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Long-term treatment with 6-thioguanine (6-TG) for pediatric acute lymphoblastic leukemia (ALL) is associated with high rates of hepatic sinusoidal obstruction syndrome (SOS). Nevertheless, current treatment continues to use short-term applications of 6-TG with only sparse information on toxicity. 6-TG is metabolized by thiopurine methyltransferase (TPMT) which underlies clinically relevant genetic polymorphism. We analyzed the association between hepatic SOS reported as a serious adverse event (SAE) and short-term 6-TG application in 3983 pediatric ALL patients treated on trial AIEOP-BFM ALL 2000 (derivation cohort) and defined the role of TPMT genotype in this relationship. We identified 17 patients (0.43%) with hepatic SOS, 13 of which with short-term exposure to 6-TG (P < 0.0001). Eight of the 13 patients were heterozygous for low-activity TPMT variants, resulting in a 22.4-fold (95% confidence interval 7.1-70.7; P ≤ 0.0001) increased risk of hepatic SOS for heterozygotes in comparison to TPMT wild-type patients. Results were supported by independent replication analysis. All patients with hepatic SOS after short-term 6-TG recovered and did not demonstrate residual symptoms. Thus, hepatic SOS is associated with short-term exposure to 6-TG during treatment of pediatric ALL and SOS risk is increased for patients with low-activity TPMT genotypes., (© 2021. The Author(s).)

6-mercaptopurine (6-MP) is widely used in the treatment of acute lymphoblastic leukemia (ALL), and its cytotoxicity is primarily mediated by thioguanine nucleotide (TGN) metabolites. A recent genomewide association study has identified germline polymorphisms (e.g., rs72846714) in the NT5C2 gene associated with 6-MP metabolism in patients with ALL. However, the full spectrum of genetic variation in NT5C2 is unclear and its impact on 6-MP drug activation has not been comprehensively examined. To this end, we performed targeted sequencing of NT5C2 in 588 children with ALL and identified 121 single nucleotide polymorphisms nominally associated with erythrocyte TGN during 6-MP treatment (P < 0.05). Of these, 61 variants were validated in a replication cohort of 372 children with ALL. After considering linkage disequilibrium and multivariate analysis, we confirmed two clusters of variants, represented by rs72846714 and rs58700372, that independently affected 6-MP metabolism. Functional studies showed that rs58700372 directly altered the activity of an intronic enhancer, with the variant allele linked to higher transcription activity and reduced 6-MP metabolism (lower TGN). By contrast, rs72846714 was not located in a regulatory element and instead its association signal was explained by linkage disequilibrium with a proximal functional variant rs12256506 that activated NT5C2 transcription in-cis. Our results indicated that NT5C2 germline variation significantly contributes to interpatient variability in thiopurine drug disposition., (© 2020 The Authors. Clinical Pharmacology & Therapeutics © 2020 American Society for Clinical Pharmacology and Therapeutics.)

Purpose: Mercaptopurine (6MP) is essential to cure childhood acute lymphoblastic leukemia (ALL). A liquid 6MP formulation was recently introduced to facilitate oral 6MP administration, especially to children. Its approval and bioequivalence with 6MP tablet were based on comparative pharmacokinetics in 60 healthy adults. Due to potential pharmacokinetic differences between healthy adults and children with ALL, we compared pharmacokinetics of tablet and liquid 6MP formulations in children with ALL., Methods: Pharmacokinetics of 50 mg 6MP tablet (Puri-Nethol ® ) and 20 mg/ml 6MP liquid suspension (Xaluprine ® ) were compared in a non-blinded, random order, single-dose, cross-over study in 16 children with ALL (eight males). 6MP was administered after a 12 h fast, and 6MP plasma concentrations measured consecutively over seven hours post-dose. Pharmacokinetic outcomes were as follows: Area under the curve (AUC), maximum plasma concentration (C max ), time to maximum plasma concentration (T max ), and terminal half-life (T ½ )., Results: Liquid 6MP formulation resulted in a 26% lower AUC (p = 0.02) compared with tablet (median 1215 vs. 1805 h × nmol/l). No significant differences were observed for C max, T max and T ½ (p = 0.28, p = 0.09, p = 0.41, respectively). Based on criteria declared by the World Health Organization the results did not establish non-inferiority of liquid 6MP formulation compared with 6MP tablet., Conclusion: Non-inferiority of liquid 6MP formulation compared with 6MP tablet was not demonstrated. Yet, maintenance therapy doses are adjusted by degree of myelosuppression and not by 6MP dose. Thus, in spite of a lower bioavailability, a liquid 6MP formulation is still desirable in a clinical setting, especially for children. However, if shifting between 6MP formulation is indicated, dose adjustments should be anticipated to maintain equivalent treatment intensity in children with ALL. The study is registered on clinicaltrials.gov (NCT01906671). Date of registration: 24.07.13.

Background: The recently established association between higher levels of DNA-incorporated thioguanine nucleotides and lower relapse risk in childhood acute lymphoblastic leukaemia (ALL) calls for reassessment of prolonged 6-thioguanine (6TG) treatment, while avoiding the risk of hepatotoxicity., Objectives: To assess the incidence of hepatotoxicity in patients treated with 6TG, and to explore if a safe dose of continuous 6TG can be established., Data Sources: Databases, conference proceedings, and reference lists of included studies were systematically searched for 6TG and synonyms from 1998-2018., Methods: We included studies of patients with ALL or inflammatory bowel disorder (IBD) treated with 6TG, excluding studies with 6TG as part of an intensive chemotherapy regimen. We uploaded a protocol to PROSPERO (registration number CRD42018089424). Database and manual searches yielded 1823 unique records. Of these, 395 full-texts were screened for eligibility. Finally, 134 reports representing 42 studies were included., Results and Conclusions: We included data from 42 studies of ALL and IBD patients; four randomised controlled trials (RCTs) including 3,993 patients, 20 observational studies including 796 patients, and 18 case reports including 60 patients. Hepatotoxicity in the form of sinusoidal obstruction syndrome (SOS) occurred in 9-25% of the ALL patients in two of the four included RCTs using 6TG doses of 40-60 mg/m2/day, and long-term hepatotoxicity in the form of nodular regenerative hyperplasia (NRH) was reported in 2.5%. In IBD patients treated with 6TG doses of approximately 23 mg/m2/day, NRH occurred in 14% of patients. At a 6TG dose of approximately 12 mg/m2/day, NRH was reported in 6% of IBD patients, which is similar to the background incidence. According to this review, doses at or below 12 mg/m2/day are rarely associated with notable hepatotoxicity and can probably be considered safe., Competing Interests: The authors have declared that no competing interests exist.

Thiopurine methyltransferase (TPMT) activity exhibits a monogenic codominant inheritance and catabolizes thiopurines. TPMT variant alleles are associated with low enzyme activity and pronounced pharmacologic effects of thiopurines. Loss-of-function alleles in the NUDT15 gene are common in Asians and Hispanics and reduce the degradation of active thiopurine nucleotide metabolites, also predisposing to myelosuppression. We provide recommendations for adjusting starting doses of azathioprine, mercaptopurine, and thioguanine based on TPMT and NUDT15 genotypes (updates on www.cpicpgx.org)., (© 2018 The Authors Clinical Pharmacology & Therapeutics © 2018 American Society for Clinical Pharmacology and Therapeutics.)

Purpose: Methotrexate polyglutamates (MTXpg) facilitate incorporation of thioguanine nucleotides into DNA (DNA-TG, the primary cytotoxic thiopurine metabolite and outcome determinant in MTX/6-mercaptopurine treatment of childhood ALL). We hypothesized that mapping erythrocyte levels of MTXpg with 1-6 glutamates and their associations with DNA-TG formation would facilitate future guidelines for maintenance therapy dosing., Methods and Results: Summed MTX with 1-6 glutamates resolved by LCMS [median (interquartile): 5.47 (3.58-7.69) nmol/mmol hemoglobin] was in agreement with total MTX by radio ligand assay. In 16,389 blood samples from 1426 ALL maintenance therapy patients, MTXpg3 21.0 (15.2-27.4)% was the predominant metabolite, and MTXpg1 (the maternal drug) constituted 38.6 (27.2-50.2)% of MTXpg1-6. All subsets correlated; the strongest associations were between metabolites with similar polyglutamate lengths. Correlations of MTXpg1 with MTXpg2 and MTXpg3,4,5,6 were r s  = 0.68 and r s  = 0.25-0.42, respectively. Intercorrelations of MTXpg3,4,5,6 were all r s  ≥ 0.51. MTXpg4 accounted for 29.8 (24.7-33.3)% of MTXpg3-6, yet explained 96% of the summed MTXpg3-6 variation. MTXpg1-4, MTXpg1-6, MTXpg2-6 and MTXpg3 were all associated with DNA-TG levels (p < 0.00001), but collinearity precluded identification of the most informative subset., Conclusions: Measuring erythrocyte MTXpg4 simplifies and can replace longer chain MTXpg monitoring. Resolving individual MTXpg identifies samples that are unsuitable for dose guidance due to high levels of MTXpg1 remaining in the plasma fraction because of recent MTX intake. All tested MTXpg subsets correlated with DNA-TG and may be used for ALL maintenance therapy dose adjustments, but the most informative subset remains to be identified.

Liposomal cytarabine is currently being tested clinically as an alternative to intrathecal (IT) methotrexate (MTX) for preventing relapse within the central nervous system among patients with acute lymphoblastic leukemia. To compare the toxicity and cognitive deficits caused by IT MTX versus liposomal cytarabine, juvenile Long Evans rats were treated with IT injections of MTX 1 mg/kg×4 doses over 8 days, or liposomal cytarabine 0.8 mg once. Mean concentrations of free cytarabine in cerebrospinal fluid remained above the cytotoxic threshold of 0.4 μM for 2 weeks after dosing. Animals treated with liposomal cytarabine exhibited normal recognition and spatial memory 4 weeks after injection. In contrast, exposure to IT MTX led to impaired cognitive function. In addition, mean hematocrit on day 11 was significantly lower in the MTX-treated animals (30.8%; 95% confidence interval, 27.0%-34.7%; n=6) compared with that in the liposomal cytarabine-treated animals (39.5%; 95% confidence interval, 38.4%-40.6%; n=6; P<0.0001). Our data suggest that liposomal cytarabine induces fewer neurocognitive deficits and less acute hematologic toxicity compared with IT MTX. Liposomal cytarabine may therefore have therapeutic advantages over IT MTX, if it is equally effective in preventing relapse.

Objectives: This randomized controlled trial tested the hypothesis that children with non-high-risk acute lymphoblastic leukemia could benefit from individualized 6-mercaptopurine increments during consolidation therapy (NCT00816049). Primary and secondary end points were end of consolidation minimal residual disease (MRD) positivity and event-free survival., Methods: 392 patients were randomized to experimental and 396 to standard therapy. Patients allocated to standard therapy received oral 6-mercaptopurine (25 mg/m 2 /day) from days 30 to 85, while the experimental arm received stepwise increments of additional 25 mg/m 2 /day beginning on days 50 and/or 71 unless dose-limiting myelosuppression had occurred., Results: In the experimental arm, 166 patients (42%) received one dose increment, and 62 (16%) received two. Fifty-seven of 387 (15%) patients in the experimental arm were MRD positive at end of consolidation vs 77 of 389 (20%) in the control arm (P = .08). Five-year probability of event-free survival was 0.89 (95% CI: 0.85-0.93) in the experimental arm vs 0.93 (0.90-0.96) in the control arm (P = .13). The median accumulated length of 6-mercaptopurine treatment interruptions was 7 (IQR 2-12) in the experimental arm vs 4 (IQR 0-10) in the control arm (P = .002)., Conclusion: This study found no benefit from individualized 6-mercaptopurine increments compared to standard therapy., (© 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Acute kidney injury due to high-dose methotrexate (HDMTX) is a serious, life-threatening toxicity that can occur in pediatric and adult patients. Glucarpidase is a treatment approved by the Food and Drug Administration for high methotrexate concentrations in the context of kidney dysfunction, but the guidelines for when to use it are unclear. An expert panel was convened to provide specific, expert consensus guidelines for the use of glucarpidase in patients who develop HDMTX-induced nephrotoxicity and delayed methotrexate excretion. The guideline provides recommendations to identify the population of patients who would benefit from glucarpidase rescue by more precisely defining the absolute methotrexate concentrations associated with risk for severe or life-threatening toxicity at several time points after the start of an HDMTX infusion. For an HDMTX infusion ≤24 hours, if the 36-hour concentration is above 30 µM, 42-hour concentration is above 10 µM, or 48-hour concentration is above 5 µM and the serum creatinine is significantly elevated relative to the baseline measurement (indicative of HDMTX-induced acute kidney injury), glucarpidase may be indicated. After a 36- to 42-hour HDMTX infusion, glucarpidase may be indicated when the 48-hour methotrexate concentration is above 5 µM. Administration of glucarpidase should optimally occur within 48-60 hours from the start of the HDMTX infusion, because life-threatening toxicities may not be preventable beyond this time point., Implications for Practice: Glucarpidase is a rarely used medication that is less effective when given after more than 60 hours of exposure to high-dose methotrexate, so predicting early which patients will need it is imperative. There are no currently available consensus guidelines for the use of this medication. The indication on the label does not give specific methotrexate concentrations above which it should be used. An international group of experts was convened to develop a consensus guideline that was specific and evidence-based to identify the population of patients who would benefit from glucarpidase., Competing Interests: Disclosures of potential conflicts of interest may be found at the end of this article., (© AlphaMed Press 2017.)

Sub-acute neurotoxicity is a well-known complication to high-dose and intrathecal methotrexate (MTX) treatment of children with leukemia. Symptoms can be treated safely by dextromethorphan, a non-competitive antagonist to N-methyl-D-aspartic acid receptor (NMDAR). In a female with subacute MTX neurotoxicity, we observed an electroencephalographic (EEG) with extreme delta brush. Extreme delta brush is an EEG pattern previously described in patients with NMDAR autoimmune encephalitis. The observations suggest that the mechanism of this neurotoxicity may be mediated by the NMDAR. Furthermore, extreme EEG delta brush should suggest a diagnosis of MTX associated subacute neurotoxicity., (Copyright © 2017 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved.)

Background: Carboxypeptidase G2 (CPDG 2 ) can be used as rescue treatment in cases of delayed methotrexate elimination (DME) and Mtx-induced nephrotoxicity., Procedure: Between July 2008 and December 2014, all children (1.0-17.9 years) in the Nordic countries diagnosed with Philadelphia chromosome negative acute lymphoblastic leukemia (ALL) were treated according to the Nordic Organization for Pediatric Hematology and Oncology (NOPHO) ALL 2008 protocol, including administration of six to eight high-dose (5 g/m 2 /24 hr) Mtx (HDMtx) courses. The protocol includes recommendations for CPDG 2 administration in cases of DME (clinicaltrials.gov NCT01305655)., Results: Forty-seven of the 1,286 children (3.6%) received CPDG 2 during 50 HDMtx courses at a median dose of 50 IU/kg. In 49% of the cases, CPDG 2 was used during the first HDMtx course. Within a median of 6 hr from CPDG 2 administration, the Mtx concentration decreased by 75% when measured with immune-based methods, and by 100% when measured with high-performance liquid chromatography. The median time from the start of Mtx infusion to plasma levels ≤ 0.2 μM was 228 hr (range: 48-438). The maximum increase in plasma creatinine was 375% (range: 100-1,310). Creatinine peaked after a median of 48 hr (range: 36-86). Mtx elimination time was shorter in patients with body surface area < 1 m 2 (median 198.5 vs. 257 hr; P = 0.004) and was inversely correlated to the maximum creatinine increase (209 vs. 258 hr; P = 0.034). All patients normalized their renal function as measured with s-creatinine., Conclusions: CPDG 2 administration is highly effective as rescue in case of delayed Mtx clearance. Subsequent HDMtx courses could be administered without events in most of the patients., (© 2016 Wiley Periodicals, Inc.)

Widely used as anticancer and immunosuppressive agents, thiopurines have narrow therapeutic indices owing to frequent toxicities, partly explained by TPMT genetic polymorphisms. Recent studies identified germline NUDT15 variation as another critical determinant of thiopurine intolerance, but the underlying molecular mechanisms and the clinical implications of this pharmacogenetic association remain unknown. In 270 children enrolled in clinical trials for acute lymphoblastic leukemia in Guatemala, Singapore and Japan, we identified four NUDT15 coding variants (p.Arg139Cys, p.Arg139His, p.Val18Ile and p.Val18&#95;Val19insGlyVal) that resulted in 74.4-100% loss of nucleotide diphosphatase activity. Loss-of-function NUDT15 diplotypes were consistently associated with thiopurine intolerance across the three cohorts (P = 0.021, 2.1 × 10(-5) and 0.0054, respectively; meta-analysis P = 4.45 × 10(-8), allelic effect size = -11.5). Mechanistically, NUDT15 inactivated thiopurine metabolites and decreased thiopurine cytotoxicity in vitro, and patients with defective NUDT15 alleles showed excessive levels of thiopurine active metabolites and toxicity. Taken together, these results indicate that a comprehensive pharmacogenetic model integrating NUDT15 variants may inform personalized thiopurine therapy., Competing Interests: Statement The authors have no competing financial interest to disclose.

Background: 6-mercaptopurine (6-MP), a key drug for treatment of acute lymphoblastic leukemia (ALL), has until recently had no adequate formulation for pediatric patients. Several approaches have been taken but the only oral paraben-free 6-MP liquid formulation named Loulla was developed and evaluated in the target population. Preclinical and clinical evaluations were performed according to a Pediatric Investigation Plan, in order to apply for a Pediatric Use Marketing Authorization., Methods: The pre-clinical study assessed the maximum tolerated dosage-volume and evaluated local mucosal toxicity of 28 daily administrations in treated compared to controls gold hamsters. The multi-centre clinical study was single-dose, open-label, crossover trial, conducted in 15 ALL children during maintenance therapy. The bioavailability and palatability of a single 50mg fixed dose of Loulla compared to 50mg registered tablets were evaluated in a random order on two consecutive days. Seven blood samples over 9h were obtained each day to determine 6-MP pharmacokinetic parameters, including Tmax, Cmax, AUC0-9 and AUC0-∞. A questionnaire adapted to children testing Loulla palatability and preference for either Loulla or the usual 6-MP tablet was completed. Occurrence of adverse events was determined at study visits by vital sign measurements, patient's spontaneous reporting, investigator's questioning and clinical examination., Results: The preclinical study in gold hamsters showed that dosage-volume of 75 mg/kg/day was well tolerated. The relative bioavailability of liquid Loulla formulation compared to the reference presentation is 76% for AUC0-9 and AUC0-∞ and 80% for Cmax. The taste of Loulla and the mouth feeling after ingestion compare favorably to the tablet. No adverse event occurred., Conclusion: Pharmacokinetic, palatability and safety data support the use of Loulla in children., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Introduction: We describe a patient diagnosed with acute myeloid leukemia (AML) and low activity of thiopurine methyltransferase (TPMT) who developed secondary myelodysplastic syndrome after treatment., Observation: A 10-year-old boy presented with AML-M2 with t(8;21)(q22;q22) and genotyping revealing 3*B TPMT heterozygosity. The patient was treated according to the NOPHO-AML 2004 protocol. Two years after the treatment, the patient presented with neutropenia and thrombocytopenia. Bone marrow, including fluorescent in situ hybridization and retrospective aCGH analysis, verified therapy-related myelodysplastic syndrome with ring chromosome 6., Discussion: The clinical course of this patient raises the possibility that low-activity TPMT genotypes may influence 6TG toxicity in patients with AML and lead to an increased risk of developing secondary malignant neoplasms.

Methotrexate/6-mercaptopurine maintenance therapy of childhood acute lymphoblastic leukemia is challenged by treatment-related hepatotoxicity, failure to achieve the myelosuppressive target, and lack of direct parameters for monitoring treatment efficacy or even intensity. Patients with low thiopurine methyltransferase (TPMT) activity have lower levels of hepatotoxic methylated thiopurine metabolites (MeMPs), higher levels of thioguanine nucleotides (TGNs), and reduced relapse rates. Addition of 6-thioguanine to maintenance therapy of a child with ALL and high TPMT activity increased the TGN/MeMP index in erythrocytes 5.5-fold, mimicking the more favorable thiopurine metabolism seen in patients with low TPMT activity.

Increased risks of lymphoma and skin cancer associated with thiopurine use among patients with inflammatory bowel disease have been shown, but data on the overall cancer risk are limited. We conducted a historical cohort study of 45,986 patients with inflammatory bowel disease (of whom, 5,197 (11%) used azathioprine) in Denmark from 1997 to 2008. We linked registry data on filled drug prescriptions, cancer diagnoses, and covariates and compared rates of overall incident cancer and cancer subgroups between users and nonusers of azathioprine, adjusting for propensity scores. During a median 7.9 (interquartile range: 3.5-12.0) person-years of follow-up, 2,596 incident cases of cancer were detected. Azathioprine use was associated with an increased risk of overall cancer (rate ratio = 1.41, 95% confidence interval: 1.15, 1.74), whereas former use of azathioprine (rate ratio = 1.02, 95% confidence interval: 0.83, 1.25) or increasing cumulative received doses (increase in rate ratio per 365 additional defined daily doses = 1.06, 95% confidence interval: 0.89, 1.27) were not. In subgroup analyses, azathioprine use was associated with increased risk of lymphoid tissue cancer (rate ratio = 2.40, 95% confidence interval: 1.13, 5.11) and urinary tract cancer (rate ratio = 2.84, 95% confidence interval: 1.24, 6.51). In conclusion, azathioprine use was associated with an increased risk of overall cancer in patients with inflammatory bowel disease, although these data cannot establish causality.

As the cure rates for haematological malignancies have improved, the exploration of the balance between efficacy and side effects has become a major research target. The antifolate methotrexate is widely used in the treatment of acute lymphoblastic leukaemia, non-Hodgkin lymphoma, and osteosarcoma. Even when given identical methotrexate doses, patients vary significantly in their response and pattern of toxicities. This diversity can, to some extent, be linked to sequence variations in genes involved in drug absorption, metabolism, excretion, cellular transport, and effector targets or target pathways. In the coming years pharmacogenomics is expected to change our approaches to individualised therapy with methotrexate. However, genetic polymorphisms affect the pharmacokinetics and dynamics of all the drugs a patient receive as well as the normal tissues tolerance to a given drug exposure. Thus, although high-throughput techniques will allow mapping of tens of thousands of genetic polymorphisms in one run, it will be a major challenge to dissect out which of these have the strongest impact on efficacy and toxicity and hence should be the targets for intervention. This paper discusses the pharmacology of methotrexate and reviews studies on haematological malignancies that have attempted to predict the risk of toxicity by specific clinical or genetic features.

The importance of maintenance therapy for higher risk childhood acute lymphoblastic leukemia (ALL) is uncertain. Between 1992 and 2001 the Nordic Society for Pediatric Haematology/Oncology compared in a nonrandomized study conventional oral methotrexate (MTX)/6-mercaptopurine (6MP) maintenance therapy with a multidrug cyclic LSA2L2 regimen. 135 children with B-lineage ALL and a white blood count > or =50 x 10/L and 98 children with T-lineage ALL were included. Of the 234 patients, the 135 patients who received MTX/6MP maintenance therapy had a lower relapse risk than the 98 patients who received LSA2L2 maintenance therapy, which was the case for both B-lineage (27%+/-5% vs. 45%+/-9%; P=0.02) and T-lineage ALL (8%+/-5% vs. 21%+/-5%; P=0.12). In multivariate Cox regression analysis stratified for immune phenotype, a higher white blood count (P=0.01) and administration of LSA2L2 maintenance therapy (P=0.04) were both related to an increased risk of an event (overall P value of the Cox model: 0.003), whereas neither sex, age at diagnosis, administration of central nervous system irradiation, nor presence of a day 15 bone marrow with > or =25% versus <25% lymphoblasts were of statistical significance. These results indicate that oral MTX/6MP maintenance therapy administered after the first year of remission can improve the cure rates of children with T-lineage or with higher risk B-lineage ALL.

Myelotoxicity during thiopurine therapy is enhanced in patients, who because of single nucleotide polymorphisms have decreased activity of the enzyme thiopurine methyltransferase (TPMT) and thus more thiopurine converted into 6-thioguanine nucleotides. Of 601 children with acute lymphoblastic leukemia (ALL) who were treated by the NOPHO ALL-92 protocol, 117 had TPMT genotype determined, whereas for 484 patients only erythrocyte TPMT activity was available. The latter were classified as heterozygous, if TPMT activity was <14 IU/ml, or deficient (<1.0 IU/ml). 526 patients had TPMT wild type, 73 were presumed heterozygous, and two were TPMT deficient. Risk of relapse was higher for the 526 TPMT wild type patients than for the remaining 75 patients (18 vs 7%, P=0.03). In Cox multivariate regression analysis, sex (male worse; P=0.06), age (higher age worse, P=0.02), and TPMT activity (wild type worse; P=0.02) were related to risk of relapse. Despite a lower probability of relapse, patients in the low TPMT activity group did not have superior survival (P=0.82), possibly because of an excess of secondary cancers among these 75 patients (P=0.07). These data suggest that children with ALL and TPMT wild type might have their cure rate improved, if the pharmacokinetics/-dynamics of TPMT low-activity patients could be mimicked without a concurrent excessive risk of second cancers.

We studied the pharmacokinetics of 6-thioguanine (6TG) in 50 children treated for newly diagnosed acute myeloid leukemia, four of them with Down syndrome (DS). They received oral 6TG 100 mg/m2 body surface area twice daily for 4 days. Etoposide, 100 mg/m2/24 h, and cytarabine, 200 mg/m2/24 h, were administered concomitantly by intravenous infusion. On day 5, doxorubicin 75 mg/m2 was given as an 8-h infusion. The concentration of thioguanine nucleotides (TGN) in erythrocytes, the active metabolites of 6TG, was determined by high-performance liquid chromatography. The mean TGN concentration from 72, 95, and 106-h samples was used as a measure of drug exposure for each individual. The median TGN concentration in non-DS children above 2 years of age was 2.30 micromol/mmol Hb (range 0.57-25.3). The TGN concentrations varied widely (30-fold) also after dose normalization. We found no correlation with demographic, clinical, or biochemical parameters, and differences in bioavailability might be the most important explanation to interpatient variability. Children with high TGN concentration tended to have longer treatment interval to the next course, but we found no correlation with our predefined parameters for clinical response, that is, remission and relapse rate. Therefore, 6TG does not seem to be a candidate for therapeutic drug monitoring by TGN measurement, at least not in the setting of short multidrug treatment courses. Children with DS had significantly higher TGN concentrations, indicating that dose reduction might be considered to reach the same drug exposure as in non-DS children.

Background and Objective: Through interruption of maintenance treatment with 6-mercaptopurine (6MP), toxicity after high-dose methotrexate (HDMTX) may compromise the efficiency of the treatment of children with acute lymphocytic leukaemia (ALL). We investigated the influence of polymorphisms in the methylene tetrahydrofolate reductase (MTHFR) gene and coadministration of antimetabolites on post-HDMTX toxicity., Methods: Toxicity was retrospectively analysed after 656 HDMTX courses administered to 88 paediatric ALL patients at a single treatment centre., Results: High-dose methotrexate with high-intensity co-treatment (6MP 75 mg/m(2)/d + MTX 20 mg/m(2)/wk) was found associated with increased odds of haematological toxicity (OR's: 3.47-7.88; P's: <0.001), hepatic toxicity (OR = 6.91; P < 0.001), hospitalization with fever (OR = 2.2; P = 0.004) and interruption maintenance treatment (OR = 15.9; P < 0.001) compared to HDMTX with low-intensity co-treatment (6MP 25 mg/m(2)/d). Addition of cytarabine to the low-intensity co-treatment increased the odds of neutropenia (OR = 3.51; P = 0.002), thrombocytopenia (OR = 6.56; P < 0.001), hepatic toxicity (OR = 3.84; P = 0.012) and interruption of maintenance treatment (OR = 4.25; P = 0.002). Alterations in 6MP dose were associated with significant changes in toxicity. Dose reduction reduced the odds of haematological toxicity (OR's: 0.22-0.34; P's: <0.001-0.020), while dose increase increased the odds of haematological toxicity (OR's: 2.72-7.42; P's: 0.006-0.027), fever (OR = 2.65; P = 0.037) and interruption of maintenance treatment (OR = 3.04; P = 0.032). No convincing associations were found between the MTHFR C677T or A1298C polymorphisms and toxicity., Conclusion: Our findings demonstrate that toxicity after HDMTX is influenced by coadministrated antimetabolites, and modifiable by alterations in 6MP dose. Prevention of toxicity related withdrawals through 6MP dose reduction could be a way of increasing total dose intensity.

We explored the relationship between time to relapse and different exposure variables (serum methotrexate (S-MTX) 23, 36 and 42 h after start of administration, MTX elimination time and leucovorin (LV) dose) during high-dose MTX (HDM) treatment of 445 children with acute lymphoblastic leukemia. MTX was infused at 5 g/m2 (non-high risk) or 8 g/m2 (high risk) over 24 h, 2-9 times per patient. LV rescue dose was adjusted according to the S-MTX concentration. Time from end of the last HDM to relapse was analyzed by Cox regression analysis with the logarithms of S-MTX and LV dose as exposures. The combined results from all risk groups suggest that high LV dose is related to higher risk for relapse. Doubling of the LV dose increased the relapse risk by 22% (95% confidence interval 1-49%, P = 0.037). High LV doses correlated with high MTX levels at 23, 36 and 42 h and longer elimination time. The results suggest that high doses of LV increase the risk for relapse despite the fact that they were correlated with high MTX levels and longer MTX elimination time. The choice of MTX and LV doses may be regarded as an intricate balance between effect and counter-effect.

Background: During therapy consisting of 6MP and MTX, metabolites accumulate in the erythrocytes. The erythrocyte levels of metabolites reflect the intensity of therapy. Whether they are associated with hepatotoxicity manifested as histological liver changes is not known. We studied the association of the metabolites and cumulative doses of 6MP and MTX with histological liver disease., Methods: Serial measurements of E-TGN, E-MTX, and ALT during maintenance therapy were performed and cumulative doses of 6MP and MTX were calculated as g/m2 in 16 children with ALL. Each subject underwent a percutaneous liver biopsy at the end of therapy to screen for histological liver disease., Results: No differences in E-TGN, E-MTX, or cumulative doses of 6MP or MTX were detected in the children with ALL with liver fibrosis compared to those without fibrosis, or in the children with less liver fatty change compared to those with more fatty change. Serum median ALT levels correlated significantly positively with cumulative doses of 6MP during therapy (rS = 0.527, P = 0.036), but not with cumulative doses of MTX, or E-TGN, or E-MTX., Conclusions: Erythrocyte levels of the metabolites or the cumulative doses of 6MP and MTX do not predict histological liver disease in children treated for ALL., ((c) 2006 Wiley-Liss, Inc.)

In this population-based material from the five Nordic countries (Denmark, Finland, Iceland, Norway and Sweden), 2860 children below 15 years of age were diagnosed with acute lymphoblastic leukemia (ALL) from July 1981 to June 1998. The annual incidence was 3.9/100,000 children and was stable throughout the study period. The development from regional or national protocols to common Nordic treatment protocols for all risk groups was completed in 1992 through a successive intensification with multidrug chemotherapy, including pulses of methotrexate in high doses and avoidance of cranial irradiation in most children. The overall event-free survival (EFS) at 5 years has increased from 56.5 +/- 1.7% in the early 1980s to 77.6 +/- 1.4% during the 1990s. The main improvements were seen in children with non-high risk leukemia. In high-risk patients, progress has been moderate, especially in children with high WBC (> or =100 x 10(9)/l) at diagnosis. During the last time period (January 1992-June 1998), only 10% of the patients have received cranial irradiation in first remission, while 90% of the patients have received pulses of high dose methotrexate (5-8 g/m2) isolated or combined with high-dose cytosine arabinoside (total dose 12 g/m2) plus multiple intrathecal injections of methotrexate as CNS-targeted treatment, not translating into increased cumulative incidence of CNS relapse.

Purpose: To study the risk of non-B-cell acute lymphoblastic leukemia (ALL) relapse in relation to the routines of administration of oral methotrexate (MTX) and 6-mercaptopurine (6MP) and to the erythrocyte (E) levels of the intracellular cytotoxic metabolites, that is, MTX polyglutamates and 6-thioguanine nucleotides (E-MTX and E-6TGN)., Patients and Methods: E-MTX and E-6TGN levels were measured at least three times (medians, eight and nine) in 294 children with non-B-cell ALL during oral MTX and 6MP therapy. For each patient, we registered (a) the individual circadian schedule of drug administration and (b) the coadministration of food, and (c) calculated a mean (m) of all E-MTX and E-6TGN measurements and (d) the product of mE-MTX and mE-6TGN (mE-MTX*6TGN), due to their synergistic action., Results: A total of 42 patients were on a morning schedule, 219 were on an evening schedule, and 33 had miscellaneous routines. A total of 149 patients took the drugs with meals, 106 took the drugs between meals, and 39 had varying routines. With a median follow-up of 78 months, ALL has recurred in 66 patients. The patients on an evening schedule had a superior outcome [probability of event-free survival (pEFS) = 0.82 +/- 0.03 vs. 0.57 +/- 0.08; p = 0.0002], whereas the coadministration of food did not significantly influence outcome. Patients with a mE-MTX*6TGN < 813 [product of median mE-MTX (4.7 nmol/mmol Hb) and mE-6TGN (173 nmol/mmol Hb)] had an inferior outcome (pEFS = 0.70 +/- 0.04 vs. 0.85 +/- 0.03; p = 0.003), even if only patients on an evening schedule were analyzed. Thus, 109 patients on the MTX/6MP evening schedule with an mE-MTX*6TGN < or = 813 (nmol/mmol Hb)2 had a pEFS of 0.89 +/- 0.03 and a probability of continuous hematopoietic remission of 0.91 +/- 0.03., Conclusions: An evening schedule should be recommended for oral MTX/6MP maintenance therapy. The value of individual dose adjustments by E-MTX and E-6TGN remains to be determined in prospective randomized trials.