Identification of cancer stem-like cells in osteosarcoma: Implications in radioresistance

Recent studies suggest that many tumors contain a small subset of cells with stem-like properties that are responsible for tumor initiation and progression and resistance to conventional treatments. We aimed to identify the presence of putative cancer stem-like cells in a human osteosarcoma cell line and to evaluate their responsiveness to ionizing radiation. The isolated cells formed sphere-clusters, were positive for mesenchymal stem cell markers, differentiated into osteoblasts and developed tumors in immunocompromised mice. [¹⁸F]fluoro 2-deoxyglucose uptake in cancer stem-like cells was significantly lower than that in the original parental cell line and the median lethal dose was significantly higher. Production of reactive oxygen species was higher in the parental cell line. The cell-cycle progression in isolated cancer stem-like cells remained almost unaltered with irradiation, while parental cells arrested in G₂/M phase.