Breast epithelial cell coculture on top of an endothelial monolayer decreased endothelial cell number. (A) 10000 MCF10A or MCF10A-NeuN cells were seeded on confluent HUVEC monolayers (orange). After 24 h, cells were fixed, labeled for nuclei (blue, endothelial and breast cells) and integrin α6 (green, breast cells), and imaged by confocal microscopy. Representative confocal microscopy images and (B) HUVEC cell number quantification. (C) HUVEC monolayer cocultured with 10000 MDA-MB-231 cells was labeled with a cytotoxicity indicator and imaged over time in an Incucyte Live Cell Analysis System. (D) GFP-HUVEC cell number in coculture with RFP-MDA-MB-231 cell number, and (E) RFP-MDA-MB-231 in coculture with GFP-HUVEC. *p < 0.01 compared to HUVEC or MDA-MB-231 alone. Scale bar: 20 μm.