title: Variable mercaptopurine metabolism and treatment outcome in childhood lymphoblastic leukemia.
abstract: Intracellular thioguanine nucleotides (6-TGN) are the major cytotoxic metabolites of mercaptopurine (6-MP). Red blood cell (RBC) 6-TGN concentrations were measured in a group of 120 consecutive children with lymphoblastic leukemia (ALL) to assess interpatient variability and its clinical importance. Assays were performed after at least 2 months 6-MP maintanance chemotherapy and a minimum 7 days unattenuated protocol dose of 75 mg/m2. Observed 6-TGN concentrations ranged from 126 to 832 pmol/8 x 10(8) RBCs (median, 275). There was a correlation between 6-TGN and neutropenia 14 days postassay (rs = .51; P less than .0005), and an inverse correlation between 6-TGN and the length of time uninterrupted full protocol dose was tolerated without neutropenia (rs = -.3; P less than .01). After a median follow-up of 49 months, 19 children had relapsed, of whom 17 (89%) had 6-TGN concentrations below the group median (log-rank chi 2 = 11.9; P less than .001). Multivariate analysis using Cox's proportional hazards regression showed the 6-TGN effect on disease control to be independent of diagnostic WBC count, sex, age, immunological cell type, French-American-British (FAB) type, variation in other antineoplastic therapy, and duration of remission at the time of 6-TGN assay. Children with ALL taking the same dose of 6-MP show great variability in its measurable cytotoxic effect, and this variability is apparently important in predicting treatment outcome.
authors.affiliation: Department of Pharmacology and Therapeutics, University of Sheffield, United Kingdom.
authors.forename: L
authors.initials: L
authors.lastname: Lennard
authors.forename: J S
authors.initials: JS
authors.lastname: Lilleyman
mesh_terms: D000293:Adolescent; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D002648:Child; D002675:Child, Preschool; D004912:Erythrocytes / Q000378:metabolism; D006801:Humans; D007958:Leukocyte Count; D015122:Mercaptopurine / Q000008:administration & dosage / Q000378:metabolism*; D008727:Methotrexate / Q000008:administration & dosage; D009504:Neutrophils / Q000166:cytology; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy / Q000378:metabolism*; D011379:Prognosis; D016019:Survival Analysis; D013866:Thioguanine / Q000097:blood*
chemical_list: D015122:Mercaptopurine; D013866:Thioguanine; D008727:Methotrexate