Focused ultrasound (HIFU) induces localized enhancement of reporter gene expression in rabbit carotid artery

Immunomodulation and targeted drug delivery with high intensity focused ultrasound (HIFU): Principles and mechanisms

High intensity focused ultrasound (HIFU) is a non-invasive and non-ionizing sonic energy-based therapeutic technology for inducing thermal and non-thermal effects in tissues. Depending on the parameters, HIFU can ablate tissues by heating them to >55 °C to induce denaturation and coagulative necrosis, improve radio- and chemo-sensitizations and local drug delivery from nanoparticles at moderate hyperthermia (~41-43 °C), and mechanically fragment cells using acoustic cavitation (also known as histotripsy). HIFU has already emerged as an attractive modality for treating human prostate cancer, veterinary cancers, and neuromodulation. Herein, we comprehensively review the role of HIFU in enhancing drug delivery and immunotherapy in soft and calcified tissues. Specifically, the ability of HIFU to improve adjuvant treatments from various classes of drugs is described. These crucial insights highlight the opportunities and challenges of HIFU technology and its potential to support new clinical trials and translation to patients.

Synergies between therapeutic ultrasound, gene therapy and immunotherapy in cancer treatment

Due to the ease of use and excellent safety profile, ultrasound is a promising technique for both diagnosis and site-specific therapy. Ultrasound-based techniques have been developed to enhance the pharmacokinetics and efficacy of therapeutic agents in cancer treatment. In particular, transfection with exogenous nucleic acids has the potential to stimulate an immune response in the tumor microenvironment. Ultrasound-mediated gene transfection is a growing field, and recent work has incorporated this technique into cancer immunotherapy. Compared with other gene transfection methods, ultrasound-mediated gene transfection has a unique opportunity to augment the intracellular uptake of nucleic acids while safely and stably modulating the expression of immunostimulatory cytokines. The development and commercialization of therapeutic ultrasound systems further enhance the potential translation. In this Review, we introduce the underlying mechanisms and ongoing preclinical studies of ultrasound-based techniques in gene transfection for cancer immunotherapy. Furthermore, we expand on aspects of therapeutic ultrasound that impact gene therapy and immunotherapy, including tumor debulking, enhancing cytokines and chemokines and altering nanoparticle pharmacokinetics as these effects of ultrasound cannot be fully dissected from targeted gene therapy. We finally explore the outlook for this rapidly developing field.

Focal therapy for localized cancer: a patent review

INTRODUCTION

Conventional cancer treatments such as radical surgery and systemic therapy targeting the organ or organ system might have side effects because of damage to the surrounding tissue. For this reason, there is a need for new instruments that focally treat cancer.

AREAS COVERED

This review provides a comprehensive overview of the patent literature on minimally and noninvasive focal therapy instruments to treat localized cancer. The medical section of the Google Patents database was scanned, and 128 patents on focal therapy instruments published in the last two decades (2000-2021) were retrieved and classified. The classification is based on the treatment target (cancer cell or network of cancer cells), treatment purpose (destroy the cancerous structure or disable its function), and treatment means (energy, matter, or a combination of both).

EXPERT OPINION

We found patents describing instruments for all groups, except for the instruments that destroy a cancer cell network structure by applying matter (e.g. particles) to the network. The description of the different treatment types may serve as a source of inspiration for new focal therapy instruments to treat localized cancer.

Amino-acid functionalized porous silicon nanoparticles for the delivery of pDNA

Porous silicon nanoparticles as a novel platform in gene therapy, have shown to be an efficient vehicle for the delivery of nucleic acids in cells. For the first time, a family of porous silicon nanoparticles has been produced featuring an amino-acid functionalized cationic external surface aiming at pDNA complexation. The amino acid-based pDNA nanocarriers, displaying an average diameter of 295 nm, succeeded in transfection of HEK293 cells with an efficiency 300 times superior to "bare" porous silicon nanoparticles.

Ultrasound triggered drug delivery with liposomal nested microbubbles

When ultrasound contrast agent microbubbles are nested within a liposome, damage to the liposome membrane caused by both stable and inertial cavitation of the microbubble allows for release of the aqueous core of the liposome. Triggered release was not accomplished unless microbubbles were present within the liposome. Leakage was tested using fluorescence assays developed specifically for this drug delivery vehicle and qualitative measurements using an optical microscope. These studies were done using a 1 MHz focused ultrasound transducer while varying parameters including peak negative ultrasound pressure, average liposome diameter, and microbubble concentration. Two regimes exist for membrane disruption caused by cavitating microbubbles. A faster release rate, as well as permanent membrane damage are seen for samples exposed to high pressure (2.1-3.7 MPa). A slower release rate and dilation/temporary poration are characteristic of stable cavitation for low pressure studies (0.54-1.7 MPa).

Investigation of temporal vascular effects induced by focused ultrasound treatment with speckle-variance optical coherence tomography

Focused ultrasound (FUS) can be used to locally and temporally enhance vascular permeability, improving the efficiency of drug delivery from the blood vessels into the surrounding tissue. However, it is difficult to evaluate in real time the effect induced by FUS and to noninvasively observe the permeability enhancement. In this study, speckle-variance optical coherence tomography (SVOCT) was implemented for the investigation of temporal effects on vessels induced by FUS treatment. With OCT scanning, the dynamic change in vessels during FUS exposure can be observed and studied. Moreover, the vascular effects induced by FUS treatment with and without the presence of microbubbles were investigated and quantitatively compared. Additionally, 2D and 3D speckle-variance images were used for quantitative observation of blood leakage from vessels due to the permeability enhancement caused by FUS, which could be an indicator that can be used to determine the influence of FUS power exposure. In conclusion, SVOCT can be a useful tool for monitoring FUS treatment in real time, facilitating the dynamic observation of temporal effects and helping to determine the optimal FUS power.

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.

Inhibitory effects of subcutaneous tumors in nude mice mediated by low-frequency ultrasound and microbubbles

The aim of the present study was to investigate the sonication effects of 21-kHz ultrasound (US) with microbubbles (MBs) on the subcutaneous prostate tumors of nude mice. In total, 15 tumor-bearing nude mice were divided into three groups: The control group, the low-frequency US group and the US+MB group. The MBs used were from US contrast agent SonoVue. The parameters of the US were as follows: 21 kHz, 26 mW/cm² and a 40% duty cycle (2 sec on, 3 sec off) for 3 min, once every other day for 2 weeks. Color Doppler flow imaging, hematoxylin and eosin (HE) staining, immunoblotting and transmission electron microscopy (TEM) were used to evaluate the results. Following 2 weeks of treatment, the blood flow signal disappeared in the US+MB group only, and the tumor size was smaller when compared with the control and US groups. For the immunoblotting, the intensity of cyclooxygenase-2 and vascular endothelial growth factor in the US+MB group was lower compared with the other two groups. Tumor necrosis was present and the nucleus disappeared upon HE staining in the US+MB group. Upon TEM analysis, increased cytoplasmic vacuolation and dilatation of the perinuclear cisternae of the tumor cells were found in the US+MB group. In the control and US groups, the tumors had intact vascular endothelia and vessel lumens. However, lumen occlusion of the vessels was observed in the US+MB group. In conclusion, 21-kHz low-intensity US with MBs may result in vessel occlusion and growth inhibitory effects in the subcutaneous tumors of nude mice.

MR-guided focused ultrasound surgery, present and future

MR-guided focused ultrasound surgery (MRgFUS) is a quickly developing technology with potential applications across a spectrum of indications traditionally within the domain of radiation oncology. Especially for applications where focal treatment is the preferred technique (for example, radiosurgery), MRgFUS has the potential to be a disruptive technology that could shift traditional patterns of care. While currently cleared in the United States for the noninvasive treatment of uterine fibroids and bone metastases, a wide range of clinical trials are currently underway, and the number of publications describing advances in MRgFUS is increasing. However, for MRgFUS to make the transition from a research curiosity to a clinical standard of care, a variety of challenges, technical, financial, clinical, and practical, must be overcome. This installment of the Vision 20∕20 series examines the current status of MRgFUS, focusing on the hurdles the technology faces before it can cross over from a research technique to a standard fixture in the clinic. It then reviews current and near-term technical developments which may overcome these hurdles and allow MRgFUS to break through into clinical practice.

Insight concerning the mechanism of therapeutic ultrasound facilitating gene delivery: increasing cell membrane permeability or interfering with intracellular pathways?

Nonviral gene delivery methods encounter major barriers in plasmid DNA (pDNA) trafficking toward the nucleus. The present study aims to understand the role and contribution of therapeutic ultrasound (TUS), if any, in pDNA trafficking in primary cells such as fibroblasts and cell lines (e.g., baby hamster kidney [BHK]) during the transfection process. Using compounds that alter the endocytic pathways and the cytoskeletal network, we show that after TUS application, pDNA trafficking in the cytoplasm is not mediated by endocytosis or by the cytoskeletal network. Transfection studies and confocal analyses showed that the actin fibers impeded TUS-mediated transfection in BHK cells, but not in fibroblasts. Flow cytometric analyses indicated that pDNA uptake by cells occurs primarily when the pDNA is added before and not after TUS application. Taken together, these results suggest that TUS by itself operates as a mechanical force driving the pDNA through the cell membrane, traversing the cytoplasmic network and into the nucleus.

Ultrasound and microbubble-assisted gene delivery: recent advances and ongoing challenges

Having first been developed for ultrasound imaging, nowadays, microbubbles are proposed as tools for ultrasound-assisted gene delivery, too. Their behavior during ultrasound exposure causes transient membrane permeability of surrounding cells, facilitating targeted local delivery. The increased cell uptake of extracellular compounds by ultrasound in the presence of microbubbles is attributed to a phenomenon called sonoporation. Sonoporation has been successfully applied to deliver nucleic acids in vitro and in vivo in a variety of therapeutic applications. However, the biological and physical mechanisms of sonoporation are still not fully understood. In this review, we discuss recent data concerning microbubble--cell interactions leading to sonoporation and we report on the progress in ultrasound-assisted therapeutic gene delivery in different organs. In addition, we outline ongoing challenges of this novel delivery method for its clinical use.

Efficient microbubble- and ultrasound-mediated plasmid DNA delivery into a specific rat liver lobe via a targeted injection and acoustic exposure using a novel ultrasound system

To develop efficient gene delivery in larger animals, based on a previous mouse study, we explored the luciferase reporter gene transfer in rats by establishing a novel unfocused ultrasound system with simultaneous targeted injection of a plasmid and microbubble mixture into a specific liver lobe through a portal vein branch. Luciferase expression was significantly enhanced over 0-30 vol % of the Definity microbubbles, with a plateau between 0.5 and 30 vol %. The increase of gene delivery efficiency also depended on the acoustic peak negative pressure, achieving over 100-fold enhancement at 2.5 MPa compared with plasmid only controls. Transient, modest liver damage following treatment was assessed by transaminase assays and histology, both of which correlated with gene expression induced by acoustic cavitation. In addition, pulse-train ultrasound exposures (i.e., with relatively long quiescent periods between groups of pulses to allow tissue refill with microbubbles) produced gene expression levels comparable to the standard US exposure but reduced the extent of liver damage. These results indicated that unfocused high intensity therapeutic ultrasound exposure with microbubbles is highly promising for safe and efficient gene delivery into the liver of rats or larger animals.

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.

In vivo gene transfer into the ocular ciliary muscle mediated by ultrasound and microbubbles

This study aimed to assess application of ultrasound (US) combined with microbubbles (MB) to transfect the ciliary muscle of rat eyes. Reporter DNA plasmids encoding for Gaussia luciferase, β-galactosidase or the green fluorescent protein (GFP), alone or mixed with 50% Artison MB, were injected into the ciliary muscle, with or without US exposure (US set at 1 MHz, 2 W/cm(2), 50% duty cycle for 2 min). Luciferase activity was measured in ocular fluids at 7 and 30 days after sonoporation. At 1 week, the US+MB treatment showed a significant increase in luminescence compared with control eyes, injected with plasmid only, with or without MB (×2.6), and, reporter proteins were localized in the ciliary muscle by histochemical analysis. At 1 month, a significant decrease in luciferase activity was observed in all groups. A rise in lens and ciliary muscle temperature was measured during the procedure but did not result in any observable or microscopic damages at 1 and 8 days. The feasibility to transfer gene into the ciliary muscle by US and MB suggests that sonoporation may allow intraocular production of proteins for the treatment of inflammatory, angiogenic and/or degenerative retinal diseases.

Clinical and future applications of high intensity focused ultrasound in cancer

High intensity focused ultrasound (HIFU) or focused ultrasound (FUS) is a promising modality to treat tumors in a complete, non invasive fashion where online image guidance and therapy control can be achieved by magnetic resonance imaging (MRI) or diagnostic ultrasound (US). In the last 10 years, the feasibility and the safety of HIFU have been tested in a growing number of clinical studies on several benign and malignant tumors of the prostate, breast, uterine, liver, kidney, pancreas, bone, and brain. For certain indications this new treatment principle is on its verge to become a serious alternative or adjunct to the standard treatment options of surgery, radiotherapy, gene therapy and chemotherapy in oncology. In addition to the now clinically available thermal ablation, in the future, focused ultrasound at much lower intensities may have the potential to become a major instrument to mediate drug and gene delivery for localized cancer treatment. We introduce the technology of MRI guided and ultrasound guided HIFU and present a critical overview of the clinical applications and results along with a discussion of future HIFU developments.

Induction of luciferase activity under the control of an hsp70 promoter using high-intensity focused ultrasound: combination of bioluminescence and MRI imaging in three different tumour models

The in vivo temporal changes of luciferase activity were investigated under the control of an hsp70 promoter in three tumour models after the application of different intensities of high-intensity focused ultrasound (HIFU). Three cell lines, SCCVII, NIH3T3 and M21 were stably transfected with a plasmid containing the hsp70 promoter and luciferase reporter gene, and tumours were subcutaneously initiated into mice. At a size of 1300 ± 234 mm(3), the tumours were exposed to five intensities of continuous HIFU (802-1401-2157-3067-4133 W/cm(2)) for 20 sec. Bioluminescence and MR imaging were performed to assess luciferase activity and signal intensity changes in the tissue. The MRI scan protocol was pre- and post-contrast T1-wt-SE, T2-wt-FSE, DCE-MRI, diffusion-wt STEAM sequence, T2 relaxation time determination obtained on a 1.5-T GE MRI scanner. The NIH3T3 tumours showed the highest luciferase activity of 328.1 ± 7.1 fold at 24 h at a HIFU intensity of 3067 W/cm(2), the M21 tumours of 3.2 ± 0.6 fold 8 hours and the SCCVII tumours 2.9 ± 0.9 fold 4 hours post-HIFU at 2157 W/cm(2). The greatest increase in T2 signal intensity and T2 relaxation time of 20.7 ± 3.4% was seen in the SCCVII tumours. The highest contrast medium uptake of 10.1 ± 1.1% was noted in the M21 tumours, and 14.8 ± 1.9% in the SCCVII tumours. In all tumours, a significant increase in the diffusion coefficient was seen with increased HIFU intensity, the highest of which was 40.3 ± 4.1% in the SCCVII tumours. The three tumour cell lines stably transfected with the hsp70/luciferase gene showed differential luciferase activity, which peaked at different times after the application of HIFU and was dependant on tumour type and HIFU energy deposition.

Ultrasound-mediated intracellular drug delivery using microbubbles and temperature-sensitive liposomes

A novel two-step protocol for intracellular drug delivery has been evaluated in vitro. As a first step TO-PRO-3 (a cell-impermeable dye that displays a strong fluorescence enhancement upon binding to nucleic acids) encapsulated in thermosensitive liposomes was released after heating to 42°C. A second step consisted of ultrasound-mediated local permeabilization of cell membrane allowing TO-PRO-3 internalization observable as nuclear staining. Only the combination of two consecutive steps - heating and sonication in the presence of SonoVue microbubbles led to the model drug TO-PRO-3 release from the thermosensitive liposomes and its intracellular uptake. This protocol is potentially beneficial for the intracellular delivery of cell impermeable drugs that suffer from rapid clearance and/or degradation in blood and are not intrinsically taken up by cells.

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 fluorescent chromophore TOTO-3 as a 'smart probe' for the assessment of ultrasound-mediated local drug delivery in vivo

Many potent anti-cancer drugs have an intracellular mode of action, but are limited in crossing the cell membrane, resulting in a reduced clinical efficacy. Ultrasound (US) is known to facilitate the penetration of drugs into tumors cells. However (molecular) imaging techniques that monitor in vivo the underlying processes of US-triggered drug delivery are lacking. The objective of this study was to demonstrate the feasibility of using a fluorescent nuclear acid stain (TOTO-3) as a model drug to monitor in real-time US-mediated delivery by in vivo fluorescence imaging. Following co-injection of TOTO-3 and microbubbles US was applied to the tumor. The time course of the drug delivery process was monitored by fluorescence imaging. Immunohistological analysis and in vitro experiments were performed to investigate the results in more detail. A significant signal intensity enhancement of the US-treated tumor was observed that indicates intracellular delivery of the dye. In the control tumor TOTO-3 signal was strongly associated with macrophages, which was not the case for the sonicated tumor. The capability of macrophages to uptake TOTO-3 was confirmed in vitro. This study demonstrates that an optical contrast agent with similar characteristics to an anti-cancer drug may be used for continuous in vivo monitoring of the drug delivery process.

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.

Ultrasound-assisted microbubbles gene transfer in tendons for gene therapy

Our study aimed at evaluating the use of ultrasound-assisted microbubbles gene transfer in mice Achilles tendons. Using a plasmid encoding luciferase gene, it was found that an efficient and stable gene expression for more than two weeks was obtained when tendons were injected with 10 microg of plasmid in the presence of 5x10(5) BR14 microbubbles with the following acoustic parameters: 1 MHz, 200 kPa, 40% duty cycle and 10 min of exposure time. The rate of gene expression was 100-fold higher than that obtained with naked plasmid injected alone without ultrasound or with ultrasound in absence of microbubbles. The long term expression of transgene makes ultrasound-assisted microbubble a suitable method for gene therapy in tendons.

Ultrasonic-activated micellar drug delivery for cancer treatment

The use of nanoparticles and ultrasound in medicine continues to evolve. Great strides have been made in the areas of producing micelles, nanoemulsions, and solid nanoparticles that can be used in drug delivery. An effective nanocarrier allows for the delivery of a high concentration of potent medications to targeted tissue while minimizing the side effect of the agent to the rest of the body. Polymeric micelles have been shown to encapsulate therapeutic agents and maintain their structural integrity at lower concentrations. Ultrasound is currently being used in drug delivery as well as diagnostics, and has many advantages that elevate its importance in drug delivery. The technique is noninvasive, thus no surgery is needed; the ultrasonic waves can be easily controlled by advanced electronic technology so that they can be focused on the desired target volume. Additionally, the physics of ultrasound are widely used and well understood; thus ultrasonic application can be tailored towards a particular drug delivery system. In this article, we review the recent progress made in research that utilizes both polymeric micelles and ultrasonic power in drug delivery.

The effect of high intensity focused ultrasound on luciferase activity on two tumor cell lines in vitro, under the control of a CMV promoter

In this study, we compared the effect of high intensity focused ultrasound (HIFU) and thermal stress on the luciferase activity, controlled by a cytomegaly virus (CMV) promoter in an in vitro model using two tumor cell lines (M21, SCCVII). HIFU was applied in a pulsed-wave mode with increasing voltage at constant pulse duration, or thermal stress was delivered over a range of temperatures (36-52 degrees C) for 5 min. The resulting luciferase activity was measured in live cells using a cooled CCD camera. Luciferase activity was measured at set time intervals over a total of 48 h post-stress. Compared to baseline, the luciferase activity of the M21 tumor cell line when exposed to HIFU was approximately 54.2+/-67.5% (p<0.01) higher at a temperature of 42 degrees C, and approximately 52.9+/-128.5% (p<0.01) higher at 44 degrees C. In the SCCVII tumor cell line, the luciferase activity after HIFU application was 55.4+/-66.6% (p<0.01) higher compared to baseline at a temperature of 42 degrees C. The M21 and SCCVII tumor cell line when exposed to thermal stress alone did not increase the luciferase activity. M21 and SCCVII tumor cells exposed to HIFU showed a maximum decrease in cell viability to 45.3+/-7.5% and 10.3+/-7.5%, respectively, and when exposed to thermal stress to 85.3+/-3.5% and 20.4+/-6.5%, respectively, compared to the untreated control. In M21 and SCCVII cells exposed to HIFU, free radicals could be detected using the dichlorofluorescein dye. Our findings demonstrate that HIFU can enhance the luciferase activity controlled by a CMV promoter. However it also has a higher damaging effect on the cells.

Physical methods of nucleic acid transfer: general concepts and applications

Physical methods of gene (and/or drug) transfer need to combine two effects to deliver the therapeutic material into cells. The physical methods must induce reversible alterations in the plasma membrane to allow the direct passage of the molecules of interest into the cell cytosol. They must also bring the nucleic acids in contact with the permeabilized plasma membrane or facilitate access to the inside of the cell. These two effects can be achieved in one or more steps, depending upon the methods employed. In this review, we describe and compare several physical methods: biolistics, jet injection, hydrodynamic injection, ultrasound, magnetic field and electric pulse mediated gene transfer. We describe the physical mechanisms underlying these approaches and discuss the advantages and limitations of each approach as well as its potential application in research or in preclinical and clinical trials. We also provide conclusions, comparisons, and projections for future developments. While some of these methods are already in use in man, some are still under development or are used only within clinical trials for gene transfer. The possibilities offered by these methods are, however, not restricted to the transfer of genes and the complementary uses of these technologies are also discussed. As these methods of gene transfer may bypass some of the side effects linked to viral or biochemical approaches, they may find their place in specific clinical applications in the future.

Sonoporation of the minicircle-VEGF(165) for wound healing of diabetic mice

PURPOSE

The purpose of this study is to examine the efficiency of sonoporation with minicircle DNA for the skin wound healing in diabetic mice.

METHODS

Minicircle DNA containing the human VEGF(165) was constructed and tested in vitro. Diabetes was induced in 2-week old male C57BL/6J mice via streptozotocin (STZ) injection. 6 mm circular skin wounds were made on the mice back. After the subcutaneous injection of the minicircle DNA at the edge of the wound, the mice were exposed to the ultrasound irradiation for the sonoporation. Wound areas were analyzed until the day 12. Blood perfusion and angiogenesis were evaluated using a laser Doppler imaging and CD31 immunostaining, respectively. Re-epithelialization was assessed by histochemical analysis using hematoxylin and eosin staining.

RESULTS

Accelerated wound closure was observed in the mice receiving sonoporation of minicircle-VEGF(165), which corresponds to the markedly increased skin blood perfusion and CD31 expression. Histological analysis revealed that the minicircle treated wound tissues showed fully restored normal architectures as compared with the non-treated diabetic controls with the markedly edematous and chaotic morphologies.

CONCLUSIONS

Ultrasound mediated gene therapy with the minicircle-VEGF(165) is effective for the healing of the skin wound of the diabetic mice.

Ultrasound mediated delivery of drugs and genes to solid tumors

It has long been shown that therapeutic ultrasound can be used effectively to ablate solid tumors, and a variety of cancers are presently being treated in the clinic using these types of ultrasound exposures. There is, however, an ever-increasing body of preclinical literature that demonstrates how ultrasound energy can also be used non-destructively for increasing the efficacy of drugs and genes for improving cancer treatment. In this review, a summary of the most important ultrasound mechanisms will be given with a detailed description of how each one can be employed for a variety of applications. This includes the manner by which acoustic energy deposition can be used to create changes in tissue permeability for enhancing the delivery of conventional agents, as well as for deploying and activating drugs and genes via specially tailored vehicles and formulations.

In vitro effect of focused ultrasound or thermal stress on HSP70 expression and cell viability in three tumor cell lines

RATIONALE AND OBJECTIVES

In this study, we compared the effect of focused ultrasound with the effect of thermal stress on the induction of a heat inducible promoter in an in vitro model using three tumor cell lines (M21, SCCVII, and NIH3T3).

MATERIALS AND METHODS

We used a reporter construct that was generated using the stress-inducible promoter from the gene encoding a murine 70-kilodalton heat shock protein (Hsp70A.1) and a luciferase (luc) reporter plasmid. High-intensity focused ultrasound (HIFU) was applied in two different modes. In the first mode, an increasing voltage at constant pulse duration and in the second mode a constant voltage at increasing pulse duration was applied. HIFU or thermal stress was delivered over a range of temperatures (36-52 degrees C) for 5 minutes, and resulting luciferase activity was measured in live cells using a cooled charge-coupled device camera as a measure of reporter gene transcription. Luciferase activity was measured at set time intervals for a total of 108 hours post-stress.

RESULTS

Both methods induced the hsp70 promoter; however, the luciferase activity under the influence of HIFU, independent of the applied mode, and thermal stress differs despite the fact that the temperature was the same. In the M21 tumor cell line, the maximum luciferase activity after focused ultrasound application was 4818 +/- 1521% at a temperature of 48 degrees C and after thermal stress 4468.2 +/- 1890.2% at a temperature of 52 degrees C with a viability of 72.3 +/- 5.2% and 85 +/- 3.4%, respectively. In the SCC tumor cell line, the maximum luciferase activity after focused ultrasound application was 6743.0 +/- 3281.4% and after only thermal stress exposure was 3910.6 +/- 2189.0% at a temperature of 44 degrees C and 50 degrees C, respectively. At the highest luciferase activity, the portion of vital cells was 72.5 +/- 8.4% and 72.5 +/- 5.9% respectively. In the NIH3T3 tumor cell line the highest luciferase activity of 428510.6 +/- 26526.8% was seen at a temperature of 42 degrees C applying focused ultrasound. Under thermal stress it was 29221.3 +/- 7205.0% at a temperature of 50 degrees C. At the highest luciferase activity, the viability analysis showed 75.3 +/- 9.2% and 72.3 +/- 7.9% viable cells, respectively.

CONCLUSIONS

Focused ultrasound induces hsp70 expression like thermal stress alone; however, HIFU is capable of inducing expression at lower temperatures than heat stress alone, indicating that nonthermal effects also play a role on the induction of hsp70.

Key factors that affect sonoporation efficiency in in vitro settings: the importance of standing wave in sonoporation

Ultrasound-induced intracellular drug delivery, sonoporation, is an appealing and promising technique for next generation drug delivery system. Many types of molecules, such as plasmid DNAs, siRNAs and peptides, have been demonstrated to be delivered into the cell by ultrasound with the aid of microbubbles both in vitro and in vivo. Although there are many reports on in vitro sonoporation, the efficiency of successful sonoporation and the viabilities of cells after the procedure documented in each report vary in a wide range, and the reasons for these differences are not fully understood. In this study, we have investigated how different experimental settings would affect sonoporation efficiency and cell viabilities after the procedure. Our results show that the fashion of cell culture (e.g. in suspension or in monolayer culture) and the presence of standing wave have a great impact on the overall results. These results indicate that in vitro sonoporation settings should be carefully evaluated in each experiment. The fact that standing wave is necessary to achieve high sonoporation efficiency may be a problematic issue for clinical application of sonoporation, as it may be difficult (although not impossible) to create standing wave in a human body.

Multiphoton imaging of ultrasound/Optison mediated cerebrovascular effects in vivo

Ultrasound (US) enhanced with microbubble contrast agents may transiently disrupt the blood-brain barrier (BBB) with minimal damage, providing a technique for noninvasive, localized drug-delivery deep within the brain. The mechanism and temporal profile of disruption are not understood, owing to the limitations of imaging modalities used previously. In this study, we monitored US-induced BBB disruption with multiphoton microscopy, providing high-resolution temporal and spatial information about the permeabilization mechanism and immediate effects of US exposure. Anesthetized C57 mice were prepared with a craniotomy and injected intravenously with fluorescent dyes to permit visualization of the vasculature and BBB integrity. The animals were imaged through a cranial window while exposed to low-intensity US (f=1.029 MHz, power=0.2 W) with a coincident intravenous injection of Optison (a microbubble contrast agent). We observed arteriolar vasoconstriction on US exposure that disrupted blood flow and lasted up to 5 mins; BBB disruption occurred via two characteristically distinct processes-perivascular fluorescence gradually increased (over minutes) along the length of the affected vessel without apparent rupture of the vessel wall or rapidly (seconds) increased in select, focal regions. These data corroborated previous studies suggesting increased endothelial transcytosis and breached tight junctions and demonstrated vasoconstriction, which might alter BBB permeability by modifying cerebral blood flow.

Ultrasonically targeted delivery into endothelial and smooth muscle cells in ex vivo arteries

This study tested the hypothesis that ultrasound can target intracellular uptake of drugs into vascular endothelial cells (ECs) at low to intermediate energy and into smooth muscle cells (SMCs) at high energy. Ultrasound-enhanced delivery has been shown to enhance and target intracellular drug and gene delivery in the vasculature to treat cardiovascular disease, but quantitative studies of the delivery process are lacking. Viable ex vivo porcine carotid arteries were placed in a solution containing a model drug, TO-PRO(R)-1, and Optison microbubbles. Arteries were exposed to ultrasound at 1.1 MHz and acoustic energies of 5.0, 66, or 630 J/cm(2). Using confocal microscopy and fluorescent labeling of cells, the artery endothelium and media were imaged to determine the localization and to quantify intracellular uptake and cell death. At low to intermediate ultrasound energy, ultrasound was shown to target intracellular delivery into viable cells that represented 9-24% of exposed ECs. These conditions also typically caused 7-25% EC death. At high energy, intracellular delivery was targeted to SMCs, which was associated with denuding or death of proximal ECs. This work represents the first known in-depth study to evaluate intracellular uptake into cells in tissue. We conclude that significant intracellular uptake of molecules can be targeted into ECs and SMCs by ultrasound-enhanced delivery suggesting possible applications for treatment of cardiovascular diseases and dysfunctions.

Microbubble-enhanced ultrasound to deliver an antisense oligodeoxynucleotide targeting the human androgen receptor into prostate tumours

We have shown recently that downregulation of the androgen receptor (AR), one of the key players in prostate tumor cells, with short antisense oligodeoxynucleotides (ODNs) results in inhibition of prostate tumor growth. Particularly with regard to an application of these antisense drugs in vivo, we now investigated the usefulness of microbubble-enhanced ultrasound to deliver these ODNs into prostate cancer cells. Our short antisense AR ODNs were loaded onto the lipid surface of cationic gas-filled microbubbles by ion charge binding, and delivered into the cells by bursting the loaded microbubbles with ultrasound. In vitro experiments were initially performed to show that this kind of delivery system works in principle. In fact, transfection of prostate tumor cells with antisense AR ODNs using microbubble-enhanced ultrasound resulted in 49% transfected cells, associated with a decrease in AR expression compared to untreated controls. In vivo, uptake of a digoxigenin-labelled ODN was found in prostate tumour xenografts in nude mice following intratumoral or intravenous injection of loaded microbubbles and subsequent exposure of the tumour to ultrasound, respectively. Our results show that ultrasound seems to be the driving force of this delivery system. Uptake of the ODN was also observed in tumors after treatment with ultrasound alone, with only minor differences compared to the combined use of microbubbles and ultrasound.

Potential role of pulsed-high intensity focused ultrasound in gene therapy

As the understanding of human cancer biology increases, new potential strategies for gene therapy are being proposed and evaluated. However, safe and efficient gene transfer continues to be the major hurdle for its implementation in the clinic. Preclinical studies have shown how pulsed-high intensity focused ultrasound (HIFU) exposures can be combined with different modes of administration (local, intravascular and systemic) to improve local delivery of genes and other therapeutic agents. Using image guidance, exposures are given, where short pulses of energy create predominantly mechanical/structural effects in the tissues as opposed to thermal ones. The result is an increase in both extravasation and interstitial diffusion of macromolecules, which occur non-destructively and reversibly. Ultrasound contrast agents can also be added, which enhance acoustic cavitation activity and consequently sonoporation. By being able to locally increase the uptake and expression of DNA, pulsed-HIFU holds much promise to further the use and applications of gene therapy for treating cancer and other pathological conditions.

Using magnetic forces to enhance non-viral gene transfer to airway epithelium in vivo

We have assessed whether magnetic forces (magnetofection) can enhance non-viral gene transfer to the airways. TransMAG(PEI), a superparamagnetic particle was coupled to Lipofectamine 2000 or cationic lipid 67 (GL67)/plasmid DNA (pDNA) liposome complexes. In vitro transfection with these formulations resulted in approximately 300- and 30-fold increase in reporter gene expression, respectively, after exposure to a magnetic field, but only at suboptimal pDNA concentrations. Because GL67 has been formulated for in vivo use, we next assessed TransMAG(PEI) in the murine nasal epithelium in vivo, and compared this to naked pDNA. At the concentrations required for in vivo experiments, precipitation of magnetic complexes was seen. After extensive optimization, addition of non-precipitated magnetic particles resulted in approximately seven- and 90-fold decrease in gene expression for naked pDNA and GL67/pDNA liposome complexes, respectively, compared to non-magnetic particles. Thus, whereas exposure to a magnetic field improved in vitro transfection efficiency, translation to the in vivo setting remains difficult.

Mechanism of intracellular delivery by acoustic cavitation

Using conditions different from conventional medical imaging or laboratory cell lysis, ultrasound has recently been shown to reversibly increase plasma membrane permeability to drugs, proteins and DNA in living cells and animals independently of cell or drug type, suggesting a ubiquitous mechanism of action. To determine the mechanism of these effects, we examined cells exposed to ultrasound by flow cytometry coupled with electron and fluorescence microscopies. The results show that cavitation generated by ultrasound facilitates cellular incorporation of macromolecules up to 28 nm in radius through repairable micron-scale disruptions in the plasma membrane with lifetimes >1 min, which is a period similar to the kinetics of membrane repair after mechanical wounding. Further data suggest that cells actively reseal these holes using a native healing response involving endogenous vesicle-based membrane resealing. In this way, noninvasively focused ultrasound could deliver drugs and genes to targeted tissues, thereby minimizing side effects, lowering drug dosages, and improving efficacy.

The effects of albumin-coated microbubbles in DNA delivery mediated by therapeutic ultrasound

The application of therapeutic ultrasound (TUS) in combination with contrast agents (USCA) to mediate gene delivery relies on the understanding of the bioeffects involved. The objective of this study was to evaluate the various bioeffects generated by albumin-coated microbubbles: Optison, an USCA, when applied with TUS operated for 10-30 min, on cells and on DNA transfection. This study reveals that Optison microbubbles were still acoustically active after long-term TUS application of 30 min. Optison enhances TUS-gene transfection by increasing the number of plasmids in the cells and also by distributing the plasmids to more cells, without significant decrease in cell viability. Optison also interacts with the DNA to further enhance transfection in a mechanism not necessarily involving cavitation. However, Optison affects mainly the cell cytoplasmatic membrane, without interfering with DNA intracellular trafficking. Using high-resolution scanning electron microscopy (HRSEM), the bioeffects on cell membrane induced by TUS-Optison were observed, demonstrating that Optison lead to a rougher surface, characterized by depressions that are reversible within 24-h post TUS. These effects are different from those observed when only TUS was applied. The findings from this study suggest that albumin-coated microbubbles enhances transfection when using TUS for 10-30 min, and that microbubbles play a major role in elevating cell transfection level and efficiency.

Combination of HIFU therapy with contrast-enhanced sonography for quantitative assessment of therapeutic efficiency on tumor grafted mice

The objective was to evaluate treatment efficiency of a new high-intensity focused ultrasound (HIFU) prototype combining a therapeutic transducer with a sonographic probe. The optimal HIFU sequence was defined on ex vivo samples before in vivo evaluation of tumor ablation was performed by perfusion quantification after contrast agent injection. The original feature of this prototype is a 9-MHz sonographic probe in a HIFU device and connected to an Aplio (Toshiba) sonograph. Acoustical power and treatment time were determined on ex vivo livers to generate 1-cm-long lesions. Lesion reproducibility was assessed for the power and treatment time selected. The gap between lesions and HIFU displacement shot procedures were optimized to ablate a 1-cm3 volume. The optimized protocol was applied to five murine tumors in vivo. Tumor ablation was quantified according to (1) contrast uptake (CU) after HIFU using perfusion software (Toshiba) in "vascular recognition imaging" mode and Sonovue (Bracco) contrast agent, and (2) the percentage of necrosis quantified on histologic slides. Ex vivo results: optimized settings, at 442 W/cm2 applied during three cycles (3 s on/5 s off) generated 10 identical elementary lesions measuring 9.78 (+/-0.66) * 2.11 (+/-0.33) mm2. A 4-mm gap between adjacent lesions and a 2-min pause between shot lines were found optimal. In vivo results: 60 % (+/-22) mean reduction in CU after HIFU and tumor necrosis histologically estimated at 58 % (+/-5.7) were quantified for the five animals. The therapeutic potential of this HIFU prototype was demonstrated in vivo through objective quantification of tumor ablation based on CU.

The role of cavitation in acoustically activated drug delivery

Pluronic P105 micelles are potential candidates as chemotherapy drug delivery vehicles using ultrasonic stimulation as a release trigger. Acoustic power has been previously shown to release two anthracycline agents from these polymeric carriers. In this study, an ultrasonic exposure chamber with fluorescence detection was used to examine the mechanism of doxorubicin release from P105 micelles. Acoustic spectra were collected and analyzed, at the same spatial position as fluorescence data, to probe the role of cavitation in drug release. Our study showed a strong correlation between percent drug release and subharmonic acoustic emissions, and we attribute the drug release to collapse cavitation that perturbs the structure of the micelle and releases drug.

Focal Gene Induction in the Liver of Rats by a Heat-Inducible Promoter Using Focused Ultrasound Hyperthermia

OBJECTIVE

We sought to examine high-intensity focused ultrasound (HIFU)-induced hyperthermia in the liver of a rat model to focally induce green-fluorescent protein (GFP).

MATERIALS AND METHODS

A total of 25 Copenhagen rats were included in this study. Rats were divided into groups treated with an adenovirus coding for green fluorescent protein (GFP) under the control of a hsp70B promoter and a CMV promoter. Ad-CMV-GFP-treated rats served as positive control. Untreated controls only subjected to MRI +/- HIFU-treatment served to find out optimal power of HIFU in the target area of the liver. Temperature was noninvasively monitored by temperature sensitive magnetic resonance imaging (MRI).

RESULTS

Rats treated with Ad-hsp70B-GFP demonstrated localized gene induction within the liver parenchyma, in good correlation with MRI and histology. Applying an acoustic power of 1.92 W a relatively uniform focal temperature up to 42 +/- 5 degrees C within the liver parenchyma could be documented. 3 x 10(9) plaque-forming units proved to account for a very homogeneous liver infection. Number of fluorescent cells in the region of hyperthermia was similar to the control group treated with Ad-CMV-GFP.

CONCLUSION

Using the introduced parameters spatially controlled gene induction within a parenchymal organ such as the liver in rats using HIFU under control of MRI is feasible.

Therapeutic ultrasound optimization for gene delivery: A key factor achieving nuclear DNA localization

When applying therapeutic-ultrasound (TUS) for gene-delivery, there is a great need to understand the contribution of different parameters to the transfection process. The aim of this study is to optimize a wide range of parameters associated with the TUS system concurrent with parameters associated with the transfection, achieving high transfection level and efficiency (total number of cells), while localizing the DNA in the nucleus. Exposure of different cell-types (BHK, LNCaP, BCE) to TUS resulted in high gene expression (1200 fold) and efficiency (28%) with minimal loss in cell viability (<20%). The optimal transfection level and efficiency was achieved using TUS at 2 W/cm2 (0.159 MPa), 30% duty cycle (DC) for 30 min (1080 J/cm2), by placing the transducer above the cells. Long-term TUS application was found to overcome the rate-limiting step of this technology-driving DNA to the cell nucleus. The effect of cell density and DNA concentrations were studied. Increasing DNA concentration contributes to the increase in total gene expression, but not necessarily to transfection efficiency. Our findings support the feasibility of TUS to deliver genes to cells and contribute to the understanding of wide range of parameters that affect the capability of TUS to efficiently deliver genes.

A novel method for the intracellular delivery of siRNA using microbubble-enhanced focused ultrasound

Short interfering RNA (siRNA) has attracted much attention for clinical use in various diseases. However, its delivery, especially through the cell membrane, continues to present a challenge. Advances in ultrasound- and ultrasound contrast-agent technologies have made it possible to change transiently the permeability of the cell membrane and, using a focused ultrasound transducer, to narrow and focus the ultrasound energy on a small target, thereby avoiding damage to surrounding tissue. In this in vitro study, we demonstrate that it is possible to deliver siRNA intracellularly via microbubble-enhanced focused ultrasound. Although further optimization is necessary, our novel method for siRNA transduction represents a powerful tool for using siRNA in vivo and possibly in the clinical setting.

MR imaging-controlled focused ultrasound ablation: a noninvasive image-guided surgery

The history of MR-guided FUS demonstrates the need for merging advanced therapy technology with advanced imaging. Without the ability of MR imaging to localize the tumor margins and without the temperature-sensitive imaging that provides the closed-loop control of energy deposition, this method is inadequate for most clinical applications. Given these limitations,high-intensity focused ultrasound initially appeared to have a narrow application area and was not able to compete with other surgical or ablation methods. Today, MR imaging-guided FUS has become a safe and effective means of performing probe-delivered thermal ablations and minimally invasive surgery. Moreover, it has the potential to replace treatments that use ionizing radiation such as radiosurgery and brachytherapy. Although the cost of integrating"big ticket" MR imaging systems with complex and expensive phased arrays is high, this expenditure will largely be offset by eliminating hospitalization and anesthesia and by reducing complications. In effect, an investment in this emerging technology will ultimately redound to the benefit of the health care delivery system and, most important, to the patient. The FUS system provides a safe, repeatable treatment approach for benign tumors (eg, uterine fibroid and breast fibroadenoma) that do not require an aggressive approach. MR-guided FUS can also be used for debulking cancerous tissue. It has already been tested as a breast cancer treatment; its application for other malignancies in the brain, liver, and prostate is under development. MR-guided FUS offers an attractive alternative to conventional surgery because it incorporates intraoperative MR imaging, which provides far more precise target definition than is possible with the surgeon's direct visualization of the lesion. MR-guided FUS is undeniably the most promising interventional MR imaging method in the field of image-guided therapy today. It is applicable not only in the thermal coagulative treatment of tumors but also in several other medical situations for which invasive surgery or radiation may not be treatment options. The use of FUS for treating vascular malformation or functional disorders of the brain is also exciting. It is uniquely applicable for image-guided therapy using targeted drug delivery methods and gene therapy. Further advances in this technology will no doubt improve energy deposition and reduce treatment times. In the near future, FUS will offer a viable alternative to conventional surgery and radiation therapy; in the longer-term, it may also enable a host of targeted treatment methods aimed at eradicating or arresting heretofore intractable diseases such as certain brain malignancies and forms of epilepsy.

Nonviral gene transfer to skeletal, smooth, and cardiac muscle in living animals

The study of muscle physiology has undergone many changes over the past 25 years and has moved from purely physiological studies to those intimately intertwined with molecular and cell biological questions. To ask these questions, it is necessary to be able to transfer genetic reagents to cells both in culture and, ultimately, in living animals. Over the past 10 years, a number of different chemical and physical approaches have been developed to transfect living skeletal, smooth, and cardiac muscle systems with varying success and efficiency. This review provides a survey of these methods and describes some more recent developments in the field of in vivo gene transfer to these various muscle types. Both gene delivery for overexpression of desired gene products and delivery of nucleic acids for downregulation of specific genes and their products are discussed to aid the physiologist, cell biologist, and molecular biologist in their studies on whole animal biology.

Intracellular delivery of Bak BH3 peptide by microbubble-enhanced ultrasound

PURPOSE

To investigate the possibility of intracellular delivery of Bak BH3 peptide using sonoporation effect by microbubble-enhanced ultrasound.

METHODS

HeLa and BJAB cells were exposed to 1.696-Mhz focused ultrasound with 2% microbubble contrast agents (OPTISON). Cell-impermeable calcein was used as an indicator for successful sonoporation, and propidium iodide staining was used for cell viability assessment. Peptides were also exposed to ultrasound with OPTISON and analyzed with mass spectrometry for evaluation of stability under ultrasound exposure. The effect of transduced Bak BH3 peptide was evaluated by the cell viability of successfully sonoporated cells.

RESULTS

Bak BH3 peptides did not undergo mechanical degradation with microbubble-enhanced ultrasound exposure. With the increase of acoustic energy exposure, the sonoporation efficiency saturated both in BJAB and HeLa cells, while direct cell death rate by ultrasound exposure tended to increase. When BJAB cells were treated with 100 microM Bak BH3 peptides, and ultrasound exposure with ultrasound contrast agents (OPTISON), an increased 35% cell death was confirmed. On the other hand, although HeLa cells had a similar trend, they failed to exhibit statistical significance.

CONCLUSIONS

Our results suggest that microbubble-enhanced focused ultrasound peptide transduction is possible. Further optimization of ultrasound exposure conditions may be necessary.

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

PURPOSE

To determine whether exposures to pulsed high-intensity focused ultrasound can enhance local delivery and expression of a reporter gene, administered with systemic injection of naked DNA, in tumors in mice.

MATERIALS AND METHODS

The study was performed according to an approved animal protocol and in compliance with guidelines of the institutional animal care and use committee. Squamous cell carcinoma (SCC7) tumors were induced subcutaneously in both flanks of female C3H mice (n = 3) and allowed to grow to average size of 0.4 cm(3). In each mouse, one tumor was exposed to pulsed high-intensity focused ultrasound while a second tumor served as a control. Immediately after ultrasound exposure, a solution containing a cytomegalovirus-green fluorescent protein (GFP) reporter gene construct was injected intravenously via the tail vein. The mouse was sacrificed 24 hours later. Tissue specimens were viewed with fluorescence microscopy to determine the presence of GFP expression, and Western blot analysis was performed, at which signal intensities of expressed GFP were quantitated. A paired Student t test was used to compare mean values in controls with those in treated tumors. Histologic analyses were performed with specific techniques (hematoxylin-eosin staining, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling) to determine whether tumor cells had been damaged by ultrasound exposure.

RESULTS

GFP expression was present in all sections of tumors that received ultrasound exposure but not in control tumors. Results of signal intensity measurement at Western blot analysis showed expressed GFP to be nine times greater in ultrasound-exposed tumors (160.2 +/- 24.5 [standard deviation]) than in controls (17.4 +/- 11.8) (P = .004, paired Student t test). Comparison of histologic sections from treated tumors with those from controls revealed no destructive effects from ultrasound exposure.

CONCLUSION

Local exposure to pulsed high-intensity focused ultrasound in tumors can enhance the delivery and expression of systemically injected naked DNA.