Inhibition of hypoxia-inducible factor-1 alpha radiosensitized MG-63 human osteosarcoma cells in vitro

Aims and background: Hypoxia is a fundamental microenvironmental component of osteosarcoma which induces activation of the hypoxia-inducible factor-1 (HIF-1) pathway. Overexpression of HIF-1 alpha has been linked to tumor resistance to radio- or chemotherapy. However, little is known about the effects of HIF-1 alpha inhibition on hypoxic radioresistance of human osteosarcoma cells. Here, we investigated the effects of HIF-1 alpha inhibition on cell survival and radiosensitivity in the MG-63 human osteosarcoma cell line. Methods: HIF-1 alpha inhibition was achieved by small interfering RNA (siRNA) targeting of HIF-1 alpha or via chetomin. Inhibition of the HIF-1 pathway was determined by monitoring the expression levels of HIF-1 alpha, carbonic anhydrase 9 (CA9) and vascular endothelial growth factor (VEGF) using quantitative real-time PCR and Western blot analyses. Clonogenic assay was performed after irradiation (2-10 Gy) to investigate the effect of HIF-1 alpha inhibition on the radiosensitivity of human osteosarcoma cells under normoxic and hypoxic conditions. Results: Compared to the control groups, treatment with HIF-1 alpha siRNA or chetomin significantly reduced the hypoxia-inducible radioresistance of MG-63 cells. However, siRNA and chetomin showed different effects on the radiosensitivity under normoxic conditions. Conclusions: Our results indicate that inhibition of HIF-1 alpha effectively decreases hypoxia-induced transcription and radiosensitizes hypoxic MG-63 human osteosarcoma cells in vitro.