Cancer stem cell-like cells exist in mucoepidermoid carcinoma cell line MC3

Strong evidence for the presence of cancer stem cells (CSCs) in tumors exists. CSCs play an important role in the development, invasion, and drug resistance of carcinoma. Poorly differentiated mucoepidermoid carcinoma (MEC) is a lethal malignancy of human salivary gland tumors. However, whether there are CSCs in MEC and their phenotypes remains unclear. We isolated side population (SP) and sphere-forming cells from the MEC cell line MC3 and identified their characteristics. The results showed that sphere-forming assays could enrich stem cell-like cells, with this group of cells exhibiting high cloning efficiency, possessing strong tumorigenic ability, and highly expressing Oct4 based on PCR and immunocytochemistry assays. They also highly expressed CD44 and lowly expressed CD24 according to PCR, immunocytochemistry assays, and fluorescence-activated cell sorting analysis. Higher cloning efficiency was observed in the SP cells, but PCR revealed that the SP and non-SP cells did not statistically differ in their expression of ABCG2, Oct4, CD44, and CD24. In spite of these, the findings were not conclusive on whether SP cells are stem cell-like cells. In conclusion, CSC-like cells do exist in the MC3 cell line, and sphere-forming assays could enrich them, sphere-forming and SP cells are not the same kind of cell subpopulations, and the characteristics of SP cells need to be further investigated.