Ultrasound-enhanced delivery of multifunctional nanoparticles: Improving therapy of cancer and diseases in the central nervous system

Nanotechnology has made it possible to make nanoparticles which improve diagnostics and treatment of several diseases. Cancer is one such disease. A challenge in treating cancer is that the drugs are not specific towards cancer cells, but also kills normal tissue. Encapsulating the drug into a nanoparticle increases the accumulation of nanoparticles in the tumour, but not in normal tissue. The reason is that blood vessels in a tumour are rather leaky compared to normal blood vessels. Thus, nanoparticles will cross the blood vessel wall in a tumour, but not in normal tissue. However, nanoparticle-based cancer treatment is not always successful, because the nanoparticles and drugs do not reach all part of the tumour. The nanoparticles need help to penetrate throughout the tumour. Ultrasound alone or in combination with gas bubbles can help, pushing the nanoparticles into tumor tissue and reach to many more cancer cells. We have made new nanoparticles that form a shell on the surface of gas bubbles. We are continuously optimizing these nanoparticles. We have achieved very promising results when injecting drug containing nanoparticles-gas bubbles into mice and treating the tumour with focused ultrasound. All tumours disappeared and the mice were cured. Now we are studying the mechanism behind these promising results. The effect of ultrasound is ether thermal (heating) or mechanical. One mechanical effect is called cavitation, which occurs when ultrasound waves hit the gas bubble and the bubble oscillates, collapses and forms microstreams and jet-streams that can make pores in the blood vessel wall. Thus, the blood vessel wall becomes even more leaky. Another mechanical effect is acoustic radiation force, which can push nanoparticles directly or induce acoustic streaming that moves the nanoparticles. We are combining experimental approach using both gels as models for tissue and tissue growing in mice with mathematical models and computer simulation, to understand whether acoustic radiation force improves the distribution of nanoparticles in tumor tissue. To understand the mechanisms, it is essential to know how the gas bubbles and nanoparticles behave during and after ultrasound exposure. We use advanced fluorescence microscopy to image tumours that grow in window chambers in mice. Through the window, we can study how injected nanoparticles-gas bubbles behaves when the tumors are exposed to focused ultrasound. We have shown that the nanoparticles leave the blood vessels in a process resembling an ?explosion?. These ?explosions? occur at vessel branching points. Furthermore, we obtain information on how far and how fast from the blood vessel wall into the extracellular matrix the nanoparticles are pushed under different acoustic intensities. Diseases in the brain are very difficult to treat due to the so called blood-brain barrier which stops drugs from entering into brain tissue. The blood-brain barrier is caused both by the tight junctions between the endothelial cells and the protein pump in the vessel wall pumping drugs back to the blood. We have shown that we can use our nanoparticle-gas bubble in combination with ultrasound to make small openings in the blood-brain barrier so that nanoparticles can pass through. The next step was to encapsulate the drug cabazitaxel into the nanoparticles and treat brain tumours (glioma) with focused ultrasound combined with nanoparticle containing drug and microbubbles. We found that free cabazitaxel crossed the blood-brain barrier and reduced the tumour growth to the same extent as ultrasound plus nanoparticle-microbubbles. We found the amount of pumps pumping drugs back to the blood was much lower in tumour tissue than in normal tissue and that this can explain the promising therapeutic effect of the drug. Successful opening of the blood- brain barrier has also been achieved using another microbubble. These microbubbles are developed by the company Phoenix Solution AS and are based on formation of a large microbubble that upon ultrasound exposure temporary will block the capillaries and induce biomechanical effects on the blood vessel wall. Alzheimer is a disease many people are suffering from. We are studying how to improve detection of Alzheimer plaques. We have previously developed a special probe, a small fluorescent molecule called oliogothiophene and shown that this probe can cross the blood-brain barrier and recognize and bind to Alzheimer plaque in mice. Now we have been able to conjugate a gadolinium based magnetic resonance imaging (MRI) contrast agent to the probe, and we find that the enhancement of MRI contrast correlates with the fluorescence from plaques in the brain in mice. Our aim was to detect plaque before cognitive changes appeared, but we were not successful. However, we think that the new probe can be useful for non-invasive detection of Alzheimer plaque.

-The nanoparticle-microbbuble platform and focus ultrasound show promising therapeutic results in human tumours growing under the skin in mice. However, more relevant tumour and mouse models need to be tested. -New knowledge on the mechanisms of ultrasound-mediated delivery of nanoparticles have been obtained by imaging for the first time the behaviour of the NPs in tumour tissue in real time during US exposure. -Our results, together with promising preclinical results from other international research groups, have laid the ground for clinical studies. At St. Olavs hospital in Trondheim, we are now performing two clinical studies to investigate whether treatment with cytotoxic drugs in cancer patients is more efficient when combined with FUS and clinically used MBs.

Nanotechnology has made it possible to develop multifunctional nanoparticles (NP) used for imaging and therapy. Treatment of cancer has obtained most attention, but if the blood-brain barrier (BBB) could be opened, treatment of diseases in the central nervous system (CNS) that today is not possible to cure will have the potential of being treated. One of the major challenges in treating diseases in the CNS is the delivery of drugs to the brain due to the specialized and tight capillary endothelium that constitutes the BBB. NPs improve the delivery of drugs to tumours and reduce toxic effects towards normal tissue due to the leaky tumour blood vessels. However, the uptake and distribution of NPs is low and heterogeneous. Thus, it is essential to improve the delivery to solid tumours and to penetrate the BBB. We have developed a novel NP-MB platform consisting of a polymeric NP forming a shell around gas bubbles. Recently, we demonstrated that these integrated NP-MBs in combination with focused ultrasound (FUS) improved the delivery of NPs to prostate xenografts in mice, and safely opened the BBB in rats temporarily. Now these promising NP-MBs will be used to improve cancer therapy and treat disorders in the CNS. Various drugs will be encapsulated in the NP and the NP-MBs have to be characterized after the encapsulation. The delivery of NP to solid tumours depends on the vascular density and vascular permeability. Tumour models which have different vascularity will be used to determine which, if not all, tumour types can be treated and thereby which patients can benefit from FUS-mediated delivery of NP. The NP-MBs will be used to study the delivery of NP and drugs to gliomas growing in rats, and to study the therapeutic effect on gliomas. Furthermore, we want to open the BBB using FUS and MBs for another NP being a MRI contrast agents and functionalized with luminescent conjugated oligothiophenes which have high affinity toward in plaques in Alzheimer's disease.