Exploiting differential effects of actomyosin contractility to control cell sorting among breast cancer cells.

To gain a greater understanding of the factors that drive spatial organization in multicellular aggregates of cancer cells, we investigate the segregation patterns of 6 breast cell lines (MDA-MB-231, MDA-MB-468, MDA-MB-436, MDA-MB-157, ZR-75-1, and MCF-10A) of varying degree of mesenchymal character during formation of mixed aggregates. We consider cell sorting in the context of available adhesion proteins and cellular contractility, biophysical properties that are typically considered in models of cell sorting. We characterize the mechanisms of spheroid formation as being primarily cadherin- or integrin-driven. The primary compaction mediator for a given cell type plays an important role in compaction speed, which in turn is the major factor dictating preference for interior or exterior position within mixed aggregates. In particular, cadherin-deficient, invasion-competent cells tend to position towards the outside of aggregates, facilitating access to extracellular matrix. We show that reducing actomyosin contractility has a differential effect on spheroid formation depending on the compaction mechanism. Inhibition of contractility has a significant stabilizing effect on cell-cell adhesions in integrin-driven aggregation and a mildly destabilizing effect in cadherin-based aggregation. This differential response is exploited as a spheroid formation method and as a method through which to statically control aggregate organization and dynamically rearrange cells in pre-formed aggregates. Sequestration of invasive cells in the interior of spheroids provides a physical barrier that reduces invasion in three-dimensional culture, revealing a potential strategy for containment of invasive cell types. [Media: see text] [Media: see text] [Media: see text].