A general chemical synthesis platform for crosslinking multivalent single chain variable fragments

Cross-Linked Hyaluronan Derivatives in the Delivery of Phycocyanin

An easy and viable crosslinking technology, based on the "click-chemistry" reaction copper(I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition (click-crosslinking), was applied to graft copolymers of medium molecular weight (i.e., 270 kDa) hyaluronic acid (HA) grafted with ferulic acid (FA) residues bearing clickable propargyl groups, as well as caffeic acid derivatives bearing azido-terminated oligo(ethylene glycol) side chains. The obtained crosslinked materials were characterized from the point of view of their structure and aggregation liability to form hydrogels in a water environment. The most promising materials showed interesting loading capability regarding the antioxidant agent phycocyanin (PC). Two novel materials complexes (namely HA(270)-FA-TEGEC-CL-20/PC and HA(270)-FA-HEGEC-CL-20/PC) were obtained with a drug-to-material ratio of 1:2 (w/w). Zeta potential measurements of the new complexes (-1.23 mV for HA(270)-FA-TEGEC-CL-20/PC and -1.73 mV for HA(270)-FA-HEGEC-CL-20/PC) showed alterations compared to the zeta potential values of the materials on their own, suggesting the achievement of drug-material interactions. According to the in vitro dissolution studies carried out in different conditions, novel drug delivery systems (DDSs) were obtained with a variety of characteristics depending on the desired route of administration and, consequently, on the pH of the surrounding environment, thanks to the complexation of phycocyanin with these two new crosslinked materials. Both complexes showed excellent potential for providing a controlled/prolonged release of the active pharmaceutical ingredient (API). They also increased the amount of drug that reach the target location, enabling pH-dependent release. Importantly, as demonstrated by the DPPH free radical scavenging assay, the complexation process, involving freezing and freeze-drying, showed no adverse effects on the antioxidant activity of phycocyanin. This activity was preserved in the two novel materials and followed a concentration-dependent pattern similar to pure PC.

Chemical and Enzymatic Methods for Post-Translational Protein-Protein Conjugation

Fusion proteins play an essential role in the biosciences but suffer from several key limitations, including the requirement for N-to-C terminal ligation, incompatibility of constituent domains, incorrect folding, and loss of biological activity. This perspective focuses on chemical and enzymatic approaches for the post-translational generation of well-defined protein-protein conjugates, which overcome some of the limitations faced by traditional fusion techniques. Methods discussed range from chemical modification of nucleophilic canonical amino acid residues to incorporation of unnatural amino acid residues and a range of enzymatic methods, including sortase-mediated ligation. Through summarizing the progress in this rapidly growing field, the key successes and challenges associated with using chemical and enzymatic approaches are highlighted and areas requiring further development are discussed.

π-Clamp-Mediated Homo- and Heterodimerization of Single-Domain Antibodies via Site-Specific Homobifunctional Conjugation

Post-translational protein–protein conjugation produces bioconjugates that are unavailable via genetic fusion approaches. A method for preparing protein–protein conjugates using π-clamp-mediated cysteine arylation with pentafluorophenyl sulfonamide functional groups is described. Two computationally designed antibodies targeting the SARS-CoV-2 receptor binding domain were produced (K_D = 146, 581 nM) with a π-clamp sequence near the C-terminus and dimerized using this method to provide a 10–60-fold increase in binding (K_D = 8–15 nM). When two solvent-exposed cysteine residues were present on the second protein domain, the π-clamp cysteine residue was selectively modified over an Asp-Cys-Glu cysteine residue, allowing for subsequent small-molecule conjugation. With this strategy, we build molecule–protein–protein conjugates with complete chemical control over the sites of modification.

Synthesis and characterization of pentaerythritol derived glycoconjugates as supramolecular gelators

Three series of glycoclusters were synthesized and studied and we found that covalently linking three or four monomeric glycosyl triazoles led to effective supramolecular gelation.

Interferon dimers: IFN-PEG-IFN

Increasingly complex proteins can be made by a recombinant chemical approach where proteins that can be made easily can be combined by site-specific chemical conjugation to form multifunctional or more active protein therapeutics. Protein dimers may display increased avidity for cell surface receptors. The increased size of protein dimers may also increase circulation times. Cytokines bind to cell surface receptors that dimerise, so much of the solvent accessible surface of a cytokine is involved in binding to its target. Interferon (IFN) homo-dimers (IFN-PEG-IFN) were prepared by two methods: site-specific bis-alkylation conjugation of PEG to the two thiols of a native disulphide or to two imidazoles on a histidine tag of two His₈-tagged IFN (His₈IFN). Several control conjugates were also prepared to assess the relative activity of these IFN homo-dimers. The His₈IFN-PEG₂₀-His₈IFN obtained by histidine-specific conjugation displayed marginally greater in vitro antiviral activity compared to the IFN-PEG₂₀-IFN homo-dimer obtained by disulphide re-bridging conjugation. This result is consistent with previous observations in which enhanced retention of activity was made possible by conjugation to an N-terminal His-tag on the IFN. Comparison of the antiviral and antiproliferative activities of the two IFN homo-dimers prepared by disulphide re-bridging conjugation indicated that IFN-PEG₁₀-IFN was more biologically active than IFN-PEG₂₀-IFN. This result suggests that the size of PEG may influence the antiviral activity of IFN-PEG-IFN homo-dimers.

Two-step functionalization of oligosaccharides using glycosyl iodide and trimethylene oxide and its applications to multivalent glycoconjugates

Oligosaccharide conjugates, such as glycoproteins and glycolipids, are potential chemotherapeutics and also serve as useful tools for understanding the biological roles of carbohydrates. With many modern isolation and synthetic technologies providing access to a wide variety of free sugars, there is increasing need for general methodologies for carbohydrate functionalization. Herein, we report a two-step methodology for the conjugation of per-O-acetylated oligosaccharides to functionalized linkers that can be used for various displays. Oligosaccharides obtained from both synthetic and commercial sources were converted to glycosyl iodides and activated with I2 to form reactive donors that were subsequently trapped with trimethylene oxide to form iodopropyl conjugates in a single step. The terminal iodide served as a chemical handle for further modification. Conversion into the corresponding azide followed by copper-catalyzed azide-alkyne cycloaddition afforded multivalent glycoconjugates of Gb3 for further investigation as anti-cancer therapeutics.

Tailoring chimeric ligands for studying and biasing ErbB receptor family interactions

Described is the development and application of a versatile semisynthetic strategy, based on a combination of sortase-mediated coupling and tetrazine ligation chemistry, which can be exploited for the efficient incorporation of tunable functionality into chimeric recombinant proteins. To demonstrate the scope of the method, the assembly of a set of bivalent ligands, which integrate members of the epidermal growth factor (EGF) ligand family, is described. By using a series of bivalent EGFs with variable intraligand spacing, the differences in structure were correlated with the ability to bias signaling in the ErbB receptor family in a cell motility assay. Biasing away from EGFR-HER2 dimerization with a bivalent EGF was observed to reduce cell motility in an intraligand distance-dependent fashion, thus demonstrating the utility of the approach for acutely perturbing receptor-mediated cell signaling pathways.

Preparation of unnatural N-to-N and C-to-C protein fusions

Standard genetic approaches allow the production of protein composites by fusion of polypeptides in head-to-tail fashion. Some applications would benefit from constructions that are genetically impossible, such as the site-specific linkage of proteins via their N or C termini, when a remaining free terminus is required for biological activity. We developed a method for the production of N-to-N and C-to-C dimers, with full retention of the biological activity of both fusion partners and without inflicting chemical damage on the proteins to be joined. We use sortase A to install on the N or C terminus of proteins of interest the requisite modifications to execute a strain-promoted copper-free cycloaddition and show that the ensuing ligation proceeds efficiently. Applied here to protein-protein fusions, the method reported can be extended to connecting proteins with any entity of interest.