Higher cell stiffness indicating lower metastatic potential in B16 melanoma cell variants and in (-)-epigallocatechin gallate-treated cells

To understand how nanomechanical stiffness affects metastatic potential, we studied the relationship between cell migration, a characteristic of metastasis, and cell stiffness using atomic force microscopy (AFM), which can measure stiffness (elasticity) of individual living cells. Migration and cell stiffness of three metastatic B16 melanoma variants (B16-F10, B16-BL6, and B16-F1 cells), and also effects of (-)-epigallocatechin gallate (EGCG), were studied using Transwell assay and AFM. Migration of B16-F10 and B16-BL6 cells was 3 and 2 times higher than that of B16-F1 cells in Transwell assay, and cell stiffness determined by AFM was also different among the three variants, although they have similar morphologies and the same growth rates: Means of Young's modulus were 350.8 +/- A 4.8 Pa for B16-F10 cells, 661.9 +/- A 16.5 Pa for B16-BL6 cells, and 727.2 +/- A 13.0 Pa for B16-F1 cells. AFM measurements revealed that highly motile B16-F10 cells have low cell stiffness, and low motile and metastatic B16-F1 cells have high cell stiffness: Nanomechanical stiffness is inversely correlated with migration potential. Treatment of highly motile B16-F10 cells with EGCG increased cell stiffness 2-fold and inhibited migration of the cells. Our study with AFM clearly demonstrates that cell stiffness is a reliable quantitative indicator of migration potential, and very likely metastatic potential, even in morphologically similar cells. And increased cell stiffness may be a key nanomechanical feature in inhibition of metastasis.