Temozolomide increases the number of mismatch repair-deficient intestinal crypts and accelerates tumorigenesis in a mouse model of Lynch syndrome.

BACKGROUND & AIMS: Lynch syndrome, a nonpolyposis form of hereditary colorectal cancer, is caused by inherited defects in DNA mismatch repair (MMR) genes. Most patients carry a germline mutation in 1 allele of the MMR genes MSH2 or MLH1. With spontaneous loss of the wild-type allele, cells with defects in MMR exist among MMR-proficient cells, as observed in healthy intestinal tissues from patients with Lynch syndrome. We aimed to create a mouse model of this situation to aid in identification of environmental factors that affect MMR-defective cells and their propensity for oncogenic transformation. METHODS: We created mice in which the MMR gene Msh2 can be inactivated in a defined fraction of crypt base columnar stem cells to generate MSH2-deficient intestinal crypts among an excess of wild-type crypts (Lgr5-CreERT2;Msh2(flox/-) mice). Intestinal tissues were collected; immunohistochemical analyses were performed for MSH2, along with allele-specific PCR assays. We traced the fate of MSH2-deficient crypts under the influence of different external factors. RESULTS: Lgr5-CreERT2;Msh2(flox/-) mice developed more adenomas and adenocarcinomas than control mice; all tumors were MSH2 deficient. Exposure of Lgr5-CreERT2;Msh2(flox/-) mice to the methylating agent temozolomide caused MSH2-deficient intestinal stem cells to proliferate more rapidly than wild-type stem cells. The MSH2-deficient intestinal stem cells were able to colonize the intestinal epithelium and many underwent oncogenic transformation, forming intestinal neoplasias. CONCLUSIONS: We developed a mouse model of Lynch syndrome (Lgr5-CreERT2;Msh2(flox/-) mice) and found that environmental factors can modify the number and mutability of the MMR-deficient stem cells. These findings provide evidence that environmental factors can promote development of neoplasias and tumors in patients with Lynch syndrome.

Sulindac effects on inflammation and tumorigenesis in the intestine of mice with Apc and Mlh1 mutations.

We have previously reported that sulindac, a non-steroidal anti-inflammatory drug, inhibited tumor formation in the small intestine but increased tumors in the colon of Apc(Min/+) mice, a model of human familial adenomatous polyposis. To further explore intestinal regional responses, we studied effects of sulindac on additional gene-targeted mouse models of human intestinal tumorigenesis; these were (i) Apc(1638N/+) mouse (chain termination mutation in exon 15 of the Apc gene); (ii) Mlh1(+/-) mouse (DNA mismatch repair deficiency, a mouse model of human hereditary non-polyposis colorectal cancer) and (iii) double-heterozygous Mlh1(+/-)Apc(1638N/+) mutant mouse. Mice were fed AIN-76A control diet with or without 0.02% sulindac for 6 months. Intestinal regional tumor incidence, multiplicity, volume and degree of inflammation were used as end points. The results showed the following: (i) sulindac inhibited tumor development in the small intestine of Apc(1638N/+) mice; (ii) in contrast, sulindac increased tumors in the small intestine of Mlh1 mutant mice, a neoplastic effect which persisted in heterozygous compound Mlh1(+/-)Apc(1638N/+) mutant mice; (iii) sulindac increased tumors in the cecum of all mice regardless of genetic background; (iv) sulindac decreased inflammation in the small intestine of Apc(1638N/+) mice, but it increased inflammation in the small intestine of Mlh1(+/-) mice and Mlh1(+/-)Apc(1638N/+) mice and (v) sulindac enhanced inflammation in the cecum of all mutant mice. Findings indicate that the effects of sulindac in the intestine of these mutant mouse models are probably related to genetic background and appear to be associated with its inflammatory-inducing response.