Membrane perforation and recovery dynamics in microbubble-mediated sonoporation

A vortex-based hydrodynamic cavitation manufacturing platform to generate albumin microbubbles for delivery of chemotherapies to cancerous tumours

A novel approach was developed to create stable protein-based microbubbles using a vortex-driven hydrodynamic cavitation device. Such microbubbles, tiny gas-filled spheres, combined with ultrasound, can enhance drug uptake leading to inhibition of cancerous cell growth, boosting the effectiveness of anti-cancer drug molecules. The optimal conditions for the fabrication of stable bovine serum albumin (BSA) microbubbles were found to be a 15 wt% bovine serum albumin (BSA) solution at 60 °C with a pH of 6 and an ionic strength of 1.0 M. This resulted in stable BSA microbubbles with an approximate diameter of 7 μm. Curcumin-encapsulated BSA microbubbles (CBMs, 63 ± 1 μM curcumin per 101⁰ microbubbles) were created using these optimised fabrication parameters as a model system for delivering chemotherapeutic agents. The maximum percentage of curcumin release from the CBMs into phosphate buffered saline with sonication (85 %) was significantly greater than without sonication (24 %). These microbubbles were then tested to assess their effectiveness in delivering curcumin to triple-negative breast cancer cells (MDAMB-231) using a cell-to-MB ratio of 1:100, an ultrasound intensity of 0.5 W/cm2, and an ultrasound exposure time of 10 s to maximise uptake. Kinetic studies demonstrated a significant enhancement in the uptake of curcumin by MDAMB-231 cells when encapsulated into the microbubbles with ultrasound application. A substantial reduction in cellular proliferation was observed in both 2D cell culture and 3D tumour spheroid models when MDAMB-231 cells were exposed to microbubbles loaded with curcumin and ultrasound was applied. The vortex-based hydrodynamic cavitation device successfully generated curcumin loaded microbubbles with a long shelf life (120 days at 4 °C), mild preparation conditions, and enhanced uptake into cancerous tumour spheroid models. This data demonstrates the potential of this device for the commercial manufacture of drug loaded microbubble-based delivery systems.

Finely controlled bioceramic granules and sonoporation for osteogenic bone defect repair and reconstruction

Osteoporotic fractures caused by imbalance in bone homeostasis like chemotherapy, loss of ovarian function，glucocorticoid use and aging require special surgical procedure to treat and restore anatomical function. However, due to escalating bone weakness and impairment, it remains a clinical challenge to treat these types of fracture defects through conventional means. Herein, we fabricated a novel calcium silicate‑strontium (CS-Sr35) bioceramic granules with high biological properties and combined it with ultrasound aided sonoporation (sono) in augmenting osteoporotic critical-sized bone defect. The use of sonoporation mediated by microbubble was to influence efficient response for tissue permeability and delivery of bioactive ions from the bioceramic scaffold. The graded robust granule with adjustable microstructure exhibited physiochemical and biointegration properties favorable for ion release in vitro and osteogenic related activities in vivo. Herein, we compared the treatment of bone defect repair using (i) no scaffold (ii) CS-Sr35 only and (iii) CS-Sr35 + sono. The gradual bone repair process was elucidated by X-ray, histology and micro-CT analyses. Overall, our results showed that the CS-Sr35 + sono exhibited a tailored biodissolution behavior with complete defect repair and reconstruction. Meanwhile, the group with only CS-Sr35 granules had less osteoblastic healing while the blank group showed inadequate critical-sized defect repair throughout the study. Our study suggests that, the synergistic technique of combining bioceramic granule with sonoporation significantly optimizes osteogenic activity and biomineralization ability of the bioceramic granule for new bone growth in osteoporotic pathology and also this tailored technique provides versatile approach for improving the biological effect for next generation reconstruction and repair of diseased bone defect.

Flow rate modulates focused ultrasound-mediated vascular delivery of microRNA

Gene therapy targeting ischemic heart disease is a promising therapeutic avenue, but it is mostly restricted to viral-based delivery approaches which are limited due to off-target immunological responses. Focused ultrasound presents a non-viral, image-guided technique in which circulating intravascular microbubble contrast agents can reversibly enhance vascular permeability and gene penetration. Here, we explore the influence of flow rate on the microbubble-assisted delivery of miR-126, a potent pro-angiogenic biologic, using a custom acoustically coupled pressurized mesenteric artery model. We demonstrate that under the same ultrasound conditions, increased flow rates enhance microbubble-mediated cell permeability; yet, miR-126 delivery itself exhibits a negative correlation with increasing flow velocity. Post-ultrasound assays confirmed vessel vasoreactivity, maintaining vasoconstriction and vasodilation capacities. These findings underscore the critical role microbubble flow rate plays in focused ultrasound gene therapy, especially notable for applications in which blood velocity itself is a salient pathophysiological indicator of disease progression, including ischemia.

Overview of Therapeutic Ultrasound Applications and Safety Considerations: 2024 Update

A 2012 review of therapeutic ultrasound was published to educate researchers and physicians on potential applications and concerns for unintended bioeffects (doi: 10.7863/jum.2012.31.4.623). This review serves as an update to the parent article, highlighting advances in therapeutic ultrasound over the past 12 years. In addition to general mechanisms for bioeffects produced by therapeutic ultrasound, current applications, and the pre-clinical and clinical stages are outlined. An overview is provided for image guidance methods to monitor and assess treatment progress. Finally, other topics relevant for the translation of therapeutic ultrasound are discussed, including computational modeling, tissue-mimicking phantoms, and quality assurance protocols.

Focused Ultrasound: Noninvasive Image-Guided Therapy

ABSTRACT

Invasive open surgery used to be compulsory to access tumor mass to perform excision or resection. Development of minimally invasive laparoscopic procedures followed, as well as catheter-based approaches, such as stenting, endovascular surgery, chemoembolization, brachytherapy, which minimize side effects and reduce the risks to patients. Completely noninvasive procedures bring further benefits in terms of reducing risk, procedure time, recovery time, potential of infection, or other side effects. Focusing ultrasound waves from the outside of the body specifically at the disease site has proven to be a safe noninvasive approach to localized ablative hyperthermia, mechanical ablation, and targeted drug delivery. Focused ultrasound as a medical intervention was proposed decades ago, but it only became feasible to plan, guide, monitor, and control the treatment procedures with advanced radiological imaging capabilities. The purpose of this review is to describe the imaging capabilities and approaches to perform these tasks, with the emphasis on magnetic resonance imaging and ultrasound. Some procedures already are in clinical practice, with more at the clinical trial stage. Imaging is fully integrated in the workflow and includes the following: (1) planning, with definition of the target regions and adjacent organs at risk; (2) real-time treatment monitoring via thermometry imaging, cavitation feedback, and motion control, to assure targeting and safety to adjacent normal tissues; and (3) evaluation of treatment efficacy, via assessment of ablation and physiological parameters, such as blood supply. This review also focuses on sonosensitive microparticles and nanoparticles, such as microbubbles injected in the bloodstream. They enable ultrasound energy deposition down to the microvascular level, induce vascular inflammation and shutdown, accelerate clot dissolution, and perform targeted drug delivery interventions, including focal gene delivery. Especially exciting is the ability to perform noninvasive drug delivery via opening of the blood-brain barrier at the desired areas within the brain. Overall, focused ultrasound under image guidance is rapidly developing, to become a choice noninvasive interventional radiology tool to treat disease and cure patients.

MTMR regulates KRAS function by controlling plasma membrane levels of phospholipids

KRAS, a small GTPase involved in cell proliferation and differentiation, frequently gains activating mutations in human cancers. For KRAS to function, it must bind the plasma membrane (PM) via interactions between its membrane anchor and phosphatidylserine (PtdSer). Therefore, depleting PM PtdSer abrogates KRAS PM binding and activity. From a genome-wide siRNA screen to identify genes regulating KRAS PM localization, we identified a set of phosphatidylinositol (PI) 3-phosphatases: myotubularin-related proteins (MTMR) 2, 3, 4, and 7. Here, we show that silencing MTMR 2/3/4/7 disrupts KRAS PM interactions by reducing PM PI 4-phosphate (PI4P) levels, thereby disrupting the localization and operation of ORP5, a lipid transfer protein maintaining PM PtdSer enrichment. Concomitantly, silencing MTMR 2/3/4/7 elevates PM PI3P levels while reducing PM and total PtdSer levels. We also observed MTMR 2/3/4/7 expression is interdependent. We propose that the PI 3-phosphatase activity of MTMR is required for generating PM PI, necessary for PM PI4P synthesis, promoting the PM localization of PtdSer and KRAS.

eTOC summary

We discovered that silencing the phosphatidylinositol (PI) 3-phosphatase, MTMR , disrupts the PM localization of PtdSer and KRAS. We propose a model, where MTMR loss depletes PM PI needed for PM PI4P synthesis, an essential phospholipid for PM PtdSer enrichment, thereby impairing KRAS PM localization.

Recent Advances and Future Directions in Sonodynamic Therapy for Cancer Treatment

Deep-tissue solid cancer treatment has a poor prognosis, resulting in a very low 5-year patient survival rate. The primary challenges facing solid tumor therapies are accessibility, incomplete surgical removal of tumor tissue, the resistance of the hypoxic and heterogeneous tumor microenvironment to chemotherapy and radiation, and suffering caused by off-target toxicities. Here, sonodynamic therapy (SDT) is an evolving therapeutic approach that uses low-intensity ultrasound to target deep-tissue solid tumors. The ability of ultrasound to deliver energy safely and precisely into small deep-tissue (>10 cm) volumes makes SDT more effective than conventional photodynamic therapy. While SDT is currently in phase 1/2 clinical trials for glioblastoma multiforme, its use for other solid cancer treatments, such as breast, pancreatic, liver, and prostate cancer, is still in the preclinical stage, with further investigation required to improve its therapeutic efficacy. This review, therefore, focuses on recent advances in SDT cancer treatments. We describe the interaction between ultrasound and sonosensitizer molecules and the associated energy transfer mechanism to malignant cells, which plays a central role in SDT-mediated cell death. Different sensitizers used in clinical and preclinical trials of various cancer treatments are listed, and the critical ultrasound parameters for SDT are reviewed. We also discuss approaches to improve the efficacies of these sonosensitizers, the role of the 3-dimensional spheroid in vitro investigations, ultrasound-controlled CAR-T cell and SDT-based multimodal therapy, and machine learning for sonosensitizer optimization, which could facilitate clinical translation of SDT.

Innovative Approaches to Brain Cancer: The Use of Magnetic Resonance-guided Focused Ultrasound in Glioma Therapy

Gliomas are a wide group of common brain tumors, with the most aggressive type being glioblastoma multiforme (GBM), with a 5-year survival rate of less than 5% and a median survival time of approximately 12-14 months. The standard treatment of GBM includes surgical excision, radiotherapy, and chemotherapy with temozolomide (TMZ). However, tumor recurrence and progression are common. Therefore, more effective treatment for GBM should be found. One of the main obstacles to the treatment of GBM and other gliomas is the blood-brain barrier (BBB), which impedes the penetration of antitumor chemotherapeutic agents into glioblastoma cells. Nowadays, one of the most promising novel methods for glioma treatment is Magnetic Resonance-guided Focused Ultrasound (MRgFUS). Low-intensity FUS causes the BBB to open transiently, which allows better drug delivery to the brain tissue. Under magnetic resonance guidance, ultrasound waves can be precisely directed to the tumor area to prevent side effects in healthy tissues. Through the open BBB, we can deliver targeted chemotherapeutics, anti-tumor agents, immunotherapy, and gene therapy directly to gliomas. Other strategies for MRgFUS include radiosensitization, sonodynamic therapy, histotripsy, and thermal ablation. FUS can also be used to monitor the treatment and progression of gliomas using blood-based liquid biopsy. All these methods are still under preclinical or clinical trials and are described in this review to summarize current knowledge and ongoing trials.

Characterizing Microbubble-Mediated Permeabilization in a Vessel-on-a-Chip Model

Drug transport from blood to extravascular tissue can locally be achieved by increasing the vascular permeability through ultrasound-activated microbubbles. However, the mechanism remains unknown, including whether short and long cycles of ultrasound induce the same onset rate, spatial distribution, and amount of vascular permeability increase. Accurate models are necessary for insights into the mechanism so a microvessel-on-a-chip is developed with a membrane-free extravascular space. Using these microvessels-on-a-chip, distinct differences between 2 MHz ultrasound treatments are shown with 10 or 1000 cycles. The onset rate is slower for 10 than 1000 cycles, while both cycle lengths increase the permeability in spot-wise patterns without affecting microvessel viability. Significantly less vascular permeability increase and sonoporation are induced for 10 versus 1000 cycles at 750 kPa (i.e., the highest studied peak negative acoustic pressure (PNP)). The PNP threshold for vascular permeability increases is 750 versus 550 kPa for 10 versus 1000 cycles, while this is 750 versus 220 kPa for sonoporation. Vascular permeability increases do not correlate with αvβ3-targeted microbubble behavior, while sonoporation correlates with αvβ3-targeted microbubble clustering. In conclusion, the further mechanistic unraveling of vascular permeability increase by ultrasound-activated microbubbles in a developed microvessel-on-a-chip model aids the safe and efficient development of microbubble-mediated drug transport.

Navigating the intricate in-vivo journey of lipid nanoparticles tailored for the targeted delivery of RNA therapeutics: a quality-by-design approach

RNA therapeutics, such as mRNA, siRNA, and CRISPR-Cas9, present exciting avenues for treating diverse diseases. However, their potential is commonly hindered by vulnerability to degradation and poor cellular uptake, requiring effective delivery systems. Lipid nanoparticles (LNPs) have emerged as a leading choice for in vivo RNA delivery, offering protection against degradation, enhanced cellular uptake, and facilitation of endosomal escape. However, LNPs encounter numerous challenges for targeted RNA delivery in vivo, demanding advanced particle engineering, surface functionalization with targeting ligands, and a profound comprehension of the biological milieu in which they function. This review explores the structural and physicochemical characteristics of LNPs, in-vivo fate, and customization for RNA therapeutics. We highlight the quality-by-design (QbD) approach for targeted delivery beyond the liver, focusing on biodistribution, immunogenicity, and toxicity. In addition, we explored the current challenges and strategies associated with LNPs for in-vivo RNA delivery, such as ensuring repeated-dose efficacy, safety, and tissue-specific gene delivery. Furthermore, we provide insights into the current clinical applications in various classes of diseases and finally prospects of LNPs in RNA therapeutics.

Manipulating long-term fates of sonoporated cells by regulating intracellular calcium for improving sonoporation-based delivery

Sonoporation-based delivery has great promise for noninvasive drug and gene therapy. After short-term membrane resealing, the long-term function recovery of sonoporated cells affects the efficiency and biosafety of sonoporation-based delivery. It is necessary to identify the key early biological signals that influence cell fate and to develop strategies for manipulating the long-term fates of sonoporated cells. Here, we used a customized experimental platform with a single cavitating microbubble induced by a single ultrasound pulse (frequency: 1.5 MHz, pulse length:13.33 μs, peak negative pressure: ∼0.40 MPa) to elicit single-site reversible sonoporation on a single HeLa cell model. We used a living-cell microscopic imaging system to trace the long-term fates of sonoporated HeLa cells in real-time for 48 h. Fluorescence from intracellular propidium iodide and Fluo-4 was used to evaluate the degree of sonoporation and intracellular calcium fluctuation (ICF), respectively. Changes in cell morphology were used to assess the long-term cell fates (i.e., proliferation, arrest, or death). We found that heterogeneously sonoporated cells had different long-term fates. With increasing degree of sonoporation, the probability of normal (proliferation) and abnormal fates (arrest and death) in sonoporated cells decreased and increased, respectively. We identified ICF as an important early event for triggering different long-term fates. Reversibly sonoporated cells exhibited stronger proliferation and restoration at lower extents of ICF. We then regulated ICF dynamics in sonoporated cells using 2-APB or BAPTA treatment to reduce calcium release from intracellular organelles and enhance intracellular calcium clearance, respectively. This significantly enhanced the proliferation and restoration of sonoporated cells and reduced the occurrence of cell-cycle arrest and death. Finally, we found that the long-term fates of sonoporated cells at multiple sites and neighboring cells were also dependent on the extent of ICF, and that 2-APB significantly enhanced their viability and reduced death. Thus, using a single HeLa cell model, we demonstrated that regulating intracellular calcium can effectively enhance the proliferation and restoration capabilities of sonoporated cells, therefore rescuing the long-term viability of sonoporated cells. These findings add to our understanding of the biophysical process of sonoporation and help design new strategies for improving the efficiency and biosafety of sonoporation-based delivery.

Recent Advancements in High-Frequency Ultrasound Applications from Imaging to Microbeam Stimulation

Ultrasound is a versatile and well-established technique using sound waves with frequencies higher than the upper limit of human hearing. Typically, therapeutic and diagnosis ultrasound operate in the frequency range of 500 kHz to 15 MHz with greater depth of penetration into the body. However, to achieve improved spatial resolution, high-frequency ultrasound (>15 MHz) was recently introduced and has shown promise in various fields such as high-resolution imaging for the morphological features of the eye and skin as well as small animal imaging for drug and gene therapy. In addition, high-frequency ultrasound microbeam stimulation has been demonstrated to manipulate single cells or microparticles for the elucidation of physical and functional characteristics of cells with minimal effect on normal cell physiology and activity. Furthermore, integrating machine learning with high-frequency ultrasound enhances diagnostics, including cell classification, cell deformability estimation, and the diagnosis of diabetes and dysnatremia using convolutional neural networks (CNNs). In this paper, current efforts in the use of high-frequency ultrasound from imaging to stimulation as well as the integration of deep learning are reviewed, and potential biomedical and cellular applications are discussed.

Cardiac gene delivery using ultrasound: State of the field

Over the past two decades, there has been tremendous and exciting progress toward extending the use of medical ultrasound beyond a traditional imaging tool. Ultrasound contrast agents, typically used for improved visualization of blood flow, have been explored as novel non-viral gene delivery vectors for cardiovascular therapy. Given this adaptation to ultrasound contrast-enhancing agents, this presents as an image-guided and site-specific gene delivery technique with potential for multi-gene and repeatable delivery protocols-overcoming some of the limitations of alternative gene therapy approaches. In this review, we provide an overview of the studies to date that employ this technique toward cardiac gene therapy using cardiovascular disease animal models and summarize their key findings.

Mesenchymal stem cell cryopreservation with cavitation-mediated trehalose treatment

Dimethylsulfoxide (DMSO) has conventionally been used for cell cryopreservation both in research and in clinical applications, but has long-term cytotoxic effects. Trehalose, a natural disaccharide, has been proposed as a non-toxic cryoprotectant. However, the lack of specific cell membrane transporter receptors inhibits transmembrane transport and severely limits its cryoprotective capability. This research presents a method to successfully deliver trehalose into mesenchymal stem cells (MSCs) using ultrasound in the presence of microbubbles. The optimised trehalose concentration was shown to be able to not only preserve membrane integrity and cell viability but also the multipotency of MSCs, which are essential for stem cell therapy. Confocal imaging revealed that rhodamine-labelled trehalose was transported into cells rather than simply attached to the membrane. Additionally, the membranes were successfully preserved in lyophilised cells. This study demonstrates that ultrasonication with microbubbles facilitated trehalose delivery, offering promising cryoprotective capability without the cytotoxicity associated with DMSO-based methods.

Biomodulatory Effects of Molecular Delivery in Human T Cells Using 3D-Printed Acoustofluidic Devices

OBJECTIVE

Cell-based therapies have shown significant promise for treating many diseases, including cancer. Current cell therapy manufacturing processes primarily utilize viral transduction to insert genomic material into cells, which has limitations, including variable transduction efficiency and extended processing times. Non-viral transfection techniques are also limited by high variability or reduced molecular delivery efficiency. Novel 3D-printed acoustofluidic devices are in development to address these challenges by delivering biomolecules into cells within seconds via sonoporation.

METHODS

In this study, we assessed biological parameters that influence the ultrasound-mediated delivery of fluorescent molecules (i.e., calcein and 150 kDa FITC-Dextran) to human T cells using flow cytometry and confocal imaging.

RESULTS

Low cell plating densities (100,000 cells/mL) enhanced molecular delivery compared to higher cell plating densities (p < 0.001), even though cells were resuspended at equal concentrations for acoustofluidic processing. Additionally, cells in the S phase of the cell cycle had enhanced intracellular delivery compared to cells in the G2/M phase (p < 0.001) and G0/G1 phase (p < 0.01), while also maintaining higher viability compared to G0/G1 phase (p < 0.001). Furthermore, the calcium chelator (EGTA) decreased overall molecular delivery levels. Confocal imaging indicated that the actin cytoskeleton had important implications on plasma membrane recovery dynamics after sonoporation. In addition, confocal imaging indicates that acoustofluidic treatment can permeabilize the nuclear membrane, which could enable rapid intranuclear delivery of nucleic acids.

CONCLUSIONS

The results of this study demonstrate that a 3D-printed acoustofluidic device can enhance molecular delivery to human T cells, which may enable improved techniques for non-viral processing of cell therapies.

Shear stress preconditioning and microbubble flow pattern modulate ultrasound-assisted plasma membrane permeabilization

The recent and exciting success of anti-inflammatory therapies for ischemic heart disease (e.g. atherosclerosis) is hindered by the lack of site-specific and targeted therapeutic deposition. Microbubble-mediated focused ultrasound, which uses circulating, lipid-encapsulated intravascular microbubbles to locally enhance endothelial permeability, offers an exciting approach. Atherosclerotic plaques preferentially develop in regions with disturbed blood flow, and microbubble-endothelial cell membrane interactions under such flow conditions are not well understood. Here, using an acoustically-coupled microscopy system, endothelial cells were sonicated (1 MHz, 20 cycle bursts, 1 ms PRI, 4 s duration, 300 kPa peak-negative pressure) under perfusion with Definity™ bubbles to examine microbubble-mediated endothelial permeabilization under a range of physiological conditions. Endothelial preconditioning under prolonged shear influenced physiology and the secretome, inducing increased expression of pro-angiogenesis analytes, decreasing levels of pro-inflammatory ones, and increasing the susceptibility of ultrasound therapy. Ultrasound treatment efficiency was positively correlated with concentrations of pro-angiogenic cytokines (e.g. VEGF-A, EGF, FGF-2), and negatively correlated with pro-inflammatory chemokines (e.g. MCP-1, GCP-2, SDF-1). Furthermore, ultrasound therapy under non-reversing pulsatile flow (∼4-8 dyne/cm2, 0.5-1 Hz) increased permeabilization up to 2.4-fold compared to shear-matched laminar flow, yet treatment under reversing oscillatory flow resulted in more heterogeneous modulation. This study provides insight into the role of vascular physiology, including endothelial biology, into the design of a localized ultrasound drug delivery system for ischemic heart disease.

Engineered microbubbles decorated with red emitting carbon nanoparticles for efficient delivery and imaging

Altering the route of uptake by the cells is an attractive strategy to overcome drug-receptor adaptation problems. Carbon nanoparticles (CNPs) with emission beyond tissue autofluorescence for imaging biological tissues were used to study the phenomenon of uptake by the cells. In this regard, red-emitting carbon nanoparticles (CNPs) were synthesized and incorporated onto lipid microbubbles (MBs). The CNPs showed red emissions in the range of 640 nm upon excitation with 480 nm wavelength of light. Atomic force microscopic and confocal microscopic images showed the successful loading of CNPs onto the MB. Carbon nanoparticle loaded microbubbles (CNP-MBs) were treated with NIH 3 T3 cells at different concentrations. Confocal microscopic imaging studies confirm the presence of CNPs inside the treated cells. Cytotoxicity studies revealed that the CNPs showed minimal toxicity towards cells after loading onto MBs. The CNPs are usually taken up by the cells through the clathrin-mediated (CME) pathway, but when loaded onto MBs, the mechanism of uptake of CNPs is altered, and the uptake by the cells was observed even in the presence of inhibitors for the CME pathway. Loading CNPs onto MBs resulted in the uptake of CNPs by the cell through micropinocytosis and sonophoresis in the presence of ultrasound. The in vivo uptake CNP-MBs were performed in Danio rerio (Zebrafish larvae). This study provides insights into altering the uptake pathway through reformulation by loading nanoparticles onto MBs.

Focused ultrasound-assisted delivery of immunomodulating agents in brain cancer

Focused ultrasound (FUS) combined with intravascularly circulating microbubbles can transiently increase the permeability of the blood-brain barrier (BBB) to enable targeted therapeutic delivery to the brain, the clinical testing of which is currently underway in both adult and pediatric patients. Aside from traditional cancer drugs, this technique is being extended to promote the delivery of immunomodulating therapeutics to the brain, including antibodies, immune cells, and cytokines. In this manner, FUS approaches are being explored as a tool to improve and amplify the effectiveness of immunotherapy for both primary and metastatic brain cancer, a particularly challenging solid tumor to treat. Here, we present an overview of the latest groundbreaking research in FUS-assisted delivery of immunomodulating agents to the brain in pre-clinical models of brain cancer, and place it within the context of the current immunotherapy approaches. We follow this up with a discussion on new developments and emerging strategies for this rapidly evolving approach.

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.

From concept to early clinical trials: 30 years of microbubble-based ultrasound-mediated drug delivery research

Ultrasound mediated drug delivery, a promising therapeutic modality, has evolved remarkably over the past three decades. Initially designed to enhance contrast in ultrasound imaging, microbubbles have emerged as a main vector for drug delivery, offering targeted therapy with minimized side effects. This review addresses the historical progression of this technology, emphasizing the pivotal role microbubbles play in augmenting drug extravasation and targeted delivery. We explore the complex mechanisms behind this technology, from stable and inertial cavitation to diverse acoustic phenomena, and their applications in medical fields. While the potential of ultrasound mediated drug delivery is undeniable, there are still challenges to overcome. Balancing therapeutic efficacy and safety and establishing standardized procedures are essential areas requiring attention. A multidisciplinary approach, gathering collaborations between researchers, engineers, and clinicians, is important for exploiting the full potential of this technology. In summary, this review highlights the potential of using ultrasound mediated drug delivery in improving patient care across various medical conditions.

Ultrasound robotics for precision therapy

In recent years, the application of microrobots in precision therapy has gained significant attention. The small size and maneuverability of these micromachines enable them to potentially access regions that are difficult to reach using traditional methods; thus, reducing off-target toxicities and maximizing treatment effectiveness. Specifically, acoustic actuation has emerged as a promising method to exert control. By harnessing the power of acoustic energy, these small machines potentially navigate the body, assemble at the desired sites, and deliver therapies with enhanced precision and effectiveness. Amidst the enthusiasm surrounding these miniature agents, their translation to clinical environments has proven difficult. The primary objectives of this review are threefold: firstly, to offer an overview of the fundamental acoustic principles employed in the field of microrobots; secondly, to assess their current applications in medical therapies, encompassing tissue targeting, drug delivery or even cell infiltration; and lastly, to delve into the continuous efforts aimed at integrating acoustic microrobots into in vivo applications.

Improving DNA vaccination performance through a new microbubble design and an optimized sonoporation protocol

As a non-viral transfection method, ultrasound and microbubble-induced sonoporation can achieve spatially targeted gene delivery with synergistic immunostimulatory effects. Here, we report for the first time the application of sonoporation for improving DNA vaccination performance. This study developed a new microbubble design with nanoscale DNA/PEI complexes loaded onto cationic microbubbles to attain significant increases in DNA-loading capacity (0.25 pg per microbubble) and in vitro transfection efficiency. Using live-cell imaging, we revealed the membrane perforation and cellular delivery characteristics of sonoporation. Using luciferase reporter gene for in vivo transfection, we showed that sonoporation increased the transfection efficiency by 40.9-fold when compared with intramuscular injection. Moreover, we comprehensively optimized the sonoporation protocol and further increased the transfection efficiency by 43.6-fold. Immunofluorescent staining results showed that sonoporation effectively activated the MHC-II+ immune cells. Using a hepatitis B DNA vaccine, sonoporation induced significantly higher serum antibody levels when compared with intramuscular injection, and the antibodies sustained for 56 weeks. In addition, we recorded the longest reported expression period (400 days) of the sonoporation-delivered gene. Whole genome resequencing confirmed that the gene with stable expression existed in an extrachromosomal state without integration. Our results demonstrated the potential of sonoporation for efficient and safe DNA vaccination.

Mechanistic study of ultrasound and microbubble enhanced cancer therapy in a 3D vascularized microfluidic cancer model

Accumulating evidence has shown that ultrasound exposure combined with microbubbles can enhance cancer therapy. However, the underlying mechanisms at the tissue level have not been fully understood yet. The conventional cell culture in vitro lacks complex structure and interaction, while animal studies cannot provide micron-scale dynamic information. To bridge the gap, we designed and assembled a 3D vascularized microfluidic cancer model, particularly suitable for ultrasound and microbubble involved mechanistic studies. Using this model, we first studied SonoVue microbubble traveling dynamics in 3D tissue structure, then resolved SonoVue microbubble cavitation dynamics in tissue mimicking agarose gels at a frame rate of 0.675 M fps, and finally explored the impacts of ultrasound and microbubbles on cancer cell spheroids. Our results demonstrate that microbubble penetration in agarose gel was enhanced by increasing microbubble concentration, flow rate and decreasing viscosity of the gel, and little affected by mild acoustic radiation force. SonoVue microbubble exhibited larger expansion amplitudes in 2 %(w/v) agarose gels than in water, which can be explained theoretically by the relaxation of the cavitation medium. The immediate impacts of ultrasound and SonoVue microbubbles to cancer cell spheroids in the 3D tissue model included improved cancer cell spheroid penetration in micron-scale and sparse direct permanent cancer cell damage. Our study provides new insights of the mechanisms for ultrasound and microbubble enhanced cancer therapy at the tissue level.

Sonosensitive Cavitation Nuclei-A Customisable Platform Technology for Enhanced Therapeutic Delivery

Ultrasound-mediated cavitation shows great promise for improving targeted drug delivery across a range of clinical applications. Cavitation nuclei-sound-sensitive constructs that enhance cavitation activity at lower pressures-have become a powerful adjuvant to ultrasound-based treatments, and more recently emerged as a drug delivery vehicle in their own right. The unique combination of physical, biological, and chemical effects that occur around these structures, as well as their varied compositions and morphologies, make cavitation nuclei an attractive platform for creating delivery systems tuned to particular therapeutics. In this review, we describe the structure and function of cavitation nuclei, approaches to their functionalization and customization, various clinical applications, progress toward real-world translation, and future directions for the field.

Ultrasound meets the cell membrane: for enhanced endocytosis and drug delivery

Endocytosis plays a crucial role in drug delivery for precision therapy. As a non-invasive and spatiotemporal-controllable stimulus, ultrasound (US) has been utilized for improving drug delivery efficiency due to its ability to enhance cell membrane permeability. When US meets the cell membrane, the well-known cavitation effect generated by US can cause various biophysical effects, facilitating the delivery of various cargoes, especially nanocarriers. The comprehension of recent progress in the biophysical mechanism governing the interaction between ultrasound and cell membranes holds significant implications for the broader scientific community, particularly in drug delivery and nanomedicine. This review will summarize the latest research results on the biological effects and mechanisms of US-enhanced cellular endocytosis. Moreover, the latest achievements in US-related biomedical applications will be discussed. Finally, challenges and opportunities of US-enhanced endocytosis for biomedical applications will be provided.

Molecular modelling of shockwave-mediated delivery of paclitaxel aggregates across the neuronal plasma membrane

Shock-assisted paclitaxel (PTX) transport across the blood-brain barrier offers a promising treatment strategy for brain tumors. Here, based on a realistically complex human brain plasma membrane (PM) model, we investigated the dynamic transmembrane behavior of a PTX cluster by shock induced bubble collapse, focusing on the effect of impulse (I), bubble diameter (D) and arrays. The results show that all three factors can control the transport depth (ΔDPM) of PTX. For a fixed D, the ΔDPM grows exponentially with I, ΔDPM ∼ exp (I), and eventually reaches a critical depth. But the depth, ΔDPM, can be adjusted linearly in a wider range of D. This mainly depends on the size of jets from bubble collapse. For bubble arrays, the bubbles in series can transport PTX deeper than a single bubble, while the parallel does the opposite. In addition, only PTX clusters in the range of jet action can be successfully transported. Finally, the absorption of PTX clusters was examined via recovery simulation. Not all PTX clusters across the membrane can be effectively absorbed by cells. The shallow PTX clusters are quickly attracted by the membrane and embedded into it. The critical depth at which PTX clusters can be effectively absorbed is about 20 nm. These molecular-level mechanisms and dynamic processes of PTX clusters crossing the PM membrane may be helpful in optimizing the application of shock-induced bubble collapse for the delivery of PTX to tumor cells.

Loading Intracranial Drug-Eluting Reservoirs Across the Blood-Brain Barrier With Focused Ultrasound

OBJECTIVE

Efficient, sustained and long-term delivery of therapeutics to the brain remains an important challenge to treatment of diseases such as brain cancer, stroke and neurodegenerative disease. Focused ultrasound can assist movement of drugs into the brain, but frequent and long-term use has remained impractical. Single-use intracranial drug-eluting depots show promise but are limited for the treatment of chronic diseases as they cannot be refilled non-invasively. Refillable drug-eluting depots could serve as a long-term solution, but refilling is hindered by the blood-brain barrier (BBB), which prevents drug refills from accessing the brain. In this article, we describe how focused ultrasound enables non-invasive loading of intracranial drug depots in mice.

METHODS

Female CD-1 mice (n = 6) were intracranially injected with click-reactive and fluorescent molecules that are capable of anchoring in the brain. After healing, animals were treated with high-intensity focused ultrasound and microbubbles to temporarily increase the permeability of the blood-brain barrier and deliver dibenzocyclooctyne (DBCO)-Cy7. The mice were perfused, and the brains were imaged via ex vivo fluorescence imaging.

RESULTS

Fluorescence imaging indicated small molecule refills are captured by intracranial depots as long as 4 wk after administration and are retained for up to 4 wk based on fluorescence imaging. Efficient loading was dependent on both focused ultrasound and the presence of refillable depots in the brain as absence of either prevented intracranial loading.

CONCLUSION

The ability to target and retain small molecules at predetermined intracranial sites with pinpoint accuracy provides opportunities to continuously deliver drugs to the brain over weeks and months without excessive BBB opening and with minimal off-target side effects.

Janus polymer-grafted nanoparticles mimicking membrane repair proteins for the prevention of lipid membrane rupture

Plasma membrane rupture often leads to cell damage, especially when there is a lack of membrane repair proteins near the wounds due to genetic mutations in organisms. To efficiently promote the repair of the injured lipid membrane, nanomedicines may act as a promising alternative to membrane repair proteins, but the related research is still in its infancy. Herein, using dissipative particle dynamics simulations, we designed a class of Janus polymer-grafted nanoparticles (PGNPs) that can mimic the function of membrane repair proteins. The Janus PGNPs comprise both hydrophobic and hydrophilic polymer chains grafted on nanoparticles (NPs). We track the dynamic process of the adsorption of Janus PGNPs at the damaged site in the lipid membrane and systematically assess the driving forces for this process. Our results reveal that tuning the length of the grafted polymer chains and the surface polarity of the NPs can efficiently enhance the adsorption of Janus PGNPs at the site of the damaged membrane to reduce membrane stress. After repair, the adsorbed Janus PGNPs can be successfully detached from the membrane, leaving the membrane untouched. These results provide valuable guidelines for designing advanced nanomaterials for the repair of damaged lipid membranes.

Radioenhancement with the Combination of Docetaxel and Ultrasound Microbubbles: In Vivo Prostate Cancer

Using an in vitro prostate cancer model, we previously demonstrated the significant enhancement of radiotherapy (XRT) with the combined treatment of docetaxel (Taxotere; TXT) and ultrasound-microbubbles (USMB). Here, we extend these findings to an in vivo cancer model. Severe combined immune-deficient male mice were xenografted with the PC-3 prostate cancer cell line in the hind leg and treated with USMB, TXT, radiotherapy (XRT), and their combinations. The tumors were imaged with ultrasound pre-treatment and 24 h post-treatment, following which they were extracted for the histological analysis of the tumor-cell death (D_N; H&E) and apoptosis (D_A; TUNEL). The tumors' growths were assessed for up to ~6 weeks and analysed using the exponential Malthusian tumor-growth model. The tumors' doubling time (V_T) was characterized as growth (positive) or shrinkage (negative). The cellular death and apoptosis increased ~5-fold with the TXT + USMB + XRT (D_n = 83% and D_a = 71%) compared to the XRT alone (D_n = 16% and D_a = 14%), and by ~2-3-fold with the TXT + XRT (D_n = 50% and D_a = 38%) and USMB + XRT (D_n = 45% and D_a = 27%) compared to the XRT. The USMB enhanced the cellular bioeffects of the TXT by ~2-5-fold with the TXT + USMB (D_n = 42% and D_a = 50%), compared with the TXT alone (D_n = 19% and D_a = 9%). The USMB alone caused cell death (D_n = 17% and D_a = 10%) compared to the untreated control (D_n = 0.4% and D_a = 0%). The histological cellular bioeffects were correlated with the changes in the ultrasound RF mid-band-fit data, which were associated with the cellular morphology. The linear regression analysis displayed a positive linear correlation between the mid-band fit and the overall cell death (R² = 0.9164), as well as a positive linear correlation between the mid-band fit and the apoptosis (R² = 0.8530). These results demonstrate a correlation between the histological and spectral measurements of the tissue microstructure and that cellular morphological changes can be detected by ultrasound scattering analysis. In addition, the tumor volumes from the triple-combination treatment were significantly smaller than those from the control, XRT, USMB + XRT, and TXT + XRT, from day 2 onward. The TXT + USMB + XRT-treated tumors shrank from day 2 and at each subsequent time-point measured (V_T ~-6 days). The growth of the XRT-treated tumors was inhibited during the first 16 days, following which the tumors grew (V_T ~9 days). The TXT + XRT and USMB + XRT groups displayed an initial decrease in tumor size (day 1-14; TXT + XRT V_T ~-12 days; USMB + XRT V_T ~-33 days), followed by a growth phase (day 15-37; TXT + XRT V_T ~11 days; USMB + XRT V_T ~22 days). The triple-combination therapy induced tumor shrinkage to a greater extent than any of the other treatments. This study demonstrates the in vivo radioenhancement potential of chemotherapy combined with therapeutic ultrasound-microbubble treatment in inducing cell death and apoptosis, as well as long-term tumor shrinkage.

Cell-cycle dependent nuclear gene delivery enhances the effects of E-cadherin against tumor invasion and metastasis

Gene delivery is the process by which foreign DNA is transferred to host cells, released from intracellular vesicles, and transported to the nuclei for transcription. This process is frequently inefficient and difficult to control spatiotemporally. We developed a gene delivery strategy that uses ultrasound to directly deliver plasmid DNA into nuclei via gas vesicles (GVs)-based intracellular cavitation. pDNA-binding GVs can be taken up by cells and cause intracellular cavitation when exposed to acoustic irradiation and delivering their pDNA payloads into nuclei. Importantly, GVs can remain stable in the cytoplasm in the absence of acoustic irradiation, allowing for temporally controlled nuclear gene delivery. We were able to achieve spatiotemporal control of E-cadherin nuclear gene delivery in this manner, demonstrating its efficacy in tumor invasion and metastasis inhibition. Interestingly, we discovered that nuclear gene delivery of E-cadherin during the G2/M phase of the cell cycle in C6 tumor cells inhibited tumor invasion and metastasis more effectively than during the G1 and S phases. The gene delivery of E-cadherin at the G2/M phase resulted in significantly lower expression of Fam50a, which reduced Fam50a/Runx2 interaction and led to reduced transactivation of MMP13, an important factor for epithelial-mesenchymal transition, as observed in a molecular mechanism assay. Thus, using remote acoustic control of intracellular cavitation of pDNA-GVs, we developed a high spatiotemporally controllable gene delivery strategy and achieved stronger tumor invasion and metastasis inhibition effects by delivering the E-cadherin gene at the G2/M phase.

Barrier-breaking effects of ultrasonic cavitation for drug delivery and biomarker release

Recently, emerging evidence has demonstrated that cavitation actually creates important bidirectional channels on biological barriers for both intratumoral drug delivery and extratumoral biomarker release. To promote the barrier-breaking effects of cavitation for both therapy and diagnosis, we first reviewed recent technical advances of ultrasound and its contrast agents (microbubbles, nanodroplets, and gas-stabilizing nanoparticles) and then reported the newly-revealed cavitation physical details. In particular, we summarized five types of cellular responses of cavitation in breaking the plasma membrane (membrane retraction, sonoporation, endocytosis/exocytosis, blebbing and apoptosis) and compared the vascular cavitation effects of three different types of ultrasound contrast agents in breaking the blood-tumor barrier and tumor microenvironment. Moreover, we highlighted the current achievements of the barrier-breaking effects of cavitation in mediating drug delivery and biomarker release. We emphasized that the precise induction of a specific cavitation effect for barrier-breaking was still challenged by the complex combination of multiple acoustic and non-acoustic cavitation parameters. Therefore, we provided the cutting-edge in-situ cavitation imaging and feedback control methods and suggested the development of an international cavitation quantification standard for the clinical guidance of cavitation-mediated barrier-breaking effects.

The role of acoustofluidics and microbubble dynamics for therapeutic applications and drug delivery

Targeted drug delivery is proposed to reduce the toxic effects of conventional therapeutic methods. For that purpose, nanoparticles are loaded with drugs called nanocarriers and directed toward a specific site. However, biological barriers challenge the nanocarriers to convey the drug to the target site effectively. Different targeting strategies and nanoparticle designs are used to overcome these barriers. Ultrasound is a new, safe, and non-invasive drug targeting method, especially when combined with microbubbles. Microbubbles oscillate under the effect of the ultrasound, which increases the permeability of endothelium, hence, the drug uptake to the target site. Consequently, this new technique reduces the dose of the drug and avoids its side effects. This review aims to describe the biological barriers and the targeting types with the critical features of acoustically driven microbubbles focusing on biomedical applications. The theoretical part covers the historical developments in microbubble models for different conditions: microbubbles in an incompressible and compressible medium and bubbles encapsulated by a shell. The current state and the possible future directions are discussed.

Ultrasound nanotheranostics: Toward precision medicine

Ultrasound (US) is a mechanical wave that can penetrate biological tissues and trigger complex bioeffects. The mechanisms of US in different diagnosis and treatment are different, and the functional application of commercial US is also expanding. In particular, recent developments in nanotechnology have led to a wider use of US in precision medicine. In this review, we focus on US in combination with versatile micro and nanoparticles (NPs)/nanovesicles for tumor theranostics. We first introduce US-assisted drug delivery as a stimulus-responsive approach that spatiotemporally regulates the deposit of nanomedicines in target tissues. Multiple functionalized NPs and their US-regulated drug-release curves are analyzed in detail. Moreover, as a typical representative of US therapy, sonodynamic antitumor strategy is attracting researchers' attention. The collaborative efficiency and mechanisms of US and various nano-sensitizers such as nano-porphyrins and organic/inorganic nanosized sensitizers are outlined in this paper. A series of physicochemical processes during ultrasonic cavitation and NPs activation are also discussed. Finally, the new applications of US and diagnostic NPs in tumor-monitoring and image-guided combined therapy are summarized. Diagnostic NPs contain substances with imaging properties that enhance US contrast and photoacoustic imaging. The development of such high-resolution, low-background US-based imaging methods has contributed to modern precision medicine. It is expected that the integration of non-invasive US and nanotechnology will lead to significant breakthroughs in future clinical applications.

Comparison of Acoustofluidic and Static Systems for Ultrasound-Mediated Molecular Delivery to T Lymphocytes

Continuous-flow acoustofluidic technologies can potentially improve processing of T lymphocytes for cell therapies by addressing the limitations with viral and non-viral delivery methods. The objective of this study was to assess the intracellular delivery efficiency with acoustofluidic treatment compared with that of static ultrasound treatment. Optimization of parameters in acoustofluidic and static configurations was performed by assessing intracellular delivery of a fluorescent compound (calcein) in viable human Jurkat T lymphocytes. Ultrasound pressure and the concentration of cationic phospholipid-coated microbubbles influenced calcein delivery in both systems. In the static system, a treatment time of 45 s increased molecular delivery compared with 0-30 s (p < 0.01). Refined parameters were used to assess molecular delivery of small and large compounds (0.6-kDa calcein and 150-kDa fluorescein isothiocyanate-dextran, respectively) after ultrasound treatment with the acoustofluidic or static systems. Molecular delivery was similar with refined parameters for acoustofluidic treatment and static treatment (p > 0.05), even though acoustofluidic treatment had lower microbubble concentration (24 μg/mL vs. 94 μg/mL) and shorter treatment time (∼2-3 s vs. 45 s). This study indicates that the acoustofluidic system can significantly enhance intracellular molecular delivery, which could potentially enable acoustofluidic cell transfection during continuous flow processing for manufacture of cell therapies or other applications.

Strategies and challenges for non-viral delivery of non-coding RNAs to the heart

Non-coding RNAs (ncRNAs), such as miRNAs and long non-coding RNAs (lncRNAs) have been reported as regulators of cardiovascular pathophysiology. Their transient effect and diversified mechanisms of action offer a plethora of therapeutic opportunities for cardiovascular diseases (CVDs). However, physicochemical RNA features such as charge, stability, and structural organization hinder efficient on-target cellular delivery. Here, we highlight recent preclinical advances in ncRNA delivery for the cardiovascular system using non-viral approaches. We identify the unmet needs and advance possible solutions towards clinical translation. Finding the optimal delivery vehicle and administration route is vital to improve therapeutic efficacy and safety; however, given the different types of ncRNAs, this may ultimately not be frameable within a one-size-fits-all approach.

Effect of acoustic cluster therapy (ACT®) combined with chemotherapy in a patient-derived xenograft mouse model of pancreatic cancer

Pancreatic ductal adenocarcinomas respond poorly to chemotherapy, in part due to the dense tumor stroma that hinders drug delivery. Ultrasound (US) in combination with microbubbles has previously shown promise as a means to improve drug delivery, and the therapeutic efficacy of ultrasound-mediated drug delivery is currently being evaluated in multiple clinical trials. However, most of these utilize echogenic contrast agents engineered for imaging, which might not be optimal compared to specialized formulations tailored for drug delivery. In this study, we evaluated the in vivo efficacy of phase-shifting microbubble-microdroplet clusters that, upon insonation, form bubbles in the size range of 20-30 μm. We developed a patient-derived xenograft model of pancreatic cancer implanted in mice that largely retained the stromal content of the originating tumor and compared tumor growth in mice given chemotherapeutics (nab-paclitaxel plus gemcitabine or liposomal irinotecan) with mice given the same chemotherapeutics in addition to ultrasound and acoustic cluster therapy. We found that acoustic cluster therapy significantly improved the effect of both chemotherapeutic regimens and resulted in 7.2 times higher odds of complete remission of the tumor compared to the chemotherapeutics alone.

The influence of inter-bubble spacing on the resonance response of ultrasound contrast agent microbubbles

Ultrasound-driven microbubbles, typically between 1 and 8 µm in diameter, are resonant scatterers that are employed as diagnostic contrast agents and emerging as potentiators of targeted therapies. Microbubbles are administered in populations whereby their radial dynamics - key to their effectiveness - are greatly affected by intrinsic (e.g. bubble size) and extrinsic (e.g. boundaries) factors. In this work, we aim to understand how two neighbouring microbubbles influence each other. We developed a finite element model of a system of two individual phospholipid-encapsulated microbubbles vibrating in proximity to each other to study the effect of inter-bubble distance on microbubble radial resonance response. For the case of two equal-sized and identical bubbles, each bubble exhibits a decrease between 7 and 10% in the frequency of maximum response (f_MR) and an increase in amplitude of maximum response (A_MR) by 9-11% as compared to its isolated response in free-space, depending on the bubble size examined. For a system of two unequal-sized microbubbles, the large bubble shows no significant change, however the smaller microbubble shows an increase in f_MR by 7-11% and a significant decrease in A_MR by 38-52%. Furthermore, in very close proximity the small bubble shows a secondary off-resonance peak at the corresponding f_MR of its larger companion microbubble. Our work suggests that frequency-dependent microbubble response is greatly affected by the presence of another bubble, which has implications in both imaging and therapy applications. Furthermore, our work suggests a mechanism by which nanobubbles show significant off-resonance vibrations in the clinical frequency range, a behaviour that has been observed experimentally but heretofore unexplained.

Applications of Focused Ultrasound for the Treatment of Glioblastoma: A New Frontier

Glioblastoma (GBM) is an aggressive primary astrocytoma associated with short overall survival. Treatment for GBM primarily consists of maximal safe surgical resection, radiation therapy, and chemotherapy using temozolomide. Nonetheless, recurrence and tumor progression is the norm, driven by tumor stem cell activity and a high mutational burden. Focused ultrasound (FUS) has shown promising results in preclinical and clinical trials for treatment of GBM and has received regulatory approval for the treatment of other neoplasms. Here, we review the range of applications for FUS in the treatment of GBM, which depend on parameters, including frequency, power, pulse duration, and duty cycle. Low-intensity FUS can be used to transiently open the blood-brain barrier (BBB), which restricts diffusion of most macromolecules and therapeutic agents into the brain. Under guidance from magnetic resonance imaging, the BBB can be targeted in a precise location to permit diffusion of molecules only at the vicinity of the tumor, preventing side effects to healthy tissue. BBB opening can also be used to improve detection of cell-free tumor DNA with liquid biopsies, allowing non-invasive diagnosis and identification of molecular mutations. High-intensity FUS can cause tumor ablation via a hyperthermic effect. Additionally, FUS can stimulate immunological attack of tumor cells, can activate sonosensitizers to exert cytotoxic effects on tumor tissue, and can sensitize tumors to radiation therapy. Finally, another mechanism under investigation, known as histotripsy, produces tumor ablation via acoustic cavitation rather than thermal effects.

Landscape of Cellular Bioeffects Triggered by Ultrasound-Induced Sonoporation

Sonoporation is the process of transient pore formation in the cell membrane triggered by ultrasound (US). Numerous studies have provided us with firm evidence that sonoporation may assist cancer treatment through effective drug and gene delivery. However, there is a massive gap in the body of literature on the issue of understanding the complexity of biophysical and biochemical sonoporation-induced cellular effects. This study provides a detailed explanation of the US-triggered bioeffects, in particular, cell compartments and the internal environment of the cell, as well as the further consequences on cell reproduction and growth. Moreover, a detailed biophysical insight into US-provoked pore formation is presented. This study is expected to review the knowledge of cellular effects initiated by US-induced sonoporation and summarize the attempts at clinical implementation.

NIR-Active Porphyrin-Decorated Lipid Microbubbles for Enhanced Therapeutic Activity Enabled by Photodynamic Effect and Ultrasound in 3D Tumor Models of Breast Cancer Cell Line and Zebrafish Larvae

Porphyrin is known to enable the photodynamic effect during cancer drug delivery and molecular imaging. However, its hydrophobicity and tendency to aggregate in an aqueous medium create a significant hurdle for its use as an anticancer drug. Loading porphyrin onto biocompatible delivery vehicles can enhance its efficacy. This can be achieved by using gas-filled microbubbles that can be administered intravenously. This study aimed at developing near-infrared (NIR)-active porphyrin-loaded lipid microbubbles with anticancer activity enhanced by sonodynamic and photodynamic effects. The porphyrin-loaded microbubbles were studied for their cell toxicity, cellular uptake of porphyrin, and effect on cellular three-dimensional (3D) invasion of breast cancer cells (MDA-MB-231) in cellulo. Toxicity studies in zebrafish larvae (Danio rerio) in the presence and absence of photodynamic and sonodynamic therapy were also conducted. The results suggest that with a higher concentration of porphyrin loaded on microbubbles, the porphyrin-loaded microbubbles display a higher therapeutic effect facilitated by photodynamic and sonodynamic therapy, which results in enhanced cellular uptake and cellular toxicity. A lower concentration of loaded porphyrin microbubbles exhibits high cellular viability and good fluorescence intensity in the NIR region, which can be exploited for bioimaging applications.

Vibropolyfection: coupling polymer-mediated gene delivery to mechanical stimulation to enhance transfection of adherent cells

BACKGROUND

With the success of recent non-viral gene delivery-based COVID-19 vaccines, nanovectors have gained some public acceptance and come to the forefront of advanced therapies. Unfortunately, the relatively low ability of the vectors to overcome cellular barriers adversely affects their effectiveness. Scientists have thus been striving to develop ever more effective gene delivery vectors, but the results are still far from satisfactory. Therefore, developing novel strategies is probably the only way forward to bring about genuine change. Herein, we devise a brand-new gene delivery strategy to boost dramatically the transfection efficiency of two gold standard nucleic acid (NA)/polymer nanoparticles (polyplexes) in vitro.

RESULTS

We conceived a device to generate milli-to-nanoscale vibrational cues as a function of the frequency set, and deliver vertical uniaxial displacements to adherent cells in culture. A short-lived high-frequency vibrational load (t = 5 min, f = 1,000 Hz) caused abrupt and extensive plasmalemma outgrowths but was safe for cells as neither cell proliferation rate nor viability was affected. Cells took about 1 hr to revert to quasi-naïve morphology through plasma membrane remodeling. In turn, this eventually triggered the mechano-activated clathrin-mediated endocytic pathway and made cells more apt to internalize polyplexes, resulting in transfection efficiencies increased from 10-to-100-fold. Noteworthy, these results were obtained transfecting three cell lines and hard-to-transfect primary cells.

CONCLUSIONS

In this work, we focus on a new technology to enhance the intracellular delivery of NAs and improve the transfection efficiency of non-viral vectors through priming adherent cells with a short vibrational stimulation. This study paves the way for capitalizing on physical cell stimulation(s) to significantly raise the effectiveness of gene delivery vectors in vitro and ex vivo.

State-of-the-art of ultrasound-triggered drug delivery from ultrasound-responsive drug carriers

INTRODUCTION

The development of new tools to locally and non-invasively transferring therapeutic substances at the desired site in deep living tissue has been a long sought-after goal within the drug delivery field. Among the established methods, ultrasound (US) with US-responsive carriers holds great promise and demonstrates on-demand delivery of a variety of functional substances with spatial precision of several millimeters in deep-seated tissues in animal models and humans. These properties have motivated several explorations of US with US responsive carriers as a modality for neuromodulation and the treatment of various diseases, such as stroke and cancer.

AREAS COVERED

This article briefly discussed three specific mechanisms that enhance in vivo drug delivery via US with US-responsive carriers: 1) permeabilizing cellular membrane, 2) increasing the permeability of vessels, and 3) promoting cellular endocytotic uptake. Besides, a series of US-responsive drug carriers are discussed, with an emphasis on the relation between structural feature and therapeutic outcome.

EXPERT OPINION

This article summarized current development for each of US-responsive drug carrier, focusing on the routes of enhancing delivery and applications. The mechanisms of interaction between US-responsive carriers and US energy, such as cavitation, hyperthermia, and reactive oxygen species, as well as how these interactions can improve drug delivery into target cell/tissue. It can be expected that there are serval efforts to further identification of US-responsive particles, design of novel US waveform sequence, and survey of optimal combination between US parameters and US-responsive carriers for better controlling the spatiotemporal drug release profile, stability, and safety in vivo. The authors believe these will provide novel tools for precisely designing treatment strategies and significantly benefit the clinical management of several diseases.

Sonoporation of Immune Cells: Heterogeneous Impact on Lymphocytes, Monocytes and Granulocytes

Microbubble-mediated ultrasound (MB-US) can be used to realize sonoporation and, in turn, facilitate the transfection of leukocytes in the immune system. Nevertheless, the bio-effects that can be induced by MB-US exposure on leukocytes have not been adequately studied, particularly for different leukocyte lineage subsets with distinct cytological characteristics. Here, we describe how that same set of MB-US exposure conditions would induce heterogeneous bio-effects on the three main leukocyte subsets: lymphocytes, monocytes and granulocytes. MB-US exposure was delivered by applying 1-MHz pulsed ultrasound (0.50-MPa peak negative pressure, 10% duty cycle, 30-s exposure period) in the presence of microbubbles (1:1 cell-to-bubble ratio); sonoporated and non-viable leukocytes were respectively labeled using calcein and propidium iodide. Flow cytometry was then performed to classify leukocytes into their corresponding subsets and to analyze each subset's post-exposure viability, sonoporation rate, uptake characteristics and morphology. Results revealed that, when subjected to MB-US exposure, granulocytes experienced the highest loss of viability (64.0 ± 11.0%) and the lowest sonoporation rate (6.3 ± 2.5%), despite maintaining their size and granularity. In contrast, lymphocytes exhibited the lowest loss of viability (20.9 ± 7.0%), while monocytes had the highest sonoporation rate (24.1 ± 13.6%). For these two sonoporated leukocyte subsets, their cell size and granularity were found to be reduced. Also, they exhibited graded levels of calcein uptake, whereas sonoporated granulocytes achieved only mild calcein uptake. These heterogeneous bio-effects should be accounted for when using MB-US and sonoporation in immunomodulation applications.

Modelling of magnetic microbubbles to evaluate contrast enhanced magnetomotive ultrasound in lymph nodes - a pre-clinical study

OBJECTIVES

Despite advances in MRI the detection and characterisation of lymph nodes in rectal cancer remains complex, especially when assessing the response to neoadjuvant treatment. An alternative approach is functional imaging, previously shown to aid characterisation of cancer tissues. We report proof of concept of the novel technique Contrast-Enhanced Magneto-Motive Ultrasound (CE-MMUS) to recover information relating to local perfusion and lymphatic drainage, and interrogate tissue mechanical properties through magnetically induced deformations.

METHODS

The feasibility of the proposed application was explored using a combination of experimental animal and phantom ultrasound imaging, along with finite element analysis. First, contrast-enhanced ultrasound imaging on one wild type mouse recorded lymphatic drainage of magnetic microbubbles after bolus injection. Second, tissue phantoms were imaged using MMUS to illustrate the force- and elasticity dependence of the magnetomotion. Third, the magnetomechanical interactions of a magnetic microbubble with an elastic solid were simulated using finite element software.

RESULTS

Accumulation of magnetic microbubbles in the inguinal lymph node was verified using contrast enhanced ultrasound, with peak enhancement occurring 3.7 s post-injection. The magnetic microbubble gave rise to displacements depending on force, elasticity, and bubble radius, indicating an inverse relation between displacement and the latter two.

CONCLUSION

Combining magnetic microbubbles with MMUS could harness the advantages of both techniques, to provide perfusion information, robust lymph node delineation and characterisation based on mechanical properties.

ADVANCES IN KNOWLEDGE

(a) Lymphatic drainage of magnetic microbubbles visualised using contrast-enhanced ultrasound imaging and (b) magnetomechanical interactions between such bubbles and surrounding tissue could both contribute to (c) robust detection and characterisation of lymph nodes.

Involvement of Ceramide Signalling in Radiation-Induced Tumour Vascular Effects and Vascular-Targeted Therapy

Sphingolipids are well-recognized critical components in several biological processes. Ceramides constitute a class of sphingolipid metabolites that are involved in important signal transduction pathways that play key roles in determining the fate of cells to survive or die. Ceramide accumulated in cells causes apoptosis; however, ceramide metabolized to sphingosine promotes cell survival and angiogenesis. Studies suggest that vascular-targeted therapies increase endothelial cell ceramide resulting in apoptosis that leads to tumour cure. Specifically, ultrasound-stimulated microbubbles (USMB) used as vascular disrupting agents can perturb endothelial cells, eliciting acid sphingomyelinase (ASMase) activation accompanied by ceramide release. This phenomenon results in endothelial cell death and vascular collapse and is synergistic with other antitumour treatments such as radiation. In contrast, blocking the generation of ceramide using multiple approaches, including the conversion of ceramide to sphingosine-1-phosphate (S1P), abrogates this process. The ceramide-based cell survival "rheostat" between these opposing signalling metabolites is essential in the mechanotransductive vascular targeting following USMB treatment. In this review, we aim to summarize the past and latest findings on ceramide-based vascular-targeted strategies, including novel mechanotransductive methodologies.

Characterization of Acoustic, Cavitation, and Thermal Properties of Poly(vinyl alcohol) Hydrogels for Use as Therapeutic Ultrasound Tissue Mimics

The thermal and mechanical effects induced in tissue by ultrasound can be exploited for therapeutic applications. Tissue-mimicking materials (TMMs), reflecting different soft tissue properties, are required for experimental evaluation of therapeutic potential. In the study described here, poly(vinyl alcohol) (PVA) hydrogels were characterized. Hydrogels prepared using different concentrations (5%-20% w/w) and molecular weights of PVA ± cellulose scatterers (2.5%-10% w/w) were characterized acoustically (sound speed, attenuation) as a function of temperature (25°C-45°C), thermally (thermal conductivity, specific heat capacity) and in terms of their cavitation thresholds. Results were compared with measurements in fresh sheep tissue (kidney, liver, spleen). Sound speed depended most strongly on PVA concentration, and attenuation, on cellulose content. For the range of formulations investigated, the PVA gel acoustic properties (sound speed: 1532 ± 17 to 1590 ± 9 m/s, attenuation coefficient: 0.08 ± 0.01 to 0.37 ± 0.02 dB/cm) fell within those measured in fresh tissue. Cavitation thresholds for 10% PVA hydrogels (50% occurrence: 4.1-5.4 MPa, 75% occurrence: 5.4-8.2 MPa) decreased with increasing cellulose content. In summary, PVA cellulose composite hydrogels may be suitable mimics of acoustic, cavitation and thermal properties of soft tissue for a number of therapeutic ultrasound applications.

Dispersing and Sonoporating Biofilm-Associated Bacteria with Sonobactericide

Bacteria encased in a biofilm poses significant challenges to successful treatment, since both the immune system and antibiotics are ineffective. Sonobactericide, which uses ultrasound and microbubbles, is a potential new strategy for increasing antimicrobial effectiveness or directly killing bacteria. Several studies suggest that sonobactericide can lead to bacterial dispersion or sonoporation (i.e., cell membrane permeabilization); however, real-time observations distinguishing individual bacteria during and directly after insonification are missing. Therefore, in this study, we investigated, in real-time and at high-resolution, the effects of ultrasound-induced microbubble oscillation on Staphylococcus aureus biofilms, without or with an antibiotic (oxacillin, 1 μg/mL). Biofilms were exposed to ultrasound (2 MHz, 100-400 kPa, 100-1000 cycles, every second for 30 s) during time-lapse confocal microscopy recordings of 10 min. Bacterial responses were quantified using post hoc image analysis with particle counting. Bacterial dispersion was observed as the dominant effect over sonoporation, resulting from oscillating microbubbles. Increasing pressure and cycles both led to significantly more dispersion, with the highest pressure leading to the most biofilm removal (up to 83.7%). Antibiotic presence led to more variable treatment responses, yet did not significantly impact the therapeutic efficacy of sonobactericide, suggesting synergism is not an immediate effect. These findings elucidate the direct effects induced by sonobactericide to best utilize its potential as a biofilm treatment strategy.

Spatiotemporal Dynamics and Mechanisms of Actin Cytoskeletal Re-modeling in Cells Perforated by Ultrasound-Driven Microbubbles

To develop new strategies for improving the efficacy and biosafety of sonoporation-based macromolecule delivery, it is essential to understand the mechanisms underlying plasma membrane re-sealing and function recovery of the cells perforated by ultrasound-driven microbubbles. However, we lack a clear understanding of the spatiotemporal dynamics of the disrupted actin cytoskeleton and its role in the re-sealing of sonoporated cells. Here we used a customized experimental setup for single-pulse ultrasound (133.33-µs duration and 0.70-MPa peak negative pressure) exposure to microbubbles and for real-time recording of single-cell (human umbilical vein endothelial cell) responses by laser confocal microscopic imaging. We found that in reversibly sonoporated cells, the locally disrupted actin cytoskeleton, which was spatially correlated with the perforated plasma membrane, underwent three successive phases (expansion; contraction and re-sealing; and recovery) to re-model and that each phase of the disrupted actin cytoskeleton was approximately synchronized with that of the perforated plasma membrane. Moreover, compared with the closing time of the perforated plasma membrane, the same time was used for the re-sealing of the actin cytoskeleton in mildly sonoporated cells and a longer time was required in moderately sonoporated cells. Further, the generation, directional migration, accumulation and re-polymerization of globular actin polymers during the three phases drove the re-modeling of the actin cytoskeleton. However, in irreversibly sonoporated cells, the actin cytoskeleton, which underwent expansion and no contraction, was progressively de-polymerized and could not be re-sealed. Finally, we found that intracellular calcium transients were essential for the recruitment of globular actin and the re-modeling of the actin cytoskeleton. These results provide new insight into the role of actin cytoskeleton dynamics in the re-sealing of sonoporated cells and serve to guide the design of new strategies for sonoporation-based delivery.

An Overview of Cell Membrane Perforation and Resealing Mechanisms for Localized Drug Delivery

Localized and reversible plasma membrane disruption is a promising technique employed for the targeted deposition of exogenous therapeutic compounds for the treatment of disease. Indeed, the plasma membrane represents a significant barrier to successful delivery, and various physical methods using light, sound, and electrical energy have been developed to generate cell membrane perforations to circumvent this issue. To restore homeostasis and preserve viability, localized cellular repair mechanisms are subsequently triggered to initiate a rapid restoration of plasma membrane integrity. Here, we summarize the known emergency membrane repair responses, detailing the salient membrane sealing proteins as well as the underlying cytoskeletal remodeling that follows the physical induction of a localized plasma membrane pore, and we present an overview of potential modulation strategies that may improve targeted drug delivery approaches.

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.