Acoustically-active microbubbles conjugated to liposomes: Characterization of a proposed drug delivery vehicle

Abstract

A new acoustically-active delivery vehicle was developed by conjugating liposomes and microbubbles, using the high affinity interaction between avidin and biotin. Binding between microbubbles and liposomes each containing 5% DSPE-PEG2kBiotin was highly dependent on avidin concentration and observed above an avidin concentration of 10 nM. With an optimized avidin and liposome concentration, we measured and calculated as high as 1000 to 10,000 liposomes with average diameters of 200 and 100 nm, respectively, attached to each microbubble. Replacing avidin with neutravidin resulted in 3-fold higher binding, approaching the calculated saturation level. Highspeed photography of this new drug delivery vehicle demonstrated that the liposome-bearing microbubbles oscillate in response to an acoustic pulse similar to microbubble contrast agents. Additionally, microbubbles carrying liposomes could be spatially concentrated on a monolayer of PC-3 cells at the focal point of ultrasound beam. As a result of cell-vehicle contact, the liposomes fused with the cells and internalization of NBD-cholesterol occurred shortly after incubation at 37°C, with internalization of NBD-cholesterol substantially enhanced in the acoustic focus.

Driving delivery vehicles with ultrasound

“…The lipid shell expands, buckles and compresses with each acoustic cycle, recoating as needed to cover bubble fragments [27][28][29][30][31][32]. A thick layer of DNA can be applied to the surface or, alternatively, liposomes or other nanoparticles can be attached to the membrane, each enhancing the payload [16,33,34]. Protein and polymer-shelled microbubbles have also been functionalized to carry targeting ligands [35] and genetic payloads [36,37].…”

The role of ultrasound and magnetic resonance in local drug delivery

“…In this case the destruction of microbubbles leads to the release of the drug and ex-travasation of the drug due to the increased number of pores in the vasculature. Recent examples of this strategy are the delivery of the antisense androgen receptor oligodeoxynucleotide in vivo, resulting in inhibition of prostate tumor growth (79), and the use of a conjugation between microbubbles and liposomes carrying the payload (80). The feasibility of both strategies has been proven mainly by using (reporter) genes as payload (81)(82)(83).…”

Microbubbles coupled to methotrexate-loaded liposomes for ultrasound-mediated delivery of methotrexate across the blood–brain barrier

“…Efforts have been made to improve drug loading by incorporating phospholipids 20 or surfactants 21 into the shell, or coupling drug-loaded liposomes to the microbubble surface. 18,22 The latter approach takes full advantage of the high drug-loading capacity of liposomes and the ultrasound-mediated BBB disruption effect of microbubbles. For example, Lentacker et al 18 coupled doxorubicin-loaded liposomes to microbubbles via a biotin-avidin linkage.…”