Development of an inflammation-associated colorectal cancer model and its application for research on carcinogenesis and chemoprevention

Abstract

Chronic inflammation is a well-recognized risk factor for development of human cancer in several tissues, including large bowel. Inflammatory bowel disease, including ulcerative colitis and Crohn's disease, is a longstanding inflammatory disease of intestine with increased risk for colorectal cancer development. Several molecular events involved in chronic inflammatory process may contribute to multistep carcinogenesis of human colorectal cancer in the inflamed colon. They include overproduction of reactive oxygen and nitrogen species, overproduction and upregulation of productions and enzymes of arachidonic acid biosynthesis pathway and cytokines, and intestinal immune system dysfunction. In this paper, I will describe several methods to induce colorectal neoplasm in the inflamed colon. First, I will introduce a protocol of a novel inflammation-associated colon carcinogenesis in mice. In addition, powerful tumor-promotion/progression activity of dextran sodium sulfate in the large bowel of Apc(Min/+) mice will be described. Finally, chemoprevention of inflammation-associated colon carcinogenesis will be mentioned.

Figure 1

UC patients are high-risk groups of colorectal cancer (CRC) development.

Figure 2

Risk of colorectal cancer.

Figure 3

Carcinogenic steps of four types of human colorectal cancer.

Figure 4

Chemical structure of dextran sulfate sodium (DSS), a sulfated polysaccharide, and its biological activities. DSS (1–5% in drinking water or diet) induces colitis in rodents. Treatment with DSS (1% in diet) after DMH exposure produces colonic adenocarcinoma [44]. The tumorigenicityof DSS is non-genotoxic effects [20]. Cycle treatment with 3% DSS (MW 54,000, 7 days) and distilled water (14 days) produces colonic tumors [45]. DSS increases the number of ACF induced by AOM [19].

Figure 5

Experimental protocol to develop an inflammation-associated mouse colon carcinogenesis model, to develop a new inflammation-related mouse colon carcinogenesis model [12].

Figure 6

Macroscopic view, incidence, and histopathology of colonic tumors in the groups of mice that received four different treatment schedules of AOM and DSS.

Figure 7

Experimental protocol for determining dose-response of DSS in mice initiated with AOM [21].

Figure 8

Macroscopic view and histopathology of colonic tumors developed in mice that received AOM and DSS (0.5%, 1%, or 2% DSS in drinking water).

Figure 9

Inflammation and nitrotyrosine-positive scores in the colon of mice that received AOM and/or DSS (0.1%, 0.25%, 0.5%, 1%, or 2% DSS in drinking water). (a) Significantly different: a (P < 0.05), versus AOM→0.5% DSS group; b (P < 0.05), versus AOM→0.1% DSS group; c (P < 0.01) and d (P < 0.05), versus AOM alone group; e (P < 0.05), versus 2% DSS alone group; and f (P < 0.001), g (P < 0.005), h (P < 0.01), and i (P < 0.05), versus no treatment group. (b) Significantly different: a (P < 0.001), versus AOM→0.5% DSS group; b (P < 0.001) and c (P < 0.05), versus AOM→0.25% DSS group; d (P < 0.001) and e (P < 0.01), versus AOM→0.1% DSS group; f (P < 0.001) and g (P < 0.05), versus AOM alone group; h (P < 0.005), versus 2% DSS alone group; and i (P < 0.001) and j (P < 0.05), versus no treatment group.

Figure 10

Experimental protocol of time-course observation of AOM/DSS-induce inflammation-associated colorectal carcinogenesis and tumor development (incidence and multiplicity) during the study [11].

Figure 11

Scores of nitrotyrosine-positivity and inflammation in the inflamed colon and colonic tubular adenocarcinoma.

Figure 12

Real-time PCR analysis of iNOS and PPARγ in the colonic mucosa of mice that received AOM and DSS at weeks 6 and 10.

Figure 13

DSS is a powerful promoter in colon carcinogenesis in mice initiated with various colonic carcinogens, azoxymethane (AOM), 1,2-dimethylhydrazine (DMH), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) [, –24, 26].

Figure 14

Immunohistochemistry of PCNA, β-catenin, COX-2, and iNOS in colonic adenocarcinomas of mice induced by AOM and DSS.

Figure 15

Mutations in the GSK-3β phosphorylation consensus motif of the β-catenin gene in adenocarcinomas of mice induced by AOM/DSS, DMH/DSS, PhIP/DSS, and 2-amino-3,8-dimethylimidazo-[4,5-f]-quinoxaline (MeIQx)/DSS. PhIP and MeIQx are heterocyclic amines.

Figure 16

Macroscopic view of large bowel of four strains (Balb/c, C57BL/6N, C3H/HeN, and DBA/2N) of mice that received AOM and DSS.

Figure 17

Colonic polyps in a familial adenomatous polyposis (FAP) patient and small intestinal polyps in an APC^{Min /+} mouse (a). Experimental protocol for determining whether DSS promotes the growth of colonic dysplastic crypts in APC^{Min /+} mice (b) [29].

Figure 18

Macroscopic view and histopathology of colonic tumors and dysplastic crypts in APC^{Min /+} mice that received 2% DSS for one week. Graphs show developments of these lesions during the study (up to 5 weeks).

Figure 19

Immunohistochemistry of β-catenin, COX-2, iNOS, and p53 in the colonic adenocarcinoma and dysplastic crypts developed in male Apc^{Min /+} mice that received 2% DSS (upper panel). Apc allelic loss and gene mutations of β-catenin and K-ras in the colonic adenocarcinoma from male Apc^Min/+   mice (lower panel).