Affinity Polymers Tailored for the Protein A Binding Site of Immunoglobulin G Proteins

Bioactive Synthetic Polymers

Synthetic polymers are omnipresent in society as textiles and packaging materials, in construction and medicine, among many other important applications. Alternatively, natural polymers play a crucial role in sustaining life and allowing organisms to adapt to their environments by performing key biological functions such as molecular recognition and transmission of genetic information. In general, the synthetic and natural polymer worlds are completely separated due to the inability for synthetic polymers to perform specific biological functions; in some cases, synthetic polymers cause uncontrolled and unwanted biological responses. However, owing to the advancement of synthetic polymerization techniques in recent years, new synthetic polymers have emerged that provide specific biological functions such as targeted molecular recognition of peptides, or present antiviral, anticancer, and antimicrobial activities. In this review, the emergence of this generation of bioactive synthetic polymers and their bioapplications are summarized. Finally, the future opportunities in this area are discussed.

Review of Recent Advances and Their Improvement in the Effectiveness of Hydrogel-Based Targeted Drug Delivery: A Hope for Treating Cancer

Using hydrogels for delivering cancer therapeutics is advantageous in pharmaceutical usage as they have an edge over traditional delivery, which is tainted due to the risk of toxicity that it imbues. Hydrogel usage leads to the development of a more controlled drug release system owing to its amenability for structural metamorphosis, its higher porosity to seat the drug molecules, and its ability to shield the drug from denaturation. The thing that makes its utility even more enhanced is that they make themselves more recognizable to the body tissues and hence can stay inside the body for a longer time, enhancing the efficiency of the delivery, which otherwise is negatively affected since the drug is identified by the human immunity as a foreign substance, and thus, an attack of the immunity begins on the drug injected. A variety of hydrogels such as thermosensitive, pH-sensitive, and magnetism-responsive hydrogels have been included and their potential usage in drug delivery has been discussed in this review that aims to present recent studies on hydrogels that respond to alterations under a variety of circumstances in "reducing" situations that mimic the microenvironment of cancerous cells.

Abiotic Stimuli-Responsive Protein Affinity Reagent for IgG

We describe an approach for the discovery of protein affinity reagents (PARs). Abiotic synthetic hydrogel copolymers can be "tuned" for selective protein capture by the type and ratios of functional monomers included in their polymerization and by the polymerization conditions (i.e., pH). By screening libraries of hydrogel nanoparticles (NPs) containing charged and hydrophobic groups against a protein target (IgG), a stimuli-responsive PAR is selected. The robust carbon backbone synthetic copolymer is rapidly synthesized in the chemistry laboratory from readily available monomers. The production of the PAR does not require living cells and is free from biological contamination. The capture and release of the protein by the copolymer NP is reversible. IgG is sequestered from human serum at pH 6.5 and following a wash step, the purified protein is released by elevating the pH to 7.3. The binding and release of the protein occur without denaturation. The abiotic material functions as a selective PAR for the F(ab')₂ domain of IgG for pull-down and immunoprecipitation experiments and for isolation and purification of proteins from complex biological mixtures.

Abiotic Mimic of Endogenous Tissue Inhibitors of Metalloproteinases: Engineering Synthetic Polymer Nanoparticles for Use as a Broad-Spectrum Metalloproteinase Inhibitor

We describe a process for engineering a synthetic polymer nanoparticle (NP) that functions as an effective, broad-spectrum metalloproteinase inhibitor. Inhibition is achieved by incorporating three functional elements in the NP: a group that interacts with the catalytic zinc ion, functionality that enhances affinity to the substrate-binding pocket, and fine-tuning of the chemical composition of the polymer to strengthen NP affinity for the enzyme surface. The approach is validated by synthesis of a NP that sequesters and inhibits the proteolytic activity of snake venom metalloproteinases from five clinically relevant species of snakes. The mechanism of action of the NP mimics that of endogenous tissue inhibitors of metalloproteinases. The strategy provides a general design principle for synthesizing abiotic polymer inhibitors of enzymes.

Design of Synthetic Polymer Nanoparticles Specifically Capturing Indole, a Small Toxic Molecule

Synthetic polymers are of interest as stable and cost-effective biomolecule-affinity reagents, since these polymers interact with target biomolecules both in vitro and in the bloodstream. However, little has been reported about orally administered polymers capable of capturing a target molecule and inhibiting its intestinal absorption. Here, we describe the design of synthetic polymer nanoparticles (NPs) specifically capturing indole, a major factor exacerbating chronic kidney disease, in the intestine. N-isopropylacrylamide-based NPs were prepared with various hydrophobic monomers. The amounts of indole captured by NPs depended on the structures and feed ratios of the hydrophobic monomers and the polymer density but not on the particle size. The combination of hydrophobic and quadrupole interaction was effective to enhance the affinity and specificity of NPs for indole. The optimized NPs specifically inhibited intestinal absorption of orally administered indole in mice. These results showed the potential of synthetic polymer NPs for inhibiting the intestinal absorption of a target molecule.

Analyte-Responsive Hydrogels: Intelligent Materials for Biosensing and Drug Delivery

Nature has mastered the art of molecular recognition. For example, using synergistic non-covalent interactions, proteins can distinguish between molecules and bind a partner with incredible affinity and specificity. Scientists have developed, and continue to develop, techniques to investigate and better understand molecular recognition. As a consequence, analyte-responsive hydrogels that mimic these recognitive processes have emerged as a class of intelligent materials. These materials are unique not only in the type of analyte to which they respond but also in how molecular recognition is achieved and how the hydrogel responds to the analyte. Traditional intelligent hydrogels can respond to environmental cues such as pH, temperature, and ionic strength. The functional monomers used to make these hydrogels can be varied to achieve responsive behavior. For analyte-responsive hydrogels, molecular recognition can also be achieved by incorporating biomolecules with inherent molecular recognition properties (e.g., nucleic acids, peptides, enzymes, etc.) into the polymer network. Furthermore, in addition to typical swelling/syneresis responses, these materials exhibit unique responsive behaviors, such as gel assembly or disassembly, upon interaction with the target analyte. With the diverse tools available for molecular recognition and the ability to generate unique responsive behaviors, analyte-responsive hydrogels have found great utility in a wide range of applications. In this Account, we discuss strategies for making four different classes of analyte-responsive hydrogels, specifically, non-imprinted, molecularly imprinted, biomolecule-containing, and enzymatically responsive hydrogels. Then we explore how these materials have been incorporated into sensors and drug delivery systems, highlighting examples that demonstrate the versatility of these materials. For example, in addition to the molecular recognition properties of analyte-responsive hydrogels, the physicochemical changes that are induced upon analyte binding can be exploited to generate a detectable signal for sensing applications. As research in this area has grown, a number of creative approaches for improving the selectivity and sensitivity (i.e., detection limit) of these sensors have emerged. For applications in drug delivery systems, therapeutic release can be triggered by competitive molecular interactions or physicochemical changes in the network. Additionally, including degradable units within the network can enable sustained and responsive therapeutic release. Several exciting examples exploiting the analyte-responsive behavior of hydrogels for the treatment of cancer, diabetes, and irritable bowel syndrome are discussed in detail. We expect that creative and combinatorial approaches used in the design of analyte-responsive hydrogels will continue to yield materials with great potential in the fields of sensing and drug delivery.

Protein Camouflage: Supramolecular Anion Recognition by Ubiquitin

Progress in the field of bio-supramolecular chemistry, the bottom-up assembly of protein-ligand systems, relies on a detailed knowledge of molecular recognition. To address this issue, we have characterised complex formation between human ubiquitin (HUb) and four supramolecular anions. The ligands were: pyrenetetrasulfonic acid (4PSA), p-sulfonato-calix[4]arene (SCLX4), bisphosphate tweezers (CLR01) and meso-tetrakis (4-sulfonatophenyl)porphyrin (TPPS), which vary in net charge, size, shape and hydrophobicity. All four ligands induced significant changes in the HSQC spectrum of HUb. Chemical shift perturbations and line-broadening effects were used to identify binding sites and to quantify affinities. Supporting data were obtained from docking simulations. It was found that these weakly interacting ligands bind to extensive surface patches on HUb. A comparison of the data suggests some general indicators for the protein-binding specificity of supramolecular anions. Differences in binding were observed between the cavity-containing and planar ligands. The former had a preference for the arginine-rich, flexible C terminus of HUb.