title: Radiosensitization by 5-fluorocytosine of human colorectal carcinoma cells in culture transduced with cytosine deaminase gene.
abstract: Recently, use of the suicide gene, cytosine deaminase (CD), has shown a selective antitumor activity of 5-fluorocytosine (5-FC) on human colorectal carcinoma cells grown in vitro and in vivo. We hypothesized that the radiosensitivity of human colorectal carcinoma cells transduced with a retroviral vector encoding the bacterial CD gene would be selectively enhanced by the nontoxic prodrug 5-FC. The radiobiological rationale of using suicide gene therapy is based on the fact that a toxic metabolite of 5-FC, 5-fluorouracil, is a well-known radiation enhancer for the treatment of gastrointestinal and other tumors. 5-FC was found to enhance selectively the radiation cytotoxicity of human colorectal carcinoma cells expressing the CD gene. Colorectal carcinoma cells transduced with the CD gene (WiDr-CD) were highly sensitive to radiation compared with parental cells (WiDr) when exposed to 20 microgram/ml 5-FC for 72 h prior to irradiation. The sensitization enhancement ratio was 2.38. This magnitude of radiation enhancement is comparable to that obtained with 5-fluorouracil. These results suggest that the addition of radiation would substantially improve the therapeutic potential of CD gene therapy for the treatment of locally advanced colorectal carcinomas.
authors.affiliation: Department of Radiation Oncology, Henry Ford Hospital, Detroit, Michigan 48202, USA.
authors.forename: M S
authors.initials: MS
authors.lastname: Khil
authors.forename: J H
authors.initials: JH
authors.lastname: Kim
authors.forename: C A
authors.initials: CA
authors.lastname: Mullen
authors.forename: S H
authors.initials: SH
authors.lastname: Kim
authors.forename: S O
authors.initials: SO
authors.lastname: Freytag
mesh_terms: D002470:Cell Survival / Q000528:radiation effects; D015179:Colorectal Neoplasms / Q000628:therapy*; D003131:Combined Modality Therapy; D043525:Cytosine Deaminase; D005437:Flucytosine / Q000494:pharmacology*; D018014:Gene Transfer Techniques; D015316:Genetic Therapy; D006801:Humans; D009700:Nucleoside Deaminases / Q000235:genetics*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D011838:Radiation-Sensitizing Agents; D005437:Flucytosine; D009700:Nucleoside Deaminases; D043525:Cytosine Deaminase