6-thioguanine Nucleotides Research Articles

P56 Azathioprine-induced alopecia totalis and knuckle hyperpigmentation in a child with uveitis: test before you leap!

Abstract Introduction Azathioprine is a common disease-modifying anti-rheumatic drug used in non-infectious uveitis. Although unusual, it has been associated with myelosuppression in genetically predisposed individuals who exhibit mutations in thiopurine S-methyltransferase (TPMT) and nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15) genes. Alopecia secondary to azathioprine treatment is rare, and is an early marker of azathioprine-induced myelosuppression. It usually precedes the onset of myelosuppression, but can also occur simultaneously with pancytopenia. Knuckle pad hyperpigmentation is strongly associated with megaloblastic anemia. We report a patient of panuveitis with both alopecia totalis and knuckle pad hyperpigmentation secondary to azathioprine-induced myelosuppression. Case description A 13-year-old girl presented with acute-onset pain, redness and blurred of both eyes. Ophthalmological evaluation revealed bilateral granulomatous panuveitis. Visual acuity was 6/12 in both eyes, and anterior chamber had 2+ cells. Extensive evaluation for infective and autoimmune causes did not yield any aetiology. Following laboratory tests, a diagnosis of non-infectious panuveitis was made, and oral corticosteroids (2 mg/kg followed by taper) were started. As steroid sparing agents, subcutaneous methotrexate (15 mg/m2/week) and azathioprine (2 mg/kg) were also started after a normal baseline hemogram [Hb: 132 g/L, total leucocyte count (TLC) 12 x 109/L and platelet count: 310 x 109/L]. Two weeks later, she presented with complete loss of hair (alopecia totalis) and knuckle pad hyperpigmentation. Hemogram revealed pancytopenia (Hb: 86 g/L, TLC: 1.7 x 109/L and platelet count: 25 x 109/L). Considering drug-induced myelosuppression, azathioprine was stopped. Subcutaneous injections of Granulocyte colony-stimulating factor (G-CSF) (300 day) were given for two weeks. Mycophenolate mofetil (1200 mg/m2/day) was added. Quantitative polymerase-chain reaction genotyping assay showed a homozygous variant in NUDT15 gene (c.415 C>T). Normalization of hemogram was seen after two weeks (Hb: 120 g/L, TLC: 10.44 x 109/L and platelet count: 199 x 109/L). Reversal of hair loss and knuckle hyperpigmentation was nearly complete at five months and six weeks of follow-up, respectively. Panuveitis remained resolved on methotrexate and mycophenolate, with 6/6 vision and no recurrence at 16-months of follow up. Discussion In India, the prevalence of TPMT mutations (heterozygous 1.2-10%, and homozygous <1%), and NUDT15 mutations (heterozygous 11.6%, and homozygous 1.4%) is low, and the tests are expensive. In routine clinical practice, monitoring of blood counts is recommended in patients on azathioprine (two weekly initially, and then four weekly). Both TPMT and NUDT15 enzymes influence metabolism of azathioprine. Their polymorphisms result in accumulation of active 6-mercaptopurine, which gets converted to 6-thioguanine nucleotide metabolites, producing cytotoxic effects. As a result of disruption in mitotic activity of actively growing hair (anagen), more catagen follicles are seen than anagen, leading to hair loss. While massive hair loss is well recognized secondary to azathioprine, there is no report of knuckle pad hyperpigmentation as a direct adverse reaction of azathioprine. Both knuckle pad hyperpigmentation and azathioprine toxicity are associated with megaloblastic anemia. Knuckle pad hyperpigmentation may be explained by vitamin B12deficiency, with decreased intracellular glutathione. As a result, melanin deposition increases due to loss of tyrosinase inhibition. In addition, melanocyte pigmentary incontinence may also contribute to knuckle pad hyperpigmentation in such cases. Key learning points • While alopecia is often massive, knuckle pad hyperpigmentation may often be overlooked as a clinical sign in patients with azathioprine-induced megaloblastic anemia. Our case highlights the significance of two simple clinical cutaneous signs (alopecia totalis and knuckle pad hyperpigmentation) as clinical indicators of impending, and potentially fatal complication of pancytopenia secondary to azathioprine. In developed countries, genetic analysis is often performed for identifying variants in TPMT and NUDT15 genes before initiation of azathioprine. However, in resource-constrained settings, regular and close monitoring of hemogram, and prompt identification of clinical clues such as alopecia and knuckle pad hyperpigmentation may be a practical method to anticipate azathioprine-induced toxicity including myelosuppression.

A case of rapidly progressive hair loss due to azathioprine, and the prevalence of NUDT15 variants among Japanese patients with autoimmune blistering diseases: A single-center retrospective observational study.

Autoimmune blistering diseases (AIBDs), classified into pemphigus and pemphigoid, consist of relatively rare skin disorders caused by autoantibodies that target desmosomal and hemidesmosomal proteins, respectively. Although systemic corticosteroids are used as a first-line treatment for AIBDs, azathioprine is frequently co-administered as a steroid-sparing agent. Azathioprine is metabolized into thioguanine nucleotides (TGNs) which are its major active metabolites. The enzyme nudix hydrolase 15 (NUDT15) plays a key role in regulating TGNs. Serious side effects of azathioprine, including leukopenia and alopecia, are known to be particularly problematic in individuals with NUDT15 variants. The single-nucleotide polymorphism c.415C >T (p.Arg139Cys) is one of the most frequent NUDT15 variants associated with severe thiopurine toxicity. Recently, we treated a case of pemphigus vulgaris in a patient with NUDT15 variants in which the patient developed rapidly progressive diffuse hair loss and myelosuppression while receiving azathioprine. Previous reports on NUDT15 polymorphisms mainly focused on patients with inflammatory bowel disease or hematological malignancies, and the prevalence of NUDT15 polymorphisms remains unknown in AIBDs. This highlights the urgent need for research on NUDT15 polymorphisms in AIBDs to achieve a better understanding of the genetic factors influencing adverse reactions to azathioprine. To clarify the prevalence of NUDT15 variants in Japanese patients with AIBDs, we retrospectively reviewed the medical records of 78 patients with AIBDs (26 with bullous pemphigoid, 26 with pemphigus vulgaris, 17 with pemphigus foliaceus, and nine with other AIBDs) who had come to Hokkaido University Hospital between 2018 and 2023. The frequencies of NUDT15 variants of Arg/Arg, Arg/Cys, and Cys/Cys in these patients were approximately 72%, 23%, and 5%, respectively. Our findings indicate a prevalence of NUDT15 variants in AIBD patients that is similar to the prevalences of previous studies on patients with other diseases. These results emphasize the importance of screening for NUDT15 variants prior to initiating azathioprine treatment in Japanese patients with AIBDs.

Agranulocytosis Induced by Overdosage of Mercaptopurine: A Case Report

Drug-induced agranulocytosis (DIAG) is a rare but potentially fatal hematological complication. Thiopurines, such as mercaptopurine (6-MP), are widely used in the treatment of chronic inflammatory bowel diseases (IBD), but can cause myelotoxicity due to the accumulation of active metabolites. We report the case of a 48-year-old woman with ulcerative colitis who developed severe agranulocytosis following an accidental overdose of 6-MP. The patient presented with febrile pancytopenia with a neutrophil count of 0.04 G/L. Bone marrow examination revealed normal cellularity with an inversion of the maturation pyramid of the granulocyte lineage. A treatment combining growth factors (filgrastim) and antibiotics (tazobactam) was initiated, leading to progressive improvement over 5 weeks. The toxicity of 6-MP is mainly due to the accumulation of 6-thioguanine nucleotides (6-TGN). The polymorphism of the gene encoding the enzyme thiopurine S-methyltransferase (TPMT) can influence the risk of myelotoxicity. Two strategies are proposed to minimize this risk: evaluation of TPMT activity with dosage adjustment, or regular monitoring of blood counts with gradual dose increase. This case highlights the importance of rigorous biological monitoring when initiating 6-MP treatment, regardless of the TPMT test. Increased vigilance is necessary when using immunosuppressive drugs in the treatment of IBD to optimize efficacy and minimize toxicity.

Early therapeutic drug monitoring helps to identify inflammatory bowel disease patients with a high risk to fail thiopurine treatment.

Conventional thiopurines (azathioprine and mercaptopurine) remain standard therapy to maintain steroid sparing remission in inflammatory bowel disease (IBD), but are regularly discontinued due to adverse drug reactions (ADRs). Measurement of the metabolites 6-thioguanine nucleotides (6-TGN), 6-methylmercaptopurine ribonucleotides (6-MMPR) and the 6-MMPR/6-TGN ratio, may predict the development of these ADRs. Our aim was to evaluate whether early thiopurine metabolite measurements were associated with clinical outcomes. A post-hoc analysis was conducted of a multicentre, prospective, observational study on thiopurine-induced hepatotoxicity. IBD patients who initiated thiopurine therapy were included and thiopurine metabolite concentrations were assessed after 7days (±1) (T1). Patients were monitored for 12 weeks to document the occurrence of ADRs, early treatment discontinuation and effectiveness. In total, 181 patients were evaluated. At T1, 6-MMPR concentrations and 6-TGN/6-MMPR ratios were independently related to treatment discontinuation within 12 weeks after correction for sex, age and body mass index (BMI) (P= .034 and .002, respectively). The largest effects were observed for 6-MMPR ≥3000pmol/8 × 108 RBC and 6-TGN/6-MMPR ratio ≥17. Furthermore, 6-MMPR concentrations and 6-TGN/6-MMPR ratios at T1 were independently related to skewed metabolism at steady state (Week 8, 6-MMPR/-6TGN ratio ≥11 and ≥20) (both P< .001). The occurrence of ADRs and effectiveness were not independently related to T1 thiopurine metabolite concentrations. Thiopurine metabolite concentrations at T1 were related to early treatment discontinuation and skewed metabolism at steady state, but not to effectiveness, helping to identify patients with a high risk of thiopurine treatment failure.

Innovating Thiopurine Therapeutic Drug Monitoring: A Systematic Review and Meta-Analysis on DNA-Thioguanine Nucleotides (DNA-TG) as an Inclusive Biomarker in Thiopurine Therapy.

Thioguanine (TG), azathioprine (AZA), and mercaptopurine (MP) are thiopurine prodrugs commonly used to treat diseases, such as leukemia and inflammatory bowel disease (IBD). 6-thioguanine nucleotides (6-TGNs) have been commonly used for monitoring treatment. High levels of 6-TGNs in red blood cells (RBCs) have been associated with leukopenia, the cutoff levels that predict this side effect remain uncertain. Thiopurines are metabolized and incorporated into leukocyte DNA. Measuring levels of DNA-incorporated thioguanine (DNA-TG) may be a more suitable method for predicting clinical response and toxicities such as leukopenia. Unfortunately, most methodologies to assay 6-TGNs are unable to identify the impact of NUDT15 variants, effecting mostly ethnic populations (e.g., Chinese, Indian, Malay, Japanese, and Hispanics). DNA-TG tackles this problem by directly measuring thioguanine in the DNA, which can be influenced by both TPMT and NUDT15 variants. While RBC 6-TGN concentrations have traditionally been used to optimize thiopurine therapy due to their ease and affordability of measurement, recent developments in liquid chromatography-tandem mass spectrometry (LC-MS/MS) techniques have made measuring DNA-TG concentrations in lymphocytes accurate, reproducible, and affordable. The objective of this systematic review was to assess the current evidence of DNA-TG levels as marker for thiopurine therapy, especially with regards to NUDT15 variants. A systematic review and meta-analysis were performed on the current evidence for DNA-TG as a marker for monitoring thiopurine therapy, including methods for measurement and the illustrative relationship between DNA-TG and various gene variants (such as TPMT, NUDT15, ITPA, NT5C2, and MRP4). PubMed and Embase were systematically searched up to April 2024 for published studies, using the keyword "DNA-TG" with MeSH terms and synonyms. The electronic search strategy was augmented by a manual examination of references cited in articles, recent reviews, editorials, and meta-analyses. A meta-analysis was performed using R studio 4.1.3. to investigate the difference between the coefficients (Fisher's z-transformed correlation coefficient) of DNA-TG and 6-TGNs levels. A meta-analysis was performed using RevMan version 5.4 to investigate the difference in DNA-TG levels between patients with or without leukopenia using randomized effect size model. The risk of bias was assessed using the Newcastle-Ottowa quality assessment scale. In this systematic review, 21 studies were included that measured DNA-TG levels in white blood cells for either patients with ALL (n = 16) or IBD (n = 5). In our meta-analysis, the overall mean difference between patients with leukopenia (ALL + IBD) versus no leukopenia was 134.15 fmol TG/µg DNA [95% confidence interval (CI) (83.78-184.35), P < 0.00001; heterogeneity chi squared of 5.62, I2 of 47%]. There was a significant difference in DNA-TG levels for patients with IBD with and without leukopenia [161.76 fmol TG/µg DNA; 95% CI (126.23-197.29), P < 0.00001; heterogeneity chi squared of 0.20, I2 of 0%]. No significant difference was found in DNA-TG level between patients with ALL with or without leukopenia (57.71 fmol TG/µg DNA [95% CI (-22.93 to 138.35), P < 0.80]). DNA-TG monitoring was found to be a promising method for predicting relapse rates in patients with ALL, and DNA-TG levels are likely a better predictor for leukopenia in patients with IBD than RBC 6-TGNs levels. DNA-TG levels have been shown to correlate with various gene variants (TPMT, NUDT15, ITPA, and MRP4) in various studies, points to its potential as a more informative marker for guiding thiopurine therapy across diverse genetic backgrounds. This systematic review strongly supports the further investigation of DNA-TG as a marker for monitoring thiopurine therapy. Its correlation with treatment outcomes, such as relapse-free survival in ALL and the risk of leukopenia in IBD, underscores its role in enhancing personalized treatment approaches. DNA-TG effectively identifies NUDT15 variants and predicts late leukopenia in patients with IBD, regardless of their NUDT15 variant status. The recommended threshold for late leukopenia prediction in patients with IBD with DNA-TG is suggested to be between 320 and 340 fmol/µg DNA. More clinical research on DNA-TG implementation is mandatory to improve patient care and to improve inclusivity in thiopurine treatment.

Effects of genetic and clinical factors on thiopurine drugs pharmacokinetics in Tunisian patients.

Aim: Thiopurine drugs are used in the treatment of various diseases including inflammatory bowel disease. Thiopurine-S-methyltransferase (TPMT) and inosine triphosphate pyrophosphatase (ITPA) are the crucial enzymes involved in thiopurines metabolism. The present study aims to investigate in Tunisian patients, the influence of genetic and nongenetic factors on thiopurine drugs pharmacokinetics.Experimental approach: We have included patients having received thiopurine drugs and have undergone 6-thioguanine nucleotides (6-TGN) concentration monitoring. The identification of TPMT and ITPA polymorphisms was performed using the polymerase chain reaction-restriction fragment length polymorphism method. The impact of both genetic and nongenetic factors on the variability of the 6-TGN C/D ratio was analyzed through a stepwise multiple regression model.Key results: One hundred and twenty-three patients were included in the study. For TPMT, the most frequent variant allele was TPMT*3B (3.3%). For ITPA, the predominant polymorphism was the c.IVS2+21A> C (7%). We have demonstrated that only gender, the TPMT*3A and TPMT*3C alleles are significantly involved on the variability of thiopurines pharmacokinetics.Conclusion: Our study is the first to evaluate, in African patients, the impact of both genetic and nongenetic factors on the thiopurine drugs pharmacokinetics. Considering the narrow therapeutic range of these drugs, TPMT genotyping combined with 6-TGN blood concentration monitoring may enhance their efficacy and safety.

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.

Effects of allopurinol on 6-mercaptopurine metabolism in unselected patients with pediatric acute lymphoblastic leukemia: a prospective phase II study.

Allopurinol can be used in maintenance therapy (MT) for pediatric acute lymphoblastic leukemia (ALL) to mitigate hepatic toxicity in patients with skewed 6-mercaptopurine metabolism. Allopurinol increases the erythrocyte levels of thioguanine nucleotides (e-TGN), which is the proposed main mediator of the antileukemic effect and decreases methyl mercaptopurine (e-MeMP) levels, associated with hepatotoxicity. We investigated the effects of allopurinol in thiopurine methyltransferase (TPMT) wild-type patients without previous clinical signs of skewed 6-mercaptopurine metabolism. Fifty-one patients from Sweden and Finland were enrolled in this prospective before-after trial during ALL MT. Mean e-TGN increased from 280 nmol/mmol hemoglobin (Hb) after 12 weeks of standard MT to 440 after 12 weeks of MT with addition of allopurinol 50 mg/ m2 (P<0.001). Mean e-MeMP decreased simultaneously from 9,481 nmol/mmol Hb to 2,791 (P<0.001) and mean alanine aminotransferase declined by almost 50%. Primary endpoint, defined as e-TGN >200 nmol/mmol Hb, was reached for 91% of the patients after 12 weeks of allopurinol (week 25) compared to 67% before (week 13) (P<0.001). This level was chosen as the median e-TGN in a previous NOPHO ALL-2008 study was just below 200 nmol/mmol Hb. During weeks on allopurinol a slightly higher proportion of the patients had a white blood cell count within target 1.5-3.0×109/L. Allopurinol did not increase severe adverse events and no life-threatening events were reported. In conclusion, allopurinol add-on treatment is safe and leads to increased e-TGN and reduced e-MeMP also in ALL-patients without previous signs of skewed thiopurine metabolism and is a promising approach to increase antileukemic effect and reduce toxicity.

P798 Study of the concordance between the enzymatic activity of Thiopurine S-methyltransferase and polymorphisms in the TPMT gene in patients with Inflammatory Bowel Disease

Abstract Background Thiopurine therapy is associated with an increased risk of serious adverse events in patients with Inflammatory Bowel Disease (IBD). Thiopurine S-methyltransferase (TPMT) is the enzyme responsible for metabolism, and its determination helps identify patients at risk of toxicity. This study aims to explore the level of correspondence between the TPMT genotype and enzymatic activity (phenotype) with the objective of preventing adverse events prior to the commencement of thiopurine therapy. Methods Consecutive patients with IBD, Crohn’s Disease (CD) or Ulcerative Colitis (UC), were included. Genotype was conducted for the most prevalent TPMT variants (TPMT*2, TPMT*3B, TPMT*3C), TPMT enzymatic activity assessment, and quantification of 6-thioguanine nucleotide (6-TGN) levels. Adverse effects were documented, along with the administration of biologics, mesalazine, ACE inhibitors or allopurinol. The primary objective was to evaluate the concordance between TPMT genotype and phenotype. Secondary objectives included determining the prevalence of genotype and phenotype within our patient cohort, 6-TGN serum levels, the prevalence of adverse events and identifying potential pharmacological inducers of the phenotype. Results A total of 218 patients were included (131 with CD and 81 with UC). Thirteen patients did not initiate thiopurines, and 34.63% (71/205) had discontinued treatment. The most observed adverse events were myelotoxicity (15.12%), gastrointestinal toxicity (12.20%), and hepatic toxicity (5.37%). TPMT activity exhibited a trimodal distribution, with 87.61% (191/218) having normal activity, 11.47% having intermediate activity, and 1% having low activity. Genotypically, 90.83% (198/218) had a wild-type genotype, 8.72% (18/218) had a heterozygous genotype, and 0.5% (1/218) had a homozygous genotype. The concordance index between phenotype and genotype was calculated at 0.57. Significantly, myelotoxicity was associated with the presence of genotypic variants (p=0.004). 6-TGN levels did not correlate with TPMT activity and concurrent medications did not affect TPMT activity . Conclusion The proactive assessment of TPMT (phenotype or genotype) before initiating thiopurine therapy effectively mitigates the occurrence of myelotoxicity in IBD patients. Importantly, the level of concordance between TPMT activity and genotype is moderate, with genotyping serving as the more reliable approach for preselecting patients susceptible to myelotoxic reactions.

Determination of Deleterious SNPs in NUDT15 Gene Related to Acute Lymphoblastic Leukemia by using Bioinformatics Tools

Aim: In acute lymphoblastic leukemia (ALL), thiopurine group drugs are the most basic drugs and are included in almost all treatment protocols, especially in maintenance treatment. The mechanism of action of thioguanine nucleotides is to enter the DNA structure in cells, disrupt DNA synthesis, and trigger programmed cell death. The impact of deleterious SNPs on nucleotide triphosphate diphosphatase protein regarding ALL is not yet fully understood. In this study, it was aimed to determine the possible deleterious impacts of missense variants in the NUDT15 gene on protein structure and stabilization that play a significant role in susceptibility to the disease, using modern bioinformatics software. Method: To access SNPs in the NUDT15, it was used National Center for Biotechnology Information (NCBI), Single Nucleotide Polymorphism Database (dbSNP). In bioinformatics tools used in this study included SIFT, PolyPhen-2, PROVEAN, SNAP2, and PANTHER, followed by I-Mutant, HOPE, and STRING. Results: The results of the analysis showed that in a total of 6663 SNPs in the NUDT15, 6 variants have been identified as ‘deleterious’. According to the I-Mutant software, 4 deleterious SNPs decreased protein stability while 2 deleterious SNPs increased protein stability. In the HOPE database analysis, E115G, E57G, F52L, and K33N mutant amino acids were found to be smaller and more hydrophobic than wild-type amino acids, while G53R and G145D mutant amino acids were found to be larger. Thus, all variations resulted in alterations in the net charge on the NUDT15 protein. Conclusion: Data on NUDT15 variants will contribute to the prediction of the patient’s response to thiopurine drugs in future studies, to a better understanding of the patient’s susceptibility to drug interactions, and ultimately to obtaining information about the prognosis.

The drug-survival of low-dose thioguanine in patients with inflammatory bowel disease: a retrospective observational study.

Thiopurines are commonly used to treat inflammatory bowel disease but withdrawal due to side effects are common. Thioguanine has been suggested to be better tolerated than conventional thiopurines. We studied drug-survival of low dose of thioguanine in real-life clinical practice in comparison to conventional thiopurines. Retrospective observational study. All patients born 1956 and later, and who at least once started thiopurine treatment between 2006 and 2022 were included. A medical chart review was performed that noted drug-survival for every thiopurine treatment attempt. The Mantel-Cox rank test was used to test differences in drug-survival for different thiopurines. Blood chemistry analysis and faecal calprotectin levels were registered for the first 5 years of treatment. In the study population, there was 379 initiated thiopurine treatments (210 for Crohn's disease and 169 for ulcerative colitis) in 307 patients with inflammatory bowel disease (IBD). Low-dose thioguanine (median dose 11 mg; 25-75th percentile 7-19 mg) had been initiated in 31 patients. Overall, when including all thiopurine attempts, thioguanine had the longest drug-survival [Mantel-Cox rank test: thioguanine versus azathioprine p = 0.014; thioguanine versus 6-mercaptopurine (6-MP) p < 0.001]. For second-line thiopurine treatment thioguanine had longer drug-survival than 6-MP (Mantel-Cox rank test: p = 0.006). At 60 months, 86% of the patients who started low-dose thioguanine were still on treatment compared to 42% of the patients who started 6-MP (p = 0.022). The median 6-thioguanine nucleotide levels in patients treated with thioguanine was 364 pmol/8 × 108. Patients on thioguanine treatment showed significantly lower values of median mean corpuscular volume at follow-up than patients treated with azathioprine and 6-MP. Patients treated with 6-MP showed significantly lower levels of FC in the third year of treatment compared to patient treated with azathioprine (59 versus 109 µg/g; p = 0.023), but there was no significant difference in FC levels for thioguanine compared to azathioprine (50 versus 109 µg/g; p = 0.33). Treatment with a low dose of thioguanine is well-tolerated in patients with IBD and had a significantly higher drug-survival than conventional thiopurines.

Azathioprine metabolite levels and outcomes during pregnancies with rheumatic disease

ObjectiveDespite widespread use of azathioprine (AZA) during pregnancy, no studies evaluated the impact of pregnancy on AZA metabolites 6-thioguanine nucleotide (6-TGN) and 6-methylmercaptopurine nucleotide (6-MMPN) disposition in rheumatic diseases. This...

Quantification of Thiopurine Metabolites in Human Erythrocytes by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS).

The thiopurine drugs, azathioprine, mercaptopurine, and thioguanine, are widely used in the treatment of several malignant and nonmalignant diseases. These inactive prodrugs undergo extensive metabolism to form active cytotoxic metabolites, which act mainly by incorporating into DNA and affecting cell replication. Thiopurine methyltransferase is a highly variable cytosolic enzyme that catalyzes the S-methylation of the thiopurine bases-an inactivating pathway. Patients with low-activity variants of TPMT can be affected by pronounced pharmacologic effects when receiving thiopurine medications. Clinical studies have reported significant interpatient variability in intracellular thiopurine metabolite concentrations in patients receiving thiopurine therapy. In this chapter, we present an LC-MS/MS method to monitor the thiopurine metabolites: 6-thioguanine nucleotides and 6-methylmercaptopurine derivatives in human erythrocytes. This method utilizes acid hydrolysis to release the bases and improves upon previously published procedures by utilizing stable isotope internal standards and a more efficient chromatographic separation.

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

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

Erythrocyte-incorporated 6-mercaptopurine metabolite levels are not affected by recent drug administration during maintenance therapy for childhood acute lymphoblastic leukemia

BackgroundChildhood acute lymphoblastic leukemia (ALL) maintenance therapy with oral 6-mercaptopurine (6-MP) and methotrexate prevents leukemic relapse by acting against residual lymphoblasts. Non-adherence to oral maintenance therapy significantly increases ALL relapse risk. The levels of intracellular 6-MP metabolites erythrocyte incorporated (ery-) thioguanine nucleotides (ery-TGN) and methylated 6-MP metabolites (ery-MeMP) can be used to evaluate adherence to 6-MP, however, little is known on their short-term pharmacokinetics. The aim of this study was to assess the changes between trough levels and the levels at 2-hours after 6-MP intake when the 6-MP levels in plasma is expected to have peaked. Materials and methodsTen ALL patients with stable 6-MP dose were prospectively included. Two blood samples were collected for ery-TGN and ery-MeMP analysis (before 6-MP intake and 2 h after). ResultsThe median trough ery-TGN was 173 (range 126–299) nmol/mmol hemoglobin (HGB), and 2 h after 6-MP intake the median level was 175 (range 120–293) nmol/mmol HGB. For ery-MeMP, the median trough and 2 h-concentrations were 9 239 (range 1 278–19 645) nmol/mmol HGB and 9 216 (range 1 215–19 519) nmol/mmol HGB, respectively. The median absolute percentual change for both ery-TGN and ery-MeMP were not statistically different from 0, p = 0.28 and p = 0.06, respectively. ConclusionsIntracellular 6-MP metabolites, ery-MeMP and ery-TGN, remain stable 2 h after oral 6-MP intake in patients with a stable 6-MP dose. This data support that blood samples may be used to assess patient adherence irrespective of the timing of 6-MP intake.

Key factors associated with 6-thioguanine and 6-methylmercaptopurine nucleotide concentrations in children treated by thiopurine for acute leukaemia and inflammatory bowel disease.

Azathioprine (AZA) and 6-mercaptopurine are prescribed in acute lymphoblastic leukaemia (ALL) and inflammatory bowel diseases (IBD). Metabolism to active 6-thioguanine (6TGN) and 6-methylmercaptopurine nucleotides (6MMPN) is variable but therapeutic drug monitoring (TDM) remains debatable. This study reports on factors impacting on red blood cell (RBC) metabolites concentrations in children to facilitate TDM interpretation. The first paediatric TDM samples received during year 2021 were analysed, whatever indication and thiopurine drug. Target concentration ranges were 200-500, <6000 pmol/8× 108 RBC for 6TGN and 6MMPN. Children (n= 492) had IBD (64.8%), ALL (22.6%) or another autoimmune disease (12.6%): mean ages at TDM were 7.5 in ALL and 13.7years in IBD (P <.0001). ALL received 6-mercaptopurine (mean dose 1.7mg/kg/d with methotrexate), IBD received AZA (1.9mg/kg/d with anti-inflammatory drugs and/or monoclonal antibodies). Median 6TGN and 6MMPN concentrations were 213.7 [interquartile range: 142.5; 309.6] and 1144.6 [419.4; 3574.3] pmol/8× 108 RBC, 38.8% of patients were in the recommended therapeutic range for both compounds. Aminotransferases and blood tests were abnormal in 57/260 patients: 8.1% patients had high alanine aminotransaminase, 3.4% of patients had abnormal blood count. Factors associated with increased 6TGN were age at TDM and thiopurine methyltransferase genotype in ALL and AZA dose in IBD. The impact of associated treatment in IBD patients was also significant. TDM allowed identification of children who do not reach target levels or remain over treated. Including TDM in follow-up may help physicians to adjust dosage with the aim of reducing adverse effects and improve treatment outcome.

Development of innovative methodology for determination of 6-thioguanine in whole blood erythrocytes by HPLC–PDA-based technique for medical diagnostics purposes

6-Thioguanine is an immunosuppressive drug, an analogue of guanine, applied to treat acute leukemia and inflammatory bowel disease. Excessive use of 6-thioguanine during clinical treatment may cause side effects. Moreover, providing a dose too low will be ineffective. Therefore, there is a critical need for a rapid, selective and routine approach to quantifying 6-thioguanine in body fluids to support a clinical application. A fully validated HPLC method has been developed to determine 6-thioguanine in whole blood samples using 5-bromouracil as an internal standard. 6-Thioguanine nucleotides were released from erythrocytes by perchloric acid, and then hydrolysed at 100 °C to the parent thiopurine, 6-thioguanine. The following validation parameters of the method were determined: specificity/selectivity, linearity range (479–17,118 ng/mL, R > 0.992), limits of detection (150 ng/mL) and quantification (479 ng/mL), accuracy (− 5.6 < Bias < 14.7), repeatability (CV 1.30–3.24%), intermediate precision (CV 4.19–5.78%), extraction recovery (79.1–103.6%) and carryover. Furthermore, the stability of the drug in whole blood samples under various storage conditions was investigated. The suggested method is suitable for determining 6-thioguanine in whole blood erythrocyte samples for drug level monitoring, thus correct dosing.

Pharmacokinetic–pharmacodynamic modeling of maintenance therapy for childhood acute lymphoblastic leukemia

In the treatment of childhood acute lymphoblastic leukemia (ALL), current protocols combine initial high-dose multiagent chemotherapy with prolonged oral therapy with 6-mercaptopurine (6MP) and low-dose methotrexate (MTX) maintenance therapy. Decades of research on ALL treatment have resulted in survival rates of approximately 90%. However, dose-response relationships vary widely between patients and insight into the influencing factors, that would allow for improved personalized treatment management, is insufficient. We use a detailed data set with measurements of thioguanine nucleotides and MTX in red blood cells and absolute neutrophil count (ANC) to develop pharmacokinetic models for 6MP and MTX, as well as a pharmacokinetic–pharmacodynamic (PKPD) model capable of predicting individual ANC levels and thus contributing to the development of personalized treatment strategies. Here, we show that integrating metabolite measurements in red blood cells into the full PKPD model improves results when less data is available, but that model predictions are comparable to those of a fixed pharmacokinetic model when data availability is not limited, providing further evidence of the quality of existing models. With this comprehensive model development leading to dynamics similar to simpler models, we validate the suitability of this model structure and provide a foundation for further exploration of maintenance therapy strategies through simulation and optimization.

Analysis of the NUDT15 gene and metabolites of azathioprine in Japanese patients with inflammatory bowel disease

BackgroundThiopurines continue to play an important role in the treatment of inflammatory bowel disease (IBD). It is well known that thiopurines can cause several adverse reactions. Especially, hematopoietic toxicity may lead to severe agranulocytosis. In a previous prospective study, we investigated the relationship between inosine triphosphate pyrophosphatase (ITPA) c.94c > a polymorphism, 6-thioguanine nucleotide (6-TGN) concentration and toxicity.MethodsTo clarify the cause of thiopurine toxicity, we analysed nucleoside disphosphate-linked moiety X-type motif 15 (NUDT15) gene polymorphisms, i.e., R139C, V18I, and V19_V19insGV, and measured 6-mercaptopurines and 6-methylmercaptopurines (6-MMP) using the archived blood samples collected from 49 IBD patients for our previous study.ResultsThe ITPA c.94c > a polymorphism was detected in 19 patients (38.7%, all heterozygous). The R139C polymorphism was found in 10 patients (20.4%, 1 homozygous, 9 heterozygous), V18_V19insGV in 7 patients (14.3%, all heterozygous), and V18I in 2 patients (4.08%, all heterozygous). Although R139C was more strongly associated with leukopenia than c.94c > a, there were no significant correlations with 6-TGN and 6-MMP levels, as for c.94c > a. The leukopenia incidence rates for each gene polymorphism were 0% in those with all wild-type genes, 21.4% for c.94c > a only, 42.9% for NUDT15 polymorphism (s) only, and 80.0% for both polymorphisms.ConclusionsAll cases of leukopenia were associated with ITPA c.94c > a and/or polymorphism of NUDT15 and the risk of developing leukopenia was synergistically increased by ITPA and NUDT15 gene polymorphism. However, there was no association between the level of azathioprine metabolites and these polymorphisms.

Association between 6-thioguanine nucleotide levels and preventing production of antibodies to infliximab in patients with inflammatory bowel disease

ObjectiveCombination therapy with infliximab and a thiopurine has been shown to be more effective than monotherapy in patients with inflammatory bowel disease (IBD). The therapeutic efficacy of thiopurines is correlated...