Abstract 3710: Targeted inhibition of arginase-1 may underline the suppression of the development of colonic neoplasia in a transgenic APC Min mouse model.

Abstract

Colorectal cancer (CRC) is the third-leading malignancy in the United States. This year alone, about 141,210 new cases of colorectal cancer will be diagnosed and more than 49,380 people will die from the disease. Strategies have focused on early screening practices and the prevention of the development of colonic adenomas that serve as precursors of invasive colon cancers. We have recently showed that chloroquine (CQ) an anti-malarial and anti-rheumatoid agent has the capacity to competitively inhibit intracellular arginase-1 (ARG-1) and that this inhibition increases the nuclear localization of the cell cycle regulator p53 protein in colon cancer cell lines. However, the mechanism of CQ-induced inhibition of ARG-1 that results in the up-regulation of p53 is unclear. The goal of the current study was to examine the chemopreventive efficacy of CQ in the development of colonic neoplasia and to further evaluate the possible mechanism(s) of action. In this regard, six weeks old Apc(Min/+) mice were treated daily (except Saturdays and Sundays) with 0-50 mg CQ/kg body wt. via oral gavage for forty days. Post-treatment, mice were sacrificed and jejunum and colon were retrieved and preserved in 10% formalin for observation of any gross pathological changes. The results of this study showed an increased in prevalence of colonic adenomas in untreated mice compared with treated mice (< 0.05). Interestingly, histochemical analysis showed significant numbers of adenomas with high-grade dysplasia (as evidenced by the presence of increased fibrous tissue core) in untreated control mice in comparison with drug-treated mice (<0.05).Since emerging studies have identified the overexpression of ARG-1 in a variety of human malignancies, including cancer of the colon, we then investigated the impact of CQ on ARG-1 levels. To this end, HT-29 cells were co-incubated with CQ (0-50 μM) for 24 h and the levels of ARG-1 were determined by western blot assay. Surprisingly, our result showed that CQ-induced inhibition of ARG-1 level corresponded to the diminution of β-catenin protein via to its phosphorylation. Further immuno- fluorescence analysis showed an increased level of nuclear localization of GFP tagged p53 (GFP-p53) and p21 in transiently transfected HT-29 cells upon CQ treatment. The observation that targeting ARG-1 results in a corresponding decrease in β-catenin level is intriguing, since the Wnt/β-catenin signaling is fundamental to colon carcinogenesis and spontaneous tumorigenesis in Apc(Min/+) mice and patients with familial adenomatous polyposis.In conclusion, our cumulative findings indicate that CQ ameliorates the development of colonic neoplasia and that the inhibition of ARG-1 and β-catenin may contribute to its chemopreventive effects in intestinal tumorigenesis. Citation Format: Efe W. Iyamu, Mohammad S. Niaz, Aramandla Ramesh, Amos Sakwe, Kieosha Williams, Billy R. Ballard, Samuel E. Adunyah. Targeted inhibition of arginase-1 may underline the suppression of the development of colonic neoplasia in a transgenic APC Min mouse model. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3710. doi:10.1158/1538-7445.AM2013-3710