Ligand- based strategies to modified NPs surface for blood-brain barrier crossing

The main limitation in the treatment of neurological diseases consists of the presence of the blood–brain barrier (BBB), which precludes the entry of therapeutic molecules from blood to brain. Specifically engineered nanoparticles (NPs) have gained interest as drug carriers able to ensure an effective brain targeting, overcoming the BBB and carrying drugs to the central nervous system (CNS). Our research group focused on biocompatible and biodegradable poly(d,l-lactide-co-glycolide) (PLGA) nanocarriers, engineered with different specific ligands able to promote the brain targeting taking advantage of the BBB crossing pathways, such as endocytosis or transcytosis (1-2). In particular, we explored different ligand to favor the BBB crossing and the cellular interaction; i) a g7 peptide ( H 2 N – Gly- L -Phe- D -Thr-Gly- L -Phe- L -Leu – L -Ser – O- - D -glucose-CONH 2) ii) a sequence 12–32 (g21) of leptin iii) both glycopeptide (g7) for blood brain barrier (BBB) crossing and SA residue for interaction with brain receptors. The brain localization of engineered nanoparticles NPs was evaluated in rats after intravenous administration, by confocal microscopy, fluorescence microscopy and electron microscopy. Studies to evaluate the biodistribution of modified NPs in comparison to the unmodified NPs were also carried out. Results: i) g7-NPs were able to cross the BBB (2): in particular, the biodistribution of these NPs showed a localization into the CNS in a quantity about two orders of magnitude greater than that found with the other known NP drug carriers. Not only, the results obtained by quantitative brain biodistribution of Rhodamine-123 loaded g7-NPs (15% of the injected dose) are comparable with the results obtained by antinociceptive assays with loperamide loaded into g7-NPs (at least 13% of the injected dose inferred by ICV studies). ii) After intravenous administration in rats, the g21-NPs were able to cross the BBB and to enter the brain parenchyma. The biodistribution studies of both unmodified and modified NPs pointed out an uptake at liver and spleen level, whereas only the g21-NPs showed brain localization. The food-intake experiments pointed out that the intravenous administration of g21 conjugated to the NP surface did not produce any anorectic effect in the rats. iii) the double-covered NPs (with SA and glycopeptide) crossed the BBB owing to the presence of glycopeptide on the NPs’ surface, followed by endocytosis as the BBB crossing mechanism. Then, as a consequence of the presence of SA moiety on the NPs’ surface, the double-covered NPs could interact with brain SA-specific receptors, thus explaining both the prolonged activity of loperamide delivered by NPs and the prolonged NP brain residence time. Biodistribution studies showed high NP localization (6% of the injected dose into the CNS) over a prolonged time (24 h) along with the qualitative evaluation of the NPs’ visualization within the brain, kidney, liver, spleen and lung tissue parenchyma