Intracellular delivery of Bak BH3 peptide by microbubble-enhanced ultrasound

Purpose To investigate the possibility of intracellular delivery of Bak BH3 peptide using sonoporation effect by microbubble-enhanced ultrasound. Methods HeLa and BJAB cells were exposed to 1.696-Mhz focused ultrasound with 2% microbubble contrast agents (OPTISON (R)). Cell- impermeable calcein was used as an indicator for successful sonoporation, and propidium iodide staining was used for cell viability assessment. Peptides were also exposed to ultrasound with OPTISON (R) and analyzed with mass spectrometry for evaluation of stability under ultrasound exposure. The effect of transduced Bak BH3 peptide was evaluated by the cell viability of successfully sonoporated cells. Results Bak BH3 peptides did not undergo mechanical degradation with microbubble-enhanced ultrasound exposure. With the increase of acoustic energy exposure, the sonoporation efficiency saturated both in BJAB and HeLa cells, while direct cell death rate by ultrasound exposure tended to increase. When BJAB cells were treated with 100 mu M Bak BH3 peptides, and ultrasound exposure with ultrasound contrast agents (OPTISON (R)), an increased 35% cell death was confirmed. On the other hand, although HeLa cells had a similar trend, they failed to exhibit statistical significance. Conclusions Our results suggest that microbubble-enhanced focused ultrasound peptide transduction is possible. Further optimization of ultrasound exposure conditions may be necessary.