title: Thiopurine metabolism and identification of the thiopurine metabolites transported by MRP4 and MRP5 overexpressed in human embryonic kidney cells.
abstract: Mercaptopurines have been used as anticancer agents for more than 40 years, and most acute lymphoblastic leukemias are treated with 6-mercaptopurine (6MP) or 6-thioguanine (TG). Overexpression of the two related multidrug resistance proteins MRP4 and MRP5 has been shown to confer some resistance against mercaptopurines, which has been attributed to extrusion of mercaptopurine metabolites by these transporters. We have analyzed the mercaptopurine metabolites formed in human embryonic kidney cells and determined which metabolites are extruded by MRP4 and MRP5. Incubation with 6MP led to the formation of thioinosine and thioxanthosine metabolites and we found that thio-IMP was transported by both MRP4 and MRP5; MRP5 showed the highest transport rate. In contrast, only MRP5 transported thioxanthosine monophosphate (tXMP). During incubation with TG, the monophosphorylated form of thioguanosine was transported by both MRP4 and MRP5; the highest transport rate was for MRP4. Similarly, only 6-methyl-thio-IMP was formed during incubation with 6-methyl mercaptopurine riboside. This compound was a substrate for both MRP4 and MRP5; MRP4 showed the highest transport rate. Our results show that all major thiopurine monophosphates important in the efficacy of mercaptopurine treatment are transported by MRP4 and MRP5, although the substrate specificity of the two transporters differs in detail.
authors.affiliation: Division of Molecular Biology and Center for Biomedical Genetics, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
authors.forename: P R
authors.initials: PR
authors.lastname: Wielinga
authors.forename: G
authors.initials: G
authors.lastname: Reid
authors.forename: E E
authors.initials: EE
authors.lastname: Challa
authors.forename: I
authors.initials: I
authors.lastname: van der Heijden
authors.forename: L
authors.initials: L
authors.lastname: van Deemter
authors.forename: M
authors.initials: M
authors.lastname: de Haas
authors.forename: C
authors.initials: C
authors.lastname: Mol
authors.forename: A J
authors.initials: AJ
authors.lastname: Kuil
authors.forename: E
authors.initials: E
authors.lastname: Groeneveld
authors.forename: J D
authors.initials: JD
authors.lastname: Schuetz
authors.forename: C
authors.initials: C
authors.lastname: Brouwer
authors.forename: R A
authors.initials: RA
authors.lastname: De Abreu
authors.forename: J
authors.initials: J
authors.lastname: Wijnholds
authors.forename: J H
authors.initials: JH
authors.lastname: Beijnen
authors.forename: P
authors.initials: P
authors.lastname: Borst
mesh_terms: D001692:Biological Transport; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D004347:Drug Interactions; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000196:embryology; D007700:Kinetics; D015122:Mercaptopurine / Q000378:metabolism* / Q000494:pharmacology; D008778:Methylthioinosine / Q000494:pharmacology; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000096:biosynthesis / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000096:biosynthesis / Q000378:metabolism*; D013866:Thioguanine / Q000378:metabolism* / Q000494:pharmacology; D014162:Transfection
chemical_list: D015122:Mercaptopurine; D008778:Methylthioinosine; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012269:Ribosomal Proteins; D013866:Thioguanine; C073492:ABCC4 protein, human; C120809:ABCC5 protein, human