Discovering Cell‐Targeting Ligands and Cell‐Surface Receptors by Selection of DNA‐Encoded Chemical Libraries against Cancer Cells without Predefined Targets

Small molecules that can bind to specific cells have broad applications in cancer diagnosis and treatment. Screening large chemical libraries against live cells is an effective strategy for discovering cell‐targeting ligands. The DNA‐encoded chemical library (DEL or DECL) technology has emerged as a robust tool in drug discovery and has been successfully utilized in identifying ligands for biological targets. However, nearly all DEL selections have predefined targets, while target‐agnostic DEL selections interrogating the entire cell surface remain underexplored. Herein, we systematically optimized a cell‐based DEL selection method against cancer cells without predefined targets. A 104.96‐million‐member DEL was selected against MDA‐MB‐231 and MCF‐7 breast cancer cells, representing high and low metastatic properties, respectively, which led to the identification of cell‐specific small molecules. We further demonstrated cell‐targeting applications of these ligands in cancer photodynamic therapy and targeted drug delivery. Finally, leveraging the DNA tag of DEL compounds, we identified α‐enolase (ENO1) as the cell surface receptor of one of the ligands targeting the more aggressive MDA‐MB‐231 cells. Overall, this work offers an efficient approach for discovering cell‐targeting small molecule ligands by using DELs and demonstrates that DELs can be a useful tool to identify specific surface receptors on cancer cells.