Cysteinyl leukotriene receptor 1 facilitates tumorigenesis in a mouse model of colitis-associated colon cancer.

Cysteinyl leukotriene receptor 1 (CysLT1R) has been shown to be up-regulated in the adenocarcinomas of colorectal cancer patients, which is associated with a poor prognosis. In a spontaneous model of colon cancer, CysLT1R disruption was associated with a reduced tumor burden in double-mutant female mice (ApcMin/+/Cysltr1-/-) compared to ApcMin/+ littermates. In the current study, we utilized a genetic approach to investigate the effect of CysLT1R in the induced azoxymethane/dextran sulfate sodium (AOM/DSS) model of colitis-associated colon cancer. We found that AOM/DSS female mice with a global disruption of the Cysltr1 gene (Cysltr1-/-) had a higher relative body weight, a more normal weight/length colon ratio and smaller-sized colonic polyps compared to AOM/DSS wild-type counterparts. The Cysltr1-/- colonic polyps exhibited low-grade dysplasia, while wild-type polyps had an adenoma-like phenotype. The Cysltr1-/- colonic polyps exhibited significant decreases in nuclear ß-catenin and COX-2 protein expression, while the normal crypts surrounding the polyps exhibited increased Mucin 2 expression. Furthermore, Cysltr1-/- mice exhibited an overall reduction in inflammation, with a significant decrease in proinflammatory cytokines, polyp 5-LOX expression and infiltration of CD45 leukocytes and F4/80 macrophages. In conclusion, the present genetic approach in an AOM/DSS model further supports an important role for CysLT1R in colon tumorigenesis.

The eicosanoids leukotriene D4 and prostaglandin E2 promote the tumorigenicity of colon cancer-initiating cells in a xenograft mouse model.

BACKGROUND: Colorectal cancer is one of the most common types of cancers worldwide. Recent studies have identified cancer-initiating cells (CICs) as a subgroup of replication-competent cells in the development of colorectal cancer. Although it is understood that an inflammation-rich tumor microenvironment presumably supports CIC functions, the contributory factors are not very well defined. The present study advances our understanding of the role of the eicosanoids leukotriene D4 (LTD4) and prostaglandin E2 (PGE2) in the tumorigenic ability of CICs and investigates the consequential changes occurring in the tumor environment that might support tumor growth. METHODS: In this study we used human HCT-116 colon cancer ALDH(+) cells in a nude mouse xenograft model. Protein expression and immune cell was determined in tumor-dispersed cells by flow cytometry and in tumor sections by immunohistochemistry. mRNA expressions were quantified using RT-q-PCR and plasma cytokine levels by Multiplex ELISA. RESULTS: We observed that LTD4 and PGE2 treatment augmented CIC-induced tumor growth. LTD4-and PGE2-treated xenograft tumors revealed a robust increase in ALDH and Dclk1 protein expression, coupled with activated ß-catenin signaling and COX-2 up-regulation. Furthermore, LTD4 or PGE2 accentuated the accumulation of CD45 expressing cells within xenograft tumors. Further analysis revealed that these infiltrating immune cells consisted of neutrophils (LY6G) and M2 type macrophages (CD206(+)). In addition, LTD4 and PGE2 treatment significantly elevated the plasma levels of cysteinyl leukotrienes and PGE2, as well as levels of IL-1ß, IL-2, IL-6, TNF-α and CXCL1/KC/GRO. In addition, increased mRNA expression of IL-1ß, IL-6 and IL-10 were detected in tumors from mice that had been treated with LTD4 or PGE2. CONCLUSION: Our data suggest that both LTD4 and PGE2 promote CICs in initiating tumor growth by allowing modifications in the tumor environment. Our data indicate that new therapeutic strategies targeting eicosanoids, specifically LTD4 and PGE2, could be tested for better therapeutic management of colon cancer.

Cysteinyl leukotriene 1 receptor influences intestinal polyp incidence in a gender-specific manner in the ApcMin/+ mouse model.

There is emerging literature emphasizing the role of inflammatory eicosanoids, including prostaglandins and leukotrienes, in cancer development. Increased expression of both the cysteinyl leukotriene receptor 1 (CysLTR1) and the enzyme responsible for the production of leukotrienes, 5-lipoxygenase, is associated with poor prognosis in patients with colorectal adenocarcinomas. Apc mutation is an early event in the development of sporadic and hereditary (familial adenomatous polyposis) colorectal cancer. We utilized the Apc(Min/+) mouse model of familial adenomatous polyposis/sporadic colorectal cancer to investigate the role of CysLTR1 in intestinal tumorigenesis by crossing Apc(Min/+) mice with mice lacking the Cysltr1 gene. We could observe a reduced tumor burden in the small intestine of double-mutant female (Cysltr1 (-/-) Apc (Min/+) ) but not double-mutant male mice, compared with gender-matched single-mutant (Cysltr1 (+/+) Apc (Min/+) ) mice. This reduction was in a Cysltr1-dependent manner, female double-mutant mice having significantly reduced tumor formation compared with control littermates. The female double-mutant phenotype was accompanied with decreased systemic inflammation, as evidenced by significantly reduced serum levels of prostaglandin E2 and CysLTs, as well as increased CD3(+)CD8(+) T-cell tumor infiltration. Furthermore, the reduced formation of polyps in double-mutant (Cysltr1 (-/-) Apc (Min/+) ) female mice could in part be explained by the cytotoxic action of CD3(+)CD8(+) T cells in the polyp and reduced nuclear accumulation of ß-catenin in the epithelium of small intestinal polyps. Our results stress the important role that CysLTR1 plays in colorectal cancer and its potential as a therapeutic target in cancer therapy.