Osteosarcoma contains a subpopulation of cancer stem-like cells that are highly resistant to radiotherapy
© Neves et al; licensee BioMed Central Ltd. 2010
Published: 24 September 2010
The cancer stem cell (CSC) theory states that tumors contain a subset of cells responsible for tumor initiation and growth and recurrence after treatments. We aimed to identify the presence of putative CSCs in a human MNNG/HOS osteosarcoma cell line and investigate their role in response to radiotherapy.
The isolation of CSCs was performed using the sphere formation assay in serum-free medium in non-adherent conditions. The cells were characterized for the expression of mesenchymal stem cell markers (CD90+/CD105+/CD73+) by flow cytometry. MNNG/HOS and CSCs were irradiated with X-rays at different doses (0-20Gy). The sensitivity to ionizing radiation was evaluated using the MTT assay after 7 days. Cell-cycle responses were studied at 24h post-irradiation using propidium iodide staining.
A subset of CSCs was identified in the MNNG/HOS cell line. The isolated cells formed sphere-clusters and were positive for MSC markers. The mean lethal dose (LD50) obtained for CSCs was of 8.0 ± 3.0Gy, significantly higher than for MNNG/HOS cells (LD50 = 3.4 ± 0.6Gy, p < 0.05). It was observed a dose dependent cell-cycle arrest in G2/M phase at 24h, in the MNNG/HOS cells. CSCs cell-cycle progression remained unaltered.
Osteosarcoma contains a subset of cells with stem-like properties that are relatively resistant to radiation. The absence of alterations in cell-cycle progression of CSCs suggests that these cells may have higher capacity to repair the irradiation-induced DNA lesions and increased DNA damage checkpoints signaling. These results suggest that radiotherapy may not address the CSCs subpopulation allowing them to survive and regenerate the tumor.
This article is published under license to BioMed Central Ltd.