Characterizing optical coherence tomography speckle fluctuation spectra of mammary organoids during suppression of intracellular motility

Background: An understanding of how the mammary gland responds to toxicant and drug exposures can shed light on mechanisms of breast cancer initiation/progression and therapeutic effectiveness, respectively. In this study, we employed noninvasive, label-free and high-throughput optical coherence tomography speckle fluctuation spectroscopy (OCT-SFS) to track exposure-response relationships in three-dimensional (3D) mammary epithelial organoid models. Methods: OCT-SFS is sensitive to relatively high speed (similar to 0.16-8 mu m/min) motions of subcellular light scattering components occurring over short (similar to 2-114 s) time scales, termed intracellular motility. In this study, OCT speckle fluctuation spectra are quantified by two metrics: the intracellular motility amplitude, M, and frequency-dependent motility roll-off, alpha. OCT-SFS was performed on human mammary organoid models comprised of pre-malignant MCF10DCIS.com cells or MCF7 adenocarcinoma cells over 6 days of exposure to either a microtubule inhibitor (Paclitaxel, Taxol) or a myosin II inhibitor (Blebbistatin). Raw values of alpha and M were normalized to a dynamic range corresponding to fixed (0%) and live/homeostatic (100%) organoids for each cell line. Results: In this work, we observed a significant decrease in both M and a of MCF10DCIS.com organoids after 24 hours of exposure to Taxol (P<0.001), and a significant decrease only in alpha for MCF7 organoids after 48 hours of exposure (P<0.0001). We also observed a significant decrease in both M and alpha of MCF7 organoids at the longest exposure time of 6 days to Blebbistatin (P<0.0001), and a significant decrease only in M for MCF10DCIS.com organoids after 24 hours of exposure (P<0.01). Conclusions: OCT-SFS revealed cell line-specific response patterns, in terms of intracellular motility, to different motility suppression mechanisms. This provides a foundation for future OCT-SFS studies of longitudinal responses of the mammary gland in toxicology and drug research.