Ultrasound targeted microbubble destruction increases capillary permeability in hepatomas.

Ultrasound-targeted microbubble destruction (UTMD) has evolved as a promising tool for organ-specific gene and drug delivery. Taking advantage of high local concentrations of therapeutic substances and transiently increased capillary permeability, UTMD could be used for the treatment of ultrasound accessible tumors. The aim of this study was to evaluate if UTMD can locally increase capillary permeability in a hepatoma model of the rat. Furthermore, we evaluated whether UTMD can transfect DNA into such tumors. Subcutaneous Morris hepatomas were induced in both hind limbs of ACI rats by cell injection. A total of 18 rats were divided into three groups. Only one tumor per rat was treated by ultrasound. The first group received injection of Evans blue, followed by UTMD. The second group received a phosphate-buffered saline solution infusion and ultrasound to the target tumor after Evans blue injection. The third group received UTMD first, followed by Evans blue injection. Tumors and control organs were harvested, and Evans blue extravasation was quantified. Another 12 rats received DNA-loaded microbubbles by UTMD to one tumor, encoding for luciferase. Evans blue injection followed by UTMD showed about fivefold higher Evans blue amount in the target tumors compared with the control tumors. In contrast, no significant difference in Evans blue content was detected between target and control tumors when ultrasound was applied without microbubbles or when UTMD was performed before Evans blue injection. Plasmid transfection was not successful. In conclusion, ultrasound targeted microbubble destruction is able to transiently increase capillary permeability in hepatomas. Using naked DNA, this technique does not seem to be feasible for noninvasive transfection of hepatomas.

Spatial distribution of ultrasound targeted microbubble destruction increases cardiac transgene expression but not capillary permeability.

Ultrasound targeted microbubble destruction (UTMD) has evolved as a promising tool for organ specific gene and drug delivery. Using DNA-loaded microbubbles, cardiac transfection has been shown to be feasible. However, two-dimensional properties of the ultrasound beam limit cardiac transgene expression to the focal zone, thus, reducing its potential therapeutic effect. The aim of this study was to test if spatial distribution of ultrasound targeted microbubble destruction in the heart could lead to augmented transgene expression or increased capillary permeability. Lipid microbubbles containing plasmids with a luciferase transgene were used to target rat hearts. The diagnostic ultrasound probe was fixed in a mid-short axis view with a gel stand-off between the chest and probe. Ultrasound (1.3 MHz) with a mechanical index of 1.6 was intermittently applied to rats during microbubble infusion. Rats were randomized to either stay in that position or move horizontally in a cranio-caudal direction (3 mm sweep) relative to the ultrasound probe during UTMD. After 4 days, organs were harvested and analyzed for reporter gene expression. Another group of rats received Evans Blue, followed by UTMD with unloaded microbubbles. Again, rats were randomized into a static or moving group. Hearts were harvested to evaluate extravasation of Evans Blue. Moving rats in a cranio-caudal direction significantly increased transgene expression by 19-fold in the anterior heart, by sixfold in the posterior heart and by 32-fold in the apex. Interestingly, Evans Blue extravasation was not augmented in the moving group. Spatial distribution of UTMD may increase transgene expression due to sonication of larger areas in the heart. In contrast, capillary permeability does not increase, indicating less capillary damage.

Ultrasound-targeted microbubble destruction augments protein delivery into testes.

OBJECTIVES: Gas-filled microbubbles have become an important tool as ultrasound contrast agents. In recent years, ultrasound-targeted microbubble destruction (UTMD) has evolved into a new tool for organ-specific gene and drug delivery. Although many studies have been performed in well-perfused target organs such as the heart or kidney, no study has yet investigated the feasibility of UTMD for delivery of bioactive substances in the testis. Thus, the aim of this study was to determine whether UTMD is a feasible and safe technique to deliver a reporter protein to the testes. METHODS: Different groups of rats received 2 microg of luciferase protein at varying protocols. One group received luciferase-loaded microbubbles infused intravenously while ultrasound was applied to the right testis. Another group received luciferase without microbubbles but with ultrasound applied to the right testis. Protein uptake was quantified by luciferase assay. Also, to rule out UTMD-induced damage, the testes were analyzed histologically. RESULTS: The testes that received ultrasound and luciferase-loaded microbubbles showed about twofold greater luciferase activity compared with testes without ultrasound or without microbubbles. No hemorrhage or microscopic damage was detected. CONCLUSIONS: The results of our study have shown that UTMD is a safe and feasible technique to augment delivery of bioactive substances to the testes.