Targeted delivery of doxorubicin to the rat brain at therapeutic levels using MRI-guided focused ultrasound

The role of focused ultrasound for pediatric brain tumors: current insights and future implications on treatment strategies

INTRODUCTION

Focused ultrasound (FUS) is an innovative and emerging technology for the treatment of adult and pediatric brain tumors and illustrates the intersection of various specialized fields, including neurosurgery, neuro-oncology, radiation oncology, and biomedical engineering.

OBJECTIVE

The authors provide a comprehensive overview of the application and implications of FUS in treating pediatric brain tumors, with a special focus on pediatric low-grade gliomas (pLGGs) and the evolving landscape of this technology and its clinical utility.

METHODS

The fundamental principles of FUS include its ability to induce thermal ablation or enhance drug delivery through transient blood-brain barrier (BBB) disruption, emphasizing the adaptability of high-intensity focused ultrasound (HIFU) and low-intensity focused ultrasound (LIFU) applications.

RESULTS

Several ongoing clinical trials explore the potential of FUS in offering alternative therapeutic strategies for pathologies where conventional treatments fall short, specifically centrally-located benign CNS tumors and diffuse intrinsic pontine glioma (DIPG). A case illustration involving the use of HIFU for pilocytic astrocytoma is presented.

CONCLUSION

Discussions regarding future applications of FUS for the treatment of gliomas include improved drug delivery, immunomodulation, radiosensitization, and other technological advancements.

The road ahead to successful BBB opening and drug-delivery with focused ultrasound

This review delves into the innovative technology of Blood-Brain Barrier (BBB) opening with low-intensity focused ultrasound in combination with microbubbles (LIFU-MB), a promising therapeutic modality aimed at enhancing drug delivery to the central nervous system (CNS). The BBB's selective permeability, while crucial for neuroprotection, significantly hampers the efficacy of pharmacological treatments for CNS disorders. LIFU-MB emerges as a non-invasive and localized method to transiently increase BBB permeability, facilitating the delivery of therapeutic molecules. Here, we review the procedural stages of LIFU-MB interventions, including planning and preparation, sonication, evaluation, and delivery, highlighting the technological diversity and methodological challenges encountered in current clinical applications. With an emphasis on safety and efficacy, we discuss the crucial aspects of ultrasound delivery, microbubble administration, acoustic feedback monitoring and assessment of BBB permeability. Finally, we explore the critical choices for effective BBB opening with LIFU-MB, focusing on selecting therapeutic agents, optimizing delivery methods, and timing for delivery. Overcoming existing barriers to integrate this technology into clinical practice could potentially revolutionize CNS drug delivery and treatment paradigms in the near future.

Recent advances of focused ultrasound induced blood-brain barrier opening for clinical applications of neurodegenerative diseases

With the aging population on the rise, neurodegenerative disorders have taken center stage as a significant health concern. The blood-brain barrier (BBB) plays an important role to maintain the stability of central nervous system, yet it poses a formidable obstacle to delivering drugs for neurodegenerative disease therapy. Various methods have been devised to confront this challenge, each carrying its own set of limitations. One particularly promising noninvasive approach involves the utilization of focused ultrasound (FUS) combined with contrast agents-microbubbles (MBs) to achieve transient and reversible BBB opening. This review provides a comprehensive exploration of the fundamental mechanisms behind FUS/MBs-mediated BBB opening and spotlights recent breakthroughs in its application for neurodegenerative diseases. Furthermore, it addresses the current challenges and presents future perspectives in this field.

Focused ultrasound as a treatment modality for gliomas

Ultrasound waves were initially used as a diagnostic tool that provided critical insights into several pathological conditions (e.g., gallstones, ascites, pneumothorax, etc.) at the bedside. Over the past decade, advancements in technology have led to the use of ultrasound waves in treating many neurological conditions, such as essential tremor and Parkinson's disease, with high specificity. The convergence of ultrasound waves at a specific region of interest/target while avoiding surrounding tissue has led to the coined term "focused ultrasound (FUS)." In tumor research, ultrasound technology was initially used as an intraoperative guidance tool for tumor resection. However, in recent years, there has been growing interest in utilizing FUS as a therapeutic tool in the management of brain tumors such as gliomas. This mini-review highlights the current knowledge surrounding using FUS as a treatment modality for gliomas. Furthermore, we discuss the utility of FUS in enhanced drug delivery to the central nervous system (CNS) and highlight promising clinical trials that utilize FUS as a treatment modality for gliomas.

Nanotechnology-enabled sonodynamic therapy against malignant tumors

Sonodynamic therapy (SDT) is an emerging approach for malignant tumor treatment, offering high precision, deep tissue penetration, and minimal side effects. The rapid advancements in nanotechnology, particularly in cancer treatment, have enhanced the efficacy and targeting specificity of SDT. Combining sonodynamic therapy with nanotechnology offers a promising direction for future cancer treatments. In this review, we first systematically discussed the anti-tumor mechanism of SDT and then summarized the common nanotechnology-related sonosensitizers and their recent applications. Subsequently, nanotechnology-related therapies derived using the SDT mechanism were elaborated. Finally, the role of nanomaterials in SDT combined therapy was also introduced.

Ultrasound-responsive microbubbles and nanodroplets: A pathway to targeted drug delivery

Ultrasound-responsive agents have shown great potential as targeted drug delivery agents, effectively augmenting cell permeability and facilitating drug absorption. This review focuses on two specific agents, microbubbles and nanodroplets, and provides a sequential overview of their drug delivery process. Particular emphasis is given to the mechanical response of the agents under ultrasound, and the subsequent physical and biological effects on the cells. Finally, the state-of-the-art in their pre-clinical and clinical implementation are discussed. Throughout the review, major challenges that need to be overcome in order to accelerate their clinical translation are highlighted.

Saturated Fatty Acid Emulsions Open the Blood-Brain Barrier and Promote Drug Delivery in Rat Brains

We performed this study to evaluate whether saturated fatty acid (SFA) emulsions affect the BBB and determine the duration of BBB opening, thereby promoting drug delivery to the brain. Butyric, valeric, caproic, enanthic, and caprylic acid emulsions were infused into the carotid artery of the rat model. We evaluated the BBB opening and drug delivery over time. The trypan blue and doxorubicin delivery studies were repeated from 30 min to 6 h. In the 1 h rats in each group, transmission electron microscopy (TEM) was performed to morphologically evaluate tight junctions, and the delivery of temozolomide was assessed by desorption electrospray ionization mass spectrometry. The ipsilateral hemisphere was positive for trypan blue staining in all the five SFA emulsion groups. In the valeric, enanthic, and caprylic acid emulsion groups, RGB ratios were significantly higher at 30 min and decreased thereafter. Doxorubicin delivery increased in all emulsion groups at all time points. Tight junctions were observed to be open in all groups. TMZ delivery was significantly higher in the ipsilateral hemisphere. In conclusion, intra-arterially infused SFA emulsions opened the BBB and promoted drug delivery within 30 min, which decreased thereafter. Therefore, SFA emulsions may aid BBB research and promote drug delivery to the brain.

Targeting diffuse midline gliomas: The promise of focused ultrasound-mediated blood-brain barrier opening

Diffuse midline gliomas (DMGs), including diffuse intrinsic pontine glioma, have among the highest mortality rates of all childhood cancers, despite recent advancements in cancer therapeutics. This is partly because, unlike some CNS tumors, the blood-brain barrier (BBB) of DMG tumor vessels remains intact. The BBB prevents the permeation of many molecular therapies into the brain parenchyma, where the cancer cells reside. Focused ultrasound (FUS) with microbubbles has recently emerged as an innovative and exciting technology that non-invasively permeabilizes the BBB in a small focal region with millimeter precision. In this review, current treatment methods and biological barriers to treating DMGs are discussed. State-of-the-art FUS-mediated BBB opening is then examined, with a focus on the effects of various ultrasound parameters and the treatment of DMGs.

Engineering Versatile Nanomedicines for Ultrasonic Tumor Immunotherapy

Due to the specific advantages of ultrasound (US) in therapeutic disease treatments, the unique therapeutic US technology has emerged. In addition to featuring a low-invasive targeted cancer-cell killing effect, the therapeutic US technology has been demonstrated to modulate the tumor immune landscape, amplify the therapeutic effect of other antitumor therapies, and induce immunosensitization of tumors to immunotherapy, shedding new light on the cancer treatment. Tremendous advances in nanotechnology are also expected to bring unprecedented benefits to enhancing the antitumor efficiency and immunological effects of therapeutic US, as well as therapeutic US-derived bimodal and multimodal synergistic therapies. This comprehensive review summarizes the immunological effects induced by different therapeutic US technologies, including ultrasound-mediated micro-/nanobubble destruction (UTMD/UTND), sonodynamic therapy (SDT), and focused ultrasound (FUS), as well as the main underlying mechanisms involved. It is also discussed that the recent research progress of engineering intelligent nanoplatform in improving the antitumor efficiency of therapeutic US technologies. Finally, focusing on clinical translation, the key issues and challenges currently faced are summarized, and the prospects for promoting the clinical translation of these emerging nanomaterials and ultrasonic immunotherapy in the future are proposed.

A Systematic Review of Nanomedicine in Glioblastoma Treatment: Clinical Efficacy, Safety, and Future Directions

(1) Background: Glioblastoma (GBM) is categorized as a grade IV astrocytoma by the World Health Organization (WHO), representing the most aggressive and prevalent form of glioma. It presents a significant clinical challenge, with limited treatment options and poor prognosis. This systematic review evaluates the efficacy and safety of various nanotherapy approaches for GBM and explores future directions in tumor management. Nanomedicine, which involves nanoparticles in the 1-100 nm range, shows promise in improving drug delivery and targeting tumor cells. (2) Methods: Following PRISMA guidelines, a systematic search of databases including Google Scholar, NCBI PubMed, Cochrane Library, and ClinicalTrials.gov was conducted to identify clinical trials on GBM and nanomedicine. The primary outcome measures were median overall survival, progression-free survival, and quality of life assessed through Karnofsky performance scores. The safety profile was assessed by adverse events. (3) Results: The analysis included 225 GBM patients, divided into primary and recurrent sub-populations. Primary GBM patients had a median overall survival of 6.75 months, while recurrent GBM patients had a median overall survival of 9.7 months. The mean PFS period was 2.3 months and 3.92 months in primary GBM and recurrent GBM patients, respectively. Nanotherapy showed an improvement in quality of life, with KPS scores increasing after treatment in recurrent GBM patients. Adverse events were observed in 14.2% of patients. Notably, Bevacizumab therapy exhibited better survival outcomes but with a higher incidence of adverse events. (4) Conclusions: Nanotherapy offers a modest increase in survival with fewer severe side effects. It shows promise in improving the quality of life, especially in recurrent GBM patients. However, it falls short in terms of overall survival compared to Bevacizumab. The heterogeneous nature of treatment protocols and reporting methods highlights the need for standardized multicenter trials to further evaluate the potential of nanomedicine in GBM management.

Methodological and ethical challenges in the use of focused ultrasound for blood-brain barrier disruption in neuro-oncology

BACKGROUND

Focused ultrasound (FUS) shows promise for enhancing drug delivery to the brain by temporarily opening the blood-brain barrier (BBB), and it is increasingly used in the clinical setting to treat brain tumours. It remains however unclear whether FUS is being introduced in an ethically and methodologically sound manner. The IDEAL-D framework for the introduction of surgical innovations and the SYRCLE and ROBINS-I tools for assessing the risk of bias in animal studies and non-randomized trials, respectively, provide a comprehensive evaluation for this.

OBJECTIVES AND METHODS

A comprehensive literature review on FUS in neuro-oncology was conducted. Subsequently, the included studies were evaluated using the IDEAL-D framework, SYRCLE, and ROBINS-I tools.

RESULTS

In total, 19 published studies and 12 registered trials were identified. FUS demonstrated successful BBB disruption, increased drug delivery, and improved survival rates. However, the SYRCLE analysis revealed a high risk of bias in animal studies, while the ROBINS-I analysis found that most human studies had a high risk of bias due to a lack of blinding and heterogeneous samples. Of the 15 pre-clinical stage 0 studies, only six had formal ethical approval, and only five followed animal care policies. Both stage 1 studies and stage 1/2a studies failed to provide information on patient data confidentiality. Overall, no animal or human study reached the IDEAL-D stage endpoint.

CONCLUSION

FUS holds promise for enhancing drug delivery to the brain, but its development and implementation must adhere to rigorous safety standards using the established ethical and methodological frameworks. The complementary use of IDEAL-D, SYRCLE, and ROBINS-I tools indicates a high risk of bias and ethical limitations in both animal and human studies, highlighting the need for further improvements in study design for a safe implementation of FUS in neuro-oncology.

Focused ultrasound combined with radiotherapy for malignant brain tumor: a preclinical and clinical study

INTRODUCTION

Blood-brain barrier (BBB) remains to be the major obstacle to conquer in treating patients with malignant brain tumors. Radiation therapy (RT), despite being the mainstay adjuvant modality regardless of BBB, the effect of radiation induced cell death is hindered by the hypoxic microenvironment. Focused ultrasound (FUS) combined with systemic microbubbles has been shown not only to open BBB but also potentially increased regional perfusion. However, no clinical study has investigated the combination of RT with FUS-BBB opening (RT-FUS).

METHODS

We aimed to provide preclinical evidence of RT-FUS combination in GBM animal model, and to report an interim analysis of an ongoing single arm, prospective, pilot study (NCT01628406) of combining RT-FUS for recurrent malignant high grade glioma patients, of whom re-RT was considered for disease control. In both preclinical and clinical studies, FUS-BBB opening was conducted within 2 h before RT. Treatment responses were evaluated by objective response rate (ORR) using magnetic resonance imaging, progression free survival, and overall survival, and adverse events (AE) in clinical study. Survival analysis was performed in preclinical study and descriptive analysis was performed in clinical study.

RESULTS

In mouse GBM model, the survival analysis showed RT-FUS (2 Gy) group was significantly longer than RT (2 Gy) group and control, but not RT (5 Gy) group. In the pilot clinical trial, an interim analysis of six recurrent malignant high grade glioma patients underwent a total of 24 RT-FUS treatments was presented. Three patients had rapid disease progression at a mean of 33 days after RT-FUS, while another three patients had at least stable disease (mean 323 days) after RT-FUS with or without salvage chemotherapy or target therapy. One patient had partial response after RT-FUS, making the ORR of 16.7%. There was no FUS-related AEs, but one (16.7%) re-RT-related grade three radiation necrosis.

CONCLUSION

Reirradiation is becoming an option after disease recurrence for both primary and secondary malignant brain tumors since systemic therapy significantly prolongs survival in cancer patients. The mechanism behind the synergistic effect of RT-FUS in preclinical model needs further study. The clinical evidence from the interim analysis of an ongoing clinical trial (NCT01628406) showed a combination of RT-FUS was safe (no FUS-related adverse effect). A comprehensive analysis of radiation dosimetry and FUS energy distribution is expected after completing the final recruitment.

A Bibliometric Analysis for Low-Intensity Ultrasound Study Over the Past Three Decades

Low-intensity ultrasound (LI-US) is a non-invasive stimulation technique that has emerged in recent years and has been shown to have positive effects on neuromodulation, fracture healing, inflammation improvement, and metabolic regulation. This study reports the conclusions of a bibliometric analysis of LI-US. Input data for the period between 1995 and 2022, including 7209 related articles in the field of LI-US, were collected from the core library of the Web of Science (WOS) database. Using these data, a set of bibliometric indicators was obtained to gain knowledge on different aspects: global production, research areas, and sources analysis, contributions of countries and institutions, author analysis, citation analysis, and keyword analysis. This study combined the data analysis capabilities provided by the WOS database, making use of two bibliometric software tools: R software and VOS viewer to achieve analysis and data exploration visualization, and predicted the further development trends of LI-US. It turns out that the United States and China are co-leaders while Zhang ZG is the most significant author in LI-US. In the future, the hot spots of LI-US will continue to focus on parameter research, mechanism discussion, safety regulations, and neuromodulation applications.

Focused ultrasound for brain metastases: an update on global clinical trials

BACKGROUND

Despite advances in immunotherapy and targeted treatments for malignancies of the central nervous system (CNS), the treatment of brain metastases (BMs) remains a formidable challenge, due largely to difficulties in crossing the blood-brain barrier (BBB), drug resistance, and molecular discrepancies. Focused ultrasound (FUS) is a non-invasive tool for BBB breaching, tumor ablation, enhancing drug delivery, promoting the release of tumor biomarkers for liquid biopsy, or the tumor microenvironment disruption. This paper presents a comprehensive review of the current literature related to FUS and its application in the treatment of brain metastasis.

METHODS

This review of the current literature via PubMed, Google Scholar, and Clincaltrials.gov focused on clinical trials in which FUS is used in the intracranial treatment of metastatic tumor, glioma, or GBM.

RESULTS

FUS is safe and effective for treatment of primary or metastatic brain tumors. FUS-augmented drug delivery can open BBB to facilitate the transport of chemotherapeutic agents, immunotherapies, and targeted treatments. The integration of FUS with liquid biopsy has considerable potential for early tumor detection, precise gene profiling, and personalized therapy. Sonodynamic therapy can induce tumor cell apoptosis and could potentially be used to enhance the outcomes of other tumor treatments, such as surgery and chemotherapy.

CONCLUSION

Further work is required to establish FUS as a standard therapy for BMs. FUS has the potential to transform brain tumor treatment, particularly when combined with immunotherapy and targeted therapy as a non-invasive alternative to surgery and radiation therapy.

Quantitative estimation of phospholipid molecules desorbed from a microbubble surface under ultrasound irradiation

Microbubbles have potential applications as drug and gene carriers, and drug release can be triggered by externally applied ultrasound irradiation while inside blood vessels. Desorption of molecules forming the microbubble shell can be observed under ultrasound irradiation of a single isolated microbubble, and the volume of desorbed molecules can be quantitatively estimated from the contact angle between the bubble and a glass plate. Microbubbles composed of a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) shell and a poorly-soluble gas are created. When the microbubbles are exposed to a pulsed ultrasound, the contact angles increase dramatically; the percentage of DMPC molecules desorbed from the bubble surface reaches 70%. Vibration of a single bubble in the radial direction is measured using a laser Doppler vibrometer. The relationship between the vibrational characteristics and the amount of molecular desorption reveals that a larger vibrational amplitude of the bubble around the resonance size induces a larger amount of molecular desorption. These results support the possibility of controlling molecular desorption with pulsed ultrasound.

Miniaturized MR-compatible ultrasound system for real-time monitoring of acoustic effects in mice using high-resolution MRI

Visualization of focused ultrasound in high spatial and temporal resolution is crucial for accurately and precisely targeting brain regions noninvasively. Magnetic resonance imaging (MRI) is the most widely used noninvasive tool for whole-brain imaging. However, focused ultrasound studies employing high-resolution (> 9.4 T) MRI in small animals are limited by the small size of the radiofrequency (RF) volume coil and the noise sensitivity of the image to external systems such as bulky ultrasound transducers. This technical note reports a miniaturized ultrasound transducer system packaged directly above a mouse brain for monitoring ultrasound-induced effects using high-resolution 9.4 T MRI. Our miniaturized system integrates MR-compatible materials with electromagnetic (EM) noise reduction techniques to demonstrate echo-planar imaging (EPI) signal changes in the mouse brain at various ultrasound acoustic intensities. The proposed ultrasound-MRI system will enable extensive research in the expanding field of ultrasound therapeutics.

Cutting-edge advances in modeling the blood-brain barrier and tools for its reversible permeabilization for enhanced drug delivery into the brain

The blood-brain barrier (BBB) is a sophisticated structure whose full functionality is required for maintaining the executive functions of the central nervous system (CNS). Tight control of transport across the barrier means that most drugs, particularly large size, which includes powerful biologicals, cannot reach their targets in the brain. Notwithstanding the remarkable advances in characterizing the cellular nature of the BBB and consequences of BBB dysfunction in pathology (brain metastasis, neurological diseases), it remains challenging to deliver drugs to the CNS. Herein, we outline the basic architecture and key molecular constituents of the BBB. In addition, we review the current status of approaches that are being explored to temporarily open the BBB in order to allow accumulation of therapeutics in the CNS. Undoubtedly, the major concern in field is whether it is possible to open the BBB in a meaningful way without causing negative consequences. In this context, we have also listed few other important key considerations that can improve our understanding about the dynamics of the BBB.

An in-vivo study of the combined therapeutic effects of pulsed non-thermal focused ultrasound and radiation for prostate cancer

PURPOSE

The purpose of this study was to investigate the in vivo combined effects of pulsed focused ultrasound (pFUS) and radiation (RT) for prostate cancer treatment.

MATERIALS AND METHODS

An animal prostate tumor model was developed by implanting human LNCaP tumor cells in the prostates of nude mice. Tumor-bearing mice were treated with pFUS, RT or both (pFUS + RT) and compared with a control group. Non-thermal pFUS treatment was delivered by keeping the body temperature below 42 °C as measured real-time by MR thermometry and using a pFUS protocol (1 MHz, 25 W focused ultrasound; 1 Hz pulse rate with a 10% duty cycle for 60 sec for each sonication). Each tumor was covered entirely using 4-8 sonication spots. RT treatment with a dose of 2 Gy was delivered using an external beam (6 MV photon energy with dose rate 300MU/min). Following the treatment, mice were scanned weekly with MRI for tumor volume measurement.

RESULTS

The results showed that the tumor volume in the control group increased exponentially to 142 ± 6%, 205 ± 12%, 286 ± 22% and 410 ± 33% at 1, 2, 3 and 4 weeks after treatment, respectively. In contrast, the pFUS group was 29% (p < 0.05), 24% (p < 0.05), 8% and 9% smaller, the RT group was 7%, 10%, 12% and 18% smaller, and the pFUS + RT group was 32%, 39%, 41% and 44% (all with p < 0.05) smaller than the control group at 1, 2, 3, and 4 weeks post treatment, respectively. Tumors treated by pFUS showed an early response (i.e. the first 2 weeks), while the RT group showed a late response. The combined pFUS + RT treatment showed consistent response throughout the post-treatment weeks.

CONCLUSIONS

These results suggest that RT combined with non-thermal pFUS can significantly delay the tumor growth. The mechanism of tumor cell killing between pFUS and RT may be different. Pulsed FUS shows early tumor growth delay, while RT contributes to the late effect on tumor growth delay. The addition of pFUS to RT significantly enhanced the therapeutic effect for prostate cancer treatment.

Intercellular Calcium Waves and Permeability Change Induced by Vertically Deployed Surface Acoustic Waves in a Human Cerebral Microvascular Endothelial Cell Line (hCMEC/D3) Monolayer

OBJECTIVE

The ultrasound-mediated blood-brain barrier (BBB) opening with microbubbles has been widely employed, while recent studies also indicate the possibility that ultrasound alone can open the BBB through a direct mechanical effect. However, the exact mechanisms through which ultrasound interacts with the BBB and whether it can directly trigger intracellular signaling and a permeability change in the BBB endothelium remain unclear.

METHODS

Vertically deployed surface acoustic waves (VD-SAWs) were applied on a human cerebral microvascular endothelial cell line (hCMEC/D3) monolayer using a 33-MHz interdigital transducer that exerts shear stress-predominant stimulation. The intracellular calcium response was measured by fluorescence imaging, and the permeability of the hCMEC/D3 monolayer was assessed by transendothelial electrical resistance (TEER).

DISCUSSION

At a certain intensity threshold, VD-SAWs induced an intracellular calcium surge that propagated to adjacent cells as intercellular calcium waves. VD-SAWs induced a TEER decrease in a pulse repetition frequency-dependent manner, thereby suggesting possible involvement of the mechanosensitive ion channels.

CONCLUSION

The unique VD-SAW system enables more physiological mechanical stimulation of the endothelium monolayer. Moreover, it can be easily combined with other measurement devices, providing a useful platform for further mechanistic studies on ultrasound-mediated BBB opening.

Focused ultrasound for treatment of peripheral brain tumors

Malignant brain tumors are the leading cause of cancer-related death in children and remain a significant cause of morbidity and mortality throughout all demographics. Central nervous system (CNS) tumors are classically treated with surgical resection and radiotherapy in addition to adjuvant chemotherapy. However, the therapeutic efficacy of chemotherapeutic agents is limited due to the blood-brain barrier (BBB). Magnetic resonance guided focused ultrasound (MRgFUS) is a new and promising intervention for CNS tumors, which has shown success in preclinical trials. High-intensity focused ultrasound (HIFU) has the capacity to serve as a direct therapeutic agent in the form of thermoablation and mechanical destruction of the tumor. Low-intensity focused ultrasound (LIFU) has been shown to disrupt the BBB and enhance the uptake of therapeutic agents in the brain and CNS. The authors present a review of MRgFUS in the treatment of CNS tumors. This treatment method has shown promising results in preclinical trials including minimal adverse effects, increased infiltration of the therapeutic agents into the CNS, decreased tumor progression, and improved survival rates.

Characteristics of Focused Ultrasound Mediated Blood-Brain Barrier Opening in Magnetic Resonance Images

OBJECTIVE

The blood-brain barrier (BBB) is an obstacle for molecules to pass through from blood to the brain. Focused ultrasound is a new method which temporarily opens the BBB, which makes pharmaceutical delivery or removal of neurodegenerative proteins possible. This study was demonstrated to review our BBB opening procedure with magnetic resonance guided images and find specific patterns in the BBB opening.

METHODS

In this study, we reviewed the procedures and results of two clinical studies on BBB opening using focused ultrasound regarding its safety and clinical efficacy. Magnetic resonance images were also reviewed to discover any specific findings.

RESULTS

Two clinical trials showed clinical benefits. All clinical trials demonstrated safe BBB opening, with no specific side effects. Magnetic resonance imaging showed temporary T1 contrast enhancement in the sonication area, verifying the BBB opening. Several low-signal intensity spots were observed in the T2 susceptibility-weighted angiography images, which were also reversible and temporary. Although these spots can be considered as microbleeding, evidence suggests these are not ordinary microbleeding but an indicator for adequate BBB opening.

CONCLUSION

Magnetic resonance images proved safe and efficient BBB opening in humans, using focused ultrasound.

Ultrasound-mediated delivery of flexibility-tunable polymer drug conjugates for treating glioblastoma

Effective chemotherapy delivery for glioblastoma multiforme (GBM) is limited by drug transport across the blood-brain barrier and poor efficacy of single agents. Polymer-drug conjugates can be used to deliver drug combinations with a ratiometric dosing. However, the behaviors and effectiveness of this system have never been well investigated in GBM models. Here, we report flexible conjugates of hyaluronic acid (HA) with camptothecin (CPT) and doxorubicin (DOX) delivered into the brain using focused ultrasound (FUS). In vitro toxicity assays reveal that DOX-CPT exhibited synergistic action against GBM in a ratio-dependent manner when delivered as HA conjugates. FUS is employed to improve penetration of DOX-HA-CPT conjugates into the brain in vivo in a murine GBM model. Small-angle x-ray scattering characterizations of the conjugates show that the DOX:CPT ratio affects the polymer chain flexibility. Conjugates with the highest flexibility yield the highest efficacy in treating mouse GBM in vivo. Our results demonstrate the association of FUS-enhanced delivery of combination chemotherapy and the drug-ratio-dependent flexibility of the HA conjugates. Drug ratio in the polymer nanocomplex may thus be employed as a key factor to modulate FUS drug delivery efficiency via controlling the polymer flexibility. Our characterizations also highlight the significance of understanding the flexibility of drug carriers in ultrasound-mediated drug delivery systems.

Ultrasound-mediated nano drug delivery for treating cancer: Fundamental physics to future directions

The application of biocompatible nanocarriers in medicine has provided several benefits over conventional treatment methods. However, achieving high treatment efficacy and deep penetration of nanocarriers in tumor tissue is still challenging. To address this, stimuli-responsive nano-sized drug delivery systems (DDSs) are an active area of investigation in delivering anticancer drugs. While ultrasound is mainly used for diagnostic purposes, it can also be applied to affect cellular function and the delivery/release of anticancer drugs. Therapeutic ultrasound (TUS) has shown potential as both a stand-alone anticancer treatment and a method to induce targeted drug release from nanocarrier systems. TUS approaches have been used to overcome various physiological obstacles, including endothelial barriers, the tumor microenvironment (TME), and immunological hurdles. Combining nanomedicine and ultrasound as a smart DDS can increase in situ drug delivery and improve access to impermeable tissues. Furthermore, smart DDSs can perform targeted drug release in response to distinctive TMEs, external triggers, or dual/multi-stimulus. This results in enhanced treatment efficacy and reduced damage to surrounding healthy tissue or organs at risk. Integrating DDSs and ultrasound is still in its early stages. More research and clinical trials are required to fully understand ultrasound's underlying physical mechanisms and interactions with various types of nanocarriers and different types of cells and tissues. In the present review, ultrasound-mediated nano-sized DDS, specifically focused on cancer treatment, is presented and discussed. Ultrasound interaction with nanoparticles (NPs), drug release mechanisms, and various types of ultrasound-sensitive NPs are examined. Additionally, in vitro, in vivo, and clinical applications of TUS are reviewed in light of the critical challenges that need to be considered to advance TUS toward an efficient, secure, straightforward, and accessible cancer treatment. This study also presents effective TUS parameters and safety considerations for this treatment modality and gives recommendations about system design and operation. Finally, future perspectives are considered, and different TUS approaches are examined and discussed in detail. This review investigates drug release and delivery through ultrasound-mediated nano-sized cancer treatment, both pre-clinically and clinically.

Preclinical Research on Focused Ultrasound-Mediated Blood-Brain Barrier Opening for Neurological Disorders: A Review

Several therapeutic agents for neurological disorders are usually not delivered to the brain owing to the presence of the blood-brain barrier (BBB), a special structure present in the central nervous system (CNS). Focused ultrasound (FUS) combined with microbubbles can reversibly and temporarily open the BBB, enabling the application of various therapeutic agents in patients with neurological disorders. In the past 20 years, many preclinical studies on drug delivery through FUS-mediated BBB opening have been conducted, and the use of this method in clinical applications has recently gained popularity. As the clinical application of FUS-mediated BBB opening expands, it is crucial to understand the molecular and cellular effects of FUS-induced microenvironmental changes in the brain so that the efficacy of treatment can be ensured, and new treatment strategies established. This review describes the latest research trends in FUS-mediated BBB opening, including the biological effects and applications in representative neurological disorders, and suggests future directions.

Past, present and future of Focused Ultrasound as an adjunct or complement to DIPG/DMG therapy: A consensus of the 2021 FUSF DIPG meeting

Diffuse Intrinsic Pontine Glioma (DIPG), now known as Diffuse Midline Glioma (DMG) is a devastating pediatric brain tumor with limited treatment options and a very poor prognosis. Despite more than 250 clinical trials aimed to treat children diagnosed with DMG, no curative therapies currently exist for this patient population. A major obstacle has been the intact blood brain barrier (BBB) which prevents most therapeutics from crossing into the tumor bed. Focused Ultrasound (FUS) is an emerging, noninvasive medical technology which has been shown in both preclinical and clinical research to disrupt the blood brain barrier safely and temporarily. FUS blood brain barrier opening has been studied in combination with chemotherapies in preclinical DMG models, and this technology is now being investigated in clinical trials for the treatment of pediatric brain tumors. Focused ultrasound has additional mechanisms of action, including sonodynamic therapy and radiation sensitization, that hold promise as future DMG therapies as well. This paper, largely based off the proceedings from a workshop held by the Focused Ultrasound Foundation in October of 2021, summarizes the current state of the field of focused ultrasound for DIPG/DMG, including preclinical, technical, and clinical summaries in addition to recommended next steps for continued advancement of the game changing technology of Focused Ultrasound.

The new insight into the inflammatory response following focused ultrasound-mediated blood-brain barrier disruption

BACKGROUND

Despite the great potential of FUS-BBB disruption (FUS-BBBD), it is still controversial whether FUS-BBBD acts as an inducing factor of neuro-inflammation or not, and the biological responses after FUS-BBBD triggers the inflammatory process are poorly understood. The aim of this study is to investigate the safety window for FUS levels based on a comprehensive safety assessment.

METHODS

The mice were treated with two different ultrasound parameters (0.25 MPa and 0.42 MPa) in the thalamus region of brain. The efficacy of BBB opening was verified by dynamic contrast-enhanced MRI (DCE-MRI) and the cavitation monitoring. The transcriptome analysis was performed to investigate the molecular response for the two BBBD conditions after FUS-mediated BBB opening in time-dependent manners. Histological analysis was used for evaluation of the tissue damage, neuronal degeneration, and activation of glial cells induced by FUS-BBBD.

RESULTS

The BBBD, as quantified by the K_trans, was approximately threefold higher in 0.42 MPa-treated group than 0.25 MPa-treated group. While the minimal tissue/cellular damage was found in 0.25 MPa-treated group, visible damages containing microhemorrhages and degenerating neurons were detected in 0.42 MPa-treated group in accordance with the extent of BBBD. In transcriptome analysis, 0.42 MPa-treated group exhibited highly dynamic changes in the expression levels of an inflammatory response or NF-κB pathway-relative genes in a time-dependent manner whereas, 0.25 MPa was not altered. Interestingly, although it is clear that 0.42 MPa induces neuroinflammation through glial activation, neuroprotective properties were evident by the expression of A2-type astrocytes.

CONCLUSIONS

Our findings propose that a well-defined BBBD parameter of 0.25 MPa could ensure the safety without cellular/tissue damage or sterile inflammatory response in the brain. Furthermore, the fact that the excessive sonication parameters at 0.42 MPa could induce a sterile inflammation response via glial activation suggested the possibility that could lead to tissue repair toward the homeostasis of the brain microenvironment through A2-type reactive astrocytes.

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.

Cavitation Feedback Control of Focused Ultrasound Blood-Brain Barrier Opening for Drug Delivery in Patients with Parkinson's Disease

Magnetic resonance-guided focused ultrasound (MRgFUS), in conjunction with circulating microbubbles, is an emerging technology that can transiently enhance the permeability of the blood-brain barrier (BBB) locally and non-invasively to facilitate targeted drug delivery to the brain. In this clinical trial, the feasibility and safety of BBB modulation in the putamen were evaluated for biweekly therapeutic agent delivery in patients with Parkinson's disease. The performance of the clinical MRgFUS system's cavitation feedback controller for active power modulation throughout the exposures was examined. The putamen was targeted unilaterally by an ExAblate Neuro MRgFUS system operating at 220 kHz. Definity microbubbles were infused via a saline bag gravity drip at a rate of 4 µL/kg per 5 min. A cavitation emissions-based feedback controller was employed to modulate the acoustic power automatically according to prescribed target cavitation dose levels. BBB opening was measured by Gadolinium (Gd)-enhanced T1-weighted MR imaging, and the presence of potential micro-hemorrhages induced by the exposures was assessed via T2*-weighted MR imaging. A total of 12 treatment sessions were carried out across four patients, with target cavitation dose levels ranging from 0.20-0.40. BBB permeability in the targeted putamen was elevated successfully in all treatments, with a 14% ± 6% mean increase in Gd-enhanced T1-weighted MRI signal intensity relative to the untreated contralateral side. No indications of red blood cell extravasations were observed on MR imaging scans acquired one day following each treatment session. The cavitation emissions-based feedback controller was effective in modulating acoustic power levels to ensure BBB permeability enhancement while avoiding micro-hemorrhages, however, further technical advancements are warranted to improve its performance for use across a wide variety of brain diseases.

Focused Delivery of Chemotherapy to Augment Surgical Management of Brain Tumors

Chemotherapy as an adjuvant therapy that has largely failed to significantly improve outcomes for aggressive brain tumors; some reasons include a weak blood brain barrier penetration and tumor heterogeneity. Recently, there has been interest in designing effective ways to deliver chemotherapy to the tumor. In this review, we discuss the mechanisms of focused chemotherapies that are currently under investigation. Nanoparticle delivery demonstrates both a superior permeability and retention. However, thus far, it has not demonstrated a therapeutic efficacy for brain tumors. Convection-enhanced delivery is an invasive, yet versatile method, which appears to have the greatest potential. Other vehicles, such as angiopep-2 decorated gold nanoparticles, polyamidoamine dendrimers, and lipid nanostructures have demonstrated efficacy through sustained release of focused chemotherapy and have either improved cell death or survival in humans or animal models. Finally, focused ultrasound is a safe and effective way to disrupt the blood brain barrier and augment other delivery methods. Clinical trials are currently underway to study the safety and efficacy of these methods in combination with standard of care.

Microbubble–Nanoparticle Complexes for Ultrasound-Enhanced Cargo Delivery

Targeted delivery of therapeutics to specific tissues is critically important for reducing systemic toxicity and optimizing therapeutic efficacy, especially in the case of cytotoxic drugs. Many strategies currently exist for targeting systemically administered drugs, and ultrasound-controlled targeting is a rapidly advancing strategy for externally-stimulated drug delivery. In this non-invasive method, ultrasound waves penetrate through tissue and stimulate gas-filled microbubbles, resulting in bubble rupture and biophysical effects that power delivery of attached cargo to surrounding cells. Drug delivery capabilities from ultrasound-sensitive microbubbles are greatly expanded when nanocarrier particles are attached to the bubble surface, and cargo loading is determined by the physicochemical properties of the nanoparticles. This review serves to highlight and discuss current microbubble–nanoparticle complex component materials and designs for ultrasound-mediated drug delivery. Nanocarriers that have been complexed with microbubbles for drug delivery include lipid-based, polymeric, lipid–polymer hybrid, protein, and inorganic nanoparticles. Several schemes exist for linking nanoparticles to microbubbles for efficient nanoparticle delivery, including biotin–avidin bridging, electrostatic bonding, and covalent linkages. When compared to unstimulated delivery, ultrasound-mediated cargo delivery enables enhanced cell uptake and accumulation of cargo in target organs and can result in improved therapeutic outcomes. These ultrasound-responsive delivery complexes can also be designed to facilitate other methods of targeting, including bioactive targeting ligands and responsivity to light or magnetic fields, and multi-level targeting can enhance therapeutic efficacy. Microbubble–nanoparticle complexes present a versatile platform for controlled drug delivery via ultrasound, allowing for enhanced tissue penetration and minimally invasive therapy. Future perspectives for application of this platform are also discussed in this review.

Ultrasound-mediated blood-brain barrier opening: An effective drug delivery system for theranostics of brain diseases

Blood-brain barrier (BBB) remains a significant obstacle to drug therapy for brain diseases. Focused ultrasound (FUS) combined with microbubbles (MBs) can locally and transiently open the BBB, providing a potential strategy for drug delivery across the BBB into the brain. Nowadays, taking advantage of this technology, many therapeutic agents, such as antibodies, growth factors, and nanomedicine formulations, are intensively investigated across the BBB into specific brain regions for the treatment of various brain diseases. Several preliminary clinical trials also have demonstrated its safety and good tolerance in patients. This review gives an overview of the basic mechanisms, ultrasound contrast agents, evaluation or monitoring methods, and medical applications of FUS-mediated BBB opening in glioblastoma, Alzheimer's disease, and Parkinson's disease.

Harnessing Ultrasound for Targeting Drug Delivery to the Brain and Breaching the Blood–Brain Tumour Barrier

Despite significant advances in developing drugs to treat brain tumours, achieving therapeutic concentrations of the drug at the tumour site remains a major challenge due to the presence of the blood–brain barrier (BBB). Several strategies have evolved to enhance brain delivery of chemotherapeutic agents to treat tumours; however, most approaches have several limitations which hinder their clinical utility. Promising studies indicate that ultrasound can penetrate the skull to target specific brain regions and transiently open the BBB, safely and reversibly, with a high degree of spatial and temporal specificity. In this review, we initially describe the basics of therapeutic ultrasound, then detail ultrasound-based drug delivery strategies to the brain and the mechanisms by which ultrasound can improve brain tumour therapy. We review pre-clinical and clinical findings from ultrasound-mediated BBB opening and drug delivery studies and outline current therapeutic ultrasound devices and technologies designed for this purpose.

Opportunities and challenges in delivering biologics for Alzheimer's disease by low-intensity ultrasound

Low-intensity ultrasound combined with intravenously injected microbubbles (US^+MB) is a novel treatment modality for brain disorders, including Alzheimer's disease (AD), safely and transiently allowing therapeutic agents to overcome the blood-brain barrier (BBB) that constitutes a major barrier for therapeutic agents. Here, we first provide an update on immunotherapies in AD and how US^+MB has been applied to AD mouse models and in clinical trials, considering the ultrasound and microbubble parameter space. In the second half of the review, we compare different in vitro BBB models and discuss strategies for combining US^+MB with BBB modulators (targeting molecules such as claudin-5), and highlight the insight provided by super-resolution microscopy. Finally, we conclude with a short discussion on how in vitro findings can inform the design of animal studies, and how the insight gained may aid treatment optimization in the clinical ultrasound space.

Guiding and monitoring focused ultrasound mediated blood-brain barrier opening in rats using power Doppler imaging and passive acoustic mapping

The blood-brain barrier (BBB) prevents harmful toxins from entering brain but can also inhibit therapeutic molecules designed to treat neurodegenerative diseases. Focused ultrasound (FUS) combined with microbubbles can enhance permeability of BBB and is often performed under MRI guidance. We present an all-ultrasound system capable of targeting desired regions to open BBB with millimeter-scale accuracy in two dimensions based on Doppler images. We registered imaging coordinates to FUS coordinates with target registration error of 0.6 ± 0.3 mm and used the system to target microbubbles flowing in cellulose tube in two in vitro scenarios (agarose-embedded and through a rat skull), while receiving echoes on imaging transducer. We created passive acoustic maps from received echoes and found error between intended location in imaging plane and location of pixel with maximum intensity after passive acoustic maps reconstruction to be within 2 mm in 5/6 cases. We validated ultrasound-guided procedure in three in vivo rat brains by delivering MRI contrast agent to cortical regions of rat brains after BBB opening. Landmark-based registration of vascular maps created with MRI and Doppler ultrasound revealed BBB opening inside the intended focus with targeting accuracy within 1.5 mm. Combined use of power Doppler imaging with passive acoustic mapping demonstrates an ultrasound-based solution to guide focused ultrasound with high precision in rodents.

Delivery of DNA octahedra enhanced by focused ultrasound with microbubbles for glioma therapy

DNA nanostructures, with good biosafety, highly programmable assembly, flexible modification, and precise control, are tailored as drug carriers to deliver therapeutic agents for cancer therapy. However, they face considerable challenges regarding their delivery into the brain, mainly due to the blood-brain barrier (BBB). By controlling the acoustic parameters, focused ultrasound combined with microbubbles (FUS/MB) can temporarily, noninvasively, and reproducibly open the BBB in a localized region. We investigated the delivery outcome of pH-responsive DNA octahedra loading Epirubicin (Epr@DNA-Octa) via FUS/MB and its therapeutic efficiency in a mouse model bearing intracranial glioma xenograft. Using FUS/MB to locally disrupt the BBB or the blood-tumor barrier (BTB) and systemic administration of Epr@DNA-Octa (Epr@DNA-Octa + FUS/MB) (2 mg/kg of loaded Epr), we achieved an Epr concentration of 292.3 ± 10.1 ng/g tissue in glioma, a 4.4-fold increase compared to unsonicated animals (p < 0.001). The in vitro findings indicated that Epr released from DNA strands accumulated in lysosomes and induced enhanced cytotoxicity compared to free Epr. Further two-photon intravital imaging of spatiotemporal patterns of the DNA-Octa leakage revealed that the FUS/MB treatment enhanced DNA-Octa delivery across several physiological barriers at microscopic level, including the first extravasation across the BBB/BTB and then deep penetration into the glioma center and engulfment of DNA-Octa into the tumor cell body. Longitudinal in vivo bioluminescence imaging and histological analysis indicated that the intracranial glioma progression in nude mice treated with Epr@DNA-Octa + FUS/MB was effectively retarded compared to other groups. The beneficial effect on survival was most significant in the Epr@DNA-Octa + FUS/MB group, with a 50% increase in median survival and a 73% increase in the maximum survival compared to control animals. Our work demonstrates the potential viability of FUS/MB as an alternative strategy for glioma delivery of anticancer drugs using DNA nanostructures as the drug delivery platform for brain cancer therapy.

The influence of the blood-brain barrier in the treatment of brain tumours

Brain tumours have a poor prognosis and lack effective treatments. The blood-brain barrier (BBB) represents a major hurdle to drug delivery to brain tumours. In some locations in the tumour, the BBB may be disrupted to form the blood-brain tumour barrier (BBTB). This leaky BBTB enables diagnosis of brain tumours by contrast enhanced magnetic resonance imaging; however, this disruption is heterogeneous throughout the tumour. Thus, relying on the disrupted BBTB for achieving effective drug concentrations in brain tumours has met with little clinical success. Because of this, it would be beneficial to design drugs and drug delivery strategies to overcome the 'normal' BBB to effectively treat the brain tumours. In this review, we discuss the role of BBB/BBTB in brain tumour diagnosis and treatment highlighting the heterogeneity of the BBTB. We also discuss various strategies to improve drug delivery across the BBB/BBTB to treat both primary and metastatic brain tumours. Recognizing that the BBB represents a critical determinant of drug efficacy in central nervous system tumours will allow a more rapid translation from basic science to clinical application. A more complete understanding of the factors, such as BBB-limited drug delivery, that have hindered progress in treating both primary and metastatic brain tumours, is necessary to develop more effective therapies.

Ultrasound-assisted brain delivery of nanomedicines for brain tumor therapy: advance and prospect

Nowadays, brain tumors are challenging problems, and the key of therapy is ensuring therapeutic drugs cross the blood-brain barrier (BBB) effectively. Although the efficiency of drug transport across the BBB can be increased by innovating and modifying nanomedicines, they exert insufficient therapeutic effects on brain tumors due to the complex environment of the brain. It is worth noting that ultrasound combined with the cavitation effect of microbubbles can assist BBB opening and enhance brain delivery of nanomedicines. This ultrasound-assisted brain delivery (UABD) technology with related nanomedicines (UABD nanomedicines) can safely open the BBB, facilitate the entry of drugs into the brain, and enhance the therapeutic effect on brain tumors. UABD nanomedicines, as the main component of UABD technology, have great potential in clinical application and have been an important area of interest in the field of brain tumor therapy. However, research on UABD nanomedicines is still in its early stages despite the fact that they have been associated with many disciplines, including material science, brain science, ultrasound, biology, and medicine. Some aspects of UABD theory and technology remain unclear, especially the mechanisms of BBB opening, relationship between materials of nanomedicines and UABD technology, cavitation and UABD nanomedicines design theories. This review introduces the research status of UABD nanomedicines, investigates their properties and applications of brain tumor therapy, discusses the advantages and drawbacks of UABD nanomedicines for the treatment of brain tumors, and offers their prospects. We hope to encourage researchers from various fields to participate in this area and collaborate on developing UABD nanomedicines into powerful tools for brain tumor therapy.

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.

Drug delivery across the blood-brain barrier for the treatment of pediatric brain tumors - An update

Even though the last decade has seen a surge in the identification of molecular targets and targeted therapies in pediatric brain tumors, the blood brain barrier (BBB) remains a significant challenge in systemic drug delivery. This continues to undermine therapeutic efficacy. Recent efforts have identified several strategies that can facilitate enhanced drug delivery into pediatric brain tumors. These include invasive methods such as intra-arterial, intrathecal, and convection enhanced delivery and non-invasive technologies that allow for transient access across the BBB, including focused ultrasound and nanotechnology. This review discusses current strategies that are being used to enhance delivery of different therapies across the BBB to the tumor site - a major unmet need in pediatric neuro-oncology.

New Drug Delivery Systems Developed for Brain Targeting

The blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (B_CSF) are two of the most complex and sophisticated concierges that defend the central nervous system (CNS) by numerous mechanisms. While they maintain the neuro-ecological homeostasis through the regulated entry of essential biomolecules, their conservative nature challenges the entry of most of the drugs intended for CNS delivery. Targeted delivery challenges for a diverse spectrum of therapeutic agents/drugs (non-small molecules, small molecules, gene-based therapeutics, protein and peptides, antibodies) are diverse and demand specialized delivery and disease-targeting strategies. This review aims to capture the trends that have shaped the current brain targeting research scenario. This review discusses the physiological, neuropharmacological, and etiological factors that participate in the transportation of various drug delivery cargoes across the BBB/B_CSF and influence their therapeutic intracranial concentrations. Recent research works spanning various invasive, minimally invasive, and non-invasive brain- targeting approaches are discussed. While the pre-clinical outcomes from many of these approaches seem promising, further research is warranted to overcome the translational glitches that prevent their clinical use. Non-invasive approaches like intranasal administration, P-glycoprotein (P-gp) inhibition, pro-drugs, and carrier/targeted nanocarrier-aided delivery systems (alone or often in combination) hold positive clinical prospects for brain targeting if explored further in the right direction.

Application of Ultrasound Combined with Microbubbles for Cancer Therapy

At present, cancer is one of the leading causes of death worldwide. Treatment failure remains one of the prime hurdles in cancer treatment due to the metastatic nature of cancer. Techniques have been developed to hinder the growth of tumours or at least to stop the metastasis process. In recent years, ultrasound therapy combined with microbubbles has gained immense success in cancer treatment. Ultrasound-stimulated microbubbles (USMB) combined with other cancer treatments including radiation therapy, chemotherapy or immunotherapy has demonstrated potential improved outcomes in various in vitro and in vivo studies. Studies have shown that low dose radiation administered with USMB can have similar effects as high dose radiation therapy. In addition, the use of USMB in conjunction with radiotherapy or chemotherapy can minimize the toxicity of high dose radiation or chemotherapeutic drugs, respectively. In this review, we discuss the biophysical properties of USMB treatment and its applicability in cancer therapy. In particular, we highlight important preclinical and early clinical findings that demonstrate the antitumour effect combining USMB and other cancer treatment modalities (radiotherapy and chemotherapy). Our review mainly focuses on the tumour vascular effects mediated by USMB and these cancer therapies. We also discuss several current limitations, in addition to ongoing and future efforts for applying USMB in cancer treatment.

Ultrasound-Mediated Blood-Brain Barrier Disruption for Drug Delivery: A Systematic Review of Protocols, Efficacy, and Safety Outcomes from Preclinical and Clinical Studies

Ultrasound-mediated blood-brain barrier (BBB) disruption has garnered focus as a method of delivering normally impenetrable drugs into the brain. Numerous studies have investigated this approach, and a diverse set of ultrasound parameters appear to influence the efficacy and safety of this approach. An understanding of these findings is essential for safe and reproducible BBB disruption, as well as in identifying the limitations and gaps for further advancement of this drug delivery approach. We aimed to collate and summarise protocols and parameters for achieving ultrasound-mediated BBB disruption in animal and clinical studies, as well as the efficacy and safety methods and outcomes associated with each. A systematic search of electronic databases helped in identifying relevant, included studies. Reference lists of included studies were further screened to identify supplemental studies for inclusion. In total, 107 articles were included in this review, and the following parameters were identified as influencing efficacy and safety outcomes: microbubbles, transducer frequency, peak-negative pressure, pulse characteristics, and the dosing of ultrasound applications. Current protocols and parameters achieving ultrasound-mediated BBB disruption, as well as their associated efficacy and safety outcomes, are identified and summarised. Greater standardisation of protocols and parameters in future preclinical and clinical studies is required to inform robust clinical translation.

Translation of focused ultrasound for blood-brain barrier opening in glioma

Survival outcomes for patients with glioblastoma multiforme (GBM) have remained poor for the past 15 years, reflecting a clear challenge in the development of more effective treatment strategies. The efficacy of systemic therapies for GBM is greatly limited by the presence of the blood-brain barrier (BBB), which prevents drug penetration and accumulation in regions of infiltrative tumour, as represented in a consistent portion of GBM lesions. Focused ultrasound (FUS) - a technique that uses low-frequency ultrasound waves to induce targeted temporary disruption of the BBB - promises to improve survival outcomes by enhancing drug delivery and accumulation to infiltrating tumour regions. In this review we discuss the current state of preclinical investigations using FUS to enhance delivery of systemic therapies to intracranial neoplasms. We highlight critical methodological inconsistencies that are hampering clinical translation of FUS and we provide guiding principles for future preclinical studies. Particularly, we focus our attention on the importance of the selection of clinically relevant animal models and to the standardization of methods for FUS delivery, which will be paramount to the successful clinical translation of this promising technology for treatment in GBM patients. We also discuss how preclinical FUS research can benefit the development of GBM immunotherapies.

Ultrasound and nanomaterial: an efficient pair to fight cancer

Ultrasounds are often used in cancer treatment protocols, e.g. to collect tumor tissues in the right location using ultrasound-guided biopsy, to image the region of the tumor using more affordable and easier to use apparatus than MRI and CT, or to ablate tumor tissues using HIFU. The efficacy of these methods can be further improved by combining them with various nano-systems, thus enabling: (i) a better resolution of ultrasound imaging, allowing for example the visualization of angiogenic blood vessels, (ii) the specific tumor targeting of anti-tumor chemotherapeutic drugs or gases attached to or encapsulated in nano-systems and released in a controlled manner in the tumor under ultrasound application, (iii) tumor treatment at tumor site using more moderate heating temperatures than with HIFU. Furthermore, some nano-systems display adjustable sizes, i.e. nanobubbles can grow into micro-bubbles. Such dual size is advantageous since it enables gathering within the same unit the targeting properties of nano bubbles via EPR effect and the enhanced ultrasound contrasting properties of micro bubbles. Interestingly, the way in which nano-systems act against a tumor could in principle also be adjusted by accurately selecting the nano-system among a large choice and by tuning the values of the ultrasound parameters, which can lead, due to their mechanical nature, to specific effects such as cavitation that are usually not observed with purely electromagnetic waves and can potentially help destroying the tumor. This review highlights the clinical potential of these combined treatments that can improve the benefit/risk ratio of current cancer treatments.

Delivering Therapeutics to Glioblastoma: Overcoming Biological Constraints

Glioblastoma multiforme is the most lethal intrinsic brain tumor. Even with the existing treatment regimen of surgery, radiation, and chemotherapy, the median survival time is only 15–23 months. The invasive nature of this tumor makes its complete removal very difficult, leading to a high recurrence rate of over 90%. Drug delivery to glioblastoma is challenging because of the molecular and cellular heterogeneity of the tumor, its infiltrative nature, and the blood–brain barrier. Understanding the critical characteristics that restrict drug delivery to the tumor is necessary to develop platforms for the enhanced delivery of effective treatments. In this review, we address the impact of tumor invasion, the molecular and cellular heterogeneity of the tumor, and the blood–brain barrier on the delivery and distribution of drugs using potential therapeutic delivery options such as convection-enhanced delivery, controlled release systems, nanomaterial systems, peptide-based systems, and focused ultrasound.

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

BACKGROUND

Single-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.

METHODS

Pulsed 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.

RESULTS

Contrast 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.

CONCLUSIONS

The 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.