title: Effects and interaction of 7-hydroxy methotrexate and methotrexate in leukaemic cells ex vivo measured by the thymidylate synthase inhibition assay.
abstract: In high dose therapy with methotrexate (MTX) the main metabolite 7-hydroxy-methotrexate (7-OH MTX) exceeds the plasma concentration of MTX achieving about tenfold higher levels. To investigate the interaction between 7-OH MTX and MTX ex vivo, the thymidylate synthase inhibition assay was used to quantify antifolate effects in patient blast samples, measuring the inhibition of the key enzyme thymidylate synthase (TS). In 18 leukemic samples (7 ALL, 11 AML) no dose-dependent TS inhibition was observed for 7-OH MTX. However, a statistically significant increase of TS inhibition (p<0.05) was observed for a 1:1 mixture of MTX and 7-OH MTX as compared to the effect of MTX alone. The half-maximal inhibitory concentrations in the short-exposure assay were 0.857 microM for MTX alone versus 0.088 microM for the 1:1 mixture with 7-OH MTX, respectively (p< or =0.05). This interaction was not observed with an excess of 7-OH MTX. Similar results were obtained in long exposure experiments. We conclude that there is a dose-dependent interaction between 7-OHMTX and MTX, despite the lack of TS inhibitory effects of the metabolite alone.
authors.affiliation: Klinik und Poliklinik für Kinder- und Jugendmedizin, Pädiatrische Hämatologie/Onkologie Universitätsklinikum Münster, Pädiatrische Hämatologie/Onkologie, Münster, Germany.
authors.forename: R M
authors.initials: RM
authors.lastname: Lingg
authors.forename: G
authors.initials: G
authors.lastname: Hempel
authors.forename: M G
authors.initials: MG
authors.lastname: Rots
authors.forename: C H
authors.initials: CH
authors.lastname: Van Zantwijk
authors.forename: J
authors.initials: J
authors.lastname: Boos
authors.forename: G J L
authors.initials: GJ
authors.lastname: Kaspers
mesh_terms: D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005493:Folic Acid Antagonists / Q000494:pharmacology*; D006801:Humans; D015470:Leukemia, Myeloid, Acute / Q000188:drug therapy* / Q000201:enzymology; D008727:Methotrexate / Q000031:analogs & derivatives* / Q000494:pharmacology*; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000188:drug therapy* / Q000201:enzymology; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors*; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D000964:Antimetabolites, Antineoplastic; D004791:Enzyme Inhibitors; D005493:Folic Acid Antagonists; D013940:Thymidylate Synthase; C011864:7-hydroxymethotrexate; D008727:Methotrexate