Molecular Weight-Independent "Polysoap" Nanostructure Characterized via In Situ Resonant Soft X-ray Scattering

Studying polymer micelle structure and loading dynamics under environmental conditions is critical for nanocarrier applications but challenging due to a lack of in situ nanoprobes. Here, the structure and loading of amphiphilic polyelectrolyte copolymer micelles, formed by 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and n-dodecyl acrylamide (DDAM), were investigated using a multimodal approach centered around in situ resonant soft X-ray scattering (RSoXS). We observe aqueous micelles formed from polymers of wide-ranging molecular weights and aqueous concentrations. Despite no measurable critical micelle concentration (CMC), structural analyses point toward multimeric structures for most molecular weights, with the lowest molecular weight micelles containing mixed coronas and forming loose micelle clusters that enhance hydrocarbon uptake. The sizes of the micelle substructures are independent of both the concentration and molecular weight. Combining these results with a measured molecular weight-invariant surface charge and zeta potential strengthens the link between the nanoparticle size and ionic charge in solution that governs the polysoap micelle structure. Such control would be critical for nanocarrier applications, such as drug delivery and water remediation.

Synthesis approaches of amphiphilic copolymers for spherical micelle preparation: application in drug delivery

The formation of polymeric micelles in aqueous environments through the self-assembly of amphiphilic polymers can provide a versatile platform to increase the solubility and permeability of hydrophobic drugs and pave the way for their administration. In comparison to various self-assembly-based vehicles, polymeric micelles commonly have a smaller size, spherical morphology, and simpler scale up process. The use of polymer-based micelles for the encapsulation and carrying of therapeutics to the site of action triggered a line of research on the synthesis of various amphiphilic polymers in the past few decades. The extended knowledge on polymers includes biocompatible smart amphiphilic copolymers for the formation of micelles, therapeutics loading and response to external stimuli, micelles with a tunable drug release pattern, etc. Different strategies such as ring-opening polymerization, atom transfer radical polymerization, reversible addition-fragmentation chain-transfer, nitroxide mediated polymerization, and a combination of these methods were employed to synthesize copolymers with diverse compositions and topologies with the proficiency of self-assembly into well-defined micellar structures. The current review provides a summary of the important polymerization techniques and recent achievements in the field of drug delivery using micellar systems. This review proposes new visions for the design and synthesis of innovative potent amphiphilic polymers in order to benefit from their application in drug delivery fields.

Protection of Double-Stranded RNA via Complexation with Double Hydrophilic Block Copolymers: Influence of Neutral Block Length in Biologically Relevant Environments

Interaction between the anionic phosphodiester backbone of DNA/RNA and polycations can be exploited as a means of delivering genetic material for therapeutic and agrochemical applications. In this work, quaternized poly(2-(dimethylamino)ethyl methacrylate)-block-poly(N,N-dimethylacrylamide) (PQDMAEMA-b-PDMA_m) double hydrophilic block copolymers (DHBCs) were synthesized via reversible addition–fragmentation chain-transfer (RAFT) polymerization as nonviral delivery vehicles for double-stranded RNA. The assembly of DHBCs and dsRNA forms distinct polyplexes that were thoroughly characterized to establish a relationship between the length of the uncharged poly(N,N-dimethylacrylamide) (PDMA) block and the polyplex size, complexation efficiency, and colloidal stability. Dynamic light scattering reveals the formation of smaller polyplexes with increasing PDMA lengths, while gel electrophoresis confirms that these polyplexes require higher N/P ratio for full complexation. DHBC polyplexes exhibit enhanced stability in low ionic strength environments in comparison to homopolymer-based polyplexes. In vitro enzymatic degradation assays demonstrate that both homopolymer and DHBC polymers efficiently protect dsRNA from degradation by RNase A enzyme.

Thiocarbonyl Chemistry in Polymer Science

Organised by reaction type, this review highlights the unique reactivity of thiocarbonyl (C=S) groups with radicals, anions, nucleophiles, electrophiles, in pericyclic reactions, and in the presence of light. In the...

Label-free characterization of organic nanocarriers reveals persistent single molecule cores for hydrocarbon sequestration

Self-assembled molecular nanostructures embody an enormous potential for new technologies, therapeutics, and understanding of molecular biofunctions. Their structure and function are dependent on local environments, necessitating in-situ/operando investigations for the biggest leaps in discovery and design. However, the most advanced of such investigations involve laborious labeling methods that can disrupt behavior or are not fast enough to capture stimuli-responsive phenomena. We utilize X-rays resonant with molecular bonds to demonstrate an in-situ nanoprobe that eliminates the need for labels and enables data collection times within seconds. Our analytical spectral model quantifies the structure, molecular composition, and dynamics of a copolymer micelle drug delivery platform using resonant soft X-rays. We additionally apply this technique to a hydrocarbon sequestrating polysoap micelle and discover that the critical organic-capturing domain does not coalesce upon aggregation but retains distinct single-molecule cores. This characteristic promotes its efficiency of hydrocarbon sequestration for applications like oil spill remediation and drug delivery. Such a technique enables operando, chemically sensitive investigations of any aqueous molecular nanostructure, label-free.

Strategies, design, and chemistry in siRNA delivery systems

Emerging therapeutics that utilize RNA interference (RNAi) have the potential to treat broad classes of diseases due to their ability to reversibly silence target genes. In August 2018, the FDA approved the first siRNA therapeutic, called ONPATTRO™ (Patisiran), for the treatment of transthyretin-mediated amyloidosis. This was an important milestone for the field of siRNA delivery that opens the door for additional siRNA drugs. Currently, >20 small interfering RNA (siRNA)-based therapies are in clinical trials for a wide variety of diseases including cancers, genetic disorders, and viral infections. To maximize therapeutic benefits of siRNA-based drugs, a number of chemical strategies have been applied to address issues associated with efficacy, specificity, and safety. This review focuses on the chemical perspectives behind non-viral siRNA delivery systems, including siRNA synthesis, siRNA conjugates, and nanoparticle delivery using nucleotides, lipids, and polymers. Tracing and understanding the chemical development of strategies to make siRNAs into drugs is important to guide development of additional clinical candidates and enable prolonged success of siRNA therapeutics.

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).

Thermoresponsive and Reducible Hyperbranched Polymers Synthesized by RAFT Polymerisation

Here, we report the synthesis of new thermoresponsive hyperbranched polymers (HBPs) via one-pot reversible addition-fragmentation chain transfer (RAFT) copolymerisation of poly(ethylene glycol)methyl ether methacrylate (PEGMEMA, Mn = 475 g/mol), poly(propylene glycol)methacrylate (PPGMA, Mn = 375 g/mol), and disulfide diacrylate (DSDA) using 2-cyanoprop-2-yl dithiobenzoate as a RAFT agent. DSDA was used as the branching agent and to afford the HBPs with reducible disulfide groups. The resulting HBPs were characterised by Nuclear Magnetic Resonance Spectroscopy (NMR) and Gel Permeation Chromatography (GPC). Differential Scanning Calorimetry (DSC) was used to determine lower critical solution temperatures (LCSTs) of these copolymers, which are in the range of 17⁻57 °C. Moreover, the studies on the reducibility of HBPs and swelling behaviours of hydrogels synthesized from these HBPs were conducted. The results demonstrated that we have successfully synthesized hyperbranched polymers with desired dual responsive (thermal and reducible) and crosslinkable (via thiol-ene click chemistry) properties. In addition, these new HBPs carry the multiplicity of reactive functionalities, such as RAFT agent moieties and multivinyl functional groups, which can afford them with the capacity for further bioconjugation and structure modifications.

Fentanyl Initiated Polymers Prepared by ATRP for Targeted Delivery

The targeted delivery of polymers to neurons is a challenging yet important goal for polymer based drug delivery. We prepared a fentanyl based atom transfer radical polymerization (ATRP) initiator to target the Mu opioid receptor (MOR) for neuronal targeting. We incorporated our recently discovered rigid acrylate linking group into the initiator to retain a high degree of binding to the MOR and grafted random or block copolymers of poly(oligo(ethylene oxide) methacrylate)-block-(glycidyl methacrylate). Trifluoroethanol promoted amine ring opening of the glycidyl methacrylate was used for post-polymerization modification of the fentanyl initiated polymers to attach a near-infrared fluorescent dye (ADS790WS) or to build a targeted siRNA delivery system via modification with secondary amines. We examined the biocompatibility, cellular internalization, and siRNA binding properties of our polymer library in a green fluorescent protein expressing SY SH5Y neuroblastoma cell-line.

Polymers in the Delivery of siRNA for the Treatment of Virus Infections

Viral diseases remain a major cause of death worldwide. Despite advances in vaccine and antiviral drug technology, each year over three million people die from a range of viral infections. Predominant viruses include human immunodeficiency virus, hepatitis viruses, and gastrointestinal and respiratory viruses. Now more than ever, robust, easily mobilised and cost-effective antiviral strategies are needed to combat both known and emerging disease threats. RNA interference and small interfering (si)RNAs were initially hailed as a “magic bullet”, due to their ability to inhibit the synthesis of any protein via the degradation of its complementary messenger RNA sequence. Of particular interest was the potential for attenuating viral mRNAs contributing to the pathogenesis of disease that were not able to be targeted by vaccines or antiviral drugs. However, it was soon discovered that delivery of active siRNA molecules to the infection site in vivo was considerably more difficult than anticipated, due to a number of physiological barriers in the body. This spurred a new wave of investigation into nucleic acid delivery vehicles which could facilitate safe, targeted and effective administration of the siRNA as therapy. Amongst these, cationic polymer delivery vehicles have emerged as a promising candidate as they are low-cost and easy to produce at an industrial scale, and bind to the siRNA by non-specific electrostatic interactions. These nanoparticles (NPs) can be functionally designed to target the infection site, improve uptake in infected cells, release the siRNA inside the endosome and facilitate delivery into the cell cytoplasm. They may also have the added benefit of acting as adjuvants. This chapter provides a background around problems associated with the translation of siRNA as antiviral treatments, reviews the progress made in nucleic acid therapeutics and discusses current methods and progress in overcoming these challenges. It also addresses the importance of combining physicochemical characterisation of the NPs with in vitro and in vivo data.

Phosphonium polymers for gene delivery

Phosphonium salt-containing polymers have very recently started to emerge as attractive materials for engineering non-viral gene delivery systems.

Rapid synthesis of ultrahigh molecular weight and low polydispersity polystyrene diblock copolymers by RAFT-mediated emulsion polymerization

An environmentally friendly emulsion technique produces uniform nanoparticles with precise control over molecular weight and particle size.

One-dimensional assembly of polymeric ionic liquid capped gold nanoparticles driven by electrostatic dipole interaction

Core–shell particles, comprising an Au NP core and a PIL shell, can be assembled into chain-like nanostructures through HPO₄²⁻ electrostatic coupling between two imidazolium cations from adjacent particles.

Surface modification of electrospun cellulose acetate nanofibers via RAFT polymerization for DNA adsorption

We report on a facile and robust method by which surface of electrospun cellulose acetate (CA) nanofibers can be chemically modified with cationic polymer brushes for DNA adsorption. The surface of CA nanofibers was functionalized by growing poly[(ar-vinylbenzyl)trimethylammonium chloride)] [poly(VBTAC)] brushes through a multi-step chemical sequence that ensures retention of mechanically robust nanofibers. Initially, the surface of the CA nanofibers was modified with RAFT chain transfer agent. Poly(VBTAC) brushes were then prepared via RAFT-mediated polymerization from the nanofiber surface. DNA adsorption capacity of CA nanofibrous web surface functionalized with cationic poly(VBTAC) brushes was demonstrated. The reusability of these webs was investigated by measuring the adsorption capacity for target DNA in a cyclic manner. In brief, CA nanofibers surface-modified with cationic polymer brushes can be suitable as membrane materials for filtration, purification, and/or separation processes for DNA.

Glucose-containing diblock polycations exhibit molecular weight, charge, and cell-type dependence for pDNA delivery

A series of diblock glycopolycations were created by polymerizing 2-deoxy-2-methacrylamido glucopyranose (MAG) with either a tertiary amine-containing monomer, N-[3-(N,N-dimethylamino) propyl] methacrylamide (DMAPMA), or a primary amine-containing unit, N-(2-aminoethyl) methacrylamide (AEMA). Seven structures were synthesized via aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization that varied in the block lengths of MAG, DMAPMA, and AEMA along with two homopolymer controls of DMAPMA and AEMA that lacked a MAG block. The polymers were all able to complex plasmid DNA into polyplex structures and to prevent colloidal aggregation of polyplexes in physiological salt conditions. In vitro transfection experiments were performed in both HeLa (human cervix adenocarcinoma) cells and HepG2 (human liver hepatocellular carcinoma) cells to examine the role of charge type, block length, and cell type on transfection efficiency and toxicity. The glycopolycation vehicles with primary amine blocks and PAEMA homopolymers revealed much higher transfection efficiency and lower toxicity when compared to analogs created with DMAPMA. Block length was also shown to influence cellular delivery and toxicity; as the block length of DMAPMA increased in the glycopolycation-based polyplexes, toxicity increased while transfection decreased. While the charge block played a major role in delivery, the MAG block length did not affect these cellular parameters. Lastly, cell type played a major role in efficiency. These glycopolymers revealed higher cellular uptake and transfection efficiency in HepG2 cells than in HeLa cells, while homopolycations (PAEMA and PDMAPMA) lacking the MAG blocks exhibited the opposite trend, signifying that the MAG block could aid in hepatocyte transfection.

Inhibition of influenza virus in vivo by siRNA delivered using ABA triblock copolymer synthesized by reversible addition-fragmentation chain-transfer polymerization

AIM

Influenza virus remains a major threat, with outbreaks continuing to occur. Few treatment options are available and drug resistance can emerge rapidly. New drugs that can quickly be adapted to virus mutations are needed. Several highly effective siRNAs targeting influenza that inhibit virus replication are known; however, effective delivery of these siRNAs remains a challenge. The aim of this study was to demonstrate the safety and efficacy of ABA triblock copolymer-delivered siRNA to inhibit influenza virus replication in vivo.

MATERIALS & METHODS

We report on the delivery of a siRNA targeting the influenza virus in chicken embryos using an ABA triblock copolymer prepared by reversible addition-fragmentation chain-transfer polymerization, containing a central cationic block and two outer hydrophilic polyethylene glycol blocks.

RESULTS

A significant reduction of virus titer was observed with the polymer/anti-influenza siRNA complexes, whereas the control with polymer/control siRNA complexes showed no effect.

CONCLUSION

These data suggest that a reversible addition-fragmentation chain transfer-based siRNA delivery platform may be suitable for combating infectious diseases in vivo.

Endolytic, pH-responsive HPMA-b-(L-Glu) copolymers synthesized via sequential aqueous RAFT and ring-opening polymerizations

A facile synthetic pathway for preparing block copolymers with pH-responsive L-glutamic acid segments for membrane disruption is reported. Aqueous reversible addition-fragmentation chain transfer (aRAFT) polymerization was first used to prepare biocompatible, nonimmunogenic poly[N-(2-hydroxypropyl)methacrylamide]. This macro chain transfer agent (CTA) was then converted into a macroinitiator via simultaneous aminolysis and thiol-ene Michael addition using the primary amine substituted N-(3-aminopropyl)methacrylamide. This macroinitiator was subsequently utilized in the ring-opening polymerization of the N-carboxyanhydride monomer of γ-benzyl-L-glutamate. After deprotection, the pH-dependent coil-to-helix transformations of the resulting HPMA-b-(L-Glu) copolymers were monitored via circular dichroism spectroscopy. HPMA segments confer water solubility and biocompatibility while the L-glutamic acid repeats provide reversible coil-to-helix transitions at endosomal pH values (~5-6). The endolytic properties of these novel [HPMA-b-(L-Glu)] copolymers and their potential as modular components in drug carrier constructs was demonstrated utilizing red blood cell hemolysis and fluorescein release from POPC vesicles.

Star polymers with a cationic core prepared by ATRP for cellular nucleic acids delivery

Poly(ethylene glycol) (PEG)-based star polymers with a cationic core were prepared by atom transfer radical polymerization (ATRP) for in vitro nucleic acid (NA) delivery. The star polymers were synthesized by ATRP of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and ethylene glycol dimethacrylate (EGDMA). Star polymers were characterized by gel permeation chromatography, zeta potential, and dynamic light scattering. These star polymers were combined with either plasmid DNA (pDNA) or short interfering RNA (siRNA) duplexes to form polyplexes for intracellular delivery. These polyplexes with either siRNA or pDNA were highly effective in NA delivery, particularly at relatively low star polymer weight or molar ratios, highlighting the importance of NA release in efficient delivery systems.

An influenza virus-inspired polymer system for the timed release of siRNA

Small interfering RNA silences specific genes by interfering with mRNA translation, and acts to modulate or inhibit specific biological pathways; a therapy that holds great promise in the cure of many diseases. However, the naked small interfering RNA is susceptible to degradation by plasma and tissue nucleases and due to its negative charge unable to cross the cell membrane. Here we report a new polymer carrier designed to mimic the influenza virus escape mechanism from the endosome, followed by a timed release of the small interfering RNA in the cytosol through a self-catalyzed polymer degradation process. Our polymer changes to a negatively charged and non-toxic polymer after the release of small interfering RNA, presenting potential for multiple repeat doses and long-term treatment of diseases.

Glucose-Sensitivity of Boronic Acid Block Copolymers at Physiological pH

Well-defined boronic acid block copolymers were demonstrated to exhibit glucose-responsive disassembly at physiological pH. A boronic acid-containing acrylamide monomer with an electron-withdrawing substituent on the pendant phenylboronic acid moiety was polymerized by reversible addition-fragmentation chain transfer (RAFT) polymerization to yield a polymer with a boronic acid pK_a = 8.2. Below this value, a block copolymer of this monomer with poly(N,N-dimethylacrylamide) self-assembled into aggregates. Addition of base to yield a pH > pK_a or addition of glucose at pH = 7.4 resulted in aggregate dissociation that may prove promising for controlled delivery applications under physiological relevant conditions.

Cationic nanohydrogel particles as potential siRNA carriers for cellular delivery

Oligonucleotides such as short, double-stranded RNA (siRNA) or plasmid DNA (pDNA) promise high potential in gene therapy. For pharmaceutical application, however, adequate drug carriers are required. Among various concepts progressing in the market or final development, nanosized hydrogel particles may serve as novel transport media especially for siRNA. In this work, a new concept of synthesizing polymeric cationic nanohydrogels was developed, which offers a promising strategy to complex and transport siRNA into cells. For this purpose, amphiphilic reactive ester block copolymers were synthesized by RAFT polymerization of pentafluorophenyl methacrylate as reactive ester monomer together with tri(ethylene glycol)methyl ether methacrylate. In polar aprotic solvents, a self-assembly of these polymers could be observed leading to the formation of nanometer-sized polymer aggregates. The resulting superstructures were used to convert the reactive precursor block copolymers with amine-containing cross-linker molecules into covalently stabilized hydrogel particles. Detailed dynamic light scattering studies showed that the structure of the self-assembled aggregates can permanently be locked-in by this process. This method offers a new possibility to synthesize precise nanohydrogels of different size starting from various block copolymers. Moreover, via reactive ester approach, further functionalities could be attached to the nanoparticle, such as fluorescent dyes, which allowed distinct tracing of the hydrogels during complexation with siRNA or cell uptake experiments. In this respect, cellular uptake of the particles themselves as well as with its payload could be detected successfully. Looking ahead, these novel cationic nanohydrogel particles may serve as a new platform for proper siRNA delivery systems.