title: DNA-thioguanine nucleotide concentration and relapse-free survival during maintenance therapy of childhood acute lymphoblastic leukaemia (NOPHO ALL2008): a prospective substudy of a phase 3 trial.
abstract: Adjustment of mercaptopurine and methotrexate maintenance therapy of acute lymphoblastic leukaemia by leucocyte count is confounded by natural variations. Cytotoxicity is primarily mediated by DNA-incorporated thioguanine nucleotides (DNA-TGN). The aim of this study was to establish whether DNA-TGN concentrations in blood leucocytes during maintenance therapy are associated with relapse-free survival.
  
  
  
  In this substudy of the NOPHO ALL2008 phase 3 trial done in 23 hospitals in seven European countries (Denmark, Estonia, Finland, Iceland, Lithuania, Norway, and Sweden), we analysed data from centralised and blinded analyses of 6-mercaptopurine and methotrexate metabolites in blood samples from patients with non-high-risk childhood acute lymphoblastic leukaemia. Eligible patients were aged 1·0-17·9 years; had been diagnosed with non-high-risk precursor B-cell or T-cell leukaemia; had been treated according to the Nordic Society of Pediatric Hematology and Oncology ALL2008 protocol; and had reached maintenance therapy in first remission. Maintenance therapy was (mercaptopurine 75 mg/m2once per day and methotrexate 20 mg/m2once per week, targeted to a leucocyte count of 1·5-3·0 × 109cells per L). We measured DNA-TGN and erythrocyte concentrations of TGN nucleotides, methylated mercaptopurine metabolites, and methotrexate polyglutamates. The primary objective was the association of DNA-TGN concentrations and 6-mercaptopurine and methotrexate metabolites with relapse-free survival. The secondary endpoint was the assessment of DNA-TGN concentration and 6-mercaptopurine and methotrexate metabolites during maintenance therapy phase 2.
  
  
  
  Between Nov 26, 2008 and June 14, 2016, 1509 patients from the NOPHO ALL2008 study were assessed for eligibility in the DNA-TGN substudy, of which 918 (89%) of 1026 eligible patients had at least one DNA-TGN measurement and were included in the analyses. Median follow-up was 4·6 years (IQR 3·1-6·1). Relapse-free survival was significantly associated with DNA-TGN concentration (adjusted hazard ratio 0·81 per 100 fmol/μg DNA increase, 95% CI 0·67-0·98; p=0·029). In patients with at least five blood samples, erythrocyte concentrations of TGN, methylated mercaptopurine metabolites, and methotrexate polyglutamates were associated with DNA-TGN concentration (all p<0·0001).
  
  
  
  Our results suggest the need for intervention trials to identify clinically applicable strategies for individualised drug dosing to increase DNA-TGN concentration, and randomised studies to investigate whether such strategies improve cure rates compared with current dose adjustments based on white blood cell counts.
  
  
  
  Danish Cancer Society, Childhood Cancer Foundation (Denmark), Childhood Cancer Foundation (Sweden), Nordic Cancer Union, Otto Christensen Foundation, University Hospital Rigshospitalet, and Novo Nordic Foundation.
authors.affiliation: Department of Pediatrics and Adolescent Medicine, University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Stine Nygaard
authors.initials: SN
authors.lastname: Nielsen
authors.affiliation: Department of Pediatrics and Adolescent Medicine, University Hospital, Rigshospitalet, Copenhagen, Denmark; Section of Biostatistics, Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Kathrine
authors.initials: K
authors.lastname: Grell
authors.affiliation: Department of Pediatrics and Adolescent Medicine, University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Jacob
authors.initials: J
authors.lastname: Nersting
authors.affiliation: Department of Pediatrics, Institution for Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Jonas
authors.initials: J
authors.lastname: Abrahamsson
authors.affiliation: Department of Pediatrics, St Olavs Hospital, Trondheim, Norway; Department of Laboratory Medicine, Children's and Women's Health, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: Bendik
authors.initials: B
authors.lastname: Lund
authors.affiliation: Children's Hospital, Helsinki University Central Hospital and University of Helsinki, Helsinki, Finland.
authors.forename: Jukka
authors.initials: J
authors.lastname: Kanerva
authors.affiliation: Pediatric Hematology-Oncology, Barnaspitali Hringsins, Landspitali University Hospital, Reykjavik, Iceland.
authors.forename: Ólafur Gísli
authors.initials: ÓG
authors.lastname: Jónsson
authors.affiliation: Centre for Paediatric Oncology and Haematology, University Children's Hospital, Vilnius, Lithuania.
authors.forename: Goda
authors.initials: G
authors.lastname: Vaitkeviciene
authors.affiliation: Department of Oncology and Haematology, Tallinn Children's Hospital, Tallinn, Estonia.
authors.forename: Kaie
authors.initials: K
authors.lastname: Pruunsild
authors.affiliation: Department of Pediatrics and Adolescent Medicine, University Hospital, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Lisa Lyngsie
authors.initials: LL
authors.lastname: Hjalgrim
authors.affiliation: Department of Pediatrics and Adolescent Medicine, University Hospital, Rigshospitalet, Copenhagen, Denmark; Institute of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark. Electronic address: kjeld.schmiegelow@regionh.dk.
authors.forename: Kjeld
authors.initials: K
authors.lastname: Schmiegelow
mesh_terms: D000293:Adolescent; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000097:blood* / Q000627:therapeutic use*; D002648:Child; D002675:Child, Preschool; D004247:DNA / Q000737:chemistry*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007223:Infant; D008297:Male; D015122:Mercaptopurine / Q000008:administration & dosage; D008727:Methotrexate / Q000008:administration & dosage / Q000031:analogs & derivatives; D009364:Neoplasm Recurrence, Local / Q000097:blood / Q000188:drug therapy / Q000401:mortality*; D009367:Neoplasm Staging; D011099:Polyglutamic Acid / Q000008:administration & dosage / Q000031:analogs & derivatives; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000097:blood / Q000188:drug therapy / Q000401:mortality*; D011379:Prognosis; D011446:Prospective Studies; D015996:Survival Rate; D013866:Thioguanine / Q000097:blood* / Q000737:chemistry
chemical_list: D011099:Polyglutamic Acid; C014085:methotrexate polyglutamate; D004247:DNA; D015122:Mercaptopurine; D013866:Thioguanine; D008727:Methotrexate