title: Radiosensitization of gliomas by intracellular generation of 5-fluorouracil potentiates prodrug activator gene therapy with a retroviral replicating vector.
abstract: A tumor-selective non-lytic retroviral replicating vector (RRV), Toca 511, and an extended-release formulation of 5-fluorocytosine (5-FC), Toca FC, are currently being evaluated in clinical trials in patients with recurrent high-grade glioma (NCT01156584, NCT01470794 and NCT01985256). Tumor-selective propagation of this RRV enables highly efficient transduction of glioma cells with cytosine deaminase (CD), which serves as a prodrug activator for conversion of the anti-fungal prodrug 5-FC to the anti-cancer drug 5-fluorouracil (5-FU) directly within the infected cells. We investigated whether, in addition to its direct cytotoxic effects, 5-FU generated intracellularly by RRV-mediated CD/5-FC prodrug activator gene therapy could also act as a radiosensitizing agent. Efficient transduction by RRV and expression of CD were confirmed in the highly aggressive, radioresistant human glioblastoma cell line U87EGFRvIII and its parental cell line U87MG (U87). RRV-transduced cells showed significant radiosensitization even after transient exposure to 5-FC. This was confirmed both in vitro by a clonogenic colony survival assay and in vivo by bioluminescence imaging analysis. These results provide a convincing rationale for development of tumor-targeted radiosensitization strategies utilizing the tumor-selective replicative capability of RRV, and incorporation of radiation therapy into future clinical trials evaluating Toca 511 and Toca FC in brain tumor patients.
authors.affiliation: Department of Medicine, University of California Los Angeles (UCLA), Los Angeles, California, USA.
authors.forename: Masamichi
authors.initials: M
authors.lastname: Takahashi
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles (UCLA), Los Angeles, California, USA.
authors.forename: Gilmer
authors.initials: G
authors.lastname: Valdes
authors.affiliation: Department of Medicine, University of California Los Angeles (UCLA), Los Angeles, California, USA.
authors.forename: Kei
authors.initials: K
authors.lastname: Hiraoka
authors.affiliation: Department of Medicine, University of California Los Angeles (UCLA), Los Angeles, California, USA.
authors.forename: Akihito
authors.initials: A
authors.lastname: Inagaki
authors.affiliation: Department of Medicine, University of California Los Angeles (UCLA), Los Angeles, California, USA.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Kamijima
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles (UCLA), Los Angeles, California, USA.
authors.forename: Ewa
authors.initials: E
authors.lastname: Micewicz
authors.affiliation: Tocagen Inc., San Diego, California, USA.
authors.forename: Harry E
authors.initials: HE
authors.lastname: Gruber
authors.affiliation: Tocagen Inc., San Diego, California, USA.
authors.forename: Joan M
authors.initials: JM
authors.lastname: Robbins
authors.affiliation: Tocagen Inc., San Diego, California, USA.
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Jolly
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles (UCLA), Los Angeles, California, USA.
authors.forename: William H
authors.initials: WH
authors.lastname: McBride
authors.affiliation: Department of Radiation Oncology, University of California Los Angeles (UCLA), Los Angeles, California, USA.
authors.forename: Keisuke S
authors.initials: KS
authors.lastname: Iwamoto
authors.affiliation: Department of Medicine, University of California Los Angeles (UCLA), Los Angeles, California, USA.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Kasahara
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D043525:Cytosine Deaminase / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D004307:Dose-Response Relationship, Radiation; D005260:Female; D005472:Fluorouracil / Q000378:metabolism* / Q000494:pharmacology; D015870:Gene Expression; D023061:Gene Order; D018014:Gene Transfer Techniques; D017930:Genes, Reporter; D041722:Genes, Transgenic, Suicide; D015316:Genetic Therapy; D005822:Genetic Vectors / Q000235:genetics*; D005910:Glioma / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology / Q000628:therapy; D006801:Humans; D051379:Mice; D011355:Prodrugs / Q000378:metabolism* / Q000494:pharmacology; D011836:Radiation Tolerance / Q000235:genetics*; D012190:Retroviridae / Q000235:genetics*; D014161:Transduction, Genetic; D014779:Virus Replication; D023041:Xenograft Model Antitumor Assays
chemical_list: D011355:Prodrugs; D043525:Cytosine Deaminase; D005472:Fluorouracil