Comparison of the abnormal diffusion characteristics of tumor cells

The random dynamics of two different tumor cell types on a substrate were observed under a microscope and analyzed based on three parameters—mean square displacement (MSD), turning angle distribution (TAD), and velocity autocorrelation function (VACF)—under well-controlled experimental conditions wherein only thermal energy existed. A two-dimensional analysis on the substrate showed linear MSD but a lowered diffusion coefficient compared to the prediction by Stokes–Einstein equation due to particle substrate interaction. Moreover, anomalous characteristics based on the MSD and TAD of the two different cells, A549 (adenocarcinomic human alveolar basal epithelial cells) and MCF-7 (breast cancer cell line; estrogen, progesterone receptors +, HER2 −), were observed, and the nonlinear MSD at a short time scale was detected. This result is attributed to the localization error from the bright-field image of a different cell taken, while the cell moved randomly on the substrate. Parameters related to random process and localization errors were employed to distinguish the two cell types. This study could be useful for the characterization of cellular properties and cell types.