Peter R. Wich

Polyphosphonium polymers for siRNA delivery: an efficient and nontoxic alternative to polyammonium carriers.

A water-soluble polyphosphonium polymer was synthesized and directly compared with its ammonium analog in terms of siRNA delivery. The triethylphosphonium polymer shows transfection efficiency up to 65% with 100% cell viability, whereas the best result obtained for the ammonium analog reaches only 25% transfection with 85% cell viability. Moreover, the nature of the alkyl substituents on the phosphonium cations is shown to have an important influence on the transfection efficiency and toxicity of the polyplexes. The present results show that the use of positively charged phosphonium groups is a worthy choice to achieve a good balance between toxicity and transfection efficiency in gene delivery systems.

Reversible and Noncompetitive Inhibition of β-Tryptase by Protein Surface Binding of Tetravalent Peptide Ligands Identified from a Combinatorial Split–Mix Library†

Molecular plug: On-bead screening of a combinatorial library of 216 tetravalent oligopeptides reveals highly specific, noncompetitive inhibitors of the serine protease β-tryptase with nanomolar affinity. The ligands most likely bind to the protein surface and act as a molecular plug that blocks access to the active sites, which are buried inside a central cavity.

The Development of Artificial Receptors for Small Peptides Using Combinatorial Approaches

In this article we describe some examples how combinatorial libraries are applied in supramolecular chemistry e.g. to identify artificial receptors for peptide binding in aqueous solvent. Whereas in the classical combinatorial approach mainly large but completely random libraries are used, nowadays also the use of small but focused libraries is coming into focus. We discuss the pros and cons of these two different approaches, using examples from literature work and our own studies in this field.

Combinatorial receptor finding—large and random vs. small and focused libraries

Whereas in the classical combinatorial approach mainly large but completely random libraries are used, nowadays also the use of small but designed libraries is coming into focus. We discuss the pros and cons of these two different approaches, using examples from literature work and our own studies showing how combinatorial libraries are applied in supramolecular chemistry e.g. to identify artificial receptors for peptide binding in aqueous solvent.

UV resonance Raman spectroscopic monitoring of supramolecular complex formation: peptide recognition in aqueous solution

The formation of a supramolecular complex between a tetrapeptide and an artificial receptor , is monitored at submillimolar concentrations in water by UV resonance Raman spectroscopy. Using 275 nm excitation, we selectively probe the carboxylate binding site (CBS) within the receptor, a moiety which is very efficient in binding the carboxy terminus of peptides in aqueous media. Complexation of the receptor with the tetrapeptide involves the formation of a H-bond enforced ion pair, resulting in significant changes in the corresponding UV resonance Raman spectra. Our qualitative interpretation is based on experimental reference and calculated Raman spectra on model systems. First preliminary calculations show that for a quantitative analysis, also the distinct contributions of multiple CBS conformers must be considered in addition to the H-bond induced changes upon complexation.

Quantum Chemical-Based Protocol for the Rational Design of Covalent Inhibitors

We propose a structure-based protocol for the development of customized covalent inhibitors. Starting from a known inhibitor, in the first and second steps appropriate substituents of the warhead are selected on the basis of quantum mechanical (QM) computations and hybrid approaches combining QM with molecular mechanics (QM/MM). In the third step the recognition unit is optimized using docking approaches for the noncovalent complex. These predictions are finally verified by QM/MM or molecular dynamic simulations. The applicability of our approach is successfully demonstrated by the design of reversible covalent vinylsulfone-based inhibitors for rhodesain. The examples show that our approach is sufficiently accurate to identify compounds with the desired properties but also to exclude nonpromising ones.

Amphiphilic Polysaccharide Block Copolymers for pH-Responsive Micellar Nanoparticles

A full polysaccharide amphiphilic block copolymer was prepared from end group-functionalized dextrans using copper-mediated azide-alkyne click chemistry. Sufficient modification of the reducing end in both blocks was achieved by microwave-enhanced reductive amination in a borate-buffer/methanol solvent system. The combination of a hydrophilic dextran block with a hydrophobic acetalated dextran block results in an amphiphilic structure that turns water-soluble upon acid treatment. The material has a low critical micelle concentration and self-assembles in water to spherical micellar nanoparticles. The formed nanoparticles have a narrow size distribution below 70 nm in diameter and disassemble in slightly acidic conditions. The amphiphilic polysaccharide system shows low toxicity and can stabilize the hydrophobic model drug curcumin in aqueous solutions over extended time periods.

Development of Novel Peptide-Based Michael Acceptors Targeting Rhodesain and Falcipain-2 for the Treatment of Neglected Tropical Diseases (NTDs)

This paper describes the development of a class of peptide-based inhibitors as novel antitrypanosomal and antimalarial agents. The inhibitors are based on a characteristic peptide sequence for the inhibition of the cysteine proteases rhodesain of Trypanosoma brucei rhodesiense and falcipain-2 of Plasmodium falciparum. We exploited the reactivity of novel unsaturated electrophilic functions such as vinyl-sulfones, -ketones, -esters, and -nitriles. The Michael acceptors inhibited both rhodesain and falcipain-2, at nanomolar and micromolar levels, respectively. In particular, the vinyl ketone 3b has emerged as a potent rhodesain inhibitor (k2nd = 67 × 106 M-1 min-1), endowed with a picomolar binding affinity (Ki = 38 pM), coupled with a single-digit micromolar activity against Trypanosoma brucei brucei (EC50 = 2.97 μM), thus being considered as a novel lead compound for the discovery of novel effective antitrypanosomal agents.

Surface Modification of Polysaccharide-Based Nanoparticles with PEG and Dextran and the Effects on Immune Cell Binding and Stimulatory Characteristics

Surface modifications of nanoparticles can alter their physical and biological properties significantly. They effect particle aggregation, circulation times, and cellular uptake. This is particularly critical for the interaction with primary immune cells due to their important role in particle processing. We can show that the introduction of a hydrophilic PEG layer on the surface of the polysaccharide-based nanoparticles prevents unwanted aggregation under physiological conditions and decreases unspecific cell uptake in different primary immune cell types. The opposite effect can be observed with a parallel-performed introduction of a layer of low molecular weight dextran (3.5 and 5 kDa) on the particle surface (DEXylation) that encourages the nanoparticle uptake by antigen-presenting cells like macrophages and dendritic cells. Binding of DEXylated particles to these immune cells results in an upregulation of surface maturation markers and elevated production of proinflammatory cytokines, reflecting cell activation. Hence, DEXylated particles can potentially be used for passive targeting of antigen presenting cells with inherent adjuvant function for future immunotherapeutic applications.

Protein-Based Nanoparticles for the Delivery of Enzymes with Antibacterial Activity

Proteins represent a versatile biopolymer material for the preparation of nanoparticles due to their biocompatibility, biodegradability, and low immunogenicity. This study presents a protein-based nanoparticle system consisting of high surface PEGylated lysozyme polyethylene glycol-modified lysozyme (LYZmPEG ). This protein modification leads to a solubility switch, which allows a nanoparticle preparation using a mild double emulsion method without the need of surfactants. The method allows the encapsulation of large hydrophilic payloads inside of the protein-based nanoparticle system. Native lysozyme (LYZ) was chosen as payload because of its innate activity as natural antibiotic. The mild particle preparation procedure retains the structure and activity of the enzyme which was successfully tested against the gram-positive bacteria strain M. Luteus. In comparison, the particle system shows no toxicity to human cells. This first report of a full protein-based particle material for the transport of large hydrophilic payloads opens up new therapeutic applications for biopolymer-based delivery systems.