Multivalent Peptide-Nanoparticle Conjugates for Influenza-Virus Inhibition.

To inhibit binding of the influenza A virus to the host cell glycocalyx, we generate multivalent peptide-polymer nanoparticles binding with nanomolar affinity to the virus via its spike protein hemagglutinin. The chosen dendritic polyglycerol scaffolds are highly biocompatible and well suited for a multivalent presentation. We could demonstrate in vitro that by increasing the size of the polymer scaffold and adjusting the peptide density, viral infection is drastically reduced. Such a peptide-polymer conjugate qualified also in an in vivo infection scenario. With this study we introduce the first non-carbohydrate-based, covalently linked, multivalent virus inhibitor in the nano- to picomolar range by ensuring low peptide-ligand density on a larger dendritic scaffold.

Amino Acid-Functionalized Dendritic Polyglycerol for Safe and Effective siRNA Delivery.

The development of safe and effective delivery vectors is a great challenge for the medicinal application of RNA interference (RNAi). In this study, we aimed to develop new synthetic transfection agents based on dendritic polyglycercol (dPG), which has shown great biocompatibility in several biomaterial applications. Histidine and aromatic amino acids were conjugated to the amine-terminated dPGs through amide bonds. We systematically tuned the amino acid combination, functionalization ratio, ligand density, and dPG core size to find optimal vectors. It was found that histidine-tryptophan-functionalized dPGs exhibited improved delivery efficiency and greatly reduced toxicity over simple amine-terminated dPGs. Furthermore, the optimized vectors exhibited strong siRNA binding and high transfection efficiency in serum containing media. The results indicate that the current amino acid-functionalized dPG system is a promising candidate for in vivo siRNA delivery applications.

Dendritic Polyglycerol Amine: An Enhanced Substrate to Support Long-Term Neural Cell Culture.

Long-term stable cell culture is a critical tool to better understand cell function. Most adherent cell culture models require a polymer substrate coating of poly-lysine or poly-ornithine for the cells to adhere and survive. However, polypeptide-based substrates are degraded by proteolysis and it remains a challenge to maintain healthy cell cultures for extended periods of time. Here, we report the development of an enhanced cell culture substrate based on a coating of dendritic polyglycerol amine (dPGA), a non-protein macromolecular biomimetic of poly-lysine, to promote the adhesion and survival of neurons in cell culture. We show that this new polymer coating provides enhanced survival, differentiation and long-term stability for cultures of primary neurons or neurons derived from human induced pluripotent stem cells (hiPSCs). Atomic force microscopy analysis provides evidence that greater nanoscale roughness contributes to the enhanced capacity of dPGA-coated surfaces to support cells in culture. We conclude that dPGA is a cytocompatible, functionally superior, easy to use, low cost and highly stable alternative to poly-cationic polymer cell culture substrate coatings such as poly-lysine and poly-ornithine. Summary statementHere, we describe a novel dendritic polyglycerol amine-based substrate coating, demonstrating superior performance compared to current polymer coatings for long-term culture of primary neurons and neurons derived from induced pluripotent stem cells.

Systematic adjustment of charge densities and size of polyglycerol amines reduces cytotoxic effects and enhances cellular uptake.

Excessive cationic charge density of polyplexes during cellular uptake is still a major hurdle in the field of non-viral gene delivery. The most efficient cationic vectors such as polyethylene imine (PEI) or polyamidoamine (PAMAM) can be highly toxic and may induce strong side effects due to their high cationic charge densities. Alternatives like polyethylene glycol (PEG) are used to 'shield' these charges and thus to reduce the cytotoxic effects known for PEI/PEG-core-shell architectures. In this study, we compared the ability of hyperbranched polyglycerol amines (hPG amines) with different amine densities and molecular weights as non-viral cationic vectors for DNA delivery. By adjusting the hydroxyl to amine group ratio on varying molecular weights, we were able to perform a systematic study on the cytotoxic effects caused by the effective charge density in correlation to size. We could demonstrate that carriers with moderate charge density have a higher potential for effective DNA delivery as compared to high/low charged ones independent of their size, but the final efficiency can be optimized by the molecular weight. We analyzed the physicochemical properties and cellular uptake capacity as well as the cytotoxicity and transfection efficiency of these new vector systems.

Optimized effective charge density and size of polyglycerol amines leads to strong knockdown efficacy in vivo.

RNA interference (RNAi)-based therapy extends the range of "druggable" targets beyond existing pharmacological drugs and enables the development of new treatment strategies for various diseases. A prerequisite are non-viral polyvalent gene delivery vectors capable for safe and effective siRNA delivery to cells in vivo allowing a broad clinical application. We synthesized hyperbranched polyglycerol amines (hPG amines) which varied in their charge density, multiplicity (absolute frequency of amine groups) and core size to successfully develop potent and safe siRNA transfer vectors. The characterization of hyperbranched polyglycerol amines with an invariable core size (8 kDa) but different amine loading revealed a correlation between the effective charge density and the transfection efficacy without impacting the cell viability in vitro. However, this correlation was not seen in tumor bearing mice in vivo treated with 8 kDa hPG amine-siRNA complexes. Improving the effective charge density and the multiplicity of amine functionalities by increasing the molecular weight (43 kDa) revealed comparable transfection efficacy in vitro but less toxic side effects after systemic administration in vivo compared to the respective hPG amine (8 kDa). In addition, in vivo delivery of 43 kDa hPG amine-siRNA-polyplexes in tumors resulted in a highly specific and significant knockdown effect. These findings demonstrate that hyperbranched polyglycerol amines with a balanced effective charge density, multiplicity and core size are promising gene delivery vectors for siRNA therapy which enable to address so far "undruggable" targets due to high tolerability and effective siRNA delivery.

Functionalized polyglycerol amine nanogels as nanocarriers for DNA.

Polyglycerol based nanogels (nPG) can function as cellular delivery systems. These nPGs are synthesized with different amine densities (nPG amines) by acid-catalyzed epoxide-opening polymerization using a mini-emulsion approach and surface modification. All the synthesized nanogels are characterized by NMR, dynamic light scattering, and ζ-potential, showing slightly positive surface charge and a homogeneous size of ≈100 nm. The use of these systems for delivery applications is demonstrated with regard to polyplex formation, cytotoxicity, and cellular uptake studies. It is depicted that the CE50 value of the high loaded nPG amines is eight times higher than the low loaded ones. The influence of the amine loading percentage on the nanogel and the effects of polyvalency in these architecture is discussed.