Intensification of mercaptopurine/methotrexate maintenance chemotherapy may increase the risk of relapse for some children with acute lymphoblastic leukemia.

Schmiegelow K, Bjork O, Glomstein A, Gustafsson G, Keiding N, Kristinsson J, Makipernaa A, Rosthoj S, Szumlanski C, Sorensen TM, Weinshilboum R.

Departments of Pediatrics and of Biostatistics, The University Hospital and The University of Copenhagen, Denmark.

Purpose: Thioguanine nucleotides (TGNs) mediate the cytotoxicity of mercaptopurine (MP). Methylated MP metabolites (formed by thiopurine methyltransferase [TPMT]) and methotrexate (MTX) polyglutamates can inhibit de novo purine synthesis. We explored whether dose adjustment of MP and MTX by erythrocyte (E) levels of TGN and MTX (including polyglutamates) could improve outcome in childhood acute lymphoblastic leukemia (ALL). Patients and Methods: A total of 538 children with ALL were randomly assigned to have their oral MP/MTX maintenance therapy adjusted by white cell counts (WBC), E-TGN, and E-MTX (pharmacology group), or by WBC only (control group). Results: After a median follow-up of 7.8 years, 79 patients had relapsed. Cox regression analysis showed an increased risk of relapse for boys (P =.00003), high WBC at diagnosis (P =.03), pharmacology arm (6.6 times increased relapse hazard for girls), high TPMT activity (P =.002), and high average neutrophil counts during maintenance therapy (P =.0009), with a significant interaction between sex and randomization group (P =.0007). For girls, the relapse risk was 5% in the control group and 19% in the pharmacology group (P =.001) because of an increased relapse hazard during the first year after cessation of therapy. TPMT activity was the most significant predictor of relapses among girls in the pharmacology arm (P <.0001). Overall, the TPMT activity was higher for patients who relapsed after cessation of therapy compared with those who stayed in remission (girls 19.5 v 17.4 U/mL, P =.03; boys 19.3 v 18.0 U/mL, P =.04). Conclusion: Adding pharmacologically guided treatment intensification to dose adjustments by blood counts may not be warranted for girls, whereas new approaches to optimize maintenance therapy are needed for boys.

PMID: 12663723 [PubMed - in process]

Continuing therapy for childhood acute lymphoblastic leukaemia: clinical and cellular pharmacology of methotrexate, 6-mercaptopurine and 6-thioguanine.

Estlin EJ.

Department of Paediatric Oncology, Royal Manchester Children's Hospital, Pendlebury, Manchester M27 4HA, UK. eestlin@mch.srht.nwest.nhs.uk

Across the world, therapy with 6-mercaptopurine (6-MP) and methotrexate (MTX) forms the basis of the continuing therapy of childhood acute lymphoblastic leukaemia (ALL). In this review, the pharmacological determinants of the sensitivity of human leukaemia cell lines and lymphoblasts derived from children with ALL will be discussed. In addition, clinical pharmacological studies of 6-MP and MTX in relation to the continuing therapy with childhood ALL will be reviewed. For 6-MP in vitro, prolonged exposure times to relatively high extracellular drug concentrations are necessary for cytotoxicity, and these concentrations are much higher than those achieved during continuing therapy for childhood ALL. For MTX, plasma concentrations are achieved during continuing therapy that would be cytotoxic to human leukaemia cells during prolonged exposures in vitro. For both MTX and 6-MP, wide inter- and intrapatient variation in plasma pharmacokinetic parameters has been described. For 6-MP and MTX, cellular pharmacological studies have been largely restricted to erythrocytes as a surrogate of the possible effects in leukaemic blasts. Although measures of the pharmacology of 6-MP and MTX in erythrocytes has been related to prognosis in many studies, 6-MP systemic exposure and the dose intensity of 6-MP and MTX actually received by children during this phase of therapy seems to be the most important determinant of efficacy. Further studies will be needed to determine the importance of pharmacokinetic variability during continuing therapy as a determinant of outcome for children with ALL. In this respect, minimal residual disease status during this phase of treatment may prove to be a useful pharmacodynamic endpoint. Copyright 2002, Elsevier Science Ltd. All rights reserved.

Publication Types: Review Review, Tutorial

PMID: 11908928 [PubMed - indexed for MEDLINE]

Effect of methotrexate polyglutamates on thioguanine nucleotide concentrations during continuation therapy of acute lymphoblastic leukemia with mercaptopurine.

Dervieux T, Hancock M, Evans W, Pui CH, Relling MV.

Department of Pharmaceutical Sciences, St Jude Children's Research Hospital, Memphis, TN 38105, USA.

Methotrexate is widely administered with mercaptopurine, a prodrug requiring activation into thioguanine nucleotides (TGN) to exert antileukemic effects. In vitro, methotrexate enhances TGN formation, but in vivo, such enhancement has yet to be demonstrated. We investigated whether TGN concentrations were related to methotrexate concentrations in children with acute lymphoblastic leukemia who received a weekly intravenous methotrexate (40 mg/m(2)) dose combined with daily mercaptopurine (75 mg/m(2)). A total of 141 erythrocyte TGN concentrations were measured with erythrocyte methotrexate polyglutamates (MTX-PG) concentrations in 87 patients. Average TGN concentrations ranged from 137 to 958 pmol/8 x 10(8) cells (median 389), average total MTX-PG concentrations (MTX- PG(1-7)) from 0.60 to 97.7 pmol/10(9)cells (median 29), and average long chain polyglutamate concentrations (MTX-PG(5-7)) from 0 to 8.35 pmol/10(9) cells (median 2.43). Higher TGN concentrations correlated with higher MTX-PG(5-7) concentrations (P = 0.002). These data support the practice of administering methotrexate with mercaptopurine during continuation therapy of acute lymphoblastic leukemia.

PMID: 11840287 [PubMed - indexed for MEDLINE]

Comparative pharmacokinetics of oral 6-mercaptopurine and intravenous 6-mercaptopurine riboside in children.

Mawatari H, Unei K, Nishimura S, Sakura N, Ueda K.

Department of Pediatrics, Hiroshima University School of Medicine, Kasumi 1-2-3, Minami-ku, Hiroshima, 734-8551, Japan. mawatari@triton.ocn.ne.jp

BACKGROUND: The poor absorption of orally administered 6-mercaptopurine (6MP) causes a wide variation in its cytotoxic efficacy. An i.v. dosage form would eliminate this problem. Our objective was to compare the pharmacokinetics of 6MP administered orally with those of an i.v. dosage form 6-mercaptopurine riboside (6MPR), in children with acute lymphoblastic leukemia or malignant lymphoma. METHODS: A total of 10 children were treated with oral 6MP, 50 mg/m(2) per day, while five children were treated with 6MPR, 50 mg/m(2) per day, administered by rapid i.v. injection. The plasma concentrations of 6MP and of 6MPR were measured on day 0, while the concentrations of 6-thioguanine nucleotides (6TGN) in red blood cells (RBC) were measured on day 2. The area under the plasma concentration-time curve (AUC1-5) was calculated from 1 to 5 h after drug administration. RESULTS: With the intravenously administered 6MPR, the AUC1-5 ranged from 124 to 186 (1.5-fold range, median 145) microM min; only two samples were obtained for the RBC concentration of 6TGN, and were 121 and 273 pmol per 25 mg hemoglobin. With the orally administered 6MP, the AUC1-5 ranged from 23 to 65 microM min (2.8-fold range, median 56); the RBC concentration of 6TGN ranged from 18 to 152 pmol per 25 mg hemoglobin (median 75). CONCLUSION: The i.v. administration of 6MPR showed less interindividual variation in the AUC1-5 coupled with a higher RBC level of 6TGN as compared with those by oral 6MP. We conclude that the i.v. administration of 6MPR achieves stable blood levels of active drug in children undergoing cancer chemotherapy.

PMID: 11737747 [PubMed - indexed for MEDLINE]

Possible implication of thiopurine S-methyltransferase in occurrence of infectious episodes during maintenance therapy for childhood lymphoblastic leukemia with mercaptopurine.

Dervieux T, Medard Y, Verpillat P, Guigonis V, Duval M, Lescoeur B, Suciu S, Vilmer E, Jacqz-Aigrain E.

Service de Pharmacologie Pediatrique et Pharmacogenetique, Hjpital Robert Debre, Paris, France.

6-Mercaptopurine (6-MP) is metabolized by thiopurine S-methyltransferase (TPMT), an enzyme subject to genetic polymorphism. We investigated the relationships between the TPMT locus (TPMT activity and genotype) and the pharmacological response to 6-MP during maintenance therapy of 78 children with acute lymphoblastic leukemia (ALL). For each patient, 6-MP dosage, leukocyte counts and occurrence of infectious episodes were monitored on an 8 week basis. Higher 6-MP dosage was associated with higher TPMT activity (P = 0.03) and higher average leukocyte counts (P < 0.01). Eight patients (10%) carrying a TPMT mutant genotype (one homozygous and seven heterozygous) received lower 6-MP doses (average: 48 vs 65 mg/m2/day; P = 0.02) and had on average lower leukocyte counts (2834 vs 3398 cells/mm3; P = 0.003) than patients carrying the wild-type TPMT genotype. Higher occurrence of infectious episodes graded 2 or 3 was correlated with higher 6-MP dosage (P < 0.01) but no difference was observed between TPMT mutants and TPMT wild-type patients. Patients who received 6-MP dosage above the group median (62 mg/m2/day) or having a TPMT activity above the group median (21.5 nmol/h/ml) had a higher percentage of 8 week periods with infectious episodes requiring treatment (34% vs 17% and 33% vs 19%, respectively) than those with 6-MP dose or TPMT activity below the group median (P < 0.01). In the last 25 patients enrolled in the study, steady-state erythrocyte thioguanine nucleotide (TGN) concentrations were associated with lower leukocyte counts (P= 0.01) but not with a higher occurrence of infectious episodes. In contrast, higher steady-state erythrocyte methylmercaptopurine nucleotide (MeMPN) concentrations were associated with higher 6-MP dosage (P< 0.01) and higher occurrence of infectious episodes (P < 0.001). In conclusion, during maintenance therapy of ALL, children with higher TPMT activity receive a higher 6-MP dosage and may have infectious episodes caused by metabolism of 6-MP into methylmercaptopurine nucleotides.

Publication Types: Clinical Trial

PMID: 11681411 [PubMed - indexed for MEDLINE]

Pneumocystis carinii pneumonia during maintenance treatment of childhood acute lymphoblastic leukemia.

Poulsen A, Demeny AK, Bang Plum C, Gjerum Nielsen K, Schmiegelow K.

Section of Pediatric Hematology and Oncology, Pediatric Clinic II, The Juliane Marie Center, The Copenhagen University Hospital, Rigshospitalet, Denmark.

BACKGROUND: Pneumocystis carinii pneumonia (PCP) is a wellknown risk among patients with deficient T-cell function such as children treated for acute lymphoblastic leukemia (ALL). The purpose of this study was to estimate the risk for PCP during maintenance treatment (MT) to identify patients at risk who could benefit from prophylaxis. PROCEDURE: We registered all episodes of PCP during MT in 71 children diagnosed between January 1992 and June 1997 with non-B-cell ALL at The Copenhagen University Hospital. Sulphametoxazole and trimetroprim (SMX/TMP) prophylaxis against PCP was given during induction and consolidation therapy but stopped prior to MT with oral methotrexate/6-mercaptopurine. Patients with standard (SR), intermediate (IR), and high risk (HR) ALL started MT at 3, 8, and 15 months from diagnosis, respectively. RESULTS: The HR group had a cumulated risk of 70% for developing PCP, whereas the risk for PCP in children with IR and the SR was 11 and 8%, respectively (P < 0.0001). All but one of these 13 cases of PCP occurred within 8 months after cessation of SMX-TMP prophylaxis. CONCLUSIONS: The higher incidence of PCP among HR compared to non-HR patients following cessation of SMX/TMP prophylaxis probably reflects the significantly longer T-cell suppressive consolidation therapy in this group. The very low incidence of PCP during the later part of MT emphasizes that methotrexate/6-mercaptopurine MT have more impact on B-cell than on T-cell function. TMP/SMX prophylaxis should be recommended for all children treated for ALL. Copyright 2001 Wiley-Liss, Inc.

PMID: 11466718 [PubMed - indexed for MEDLINE]

6-mercaptopurine dosage and pharmacokinetics influence the degree of bone marrow toxicity following high-dose methotrexate in children with acute lymphoblastic leukemia.

Schmiegelow K, Bretton-Meyer U.

The Laboratory for Pediatric Oncology, The Pediatric Clinic II, The Juliane Marie Centre, The National University Hospital, Rigshospitalet, Copenhagen, Denmark.

Through inhibition of purine de novo synthesis and enhancement of 6-mercaptopurine (6MP) bioavailability high-dose methotrexate (HDM) may increase the incorporation into DNA of 6-thioguanine nucleotides (6TGN), the cytoxic metabolites of 6MP. Thus, coadministration of 6MP could increase myelotoxicity following HDM. Twenty-one children with standard risk (SR) and 25 with intermediate risk (IR) acute lymphoblastic leukemia (ALL) were studied. During consolidation therapy they received either three courses of HDM at 2 week intervals without concurrent oral 6MP (SR-ALL) or four courses of HDM given at 2 week intervals with 25 mg/m2 of oral 6MP daily (IR-ALL). During the first year of maintenance with oral 6MP (75 mg/m2/day) and oral MTX (20 mg/m2/week) they all received five courses of HDM at 8 week intervals. In all cases, HDM consisted of 5,000 mg of MTX/m2 given over 24 h with intraspinal MTX and leucovorin rescue. Erythrocyte levels of 6TGN (E-6TGN) and methotrexate (E-MTX) were, on average, measured every second week during maintenance therapy. When SR consolidation (6MP: 0 mg), IR consolidation (6MP: 25 mg/m2), and SR/IR maintenance therapy (6MP: 75 mg/m2) were compared, white cell and absolute neutrophil count (ANC) nadir, lymphocyte count nadir, thrombocyte count nadir, and hemoglobin nadir after HDM decreased significantly with increasing doses of oral 6MP. Three percent of the HDM courses given without oral 6MP (SR consolidation) were followed by an ANC nadir <0.5 x 10(9)/l compared to 50% of the HDM courses given during SR/IR maintenance therapy. Similarly, only 13% of the HDM courses given as SR-ALL consolidation induced a thrombocyte count nadir <100 x 10(9)/l compared to 58% of the HDM courses given during maintenance therapy. The best-fit model to predict the ANC nadir following HDM during maintenance therapy included the dose of 6MP prior to HDM (beta = -0.017, P= 0.001), the average ANC level during maintenance therapy (beta = 0.82, P = 0.004), and E-6TGN (beta = -0.0029, P= 0.02). The best-fit model to predict the thrombocyte nadir following HDM during maintenance therapy included only mPLATE (beta = 0.0057, P = 0.046). In conclusion, the study indicates that reductions of the dose of concurrently given oral 6MP could be one way of reducing the risk of significant myelotoxicity following HDM during maintenance therapy of childhood ALL.

Publication Types: Clinical Trial

PMID: 11243403 [PubMed - indexed for MEDLINE]

Variable correlation between 6-mercaptopurine metabolites in erythrocytes and hematologic toxicity: implications for drug monitoring in children with acute lymphoblastic leukemia.

Innocenti F, Danesi R, Favre C, Nardi M, Menconi MC, Di Paolo A, Bocci G, Fogli S, Barbara C, Barachini S, Casazza G, Macchia P, Del Tacca M.

Department of Oncology, University of Pisa, Italy.

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.

PMID: 10942174 [PubMed - indexed for MEDLINE]

Myelotoxicity, pharmacokinetics, and relapse rate with methotrexate/6-mercaptopurine maintenance therapy of childhood acute lymphoblastic leukemia.

Comment in: Pediatr Hematol Oncol. 1996 Sep-Oct;13(5):vii-x.

Schmiegelow K, Ifversen M.

Section of Pediatric Hematology and Oncology, Juliane Marie Centre, National University Hospital, Copenhagen, Denmark.

White blood cell and absolute neutrophil counts (WBC, ANC), aminotransferase (AT) levels, methotrexate (MTX) and 6-mercaptopurine (6MP) doses, metabolites in erythrocytes (E-MTX and E-6TGN), and the prognostic significance of these parameters were studied in 58 children receiving MTX/6MP maintenance therapy for acute lymphoblastic leukemia diagnosed from July 1986 to December 1991. At the end of follow-up July 1995, 13 patients had relapsed (pEFS = 0.77). Weighted means of AT, WBC, and ANC during and after maintenance therapy (mAT, mWBCON, mWBCOFF, mANCON, mANCOFF), E-MTX (mE-MTX), and E-6TGN (mE-6TGN) were calculated, as well as the product of mE-MTX and mE-6TGN (mE-MTX*6TGN), as MTX and 6MP probably act synergistically. Beyond higher MTX and 6MP doses to patients with high mWBCON, neither mWBCON, (median 3.5 x 10(9)/L), mANCON, nor mAT was correlated with the dose of MTX and 6MP, mE-MTX, mE-6TGN, or risk of relapse. Patients with mE-MTX*6TGN above or below 828 (nmol/mmol Hb)2 (median value) had pEFS values of 0.84 and 0.70, respectively (P = .16). All 5 patients who relapsed during therapy had mE-MTX*6TGN < 828 (nmol/mmol Hb)2 (P = .03). mWBCOFF and the degree of myelosuppression (= mWBCSHIFT = mWBCOFF - mWBCON; median: 2.5 x 10(9)/L) were related to age (rs = -0.50, P = .001 and rs = -0.40, P = .006, respectively). All eight relapses off therapy occurred in patients with mWBCSHIFT < 2.5 x 10(9)/L (P = .02). WBC levels during MTX/6MP therapy may underestimate the degree of MTX/6MP treatment intensity, especially in order children. Pharmacokinetic monitoring could be useful for optimizing MTX/6MP maintenance therapy.

PMID: 10897815 [PubMed - indexed for MEDLINE]

Six months of maintenance chemotherapy after intensified treatment for acute lymphoblastic leukemia of childhood.

Toyoda Y, Manabe A, Tsuchida M, Hanada R, Ikuta K, Okimoto Y, Ohara A, Ohkawa Y, Mori T, Ishimoto K, Sato T, Kaneko T, Maeda M, Koike K, Shitara T, Hoshi Y, Hosoya R, Tsunematsu Y, Bessho F, Nakazawa S, Saito T.

Department of Oncology, Kanagawa Children's Medical Center, and Department of Pediatrics, Yokohama City University School of Medicine, Yokohama, Japan.

PURPOSE: We postulated that intensification of chemotherapy immediately after remission induction might reduce the leukemic cell burden sufficiently to allow an abbreviated period of antimetabolite therapy. PATIENTS AND METHODS: Three hundred forty-seven children (ages 1 to 15 years) with previously untreated acute lymphoblastic leukemia (ALL) were enrolled onto the Tokyo L92-13 study, which excluded patients with mature B-cell ALL and patients less than 1 year old. One hundred twenty-four patients were classified as standard risk, 122 as high risk, and 101 as extremely high risk, according to age, peripheral-blood leukocyte count, selected genetic abnormalities, and immunophenotype. All subjects received four drugs for remission induction, followed by a risk-directed multidrug intensification phase and therapy for presymptomatic leukemia in the CNS. Maintenance chemotherapy with oral mercaptopurine and methotrexate was administered for 6 months, with all treatment stopped by 1 year after diagnosis. RESULTS: The mean (+/- SD) event-free survival (EFS) and overall survival rates for all patients were 59.5% +/- 3.4% and 81.5% +/- 2.2%, respectively, at 5. 5 years after diagnosis. EFS rates by risk category were similar (60. 2% +/- 6.0% for standard risk, 57.7% +/- 5.6% for high risk, and 62. 5% +/- 5.7% for extremely high risk), whereas overall survival rates differed significantly (91.2% +/- 2.7%, 80.0% +/- 4.1%, and 72.1% +/- 4.5%, respectively, P <.0001 by the log-rank test). There were 107 relapses. Eighty-five (79.4%) of these 107 patients achieved second complete remissions, with subsequent EFS rates of 61.5% +/- 7. 9% (standard risk), 42.6% +/- 8.1% (high risk), and 9.6% +/- 6.4% (extremely high risk). Of the five risk factors analyzed, only the response to prednisolone monotherapy among extremely high-risk patients proved important. CONCLUSION: Early treatment intensification did not compensate for a truncated phase of maintenance chemotherapy in children with standard- or high-risk ALL. However, 6 months of antimetabolite treatment seemed adequate for extremely high-risk patients who were good responders to prednisolone and received intensified chemotherapy that included high-dose cytarabine early in the clinical course.

Publication Types: Clinical Trial

PMID: 10735899 [PubMed - indexed for MEDLINE]

Delayed cytotoxicity of 6-mercaptopurine is compatible with mitotic death caused by DNA damage due to incorporation of 6-thioguanine into DNA as 6-thioguanine nucleotide.

Inamochi H, Higashigawa M, Shimono Y, Nagata T, Cao DC, Mao XY, M'soka T, Hori H, Kawasaki H, Sakurai M.

Dept. of Pediatrics, Mie University School of Medicine, Tsu-city, Japan.

Many protocol studies have shown that low dose 6-mercaptopurine (6MP) in maintenance chemotherapy for childhood acute lymphoblastic leukemia (ALL) can be utilized to cure the disease. Mitotic or reproductive cell death has been recognized after G2 arrest when cells are treated with antitumor agents. The precise mechanism of mode of action of 6MP still remains unclear. We found delayed cytotoxic effect of 6MP in P388 murine leukemic cells. Morphological study showed that 6MP induced delayed death was characterized by an enlargement of cell size and multinucleated nuclei. Agarose gel electrophoresis of fragmented DNA from cells treated with 6MP showed the typical ladder pattern. These findings were compatible with mitotic death. Our results make us hypothesize that the delayed cytotoxicity of 6MP is one of the drug induced mitotic deaths caused by DNA damage due to incorporation of 6-thioguanine (6TG) into DNA as thioguanine nucleotide (TGN). Mitotic death may be a mechanism for killing the cycling cells from residual leukemic cells in G0 or long G1 phases in the treatment of childhood ALL.

PMID: 10606189 [PubMed - indexed for MEDLINE]

Mercaptopurine therapy intolerance and heterozygosity at the thiopurine S-methyltransferase gene locus.

Comment in: J Natl Cancer Inst. 1999 Dec 1;91(23):1983-5.

Relling MV, Hancock ML, Rivera GK, Sandlund JT, Ribeiro RC, Krynetski EY, Pui CH, Evans WE.

Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, TN 38105, USA. mary.relling@stjude.org

BACKGROUND: Patients with acute lymphoblastic leukemia are often treated with 6-mercaptopurine, and those with homozygous deficiency in thiopurine S-methyltransferase (TPMT) enzyme activity have an extreme sensitivity to this drug as a result of the accumulation of higher cellular concentrations of thioguanine nucleotides. We studied the metabolism, dose requirements, and tolerance of 6-mercaptopurine among patients with different TPMT phenotypes. METHODS: We compared, by use of statistical modeling, 6-mercaptopurine pharmacology and tolerance in 180 patients who achieved remission on St. Jude Children's Research Hospital Protocol Total XII composed of weekly methotrexate (40 mg/m(2)) and daily oral 6-mercaptopurine (75 mg/m(2)) given for 2.5 years, interrupted every 6 weeks during the first year for treatment with either high-dose methotrexate or teniposide plus cytarabine. Statistical tests were two-sided. RESULTS: Erythrocyte concentrations of thioguanine nucleotides (pmol/8 x 10(8) erythrocytes) were inversely related to TPMT enzyme activity (P<.01), with averages (+/- standard deviations) of 417 (+/-179), 963 (+/-752), and 3565 (+/-1282) in TPMT homozygous wild-type (n = 161), heterozygous (n = 17), and homozygous-deficient (n = 2) patients, respectively. There was complete concordance between TPMT genotype and phenotype in a subset of 28 patients for whom TPMT genotype was determined. There were no sex differences in thioguanine nucleotide concentrations (P =.24), TPMT enzyme activity (P =.22), or average weekly prescribed dose of 6-mercaptopurine (P=.49). The cumulative incidence of 6-mercaptopurine dose reductions due to toxicity was highest among patients homozygous for mutant TPMT (100%), intermediate among heterozygous patients (35%), and lowest among wild-type patients (7%) (P<.001), with average (+/- standard deviation) final weekly 6-mercaptopurine doses of 72 (+/-60), 449 (+/-160), and 528 (+/-90) mg/m(2), respectively. Lowering doses of 6-mercaptopurine in TPMT heterozygotes and in deficient patients allowed administration of full protocol doses of other chemotherapy while maintaining high thioguanine nucleotide concentrations. CONCLUSION: We conclude that genetic polymorphism in TPMT is an important determinant of mercaptopurine toxicity, even among patients who are heterozygous for this trait.

Publication Types: Clinical Trial Randomized Controlled Trial

PMID: 10580024 [PubMed - indexed for MEDLINE]

The interaction of 6-mercaptopurine (6-MP) and methotrexate (MTX).

Giverhaug T, Loennechen T, Aarbakke J.

Department of Pharmacology, Institute of Pharmacy, University of Tromso, Norway. trudeg@farmasi.uit.no

The antimetabolites 6-mercaptopurine (6-MP) and methotrexate (MTX) are the cornerstones in the maintenance treatment of children's acute lymphoblastic leukemia (ALL). The biochemical mechanisms underlying the increased therapeutic efficacy of the combination of these drugs have not yet been elucidated. However, both drugs interact with important pathways. such as purine de novo synthesis (PDNS), purine salvage, and methylation reactions. A review of the mechanistic aspects of the interactions between 6-MP and MTX is given.

Publication Types: Review Review, Tutorial

PMID: 10523073 [PubMed - indexed for MEDLINE]

In vitro metabolism of 6-mercaptopurine by human liver cytosol.

Rowland K, Lennard L, Lilleyman JS.

University of Sheffield, Division of Clinical Sciences (CSUH), Royal Hallamshire Hospital, UK.

1. The aim of this study was to investigate 6-mercaptopurine (6MP) metabolism by human liver cytosol in vitro. 2. Cytosol was prepared from seven human livers (A-G). A single cytosol (C) was used to optimize incubation conditions. 3. Cytosols A-G were incubated with 6MP at 2, 10 and 500 microM for two fixed times (5 and 48 h). Parent drug, thiopurine and thionucleotide metabolites were quantitated by high performance liquid chromatography at all time points. 4. At 5 and 48 h the 2 microM and 10 microM 6MP incubations contained both 6MP and its initial nucleotide metabolite, thioinosine 5'-monophosphate (TIMP). In addition, the 10 microM 6MP 48 h incubates contained small amounts of 6-thioguanine (6TG, median 0.12 microM). At 500 microM 6MP all seven liver incubates produced a range of metabolites. At 48 h these included thiouric acid, 8-hydroxy-6-mercaptopurine and 6-methylmercaptopurine (median 31, 19.5 and 8.8 microM respectively), with TIMP, 6TG, thioxanthine and thioxanthine nucleotide at median concentrations of 61, 0.79, 2.11 and 0.80 microM respectively. Thioguanine nucleotides, major metabolites measured in vivo, were not detected. 5. These results indicate that the human liver 6MP metabolic profile is dependent upon drug concentration.

PMID: 10426560 [PubMed - indexed for MEDLINE]

Prognostic importance of 6-mercaptopurine dose intensity in acute lymphoblastic leukemia.

Relling MV, Hancock ML, Boyett JM, Pui CH, Evans WE.

Departments of Pharmaceutical Sciences, Hematology/Oncology, and Biostatistics and Epidemiology, St Jude Children's Research Hospital, Memphis, TN, USA.

6-Mercaptopurine (6MP) and methotrexate are the backbone of continuation therapy for childhood acute lymphoblastic leukemia (ALL). In studies of oral 6MP and methotrexate, indices of chronic systemic exposure to active metabolites of these agents, namely, red blood cell (RBC) concentrations of methotrexate polyglutamates (MTXPGs) and thioguanine nucleotides (TGNs) have positively correlated with event-free survival (EFS). Our objective was to evaluate whether MTXPGs, TGNs, and the dose intensity of administered methotrexate and 6MP were prognostic in the setting of a treatment protocol in which all treatment was coordinated through a single center, and the weekly doses of methotrexate were given parenterally. On protocol Total XII, 182 children achieved remission and received weekly methotrexate 40 mg/m2 parenterally and daily oral 6MP, interrupted every 6 weeks during the first year by pulse chemotherapy. A total of 709 TGN, 418 MTX-PG, and 267 thiopurine methyltransferase (TPMT) measurements, along with complete dose intensity information (dose received divided by protocol dose per week) for 19,046 weeks of 6MP and methotrexate, were analyzed. In univariate analyses, only higher dose intensity of 6MP and of weekly methotrexate were significant predictors of overall EFS (P =.006 and .039, respectively). The occurrence of neutropenia was associated with worse outcome (P =.040). In a multivariate analysis, only higher dose intensity of 6MP (P =.020) was a significant predictor of EFS, with lower TPMT activity (P =.096) tending to associate with better outcome. 6MP dose intensity was also associated (P =.007) with EFS among patients with homozygous wild-type TPMT phenotype. Lower 6MP dose intensity was primarily due to missed weeks of therapy and not to reductions in daily dose. We conclude that increased dose-intensity of oral 6MP is an important determinant of EFS in ALL, particularly among those children with a homozygous wild-type TPMT phenotype. However, increasing intensity of therapy such that neutropenia precludes chemotherapy administration may be counterproductive.

Publication Types: Clinical Trial

PMID: 10216075 [PubMed - indexed for MEDLINE]

Pharmacokinetics and pharmacodynamics of oral methotrexate and mercaptopurine in children with lower risk acute lymphoblastic leukemia: a joint children's cancer group and pediatric oncology branch study.

Balis FM, Holcenberg JS, Poplack DG, Ge J, Sather HN, Murphy RF, Ames MM, Waskerwitz MJ, Tubergen DG, Zimm S, Gilchrist GS, Bleyer WA.

Pediatric Oncology Branch, National Cancer Institute, Bethesda, MD; and the Children's Cancer Group, Arcadia, CA, USA. balisf@nih.gov

We prospectively assessed the pharmacokinetics of methotrexate, mercaptopurine, and erythrocyte thioguanine nucleotide levels in a homogenous population of children with lower risk acute lymphoblastic leukemia and correlated pharmacokinetic parameters with disease outcome. The maintenance therapy regimen included daily oral mercaptopurine (75 mg/m2) and weekly oral methotrexate (20 mg/m2). One hundred ninety-one methotrexate doses and 190 mercaptopurine doses were monitored in 89 patients. Plasma drug concentrations of both agents were highly variable. The area under the plasma concentration-time curve (AUC) of methotrexate ranged from 0.63 to 12 micromol*h/L, and the AUC of mercaptopurine ranged from 0.11 to 8 micromol*h/L. Drug dose, patient age, and duration of therapy did not account for the variability. Methotrexate AUC was significantly higher in girls than boys (P =.007). There was considerable intrapatient variability for both agents. Erythrocyte thioguanine nucleotide levels were also highly variable (range, 0 to 10 pmol/g Hgb) and did not correlate with mercaptopurine dose or AUC. A Cox regression analysis showed that mercaptopurine AUC was a marginally significant (P =.043) predictor of outcome, but a direct comparison of mercaptopurine AUC in the remission and relapsed patient groups failed to show a significant difference. Methotrexate and mercaptopurine plasma concentrations and erythrocyte thioguanine nucleotide levels were highly variable, but measurement of these pharmacokinetic parameters at the start of maintenance will not distinguish patients who are more likely to relapse.

Publication Types: Multicenter Study

PMID: 9808549 [PubMed - indexed for MEDLINE]

Pharmacokinetics and metabolism of thiopurines in children with acute lymphoblastic leukemia receiving 6-thioguanine versus 6-mercaptopurine.

Erb N, Harms DO, Janka-Schaub G.

Department of Pediatric Hematology and Oncology, Children's University Hospital, Hamburg, Germany.

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.

Publication Types: Clinical Trial Multicenter Study Randomized Controlled Trial

PMID: 9744770 [PubMed - indexed for MEDLINE]

Continuing (maintenance) therapy in lymphoblastic leukaemia: lessons from MRC UKALL X. Medical Research Council Working Party in Childhood Leukaemia.

Chessells JM, Harrison G, Lilleyman JS, Bailey CC, Richards SM.

Haematology/Oncology Department, Institute of Child Health, London.

The relationship between the prescribed dose of drugs during continuing (maintenance) therapy, the degree of marrow suppression caused, and subsequent event-free survival was examined in a cohort of 740 children with lymphoblastic leukaemia treated on MRC UKALL X. Girls, younger children, and patients who had received intensification treatment, were prescribed lower doses of mercaptopurine, became neutropenic more readily, and had more interruptions of treatment. Children who had one or more episodes of neutropenia with a count of <0.5 x 10(9)/l had a better prognosis than those who never became neutropenic. We conclude that early intensification treatment influences the probability of neutropenia during continuing treatment and that patients exhibiting myelosuppression during this phase of treatment have a better chance of prolonged remission.

Publication Types: Clinical Trial Randomized Controlled Trial

PMID: 9326194 [PubMed - indexed for MEDLINE]

Pharmacokinetics of mercaptopurine: plasma drug and red cell metabolite concentrations after an oral dose.

Welch J, Lennard L, Morton GC, Lilleyman JS.

University of Sheffield, Department of Paediatrics, Children's Hospital Sheffield, United Kingdom.

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.

PMID: 9263376 [PubMed - indexed for MEDLINE]

Thiopurine methyltransferase deficiency in childhood lymphoblastic leukaemia: 6-mercaptopurine dosage strategies.

Lennard L, Lewis IJ, Michelagnoli M, Lilleyman JS.

Department of Medicine and Pharmacology, Royal Hallamshire Hospital, Sheffield, U.K.

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.

PMID: 9251729 [PubMed - indexed for MEDLINE]

Profile of non-compliance in lymphoblastic leukaemia.

Lancaster D, Lennard L, Lilleyman JS.

Department of Paediatric Oncology, St Bartholomew's Hospital, London.

A nationwide study of intracellular drug metabolite concentrations in children prescribed 6-mercaptopurine for the treatment of lymphoblastic leukaemia was carried out to assess interpatient variability at a standardised dose. Nine children (2% of the total) had completely undetectable metabolites, indicative of non-compliance. Five were adolescents, but otherwise they had no obvious distinguishing characteristics. Not taking any 6-mercaptopurine at all is uncommon, but the problem cannot be predicted. The total number of children who do not comply cannot be determined from this study, but the nine children described represent only a fraction of these.

PMID: 9166035 [PubMed - indexed for MEDLINE]

Impact of morning versus evening schedule for oral methotrexate and 6-mercaptopurine on relapse risk for children with acute lymphoblastic leukemia. Nordic Society for Pediatric Hematology and Oncology (NOPHO).

Schmiegelow K, Glomstein A, Kristinsson J, Salmi T, Schroder H, Bjork O.

Section of Clinical Hematology and Oncology, Juliane Marie Center, University Hospital, Copenhagen, Denmark.

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.

PMID: 9149738 [PubMed - indexed for MEDLINE]

Mercaptopurine in childhood leukaemia: the effects of dose escalation on thioguanine nucleotide metabolites.

Lennard L, Welch J, Lilleyman JS.

University of Sheffield Department of Medicine and Pharmacology, Royal Hallamshire Hospital, Sheffield.

The current U.K. trial protocol (UKALL XI) for childhood lymphoblastic leukaemia demands mercaptopurine (MP) dose escalation in children who tolerate daily 75 mg/m2 MP (100% dose) without cytopenias. The previous trial (UKALL X) did not. MP metabolism was studied in a group of UKALL XI children (n = 21) who tolerated 100% dosages and who were matched in this respect with a similar group of UKALL X children. Red blood cell MP derived thioguanine nucleotide (TGN) concentrations were measured in both groups under comparable conditions; at 75 mg/m2 MP there was no significant difference. MP dose escalation in the UKALL XI children produced higher TGN concentrations (TGNs at 100% vs 125% dosages, median difference 90 pmol/8 x 10(8) RBCs, 95% CI 25 to 165 pmol, P < 0.02). Assayed at the time of cytopenia induced dose reduction, the UKALL XI children had accumulated significantly higher TGN concentrations than the UKALL X children (median difference 78 pmol/8 x 10(8) RBCs, 95% CI 20 to 144, P < 0.02). These findings indicate that dose escalation in children tolerant of 100% MP dosages produces higher peak TGN concentrations.

PMID: 8904630 [PubMed - indexed for MEDLINE]

6-Mercaptopurine dose escalation and its effect on drug tolerance in childhood lymphoblastic leukaemia.

Welch JC, Lilleyman JS.

University of Sheffield, Department of Paediatrics, The Children's Hospital, UK.

Daily oral 6-mercaptopurine (6MP) is important in the treatment of childhood lymphoblastic leukaemia (ALL), but there is great inter-patient variability in the pattern of evident drug effect (myelosuppression) seen at a standard dose. In an attempt to reduce that variability the current practise in the United Kingdom for the last 4 years has been to escalate the amount prescribed in patients who do not experience cytopenias at 75 mg/m2. We undertook a study to see whether that strategy would increase the total dose of 6MP prescribed in such patients and whether it would alter the pattern of myelosuppression. Over a 6-month period we studied 44 children treated conventionally (without escalation) and compared them with another 44 (matched for sex) who were treated on the same protocol but where doses were increased in monthly 25% steps if 75 mg/m2 was tolerated without cytopenias. We then compared the two groups for the total dose of drug prescribed and the frequency and duration of neutropenia or thrombocytopenia. The median cumulative dose of 6MP received by the conventionally treated children (10,002 mg/m2) was not significantly different from that of the children treated with dose escalation (9,429 mg/m2). In a comparison of the 30 children who actually received inflated doses of 6MP with the 37 from the conventional cohort who would have been eligible to do so, it was again found that the cumulative median doses were similar (10,460 versus 10,916 mg/m2). There was a difference between the two groups in the pattern of myelosuppression -- the escalated group spent significantly more time off 6MP than did the non-escalated group (median 4.5 versus 3 weeks; P<0.005, 95% CI from -1 to -3). These findings imply that the method of dose escalation employed does not allow more 6MP to be prescribed in children tolerant of the standard dose. The chief effect seems to be to generate longer periods off therapy, and this could paradoxically decrease the anti-neoplastic activity of the drug. Alternative ways of prescribing should be explored.

Publication Types: Clinical Trial Controlled Clinical Trial

PMID: 8603445 [PubMed - indexed for MEDLINE]

Clinical and experimental pharmacokinetic interaction between 6-mercaptopurine and methotrexate.

Innocenti F, Danesi R, Di Paolo A, Loru B, Favre C, Nardi M, Bocci G, Nardini D, Macchia P, Del Tacca M.

Institute of Medical Pharmacology, University of Pisa, Italy.

Clinical and experimental pharmacokinetic interaction between 6-mercaptopurine (6-MP) and methotrexate (MTX) was investigated in patients as well as in rats and in HL-60 human leukemic cells. Ten children affected by acute lymphoblastic leukemia (ALL) in remission received daily doses of 6-MP given at 25 mg/m2 and i.v. infusion of high-dose MTX at 2 or 5 g/m2 once every other week. When 6-MP was given alone, the mean peak plasma concentration (Cmax) and area under the curve (AUC) of 6-MP were 72.5 ng/ml and 225.3 h ng ml(-1). Concurrent treatment with MTX at 2 or 5 g/m2 resulted in a mean increase of 108% and 121% in the Cmax and of 69% and 93% in the AUC, respectively. In rats treated with an oral dose of 6-MP at 75 mg/m2, MTX given i.p. at 5 g/m2 produced mean increases of 110% and 230% in the Cmax and AUC of 6-MP, respectively. In HL-60 human leukemic cells incubated with 6-MP at 250 ng/ml, the cumulative intracellular concentration of 6-thioguanine and 6-MP nucleotides was not significantly modified by treatment with 20 micrograms/ml of MTX. The present findings indicate that high-dose MTX enhances the bioavailability of 6-MP as evidenced by the observed increases in the plasma Cmax and AUC of 6-MP in humans and animals.

PMID: 8599862 [PubMed - indexed for MEDLINE]

Hepatotoxicity of 6-mercaptopurine in childhood acute lymphocytic leukemia: pharmacokinetic characteristics.

Berkovitch M, Matsui D, Zipursky A, Blanchette VS, Verjee Z, Giesbrecht E, Saunders EF, Evans WE, Koren G.

Division of Clinical Pharmacology and Toxicology, Hospital for Sick Children, Toronto, Canada.

Treatment with 6-mercaptopurine (6MP) is associated with adverse gastrointestinal (GI) and hepatic effects. Four patients, ages 6.9 +/- 2.6 (mean +/- S.D.) years, with acute lymphocytic leukemia (ALL) on maintenance chemotherapy including 6MP, developed nausea, vomiting, abdominal pain, elevated liver enzymes, and hyperbilirubinemia after 1.4 +/- 1.0 (range 0.5-2) years. Liver biopsy in 1 patient was suggestive of drug-induced intrahepatic cholestatis. Symptoms resolved and liver function returned to normal after discontinuation of 6MP. Pharmacokinetic data of the symptomatic patients were compared with those of 25 ALL patients on the same protocol but without GI symptoms or hepatotoxicity. Levels of 6-thioguanine nucleotides (6-TGN) and the methylated metabolites of 6MP in red blood cells of the patients with hepatotoxicity, were not significantly different when compared to patients without hepatotoxicity, suggesting similar absorption of 6MP in both groups. Time to achieve peak 6MP levels was significantly longer in the symptomatic patients compared to the asymptomatic patients (P = 0.005). Peak levels and standardized concentration versus time curve (AUC) per 1 mg of 6MP per m2 of body surface area were significantly lower in the patients with hepatotoxicity (P = 0.016; P = 0.037, respectively). A significant correlation between peak 6MP levels and standardized AUC (r = 0.729, P < 0.0001) was found. These results suggest accumulation of 6MP and its metabolites in the liver of the patients with GI symptoms, leading to hepatotoxicity.

PMID: 8531858 [PubMed - indexed for MEDLINE]

Cellular pharmacology of 6-mercaptopurine in acute lymphoblastic leukemia.

Bostrom B, Erdmann G.

Division of Pediatric Hematology and Oncology, Minneapolis Children's Medical Center, MN.

PURPOSE: The cellular pharmacology of 6-Mercaptopurine (6MP) in acute lymphoblastic leukemia (ALL) is reviewed. DESIGN: Relevant studies on the clinical pharmacology of 6MP were reviewed. RESULTS: 6MP is one of the major drugs used in maintenance therapy of acute lymphoblastic leukemia (ALL). It is also used to treat steroid unresponsive inflammatory bowel disease. 6MP is an inactive prodrug that requires absorption, cellular uptake, and intracellular anabolism to nucleotides for cytotoxic activity. These nucleotides are ultimately incorporated into DNA and RNA, resulting in cell death. Two analogs of 6MP, azathioprine and 6-thioguanine, are also anabolized to the same intracellular metabolites, suggesting they should be therapeutically equivalent to 6MP. 6MP may be anabolized to nonmethylated nucleotides or may undergo methylation by the enzyme thiopurine methyltransferase to S-methylated nucleotides, which are also cytotoxic. CONCLUSION: Recent studies of 6MP pharmacokinetics in children with ALL have suggested that a higher systemic exposure, as measured by a greater area under the plasma concentration time curve or a higher concentration of 6MP metabolites in red blood cells, is associated with a decreased risk of relapse.

Publication Types: Review Review, Tutorial

PMID: 8447563 [PubMed - indexed for MEDLINE]

Is 6-thioguanine more appropriate than 6-mercaptopurine for children with acute lymphoblastic leukaemia?

Lennard L, Davies HA, Lilleyman JS.

University of Sheffield Department of Medicine, Royal Hallamshire Hospital, UK.

The cytotoxic activity of 6-mercaptopurine (6-MP) is affected by thiopurine methyltransferase (TPMT), a genetically regulated and variable intracellular enzyme. 6-Thioguanine (6-TG), a closely related thiopurine, is less affected by that enzyme and so it may be a more reliable drug-at least for patients with constitutionally high TPMT activity. We attempted to assess its suitability as an alternative by comparing the pharmacokinetics of both drugs in a small group of children with lymphoblastic leukaemia (ALL). Patients were included who were in their second or subsequent remission, who would otherwise have received 6-MP, and on whom pharmacokinetic data concerning 6-MP metabolism had been collected in a previous remission. Plasma 6-TG concentrations were assayed following an oral dose of 40 mg m-2, and the accumulation and fluctuation of intracellular (erythrocyte, RBC) 6-TG nucleotides (6-TGNs) were measured at regular intervals during daily oral therapy. Seven children were studied. Plasma 6-TG concentrations were low and cleared within 6 h of oral dosing. At 7 days, 6-TGN concentrations ranged from 959 to 2361 pmol 8 x 10(-8) RBCs, in all cases significantly higher (P = 0.002) than those produced by the same patients on 6-MP. After a total therapy time of 35 patient months, a modest rise of alanine aminotransferase was seen on one occasion, otherwise no toxicity apart from myelosuppression was encountered. In the context used, 6-TG appears well tolerated and produces higher concentrations of intracellular cytotoxic metabolites than 6-MP. For children constitutionally 'resistant' to the traditional drug, if not all, it may be a preferable alternative.

Publication Types: Clinical Trial

PMID: 8318412 [PubMed - indexed for MEDLINE]

Plasma and urine levels of methotrexate and 7-hydroxymethotrexate in children with ALL during maintenance therapy with weekly oral methotrexate.

Skoglund KA, Soderhall S, Beck O, Peterson C, Wennberg M, Hayder S, Bjork O.

Department of Pediatric Oncology, Karolinska Hospital, Stockholm, Sweden.

A new high-performance liquid chromatographic assay was used to determine methotrexate (MTX) and its main metabolite, 7-hydroxymethotrexate (7-OH-MTX), in the plasma (n = 17) and urine (n = 14) of children (age 3-12 years) on maintenance therapy for acute lymphocytic leukemia (n = 14) or non-Hodgkin's lymphoma (n = 3). Each child received oral doses of weekly MTX (4.0-29 mg/m2) and daily 6-mercaptopurine (40-111 mg/m2). Plasma samples were collected daily from two children during the 1-week dose interval. A limited sampling strategy was designed, whereby 2 days of blood sampling were used in the other 15 patients. Morning urine samples were collected daily for 1 week following MTX intake from 14 of the children. MTX was detectable in all plasma and urine samples for the entire dose interval. The main metabolite, 7-OH-MTX, could be detected in plasma and urine from all patients on the first day after dose intake but only in a few patients during the whole dose interval. Interpatient variability of MTX and 7-OH-MTX levels was high at all points during the week. Significant correlation were found between the urinary MTX levels on days 2 and 7 and plasma MTX levels on day 2 after intake. No significant correlation was found between drug levels in plasma or urine and liver function tests in the children showing signs of mild liver injury. This assay provides a tool for further studies on the role of pharmacokinetics for the clinical effects of weekly oral low-dose MTX given alone or in combination with 6-mercaptopurine.

Publication Types: Clinical Trial

PMID: 8272008 [PubMed - indexed for MEDLINE]

Liver function studies in children with acute lymphocytic leukemia after cessation of therapy.

Bessho F, Kinumaki H, Yokota S, Hayashi Y, Kobayashi M, Kamoshita S.

Department of Pediatrics, University of Tokyo Hospital, Japan.

We investigated liver function in 27 children with acute lymphocytic leukemia (ALL) after cessation of therapy. Induction therapy consisted of prednisolone+vincristine (VP regimen) alone (16 patients) or with addition of daunorubicin (4 patients) or L-asparaginase (7 patients). Patients treated with VP regimen received short courses of VP regimen every 12 weeks for the first year of maintenance. Twenty-five patients remained in first complete remission and had completed 3-year maintenance therapy with methotrexate (MTX) and 6-mercaptopurine (6-MP) 1-7 years prior to this study. Twenty-three patients had received transfusions of packed red blood cells or fresh whole blood (1-11 units; median: 2 units) but none had evidence of either hepatitis B or hepatitis C. Alanine aminotransferase (ALT), which was measured every 3 months during maintenance therapy, had values more than three times the upper limit of the normal range in 25% of the measurements in more than half of the patients. However, by 3 months after the completion of maintenance therapy, ALT had normalized in all patients and remained normal in all but two patients until the time of this study. Serum bilirubin, serum albumin, and prothrombin time were all within normal limits. Fasting and 2-hour postprandial total serum bile acids were high in 5 of 13 patients and in 6 of 13 patients, respectively. The ratio of cholic acids+deoxycholic acids to chenodeoxycholic acids+lithocholic acids was below 1 in all but two patients, whereas this ratio was above 1 in all controls. Our bile acid profile results indicate the necessity of careful long-term follow-up of survivors of ALL treated with hepatotoxic chemotherapy during childhood.

PMID: 8202032 [PubMed - indexed for MEDLINE]

6-Mercaptopurine cumulative dose: a critical factor of maintenance therapy in average risk childhood acute lymphoblastic leukemia.

Dibenedetto SP, Guardabasso V, Ragusa R, Di Cataldo A, Miraglia V, D'Amico S, Ippolito AM.

Division of Pediatric Hematology-Oncology, University of Catania, Italy.

A multivariate survival analysis including gender, age, log white blood cell (WBC) count, liver and spleen size at diagnosis, mean log WBC count during maintenance therapy, and the prescribed cumulative doses of 6-mercaptopurine (6-MP), methotrexate (MTX), vincristine (VCR), and prednisone (PDN) during maintenance therapy was performed on 53 children with average-risk acute lymphoblastic leukemia (ALL). The 6-MP cumulative dose prescribed during maintenance therapy resulted in the most important statistically significant independent prognostic factor. Patients who received less than the median cumulative dose of 6-MP (86% of planned protocol dose) fared significantly worse than the other patients, regardless of WBC count at diagnosis, gender, age, and other factors studied. Therefore, 6-MP cumulative dose during maintenance therapy may be the critical factor for effective maintenance therapy in childhood ALL.

PMID: 8060809 [PubMed - indexed for MEDLINE]

Methotrexate and 6-mercaptopurine maintenance therapy for childhood acute lymphoblastic leukemia: dose adjustments by white cell counts or by pharmacokinetic parameters?

Schmiegelow K, Schroder H, Schmiegelow M.

Department of Pediatrics, University Hospital, Rigshospitalet, Copenhagen, Denmark.

In a consecutive study of 14 boys and 17 girls with non-B-cell ALL who were > or = 1 year of age at diagnosis, the degree of myelosuppression during the last year of MTX/6MP maintenance therapy was analyzed in relation to the erythrocyte concentration of MTX polyglutamates and 6-thioguanine nucleotides (E-MTX and E-6TGN, the respective major cytotoxic metabolites of MTX and 6MP). For each patient, E-MTX and E-6TGN levels were measured 2-15 (median, 6) and 2-17 (median, 7) times, respectively. From these measurements, arithmetic means of E-MTX and E-6TGN were calculated (mE-MTX and mE-6TGN, respectively). Since MTX and 6MP probably work synergistically, the product of mE-MTX and mE-6TGN was calculated for each patient (mE-MTX x 6TGN). The degree of myelosuppression was registered as the mean WBC determined following cessation of the therapy minus the mean WBC measured during the therapy (mWBCshift). The mean WBCs measured on therapy (mWBC(on)) and off therapy were highly correlated (r = 0.48, P = 0.009). The median mWBCshift was 2.7 x 10(9)/l (range, 1.4-4.8 x 10(9)/l). In a multivariate regression analysis, the best-fit model to predict the mWBCshift included mE-MTX x 6TGN, age at drug withdrawal, and mWBC in the order given [mWBCshift = 4.3 + 0.00089 x (mE-MTX x 6TGN) - 0.097 x age - 0.41 x mWBC(on); global rs = 0.66, P = 0.0002]. Thus, the patients with higher mE-MTX x 6TGN values, the younger patients, and the patients with the lowest WBC during therapy had the most pronounced degree of myelosuppression as measured by mWBCshift. These results indicate that E-MTX and E-6TGN may give a better reflection of the treatment intensity than do the WBCs alone.

PMID: 8004753 [PubMed - indexed for MEDLINE]

6-Thioguanine-induced growth arrest in 6-mercaptopurine-resistant human leukemia cells.

Morgan CJ, Chawdry RN, Smith AR, Siravo-Sagraves G, Trewyn RW.

Tulane University School of Medicine, Department of Surgery, New Orleans, Louisiana 70112.

The thiopurines 6-thioguanine (6TG) and 6-mercaptopurine (6MP) are cytotoxic to proliferating cells by a mechanism involving incorporation into DNA via the purine salvage pathway, and resistance to these agents can be conferred by lack of the salvage pathway enzyme hypoxanthine-guanine phosphoribosyltransferase. However, human and murine hypoxanthine-guanine phosphoribosyltransferase-deficient leukemia cell lines have been shown to respond to 6TG by growth arrest and differentiation by a mechanism apparently not involving incorporation of 6TG into DNA. If so, leukemia cells resistant to 6MP should still respond to 6TG by growth arrest via an undescribed epigenetic mechanism. To test this, polyclonal 6MP-resistant variants were produced from three human leukemia cell lines, HL-60, U937, and CCRF-CEM. Treatment of both sensitive and resistant cells with 6TG induced growth arrest. The effect of 6TG in the 6MP-sensitive HL-60 and U937 cells was associated with significant loss of viability and DNA fragmentation. In contrast, the 6TG-treated 6MP-resistant cells exhibited a slower decline in viability and no DNA fragmentation. To identify the mechanism by which 6TG may induce growth arrest, tRNA was isolated from 6MP-resistant cells cultured for 48 h with 6TG. 6TG was found to be incorporated into tRNAs normally containing queuine in the anticodon wobble position. These studies may provide a basis for the development of new therapeutic regimens for the treatment of leukemia.

PMID: 7923170 [PubMed - indexed for MEDLINE]

Mercaptopurine metabolism and risk of relapse in childhood lymphoblastic leukaemia.

Lilleyman JS, Lennard L.

Department of Haematology, Children's Hospital, Sheffield, UK.

Many months' treatment with daily oral mercaptopurine is an important part of therapy for nearly all children with lymphoblastic leukaemia (ALL). Even when prescribed the same dose based on body surface area, patients have widely different intracellular concentrations of drug metabolites. Whether this variation matters in terms of disease control is not yet clear. To find out, we followed up a large group of children with ALL in whom mercaptopurine-derived thioguanine nucleotides in the red cells were measured during treatment with an identical dose of mercaptopurine early in first remission. 172 unselected children (100 boys, 72 girls) were recruited between 1980 and 1992. At median follow-up of 5 years from diagnosis 42 (24%) had relapsed; 30 had erythrocyte thioguanine nucleotide concentrations below the group median (284 pmol per 8 x 10(8) erythrocytes) and 12 had values above the median. The actuarial relapse-free survival at 5 years was 63% in the below-median group and 84% in the above-median group (difference 21% [95% CI 3-39%], p = 0.0018). Multivariate analysis showed that erythrocyte thioguanine nucleotide concentration was independent of other prognostic variables including age, leukaemia immunophenotype, white-blood-cell count at diagnosis, trial protocol, and sex. Whatever the cause, in childhood ALL variable formation of intracellular mercaptopurine metabolites seems to be clinically important. Therapeutic schedules that include long-term daily oral mercaptopurine might be more effective if such metabolites are monitored.

PMID: 7909868 [PubMed - indexed for MEDLINE]

Intracellular metabolites of mercaptopurine in children with lymphoblastic leukaemia: a possible indicator of non-compliance?

Lennard L, Welch J, Lilleyman JS.

University of Sheffield Department of Medicine and Pharmacology, Royal Hallamshire Hospital, UK.

As part of a programme assessing the pharmacokinetics of oral thiopurines given for lymphoblastic leukaemia, we assayed intracellular metabolites of mercaptopurine in children from all over the United Kingdom who were given a standard dose of the drug. The metabolites we measured, thioguanine nucleotides and methylmercaptopurines, are products of two competing metabolic pathways and would be expected to show an inverse correlation. A total of 327 children from 17 centres in the UK were studied. All were on the same therapeutic schedule of mercaptopurine. All had been on an unattenuated full protocol-directed dose (at least 75 mg m-2) for a minimum of 7 days before assay. There was a very wide variation in the concentration of the two metabolites measured; the thioguanine nucleotides ranged from 0 to 1255 pmol per 8 x 10(8) red cells (median 289, lower quartile 210, upper quartile 377) and the methylmercaptopurine metabolites ranged from 0 to 46.3 nmol per 8 x 10(8) red cells (median 5.18, lower quartile 2.31, upper quartile 11.59). The anticipated negative correlation was not apparent, but the ratio between the two was not randomly distributed. No child had both metabolite concentrations in the upper quartiles, but in 32 (10%) children the concentration of both metabolites was in the lower quartile. Of the 32, only one metabolite was detected in four and none at all in six. The most likely explanation for these findings is that a minority of children with lymphoblastic leukaemia fail to take oral mercaptopurine either totally or intermittently. The extent of the problem is unknown, but we suspect it may be clinically important in at least 10% of patients.

PMID: 7547211 [PubMed - indexed for MEDLINE]

Methotrexate in neutrophils in children with acute lymphoblastic leukemia.

Schroder H.

Methotrexate (MTX) and 6-mercaptopurine (6-MP) are used for maintenance therapy of acute lymphoblastic leukemia (ALL) of childhood, and both are myelotoxic. Clinically the individual tolerance to the two drugs is variable. In order to study to what extent the MTX accumulation in circulating neutrophils is related to the absolute neutrophil count (ANC), neutrophils were isolated on a discontinuous two-step Percoll gradient in 16 children with ALL in maintenance therapy. The MTX concentration in the neutrophils was determined with a sensitive radioligand binding assay. In all children except one who admitted noncompliance, MTX was found in the neutrophils in concentrations (56-460 pmol/10(9) cells) positively correlated with the weekly dose of MTX (r = 0.51, p less than 0.01). The interindividual variation was large. Children with relatively low neutrophil MTX exhibited the widest intraindividual variation of neutrophil MTX upon reexamination during continued MTX administration with the same dosage schedule. Increases in the weekly dose of MTX resulted in proportional increases in the neutrophil MTX. In half the cases the ANC was less than 1.5 X 10(9)/l. The ANC was not related to the weekly MTX dose or the daily 6-MP dose. In children with ANC greater than 1.5 X 10(9)/l there was a significant inverse correlation between the ANC and the neutrophil MTX (r = -0.71, P less than 0.01), which was not found in the group of children with ANC less than 1.5 X 10(9)/l. These findings may be explained by differences in the kinetics of the granulopoiesis between children with high and children with low neutrophil counts.

PMID: 3474084 [PubMed - indexed for MEDLINE]

The effect of methotrexate on the bioavailability of oral 6-mercaptopurine.

Balis FM, Holcenberg JS, Zimm S, Tubergen D, Collins JM, Murphy RF, Gilchrist GS, Hammond D, Poplack DG.

Fourteen children (aged 3 to 14 years) with average-risk acute lymphoblastic leukemia were studied after an oral dose of 6-mercaptopurine (6-MP) (75 mg/m2) administered alone and, on the next day, concurrently with oral methotrexate (20 mg/m2). When 6-MP was administered alone, both the peak plasma concentration (15 to 150 ng X ml-1) and the AUC (36 to 340 ng X ml-1 X hr) were highly variable. Concurrent methotrexate resulted in a 31% increase in the AUC (P less than 0.01) and a 26% increase in peak plasma levels (P less than 0.05) of 6-MP. The AUC of methotrexate correlated with the degree of increase in 6-MP plasma concentrations. These findings are consistent with previous in vitro studies demonstrating that methotrexate is an inhibitor of xanthine oxidase, the enzyme that catabolizes 6-MP to the inactive metabolite thiouric acid. Although the increases in 6-MP AUC and peak plasma concentrations resulting from concurrent methotrexate administration were statistically significant, this interaction is probably not clinically significant at standard low oral doses of methotrexate in light of the wide interpatient variability in these pharmacokinetic parameters of 6-MP.

PMID: 3470165 [PubMed - indexed for MEDLINE]

The pharmacology of orally administered chemotherapy. A reappraisal.

Poplack DG, Balis FM, Zimm S.

Rational treatment of pediatric malignancies requires a detailed knowledge of the clinical pharmacology of those antineoplastic agents used therapeutically. A number of different agents are administered by the oral route. Recently, the clinical pharmacology of 6-mercaptopurine (6-MP) and methotrexate (MTX), the two agents that are the mainstay of maintenance chemotherapy in acute lymphoblastic leukemia (ALL), were investigated. Studies of oral 6-MP indicate that, contrary to previous information, the bioavailability of this drug is relatively poor after oral administration, and that plasma 6-MP concentrations achieved after uniform oral dosing are highly variable. Similarly, study of the pharmacology of orally administered MTX indicates that there is little correlation between MTX dose and the peak serum level achieved. These findings suggest that some patients may not be exposed to adequate systemic concentrations of 6-MP and/or MTX after oral administration, and raise the possibility that the development of relapse in some patients with ALL may be the result of a pharmacologic failure of oral maintenance therapy. A comprehensive prospective study of the clinical pharmacology of MTX and 6-MP in patients with ALL undergoing maintenance chemotherapy is currently in progress.

PMID: 3459570 [PubMed - indexed for MEDLINE]

Bioavailability of low-dose vs high-dose 6-mercaptopurine.

Arndt CA, Balis FM, McCully CL, Jeffries SL, Doherty K, Murphy R, Poplack DG.

Pediatric Branch, National Cancer Institute, Bethesda, MD 20892.

The bioavailability of oral 6-mercaptopurine (6MP) at standard doses is very low, largely as a result of extensive first-pass metabolism by xanthine oxidase. Fewer than one third of patients achieve 6MP plasma concentrations known to be cytocidal in vitro (greater than 1 mumol/L). Studies in vitro have suggested that first-pass metabolism can be saturated at higher doses of 6MP. To determine whether saturation occurs in vivo at clinically used doses and whether bioavailability can be enhanced by increasing the dose, the bioavailability of different doses of 6MP was studied first in rhesus monkeys and then in children with acute lymphoblastic leukemia in remission. In monkeys a higher dose of 6MP resulted in enhanced bioavailability, whereas in patients the mean relative bioavailability at the higher dose was significantly less. However, all patients achieved cytocidal (greater than 1 to 10 mumol/L) plasma concentrations at the higher dose without manifesting significant clinical toxicity. Therefore cytocidal levels of 6MP can be achieved in patients with oral 6MP without the risk of unexpectedly high levels caused by saturation of first-pass metabolism.

PMID: 3365920 [PubMed - indexed for MEDLINE]

Influence of food intake on bioavailability of oral 6-mercaptopurine in children with acute lymphoblastic leukemia.

Riccardi R, Balis FM, Ferrara P, Lasorella A, Poplack DG, Mastrangelo R.

Division of Pediatric Oncology, Catholic University of Rome, Italy.

Plasma levels of 6-mercaptopurine (6-MP) were measured after oral administration in 17 children with acute lymphoblastic leukemia (ALL). In the fasting state or after a breakfast consisting of 250 ml milk and 50 g biscuits, 6-MP was administered at a dose of 75 mg/m2. In patients studied in a fasting state, the mean time to plasma peak (tmax) level was 1.2 h, whereas in patient studied after breakfast the mean tmax was 2.3 h. This difference is statistically significant (p less than 0.001). Moreover, the 6-MP peak plasma concentration (cmax) and the areas under the plasma concentration time curves (AUC) were significantly reduced when the drug was administered after breakfast. The mean Cmax +/- SD were 0.98 +/- 0.54 microM and 0.63 +/- 0.48 microM, respectively (p less than 0.05). The mean 6-MP AUC +/- SD in patients studied in a fasting state and after breakfast were 143 +/- 69 microM min and 105 +/- 68 microM, respectively (p less than 0.01). These results indicated that 6-MP should be taken in a fasting state to optimize drug absorption in children undergoing chemotherapy for ALL.

PMID: 3153245 [PubMed - indexed for MEDLINE]

Chronopharmacokinetics of oral methotrexate and 6-mercaptopurine: is there diurnal variation in the disposition of antileukemic therapy?

Balis FM, Jeffries SL, Lange B, Murphy RF, Doherty KM, Arndt CA, Luery N, Poplack DG.

Pediatric Branch, National Cancer Institute, Bethesda, Maryland 20892.

The chronopharmacokinetics of the orally administered antileukemic drugs, 6-mercaptopurine and methotrexate, were examined in 13 children with acute lymphoblastic leukemia (ALL) to establish if there is a pharmacokinetic basis for the lower relapse rate associated with administration of these agents in the evening. Children with ALL in complete remission had plasma drug concentrations monitored for 8 h following an oral dose of either methotrexate or 6-mercaptopurine administered in the morning (8 a.m.) and the evening (8 p.m.). Total drug exposure to oral methotrexate, as measured by the mean area under the plasma concentration-time curve (AUC), was 2.75 microM.h following the morning dose and 2.77 microM.h in the evening. For 6-mercaptopurine, the mean morning AUC (198 ng.h/ml) was higher than that following the evening dose (167 ng.h/ml) (p greater than 0.05); but compared to the wide interpatient variability observed with this drug, this 20% difference is not likely to be clinically significant. These results indicate that the suggested benefit of evening drug administration is not likely to be a result of diurnal variation in drug disposition.

PMID: 2782561 [PubMed - indexed for MEDLINE]

Oral mercaptopurine in childhood leukemia: influence of food intake on bioavailability.

Lonnerholm G, Kreuger A, Lindstrom B, Myrdal U.

Department of Pediatrics, Uppsala University, Akademiska Sjukhuset, Sweden.

Plasma concentrations of 6-mercaptopurine (6-MP) were determined by gas chromatography-mass spectrometry. Ten children (nine with acute lymphatic leukemia) were studied on 2 consecutive days after oral intake of 6-MP. On one day the drug was administered in the fasting state and on the other (in random order) together with breakfast. The peak plasma concentrations of 6-MP after the dose intake with breakfast in percent of that in the fasting state (meal in % of fasting for each individual) varied between 33 and 181% (mean 111), and the area under the plasma concentration-time curve varied between 47 and 186% (mean 103). Thus, there were considerable variations among patients, but, for the group as a whole, there were no statistically significant differences between the two experimental conditions. This study cannot therefore form the basis for a recommendation as to whether 6-MP should be administered on an empty stomach or together with food.

Publication Types: Clinical Trial Randomized Controlled Trial

PMID: 2702064 [PubMed - indexed for MEDLINE]

Milk could decrease the bioavailability of 6-mercaptopurine.

Rivard GE, Lin KT, Leclerc JM, David M.

Centre de Recherche Pediatrique, Hopital Sainte-Justine, Montreal, Quebec, Canada.

The bioavailability of 6-mercaptopurine (6-MP) administered orally for maintenance therapy of children with acute lymphoblastic leukemia is highly variable. Xanthine oxidase (XO) can transform 6-MP into 6-thioxanthine (6-TX) and 6-thiouric acid (6-TUA), which have no therapeutic value. XO is found in high concentration in cow's milk. Incubation at 37 degrees C for 30 min with commercial preparations of pasteurized cow's milk results in transformation of 30% of a clinically relevant concentration of 6-MP into 6-TUA. Milk boiled for 5 min has no effect on the 6-MP. Addition of gastric juice at ratios likely to be seen in children has negligible inhibitory effect on the 6-MP destroying activity of milk. Conversely, folic acid and allopurinol markedly inhibit this effect at clinically relevant concentrations. These observations may help to optimize modalities of administration of 6-MP.

PMID: 2618973 [PubMed - indexed for MEDLINE]

Variability of 6-mercaptopurine pharmacokinetics during oral maintenance therapy of children with acute leukemia.

Lafolie P, Bjork O, Hayder S, Ahstrom L, Peterson C.

Department of Clinical Pharmacology, Karolinska Hospital, Stockholm, Sweden.

The effects of some environmental and genetic factors on the inter- and intraindividual variations of 6-mercaptopurine (6-MP) pharmacokinetics were studied in children on oral remission maintenance therapy for acute lymphoblastic leukemia or non-Hodgkin's lymphoma. Blood samples were obtained 0-4 h after drug intake. 6-MP concentrations were determined in plasma and in erythrocyte concentrates. The influence of food on the pharmacokinetics was examined in a prospective study of 15 children. Each child was examined four times, twice in the fasted state and twice after intake of a standardized, milky, breakfast. There were pronounced inter- and intraindividual variations. Food intake seemed to reduce these variations but there were no significant changes in peak concentrations and area under the plasma concentration vs time curves (AUC) between the fasted and fed states. Food intake reduced the time to peak concentration both in plasma, from 1.8 h to 1.1 h (P less than 0.01) and in red blood cells, from 1.8 h to 1.3 h (P less than 0.01). Retrospective subdivision of the patients indicated a tendency for different pharmacokinetic patterns according to dose; five out of seven patients receiving greater than 70 mg m-2 had a higher AUC in the fasting state, while five out of eight patients receiving less than 70 mg m-2 had a higher AUC in the fed state. The cytochrome P-450-dependent hydroxylation capacity was evaluated with debrisoquine but no correlation was found to the pharmacokinetics of 6-MP.

PMID: 2615529 [PubMed - indexed for MEDLINE]

Disposition of oral methotrexate in children with acute lymphoblastic leukemia and its relation to 6-mercaptopurine pharmacokinetics.

Koren G, Solh H, Klein J, Soldin SJ, Greenberg M.

Division of Hematology-Oncology, Toronto, Ontario, Canada.

We studied the disposition pharmacokinetics of methotrexate (MTX) given orally to 16 children with acute lymphoblastic leukemia (ALL) and its relation to the pharmacokinetics of 6-mercaptopurine (6MP) in the same children. There was an eightfold variability in area-under-concentration time-curve (AUC) of MTX achieved by the same dose. Excellent correlation existed between peak concentrations and AUC0----infinity (r = 0.95, P less than 0.001). Elimination T1/2 was between 1.34 and 5 hours (mean 2.16 +/- 0.23 hr, mean +/- SE). A weak correlation existed between AUC achieved by 1 mg/m2 MTX and patients' age or body weight. Weak but significant correlation existed between AUC achieved by 1 mg/m2 of MTX vs. 6MP (r = 0.54, P less than 0.05). In 13/16 patients peak concentrations were achieved at 60 minutes. There was a significantly larger AUC of 6MP achieved by a standardized dose in longer therapy (greater than 15 mo) vs. short therapy (less than 12 mo) (462 +/- 75 and 246 +/- 58 ng.ml-1.min.mg-1.m2, P less than 0.025). No statistical differences in AUC of MTX were found between short and long therapy. The large interpatient variability in MTX pharmacokinetics supports the possibility that differences in absorption and/or clearance of the drug may affect the clinical response. Because of the excellent correlation between peak and AUC of MTX, and because 3 measurements, at 30, 60, and 90 minutes will almost invariably identify the peak, this measurement can be used to estimate AUC for purpose of correlation with clinical outcome.

PMID: 2586358 [PubMed - indexed for MEDLINE]

Purine de novo synthesis as the basis of synergism of methotrexate and 6-mercaptopurine in human malignant lymphoblasts of different lineages.

Bokkerink JP, Bakker MA, Hulscher TW, De Abreu RA, Schretlen ED.

Department of Pediatrics, St Radboud Hospital, University of Nijmegen, The Netherlands.

Methotrexate (MTX) causes an inhibition of purine de novo synthesis (PDNS), resulting in increased intracellular availability of 5-phosphoribosyl-1-pyrophosphate (PRPP) in human malignant lymphoblasts with an active PDNS. Normal bone marrow cells and peripheral blood lymphocytes lack this capacity. The increased levels of PRPP can be used for enhanced incorporation of 6-mercaptopurine (6MP), indicating a potential time-, sequence- and dose-dependent synergism of both drugs. The effects of 0.02 microM and 0.2 microM MTX on the PDNS of MOLT-4 (T-), RAJI (B-) and KM-3 (non-B-non-T-) human malignant lymphoblasts were studied with respect to PRPP levels, aminoimidazolecarboxamide ribonucleosidemonophosphate (AICAR) levels and the incorporation of labeled glycine into purine metabolites. These results were correlated with the activity of the PDNS (labeled glycine incorporation) and the purine salvage pathway (labeled hypoxanthine incorporation) in untreated cells. Inhibition of PDNS by 0.02 microM MTX was complete in KM-3 cells with a moderately active PDNS and salvage pathway. RAJI cells, with a relatively low PDNS and high salvage pathway, demonstrated an incomplete, but increasing inhibition of PDNS, whereas inhibition of PDNS in MOLT-4 cells with both pathways active was minimal and recovered in time. Treatment with 0.2 microM MTX resulted in a complete inhibition of PDNS in all cell lines. After treatment with MTX an enhanced incorporation of labeled hypoxanthine and 6MP was noticed, confirming the potential rescue from MTX cytotoxicity by hypoxanthine and a potential synergism of MTX and 6MP on cytotoxicity. The enhanced incorporation of 6MP was more obvious in RAJI and KM-3 cells in comparison with MOLT-4 cells. These data demonstrate the important role of both the activities of the PDNS and the purine salvage pathway in malignant lymphoblasts of different subclasses with respect to the synergism of MTX and 6MP.

PMID: 2455519 [PubMed - indexed for MEDLINE]

Systemic exposure to mercaptopurine as a prognostic factor in acute lymphocytic leukemia in children.

Comment in: N Engl J Med. 1990 Nov 29;323(22):1565-6.

Koren G, Ferrazini G, Sulh H, Langevin AM, Kapelushnik J, Klein J, Giesbrecht E, Soldin S, Greenberg M.

Division of Clinical Pharmacology, Hospital for Sick Children, Toronto, ON, Canada.

BACKGROUND. Despite a success rate of more than 90 percent in inducing remission in children with acute lymphocytic leukemia, 30 to 40 percent of such children relapse. Maintenance therapy during remission usually includes oral mercaptopurine and methotrexate. Recently, wide variability in the bioavailability of oral mercaptopurine has been demonstrated, and there is concern that this may affect the risk of relapse. METHODS. To investigate whether lower systemic exposure to mercaptopurine may increase the risk of relapse in acute lymphocytic leukemia, we prospectively studied 23 children receiving maintenance therapy. On the basis of disease features, 11 were classified as being at low risk of relapse, and 12 at standard risk. Those who relapsed (n = 10) did not differ from those who did not in their mean age, hemoglobin level, mean daily dose of mercaptopurine and weekly dose of methotrexate, or the total number of days during which mercaptopurine and methotrexate therapy was interrupted. RESULTS. There was a significant difference in the mean (+/- SEM) area under the mercaptopurine concentration-time curve achieved by a dose of 1 mg of mercaptopurine per square meter of body-surface area: 1636 +/- 197 nmol per liter x minutes in those who relapsed, as compared with 2424 +/- 177 nmol per liter x minutes in those who did not (P less than 0.005). This caused a significantly lower total daily systemic exposure to mercaptopurine in those who relapsed (104,043 +/- 12,812 nmol per liter x minutes) than in those who did not (168,862 +/- 18,830 nmol per liter x minutes) (P less than 0.005). An identical tendency prevailed when patients at low risk and patients at standard risk were analyzed separately. Kaplan-Meier analysis revealed that children in whom an area under the curve of less than 1971 nmol per liter x minutes was achieved by a dose of 1 mg of mercaptopurine per square meter had a significantly poorer prognosis than those with larger areas under the curve (P less than 0.01). Similarly, those with a total daily systemic exposure of more than 137,970 nmol per liter x minutes had a significantly better prognosis than those with a lower exposure (P less than 0.005). CONCLUSIONS. Low systemic exposure to oral mercaptopurine during maintenance therapy for acute lymphocytic leukemia in childhood adversely affects prognosis. Children should be studied at the beginning of maintenance therapy to establish the pharmacokinetics of mercaptopurine, and the dose should be tailored to achieve an appropriate systemic exposure.

PMID: 2355954 [PubMed - indexed for MEDLINE]

Maintenance chemotherapy for childhood acute lymphoblastic leukemia: should dosage be guided by white blood cell counts?

Schmiegelow K, Pulczynska MK.

Department of Pediatrics, University Hospitals, Copenhagen, Denmark.

In a retrospective population-based study of 122 children with non-B-cell acute lymphoblastic leukemia (ALL), we analyzed the relation between risk of relapse and the degree of leukopenia achieved during oral methotrexate (MTX) and 6-mercaptopurine (6MP) maintenance chemotherapy (MT). After a median follow-up of 62 months for patients still in remission, 43 patients had relapsed (including 28 bone marrow relapses). Patients with a mean white blood cell count during MT (mWBCMT) of less than or equal to 3.5 x 10(9)/L had a significantly lower risk of hematological relapse (p = 0.007) as well as of any relapse (p = 0.02) compared to patients with higher mWBCMT. The clinical advantage of leukopenia could be demonstrated for all risk groups and was not explained by differences in year of diagnosis, gender, age, and white blood cell count at diagnosis, or the prescribed dose of MTX and 6MP. Although prospective studies are needed to establish the benefit of upward dose adjustments to achieve leukopenia, these results indicate a clinical advantage of keeping WBCs low during MT.

PMID: 2285127 [PubMed - indexed for MEDLINE]

Fat body mass and pharmacokinetics of oral 6-mercaptopurine in children with acute lymphoblastic leukemia.

Zuccaro P, Guandalini S, Pacifici R, Pichini S, Di Martino L, Guiducci M, Giuliano M, Di Tullio MT, Pettoello Mantovani M.

Department of Pediatrics, University of Naples, Italy.

To evaluate the reasons for the wide variability in bioavailability of orally administered 6-mercaptopurine in children with acute lymphoblastic leukemia, we studied several pharmacokinetic parameters of the drug in 18 affected children receiving remission maintenance therapy, and compared them with their anthropometric data and with the results of intestinal function tests. No correlation was found between estimates of small intestinal absorption (the oral lactose tolerance test and 1 h blood xylose test) and 6-mercaptopurine serum levels. Of the anthropometric measurements considered, only the weight/height percentile (an index of the fat body mass) strongly and linearly correlated with the area under the curve of 6-mercaptopurine. The dose of 75 mg of 6-mercaptopurine/m2 of body surface resulted in higher serum concentrations in children below the 75th percentile than in those with a weight/height ratio exceeding the 75th percentile. In conclusion, these data caution about the risk of underdosing 6-mercaptopurine in overweight children when administering it on the basis of body surface area.

PMID: 2057989 [PubMed - indexed for MEDLINE]

Importance of 6-mercaptopurine dose in lymphoblastic leukaemia.

Hale JP, Lilleyman JS.

Department of Haematology, Children's Hospital, Western Bank, Sheffield.

To explore the possibility that higher total dosage of 'maintenance' treatment may have contributed to the recent improvement in outlook of children in the United Kingdom with lymphoblastic leukaemia, details of the amount of 6-mercaptopurine prescribed during the first two years of treatment were studied in an unselected cohort of children diagnosed between 1973 and 1987. Eighty five patients were studied, 30 diagnosed before and 55 after 1980. The group diagnosed after 1980 showed an 18% improvement in relapse free survival at five years. Their median total dose of 6-mercaptopurine had increased by 22%, whereas according to the protocol it should have risen by an average of only 9%. After 1980 boys were prescribed significantly more 6-mercaptopurine than girls, and had fewer dose reductions because of myelosuppression. These findings support the clinical impression that after 1980 an important therapeutic difference resulting from the new United Kingdom acute lymphoblastic leukaemia protocols was an increase in the amount of 6-mercaptopurine that children actually received as a result of changes in prescribing guidelines rather than dose. They also provide further evidence that boys tolerate 6-mercaptopurine better than girls, which may be related to the still unexplained difference in prognosis between the sexes.

PMID: 2031601 [PubMed - indexed for MEDLINE]

Intraindividual variation in 6-mercaptopurine pharmacokinetics during oral maintenance therapy of children with acute lymphoblastic leukaemia.

Lafolie P, Hayder S, Bjork O, Peterson C.

Department of Clinical Pharmacology, Karolinska Hospital, Stockholm, Sweden.

Intraindividual variation in 6-mercaptopurine (6-MP) kinetics has been little studied. It has now been examined in 18 children with acute lymphoblastic leukaemia (ALL). On 2 to 4 occasions in each patient drug concentrations in plasma and red cells were followed for 4 h after administration by means of HPLC. The mean individual coefficient of variation (C.V.) in AUC was 57.9% and it was not related to dose or concentration. The variation was the same in plasma and in red cells. It is concluded that regular monitoring of 6-mercaptopurine concentration would identify periods when a patient deviates strongly from the mean range. Both undertreatment and concentration-dependent toxicity could then be corrected.

PMID: 1884741 [PubMed - indexed for MEDLINE]

Dose-dependent kinetics of orally administered 6-mercaptopurine in children with leukemia.

Kato Y, Matsushita T, Chiba K, Hijiya N, Yokoyama T, Ishizaki T.

Department of Hospital Pharmacy, Clinical Research Institute, National Medical Center, Tokyo, Japan.

To determine whether the pharmacokinetics of 6-mercaptopurine (6-MP) would show dose dependency, we studied three different single oral doses in eight children (aged 3.6 to 15.1 years) with acute leukemia in remission. Marked interindividual differences in maximum plasma concentration (Cmax) and the area under the plasma concentration-time curve (AUC) were observed when children received the 50 mg/m2 dose. This variability decreased when the doses were increased. Six of the eight children showed a disproportionate increase in the AUC with increasing doses; the other two had a proportionate relationship between the AUC and dose. Overall mean (+/- SD) Cmax and AUC values increased disproportionately (88 +/- 123, to 326 +/- 194, to 653 +/- 344 ng/ml for Cmax, and 147 +/- 180, to 451 +/- 177, to 1291 +/- 415 ng/ml per hour for AUC, respectively) when the dose increased from 50 to 87.5 mg/m2 and then to 175 mg/m2. The results suggest that a saturable first-pass metabolism of oral 6-MP occurs with increasing oral doses in some, but not all, children. Whether and to what extent this pharmacokinetic character of oral 6-MP affects the interindividual difference in systemic exposure to the drug in children with leukemia receiving maintenance therapy require further studies.

PMID: 1861221 [PubMed - indexed for MEDLINE]

Prognostic significance of methotrexate and 6-mercaptopurine dosage during maintenance chemotherapy for childhood acute lymphoblastic leukemia.

Erratum in: Pediatr Hematol Oncol 1992 Apr-Jun;9(2):following 198

Schmiegelow K.

Department of Pediatrics, University Hospital, Copenhagen, Denmark.

Tolerance of full-dose methotrexate/6-mercaptopurine (MTX/6MP) maintenance therapy for childhood acute lymphoblastic leukemia (ALL) without side effects could reflect insufficient systemic drug exposure, and drug withdrawals due to toxicity might reduce the chance of cure. The present study included 122 children with non-B cell acute lymphoblastic leukemia with a median follow-up of 84 months. Leukopenia and hepatotoxicity were calculated as weighted means of all white cell counts and all serum aminotransferase measurements, respectively, registered for each patient. Forty-five patients relapsed (30 in bone marrow). Patients tolerating an average dose of MTX of more than 75% of the recommended protocol doses and having cumulated drug withdrawals of less than 1% of the period of maintenance therapy had an increased risk of hematological relapse (p = 0.008) as well as of any relapse (p = 0.03) when compared to the remaining patients. Patients with a cumulative withdrawal of MTX or of 6MP for greater than 10% of the maintenance therapy period had an increased risk of hematological relapse (MTX: p = 0.009, 6MP: p less than 0.0001) and of any relapse (MTX: p = 0.16, 6MP: p = 0.0002). Liver toxicity was the main reason for cumulative long-term drug withdrawals. However, patients with a mean aminotransferase level above the upper normal limit (40 IU/l) who were kept on therapy (cumulative withdrawals of neither drug for more than 5% of their maintenance therapy period) had a significantly lower risk of hematological relapse (p = 0.02) as well as of any relapse (p = 0.06) than the remaining children. The concept of treating to toxicity seems warranted for maintenance therapy of childhood lymphoblastic leukemia.

PMID: 1782110 [PubMed - indexed for MEDLINE]

Chronopharmacology of methotrexate pharmacokinetics in childhood leukemia.

Koren G, Ferrazzini G, Sohl H, Robieux I, Johnson D, Giesbrecht E.

Division of Clinical Pharmacology, Hospital for Sick Children, Toronto, Ontario, Canada.

Survival has been shown to improve when maintenance therapy for acute lymphocytic leukemia in children is given at night rather during the day. We examined the possibility that diurnal variation in methotrexate pharmacokinetics may contribute to this improvement. In a crossover study, we determined the pharmacokinetics of intravenous methotrexate at 10:00 and 21:00 h in six children with standard or high-risk leukemia. During the study, children refrained from concomitant drugs (6-mercaptopurine and trimethoprim sulfamethoxazole). There was a significant fall in methotrexate plasma clearance at night (from 5.6 +/- 3 ml/min/kg to 4.7 +/- 2.3 ml/min/kg p < 0.05). Renal clearance of methotrexate tended to decrease at night and unbound renal clearance decreased significantly (from 17.5 +/- 1.7 ml/min/kg to 8.5 +/- 3.6 ml/min/kg p < 0.05). Creatinine clearance did not exhibit diurnal variation, when comparing two 12-h collections, but there was a significant decrease in the nonglomerular clearance of methotrexate (from 14.8 +/- 5.2 to 6 +/- 4 ml/min/kg). Because it is a weak organic acid, the tubular secretion of methotrexate depends on urinary pH. At night urinary pH is more acidic. This may result in more reabsorption and hence reduced renal clearance.

PMID: 1473196 [PubMed - indexed for MEDLINE]

On the biochemical modulation of 6-mercaptopurine by methotrexate in murine WEHI-3b leukemia cells in vitro.

Liliemark J, Pettersson B, Peterson C.

Department of Medicine, Karolinska Institute, Huddinge Hospital, Stockholm, Sweden.

The chemicals 6-mercaptopurine (6-MP) and methotrexate (MTX) are the cornerstones in the maintenance treatment of acute lymphoblastic leukemia. The intracellular metabolism of 6-MP to 6-thioguanosine nucleotides (TGN) via 6-thioinosine 5'-monophosphate (TIMP) is crucial for its cytotoxic effect. MTX inhibits purine de novo synthesis and thereby increases the intracellular PRPP being a substrate for the phosphoribosylation of 6-MP to TIMP. Hypoxanthine has been shown to inhibit the uptake of 6-MP over the cell membrane and the phosphoribosylation of 6-MP to TIMP. We have previously shown that the conversion of TIMP to TGN decreases at 6-MP concentrations above 5 microM in vitro. The aim of the present study was therefore to investigate the effect of MTX increasing the PRPP and TIMP concentrations and of hypoxanthine decreasing the TIMP concentration on the formation of TGN from TIMP. Murine myelomonocytic leukemia cells (WEHI-3b) were treated with 6-MP in vitro. The drug concentration was kept constant by continuous addition of 6-MP during the experiment. With this technique, the concentration of TGN begins to decrease already at 6-MP concentrations above 2 microM. The addition of 0.2 microM MTX 6 h before 6-MP strongly inhibited the purine de novo synthesis, decreased the ATP, and increased the PRPP concentration 4-fold. The intracellular concentrations of TIMP and to a lesser extent TXMP also increased. The concentrations of the TGN were, however, basically unaffected by the preincubation with MTX. Simultaneous addition of 20-50 microM hypoxanthine and 6-MP decreased the accumulation of all cellular 6-MP metabolites. It is concluded that the synergistic cytotoxic effect of the combination of 6-MP and MTX is not based on biochemical modulation of the 6-MP metabolism by MTX.

PMID: 1373210 [PubMed - indexed for MEDLINE]