HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) All Versions of this Article: 2363041021v1 236/3/939    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Du, X. Articles by Yang, X. Search for Related Content PubMed PubMed Citation Articles by Du, X. Articles by Yang, X.

Radiofrequency-enhanced Vascular Gene Transduction and Expression for Intravascular MR Imaging–guided Therapy: Feasibility Study in Pigs¹

¹ From the Departments of Radiology (X.D., B.Q., F.G., L.V.H., X.Y.), Oncology (X.Z., L.C.), and Pediatrics (A.K., S.C.), Johns Hopkins University School of Medicine, Traylor Bldg, Room 330, 720 Rutland Ave, Baltimore, MD 21205. Received June 7, 2004; revision requested August 23; revision received September 21; accepted October 22. Supported by National Institutes of Health grant R01 HL 66187. Address correspondence to X.Y. (e-mail: xyang{at}mri.jhu.edu).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
PURPOSE: To evaluate the feasibility of radiofrequency (RF)-enhanced vascular gene transduction and expression by using a magnetic resonance (MR) imaging–heating guidewire as an intravascular heating vehicle during MR imaging–guided therapy.

MATERIALS AND METHODS: The institutional committee for animal care and use approved the experimental protocol. The study included in vitro evaluation of the use of RF energy to enhance gene transduction and expression in vascular cells, as well as in vivo validation of the feasibility of intravascular MR imaging–guided RF-enhanced vascular gene transduction and expression in pig arteries. For in vitro experiments, approximately 10⁴ vascular smooth muscle cells were seeded in each of four chambers of a cell culture plate. Next, 1 mL of a green fluorescent protein gene (gfp)-bearing lentivirus was added to each chamber. Chamber 4 was heated at approximately 41°C for 15 minutes by using an MR imaging–heating guidewire connected to a custom RF generator. At day 6 after transduction, the four chambers were examined and compared at confocal microscopy to determine the efficiency of gfp transduction and expression. For the in vivo experiments, a lentivirus vector bearing a therapeutic gene, vascular endothelial growth factor 165 (VEGF-165), was transferred by using a gene delivery balloon catheter in 18 femoral-iliac arteries (nine artery pairs) in domestic pigs and Yucatan pigs with atherosclerosis. During gene infusion, one femoral-iliac artery in each pig was heated to approximately 41°C with RF energy transferred via the intravascular MR imaging–heating guidewire, while the contralateral artery was not heated (control condition). At day 6, the 18 arteries were harvested for quantitative Western blot analysis to compare VEGF-165 transduction and expression efficiency between RF-heated and nonheated arterial groups.

RESULTS: Confocal microscopy showed gfp expression in chamber 4 that was 293% the level of expression in chamber 1 (49.6% ± 25.8 vs 16.8% ± 8.0). Results of Western blot analysis showed VEGF-165 expression for normal arteries in the RF-heated group that was 300% the level of expression in the nonheated group (70.4 arbitrary units [au] ± 107.1 vs 23.5 au ± 29.8), and, for atherosclerotic arteries in the RF-heated group, 986% the level in the nonheated group (129.2 au ± 100.3 vs 13.1 au ± 4.9).

CONCLUSION: Simultaneous monitoring and enhancement of vascular gene delivery and expression is feasible with the MR imaging–heating guidewire.

© RSNA, 2005

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
Atherosclerotic cardiovascular disease is the leading cause of death in developed countries (1). Gene therapy presents great potential for the treatment of atherosclerotic cardiovascular disease (2–5). The rate of in vivo transfection and transduction of genes in vessels, however, has been very low with currently used techniques: For example, it is approximately only 1% for nonviral gene-carrying vectors (2,6). The low rate of transfection and transduction is one of the major obstacles to the clinical application of vascular gene therapy.

In a few in vitro studies, researchers have demonstrated that controlled heating can improve gene transfection (7,8). The proposed explanations for increased transfection include the fact that heating can fracture tissues, increase the cell membrane permeability and the cell metabolism, and increase the activity of heat-sensitive heat shock proteins (8–11). In clinical practice, it would be desirable to have an imaging-guided method for local heating in targeted vascular segments only. One way to accomplish targeted local heating is to develop an internal heating source, which should be small enough to be easily placed into a local target via the naturally existing anatomic channel (blood vessel).

For this purpose, we developed a magnetic resonance (MR) imaging–heating guidewire. The MR imaging–heating guidewire was designed to fulfill three functions simultaneously: to serve as a receiver antenna for generating high-spatial-resolution MR images of vessel walls and plaques, a conventional guidewire for guiding endovascular interventions such as balloon angioplasty and vascular gene transfer performed during MR imaging (12,13), and a potential intravascular heating source for local heating in targeted vessel segments (14). Simultaneous application of the three functions (imaging, heating, and guiding) of the MR imaging–heating guidewire should benefit the overall usefulness of MR technology for monitoring, enhancing, and guiding vascular gene therapy.

The imaging and guiding functions of the MR imaging–heating guidewire were extensively investigated in previous studies (12,13,15,16). Thus, the purpose of the current study was to evaluate the feasibility of in vivo radiofrequency (RF)-enhanced vascular gene transduction and expression by using the MR imaging–heating guidewire as an intravascular heating vehicle.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
MR Imaging–Heating System
To efficiently deliver external RF energy to the targeted vessel segments with minimal power loss in transit, we produced a copper-based MR imaging–heating guidewire of a size commonly used in the clinical setting, 0.014 inch in diameter and 5 feet in length. The MR imaging–heating guidewire was designed to be connected to the common port of a custom filter box, or duplexer, to enable simultaneous MR imaging and RF heating with the same MR imaging–heating guidewire (Fig 1). The filter box contained a low-pass filter (upper-limit cutoff frequency, 90 MHz) that allowed the generation of an MR signal (Signa c/I; GE Medical Systems, Milwaukee, Wis) with a 64-MHz frequency, and a high-pass filter (lower-limit cutoff frequency, 150 MHz) that allowed the generation of a 180-MHz-frequency RF wave with a custom external RF generator to simultaneously deliver RF thermal energy to the targeted vessel segments. The MR imaging–heating guidewire was a coaxial cable with a 4.5-cm-long extension of the inner conductor (Microstock, West Point, Pa). The junction of the inner conductor extension with the outer conductor was the most active point (hot spot) for both MR imaging and RF heating.

View larger version (47K): [in this window] [in a new window] [Download PPT slide]   Figure 1. Schema of system for simultaneous MR imaging and RF heating with the MR imaging–heating guidewire (MRIHG). The MR imaging–heating guidewire is connected to the duplexer, which consists of a low-pass filter (LPF) to generate MR signal and a high-pass filter (HPF) to simultaneously deliver RF energy from an external RF generator to the targeted vessel as heat, thus enhancing catheter-based gene transduction in arterial plaques.

In Vitro Evaluation
Cell culture preparation.—We used a four-chamber cell culture plate (Lab-Tek Chamber Slide; Nalge Nunc International, Rochester, NY) (Fig 2a). The MR imaging–heating guidewire was attached under the bottom of chamber 4 of the cell culture plate, with the hot spot of the MR imaging–heating guidewire located at the center of the chamber bottom. Next, the MR imaging–heating guidewire was connected to the custom RF generator for heating. To measure the temperature changes in the four chambers, two authors (X.D., B.Q.), working together, attached 0.6-mm fiberoptic thermal sensors (FISO Technologies, Quebec, Canada) to the bottom of each of the four chambers. The thermal sensors were then connected to a multichannel thermometer (FISO Technologies) to record the temperature changes during RF heating mediated by the MR imaging–heating guidewire. When the cell culture plate was placed in a 37°C water bath, chamber 4 could be heated to approximately 41°C by applying 25 W of RF power to the MR imaging–heating guidewire. In each of the four chambers, approximately 10⁴ vascular smooth muscle cells were seeded. Then, 1 mL of gfp-lentivirus was added to each chamber, and chamber 4 was heated at approximately 41°C for 15 minutes. Subsequently, untransduced gfp-lentivirus supernatant was removed by washing the chambers five times with phosphate-buffered saline, and the smooth muscle cells were further incubated for 5 days to allow sufficient gfp expression.

View larger version (80K): [in this window] [in a new window] [Download PPT slide]   Figure 2a. In vitro gfp transduction and expression with different RF heating protocols. (a) Photograph shows cell culture plate with four chambers (1–4) in which smooth muscle cells were cultured. The bottom of chamber 4 was heated with RF energy via the MR imaging–heating guidewire (arrow). (b) Graph of temperature increases shows that when the temperature reached approximately 41°C in chamber 4, there was almost no temperature increase in chamber 1. (c) Graph of gfp transduction values shows higher transduction in chamber 4 than in the other three. (d) Confocal micrographs of cell cultures show smooth muscle cell nuclei as areas of blue stain, while expressed gfp manifests as green fluorescent light. Expression of gfp is more extensive in chamber 4 than in the other three.

In Vivo Validation
Arteries and animals.—Twelve femoral-iliac arterial segments (six bilateral artery pairs) from domestic pigs and six femoral-iliac arterial segments (three bilateral artery pairs) from Yucatan pigs were used in the in vivo validation study. The domestic pigs were primarily used to test the effectiveness of the intravascular MR imaging–RF heating protocol for enhancement of vascular gene transduction and expression, while the Yucatan pigs were primarily used to validate the applicability of the technique in a more clinical setting (ie, in atherosclerotic arteries). In Yucatan pigs, atherosclerotic stenoses and plaques in bilateral femoral-iliac arteries were created with balloon denudation followed by a high-cholesterol diet for 18–24 months (18,19). Once the atherosclerotic stenoses were created in the arteries, we began to perform catheter-based gene transfer. All animals were treated according to the Principles of Laboratory Animal Care of the National Society for Medical Research and the revised 1985 edition of the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. The animal care and use committee at our institution approved the experimental protocol.

Gene-lentivirus delivery.—Through a surgical cutdown in the left carotid artery, a 7-F introducer sheath was placed in the upper abdominal aorta. Heparin (Elkins-Sinn, Cherry Hill, NJ) was intravenously administered (100 IU/kg) to initiate anticoagulation. We then obtained an angiogram of the pelvic and bilateral femoral arteries. According to the appearance of the arteries on the angiogram, we selected either two or four vessel segments, one or two in each femoral-iliac artery, respectively, as the targets for gene delivery in each animal. Then, by using a gene delivery balloon catheter (Remedy; Scimed/Boston Scientific, Maple Grove, Minn), we delivered 1.4 mL of the gene-lentivirus into the wall of each targeted vessel. The gene delivery catheter consisted of an angioplasty balloon that was surrounded by multiple gene delivery–infusion channels with 30–100-µm micropores in their surfaces. The inflation of the angioplasty balloon with saline at a temperature of 37°C and pressure of 4 atm stopped the blood flow completely in the vessel and simultaneously propelled the multiple gene delivery–infusion channels against the targeted vessel wall. Thus, subsequent infusion of the gene-lentivirus material caused, via an orifice-mediated jet effect, the disruption of the physical barriers imposed by the continuous endothelium and the internal elastic lamina, and, thereby, the delivery of the gene-lentivirus with high infusion pressure into the media of the targeted vessel wall (20). The gene-lentivirus infusion was maintained by using a syringe pump (Harvard Apparatus, Holliston, Mass). Gene delivery procedures in all arteries were successful, and all pigs survived the procedures with no clinical abnormalities.

RF heating.—During the gene-lentivirus infusion, the targeted artery segments in one femoral-iliac artery were not heated and instead served as controls, while the targeted segments in the contralateral femoral-iliac artery were heated with the 0.014-inch MR imaging–heating guidewire that was connected to the external RF generator. In this experimental setting, we achieved a temperature increase to approximately 41°C from 37°C in the targeted femoral-iliac arteries by operating the 180-MHz RF generator at 4 W (B. Qiu et al, unpublished data, October 9, 2002). We used one of two infusion parameters: (a) a constant 8.5-minute infusion at a flow rate of 10 mL/h or (b) an intermittent 8-minute infusion, administered in four increments of 2 minutes each, with a 2-minute interval between increments, at a flow rate of 21 mL/h. In the intermittent infusion, the 2-minute intervals permitted deflation of the gene delivery balloon, which restored the blood flow through the targeted vessels. RF heating was maintained at a constant temperature throughout the infusion period and was prolonged for an additional 11 to 12 minutes after the initial infusion.

We then kept the pigs alive for 5 days to permit sufficient gene expression. At day 6 after the gene-vector infusion, all 18 targeted vessel segments were harvested for quantitative Western blot analysis. Since this study focused only on technical development, we did not investigate the long-term function of gene expression or the therapeutic effect of the VEGF gene.

Quantitative Western Blot Analysis
Two authors (A.K., S.C.) together homogenized the harvested arterial tissues in a Wheaton grinder and extracted proteins with a lysis buffer (50 mmol Tris-HCl, pH of 7.4; 1% nonylphenyl polyethylene glycol; 0.5% sodium deoxycholate; and 150 mmol NaCl) and a cocktail of protease inhibitors (2 mmol phenylmethylsulfonyl fluoride, 2 µg/mL leupeptin, 2 µg/mL aprotinin, 1 mmol Na₃VO_4, and 1 mmol NaF). Next, the homogenate was centrifuged at 10 000g and 4°C, and protein concentration in the supernatant was determined with a bicinchoninic acid protein assay kit (Pierce Biotechnology, Rockford, Ill). Supernatants (100 µg of proteins) were separated with gel electrophoresis by using 4%–15% gradient polyacrylamide in denaturing conditions and were transferred electrophoretically to nitrocellulose membranes. Membranes were blocked in 5% milk at room temperature for 1 hour. Western blot analysis was performed by using anti-VEGF rabbit polyclonal immunoglobulin G (Upstate Biotechnology, Lake Placid, NY) at a dilution of 1:1000, and horseradish peroxidase–conjugated anti–rabbit antibody (Amersham Pharmacia Biotech, Piscataway, NJ). Blots were prepared by using an enhanced chemiluminescence detection kit for Western blot analysis (Amersham Pharmacia Biotech) and were examined with laser densitometry. The intensity of the signals was subsequently quantified by using software (ImageQuant; Molecular Dynamics, Sunnyvale, Calif).

Data Analysis
For in vitro studies, three investigators (X.D., B.Q., X.Y.) independently counted the number of gfp-positive cells and compared it with the total number of cells at 10 randomly selected regions of interest in each of the four cell culture chambers. For in vivo studies, two authors (A.K., S.C.) together assessed the VEGF transduction and expression efficiency by using laser densitometry to measure the intensity of the immunoblot bends derived from each of the arterial specimens. VEGF transduction and expression efficiency levels were compared between the nine pairs of RF-heated and nonheated arteries. Data were expressed as the mean ± standard deviation.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
In Vitro Experiments
In the in vitro experiments with smooth muscle cells, RF heating mediated by the MR imaging–heating guidewire produced a temperature gradient across the four chambers of the cell culture plate: A desired temperature increase to approximately 41°C was achieved in chamber 4, while there was almost no temperature increase in chamber 1 (37°C) (Fig 2a, 2b). RF heating generated gfp expression in chamber 4 that was 293% the level of expression achieved in chamber 1 (49.6% ± 25.9 vs 16.8% ± 8.0) (Fig 2c, 2d).

View larger version (8K): [in this window] [in a new window] [Download PPT slide]   Figure 2b. In vitro gfp transduction and expression with different RF heating protocols. (a) Photograph shows cell culture plate with four chambers (1–4) in which smooth muscle cells were cultured. The bottom of chamber 4 was heated with RF energy via the MR imaging–heating guidewire (arrow). (b) Graph of temperature increases shows that when the temperature reached approximately 41°C in chamber 4, there was almost no temperature increase in chamber 1. (c) Graph of gfp transduction values shows higher transduction in chamber 4 than in the other three. (d) Confocal micrographs of cell cultures show smooth muscle cell nuclei as areas of blue stain, while expressed gfp manifests as green fluorescent light. Expression of gfp is more extensive in chamber 4 than in the other three.

View larger version (9K): [in this window] [in a new window] [Download PPT slide]   Figure 2c. In vitro gfp transduction and expression with different RF heating protocols. (a) Photograph shows cell culture plate with four chambers (1–4) in which smooth muscle cells were cultured. The bottom of chamber 4 was heated with RF energy via the MR imaging–heating guidewire (arrow). (b) Graph of temperature increases shows that when the temperature reached approximately 41°C in chamber 4, there was almost no temperature increase in chamber 1. (c) Graph of gfp transduction values shows higher transduction in chamber 4 than in the other three. (d) Confocal micrographs of cell cultures show smooth muscle cell nuclei as areas of blue stain, while expressed gfp manifests as green fluorescent light. Expression of gfp is more extensive in chamber 4 than in the other three.

View larger version (57K): [in this window] [in a new window] [Download PPT slide]   Figure 2d. In vitro gfp transduction and expression with different RF heating protocols. (a) Photograph shows cell culture plate with four chambers (1–4) in which smooth muscle cells were cultured. The bottom of chamber 4 was heated with RF energy via the MR imaging–heating guidewire (arrow). (b) Graph of temperature increases shows that when the temperature reached approximately 41°C in chamber 4, there was almost no temperature increase in chamber 1. (c) Graph of gfp transduction values shows higher transduction in chamber 4 than in the other three. (d) Confocal micrographs of cell cultures show smooth muscle cell nuclei as areas of blue stain, while expressed gfp manifests as green fluorescent light. Expression of gfp is more extensive in chamber 4 than in the other three.

View larger version (66K): [in this window] [in a new window] [Download PPT slide]   Figure 3. Experimental creation of atherosclerotic stenosis in pigs. A, B, Gross specimens of, A, normal and, B, atherosclerotic aorta and arteries. C, D, Cross sections of, C, normal and, D, atherosclerotic femoral-iliac arteries. Note severe stenosis due to plaque in D. E, Photomicrograph of arterial cross section shows plaque (arrow) that narrows the lumen (L) of the femoral-iliac artery, as well as calcification (c) leaching due to the slide preparation process. (Hematoxylin-eosin stain; original magnification, x1.)

View larger version (14K): [in this window] [in a new window] [Download PPT slide]   Figure 4a. Results of quantitative Western blot analysis of VEGF expression in (a) normal and (b) atherosclerotic arteries. Graphs show higher expression in RF-heated arteries than in nonheated arteries. au = arbitrary units.

View larger version (16K): [in this window] [in a new window] [Download PPT slide]   Figure 4b. Results of quantitative Western blot analysis of VEGF expression in (a) normal and (b) atherosclerotic arteries. Graphs show higher expression in RF-heated arteries than in nonheated arteries. au = arbitrary units.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

To precisely deliver genes into the targeted vessel wall, we used a catheter-based local gene delivery approach. The pressure-driven gene delivery catheter permitted us to concentrate high doses of the gene-vector at the targeted vessel wall only, thereby avoiding the toxic effects to different organs that could be caused by systemic administration of the gene-vector.

A few attempts have been made to use low-frequency ultrasound to efficiently transfect and transduce a gene-vector into targeted vascular cells, to enhance vascular gene expression (21,22). However, low-frequency ultrasound does not enable high-spatial-resolution ultrasonographic imaging of the gene-targeted vessel wall and may be technically feasible only in treating superficial vessels, because of difficulties in precisely focusing the ultrasound energy on deep structures. The concept of heat-enhanced gene transfection motivated us to develop an alternative to ultrasound by using an intravascular MR imaging–heating guidewire to enable simultaneous imaging and heating.

The results of the current study conducted in vitro with vascular cells and in vivo with both normal and atherosclerotic arteries provide the first evidence that RF heating can enhance catheter-based vascular gene transduction and expression. We used the MR imaging–heating guidewire as a unique endovascular vehicle to deliver external RF energy into the vessel and thus create local heat in the targeted vessel segment only, which enabled us to successfully enhance local vascular gene transduction and expression. The results of a previous study confirmed that the power distribution pattern of the hot spot of the MR imaging–heating guidewire was cylindrically symmetric, analogous to the geometry of vessels, and localized to the targeted vessel area only, with no thermal damage to the vessels or the adjacent tissues and organs when the MR imaging–heating guidewire was operated at approximately 41°C (14).

For experimental purposes, to achieve sufficient gene transduction and expression, we intended to deliver the gene-lentivirus by using a constant 8.5-minute infusion protocol at a 10 mL/h flow rate. This constant infusion protocol, however, is not practical in a clinical setting. Therefore, we investigated the feasibility of using an intermittent 2-minute infusion at 2-minute intervals with a 21 mL/h flow rate. This intermittent infusion protocol enabled us to deliver the same amount (1.4 mL) of gene-lentivirus into the targeted vessels as the constant 8.5-minute infusion protocol, while blood circulation was still established intermittently via the target to distal organs.

There are many advantages of MR technology for vascular gene therapy. First, intravascular MR imaging with the MR imaging–heating guidewire allows the performance of endovascular interventions, including gene therapy, with MR guidance (12). Second, the high-spatial-resolution MR imaging technique with the MR imaging–heating guidewire provides an effective imaging tool to monitor the location and distribution of the delivered gene-vector in the targeted vessel wall (13). Third, it would be beneficial to use the MR thermometer technique as a noninvasive tool to monitor and control RF heat in the targeted vessels during RF-enhanced vascular gene therapy. Fourth, existing MR imaging techniques, such as MR angiography and functional perfusion MR imaging performed before and after MR imaging–guided vascular gene therapies, should enable prompt assessment of the success of intervention.

The current study was focused initially on only technical development, on the use of the MR imaging–heating guidewire as an intravascular RF heating vehicle to enhance vascular gene transduction and expression. Thus, a limitation of this study was that we did not investigate why greater gene expression was observed in atherosclerotic arteries than in normal arteries. This difference in gene expression might have been caused by a difference between atherosclerotic and normal arteries in vessel permeability during gene-vector transfer with the jet effect via the gene delivery balloon catheter. In addition to investigating the cause of this difference, further studies should be aimed at optimizing the intravascular RF heating protocol and evaluating the safety of this technique by using quantification in different experimental groups. They also should combine this technique with other MR techniques, including intravascular high-spatial-resolution MR imaging of the gene-targeted vessel wall to monitor gene delivery and localization at the target, and with the use of an MR thermometer to noninvasively control the distribution and level of local heating mediated by the intravascular MR imaging–heating guidewire.

In conclusion, we present a technique of intravascular RF heating–enhanced local vascular gene transduction and expression mediated by an MR imaging–heating guidewire.

One of the current limitations to clinical application of vascular gene therapy is the very low rate of transfection and transduction in vivo. This study demonstrated the potential use of intravascular MR imaging and RF-mediated heating to enhance local vascular gene transduction and expression. The combination of this technique with other advantages of MR technology should benefit MR-based vascular gene therapy.

	FOOTNOTES

 

Abbreviations: gfp = green fluorescent protein gene • RF = radiofrequency • VEGF = vascular endothelial growth factor

Authors stated no financial relationship to disclose.

Author contributions: Guarantors of integrity of entire study, X.D., L.C., S.C., X.Y.; study concepts, X.D., B.Q., X.Y.; study design, X.D., B.Q., S.C., X.Y.; literature research, X.D., B.Q., X.Y.; experimental studies, all authors; data acquisition, X.D., B.Q., A.K.; data analysis/interpretation, X.D., B.Q., A.K., S.C., X.Y.; manuscript preparation, X.D., B.Q., X.Y.; manuscript definition of intellectual content, X.D., B.Q., X.Z., L.C., S.C., X.Y.; manuscript revision/review and editing, X.D., B.Q., X.Z., L.V.H., L.C., S.C., X.Y.; manuscript final version approval, all authors

	References

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 

1. American Heart Association. 2003 Heart and stroke statistical update. Dallas, Tex: American Heart Association, 2003.
2. Nabel E, Leiden J. Gene transfer approaches for cardiovascular disease. In: Chien K, ed. Molecular basis of cardiovascular disease. Philadelphia, Pa: Saunders, 1999; 86–112.
3. Thomas JW, Kuo MD, Chawla M, et al. Vascular gene therapy. RadioGraphics 1998;18:1373–1394.[Abstract]
4. Francis SC, Raizada MK, Mangi AA, et al. Genetic targeting for cardiovascular therapeutics: are we near the summit or just beginning the climb? Physiol Genomics 2001;7:79–94.
5. Yang X. Imaging of vascular gene therapy. Radiology 2003;228:36–49.[Abstract/Free Full Text]
6. Yla-Herttuala S, Martin J. Cardiovascular gene therapy. Lancet 2000;355:213–222.[CrossRef][Medline]
7. Takai T, Ohmori H. Enhancement of DNA transfection efficiency by heat treatment of cultured mammalian cells. Biochim Biophys Acta 1992;1129:161–165.[Medline]
8. Madio D, van-Gelderen P, DesPres D, et al. On the feasibility of MRI-guided focused ultrasound for local induction of gene expression. J Magn Reson Imaging 1998;8:101–104.[Medline]
9. Tang MX, Redemann CT, Szoka FC Jr. In vitro gene delivery by degraded polyamidoamine dendrimers. Bioconjug Chem 1996;7:703–714.[CrossRef][Medline]
10. Doukas AG, Flotte TJ. Physical characteristics and biological effects of laser-induced stress waves. Ultrasound Med Biol 1996;22:151–164.[CrossRef][Medline]
11. Li CY, Dewhirst MW. Hyperthermia-regulated immunogene therapy. Int J Hyperthermia 2002;18:586–596.[CrossRef][Medline]
12. Yang X, Atalar E. Intravascular MR-guided balloon angioplasty with an MR imaging guide wire: feasibility study in rabbits. Radiology 2000;217:501–506.[Abstract/Free Full Text]
13. Yang X, Atalar E, Li D, et al. Magnetic resonance imaging permits in vivo monitoring of catheter-based vascular gene delivery. Circulation 2001;104:1588–1590.[Abstract/Free Full Text]
14. Qiu B, Yeung C, Du X, Atalar E, Yang X. Development of an intravascular heating source using an MR imaging-guidewire. J Magn Reson Imaging 2002;16:716–720.[CrossRef][Medline]
15. Ocali O, Atalar E. Intravascular magnetic resonance imaging using a loopless catheter antenna. Magn Reson Med 1997;37:112–118.[Medline]
16. Serfaty JM, Yang X, Foo TK, Kumar A, Derbyshire A, Atalar E. MRI-guided coronary catheterization and PTCA: a feasibility study on a dog model. Magn Reson Med 2003;49:258–263.[CrossRef][Medline]
17. Cui Y, Golob J, Kelleher E, Ye Z, Pardoll D, Cheng L. Targeting transgene expression to antigen-presenting cells derived from lentivirus-transduced engrafting human hematopoietic stem/progenitor cells. Blood 2002;99:399–408.[Abstract/Free Full Text]
18. White C, Ramee S. Swine models of atherosclerosis. In: White R, ed. Atherosclerosis and arteriosclerosis: human pathology and experimental animal methods and models. Boca Raton, Fla: CRC, 1989; 207–234.
19. Augier T, Charpiot P, Chareyre C, Remusat M, Rolland P, Carcon D. Medial elastic structure alterations in atherosclerotic arteries in minipigs: plaque proximity and arterial site specificity. Matrix Biol 1997;15:455–567.[CrossRef][Medline]
20. Varenne O, Gerard R, Sinnaeve P, Gillijns H, Collen D, Janssens S. Percutaneous adenoviral gene transfer into porcine coronary arteries: is catheter-based gene delivery adapted to coronary circulation? Hum Gene Ther 1999; 10:1105–1115.[CrossRef][Medline]
21. Lawrie A, Brisken A, Francis S, et al. Ultrasound enhances reporter gene expression after transfection of vascular cells in vitro. Circulation 1999;99:2617–2620.[Abstract/Free Full Text]
22. Amabile PG, Waugh JM, Lewis TN, Elkins CJ, Janas W, Dake MD. High-efficiency endovascular gene delivery via therapeutic ultrasound. J Am Coll Cardiol 2001;37:1975–1980.[Abstract/Free Full Text]

This Article Abstract Figures Only Full Text (PDF) All Versions of this Article: 2363041021v1 236/3/939    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Du, X. Articles by Yang, X. Search for Related Content PubMed PubMed Citation Articles by Du, X. Articles by Yang, X.