Inhibiting DNA-PK_CS radiosensitizes human osteosarcoma cells

Osteosarcoma survival rate has not improved over the past three decades, and the debilitating side effects of the surgical treatment suggest the need for alternative local control approaches. Radiotherapy is largely ineffective in osteosarcoma, indicating a potential role for radiosensitizers. Blocking DNA repair, particularly by inhibiting the catalytic subunit of DNA-dependent protein kinase (DNA-PK_CS), is an attractive option for the radiosensitization of osteosarcoma. In this study, the expression of DNA-PK_CS in osteosarcoma tissue specimens and cell lines was examined. Moreover, the small molecule DNA-PK_CS inhibitor, KU60648, was investigated as a radiosensitizing strategy for osteosarcoma cells in vitro. DNA-PK_CS was consistently expressed in the osteosarcoma tissue specimens and cell lines studied. Additionally, KU60648 effectively sensitized two of those osteosarcoma cell lines (143B cells by 1.5-fold and U2OS cells by 2.5-fold). KU60648 co-treatment also altered cell cycle distribution and enhanced DNA damage. Cell accumulation at the G2/M transition point increased by 55% and 45%, while the percentage of cells with >20 γH2AX foci were enhanced by 59% and 107% for 143B and U2OS cells, respectively. These results indicate that the DNA-PK_CS inhibitor, KU60648, is a promising radiosensitizing agent for osteosarcoma.