Diamond-based quantum sensing of free radicals in migrating human breast cancer cells

Cell migration is a crucial parameter for disease progression in cancer. Reactive oxygen species (ROS) levels are involved in the regulation of the migration process, however, the exact role of free radical generation and where it occurs is unknown. Here we use a diamond-based quantum sensing technique to detect free radicals during cancer cell migration in real time with subcellular resolution. We investigated metastatic MDA-MB-231 human breast cancer cells and observed free radical formation after 16 h of starvation and 24 h of migration under low-serum conditions. Intracellular diamond dynamics were monitored at different migration points (0, 12, and 24 h), and cell morphology was evaluated. Additionally, the number of focal adhesions was analyzed as an indicator of the migratory potential of the cells. We further measured free radical generation under nicotinamide adenine dinucleotide phosphate hydrogen NADPH oxidases 2 (NOX2) inhibition by apocynin. We found that free radical levels decreased after 24 h treatment with 36 μg/mL apocynin while the levels of ROS and the migratory capacity of the cells increased. Our results evidence the complexity of the redox regulation in migrating cancer cells and offer a novel approach to specifically and locally interrogate pivotal players of the oxidative network behind metastatic success.