title: Inhibition of DNA methylation in malignant MOLT F4 lymphoblasts by 6-mercaptopurine.
abstract: Treatment of MOLT F4 lymphoblasts with 6-mercaptopurine (6-MP) resulted in a decrease of ATP and a depletion of S-adenosylmethionine (AdoMet). To investigate whether this might affect the methylation of DNA, we treated MOLT F4 lymphoblasts with increasing concentrations of 6-MP, followed by labeling with [methyl-14C]methionine and [methyl-3H]thymidine. After DNA isolation, we measured the incorporated radioactivity and determined the 14C/3H ratio as a measure for the methylation of newly formed DNA. The 14C/3H ratio was decreased by 17% with 1 mumol/L 6-MP; treatment with increasing concentrations of 6-MP up to 10 mumol/L showed a further decrease to 70%, in comparison with untreated cells. To demonstrate that the methylation of deoxycytidine residues in DNA was reduced, we quantified hydrolyzed DNA by HPLC. The 14C/3H ratio showed a decrease with increasing 6-MP concentrations, indicating that treatment with 6-MP resulted in hypomethylation of DNA.
authors.affiliation: Center for Pediatric Oncology SE Netherlands, Department of Pediatrics, St. Radboud University Hospital of Nijmegen, The Netherlands.
authors.forename: L H
authors.initials: LH
authors.lastname: Lambooy
authors.forename: P A
authors.initials: PA
authors.lastname: Leegwater
authors.forename: L P
authors.initials: LP
authors.lastname: van den Heuvel
authors.forename: J P
authors.initials: JP
authors.lastname: Bökkerink
authors.forename: R A
authors.initials: RA
authors.lastname: De Abreu
mesh_terms: D002250:Carbon Radioisotopes; D019175:DNA Methylation / Q000187:drug effects*; D004273:DNA, Neoplasm / Q000096:biosynthesis*; D006801:Humans; D008214:Lymphocytes; D015122:Mercaptopurine / Q000494:pharmacology*; D008715:Methionine / Q000378:metabolism; D011865:Radioisotope Dilution Technique; D013936:Thymidine / Q000378:metabolism; D014316:Tritium; D014407:Tumor Cells, Cultured
chemical_list: D002250:Carbon Radioisotopes; D004273:DNA, Neoplasm; D014316:Tritium; D008715:Methionine; D015122:Mercaptopurine; D013936:Thymidine