Enhanced gene transfection of plasmid DNA in the liver with ultrasound and microbubbles

Abstract

Ultrasound mediated delivery (USMD) in the presence of microbubbles is a potentially safe and effective method for gene therapy, offering many desired characteristics such as low toxicity, potential for repeated treatment, as well as organ specificity. In this study we tested the capability of USMD to improve gene transfection to mice livers for treating a rare genetic disorder, Glycogen Storage Disease Type 1a. An image guided therapeutic ultrasound system (TIPS, Philips) was used to provide therapeutic ultrasound to mice liver under IACUC approved protocols. Anesthetized healthy mice were placed supine on a heated pad and coupled to the TIPS transducer. Therapeutic plasmid DNA (FLAG-pG6Pase) was injected and microbubbles infused via the tail vein. Treated animals (n=4) received therapeutic ultrasound pulses (1 MHz, 2.5 MPa) over the entire liver. Control animals (n=5) received pDNA but not ultrasound treatment. Post treatment the animals were left to recover and subsequently sacrificed after 5 days. Tissues from the left, middle, caudal, right anterior, and right posterior liver lobes were harvested and stored. Quantitative PCR assays were then performed on the samples to quantify gene transfection. Ultrasound treated animals showed significantly higher levels of G6Pase transfection compared to control animals (p<0.05) in all five lobes of the liver. On average, the treated animals showed 5.4 times more pDNA accumulation in the liver compared to controls. Immunohistochemistry staining for FLAG tag showed increased transgene expression especially around the blood vessels in treated animals. No evidence of toxicity was found up to 5 days post treatment.