Thiopurine methyltransferase activity in Spain: a study of 14,545 patients

Transcriptome analysis reveals involvement of thiopurine S-methyltransferase in oxidation-reduction processes

Thiopurine S-methyltransferase (TPMT) is an important enzyme involved in the deactivation of thiopurines and represents a major determinant of thiopurine-related toxicities. Despite its well-known importance in thiopurine metabolism, the understanding of its endogenous role is lacking. In the present study, we aimed to gain insight into the molecular processes involving TPMT by applying a data fusion approach to analyze whole-genome expression data. The RNA profiling was done on whole blood samples from 1017 adult male and female donors to the Estonian biobank using Illumina HTv3 arrays. Our results suggest that TPMT is closely related to genes involved in oxidoreductive processes. The in vitro experiments on different cell models confirmed that TPMT influences redox capacity of the cell by altering S-adenosylmethionine (SAM) consumption and consequently glutathione (GSH) synthesis. Furthermore, by comparing gene networks of subgroups of individuals, we identified genes, which could have a role in regulating TPMT activity. The biological relevance of identified genes and pathways will have to be further evaluated in molecular studies.

Population-scale predictions of DPD and TPMT phenotypes using a quantitative pharmacogene-specific ensemble classifier

BACKGROUND

Inter-individual differences in dihydropyrimidine dehydrogenase (DPYD encoding DPD) and thiopurine S-methyltransferase (TPMT) activity are important predictors for fluoropyrimidine and thiopurine toxicity. While several variants in these genes are known to decrease enzyme activities, many additional genetic variations with unclear functional consequences have been identified, complicating informed clinical decision-making in the respective carriers.

METHODS

We used a novel pharmacogenetically trained ensemble classifier to analyse DPYD and TPMT genetic variability based on sequencing data from 138,842 individuals across eight populations.

RESULTS

The algorithm accurately predicted in vivo consequences of DPYD and TPMT variants (accuracy 91.4% compared to 95.3% in vitro). Further analysis showed high genetic complexity of DPD deficiency, advocating for sequencing-based DPYD profiling, whereas genotyping of four variants in TPMT was sufficient to explain >95% of phenotypic TPMT variability. Lastly, we provided population-scale profiles of ethnogeographic variability in DPD and TPMT phenotypes, and revealed striking interethnic differences in frequency and genetic constitution of DPD and TPMT deficiency.

CONCLUSION

These results provide the most comprehensive data set of DPYD and TPMT variability published to date with important implications for population-adjusted genetic profiling strategies of fluoropyrimidine and thiopurine risk factors and precision public health.

Gender Differences in Cardiovascular Pharmacotherapy-the Example of Hypertension: A Mini Review

Cardiovascular disease (CVD) is the leading cause of mortality worldwide in both sexes. Despite considerable progress in better understanding the patterns of disease in women, they are still often undertreated and benefit less from evidence-based treatment. Hypertension is a key contributor to CVD and is also one of the most potent risk factors for heart failure in women. Even with the wide variety of available drugs, blood pressure control is globally suboptimal. Current guidelines do not suggest differential treatment of hypertension for women; however, a growing body of research suggests gender dimorphism in the pathophysiology of hypertension and pharmacological response to cardiovascular drugs. The clinical relevance of theses sex-divergent effects of drugs is still under investigation. Owing to the exponential relationship between blood pressure and cardiovascular mortality, even a modest decrease in blood pressure or therapeutic adhesion could be clinically \relevant. In this review, we explore the known pharmacological and pharmacokinetic sex differences with special attention to the main classes of antihypertensive treatment. Current data shows frequently higher drug exposures in women and more frequent adverse drug reactions in all antihypertensive drug groups. As far as cardiovascular prevention is concerned, sex-specific data is often lacking in clinical trials, highlighting the necessity to further study CVD and their treatment in both men and women.

Myasthenia gravis and azathioprine treatment: Adverse events related to thiopurine S-methyl-transferase (TPMT) polymorphisms

Azathioprine (AZA) is the most common immunosuppressive drug used to treat myasthenia gravis (MG). To analyses the prevalence of thiopurine S-methyl-transferase (TPMT) genotypes and their association with adverse events due to azathioprine therapy in MG patients. Allele-specific polymerase chain reaction (PCR) and PCR with restriction fragment length polymorphism (RFLP) analysis were carried out to determine the prevalence of the most common TPMT genotypes (*2, *3A, *3B and *3C) in 50 MG patients from Southern Brazilian. The frequency of adverse reactions due to azathioprine therapy was analysed and correlated with different genotypes groups. The prevalence of TPMT gene variants was 12%. The allelic frequency of variant TPMT*2 (C238G), TPMT*3A (G460A/A719G), TPMT*3B (G460A), and TPMT*3C (A719G) genotypes was 1, 3, 2 and 1%, respectively. Adverse events occurred in 44%, of MG patients, of which 86% were minor and 14% were major. One patient, who presented a major adverse event (bone marrow suppression), was homozygous for the TPMT*3A genotype. Our study estimated the prevalence of TPMT genotypes for Brazilian MG patients. The profile of TPMT genotypes was different from other Brazilian populations. Hardy-Weinberg equilibrium and allelic frequencies of TPMT*3A and TPMT*3B, respectively, were different than expected, a finding that suggests a possible founder effect. Major adverse events were statistically significant for TPMT genotypes compared to wild-type. Although TPMT genotype has been associated with AZA-related adverse events, since no statistically significant difference among wild-type and other TPMT genotypes for minor adverse events, our study supports the view that TPMT genotype alone is not enough to adequately personalise the AZA therapy in MG patients. In conclusion, these results were important to characterise the prevalence of TPMT gene variants in MG patients treated with AZA and correlate the adverse events of this therapy in a real-world outpatient clinic from Southern Brazil.

Autoimmune hepatitis: Current and future therapeutic options

Autoimmune hepatitis (AIH) is a rare immune-mediated liver disease with few major advances in treatment options over the last several decades. Available options are effective in most patients albeit are imprecise in their mechanisms. Novel and more tolerable induction regimens and alternative options for management of patients intolerant or with suboptimal response to traditional therapies including in the post-transplant setting remain an important unmet need. This review aims to summarize recent data on pharmacological options and investigational drugs in development for patients with AIH. Standard therapy using prednisone with or without azathioprine remains the mainstay of therapy and is effective in most patients. Budesonide may be considered for induction in early disease and in those with mild fibrosis, but has not been approved for maintenance therapy. Mycophenolate mofetil (MMF) in combination with steroids might be an alternative first-line therapy, but results from a randomized trial are awaited. MMF as a second-line maintenance agent has moderate efficacy though more frequent adverse events in patients with cirrhosis may be seen. Tacrolimus may be an equally effective second-line option particularly in non-responders, but data remain limited. Management of recurrent AIH post-liver transplantation remains controversial with insufficient data to support long-term steroid use. Moving forward, expanding the scope of therapeutic options to include biologics including B-cell depleting agents may be a promising step. Recent insights in understanding the pathogenesis of AIH could serve as a basis for future therapies, including the elucidation of different immunoregulatory pathways and the potential role of the intestinal microbiome.

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.

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.

Recommendations of the Spanish Working Group on Crohn's Disease and Ulcerative Colitis (GETECCU) on the use of thiopurines in inflammatory bowel disease

Thiopurines (azathioprine and mercaptopurine) are widely used in patients with inflammatory bowel disease. In this paper, we review the main indications for their use, as well as practical aspects on efficacy, safety and method of administration. They are mainly used to maintain remission in steroid-dependent disease or with ciclosporin to control a severe ulcerative colitis flare-up, as well as to prevent postoperative Crohn's disease recurrence, and also in combination therapy with biologics. About 30-40% of patients will not respond to treatment and 10-20% will not tolerate it due to adverse effects. Before they are prescribed, immunisation status against certain infections should be checked. Determination of thiopurine methyltransferase activity (TPMT) is not mandatory but it increases initial safety. The appropriate dose is 2.5mg/kg/day for azathioprine and 1.5mg/kg/day for mercaptopurine. Some adverse effects are idiosyncratic (digestive intolerance, pancreatitis, fever, arthromyalgia, rash and some forms of hepatotoxicity). Others are dose-dependent (myelotoxicity and other types of hepatotoxicity), and their surveillance should never be interrupted during treatment. If therapy fails or adverse effects develop, management can include switching from one thiopurine to the other, reducing the dose, combining low doses of azathioprine with allopurinol and assessing metabolites, before their use is ruled out. Non-melanoma skin cancer, lymphomas and urinary tract tumours have been linked to thiopurine therapy. Thiopurine use is safe during conception, pregnancy and breastfeeding.

Combined Detection of NUDT15 Variants Could Highly Predict Thiopurine-induced Leukopenia in Chinese Patients with Inflammatory Bowel Disease: A Multicenter Analysis

BACKGROUND

NUDT15 c.415C>T was a novel genetic marker confirmed in our center for thiopurine-induced leukopenia in Chinese inflammatory bowel disease (IBD). For validation, a large cohort study is needed. Meanwhile, the newly discovered NUDT15 coding variants (c.36_37insGGAGTC and c.52 G>A) have not been studied in patients with IBD. We aimed to further confirm the influence of 3 NUDT15 variants (c.415C>T, c.36_37insGGAGTC, and c.52G>A) on thiopurine-induced leukopenia in Chinese patients with IBD.

METHODS

Patients prescribed on thiopurines for at least 2 weeks were recruited from 4 tertiary hospitals. Clinical data were collected. NUDT15 genotypes were determined with polymerase chain reaction-RFLP and sequencing. The interactions between variants and leukopenia were analyzed.

RESULTS

A total of 732 patients were included, 177 (24.3%) of whom developed leukopenia. There were strong associations of NUDT15 c.415C>T, c.36_37insGGAGTC, and c.52G>A with thiopurine-induced leukopenia (P = 1.81 × 10, P = 4.74 × 10 and P = 0.04, respectively), whereas there was no relevance for thiopurine S-methyltransferase genotypes (P = 0.25). The predictive sensitivity of NUDT15 c.415C>T was 49.2%, whereas it increased to 55.4% when combined analysis with c.36_37insGGAGTC and c.52G>A. Notably, not only the homozygotes with NUDT15 c.415C>T but also the heterozygotes both carrying c.415C>T and c.52G>A developed early leukopenia. The median dosage for NUDT15 c.415C>T carriers was significantly lower than that for wild-type (P < 0.001).

CONCLUSIONS

We confirmed that NUDT15 c.415C>T, c.36_37insGGAGTC, and c.52G>A variants were risk factors for thiopurine-induced leukopenia. Combined detection of the 3 variants could increase the predictive sensitivity of thiopurine-induced leukopenia and help to distinguish early leukopenia in heterozygote of c.415C>T in Chinese patients with IBD. Treatment monitoring by NUDT15 variants may be promising in individualized therapy.

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.

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.

Monitoring thiopurine metabolites in inflammatory bowel disease

Thiopurines (azathioprine and mercaptopurine) are one of the immunosuppressive mainstays for the treatment of inflammatory bowel disease. In spite of its widespread use, thiopurine metabolism is still not fully understood, and a significant proportion of patients suffer toxicity or lack of efficacy. Different enzymatic pathways with individual variations constitute a pharmacogenetic model that seems to be suitable for monitoring and therapeutic intervention. This review is focused on current concepts and recent research that may help clinicians to rationally optimise thiopurine treatment in patients with inflammatory bowel disease.

Clinical features, pathogenesis, and treatment of myasthenia gravis: a supplement to the Guidelines of the German Neurological Society

Myasthenia gravis (MG) is an autoimmune antibody-mediated disorder of neuromuscular synaptic transmission. The clinical hallmark of MG consists of fluctuating fatigability and weakness affecting ocular, bulbar and (proximal) limb skeletal muscle groups. MG may either occur as an autoimmune disease with distinct immunogenetic characteristics or as a paraneoplastic syndrome associated with tumors of the thymus. Impairment of central thymic and peripheral self-tolerance mechanisms in both cases is thought to favor an autoimmune CD4(+) T cell-mediated B cell activation and synthesis of pathogenic high-affinity autoantibodies of either the IgG1 and 3 or IgG4 subclass. These autoantibodies bind to the nicotinic acetylcholine receptor (AchR) itself, or muscle-specific tyrosine-kinase (MuSK), lipoprotein receptor-related protein 4 (LRP4) and agrin involved in clustering of AchRs within the postsynaptic membrane and structural maintenance of the neuromuscular synapse. This results in disturbance of neuromuscular transmission and thus clinical manifestation of the disease. Emphasizing evidence from clinical trials, we provide an updated overview on immunopathogenesis, and derived current and future treatment strategies for MG divided into: (a) symptomatic treatments facilitating neuromuscular transmission, (b) antibody-depleting treatments, and

A study of the utility of azathioprine metabolite testing in myasthenia gravis

Myasthenia gravis (MG) is an autoimmune neuromuscular disorder characterised by fatigable voluntary skeletal muscle weakness. The underlying pathogenesis is complex involving adaptive autoimmune responses. Azathioprine remains a first line broad acting immunosuppressant for MG. Due to varied clinical responses to azathioprine we aimed to investigate the relationship between azathioprine metabolites and symptom control. Mild correlations between Quantitative Myasthenia Gravis Score (QMG) vs. 6-thioguanine nucleotides (R=-0.317 p=0.186) and QMG vs. lymphocyte count (R=0.402 p=0.08) were found. Azathioprine metabolite measurement should be considered in MG patients with; pancytopenia, deranged liver function or recurrent infections.

The clinical effectiveness and cost-effectiveness of treatments for idiopathic pulmonary fibrosis: a systematic review and economic evaluation

BACKGROUND

Idiopathic pulmonary fibrosis (IPF) is a life-limiting lung disease that generally affects people over 60 years old. The main symptoms are shortness of breath and cough, and as the disease progresses there is a considerable impact on day-to-day life. Few treatments are currently available.

OBJECTIVES

To conduct a systematic review of clinical effectiveness and an analysis of cost-effectiveness of treatments for IPF based on an economic model informed by systematic reviews of cost-effectiveness and quality of life.

DATA SOURCES

Eleven electronic bibliographic databases, including MEDLINE, EMBASE, Web of Science, and The Cochrane Library and the Centre for Reviews and Dissemination databases, were searched from database inception to July 2013. Reference lists of relevant publications were also checked and experts consulted.

METHODS

Two reviewers independently screened references for the systematic reviews, extracted and checked data from the included studies and appraised their risk of bias. An advisory group was consulted about the choice of interventions until consensus was reached about eligibility. A narrative review with meta-analysis was undertaken, and a network meta-analysis (NMA) was performed. A decision-analytic Markov model was developed to estimate cost-effectiveness of pharmacological treatments for IPF. Parameter values were obtained from NMA and systematic reviews. Univariate and probabilistic sensitivity analyses were undertaken. The model perspective is NHS and Personal Social Services, and discount rate is 3.5% for costs and health benefits.

RESULTS

Fourteen studies were included in the review of clinical effectiveness, of which one evaluated azathioprine, three N-acetylcysteine (NAC) (alone or in combination), four pirfenidone, one BIBF 1120, one sildenafil, one thalidomide, two pulmonary rehabilitation, and one a disease management programme. Study quality was generally good, with a low risk of bias. The current evidence suggests that some treatments appear to be clinically effective. The model base-case results show increased survival for five pharmacological treatments, compared with best supportive care, at increased cost. General recommendations cannot be made of their cost-effectiveness owing to limitations in the evidence base.

LIMITATIONS

Few direct comparisons of treatments were identified. An indirect comparison through a NMA was performed; however, caution is recommended in the interpretation of these results. In relation to the economic model, there is an assumption that pharmacological treatments have a constant effect on the relative rate of per cent predicted forced vital capacity decline.

CONCLUSIONS

Few interventions have any statistically significant effect on IPF and a lack of studies on palliative care approaches was identified. Research is required into the effects of symptom control interventions, in particular pulmonary rehabilitation and thalidomide. Other research priorities include a well-conducted randomised controlled trial on inhaled NAC therapy and an updated evidence synthesis once the results of ongoing studies are reported.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42012002116.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Getting the best out of thiopurine therapy: thiopurine S-methyltransferase and beyond

Thiopurines are the cornerstone of treatment for a wide variety of medical disorders, ranging from pediatric leukemia to inflammatory bowel disease. Because of their complex metabolism and potential toxicities, the use of biomarkers to predict risk and response is paramount. Thiopurine S-methyltransferase and thiopurine metabolite levels have emerged as companion diagnostics with crucial roles in facilitating safe and effective treatment. This review serves to update the reader on how these tools are being developed and implemented in clinical practice. A useful paradigm in thiopurine therapeutic strategy is presented, along with fresh insights into the mechanisms underlying these approaches. We elaborate on potential future developments in the optimization of thiopurine therapy.

Clinical predictors of thiopurine-related adverse events in Crohn's disease

AIM: To determine the incidence and predictors of thiopurine-related adverse events.

METHODS: Subjects with Crohn’s disease who were followed in the Alberta Inflammatory Bowel Disease Consortium patient database registry were identified. Retrospective chart review was conducted between August 5^th, 2010 and June 1^st, 2012. We collected data on: age at diagnosis; sex; disease location and behaviour at time of prescribing thiopurine; perianal fistulising disease at or prior to thiopurine prescription; smoking status at time of thiopurine prescription, use of corticosteroid within 6 mo of diagnosis; dosage, age at onset, and cessation of 5-aminosalicyclic acid (5-ASA); anti-tumour necrosis factor medication exposure and intestinal resection before thiopurine prescription. The primary outcome of interest was the first adverse event that led to discontinuation of the first thiopurine medication used. Logistic regression models were used to associate clinical characteristics with outcomes after adjusting for potential confounders. Risk estimates were presented as odds ratios (OR) with 95% CI. Effect modification by age and sex were explored.

RESULTS: Our cohort had a median follow-up duration of 5.8 years [interquartile range (IQR 25^th-75^th) 2.7-9.1]. Thiopurine therapy was discontinued in 31.3% of patients because of: hypersensitivity reactions (7.1%), acute pancreatitis (6.2%), gastrointestinal intolerance (5.4%), leucopenia (3.7%), hepatotoxicity (3.4%), infection (1.1%) and other reasons (4.3%). A higher incidence of thiopurine withdrawal was observed in patients over the age of 40 (39.4%, P = 0.007). A sex-by-age interaction (P = 0.04) was observed. Females older than 40 years of age had an increased risk of thiopurine discontinuation due to an adverse event (age above 40 vs age below 40, adjusted OR = 2.8; 95%CI: 1.4-5.6). In contrast, age did not influence thiopurine withdrawal in males (age above 40 vs below 40, adjusted OR = 0.9; 95%CI: 0.4-2.1). Other clinical variables (disease location and phenotype, perianal disease, smoking history, history of intestinal resection and prior 5-ASA or corticosteroid use) were not associated with an increased risk an adverse event leading to therapy cessation.

CONCLUSION: Thiopurine withdrawal due to adverse events is commoner in women over the age of 40 at prescription. These findings need to be replicated in other cohorts.

Interindividual variability in TPMT enzyme activity: 10 years of experience with thiopurine pharmacogenetics and therapeutic drug monitoring

BACKGROUND & AIMS

TPMT activity and metabolite determination (6-thioguanine nucleotides [6-TGN] and 6-methylmercaptopurine nucleotides [6-MMPN]) remain controversial during thiopurine management. This study assessed associations between patient characteristics and TPMT activity, and their impact on metabolite levels.

PATIENTS & METHODS

A retrospective review of the laboratory database from a French university hospital identified 7360 patients referred for TPMT phenotype/genotype determination, and/or for 6-TGN/6-MMPN monitoring.

RESULTS

Four TPMT phenotypes were identified according to TPMT activity distribution: low, intermediate, normal/high and very high. Based on 6775 assays, 6-TGN concentrations were 1.6-fold higher in TPMT-deficient patients compared with TPMT-normal patients. Azathioprine dose and TPMT genotype were significant predictors of metabolite levels. Furthermore, 6-MMPN and 6-MMPN: 6-TGN ratios were, respectively, 1.6- and 2.2-fold higher in females than in males, despite similar TPMT, 6-TGN and azathioprine doses. An unfavorable ratio (≥20) was associated with a slightly higher TPMT activity.

CONCLUSION

These results illustrate the usefulness of pharmacogenomics and metabolite measurement to improve the identification of noncompliance and patients at high risk for toxicity or therapeutic resistance. Original submitted 13 November 2013; Revision submitted 30 January 2014.

Germline oncopharmacogenetics, a promising field in cancer therapy

Pharmacogenetics (PGx) is the study of the relationship between inter-individual genetic variation and drug responses. Germline variants of genes involved in drug metabolism, drug transport, and drug targets can affect individual response to medications. Cancer therapies are characterized by an intrinsically high toxicity; therefore, the application of pharmacogenetics to cancer patients is a particularly promising method for avoiding the use of inefficacious drugs and preventing the associated adverse effects. However, despite continuing efforts in this field, very few labels include information about germline genetic variants associated with drug responses. DPYD, TPMT, UGT1A1, G6PD, CYP2D6, and HLA are the sole loci for which the European Medicines Agency (EMA) and the US Food and Drug Administration (FDA) report specific information. This review highlights the germline PGx variants that have been approved to date for anticancer treatments, and also provides some insights about other germline variants with potential clinical applications. The continuous and rapid evolution of next-generation sequencing applications, together with the development of computational methods, should help to refine the implementation of personalized medicine. One day, clinicians may be able to prescribe the best treatment and the correct drug dosage based on each patient's genotype. This approach would improve treatment efficacy, reduce toxicity, and predict non-responders, thereby decreasing chemotherapy-associated morbidity and improving health benefits.

Implementation of TPMT testing

The activity of the enzyme thiopurine methyltransferase (TPMT) is regulated by a common genetic polymorphism. One in 300 individuals lack enzyme activity and 11% are heterozygous for a variant low activity allele and have an intermediate activity. The thiopurine drugs azathioprine, mercaptopurine and thioguanine are substrates for TPMT; these drugs exhibit well documented myelosuppressive effects on haematopoietic cells and have a track record of idiosyncratic drug reactions. The development of severe bone marrow toxicity, in patients taking standard doses of thiopurine drugs, is associated with TPMT deficiency whilst the TPMT heterozygote is at an increased risk of developing myelosuppression. Factors influencing TPMT enzyme activity, as measured in the surrogate red blood cell, are discussed in this review to enable an appreciation of why concordance between TPMT genotype and phenotype is not 100%. This is particularly important for lower/intermediate TPMT activities to avoid misclassification of TPMT status. TPMT testing is now widely available in routine service laboratories. The British National Formulary suggests TPMT testing before starting thiopurine drugs. Dermatologists were quick to adopt routine TPMT testing whilst gastroenterologists do not specifically recommend TPMT screening. TPMT testing is mandatory prior to the use of mercaptopurine in childhood leukaemia. Thiopurine drug dose and other treatment related influences on cell counts explain some of the differing recommendations between clinical specialities. TPMT testing is cost-effective and the major role is in the identification of the TPMT deficient individual prior to the start of thiopurine drugs.

Thiopurine methyltransferase genotype-phenotype discordance and thiopurine active metabolite formation in childhood acute lymphoblastic leukaemia

AIMS

In children with acute lymphoblastic leukaemia (ALL) bone marrow activity can influence red blood cell (RBC) kinetics, the surrogate tissue for thiopurine methyltransferase (TPMT) measurements. The aim of this study was to investigate TPMT phenotype-genotype concordance in ALL, and the influence of TPMT on thiopurine metabolite formation.

METHODS

We measured TPMT (activity, as units ml(-1) packed RBCs and genotype) at diagnosis (n = 1150) and TPMT and thioguanine nucleotide (TGN) and methylmercaptopurine nucleotide (MeMPN) metabolites (pmol/8 × 10(8) RBCs) during chemotherapy (n = 1131) in children randomized to thioguanine or mercaptopurine on the United Kingdom trial ALL97.

RESULTS

Median TPMT activity at diagnosis (8.5 units) was significantly lower than during chemotherapy (13.8 units, median difference 5.1 units, 95% confidence interval (CI) 4.8, 5.4, P < 0.0001). At diagnosis genotype-phenotype was discordant. During chemotherapy the overall concordance was 92%, but this fell to 55% in the intermediate activity cohort (45% had wild-type genotypes). For both thiopurines TGN concentrations differed by TPMT status. For mercaptopurine, median TGNs were higher in TPMT heterozygous genotype (754 pmol) than wild-type (360 pmol) patients (median difference 406 pmol, 95% CI 332, 478, P < 0.0001), whilst median MeMPNs, products of the TPMT reaction, were higher in wild-type (10 650 pmol) than heterozygous patients (3868 pmol) (P < 0.0001). In TPMT intermediate activity patients with a wild-type genotype, TGN (median 366 pmol) and MeMPN (median 8590 pmol) concentrations were similar to those in wild-type, high activity patients.

CONCLUSIONS

In childhood ALL, TPMT activity should not be used to predict heterozygosity particularly in blood samples obtained at disease diagnosis. Genotype is a better predictor of TGN accumulation during chemotherapy.

Clinical implications of ageing for the management of IBD

As the global population ages, the number of older people (≥65 years) living with IBD is expected to increase. IBD therapeutics have advanced considerably over the past few decades with the introduction of multiple steroid-sparing agents as well as numerous clinical trials that have tested new therapeutic targets. However, the current paradigms for IBD management might not be directly translatable to older patients with IBD. Age-related factors such as immunodeficiency relative to younger patients, comorbidity, polypharmacy and diminished physical reserve directly or indirectly affect the natural history of their disease. This Review highlights how these age-associated variables can affect older patients with IBD and also illustrates the multiple gaps in our current knowledge of IBD in the elderly.

Relationship between azathioprine dosage and thiopurine metabolites in pediatric IBD patients: identification of covariables using multilevel analysis

BACKGROUND

Previous studies have reported no or only a very poor correlation between 6-methylmercaptopurine/6-thioguanine nucleotide (6-MeMPN/6-TGN) and azathioprine (AZA) dose in the treatment of inflammatory bowel disease (IBD). However, metabolite levels are often repeatedly measured yielding a hierarchical data structure that requires more appropriate data analysis.

METHODS

This study explored the relationship between the weight-based dosage of AZA and metabolites levels in 86 pediatric IBD patients using multilevel analysis. Other covariates related to patient characteristics and treatment were evaluated.

RESULTS

This is the first study to demonstrate positive correlations between AZA dose and 6-TGN and 6-MeMPN levels and 6-MeMPN/6-TGN ratio (P < 0.001) in IBD children. Other novel predictors of metabolites were reported. Younger children exhibited lower 6-TGN and 6-MeMPN levels, probably suggesting age-related differences in metabolism and/or absorption of thiopurines. Coadministration of infliximab resulted in a significant increase in 6-TGN levels (P = 0.023). Moreover, alanine aminotransferase values positively correlated with 6-MeMPN levels (P = 0.032). The duration of AZA therapy, gender, and thiopurine methyltransferase activity were associated with metabolite levels. The wide interindividual variability in metabolite levels that accounted for 67.7%, 48.6%, and 49.4% of variance in the 6-TGN and 6-MeMPN levels and the ratio, respectively, were confirmed.

CONCLUSIONS

The reliable AZA dose-metabolites relationship is useful for clinicians to guide the dosing regimen to maximize clinical response and minimize side effects or to consider alternative therapies when patients have preferential production of the toxic 6-MeMPN. These results may be of potential interest for optimizing thiopurine therapy to achieve safe and efficacious AZA use in pediatric IBD patients.

Practical guidelines for the use of steroid-sparing agents in the treatment of chronic pruritus

Chronic pruritus in the adult patient is both an underappreciated and a difficult to treat condition. In the vast majority of cases, itch is the result of inflammatory skin disease and therefore may be responsive to systemic anti-inflammatory therapies. Urticarial dermatitis is an under-recognized cause of chronic itch in the adult population. Patients with this disorder are characterized by prolonged, prednisone-responsive pruritus, often in the absence of substantial cutaneous findings. Skin findings, when present, can range from subtle, persistent urticarial lesions to excoriated papules, often intermixed with urticaria, eczematous change, and lichenification secondary to chronic scratching. Hereby, we describe our algorithm for evaluation and management of adult patients with refractory pruritus (urticarial dermatitis in particular), including evaluation for other etiologies of pruritus, pre-immunosuppression workup, and the use of azathioprine and other steroid-sparing agents for treatment of recalcitrant itch.

New genetic associations in thiopurine-related bone marrow toxicity among inflammatory bowel disease patients

Background: The toxicity related to thiopurine drug therapy for inflammatory bowel disease (IBD) varies widely among patients. Almost 15–30% of patients with IBD develop side effects during treatment, often bone marrow suppression. Several factors have been implicated in determining this toxicity, mainly individual genetic variation related to formation of active thiopurine metabolites. The aim was to identify genes involved in thiopurine-related myelosuppression. Materials & methods: A two-stage investigation of 19,217 coding SNPs (cSNPs) was performed in a Spanish (Inflammatory Bowel Disease Group of Galicia [EIGA]) cohort of 173 IBD patients, 15 with bone marrow suppression. The top 20 cSNPs identified in the first stage with p < 10-3 for allelic test association and SNPs that define the common TPMT alleles were replicated in a different Spanish (ENEIDA) cohort (87 patients, 29 with bone marrow suppression). Results: Several cSNPs showed a significant p-value in the allelic joint analysis (p-Cochran–Mantel–Haenszel test ≤2.55 × 10-3) despite no cSNP passing correction for multiple testing in the first cohort. Of note is rs3729961 in the gene IL6ST, a transducer signal chain shared by many cytokines including IL6 (p-value combined = 2.36 × 10-4, odds ratio [95% CI]: 3.41 [1.71–6.78]). In addition, we detected association with rs3749598 in the FSTL5 gene that appears to interact with metalloproteases at the extracellular matrix level (p-value combined = 4.89 × 10-4), odds ratio (95% CI): 3.67 (1.68–8.01). Conclusion: We have identified IL6ST and FSLT5 as new bone marrow suppression susceptibility candidate genes after thiopurine treatment in IBD patients. This is the first report of variants associated with thiopurine-related myelosuppression that was identified by a genome-wide association study. Its validation awaits functional analyses and replication in additional studies.

Original submitted 14 September 2012; Revision submitted 13 February 2013

Thiopurines in inflammatory bowel disease revisited

Although a great variety of new drugs have been introduced for the therapy of inflammatory bowel diseases so far, a definite cure of the disease is still out of scope. An anti-inflammatory approach to induce remission followed by maintenance therapy with immunosupressants is still the mainstay of therapy. Thiopurines comprising azathioprine and its active metabolite mercaptopurine as well as tioguanine, are widely used in the therapy of chronic active inflammatory bowel disease (IBD). Their steroid sparing potential and efficacy in remission maintenance are out of doubt. Unfortunately, untoward adverse events are frequently observed and may preclude further administration or be life threatening. This review will focus on new aspects of thiopurine therapy in IBD, its efficacy and safety.

Current concepts in the diagnosis and management of autoimmune hepatitis

Autoimmune hepatitis (AIH) is a progressive necroinflammatory liver disease associated with significant morbidity and mortality. Mainly affecting females, AIH has a varied clinical presentation from minor symptomatology to acute liver failure. The diagnosis should be considered in anyone with abnormal liver function tests. Diagnostic features include biochemical evidence of transaminitis, elevated IgG and positive autoantibodies. Liver biopsy may show interface hepatitis with portal-based plasma cell infiltrates. A clinical and pathological spectrum of disease exists with other autoimmune liver disease in rare cases. AIH responds promptly to immunosuppression therapy, including corticosteroids (prednis(ol)one or budesonide) with azathioprine. Treatment failure can be addressed with several second-line immunosuppressive agents. Liver transplantation remains a successful salvage therapy for acute autoimmune liver failure or treatment failure in chronic AIH complicated by synthetic dysfunction, portal hypertension or hepatocellular carcinoma.

Usefulness of salicylate and thiopurine coprescription in steroid-dependent ulcerative colitis and withdrawal strategies

5-aminosalicylic acid (5-ASA) and thiopurines (azathioprine and mercaptopurine) are the most common drugs used as a maintenance treatment for ulcerative colitis. A considerable proportion of these patients develop corticosteroid dependency, and thiopurines are the standard treatment in this scenario. Dual prescriptions of both thiopurines and 5-ASA are common practice in steroid-dependent ulcerative colitis, in an attempt to optimize the efficacy of therapy. On the one hand, the potential protective role of 5-ASA against colorectal cancer argues in favour of prescription of both medications. The possible synergism between the two drugs, because of the inhibition of thiopurine methyltransferase (TPMT) enzyme activity by 5-ASA, has been postulated as another justification for dual prescription. However, existing evidence does not support that this combined strategy is superior to monotherapy with thiopurines. On the other hand, in patients showing prolonged disease remission, the possibility of discontinuing maintenance treatment can be considered on an individualized basis. The high frequency of relapses after thiopurine withdrawal should always be taken into account, but the potential adverse effects of the medication also need to be considered. A properly indicated treatment with thiopurines may need to be continued for life in many patients.

Nutritional therapy versus 6-mercaptopurine as maintenance therapy in patients with Crohn's disease

BACKGROUND

6-Mercaptopurine is often used as maintenance therapy in patients with Crohn's disease. However, toxicities like myelosuppression limit its clinical benefit.

AIMS

To evaluate the efficacy of elemental diet versus 6-mercaptopurine as maintenance therapy in Crohn's disease.

METHODS

Ninety-five eligible patients with Crohn's disease activity index ≤150 were randomly assigned to: 6-mercaptopurine (0.5-1.5mg/kg/day, n=30); Elental as an elemental diet (≥900 kcal/day, n=32); none (control, n=33). In the three groups, patients were and remained on 5-aminosalicylic acid (2250-3000 mg/day). Patients were observed for 2 years and the rate of relapse (Crohn's disease activity index ≥200) was monitored.

RESULTS

At 24 months, the fractions of patients who had maintained remission were 60%, 46.9% and 27.2% for 6-mercaptopurine, Elental and the control groups, respectively. Log-rank test showed better efficacy for 6-mercaptopurine (P=0.0041) and Elental (P=0.0348) versus control. No significant difference was found between 6-mercaptopurine and Elental. Further, in the 6-mercaptopurine group, 2 patients experienced liver injury and one developed alopecia.

CONCLUSIONS

This 24 months comparison study showed that Elental as maintenance therapy in Crohn's disease patients was as effective as 6-mercaptopurine. Elental should be useful for long-term maintenance therapy in Crohn's disease. This is the first comparison study evaluating nutritional therapy versus 6-mercaptopurine.

Diagnosis and treatment of autoimmune hepatitis

Autoimmune hepatitis is a chronic liver disease characterized by elevated aminotransferase levels, autoantibodies, increased γ-globulin or IgG levels and biopsy evidence of interface hepatitis. Recent advances include new practice guidelines that redefine criteria for remission to require complete biochemical and histological normalization on therapy; comparisons between the revised original and simplified diagnostic scoring systems; refined characterization of autoantibodies and their diagnostic performance parameters; proof of the safety and efficacy of combination budesonide and azathioprine therapy for non-cirrhotic patients; scrutiny of overlap syndromes; further analyses of the outcomes of orthotopic liver transplantation and the diagnosis and treatment of recurrent and de novo autoimmune hepatitis after transplantation. Anticipated consequences of the application of the new definition of therapeutic remission include a reduction in the proportion of patients achieving remission with conventional immunosuppression regimens and a corresponding increase in the need for alternative therapies.

High prevalence of polymorphism and low activity of thiopurine methyltransferase in patients with inflammatory bowel disease

BACKGROUND

Gene polymorphism of thiopurine methyltransferase (TPMT) correlates with decreased enzyme activity which determines a significant risk of adverse effect reactions (ADR) in patients treated with thiopurines. The aim of this study was to investigate TPMT genotype and phenotype status in patients with inflammatory bowel diseases (IBD).

METHODS

Fifty-one consecutive out-patients with IBD were genotyped for the following allelic variants: rs1800462 (referred as TPMT 2 allele), rs1800460 (referred as TPMT 3B allele), and 1142345 (referred as TPMT 3C allele). Red blood cell TPMT activity was measured using a competitive micro-well immunoassay for the semi-quantitative determination of TPMT activity in red blood cells (RBC) by means of a 6-MP substrate.

RESULTS

Polymorphism of TPMT was found in 5 out of 51 patients (10%; 95% CI 2%-18%), three heterozygous and two homozygous carriers. Six patients (11.8%; 95% CI 2.4%-19.5%) displayed very low, 12 (23.5%; 95% CI 11.4%-34.5%) intermediate, and 33 (64.7%; 95% CI 52%-78%) normal/high TPMT activity. There were no differences between TPMT genotype and phenotype groups according to age, type of disease, smoking, and chronic medications. A 71% (95% CI 61%-81%; κ=0.45) concordance rate was found between genotype and phenotype status. Six out of 27 (22%) current or past users of azathioprine developed ADR, with three (50%) displaying TPMT genotype and/or phenotype alterations.

CONCLUSION

Compared to the general population, IBD patients may have significantly higher prevalence of TPMT polymorphism and, even more, low activity. Phenotypic more than genotypic TPMT analysis could be useful to better manage IBD therapy with thiopurines.

Validation of a genotyping method for analysis of TPMT polymorphisms

BACKGROUND

Thiopurine methyltransferase (TPMT) catalyzes the methylation of thiopurine drugs such as azathioprine and 6-mercaptopurine. Several mutations in the TPMT gene correlate with low enzyme activity and adverse effects such as myelotoxicity. Hence, genotyping TPMT makes it possible to identify patients at high risk for drug toxicity.

OBJECTIVE

The aim of this study was to validate a TPMT genotyping method by comparing it with a conventional polymerase chain reaction (PCR) approach.

METHODS

LightSNiP is a real-time PCR method for the detection of TPMT*2, *3B, and *3C without a sequencing step. We evaluated the frequencies of 3 TPMT alleles in 111 white adult patients by comparing genotyping by LightSNiP with conventional PCR (sequencing).

RESULTS

No differences were observed between conventional genotyping with sequencing and LightSNiP for *2, *3B, and *3C, suggesting the validity of this method.

CONCLUSIONS

Compared with the conventional PCR sequencing method, the data suggest that LightSNiP correctly detected the TPMT *2, *3B, and *3C in this select population.

Thiopurine methyltransferase genotype and thiopurine S-methyltransferase activity in Greek children with inflammatory bowel disease

BACKGROUND

Azathioprine (AZA) and 6-mercaptopurine (6MP) are used in the treatment of pediatric inflammatory bowel disease (IBD). Genetic variations in thiopurine S-methyltranfarase (TPMT) gene have been correlated with enzyme activity and with the occurrence of adverse events to AZA and 6MP. The aim of the present study was to examine the sensitivity and specificity of TPMT genotyping for TPMT enzymatic activity, reducing harm from thiopurine by pretesting, and the association of thiopurine toxicity with TPMT status in children with IBD.

METHODS

TPMT red blood cell (RBC) activity was measured by using a radiochemical method and genotype was determined for the TPMT alleles *2, *3A, *3B and *3C in 108 thiopurinetreated pediatric IBD patients with a mean age of 11.3 years (range 3-16).

RESULTS

Significant TPMT activity differences between wild-type and heterozygous and homozygous mutated subjects were observed. We divided TPMT activity into three categories according to frequency distribution: low (16.67%), intermediate (25.92%) and high (57.41%). The whole population included a total of 77.78% of homozygous wild-type subjects, 15.74% heterozygous variants, 1.85% homozygous variants and five (4.63%) compound heterozygous variant TPMT*3B/*3C. The overall concordance rate between TPMT genotypes and phenotypes was 88.2%. Seven carriers of at least one variant allele and low or intermediate TPMT activity developed adverse effects.

CONCLUSIONS

Our findings suggest that carriers of at least one variant allele and both intermediate and absent TPMT activity have an increased risk of developing thiopurine-induced myelotoxicity compared with individuals with normal genotype and TPMT activity.

Review article: the benefits of pharmacogenetics for improving thiopurine therapy in inflammatory bowel disease

BACKGROUND

Thiopurines represent an effective and widely prescribed therapy in inflammatory bowel disease (IBD). Concerns about toxicity, mainly resulting from a wide inter-individual variability in thiopurine metabolism, restrict their use. Optimal thiopurine dosing is challenging for preventing adverse drug reactions and improving clinical response.

AIM

To review efficacy and toxicity of thiopurines in IBD. To provide pharmacogenetic-based therapeutic recommendations.

METHODS

We conducted a query on PubMed database using 'inflammatory bowel disease', 'thiopurine', 'azathioprine', '6-mercaptopurine', 'TPMT', 'pharmacogenetics', 'TDM', and selected relevant articles, especially clinical studies.

RESULTS

Thiopurine metabolism - key enzyme: thiopurine S-methyltransferase (TPMT) - modulates clinical response, as it results in production of the pharmacologically active and toxic metabolites, the thioguanine nucleotides (6-TGN). Adjusting dosage according to TPMT status and/or metabolite blood levels is recommended for optimising thiopurine therapy (e.g. improving response rate up to 30% or decreasing haematological adverse events of 25%). Other enzymes or transporters of interest, as inosine triphosphatase (ITPase), glutathione S-transferase (GST), xanthine oxidase (XO), aldehyde oxidase (AOX), methylene tetrahydrofolate reductase (MTHFR) and ATP-binding cassette sub-family C member 4 (ABCC4) are reviewed and discussed for clinical relevance.

CONCLUSIONS

Based on the literature data, we provide a therapeutic algorithm for thiopurines therapy with starting dose recommendations depending on TPMT status and thereafter dose adjustments according to five metabolite profiles identified with therapeutic drug monitoring (TDM). This algorithm allows a dosage individualisation to optimise the management of patients under thiopurine. Furthermore, identification of new pharmacogenetic biomarkers is promising for ensuring maximal therapeutic response to thiopurines with a minimisation of the risk for adverse events.

Thiopurine methyl-transferase activity and azathioprine metabolite concentrations do not predict clinical outcome in thiopurine-treated inflammatory bowel disease patients

BACKGROUND

Low thiopurine-methyl-transferase (TPMT) activity and high 6-thioguanine-nucleotide (6TGN) concentrations have been linked to therapeutic success in inflammatory bowel disease patients treated with thiopurines; however, this has not been implemented in clinical practice.

AIM

To identify a therapeutic threshold value for TPMT or 6TGN concentrations, and their capability to predict treatment safety and efficacy.

METHODS

Prospective multicentre study including steroid-resistant/dependent patients starting thiopurines. The TPMT activity was determined at inclusion (>5 U/mL required). Azathioprine metabolites [6TGN, 6-methyl-mercaptopurine ribonucleotides (6MMP), and 6TGN/6MMP and 6TGN/TPMT ratios] were periodically monitored during steroid tapering and after withdrawal for 6 months or until a new flare occurred.

RESULTS

A total of 113 patients were analysed (62% clinical response). Areas under the receiver operating characteristic (ROC) curve (AUC) relating clinical response and metabolite levels at 2, 4 and 6 months after steroid withdrawal were less than 0.7. The AUCs relating final response and initial TPMT activity or metabolite concentrations at 2, 4, 8 and 16 weeks after starting thiopurines were less than 0.7. No cut-off point with worthwhile sensitivity/specificity was found. Eight (7%) patients developed thiopurine-related toxicity that could not be linked to TPMT activity or 6TGN levels.

CONCLUSIONS

Our results do not support determination of TPMT activity or 6TGN concentrations to predict treatment outcome, and no useful serum metabolites threshold value to adjust the drug's dose was identified.

Common misconceptions about 5-aminosalicylates and thiopurines in inflammatory bowel disease

Misconceptions are common in the care of patients with inflammatory bowel disease (IBD). In this paper, we state the most commonly found misconceptions in clinical practice and deal with the use of 5-aminosalicylates and thiopurines, to review the related scientific evidence, and make appropriate recommendations. Prevention of errors needs knowledge to avoid making such errors through ignorance. However, the amount of knowledge is increasing so quickly that one new danger is an overabundance of information. IBD is a model of a very complex disease and our goal with this review is to summarize the key evidence for the most common daily clinical problems. With regard to the use of 5-aminosalicylates, the best practice may to be consider abandoning the use of these drugs in patients with small bowel Crohn’ s disease. The combined approach with oral plus topical 5-aminosalicylates should be the first-line therapy in patients with active ulcerative colitis; once-daily treatment should be offered as a first choice regimen due to its better compliance and higher efficacy. With regard to thiopurines, they seem to be as effective in ulcerative colitis as in Crohn’ s disease. Underdosing of thiopurines is a form of undertreatment. Thiopurines should probably be continued indefinitely because their withdrawal is associated with a high risk of relapse. Mercaptopurine is a safe alternative in patients with digestive intolerance or hepatotoxicity due to azathioprine. Finally, thiopurine methyltransferase (TPMT) screening cannot substitute for regular monitoring because the majority of cases of myelotoxicity are not TPMT-related.

Pre-analytic and analytic sources of variations in thiopurine methyltransferase activity measurement in patients prescribed thiopurine-based drugs: A systematic review

OBJECTIVES

Low thiopurine S-methyltransferase (TPMT) enzyme activity is associated with increased thiopurine drug toxicity, particularly myelotoxicity. Pre-analytic and analytic variables for TPMT genotype and phenotype (enzyme activity) testing were reviewed.

DESIGN AND METHODS

A systematic literature review was performed, and diagnostic laboratories were surveyed.

RESULTS

Thirty-five studies reported relevant data for pre-analytic variables (patient age, gender, race, hematocrit, co-morbidity, co-administered drugs and specimen stability) and thirty-three for analytic variables (accuracy, reproducibility). TPMT is stable in blood when stored for up to 7 days at room temperature, and 3 months at -30°C. Pre-analytic patient variables do not affect TPMT activity. Fifteen drugs studied to date exerted no clinically significant effects in vivo. Enzymatic assay is the preferred technique. Radiochemical and HPLC techniques had intra- and inter-assay coefficients of variation (CVs) below 10%.

CONCLUSION

TPMT is a stable enzyme, and its assay is not affected by age, gender, race or co-morbidity.

Adverse events of thiopurine immunomodulators in patients with inflammatory bowel disease

BACKGROUND

Thiopurine immunomodulators are the most commonly used immunosuppressants in inflammatory bowel disease.

AIMS

To evaluate the incidence of adverse events (AE) in patients with inflammatory bowel disease treated with azathioprine (AZA) or 6-mercaptopurine (MP) in our hospital, the features of these effects, the distribution of socio-demographic factors, and the possible predisposing factors.

METHODS

We included 377 patients with inflammatory bowel disease who were diagnosed through 2008 and who received AZA or MP during the course of their disease. We collected retrospective demographic, clinical, and laboratory data about their disease and detailed information on any AE.

RESULTS

Fifty-one patients had some form of AE with AZA or MP (13.5%) and 11% discontinued therapy because of toxicity. Statistically significant association with Crohn's disease was found (P = .008). Myelotoxicity occurred in 18 patients (4.8%) with a mean time of laboratory abnormalities appearing after 16 months. Nine patients had hepatotoxicity secondary to these drugs (2.4%); one of them developed nodular regenerative hyperplasia and portal hypertension. Ten patients had acute pancreatitis (2.7%) with a mean time occurrence of 27 days and a statistically significant association with Crohn's disease (P = .03) and smoking (P = .01). Fifteen patients had gastrointestinal intolerance (4%) but 5 were able to continue with medication given in divided doses or switching to MP.

CONCLUSIONS

Thiopurine immunomodulators have a significant percentage of AE (13.5%), which, although usually mild, forced us to follow up all cases and sometimes even suspend treatment.

Pharmacological management of autoimmune hepatitis

INTRODUCTION

Without prompt immunosuppressive treatment, autoimmune hepatitis is a devastating, albeit rare, liver disease. It affects both adults and children, being particularly aggressive in the latter. Eighty per cent of patients respond satisfactorily to treatment; the other 20% progress to end-stage liver disease and require transplantation.

AREAS COVERED

This review emphasizes the importance of a timely diagnosis of autoimmune hepatitis and provides a practical guide for its treatment. The authors summarize the treatment options available for autoimmune hepatitis and stress that most patients respond successfully to standard treatment with prednisolone and azathioprine, two well-tried and inexpensive drugs. The authors also review the options for difficult-to-treat patients (non-responders and frequent relapsers), for whom newer immunosuppressive agents--usually employed as anti-rejection drugs--have been tried with variable success.

EXPERT OPINION

Autoimmune hepatitis is exquisitely responsive to immunosuppression but treatment must be started as soon as possible to achieve full remission and halt progression of liver disease. New strategies aiming at treating the unresponsive patients and at specifically curbing the liver autoimmune attack, without provoking unwanted systemic side effects, are being investigated and may be available within the next 5 years.

Influences of thiopurine methyltransferase genotype and activity on thiopurine-induced leukopenia in Korean patients with inflammatory bowel disease: a retrospective cohort study

BACKGROUND AND AIM

Myelotoxicity has been shown to be very common in Korean patients with inflammatory bowel disease (IBD) during azathioprine (AZA) or 6-mercaptopurine (6-MP) treatment. The purpose of this study was to investigate the relative risk of the thiopurine methyltransferase (TPMT) and inosine triphosphate pyrophosphatase (ITPA) genotypes and TPMT activity for the development of leukopenia in Korean IBD patients during AZA/6-MP treatment.

METHODS

We retrospectively analyzed 286 Korean patients with IBD who had been treated with AZA/6-MP for at least 6 months between June 1996 and September 2006. Common TPMT mutations, including TPMT*1, *2, *3A, *3B, and *3C, and ITPA mutations, including 94C>A and IVS2+21A>C, were determined using a high-performance liquid chromatography method. TPMT activity was measured using liquid chromatography with coupled mass spectrometry/mass spectrometry.

RESULTS

Leukopenia occurred in 118 cases (41.3%). TPMT *1/*3C was detected in 7 cases (2.4%), and ITPA 94 C>A was detected in 66 cases (23.1%), including 63 heterozygotes (22.1%) and 3 homozygotes (1.0%). The median TPMT activity was 9.3 U/mL (interquartile range 10.4, range 2.1 to 76.2). Cox regression analysis revealed that patients with heterozygous *3C type TPMT had a higher probability of leukopenia than those with wild type TPMT (P=0.02). Patients with intermediate TPMT activity had a lower probability of leukopenia than those with low activity (P=0.01). However, the ITPA genotype did not affect the risk of leukopenia.

CONCLUSIONS

Our data showed that it could be helpful to examine TPMT genotypes and to measure TPMT activity in Korean patients taking AZA/6-MP to predict the development of leukopenia.

Thiopurines in Crohn's disease, is there something new?

IMPORTANCE OF THE FIELD

traditional immunosuppressants, including azathioprine, remain the mainstay of therapy in steroid dependent/refractory patients with inflammatory bowel diseases (IBD). The main limitations of its use are its side effects appearing in about a fifth of the patients, including myelosuppression and liver toxicity. Major complications occur in patients with low thiopurine-S-methyltransferase (TPMT) enzyme activity; however, the clinical relevance of these tests remains conflictive.

AREAS COVERED IN THIS REVIEW

in this review, the authors aim to summarize the new data regarding the relationship between the pharmacology of thiopurines and pathogenesis of adverse events.

WHAT THE READER WILL GAIN

readers will gain an understanding of the metabolism of thiopurines, side effect profile, pharmacological background of side effects, importance of metabolite monitoring, clinical relevance of inherited differences in drug metabolism and other conditions (e.g., concomitant use of allopurinol) which can modify enzyme activity. By gaining an understanding of the pharmacology and metabolism of thiopurines, clinicians will be able to optimize thiopurine therapy in IBD.

TAKE HOME MESSAGE

TPMT testing and metabolite monitoring are still not considered the standard of care, and clinicians will continue to choose the approach that best suits their clinical practice and patient needs. Regardless of what strategy is chosen, patients need to be carefully monitored and well informed about the potential risks.

Thiopurine maintenance therapy for ulcerative colitis: the clinical significance of monitoring 6-thioguanine nucleotide

BACKGROUND

6-Mercaptopurine (6-MP) is an effective maintenance medication in patients with ulcerative colitis (UC), but toxic effects like myelosuppression limit its clinical benefit. In the blood, 6-thioguanine (6-TGN) is formed from 6-MP and mediates the therapeutic efficacy and most of the toxicities of 6-MP. The level of 6-TGN depends on the activity of thiopurine methyltransferase (TPMT), inherited as 1 of its 3 polymorphic forms with low, moderate, or normal/high activity. Accordingly, the 6-MP dose needs to be pharmacogenetically guided.

METHODS

Patients with quiescent UC received 6-MP as maintenance therapy and 6-TGN was assayed as its concentrations in red blood cells (RBCs) done by high-performance liquid chromatography. In a preliminary investigation, 30 mg/day 6-MP (n = 50) was given orally over 12 weeks to determine the time course of blood 6-TGN level. Then 257 patients were given 6-MP at 15-80 mg/day in a stepwise manner based on RBC 6-TGN, white blood cell count, and body weight to monitor 6-MP efficacy and safety profiles.

RESULTS

At 30 mg/day 6-MP, RBC 6-TGN peaked over 4-8 weeks. In the main dosing study, the mean RBC 6-TGN level in patients who remained in remission during the 1-year observation time (n = 151) was 322.3 +/- 119.5 pmole/8 x 10(8) RBC versus 204.8 +/- 78.7 pmole/8 x 10(8) RBC in patients (n = 19) who relapsed (P < 0.001). Bone marrow suppression was seen almost exclusively at high 6-TGN concentration ranges. Further, a regression plot showed an inverse relationship between 6-TGN levels in RBC and TPMT enzyme activity.

CONCLUSIONS

By regularly measuring RBC 6-TGN in patients with quiescent UC receiving 6-MP as maintenance therapy, we could monitor bone marrow suppression as well as other toxic side effects. Potentially, this strategy should enable physicians to avoid thiopurine-related adverse effects and identify individuals who may benefit most from 6-MP maintenance therapy.

Thiopurine S- methyltransferase [corrected] testing in idiopathic pulmonary fibrosis: a pharmacogenetic cost-effectiveness analysis

Azathioprine in combination with N-acetylcysteine (NAC) and steroids is a standard therapy for idiopathic pulmonary fibrosis (IPF). Its use, however, is limited by its side effects, principally leukopenia. A genotypic assay, thiopurine S-methyltransferase (TPMT), has been developed that can potentially identify those at risk for developing leukopenia with azathioprine, and thereby limit its toxicity. In those with abnormal TPMT activity, azathioprine can be started at lower dose or an alternate regimen selected. Determine the cost-effectiveness of a treatment strategy using TPMT testing before initiation of azathioprine, NAC, and steroids in IPF by performing a computer-based simulation. We developed a decision analytic model comparing three strategies: azathioprine, NAC and steroids with and without prior TPMT testing, and conservative therapy, consisting of only supportive measures. Prevalence of abnormal TPMT alleles and complication rates of therapy were taken from the literature. We assumed a 12.5% incidence of abnormal TPMT alleles, 4% overall incidence of leukopenia while taking azathioprine, and that azathioprine, NAC, and steroids in combination reduced IPF disease progression by 14% during 12 months. TPMT testing before azathioprine, NAC, and steroids was the most effective and most costly strategy. The marginal cost-effectiveness of the TPMT testing strategy was $49,156 per quality adjusted life year (QALY) gained versus conservative treatment. Compared with azathioprine, NAC and steroids without prior testing, the TPMT testing strategy cost only $29,662 per QALY gained. In sensitivity analyses, when the prevalence of abnormal TPMT alleles was higher than our base case, TPMT was "cost-effective." At prevalence rates lower than our base case, it was not. TPMT testing before initiating therapy with azathioprine, NAC, and steroids is a cost-effective treatment strategy for IPF.

Managing the risks of IBD therapy

Successful management of the patient with inflammatory bowel disease (IBD) involves not only the induction and maintenance of remission, but also the optimization of the benefit-to-risk equation to achieve the greatest gain in quality of life. These risks range from intolerance to prescribed medications to potentially life-threatening sequelae (eg, sepsis) of immune suppression. A proper awareness of risk on the part of the physician and education of the patient can lead to early detection and institution of an appropriate management plan, including risk management and, optimally, primary prevention (eg, prophylactic vaccination). One should take the opportunity regularly to reassess the utility and efficacy of existing therapy, with the provision of ineffective therapies mandating urgent review. Overall, optimal management of the patient with IBD requires open dialogue between clinician and patient so that both are cognizant of the goals, benefits, and potential risks of therapy.

Thiopurine S-methyltransferase pharmacogenetics in a large-scale healthy Italian-Caucasian population: differences in enzyme activity

AIMS

To investigate the influence of genotype, age and gender on the thiopurine S-methyltransferase (TPMT) phenotype in healthy Italian-Caucasian subjects.

MATERIALS & METHODS

The study investigated the TPMT genotype and the TPMT phenotype of 943 healthy Italian-Caucasian subjects of different age and gender (age range: 0.08-68 years; 623 males 320 females). TPMT red blood cell activity was measured in all samples and genotype was determined for the TPMT alleles *2, *3A, *3B and *3C.

RESULTS

TPMT activity levels in our whole population ranged from 1.6 up to 75.2 U/gHb. Significant TPMT activity differences between wild-type and heterozygous subjects were observed. We divided our TPMT activity into four categories according to our frequency distribution: low (0.1%), intermediate (32.9%), normal (60%) and high (7%), with arbitrary cut-off values of 8.0, 19.4 and 37.0 U/gHb, respectively. The whole population had a total of 94.5% of homozygous wild-type subjects, 5.4% heterozygous variants and one (0.1%) compound heterozygous variant TPMT*3B/*3C. The overall concordance rate between TPMT genotypes and phenotypes was 71.6%. The TPMT activity was significantly higher in wild-type children (0.08-17 years) than in wild-type adults (aged 18-68 years). Moreover, it was noted that wild-type infants from 0.08 to 5 years had a 9% higher average TPMT activity than the other wild-type groups, and only in children from 0.08 to 2 years was the TPMT activity higher in males than in females.

CONCLUSION

The data obtained in this study show that genetic factors seem to be the major aspect in TPMT phenotype variability in adults, whilst, in children, other physiological factors should be taken into consideration when assessing the TPMT phenotype, such as age and gender.