Sonothrombolysis with Magnetically Targeted Microbubbles.

Microbubble-enhanced sonothrombolysis is a promising approach to increasing the tolerability and efficacy of current pharmacological treatments for ischemic stroke. Maintaining therapeutic concentrations of microbubbles and drugs at the clot site, however, poses a challenge. The objective of this study was to investigate the effect of magnetic microbubble targeting upon clot lysis rates in vitro. Retracted whole porcine blood clots were placed in a flow phantom of a partially occluded middle cerebral artery. The clots were treated with a combination of tissue plasminogen activator (0.75 µg/mL), magnetic microbubbles (∼107 microbubbles/mL) and ultrasound (0.5 MHz, 630-kPa peak rarefactional pressure, 0.2-Hz pulse repetition frequency, 2% duty cycle). Magnetic targeting was achieved using a single permanent magnet (0.08-0.38 T and 12-140 T/m in the region of the clot). The change in clot diameter was measured optically over the course of the experiment. Magnetic targeting produced a threefold average increase in lysis rates, and linear correlation was observed between lysis rate and total energy of acoustic emissions.

Probing supramolecular protein assembly using covalently attached fluorescent molecular rotors.

Changes in microscopic viscosity and macromolecular crowding accompany the transition of proteins from their monomeric forms into highly organised fibrillar states. Previously, we have demonstrated that viscosity sensitive fluorophores termed 'molecular rotors', when freely mixed with monomers of interest, are able to report on changes in microrheology accompanying amyloid formation, and measured an increase in rigidity of approximately three orders of magnitude during aggregation of lysozyme and insulin. Here we extend this strategy by covalently attaching molecular rotors to several proteins capable of assembly into fibrils, namely lysozyme, fibrinogen and amyloid-ß peptide (Aß(1-42)). We demonstrate that upon covalent attachment the molecular rotors can successfully probe supramolecular assembly in vitro. Importantly, our new strategy has wider applications in cellulo and in vivo, since covalently attached molecular rotors can be successfully delivered in situ and will colocalise with the aggregating protein, for example inside live cells. This important advantage allowed us to follow the microscopic viscosity changes accompanying blood clotting and during Aß(1-42) aggregation in live SH-SY5Y cells. Our results demonstrate that covalently attached molecular rotors are a widely applicable tool to study supramolecular protein assembly and can reveal microrheological features of aggregating protein systems both in vitro and in cellulo not observable through classical fluorescent probes operating in light switch mode.

Ultrasound-Enhanced siRNA Delivery Using Magnetic Nanoparticle-Loaded Chitosan-Deoxycholic Acid Nanodroplets.

Small interfering RNA (siRNA) has significant therapeutic potential but its clinical translation has been severely inhibited by a lack of effective delivery strategies. Previous work has demonstrated that perfluorocarbon nanodroplets loaded with magnetic nanoparticles can facilitate the intracellular delivery of a conventional chemotherapeutic drug. The aim of this study is to determine whether a similar agent can provide a means of delivering siRNA, enabling efficient transfection without degradation of the molecule. Chitosan-deoxycholic acid nanoparticles containing perfluoropentane and iron oxide (d 0 = 7.5 ± 0.35 nm) with a mean hydrodynamic diameter of 257.6 ± 10.9 nm are produced. siRNA (AllStars Hs cell death siRNA) is electrostatically bound to the particle surface and delivery to lung cancer cells and breast cancer cells is investigated with and without ultrasound exposure (500 kHz, 1 MPa peak-to-peak focal pressure, 40 cycles per burst, 1 kHz pulse repetition frequency, 10 s duration). The results show that siRNA functionality is not impaired by the treatment protocol and that the nanodroplets are able to successfully promote siRNA uptake, leading to significant apoptosis (52.4%) 72 h after ultrasound treatment.

Nanoparticle-Loaded Protein-Polymer Nanodroplets for Improved Stability and Conversion Efficiency in Ultrasound Imaging and Drug Delivery.

A new formulation of volatile nanodroplets stabilized by a protein and polymer coating and loaded with magnetic nanoparticles is developed. The droplets show enhanced stability and phase conversion efficiency upon ultrasound exposure compared with existing formulations. Magnetic targeting, encapsulation, and release of an anticancer drug are demonstrated in vitro with a 40% improvement in cytotoxicity compared with free drug.

Properties, characteristics and applications of microbubbles for sonothrombolysis.

INTRODUCTION: Ultrasound enhancement of thrombolysis (sonothrombolysis) is further potentiated by administration of acoustically active microbubbles, which may be developed into powerful adjuvant therapies for thrombolytic treatment of occlusive conditions such as ischaemic stroke. AREAS COVERED: The role of microbubbles in sonothrombolysis is evaluated based on published in vitro and in vivo evidence and a critical review of clinical trials to date. Microbubble, ultrasound and drug parameters compiled from a broad search of the existing literature are tabulated. Mechanisms of microbubble-enhanced sonothrombolysis are discussed, with particular focus on acoustic cavitation and thermal effects. A number of challenges to widespread clinical adoption are identified. Key factors for future optimisation of treatment and microbubble design are proposed. EXPERT OPINION: Microbubble enhancement of thrombolysis is supported by a broad range of in vitro and in vivo evidence that demonstrates improved lysis compared to conventional drug treatment or ultrasound without microbubbles. Clinically, this is shown by accelerated recanalisation of occluded arteries; however, further research is needed to ensure patient safety. Before such techniques can enter widespread clinical practice, an improved understanding of the role of microbubbles in sonothrombolysis is required, in addition to demonstration of significant improvement over existing treatments and the development of reliable real-time monitoring protocols.