Establishment of a novel mouse model of colorectal cancer by orthotopic transplantation.

Background: Colorectal cancer (CRC) represents a major malignancy that poses a significant threat to human health worldwide. The establishment of a reliable and pathologically relevant orthotopic model of CRC is crucial for gaining a deeper understanding of its molecular mechanisms and for developing more effective therapies. Nonetheless, the development of such models is fraught with challenges primarily owing to the technical complexities associated with the transplantation of CRC cells into the intestinal epithelium.

Methods: The luminal surface of the cecum was externalized to visualize the entire process involved in the transplantation of CRC cells into the cecal epithelium of BALB/c athymic nude mice. The cecal epithelium was mechanically removed, preserving the integrity of the submucosal layer. Caco-2 CRC cells were subsequently inoculated onto the epithelium-depleted surface of the cecum to reproduce the development of CRC within the epithelial layer. The successful removal of the epithelium and transplantation of Caco-2 cells were verified through the use of appropriate fluorescent labeling techniques and examination with a fluorescence stereoscopic microscope.

Results: Following orthotopic transplantation, Caco-2 cells formed tumors in the cecum, where tumors progressed from a flat monolayer epithelium to thickened aberrant crypt foci, and then to protruding polyps, aided by mesenchymal cells infiltrating the tumors to form a stalk region, and eventually to large tumors invading the submucosa. Throughout this process, Caco-2 cells retained stem cell and fetal intestinal signatures, regardless of their location within the tumors or their proliferative status. Histopathological analysis further suggested that interactions between the transplanted Caco-2 cells and the surrounding normal epithelial and mesenchymal cells play critical roles in tumor development and in the elimination of normal epithelial cells from the tumor in this model.

Conclusions: This study established a novel orthotopic model of CRC within the mouse cecum. Tumor development and progression in this model include sequential morphological changes from a flat monolayer to large invasive tumors. The establishment of this orthotopic CRC model, which mimics tumor development in a more natural microenvironment, provides new opportunities to investigate the molecular mechanisms underlying CRC and to evaluate novel anticancer therapies in pathologically relevant contexts.