Comparison of 2 different mouse models of colorectal cancer and their application

Abstract

Objective To establish and compare the characteristics of mouse models of colorectal cancer (CRC) induced by inflammation and gene mutation. Methods Inflammation-induced colorectal cancer mouse model was established using azoxymethane (AOM) combined with dextran sodium sulfate (DSS). The transgenic CRC mouse model carrying Kras gene mutation and Apc conditional knockout mutation was established by intraperitoneal injection of 100 mg/kg tamoxifen into KPC mice. The changes of body weight, fecal appearance and blood feces were observed during the modeling period. Colonic tissue samples were collected during the time points of CRC modeling, and then embedded and sectioned to observe tumor formation. HE and immunohistochemical staining of Ki67 were used to observe the pathological changes. Tandem dimer Tomato (tdTomato) was employed to determine the CDX2 expression in the colonic epithelial cells. CRC crypts were isolated and cultured to get tumor organoids, then compared with healthy colonic enteroids. Results It took about 50 d to establish AOM/DSS-induced CRC model, and the visible tumors were mainly observed at the distal colon close to the anus and at the middle section of colon. However, only about 8 d was needed for KPC mice to develop CRC, with the masses mostly locating in the proximal colon. In AOM/DSS model, disordered structure was observed in the distal tumor sites, and the KPC model had thickened and disrupted proximal mucosa and irregularly arranged tissues, with many undifferentiated epithelial cells. There were more Ki67+ proliferative cells in the tumor tissues than the para-tumor tissues in AOM/DSS model, and larger amount of these cells were seen in the tumor in proximal section, but the distal colonic epithelium remained healthy proliferation. In addition, tdTomato+CDX2-expressing colonic epithelia cells were observed mainly at the proximal colonic epithelium. Both AOM/DSS and KPC mice were capable to culture organoids of CRC. Conclusion AOM/DSS-induced CRC model presents the inflammatory process of CRC development, and it is suitable to the CRC study concerning chronic inflammation. The KPC CRC model is due to higher proliferative capacity of proximal colonic segment, in which CDX2 expressing higher than in the distal segment, so it is more convenient to Kras mutation related CRC study. These 2 CRC models can be alternatively adopted depending on different aims.

Keywords

• colorectal cancer
• animal model
• azoxymethane
• dextran sodium sulfate
• kras
• apc