Hyperthermia enhances the effect of beta beta-lapachone to cause gamma gamma H2AX formations and cell death in human osteosarcoma cells

Materials and methods: The effects of beta beta-lap alone, hyperthermia alone and in combination to cause clonogenic death and apoptosis in HOS cells were elucidated. The effect of heating on the NQO1expression was evaluated with western blot analysis. The effect of beta beta-lap on the cell cycle distribution was elucidated with flow cytometry and to cause DNA damage was determined by assessing the gamma gamma H2AX foci formation. Results: Treatment of HOS cells with beta beta-lap at 42 degrees A degrees C was markedly more effective than that at 37 degrees A degrees C in causing clonogenic cell death. Heating caused a long-lasting up-regulation of NQO1 in the cells, and sensitised the cells to beta beta-lap. The gamma gamma H2AX foci formation was increased immediately after beta beta-lap treatment and preheating increased the beta beta-lap-induced gamma gamma H2AX foci formation. Conclusions: The sensitivity of HOS cells to beta beta-lap was increased not only during heating but also after heating as demonstrated by the increase in the clonogenic cell death and gamma gamma H2AX foci formation. The increase in beta beta-lap sensitivity after heating appeared to be due to the heat-induced elevation of NQO1 activity.