K. P. Terracina1, T. Aoyagi3, W. Huang1, A. Yamada4, M. Nagahashi2, K. Takabe1 1Virginia Commonwealth University,Surgical Oncology,Richmond, VA, USA 2Nigata University,Surgery,Nigata, , Japan 3Chiba University,Surgery,Chiba, , Japan 4Yokohama City University,Surgery,Yokohama, , Japan
Introduction: Over the past several decades, it has become clear that the murine xenograft models, which implant human cancer cells into immune-deficient nude mice, used in the majority of preclinical studies, poorly predict the outcome of human clinical trials. The emerging understanding of the important role of immune responses in the tumor microenvironment for cancer progression necessitates animal models that do not preclude the immune response. As new targets for cancer treatment are discovered and investigated, preclinical studies should be conducted with murine models that include intact immune responses, and that allow real time monitoring of cancer progression to provide a closer correlation with human cancer. In our laboratory, we have recently developed a modified syngeneic orthotopic murine colon cancer model that mimics human colon cancer progression with consistent results.
Methods: We have genetically engineered a murine colon adenocarcinoma cell line, CT26, to overexpress the firefly luciferase gene (CT26-luc1), which allowed real time in vivo monitoring of tumor burden when the substrate, D-luciferin, was injected intraperitoneally using In Vivo Imaging System (IVIS). We have established a syngeneic orthotopic colon cancer model using CT26-luc1 cells suspended in matrigel and either injected submucosally into the cecum wall under direct visualization, or directly injected into the cecum wall as a control.
Results: Our syngeneic orthotopic colon cancer submucosal injection model has demonstrated consistent implantation in the cecum compared to the direct injection technique. In contrast, the direct injection model demonstrated complications such as premature peritoneal carcinomatosis prior to development of lymph node metastasis. In vivo bioluminescence allowed real time monitoring of total tumor burden. We have also found that perioperative care has a significant impact on reproducibility of the model. Finally, we found that total tumor burden quantified with bioluminescence enabled us to estimate lymph node metastasis in vivo.
Conclusion: Our newly established method that maintains intact immune response in the tumor microenvironment is expected to provide an invaluable murine metastatic colon cancer model particularly in preclinical studies for drug development targeting those mechanisms.