Jiong Zou

Improving paclitaxel delivery: in vitro and in vivo characterization of PEGylated polyphosphoester-based nanocarriers.

Nanomaterials have great potential to offer effective treatment against devastating diseases by providing sustained release of high concentrations of therapeutic agents locally, especially when the route of administration allows for direct access to the diseased tissues. Biodegradable polyphosphoester-based polymeric micelles and shell cross-linked knedel-like nanoparticles (SCKs) have been designed from amphiphilic block-graft terpolymers, PEBP-b-PBYP-g-PEG, which effectively incorporate high concentrations of paclitaxel (PTX). Well-dispersed nanoparticles physically loaded with PTX were prepared, exhibiting desirable physiochemical characteristics. Encapsulation of 10 wt% PTX, into either micelles or SCKs, allowed for aqueous suspension of PTX at concentrations up to 4.8 mg/mL, as compared to <2.0 μg/mL for the aqueous solubility of the drug alone. Drug release studies indicated that PTX released from these nanostructures was defined through a structure-function relationship, whereby the half-life of sustained PTX release was doubled through cross-linking of the micellar structure to form SCKs. In vitro, physically loaded micellar and SCK nanotherapeutics demonstrated IC50 values against osteosarcoma cell lines, known to metastasize to the lungs (CCH-OS-O and SJSA), similar to the pharmaceutical Taxol formulation. Evaluation of these materials in vivo has provided an understanding of the effects of nanoparticle structure-function relationships on intratracheal delivery and related biodistribution and pharmacokinetics. Overall, we have demonstrated the potential of these novel nanotherapeutics toward future sustained release treatments via administration directly to the sites of lung metastases of osteosarcoma.

Poly(ethylene oxide)-block-polyphosphester-based Paclitaxel Conjugates as a Platform for Ultra-high Paclitaxel-loaded Multifunctional Nanoparticles.

A new type of degradable, nanoscopic polymer assembly containing ultra-high levels of drug loading via covalent attachment within amphiphilic core-shell nanoparticle morphology has been generated as a potentially effective and safe anti-cancer agent. Poly(ethylene oxide)-block-polyphosphoester-based paclitaxel drug conjugates (PEO-b-PPE-g-PTX) were synthesized by rapid, scalable and versatile approach that involves only two steps: organocatalyst-promoted ring-opening-polymerization followed by click reaction-based conjugation of a PTX prodrug. Variations in the polymer-to-PTX stoichiometries allowed for optimization of the conjugation efficiency, the PTX drug loading and the resulting water solubilities of the entire polymer and the PTX content. The PEO-b-PPE-g-PTX formed well-defined micelles in aqueous solution, with a PTX loading capacity as high as 65 wt%, and a maximum PTX concentration of 6.2 mg/mL in water, which is 25000-fold higher than the aqueous solubility of free PTX. The positive cell-killing activity of PEO-b-PPE-g-PTX against several cancer cell lines is demonstrated, and the presence of pendant reactive functionality provides a powerful platform for future work to involve conjugation of multiple drugs and imaging agents to achieve chemotherapy and bioimaging.

Poly(ethylene oxide)-block-polyphosphoester-graft-paclitaxel conjugates with acid-labile linkages as a pH-sensitive and functional nanoscopic platform for paclitaxel delivery.

There has been an increasing interest to develop new types of stimuli-responsive drug delivery vehicles with high drug loading and controlled release properties for chemotherapeutics. An acid-labile poly(ethylene oxide)-block-polyphosphoester-graft-PTX drug conjugate (PEO-b-PPE-g-PTX G2) degradable, polymeric paclitaxel (PTX) conjugate containing ultra-high levels of PTX loading is improved significantly, in this second-generation development, which involves connection of each PTX molecule to the polymer backbone via a pH-sensitive β-thiopropionate linkage. The PEO-b-PPE-g-PTX G2 forms well-defined nanoparticles in an aqueous solution, by direct dissolution into water, with a number-averaged hydrodynamic diameter of 114 ± 31 nm, and exhibits a PTX loading capacity as high as 53 wt%, with a maximum PTX concentration of 0.68 mg mL(-1) in water (vs 1.7 μg mL(-1) for free PTX). The PEO-b-PPE-g-PTX G2 shows accelerated drug release under acidic conditions (≈50 wt% PTX released in 8 d) compared with neutral conditions (≈20 wt% PTX released in 8 d). Compared to previously reported polyphosphoester-based PTX drug conjugates, PEO-b-PPE-g-PTX G1 without the β-thiopropionate linker, the PEO-b-PPE-g-PTX G2 shows pH-triggered drug release property and 5- to 8-fold enhanced in vitro cytotoxicity against two cancer cell lines.

Tunable mechano-responsive organogels by ring-opening copolymerizations of N -carboxyanhydrides

The simple copolymerization of N-carboxyanhydride (NCA) monomers is utilized to generate copolypeptides having a combination of α-helix and β-sheet sub-structures that, when grown from a solvophilic synthetic polymer block segment, are capable of driving mechano-responsive supramolecular sol-to-gel-to-sol and sol-to-gel-to-gel transitions reversibly, which allow also for injection-based processing and self-healing behaviors. A new type of polypeptide-based organogelator, methoxy poly(ethylene glycol)-block-poly(γ-benzyl-l-glutamate-co-glycine) (mPEG-b-P(BLG-co-Gly)), is facilely synthesized by statistical ring-opening copolymerizations (ROPs) of γ-benzyl-l-glutamate (BLG) and glycine (Gly) NCAs initiated by mPEG-amine. These systems exhibit tunable secondary structures and result in sonication stimulus responsiveness of the organogels with the polypeptide segment variation, controlled by varying the ratio of BLG NCA to Gly NCA during the copolymerizations. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) studies indicate the α-helical component decreases while the β-sheet content increases systematically with a higher mole fraction of Gly in the polypeptide segment. The supramolecular assembly of β-sheet nanofibrils, having a tunable width over the range of 10.4 - 14.5 nm with varied BLG to Gly ratio, are characterized by transmission electron microscopy (TEM). The further self-assembly of these nanostructures into 3-D gel networks within N,N-dimethylformamide (DMF) occurs at low critical gelation concentrations (CGC) (lowest ca. 0.6 wt %). Increased BLG to Gly ratios lead to an increase of the α-helical component in the secondary structures of the polypeptide segments, resulting in wider and more flexible nanofibrils. The presence of α-helical component in the polymers enhances the stability of the organogels against sonication, and instantaneous gel-to-gel transitions are observed as in situ reconstruction of networks occurs within the gelled materials after sonication. In marked contrast, the β-sheet-rich gel, prepared from mPEG-b-PGly, exhibits an instant gel-to-sol transition after sonication is applied. The CGC concentration and stiffness of this mPEG-b-P(BLG-co-Gly) organogel system can be tuned by simply varying the percentages of α-helix and β-sheet in the secondary structures through control of the BLG to Gly ratio during synthesis. The mechanical properties of these organogels are studied by dynamic mechanical analyses (DMA), having storage moduli of ca. 12.1 kPa at room temperature. The injectability and self-healing capabilities are demonstrated by direct observation of the macroscopic self-healing behavior experiment.

Multi-responsive Hydrogels Derived from the Self-assembly of Tethered Allyl-functionalized Racemic Oligopeptides

A multi-responsive triblock hydrogelator oligo(dl-allylglycine)-block-poly(ethylene glycol)-block-oligo(dl-allylglycine) (ODLAG-b-PEG-b-ODLAG) was synthesized facilely by ring-opening polymerization (ROP) of DLAG N-carboxyanhydride (NCA) with a diamino-terminated PEG as the macroinitiator. This system exhibited heat-induced sol-to-gel transitions and either sonication- or enzyme-induced gel-to-sol transitions. The β-sheeting of the oligopeptide segments was confirmed by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and wide-angle X-ray scattering (WAXS). The β-sheets further displayed tertiary ordering into fibrillar structures that, in turn generated a porous and interconnected hydrogel matrix, as observed via transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The reversible macroscopic sol-to-gel transitions triggered by heat and gel-to-sol transitions triggered by sonication were correlated with the transformation of nanostructural morphologies, with fibrillar structures observed in gel and spherical aggregates in sol, respectively. The enzymatic breakdown of the hydrogels was also investigated. This allyl-functionalized hydrogelator can serve as a platform for the design of smart hydrogels, appropriate for expansion into biological systems as bio-functional and bio-responsive materials.

pH-Triggered reversible morphological inversion of orthogonally-addressable poly(3-acrylamidophenylboronic acid)-block-poly(acrylamidoethylamine) micelles and their shell crosslinked nanoparticles

Functionally-responsive amphiphilic core-shell nanoscopic objects, capable of either complete or partial inversion processes, were produced by the supramolecular assembly of pH-responsive block copolymers, without or with covalent crosslinking of the shell layer, respectively. A new type of well-defined, dual-functionalized boronic acid- and amino-based diblock copolymer poly(3-acrylamidophenylboronic acid)(30)-block-poly(acrylamidoethylamine)(25) (PAPBA(30)-b-PAEA(25)) was synthesized by sequential reversible addition-fragmentation chain transfer (RAFT) polymerization and then assembled into cationic micelles in aqueous solution at pH 5.5. The micelles were further cross-linked throughout the shell domain comprised of poly(acrylamidoethylamine) by reaction with a bis-activated ester of 4,15-dioxo-8,11-dioxa-5,14-diazaoctadecane-1,18-dioic acid, upon increase of the pH to 7, to different cross-linking densities (2%, 5% and 10%), forming well-defined shell cross-linked nanoparticles (SCKs) with hydrodynamic diameters of ca. 50 nm. These smart micelles and SCKs presented switchable cationic, zwitterionic and anionic properties, and existed as stable nanoparticles with high positive surface charge at low pH (pH = 2, zeta potential ~ +40 mV) and strong negative surface charge at high pH (pH = 12, zeta potential ~ -35 mV). (1)H NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), dynamic light scattering (DLS), transmission electron microscopy (TEM), atomic force microscopy (AFM), and zeta potential, were used to characterize the chemical compositions, particle sizes, morphologies and surface charges. Precipitation occurred near the isoelectric points (IEP) of the polymer/particle solutions, and the IEP values could be tuned by changing the shell cross-linking density. The block copolymer micelles were capable of full reversible morphological inversion as a function of pH, by orthogonal protonation of the PAEA and hydroxide association with the PAPBA units, whereas the SCKs underwent only reptation of the PAPBA chain segments through the crosslinked shell of PAEA as the pH was elevated. Further, these nanomaterials also showed D-glucose-responsive properties.

Responsive organogels formed by supramolecular self assembly of PEG-block-allyl-functionalized racemic polypeptides into β-sheet-driven polymeric ribbons

A chemically reactive hybrid diblock polypeptide gelator poly(ethylene glycol)-block-poly(dl-allylglycine) (PEG-b-PDLAG) is an exceptional material, due to the characteristics of thermo-reversible organogel formation driven by the combination of a hydrophilic polymer chain linked to a racemic oligomeric homopeptide segment in a range of organic solvents. One-dimensional stacking of the block copolymers is demonstrated by ATR-FTIR spectroscopy, wide-angle X-ray scattering to be driven by the supramolecular assembly of β-sheets in peptide blocks to afford well-defined fiber-like structures, resulting in gelation. These supramolecular interactions are sufficiently strong to achieve ultra low critical gelation concentrations (ca. 0.1 wt%) in N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and methanol. The critical gel transition temperature was directly proportional to the polymer concentration, so that at low concentrations, thermoreversibility of gelation was observed. Dynamic mechanical analysis studies were employed to determine the organogel mechanical properties, having storage moduli of ca. 15.1 kPa at room temperature.

Construction of a versatile and functional nanoparticle platform derived from a helical diblock copolypeptide-based biomimetic polymer

Sequential polymerization of N-carboxyanhydrides accelerated by nitrogen flow is utilized to generate a novel well-defined diblock copolypeptide (PDI = 1.08), with incorporation of alkyne-functionalized side-chain groups allowing for rapid and efficient thiol-yne click-type modifications, followed by self-assembly into nanopure water to construct a helical polypeptide-based versatile and functional nanoparticle platform.

Polyphosphoester‐Based Cationic Nanoparticles Serendipitously Release Integral Biologically‐Active Components to Serve as Novel Degradable Inducible Nitric Oxide Synthase Inhibitors

A degradable polyphosphoester (PPE)-based cationic nanoparticle (cSCK), which is integrated constructed as a novel degradable drug device, demonstrates surprisingly efficient inhibition of inducible nitric oxide synthase (iNOS) transcription, and eventually inhibits nitric oxide (NO) over-production, without loading of any specific therapeutic drugs. This system may serve as a promising anti-inflammatory agent toward the treatment of acute lung injury.

Two-Dimensional Controlled Syntheses of Polypeptide Molecular Brushes via N-Carboxyanhydride Ring-Opening Polymerization and Ring-Opening Metathesis Polymerization

Well-defined molecular brushes bearing polypeptides as side chains were prepared by a “grafting through” synthetic strategy with two-dimensional control over the brush molecular architectures. By integrating N-carboxyanhydride ring-opening polymerizations (NCA ROPs) and ring-opening metathesis polymerizations (ROMPs), desirable segment lengths of polypeptide side chains and polynorbornene brush backbones were independently constructed in controlled manners. The N2 flow accelerated NCA ROP was utilized to prepare polypeptide macromonomers with different lengths initiated from a norbornene-based primary amine, and those macromonomers were then polymerized via ROMP. It was found that a mixture of dichloromethane and an ionic liquid were required as the solvent system to allow for construction of molecular brush polymers having densely-grafted peptide chains emanating from a polynorbornene backbone, poly(norbornene-graft-poly(β-benzyl-l-aspartate)) (P(NB-g-PBLA)). Highly efficient postpolymerization modification was achieved by aminolysis of PBLA side chains for facile installment of functional moieties onto the molecular brushes.