Mechanical properties of Bio-Ferrography isolated cancerous cells studied by atomic force microscopy

Detecting the presence of circulating tumor cells (CTCs) in peripheral blood can be useful for monitoring treatment in patients, metastasis prognosis, and even early detection. The epidermal growth factor receptor (EGFR) is overexpressed in carcinoma, e.g. in colorectal cancer. Here, we use atomic force microscopy (AFM) force spectroscopy to study the mechanical properties of A431 cells, which simulate EGFR-overexpressing epithelial CTCs and were magnetically isolated by Bio-Ferrography (BF). BF is found useful in isolating individual cancerous cells for mechanical testing, thus avoiding cell-cell interactions. Different stages in the pre-isolation sample preparation steps (namely, cell fixation, PLL coating of the glass substrate, and immunomagnetic labeling) are found to affect the estimated Young's modulus. The BF magnetic isolation step itself does not change the elasticity of the captured cells in comparison to the pre-isolated microbeads-bound cells. The reported increase in the estimated Young's modulus between BF-isolated target cells and fixed cells that are not bound to magnetic microbeads can be used as a quantitative mechanical indicator for objective detection of CTCs. Furthermore, we report a 2.8-fold increase in the adhesion force between the AFM tip and the BF-isolated cells compared to the pre-isolated magnetic microbead-bound A431 fixed cells. This adhesion force correlation could potentially serve as an additional quantitative mechanical indicator for distinguishing between the target and background cells, without the use of cell staining assay and subjective analysis by an expert pathologist. This study demonstrates the powerful combination of the highly sensitive cell isolation by BF and the subsequent analysis of mechanical properties of individual captured cancerous cells by AFM. This combination has potential use in cancer research.