Peihong Ni

Galactosylated reduction and pH dual-responsive triblock terpolymer Gal-PEEP-a-PCL-ss-PDMAEMA: a multifunctional carrier for the targeted and simultaneous delivery of doxorubicin and DNA

Novel galactosamine (Gal)-modified polymeric micelles which were responsive to both reduction (via the disulfide group, -ss-) and pH (acetal group, -a-) were constructed from poly(ethylethylene phosphate)-a-poly(e-caprolactone)-ss-poly[2-(dimethylamino)ethyl methacrylate] (Gal-PEEP-a-PCL-ss-PDMAEMA) terpolymers in order to develop a multifunctional bioreducible system for the targeted co-delivery of anticancer drugs and DNA. These multifunctional terpolymers were synthesized via a combination of ring-opening polymerization (ROP), atom transfer radical polymerization (ATRP) and a Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) “click” reaction. The chemical structures, chemical compositions, the molecular weights and molecular weight distributions of these terpolymers have been fully characterized, and their self-assembly behavior was studied in detail. The interaction between the terpolymers and DNA was studied by an agarose gel retardation assay. The physical properties of the resulting polyplexes were further determined by zeta potential, dynamic light scattering (DLS) and TEM analyses. The micelles containing the acetal and disulfide groups could be dissociated in an intracellular environment. The reduction- and pH-triggered release of doxorubicin (DOX) from DOX-loaded micelles showed that the release of DOX was accelerated at pH 5.0 and pH 7.4 with 10 mM cytoplasmic glutathione (GSH), and that the release rate was further enhanced at pH 5.0 with 10 mM GSH. A methyl thiazolyl tetrazolium (MTT) assay indicated that the blank micelles displayed relatively low cytotoxicity towards HeLa and HepG2 cells. Although the DOX-loaded micelles could efficiently prohibit the growth of both cell types, they exhibited much higher cytotoxicity towards HepG2 cells than HeLa cells. In addition, the intracellular uptake and transfection of Gal-PEEP-a-PCL-ss-PDMAEMA/DNA/DOX polyplexes into HepG2 cells was more efficient than that into HeLa cells, as revealed by a live cell imaging system, owing to specific ligand–receptor interactions between Gal and asialoglycoprotein receptors overexpressed on the surface of HepG2 cells. These results provide a facile strategy for the preparation of multifunctional biodegradable polymeric micelles that may act as a promising platform for the targeted intracellular co-delivery of hydrophobic drugs and nucleic acids.

Novel fluoroalkyl end-capped amphiphilic diblock copolymers with pH/temperature response and self-assembly behavior.

A series of fluoroalkyl end-capped diblock copolymers of poly[2-(N,N-dimethylamino)ethyl methacrylate] (PDMAEMA or PDMA) and poly[2-(N,N-diethylamino)ethyl methacrylate] (PDEAEMA or PDEA) have been synthesized via oxyanion-initiated polymerization, in which a potassium alcoholate of 4,4,5,5,6,6,7,7,7-nonafluoro-1-heptanol (NFHOK) was used as an initiator. The chemical structures of the NFHO-PDMA-b-PDEA and NFHO-PDEA-b-PDMA depended on the addition sequence of the two monomers and the feeding molar ratios of [DMA] to [DEA] during the polymerization process. These copolymers have been characterized by (1)H NMR and (19)F NMR spectroscopy and gel permeation chromatography (GPC). The aggregation behavior of these copolymers in aqueous solutions at different pH media was studied using a combination of surface tension, fluorescence probe, and transmission electron microscopy (TEM). Both diblock copolymers exhibited distinct pH/temperature-responsive properties. The critical aggregation concentrations (cacs) of these copolymers have been investigated, and the results showed that these copolymers possess excellent surface activity. Besides, these fluoroalkyl end-capped diblock copolymers showed pH-induced lower critical solution temperatures (LCSTs) in water. TEM analysis indicated that the NFHO-PDMA(30)-b-PDEA(10) diblock copolymers can self-assemble into the multicompartment micelles in aqueous solutions under basic conditions, in which the pH value is higher than the pKa values of both PDMA and PDEA homopolymers, while the NFHO-PDEA(10)-b-PDMA(30) diblock copolymers can form flowerlike micelles in basic aqueous solution.

Fluorinated polyhedral oligomeric silsesquioxane-based shape amphiphiles: molecular design, topological variation, and facile synthesis

This paper reports the design and synthesis of fluoroalkyl-functionalized polyhedral oligomeric silsesquioxane (FPOSS)-based shape amphiphiles with two distinct topologies: (i) mono-tethered FPOSS-poly(e-caprolactone) (PCL) and (ii) FPOSS tethered with two polymer chains possessing different compositions, namely, polystyrene (PS) and PCL, denoted as PS–(FPOSS)–PCL. The synthetic strategy features an efficient “growing-from” and “click-functionalization” approach. From a monohydroxyl-functionalized heptavinyl POSS, a PCL chain was grown via ring opening polymerization (ROP) of e-caprolactone; subsequent thiol–ene “click” chemistry with 1H,1H,2H,2H-perfluoro-1-decanethiol allowed the facile introduction of seven perfluorinated alkyl chains onto the POSS head. Similarly, PS–(FPOSS)–PCL was synthesized from a PS precursor bearing both hydroxyl group and heptavinyl POSS at the ω-end, which was prepared by living anionic polymerization and hydrosilylation. The compounds were fully characterized by 1H NMR, 13C NMR, FT-IR spectroscopy, MALDI-TOF mass spectrometry, and size exclusion chromatography. The introduction of perfluorinated molecular cluster into polymers is expected to make them surface-active while the interplay between crystallization and fluorophobic/fluorophilic bulk phase separation in these shape amphiphiles shall lead to intriguing self-assembly behavior and novel hierarchical structures. This study has demonstrated FPOSS as a versatile building block in the construction of shape amphiphiles and established a general and efficient method to introduce such fluorous molecular clusters into polymers.

Geometry induced sequence of nanoscale Frank–Kasper and quasicrystal mesophases in giant surfactants

Significance How far can we push self-assembly toward unusual nanostructures? Frank–Kasper and quasicrystal phases represent unconventional phases of ordered spheroids originally identified in metal alloys. We report that Frank–Kasper and quasicrystal phases and their transition sequence are observed in one-component giant surfactants by introducing variations in molecular geometry. Both X-ray scattering and electron microscopy techniques are used to identify the self-assembled nanostructures. Combining molecular dynamics simulations, we attribute the appearance of these phases to molecular geometry as a result of tail number variation. Our findings lay the foundation for rational design of unconventional soft-matter phases and for exploiting them for unusual properties and functions. Frank–Kasper (F-K) and quasicrystal phases were originally identified in metal alloys and only sporadically reported in soft materials. These unconventional sphere-packing schemes open up possibilities to design materials with different properties. The challenge in soft materials is how to correlate complex phases built from spheres with the tunable parameters of chemical composition and molecular architecture. Here, we report a complete sequence of various highly ordered mesophases by the self-assembly of specifically designed and synthesized giant surfactants, which are conjugates of hydrophilic polyhedral oligomeric silsesquioxane cages tethered with hydrophobic polystyrene tails. We show that the occurrence of these mesophases results from nanophase separation between the heads and tails and thus is critically dependent on molecular geometry. Variations in molecular geometry achieved by changing the number of tails from one to four not only shift compositional phase boundaries but also stabilize F-K and quasicrystal phases in regions where simple phases of spheroidal micelles are typically observed. These complex self-assembled nanostructures have been identified by combining X-ray scattering techniques and real-space electron microscopy images. Brownian dynamics simulations based on a simplified molecular model confirm the architecture-induced sequence of phases. Our results demonstrate the critical role of molecular architecture in dictating the formation of supramolecular crystals with “soft” spheroidal motifs and provide guidelines to the design of unconventional self-assembled nanostructures.

Facile Approach for DNA Encapsulation in Functional Polyion Complex for Triggered Intracellular Gene Delivery: Design, Synthesis, and Mechanism

A facile route for DNA encapsulation in triggered intracellular degradable polymer microcapsules has been achieved via electrostatic interaction, using a polycation, that is, poly[(dimethylamino)ethyl methacrylate] end-capped with cholesterol moiety (Chol-PDMAEMA(30)), along with a polyanion named MePEG2000-block-poly(methacrylic acid) carring partial thiol groups (MePEG2000-b-PMAA(SH)). The encapsulation procedure involves three steps: (i) DNA was first complexed with the polycation (Chol-PDMAEMA(30)); (ii) the complex was then further set into interaction with the anion-containing MePEG2000-b-PMAA(SH); and (iii) the compound carrier was subsequently obtained by cross-linking the thiol groups of the MePEG2000-b-PMAA(SH) to form disulfide linkages. The interactions between every pair among calf thymus DNA, Chol-PDMAEMA(30), and MePEG2000-b-PMAA(SH) were studied by agarose gel retardation assay and ethidium bromide displacement assay. The results indicate that the prepared microcapsules may remain stable during systemic circulation, but degrade and release the carried DNA in a cellular reducing environment. Furthermore, the biophysical properties of the microcapsule have been investigated by zeta-potential, laser light scattering, and transmission electron microscopy (TEM) measurements.

Synthesis and characterization of a new multifunctional polymeric prodrug paclitaxel–polyphosphoester–folic acid for targeted drug delivery

We report here a strategy that allows the preparation of a novel water-soluble polymeric prodrug, paclitaxel–poly(ethyl ethylene phosphate) conjugated with folic acid molecules (abbreviated as PTX–PEEP–FA). PTX was directly used as an initiator for the ring-opening polymerization (ROP) of 2-ethoxy-2-oxo-1,3,2-dioxaphospholane (EOP) under the catalysis of Sn(Oct)2 to fabricate an amphiphilic PTX–PEEP, followed by covalently conjugating a FA moiety via esterification to obtain the biodegradable and targeted polymeric prodrug PTX–PEEP–FA. The chemical structure of the prodrug was characterized by 1H NMR and MALDI-TOF mass spectroscopy. TEM and DLS measurements showed that these prodrugs could self-assemble in aqueous solution to form micelles with PTX as the core and PEEP–FA as the corona, and the average particle size was less than 130 nm. The hydrophobic PTX core could be further used to load more water-insoluble anti-cancer drugs, such as PTX or doxorubicin (DOX), while the hydrophilic PEEP–FA chain endowed micelles with good stability during systemic circulation and significantly improved controlled-release properties compared to free PTX or DOX. Live cell imaging system was utilized to monitor the cellular uptake process of DOX-loaded PTX–PEEP–FA micelles for HeLa and KB cells, respectively. The results revealed that these drug-loaded micelles with FA on their surface could remarkably improve cell endocytosis. In vitro biological evaluations confirmed that PTX–PEEP–FA, simultaneously acted as both a prodrug and drug delivery carrier, could achieve the aims of increased drug loading efficiency, reduced cytotoxicity, and enhanced targeting efficacy.

Rapidly in situ forming polyphosphoester-based hydrogels for injectable drug delivery carriers

In situ forming hydrogels allow the modulation of physicochemical properties and are providing new opportunities for biomedical applications. Here, the preparation and characterization of a series of rapidly in situ forming and pH-responsive hydrogels with different crosslinking degrees are reported, which were achieved by accelerated free radical copolymerization of polyphosphoester-based macrocrosslinker and 2-(dimethylamino)ethyl methacrylate (DMAEMA) monomer. The hydrogel formation can be completed very quickly under mild conditions, ranging from several to tens of minutes with varying concentrations of components. The polyphosphoester-based macrocrosslinker was synthesized via a combination of ring-opening polymerization and post-polymerization modification, and it was characterized by 1H NMR, 31P NMR, and GPC measurements. The sol–gel transition was monitored by dynamic time sweep rheological analysis. Moreover, the swelling kinetics, interior morphology, pH-responsive property, in vitro cytotoxicity and drug release of these hydrogels were characterized. The results indicate that these hydrogels show great potential as injectable drug delivery system.

A new pathway towards polymer modified cellulose nanocrystals via a “grafting onto” process for drug delivery

Poly(ethyl ethylene phosphate) (PEEP) modified cellulose nanocrystals (CNCs) (CNC-g-PEEP) were synthesized through a “grafting onto” process, in which a combination of ring-opening polymerization (ROP) and Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) “click” chemistry was utilized. The resulting suspension of negatively-charged CNC-g-PEEP nanocrystals could be used to encapsulate doxorubicin (DOX) by electrostatic interactions and release the drug in the tumor cell environment.

Synthesis of an acid-labile polymeric prodrug DOX-acetal-PEG-acetal-DOX with high drug loading content for pH-triggered intracellular drug release

In this study, three PEGylated doxorubicin (DOX) prodrugs with acid-labile acetal and carbamate linkages have been prepared via the combination of Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition of alkyne and azide (CuAAC) “click” reaction and ammonolysis reaction. The chemical structures of the prodrugs and the drug contents were characterized by 1H NMR, FT-IR and HPLC analyses. To avoid some side effects caused by the acidic degradation products from conventional hydrophobic polymers, DOX was directly linked to the PEG chain. These prodrugs could self-assemble into micelles in aqueous solution with DOX as the core and PEG chains as the corona. The dissociation of prodrug micelles was confirmed by monitoring the size change as a function of time through DLS analysis. Compared with free DOX, the pH-triggered DOX release of prodrugs exhibited a well-controlled and faster release behavior at pH 5.0 than at pH 7.4. In vitro cytotoxicity tests against HeLa cells by MTT assay demonstrated that these prodrugs displayed the desirable antitumor activity. The intracellular drug release was observed by a live cell imaging system at different DOX dosages. This work provides a strategy for the preparation of a new type of pH-cleavable and water-soluble antitumor prodrug for cancer chemotherapy.

Polymeric prodrugs conjugated with reduction-sensitive dextran–camptothecin and pH-responsive dextran–doxorubicin: an effective combinatorial drug delivery platform for cancer therapy

Multiple drugs in combinatory therapy can improve the treatment of cancer due to their efficient reduction of multidrug resistance (MDR) of tumor cells. In this paper, we first synthesized a reduction-sensitive dextran-ss-camptothecin (Dex-ss-CPT, or Dex-CPT) prodrug conjugated by a disulfide bond, and a pH-responsive dextran-hyd-doxorubicin (Dex-hyd-DOX, or Dex-DOX) prodrug linked with an acid-cleavable hydrazone group. The chemical structures of the intermediate polymers and polymeric prodrugs have been fully characterized by 1H NMR, FT-IR, UV-Vis and HPLC analyses, respectively. Both prodrugs could self-assemble into uniform particles in aqueous solution. Subsequently, in vitro synergistic drug release of the two prodrugs was studied by methyl thiazolyl tetrazolium (MTT) assay. The reduction of a disulfide linker generates a thiol intermediate that is followed by intramolecular cyclization and the cleavage of the neighboring carbonate bridge, thus releasing native CPT molecules from the Dex-ss-CPT micelles. Similarly, the pH-sensitive hydrazone bond is broken under intracellular acidic conditions and the DOX parent drug is released from the Dex-hyd-DOX micelles. Finally, in vivo pharmacokinetics and biodistribution were investigated via intravenous administration with various formulations to treat 4T1 tumor-bearing mice. Meanwhile, the antitumor activity was also studied. This work demonstrates an effective anti-cancer prodrug design platform, which is expected to be useful for the treatment of various tumors.