title: Expression of MRP4 confers resistance to ganciclovir and compromises bystander cell killing.
abstract: The multidrug resistance protein MRP4, a member of the ATP-binding cassette superfamily, confers resistance to purine-based antiretroviral agents. However, the antiviral agent ganciclovir (GCV) has not been shown to be a substrate of MRP4. GCV is important not only in antiviral therapy, but also in the selective killing of tumor cells modified to express herpes simplex virus thymidine kinase (HSV-TK). We therefore tested the effect of MRP4 on the cytotoxicity of GCV, on the ability of GCV to kill cells genetically modified to express HSV-TK, and on the bystander effect in which unmodified target cells are killed by GCV. Cells overexpressing MRP4 had markedly increased resistance to the cytotoxicity of GCV. Although, expression of recombinant HSV-TK increased the intracellular concentration of GCV nucleotide, cells were rescued by the cytoprotective effect of MRP4. In cells that overexpressed MRP4, intracellular accumulation of GCV metabolites was reduced, efflux of these metabolites was increased, and resistance to bystander killing was increased. Therefore, MRP4 can strongly reduce the susceptibility of HSV-TK-expressing cells to GCV, and its overexpression in adjacent cells protects them from bystander cell death. These findings indicate that a nucleotide transporter, such as MRP4, modulates the cellular response to GCV and thus may influence not only the efficacy of antiviral therapy, but also prodrug-based gene therapy, which is critically dependent upon bystander cell killing.
authors.affiliation: Department of Pharmaceutical Sciences, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
authors.forename: Masashi
authors.initials: M
authors.lastname: Adachi
authors.forename: Janardhan
authors.initials: J
authors.lastname: Sampath
authors.forename: Lu-bin
authors.initials: LB
authors.lastname: Lan
authors.forename: Daxi
authors.initials: D
authors.lastname: Sun
authors.forename: Philip
authors.initials: P
authors.lastname: Hargrove
authors.forename: Robin
authors.initials: R
authors.lastname: Flatley
authors.forename: Ann
authors.initials: A
authors.lastname: Tatum
authors.forename: Mary Z
authors.initials: MZ
authors.lastname: Edwards
authors.forename: Michele
authors.initials: M
authors.lastname: Wezeman
authors.forename: Larry
authors.initials: L
authors.lastname: Matherly
authors.forename: Richard
authors.initials: R
authors.lastname: Drake
authors.forename: John
authors.initials: J
authors.lastname: Schuetz
mesh_terms: D000998:Antiviral Agents / Q000378:metabolism / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D024201:Bystander Effect / Q000187:drug effects*; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D018432:Drug Resistance, Multiple; D015774:Ganciclovir / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D008969:Molecular Sequence Data; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D018139:Simplexvirus / Q000201:enzymology / Q000235:genetics; D013601:T-Lymphocytes / Q000378:metabolism; D013937:Thymidine Kinase / Q000235:genetics / Q000378:metabolism
chemical_list: D000998:Antiviral Agents; D015774:Ganciclovir; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D011994:Recombinant Proteins; D013937:Thymidine Kinase; C073492:ABCC4 protein, human