ABCG2-meditated multidrug resistance and tumor-initiating capacity of side population cells from colon cancer.

BACKGROUND: Recent studies have reported that the presence of cancer stem cells (CSCs) has major implications in the treatment of cancer and is responsible for tumor relapse. In the current study, we identified and characterized colon CSC-like side population (SP) cells from colon cancer tissue.

MATERIALS AND METHODS: The colon cancer samples were subjected to fluorescence-activated cell sorting (FACS) based on Hoechst 33342 dye exclusion for the purification of SP cells. The sorted SP cells were subjected to further characterization by immunofluorescence, real-time polymerase chain reaction (RT-PCR), multidrug resistance, and sphere formation assays.

RESULTS: We identified a fraction of 3.3% of SP cells in the colon cancer cell samples, which was reduced to 0.6% upon treatment with verapamil. The sorted SP cells showed high positivity with regard to CD133, CD44, CD147, and EpCAM, by fluorescence microscopic analysis. Further, these SP cells were highly resistant to multidrug treatment due to overexpression of the multidrug resistance 1 (MDR1) transporter protein ABCG2.

CONCLUSION: Our findings suggest that the overexpression of ABCG2 and the expression of stem cell surface markers are collectively responsible for chemotherapy failure, tumor recurrence, and invasion in colon cancer.