title: Cytosine deaminase/5-fluorocytosine-based vaccination against liver tumors: evidence of distant bystander effect.
abstract: BACKGROUND
  The cytosine deaminase gene of Escherichia coli converts the nontoxic compound 5-fluorocytosine into 5-fluorouracil (5-FU), thereby acting as a suicide gene when introduced into cancer cells, killing the cells when they are exposed to 5-fluorocytosine. We analyzed the efficacy of using cytosine deaminase-bearing cancer cells as an autologous tumor vaccine in a rat model that mimics liver metastasis from colon carcinoma.
  
  
  METHODS
  We introduced a plasmid vector containing the E. coli cytosine deaminase gene into a BDIX rat colon carcinoma cell line. Intrahepatic injection of the modified cells in syngeneic animals generates a single experimental liver "suicide tumor." We then analyzed the effect of 5-fluorocytosine treatment in terms of regression of cytosine deaminase-expressing cells in vivo as well as protection against wild-type cancer cells.
  
  
  RESULTS
  Treatment with 5-fluorocytosine induced regression of cytosine deaminase-expressing (CD+) tumors, with seven of 11 treated animals being tumor free at the end of 30 days and a statistically significant difference in tumor volumes between treated and control animals (two-sided P<.0001). Intrahepatic injection of CD+ cells followed by 5-fluorocytosine treatment rendered the treated animals resistant to challenge with wild-type tumor cells, with no (zero of seven) treated animals developing wild-type tumors in contrast to all (four of four) control animals. Moreover, in animals with established wild-type liver tumors, injection of CD+ tumor cells followed by 5-fluorocytosine treatment produced a statistically significant increase in survival time (two-sided P<.0001). In vivo immunodepletion and immunohistologic analysis of experimental tumors indicate that natural killer cells are the major immune component involved in this antitumor effect.
  
  
  CONCLUSIONS
  Taken together, these results suggest the potential use of suicide gene-modified tumor cells as therapeutic vaccines against liver metastasis from colon carcinoma.
authors.affiliation: V. Pierrefite-Carle, B. Rossi, Unité INSERM 364, Faculté de Médecine, Nice, France. pierrefi@unice.fr
authors.forename: V
authors.initials: V
authors.lastname: Pierrefite-Carle
authors.forename: P
authors.initials: P
authors.lastname: Baqué
authors.forename: A
authors.initials: A
authors.lastname: Gavelli
authors.forename: M
authors.initials: M
authors.lastname: Mala
authors.forename: M
authors.initials: M
authors.lastname: Chazal
authors.forename: J
authors.initials: J
authors.lastname: Gugenheim
authors.forename: A
authors.initials: A
authors.lastname: Bourgeon
authors.forename: G
authors.initials: G
authors.lastname: Milano
authors.forename: P
authors.initials: P
authors.lastname: Staccini
authors.forename: B
authors.initials: B
authors.lastname: Rossi
mesh_terms: D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology*; D000963:Antimetabolites / Q000494:pharmacology*; D000970:Antineoplastic Agents; D019496:Cancer Vaccines / Q000494:pharmacology; D003110:Colonic Neoplasms / Q000473:pathology; D043525:Cytosine Deaminase; D004926:Escherichia coli / Q000201:enzymology; D005434:Flow Cytometry; D005437:Flucytosine / Q000494:pharmacology*; D005472:Fluorouracil; D015316:Genetic Therapy; D007694:Killer Cells, Natural; D008113:Liver Neoplasms / Q000276:immunology / Q000556:secondary / Q000628:therapy*; D008297:Male; D009700:Nucleoside Deaminases / Q000235:genetics*; D051381:Rats; D014162:Transfection; D014407:Tumor Cells, Cultured
chemical_list: D000935:Antifungal Agents; D000963:Antimetabolites; D000970:Antineoplastic Agents; D019496:Cancer Vaccines; D005437:Flucytosine; D009700:Nucleoside Deaminases; D043525:Cytosine Deaminase; D005472:Fluorouracil