(7h) Dendrimer-Based Therapeutic Delivery for Cerebral Palsy: Mechanism of Nanoparticle Uptake

Cerebral palsy is a chronic childhood disorder that currently has no effective cure. Injury to the developing brain that occurs either in utero or soon after birth can result in motor, sensory and cognitive deficits as seen in cerebral palsy, with neuroinflammation playing a key role in the pathophysiology. Nanoparticles such asdendrimers provide opportunities for the targeted delivery of multiple drugs that can mitigate pathways involved in injury and can be delivered selectively to cells that are responsible for neuroinflammation and injury. We have previously demonstrated that a systemic, postnatal  therapy with dendrimer-drug nanodevices in rabbit kits with CP,can cross the disrupted BBB and localize in activated microglia and astrocytes, resulting in an improvement in motor deficits (1).

Understanding factors affecting uptake will allow for better design and more efficient delivery of dendrimer platforms to diseased cells, further increasing therapeutic efficacy. In this work, we used a combination of in vivo and ex vivo methods to study the effect of dendrimer size (generation 4 (G4), ~4nm in size) and surface charge (-OH terminated neutral vs -NH2 terminated cationic dendrimers) on the ability to cross an impaired BBB, diffuse within the brain parenchyma, and selectively uptake in microglia cells in rabbit kits exposed to endotoxin in utero. In brain slices from endotoxin kits, the neutral G4-OH-Cy5 dendrimer could diffuse through the brain parenchyma, preferentially accumulating in microglia, whereas the cationic G4-NH2-FITC dendrimers did not diffuse in slices. Following intracranial administration into an endotoxin day 1 kit, G4-OH dendrimer was found distributed in the parenchyma at 4 hrs and 24 hrs, and localized in microglial cells at 24 hrs. In age-matched healthy controls, minimal uptake in microglia was seen in either white matter or cortical regions; however, dendrimer was spread throughout the parenchyma at 24 hours confirming the diffusive nature of these particles. Following intravenous (IV) administration, G4-OH-Cy5 dendrimer penetrate a disrupted BBB in endotoxin kits and were found within the parenchyma at 4 hours, and within microglial cells at 24 hours. Polystyrene nanoparticles (20nm) did not cross the BBB or selectively uptake into microglia cells. Dendrimer was not found in the brain in age-matched healthy controls following systemic administration. These results suggest that appropriate tailoring of the physicochemical properties of the dendrimer nanodevice to optimize targeting and localization can lead to improvement in drug delivery to the brain. 

1. S Kannan, H Dai, RS Navath, B Balakrishnan, A Jyoti, J Janisse, R Romero, RM Kannan (2012). 'Dendrimer-based postnatal therapy for neuroinflammation and cerebral palsy in a rabbit model'. Science Translational Medicine, 4(130), p. 130ra46. Highlighted in Nature, Science, Nature Review Drug Discovery.