Expanding the materials space of DNA via organic-phase ring-opening metathesis polymerization

Synthesis of Antifouling Poly(ethylene glycol) Brushes via "Grafting to" Approach for Improved Biodistribution

Polyethylene glycol (PEG) modification of materials has been identified to mitigate the challenge of biofouling. However, the practical application of PEGylation has been hampered by a low PEGylation density on the material surface. Therefore, developing efficient strategies to promote the PEGylation density is crucial. In this study, PEG brushes (PBs) with various structures were synthesized and their physicochemical properties and biomedical applications were investigated. Compared to benzaldehyde (BA), o-phthalaldehyde (OPA) exhibited higher reactivity with amine groups, resulting in increased grafting density (as high as 96.3%) and improved antifouling properties of PEG brushes. Bottlebrushes fabricated by PEG-OPA and polylysine demonstrated a prolonged circulation time in blood and enhanced potential for magnetic resonance imaging of tumors. Furthermore, the rigidity of the backbone was found to be crucial for the antifouling properties of PEG brushes both in vitro and in vivo. These findings are significant and provide valuable insights into designing biomaterials with superior antifouling performance.

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.

Supramolecular DNA-based catalysis in organic solvents

The distinct folding accompanied by its polymorphic character renders DNA G-quadruplexes promising biomolecular building blocks to construct novel DNA-based and supramolecular assemblies. However, the highly polar nature of DNA limits the use of G-quadruplexes to water as a solvent. In addition, the archetypical G-quadruplex fold needs to be stabilized by metal-cations, which is usually a potassium ion. Here, we show that a noncovalent PEGylation process enabled by electrostatic interactions allows the first metal-free G-quadruplexes in organic solvents. Strikingly, incorporation of an iron-containing porphyrin renders the self-assembled metal-free G-quadruplex catalytically active in organic solvents. Hence, these "supraG4zymes" enable DNA-based catalysis in organic media. The results will allow the broad utilization of DNA G-quadruplexes in nonaqueous environments.

Nucleic Acid-Binding Dyes as Versatile Photocatalysts for Atom-Transfer Radical Polymerization

Nucleic acid-binding dyes (NuABDs) are fluorogenic probes that light up after binding to nucleic acids. Taking advantage of their fluorogenicity, NuABDs have been widely utilized in the fields of nanotechnology and biotechnology for diagnostic and analytical applications. We demonstrate the potential of NuABDs together with an appropriate nucleic acid scaffold as an intriguing photocatalyst for precisely controlled atom-transfer radical polymerization (ATRP). Additionally, we systematically investigated the thermodynamic and electrochemical properties of the dyes, providing insights into the mechanism that drives the photopolymerization. The versatility of the NuABD-based platform was also demonstrated through successful polymerizations using several NuABDs in conjunction with diverse nucleic acid scaffolds, such as G-quadruplex DNA or DNA nanoflowers. This study not only extends the horizons of controlled photopolymerization but also broadens opportunities for nucleic acid-based materials and technologies, including nucleic acid-polymer biohybrids and stimuli-responsive ATRP platforms.

Biomass RNA for the Controlled Synthesis of Degradable Networks by Radical Polymerization

Nucleic acids extracted from biomass have emerged as sustainable and environmentally friendly building blocks for the fabrication of multifunctional materials. Until recently, the fabrication of biomass nucleic acid-based structures has been facilitated through simple crosslinking of biomass nucleic acids, which limits the possibility of material properties engineering. This study presents an approach to convert biomass RNA into an acrylic crosslinker through acyl imidazole chemistry. The number of acrylic moieties on RNA was engineered by varying the acylation conditions. The resulting RNA crosslinker can undergo radical copolymerization with various acrylic monomers, thereby offering a versatile route for creating materials with tunable properties (e.g., stiffness and hydrophobic characteristics). Further, reversible-deactivation radical polymerization methods, such as atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT), were also explored as additional approaches to engineer the hydrogel properties. The study also demonstrated the metallization of the biomass RNA-based material, thereby offering potential applications in enhancing electrical conductivity. Overall, this research expands the opportunities in biomass-based biomaterial fabrication, which allows tailored properties for diverse applications.

Synthesis of RNA-Amphiphiles via Atom Transfer Radical Polymerization in the Organic Phase

The combination of hydrophobic polymers with nucleic acids is a fascinating way to engineer the self-assembly behavior of nucleic acids into diverse nanostructures such as micelles, vesicles, nanosheets, and worms. Here we developed a robust route to synthesize a RNA macroinitiator with protecting groups on the 2'-hydroxyl groups in the solid phase using an oligonucleotide synthesizer. The protecting groups successfully solubilized the RNA macroinitiator, enabling atom transfer radical polymerization (ATRP) of hydrophobic monomers. As a result, the RNA-polymer hybrids obtained by ATRP exhibited enhanced chemical stability by suppressing cleavage. In addition, we demonstrated evidence of controlled polymerization behavior as well as control over the molecular weight of the hydrophobic polymers grown from RNA. We envision that this methodology will expand the field of RNA-polymer conjugates while vastly enhancing the possibility to alter and engineer the properties of RNA-based polymeric materials.

Polymer-drug conjugates: Design principles, emerging synthetic strategies and clinical overview

Adagen, an enzyme replacement treatment for adenosine deaminase deficiency, was the first protein-polymer conjugate to be approved in early 1990s. Post this regulatory approval, numerous polymeric drugs and polymeric nanoparticles have entered the market as advanced or next-generation polymer-based therapeutics, while many others have currently been tested clinically. The polymer conjugation to therapeutic moiety offers several advantages, like enhanced solubilization of drug, controlled release, reduced immunogenicity, and prolonged circulation. The present review intends to highlight considerations in the design of therapeutically effective polymer-drug conjugates (PDCs), including the choice of linker chemistry. The potential synthetic strategies to formulate PDCs have been discussed along with recent advancements in the different types of PDCs, i.e., polymer-small molecular weight drug conjugates, polymer-protein conjugates, and stimuli-responsive PDCs, which are under clinical/preclinical investigation. Current impediments and regulatory hurdles hindering the clinical translation of PDC into effective therapeutic regimens for the amelioration of disease conditions have been addressed.

Exploring the Structural Diversity of DNA Bottlebrush Polymers Using an Oligonucleotide Macromonomer Approach

Herein, we demonstrate that macromonomers consisting of organics-soluble, chemically protected oligonucleotides (protDNA) and poly(ethylene glycol) (PEG) chains can be converted into bottlebrush polymers of distinct architectures via ring-opening metathesis polymerization (ROMP). Using a custom norbornene-containing phosphoramidite, two types of macromonomers were obtained: a linear norbornene-protDNA-PEG structure and a Y-shaped structure where the polymerizable norbornene group is situated at the junction where protDNA and PEG meet. With this strategy, the PEG chains can be placed either near the backbone of the bottlebrush or on its periphery, and in principle anywhere between these two extremes by adjusting the norbornene location, which makes this strategy attractive for constructing architecturally sophisticated oligonucleotide-containing copolymers.

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

Peptide-brush polymers (PBPs), wherein every side-chain of the polymers is peptidic, represent a new class of proteomimetic with unusually high proteolytic resistance while maintaining bioactivity. Here, we sought to determine the origin of this behavior and to assess its generality via a combined theory and experimental approach. A series of PBPs with various polymer backbone structures were prepared and examined for their proteolytic stability and bioactivity. We discovered that an increase in the hydrophobicity of the polymer backbones is predictive of an elevation in proteolytic stability of the side-chain peptides. Computer simulations, together with small-angle X-ray scattering (SAXS) analysis, revealed globular morphologies for these polymers, in which pendant peptides condense around hydrophobic synthetic polymer backbones driven by the hydrophobic effect. As the hydrophobicity of the polymer backbones increases, the extent of solvent exposure of peptide cleavage sites decreases, reducing their accessibility to proteolytic enzymes. This study provides insight into the important factors driving PBP aqueous-phase structures to behave as globular, synthetic polymer-based proteomimetics.

Degradable polymers via olefin metathesis polymerization

The development of degradable polymers has commanded significant attention over the past half century. Approaches have predominantly relied on ring-opening polymerization of cyclic esters (e.g., lactones, lactides) and N-carboxyanhydrides, as well as radical ring-opening polymerizations of cyclic ketene acetals. In recent years, there has been a significant effort applied to expand the family of degradable polymers accessible via olefin metathesis polymerization. Given the excellent functional group tolerance of olefin metathesis polymerization reactions generally, a broad range of conceivable degradable moieties can be incorporated into appropriate monomers and thus into polymer backbones. This approach has proven particularly versatile in synthesizing a broad spectrum of degradable polymers including poly(ester), poly(amino acid), poly(acetal), poly(carbonate), poly(phosphoester), poly(phosphoramidate), poly(enol ether), poly(azobenzene), poly(disulfide), poly(sulfonate ester), poly(silyl ether), and poly(oxazinone) among others. In this review, we will highlight the main olefin metathesis polymerization strategies that have been used to access degradable polymers, including (i) acyclic diene metathesis polymerization, (ii) entropy-driven and (iii) enthalpy-driven ring-opening metathesis polymerization, as well as (iv) cascade enyne metathesis polymerization. In addition, the livingness or control of polymerization reactions via different strategies are highlighted and compared. Potential applications, challenges and future perspectives of this new library of degradable polyolefins are discussed. It is clear from recent and accelerating developments in this field that olefin metathesis polymerization represents a powerful synthetic tool towards degradable polymers with novel structures and properties inaccessible by other polymerization approaches.

DNA-polymer conjugates via the graft-through polymerisation of native DNA in water

The direct, graft-through, ring-opening metathesis polymerisation (ROMP) of unprotected DNA macromonomers is reported. By tuning the polymerisation conditions, good control is achieved, enabling the rapid and efficient synthesis of DNA-containing bottlebrush copolymers, without the need for protection of the DNA bases.

Synthetic Approaches for Copolymers Containing Nucleic Acids and Analogues: Challenges and Opportunities

A deep integration of nucleic acids with other classes of materials have become the basis of many useful technologies. Among these biohybrids, nucleic acid-containing copolymers has seen rapid development in both chemistry and application. This review focuses on the various synthetic approaches to access nucleic acid-polymer biohybrids spanning post-polymerization conjugation, nucleic acids in polymerization, solid-phase synthesis, and nucleoside/nucleobase-functionalized polymers. We highlight the challenges associated with working with nucleic acids with each approach and the ingenuity of the solutions, with the hope of lowering the entry barrier and inpsiring further investigations in this exciting area.

Programmable Repurposing of Existing Drugs as Pharmaceutical Elements for the Construction of Aptamer-Drug Conjugates

Converting marketed drug molecules into phosphoramidites may present a potential strategy to facilitate the development of aptamer-drug conjugates (ApDCs) by a DNA synthesizer in a programmable way; however, quite limited methods were reported. Herein, we demonstrated a general approach by repurposing camptothecin (CPT) species. Commonly used inactive ingredients in pharmaceuticals are investigated and selected as a bonding moiety, from which 2-mercaptoethoxy ethanol and thioglycerol were efficiently incorporated with CPT to give the precursors. Cell viability and molecular docking results of the precursors supported that incorporation of the bonding moiety would not interrupt the inhibitory activity. Therefore, corresponding phosphoramidites were prepared as pharmaceutical elements, and a series of ApDCs were constructed automatically by solid-phase synthesis. Biological studies revealed that CPT elements could be specifically delivered to HCT116 cells by an aptamer and released inside cells. This kind of programmable repurposing may take advantage of established safety data and efficacy of existing drugs resulting in a faster development of ApDCs.

Combination of DNA with polymers

The preparation and applications of DNA containing polymers are comprehensively reviewed, and they are in the form of DNA−polymer covalent conjugators, supramolecular assemblies and hydrogels for advanced materials with promising features.

Programmable Cocrystallization of DNA Origami Shapes

Assembly of distinct types of species, particularly possessing anisotropic configurations, is the premise to broaden structural diversity and explore materials' collective properties. However, it remains a great challenge to programmably cocrystallize manifold anisotropic nanoparticles with the desired assembly mode, because it requires not only the complementarity of both sizes and shapes but also the control over their directional interactions. Here, by introducing DNA origami technique into lattice engineering, we synthesize two types of DNA nano-objects with different symmetries and program the heterogeneous functional patches precisely on their surfaces with nanometer-level precision, which could guide further assembly of these nano-objects. We show that these anisotropic DNA nano-objects could be cocrystallized along specified modes via modulating the combination of surface patches. The highly ordered DNA crystals were thoroughly evidenced by techniques including small-angle X-ray scattering and electron microscopy after careful encapsulation of a thin layer of silica on these DNA nano-objects. Our strategy endows distinct shapes of organic DNA origami structures with regulation features to control the sophisticated modes of cocrystallization of these diverse components, laying a foundation for designing and fabricating customized three-dimensional structures with given optical and mechanical properties.

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.

Degradable Polyphosphoramidate via Ring-Opening Metathesis Polymerization

We report the synthesis of a degradable polyphosphoramidate via ring-opening metathesis polymerization (ROMP) with the Grubbs initiator (IMesH2)(C5H5N)2(Cl)2Ru═CHPh. Controlled ROMP of a low ring strain diazaphosphepine-based cyclic olefin was achieved at low temperatures to afford well-defined polymers that readily undergo degradation in acidic conditions via the cleavage of the acid-labile phosphoramidate linkages. The diazaphosphepine monomer was compatible in random and block copolymerizations with phenyl and oligo(ethylene glycol) bearing norbornenes. This approach introduced partial or complete degradability into the polymer backbones. With this chemistry, we accessed amphiphilic poly(diazaphosphepine-norbornene) copolymers that could be used to prepare micellar nanoparticles.

Well-Defined DNA-Polymer Miktoarm Stars for Enzyme-Resistant Nanoflares and Carrier-Free Gene Regulation

Herein, we report a star-architectured poly(ethylene glycol) (PEG)-oligonucleotide nanoconjugate of a well-defined molecular structure. Based upon fullerene C₆₀ cores, each star bears precisely 1 DNA strand and 11 polymer chains. The elevated PEG density provides the DNA with steric selectivity: the DNA is significantly more resistant to nuclease digestion while remaining able to hybridize with a complementary sequence. The degree of resistance increases as the centers of mass for the DNA and fullerene are closer together. Such steric selectivity reduces protein-related background signals of the nanoflares synthesized from these miktoarm star polymers. Importantly, the stars improve cellular uptake and regulate gene expression as a non-cytotoxic, single-entity antisense agent without the need for a transfection carrier.