High-Content Drug Discovery Screening of Endocytosis Pathways

Endocytosis is the dynamic internalization of cargo (receptors, hormones, viruses) for cellular signaling or processing. It involves multiple mechanisms, classified depending on critical proteins involved, speed, morphology of the derived intracellular vesicles, or substance trafficked. Pharmacological targeting of specific endocytosis pathways has a proven utility for diverse clinical applications from epilepsy to cancer. A multiplexable, high-content screening assay has been designed and implemented to assess various forms of endocytic trafficking and the associated impact of potential small molecule modulators. The applications of this assay include (1) drug discovery in the search for specific, cell-permeable endocytosis pathway inhibitors (and associated analogues from structure-activity relationship studies), (2) deciphering the mechanism of internalization for a novel ligand (using pathway-specific inhibitors), (3) assessment of the importance of specific proteins in the trafficking process (using CRISPR-Cas9 technology, siRNA treatment, or transfection), and (4) identifying whether endocytosis inhibition is an off-target for novel compounds designed for alternative purposes. We describe this method in detail and provide a range of troubleshooting options and alternatives to modify the protocol for lab-specific applications.