Yu-Mei Shen

Redox-responsive micelles self-assembled from dynamic covalent block copolymers for intracellular drug delivery.

Redox-responsive micelles self-assembled from dynamic covalent block copolymers with double disulfide linkage in the backbone have been developed successfully. The amphiphilic block copolymers PEG-PLA associated with complementary H-bonding sequences can self-assemble into spherical micelles in aqueous media with sizes from 34 nm to 107 nm with different molar mass of PEG and PLA. Moreover, in vitro drug release analyses indicate that reductive environment can result in triggered drug release profiles. The glutathione (GSH) mediated intracellular drug delivery was investigated against HeLa human cervical carcinoma cell line. Flow cytometry and fluorescence microscopy measurements demonstrated that the micelles exhibited faster drug release in glutathione monoester (GSH-OEt) pretreated HeLa cells than that in the nonpretreated cells. Cytotoxicity assay of DOX-loaded micelles indicated the higher cellular proliferation inhibition against 10 mM of GSH-OEt pretreated HeLa cells than that of the nonpretreated ones. These reduction-responsive, biodegradable and biocompatibility micelles could provide a favorable platform to construct excellent drug delivery systems for cancer therapy.

Chitosan oligosaccharide copolymer micelles with double disulphide linkage in the backbone associated by H-bonding duplexes for targeted intracellular drug delivery

A folic acid (FA) conjugated chitosan oligosaccharide (CSO) polylactic acid (PLA) copolymer FA-CSO-PLA with double disulphide linkage in the backbone directed by H-bonding association duplex was synthesized, and its self-assembled micelles were evaluated as smart targeted drug delivery carriers. Both of the intermediates and the terminal copolymers were characterized by 1H-NMR and gel permeation chromatography (GPC). The critical micelle concentration (CMC) value is 0.045 mg mL−1 which suggests the micelles are highly stable in dilute solution. TEM and DLS further confirmed the successful formation of micelles with an average size of 61 and 100 nm, PDI of 0.209 and 0.230 for blank and DOX loaded micelles, respectively. The micelles were destructed under a reductive environment, leading to encapsulated drug release. Moreover, fluorescence microscopy demonstrated that the micelles exhibited both a passive and active targeting ability in HeLA cells due to an EPR effect and folate-mediated endocytosis. These results suggested the micelles would provide a favourable platform for constructing excellent drug delivery systems for cancer therapy.

Chitosan-based core-shell nanomaterials for pH-triggered release of anticancer drug and near-infrared bioimaging

As a naturally-abundant biopolymer, chitosan (CS) exhibit pH-sensitive structural transformation within a narrow pH range. Integrating hydrophobic groups to CS molecules gives modified CS polymers with more adjustable pH responsiveness. In this paper, near-infrared (NIR) photoluminescent Ag2S QDs capped by long-chain carboxylic acid were synthesized and then conjugated with CS via esterification reaction. The anticancer drug doxorubicin (DOX) has an affinity for the hydrophobic oleoyl groups and was entrapped by them to produce Ag2S(DOX)@CS nanospheres. A variety of experiments were performed to characterize the nanospheres. In vitro and in vivo experiments showed that the nanospheres can release DOX at lowered pH in tumor cells and have high antitumor efficacy. In addition, the strong NIR signal derived from the encapsulated Ag2S QDs makes real-time monitoring of the nanosphere distribution in a body possible. This study provides a new CS-based nanocomposite drug carrier for efficient cancer therapy.

Synthesis and micellization of redox-responsive dynamic covalent multi-block copolymers

Multi-block copolymers, which are composed of two or more covalent interconnected polymeric segments of different types, offer unparalleled opportunities for designing new nanostructured materials with enhanced functionality and properties. Using double disulfide linkages coupling with complementary double H-bonding sequences, we demonstrated a new synthetic approach to multi-block copolymers that produces alternating architectures. It offers a new synthetic strategy for synthesizing multi-block copolymers which not only applies to PLA and PEG blocks for multi-block copolymers, but also to other kinds of polymers especially for those hard to be linked by a traditional method. In this study, we synthesized an amphiphilic multi-block copolymer [PLA-PEG]t containing redox-responsive disulfide linkages. Their structures were confirmed by 1H NMR and GPC. These amphiphilic multi-block copolymers can self-assemble into spherical micelles in aqueous media. Compared with di-block copolymers reported in our previous work, multi-block copolymer micelles have a higher drug loading content (DLC), higher stability and more compact spherical structure, whilst maintaining excellent redox-responsive properties and are able to release drugs triggered by intracellular GSH. Fluorescence microscopy measurements and MTT assay demonstrated that the micelle exhibited faster drug release and higher cellular proliferation inhibition due to intracellular GSH responsiveness. These results suggested that the micelles would provide a favorable platform to construct drug delivery systems for cancer therapy.

Facile Assembly of Oppositely Charged Silver Sulfide Nanoparticles into Photoluminescent Mesoporous Nanospheres

Inorganic mesoporous materials have been attracting increasing attention during the past decade. In the present work, photoluminescent Ag2S nanospheres with mesoporous structures were prepared by assembling Ag2S nanoparticles with opposite charges in aqueous phase. Without structure-directing templates, mesoporous Ag2S with well-ordered face-centered cubic superlattice structures and high specific surface area was obtained. The mesoporous Ag2S nanospheres had the same crystal phase as their precursors Ag2S nanoparticles. Different from their near-infrared emitting precursors, the mesoporous Ag2S nanospheres exhibited cyan emission under ultraviolet excitation. The large number of sulfur-related defects existing in the mesostructures is most likely responsible for the photoluminescence. This work provides new insights into fabricating photoluminescent mesostructured materials via scale-up strategy.

Controllable release of nitric oxide and doxorubicin from engineered nanospheres for synergistic tumor therapy

NaYF4:Yb,Er upconversion nanoparticles (UCNPs) capped with long-chain carboxylic acid were synthesized and then conjugated with chitosan (CS) in the aid of N-hydroxysuccinimide. The resultant nanocompound was integrated with doxorubicin (DOX) and Roussins black salt (RBS), a photosensitive nitric oxide (NO) donor to produce stimuli-responsive UCNPs(DOX)@CS-RBS nanospheres as nanocarriers for controllable drug delivery. On the one hand, the encapsulated UCNPs can efficiently absorb NIR photons and convert them into visible photons to trigger NO release. On the other hand, the entrapped DOX can be released at lowered pH from the swollen nanospheres caused by stretched oleoyl-CS chains under acidic conditions. The UCNPs(DOX)@CS-RBS nanospheres exhibit great therapeutic efficacy, which is attributable to the combination of NO and DOX releases based on NO dose-dependent mechanisms. This study highlights the controllable release of NO and DOX from the same nanocarriers and the synergistic therapeutic effect on tumors, which could give new insights into improving cancer nanotherapeutics. STATEMENT OF SIGNIFICANCE In this paper, core-shell structured UCNPs(DOX)@CS-RBS nanospheres have been designed and synthesized via a step-by-step procedure. The stimuli-responsive UCNPs(DOX)@CS-RBS nanospheres act as nanocarriers for controllable drug delivery towards cancer therapy. The encapsulated UCNPs can efficiently absorb NIR photons and convert them into visible light to trigger NO release. Meanwhile, the entrapped DOX can be released from the swollen nanospheres caused by stretched oleoyl-CS chains at lowered pH typical of intracellular environment. Synergistic cancer therapy will be achieved through the combination of NO and DOX releases based on NO dose-dependent mechanisms. This study provides new drug nanocarriers with high antitumor efficacy for synergistic cancer therapy.

Reductive triblock copolymer micelles with a dynamic covalent linkage deliver antimiR-21 for gastric cancer therapy

A reductive tri-block copolymer PEG-SS-PLA-SS-PEI with a double disulphide linkage in the backbone directed by H-bonding association was synthesized and self-assembled into cationic polymeric nanomicellar particles for in vivo antimiRNA delivery with an average diameter of 68 nm and a zeta potential of approximately 39 mV. The chemical structure of the copolymer was well characterized by 1H NMR and GPC. The cationic polymeric nanomicellar particles could be unpacked in an intracellular reductive environment (GSH) leading to the release of encapsulated antimiRNA. MTT assays in vitro showed no significant cytotoxicity of SGC7901 gastric cancer cells incubated with PEG-SS-PLA-SS-PEI micelles. The in vitro study indicated that the micelle-based antimiR-21 delivery system could effectively facilitate cellular uptake and greatly down-regulate the expression level of miR-21 in SGC7901 cell lines, which was comparable to Lipofectamine™ 2000. The down regulation of miR-21 remarkably induced apoptosis, suppressed the tumor cell migration and invasion, and increased the expression of target genes such as phosphatase and tensin homolog deleted on chromosome ten (PTEN) and Programmed Cell Death Protein 4 (PDCD4). More importantly, the in vivo systemic administration of the micelles/antimiR-21 complex in a gastric cancer model significantly inhibited tumor growth and increased the expression of target genes. The nanoparticle based on the PEG-SS-PLA-SS-PEI copolymer would be a safe and efficient carrier for delivery of therapeutic antimiRNA, which shows a prospective therapy method in gastric cancer.

Dynamic covalent linked triblock copolymer micelles for glutathione-mediated intracellular drug delivery

Redox-responsive linkages dispersed in the backbones of the synthetic polymers, while young in the current spectrum of the biomedical application, are rapidly extending into their niche. In the present work, triblock copolymer PEG-PLA-PEG synthesized and characterized by 1H -NMR and SEC can self-assemble into redox-responsive micelles in aqueous media with nanosized 33nm and 47nm. And the copolymers PEG2000-PLA3000-PEG2000 and PEG2000-PLA5000-PEG2000 present lower CMC with 0.034 and 0.022mg/mL, and higher DLC of 4.28% and 5.14% respectively, compared with that of diblock copolymer. Moreover, drug release from the micelles can be triggered and significantly accelerated in reductive environment. The low cytotoxicity of redox-responsive micelles was confirmed by MTT assay against NIH 3T3 cells. All of these results demonstrated that these polymeric micelles self-assembled from double-disulfide tethered block copolymers are promising carriers for the redox-responsive intracellular delivery of hydrophobic anticancer drugs.

Design and Synthesis of New Acid Cleavable Linkers for DNA Sequencing by Synthesis

A new kind of acid sensitive tetrahydrofuranyl (THF) linker was synthesized and then reacted with 5-(6)-carboxytetramethylrhodaminesuccinimidyl ester (5(6)-TAMRA, SE), followed by di(N-succinimidyl) carbonate (DSC) and modified 2′-deoxyuridine triphosphate (dUTP); the final product, as a reversible terminator for DNA sequencing by synthesis (DNA SBS), was given obtained and confirmed by 1H-NMR, 31P-NMR, and HRMS with purity of up to 99%. The synthesized dye-labeled terminator incorporated into DNA strand successfully, and the fluorophore was cleaved completely under acidic conditions. The preliminary results encourage us to explore more acid-sensitive linkers for DNA SBS to increase the cleavage efficiency under weakly acidic conditions.