Background: The delivery of therapeutics across the blood-brain barrier (BBB) constitutes a significant hurdle for the treatment of patients suffering from CNS disorders. This is especially evident for neurodegenerative diseases such as Alzheimer's and Parkinson's disease, since the BBB limits the treatment options to small lipophilic drugs, which has a limited therapeutic potential. Therefore several nanoparticulate drug delivery systems are being investigated to enable macromolecular drug delivery to the CNS and thereby improving the treatment options.

Methods: The purpose of this study was to construct a magnetic responsive drug delivery system to enable drug delivery across the BBB. The starting platform was starch coated magnetic nanoparticles (S-MNPs), which were encapsulated in phospholipids to yield magnetoliposomes (MLs). Finally OX26 antibodies, targeting the transferrin receptor, was purified from an in-house hybridoma cell culture and utilized to produce OX26 conjugated magnetoliposomes (OX26-MLs). Initially cellular uptake of all particle types were screened in vitro in rat brain endothelial cells (RBE4 cells). The biodistribution of MLs and OX26-MLs was investigated after intravenous injection in 16 day old rats (P16). The morphological biodistribution was studied on tissue sections from brain, liver, spleen, lungs, and kidneys by fluorescence microscopy. Finally the ability of MLs and OX26-MLs to traverse the BBB both with and without the application of a magnetic field was tested on P16 rats using the in situ brain perfusion method (n = 10). Traversal of the BBB was evaluated by immunohistochemical staining of laminin in the basement membrane of the capillary bed, and sections were then analyzed by fluorescence microscopy to detect particles beyond the BBB. P16 rats were used due to their high expression and recycling rate of transferrin receptors in the brain capillary endothelial cells (BCECs).

Results: In vitro screening of the cellular uptake in RBE4 cells revealed a 4.3 fold and 7.3 fold increase in median cell fluorescence intensity for MLs and OX26-MLs compared to S-MNPs, respectively. Furthermore OX26-MLs demonstrated a 1.6 fold increase compared to MLs. Mann-Whitney-U tests revealed that all groups were significantly different from each other (p < 0.05). The biodistribution revealed a preferential uptake of both MLs and OX26-MLs in the liver and spleen, whereas a small amount of particles were present in the lungs and virtually absent in the kidney. Surprisingly no significant accumulation of both MLs and OX26-MLs were seen in the brain capillaries. In situ brain perfusion experiments revealed, that OX26-MLs demonstrated a good potential as a drug delivery system to the BCECs with enhanced uptake compared to MLs. Furthermore the uptake did not dependent on an external magnetic field and hence OX26-MLs are probably transported into the BCECs by receptor mediated endocytosis. When investigating the permeation of OX26-MLs under the influence of a magnetic field a small amount of OX26-MLs was found beyond the BBB, which suggests transcytosis occurred. However, no convincing and consistent evidence was found for this phenomenon to support widespread transcytosis and cellular accumulation of OX26-MLs beyond the BBB.

Conclusion: OX26-MLs were synthesized and constitute a novel drug delivery system, which has the ability to target the BCECs. This suggests that OX26-MLs are suitable for blood to endothelium transport. However, the potential of OX26-MLs to enhance the permeation of the BBB remains obscure. Furthermore the stability in blood must be improved to make intravenous administration feasible.