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.

New doxorubicin-loaded phospholipid microbubbles for targeted tumor therapy: Part I--Formulation development and in-vitro characterization.

Despite high antitumor efficacy and a broad application spectrum, clinical treatment with anthracycline chemotherapeutics is often limited by severe adverse effects such as cardiotoxicity and myelosupression. In recent years, tumor drug targeting has evolved as a promising strategy to increase local drug concentration and reduce systemic side effects. One recent approach for targeting solid tumors is the application of microbubbles, loaded with chemotherapeutic drugs. These advanced drug carriers can be safely administered to the patient by intravenous infusion, and will circulate through the entire vasculature. Their drug load can be locally released by ultrasound targeted microbubble destruction. In addition, tumors can be precisely localized by diagnostic ultrasound since microbubbles act as contrast agents. In the present work a novel microbubble carrier for doxorubicin has been developed and characterized in-vitro. In contrast to many recent tumor-targeting MB designs the newly developed doxorubicin-loaded microbubbles possess a soft but stable phospholipid monolayer shell. Importantly, the active drug is embedded in the microbubble shell and is complexed to the phospholipids by both electrostatic and hydrophobic interactions. Despite their drug load, these novel microbubbles retained all important physical characteristics for ultrasound targeted microbubble destruction, comparable with the commercially available ultrasound contrast agents. In cell culture studies doxorubicin-loaded microbubbles in combination with ultrasound demonstrated an about 3 fold increase of the anti-proliferative activity compared to free doxorubicin and doxorubicin-loaded liposomes. For the first time in the literature the intracellular partition of free doxorubicin and phospholipid-complexed doxorubicin were compared. In conclusion, new doxorubicin-loaded microbubbles with ideal physical characteristics were developed. In-vitro studies show enhanced cytotoxic activity compared to free doxorubicin and doxorubicin-loaded liposomes.

New doxorubicin-loaded phospholipid microbubbles for targeted tumor therapy: in-vivo characterization.

Doxorubicin(DOX) is a potent chemotherapy drug that is often limited by severe adverse effects such as cardiac toxicity and myelosupression. Drug targeting with non invasive techniques would be desirable, aiming at increased local drug concentration and reduced systemic side effects. Ultrasound(US) targeted destruction of drug loaded microbubbles(MBs) has evolved as a promising strategy for non invasive local gene and drug delivery. A recently developed novel DOX-loaded microbubble (DOX-MB) formulation was previously tested in-vitro, with optimal DOX loading capacity, ideal physical characteristics and preserved antiproliferative efficacy. The aim of this study was to evaluate applicability and efficacy of DOX-loaded MBs in a pancreas carcinoma model of the rat. First, immediate toxicity was tested in rats ruling out in-vivo MB agglomeration/capillary adhesion with subsequent embolisation/occlusion of the pulmonary vasculature. In a second set of experiments, tumors derived from pancreas carcinomas were implanted in both flanks of Lewis rats. After establishing the tumors, DOX-MBs were administered intravenously while one of the two tumors was exposed to US (1.3 MHz; mechanical index 1.6). DOX tissue concentration was measured in tumors and control organs after the experiment. Finally, efficacy of US targeted destruction of DOX-MBs in tumors was studied, looking at tumor growth after two therapeutic applications. All rats survived the DOX-MB administration without any sign of embolisation/occlusion of the pulmonary vasculature. US targeted destruction of DOX-MBs leads to a 12-fold higher tissue concentration of DOX and a significantly lower tumor growth in the target tumor compared to the contralateral control tumor. In conclusion, novel DOX-loaded MBs can be safely administered to rats, leading to a relevant increase in local drug concentration and reduction in tumor growth.

Microbubbles as ultrasound triggered drug carriers.

Originally developed as contrast agents for ultrasound imaging and diagnostics, in the past years, microbubbles have made their way back from the patients' bedside to the researcher's laboratory. Microbubbles are currently believed to have great potential as carriers for drugs, small molecules, nucleic acids, and proteins. This review provides insight into this intriguing new frontier from the perspective of the pharmaceutical scientist. First, basic aspects on the application of ultrasound-targeted microbubble destruction for drug delivery will be presented. Next, we will review the recently applied approaches for manufacturing and drug-loading microbubbles. Important quality issues and characterization techniques for advanced microbubble formulation will be discussed. Finally, we will provide an assessment of the prospects for microbubbles in drug and gene therapy, illustrating the problems and requirements for their future development.