Combinatorial evaluation of cations, pH-sensitive and hydrophobic moieties for polymeric vector design

pH-sensitive cationic nanoparticles for endosomal cell-free DNA scavenging against acute inflammation

Cell-free DNA (cfDNA) released from dead cells could be a player in some autoimmune disorders by activating Toll-like receptor 9 (TLR9) and inducing proinflammatory cytokines. Cationic nanoparticles (cNPs) address cfDNA clearance, yet challenges persist, including toxicity, low specificity and ineffectiveness against endocytosed cfDNA. This study introduced pH-sensitive cNPs, reducing off-target effects and binding cfDNA at inflammatory sites. This unique approach inhibits the TLR9 pathway, offering a novel strategy for inflammation modulation. Synthesized cNPs, with distinct cationic moieties, exhibit varied pKa values, enhancing cfDNA binding. Comprehensive studies elucidate the mechanism, demonstrating minimal extracellular binding, enhanced endosomal DNA binding, and optimal tumor necrosis factor-α suppression. In a traumatic brain injury mice model, pH-sensitive cNPs effectively suppress inflammatory cytokines, highlighting their potential in acute inflammation regulation.

Postpolymerization Modification of Poly(2-vinyl-4,4-dimethyl azlactone) as a Versatile Strategy for Drug Conjugation and Stimuli-Responsive Release

Postpolymerization modification of highly defined "scaffold" polymers is a promising approach for overcoming the existing limitations of controlled radical polymerization such as batch-to-batch inconsistencies, accessibility to different monomers, and compatibility with harsh synthesis conditions. Using multiple physicochemical characterization techniques, we demonstrate that poly(2-vinyl-4,4-dimethyl azlactone) (PVDMA) scaffolds can be efficiently modified with a coumarin derivative, doxorubicin, and camptothecin small molecule drugs. Subsequently, we show that coumarin-modified PVDMA has a high cellular biocompatibility and that coumarin derivatives are liberated from the polymer in the intracellular environment for cytosolic accumulation. In addition, we report the pharmacokinetics, biodistribution, and antitumor efficacy of a PVDMA-based polymer for the first time, demonstrating unique accumulation patterns based on the administration route (i.e., intravenous vs oral), efficient tumor uptake, and tumor growth inhibition in 4T1 orthotopic triple negative breast cancer (TNBC) xenografts. This work establishes the utility of PVDMA as a versatile chemical platform for producing polymer-drug conjugates with a tunable, stimuli-responsive delivery.

Chemically Tuned Intracellular Gene Delivery by Core-Shell Nanoparticles: Effects of Proton Buffering, Acid Degradability, and Membrane Disruption

Nanoparticles consisting of a condensed nucleic acid core surrounded by protective layers which aid to overcome extracellular and intracellular hurdles to gene delivery (i. e., core-shell nanoparticles, CSNPs) synthetically mimic viruses. The outer shells shield the core and are particularly designed to enable facilitated release of the gene payload into the cytoplasm, the major limiting step in intracellular gene delivery. The hypothetical proton sponge effect and degradability in response to a stimulus (i. e., mildly acidic pH in the endosome) are two prevailing, although contested, principles in designing effective carriers for intracellular gene delivery via endosomal escape. Utilizing the highly flexible chemical-tuning of the polymeric shell via surface-initiated photo-polymerization of the various monomers at different molecular ratios, the effects of proton buffering capacity, acid-degradability, and endosomal membrane-lysis property on intracellular delivery of plasmid DNA by CSNPs were investigated. This study demonstrated the equivalently critical roles of proton buffering and acid-degradability in achieving efficient intracellular gene delivery, independent of cellular uptake. Extended proton buffering resulted in further improved transfection as long as the core structure was not compromised. The results of the study present a promising synthetic strategy to the development of an efficient, chemically-tunable gene delivery carrier.

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.

Tuning the Surface Charge of Self-Assembled Polydiacetylene Vesicles to Control Aggregation and Cell Binding

Polydiacetylene vesicles of various compositions were assembled using a two-part mixture of 10,12-pentacosadiynoic acid (PCDA) and ethylenedioxy-bis-ethylamine (EDEA)-labeled PCDA in order to control surface charge and stability within a desired pH range. Investigation of the interaction of the vesicles with mammalian cells as a function of surface charge was carried out and identified a clear correlation in cell–vesicle association and corresponding cell death for vesicles with positive surface charge. The binding behavior of the vesicles was found to be tunable by regulating the proportion of anionic PCDA relative to cationic PCDA–EDEA content within vesicles as to control the surface charge as a function of pH. Association of vesicles with cells thus depended on the corresponding charge of the vesicles and cell surface. The prospect of this work may serve as a step toward future vesicle designs to allow triggered uptake of vesicles locally within low pH tumor microenvironments.

Histone-Mimetic Gold Nanoparticles as Versatile Scaffolds for Gene Transfer and Chromatin Analysis

Histone-inspired polymer assemblies (polyplexes) can regulate gene expression and subcellular transport in plasmids by harnessing the cellular machinery normally used for histone proteins. When grafted to polyplexes, histone tails promote nuclear accumulation, trigger plasmid DNA (pDNA) release, and enhance transcription. Herein, we developed multifunctional gold nanoparticles (AuNPs) decorated by histone motifs as histone-inspired scaffolds with improved pDNA binding, easy bioimaging, and increased potential for gene delivery and chromatin analysis applications. We hypothesized that polycationic AuNPs coupled to histone motifs would mimic the native presentation of these sequences on the histone octamer and thereby create structures with the capacity to both engage native histone effectors and condense pDNA into nucleosome-inspired nanostructures. AuNPs bearing ∼2 nm cores were prepared based on the well-established Brust-Schiffrin two-phase method involving tetrachloroaurate reduction in the presence of 1-pentanethiol. Solid phase peptide synthesis was employed to generate thiolated polycationic ligands and histone tail motifs, and the AuNPs and peptide ligands were combined in a two-step Murray place exchange reaction at various ratios to produce a collection of polycationic AuNPs modified with varying amounts of histone tails. Electron microscopy and thermal analyses demonstrated that these modified AuNPs exhibited tunable biochemical and biophysical properties that closely mimicked the properties of native histones. The histone-mimetic nanoscaffolds efficiently and sequence-specifically engaged histone effectors responsible for activating transcription. In addition, the nanoscaffolds condensed pDNA into complexes with high stability in the presence of physiological concentrations of heparin, a common extracellular polyanion. These combined properties of histone engagement and high stability led to a ∼6-fold enhancement in transfection efficiency as compared with typical polymeric transfection reagents, with the increased transfection efficiency correlated to the presence and amount of histone tails displayed on the surface of the nanoscaffolds. These findings demonstrate the utility of employing a biomimetic materials design approach to develop more effective and stable delivery vehicles for gene transfer and chromatin analysis applications.

Arginine-based poly(ester amide) nanoparticle platform: From structure-property relationship to nucleic acid delivery

Many different types of polycations have been vigorously studied for nucleic acid delivery, but a systematical investigation of the structure-property relationships of polycations for nucleic acid delivery is still lacking. In this study, a new library of biodegradable and biocompatible arginine-based poly(ester amide) (Arg-PEA) biomaterials was designed and synthesized with a tunable structure for such a comprehensive structure-property research. Nanoparticle (NP) complexes were formed through the electrostatic interactions between the polycationic Arg-PEAs and anionic nucleic acids. The following structure effects of the Arg-PEAs on the transfection efficiency of nucleic acids were investigated: 1) the linker/spacer length (length effect and odd-even effect); 2) salt type of arginine; 3) the side chain; 4) chain stiffness; 5) molecular weight (MW). The data obtained revealed that a slight change in the Arg-PEA structure could finely tune its physicochemical property such as hydrophobicity, and this could subsequently affect the nanoparticle size and zeta potential, which, in turn, regulate the transfection efficiency and silencing outcomes. A further study of the Arg-PEA/CpG oligodeoxynucleotide NP complexes indicated that the polymer structure could precisily regulate the immune response of CpG, thus providing a new potential nano-immunotherapy strategy. The in vitro data have further confirmed that the Arg-PEA NPs showed a satisfactory delivery performance for a variety of nucleic acids. Therefore, the data from the current study provide comprehensive information about the Arg-PEA structure-transfection property relationship; the tunable property of the library of Arg-PEA biomaterials can be one of the promising candidates for nucleic acid delivery and other biomedical applications.

STATEMENT OF SIGNIFICANCE

Polycations have being intensive utilized for nucleic acid delivery. However, there has not been elucidated about the relationship between polycation's structure and the physicochemical properties/biological function. In this timely report, an arginine based poly(ester amide) (Arg-PEA) library was prepared with finely tunable structure to systematically investigate the structure-property relationships of polycations for nucleic acid delivery. The results revealed that slight change of Arg-PEA structure could finely tune the physicochemical property (such as hydrophobicity), which subsequently affect the size and zeta potential of Arg-PEA/nucleic acid nanoparticles(NPs), and finally regulate the resulting transfection or silencing outcomes. Further study of Arg-PEA/CpG NPs indicated that the polymer structure could precisely regulate immuno response of CpG, providing new potential nano-immunotherapy strategy. In vitro evaluations confirmed that the NPs showed satisfied delivery performance for a variety types of nucleic acids. Therefore, these studies provide comprehensive information of Arg-PEA structure-property relationship, and the tunable properties of Arg-PEAs make them promising candidates for nucleic acid delivery and other biomedical applications. Overall, we have shown enough significance and novelty in terms of nucleic acid delivery, biomaterials, pharmaceutical science and nanomedicine.

Block Copolymer Micelles in Nanomedicine Applications

Polymeric micelles are demonstrating high potential as nanomedicines capable of controlling the distribution and function of loaded bioactive agents in the body, effectively overcoming biological barriers, and various formulations are engaged in intensive preclinical and clinical testing. This Review focuses on polymeric micelles assembled through multimolecular interactions between block copolymers and the loaded drugs, proteins, or nucleic acids as translationable nanomedicines. The aspects involved in the design of successful micellar carriers are described in detail on the basis of the type of polymer/payload interaction, as well as the interplay of micelles with the biological interface, emphasizing on the chemistry and engineering of the block copolymers. By shaping these features, polymeric micelles have been propitious for delivering a wide range of therapeutics through effective sensing of targets in the body and adjustment of their properties in response to particular stimuli, modulating the activity of the loaded drugs at the targeted sites, even at the subcellular level. Finally, the future perspectives and imminent challenges for polymeric micelles as nanomedicines are discussed, anticipating to spur further innovations.

Combinatorial approaches in post-polymerization modification for rational development of therapeutic delivery systems

The combinatorial polymer library approach has been proven to be effective for the optimization of therapeutic delivery systems. The library of polymers with chemical diversity has been synthesized by (i) polymerization of functionalized monomers or (ii) post-polymerization modification of reactive polymers. Most scientists have followed the first approach so far, and the second method has emerged as a versatile approach for combinatorial biomaterials discovery. This review focuses on the second approach, especially discussing the post-modifications that employ reactive polymers as templates for combinatorial synthesis of a library of functional polymers with distinct structural diversity or a combination of different functionalities. In this way, the functional polymers have a consistent chain length and distribution, which allows for systematic optimization of therapeutic delivery polymers for the efficient delivery of genes, small-molecule drugs, and protein therapeutics. In this review, the modification of representative reactive polymers for the delivery of different therapeutic payloads are summarized. The recent advances in rational design and optimization of therapeutic delivery systems based on reactive polymers are highlighted. This review ends with a summary of the current achievements and the prospect on future directions in applying the approach of post-polymerization modification of polymers to accelerate the development of therapeutic delivery systems.

STATEMENT OF SIGNIFICANCE

A strategy to rationally design and systematically optimize polymers for the efficient delivery of specific therapeutics is highly needed. The combinatorial polymer library approach could be an effective way to this end. The post-polymerization modification of reactive polymer precursors is applicable for the combinatorial synthesis of a library of functional polymers with distinct structural diversity across a consistent degree of polymerization. This allows for parallel comparison and systematic evaluation/optimization of functional polymers for efficient therapeutic delivery. This review summarizes the key elements of this combinatorial polymer synthesis approach realized by post-polymerization modification of reactive polymer precursors towards the development and identification of optimal polymers for the efficient delivery of therapeutic agents.

Aerosol delivery of stabilized polyester-siRNA nanoparticles to silence gene expression in orthotopic lung tumors

Tremendous progress has been made in the development of delivery carriers for small RNA therapeutics. However, most achievements have focused on the treatment of liver-associated diseases because conventional lipid and lipidoid nanoparticles (LNPs) readily accumulate in the liver after intravenous (i.v.) administration. Delivering RNAs to other organs and tumor tissues remains an ongoing challenge. Here, we utilized a 540-member combinatorial functional polyester library to discover nanoparticles (NPs) that enable efficacious siRNA delivery to A549 lung cancer cells in vitro and in vivo. PE4K-A13-0.33C6 and PE4K-A13-0.33C10 NPs were efficiently internalized into A549-Luc cells within 4 h. The addition of PEG 2000 DMG lipid or Pluronic F-127 onto the surface of the polyplexes reduced the surface charge of NPs, resulting in an increase of serum stability. We then explored aerosol delivery of stabilized PE4K-A13-0.33C6 and PE4K-A13-0.33C10 NPs to implanted orthotopic lung tumors. We found that by altering the administration route from i.v. to aerosol, the NPs could avoid liver accumulation and instead be specifically localized only in the lungs. This resulted in significant gene silencing in the A549 orthotopic lung tumors. Due to the ability to deliver siRNA to non-liver targets, this approach provides a privileged route for gene silencing in the lungs.

Self-aggregating 1.8kDa polyethylenimines with dissolution switch at endosomal acidic pH are delivery carriers for plasmid DNA, mRNA, siRNA and exon-skipping oligonucleotides

Efficiency of polyethylenimine (PEI) for nucleic acid delivery is affected by the size of the carrier and length of the nucleic acids. For instance, PEIs with molecular weights between 10-30kDa provide optimal DNA delivery activity whereas PEIs with molecular weights below 1.8kDa are ineffective. The activity of PEI is also severely diminished by substitution of DNA for shorter nucleic acids such as mRNA or siRNA. Here, through chemical modification of the primary amines to aromatic domains we achieved nucleic acid delivery by the 1.8kDa polyethylenimine (PEI) particles. This modification did not affect the PEI buffering abilities but enhanced its pH-sensitive aggregation, enabling stabilization of the polyplex outside the cell while still allowing nucleic acid release following cellular entry. The aromatic PEIs were then evaluated for their gene, mRNA, siRNA and 2'O-methyl phosphorothioate oligonucleotide in vitro transfection abilities. The salicylamide-grafted PEI showed to be a reliable carrier for delivering nucleic acids with cytoplasmic activity such as the mRNA and siRNA or nuclear diffusible oligonucleotide. It was then further equipped with polyethyleneglycol (PEG) and the delivery efficiency of the copolymer was tested in vivo for regeneration of dystrophin in the muscle of mdx mouse through a 2'O-methyl phosphorothioate-mediated splicing modulation. Intramuscular administration of polyplexes resulted in dystrophin-positive fibers in a mouse model of Duchenne muscular dystrophy without apparent toxicity. These findings indicate that precise modifications of low molecular weight PEI improve its bio-responsiveness and yield delivery vehicles for nucleic acids of various types in vitro and in vivo.

Polymeric Nanostructure Compiled with Multifunctional Components To Exert Tumor-Targeted Delivery of Antiangiogenic Gene for Tumor Growth Suppression

Nucleic acid-based therapy has emerged as a revolutionary methodology for treatment of the diseases related to protein dysfunction; however, lack of systemically applicable synthetic delivery systems limits its current usage in local applications, particularly for DNA-based therapy with regard to the poor bioavailability in the systemic administrations. To overcome this obstacle, we compiled multiple chemistry-based strategies into the manufacture of the gene delivery formulations to pursue improved tolerability of DNA to the enzymatic degradation in the biological milieu and prolonged retention in the systemic circulation. Here, we constructed a distinctive multilayered functional architecture: plasmid DNA (pDNA) was electrostatically complexed with cationic poly(lysine) (polyplex) as the interior pDNA reservoir, which was further cross-linked by redox-responsive disulfide cross-linking to minimize the occurrence of polyplex disassembly through exchange reaction with the biological charged components. Still, the pDNA reservoir was spatially protected by a sequential thermoresponsive poly(N-isopropylacrylamide) palisade as the intermediate barrier and a biocompatible hydrophilic poly(ethylene glycol) (PEG) shell with the aim of preventing the accessibility of the biological species, particularly the nuclease degradation to the pDNA payload. Subsequent investigations validated the utilities of these strategies in accomplishing prolonged blood retention. In an attempt to apply this method for tumor therapy, ligand cyclic (Arg-Gly-Asp) peptide was attached at the distal end of PEG, validating prompted tumor-targeted delivery and gene expression of the loaded antiangiogenic gene at the targeted tumor cells and accordingly exerting antiangiogenesis of the tumors for abrogation of tumor growth. Together with its excellent safe profile, the proposed formulation suggests potential utility as a practical gene delivery system for treatment of intractable diseases.

Exploring the role of polymer structure on intracellular nucleic acid delivery via polymeric nanoparticles

Intracellular nucleic acid delivery has the potential to treat many genetically-based diseases, however, gene delivery safety and efficacy remains a challenging obstacle. One promising approach is the use of polymers to form polymeric nanoparticles with nucleic acids that have led to exciting advances in non-viral gene delivery. Understanding the successes and failures of gene delivery polymers and structures is the key to engineering optimal polymers for gene delivery in the future. This article discusses the polymer structural features that enable effective intracellular delivery of DNA and RNA, including protection of nucleic acid cargo, cellular uptake, endosomal escape, vector unpacking, and delivery to the intracellular site of activity. The chemical properties that aid in each step of intracellular nucleic acid delivery are described and specific structures of note are highlighted. Understanding the chemical design parameters of polymeric nucleic acid delivery nanoparticles is important to achieving the goal of safe and effective non-viral genetic nanomedicine.

Co-delivery of paclitaxel and gemcitabine via CD44-targeting nanocarriers as a prodrug with synergistic antitumor activity against human biliary cancer

Multi-drug delivery focuses on different signaling pathways in cancer cells that have synergistic anti-proliferative effects. In this study, we developed multi-prodrug nanocarriers (MPDNCs) consisting of poly (l-lysine)-carboxylate PTX (PLL-PTX) and hyaluronic acid-conjugated GEM (HA-GEM) for CD44-targeted synergistic biliary cancer therapy. An in vitro study of cell viability and mRNA expression levels and an in vivo study showed that MPDNCs more effectively inhibit proliferation in CD44-overexpressing cancer cells (HuCCT1) than in cells with lower CD44 expression (SCK) by synergistically inducing apoptosis. Consequently, these results demonstrate that MPDNCs are prodrugs with synergistic cancer therapeutic efficacy and effective cellular uptake at target cells compared to free drugs, indicating their strong potential as efficient multi-drug-carrying nano-platforms for cancer treatment.

Strategies on the nuclear-targeted delivery of genes

To improve the nuclear-targeted delivery of non-viral vectors, extensive effort has been carried out on the development of smart vectors which could overcome multiple barriers. The nuclear envelope presents a major barrier to transgene delivery. Viruses are capable of crossing the nuclear envelope to efficiently deliver their genome into the nucleus through the specialized protein components. However, non-viral vectors are preferred over viral ones because of the safety concerns associated with the latter. Non-viral delivery systems have been designed to include various types of components to enable nuclear translocation at the periphery of the nucleus. This review summarizes the progress of research regarding nuclear transport mechanisms. "Smart" non-viral vectors that have been modified by peptides and other small molecules are able to facilitate the nuclear translocation and enhance the efficacy of gene expression. The resulting technology may also enhance delivery of other macromolecules to the nucleus.

DNA delivery with hyperbranched polylysine: a comparative study with linear and dendritic polylysine

PEI and polylysine are among the most investigated synthetic polymeric carriers for DNA delivery. Apart from their practical use, these 2 classes of polymers are also of interest from a fundamental point of view as they both can be prepared in different architectures (linear and branched/dendritic) and in a wide range of molecular weights, which is attractive to establish basic structure-activity relationships. This manuscript reports the results of an extensive study on the influence of molecular weight and architecture of a library of polylysine variants that includes linear, dendritic and hyperbranched polylysine. Hyperbranched polylysine is a new polylysine-based carrier that is structurally related to dendritic polylysine but possesses a randomly branched structure. Hyperbranched polylysine is attractive as it can be prepared in a one-step process on a large scale. The performance of these 3 classes of polylysine analogs was evaluated by assessing eGFP and IgG production in transient gene expression experiments with CHO DG44 cells, which revealed that protein production generally increased with increasing molecular weight and that at comparable molecular weight, the hyperbranched analogs were superior as compared to the dendritic and linear polylysines. To understand the differences between the gene delivery properties of the hyperbranched polylysine analogs on the one hand and the dendritic and linear polylysines on the other hand, the uptake and trafficking of the corresponding polyplexes were investigated. These experiments allowed us to identify (i) polyplex-external cell membrane binding, (ii) free, unbound polylysine coexisting with polyplexes as well as (iii) polymer buffer capacity as three possible factors that may contribute to the superior transfection properties of the hyperbranched polylysines as compared to their linear and dendritic analogs. Altogether, the results of this study indicate that hyperbranched polylysine is an interesting, alternative synthetic gene carrier. Hyperbranched polylysine can be produced at low costs and in large quantities, is partially biodegradable, which may help to prevent cumulative cytotoxicity, and possesses transfection properties that can approach those of PEI.

Rapid discovery of potent siRNA-containing lipid nanoparticles enabled by controlled microfluidic formulation

The discovery of potent new materials for in vivo delivery of nucleic acids depends upon successful formulation of the active molecules into a dosage form suitable for the physiological environment. Because of the inefficiencies of current formulation methods, materials are usually first evaluated for in vitro delivery efficacy as simple ionic complexes with the nucleic acids (lipoplexes). The predictive value of such assays, however, has never been systematically studied. Here, for the first time, by developing a microfluidic method that allowed the rapid preparation of high-quality siRNA-containing lipid nanoparticles (LNPs) for a large number of materials, we have shown that gene silencing assays employing lipoplexes result in a high rate of false negatives (~90%) that can largely be avoided through formulation. Seven novel materials with in vivo gene silencing potencies of >90% at a dose of 1.0 mg/kg in mice were discovered. This method will facilitate the discovery of next-generation reagents for LNP-mediated nucleic acid delivery.

Discovery of cationic polymers for non-viral gene delivery using combinatorial approaches

Gene therapy is an attractive treatment option for diseases of genetic origin, including several cancers and cardiovascular diseases. While viruses are effective vectors for delivering exogenous genes to cells, concerns related to insertional mutagenesis, immunogenicity, lack of tropism, decay and high production costs necessitate the discovery of non-viral methods. Significant efforts have been focused on cationic polymers as non-viral alternatives for gene delivery. Recent studies have employed combinatorial syntheses and parallel screening methods for enhancing the efficacy of gene delivery, biocompatibility of the delivery vehicle, and overcoming cellular level barriers as they relate to polymer-mediated transgene uptake, transport, transcription, and expression. This review summarizes and discusses recent advances in combinatorial syntheses and parallel screening of cationic polymer libraries for the discovery of efficient and safe gene delivery systems.

Azlactone-Functionalized Polymers as Reactive Platforms for the Design of Advanced Materials: Progress in the Last Ten Years

Polymers functionalized with azlactone (or oxazolone) functionality have become increasingly useful for the rapid and modular design of functional materials. Because azlactones can react via ring-opening reactions with a variety of different nucleophilic species (e.g., primary amines, hydroxyl groups, and thiol functionality), azlactone-functionalized materials can serve as convenient 'reactive' platforms for the post-synthesis or post-fabrication introduction of a broad range of chemical functionality to soluble polymers, insoluble supports, and surfaces/interfaces. The last decade has seen an increase in both the number and the variety of reports that exploit the properties and the reactivities of azlactone-functionalized polymers. Here, we highlight recent work from several different laboratories, including our own, toward the design and characterization of azlactone-functionalized polymers, with a particular emphasis on: (i) new synthetic approaches for the preparation of well-defined azlactone-functionalized polymers using living/controlled methods of polymerization, (ii) the design and modular synthesis of side-chain functionalized polymers and block copolymers via post-polymerization modification of azlactone-functionalized polymers, (iii) the development of reactive polymeric supports useful in the contexts of separations and catalysis, and (iv) methods for the fabrication of reactive thin films and other approaches to the immobilization of azlactone functionality on surfaces and interfaces. Examples discussed herein reveal a growing awareness of azlactone functionality as a useful tool for polymer chemists, and highlight several ways that the unique reactivity of these materials can both complement and provide useful alternatives to other reactive polymers currently used to design functional materials.

Enhancement of airway gene transfer by DNA nanoparticles using a pH-responsive block copolymer of polyethylene glycol and poly-L-lysine

Highly compacted DNA nanoparticles, composed of single molecules of plasmid DNA compacted with block copolymers of polyethylene glycol and poly-L-lysine (PEG-CK(30)), have shown considerable promise in human gene therapy clinical trials in the nares, but may be less capable of transfecting cells that lack surface nucleolin. To address this potential shortcoming, we formulated pH-responsive DNA nanoparticles that mediate gene transfer via a nucleolin-independent pathway. Poly-L-histidine was inserted between PEG and poly-L-lysine to form a triblock copolymer system, PEG-CH(12)K(18). Inclusion of poly-L-histidine increased the buffering capacity of PEG-CH(12)K(18) to levels comparable with branched polyethyleneimine. PEG-CH(12)K(18) compacted DNA into rod-shaped DNA nanoparticles with similar morphology and colloidal stability as PEG-CK(30) DNA nanoparticles. PEG-CH(12)K(18) DNA nanoparticles entered human bronchial epithelial cells (BEAS-2B) that lack surface nucleolin by a clathrin-dependent endocytic mechanism followed by endo-lysosomal processing. Despite trafficking through the degradative endo-lysosomal pathway, PEG-CH(12)K(18) DNA nanoparticles improved the in vitro gene transfer by ~20-fold over PEG-CK(30) DNA nanoparticles, and in vivo gene transfer to lung airways in BALB/c mice by ~3-fold, while maintaining a favorable toxicity profile. These results represent an important step toward the rational development of an efficient gene delivery platform for the lungs based on highly compacted DNA nanoparticles.

Poly(2-aminoethyl methacrylate) with well-defined chain length for DNA vaccine delivery to dendritic cells

Poly(2-aminoethyl methacrylate) (PAEM) homopolymers with defined chain length and narrow molecular weight distribution were synthesized using atom transfer radical polymerization (ATRP), and a comprehensive study was conducted to evaluate the colloidal properties of PAEM/plasmid DNA polyplexes, the uptake and subcellular trafficking of polyplexes in antigen-presenting dendritic cells (DCs), and the biological performance of PAEM as a potential DNA vaccine carrier. PAEM of different chain length (45, 75, and 150 repeating units) showed varying strength in condensing plasmid DNA into narrowly dispersed nanoparticles with very low cytotoxicity. Longer polymer chain length resulted in higher levels of overall cellular uptake and nuclear uptake of plasmid DNA, but shorter polymer chains favored intracellular and intranuclear release of free plasmid from the polyplexes. Despite its simple chemical structure, PAEM transfected DCs very efficiently in vitro in media with or without serum and led to phenotypic maturation of DCs. When a model antigen-encoding ovalbumin plasmid was used, transfected DCs stimulated the activation of naïve CD8(+) T cells to produce high levels of interferon-γ. The efficiency of transfection, DC maturation, and CD8(+) T cell activation showed varying degrees of polymer chain-length dependence. These structurally defined cationic polymers may have much potential as efficient DNA vaccine carriers and immunostimulatory adjuvants. They may also serve as a model material system for elucidating structural and intracellular mechanisms of polymer-mediated DNA vaccine delivery.

Combinatorial synthesis of chemically diverse core-shell nanoparticles for intracellular delivery

Analogous to an assembly line, we employed a modular design for the high-throughput study of 1,536 structurally distinct nanoparticles with cationic cores and variable shells. This enabled elucidation of complexation, internalization, and delivery trends that could only be learned through evaluation of a large library. Using robotic automation, epoxide-functionalized block polymers were combinatorially cross-linked with a diverse library of amines, followed by measurement of molecular weight, diameter, RNA complexation, cellular internalization, and in vitro siRNA and pDNA delivery. Analysis revealed structure-function relationships and beneficial design guidelines, including a higher reactive block weight fraction, stoichiometric equivalence between epoxides and amines, and thin hydrophilic shells. Cross-linkers optimally possessed tertiary dimethylamine or piperazine groups and potential buffering capacity. Covalent cholesterol attachment allowed for transfection in vivo to liver hepatocytes in mice. The ability to tune the chemical nature of the core and shell may afford utility of these materials in additional applications.

An in-depth analysis of polymer-analogous conjugation using DMTMM

Combinatorial libraries have become increasingly popular in the field of functional biomaterials. One approach for creating diverse polymer libraries is polymer-analogous conjugation of functional groups to polymer scaffolds. In this study, we show that a water-soluble condensing agent, 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM), can be employed to conjugate two disparate model ligands, d-(+)-galactosamine (Gal) and agmatine (Agm), to the side chains of either poly(methacrylic acid) (pMAA) or poly(acrylic acid) (pAA) at various substitution ratios. The degree of substitution was found to be directly influenced by media pH, polymer concentration, structure of ligands, and polymer precursor. A nearly 2-fold increase in conjugation efficiencies for both ligands to pAA was achieved as compared to pMAA under identical conditions reaching up to 56% and 78% of Gal and Agm of total content, respectively. These two structurally similar polymers showed remarkably different performances, which reveals that the selection of a polymer precursor is crucial for the optimal design of polymeric libraries, particularly when complex structural ligands are involved. The approach employed provides a basis from which larger and more diverse combinatorial libraries of functionalized polymers with multiple moieties can be generated.

Charge density and molecular weight of polyphosphoramidate gene carrier are key parameters influencing its DNA compaction ability and transfection efficiency

A series of polyphosphoramidates (PPAs) with different molecular weights (MWs) and charge densities were synthesized and examined for their DNA compaction ability and transfection efficiency. A strong correlation was observed between the transfection efficiency of PPA/DNA nanoparticles and the MW and net positive charge density of the PPA gene carriers in three different cell lines (HeLa, HEK293, and HepG2 cells). An increase in MW and net positive charge density of PPA carrier yielded higher DNA compaction capacity, smaller nanoparticles with higher surface charges, and higher complex stability against challenges by salt and polyanions. These favorable physicochemical properties of nanoparticles led to enhanced transfection efficiency. PPA/DNA nanoparticles with the highest complex stability showed comparable transfection efficiency as PEI/DNA nanoparticles likely by compensating the low buffering capacity with higher cellular uptake and affording higher level of protection to DNA in endolysosomal compartment. The differences in transfection efficiency were not attributed by any difference in cytotoxicity among the carriers, as all nanoparticles showed a minimal level of cytotoxicity under the transfection conditions. Using PPA as a model system, we demonstrated the structural dependence of transfection efficiency of polymer gene carrier. These results offer more insights into nanoparticle engineering for nonviral gene delivery.

Azlactone-functionalized polymers as reactive templates for parallel polymer synthesis: synthesis and screening of a small library of cationic polymers in the context of DNA delivery

Azlactone-functionalized polymers are used as reactive templates for the synthesis of a library of amine-functionalized polymers of interest in the context of DNA delivery and other applications.

A family of bioreducible poly(disulfide amine)s for gene delivery

A family of bioreducible poly(disulfide amine)s, which differ in the length of polymethylene spacer [-(CH(2))(n)-] in the main chain and the side chain, has been synthesized. These bioreducible poly(disulfide amine)s exhibit local environment specific degradability and are associated with lower cytotoxicity than branched poly(ethylenimine) (bPEI, 25 kDa). These cationic polymers also show higher buffering capacity and protonation degree than bPEI, facilitating the endosomal escape of carried genetic materials. The transfection efficiency of these agents is oligomethylene length dependent. Poly(cystaminebisacrylamide-spermine) [poly(CBA-SP)], poly(cystaminebisacrylamide-bis(3-aminopropyl)-1,3-propanediamine) [poly(CBA-APPD)], and poly(cyxtaminebisacrylamide-bis(3-aminopropyl)-ethylenediamine) [ploy(CBA-APED)] with longer propylene [-(CH(2))(3)-] side spacer, demonstrate higher transfection efficacy than the counterpart poly(cystaminebisacrylamide-bis(2-aminoethyl)-1,3-propanediamine) [poly(CBA-AEPD)] and poly(cystaminebisacrylamide-triethylenetetramine) [poly(CBA-TETA)], which have shorter ethylene [-(CH(2))(2)-] side spacer. The poly(CBA-SP), poly(CBA-APPD), poly(CBA-APED) with the main chain spacer of -(CH(2))(4)-, -(CH(2))(3)-, -(CH(2))(2)- demonstrate similar transfection efficiency, indicating the length of polymer main chain spacer has less influence on transfection efficiency. However, with the same short ethylene [-(CH(2))(2)-] side spacer, poly(CBA-AEPD), with the longer main chain oligomethylene units [-(CH(2))(3)-], showed relatively higher transfection efficiency than poly(CBA-TETA), having shorter main chain oligomethylene units [-(CH(2))(2)-]. Of these polymeric carriers, poly(CBA-SP) demonstrated the highest transfection in the C2C12 cell line, while poly(CBA-APED) showed the highest transfection in the HeLa cell line. All of these agents showed greater transfection activity than commercialized bPEI 25 kDa. The poly(disulfide amine)s are promising safe and efficient non-viral vectors for gene delivery.