Enhanced gene transfection in vivo using magnetic localisation ofultrasound contrast agents: Preliminary results
Mulvana H., Eckersley RJ., Browning R., Hajnal JV., Stride E., Barrack T., Tang M., Pankhurst Q., Wells D.
In previous work we demonstrated that microbubble mediated gene deliverycan be enhanced in vitro through simultaneous exposure of cells to ultrasoundand magnetic fields in the presence of magnetically loaded microbubbleultrasound contrast agents. The aim of this preliminary study was to investigatethe feasibility of the technique for in vivo applications. Phospholipid coatedmicrobubbles loaded with a hydrocarbon suspension of magnetic nanoparticles wereprepared through sonication and sized using optical microscopy (concentration1.4 10 8 bubbles/ml). Plasmid pGL4.13, which encodes for fireflyluciferase, was prepared at a concentration of 4 g/l in endotoxin-free water. ASiemens Acuson Sequioa clinical imaging system with a 26 mm linear arraytransducer (15L8) was used throughout the investigation. 20, 6-8 week old CD1female mice were injected with of 150 l of microbubble suspension and 50 lplasmid intra-venously through the tail vein. Mice were anaesthetized usingisoflurance and imaged with the transducer above the left lung (14 MHz, 0.06 MI)to locate the thoracic region. Immediately following injection, a NdFeBpermanent magnet was positioned over the right lung and the acoustic output wasincreased (H7MHz, 1.7 MI, focal depth 7.5 mm). Exposure to ultrasound and/ormagnetic field was maintained for two minutes. 20 mice were exposed toultrasound and magnetic field, two to ultrasound only and two to magnetic fieldonly. On the third day post treatment, luciferase substrate (D-luciferin) wasadministered through intra-peritoneal injection and allowed to catalyse thetransfected substrate for 10 minutes before animals were sacrificed and theirorgans recovered for individual bioluminescence imaging (IVIS 100, Xenogen) andquantification (Living Image Software, Xenogen). Animals treated with bothultrasound and the magnetic field showed transfection in the right lung, whileno animals showed transfection in the contralateral organs. Of the 20 micetreated, 17 showed transfection at a level greater than for ultrasound alone and12 greater than that of magnetic field alone. The results of this preliminarystudy indicate that microbubbles which include magnetic nanoparticles withintheir shells may be used to control the location of transfection in vivo.Further work is required to improve microbubble formulations and magnetic arraydesign to allow more accurate targeting of transfection. © 2010 IEEE.