title: Polyplex-microbubble hybrids for ultrasound-guided plasmid DNA delivery to solid tumors.
abstract: 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.
authors.affiliation: Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Shashank R
authors.initials: SR
authors.lastname: Sirsi
authors.forename: Sonia L
authors.initials: SL
authors.lastname: Hernandez
authors.forename: Lukasz
authors.initials: L
authors.lastname: Zielinski
authors.forename: Henning
authors.initials: H
authors.lastname: Blomback
authors.forename: Adel
authors.initials: A
authors.lastname: Koubaa
authors.forename: Milo
authors.initials: M
authors.lastname: Synder
authors.forename: Shunichi
authors.initials: S
authors.lastname: Homma
authors.forename: Jessica J
authors.initials: JJ
authors.lastname: Kandel
authors.forename: Darrell J
authors.initials: DJ
authors.lastname: Yamashiro
authors.forename: Mark A
authors.initials: MA
authors.lastname: Borden
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D003287:Contrast Media / Q000737:chemistry / Q000493:pharmacokinetics*; D004247:DNA / Q000008:administration & dosage / Q000493:pharmacokinetics; D005260:Female; D018014:Gene Transfer Techniques; D006801:Humans; D007668:Kidney / Q000000981:diagnostic imaging / Q000378:metabolism; D008301:Maleimides / Q000737:chemistry / Q000493:pharmacokinetics*; D051379:Mice; D008819:Mice, Nude; D045423:Microbubbles; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism; D010957:Plasmids; D011092:Polyethylene Glycols / Q000737:chemistry; D011094:Polyethyleneimine / Q000737:chemistry / Q000493:pharmacokinetics*; D014463:Ultrasonography
chemical_list: D003287:Contrast Media; D008301:Maleimides; D011092:Polyethylene Glycols; D011094:Polyethyleneimine; D004247:DNA