Genetic variants in 6-mercaptopurine pathway as potential factors of hematological toxicity in acute lymphoblastic leukemia patients

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.

Genetic variants of genes involved in thiopurine metabolism pathway are associated with 6-mercaptopurine toxicity in pediatric acute lymphoblastic leukemia patients from Ethiopia

Introduction: Genetic variation in the thiopurine S-methyltransferase (TPMT) gene by and large predicts variability in 6-mercaptopurine (6-MP) related toxicities. However, some individuals without genetic variants in TPMT still develop toxicity that necessitates 6-MP dose reduction or interruption. Genetic variants of other genes in the thiopurine pathway have been linked to 6-MP related toxicities previously. Objective: The aim of this study was to evaluate the effect of genetic variants in ITPA, TPMT, NUDT15, XDH, and ABCB1 on 6-MP related toxicities in patients with acute lymphoblastic leukemia (ALL) from Ethiopia. Methods: Genotyping of ITPA, and XDH was performed using KASP genotyping assay, while that of TPMT, NUDT15, and ABCB1 with TaqMan^® SNP genotyping assays. Clinical profile of the patients was collected for the first 6 months of the maintenance phase treatment. The primary outcome was the incidence of grade 4 neutropenia. Bivariable followed by multivariable cox regression analysis was performed to identify genetic variants associated with the development of grade 4 neutropenia within the first 6 months of maintenance treatment. Results: In this study, genetic variants in XDH and ITPA were associated with 6-MP related grade 4 neutropenia and neutropenic fever, respectively. Multivariable analysis revealed that patients who are homozygous (CC) for XDH rs2281547 were 2.956 times (AHR 2.956, 95% CI = 1.494-5.849, p = 0.002) more likely to develop grade 4 neutropenia than those with the TT genotype. Conclusion: In conclusion, in this cohort, XDH rs2281547 was identified as a genetic risk factor for grade 4 hematologic toxicities in ALL patients treated with 6-MP. Genetic polymorphisms in enzymes other than TPMT involved in the 6-mercaptopurine pathway should be considered during its use to avoid hematological toxicity.

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.

The Role of SLC22A1 and Genomic Ancestry on Toxicity during Treatment in Children with Acute Lymphoblastic Leukemia of the Amazon Region

In Brazil, Acute lymphoid leukemia (ALL) is the leading cause of cancer deaths in children and adolescents. Treatment toxicity is one of the reasons for stopping chemotherapy. Amerindian genomic ancestry is an important factor for this event due to fluctuations in frequencies of genetic variants, as in the NUDT15 and SLC22A1 genes, which make up the pharmacokinetic and pharmacodynamic pathways of chemotherapy. This study aimed to investigate possible associations between NUDT15 (rs1272632214) and SLC22A1 (rs202220802) gene polymorphism and genomic ancestry as a risk of treatment toxicities in patients with childhood ALL in the Amazon region of Brazil. The studied population consisted of 51 patients with a recent diagnosis of ALL when experiencing induction therapy relative to the BFM 2009 protocol. Our results evidenced a significant association of risk of severe infectious toxicity for the variant of the SLC22A1 gene (OR: 3.18, p = 0.031). Genetic ancestry analyses demonstrated that patients who had a high contribution of African ancestry had a significant protective effect for the development of toxicity (OR: 0.174; p = 0.010), possibly due to risk effects of the Amerindian contribution. Our results indicate that mixed populations with a high degree of African ancestry have a lower risk of developing general toxicity during induction therapy for ALL. In addition, individuals with the SLC22A1 variant have a higher risk of developing severe infectious toxicity while undergoing the same therapy.

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.

Pharmacogenomics in Cytotoxic Chemotherapy of Cancer

Pharmacogenetic testing in patients with cancer requiring cytotoxic chemotherapy offers the potential to predict, prevent, and mitigate chemotherapy-related toxicities. While multiple drug-gene pairs have been identified and studied, few drug-gene pairs are currently used routinely in the clinical status. Here we review what is known, theorized, and unknown regarding the use of pharmacogenetic testing in cancer.

Frequency and impact of DHODH, ABCG2 and CYP2C19 SNPs on the therapeutic efficacy, tolerability and toxicity of leflunomide

Introduction: Leflunomide is one of the commonly used drugs in treatment of rheumatoid arthritis (RA), which on administration is converted into its active metabolite teriflunomide. Aim: Our aim is to evaluate the frequencies of dihydrooroate dehydrogenase (DHODH) (rs3213422), ABCG2 (rs2231142) and CYP2C19 (rs4244285) allele distribution among patients receiving leflunomide for RA and their possible impact on leflunomide performance in disease control. Patients & methods: Patients (>18 years) who fulfilled the 2010 ACR classification criteria for RA receiving leflunomide (20 mg/day) were included in the study. Disease activity score 28 was used to assess patients disease activity. Blood samples were collected for full blood count and blood chemistry. Genomic DNA was extracted from peripheral blood. The selection of SNPs was based on the criteria of minor allele frequency among Caucasians. Results: A significant association between the therapeutic outcome of leflunomide and DHODH genotyping was observed but not with CYP2C19 and ABCG2. Importantly, there is a significant association between DHODH (rs3213422) CC genotype and the number of patients with controlled disease. Conclusion: We strongly suggest that polymorphisms in the DHODH are the major factor affecting leflunomide pharmacogenetics and therapeutic efficacy.

Biomarkers for gastrointestinal adverse events related to thiopurine therapy

Thiopurines are immunomodulators used in the treatment of acute lymphoblastic leukemia and inflammatory bowel diseases. Adverse reactions to these agents are one of the main causes of treatment discontinuation or interruption. Myelosuppression is the most frequent adverse effect; however, approximately 5%-20% of patients develop gastrointestinal toxicity. The identification of biomarkers able to prevent and/or monitor these adverse reactions would be useful for clinicians for the proactive management of long-term thiopurine therapy. In this editorial, we discuss evidence supporting the use of PACSIN2, RAC1, and ITPA genes, in addition to TPMT and NUDT15, as possible biomarkers for thiopurine-related gastrointestinal toxicity.

Understanding thiopurine methyltransferase polymorphisms for the targeted treatment of hematologic malignancies

INTRODUCTION

Thiopurine methyltransferase (TPMT) catalyzes the S-methylation of thiopurines (mercaptopurine (MP) and tioguanine (TG)), chemotherapeutic agents used in the treatment of acute lymphoblastic leukemia (ALL). Polymorphisms in TPMT gene encode diminished activity enzyme, enhancing accumulation of active metabolites, and partially explaining the inter-individual differences in patients' clinical response.

AREAS COVERED

This review gives an overview on TPMT gene and function, and discusses the pharmacogenomic implications of TPMT variants in the prevention of severe thiopurine-induced hematological toxicities and the less known implication on TG-induced sinusoidal obstruction syndrome. Additional genetic and non-genetic factors impairing TPMT activity are considered. Literature search was done in PubMed for English articles published since1990, and on PharmGKB.

EXPERT OPINION

To titrate thiopurines safely and effectively, achieve the right degree of lymphotoxic effect and avoid excessive myelosuppression, the optimal management will combine a preemptive TPMT genotyping to establish a safe initial dose with a close phenotypic monitoring of TPMT activity and/or of active metabolites during long-term treatment. Compared to current ALL protocols, replacement of TG by MP during reinduction phase in TPMT heterozygotes and novel individualized TG regimens in maintenance for TPMT wild-type subjects could be investigated to improve outcomes while avoiding risk of severe hepatotoxicity.

Novel Targeted Photosensitizer as an Immunomodulator for Highly Efficient Therapy of T-Cell Acute Lymphoblastic Leukemia

Dasatinib is a kinase-targeted drug used in the treatment of leukemia. Regrettably, it remains far from optimal medicine due to insurmountable drug resistance and side effects. Photodynamic therapy (PDT) has proven that it can induce systemic immune responses. However, conventional photosensitizers as immunomodulators produce anticancer immunities, which are inadequate to eliminate residual cancer cells. Herein, a novel compound 4 was synthesized and investigated, which introduces dasatinib and zinc(II) phthalocyanine as the targeting and photodynamic moiety, respectively. Compound 4 exhibits a high affinity to CCRF-CEM cells/tumor tissues, which overexpress lymphocyte-specific protein tyrosine kinase (LCK), and preferential elimination from the body. Meanwhile, compound 4 shows excellent photocytotoxicity and tumor regression. Significantly, compound 4-induced PDT can obviously enhance immune responses, resulting in the production of more immune cells. We believe that the proposed manner is a potential strategy for the treatment of T-cell acute lymphoblastic leukemia.

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.

Chemoresponsive polymer systems for selective molecular recognition of organic molecules in biological systems

Smart polymer materials that respond to a chemical stimulus are applied for the construction of biomedical devices and purification/separation systems. Small organic molecules are a particular type of stimulus. Their abnormal concentration indisputably indicates certain diseases. They are also hazardous environment contaminants. Polymer materials, which structure is selectively changed in the presence of a defined organic compound are promising in view of regulation of certain biomedical functions, as well as in view of chemical detectors construction. This review summarizes the state of the art in the self-assemblies of amphiphilic copolymers and polymer networks sensitive toward organic species, with an emphasis on the reports from the last decade. We focus on the relationship between the selectivity of introduced receptor moieties responsible for the change of material structure, the overall structure of material and its functionality.

Extremely low dose of 6-mercaptopurine in a Chinese child with acute lymphoblastic leukaemia and multiple pharmacogenetic mutations

WHAT IS KNOWN AND OBJECTIVES

Thiopurines are cornerstone drugs in the treatment of acute lymphoblastic leukaemia (ALL), but their use can be complicated by the incidence of life-threatening leucopenia.

CASE DESCRIPTION

We describe a case of a 6-year-old Chinese boy with B-ALL receiving extremely low dose of 6-mercaptopurine (only 4% of recommended dose) during the ALL maintenance therapy phase.

WHAT IS NEW AND CONCLUSION

Complex pharmacogenetic tests and TDM should be recommended in children with complicated ALL to highlight the large individual variability in the responses to 6-MP exposure and the associated adverse effects.

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.

Characterization of pharmacogenetic markers related to Acute Lymphoblastic Leukemia toxicity in Amazonian native Americans population

Acute Lymphoblastic Leukemia (ALL) is the most common cancer in children. Differences are found among ethnic groups in the results of the treatment of pediatric ALL. In general, children with a high level of native American ancestry tend to respond less positively to ALL treatments, which may be related to specific genomic variants found in native American groups. Despite the evidence, few data are available on the distribution of the pharmacogenomic variants relevant to the treatment of ALL in traditional Amerindian populations, such the those of the Amazon region. Given this, the present study investigated 27 molecular markers related to the treatment of ALL in Amerindians from Brazilian Amazonia and compared the frequencies with those recorded previously on five continents, that are available in the 1,000 Genomes database. The variation in the genotype frequencies among populations was evaluated using Fisher's exact test. The False Discovery Rate method was used to correct the results of the multiple analyses. Significant differences were found in the frequencies of the majority of markers between the Amerindian populations and those of other regions around the world. These findings highlight the unique genetic profile of the indigenous population of Brazilian Amazonia, which may reflect a distinct therapeutic profile for the treatment of ALL in these populations.

Gene-Based Dose Optimization in Children

Pharmacogenetics is a key component of precision medicine. Genetic variation in drug metabolism enzymes can lead to variable exposure to drugs and metabolites, potentially leading to inefficacy and drug toxicity. Although the evidence for pharmacogenetic associations in children is not as extensive as for adults, there are several drugs across diverse therapeutic areas with robust pediatric data indicating important, and relatively common, drug-gene interactions. Guidelines to assist gene-based dose optimization are available for codeine, thiopurine drugs, selective serotonin reuptake inhibitors, atomoxetine, tacrolimus, and voriconazole. For each of these drugs, there is an opportunity to clinically implement precision medicine approaches with children for whom genetic test results are known or are obtained at the time of prescribing. For many more drugs that are commonly used in pediatric patients, additional investigation is needed to determine the genetic factors influencing appropriate dose.

Sgc8 aptamer targeted glutathione-responsive nanoassemblies containing Ara-C prodrug for the treatment of acute lymphoblastic leukemia

Cytarabine (Ara-C) is an essential medicine used in the clinical treatment of acute lymphoblastic leukemia. However, Ara-C suffers from high hydrophilicity, rapid plasma degradation and significant side effects. Thus, herein, to eliminate the limitations of Ara-C in the treatment of leukemia, Sgc8 aptamer targeting and glutathione (GSH)-responsive polymeric micelles (PCL-ss-Ara@Sgc8-BSA) were prepared. The prodrug was synthesized via covalent bond formation between acryloyl chloride-terminal PCL-ss-PCL and Ara-C, and surface decoration with Sgc8-bovine serum albumin (Sgc8-BSA). The obtained PCL-ss-Ara@Sgc8-BSA exhibited good GSH-responsive drug release behavior, obvious targetability and sufficient antitumor effect to acute lymphoblastic leukemia (ALL) cells (CCRF-CEM). A hemolysis test was further carried out to demonstrate that these polymeric micelles are safe to be administrated intravenously. Compared with free Ara-C, PCL-ss-Ara@Sgc8-BSA significantly enhanced tumor growth inhibition in mice bearing CCRF-CEM xenograft tumors, while causing little side effects, and improved the survival rate of CCRF-CEM tumor-bearing mice in vivo. Therefore, this new self-assembling small molecular prodrug equipped with Sgc8 targeting function is a potential treatment for the targeted therapy of acute lymphoblastic leukemia.

Revisiting the Role of Thiopurines in Inflammatory Bowel Disease Through Pharmacogenomics and Use of Novel Methods for Therapeutic Drug Monitoring

Azathioprine and 6-mercaptopurine, often referred to as thiopurine compounds, are commonly used in the management of inflammatory bowel disease. However, patients receiving these drugs are prone to developing adverse drug reactions or therapeutic resistance. Achieving predefined levels of two major thiopurine metabolites, 6-thioguanine nucleotides and 6-methylmercaptopurine, is a long-standing clinical practice in ensuring therapeutic efficacy; however, their correlation with treatment response is sometimes unclear. Various genetic markers have also been used to aid the identification of patients who are thiopurine-sensitive or refractory. The recent discovery of novel Asian-specific DNA variants, namely those in the NUDT15 gene, and their link to thiopurine toxicity, have led clinicians and scientists to revisit the utility of Caucasian biomarkers for Asian individuals with inflammatory bowel disease. In this review, we explore the limitations associated with the current methods used for therapeutic monitoring of thiopurine metabolites and how the recent discovery of ethnicity-specific genetic markers can complement thiopurine metabolites measurement in formulating a strategy for more accurate prediction of thiopurine response. We also discuss the challenges in thiopurine therapy, alongside the current strategies used in patients with reduced thiopurine response. The review is concluded with suggestions for future work aiming at using a more comprehensive approach to optimize the efficacy of thiopurine compounds in inflammatory bowel disease.

Pharmacogenomics and variations in the risk of toxicity during the consolidation/maintenance phases of the treatment of pediatric B-cell leukemia patients from an admixed population in the Brazilian Amazon

The treatment of Acute Lymphoblastic Leukemia (ALL) in children has a high clinical success rate, although toxicological complications are frequent, and often result in the interruption of the treatment. Various studies have shown that toxicities resulting from the treatment are influenced by pharmacogenetic variants. Most of this research has focused on relatively homogeneous populations, and the influence of these variants in highly admixed populations, such as that of Brazil, is still poorly understood. The present study investigated the association between pharmacogenetic variants and severe toxicities in pediatric B-cell ALL patients from an admixed population of the Brazilian Amazon. The rs2306283 (of SLCO1B1) mutant allele increased the risk of neurotoxicity threefold, and the homozygous mutant rs9895420 (of ABCC3) genotype was associated with a fivefold increase in protection against severe gastrointestinal toxicity. This indicates that the rs2306283 and rs9895420 polymorphisms may be relevant to the prediction of severe toxicity in pediatric ALL patients.

ITPA Activity in Adults and Children Treated With or Without Azathioprine: Relationship Between TPMT Activity, Thiopurine Metabolites, and Co-medications

BACKGROUND

The implication of inosine triphosphate pyrophosphatase (ITPA) on thiopurine drug response variability has been investigated but little data are available on its role on thiopurine metabolites. The ability of ITPA to modify the thiopurine metabolite levels is currently used to optimize azathioprine (AZA) therapy in relation to thiopurine S-methyltransferase (TPMT) activity, the aim of this study is to investigate ITPA phenotype in a large population and to evaluate the relation between ITPA and TPMT activities and thiopurine metabolites.

METHODS

ITPA activity was determined in 183 adults and 138 children with or without AZA therapy. 6-thioguanine nucleotides (6-TGN), 6-methylmercaptopurine nucleotides (6-MeMPN) levels, and ITPA as well as TPMT activities were measured in red blood cells. Using the Gaussian mixture model, distribution of ITPA activity was evaluated. Intraindividual variability and influence of age, sex, AZA treatment and associated co-medications on ITPA activity were also assessed.

RESULTS

This retrospective study shows a quadrimodal distribution in ITPA activity. No influence of age, sex, AZA therapy, and co-medications was found. In adults, ITPA activity was not significantly associated with 6-TGN or 6-MeMPN concentrations, whereas a weak negative correlation was observed with 6-MeMPN levels in pediatric populations (rs = -0.261; P = 0.024). A weak positive correlation was observed between ITPA and TPMT activities in children (rs = 0.289; P = 0.001).

CONCLUSIONS

ITPA activity was poorly influenced by nongenetic parameters and has no influence on 6-TGN and 6-MeMPN concentrations in adults and only a weak correlation with 6-MeMPN and TPMT activity in children. These results demonstrate that ITPA is not a rate-limiting enzyme in the formation of 6-TGN but suggest that a decrease in ITPA activity in children may be a risk factor for accumulation of 6-MeMPN in cells.

Role of TPMT and ITPA variants in mercaptopurine disposition

PURPOSE

To explore the levels of thioguanine incorporated into DNA (DNA-TG), and erythrocyte levels of 6-thioguanine nucleotides (Ery-TGN) and methylated metabolites (Ery-MeMP) during 6-mercaptopurine (6MP)/Methotrexate (MTX) therapy of childhood acute lymphoblastic leukemia (ALL) and the relation to inosine triphosphatase (ITPA) and thiopurine methyltransferase (TPMT) gene variants.

METHODS

Blood samples were drawn during 6MP/MTX maintenance therapy from 132 children treated for ALL at Rigshospitalet, Copenhagen. The samples were analysed for thiopurine metabolites and compared to TPMT (rs1800460 and rs1142345) and ITPA (rs1127354) genotypes.

RESULTS

Median DNA-TG (mDNA-TG) levels were higher in TPMT and ITPA low-activity patients as compared to wildtype patients (TPMTLA 549 vs. 364 fmol/µg DNA, p = 0.007, ITPALA 465 vs. 387 fmol/µg DNA, p = 0.04). mDNA-TG levels were positively correlated to median Ery-TGN (mEry-TGN)(rs = 0.37, p = 0.001), but plateaued at higher mEry-TGN levels. DNA-TG indices (mDNA-TG/mEry-TGN) were 42% higher in TPMTWT patients as compared to TPMTLA patients but no difference in DNA-TG indices was observed between ITPAWT and ITPALA patients (median 1.7 vs. 1.6 fmol/µg DNA/ nmol/mmol Hb, p = 0.81). DNA-TG indices increased with median Ery-MeMP (mEry-MeMP) levels (rs = 0.25, p = 0.001).

CONCLUSIONS

TPMT and ITPA genotypes significantly influence the metabolism of 6MP. DNA-TG may prove to be a more relevant pharmacokinetic parameter for monitoring 6MP treatment intensity than cytosolic metabolites. Prospective trials are needed to evaluate the usefulness of DNA-TGN for individual dose adjustments in childhood ALL maintenance therapy.

ITPA Activity in Children Treated by Azathioprine: Relationship to the Occurrence of Adverse Drug Reactions and Inflammatory Response

Azathioprine (AZA), a thiopurine drug, is widely used in the treatment of children with immunological diseases such as inflammatory bowel disease (IBD) and autoimmune hepatitis (AIH); however, interindividual variability in the occurrence of adverse drug reactions (ADRs) and drug response is observed. This study investigated (i) the relationships between inosine triphosphate pyrophosphatase (ITPA) activity, an enzyme involved in thiopurine metabolism, and the occurrence of ADRs in children with immunological disease on AZA therapy, and (ii) the relationship between ITPA activity and the inflammatory activity observed in children with IBD. ITPA and TPMT activities were determined in 106 children with immunological disease on AZA therapy. Markers of hepatotoxicity, myelotoxicity, pancreatitis and inflammation as well as clinical information were retrospectively collected during regular medical visits. No significant association was found between ITPA activity and hepatotoxicity or clinical ADRs such as cutaneous reactions, arthralgia, flulike symptoms and gastrointestinal disorders. Concerning myelotoxicity, a significant relation was observed between ITPA activity and RBC mean corpuscular volume (MCV; p=0.003). This observation may be related to the significant relationship found between high ITPA activity and the increase in γ-globulin level reflecting inflammation (p=0.005). In our study, ITPA activity was not associated with occurrence of ADRs, but a relationship between high ITPA activity and γ-globulin, a marker of inflammation, was found in children with IBD. Therefore, measurement of ITPA activity may help to identify children with IBD predisposed to residual inflammation on AZA therapy. Further prospective studies are needed to confirm this result.

Design and fabrication of poly(HPMA)–6-mercaptopurine conjugates and their in vitro anticancer effect

A polymeric prodrug of poly(HPMA)–6MP was synthesized by grafting 6MP on poly(HPMA) and it exhibited an enhanced therapeutic effect.

LC-MS/MS Analysis of Erythrocyte Thiopurine Nucleotides and Their Association With Genetic Variants in Patients With Neuromyelitis Optica Spectrum Disorders Taking Azathioprine

BACKGROUND

Azathioprine is a first-line drug in treating neuromyelitis optica spectrum disorders (NMOSD). To exhibit its bioactivity, azathioprine needs to be converted to thiopurine nucleotides (TPNs) including 6-thioguanine nucleotides (6-TGNs) and 6-methylmercaptopurine nucleotides (6-MMPNs) that are affected by genetic polymorphisms. This study aims to develop an LC-MS/MS method for the analysis of erythrocyte concentrations of TPNs and to evaluate their associations with variants of various genes (MTHFR, TPMT, HLA, SLC29A1, SLC28A2, SLC28A3, ABCB1, and ABCC4) in patients with NMOSD.

METHODS

Erythrocyte 6-TGNs and 6-MMPNs were converted to their free bases 6-thioguanine and 6-methylmercaptopurine derivative by 1-hour acid hydrolysis at 95°C. An LC-MS/MS method was developed, validated, and used to study 32 patients with NMOSD to determine these free bases. Genetic variants were identified by MassARRAY (Sequenom) and multiple SNaPshot techniques. The associations between genetic variants and the concentrations of TPNs or the 6-MMPNs:6-TGNs ratio were evaluated by PLINK software using linear regression.

RESULTS

Methanol and water were used for separation with a total run time of 6.5 minutes. The lowest limit of quantification was 0.1 μmol/L with an injection volume of 10 μL. rs10868138 (SLC28A3) was associated with a higher erythrocyte concentration of 6-TGNs (P = 0.031), whereas rs12378361 (SLC28A3) was associated with a lower erythrocyte concentration of 6-TGNs (P = 0.0067). rs507964 (SLC29A1) was significantly associated with a lower erythrocyte concentration of 6-MMPNs (P = 0.024) and a lower 6-MMPNs:6-TGNs ratio (P = 0.029).

CONCLUSIONS

An LC-MS/MS method for the analysis of erythrocyte TPNs was developed, validated, and used to study 32 patients with NMOSD. SLC29A1 and SLC28A3 were associated with the erythrocyte concentrations of TPNs and 6-MMPNs:6-TGNs ratio. Further studies are needed to confirm these results.

Analysis of Thiopurine S-Methyltransferase Deficient Alleles in Acute Lymphoblastic Leukemia Patients in Mexican Patients

BACKGROUND AND AIMS

It has been demonstrated that heterozygote and homozygote thiopurine S-methyltransferase (TPMT) mutant allele carriers are at high risk to develop severe and potentially fatal hematopoietic toxicity after treatment with standard doses of 6-mercaptopurine (6-MP) and methotrexate (MX). Those drugs are the backbone of acute lymphoblastic leukemia (ALL) and several autoimmune disease treatments. We undertook this study to determine the frequency of the TPMT deficient alleles in children with ALL and non-ALL subjects from Mexico City and Yucatan, Mexico.

METHODS

We included 849 unrelated subjects, of which 368 ALL children and 342 non-ALL subjects were from Mexico City, and 60 ALL cases and 79 non-ALL individuals were from Yucatan. Genotyping of the rs1800462, rs1800460 and rs1142345 SNPs was performed by 5'exonuclease technique using TaqMan probes (Life Technologies Foster City, CA).

RESULTS

The mutant TPMT alleles were present in 4.8% (81/1698 chromosomes) and only 0.2% were homozygote TPMT*3A/TPMT*3A. We did not find statistically significant differences in the distribution of the mutant alleles between patients from Mexico City and Yucatan in either ALL cases or non-ALL. Nonetheless, the TPMT*3C frequency in ALL patients was higher than non-ALL subjects (p = 0.03). To note, the null homozygous TPMT*3A/TPMT*3A genotype was found in 2.5% of the non-ALL subjects.

CONCLUSIONS

TPMT mutant alleles did not exhibit differential distribution between both evaluated populations; however, TPMT*3C is overrepresented in ALL cases in comparison with non-ALL group. Assessing the TPMT mutant alleles could benefit the ALL children and those undergoing 6-MP and MX treatment.

Effects of cytochrome P450 family 3 subfamily A member 5 gene polymorphisms on daunorubicin metabolism and adverse reactions in patients with acute leukemia

The present study aimed to investigate the association between the genetic polymorphism of cytochrome P450 family 3 subfamily A member 5 (CYP3A5) and the activity of CYP3A and plasma concentrations of daunorubicin (DNR) in patients with acute leukemia. A total of 36 children with newly diagnosed acute lymphoblastic leukemia were enrolled in the study. Polymerase chain reaction (PCR)‑restriction fragment length polymorphism and PCR product sequencing were used to detect the genotype of CYP3A5*3. PCR was then used to express the mRNA expression of CYP3A5. A midazolam probe method was used to detect CYP3A enzyme activity, and DNR concentrations were measured using high performance liquid chromatography. Children with different genotypes had different mRNA expression levels of CYP3A5, and CYP3A enzyme activity in children with the CYP3A5*1 allele was higher, compared with that in children with the CYP3A5*3 allele. In addition, the area under the curve (AUC)0‑24 h and AUC0‑∞ of DNR were significantly different in children with different genotypes, however, no statistically significant differences were found in half‑life or maximum concentration. The AUC of DNR was increased in children with acute lymphatic leukemia who suffered from cardiotoxicity, compared with those in the normal group. The CYP3A5*3 gene polymorphism was closely associated with the mRNA expression of CYP3A5, CYP3A enzyme activity and DNR plasma drug concentration, and exhibited different drug adverse reactions.

Genetic Polymorphisms Associated to Folate Transport as Predictors of Increased Risk for Acute Lymphoblastic Leukemia in Mexican Children

Acute lymphoblastic leukemia (ALL) is a frequent neoplasia occurring in children. The most commonly used drug for the treatment of ALL is methotrexate (MTX), an anti-folate agent. Previous studies suggest that folate transporters play a role in ALL prognosis and that genetic polymorphism of genes encoding folate transporters may increase the risk of ALL. Therefore, the main goal of this study was to determine the associations among six genetic polymorphisms in four genes related with the folate transporter pathway to determine a relationship with the occurrence of ALL in Mexican children. A case-control study was performed in 73 ALL children and 133 healthy children from Northern and Northwestern Mexico. COL18A1 (rs2274808), SLC19A1 (rs2838956), ABCB1 (rs1045642 and rs1128503), and ABCC5 (rs9838667 and rs3792585). Polymorphisms were assayed through qPCR. Our results showed an increased ALL risk in children carrying CT genotype (OR = 2.55, CI 95% 1.11–5.83, p = 0.0001) and TT genotype (OR = 21.05, CI 95% 5.62–78.87, p < 0.0001) of COL18A1 rs2274808; in SLC19A1 rs2838956 AG carriers (OR = 44.69, CI 95% 10.42–191.63, p = 0.0001); in ABCB1 rs1045642 TT carriers (OR = 13.76, CI 95% 5.94–31.88, p = 0.0001); in ABCC5 rs9838667 AC carriers (OR = 2.61, CI 95% 1.05–6.48, p < 0.05); and in ABCC5 rs3792585 CC carriers (OR = 9.99, CI 95% 3.19–31.28, p = 0.004). Moreover, several combinations of genetic polymorphisms were found to be significantly associated with a risk for ALL. Finally, two combinations of ABCC5 polymorphisms resulted in protection from this neoplasia. In conclusion, certain genetic polymorphisms related to the folate transport pathway, particularly COL18A1 rs2274808, SLC19A1 rs2838956, ABCB1 rs1045642, and ABCC5 rs3792585, were associated with an increased risk for ALL in Mexican children.