Generation of a model colon cancer stem cell system provides novel therapeutic opportunities

A99 Increasing evidence suggests that tumors depend on a subpopulation of cells termed cancer stem cells (CSCs) for tumor initiation and resistance to therapeutic intervention. Targeting the elimination of cancer stem cells therefore presents an opportunity for the development of more effective cancer treatments. A significant obstacle to characterizing cancer stem cells however is the limited ability to expand sufficient clonal populations for phenotypic characterization. Previously it has been demonstrated that CSC populations can be isolated and expanded as 3D tumorospheres from glioblastoma (Bao et al., Nature. 2006; 444:756) and melanoma (Fang et al., Cancer Research, 2005; 65:9328). More recently, CSC populations from colon carcinoma have been isolated based on their expression of the stem cell marker CD133 and expanded as 3D tumorospheres (Ricci-Vitiani et al., Nature 2007; 445:106). Here, we independently demonstrate isolation of tumorospheres from nine out of thirteen surgically resected colon tumor specimens of varying pathology stage and confirm that spheroid formation resides within the CD133 expressing population. Prolonged culturing of tumorospheres in an undifferentiated state was achieved for 3 independent colon cancer specimens with one in culture for over 22 months showing no notable senescence but retaining the ability to self-renew and differentiate towards an adherent epitheloid morphology. The long term spheroid cultures grow in an anchorage independent manner indicating their tumorogenic capacity. Expression of the stem cell markers nestin, BMI-1 and mushahsi-1 support their use as a model for stem cells. Significantly, they also displayed resistance to the growth inhibititory and apoptotic effects mediated by the chemotherapeutic irinotecan. To further characterize the tumorospheres, cell surface proteins were captured and subjected to LC-MS based quantitative proteomic analyses revealing enriched expression of CD133 and CD44. Taken together the characteristics of the expanded CD133 expressing colon cancer tumorospheres isolated suggest they have the potential to serve as a novel model system in which to identify and characterize treatments for colorectal cancer that are capable of targeting cancer stem cells.