(208e) Utilizing Novel Microbubbles for Efficient Delivery of Plasmid DNA to Tumors

Microbubble ultrasound contrast agents have been frequently cited as potential gene and drug carriers for targeted delivery applications. Microbubbles have been shown to be especially useful for non-viral gene delivery by improving the efficiency of plasmid DNA transfection in cells. When circulating in the bloodstream, acoustic energy can cause microbubble destruction by cavitation that transiently increases the permeability of the endothelial vasculature, allowing macromolecules such as plasmids to be delivered to target cells. This technique is especially useful for targeted plasmid DNA delivery to tumors. Despite intense research efforts in this area, an optimized microbubble carrier of plasmid DNA for delivery to tumors has yet to be developed.

In this study, we have synthesized novel microbubbles capable of more efficiently binding plasmid DNA and delivering it to tumors expressed within mice. High molecular weight polyethlyeneimine (PEI) was thiolated and mixed with anionic plasmid DNA expressing luciferase to form so-called polyplex structures. Polyplexes were covalently attached to the microbubble surface by malemide chemistry and subsequently injected into tumor bearing mice. Ultrasound was applied over the area of the tumor immediately after the injection. Plasmid DNA adsorbed to cationic microbubbles significantly increased the transfection efficiency of plasmid DNA within tumor cells compared to plasmid DNA alone. Importantly, the expression of luciferase was almost exclusively expressed within the focal region of the ultrasound beam. Utilizing the polyplex- loaded microbubbles as a contrast agent, we are also able to image them within the body in order to determine their persistence in the bloodstream. This approach is particularly advantageous for further developing longer circulating contrast agents and improving the efficiency of plasmid DNA delivery to tumor cells.