Remodeling of Adhesion Network within Cancer Spheroids via Cell-Polymer Interaction

3D spheroids are considered as the improved in vitro model to mimic the distinct arrangements of the cells in vivo. To date, low-attachment surfaces have been most widely used to induce the spontaneous aggregation of cells in suspension by simply tuning the relative strength of the cell-cell adhesion over cell-substrate adhesion. However, aggregating cancer cells into 3D clusters should mean more than just adjoining the cells in the physical proximity. The tumor cell functionality is strongly affected by the adhesion networks between cancer cells and extracellular matrix (ECM). Here, we performed an in-depth analysis of how the nonmetastatic breast cancer cells (MCF7) can be transformed to gain invasive phenotypes through compact aggregation into 3D spheroids on a functional polymer film surface, poly(2,4,6,8-tetravinyl-2,4,6,8-tetramethyl cyclotetrasiloxane) (pV4D4). By comparing the adhesion networks and invasion dynamics between 3D spheroids cultured on the pV4D4 surface with those cultured on conventional ultra-low-attachment (ULA) dishes, we report that only spheroids on the pV4D4 display active and sporadic cell-surface binding activities via dynamic protrusions, which correlates strongly with an increase in integrin β1. Moreover, localized laminin expression at the core of the pV4D4-cultured spheroids confirms the prominence of the intimate integrin-laminin interactions prompted by the exposure to pV4D4. This study suggests that structurally and functionally dissimilar 3D spheroids can be generated from the same type of cells on the surfaces of different physicochemical properties without any chemical treatment or genetic manipulation.