Purpose: The anti-cancer effect of β-lapachone (β-lap) is positively related to the cellular activity of NAD(P)H:quinone oxidoreductase (NQO1). Heat shock has been reported to elevate cellular NQO1. The effect of heating on the NQO1 expression in human osteosarcoma cells (HOS) and the response of the cells to the combined treatment with β-lap and hyperthermia was investigated.
Materials and methods: The effects of β-lap alone, hyperthermia alone and in combination to cause clonogenic death and apoptosis in HOS cells were elucidated. The effect of heating on the NQO1 expression was evaluated with western blot analysis. The effect of β-lap on the cell cycle distribution was elucidated with flow cytometry and to cause DNA damage was determined by assessing the γH2AX foci formation.
Results: Treatment of HOS cells with β-lap at 42°C was markedly more effective than that at 37°C in causing clonogenic cell death. Heating caused a long-lasting up-regulation of NQO1 in the cells, and sensitised the cells to β-lap. The γH2AX foci formation was increased immediately after β-lap treatment and preheating increased the β-lap-induced γH2AX foci formation.
Conclusions: The sensitivity of HOS cells to β-lap was increased not only during heating but also after heating as demonstrated by the increase in the clonogenic cell death and γH2AX foci formation. The increase in β-lap sensitivity after heating appeared to be due to the heat-induced elevation of NQO1 activity.