Polyplex-microbubble hybrids for ultrasound-guided plasmid DNA delivery to solid tumors

J Control Release. 2012 Jan 30;157(2):224-34. doi: 10.1016/j.jconrel.2011.09.071. Epub 2011 Sep 17.


Microbubble ultrasound contrast agents are being developed as image-guided gene carriers for targeted delivery in vivo. In this study, novel polyplex-microbubbles were synthesized, characterized and evaluated for systemic circulation and tumor transfection. Branched polyethylenimine (PEI; 25 kDa) was modified with polyethylene glycol (PEG; 5 kDa), thiolated and covalently attached to maleimide groups on lipid-coated microbubbles. The PEI-microbubbles demonstrated increasingly positive surface charge and DNA loading capacity with increasing maleimide content. The in vivo ultrasound contrast persistence of PEI-microbubbles was measured in the healthy mouse kidney, and a two-compartment pharmacokinetic model accounting for free and adherent microbubbles was developed to describe the anomalous time-intensity curves. The model suggested that PEI loading dramatically reduced free circulation and increased nonspecific adhesion to the vasculature. However, DNA loading to form polyplex-microbubbles increased circulation in the bloodstream and decreased nonspecific adhesion. PEI-microbubbles coupled to a luciferase bioluminescence reporter plasmid DNA were shown to transfect tumors implanted in the mouse kidney. Site-specific delivery was achieved using ultrasound applied over the tumor area following bolus injection of the DNA/PEI-microbubbles. In vivo imaging showed over 10-fold higher bioluminescence from the tumor region compared to untreated tissue. Ex vivo analysis of excised tumors showed greater than 40-fold higher expression in tumor tissue than non-sonicated control (heart) tissue. These results suggest that the polyplex-microbubble platform offers improved control of DNA loading and packaging suitable for ultrasound-guided tissue transfection.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line, Tumor
  • Contrast Media / chemistry
  • Contrast Media / pharmacokinetics*
  • DNA / administration & dosage
  • DNA / pharmacokinetics
  • Female
  • Gene Transfer Techniques*
  • Humans
  • Kidney / diagnostic imaging
  • Kidney / metabolism
  • Maleimides / chemistry
  • Maleimides / pharmacokinetics*
  • Mice
  • Mice, Nude
  • Microbubbles*
  • Neoplasms / diagnostic imaging*
  • Neoplasms / metabolism
  • Plasmids
  • Polyethylene Glycols / chemistry
  • Polyethyleneimine / chemistry
  • Polyethyleneimine / pharmacokinetics*
  • Ultrasonography


  • Contrast Media
  • Maleimides
  • Polyethylene Glycols
  • Polyethyleneimine
  • DNA