title: Decrease in S-adenosylmethionine synthesis by 6-mercaptopurine and methylmercaptopurine ribonucleoside in Molt F4 human malignant lymphoblasts.
abstract: 6-Mercaptopurine (6-MP) and methylmercaptopurine ribonucleoside (Me-MPR) are purine anti-metabolites which are both metabolized to methylthio-IMP (Me-tIMP), a strong inhibitor of purine synthesis de novo. Me-MPR is converted directly into Me-tIMP by adenosine kinase. 6-MP is converted into tIMP, and thereafter it is methylated to Me-tIMP by thiopurine methyltransferase, an S-adenosylmethionine (S-Ado-Met)-dependent conversion. S-Ado-Met is formed from methionine and ATP by methionine adenosyltransferase, and is a universal methyl donor, involved in methylation of several macromolecules, e.g. DNA and RNA. Therefore, depletion of S-Ado-Met could result in an altered methylation state of these macromolecules, thereby affecting their functionality, leading to dysregulation of cellular processes and cytotoxicity. In this study the effects of 6-MP and Me-MPR on S-Ado-Met, S-adenosylhomocysteine (S-Ado-Hcy), homocysteine and methionine concentrations are determined. Both drugs cause a decrease in intracellular S-Ado-Met concentrations and an increase in S-Ado-Hcy and methionine concentrations in Molt F4 human malignant lymphoblasts. The effects of both 6-MP and Me-MPR can be ascribed to a decreased conversion of methionine into S-Ado-Met, due to the ATP depletion induced by the inhibition of purine synthesis de novo by Me-tIMP. Both 6-MP and Me-MPR thus affect the methylation state of the cells, and this may result in dysregulation of cellular processes and may be an additional mechanism of cytotoxicity for 6-MP and Me-MPR.
authors.affiliation: Department of Pediatrics, St. Radboud University Hospital of Nijmegen, The Netherlands.
authors.forename: E H
authors.initials: EH
authors.lastname: Stet
authors.forename: R A
authors.initials: RA
authors.lastname: De Abreu
authors.forename: J P
authors.initials: JP
authors.lastname: Bökkerink
authors.forename: H J
authors.initials: HJ
authors.lastname: Blom
authors.forename: L H
authors.initials: LH
authors.lastname: Lambooy
authors.forename: T M
authors.initials: TM
authors.lastname: Vogels-Mentink
authors.forename: A C
authors.initials: AC
authors.lastname: de Graaf-Hess
authors.forename: B
authors.initials: B
authors.lastname: van Raay-Selten
authors.forename: F J
authors.initials: FJ
authors.lastname: Trijbels
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D006801:Humans; D015459:Leukemia-Lymphoma, Adult T-Cell / Q000378:metabolism / Q000473:pathology; D015122:Mercaptopurine / Q000494:pharmacology*; D012436:S-Adenosylmethionine / Q000096:biosynthesis*; D013872:Thionucleosides / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D013872:Thionucleosides; D012436:S-Adenosylmethionine; D000255:Adenosine Triphosphate; D015122:Mercaptopurine