[Mouse models for human colorectal cancer with liver metastasis]

Objective: To established Apc(loxp/loxp)+Kras(LSL-G12D/-)+Smad4(loxp/loxp) transgenic mouse model that mimick the occurrence and development of human sporadic colorectal cancer(CRC) and its liver metastasis. Methods: C57BL/6-Apc(tm1Tyj)/J(Apc(loxP)), B6.129S4-Kras(tm4Tyj)/J(Kras(LSL-G12D)), 129S6-Smad4(tm2.1Cxd)/J(Smad4(loxP)) and C57BL/6J mice were crossed, and genotype with Apc(loxP/loxP)+Kras(LSL-G12D/-)and Apc(loxP/loxP)+Kras(LSL-G12D/-)+Smad4(loxP/loxP)were generated. Genotypes of the mice were identified by PCR and real-time quantitative PCR. The mice were divided into Apc(loxP/loxP)+Kras(LSL-G12D/-)+Smad4(loxP/loxP) group (n=20) and Apc(loxP/loxP)+Kras(LSL-G12D/-)group(n=24). Lentivirus expressing Cre enzyme and IRES-luciferase were injected into the submucosa of colon or rectum of the transgenic mice under colonoscopy. Intraabdominal injection of D-luciferase into mice every 4 weeks, imaging with small animal in vivo imaging system(IVIS). The tumor size, tumorigenesis rate and metastasis ratio were analyzed. At the end of the 20th week, the colorectal lesions and metastatic tissues of mice were stained with hematoxylin-eosin(HE) and the pathological changes were observed under microscope. Results: Apc(loxp/loxp)+Kras(LSL-G12D/-)+Smad4(loxp/loxp) and Apc(loxp/loxp)+Kras(LSL-G12D/-)transgenic mice were successfully bred. The colorectal stem cells of the transgenic mouse mutated leading tumor lesion and liver metastatic under the induction of Lentivirus(Cre-IRES-luciferase). The primary and metastatic foci of colorectal carcinoma and liver metastasis in mice were proved to be adenocarcinoma and liver metastatic carcinoma by histopathological examination. The primary tumor size inApc(loxP/loxP)+Kras(LSL-G12D/-)+Smad4(loxP/loxP) group and Apc(loxP/loxP)+Kras(LSL-G12D/-)group was(3.52±0.26) and(3.45±0.20)mm, respectively,without significant difference(t=0.872, P=0.388).The tumorigenesis rate was 70.0% and 50.0% respectively, and there was no significant difference between the two groups(χ(2)=0.440, P=0.507). The metastasis rate of two groups were 58.3% and 8.3%respectively(Fisher's exact test, P=0.027). Conclusions: In this study, the colorectal carcinogenesis and its spontaneously metastasis to the liver of CRC were induced by Lentivirus(Cre-IRES-luciferase) in our established transgenic mice,which successfully simulated the occurrence and development of human sporadic CRC and its liver metastasis.