Ultrasound with microbubbles enhances gene expression of plasmid DNA in the liver via intraportal delivery

Current ultrasound (US)-mediated gene delivery methods are inefficient due, in part, to a lack of US optimization. We systematically explored the use of microbubbles (MBs), US parameters and plasmid delivery routes to improve gene transfer into the mouse liver. Co-presentation of plasmid DNA (pDNA), 10% Optison MBs and pulsed 1-MHz US at a peak negative pressure of 4.3 MPa significantly increased luciferase gene expression with pDNA delivered by intrahepatic injection to the left liver lobe. Intraportal injection delivered pDNA and MBs to the whole liver; with insonation, all lobes expressed the transgene, thus increasing total gene expression. Gene expression was also dependent on acoustic pressure over the range of 0-4.3 MPa, with a peak effect at 3 MPa. An average of 85-fold enhancement in gene delivery was achieved. No enhancement was observed below 0.25 MPa. Increasing pulse length while decreasing pulse repetition frequency and exposure time to maintain a constant total energy during exposure did not further improve transfection efficiency, nor did extend the US exposure pre- or postinjection of pDNA. The results indicate that coupled with MBs, US can more efficiently and dose-dependently enhance gene expression from pDNA delivered via portal vein injection by an acoustic mechanism of inertial cavitation.