Dissection of Melanoma Drug Resistance and Heterogeneity using Live Cell Interferometry

Cell-cycle dysregulation and increased proliferation are common in cancer. Accordingly, many cancer treatments target mitosis using small molecule mitotic inhibitors. In vivo, mitotic inhibitor levels show great temporal and spatial variability due to many factors, including varied intratumoral vasculature and diffusion rates. Exposure to mitotic inhibitors at sub-optimal concentrations can drive cancer cell fates other than the desired apoptosis, senescence, or terminal differentiation, including multi-polar mitoses and cell endocycling. These unwanted fates may pair with chromosomal instability to promote cancer cell drug resistance. We therefore developed a high throughput, quantitative approach based on live cell interferometry (LCI) to dissect dose-dependent cell fate responses to mitotic inhibitors. LCI provides precise quantification of cell biophysical properties, such as cell dry mass, by measuring the phase shift of light as it passes through and interacts with cell matter. As proof-of-principle, we tracked thousands of cell-cycle synchronized HeLa cervical carcinoma and M202 patient-derived melanoma cells during 24 hour treatments with escalating doses of taxol, colchicine and VX680, an aurora-kinase B inhibitor. Cell fate, mitotic entry time and duration of mitotic arrest were examined for each cell by quantifying cell biomass and average mass per projected area, a sensitive measure of mitosis-associated morphology changes. The data reveal features missed by standard multi-day viability assays, including the percentage of cells exhibiting each identified cell fate. Our results show that LCI can be used to identify optimal drug combinations and concentrations that most efficiently drive cancer cells to death and, more generally, perturbations that drive desired cell fate outcomes. When combined with cell isolation, LCI shows promise to identify and molecularly dissect cells with different fate outcomes, which could provide key information on mechanisms of therapeutic success or resistance.