Ultrasound Enhances Gene Delivery of Human Factor IX Plasmid

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Abstract
Delivery of plasmid DNA can be enhanced by treatment with ultrasound (US); acoustic cavitation appears to play an important role in the process. Ultrasound contrast agents (UCAs; stabilized microbubbles) nucleate acoustic cavitation, and lower the acoustic pressure threshold for inertial cavitation occurrence. Fifty micrograms of a liver-specific, high-expressing human factor IX plasmid, pBS-HCRHP-FIXIA, mixed with UCA or phosphate-buffered saline was delivered to mouse livers by intrahepatic injection, with simultaneous exposure to 1 MHz-pulsed US using various acoustic protocols. Variable pulse duration (PD) at constant treatment time, pulse repetition frequency, and an acoustic peak negative pressure amplitude of 1.8 MPa produced 2- to 13-fold enhancements in hFIX gene expression, but PD was not a strong determinant. In contrast, a dose–response relationship was demonstrated for the peak negative pressure (P−), with significant enhancement of gene transduction at P− ≥ 2 MPa. Up to 63 ng/ml (approaching the therapeutic range for treating hemophilia patients) could be achieved by transducing one liver lobe at 4-MPa P−, corresponding to a 66- fold increment relative to treatment with naked DNA alone. Under the same conditions, mouse livers could also be transduced with a GFP plasmid. Histology showed transient liver damage caused by intrahepatic injection and US exposure at 4-MPa P−; however, the damage was repaired in a few days. We conclude that therapeutic US in combination with UCA has the potential to promote safe and efficient nonviral gene transfer of hFIX for the treatment of hemophilia.