Combined use of carboxyl-directed protein pegylation and vector-mediated blood-brain barrier drug delivery system optimizes brain uptake of brain-derived neurotrophic factor following intravenous administration.

Purpose: Peptide drug delivery to the brain requires optimization of (a) plasma pharmacokinetics and (b) blood-brain barrier (BBB) permeability. In the present studies, plasma pharmacokinetics are improved with protein pegylation and BBB transport is facilitated with the use of vector-mediated drug delivery using the OX26 monoclonal antibody (MAb) to the rat transferrin receptor, which undergoes receptormediated transcytosis through the BBB in vivo.

Methods: A conjugate of OX26 and streptavidin (SA), designated OX26/SA, was prepared in parallel with the carboxyl-directed pegylation of brain-derived neurotrophic factor (BDNF). A novel bifunctional polyethyleneglycol (PEG) was used in which a hydrazide (Hz) was attached at one end and a biotin moiety was attached to the other end. This allowed for conjugation of BDNF-PEG-biotin to OX26/SA.

Results: The brain uptake of BDNF-PEG-biotin was increased following conjugation to OX26/SA to a level of 0.144 +/- 0.004% injected dose per g brain and a BBB permeability-surface area product of 2.0 +/- 0.2 microL/min/g.

Conclusions: These studies demonstrate that peptide drug delivery to the brain can be achieved with advanced formulation of protein-based therapeutics. The formulation is intended to (a) minimize rapid systemic clearance of the peptide, and (b) allow for vector-mediated drug delivery through the BBB in vivo. Following this dual formulation, the brain uptake of a neurotrophin such as BDNF achieves a value that is approximately 2-fold greater than that of morphine, a neuroactive small molecule.