The Use of Ultrasound to Facilitate the Delivery of Genetic-based Therapeutic Strategies

Gene therapy is the introduction of exogenous genes to a cell to "fool" the cell into producing the coding protein. There are ongoing studies in cancer-killing gene therapies, kidney cell regeneration and many genetic disorders such as cystic fibrosis and severe combined immunodeficiency (SCID). However, it has been discovered that developing the therapy is not enough. A method to deliver the drugs is equally important. The objective of this work was to explore two potential uses of ultrasound for gene delivery. The first is to determine if ultrasound-induced cavitation can be used to enhance in vivo transfection of gene therapy. Second, to use non-invasive ultrasonic heating to spatially control gene therapy expression in vivo after delivery. In the first phase of this project, feasibility experiments were performed to show an increase in transfection efficiency occurred when using microbubbles, ultrasound, plasmid and genes compared to plasmid and genes alone. An ultrasound transducer was then designed to optimize experimental conditions for invasive in vivo experiments taking into consideration optimal transducer size, focal distance, and frequency. When testing the transducer, a potential side effect to using ultrasound to increase transfection was discovered. In the second phase of exploration, the use of MRI-monitored ultrasound to induce enhanced expression of luciferase after local injection of the gene construct Ad-HSP-Luc was explored. Using a construct that includes an hsp promoter allows the activation of the associated transgene only in areas that are subsequently heated after injection. Increased luciferase expression was observed in areas that were exposed to ultrasonic heating. It is hoped that the positive results of these preliminary experiments will eventually lead to a clinical methodology where ultrasound-enhanced gene therapy transfection would be followed with ultrasound-directed spatial control of gene expression. Thesis Supervisor: Kullervo Hynynen Title: Professor of Radiology, Harvard Medical School