Identification of novel blood brain barrier penetrating peptides using one‐bead‐two‐compound combinatorial library technology

Successful development of therapeutics for neurological diseases is limited by the ability of compounds to cross the blood brain barrier (BBB). Brain capillary endothelial cells are sealed by tight junctions forming the BBB which express high levels of efflux transport proteins. This results in molecules like gene based or recombinant protein therapies that cannot cross the BBB. Combinatorial chemistry, namely the one bead two compound (OB2C) method, is a powerful tool to identify brain endothelial cell penetrating peptides. We designed releasable OB2C libraries to discover ligands that specifically penetrate brain endothelial cells (bEnd.3). Screening the libraries, we identified 17 peptides that facilitate the uptake of quantum dot by brain endothelial cells. These peptides were resynthesized in soluble form and its cell penetrating abilities were confirmed by the successful delivery of impenetrable compounds, saporin and imaging agents. One peptide, LBL7, showed uptake specifically in bEnd.3 but not 3T3 or SVEC4–10 cell lines. A different cell entry mechanism is involved since the application of endocytosis inhibitors did not affect uptake. We have successfully used OB2C to identify a series of peptides that can penetrate brain endothelial cells. Our studies indicate LBL7 can carry imaging agents and therapeutics to the BBB thereby showing great promise as a vehicle for CNS delivery. Funding: Department