Origin of Proteolytic Stability of Peptide-Brush Polymers as Globular Proteomimetics

Synthesis of Fucoidan-Biomimetic Glycopolymers with Flexible Skeletons for Enhanced Anti-Herpes Virus Efficacy

Synthetic glycopolymers can be designed to mimic the structure and biological function of natural polysaccharides, offering a wide range of potential applications in the pharmaceutical and medicine. Nevertheless, amphiphilic synthetic glycopolymers commonly form biologically inert nanomicelle structures in aqueous solutions through spontaneous self-assembly. Envisioning that preventing self-assembly is pivotal to the full realization of the biological activities of the glycopolymers, we design and prepare a class of norbornene-derived hydrophilic glycopolymers containing sulfated fucose amenable to skeleton modification through ring-opening metathesis polymerization (ROMP). The skeleton of the fucoidan glycopolymers was chemically modified with hydrogen reduction, dihydroxylation, and oxidation following subsequent sulfation. We conducted physicochemical property characterization of the skeleton-modified glycopolymers to demonstrate that the hydrophilic glycopolymers have a more flexible structure compared to conventional polymers, and the sulfated fucoidan glycopolymers form a non-assembly morphology similar to the natural polysaccharides. Furthermore, the non-assembly glycopolymers exhibit significantly enhanced anti-HSV-1 activities. Our findings underscore the significance of the rational design of polymer skeletons in the development of structural and functional mimics of natural polysaccharides.

Protein-Like Polymers Targeting Keap1/Nrf2 as Therapeutics for Myocardial Infarction

Myocardial infarction (MI) results in oxidative stress to the myocardium and frequently leads to heart failure (HF). There is an unmet clinical need to develop therapeutics that address the inflammatory stress response and prevent negative left ventricular remodeling. Here, the Keap1/Nrf2 protein-protein interaction is specifically targeted, as Nrf2 activation is known to mitigate the inflammatory response following MI. This is achieved using a Nrf2-mimetic protein-like polymer (PLP) to inhibit the Keap1-Nrf2 interaction. The PLP platform technology provides stability in vivo, potent intracellular bioactivity, and multivalency leading to high avidity Keap1 binding. In vitro and in vivo assays to probe cellular activity and MI therapeutic utility are employed. These Keap1-inhibiting PLPs (Keap1i-PLPs) impart cytoprotection from oxidative stress via Nrf2 activation at sub-nanomolar concentrations in primary cardiomyocytes. Single-digit mg kg-1, single-dose, intravenous PLP administration significantly improves cardiac function in rats post-MI through immunomodulatory, anti-apoptotic, and angiogenic mechanisms. Thus Keap1i-PLPs disrupt key intracellular protein-protein interactions following intravenous, systemic administration in vivo. These results have broad implications not only for MI but also for other oxidative stress-driven diseases and conditions.

Heterobifunctional proteomimetic polymers for targeted protein degradation

The burgeoning field of targeted protein degradation (TPD) has opened new avenues for modulating the activity of previously undruggable proteins of interest. To date, TPD has been dominated by small molecules containing separate linked domains for protein engagement and recruitment of cellular degradation machinery. The process of identifying active compounds has required tedious optimization and has been successful largely against a limited set of targets with well-defined, suitable docking pockets. Here we present a polymer chemistry approach termed the HYbrid DegRAding Copolymer (HYDRAC) to overcome standing challenges associated with the development of TPD. These copolymers densely display either peptide-based or small molecule-derived degradation inducers and target-binding peptide sequences for the selective degradation of disease-associated proteins. HYDRACs are synthesized in a facile manner, are modular in design, and are highly selective. Using the intrinsically disordered transcription factor MYC as an initial proof-of-concept, difficult to drug protein target, HYDRACs containing a MYC-inhibitory peptide copolymerized with a validated degron, showed robust and selective degradation of the target protein. Treatment of tumor-bearing mice with MYC-targeted HYDRACs showed decreased cell proliferation and increased tumor apoptosis, leading to significantly suppressed tumor growth in vivo . The versatility of the platform was demonstrated by substituting the degron for recruiters of three different E3 ligases (VHL, KEAP1, and CRBN), which all maintained MYC degradation. To demonstrate generalizability, HYDRACs were further designed against a second elusive target of clinical interest, KRAS, by employing a consensus RAS binding motif. RAS-targeted HYDRACs showed degradation in two cell lines harboring separate KRAS alleles, suggesting potential pan-KRAS activity. We envision the HYDRAC platform as a generalizable approach to developing degraders of proteins of interest, greatly expanding the therapeutic armamentarium for TPD.

Responsive Degradable Bottlebrush Polymers Enable Drugs With Superior Efficacy and Minimal Systemic Toxicity

Bottlebrush polymers (BBPs) have garnered significant attention as advanced drug delivery systems, capable of transporting a diverse range of therapeutic agents, including both chemical drugs and biologics. Despite their effectiveness, the empty BBP vectors post-drug release may pose long-term safety risks due to their difficult systemic clearance. Here, a responsive degradable BBP platform for cancer therapy is developed, featuring a poly(disulfide) backbone grafted with fluorine-terminated zwitterionic side chains. Anti-cancer drugs are tethered to the backbone via a clinically approved valine-citrulline (VC) linker. This design leverages the tumor's reductive environment and Cathepsin B overexpression for BBP rapid degradation and precise drug release restricted within tumor cells, thereby addressing systemic safety concerns over synthetic BBP and expanding the therapeutic window of anti-cancer drugs simultaneously. Surface fluorination of BBP further enhances tumor accumulation and deep penetration. In vivo studies with monomethyl auristatin E (MMAE)-loaded BBP in tumor-bearing mice demonstrate substantial tumor suppression with minimal side effects. Together, these findings highlight the potential of responsive degradable BBP as a versatile unimolecular platform for cancer drug delivery, addressing existing challenges associated with synthetic BBP nanomedicines.

The Precise Synthesis of Ultradense Bottlebrush Polymers Unearths Unique Trends in Lyotropic Ordering

Biomacromolecular networks with multiscale fibrillar structures are characterized by exceptional mechanical properties, making them attractive architectures for synthetic materials. However, there is a dearth of synthetic polymeric building blocks capable of forming similarly structured networks. Bottlebrush polymers (BBPs) are anisotropic graft polymers with the potential to mimic and replace biomacromolecules such as tropocollagen for the fabrication of synthetic fibrillar networks; however, a longstanding limitation of BBPs has been the lack of rigidity necessary to access the lyotropic ordering that underpins the formation of collagenous networks. While the correlation between BBP rigidity and grafting density is well established, synthetic approaches to rigidify BBPs by increased grafting density are underdeveloped. To address this gap in synthetic capability, we report the synthesis of novel macroinitiators that provide well-defined BBPs with an unprecedentedly high grafting density. A suite of light scattering techniques are used to correlate macromolecular rigidity with grafting architecture and density and demonstrate for the first time that poly(norbornene) BBPs exhibit long-range lyotropic ordering as a result of their rodlike character. Specifically, the newly reported ultradensely grafted structures, preparable on multigram scale, form hexagonal arrays while conventional BBPs do not, despite showing long-range spatial correlations. These results implicate the central role of density and entanglement in the solution phase assembly of BBPs and provide new fundamental insight that is broadly relevant to the fabrication and performance of BBP-derived materials, spanning biomedical research to photonic materials and thermal management technologies. Furthermore, these newly reported liquid crystalline BBPs provide a structural template to explore the untapped potential of the bottom-up assembly of semiflexible networks and are ultimately intended to provide a modular route to hierarchically structured biomimetic materials.

Proteomimetic polymer blocks mitochondrial damage, rescues Huntington's neurons, and slows onset of neuropathology in vivo

Recently, it has been shown that blocking the binding of valosin-containing protein (VCP) to mutant huntingtin (mtHtt) can prevent neuronal mitochondrial autophagy in Huntington's disease (HD) models. Herein, we describe the development and efficacy of a protein-like polymer (PLP) for inhibiting this interaction in cellular and in vivo models of HD. PLPs exhibit bioactivity in HD mouse striatal cells by successfully inhibiting mitochondrial destruction. PLP is notably resilient to in vitro enzyme, serum, and liver microsome stability assays, which render analogous control oligopeptides ineffective. PLP demonstrates a 2000-fold increase in circulation half-life compared to peptides, exhibiting an elimination half-life of 152 hours. In vivo efficacy studies in HD transgenic mice (R6/2) confirm the superior bioactivity of PLP compared to free peptide through behavioral and neuropathological analyses. PLP functions by preventing pathologic VCP/mtHtt binding in HD animal models; exhibits enhanced efficacy over the parent, free peptide; and implicates the PLP as a platform with potential for translational central nervous system therapeutics.

Conformational modulation and polymerization-induced folding of proteomimetic peptide brush polymers

Peptide-brush polymers generated by graft-through living polymerization of peptide-modified monomers exhibit high proteolytic stability, therapeutic efficacy, and potential as functional tandem repeat protein mimetics. Prior work has focused on polymers generated from structurally disordered peptides that lack defined conformations. To obtain insight into how the structure of these polymers is influenced by the folding of their peptide sidechains, a set of polymers with varying degrees of polymerization was prepared from peptide monomers that adopt α-helical secondary structure for comparison to those having random coil structures. Circular dichroism and nuclear magnetic resonance spectroscopy confirm the maintenance of the secondary structure of the constituent peptide when polymerized. Small-angle X-ray scattering (SAXS) studies reveal the solution-phase conformation of PLPs in different solvent environments. In particular, X-ray scattering shows that modulation of solvent hydrophobicity, as well as hydrogen bonding patterns of the peptide sidechain, plays an important role in the degree of globularity and conformation of the overall polymer, with polymers of helical peptide brushes showing less spherical compaction in conditions where greater helicity is observed. These structural insights into peptide brush folding and polymer conformation inform the design of these proteomimetic materials with promise for controlling and predicting their artificial fold and morphology.

Tips and Tricks in the Modeling of Supramolecular Peptide Assemblies

Supramolecular peptide assemblies (SPAs) hold promise as materials for nanotechnology and biomedicine. Although their investigation often entails adapting experimental techniques from their protein counterparts, SPAs are fundamentally distinct from proteins, posing unique challenges for their study. Computational methods have emerged as indispensable tools for gaining deeper insights into SPA structures at the molecular level, surpassing the limitations of experimental techniques, and as screening tools to reduce the experimental search space. However, computational studies have grappled with issues stemming from the absence of standardized procedures and relevant crystal structures. Fundamental disparities between SPAs and protein simulations, such as the absence of experimentally validated initial structures and the importance of the simulation size, number of molecules, and concentration, have compounded these challenges. Understanding the roles of various parameters and the capabilities of different models and simulation setups remains an ongoing endeavor. In this review, we aim to provide readers with guidance on the parameters to consider when conducting SPA simulations, elucidating their potential impact on outcomes and validity.

Proteomimetic Polymers Trigger Potent Antigen-Specific T Cell Responses to Limit Tumor Growth

Elicitation of effective antitumor immunity following cancer vaccination requires the selective activation of distinct effector cell populations and pathways. Here we report a therapeutic approach for generating potent T cell responses using a modular vaccination platform technology capable of inducing directed immune activation, termed the Protein-like Polymer (PLP). PLPs demonstrate increased proteolytic resistance, high uptake by antigen-presenting cells (APCs), and enhanced payload-specific T cell responses. Key design parameters, namely payload linkage chemistry, degree of polymerization, and side chain composition, were varied to optimize vaccine formulations. Linking antigens to the polymer backbone using an intracellularly cleaved disulfide bond copolymerized with a diluent amount of oligo(ethylene glycol) (OEG) resulted in the highest payload-specific potentiation of antigen immunogenicity, enhancing dendritic cell (DC) activation and antigen-specific T cell responses. Vaccination with PLPs carrying either gp100, E7, or adpgk peptides significantly increased the survival of mice inoculated with B16F10, TC-1, or MC38 tumors, respectively, without the need for adjuvants. B16F10-bearing mice immunized with gp100-carrying PLPs showed increased antitumor CD8+ T cell immunity, suppressed tumor growth, and treatment synergy when paired with two distinct stimulator of interferon gene (STING) agonists. In a human papillomavirus-associated TC-1 model, combination therapy with PLP and 2'3'-cGAMP resulted in 40% of mice completely eliminating implanted tumors while also displaying curative protection from rechallenge, consistent with conferment of lasting immunological memory. Finally, PLPs can be stored long-term in a lyophilized state and are highly tunable, underscoring the unique properties of the platform for use as generalizable cancer vaccines.

Controlled adsorption of multiple bioactive proteins enables targeted mast cell nanotherapy

Protein adsorption onto nanomaterials often results in denaturation and loss of bioactivity. Controlling the adsorption process to maintain the protein structure and function has potential for a range of applications. Here we report that self-assembled poly(propylene sulfone) (PPSU) nanoparticles support the controlled formation of multicomponent enzyme and antibody coatings and maintain their bioactivity. Simulations indicate that hydrophobic patches on protein surfaces induce a site-specific dipole relaxation of PPSU assemblies to non-covalently anchor the proteins without disrupting the protein hydrogen bonding or structure. As a proof of concept, a nanotherapy employing multiple mast-cell-targeted antibodies for preventing anaphylaxis is demonstrated in a humanized mouse model. PPSU nanoparticles displaying an optimized ratio of co-adsorbed anti-Siglec-6 and anti-FcεRIα antibodies effectively inhibit mast cell activation and degranulation, preventing anaphylaxis. Protein immobilization on PPSU surfaces provides a simple and rapid platform for the development of targeted protein nanomedicines.

Inhibiting the Keap1/Nrf2 Protein-Protein Interaction with Protein-Like Polymers

Successful and selective inhibition of the cytosolic protein-protein interaction (PPI) between nuclear factor erythroid 2-related factor 2 (Nrf2) and Kelch-like ECH-associating protein 1 (Keap1) can enhance the antioxidant response, with the potential for a therapeutic effect in a range of settings including in neurodegenerative disease (ND). Small molecule inhibitors have been developed, yet many have off-target effects, or are otherwise limited by poor cellular permeability. Peptide-based strategies have also been attempted to enhance specificity, yet face challenges due to susceptibility to degradation and lack of cellular penetration. Herein, these barriers are overcome utilizing a polymer-based proteomimetics. The protein-like polymer (PLP) consists of a synthetic, lipophilic polymer backbone displaying water soluble Keap1-binding peptides on each monomer unit forming a brush polymer architecture. The PLPs are capable of engaging Keap1 and displacing the cellular protective transcription factor Nrf2, which then translocates to the nucleus, activating the antioxidant response element (ARE). PLPs exhibit increased Keap1 binding affinity by several orders of magnitude compared to free peptides, maintain serum stability, are cell-penetrant, and selectively activate the ARE pathway in cells, including in primary cortical neuronal cultures. Keap1/Nrf2-inhibitory PLPs have the potential to impact the treatment of disease states associated with dysregulation of oxidative stress, such as NDs.

Chemical recycling of polyolefins via ring-closing metathesis depolymerization

The current insufficient recycling of commodity polymer waste has resulted in pressing environmental and human health issues in our modern society. In the quest for next-generation polymer materials, chemists have recently shifted their attention to the design of chemically recyclable polymers that can undergo depolymerization to regenerate monomers under mild conditions. During the past decade, ring-closing metathesis reactions have been demonstrated to be a robust approach for the depolymerization of polyolefins, producing low-strain cyclic alkene products which can be repolymerized back to new batches of polymers. In this review, we aim to highlight the recent advances in chemical recycling of polyolefins enabled by ring-closing metathesis depolymerization (RCMD). A library of depolymerizable polyolefins will be covered based on the ring size of their monomers or depolymerization products, including five-membered, six-membered, eight-membered, and macrocyclic rings. Moreover, current limitations, potential applications, and future opportunities of the RCMD approach will be discussed. It is clear from recent research in this field that RCMD represents a powerful strategy towards closed-loop chemical recycling of novel polyolefin materials.

Thrombospondin-1 proteomimetic polymers exhibit anti-angiogenic activity in a neovascular age-related macular degeneration mouse model

Neovascular age-related macular degeneration (nAMD) is the leading cause of blindness in the developed world. Current therapy includes monthly intraocular injections of anti-VEGF antibodies, which are ineffective in up to one third of patients. Thrombospondin-1 (TSP1) inhibits angiogenesis via CD36 binding, and its down-regulated expression is negatively associated with the onset of nAMD. Here, we describe TSP1 mimetic protein-like polymers (TSP1 PLPs). TSP1 PLPs bind CD36 with high affinity, resist degradation, show prolonged intraocular half-lives (13.1 hours), have no toxicity at relevant concentrations in vivo (40 μM), and are more efficacious in ex vivo choroidal sprouting assays compared to the peptide sequence and Eylea (aflibercept), the current standard of care anti-VEGF treatment. Furthermore, PLPs exhibit superior in vivo efficacy in a mouse model for nAMD compared to control PLPs consisting of scrambled peptide sequences, using fluorescein angiography and immunofluorescence. Since TSP-1 inhibits angiogenesis by VEGF-dependent and independent mechanisms, TSP1 PLPs are a potential therapeutic for patients with anti-VEGF treatment-resistant nAMD.

Lipidation Alters the Structure and Hydration of Myristoylated Intrinsically Disordered Proteins

Lipidated proteins are an emerging class of hybrid biomaterials that can integrate the functional capabilities of proteins into precisely engineered nano-biomaterials with potential applications in biotechnology, nanoscience, and biomedical engineering. For instance, fatty-acid-modified elastin-like polypeptides (FAMEs) combine the hierarchical assembly of lipids with the thermoresponsive character of elastin-like polypeptides (ELPs) to form nanocarriers with emergent temperature-dependent structural (shape or size) characteristics. Here, we report the biophysical underpinnings of thermoresponsive behavior of FAMEs using computational nanoscopy, spectroscopy, scattering, and microscopy. This integrated approach revealed that temperature and molecular syntax alter the structure, contact, and hydration of lipid, lipidation site, and protein, aligning with the changes in the nanomorphology of FAMEs. These findings enable a better understanding of the biophysical consequence of lipidation in biology and the rational design of the biomaterials and therapeutics that rival the exquisite hierarchy and capabilities of biological systems.

Molecular polymer bottlebrushes in nanomedicine: therapeutic and diagnostic applications

Molecular polymer bottlebrushes are densely grafted, individual macromolecules with nanoscale proportions. The last decade has seen an increased focus on this material class, especially in nanomedicine and for biomedical applications. This Feature Article provides an overview of major developments in this area to highlight the many opportunities that these polymer architectures bring to nano-bio research. The article covers aspects of bottlebrush synthesis and summarises their use in drug and gene delivery, imaging, as theranostics and as prototype materials to correlate nanoparticle structure and composition to biological function and behaviour. Areas for future research in this area are discussed.