Cell cycle analysis of the CD133⁺ and CD133^- cells isolated from human colorectal cancer

Aim: The CD133 antigen has been identified as a putative stem cell marker in colorectal cancer tissues. The aim of this study was to investigate the cell cycle state of CD133⁺ and CD133^- cells, isolated from primary human colorectal tumors. Materials and Methods: After mechanical and enzymatic dissociation of the tumor samples, CD133⁺ and CD133 ^- subsets were identified and separated by magnetic cell sorting. Flow cytometric analysis was performed to compare the cell cycle of both CD133⁺ and CD133^- cells isolated from primary and liver metastatic cancer cells. Results: The results indicated that CD133⁺ cells isolated from both primary and liver metastatic colorectal cancers were found in higher percentage in the G0/G1 phases. However, the CD133^- cells isolated from primary colorectal cancers were predominantly found in the S and G2/M phases. Surprisingly, the CD133^- cells isolated from liver metastatic colorectal cancers were mostly found in the G0/G1 phase. Conclusion: The present study provides evidence that CD133⁺ cells are in a quiescent state in colorectal cancer, representing a mechanism that would at least partially explain chemotherapy resistance and tumor recurrence in post-Therapy patients.