title: (E)-5-(2-bromovinyl)-2'-deoxyuridine potentiates ganciclovir-mediated cytotoxicity on herpes simplex virus-thymidine kinase--expressing cells.
abstract: Tumor cells expressing the thymidine kinase gene of the herpes simplex virus (HSV-tk) are rendered highly susceptible to the cytotoxic effects of different antiherpes drugs. In an attempt to enhance cytotoxicity of this therapeutic approach in glioma and other tumor cell lines transduced with the HSV-tk gene, we evaluated tumor cell killing following co-administration of two different prodrugs metabolized by HSV-tk, (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU), and ganciclovir (GCV). In 8 of 12 cell lines investigated, addition of BVDU in concentrations showing no cytotoxic effect or only limited cytotoxicity could enhance GCV-mediated cell killing by as much as one order of magnitude. In co-cultures consisting of HSV-tk(+) (9L STK) and HSV-tk(-) (9L wild-type) cells, we also observed potentiation of GCV-mediated cytotoxicity in the presence of BVDU, suggesting strongly enhanced bystander cell killing. BVDU is thought to exert its cytotoxic effect through inhibition of thymidylate synthase activity or by incorporation into replicating DNA. Both effects could be observed in all HSV-tk--expressing cells investigated, including cell lines which did not exhibit cytotoxicity after incubation with BVDU. These findings argue against current concepts of BVDU-mediated cytotoxicity in HSV-tk--expressing cells. Taken together, our data suggest that gene therapy utilizing prodrug activating enzymes may be rendered more effective by simultaneous treatment with two different prodrugs metabolized by the same enzyme.
authors.affiliation: Preuss Laboratory for Molecular Neuro-Oncology, Brain Tumor Research Center, HSE-722, University of California, San Francisco, California 94143-0520, USA. hamelw@nch.uni-kiel.de
authors.forename: W
authors.initials: W
authors.lastname: Hamel
authors.forename: D
authors.initials: D
authors.lastname: Zirkel
authors.forename: H M
authors.initials: HM
authors.lastname: Mehdorn
authors.forename: M
authors.initials: M
authors.lastname: Westphal
authors.forename: M A
authors.initials: MA
authors.lastname: Israel
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000378:metabolism; D000998:Antiviral Agents / Q000494:pharmacology*; D001973:Bromodeoxyuridine / Q000031:analogs & derivatives / Q000494:pharmacology*; D016923:Cell Death; D004351:Drug Resistance; D004357:Drug Synergism; D004790:Enzyme Induction; D015774:Ganciclovir / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D018139:Simplexvirus / Q000201:enzymology*; D013937:Thymidine Kinase / Q000378:metabolism*; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors; D014407:Tumor Cells, Cultured / Q000187:drug effects* / Q000201:enzymology
chemical_list: D000964:Antimetabolites, Antineoplastic; D000998:Antiviral Agents; C020235:brivudine; D013940:Thymidylate Synthase; D013937:Thymidine Kinase; D001973:Bromodeoxyuridine; D015774:Ganciclovir