title: Combination therapy in childhood leukaemia: in vitro studies of thiopurines and inhibitors of purine metabolism on apoptosis.
abstract: BACKGROUND
  Methotrexate (MTX) followed by 6-mercaptopurine (6MP) is one of the best known combinations for the treatment of childhood acute lymphoblastic leukaemia. Tiazofurin (TF) and 6-thioguanine (TG) are also used as chemotherapy agents in the treatment of malignancies. We have examined the induction of apoptosis by combinations of these drugs to gain more insights into their efficacy in the treatment of malignancies.
  
  
  METHODS
  The induction of apoptosis was examined in Molt-4, a human malignant acute lymphoblastic T-cell line. The cells were exposed to increasing drug concentrations at various exposure times. Annexin V/FITC and propidium iodide (PI) were used as markers for apoptosis and cell death. Annexin V/FITC positive and PI positive cells were detected by flow-cytometric analysis.
  
  
  RESULTS
  Sequential 24-h exposure with MTX (0.005-0.02 micro mol) followed by 6MP (1-10 micro mol) and 24-h exposure with TF (5-20 micro mol) followed by TG (0.5-2 micro mol) showed a more than additive induction of apoptosis compared with single-drug exposure. Simultaneous administration of the drugs does not show an additive effect on apoptosis.
  
  
  CONCLUSIONS
  The results of this study indicate that sequential administration of MTX before 6MP and of TF before TG may be essential for therapeutic success in the treatment of leukaemia.
authors.affiliation: University Medical Center St Radboud, Department of Pediatrics, Laboratory of Pediatrics and Neurology, PO Box 9101, 6500 HB Nijmegen, The Netherlands. r.deabreu@cukz.umcn.nl
authors.forename: Ronney A
authors.initials: RA
authors.lastname: De Abreu
authors.forename: Robert C
authors.initials: RC
authors.lastname: Trueworthy
authors.forename: André B P
authors.initials: AB
authors.lastname: van Kuilenburg
authors.forename: Trude M
authors.initials: TM
authors.lastname: Vogels-Mentink
authors.forename: Lambert H J
authors.initials: LH
authors.lastname: Lambooy
authors.forename: Albert H
authors.initials: AH
authors.lastname: van Gennip
mesh_terms: D017304:Annexin A5 / Q000494:pharmacology; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D017209:Apoptosis; D002470:Cell Survival; D002648:Child; D004396:Coloring Agents / Q000494:pharmacology; D006801:Humans; D007938:Leukemia / Q000628:therapy*; D015122:Mercaptopurine / Q000627:therapeutic use*; D008727:Methotrexate / Q000627:therapeutic use; D008954:Models, Biological; D011687:Purines / Q000378:metabolism*; D012254:Ribavirin / Q000031:analogs & derivatives / Q000627:therapeutic use; D013866:Thioguanine / Q000627:therapeutic use; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: D017304:Annexin A5; D004396:Coloring Agents; D011687:Purines; D012254:Ribavirin; D015122:Mercaptopurine; D013866:Thioguanine; C033706:tiazofurin; D008727:Methotrexate