Chemical optimization of new ligands of the low-density lipoprotein receptor as potential vectors for central nervous system targeting.

Drug delivery to the central nervous system is hindered by the presence of physiological barriers such as the blood-brain barrier. To accomplish the task of nutrient transport, the brain endothelium is endowed with various transport systems, including receptor-mediated transcytosis (RMT). This system can be used to shuttle therapeutics into the central nervous system (CNS) in a noninvasive manner. Therefore, the low-density lipoprotein receptor (LDLR) is a relevant target for delivering drugs. From an initial phage display biopanning, a series of peptide ligands for the LDLR was optimized leading to size reduction and improved receptor binding affinity with the identification of peptide 22 and its analogues. Further real-time biphoton microscopy experiments on living mice demonstrated the ability of peptide 22 to efficiently and quickly cross CNS physiological barriers. This validation of peptide 22 led us to explore its binding on the extracellular LDLR domain from an NMR-oriented structural study and docking experiments.