Triggered destabilisation of polymeric micelles and vesicles by changing polymers polarity: an attractive tool for drug delivery

Radiation-sensitive diselenide block co-polymer micellar aggregates: toward the combination of radiotherapy and chemotherapy

We have developed a potential radiation-sensitive drug-delivery system using active diselenide-containing block co-polymer aggregates in aqueous solution that can load and release anticancer drugs. These aggregates were sensitive to even a low dose of γ-radiation, such as 5 Gy, which is close to the radiation dose received by patients during a single radiotherapy treatment. This line of research may open an avenue for the combination of radiotherapy and chemotherapy.

Multi-responsive nanogels containing motifs of ortho ester, oligo(ethylene glycol) and disulfide linkage as carriers of hydrophobic anti-cancer drugs

A family of multi-responsive nanogels with different compositions and crosslinking degrees have been prepared by the miniemulsion copolymerization of monomethyl oligo(ethylene glycol) acrylate (OEGA) and an ortho ester-containing acrylic monomer, 2-(5,5-dimethyl-1,3-dioxan-2-yloxy) ethyl acrylate (DMDEA), with bis(2-acryloyloxyethyl) disulfide (BADS) as a crosslinker. These nanogels are thermoresponsive and labile in the weakly acidic or reductive environments. The thermoresponsive behaviors, acid-triggered hydrolysis, and reduction-induced degradation of these nanogels were studied by means of dynamic light scattering (DLS), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results indicate that the volume phase transition temperature (VPTT), thermally induced deswelling ratio, and acid-triggered swelling ratio of the nanogels are closely relevant to their compositions and crosslinking degrees. Although these nanogels could be reductively disrupted by dithiothreitol (DTT), single polymer chains with sizes smaller than 20 nm were not detected by DLS. This is probably due to the existence of some unbreakable linkages formed by chain transfer to the disulfide bond during the radical polymerization. These nanogels are capable of encapsulating hydrophobic compounds. The loading capability of the nanogels for Nile Red (NR), paclitaxel (PTX), and doxorubicin (DOX), and the release behaviors of the drug-loaded nanogels were investigated by UV-vis spectrometry and HPLC. As expected, drug release can be greatly accelerated by a cooperative effect of both acid-triggered hydrolysis and DTT-induced degradation. Finally, the PTX-loaded nanogels exhibit a concentration-dependent toxicity to MCF-7 cells while the intact unloaded nanogels are non-toxic, thereby they may be used as potential carriers for hydrophobic anticancer drugs.

Enzyme-inspired controlled release of cucurbit[7]uril nanovalves by using magnetic mesoporous silica

The controlled release of drugs by biostimuli is highly desirable under physiological conditions for their potential use in advanced applications. The enzyme-inspired controlled release of cucurbituril nanovalves by using magnetic mesoporous silica nanoparticles (MSNs) in near-neutral aqueous solutions is reported for the first time. The encirclement of cucurbit[7]uril (CB[7]) onto the protonated 1,4-butanediamine stalks tethered to the external surfaces of superparamagnetic Fe(3) O(4) -embedded mesoporous silica particles leads to tight blocking of the nanopores. The supramolecular nanovalves are activated by the enzymatic decarboxylation products of lysine, cadaverine (in the protonated form), which has a high affinity for CB[7], so that the encapsulated guest molecules, calcein, in the nanopores are released into the bulk solution. The release of calcein can be controlled in small portions on command by alternating changes in enzymatic decarboxylation products and CB[7]. The amino acid derived polyamines have long been associated with cell growth and cancers. The guest molecules released from the delivery system of magnetic MSNs can act not only on sensing probes for levels of decarboxylases and polyamines, but also on efficacious drugs to specific tissues and cells for regulation of polyamine synthesis.

Stearic acid-g-chitosan polymeric micelle for oral drug delivery: in vitro transport and in vivo absorption

Stearic acid-g-chitosan (low molecular weight chitosan CS-SA) with different amino-substituted degrees was synthesized and evaluated as an oral delivery vehicle in this paper. Synthesized CS-SA with 4.47%, 24.36% and 40.36% amino-substituted degree (SD) could form micelles by self-aggregation in aqueous medium. The critical micelle concentration (CMC) ranged from about 0.16 to 0.25 mg/mL, which decreased with the increased SD of CS-SA. The CS-SA micelles had 33.4-130.9 nm size and 22.9- 48.4 mV zeta potential. CS-SA with higher SD had the smaller size and the higher zeta potential. The permeability and possible transport route of CS-SA micelles across the gastrointestinal tract was investigated by in vitro model Caco-2 cells. The results exhibited that the CS-SA micelles had good permeability, and the permeability enhanced with increasing SD of the CS-SA. The transport of the micelles showed energy, pH and concentration dependent transcytosis process, mainly through macropinocytosis and partly via fluid-phase transcytosis and caveolar route. The reversible decrease in transepithelial electrical resistance (TEER) by treatment of micelles suggested that paracellular transport pathway was another route of the micelles crossing the gastrointestinal tract. Using doxorubicin (DOX) as a model drug, the permeation results further demonstrated that the DOX transport mediated by CS-SA micelles could avoid efflux via P-glycoprotein. In vivo study demonstrated that the micelles could significantly improve the bioavailability of encapsulated drug. The results presented that the CS-SA with higher SD was a promising vehicle for oral drugs.

Polymeric micelles in anticancer therapy: targeting, imaging and triggered release

Micelles are colloidal particles with a size around 5-100 nm which are currently under investigation as carriers for hydrophobic drugs in anticancer therapy. Currently, five micellar formulations for anticancer therapy are under clinical evaluation, of which Genexol-PM has been FDA approved for use in patients with breast cancer. Micelle-based drug delivery, however, can be improved in different ways. Targeting ligands can be attached to the micelles which specifically recognize and bind to receptors overexpressed in tumor cells, and chelation or incorporation of imaging moieties enables tracking micelles in vivo for biodistribution studies. Moreover, pH-, thermo-, ultrasound-, or light-sensitive block copolymers allow for controlled micelle dissociation and triggered drug release. The combination of these approaches will further improve specificity and efficacy of micelle-based drug delivery and brings the development of a 'magic bullet' a major step forward.

Self-assembled nanogel made of mannan: synthesis and characterization

Amphiphilic mannan (mannan-C(16)) was synthesized by the Michael addition of hydrophobic 1-hexadecanethiol (C(16)) to hydroxyethyl methacrylated mannan (mannan-HEMA). Mannan-C(16) formed nanosized aggregates in water by self-assembly via the hydrophobic interaction among C(16) molecules as confirmed by hydrogen nuclear magnetic resonance ((1)H NMR), fluorescence spectroscopy, cryo-field emission scanning electron microscopy (cryo-FESEM), and dynamic light scattering (DLS). The mannan-C(16) critical aggregation concentration (cac), calculated by fluorescence spectroscopy with Nile red and pyrene, ranged between 0.04 and 0.02 mg/mL depending on the polymer degree of substitution of C(16) relative to methacrylated groups. Cryo-FESEM micrographs revealed that mannan-C(16) formed irregular spherical macromolecular micelles, in this work designated as nanogels, with diameters ranging between 100 and 500 nm. The influence of the polymer degree of substitution, DS(HEMA) and DS(C(16)), on the nanogel size and zeta potential was studied by DLS at different pH values and ionic strength and as a function of mannan-C(16) and urea concentrations. Under all tested conditions, the nanogel was negatively charged with a zeta potential close to zero. Mannan-C(16) with higher DS(HEMA) and DS(C(16)) values formed larger nanogels and were also less stable over a 6 month storage period and at concentrations close to the cac. When exposed to solutions of different pH and aggressive conditions of ionic strength and urea concentration, the size of mannan-C(16) varied to some extent but was always in the nanoscale range.

The pH-induced thermosensitive poly (NIPAAm-co-AAc-co-HEMA)-g-PCL micelles used as a drug carrier

The macromonomer of 2-hydroxyethyl methyacrylate-caprolactone (HPCL) was synthesized by the ring-opening polymerization (ROP) of epsilon-caprolactone, which was initiated by 2-hydroxyethyl methyacrylate (HEMA). Then, the graft terpolymers of NIPAAm-co-AAc-co-HEMA-g-PCL (PHNA-CL) with varying mole ratios were subsequently synthesized by free radical polymerization of HEMA-PCL, N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc). PHNA-CL was further self-assembled in different types of solvent. All the as-prepared copolymers were characterized by 1H NMR, FT-IR and GPC. Micellization behaviors of micelles were studied by TEM and DLS. The micelles exhibited a phase transition temperature which can be readily adjusted by changing pH value of the micellization system. Micelle loaded with doxorubicin (DOX) was used to evaluate the drug release behavior. The release of DOX from micelles could be controlled by changing pH value and temperature in buffer solutions. The micelles are potentially to be used as a new anticancer drug carrier for intracellular delivery.

Dual redox responsive assemblies formed from diselenide block copolymers

A block copolymer with diselenide bonds in the polymer backbone was reported. This block copolymer was capable of forming micellar aggregates that were responsive to redox stimuli. Compared with other redox responsive aggregates, this type of diselenide-containing block copolymer aggregates could be responsive to both oxidants and reductants even in a solution with a very low concentration under mild conditions.

Multifunctional nanoassemblies of block copolymers for future cancer therapy

Nanoassemblies from amphiphilic block copolymers are promising nanomedicine platforms for cancer diagnosis and therapy due to their relatively small size, high loading capacity of drugs, controlled drug release, in vivo stability and prolonged blood circulation. Recent clinical trials with self-assembled polymeric micelles incorporating anticancer drugs have shown improved antitumor activity and decreased side effects encouraging the further development of nanoassemblies for drug delivery. This review summarizes recent approaches considering stimuli-responsive, multifunctionality and more advanced architectures, such as vesicles or worm-like micelles, for tumor-specific drug and gene delivery.