In vitro models mimicking capillary sprouting are important tools to investigate the tumor angiogenesis, developmental blood vessel formation, and pathophysiological remodeling processes of the capillary system in the adult. With this focus, in 1998 Korff et al. introduced endothelial cell (EC) spheroids as a three-dimensional in vitro model resembling angiogenic responses and sprouting behavior [1]. As such, EC spheroids are capable of giving rise to capillary-like sprouts which are relatively close to the physiologically and genetically programmed arrangement of endothelial cells in vessels. Co-culture spheroids consisting of endothelial cells and smooth muscle cells form a spheroidal core composed of smooth muscle cells and an outer monolayer of endothelial cells, similar to the physiological architecture of larger blood vessels. In practise, a defined number of endothelial cells are cultured in a round-bottom well plate or in "hanging drops" to allow the formation and arrangement of the spheroidal three-dimensional structure. Subsequently, they are harvested and embedded in a collagen gel to allow outgrowth of endothelial cell sprouts originating from each spheroid. To evaluate the pro- or antiangiogenic impact of a cytokine or compound, the number and length of sprouts is determined.
Keywords: Angiogenesis; Angiogenic stimuli; Endothelial cells; Spheroids; Sprouting; Vascular.