Anti-inflammatory drug resistance selects putative cancer stem cells in a cellular model for genetically predisposed colon cancer

Abstract

Mutations in the adenomatous polyposis coli (Apc) tumor suppressor gene represent the primary genetic defect in colon carcinogenesis. Apc+/- mouse models exhibit pre-invasive small intestinal adenomas. Cell culture models exhibiting Apc defects in the colon and quantifiable cancer risk provide a novel clinically relevant approach. The tumor-derived Apc-/- colonic epithelial cell line 1638N COL-Pr1 represented the experimental model. The anti-inflammatory drugs sulindac (SUL) and celecoxib (CLX) represented the test compounds. Compared with non-tumorigenic Apc+/+ C57COL cells, the Apc+/- 1638N COL cells and Apc-/- 1638N COL-Pr1 cells exhibited progressive loss of homeostatic growth control. Compared with Apc+/- cells, Apc-/- cells displayed increased expression of biomarkers specific for hyper-proliferation. Treatment of Apc-/- cells with SUL and CLX resulted in inhibition of anchorage-independent colony formation in vitro, which is indicative of reduced cancer risk in vivo. Mechanistically, SUL and CLX suppressed the expression of the Apc target genes β-catenin, cyclin D1, c-Myc and cyclooxygenase-2. Long-term treatment with high concentrations of SUL and CLX led to the selection of hyper-proliferative drug-resistant phenotypes. The Apc-/- SUL-resistant phenotype displayed spheroid formation and enhanced the expression of the stem cell-specific molecular markers CD44, CD133 and c-Myc. These data demonstrated the growth-inhibitory efficacy of SUL and CLX and indicated that drug resistance leads to the selection of a putative cancer stem cell phenotype. The study outcome validates a stem cell-targeted mechanistic approach to identify testable alternative leads for chemotherapy-resistant colon cancer.