  Cellular microrheology has shown that cancer cells with high metastatic
potential are softer compared to non-tumorigenic normal cells. These findings
rely on measuring the apparent Young modulus of whole cells using primarily
atomic force microscopy. This study aims to explore whether alternative
mechanical parameters have discriminating features with regard to metastatic
potential. Magnetic rotational spectroscopy (MRS) is employed in the
examination of mammary epithelial cell lines: MCF-7 and MDA-MB-231,
representing low and high meta-static potential, alongside normal-like MCF-10A
cells. MRS utilizes active micron-sized magnetic wires in a rotating magnetic
field to measure the viscosity and elastic modulus of the cy-toplasm. All three
cell lines display viscoelastic behavior, with cytoplasmic viscosities ranging
from 10-70 Pa s and elastic moduli from 30-80 Pa. It is found that the
tumorigenic MCF-7 and MDA-MB-231 cells are softer than the MCF-10A cells, with
a twofold decrease in elastic modulus. To differentiate cells with low and high
malignancy however, viscosity emerges as the more discriminating parameter, as
MCF-7 exhibits a 5 times higher viscosity as compared to MDA-MB-231. These
findings highlight the sensitivity of cytoplasmic viscosity to metastatic
potential, suggesting its potential utility as a mechanical marker for
malignant cancer cells.
