Biodegradable amphiphilic copolymer containing nucleobase: synthesis, self-assembly in aqueous solutions, and potential use in controlled drug delivery

Photoreactive silver-containing supramolecular polymers that form self-assembled nanogels for efficient antibacterial treatment

In this study, an efficient synthetic strategy and potential route to obtain a photo-reactive silver-containing cytosine-functionalized polypropylene glycol polymer (Ag-Cy-PPG) was developed by combining a hydrophilic oligomeric polypropylene glycol (PPG) backbone with dual pH-sensitive/photo-reactive cytosine-silver-cytosine (Cy-Ag-Cy) linkages. The resulting photo-responsive Ag-Cy-PPG holds great promise as a multifunctional biomedical material that generates spherical-like nanogels in water; the nanogels exhibit high antibacterial activity and thus may significantly enhance the efficacy of antibacterial treatment. Due to the formation of photo-dimerized Cy-Ag-Cy cross-linkages after UV irradiation, Ag-Cy-PPG converts into water-soluble cross-linked nanogels that possess a series of interesting chemical and physical properties, such as intense and stable fluorescence behavior, highly sensitive pH-responsive characteristics, on/off switchable phase transition behavior, and well-controlled release of silver ions (Ag+) in mildly acidic aqueous solution. Importantly, antibacterial tests clearly demonstrated that irradiated Ag-Cy-PPG nanogels exhibited strong antibacterial activity at low doses (MIC values of < 50 μg/mL) against gram-positive and gram-negative bacterial pathogens, whereas non-irradiated Ag-Cy-PPG nanogels did not inhibit the viability of bacterial pathogens. These results indicate that irradiated Ag-Cy-PPG nanogels undergo a highly sensitive structural change in the bacterial microenvironment due to their relatively unstable π-conjugated structures (compared to non-irradiated nanogels); this change results in a rapid structural response that promotes intracellular release of Ag+ and induces potent antibacterial ability. Overall, this newly created metallo-supramolecular system may potentially provide an efficient route to dramatically enhance the therapeutic effectiveness of antibacterial treatments.

Photoreactive Mercury-Containing Metallosupramolecular Nanoparticles with Tailorable Properties That Promote Enhanced Cellular Uptake for Effective Cancer Chemotherapy

A new potential route to enhance the efficiency of supramolecular polymers for cancer chemotherapy was successfully demonstrated by employing a photosensitive metallosupramolecular polymer (Hg-BU-PPG) containing an oligomeric poly(propylene glycol) backbone and highly sensitive pH-responsive uracil-mercury-uracil (U-Hg-U) bridges. This route holds great promise as a multifunctional bioactive nano-object for development of more efficient and safer cancer chemotherapy. Owing to the formation of uracil photodimers induced by ultraviolet irradiation, Hg-BU-PPG can form a photo-cross-linked structure and spontaneously forms spherical nanoparticles in aqueous solution. The irradiated nanoparticles possess many unique characteristics, such as unique fluorescence behavior, highly sensitive pH-responsiveness, and intriguing phase transition behavior in aqueous solution as well as high structural stability and antihemolytic activity in biological media. More importantly, a series of cellular studies clearly confirmed that the U-Hg-U photo-cross-links in the irradiated nanoparticles substantially enhance their selective cellular uptake by cancer cells via macropinocytosis and the mercury-loaded nanoparticles subsequently induce higher levels of cytotoxicity in cancer cells (compared to non-irradiated nanoparticles), without harming normal cells. These results are mainly attributed to cancer cell microenvironment-triggered release of mercury ions from disassembled nanoparticles, which rapidly induce massive levels of apoptosis in cancer cells. Overall, the pH-sensitive U-Hg-U photo-cross-links within this newly discovered supramolecular system are an indispensable factor that offers a potential path to remarkably enhance the selective therapeutic effects of functional nanoparticles toward cancer cells.

Photoreactive Cytosine-Functionalized Self-Assembled Micelles with Enhanced Cellular Uptake Capability for Efficient Cancer Chemotherapy

Design, fabrication, and control of photoreactive supramolecular macromers─which are composed of a thermoresponsive polymer backbone and photoreactive nucleobase end-groups─to achieve the desired physical-chemical performance and provide the high efficiency required for chemotherapy drug delivery purposes still present challenges. Herein, a difunctional cytosine-terminated supramolecular macromer was successfully obtained at high yield. UV-irradiation induces the formation of cytosine photodimers within the structure. The irradiated macromer can self-assemble into nanosized spherical micelles in water that possess a number of interesting and unique features, such as desired micellar size and morphology, tunable drug-loading capacity, and excellent structural stability in serum-containing medium, in addition to well-controlled drug-release behaviors in response to changes in environmental temperature and pH; these extremely desirable, rare features are required to augment the functions of polymeric nanocarriers for drug delivery. Importantly, a series of in vitro studies demonstrated that photodimerized cytosine moieties within the drug-loaded micelles substantially enhance their internalization and accumulation inside cells via endocytosis and subsequently lead to induction of massive apoptotic cell death compared with the corresponding nonirradiated micelles. Thus, this newly developed "photomodified" nanocarrier system could provide a potentially fruitful route to enhance the drug delivery performance of nanocages without the need to introduce targeting moieties or additional components.

Complementary Nucleobase Interactions Drive Co-Assembly of Drugs and Nanocarriers for Selective Cancer Chemotherapy

A new concept in cooperative adenine-uracil (A-U) hydrogen bonding interactions between anticancer drugs and nanocarrier complexes was successfully demonstrated by invoking the co-assembly of water soluble, uracil end-capped polyethylene glycol polymer (BU-PEG) upon association with the hydrophobic drug adenine-modified rhodamine (A-R6G). This concept holds promise as a smart and versatile drug delivery system for the achievement of targeted, more efficient cancer chemotherapy. Due to A-U base pairing between BU-PEG and A-R6G, BU-PEG has high tendency to interact with A-R6G, which leads to the formation of self-assembled A-R6G/BU-PEG nanogels in aqueous solution. The resulting nanogels exhibit a number of unique physical properties, including extremely high A-R6G-loading capacity, well-controlled, pH-triggered A-R6G release behavior, and excellent structural stability in biological media. Importantly, a series of in vitro cellular experiments clearly demonstrated that A-R6G/BU-PEG nanogels improved the selective uptake of A-R6G by cancer cells via endocytosis and promoted the intracellular release of A-R6G to subsequently induce apoptotic cell death, while control rhodamine/BU-PEG nanogels did not exert selective toxicity in cancer or normal cell lines. Overall, these results indicate that cooperative A-U base pairing within nanogels is a critical factor that improves selective drug uptake and effectively promotes apoptotic programmed cell death in cancer cells.

Stimuli-Responsive Aliphatic Polycarbonate Nanocarriers for Tumor-Targeted Drug Delivery

Nanoparticles based on amphiphilic copolymers with tunable physicochemical properties can be used to encapsulate delicate pharmaceutics while at the same time improving their solubility, stability, pharmacokinetic properties, reducing immune surveillance, or achieving tumor-targeting ability. Those nanocarriers based on biodegradable aliphatic polycarbonates are a particularly promising platform for drug delivery due to flexibility in the design and synthesis of appropriate monomers and copolymers. Current studies in this field focus on the design and the synthesis of new effective carriers of hydrophobic drugs and their release in a controlled manner by exogenous or endogenous factors in tumor-specific regions. Reactive groups present in aliphatic carbonate copolymers, undergo a reaction under the action of a stimulus: e.g., acidic hydrolysis, oxidation, reduction, etc. leading to changes in the morphology of nanoparticles. This allows the release of the drug in a highly controlled manner and induces a desired therapeutic outcome without damaging healthy tissues. The presented review summarizes the current advances in chemistry and methods for designing stimuli-responsive nanocarriers based on aliphatic polycarbonates for controlled drug delivery.

Functional Systems Derived from Nucleobase Self-assembly

Dynamic and reversible non-covalent interactions endow synthetic systems and materials with smart adaptive functions that allow them to response to diverse stimuli, interact with external agents, or repair structural defects. Inspired by the outstanding performance and selectivity of DNA in living systems, scientists are increasingly employing Watson-Crick nucleobase pairing to control the structure and properties of self-assembled materials. Two sets of complementary purine-pyrimidine pairs (guanine:cytosine and adenine:thymine(uracil)) are available that provide selective and directional H-bonding interactions, present multiple metal-coordination sites, and exhibit rich redox chemistry. In this review, we highlight several recent examples that profit from these features and employ nucleobase interactions in functional systems and materials, covering the fields of energy/electron transfer, charge transport, adaptive nanoparticles, porous materials, macromolecule self-assembly, or polymeric materials with adhesive or self-healing ability.

Hydrogen-bonded supramolecular micelle-mediated drug delivery enhances the efficacy and safety of cancer chemotherapy

Multiple hydrogen-bonded supramolecular polymers tend to form stable spherical micelles with oppositely charged anticancer drugs in biological environments, which improves cellular drug uptake and more effectively induces apoptosis in cancer cells.

Dextran-Benzoporphyrin Derivative (BPD) Coated Superparamagnetic Iron Oxide Nanoparticle (SPION) Micelles for T2-Weighted Magnetic Resonance Imaging and Photodynamic Therapy

Photodynamic therapy (PDT) has attracted extensive attention in recent years as a noninvasive and locally targeted cancer treatment approach. Nanoparticles have been used to improve the solubility and pharmacokinetics of the photosensitizers required for PDT; however, nanoparticles also suffer from many shortcomings including uncontrolled drug release and low tumor accumulation. Herein, we describe a novel biodegradable nanoplatform for the delivery of the clinically used PDT photosensitizer benzoporphyrin derivative monoacid ring A (BPD-MA) to tumors. Specifically, the hydrophobic photosensitizer BPD was covalently conjugated to the amine groups of a dextran-b-oligo (amidoamine) (dOA) dendron copolymer, forming amphiphilic dextran-BPD conjugates that can self-assemble into nanometer-sized micelles in water. To impart additional imaging capabilities to these micelles, superparamagnetic iron oxide nanoparticles (SPIONs) were encapsulated within the hydrophobic core to serve as a magnetic resonance imaging (MRI) contrast agent. The use of a photosensitizer as a hydrophobic building block enabled facile and reproducible synthesis and high drug loading capacity (∼30%, w/w). Furthermore, covalent conjugation of BPD to dextran prevents the premature release of drug during systemic circulation. In vivo studies show that the intravenous administration of dextran-BPD coated SPION nanoparticles results in significant MR contrast enhancement within tumors 24 h postinjection and PDT led to a significant reduction in the tumor growth rate.

Entrapment of an adenine derivative by a photo-irradiated uracil-functionalized micelle confers controlled self-assembly behavior

HYPOTHESIS

Invoking cooperative assembly of the uracil-functionalized supramolecular polymer BU-PPG [uracil end-capped poly(propylene glycol)] upon association with the nucleobase adenine derivative A-MA [methyl 3-(6-amino-9H-purin-9-yl)propanoate] as a model drug provides a new concept to control and tune the properties of supramolecular complexes and holds significant potential for the development of safer, more effective drug delivery systems.

EXPERIMENTS

BU-PPG and A-MA were successfully developed and exhibited specific recognition and high affinity, which enabled reversible complementary adenine-uracil (A-U) hydrogen bonding-induced formation of spherical micelles in aqueous solution. The self-assembly and controllable A-MA release behavior of BU-PPG/A-MA micelles were studied using morphological analysis and optical and light scattering techniques to investigate the effect of photoirradiation and temperature on the complementary hydrogen bond interactions between BU-PPG and A-MA.

FINDINGS

The resulting micelles possess unusual physical properties, including controlled photoreactivity kinetics, controllable self-assembled morphology and low cytotoxicity in vitro, as well as reversible temperature-responsive behavior. Importantly, irradiated micelles exhibited excellent long-term structural stability under normal physiological conditions and serum disturbance. Increasing the temperature triggered rapid release of A-MA by disrupting A-U complexes. These findings represent an entirely new, promising strategy for the development of multi-controlled release drug delivery nanocarriers based on complementary hydrogen bonding interactions.

Functional biodegradable polymers via ring-opening polymerization of monomers without protective groups

Biodegradable polymers are of current interest and chemical functionality in such materials is often demanded in advanced biomedical applications. Functional groups often are not tolerated in the polymerization process of ring-opening polymerization (ROP) and therefore protective groups need to be applied. Advantageously, several orthogonally reactive functions are available, which do not demand protection during ROP. We give an insight into available, orthogonally reactive cyclic monomers and the corresponding functional synthetic and biodegradable polymers, obtained from ROP. Functionalities in the monomer are reviewed, which are tolerated by ROP without further protection and allow further post-modification of the corresponding chemically functional polymers after polymerization. Synthetic concepts to these monomers are summarized in detail, preferably using precursor molecules. Post-modification strategies for the reported functionalities are presented and selected applications highlighted.

Self-Assembled pH-Responsive Polymeric Micelles for Highly Efficient, Noncytotoxic Delivery of Doxorubicin Chemotherapy To Inhibit Macrophage Activation: In Vitro Investigation

Self-assembled pH-responsive polymeric micelles, a combination of hydrophilic poly(ethylene glycol) segments and hydrogen bonding interactions within a biocompatible polyurethane substrate, can spontaneously self-assemble into highly controlled, nanosized micelles in aqueous solution. These newly developed micelles exhibit excellent pH-responsive behavior and biocompatibility, highly controlled drug (doxorubicin; DOX) release behavior, and high drug encapsulation stability in different aqueous environments, making the micelles highly attractive potential candidates for safer, more effective drug delivery in applications such as cancer chemotherapy. In addition, in vitro cell studies revealed the drug-loaded micelles possessed excellent drug entrapment stability and low cytotoxicity toward macrophages under normal physiological conditions (pH 7.4, 37 °C). When the pH of the culture media was reduced to 6.0 to mimic the acidic tumor microenvironment, the drug-loaded micelles triggered rapid release of DOX within the cells, which induced potent antiproliferative and cytotoxic effects in vitro. Importantly, fluorescent imaging and flow cytometric analyses confirmed the DOX-loaded micelles were efficiently delivered into the cytoplasm of the cells via endocytosis and then subsequently gradually translocated into the nucleus. Therefore, these multifunctional micelles could serve as delivery vehicles for precise, effective, controlled drug release to prevent accumulation and activation of tumor-promoting tumor-associated macrophages in cancer tissues. Thus, this unique system may offer a potential route toward the practical realization of next-generation pH-responsive therapeutic delivery systems.

Photo-responsive polymeric micelles and prodrugs: synthesis and characterization

Bio-recognizable and photocleavable amphiphilic glycopolymers and prodrugs containing photodegradable linkers (i.e. 5-hydroxy-2-nitrobenzyl alcohol) as junction points between bio-recognizable hydrophilic glucose (or maltose) and hydrophobic poly(α-azo-ε-caprolactone)-grafted alkyne or drug chains were synthesized by combining ring-opening polymerization, nucleophilic substitution, and “click” post-functionalization with alkynyl-pyrene and 2-nitrobenzyl-functionalized indomethacin (IMC). The block-grafted glycocopolymers could self-assemble into spherical photoresponsive micelles with hydrodynamic sizes of <200 nm. Fluorescence emission measurements indicated the release of Nile red, a hydrophobic dye, encapsulated by the Glyco-ONB-P(αN₃CL-g-alkyne)_n micelles, in response to irradiation caused by micelle disruption. Light-triggered bursts were observed for IMC-loaded or -conjugated micelles during the first 5 h. Following light irradiation, the drug release rate of IMC-conjugated micelles was faster than that of IMC-loaded micelles. Selective lectin binding experiments confirmed that glycosylated Glyco-ONB-P(αN₃CL-g-alkyne)_n could be used in bio-recognition applications. The nano-prodrug with and without UV irradiation was associated with negligible levels of toxicity at concentrations of less than 30 μg mL⁻¹. The confocal microscopy and flow cytometry results indicated that the uptake of doxorubicin (DOX)-loaded micelles with UV irradiation by HeLa cells was faster than without UV irradiation. The DOX-loaded Gluco-ONB-P(αN₃CL-g-PONBIMC)₁₀ micelles effectively inhibited HeLa cells' proliferation with a half-maximal inhibitory concentration of 8.8 μg mL⁻¹.

Bio-recognizable and photocleavable amphiphilic glycopolymers and prodrugs containing photodegradable linkers as junction points between hydrophilic glycose and hydrophobic poly(α-azo-ε-caprolactone)-grafted alkyne or drug chains were synthesized.

Sodium cholate-enhanced polymeric micelle system for tumor-targeting delivery of paclitaxel

PURPOSE

Polymeric micelles are attractive nanocarriers for tumor-targeted delivery of paclitaxel (PTX). High antitumor efficacy and low toxicity require that PTX mainly accumulated in tumors with little drug exposure to normal tissues. However, many PTX-loaded micelle formulations suffer from low stability, fast drug release, and lack of tumor-targeting capability in the circulation. To overcome these challenges, we developed a micellar formulation that consists of sodium cholate (NaC) and monomethoxy poly (ethylene glycol)-block-poly (d,l-lactide) (mPEG-PDLLA).

METHODS

PTX-loaded NaC-mPEG-PDLLA micelles (PTX-CMs) and PTX-loaded mPEG-PDLLA micelles (PTX-Ms) were formulated, and their characteristics, particle size, surface morphology, release behavior in vitro, pharmacokinetics and in vivo biodistributions were researched. In vitro and in vivo tumor inhibition effects were systematically investigated. Furthermore, the hemolysis and acute toxicity of PTX-CMs were also evaluated.

RESULTS

The size of PTX-CMs was 53.61±0.75 nm and the ζ-potential was -19.73±0.68 mV. PTX was released much slower from PTX-CMs than PTX-Ms in vitro. Compared with PTX-Ms, the cellular uptake of PTX-CMs was significantly reduced in macrophages and significantly increased in human cancer cells, and therefore, PTX-CMs showed strong growth inhibitory effects on human cancer cells. In vivo, the plasma AUC0-t of PTX-CMs was 1.8-fold higher than that of PTX-Ms, and 5.2-fold higher than that of Taxol. The biodistribution study indicated that more PTX-CMs were accumulated in tumor than PTX-Ms and Taxol. Furthermore, the significant antitumor efficacy of PTX-CMs was observed in mice bearing BEL-7402 hepatocellular carcinoma and A549 lung carcinoma. Results from drug safety assessment studies including acute toxicity and hemolysis test revealed that the PTX-CMs were safe for in vivo applications.

CONCLUSION

These results strongly revealed that NaC-mPEG-PDLLA micelles can tumor-target delivery of PTX and enhance drug penetration in tumor, suggesting that NaC-mPEG-PDLLA micelles are promising nanocarrier systems for anticancer drugs delivery.

α-Cyclodextrin concentration-controlled thermo-sensitive supramolecular hydrogels

Supramolecular hydrogels (SHGs) built from inclusion complex of macrocyclic compound α-cyclodextrin (α-CD) and poly(ethylene glycol) (PEG) have attracted much interest due to their excellent biocompatibility and great potential for biomedical applications. In this work, the hydrogen bond of nucleic acid was introduced into the above-mentioned SHG by syntheses of nucleobase guanine/cytosine (G/C)-terminated PEG (G-PEG-G/C-PEG-C). The base-pairing interaction between G and C as an additional network junction effectively enhanced storage moduli (G's) of the hydrogels. Moreover, the prepared hydrogels exhibited excellent cytocompatibility and property for controlled drug release, outlining the potential of thermo-sensitive construct for biomedical applications, such as local chemotherapy of cancers.

Temperature, ultrasound and redox triple-responsive poly(N-isopropylacrylamide) block copolymer: synthesis, characterization and controlled release

Triple stimuli-responsive polymers PNiPAAm-S-S-PXCL containing a disulfide (–S–S–) bond as a junction point between hydrophilic and hydrophobic chains were synthesized and characterized.

Mesoporous silica nanoparticles with lactose-mediated targeting effect to deliver platinum(iv) prodrug for liver cancer therapy

A mesoporous silica nanoparticle system with a lactose-mediated targeting effect was demonstrated to deliver a platinum(iv) prodrug for liver cancer therapy.

CO2-Driven stereochemical inversion of sugars to create thymidine-based polycarbonates by ring-opening polymerisation

A strategy using CO₂ to invert the stereochemistry and cyclise natural sugars is presented and applied towards thymidine-based polymers by ring-opening polymerisation.

Pluronic F68-Linoleic Acid Nano-spheres Mediated Delivery of Gambogic Acid for Cancer Therapy

Gambogic acid (GA), a natural compound from gamboge resin, has been introduced as a promising antitumor drug contributing to its broad spectrum of antitumor activity. However, the poor aqueous solubility and short half-life hinder its clinical application. Pluronic F68 (F68) is a well-known amphiphilic block copolymer consisting of hydrophobic propylene oxide units and hydrophilic ethylene oxide. Although F68 has an amphiphilic structure, its short propylene oxide segment limits its dilution stability and drug-loading capacity. To overcome this limitation, we modified F68 by conjugating linoleic acid, a hydrophobic fatty acid, to increase the hydrophilic-hydrophobic interaction and thus improve the stability of F68 nano-spheres. This F68-linoleic acid (F68-LA) conjugate was synthesized and was used to load GA to improve its anticancer effects. GA-loaded F68-LA nano-spheres were stable for 6 days, with a mean diameter of 159.3 nm and zeta potential of -23.2 mV. The entrapment efficiency of GA in F68-LA nano-spheres was as high as 92.0%. Furthermore, F68-LA/GA nano-spheres exhibited an enhanced cytotoxic activity and proapoptotic effect against human ovarian cancer A2780 cells, compared with free GA. Our results showed that the F68-LA/GA nano-spheres might be a promising cancer-targeted drug delivery system in ovarian cancer therapy.

Synthesis of Polylactide-Based Core-Shell Interface Cross-Linked Micelles for Anticancer Drug Delivery

Well-defined poly(ethylene glycol)-b-allyl functional polylactide-b-polylactides (PEG-APLA-PLAs) are synthesized through sequential ring-opening polymerization. PEG-APLA-PLAs that have amphiphilic properties and reactive allyl side chains on their intermediate blocks are successfully transferred to core-shell interface cross-linked micelles (ICMs) by micellization and UV-initiated irradiation. ICMs have demonstrated enhanced colloidal stability in physiological-mimicking media. Hydrophobic molecules such as Nile Red or doxorubicin (Dox) are readily loaded into ICMs; the resulting drug-ICM formulations possess slow and sustained drug release profiles under physiological-mimicking conditions. ICMs exhibit negligible cytotoxicity in human uterine sarcoma cancer cells by using biodegradable aliphatic polyester as the hydrophobic segments. Relative to free Dox, Dox-loaded ICMs show a reduced cytotoxicity due to the late intracellular release of Dox from ICMs. Overall, ICMs represent a new type of biodegradable cross-linked micelle and can be employed as a promising platform for delivering a broad variety of hydrophobic drugs.

Postpolymerization Modifications of Alkene-Functional Polycarbonates for the Development of Advanced Materials Biomaterials

Functional aliphatic polycarbonates have attracted significant attention as materials for use as biomedical polymers in recent years. The incorporation of pendent functionality offers a facile method of modifying materials postpolymerization, thus enabling functionalities not compatible with ring-opening polymerization (ROP) to be introduced into the polymer. In particular, polycarbonates bearing alkene-terminated functional groups have generated considerable interest as a result of their ease of synthesis, and the wide range of materials that can be obtained by performing simple postpolymerization modifications on this functionality, for example, through radical thiol-ene addition, Michael addition, and epoxidation reactions. This review presents an in-depth appraisal of the methods used to modify alkene-functional polycarbonates postpolymerization, and the diversity of practical applications for which these materials and their derivatives have been used.

Use of complementary nucleobase-containing synthetic polymers to prepare complex self-assembled morphologies in water

Amphiphilic nucleobase-containing block copolymers with poly(oligo(ethylene glycol) methyl ether methacrylate) as the hydrophilic block and nucleobase-containing blocks as the hydrophobic segments were successfully synthesized using RAFT polymerization and then self-assembled via solvent switch in aqueous solutions. Effects of the common solvent on the resultant morphologies of the adenine (A) and thymine (T) homopolymers, and A/T copolymer blocks and blends were investigated. These studies highlighted that depending on the identity of the common solvent, DMF or DMSO, spherical micelles or bicontinuous micelles were obtained. We propose that this is due to the presence of A-T interactions playing a key role in the morphology and stability of the resultant nanoparticles, which resulted in a distinct system compared to individual adenine or thymine polymers. Finally, the effects of annealing on the self-assemblies were explored. It was found that annealing could lead to better-defined spherical micelles and induce a morphology transition from bicontinuous micelles to onion-like vesicles, which was considered to occur due to a structural rearrangement of complementary nucleobase interactions resulting from the annealing process.

Highly efficient drug delivery systems based on functional supramolecular polymers: In vitro evaluation

The novel concept of modifying and enhancing the properties of existing functional micelles through self-complementary interactions has significant potential. In this study, a practical approach to living polymerization of functionalized thermoresponsive monomers enabled the incorporation of self-constituted multiple hydrogen bonded groups into micelles that have potential as supramolecular drug-delivery systems. Phase transitions and morphological studies in aqueous solution showed that the microstructure can be controlled to achieve well-defined vesicle-like micelles with respect to the strength of the hydrogen bond segment. Thus, the resulting micelles have a very low critical micellization concentration and very high loading capacity (16.1%), making the loading process extremely stable and efficient. Incorporation of the anticancer drug doxorubicin (DOX) affected the micellization process in aqueous solution and enabled fine-tuning of drug loading and precise control of drug release rate with excellent sensitivity. Release studies in vitro showed that DOX-loaded micelles exerted dose-dependent cytotoxicity against human liver carcinoma (HepG2) cells at the physiological temperature of 37°C. In addition, DOX-loaded micelles were efficiently endocytosed by the cancer cells, which may enable the micelles to serve as suitable vehicles for effective delivery of anticancer drugs to primary tumors and metastatic disease. This newly developed material may provide a potential route towards next-generation drug delivery vehicles.

STATEMENT OF SIGNIFICANCE

A breakthrough innovation in water-based thermo-responsive polymers has enabled significant progress in developing smart stimuli-responsive nanocarriers by generating novel "supramolecular polymeric micelles" via self-complementary hydrogen-bonding interactions. These newly developed micelles exhibit extremely high micellar stability and drug loading capacity (up to 16%), excellent thermo-responsive behavior and precise control of drug release rate due to hydrogen-bond-induced physical cross-linking. In addition, doxorubicin-loaded micelles were efficiently endocytosed by the cancer cells, which allows them to serve as suitable vehicles for effective delivery of anticancer drugs to primary tumors and metastatic disease. Thus, this work provides a potential route for the development of next generation multifunctional nanocarriers that have improved safety and to increase the therapeutic efficacy of anticancer therapy.

Dual-stimuli-responsive glycopolymer bearing a reductive and photo-cleavable unit at block junction

Dual-stimuli-cleavable glycopolymers bearing a reductive and photo-cleavable unit at block junction were synthesized and characterization.

Polymeric micelles from block copolymers containing 2,6-diacylaminopyridine units for encapsulation of hydrophobic drugs

New polymers are described that can form micelles in water and can be envisaged as nanocarriers for drug delivery applications.

Micellar nanoparticles with tuneable morphologies through interactions between nucleobase-containing synthetic polymers in aqueous solution

Herein, we report the preparation of nucleobase-containing synthetic amphiphilic diblock copolymers using RAFT polymerization.

Polycarbonate-based biodegradable copolymers for stimuli responsive targeted drug delivery

The newly developed polymeric nanocarrier could open a new avenue for cancer therapy, due to its unique design as well as, most importantly, its biocompatible and biodegradable nature.

A dextran-platinum(iv) conjugate as a reduction-responsive carrier for triggered drug release

Reduction-responsive nano-carriers have been confirmed to be promising for intracellular drug delivery. To develop multifunctional polymer-based drug delivery system, a novel dextran-Pt(iv) conjugate was synthesized by conjugating Pt(iv) to the side chains of the hydrophilic dextran and used for doxorubicin (DOX) delivery. Pt(iv) conjugation could change the hydrophilicity of dextran, leading to the self-assembly of dextran-Pt(iv) conjugates with different morphologies. Pt(iv) segments served as the key components in assembly formation and as the antitumor prodrug. Under a reductive environment, Pt(iv) was found to be reduced to its active Pt(ii) form and cleaved from dextran, shifting the hydrophilic-hydrophobic balance of the dextran-Pt(iv) conjugate. The collapse of the assembly structure due to the partial or complete recovery of the hydrophilicity of dextran led to triggered release of DOX. The DOX-loaded dextran-Pt(iv) conjugate obtained by combining the released hydrophobic DOX and recovered hydrophilic Pt(ii), was found to be very effective as an antitumor agent as demonstrated in in vitro cytotoxicity evaluations. This DOX-loaded dextran-Pt(iv) conjugate system provided a new strategy to trigger the release of hydrophobic and hydrophilic drugs at the same time via single reduction-responsive control to provide an enhanced anti-tumor effect.

Nanostructured Amphiphilic Star-Hyperbranched Block Copolymers for Drug Delivery

A robust drug delivery system based on nanosized amphiphilic star-hyperbranched block copolymer, namely, poly(methyl methacrylate-block-poly(hydroxylethyl methacrylate) (PMMA-b-PHEMA) is described. PMMA-b-PHEMA was prepared by sequential visible light induced self-condensing vinyl polymerization (SCVP) and conventional vinyl polymerization. All of the synthesis and characterization details of the conjugates are reported. To accomplish tumor cell targeting property, initially cell-targeting (arginylglycylaspactic acid; RGD) and penetrating peptides (Cys-TAT) were binding to each other via the well-known EDC/NHS chemistry. Then, the resulting peptide was further incorporated to the surface of the amphiphilic hyperbranched copolymer via a coupling reaction between the thiol (-SH) group of the peptide and the hydroxyl group of copolymer by using N-(p-maleinimidophenyl) isocyanate as a heterolinker. The drug release property and targeting effect of the anticancer drug (doxorobucin; DOX) loaded nanostructures to two different cell lines were evaluated in vitro. U87 and MCF-7 were chosen as integrin αvβ3 receptor positive and negative cells for the comparison of the targeting efficiency, respectively. The data showed that drug-loaded copolymers exhibited enhanced cell inhibition toward U87 cells in compared to MCF-7 cells because targeting increased the cytotoxicity of drug-loaded copolymers against integrin αvβ3 receptor expressing tumor cells.

Supramolecular nanoassemblies of an amphiphilic porphyrin-cyclodextrin conjugate and their morphological transition from vesicle to network

An amphiphilic compound, 5-(4'-dodecyloxyphenyl)-10,15,20-tri(permethyl-β-CD)-modified Zn(II)-porphyrin (1; β-CD = β-cyclodextrin), was synthesized by means of the click reaction of an alkylated Zn-porphyrin derivative with 6-deoxy-6-azidopermethyl-β-CD. The complexation between 1 and tetrasodium tetraphenylporphyrintetrasulfonate (5) with different molar ratios led to the formation of two distinctly different nanoarchitectures, which were proven to be vesicle and network aggregates, respectively, by using dynamic light scattering, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. On the basis of the results of the time-dependent TEM studies, fluorescence, and NMR spectroscopic measurements, we have determined that the mechanism of the morphology transition from vesicles to networks is controlled by the stepwise complexation of 1 with 5. Furthermore, these supramolecular nanoarchitectures show the controlled- release property of doxorubicin as potential candidates for drug delivery.

Self-organization in water of well-defined amphiphilic poly(vinyl acetate)-b-poly(vinyl alcohol) diblock copolymers

Self-organization of well-defined poly(vinyl acetate)-b-poly(vinyl alcohol) (PVAc-b-PVA) amphiphilic diblock copolymers with different hydrophilic block sizes was reported.

Double pH-responsive supramolecular copolymer micelles based on the complementary multiple hydrogen bonds of nucleobases and acetalated dextran for drug delivery

The formation and destabilization of supramolecular micelles based on hydrogen bonding between nucleobases and acetalated dextran.