Augmentation of cardiac protein delivery using ultrasound targeted microbubble destruction

Non-viral in vivo cytidine base editing in hepatocytes using focused ultrasound targeted microbubbles

CRISPR-Cas9-based genome editing technologies, such as base editing, have the potential for clinical translation, but delivering nucleic acids into target cells in vivo is a major obstacle. Viral vectors are widely used but come with safety concerns, while current non-viral methods are limited by low transfection efficiency. Here we describe a new method to deliver CRISPR-Cas9 base editing vectors to the mouse liver using focused ultrasound targeted microbubble destruction (FUTMD). We demonstrate, using the example of cytosine base editing of the Pde3b gene, that FUTMD-mediated delivery of cytosine base editing vectors can introduce stop codons (up to ∼2.5% on-target editing) in mouse liver cells in vivo. However, base editing specificity is less than one might hope with these DNA constructs. Our findings suggest that FUTMD-based gene editing tools can be rapidly and transiently deployed to specific organs and sites, providing a powerful platform for the development of non-viral genome editing therapies. Non-viral delivery also reveals greater off-target base exchange in vivo than in vitro.

Ultrasound-targeted microbubble destruction mediates PDE5i/NO integration for cavernosum remodeling and penile rehabilitation

Erectile dysfunction (ED) caused by cavernous nerve injury (CNI) is refractory to heal mainly ascribed to the adverse remodeling of the penis induced by ineffectual microvascular perfusion, fibrosis, and neurotrophins scarcity in cavernosum. Phosphodiesterase type V inhibitors (PDE5i) have been regarded as an alternative candidate drug for avoiding penile neuropathy. However, the therapeutic efficacy is severely limited due to poor accumulation under systemic medication and endogenous nitric oxide (NO) deficiency in cavernosum. Herein, an innovative liposomal microbubble (MB) loaded with both Sildenafil (one of PDE5i) and NO was designed. Ultrasound-targeted MB destruction (UTMD)-mediated efficient release and integration erectogenic agents into corpus cavernosum with high biosafety. On a bilateral CNI rat model, the multifunctional MB-cooperated UTMD improved microvascular perfusion in penis, simultaneously, alleviated hypoxia and oxidative stress, indicating successful activation of NO-cyclic guanosine monophosphate pathway. Also, evaluation of the endothelial/muscular composition, intracavernosal pressure, and neural integrity in the penis proved that coordinated intervention reversed the abnormal structural remodeling and promoted the recovery of functional erection. Our work demonstrates that MB loading Sildenafil and NO combined with UTMD hold great promise to "awaken" the efficacy of PDE5i in neurogenic ED, which provided a superior option for ensuring penile rehabilitation.

Ultrasound-Triggered Microbubbles: Novel Targeted Core-Shell for the Treatment of Myocardial Infarction Disease

Myocardial infarction (MI) is known as a main cardiovascular disease that leads to extensive cell death by destroying vasculature in the affected cardiac muscle. The development of ultrasound-mediated microbubble destruction has inspired extensive interest in myocardial infarction therapeutics, targeted delivery of drugs, and biomedical imaging. In this work, we describe a novel therapeutic ultrasound system for the targeted delivery of biocompatible microstructures containing basic fibroblast growth factor (bFGF) to the MI region. The microspheres were fabricated using poly(lactic-co-glycolic acid)-heparin-polyethylene glycol- cyclic arginine-glycine-aspartate-platelet (PLGA-HP-PEG-cRGD-platelet). The micrometer-sized core-shell particles consisting of a perfluorohexane (PFH)-core and a PLGA-HP-PEG-cRGD-platelet-shell were prepared using microfluidics. These particles responded adequately to ultrasound irradiation by triggering the vaporization and phase transition of PFH from liquid to gas in order to achieve microbubbles. Ultrasound imaging, encapsulation efficiency cytotoxicity, and cellular uptake of bFGF-MSs were evaluated using human umbilical vein endothelial cells (HUVECs) in vitro. In vivo imaging demonstrated effective accumulation of platelet- microspheres injected into the ischemic myocardium region. The results revealed the potential use of bFGF-loaded microbubbles as a noninvasive and effective carrier for MI therapy.

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.

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

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

Release of vascular agonists from liposome-microbubble conjugate by ultrasound-mediated microbubble destruction: effect on vascular function

The endothelium is a single cell layer of the vessel wall and a key regulator of blood flow in vascular beds. Local and systemic pathologies have been associated with alterations in endothelial function. However, targeting the endothelium with vasoconstrictor or vasodilator drugs is often accompanied by systemic effects. Here, we evaluated a liposome-microbubble delivery system as a vascular hydrophilic agonist carrier. Phenylephrine (Phe) or acetylcholine (Ach)-loaded liposomes were conjugated to microbubbles. The drug release was triggered by ultrasound (US), and the vascular response was assessed in rat aortic rings using an isolated organ chamber. Aortic rings incubated with Phe-liposome-microbubble conjugate, exposed to US showed a marked contractile response (0.79 ± 0.04 g) compared to empty liposomes conjugated to microbubbles, aortic rings exposed only to US, and Phe-liposome-microbubble conjugate without US exposure that elicited a minimal or no response. Expressed as %, contractile responses were 85.24 ± 4.31% and 12.62 ± 3.23% for Phe-Chol-liposome-microbubble conjugate and empty Chol-liposome-microbubble conjugate exposed to US, respectively. Addition of 1 × 10^-5 M Ach to pre-contracted aortic rings decreased the contraction response from 1 to 0.21 g. The addition of Ach-liposome conjugate and exposure to US decreased the contraction response to 0.32 g. Additionally, the ED50 values for Phe and Ach released by US from liposome-microbubble conjugates were 3.6 × 10^-8 M ± 2.8 × 10^-9 M for Phe and 2.0 × 10^-8 M ± 1.8 × 10^-9 M. In conclusion, we evaluated a hybrid delivery system that consisted of loaded liposomes conjugated to microbubbles to deliver and release vascular agonists using UMMD.

Ultrasound-Responsive Nanocarriers in Cancer Treatment: A Review

The safe and effective delivery of anticancer agents to diseased tissues is one of the significant challenges in cancer therapy. Conventional anticancer agents are generally cytotoxins with poor pharmacokinetics and bioavailability. Nanocarriers are nanosized particles designed for the selectivity of anticancer drugs and gene transport to tumors. They are small enough to extravasate into solid tumors, where they slowly release their therapeutic load by passive leakage or biodegradation. Using smart nanocarriers, the rate of release of the entrapped therapeutic(s) can be increased, and greater exposure of the tumor cells to the therapeutics can be achieved when the nanocarriers are exposed to certain internally (enzymes, pH, and temperature) or externally (light, magnetic field, and ultrasound) applied stimuli that trigger the release of their load in a safe and controlled manner, spatially and temporally. This review gives a comprehensive overview of recent research findings on the different types of stimuli-responsive nanocarriers and their application in cancer treatment with a particular focus on ultrasound.

Regulation of Proteins to the Cytosol Using Delivery Systems with Engineered Polymer Architecture

Intracellular protein delivery enables selective regulation of cellular metabolism, signaling, and development through introduction of defined protein quantities into the cell. Most applications require that the delivered protein has access to the cytosol, either for protein activity or as a gateway to other organelles such as the nucleus. The vast majority of delivery vehicles employ an endosomal pathway however, and efficient release of entrapped protein cargo from the endosome remains a challenge. Recent research has made significant advances toward efficient cytosolic delivery of proteins using polymers, but the influence of polymer architecture on protein delivery is yet to be investigated. Here, we developed a family of dendronized polymers that enable systematic alterations of charge density and structure. We demonstrate that while modulation of surface functionality has a significant effect on overall delivery efficiency, the endosomal release rate can be highly regulated by manipulating polymer architecture. Notably, we show that large, multivalent structures cause slower sustained release, while rigid spherical structures result in rapid burst release.

A review of ultrasound-mediated microbubbles technology for cancer therapy: a vehicle for chemotherapeutic drug delivery

Background:

The unique behaviour of microbubbles under ultrasound acoustic pressure makes them useful agents for drug and gene delivery. Several studies have demonstrated the potential application of microbubbles as a non-invasive, safe and effective technique for targeted delivery of drugs and genes. The drugs can be incorporated into the microbubbles in several different approaches and then carried to the site of interest where it can be released by destruction of the microbubbles using ultrasound to achieve the required therapeutic effect.

Methods:

The objective of this article is to report on a review of the recent advances of ultrasound-mediated microbubbles as a vehicle for delivering drugs and genes and its potential application for the treatment of cancer.

Conclusion:

Ultrasound-mediated microbubble technology has the potential to significantly improve chemotherapy drug delivery to treatment sites with minimal side effects. Moreover, the technology can induce temporary and reversible changes in the permeability of cells and vessels, thereby allowing for drug delivery in a spatially localised region which can improve the efficiency of drugs with poor bioavailability due to their poor absorption, rapid metabolism and rapid systemic elimination.

Photo- and Sono-Dynamic Therapy: A Review of Mechanisms and Considerations for Pharmacological Agents Used in Therapy Incorporating Light and Sound

As irreplaceable energy sources of minimally invasive treatment, light and sound have, separately, laid solid foundations in their clinic applications. Constrained by the relatively shallow penetration depth of light, photodynamic therapy (PDT) typically involves involves superficial targets such as shallow seated skin conditions, head and neck cancers, eye disorders, early-stage cancer of esophagus, etc. For ultrasound-driven sonodynamic therapy (SDT), however, to various organs is facilitated by the superior... transmission and focusing ability of ultrasound in biological tissues, enabling multiple therapeutic applications including treating glioma, breast cancer, hematologic tumor and opening blood-brain-barrier (BBB). Considering the emergence of theranostics and precision therapy, these two classic energy sources and corresponding sensitizers are worth reevaluating. In this review, three typical therapies using light and sound as a trigger, PDT, SDT, and combined PDT and SDT are introduced. The therapeutic dynamics and current designs of pharmacological sensitizers involved in these therapies are presented. By introducing both the history of the field and the most up-to-date design strategies, this review provides a systemic summary on the development of PDT and SDT and fosters inspiration for researchers working on 'multi-modal' therapies involving light and sound.

Ultrasound Imaging of Microbubble Activity during Sonoporation Pulse Sequences

Ultrasound-mediated drug delivery using the mechanical action of oscillating and/or collapsing microbubbles has been studied on many different experimental platforms, both in vitro and in vivo; however, the mechanisms remain to be elucidated. Many groups use sterile, enclosed chambers, such as Opticells and Clinicells, to optimize acoustic parameters in vitro needed for effective drug delivery in vivo, as well as for mechanistic investigation of sonoporation or the use of sound to permeate cell membranes. In these containers, cell monolayers are seeded on one side, and the remainder of the volume is filled with a solution containing microbubbles and a model drug. Ultrasound is then applied to study the effect of different parameters on model drug uptake in cell monolayers. Despite the simplicity of this system, the field has been unable to appropriately address what parameters and microbubble concentrations are most effective at enhancing drug uptake and minimizing cellular toxicity. In this work, a common in vitro sonoporation experimental setup was characterized through quantitative analysis of microbubble-dependent acoustic attenuation in combination with high-frame-rate and high-resolution imaging of bubble activity during sonoporation pulse sequences. The goal was to visualize the effect that ultrasound parameters have on microbubble activity. It was observed that under literature-derived sonoporation conditions (0.1-1 MPa, 20-1000 cycles and 10,000 to 10,000,000 microbubbles/mL), there is strong and non-linear acoustic attenuation, as well as bubble destruction, gas diffusion and bubble motion resulting in spatiotemporal pressure and concentration gradients. Ultimately, it was found that the acoustic conditions in common in vitro sonoporation setups are much more complex and confounding than often assumed.

Microbubble Formulations: Synthesis, Stability, Modeling and Biomedical Applications

Microbubbles are increasingly being used in biomedical applications such as ultrasonic imaging and targeted drug delivery. Microbubbles typically range from 0.1 to 10 µm in size and consist of a protective shell made of lipids or proteins. The shell encapsulates a gaseous core containing gases such as oxygen, sulfur hexafluoride or perfluorocarbons. This review is a consolidated account of information available in the literature on research related to microbubbles. Efforts have been made to present an overview of microbubble synthesis techniques; microbubble stability; microbubbles as contrast agents in ultrasonic imaging and drug delivery vehicles; and side effects related to microbubble administration in humans. Developments related to the modeling of microbubble dissolution and stability are also discussed.

Improving acute cardiac transplantation rejection therapy using ultrasound-targeted FK506-loaded microbubbles in rats

FK506-MBs combined with the UTMD technique increased drug concentrations in transplanted hearts and enhanced the therapeutic effect.

Ultrasound Microbubble Delivery Targeting Intraplaque Neovascularization Inhibits Atherosclerotic Plaque in an APOE-deficient Mouse Model

BACKGROUND/AIM

Intraplaque neovascularization is often associated with plaque formation, development and instability, and clinical symptoms in atherosclerosis. The aim of the present study was to investigate a new strategy for treating athrosclerosis by ultrasound-targeted microbubble delivery (UTMD) targeting intraplaque neovascularization in an APOE-deficient mouse model of atherosclerosis.

MATERIALS AND METHODS

A mouse model of atherosclerosis was induced by feeding Apoe^-/- mice a hypercholesterolemic diet and was verified with hematoxylin and eosin staining and intercellular adhesion molecule 1 (ICAM-1) expression. Targeted microbubbles (MB) were prepared by conjugating microbubbles with biotinylated antibody to ICAM1 (MBi) or with both biotinylated anti-ICAM1 and the angiogenesis inhibitor Endostar (MBie). The targeted microbubbles were analyzed with epifluorescence microscopy and flow cytometry. The animals with induced atherosclerotic plaques received MBi or MBie followed by UTMD treatment. Endostar treatment alone was given to other animals for comparison. Morphological assessment of atherosclerotic plaques was performed after treatment. The expression of angiogenesis marker CD31 was detected by immunohistochemical analysis.

RESULTS

Atherosclerotic plaques developed in the entire aorta with significant intraplaque ICAM-1 expression in the APOE-deficient mice following a 30-week hypercholesterolemic diet. Microbubbles were successfully conjugated with anti-ICAM-1 and Endostar, with a conjugation rate of 98.3% and 63.5%, respectively. UTMD with MBie significantly reduced the area of atherosclerotic plaque as compared to the model control (p<0.05). Treatment with Endostar and UTMD with MBie significantly reduced CD31 expression compared with the model control group (p<0.01). Greater significant inhibitory effect on CD31 expression was found in the group treated with UTMD and MBie compared to the Endostar- and UTMD with MBi groups (p<0.01).

CONCLUSION

UTMD targeting intraplaque neovascularization was found to inhibit atherosclerotic plaque in a mouse model of atherosclerosis, suggesting the potential of microbubble-mediated ultrasound technology in aiding drug delivery for atherosclerosis treatment.

Concurrent Treatment with Anti-DLL4 Enhances Antitumor and Proapoptotic Efficacy of a γ-Secretase Inhibitor in Gastric Cancer

The Notch signaling pathway has been identified as a therapeutic target for cancers. γ-Secretase inhibitors (GSIs) have been progressively recognized as potential anticancer drugs. The present study aimed to investigate the effects of anti-delta like legend 4 (anti-DLL4) treatment on the anticancer efficacy of GSIs in gastric cancer. SGC-7901-GFP human gastric cancer cells were tested for DLL4 expression by rosette formation test and immunofluorescence, and then were treated with anti-DLL4 antibody N-[N-(3,5-difluorophenacetyl)-L-ananyl]-S-phenylglycine t-butyl ester (DAPT, a type of GSI), or a combination of anti-DLL4 antibody and DAPT. The effects of in vitro treatments on cell apoptosis, cell cycle, and cell invasion were analyzed. For in vivo study, an orthotopic mouse model of gastric cancer was established with green fluorescence expressing SGC-7901. Ultrasound targeted microbubble destruction was used to treat tumor-bearing mice with anti-DLL4 antibody conjugated microbubbles, DAPT, and a combination of the two. Real-time fluorescence imaging was performed to assess tumor cell inhibition in each group. Following in vivo treatments, apoptosis of tumor cells and the expression of apoptosis-related genes BAX, Bcl-2, and P53 were detected by TUNEL and immunohistochemical staining. In vivo combined treatment of anti-DLL4 and DAPT led to a higher rate of cell apoptosis and greater inhibition of cell invasion than that observed with DAPT treatment alone. DAPT and anti-DLL4 combination therapy resulted in decreased cell distribution at G1 phase and increased cell distribution at S phase, compared to the untreated control group (P < .01). In vivo combined therapy with anti-DLL4 and DAPT significantly increased tumor growth inhibition and tumor cell apoptosis when compared to DAPT therapy alone (P < .05). In addition, combined treatment significantly increased expression of BAX and P53 and reduced Bcl-2 expression (P < .05). Conversely, treatment with DAPT alone only increased expression of BAX and P53 (P < .05), suggesting that the reduction of Bcl-2 expression may play an important role in the synergetic antitumor and proapoptosis effects of the combined treatment. Concurrent treatment with anti-DLL4 enhances the antitumor and proapoptotic efficacy of the γ-secretase inhibitor in gastric cancer both in vitro and in vivo.

A novel local drug delivery system: Superhydrophobic titanium oxide nanotube arrays serve as the drug reservoir and ultrasonication functions as the drug release trigger

A local drug delivery system consisting of superhydrophobic titanium oxide nanotube (S-TNTs) arrays and ultrasonic-controlled release trigger was developed in this work. Hydrophilic TNTs arrays are converted into superhydrophobic after being treated by 1H,1H,2H,2H- perfluorooctyl-triethoxysilane (POTS). S-TNTs arrays serving as a drug-carrying vehicle require no extra sealing treatment due to the excellent isolation effect from the trapped air layer on the surface. Different amounts of drugs could be loaded into S-TNTs arrays by control of the structure of arrays (including length and diameter of tubes) and the original amount of drug in the drug-loading solution. The relation between surface morphology of TNTs arrays and superhydrophobicity (isolation effect) was thoroughly investigated. To achieve a stimulus-responsive drug delivery system, ultrasonication was employed as an efficient drug release trigger. Trapped air layer could be selectively removed by ultrasonication, and therefore the loaded drug could be released in a multiple and controlled manner. Any drugs that can dissolve in nonpolar solutions are expected to be suitable for this local drug delivery system.

Ultrasound-Responsive Polymeric Micelles for Sonoporation-Assisted Site-Specific Therapeutic Action

Targeting drug delivery remains a challenge in various disease treatment including cancer. The local drug deposit could be greatly enhanced by some external stimuli-responsive systems. Here we develop pluronic P123/F127 polymeric micelles (M) encapsulating curcumin (Cur) that are permeabilized directly by focused ultrasound, in which ultrasound triggers drug release. Tumor preferential accumulation and site-specific sonochemotherapy were then evaluated. Cur-loaded P123/F127 mixed micelles (Cur-M) exhibited longer circulating time and increased cellular uptake compared to free Cur. With the assistance of focused ultrasound treatment, Cur-M showed tumor-targeting deposition in a time-dependent manner following systemic administration. This was due to enhanced permeabilization of tumor regions and increased penetration of Cur-M in irradiated tumor cells by ultrasound sonoporation. Furthermore, Cur-M self-assembly could be regulated by ultrasound irradiation. In vitro Cur release from mixed micelles was greatly dependent on ultrasound intensity but not on duration, suggesting the cavitational threshold was necessary to initiate subsequent sonochemotherapy. In vivo site-specific drug release was demonstrated in dual-tumor models, which showed spatial-temporal release of entrapped drugs following intratumoral injection. The sonoporation-assisted site-specific chemotherapy significantly inhibited tumor growth and the decrease in tumor weight was approximately 6.5-fold more than without exposure to ultrasound irradiation. In conclusion, the established ultrasound-guided nanomedicine targeting deposit and local release may represent a new strategy to improve chemotherapy efficiency.

Fabrication of ultrasound-responsive microbubbles via coaxial electrohydrodynamic atomization for triggered release of tPA

A single-step fabrication method, coaxial electrohydrodynamic atomization (CEHDA), was developed to synthesize drug-loaded microbubbles (MBs) for combination treatment of ischemic stroke. The bioactivity of therapeutic agent (tPA, tissue plasminogen activator) after preparation was evaluated, showing that CEHDA could be very promising method for producing MBs with therapeutic functions. The bubble performance and tPA release profiles were also examined by exposing the bubbles to 2MHz ultrasound of various intensities. The results showed that the mean diameter of tPA-loaded MBs was found to fluctuate about its original diameter when exposed to ultrasound and higher intensity ultrasound was more effective in triggering the burst of CEHDA MBs. High ultrasound-triggered bubble disintegration effectiveness in a short period (first 5min) fits well with the requirement of short ultrasound exposure time for human brain. Moreover, a numerical model was also applied to investigate the stability of the fabricated MBs in the bloodstream. It was found that MB dissolution time increased with initial radius, decreased with initial surface tension and increased with initial shell resistance but it was barely affected by the average excessive bloodstream pressure.

Materials Chemistry of Nanoultrasonic Biomedicine

As a special cross-disciplinary research frontier, nanoultrasonic biomedicine refers to the design and synthesis of nanomaterials to solve some critical issues of ultrasound (US)-based biomedicine. The concept of nanoultrasonic biomedicine can also overcome the drawbacks of traditional microbubbles and promote the generation of novel US-based contrast agents or synergistic agents for US theranostics. Here, we discuss the recent developments of material chemistry in advancing the nanoultrasonic biomedicine for diverse US-based bio-applications. We initially introduce the design principles of novel nanoplatforms for serving the nanoultrasonic biomedicine, from the viewpoint of synthetic material chemistry. Based on these principles and diverse US-based bio-application backgrounds, the representative proof-of-concept paradigms on this topic are clarified in detail, including nanodroplet vaporization for intelligent/responsive US imaging, multifunctional nano-contrast agents for US-based multi-modality imaging, activatable synergistic agents for US-based therapy, US-triggered on-demand drug releasing, US-enhanced gene transfection, US-based synergistic therapy on combating the cancer and potential toxicity issue of screening various nanosystems suitable for nanoultrasonic biomedicine. It is highly expected that this novel nanoultrasonic biomedicine and corresponding high performance in US imaging and therapy can significantly promote the generation of new sub-discipline of US-based biomedicine by rationally integrating material chemistry and theranostic nanomedicine with clinical US-based biomedicine.

Ultrasound-Targeted Microbubble Destruction for Cardiac Gene Delivery

Ultrasound targeted microbubble destruction (UTMD) is a novel technique that is used to deliver a gene or other bioactive substance to organs of living animals in a noninvasive manner. Plasmid DNA binding with cationic liposome into nanoparticles are assembled into the shell of microbubbles, which are circulated by intravenous injection. Intermittent bursts of ultrasound with low frequency and high mechanical index destroys the microbubbles and releases the nanoparticles into targeted organ to transfect local organ cells. Cell-specific promoters can be used to further enhance cell specificity. Here we describe UTMD applied to cardiac gene delivery.

Activation of microbubbles by low-intensity pulsed ultrasound enhances the cytotoxicity of curcumin involving apoptosis induction and cell motility inhibition in human breast cancer MDA-MB-231 cells

Ultrasound and microbubbles-mediated drug delivery has become a promising strategy to promote drug delivery and its therapeutic efficacy. The aim of this research was to assess the effects of microbubbles (MBs)-combined low-intensity pulsed ultrasound (LPUS) on the delivery and cytotoxicity of curcumin (Cur) to human breast cancer MDA-MB-231 cells. Under the experimental condition, MBs raised the level of acoustic cavitation and enhanced plasma membrane permeability; and cellular uptake of Cur was notably improved by LPUS-MBs treatment, aggravating Cur-induced MDA-MB-231 cells death. The combined treatment markedly caused more obvious changes of cell morphology, F-actin cytoskeleton damage and cell migration inhibition. Our results demonstrated that combination of MBs and LPUS may be an efficient strategy for improving anti-tumor effect of Cur, suggesting a potential effective method for antineoplastic therapy.

Molecular Imaging of Vulnerable Atherosclerotic Plaques in Animal Models

Atherosclerosis is characterized by intimal plaques of the arterial vessels that develop slowly and, in some cases, may undergo spontaneous rupture with subsequent heart attack or stroke. Currently, noninvasive diagnostic tools are inadequate to screen atherosclerotic lesions at high risk of acute complications. Therefore, the attention of the scientific community has been focused on the use of molecular imaging for identifying vulnerable plaques. Genetically engineered murine models such as ApoE^−/− and ApoE^−/−Fbn1C1039G^+/− mice have been shown to be useful for testing new probes targeting biomarkers of relevant molecular processes for the characterization of vulnerable plaques, such as vascular endothelial growth factor receptor (VEGFR)-1, VEGFR-2, intercellular adhesion molecule (ICAM)-1, P-selectin, and integrins, and for the potential development of translational tools to identify high-risk patients who could benefit from early therapeutic interventions. This review summarizes the main animal models of vulnerable plaques, with an emphasis on genetically altered mice, and the state-of-the-art preclinical molecular imaging strategies.

Theragnostic ultrasound using microbubbles in the treatment of prostate cancer

The use of gas-filled microbubbles in perfusion monitoring as intravascular ultrasound contrast agents has recently become more common. Additionally, microbubbles are employed as carriers of pharmaceutical substances or genes. Microbubbles have great potential to improve the delivery of therapeutic materials into cells and to modify vascular permeability, causing increased extravasation of drugs and drug carriers. Prostate cancer is the most common neoplasm in Europe and America, with an incidence twice to three times that of lung and colorectal cancer. Its incidence is still rising in Asian countries, including Japan and Korea. In this review, we present current strategies regarding the synthesis of microbubbles with targeted ligands on their surfaces, with a focus on prostate cancer.

Accurate measurement of microbubble response to ultrasound with a diagnostic ultrasound scanner

Ultrasound and microbubbles are often used to enhance drug delivery and the suggested mechanisms are extravasation and sonoporation. Drug delivery schemes with ultrasound and microbubbles at both low and high acoustic amplitudes have been suggested. A diagnostic ultrasound scanner may play a double role as both an imaging and a therapy device. It was not possible to accurately measure microbubble response with an ultrasound scanner for a large range of acoustic pressures and microbubble concentrations until now, mainly because of signal saturation issues. A method for continuously adjusting the receive gain of a scanner and limiting signal saturation was developed to accurately measure backscattered echoes from microbubbles for mechanical indexes (MIs) up to 2.1. The intensity of backscattered echoes from microbubbles increased quarticly with MI without reaching any limit. The signal intensity from microbubbles was found to be linear with concentration at both low and high MIs. However, at very high concentrations, acoustic shadowing occurs which limits the delivered acoustic pressure in deeper areas. The contrastto- tissue ratio was also measured and found to stay constant with MI. These results can be used to better guide drug delivery approaches and to also develop imaging techniques for therapy procedures.

Ultrasound and microbubble mediated drug delivery: acoustic pressure as determinant for uptake via membrane pores or endocytosis

Although promising results are achieved in ultrasound mediated drug delivery, its underlying biophysical mechanisms remain to be elucidated. Pore formation as well as endocytosis has been reported during ultrasound application. Due to the plethora of ultrasound settings used in literature, it is extremely difficult to draw conclusions on which mechanism is actually involved. To our knowledge, we are the first to show that acoustic pressure influences which route of drug uptake is addressed, by inducing different microbubble-cell interactions. To investigate this, FITC-dextrans were used as model drugs and their uptake was analyzed by flow cytometry. In fluorescence intensity plots, two subpopulations arose in cells with FITC-dextran uptake after ultrasound application, corresponding to cells having either low or high uptake. Following separation of the subpopulations by FACS sorting, confocal images indicated that the low uptake population showed endocytic uptake. The high uptake population represented uptake via pores. Moreover, the distribution of the subpopulations shifted to the high uptake population with increasing acoustic pressure. Real-time confocal recordings during ultrasound revealed that membrane deformation by microbubbles may be the trigger for endocytosis via mechanostimulation of the cytoskeleton. Pore formation was shown to be caused by microbubbles propelled towards the cell. These results provide a better insight in the role of acoustic pressure in microbubble-cell interactions and the possible consequences for drug uptake. In addition, it pinpoints the need for a more rational, microbubble behavior based choice of acoustic parameters in ultrasound mediated drug delivery experiments.

High-frequency ultrasound-guided disruption of glycoprotein VI-targeted microbubbles targets atheroprogressison in mice

Targeted contrast-enhanced ultrasound (CEU) using microbubble agents is a promising non-invasive imaging technique to evaluate atherosclerotic lesions. In this study, we decipher the diagnostic and therapeutic potential of targeted-CEU with soluble glycoprotein (GP)-VI in vivo. Microbubbles were conjugated with the recombinant fusion protein GPVI-Fc (MBGPVI) that binds with high affinity to atherosclerotic lesions. MBGPVI or control microbubbles (MBC) were intravenously administered into ApoE(-/-) or wild type mice and binding of the microbubbles to the vessel wall was visualized by high-resolution CEU. CEU molecular imaging signals of MBGPVI were substantially enhanced in the aortic arch and in the truncus brachiocephalicus in ApoE(-/-) as compared to wild type mice. High-frequency ultrasound (HFU)-guided disruption of MBGPVI enhanced accumulation of GPVI in the atherosclerotic lesions, which may interfere with atheroprogression. Thus, we establish targeted-CEU with soluble GPVI as a novel non-invasive molecular imaging method for atherosclerosis. Further, HFU-guided disruption of GPVI-targeted microbubbles is an innovate therapeutic approach that potentially prevents progression of atherosclerotic disease.

Ultrasound and microbubble guided drug delivery: mechanistic understanding and clinical implications

Ultrasound mediated drug delivery using microbubbles is a safe and noninvasive approach for spatially localized drug administration. This approach can create temporary and reversible openings on cellular membranes and vessel walls (a process called "sonoporation"), allowing for enhanced transport of therapeutic agents across these natural barriers. It is generally believed that the sonoporation process is highly associated with the energetic cavitation activities (volumetric expansion, contraction, fragmentation, and collapse) of the microbubble. However, a thorough understanding of the process was unavailable until recently. Important progress on the mechanistic understanding of sonoporation and the corresponding physiological responses in vitro and in vivo has been made. Specifically, recent research shed light on the cavitation process of microbubbles and fluid motion during insonation of ultrasound, on the spatio-temporal interactions between microbubbles and cells or vessel walls, as well as on the temporal course of the subsequent biological effects. These findings have significant clinical implications on the development of optimal treatment strategies for effective drug delivery. In this article, current progress in the mechanistic understanding of ultrasound and microbubble mediated drug delivery and its implications for clinical translation is discussed.

Enhancement of the cytotoxicity and selectivity of doxorubicin to hepatoma cells by synergistic combination of galactose-decorated γ-poly(glutamic acid) nanoparticles and low-intensity ultrasound

Specific drug delivery to solid tumors remains one of the challenges in cancer therapy. The aim of this study was to combine three drug-targeting strategies, polymer-drug conjugate, ligand presentation and ultrasound treatment, to enhance the efficacy and selectivity of doxorubicin (DXR) to hepatoma cells. The conjugation of DXR to γ-poly(glutamic acids) (γ-PGA) decreased the cytotoxicity of DXR, while the conjugation of galactosamine (Gal) to the γ-PGA-DXR conjugate restored the cytotoxic efficacy of DXR on hepatoma cells due to increased uptake of DXR. Furthermore, low-intensity ultrasound treatment increased the cell-killing ability of γ-PGA-DXR conjugates by 20%. The in vitro results showed the potential of the γ-PGA-DXR-Gal conjugate for future clinical applications.

Functional and pathological improvements of the hearts in diabetes model by the combined therapy of bFGF-loaded nanoparticles with ultrasound-targeted microbubble destruction

Diabetic cardiomyopathy (DCM) is the leading cause of morbidity and mortality among the diabetic patients and currently there is no effective means to reverse its pathological progress. Basic fibroblast growth factor (bFGF) has shown promise as a molecular therapy for DCM, but its delivery is inefficient and non-specific. In the present study, a therapy combining nanoparticle (NP) carrier and ultrasound-targeted microbubble destruction (UTMD) was reported the first time for bFGF delivery to the heart of diabetic rats. bFGF-loaded NP (bFGF-NP) were prepared with Poloxamer 188-grafted heparin copolymer using water-in-water technique, and the morphology, encapsulation efficiency, and bioactivity of bFGF-NP were studied. The cellular uptake and cytotoxicity of bFGF-NP were evaluated with primary cultures of the left ventricular (LV) cardiomyocytes in vitro. Therapeutic effects of bFGF-NP/UTMD on the heart of DCM rats were studied by measuring LV systolic and diastolic functions, hemodynamic characteristics and indicators of cardiac remodeling including myocardial collagen volume fraction and capillary density. Results demonstrated that bFGF-NP showed good round morphology, efficient bFGF encapsulation and stable bioactivity of bFGF in vitro. bFGF-NP/UTMD combined treatment significantly enhanced the efficiency of bFGF cellular uptake (P<0.05) without obvious cytotoxicity. Significant improvements (P<0.05) in both cardiac functions and tissue morphology in the DCM rats were observed in bFGF-NP/UTMD group. These were not achievable using free bFGF, bFGF-NP or UTMD treatment alone. Our results show that combining a non-viral vector with UTMD technique is an effective strategy to deliver bFGF to the heart, and the resulting growth factor therapy has demonstrated potential to reverse the progress of DCM by restoring the cardiac functions and even the structure of damaged cardiac tissues.

Development of therapeutic microbubbles for enhancing ultrasound-mediated gene delivery

Ultrasound (US)-mediated gene delivery has emerged as a promising non-viral method for safe and selective gene delivery. When enhanced by the cavitation of microbubbles (MBs), US exposure can induce sonoporation that transiently increases cell membrane permeability for localized delivery of DNA. The present study explores the effect of generalizable MB customizations on MB facilitation of gene transfer compared to Definity®, a clinically available contrast agent. These modifications are 1) increased MB shell acyl chain length (RN18) for elevated stability and 2) addition of positive charge on MB (RC5K) for greater DNA associability. The MB types were compared in their ability to facilitate transfection of luciferase and GFP reporter plasmid DNA in vitro and in vivo under various conditions of US intensity, MB dosage, and pretreatment MB-DNA incubation. The results indicated that both RN18 and RC5K were more efficient than Definity®, and that the cationic RC5K can induce even greater transgene expression by increasing payload capacity with prior DNA incubation without compromising cell viability. These findings could be applied to enhance MB functions in a wide range of therapeutic US/MB gene and drug delivery approach. With further designs, MB customizations have the potential to advance this technology closer to clinical application.

A novel cationic microbubble coated with stearic acid-modified polyethylenimine to enhance DNA loading and gene delivery by ultrasound

A novel cationic microbubble (MB) for improvement of the DNA loading capacity and the ultrasound-mediated gene delivery efficiency has been developed; it has been prepared with commercial lipids and a stearic acid modified polyethylenimine 600 (Stearic-PEI600) polymer synthesized via acylation reaction of branched PEI600 and stearic acid mediated by N, N'-carbonyldiimidazole (CDI). The MBs’ concentration, size distribution, stability and zeta potential (ζ-potential) were measured and the DNA loading capacity was examined as a function of the amount of Stearic-PEI600. The gene transfection efficiency and cytotoxicity were also examined using breast cancer MCF-7 cells via the reporter plasmid pCMV-Luc, encoding the firefly luciferase gene. The results showed that the Stearic-PEI600 polymer caused a significant increase in magnitude of ζ-potential of MBs. The addition of DNA into cationic MBs can shift ζ-potentials from positive to negative values. The DNA loading capacity of the MBs grew linearly from (5±0.2) ×10⁻³ pg/µm² to (20±1.8) ×10⁻³ pg/µm² when Stearic-PEI600 was increased from 5 mol% to 30 mol%. Transfection of MCF-7 cells using 5% PEI600 MBs plus ultrasound exposure yielded 5.76±2.58×10³ p/s/cm²/sr average radiance intensity, was 8.97- and 7.53-fold higher than those treated with plain MBs plus ultrasound (6.41±5.82) ×10² p/s/cm²/sr, (P<0.01) and PEI600 MBs without ultrasound (7.65±6.18) ×10² p/s/cm²/sr, (P<0.01), respectively. However, the PEI600 MBs showed slightly higher cytotoxicity than plain MBs. The cells treated with PEI600-MBs and plain MBs plus ultrasound showed 59.5±6.1% and 71.4±7.1% cell viability, respectively. In conclusion, our study demonstrated that the novel cationic MBs were able to increase DNA loading capacity and gene transfection efficiency and could be potentially applied in targeted gene delivery and therapy.

Lung surfactant microbubbles increase lipophilic drug payload for ultrasound-targeted delivery

The cavitation response of circulating microbubbles to targeted ultrasound can be used for noninvasive, site-specific delivery of shell-loaded materials. One challenge for microbubble-mediated delivery of lipophilic compounds is the limitation of drug loading into the microbubble shell, which is commonly a single phospholipid monolayer. In this study, we investigated the use of natural lung surfactant extract (Survanta^®, Abbott Nutrition) as a microbubble shell material in order to improve drug payload and delivery. Pulmonary surfactant extracts such as Survanta contain hydrophobic surfactant proteins (SP-B and SP-C) that facilitate lipid folding and retention on lipid monolayers. Here, we show that Survanta-based microbubbles exhibit wrinkles in bright-field microscopy and increased lipid retention on the microbubble surface in the form of surface-associated aggregates observed with fluorescence microscopy. The payload of a model lipophilic drug (DiO), measured by flow cytometry, increased by over 2-fold compared to lipid-coated microbubbles lacking SP-B and SP-C. Lung surfactant microbubbles were highly echogenic to contrast enhanced ultrasound imaging at low acoustic intensities. At higher ultrasound intensity, excess lipid was observed to be acoustically cleaved for localized release. To demonstrate targeting, a biotinylated lipopolymer was incorporated into the shell, and the microbubbles were subjected to a sequence of radiation force and fragmentation pulses as they passed through an avidinated hollow fiber. Lung surfactant microbubbles showed a 3-fold increase in targeted deposition of the model fluorescent drug compared to lipid-only microbubbles. Our results demonstrate that lung surfactant microbubbles maintain the acoustic responsiveness of lipid-coated microbubbles with the added benefit of increased lipophilic drug payload.

Enhancement of recombinant adeno-associated virus mediated transgene expression by targeted echo-contrast agent

Ultrasound-targeted microbubble destruction (UTMD) has been recently developed for destroying bubbles carrying drugs or genes, thereby permitting local release of these target molecules. We investigated whether SonoVue®, a new contrast agent that contains phospholipid-stabilized microbubbles filled with sulfur hexafluoride vapor, is effective at delivering a recombinant adeno-associated viral (rAAV) vector to the rat heart by UTMD. Serotype-2 (rAAV2) marked with green fluorescent protein (GFP) as a reporter gene was attached to the surface of sulfur hexafluoride-filled microbubbles. Microbubbles were infused into the tail vein of rats with or without simultaneous echocardiography. Additional controls included ultrasound microbubbles that did not contain virus, virus alone, and virus plus ultrasound. One group underwent echocardiographic destruction of microbubbles followed by rAAV2-GFP infusion. Rats were killed after 4 weeks and examined for GFP expression. Green fluorescence was detected in all groups that received the rAAV2-GFP vector, indicating expression of the rAAV2 transgene; however, GFP expression in the UTMD group was significantly higher than that in control groups. We conclude that ultrasound-mediated destruction mediated by SonoVue is a promising method for delivery of rAAV2 to the heart in vivo.

Ultrasound-mediated drug delivery for cardiovascular disease

INTRODUCTION

Ultrasound (US) has been developed as both a valuable diagnostic tool and a potent promoter of beneficial tissue bioeffects for the treatment of cardiovascular disease. These effects can be mediated by mechanical oscillations of circulating microbubbles, or US contrast agents, which may also encapsulate and shield a therapeutic agent in the bloodstream. Oscillating microbubbles can create stresses directly on nearby tissue or induce fluid effects that effect drug penetration into vascular tissue, lyse thrombi or direct drugs to optimal locations for delivery.

AREAS COVERED

The present review summarizes investigations that have provided evidence for US-mediated drug delivery as a potent method to deliver therapeutics to diseased tissue for cardiovascular treatment. In particular, the focus will be on investigations of specific aspects relating to US-mediated drug delivery, such as delivery vehicles, drug transport routes, biochemical mechanisms and molecular targeting strategies.

EXPERT OPINION

These investigations have spurred continued research into alternative therapeutic applications, such as bioactive gas delivery and new US technologies. Successful implementation of US-mediated drug delivery has the potential to change the way many drugs are administered systemically, resulting in more effective and economical therapeutics, and less-invasive treatments.

Advances in ultrasound mediated gene therapy using microbubble contrast agents

Microbubble ultrasound contrast agents have the potential to dramatically improve gene therapy treatments by enhancing the delivery of therapeutic DNA to malignant tissue. The physical response of microbubbles in an ultrasound field can mechanically perturb blood vessel walls and cell membranes, enhancing drug permeability into malignant tissue. In this review, we discuss literature that provided evidence of specific mechanisms that enhance in vivo gene delivery utilizing microbubble contrast agents, namely their ability to 1) improving cell membrane permeability, 2) modulate vascular permeability, and 3) enhance endocytotic uptake in cells. Additionally, we review novel microbubble vectors that are being developed in order to exploit these mechanisms and deliver higher gene payloads with greater target specificity. Finally, we discuss some future considerations that should be addressed in the development of next-generation microbubbles in order to improve in vivo microbubble gene delivery. Overall, microbubbles are rapidly gaining popularity as efficient gene carriers, and combined with their functionality as imaging contrast agents, they represent powerful theranostic tools for image guided gene therapy applications.

Ultrasound-based molecular imaging and specific gene delivery to mesenteric vasculature by endothelial adhesion molecule targeted microbubbles in a mouse model of Crohn's disease

Crohn's disease (CD) is a chronic inflammatory disorder of the gastrointestinal tract (GI) for which treatments with immunosuppressive drugs have significant side-effects. Consequently, there is a clinical need for site-specific and non-toxic delivery of therapeutic genes or drugs for CD and related disorders such as inflammatory bowel disease. The aim of this study was to validate a gene delivery platform based on ultrasound-activated lipid-shelled microbubbles (MBs) targeted to inflamed mesenteric endothelium in the CD-like TNFΔARE mouse model. MBs bearing luciferase plasmid were functionalized with antibodies to MAdCAM-1 (MB-M) or VCAM-1 (MB-V), biomarkers of gut endothelial cell inflammation and evaluated in an in vitro flow chamber assay with appropriate ligands to confirm targeting specificity. Following MB retro-orbital injection in TNFΔARE mice, the mean contrast intensity in the ileocecal region from accumulated MB-M and MB-V was 8.5-fold and 3.6-fold greater, respectively, compared to MB-C. Delivery of luciferase plasmid to the GI tract in TNFΔARE mice was achieved by insonating the endothelial cell-bound agents using a commercial sonoporator. Luciferase expression in the midgut was detected 48 h later by bioluminescence imaging and further confirmed by immunohistochemical staining. The liver, spleen, heart, and kidney had no detectable bioluminescence following insonation. Transfection of the microcirculation guided by a targeted, acoustically-activated platform such as an ultrasound contrast agent microbubble has the potential to be a minimally-invasive treatment strategy to ameliorate CD and other inflammatory conditions.

Efficient microbubble- and ultrasound-mediated plasmid DNA delivery into a specific rat liver lobe via a targeted injection and acoustic exposure using a novel ultrasound system

To develop efficient gene delivery in larger animals, based on a previous mouse study, we explored the luciferase reporter gene transfer in rats by establishing a novel unfocused ultrasound system with simultaneous targeted injection of a plasmid and microbubble mixture into a specific liver lobe through a portal vein branch. Luciferase expression was significantly enhanced over 0-30 vol % of the Definity microbubbles, with a plateau between 0.5 and 30 vol %. The increase of gene delivery efficiency also depended on the acoustic peak negative pressure, achieving over 100-fold enhancement at 2.5 MPa compared with plasmid only controls. Transient, modest liver damage following treatment was assessed by transaminase assays and histology, both of which correlated with gene expression induced by acoustic cavitation. In addition, pulse-train ultrasound exposures (i.e., with relatively long quiescent periods between groups of pulses to allow tissue refill with microbubbles) produced gene expression levels comparable to the standard US exposure but reduced the extent of liver damage. These results indicated that unfocused high intensity therapeutic ultrasound exposure with microbubbles is highly promising for safe and efficient gene delivery into the liver of rats or larger animals.

Efficiency of drug delivery enhanced by acoustic pressure during blood-brain barrier disruption induced by focused ultrasound

Purpose

We evaluated the delivery efficiency of intravenously injected large molecular agents, before and after disruption of the blood–brain barrier (BBB-D), induced by focused ultrasound (FUS) using various acoustic parameters.

Materials and methods

Male Sprague-Dawley rats were injected intravenously with Evans blue (EB) before or after BBB-D induction by pulsed FUS. We used a 1.0 MHz pulsed FUS with four acoustic power settings and an ultrasound contrast agent (UCA) at four different doses to induce BBB-D resulting from cavitation. The permeability of the BBB was assessed quantitatively based on the extravasation of EB. Contrast enhanced magnetic resonance imaging (MRI) was used to monitor the gadolinium deposition associated with FUS. Histological analysis was performed to examine tissue damage.

Results

The accumulation of EB in rat brain was found to be dependent on acoustic power and UCA dosage, regardless of whether EB administration occurred before or after FUS-induced BBB-D. Administration of EB followed by sonication resulted in greater EB extravasation than that for rats subjected to sonication prior to EB injection. To reduce tissue damage, EB extravasation was enhanced by first administering EB by intravenous injection, followed by sonication at reduced acoustic power or UCA dosage. The normalized signal intensity change in rat brains that received the same dose of UCA and sonicated after gadolinium injection was significantly greater than in rats undergoing sonication followed by gadolinium administration. Moreover, contrast enhanced MRI showed a more precise distribution of gadolinium in the brain when gadolinium was administered before sonication.

Conclusion

We demonstrated that a compound administered prior to sonication treatment promotes extravasation of the sonicated region. Thus, it is possible to optimize ultrasound parameters for lower sonication and reduced UCA doses, to induce BBB-D while minimizing damage to normal brain tissue.

Investigation of microbubble response to long pulses used in ultrasound-enhanced drug delivery

In current drug delivery approaches, microbubbles and drugs can be co-administered while ultrasound is applied. The mechanism of microbubble interaction with ultrasound, the drug and the cells is not fully understood. The aim of this study was to investigate microbubble response to long ultrasonic pulses used in drug delivery approaches. Two different in vitro set-ups were considered: with the microbubbles diluted in an enclosure and with the microbubbles flowing in a capillary tube. Acoustic streaming, which influences the observed bubble response, was observed in "typical" drug delivery conditions in the first set-up. With the capillary set-up, streaming effects were avoided and accurate bubble responses were recorded. The diffraction pattern of the source greatly influences the bubble response and in different locations of the field different bubble responses are observed. At low nondestructive pressures, microbubbles can oscillate for thousands of cycles repeatedly. At high acoustic pressures (at 1 MHz), most bubble activity disappeared within about 100 μs despite the length of the pulse, mainly due to violent bubble destruction and subsequent accelerated diffusion.

Ultrasound- and liposome microbubble-mediated targeted gene transfer to cardiomyocytes in vivo accompanied by polyethylenimine

OBJECTIVES

Gene transfer to cardiomyocytes in vivo has received much research attention in the last decade but remains a substantial hurdle. Gene transfer using ultrasound-targeted microbubble destruction is a promising tool for gene therapy. Little data have shown the feasibility and optimization of this method for primary myocardial disease. In this study, we sought to determine the feasibility and efficiency of in vivo gene transfer to the myocardium mediated by ultrasound-targeted microbubble destruction accompanied by polyethylenimine.

METHODS

Three plasmids (luciferase reporter, red fluorescent protein reporter, and enhanced green fluorescent protein reporter) were used in this study. The ultrasound parameters were also optimized. A solution containing phosphate-buffered saline, a plasmid, plasmid complex, or polyethylenimine/plasmid, and liposome microbubbles was injected via a tail vein with (study) or without (control) transthoracic ultrasound irradiation. The efficiency of reporter gene transfer was determined by detection of luciferase activity or microscopy, and histologic investigations of the tissue specimens were performed.

RESULTS

Ultrasound-targeted microbubble destruction significantly increased luciferase activity in vivo compared to plasmids and microbubbles alone (P < .001). More importantly, the increase in transgene expression was significantly related to ultrasound-targeted microbubble destruction in the presence of polyethylenimine (P < .001). In addition, fluorescein expression was present in all sections that received ultrasound-targeted microbubble destruction. The fluorescent reporter genes and luciferase plasmid all had similar results. Regardless of ultrasound exposure, expression in other organs was close to a background level except for the liver and lung. Hematoxylin-eosin staining showed no notable myocardial injury or death in control and treated mice.

CONCLUSIONS

An atraumatic targeted gene delivery technique based on ultrasound-targeted microbubble destruction and polyethylenimine has been developed to transfect cardiomyocytes in vivo. If a suitable target gene is added, the novel technique could be highly effective in many kinds of heart disease.

Explorations of high-intensity therapeutic ultrasound and microbubble-mediated gene delivery in mouse liver

Ultrasound (US) combined with microbubbles (MBs) is a promising technology for non-viral gene delivery. Significant enhancements of gene expression have been obtained in our previous studies. To optimize and prepare for application to larger animal models, the luciferase reporter gene transfer efficacy of lipid-based Definity MBs of various concentrations, pressure amplitudes and a novel unfocused high-intensity therapeutic US (HITU) system were explored. Luciferase expression exhibited a dependence on MB dose over the range of 0-25 vol%, and a strong dependence on acoustic peak negative pressure at over the range of 0-3.2 MPa. Gene expression reached an apparent plateau at MB concentration ≥2.5 vol% or at negative pressures >1.8 MPa. Maximum gene expression in treated animals was 700-fold greater than in negative controls. Pulse train US exposure protocols produced an upward trend of gene expression with increasing quiescent time. The hyperbolic correlation of gene expression and transaminase levels suggested that an optimum gene delivery effect can be achieved by maximizing acoustic cavitation-induced enhancement of DNA uptake and minimizing unproductive tissue damage. This study validated the new HITU system equipped with an unfocused transducer with a larger footprint capable of scanning large tissue areas to effectively enhance gene transfer efficiencies.

Effects of a novel ultrasound contrast agent with long persistence on right ventricular pressure: Comparison with SonoVue

This work investigated the effect of infusion of a self-made ultrasound contrast agent with long persistence (named ZHIFUXIAN) on rat right ventricular pressure and made a preliminary evaluation on the relative safety of the novel microbubbles. Normal saline, SonoVue and ZHIFUXIAN were injected through caudal vein at the total volume of 0.5ml for each injection. The right ventricular systolic pressure (RVSP) and end-diastolic pressure (RVEDP) were monitored and the changes of the pressure were compared with baseline readings. RVSP increased when saline, SonoVue or ZHIFUXIAN were injected, the greatest change being after SonoVue (about 2mmHg), but there was no statistical significance compared with baseline (P>0.05). There was no significant difference in RVSP between saline, SonoVue and ZHIFUXIAN at any time point. Also, there was no significant difference in RVEDP between groups at each time point and between different time points in each group. The results indicate that the self-made microbubbles effect on right ventricular hemodynamics is equivalent to that of normal saline at the same volume needed for effective enhanced imaging, demonstrating that it does not produce changes in right ventricular blood pressure under the study conditions. Pathological examination also showed it had no obvious influence on lung, liver and kidney.

Sonoporation, drug delivery, and gene therapy

Ultrasound is a very effective modality for drug delivery and gene therapy because energy that is non-invasively transmitted through the skin can be focused deeply into the human body in a specific location and employed to release drugs at that site. Ultrasound cavitation, enhanced by injected microbubbles, perturbs cell membrane structures to cause sonoporation and increases the permeability to bioactive materials. Cavitation events also increase the rate of drug transport in general by augmenting the slow diffusion process with convective transport processes. Drugs and genes can be incorporated into microbubbles, which in turn can target a specific disease site using ligands such as the antibody. Drugs can be released ultrasonically from microbubbles that are sufficiently robust to circulate in the blood and retain their cargo of drugs until they enter an insonated volume of tissue. Local drug delivery ensures sufficient drug concentration at the diseased region while limiting toxicity for healthy tissues. Ultrasound-mediated gene delivery has been applied to heart, blood vessel, lung, kidney, muscle, brain, and tumour with enhanced gene transfection efficiency, which depends on the ultrasonic parameters such as acoustic pressure, pulse length, duty cycle, repetition rate, and exposure duration, as well as microbubble properties such as size, gas species, shell material, interfacial tension, and surface rigidity. Microbubble-augmented sonothrombolysis can be enhanced further by using targeting microbubbles.

Formulation and characterization of echogenic lipid-Pluronic nanobubbles

The advent of microbubble contrast agents has enhanced the capabilities of ultrasound as a medical imaging modality and stimulated innovative strategies for ultrasound-mediated drug and gene delivery. While the utilization of microbubbles as carrier vehicles has shown encouraging results in cancer therapy, their applicability has been limited by a large size which typically confines them to the vasculature. To enhance their multifunctional contrast and delivery capacity, it is critical to reduce bubble size to the nanometer range without reducing echogenicity. In this work, we present a novel strategy for formulation of nanosized, echogenic lipid bubbles by incorporating the surfactant Pluronic, a triblock copolymer of ethylene oxide copropylene oxide coethylene oxide into the formulation. Five Pluronics (L31, L61, L81, L64 and P85) with a range of molecular weights (M(w): 1100 to 4600 Da) were incorporated into the lipid shell either before or after lipid film hydration and before addition of perfluorocarbon gas. Results demonstrate that Pluronic-lipid interactions lead to a significantly reduced bubble size. Among the tested formulations, bubbles made with Pluronic L61 were the smallest with a mean hydrodynamic diameter of 207.9 +/- 74.7 nm compared to the 880.9 +/- 127.6 nm control bubbles. Pluronic L81 also significantly reduced bubble size to 406.8 +/- 21.0 nm. We conclude that Pluronic is effective in lipid bubble size control, and Pluronic M(w), hydrophilic-lipophilic balance (HLB), and Pluronic/lipid ratio are critical determinants of the bubble size. Most importantly, our results have shown that although the bubbles are nanosized, their stability and in vitro and in vivo echogenicity are not compromised. The resulting nanobubbles may be better suited for contrast enhanced tumor imaging and subsequent therapeutic delivery.

Chitosan-based systems for molecular imaging

Molecular imaging enables the non-invasive assessment of biological and biochemical processes in living subjects. Such technologies therefore have the potential to enhance our understanding of disease and drug activity during preclinical and clinical drug development. Molecular imaging allows a repetitive and non-invasive study of the same living subject using identical or alternative biological imaging assays at different time points, thus harnessing the statistical power of longitudinal studies, and reducing the number of animals required and cost. Chitosan is a hydrophilic and non-antigenic biopolymer and has a low toxicity toward mammalian cells. Hence, it has great potential as a biomaterial because of its excellent biocompatibility. Conjugated to additional materials, chitosan composites result in a new class of biomaterials that possess mechanical, physicochemical and functional properties, which have potential for use in advanced biomedical imaging applications. The present review will discuss the strengths, limitations and challenges of molecular imaging as well as applications of chitosan nanoparticles in the field of molecular imaging.