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Electrotransfer at MR Imaging: Tool for Optimization of Gene Transfer Protocols—Feasibility Study in Mice¹

¹ From INSERM U 582 (M.P.J., J.T.V., K.S.) and Laboratoire de RMN (AFM-CEA) (E.P., G.V., P.G.C., C.W., A.L.W.), Institut de Myologie, Hôpital de la Pitié-Salpêtrière, 47 Boulevard de l’Hôpital, 75651 Paris, France; and Service de Radiologie, Hôpital Saint-Louis, Paris, France (E.d.K.). Received April 26, 2002; revision requested July 9; final revision received December 4; accepted January 13, 2003. Supported by the Association Française contre les Myopathies, the Institut Fédératif de Recherche 14, the Institut National de la Santé et de la Recherche Médicale, the Commissariat à l’Energie Atomique, and the Centre National de la Recherche Scientifique. E.P. supported by the Ministère de la Recherche. Address correspondence to A.L.W. (e-mail: a.leroywillig@myologie.chups.jussieu.fr).

PURPOSE: To test, by using an electrotransfer protocol for the transfection of skeletal muscle with naked plasmid complementary DNA, whether in vivo magnetic resonance (MR) imaging can help delineate either the spatial extent of the electric field when contrast agent is injected intraperitoneally or the transfection area when contrast agent is injected locally.

MATERIALS AND METHODS: Three groups of five mice each were examined at 4 T. Gadopentetate dimeglumine was injected intraperitoneally before electroporation in group 1 and after electroporation in group 2. In group 3, gadopentetate dimeglumine was coinjected in situ with plasmid pCMV-ßGal in the gastrocnemius muscle before electroporation. MR imaging and muscle preparation for histologic examination were performed 3 days later. On T1-weighted images, increase of muscle signal intensity was determined in regions of interest (ROIs) of treated legs and compared with contralateral ROIs. Comparison of signal intensity increase between groups 1 and 2 was performed with Kruskal-Wallis test.

RESULTS: In groups 1 and 3, T1-weighted images of treated muscle showed zones of strongly increased signal intensity. In corresponding ROIs of groups 1, 2, and 3, the mean T1-weighted signal intensity increase at day 3 was 1.64 ± 0.20 (SD), 1.16 ± 0.06, and 1.58 ± 0.17, respectively. The difference between groups 1 and 2 (ie, gadopentetate dimeglumine injected before and after electrotransfer) was significant (P < .001) both without and with correction for T2 variation (1.47 ± 0.19 and 1.04 ± 0.09, respectively). In group 3, after in situ coinjection of gadopentetate dimeglumine and plasmid, the area of increased signal intensity revealed at ex vivo MR imaging of the muscle showed a reasonable concordance with the transfected area revealed with ß-galactosidase on histologic sections.

CONCLUSION: In vivo and ex vivo results indicate that atraumatic visualization of the permeabilized and transfected area is possible.

© RSNA, 2003

Index terms: Animals • Genes and genetics • Magnetic resonance (MR), experimental studies, 45.121411, 45.12143 • Therapeutic radiology, experimental studies