Malisetty V. Swamy

Slippage of Mitotic Arrest and Enhanced Tumor Development in Mice with BubR1 Haploinsufficiency

A compromised spindle checkpoint is thought to play a key role in genetic instability that predisposes cells to malignant transformation. Loss of function mutations of BubR1, an important component of the spindle checkpoint, have been detected in human cancers. Here we show that BubR1+/− mouse embryonic fibroblasts are defective in spindle checkpoint activation, contain a significantly reduced amount of securin and Cdc20, and exhibit a greater level of micronuclei than do wild-type cells. RNA interference-mediated down-regulation of BubR1 also greatly reduced securin level. Moreover, compared with wild-type littermates, BubR1+/− mice rapidly develop lung as well as intestinal adenocarcinomas in response to challenge with carcinogen. BubR1 is thus essential for spindle checkpoint activation and tumor suppression.

Low doses of β-carotene and lutein inhibit AOM-induced rat colonic ACF formation but high doses augment ACF incidence

Epidemiological studies suggest that carotenoids such as β‐carotene and lutein play an important role in reducing the risk for several cancers. However, in colon cancer there is ambiguity with regard to the role of these compounds in that both preventive effects and tumor promotion have been observed. In the present study we observed that male F344 rats were able to tolerate up to 2,500 ppm of β‐carotene as well as of lutein. We have then assessed the chemopreventive efficacy of β‐carotene and lutein at dose levels of ∼4 and 8% of the 2,500 ppm tolerated dose (TD) and also ∼40 and 80% of the TD on azoxymethane (AOM)‐induced colon carcinogenesis, using aberrant crypt foci (ACF) as a surrogate biomarker for colon cancer. Throughout the experiments, 5‐week‐old male F344 rats were fed the control diet (modified AIN‐76A) or experimental diets containing 100 or 200 ppm (∼4 or 8% of the 2,500 ppm TD), or 1,000 or 2,000 ppm (∼40 or 80% of the 2,500 ppm TD) of β‐carotene and lutein (n=10 rats/group). After 2 weeks on the experimental or control diets, all animals were injected with AOM (15 mg/kg body wt., once weekly for 2 weeks). At 14 weeks of age, all rats were killed, and their colons were evaluated for ACF. Administration of 100 or 200 ppm of β‐carotene inhibited AOM‐induced total colonic ACF formation by 24% (p<0.01) and 36% (p<0.001), respectively, whereas lutein at 200 ppm produced a 27% inhibition (p<0.01) yet had no significant effect at the 100 ppm dose level. Surprisingly, administration of 1,000 or 2,000 ppm of β‐carotene and lutein increased colonic ACF formation in a dose‐dependent manner, i.e., to 124% and 144% for the former and 110% and 159% for the latter. These results clearly suggest that further studies are warranted to determine whether the increase in ACF incidence by high doses of β‐carotene and lutein will also lead to an increase in tumor outcome. Taken together these data indicate that the chemopreventive activity of β‐carotene and lutein against colon carcinogenesis depends on the dose level.

Abstract 954: A selective iNOS inhibitor N 6 -iminoethyl-lysine tetrazoleamide (NILT), suppress invasive colonic cancers and improves preventive efficacy of low-dose COX-2 inhibitor, celecoxib in F344 rats

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 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.