Recent Advances in the Use of Focused Ultrasound for Magnetic Resonance Image-Guided Therapeutic Nanoparticle Delivery to the Central Nervous System

Safety and efficacy of unilateral focused ultrasound pallidotomy on motor complications in Parkinson's disease (PD): a systematic review and meta-analysis

To systematically review and conduct a meta-analysis to evaluate the safety and efficacy of the unilateral focused ultrasound (FUS) pallidotomy on motor complications in Parkinson's disease (PD) patients. A comprehensive search strategy was implemented through August 15, 2023, and updated on February 13, 2024, across six databases, identifying studies relevant to unilateral focused ultrasound pallidotomy and PD. Eligibility criteria included observational studies, clinical trials, and case series reporting on the impact of the intervention on motor complications in PD patients. The screening and data extraction were done by two independent reviewers. Risk of bias assessment utilized appropriate tools for different study designs. Statistical analysis involved narrative synthesis and meta-analysis. Subgroup analyses and leave-one-out analyses were performed. Five studies were included in our study, involving 112 PD patients undergoing FUS pallidotomy. UPDRS-II analysis revealed a significant improvement from baseline (mean difference (MD): -3.205, 95% CI: -4.501, -1.909, P < 0.001). UPDRS-III overall change was significant (MD: -10.177, 95% CI: [-12.748, -7.606], P < 0.001). UPDRS-IV showed a significant change from baseline (MD: -5.069, 95% CI: [-5.915, -4.224], P < 0.001). UDysRS demonstrated a significant overall improvement (MD: -18.895, 95% CI: [-26.973, -10.818], P < 0.001). The effect of FUS pallidotomy on motor complications in PD patients was effective, with a significant decrease in the UPDRS and UDysRS, reflecting improvement. The incidence of adverse events (headaches, pin-site pain, difficulty walking, and sonication-related head pain) of the FUS pallidotomy was not statistically significant, indicating its safety.

Focused Ultrasound Impels the Delivery and Penetration of Model Therapeutics into Cerebral Cavernous Malformations

BACKGROUND

Cerebral cavernous malformations (CCMs) are vascular neoplasms in the brain that can cause debilitating symptoms. Current treatments pose significant risks to some patients, motivating the development of new nonsurgical options. We recently discovered that focused ultrasound-mediated blood-brain barrier opening (FUS) arrests CCM formation and growth. Here, we build on this discovery and assess the ability of FUS to deliver model therapeutics into CCMs.

METHODS

Quantitative T1 mapping MRI sequences were used with 1 kDa (MultiHance; MH) and 17 kDa (GadoSpin D; GDS) contrast agents to assess the FUS-mediated delivery and penetration of model small molecule drugs and biologics, respectively, into CCMs of Krit1 mutant mice.

RESULTS

FUS elevated the rate of MH delivery to both the lesion core (4.6-fold) and perilesional space (6.7-fold). Total MH delivery more than doubled in the lesion core and tripled in the perilesional space when FUS was applied immediately prior to MH injection. For the model biologic drug (i.e. GDS), FUS was of greater relative benefit, resulting in 21.7-fold and 3.8-fold delivery increases to the intralesional and perilesional spaces, respectively.

CONCLUSIONS

FUS is capable of impelling the delivery and penetration of therapeutics into the complex and disorganized CCM microenvironment. Benefits to small molecule drug delivery are more evident in the perilesional space, while benefits to biologic delivery are more evident in CCM cores. These findings, when combined with ability of FUS alone to control CCMs, highlight the potential of FUS to serve as a powerful non-invasive therapeutic platform for CCM.

Nanomaterial-Based Strategies for Attenuating T-Cell-Mediated Immunodepression in Stroke Patients: Advancing Research Perspectives

This review article discusses the potential of nanomaterials in targeted therapy and immunomodulation for stroke-induced immunosuppression. Although nanomaterials have been extensively studied in various biomedical applications, their specific use in studying and addressing immunosuppression after stroke remains limited. Stroke-induced neuroinflammation is characterized by T-cell-mediated immunodepression, which leads to increased morbidity and mortality. Key observations related to immunodepression after stroke, including lymphopenia, T-cell dysfunction, regulatory T-cell imbalance, and cytokine dysregulation, are discussed. Nanomaterials, such as liposomes, micelles, polymeric nanoparticles, and dendrimers, offer advantages in the precise delivery of drugs to T cells, enabling enhanced targeting and controlled release of immunomodulatory agents. These nanomaterials have the potential to modulate T-cell function, promote neuroregeneration, and restore immune responses, providing new avenues for stroke treatment. However, challenges related to biocompatibility, stability, scalability, and clinical translation need to be addressed. Future research efforts should focus on comprehensive studies to validate the efficacy and safety of nanomaterial-based interventions targeting T cells in stroke-induced immunosuppression. Collaborative interdisciplinary approaches are necessary to advance the field and translate these innovative strategies into clinical practice, ultimately improving stroke outcomes and patient care.

Smart/stimuli-responsive chitosan/gelatin and other polymeric macromolecules natural hydrogels vs. synthetic hydrogels systems for brain tissue engineering: A state-of-the-art review

Currently, there are no viable curative treatments that can enhance the central nervous system's (CNS) recovery from trauma or illness. Bioengineered injectable smart/stimuli-responsive hydrogels (SSRHs) that mirror the intricacy of the CNS milieu and architecture have been suggested as a way to get around these restrictions in combination with medication and cell therapy. Additionally, the right biophysical and pharmacological stimuli are required to boost meaningful CNS regeneration. Recent research has focused heavily on developing SSRHs as cutting-edge delivery systems that can direct the regeneration of brain tissue. In the present article, we have discussed the pathology of brain injuries, and the applicable strategies employed to regenerate the brain tissues. Moreover, the most promising SSRHs for neural tissue engineering (TE) including alginate (Alg.), hyaluronic acid (HA), chitosan (CH), gelatin, and collagen are used in natural polymer-based hydrogels and thoroughly discussed in this review. The ability of these hydrogels to distribute bioactive substances or cells in response to internal and external stimuli is highlighted with particular attention. In addition, this article provides a summary of the most cutting-edge techniques for CNS recovery employing SSRHs for several neurodegenerative diseases.

Focused Ultrasound Blood-Brain Barrier Opening Arrests the Growth and Formation of Cerebral Cavernous Malformations

BACKGROUND

Cerebral cavernous malformations (CCM) are vascular lesions within the central nervous system, consisting of dilated and hemorrhage-prone capillaries. CCMs can cause debilitating neurological symptoms, and surgical excision or stereotactic radiosurgery are the only current treatment options. Meanwhile, transient blood-brain barrier opening (BBBO) with focused ultrasound (FUS) and microbubbles is now understood to exert potentially beneficial bioeffects, such as stimulation of neurogenesis and clearance of amyloid-β. Here, we tested whether FUS BBBO could be deployed therapeutically to control CCM formation and progression in a clinically-representative murine model.

METHODS

CCMs were induced in mice by postnatal, endothelial-specific Krit1 ablation. FUS was applied for BBBO with fixed peak-negative pressures (PNPs; 0.2-0.6 MPa) or passive cavitation detection-modulated PNPs. Magnetic resonance imaging (MRI) was used to target FUS treatments, evaluate safety, and measure longitudinal changes in CCM growth after BBBO.

RESULTS

FUS BBBO elicited gadolinium accumulation primarily at the perilesional boundaries of CCMs, rather than lesion cores. Passive cavitation detection and gadolinium contrast enhancement were comparable in CCM and wild-type mice, indicating that Krit1 ablation does not confer differential sensitivity to FUS BBBO. Acutely, CCMs exposed to FUS BBBO remained structurally stable, with no signs of hemorrhage. Longitudinal MRI revealed that FUS BBBO halted the growth of 94% of CCMs treated in the study. At 1 month, FUS BBBO-treated lesions lost, on average, 9% of their pre-sonication volume. In contrast, non-sonicated control lesions grew to 670% of their initial volume. Lesion control with FUS BBBO was accompanied by a marked reduction in the area and mesenchymal appearance of Krit mutant endothelium. Strikingly, in mice receiving multiple BBBO treatments with fixed PNPs, de novo CCM formation was significantly reduced by 81%. Mock treatment plans on MRIs of patients with surgically inaccessible lesions revealed their lesions are amenable to FUS BBBO with current clinical technology.

CONCLUSIONS

Our results establish FUS BBBO as a novel, non-invasive modality that can safely arrest murine CCM growth and prevent their de novo formation. As an incisionless, MR image-guided therapy with the ability to target eloquent brain locations, FUS BBBO offers an unparalleled potential to revolutionize the therapeutic experience and enhance the accessibility of treatments for CCM patients.

Nonviral nanoparticle gene delivery into the CNS for neurological disorders and brain cancer applications

Nonviral nanoparticles have emerged as an attractive alternative to viral vectors for gene therapy applications, utilizing a range of lipid-based, polymeric, and inorganic materials. These materials can either encapsulate or be functionalized to bind nucleic acids and protect them from degradation. To effectively elicit changes to gene expression, the nanoparticle carrier needs to undergo a series of steps intracellularly, from interacting with the cellular membrane to facilitate cellular uptake to endosomal escape and nucleic acid release. Adjusting physiochemical properties of the nanoparticles, such as size, charge, and targeting ligands, can improve cellular uptake and ultimately gene delivery. Applications in the central nervous system (CNS; i.e., neurological diseases, brain cancers) face further extracellular barriers for a gene-carrying nanoparticle to surpass, with the most significant being the blood-brain barrier (BBB). Approaches to overcome these extracellular challenges to deliver nanoparticles into the CNS include systemic, intracerebroventricular, intrathecal, and intranasal administration. This review describes and compares different biomaterials for nonviral nanoparticle-mediated gene therapy to the CNS and explores challenges and recent preclinical and clinical developments in overcoming barriers to nanoparticle-mediated delivery to the brain. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Functionalized Carbon Nanoparticles as Theranostic Agents and Their Future Clinical Utility in Oncology

Over the years, research of nanoparticle applications in pre-clinical and clinical applications has greatly advanced our therapeutic and imaging approaches to many diseases, most notably neoplastic disorders. In particular, the innate properties of inorganic nanomaterials, such as gold and iron oxide, as well as carbon-based nanoparticles, have provided the greatest opportunities in cancer theranostics. Carbon nanoparticles can be used as carriers of biological agents to enhance the therapeutic index at a tumor site. Alternatively, they can also be combined with external stimuli, such as light, to induce irreversible physical damaging effects on cells. In this review, the recent advances in carbon nanoparticles and their use in cancer theranostics will be discussed. In addition, the set of evaluations that will be required during their transition from laboratory investigations toward clinical trials will be addressed.

Ultrasound Responsive Smart Implantable Hydrogels for Targeted Delivery of Drugs: Reviewing Current Practices

Over the last two decades, the process of delivering therapeutic drugs to a patient with a controlled release profile has been a significant focus of drug delivery research. Scientists have given tremendous attention to ultrasound-responsive hydrogels for several decades. These smart nanosystems are more applicable than other stimuli-responsive drug delivery vehicles (ie UV-, pH- and thermal-, responsive materials) because they enable more efficient targeted treatment via relatively non-invasive means. Ultrasound (US) is capable of safely transporting energy through opaque and complex media with minimal loss of energy. It is capable of being localized to smaller regions and coupled to systems operating at various time scales. However, the properties enabling the US to propagate effectively in materials also make it very difficult to transform acoustic energy into other forms that may be used. Recent research from a variety of domains has attempted to deal with this issue, proving that ultrasonic effects can be used to control chemical and physical systems with remarkable specificity. By obviating the need for multiple intravenous injections, implantable US responsive hydrogel systems can enhance the quality of life for patients who undergo treatment with a varied dosage regimen. Ideally, the ease of self-dosing in these systems would lead to increased patient compliance with a particular therapy as well. However, excessive literature has been reported based on implanted US responsive hydrogel in various fields, but there is no comprehensive review article showing the strategies to control drug delivery profile. So, this review was aimed at discussing the current strategies for controlling and targeting drug delivery profiles using implantable hydrogel systems.

Polymeric Nanoparticles in Brain Cancer Therapy: A Review of Current Approaches

Translation of novel therapies for brain cancer into clinical practice is of the utmost importance as primary brain tumors are responsible for more than 200,000 deaths worldwide each year. While many research efforts have been aimed at improving survival rates over the years, prognosis for patients with glioblastoma and other primary brain tumors remains poor. Safely delivering chemotherapeutic drugs and other anti-cancer compounds across the blood-brain barrier and directly to tumor cells is perhaps the greatest challenge in treating brain cancer. Polymeric nanoparticles (NPs) are powerful, highly tunable carrier systems that may be able to overcome those obstacles. Several studies have shown appropriately-constructed polymeric NPs cross the blood-brain barrier, increase drug bioavailability, reduce systemic toxicity, and selectively target central nervous system cancer cells. While no studies relating to their use in treating brain cancer are in clinical trials, there is mounting preclinical evidence that polymeric NPs could be beneficial for brain tumor therapy. This review includes a variety of polymeric NPs and how their associated composition, surface modifications, and method of delivery impact their capacity to improve brain tumor 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.

Low-Intensity Focused Ultrasound Technique in Glioblastoma Multiforme Treatment

Glioblastoma is one of the central nervous system most aggressive and lethal cancers with poor overall survival rate. Systemic treatment of glioblastoma remains the most challenging aspect due to the low permeability of the blood-brain barrier (BBB) and blood-tumor barrier (BTB), limiting therapeutics extravasation mainly in the core tumor as well as in its surrounding invading areas. It is now possible to overcome these barriers by using low-intensity focused ultrasound (LIFU) together with intravenously administered oscillating microbubbles (MBs). LIFU is a non-invasive technique using converging ultrasound waves which can alter the permeability of BBB/BTB to drug delivery in a specific brain/tumor region. This emerging technique has proven to be both safe and repeatable without causing injury to the brain parenchyma including neurons and other structures. Furthermore, LIFU is also approved by the FDA to treat essential tremors and Parkinson's disease. It is currently under clinical trial in patients suffering from glioblastoma as a drug delivery strategy and liquid biopsy for glioblastoma biomarkers. The use of LIFU+MBs is a step-up in the world of drug delivery, where onco-therapeutics of different molecular sizes and weights can be delivered directly into the brain/tumor parenchyma. Initially, several potent drugs targeting glioblastoma were limited to cross the BBB/BTB; however, using LIFU+MBs, diverse therapeutics showed significantly higher uptake, improved tumor control, and overall survival among different species. Here, we highlight the therapeutic approach of LIFU+MBs mediated drug-delivery in the treatment of glioblastoma.

Crossing the Blood-Brain Barrier: Advances in Nanoparticle Technology for Drug Delivery in Neuro-Oncology

The blood-brain barrier (BBB) constitutes a microvascular network responsible for excluding most drugs from the brain. Treatment of brain tumors is limited by the impermeability of the BBB and, consequently, survival outcomes for malignant brain tumors remain poor. Nanoparticles (NPs) represent a potential solution to improve drug transport to brain tumors, given their small size and capacity to target tumor cells. Here, we review the unique physical and chemical properties of NPs that aid in BBB transport and discuss mechanisms of NP transport across the BBB, including paracellular transport, carrier-mediated transport, and adsorptive- and receptor-mediated transcytosis. The major types of NPs investigated for treatment of brain tumors are detailed, including polymeric NPs, liposomes, solid lipid NPs, dendrimers, metals, quantum dots, and nanogels. In addition to their role in drug delivery, NPs can be used as imaging contrast agents and can be conjugated with imaging probes to assist in visualizing tumors, demarcating lesion boundaries and margins, and monitoring drug delivery and treatment response. Multifunctional NPs can be designed that are capable of targeting tumors for both imaging and therapeutic purposes. Finally, limitations of NPs for brain tumor treatment are discussed.

Bioactive injectable hydrogels for on demand molecule/cell delivery and for tissue regeneration in the central nervous system

Currently there are no potential curative therapies that can improve the central nervous system (CNS) regeneration after traumatic injuries or diseases. Indeed, the regeneration of CNS is greatly impaired by limited drug penetration across the blood brain barrier (BBB), poor drug targeting, deficient progenitor neural cells and limited proliferation of mature neural cells. To overcome these limitations, bioengineered injectable hydrogels in combination with drug and cell therapy have been proposed to mimic the complexity of the CNS microenvironment and architecture. Additionally, to enhance relevant CNS regeneration, proper biophysical and biochemical cues are needed. Recently, great efforts have been devoted to tailor stimuli-responsive hydrogels as novel carrier systems which are able to guide neural tissue regeneration. This review provides an extensive overview on the most promising injectable hydrogels for neural tissue engineering. A special emphasis is made to highlight the ability of these hydrogels to deliver bioactive compounds/cells upon the exposure to internal and external stimuli. Bioactive injectable hydrogels have a broad application in central nervous system's (CNS) regeneration. This review gives an overview of the latest pioneering approaches in CNS recovery using stimuli-responsive hydrogels for several neurodegenerative disorders. STATEMENT OF SIGNIFICANCE: This review summarizes the latest innovations on bioactive injectable hydrogels, focusing on tailoring internal/external stimuli-responsive hydrogels for the new injectable systems design, able to guide neural tissue response. The purpose is to highlight the advantages and the limitations of thermo-responsive, photo responsive, magnetic responsive, electric responsive, ultrasound responsive and enzymes-triggered injectable hydrogels in developing customizable neurotherapies. We believe that this comprehensive review will help in identifying the strengths and gaps in the existing literature and to further support the use of injectable hydrogels in stimulating CNS regeneration.

Nanotherapeutics and the Brain

Brain disease remains a significant health, social, and economic burden with a high failure rate of translation of therapeutics to the clinic. Nanotherapeutics have represented a promising area of technology investment to improve drug bioavailability and delivery to the brain, with several successes for nanotherapeutic use for central nervous system disease that are currently in the clinic. However, renewed and continued research on the treatment of neurological disorders is critically needed. We explore the challenges of drug delivery to the brain and the ways in which nanotherapeutics can overcome these challenges. We provide a summary and overview of general design principles that can be applied to nanotherapeutics for uptake and penetration in the brain. We next highlight remaining questions that limit the translational potential of nanotherapeutics for application in the clinic. Lastly, we provide recommendations for ongoing preclinical research to improve the overall success of nanotherapeutics against neurological disease. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 13 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Preparation, characterization, and antibacterial activity of tigecycline-loaded, ultrasound-activated microbubbles

Central nervous system infectious disease caused by the multidrug-resistant Acinetobacter baumannii (AB) seriously threatens human life in clinic. Tigecycline has good sensitivity in killing AB, but due to its wide tissue distribution and blood-brain barrier, concentration in cerebrospinal fluid is low, therefore, the clinical effect is limited. Herein, we designed micro-bubbled tigecycline, aimed to enhance its anti-MDRAB effects under ultrasound. The lipid microbubbles with different ratios of lipids to drugs (a ratio of 10:1, 20:1, and 40:1) were prepared by the mechanical shaking method. The morphology, zeta potential and particle size of microbubbles were tested to screen out the much better formulation. Encapsulation efficiency and drug loading amount were determined by ultracentrifugation combined with high-performance liquid chromatography. Then the in vitro antibacterial activity against AB was conducted using the selected ultrasound-activated microbubble. Results showed the selected microbubbles with high encapsulation efficiency and good stability. The mechanical shaking method is feasible for preparation of drug-loaded and ultrasound-activated lipid microbubbles. Using 0.2 mg/mL microbubbles, combined with 1 MHz, 2.5 W/cm² and 1 min of ultrasound exhibited a potent anit-AB in vitro. This study indicates that tigecycline treatment in form of ultrasound-activated microbubble is a promising strategy against AB infections.

Blood-Brain Barrier in Brain Tumors: Biology and Clinical Relevance

The presence of barriers, such as the blood–brain barrier (BBB) and brain–tumor barrier (BTB), limits the penetration of antineoplastic drugs into the brain, resulting in poor response to treatments. Many techniques have been developed to overcome the presence of these barriers, including direct injections of substances by intranasal or intrathecal routes, chemical modification of drugs or constituents of BBB, inhibition of efflux pumps, physical disruption of BBB by radiofrequency electromagnetic radiation (EMP), laser-induced thermal therapy (LITT), focused ultrasounds (FUS) combined with microbubbles and convection enhanced delivery (CED). However, most of these strategies have been tested only in preclinical models or in phase 1–2 trials, and none of them have been approved for treatment of brain tumors yet. Concerning the treatment of brain metastases, many molecules have been developed in the last years with a better penetration across BBB (new generation tyrosine kinase inhibitors like osimertinib for non-small-cell lung carcinoma and neratinib/tucatinib for breast cancer), resulting in better progression-free survival and overall survival compared to older molecules. Promising studies concerning neural stem cells, CAR-T (chimeric antigen receptors) strategies and immunotherapy with checkpoint inhibitors are ongoing.

Ultrasound-targeted nucleic acid delivery for solid tumor therapy

Depending upon multiple factors, malignant solid tumors are conventionally treated by some combination of surgical resection, radiation, chemotherapy, and immunotherapy. Despite decades of research, therapeutic responses remain poor for many cancer indications. Further, many current therapies in our armamentarium are either invasive or accompanied by toxic side effects. In lieu of traditional pharmaceutics and invasive therapeutic interventions, gene therapies offer more flexible and potentially more durable approaches for new anti-cancer therapies. Nonetheless, many current gene delivery approaches suffer from low transfection efficiency due to physiological barriers limiting extravasation and uptake of genetic material. Additionally, systemically administered gene therapies may lack target-specificity, which can lead to off-target effects. To overcome these challenges, many preclinical studies have shown the utility of focused ultrasound (FUS) to increase macromolecule uptake in cells and tissue under image guidance, demonstrating promise for improved delivery of therapeutics to solid tumors. As FUS-based drug delivery is now being tested in several clinical trials around the world, FUS-targeted gene therapy for solid tumor therapy may not be far behind. In this review, we comprehensively cover the literature pertaining to preclinical attempts to more efficiently deliver therapeutic genetic material with FUS and offer perspectives for future studies and clinical translation.

Functional intersections between extracellular vesicles and oncolytic therapies

Minimally invasive focal therapies for nonviral oncolysis are a cornerstone of cancer therapeutics. Our ability to optimally deploy oncolytic therapies and identify synergistic combination approaches requires a deeper understanding of elicited biological responses. Extracellular vesicles (EV), which orchestrate a variety of pathophysiological processes and have a critical role in the evolution of primary and disseminated tumors, are now known to be potently modulated by oncolytic focal therapies, such as radiotherapy, photodynamic therapy (PDT), and therapeutic ultrasound (TUS). In this review, we summarize the diverse impacts of the aforementioned therapeutic modalities on EV biology, and highlight the most recent advances in EV-based drug delivery systems leveraging these modalities.

Polymeric magnetic nanoparticles: a multitargeting approach for brain tumour therapy and imaging

The most challenging task in targeting the brain is trespassing the blood-brain barrier (BBB) which restricts the movement of about 98% small molecules. Targeting the central nervous system using magnetic nanoparticles may deliver the drug to the target site along with a contrast imaging property. The use of magnetic nanoparticles can become non-invasive drug targeting and a bio-imaging method for brain cancer. The strategy to apply polymeric nanoparticles as a carrier of magnetic iron oxide nanoparticles can be a promising tool as a multitherapeutic drug delivery approach involving delivery of chemotherapeutic drugs with a magnetic targeting approach, imaging, and hyperthermia. This review will highlight the existing difficulties/barriers in crossing the BBB, types of magnetic materials, polymeric carriers for functionalization of magnetic nanoparticles, and targeting strategies as therapeutic and imaging modalities. Utilization of polymeric magnetic nanoparticles as an efficient targeting platform for better drug delivery and imaging for brain cancer and future prospects are also discussed. Polymeric magnetic nanoparticles as a drug delivery and bio-imaging vehicle for brain cancer.

Glioblastoma multiforme (GBM): An overview of current therapies and mechanisms of resistance

Glioblastoma multiforme (GBM) is a WHO grade IV glioma and the most common malignant, primary brain tumor with a 5-year survival of 7.2%. Its highly infiltrative nature, genetic heterogeneity, and protection by the blood brain barrier (BBB) have posed great treatment challenges. The standard treatment for GBMs is surgical resection followed by chemoradiotherapy. The robust DNA repair and self-renewing capabilities of glioblastoma cells and glioma initiating cells (GICs), respectively, promote resistance against all current treatment modalities. Thus, durable GBM management will require the invention of innovative treatment strategies. In this review, we will describe biological and molecular targets for GBM therapy, the current status of pharmacologic therapy, prominent mechanisms of resistance, and new treatment approaches. To date, medical imaging is primarily used to determine the location, size and macroscopic morphology of GBM before, during, and after therapy. In the future, molecular and cellular imaging approaches will more dynamically monitor the expression of molecular targets and/or immune responses in the tumor, thereby enabling more immediate adaptation of tumor-tailored, targeted therapies.

Citrate-Coated Magnetic Polyethyleneimine Composites for Plasmid DNA Delivery into Glioblastoma

Several ternary composites that are based on branched polyethyleneimine (bPEI 25 kDa, polydispersity 2.5, 0.1 or 0.2 ng), citrate-coated ultrasmall superparamagnetic iron oxide nanoparticles (citrate-NPs, 8-10 nm, 0.1, 1.0, or 2.5 µg), and reporter circular plasmid DNA pEGFP-C1 or pRL-CMV (pDNA 0.5 µg) were studied for optimization of the best composite for transfection into glioblastoma U87MG or U138MG cells. The efficiency in terms of citrate-NP and plasmid DNA gene delivery with the ternary composites could be altered by tuning the bPEI/citrate-NP ratios in the polymer composites, which were characterized by Prussian blue staining, in vitro magnetic resonance imaging as well as green fluorescence protein and luciferase expression. Among the composites prepared, 0.2 ng bPEI/0.5 μg pDNA/1.0 µg citrate-NP ternary composite possessed the best cellular uptake efficiency. Composite comprising 0.1 ng bPEI/0.5 μg pDNA/0.1 μg citrate-NP gave the optimal efficiency for the cellular uptake of the two plasmid DNAs to the nucleus. The best working bPEI concentration range should not exceed 0.2 ng/well to achieve a relatively low cytotoxicity.

A Comparison of Focused and Unfocused Ultrasound for Microbubble-Mediated Gene Delivery

We compared focused and unfocused ultrasound-targeted microbubble destruction (UTMD) for delivery of reporter plasmids to the liver and heart in mice. Optimal hepatic expression was seen with double-depth targeting at 5 and 13 mm in vivo, incorporating a low pulse repetition frequency and short pulse duration. Reporter expression was similar, but the transfection patterns were distinct, with intense foci of transfection using focused UTMD (F-UTMD). We then compared both approaches for cardiac delivery and found 10-fold stronger levels of reporter expression for F-UTMD and observed small areas of intense luciferase expression in the left ventricle. Non-linear contrast imaging of the liver before and after insonation also showed a substantially greater change in signal intensity for F-UTMD, suggesting distinct cavitation mechanisms for both approaches. Overall, similar levels of hepatic transgene expression were observed, but cardiac-directed F-UTMD was substantially more effective. Focused ultrasound presents a new frontier in UTMD-directed gene therapy.

Development of Polymeric Nanoparticles for Blood-Brain Barrier Transfer-Strategies and Challenges

Neurological disorders such as Alzheimer's disease, stroke, and brain cancers are difficult to treat with current drugs as their delivery efficacy to the brain is severely hampered by the presence of the blood-brain barrier (BBB). Drug delivery systems have been extensively explored in recent decades aiming to circumvent this barrier. In particular, polymeric nanoparticles have shown enormous potentials owing to their unique properties, such as high tunability, ease of synthesis, and control over drug release profile. However, careful analysis of their performance in effective drug transport across the BBB should be performed using clinically relevant testing models. In this review, polymeric nanoparticle systems for drug delivery to the central nervous system are discussed with an emphasis on the effects of particle size, shape, and surface modifications on BBB penetration. Moreover, the authors critically analyze the current in vitro and in vivo models used to evaluate BBB penetration efficacy, including the latest developments in the BBB-on-a-chip models. Finally, the challenges and future perspectives for the development of polymeric nanoparticles to combat neurological disorders are discussed.

Development of a multi-functional preclinical device for the treatment of glioblastoma

Glioblastoma multiforme (GBM) is one of the most common and aggressive malignant primary brain tumors in adults. The treatment of GBM is limited by the blood-brain barrier (BBB), which limits the diffusion of appropriate concentrations of therapeutic agents at the tumor site. Among experimental therapies, photo-thermal therapy (PTT) mediated by nanoparticles is a promising strategy. To propose a preclinical versatile research instrument for the development of new PTT for GBM, a multipurpose integrated preclinical device was developed. The setup is able to perform: i) BBB permeabilization by focused ultrasound sonication (FUS); ii) PTT with continuous wave laser; iii) in situ temperature monitoring with photo-acoustic (PA) measurements. In vivo preliminary subcutaneous and transcranial experiments were conducted on healthy or tumor-bearing mice. Transcranial FUS-induced BBB permeabilization was validated using single photon emission computed tomography (SPECT) imaging. PTT capacities were monitored by PA thermometry, and are illustrated through subcutaneous and transcranial in vivo experiments. The results show the therapeutic possibilities and ergonomy of such integrated device as a tool for the validation of future treatments.

Single-cell analysis reveals effective siRNA delivery in brain tumors with microbubble-enhanced ultrasound and cationic nanoparticles

RNA-based therapies offer unique advantages for treating brain tumors. However, tumor penetrance and uptake are hampered by RNA therapeutic size, charge, and need to be "packaged" in large carriers to improve bioavailability. Here, we have examined delivery of siRNA, packaged in 50-nm cationic lipid-polymer hybrid nanoparticles (LPHs:siRNA), combined with microbubble-enhanced focused ultrasound (MB-FUS) in pediatric and adult preclinical brain tumor models. Using single-cell image analysis, we show that MB-FUS in combination with LPHs:siRNA leads to more than 10-fold improvement in siRNA delivery into brain tumor microenvironments of the two models. MB-FUS delivery of Smoothened (SMO) targeting siRNAs reduces SMO protein production and markedly increases tumor cell death in the SMO-activated medulloblastoma model. Moreover, our analysis reveals that MB-FUS and nanoparticle properties can be optimized to maximize delivery in the brain tumor microenvironment, thereby serving as a platform for developing next-generation tunable delivery systems for RNA-based therapy in brain tumors.

Acupoint-brain (acubrain) mapping: Common and distinct cortical language regions activated by focused ultrasound stimulation on two language-relevant acupoints

Acupuncture, taking the advantage of modality-specific neural pathways, has shown promising results in the treatment of brain disorders that affect different modalities such as pain and vision. However, the precise underlying mechanisms of within-modality neuromodulation of acupoints on human high-order cognition remain largely unknown. In the present study, we used a non-invasive and easy-operating method, focused ultrasound, to stimulate two language-relevant acupoints, namely GB39 (Xuanzhong) and SJ8 (Sanyangluo), of thirty healthy adults. The effect of focused ultrasound stimulation (FUS) on brain activation was examined by functional magnetic resonance imaging (fMRI). We found that stimulating GB39 and SJ8 by FUS evoked overlapping but distinct brain activation patterns. Our findings provide a major step toward within-modality (in this case, language) acupoint-brain (acubrain) mapping and shed light on to the potential use of FUS as a personalized treatment option for brain disorders that affect high-level cognitive functions.

Central nervous system delivery of molecules across the blood-brain barrier

Therapies targeting neurological conditions such as Alzheimer's or Parkinson's diseases are hampered by the presence of the blood-brain barrier (BBB). During the last decades, several approaches have been developed to overcome the BBB, such as the use of nanoparticles (NPs) based on biomaterials, or alternative methods to open the BBB. In this review, we briefly highlight these strategies and the most recent advances in this field. Limitations and advantages of each approach are discussed. Combination of several methods such as functionalized NPs targeting the receptor-mediated transcytosis system with the use of magnetic resonance imaging-guided focused ultrasound (FUS) might be a promising strategy to develop theranostic tools as well as to safely deliver therapeutic molecules, such as drugs, neurotrophic factors or antibodies within the brain parenchyma.

MR-labelled liposomes and focused ultrasound for spatiotemporally controlled drug release in triple negative breast cancers in mice

Rationale: Image-guided, triggerable, drug delivery systems allow for precisely placed and highly localised anti-cancer treatment. They contain labels for spatial mapping and tissue uptake tracking, providing key location and timing information for the application of an external stimulus to trigger drug release. High Intensity Focused Ultrasound (HIFU or FUS) is a non-invasive approach for treating small tissue volumes and is particularly effective at inducing drug release from thermosensitive nanocarriers. Here, we present a novel MR-imageable thermosensitive liposome (iTSL) for drug delivery to triple-negative breast cancers (TNBC). Methods: A macrocyclic gadolinium-based Magnetic Resonance Imaging (MRI) contrast agent was covalently linked to a lipid. This was incorporated at 30 mol% into the lipid bilayer of a thermosensitive liposome that was also encapsulating doxorubicin. The resulting iTSL-DOX formulation was assessed for physical and chemical properties, storage stability, leakage of gadolinium or doxorubicin, and thermal- or FUS-induced drug release. Its effect on MRI relaxation time was tested in phantoms. Mice with tumours were used for studies to assess both tumour distribution and contrast enhancement over time. A lipid-conjugated near-infrared fluorescence (NIRF) probe was also included in the liposome to facilitate the real time monitoring of iTSL distribution and drug release in tumours by NIRF bioimaging. TNBC (MDA-MB-231) tumour-bearing mice were then used to demonstrate the efficacy at retarding tumour growth and increasing survival. Results: iTSL-DOX provided rapid FUS-induced drug release that was dependent on the acoustic power applied. It was otherwise found to be stable, with minimum leakage of drug and gadolinium into buffers or under challenging conditions. In contrast to the usually suggested longer FUS treatment we identified that brief (~3 min) FUS significantly enhanced iTSL-DOX uptake to a targeted tumour and triggered near-total release of encapsulated doxorubicin, causing significant growth inhibition in the TNBC mouse model. A distinct reduction in the tumours' average T1 relaxation times was attributed to the iTSL accumulation. Conclusions: We demonstrate that tracking iTSL in tumours using MRI assists the application of FUS for precise drug release and therapy.

Advancements in the Blood-Brain Barrier Penetrating Nanoplatforms for Brain Related Disease Diagnostics and Therapeutic Applications

Noninvasive treatments to treat the brain-related disorders have been paying more significant attention and it is an emerging topic. However, overcoming the blood brain barrier (BBB) is a key obstacle to most of the therapeutic drugs to enter into the brain tissue, which significantly results in lower accumulation of therapeutic drugs in the brain. Thus, administering the large quantity/doses of drugs raises more concerns of adverse side effects. Nanoparticle (NP)-mediated drug delivery systems are seen as potential means of enhancing drug transport across the BBB and to targeted brain tissue. These systems offer more accumulation of therapeutic drugs at the tumor site and prolong circulation time in the blood. In this review, we summarize the current knowledge and advancements on various nanoplatforms (NF) and discusses the use of nanoparticles for successful cross of BBB to treat the brain-related disorders such as brain tumors, Alzheimer's disease, Parkinson's disease, and stroke.

Current Status and Challenges Associated with CNS-Targeted Gene Delivery across the BBB

The era of the aging society has arrived, and this is accompanied by an increase in the absolute numbers of patients with neurological disorders, such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). Such neurological disorders are serious costly diseases that have a significant impact on society, both globally and socially. Gene therapy has great promise for the treatment of neurological disorders, but only a few gene therapy drugs are currently available. Delivery to the brain is the biggest hurdle in developing new drugs for the central nervous system (CNS) diseases and this is especially true in the case of gene delivery. Nanotechnologies such as viral and non-viral vectors allow efficient brain-targeted gene delivery systems to be created. The purpose of this review is to provide a comprehensive review of the current status of the development of successful drug delivery to the CNS for the treatment of CNS-related disorders especially by gene therapy. We mainly address three aspects of this situation: (1) blood-brain barrier (BBB) functions; (2) adeno-associated viral (AAV) vectors, currently the most advanced gene delivery vector; (3) non-viral brain targeting by non-invasive methods.

Activation Strategies in Image-Guided Nanotherapeutic Delivery

Therapeutic nanomaterials serve as an important platform for drug delivery under image guidance. Despite significant growth and broad applications, their design specifics remain a subject of continued interest primarily due to multifunctional factors involved, ranging from nanomaterial properties, imaging modalities, and therapeutic agents to activation strategies. This review article summarizes key findings on their design characteristics with a particular interest in strategies developed for therapeutic activation (release). First, their activation can be controlled using either an endogenous factor including low pH and glutathione or an external stimulation by light, ultrasound, or electromagnetic field. The former is passively controlled from a spatiotemporal aspect compared to the latter, which is otherwise actively controlled through drug linker photolysis, nanomaterial disassembly, or gate opening. Second, light stimulation serves a most notable strategy due to its essential role in controlled drug release, photothermal activation (hyperthermia), and photodynamic production of reactive oxygen species (ROS). Third, some of those activation strategies that rely on ultrasound, photothermal, photoacoustic, magnetic field, or X-ray radiation are dually functional due to their role in imaging modalities. In summary, this review article presents recent advances and new insights that pertain to nanotherapeutic delivery systems. It also addresses their technical limitations associated with tissue penetration (light), spatial resolution (ultrasound, hyperthermia), and occurrence of cellular resistance (ROS).

Recent Advances on Ultrasound Contrast Agents for Blood-Brain Barrier Opening with Focused Ultrasound

The blood-brain barrier is the primary obstacle to efficient intracerebral drug delivery. Focused ultrasound, in conjunction with microbubbles, is a targeted and non-invasive way to disrupt the blood-brain barrier. Many commercially available ultrasound contrast agents and agents specifically designed for therapeutic purposes have been investigated in ultrasound-mediated blood-brain barrier opening studies. The new generation of sono-sensitive agents, such as liquid-core droplets, can also potentially disrupt the blood-brain barrier after their ultrasound-induced vaporization. In this review, we describe the different compositions of agents used for ultrasound-mediated blood-brain barrier opening in recent studies, and we discuss the challenges of the past five years related to the optimal formulation of agents.

Nanoparticles for drug delivery in Parkinson's disease

Although effective symptomatic treatments for Parkinson's disease (PD) have been available for some time, efficient and well-controlled drug delivery to the brain has proven to be challenging. The emergence of nanotechnology has created new opportunities not only for improving the pharmacokinetics of conventional therapies but also for developing novel treatment approaches and disease modifying therapies. Several exciting strategies including drug carrier nanoparticles targeting specific intracellular pathways and structural reconformation of tangled proteins as well as introducing reprogramming genes have already shown promise and are likely to deliver more tailored approaches to the treatment of PD in the future. This paper reviews the role of nanoparticles in PD including a discussion of both their composition and functional capacity as well as their potential to deliver better therapeutic agents.

A Comprehensive View on MRI Techniques for Imaging Blood-Brain Barrier Integrity

The blood-brain barrier (BBB) is the interface between the blood and brain tissue, which regulates the maintenance of homeostasis within the brain. Impaired BBB integrity is increasingly associated with various neurological diseases. To gain a better understanding of the underlying processes involved in BBB breakdown, magnetic resonance imaging (MRI) techniques are highly suitable for noninvasive BBB assessment. Commonly used MRI techniques to assess BBB integrity are dynamic contrast-enhanced and dynamic susceptibility contrast MRI, both relying on leakage of gadolinium-based contrast agents. A number of conceptually different methods exist that target other aspects of the BBB. These alternative techniques make use of endogenous markers, such as water and glucose, as contrast media. A comprehensive overview of currently available MRI techniques to assess the BBB condition is provided from a scientific point of view, including potential applications in disease. Improvements that are required to make these techniques clinically more easily applicable will also be discussed.

Tetravalent Bispecific Tandem Antibodies Improve Brain Exposure and Efficacy in an Amyloid Transgenic Mouse Model

Most antibodies display very low brain exposure due to the blood-brain barrier (BBB) preventing their entry into brain parenchyma. Transferrin receptor (TfR) has been used previously to ferry antibodies to the brain by using different formats of bispecific constructs. Tetravalent bispecific tandem immunoglobulin Gs (IgGs) (TBTIs) containing two paratopes for both TfR and protofibrillar forms of amyloid-beta (Aβ) peptide were constructed and shown to display higher brain penetration than the parent anti-Aβ antibody. Additional structure-based mutations on the TfR paratopes further increased brain exposure, with maximal enhancement up to 13-fold in wild-type mice and an additional 4–5-fold in transgenic (Tg) mice harboring amyloid plaques, the main target of our amyloid antibody. Parenchymal target engagement of extracellular amyloid plaques was demonstrated using in vivo and ex vivo fluorescence imaging as well as histological methods. The best candidates were selected for a chronic study in an amyloid precursor protein (APP) Tg mouse model showing efficacy at reducing brain amyloid load at a lower dose than the corresponding monospecific antibody. TBTIs represent a promising format for enhancing IgG brain penetration using a symmetrical construct and keeping bivalency of the payload antibody.

Nanocarriers as Potential Drug Delivery Candidates for Overcoming the Blood-Brain Barrier: Challenges and Possibilities

The design of a drug that successfully overcomes the constraints imposed by the blood-brain barrier (BBB, which acts as a gatekeeper to the entry of substances into the brain) requires an understanding of the biological firewall. It is also of utmost importance to understand the physicochemical properties of the said drug and how it engages the BBB to avoid undesired side effects. Since fewer than 5% of the tested molecules can pass through the BBB, drug development pertaining to brain-related disorders takes inordinately long to develop. Furthermore, in most cases it is also unsuccessful for allied reasons. Several drug delivery systems (DDSs) have shown excellent potential in drug delivery across the BBB while demonstrating minimal side effects. This mini-review summarizes key features of the BBB, recapitulates recent advances in our understanding of the BBB, and highlights existing strategies for the delivery of drug to the brain parenchyma.

Nanotherapeutic modulation of excitotoxicity and oxidative stress in acute brain injury

Excitotoxicity is a primary pathological process that occurs during stroke, traumatic brain injury (TBI), and global brain ischemia such as perinatal asphyxia. Excitotoxicity is triggered by an overabundance of excitatory neurotransmitters within the synapse, causing a detrimental cascade of excessive sodium and calcium influx, generation of reactive oxygen species, mitochondrial damage, and ultimately cell death. There are multiple potential points of intervention to combat excitotoxicity and downstream oxidative stress, yet there are currently no therapeutics clinically approved for this specific purpose. For a therapeutic to be effective against excitotoxicity, the therapeutic must accumulate at the disease site at the appropriate concentration at the right time. Nanotechnology can provide benefits for therapeutic delivery, including overcoming physiological obstacles such as the blood–brain barrier, protect cargo from degradation, and provide controlled release of a drug. This review evaluates the use of nano-based therapeutics to combat excitotoxicity in stroke, TBI, and hypoxia–ischemia with an emphasis on mitigating oxidative stress, and consideration of the path forward toward clinical translation.