Gene therapy, particularly microRNA (miRNA), is a promising candidate in the treatment of cancer; however, it is challenging to develop gene delivery systems. Ultrasound microbubbles have been used for gene delivery with excellent results. The present study aimed to investigate the transfection efficiency of HepG2 cells using ultrasound microbubbles. The effects of three miRNAs (miR-21, miR-221 and miR-199a) on HepG2 cells were also determined by performing ultrasound microbubble-mediated gene transfection. Three recombinant plasmids containing anti-miR-21, anti-miR-221 and miR-199a were fused with enhanced green fluorescent protein. For the transfection of genes, the type of contrast agent, the concentration of microbubble contrast agent and the exposure intensity of ultrasound were optimized. The expression of miRNAs was detected using reverse transcription-polymerase chain reaction. To determine the effect of anti-miR-21, anti-miR-221 and miR-199a on HepG2 cells, MTT, cell cycle analysis and Annexin V-PE/7-ADD apoptosis assays were performed. The optimal condition was 10% sulfur hexafluoride microbubbles at an ultrasound frequency of 2.0 MHz and mechanical index of 0.28. When cells were transfected with three recombinant plasmids using ultrasound microbubbles, there was significant downregulation of miR-21 and miR-221 and upregulation of miR-199a (P<0.05). All three treatments inhibited cell proliferation and promoted the apoptosis of cells. The present data indicated that the delivery of anti-miR-21, anti-miR-221 and miR-199a may be mediated by ultrasound microbubble contrast agents. With this approach, cell proliferation may be effectively inhibited and cell apoptosis may be induced. These are novel cancer therapy targets.
Keywords: apoptosis; gene delivery; microRNA; ultrasound microbubbles.