The correlation between acoustic cavitation and sonoporation involved in ultrasound-mediated DNA transfection with polyethylenimine (PEI) in vitro

Previous studies have demonstrated that the efficiency of gene/drug delivery can be enhanced under ultrasound (US) exposure with the presence of US contrast agent microbubbles, due to the acoustic cavitation-induced sonoporation. However, obstacles still remain to achieve controllable sonoporation outcome. The general hypotheses guiding present studies were that inertial cavitation (IC) activities accumulated during US exposure could be quantified as IC dose (ICD) based on passive cavitation detection (PCD), and the assessment of sonoporation outcome should be correlated with ICD measurements. In current work, MCF-7 cells mixed with PEI:DNA complex and UCD microbubbles were exposed to 1-MHz US pulses with 20-cycle pulse and varied acoustic peak negative pressure (P-; 0 (sham), 0.3, 0.75, 1.4, 2.2 or 3.0 MPa), total treatment time (0, 5, 10, 20, 40 or 60 s), and pulse-repetition-frequency (PRF; 0, 20, 100, 250, 500, or 1000 Hz). Then, four series experiments were conducted: (1) the IC activities were detected using a PCD system and quantified as ICD; (2) the DNA transfection efficiency was evaluated with flow cytometry; (3) the cell viability was examined by PI dying then measured using flow cytometry; and (4) scan electron microscopy was used to investigate the sonoporation effects on the cell membrane. The results showed that: (1) the ICD generated during US exposure could be affected by US parameters (e.g., P-, total treatment time, and PRF); (2) the pooled data analyses demonstrated that DNA transfection efficiency initially increased linearly with the increasing ICD, then it tended to saturate instead of trying to achieve a maximum value while the ICD kept going up; and (3) the measured ICD, sonoporation pore size, and cell viability exhibited high correlation among each other. All the results indicated that IC activity should play an important role in the US-mediated DNA transfection through sonoporation, and ICD could be used as an effective tool to monitor and control the US-mediated gene/drug delivery effect. (C) 2010 Elsevier B.V. All rights reserved.