Interaction between NUDT15 and ABCC4 variants enhances intolerability of 6-mercaptopurine in Japanese patients with childhood acute lymphoblastic leukemia

Association between genetic variants of membrane transporters and the risk of high-grade hematologic adverse events in a cohort of Mexican children with B-cell acute lymphoblastic leukemia

Background

Advances in the understanding of the pathobiology of childhood B-cell acute lymphoblastic leukemia (B-ALL) have led towards risk-oriented treatment regimens and markedly improved survival rates. However, treatment-related toxicities remain a major cause of mortality in developing countries. One of the most common adverse effects of chemotherapy in B-ALL is the hematologic toxicity, which may be related to genetic variants in membrane transporters that are critical for drug absorption, distribution, and elimination. In this study we detected genetic variants present in a selected group genes of the ABC and SLC families that are associated with the risk of high-grade hematologic adverse events due to chemotherapy treatment in a group of Mexican children with B-ALL.

Methods

Next generation sequencing (NGS) was used to screen six genes of the ABC and seven genes of the SLC transporter families, in a cohort of 96 children with B-ALL. The grade of hematologic toxicity was classified according to the National Cancer Institute's Common Terminology Criteria for Adverse Events (CTCAE) version 5.0, Subsequently, two groups of patients were formed: the null/low-grade (grades 1 and 2) and the high-grade (grades 3 to 5) adverse events groups. To determine whether there is an association between the genetic variants and high-grade hematologic adverse events, logistic regression analyses were performed using co-dominant, dominant, recessive, overdominant and log-additive inheritance models. Odds ratio (OR) and 95% confidence intervals (95% CI) were calculated.

Results

We found two types of associations among the genetic variants identified as possible predictor factors of hematologic toxicity. One group of variants associated with high-grade toxicity risk: ABCC1 rs129081; ABCC4 rs227409; ABCC5 rs939338, rs1132776, rs3749442, rs4148575, rs4148579 and rs4148580; and another group of protective variants that includes ABCC1 rs212087 and rs212090; SLC22A6 rs4149170, rs4149171 and rs955434.

Conclusion

There are genetic variants in the SLC and ABC transporter families present in Mexican children with B-ALL that can be considered as potential risk markers for hematologic toxicity secondary to chemotherapeutic treatment, as well as other protective variants that may be useful in addition to conventional risk stratification for therapeutic decision making in these highly vulnerable patients.

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.

Single-Nucleotide Polymorphisms, c.415C > T (Arg139Cys) and c.416G > A (Arg139His), in the NUDT15 Gene Are Associated with Thiopurine-Induced Leukopenia

While nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15) gene polymorphism Arg139Cys (rs116855232) is known to be a risk factor for thiopurine-induced severe leukopenia, association with the NUDT15 gene polymorphism Arg139His (rs147390019) has not yet been clarified. In addition, the accuracy of TaqMan PCR to assess these two polymorphisms has not been investigated. In this study, we evaluated TaqMan PCR for detection of the NUDT15 single-nucleotide polymorphisms (SNPs) and examined the clinical impact of Arg139His on thiopurine-induced leukopenia. First, we demonstrated that a TaqMan PCR assay successfully detected the Arg139His polymorphism of NUDT15 in clinical samples. Next, the NUDT15 gene polymorphisms (Arg139Cys and Arg139His) were separately analyzed by TaqMan Real-Time PCR in 189 patients from August 2018 to July 2019. The incidences of leukopenia within 2 years were 16.2, 57.9, and 100% for arginine (Arg)/Arg, Arg/cysteine (Cys), and Arg/histidine (His), respectively. The leukopenia was significantly increased in Arg/Cys and Arg/His compared with Arg/Arg. This retrospective clinical study indicated that, in addition to Arg139Cys, Arg139His may be clinically associated with a high risk of leukopenia. Pharmacogenomics will help in selecting drugs and determining the individualized dosage of thiopurine drugs.

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.

Prominence of NUDT15 genetic variation associated with 6-mercaptopurine tolerance in a genome-wide association study of Japanese children with acute lymphoblastic leukaemia

Inherited genetic variation is associated with 6-mercaptopurine (6-MP) dose reduction and frequent toxicities induced by 6-MP. However, the tolerable dose for 6-MP is not fully predicted by the known variation in NUDT15 and TPMT among Asian children with acute lymphoblastic leukaemia (ALL). We performed a genome-wide association study (GWAS) related to 6-MP dose among Japanese children with ALL. This GWAS comprised 224 patients previously enrolled in Tokyo Children's Cancer Study Group clinical studies with replication attempted in 55 patients. Genome-wide single nucleotide polymorphism (SNP) genotypes were evaluated for association with average 6-MP dose during the initial 168 days of maintenance therapy. Possible associations were observed across five gene-coding regions, among which only variants at 13q14.2 were significant and replicated genome-wide (rs116855232, NUDT15, β = -10.99, p = 3.7 × 10^-13 ). Notable findings were observed for variants in AFF3 (rs75364948, p = 2.05 × 10^-6 ) and CHST11 (rs1148407, p = 2.09 × 10^-6 ), but were not replicated possibly due to small numbers. A previously reported candidate SNP in MTHFR was associated with higher average 6-MP dose (rs1801133, p = 0.045), and FOLH1 (rs12574928) was associated in an evaluation of candidate regions (p_adjust  = 0.013). This study provides strong evidence that rs116855232 in NUDT15 is the genetic factor predominantly associated with 6-MP tolerable dose in children in Japan.

Role of Drug Transporters in Elucidating Inter-Individual Variability in Pediatric Chemotherapy-Related Toxicities and Response

Pediatric cancer treatment has evolved significantly in recent decades. The implementation of risk stratification strategies and the selection of evidence-based chemotherapy combinations have improved survival outcomes. However, there is large interindividual variability in terms of chemotherapy-related toxicities and, sometimes, the response among this population. This variability is partly attributed to the functional variability of drug-metabolizing enzymes (DME) and drug transporters (DTS) involved in the process of absorption, distribution, metabolism and excretion (ADME). The DTS, being ubiquitous, affects drug disposition across membranes and has relevance in determining chemotherapy response in pediatric cancer patients. Among the factors affecting DTS function, ontogeny or maturation is important in the pediatric population. In this narrative review, we describe the role of drug uptake/efflux transporters in defining pediatric chemotherapy-treatment-related toxicities and responses. Developmental differences in DTS and the consequent implications are also briefly discussed for the most commonly used chemotherapeutic drugs in the pediatric population.

ABCC4, ITPA, NUDT15, TPMT and their interaction as genetic predictors of 6-mercaptopurine intolerance in chinese patients with acute lymphoblastic leukemia

Inter-individual variance in 6-mercaptopurine (6-MP) dose intensity is common in patients with acute lymphoblastic leukemia (ALL). We aimed to evaluate the association of common variants of ABCC4, ITPA, NUDT15, and TPMT with 6-MP dose intensity and toxicity in pediatric ALL patients. In this cohort, 13.8% of patients were intolerant to 6-MP with actual dosage less than 50% of scheduled dose. Twenty percent of patients were found to be heterozygous or homozygous mutated with NUDT15. NUDT15 c.415C > T and the genotype-predicted NUDT15 activity were significantly associated with 6-MP intolerance. TPMT*3C variants were not common in this cohort (2.8%). NUDT15 polymorphisms and genotype predicted NUDT15 activity were significantly associated with 6-MP dose intensity and leukopenia episodes. Combination of ABCC4 and ITPA variants (ABCC4 c.912G > T and ITPA c.94C > A) also showed significant positive association with 6-MP intolerance in Chinese children with ALL. Further study on pharmacogenetic screening for ALL patients to avoid 6-MP induced toxicity is recommended.Supplemental data for this article is available online at https://doi.org/10.1080/08880018.2021.1973628.

Effect of ITPA Polymorphism on Adverse Drug Reactions of 6-Mercaptopurine in Pediatric Patients with Acute Lymphoblastic Leukemia: A Systematic Review and Meta-Analysis

6-Mercaptopurine (6-MP) is a cornerstone of the maintenance regimen for pediatric acute lymphoblastic leukemia (ALL). Inosine triphosphate pyrophosphatase (ITPA) is considered a candidate pharmacogenetic marker that may affect metabolism and 6-MP-induced toxicities; however, the findings are inconsistent. Therefore, we attempted to evaluate the effect of ITPA 94C>A polymorphism on 6-MP-induced hematological toxicity and hepatotoxicity through a systematic review and meta-analysis. A literature search for qualifying studies was conducted using the PubMed, Web of Science, and Embase databases until October 2021. Overall, 10 eligible studies with 1072 pediatric ALL patients were included in this meta-analysis. The results indicated that ITPA 94C>A was significantly associated with 6-MP-induced neutropenia (OR 2.38, 95% CI: 1.56−3.62; p = 0.005) and hepatotoxicity (OR 1.98, 95% CI: 1.32−2.95; p = 0.0009); however, no significant association was found between the ITPA 94C>A variant and 6-MP-induced leukopenia (OR 1.75, 95% CI: 0.74−4.12; p = 0.20). This meta-analysis demonstrated that ITPA 94C>A polymorphism could affect 6-MP-induced toxicities. Our findings suggested that ITPA genotyping might help predict 6-MP-induced myelosuppression and hepatotoxicity.

Association of ITPA gene polymorphisms with adverse effects of AZA/6-MP administration: a systematic review and meta-analysis

Azathioprine (AZA) and its metabolite, mercaptopurine (6-MP), are widely used immunosuppressant drugs. Polymorphisms in genes implicated in AZA/6-MP metabolism, reportedly, could account in part for their potential toxicity. In the present study we performed a systematic review and a meta-analysis, comprising 30 studies and 3582 individuals, to investigate the putative genetic association of two inosine triphosphatase (ITPA) polymorphisms with adverse effects in patients treated with AZA/6-MP. We found that rs1127354 is associated with neutropenia in general populations and in children (OR: 2.39, 95%CI: 1.97-2.90, and OR: 2.43, 95%CI: 2.12-2.79, respectively), and with all adverse effects tested herein in adult populations (OR: 2.12, 95%CI: 1.22-3.69). We also found that rs7270101 is associated with neutropenia and leucopenia in all-ages populations (OR: 2.93, 95%CI: 2.36-3.63, and OR: 2.82, 95%CI: 1.76-4.50, respectively) and with all adverse effects tested herein in children (OR: 1.74, 95%CI: 1.06-2.87). Stratification according to background disease, in combination with multiple comparisons corrections, verified neutropenia to be associated with both polymorphisms, in acute lymphoblastic leukemia (ALL) patients. These findings suggest that ITPA polymorphisms could be used as predictive biomarkers for adverse effects of thiopurine drugs to eliminate intolerance in ALL patients and clarify dosing in patients with different ITPA variants.

NUDT15 is a key genetic factor for prediction of hematotoxicity in pediatric patients who received a standard low dosage regimen of 6-mercaptopurine

6-Mercaptopurine (6-MP) is commonly used for treatment of acute lymphoblastic leukemia (ALL). The incidence of hematotoxicity caused by this drug is quite high in Asians even using a standard low dosage regimen. The present study was aimed to elucidate the impact of thiopurine S-methyltransferase (TPMT), a nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15), inosine triphosphatase (ITPA) and ATP Binding Cassette Subfamily C Member 4 (ABCC4) polymorphisms on hematotoxicity in pediatric patients who received a standard low starting dose of 6-MP. One hundred and sixty-nine pediatric patients were enrolled and their genotypes were determined. Patients who carried NUDT15^∗3 and NUDT15^∗2 genotypes were at a 10-15 fold higher risk of severe neutropenia than those of the wild-type during the early months of the maintenance phase. Risk of neutropenia was not significantly increased in patients with other NUDT15 variants as well as in patients with TPMT, ITPA or ABCC4 variants. These results suggest that NUDT15 polymorphisms particularly, NUDT15^∗3 and NUDT15^∗2, play major roles in 6-MP-induced severe hematotoxicity even when using a standard low dosage of 6-MP and genotyping of these variants is necessary in order to obtain precise tolerance doses and avoid severe hematotoxicity in pediatric patients.

Meta-Analysis of NUDT15 Genetic Polymorphism on Thiopurine-Induced Myelosuppression in Asian Populations

Backgound: The high incidence of thiopurine-induced myelosuppression in Asians is known to be attributable to genetic variation in thiopurine metabolism. A quantitative synthesis to summarize the genetic association with thiopurine-induced myelosuppression in Asians was therefore conducted.

Methods: A Literature search was performed from January 2016 to May 2021 in the following databases: PubMed, Web of Science, and Embase and addition search included the studies from Zhang et al. Two reviewers independently extracted the following data: the author’s name, year of publication, ethnicity, drugs, diseases, genetic polymorphisms, onset, type of myelosuppression and results of Hardy-Weinberg equilibrium. The Newcastle-Ottawa Scale was used to assess the quality of the studies. The pooled odds ratios (OR) and 95% confidence intervals (CI) were calculated to evaluate the associations of NUDT15 and the risk of thiopurine-induced myelosuppression stratified by onset and type of myelosuppressive. Subgroup analysis by NUDT15 genetic polymorphisms was performed.

Results: A total of 30 studies was included in this meta-analysis. The overall OR for the relationship between NUDT15 genetic polymorphisms and thiopurine-induced early onset of leukopenia and neutropenia in Asian populations were 11.43 (95% CI 7.11–18.35) and 16.35 (95% CI 10.20–26.22). Among NUDT15 polymorphisms, NUDT15*3 showed a significantly increased risk of early leukopenia (OR 15.31; 95% CI 9.65–24.27) and early neutropenia (OR 15.85; 95% CI 8.80–28.53). A significantly higher thiopurine-induced early neutropenic risk was also found for NUDT15*2 (OR 37.51; 95% CI 1.99–708.69). Whereas, NUDT15*5 and NUDT15*6 variants showed a lower risk of leukopenia.

Conclusion: This study suggests that NUDT15*3 and NUDT15*2 are important genetic markers of thiopurine-induced early onset of myelotoxicity in Asians, therefore, early detection of these variants before initiating thiopurine therapy is necessary.

[Effect of genetic polymorphism of TPMT and NUDT15 on the tolerance of 6-mercaptopurine therapy in adult acute lymphoblastic leukemia]

Objective: To investigate the effect of genetic polymorphisms of TPMT*2 rs1800462, TPMT*3B rs1800460, TPMT*3C rs1142345, and NUDT15 rs116855232 on the tolerance of 6-mercaptopurine (6-MP) therapy in adult acute lymphoblastic leukemia (ALL) . Methods: A total of 216 adult patients who were diagnosed with ALL and treated with cyclophosphamide, cytarabine, and 6-MP [complementary and alternative medicine (CAM) regimen] from September 2015 to December 2019 were included. Polymorphisms were detected by TaqMan SNP Genotyping Assay. Combined with clinical data, the influence of genetic polymorphism on the tolerance of 6-MP in the treatment of ALL was analyzed. Results: Among the 216 patients, 185 (85.65%) patients had B-ALL and 31 (14.35%) patients had T-ALL. 216 (100%) patients had CC genotype for both TPMT*2 rs1800462 and TPMT*3B rs1800460. The number of TT and TC genotypes for TPMT*3C rs1142345 was 209 (96.76%) and 7 (3.24%) , respectively. The allele frequency was 1.62% for TPMT*3C rs1142345. The number of CC, CT, and TT genotypes for NUDT15 rs116855232 was 166 (76.85%) , 48 (22.22%) , and 2 (0.93%) , respectively. The allele frequency was 12.04% for NUDT15 rs116855232. The TPMT*3C rs1142345 mutant group (TC+CC genotype) had less transfusion volume of packed red blood cell than the wild group (CC genotype) (P=0.036) , and the mutant group (TC+CC genotype) had a higher risk to develop hepatotoxicity (increased aspartate aminotransferase) than the wild group (CC genotype) (OR=9.559, 95% CI 1.135-80.475, P=0.038) . The durations of white blood cells (WBC) <1×10(9)/L and absolute neutrophil count (ANC) <0.5×10(9)/L in the NUDT15 rs116855232 mutation group (CT+TT genotype) were longer than that in the wild group (CC genotype) (P=0.005, P=0.007) , and the transfusion volume of apheresis-derived platelets in the mutant group (CT+TT type) was greater than that in the wild group (CC genotype) (P=0.014) . Conclusion: Genetic polymorphism of TMPT and NUDT15 has an effect on the tolerance of 6-MP in the treatment of adult ALL. Detecting genotypes of patients with ALL before treatment helps to optimize the dosage of 6-MP, which may help shorten the bone marrow suppression duration and reduce blood transfusion volume.

NUDT15 genetic testing-guided 6-mercaptopurine dosing in children with ALL likely to be cost-saving in China

OBJECTIVE

The cost-effectiveness of NUDT15 genetic testing-guided initial 6-mercaptopurine (6-MP) dosing in children with acute lymphoblastic leukemia (ALL) was evaluated.

METHODS

A decision tree model was used to evaluate the cost to China's medical system per quality-adjusted life-year (QALY) gained and cost per case of severe leukopenia avoided of NUDT15 genetic testing using public clinical data.

RESULTS

Genetic testing-guided initial 6-MP dosing reduced overall costs by $518.61, and prevented 0.221 cases of Grade III-IV leukopenia and increased QALY by 0.00136 per patient. Results were robust in one-way analyses and probabilistic sensitivity analyses.

CONCLUSION

NUDT15 genetic testing prior to the initial administration of 6-MP in pediatric ALL patients in China is less expensive than standard dosing without genetic testing.

NUDT15 polymorphism in healthy children with Bai nationality in Yunnan of China

BACKGROUND

Thiopurine methyltransferase (TPMT) polymorphism is one of the causes of the toxicity of thiopurines, but this is rarely seen in Asian populations. Rather, the nucleoside diphosphate-linked X-component motif 15 (NUDT15) gene is frequently linked to mercaptopurine (MP) intolerance and myelotoxicity in children with acute lymphoblastic leukemia (ALL) in East Asians; however, little is known about the NUDT15 polymorphism in healthy children, especially in ethnic minorities in China.

METHODS

A total of 162 cases of healthy children with Bai nationality were enrolled for NUDT15 genotyping.

RESULTS

Three coding variants were identified in the NUDT15 gene including rs186364861, rs746071566 and rs116855232. Notably, the rs746071566 and rs116855232 in NUDT15 showed much higher frequencies in healthy children with Bai nationality compared with healthy East Asian populations, suggesting a concentrated distribution of these variants in the Bai ethnic group.

CONCLUSIONS

This finding reveals the genetic polymorphism of NUDT15 in children with Chinese Bai nationality, providing a biological genetic background for the individualized therapy of thiopurines for children with Bai nationality in China.

Association Between Genetic Polymorphisms of Metabolic Enzymes and Azathioprine-Induced Myelosuppression in 1,419 Chinese Patients: A Retrospective Study

The aim of this study was to investigate the correlation between genetic polymorphisms of azathioprine-metabolizing enzymes and adverse reactions of myelosuppression. To this end, a retrospective analysis was performed on 1,419 Chinese patients involving 40 different diseases and 3 genes: ITPA (94C>A), TPMT*3 (T>C), and NUDT15 (415C>T). Strict inclusion and exclusion criteria were established to collect the relative cases, and the correlation between azathioprine and myelosuppression was evaluated by adverse drug reaction criteria. The mutation rates of the three genes were 29.32, 3.73, and 21.92% and grades I to IV myelosuppression occurred in 54 (9.28%) of the 582 patients who took azathioprine. The highest proportion of myelosuppression was observed in 5 of the 6 (83.33%) patients carrying the NUDT15 (415C>T) TT genotype and 12 of the 102 (11.76%) patients carrying the NUDT15 (415C>T) CT genotype. Only the NUDT15 (415C>T) polymorphism was found to be associated with the adverse effects of azathioprine-induced myelosuppression (odds ratio [OR], 51.818; 95% CI, 5.280–508.556; p = 0.001), which suggested that the NUDT15 (415C>T) polymorphism could be an influencing factor of azathioprine-induced myelosuppression in the Chinese population. Epistatic interactions between ITPA (94C>A) and NUDT15 (415C>T) affect the occurrence of myelosuppression. Thus, it is recommended that the genotype of NUDT15 (415C>T) and ITPA (94C>A) be checked before administration, and azathioprine should be avoided in patients carrying a homozygous NUDT15 (415C>T) mutation. This study is the first to investigate the association between genetic polymorphisms of these three azathioprine-metabolizing enzymes and myelosuppression in a large number of cases with a diverse range of diseases.

Pharmacogenetic evaluation of 6-mercaptopurine-mediated toxicity in pediatric acute lymphoblastic leukemia patients from a South Indian population

Aim: To evaluate the variants in the genes coding for the proteins involved in thiopurine and folate metabolism with treatment related adverse effects (TRAEs). Materials & methods: Eleven variants in seven candidate genes were genotyped in 127 pediatric acute lymphoblastic leukemia patients under 6-mercaptopurine (6-MP) treatment to infer the association of selected genotypes with TRAEs. Results: Among the genotypes inspected, NUDT15 (c.415C>T) and SLC19A1 (c.80G>A) showed a significant association with the TRAEs (odds ratio = 4.01, p = 0.002 and odds ratio = 7.78, p = 0.002). Conclusion: SLC19A1 and NUDT15 play an important role in the metabolism of 6-MP and it is necessary to spot other variants in associated pathways and investigate the factors that can impact 6-MP metabolism.

Genetic Polymorphisms of Drug-Metabolizing Enzymes Involved in 6-Mercaptopurine-Induced Myelosuppression in Thai Pediatric Acute Lymphoblastic Leukemia Patients

Genetic polymorphisms of thiopurine S-methyltransferase (TPMT) and nucleoside diphosphate-linked moiety X-type motif 15 ( NUDT15 ) genes have been proposed as key determinants of 6-mercaptopurine (6-MP)-induced myelosuppression in pediatric acute lymphoblastic leukemia (ALL). In the present study, genotypes of TPMT and NUDT15 were investigated in 178 Thai pediatric patients with ALL by the TaqMan SNP genotyping assay and DNA sequencing. The frequency of TPMT*3C was 0.034. Among NUDT15 variants, NUDT15*3 is the most common variant with the allele frequency of 0.073, whereas those of NUDT15*2 , NUDT15*5 , and NUDT15*6 variants were 0.022, 0.011, and 0.039. These data suggest that a high proportion of Thai pediatric ALL patients may be at risk of thiopurine-induced myelosuppression.

Childhood acute lymphoblastic leukemia mercaptopurine intolerance is associated with NUDT15 variants

BACKGROUND

Mercaptopurine-induced neutropenia can interrupt chemotherapy and expose patients to infection during childhood acute lymphoblastic leukemia (ALL) treatment. Previously, six candidate gene variants associated with mercaptopurine intolerance were reported. Herein, we investigated the association between the mean tolerable dose of mercaptopurine and these genetic variants in Taiwanese patients.

METHODS

In total, 294 children with ALL were treated at the National Taiwan University Hospital from April 1997 to December 2017. Germline variants were analyzed for NUDT15, SUCLA2, TPMT, ITPA, PACSIN2, and MRP4. Mean daily tolerable doses of mercaptopurine in the continuation phase of treatment were correlated with these genetic variants.

RESULTS

Mercaptopurine intolerance was significantly associated with polymorphisms in NUDT15 (P value < 0.0001). Patients with SUCLA2 variants received lower mercaptopurine doses (P value = 0.0119). The mean mercaptopurine doses did not differ among patients with TPMT, ITPA, MRP4, and PACSIN2 polymorphisms (P value = 0.9461, 0.5818, and 0.7951, respectively). After multivariable linear regression analysis, only NUDT15 variants retained their clinically significant correlation with mercaptopurine intolerance (P value < 0.0001).

CONCLUSION

In this cohort, the major genetic determinant of mercaptopurine intolerance was NUDT15 in Taiwanese patients.

IMPACT

NUDT15 causes mercaptopurine intolerance in children with ALL. The NUDT15 variant is a stronger predictor of mercaptopurine intolerance than TPMT in a Taiwanese cohort. This finding is similar with studies performed on Asian populations rather than Caucasians. Pre-emptive genotyping of the patients' NUDT15 before administering mercaptopurine may be more helpful than genotyping TPMT in Asians.

Promising genes and variants to reduce chemotherapy adverse effects in acute lymphoblastic leukemia

Almost two decades ago, the sequencing of the human genome and high throughput technologies came to revolutionize the clinical and therapeutic approaches of patients with complex human diseases. In acute lymphoblastic leukemia (ALL), the most frequent childhood malignancy, these technologies have enabled to characterize the genomic landscape of the disease and have significantly improved the survival rates of ALL patients. Despite this, adverse reactions from treatment such as toxicity, drug resistance and secondary tumors formation are still serious consequences of chemotherapy, and the main obstacles to reduce ALL-related mortality. It is well known that germline variants and somatic mutations in genes involved in drug metabolism impact the efficacy of drugs used in oncohematological diseases therapy. So far, a broader spectrum of clinically actionable alterations that seems to be crucial for the progression and treatment response have been identified. Although these results are promising, it is necessary to put this knowledge into the clinics to help physician make medical decisions and generate an impact in patients' health. This review summarizes the gene variants and clinically actionable mutations that modify the efficacy of antileukemic drugs. Therefore, knowing their genetic status before treatment is critical to reduce severe adverse effects, toxicities and life-threatening consequences in ALL patients.

Ancestry and TPMT-VNTR Polymorphism: Relationship with Hematological Toxicity in Uruguayan Patients with Acute Lymphoblastic Leukemia

6-Mercaptopurine (6-MP) is a thiopurine drug widely used in childhood acute lymphoblastic leukemia (ALL) therapy. Genes such as TPMT and NUDT15 have an outstanding role in 6-MP metabolism. Mutations in both genes explain a significant portion of hematological toxicities suffered by ALL Uruguayan pediatric patients. A variable number tandem repeat in the TPMT promoter (TPMT-VNTR) has been associated with TPMT expression. This VNTR has a conservative architecture (AnBmC). To explore new causes of hematological toxicities related to ALL therapy, we genotyped the TPMT-VNTR of 130 Uruguayan pediatric patients. Additionally, individual genetic ancestry was estimated by 45 ancestry-informative markers (AIMs). Hematological toxicity was measured as the number of leukopenia events and 6-MP dose along the maintenance phase. As previously reported, we found TPMT*2 and TPMT*3C alleles were associated to TPMT-VNTR A2BC and AB2C, respectively. However, contrasting with other reports, TPMT*3A allele was found in a heterogeneous genetic background in linkage equilibrium. Patients carrying more than 5 A repeats present a significant higher number of leukopenia events among patients without TPMT and/or NUDT15 variants. Native American ancestry and the number of A repeats were significantly correlated with the number of leukopenia events. However, the correlation between Native American ancestry and the number of leukopenia events was lost when the number of A repeats was considered as covariate. This suggests that TPMT-VNTR alleles are more relevant than Native American ancestry in the hematological toxicity. Our results emphasize that TPMT-VNTR may be used as a pharmacogenetic biomarker to predict 6-MP-related hematological toxicity in ALL childhood therapy.

Simultaneous UPLC-MS/MS Determination of 6-mercaptopurine, 6-methylmercaptopurine and 6-thioguanine in Plasma: Application to the Pharmacokinetic Evaluation of Novel Dosage forms in Beagle Dogs

BACKGROUND

6-Mercaptopurine (6-MP) is widely used to treat pediatric acute lymphoblastic leukemia (ALL). Mini-tablets of 5 mg per tablet were developed for precision individual therapy for children and individuals with poor thiopurine S-methyltransferase (TPMT) or nucleoside diphophate-linked moiety X-type motif 15 (NUDT15) metabolism. This study investigated the pharmacokinetic profiles of mini-tablets and conventional tablets with an improved ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method.

METHODS

After giving 8 healthy beagle dogs 50 mg 6-MP in different dosage forms, plasma samples collected at different time points were analyzed for pharmacokinetic evaluation. The samples were precipitated by methanol with 0.05% formic acid and separated on a Waters Atlantis T3 column (2.1 × 150 mm, 3 μm particles) using 0.1% formic acid in water and methanol at a flow rate of 0.4 mL/min in 4 min.

RESULTS

This method showed good linearity, accuracy, precision and stability with a detection range of 5.0-500.0 ng/mL for 6-MP, 6-methylmercaptopurine (6-MMP) and 6-thioguanine (6-TG). The main parameters, half-life of apparent terminal disposition, maximum observed plasma concentration, total AUC extrapolated to infinity, AUC since initiation of the experiment, mean residence time, distribution volume and clearance were 1.62 ± 0.87 hours, 90.58 ± 60.43 ng/mL, 151.20 ± 94.18 ng·h/mL, 292.06 ± 184.02 ng·h2/mL, 1.90 ± 0.92 hours, 864.08 ± 538.52 L, and 432.75 ± 360.64 L/h for conventional tablets and 1.70 ± 1.10 hours, 84.15 ± 39.50 ng/mL, 147.70 ± 51.80 ng·h/mL, 300.92 ± 124.48 ng·h2/mL, 2.07 ± 0.50 hours, 756.90 ± 324.00 L, and 340.75 ± 125.81 L/h for minitablets, respectively. Paired t-tests showed no significant difference in any of the evaluated pharmacokinetic parameters between the two types tablets (P > 0.05).

CONCLUSION

Two dosage forms showed the same pharmacokinetic characteristics. This developing, novel formulation will help to provide a more accurate and optimal dosing regimen of 6-MP for humans in the future.

Determination of NUDT15 variants by targeted sequencing can identify compound heterozygosity in pediatric acute lymphoblastic leukemia patients

Mercaptopurine intolerance is an adverse effect of mercaptopurine administration in pediatric acute lymphoblastic leukemia. Recently, NUDT15 variants were identified as a major determinant of mercaptopurine intolerance. Two NUDT15 variants, c.36_37insGGAGTC and c.415C > T, are located on exons 1 and 3, respectively. Patients with heterozygous c.36_37insGGAGTC and c.415C > T can be either compound heterozygous with two variants on different alleles or heterozygous with both variants on the same allele. Because patients with biallelic NUDT15 variants are extremely sensitive to mercaptopurine, clinical identification of NUDT15 diplotype would be advantageous. A cohort of 37 patients with c.36_37insGGAGTC and c.415C > T NUDT15 variants were selected for haplotyping by targeted sequencing. NUDT15 complementary DNA was amplified and sequenced by 300-bp paired-end sequencing on Illumina MiSeq. Of the 37 patients carrying NUDT15 variants, 35 had heterozygous NUDT15*1/*2 variants and two had compound heterozygous NUDT15*3/*6 and NUDT15*2/*7 variants. These two patients with compound heterozygous variants could only tolerate low doses of mercaptopurine, similar to patients with homozygous NUDT15 variants. Targeted sequencing of NUDT15 cDNA can be used to determine NUDT15 diplotype and identify patients with compound heterozygous NUDT15 variants.

Implementation of Pharmacogenetics to Individualize Treatment Regimens for Children with Acute Lymphoblastic Leukemia

Despite major advances in the management and high cure rates of childhood acute lymphoblastic leukemia (ALL), patients still suffer from many drug-induced toxicities, sometimes necessitating dose reduction, or halting of cytotoxic drugs with a secondary risk of disease relapse. In addition, investigators have noted significant inter-individual variability in drug toxicities and disease outcomes, hence the role of pharmacogenetics (PGx) in elucidating genetic polymorphisms in candidate genes for the optimization of disease management. In this review, we present the PGx data in association with main toxicities seen in children treated for ALL in addition to efficacy, with a focus on the most plausible germline PGx variants. We then follow with a summary of the highest evidence drug-gene annotations with suggestions to move forward in implementing preemptive PGx for the individualization of treatment regimens for children with ALL.

Pharmacogenomics as a Tool to Limit Acute and Long-Term Adverse Effects of Chemotherapeutics: An Update in Pediatric Oncology

In the past decades, new cancer treatments have been introduced in pediatric oncology leading to improvement in clinical outcomes and survival rates. However, due to inter-individual differences, some children experience severe chemotherapy-induced toxicities or a poor clinical outcome. An explanation for the diversity in response to chemotherapy is genetic variation, leading to differences in expression and activity of metabolizing and transport enzymes as well as drug targets. Pharmacogenetic testing has emerged as a promising tool to predict and limit acute and long-term adverse effects in patients. However, in pediatric oncology, limited number of patients and a considerable diversity in study results complicate the interpretation of test results and its clinical relevance. With this review, we provide an overview of new developments over the past four years regarding relevant polymorphisms related to toxicity in pediatric oncology. The following chemotherapeutics and associated toxicities are discussed: alkylating agents, anthracyclines, asparaginase, methotrexate, platinum compounds, steroids, thiopurines, topoisomerase inhibitors, and vinca alkaloids. Our review identifies several questions regarding the role of genetic variants in chemotherapy-induced toxicities. Ambiguities in the literature stem from small population sizes, differences in (statistical) interpretation and variations in sequencing technologies as well as different clinical outcome definitions. Standardization of clinical outcome data and toxicity definitions within electronic health records combined with the increased availability of genomic sequence techniques in clinical practice will help to validate these models in upcoming years.

Lack of the multidrug transporter MRP4/ABCC4 defines the PEL-negative blood group and impairs platelet aggregation

The rare PEL-negative phenotype is one of the last blood groups with an unknown genetic basis. By combining whole-exome sequencing and comparative global proteomic investigations, we found a large deletion in the ABCC4/MRP4 gene encoding an ATP-binding cassette (ABC) transporter in PEL-negative individuals. The loss of PEL expression on ABCC4-CRISPR-Cas9 K562 cells and its overexpression in ABCC4-transfected cells provided evidence that ABCC4 is the gene underlying the PEL blood group antigen. Although ABCC4 is an important cyclic nucleotide exporter, red blood cells from ABCC4null/PEL-negative individuals exhibited a normal guanosine 3',5'-cyclic monophosphate level, suggesting a compensatory mechanism by other erythroid ABC transporters. Interestingly, PEL-negative individuals showed an impaired platelet aggregation, confirming a role for ABCC4 in platelet function. Finally, we showed that loss-of-function mutations in the ABCC4 gene, associated with leukemia outcome, altered the expression of the PEL antigen. In addition to ABCC4 genotyping, PEL phenotyping could open a new way toward drug dose adjustment for leukemia treatment.

Association of NUDT15*3 and FPGS 2572C>T Variants with the Risk of Early Hematologic Toxicity During 6-MP and Low-Dose Methotrexate-Based Maintenance Therapy in Indian Patients with Acute Lymphoblastic Leukemia

Genetic variants influencing the pharmacokinetics and/or pharmacodynamics of the chemotherapeutic drugs used in Acute Lymphoblastic Leukemia (ALL) therapy often contribute to the occurrence of treatment related toxicity (TRT). In this study, we explored the association of candidate genetic variants with early hematological TRT (grade 3–4) occurring within the first 100 days of low-dose methotrexate and 6-mercaptopurine based maintenance therapy (n = 73). Fourteen variants in the following candidate genes were genotyped using allele discrimination assay by real-time PCR: ABCB1, DHFR, GGH, FPGS, MTHFR, RFC1, SLCO1B1, TPMT, and NUDT15. Methotrexate polyglutamate (MTXPG3-5) levels in red blood cells were measured by LC-MS/MS. Early hematological TRT (grade 3–4) was seen in 54.9% of patients. The NUDT15c.415T allele was associated with early TRT occurrence [HR: 3.04 (95% CI: 1.5–6.1); p = 0.007]. Sensitivity of early TRT prediction improved (from 30.7% to 89.7%) by considering FPGS variant (rs1544105’T’) carrier status along with NUDT15c.415T allele [HR = 2.7 (1.5–4.7, p = 0.008)]. None of the considered genetic variants were associated with MTXPG3-5 levels, which in turn were not associated with early TRT. NUDT15c.415T allele carrier status could be used as a stratifying marker for Indian ALL patients to distinguish patients at high or low risk of developing early hematological TRT.

Association between the c.415C > T, c.52G > A, and 36_37insGGAGTC polymorphisms of NUDT 15 and thiopurine-induced leukopenia, thiopurine intolerance, and severe hair loss: an updated meta-analysis

Purpose

As a common immunosuppressive and anticancer drug, thiopurine has achieved remarkable clinical success. However, higher inter-individual dose variability and unpredictable toxicity still challenge its use in clinical practices. Some studies indicate that NUDT 15 polymorphisms are associated with this variation, but specific correlation remains controversial. This meta-analysis assessed the association between three polymorphisms of NUDT 15 and thiopurine-induced toxicities.

Methods

Three databases were electronically searched: PubMed, Embase, and Web of Science. Only case–control studies and cohort studies were eligible. The overall pooled ORs and corresponding 95% CIs were used to represent the results.

Findings

We included 16 studies that focus on NUDT 15 c.415C > T, c.52G > A, and 36_37insGGAGTC polymorphisms in patients treated with thiopurine. Significant associations between NUDT 15 c.415C > T polymorphism and leukopenia were found in all genetic models (TC/TT vs CC, OR: 7.64, 95% CI: (6.19, 9.44), P<0.00001; TT vs CC/TC, OR: 29.66, 95% CI: (12.31, 71.46), P<0.00001; TT vs CC, OR: 45.60, 95% CI: (18.84, 110.37), P<0.00001; TC vs CC, OR: 6.41, 95% CI: (5.19, 7.94), P<0.00001; TT vs TC, OR: 6.38, 95% CI: (2.59, 15.72), P<0.00001), early/late leukopenia (in recessive and co-dominant model), leukopenia (grade 3–4), and severe hair loss in all genetic models. Besides, c.52G > A and 36_37insGGAGTC polymorphisms were also significantly associated with leukopenia. No significant association between NUDT 15 c.415C > T polymorphism and early/late leukopenia in the Chinese population was determined in the co-dominant model (TC vs CC).

Implications

NUDT 15 c.415C > T polymorphism could increase the risk of leukopenia, early/late leukopenia, leukopenia (grade 3–4), and severe hair loss. Meanwhile, c.52G > A and c.36_37insGGAGTC mutations also probably increase the risk of leukopenia. Preemptive tests for NUDT 15 polymorphisms are highly recommended to individualize the treatment of thiopurine for a better outcome with less toxicity.

Somatic and germline genomics in paediatric acute lymphoblastic leukaemia

Advances in genomic research and risk-directed therapy have led to improvements in the long-term survival and quality of life outcomes of patients with childhood acute lymphoblastic leukaemia (ALL). The application of next-generation sequencing technologies, especially transcriptome sequencing, has resulted in the identification of novel molecular subtypes of ALL with prognostic and therapeutic implications, as well as cooperative mutations that account for much of the heterogeneity in clinical responses observed among patients with specific ALL subtypes. In addition, germline genetic variants have been shown to influence the risk of developing ALL and/or the responses of non-malignant and leukaemia cells to therapy; shared pathways for drug activation and metabolism are implicated in treatment-related toxicity and drug sensitivity or resistance, depending on whether the genetic changes are germline, somatic or both. Indeed, although once considered a non-hereditary disease, genomic investigations of familial and sporadic ALL have revealed a growing number of genetic alterations or conditions that predispose individuals to the development of ALL and treatment-related second cancers. The identification of these genetic alterations holds the potential to direct genetic counselling, testing and possibly monitoring for the early detection of ALL and other cancers. Herein, we review these advances in our understanding of the genomic landscape of childhood ALL and their clinical implications.

Associations between the NUDT15 R139C polymorphism and susceptibility to thiopurine-induced leukopenia in Asians: a meta-analysis

Background and aim

Despite several studies being conducted to examine the associations between the NUDT15 R139C polymorphism and thiopurine-induced leukopenia in the Asian population, the results remain inconsistent. This meta-analysis determined the risk of thiopurine-induced leukopenia conferred by the NUDT15 R139C polymorphism.

Materials and methods

All eligible studies published in English up to May 2018 were identified by searching PubMed, Web of Science, Embase, and the Cochrane Library. Pooled OR and 95% CI were calculated using fixed- or random-effect model.

Results

In all, total of 14 studies containing 918 patients and 2,341 controls were included; of these, 8 studies concerned inflammatory bowel disease (IBD) and 4 concerned acute lymphoblastic leukemia (ALL). Overall, the results indicated that the NUDT15 R139C polymorphism was associated with leukopenia induced by thiopurines (OR =9.04, 95% CI 6.05–13.50, P<0.001 for the dominant model; OR =24.26, 95% CI 11.38–51.71, P<0.001 for the recessive model; OR =7.60, 95% CI 4.97–11.61, P<0.001 for the CT vs TT model; OR =38.47, 95% CI 17.78–83.24, P<0.001 for the CC vs TT model). In subgroup analyses, significant associations were found among patients with IBD (OR =7.57, 95% CI 5.16–11.12, P<0.001 for the dominant model), ALL (OR =13.13, 95% CI 3.43–50.23 P<0.001 for the dominant model), and other diseases (OR =31.22, 95% CI 1.20–814.07, P=0.04 for the dominant model). In addition, the R139C variant was strongly associated with early (<8 weeks) (OR =15.53, 95% CI 7.91–30.50, P<0.001 for the dominant model) and late leukopenia (≥8 weeks) (OR =2.92, 95% CI 2.01–4.24, P<0.001 for the dominant model). Moreover, these findings were sufficiently robust when studies without Hardy–Weinberg equilibrium test were excluded.

Conclusion

This meta-analysis verified the strong association between the NUDT15 R139C polymorphism and thiopurine-induced leukopenia (both early and late leukopenia) in an Asian population with IBD, ALL, and other diseases. NUDT15 R139C genotyping should be prioritized to predict leukopenia among Asians.

Development and application of a rapid and sensitive genotyping method for pharmacogene variants using the single-stranded tag hybridization chromatographic printed-array strip (STH-PAS)

Genetic polymorphisms contribute to inter-individual variability in the metabolism of multiple clinical drugs, including warfarin, thiopurines, primaquine, and aminoglycosides. A rapid and sensitive clinical assessment of various genome biomarkers is, therefore, required to predict the individual responsiveness of each patient to these drugs. In this study, we developed a novel genotyping method for the detection of nine pharmacogene variants that are important in the prediction of drug efficiency and toxicity. This genotyping method uses competitive allele-specific PCR and a single-stranded tag hybridization chromatographic printed-array strip (STH-PAS) that can unambiguously determine the presence or absence of the gene variant by displaying visible blue lines on the chromatographic printed-array strip. Notably, the results of our STH-PAS method were in 100% agreement with those obtained using standard Sanger sequencing and KASP assay genotyping methods for CYP4F2 gene deletion. Moreover, the results were obtained within 90 min, including the PCR amplification and signal detection processes. The sensitive and rapid nature of this novel method make it ideal for clinical genetic testing to predict drug efficacy and toxicity, and in doing so will aid in the development of individualized medicine and better patient care.

Pharmacogenetics: Applications to Pediatric Patients

Individual genomic differences may affect drug disposition and effects of many drugs, and identification of biomarkers are crucial to personalize dosage and optimize response. In children, developmental changes associated with growth and maturation translate into different relationships between genotype and phenotype and different responses to treatment compared to adults. This review aims to summarize some developmental aspects of pharmacogenetics, based on practical examples.

Cell Migration Related to MDR-Another Impediment to Effective Chemotherapy?

Multidrug resistance, mediated by members of the ATP-binding cassette (ABC) proteins superfamily, has become one of the biggest obstacles in conquering tumour progression. If the chemotherapy outcome is considered successful, when the primary tumour volume is decreased or completely abolished, modulation of ABC proteins activity is one of the best methods to overcome drug resistance. However, if a positive outcome is represented by no metastasis or, at least, elongation of remission-free time, then the positive effect of ABC proteins inhibition should be compared with the several side effects it causes, which may inflict cancer progression and decrease overall patient health. Clinical trials conducted thus far have shown that the tested ABC modulators add limited or no benefits to cancer patients, as some of them are merely toxic and others induce unwanted drug–drug interactions. Moreover, the inhibition of certain ABC members has been recently indicated as potentially responsible for increased fibroblasts migration. A better understanding of the complex role of ABC proteins in relation to cancer progression may offer novel strategies in cancer therapy.

Pharmacogenetics of thiopurines for inflammatory bowel disease in East Asia: prospects for clinical application of NUDT15 genotyping

The thiopurine drugs 6-mercaptopurine (6-MP) and azathiopurine (AZA) are widely used to treat inflammatory bowel disease. However, the incidence of adverse reactions is high, particularly in Asia, and the mechanisms of toxicity in Asian populations remain unclear. Thiopurine S-methyltransferase (TPMT) is a well-known enzyme that inactivates AZA or 6-MP through methylation and is one of the few pharmacogenetic predictors used in clinical settings in Western countries. Individuals carrying TPMT-deficient genetic variants require reduced drug doses, but this treatment modification is are not applicable to East Asian populations. Several genes code thiopurine-metabolizing enzymes, including TPMT, multidrug-resistance protein 4, and inosine triphosphatase. These genes have been studied as candidate pharmacogenetic markers; however, it remains unclear why Asian populations seem to be more intolerant than other ethnic groups to a full dose of thiopurines. A genome-wide association approach to identify Asian-specific pharmacogenetic markers in Korean patients with Crohn's disease revealed that a non-synonymous single nucelotide polymorphism in nucleoside diphosphate-linked moiety X-type motif 15 (NUDT15) which causes p.Arg139Cys was strongly associated with thiopurine-induced early leukopenia. Six common haplotypes of NUDT15 were reported, and five variants showed medium-to-low enzyme activities, compared with the wild haplotype. NUDT15 hydrolyzes the thiopurine active metabolites 6-thio-GTP and 6-thio-dGTP; variants of NUDT15 had lower enzyme activities, causing higher levels of thiopurine active metabolites, resulting in thiopurine-induced leukopenia. In clinical application, NUDT15 genotyping is a good candidate for predicting thiopurine toxicity in East Asian populations. However, the association of NUDT15 diplotypes with thiopurine toxicity remains unclear. Further analyses with large cohorts to confirm the clinical effects of each haplotype are planned.

NUDT15 codon 139 is the best pharmacogenetic marker for predicting thiopurine-induced severe adverse events in Japanese patients with inflammatory bowel disease: a multicenter study

BACKGROUND

Despite NUDT15 variants showing significant association with thiopurine-induced adverse events (AEs) in Asians, it remains unclear which variants of NUDT15 or whether additional genetic variants should be tested to predict AEs. To clarify the best pharmacogenetic test to be used clinically, we performed association studies of NUDT15 variants and haplotypes with AEs, genome-wide association study (GWAS) to discover additional variants, and ROC analysis to select the model to predict severe AEs.

METHODS

Overall, 2630 patients with inflammatory bowel disease (IBD) were enrolled and genotyped for NUDT15 codon 139; 1291 patients were treated with thiopurines. diplotypes were analyzed in 970 patients, and GWASs of AEs were performed with 1221 patients using population-optimized genotyping array and imputation.

RESULTS

We confirmed the association of NUDT15 p.Arg139Cys with leukopenia and alopecia (p = 2.20E-63, 1.32E-69, OR = 6.59, 12.1, respectively), and found a novel association with digestive symptoms (p = 6.39E-04, OR = 1.89). Time to leukopenia was significantly shorter, and when leukopenia was diagnosed, thiopurine doses were significantly lower in Arg/Cys and Cys/Cys than in Arg/Arg. In GWASs, no additional variants were found to be associated with thiopurine-induced AEs. Despite strong correlation of leukopenia frequency with estimated enzyme activities based on the diplotypes (r² = 0.926, p = 0.0087), there were no significant differences in the AUCs of diplotypes from those of codon 139 to predict severe AEs (AUC = 0.916, 0.921, for acute severe leukopenia, AUC = 0.990, 0.991, for severe alopecia, respectively).

CONCLUSIONS

Genotyping of NUDT15 codon 139 was sufficient to predict acute severe leukopenia and alopecia in Japanese patients with IBD.

Antituberculosis Drug-Induced Adverse Events in the Liver, Kidneys, and Blood: Clinical Profiles and Pharmacogenetic Predictors

Antituberculosis drug‐induced adverse drug reactions (ATD‐ADRs) are increasing globally, and it is key to identify candidate ATD‐ADRs loci for clinical management. We prospectively enrolled 1,235 highly suspicious tuberculosis (TB) inpatients to investigate the profiles and genetic risk factors of ATD‐ADRs in the liver, kidneys, and blood. Overall, 644 subjects were eligible and genotyped for seven polymorphisms in drug‐metabolizing enzymes and transporter genes. Clinical follow‐up and blood analysis were performed regularly. We found that a notable rate of ATD‐ADRs (incidence: 16.5%, drug intervention rate: 10.4%), mainly involving hepatotoxicity (10.6%) and leukopenia (3.3%) in western China. CYP2D6 rs1135840 and NUDT15 rs116855232 increased the risks of hepatotoxicity and leukopenia with an odds ratio of 2.52 and 4.97, respectively. Both variants showed excellent negative predictive values (93.7% and 98.1%, respectively) but moderate sensitivities (72.7% and 52.4%, respectively). These data provide new insight into ATD‐ADRs in the Chinese population and may offer future leads for diagnosis and treatment.