Novel orthotopic transplantation mouse models to study sporadic distant CRC metastasis

Colorectal cancer (CRC) was the 3rd most frequently diagnosed cancer, killing over 900,000 patients worldwide in 2020. The prognosis of CRC patients is mainly determined by the development of distant metastasis. Tumor mouse models are common tools to study mechanisms of tumor initiation and progression. Conventional CRC mouse models failed to replicate distant metastasis in immunocompetent mouse models as yet. Novel 3D cell cultures of tumor cells, so called “tumor spheroids” or “organoids” can be derived from primary lesions of genetically modified mouse models (GEMMs) and may result in distant metastasis after implantation into mice. In this thesis, recently developed organoids were orthotopically injected into the colon submucosa of immunocompetent mice with the aim to establish models of distant metastatic CRC for future experiments. The utilized organoids (“KPN”, “VAKPT” and “APTKA”), were all derived from syngeneic C57BL/6 mice and harbor mutations that account for a high invasive and metastatic potential. The experimental mice were observed over three months and received weekly colonoscopy, revealing a faster tumor growth in mice injected with KPN and VAPKT than in mice injected with APTKA organoids. After three months, the lungs, livers, spleen, colons and kidneys were analyzed using hematoxylin and eosin (HE) stained tissue sections. A high take rate was detected with 24 (88.8%) of 27 mice injected developing a primary tumor in the colon, two mice developed tumors in the kidney capsule and peritoneal cavity and one mouse did not harbor a tumor. Distant metastasis in the liver and/or in the lungs was found in 15 of the 24 mice (62.5%) with primary colon tumors. Mice injected with VAKPT organoids showed the highest rate of metastasis in the liver and lungs. Mice (n=5) injected with MC38 cells showed no tumor development. In conclusion, orthotopic implantation of the syngeneic CRC organoids KPN, VAKPT and APTKA resembled the human situation more accurately as compared to previous mouse models which are mostly lacking distant metastasis. The presented models are also highly efficient in terms of take rate, speed of primary tumor growth as well as rates of distant metastasis and at the same time only require less than three months to be conducted.