The role of CysLT1R in animal models of colorectal cancer

Abstract: Cysteinyl leukotrienes (LTC4, LTD4 and LTE4) are potent pro-inflammatory lipids derived from arachidonic acid and mediate their effect through CysLT1R and CysLT2R. There is a strong correlation between long-standing inflammatory bowel disease where these pro-inflammatory mediators are abundant and colorectal cancer. We have shown that LTD4 via its receptor CysLT1 induces expression of proteins associated with colorectal cancer and promotes proliferation, survival and migration in intestinal epithelial cells. In addition, we have demonstrated that that high expression of CysLT1R in colorectal adenocarcinomas predicts poor prognosis in patients. In the presented papers in this thesis we investigated the role of CysLT1R in different mouse models of colorectal cancer. In the mouse xenograft model of colon cancer, we were able to observe a reduced tumor growth in response to CysLT1R antagonist treatment. The inhibition of the tumor growth was accompanied with changes in proliferation and apoptosis as determined by reduced Ki-67 expression, increased expression of p21WAF/Cip1, cleaved caspase 3 and caspase-cleaved keratin 18. An impaired tumor angiogenesis was also demonstrated by detection of increased levels of VEGF and reduced vessel size. We also investigated the role of CysLT1R in 1) FAP/sporadic colorectal cancer by crossing ApcMin/+ mice with mice lacking CysLT1R expression and in 2) colitis-associated colorectal cancer by employing the AOM/DSS-model on mice lacking CysLT1R expression. Interestingly, a reduced polyp formation in a gender-specific manner could be observed in both models. CysLT1R knockout female mice, but not male mice exhibited a reduced polyp formation in the small intestine and colon, respectively. Also, a decreased nuclear expression of β-catenin within the epithelial tumor compartment was determined for CysLT1R mutant female mice in both models. However, the mechanism of tumor progression in FAP/sporadic colorectal cancer and in colitis-associated colorectal cancer might differ as indicated by reduced tumor expression of COX-2 and reduced serum levels of PGE2 in the female double mutant (CysLT1R−/− ApcMin/+) mice, whereas AOM/DSS-treated female single mutant (CysLT1R−/−) mice demonstrated increased serum levels of PGE2. In conclusion, the presented mouse models of colorectal cancer further strengthen our previous in vitro findings and highlight the prospect of CysLT1R as an alternative therapeutic approach.