Development of a high-throughput molecular delivery method using microbubbles and ultrasound and its application to cancer gene therapy

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Non-invasive, tissue-specific molecular delivery is crucial for the efficiency and reduced side effects of a wide range of treatments. A physical method that combines microbubbles (MB) with ultrasound (US) has been regarded as one of the few methods capable of delivering genes into target sites non-invasively. Applied to cancer gene therapy, this method could efficiently target cancer, and may be more efficient than immune gene therapy, as patients are often immunocompromised. However, several essential aspects remain unexplored. First, cavitation bubbles are believed to be a major cause for molecular delivery; however, the relation between wave characteristics and subsequent generation and collapse of cavitation bubbles has not been elucidated, therefore gene transfer has not been optimized. In addition, molecular delivery and subsequent gene expression have not been quantified in vivo. In the present study, these parameters in vitro and in vivo were optimized, and the mechanism of mo … More lecular delivery with theoretical and computer analysis were elucidated. Hypothesizing that free cavitation bubbles were generated from cavitation nuclei created by fragmented MB shells, we estimated the shock wave propagation distance that would induce cell membrane damage from the center of the cavitation bubble. Next, we investigated the structural change of a phospholipid bilayer in water under the action of a shock wave with molecular dynamics simulations. The resulting collapse and rebound of the bilayer followed by the penetration of water molecules into the hydrophobic region of the bilayer induced after the shock wave interaction were demonstrated. Finally, we evaluated the application of this technology to cancer gene therapy using herpes simplex virus thymidine kinase-mediated suicide gene therapy. We observed dramatic reductions of the tumor size by US/MB-mediated transfer. These data demonstrate the potential of US/MB as a new physical gene delivery method for cancer gene therapy. Less