Investigations of microbubble-cell interactions during the sonoporation process

International audienceUltrasound (US) stimulation coupled to gaseous microbubbles (MB) is a new technique for efficient drug/gene delivery. Upon US exposure, MBs can be expanded, moved and even destroyed. These properties offer the opportunity of site-specific local drug delivery.A key to success of this technique lies in understanding mechanisms governing microbubble- cells interactions. Several studies suggest that pore formation is less likely to be the dominant mechanism. However, recent data have suggested that endocytosis mechanisms might also be in- volved. Real time experiments of sonoporation were performed to investigate how MB behaves towards cells, under optimal conditions that allow an efficient gene transfer. Studies have been done with a specific experimental set-up combining a CCD of a PHOTRON FastCam MC-2.1 high-speed camera connected to LSM 500 META Zeiss fluorescence confocal microscope. The transducer was placed in a custom-built sonoporation chamber mounted on the confocal microscopy. Bubbles and plasmid encoding the gene of interest (pDNA) were fluorescent-labelled. Our data showed that small size bubbles were pushed and entered the cell during the sonoporation processes. Optical sec- tions of the cell support this entry. The intracellular fate of MB and pDNA following sonoporation was investigated by confocal microscopy investigations on cells that express different fluorescent markers of cellular compartments. We observed that molecule with large size as pDNA (3 MDa) was mainly localized close at plasma membrane straightaway following insonation. At later time, punctuate staining like vesicles were progressively moved towards the nucleus. They were localized in late endosomes 3h post insonation and very few reached the nucleus after 6h. We are currently investigating if there is a specific plasma membrane area that is prone to be destabilized by sono- poration. Data emerging from these different studies will allow specifying limitations of US assist- ed MB delivery and to fine tune MB composition for gene delivery