In vivo phage display screen for peptide sequences that cross the blood-cerebrospinal-fluid barrier

There is lack of a barrier between CSF and brain, thus peptide that can cross the blood-cerebrospinal-fluid barrier (BCSFB) will have a greater chance of providing access to the brain. In this study, we screened for a novel peptide sequence that can cross the BCSFB from the systemic circulation using phage display. We applied a 12-mer phage display peptide library (Ph.D.-12) intravenously in rats and recovered phage from the cerebrospinal fluid. A longer circulation time was used according to the biodistributive CSF/blood ratio of the phage particles. Following sequential rounds of isolation, several phages were sequenced, and a peptide sequence (TPSYDTYAAELR, referred to as the TPS peptide) was identified. Clone 12-1, which encoded the TPS peptide, was enriched approximately 53 times greater than the random library phage. After labeling with FITC, the TPS peptide demonstrated significantly greater brain accumulation efficiency. This study demonstrates the feasibility of using in vivo phage display to screen for peptides that can cross the BCSFB from the systemic circulation. In conclusion, the TPS peptide represents a previously unreported promising motif that can be used to design a drug delivery system that can cross the BCSFB.