Recent developments in peptide drug delivery to the brain.

Peptide-based therapeutics are highly water-soluble compounds that do not readily enter brain from blood owing to poor transport through the brain capillary endothelial wall, i.e., the blood-brain barrier (BBB). Strategies available for peptide drug delivery to brain include: (a) neurosurgical-based (intraventricular drug infusion, hyperosmotic opening of the BBB); (b) pharmacological-based (peptide lipidization, liposomes); and (c) physiological-based (biochemical opening of the BBB, chimeric peptides). Chimeric peptides are formed by the covalent coupling of a pharmaceutical peptide (that is normally not transported through the BBB) to a brain transport vector that undergoes absorptive-mediated or receptor-mediated transcytosis through the BBB. The most efficient brain transport vector known to date is a monoclonal antibody to the transferrin receptor, and this vector achieves a brain volume of distribution approximately 18-fold greater than the plasma space by 5 hr after a single intravenous injection of antibody. The chimeric peptides are formed generally with chemical-based linkers. However, avidin/biotin-based linkers allow for high yield coupling of drug to vector, and for the release of biologically-active peptide following cleavage of the chimeric peptide linker. These strategies may also be used for the delivery of antisense oligonucleotide-based therapeutics to brain. In conclusion, the development of efficacious neuropharmaceuticals in the future will require the development of both drug delivery and drug discovery strategies that operate in parallel.