Longitudinal micro-endoscopic monitoring of high-success intramucosal xenografts for mouse models of colorectal cancer

Colorectal cancer (CRC) is one of the most frequently lethal forms of cancer. Intramucosal injection allows development of better mouse models of CRC, as orthotopic xenografts allow development of adenocarcinoma in the submucosa of the mouse colon wall. In this paper, a method of orthotopic injection is monitored longitudinally using cellular-resolution real-time in vivo fluorescence microendoscopy, following the injection of three different cell lines: 3T3-GFP to confirm immunosuppression and HCT116-RFP cells to model CRC. Adenoma formation is first observable after 7 to 10 days, and by use of 33 G needles a tumor induction rate of greater than 85% is documented. An additional experiment on the injection of rapamycin reveals drug efficacy and localization between 24 and 48 hours, and suggests the promise of real-time cellular-resolution fluorescence micro-endoscopy for developing longitudinal therapy regimes in mural models of CRC.

Subcutaneous preconditioning increases invasion and metastatic dissemination in mouse colorectal cancer models

Mouse colorectal cancer (CRC) models generated by orthotopic microinjection of human CRC cell lines reproduce the pattern of lymphatic, haematological and transcoelomic spread but generate low metastatic efficiency. Our aim was to develop a new strategy that could increase the metastatic efficiency of these models. We used subcutaneous implantation of the human CRC cell lines HCT116 or SW48 prior to their orthotopic microinjection in the cecum of nude mice (SC+ORT). This subcutaneous preconditioning significantly enhanced metastatic dissemination. In the HCT116 model it increased the number and size of metastatic foci in lymph nodes, lung, liver and peritoneum, whereas, in the SW48 model, it induced a shift from non-metastatic to metastatic. In both models the number of apoptotic bodies in the primary tumour in the SC+ORT group was significantly reduced compared with that in the direct orthotopic injection (ORT) group. Moreover, in HCT116 tumours the number of keratin-positive tumour buddings and single epithelial cells increased at the invasion front in SC+ORT mice. In the SW48 tumour model, we observed a trend towards a higher number of tumour buds and single cells in the SC+ORT group but this did not reach statistical significance. At a molecular level, the enhanced metastatic efficiency observed in the HCT116 SC+ORT model was associated with an increase in AKT activation, VEGF-A overexpression and downregulation of β1 integrin in primary tumour tissue, whereas, in SW48 SC+ORT mice, the level of expression of these proteins remained unchanged. In summary, subcutaneous preconditioning increased the metastatic dissemination of both orthotopic CRC models by increasing tumour cell survival and invasion at the tumour invasion front. This approach could be useful to simultaneously study the mechanisms of metastases and to evaluate anti-metastatic drugs against CRC.