PEG-stabilized micellar system with positively charged polyester core for fast pH-responsive drug release.

PURPOSE: To design functional drug carriers for fast pH-responsive drug release. METHODS: Functional diblock terpolymers of monomethoxy poly(ethylene glycol)-block- copoly(6,14-dimethyl-1,3,9,11-tetraoxa-6,14-diaza-cyclohexadecane-2,10-dione-co-ε-caprolactone) [mPEG-b-poly(ADMC-co-CL)] were fabricated via biosynthetic pathway. The self-assembled nanosphere and drug-loaded micelles of the copolymers were further prepared by dialysis method. The pH-tunable morphology variation and drug release pattern were observed at different pH. RESULTS: A collection of three PEGylated terpolymers with varied compositions in poly(ADMC-co-CL) block was designed with high cell-biocompatibility. The copolymers could readily self-assemble into nanoscale micelles (~ 100 nm) in aqueous medium and exhibit high stability over 80-h incubation in different mediums including deionized water, neutral NaCl solution, and heparin sodium solution. Due to the protonation-deprotonation of tertiary amine groups in ADMC units, acid-induced structural deformation of micelles was disclosed in terms of the variation in CAC value and hydrodynamic size at different pH. Drug loading efficiency was comparable to that of reported PEG-polyester micelles with specifically designed structures purposed for drug-loading improvement. Remarkably accelerated drug release triggered by acidity was distinctly detected for ibuprofen-loaded mPEG-b-poly(ADMC-co-CL) micelle system, suggesting a fast pH-responsive characteristic. CONCLUSION: Functional PEG-stabilized micellar carriers with positively charged polyester core were successfully developed for fast pH-responsive drug release.

Hyperbranched polycarbonate-based multimolecular micelle with enhanced stability and loading efficiency.

We herein develop a facile catalyst-free method to prepare hyperbranched hydroxyl-enriched aliphatic polycarbonate according to SCROP strategy. PEG-attached multiarm hyperbranched copolymer HEHDO-star-mPEG was further designed. It was found that HEHDO-star-mPEG can self-assemble into supramolecular multimolecular micelles in water. HEHDO-star-mPEG micelle showed excellent stability with respect to micellar size upon dilution, and displayed good cell-biocompatibility. An anticancer drug of doxorubicin with hydrogen-bonding functionality was incorporated into obtained micelles to establish a drug delivery system model. A high drug-loading content as well as sustained release pattern for HEHDO-star-mPEG based delivery system was achieved.

Biocatalytic fabrication of fast-degradable, water-soluble polycarbonate functionalized with tertiary amine groups in backbone.

Degradable polymers with specifically designed functionality have wide applications in biomedical fields. We reported herein the synthesis and characterization of a water-soluble and fast-degradable polycarbonate, functionalized with tertiary amine groups in the backbone. A novel cyclic carbonate monomer, namely, 6,14-dimethyl-1,3,9,11-tetraoxa-6,14-diaza-cyclohexadecane-2,10-dione (ADMC)(2), was synthesized and polymerized to provide the title polycarbonate [poly(ADMC)] via Novozym-435 lipase or tin(II) 2-ethylheaxanoate [Sn(Oct)(2)] catalyzed ring-opening polymerization (ROP). Novozym-435 lipase exhibited high activity toward the ROP in terms of molecular weight (M(n)) and monomer conversion, whereas the attempt with Sn(Oct)(2) failed. In the presence of molecular sieves-4 Å, the highest M(n) value of 1.2 × 10(4) g/mol was obtained in toluene with an initial monomer concentration of 0.58 M at 75 °C in the presence of 10 wt % of Novozym-435 to the monomer. Parameters that influence the polymerization, including reaction temperature, enzyme concentration, monomer concentration, and solvent composition, were investigated systematically. The resultant data suggested "living" characteristics for this enzyme-catalyzed polymerization, and the "living" feature seemed independent of the lipase concentration. The polymerization conducted in mixed solvents (toluene/isooctane) showed that product M(n)s were heavily dependent on the solvent composition. Poly(ADMC) was demonstrated to be amorphous by DSC technique. The obtained poly(ADMC) was found to be soluble in most of the organic solvents and interestingly in H(2)O as well. In vitro hydrolytic degradation of poly(ADMC) as monitored by GPC indicated the degradation was a relatively fast process. HPLC-ESI/MS and (1)H NMR analyses demonstrated that N-methyl diethanolamine was the main product after degradation. Poly(ADMC) presented low cytotoxicity toward human cervix carcinoma (HeLa) cells and hepatoblastoma cells (Hep G2), as demonstrated by MTT assay.

Acidity-promoted cellular uptake and drug release mediated by amine-functionalized block polycarbonates prepared via one-shot ring-opening copolymerization.

This paper reports a drug nanovehicle self-assembled from an amine-functionalized block copolymer poly(6,14-dimethyl-1,3,9,11-tetraoxa-6,14-diaza-cyclohexadecane-2,10-dione)-block-poly(1,3-dioxepan-2-one) (PADMC-b-PTeMC), which is prepared by controlable ring-opening block copolymerization attractively in a "one-shot feeding" pathway. The copolymers display high cell-biocompatibility with no apparent cytotoxicities detected in 293T and HeLa cells. Due to their amphiphilic nature, PADMC-b-PTeMC copolymers can self-assemble into nanosized micelles capable of loading anticancer drugs such as camptothecin (CPT) and doxorubicin (DOX). In particular, the outer PADMC shell endows the PADMC-b-PTeMC nanomicelles with pH-dependent control over the micellar morphology, cell uptake efficiency, and the drug release pattern. Confocal inspection reveals the remarkably enhanced cellular internalization of drug loaded micelles by cancerous HeLa cells at relatively lower pH 5.8 simulating the mildly acid microenvironment in tumors. Along with the acidity-triggered volume expansion of micelles, an accelerated CPT release in vitro occurs. The obtained results adumbrate the possibility of completely biodegradable PADMC-b-PTeMC as pH-sensitive drug carriers for tumor chemotherapy.

A smart micellar system with an amine-containing polycarbonate shell.

The present paper reports the design and preparation of an amphiphilic triblock co-polymer poly(ε-caprolactone) (PCL)-poly(6,14-dimethyl-1,3,9,11-tetraoxa-6,14-diaza-cyclohexadecane-2,10-dione) (PADMC)-PCL and the use of micelles composed of them as carriers for pH-sensitive drug release. The triblock co-polymers were synthesized via two-step ring-opening polymerization with catalysis by Novozym-435 lipase. By adjusting the feed ratio, three co-polymers with different PCL lengths and the same PADMC length were produced. The block structure of the co-polymers obtained was confirmed by comparative studies on PCL-PADMC-PCLs and the corresponding random poly(ε-caprolactone-random-6,14-dimethyl-1,3,9,11-tetraoxa-6,14-diaza-cyclohexadecane-2,10-dione) (poly(CL-r-ADMC)) by means of nuclear magnetic resonance and differential scanning calorimetry. Cell cytotoxicity tests showed that the co-polymer displayed no apparent cytotoxicity to 293T and HeLa cells. Transmissions electron microscopy indicates that the self-assembled micelles exhibited a well-defined spherical shape with a diameter between ∼30 and 50 nm. The critical aggregation concentration was dependent on the block composition. Due to the presence of ionizable tertiary amine groups in the PADMC block, acid-induced variation in the micellar morphology was evident with respect to micelle size and size distribution. The size-pH curve was characterized by a smooth sigmoid form, and had a dramatic upward shift with decreasing pH from 6.5 to 4.5, which correlated well with the buffer range of hydrophilic PADMC. As a demonstration of the potential of PCL-PADMC-PCL micelles to control drug delivery, acid induced drug release for prednisone acetate-loaded micelles was explored. PCL-PADMC-PCL micelles show good promise as smart drug carriers, sensing the local specific pH decrease around lesion sites.

One-step preparation and pH-tunable self-aggregation of amphoteric aliphatic polycarbonates bearing plenty of amine and carboxyl groups.

This paper reports a novel amphoteric aliphatic polycarbonate bearing both amine and carboxyl groups. In the absence of protection-deprotection chemistry, the multi-functionalized copolymer is synthesized by one-step enzymatic copolymerization. The influences of the reaction conditions including monomer feed ratio and polymerization time are explored. The simultaneous incorporation of amine and carboxyl functionalities provides the copolymer with a pH-tunable self-aggregation feature, leading to various aggregation states including precipitated agglomerate, well-dispersed positively or negatively charged nanoparticles in a controlled manner. The copolymer displays minimal cytotoxicity to 293T and HeLa cells.

A strategy to improve serum-tolerant transfection activity of polycation vectors by surface hydroxylation.

The aim of this contribution is to develop a universal method to promote the serum-tolerant capability of polycation-based gene delivery system. A "hydroxylation camouflage" strategy was put forward by coating the polycation vectors with hydroxyl-enriched "skin". Branched polyethyleneimine (PEI) was herein used as the polycation model and modified via the catalyst-free aminolysis reaction with 5-ethyl-5-(hydroxymethyl)-1,3-dioxan-2-oxo (EHDO). PEI-g-EHDO, PEI and alkylated PEI derivative termed as PEI-g-DPA were comparatively explored with respect to the transfection efficiency in the serum-free and serum-conditioned medium. The resultant data indicate that the serum-tolerant capability largely depended on the surface composition and substitution degree. In addition to the reduced surface charge, the introduced function caused by hydroxyl coating is believed to play a crucial role for the improved properties of PEI-g-EHDOs. The EHDO modification can effectively inhibit the adsorption of BSA proteins onto polyplexes surface. And the polyplexes stability was remarkably enhanced in the presence of DNase and heparin after EHDO modification. Note that the transfection activity of PEI-g-EHDO(34.5%) in the serum-conditioned medium was even higher than that without serum addition. In contrast, serum addition led to appreciable reduction in the transfection efficiency mediated by PEI and PEI-g-DPAs. Specifically, as far as the transfection activity in the presence of serum is concerned, PEI-g-EHDO could be up to 30-fold higher than unmodified PEI25k. PEI-g-EHDO(34.5%) displayed little to no hemolytic effect and high cell-biocompatibility with nearly no cytotoxicity detected in 293T cells and HeLa cells. Taking into account the high biocompatibility and serum-tolerant transfection activity, PEI-g-EHDO(34.5%) holds great potential for the use as efficient gene vector. More importantly, it is expected that such "hydroxylation camouflage" strategy may be universally applicable for a majority of existing polycation vectors.

PEGylated PEI-based biodegradable polymers as non-viral gene vectors.

Novel functional biodegradable gene vectors, poly(L-succinimide)-g-polyethylenimines-g-poly(ethylene glycol) (PSI-g-PEI-g-PEGs) were synthesized by conjugating methoxy poly(ethylene glycol) (mPEG, M(w)=750 Da) to PEI segments (M(w)=800 Da) of PSI-g-PEI. The physicochemical properties of PSI-g-PEI-g-PEGs, including buffering capability, pDNA binding ability, cytotoxicity, zeta potential and the particle size of polymer/pDNA complexes, were explored. The influence of PEGylation was discussed based on a comparative study of PSI-g-PEI-g-PEGs, PSI-g-PEI and PEI25k (M(w)=25 kDa). SEM images revealed that PSI-g-PEI-g-PEG/pDNA particles have a regular shape with the diameter ranging from 70 to 170 nm. PEGylation could suppress the aggregation occurrence between complexes, resulting in a reduction of the polymer/pDNA complex size. PSI-g-PEI-g-PEGs exhibited remarkably lower cytotoxicity compared to PSI-g-PEI and PEI25k. In 293T and HeLa cells, the obtained PSI-g-PEI-g-PEGs showed very high transfection efficiency compared to PEI25k. Fluorescent confocal microscopy demonstrated that PSI-g-PEI-g-PEGs could effectively transport pGL-3 plasmids into the nuclei of HeLa cells. Taking into account the continued high transfection efficacy and decreased toxicity after PEG modification, PSI-g-PEI-g-PEGs show great potential as the non-viral vectors for gene transfection.

Facile fabrication of diblock methoxy poly(ethylene glycol)-poly(tetramethylene carbonate) and its self-assembled micelles as drug carriers.

AB type diblock methoxy poly(ethylene glycol)-b-poly(tetramethylene carbonate) (mPEG-PTeMC) copolymers were designed for the first time and used as carriers for the sustained release of the hydrophobic drug ibuprofen. In this paper, we developed a facile ring-opening polymerization (ROP) method to prepare mPEG-PTeMC copolymers under the catalysis of Novozym-435 lipase. Attractively, the polymerization has been successfully performed at 30 degrees C, close to room temperature. The data show that the copolymer compositions agree well with the feed ratio of TeMC to mPEG, indicating the controllable feature of the polymerization. The copolymer structures were characterized by (1)H NMR, IR, SEC, and DSC measurements. mPEG-PTeMC exhibits no apparent in vitro cytotoxicity toward human embryonic kidney transformed 293T cells. Those amphiphilic copolymers can readily self-assemble into nanosized micelles (about 150 nm) in aqueous solution. Their critical micelle concentrations are in the range of (1.6-9.3) x 10(-7) mol/L, determined by fluorescence spectroscopy. The micelles present high stability in PBS solution, with no obvious change in micelle diameters over 5 days. Ibuprofen can be loaded effectively in mPEG-PTeMC micelles, and its sustained release behavior is observed. Transmission electron microscopy shows that the well-dispersed spherical micelles are around 25 nm in diameter, while the diameter is 30 nm after loading ibuprofen. The release rate increases when the chain length of the PTeMC block decreases. These properties show that the micelles self-assembled from mPEG-PTeMC copolymers would have great potential as carriers for the effective encapsulation as well as sustained release of hydrophobic drugs.