Pulsed High-Intensity Focused Ultrasound Enhances Systemic Administration of Naked DNA in Squamous Cell Carcinoma Model: Initial Experience

Multifunctional Theranostic Nanoparticles for Enhanced Tumor Targeted Imaging and Synergistic FUS/Chemotherapy on Murine 4T1 Breast Cancer Cell

Purpose

Triple negative breast cancer (TNBC) is challenging for effective remission due to its very aggressive, extremely metastatic and resistant to conventional chemotherapy. Herein, a multifunctional theranostic nanoparticle was fabricated to enhance tumor targeted imaging and promote focused ultrasound (FUS) ablation and chemotherapy and sonodynamic therapy (SDT). A multi-modal synergistic therapy can improve the therapeutic efficacy and prognosis of TNBC.

Methods

AS1411 aptamer modified PEG@PLGA nanoparticles encapsulated with perfluorohexane (PFH) and anti-cancer drug doxorubicin (DOX) were constructed (AS1411-DOX/PFH-PEG@PLGA) to enhance tumor targeted imaging to guide ablation and synergistic effect of FUS/chemotherapy. FUS was utilized to trigger the co-release of doxorubicin and simultaneously PFH phase transition and activate DOX for SDT effect. The physicochemical, phase-changeable imaging capability, biosafety of nanoparticles and multi-mode synergistic effects on growth of TNBC were thoroughly evaluated in vivo and in vitro.

Results

The synthesized AS1411-DOX/PFH-PEG@PLGA (A-DPPs) nanoparticles are uniformly round with an average diameter of 306.03 ± 5.35 nm and the zeta potential of −4.05 ± 0.13 mV, displaying high biosafety and FUS-responsive drug release in vitro and in vivo. AS1411 modified NPs specifically bind to 4T1 cells and elevate the ultrasound contrast agent (UCA) image contrast intensity via PFH phase-transition after FUS exposure. Moreover, the combined treatment of A-DPPs nanoparticles with FUS exhibited significantly higher apoptosis rate, stronger inhibitory effect on 4T1 cell invasion in vitro, induced more reactive oxygen species (ROS), and enhanced anti-tumor effect compared to a single therapy (p < 0.05). Additionally, the joint strategy resulted in more intense cavitation effect and larger ablated areas and reduced energy efficiency factor (EEF) both in vitro and in vivo.

Conclusion

The multifunctional AS1411-DOX/PFH-PEG@PLGA nanoparticles can perform as a marvelous synergistic agent for enhanced FUS/chemotherapy, promote real-time contrast enhanced US imaging and improve the therapeutic efficacy and prognosis of TNBC.

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.

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 Microbubble Delivery Targeting Intraplaque Neovascularization Inhibits Atherosclerotic Plaque in an APOE-deficient Mouse Model

BACKGROUND/AIM

Intraplaque neovascularization is often associated with plaque formation, development and instability, and clinical symptoms in atherosclerosis. The aim of the present study was to investigate a new strategy for treating athrosclerosis by ultrasound-targeted microbubble delivery (UTMD) targeting intraplaque neovascularization in an APOE-deficient mouse model of atherosclerosis.

MATERIALS AND METHODS

A mouse model of atherosclerosis was induced by feeding Apoe^-/- mice a hypercholesterolemic diet and was verified with hematoxylin and eosin staining and intercellular adhesion molecule 1 (ICAM-1) expression. Targeted microbubbles (MB) were prepared by conjugating microbubbles with biotinylated antibody to ICAM1 (MBi) or with both biotinylated anti-ICAM1 and the angiogenesis inhibitor Endostar (MBie). The targeted microbubbles were analyzed with epifluorescence microscopy and flow cytometry. The animals with induced atherosclerotic plaques received MBi or MBie followed by UTMD treatment. Endostar treatment alone was given to other animals for comparison. Morphological assessment of atherosclerotic plaques was performed after treatment. The expression of angiogenesis marker CD31 was detected by immunohistochemical analysis.

RESULTS

Atherosclerotic plaques developed in the entire aorta with significant intraplaque ICAM-1 expression in the APOE-deficient mice following a 30-week hypercholesterolemic diet. Microbubbles were successfully conjugated with anti-ICAM-1 and Endostar, with a conjugation rate of 98.3% and 63.5%, respectively. UTMD with MBie significantly reduced the area of atherosclerotic plaque as compared to the model control (p<0.05). Treatment with Endostar and UTMD with MBie significantly reduced CD31 expression compared with the model control group (p<0.01). Greater significant inhibitory effect on CD31 expression was found in the group treated with UTMD and MBie compared to the Endostar- and UTMD with MBi groups (p<0.01).

CONCLUSION

UTMD targeting intraplaque neovascularization was found to inhibit atherosclerotic plaque in a mouse model of atherosclerosis, suggesting the potential of microbubble-mediated ultrasound technology in aiding drug delivery for atherosclerosis treatment.

Concurrent Treatment with Anti-DLL4 Enhances Antitumor and Proapoptotic Efficacy of a γ-Secretase Inhibitor in Gastric Cancer

The Notch signaling pathway has been identified as a therapeutic target for cancers. γ-Secretase inhibitors (GSIs) have been progressively recognized as potential anticancer drugs. The present study aimed to investigate the effects of anti-delta like legend 4 (anti-DLL4) treatment on the anticancer efficacy of GSIs in gastric cancer. SGC-7901-GFP human gastric cancer cells were tested for DLL4 expression by rosette formation test and immunofluorescence, and then were treated with anti-DLL4 antibody N-[N-(3,5-difluorophenacetyl)-L-ananyl]-S-phenylglycine t-butyl ester (DAPT, a type of GSI), or a combination of anti-DLL4 antibody and DAPT. The effects of in vitro treatments on cell apoptosis, cell cycle, and cell invasion were analyzed. For in vivo study, an orthotopic mouse model of gastric cancer was established with green fluorescence expressing SGC-7901. Ultrasound targeted microbubble destruction was used to treat tumor-bearing mice with anti-DLL4 antibody conjugated microbubbles, DAPT, and a combination of the two. Real-time fluorescence imaging was performed to assess tumor cell inhibition in each group. Following in vivo treatments, apoptosis of tumor cells and the expression of apoptosis-related genes BAX, Bcl-2, and P53 were detected by TUNEL and immunohistochemical staining. In vivo combined treatment of anti-DLL4 and DAPT led to a higher rate of cell apoptosis and greater inhibition of cell invasion than that observed with DAPT treatment alone. DAPT and anti-DLL4 combination therapy resulted in decreased cell distribution at G1 phase and increased cell distribution at S phase, compared to the untreated control group (P < .01). In vivo combined therapy with anti-DLL4 and DAPT significantly increased tumor growth inhibition and tumor cell apoptosis when compared to DAPT therapy alone (P < .05). In addition, combined treatment significantly increased expression of BAX and P53 and reduced Bcl-2 expression (P < .05). Conversely, treatment with DAPT alone only increased expression of BAX and P53 (P < .05), suggesting that the reduction of Bcl-2 expression may play an important role in the synergetic antitumor and proapoptosis effects of the combined treatment. Concurrent treatment with anti-DLL4 enhances the antitumor and proapoptotic efficacy of the γ-secretase inhibitor in gastric cancer both in vitro and in vivo.

High intensity focused ultrasound inhibits melanoma cell migration and metastasis through attenuating microRNA-21-mediated PTEN suppression

High intensity focused ultrasound (HIFU) technology is becoming a potential noninvasive treatment for solid tumor. To explore whether HIFU can be applied to treat melanoma and its metastasis, we investigated the effect of HIFU on murine melanoma model. While there was little influence on cell survival, viability or apoptosis, HIFU exposure suppressed melanoma cell migration in vitro and metastasis in vivo. The expression of microRNA-21(miR-21) was down-regulated and PTEN expression was up-regulated in response to HIFU exposure, which was in concomitant with the reduction of AKT activity. Furthermore, ectopic miR-21 expression suppressed this effect of HIFU. These results demonstrate that HIFU exposure can inhibit AKT-mediated melanoma metastasis via miR-21 inhibition to restore PTEN expression. Therefore, targeting the miR-21/PTEN/AKT pathway might be a novel strategy of HIFU in treatment of melanoma.

Delivery of the gene encoding the tumor suppressor Sef into prostate tumors by therapeutic-ultrasound inhibits both tumor angiogenesis and growth

Carcinomas constitute over 80% of all human cancer types with no effective therapy for metastatic disease. Here, we demonstrate, for the first time, the efficacy of therapeutic-ultrasound (TUS) to deliver a human tumor suppressor gene, hSef-b, to prostate tumors in vivo. Sef is downregulated in various human carcinomas, in a manner correlating with tumor aggressiveness. In vitro, hSef-b inhibited proliferation of TRAMP C2 cells and attenuated activation of ERK/MAPK and the master transcription factor NF-κB in response to FGF and IL-1/TNF, respectively. In vivo, transfection efficiency of a plasmid co-expressing hSef-b/eGFP into TRAMP C2 tumors was 14.7 ± 2.5% following a single TUS application. Repeated TUS treatments with hSef-b plasmid, significantly suppressed prostate tumor growth (60%) through inhibition of cell proliferation (60%), and reduction in blood vessel density (56%). In accordance, repeated TUS-treatments with hSef-b significantly inhibited in vivo expression of FGF2 and MMP-9. FGF2 is a known mitogen, and both FGF2/MMP-9 are proangiogenic factors. Taken together our results strongly suggest that hSef-b acts in a cell autonomous as well as non-cell autonomous manner. Moreover, the study demonstrates the efficacy of non-viral TUS-based hSef-b gene delivery approach for the treatment of prostate cancer tumors, and possibly other carcinomas where Sef is downregulated.

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: 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.

Enhanced Therapeutic Epidermal Growth Factor Receptor (EGFR) Antibody Delivery via Pulsed Ultrasound with Targeting Microbubbles for Glioma Treatment

Pulsed-mode ultrasound (pUS) in combination with intravenously (IV) administered microbubbles (MBs) can enhance local drug delivery by temporarily enhancing capillary permeability. This study evaluates the use of epidermal growth factor receptor (EGFR)-targeting MBs after pUS treatment to enhance the effects of therapeutic-EGFR antibody delivery to glioma tumor cells in mice. Three animal groups were compared: (1) IV-injected non-targeting MBs, (2) IV-injected targeting MBs, and (3) IV-injected targeting MBs combined with pUS treatment. All animals were analyzed using high-frequency small-animal US imaging. The mean halftime of circulating targeting MBs was significantly increased from 3.13 min of targeting bubble alone to 5.86 min by targeting MBs combined with pUS treatment, compared to 2.34 min for non-targeting MBs. Compared to targeting bubble administration alone, pUS exposure prior to injection of targeting MBs was also significantly better at suppressing tumor growth when monitored for up to 35 days (p < 0.05). The final relative tumor volumes were 2664, 700, and 188 mm³ for non-targeting MBs, targeting MBs, and targeting MBs combined with pUS treatment, respectively. pUS treatment prolonged the mean circulatory halftime of targeting MBs and enhanced the anti-tumor effect of EGFR antibodies in a human glioma model in mice. Targeting MBs combined with pUS treatment thus has potential for enhanced therapeutic antibody delivery for facilitating anti-glioma treatment.

An in-vivo investigation of the therapeutic effect of pulsed focused ultrasound on tumor growth

PURPOSE

High-intensity focused ultrasound (HIFU) has been investigated for ablative therapy and drug enhancement for gene therapy and chemotherapy. The aim of this work is to explore the feasibility of pulsed focused ultrasound (pFUS) for cancer therapy using an in vivo animal model.

METHODS

A clinical HIFU system (InSightec ExAblate 2000) integrated with a 1.5 T GE MR scanner was used in this study. Suitable ultrasound parameters were investigated to perform nonthermal sonications, keeping the temperature elevation below 4 °C as measured in real time by MR thermometry. LNCaP cells (10(6)) were injected into the prostates of male mice (n = 20). When tumors reached a diameter of about 5 mm in 3D as measured on magnetic resonance imaging (MRI), the tumor-bearing mice (n = 8) were treated with pFUS (1 MHz frequency; 25 W acoustic power; 0.1 duty cycle; 60 s duration). A total of 4-6 sonications were used to cover the entire tumor volume under MR image guidance. The animals were allowed to survive for 4 weeks after the treatment. The tumor growth was monitored on high-resolution (0.2 mm) MRI weekly post treatment and was compared with that of the control group (n = 12).

RESULTS

Significant tumor growth delay was observed in the tumor-bearing mice treated with pFUS. The mean tumor volume for the pFUS treated mice remained the same 1 week after the treatment while the mean tumor volume of the control mice grew 42% over the same time. Two weeks after the pFUS treatment, the control group had a mean tumor volume 40% greater than that of the treated group. There was a greater variation in tumor volume at 4 weeks post treatment for both treated and control mice and a slightly faster tumor growth for the pFUS treated mice.

CONCLUSIONS

The authors' results demonstrated that pFUS may have a great potential for cancer therapy. Further experiments are warranted to understand the predominantly nonthermal cell killing mechanisms of pFUS and to derive optimal ultrasound parameters and fractionation schemes to maximize the therapeutic effect of pFUS.

Modulation of the interstitial fluid pressure by high intensity focused ultrasound as a way to alter local fluid and solute movement: insights from a mathematical model

High intensity focused ultrasound (HIFU) operated in thermal mode has been reported to reduce interstitial fluid pressure and improve the penetration of large macromolecules and nanoparticles in tumor and normal tissue. Little is understood about how the interstitial fluid pressure and velocity as well as the interstitial macromolecule transport are affected by HIFU exposure. A mathematical model is presented here which sheds light on the initial biophysical changes brought about HIFU. Our continuum model treats tissue as an effective poro-elastic material that reacts to elevated temperatures with a rapid drop in interstitial elastic modulus. Using parameters from the literature, the model is extrapolated to derive information on the effect in tumors, and to predict its impact on the convective and diffusive transport of macromolecular drugs. The model is first solved using an analytical approximation with step-wise changes at each boundary, and then solved numerically starting from a Gaussian beam approximation of the ultrasound treatment. Our results indicate that HIFU causes a rapid drop in interstitial fluid pressure that may be exploited to facilitate convection of macromolecules from vasculature to the exposed region. However, following a short recovery period in which the interstitial fluid pressure is normalized, transport returns to normal and the advantages disappear over time. The results indicate that this effect is strongest for the delivery of large molecules and nanoparticles that are in the circulation at the time of treatment. The model may be easily applied to more complex situations involving effects on vascular permeability and diffusion.

Portable high-intensity focused ultrasound system with 3D electronic steering, real-time cavitation monitoring, and 3D image reconstruction algorithms: a preclinical study in pigs

PURPOSE

The aim of this study was to evaluate the safety and accuracy of a new portable ultrasonography-guided high-intensity focused ultrasound (USg-HIFU) system with a 3-dimensional (3D) electronic steering transducer, a simultaneous ablation and imaging module, real-time cavitation monitoring, and 3D image reconstruction algorithms.

METHODS

To address the accuracy of the transducer, hydrophones in a water chamber were used to assess the generation of sonic fields. An animal study was also performed in five pigs by ablating in vivo thighs by single-point sonication (n=10) or volume sonication (n=10) and ex vivo kidneys by single-point sonication (n=10). Histological and statistical analyses were performed.

RESULTS

In the hydrophone study, peak voltages were detected within 1.0 mm from the targets on the y- and z-axes and within 2.0-mm intervals along the x-axis (z-axis, direction of ultrasound propagation; y- and x-axes, perpendicular to the direction of ultrasound propagation). Twenty-nine of 30 HIFU sessions successfully created ablations at the target. The in vivo porcine thigh study showed only a small discrepancy (width, 0.5-1.1 mm; length, 3.0 mm) between the planning ultrasonograms and the pathological specimens. Inordinate thermal damage was not observed in the adjacent tissues or sonic pathways in the in vivo thigh and ex vivo kidney studies.

CONCLUSION

Our study suggests that this new USg-HIFU system may be a safe and accurate technique for ablating soft tissues and encapsulated organs.

Micro- and nanobubbles: a versatile non-viral platform for gene delivery

Micro- and nanobubbles provide a promising non-viral strategy for ultrasound mediated gene delivery. Microbubbles are spherical gas-filled structures with a mean diameter of 1-8 μm, characterised by their core-shell composition and their ability to circulate in the bloodstream following intravenous injection. They undergo volumetric oscillations or acoustic cavitation when insonified by ultrasound and, most importantly, they are able to resonate at diagnostic frequencies. It is due to this behaviour that microbubbles are currently being used as ultrasound contrast agents, but their use in therapeutics is still under investigation. For example, microbubbles could play a role in enhancing gene delivery to cells: when combined with clinical ultrasound exposure, microbubbles are able to favour gene entry into cells by cavitation. Two different delivery strategies have been used to date: DNA can be co-administered with the microbubbles (i.e. the contrast agent) or 'loaded' in purposed-built bubble systems - indeed a number of different technological approaches have been proposed to associate genes within microbubble structures. Nanobubbles, bubbles with sizes in the nanometre order of magnitude, have also been developed with the aim of obtaining more efficient gene delivery systems. Their small sizes allow the possibility of extravasation from blood vessels into the surrounding tissues and ultrasound-targeted site-specific release with minimal invasiveness. In contrast, microbubbles, due to their larger sizes, are unable to extravasate, thus and their targeting capacity is limited to specific antigens present within the vascular lumen. This review provides an overview of the use of microbubbles as gene delivery systems, with a specific focus on recent research into the development of nanosystems. In particular, ultrasound delivery mechanisms, formulation parameters, gene-loading approaches and the advantages of nanometric systems will be described.

Targeted manipulation of apoptotic pathways by using High Intensity Focused Ultrasound in cancer treatment

Apoptosis, or programmed cell death, is a mechanism of cell death, which has been exploited for the treatment of cancers over the past few years. The understanding of apoptosis pathways (intrinsic and extrinsic) has led to discovery of treatment strategies which selectively target the cancer cells and spare the normal ones. This article reviews the current understanding of the apoptotic pathways which are utilized for targeting cancer cells using High Intensity Focused Ultrasound (HIFU).

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.

Magnetic resonance-guided focused ultrasound surgery: Part 2: A review of current and future applications

Magnetic resonance-guided focused ultrasound surgery (MRgFUS) is a novel combination of technologies that is actively being realized as a noninvasive therapeutic tool for a myriad of conditions. These applications are reviewed with a focus on neurological use. A combined search of PubMed and MEDLINE was performed to identify the key events and current status of MRgFUS, with a focus on neurological applications. MRgFUS signifies a potentially ideal device for the treatment of neurological diseases. As it is nearly real time, it allows monitored provision of treatment location and energy deposition; is noninvasive, thereby limiting or eliminating disruption of normal tissue; provides focal delivery of therapeutic agents; enhances radiation delivery; and permits modulation of neural function. Multiple clinical applications are currently in clinical use and many more are under active preclinical investigation. The therapeutic potential of MRgFUS is expanding rapidly. Although clinically in its infancy, preclinical and early-phase I clinical trials in neurosurgery suggest a promising future for MRgFUS. Further investigation is necessary to define its true potential and impact.

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.

Targeted microbubbles in the experimental and clinical setting

BACKGROUND

Microbubbles have improved ultrasonography imaging techniques over the past 2 decades. Their safety, versatility, and easiness of use have rendered them equal or even superior in some instances to other imaging modalities such as computed tomography and magnetic resonance imaging. Herein, we conducted a literature review to present their types, general behavior in tissues, and current and potential use in clinical practice.

METHODS

A literature search was conducted for all preclinical and clinical studies involving microbubbles and ultrasonography.

RESULTS

Different types of microbubbles are available. These generally improve the enhancement of tissues during ultrasonography imaging. They also can be attached to ligands for the target of several conditions such as inflammation, angiogenesis, thrombosis, apoptosis, and might have the potential of carrying toxic drugs to diseased sites, thereby limiting the systemic adverse effects.

CONCLUSIONS

The use of microbubbles is evolving rapidly and can have a significant impact on the management of various conditions. The potential for their use as targeting agents and gene and drug delivery vehicles looks promising.

Quantitative study of focused ultrasound enhanced doxorubicin delivery to prostate tumor in vivo with MRI guidance

PURPOSE

The purpose of this study was to investigate the potential of MR-guided pulsed focused ultrasound (pFUS) for the enhancement of drug uptake in prostate tumors in vivo using doxorubicin (Dox).

METHODS

An antitumor drug Dox, an orthotopic animal prostate tumor model using human prostate cancer, LNCaP cell line, and a clinical FUS treatment system (InSightec ExAblate 2000) with a 1.5T GE MR scanner were used in this study. First, experiments on a tissue mimic phantom to determine the optimal acoustic power and exposure durations with a 10% duty cycle and a 1 Hz pulse rate were performed. The temperature variation was monitored using real-time MR thermometry. Second, tumor-bearing animals were treated with pFUS. There were three groups (n = 8/group): group 1 received pFUS + Dox (10 mg/kg i.v. injection immediately after pFUS exposure), group 2 received Dox only (10 mg/kg i.v. injection), and group 3 was a control. Animals were euthanized 2 h after the pFUS treatment. The Dox concentration in the treated tumors was measured by quantifying fluorescent tracers using a fluorometer. Third, the histological changes of tumors with and without pFUS treatments were evaluated. Finally, experiments were performed to study the spatial drug distribution in tumors after the pFUS treatment, in which two animals received pFUS + Dox, two animals received Dox only, and one animal was used as control. Two hours following the treatment, animals were euthanized and processed. The Dox distribution was determined using a fluorescence microscope.

RESULTS

Parametric measurements using a tissue phantom showed that the temperature increased with an increasing acoustic power (from 10 to 50 W) or sonication duration (from 10 to 60 s) with a given acoustic frequency of 1 MHz, duty cycle 10%, and pulse rate 1 Hz. A set of ultrasound parameters was identified with which the temperature elevation was less than 5 °C, which was used for nonthermal pFUS sonication. Increased Dox concentration (14.9 ± 2.5 μg/g) was measured in the pFUS-treated group compared to the Dox-only group (9.5 ± 1.6 μg/g), indicating an approximate 60% increase with p = 0.05. The results were consistent with the increased spatial drug distributions by fluorescence imaging. Histological analysis showed increased extravasation in pFUS-treated prostate tumors suggesting increased drug delivery with pFUS.

CONCLUSIONS

The results showed that pFUS-enhanced drug uptake in prostate tumors was significant. This increased uptake may be due to increased extravasation by pFUS. Optimal pFUS parameters may exist to maximize the drug uptake, and this study using Dox demonstrated a quantitative method for such systematic parametric studies. In addition, this study may provide useful data for the potential application of pFUS-mediated Dox delivery for prostate tumor therapy.

In vivo temperature controlled ultrasound-mediated intracellular delivery of cell-impermeable compounds

Many chemotherapeutic drugs are characterized by high systemic toxicity and/or suffer from limited bioavailability. Thermosensitive liposomes (TSLs) encapsulating drugs in their aqueous lumen are promising activatable nanocarriers for ultrasound (US)-mediated drug delivery in response to mild hyperthermia. On the other hand, US is known to locally break biological barriers and as a consequence enable internalization of molecules. In this work, a two-step protocol for intracellular delivery of cell-impermeable molecules comprising of US-induced permeabilization followed by temperature-controlled release of the model drug from thermosensitive liposomes has been developed. TSLs containing TO-PRO-3, a cell-impermeable molecule that displays a significant increase in fluorescence upon binding to nucleic acids thus serving as a 'sensor' for internalization have been prepared and characterized in detail. US-mediated permeabilization followed by temperature-controlled release was applied to tumor bearing mice following i.v. injection of TSLs and microbubbles. The efficacy of this approach was evaluated by in vivo fluorescence imaging followed by histological analysis. A 2.4-fold increase of fluorescence signal was observed and intracellular delivery of TO-PRO-3 was confirmed by a characteristic nuclear staining. These results demonstrate the feasibility of novel drug delivery system to tumors comprising of local cell permeabilization by US followed by in situ release of the payload from thermosensitive liposomes. Possible applications include local and controlled intracellular delivery of molecules with otherwise limited bioavailability.

MR-guided pulsed high intensity focused ultrasound enhancement of docetaxel combined with radiotherapy for prostate cancer treatment

The purpose of this study is to evaluate the efficacy of the enhancement of docetaxel by pulsed focused ultrasound (pFUS) in combination with radiotherapy (RT) for treatment of prostate cancer in vivo. LNCaP cells were grown in the prostates of male nude mice. When the tumors reached a designated volume by MRI, tumor bearing mice were randomly divided into seven groups (n = 5): (1) pFUS alone; (2) RT alone; (3) docetaxel alone; (4) docetaxel + pFUS; (5) docetaxel + RT; (6) docetaxel + pFUS + RT, and (7) control. MR-guided pFUS treatment was performed using a focused ultrasound treatment system (InSightec ExAblate 2000) with a 1.5T GE MR scanner. Animals were treated once with pFUS, docetaxel, RT or their combinations. Docetaxel was given by i.v. injection at 5 mg kg(-1) before pFUS. RT was given 2 Gy after pFUS. Animals were euthanized 4 weeks after treatment. Tumor volumes were measured on MRI at 1 and 4 weeks post-treatment. Results showed that triple combination therapies of docetaxel, pFUS and RT provided the most significant tumor growth inhibition among all groups, which may have potential for the treatment of prostate cancer due to an improved therapeutic ratio.

Estimation of thermal dose from MR thermometry during application of nonablative pulsed high intensity focused ultrasound

PURPOSE

To evaluate whether MR thermometry is sufficiently fast, accurate, and spatially resolved for monitoring the thermal safety of nonablative pulsed high intensity ultrasound (pHIFU) treatments.

MATERIALS AND METHODS

A combination of real MR thermometry data and modeling was used to analyze the effects of temporal and spatial averaging as well as noise on the peak temperatures and thermal doses that would be measured by MR thermometry.

RESULTS

MR thermometry systematically underestimates the temperature and thermal doses during pHIFU treatment. Small underestimates of peak temperature can lead to large underestimates of thermal dose. Spatial averaging errors are small for ratios of pixel dimension to heating zone radius less than 0.25, which may be achieved by reducing the voxel size or steering the acoustic beam. Thermal dose might also be underestimated for very short, high power pulses due to temporal averaging. A simple correction factor based on the applied power and duty cycle may be applied to determine the upper bound of this effect.

CONCLUSION

The temperature and thermal dose measured using MR thermometry during pulsed HIFU treatment is probably sufficient in most instances. Simple corrections may be used to calculate an upper bound where this is a critical factor.

Increased accumulation of paclitaxel and doxorubicin in proliferating capillary cells and prostate cancer cells following ultrasound exposure

INTRODUCTION

We have previously reported enhanced cytotoxic effects of both doxorubicin and antisense oligonucleotides using an optimized ultrasound regime of a single 10s exposure in burst-mode (4 MHz, 32 W/cm(2)(SaTa), 50 ms burst period) in both PC3 (prostate cancer) cells and angiogenic Huvec (human umbilical cord endothelial cells). The objective of this study was to investigate the effect of ultrasound on the cellular uptake of both hydrophilic agents (rhodamine R123, doxorubicin hydrochloride and mannitol) and hydrophobic agents (rhodamine R6G and paclitaxel) using the same 4 MHz ultrasound exposure system.

METHODS

PC3 cells and Huvec were incubated with solutions of radioactive or fluorescent compounds for 1h and ultrasound was then applied to cells. Following washing and lysis of cells, the degree of drug uptake was measured using liquid scintillation counting or fluorescence spectroscopy.

RESULTS

Ultrasound exposure resulted in the enhanced uptake of both hydrophilic and hydrophobic compounds into cells. For paclitaxel, approximately 100% increased uptake was observed when the drug was encapsulated in a nanoparticulate micellar formulation compared to approximately 50% for free drug.

CONCLUSIONS

The 4 MHz, 32 W/cm(2) ultrasound exposure regime (using burst-mode with 50 ms burst period) allows for the enhanced uptake of both water soluble and insoluble compounds into proliferating cancer and angiogenic cells.

Emerging local ablation techniques

Local ablation technologies for hepatic malignancy have developed rapidly in the past decade, with advances in several percutaneous or externally delivered treatment methods including radiofrequency ablation, microwave ablation, laser ablation, and high-intensity focused ultrasound. Research has focused on increasing the size of the ablation zone and minimizing heat-sink effects. More recent developments include improvements in treatment planning and navigation with integration of several imaging modalities, as well as automated delivery of the ablation through robotics. These improvements will allow increased consistency in treatment delivery and will facilitate translation to the community setting. Combination therapies with multimodality guidance are on the cutting edge of image-guided, minimally invasive cancer therapies. Local ablation is being combined with regional therapies, such as arterial chemoembolization and local activation of systemically administered drugs, with promising results. Potential combinations with local ablation also include external radiation therapy and antitumor immune modulation. Image-guided oncology is emerging as an important part of the interventional radiology practice, thanks in part to the innovation and imaging background that lies at the roots of our discipline.

Evaluation of the temporal window for drug delivery following ultrasound-mediated membrane permeability enhancement

PURPOSE

Ultrasound-induced cavitation facilitates cellular uptake of drugs via increased membrane permeability. Here, the purpose was to evaluate the duration of enhanced membrane permeability following ultrasound treatment in cell culture.

PROCEDURES

Optical chromophores with fluorescence intensity increasing 100-1,000-fold upon intercalation with nucleic acids served as smart agents for reporting cellular uptake. Opticell chambers with a monolayer of C6 cells were subjected to ultrasound in the presence of microbubbles followed by varying delays between 0 and 24 h before addition of Sytox Green optical contrast agent. Micro- and macroscopic fluorescence were used for qualitative and quantitative analysis.

RESULTS

Up to 25% of viable cells showed uptake of contrast agent with a half time of 8 h, with cellular uptake persisting even at 24 h. Only cells exposed to ultrasound showed the effect.

CONCLUSION

The temporal window of increased membrane permeability is much longer in these studies than previously suggested. This may have important repercussions for in vivo studies in which membrane permeability may be temporally separated from drug delivery.

Explorations of high-intensity therapeutic ultrasound and microbubble-mediated gene delivery in mouse liver

Ultrasound (US) combined with microbubbles (MBs) is a promising technology for non-viral gene delivery. Significant enhancements of gene expression have been obtained in our previous studies. To optimize and prepare for application to larger animal models, the luciferase reporter gene transfer efficacy of lipid-based Definity MBs of various concentrations, pressure amplitudes and a novel unfocused high-intensity therapeutic US (HITU) system were explored. Luciferase expression exhibited a dependence on MB dose over the range of 0-25 vol%, and a strong dependence on acoustic peak negative pressure at over the range of 0-3.2 MPa. Gene expression reached an apparent plateau at MB concentration ≥2.5 vol% or at negative pressures >1.8 MPa. Maximum gene expression in treated animals was 700-fold greater than in negative controls. Pulse train US exposure protocols produced an upward trend of gene expression with increasing quiescent time. The hyperbolic correlation of gene expression and transaminase levels suggested that an optimum gene delivery effect can be achieved by maximizing acoustic cavitation-induced enhancement of DNA uptake and minimizing unproductive tissue damage. This study validated the new HITU system equipped with an unfocused transducer with a larger footprint capable of scanning large tissue areas to effectively enhance gene transfer efficiencies.

A Multi-Phasic, Continuum Damage Mechanics Model of Mechanically Induced Increased Permeability in Tissues

Recently, we have reported enhanced permeability of tissues due to in vivo treatment with pulsed high intensity focused ultrasound (pHIFU). This new therapy has shown promise as a way of increasing the penetration of large drug molecules, both out of the vasculature and through the tissue. To date, no clear physical model of tissue exists that can account for these effects.

A new model is proposed that clearly establishes the link between tissue structure and fluid flow properties on one hand, and the history of applied mechanical forces on the other. The model draws inspiration from two different theoretical fields of materials science, multi-phase theory and continuum damage mechanics. The theory differs from the traditional bi-phasic solid-fluid model of tissues in that the fluid part here is broken into trapped (moving with the solid) and free (moving through the solid) parts. A damage-like variable links the effective elasticity of the tissue to the ratio of the trapped to free fluids. As the damage increases, the tissue becomes, in effect, less stiff and more permeable. Release of elastic energy drives the process. A distribution of energy barriers opposes the process and governs how the fluid is released as damage increases.

Targeted gene delivery in tumor xenografts by the combination of ultrasound-targeted microbubble destruction and polyethylenimine to inhibit survivin gene expression and induce apoptosis

Background

Noninvasive and tissue-specific technologies of gene transfection would be valuable in clinical gene therapy. This present study was designed to determine whether it could enhance gene transfection in vivo by the combination of ultrasound-targeted microbubble destruction (UTMD) with polyethylenimine (PEI) in tumor xenografts, and illuminate the effects of gene silencing and apoptosis induction with short hairpin RNA (shRNA) interference therapy targeting human survivin by this novel technique.

Methods

Two different expression vectors (pCMV-LUC and pSIREN) were incubated with PEI to prepare cationic complexes (PEI/DNA) and confirmed by the gel retardation assay. Human cervical carcinoma (Hela) tumors were planted subcutaneously in both flanks of nude mice. Tumor-bearing mice were administered by tail vein with PBS, plasmid, plasmid and SonoVue microbubble, PEI/DNA and SonoVue microbubble. One tumor was exposed to ultrasound irradiation, while the other served as control. The feasibility of targeted delivery and tissue specificity facilitated by UTMD and PEI were investigated. Moreover, immunohistochemistry analyses about gene silencing and apoptosis induction were detected.

Results

Electrophoresis experiment revealed that PEI could condense DNA efficiently. The application of UTMD significantly increases the tissue transfection. Both expression vectors showed that gene expressions were present in all sections of tumors that received ultrasound exposure but not in control tumors. More importantly, the increases in transgene expression were related to UTMD with the presence of PEI significantly. Silencing of the survivin gene could induce apoptosis effectively by downregulating survivin and bcl-2 expression, also cause up-regulation of bax and caspase-3 expression.

Conclusions

This noninvasive, novel combination of UTMD with PEI could enhance targeted gene delivery and gene expression in tumor xenografts at intravenous administration effectively without causing any apparently adverse effect, and might be a promising candidate for gene therapy. Silencing of survivin gene expression with shRNA could be facilitated by this non-viral technique, and lead to significant cell apoptosis.

Immunological therapy in urological malignancy: novel combination strategies

At present, immunotherapy in urological malignancy is experiencing a renaissance, particularly with the emergence of a host of innovative cancer vaccines. Herein, we will review promising immunotherapeutic approaches and evaluate the data supporting their inclusion in novel combination strategies.

An optimum method for pulsed high intensity focused ultrasound treatment of large volumes using the InSightec ExAblate® 2000 system

Pulsed high intensity focused ultrasound (pHIFU) is a method for delivering ultrasound to tissue while avoiding high temperatures. The technique has been suggested for non-destructively enhancing local uptake of drugs. Side effects include thermal necrosis; therefore, real-time monitoring of tissue temperature is advantageous. This paper outlines a method for improving the treatment efficiency of pHIFU using the MR image-guided InSightec ExAblate® 2000 system, an ultrasound system integrated into a whole body human MRI scanner with the ability to measure temperature at the treatment location in near real time. Thermal measurements obtained during treatment of a tissue phantom were used to determine appropriate heating parameters, and compared to in vivo treatment of rabbit muscle. Optimization of the treatment procedure and ultrasound transducer steering patterns was then conducted with the goal of minimizing treatment time while avoiding overheating. The optimization was performed on the basis of approximate solutions to the standard bioheat equation. The commercial system software of the Exablate® system was modified to assist in this optimization. Depending on the size of the treatment volume, the presented results demonstrate that it is possible to use the technique described to cut treatment times significantly, up to one-third of that required by the current standard treatment cycle.

DNA vaccines for the treatment of prostate cancer

Prostate cancer is a significant public health problem, and the most commonly diagnosed cancer in the USA. The long natural history of prostate cancer, the presence of a serum biomarker that can be used to detect very early recurrences, and the previous identification of multiple potential tissue-specific target antigens are all features that make this disease suitable for the development of anti-tumor vaccines. To date, many anti-tumor vaccines have entered clinical testing for patients with prostate cancer, and some have demonstrated clinical benefit. DNA vaccines represent one vaccine approach that has been evaluated in multiple preclinical models and clinical trials. The safety, specificity for the target antigen, ease of manufacturing and ease of incorporating other immune-modulating approaches make DNA vaccines particularly relevant for future development. This article focuses on DNA vaccines specifically in the context of prostate cancer treatment, focusing on antigens targeted in preclinical models, recent clinical trials and efforts to improve the potency of these vaccines.

Sonoporation, drug delivery, and gene therapy

Ultrasound is a very effective modality for drug delivery and gene therapy because energy that is non-invasively transmitted through the skin can be focused deeply into the human body in a specific location and employed to release drugs at that site. Ultrasound cavitation, enhanced by injected microbubbles, perturbs cell membrane structures to cause sonoporation and increases the permeability to bioactive materials. Cavitation events also increase the rate of drug transport in general by augmenting the slow diffusion process with convective transport processes. Drugs and genes can be incorporated into microbubbles, which in turn can target a specific disease site using ligands such as the antibody. Drugs can be released ultrasonically from microbubbles that are sufficiently robust to circulate in the blood and retain their cargo of drugs until they enter an insonated volume of tissue. Local drug delivery ensures sufficient drug concentration at the diseased region while limiting toxicity for healthy tissues. Ultrasound-mediated gene delivery has been applied to heart, blood vessel, lung, kidney, muscle, brain, and tumour with enhanced gene transfection efficiency, which depends on the ultrasonic parameters such as acoustic pressure, pulse length, duty cycle, repetition rate, and exposure duration, as well as microbubble properties such as size, gas species, shell material, interfacial tension, and surface rigidity. Microbubble-augmented sonothrombolysis can be enhanced further by using targeting microbubbles.

Differences in gene expression between sonoporation in tumor and in muscle

BACKGROUND

Ultrasound (US) is a novel and effective tool for the local delivery of genes into target tissues. US can temporarily change the permeability of a cell membrane and thus enhance the delivery of naked DNA into cells. In the present study, the efficiencies of gene expression mediated by US delivery in orthotopic liver tumor, subcutaneous tumor and muscle tissue were evaluated by changing the contrast agent concentrations and US exposure durations.

METHODS

Plasmid DNA coding for luciferase, interleukin-12 or enhanced green fluorescence protein was mixed with SonoVue and injected intratumorally or intramuscularly. The injection sites were then exposed to US (20% duty cycle and 0.4 W/cm(2) intensity).

RESULTS

The results obtained showed that the optimal condition was 50% SonoVue for tumors and 30% for muscle, with 10 min of US exposure. The expression levels of the transfected DNAs were in the order: muscle > subcutaneous tumor > orthotopic liver tumor.

CONCLUSIONS

The present study indicates that muscle tissue is a good target site for producing large amounts of gene products for the purpose of gene therapy.

Investigations into pulsed high-intensity focused ultrasound-enhanced delivery: preliminary evidence for a novel mechanism

Pulsed high-intensity focused ultrasound (HIFU) exposures without ultrasound contrast agents have been used for noninvasively enhancing the delivery of various agents to improve their therapeutic efficacy in a variety of tissue models in a nondestructive manner. Despite the versatility of these exposures, little is known about the mechanisms by which their effects are produced. In this study, pulsed-HIFU exposures were given in the calf muscle of mice, followed by the administration of a variety of fluorophores, both soluble and particulate, by local or systemic injection. In vivo imaging (whole animal and microscopic) was used to quantify observations of increased extravasation and interstitial transport of the fluorophores as a result of the exposures. Histological analysis indicated that the exposures caused some structural alterations such as enlarged gaps between muscle fiber bundles. These effects were consistent with increasing the permeability of the tissues; however, they were found to be transient and reversed themselves gradually within 72 h. Simulations of radiation force-induced displacements and the resulting local shear strain they produced were carried out to potentially explain the manner by which these effects occurred. A better understanding of the mechanisms involved with pulsed HIFU exposures for noninvasively enhancing delivery will facilitate the process for optimizing their use.