5 Acknowledgements
3.3 Cellular Uptake Studies
Figure 3. Reversal of zeta potential with addition of successive polyelectrolyte layers. (n=6, error bars represent standard deviations).
3.3 Cellular Uptake Studies
Cellular uptake of double‐chambered nanoparticles by MDCK cells was qualitatively investigated employing confocal fluorescence imaging as shown in Figure 4. Images were recorded in 3 channels: the blue channel (DAPI) shows cell nuclei covering the slide. The green channel shows fluorescence signal of Flu, which is the signal of the model small molecule loaded in the core (inner chamber). The red channel shows the fluorescence signal of Lys‐RhD, which is the signal of the
model labelled protein loaded in the outer LbL layer (external chamber). Figure 4 shows a gallery of confocal images in which (a) to (g) represent progressive sections from the top downwards throughout the cell layer thickness, each spaced by 1 µm. Obvious fluorescence signal in the perinuclear region in both green and red channels indicate particle uptake. Going through stacks from (a) to (g) shows stronger signals in the mid focal planes, clearly pointing out that particles were internalized and not only adsorbed at the cell surface. Furthermore, by overlaying both fluorescent channels, we observed that fluorescent spots are superimposed, as evident by the appearance of yellow color, indicating co‐localization of both compounds into same cells.
Moreover, the particles appear to aggregate in an intracellular compartment, some appear sharply defined, some appear more diffused indicating that some particles already started releasing the compounds intracellularly after 4h of incubation.
Figure 4. Confocal laser scanning microscopy images showing progressive sections from the top downwards at 1 µm intervals (a)‐(g). Scale bar indicates 20 µm.
4 Conclusions
In this report, a simple and time‐efficient method for LbL deposition is described, resolving issues related to coating of small charged nanoparticles. The new method depends on the use of concentration tubes to remove excess liquid instead of particle precipitation, especially advantageous when charged nanocores (e.g., PLGA nanoparticles) tend to aggregate under high centrifugation speeds. This method was used to develop a double chambered nanocarrier system capable of carrying two different species of model compounds, a protein and a small molecule, in 2 defined and separated compartments. The produced particles were shown to be internalized by MDCK cells. This LbL technique allows the coating of many types of delicate cores and opens the door for more versatile applications of this technology.
5 References
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Final Conclusions and Outlook
Layer‐by‐Layer technology (LbL), a technique based on the deposition of oppositely charged polyelectrolytes layer‐wise on the surface of interest, has gained increasing interest in the field of drug delivery. The presented work in this thesis explores new applications for Layer‐by‐Layer (LbL) technology in the field of controlled protein delivery. The basic motives for these studies were the protein‐friendly mild formulation conditions where only aqueous solutions are used, in contrast to organic solvents typically employed in the fabrication of many other protein formulations, thus correct protein folding and activity are preserved.
In the first chapter, LbL structures encapsulating enzymes as a representative of functional proteins were reviewed. We could show the versatility and flexibility of the technology and the different added values it brings to the formulation such as; increased stability, response control functionality and sequential action when loading 2 different enzymes. In addition, special attention was paid to show different common techniques used to characterize LbL structures, such as studying layer deposition by UV absorbance and quartz crystal microbalance (QCM), showing charge reversal using zeta potential measurements, and different imaging techniques like scanning electron microscopy (SEM), atomic force microscopy (AFM) beside several enzyme‐specific activity tests.
The second chapter reviews the use of biopolymer‐based delivery systems as carriers for intracellular delivery of siRNA molecules into target cells. The recent progress in polymer science led to a paradigm shift where biopolymers are not feared to suffer from poorly controlled and irreproducible properties as they used to be, allowing to obtain pharma grade biopolymers. Several biopolymers and modified biopolymers of interesting biocompatibility and/or biodegradability were discussed as vectors for siRNA delivery. The biocompatibility, high tolerability and versatility of these biopolymers are the main driving forces behind the interest of many scientific groups in biopolymer‐based delivery systems. However, progress to clinical trials is still significantly delayed.
In our point of view, the most important unmet challenge is efficient delivery of siRNA cargo intracellularly to target cells, at sufficient doses needed for optimal effect. This should be preferably done by systemic administration and with a sustained mode of action as the patient in a real word setting cannot tolerate frequent injections.
In the third chapter, the feasibility of LbL coatings to sustain the release of a model protein (lysozyme) from microspheres was studied. LbL coating was composed of chondroitin sulfate as a negatively charged polyelectrolyte and a biocompatible, hydrolytically degradable poly β‐amino
ester as a positively charged polyelectrolyte. Lys was loaded effectively on hydrogel microspheres achieving about 9mg protein/100 mg wet spheres. Fluorescence imaging showed that lysozyme was adsorbed homogenously on the microspheres surface. After loading, a series of LbL coatings of different thicknesses were deposited and proved by reversal of zeta potential after each layer deposition. In vitro release studies showed sustained release profiles that depend on the thickness of the deposited coat, with t50% extended from 4.9h to 143.9h. More importantly, released Lys possessed a high degree of biological activity during the course of release maintaining at least 72%
of initial activity.
These results were motivating to move from model protein into a real protein case. The presented work in the fourth chapter investigates the feasibility of loading the clinically used embolic beads (DC Bead®) with Bevacizumab (BEV), an anti‐VEGF antibody, and control its release kinetics via Layer‐by‐Layer (LbL) coating. This strategy has the aim to achieve high, localized and sustained concentrations of BEV at the tumor site and reduce drug exposure in the systemic circulation. High loading of BEV on lyophilized beads of about 76 mg BEV / DC Bead vial was achieved. LbL coating was carried out by depositing alternating layers of the biocompatible polymers alginate and poly‐L‐
lysine. Coating was proven successful by monitoring the reversal of zeta potential after addition of each layer. Morphological changes of the bead surface before and after coating were illustrated using SEM imaging. Moreover, release profiles from different formulations were studied and results showed that optimizing the number of deposited layers effectively slows the release of BEV for three days. Activity of released BEV was studied in different 2D and 3D cell based assays.
Interestingly, released BEV fractions showed comparable activity to fresh BEV solution used as control after 3 days.
The fifth chapter tackles the issue of co‐delivery of a protein and a small molecule drug into target cells. The preparation of a novel double chambered, nanoparticulate system is described, applying a simple and less time‐consuming LbL fabrication method using concentration tubes. Small poly lactide‐co‐glycolide (PLGA) nanoparticles loaded with fluorescein base as a model small hydrophobic molecule, represents the “internal chamber” while the “external chamber” is formed of alternating polyelectrolyte layers containing lysozyme as a model protein. These nanocarriers were taken up by MDCK cells in vitro, where a co‐localization of both model compounds was shown by confocal imaging.
To conclude, LbL technology provides an interesting option for controlling the release of active biologicals from coated surfaces while retaining their activity. The presented work in this thesis lays the foundation and provides a proof of concept that should to be taken further on. Some major questions are still unanswered concerning the interaction between the drug and the layers, the layers and beads surface and how these interactions control the release of the drug which is apparently a process controlled by several factors. In addition, in vivo studies should be launched to examine the behaviour of LbL formulations in biological systems. However, a major challenge is developing a better production technique that enables large scale production of LbL structures. The current used processes depend mainly on successive cycles of suspension/centrifugation/
resuspension, which makes the production time too lengthy. In addition, the large volumes needed and wasted during production is quite a challenge.
Working in the field of chemoembolization for about 3 years granted me a considerable amount of knowledge that I aim to build on in the years to come. Apart from my PhD project herein described, I developed a pharmaceutical formulation to face the challenge of loading water insoluble drugs to embolic beads which is not doable using current technology. The formulation underwent several in vitro investigations and was proven to be promising enough to win the University of Geneva Innogap Award of novel product design (July 2014). This formulation depends greatly on lessons learned during my work in the field of LbL technology. More research and investigations are due to take this product to clinical trials. Interestingly, the case of this formulation product won the “Best Business Concept Award” in the CTI competition (May 2015). Results of this work have not be added to my thesis due to the ongoing patenting process.
Résumé
La technologie d’assemblage couche‐par‐couche (LbL) est une technique basée sur le dépôt de polyélectrolytes de charges opposées par couches sur une surface d’intérêt. Celle‐ci a rencontré un intérêt croissant dans le domaine de l’administration des médicaments. Le travail présenté dans cette thèse explore de nouvelles applications de la technique d’assemblage couche par couche (LbL) dans le domaine du relargage contrôlé de protéines. Une motivation pour ces études était les conditions douces de formulations de protéines, où seulement des solutions aqueuses sont utilisées, évitant les solvants organiques employés lors de la fabrication de multiples autres formulations de protéines. De cette manière, le repliement correct et l’activité des protéines sont préservés.
Dans le premier chapitre, nous présentons une revue du domaine de cette technologie couche‐par‐
couche (LbL) en termes de structures d’encapsulation d’enzymes comme modèles de protéines fonctionnelles. Nous avons pu montrer la polyvalence et la flexibilité de cette technologie et les différentes valeurs ajoutées qu’elle apporte à la formulation telle qu’une stabilité accrue, un contrôle de la réponse et une libération séquentielle lors du chargement de deux enzymes différentes. En outre, une attention particulière a été accordée pour présenter les différentes techniques courantes utilisées pour caractériser les structures multicouches, telles que l’étude de dépôt de couches par absorption UV et microbalance à quartz (QCM), la caractérisation d’une inversion de charge au cours du dépôt LbL en utilisant des mesures de potential zêta, ou différentes techniques d’imagerie telles que la microscopie électronique à balayage (SEM), la microscopie à force atomique (AFM) ainsi que plusieurs tests d’activité spécifiques à une enzyme.
Le second chapitre passe en revue l’utilisation de systèmes d’administration à base de biopolymères destinés à l’administration intracellulaire de molécules siARN dans des cellules‐cibles.
Les progrès récents en science des polymères ont conduit à un changement de paradigme, selon lequel on ne craint plus que les biopolymères souffrent de propriétés mal définies et peu reproductibles, comme auparavant, permettant ainsi d’obtenir des biopolymères de qualité pharmaceutique. Plusieurs biopolymères, modifiés ou non, possédant des propriétés de biocompatibilité et biodégradabilité d’intérêt, sont discutés en tant que vecteurs pour l’administration de siARN. La biocompatibilité, une haute tolérabilité ainsi que la polyvalence de ces biopolymères sont les principaux moteurs de l’intérêt que de nombreux groupes scientifiques portent à ce type de système d’administration. Toutefois, la progression vers des essais cliniques continue d’être retardée de façon significative. De notre point de vue, le plus important défi qui