Glycopolymer Self-Assemblies with Gold(I) Complexed to the Core as a Delivery System for Auranofin

A new glycomonomer <b>1</b> containing a thioacetate group in the anomeric position and mimicking the thiosugar ligand of the gold-based drug auranofin was designed and synthesized in four steps from d-glucose. Both CPADB-mediated homopolymerization and chain extension of a hydrophilic poly­(OEGMEMA) macroRAFT agent were well-controlled with dispersities (<i><i><i>Đ</i></i></i>) below 1.2, highlighting the suitability of thioacetate as a thiol protecting group in RAFT polymerization. Using the homopolymer as a test system, the thioacetate protective groups were selectively removed using hydrazine acetate, and AuPEt₃Cl was subsequently complexed to the exposed thiols to generate a polymeric auranofin analogue with 52% complexation efficiency. Extension of this successful procedure to three block copolymers with differing hydrophobic block lengths, poly­(OEGMEMA)₃₄-<i>b</i>-poly­(<b>1</b>)₄₇, poly­(F-OEGMEMA)₃₂-<i>b</i>-poly­(<b>1</b>)₂₇, and poly­(F-OEGMEMA)₃₂-<i>b</i>-poly­(<b>1</b>)₇ (where “F” in the last two indicates the incorporation of 2 wt % fluorescein methacrylate into the hydrophilic block), produced well-defined complexed block copolymers with complexation efficiencies comparable to that of the homopolymer. Self-assembly of the longest complexed polymer poly­(OEGMEMA)₃₄-<i>b</i>-poly­(<b>1</b>-AuPEt₃)₄₇ generated spherical micelles with a hydrodynamic diameter <i>D</i>_h of 28 nm when prepared by slow water addition to a dilute DMF solution. The IC₅₀ value against OVCAR-3 cells in a serum-free media was 44 μM on a gold concentration basis, compared to 0.3 μM for auranofin itself. The two shorter fluorescent complexed block copolymers formed spherical micelles with <i>D</i>_h 23 and 9 nm, respectively, and proved more cytotoxic than their longer counterpart, both displaying IC₅₀ values of 13.5 μM. The addition of serum to the cell growth medium reduced the cytotoxicity of auranofin by a factor of 3.6 but had a less marked effect on the fluorescent micellar systems, reducing their toxicities by between 2.4 and 2.8 times. These micellar systems therefore show less susceptibility to deactivation by serum proteins (which is the primary limitation to auranofin’s <i>in vivo</i> effectiveness) than the free auranofin, suggesting some protective benefit offered by the hydrophilic shell. Fluorescence microscopy of the two fluorescent systems revealed an accumulation in the lysosomes of the OVCAR-3 cells. The cytotoxicity mechanism may therefore differ from that of auranofin, which is known to interact with mitochondrial proteins

Origami with ABC Triblock Terpolymers Based on Glycopolymers: Creation of Virus-Like Morphologies

Morphologies, that resemble viruses, were created using a single ABC triblock terpolymer poly­(2-acryloylethyl-α-d-mannopyranoside)-<i>b</i>-poly­(<i>n</i>-butyl acrylate)-<i>b</i>-poly­(4-vinylpyridine) (PAcManA₇₀-<i>b</i>-PBA₃₆₉-<i>b</i>-PVP₃₇₀). Morphologies ranging from flower-like micelles, cylindrical micelles, raspberry-like morphologies to nanocaterpillars were obtained by adjusting the pH value during the self-assembly process. The resulting nanoparticles had an abundance of mannose on the surface, which were recognized by the mannose receptors of RAW264.7, a macrophage cell line that can be used as a model for virus entry

Synthesis and Lectin Recognition of Glyco Star Polymers Prepared by “Clicking” Thiocarbohydrates onto a Reactive Scaffold

Glycopolymers with a four-arm star architecture were prepared from poly(vinyl benzyl chloride) (PVBC) star polymers as reactive scaffold and 1-thio-β-d-glucose sodium salt. The star polymer was prepared via RAFT polymerization using 1,2,4,5-tetrakis(thiobenzoylthiomethyl)benzene as a rate-retarding RAFT agent at a polymerization temperature of 120 °C. The occurrence of known side reactions such as star−star coupling was partly suppressed by optimizing the reaction conditions. The molecular weight distribution in the early stages of the polymerization (1H NMR, confirming full conversion after a reaction time of 110 h. Six different glyco star polymers with number of repeating units N ranging from 40 to 680 were tested regarding their ability to bind to Concanavalin A (ConA) using turbidity assay. The rate of reaction and t1/2, the time to reach half of the maximum absorption, was found to reach a maximum and minimum, respectively, at a medium molecular weight. The same molecular weight dependency was obtained using precipitation assay, which determines the amount of ConA conjugated to the glycopolymer. Comparison with linear glycopolymers reveals however that the amount of bound ConA and the rate of clustering are not superior in the star architecture

PET-RAFT Enables Efficient and Automated Multiblock Star Synthesis

We show that photoinitiated electron/energy transfer–reversible addition–fragmentation chain transfer (PET-RAFT) enables vastly superior control over the polymerization of multiblock star copolymers compared to conventional techniques. Monomodal distributions with dispersities <1.3 could be achieved after the 10th block despite pushing the polymerization to >95% conversion in each block extension. The improvement in control is likely due to the reabsorption of the free radical at the propagating chain end by the excited catalyst, which would otherwise lead to a termination product. Simple modeling shows the dramatic effect that this has in the case of star polymerizations. Because PET-RAFT is also tolerant to oxygen, we were able to automate the synthesis of up to heptablock stars at short block lengths, providing a useful technique for screening the effect of polymer composition on the solution structure

Inverse Miniemulsion Periphery RAFT Polymerization: A Convenient Route to Hollow Polymeric Nanoparticles with an Aqueous Core

The recently developed [Chem. Commun. 2012, 48, 11103−11105] inverse miniemulsion periphery RAFT polymerization (IMEPP) approach to prepare hollow polymeric nanoparticles (∼200 nm) with an aqueous core has been explored in detail. The method is based on an amphiphilic macroRAFT agent acting as stabilizer of water droplets in an organic continuous phase while also mediating cross-linking chain growth in a controlled/living manner on the outer periphery of the droplets. The macroRAFT agent comprised a hydrophilic block of poly­(<i>N</i>-(2-hydroxypropyl)­methacrylamide) and a hydrophobic block of either polystyrene or poly­(methyl methacrylate), and the cross-linked shell was formed on polymerization of styrene/divinylbenzene or methyl methacrylate/ethylene glycol dimethacrylate, respectively. The effects of various reaction parameters on the resulting hollow nanoparticles have been systematically investigated, and it has been demonstrated that the shell thickness can be tuned based on initial stoichiometry and monomer conversion. This method is particularly relevant for encapsulation of proteinssuccessful incorporation of proteins (bovine serum albumin) into the miniemulsion did not negatively affect the droplet size and stability

Maximizing Aqueous Drug Encapsulation: Small Nanoparticles Formation Enabled by Glycopolymers Combining Glucose and Tyrosine

Highly potent heterocyclic drugs are frequently poorly water soluble, leading to limited or abandoned further drug development. Nanoparticle technology offers a powerful delivery approach by enhancing the solubility and bioavailability of hydrophobic therapeutics. However, the common usage of organic solvents causes unwanted toxicity and process complexity, therefore limiting the scale-up of nanomedicine technology for clinical translation. Here, we show that an organic-solvent-free methodology for hydrophobic drug encapsulation can be obtained using polymers based on glucose and tyrosine. An aqueous solution based on a tyrosine-containing glycopolymer is able to dissolve solid dasatinib directly without adding an organic solvent, resulting in the formation of very small nanoparticles of around 10 nm loaded with up to 16 wt % of drug. This polymer is observed to function as both a drug solubilizer and a nanocarrier at the same time, offering a simple route for the delivery of insoluble drugs

Covalent Tethering of Temperature Responsive pNIPAm onto TEMPO-Oxidized Cellulose Nanofibrils via Three-Component Passerini Reaction

A critical challenge in the application of functional cellulose fibrils is to perform efficient surface modification without disrupting the original properties. Three-component Passerini reaction (Passerini 3-CR) is regarded as an effective functionalization approach which can be carried out under mild and fast reaction condition. In this study, we investigated the application of Passerini 3-CR for the synthesis of thermoresponsive cellulose fibrils by covalently tethering poly­(<i>N</i>-isopropylacrylamide) in aqueous condition at ambient temperature. The three components, a TEMPO-oxidized cellulose nanofiber bearing carboxylic acid moieties (TOCN-COOH), a functionalized polymer with aldehyde group (pNIPAm-COH) and a cyclohexyl isocyanide, were reacted in one pot resulting in 36% of grafting efficiency within 30 min. The chemical coupling was evidenced by improved aqueous dispersibility, which was further confirmed by FT-IR, TGA, UV–vis, and turbidity study. It was observed that the grafting efficiency is strongly dependent on the chain length of the polymer. Furthermore, AFM and X-ray diffraction measurements affirmed the suitability of the proposed method for chemical modification of cellulose nanofibers without significantly compromising the original morphology and structural integrity

Enhanced Delivery of the RAPTA‑C Macromolecular Chemotherapeutic by Conjugation to Degradable Polymeric Micelles

Macromolecular ruthenium complexes are a promising avenue to better and more selective chemotherapeutics. We have previously shown that RAPTA-C [RuCl₂(<i>p</i>-cymene)­(PTA)], with the water-soluble 1,3,5-phosphaadamantane (PTA) ligand, could be attached to a polymer moiety via nucleophilic substitution of an available iodide with an amide in the PTA ligand. To increase the cell uptake of this macromolecule, we designed an amphiphilic block copolymer capable of self-assembling into polymeric micelles. The block copolymer was prepared by ring-opening polymerization of d,l-lactide (3,6-dimethyl-1,4-dioxane-2,5-dione) using a RAFT agent with an additional hydroxyl functionality, followed by the RAFT copolymerization of 2-hydroxyethyl acrylate (HEA) and 2-chloroethyl methacrylate (CEMA). The Finkelstein reaction and reaction with PTA led to polymers that can readily react with the dimer of RuCl₂(<i>p</i>-cymene) to create a macromolecular RAPTA-C drug. RAPTA-C conjugation, micellization, and subsequent cytotoxicity and cell uptake of these polymeric moieties was tested on ovarian cancer A2780, A2780cis, and Ovcar-3 cell lines. Confocal microscopy images confirmed cell uptake of the micelles into the lysosome of the cells, indicative of an endocytic pathway. On average, a 10-fold increase in toxicity was found for the macromolecular drugs when compared to the RAPTA-C molecule. Furthermore, the cell uptake of ruthenium was analyzed and a significant increase was found for the micelles compared to RAPTA-C. Notably, micelles prepared from the polymer containing fewer HEA units had the highest cytotoxicity, the best cell uptake of ruthenium and were highly effective in suppressing the colony-forming ability of cells

Polymeric Micelles with Pendant Dicarboxylato Chelating Ligands Prepared via a Michael Addition for <i>cis</i>-Platinum Drug Delivery

A new monomer with a neighboring carboxylate functional group was prepared via carbon Michael addition between ethylene glycol dimethacrylate and malonate. The monomer, 1,1-di-tert-butyl 3-(2-(methacryloyloxy)ethyl) butane-1,1,3-tricarboxylate (MAETC), was polymerized in a controlled manner using RAFT polymerization. After deprotection and the conjugation of platinum drugs, a macromolecular Pt complex was created, which was found to be insoluble in water. 195Pt NMR revealed that the desired complex has been formed next to a minor fraction of other Pt complexes. Block copolymers were prepared using poly[oligo(ethylene glycol) methyl ether methacrylate] (POEGMEMA) as macroRAFT agent for chain extension with the synthesized monomer to yield three different block copolymers with varying PMAETC block lengths. Subsequent conjugation to platinum resulted in amphiphilic block copolymers, which can ultimately generate micelles. The length of the core block had significant contribution to the micelle sizes with the micelle size increasing with an increase of the hydrophobic block length. The polymers prior to platinum conjugation were found to be nontoxic when in contact with A549, a lung cancer cell line. After conjugation with the platinum drug, the micelle with the shortest PMAETC block length was found to have the highest toxicity, which may be due to the fastest cisplatin release when compared to the longer PMAETC block lengths

Maximizing Aqueous Drug Encapsulation: Small Nanoparticles Formation Enabled by Glycopolymers Combining Glucose and Tyrosine

Highly potent heterocyclic drugs are frequently poorly water soluble, leading to limited or abandoned further drug development. Nanoparticle technology offers a powerful delivery approach by enhancing the solubility and bioavailability of hydrophobic therapeutics. However, the common usage of organic solvents causes unwanted toxicity and process complexity, therefore limiting the scale-up of nanomedicine technology for clinical translation. Here, we show that an organic-solvent-free methodology for hydrophobic drug encapsulation can be obtained using polymers based on glucose and tyrosine. An aqueous solution based on a tyrosine-containing glycopolymer is able to dissolve solid dasatinib directly without adding an organic solvent, resulting in the formation of very small nanoparticles of around 10 nm loaded with up to 16 wt % of drug. This polymer is observed to function as both a drug solubilizer and a nanocarrier at the same time, offering a simple route for the delivery of insoluble drugs