Title

Early detection and non-steroidal anti-inflammatory drug chemoprevention of colorectal cancer

Date of Completion

January 2010

Keywords

Biology, Cell

Degree

Ph.D.

Abstract

Early detection and removal of pre-cancerous adenomas and polyps through endoscopic techniques remains the most effective method for reducing the morbidity and mortality associated with colorectal cancer (CRC). Aberrant crypt foci (ACF) are microscopic surface abnormalities that are putative precursors to adenomas and CRC. ACF exhibit similar histological and molecular abnormalities to adenomas and CRC and potentially represent useful biomarkers of cancer risk. We examined ACF from subjects undergoing screening colonoscopies. Notably, no patients included in the study had a concurrent colon cancer. Genomic DNA, isolated by laser capture microdissection, was prepared from ACF and adjacent normal colonic epithelium. We show that K-ras mutations, promoter hypermethylation of RASSF1A, hMLH1 and MGMT, and microsatellite instability (MSI) can all be detected in ACF in the absence of synchronous colon tumors and are not accompanied by field effects into the surrounding epithelium. Also, all ACF with MGMT hypermethylation displayed an MSI-low phenotype. These lesions may be precursors to MSI-low CRC, providing a potential early biomarker to assess the effects of cancer prevention strategies. ^ Chemoprevention has emerged as a complementary and even first-line strategy in high-risk subjects for the prevention of CRC, using agents that target cancer-associated pathways to delay, prevent or reverse the development of adenomas. Among the most promising chemopreventive approaches are non-steroidal anti-inflammatory drugs (NSAIDs), which inhibit the COX-1 and -2 enzymes and can induce apoptosis in colon cancer cells through multiple mechanisms. We show that the NSAID sulindac significantly inhibits small intestinal tumors in ApcMin/+ mice, but actually increases colon tumor multiplicity. Importantly, p21WAF1/cip1 and PPARγ expression were absent in colon tumors from sulindac-treated mice, suggesting that loss of these proteins is necessary for drug resistance. These observations may be translatable to designing novel clinical therapies utilizing combinations of agents that target multiple molecular pathways to overcome sulindac resistance. We also show that the NSAID ibuprofen inhibits nuclear β-catenin expression in human sporadic colon adenomas as well as in colon cancer cell lines. These data demonstrate that this drug can target a key pathway associated with colon carcinogenesis and may be a good candidate for future clinical trials for CRC chemoprevention. ^