The Chick Chorioallantoic Membrane (CAM) Assay as a Three-dimensional Model to Study Autophagy in Cancer Cells

The chick chorioallantoic membrane (CAM) is an extra-embryonic organ and thus well accessible for seeding and harvesting 3D cell cultures. Samples from CAM assays are suitable for protein and gene expression analysis as well as for immuno-histochemical studies. Here we present the CAM assay as a possible model to study autophagy in different types of cancer using immunohistochemistry. Compared with other 3D and xenograft models, the CAM assay displays several advantages such as lower costs, shorter experimental times, physiological environment and reproducibility. Macroautophagy hereafter simply referred to as "autophagy" is a conserved cellular catabolic process that degrades and recycles cellular components. Under basal conditions, autophagy contributes to the maintenance of cellular homeostasis whereas under cellular stress, such as starvation or hypoxia, autophagy is activated as a survival mechanism. Dysregulation of autophagy has been described in many diseases. In cancer, autophagy has been suggested to play a dual role. Whereas autophagy has been reported to play a tumor suppressive role in early stages, it seems to be rather tumor supportive in later stages. Here we provide a method to study autophagy in 3D microtumors of cancer cells grown on the CAM.