Heteromultivalent Nanoparticles for Selective Targeting of Renal Cells

Maximizing drug concentration at the site of disease while minimizing undesiredsystemic drug effects is regarded the ideal conception for pharmacotherapy. This is of particular importance when the therapeutic target is confined to a defined tissue which is the case for various cancers, vitreoretinal diseases or diabetic nephropathy. Targeted drug delivery is widely regarded the most potent tool to make this vision come true (Chapter 1). In particular, polymeric nanoparticles (NPs) have tremendous potential for targeted delivery as they are biocompatible, degradable and possess unique and highly tunable physicochemical properties. However, their bench to bedside transition proceeds slowly which is attributed to several limiting factors: (1) lack of manufacturing platforms that allow for a controlled and scalable synthesis, (2) inadequate knowledge of events at the nano bio interface both in vitro and in vivo, (3) the limited understanding of their fate in the body due to their poor detectability in biological environments, (4) incomplete knowledge of critical targeting factors, and (5) insufficient selectivity and efficiency of targeted NPs in vivo. The aim of this work was to design and characterize core/shell structured multivalent polymeric NPs intended for selective targeting of mesangial cells with special focus on addressing the abovementioned challenges. The development of therapeutic colloids intended for selective targeting requires the precise control of NP attributes. Particle size is widely considered a key factor since it determines the interfacial contact area and therefore, has a major impact on multivalent binding to target cells. In Chapter 3, microfluidic synthesis of multicomponent polymeric colloids was evaluated and compared to bulk nanoprecipitation, which is considered the gold standard in the field. It was found that nanoprecipitation generally results in formation of larger particles with a wide size distribution, whereas microfluidic synthesis allowed for the manufacturing of highly monodisperse NPs of defined size. The majority of efforts in the area of polymeric nanocarriers is aimed at providing controlled drug delivery in vivo. Therefore, it is essential to understand the delicate interplay of polymeric NPs with serum proteins. In Chapter 4, the impact of particle charge (negative, positive, zwitterionic) and hydrophobicity (non-charged) on the interaction with serum proteins was studied. Due to strong attractive electrostatic interactions, positively charged NPs formed the most distinct protein corona, followed by uncharged and negatively charged NPs, and finally zwitterionic NPs with the lowest amount of deposited protein. This enhanced interaction with serum proteins significantly impaired the colloidal integrity because the lipophilic cargo was continuously leached out of the hydrophobic NP core. Surface functionalization with high-affinity ligands is commonly considered the major determinant for controlling the uptake efficiency in vitro and in vivo. However, it is often not sufficiently taken into consideration that cellular uptake of targeted colloids is governed by a complex interplay between different particle features. In Chapter 5, the combinational influence of ligand density and linker length on the specific receptor binding was investigated. When NPs with complete surface functionalization and short versus long linkers were compared, short poly(ethylene glycol) PEG chains displayed a significantly higher tendency to form colloidal clusters which facilitated cooperative binding to integrin receptors on the cell membrane. In contrast, the use of longer and more flexible PEG chains enhanced the chance of ligand shrouding which significantly impeded ligand-receptor interactions. There are numerous examples where nature has inspired researchers to create high performance materials for medicine, engineering and other fields. For targeted delivery, viruses could serve as blueprints to optimize selective targeting of NPs. To mimic the binding sequence of viruses and utilize this selective targeting strategy for the treatment of renal diseases, polymeric core/shell structured nanocarriers were surface-decorated with two mesangial cell-specific targeting ligands. In this system, the primary ligand (AT1R blocker) was used for the first recognition of the target cell via binding to the AT1R, whereas the secondary ligand (cRGD) was initially “invisible” for the cell and interacted with the secondary receptor (avβ3 integrin) in a time-shifted manner and triggered endocytosis. In contrast to NPs decorated with a single type of targeting ligand, dual targeted NPs displayed synergistic targeting effects with enhanced selectivity and efficiency (Chapter 6). Nanoparticles made of organic materials offer the advantage of high biocompatibility but suffer frequently from poor visibility in biological environments. To overcome this restraint, 2.2 nm gold nanoparticles were introduced as a contrast agent at the interface between the hydrophobic fluorophore loaded core and the hydrophilic shell of polymeric nanoparticles. Due to the spatially controlled stratified composition these hybrid NPs exhibited outstanding detectability in transmission electron microscopy, even without the addition of contrast agents. Combination with an additional fluorescence label resulted in a negligible degree of fluorescence quenching which allowed for concomitant detection of the gold and the fluorescent label by optical microscopy. Moreover, the gold content of hybrid NPs is sufficiently high for future quantification in tissues after systemic administration (Chapter 7). In summary, various novel concepts have been established in this work that will facilitate the development of effective nanomedicines or improve existing delivery strategies