Artificial cavitation nuclei significantly enhance acoustically induced cell transfection

Focused ultrasound gene delivery for the treatment of neurological disorders

The transformative potential of gene therapy has been demonstrated in humans. However, there is an unmet need for non-invasive targeted gene delivery and regulation in the treatment of brain disorders. Transcranial focused ultrasound (FUS) has gained tremendous momentum to address these challenges. FUS non-invasively modulates brain cells and their environment, and is a powerful tool to facilitate gene delivery across the blood-brain barrier (BBB) with millimeter precision and promptly regulate transgene expression. This review highlights technical aspects of FUS-mediated gene therapies for the central nervous system (CNS) and lessons learned from discoveries in other organs. Understanding the possibilities and remaining obstacles of FUS-mediated gene therapy will be necessary to harness remarkable technologies and create life-changing treatments for neurological disorders.

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.

Development of a Gene and Nucleic Acid Delivery System for Skeletal Muscle Administration via Limb Perfusion Using Nanobubbles and Ultrasound

Strategies for gene and nucleic acid delivery to skeletal muscles have been extensively explored to treat Duchenne muscular dystrophy (DMD) and other neuromuscular diseases. Of these, effective intravascular delivery of naked plasmid DNA (pDNA) and nucleic acids into muscles is an attractive approach, given the high capillary density in close contact with myofibers. We developed lipid-based nanobubbles (NBs) using polyethylene-glycol-modified liposomes and an echo-contrast gas and found that these NBs could improve tissue permeability by ultrasound (US)-induced cavitation. Herein, we delivered naked pDNA or antisense phosphorodiamidate morpholino oligomers (PMOs) into the regional hindlimb muscle via limb perfusion using NBs and US exposure. pDNA encoding the luciferase gene was injected with NBs via limb perfusion into normal mice with application of US. High luciferase activity was achieved in a wide area of the limb muscle. DMD model mice were administered PMOs, designed to skip the mutated exon 23 of the dystrophin gene, with NBs via intravenous limb perfusion, followed by US exposure. The number of dystrophin-positive fibers increased in the muscles of mdx mice. Combining NBs and US exposure, which can be widely delivered to the hind limb muscles via the limb vein, could be an effective therapeutic approach for DMD and other neuromuscular disorders.

LB, Endo H, Itaka K, Tachibana K. Efficient mRNA Delivery with Lyophilized Human Serum Albumin-Based Nanobubbles

In this study, we developed an efficient mRNA delivery vehicle by optimizing a lyophilization method for preserving human serum albumin-based nanobubbles (HSA-NBs), bypassing the need for artificial stabilizers. The morphology of the lyophilized material was verified using scanning electron microscopy, and the concentration, size, and mass of regenerated HSA-NBs were verified using flow cytometry, nanoparticle tracking analysis, and resonance mass measurements, and compared to those before lyophilization. The study also evaluated the response of HSA-NBs to 1 MHz ultrasound irradiation and their ultrasound (US) contrast effect. The functionality of the regenerated HSA-NBs was confirmed by an increased expression of intracellularly transferred Gluc mRNA, with increasing intensity of US irradiation. The results indicated that HSA-NBs retained their structural and functional integrity markedly, post-lyophilization. These findings support the potential of lyophilized HSA-NBs, as efficient imaging, and drug delivery systems for various medical applications.

Immunomodulation and targeted drug delivery with high intensity focused ultrasound (HIFU): Principles and mechanisms

High intensity focused ultrasound (HIFU) is a non-invasive and non-ionizing sonic energy-based therapeutic technology for inducing thermal and non-thermal effects in tissues. Depending on the parameters, HIFU can ablate tissues by heating them to >55 °C to induce denaturation and coagulative necrosis, improve radio- and chemo-sensitizations and local drug delivery from nanoparticles at moderate hyperthermia (~41-43 °C), and mechanically fragment cells using acoustic cavitation (also known as histotripsy). HIFU has already emerged as an attractive modality for treating human prostate cancer, veterinary cancers, and neuromodulation. Herein, we comprehensively review the role of HIFU in enhancing drug delivery and immunotherapy in soft and calcified tissues. Specifically, the ability of HIFU to improve adjuvant treatments from various classes of drugs is described. These crucial insights highlight the opportunities and challenges of HIFU technology and its potential to support new clinical trials and translation to patients.

Influence of Nanobubble Size Distribution on Ultrasound-Mediated Plasmid DNA and Messenger RNA Gene Delivery

The use of nanobubbles (NBs) for ultrasound-mediated gene therapy has recently attracted much attention. However, few studies have evaluated the effect of different NB size distribution to the efficiency of gene delivery into cells. In this study, various size of albumin stabilized sub-micron bubbles were examined in an in vitro ultrasound (1 MHz) irradiation setup in the aim to compare and optimize gene transfer efficiency. Results with pDNA showed that gene transfer efficiency in the presence of NB size of 254.7 ± 3.8 nm was 2.5 fold greater than those with 187.3 ± 4.8 nm. Similarly, carrier-free mRNA transfer efficiency increased in the same conditions. It is suggested that NB size greater than 200 nm contributed more to the delivery of genes into the cytoplasm with ultrasound. Although further experiments are needed to understand the underlying mechanism for this phenomenon, the present results offer valuable information in optimizing of NB for future ultrasound-mediate gene therapy.

Ultrasound-induced biophysical effects in controlled drug delivery

Ultrasound is widely used in biomedical engineering and has applications in conventional diagnosis and drug delivery. Recent advances in ultrasound-induced drug delivery have been summarized previously in several reviews that have primarily focused on the fabrication of drug delivery carriers. This review discusses the mechanisms underlying ultrasound-induced drug delivery and factors affecting delivery efficiency, including the characteristics of drug delivery carriers and ultrasound parameters. Firstly, biophysical effects induced by ultrasound, namely thermal effects, cavitation effects, and acoustic radiation forces, are illustrated. Secondly, the use of these biophysical effects to enhance drug delivery by affecting drug carriers and corresponding tissues is clarified in detail. Thirdly, recent advances in ultrasound-triggered drug delivery are detailed. Safety issues and optimization strategies to improve therapeutic outcomes and reduce side effects are summarized. Finally, current progress and future directions are discussed.

A 3D finite element model to study the cavitation induced stresses on blood-vessel wall during the ultrasound-only phase of photo-mediated ultrasound therapy

Photo-mediated ultrasound therapy (PUT) is a novel technique utilizing synchronized ultrasound and laser to generate enhanced cavitation inside blood vessels. The enhanced cavitation inside blood vessels induces bio-effects, which can result in the removal of micro-vessels and the reduction in local blood perfusion. These bio-effects have the potential to treat neovascularization diseases in the eye, such as age-related macular degeneration and diabetic retinopathy. Currently, PUT is in the preclinical stage, and various PUT studies on in vivo rabbit eye models have shown successful removal of micro-vessels. PUT is completely non-invasive and particle-free as opposed to current clinical treatments such as anti-vascular endothelial growth factor therapy and photodynamic therapy, and it precisely removes micro-vessels without damaging the surrounding tissue, unlike laser photocoagulation therapy. The stresses produced by oscillating bubbles during PUT are responsible for the induced bio-effects in blood vessels. In our previous work, stresses induced during the first phase of PUT due to combined ultrasound and laser irradiation were studied using a 2D model. In this work, stresses induced during the third or last phase of PUT due to ultrasound alone were studied using a 3D finite element method-based numerical model. The results showed that the circumferential and shear stress increased as the bubble moves from the center of the vessel toward the vessel wall with more than a 16 times increase in shear stress from 1.848 to 31.060 kPa as compared to only a 4 times increase in circumferential stress from 211 to 906 kPa for a 2 µm bubble placed inside a 10 µm vessel on the application of 1 MHz ultrasound frequency and 130 kPa amplitude. In addition, the stresses decreased as the bubble was placed in smaller sized vessels with a larger decrease in circumferential stress. The changes in shear stress were found to be more dependent on the bubble-vessel wall distance, and the changes in circumferential stress were more dependent on the bubble oscillation amplitude. Moreover, the bubble shape changed to an ellipsoidal with a higher oscillation amplitude in the vessel's axial direction as it was moved closer to the vessel wall, and the bubble oscillation amplitude decreased drastically as it was placed in vessels of a smaller size.

Ultrasounds in cancer therapy: A summary of their use and unexplored potential

Ultrasounds (US) are a non-ionizing mechanical wave, with less adverse effects than conventional pharmacological or surgical treatments. Different biological effects are induced in tissues and cells by ultrasound actuation depending on acoustic parameters, such as the wave intensity, frequency and treatment dose. This non-ionizing radiation has considerable applications in biomedicine including surgery, medical imaging, physical therapy and cancer therapy. Depending on the wave intensity, US are applied as high-intensity ultrasounds (HIUS) and low-intensity pulsed ultrasounds (LIPUS), with different effects on cells and tissues. HIUS produce thermal and mechanical effects, resulting in a large localized temperature increase, leading to tissue ablation and even tumor necrosis. This can be achieved by focusing low intensity waves emitted from different electrically shifted transducers, known as high-intensity focused ultrasounds (HIFU). LIPUS have been used extensively as a therapeutic, surgical and diagnostic tool, with diverse biological effects observed in tissues and cultured cells. US represent a non-invasive treatment strategy that can be applied to selected areas of the body, with limited adverse effects. In fact, tumor ablation using HIFU has been used as a curative treatment in patients with an early-stage pancreatic tumor and is an effective palliative treatment in patients with advanced stage disease. However, the biological effects, dose standardization, benefit-risk ratio and safety are not fully understood. Thus, it is an emerging field that requires further research in order to reach its full potential.

The cellular response to plasma membrane disruption for nanomaterial delivery

Delivery of nanomaterials into cells is of interest for fundamental cell biological research as well as for therapeutic and diagnostic purposes. One way of doing so is by physically disrupting the plasma membrane (PM). Several methods that exploit electrical, mechanical or optical cues have been conceived to temporarily disrupt the PM for intracellular delivery, with variable effects on cell viability. However, apart from acute cytotoxicity, subtler effects on cell physiology may occur as well. Their nature and timing vary with the severity of the insult and the efficiency of repair, but some may provoke permanent phenotypic alterations. With the growing palette of nanoscale delivery methods and applications, comes a need for an in-depth understanding of this cellular response. In this review, we summarize current knowledge about the chronology of cellular events that take place upon PM injury inflicted by different delivery methods. We also elaborate on their significance for cell homeostasis and cell fate. Based on the crucial nodes that govern cell fitness and functionality, we give directions for fine-tuning nano-delivery conditions.

Microfluidic and Nanofluidic Intracellular Delivery

Innate cell function can be artificially engineered and reprogrammed by introducing biomolecules, such as DNAs, RNAs, plasmid DNAs, proteins, or nanomaterials, into the cytosol or nucleus. This process of delivering exogenous cargos into living cells is referred to as intracellular delivery. For instance, clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 gene editing begins with internalizing Cas9 protein and guide RNA into cells, and chimeric antigen receptor-T (CAR-T) cells are prepared by delivering CAR genes into T lymphocytes for cancer immunotherapies. To deliver external biomolecules into cells, tools, including viral vectors, and electroporation have been traditionally used; however, they are suboptimal for achieving high levels of intracellular delivery while preserving cell viability, phenotype, and function. Notably, as emerging solutions, microfluidic and nanofluidic approaches have shown remarkable potential for addressing this open challenge. This review provides an overview of recent advances in microfluidic and nanofluidic intracellular delivery strategies and discusses new opportunities and challenges for clinical applications. Furthermore, key considerations for future efforts to develop microfluidics- and nanofluidics-enabled next-generation intracellular delivery platforms are outlined.

Ultrasound image-guided gene delivery using three-dimensional diagnostic ultrasound and lipid-based microbubbles

Gene therapy is a promising technology for genetic and intractable diseases. Drug delivery carriers or systems for genes and nucleic acids have been studied to improve transfection efficiency and achieve sufficient therapeutic effects. Ultrasound (US) and microbubbles have also been combined for use in gene delivery. To establish a clinically effective gene delivery system, exposing the target tissues to US is important. The three-dimensional (3D) diagnostic probe can three-dimensionally scan the tissue with mechanical regulation, and homogenous US exposure to the targeted tissue can be expected. However, the feasibility of therapeutically applying 3D probes has not been evaluated, especially gene delivery. In this study, we evaluated the characteristics of a 3D probe and lipid-based microbubbles (LB) for gene delivery and determined whether the 3D probe in the diagnostic US device could be used for efficient gene delivery to the targeted tissue using a mouse model. The 3D probe RSP6-16 with LB delivered plasmid DNA (pDNA) to the kidney after systemic injection with luciferase activity similar to that of probes used in previously studies. No toxicity was observed after treatment and, therefore, the combined 3D probe and LB would deliver genes to targeted tissue safely and efficiently.

A Comprehensive Review on Intracellular Delivery

Intracellular delivery is considered an indispensable process for various studies, ranging from medical applications (cell-based therapy) to fundamental (genome-editing) and industrial (biomanufacture) approaches. Conventional macroscale delivery systems critically suffer from such issues as low cell viability, cytotoxicity, and inconsistent material delivery, which have opened up an interest in the development of more efficient intracellular delivery systems. In line with the advances in microfluidics and nanotechnology, intracellular delivery based on micro- and nanoengineered platforms has progressed rapidly and held great promises owing to their unique features. These approaches have been advanced to introduce a smorgasbord of diverse cargoes into various cell types with the maximum efficiency and the highest precision. This review differentiates macro-, micro-, and nanoengineered approaches for intracellular delivery. The macroengineered delivery platforms are first summarized and then each method is categorized based on whether it employs a carrier- or membrane-disruption-mediated mechanism to load cargoes inside the cells. Second, particular emphasis is placed on the micro- and nanoengineered advances in the delivery of biomolecules inside the cells. Furthermore, the applications and challenges of the established and emerging delivery approaches are summarized. The topic is concluded by evaluating the future perspective of intracellular delivery toward the micro- and nanoengineered approaches.

Therapeutic ultrasound experiments in vitro: Review of factors influencing outcomes and reproducibility

Current in vitro sonication experiments show immense variability in experimental set-ups and methods used. As a result, there is uncertainty in the ultrasound field parameters experienced by sonicated samples, poor reproducibility of these experiments and thus reduced scientific value of the results obtained. The scope of this narrative review is to briefly describe mechanisms of action of ultrasound, list the most frequently used experimental set-ups and focus on a description of factors influencing the outcomes and reproducibility of these experiments. The factors assessed include: proper reporting of ultrasound exposure parameters, experimental geometry, coupling medium quality, influence of culture vessels, formation of standing waves, motion/rotation of the sonicated sample and the characteristics of the sample itself. In the discussion we describe pros and cons of particular exposure geometries and factors, and make a few recommendations as to how to increase the reproducibility and validity of the experiments performed.

Sonoporation as an Approach for siRNA delivery into T cells

Delivery of small interfering RNAs (siRNAs) into primary T cells is quite challenging because they are non-proliferating cells and are difficult to transfect with non-viral approaches. Because sonoporation is independent of the proliferation status of cells and siRNA acts in the cell cytoplasm, we investigated whether sonoporation could be used to deliver siRNA into mouse and human T cells. Cells mixed with Definity microbubbles and siRNA were sonicated with a non-focused transducer of center frequency 2.20 MHz producing ultrasound at a 10% duty cycle, pulse repetition frequency of 2.20 kHz and spatial average temporal average ultrasound intensity of 1.29 W/cm² for 5 s and then examined for siRNA fluorescence by flow cytometry analysis. These sonoporation conditions resulted in high-efficiency transfection of siRNA in mouse and human T cells. Further, the efficacy of siRNA delivery by sonoporation was illustrated by the successful visualization of decreased methylation-controlled J protein expression in mouse and human CD8 T cells via Western blot analysis. The results provide the first evidence that sonoporation is a novel approach to delivery of siRNA into fresh isolated mouse and human T cells in vitro, and might be used for in vivo studies in the future.

Enhanced Proliferation of Endothelial Progenitor Cells Post-Ultrasonic Microbubble Transfection Is Plasmid DNA Size Dependent and Contributed by Interleukin-6 Generation

We investigated whether ultrasonic microbubble transfection (UMT) would enhance the transfection of large-sized luciferase plasmids (5.6, 9.2 and 33 kb) and biological impacts. Porcine venous blood endothelial progenitor cells (EPCs) were cultured in a medium containing plasmid DNA (pDNA) of different sizes followed by UMT and functional assays. Real-time polymerase chain reaction was conducted to investigate the effects of transfection of pDNA on multiple molecules central to endothelial function. The results indicated enhanced luciferase expression after UMT but the enhancement declined with increase in the size of the plasmid. UMT of pDNAs sized 5.6 and 9.2 kb into EPCs led to significant enhancement of proliferation. The interleukin-6 (IL-6) secreted from UMT of EPCs also increased in the 5.6- and 9.2-kb pDNA groups. Treatment of the transfected EPCs with anti-IL-6 antibody neutralized the proliferation. In conclusion, UMT of pDNAs sized 5.6 and 9.2 kb into EPCs increased the secretion of IL-6, which in turn enhanced cell proliferation.

Advanced nanostructures for cell membrane poration

Nanostructured devices are able to foster the technology for cell membrane poration. With the size smaller than a cell, nanostructures allow efficient poration on the cell membrane. Emerging nanostructures with various physical transduction have been demonstrated to accommodate effective intracellular delivery. Aside from improving poration and intracellular delivery performance, nanostructured devices also allow for the discovery of novel physiochemical phenomena and the biological response of the cell. This article provides a brief introduction to the principles of nanostructured devices for cell poration and outlines the intracellular delivery capability of the technology. In the future, we envision more exploration on new nanostructure designs and creative applications in biomedical fields.

Exon Skipping by Ultrasound-Enhanced Delivery of Morpholino with Bubble Liposomes for Myotonic Dystrophy Model Mice

Abnormal splicing of the chloride channel 1 (CLCN1) gene causes myotonic dystrophy type 1 (DM1). Therefore, controlling the alternative splicing process of this gene by antisense oligonucleotides can be a promising treatment for DM1. In this study, we describe an efficient phosphorodiamidate morpholino oligomer (PMO) delivery method by ultrasound-mediated bubble liposomes, which is a known gene delivery tool with ultrasound exposure, to treat skeletal muscles in a DM1 mouse model, HSA^LR. Effective delivery of PMO using this technique can help control the alternative splicing of the Clcn1 gene via exon skipping and enhance the expression of Clcn1 protein in skeletal muscles and the amelioration of myotonia. Thus, exon skipping by PMO delivery with ultrasound-mediated BLs may be feasible in myotonic dystrophy model mice.

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Ultrasound-mediated nanobubble destruction (UMND) facilitates the delivery of A10-3.2 aptamer targeted and siRNA-loaded cationic nanobubbles for therapy of prostate cancer

The Forkhead box M1 (FoxM1) transcription factor is an important anti-tumor target. A novel targeted ultrasound (US)-sensitive nanobubble that is likely to make use of the physical energy of US exposure for the improvement of delivery efficacy to target tumors and specifically silence FoxM1 expression appears as among the most potential nanocarriers in respect of drug delivery. In this study, we synthesized a promising anti-tumor targeted FoxM1 siRNA-loaded cationic nanobubbles (CNBs) conjugated with an A10-3.2 aptamer (siFoxM1-Apt-CNBs), which demonstrate high specificity when binding to prostate-specific membrane antigen (PSMA) positive LNCaP cells. Uniform nanoscaled siFoxM1-Apt-CNBs were developed using a thin-film hydration sonication, carbodiimide chemistry approaches, and electrostatic adsorption methods. Fluorescence imaging as well as flow cytometry evidenced the fact that the siFoxM1-Apt-CNBs were productively developed and that they specifically bound to PSMA-positive LNCaP cells. siFoxM1-Apt-CNBs combined with ultrasound-mediated nanobubble destruction (UMND) significantly improved transfection efficiency, cell apoptosis, and cell cycle arrest in vitro while reducing FoxM1 expression. In vivo xenografts tumors in nude-mouse model results showed that siFoxM1-Apt-CNBs combined with UMND led to significant inhibition of tumor growth and prolonged the survival of the mice, with low toxicity, an obvious reduction in FoxM1 expression, and a higher apoptosis index. Our study suggests that siFoxM1-Apt-CNBs combined with UMND might be a promising targeted gene delivery strategy for therapy of prostate cancer.

Advances in mechanism studies on ultrasonic gene delivery at cellular level

Ultrasound provides a means for intracellular gene delivery, contributing to a noninvasive and spatiotemporally controllable strategy suitable for clinical applications. Many studies have been done to provide mechanisms of ultrasound-mediated gene delivery at the cellular level. This review summarizes the studies on the important aspects of the mechanisms, providing an overview of recent progress in cellular experiment of ultrasound-mediated gene delivery.

PMO Delivery System Using Bubble Liposomes and Ultrasound Exposure for Duchenne Muscular Dystrophy Treatment

Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by progressive muscle degeneration, caused by nonsense or frameshift mutations in the dystrophin (DMD) gene. Antisense oligonucleotides can be used to induce specific exon skipping; recently, a phosphorodiamidate morpholino oligomer (PMO) has been approved for clinical use in DMD. However, an efficient PMO delivery strategy is required to improve the therapeutic efficacy in DMD patients. We previously developed polyethylene glycol (PEG)-modified liposomes containing ultrasound contrast gas, "Bubble liposomes" (BLs), and found that the combination of BLs with ultrasound exposure is a useful gene delivery tool. Here, we describe an efficient PMO delivery strategy using the combination of BLs and ultrasound exposure to treat muscles in a DMD mouse model (mdx). This ultrasound-mediated BL technique can increase the PMO-mediated exon-skipping efficiency, leading to significantly increased dystrophin expression. Thus, the combination of BLs and ultrasound exposure may be a feasible PMO delivery method to improve therapeutic efficacy and reduce the PMO dosage for DMD treatment.

The synergistic bactericidal effect of vancomycin on UTMD treated biofilm involves damage to bacterial cells and enhancement of metabolic activities

In this study, the synergistic effect of vancomycin, a cell wall synthesis inhibitor, and ultrasound-targeted microbubble destruction (UTMD), on cell viability of Staphylococcus epidermidis, embedded in biofilm, was investigated. Biofilms are the leading causes of antibiotic-resistant bacterial infections of medical implants and prosthetics worldwide. The antibiotic-resistant nature of biofilm-embedded pathogens poses a critical challenge to the medical community. Previously, studies have demonstrated the efficacy of using ultrasound waves and UTMD in circumventing this problem. However, the mechanism(s) underlying this phenomenon was not clear. Here, the present study showed that both ultrasound and UTMD damaged the cell wall structure of S. epidermidis, and floccules and fragments from damaged cells were observed on transmission electron microscope micrograph. However, the cell membrane integrity was not seriously affected by treatments, and the treatment increased the metabolic activity levels of the dormant biofilm-embedded bacteria, detected by confocal laser scanning microscope and flow cytometry, which could make them susceptible to the effect of the antibiotic. Thus, the biological mechanism underlying the efficacy of the combined treatment involving UTMD and vancomycin in the case of S. epidermidis biofilm was dissected, which may be utilized for further investigations on other biofilm pathogens before clinical use.

High-Speed In Situ Observation System for Sonoporation of Cells With Size- and Position-Controlled Microbubbles

A high-speed in situ microscopic observation system developed for basic studies on mechanisms of sonoporation is introduced in this paper. The main part of the system is an inverted-type fluorescence microscope, and a high-speed camera of 20 MHz in a maximum framing rate was used to visualize the dynamics of cavitation bubbles that causes a sonoporation effect. Differential interference contrast and fluorescence techniques were used for sensitive visualization of cell changes during sonoporation. The system is also equipped with optical tweezers that can move a microbubble of several microns in size by using a donut-shaped light beam. In situ microscopic observation of sonoporation was carried out using a cell with a size- and position-controlled microbubble. The experimental results showed that the ability of cells to repair sonoporation-induced damage depends on their membrane tension, indicating the usefulness of the observation system as a basic tool for the investigation of sonoporation phenomena.

Characterisation of Liposome-Loaded Microbubble Populations for Subharmonic Imaging

Therapeutic microbubbles could make an important contribution to the diagnosis and treatment of cancer. Acoustic characterisation was performed on microfluidic generated microbubble populations that either were bare or had liposomes attached. Through the use of broadband attenuation techniques (3-8 MHz), the shell stiffness was measured to be 0.72 ± 0.01 and 0.78 ± 0.05 N/m and shell friction was 0.37 ± 0.05 and 0.74 ± 0.05 × 10^-6 kg/s for bare and liposome-loaded microbubbles, respectively. Acoustic scatter revealed that liposome-loaded microbubbles had a lower subharmonic threshold, occurring from a peak negative pressure of 50 kPa, compared with 200 kPa for equivalent bare microbubbles. It was found that liposome loading had a negligible effect on the destruction threshold for this microbubble type, because at a mechanical index >0.4 (570 kPa), 80% of both populations were destroyed.

Localized Delivery of shRNA against PHD2 Protects the Heart from Acute Myocardial Infarction through Ultrasound-Targeted Cationic Microbubble Destruction

Hypoxia-inducible factor 1α (HIF-1α) plays a critical protective role in ischemic heart disease. Under normoxic conditions, HIF-1α was degraded by oxygen-dependent prolyl hydroxylase-2 (PHD2). Gene therapy has become a promising strategy to inhibit the degradation of HIF-1α and to improve cardiac function after ischemic injury. However, conventional gene delivery systems are difficult to achieve a targeted and localized gene delivery into the ischemic myocardia. Here, we report the localized myocardial delivery of shRNA against PHD2 through ultrasound-targeted microbubble destruction (UTMD) for protection the heart from acute myocardial infarction. In this study, a novel cationic microbubble was fabricated by using of the thin-film hydration and sonication method. The resulting microbubbles had a 28.2 ± 2.21 mV surface zeta potential and could greatly improve DNA binding performance, achieving 17.81 ± 1.46 μg of DNA loading capacity per 5 × 10⁸ microbubbles. Combined with these cationic microbubbles, UTMD-mediated gene delivery was evaluated and the gene transfection efficiency was optimized in the H9C2 cardiac cells. Knockdown of PHD2 gene was successfully realized by UTMD-mediated shPHD2 transfection, resulting in HIF-1α-dependent protective effects on H9C2 cells through increasing the expression of HIF-1α, VEGF and bFGF. We further employed UTMD-mediated shPHD2 transfection into the localized ischemic myocardia in a rat ischemia model, demonstrating significantly reduced infarct size and greatly improved the heart function. The silencing of PHD2 and the up-regulation of its downstream genes in the treated myocardia were confirmed. Histological analysis further revealed numbers of HIF-1α- and VEGF-, and CD31-positive cells/mm² in the shPHD2-treated group were significantly greater than those in the sham or control vector groups (P < 0.05). In conclusion, our study provides a promising strategy to realize ultrasound-mediated localized myocardial shRNA delivery to protect the heart from acute myocardial infarction via cationic microbubbles.

Enhancement and Passive Acoustic Mapping of Cavitation from Fluorescently Tagged Magnetic Resonance-Visible Magnetic Microbubbles In Vivo

Previous work has indicated the potential of magnetically functionalized microbubbles to localize and enhance cavitation activity under focused ultrasound exposure in vitro. The aim of this study was to investigate magnetic targeting of microbubbles for promotion of cavitation in vivo. Fluorescently labelled magnetic microbubbles were administered intravenously in a murine xenograft model. Cavitation was induced using a 0.5-MHz focused ultrasound transducer at peak negative focal pressures of 1.2-2.0 MPa and monitored in real-time using B-mode imaging and passive acoustic mapping. Magnetic targeting was found to increase the amplitude of the cavitation signal by approximately 50% compared with untargeted bubbles. Post-exposure magnetic resonance imaging indicated deposition of magnetic nanoparticles in tumours. Magnetic targeting was similarly associated with increased fluorescence intensity in the tumours after the experiments. These results suggest that magnetic targeting could potentially be used to improve delivery of cavitation-mediated therapy and that passive acoustic mapping could be used for real-time monitoring of this process.

Non-Viral Nucleic Acid Delivery Strategies to the Central Nervous System

With an increased prevalence and understanding of central nervous system (CNS) injuries and neurological disorders, nucleic acid therapies are gaining promise as a way to regenerate lost neurons or halt disease progression. While more viral vectors have been used clinically as tools for gene delivery, non-viral vectors are gaining interest due to lower safety concerns and the ability to deliver all types of nucleic acids. Nevertheless, there are still a number of barriers to nucleic acid delivery. In this focused review, we explore the in vivo challenges hindering non-viral nucleic acid delivery to the CNS and the strategies and vehicles used to overcome them. Advantages and disadvantages of different routes of administration including: systemic injection, cerebrospinal fluid injection, intraparenchymal injection and peripheral administration are discussed. Non-viral vehicles and treatment strategies that have overcome delivery barriers and demonstrated in vivo gene transfer to the CNS are presented. These approaches can be used as guidelines in developing synthetic gene delivery vectors for CNS applications and will ultimately bring non-viral vectors closer to clinical application.

Gene delivery systems by the combination of lipid bubbles and ultrasound

Gene therapy is promising for the treatment of many diseases including cancers and genetic diseases. From the viewpoint of safety, ultrasound (US)-mediated gene delivery with nano/ microbubbles was recently developed as a novel non-viral vector system. US-mediated gene delivery using nano/microbubbles are able to produce transient changes in the permeability of the cell membrane after US-induced cavitation while reducing cellular damage and enables the tissue-specific or the site-specific intracellular delivery of gene both in vitro and in vivo. We have recently developed novel lipid nanobubbles (Lipid Bubbles). These nanobubbles can also be used to enhance the efficacy of the US-mediated genes (plasmid DNA, siRNA, and miRNA etc.) delivery. In this review, we describe US-mediated delivery systems combined with nano/microbubbles and discuss their feasibility as non-viral vector systems.

Image-guided ultrasound phased arrays are a disruptive technology for non-invasive therapy

Focused ultrasound offers a non-invasive way of depositing acoustic energy deep into the body, which can be harnessed for a broad spectrum of therapeutic purposes, including tissue ablation, the targeting of therapeutic agents, and stem cell delivery. Phased array transducers enable electronic control over the beam geometry and direction, and can be tailored to provide optimal energy deposition patterns for a given therapeutic application. Their use in combination with modern medical imaging for therapy guidance allows precise targeting, online monitoring, and post-treatment evaluation of the ultrasound-mediated bioeffects. In the past there have been some technical obstacles hindering the construction of large aperture, high-power, densely-populated phased arrays and, as a result, they have not been fully exploited for therapy delivery to date. However, recent research has made the construction of such arrays feasible, and it is expected that their continued development will both greatly improve the safety and efficacy of existing ultrasound therapies as well as enable treatments that are not currently possible with existing technology. This review will summarize the basic principles, current statures, and future potential of image-guided ultrasound phased arrays for therapy.

Ultrasound-mediated gene delivery systems by AG73-modified Bubble liposomes

Targeted gene delivery to neovascular vessels in tumors is considered a promising strategy for cancer therapy. We previously reported that "Bubble liposomes" (BLs), which are ultrasound (US) imaging gas-encapsulating liposomes, were suitable for US imaging and gene delivery. When BLs are exposed to US, the bubble is destroyed, creating a jet stream by cavitation, and resulting in the instantaneous ejection of extracellular plasmid DNA (pDNA) or other nucleic acids into the cytosol. We developed AG73 peptide-modified Bubble liposomes (AG73-BL) as a targeted US contrast agent, which was designed to attach to neovascular tumor vessels and to allow specific US detection of angiogenesis (Negishi et al., Biomaterials 2013, 34, 501-507). In this study, to evaluate the effectiveness of AG73-BL as a gene delivery tool for neovascular vessels, we examined the gene transfection efficiency of AG73-BL with US exposure in primary human endothelial cells (HUVEC). The transfection efficiency was significantly enhanced if the AG73-BL attached to the HUVEC was exposed to US compared to the BL-modified with no peptide or scrambled peptide. In addition, the cell viability was greater than 80% after transfection with AG73-BL. These results suggested that after the destruction of the AG73-BL with US exposure, a cavitation could be effectively induced by the US exposure against AG73-BL binding to the cell surface of the HUVEC, and the subsequent gene delivery into cells could be enhanced. Thus, AG73-BL may be useful for gene delivery as well as for US imaging of neovascular vessels.

Inhibitory effects of shRNA on expression of JNK1 and migration and invasion in mouse hepatocellular carcinoma cell lines mediated by ultrasound-targeted microbubble destruction

AIM

The inhibitory effects on expression of JNK1 in mouse hepatocellular carcinoma cell lines and cell migration and invasion were mediated by ultrasound-targeted microbubble destruction (UTMD).

MATERIALS AND METHODS

The best shRNA vector was built and screened. The hepatocellular carcinoma cell lines were cultured in vitro and divided into five groups: the group of normal Hca-F cells, the group of shRNA plasmid (already selected from the above procedure), the group of Lipofectamine, the group of UTMD (ultrasound microbubbles combined with ultrasound exposure) and the group of Lipofectamine and UTMD. The transfection rate was observed by inverted fluorescence microscope. The expression levels of JNK1 mRNA and protein were evaluated by fluorescence quantitative PCR and Western Blot respectively. The cell proliferation was detected by CCK-8. The ability of migration and invasion in vitro was detected by transwell assay.

RESULTS

The best shRNA vector was established. The comparison of the transfection rate: The group of Lipofectamine and UTMD was larger than that of the groups of shRNA plasmid, Lipofectamine lipofection and UTMD (all P<0.05). There was no significant difference between the group of Lipofectamine and the group of UTMD (P>0.05). The comparison of the expression levels of JNK1 mRNA and protein: Both of the mRNA and protein expression levels were lowest in the group of Lipofectamine and UTMD (all P<0.05). CCK-8 showed that cell viability decreased most in the group of Lipofectamine and UTMD (all P<0.05); Transwell assay showed that the abilities of migration and invasion decreased most in the group of Lipofectamine and UTMD (all P<0.05).

CONCLUSION

The transfection rate of JNK1 shRNA can be improved through the combination of lipofection and UTMD in mouse hepatocellular carcinoma cell lines, therefore enhancing the inhibitory effects of gene expression. The inhibitory effects of cell proliferation, migration and invasion can also be enhanced.

Microbubbles and ultrasound increase intraventricular polyplex gene transfer to the brain

Neurons in the brain can be damaged or lost from neurodegenerative disease, stroke, or traumatic injury. Although neurogenesis occurs in mammalian adult brains, the levels of natural neurogenesis are insufficient to restore function in these cases. Gene therapy has been pursued as a promising strategy to induce differentiation of neural progenitor cells into functional neurons. Non-viral vectors are a preferred method of gene transfer due to potential safety and manufacturing benefits but suffer from lower delivery efficiencies compared to viral vectors. Since the neural stem and progenitor cells reside in the subventricular zone of the brain, intraventricular injection has been used as an administration route for gene transfer to these cells. However, the choroid plexus epithelium remains an obstacle to delivery. Recently, transient disruption of the blood-brain barrier by microbubble-enhanced ultrasound has been used to successfully improve drug delivery to the brain after intravenous injection. In this work, we demonstrate that microbubble-enhanced ultrasound can similarly improve gene transfer to the subventricular zone after intraventricular injection. Microbubbles of different surface charges (neutral, slightly cationic, and cationic) were prepared, characterized by acoustic flow cytometry, and evaluated for their ability to increase the permeability of immortalized choroid plexus epithelium monolayers in vitro. Based on these results, slightly cationic microbubbles were evaluated for microbubble and ultrasound-mediated enhancement of non-viral gene transfer in vivo. When coupled with our previously reported gene delivery vehicles, the slightly cationic microbubbles significantly increased ultrasound-mediated transfection of the murine brain when compared to commercially available Definity® microbubbles. Temporary disruption of the choroid plexus by microbubble-enhanced ultrasound is therefore a viable way of enhancing gene delivery to the brain and merits further research.

Direct and sustained intracellular delivery of exogenous molecules using acoustic-transfection with high frequency ultrasound

Controlling cell functions for research and therapeutic purposes may open new strategies for the treatment of many diseases. An efficient and safe introduction of membrane impermeable molecules into target cells will provide versatile means to modulate cell fate. We introduce a new transfection technique that utilizes high frequency ultrasound without any contrast agents such as microbubbles, bringing a single-cell level targeting and size-dependent intracellular delivery of macromolecules. The transfection apparatus consists of an ultrasonic transducer with the center frequency of over 150 MHz and an epi-fluorescence microscope, entitled acoustic-transfection system. Acoustic pulses, emitted from an ultrasonic transducer, perturb the lipid bilayer of the cell membrane of a targeted single-cell to induce intracellular delivery of exogenous molecules. Simultaneous live cell imaging using HeLa cells to investigate the intracellular concentration of Ca²⁺ and propidium iodide (PI) and the delivery of 3 kDa dextran labeled with Alexa 488 were demonstrated. Cytosolic delivery of 3 kDa dextran induced via acoustic-transfection was manifested by diffused fluorescence throughout whole cells. Short-term (6 hr) cell viability test and long-term (40 hr) cell tracking confirmed that the proposed approach has low cell cytotoxicity.

Reparable Cell Sonoporation in Suspension: Theranostic Potential of Microbubble

The conjunction of low intensity ultrasound and encapsulated microbubbles can alter the permeability of cell membrane, offering a promising theranostic technique for non-invasive gene/drug delivery. Despite its great potential, the biophysical mechanisms of the delivery at the cellular level remains poorly understood. Here, the first direct high-speed micro-photographic images of human lymphoma cell and microbubble interaction dynamics are provided in a completely free suspension environment without any boundary parameter defect. Our real-time images and theoretical analyses prove that the negative divergence side of the microbubble's dipole microstreaming locally pulls the cell membrane, causing transient local protrusion of 2.5 µm in the cell membrane. The linear oscillation of microbubble caused microstreaming well below the inertial cavitation threshold, and imposed 35.3 Pa shear stress on the membrane, promoting an area strain of 0.12%, less than the membrane critical areal strain to cause cell rupture. Positive transfected cells with pEGFP-N1 confirm that the interaction causes membrane poration without cell disruption. The results show that the overstretched cell membrane causes reparable submicron pore formation, providing primary evidence of low amplitude (0.12 MPa at 0.834 MHz) ultrasound sonoporation mechanism.

Sonothrombolysis

Thrombo-occlusive disease is a leading cause of morbidity and mortality. In this chapter, the use of ultrasound to accelerate clot breakdown alone or in combination with thrombolytic drugs will be reported. Primary thrombus formation during cardiovascular disease and standard treatment methods will be discussed. Mechanisms for ultrasound enhancement of thrombolysis, including thermal heating, radiation force, and cavitation, will be reviewed. Finally, in-vitro, in-vivo and clinical evidence of enhanced thrombolytic efficacy with ultrasound will be presented and discussed.

Co-administration of Microbubbles and Drugs in Ultrasound-Assisted Drug Delivery: Comparison with Drug-Carrying Particles

There are two alternative approaches to ultrasound-assisted drug delivery. First, the drug can be entrapped into or attached onto the ultrasound-responsive particles and administered in the vasculature, to achieve ultrasound-triggered drug release from the particles and localized tissue deposition in response to ultrasound treatment of the target zone. Second, the drug can be co-administered with the microbubbles or other sonosensitive particles. In this case, the action of ultrasound on the particles (which act as cavitation nuclei) results in the transient improvement of permeability of the physiological barriers, so that the circulating drug can exit the bloodstream and get into the target tissues and cells. We discuss and compare both of these approaches, their characteristic advantages and disadvantages for the specific drug delivery scenarios. Clearly, the system based on the off-label use of the existing approved microbubbles and drugs (or drug carriers) will have a chance of getting to clinical trials faster and with lesser resources spent. However, if a superior curative potential of a sonosensitive drug carrier is proven, and formulation stability problems are addressed properly, this approach may find its way to practical use, especially for nucleic acid delivery scenarios.

Ultrasound triggered drug delivery with liposomal nested microbubbles

When ultrasound contrast agent microbubbles are nested within a liposome, damage to the liposome membrane caused by both stable and inertial cavitation of the microbubble allows for release of the aqueous core of the liposome. Triggered release was not accomplished unless microbubbles were present within the liposome. Leakage was tested using fluorescence assays developed specifically for this drug delivery vehicle and qualitative measurements using an optical microscope. These studies were done using a 1 MHz focused ultrasound transducer while varying parameters including peak negative ultrasound pressure, average liposome diameter, and microbubble concentration. Two regimes exist for membrane disruption caused by cavitating microbubbles. A faster release rate, as well as permanent membrane damage are seen for samples exposed to high pressure (2.1-3.7 MPa). A slower release rate and dilation/temporary poration are characteristic of stable cavitation for low pressure studies (0.54-1.7 MPa).

Enhancement of Blood-Brain Barrier Permeability and Delivery of Antisense Oligonucleotides or Plasmid DNA to the Brain by the Combination of Bubble Liposomes and High-Intensity Focused Ultrasound

The blood–brain barrier (BBB) is a major obstacle that prevents therapeutic drugs or genes from being delivered to the central nervous system. Therefore, it is important to develop methods to enhance the permeability of the BBB. We have developed echo-contrast gas (C₃F₈) entrapping liposomes (Bubble liposomes, BLs) that can work as a gene delivery tool in combination with ultrasound (US) exposure. Here, we studied whether the permeability of the BBB can be enhanced by the combination of BLs and high-intensity focused ultrasound (HIFU). Mice were intravenously injected with Evans blue (EB). BLs were subsequently injected, and the right hemispheres were exposed to HIFU. As a result, the accumulation of EB in the HIFU-exposed brain hemispheres was increased over that observed in the non-HIFU-exposed hemispheres, depending on the intensity and the duration of the HIFU. Similarly, the combination of BLs and HIFU allowed fluorescent-labeled antisense oligonucleotides to be delivered into the HIFU-exposed left hemispheres of the treated mice. Furthermore, a firefly luciferase-expressing plasmid DNA was delivered to the brain by the combination method of BLs and HIFU, which resulted in the increased gene expression in the brain at the focused-US exposure site. These results suggest that the method of combining BLs and HIFU together serves as a useful means for accelerating the permeability of BBB and thereby enabling antisense oligonucleotides or genes to be delivered to the focused brain site.

Targeted antiangiogenesis gene therapy using targeted cationic microbubbles conjugated with CD105 antibody compared with untargeted cationic and neutral microbubbles

Objective This study aimed to develop targeted cationic microbubbles conjugated with a CD105 antibody (CMB105) for use in targeted vascular endothelial cell gene therapy and ultrasound imaging. We compared the results with untargeted cationic microbubbles (CMB) and neutral microbubbles (NMB).

Methods CMB105 were prepared and compared with untargeted CMB and NMB. First, the microbubbles were characterized in terms of size, zeta-potential, antibody binding ability and plasmid DNA loading capacity. A tumor model of subcutaneous breast cancer in nude mice was used for our experiments. The ability of different types of microbubbles to target HUVECs in vitro and tumor neovascularization in vivo was measured. The endostatin gene was selected for its outstanding antiangiogenesis effect. For in vitro experiments, the transfection efficiency and cell cycle were analyzed using flow cytometry, and the transcription and expression of endostatin were measured by qPCR and Western blotting, respectively. Vascular tube cavity formation and tumor cell invasion were used to evaluate the antiangiogenesis gene therapy efficiency in vitro. Tumors were exposed to ultrasound irradiation with different types of microbubbles, and the gene therapy effects were investigated by detecting apoptosis induction and changes in tumor volume.

Results CMB105 and CMB differed significantly from NMB in terms of zeta-potential, and the DNA loading capacities were 16.76±1.75 μg, 18.21±1.22 μg, and 0.48±0.04 μg per 5×10⁸ microbubbles, respectively. The charge coupling of plasmid DNA to CMB105 was not affected by the presence of the CD105 antibody. Both CMB105 and CMB could target to HUVECs in vitro, whereas only CMB105 could target to tumor neovascularization in vivo. In in vitro experiments, the transfection efficiency of CMB105 was 24.7-fold higher than the transfection efficiency of NMB and 1.47-fold higher than the transfection efficiency of CMB (P<0.05). With ultrasound-targeted microbubble destruction (UTMD)-mediated gene therapy, the transcription and expression of endostatin were the highest in the CMB105 group (P<0.001); the antiangiogenesis effect and inhibition of tumor cells invasion was better with CMB105 than CMB or NMB in vitro (P<0.01). After gene therapy, the tumor volumes of CMB105 group were significantly smaller than that of CMB and NMB, and many tumor cells had begun apoptosis in the CMB105 group, which had the highest apoptosis index (P<0.001).

Conclusions As a contrast agent and plasmid carrier, CMB105 can be used not only for targeted ultrasound imaging but also for targeted gene therapy both in vitro and in vivo. The plasmid DNA binding ability of the CMB was not affected by conjugation of the CMB with the CD105 antibody, and because of its targeting ability, the gene transfection efficiency and therapeutic effect were better compared with the untargeted CMB and NMB. The advantages of targeted gene therapy with CMB105 in vivo were more prominent than with CMB or NMB because neither can target the endothelia in vivo.

Enhancing acoustic cavitation using artificial crevice bubbles

We study the response of pre-defined cavitation nuclei driven continuously in the kHz regime (80, 100 and 200 kHz). The nuclei consist of stabilized gaspockets in cylindrical pits of 30 μm diameter etched in silicon or glass substrates. It is found that above an acoustic pressure threshold the dynamics of the liquid-gas meniscus switches from a stable drum-like vibration to expansion and deformation, frequently resulting in detachment of microbubbles. Just above this threshold small bubbles are continuously and intermittently ejected. At elevated input powers bubble detachment becomes more frequent and cavitation bubble clouds are formed and remain in the vicinity of the pit bubble. Surprisingly, the resulting loss of gas does not lead to deactivation of the pit which can be explained by a rectified gas diffusion process.

Bi-modal cancer treatment utilizing therapeutic ultrasound and an engineered therapeutic nanobubble

We developed a bi-modal cancer therapy comprising a sorafenib loaded ultra-sonic responsive nanobubble (SRF-NB) for ultrasonic assisted delivery in hepatocellular carcinoma.

Physical methods for gene transfer

The key impediment to the successful application of gene therapy in clinics is not the paucity of therapeutic genes. It is rather the lack of nontoxic and efficient strategies to transfer therapeutic genes into target cells. Over the past few decades, considerable progress has been made in gene transfer technologies, and thus far, three different delivery systems have been developed with merits and demerits characterizing each system. Viral and chemical methods of gene transfer utilize specialized carrier to overcome membrane barrier and facilitate gene transfer into cells. Physical methods, on the other hand, utilize various forms of mechanical forces to enforce gene entry into cells. Starting in 1980s, physical methods have been introduced as alternatives to viral and chemical methods to overcome various extra- and intracellular barriers that limit the amount of DNA reaching the intended cells. Accumulating evidence suggests that it is quite feasible to directly translocate genes into cytoplasm or even nuclei of target cells by means of mechanical force, bypassing endocytosis, a common pathway for viral and nonviral vectors. Indeed, several methods have been developed, and the majority of them share the same underlying mechanism of gene transfer, i.e., physically created transient pores in cell membrane through which genes get into cells. Here, we provide an overview of the current status and future research directions in the field of physical methods of gene transfer.

Nonviral gene delivery systems by the combination of bubble liposomes and ultrasound

The combination of therapeutic ultrasound (US) and nano/microbubbles is an important system for establishing a novel and noninvasive gene delivery system. Genes are delivered more efficiently using this system compared with a conventional nonviral vector system such as the lipofection method, resulting in higher gene expression. This higher efficiency is due to the gene being delivered into the cytosol and bypassing the endocytosis pathway. Many in vivo studies have demonstrated US-mediated gene delivery with nano/microbubbles, and several gene therapy feasibility studies for various diseases have been reported. In addition, nano/microbubbles can deliver genes site specifically by the control of US exposure site. In the present review, we summarize the gene delivery systems by the combination of nano/microbubbles and US, describe their properties, and assess applications and challenges of US theranostics.

Nucleic acid delivery with microbubbles and ultrasound

Nucleic acid-based therapy is a growing field of drug delivery research. Although ultrasound has been suggested to enhance transfection decades ago, it took a combination of ultrasound with nucleic acid carrier systems (microbubbles, liposomes, polyplexes, and viral carriers) to achieve reasonable nucleic acid delivery efficacy. Microbubbles serve as foci for local deposition of ultrasound energy near the target cell, and greatly enhance sonoporation. The major advantage of this approach is in the minimal transfection in the non-insonated non-target tissues. Microbubbles can be simply co-administered with the nucleic acid carrier or can be modified to carry nucleic acid themselves. Liposomes with embedded gas or gas precursor particles can also be used to carry nucleic acid, release and deliver it by the ultrasound trigger. Successful testing in a wide variety of animal models (myocardium, solid tumors, skeletal muscle, and pancreas) proves the potential usefulness of this technique for nucleic acid drug delivery.

Ultrasound induced cancer immunotherapy

Recently, the use of ultrasound (US) has been shown to have potential in cancer immunotherapy. High intensity focused US destruction of tumors may lead to immunity forming in situ in the body by immune cells being exposed to the tumor debris and immune stimulatory substances that are present in the tumor remains. Another way of achieving anti-cancer immune responses is by using US in combination with microbubbles and nanobubbles to deliver genes and antigens into cells. US leads to bubble destruction and the forces released to direct delivery of the substances into the cytoplasm of the cells thus circumventing the natural barriers. In this way tumor antigens and antigen-encoding genes can be delivered to immune cells and immune response stimulating genes can be delivered to cancer cells thus enhancing immune responses. Combination of bubbles with cell-targeting ligands and US provides an even more sophisticated delivery system whereby the therapy is not only site specific but also cell specific. In this review we describe how US has been used to achieve immunity and discuss the potential and possible obstacles in future development.

Effects of low-intensity ultrasound on gramicidin D-induced erythrocyte edema

OBJECTIVES

To determine whether low-intensity ultrasound (US) can reduce red blood cell (RBC) edema and, if so, whether the US activity is associated with aquaporin 1 (AQP-1), a water channel in the cell membrane.

METHODS

Red blood cell edema was induced by gramicidin D treatment at 40 ng/mL for 20 minutes and evaluated by a hematocrit assay. Low-intensity continuous wave US at 1 MHz was applied to RBCs for the last 10 minutes of gramicidin D treatment. To determine whether US activity was associated with AQP-1, RBCs were treated with 40 μM mercuric chloride (HgCl(2)), an AQP-1 inhibitor, for 20 minutes at the time of gramicidin D treatment. Posttreatment morphologic changes in RBCs were observed by actin staining with phalloidin.

RESULTS

Red blood cell edema increased significantly with gramicidin D at 20 (1.8%), 40 (6.7%), 60 (16.7%), and 80 (11.3%) ng/mL, reaching a peak at 60 ng/mL, compared to the control group (20 ng/mL, P = .019; 40, 60, and 80 ng/mL, P < .001). No significant RBC hemolysis was observed in any group. Edema induced by gramicidin D at 40 ng/mL was significantly reduced by US at 30 (3.4%; P = .003), 70 (4.4%; P = .001), and 100 (2.9%; P = .001) mW/cm(2). Subsequent experiments showed that edema reduction by US ranged from 7% to 10%. Cotreatment with HgCl(2) partially reversed the US effect and showed a significantly different level of edema compared to gramicidin D-alone and US-cotreated groups (P = .001). These results were confirmed by microscopic observation of RBC morphologic changes.

CONCLUSIONS

Low-intensity US could reduce gramicidin D-induced RBC edema, and its effect appeared to at least partly involve regulation of AQP-1 activity. These results suggest that low-intensity US can be used as an alternative treatment to control edema and related disorders.

Tertiary-amine functionalized polyplexes enhanced cellular uptake and prolonged gene expression

Ultrasound (US) has been found to facilitate the transport of DNA across cell membranes. However, the transfection efficiency is generally low, and the expression duration of the transfected gene is brief. In this study, a tertiary polycation, Poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA), was used as a carrier for US-mediated gene transfection. Its in-vitro and in-vivo effects on the transfection efficiency and the expression duration were evaluated. A mixture of pCI-neo-luc and PDMAEMA was transfected to cultured cells or mouse muscle by exposure to 1-MHz pulse US. A strong expression of luciferase was found 10 days after the transfection in vitro regardless of US exposure. However, effective transfection only occurred in the US groups in vivo. The transfection ability depended on the weight ratio of PDMAEMA to DNA, and was different for the in-vitro and in-vivo conditions. Lower weight ratios, e.g., 0.25, exhibited better in-vivo expression for at least 45 days.