI: 16-24%] and Chinese patients [18%, 95% CI: 12-27%]. The incidence of early leukopenia was 20% [95% CI: 16-26%] in *1/*3 patients, 99% [95% CI: 7-100%] in *3/*3 patients, and 49% [95% CI: 29-69%] in *1/*6 patients. The incidence of late leukopenia was 36% [95% CI: 26-49%] in *1/*3 patients.

CONCLUSIONS

NUDT15 variants are common and strongly predict TIL in IBD patients. Pre-treatment NUDT15 genotyping should be considered particularly in Asian populations, to guide thiopurine dosing and prevent myelotoxicity.

Usefulness and difficulties with the thiopurine pharmacogenomic NUDT15 genotyping test: Analysis of real-world data in Japan

The usefulness of NUDT15 genotyping as a pharmacogenomic test for thiopurine has been established. The first such test developed to date, NUDT15 genotyping was approved for reimbursement in Japan in February 2019 for all indicated patients. We retrospectively examined claims data in Japan and confirmed that the proportion of patients who undergo genotyping before initiating a new thiopurine regimen has increased; furthermore, genotyping has improved the rate of treatment continuation and reduced on-treatment hospitalization. However, the genotyping rate before thiopurine induction was >50% for patients with inflammatory bowel disease and <20% for those with other immune-related diseases, indicating significant variation by disease field. Additionally, over 10% of tests were found to have been performed inappropriately, such as multiple genotyping of the same patient or testing more than 2 weeks after starting treatment. Although NUDT15 genotyping for patients requiring thiopurine treatment has been shown to improve thiopurine treatment continuation rate, measures are required to address the systematic issues identified in our analysis.

The Role of Pharmacogenetics in the Therapeutic Response to Thiopurines in the Treatment of Inflammatory Bowel Disease: A Systematic Review

This study focuses on the use of thiopurines for treating inflammatory bowel diseases (IBD). These drugs undergo enzymatic changes within the body, resulting in active and inactive metabolites that influence their therapeutic effects. The research examines the role of genetic polymorphisms in the enzyme thiopurine S-methyltransferase (TPMT) in predicting the therapeutic response and adverse effects of thiopurine treatment. The TPMT genotype variations impact the individual responses to thiopurines. Patients with reduced TPMT activity are more susceptible to adverse reactions (AEs), such leukopenia, hepatotoxicity, pancreatitis, and nausea, which are common adverse effects of thiopurine therapy. The therapeutic monitoring of the metabolites 6-thioguanine nucleotides (6-TGN) and 6-methyl mercaptopurine (6-MMP) is proposed to optimize treatment and minimize AEs. Patients with higher 6-TGN levels tend to have better clinical responses, while elevated 6-MMP levels are linked to hepatotoxicity. Genotyping for TPMT before or during treatment initiation is suggested to tailor dosing strategies and enhance treatment efficacy while reducing the risk of myelosuppression. In conclusion, this study highlights the importance of considering genetic variations and metabolite levels in optimizing thiopurine therapy for IBD patients, focusing on balance therapeutic efficacy with the prevention of adverse effects and contributing to personalized treatment and better patient outcomes.

Time to incorporate preemptive NUDT15 testing before starting thiopurines in inflammatory bowel disease in Asia and beyond: a review

INTRODUCTION

Thiopurine toxicity is related to genetic polymorphism. Thiopurine methyltransferase (TPMT) variants do not explain thiopurine toxicity in more than half of patients. Asians, despite the low prevalence of TPMT variants, are more susceptible to thiopurine toxicity. Since 2014, studies from many Asian countries have shown a strong association between nucleoside diphosphate-linked moiety X-type motif (NUDT) 15 polymorphism and thiopurine-induced myelotoxicity.

AREAS COVERED

An English language literature search was performed for TPMT and NUDT15 genetic variants in inflammatory bowel disease and other diseases. This article discusses the merits of preemptive NUDT15 and TPMT testing in Asian and non-Asian IBD populations.

EXPERT OPINION

The NUDT polymorphism occurs in up to 27% of the Asian and Hispanic population. Hematological toxicity occurs in up to one-third of patients with this genetic variant. Given this, preemptive testing for NUDT15 variant is worthwhile and is probably more cost-effective than TPMT testing in these groups. Prevalence of NUDT15 variants is low in non-Finnish European population, but NUDT15 variants have been linked to myelotoxicity along with TPMT genetic variants. NUDT15 preemptive testing should be considered in the migrant Asian population in Europe and North America and in Caucasian populations who develop myelotoxicity.

Safety and efficacy of personalized versus standard initial dosing of thiopurines: Systematic review and meta-analysis of randomized trials

BACKGROUND

Pretherapy assessment of specific genetic polymorphism (TPMT, NUDT15, FTO, RUNX1, etc) or enzyme levels (for TPMT) may help personalize the dose of thiopurines and avoid adverse effects.

RESEARCH DESIGN AND METHODS

A systematic review of randomized controlled trials (RCTs) comparing personalized versus standard strategy for initial thiopurine dosing was performed. The electronic databases were searched on 27 September 2022. The outcomes were overall adverse effects, myelotoxicity, drug interruptions, and therapeutic efficacy with either strategy. The certainty of evidence was assessed using GRADE methodology.

RESULTS

We included six randomized trials, done dominantly in patients with inflammatory bowel disease (IBD). The personalized strategies were genotype testing in 4 trials (TPMT in three trials, NUDT15 in two) and enzyme levels for TPMT in two trials. The pooled risk of myelotoxicity in personalized dosing was lower [RR = 0.72 (95%CI, 0.55-0.94, I2 = 0%)]. The pooled risk of pancreatitis (RR = 1.10I, 0.78-1.56, I2 = 0%), hepatotoxicity (RR = 1.13, 0.69-1.88, I2 = 45), and GI intolerance (RR = 1.01, 0.92-1.10, I2 = 0) were similar in two groups. The pooled risk of drug interruption in individualized dosing was similar to the standard dosing group (RR = 0.97, I2 = 68%).

CONCLUSION

Personalized testing-based initial thiopurine dosing is protective against myelotoxicity as compared to standard weight-based dosing.

m6A modification in inflammatory bowel disease provides new insights into clinical applications

Inflammatory bowel disease (IBD) results from a complex interplay between genetic predisposition, environmental factors, and gut microbes. The role of N6-methyladenosine (m6A) methylation in the pathogenesis of IBD has attracted increasing attention. m6A modification not only regulates intestinal mucosal immunity and intestinal barrier function, but also affects apoptosis and autophagy in intestinal epithelial cells. Additionally, m6A modification participated in the interaction between gut microbes and the host, providing a novel direction to explore the molecular mechanisms of IBD and the theoretical basis for specific microorganism-oriented prevention and treatment measures. m6A regulators are expected to be biomarkers for predicting the prognosis of IBD patients. m6A methylation may be utilized as a novel target in the management of IBD. This review focused on the recent advances in how m6A modification causes the initiation and development of IBD, and provided new insights into optimal prevention and treatment measures for IBD.

[Treatment of Autoimmune Hepatitis]

Autoimmune hepatitis (AIH) is a chronic liver disease, characterized by elevated levels of transaminases, immunoglobulin G, and positive autoantibodies. The disease course is dynamic and presents heterogeneous disease manifestations at diagnosis. This review summarizes the issues regarding the treatment and monitoring of AIH in adult patients. Glucocorticoids and azathioprine are the first line of treatment. Alternative first-line treatments include budesonide or mycophenolate mofetil (MMF). Although no randomized controlled trials have been performed, MMF, cyclosporine, tacrolimus, 6-mercaptopurine, 6-thioguanine, allopurinol, sirolimus, everolimus, infliximab, or rituximab have been attempted in patients not responding to or intolerant to first-line treatments. Most patients require life-long special monitoring, with or without maintenance treatment.

DNA-Thioguanine Nucleotides as a Marker for Thiopurine Induced Late Leukopenia after Dose Optimizing by NUDT15 C415T in Chinese Patients with IBD

Thiopurine dose optimization by thiopurine-S-methyltransferase (TPMT) or nudix hydrolase-15 (NUDT15) significantly reduced early leucopenia in Asia. However, it fails to avoid the late incidence (> 2 months). Although laboratory monitoring of 6-thioguanine nucleotides (6TGN) to optimize thiopurine dose was suggested in White patients the exact association between leucopenia and 6TGN was controversial in Asian patients. In the present study, we aimed to explore whether DNA-thioguanine nucleotides (DNA-TGs) in leukocytes, compared with 6TGN in erythrocytes, can be a better biomarker for late leucopenia. This was a prospective, observational study. Patients with inflammatory bowel disease (IBD) prescribed thiopurine from February 2019 to December 2019 were recruited. Thiopurine dose was optimized by NUDT15 C415T (rs116855232). DNA-TG and 6TGN levels were determined at the time of late leucopenia or 2 months after the stable dose was obtained. A total of 308 patients were included. Thiopurine induced late leucopenia (white blood cells < 3.5 × 10⁹ /L) were observed in 43 patients (14.0%), who had significantly higher DNA-TG concentration than those without leucopenia (P = 4.1 × 10^-9 , 423.3 (~ 342.2 to 565.7) vs. 270.5 (~ 188.1 to 394.3) fmol/μg DNA). No difference in 6TGN concentrations between leucopenia and non-leucopenia was found. With a DNA-TG threshold of 340.1 fmol/μg DNA, 83.7% of leucopenia cases could be identified. Multivariate analysis showed that DNA-TG was an independent risk factor for late leucopenia. Quantification of DNA-TG, rather than 6TGN, can be applied to gauge thiopurine therapy after NUDT15 screening in Chinese patients with IBD.

Role of Pharmacogenomics in the Efficacy and Safety of Thiopurines in Inflammatory Bowel Disease: A Systematic Review and Meta-analysis

BACKGROUND

Thiopurines' toxicity often leads to dose reduction or discontinuation. This systematic review aims to synthesize the evidence on the effect of genotype-based dosing of thiopurines on treatment efficacy and safety in inflammatory bowel disease (objective #1), and the association between genotype status and the efficacy and safety profile (objective #2).

METHODS

The Cochrane Library, MEDLINE, and EMBASE were searched in August 2021. A total of 80 studies (19,859 individuals) were included. Meta-analyses for mortality, different types of adverse events (AEs), withdrawal due to AE, change in disease activity and clinical remission were performed following mainly a fixed-effects model. PROSPERO registration: CRD42020148130.

RESULTS

Genotype-based dosing was associated to a significantly lower incidence of hematologic AEs (risk ratio=0.71; 95% CI: 0.56-0.90; I2: 47%; 4 randomized controlled trials; moderate quality), which may be attributable to nudix hydrolase 15 (NUDT15) testing more than to thiopurine methyltransferase (TPMT) genotyping. No differences were found in other outcomes. Mutations in TPMT and NUDT15 genes were associated to a higher probability of serious AEs [odds ratio (OR) TPMT=4.98; OR NUDT15=11.44], hematologic AEs (OR TPMT=3.18), and serious hematologic AEs (OR TPMT=7.88; OR NUDT15=12.83). TPMT was also associated with a higher risk of withdrawals due to AEs (OR=3.38), and NUDT15 with gastrointestinal AEs (OR=2.04). Mutations in the ITPA gene did not lead to significant differences. Evidence of an association between other genes and clinical outcomes is still scarce.

CONCLUSIONS

Mutations in TPMT and NUDT15 genes predispose patients to suffer thiopurine-induced toxicity, and genotype-guided treatment has been shown to contribute to the prevention of thiopurine-induced toxicity, especially in the case of NUDT15 in Asians.

Updates on conventional therapies for inflammatory bowel diseases: 5-aminosalicylates, corticosteroids, immunomodulators, and anti-TNF-α

The incidence and prevalence of inflammatory bowel diseases (IBDs) are rapidly increasing worldwide. IBDs are considered an emerging problem not only in Western countries but also in developing counties. The relapses and complications of active IBD mandate various medications. Nevertheless, hospitalization, emergency room visits, or surgery may be required, resulting in a socioeconomic burden. Great advances have been made in the development of new therapeutic options for IBD to achieve induction and maintenance remission. Nevertheless, conventional therapy is still the mainstay in the treatment of IBD. This review article provides an update on recent advances in conventional therapies, including 5-aminosalicylates, corticosteroids, immunomodulators, and anti-tumor necrosis factor-α agents to treat IBD.

A case of azathioprine-induced aplastic anemia

Azathioprine (AZA) is an immunosuppressant that is widely used to treat many disease states including rheumatoid arthritis. We present a patient who was treated with AZA for rheumatoid arthritis and subsequently hospitalized for severe myelosuppression due to acquired aplastic anemia. Upon genetic testing it was found that the patient was thiopurine methyltransferase (TMPT) deficient, a well-documented risk factor for myelosuppression in patients taking azathioprine. We advocate for TPMT and nudix hydrolase 15 (NUDT15) testing prior to initiation of AZA treatment, or close monitoring with a complete blood count post-AZA initiation to avoid these serious side effects.

Cytotoxicity of Thiopurine Drugs in Patients with Inflammatory Bowel Disease

The effectiveness of thiopurine drugs in inflammatory bowel disease (IBD) was confirmed more than a half-century ago. It was proven that these can be essential immunomodulatory medications. Since then, they have been used routinely to maintain remission of Crohn’s disease (CD) and ulcerative colitis (UC). The cytotoxic properties of thiopurines and the numerous adverse effects of the treatment are controversial. However, the research subject of their pharmacology, therapy monitoring, and the search for predictive markers are still very relevant. In this article, we provide an overview of the current knowledge and findings in the field of thiopurines in IBD, focusing on the aspect of their cytotoxicity. Due to thiopurines’ benefits in IBD therapy, it is expected that they will still constitute an essential part of the CD and UC treatment algorithm. More studies are still required on the modulation of the action of thiopurines in combination therapy and their interaction with the gut microbiota.

Association of Preterm Birth with Inflammatory Bowel Disease and Salivary Gland Disease: Machine Learning Analysis Using National Health Insurance Data

This study employs machine learning and population data for testing the associations of preterm birth with inflammatory bowel disease (IBD), salivary gland disease, socioeconomic status and medication history, including proton pump inhibitors. The source of population-based retrospective cohort data was the Korea National Health Insurance Service claims data for all women aged 25–40 years and who experience their first childbirths as singleton pregnancy during 2015 to 2017 (402,092 women). These participants were divided into the Ulcerative Colitis (UC) Group (1782 women), the Crohn Group (1954 women) and the Non-IBD Group (398,219 women). For each group, the dependent variable was preterm birth during 2015–2017, and 51 independent variables were included. Random forest variable importance was employed for investigating the main factors of preterm birth and testing its associations with salivary gland disease, socioeconomic status and medication history for each group. The proportion of preterm birth was higher for the UC Group and the Non-IBD Group than for the Crohn Group: 7.86%, 7.17% vs. 6.76%. Based on random forest variable importance, salivary gland disease was a top 10 determinant for the prediction of preterm birth for the UC Group, but this was not the case for the Crohn Group or the Non-IBD Group. The top 5 variables of preterm birth for the UC Group during 2015–2017 were socioeconomic status (8.58), age (8.00), proton pump inhibitors (2.35), progesterone (2.13) and salivary gland disease in 2014 (1.72). In conclusion, preterm birth has strong associations with ulcerative colitis, salivary gland disease, socioeconomic status and medication history including proton pump inhibitors.

Pharmacogenetics-based personalized treatment in patients with inflammatory bowel disease: A review

The development of treatment options has revolutionized the prognosis of inflammatory bowel disease (IBD). However, a particular group of patients still experience therapeutic failure or drug side effects. Although the high inter-patient variability in therapy is associated with clinical factors, including age, disease behavior, and disease duration, they attribute only a small proportion of inter-individual variability. Thus, pharmacogenetics evaluating associations between specific genetic variations and drug responses or side effects have focused on optimizing therapeutic efficacy and minimizing toxicity in IBD treatment. Thiopurine S-methyltransferase (TPMT) and nudix hydrolase 15 (NUDT15) are well-established predictive markers of thiopurine-induced myelosuppression. Low TPMT activity is related to increased 6-thioguanine nucleotide levels, subsequently leading to myelotoxicity. NUDT15 variants are strongly associated with thiopurine-induced early leukopenia in Asians, with a lower incidence of TPMT-deficient allele. The Korean Association for the Study of Intestinal Diseases guidelines recommend pretreatment determination of NUDT15 genotypes, especially in East Asians, and NUDT15 R139C measurement has been approved for clinical use since 2019. Several studies have attempted to identify powerful genetic markers for personalized medicine. In this article, we review the identified pharmacogenetics of currently available drugs, focusing on 5-aminosalicylic acid, glucocorticosteroids, thiopurines, and anti-tumor necrosis factor-alpha agents.

Randomised clinical trial: dose optimising strategy by NUDT15 genotyping reduces leucopenia during thiopurine treatment of Crohn's disease

INTRODUCTION

Thiopurine S-methyltransferase (TPTM) is a well known biomarker for thiopurine-induced leucopenia, which has limited value in Asia. Instead, NUDT15 C415T is a promising predictor in Asia.

AIMS

To explore whether an optimised strategy based on NUDT15 C415T genotypes affects thiopurine-induced leucopenia, as well as efficacy in Chinese patients with Crohn's disease.

METHODS

Patients with Crohn's disease and indications for thiopurines were included from two hospitals in China. They were randomly assigned to either the intervention or the control group. In the intervention group, those with genotype CC received a standard dose (control group), those with CT genotype received 50% of the standard dose, those with TT genotype received alternative drugs. The primary endpoint was thiopurine-induced leucopenia (<3.5 × 10⁹ /L). Secondary outcomes were the incidence of other adverse events and the efficacy for maintaining steroid-free remission at week 36.

RESULTS

The rate of thiopurine-induced leucopenia was lower in the intervention group (n = 52) than in the control group (n = 66) (23.7% vs 32.4%, P = 0.049, RR = 0.73, 95% CI 0.53-1.00). In CT subgroup, the incidence of leucopenia in the intervention group (n = 10) was significantly lower than in the control group (n = 28) (31.3% vs 65.1%, RR = 0.48, 95% CI 0.28-0.84). Neither other adverse events nor treatment efficacy was significantly different between the two groups during follow-up.

CONCLUSIONS

Among Chinese patients with Crohn's disease, dose optimisation by NUDT15 C415T reduced the rate of thiopurine-induced leucopenia, without significant influence on efficacy. Using 50% dose reduction for heterozygotes, and alternative drugs for homozygotes, are practicable strategies. Clinical trial number: NCT02929706.

Increased DNA-incorporated thiopurine metabolite as a possible mechanism for leukocytopenia through cell apoptosis in inflammatory bowel disease patients with NUDT15 mutation

BACKGROUND AND AIMS

Polymorphisms in the nucleotide diphosphate-linked moiety X-type motif 15 (NUDT15) gene are associated with thiopurine-induced leukopenia in patients with inflammatory bowel disease (IBD). NUDT15-associated subcellular thiopurine metabolism has not been investigated in primary lymphocytes. We hypothesized that NUDT15 mutation increases DNA-incorporated deoxythioguanosine (dTG) and induces apoptosis in lymphocytes.

METHODS

DNA-incorporated dTG in peripheral blood mononuclear cells (PBMCs) and 6-thioguanine nucleotides (6-TGN) in red blood cells were measured in patients with IBD undergoing thiopurine treatment. The association of a single nucleotide polymorphism for NUDT15 (rs116855232) with dTG^PBMC was examined. The pro-apoptotic effect of DNA-incorporated dTG was examined ex vivo in association with NUDT15 genotypes by co-culturing patient-derived peripheral CD4⁺ T lymphocytes with 6-thioguanine (6-TG).

RESULTS

dTG^PBMC was significantly higher in NUDT15 variants than in non-variants. dTG^PBMC, but not 6-TGN^RBC, negatively correlated with peripheral lymphocyte counts (r =  - 0.31 and  - 0.12, p = 0.012 and 0.173, respectively). DNA-incorporated dTG significantly accumulated to a greater extent in lymphocytes from NUDT15 variants when co-cultured with 6-TG ex vivo than in those from non-variants and was associated with decreased proliferation and increased apoptosis.

CONCLUSION

Increased DNA-incorporated dTG may be responsible for thiopurine-induced leukocytopenia through cell apoptosis in IBD patients with NUDT15 mutation.

Evolving Role of Thiopurines in Inflammatory Bowel Disease in the Era of Biologics and New Small Molecules

In recent years, with the increasing availability of biologic therapies and due to safety concerns, the role of thiopurines in the management of inflammatory bowel disease has been questioned. While acknowledging that the benefit/risk ratio of biologic therapies is very high, they are expensive and are not required by a majority of patients. Therefore, thiopurines do retain an important role as steroid-sparing and maintenance agents when used as monotherapy, and in combination therapy with biologics due to their clinical and pharmacokinetic optimization of anti-tumor necrosis factor agents in particular. Safety concerns with thiopurines are real but also relatively rare, and with careful pre-treatment screening and ongoing monitoring thiopurine benefits outweigh risks in the majority of appropriately selected patients. Measurement of newer pharmacogenomic markers such as nudix hydrolase 15 (NUDT15), when combined with knowledge of existing known mutations (e.g., thiopurine S-methyltransferase-TPMT), will hopefully minimize the risk of potentially life-threatening leukopenia by allowing for pre-treatment dosing stratification. Further optimization of thiopurine dosing via measurement of thiopurine metabolites should be performed routinely and is superior to weight-based dosing. The association of thiopurines with malignancies including lymphoproliferative disorders needs to be recognized in all patients and individualized in each patient. The decrease in lymphoma risk after thiopurine cessation provides an incentive for thiopurine de-escalation in appropriate patients after a period of prolonged deep remission. This review will summarize the current role of thiopurines in inflammatory bowel disease management and provide recommendations for commencing and monitoring therapy, and when to consider de-escalation.

Thiopurine pharmacogenomics and pregnancy in inflammatory bowel disease

The thiopurine drugs azathioprine and 6-mercaptopurine are widely used for the maintenance of clinical remission in steroid-dependent inflammatory bowel disease (IBD). Thiopurines are recommended to be continued throughout pregnancy in IBD patients, but conclusive safety data in pregnant patients remain still insufficient. On the other hand, a strong association between a genetic variant of nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15 p.Arg139Cys) and thiopurine-induced myelotoxicity has been identified. Pharmacokinetic studies have revealed that thiopurine metabolism is altered in pregnant IBD patients and suggested that the fetus may be exposed to the active-thiopurine metabolite, 6-thioguaninetriphosphate, in the uterus. A recent study using knock-in mice harboring the p.Arg138Cys mutation which corresponds to human p.Arg139Cys showed that oral administration of 6-MP at clinical dose induces a severe toxic effect on the fetus harboring the homozygous or heterozygous risk allele. This suggests that NUDT15 genotyping may be required in both women with IBD who are planning pregnancy (or pregnant) and their partner to avoid adverse outcomes for their infant. The risk to the fetus due to maternal thiopurine use is minimal but there are some concerns that are yet to be clarified. In particular, a pharmacogenomic approach to the fetus is considered necessary.

TPMT and NUDT15 polymorphisms in thiopurine induced leucopenia in inflammatory bowel disease: a prospective study from India

BACKGROUND

Polymorphisms in thiopurine methyltransferase (TPMT) and Nudix hydrolase-15 (NUDT15) have been implicated as the predominant cause of thiopurine induced leukopenia in the Western countries and East Asia respectively. Exact role of these polymorphisms in South Asian population with inflammatory bowel disease (IBD) is uncertain.

METHODS

We included consecutive patients with IBD who were initiated on thiopurines at a center in North India. The dosage of thiopurines was titrated using regular monitoring of hemogram and liver function tests. Three TPMT polymorphisms (c.238 G > C, c.460 G > A, and c.719A > G) and one NUDT15 polymorphism (c.415 C > T) were assessed. Comparison regarding incidence of leukopenia and maximum tolerated thiopurine dosage was performed between those with wild polymorphism and those with TPMT and NUDT15 polymorphisms, respectively.

RESULTS

Of the 119 patients (61 males, mean age 36.8 ± 13.5 years), 105 (88.2%) had ulcerative colitis and 14 (11.8%) had Crohn's disease. Leukopenia was noted in 33 (27.7%), gastrointestinal intolerance in 5 (4.2%) and pancreatitis in 2 (1.6%). TPMT polymorphisms were detected amongst five patients of whom 1 developed leukopenia. NUDT15 polymorphism was noted in 13 patients of whom 7 had leukopenia. The odds of developing leukopenia in TPMT polymorphism were non-significant (0.77, 95% CI:0.0822 to 7.2134, P = 0.819) but were significantly higher in those with NUDT15 polymorphism (3.5933, 1.1041 to 11.6951, P value: = 0.0336).

CONCLUSION

NUDT15 polymorphism was more frequent than TPMT polymorphisms and was associated with thiopurine induced leukopenia. However, the tested polymorphisms account for only 24.2% of the risk of thiopurine induced leukopenia.

Importance of NUDT15 Polymorphisms in Thiopurine Treatments

Thiopurines, mercaptopurine, and azathioprine are used as immunosuppressants in the treatments of inflammatory bowel disease, rheumatoid arthritis, and organ transplantation and as chemotherapeutic drugs for the treatment of acute leukemia and chronic myeloid leukemia. This drug class sometimes causes severe adverse reactions, including bone marrow suppression and hair loss. Genetic polymorphisms of the metabolizing enzyme thiopurine S-methyltransferase have been used for predicting these reactions in Caucasians, but these allele frequencies are less frequently observed in Asian populations. Recently, nudix hydrolase 15 (NUDT15) polymorphisms have been shown to play an important role in thiopurine-induced adverse reactions in Asians. In this review, we summarize the NUDT15 studies, mainly in Asian countries, and their implementation in several countries.

Thiopurines in Inflammatory Bowel Disease. How to Optimize Thiopurines in the Biologic Era?

Thiopurines have been a cornerstone in the treatment of inflammatory bowel disease (IBD). Although they have been used for more than 50 years, there are still some unsolved issues about their efficacy and, also, some safety concerns, mainly the risk of myelosuppression and life-threatening lymphoproliferative disorders. Furthermore, the development of biological therapy raises the question whether there is still a role for thiopurines in the IBD treatment algorithm. On the other hand, limited cost and wide availability make thiopurines a reasonable option in settings of limited resources and increasing prevalence of IBD. In fact, there is a growing interest in optimizing thiopurine therapy, since pharmacogenomic findings suggest that a personalized approach based on the genotyping of some molecules involved in its metabolism could be useful to prevent side effects. Polymorphisms of thiopurine methyltransferase enzyme (TPMT) that result in low enzymatic activity have been associated with an increased risk of myelotoxicity, especially in Caucasians; however, in Asians it is assumed that the variants of nudix hydrolase 15 (NUDT15) are more relevant in the development of toxicity. Age is also important, since in elderly patients the risk of complications seems to be increased. Moreover, the primo-infection of Epstein Barr virus and cytomegalovirus under thiopurine treatment has been associated with severe lymphoproliferative disorders. In addition to assessing individual characteristics that may influence thiopurines treatment outcomes, this review also discusses other strategies to optimize the therapy. Low-dose thiopurines combined with allopurinol can be used in hypermethylators and in thiopurine-related hepatotoxicity. The measurement of metabolites could be useful to assess compliance, identify patients at risk of adverse events and also facilitating the management of refractory patients. Thioguanine is also a rescue therapy in patients with toxicity related to conventional thiopurine therapy. Finally, the current indications for thiopurines in monotherapy or in combination with biologics, as well as the optimal duration of treatment, are also reviewed.

Bone marrow inhibition induced by azathioprine in a patient without mutation in the thiopurine S-methyltransferase pathogenic site: A case report

BACKGROUND

Azathioprine (AZA) and its close analog 6-mercaptopurine are thiopurines widely used in the treatment of patients with cancer, organ transplantation, and autoimmune or inflammatory diseases, including systemic lupus erythematosus. Bone marrow inhibition is a common side effect of AZA, and severe bone marrow inhibition is related to decreased thiopurine S-methyltransferase (TPMT) activity.

CASE SUMMARY

We herein report a patient with proliferative lupus nephritis who was using AZA for maintenance therapy, had no common TPMT pathogenic site mutations, and exhibited severe bone marrow inhibition on the 15^th day after oral administration.

CONCLUSION

This report alerts physicians to the fact that even though the TPMT gene has no common pathogenic site mutation, severe myelosuppression may also occur.

Advances in Management of Intestinal Behçet's Disease: A Perspective From Gastroenterologists

Intestinal Behçet's disease (intestinal BD) is a rare chronic inflammatory disorder of the intestine that is characterized by recurrent intestinal manifestations with other systemic features of BD. Intestinal BD is diagnosed when a typically shaped ulcer is observed in the gastrointestinal tract, and the clinical findings meet the diagnostic criteria for BD. Owing to the small number of patients, intestinal BD is easily underestimated. On the other hand, but it often requires surgical treatment because of severe complications, including intestinal perforations or massive bleeding. The same treatment strategies used for inflammatory bowel diseases, such as Crohn's disease and ulcerative colitis, are used for intestinal BD. 5-Aminosalicylic acids, corticosteroids, and immunomodulators are considered conventional therapies, but a considerable number of patients eventually become unresponsive to these pharmaceutical treatments. Recently, biologic agents, such as anti-tumor necrosis factor-alpha inhibitors, have also been suggested as a new treatment option for intestinal BD. This article reviews the pathogenesis and diagnosis of intestinal BD and the current treatment strategies that are expected to be useful for rheumatologic specialists.

Safety of Thiopurine Use in Paediatric Gastrointestinal Disease

Thiopurines, alone or in combination with other agents, have a pivotal role in the treatment of specific gastrointestinal and hepatological disorders. In inflammatory bowel disease and autoimmune hepatitis thiopurines have proven their value as steroid sparing agents for the maintenance of remission and may be considered for preventing postoperative Crohn disease recurrence where there is moderate risk of this occurring. Their use with infliximab therapy reduces antibody formation and increases biologic drug levels. The routine clinical use of thiopurines has, however, been questioned due to a number of potential adverse effects. The aim of this article is to provide information regarding the use, and in particular, safety of these agents in clinical practice in the light of such potentially severe, albeit rare, effects.

Precision medicine for rheumatologists: lessons from the pharmacogenomics of azathioprine

Precision medicine aims to personalize treatment for both effectiveness and safety. As a critical component of this emerging initiative, pharmacogenomics seeks to guide drug treatment based on genetics. In this review article, we give an overview of pharmacogenomics in the setting of an immunosuppressant frequently prescribed by rheumatologists, azathioprine. Azathioprine has a narrow therapeutic index and a high risk of adverse events. By applying candidate gene analysis and unbiased approaches, researchers have identified multiple variants associated with an increased risk for adverse events associated with azathioprine, particularly bone marrow suppression. Variants in two genes, TPMT and NUDT15, are widely recognized, leading drug regulatory agencies and professional organizations to adopt recommendations for testing before initiation of azathioprine therapy. As more gene-drug interactions are discovered, our field will continue to face the challenge of balancing benefits and costs associated with genetic testing. However, novel approaches in genomics and the integration of clinical and genetic factors into risk scores offer unprecedented opportunities for the application of pharmacogenomics in routine practice. Key Points • Pharmacogenomics can help us understand how individuals' genetics may impact their response to medications. • Azathioprine is a success story for the clinical implementation of pharmacogenomics, particularly the effects of TPMT and NUDT15 variants on myelosuppression. • As our knowledge advances, testing and dosing recommendations will continue to evolve, with our field striving to balance costs and benefits to patients. • As we aim toward the goals of precision medicine, future research may integrate increasingly individualized traits-including clinical and genetic characteristics-to predict the safety and efficacy of particular medications for individual patients.

NUDT15 gene variants and thiopurine-induced leukopenia in patients with inflammatory bowel disease

Thiopurine has been used to maintain remission and to reduce antidrug antibody formation in monoclonal antibody therapy in patients with inflammatory bowel disease (IBD). The use of thiopurine is limited by side effects such as leukopenia. Thiopurine S-methyltransferase (TPMT) variants are associated with thiopurine-induced leukopenia in Westerners, but the frequency of the risk alleles is low in Asians. Recently, a variant in the nudix hydrolase 15 (NUDT15) gene (R139C, c.415C > T) was reported to be associated with early severe leukopenia in Asians. NUDT15 is an enzyme that converts 6-thio-(deoxy)guanosine triphosphate (6-T(d)GTP) to 6-thio-(deoxy)guanosine monophosphate (6-T(d)GMTP). The R139C variant impairs the stability of the protein and increases incorporation of 6-TGTP and 6-TdGTP into RNA and DNA, respectively, resulting in leukopenia. The frequency of C/C, C/T, and T/T are approximately 80%, 20%, and 1%, respectively in East Asians. Early leukopenia occurred in less than 3% of patients with C/C and in around 20% of those with C/T, whereas it occurred in almost all patients with T/T. Patients homozygous for this variant also develop severe hair loss. The measurement of NUDT15 R139C can increase the safety of thiopurine dramatically and is a successful example of personalized medicine in the field of IBD.

Identification of NUDT15 gene variants in Amazonian Amerindians and admixed individuals from northern Brazil

INTRODUCTION

The nudix hydrolase 15 (NUDT15) gene acts in the metabolism of thiopurine, by catabolizing its active metabolite thioguanosine triphosphate into its inactivated form, thioguanosine monophosphate. The frequency of alternative NUDT15 alleles, in particular those that cause a drastic loss of gene function, varies widely among geographically distinct populations. In the general population of northern Brazilian, high toxicity rates (65%) have been recorded in patients treated with the standard protocol for acute lymphoblastic leukemia, which involves thiopurine-based drugs. The present study characterized the molecular profile of the coding region of the NUDT15 gene in two groups, non-admixed Amerindians and admixed individuals from the Amazon region of northern Brazil.

METHODS

The entire NUDT15 gene was sequenced in 64 Amerindians from 12 Amazonian groups and 82 admixed individuals from northern Brazil. The DNA was extracted using phenol-chloroform. The exome libraries were prepared using the Nextera Rapid Capture Exome (Illumina) and SureSelect Human All Exon V6 (Agilent) kits. The allelic variants were annotated in the ViVa® (Viewer of Variants) software.

RESULTS

Four NUDT15 variants were identified: rs374594155, rs1272632214, rs147390019, andrs116855232. The variants rs1272632214 and rs116855232 were in complete linkage disequilibrium, and were assigned to the NUDT15*2 genotype. These variants had high frequencies in both our study populations in comparison with other populations catalogued in the 1000 Genomes database. We also identified the NUDT15*4 haplotype in our study populations, at frequencies similar to those reported in other populations from around the world.

CONCLUSION

Our findings indicate that Amerindian and admixed populations from northern Brazil have high frequencies of the NUDT15 haplotypes that alter the metabolism profile of thiopurines.