Effective ultrasound-targeted microbubble destruction (UTMD)-mediated gene transfer into the livers of small and large animals

Ultrasound (US)-targeted microbubble (MB) destruction (UTMD) can significantly enhance gene delivery in mouse livers when pDNA/MBs were injected into the portal vein (PV) with simultaneous US exposure using a focused transducer. However, this transducer was ineffective in enhancing gene transfer into rats. A 13-mm diameter unfocused transducer was designed and the delivery route of pDNA/MBs was modified into a specific liver lobe, resulting in >100-fold increase in luciferase expression in rats. To facilitate the translation into human applications, many technical issues were explored in large animal models. We applied 1.1 MHz US to targeted canine and swine liver lobes with simultaneous injection of pDNA/MBs into a PV segmental branch and occlusion of the inferior vena cava. For more effective treatment of large tissue volumes, a 52-mm apodized, dual element unfocused transducer was specifically constructed to reduce the near field transaxial pressure variations, producing a uniform field of US exposure. Together with a 15 kW-capacity US amplifier, a 692-fold and 1800-fold increases of gene expression in canines and swines were achieved at 2.7-MPa, respectively. Transaminase levels and histology analysis indicated minimal tissue damage. These results demonstrated that UTMD is highly promising for safe and efficient gene delivery into the liver.