QCM-D Investigations on Cholesterol–DNA Tethering of Liposomes to Microbubbles for Therapy

Abstract

Lipid-shelled microbubbles (MBs) offer potential as theranostic agents, capable of providing both contrast enhancement in ultrasound imaging as well as a route for triggered drug release and improved localized drug delivery. A common motif in the design of such therapeutic vehicles is the attachment of the drug carrier, often in the form of liposomes, to the microbubble. Traditionally, such attachments have been based around biotin−streptavidin and maleimide−PDP chemistries. Comparatively, the use of DNA−lipid tethers offers potential advantage. First, their specificity permits the construction of more complex architectures that might include bespoke combinations of different drugloaded liposomes and/or targeting groups, such as affimers or antibodies. Second, the use of dual-lipid tether strategies should increase the strength of the individual tethers tethering the liposomes to the bubbles. The ability of cholesterol−DNA (cDNA) tethers for conjugation of liposomes to supported lipid bilayers has previously been demonstrated. For in vivo applications, bubbles and liposomes often contain a proportion of polyethylene glycol (PEG) to promote stealth-like properties and increase lifetimes. However, the associated steric effects may hinder tethering of the drug payload. We show that while the presence of PEG reduced the tethering affinity, cDNA can still be used for the attachment of liposomes to a supported lipid bilayer (SLB) as measured via QCM-D. Importantly, we show, for the first time, that QCM-D can be used to study the tethering of microbubbles to SLBs using cDNA, signified by a decrease in the magnitude of the frequency shift compared to liposomes alone due to the reduced density of the MBs. We then replicate this tethering interaction in the bulk and observe attachment of liposomes to the shell of a central MB and hence formation of a model therapeutic microbubble.

Maleimide–Thiol Linkages Alter the Biodistribution of SN38 Therapeutic Microbubbles Compared to Biotin–Avidin While Preserving Parity in Tumoral Drug Delivery

“…In addition, the VEGFR2 target is on the tumour vasculature so much more easily accessible to vascular contrast agents compared to antibody drug conjugates that need time to extravasate from blood vessels deep into tissue. However, any free-flowing liposomes attached to VEGFR2 antibody (and lipids from a dissipated liposome) may require longer-term linkages to allow further uptake via endocytosis and other methods that would have rapid clinical translation are being investigated [ 28 ]. Although this study has shown equivalence of thMB binding in vitro, this could be further defined in vivo using flash-replenishment studies [ 7 ].…”

Physicochemical Features and Applicability of Newly Fabricated Phytopharmaceutical‐Loaded Hydrogel Alginate Microcarriers with Viscoelastic Polyelectrolyte Coatings

“…Applying QCM−D provides the measurement of PE mass adsorbed on the crystal surface. The high sensitivity of the QCM−D device allows for monitoring of the formation of PE films in time [31,32] . It permits an understanding of the mechanism of PE film deposition and gives an insight into the composition and internal structure of the resulting coatings by studying the adsorption behaviour of PE layers, their growth, viscoelastic properties, as well as the interactions between deposited PEs.…”

“…The high sensitivity of the QCMÀ D device allows for monitoring of the formation of PE films in time. [31,32] It permits an understanding of the mechanism of PE film deposition and gives an insight into the composition and internal structure of the resulting coatings by studying the adsorption behaviour of PE layers, their growth, viscoelastic properties, as well as the interactions between deposited PEs. Simultaneous monitoring of the oscillation frequency ( ~f) changes of quartz crystal and the dissipated energy ( ~D) offers an insight into the multilayer assembly and structural features of the PE films.…”

Microfluidic fabrication of monodisperse microcapsules with gas cores

“…To date, several methods have been developed for preparing gas-core microcarriers, mainly including stirring emulsification, 10,[32][33][34] ultrasonic emulsification 3 and microfluidic emulsification. 7,[35][36][37] The stirring emulsification and ultrasonic emulsification methods mainly use mechanical stirring or ultrasound to mix a gas with a liposome solution, and then form liposome microstructures that encapsulate microbubbles.…”