Thiopurine Dose Research Articles

Genetic profiling of NUDT15 in the Slovenian population.

Determining variant TPMT alleles to predict patient response to thiopurine therapy represents one of the first successful implementations of pharmacogenomics in clinical practice. However, despite the TPMT-adjusted thiopurine dosing, some TPMT wild-type patients still exhibit toxicity at standard doses. Over the past decade, the pharmacogene NUDT15 has emerged as a significant co-modulator of thiopurine therapy. Initially, NUDT15 was considered important predominantly in Asian populations, but recent studies have highlighted its relevance in European populations as well.To evaluate the pharmacogenetic significance of NUDT15 in the Slovenian population, we sequenced extended regions of exon 1 and exon 3 in 109 healthy individuals and 37 patients with acute lymphoblastic leukemia.We identified eight variants, including one with established clinical significance (allele *3) and one extremely rare variant (Chr13 at 48045861; GRCh38, NC_000013.11). The frequencies of most previously described variants in both the general population and in the ALL cohort were consistent with those reported in other European populations, except for rs45465203, which was less frequent in the Slovenian population. None of the variants, except for NUDT15*3, were associated with cumulative thiopurine doses in ALL patients. However, these variants warrant further investigation in larger ALL cohorts.

Effectiveness of Early Thiopurine Use in Korean Patients With Moderate-to-Severe Ulcerative Colitis: A Prospective Multicenter Cohort (MOSAIK) Study.

Thiopurines play an important role in the management of steroid-refractory and steroid-dependent ulcerative colitis. However, the effectiveness of the early use of thiopurines in ulcerative colitis remains controversial. In this multicenter prospective cohort (MOSAIK) study, we divided patients with ulcerative colitis into those who underwent early (within 6mo of diagnosis) and late (6mo after diagnosis) thiopurine therapy to determine the effectiveness of early thiopurine treatment. The primary outcome was the cumulative rate of clinical relapse (Mayo score >2 points). Multivariate Cox proportional hazards regression was used to identify independent clinical factors associated with the outcomes. Overall, 333 patients with moderate-to-severe ulcerative colitis were included. Of the 118 patients treated with thiopurines, 65 (55.1%) and 53 (44.9%) received thiopurine therapy within and after 6 months of diagnosis. The cumulative use rate of thiopurines was 38.9% at 3 years after diagnosis. The median initial dose of thiopurines was 0.7mg/kg (0.3 to 2.0); the median maintenance dose was 1.1mg/kg (0.3 to 2.4). The cumulative rate of clinical relapse was not significantly different between patients who started thiopurine therapy within 6 months of diagnosis and those who started therapy 6 months after diagnosis (P=0.712). The presence of extraintestinal manifestations (hazard ratio: 4.674, 95% CI: 1.210-18.061, P=0.025) independently predicted an increased risk of clinical relapse. Patients with ulcerative colitis who received early thiopurine therapy did not differ significantly in terms of clinical relapse compared with those who received late therapy.

Genotype and Phenotype Correlation of the TPMT∗8 Allele in Thiopurine Metabolism

Thiopurine 6-mercaptopurine (6-MP) is metabolized by thiopurine methyl transferase (TPMT). TPMT genetic variation results in some individuals having reduced or absent TPMT enzyme activity. If these individuals take a full thiopurine dose, life-threatening adverse events can occur. Testing identifies patients with reduced or absent TPMT activity and is recommended prior to initiation of therapy. The TPMT*8 allele, defined by c.644G>A (p.Arg215His), is common among individuals of African ancestry (∼2.3% minor allele frequency), but is not included in genotyping recommendations due to its uncertain function. Here, a clinical TPMT enzyme activity assay was used to assess TPMT activity in red blood cells from 982 patients, including those with *1/*8 (n=22), *3A/*8 (n=1), and *3C/*8 (n=1) TPMT diplotypes. The average 6-MMP production (primary TPMT product measured clinically) was 3.08 ± 0.16 nmol/mL/hr for *1/*8 individuals, compared to 3.77 ± 0.03 nmol/mL/hr for normal metabolizers (p=0.0001) and 2.39 ± 0.06 nmol 6-MMP/mL/hr for intermediate metabolizers (p<0.0001). Individuals with a TPMT*1/*8 diplotype demonstrated reduced 6-MP metabolism between that of normal metabolizers and intermediate metabolizers, suggesting that TPMT*8 is a reduced function allele.

A systematic review of aspects of NUDT15 pharmacogenomic variants and thiopurine-induced myelosuppression

Abstract Objectives Evidence for NUDT15 pharmacogenomic variants and thiopurine-induced myelosuppression (TIM), consists predominantly of association data in Asian, mixed variant homozygote/heterozygote populations. We therefore sought evidence on; (i) NUDT15 genotype-guided thiopurine dosing. (ii) Association data for TIM in NUDT15 variant heterozygotes with inflammatory bowel disease. (iii) Association data for NUDT15 variants with TIM in Europeans. (iv) Health economic data for NUDT15 genotyping in inflammatory bowel disease. Methods A systematic review was conducted, consisting of database searches, screening against pre-defined inclusion/exclusion criteria, and assessment of risk of bias using study-specific appraisal tools. Key findings Titles/abstracts of 493 articles were screened, with 29 studies included. (i) Significant reductions in TIM with genotype-guided thiopurine dosing were reported by both trials and a cohort study. (ii) TIM rates were significantly higher in NUDT15*3 heterozygotes vs. wild type. Data were conflicting for rarer variants. (iii) Four of five studies reported an association with TIM for at least one or a combination of NUDT15 variants in Europeans (OR 9.5–38.2), but data were conflicting. (iv) Both health economic analyses found TPMT/NUDT15 genotyping cost-effective in Asian populations, but not when a European population was considered. Conclusion Limited data showed an association with TIM in NUDT15 variant heterozygotes and Europeans and the potential for genotype-guided dosing to reduce TIM. Studies were generally small, heterogenous, and of variable quality. The low prevalence of rarer NUDT15 variants/variants in Europeans likely contributed to contradictory findings. Further research on the clinical utility of genotyping in diverse populations will help inform future economic analyses.

Optimizing thiopurine therapy in autoimmune hepatitis: A multicenter study on monitoring metabolite profiles and co-therapy with allopurinol.

In autoimmune hepatitis, achieving complete biochemical remission (CBR) with current weight-based thiopurine dosing is challenging. We investigated whether patients could be stratified regarding CBR according to a target range of thiopurine metabolites. Moreover, we explored the effects of azathioprine dosage increases and co-therapy of allopurinol with low-dose thiopurines on metabolite profiles and treatment response. The relation between metabolites and treatment response was assessed in 337 individuals from 4 European centers. In a global, cross-sectional analysis, active metabolites 6-thioguanine nucleotides (6TGN) were similar in those with and without CBR. However, analyzing patients with sequential measurements over 4 years (N = 146) revealed higher average 6TGN levels in those with stable CBR (260pmol/0.2mL) compared to those failing to maintain CBR (181pmol/0.2mL; p = 0.0014) or never achieving CBR (153pmol/0.2mL; p < 0.0001), with an optimal 6TGN cutoff of ≥223pmol/0.2mL (sensitivity: 76% and specificity: 78%). Only 42% exhibited 6TGN ≥223pmol/0.2mL following weight-based dosing, as doses weakly correlated with 6TGN but with 6-methylmercaptopurine (6MMP), a metabolite associated with toxicity. Azathioprine dose increases led to preferential 6MMP formation (+127% vs. 6TGN +34%; p < 0.0001). Conversely, adding allopurinol to thiopurines in difficult-to-treat patients (N = 36) raised 6TGN (168→321pmol/0.2mL; p < 0.0001) and lowered 6MMP (2125→184pmol/0.2mL; p < 0.0001), resulting in improved transaminases in all patients and long-term CBR in 75%. Maintaining CBR in autoimmune hepatitis was associated with 6TGN ≥223pmol/0.2mL. For patients who fail to achieve CBR and therapeutic 6TGN levels despite thiopurine dose increase due to preferential 6MMP formation, comedication of allopurinol alongside low-dose thiopurines represents an efficient alternative.

Landscape of TPMT and NUDT15 Pharmacogenetic Variation in a Cohort of Canadian Pediatric Inflammatory Bowel Disease Patients.

Patients with inflammatory bowel disease (IBD) exhibit considerable interindividual variability in medication response, highlighting the need for precision medicine approaches to optimize and tailor treatment. Pharmacogenetics (PGx) offers the ability to individualize dosing by examining genetic factors underlying the metabolism of medications such as thiopurines. Pharmacogenetic testing can identify individuals who may be at risk for thiopurine dose-dependent adverse reactions including myelosuppression. We aimed to evaluate PGx variation in genes supported by clinical guidelines that inform dosing of thiopurines and characterize differences in the distribution of actionable PGx variation among diverse ancestral groups. Pharmacogenetic variation in TPMT and NUDT15 was captured by genome-wide genotyping of 1083 pediatric IBD patients from a diverse Canadian cohort. Genetic ancestry was inferred using principal component analysis. The proportion of PGx variation and associated metabolizer status phenotypes was compared across 5 genetic ancestral groups within the cohort (Admixed American, African, East Asian, European, and South Asian) and to prior global estimates from corresponding populations. Collectively, 11% of the cohort was categorized as intermediate or poor metabolizers of thiopurines, which would warrant a significant dose reduction or selection of alternate therapy. Clinically actionable variation in TPMT was more prevalent in participants of European and Admixed American/Latino ancestry (8.7% and 7.5%, respectively), whereas variation in NUDT15 was more prevalent in participants of East Asian and Admixed American/Latino ancestry (16% and 15% respectively). These findings demonstrate the considerable interpopulation variability in PGx variation underlying thiopurine metabolism, which should be factored into testing diverse patient populations.

Mechanisms and management of loss of response to anti-TNF therapy for patients with Crohn's disease: 3-year data from the prospective, multicentre PANTS cohort study

We sought to report the effectiveness of infliximab and adalimumab over the first 3 years of treatment and to define the factors that predict anti-TNF treatment failure and the strategies that prevent or mitigate loss of response. Personalised Anti-TNF therapy in Crohn's disease (PANTS) is a UK-wide, multicentre, prospective observational cohort study reporting the rates of effectiveness of infliximab and adalimumab in anti-TNF-naive patients with active luminal Crohn's disease aged 6 years and older. At the end of the first year, sites were invited to enrol participants still receiving study drug into the 2-year PANTS-extension study. We estimated rates of remission across the whole cohort at the end of years 1, 2, and 3 of the study using a modified survival technique with permutation testing. Multivariable regression and survival analyses were used to identify factors associated with loss of response in patients who had initially responded to anti-TNF therapy and with immunogenicity. Loss of response was defined in patients who initially responded to anti-TNF therapy at the end of induction and who subsequently developed symptomatic activity that warranted an escalation of steroid, immunomodulatory, or anti-TNF therapy, resectional surgery, or exit from study due to treatment failure. This study was registered with ClinicalTrials.gov, NCT03088449, and is now complete. Between March 19, 2014, and Sept 21, 2017, 389 (41%) of 955 patients treated with infliximab and 209 (32%) of 655 treated with adalimumab in the PANTS study entered the PANTS-extension study (median age 32·5 years [IQR 22·1-46·8], 307 [51%] of 598 were female, and 291 [49%] were male). The estimated proportion of patients in remission at the end of years 1, 2, and 3 were, for infliximab 40·2% (95% CI 36·7-43·7), 34·4% (29·9-39·0), and 34·7% (29·8-39·5), and for adalimumab 35·9% (95% CI 31·2-40·5), 32·9% (26·8-39·2), and 28·9% (21·9-36·3), respectively. Optimal drug concentrations at week 14 to predict remission at any later timepoints were 6·1-10·0 mg/L for infliximab and 10·1-12·0 mg/L for adalimumab. After excluding patients who had primary non-response, the estimated proportions of patients who had loss of response by years 1, 2, and 3 were, for infliximab 34·4% (95% CI 30·4-38·2), 54·5% (49·4-59·0), and 60·0% (54·1-65·2), and for adalimumab 32·1% (26·7-37·1), 47·2% (40·2-53·4), and 68·4% (50·9-79·7), respectively. In multivariable analysis, loss of response at year 2 and 3 for patients treated with infliximab and adalimumab was predicted by low anti-TNF drug concentrations at week 14 (infliximab: hazard ratio [HR] for each ten-fold increase in drug concentration 0·45 [95% CI 0·30-0·67], adalimumab: 0·39 [0·22-0·70]). For patients treated with infliximab, loss of response was also associated with female sex (vs male sex; HR 1·47 [95% CI 1·11-1·95]), obesity (vs not obese 1·62 [1·08-2·42]), baseline white cell count (1·06 [1·02-1·11) per 1 × 109 increase in cells per L), and thiopurine dose quartile. Among patients treated with adalimumab, carriage of the HLA-DQA1*05 risk variant was associated with loss of response (HR 1·95 [95% CI 1·17-3·25]). By the end of year 3, the estimated proportion of patients who developed anti-drug antibodies associated with undetectable drug concentrations was 44·0% (95% CI 38·1-49·4) among patients treated with infliximab and 20·3% (13·8-26·2) among those treated with adalimumab. The development of anti-drug antibodies associated with undetectable drug concentrations was significantly associated with treatment without concomitant immunomodulator use for both groups (HR for immunomodulator use: infliximab 0·40 [95% CI 0·31-0·52], adalimumab 0·42 [95% CI 0·24-0·75]), and with carriage of HLA-DQA1*05 risk variant for infliximab (HR for carriage of risk variant: infliximab 1·46 [1·13-1·88]) but not for adalimumab (HR 1·60 [0·92-2·77]). Concomitant use of an immunomodulator before or on the day of starting infliximab was associated with increased time without the development of anti-drug antibodies associated with undetectable drug concentrations compared with use of infliximab alone (HR 2·87 [95% CI 2·20-3·74]) or introduction of an immunomodulator after anti-TNF initiation (1·70 [1·11-2·59]). In years 2 and 3, 16 (4%) of 389 patients treated with infliximab and 11 (5%) of 209 treated with adalimumab had adverse events leading to treatment withdrawal. Nine (2%) patients treated with infliximab and two (1%) of those treated with adalimumab had serious infections in years 2 and 3. Only around a third of patients with active luminal Crohn's disease treated with an anti-TNF drug were in remission at the end of 3 years of treatment. Low drug concentrations at the end of the induction period predict loss of response by year 3 of treatment, suggesting higher drug concentrations during the first year of treatment, particularly during induction, might lead to better long-term outcomes. Anti-drug antibodies associated with undetectable drug concentrations of infliximab, but not adalimumab, can be predicted by carriage of HLA-DQA1*05 and mitigated by concomitant immunomodulator use for both drugs. Guts UK, Crohn's and Colitis UK, Cure Crohn's Colitis, AbbVie, Merck Sharp and Dohme, Napp Pharmaceuticals, Pfizer, and Celltrion Healthcare.

Thiopurine Metabolite Shunting in Late Pregnancy Increases the Risk of Intrahepatic Cholestasis of Pregnancy in Women With Inflammatory Bowel Disease, and Can be Managed With Split Dosing.

The risk of intrahepatic cholestasis of pregnancy [ICP] is increased in thiopurine-exposed pregnancies. Thiopurine 'shunting', with a 6-methylmercaptopurine [MMP] to 6-thioguanine [TGN] ratio of >11, progresses over pregnancy, and may promote ICP development. We aimed to explore the association between thiopurine exposure and ICP, including the hypothesised impact of thiopurine shunting, and identify risk minimisation strategies. This prospective multicentre cohort study compared thiopurine and biologic monotherapy-exposed pregnant participants. Disease activity and obstetric outcome data, thiopurine metabolites, bile acids, and transaminases were obtained before conception, in each trimester, at delivery, and postpartum. Thiopurine dose management was at the discretion of the treating physician. Included were 131 thiopurine and 147 biologic monotherapy-exposed pregnancies. MMP/TGN ratio increased from preconception to third trimester [p <0.01], with approximately 25% of participants shunting in pregnancy. Second trimester split dosing led to a decrease in the median MMP/TGN ratio from 18 (interquartile range [IQR] 6-57) to 3 [IQR 2-3.5] at delivery [p = 0.04]. The risk of ICP was increased in thiopurine-exposed pregnancies (6.7% [7/105] vs 0% [0/112], p <0.001), with all ICP cases occurring in the setting of antenatal thiopurine shunting. Thiopurine dose increases (risk ratio [RR] 8.10, 95% confidence interval [CI] 1.88-34.85, p = 0.005) and shunting in third trimester [6.20, 1.21-30.73, p = 0.028] and at delivery [14.18, 1.62-123.9, p = 0.016] were associated with an increased risk of ICP. Thiopurine exposure is associated with an increased risk of ICP, particularly following dose increases antenatally and with shunting in late pregnancy. The latter may be effectively managed with split dosing, although further studies are warranted.

NUDT15 and TPMT polymorphisms in three distinct native populations of the Brazilian Amazon.

This is the first report of the distribution of TPMT and NUDT15 single nucleotide polymorphisms and metabolic phenotypes associated with cytotoxicity of thiopurine drugs, in indigenous groups of Brazilian Amazon: Munduruku, Paiter-Suruí and Yanomami. The minor allele frequency (MAF) of NUDT15 rs116855232 did not differ significantly across the groups; TPMT rs1800462 was absent, while rs1800460 and rs1142345 were in strong linkage disequilibrium, and 10- and 30-fold more common in Paiter-Suruí. Indeed, the MAFs in Paiter-Surui (0.193 and 0.188) are the largest report globally. The distribution of combined NUDT15/TPMT metabolic phenotypes differed significantly (p < 0.0001) and largely (Cramér´s V = 0.37) across cohorts. This has important pharmacogenetic implications: the Clinical Pharmacogenetics Implementation Consortium recommendations to reduce or consider reduction of thiopurine dose applies to 4.4% Yanomami, 5.6% Munduruku, versus 41% Paiter-Suruí. The proportion of Paiter-Suruí at risk of thiopurine intolerance is 3- to 4-fold higher than any other population worldwide.

P617 Persistent active inflammation may predict non-improvement in bone mass density in patients with Crohn's disease

Abstract Background Osteopenia and osteoporosis are associated with Crohn’s disease (CD). Diagnosis is made by dual-energy X-ray absorptiometry scan (DEXA). Pathophysiology of osteoporosis may reflect an interplay between persistent inflammation, steroid usage, as well as risk factors similar to general population. We aimed to identify factors associated with low or deteriorating bone mineral density (BMD) among patients. Methods A retrospective case-control study, included patients with CD followed at our IBD clinic from January 2000 to February 2023, with ≥ 2 DEXA scans. The observation started one year before the initial DEXA scan and extended until one year after the second scan. Demographic, clinical and laboratory data as well as medication exposure were collected before and during F/U. Patients were classified into three groups based on change in DEXA results: improved, worsened and no change. Multivariable proportional odds regression model was built to assess independent predictors of change in BMD. Results 121 patients [60 (49.6%) females, median age 33 years (IQR 23-43), median disease duration 5 years (IQR 0-35), median baseline BMI 22.4 kg/m2 (IQR 12.9-39.3), baseline CRP 1.4 ULN (IQR 0.5-4.5), baseline vitamin D 54.2 nmol/L (IQR 40.9-67.5)], were enrolled and followed for a median of 48 (IQR 29-71) months. At baseline, patients with osteoporosis had a lower BMI (18.5 kg/m2) than patients with normal BMD (26 kg/m2) and osteopenia (22.4 kg/m2), p&amp;lt;0.001. During F/U 63%, 59% and 66% of patients were exposed to high dose CS, anti-TNF and thiopurines respectively. At the end of F/U,19 (15.7%) patients had deterioration in BMD status while 78 (64.5%) remained unchanged, and in 24 (19.8%) BMD improved. Baseline vitamin D levels (in nmol/L) were higher in patients with improvement in BMD status at the end of the F/U compared to those with maintained or deterioration in BMD (66, 54.2, 41.2; p=0.001, Figure 1). Active smoking was associated with decline in BMD status (p=0.03). No correlation was found between different types of medication exposure and changes in BMD status. In multivariable analysis, elevated CRP was the only independent variable associated with lower odds of improvement in BMD (OR=0.45 (CI 0.2-1.0), p=0.05,Table 1). Conclusion Low BMI, low baseline vitamin D levels, and active smoking were found to be risk factors for low BMD status. Elevated CRP was associated with lack of improvement in BMD during the F/U. No correlation was found between different medications and changes in BMD status.

P631 Effectiveness of Early Thiopurine Use in Korean Patients with Moderate-to-Severe Ulcerative Colitis: A Prospective Multicenter Cohort (MOSAIK) study

Abstract Background Thiopurines play an important role in the management of steroid-refractory steroid-dependent ulcerative colitis (UC). However, the effectiveness of the early use of thiopurines in UC remains controversial. Methods In this multicenter prospective cohort study, we divided patients with UC into those who underwent early (within 6 months of diagnosis) and late (6 months after diagnosis) thiopurine therapy to determine the effectiveness of early thiopurine treatment. The primary outcome was the cumulative rate of clinical relapse (Mayo score &amp;gt;2 points). Multivariate Cox proportional hazards regression was used to identify independent clinical factors associated with the outcomes. Results Overall, 333 patients with moderate-to-severe UC were included in the MOSAIK study. Of the 118 patients treated with thiopurines, 65 (55.1%) and 53 (44.9%) received thiopurine therapy within and after 6 months of diagnosis. The cumulative use rate of thiopurines was 38.96% at 3 years after diagnosis. The median initial dose of thiopurines was 0.7 mg/kg (0.3–2.0), and the median maintenance dose was 1.1 mg/kg (0.3–2.4). The cumulative rate of clinical relapse was not significantly different between patients who started thiopurine therapy within 6 months of diagnosis and those who started therapy 6 months after diagnosis during a 3–year period (p = 0.712). Multivariate analysis showed that the presence of extraintestinal manifestations (hazard ratio [HR]: 4.674, 95% CI: 1.210–18.061, p = 0.025) independently predicted an increased risk of clinical relapse. Conclusion Patients with UC who received early thiopurine therapy did not differ significantly in terms of clinical relapse compared with those who received late therapy.

OP11 Exploring the potential clinical utility of NUDT15 pharmacogenetic testing in clinical practice: a ‘focused reverse phenotyping’ study in the UK IBD Bioresource

Abstract Background In a previous study we recruited patients with inflammatory bowel disease (IBD) and a history of thiopurine induced myelosuppression (TIM) and identified associated variants in NUDT15. This widely used phenotype-first approach, is limited by ascertainment and recall bias, which impacts understanding of penetrance, expressivity, and variant pathogenicity that are key to clinical implementation. The United Kingdom (UK) National Institute for Health Research (NIHR) IBD Bioresource allows investigators to select large numbers of subjects based on genomic variants of interest, rather than phenotypes, to overcome these biases. Using this ‘focused reverse phenotyping’ approach we sought to investigate the cumulative 6-month risk of myelosuppression in patients with NUDT15 variants. Methods Cases and controls were identified from whole exome sequencing data. Cases included all participants with a loss of function NUDT15 variant (*2, *3, *4, *5, *6 and *9). Control subjects were selected based on wild-type carriage of NUDT15 and TPMT, matched for ethnicity. Our primary outcome measure was time to TIM. Myelosuppression was defined as a white cell count (WCC) &amp;lt;3.5x109/L or a neutrophil count &amp;lt;2.0x109/L that occurred within six months of achieving the maximum thiopurine dose, or in the absence of blood test results, a decision to reduce the dose of or withdraw the thiopurine due to myelosuppression. Severe myelosuppression was defined as a WCC &amp;lt;2.5x109/L or neutrophil count &amp;lt;1.0x109/L and a decision to either reduce the dose of or stop the thiopurine. Results We screened 23,082 patients recruited to the UK NIHR IBD bioresource with whole exome sequence data and identified 451 patients with a loss of function NUDT15 variant. We matched, based on ethnicity, these patients to 916 controls. Overall, 271/21,136 (1.3%) Caucasians and 127/1,089 (11.7%) South Asian carried an NUDT15 variant allele. 239/451 (60%) cases had a history of thiopurine exposure. The median weight-adjusted maximum thiopurine dose amongst cases and controls was 1.78 and 1.79 mg/kg/day, respectively. The time to myelosuppression was shorter in patients with NUDT15 variants as shown in Figure 1. The risk of myelosuppression, severe myelosuppression, and hospitalisation was also higher in patients with NUDT15 variants as shown in table 1. Conclusion In this reverse phenotyping study, the time to myelosuppression was significantly shorter in patients who carried a loss of function NUDT15 variant. The overall risk of myelosuppression was lower than previously observed in phenotype-first studies. Prior to implementation further analysis of the cost-effectiveness of NUDT15 testing is required.

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

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). 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. 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. 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.

Cumulative thiopurine dosing and keratinocyte skin cancer in inflammatory bowel disease: a case-control study.

Patients with inflammatory bowel disease (IBD) treated with thiopurines are at increased risk of keratinocyte skin cancer (KSC). Most international guidelines recommend yearly dermatological screening of thiopurine-treated patients. Whether the association between the development of KSC and the use of thiopurines is dose-dependent remains unclear. The aim of this study was to investigate the association between the cumulative thiopurine dose and KSC development in patients with IBD which can be helpful to assist in further skin cancer risk stratification and personalization of screening recommendations in patients with IBD. We performed a single-center case-control study, including patients with IBD with and without a history of KSC (cases and controls, respectively). The primary outcome was the association of cumulative azathioprine, mercaptopurine and thioguanine dose with KSC development. Univariable and multivariable logistic regression analyses were performed, the latter corrected for age and smoking, known risk factors of KSC. We included 50 cases and 150 controls, predominantly white population. Age and current azathioprine use were univariably significantly associated with KSC development. In multivariable logistic regression analyses, age at inclusion remained significantly associated. Cumulative doses of thiopurines (separate or combined) or duration of thiopurine use did not impact KSC risk, also after correcting for age and smoking. Cumulative thiopurine dose and duration did not show an association with KSC development. Future KSC risk stratification, based on all available KSC risk factors, may aid in selecting individuals who can benefit most from dermatologic screening programs.

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

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. 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. 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. 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.

A Simple, Rapid, and Cost-Effective PCR Procedure for Detection of NUDT15 Gene Variants in Vietnamese Patients with Acute Lymphoblastic Leukemia.

Objective The NUDT15 variants impact thiopurine dose selection in acute lymphoblastic leukemia patients. The ability to rapidly detect variants is important in clinical practice. This study aims to develop a simple polymerase chain reaction (PCR) procedure for detecting NUDT15 variants in Vietnamese patients. Materials and Methods Sanger sequencing was used to determine NUDT15 variants from 200 patients. We designed primers and optimized the PCR procedure for detection of wild-type and variant alleles and compared with Sanger sequencing results. Results The inserted variant c.55_56insGAGTCG was detected by differences in size through conventional PCR. The tetra-primer amplification refractory mutation system PCR was successful in detecting two variations, c.52G > A and c.415C > T. The sensitivity and specificity of PCR procedure achieved 100% when compared to 200 Sanger sequencing results. Conclusion Our PCR procedure is suitable for replacing Sanger sequencing to detect the NUDT15 variants in clinical setting.

Systematic review: The effectiveness of 6-thioguanine nucleotide-based dose optimisation of thiopurines in the treatment of inflammatory bowel disease

Introduction: Clinical guidelines highlight the potential utility of metabolite-based thiopurine dose optimisation strategies in inflammatory bowel disease (IBD). The aim of this review was to summarise the evidence of effectiveness and safety of a 6-thioguanine nucleotide (6-TGN) metabolite-based dosing strategy for maintenance of remission using azathioprine or mercaptopurine in Crohn's disease and ulcerative colitis. Methods: We searched the Cochrane central register of controlled trials, EMBASE, clinicaltrials.gov, the WHO international clinical trials registry platform, and relevant grey literature, up to 1 December 2021. Inclusion criteria were: all randomised (active comparator) controlled trials of azathioprine or mercaptopurine used for the purposes of maintenance of remission in Crohn's disease or ulcerative colitis where the dose in the intervention arm was optimised based on 6-TGN metabolite assay results. Studies of any duration were eligible for inclusion, and no age restrictions were applied. Results: No studies met the eligibility criteria for this review. Four randomised controlled studies (two of which are currently underway) were identified that assessed the effectiveness of metabolite-based dose optimisation for thiopurine therapy, but were not eligible either because they did not differentiate between induction and maintenance therapy or because of a lack of an appropriate active comparator. Conclusions: There is no RCT-based evidence for dose optimisation using a 6-TGN metabolite-based dosing strategy for maintenance of remission in Crohn's disease or ulcerative colitis. Where evidence is available from combination induction and maintenance trials, it suggests that such a strategy is no better than weight-based dosing. Cochrane protocol registration: CD014795

P440 Prevalence of NUDT15 polymorphisms and incidence of thiopurine-induced leukopenia in Inflammatory Bowel Disease patients: A systematic review and meta-analysis

Abstract Background Nudix hydrolase 15 (NUDT15) genetic polymorphisms confer an increased risk of thiopurine-induced myelosuppression (TIM). Thiopurines continue to be widely used as maintenance therapy for inflammatory bowel disease (IBD) in patients worldwide. However, the global prevalence of NUDT15 variants and incidence of TIM in IBD remains unclear. We aimed to evaluate the global prevalence of NUDT15 polymorphisms in IBD patients and incidence of thiopurine-induced leukopenia in patients with these polymorphisms. Methods We searched Medline, Embase, Emcare, CINAHL, APA PsycInfo and the Cochrane Library databases from inception until 7 July 2022. Full-text articles and conference abstracts reporting the frequency of any NUDT15 polymorphism and/or frequency of leukopenia in adult IBD patients with these variants, were included. Studies that examined paediatric populations or mixed disease populations, or reported duplicate data, were excluded. A random effects model was performed to estimate the pooled prevalence of NUDT15 variants, pooled prevalence of early (≤8 weeks) and late (&amp;gt;8 weeks) leukopenia and relative risk (RR) of developing leukopenia. Results 20 studies comprising 5232 IBD patients were included. The pooled prevalence of the *1/*1 wild type genotype was 83% (95% CI: 0.78-0.88). The pooled prevalence of the *1/*3 c.415C&amp;gt;T C/T variant was 13% (95% CI: 0.10-0.18), *3/*3 c.415C&amp;gt;T T/T variant was 2% (95% CI: 0.01-0.02), *1/*5 c.52G&amp;gt;A G/A variant was 2% (95% CI: 0.01-0.03) and *1/*6 c.36_37insGGAGTC ins/- variant was 7% (95% CI: 0.04-0.12). Subgroup analyses showed a higher pooled prevalence of the *1/*3 c.415C&amp;gt;T C/T variant in Japanese (20%, 95% CI: 0.16-0.24) and Chinese patients (18%, 95% CI: 0.12-0.27). Patients with the *1/*3 c.415C&amp;gt;T C/T variant had a RR of 4.12 (95% CI: 2.87-5.91) of developing leukopenia relative to the *1/*1 genotype, and the pooled prevalence of early leukopenia was 20% (95% CI: 0.16-0.26) and late leukopenia was 36% (95% CI: 0.26-0.49). Patients with the *3/*3 c.415C&amp;gt;T T/T variant had a RR of 9.38 (95% CI: 5.17-17.01) of developing leukopenia relative to the *1/*1 genotype, and the pooled prevalence of early leukopenia was 99% (95% CI: 0.07-1.00). The pooled prevalence of early leukopenia was 49% (95% CI: 0.29-0.69) in patients with the *1/*6 c.36_37insGGAGTC ins/- variant. Conclusion NUDT15 polymorphisms are common in IBD patients and strongly predict thiopurine-induced leukopenia. The most common variant was the *1/*3 c.415C&amp;gt;T C/T variant and the *3/*3 c.415C&amp;gt;T T/T variant was associated with the highest risk of leukopenia. Pre-treatment genotyping for NUDT15 variants should be considered particularly in Asian populations, to guide individualised thiopurine dosing and avoid myelotoxicity.

The role of therapeutic drug monitoring in the management of inflammatory bowel disease

Therapeutic drug monitoring (TDM) is performed when a drug has a narrow therapeutic range (e.g., thiopurines) or there is no linear drug response relationship (biologic agents). TDM is the measurement of drug and/or antibody concentration and individualizing the dose to maintain the drug concentration in the target range. Maintaining serum drug concentration in a therapeutic range is associated with a higher rate of favorable outcomes. Reactive drug monitoring is performed when the disease is active, and proactive drug monitoring is performed when the disease is in remission. Thiopurines still form an important therapeutic armamentarium in the treatment of inflammatory bowel disease (IBD) but have a narrow therapeutic range. Preemptive thiopurine methyl transferase and nucleoside diphosphate-linked moiety X-type motif (NUDT) genotype measurement can reduce the toxicity with appropriate dose initiation and thiopurine metabolite measurement can optimize the dose and reduce the toxicity. Antitumor necrosis factor agents brought about a paradigm shift in the management of moderate-to-severe IBD at the turn of the past century. Despite their efficacy, up to half the patients discontinue the biologic agents at the end of 1 year due to primary nonresponse or secondary loss of response. TDM can optimize the drug level and improve clinical response, reduce antibody formation, reduce cost, and can improve corticosteroid- free clinical remission. Despite postulated benefits and guidelines, the evidence for objective benefits from meta-analysis is mixed. This article reviews the current concepts regarding TDM.

Optimizing thiopurine therapy in children with acute lymphoblastic leukemia: A promising "MINT" sequencing strategy and therapeutic "DNA-TG" monitoring.

Thiopurines, including thioguanine (TG), 6-mercaptopurine (6-MP), and azathioprine (AZA), are extensively used in clinical practice in children with acute lymphoblastic leukemia (ALL) and inflammatory bowel diseases. However, the common adverse effects caused by myelosuppression and hepatotoxicity limit their application. Metabolizing enzymes such as thiopurine S-methyltransferase (TPMT), nudix hydrolase 15 (NUDT15), inosine triphosphate pyrophosphohydrolase (ITPA), and drug transporters like multidrug resistance-associated protein 4 (MRP4) have been reported to mediate the metabolism and transportation of thiopurine drugs. Hence, the single nucleotide polymorphisms (SNPs) in those genes could theoretically affect the pharmacokinetics and pharmacological effects of these drugs, and might also become one of the determinants of clinical efficacy and adverse effects. Moreover, long-term clinical practices have confirmed that thiopurine-related adverse reactions are associated with the systemic concentrations of their active metabolites. In this review, we mainly summarized the pharmacogenetic studies of thiopurine drugs. We also evaluated the therapeutic drug monitoring (TDM) research studies and focused on those active metabolites, hoping to continuously improve monitoring strategies for thiopurine therapy to maximize therapeutic efficacy and minimize the adverse effects or toxicity. We proposed that tailoring thiopurine dosing based on MRP4, ITPA, NUDT15, and TMPT genotypes, defined as “MINT” panel sequencing strategy, might contribute toward improving the efficacy and safety of thiopurines. Moreover, the DNA-incorporated thioguanine nucleotide (DNA-TG) metabolite level was more suitable for red cell 6-thioguanine nucleotide (6-TGNs) monitoring, which can better predict the efficacy and safety of thiopurines. Integrating the panel “MINT” sequencing strategy with therapeutic “DNA-TG” monitoring would offer a new insight into the precision thiopurine therapy for pediatric acute lymphoblastic leukemia patients.