Localized ultrasound enhances delivery of rapamycin from microbubbles to prevent smooth muscle proliferation

Gelatin microgel-coated balloon catheter with enhanced delivery of everolimus for long-term vascular patency

In-stent restenosis (ISR) after percutaneous coronary intervention is a major reason for limited long-term patency due to complex neointimal proliferation caused by vascular injury. Drug-coated balloon (DCB) has been developed to treat various cardiovascular diseases including ISR by providing anti-proliferative drugs into blood vessel tissues. However, a significant proportion of the drug is lost during balloon tracking, resulting in ineffective drug delivery to the target region. In this study, we report an everolimus-coated balloon (ECB) using everolimus-loaded gelatin-hydroxyphenyl propionic acid microgel (GM) with enhanced everolimus delivery to vascular walls for long-term patency. GM with high drug loading (> 97%) was simply prepared by homogenizing enzyme-mediated crosslinked hydrogels. The optimal condition to prepare GM-coated ECB (GM-ECB) was established by changing homogenization time and ethanol solvent concentration (30 ∼ 80%). In vitro sustained everolimus release for 30 d, and cellular efficacy using smooth muscle cells and vascular endothelial cells were evaluated. Additionally, an in vivo drug transfer levels of GM-ECB using rabbit femoral arteries were assessed with reduced drug loss and efficient drug delivery capability. Finally, using ISR-induced porcine models, effective in vivo vascular patency 4 weeks after treatment of ECBs was also confirmed. Thus, this study strongly demonstrates that GM can be used as a potential drug delivery platform for DCB application. STATEMENT OF SIGNIFICANCE: We report an ECB using everolimus-loaded GM prepared by homogenization of enzymatic cross-linked hydrogel. GM showed efficient drug loading (> 97 %) and controllable size. GM-ECB exhibited potential to deliver everolimus in a sustained manner to target area with drug efficacy and viability against SMC and EC. Although GM-ECB had much lower drug content compared to controls, animal study demonstrated enhanced drug transfer and reduced drug loss of GM-ECB due to the protection of encapsulated drugs by GM, and the possible interaction between GM and endothelium. Finally, vascular patency and safety were assessed using ISR-induced porcine models. We suggest an advanced DCB strategy to alleviate rapid drug clearance by bloodstream while improving drug delivery for a long-term vascular patency.

Sirolimus-Coated Balloon With a Microsphere-Based Technology for the Treatment of De Novo or Restenotic Coronary Lesions

BACKGROUND

Non stent-based local drug delivery with drug-coated balloon (DCB) is an alternative to drug-eluting stent with favorable clinical applicability in the treatment of selected coronary lesions. Our purpose was to report the initial performance, safety and efficacy evaluations of a novel sirolimus-coated balloon in the treatment of coronary lesions.

METHODS

This was a phase I (first-in-man), prospective, multicenter, single-arm trial evaluating the novel SELUTION SLR™ DCB (M.A. Med Alliance SA, Nyon, Switzerland), which incorporates a polymeric microsphere-based technology for controlled and continuous release of sirolimus, in the treatment of de novo or restenotic lesions.

RESULTS

A total of 56 patients/lesions were enrolled between November/2018 and March/2019. Diabetes was found in 46.6 %, and de novo lesions represented 79.6 % of cases. Device and procedural/clinical success were 100 % and 96.4 %, respectively. There was only one major adverse cardiac event (target lesion revascularization) reported at late follow-up. By quantitative coronary angiography analysis, mean % diameter stenosis was 30.5 ± 16.7 %, late lumen loss was 0.26 ± 0.45 mm and angiographic binary restenosis occurred in 4 of 45 cases at 6-month angiographic follow-up.

CONCLUSION

The novel SELUTION sirolimus-coated balloon demonstrated safety and efficacy in the treatment of diseased coronary vessels, including absence of mortality and relatively low late lumen loss at late follow-up.

Non-Viral Delivery of CRISPR/Cas Cargo to the Retina Using Nanoparticles: Current Possibilities, Challenges, and Limitations

The discovery of the CRISPR/Cas system and its development into a powerful genome engineering tool have revolutionized the field of molecular biology and generated excitement for its potential to treat a wide range of human diseases. As a gene therapy target, the retina offers many advantages over other tissues because of its surgical accessibility and relative immunity privilege due to its blood-retinal barrier. These features explain the large advances made in ocular gene therapy over the past decade, including the first in vivo clinical trial using CRISPR gene-editing reagents. Although viral vector-mediated therapeutic approaches have been successful, they have several shortcomings, including packaging constraints, pre-existing anti-capsid immunity and vector-induced immunogenicity, therapeutic potency and persistence, and potential genotoxicity. The use of nanomaterials in the delivery of therapeutic agents has revolutionized the way genetic materials are delivered to cells, tissues, and organs, and presents an appealing alternative to bypass the limitations of viral delivery systems. In this review, we explore the potential use of non-viral vectors as tools for gene therapy, exploring the latest advancements in nanotechnology in medicine and focusing on the nanoparticle-mediated delivery of CRIPSR genetic cargo to the retina.

Molecular Imaging and Non-molecular Imaging of Atherosclerotic Plaque Thrombosis

Thrombosis in the context of atherosclerosis typically results in life-threatening consequences, including acute coronary events and ischemic stroke. As such, early detection and treatment of thrombosis in atherosclerosis patients is essential. Clinical diagnosis of thrombosis in these patients is typically based upon a combination of imaging approaches. However, conventional imaging modalities primarily focus on assessing the anatomical structure and physiological function, severely constraining their ability to detect early thrombus formation or the processes underlying such pathology. Recently, however, novel molecular and non-molecular imaging strategies have been developed to assess thrombus composition and activity at the molecular and cellular levels more accurately. These approaches have been successfully used to markedly reduce rates of atherothrombotic events in patients suffering from acute coronary syndrome (ACS) by facilitating simultaneous diagnosis and personalized treatment of thrombosis. Moreover, these modalities allow monitoring of plaque condition for preventing plaque rupture and associated adverse cardiovascular events in such patients. Sustained developments in molecular and non-molecular imaging technologies have enabled the increasingly specific and sensitive diagnosis of atherothrombosis in animal studies and clinical settings, making these technologies invaluable to patients' health in the future. In the present review, we discuss current progress regarding the non-molecular and molecular imaging of thrombosis in different animal studies and atherosclerotic patients.

Immunomodulatory nanosystems for treating inflammatory diseases

Inflammatory disease (ID) is an umbrella term encompassing all illnesses involving chronic inflammation as the central manifestation of pathogenesis. These include, inflammatory bowel diseases, hepatitis, pulmonary disorders, atherosclerosis, myocardial infarction, pancreatitis, arthritis, periodontitis, psoriasis. The IDs create a severe burden on healthcare and significantly impact the global socio-economic balance. Unfortunately, the standard therapies that rely on a combination of anti-inflammatory and immunosuppressive agents are palliative and provide only short-term relief. In contrast, the emerging concept of immunomodulatory nanosystems (IMNs) has the potential to address the underlying causes and prevent reoccurrence, thereby, creating new opportunities for treating IDs. The IMNs offer exquisite ability to precisely modulate the immune system for a therapeutic advantage. The nano-sized dimension of IMNs allows them to efficiently infiltrate lymphatic drainage, interact with immune cells, and subsequently to undergo rapid endocytosis by hyperactive immune cells (HICs) at inflamed sites. Thus, IMNs serve to restore dysfunctional or HICs and alleviate the inflammation. We identified that different IMNs exert their immunomodulatory action via either of the seven mechanisms to modulate; cytokine production, cytokine neutralization, cellular infiltration, macrophage polarization, HICs growth inhibition, stimulating T-reg mediated tolerance and modulating oxidative-stress. In this article, we discussed representative examples of IMNs by highlighting their rationalization, design principle, and mechanism of action in context of treating various IDs. Lastly, we highlighted technical challenges in the application of IMNs and explored the future direction of research, which could potentially help to overcome those challenges.

Visualized podocyte-targeting and focused ultrasound responsive glucocorticoid nano-delivery system against immune-associated nephropathy without glucocorticoid side effect

Glucocorticoids are widely used in the treatment of nephritis, however, its dose-dependent side effects, such as the increased risk of infection and metabolic disturbances, hamper its clinical use. This study reports a visualized podocyte-targeting and focused ultrasound responsive glucocorticoid nano-delivery system (named as Dex/PFP@LIPs-BMS-α), which specific delivers dexamethasone (Dex) to podocyte targets and reduces systemic side effects.

Methods: The glucocorticoid nano-delivery system was synthesized by a lipid thin film and a simple facile acoustic-emulsification method. This glucocorticoid nano-delivery system used BMS-470539 (BMS-α), a synthetic compound, as a “navigator” to specifically identify and target the melanocortin-1 receptor (MC-1R) on podocytes. The loaded perfluoropentane (PFP) realizes the directed "explosion effect" through ultrasound-targeted microbubble destruction (UTMD) technology under the coordination of low intensity focused ultrasound (LIFU) to completely release Dex.

Results: Both in vitro and in vivo experiments have demonstrated that Dex/PFP@LIPs-BMs-α accurately gathered to podocyte targets and improved podocyte morphology. Moreover, in vivo, proteinuria and serum creatinine levels were significantly reduced in the group treated with Dex/PFP@LIPs-BMS-α, and no severe side effects were detected. Furthermore, Dex/PFP@LIPs-BMS-α, with capabilities of ultrasound, photoacoustic and fluorescence imaging, provided individualized visual guidance and the monitoring of treatment.

Conclusion: This study provides a promising strategy of Dex/PFP@LIPs-BMS-α as effective and safe against immune-associated nephropathy.

Comparison of Bubble Size Distributions Inferred from Acoustic, Optical Visualisation, and Laser Diffraction

Bubble measurement has been widely discussed in the literature and comparison studies have been widely performed to validate the results obtained for various forms of bubble size inferences. This paper explores three methods used to obtain a bubble size distribution—optical detection, laser diffraction and acoustic inferences—for a bubble cloud. Each of these methods has advantages and disadvantages due to their intrinsic inference methodology or design flaws due to lack of specificity in measurement. It is clearly demonstrated that seeing bubbles and hearing them are substantially and quantitatively different. The main hypothesis being tested is that for a bubble cloud, acoustic methods are able to detect smaller bubbles compared to the other techniques, as acoustic measurements depend on an intrinsic bubble property, whereas photonics and optical methods are unable to “see” a smaller bubble that is behind a larger bubble. Acoustic methods provide a real-time size distribution for a bubble cloud, whereas for other techniques, appropriate adjustments or compromises must be made in order to arrive at robust data. Acoustic bubble spectrometry consistently records smaller bubbles that were not detected by the other techniques. The difference is largest for acoustic methods and optical methods, with size differences ranging from 5–79% in average bubble size. Differences in size between laser diffraction and optical methods ranged from 5–68%. The differences between laser diffraction and acoustic methods are less, and range between 0% (i.e., in agreement) up to 49%. There is a wider difference observed between the optical method, laser diffraction and acoustic methods whilst good agreement between laser diffraction and acoustic methods. The significant disagreement between laser diffraction and acoustic method (35% and 49%) demonstrates the hypothesis, as there is a higher proportion of smaller bubbles in these measurements (i.e., the smaller bubbles ‘hide’ during measurement via laser diffraction). This study, which shows that acoustic bubble spectrometry is able to detect smaller bubbles than laser diffraction and optical techniques. This is supported by heat and mass transfer studies that show enhanced performance due to increased interfacial area of microbubbles, compared to fine bubbles.

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.

Cold plasma gas loaded microbubbles as a novel ultrasound contrast agent

Nowadays, cold atmospheric plasma (CAP) that contains lots of active free radicals has tremendous potential applications in biomedical engineering, and target delivery of a controllable dose of plasma gas is highly desired in clinical use. In this conceptual study, we developed a novel microbubble loaded by plasma gas and proposed an ultrasound-triggered strategy for the ultrasound-triggered release of free radicals from the microbubbles. The plasma microbubbles (PMBs) were fabricated by mixing plasma gas in the core of the surfactant microbubbles by a modified emulsification process. The resulting PMBs with an average size of 2.54 ± 2.28 μm were successfully fabricated using the proposed approach and the experimental result showed that PMBs exhibited a satisfactory ability to meet the requirement of ultrasound contrast-enhanced imaging. Furthermore, we depicted that ultrasound induced PMB destruction to release the plasma gas and PMBs with ultrasound stimulation could significantly improve the concentration of nitric oxide and hydrogen peroxide compared with the control group. In addition, Dil acting as a model drug was loaded into the PMBs and an in vitro cell experiment showed that Dil and plasma gas could be released from PMBs and internalized by PIEC cells with ultrasound mediation. Our experimental results showed that ultrasound induced PMB destruction could successfully release many active free radicals in plasma gas, including nitric oxide and hydrogen peroxide. The developed novel microbubbles demonstrated the technical potential of plasma gas loaded MBs for disease diagnostics and therapy with ultrasound imaging guidance.

A versatile method for the preparation of particle-loaded microbubbles for multimodality imaging and targeted drug delivery

Microbubbles are currently in clinical use as ultrasound contrast agents and under active investigation as mediators of ultrasound therapy. To improve the theranostic potential of microbubbles, nanoparticles can be attached to the bubble shell for imaging, targeting and/or enhancement of acoustic response. Existing methods for fabricating particle-loaded bubbles, however, require the use of polymers, oil layers or chemical reactions for particle incorporation; embed/attach the particles that can reduce echogenicity; impair biocompatibility; and/or involve multiple processing steps. Here, we describe a simple method to embed nanoparticles in a phospholipid-coated microbubble formulation that overcomes these limitations. Magnetic nanoparticles are used to demonstrate the method with a range of different microbubble formulations. The size distribution and yield of microbubbles are shown to be unaffected by the addition of the particles. We further show that the microbubbles can be retained against flow using a permanent magnet, can be visualised by both ultrasound and magnetic resonance imaging (MRI) and can be used to transfect SH-SY5Y cells with fluorescent small interfering RNA under the application of a magnetic field and ultrasound field.

Lipid microbubbles as a vehicle for targeted drug delivery using focused ultrasound-induced blood-brain barrier opening

Focused ultrasound in conjunction with lipid microbubbles has fully demonstrated its ability to induce non-invasive, transient, and reversible blood-brain barrier opening. This study was aimed at testing the feasibility of our lipid-coated microbubbles as a vector for targeted drug delivery in the treatment of central nervous system diseases. These microbubbles were labeled with the fluorophore 5-dodecanoylaminfluorescein. Focused ultrasound targeted mouse brains in vivo in the presence of these microbubbles for trans-blood-brain barrier delivery of 5-dodecanoylaminfluorescein. This new approach, compared to previously studies of our group, where fluorescently labeled dextrans and microbubbles were co-administered, represents an appreciable improvement in safety outcome and targeted drug delivery. This novel technique allows the delivery of 5-dodecanoylaminfluorescein at the region of interest unlike the alternative of systemic exposure. 5-dodecanoylaminfluorescein delivery was assessed by ex vivo fluorescence imaging and by in vivo transcranial passive cavitation detection. Stable and inertial cavitation doses were quantified. The cavitation dose thresholds for estimating, a priori, successful targeted drug delivery were, for the first time, identified with inertial cavitation were concluded to be necessary for successful delivery. The findings presented herein indicate the feasibility and safety of the proposed microbubble-based targeted drug delivery and that, if successful, can be predicted by cavitation detection in vivo.

Characterization of Bioeffects on Endothelial Cells under Acoustic Droplet Vaporization

Gas embolotherapy is achieved by locally vaporizing microdroplets through acoustic droplet vaporization, which results in bubbles that are large enough to occlude blood flow directed to tumors. Endothelial cells, lining blood vessels, can be affected by these vaporization events, resulting in cell injury and cell death. An idealized monolayer of endothelial cells was subjected to acoustic droplet vaporization using a 3.5-MHz transducer and dodecafluoropentane droplets. Treatments included insonation pressures that varied from 2 to 8 MPa (rarefactional) and pulse lengths that varied from 4 to 16 input cycles. The bubble cloud generated was directly dependent on pressure, but not on pulse length. Cellular damage increased with increasing bubble cloud size, but was limited to the bubble cloud area. These results suggest that vaporization near the endothelium may impact the vessel wall, an effect that could be either deleterious or beneficial depending on the intended overall therapeutic application.

Reducing Neointima Formation in a Swine Model with IVUS and Sirolimus Microbubbles

Potent therapeutic compounds with dose dependent side effects require more efficient and selective drug delivery to reduce systemic drug doses. Here, we demonstrate a new platform that combines intravascular ultrasound (IVUS) and drug-loaded microbubbles to enhance and localize drug delivery, while enabling versatility of drug type and dosing. Localization and degree of delivery with IVUS and microbubbles was assessed using fluorophore-loaded microbubbles and different IVUS parameters in ex vivo swine arteries. Using a swine model of neointimal hyperplasia, reduction of neointima formation following balloon injury was evaluated when using the combination of IVUS and sirolimus-loaded microbubbles. IVUS and microbubble enhanced fluorophore delivery was greatest when applying low amplitude pulses in the ex vivo model. In the in vivo model, neointima formation was reduced by 50% after treatment with IVUS and the sirolimus-loaded microbubbles. This reduction was achieved with a sirolimus whole blood concentration comparable to a commercial drug-eluting stent (0.999 ng/mL). We anticipate this therapy will find clinical use localizing drug delivery for numerous other diseases in addition to serving as an adjunct to stents in treating atherosclerosis.

Localized in vivo model drug delivery with intravascular ultrasound and microbubbles

An intravascular ultrasound (IVUS) and microbubble drug delivery system was evaluated in both ex vivo and in vivo swine vessel models. Microbubbles with the fluorophore DiI embedded in the shell as a model drug were infused into ex vivo swine arteries at a physiologic flow rate (105 mL/min) while a 5-MHz IVUS transducer applied ultrasound. Ultrasound pulse sequences consisted of acoustic radiation force pulses to displace DiI-loaded microbubbles from the vessel lumen to the wall, followed by higher-intensity delivery pulses to release DiI into the vessel wall. Insonation with both the acoustic radiation force pulse and the delivery pulse increased DiI deposition 10-fold compared with deposition with the delivery pulse alone. Localized delivery of DiI was then demonstrated in an in vivo swine model. The theoretical transducer beam width predicted the measured angular extent of delivery to within 11%. These results indicate that low-frequency IVUS catheters are a viable method for achieving localized drug delivery with microbubbles.

Acoustic behavior of microbubbles and implications for drug delivery

Ultrasound contrast agents are valuable in diagnostic ultrasound imaging, and they increasingly show potential for drug delivery. This review focuses on the acoustic behavior of flexible-coated microbubbles and rigid-coated microcapsules and their contribution to enhanced drug delivery. Phenomena relevant to drug delivery, such as non-spherical oscillations, shear stress, microstreaming, and jetting will be reviewed from both a theoretical and experimental perspective. Further, the two systems for drug delivery, co-administration and the microbubble as drug carrier system, are reviewed in relation to the microbubble behavior. Finally, future prospects are discussed that need to be addressed for ultrasound contrast agents to move from a pre-clinical tool into a clinical setting.

Ultrasound and microbubble-targeted delivery of small interfering RNA into primary endothelial cells is more effective than delivery of plasmid DNA

Ultrasound and microbubble-targeted delivery (UMTD) is a promising non-viral technique for genetic-based therapy. We found that UMTD of small interfering RNA (siRNA) is more effective than delivery of plasmid DNA (pDNA). UMTD (1 MHz, 0.22 MPa) of fluorescently labeled siRNA resulted in 97.9 ± 1.5% transfected cells, with siRNA localized homogenously in the cytoplasm directly after ultrasound exposure. UMTD of fluorescently labeled pDNA resulted in only 43.0 ± 4.2% transfected cells, with localization mainly in vesicular structures, co-localizing with endocytosis markers clathrin and caveolin. Delivery of siRNA against GAPDH (glyceraldehyde-3-phosphate dehydrogenase) effectively decreased protein levels to 24.3 ± 7.9% of non-treated controls (p < 0.01). In contrast, 24 h after delivery of pDNA encoding GAPDH, no increase in protein levels was detected. Transfection efficiency, verified with red fluorescently labeled pDNA encoding enhanced green fluorescent protein, revealed that of the transfected cells, only 2.0 ± 0.7% expressed the transgene. In conclusion, the difference in localization between siRNA and pDNA after UMTD is an important determinant of the effectiveness of these genetic-based technologies.

Encapsulated microbubbles and echogenic liposomes for contrast ultrasound imaging and targeted drug delivery

Micron- to nanometer-sized ultrasound agents, like encapsulated microbubbles and echogenic liposomes, are being developed for diagnostic imaging and ultrasound mediated drug/gene delivery. This review provides an overview of the current state of the art of the mathematical models of the acoustic behavior of ultrasound contrast microbubbles. We also present a review of the in vitro experimental characterization of the acoustic properties of microbubble based contrast agents undertaken in our laboratory. The hierarchical two-pronged approach of modeling contrast agents we developed is demonstrated for a lipid coated (Sonazoid™) and a polymer shelled (poly D-L-lactic acid) contrast microbubbles. The acoustic and drug release properties of the newly developed echogenic liposomes are discussed for their use as simultaneous imaging and drug/gene delivery agents. Although echogenicity is conclusively demonstrated in experiments, its physical mechanisms remain uncertain. Addressing questions raised here will accelerate further development and eventual clinical approval of these novel technologies.

Current status and prospects for microbubbles in ultrasound theranostics

Encapsulated microbubbles have been developed over the past two decades to provide improvements both in imaging as well as new therapeutic applications. Microbubble contrast agents are used currently for clinical imaging where increased sensitivity to blood flow is required, such as echocardiography. These compressible spheres oscillate in an acoustic field, producing nonlinear responses which can be uniquely distinguished from surrounding tissue, resulting in substantial enhancements in imaging signal-to-noise ratio. Furthermore, with sufficient acoustic energy the oscillation of microbubbles can mediate localized biological effects in tissue including the enhancement of membrane permeability or increased thermal energy deposition. Structurally, microbubbles are comprised of two principal components--an encapsulating shell and an inner gas core. This configuration enables microbubbles to be loaded with drugs or genes for additional therapeutic effect. Application of sufficient ultrasound energy can release this payload, resulting in site-specific delivery. Extensive preclinical studies illustrate that combining microbubbles and ultrasound can result in enhanced drug delivery or gene expression at spatially selective sites. Thus, microbbubles can be used for imaging, for therapy, or for both simultaneously. In this sense, microbubbles combined with acoustics may be one of the most universal theranostic tools.

Enhanced intracellular delivery of a model drug using microbubbles produced by a microfluidic device

Focal drug delivery to a vessel wall facilitated by intravascular ultrasound and microbubbles holds promise as a potential therapy for atherosclerosis. Conventional methods of microbubble administration result in rapid clearance from the bloodstream and significant drug loss. To address these limitations, we evaluated whether drug delivery could be achieved with transiently stable microbubbles produced in real time and in close proximity to the therapeutic site. Rat aortic smooth muscle cells were placed in a flow chamber designed to simulate physiological flow conditions. A flow-focusing microfluidic device produced 8 μm diameter monodisperse microbubbles within the flow chamber, and ultrasound was applied to enhance uptake of a surrogate drug (calcein). Acoustic pressures up to 300 kPa and flow rates up to 18 mL/s were investigated. Microbubbles generated by the flow-focusing microfluidic device were stabilized with a polyethylene glycol-40 stearate shell and had either a perfluorobutane (PFB) or nitrogen gas core. The gas core composition affected stability, with PFB and nitrogen microbubbles exhibiting half-lives of 40.7 and 18.2 s, respectively. Calcein uptake was observed at lower acoustic pressures with nitrogen microbubbles (100 kPa) than with PFB microbubbles (200 kPa) (p < 0.05, n > 3). In addition, delivery was observed at all flow rates, with maximal delivery (>70% of cells) occurring at a flow rate of 9 mL/s. These results demonstrate the potential of transiently stable microbubbles produced in real time and in close proximity to the intended therapeutic site for enhancing localized drug delivery.

Real time dynamic imaging and current targeted therapies in the war on cancer: a new paradigm

In biology, as every science student is made to learn, ontology recapitulates phylogeny. In medicine, however, oncology recapitulates polemology, the science of warfare: The medical establishment is transitioning from highly toxic poisons that kill rapidly dividing normal and malignant cells with little specificity to tailored therapies that target the tumors with the lethality of the therapeutic warhead. From the advent of the information age with the incorporation of high-tech intelligence, reconnaissance, and surveillance has resulted in "data fusion" where a wide range of information collected in near real-time can be used to redesign most of the treatment strategies currently used in the clinic. The medical community has begun to transition from the 'black box' of tumor therapy based solely on the clinical response to the 'glass box' of dynamic imaging designed to bring transparency to the clinical battlefield during treatment, thereby informing the therapeutic decision to 'retreat or repeat'. The tumor microenvironment is dynamic, constantly changing in response to therapeutic intervention, and therefore the therapeutic assessment must map to this variable and ever-changing landscape with dynamic and non-static imaging capabilities. The path to personalized medicine will require incorporation and integration of dynamic imaging at the bedside into clinical practice for real-time, interactive assessment of response to targeted therapies. The application of advanced real time imaging techniques along with current molecularly targeted anticancer therapies which alter cellular homeostasis and microenvironment can enhance therapeutic interventions in cancer patients and further improve the current status in clinical management of patients with advanced cancers.

Current status and prospects for microbubbles in ultrasound theranostics

Encapsulated microbubbles have been developed over the past two decades to provide improvements both in imaging as well as new therapeutic applications. Microbubble contrast agents are used currently for clinical imaging where increased sensitivity to blood flow is required, such as echocardiography. These compressible spheres oscillate in an acoustic field, producing nonlinear responses which can be uniquely distinguished from surrounding tissue, resulting in substantial enhancements in imaging signal-to-noise ratio. Furthermore, with sufficient acoustic energy the oscillation of microbubbles can mediate localized biological effects in tissue including the enhancement of membrane permeability or increased thermal energy deposition. Structurally, microbubbles are comprised of two principal components--an encapsulating shell and an inner gas core. This configuration enables microbubbles to be loaded with drugs or genes for additional therapeutic effect. Application of sufficient ultrasound energy can release this payload, resulting in site-specific delivery. Extensive preclinical studies illustrate that combining microbubbles and ultrasound can result in enhanced drug delivery or gene expression at spatially selective sites. Thus, microbbubles can be used for imaging, for therapy, or for both simultaneously. In this sense, microbubbles combined with acoustics may be one of the most universal theranostic tools.

Preliminary observations on the spatial correlation between short-burst microbubble oscillations and vascular bioeffects

The objective of this preliminary study was to examine the spatial correlation between microbubble (MB)-induced vessel wall displacements and resultant microvascular bioeffects. MBs were injected into venules in ex vivo rat mesenteries and insonated by a single short ultrasound pulse with a center frequency of 1 MHz and peak negative pressures spanning the range of 1.5-5.6 MPa. MB and vessel dynamics were observed under ultra-high speed photomicrography. The tissue was examined by histology or transmission electron microscopy for vascular bioeffects. Image registration allowed for spatial correlation of MB-induced vessel wall motion to corresponding vascular bioeffects, if any. In cases in which damage was observed, the vessel wall had been pulled inward by more than 50% of the its initial radius. The observed damage was characterized by the separation of the endothelium from the vessel wall. Although the study is limited to a small number of observations, analytic statistical results suggest that vessel invagination comprises a principal mechanism for bioeffects in venules by microbubbles.

Intravascular ultrasound catheter to enhance microbubble-based drug delivery via acoustic radiation force

Previous research has demonstrated that acoustic radiation force enhances intravascular microbubble adhesion to blood vessels in the presence of flow for moleculartargeted ultrasound imaging and drug delivery. A prototype acoustic radiation force intravascular ultrasound (ARFIVUS) catheter was designed and fabricated to displace a microbubble contrast agent in flow representative of conditions encountered in the human carotid artery. The prototype ARFIVUS transducer was designed to match the resonance frequency of 1.4- to 2.6-μm-diameter microbubbles modeled by an experimentally verified 1-D microbubble acoustic radiation force translation model. The transducer element was an elongated Navy Type I (hard) lead zirconate titanate (PZT) ceramic designed to operate at 3 MHz. Fabricated devices operated with center frequencies of 3.3 and 3.6 MHz with -6-dB fractional bandwidths of 55% and 50%, respectively. Microbubble translation velocities as high as 0.86 m/s were measured using a high-speed streak camera when insonating with the ARFIVUS transducer. Finally, the prototype was used to displace microbubbles in a flow phantom while imaging with a commercial 45-MHz imaging IVUS transducer. A sustained increase of 31 dB in average video intensity was measured following insonation with the ARFIVUS, indicating microbubble accumulation resulting from the application of acoustic radiation force.

Intravascular ultrasound detection and delivery of molecularly targeted microbubbles for gene delivery

We are investigating the combination of microbubble-based targeted drug delivery and intravascular ultrasound (IVUS) imaging as a potential therapy to reduce incidence of restenosis following stent placement in atherosclerotic coronary arteries. The goal of these studies was to determine whether IVUS could be used to detect targeted microbubbles and enhance drug/gene delivery through targeting. Quiescent vascular smooth muscle cells (SMCs) were stimulated with cytokine IL-1β to induce the inflammatory cell surface marker vascular cell adhesion molecule 1 (VCAM-1). Molecular-targeted (VCAM-1 Ab or IgG control Ab), fluorescent-labeled microbubbles were conjugated with plasmid DNA expressing green fluorescent protein (GFP, pMax-GFP) and exposed to the inflamed SMCs under flow to measure adhesion compared with control microbubbles. Gene delivery was performed using a modified IVUS catheter to generate 1.5-MHz ultrasound at 200 kPa. Detection of adherent microbubbles to inflamed SMCs in culture and flow chambers was measured using an IVUS catheter and scanner. VCAM-1-targeted microbubbles enhanced adhesion to inflamed SMCs 100-fold over nontargeted microbubbles. Compared with noninflamed SMCs, VCAM-1-targeted microbubbles exhibited a 7.9-fold increase in adhesion to IL-1β-treated cells. Targeted microbubbles resulted in a 5.5-fold increase in plasmid DNA transfection over nontargeted microbubbles in conjunction with a focused 2.54-cm (1-in) diameter 1-MHz transducer and also enhanced transfection by the modified IVUS transducer at 1.5 MHz. Targeted microbubbles (at a density of 3 × 10⁴ microbubbles/mm²) increased IVUS image intensity 13.2 dB over non-microbubble-coated surfaces. Rupture of microbubbles from the modified IVUS transducer resulted in a 53% reduction in image intensity. Taken together, these results indicate that IVUS may be used to detect targeted microbubbles to inflamed vasculature and subsequently deliver a gene/drug locally.

Focused ultrasound-mediated drug delivery from microbubbles reduces drug dose necessary for therapeutic effect on neointima formation--brief report

OBJECTIVE

We hypothesized that (1) neointima formation in a rat carotid balloon injury model could be reduced in vivo following targeted ultrasound delivery of rapamycin microbubbles (RMBs), and (2) the addition of dual-mode ultrasound decreases the total amount of drug needed to reduce neointima formation.

METHODS AND RESULTS

Balloon injury was performed in rat carotids to induce neointima formation. High or low doses of RMBs were injected intravenously and ruptured at the site of injury with ultrasound. Compared with nontreated injured arteries, neointima formation was reduced by 0% and 35.9% with 10(8) RMBs and by 28.7% and 34.9% in arteries treated with 10(9) RMBs with and without ultrasound, respectively.

CONCLUSIONS

Without ultrasound, 10-fold higher concentrations of RMBs were needed to reduce neointima formation by at least 28%, whereas 10(8) RMBs combined with ultrasound were sufficient to achieve the same therapeutic effect, demonstrating that this technology may have promise for localized potent drug therapy.