PROJECT SUMMARY/ABSTRACT Breast cancer the 4th leading cause of death in the US. Unchecked progression of breast cancer and therapeutic resistance leads to poor patient prognosis. Recent studies have suggested that aberrant growth is not the primary mediator of aggressive cancer growth, rather, the ability of cancer cells to migrate. Furthermore, the type of migration is also important: cell cohesively migrating together have been shown to be more invasive than single cells migrating. Therefore, understanding why and how cells collectively migrate could lead to new therapeutic interventions that would better prevent breast tumor progression. Our group recently discovered a phenomenon, cellular jamming, that may explain collective migration in epithelial monolayers. Collective cellular motion could be either described as non-migratory and solid-like for a jammed state, or migratory and fluid-like for an unjammed state. The theory of cell jamming shows how cell-cell adhesion and cell cortical tension interact to control changes of cell shape and to regulate collective cellular migration. It does not, however, include contributions by cell-matrix interactions. This is a critical gap in understanding collective migration, because cell-matrix adhesion proteins are directly coupled to cell-cell adhesion proteins. This proposal will test the currently developed metrics of cellular jamming in breast tumorigenesis and furthermore, test how the addition of cell-matrix adhesions would modulate collective behavior. In Aim 1, we will test models of both normal and malignant breast epithelial monolayers and their tendency to jam (or remain unjammed) by measuring cell-cell forces, cell-matrix forces, and kinetics of cellular motion. Our group has shown that increases in cell-cell adhesion forces leads to unjamming cells. A possible mechanism of altered cell-cell adhesion is enhanced Abl signaling, which has been shown to regulate invasive cancer cell motility and differential cell-cell adhesion protein activation. Aim 2 will test the contributions of Abl kinase activity to cellular unjamming. Furthermore, as cell-cell adhesions are intrinsically coupled to cell-matrix adhesions, understanding contributions from cell-matrix adhesions in a 3D model, is critical to developing a complete physical picture of how cellular unjamming leads to collective migration. Therefore, Aim 3 will utilize spheroids of both normal and malignant breast epithelial cells as a model of cells would escape from a 3D spheroid by unjamming and spreading when modulating cell-matrix adhesions. This proposed work will elucidate the physical mechanism(s) by which breast epithelial collectives migrate, and thus could lead to a new direction in breast cancer therapy development, from targeting growth factors such as HER2 to targeting migratory factors.