Guolin Wu

Magnetic and pH-sensitive nanoparticles for antitumor drug delivery

A dually responsive nanocarrier with multilayer core-shell architecture was prepared based on Fe(3)O(4)@SiO(2) nanoparticles coated with mPEG-poly(l-Asparagine). Imidazole groups (pK(a)∼6.0) were tethered to the side chains of poly(l-Asparagine) segments by aminolysis. These nanoparticles were expected to be sensitive to both magnetic field and pH environment. The obtained materials were characterized with FTIR, dynamic light scattering, ζ-potential, TEM, TGA and hysteresis loop analysis. It was found that this Fe(3)O(4)@SiO(2)-polymer complex can form nano-scale core-shell-corona trilayer particles (∼250 nm) in aqueous solution. The Fe(3)O(4)@SiO(2), poly(L-Asparagine) and mPEG segments serve as a super-paramagnetic core, a pH-sensitive shell, and a hydrophilic corona, respectively. An antitumor agent, doxorubicin (DOX), was successfully loaded into the nanocarrier via combined actions of hydrophobic interaction and hydrogen bonding. The drug release profiles displayed a pH-dependent behavior. DOX release rate increased significantly as the ambient pH dropped from the physiological pH (7.4) to acidic (5.5). This is most likely due to protonation and a change in hydrophilicity of the imidazole groups in the poly(l-Asparagine) segments. This new approach may serve as a promising platform to formulate magnetic targeted drug delivery systems.

Biodegradable and temperature-responsive polyurethanes for adriamycin delivery

To develop biodegradable polymers with temperature-sensitivity, a series of polyurethanes consisting of poly (ethylene glycol) (PEG) and L-lysine ester diisocyanate (LDI) were synthesized, and the structure and molecule weight of the polymers were examined by (1)H NMR, FT-IR, gel permeation chromatography (GPC). The solution properties of the copolymers were studied by turbidity measurement and size measurement. Polyurethanes could form nanoparticles by sonication in water. No temperature-sensitivity was observed with the polyurethane nanoparticles composed of PEG1000 and PEG1500. On the contrary, LDI-PEG600 exhibited a reversible temperature-responsive behavior in aqueous solution. The transition temperature (T(c)) of LDI-PEG600 with methyl ester of LDI was higher than that of LDI-PEG600 with butyl ester side chain. The polymers were then used to encapsulate adriamycin (ADR) by the dialyzing method from dimethylformamide solution against water. ADR could be successfully encapsulated into the polyurethane nanoparticles. The ratio of ADR release from polymeric nanoparticles increased sharply above the T(c), while the release was suppressed below the T(c).

A novel delivery system of doxorubicin with high load and pH-responsive release from the nanoparticles of poly (α,β-aspartic acid) derivative.

A poly (amino acid)-based amphiphilic copolymer was utilized to fabricate a better micellar drug delivery system (DDS) with improved compatibility and sustained release of doxorubicin (DOX). First, poly (ethylene glycol) monomethyl ether (mPEG) and DOX were conjugated onto polyasparihyazide (PAHy), prepared by hydrazinolysis of the poly (succinimide) (PSI), to afford an amphiphilic polymer [PEG-hyd-P (AHy-hyd-DOX)] with acid-liable hydrazone bonds. The DOX, chemically conjugated to the PAHy, was designed to supply hydrophobic segments. PEGs were also grafted to the polymer via hydrazone bonds to supply hydrophiphilic segments and prolong its lifetime in blood circulation. Free DOX molecules could be entrapped into the nanoparticles fabricated by such an amphiphilic polymer (PEG-hyd-P (AHy-hyd-DOX)), via hydrophobic interaction and π-π stacking between the conjugated and free DOX molecules to obtain a pH responsive drug delivery system with high DOX loaded. The drug loading capacity, drug release behavior, and morphology of the micelles were investigated. The biological activity of micelles was evaluated in vitro. The drug loading capacity was intensively augmented by adjusting the feed ratio, and the maximum loading capacity was as high as 38%. Besides, the DOX-loaded system exhibited pH-dependent drug release profiles in vitro. The cumulative release of DOX was much faster at pH 5.0 than that at pH 7.4. The DOX-loaded system kept highly antitumor activity for a long time, compared with free DOX. This easy-prepared DDS, with features of biocompatibility, biodegradability, high drug loading capacity and pH-responsiveness, was a promising controlled release delivery system for DOX.

Preparation and tunable temperature sensitivity of biodegradable polyurethane nanoassemblies from diisocyanate and poly(ethylene glycol)

The development of temperature-responsive and biodegradable polymeric nanoparticles with tunable temperature sensitivity is of great interest. In this study, alternating polyurethanes were synthesized from diisocyanate (L-lysine ethyl ester diisocyanate (LDI) or hexamethylene diisocyanate (HDI)) and poly(ethylene glycol) (PEG) of different molecular weights. The resulting polyurethanes were then used to prepare nanoparticles either by direct dispersion in water or by nanoprecipitation. The temperature-responsive property of the polyurethane nanoparticles was evaluated by UV-visible transmittance experiments and dynamic light scattering. During the heating–cooling cycling, the LDI-PEG series showed almost no change except LDI-PEG600, but the HDI-PEG series exhibited reversible dispersion–aggregation changes. The nanoparticles were spherical at temperatures below or above the cloud point, as observed by transmission electron microscopy. The cloud point temperature of the alternative polymers was found to depend on both the hydrophilic–hydrophobic balance of the alternative chain and polymer concentration. The degradation test in vitro revealed a fall of less than 20% of polymer molecular weight within 12 days. The transition temperature was close to human body temperature, which could have great potential in biomedical fields.

Polyelectrolyte complex nanoparticles of amino poly(glycerol methacrylate)s and insulin.

Amino poly(glycerol methacrylate)s (PGOHMAs) were synthesized from linear or star-shaped poly(glycidyl methacrylate)s (PGMA)s via ring opening reactions with 1,2-ethanediamine, 1,4-butanediamine and diethylenetriamine, respectively. The resulting cationic polymers were employed to form polyelectrolyte complexes (PECs) with insulin. Parameters influencing complex formation were investigated by dynamic light scattering (DLS). PECs in the size range of 100-200 nm were obtained under optimal conditions, i.e., the pH value of PECs was 5.58-6.27, the concentration of NaCl was 0.02 mol/L, and insulin-polymer weight ratio was 0.8. The insulin association efficiency (AE) of current system increased with zeta potentials of PECs. Circular dichroism (CD) analysis corroborated that the structure of insulin in the PEC nanoparticles was preserved after lyophilization. Fourier transform infrared (FT-IR) and X-ray diffraction (XRD) experiments demonstrated that weak physical interactions between insulin and amino PGOHMAs play an important role in the formation of PECs. The release of insulin depends on both structure and architecture of amino PGOHMAs. These PECs would be potentially useful for mucosal administration.

An injectable and biodegradable hydrogel based on poly(α,β-aspartic acid) derivatives for localized drug delivery

An injectable hydrogel via hydrazone cross-linking was prepared under mild conditions without addition of cross-linker or catalyst. Hydrazine and aldehyde modified poly(aspartic acid)s were used as two gel precursors. Both of them are water-soluble and biodegradable polymers with a protein-like structure, and obtained by aminolysis reaction of polysuccinimide. The latter can be prepared by thermal polycondensation of aspartic acid. Hydrogels were prepared in PBS solution and characterized by different methods including gel content and swelling, Fourier transformed-infrared spectroscopy, and in vitro degradation experiment. A scanning electron microscope viewed the interior morphology of the obtained hydrogels, which showed porous three-dimensional structures. Different porous sizes were present, which could be well controlled by the degree of aldehyde substitution in precursor poly(aspartic acid) derivatives. The doxorubicin-loaded hydrogels were prepared and showed a pH-sensitive release profile. The release rate can be accelerated by decreasing the environmental pH from a physiological to a weak acidic condition. Moreover, the cell adhesion and growth behaviors on the hydrogel were studied and the polymeric hydrogel showed good biocompatibility.

Layer-by-layer assembled polyaspartamide nanocapsules for pH-responsive protein delivery

Biodegradable shell cross-linked nanocapsules were prepared via layer-by-layer assembly of PADH (tertiary amine and hydrazide grafted polyaspartamide) and PACA (carboxyl and aldehyde grafted polyaspartamide) on silica spheres. Both of the polyaspartamide derivatives are water-soluble and biodegradable polymers with a protein-like structure, and obtained by aminolysis reaction of polysuccinimide. The latter is prepared by thermal polycondensation of aspartic acid. Dynamic light scattering and zeta potential measurements were used to analyze the layer-by-layer assembly process. Bovine serum albumin (BSA), as a model protein, was entrapped in the nanocapsules via electrostatic adsorption. Nanocapsules encapsulating BSA were prepared via layer-by-layer assembly on protein-entrapping amino-functionalized silica spheres, hydrazone cross-linking and silica core removal. The BSA release profiles exhibited a pH-dependent behavior. BSA release rate increased significantly as the ambient pH dropped from the physiological pH to acidic. Cell viability study suggests that the obtained polymeric nanocapsules have good biocompatibility. These kinds of novel composite nanocapsules may offer a promising delivery system for proteins.

Amino poly(glycerol methacrylate)s for oligonucleic acid delivery with enhanced transfection efficiency and low cytotoxicity

To improve the transfection activity and reduce cell cytotoxicity of polycations with antisense oligonucleotide (AON), poly(glycidyl methacrylate)s (PGMAs) were modified with different amines, i.e., methylethylamine (MEA), 2-amino-1-butanol (2-ABO) and 4-amino-1-butanol (4-ABO). The structures of resulting polymers were well characterized and their thermal properties were studied by differential scanning calorimetry (DSC). The amino PGMA could self-assemble with AON in a Tris buffer solution, resulting in narrowly distributed polymer/AON complexes with a size of 0.1–0.3 μm at an amine-group-of-polymer/phosphate-group-of-nucleotide ratio (N/P ratio) of 0.5–3. Spherical nanoparticles of the complexes were visualized using atomic force microscopy (AFM), and the gel electrophoresis and zeta potential assay evidenced the formation of complexes at relatively low N/P ratios. Stability of the complexes towards dissociation was tested using ethidium bromide displacement assay. Protection of the incorporated AON against DNase I degradation was also evaluated. An increased charge ratio and a synergistic effect of hydrogen bonding in this system contributed to the increased stability of the complex, which prevents the incorporated AON from nuclease degradation. In vitro cytotoxicity experiments on COS-7 cells showed that all amino PGMAs displayed lower toxicity compared to the control PEI25k, except for the polymers with a relatively high molecular weight (30 kDa). In addition, the MEA modified linear and star-shaped PGMA (Mn in the range of 15–20 kDa) as well as 4-ABO modified linear PGMA complexes exhibited higher transfection efficiencies in vitro, compared to PEI25k. These results demonstrated that amino PGMAs with suitable amine groups and molecular weight can be used as safe and efficient AON delivery polymers.

Temperature-responsive drug delivery systems based on polyaspartamides with isopropylamine pendant groups

To develop poly(amino acid)s with temperature-sensitivity, a series of polyaspartamides with isopropylamide and hydroxyalkylamide pendant groups were synthesized by a successive aminolysis reaction of polysuccinimide. The structure of the resulting polymers was examined by 1H NMR and FT-IR. The polyaspartamide derivatives self-assembled into nanoparticles in water and showed sharp temperature-responsive phase transition behaviour. The phase transition temperature (Tp) could be modulated by the hydrophilic–hydrophobic balance of the copolymer controlled by altering the composition of both pendants. Besides, an antitumor agent, doxorubicin, was successfully loaded into the polymeric nanoparticles via a dialyzing method. The drug release profile was temperature-dependent accelerating significantly above the Tp and decelerating below the Tp. This easily prepared polymeric nanoparticle with excellent biocompatibility and tunable temperature responsiveness has significant potential for controlled drug release applications.

Post-modification of poly(glycidyl methacrylate)s with alkyl amine and isothiocyanate for effective pDNA delivery

Thiourea has been shown to interact actively with phosphate groups of DNA. To this end, linear and five-arm poly(glycidyl methacrylate)s (PGMA)s are post-modified with 1,2-ethanediamine (E), 1,4-butanediamine (B) and diethylenetriamine (D) via ring opening reactions to obtain various amino poly(glycidyl methacrylate)s (PGOHMAs), namely L–E, S5–E, S5–B, L–B, and L–D (L represents linear polymer, S5 represents five-arm polymer, E is short for 1,2-ethanediamine, B is short for 1,4-butanediamine, and D is short for diethylenetriamine). These amino PGOHMAs are further functionalized with methyl isothiocyanate (M) to give thiourea-modified PGOHMAs (TPGOHMAs), L–EM, S5–EM, L–DM, L–BM, S5–BM, L–EM and S5–EM, with propyl isothiocyanate (P) to give L–BP. Both the amino PGOHMAs and TPGOHMAs are used as gene vectors. The mean hydrodynamic diameter of amino PGOHMA/plasmid DNA (pDNA) and TPGMP/pDNA complexes is in the range of 65–195 nm, as determined by dynamic light scattering, and decreases with increasing nitrogen-to-phosphate (N/P) ratio. At the same N/P ratio, TPGOHMA/pDNA complexes exhibit lower values of zeta potentials than its amino PGOHMA counterpart when zeta potentials turned into positive. Gel electrophoresis indicates that TPGOHMA polymers can condense pDNA at lower N/P ratios than amino PGOHMAs. MTT assay suggests that TPGOHMAs have obviously lower cytotoxicity than amino PGOHMAs against Huh-7 cells. Subsequently, in vitro gene transfection studies against Huh-7 cells show that TPGOHMA/pDNA exhibits lower transfection efficiency than amino PGOHMAs, except for L–DM/pDNA complexes. Confocal laser scanning microscopy reveals that L–DM/pDNA complexes achieve endosomal escape more effectively than L–D/pDNA complexes. This study revealed the effect of thiourea-modification of amino PGOHMA on its gene transfection properties. L–DM, with enhanced transfection efficiency and reduced cytotoxicity, is an interesting material for further investigation as a nucleic acid delivery vehicle.