Abstract B55: Multitargeted low-dose combination chemoprevention: A novel, ideal, and promising approach to combat colon carcinogenesis

Abstract

Abstract Colon cancer is the second to third most common causes of cancer deaths in U.S. Identifying strategies that interrupt process of carcinogenesis without undue side effects, maintaining balance between efficacy and toxicity of interventions is critical to long term successful application of chemoprevention to high risk population. Different modes of action exerted by combination regimens offer promise and represent a practical approach for improving synergistic tumor inhibitory effects without unwanted side effects as they allow use of low doses for blocking multiple signaling pathways. Preclinical studies have previously shown that gefitinib (G), licofelone (L), atorvastatin (A) and DFMO (D), as promising colon cancer chemopreventive agents. These drugs are currently in different phases of various clinical trials for treatment of colon/lung cancers or arthritis. As these drugs (GLAD) target critical pathways of colon carcinogenesis, we decided to test the low dose combination of these four classes of agents for prevention of colon cancer. Experiments were designed to assess the toxicity of GLAD in C57BL/6J wild type mice and chemopreventive efficacy for suppression of intestinal tumorigenesis in ApcMin/+ mice. Six-week old male and female wild type (6/group) and ApcMin/+ mice (10/Group) fed with modified AIN-76A diets with or without GLAD (25+50+50+500 ppm) for 100 days (∼14 weeks). At the termination, both small intestinal and colonic tumors were evaluated for number, size and location; and multiple samples of normal appearing mucosa and tumors harvested from small intestine and colon were evaluated histopathologically. Expression levels of markers for proliferation (PCNA), apoptosis(TUNEL,p21,caspase-3), Cav-1, p2X7, COX-2, 5LOX, β-catenin, Cyclin B1, cyclin D1, p38 and serum inflammatory cytokines were determined by IHC, western blotting, RT-PCR and/or Elisa. Our results suggest that dietary GLAD had no signs of toxicity based on organ pathology, liver enzyme profile in mice. Dietary GLAD significantly inhibited (p<0.0001) total intestinal tumor multiplicity and size in both in male and female APCmin/+mice (mean ± SEM tumors for 0 ppm, and GLAD had 67.1±5.4, 11.3±1.1 respectively, in male mice; and 72.3± 8.9, 14.5±2.8 respectively, in female mice). Importantly, GLAD showed 80-85% (P<0.0001) intestinal tumor inhibition in both genders. Remarkably, mice fed GLAD had >95% less polyps with size of >2mm compared to control mice polyps. Male and female mice fed with GLAD showed 75% and 85% inhibition of colonic tumors respectively. Intestinal tumors of mice fed GLAD diet showed significantly reduced PCNA expression, increased TUNEL positive cells. Also, mice fed with GLAD diets showed significant suppression of Cav-1, p2X7, β-catenin, cyclin B1 and Inflammatory cytokines, and, increase in p21, caspase-3 cleavage (p<0.0001). However, we did not observe any significant difference in the expression levels of COX-2, 5LOX, cyclin D1 and p38. These observations demonstrate for the first time that GLAD, a novel cocktail mixture of chemopreventive agents at very low doses suppress SI and colonic tumor formation in ApcMin/+ mice with no toxicity. This novel strategy to prevent colorectal cancer is an important step in developing chemopreventive agents with high efficacy without unwanted side effects. {Supported by NCI-CN-53300} Citation Information: Cancer Prev Res 2010;3(12 Suppl):B55.