Rapid Assessment of Mitochondrial Complex I Activity and Metabolic Phenotyping of Breast Cancer Cells by NAD(p)H Cytometry.

Cancer cells are known to display a variety of metabolic reprogramming strategies to fulfill their own growth and proliferative agenda. With the advent of high resolution imaging strategies, metabolomics techniques, and so forth, there is an increasing appreciation of critical role that tumor cell metabolism plays in the overall breast cancer (BC) growth. In this report, we demonstrate a sensitive, flow-cytometry-based assay for rapidly assessing the metabolic phenotypes in isolated suspensions of breast cancer cells. By measuring the temporal variation of NAD(p)H signals in unlabeled, living cancer cells, and by measuring mitochondrial membrane potential {Δψm } in fluorescently labeled cells, we demonstrate that these signals can reliably distinguish the metabolic phenotype of human breast cancer cells and can track the cellular sensitivity to drug candidates. We further show the utility of this metabolic ratio {Δψm /NAD(p)H} in monitoring mitochondrial functional improvement as well as metabolic heterogeneity in primary murine tumor cells isolated from tumor biopsies. Together, these results demonstrate a novel possibility for rapid metabolic functional screening applications as well as a metabolic phenotyping tool for determining drug sensitivity in living cancer cells.