Abstract 954: A selective iNOS inhibitor N6-iminoethyl-lysine tetrazoleamide (NILT), suppress invasive colonic cancers and improves preventive efficacy of low-dose COX-2 inhibitor, celecoxib in F344 rats

Abstract

Abstract Clinical and preclinical studies suggest that NSAIDs and cyclooxygenase (COX)-2 inhibitors such as celecoxib, reduce the risk of colorectal cancer. However, at high doses celecoxib causes gastrointestinal toxicity and an increased cardiovascular risk. Inducible nitric oxide synthase (iNOS), similar to COX-2, is overexpressed in colon tumors, and nitric oxide is shown to stimulate COX-2 activity and contributes to the tumor invasiveness. Thus, in the present study we tested a novel iNOS-selective inhibitor NILT for colon cancer inhibition and invasiveness in F344 rats and evaluated the combined low dose effects of NILT and celecoxib, to improve the chemopreventive efficacy in rats. Seven week old male F344 rats (36/group) were fed control AIN-76A diet and colon cancer was induced by administering azoxymethane (AOM), s.c., a single dose at week 8 and 9. Four weeks after the AOM treatment, groups of rats were fed experimental diets containing either 0, 100, 200 ppm of NILT or 250 and 500 ppm of celecoxib or a combination of 100 ppm NILT and 250 ppm celecoxib. Forty eight weeks after AOM treatment, rats were killed and the colonic tumors were evaluated. Multiple samples of colonic tumors from each group were assayed for activity levels of iNOS, COX-2, and expression levels of cytokines, chemokine and markers of apoptosis and cell proliferation. We found that dietary administration of 200 ppm NILT suppressed both colon adenocarcinoma incidence by 40% (p<0.02) and multiplicity by 46 % (p<0.02); whereas 100 ppm NILT showed ∼33% of colon adenocarcinoma incidence and multiplicity (p<0.06). Importantly, 100 ppm and 200 ppm iNOS inhibitor suppressed invasive adenocarcinomas multiplicities by 52% and 67% (P<0.007). Celecoxib at both the doses (250 and 500 ppm) significantly suppressed colon adenocarcinoma incidence (55 − 77%, p<0.002 − 0.0001) and multiplicity (66 − 82% (p<0.002 − 0.0002). Furthermore, low dose combination of 100 ppm NILT plus 250 ppm celecoxib suppressed colon adenocarcinoma incidence by 70% and multiplicity by 77%. Low dose combinations of NILT and celecoxib showed improved efficacy over NILT alone. In colonic tumors of rats fed NILT and/or combination of 100 ppm NILT plus 250 ppm celecoxib showed a significantly low levels of iNOS and COX-2 activities and increased p53, p21, BAX, Caspase −3 and PARP expressions, along with significant decreased levels of Bcl-2, inflammatory cytokines and chemokine expression. Significant levels of apoptotic cells were also observed in treated tumors. These results demonstrate the chemopreventive efficacy of novel iNOS inhibitor against the colon adenocarcinoma, in particular, invasive cancers and increased efficacy when combined with low-dose celecoxib. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 954.