A polymeric microbubble platform for ultrasound-mediated drug delivery

• Eine polymere Mikrobläschen Plattform für den Ultraschall vermittelten Wirkstofftransport

Appold, Lia; Pich, Andrij (Thesis advisor); Lammers, Twan (Thesis advisor); Elling, Lothar (Thesis advisor)

Aachen (2018, 2019)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2018

Abstract

In this dissertation, I describe the synthesis and characterization of poly(butyl cyanoacrylate) (PBCA) microbubbles (MB), which were applied as ultrasound (US) contrast agents and drug delivery systems to tumors or across the blood brain barrier (BBB) in preclinical settings. The MB were prepared by an established protocol in one-batch synthesis, which comprised the polymerization of butyl cyanoacrylate in water at a pH of 2.5. The resulted PBCA polymer chains attached to each other due to hydrophobic interactions, thus forming a round shell, encapsulating air. Different synthesis parameters such as stirring time/speed, pH and surfactant were varied to evaluate their influence on the MB properties like size (distribution), molecular weight (distribution) of the PBCA chains, shell thickness, and acoustic properties. The physicochemical properties of MB were evaluated with various techniques: Coulter counter, dynamic light scattering (DLS), gel permeation chromatography (GPC), and electron/fluorescence microscopy. The results showed that stirring time had a high impact on MB size distribution, while pH and surfactant mainly influenced shell thickness and molecular weight of the PBCA chains. Acoustic properties were analyzed at different US frequencies and PBCA MB showed a better acoustic response at 5 MHz in the non-linear US mode compared to commercial micromarker lipid MB. For their in vitro and in vivo application, MB were functionalized by loading fluorescent dyes, iron oxide nanoparticles and drugs within the MB shell, or oxygen in the MB core and analyzed using spectroscopic and microscopic methods. The surface of the MB was modified using fluorescent dyes, PEG or peptides/proteins. Different peptides, targeting E-selectin (a cell adhesion molecule overexpressed on activated endothelial cells in several tumor types), were screened for their binding to endothelial cells. MB conjugated to the best binding peptide were tested in a flow-chamber and showed higher binding to activated HUVEC compared to control MB.MB loaded with the vascular targeting agent combretastatin A4 were tested for their sonoporation ability compared to standard MB in tumor bearing mice. For US and MB treatment, the extravasation of a co-injected fluorescently labeled polymer increased. The results show that MB can be efficiently used as targeted drug delivery system and for ultrasound and photoacoustic imaging.