Synthesis and Noncovalent Protein Conjugation of Linear-Hyperbranched PEG-Poly(glycerol) α,ωn-Telechelics

Polyethers Based on Short-Chain Alkyl Glycidyl Ethers: Thermoresponsive and Highly Biocompatible Materials

The polymerization of short-chain alkyl glycidyl ethers (SCAGEs) enables the synthesis of biocompatible polyethers with finely tunable hydrophilicity. Aliphatic polyethers, most prominently poly(ethylene glycol) (PEG), are utilized in manifold biomedical applications due to their excellent biocompatibility and aqueous solubility. By incorporation of short hydrophobic side-chains at linear polyglycerol, control of aqueous solubility and the respective lower critical solution temperature (LCST) in aqueous solution is feasible. Concurrently, the chemically inert character in analogy to PEG is maintained, as no further functional groups are introduced at the polyether structure. Adjustment of the hydrophilicity and the thermoresponsive behavior of the resulting poly(glycidyl ether)s in a broad temperature range is achieved either by the combination of the different SCAGEs or with PEG as a hydrophilic block. Homopolymers of methyl and ethyl glycidyl ether (PGME, PEGE) are soluble in aqueous solution at room temperature. In contrast, n-propyl glycidyl ether and iso-propyl glycidyl ether lead to hydrophobic polyethers. The use of a variety of ring-opening polymerization techniques allows for controlled polymerization, while simultaneously determining the resulting microstructures. Atactic as well as isotactic polymers are accessible by utilization of the respective racemic or enantiomerically pure monomers. Polymer architectures varying from statistical copolymers, di- and triblock structures to star-shaped architectures, in combination with PEG, have been applied in various thermoresponsive hydrogel formulations or polymeric surface coatings for cell sheet engineering. Materials responding to stimuli are of increasing importance for "smart" biomedical systems, making thermoresponsive polyethers with short-alkyl ether side chains promising candidates for future biomaterials.

Water-Assisted and Protein-Initiated Fast and Controlled Ring-Opening Polymerization of Proline N-Carboxyanhydride

The production of polypeptides via the ring-opening polymerization (ROP) of N-carboxyanhydride (NCA) is usually conducted under stringent anhydrous conditions. The ROP of proline NCA (ProNCA) for the synthesis of poly-_L-proline (PLP) is particularly challenging due to the premature product precipitation as polyproline type I helices, leading to slow reactions for up to one week, poor control of the molar mass and laborious workup. Here, we report the unexpected water-assisted controlled ROP of ProNCA, which affords well-defined PLP as polyproline II helices in 2–5 minutes and almost-quantitative yields. Experimental and theoretical studies together suggest the as-yet-unreported role of water in facilitating proton shift, which significantly lowers the energy barrier of the chain propagation. The scope of initiators can be expanded from hydrophobic amines to encompass hydrophilic amines and thiol-bearing nucleophiles, including complex biomacromolecules such as proteins. Protein-mediated ROP of ProNCA conveniently affords various protein-PLP conjugates via a grafting-from approach. PLP modification not only preserves the biological activities of the native proteins, but also enhances their resistance to extreme conditions. Moreover, PLP modification extends the elimination half-life of asparaginase (ASNase) 18-fold and mitigates the immunogenicity of wt ASNase >250-fold (ASNase is a first-line anticancer drug for lymphoma treatment). This work provides a simple solution to a long-standing problem in PLP synthesis, and offers valuable guidance for the development of water-resistant ROP of other proline-like NCAs. The facile access to PLP can greatly boost the application potential of PLP-based functional materials for engineering industry enzymes and therapeutic proteins.

Poly(HPMA-co-NIPAM) copolymer as an alternative to polyethylene glycol-based pharmacokinetic modulation of therapeutic proteins

PEGylation is the standard approach for prolonging the plasma exposure of protein therapeutics but has limitations. We explored whether polymers prepared by Reversible Addition-Fragmentation chain-Transfer (RAFT) may provide better alternatives to polyethylene glycol (PEG). Four RAFT polymers were synthesised with varying compositions, molar mass (M_n), and structures, including a homopolymer of N-(2-hydroxypropyl)methacrylamide, (pHPMA) and statistical copolymers of HPMA with poly(ethylene glycol methyl ether acrylate) p(HPMA-co-PEGA); HPMA and N-acryloylmorpholine, p(HPMA-co-NAM); and HPMA and N-isopropylacrylamide, p(HPMA-co-NIPAM). The intravenous pharmacokinetics of the polymers were then evaluated in rats. The in vitro activity and in vivo pharmacokinetics of p(HPMA-co-NIPAM)-conjugated trastuzumab Fab' and full length mAb were then evaluated. p(HPMA-co-NIPAM) prolonged plasma exposure more avidly compared to the other p(HPMA) polymers or PEG, irrespective of molecular weight. When conjugated to trastuzumab-Fab', p(HPMA-co-NIPAM) prolonged plasma exposure of the Fab' similar to PEG-Fab'. The generation of anti-PEG IgM in rats 7 days after intravenous and subcutaneous dosing of p(HPMA-co-NIPAM) conjugated trastuzumab mAb was also examined and was shown to exhibit lower immunogenicity than the PEGylated construct. These data suggest that p(HPMA-co-NIPAM) has potential as a promising copolymer for use as an alternative conjugation strategy to PEG, to prolong the plasma exposure of therapeutic proteins.

Noncovalent Protection for Direct Synthesis of α-Amino-ω-hydroxyl Poly(ethylene oxide)

The synthesis of poly(ethylene oxide) (PEO) with amino end group, a key functionality for PEGylation, is a long-standing challenge. Multistep routes based on postmodification or covalent protection have been adopted to circumvent ethoxylation of the amino group by ethylene oxide (EO). Here, we report a noncovalent protection strategy for one-step synthesis of PEO amine. An amino (di)alcohol is mixed with a small amount of mild phosphazene base and excess triethylborane (Et₃B) before addition of EO. The complexation of the amino group with Et₃B guarantees that polymerization of EO occurs selectively from the hydroxyl group through the bicomponent metal-free catalysis. Simply by precipitation in diethyl ether, the protective Et₃B as well as the catalyst can be removed to afford α-amino-ω-hydroxyl PEO with controlled molar mass, low dispersity, and complete end functionality. The effect of initiator structure and retention of Et₃B on the storage (oxidative) stability of PEO amine is also revealed.

Liquid crystalline hyperbranched polyesters with phosphorus functional groups

Liquid crystalline hyperbranched poly(aryl ester)s (A2B3) were prepared by polycondensation reaction of 2-(6-oxido-6H-dibenz<c,e><1,2>oxaphosphorin-6-yl)1,4-naphthalene diol with 1,3,5-benzenetricarbonyl trichloride, taken in two different molar ratios. The chemical structure of the newly synthesized hyperbranched polymers was confirmed by FTIR, 1H NMR, 13C NMR spectroscopy. The polymers exhibited high thermal stability with initial decomposition temperature above 410–435°C and char yield at 700°C higher than 40%. Combined differential scanning calorimetry, polarized optical microscopy and wide-angle X-ray diffraction measurements were carried out to closely examine their thermal behavior and phase transitions.

Amphiphilic drug-peptide-polymer conjugates based on poly(ethylene glycol) and hyperbranched polyglycerol for epidermal growth factor receptor targeting: the effect of conjugate aggregation on in vitro activity

Numerous peptide-drug conjugates have been developed over the years to enhance the specificity and selectivity of chemotherapeutic agents for tumour cells. In our present work, epidermal growth factor receptor targeting drug-peptide conjugates were prepared using GE11 and D4 peptides. To ensure the drug release, the cathepsin B labile GFLG spacer was incorporated between the targeting peptide and the drug molecule (daunomycin), which significantly increased the hydrophobicity and thereby decreased the water solubility of the conjugates. To overcome the solubility problem, drug-peptide-polymer conjugates with systematic structural variations were prepared, by linking poly(ethylene glycol) (PEG) or a well-defined amino-monofunctional hyperbranched polyglycerol (HbPG) directly or via a pentaglycine spacer to the targeting peptides. All the drug-peptide-polymer conjugates were water-soluble as confirmed by turbidimetric measurements. The results of the in vitro cell viability and cellular uptake measurements on HT-29 human colon adenocarcinoma cells proved that the HbPG and the PEG highly influenced the biological activity. The conjugation of the hydrophilic polymer resulted in the amphiphilic character of the conjugates, which led to self-aggregation and nanoparticle formation that decreased the cellular uptake above a specific aggregation concentration. On the other hand, the hydrodynamic volume and the different polymer chain topology of the linear PEG and the compact hyperbranched HbPG also played an important role in the biological activity. Therefore, in similar systems, the investigation of the colloidal properties is inevitable for the better understanding of the biological activity, which can reveal the structure-activity relationship of amphiphilic drug-peptide-polymer conjugates for efficient tumour targeting.

Amino-functional polyethers: versatile, stimuli-responsive polymers

Amino-functional polyethers have emerged as a new class of “smart”, i.e. pH- and thermoresponsive materials. This review article summarizes the synthesis and applications of these materials, obtained from ring-opening of suitable epoxide monomers.

Nanocrystal Encapsulation, Release and Application Based on pH-Sensitive Covalent Dynamic Hyperbranched Polymers

A new strategy for nanocrystal encapsulation, release and application based on pH-sensitive covalent dynamic hyperbranched polymers is described. The covalent dynamic hyperbranched polymers, with multi-arm hydrophobic chains and a hydrophilic hyperbranched poly(amidoamine) (HPAMAM) core connected with pH-sensitive imine bonds (HPAMAM–DA), could encapsulate CdTe quantum dots (QDs) and Au nanoparticles (NPs). Benefiting from its pH response property, CdTe QDs and Au NPs encapsulated by HPAMAM–DA could be released to aqueous phase after imine hydrolysis. The released CdTe/HPAMAM and Au/HPAMAM nanocomposites exhibited excellent biological imaging behavior and high catalytic activities on p-nitrophenol hydrogenation, respectively.

Selective azo dye-based colorimetric chemosensor for F-, CH3COO- and PO43

Developing anionic receptors is a huge challenge, especially those using hydrogen bonds to interact with the analytes. Azobenzene-derivative selective chemosensor has been evaluated for anion recognition properties. 2‑(4‑Hydroxiazobenzene)benzoic acid (HABA) has two hydrogens groups available for interaction; one is the phenol group and the other is the carboxylic acid group, enabling interaction with cations and anions. Subsequently titrations of chromophore 2‑(4‑hydroxiazobenzene) benzoic acid were performed with cations and anions; however, only the interactions with fluoride, acetate, and phosphate were significant. These data demonstrated the sensitivity of the ligand HABA by these anions, characterized by the displacement of the absorbance bands at 372nm to 491nm in acetonitrile. The association constants found to fluoride, acetate, and phosphate were 1.56×10⁴±0.28, 1.25×10⁴±0.60, and 1.90×10⁴±0.67mol^-1dm³ respectively. ¹H NMR titrations data confirmed association constants values in agreement with those of UV-Vis, besides showing evidence of the analyte interaction by the hydrogen-bonding of the carboxylic acid group. Overall, UV-Vis limit of detection data for fluoride (1.05×10^-7moldm^-3), acetate (3.77×10^-8moldm^-3) and phosphate (3.00×10^-8moldm^-3), support that HABA can detect low concentration of these anions.

Lipiodol nanoemulsions stabilized with polyglycerol-polycaprolactone block copolymers for theranostic applications

BACKGROUND

Polyglycerol is an attractive hydrophilic building block of amphiphilic copolymers for biomedical and pharmaceutical applications due to its biocompatibility, facile chemical modification, and anti-fouling activity. Herein we introduce theranostic nanoemulsions incorporating anti-cancer therapeutic and contrast agents using linear polyglycerol-poly(ε-caprolactone) diblock copolymers (PG-b-PCL). Lipiodol is used as a core oil that dissolves paclitaxel and serves as a contrast agent for computer tomography (CT).

METHODS

PG-b-PCL is synthesized by three-step processes: polymerization of ethoxyethyl glycerol ether; ring-opening polymerization of ε-caprolactone; and deprotection of the PEEGE block. In vitro cytotoxicity of the polyglycerolated lipiodol nanoemulsions is demonstrated using HeLa ovarian cancer cells. The applicability of the prepared nanoemulsions as a contrast agent for CT imaging is also evaluated using micro-CT.

RESULTS

Three compositions of PG-b-PCL with different block lengths are synthesized to prepare nanoemulsions. The polyglycerolated lipiodol nanoemulsions exhibit excellent anti-cancer activities, while placebo nanoemulsions have no significant cytotoxicity under the same condition. Micro-CT imaging of the nanoemulsions confirms the ability of nanoemulsions as a contrast agent.

CONCLUSIONS

This study suggests that PG-b-PCL is a promising polymeric emulsifier for effective stabilization and surface functionalization of drug delivery nanocarriers for therapeutic and imaging agents.

Catalyst System for Hydrogenation Catalysis Based on Multiarm Hyperbranched Polymer Templated Metal (Au, Pt, Pd, Cu) Nanoparticles

With a hyperbranched poly(amidoamine) core and many water-soluble poly(ethylene glycol) monomethyl ether arms connected by pH-sensitive acylhydrazone bonds, multiarm hyperbranched polymer was used as nanoreactor and reductant to prepare metal nanoparticles endowed with intelligence and biocompatibility. The multiarm hyperbranched polymer encapsulated nanoparticles (NPs) showed excellent catalytic activity for hydrogenation, thus an excellent catalyst system for hydrogenation was established. The rate constants could reach as high as 3.48 L·s-1·m-2, which can be attributed to the lack of surface passivation afforded by the multiarm hyperbranched polymer.

Hyperbranched polyglycerols: recent advances in synthesis, biocompatibility and biomedical applications

Hyperbranched polyglycerol is one of the most widely studied biocompatible dendritic polymer and showed promising applications. Here, we summarized the recent advancements in the field.

Linear-dendritic block copolymer for drug and gene delivery

Dendrimers as a new class of polymeric materials have a highly ordered branched structure, exact molecular weight, multivalency and available internal cavities, which make them extensively used in biology and drug-delivery. Concurrent with the development of dendrimers, much more attention is drawn to a novel block copolymer which combines linear chains with dendritic macromolecules, the linear-dendritic block copolymer (LDBC). Because of the different solubility of the contrasting regions, the amphiphilic LDBCs could self-assemble to form aggregates with special core-shell structures which exhibit excellent properties different from traditional micelles, such as lower critical micelle concentration, prolonged circulation in the bloodstream, better biocompatibility, and lower toxicity. The present review briefly describes the type of LDBC, the self-assembly behavior in solution, and the application in delivery system including the application as drug carriers and gene vectors. The interactions between block copolymers and drugs are also summarized to better understand the release mechanism of drugs from the linear-dendritic block copolymers.

Soft amphiphilic polyesters obtained from PEGs and silicon fatty compounds: structural characterizations and self-assembly studies

Transesterification polymerizations between a silicon fatty ester derived from methyl 10-undecenoate and polyethylene glycol (PEG) monomers generate amphiphilic biopolyesters ​showing abilities to form micelle and fiber structures.

Fluorescent protein-reactive polymers via one-pot combination of the Ugi reaction and RAFT polymerization

Well-defined polymers containing both fluorescent and protein-reactive groups at the chain end have been facilely synthesized by the one-pot combination of the four-component Ugi reaction and RAFT polymerization.

Perfluoroalkylated linear polyglycerols and their supramolecular assemblies in aqueous solution

In this study, amphiphiles composed of linear polyglycerols (LPGs) with hydroxyl, methoxy, and ethoxy side groups and end capped with one or two perfluorooctyl chains (R_f8) have been designed to form supramolecular architectures.

Polymerization of Ethylene Oxide, Propylene Oxide, and Other Alkylene Oxides: Synthesis, Novel Polymer Architectures, and Bioconjugation

The review summarizes current trends and developments in the polymerization of alkylene oxides in the last two decades since 1995, with a particular focus on the most important epoxide monomers ethylene oxide (EO), propylene oxide (PO), and butylene oxide (BO). Classical synthetic pathways, i.e., anionic polymerization, coordination polymerization, and cationic polymerization of epoxides (oxiranes), are briefly reviewed. The main focus of the review lies on more recent and in some cases metal-free methods for epoxide polymerization, i.e., the activated monomer strategy, the use of organocatalysts, such as N-heterocyclic carbenes (NHCs) and N-heterocyclic olefins (NHOs) as well as phosphazene bases. In addition, the commercially relevant double-metal cyanide (DMC) catalyst systems are discussed. Besides the synthetic progress, new types of multifunctional linear PEG (mf-PEG) and PPO structures accessible by copolymerization of EO or PO with functional epoxide comonomers are presented as well as complex branched, hyperbranched, and dendrimer like polyethers. Amphiphilic block copolymers based on PEO and PPO (Poloxamers and Pluronics) and advances in the area of PEGylation as the most important bioconjugation strategy are also summarized. With the ever growing toolbox for epoxide polymerization, a "polyether universe" may be envisaged that in its structural diversity parallels the immense variety of structural options available for polymers based on vinyl monomers with a purely carbon-based backbone.

Supramolecular hydrogels: synthesis, properties and their biomedical applications

As a novel class of three-dimensional (3D) hydrophilic cross-linked polymers, supramolecular hydrogels not only display unique physicochemical properties (e.g., water-retention ability, drug loading capacity, biodegradability and biocompatibility, biostability) as well as specific functionalities (e.g., optoelectronic properties, bioactivity, self-healing ability, shape memory ability), but also have the capability to undergo reversible gel-sol transition in response to various environmental stimuli inherent to the noncovalent cross-linkages, thereby showing great potential as promising biomaterial scaffolds for diagnosis and therapy. In this Review, we summarized the recent progress in the design and synthesis of supramolecular hydrogels through specific, directional noncovalent interactions, with particular emphasis on the structure-property relationship, as well as their wide-ranging applications in disease diagnosis and therapy including bioimaging, biodetection, therapeutic delivery, and tissue engineering. We believe that these current achievements in supramolecular hydrogels will greatly stimulate new ideas and inspire persistent efforts in this hot topic area in future.

Functional supramolecular polymers for biomedical applications

As a novel class of dynamic and non-covalent polymers, supramolecular polymers not only display specific structural and physicochemical properties, but also have the ability to undergo reversible changes of structure, shape, and function in response to diverse external stimuli, making them promising candidates for widespread applications ranging from academic research to industrial fields. By an elegant combination of dynamic/reversible structures with exceptional functions, functional supramolecular polymers are attracting increasing attention in various fields. In particular, functional supramolecular polymers offer several unique advantages, including inherent degradable polymer backbones, smart responsiveness to various biological stimuli, and the ease for the incorporation of multiple biofunctionalities (e.g., targeting and bioactivity), thereby showing great potential for a wide range of applications in the biomedical field. In this Review, the trends and representative achievements in the design and synthesis of supramolecular polymers with specific functions are summarized, as well as their wide-ranging biomedical applications such as drug delivery, gene transfection, protein delivery, bio-imaging and diagnosis, tissue engineering, and biomimetic chemistry. These achievements further inspire persistent efforts in an emerging interdisciplin-ary research area of supramolecular chemistry, polymer science, material science, biomedical engineering, and nanotechnology.

Hyperbranched PEG-based supramolecular nanoparticles for acid-responsive targeted drug delivery

In this article acid-sensitive hyperbranched PEG-based supramolecular nanoparticles were designed and used for targeted drug delivery.

Bioapplications of hyperbranched polymers

The recent research progress in biological and biomedical applications of hyperbranched polymers has been summarized in this review.

Synthesis and therapeutic applications of biocompatible or biodegradable hyperbranched polymers

The recent progress in the synthesis, modifications and therapeutic applications of biocompatible or biodegradable hyperbranched polymers has been reviewed.

Self-assembly of supramolecularly engineered polymers and their biomedical applications

Self-assembly behavior of supramolecularly engineered polymers and their biomedical applications have been summarized.

Efficient delivery of p53 and cytochrome c by supramolecular assembly of a dendritic multi-domain delivery system

Versatile nanocarrier systems facilitating uptake of exogenous proteins are highly alluring in evaluating these proteins for therapeutic applications. The self-assembly of an efficient nano-sized protein transporter consisting of three different entities is presented: A streptavidin protein core functioning as an adapter, second generation polyamidoamine dendrons for facilitating cell uptake as well as two different therapeutic proteins (tumor suppressor p53 or pro-apoptotic cytochrome c as cargo). Well-defined dendrons containing a biotin core are prepared and display no cytotoxic behavior upon conjugation to streptavidin. The integration of biotinylated human recombinant p53 (B-p53) into the three component system allows excellent internalization into HeLa, A549 and SaOS osteosarcoma cells monitored via confocal microscopy, immunoblot analysis and co-localization studies. In addition, the conjugation of B-p53 to dendronized streptavidin preserves its specific DNA-binding in vitro, and its delivery into SaOS cells impairs cell viability with concomitant activation of caspases 3 and 7. The versatility of this system is further exhibited by the significant enhancement of the pro-apoptotic effects of internalized cytochrome c which is analyzed by flow cytometry and cell viability assays. These results demonstrate that the "bio-click" self-assembly of biotinylated dendrons and proteins on a streptavidin adapter yields a stable supramolecular complex. This efficient bionanotransporter provides an attractive platform for mediating the delivery of functional proteins of interest into living mammalian cells in a facile and rapid way.

Controlled branching of polyglycidol and formation of protein-glycidol bioconjugates via a graft-from approach with "PEG-like" arms

The control of the branching in polyglycidols as semibranched alternatives to traditional polyglycidols is presented. The relative abundance of dendritic carbons is lowered by five-fold compared to hyperbranched polyglycidols. It is the first example of tailoring the branching in polyglycidol and creating protein-glycidol bioconjugates as alternatives to pegylated biostructures.