Multifunctional nanoparticles for drug delivery across the blood-brain barrier

Nanoparticles, microbubbles and ultrasound improve delivery of drugs across the blood-brain barrier Nanotechnology has made it possible to develop multifunctional nanoparticles used for imaging and therapy. Nanoparticle assisted delivery of therapeutic agents has several advantages compared to the delivery of the drug alone, such as improved pharmacokinetics and increased specificity to the target. One important potential application of nanoparticles is treating diseases in the central nervous system. However, a challenge in delivery nanoparticles and drugs to brain tissue is the tight blood-brain barrier. The access of drugs to the brain is controlled by specialized endothelial cells constituting the blood-brain barrier, where restriction of passage results from a combination of physical, metabolic and transport barriers. The endothelial cells forming the blood-brain barrier are connected through tight junctions making it very difficult to cross the blood-brain barrier. Several approaches have been proposed to penetrate the blood-brain barrier, and focused ultrasound in the presence of gas bubbles is shown to transiently open the blood-brain barrier in animals and in humans. We have developed a polymeric nanoparticle with the unique capability to stabilize gas bubbles. These nanoparticle-gas bubbles are injected into rats or mice and the brains are exposed to focused ultrasound. Magnetic resonance imaging (MRI) is used to verify the successful delivery of co-injected MRI contrast agents, and advanced light microscopy is used to image the fluorescently labelled nanoparticles. We are testing out different ultrasound exposure and continuously optimizing the gas bubbles and nanoparticles to achieve a safe treatment. This part of the project has been successful as we are able to deliver nanoparticles to brain tissue without inducing any visible brain damage and hemorrhage. Next we performed similar study in mice having metastases in the brain. In this study we determined the amount of nanoparticles in the normal brain tissue and in the metastases, and we measured how far from the blood vessel the nanoparticles had been pushed. We could see lot of nanoparticles in the normal brain tissue, but few in the metastases. In the metastases, the nanoparticles were mainly located in the periphery of the metastases. Here we also saw most blood vessels. At this stage of the growth of the metastases, the density of blood vessels was low and this explains the low number of nanoparticles. Furthermore, to study the penetration of the blood-brain barrier, in vitro models consisting of rat brain endothelial cells from a cell line or primary brain endothelial cells from porcine are also used. These modes are valuable tools to obtain new knowledge on the mechanisms for ultrasound-mediated penetration across the blood-brain barrier, and knowledge about the importance of the different ultrasound exposure parameters (pulse length, pulse repetition frequency, acoustic power, etc). We are studying whether nanoparticles cross the blood-brain barrier between cells or through cells, or if a combination takes place. Our results indicate the last-mentioned. The nanoparticles and microbubbles are continuously optimized and characterized. We synthesize nanoparticles from various polymers and test them with respect to toxicity, circulation time in mice, the efficiency of the cellular uptake and intracellular release of the encapsulated dye that is used as a model for drug. To increase the circulation time of nanoparticles, they are coated with the molecule polyethylene glycol (PEGylation). We are studying various PEGylation-strategies with respect to circulation time and uptake in cells. Acoustic and mechanical properties of the gas bubbles are also testes, such as attenuation and backscattering of the ultrasound wave, and the stiffness of the nanoparticle-microbubbles. The project is an interdisciplinary collaboration between NTNU being the project leader, SINTEF developing the nanoparticle-gas bubbles, the University of Bergen providing interesting models for glioma and metastases in the brain, as well as international collaborators.

Nanotechnology has made it possible to develop multifunctional nanoparticles (NP) used for imaging and therapy. NP assisted delivery of therapeutic agents has several advantages compared to the delivery of the drug alone, such as improved pharmacokinetics and increased specificity to the target. One important potential application of NP is treating diseases in the central nervous system. The access of drugs to the brain is controlled by specialized endothelial cells constituting the blood-brain barrier (B BB), where restriction of passage results from a combination of physical, metabolic and transport barriers. Potentially harmful molecules entering the brain are efficiently effluxed back to the blood by transport proteins. Several approaches have been pr oposed to penetrate the BBB, and focused ultrasound in the presence of gas bubbles is shown to transiently open the BBB in animals. The novelty of our project is transporting NP across the BBB by combining 1) silencing of the efflux transporters using siR NA functionalized gold-coated-iron NP before 2) temporarily opening the BBB using focused ultrasound in combination with NP and gas bubbles. We have developed polymeric NP with the unique capability to stabilize gas bubbles. The two NP platforms will be o ptimized for respectively silencing the efflux pumps and penetrating the BBB. To study the penetration of BBB, in vitro models consisting of co-cultures of endothelial cells and astrocytes will be used as well as in vivo models of human glioma xenografts, and brain tissue in cranial window in rodents. BBB disruption in vivo and tracking of the NP will be monitored by MRI and optical imaging. Optimal ultrasound exposure (frequency, intensity exposure time) will be determined. The project addresses priority areas of NANO2021 such as applying nanotechnology to improve health, and the development of a generic method for efficient transport across the BBB has the potential for further innovation and commercialization.