A Novel Cationic Microbubble Coated with Stearic Acid-Modified Polyethylenimine to Enhance DNA Loading and Gene Delivery by Ultrasound

A novel cationic microbubble (MB) for improvement of the DNA loading capacity and the ultrasound-mediated gene delivery efficiency has been developed; it has been prepared with commercial lipids and a stearic acid modified polyethylenimine 600 (Stearic-PEI600) polymer synthesized via acylation reaction of branched PEI600 and stearic acid mediated by N, N'-carbonyldiimidazole (CDI). The MBs' concentration, size distribution, stability and zeta potential (ζ-potential) were measured and the DNA loading capacity was examined as a function of the amount of Stearic-PEI600. The gene transfection efficiency and cytotoxicity were also examined using breast cancer MCF-7 cells via the reporter plasmid pCMV-Luc, encoding the firefly luciferase gene. The results showed that the Stearic-PEI600 polymer caused a significant increase in magnitude of ζ-potential of MBs. The addition of DNA into cationic MBs can shift ζ-potentials from positive to negative values. The DNA loading capacity of the MBs grew linearly from (5±0.2) ×10⁻³ pg/µm² to (20±1.8) ×10⁻³ pg/µm² when Stearic-PEI600 was increased from 5 mol% to 30 mol%. Transfection of MCF-7 cells using 5% PEI600 MBs plus ultrasound exposure yielded 5.76±2.58×10³ p/s/cm²/sr average radiance intensity, was 8.97- and 7.53-fold higher than those treated with plain MBs plus ultrasound (6.41±5.82) ×10² p/s/cm²/sr, (P<0.01) and PEI600 MBs without ultrasound (7.65±6.18) ×10² p/s/cm²/sr, (P<0.01), respectively. However, the PEI600 MBs showed slightly higher cytotoxicity than plain MBs. The cells treated with PEI600-MBs and plain MBs plus ultrasound showed 59.5±6.1% and 71.4±7.1% cell viability, respectively. In conclusion, our study demonstrated that the novel cationic MBs were able to increase DNA loading capacity and gene transfection efficiency and could be potentially applied in targeted gene delivery and therapy.