Ultrasound-mediated blood-brain barrier disruption for targeted drug delivery in the central nervous system

Advances in acoustic monitoring and control of focused ultrasound-mediated increases in blood-brain barrier permeability

Transcranial focused ultrasound (FUS) combined with intravenously circulating microbubbles can transiently and selectively increase blood-brain barrier permeability to enable targeted drug delivery to the central nervous system, and is a technique that has the potential to revolutionize the way neurological diseases are managed in medical practice. Clinical testing of this approach is currently underway in patients with brain tumors, early Alzheimer's disease, and amyotrophic lateral sclerosis. A major challenge that needs to be addressed in order for widespread clinical adoption of FUS-mediated blood-brain barrier permeabilization to occur is the development of systems and methods for real-time treatment monitoring and control, to ensure that safe and effective acoustic exposure levels are maintained throughout the procedures. This review gives a basic overview of the oscillation dynamics, acoustic emissions, and biological effects associated with ultrasound-stimulated microbubbles in vivo, and provides a summary of recent advances in acoustic-based strategies for detecting, controlling, and mapping microbubble activity in the brain. Further development of next-generation clinical FUS brain devices tailored towards microbubble-mediated applications is warranted and required for translation of this potentially disruptive technology into routine clinical practice.

Cavitation dose painting for focused ultrasound-induced blood-brain barrier disruption

Focused ultrasound combined with microbubble for blood-brain barrier disruption (FUS-BBBD) is a promising technique for noninvasive and localized brain drug delivery. This study demonstrates that passive cavitation imaging (PCI) is capable of predicting the location and concentration of nanoclusters delivered by FUS-BBBD. During FUS-BBBD treatment of mice, the acoustic emissions from FUS-activated microbubbles were passively detected by an ultrasound imaging system and processed offline using a frequency-domain PCI algorithm. After the FUS treatment, radiolabeled gold nanoclusters, ⁶⁴Cu-AuNCs, were intravenously injected into the mice and imaged by positron emission tomography/computed tomography (PET/CT). The centers of the stable cavitation dose (SCD) maps obtained by PCI and the corresponding centers of the ⁶⁴Cu-AuNCs concentration maps obtained by PET coincided within 0.3 ± 0.4 mm and 1.6 ± 1.1 mm in the transverse and axial directions of the FUS beam, respectively. The SCD maps were found to be linearly correlated with the ⁶⁴Cu-AuNCs concentration maps on a pixel-by-pixel level. These findings suggest that SCD maps can spatially "paint" the delivered nanocluster concentration, a technique that we named as cavitation dose painting. This PCI-based cavitation dose painting technique in combination with FUS-BBBD opens new horizons in spatially targeted and modulated brain drug delivery.

Closed-loop cavitation control for focused ultrasound-mediated blood-brain barrier opening by long-circulating microbubbles

Focused ultrasound (FUS) exposure in the presence of microbubbles (MBs) has been successfully used in the delivery of various sizes of therapeutic molecules across the blood-brain barrier (BBB). While acoustic pressure is correlated with the BBB opening size, real-time control of BBB opening to avoid vascular and neural damage is still a challenge. This arises mainly from the variability of FUS-MB interactions due to the variations of animal-specific metabolic environment and specific experimental setup. In this study, we demonstrate a closed-loop cavitation control framework to induce BBB opening for delivering large therapeutic molecules without causing macro tissue damages. To this end, we performed in mice long-term (5 min) cavitation monitoring facilitated by using long-circulating MBs. Monitoring the long-term temporal kinetics of the MBs under varying level of FUS pressure allowed to identify in situ, animal specific activity regimes forming pressure-dependent activity bands. This enables to determine the boundaries of each activity band (i.e. steady oscillation, transition, inertial cavitation) independent from the physical and physiological dynamics of the experiment. However, such a calibration approach is time consuming and to speed up characterization of the in situ, animal specific FUS-MB dynamics, we tested a novel method called 'pre-calibration' that closely reproduces the results of long-term monitoring but with a much shorter duration. Once the activity bands are determined from the pre-calibration method, an operation band can be selected around the desired cavitation dose. To drive cavitation in the selected operation band, we developed an adaptive, closed-loop controller that updates the acoustic pressure between each sonication based on measured cavitation dose. Finally, we quantitatively assessed the safety of different activity bands and validated the proposed methods and controller framework. The proposed framework serves to optimize the FUS pressure instantly to maintain the targeted cavitation level while improving safety control.

Treatment Strategies in Diffuse Midline Gliomas With the H3K27M Mutation: The Role of Convection-Enhanced Delivery in Overcoming Anatomic Challenges

Diffuse midline gliomas harboring the H3 K27M mutation—including the previously named diffuse intrinsic pontine glioma (DIPG)—are lethal high-grade pediatric brain tumors that are inoperable and without cure. Despite numerous clinical trials, the prognosis remains poor, with a median survival of ~1 year from diagnosis. Systemic administration of chemotherapeutic agents is often hindered by the blood brain barrier (BBB), and even drugs that successfully cross the barrier may suffer from unpredictable distributions. The challenge in treating this deadly disease relies on effective delivery of a therapeutic agent to the bulk tumor as well as infiltrating cells. Therefore, methods that can enhance drug delivery to the brain are of great interest. Convection-enhanced delivery (CED) is a strategy that bypasses the BBB entirely and enhances drug distribution by applying hydraulic pressure to deliver agents directly and evenly into a target region. This technique reliably distributes infusate homogenously through the interstitial space of the target region and achieves high local drug concentrations in the brain. Moreover, recent studies have also shown that continuous delivery of drug over an extended period of time is safe, feasible, and more efficacious than standard single session CED. Therefore, CED represents a promising technique for treating midline tumors with the H3K27M mutation.

Photoacoustic imaging of gold nanorods in the brain delivered via microbubble-assisted focused ultrasound: a tool for in vivo molecular neuroimaging

The protective barriers of the CNS present challenges during the treatment and monitoring of diseases. In particular, the blood brain barrier is a major hindrance to the delivery of imaging contrast agents and therapeutics to the brain. In this work, we use gas microbubble-assisted focused ultrasound to transiently open the blood brain barrier and locally deliver silica coated gold nanorods across the barrier. This particular nanoagent possesses a strong optical absorption which enables in vivo and ex vivo visualization of the delivered particles using ultrasound-guided photoacoustic imaging. The results of these studies demonstrate the potential of ultrasound-guided photoacoustics to image contrast agents delivered via microbubble-assisted focused ultrasound for longitudinal diagnostic imaging and for therapeutic monitoring of neurological diseases.

Efficient treatment of Parkinson's disease using ultrasonography-guided rhFGF20 proteoliposomes

Fibroblast growth factor-20 (FGF20) is a paracrine member of the FGF family that is preferentially expressed in the substantia nigra pars compacta (SNpc). Previous studies have demonstrated that FGF20 enhances the survival of dopaminergic neurons suggesting the potential use of FGF20 to treat Parkinson’s disease (PD). However, the reduced solubility of the bacterial recombinant human FGF20 (rhFGF20) and the absence of efficient strategies to transport rhFGF20 across the blood–brain barrier (BBB) have halted its clinical application. In the present study, we have examined the efficiency of fuzing a small ubiquitin-related modifier (SUMO) to rhFGF20 to enhance its soluble expression and further investigated the efficacy of FUS-guided, rhFGF20-liposome transport across the BBB. We also examined the bioavailability and behavioral improvement in a 6-hydroxydopamine-lesioned rat model of PD following 2 weeks’ FUS-liposomal combinatorial treatment. Our results showed that, in contrast with rhFGF20 or LIP-FGF20, the FUS-LIP-rhFGF20 treatment could significantly improve the apomorphine-induced rotations by protecting against the loss of dopaminergic neurons in the SNpc. Our Results suggest that our combinatorial method would help overcome key challenges that hinder the currently available methods for the use of rhFGF20 in PD treatment.

Transvascular Delivery of Hydrophobically Modified siRNAs: Gene Silencing in the Rat Brain upon Disruption of the Blood-Brain Barrier

Effective transvascular delivery of therapeutic oligonucleotides to the brain presents a major hurdle to the development of gene silencing technologies for treatment of genetically defined neurological disorders. Distribution to the brain after systemic administrations is hampered by the low permeability of the blood-brain barrier (BBB) and the rapid clearance kinetics of these drugs from the blood. Here we show that transient osmotic disruption of the BBB enables transvascular delivery of hydrophobically modified small interfering RNA (hsiRNA) to the rat brain. Intracarotid administration of 25% mannitol and hsiRNA conjugated to phosphocholine-docosahexanoic acid (PC-DHA) resulted in broad ipsilateral distribution of PC-DHA-hsiRNAs in the brain. PC-DHA conjugation enables hsiRNA retention in the parenchyma proximal to the brain vasculature and enabled active internalization by neurons and astrocytes. Moreover, transvascular delivery of PC-DHA-hsiRNAs effected Htt mRNA silencing in the striatum (55%), hippocampus (51%), somatosensory cortex (52%), motor cortex (37%), and thalamus (33%) 1 week after administration. Aside from mild gliosis induced by osmotic disruption of the BBB, transvascular delivery of PC-DHA-hsiRNAs was not associated with neurotoxicity. Together, these findings provide proof-of-concept that temporary disruption of the BBB is an effective strategy for the delivery of therapeutic oligonucleotides to the brain.

Acoustic Transmission Factor through the Rat Skull as a Function of Body Mass, Frequency and Position

In many transcranial ultrasound studies on rats, the transmission factor is assumed to be independent of animal weight and losses resulting from non-normal incidence angles of the beam are not accounted for. In this study, we measured acoustic transmission factors through 13 excised skulls of male Sprague-Dawley rats weighing between 90 and 520g, at different positions on each skull and at 1, 1.25, 1.5, 1.75 and 2MHz. Our results revealed that insertion loss through rat skull increases linearly with both body mass and frequency and strongly depends on the position, decreasing from the front to the back and from the midline to the lateral sides. Skull thickness also scales linearly with body mass. Reflection explains the main part of the insertion loss compared with attenuation and aberration. These data are helpful in predicting the acoustic pressure at the focus in the brain.

Overcoming the Blood-Brain Barrier: The Role of Nanomaterials in Treating Neurological Diseases

Therapies directed toward the central nervous system remain difficult to translate into improved clinical outcomes. This is largely due to the blood-brain barrier (BBB), arguably the most tightly regulated interface in the human body, which routinely excludes most therapeutics. Advances in the engineering of nanomaterials and their application in biomedicine (i.e., nanomedicine) are enabling new strategies that have the potential to help improve our understanding and treatment of neurological diseases. Herein, the various mechanisms by which therapeutics can be delivered to the brain are examined and key challenges facing translation of this research from benchtop to bedside are highlighted. Following a contextual overview of the BBB anatomy and physiology in both healthy and diseased states, relevant therapeutic strategies for bypassing and crossing the BBB are discussed. The focus here is especially on nanomaterial-based drug delivery systems and the potential of these to overcome the biological challenges imposed by the BBB. Finally, disease-targeting strategies and clearance mechanisms are explored. The objective is to provide the diverse range of researchers active in the field (e.g., material scientists, chemists, engineers, neuroscientists, and clinicians) with an easily accessible guide to the key opportunities and challenges currently facing the nanomaterial-mediated treatment of neurological diseases.

Sonodynamic therapy induces oxidative stress, DNA damage and apoptosis in glioma cells

Malignant glioma remains one of the most challenging diseases to treat because of the invasive growth of glioma cells and the existence of the blood-brain barrier (BBB), which blocks drug delivery to the brain. New strategies are urgently needed to overcome these shortcomings and improve the outcomes. Ultrasound represents a promising noninvasive and reversible BBB opening approach and the related sonodynamic therapy (SDT) is rapidly emerging. This study aims to explore the ultrasound parameters for BBB opening and the cell killing effect of SDT in human glioma U373 cells by using a recently reported sonosensitizer, sinoporphyrin sodium (DVDMS). The in vitro BBB model indicated that SDT caused a time-dependent permeability increase, which peaked at 2 h post treatment and then recovered gradually. The results of toxicology tests showed significant U373 cell viability loss and apoptosis increase after DVDMS-SDT, accompanied by enhanced cleaved-caspase-3 level and DNA fragmentation, in which reactive oxygen species (ROS) were a major triggering intermediate during DVDMS-SDT. Furthermore, DVDMS-SDT produced DNA damage and the underlying mechanisms were evaluated, in order to provide a fundamental basis for DVDMS-SDT application in glioma therapy. The findings indicated that the DNA molecules could be temporarily regulated by SDT and DNA double-strand breaks (DSBs), which increased the difficulty of cellular self-repair, thus aggravating cell apoptosis and inhibiting glioma cell invasive growth. Therefore, this study supports the use of SDT as an alternative approach for glioma therapy.

Focused ultrasound combined with microbubble-mediated intranasal delivery of gold nanoclusters to the brain

Focused ultrasound combined with microbubble-mediated intranasal delivery (FUSIN) is a new brain drug delivery technique. FUSIN utilizes the nasal route for direct nose-to-brain drug administration, thereby bypassing the blood-brain barrier (BBB) and minimizing systemic exposure. It also uses FUS-induced microbubble cavitation to enhance transport of intranasally (IN) administered agents to the FUS-targeted brain location. Previous studies have provided proof-of-concept data showing the feasibility of FUSIN to deliver dextran and the brain-derived neurotrophic factor to the caudate putamen of mouse brains. The objective of this study was to evaluate the biodistribution of IN administered gold nanoclusters (AuNCs) and assess the feasibility and short-term safety of FUSIN for the delivery of AuNCs to the brainstem. Three experiments were performed. First, the whole-body biodistribution of IN administered 64Cu-alloyed AuNCs (64Cu-AuNCs) was assessed using in vivo positron emission tomography/computed tomography (PET/CT) and verified with ex vivo gamma counting. Control mice were intravenously (IV) injected with the 64Cu-AuNCs. Second, 64Cu-AuNCs and Texas red-labeled AuNCs (TR-AuNCs) were used separately to evaluate FUSIN delivery outcome in the brain. 64Cu-AuNCs or TR-AuNCs were administered to mice through the nasal route, followed by FUS sonication at the brainstem in the presence of systemically injected microbubbles. The spatial distribution of 64Cu-AuNCs and TR-AuNCs were examined by autoradiography and fluorescence microscopy of ex vivo brain slices, respectively. Third, histological analysis was performed to evaluate any potential histological damage to the nose and brain after FUSIN treatment. The experimental results revealed that IN administration induced significantly lower 64Cu-AuNCs accumulation in the blood, lungs, liver, spleen, kidney, and heart compared with IV injection. FUSIN enhanced the delivery of 64Cu-AuNCs and TR-AuNCs at the FUS-targeted brain region compared with IN delivery alone. No histological-level tissue damage was detected in the nose, trigeminal nerve, and brain. These results suggest that FUSIN is a promising technique for noninvasive, spatially targeted, and safe delivery of nanoparticles to the brain with minimal systemic exposure.

Treatment of neurodegenerative disorders through the blood-brain barrier using nanocarriers

Neurodegenerative diseases refer to disorders of the central nervous system (CNS) that are caused by neuronal degradations, dysfunctions, or death. Alzheimer's disease, Parkinson's disease, and Huntington's disease (APHD) are regarded as the three major neurodegenerative diseases. There is a vast body of literature on the causes and treatments of these neurodegenerative diseases. However, the main obstacle in developing an effective treatment strategy is the permeability of the treatment components at the blood-brain barrier (BBB). Several strategies have been developed to improve this obstruction. For example, nanomaterials facilitate drug delivery to the BBB due to their size. They have been used widely in nanomedicine and as nanoprobes for diagnosis purposes among others in neuroscience. Nanomaterials in different forms, such as nanoparticles, nanoemulsions, solid lipid nanoparticles (SLN), and liposomes, have been used to treat neurodegenerative diseases. This review will cover the basic concepts and applications of nanomaterials in the therapy of APHD.

Laser-activated perfluorocarbon nanodroplets: a new tool for blood brain barrier opening

A major obstacle in the monitoring and treatment of neurological diseases is the blood brain barrier (BBB), a semipermeable barrier that prevents the delivery of many therapeutics and imaging contrast agents to the brain. In this work, we explored the possibility of laser-activated perfluorocarbon nanodroplets (PFCnDs) to open the BBB and deliver agents to the brain tissue. Specifically, near infrared (NIR) dye-loaded PFCnDs comprised of a perfluorocarbon (PFC) core with a boiling point above physiological temperature were repeatedly vaporized and recondensed from liquid droplet to gas bubble under pulsed laser excitation. As a result, this pulse-to-pulse repeated behavior enabled the recurring interaction of PFCnDs with the endothelial lining of the BBB, allowing for a BBB opening and extravasation of dye into the brain tissue. The blood brain barrier opening and delivery of agents to tissue was confirmed on the macro and the molecular level by evaluating Evans Blue staining, ultrasound-guided photoacoustic (USPA) imaging, and histological tissue analysis. The demonstrated PFCnD-assisted pulsed laser method for BBB opening, therefore, represents a tool that has the potential to enable non-invasive, cost-effective, and efficient image-guided delivery of contrast and therapeutic agents to the brain.

Mechanisms of enhanced drug delivery in brain metastases with focused ultrasound-induced blood-tumor barrier disruption

Blood-brain/blood-tumor barriers (BBB and BTB) and interstitial transport may constitute major obstacles to the transport of therapeutics in brain tumors. In this study, we examined the impact of focused ultrasound (FUS) in combination with microbubbles on the transport of two relevant chemotherapy-based anticancer agents in breast cancer brain metastases at cellular resolution: doxorubicin, a nontargeted chemotherapeutic, and ado-trastuzumab emtansine (T-DM1), an antibody-drug conjugate. Using an orthotopic xenograft model of HER2-positive breast cancer brain metastasis and quantitative microscopy, we demonstrate significant increases in the extravasation of both agents (sevenfold and twofold for doxorubicin and T-DM1, respectively), and we provide evidence of increased drug penetration (>100 vs. <20 µm and 42 ± 7 vs. 12 ± 4 µm for doxorubicin and T-DM1, respectively) after the application of FUS compared with control (non-FUS). Integration of experimental data with physiologically based pharmacokinetic (PBPK) modeling of drug transport reveals that FUS in combination with microbubbles alleviates vascular barriers and enhances interstitial convective transport via an increase in hydraulic conductivity. Experimental data demonstrate that FUS in combination with microbubbles enhances significantly the endothelial cell uptake of the small chemotherapeutic agent. Quantification with PBPK modeling reveals an increase in transmembrane transport by more than two orders of magnitude. PBPK modeling indicates a selective increase in transvascular transport of doxorubicin through small vessel wall pores with a narrow range of sizes (diameter, 10-50 nm). Our work provides a quantitative framework for the optimization of FUS-drug combinations to maximize intratumoral drug delivery and facilitate the development of strategies to treat brain metastases.

Reversal of Aging-Induced Increases in Aortic Stiffness by Targeting Cytoskeletal Protein-Protein Interfaces

BACKGROUND

The proximal aorta normally functions as a critical shock absorber that protects small downstream vessels from damage by pressure and flow pulsatility generated by the heart during systole. This shock absorber function is impaired with age because of aortic stiffening.

METHODS AND RESULTS

We examined the contribution of common genetic variation to aortic stiffness in humans by interrogating results from the AortaGen Consortium genome-wide association study of carotid-femoral pulse wave velocity. Common genetic variation in the N-WASP (WASL) locus is associated with carotid-femoral pulse wave velocity (rs600420, P=0.0051). Thus, we tested the hypothesis that decoy proteins designed to disrupt the interaction of cytoskeletal proteins such as N-WASP with its binding partners in the vascular smooth muscle cytoskeleton could decrease ex vivo stiffness of aortas from a mouse model of aging. A synthetic decoy peptide construct of N-WASP significantly reduced activated stiffness in ex vivo aortas of aged mice. Two other cytoskeletal constructs targeted to VASP and talin-vinculin interfaces similarly decreased aging-induced ex vivo active stiffness by on-target specific actions. Furthermore, packaging these decoy peptides into microbubbles enables the peptides to be ultrasound-targeted to the wall of the proximal aorta to attenuate ex vivo active stiffness.

CONCLUSIONS

We conclude that decoy peptides targeted to vascular smooth muscle cytoskeletal protein-protein interfaces and microbubble packaged can decrease aortic stiffness ex vivo. Our results provide proof of concept at the ex vivo level that decoy peptides targeted to cytoskeletal protein-protein interfaces may lead to substantive dynamic modulation of aortic stiffness.

Protein Toxin Chaperoned by LRP-1-Targeted Virus-Mimicking Vesicles Induces High-Efficiency Glioblastoma Therapy In Vivo

Glioblastoma is a most intractable and high-mortality malignancy because of its extremely low drug accessibility resulting from the blood-brain barrier (BBB). Here, it is reported that angiopep-2-directed and redox-responsive virus-mimicking polymersomes (ANG-PS) (angiopep-2 is a peptide targeting to low-density lipoprotein receptor-related protein-1 (LRP-1)) can efficiently and selectively chaperone saporin (SAP), a highly potent natural protein toxin, to orthotopic human glioblastoma xenografts in nude mice. Unlike chemotherapeutics, free SAP has a low cytotoxicity. SAP-loaded ANG-PS displays, however, a striking antitumor activity (half-maximal inhibitory concentration, IC₅₀  = 30.2 × 10^-9 m) toward U-87 MG human glioblastoma cells in vitro as well as high BBB transcytosis and glioblastoma accumulation in vivo. The systemic administration of SAP-loaded ANG-PS to U-87 MG orthotopic human-glioblastoma-bearing mice brings about little side effects, effective tumor inhibition, and significantly improved survival rate. The protein toxins chaperoned by LRP-1-targeted virus-mimicking vesicles emerge as a novel and highly promising treatment modality for glioblastoma.

Brain-focussed ultrasound: what's the "FUS" all about? A review of current and emerging neurological applications

MR-guided focussed ultrasound surgery (MRgFUS) allows for precise non-invasive thermal ablation of target tissues for a wide range of clinical applications. It is an innovative and rapidly expanding technology, which has already established itself as an effective and safe incisionless alternative in the treatment of various soft tissue tumours, with many more research studies underway to extend its therapeutic envelope. The non-invasiveness of the procedure makes FUS particularly attractive in functional neurosurgery, where existing treatment options are not suitable for all patients. Several clinical trials have demonstrated the feasibility and favourable safety profile of MR-guided focused ultrasound surgery in essential tremor, Parkinson's disease and other neurological conditions. This article reviews the existing evidence base for the neurological applications of FUS and the evidence for its emerging roles in the treatment of a range of brain disorders.

Antidepressant-Like Effect of Low-Intensity Transcranial Ultrasound Stimulation

OBJECTIVE

Transcranial ultrasound stimulation (TUS) is a noninvasive neuromodulation technique with good spatial resolution and deep penetration. This study aims to investigate whether TUS has antidepressant-like effect to depressed rats.

METHODS

Rats were divided into five groups, including two groups (ST-Ctr and ST-Res) for evaluating the short-term impact of restraint stress and three groups (LT-Ctr-ShamTUS, LT-Res-ShamTUS and LT-Res-TUS) for studying the long-term effects of restraint and TUS stimulation. The TUS-treated rats were subjected to 15 min TUS stimulation to the prelimbic cortex every day for 2 weeks after the restraint. Then, depressive symptoms related behavioral outcomes were estimated in ST-Ctr and ST-Res groups (1 week after restraint), as well as in the other three groups (3 weeks after restraint).

RESULTS

The 48-h-restraint stress could lead to long lasting reduction of exploratory behavior (1 and 3 weeks after restraint) and protracted anhedonia (only observed 3 weeks after restraint). TUS application successfully reversed the core depressive phenotype, anhedonia, indicated by significantly higher sucrose preference index in LT-Res-TUS group [Formula: see text] than LT-Res-ShamTUS group [Formula: see text]. Furthermore, the brain derived neurotrophic factor expression in left hippocampus was significantly promoted in LT-Res-TUS group [Formula: see text] compared to LT-Res-ShamTUS group [Formula: see text]. In addition, the histologic results of hematoxylin and eosin staining showed no TUS-induced brain tissue injury.

CONCLUSION

These results demonstrated that low intensity TUS had antidepressant-like effect.

SIGNIFICANCE

TUS has been speculated to have therapeutic effect in depression. This study provide evidence for the antidepressant-like effects of TUS in rats for the first time.

Modulation of Brain Function and Behavior by Focused Ultrasound

PURPOSE OF REVIEW

The past decade has seen rapid growth in the application of focused ultrasound (FUS) as a tool for basic neuroscience research and potential treatment of brain disorders. Here, we review recent developments in our understanding of how FUS can alter brain activity, perception and behavior when applied to the central nervous system, either alone or in combination with circulating agents.

RECENT FINDINGS

Focused ultrasound in the central nervous system can directly excite or inhibit neuronal activity, as well as affect perception and behavior. Combining FUS with intravenous microbubbles to open the blood-brain barrier also affects neural activity and behavior, and the effects may be more sustained than FUS alone. Opening the BBB also allows delivery of drugs that do not cross the intact BBB including viral vectors for gene delivery.

SUMMARY

While further research is needed to elucidate the biophysical mechanisms, focused ultrasound, alone or in combination with other factors, is rapidly maturing as an effective technology for altering brain activity. Future challenges include refining control over targeting specificity, the volume of affected tissue, cell-type specificity (excitatory or inhibitory), and the duration of neural and behavioral effects.

Focused ultrasound induced opening of the blood-brain barrier disrupts inter-hemispheric resting state functional connectivity in the rat brain

Focused ultrasound (FUS) is a technology capable of delivering therapeutic levels of energy through the intact skull to a tightly localized brain region. Combining the FUS pressure wave with intravenously injected microbubbles creates forces on blood vessel walls that open the blood-brain barrier (BBB). This noninvasive and localized opening of the BBB allows for targeted delivery of pharmacological agents into the brain for use in therapeutic development. It is possible to use FUS power levels such that the BBB is opened without damaging local tissues. However, open questions remain related to the effects that FUS-induced BBB opening has on brain function including local physiology and vascular hemodynamics. We evaluated the effects that FUS-induced BBB opening has on resting state functional magnetic resonance imaging (rs-fMRI) metrics. Data from rs-fMRI was acquired in rats that underwent sham FUS BBB vs. FUS BBB opening targeted to the right primary somatosensory cortex hindlimb region (S1HL). FUS BBB opening reduced the functional connectivity between the right S1HL and other sensorimotor regions, including statistically significant reduction of connectivity to the homologous region in the left hemisphere (left S1HL). The effect was observed in all three metrics analyzed: functional connectivity between anatomically defined regions, whole brain voxel-wise correlation maps based on anatomical seeds, and spatial patterns from independent component analysis. Connectivity metrics for other regions where the BBB was not perturbed were not affected. While it is not clear whether the effect is vascular or neuronal in origin, these results suggest that even safe levels of FUS BBB opening have an effect on the physiological processes that drive the signals measured by BOLD fMRI. As such these effects must be accounted for when carrying out studies using fMRI to evaluate the effects of pharmacological agents delivered via FUS-induced BBB opening.

Layered acoustofluidic resonators for the simultaneous optical and acoustic characterisation of cavitation dynamics, microstreaming, and biological effects

The study of the effects of ultrasound-induced acoustic cavitation on biological structures is an active field in biomedical research. Of particular interest for therapeutic applications is the ability of oscillating microbubbles to promote both cellular and tissue membrane permeabilisation and to improve the distribution of therapeutic agents in tissue through extravasation and convective transport. The mechanisms that underpin the interaction between cavitating agents and tissues are, however, still poorly understood. One challenge is the practical difficulty involved in performing optical microscopy and acoustic emissions monitoring simultaneously in a biologically compatible environment. Here we present and characterise a microfluidic layered acoustic resonator (μLAR) developed for simultaneous ultrasound exposure, acoustic emissions monitoring, and microscopy of biological samples. The μLAR facilitates in vitro ultrasound experiments in which measurements of microbubble dynamics, microstreaming velocity fields, acoustic emissions, and cell-microbubble interactions can be performed simultaneously. The device and analyses presented provide a means of performing mechanistic in vitro studies that may benefit the design of predictable and effective cavitation-based ultrasound treatments.

Tumor targeting via EPR: Strategies to enhance patient responses

The tumor accumulation of nanomedicines relies on the enhanced permeability and retention (EPR) effect. In the last 5-10 years, it has been increasingly recognized that there is a large inter- and intra-individual heterogeneity in EPR-mediated tumor targeting, explaining the heterogeneous outcomes of clinical trials in which nanomedicine formulations have been evaluated. To address this heterogeneity, as in other areas of oncology drug development, we have to move away from a one-size-fits-all tumor targeting approach, towards methods that can be employed to individualize and improve nanomedicine treatments. To this end, efforts have to be invested in better understanding the nature, the complexity and the heterogeneity of the EPR effect, and in establishing systems and strategies to enhance, combine, bypass and image EPR-based tumor targeting. In the present manuscript, we summarize key studies in which these strategies are explored, and we discuss how these approaches can be employed to enhance patient responses.

Focused Ultrasound-enabled Brain Tumor Liquid Biopsy

Although blood-based liquid biopsies have emerged as a promising non-invasive method to detect biomarkers in various cancers, limited progress has been made for brain tumors. One major obstacle is the blood-brain barrier (BBB), which hinders efficient passage of tumor biomarkers into the peripheral circulation. The objective of this study was to determine whether FUS in combination with microbubbles can enhance the release of biomarkers from the brain tumor to the blood circulation. Two glioblastoma tumor models (U87 and GL261), developed by intracranial injection of respective enhanced green fluorescent protein (eGFP)-transduced glioblastoma cells, were treated by FUS in the presence of systemically injected microbubbles. Effect of FUS on plasma eGFP mRNA levels was determined using quantitative polymerase chain reaction. eGFP mRNA were only detectable in the FUS-treated U87 mice and undetectable in the untreated U87 mice (maximum cycle number set to 40). This finding was replicated in GL261 mice across three different acoustic pressures. The circulating levels of eGFP mRNA were 1,500-4,800 fold higher in the FUS-treated GL261 mice than that of the untreated mice for the three acoustic pressures. This study demonstrated the feasibility of FUS-enabled brain tumor liquid biopsies in two different murine glioma models across different acoustic pressures.

Three-dimensional transcranial microbubble imaging for guiding volumetric ultrasound-mediated blood-brain barrier opening

Focused ultrasound (FUS)-mediated blood-brain barrier (BBB) opening recently entered clinical testing for targeted drug delivery to the brain. Sources of variability exist in the current procedures, motivating the development of real-time monitoring and control techniques to improve treatment safety and efficacy. Here we used three-dimensional (3D) transcranial microbubble imaging to calibrate FUS exposure levels for volumetric BBB opening.

Methods: Using a sparse hemispherical transmit/receive ultrasound phased array, pulsed ultrasound was focused transcranially into the thalamus of rabbits during microbubble infusion and multi-channel 3D beamforming was performed online with receiver signals captured at the subharmonic frequency. Pressures were increased pulse-by-pulse until subharmonic activity was detected on acoustic imaging (p_sub), and tissue volumes surrounding the calibration point were exposed at 50-100%p_sub via rapid electronic beam steering.

Results: Spatially-coherent subharmonic microbubble activity was successfully reconstructed transcranially in vivo during calibration sonications. Multi-point exposures induced volumetric regions of elevated BBB permeability assessed via contrast-enhanced magnetic resonance imaging (MRI). At exposure levels ≥75%p_sub, MRI and histological examination occasionally revealed tissue damage, whereas sonications at 50%p_sub were performed safely. Substantial intra-grid variability of FUS-induced bioeffects was observed via MRI, prompting future development of multi-point calibration schemes for improved treatment consistency. Receiver array sparsity and sensor configuration had substantial impacts on subharmonic detection sensitivity, and are factors that should be considered when designing next-generation clinical FUS brain therapy systems.

Conclusion: Our findings suggest that 3D subharmonic imaging can be used to calibrate exposure levels for safe FUS-induced volumetric BBB opening, and should be explored further as a method for cavitation-mediated treatment guidance.

Probing the brain with molecular fMRI

One of the greatest challenges of modern neuroscience is to incorporate our growing knowledge of molecular and cellular-scale physiology into integrated, organismic-scale models of brain function in behavior and cognition. Molecular-level functional magnetic resonance imaging (molecular fMRI) is a new technology that can help bridge these scales by mapping defined microscopic phenomena over large, optically inaccessible regions of the living brain. In this review, we explain how MRI-detectable imaging probes can be used to sensitize noninvasive imaging to mechanistically significant components of neural processing. We discuss how a combination of innovative probe design, advanced imaging methods, and strategies for brain delivery can make molecular fMRI an increasingly successful approach for spatiotemporally resolved studies of diverse neural phenomena, perhaps eventually in people.

Towards Improvements for Penetrating the Blood-Brain Barrier-Recent Progress from a Material and Pharmaceutical Perspective

The blood–brain barrier (BBB) is a critical biological structure that prevents damage to the brain and maintains its bathing microenvironment. However, this barrier is also the obstacle to deliver beneficial drugs to treat CNS (central nervous system) diseases. Many efforts have been made for improvement of delivering drugs across the BBB in recent years to treat CNS diseases. In this review, the anatomical and functional structure of the BBB is comprehensively discussed. The mechanisms of BBB penetration are summarized, and the methods and effects on increasing BBB permeability are investigated in detail. It also elaborates on the physical, chemical, biological and nanocarrier aspects to improve drug delivery penetration to the brain and introduces some specific drug delivery effects on BBB permeability.

Advances in Glioblastoma Multiforme Treatment: New Models for Nanoparticle Therapy

The most lethal form of brain cancer, glioblastoma multiforme, is characterized by rapid growth and invasion facilitated by cell migration and degradation of the extracellular matrix. Despite technological advances in surgery and radio-chemotherapy, glioblastoma remains largely resistant to treatment. New approaches to study glioblastoma and to design optimized therapies are greatly needed. One such approach harnesses computational modeling to support the design and delivery of glioblastoma treatment. In this paper, we critically summarize current glioblastoma therapy, with a focus on emerging nanomedicine and therapies that capitalize on cell-specific signaling in glioblastoma. We follow this summary by discussing computational modeling approaches focused on optimizing these emerging nanotherapeutics for brain cancer. We conclude by illustrating how mathematical analysis can be used to compare the delivery of a high potential anticancer molecule, delphinidin, in both free and nanoparticle loaded forms across the blood-brain barrier for glioblastoma.

MEMS devices for drug delivery

Novel drug delivery systems based on microtechnology have advanced tremendously, but yet face some technological and societal hurdles to fully achieve their potential. The novel drug delivery systems aim to deliver drugs in a spatiotemporal- and dosage-controlled manner with a goal to address the unmet medical needs from oral delivery and hypodermic injection. The unmet needs include effective delivery of new types of drug candidates that are otherwise insoluble and unstable, targeted delivery to areas protected by barriers (e.g. brain and posterior eye segment), localized delivery of potent drugs, and improved patient compliance. After scrutinizing the design considerations and challenges associated with delivery to areas that cannot be efficiently targeted through standard drug delivery (e.g. brain, posterior eye segment, and gastrointestinal tract), this review provides a summary of recent advances that addressed these challenges and summarizes yet unresolved problems in each target area. The opportunities for innovation in devising the novel drug delivery systems are still high; with integration of advanced microtechnology, advanced fabrication of biomaterials, and biotechnology, the novel drug delivery is poised to be a promising alternative to the oral administration and hypodermic injection for a large spectrum of drug candidates.

Targeting Early Dementia: Using Lipid Cubic Phase Nanocarriers to Cross the Blood⁻Brain Barrier

Over the past decades, a frequent co-morbidity of cerebrovascular pathology and Alzheimer's disease has been observed. Numerous published studies indicate that the preservation of a healthy cerebrovascular endothelium can be an important therapeutic target. By incorporating the appropriate drug(s) into biomimetic (lipid cubic phase) nanocarriers, one obtains a multitasking combination therapeutic, which targets certain cell surface scavenger receptors, mainly class B type I (i.e., SR-BI), and crosses the blood⁻brain barrier. This targeting allows for various cell types related to Alzheimer's to be simultaneously searched out for localized drug treatment in vivo.

Passive acoustic mapping of cavitation using eigenspace-based robust Capon beamformer in ultrasound therapy

Pulse-echo imaging technique can only play a role when high intensity focused ultrasound (HIFU) is turned off due to the interference between the primary HIFU signal and the transmission pulse. Passive acoustic mapping (PAM) has been proposed as a tool for true real-time monitoring of HIFU therapy. However, the most-used PAM algorithm based on time exposure acoustic (TEA) limits the quality of cavitation image. Recently, robust Capon beamformer (RCB) has been used in PAM to provide improved resolution and reduced artifacts over TEA-based PAM, but the presented results have not been satisfactory. In the present study, we applied an eigenspace-based RCB (EISRCB) method to further improve the PAM image quality. The optimal weighting vector of the proposed method was found by projecting the RCB weighting vector onto the desired vector subspace constructed from the eigenstructure of the covariance matrix. The performance of the proposed PAM was validated by both simulations and in vitro histotripsy experiments. The results suggested that the proposed PAM significantly outperformed the conventionally used TEA and RCB-based PAM. The comparison results between pulse-echo images of the residual bubbles and cavitation images showed the potential of our proposed PAM in accurate localization of cavitation activity during HIFU therapy.

Perspectives on cavitation enhanced endothelial layer permeability

Traditional drug delivery systems, where pharmaceutical agents are conveyed to the target tissue through the blood circulation, suffer of poor therapeutic efficiency and limited selectivity largely due to the low permeability of the highly specialised biological interface represented by the endothelial layer. Examples concern cancer therapeutics or degenerative disorders where drug delivery is inhibited by the blood-brain barrier (BBB). Microbubbles injected into the bloodstream undergo volume oscillations under localised ultrasound irradiation and possibly collapse near the site of interest, with no effect on the rest of the endothelium. The resulting mechanical action induces a transient increase of the inter-cellular spaces and facilitates drug extravasation. This approach, already pursed in in vivo animal models, is extremely expensive and time-consuming. On the other hand in vitro studies using different kinds of microfluidic networks are firmly established in the pharmaceutical industry for drug delivery testing. The combination of the in vitro approach with ultrasound used to control microbubbles oscillations is expected to provide crucial information for developing cavitation enhanced drug delivery protocols and for screening the properties of the biological interface in presence of healthy or diseased tissues. Purpose of the present review is providing the state of the art in this rapidly growing field where cavitation is exploited as a viable technology to transiently modify the permeability of the biological interface. After describing current in vivo studies, particular emphasis will be placed on illustrating characteristics of micro-devices, biological functionalisation, properties of the artificial endothelium and ultrasound irradiation techniques.

In vitro models and systems for evaluating the dynamics of drug delivery to the healthy and diseased brain

The blood-brain barrier (BBB) plays a crucial role in maintaining brain homeostasis and transport of drugs to the brain. The conventional animal and Transwell BBB models along with emerging microfluidic-based BBB-on-chip systems have provided fundamental functionalities of the BBB and facilitated the testing of drug delivery to the brain tissue. However, developing biomimetic and predictive BBB models capable of reasonably mimicking essential characteristics of the BBB functions is still a challenge. In addition, detailed analysis of the dynamics of drug delivery to the healthy or diseased brain requires not only biomimetic BBB tissue models but also new systems capable of monitoring the BBB microenvironment and dynamics of barrier function and delivery mechanisms. This review provides a comprehensive overview of recent advances in microengineering of BBB models with different functional complexity and mimicking capability of healthy and diseased states. It also discusses new technologies that can make the next generation of biomimetic human BBBs containing integrated biosensors for real-time monitoring the tissue microenvironment and barrier function and correlating it with the dynamics of drug delivery. Such integrated system addresses important brain drug delivery questions related to the treatment of brain diseases. We further discuss how the combination of in vitro BBB systems, computational models and nanotechnology supports for characterization of the dynamics of drug delivery to the brain.

Focused shockwave induced blood-brain barrier opening and transfection

Despite extensive efforts in recent years, the blood-brain barrier (BBB) remains a significant obstacle for drug delivery. This study proposes using a clinical extracorporeal shockwave instrument to open the BBB, combined with a laser assisted bi-axial locating platform to achieve non-invasive, controllable-focus and reversible BBB opening in the brains of rats. Under shockwave treatment with an intensity level of 5 (P^-9.79 MPa, energy flux density (EFD) 0.21 mJ/mm²) and a pulse repetition frequency of 5 Hz, the BBB could be opened after 50 shocks without the use of an ultrasound contrast agent. With the proposed method, the BBB opening can be precisely controlled in terms of depth, size and location. Moreover, a shockwave based gene transfection was demonstrated using a luciferase gene.

Stimulus-responsive liposomes as smart nanoplatforms for drug delivery applications

Liposomes are known to be promising nanoparticles (NPs) for drug delivery applications. Among different types of self-assembled NPs, liposomes stand out for their non-toxic nature, and their possession of dual hydrophilic-hydrophobic domains. Advantages of liposomes include the ability to solubilize hydrophobic drugs, the ability to incorporate different hydrophilic and lipophilic drugs at the same time, lessening the exposure of host organs to potentially toxic drugs and allowing modification of the surface by a variety of different chemical groups. This modification of the surface, or of the individual constituents, may be used to achieve two important goals. Firstly, ligands for active targeting can be attached that are recognized by cognate receptors over-expressed on the target cells of tissues. Secondly, modification can be used to impart a stimulus-responsive or "smart" character to the liposomes, whereby the cargo is released on demand only when certain internal stimuli (pH, reducing agents, specific enzymes) or external stimuli (light, magnetic field or ultrasound) are present. Here, we review the field of smart liposomes for drug delivery applications.

Nanotherapy for Alzheimer's disease and vascular dementia: Targeting senile endothelium

Due to the complexity of Alzheimer's disease, multiple cellular types need to be targeted simultaneously in order for a given therapy to demonstrate any major effectiveness. Ultrasound-sensitive coated microbubbles (in a targeted lipid nanoemulsion) are available. Versatile small molecule drug(s) targeting multiple pathways of Alzheimer's disease pathogenesis are known. By incorporating such drug(s) into the targeted "lipid-coated microbubble" [LCM]/"nanoparticle-derived" [ND] (or LCM/ND) nanoemulsion type, one obtains a multitasking combination therapeutic for translational medicine. This multitasking therapeutic targets cell-surface scavenger receptors (mainly class B type I), or SR-BI, making possible for various Alzheimer's-related cell types to be simultaneously searched out for localized drug treatment in vivo. Besides targeting cell-surface SR-BI, the proposed LCM/ND-nanoemulsion combination therapeutic(s) include a characteristic lipid-coated microbubble [LCM] subpopulation (i.e., a stable LCM suspension); such film-stabilized microbubbles are well known to substantially reduce the acoustic power levels needed for accomplishing temporary noninvasive (transcranial) ultrasound treatment, or sonoporation, if additionally desired for the Alzheimer's patient.

Alzheimer’s Disease, Brain Injury, and C.N.S. Nanotherapy in Humans: Sonoporation Augmenting Drug Targeting

Owing to the complexity of neurodegenerative diseases, multiple cellular types need to be targeted simultaneously in order for a given therapy to demonstrate any major effectiveness. Ultrasound-sensitive coated microbubbles (in a targeted nanoemulsion) are available. Versatile small-molecule drug(s) targeting multiple pathways of Alzheimer’s disease pathogenesis are known. By incorporating such drug(s) into the targeted lipid-coated microbubble/nanoparticle-derived (LCM/ND) lipid nanoemulsion type, one obtains a multitasking combination therapeutic for translational medicine. This multitasking therapeutic targets cell-surface scavenger receptors (mainly scavenger receptor class B type I (SR-BI)), making it possible for various Alzheimer’s-related cell types to be simultaneously sought for localized drug treatment in vivo. Besides targeting cell-surface SR-BI, the proposed LCM/ND-nanoemulsion combination therapeutic(s) include a characteristic lipid-coated microbubble (LCM) subpopulation (i.e., a stable LCM suspension); such LCM substantially reduce the acoustic power levels needed for accomplishing temporary noninvasive (transcranial) ultrasound treatment, or sonoporation, if additionally desired for the Alzheimer’s patient.

Closed-loop control of targeted ultrasound drug delivery across the blood-brain/tumor barriers in a rat glioma model

Cavitation-facilitated microbubble-mediated focused ultrasound therapy is a promising method of drug delivery across the blood-brain barrier (BBB) for treating many neurological disorders. Unlike ultrasound thermal therapies, during which magnetic resonance thermometry can serve as a reliable treatment control modality, real-time control of modulated BBB disruption with undetectable vascular damage remains a challenge. Here a closed-loop cavitation controlling paradigm that sustains stable cavitation while suppressing inertial cavitation behavior was designed and validated using a dual-transducer system operating at the clinically relevant ultrasound frequency of 274.3 kHz. Tests in the normal brain and in the F98 glioma model in vivo demonstrated that this controller enables reliable and damage-free delivery of a predetermined amount of the chemotherapeutic drug (liposomal doxorubicin) into the brain. The maximum concentration level of delivered doxorubicin exceeded levels previously shown (using uncontrolled sonication) to induce tumor regression and improve survival in rat glioma. These results confirmed the ability of the controller to modulate the drug delivery dosage within a therapeutically effective range, while improving safety control. It can be readily implemented clinically and potentially applied to other cavitation-enhanced ultrasound therapies.

Getting Drugs Across Biological Barriers

The delivery of drugs to a target site frequently involves crossing biological barriers. The degree and nature of the impediment to flux, as well as the potential approaches to overcoming it, depend on the tissue, the drug, and numerous other factors. Here an overview of approaches that have been taken to crossing biological barriers is presented, with special attention to transdermal drug delivery. Technology and knowledge pertaining to addressing these issues in a variety of organs could have a significant clinical impact.

Understanding the neurovascular unit at multiple scales: Advantages and limitations of multi-photon and functional ultrasound imaging

Developing efficient brain imaging technologies by combining a high spatiotemporal resolution and a large penetration depth is a key step for better understanding the neurovascular interface that emerges as a main pathway to neurodegeneration in many pathologies such as dementia. This review focuses on the advances in two complementary techniques: multi-photon laser scanning microscopy (MPLSM) and functional ultrasound imaging (fUSi). MPLSM has become the gold standard for in vivo imaging of cellular dynamics and morphology, together with cerebral blood flow. fUSi is an innovative imaging modality based on Doppler ultrasound, capable of recording vascular brain activity over large scales (i.e., tens of cubic millimeters) at unprecedented spatial and temporal resolution for such volumes (up to 10μm pixel size at 10kHz). By merging these two technologies, researchers may have access to a more detailed view of the various processes taking place at the neurovascular interface. MPLSM and fUSi are also good candidates for addressing the major challenge of real-time delivery, monitoring, and in vivo evaluation of drugs in neuronal tissue.

Emerging strategies for delivering antiangiogenic therapies to primary and metastatic brain tumors

Five-year survival rates have not increased appreciably for patients with primary and metastatic brain tumors. Nearly 17,000 patients die from primary brain tumors, whereas approximately 200,000 cases are diagnosed with brain metastasis every year in the US alone. At the same time, with improved control of systemic disease, the incidence of brain metastasis is increasing. Thus, novel approaches for improving the treatment outcome for these uniformly fatal diseases are needed urgently. In the review, we summarize the challenges in the treatment of these diseases using antiangiogenic therapies alone or in combination with radio-, chemo- and immuno-therapies. We also discuss the emerging strategies to improve the treatment outcome using both pharmacological approaches to normalize the tumor microenvironment and physical approaches (e.g., focused ultrasound) to modulate the blood-tumor-barrier, along with limitations of each approach. Finally, we offer some new avenues of future research.

Progress in brain targeting drug delivery system by nasal route

The blood-brain barrier (BBB) restricts the transport of potential therapeutic moieties to the brain. Direct targeting the brain via olfactory and trigeminal neural pathways by passing the BBB has gained an important consideration for delivery of wide range of therapeutics to brain. Intranasal route of transportation directly delivers the drugs to brain without systemic absorption, thus avoiding the side effects and enhancing the efficacy of neurotherapeutics. Over the last several decades, different drug delivery systems (DDSs) have been studied for targeting the brain by the nasal route. Novel DDSs such as nanoparticles (NPs), liposomes and polymeric micelles have gained potential as useful tools for targeting the brain without toxicity in nasal mucosa and central nervous system (CNS). Complex geometry of the nasal cavity presented a big challenge to effective delivery of drugs beyond the nasal valve. Recently, pharmaceutical firms utilized latest and emerging nasal drug delivery technologies to overcome these barriers. This review aims to describe the latest development of brain targeted DDSs via nasal administration.

CHEMICAL COMPOUNDS STUDIED IN THIS ARTICLE

Carbopol 934p (PubChem CID: 6581) Carboxy methylcellulose (PubChem CID: 24748) Penetratin (PubChem CID: 101111470) Poly lactic-co-glycolic acid (PubChem CID: 23111554) Tween 80 (PubChem CID: 5284448).

Ultrasound-Responsive Polymeric Micelles for Sonoporation-Assisted Site-Specific Therapeutic Action

Targeting drug delivery remains a challenge in various disease treatment including cancer. The local drug deposit could be greatly enhanced by some external stimuli-responsive systems. Here we develop pluronic P123/F127 polymeric micelles (M) encapsulating curcumin (Cur) that are permeabilized directly by focused ultrasound, in which ultrasound triggers drug release. Tumor preferential accumulation and site-specific sonochemotherapy were then evaluated. Cur-loaded P123/F127 mixed micelles (Cur-M) exhibited longer circulating time and increased cellular uptake compared to free Cur. With the assistance of focused ultrasound treatment, Cur-M showed tumor-targeting deposition in a time-dependent manner following systemic administration. This was due to enhanced permeabilization of tumor regions and increased penetration of Cur-M in irradiated tumor cells by ultrasound sonoporation. Furthermore, Cur-M self-assembly could be regulated by ultrasound irradiation. In vitro Cur release from mixed micelles was greatly dependent on ultrasound intensity but not on duration, suggesting the cavitational threshold was necessary to initiate subsequent sonochemotherapy. In vivo site-specific drug release was demonstrated in dual-tumor models, which showed spatial-temporal release of entrapped drugs following intratumoral injection. The sonoporation-assisted site-specific chemotherapy significantly inhibited tumor growth and the decrease in tumor weight was approximately 6.5-fold more than without exposure to ultrasound irradiation. In conclusion, the established ultrasound-guided nanomedicine targeting deposit and local release may represent a new strategy to improve chemotherapy efficiency.

Enhanced delivery of paclitaxel liposomes using focused ultrasound with microbubbles for treating nude mice bearing intracranial glioblastoma xenografts

Paclitaxel liposomes (PTX-LIPO) are a clinically promising antineoplastic drug formulation for the treatment of various extracranial cancers, excluding glioblastoma. A main reason for this is the presence of the blood–brain barrier (BBB) or blood–tumor barrier (BTB), preventing liposomal drugs from crossing at a therapeutically meaningful level. Focused ultrasound (FUS) in conjunction with microbubbles (MBs) has been suggested in many studies to be an effective approach to increase the BBB or BTB permeability. In this study, we investigated the feasibility of enhancing the delivery of PTX-LIPO in intracranial glioblastoma-bearing nude mice using pulsed low-intensity FUS exposure in the presence of MBs. Our results showed that the delivery efficiency of PTX-LIPO could be effectively improved in terms of the penetration of both the BBB in vitro and BTB in vivo by pulsed FUS sonication with a 10 ms pulse length and 1 Hz pulse repetition frequency at 0.64 MPa peak-rarefactional pressure in the presence of MBs. Quantitative analysis showed that a 2-fold higher drug concentration had accumulated in the glioblastoma 3 h after FUS treatment, with 7.20±1.18 µg PTX per g glioma tissue. Longitudinal magnetic resonance imaging analysis illustrated that the intracranial glioblastoma progression in nude mice treated with PTX-LIPO delivered via FUS with MBs was suppressed consistently for 4 weeks compared to the untreated group. The medium survival time of these tumor-bearing nude mice was significantly prolonged by 20.8%, compared to the untreated nude mice. Immunohistochemical analysis further confirmed the antiproliferation effect and cell apoptosis induction. Our study demonstrated that noninvasive low-intensity FUS with MBs can be used as an effective approach to deliver PTX-LIPO in order to improve their chemotherapy efficacy toward glioblastoma.

Simultaneous Ultrasound Therapy and Monitoring of Microbubble-Seeded Acoustic Cavitation Using a Single-Element Transducer

Ultrasound-driven microbubble (MB) activity is used in therapeutic applications such as blood clot dissolution and targeted drug delivery. The safety and performance of these technologies are linked to the type and distribution of MB activities produced within the targeted area, but controlling and monitoring these activities in vivo and in real time has proven to be difficult. As therapeutic pulses are often milliseconds long, MB monitoring currently requires a separate transducer used in a passive reception mode. Here, we present a simple, inexpensive, integrated setup, in which a focused single-element transducer can perform ultrasound therapy and monitoring simultaneously. MBs were made to flow through a vessel-mimicking tube, placed within the transducer's focus, and were sonicated with therapeutic pulses (peak rarefactional pressure: 75-827 kPa, pulse lengths: [Formula: see text] and 20 ms). The MB-seeded acoustic emissions were captured using the same transducer. The received signals were separated from the therapeutic signal with a hybrid coupler and a high-pass filter. We discriminated the MB-generated cavitation signal from the primary acoustic field and characterized MB behavior in real time. The simplicity and versatility of our circuit could make existing single-element therapeutic transducers also act as cavitation detectors, allowing the production of compact therapeutic systems with real time monitoring capabilities.