Ultrasound-mediated Drug Delivery Research Articles

Overcoming anticancer resistance by photodynamic therapy-related efflux pump deactivation and ultrasound-mediated improved drug delivery efficiency

One of the major obstacles to successful chemotherapy is multi-drug resistance (MDR). A multi-drug resistant cancerous cell abnormally overexpresses membrane transporters that pump anticancer drugs out of the cell, resulting in low anticancer drug delivery efficiency. To overcome the limitation, many attempts have been performed to inhibit the abilities of efflux receptors chemically or genetically or to increase the delivery efficiency of anticancer drugs. However, the results have not yet been satisfactory. In this study, we developed nanoparticle-microbubble complexes (DOX-NPs/Ce6-MBs) by conjugating doxorubicin loaded human serum albumin nanoparticles (DOX-NPs) onto the surface of Chlorin e6 encapsulated microbubbles (Ce6-MBs) in order to maximize anticancer efficiency by overcoming MDR. Under the ultrasound irradiation, DOX-NPs and Ce6 encapsulating self-assembled liposomes or micelles were effectively delivered into the cells due to the sonoporation effect caused by the microbubble cavitation. At the same time, reactive oxygen (ROS) generated from intracellularly delivered Ce6 by laser irradiation arrested the activity of ABCG2 efflux receptor overexpressed in doxorubicin-resistant breast cancer cells (MCF-7/ADR), resulting in increased the chemotherapy efficacy. In addition, the total number of side population cells that exhibit the properties of cancer stem-like cells were also reduced by the combination of photodynamic therapy and chemotherapy. In conclusion, DOX-NPs/Ce6-MBs will provide a platform for simultaneously overcoming MDR and increasing drug delivery and therefore, treatment efficiency, under ultrasound irradiation.

Transcranial activation and imaging of low boiling point phase‐change contrast agents through the temporal bone using an ultrafast interframe activation ultrasound sequence

As a cavitation enhancer, low boiling point phase-change contrast agents (PCCA) offer potential for ultrasound-mediated drug delivery in applications including intracerebral hemorrhage or brain tumors. In addition to introducing cavitation, ultrasound imaging also has the ability to provide guidance and monitoring of the therapeutic process by localizing delivery events. However, the highly attenuating skull poses a challenge for achieving an image with useful contrast. In this study, the feasibility of transcranial activation and imaging of low boiling point PCCAs through the human temporal bone was investigated by using a low frequency ultrafast interframe activation ultrasound (UIAU) imaging sequence with singular value decomposition-based denoising. Lipid-shelled PCCAs filled with decafluorobutane were activated and imaged at 37°C in tissue-mimicking phantoms both without and with an ex vivo human skull using the new UIAU sequence and a low frequency diagnostic transducer array at frequencies from 1.5 to 3.5MHz. A singular value decomposition-based denoising filter was developed and used to further enhance transcranial image contrast. The contrast-to-tissue ratio (CTR) and contrast enhancement (CE) of UIAU was quantitatively evaluated and compared with the amplitude modulation pulse inversion (AMPI) and vaporization detection imaging (VDI) approaches. Image results demonstrate enhanced contrast in the phantom channel with suppressed background when the low boiling point PCCA was activated both without and with an ex vivo human skull using the UIAU sequence. Quantitative results show that without the skull, low frequency UIAU imaging provided significantly higher image contrast (CTR≥18.56dB and CE≥18.66dB) than that of AMPI and VDI (P<0.05). Transcranial imaging results indicated that the CE of UIAU (≥18.80dB) was significantly higher than AMPI for free-field activation pressures of 5 and 6MPa. The CE of UIAU is also significantly higher than that of VDI when PCCAs were activated at 2.5MHz and 3MHz (P<0.05). The CTR (23.30 [20.07-25.56]dB) of denoised UIAU increased by 12.58dB relative to the non-denoised case and was significantly higher than that of AMPI at an activation pressure of 4MPa (P<0.05). Results indicate that low boiling point PCCAs can be activated and imaged at low frequencies including imaging through the temporal bone using the UIAU sequence. The UIAU imaging approach provides higher contrast than AMPI and VDI, especially at lower activation pressures with additional removal of electronic noise.

Clinical Efficacy of Ultrasound-Mediated Transdermal Lidocaine and Capsaicin Delivery for the Treatment of Allodynia Caused by Herpes Zoster.

To investigate the efficacy of ultrasound-mediated drug delivery for allodynia caused by herpes zoster. Unblinded randomized controlled study with two treatment groups and an additional control group. Patients hospitalized with allodynia caused by herpes zoster were enrolled. Patients were randomly assigned to three groups: ultrasound-mediated transdermal drug delivery (group U), lidocaine intradermal injection (group I), or control group (group C). The primary outcome was pain intensity associated with allodynia, assessed with the visual analog scale (VAS) while brushing the skin with clothing after treatment stimulated allodynia. The secondary outcomes included an emotional functioning score (ES), average gabapentin consumption, and incidence of adverse events of each group. Sixty patients were enrolled in the study, but two of them failed to complete the treatment process. Therefore, 58 patients were included in the final analysis. All groups had lower VAS and ES scores after treatment compared with baseline. The VAS scores in groups U and I decreased significantly more than in group C (P < 0.05). Mean VAS scores in group U on days 1, 2, and 3 were lower than in group C (P < 0.01). ES was significantly lower in group U compared with groups I and C after treatment (P < 0.001). Average gabapentin consumption and incidence of adverse events in group C were higher than in the other two groups. In this study of treatment of allodynia caused by herpetic zoster, ultrasound-mediated lidocaine and capsaicin delivery provided better pain relief and improved emotional functioning compared with intradermal blockade with local anesthetics.

A Dual-Frequency Coupled Resonator Transducer.

New ultrasound-mediated drug delivery systems, such as acoustic cluster therapy or combined imaging and therapy systems, require transducers that can operate beyond the bandwidth limitation (~100%) of conventional piezoceramic transducers. In this article, a dual-frequency coupled resonator transducer (CRT) comprised of a polymeric coupling layer with a low acoustic impedance (2-5 MRayl) sandwiched between two piezoceramic layers is investigated. Depending on the electrical configuration, the CRT exhibits two usable frequency bands. The resonance frequency of the high-frequency (HF) band can be tailored to be ~3-5 times higher than that of the low-frequency (LF) band using the stiffness in the coupling layer. The CRT's LF band was analyzed analytically, and we obtained the closed-form expressions for the LF resonance frequency. A dual-frequency CRT was designed, manufactured, and characterized acoustically, and comparisons with theory showed good agreement. The HF band exhibited a center frequency of 2.5 MHz with a -3-dB bandwidth of 70% and is suited to manipulate microbubbles or for diagnostic imaging applications. The LF band exhibited a center frequency of 0.5 MHz with a -3-dB bandwidth of 13% and is suited to induce biological effects in tissue, therein manipulation of microbubbles.

Micro-Particle Image Velocimetry Investigation of Flow Fields of SonoVue Microbubbles Mediated by Ultrasound and Their Relationship With Delivery

The flow fields generated by the acoustic behavior of microbubbles can significantly increase cell permeability. This facilitates the cellular uptake of external molecules in a process known as ultrasound-mediated drug delivery. To promote its clinical translation, this study investigated the relationships among the ultrasound parameters, acoustic behavior of microbubbles, flow fields, and delivery results. SonoVue microbubbles were activated by 1 MHz pulsed ultrasound with 100 Hz pulse repetition frequency, 1:5 duty cycle, and 0.20/0.35/0.70 MPa peak rarefactional pressure. Micro-particle image velocimetry was used to detect the microbubble behavior and the resulting flow fields. Then HeLa human cervical cancer cells were treated with the same conditions for 2, 4, 10, 30, and 60 s, respectively. Fluorescein isothiocyanate and propidium iodide were used to quantitate the rates of sonoporated cells with a flow cytometer. The results indicate that (1) microbubbles exhibited different behavior in ultrasound fields of different peak rarefactional pressures. At peak rarefactional pressures of 0.20 and 0.35 MPa, the dispersed microbubbles clumped together into clusters, and the clusters showed no apparent movement. At a peak rarefactional pressure of 0.70 MPa, the microbubbles were partially broken, and the remainders underwent clustering and coalescence to form bubble clusters that exhibited translational oscillation. (2) The flow fields were unsteady before the unification of the microbubbles. After that, the flow fields showed a clear pattern. (3)The delivery efficiency improved with the shear stress of the flow fields increased. Before the formation of the microbubble/bubble cluster, the maximum shear stresses of the 0.20, 0.35, and 0.70 MPa groups were 56.0, 87.5 and 406.4 mPa, respectively, and the rates of the reversibly sonoporated cells were 2.4% ± 0.4%, 5.5% ± 1.3%, and 16.6% ± 0.2%. After the cluster formation, the maximum shear stresses of the three groups were 9.1, 8.7, and 71.7 mPa, respectively. The former two could not mediate sonoporation, whereas the last one could. These findings demonstrate the critical role of flow fields in ultrasound-mediated drug delivery and contribute to its clinical applications.

SCIDOT-07. ULTRASOUND DELIVERED ALBUMIN BOUND PACLITAXEL EXTENDS SURVIVAL IN MALIGNANT GLIOMA MODELS AND OUTPERFORMS ULTRASOUND DELIVERED CREMOPHOR PACLITAXEL IN BIO-DISTRIBUTION AND SAFETY

Abstract Paclitaxel is anti-neoplastic agent shown to be extremely potent against glioblastoma in-vitro; however, it has yet to demonstrate antitumor activity in the clinic due to its inadequate brain penetration. Ultrasound-mediated drug delivery is an emerging new technology that transiently disrupts the blood-brain barrier to allow the passage of larger molecules that under physiological conditions would not reach the brain tissue. In this preclinical study, we investigated the ability of low intensity pulsed ultrasound (LIPU), delivered with the SonoCloud System (CarThera), to increase brain paclitaxel concentrations in a murine model. LIPU increased paclitaxel concentrations in the brain 300–500% after systemic administration of two different commercially available formulations of paclitaxel; paclitaxel dissolved in Cremophor (Taxol®) and albumin-bound paclitaxel (Abraxane®). The two formulations differed in their toxicity and biodistribution profiles with albumin-bound paclitaxel exhibiting increased tolerability and brain penetration. After sonication, albumin-bound paclitaxel increased survival in an orthotropic glioma model, whereas cremophor-paclitaxel induced central nervous system toxicity. Our experiments suggest that increased paclitaxel drug delivery by opening the BBB is feasible, and an effective anti-glioma treatment. Albumin-bound paclitaxel is the preferred formulation for further investigation with the SonoCloud system in the clinical setting.

Optimization of Ultrasound-Mediated Drug Delivery for Treatment of Onychomycosis.

Onychomycosis is a fungal nail disorder that does not have a successful cure due to the poor permeability of topical anti-fungal drugs through the nail. This study utilizes ultrasound to increase the permeability of the nail to the topical drugs currently used in clinic. The first aim of this study was to optimize ultrasonic parameters within the temperature increase limits set by the American Institute of Ultrasound in Medicine (AIUM) and the British Medical Ultrasound Society (BMUS). The second aim of the study was to evaluate the optimized parameters for a cause of action of either cavitation (the creation of micrometer pores in the nail barrier) or acoustic streaming (a steady fluid motion which may help push the drug through the nail). Porcine and human nails are used in the five studies. PZFlex Modeling Software is used to model the temperature increase in the toe as a result of ultrasonic application and these results were used to develop the three parameters tested throughout the rest of the studies. The three parameters tested were 1 min of continuous ultrasonic application, 3 min of 50% ultrasonic application and 5 min of 50% ultrasonic application. In order to address the second aim of our research work, these three parameters were tested for the presence of streaming and cavitation. At the three tested parameters, the most permeation of the nail occurs with 1 min of continuous application of ultrasound to the nail. It was also found that there was limited cavitation and significant streaming at all three parameters. This suggests that streaming may be the main mechanism-of-action in ultrasound-mediated drug delivery through the nail. The parameter of 1 min of continuous ultrasonic testing will continue to be employed as the testing is moved to a rabbit model of onychomycosis.

Advances in Ultrasound Mediated Transdermal Drug Delivery.

Low frequency ultrasound-assisted drug delivery has been widely investigated as a non-invasive method to enhance the transdermal penetration of drugs. Using this technique, a brief application of ultrasound is used to permeabilize skin for a prolonged time. In this review, an overview on ultrasound is detailed to help explain the parameters that could be modulated to obtain the desired ultrasound parameters for enhanced transdermal drug delivery. The mechanisms of enhancement and the latest developments in the area of ultrasound-assisted transdermal drug delivery are discussed. Special emphasis is placed on the effects of ultrasound when used in combination with microneedles, electroporation and iontophoresis, and penetration enhancers. Further, this review summarizes the effect of ultrasound on skin integrity and the regulatory requirements for commercialization of the ultrasound based transdermal delivery instruments.

Echographic and physical characterization of albumin-stabilized nanobubbles

There has been increasing interest in using nanobubbles (NBs) for ultrasound mediated drug delivery as well as for ultrasound imaging. Albumin NBs are especially attractive for its potential of becoming a versatile platform for drug carriers and molecular targeted therapy agents. However, physical characterization of NBs is generally considered to be difficult due to various technical issues, such as concentration limitations, nanoparticle contamination, etc. In the present study, we measured the size distribution, concentration and weight density of albumin stabilized NBs by means of multiple nanoscale measurement modalities. Laser nanoparticle tracking analysis, multicolor flow cytometry, resonance mass evaluation showed consistent measurement results of the NBs with low mass weight density and diameter size ranging from 100 nm to 400 nm. Furthermore, the NB solution showed excellent images by high frequency ultrasound (30–50 MHz) in flow model acoustic phantoms. The NBs also induced acute cell disruption by low intensity ultrasound (0.8 W/cm2) irradiation. We successfully fabricated and characterized albumin stabilized NBs which could serve as an effective platform for future theranositic agents.

Thermodynamic state of the interface during acoustic cavitation in lipid suspensions

The thermodynamic state of lipid interfaces was observed during shock wave induced cavitation in water with sub-microsecond resolution, using the emission spectra of hydration-sensitive fluorescent probes co-localized at the interface. The experiments show that the cavitation threshold is lowest near a phase transition of the lipid interface. The cavitation collapse time and the maximum state change during cavitation are found to be a function of both the driving pressure and the initial state of the lipid interface. The experiments show dehydration and crystallization of lipids during the expansion phase of cavitation, suggesting that the heat of vaporization is absorbed from within the interface, which is adiabatically uncoupled from the free water. The study underlines the critical role of the thermodynamic state of the interface in cavitation dynamics, which has mechanistic implications for ultrasound-mediated drug delivery, acoustic nerve stimulation, ultrasound contrast agents, and the nucleation of ice during cavitation.

Biomedical acoustics research at the Image-Guided Ultrasound Therapeutics Laboratories

The Image-guided Ultrasound Therapeutic Laboratories (IgUTL) are located at the University of Cincinnati in the Heart, Lung, and Vascular Institute, a key component of efforts to align the UC College of Medicine and UC Health research, education, and clinical programs. These laboratories, directed by Christy K. Holland, comprise graduate and undergraduate students, postdoctoral fellows, physician-scientists, and clinical and scientific collaborators in fields including cardiology, neurosurgery, neurology, radiology, and emergency medicine. Holland’s research focuses on biomedical ultrasound including sonothrombolysis, ultrasound-mediated drug and bioactive gas delivery, development of echogenic liposomes, early detection of cardiovascular diseases, and ultrasound-image guided tissue ablation. Imaging algorithms incorporate both passive and active cavitation detection. The Biomedical Acoustics Laboratory within IgUTL, directed by T. Douglas Mast, investigates ultrasound imaging for therapy guidance, including echo decorrelation imaging for monitoring liver cancer ablation and real-time tracking of tongue motion for biofeedback in speech therapy. The Biomedical Ultrasonics and Cavitation Laboratory within IgUTL, directed by Kevin J. Haworth, employs ultrasound-mediated gas scavenging for image-guided treatment of cardiovascular disease, especially reperfusion injury. [Work supported by NIH Grants R01 NS047603, R01 HL135092, R01 HL133334, R01 CA158439, R01 DC017301, and K25 HL133452.]

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.

Engineered 3D Microvascular Networks for the Study of Ultrasound-Microbubble-Mediated Drug Delivery.

Localized and targeted drug delivery can be achieved by the combined action of ultrasound and microbubbles on the tumor microenvironment, likely through sonoporation and other therapeutic mechanisms that are not well understood. Here, we present a perfusable in vitro model with a realistic 3D geometry to study the interactions between microbubbles and the vascular endothelium in the presence of ultrasound. Specifically, a three-dimensional, endothelial-cell-seeded in vitro microvascular model was perfused with cell culture medium and microbubbles while being sonicated by a single-element 1 MHz focused transducer. This setup mimics the in vivo scenario in which ultrasound induces a therapeutic effect in the tumor vasculature in the presence of flow. Fluorescence and bright-field microscopy were employed to assess the microbubble-vessel interactions and the extent of drug delivery and cell death both in real time during treatment as well as after treatment. Propidium iodide was used as the model drug while calcein AM was used to evaluate cell viability. There were two acoustic parameter sets chosen for this work: (1) acoustic pressure: 1.4 MPa, pulse length: 500 cycles, duty cycle: 5% and (2) acoustic pressure: 0.4 MPa, pulse length: 1000 cycles, duty cycle: 20%. Enhanced drug delivery and cell death were observed in both cases while the higher pressure setting had a more pronounced effect. By introducing physiological flow to the in vitro microvascular model and examining the PECAM-1 expression of the endothelial cells within it, we demonstrated that our model is a good mimic of the in vivo vasculature and is therefore a viable platform to provide mechanistic insights into ultrasound-mediated drug delivery.

Effect of Molecular Weight on Sonoporation-Mediated Uptake in Human Cells

Ultrasound-induced microbubble destruction can enhance drug delivery to cells. The molecular weight of therapeutic compounds varies significantly (from <1 kDa for small molecule drugs, to 7–15 kDa for siRNAs/miRNAs, to >1000 kDa for DNA plasmids). Therefore, the objective of this study was to determine the relationship between uptake efficiency and molecular weight using equal molar concentrations. Uptake efficiency of fluorescent compounds with different molecular weights (0.3, 10 and 2000 kDa) was explored in vitro using human cardiac mesenchymal cells and breast cancer cells exposed to microbubbles and 2.5-MHz ultrasound pulses. Uptake by viable cells was quantified using flow cytometry. After correction for the fluorescence yield of each compound, there was a significant size-dependent difference in fluorescence intensity, indicating an inverse relationship between size and uptake efficiency. These results suggest that diffusion of therapeutic compounds across permeabilized cell membranes may be an important mechanism for ultrasound-mediated drug delivery.

Ultrasound Mediated Drug Delivery for the Management of Oral Diseases in Near Future

Ultrasound Mediated Drug Delivery for the Management of Oral Diseases in Near Future

A study on the possibility of drug delivery approach through ultrasonic sensitive nanocarriers

Physical drug delivery through smart nanocarrier and external stimulus could lead to significant improvements of drug potency as well as noticeable decrease in unwanted side effects. Currently, many external energy sources such as light, magnetic fields, ultrasound, ..., are under investigation as external stimulus for physical drug delivery. The purpose of this paper is to review most recent developments of triggered release of drugs and biomolecules under external ultrasound exposure. A special attention has also been paid to the metal nanostructures for ultrasound mediated drug delivery and also, other nanostructures were also considered. We briefly introduced ultrasound regulation and safety consideration. Further it is concluded that the use of nanostructures for delivery of active biomolecules in combination with ultrasound as a stimulus to trigger drug release from the nanocarriers and increased drug penetration has gained much attention for effective drug delivery and overcoming difficulties of multi-drug resistance of cancer.

Preliminary Investigation of Focused Ultrasound-Facilitated Drug Delivery for the Treatment of Leptomeningeal Metastases

Leptomeningeal metastases (LM) are a serious complication of cancer in the central nervous system (CNS) and are diagnosed in approximately 5% of patients with solid tumors. Effective treatment using systemically administered therapeutics is hindered by the barriers of the CNS. Ultrasound can mediate delivery of drugs through these barriers. The goal of this study was to test the feasibility of using ultrasound-mediated drug delivery to improve the treatment of LM. LM was induced in the spinal cord of athymic rats by injecting HER2-expressing breast cancer cells into the subarachnoid space of the thoracic spine. Animals were divided into three groups: no treatment (n = 5), trastuzumab only (n = 6) or trastuzumab + focused ultrasound + microbubbles (FUS + MBs) (n = 7). Animals in groups 2 and 3 were treated weekly with intravenous trastuzumab +/− FUS + MBs for three weeks. Suppression in tumor growth was qualitatively observed by MRI in the group receiving ultrasound, and was confirmed by a significant difference in the tumor volume measured from the histology data (25 ± 17 mm3 vs 8 ± 5 mm3, p = 0.04 in the trastuzumab-only vs trastuzumab + FUS + MBs). This pilot study demonstrates the potential of ultrasound-mediated drug delivery as a novel treatment for LM. Future studies will extend this work to larger cohorts and the investigation of LM arising from other cancers.

Non-spherical oscillations drive the ultrasound-mediated release from targeted microbubbles

Ultrasound-driven microbubbles are attractive for a variety of applications in medicine, including real-time organ perfusion imaging and targeted molecular imaging. In ultrasound-mediated drug delivery, bubbles decorated with a functional payload become convenient transport vehicles and offer highly localized release. How to efficiently release and transport these nanomedicines to the target site remains unclear owing to the microscopic length scales and nanoseconds timescales of the process. Here, we show theoretically how non-spherical bubble oscillations lead first to local oversaturation, thereby inducing payload release, and then to microstreaming generation that initiates transport. Experimental validation is achieved through ultra-high-speed imaging in an unconventional side-view at tens of nanoseconds timescales combined with high-speed fluorescence imaging to track the release of the payload. Transport distance and intrinsic bubble behavior are quantified and agree well with the model. These results will allow for optimizing the therapeutic use of targeted microbubbles for precision medicine.

Acoustic Characterization of a Vessel-on-a-Chip Microfluidic System for Ultrasound-Mediated Drug Delivery.

Ultrasound in the presence of gas-filled microbubbles can be used to enhance local uptake of drugs and genes. To study the drug delivery potential and its underlying physical and biological mechanisms, an in vitro vessel model should ideally include 3-D cell culture, perfusion flow, and membrane-free soft boundaries. Here, we propose an organ-on-a-chip microfluidic platform to study ultrasound-mediated drug delivery: the OrganoPlate. The acoustic propagation into the OrganoPlate was determined to assess the feasibility of controlled microbubble actuation, which is required to study the microbubble-cell interaction for drug delivery. The pressure field in the OrganoPlate was characterized non-invasively by studying experimentally the well-known response of microbubbles and by simulating the acoustic wave propagation in the system. Microbubble dynamics in the OrganoPlate were recorded with the Brandaris 128 ultrahigh-speed camera (17 million frames/s) and a control experiment was performed in an OptiCell, an in vitro monolayer cell culture chamber that is conventionally used to study ultrasound-mediated drug delivery. When insonified at frequencies between 1 and 2 MHz, microbubbles in the OrganoPlate experienced larger oscillation amplitudes resulting from higher local pressures. Microbubbles responded similarly in both systems when insonified at frequencies between 2 and 4 MHz. Numerical simulations performed with a 3-D finite-element model of ultrasound propagation into the OrganoPlate and the OptiCell showed the same frequency-dependent behavior. The predictable and homogeneous pressure field in the OrganoPlate demonstrates its potential to develop an in vitro 3-D cell culture model, well suited to study ultrasound-mediated drug delivery.

High-frequency, low-intensity ultrasound and microbubbles enhance nerve blockade

Site 1 sodium channel blockers (S1SCBs such as tetrodotoxin [TTX] and the saxitoxins) are ultrapotent local anesthetics that bind extracellular domains of voltage-dependent sodium channels [1]. S1SCBs do not cross the blood brain barrier and have low affinity for the cardiac sodium channel isoform [2,3], and so do not cause seizures [4] or arrhythmias, making TTX an attractive alternative to conventional local anesthetics [5,6]. Local anesthesia with S1SCBs has been described in numerous reports in animal models [7–11], and is now starting to be applied in humans [12] [13]. However, due to their very hydrophilic nature S1SCBs have limited penetration to peripheral nerves even with local injection, and require relatively high concentrations to achieve consistent nerve blockade [9]. Those high concentrations can be associated with systemic toxicity. One approach to enhancing the effect of S1SCBs has been to co-inject them with second or third drugs with adjuvantic effects [7,8,14,15]. However, such couplings can entail the side-effects of the second drugs, such as the local tissue toxicity of “conventional” amino-amide and amino-ester local anesthetics or the vasoconstriction and/or tachycardia seen with epinephrine. An alternative approach is to enhance the penetration of S1SCBs to the nerve. Previously we have shown that co-injection of TTX with chemical permeation enhancers could enhance the effect of S1SCBs, albeit with some adverse tissue reaction at high concentrations [16,17]. Ultrasound-mediated drug delivery has the potential to enhance nerve blockade without adverse tissue reaction. Acoustic waves can enhance drug delivery through the sclera [18], the stratum corneum [19,20], across barriers within the gastrointestinal tract [21,22], and the blood brain barrier [23,24]. The effect of high-frequency ultrasound on drug flux across skin (sonophoresis) can be enhanced by exogenous microbubbles [25,26]. In this study, we hypothesized that ultrasound treatment would increase the flux of hydrophilic molecules, such as S1SCBs, across biological barriers to the surface of the peripheral nerve. We used TTX as a model S1SCB. We studied high-frequency, low-intensity ultrasound (HFLIU), parameters similar to those used in clinical imaging. This frequency and intensity range is theoretically safe for a broad range of applications. We evaluated the effects of HFLIU with and without the addition of exogenous microbubbles on TTX-mediated nerve blockade. We also verified whether effects of ultrasound and microbubbles were applicable to local anesthetics in general by testing their effect on the amino-amide local anesthetic bupivacaine.