Establishment and characterization of a rectal cancer model in mice: Application to cytokine gene therapy

Background and aims: We established an orthotopic animal model of rectal cancer in mice and applied this model to the study of the antitumor effects of cytokine-assisted tumor vaccine. Materials and methods: The CT-26 murine colon adenocarcinoma cells were inoculated into the submucosa of the rectum of the mice to induce the rectal tumor. The tumor growth rate and the survival time of the mice were observed. The cDNA of granulocyte-macrophage colony-stimulating factor (GM-CSF) was transduced to the CT-26 cell line via a retroviral vector, and the therapeutic effects of irradiated GM-CSF secreting tumor vaccine on the rectal tumor were investigated. Results: All the mice implanted with the wild-type tumor cells had tumor growth in the rectum and died. The mean survival time of the mice was 28.9 days. Two doses of irradiated GM-CSF secreting tumor vaccine administered on days 0 and 3 after tumor cell implantation significantly prolonged the survival of the mice with rectal tumor compared with that of the control groups (P<0.0001). In contrast, no antitumor effect was observed when the treatment with GM-CSF secreting tumor vaccine was delayed to 3 days after tumor cell implantation (P>0.17). Conclusion: The results suggest that cytokine gene therapy exerts an antitumor effect on small tumors and may be considered as an adjuvant immunotherapy of rectal cancers and prevention of reimplantation of tumor cells disseminated during or following surgery. The orthotopic animal model of the rectal cancer in mice could be applied to the in vivo experimental studies of rectal cancer.