Ultrasound-mediated Drug Delivery Research Articles

Preparation of novel curcumin-loaded multifunctional nanodroplets for combining ultrasonic development and targeted chemotherapy

Recently, a new class of multifunctional nanodroplets that combine the properties of polymeric drug carriers, ultrasound imaging contrast agents, and enhancers of ultrasound-mediated drug delivery has been developed. We studied the formation mechanism of nanodroplets of a drug and its application in chemotherapy. Curcumin was loaded in polymeric micelles as a anti-cancer drug using polyethylene glycol block-poly(caprolactone) with encapsulation efficiency of 95.60%. At room temperature, the developed systems comprised perfluorocarbon nanodroplets stabilized by walls comprising biodegradable block copolymers. Upon heating to 37°C, the nanodroplets were converted to nano/microbubbles. Under ultrasound, nanobubbles cavitated and collapsed, resulting in release of the encapsulated drug. The percentage release of curcumin-loaded nanodroplets by insonation was 90.95%, showing enhancement compared with the non-ultrasound group. Nanodroplets strongly retained the loaded drugs in vivo yet, under ultrasound-mediated vaporization, they released the drugs, thereby implementing effective targeting into the tumor. The tumor inhibition of the group in which curcumin-loaded nanodroplets were combined with ultrasound was 71.30%, more than that of the group of curcumin-loaded nanodroplets (53.00%). Nanodroplets showed high enhancement of anti-cancer effects under ultrasound. Upon intravenous injection, a long-lasting, strong and selective ultrasound contrast was observed, suggesting their coalescence into larger, highly echogenic microbubbles. These multifunctional nanodroplets, which manifest excellent therapeutic and ultrasound properties, could be promising anti-cancer drug delivery systems.

Novel Central Nervous System Drug Delivery Systems

For decades, biomedical and pharmaceutical researchers have worked to devise new and more effective therapeutics to treat diseases affecting the central nervous system. The blood-brain barrier effectively protects the brain, but poses a profound challenge to drug delivery across this barrier. Many traditional drugs cannot cross the blood-brain barrier in appreciable concentrations, with less than 1% of most drugs reaching the central nervous system, leading to a lack of available treatments for many central nervous system diseases, such as stroke, neurodegenerative disorders, and brain tumors. Due to the ineffective nature of most treatments for central nervous system disorders, the development of novel drug delivery systems is an area of great interest and active research. Multiple novel strategies show promise for effective central nervous system drug delivery, giving potential for more effective and safer therapies in the future. This review outlines several novel drug delivery techniques, including intranasal drug delivery, nanoparticles, drug modifications, convection-enhanced infusion, and ultrasound-mediated drug delivery. It also assesses possible clinical applications, limitations, and examples of current clinical and preclinical research for each of these drug delivery approaches. Improved central nervous system drug delivery is extremely important and will allow for improved treatment of central nervous system diseases, causing improved therapies for those who are affected by central nervous system diseases.

Tracking of Cell Nuclei for Assessment of In Vitro Uptake Kinetics in Ultrasound-Mediated Drug Delivery Using Fibered Confocal Fluorescence Microscopy

Previously, we demonstrated the feasibility to monitor ultrasound-mediated uptake of a cell-impermeable model drug in real time with fibered confocal fluorescence microscopy. Here, we present a complete post-processing methodology, which corrects for cell displacements, to improve the accuracy of pharmacokinetic parameter estimation. Nucleus detection was performed based on the radial symmetry transform algorithm. Cell tracking used an iterative closest point approach. Pharmacokinetic parameters were calculated by fitting a two-compartment model to the time-intensity curves of individual cells. Cells were tracked successfully, improving time-intensity curve accuracy and pharmacokinetic parameter estimation. With tracking, 93% of the 370 nuclei showed a fluorescence signal variation that was well-described by a two-compartment model. In addition, parameter distributions were narrower, thus increasing precision. Dedicated image analysis was implemented and enabled studying ultrasound-mediated model drug uptake kinetics in hundreds of cells per experiment, using fiber-based confocal fluorescence microscopy.

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.

Prospects for enhancement of targeted radionuclide therapy of cancer using ultrasound

Ultrasound-mediated drug delivery is a promising means of enhancing delivery, distribution and effectiveness of drugs within tumours. In this review, prospects for exploiting ultrasound to improve the tumour delivery and distribution of radiolabelled antibodies for radioimmunotherapy and to overcome barriers imposed by tumour microenvironment are discussed.

Focused ultrasound mediated drug delivery from temperature-sensitive liposomes: in-vitro characterization and validation

Nanomedicine-based delivery with non-invasive techniques is a promising approach to increase local drug concentration and to reduce systemic side effects. Focused ultrasound (FUS) has become a promising strategy for non-invasive local drug delivery by mild hyperthermia. In this study, traditional temperature-sensitive liposomes (TTSLs) encapsulating doxorubicin (DOX) were evaluated for FUS-mediated drug delivery with an in-vitro FUS setup. In-vitro studies showed quantitative release of the DOX from the lumen of the temperature-sensitive liposomes when heated to 42 °C with FUS using 1 MHz sinusoidal waves at 1.75 MPa for 10 min. No release was observed when heated at 37 °C. Moreover, we showed that DOX released from TTSLs by FUS is as efficiently internalized by glioblastoma cells as free DOX at 37 °C. In-vitro therapeutic evaluation showed that exposure of a cell monolayer to FUS-activated TTSLs induced a 60% and a 50% decrease in cell viability compared to cell medium and to TTSLs preheated at 37 °C, respectively. Using an in-vitro 3D cell culture model, the results showed that after FUS-mediated hyperthermia, preheated liposomes induced a 1.7-fold decrease in U-87 MG spheroid growth in comparison to the preheated liposomes at 37 °C. In conclusion, our results show that in-vitro FUS allows the evaluation of TTSLs and does not modify the cellular uptake of the released DOX nor its cytotoxic activity.

Magnetic targeting of microbubbles at physiologically relevant flow rates

The localization of microbubbles to a target site has been shown to be essential to their effectiveness in ultrasound mediated drug delivery and gene therapy. The incorporation of super paramagnetic nanoparticles into the microbubble coating enables them to be manipulated using an externally applied magnetic field. Magnetic microbubbles have been shown to be effective in therapeutic delivery both in vitro and in vivo in a mouse model. The aim of this experiment was to determine under what conditions in the human body magnetic microbubbles can be successfully imaged and targeted. Different flow rates and shear rates were generated in a tissue mimicking phantom and targeting was observed using a 9.4 MHz ultrasound imaging probe. For the highest shear rates, targeting was also observed optically. Results indicate that magnetic microbubbles can be successfully targeted at shear rates found in the human capillary system (>1000/s) and at flow rates found in the veins and smaller arteries (~200 ml/s). Successful retention was also demonstrated in a perfused porcine liver model simulating conditions in vivo. This study provides further evidence for the potential of magnetic microbubbles for targeted therapeutic delivery.

Coupling of drug containing liposomes to microbubbles improves ultrasound triggered drug delivery in mice

Local extravasation and triggered drug delivery by use of ultrasound and microbubbles is a promising strategy to target drugs to their sites of action. In the past we have developed drug loaded microbubbles by coupling drug containing liposomes to the surface of microbubbles. Until now the advantages of this drug loading strategy have only been demonstrated in vitro. Therefore, in this paper, microbubbles with indocyanine green (ICG) containing liposomes at their surface or a mixture of ICG-liposomes and microbubbles was injected intravenously in mice. Immediately after injection the left hind leg was exposed to 1MHz ultrasound and the ICG deposition was monitored 1, 4 and 7days post-treatment by in vivo fluorescence imaging. In mice that received the ICG-liposome loaded microbubbles the local ICG deposition was, at each time point, about 2-fold higher than in mice that received ICG-liposomes mixed with microbubbles. We also showed that the perforations in the blood vessels allow the passage of ICG-liposomes up to 5h after microbubble and ultrasound treatment. An increase in tissue temperature to 41°C was observed in all ultrasound treated mice. However, ultrasound tissue heating was excluded to cause the local ICG deposition. We concluded that coupling of drug containing liposomes to microbubbles may increase ultrasound mediated drug delivery in vivo.

Ultrasound-mediated drug delivery using liposomes modified with a thermosensitive polymer

Ultrasound-mediated drug delivery was established using liposomes that were modified with the thermosensitive polymer (TSP) poly(NIPMAM-co-NIPAM), which sensitized the liposomes to high temperatures. TSP-modified liposomes (TSP liposomes) released encapsulated calcein under 1MHz ultrasound irradiation at 0.5W/cm2 for 120s as well as the case under incubation at 42°C for 15min. In addition, uptake of the drug released from TSP liposomes by cancer cells was enhanced by ultrasound irradiation. In a cell injury assay using doxorubicin (DOX)-loaded TSP liposomes and ultrasound irradiation, cell viability of HepG2 cells at 6h after ultrasound irradiation (1MHz, 0.5W/cm2 for 30s) with DOX-loaded TSP liposomes (TSP/lipid ratio=1) was 60%, which was significantly lower than that of the control conditions such as DOX-loaded TSP liposomes alone and DOX-loaded intact liposomes under ultrasound irradiation.

MRI-Guided Focused Ultrasound as a New Method of Drug Delivery

Ultrasound-mediated drug delivery under the guidance of an imaging modality can improve drug disposition and achieve site-specific drug delivery. The term focal drug delivery has been introduced to describe the focal targeting of drugs in tissues with the help of imaging and focused ultrasound. Focal drug delivery aims to improve the therapeutic profile of drugs by improving their specificity and their permeation in defined areas. Focused-ultrasound- (FUS-) mediated drug delivery has been applied with various molecules to improve their local distribution in tissues. FUS is applied with the aid of microbubbles to enhance the permeability of bioactive molecules across BBB and improve drug distribution in the brain. Recently, FUS has been utilised in combination with MRI-labelled liposomes that respond to temperature increase. This strategy aims to “activate” nanoparticles to release their cargo locally when triggered by hyperthermia induced by FUS. MRI-guided FUS drug delivery provides the opportunity to improve drug bioavailability locally and therefore improve the therapeutic profiles of drugs. This drug delivery strategy can be directly translated to clinic as MRg FUS is a promising clinically therapeutic approach. However, more basic research is required to understand the physiological mechanism of FUS-enhanced drug delivery.

Ultrasound-mediated drug delivery with real-time cell permeability measurements

Ultrasound-mediated drug and gene delivery offers a variety of novel possibilities for improved localized treatment of vascular- and cancer-related diseases. This therapeutic application benefits from the use of acoustic radiation force, which facilitates the exposure for enhanced binding from ligand-receptor interactions. The unique merits of ultrasound are the transient increase of cell permeability without any detrimental and irreversible side-effects. The related underlying molecular and cellular pathways of ultrasound-induced permeability and the subsequent recovery of cells are topics of on-going research. Real-time studies of cell behavior during and past-ultrasound exposure have been limited by the lack of appropriate techniques. The electric-cell impedance sensing (ECIS) technique is a suitable way of studying cell permeability changes in real-time. Its nanoscale sensitivity and speedy acquisition of data allows for the accurate and timely monitoring of cell behavior. Our preliminary results suggest that cells recover within 24–36 h post-exposure. During this time window the cells undergo drastic changes exhibiting an increased permeability of 2.4 ± 0.6 Ω•cm2 compared to 3.8 ± 0.5 Ω•cm2 that normal untreated cells exhibit.

Temperature-Dependent Biphasic Shrinkage of Lipid-Coated Bubbles in Ultrasound

Lipid-coated microbubbles and emulsions are of interest as possible ultrasound-mediated drug delivery vehicles and for their interesting behaviors and fundamental properties. We and others have noted that bubbles coated with the long chain saturated phospholipid distearoylphosphatidylcholine (DSPC) rapidly shrink to a quasistable size when repeatedly insonated with short ultrasound pulses; such stability may adversely affect the bubble's subsequent ability to deliver its pharmacological cargo. Bubbles coated with the unsaturated lipid dioleoylphosphatidylcholine (DOPC) did not show stability but did undergo an abrupt change from rapid initial shrinkage to a slow persistent shrinkage, leading ultimately to dissolution or dispersion. As DOPC and DSPC differ not only in chain saturation but also phase behavior, we performed additional studies using dimyristoyl PC (DMPC) as a coat lipid and controlled the solution temperature to study bubble behavior on exposure to repeated ultrasound pulses for the same coat, in both fluid and gel phases. We find, first, that essentially all bubbles show an initially rapid shrinkage, in which gas loss exceeds the limit imposed by gas diffusion into the surrounding medium; this rapid shrinkage may be evidence of nanoscopic bubble fragmentation. Second, upon reaching a fraction of their initial size, bubbles begin a slower shrinkage with a shrinkage rate that depends on the resting phase state of the coat lipid: fluid DMPC monolayers give a more rapid shrinkage than gel phase. DOPC-coated bubbles showed no temperature-dependent responses in the same temperature range. The results are especially interesting in that bubble compression during the pulse is likely to adiabatically heat the bubble and fluidize the coat, regardless of its initial phase state; thus, some structural feature of the resting coat, such as defect lines in the gel phase, may be important in the subsequent response to the ~3 μs ultrasound pulse.

Modelling single- and tandem-bubble dynamics between two parallel plates for biomedical applications

Carefully timed tandem microbubbles have been shown to produce directional and targeted membrane poration of individual cells in microfluidic systems, which could be of use in ultrasound-mediated drug and gene delivery. This study aims at contributing to the understanding of the mechanisms at play in such an interaction. The dynamics of single and tandem microbubbles between two parallel plates is studied numerically and analytically. Comparisons are then made between the numerical results and the available experimental results. Numerically, assuming a potential flow, a three-dimensional boundary element method (BEM) is used to describe complex bubble deformations, jet formation, and bubble splitting. Analytically, compressibility and viscous boundary layer effects along the channel walls, neglected in the BEM model, are considered while shape of the bubble is not considered. Comparisons show that energy losses modify the bubble dynamics when the two approaches use identical initial conditions. The initial conditions in the boundary element method can be adjusted to recover the bubble period and maximum bubble volume when in an infinite medium. Using the same conditions enables the method to recover the full dynamics of single and tandem bubbles, including large deformations and fast re-entering jet formation. This method can be used as a design tool for future tandem-bubble sonoporation experiments.

Ultrasound enhanced release of therapeutics from drug-releasing implants based on titania nanotube arrays

A non-invasive and external stimulus-driven local drug delivery system (DDS) based on titania nanotube (TNT) arrays loaded with drug encapsulated polymeric micelles as drug carriers and ultrasound generator is described. Ultrasound waves (USW) generated by a pulsating sonication probe (Sonotrode) in phosphate buffered saline (PBS) at pH 7.2 as the medium for transmitting pressure waves, were used to release drug-loaded nano-carriers from the TNT arrays. It was demonstrated that a very rapid release in pulsatile mode can be achieved, controlled by several parameters on the ultrasonic generator. This includes pulse length, time, amplitude and power intensity. By optimization of these parameters, an immediate drug-micelles release of 100% that spans a desirable time of 5-50 min was achieved. It was shown that stimulated release can be generated and reproduced at any time throughout the TNT-Ti implant life, suggesting considerable potential of this approach as a feasible and tunable ultrasound-mediated drug delivery system in situ via drug-releasing implants. It is expected that this concept can be translated from an in vitro to in vivo regime for therapeutic applications using drug-releasing implants in orthopedic and coronary stents.

Focused ultrasound-mediated drug delivery to pancreatic cancer in a mouse model.

BackgroundMany aspects of the mechanisms involved in ultrasound-mediated therapy remain obscure. In particular, the relative roles of drug and ultrasound, the effect of the time of ultrasound application, and the effect of tissue heating are not yet clear. The current study was undertaken with the goal to clarify these aspects of the ultrasound-mediated drug delivery mechanism.MethodsFocused ultrasound-mediated drug delivery was performed under magnetic resonance imaging guidance (MRgFUS) in a pancreatic ductal adenocarcinoma (PDA) model grown subcutaneously in nu/nu mice. Paclitaxel (PTX) was used as a chemotherapeutic agent because it manifests high potency in the treatment of gemcitabine-resistant PDA. Poly(ethylene oxide)-co-poly(d,l-lactide) block copolymer stabilized perfluoro-15-crown-5-ether nanoemulsions were used as drug carriers. MRgFUS was applied at sub-ablative pressure levels in both continuous wave and pulsed modes, and only a fraction of the tumor was treated.ResultsPositive treatment effects and even complete tumor resolution were achieved by treating the tumor with MRgFUS after injection of nanodroplet encapsulated drug. The MRgFUS treatment enhanced the action of the drug presumably through enhanced tumor perfusion and blood vessel and cell membrane permeability that increased the drug supply to tumor cells. The effect of the pulsed MRgFUS treatment with PTX-loaded nanodroplets was clearly smaller than that of continuous wave MRgFUS treatment, supposedly due to significantly lower temperature increase as measured with MR thermometry and decreased extravasation. The time of the MRgFUS application after drug injection also proved to be an important factor with the best results observed when ultrasound was applied at least 6 h after the injection of drug-loaded nanodroplets. Some collateral damage was observed with particular ultrasound protocols supposedly associated with enhanced inflammation.ConclusionThis presented data suggest that there exists an optimal range of ultrasound application parameters and drug injection time. Decreased tumor growth, or complete resolution, was achieved with continuous wave ultrasound pressures below or equal to 3.1 MPa and drug injection times of at least 6 h prior to treatment. Increased acoustic pressure or ultrasound application before or shortly after drug injection gave increased tumor growth when compared to other protocols.

Ultrasound mediated release from stimuli-responsive core-shell capsules.

Delivery systems that facilitate non-invasive, real-time control of drug release have enormous potential in a wide range of therapeutic applications. This study investigates the potential of a new type of core-shell particle for ultrasound-mediated drug delivery. The capsules were prepared using coaxial electrohydrodynamic atomization and consist of a biocompatible polymer (polymethylsilsesquioxane) shell encapsulating a core containing a volatile liquid (perfluorohexane PFH) and a dye (Evans Blue) simulating a drug. The effect of low frequency (20 kHz) ultrasound upon the rate of dye release and capsule surface morphology was investigated for a range of exposure conditions (ultrasound intensity 0.7-26 W cm-2, duty cycle 30-90% and exposure time 0-600 s). The relative proportions of the core liquids were also varied. Incorporation of PFH was found to increase the rate of dye release compared with that from capsules containing dye only. The rate of release was found to be positively correlated with intensity, duty cycle and exposure time; whilst the proportion of PFH did not appear to affect it. Changes in particle surface morphology were only discernible at the higher ultrasound intensities, with pore formation followed by surface cracking and finally shell disintegration being observed with increasing intensity. The presence of the pores was indicative of cavitation activity as was the fact that enhanced release was still observed when the exposure chamber was immersed in an ice bath to minimize heating. It was concluded that the incorporation of PFH into the particles did provide an effective means of producing ultrasound sensitivity which could be exploited in stimuli responsive drug delivery.

The impact of bubbles on measurement of drug release from echogenic liposomes

Echogenic liposomes (ELIP) encapsulate gas bubbles and drugs within lipid vesicles, but the mechanisms of ultrasound-mediated drug release from ELIP are not well understood. The effect of cavitation activity on drug release from ELIP was investigated in flowing solutions using two fluorescent molecules: a lipophilic drug (rosiglitazone) and a hydrophilic drug substitute (calcein). ELIP samples were exposed to pulsed Doppler ultrasound from a clinical diagnostic ultrasound scanner at pressures above and below the inertial and stable cavitation thresholds. Control samples were exposed to a surfactant, Triton X-100 (positive control), or to flow alone (negative control). Fluorescence techniques were used to detect release. Encapsulated microbubbles reduced the measured fluorescence intensity and this effect should be considered when assessing drug release from ELIP. The origin of this effect is not specific to ELIP. Release of rosiglitazone or calcein compared to the negative control was only observed with detergent treatment, but not with ultrasound exposure, despite the presence of stable and inertial cavitation activity. Release of rosiglitazone or calcein from ELIP exposed to diagnostic ultrasound was not observed, even in the presence of cavitation activity. Ultrasound-mediated drug delivery strategies with ELIP will thus rely on passage of the drug-loaded liposomes to target tissues.

Ultrasound-mediated targeted drug delivery: recent success and remaining challenges

The potential clinical value of developing a novel, nonviral, ultrasound-directed gene and drug delivery system is immense. Investigators soon will initiate clinical trials with the goal of treating a wide variety of maladies using noninvasive, ultrasound-based technology. The ongoing, scientific validation associated with promising preclinical success portents a novel range of therapeutics. The clinical utility and eventual clinical successes await vigorous testing. This review highlights the recent successes and challenges within the field of ultrasound-mediated drug delivery.

An introduction to the Biomedical Acoustics Technical Committee

An overview of the activities of the Biomedical Acoustics Technical Committee will be presented, along with a brief survey of some of the ongoing research projects in Biomedical Acoustics. For example, the Biomedical Acoustics Technical Committee organizes a student poster competition every year, and special sessions are arranged at each meeting to highlight some of the latest research in the diagnostic and therapeutic applications of acoustics. Some of the topics include ultrasound imaging, high intensity focused ultrasound, ultrasound mediated drug delivery, ultrasound contrast agents, ultrasound-induced cavitation, and ultrasound elastography, among several others. In this presentation, selected examples of active research topics in Biomedical Acoustics will also be described in greater detail.

Ultrasound triggered drug release from 10-hydroxycamptothecin-loaded phospholipid microbubbles for targeted tumor therapy in mice

Ultrasound targeted microbubble destruction (UTMD) was one of the most promising strategies to enhance drug delivery in cancer therapy. Microbubbles (MBs) serve as a vehicle to carry anti-tumor drugs and locally release them when exposed to therapeutic ultrasound, resulting in drug accumulation in tumor tissues and enhanced anti-tumor effect. However the ultrasound triggered drug delivery system has been seriously limited due to the poor loading capacity of MBs. Here we present a new strategy to overcome the low drug payload of MBs for ultrasound guided drug delivery. In this study, we developed a novel microbubble carrying 10-HCPT which only needs a particularly low single dose of injection (4–6mg) for tumor therapy in clinical application, therefore, the required high dosing of drug loaded MBs for ultrasound mediated drug delivery is not necessary. We subsequently investigated the combination of ultrasound application with HLMs to achieve therapeutic effect on tumor at a feasible dose of MBs. HLMs were manufactured with a high drug encapsulation and loading content and simultaneously maintained the acoustic properties as an ultrasound contrast agent. After that, tumor-bearing mice were routinely and non-invasively administered with HLMs through the tail vein and were then exposed to ultrasound, resulting in a remarkable drug accumulation in tumor tissues and a significant increase in tumor inhibition rate (70.6%) compared with HLMs alone (47.8%) as well as commercial HCPT injection (49.4). In conclusion, HLMs are expected to improve the therapeutic efficacy of MBs and are worthy of further study for UTMD mediated drug delivery.