Abstract 1922: Elasticity of stem-like and non-stem-like breast cancer cells studied by micropipette aspiration technique
Authors: Mohammadalipour Ameneh , Benencia Fabian , Burdick Monica M. , Tees David F. J. 
Published: May 2015

Abstract
It has been shown that the mechanical properties of pathological cells are different from healthy ones. Therefore, mechanical characterization of cells can be useful for investigating mechanisms and progression of disease such as cancer. In the case of cancer, the finding that cancerous cells are considerably more deformable than normal ones provides the motivation for investigating deformability differences between stem-like and non-stem-like cancerous cells. In this study, elasticity of two breast cancer cell lines with different phenotypes, Hs578T as stem-like and BT-20 as non-stem-like, was measured using the micropipette aspiration technique.
Cancer cells were aspirated one-by-one at controlled pressures into small glass micropipettes with radii Rp, while the length of the aspirated section of the cells inside the micropipette, L, was measured. The applied pressure was increased linearly using a syringe pump. The homogeneous half-space elastic model was employed to find the Young's moduli of BT-20 and Hs578T breast cancer cells. According to this model, graph of cell deformation (L/Rp) versus applied pressure is linear for small deformations. Our results showed a linear trend for small deformations for both BT-20 and Hs578T cells, in agreement with the model. However, for large deformations, the graphs were no longer linear. We related this nonlinearity to the fact that above a deformation threshold the cells were exhibiting a liquid-like behavior for which a solid model could not be applied. The effect of loading rate on cell's elasticity was also examined by applying three different aspiration pressure rates of 9, 6, and 3 Pa/s.
A comparison between the Young's moduli of BT-20 and Hs578T breast cancer cells showed that the latter are less stiff. Such a difference might be attributed to an alteration in the cell cytoskeleton organization and orientation for stem-like cancer cells. In other words, a reduction in stiffness might be the result of lower actin filament density which allows the stem-like cancer cells to be more deformable while undergoing extravasation and intravasation during the metastasic process. We also found that the aspiration rate influences the elasticity properties of the cell associated with differences in the dynamics of the actin cytoskeleton. Both cell lines showed smaller Young's moduli at slower aspiration rates and by increasing the rate, the Young's moduli increased for both cell lines. Therefore, cells appear softer when aspirated at a slower rate which is in agreement with the behavior of normal elastic materials. Our hypothesis is that the differences in the elastic properties might help to distinguish between stem-like cancer cells and non-stem-like ones by determining the cytoskeleton-related rate dependence of stiffness, which could eventually lead to a new detection and diagnostic method in cancer research.
This work was supported by NSF grant CBET-1106118.
Citation Format: Ameneh Mohammadalipour, Fabian Benencia, Monica M. Burdick, David F. J. Tees. Elasticity of stem-like and non-stem-like breast cancer cells studied by micropipette aspiration technique. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1922. doi:10.1158/1538-7445.AM2014-1922