Polyvalent side chain peptide-synthetic polymer conjugates as HIV-1 entry inhibitors

Progress in Treatment and Diagnostics of Infectious Disease with Polymers

In this era of advanced technology and innovation, infectious diseases still cause significant morbidity and mortality, which need to be addressed. Despite overwhelming success in the development of vaccines, transmittable diseases such as tuberculosis and AIDS remain unprotected, and the treatment is challenging due to frequent mutations of the pathogens. Formulations of new or existing drugs with polymeric materials have been explored as a promising new approach. Variations in shape, size, surface charge, internal morphology, and functionalization position polymer particles as a revolutionary material in healthcare. Here, an overview is provided of major diseases along with statistics on infection and death rates, focusing on polymer-based treatments and modes of action. Key issues are discussed in this review pertaining to current challenges and future perspectives.

Polymer Conjugate as the New Promising Drug Delivery System for Combination Therapy against Cancer

This review highlights the advantages of combination therapy using polymer conjugates as drug delivery systems for cancer treatment. In this review, the specific structures and materials of polymer conjugates, as well as the different types of combination chemotherapy strategies, are discussed. Specific targeting strategies, such as monoclonal antibody therapy and small molecule ligands, are also explored. Additionally, self-assembled polymer micelles and overcoming multidrug resistance are described as potential strategies for combination therapy. The assessment of combinational therapeutic efficacy and the challenges associated with polymer conjugates are also addressed. The future outlook aims to overcome these challenges and improve the effectiveness of drug delivery systems for combination therapy. The conclusion emphasizes the potential of polymer conjugates in combination therapy while acknowledging the need for further research and development in this field.

Biomolecular Densely Grafted Brush Polymers: Oligonucleotides, Oligosaccharides and Oligopeptides

In this Minireview, we describe synthetic polymers densely functionalized with sequence-defined biomolecular sidechains. We focus on synthetic brush polymers of oligonucleotides, oligosaccharides, and oligopeptides, prepared via graft-through polymerization from biomolecule functionalized monomers. The resulting structures are brush polymers wherein a biomolecular graft is positioned at each monomer backbone unit. We describe key synthetic milestones, identify synthetic opportunities, and highlight recent advances in the field, including biological applications.

A Dual Wavelength Polymerization and Bioconjugation Strategy for High Throughput Synthesis of Multivalent Ligands

Structure-function relationships for multivalent polymer scaffolds are highly complex due to the wide diversity of architectures offered by such macromolecules. Evaluation of this landscape has traditionally been accomplished case-by-case due to the experimental difficulty associated with making these complex conjugates. Here, we introduce a simple dual-wavelength, two-step polymerize and click approach for making combinatorial conjugate libraries. It proceeds by incorporation of a polymerization friendly cyclopropenone-masked dibenzocyclooctyne into the side chain of linear polymers or the α-chain end of star polymers. Polymerizations are performed under visible light using an oxygen tolerant porphyrin-catalyzed photoinduced electron/energy transfer-reversible addition-fragmentation chain-transfer (PET-RAFT) process, after which the deprotection and click reaction is triggered by UV light. Using this approach, we are able to precisely control the valency and position of ligands on a polymer scaffold in a manner conducive to high throughput synthesis.

Polymeric therapeutic delivery systems for the treatment of infectious diseases

Infectious diseases caused by germs, parasites, fungi, virus and bacteria are one of the leading causes of death worldwide. Polymeric therapeutics are nanomedicines that offer several advantages making them useful for the treatment of infectious diseases such as targeted drug release mechanism, ability to maintain the drug concentration within a therapeutic window for a desired duration, biocompatibility with low immunogenicity and reduced drug toxicity resulting in enhanced therapeutic efficacy of the incorporated drug. Although polymeric therapeutics have been evaluated for the treatment of infectious diseases in vitro and in vivo with improved therapeutic efficacy, most treatments for infectious disease have not been evaluated using polymeric therapeutics. This review will focus on the applications of polymeric therapeutics for the treatment of infectious diseases (preclinical studies and clinical trials), with particular focus on parasitic and viral infections.

Responsive Hybrid (Poly)peptide-Polymer Conjugates

(Poly)peptide-polymer conjugates continue to garner significant interest in the production of functional materials given their composition of natural and synthetic building blocks that confer select and synergistic properties. Owing to opportunities to design predefined architectures and structures with different morphologies, these hybrid conjugates enable new approaches for producing micro- or nanomaterials. Their modular design enables the incorporation of multiple responsive properties into a single conjugate. This review presents recent advances in (poly)peptide-polymer conjugates for drug-delivery applications, with a specific focus on the utility of the (poly)peptide component in the assembly of particles and nanogels, as well as the role of the peptide in triggered drug release.

Mechanisms of fast and stringent search in homologous pairing of double-stranded DNA

Self-organization in the cell relies on the rapid and specific binding of molecules to their cognate targets. Correct bindings must be stable enough to promote the desired function even in the crowded and fluctuating cellular environment. In systems with many nearly matched targets, rapid and stringent formation of stable products is challenging. Mechanisms that overcome this challenge have been previously proposed, including separating the process into multiple stages; however, how particular in vivo systems overcome the challenge remains unclear. Here we consider a kinetic system, inspired by homology dependent pairing between double stranded DNA in bacteria. By considering a simplified tractable model, we identify different homology testing stages that naturally occur in the system. In particular, we first model dsDNA molecules as short rigid rods containing periodically spaced binding sites. The interaction begins when the centers of two rods collide at a random angle. For most collision angles, the interaction energy is weak because only a few binding sites near the collision point contribute significantly to the binding energy. We show that most incorrect pairings are rapidly rejected at this stage. In rare cases, the two rods enter a second stage by rotating into parallel alignment. While rotation increases the stability of matched and nearly matched pairings, subsequent rotational fluctuations reduce kinetic trapping. Finally, in vivo chromosome are much longer than the persistence length of dsDNA, so we extended the model to include multiple parallel collisions between long dsDNA molecules, and find that those additional interactions can greatly accelerate the searching.

Protein folding and the binding of sequence dependent proteins to DNA are examples of self-assembling systems in which the binding energy varies continuously throughout the interaction. Previous theoretical work has highlighted the importance of dividing the interaction into separate stages characterized by interaction times and binding energies that vary by orders of magnitude. Insight into how such a division might naturally arise and promote accurate and efficient self-assembly is provided by our study of a simple tractable model inspired by the homology dependent pairing of double stranded DNA molecules in vivo. In the model, the binding energy is controlled by one single continuously tunable variable whose natural evolution creates stages that efficiently and accurately form stable products.

Site-Specific Polymer Attachment to HR2 Peptide Fusion Inhibitors against HIV-1 Decreases Binding Association Rates and Dissociation Rates Rather Than Binding Affinity

A popular strategy for overcoming the limited plasma half-life of peptide heptad repeat 2 (HR2) fusion inhibitors against HIV-1 is conjugation with biocompatible polymers such as poly(ethylene glycol) (PEG). However, despite improved resistance to proteolysis and reduced renal elimination, covalent attachment of polymers often causes a loss in therapeutic potency. In this study, we investigated the molecular origins of the loss in potency upon conjugation of linear, midfunctional, and hyperbranched PEG-like polymers to peptides that inhibit HIV-1-host cell membrane fusion. Fluorescence binding assays revealed that polymer conjugation imparted mass transport limitations that manifested as coexistent slower association and dissociation rates from the gp41 target on HIV-1. Furthermore, reduced association kinetics rather than affinity disruption was responsible for the loss in antiviral potency. Finally, the binding assays indicated that the unmodified HR2-derived peptide demonstrated diffusion-limited binding. The observed high potency of the unmodified peptide in HIV-1 inhibition assays was therefore attributed to rapid peptide conformational changes upon binding to the gp41 prehairpin structure. This study emphasizes that the view in which polymer ligation to therapeutic peptides inadvertently leads to loss in potency due to a loss in binding affinity requires scientific verification on a case-by-case basis and that high peptide potency may be due to rapid target-binding events.

Synthetic Aspects of Peptide– and Protein–Polymer Conjugates in the Post-click Era

Biomacromolecules offer complex and precise functions embedded in their monomer sequence such as enzymatic activity or specific interactions towards other molecules. Their informational content and capability to organize in higher ordered structures is superior to those of synthetic molecules. In comparison, synthetic polymers are easy to access even at large production scales and they are chemically more diverse. Solubilization, shielding against enzymatic degradation to more advanced functions like switchability or protein mimicry, etc., are accessible through the world of polymer chemistry. Bio-inspired hybrid materials consisting of peptides or proteins and synthetic polymers thereby combine the properties of both molecules to give rise to a new class of materials with unique characteristics and performance. To obtain well-defined bioconjugate materials, high yielding and site-specific as well as biorthogonal ligation techniques are mandatory. Since the first attempts of protein PEGylation in the 1970s and the concept of “click” chemistry arising in 2001, continuous progress in the field of peptide– and protein–polymer conjugate preparation has been gained. Herein, we provide an overview on ligation techniques to prepare functional bioconjugates published in the last decade, also referred to as “post-click” methods. Furthermore, chemoenzymatic approaches and biotransformation reactions used in peptide or protein modification, as well as highly site-specific and efficient reactions originated in synthetic macromolecular chemistry, which could potentially be adapted for bioconjugation, are presented. Finally, future perspectives for the preparation and application of bioconjugates at the interface between biology and synthetic materials are given.

Design of Self-Assembling Protein-Polymer Conjugates

Protein-polymer conjugates are of particular interest for nanobiotechnology applications because of the various and complementary roles that each component may play in composite hybrid-materials. This chapter focuses on the design principles and applications of self-assembling protein-polymer conjugate materials. We address the general design methodology, from both synthetic and genetic perspective, conjugation strategies, protein vs. polymer driven self-assembly and finally, emerging applications for conjugate materials. By marrying proteins and polymers into conjugated bio-hybrid materials, materials scientists, chemists, and biologists alike, have at their fingertips a vast toolkit for material design. These inherently hierarchical structures give rise to useful patterning, mechanical and transport properties that may help realize new, more efficient materials for energy generation, catalysis, nanorobots, etc.

Combination anti-HIV therapy via tandem release of prodrugs from macromolecular carriers

Reversible addition-fragmentation chain transfer (RAFT) polymerisation has been used to create a library of copolymers outfitted with a combination of self-immolative reverse transcriptase inhibitor prodrug pendents comprising zidovudine (AZT) and lamivudine (3TC).

Synthesis of cyclic peptide disulfide–PHPMA conjugates via sequential active ester aminolysis and CuAAC coupling

A synthetic strategy for the preparation of cyclic peptide disulfide–polymer conjugates that does not require peptide protecting groups is reported.

Designing multivalent probes for tunable superselective targeting

Specific targeting is common in biology and is a key challenge in nanomedicine. It was recently demonstrated that multivalent probes can selectively target surfaces with a defined density of surface binding sites. Here we show, using a combination of experiments and simulations on multivalent polymers, that such "superselective" binding can be tuned through the design of the multivalent probe, to target a desired density of binding sites. We develop an analytical model that provides simple yet quantitative predictions to tune the polymer's superselective binding properties by its molecular characteristics such as size, valency, and affinity. This work opens up a route toward the rational design of multivalent probes with defined superselective targeting properties for practical applications, and provides mechanistic insight into the regulation of multivalent interactions in biology. To illustrate this, we show how the superselective targeting of the extracellular matrix polysaccharide hyaluronan to its main cell surface receptor CD44 is controlled by the affinity of individual CD44-hyaluronan interactions.

Recent advances in engineering polyvalent biological interactions

Polyvalent interactions, where multiple ligands and receptors interact simultaneously, are ubiquitous in nature. Synthetic polyvalent molecules, therefore, have the ability to affect biological processes ranging from protein-ligand binding to cellular signaling. In this review, we discuss recent advances in polyvalent scaffold design and applications. First, we will describe recent developments in the engineering of polyvalent scaffolds based on biomolecules and novel materials. Then, we will illustrate how polyvalent molecules are finding applications as toxin and pathogen inhibitors, targeting molecules, immune response modulators, and cellular effectors.

Optimizing the Selectivity of Surface-Adsorbing Multivalent Polymers

Multivalent polymers are macromolecules containing multiple chemical moieties designed to bind to complementary moieties on a target; for example, a protein with multiple ligands that have affinity for receptors on a cell surface. Though the individual ligand-receptor bonds are often weak, the combinatorial entropy associated with the different possible ligand-receptor pairs leads to a binding transition that can be very sharp with respect to control parameters, such as temperature or surface receptor concentration. We use mean-field self-consistent field theory to study the binding selectivity of multivalent polymers to receptor-coated surfaces. Polymers that have their ligands clustered into a contiguous domain, either located at the chain end or chain midsection, exhibit cooperative surface adsorption and superselectivity when the polymer concentration is low. On the other hand, when the ligands are uniformly spaced along the chain backbone, selectivity is substantially reduced due to the lack of binding cooperativity and due to crowding of the surface by the inert polymer segments in the chain backbone.

Polymeric anti-HIV therapeutics

The scope of this review is to highlight the application of polymer therapeutics in an effort to curb the transmission and infection of the human immunodeficiency virus (HIV). Following a description of the HIV life cycle, the use of approved antiretroviral drugs that inhibit critical steps in the HIV infection process is highlighted. After that, a comprehensive overview of the structure and inhibitory properties of polymeric anti-HIV therapeutic agents is presented. This overview will include inhibitors based on polysaccharides, synthetic polymers, dendritic polymers, polymer conjugates as well as polymeric DC-SIGN antagonists. The review will conclude with a section that discusses the applications of polymers and polymer conjugates as systemic and topical anti-HIV therapeutics.

Superselective targeting using multivalent polymers

Despite their importance for material and life sciences, multivalent interactions between polymers and surfaces remain poorly understood. Combining recent achievements of synthetic chemistry and surface characterization, we have developed a well-defined and highly specific model system based on host/guest interactions. We use this model to study the binding of hyaluronic acid functionalized with host molecules to tunable surfaces displaying different densities of guest molecules. Remarkably, we find that the surface density of bound polymer increases faster than linearly with the surface density of binding sites. Based on predictions from a simple analytical model, we propose that this superselective behavior arises from a combination of enthalpic and entropic effects upon binding of nanoobjects to surfaces, accentuated by the ability of polymer chains to interpenetrate.

“Click” reactions: a versatile toolbox for the synthesis of peptide-conjugates

Peptides that comprise the functional subunits of proteins have been conjugated to versatile materials (biomolecules, polymers, surfaces and nanoparticles) in an effort to modulate cell responses, specific binding affinity and/or self-assembly behavior.

"Bio"-macromolecules: polymer-protein conjugates as emerging scaffolds for therapeutics

Polymer-protein conjugates are biohybrid macromolecules derived from covalently connecting synthetic polymers with polypeptides. The resulting materials combine the properties of both worlds: chemists can engineer polymers to stabilize proteins, to add functionality, or to enhance activity; whereas biochemists can exploit the specificity and complexity that Nature has bestowed upon its macromolecules. This has led to a wealth of applications, particularly within the realm of biomedicine. Polymer-protein conjugation has expanded to include scaffolds for drug delivery, tissue engineering, and microbial inhibitors. This feature article reflects upon recent developments in the field and discusses the applications of these hybrids from a biomaterials standpoint.

Tuning hemoglobin-poly(acrylic acid) interactions by controlled chemical modification with triethylenetetramine

Protein-polymer interactions play a very important role in a number of applications, but details of these interactions are not fully understood. Chemical modification was introduced here to tune protein-polymer interactions in a systematic manner, where methemoglobin (Hb) and poly(acrylic acid) (PAA) served as a model system. Under similar conditions of pH and ionic strength, the influence of protein charge on Hb/PAA interaction was studied using chemically modified Hb by isothermal titration calorimetry (ITC). A small fraction of COOH groups of Hb were amidated with triethylenetetramine (TETA) or ammonium chloride to produce the corresponding charge ladders of Hb-TETA and Hb-ammonia derivatives, respectively. All the Hb/PAA complexes produced here are bioactive, entirely soluble in water, and indicated the retention of Hb structure to a significant extent. Binding of Hb to PAA was exothermic (ΔH < 0). The binding of Hb-TETA charge ladder to PAA indicated decrease of ΔH from -8 ± 0.2 to -89 ± 4 kcal/mol, at a rate of -3.8 kcal/mol per unit charge introduced via modification. The Hb-ammonia charge ladder, in contrast, showed a decrease of ΔH from -8 ± 0.2 to -17 ± 1.5 kcal/mol, at much slower rate of -1.0 kcal/mol per unit charge. Thus, the amine used for the modification played a strong role in tuning Hb/PAA interactions, even after correcting for the charge, synergistically. Charge clustering may be responsible for this synergy, and this interesting observation may be exploited to construct protein/polymer platforms for advanced biomacromolecular applications.