Comparison of methods to measure oxygen consumption in tumor cells in vitro

The oxygen consumption rate of tumor cells affects tumor oxygenation and response to therapies. Highly sensitive methods of determining cellular oxygen consumption are therefore needed to identify treatments that can modulate this parameter. We compared the performance of three different methods of measuring cellular oxygen consumption: Electron paramagnetic resonance (EPR) oximetry, the Clark electrode, and the Mito Xpress-Xtra fluorescent assay. To compare the assays, we used K562 cells in the presence of rotenone and hydrocortisone, compounds that are known to inhibit the mitochondrial electron transport chain to different extents. The EPR method was the only method that could identify both rotenone and hydrocortisone as inhibitors of tumor cell oxygen consumption. The Clark electrode and the fluorescence assay demonstrated a significant decrease in cellular oxygen consumption after administration of the most potent inhibitor (rotenone), but failed to show any significant effect of hydrocortisone. EPR oximetry is, therefore, the most sensitive method of identifying inhibitors of oxygen consumption on cell assays, while the Clark electrode offers the unique opportunity to add external compounds during experiments, and still shows great sensitivity in studying enzyme and chemical reactions that consume oxygen (non-cell assays). Finally, the Mito Xpress-Xtra fluorescent assay has the advantage of a high-sample throughput and low bulk requirements, but at the cost of a lower sensitivity