(414b) Encapsulating Emulsions Inside Liposomes for Drug Delivery

Polymer-based nanoparticles have some advantages in drug delivery but often are toxic and problematic for in vivo use. However, liposomes and nanoemulsions made from phospholipids are much more biocompatible and can safely be used as carriers in the human body, and they may be better carriers than polymer based ones. The ability of lipid emulsions to carry poorly soluble drugs increases their application. Liposomes can effectively sequester drugs and genes to protect them from enzymatic degradation. Our research group uses ultrasound as a modality to trigger release from these carriers and to induce drug uptake by cells. We are developing a novel drug delivery liposome that breaks open upon exposure to a short burst of ultrasound. This is done by encapsulating nanoemulsions of perflurocarbons along with the drug inside a liposome. Upon exposure to the low pressure phase of the acoustic cycle, the perfluorocarbon flashes from liquid to gas. The volume expansion ruptures the liposome, thus spilling the therapeutic content only at the insonated site. We use 2 different processes to encapsulate nanoemulsions of perfluorohexane inside phospholipid liposomes. The first technique is a 2-step process to form vesosomes. This involves first making conventional liposomes using film hydration and extrusion, and adding ethanol to form bilayer sheets. Next the nanoemulsion and therapeutics (or fluorescent markers like calcein) are added. Heating above the melting temperature of the lipid bilayer forms closed vesicles containing the nanoemulsions and the therapeutics. External nanoemulsions and other materials are removed by size exclusion chromatography. The second technique is a one step process, in which a lipid layer is hydrated by perfluorocarbon emulsion suspension and then extruded and cleaned up. This presentation describes both process and their advantages and disadvantages. Once the nanoemulsions are inside the liposomes, exposure to low or mid frequency ultrasound causes rupture of the liposomes in vitro. The kinetics of release of calcein is studied (using fluorescent spectroscopy) as a function of the ultrasound parameters. This novel drug delivery technology may have application in controlled drug and gene delivery to cancerous tumors in vivo.