Characterization of cancer stem-like cells in chordoma
Chordomas are locally aggressive bone tumors known to arise from the remnants of the notochord. Because chordomas are rare, molecular studies aimed at developing new therapies are scarce and new approaches are needed. Chordoma cells and cancer stem-like cells share similar characteristics, including self-renewal, differentiation, and resistance to chemotherapy. Therefore, it seems possible that chordomas might contain a subpopulation of cancer stem-like cells. The aim of this study is to determine whether cancer stem-like cells might be present in chordomas. In this study, the authors used gene expression analysis for common cancer stem-like cellmarkers, including c-myc, SSEA-1, oct4, klf4, sox2, nanog, and brachyury, and compared chordoma cells and tissues with nucleus pulposus tissues (disc degenerated nontumorigenic tissues). Differentiation through agents such as all-trans retinoic acid and osteogenic differentiation medium was induced to the chordoma cells. Additionally, U-CH1 cells were sorted via magnetic cell sorting for stem cell markers CD133 and CD15. After separation, positive and negative cells for these markers were grown in a nonadherent environment, soft agar, to determine whether the presence of these cancer stem-like cells might be responsible for initiating chordoma. The results were compared with those of untreated cells in terms of migration, proliferation, and gene expression by using reverse transcriptase polymerase chain reaction. The results indicate that chordoma cells might be differentiating and committing into an osteogenic lineage when induced with the osteogenic differentiation agent. Chordoma cells that are induced with retinoic acid showed slower migration and proliferation rates when compared with the untreated cells. Chordoma cells that were found to be enriched by cancer stem-like cell markers, namely CD133 and CD15, were able to live in a nonadherent soft agar medium, demonstrating a self-renewal capability. To the authors' knowledge, this is the first time that cancer stem-like cell markers were also found to be expressed in chordoma cells and tissues. Cancer stem-like cell detection might be an important step in determining the recurrent and metastatic characteristics of chordoma. This finding may lead to the development of new approaches toward treatments of chordomas.