Amphiphilic Random Glycopolymer Based on Phenylboronic Acid: Synthesis, Characterization, and Potential as Glucose-Sensitive Matrix

Synthesis of Copolymers from Phenylboronic Acid-Installed Cyclic Carbonates

Organoboron polymers play important roles in biomedical applications. An ample number of monomers bearing boronic acid derivatives have been synthesized, particularly focusing on controlled free radical polymerization methods. Organoboron polymers synthesized by ring-opening polymerization (ROP) routes are far less explored. We report on the ROP of boronic acid-installed cyclic carbonates, catalyzed by DBU from a poly(ethylene glycol) macroinitiator. Controlled polymerization proceeded to relatively high conversions (∼70%) with low polydispersity. Deprotection of the copolymer to generate the boronic acid pendant group was readily achieved by displacement of the protecting group with free diboronic acid. The resulting amphiphilic copolymers self-assembled in water into spherical nanoparticles or vesicles, depending on hydrophilic/hydrophobic ratio. We envision these functional carbonates finding direct applications for core stabilization of biodegradable amphiphilic assemblies or in drug and protein encapsulation.

Emerging micro- and nanotechnology based synthetic approaches for insulin delivery

Insulin is essential for type 1 and advanced type 2 diabetics to maintain blood glucose levels and prolong lives. The traditional administration requires frequent subcutaneous insulin injections that are associated with poor patient compliance, including pain, local tissue necrosis, infection, and nerve damage. Taking advantage of emerging micro- and nanotechnologies, numerous alternative strategies integrated with chemical approaches for insulin delivery have been investigated. This review outlines recent developments in the controlled delivery of insulin, including oral, nasal, pulmonary, transdermal, subcutaneous and closed-loop insulin delivery. Perspectives from new materials, formulations and devices at the micro- or nano-scales are specifically surveyed. Advantages and limitations of current delivery methods, as well as future opportunities and challenges are also discussed.

Phenylboronate-diol crosslinked glycopolymeric nanocarriers for insulin delivery at physiological pH

Research into polymers with glucose-sensitivity in physiological conditions has expanded recently due to their therapeutic potential in diabetes. Herein, to explore the glucose-responsive properties of a new polymer under physiological conditions, we synthesized an amphiphilic block glycopolymer based on phenylboronic acid and a carbohydrate, which was named poly(d-gluconamidoethyl methacrylate-block-3-acrylamidophenylboronic acid) (p(AAPBA-b-GAMA)). Based on the cross-linking between the diol groups of the carbohydrates and phenylboronic acid, the glycopolymers self-assembled to form nanoparticles (NPs). The glucose-sensitivity was revealed by the swelling behavior of the NPs at different glucose concentrations and was found to be dependent on the glucose level. The morphology of the NPs revealed by transmission electron microscopy showed that the NPs were spherical in shape with good dispersity. The cell viability of the NPs investigated by MTT assay was more than 90%, indicating that the glycopolymers had good cytocompatibility. Insulin could be loaded onto the glycopolymer NPs with high efficiency (up to 10%), and insulin release increased with enhancement of the glucose level in the medium. Such a glucose-responsive glycopolymer is an excellent candidate that holds great potential in the treatment of diabetes.

Glucose-sensitive polyelectrolyte nanocapsules based on layer-by-layer technique for protein drug delivery

The glucose-responsive nanocapsules [CS-NAC/p(GAMA-r-AAPBA)] were readily fabricated with modified chitosan (CS-NAC) and random glycopolymer poly(D-gluconamidoethyl methacrylate-r-3-acrylamidophenylboronic acid) p(GAMA-r-AAPBA) as the alternant multilayered polyelectrolyte hybrid shell via layer-by-layer self-assembly after etching the amino functionalized SiO2 spheres by NH4F/HF. The spherical and hollow structure of nanocapsules was confirmed by TEM analysis and there was no clear collapse found after removal of the sacrificial cores. The reversible zeta potential changes of the nanocapsule materials evaluated the reversible glucose sensitivity. Besides, this system demonstrated a good capacity for encapsulation and loading insulin entrapped in nanocapsules as model protein drug. A good biocompatibility of the material was confirmed by the cell viability. In vitro release of insulin experiments revealed that no obvious release was found in acidic condition and the release could be normally conducted at physiological pH. These results implied that it was feasible for nanocapsules to be used in controlled release drug delivery system.

Stimuli-responsive nanocarriers for drug delivery

Spurred by recent progress in materials chemistry and drug delivery, stimuli-responsive devices that deliver a drug in spatial-, temporal- and dosage-controlled fashions have become possible. Implementation of such devices requires the use of biocompatible materials that are susceptible to a specific physical incitement or that, in response to a specific stimulus, undergo a protonation, a hydrolytic cleavage or a (supra)molecular conformational change. In this Review, we discuss recent advances in the design of nanoscale stimuli-responsive systems that are able to control drug biodistribution in response to specific stimuli, either exogenous (variations in temperature, magnetic field, ultrasound intensity, light or electric pulses) or endogenous (changes in pH, enzyme concentration or redox gradients).

Phenylboronic acid-functionalized polymeric micelles with a HepG2 cell targetability

Phenylboronic acid-functionalized amphiphilic block copolymer Pluronic-PMCC-BA was synthesized via ring-opening polymerization of 5-methyl-5-benzyloxycarbonyl-1,3-dioxan-2-one (MBC) with fumaric acid as a catalyst followed by the deprotection of carboxyl groups by catalyzed hydrogenation and the condensation of 3-aminophenylboronic acid with the copolymer side groups. Pluronic-PMCC-BA can form stable micelle solution by self-assembly in water. The phenylboronic acid groups are located at the shell of micelle as proved by (1)H NMR. The diameter of drug-free micelles is approximate 60 nm. Nano-spheres with narrow size distribution could be observed in the TEM image. MTT assay results show that Pluronic-PMCC-BA exhibits slight cytotoxicity when the polymer concentration is higher than 25 μg mL(-1). The toxicities of DOX@Pluronic-PMCC and DOX@Pluronic-PMCC-BA to COS7, HeLa, and HepG2 cell lines are similar with those of free DOX. Interestingly, phenylboronic acid groups located at the surface of Pluronic-PMCC-BA micelles can recognize HepG2 cells and promote the drug uptake of the cells, which are observed by confocal laser scanning microscopy (CLSM). The results imply that Pluronic-PMCC-BA would be a promising material for targeted drug delivery to the cancer cells.

Hydrogels: an interesting strategy for smart drug delivery

Hydrogels are novel delivery systems that have drawn much attention in the current pharmaceutical scenario. Of all the advantages, the most important is their versatility, which makes them optimal for any kind of molecule, adequate to be administered by any administration route and capable to modulate the desired release profile. Current research is managed to solve the limitations of this systems; mainly the low mechanical strength and lack of control of release in time and quantity, and the reversibility of the delivery. Several approaches such as the use of multi-stimuli-sensitive mechanisms, the enhancement of mechanical properties using chemical crosslinkers, development of polyelectrolyte complexes, the increment of interpenetrating networks or composite hydrogels are providing excellent results. These systems represent a promising alternative due to the countless possibilities to offer for modulating drug release.

Phenylboronic acid-functionalized glycopolymeric nanoparticles for biomacromolecules delivery across nasal respiratory

The aim of this study was to explore the potential of the mucoadhesive and enzyme-inhibitory phenylboronic acid-functionalized glycopolymeric nanoparticles as carriers for the nasal delivery of biomacromolecules. The glycopolymers were prepared by the random copolymerization of 3-acrylamidophenylboronic acid and N-acetyl glucosamine. Insulin, as a model, was encapsulated within self-assembled glypolymeric nanoparticles. Nanoparticle size, insulin loading, and insulin release were characterized. In vitro cytotoxicity experiment showed the glycopolymers were cytocompatible (≥ 80% cell viability). Adhesiveness was determined from the absorption amount of mucin, reaching up to 1180 μg/mL. Moreover, the results obtained from in vivo administration of insulin-loaded p(AAPBA-r-MAGA) nanoparticles to rats evidenced that the nanoparticles enhanced insulin absorption across the nasal mucosal barrier and did not induce irritation of nasal mucosa. Thus, insulin-loaded nanoparticles were able to significantly decrease plasma glucose levels (more than 35% reduction). These results suggest that p(AAPBA-r-MAGA) nanoparticles have potential application for the nasal delivery of biomacromolecules.

Hydrogels in mucosal delivery

The concept of mucoadhesion and the molecular design requirements for the synthesis of mucoadhesive agents are both well understood and, as a result, hydrogel formulations that may be applied to mucosal surfaces are readily accessible. Nanosized hydrogel systems that make use of biological recognition or targeting motifs, by reacting to disease-specific environmental triggers and/or chemical signals to affect drug release, are now emerging as components of a new generation of therapeutics that promise improved residence time, faster response to stimuli and triggered release.

Random amphiphilic copolymeric sub-micro particles as a carrier shielding from enzymatic attack for peptides and proteins delivery

The development of peptide drugs and therapeutic proteins is limited by their rapid clearance in liver and other body tissues by proteolytic enzymes, and consequently peptides and proteins are difficult to administer except by injection. There is a growing effort to circumvent these problems by designing strategies to deliver these drugs to specific site of the body. Among them, this peptide carrier presents several advantages for protein therapy including stability in physiological buffer and lack of toxicity. Here, we have been developing a novel bioadhesive polymer matrix that protects entrapped proteins and peptides from degradation by serine protease. Poly(2-lactobionamidoethyl methacrylate-ran-3-acrylamidophenylboronic acid-ran-methoxypolyethylene glycol methacrylate) glycopolymers were synthesized and could self-assemble into the sub-micro particles. The loading capability of insulin, as a drug model, and the insulin release from the particles were assessed. The inhibitory effect of the particles toward trypsin, elastase, and chymotrypsin was evaluated in vitro. Insulin was effectively encapsulated, up to 10%, and could be stained release in vitro. These glycopolymers displayed a strong inhibitory effect toward these exopeptidases. Therefore, novel glycopolymers with excellent inhibitory activity against proteolytic enzymes and reasonable mucoadhesivity might be a useful tool in overcoming the enzymatic barrier to the mucosal delivery (e.g. nasal and buccal) of therapeutic peptides or proteins.

pH- and glucose-sensitive glycopolymer nanoparticles based on phenylboronic acid for triggered release of insulin

Amphiphilic poly(acrylic acid-co-acrylamidophenylboronic acid)-block-poly(2-acryloxyethyl galactose)-block-poly(acrylic acid-co-acrylamidophenylboronic acid) (((PAA-co-PAAPBA)-b-)₂PAEG) copolymer was fabricated: The poly(2-acryloyloxyethyl pentaacetylgalactoside) (PAEAcG) with narrow molecular weight distributions (Mw/Mn≤1.22) was prepared by atom transfer radical polymerization (ATRP) using dibromo-p-xylene (DBX) as initiator. Then the well-defined triblock copolymer poly(t-butyl acrylate)-b-poly(2-acryloyloxyethyl pentaacetylgalactoside)-b-poly(t-butyl acrylate) (PtBA-b-PAEAcG-b-PtBA) was synthesized by ATRP of tBA using PAEAcG homopolymer with dibromo end groups as macroinitiator. After hydrolysis of t-butyl acrylate block, amide linkage and deacetylation, the final copolymer ((PAA-co-PAAPBA)-b-)₂PAEG was obtained. Because of characteristics of three different segments, amphiphilic ((PAA-co-PAAPBA)-b-)₂PAEG can self-assemble into pH- and glucose-responsive nanoparticles studied by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Furthermore, the in vitro release profiles of insulin also revealed obvious pH- and glucose-sensitivity of the nanoparticles. The analysis of cell viability suggested that the copolymer nanoparticles had good cytocompatibility.

Non inflammatory boronate based glucose-responsive insulin delivery systems

Boronic acids, known to bind diols, were screened to identify non-inflammatory cross-linkers for the preparation of glucose sensitive and insulin releasing agglomerates of liposomes (Agglomerated Vesicle Technology-AVT). This was done in order to select a suitable replacement for the previously used cross-linker, ConcanavalinA (ConA), a lectin known to have both toxic and inflammatory effects in vivo. Lead-compounds were selected from screens that involved testing for inflammatory potential, cytotoxicity and glucose-binding. These were then conjugated to insulin-encapsulating nanoparticles and agglomerated via sugar-boronate ester linkages to form AVTs. In vitro, the particles demonstrated triggered release of insulin upon exposure to physiologically relevant concentrations of glucose (10 mmoles/L–40 mmoles/L). The agglomerates were also shown to be responsive to multiple spikes in glucose levels over several hours, releasing insulin at a rate defined by the concentration of the glucose trigger.