Characterization of side population cells from laryngeal cancer cell lines.

BACKGROUND Analysis of the hematopoietic system has shown that bone marrow stem cells contain a subpopulation that effluxes the DNA binding dye, Hoechst 33342, out of the cell membrane. These cells are called side population (SP) cells and have been shown to have stem cell characteristics. SP cells have already been found in solid tumors, although there are no published reports examining the role of SP cells in human laryngeal cancer. METHODS SP cells were identified in the laryngeal cancer cell lines, AMC-HN-8 (head and neck cancer cell line 8, from the Asan Medical Center) and Hep-2 (human epithelial type 2) cell lines, by flow cytometry. Hep-2 SP cells were isolated and analyzed in proliferation assays, differentiation studies, radiotherapy resistance studies, and tumorigenesis ability. RESULTS The AMC-HN-8 and Hep-2 cell lines contained 11.8 ± 1.7% and 17.1 ± 2.0% SP cells, respectively. SP cell proportion was reduced by verapamil. Hep-2 SP cells exhibited higher self-regeneration, proliferation, radiotherapy resistance, and tumorigenicity. CONCLUSIONS SP cells purified from the Hep-2 cell line harbor cancer stem cell-like properties, and they are heterogeneous, indicating that SP cells are not identical to stem cells.