In vitro characterization of nanodrugs at model lipid membranes

Licentiate thesis, 2010

The use of nano-sized drug carriers to improve the efficiency of drug delivery has become well established during the past decades. New nanoparticle (NP) formulations for the administration of biopharmaceuticals (e.g. proteins and peptides) emerge at an increasing rate and the need for methods to evaluate their properties is expanding. Rational design of drug carriers requires understanding of their biophysical interactions with various biological barriers, e.g. cell membranes, mucus layers, or the blood brain barrier, since most carriers aim to deliver drugs across one or more of such barriers. The shape of NPs and the way they adhere to the cell membrane are important determinants for triggering of endocytosis. Another important NP parameter is their responsiveness to changes in the ambient environment when entering intracellular compartments e.g. the endosome or the cytosol. In this thesis, an in vitro screening platform for studying of NP – lipid membrane interaction is presented and used to characterize insulin-loaded polymeric NPs with respect to their interaction with differently charged supported lipid bilayers. By combining different surface sensitive techniques (quartz crystal microbalance with dissipation monitoring, reflectometry, and atomic force microscopy), structural properties of nano-sized polyelectrolyte complexes upon adsorption to model membranes were studied. From the results it is clear that electrostatic forces are important for the outcome of the NP-lipid membrane adsorption process. Polyelectrolyte complexes, which are non covalent assemblies of oppositely charged polyions, adopted different shapes on different membranes. Upon strong electrostatic attraction between the NPs and the membrane, NPs collapsed into a thin layer on top of an oppositely charged model membrane. This rearrangement process is potentially unfavorable for uptake into epithelial cells through endocytosis. NPs based on polymers with disulfide linkages in the polymer backbone were responsive to reducing agents. This property was shown by exposing membrane-adsorbed bioreducible poly(amido amine) based polyelectrolyte complexes to glutathione, mimicking an intracellular reductive environment. Similarly, the responsiveness of the NPs towards a decrease in ambient pH, mimicking the low pH in the late endosome, was shown. These results show the application of an experimental platform based on engineered supported lipid membranes and surface sensitive analytical techniques to evaluate drug carriers with respect to their membrane interactions as well as their responsiveness. The information gained from screening of novel drug carries gives important guidance during the process of design and development. An important next step in the development of the presented platform will be to establish a correlation to in vitro cell culture assays. NPs for other purposes could also be evaluated.