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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).

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