title: Hypoxia- and radiation-activated Cre/loxP 'molecular switch' vectors for gene therapy of cancer.
abstract: Although a significant negative prognostic factor, tumor hypoxia can be exploited for gene therapy. To maximize targeting within the tumor mass, we have developed synthetic gene promoters containing hypoxia-responsive elements (HREs) from the erythropoietin (Epo) gene as well as radiation-responsive CArG elements from the early growth response (Egr) 1 gene. Furthermore, to achieve high and sustained expression of the suicide gene herpes simplex virus thymidine kinase (HSVtk), our gene therapy vectors contain an expression amplification system, or 'molecular switch', based on Cre/loxP recombination. In human glioma and breast adenocarcinoma cells exposed to hypoxia and/or radiation, the HRE/CArG promoter rapidly activated Cre recombinase expression leading to selective and sustained HSVtk synthesis. Killing of transfected tumor cells was measured after incubation with the prodrug ganciclovir (GCV; converted by HSVtk into a cytotoxin). In vitro, higher and more selective GCV-mediated toxicity was achieved with the switch vectors, when compared with the same inducible promoters driving HSVtk expression directly. In tumor xenografts implanted in nude mice, the HRE/CArG-switch induced significant growth delay and tumor eradication. In conclusion, hypoxia- and radiation-activated 'molecular switch' vectors represent a promising strategy for both targeted and effective gene therapy of solid tumors.
authors.affiliation: Department of Radiation Oncology, Wayne State University and Karmanos Cancer Institute, Hudson Webber CRC, Detroit, MI, USA. o.greco@sheffield.ac.uk
authors.forename: O
authors.initials: O
authors.lastname: Greco
authors.forename: M C
authors.initials: MC
authors.lastname: Joiner
authors.forename: A
authors.initials: A
authors.lastname: Doleh
authors.forename: A D
authors.initials: AD
authors.lastname: Powell
authors.forename: G G
authors.initials: GG
authors.lastname: Hillman
authors.forename: S D
authors.initials: SD
authors.lastname: Scott
mesh_terms: D000230:Adenocarcinoma / Q000473:pathology / Q000628:therapy; D000256:Adenoviridae / Q000235:genetics*; D000818:Animals; D000998:Antiviral Agents / Q000627:therapeutic use; D001932:Brain Neoplasms / Q000473:pathology / Q000628:therapy; D001943:Breast Neoplasms / Q000473:pathology / Q000628:therapy; D016923:Cell Death; D015687:Cell Hypoxia; D003131:Combined Modality Therapy; D051766:Early Growth Response Protein 1 / Q000235:genetics; D004921:Erythropoietin / Q000235:genetics; D015774:Ganciclovir / Q000627:therapeutic use; D015972:Gene Expression Regulation, Neoplastic; D005812:Genes, Switch; D041722:Genes, Transgenic, Suicide; D005818:Genetic Engineering / Q000379:methods; D015316:Genetic Therapy / Q000379:methods*; D005822:Genetic Vectors / Q000008:administration & dosage / Q000235:genetics* / Q000528:radiation effects; D005910:Glioma / Q000473:pathology / Q000628:therapy; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000473:pathology / Q000628:therapy*; D050130:Oncolytic Virotherapy / Q000379:methods*; D011401:Promoter Regions, Genetic; D018139:Simplexvirus / Q000201:enzymology; D013937:Thymidine Kinase / Q000096:biosynthesis / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D000998:Antiviral Agents; D051766:Early Growth Response Protein 1; D004921:Erythropoietin; D013937:Thymidine Kinase; D015774:Ganciclovir