Conformation-Directed Micelle-to-Vesicle Transition of Cholesterol-Decorated Polypeptide Triggered by Oxidation

Programmable Morphology Evolution of Rod-Coil-Rod Block Copolymer Assemblies Induced by Variation of Chain Ordering

Morphology transition of block copolymer assemblies in response to external stimuli has attracted considerable attention. However, our knowledge about the mechanism of such a transition is still limited, especially for rod-coil block copolymers. Here, we report a programmable morphology evolution of assemblies induced by variation of chain ordering for rod-coil-rod triblock copolymers. A sequence of morphology transition from ellipsoids to disks, bowls, and vesicles is observed by increasing the solution temperature. At high temperatures, the mobility of the rod chain increases and the rigidity of the rod chain decreases. This gives rise to an ellipsoid-to-vesicle morphology transition. Dissipative particle dynamics theoretical simulations were performed to reveal the mechanism of this morphology transition process. It was found that the increase of rod chain mobility and the decrease of rod chain rigidity induce a decrease of chain ordering of rod blocks as temperature increases, which results in an ellipsoid-to-vesicle morphology transition. The gained information can guide the construction of nanoassemblies based on the rod-coil block copolymers.

Transition of Conformation and Solubility in β-Sheet-Structured Poly(l-cysteine)s with Methylthio or Sulfonium Pendants

Poly(l-cysteine)s with methylthio pendants (PMTLCs) were synthesized by ring-opening polymerization of a new l-cysteine-based N-carboxyanhydride. The thioether bonds of PMTLC can be readily oxidized by H₂O₂ yielding water-soluble PMTLC^OX. The methylthio groups can undergo an alkylation reaction using methyl iodide and a subsequent ion-exchange reaction yielding sulfonium-based polypeptides (PPLC-DMS-X, where X = I, BF₄). PPLC-DMS-X showed upper critical solution temperature-type thermo- and oxidation-responsive properties in aqueous solutions. Both PMTLC and PPLC-DMS-X showed oxidation-induced β-sheet to α-helix transitions. The absorbance of PPLC-DMS-I and methyl orange aqueous solution displayed a significant linear correlation with temperature, which makes the sulfonium-based polypeptides good candidates in the field of temperature sensors.

Structure and Oxidation Effects on Conformation and Thermoresponsiveness of the OEGylated Poly(glutamic acid)-Bearing Side-Chain Thioether Linkers

A series of side-chain thioether-linked OEGylated poly(glutamic acid) (PGAs) have been synthesized by "thiol-ene" synthetic methodology, where both the oligo-ethylene glycol (OEG) length and the hydrophobic linkers at the side chains are varied to learn how these structural features affect the secondary structure and thermoresponsive behaviors in water. Before side-chain oxidation, the structural factors affecting the α-helicity include the backbone length, the OEG length, and the hydrophobic linkers' length at the side chains; however, the OEG length plays the most crucial role among these factors because longer OEG around the peripheral side chains can stop water penetration into the backbone to disturb the intramolecular H bonds, which finally allows stabilizing the α-helix; after the oxidation, the polypeptides show increased α-helicity because of the enhanced hydrophilicity. More interestingly, a rare oxidation-induced conformation transition from the ordered β-sheet to the ordered α-helix can be achieved. In addition, only the OEGylated poly(glutamic acids) (PGAs) with shorter hydrophobic linkers and longer OEG can display the thermoresponsive properties before the oxidation but the subsequent oxidation can cause the polypeptides bearing longer hydrophobic linkers to exhibit the thermosensitivity since sulfone formation at the side chain can lead to final hydrophilicity-hydrophobicity balance. This work is meaningful to understand the secondary structure-associated solution behaviors of the synthetic polypeptides.

Reaction-induced phase transitions with block copolymers in solution and bulk

Reaction-induced phase transitions use chemical reactions to drive macromolecular organisation and self-assembly. This review highlights significant and recent advancements in this burgeoning field.

Tumor Microenvironment-Responsive Peptide-Based Supramolecular Drug Delivery System

Physical and biochemical differences between tumor tissues and normal tissues provide promising triggering factors that can be utilized to engineer stimuli-responsive drug delivery platforms for cancer treatment. Rationally designed peptide-based supramolecular architectures can perform structural conversion by responding to the tumor microenvironment and achieve the controlled release of antitumor drugs. This mini review summarizes recent approaches for designing internal trigger-responsive drug delivery platforms using peptide-based materials. Peptide assemblies that exhibit a stimuli-responsive structural conversion upon acidic pH, high temperature, high oxidative potential, and the overexpressed proteins in tumor tissues are emphatically introduced. We also discuss the challenges of current peptide-based supramolecular delivery platforms against cancer.

Self-Assembled Vesicles Formed by Positional Isomers of Sodium Dodecyl Benzene Sulfonate-Based Pseudogemini Surfactants

The construction of pseudogemini surfactants based on noncovalent interactions (such as electrostatic interaction and π-π stacking) was a powerful method to assemble well-defined aggregates in aqueous solution. The mixtures of butane-1,4-bis(methylimidazolium bromide) ([mim-C₄-mim]Br₂) and positional isomers of sodium dodecyl benzene sulfonate (SDBS-0,11 or SDBS-3,8) in a molar ratio of 1:2 were studied to characterize the effect of straight and branched alkyl chains on the aggregation behavior of pseudogemini surfactants. Spontaneous phase transition from micelles to vesicles was formed by these two kinds of complexes. Interestingly, a densely stacked onion-like structure (multilamellar vesicles) with more than one dozen layers was fabricated. The micelle and vesicle phases were characterized in detail by cryogenic transmission electron microscopy, polarized optical microscopy, dynamic light scattering, and rheological measurements. It can be clearly demonstrated that the structure of alkyl chain can significantly influence the surface adsorption, solution self-assembly, and aqueous two-phase system of pseudogemini surfactants. Our work provided a convenient technique to achieve controlled self-assembly by introducing positional isomers of surfactants.

pH-Responsive hyperbranched polypeptides based on Schiff bases as drug carriers for reducing toxicity of chemotherapy

Polymeric micelles have great potential in drug delivery systems because of their multifunctional adjustability, excellent stability, and biocompatibility. To further increase the drug loading efficiency and controlled release ability, a pH-responsive hyperbranched copolymer methoxy poly(ethylene glycol)-b-polyethyleneimine-poly(Nε-Cbz-l-lysine) (MPEG-PEI-PBLL) was synthesized successfully. MPEG-PEI-NH2 was synthesized to initiate the ring-opening polymerization of benzyloxycarbonyl substituted lysine N-carboxyanhydride (Z-lys NCA). The introduction of Schiff bases in the polymer make it possible to respond to the variation of pH values, which cleaved at pH 5.0 while stable at pH 7.4. As the polymer was amphiphilic, MPEG-PEI-PBLL could self-assemble into micelles. Owing to the introduction of PEI, which make the copolymer hyperbranched, the pH-responsive micelles could efficiently encapsulate theranostic agents, such as doxorubicin (DOX) for chemotherapy and NIRF dye DiD for in vivo near-infrared (NIR) imaging. The drug delivery system prolonged the drug circulation time in blood and allowed the drug accumulate effectively at the tumor site. Following the guidance, the DOX was applied in chemotherapy to achieve cancer therapeutic efficiency. All the results demonstrate that the polymer micelles have great potential for cancer theranostics.

Crosslinking Induced Reassembly of Multiblock Polymers: Addressing the Dilemma of Stability and Responsivity

Physical or chemical crosslinking of polymeric micelles has emerged as a straightforward approach to overcome the intrinsic instability of assemblies. However, the crosslinking process may compromise the responsivity of nanosystems and result in inefficient release of payloads. To address this dilemma, a crosslinking induced reassembly (CIRA) strategy is reported here to simultaneously increase the kinetic and thermodynamic stability and redox-responsivity of polymeric micelles. It is found that the click crosslinking of a model multiblock polyurethane at the micellar interface induces microphase separation between the soft and hard segments. The aggregation of hard domains gathers liable disulfide linkages around the interlayer of micelles, which could facilitate the attack of reducing agents and act as an intelligent on-off switch for high stability and triggered release. As a result, the CIRA approach enables an enhanced tumor targeting, improved biodistribution and excellent therapeutic efficacy in vivo. This work provides a facile and versatile platform for controlled delivery applications.

Synthesis of Stable Cholesteryl-Polyethylene Glycol-Peptide Conjugates with Non-Disperse Polyethylene Glycol Lengths

A method for conjugating cholesterol to peptide ligands through non-disperse polyethylene glycol (ND-PEG) through a non-hydrolysable linkage is described. The iterative addition of tetraethylene glycol macrocyclic sulfate to cholesterol (Chol) renders a family of highly pure well-defined Chol-PEG compounds with different PEG lengths from 4 up to 20 ethylene oxide units, stably linked through an ether bond. The conjugation of these Chol-PEG compounds to the cyclic (RGDfK) peptide though Lys5 side chains generates different lengths of Chol-PEG-RGD conjugates that retain the oligomer purity of the precursors, as analysis by HRMS and NMR has shown. Other derivatives were synthesized with similar results, such as Chol-PEG-OCH3 and Chol-PEG conjugated to glutathione and Tf1 peptides through maleimide-thiol chemoselective ligation. This method allows the systematic synthesis of highly pure uniform stable Chol-PEGs, circumventing the use of activation groups on each elongation step and thus reducing the number of synthesis steps.

Stimuli-responsive nanocarriers for drug delivery, tumor imaging, therapy and theranostics

In recent years, much progress has been motivated in stimuli-responsive nanocarriers, which could response to the intrinsic physicochemical and pathological factors in diseased regions to increase the specificity of drug delivery. Currently, numerous nanocarriers have been engineered with physicochemical changes in responding to external stimuli, such as ultrasound, thermal, light and magnetic field, as well as internal stimuli, including pH, redox potential, hypoxia and enzyme, etc. Nanocarriers could respond to stimuli in tumor microenvironments or inside cancer cells for on-demanded drug delivery and accumulation, controlled drug release, activation of bioactive compounds, probes and targeting ligands, as well as size, charge and conformation conversion, etc., leading to sensing and signaling, overcoming multidrug resistance, accurate diagnosis and precision therapy. This review has summarized the general strategies of developing stimuli-responsive nanocarriers and recent advances, presented their applications in drug delivery, tumor imaging, therapy and theranostics, illustrated the progress of clinical translation and made prospects.

A Novel pH-Tunable Secondary Conformation Containing Mixed Micellar System in Anticancer Treatment

In this study, for the first time, we precisely assembled the poly-γ-benzyl-l-glutamate and an amphiphilic copolymer d-α-tocopherol polyethylene glycol succinate into a mixed micellar system for the embedment of the anticancer drug doxorubicin. Importantly, the intracellular drug-releasing behaviors could be controlled by changing the secondary structures of poly-γ-benzyl-l-glutamate via the precise regulation of the buffer’s pH value. Under neutral conditions, the micellar architectures were stabilized by both α-helix secondary structures and the microcrystalline structures. Under acidic conditions (pH 4.0), the interior structures transformed into a coil state with a disordered alignment, inducing the release of the loaded drug. A remarkable cytotoxicity of the Dox-loaded mixed micelles was exhibited toward human lung cancer cells in vitro. The internalizing capability into the cancer cells, as well as the intracellular drug-releasing behaviors, were also identified and observed. The secondary structures containing Dox-loaded mixed micelles had an outstanding antitumor efficacy in human lung cancer A549 cells-bearing nude mice, while little toxicities occurred or interfered with the hepatic or renal functions after the treatments. Thus, these pH-tunable α-helix-containing mixed micelles are innovative and promising for controlled intracellular anticancer drug delivery.

Temperature-Directed Micellar Morphological Transformation Using CABC-Block Copolymers and Its Applications in Encapsulation and Hidden Segment

A temperature-directed micellar morphological transformation was developed using CABC multi-block copolymers with a hydrophobic block A, a hydrophilic block B, and a thermally responsive block C with a lower critical solution temperature (LCST). The micellar structure was switched from a star (below LCST) to a flower (above LCST). The transition temperature was tunable in a wide range (11-90 °C) by varying the C monomer composition. The large difference in the loading capacity between the star and flower enabled efficient encapsulation and controlled release of external molecules. Unlike conventional systems, the present star-to-flower transformation keeps micellar structures and hence does not liberate polymers but only external molecules selectively. Another application is a hidden functional segment. A functional segment is hidden (shielded) below the LCST and exposed to interact with external molecules or surfaces above the LCST.

Ring opening polymerization of α-amino acids: advances in synthesis, architecture and applications of polypeptides and their hybrids

This review provides a comprehensive overview of the latest advances in the synthesis, architectural design and biomedical applications of polypeptides and their hybrids.

Manipulating the helix–coil transition profile of synthetic polypeptides by leveraging side-chain molecular interactions

Based on the pH-sensitive, conformationally tunable triazole polypeptides, we reported the manipulation of helix–coil transition profile determined by the leveraging interactions of the triazole and other side-chain helix-influencing ligands.

Multivalency-assisted membrane-penetrating siRNA delivery sensitizes photothermal ablation via inhibition of tumor glycolysis metabolism

The success of photothermal therapy (PTT) is often hampered by the thermo-resistance of tumor cells mediated by over-expressed heat shock proteins (HSPs). Herein, we developed a guanidine-rich, spherical helical polypeptide (DPP) with multivalency-assisted strong membrane penetrating capability, which mediated effective RNAi against tumor glycolysis metabolism to sensitize PTT. ICG was loaded into the internal cavity of DPP, and siRNA against pyruvate kinase M2 (siPKM2) was condensed by DPP to form positively charged nanocomplexes (NCs). The NCs were further coated with human serum albumin to enhance serum stability, prolong blood circulation, and improve tumor targeting. Due to its multivalent topology, DPP exhibited stronger membrane activity yet lower cytotoxicity than its linear analogue (LPP), thus enabling efficient PKM2 silencing in MCF-7 cells in vitro (~75%) and in vivo (~70%). The PKM2 silencing inhibited tumor glycolysis metabolism and further depleted the energy supply for HSPs production, thus overcoming the heat endurance of tumor cells to strengthen ICG-mediated photothermal ablation. Additionally, siPKM2-mediated energy depletion led to tumor cell starvation, which imparted synergistic anti-cancer effect with PTT. This study therefore provides a promising strategy for designing membrane-penetrating siRNA delivery materials, and it renders a unique RNAi-mediated anti-metabolic mechanism in sensitizing PTT and enabling starvation therapy.

Moebius strips of chiral block copolymers

The Moebius topology (twisted, single-sided strip) is intriguing because of its structural elegance and distinct properties. Here we report the generation of block copolymer Moebius strips via a fast self-assembly of chiral block copolymer polystyrene-block-poly(D-lactide acid) (PS-b-PDLA) in tetrahydrofuran/water mixed solvents. The Moebius strip is formed by morphological evolution from large compound micelle (LCM) to spindle-like micelle (SLM) and then to toroid with a 180° twist along the ring. Mechanism insight reveals that a subtle balance of crystallization of PDLA and microphase separation between PS and PDLA chains dominates the formation of Moebius strips. An intriguing helix-helix transition occurs during the chiral transfer from microphase to assemblies, which is driven by relaxation of the internal stress within SLM related to orientated stretching of PS chains. Mesoporous chiral channels can be generated within Moebius strips after removal of PDLA, which are interesting in chiral recognition, separation and asymmetric catalysis.

Substrate-Assisted Visualization of Surfactant Micelles via Transmission Electron Microscopy

The visualization of the micellar morphological evolution for surfactant has drawn much attention due to its self-assemble ability to fold into various structures. However, the direct observation of the soft materials with low atomic number has been hampered because of the poor scattering contrast and complex staining process by the traditional transmission electron microscopy (TEM) techniques. Herein, we reported a novel strategy to the visualization of surfactant micelles with the assistance of layered double hydroxides (LDHs) via TEM. Owing to the uniformly distributed metal ions and positive charges in the LDHs, the surfactant at the micelle-water interface reacted with LDHs to form a stabilized architecture through electrostatic and hydrogen-bond interactions. The morphologies of the surfactant can be clearly observed through the surfactant-LDHs architectures, exhibiting high contrast by TEM techniques. Significantly, the micellar evolutions involving the spherical, rodlike, and wormlike shapes were successfully distinguished. Our results may provide great possibilities and inspirations for the visualization for morphology of soft matters.

Interfacial rheological behaviors of amphiphilic sodium cholesteryl glycylglycine

The present study was conducted to investigate the effects of the strong van der Waals interaction and sterol skeleton of surfactants on their interfacial rheological behaviors by comparing the interfacial properties of sodium cholesteryl glycylglycine (Chol-GG-Na) and sodium lauryl glycylglycine (C12-GG-Na) at the oil-aqueous interface. The interfacial dilational rheological experiment results indicate a significant increase in the interfacial activity and intermolecular interaction with the introduction of the cholesteryl group. Therefore, a compact interfacial layer with a remarkably high dilational modulus was obtained with the adsorption of Chol-GG-Na. The cholesteryl group also has a significant impact on the dynamic processes such as it slows down the motion of the molecules due to which the diffusion exchange between the bulk and the interface decreases. Besides, the rigid skeleton makes rearrangement and conformation adjustment difficult. These impacts become more pronounced when the adsorption layer approaches a close and ordered arrangement, which has been confirmed by the relaxation measurements. The reported results provide a theoretical foundation for the potential applications of cholesteryl-based surfactants in the food, pharmaceutical, cosmetic and petroleum industries.

Synthesis of water soluble and multi-responsive selenopolypeptides via ring-opening polymerization of N-carboxyanhydrides

Synthesis of selenopolypeptides via ring opening polymerization of N-carboxyanhydrides.

Cholesterol-Based Compounds: Recent Advances in Synthesis and Applications

This review reports on the latest developments (since 2014) in the chemistry of cholesterol and its applications in different research fields. These applications range from drug delivery or bioimaging applications to cholesterol-based liquid crystals and gelators. A brief overview of the most recent synthetic procedures to obtain new cholesterol derivatives is also provided, as well as the latest anticancer, antimicrobial, and antioxidant new cholesterol-based derivatives. This review discusses not only the synthetic details of the preparation of new cholesterol derivatives or conjugates, but also gives a short summary concerning the specific application of such compounds.