No abstract

18Breast cancer cells (BCC) and macrophages are known to interact via epidermal growth factor (EGF) 19produced by macrophages and colony stimulating factor-1 (CSF-1) produced by BCC. Despite 20 contradictory findings, this interaction is perceived as a paracrine loop. Further, the underlying 21 mechanism of interaction remains unclear. Here, we investigated interactions of BCC with macrophages 22in 2D and 3D. BCC did not show chemotaxis to macrophages in custom designed 3D cell-on-a-chip 23 devices, which was in agreement with ELISA results showing that macrophage-derived-EGF was not 24 secreted into macrophage-conditioned-medium. Live cell imaging of BCC in the presence and absence 25 of iressa showed that macrophages but not macrophage-derived-matrix modulated adhesion and motility 26 of BCC in 2D. 3D co-culture experiments in collagen and matrigel showed that BCC changed their 27 multicellular organization in the presence of macrophages. In custom designed 3D co-culture cell-on-a-28 chip devices, macrophages promoted and reduced migration of BCC in collagen and matrigel, 29respectively. Furthermore, adherent but not suspended BCC endocytosed EGFR when in contact with 30 macrophages. Collectively, our data revealed that macrophages showed chemotaxis towards BCC 31whereas BCC required direct contact to interact with macrophage-derived-EGF. We propose that the 32 interaction between cancer cells and macrophages is a paracrine-juxtacrine loop of CSF-1 and EGF, 33respectively. 34