Ultrasound-induced Blood-brain Barrier Disruption Research Articles

CMUT for ultrafast passive cavitation detection during ultrasound-induced blood-brain barrier disruption: proof of concept study.

Cavitation dose monitoring plays a key role in ultrasound drug delivery to the brain. The use of CMUT technology has a great potential for passive cavitation detection (PCD). 
Approach. Here, a circular (diameter 7mm) capacitive micromachined ultrasonic transducer (CMUT) centered at 5MHz was designed to be inserted into a therapeutic transducer (1.5MHz) used for ultrasound-induced blood-brain barrier (BBB) disruption on mice. CMUT-based real-time cavitation detection was performed during the ultrasound procedure (50µL intravenous injection of SonoVue microbubbles, Frequency 1.5MHz, PNP 480kPa, Duty Cycle 10%, PRF 10Hz, Duration 60s). BBB disruption were confirmed by contrast-enhanced 7T-MRI. 
Main results. The CMUT device has a fractional bandwidth of 140%, almost twice a conventional piezocomposite PCD transducer. As expected, the CMUT device was able to detect the occurrence of harmonic, subharmonic and ultraharmonic frequencies as well as the increase of broadband signal indicating inertial cavitation in a wide frequency range (from 0.75 to 6 MHz). Signal-to-noise ratio was high enough (> 40 dB) to perform ultrafast monitoring and follow the subtle intrapulse variations of frequency components at a rate of 10 kHz. 
Significance. This first in vivo proof of concept demonstrates the interest of CMUT for PCD and encourages us to develop devices for PCD in larger animals by integrating an amplifier directly to the CMUT front-end to considerably increase the signal-to-noise ratio.

Safety Profile of Low-Intensity Pulsed Ultrasound–Induced Blood–Brain Barrier Opening in Non-epileptic Mice and in a Mouse Model of Mesial Temporal Lobe Epilepsy

It is unknown whether ultrasound-induced blood-brain barrier (BBB) disruption can promote epileptogenesis and how BBB integrity changes over time after sonication. To gain more insight into the safety profile of ultrasound (US)-induced BBB opening, we determined BBB permeability as well as histological modifications in C57BL/6 adult control mice and in the kainate (KA) model for mesial temporal lobe epilepsy in mice after sonication with low-intensity pulsed ultrasound (LIPU). Microglial and astroglial changes in ipsilateral hippocampus were examined at different time points following BBB disruption by respectively analyzing Iba1 and glial fibrillary acidic protein immunoreactivity. Using intracerebral EEG recordings, we further studied the possible electrophysiological repercussions of a repeated disrupted BBB for seizure generation in nine non-epileptic mice. LIPU-induced BBB opening led to transient albumin extravasation and reversible mild astrogliosis, but not to microglial activation in the hippocampus of non-epileptic mice. In KA mice, the transient albumin extravasation into the hippocampus mediated by LIPU-induced BBB opening did not aggravate inflammatory processes and histologic changes that characterize the hippocampal sclerosis. Three LIPU-induced BBB opening did not induce epileptogenicity in non-epileptic mice implanted with depth EEG electrodes. Our experiments in mice provide persuasive evidence of the safety of LIPU-induced BBB opening as a therapeutic modality for neurological diseases.

Methylene Blue Delivery Mediated by Focused Ultrasound-Induced Blood-Brain Barrier Disruption Reduces Neural Damage and Amyloid-Beta Plaques by AQP-4 Upregulation.

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease worldwide, causing progressive cognitive decline, memory impairment, and neurological deficits. Methylene blue (MB), an antioxidant, has emerged as a potential drug for the treatment of AD owing to its cognitive improvement and neuroprotective functions. Despite the small molecular size of MB, which can cross the BBB, the therapeutic effective dosage using a BBB-permeable delivery system in a specific brain localization remains unclear. In this study, we presented magnetic resonance-guided focused ultrasound (MRgFUS) as a delivery system to enhance BBB permeability for the effective treatment of AD. MRgFUS using two ultrasound intensities (0.25 and 0.32 MPa) was used to intravenously deliver MB to the hippocampal region. Compared with treatment with 0.25 MPa FUS, treatment with 0.32 MPa FUS significantly enhanced MB brain accumulation. Deposition of amyloid-β (Aβ) plaques and neural cell damage was significantly reduced in 0.32 MPa FUS/MB-treated APP/PS1 mice. Furthermore, aquaporin-4 expression increased significantly in the 0.32 MPa FUS and 0.32 MPa FUS/MB groups without glial fibrillary acidic protein activation. The results from this study demonstrate that FUS improved MB delivery to the brain, and FUS/MB combination treatment reduced the number of Aβ plaques. This study revealed the potential of FUS-BBBD as an effective strategy to enhance the efficacy of therapeutic drugs for AD.

Incisionless targeted adeno-associated viral vector delivery to the brain by focused ultrasound-mediated intranasal administration.

SummaryBackgroundAdeno-associated viral (AAV) vectors are currently the leading platform for gene therapy with the potential to treat a variety of central nervous system (CNS) diseases. There are numerous methods for delivering AAVs to the CNS, such as direct intracranial injection (DI), intranasal delivery (IN), and intravenous injection with focused ultrasound-induced blood–brain barrier disruption (FUS-BBBD). However, non-invasive and efficient delivery of AAVs to the brain with minimal systemic toxicity remain the major challenge. This study aims to investigate the potential of focused ultrasound-mediated intranasal delivery (FUSIN) in AAV delivery to brain.MethodsMice were intranasally administered with AAV5 encoding enhanced green fluorescence protein (AAV5-EGFP) followed by FUS sonication in the presence of systemically injected microbubbles. Mouse brains and other major organs were harvested for immunohistological staining, PCR quantification, and in situ hybridization. The AAV delivery outcomes were compared with those of DI, FUS-BBBD, and IN delivery.FindingsFUSIN achieved safe and efficient delivery of AAV5-EGFP to spatially targeted brain locations, including a superficial brain site (cortex) and a deep brain region (brainstem). FUSIN achieved comparable delivery outcomes as the established DI, and displayed 414.9-fold and 2073.7-fold higher delivery efficiency than FUS-BBBD and IN. FUSIN was associated with minimal biodistribution in peripheral organs, which was comparable to that of DI.InterpretationOur results suggest that FUSIN is a promising technique for non-invasive, efficient, safe, and spatially targeted AAV delivery to the brain.FundingNational Institutes of Health (NIH) grants R01EB027223, R01EB030102, R01MH116981, and UG3MH126861.

Influence of Acoustic Parameters and Sonication Schemes on Transcranial Blood–Brain Barrier Disruption Induced by Pulsed Weakly Focused Ultrasound

Pulsed ultrasound combined with microbubbles use can disrupt the blood–brain barrier (BBB) temporarily; this technique opens a temporal window to deliver large therapeutic molecules into brain tissue. There are published studies to discuss the efficacy and safety of the different ultrasound parameters, microbubble dosages and sizes, and sonication schemes on BBB disruption, but optimal the paradigm is still under investigation. Our study is aimed to investigate how different sonication parameters, time, and microbubble dose can affect BBB disruption, the dynamics of BBB disruption, and the efficacy of different sonication schemes on BBB disruption. Method: We used pulsed weakly focused ultrasound to open the BBB of C57/B6 mice. Evans blue dye (EBD) was used to determine the degree of BBB disruption. With a given acoustic pressure of 0.56 MPa and pulse repetitive frequency of 1 Hz, burst lengths of 10 ms to 50 ms, microbubbles of 100 μL/kg to 300 μL/kg, and sonication times of 60 s to 150 s were used to open the BBB for parameter study. Brain EBD accumulation was measured at 1, 4, and 24 h after sonication for the time–response relationship study; EBD of 100 mg/kg to 200 mg/kg was administered for the dose–response relationship study; EBD injection 0 to 6 h after sonication was performed for the BBB disruption dynamic study; brain EBD accumulation induced by one sonication and two sonications was investigated to study the effectiveness on BBB disruption; and a histology study was performed for brain tissue damage evaluation. Results: Pulsed weakly focused ultrasound opens the BBB extensively. Longer burst lengths and a larger microbubble dose result in a higher degree of BBB disruption; a sonication time longer than 60 s did not increase BBB disruption; brain EBD accumulation peaks 1 h after sonication and remains 81% of the peak level 24 h after sonication; the EBD dose administered correlates with brain EBD accumulation; BBB disruption decreases as time goes on after sonication and lasts for 6 h at least; and brain EBD accumulation induced by two sonication increases 74.8% of that induced by one sonication. There was limited adverse effects associated with sonication, including petechial hemorrhages and mild neuronal degeneration. Conclusions: BBB can be opened extensively and reversibly by pulsed weakly focused ultrasound with limited brain tissue damage. Since EBD combines with albumin in plasma to form a conjugate of 83 kDa, these results may simulate ultrasound-induced brain delivery of therapeutic molecules of this size scale. The result of our study may contribute to finding the optimal paradigm of focused ultrasound-induced BBB disruption.

Single-nanometer iron oxide nanoparticles as tissue-permeable MRI contrast agents

Magnetic nanoparticles are robust contrast agents for MRI and often produce particularly strong signal changes per particle. Leveraging these effects to probe cellular- and molecular-level phenomena in tissue can, however, be hindered by the large sizes of typical nanoparticle contrast agents. To address this limitation, we introduce single-nanometer iron oxide (SNIO) particles that exhibit superparamagnetic properties in conjunction with hydrodynamic diameters comparable to small, highly diffusible imaging agents. These particles efficiently brighten the signal in T1-weighted MRI, producing per-molecule longitudinal relaxation enhancements over 10 times greater than conventional gadolinium-based contrast agents. We show that SNIOs permeate biological tissue effectively following injection into brain parenchyma or cerebrospinal fluid. We also demonstrate that SNIOs readily enter the brain following ultrasound-induced blood-brain barrier disruption, emulating the performance of a gadolinium agent and providing a basis for future biomedical applications. These results thus demonstrate a platform for MRI probe development that combines advantages of small-molecule imaging agents with the potency of nanoscale materials.

Feasibility of ultrasound-induced blood-brain barrier disruption with a single-element transducer under three different frequencies in two non-human primates in vivo: Case report

BackgroundSingle-element focused transducers applied in blood-brain barrier (BBB) disruption experiments to optimize intravascular therapies in CNS diseases have the advantage of low cost and portability. Most of the in vivo studies on non-human primates report the use of single-element transducers with an annular spherical shape and a central frequency of 500 kHz. High-frequency ultrasound has smaller focal area and less standing-wave effect but lower transcranial penetration efficiency. Our study reports the feasibility and safety concerns of BBB opening by single-element spherical transducers with central frequencies of 300, 650 and 800 kHz on two rhesus macaques. MethodsPulsed ultrasound exposure (3-minute duration, 0.5–1% duty cycle) combined with microbubble injection (SonoVue, 0.2uL/g) was used to disrupt the BBB of the monkeys under the magnetic resonance imaging (MRI) guidance. Gadolinium contrast-enhanced MRI was used to confirm and evaluate the BBB opening after sonication. T2-weighted fast spin echo and T2 * -weighted gradient echo sequences were used to check the post-sonication complications, such as edema and micro-bleeding. ResultsContrast enhancement was found on the post-sonication T1 weighted images for all experiments, showing that the BBB was successfully opened under all the three frequencies on both monkeys. The enhanced area was largest at the lowest frequency. No obvious hypo-intensity or hyper-intensity was observed on either the T2 * weighted gradient echo images or T2-weighted fast-spin echo images, implying the safety of the opening procedure. However, signal enhancement was also observed in the subarachnoid space of the sulci for all frequencies, indicating that the BBB was also disrupted in the propagation path outside the focal area. ConclusionsThe feasibility of BBB opening with single-element transducer under frequencies ranging from 300 kHz to 800 kHz was confirmed by experiments in two non-human primates in vivo. Further investigation into the off-target effects and transducer configurations is needed for safety optimization.

Localized Modification of Water Molecule Transport After Focused Ultrasound-Induced Blood-Brain Barrier Disruption in Rat Brain.

Interstitial solutes can be removed by various overlapping clearance systems, including blood–brain barrier (BBB) transport and glymphatic clearance. Recently, focused ultrasound (FUS)-induced BBB disruption (BBBD) has been applied to visualize glymphatic transport. Despite evidence that FUS–BBBD might facilitate glymphatic transport, the nature of fluid movement within the sonication region is yet to be determined. In this study, we sought to determine whether FUS–BBBD may facilitate the local movement of water molecules. Two different FUS conditions (0.60–0.65 MPa and 0.75–0.80 MPa) were used to induce BBBD in the caudate-putamen and thalamus regions of healthy Sprague–Dawley rats. The water diffusion caused by FUS–BBBD was analyzed using the apparent diffusion coefficient (ADC), axial diffusivity, radial diffusivity (RD), and fractional anisotropy, obtained at 5 min, 24 and 48 h, as well as the water channel expression of aquaporin-4 (AQP-4) immunostaining at 48 h after FUS-induced BBBD. In addition, hematoxylin and eosin histopathology and Fluoro-Jade C (FJC) immunostaining were performed to analyze brain damage. The signal changes in ADC and RD in the sonication groups showed significant and transient reduction at 5 min, with subsequent increases at 24 and 48 h after FUS-induced BBBD. When we applied higher sonication conditions, the ADC and RD showed enhancement until 48 h, and became comparable to contralateral values at 72 h. AQP-4 expression was upregulated after FUS-induced BBBD in both sonication conditions at 48 h. The results of this study provide preliminary evidence on how mechanical forces from FUS alter water dynamics through diffusion tensor imaging (DTI) measures and AQP4 expression.

HGG-17. FOCUSED ULTRASOUND-ENHANCED DELIVERY OF RADIOLABELED AGENTS TO DIFFUSE INTRINSIC PONTINE GLIOMA

Abstract Diffuse intrinsic pontine glioma (DIPG) arising in the brainstem is the deadliest pediatric brain cancer with nearly 100% fatality and a median survival of <1 year. The critical location in the brainstem and the often intact blood-brain barrier (BBB) pose significant challenges in the treatment of DIPG. The objective of this study was to demonstrate the potential for focused ultrasound-induced BBB disruption (FUS-BBBD) to improve DIPG treatment by enhancing the safe and efficient delivery of drugs. A genetically engineered mouse model of DIPG was generated using the RCAS (replication-competent avian sarcoma-leucosis virus long-terminal repeat with splice acceptor)/tumor virus A modeling system. A magnetic resonance-guided FUS (MRgFUS) system was used to induce BBB disruption in these mice with the FUS targeted at the center of the tumor. Two radiolabeled agents with different sizes were used to evaluate the delivery efficiency of the FUS-BBBD technique in DIPG mice: a small-molecular radiotracer, 68Ga-DOTA-ECL1i, and a radiolabeled nanoparticle, 64Cu-labeled copper nanoparticles (64Cu-CuNCs, ~ 5 nm in diameter). 68Ga-DOTA-ECL1i (half-life ~ 1 h) and 64Cu-CuNCs (half-life ~13 h) were intravenously injected into the mice after FUS sonication, and microPET/CT imaging was performed at 1 h and 24 h, respectively, to evaluate the spatial-temporal distribution of these two agents in the brain and quantify the delivery outcome. FUS treatment increased the uptake of 68Ga-DOTA-ECL1i and 64Cu-CuNCs to the DIPG tumor by 3.25 folds and 4.07 folds on average, respectively. These findings demonstrated, for the first time, that FUS can increase BBB permeability in a murine model of DIPG and significantly enhance the delivery of agents of different sizes into the DIPG tumor.

MRI-Guided Focused Ultrasound-Induced Blood Brain Barrier Disruption to Deliver Glial Cell Line Derived Neurotropic Factor Proteins into Brain to Treat Rat Depression.

Glial cell line derived neurotropic factor (GDNF) plays a crucial role in the development and maintenance of glial cells, serotonergic and dopaminergic neurons. A positively therapeutic effect has been demonstrated on some animal neurodegenerative diseases. However, the inability to deliver the protein across blood brain barrier (BBB) into damaged brain region limits its clinical application. Here, we developed GDNF-loaded microbubbles (MBs) and achieved a local and precise delivery of GDNF into the brain through MRI-guided focused ultrasound-induced BBB disruption. To demonstrate the therapeutic effect, rat depression model was developed by chronic mild stress treatment. Typical depression behaviors were confirmed. MRI-guided focused ultrasound was used to irradiate the GDNF-loaded MBs. Obvious BBB opening was observed in the treated rat brains and a significant higher GDNF concentration was detected in the ultrasound-treated brain tissues. Behavioral tests demonstrated the increased GDNF could reverse the depressive-like behaviors induced by chronic mild stress, improve the expression of 5-HT 1B receptor and the protein p11, and increase the number of 5-HT or TPH2 immunoreactive neurons. In conclusion, our study provided an effective approach to deliver GDNF proteins into brain to treat rat depression through MRI-guided focused ultrasound-induced destruction of blood-brain barrier.

Blood-brain barrier opening with low intensity pulsed ultrasound for immune modulation and immune therapeutic delivery to CNS tumors.

Opening of the blood-brain barrier (BBB) by pulsed low intensity ultrasound has been developed during the last decade and is now recognized as a safe technique to transiently and repeatedly open the BBB. This non- or minimally invasive technique allows for a targeted and uniform dispersal of a wide range of therapeutic substances throughout the brain, including immune cells and antibodies. In this review article, we summarize pre-clinical studies that have used BBB-opening by pulsed low intensity ultrasound to enhance the delivery of immune therapeutics and effector cell populations, as well as several recent clinical studies that have been initiated. Based on this analysis, we propose immune therapeutic strategies that are most likely to benefit from this strategy. The literature review and trial data research were performed using Medline/Pubmed databases and clinical trial registry www.clinicaltrials.gov . The reference lists of all included articles were searched for additional studies. A wide range of immune therapeutic agents, including small molecular weight drugs, antibodies or NK cells, have been safely and efficiently delivered to the brain with pulsed low intensity ultrasound in preclinical models, and both tumor control and increased survival have been demonstrated in different types of brain tumor models in rodents. Ultrasound-induced BBB disruption may also stimulate innate and cellular immune responses. Ultrasound BBB opening has just recently entered clinical trials with encouraging results, and the association of this strategy with immune therapeutics creates a new field of brain tumor treatment.

Ultrasound-induced blood-brain barrier disruption for the treatment of gliomas and other primary CNS tumors.

The treatment of primary brain tumors, especially malignant gliomas, remains challenging. The failure of most treatments for this disease is partially explained by the blood-brain barrier (BBB), which prevents circulating molecules from entering the brain parenchyma. Ultrasound-induced BBB disruption (US-BBBD) has recently emerged as a promising strategy to improve the delivery of therapeutic agents to brain tumors. A large body of preclinical studies has demonstrated that the association of low-intensity pulsed ultrasound with intravenous microbubbles can transiently open the BBB in a localized manner. The safety of this technique has been assessed in numerous preclinical studies in both small and large animal models. A large panel of therapeutic agents have been delivered to the brain in preclinical models, demonstrating both tumor control and increased survival. This technique has recently entered clinical trials with encouraging preliminary data. In this review, we describe the mechanisms and histological effects of US-BBBD and summarize the preclinical studies published to date. We furthermore provide an overview of the current clinical development and future potential of this promising technology.

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.

Pharmacokinetics of doxorubicin in glioblastoma multiforme following ultrasound-Induced blood-brain barrier disruption as determined by microdialysis

The goal of this study was to investigate the in vivo extracellular kinetics of doxorubicin (Dox) in glioblastoma multiforme (GBM)-bearing mice following focused ultrasound (FUS)-induced blood-brain barrier (BBB) disruption using microdialysis. An intracranial brain tumor model in NOD-scid mice using human brain GBM 8401 cells was used in this study. Prior to each sonication, simultaneous intravenous administration of Dox and microbubbles, and the Dox concentration in the brains was quantified by high performance liquid chromatography (HPLC). Drug administration with sonication elevated the tumor-to-normal brain Dox ratio of the target tumors by about 2.35-fold compared with the control tumors. The mean peak concentration of Dox in the sonicated GBM dialysate was 10 times greater than without sonication, and the area under the concentration-time curve was 3.3 times greater. This study demonstrates that intracerebral microdialysis is an effective means of evaluating real-time target BBB transport profiles and offers the possibility of investigating the pharmacokinetics of drug delivery in the sonicated brain.

The Effects of Oxygen on Ultrasound-Induced Blood–Brain Barrier Disruption in Mice

Numerous researchers are investigating the use of microbubble-enhanced ultrasound to disrupt the blood–brain barrier (BBB) and deliver drugs to the brain. This study investigated the impact of using oxygen as a carrier gas for anesthesia on microbubble activity and BBB disruption. Targets in mice were sonicated in combination with administration of Optison microbubbles (100 μL/kg) under isoflurane anesthesia with either oxygen or medical air. A 690-kHz focused ultrasound transducer applied 10-ms bursts at peak pressure amplitudes of 0.46–0.54 MPa (n = 2) or 0.34–0.36 MPa (n = 5). After sonication of two locations in one hemisphere, the carrier gas for the anesthesia was changed and the sonications were repeated in the contralateral hemisphere. The BBB disruption, measured via contrast-enhanced magnetic resonance imaging, was significantly greater (p < 0.001) with medical air than with oxygen. Harmonic emissions were also greater with air (p < 0.001), while the decay rate of the harmonic emissions was 1.5 times faster with oxygen. A good correlation (R2, 0.46) was observed between the harmonic emissions strength and magnetic resonance imaging signal enhancement. At 0.46–0.54 MPa, both the occurrence and strength of wideband emissions were greater with medical air. However, at lower peak pressure amplitudes of 0.34–0.36 MPa, the strength and probability for wideband emissions were higher with oxygen. Little or no effects were observed in histology at 0.34–0.36 MPa. These findings show that use of oxygen as a carrier gas can result in a substantial diminution of BBB disruption. These results should be taken into account when comparing studies from different researchers and in translating this method to humans.

Targeted delivery of GABA via ultrasound-induced blood-brain barrier disruption blocks somatosensory-evoked potentials

This study investigated whether targeted delivery of the inhibitory neurotransmitter gamma-Aminobutyric acid (GABA), a small molecule (103 Da) that normally does not reach the brain with systemic administration, can temporarily block brain activity after ultrasound-induced blood-brain barrier (BBB) disruption.

Modeling localized delivery of Doxorubicin to the brain following focused ultrasound enhanced blood-brain barrier permeability

Doxorubicin (Dox) is a well-established chemotherapeutic agent, however it has limited efficacy in treating brain malignancies due to the presence of the blood-brain barrier (BBB). Recent preclinical studies have demonstrated that focused ultrasound induced BBB disruption (BBBD) enables efficient delivery of Dox to the brain. For future treatment planning of BBBD-based drug delivery, it is crucial to establish a mathematical framework to predict the effect of transient BBB permeability enhancement on the spatiotemporal distribution of Dox at the targeted area. The constructed model considers Dox concentrations within three compartments (plasma, extracellular, intracellular) that are governed by various transport processes (e.g. diffusion in interstitial space, exchange across vessel wall, clearance by cerebral spinal fluid, uptake by brain cells). By examining several clinical treatment aspects (e.g. sonication scheme, permeability enhancement, injection mode), our simulation results support the experimental findings of optimal interval delay between two consecutive sonications and therapeutically-sufficient intracellular concentration with respect to transfer constant Ktrans range of 0.01–0.03 min−1. Finally, the model suggests that infusion over a short duration (20–60 min) should be employed along with single-sonication or multiple-sonication at 10 min interval to ensure maximum delivery to the intracellular compartment while attaining minimal cardiotoxicity via suppressing peak plasma concentration.

Pharmacokinetic Analysis and Uptake of 18F-FBPA-Fr After Ultrasound-Induced Blood–Brain Barrier Disruption for Potential Enhancement of Boron Delivery for Neutron Capture Therapy

Boronophenylalanine has been applied in clinical boron neutron capture therapy for the treatment of high-grade gliomas. The purpose of this study was to evaluate the pharmacokinetics of 4-borono-2-(18)F-fluoro-L-phenylalanine-fructose ((18)F-FBPA-Fr) in F98 glioma-bearing Fischer 344 rats by means of intravenous injection of (18)F-FBPA-Fr both with and without blood-brain barrier disruption (BBB-D) induced by focused ultrasound (FUS). Dynamic PET imaging of (18)F-FBPA-Fr was performed on the ninth day after tumor implantation. Blood samples were collected to obtain an arterial input function for tracer kinetic modeling. Ten animals were scanned for approximately 3 h to estimate the uptake of (18)F radioactivity with respect to time for the pharmacokinetic analysis. Rate constants were calculated by use of a 3-compartment model. The accumulation of (18)F-FBPA-Fr in brain tumors and the tumor-to-contralateral brain ratio were significantly elevated after intravenous injection of (18)F-FBPA-Fr with BBB-D. (18)F-FBPA-Fr administration after sonication showed that the tumor-to-contralateral brain ratio for the sonicated tumors (3.5) was approximately 1.75-fold higher than that for the control tumors (2.0). Furthermore, the K1/k2 pharmacokinetic ratio after intravenous injection of (18)F-FBPA-Fr with BBB-D was significantly higher than that after intravenous injection without BBB-D. This study demonstrated that radioactivity in tumors and the tumor-to-normal brain ratio after intravenous injection of (18)F-FBPA-Fr with sonication were significantly higher than those in tumors without sonication. The K1/k2 ratio may be useful for indicating the degree of BBB-D induced by FUS. Further studies are needed to determine whether FUS may be useful for enhancing the delivery of boronophenylalanine in patients with high-grade gliomas.

Drug delivery to the brain by focused ultrasound induced blood–brain barrier disruption: Quantitative evaluation of enhanced permeability of cerebral vasculature using two-photon microscopy

Reversible and localized blood–brain barrier disruption (BBBD) using focused ultrasound (FUS) in combination with intravascularly administered microbubbles (MBs) has been established as a non-invasive method for drug delivery to the brain. Using two-photon fluorescence microscopy (2PFM), we imaged the cerebral vasculature during BBBD and observed the extravasation of fluorescent dye in real-time in vivo. We measured the enhanced permeability upon BBBD for both 10kDa and 70kDa dextran conjugated Texas Red (TR) at the acoustic pressure range of 0.2–0.8MPa and found that permeability constants of TR10kDa and TR70kDa vary from 0.0006 to 0.0359min−1 and from 0.0003 to 0.0231min−1, respectively. For both substances, a linear regression was applied on the permeability constant against the acoustic pressure and the slope from best-fit was found to be 0.039±0.005min−1/MPa and 0.018±0.005min−1/MPa, respectively. In addition, the pressure threshold for successfully induced BBBD was confirmed to be 0.4–0.6MPa. Finally, we identified two types of leakage kinetics (fast and slow) that exhibit distinct permeability constants and temporal disruption onsets, as well as demonstrated their correlations with the applied acoustic pressure and vessel diameter. Direct assessment of vascular permeability and insights on its dependency on acoustic pressure, vessel size and leakage kinetics are important for treatment strategies of BBBD-based drug delivery.

Focused ultrasound-induced blood–brain barrier disruption enhances the delivery of cytarabine to the rat brain

To investigate the feasibility of using focused ultrasound (FUS) with microbubbles for targeted delivery of cytarabine to the brain. Sprague–Dawly rats (weighing 200–250 g) received focused ultrasound with intravenous injection microbubbles. At 0, 2, 4, 8, and 24 hours (n = 5 for each time point) after sonication, animals received intravenous administration of cytarabine at a normal dose of 4 mg/kg body weight. Additional five rats were given with a high dose (50 mg/kg body weight) of cytarabine alone. Blood–brain barrier (BBB) permeability and cerebral cytarabine were determined. FUS in conjunction with microbubbles caused a transient BBB opening. Sonication exposure promoted cytarabine accumulation at the sonicated site. Animals injected with a normal dose of cytarabine 2 hours after sonication had similar concentrations of cerebral cytarabine compared to those with higher cytarabine without sonication. FUS can temporarily open the BBB and thus facilitate the penetration of systemic cytarabine into the brain.