BackgroundOsteosarcoma is a bone-forming tumor of mesenchymal origin that presents a clinical pattern that is consistent with the cancer stem cell model. Cells with stem-like properties (CSCs) have been identified in several tumors and hypothesized as the responsible for the relative resistance to therapy and tumor relapses. In this study, we aimed to identify and characterize CSCs populations in a human osteosarcoma cell line and to explore their role in the responsiveness to conventional therapies.MethodsCSCs were isolated from the human MNNG/HOS cell line using the sphere formation assay and characterized in terms of self-renewal, mesenchymal stem cell properties, expression of pluripotency markers and ABC transporters, metabolic activity and tumorigenicity. Cell's sensitivity to conventional chemotherapeutic agents and to irradiation was analyzed and related with cell cycle-induced alterations and apoptosis.ResultsThe isolated CSCs were found to possess self-renewal and multipotential differentiation capabilities, express markers of pluripotent embryonic stem cells Oct4 and Nanog and the ABC transporters P-glycoprotein and BCRP, exhibit low metabolic activity and induce tumors in athymic mice. Compared with parental MNNG/HOS cells, CSCs were relatively more resistant to both chemotherapy and irradiation. None of the treatments have induced significant cell-cycle alterations and apoptosis in CSCs.ConclusionsMNNG/HOS osteosarcoma cells contain a stem-like cell population relatively resistant to conventional chemotherapeutic agents and irradiation. This resistant phenotype appears to be related with some stem features, namely the high expression of the drug efflux transporters P-glycoprotein and BCRP and their quiescent nature, which may provide a biological basis for resistance to therapy and recurrence commonly observed in osteosarcoma.

AimThere are growing evidences that tumors contain a subset of cells with stem like properties. These cells are referred as cancer stem cells (CSC) and are responsible for driving tumor growth and recurrence. We aimed to isolate and characterize putative CSCs in a human osteosarcoma cell line (MNNG/HOS) and to explore their role in response to chemotherapy. MethodsCSCs were isolated using the sphere-forming assay in serum-free medium under non-adherent conditions and characterized for the expression of mesenchymal stem cell markers (CD90 + , CD105 + , CD73 + ) by flow cytometry. The chemosensitity of MNNG and CSCs to doxorubicin (DOX), cisplatin (CIS) and methotrexate (MTX) was evaluated using the MTT colorimetric assay after an incubation period of 48h. Cell cycle progression was analyzed by flow cytometry with propidiun iodide. ResultsA subpopulation of tumor cells formed sphere-clusters in serum-free medium and were positive for MSC markers. These cells revealed to be more resistant to chemotherapy in comparison with MNNG/HOS cells. The half maximal inhibitory concentrations (IC 50 ) of DOX (0.66 ± 0.24 μM), CIS (13.18 ± 0.09 μM) and MTX (0.05 ± 0.01 μM) were significantly higher (p < 0.05) than those in MNNG/HOS cells (DOX: 0.30 ± 0.07 μM; CIS: 8.08 ± 3.78 μM; MTX: 0.006 ± 0.001 μM). All drugs induced a G2/M cell cycle arrest in MNNG/HOS cells. In opposite, no significant changes were observed in CSC. ConclusionsWe have identified a subset of tumor cells with stemlike properties in OS that are relatively resistant to conventional chemotherapeutic agents. Therefore conventional drugs might not address this subset of cells that can be responsible for tumor regrowth after therapy.

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.