AFM-based analysis of human metastatic cancer cells

Abstract

Recently biomechanics of cancer cells, in particular stiffness or elasticity, has been identified as an important factor relating to cancer cell function, adherence, motility, transformation and invasion. We report on the nanomechanical responses of metastatic cancer cells and benign mesothelial cells taken from human body cavity fluids using atomic force microscopy. Following our initial study (Cross et al 2007 Nat. Nanotechnol. 2 780-3), we report on the biophysical properties of patient-derived effusion cells and address the influence of cell morphology on measured cell stiffness. Using a cytocentrifugation method, which yields morphologically indistinguishable cells that can be prepared in 1 min and avoids any possible artifacts due to 12 h ex vivo culture, we find that metastatic tumor cells are more than 80% softer than benign cells with a distribution over six times narrower than that of normal cells. Consistent with our previous study, which yielded distinguishable cell populations based on ex vivo growth and morphological characteristics, our results show it is unlikely that morphology alone is sufficient to explain the difference in elastic moduli for these two cell types. Moreover, analysis of non-specific cell adhesion inherent to tumor and normal cells collected from patients show surface adhesion of tumor cells is ∼33% less adhesive compared to that of normal cells. Our findings indicate that biomechanical-based functional analysis may provide an additional platform for cytological evaluation and diagnosis of cancer in the future.

Oncogenes induce a vimentin filament collapse mediated by HDAC6 that is linked to cell stiffness

“…This is in agreement with reports that have shown that when directly comparing stiffness of adherent cancer and normal cells, cell stiffness is significantly increased in the cancer cells (40). However, there have also been contradicting reports of decreased cell stiffness and increased deformability of cancer cells (41)(42)(43)(44). Nevertheless, as these latter studies analyzed cells in suspension or nonspread cells, this discrepancy in cell stiffness changes might be explained by differences in the spreading of the analyzed cells.…”

Local mechanical properties of bladder cancer cells measured by AFM as a signature of metastatic potential

“…This is known as the "bottom effect" artefact that makes cell appear stiffer than they really are when thin samples are used. To avoid this artefact, usually the indentation is limited to 10% of the cell thickness [10]. In our study, we want to compare the local viscoelasticity of human bladder cancer cells, especially at the periphery, where the cell thickness is around 200 nm.…”

“…Several studies of a variety of diseases using different experimental techniques have shown that abnormalities are connected with the mechanical properties of cells, in particular in cancer metastasis [6,7]. In fact, this is a subject of controversy as some studies report a stiffening of cancer cells compared to benign cells [8], while others show that cancer is characterized by the decrease of the cell stiffness [9,10] i.e. metastatic cancer cells have an elastic modulus lower than that of healthy cells.…”

Background clean-up in Brillouin microspectroscopy of scattering medium

“…Thus, the medium's elastic modulus, which is directly related with the speed of sound in the medium, can be determined simply by measuring the Brillouin shift. Compared to other imaging techniques that are capable of quantifying material's mechanical properties (e.g., [8][9][10]), Brillouin spectroscopy offers a non-contact, non-invasive, and label-free contrast mechanism with microscopic spatial resolution. The microscopic elasticity of the living organisms enables investigations of cell mechanics with a sub-micron resolution, which is essential for understanding biological development and disease pathophysiology [11].…”