Synthesis of poly(meth)acrylates with thioether and tertiary sulfonium groups by ARGET ATRP and their use as siRNA delivery agents

Beyond Lipids: Exploring Advances in Polymeric Gene Delivery in the Lipid Nanoparticles Era

The recent success of gene therapy during the COVID-19 pandemic has underscored the importance of effective and safe delivery systems. Complementing lipid-based delivery systems, polymers present a promising alternative for gene delivery. Significant advances have been made in the recent past, with multiple clinical trials progressing beyond phase I and several companies actively working on polymeric delivery systems which provides assurance that polymeric carriers can soon achieve clinical translation. The massive advantage of structural tunability and vast chemical space of polymers is being actively leveraged to mitigate shortcomings of traditional polycationic polymers and improve the translatability of delivery systems. Tailored polymeric approaches for diverse nucleic acids and for specific subcellular targets are now being designed to improve therapeutic efficacy. This review describes the recent advances in polymer design for improved gene delivery by polyplexes and covalent polymer-nucleic acid conjugates. The review also offers a brief note on novel computational techniques for improved polymer design. The review concludes with an overview of the current state of polymeric gene therapies in the clinic as well as future directions on their translation to the clinic.

Main-Chain Sulfonium-Containing Homopolymers with Negligible Hemolytic Toxicity for Eradication of Bacterial and Fungal Biofilms

Antimicrobials against planktonic cells and established biofilms at low doses are in increasing demand to tackle antibiotic-resistant biofilm infections. As a promising alternative to antibiotics, cationic polymers can effectively kill planktonic microbes but usually require high concentrations to eradicate the established biofilms. Herein, we developed a series of sulfonium-based homopolymers with cationic sulfoniums and alkane spacers in the main chain. These polysulfoniums presented effective activity against planktonic fungi (Candida albicans) and bacteria (Escherichia coli and Staphylococcus aureus) with minimum inhibition concentrations (MICs) of 0.5-32 μg/mL, and the optimal composition can provide an 80-90% reduction in biofilm mass and >99% killing of Candida albicans and Escherichia coli cells in 3-day mature biofilms at 2 × MIC as well as steadily low hemolytic toxicity. The influence of amphiphilicity and charge density of polysulfonium homopolymers on their antimicrobial activity against planktonic microbes and mature biofilms was investigated to provide insights for effective antimicrobial polymer design.

Broad-Spectrum Bactericidal Activity and Remarkable Selectivity of Main-Chain Sulfonium-Containing Polymers with Alternating Sequences

Incorporation of cationic groups into polymers represents one of the most widely used strategies to prepare antibacterial materials. Sulfonium, as a typical cationic moiety, displays potent antibacterial efficacy in the form of small molecules, however, has long underperformed in polymeric systems. Herein, we developed a series of alternating polysulfoniums, where the hydrophobicity of each alternating unit can be accurately tuned by altering the monomer precursors. Excellent antibacterial activity against a broad spectrum of clinically relevant bacteria, including Methicillin-resistant Staphylococcus aureus, can be obtained in the optimal compositions with minimum bactericidal concentrations in the range of 1.25-10 μg/mL, as well as negligible hemolytic effect at polymer concentrations even up to 10000 μg/mL. Bacteria do not readily develop resistance to polysulfoniums due to the antibacterial action is possibly the membrane disrupting mechanism. This work demonstrates sulfonium-based polymers with well-defined sequences can function as a promising candidate to combat drug-resistant bacterial infection.

Main-Chain Polysulfonium Salts: Development of Non-Ammonium Antibacterial Polymers Similar in Their Activity to Antibiotic Drugs Vancomycin and Kanamycin

Typically, quaternary ammonium polymers are employed for antibacterial purposes. However, a century of use has led bacteria to develop resistance to such materials. Therefore, attention is now turning toward other cationic moieties. In this context, the present work explores sulfur-based main-chain cationic polymers. The results indicate that sulfonium polymers with a β-hydroxy motif do not suffer from structural instability issues as is commonly observed in cationic polythioethers. Furthermore, they can be highly effective toward important Gram-positive bacterial strains such as Mycobacterium smegmatis, a model organism to develop drugs against rapidly spreading tuberculosis infections. More importantly, however, more challenging Gram-negative strains such as Escherichia coli can also be targeted by the polysulfoniums with equal effectiveness. Interestingly, side-chain sulfonium polyelectrolytes are observed to be devoid of any significant antibacterial activity. Finally, a comparison with kanamycin and vancomycin suggests the present polymers to be similarly effective as the bactericidal antibiotic drugs. Overall, these results indicate the effectiveness of the main-chain trivalent β-hydroxy sulfonium motif for the development of novel antibacterial polymers with a non-ammonium structure.

Engineering of Janus-Like Dendrimers with Peptides Derived from Glycoproteins of Herpes Simplex Virus Type 1: Toward a Versatile and Novel Antiviral Platform

Novel antiviral nanotherapeutics, which may inactivate the virus and block it from entering host cells, represent an important challenge to face viral global health emergencies around the world. Using a combination of bioorthogonal copper-catalyzed 1,3-dipolar alkyne/azide cycloaddition (CuAAC) and photoinitiated thiol-ene coupling, monofunctional and bifunctional peptidodendrimer conjugates were obtained. The conjugates are biocompatible and demonstrate no toxicity to cells at biologically relevant concentrations. Furthermore, the orthogonal addition of multiple copies of two different antiviral peptides on the surface of a single dendrimer allowed the resulting bioconjugates to inhibit Herpes simplex virus type 1 at both the early and the late stages of the infection process. The presented work builds on further improving this attractive design to obtain a new class of therapeutics.

Functional Polymer Zwitterions as Reactive Surfactants for Nanoparticle Capture

We describe the synthesis of sulfothetin (ST)-containing polymer zwitterions and their use as polymer surfactants for stabilizing emulsion droplets and for capturing and transporting nanoparticles (NPs) through a flowing aqueous fluid. In contrast to conventional zwitterions, which are chemically inert, the multifunctional ST-containing copolymers we describe both participate in droplet stabilization and embed reactive functionality directly into the zwitterionic framework. Advantageously including these ST zwitterions in phosphorylcholine (PC)-containing copolymers proved particularly useful for producing surfactants that contributed characteristics of droplet stabilization and interfacial reactivity. This was demonstrated by NP pickup, or "capture", experiments that were performed by circulating ST-coated emulsion droplets across a substrate, in a flow cell, containing amine-functionalized silica NPs. The resultant NP adherence to the fluid-fluid interface of the droplets hinged on the available reactivity of both the electrophilic (from ST) and nucleophilic (from the NPs) components as well as the solution pH and extent of amine functionality on the NPs.

Polymeric Delivery of Therapeutic Nucleic Acids

The advent of genome editing has transformed the therapeutic landscape for several debilitating diseases, and the clinical outlook for gene therapeutics has never been more promising. The therapeutic potential of nucleic acids has been limited by a reliance on engineered viral vectors for delivery. Chemically defined polymers can remediate technological, regulatory, and clinical challenges associated with viral modes of gene delivery. Because of their scalability, versatility, and exquisite tunability, polymers are ideal biomaterial platforms for delivering nucleic acid payloads efficiently while minimizing immune response and cellular toxicity. While polymeric gene delivery has progressed significantly in the past four decades, clinical translation of polymeric vehicles faces several formidable challenges. The aim of our Account is to illustrate diverse concepts in designing polymeric vectors towards meeting therapeutic goals of in vivo and ex vivo gene therapy. Here, we highlight several classes of polymers employed in gene delivery and summarize the recent work on understanding the contributions of chemical and architectural design parameters. We touch upon characterization methods used to visualize and understand events transpiring at the interfaces between polymer, nucleic acids, and the physiological environment. We conclude that interdisciplinary approaches and methodologies motivated by fundamental questions are key to designing high-performing polymeric vehicles for gene therapy.

Oxidation and ATP dual-responsive block copolymer containing tertiary sulfoniums: self-assembly, protein complexation and triggered release

Alkylation of thioether-containing block copolymer simultaneously incorporated sulfoniums and phenylboronic acid moieties. The co-assembly of this cationic polymer and protein generated micelles with an H₂O₂-and ATP-responsive release profile.

Thiol-Bromo Click Reaction for One-Pot Synthesis of Star-Shaped Polymers

Star-shaped polymers have unique physical properties and they are sought after materials in industry. However, the ease of synthesis is essential for translation of these materials into large-scale applications. Herein, a highly efficient synthetic method to prepare star-shaped polymers by combination of Cu-mediated reversible deactivation radical polymerization (Cu-RDRP) and thiol-bromo click reaction is described. Well-defined linear and block polymers with a very high bromine chain end fidelity are obtained via Cu-RDRP and subsequently react with multi-functional thiol compounds. High coupling efficiencies of larger than 90% are obtained owing to the quick and efficient reaction between thiols and alkyl bromides. Moreover, the arms of the obtained star-shaped polymers are linked via thioether bonds to the core, making them susceptible for oxidative degradation.

Facile fabrication of a controlled polymer brush-type functional nanoprobe for highly sensitive determination of alpha fetoprotein

As robust functional polymers, polymer brush-based hybrid nanomaterials have potential application in the highly sensitive determination of tumor markers (TMs). Currently, there are plentiful reports on the polymerization methods of functional polymer brushes. Low ppm ATRP (activators (re)generated by electron transfer for atom transfer radical polymerization (A(R)GET ATRP), initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP) and electrochemically mediated atom transfer radical polymerization (eATRP)) is a facile and robust methodology with the advantages of simplicity, eco-friendliness and wide applicability to prepare well-defined polymeric materials. In this work, a controlled polymer brush-type functional nanoprobe is successfully fabricated by functional AGET ATRP and used as a sandwich-type electrochemical immunosensor for precise detection of TMs (alpha-fetoprotein, AFP). Using graphene oxide (GO) as an excellent conductive matrix, a GO-based poly-heterozygosis pyridine nanomaterial (GO@PHPY) is obtained by surface-initiated AGET ATRP and photocatalytic modification. The nanoprobe is assembled using GO@PHPY and a detection antibody (Ab2) to detect AFP, in which Cu(ii) serves as a signal label to coordinate with the pyridyl group. Under optimized conditions, the electrochemical sensor exhibits a good detection effect on AFP, with a detection range of 0.1 pg mL^-1 to 100 ng mL^-1 and a low detection limit of 0.08 pg mL^-1. It is worth noting that the detection platform can be applied to the detection of real human serum samples. Thus, it is a desirable platform for AFP detection in clinical diagnosis and practical applications. Meanwhile, this work proves that designing and constructing functional polymer brushes is one of the most effective methods for developing new materials for analytical scientific applications.

Photoinduced Proton-Transfer Polymerization: A Practical Synthetic Tool for Soft Lithography Applications

Proton-transfer photopolymerization through the thiol-epoxy "click" reaction is shown to be a versatile new method for the fabrication of micro- and nanosized polymeric patterns. In this approach, complexation of a guanidine base, diazabicycloundecene (DBU), with benzoylphenylpropionic acid (ketoprofen) generates a photolabile salt. Under illumination at a wavelength of 365 nm, the salt undergoes a photodecarboxylation reaction to release DBU as a base. The base-catalyzed ring opening reaction then creates cross-linked poly(β-hydroxyl thio-ether) patterns. The surface chemistry of these patterns can be altered through alkylation of the thio-ether linkages. For example, a reaction with bromoacetic acid produces a hitherto unknown sulfonium/carboxylate-based zwitterionic motif that endows antibiofouling capacity to the micropatterns.

Cationic Hyperbranched Polymers with Biocompatible Shells for siRNA Delivery

Cationic hyperbranched polymers (HBP) were prepared by self-condensing vinyl polymerization of an atom transfer radical polymerization (ATRP) inimer containing a quaternary ammonium group. Two types of biocompatible shells, poly(oligoethylene glycol) methacrylate (polyOEGMA) and poly(2-(methylsulfinyl) ethyl methacrylate) (polyDMSO), were grafted respectively from HBP core to form core-shell structures with low molecular weight dispersity and high biocompatibility, polyOEGMA-HBP and polyDMSO-HBP. Both of the structures showed low cytotoxicity and good siRNA complexing ability. The efficacy of gene silencing against Runt-related transcription factor 2 ( Runx2) expression and the long-term assessment of mineralized nodule formation in osteoblast cultures were evaluated. The biocompatible core-shell structures were crucial to minimizing undesired cytotoxicity and nonspecific gene suppression. polyDMSO-HBP showed higher efficacy of forming polyplexes than polyOEGMA-HBP due to shell with lower steric hindrance. Overall, the gene silencing efficiency of both core-shell structures was comparable to commercial agent Lipofectamine, indicating long-term potential for gene silencing to treat heterotopic ossification (HO).

The great escape: how cationic polyplexes overcome the endosomal barrier

Endo-lysosomal escape strategies of cationic polymer-mediated gene delivery at a glance.

2-(Methylthio)ethyl Methacrylate: A Versatile Monomer for Stimuli Responsiveness and Polymerization-Induced Self-Assembly in the Presence of Air

In this communication, we investigate the photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of 2-(methylthio)ethyl methacrylate (MTEMA) using 5,10,15,20-tetraphenylporphine zinc (ZnTPP) as a photocatalyst under visible red light (λ_max = 635 nm). Interestingly, the polymerization kinetics were not affected by the presence of air as near identical polymerization kinetics were observed for non-deoxygenated and deoxygenated systems, which is attributed to the singlet oxygen quenching ability of MTEMA. In both cases, well-defined polymers were obtained with good control over the molecular weight and molecular weight distribution (MWD). Furthermore, we have demonstrated that MTEMA can undergo the polymerization-induced self-assembly (PISA) process from a poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) macromolecular chain transfer agent (macro-CTA) to yield well-defined polymeric nanoparticles of various morphologies. These nanoparticles were rapidly disassembled after exposure to visible light due to the formation of singlet oxygen by the encapsulated ZnTPP and subsequent rapid oxidation of the thioether group.

Biocompatible Polymeric Analogues of DMSO Prepared by Atom Transfer Radical Polymerization

The synthesis of a sulfoxide-based water-soluble polymer, poly(2-(methylsulfinyl)ethyl acrylate) (polyMSEA), a polymeric analogue of DMSO, by atom transfer radical polymerization (ATRP) is reported. Well-defined linear polymers were synthesized using relatively low amounts of copper catalyst (1000 or 100 ppm). Two types of star polymers were synthesized by either an "arm-first" approach or a "core-first" approach using a biodegradable β-cyclodextrin core. The glass transition temperatures of both the linear polymer (16 °C) and star polymer (32 °C) were determined by differential scanning calorimetry (DSC). The lower critical solution temperature (LCST) of poly(MSEA) was estimated to be ca. 140 °C by extrapolating the LCST of a series of copolymers with NIPAM. Cytotoxicity tests revealed that both the linear and star polymers have low toxicity, even at concentrations up to 3 mg/mL.

Thermo and pH dual responsive polypeptides derived from “clickable” poly(γ-3-methylthiopropyl-l-glutamate)

Thermo and pH dual responsive polypeptides bearing sulfonium linkages and ammonium pendants were prepared from “clickable” thioether-containing polypeptides.

A stimuli-responsive methionine-based zwitterionic methacryloyl sulfonium sulfonate monomer and the corresponding antifouling polymer with tunable thermosensitivity

This report describes a dual pH- and thermo-responsive methionine-based zwitterionic methacryloyl sulfonium sulfonate monomer and the corresponding zwitterionic antifouling polymer with ion-induced tunable thermosensitivity.

Multifunctional polymers built on copper–thioether coordination

Copper–thioether coordinated block polymers were successfully constructed to form mechanically tough materials with a color response towards hydrochloric acid and hydrogen peroxide.

Biosynthetic Polymers as Functional Materials

The synthesis of functional polymers encoded with biomolecules has been an extensive area of research for decades. As such, a diverse toolbox of polymerization techniques and bioconjugation methods has been developed. The greatest impact of this work has been in biomedicine and biotechnology, where fully synthetic and naturally derived biomolecules are used cooperatively. Despite significant improvements in biocompatible and functionally diverse polymers, our success in the field is constrained by recognized limitations in polymer architecture control, structural dynamics, and biostabilization. This Perspective discusses the current status of functional biosynthetic polymers and highlights innovative strategies reported within the past five years that have made great strides in overcoming the aforementioned barriers.