Polyplex-microbubbles for ultrasound-mediated gene therapy

Sonoporation is an established method whereby acoustically stimulated microbubbles create pores in the endothelium to promote the delivery of nucleic acids and other macromolecules through the vasculature. In this presentation, we describe the development of polyplex-microbubbles to enhance delivery and intracellular trafficking to target cells beyond the endothelium following sonoporation. Our design combines the tissue targeting capability of microbubbles with the cellular targeting capability of polyplexes, which are self-assembled particles comprising nucleic acids and a cationic polymer. The first purpose of the cationic polymer (polyethylenimine, PEI) is to condense and protect the nucleic acids on the microbubble surface as it travels in circulation from the site of injection to the target tissue. Polyethylene glycol (PEG) is conjugated to the PEI to reduce immunogenicity. Ultrasound is applied to the target tissue to fragment the microbubbles and release the polyplexes and to porate the endothelium, allowing the polyplexes to extravasate. The second purpose of PEI is to promote endocytotic uptake and subsequent endosomal escape of the nucleic acids into the cytoplasm by the so-called "proton- sponge" effect. Here, we describe polyplex-microbubble fabrication and characterization, as well as in vivo testing. Our results indicate the promise of this design for cancer gene therapy.