6-thioguanylic-acid and Precursor-Cell-Lymphoblastic-Leukemia-Lymphoma

Pediatric patients with acute lymphoblastic leukemia (ALL) are treated with oral 6-mercaptopurine (6MP) for nearly 2 years, but no pediatric formulation has been available. In this study, an oral 6MP liquid suitable for pediatric use was developed and tested in the target population.. A randomized cross-over study was performed in 20 pediatric ALL patients (age 1.9 - 14.6 years), comparing pharmacokinetics and pharmacodynamics of a newly developed 6MP liquid formulation to 6MP capsules, both taken orally for 4 weeks.. Based upon trough levels of the principal active metabolite,6-thioguanine nucleotides (6-TGN),a relative bioavailability of the liquid vs. capsules of 1.01 was found (90% CI 0.86 - 1.20), demonstrating bioequivalence. This was supported by the similarly observed 6MP dosages needed for leucocyte depletion, for both formulations (35 mg/day (range 10 - 115 mg)). 75% of the parents/patients (p = 0.005) preferred the oral liquid over the capsules because of the ease of administration.. We conclude that the novel 6MP liquid is a promising treatment for ALL.

Topics: Administration, Oral; Adolescent; Antimetabolites, Antineoplastic; Biological Availability; Child; Child, Preschool; Cross-Over Studies; Female; Guanine Nucleotides; Humans; Infant; Leukocytes; Male; Mercaptopurine; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Therapeutic Equivalency; Thionucleotides; Young Adult

Topics: Antineoplastic Combined Chemotherapy Protocols; Child; DNA; Female; Genotype; Guanine Nucleotides; Humans; Male; Mercaptopurine; Methotrexate; Methyltransferases; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Thionucleotides

In children with acute lymphoblastic leukaemia (ALL) bone marrow activity can influence red blood cell (RBC) kinetics, the surrogate tissue for thiopurine methyltransferase (TPMT) measurements. The aim of this study was to investigate TPMT phenotype-genotype concordance in ALL, and the influence of TPMT on thiopurine metabolite formation.. We measured TPMT (activity, as units ml(-1) packed RBCs and genotype) at diagnosis (n = 1150) and TPMT and thioguanine nucleotide (TGN) and methylmercaptopurine nucleotide (MeMPN) metabolites (pmol/8 × 10(8) RBCs) during chemotherapy (n = 1131) in children randomized to thioguanine or mercaptopurine on the United Kingdom trial ALL97.. Median TPMT activity at diagnosis (8.5 units) was significantly lower than during chemotherapy (13.8 units, median difference 5.1 units, 95% confidence interval (CI) 4.8, 5.4, P < 0.0001). At diagnosis genotype-phenotype was discordant. During chemotherapy the overall concordance was 92%, but this fell to 55% in the intermediate activity cohort (45% had wild-type genotypes). For both thiopurines TGN concentrations differed by TPMT status. For mercaptopurine, median TGNs were higher in TPMT heterozygous genotype (754 pmol) than wild-type (360 pmol) patients (median difference 406 pmol, 95% CI 332, 478, P < 0.0001), whilst median MeMPNs, products of the TPMT reaction, were higher in wild-type (10 650 pmol) than heterozygous patients (3868 pmol) (P < 0.0001). In TPMT intermediate activity patients with a wild-type genotype, TGN (median 366 pmol) and MeMPN (median 8590 pmol) concentrations were similar to those in wild-type, high activity patients.. In childhood ALL, TPMT activity should not be used to predict heterozygosity particularly in blood samples obtained at disease diagnosis. Genotype is a better predictor of TGN accumulation during chemotherapy.

Topics: Adolescent; Antimetabolites, Antineoplastic; Child; Child, Preschool; Female; Genotype; Guanine Nucleotides; Heterozygote; Humans; Infant; Male; Mercaptopurine; Methyltransferases; Phenotype; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Thioguanine; Thionucleotides; United Kingdom

To elucidate interpatient variability in thioguanine nucleotide (TGN) concentrations in acute lymphoblastic leukemia (ALL) cells, we determined the TGN concentrations in leukemic blasts from 82 children with newly diagnosed ALL after intravenous administration of mercaptopurine (MP). Patients treated with MP alone achieved higher TGN concentrations than those treated with the combination of methotrexate plus mercaptopurine (MTX + MP). Analysis of the expression of approximately 9600 genes in ALL cells obtained at diagnosis identified 60 gene probes significantly associated with TGN accumulation in patients treated with MP alone and 75 gene probes in patients treated with MTX + MP, with no overlap between the 2 sets of genes. Genes significantly associated with intracellular TGN accumulation after MP alone included those encoding MP metabolic enzymes and transporters (eg, SLC29A1). Inhibition of SLC29A1 by nitrobenzylmercaptopurine ribonucleoside (NBMPR) caused a 33% to 45% reduction of TGN in ALL cells in vitro (P < .006), consistent with the gene expression findings. Genes associated with TGN concentration after combination therapy included those involved in protein and adenosine triphosphate (ATP)-biosynthesis. Together, these in vivo and in vitro data provide new insight into the genomic basis of interpatient differences in intracellular TGN accumulation and reveal significant differences between treatment with MP alone and treatment with MP and MTX.

Topics: Adolescent; Cell Line, Tumor; Cell Proliferation; Dose-Response Relationship, Drug; Gene Expression Profiling; Genotype; Guanine Nucleotides; Humans; Mercaptopurine; Phenotype; Phylogeny; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Thionucleotides; Tissue Distribution

6-Mercaptopurine (6MP) has been regarded as nonleukemogenic, even though the cytotoxicity of 6MP depends on the incorporation of 6-thioguanine nucleotides (6TGN) into DNA. In hematopoietic cells this pathway competes with S-methylation catalyzed by thiopurine methyltransferase (TPMT). However, methylated 6MP metabolites inhibit purine de novo synthesis and thus may enhance incorporation of 6TGN into DNA. Approximately 10% of white individuals have low TPMT activity as a result of polymorphisms in the TPMT gene. The authors attempted to test the hypothesis that the degree of DNA damage during 6MP therapy might reflect variations in 6MP metabolism and pharmacokinetics.. The authors measured TPMT activity as well as erythrocyte levels of 6TGN (E-6TGN) and methylated 6MP metabolites (E-MeMP) during 6MP therapy in 439 children with acute lymphoblastic leukemia, 5 of whom later developed secondary myelodysplasia or acute myeloid leukemia (sMDS/AML).. The patients who developed sMDS/AML had significantly lower TPMT activity compared with the remaining patients (P = 0.03). The 55 patients with TPMT activity <14 U/mL red blood cells (RBC) (antimode of the bimodal distribution) had a 5-year risk of sMDS/AML of 9 +/- 6% versus 1 +/- 1% for the remaining patients (P = 0.002). Cox regression analysis identified TPMT activity and E-MeMP level as the strongest predictors of risk for sMDS/AML (global P value = 0.02). Patients with low TPMT activity and high E-MeMP levels had the highest risk. All 5 patients with sMDS/AML had E-6TGN and/or E-MeMP levels > the 90% percentiles or had TPMT activity < 14 U/mL RBC.. These data demonstrate an increased leukemogenic risk when 6MP is administered with other cytotoxic agents in patients with low TPMT activity, and indicate that not only high 6TGN levels but also high levels of methylated metabolites may lead to DNA damage.

Topics: Adolescent; Antineoplastic Combined Chemotherapy Protocols; Bone Marrow Cells; Child; Child, Preschool; DNA Damage; Guanine Nucleotides; Humans; Immunophenotyping; Infant; Mercaptopurine; Methyltransferases; Myelodysplastic Syndromes; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Risk; Thionucleotides

Mercaptopurine (6MP) has been the standard drug for maintenance therapy of acute lymphoblastic leukemia. In a multicenter study we investigated whether thioguanine (6TG), which is converted more directly to the cytotoxic thioguanine nucleotides (TGN), offers a therapeutic advantage over 6MP. In this study (COALL-92), 6TG was randomized versus 6MP in maintenance therapy, whereby the doses of both drugs had to be adjusted to a white blood cell (WBC) count of between 2 and 3/nl. In 19 children the plasma levels of both drugs and/or the accumulation of their metabolites in red blood cells (RBC) were measured during intensive treatment in two consecutive chemotherapy blocks, and in 54 children the metabolites in RBC were measured every 3 months during daily treatment in maintenance therapy. There was a marked interindividual difference in the plasma kinetics of the two drugs; after identical doses of 100 mg/m2 an about 4-fold higher peak concentration of the parent drug was reached with 6MP. The main metabolites of 6TG were thioguanine nucleotides (TGN), whereas during 6MP treatment, methylated thioinosine nucleotides (TIN) predominated in erythrocytes. In patients receiving 6TG during maintenance therapy (22 patients) the concentration of methylated TGN reached about 40% of that of unmethylated TGN; after 6MP administration (32 patients) the methylated TIN were concentrated about 26-fold higher in RBC than were TGN. In contrast to 6TG, for 6MP the pattern of metabolites shifted toward the methylated ones with increasing dose. The median TGN concentration was about 7-fold higher in the TG branch, although the median dose was only about 70% of that of 6MP. The WBC values were equivalent in the two treatment groups. Our results suggest that the cytotoxic effect of 6MP is not based solely on the formation of TGN.

Topics: Adolescent; Antimetabolites, Antineoplastic; Child; Child, Preschool; Erythrocytes; Female; Guanine Nucleotides; Humans; Infant; Leukocyte Count; Male; Mercaptopurine; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Thioguanine; Thioinosine; Thionucleotides

We aimed to identify the impact of NUDT15 variants on thiopurine intolerance and 6-thioguanine nucleotide (6-TGN) levels in Korean children with acute lymphoblastic leukemia (ALL).. Genotyping of NUDT15 was tested in 258 patients with ALL registered at Samsung Medical Center. Patients were classified into normal-activity (wild-type), intermediate-activity (heterozygous variant), and low-activity groups (homozygous or compound heterozygous variant). Clinical and laboratory features during the first year of maintenance therapy were investigated.. A total of 182 patients were included in the final analysis. There were five (2.7%), 46 (25.3%), and 131 (72.0%) patients in low-, intermediate-, and normal-activity groups, respectively. The lowest 6-mercaptopurine (6-MP) dose (mg/m2/day) was administered to the low-activity group (low-activity group 7.5 vs. intermediate-activity group 24.4 vs. normalactivity group 31.1, p < 0.01) from three months to a year after beginning maintenance therapy. The low-activity group experienced the longest duration of therapy interruption during the first year (low-activity group 169 days vs. intermediate-activity group 30 days vs. normal-activity group 16 days, p < 0.01). They also showed the lowest blood cell counts and had a longer duration of leukopenia (low-activity group 131 days vs. intermediate-activity group 92 days vs. normal-activity group 59 days, p < 0.01). 6-TGN level and its ratio to 6-MP dose were lowest in the low-activity group.. NUDT15 variants cause hematopoietic toxicity with low 6-TGN levels. NUDT15 genotyping should be conducted before administering thiopurine, and dose adjustments require caution regardless of 6-TGN levels.

Topics: Adolescent; Child; Child, Preschool; Drug Administration Schedule; Female; Guanine Nucleotides; Humans; Infant; Male; Mercaptopurine; Pharmacogenomic Variants; Polymorphism, Single Nucleotide; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Pyrophosphatases; Republic of Korea; Retrospective Studies; Sequence Analysis, DNA; Thionucleotides; Young Adult

Mercaptopurine (6-MP), a critical component of acute lymphoblastic leukemia (ALL) therapy, is metabolized to 6-thioguanine (6-TGN) which is responsible for its anti-leukemic effect, and to 6-methylmercaptopurine nucleotides (6-MMPN/6-MMP) which can be hepatotoxic. Some patients preferentially metabolize 6-MP to 6-MMPN which may increase the risk of liver injury, reduce serum levels of 6-TGN and potentially increase the risk of relapse. The addition of allopurinol to oral 6-MP has been shown to optimize metabolism towards 6-TGN in patients with inflammatory bowel disease (IBD); however, this use has not been reported in patients undergoing treatment for ALL.

Topics: Adolescent; Allopurinol; Antimetabolites, Antineoplastic; Antineoplastic Combined Chemotherapy Protocols; Biotransformation; Chemical and Drug Induced Liver Injury; Child, Preschool; Drug Evaluation; Female; Guanine Nucleotides; Humans; Hyperbilirubinemia; Hypoxanthine Phosphoribosyltransferase; Maintenance Chemotherapy; Male; Mercaptopurine; Methotrexate; Methyltransferases; Neutropenia; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Thionucleotides; Xanthine Oxidase

To explore the DNA incorporation of 6-thioguanine nucleotide levels (DNA-6TGN) during 6-mercaptopurine (6MP) therapy of childhood acute lymphoblastic leukaemia (ALL) and non-Hodgkin lymphoma (NHL) and its relation to erythrocyte levels of their metabolites: 6-thioguanine-nucleotides (E-6TGN), methylated metabolites (E-MeMP), Methotrexate polyglutamates (E-MTX), and to thiopurine methyltransferase activity (TPMT).. We studied these metabolites in 229 blood samples from 18 children with ALL (N = 16) or NHL (N = 2) on 6MP/Methotrexate maintenance therapy.. DNA-6TGN levels were significantly correlated to E-6TGN (r (p) = 0.66, p = 0.003) with a trend to reach a plateau at high E-6TGN levels. To explore the relative DNA incorporation of 6TGN in relation to cytosol 6TGN levels, a DNA-6TGN index was calculated as DNA-6TGN/E-6TGN. The DNA-6TGN index was inversely correlated to E-6TGN (r (p) = -0.58, p = 0.012), which implies that with increasing levels of E-6TGN relatively less 6TGN are incorporated into DNA. E-MeMP levels were correlated to the DNA-TGN index (r (p) = 0.60, p = 0.008), indicating that high levels of MeMP result in enhanced DNA-6TGN incorporation, possibly due to inhibition of purine de novo synthesis, mediated by some of the methylated 6MP metabolites.. DNA-6TGN may prove to be a more relevant pharmacokinetic parameter for monitoring 6MP treatment intensity than the previously used erythrocyte 6MP metabolites levels. Prospective clinical trials are needed to evaluate the usefulness of DNA-6TGN for individual dose adjustments.

Topics: Antineoplastic Combined Chemotherapy Protocols; Child; Child, Preschool; Cytosol; DNA; Drug Monitoring; Erythrocytes; Female; Guanine Nucleotides; Humans; Infant; Lymphoma, Non-Hodgkin; Male; Mercaptopurine; Methotrexate; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Purines; Thionucleotides

To examine the allelic variation of three enzymes involved in 6-mercaptopurine/azathioprine (6-MP/AZA) metabolism and evaluate the influence of these polymorphisms on toxicity, haematological parameters and metabolite levels in patients with acute lymphoblastic leukaemia (ALL) or inflammatory bowel disease (IBD).. Clinical data and blood samples were collected from 19 ALL paediatric patients and 35 IBD patients who were receiving 6-MP/AZA therapy. All patients were screened for seven genetic polymorphisms in three enzymes involved in mercaptopurine metabolism [xanthine oxidase, inosine triphosphatase (C94-->A and IVS2+21A-->C) and thiopurine methyltransferase]. Erythrocyte and plasma metabolite concentrations were also determined. The associations between the various genotypes and myelotoxicity, haematological parameters and metabolite concentrations were determined.. Thiopurine methyltransferase variant alleles were associated with a preferential metabolism away from 6-methylmercaptopurine nucleotides (P = 0.008 in ALL patients, P = 0.038 in IBD patients) favouring 6-thioguanine nucleotides (6-TGNs) (P = 0.021 in ALL patients). Interestingly, carriers of inosine triphosphatase IVS2+21A-->C variants among ALL and IBD patients had significantly higher concentrations of the active cytotoxic metabolites, 6-TGNs (P = 0.008 in ALL patients, P = 0.047 in IBD patients). The study confirmed the association of thiopurine methyltransferase heterozygosity with leucopenia and neutropenia in ALL patients and reported a significant association between inosine triphosphatase IVS2+21A-->C variants with thrombocytopenia (P = 0.012). CONCLUSIONS; Pharmacogenetic polymorphisms in the 6-MP pathway may help identify patients at risk for associated toxicities and may serve as a guide for dose individualization.

Topics: Adolescent; Antimetabolites, Antineoplastic; Azathioprine; Child; Child, Preschool; Female; Gene Frequency; Genotype; Guanine Nucleotides; Humans; Inflammatory Bowel Diseases; Male; Mercaptopurine; Methyltransferases; Pharmacogenetics; Polymorphism, Genetic; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Thionucleotides; Treatment Outcome

A HPLC method for determination of 6-thioguanine nucleotide in DNA was developed. Leukocyte DNA was isolated from peripheral blood, derivatized with chloroacetaldehyde and the formed etheno derivatives N(2),3-etheno 6-thioguanine (epsilon6TG), 1,N(6)-etheno adenine (epsilonA) and N(2),3-etheno guanine (epsilonG) were released from the DNA backbone by hydrolysis at pH 6.0 and 80 degrees C for 60 min. After extraction of epsilon6TG by immobilized metal ion affinity chromatography (IMAC) the sample was analysed by ion-pair reversed-phase HPLC with fluorescence detection. The limit of quantification was 9.0 nM and the intra- and interday precision ranged from 2.8 to 15.5%. In a small cohort of eight children with acute lymphoblastic leukaemia (ALL), a median of one 6-thioguanine base was found for each 3000 normal bases (range 1:2000-1:11000).

Topics: Child; Chromatography, Affinity; Chromatography, High Pressure Liquid; DNA; Guanine Nucleotides; Humans; Hydrogen-Ion Concentration; Hydrolysis; Leukocytes; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Quality Control; Reproducibility of Results; Sensitivity and Specificity; Thioguanine; Thionucleotides

Nineteen pediatric patients affected by acute lymphoblastic leukemia (ALL) were examined weekly with respect to 6-mercaptopurine nucleotide (6-MPN) and 6-thioguanine nucleotide (6-TGN) levels in erythrocytes during the course of maintenance treatment with 6-MP 50 mg/m2 per d and results were related to various parameters of bone marrow function to assess, in the same individual, the level of reliability of 6-MP metabolites in predicting a later change in peripheral blood cell counts. Median values for 6-MPN and 6-TGN were 57 and 200 pmol/8 x 10(8) erythrocytes, respectively, as measured by reversed-phase high-performance liquid chromatography (HPLC). 6-TGN levels in erythrocytes were inversely related with white blood cell count (r = -0.463, p < 0.0001, n = 361), absolute neutrophil count (r = -0.386, p < 0.0001, n = 347), erythrocyte (r = -0.354, p < 0.0001, n = 287), and platelet counts (r = -0.24, p < 0.0001, n = 319) in the majority of patients (n = 10-12), while no correlation was found for 6-MPN. In the remaining children, no evidence of correlation was demonstrated between 6-TGN levels and myelotoxicity. The results confirm the role of 6-TGN as the reference cytotoxic metabolite for evaluating the exposure to 6-MP and identifying treatment compliance in ALL children but indicate the limits of a follow-up based solely on metabolite levels and suggest that a more correct approach remains the double monitoring of 6-TGN and blood cell count with differential.

Topics: Adolescent; Antimetabolites, Antineoplastic; Bone Marrow; Child; Child, Preschool; Drug Monitoring; Erythrocytes; Female; Guanine Nucleotides; Humans; Male; Mercaptopurine; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Thionucleotides

Daily 6-mercaptopurine (6MP) forms the backbone of continuing chemotherapy for childhood lymphoblastic leukaemia (ALL). A major metabolic route is catalysed by thiopurine methyltransferase (TPMT). TPMT deficiency occurs in 1 in 300 individuals and results in high concentrations of thioguanine nucleotides (TGNs), cytotoxic 6MP metabolites. A leukaemic child taking 6MP repeatedly developed profound pancytopenias. TPMT deficiency was confirmed. TGN formation was then studied on attenuated 6MP dosages. Four weekly oral doses of 75 mg/m2 6MP produced TGNs of 2348 pmol/8 x 10(8) red cells, nearly double the maximum TGNs recorded in ALL children with TPMT activity taking long term daily 75 mg/m2 6MP. Grossly elevated TGN concentrations were also produced at 10% standard 6MP dosage (7.5 mg/m2 daily), accompanied by unacceptable 6MP toxicity (neutropenia, diarrhoea, vomiting). The child was eventually stabilised on 10% alternate day therapy and after 15 weeks TGNs were 1670 pmol, just above the upper end of the TGN range for ALL children with TPMT activity.

Topics: Antimetabolites, Antineoplastic; Child; Drug Administration Schedule; Erythrocytes; Female; Guanine Nucleotides; Humans; Mercaptopurine; Methyltransferases; Neutropenia; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Thionucleotides; Thrombocytopenia

Measurement of red cell 6-mercaptopurine (MP) derived 6-thioguanine nucleotide (TGN) and methylmercaptopurine metabolites (MeMPs) can be used to monitor therapy in children who are administered MP for childhood lymphoblastic leukemia. Red cell TGNs are not influenced by the time of blood sampling in relation to the last MP dose. The purpose of this study was to find out whether the same is true for the MeMPs. Plasma MP and red cell MP metabolite pharmacokinetics were studied in seven children immediately before and for 4 hours after a protocol standardized dose of MP. Duplicate blood samples were taken, one was processed immediately whereas one was left at an ambient temperature for 24 hours. The variation in TGN and MeMP metabolites over the 0- to 4-hour period (10 time points per child) was within the error of the assays used. The coefficients of variation for the TGNs ranged from 2.7% to 7% and for the MeMPs, 4% to 10.7%. There was no difference in the TGN and MeMP concentrations measured when the blood samples were left for 24 hours. If a child takes a MP tablet immediately before a clinic appointment, it has no major influence on MeMP measurements.

Topics: Administration, Oral; Antimetabolites, Antineoplastic; Child; Child, Preschool; Erythrocytes; Female; Guanine Nucleotides; Humans; Male; Mercaptopurine; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Thionucleotides; Time Factors

During maintenance chemotherapy for childhood acute lymphoblastic leukemia (ALL), the cytotoxic metabolites of methotrexate (MTX polyglutamates) and mercaptopurine (6MP) (thioguanine nucleotides [6TGN]) accumulate intracellularly, including in erythrocytes (E-MTX and E-6TGN) with large interindividual variations. In the present Nordic Society for Pediatric Hematology and Oncology (NOPHO) study, the relation of E-MTX and E-6TGN to relapse risk was explored.. Two hundred ninety-seven patients with non-B-cell ALL, aged 1 to 14 years, on oral MTX and 6MP had E-MTX and E-6TGN levels measured three to 35 (median, eight) and three to 75 (median, nine) times, respectively. For each patient, a mean of all E-MTX (mE-MTX) and E-6TGN (mE-6TGN) measurements was calculated, as well as the product of mE-MTX and mE-6TGN (mE-MTX-6TGN), since MTX and 6MP may have synergistic action.. For patients in remission, the median mE-MTX and mE-6TGN values were 4.7 nmol/mmol hemoglobin (Hgb) (range, 0.4 to 10.3) and 173 nmol/mmol Hgb (range, 58 to 846). With a median follow-up duration of 66 months for patients in remission, 64 patients relapsed. Cox regression analysis identified mE-MTX-6TGN and sex to be the most significant parameters to predict relapse (global P = .001). Factors that predicted a better prognosis were high mE-MTX 6TGN and female sex. Patients who had a mE-MTX-6TGN less than the product of the median mE-MTX and median mE-6TGN (813 [nmol/mmol Hgb]2) had a significantly poorer event-free survival (EFS) than did patients with higher values (5-year probability of EFS [pEFS5y], 0.70 v 0.86; P = .001).. The pharmacokinetics of MTX and 6MP may have significant influence on the risk of relapse. The value of dose adjustments by E-MTX and E-6TGN remains to be determined.

Topics: Administration, Oral; Adolescent; Child; Child, Preschool; Erythrocytes; Female; Follow-Up Studies; Guanine Nucleotides; Humans; Infant; Male; Mercaptopurine; Methotrexate; Polyglutamic Acid; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Prognosis; Recurrence; Regression Analysis; Remission Induction; Risk; Thionucleotides; Time Factors

Two children with acute lymphoblastic leukaemia (ALL) taking daily 6-mercaptopurine as part of a national UK therapeutic trial repeatedly developed profound myelosuppression on 25% of the standard protocol dose. Both were found to have undetectable intracellular activity of thiopurine methyltransferase (TPMT), an enzyme controlling one of the major alternative catabolic pathways of 6-mercaptopurine, and both produced higher concentrations of cytotoxic drug metabolites at 10-25% of the protocol dose than other patients taking 100%. It is supposed that these patients represent the 0.33% of the normal population constitutionally lacking TPMT. It is important to recognise such individuals both to avoid fatal bone marrow failure through inadvertent overdosage, and to be reassured that an adequate drug effect can be achieved at around 10% of the standard dose.

Topics: Bone Marrow; Child; Child, Preschool; Female; Guanine Nucleotides; Humans; Male; Mercaptopurine; Methotrexate; Methyltransferases; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Reference Values; Thionucleotides; Vincristine

Topics: Adolescent; Child; Female; Guanine Nucleotides; Humans; Male; Mercaptopurine; Patient Compliance; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Thionucleotides

6-mercaptopurine (6-MP) can be inactivated by S-methylation, which is catalysed by thiopurine methyltransferase (TPMT). An alternative metabolic route leads to the formation of cytotoxic 6-thioguanine nucleotides (6-TGN). To investigate whether these two pathways compete with each other to affect the therapeutic response to 6-MP, 6-TGN concentrations and TPMT enzymatic activity were measured in erythrocytes (RBC) from 95 children on long-term 6-MP therapy for lymphoblastic leukaemia (ALL). RBC TPMT activities were also measured in 130 control children and 104 long-term survivors of ALL no longer on treatment. The 95 children on 6-MP showed wide interindividual differences in RBC 6-TGN concentrations at the full protocol dose of 75 mg/m2, and RBC 6-TGN concentrations correlated negatively with RBC TPMT activity. Children with 6-TGN concentrations below the group median had higher TPMT activities and a higher subsequent relapse rate. 50 of the 104 long-term survivors had been treated with "gentle" low-dose protocols, and this subgroup contained an excess of children with lower TPMT activities compared with normal controls. These results indicate that genetically determined TPMT activity may be a substantial regulator of the cytotoxic effect of 6-MP, an effect which in turn could be important in influencing the outcome of therapy for childhood ALL.

Topics: Actuarial Analysis; Administration, Oral; Adolescent; Adult; Analysis of Variance; Child; Child, Preschool; Drug Administration Schedule; Drug Evaluation; Erythrocytes; Female; Follow-Up Studies; Guanine Nucleotides; Homozygote; Humans; Male; Mercaptopurine; Methyltransferases; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Prognosis; Remission Induction; Thionucleotides; Time Factors

In the present study of 12 boys and 19 girls 2-16 years of age (median, 7 years) on oral 6-mercaptopurine (6MP) and methotrexate (MTX) maintenance therapy (MT) for non-B-cell acute lymphoblastic leukemia (ALL), we found that (a) during MT, 6-thioguanine nucleotides (6TGN) (the major cytotoxic metabolite of 6MP) accumulate in the erythrocytes (E-6TGN); (b) for patients receiving an unchanged dose of 6MP, no significant correlation could be demonstrated between the mean E-6TGN (mE-6TGN) and the dose of 6MP (r = -0.11, P = 0.28) (31 patients); (c) among 21 patients receiving 50-75 mg/m2 6MP, a variation of up to 3 orders of magnitude in mE-6TGN could be demonstrated, with the interindividual coefficient of variation (CV) in mE-6TGN for these patients being 0.31; (d) the median intraindividual CV in E-6TGN at an unchanged dose of 6MP was 0.11 (range, 0.04-0.18); and (e) the degree of myelodepression as measured by the mean white cell count was related to mE-6TGN (r = -0.55, P = 0.0006). These results indicate that E-6TGN could be a useful parameter for monitoring 6MP maintenance chemotherapy, although this needs to be explored in prospective studies.

Topics: Adolescent; Antineoplastic Combined Chemotherapy Protocols; Child; Child, Preschool; Dose-Response Relationship, Drug; Erythrocytes; Female; Guanine Nucleotides; Humans; Leukopenia; Male; Mercaptopurine; Methotrexate; Monitoring, Physiologic; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Thionucleotides