Pulsed high intensity focused ultrasound mediated nanoparticle delivery: mechanisms and efficacy in murine muscle

Present and future of metal nanoparticles in tumor ablation therapy

Cancer is an important factor affecting the quality of human life as well as causing death. Tumor ablation therapy is a minimally invasive local treatment modality with unique advantages in treating tumors that are difficult to remove surgically. However, due to its physical and chemical characteristics and the limitation of equipment technology, ablation therapy cannot completely kill all tumor tissues and cells at one time; moreover, it inevitably damages some normal tissues in the surrounding area during the ablation process. Therefore, this technology cannot be the first-line treatment for tumors at present. Metal nanoparticles themselves have good thermal and electrical conductivity and unique optical and magnetic properties. The combination of metal nanoparticles with tumor ablation technology, on the one hand, can enhance the killing and inhibiting effect of ablation technology on tumors by expanding the ablation range; on the other hand, the ablation technology changes the physicochemical microenvironment such as temperature, electric field, optics, oxygen content and pH in tumor tissues. It helps to stimulate the degree of local drug release of nanoparticles and increase the local content of anti-tumor drugs, thus forming a synergistic therapeutic effect with tumor ablation. Recent studies have found that some specific ablation methods will stimulate the body's immune response while physically killing tumor tissues, generating a large number of immune cells to cause secondary killing of tumor tissues and cells, and with the assistance of metal nanoparticles loaded with immune drugs, the effect of this anti-tumor immunotherapy can be further enhanced. Therefore, the combination of metal nanoparticles and ablative therapy has broad research potential. This review covers common metallic nanoparticles used for ablative therapy and discusses in detail their characteristics, mechanisms of action, potential challenges, and prospects in the field of ablation.

Overcoming tumor microenvironment obstacles: Current approaches for boosting nanodrug delivery

In order to achieve targeted delivery of anticancer drugs, efficacy improvement, and side effect reduction, various types of nanoparticles are employed. However, their therapeutic effects are not ideal. This phenomenon is caused by tumor microenvironment abnormalities such as abnormal blood vessels, elevated interstitial fluid pressure, and dense extracellular matrix that affect nanoparticle penetration into the tumor's interstitium. Furthermore, nanoparticle properties including size, charge, and shape affect nanoparticle transport into tumors. This review comprehensively goes over the factors hindering nanoparticle penetration into tumors and describes methods for improving nanoparticle distribution by remodeling the tumor microenvironment and optimizing nanoparticle physicochemical properties. Finally, a critical analysis of future development of nanodrug delivery in oncology is further discussed. STATEMENT OF SIGNIFICANCE: This article reviews the factors that hinder the distribution of nanoparticles in tumors, and describes existing methods and approaches for improving the tumor accumulation from the aspects of remodeling the tumor microenvironment and optimizing the properties of nanoparticles. The description of the existing methods and approaches is followed by highlighting their advantages and disadvantages and put forward possible directions for the future researches. At last, the challenges of improving tumor accumulation in nanomedicines design were also discussed. This review will be of great interest to the broad readers who are committed to delivering nanomedicine for cancer treatment.

Interstitial fluid streaming in deep tissue induced by ultrasound momentum transfer for accelerating nanoagent transport and controlling its distribution

Objective. This study aims to theoretically investigate the dynamics of ultrasound-induced interstitial fluid streaming and tissue recovery after ultrasound exposure for potentially accelerating nanoagent transport and controlling its distribution in tissue. Approach. Starting from fundamental equations, the dynamics of ultrasound-induced interstitial fluid streaming and tissue relaxation after an ultrasound exposure were modeled, derived and simulated. Also, both ultrasound-induced mechanical and thermal effects were considered in the models. Main results. The proposed new mechanism was named squeezing interstitial fluid via transfer of ultrasound momentum (SIF-TUM). It means that an ultrasound beam can squeeze the tissue in a small focal volume from all the directions, and generate a macroscopic streaming of interstitial fluid and a compression of tissue solid matrix. After the ultrasound is turned off, the solid matrix will recover and can generate a backflow. Rather than the ultrasound pressure itself or intensity, the streaming velocity is determined by the dot product of the ultrasound pressure gradient and its conjugate. Tissue and nanoagent properties also affect the streaming and recovery velocities. Significance. The mobility of therapeutic or diagnostic agents, such as drugs, drug carriers, or imaging contrast agents, in the interstitial space of many diseased tissues, such as tumors, is usually extremely low because of the inefficiency of the natural transport mechanisms. Therefore, the interstitial space is one of the major barriers hindering agent deliveries. The ability to externally accelerate agent transport and control its distribution is highly desirable. Potentially, SIF-TUM can be a powerful technology to accelerate agent transport in deep tissue and control the distribution if appropriate parameters are selected.

The role of anti-tumor immunity of focused ultrasound for the malignancies: depended on the different ablation categories

Improving anti-tumor immunity has promising outcomes in eradicating malignant tumors. Tumor cells can escape from immune surveillance and killing; therefore, various strategies are continuously developing to inhibit immune escape. Focused ultrasound (FUS) has recently emerged to play an important role in immune modulation. After FUS therapy, various tumor antigens and related signals are released. The non-thermal effect of FUS strengthens the blood and lymph circulation, increases cell permeability, and helps in crossing the physical barrier like the blood-brain barrier and blood-tumor barrier. However, the different ablation of FUS is proposed to have a different anti-tumor immune effect. Therefore, we categorized the FUS ablation into thermal and non-thermal ablation and summarized possible anti-tumor immunity mechanisms.

Mechanistic Insights and Therapeutic Delivery through Micro/Nanobubble-Assisted Ultrasound

Ultrasound with low frequency (20–100 kHz) assisted drug delivery has been widely investigated as a non-invasive method to enhance the permeability and retention effect of drugs. The functional micro/nanobubble loaded with drugs could provide an unprecedented opportunity for targeted delivery. Then, ultrasound with higher intensity would locally burst bubbles and release agents, thus avoiding side effects associated with systemic administration. Furthermore, ultrasound-mediated destruction of micro/nanobubbles can effectively increase the permeability of vascular membranes and cell membranes, thereby not only increasing the distribution concentration of drugs in the interstitial space of target tissues but also promoting the penetration of drugs through cell membranes into the cytoplasm. These advancements have transformed ultrasound from a purely diagnostic utility into a promising theragnostic tool. In this review, we first discuss the structure and generation of micro/nanobubbles. Second, ultrasound parameters and mechanisms of therapeutic delivery are discussed. Third, potential biomedical applications of micro/nanobubble-assisted ultrasound are summarized. Finally, we discuss the challenges and future directions of ultrasound combined with micro/nanobubbles.

Endovascular Chemotherapy: Selective Targeting for Brain Cancer

Establishing an effective and robust management option for brain cancers has proven to bean elusive challenge for the fields of neurosurgery and neuro-oncology. Despite decades of research efforts to improve treatment outcomes and increase patient survivability, brain cancer remains among the most fatal of all cancer classes. A significant barrier to this endeavor is the blood-brain barrier, a major protective border for brain tissue that primarily precludes the optimal delivery of chemotherapeutic drugs to the patient's brain circulation through tight junction formations and selective transporter proteins. This issue is often compounded by tumor location, particularly in inoperable regions near functional brain parenchyma. These obstacles necessitate the development of selectively targeted delivery of chemotherapeutic agents, such as endovascular super-selective intra-arterial injections. Recent experimental studies demonstrate the effectiveness of focused ultrasound to unseal the blood-brain barrier selectively and reversibly. Together, these new technologies can be leveraged to circumvent the limited permeability of the blood-brain barrier, thus improving drug delivery to tumoral locations and potentially enabling a more effective treatment alternative to surgical resection. This review attempts to place into context the necessity of these newer selective chemotherapeutic modalities by briefly highlighting commonly encountered brain cancers and explaining the prominent challenges that face chemotherapy delivery, as well as describing the current preclinical and clinical progress in the development of facilitatory focused ultrasound with selective endovascular chemotherapy.

Effect of hyperthermia and proton beam radiation as a novel approach in chordoma cells death and its clinical implication to treat chordoma

PURPOSE

Chordoma is a locally aggressive tumor that most commonly affects the base of the skull/clivus, cervical, and sacral spine. Conventional radiotherapy (RT), cannot be safely increased further to improve disease control due to the risk of toxicity to the surrounding critical structures. Tumor-targeted hyperthermia (HT) combined with Proton Beam Radiation Therapy (PBRT) is known to act as a potent radiosensitizer in cancer control. In this study, we investigated whether PBRT efficacy for chordoma can be enhanced in combination with HT as a radiosensitizer.

MATERIAL AND METHODS

Human chordoma cell lines, U-CH2 and Mug-chor1 were treated in vitro with HT followed by PBRT with variable doses. The colony-forming assay was performed, and dose-response was characterized by linear-quadratic model fits. HSP-70 and Brachyury (TBXT) biomarkers for chordoma aggression levels were quantified by western blot analysis. Gene microarray analysis was performed by U133 Arrays. Pathway Analysis was also performed using IPA bioinformatic software.

RESULTS

Our findings in both U-CH₂ and Mug-Chor1 cell lines demonstrate that hyperthermia followed by PBRT has an enhanced cell killing effect when compared with PBRT-alone (p < .01). Western blot analysis showed HT decreased the expression of Brachyury protein (p < .05), which is considered a biomarker for chordoma tumor aggression. HT with PBRT also exhibited an RT-dose-dependent decrease of Brachyury expression (p < .05). We also observed enhanced HSP-70 expression due to HT, RT, and HT + RT combined in both cell lines. Interestingly, genomic data showed 344 genes expressed by the treatment of HT + RT compared to HT (68 genes) or RT (112 genes) as individual treatment. We also identified activation of death receptor and apoptotic pathway in HT + RT treated cells.

CONCLUSION

We found that Hyperthermia (HT) combined with Proton Beam Radiation (PBRT) could significantly increase chordoma cell death by activating the death receptor pathway and apoptosis which has the promise to treat metastatic chordoma.

MRI Guided Focused Ultrasound-Mediated Delivery of Therapeutic Cells to the Brain: A Review of the State-of-the-Art Methodology and Future Applications

Stem cell and immune cell therapies are being investigated as a potential therapeutic modality for CNS disorders, performing functions such as targeted drug or growth factor delivery, tumor cell destruction, or inflammatory regulation. Despite promising preclinical studies, delivery routes for maximizing cell engraftment, such as stereotactic or intrathecal injection, are invasive and carry risks of hemorrhage and infection. Recent developments in MRI-guided focused ultrasound (MRgFUS) technology have significant implications for treating focal CNS pathologies including neurodegenerative, vascular and malignant processes. MRgFUS is currently employed in the clinic for treating essential tremor and Parkinson's Disease by producing precise, incisionless, transcranial lesions. This non-invasive technology can also be modified for non-destructive applications to safely and transiently open the blood-brain barrier (BBB) to deliver a range of therapeutics, including cells. This review is meant to familiarize the neuro-interventionalist with this topic and discusses the use of MRgFUS for facilitating cellular delivery to the brain. A detailed and comprehensive description is provided on routes of cell administration, imaging strategies for targeting and tracking cellular delivery and engraftment, biophysical mechanisms of BBB enhanced permeability, supportive proof-of-concept studies, and potential for clinical translation.

Opening doors with ultrasound and microbubbles: Beating biological barriers to promote drug delivery

Apart from its clinical use in imaging, ultrasound has been thoroughly investigated as a tool to enhance drug delivery in a wide variety of applications. Therapeutic ultrasound, as such or combined with cavitating nuclei or microbubbles, has been explored to cross or permeabilize different biological barriers. This ability to access otherwise impermeable tissues in the body makes the combination of ultrasound and therapeutics very appealing to enhance drug delivery in situ. This review gives an overview of the most important biological barriers that can be tackled using ultrasound and aims to provide insight on how ultrasound has shown to improve accessibility as well as the biggest hurdles. In addition, we discuss the clinical applicability of therapeutic ultrasound with respect to the main challenges that must be addressed to enable the further progression of therapeutic ultrasound towards an effective, safe and easy-to-use treatment tailored for drug delivery in patients.

Effect of Acoustic Radiation Force on the Distribution of Nanoparticles in Solid Tumors

Acoustic radiation force (ARF) might improve the distribution of nanoparticles (NPs) in tumors. To study this, tumors growing subcutaneously in mice were exposed to focused ultrasound (FUS) either 15 min or 4 h after the injection of NPs, to investigate the effect of ARF on the transport of NPs across the vessel wall and through the extracellular matrix. Quantitative analysis of confocal microscopy images from frozen tumor sections was performed to estimate the displacement of NPs from blood vessels. Using the same experimental exposure parameters, ARF was simulated and compared with the experimental data. Enhanced interstitial transport of NPs in tumor tissues was observed when FUS (10 MHz, acoustic power 234 W/cm², 3.3% duty cycle) was given either 15 min or 4 h after NP administration. According to acoustic simulations, the FUS generated an ARF per unit volume of 2.0×10⁶ N/m³. The displacement of NPs was larger when FUS was applied 4 h after NP injection compared with after 15 min. This study shows that ARF might contribute to a modest improved distribution of NPs into the tumor interstitium.

Ultrasound-triggered therapeutic microbubbles enhance the efficacy of cytotoxic drugs by increasing circulation and tumor drug accumulation and limiting bioavailability and toxicity in normal tissues

Most cancer patients receive chemotherapy at some stage of their treatment which makes improving the efficacy of cytotoxic drugs an ongoing and important goal. Despite large numbers of potent anti-cancer agents being developed, a major obstacle to clinical translation remains the inability to deliver therapeutic doses to a tumor without causing intolerable side effects. To address this problem, there has been intense interest in nanoformulations and targeted delivery to improve cancer outcomes. The aim of this work was to demonstrate how vascular endothelial growth factor receptor 2 (VEGFR2)-targeted, ultrasound-triggered delivery with therapeutic microbubbles (thMBs) could improve the therapeutic range of cytotoxic drugs. Methods: Using a microfluidic microbubble production platform, we generated thMBs comprising VEGFR2-targeted microbubbles with attached liposomal payloads for localised ultrasound-triggered delivery of irinotecan and SN38 in mouse models of colorectal cancer. Intravenous injection into tumor-bearing mice was used to examine targeting efficiency and tumor pharmacodynamics. High-frequency ultrasound and bioluminescent imaging were used to visualise microbubbles in real-time. Tandem mass spectrometry (LC-MS/MS) was used to quantitate intratumoral drug delivery and tissue biodistribution. Finally, 89Zr PET radiotracing was used to compare biodistribution and tumor accumulation of ultrasound-triggered SN38 thMBs with VEGFR2-targeted SN38 liposomes alone. Results: ThMBs specifically bound VEGFR2 in vitro and significantly improved tumor responses to low dose irinotecan and SN38 in human colorectal cancer xenografts. An ultrasound trigger was essential to achieve the selective effects of thMBs as without it, thMBs failed to extend intratumoral drug delivery or demonstrate enhanced tumor responses. Sensitive LC-MS/MS quantification of drugs and their metabolites demonstrated that thMBs extended drug exposure in tumors but limited exposure in healthy tissues, not exposed to ultrasound, by persistent encapsulation of drug prior to elimination. 89Zr PET radiotracing showed that the percentage injected dose in tumors achieved with thMBs was twice that of VEGFR2-targeted SN38 liposomes alone. Conclusions: thMBs provide a generic platform for the targeted, ultrasound-triggered delivery of cytotoxic drugs by enhancing tumor responses to low dose drug delivery via combined effects on circulation, tumor drug accumulation and exposure and altered metabolism in normal tissues.

Pulsed focused ultrasound lowers interstitial fluid pressure and increases nanoparticle delivery and penetration in head and neck squamous cell carcinoma xenograft tumors

Nanocarriers offer a promising approach to significantly improve therapeutic delivery to solid tumors as well as limit the side effects associated with anti-cancer agents. However, their relatively large size can negatively affect their ability to efficiently penetrate into more interior tumor regions, ultimately reducing therapeutic efficacy. Poor penetration of large agents such as nanocarriers is attributed to factors in the tumor microenvironment such as elevated interstitial fluid pressure (IFP) and fibrillar collagen in the extracellular matrix. Our previous studies reported that pretreatment of solid tumor xenografts with nondestructive pulsed focused ultrasound (pFUS) can improve the delivery and subsequent therapy of a variety of therapeutic formulations in different tumor models, where the results were associated with expanded extracellular spaces (ECS), an increase in hydraulic conductivity, and decrease in tissue stiffness. Here, we demonstrate the inverse relationship between IFP and the penetration of systemically administered nanoparticle (NP) probes, where IFP increased from the tumor periphery to their center. Furthermore, we show that pretreatment with pFUS can safely reduce IFP and improve NP delivery; especially into the center of the tumors. These results coincide with effects generated in the fibrillar collagen network microstructure in the ECS as determined by quantitative polarized light microscopy. Whole tumor and histomorphometric analysis, however, did not show significant differences in collagen area fraction or collagen feature solidity, as well as tumor cross-sectional area and aspect ratio, as a result of the treatments. We present a biophysical model connecting the experimental results, where pFUS-mediated cytoarchitectural changes are associated with improved redistribution of the interstitial fluid and lower IFP. The resulting improvement in NP delivery supports our previous therapeutic studies and may have implications for clinical applications to improve therapeutic outcomes in cancer therapy.

Ultrasound and microbubble mediated therapeutic delivery: Underlying mechanisms and future outlook

Beyond the emerging field of oncological ultrasound molecular imaging, the recent significant advancements in ultrasound and contrast agent technology have paved the way for therapeutic ultrasound mediated microbubble oscillation and has shown that this approach is capable of increasing the permeability of microvessel walls while also initiating enhanced extravasation and drug delivery into target tissues. In addition, a large number of preclinical studies have demonstrated that ultrasound alone or combined with microbubbles can efficiently increase cell membrane permeability resulting in enhanced tissue distribution and intracellular drug delivery of molecules, nanoparticles, and other therapeutic agents. The mechanism behind the enhanced permeability is the temporary creation of pores in cell membranes through a phenomenon called sonoporation by high-intensity ultrasound and microbubbles or cavitation agents. At low ultrasound intensities (0.3-3 W/cm²), sonoporation may be caused by microbubbles oscillating in a stable motion, also known as stable cavitation. In contrast, at higher ultrasound intensities (greater than 3 W/cm²), sonoporation usually occurs through inertial cavitation that accompanies explosive growth and collapse of the microbubbles. Sonoporation has been shown to be a highly effective method to improve drug uptake through microbubble potentiated enhancement of microvascular permeability. In this review, the therapeutic strategy of using ultrasound for improved drug delivery are summarized with the special focus on cancer therapy. Additionally, we discuss the progress, challenges, and future of ultrasound-mediated drug delivery towards clinical translation.

Comparison of Heat Transfer Enhancement Between Magnetic and Gold Nanoparticles During HIFU Sonication

Long procedure times and collateral damage remain challenges in high-intensity focused ultrasound (HIFU) medical procedures. Magnetic nanoparticles (mNPs) and gold nanoparticles (gNPs) have the potential to reduce the acoustic intensity and/or exposure time required in these procedures. In this research, we investigated relative advantages of using gNPs and mNPs during HIFU thermal-ablation procedures. Tissue-mimicking phantoms containing embedded thermocouples (TCs) and physiologically acceptable concentrations (0.0625% and 0.125%) of gNPs were sonicated at acoustic powers of 5.2 W, 9.2 W, and 14.5 W, for 30 s. It was observed that when the concentration of gNPs was doubled from 0.0625% to 0.125%, the temperature rise increased by 80% for a power of 5.2 W. For a fixed concentration (0.0625%), the energy absorption was 1.7 times greater for mNPs than gNPs for a power of 5.2 W. Also, for the power of 14.5 W, the sonication time required to generate a lesion volume of 50 mm3 decreased by 1.4 times using mNPs, compared with gNPs, at a concentration of 0.0625%. We conclude that mNPs are more likely than gNPs to produce a thermal enhancement in HIFU ablation procedures.

Focused ultrasound activates voltage-gated calcium channels through depolarizing TRPC1 sodium currents in kidney and skeletal muscle

Pulsed focused ultrasound (pFUS) technology is being developed for clinical neuro/immune modulation and regenerative medicine. Biological signal transduction of pFUS forces can require mechanosensitive or voltage-gated plasma membrane ion channels. Previous studies suggested pFUS is capable of activating either channel type, but their mechanistic relationship remains ambiguous. We demonstrated pFUS bioeffects increased mesenchymal stem cell tropism (MSC) by altering molecular microenvironments through cyclooxygenase-2 (COX2)-dependent pathways. This study explored specific relationships between mechanosensitive and voltage-gated Ca²⁺ channels (VGCC) to initiate pFUS bioeffects that increase stem cell tropism.

Methods: Murine kidneys and hamstring were given pFUS (1.15 or 1.125 MHz; 4MPa peak rarefactional pressure) under ultrasound or magnetic resonance imaging guidance. Cavitation and tissue displacement were measure by hydrophone and ultrasound radiofrequency data, respectively. Elastic modeling was performed from displacement measurements. COX2 expression and MSC tropism were evaluated in the presence of pharmacological ion channel inhibitors or in transient-receptor-potential-channel-1 (TRPC1)-deficient mice. Immunohistochemistry and co-immunoprecipitation examined physical channel relationships. Fluorescent ionophore imaging of cultured C2C12 muscle cells or TCMK1 kidney cells probed physiological interactions.

Results: pFUS induced tissue deformations resulting in kPa-scale forces suggesting mechanical activation of pFUS-induced bioeffects. Inhibiting VGCC or TRPC1 in vivo blocked pFUS-induced COX2 upregulation and MSC tropism to kidneys and muscle. A TRPC1/VGCC complex was observed in plasma membranes. VGCC or TRPC1 suppression blocked pFUS-induced Ca²⁺ transients in TCMK1 and C2C12 cells. Additionally, Ca²⁺ transients were blocked by reducing transmembrane Na⁺ potentials and observed Na⁺ transients were diminished by genetic TRPC1 suppression.

Conclusion: This study suggests that pFUS acoustic radiation forces mechanically activate a Na⁺-containing TRPC1 current upstream of VGCC rather than directly opening VGCC. The electrogenic function of TRPC1 provides potential mechanistic insight into other pFUS techniques for physiological modulation and optimization strategies for clinical implementation.

Numerical modeling of ultrasound heating for the correction of viscous heating artifacts in soft tissue temperature measurements

Measuring temperature during focused ultrasound (FUS) procedures is critical for characterization, calibration, and monitoring to ultimately ensure safety and efficacy. Despite the low cost and the high spatial and temporal resolutions of temperature measurements using thermocouples, the viscous heating (VH) artifact at the thermocouple-tissue interface requires reading corrections for correct thermometric analysis. In this study, a simulation pipeline is proposed to correct the VH artifact arising from temperature measurements using thermocouples in FUS fields. The numerical model consists of simulating a primary source of heating due to ultrasound absorption and a secondary source of heating from viscous forces generated by the thermocouple in the FUS field. Our numerical validation found that up to 90% of the measured temperature rise was due to VH effects. Experimental temperature measurements were performed using thermocouples embedded in fresh chicken breast samples. Temperature corrections were demonstrated for single high-intensity FUS pulses at 3.1 MHz and for multiple pulses (3.1 MHz, 100 Hz, and 500 Hz pulse repetition frequency). The VH accumulated during sonications and produced a temperature increase of 3.1 °C and 15.3 °C for the single and multiple pulse sequences, respectively. The methodology presented here enables the decoupling of the temperature increase generated by absorption and VH. Thus, more reliable temperature measurements can be extracted from thermocouple measurements by correcting for VH.

Temperature-Responsive Hydrophobic Silica Nanoparticle Ultrasound Contrast Agents Directed by Phospholipid Phase Behavior

In this paper, we report ultrasonically active nanoscale contrast agents that behave as thermometric sensors through phase change in their stabilizing phospholipid monolayer. Phospholipid-stabilized, hydrophobic mesoporous silica nanoparticles (P@hMSNs) are known to interact with high-intensity focused ultrasound (HIFU) to promote cavitation at their surfaces, which can be used for both imaging and therapy. We show that the lateral lipid phase behavior of the phosphocholine lipid dictates the acoustic contrast of the P@hMSNs. When the lipids are in the gel phase below their melting temperature, the P@hMSNs generate detectable microbubbles when exposed to HIFU. However, if the lipids exhibit a liquid expanded phase, the P@hMSNs cease to generate bubbles in response to HIFU insonation. We verify that the heating and subsequent transition of lipid coating the hMSN are associated with the loss of acoustic response by doping laurdan dye into the lipid monolayer and imaging lipid phase through red shifts in emission spectra. Similarly, cessation of cavitation was also induced by adding a fluidizing surfactant such as Triton X, which could be reversed upon washing away the excess surfactant. Finally, by controlling for the partial fluidization caused by the adsorption of protein, P@hMSNs may be used as thermometric sensors of the bulk fluid temperature. These findings not only impact the utilization of nanoscale agents as stimulus-responsive ultrasound contrast agents but also have broader implications for how cavitation may be initiated at surfaces coated by a surfactant.

Controlled Ultrasound Erosion for Transdermal Delivery and Hepatitis B Immunization

Although ultrasound is effective for transdermal delivery, it remains difficult to control the position, shape and size of localized skin transport regions. We developed an ultrasound erosion protocol to generate a single-site, circular delivery region with controlled size at the center of patched skin. We found that (i) shorter ultrasound pulses (25 cycles) with higher pulse repetition frequency (4 kHz) and higher peak negative pressure (17.0 MPa) resulted in larger (0.995 mm²) and deeper (∼300 µm) skin delivery regions with a higher success rate (94.44%); and (ii) temperature elevation of the skin increased with ultrasound exposure time, with a 30-s safety threshold. Furthermore, we found that hair follicles decreased the delivery controllability of ultrasound erosion. Therefore, we selected the skin of the hind legs of mice without dense hair follicles to deliver more than 1 μL of vaccine solution and successfully elicit immune responses against hepatitis B surface antigen.

Microbubble-Mediated Delivery for Cancer Therapy

Despite an overall improvement in survival rates for cancer, certain resistant forms of the disease still impose a significant burden on patients and healthcare systems. Standard chemotherapy in these cases is often ineffective and/or gives rise to severe side effects. Targeted delivery of chemotherapeutics could improve both tumour response and patient experience. Hence, there is an urgent need to develop effective methods for this. Ultrasound is an established technique in both diagnosis and therapy. Its use in conjunction with microbubbles is being actively researched for the targeted delivery of small-molecule drugs. In this review, we cover the methods by which ultrasound and microbubbles can be used to overcome tumour barriers to cancer therapy.

Tumour tissue transport after intraperitoneal anticancer drug delivery

Intraperitoneal (IP) drug delivery, either as an intraoperative chemoperfusion or as an adjuvant, repeated instillation, is an established treatment modality in patients with peritoneal carcinomatosis. The efficacy of IP drugs depends on its ability to penetrate the tumour stroma in order to reach their (sub)cellular target. It is known, that drug penetration after IP delivery is limited to a few millimetres. Here, we review the basic tissue transport mechanisms after IP delivery and discuss the biophysical barriers and obstacles that limit penetration distance. In addition, we review the physical and pharmaceutical interventions that have been studied in order to improve delivery of small molecular and macromolecular drugs after IP instillation. These interventions could inform the design of future clinical trials aiming at an improved efficacy of IP-based drug delivery in carcinomatosis patients.

MR-guided transcranial focused ultrasound safely enhances interstitial dispersion of large polymeric nanoparticles in the living brain

Generating spatially controlled, non-destructive changes in the interstitial spaces of the brain has a host of potential clinical applications, including enhancing the delivery of therapeutics, modulating biological features within the tissue microenvironment, altering fluid and pressure dynamics, and increasing the clearance of toxins, such as plaques found in Alzheimer's disease. Recently we demonstrated that ultrasound can non-destructively enlarge the interstitial spaces of the brain ex vivo. The goal of the current study was to determine whether these effects could be reproduced in the living brain using non-invasive, transcranial MRI-guided focused ultrasound (MRgFUS). The left striatum of healthy rats was treated using MRgFUS. Computer simulations facilitated treatment planning, and targeting was validated using MRI acoustic radiation force impulse imaging. Following MRgFUS treatments, Evans blue dye or nanoparticle probes were infused to assess changes in the interstitial space. In MRgFUS-treated animals, enhanced dispersion was observed compared to controls for 70 nm (12.8 ± 0.9 mm3 vs. 10.6 ± 1.0 mm3, p = 0.01), 200 nm (10.9 ± 1.4 mm3 vs. 7.4 ± 0.7 mm3, p = 0.01) and 700 nm (7.5 ± 0.4 mm3 vs. 5.4 ± 1.2 mm3, p = 0.02) nanoparticles, indicating enlargement of the interstitial spaces. No evidence of significant histological or electrophysiological injury was identified. These findings suggest that transcranial ultrasound can safely and effectively modulate the brain interstitium and increase the dispersion of large therapeutic entities such as particulate drug carriers or modified viruses. This has the potential to expand the therapeutic uses of MRgFUS.

Emerging Applications of Therapeutic Ultrasound in Neuro-oncology: Moving Beyond Tumor Ablation

: Transcranial focused ultrasound (FUS) can noninvasively transmit acoustic energy with a high degree of accuracy and safety to targets and regions within the brain. Technological advances, including phased-array transducers and real-time temperature monitoring with magnetic resonance thermometry, have created new opportunities for FUS research and clinical translation. Neuro-oncology, in particular, has become a major area of interest because FUS offers a multifaceted approach to the treatment of brain tumors. FUS has the potential to generate cytotoxicity within tumor tissue, both directly via thermal ablation and indirectly through radiosensitization and sonodynamic therapy; to enhance the delivery of therapeutic agents to brain tumors by transiently opening the blood-brain barrier or improving distribution through the brain extracellular space; and to modulate the tumor microenvironment to generate an immune response. In this review, we describe each of these applications for FUS, the proposed mechanisms of action, and the preclinical and clinical studies that have set the foundation for using FUS in neuro-oncology.

ABBREVIATIONS

BBB, blood-brain barrierCED, convection-enhanced delivery5-Ala, 5-aminolevulinic acidFUS, focused ultrasoundGBM, glioblastoma multiformeHSP, heat shock proteinMRgFUS, magnetic resonance-guided focused ultrasoundpFUS, pulsed focused ultrasound.

Drug Delivery Strategies for Platinum-Based Chemotherapy

Few chemotherapeutics have had such an impact on cancer management as cis-diamminedichloridoplatinum(II) (CDDP), also known as cisplatin. The first member of the platinum-based drug family, CDDP's potent toxicity in disrupting DNA replication has led to its widespread use in multidrug therapies, with particular benefit in patients with testicular cancers. However, CDDP also produces significant side effects that limit the maximum systemic dose. Various strategies have been developed to address this challenge including encapsulation within micro- or nanocarriers and the use of external stimuli such as ultrasound to promote uptake and release. The aim of this review is to look at these strategies and recent scientific and clinical developments.

Enhancing tissue permeability with MRI guided preclinical focused ultrasound system in rabbit muscle: From normal tissue to VX2 tumor

High Intensity Focused Ultrasound (HIFU) is an emerging noninvasive, nonionizing physical energy based modality to ablate solid tumors with high power, or increase local permeability in tissues/tumors in pulsed mode with relatively low power. Compared with traditional ablative HIFU, nondestructive pulsed HIFU (pHIFU) is present in the majority of novel applications recently developed for enhancing the delivery of drugs and genes. Previous studies have demonstrated the capability of pHIFU to change tissue local permeability for enhanced drug delivery in both mouse tumors and mouse muscle. Further study based on bulk tissues in large animals and clinical HIFU system revealed correlation between therapeutic effect and thermal parameters, which was absent in the previous mouse studies. In this study, we further investigated the relation between the therapeutic effect of pHIFU and thermal parameters in bulky normal muscle tissues based on a rabbit model and a preclinical HIFU system. Correlation between therapeutic effect and thermal parameters was confirmed in our study on the same bulk tissues although different HIFU systems were used. Following the study in bulky normal muscle tissues, we further created bulky tumor model with VX2 tumors implanted on both hind limbs of rabbits and investigated the feasibility to enhance tumor permeability in bulky VX2 tumors in a rabbit model using pHIFU technique. A radiolabeled peptidomimetic integrin antagonist, 111In-DOTA-IA, was used following pHIFU treatment in our study to target VX2 tumor and serve as the radiotracer for follow-up single-photon emission computed tomography (SPECT) scanning. The results have shown significantly elevated uptake of 111In-DOTA-IA in the area of VX2 tumors pretreated by pHIFU compared with the control VX2 tumors not being pretreated by pHIFU, and statistical analysis revealed averaged 34.5% enhancement 24h after systematic delivery of 111In-DOTA-IA in VX2 tumors pretreated by pHIFU compared with the control VX2 tumors.

Treatment of Movement Disorders With Focused Ultrasound

Although the use of ultrasound as a potential therapeutic modality in the brain has been under study for several decades, relatively few neuroscientists or neurologists are familiar with this technology. Stereotactic brain lesioning had been widely used as a treatment for medically refractory patients with essential tremor (ET), Parkinson disease (PD), and dystonia but has been largely replaced by deep brain stimulation (DBS) surgery, with advantages both in safety and efficacy. However, DBS is associated with complications including intracerebral hemorrhage, infection, and hardware malfunction. The occurrence of these complications has spurred interest in less invasive stereotactic brain lesioning methods including magnetic resonance imaging–guided high intensity–focused ultrasound (FUS) surgery. Engineering advances now allow sound waves to be targeted noninvasively through the skull to a brain target. High intensities of sonic energy can create a coagulation lesion similar to that of older radiofrequency stereotactic methods, but without opening the skull, recent Food and Drug Administration approval of unilateral thalamotomy for treatment of ET. Clinical studies of stereotactic FUS for aspects of PD are underway. Moderate intensity, pulsed FUS has also demonstrated the potential to safely open the blood-brain barrier for localized delivery of therapeutics including proteins, genes, and cell-based therapy for PD and related disorders. The goal of this review is to provide basic and clinical neuroscientists with a level of understanding to interact with medical physicists, biomedical engineers, and radiologists to accelerate the application of this powerful technology to brain disease

Focused Ultrasound for Essential Tremor: Review of the Evidence and Discussion of Current Hurdles

Background

While there is no breakthrough progress in the medical treatment of essential tremor (ET), in the past decades several remarkable achievements happened in the surgical field, such as radiofrequency thalamotomy, thalamic deep brain stimulation, and gamma knife thalamotomy. The most recent advance in this area is magnetic resonance-guided focused ultrasound (MRgFUS).

Methods

The purpose of this review is to discuss the new developments and trials of MRgFUS in the treatment of ET and other tremor disorders.

Results

MRgFUS is an incisionless surgery performed without anesthesia and ionizing radiation (no risk of cumulative dose and delayed side effects). Studies have shown the safety and effectiveness of unilateral MRgFUS-thalamotomy in the treatment of ET. It has been successfully used in a few patients with Parkinson’s disease-related tremor, and in fewer patients with fragile X-associated tremor/ataxia syndrome. The safety and long-term effects of the procedure are still unclear, as temporary and permanent adverse events have been reported as well as recurrence of tremor.

Discussion

MRgFUS is a promising new surgical approach with a number of unknowns and unsolved issues. It represents a valuable option particularly for patients who refused or could not be candidates for other procedures, deep brain stimulation in particular.

Focused Ultrasound: An Emerging Therapeutic Modality for Neurologic Disease

Therapeutic ultrasound is only beginning to be applied to neurologic conditions, but the potential of this modality for a wide spectrum of brain applications is high. Engineering advances now allow sound waves to be targeted through the skull to a brain region selected with real time magnetic resonance imaging and thermography, using a commercial array of focused emitters. High intensities of sonic energy can create a coagulation lesion similar to that of older radiofrequency stereotactic methods, but without opening the skull. This has led to the recent Food and Drug Administration approval of focused ultrasound (FUS) thalamotomy for unilateral treatment of essential tremor. Clinical studies of stereotactic FUS for aspects of Parkinson's disease, chronic pain, and refractory psychiatric indications are underway, with promising results. Moderate-intensity FUS has the potential to safely open the blood-brain barrier for localized delivery of therapeutics, while low levels of sonic energy can be used as a form of neuromodulation.

Cyclooxygenase-2 or tumor necrosis factor-α inhibitors attenuate the mechanotransductive effects of pulsed focused ultrasound to suppress mesenchymal stromal cell homing to healthy and dystrophic muscle

Maximal homing of infused stem cells to diseased tissue is critical for regenerative medicine. Pulsed focused ultrasound (pFUS) is a clinically relevant platform to direct stem cell migration. Through mechanotransduction, pFUS establishes local gradients of cytokines, chemokines, trophic factors (CCTF) and cell adhesion molecules (CAM) in treated skeletal muscle that subsequently infused mesenchymal stromal cells (MSC) can capitalize to migrate into the parenchyma. Characterizing molecular responses to mechanical pFUS effects revealed tumor necrosis factor-alpha (TNFα) drives cyclooxygenase-2 (COX2) signaling to locally increase CCTF/CAM that are necessary for MSC homing. pFUS failed to increase chemoattractants and induce MSC homing to treated muscle in mice pretreated with ibuprofen (nonspecific COX inhibitor) or etanercept (TNFα inhibitor). pFUS-induced MSC homing was also suppressed in COX2-knockout mice, demonstrating ibuprofen blocked the mechanically induced CCTF/CAM by acting on COX2. Anti-inflammatory drugs, including ibuprofen, are administered to muscular dystrophy (MD) patients, and ibuprofen also suppressed pFUS-induced homing to muscle in a mouse model of MD. Drug interactions with cell therapies remain unexplored and are not controlled for during clinical cell therapy trials. This study highlights potentially negative drug-host interactions that suppress stem cell homing and could undermine cell-based approaches for regenerative medicine.

MRI-guided focused ultrasound surgery in musculoskeletal diseases: the hot topics

MRI-guided focused ultrasound surgery (MRgFUS) is a minimally invasive treatment guided by the most sophisticated imaging tool available in today's clinical practice. Both the imaging and therapeutic sides of the equipment are based on non-ionizing energy. This technique is a very promising option as potential treatment for several pathologies, including musculoskeletal (MSK) disorders. Apart from clinical applications, MRgFUS technology is the result of long, heavy and cumulative efforts exploring the effects of ultrasound on biological tissues and function, the generation of focused ultrasound and treatment monitoring by MRI. The aim of this article is to give an updated overview on a "new" interventional technique and on its applications for MSK and allied sciences.

Pulsed High-Intensity Focused Ultrasound Enhances Delivery of Doxorubicin in a Preclinical Model of Pancreatic Cancer

Pancreatic cancer is characterized by extensive stromal desmoplasia, which decreases blood perfusion and impedes chemotherapy delivery. Breaking the stromal barrier could both increase perfusion and permeabilize the tumor, enhancing chemotherapy penetration. Mechanical disruption of the stroma can be achieved using ultrasound-induced bubble activity-cavitation. Cavitation is also known to result in microstreaming and could have the added benefit of actively enhancing diffusion into the tumors. Here, we report the ability to enhance chemotherapeutic drug doxorubicin penetration using ultrasound-induced cavitation in a genetically engineered mouse model (KPC mouse) of pancreatic ductal adenocarcinoma. To induce localized inertial cavitation in pancreatic tumors, pulsed high-intensity focused ultrasound (pHIFU) was used either during or before doxorubicin administration to elucidate the mechanisms of enhanced drug delivery (active vs. passive drug diffusion). For both types, the pHIFU exposures that were associated with high cavitation activity resulted in disruption of the highly fibrotic stromal matrix and enhanced the normalized doxorubicin concentration by up to 4.5-fold compared with controls. Furthermore, normalized doxorubicin concentration was associated with the cavitation metrics (P < 0.01), indicating that high and sustained cavitation results in increased chemotherapy penetration. No significant difference between the outcomes of the two types, that is, doxorubicin infusion during or after pHIFU treatment, was observed, suggesting that passive diffusion into previously permeabilized tissue is the major mechanism for the increase in drug concentration. Together, the data indicate that pHIFU treatment of pancreatic tumors when resulting in high and sustained cavitation can efficiently enhance chemotherapy delivery to pancreatic tumors. .

Localization of focused-ultrasound beams in a tissue phantom, using remote thermocouple arrays

In focused-ultrasound procedures such as vessel cauterization or clot lysis, targeting accuracy is critical. To investigate the targeting accuracy of the focused-ultrasound systems, tissue phantoms embedded with thermocouples can be employed. This paper describes a method that utilizes an array of thermocouples to localize the focused ultrasound beam. All of the thermocouples are located away from the beam, so that thermocouple artifacts and sensor interference are minimized. Beam propagation and temperature rise in the phantom are simulated numerically, and an optimization routine calculates the beam location that produces the best agreement between the numerical temperature values and those measured with thermocouples. The accuracy of the method was examined as a function of the array characteristics, including the number of thermocouples in the array and their orientation. For exposures with a 3.3-MHz source, the remote-thermocouple technique was able to predict the focal position to within 0.06 mm. Once the focal location is determined using the localization method, temperatures at desired locations (including the focus) can be estimated from remote thermocouple measurements by curve fitting an analytical solution to the heat equation. Temperature increases in the focal plane were predicted to within 5% agreement with measured values using this method.

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.

Recent advances in molecular, multimodal and theranostic ultrasound imaging

Ultrasound (US) imaging is an exquisite tool for the non-invasive and real-time diagnosis of many different diseases. In this context, US contrast agents can improve lesion delineation, characterization and therapy response evaluation. US contrast agents are usually micrometer-sized gas bubbles, stabilized with soft or hard shells. By conjugating antibodies to the microbubble (MB) surface, and by incorporating diagnostic agents, drugs or nucleic acids into or onto the MB shell, molecular, multimodal and theranostic MBs can be generated. We here summarize recent advances in molecular, multimodal and theranostic US imaging, and introduce concepts how such advanced MB can be generated, applied and imaged. Examples are given for their use to image and treat oncological, cardiovascular and neurological diseases. Furthermore, we discuss for which therapeutic entities incorporation into (or conjugation to) MB is meaningful, and how US-mediated MB destruction can increase their extravasation, penetration, internalization and efficacy.

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.

Localized micro-scale disruption of cells using laser-generated focused ultrasound

We utilize laser-generated focused ultrasound (LGFU) to create targeted mechanical disturbance on a few cells. The LGFU is transmitted through an optoacoustic lens that converts laser pulses into focused ultrasound. The tight focusing (<100 µm) and high peak pressure of the LGFU produces cavitational disturbances at a localized spot with micro-jetting and secondary shock-waves arising from micro-bubble collapse. We demonstrate that LGFU can be used as a non-contact, non-ionizing, high-precision tool to selectively detach a single cell from its culture substrate. Furthermore, we explore the possibility of biomolecule delivery in a small population of cells targeted by LGFU at pressure amplitudes below and above the cavitation threshold. We experimentally confirm that cavitational disruption is required for delivery of propidium iodide, a membrane-impermeable nucleic acid-binding dye, into cells.

Pulsed high-intensity focused ultrasound enhances apoptosis of pancreatic cancer xenograft with gemcitabine

We sought to investigate whether concurrent exposure to pulsed high-intensity focused ultrasound (HIFU) and the chemotherapeutic drug gemcitabine would enhance apoptosis in pancreatic cancer. A pancreatic cancer xenograft model was established using BALB/c nude mice and human pancreatic cancer cells (PANC-1). In the first study, mice were randomly allocated into one of four groups: control (n = 4), HIFU alone (n = 4), gemcitabine (GEM) alone (n = 28) and concurrent treatment with HIFU and gemcitabine (HIGEM) (n = 28). The GEM and HIGEM groups were subdivided into four subgroups (16 mice) according to the drug dose injected (50-200 mg/kg) and another four subgroups (16 mice) according to the time interval between drug injection and HIFU treatment (each subgroup, n = 4). Apoptosis rates were evaluated using the TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) assay and percentage of necrosis, as evaluated with Harris' hematoxylin solution and eosin Y stain, 3 d after treatment. The second study was performed to evaluate tumor growth rates of the four groups. Each group was treated weekly for 3 wk, and tumor size was periodically measured for up to 4 wk from the beginning of treatment. In the first study, overall rates of apoptosis were significantly higher in the HIGEM group than in the GEM group (p = 0.02). In a subgroup analysis, HIGEM was superior to GEM in enhancing apoptosis at gemcitabine dosages of 150-200 mg/kg gemcitabine and intervals between gemcitabine and HIFU less than 2 h (p = 0.01). In the second study, HIGEM treatment resulted in the slowest tumor growth. However, despite a visible distinction, none of the differences found between the HIGEM and GEM groups were statistically significant (p > 0.05). Treatment with both HIFU and gemcitabine might enhance cell apoptosis and reduce tumor growth in pancreatic carcinoma. For this concurrent treatment, a high dosage of gemcitabine and a short-term delay before HIFU are recommended to maximize the therapeutic effect.

Sharpening the thermal release of DNA from nanoparticles: towards a sequential release strategy

Unlike the sharp melting behavior of DNA-linked nanoparticle aggregates, the melting of DNA strands from individual gold nanoparticles is broad despite the high surface density of bound DNA. Here, it is demonstrated how sharpened melting can be achieved in colloidal nanoparticle systems using branched DNA-doubler structures hybridized with complementary DNA-doublers bound to the gold nanoparticle. Moreover, sharpened transitions are observed when DNA-doublers are hybridized with linear DNA-modified gold nanoparticles. This result suggests that the DNA density on nanoparticles is intrinsically great enough to form cooperative structures with the DNA-doublers. Finally, by introducing abasic destabilizing groups, the melting temperature of these DNA-doublers decreases without decreasing the sharpness. Consequently, by varying the temperature, two DNA-doublers with different stabilities dissociate sequentially from the gold nanoparticle surface, without overlapping and within a narrow temperature window. Owing to the excellent thermal selectivities exhibited by this system, the implementation of DNA-doublers in sequential photothermal therapies and with other nanomedicine delivery agents that rely on DNA dissociation as the mechanism of selective release is anticipated.

MRI-based prediction of pulsed high-intensity focused ultrasound effect on tissue transport in rabbit muscle

PURPOSE

To design an algorithm for optimizing pulsed high intensity focused ultrasound (p-HIFU) treatment parameters to maximize tissue transport while minimizing thermal necrosis based on MR image guidance.

MATERIALS AND METHODS

P-HIFU power, duty cycle, and treatment duration were varied to generate different levels of thermal and mechanical deposition in rabbit muscle. Changes in T2-weighted and T1 contrast-enhanced (CE) signal were assessed immediately following treatment and at 24 h. Transport parameters were extracted by means of T1-weighted dynamic contrast-enhanced MRI (DCE-MRI) technique at 0 and 24-h time points.

RESULTS

Successful p-HIFU treatment was indicated by focal hyperintensity on the T2-weighted image immediately post-treatment, suggesting increased fluid (edema), with little intensity change in CE image. After 24 h, the affected region expanded along the muscle fiber accompanied by clear hyperintensity in CE image (contrast uptake). Quantitative DCE-MRI analysis revealed statistically significant increases in both leakage rate and extracellular space, accompanied by a decrease in clearance rate.

CONCLUSION

Successful p-HIFU treatment was mainly correlated to tissue heating. Tissue transport properties following treatment success would result in improved contact between drug and targets in both time and space. MRI is the key to controlling treatment by means of thermometry and also monitoring efficacy by means of T2-weighted imaging.

Pulsed focused ultrasound exposures enhance locally administered gene therapy in a murine solid tumor model

Gene therapy by intratumoral injection is a promising approach for treating solid tumors. However, this approach has limited success due to insufficient distribution of gene vectors used for gene delivery. Previous studies have shown that pulsed-focused ultrasound (pFUS) can enhance both systemic and local delivery of therapeutic agents in solid tumors and other disease models. Here, murine squamous cell carcinoma flank tumors were treated with single intratumoral injection of naked tumor necrosis factor-alpha (TNF-α) plasmid, either with or without a preceding pFUS exposure. The exposures were given at 1 MHz, at a spatial average, temporal peak intensity of 2660 W cm(-2), using 50 ms pulses, given at a pulse repetition frequency of 1 Hz. One hundred pulses were given at individual raster points, spaced evenly over the projected surface of the tumor at a distance of 2 mm. Exposures alone had no effect on tumor growth. Significant growth inhibition was observed with injection of TNF-α plasmid, and tumor growth was further inhibited with pFUS. Improved results with pFUS correlated with larger necrotic regions in histological sections and improved distribution and penetration of fluorescent surrogate nanoparticles. Electron microscopy demonstrated enlarged gaps between cells in exposed tissue, and remote acoustic palpation showed decreases in tissue stiffness after pFUS. Combined, these results suggest pFUS effects may be reducing barriers for tissue transport and additionally lowering interstitial fluid pressure to further improve delivery and distribution of injected plasmid for greater therapeutic effects. This suggests that pFUS could potentially be beneficial for improving local gene therapy treatment of human malignancies.

Pulsed high-intensity focused ultrasound therapy enhances targeted delivery of cetuximab to colon cancer xenograft model in mice

Our aim was to evaluate whether pulsed high-intensity focused ultrasound (HIFU) therapy enhances the effect of an epidermal growth factor receptor-targeted chemotherapeutic drug, cetuximab, in treating human colon cancer xenografts in a mouse model. Balb/c nude mice with subcutaneous xenografts of HT-29 cells were randomly categorized into control (n = 9), pulsed HIFU alone (n = 10), cetuximab monotherapy (n = 8) or combined pulsed HIFU and cetuximab therapy (n = 9) group. Cetuximab, pulsed HIFU therapy, or both were administered three times per week starting from day 8 after tumor cell injection. Based on tumor growth curves up to 34 days, the combination therapy group showed more suppressed tumor growth than all other groups (p < 0.05). The final relative tumor volumes were 5.4 ± 2.1, 5.2 ± 1.3, 4.8 ± 1.8, and 3.1 ± 0.9 for control, pulsed HIFU alone, cetuximab monotherapy, and combination therapy groups, respectively. In conclusion, pulsed HIFU therapy appears to enhance the anti-tumor effect of epidermal growth factor receptor-targeted cetuximab on human colon cancer xenograft models in mice.