In vivo molecular imaging of cancer stem cells in mice with xenografted colon cancer

Objectives To monitor the behavior of cancer stem cell (CSC) in vivo, we characterized human colon cancer cell line Caco2 according to CD133 and CD44, putative CSC surface markers, and then established an in vivo molecular imaging method in a xenografted mouse model.

Methods We characterized Caco2 cells by the expression of CD133/CD44 marker using fluorescence activated cell sorting analysis according to the cell passage. By means of transfection of Caco2 cells with an enhanced firefly luciferase (effLuc) retroviral vector, we established a stable cell line (Caco2-effLuc). After separation using automated magnetic cell sorter, both CD133+ and CD133- groups were cultured in a 24-well plate and injected subcutaneously into nude mice with/without Matrigel, and then they were monitored using a luminometer for in vitro and optical imaging system for in vivo.

Results Early passage Caco2 cells expressed CD133/CD44 (passage 15: 58%/10%) highly, but dramatically decreased in the late passage (passage 25; 5.4%/1.1%). With assistance of Matrigel, both CD133+ and CD133- cells could make a xenograft, but the proliferation of the CD133+ cells were greater than that of CD133- cells, approximately 80 folds at 10 days after the injection of the cells. In contrast to CD133- cells that were non-capable of forming a xenograft without Matrigel, CD133+ cells could make a xenograft even without Matrigel though the proliferation was lagged.

Conclusions The putative CSC marker was highly expressed in the early passage Caco2 cell line. Colon cancer cells expressing CD133 might play a key role in tumor proliferation