Assessment on the use of allopurinol to improve safety and efficacy of mercaptopurine in pediatric patients with Acute Lymphoblastic Leukemia and Lymphoma during maintenance therapy.

BACKGROUND: Mercaptopurine is an important component of acute lymphoblastic leukemia (ALL) and lymphoma (LLy) maintenance therapy. The 6-thioguanine nucleosides (6-TGN) are believed to be the primary contributor to myelosuppression and immunosuppressive effects, while 6-methylmercaptopurine (6-MMPN) is believed to be responsible for several toxicities including hepatotoxicity, pancreatitis, and hypoglycemia. Previous reports suggest the addition of allopurinol may reduce these toxicities. AIMS: To assess the use of allopurinol to improve both safety and efficacy of mercaptopurine in pediatric patients with ALL and LLy during maintenance therapy. Secondary objectives included evaluating patient tolerability and skewed metabolism. In addition, we also analyzed mercaptopurine daily dose reduction upon allopurinol initiation. METHODS AND RESULTS: The primary endpoint was time within goal ANC prior to and after initiation of allopurinol. Secondary endpoints included; improvement in selective toxicities (hepatotoxicity, pancreatitis, and hypoglycemia) and 6-MMPN to 6-TGN ratio prior to and after allopurinol initiation. In addition, an exploratory endpoint assessing mercaptopurine daily dose reduction prior to and after allopurinol initiation was included. Sixteen patients met inclusion criteria and 15 (94%) of which were included in this study. Median percent of maintenance days within goal ANC prior to and after initiation of allopurinol was 27.8 (IQR 22.6-44.9) and 41.6 (IQR 20.2-58.2) respectively. All patients experienced selective toxicities; 15 (100%) hepatotoxicity, 1 (7%) pancreatitis, and 3 (20%) hypoglycemia. Improvement of toxicities was seen in 13/15 (87%), 1/1 (100%), and 2/3 (67%) respectively. Average 6-MMPN:6-TGN ratio prior to allopurinol initiation was 304:1 and after, allopurinol initiation improved to 15:1, resulting in a 95% reduction. Average mercaptopurine dose prior to and after allopurinol initiation decreased by about 56% (63 to 28 mg/m2 /day). CONCLUSION: Results suggest that the use of allopurinol in pediatric patients with ALL and LLy receiving mercaptopurine during maintenance therapy is both safe and effective.

Hypoglycemia Associated With PEG-asparaginase and 6-MP Therapy During Treatment of Acute Lymphoblastic Leukemia in Pediatric Patients: A Case Series.

BACKGROUND: Asparaginases are a mainstay treatment for pediatric acute lymphoblastic leukemia (ALL). Recent reports identified hypoglycemia associated with asparaginases. Other reports describe hypoglycemia associated with 6-mercaptopurine (6-MP), another fundamental ALL therapy. Little is known about the risk of hypoglycemia associated with ALL therapy, an adverse event that puts children at risk of decreased level of consciousness, seizures, and possibly negative neurocognitive sequelae. METHODS: We performed a retrospective chart review of 6 children with hypoglycemia during ALL treatment in our institution from May 2016 to August 2019. Timing and duration of hypoglycemia relative to polyethylene glycol (PEG)-asparaginase, 6-MP, and corticosteroids were determined. Laboratory values of the critical sample were collected. RESULTS: The median age was 2.75 (interquartile range: 1.88 to 3.63) years. Three patients had trisomy 21. The onset of hypoglycemia was 5 to 19 days after the most recent PEG-asparaginase administration or 6 to 7 months after initiating daily 6-MP. Sixteen hypoglycemic events were documented, and 9/16 had a critical sample drawn. Six events were hypoketotic, associated with PEG-asparaginase. Three were ketotic, associated with 6-MP. Two patients required treatment with diazoxide and cornstarch. CONCLUSIONS: Hypoglycemia associated with PEG-asparaginase occurred later and lasted longer than previous reports with l-asparaginase, with the likely mechanism being hyperinsulinism. 6-MP was associated with ketotic hypoglycemia.

Mercaptopurine-induced Sweet's syndrome.

Sweet's syndrome is an acute febrile neutrophilic dermatosis. Drug-induced Sweet's syndrome typically occurs soon after drug administration, with rapid resolution of symptoms with cessation of the offending agent. We report a man in his early 40s who presented with fever and widespread erythematous rash on a background of recently diagnosed mild stricturing ileal Crohn's disease. He was commenced on 6-mercaptopurine 12 days before presentation. Skin biopsy demonstrated diffuse infiltration of neutrophils in the upper dermis, dermal oedema, eosinophils and fibrin deposition. Symptoms rapidly improved with cessation of 6-mercaptopurine without requiring systemic corticosteroids.

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

AIMS: 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. METHODS: 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. RESULTS: 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 13.7 years in IBD (P < .0001). ALL received 6-mercaptopurine (mean dose 1.7 mg/kg/d with methotrexate), IBD received AZA (1.9 mg/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. CONCLUSION: 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.

The Effect of Renal Replacement Therapy in a Patient with Mercaptopurine Toxicity: Time to Revise Guidelines.

INTRODUCTION: Mercaptopurine, a thiopurine, is used in various disorders of immune regulation, such as autoimmune hepatitis. Thiopurine metabolism is complex with risk for overdosing, especially when metabolism is impaired by liver dysfunction. Hepatotoxicity may be due to mercaptopurine overdose and is often reversible after prompt cessation of the drug. CASE PRESENTATION: Treatment of thiopurine toxicity is mainly supportive and literature on enhanced elimination by renal replacement therapy is ambiguous. CONCLUSION: In this case of thiopurine toxicity, a patient with autoimmune hepatitis presents with abdominal pain, nausea, vomiting, and diarrhea. We show in this case report that renal replacement therapy had no effect on total body clearance of mercaptopurine.

A Bayesian joint model for multivariate longitudinal and time-to-event data with application to ALL maintenance studies.

The most common type of cancer diagnosed among children is the Acute Lymphocytic Leukemia (ALL). A study was conducted by Tata Translational Cancer Research Center (TTCRC) Kolkata, in which 236 children (diagnosed as ALL patients) were treated for the first two years (approximately) with two standard drugs (6MP and MTx) and were then followed nearly for the next 3 years. The goal is to identify the longitudinal biomarkers that are associated with time-to-relapse, and also to assess the effectiveness of the drugs. We develop a Bayesian joint model in which a linear mixed model is used to jointly model three biomarkers (i.e. white blood cell count, neutrophil count, and platelet count) and a semi-parametric proportional hazards model is used to model the time-to-relapse. Our proposed joint model can assess the effects of different covariates on the progression of the biomarkers, and the effects of the biomarkers (and the covariates) on time-to-relapse. In addition, the proposed joint model can impute the missing longitudinal biomarkers efficiently. Our analysis shows that the white blood cell (WBC) count is not associated with time-to-relapse, but the neutrophil count and the platelet count are significantly associated with it. We also infer that a lower dose of 6MP and a higher dose of MTx jointly result in a lower relapse probability in the follow-up period. Interestingly, we find that relapse probability is the lowest for the patients classified into the "high-risk" group at presentation. The effectiveness of the proposed joint model is assessed through the extensive simulation studies.

Individualized Use of 6-Mercaptopurine in Chinese Children with ALL: A Multicenter Randomized Controlled Trial.

Continuous 6-mercaptopurine (6-MP) dose titration is necessary because of its narrow therapeutic index and frequently encountered dose-limiting hematopoietic toxicity. However, evidence-based guidelines for gene-based 6-MP dosing have not been established for Chinese children with acute lymphoblastic leukemia (ALL). This multicenter, randomized, open-label, active-controlled clinical trial randomly assigned Chinese children with low- or intermediate-risk ALL in a 1:1 ratio to receive TPMT-NUDT15 gene-based dosing of 6-MP (N = 44, 10 to 50 mg/m2 /day) or standard dosing (N = 44, 50 mg/m2 /day) during maintenance therapy. The primary end point was the incidence of 6-MP myelosuppression in both groups. Secondary end points included frequencies of 6-MP hepatotoxicity, duration of myelosuppression and leukopenia, event-free survival, and steady-state concentrations of active metabolites (6-thioguaninenucleotides and 6-methylmercaptopurine nucleotides) in erythrocytes. A 2.2-fold decrease in myelosuppression, the primary end point, was observed in the gene-based-dose group using ~ 50% of the standard initial 6-MP dose (odds ratio, 0.26, 95% confidence interval, 0.11 to 0.64, P = 0.003). Patients in the gene-based-dose group had a significantly lower risk of developing thiopurine-induced myelosuppression and leukopenia (P = 0.015 and P = 0.022, respectively). No significant differences were observed in the secondary end points of the incidence of hepatotoxicity and steady-state concentrations of active metabolites in erythrocytes between the two groups. TPMT- and NUDT15-based dosing of 6-MP will significantly contribute toward further reducing the incidence of leukopenia in Chinese children with ALL. This trial is registered at www.clinicaltrial.gov as #NCT04228393.

Azathioprine and 6-mercaptopurine-induced intrahepatic cholestasis of pregnancy: Case report and review of the literature.

OBJECTIVE: Azathioprine, a prodrug of 6-mercaptopurine (6-MP), is used in the treatment of inflammatory bowel disease and may be continued during pregnancy. Acute cholestatic liver injury has been reported to occur with azathioprine. We aimed to examine azathioprine related cholestasis effect on pregnancy complications and outcome. CASE REPORT: We present a unique case of 6-MP-induced severe intrahepatic cholestasis of pregnancy (ICP) that required meticulous combined therapy including plasma exchange. The symptoms resolved following 6-MP withdrawal. A literature review revealed 11 pregnancies complicated by early-induced severe ICP among women treated with azathioprine or 6-MP. CONCLUSION: We recommend weekly bile acid level tests for pregnant women treated with azathioprine or 6-MP, beginning early in the second trimester of pregnancy, and the prompt discontinuation of treatment upon establishment of an ICP diagnosis.

The c.415C>T polymorphism in NUDT15 is more frequent than the polymorphisms in TPMT in Chilean patients who use thiopurine drugs.

Azathioprine (AZA) and 6-mercaptopurine (6-MP) are drugs widely used in the treatment of autoimmune diseases. Among the enzymes involved in the metabolism of AZA and 6-MP are thiopurine methyltransferase (TPMT) and nudix hydrolase 15 (NUDT15). The existence of single nucleotide polymorphisms in the genes that code for these enzymes could decreased enzymatic activity AND lead to severe myelosuppression. The most relevant polymorphism is NUDT15*3 (rs116855232), where the replacement of cytosine for thymine at position 415, which in turn leads to a loss of enzymatic activity. In a previous study, it was identified that together the polymorphisms in the TPMT gene reach an allelic frequency of 3.81%. There is no information regarding the rs116855232 polymorphism in the NUDT15 gene, so this corresponds to the objective of this report. Blood samples from Chilean adult patients with indications for the use of AZA or 6-MP for different pathologies and who had undergone a TPMT gene polymorphism study were retrospectively analyzed. A total of 253 blood samples were analyzed. Of the 253 patients, 47 presented the c.415C>T polymorphism in the NUDT15 gene, 3 being homozygous and 44 heterozygous. Four of the heterozygous patients for NUDT15 also had the *3A variant in the TPMT gene, also heterozygous. The allelic frequency of the minor T allele found (9.88%) was very similar to that found in patients of Asian origin, and much higher than that reported for the European Caucasian or Latin American population.

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

BACKGROUND: Thiopurines 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. METHODS: To 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. RESULTS: The 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. CONCLUSIONS: All 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.

Antenatal thiopurine exposure in women with IBD is associated with intrahepatic cholestasis of pregnancy.

BACKGROUND: Pregnant women with inflammatory bowel disease (IBD) continue thiopurines to maintain remission. Other studies have reported intrahepatic cholestasis of pregnancy (ICP) in IBD pregnancies exposed to thiopurines. We aimed to investigate whether thiopurines are associated with an increased risk of ICP. RESEARCH DESIGN AND METHODS: Single-center retrospective cohort study comparing incidence of ICP in thiopurine-exposed versus non-exposed patients with IBD compared with age-matched pregnant controls. RESULTS: The IBD cohort consisted of 386 pregnancies in 243 patients with IBD, with 386 age-matched controls. In patients with IBD, ICP was significantly more common among thiopurine-exposed pregnancies (9.0% vs 1.8%; odds ratio [95% confidence interval] = 5.34 [1.78-16.02]; p = 0.021). IBD patients with thiopurine exposure were significantly more likely to experience ICP compared to non-IBD controls (9.0% vs 1.3%; p < 0.001). Patients with IBD not exposed to thiopurines had a comparable ICP incidence with controls (1.8% vs 1.3%; p = 0.75). Severe ICP occurred in 80% of thiopurine-exposed ICP cases versus 40% in non-exposed (p = 0.25), versus 20% in controls (p = 0.09). CONCLUSION: Thiopurine exposure was associated with a significantly increased risk of ICP among patients with IBD compared to non-exposed IBD patients and age-matched general population controls. The course of ICP was not significantly different in thiopurine-exposed cases.

Loss of Nudt15 thiopurine detoxification increases direct DNA damage in hematopoietic stem cells.

Thiopurines, such as 6-mercaptopurine (6-MP), are widely used as cytotoxic agents and immunosuppressants for leukemia and autoimmune or inflammatory diseases. A nonsynonymous single nucleotide polymorphism (p.Arg139Cys; R139C) of the nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15) gene causes the loss of thiopurine detoxification, inducing myelosuppression. To understand such hematotoxicity, we investigate the effects of NUDT15 R139C on hematopoietic stem cells (HSCs) upon thiopurine administration. Using previously established Nudt15R138C knock-in mice, which mimic myelosuppression in NUDT15R139C homozygous or heterozygous patients following thiopurine administration, we investigated the numerical changes of HSCs and hematopoietic progenitor cells following 6-MP administration using in vivo flowcytometry and ex vivo HSC expansion. Genes differentially expressed between Nudt15+/+ HSCs and Nudt15R138C/R138C HSCs were identified using RNA-sequencing before the emergence of 6-MP-induced HSC-damage. Gene Ontology (GO) and Transcriptional Regulatory Relationships Unraveled by Sentence-based Text Mining (TRRUST) analyses were performed to elucidate the molecular effects of 6-MP on HSCs. In Nudt15R138C/R138C mice, 6-MP induced exhaustion of HSCs faster than that of multipotent progenitors and as fast as that of myeloid-committed progenitors. Ex vivo-expanded Nudt15R138C/R138C HSCs were dose- and time-dependently damaged by 6-MP. GO analysis identified the DNA damage response and cell cycle process as the most strongly influenced processes in Nudt15R138C/R138C HSCs. TRRUST analysis revealed that the Trp53-regulated transcriptional regulatory network is influenced prior to HSC exhaustion in Nudt15R138C/R138C HSCs. The loss of NUDT15 thiopurine detoxification enhances thiopurine-mediated DNA damage via the Trp53 networks in HSCs. Therefore, caution is required in long-term thiopurine use in patients with NUDT15 R139C in view of its adverse effects on HSCs in the form of DNA damage.

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

BACKGROUND AND AIMS: Nudix hydrolase 15 [NUDT15] genetic variants confer an increased risk of thiopurine-induced leukopenia [TIL]; however, their global prevalence in inflammatory bowel disease [IBD] patients is unknown. We aimed to evaluate the global prevalence of NUDT15 variants in IBD patients and incidence of TIL in these patients. METHODS: Six databases were searched from inception until July 2022. Studies reporting the frequency of any NUDT15 variant and/or frequency of leukopenia in adult IBD patients with these variants were included. A random effects model was performed to estimate the pooled prevalence of variants, incidence of early [≤8 weeks] and late [>8 weeks] leukopenia, and relative risk of developing leukopenia. RESULTS: Twenty studies comprising 5232 patients were included. The pooled prevalence of the *1/*3 c.415C > T C/T diplotype was 13% (95% confidence interval [CI]: 10-18%), *3/*3 c.415C > T T/T diplotype was 2% [95% CI: 1-2%], *1/*5 c.52G > A G/A diplotype was 2% [95% CI: 1-3%], and *1/*6 c.36_37insGGAGTC ins/- diplotype was 7% [95% CI: 4-12%]. The pooled prevalence of *1/*3 was high in Japanese [20%, 95% CI: 16-24%] and Chinese patients [18%, 95% CI: 12-27%]. The incidence of early leukopenia was 20% [95% CI: 16-26%] in *1/*3 patients, 99% [95% CI: 7-100%] in *3/*3 patients, and 49% [95% CI: 29-69%] in *1/*6 patients. The incidence of late leukopenia was 36% [95% CI: 26-49%] in *1/*3 patients. CONCLUSIONS: NUDT15 variants are common and strongly predict TIL in IBD patients. Pre-treatment NUDT15 genotyping should be considered particularly in Asian populations, to guide thiopurine dosing and prevent myelotoxicity.

Incidence and determinants of hematotoxicity in acute lymphoblastic leukemia children who received 6-mercaptopurine based maintenance therapy in Addis Ababa, Ethiopia.

INTRODUCTION: The maintenance phase of acute lymphoblastic leukemia treatment is the final and longest stage of treatment, mainly focused on antimetabolite therapy. This phase is essential to eliminate residual leukemic clones and prevent relapse. However, dose-limiting hematotoxicity is a major problem during this phase resulting in dose reduction or treatment discontinuation. OBJECTIVE: In this cohort study, the clinical features and risk factors of hematological toxicity during the maintenance phase of treatment were analyzed in pediatric patients from Ethiopia. METHODS: A total of 160 patients from Tikur Anbessa specialized hospital were included in the study of which 142 had sufficient data available for analysis. Patient characteristics as well as information about the care-givers, sides-effects as reported by the care-givers and clinical factors were collected. Bivariable followed by multivariable analysis was performed to investigate which factors were associated with hematological toxicity during the maintenance phase. RESULTS: During the first six months of maintenance phase treatment grade 4 neutropenia was detected in 52.8% of the patients. The risk of developing grade 4 neutropenia was increased by about two fold in children with the age of 6 years and less compared to those with the age of more than 6 years. Similarly, the rate of developing grade 4 neutropenia among children with less than 4,500 maintenance day 1 white blood cell counts was significantly higher than that of children with normal maintenance day 1 white blood cell counts (AHR 2.477, 95% CI = 1.461-4.200, p = 0.001). CONCLUSION: In conclusion, child's age and day 1 maintenance white blood cell/absolute neutrophil counts significantly affected the occurrence of grade 4 hematotoxicity. Close monitoring for white blood cell and absolute neutrophil counts during maintenance phase treatment is recommended for early diagnosis of hematotoxicity.

Feasibility of Reduced Clinical Monitoring in Patients with Inflammatory Bowel Disease Treated with Thiopurine Therapy.

BACKGROUND: Outpatient visits and laboratory assessments are routinely scheduled every 3 to 4 months in thiopurine-treated patients with inflammatory bowel disease (IBD) to timely detect thiopurine-related adverse events (AEs). AEs that require therapy adjustment beyond 12 months of treatment are rare. AIM AND METHODS: This single-center prospective cohort study evaluated the safety of a reduced 6-monthly monitoring strategy in steroid-free patients with quiescent IBD on stable dose of azathioprine, mercaptopurine, or thioguanine monotherapy. The primary outcome was thiopurine-related AEs requiring therapy adjustments during a follow-up period of 24 months. Secondary outcomes included all AEs including laboratory toxicity, disease flares until 12 months, and the net monetary benefit from this strategy concerning IBD-related health care use. RESULTS: We enrolled 85 patients with IBD (median age 42 years, 61% Crohn's disease, 62% female), with a median disease duration of 12.5 years and median thiopurine treatment duration of 6.7 years. During follow-up, 3 patients (4%) ceased thiopurines due to AEs: recurrent infections, non-melanoma skin cancer, and gastrointestinal complaints (nausea, vomiting). At 12 months, 25 laboratory toxicities were observed (including 13% myelotoxicity, 17% hepatotoxicity); none required therapy adjustments and all were transient. A reduced monitoring strategy had a net benefit of €136 per patient. CONCLUSION: Three patients (4%) ceased thiopurine therapy due to thiopurine-related AEs, while no laboratory toxicity required therapy adjustments. Monitoring frequency of every 6 months seems feasible in patients with stable IBD on long-term (median duration > 6 years) maintenance thiopurine therapy and may contribute to reduced patient-burden and health care costs.

DNA polymerase gamma variants and hepatotoxicity during maintenance therapy of childhood acute lymphoblastic leukemia: is there a causal relationship?

Hepatotoxicity is a frequent complication during maintenance therapy of acute lymphoblastic leukemia (ALL) with 6-mercaptopurine and methotrexate. Elevated levels of methylated 6-mercaptopurine metabolites (MeMP) are associated with hepatotoxicity. However, not all mechanisms are known that lead to liver failure in patients with ALL. Variants in the POLG gene, which encodes the catalytic subunit of mitochondrial DNA polymerase gamma (POLG1), have been related to drug-induced hepatotoxicity, for example, by sodium valproate. The association of common POLG variants with hepatotoxicity during maintenance therapy was studied in 34 patients with childhood ALL. Of the screened POLG variants, four different variants were detected in 12 patients. One patient developed severe hepatotoxicity without elevated MeMP levels and harbored a heterozygous POLG p.G517V variant, which was not found in the other patients.

Pharmacogenetics of 6-mercaptopurine in a black Zimbabwean cohort treated for acute lymphoblastic leukaemia.

Background: 6-mercaptopurine usage is associated with myelotoxicity and increased risk in patients carrying metabolism-related genetic variations. This study aimed to determine the frequency of candidate gene polymorphisms and their association with 6-mercaptopurine intolerance. Methods: A total of 41 patients on acute lymphoblastic leukaemia treatment were genotyped for TPMT and NUDT15 (rs116855232) alleles, and their association with dose intensity was analyzed. Results: The defective TPMT*3C allele frequency was 9.8%. The median maintenance dose intensity for TPMT*1/*3C participants was considerably lower (47%) when compared with the TPMT*1/*1 wild-type (77%), although not statistically significant. Conclusion: This is the first pharmacogenetics study carried out in a black Zimbabwean leukemia patient cohort. The high defective TPMT*3C (9.8%) allele frequency points to the potential utility of pharmacogenetics testing for safe usage of 6-mercaptopurine in this population.

Acute lymphoblastic leukemia (ALL) is the most common malignancy affecting children in Zimbabwe and 6-mercaptopurine is frequently used as part of its treatment. However, 6-mercaptopurine is associated with side-effects such as severe neutropenia (a condition where you have a low number of white blood cells called neutrophils in your blood), with increased risk observed in patients carrying variants in genes involved in the metabolism of 6-mercaptopurine. Therefore, this study aimed to determine the frequency of polymorphisms in specific genes as well as their association with drug intolerance. A total of 41 patients on ALL treatment were studied. Review of treatment records was done to determine the cumulative 6-mercaptopurine dose and calculate dose intensity. Genotyping (to determine the versions of a gene a patient carries) for TPMT and NUDT15 (rs116855232) was performed and results correlated with drug dose intensity. The most frequent genotype was TPMT*1/*1, occurring in 80% of the participants. The remaining 20% were carriers with two different copies of TPMT (*1/*3C). The defective TPMT*3C variation occurred at 9.8% and none had TPMT*2, *3A, *3B or NUDT15 rs116855232 variants. Comparison analysis with dose intensity was done for 23 participants (56%) who had maintenance records available. The median dose intensity of 47% for TPMT*1/*3C participants was considerably low when compared to that of a normal TPMT*1/*1 patient, which was 77%. However, no statistically significant difference was observed between TPMT genotype and dose intensity. This is the first study in a group of leukemic Zimbabweans to investigate the frequency of TPMT and NUDT15 variants. With a high variation frequency of 9.8% for the defective TPMT*3C, pharmacogenetics testing for TPMT before treatment with 6-MP is recommended in the Zimbabwean population.

Thiopurine Methyltransferase Intermediate Metabolizer Status and Thiopurine-Associated Toxicity During Maintenance Therapy in Childhood Acute Lymphoblastic Leukemia.

Mercaptopurine is a cornerstone of maintenance chemotherapy in childhood acute lymphoblastic leukemia (ALL). Its cytotoxic effects are mediated by 6-thioguanine nucleotides (TGNs) incorporation into lymphocyte DNA. Thiopurine methyltransferase (TPMT) inactivates mercaptopurine, and deficiency resulting from genetic variants increases TGN exposure and hematopoietic toxicity. Although mercaptopurine-dose reduction reduces toxicity risk without compromising relapse rate in patients with TPMT deficiency, dosing recommendations for those with moderately reduced activity (intermediate metabolizer (IM)) are less clear and their clinical impacts have yet to be established. This cohort study assessed the effect of TPMT IM status on mercaptopurine-associated toxicity and TGN blood exposure in pediatric patients with ALL initiated on standard dose mercaptopurine. Of 88 patients studied (mean age 4.8 years), 10 (11.4%) were TPMT IM, and all had undergone ≥ 3 cycles of maintenance therapy (80% completed). A larger proportion of TPMT IM than normal metabolizers (NM) had febrile neutropenia (FN) during the first two cycles of maintenance, reaching significance in the second cycle (57% vs. 15%, respectively; odds ratio = 7.33, P < 0.05). Compared to NM, FN events occurred more frequently and with prolonged duration in IM in cycles 1 and 2 (adjusted P < 0.05). IM had a 2.46-fold increased hazard ratio for FN, and about twofold higher TGN level than NM (P < 0.05). Myelotoxicity was more common in IM than NM (86% vs. 42%, respectively) during cycle 2 (odds ratio = 8.2, P < 0.05). TPMT IM initiated at a standard mercaptopurine dose are at greater risk for FN during early cycles of maintenance therapy, thus our findings support genotype-guided dose adjustment to reduce toxicity.

Thiopurines are an independent risk factor for active tuberculosis in inflammatory bowel disease patients.

The use of thiopurines is an independent risk factor for active tuberculosis in patients with inflammatory bowel disease.

The influence of NUDT15 variants on 6-mercaptopurine-induced neutropenia in Vietnamese pediatric acute lymphoblastic leukemia.

6-Mercaptopurine (6-MP) serves as the backbone of maintenance therapy in acute lymphoblastic leukemia. The nucleoside diphosphate-linked moiety X-type motif 15 genes (NUDT15) affects the metabolism of 6-MP and thiopurine-related neutropenia in the Asian population. This study reports the influence of these variants on 6MP-induced neutropenia in children with acute lymphoblastic leukemia (ALL). A total of 102 children were enrolled in this retrospective cohort study. NUDT15 variants on exon 1 and exon 3 were identified by Sanger sequencing. We divided the intermediate metabolizer group and the normal metabolizer group base on NUDT15 diplotypes. During the first 3 months of maintenance treatment, medical reports measured treatment-related toxicity (neutropenia) and 6-MP dose decreases. NUDT15 genotyping showed two categories of mutations: wild type (75.5%) and heterozygous variant (24.5%). Neutropenia during the early phase of maintenance therapy in the intermediate metabolizer group (68%) was significantly higher than the normal metabolizer group (18.2%) with 10-fold greater odds. Especially, the c.415C>T heterozygous variant was extremely associated with neutropenia compared with the C>C genotype (odds ratio [OR]: 12; 95% confidence interval [CI]: 3.5-41.7). The tolerated doses of 6-MP after the first 3 months of maintenance therapy related to the intermediate metabolizer group and the normal metabolizer group were 48.7 and 64.3 mg/m2/day, respectively (p < 0.001). One-fourth of individuals had NUDT15 variations. All NUDT15 heterozygous mutations cause neutropenia and need 6-MP dose optimization. Given the frequency of NUDT15 mutations in Vietnamese children and their connection with early neutropenia, testing is indicated.