Comparison of viscoelastic properties of breast cancer and normal cells using AFM, FLIM and ToF-SIMS techniques.

The modifications in biomechanical properties of cells and tissue are important in cancer progression, including its different aspects, e.g. invasion, migration, adhesion, signaling, interactions with microenvironment, and immune response. However, our understanding of the changes in physical characteristics of cells, and especially the molecular basis for these changes, caused by malignant transformation remains rather limited. While the differences in stiffness and viscoelasticity of tumor and normal cells have been well documented at the cellular scale, subcellular and molecular alterations have been poorly characterised. In our work, we investigated the stiffness and viscoelastic parameters, mainly determined by the actin cortex, and the microviscosity of the plasma membrane, mainly determined by its lipid profile, in normal and cancer cells. The mechanical properties of the cells were assessed using atomic force microscopy (AFM). The microviscosity of the membrane was visualized by fluorescence lifetime imaging microscopy (FLIM) with the viscosity-sensitive probe BODIPY2. Chemical analysis of cell membranes was performed by secondary ion time-of-flight mass spectrometry (ToF-SIMS). The MCF-10 A (normal epithelial cells) and MCF-7 (human breast cancer) cell lines were used in the study. It was shown that cancer cells were more deformable due to a less organized and more isotropic filamentous structure of the actin cytoskeleton. At the same time they had more viscous plasma membranes, compared to normal cells, in both in vitro and tissue conditions. In the membrane lipid profile, increased signals of sphingomyelin and saturated fatty acids and decreased signals of polyunsaturated fatty acids were detected in cancer cells, which explain the higher microviscosity of their membranes. The obtained data indicate a complex reorganization of cell biomechanics at the cellular, subcellular and molecular levels during malignant transformation, which is important for better understanding of fundamental mechanisms of tumor development.