Thermal gating in lipid membranes using thermoresponsive cyclic peptide-polymer conjugates

Supramolecular Assembly and Thermogelation Strategies Using Peptide-Polymer Conjugates

Peptide-polymer conjugates (PPCs) are of particular interest in the development of responsive, adaptive, and interactive materials due to the benefits offered by combining both building blocks and components. This review presents pioneering work as well as recent advances in the design of peptide-polymer conjugates, with a specific focus on their thermoresponsive behavior. This unique class of materials has shown great promise in the development of supramolecular structures with physicochemical properties that are modulated using soft and biorthogonal external stimuli. The temperature-induced self-assembly of PPCs into various supramolecular architectures, gelation processes, and tuning of accessible processing parameters to biologically relevant temperature windows are described. The discussion covers the chemical design of the conjugates, the supramolecular driving forces involved, and the mutual influence of the polymer and peptide segments. Additionally, some selected examples for potential biomedical applications of thermoresponsive PPCs in tissue engineering, delivery systems, tumor therapy, and biosensing are highlighted, as well as perspectives on future challenges.

Neutron reflection and scattering in characterising peptide assemblies

Self-assemblies of de novo designed short peptides at interface and in bulk solution provide potential platforms for developing applications in many medical and technological areas. However, characterising how bioinspired supramolecular nanostructures evolve with dynamic self-assembling processes and respond to different stimuli remains challenging. Neutron scattering technologies including small angle neutron scattering (SANS) and neutron reflection (NR) can be advantageous and complementary to other state-of-the-art techniques in tracing structural changes under different conditions. With more neutron sources now available, SANS and NR are becoming increasingly popular in studying self-assembling processes of diverse peptide and protein systems, but the difficulty in experimental manipulation and data analysis can deter beginners. This review will introduce the basic theory, general experimental setup and data analysis of SANS and NR, followed by provision of their applications in characterising interfacial and solution self-assemblies of representative peptides and proteins. SANS and NR are remarkably effective in determining the morphological features self-assembled short peptides, especially size and shape transitions as a result of either sequence changes or in response to environmental stimuli, demonstrating the unique capability of NR and SANS in unravelling the interactive processes. These examples highlight the potential of NR and SANS in supporting the development of novel short peptides and proteins as biopharmaceutical candidates in the fight against many diseases and infections that share common features of membrane interactive processes.

Phase transition and potential biomedical applications of thermoresponsive compositions based on polysaccharides, proteins and DNA: A review

Smart thermoresponsive polymers have long attracted attention as materials of a great potential for biomedical applications, mainly for drug delivery, tissue engineering and wound dressing, with a special interest to injectable hydrogels. Poly-N-isopropylacrylamide (PNIPAM) is the most important synthetic thermoresponsive polymer due to its physiologically relevant transition temperature. However, the use of unmodified PNIPAM encounters such problems as low biodegradability, low drug loading capacity, slow response to thermal stimuli, and insufficient mechanical robustness. The use of natural polysaccharides and proteins in combinations with PNIPAM, in the form of grafted copolymers, IPNs, microgels and physical mixtures, is aimed at overcoming these drawbacks and creating dual-functional materials with both synthetic and natural polymers' properties. When developing such compositions, special attention should be paid to preserving their key property, thermoresponsiveness. Addition of hydrophobic and hydrophilic fragments to PNIPAM is known to affect its transition temperature. This review covers various classes of natural polymers - polysaccharides, fibrous and non-fibrous proteins, DNA - used in combination with PNIPAM for the prospective biomedical purposes, with a focus on their phase transition temperatures and its relation to the natural polymer's structure.

Transmembrane Transporter Constructed from PlatinumMetal-organic Cage

A perylene diimide-based metal-organic cage (MOC4c) was found to be an efficient transmembrane transporter for ions and small molecules through the internal cavity of the cage. MOC4c could selectively transport different anions, as evidenced by vesicle-based fluorescenceassays and planar lipid bilayer-based current recordings.Furthermore, MOC4c appears tofacilitate calcein transport across the lipid bilayer membrane of a livingcell, suggesting that MOC4c could be used as a biologicaltool for small molecule drugstransmembrane transportation.

Sequence effect on the self-assembly of discrete amphiphilic co-oligomers with fluorene-azobenzene semirigid backbones

Sequences can have a dramatic impact on the unique properties and self-assembly in natural macromolecules, which has received increasing interest. Herein, we report a series of discrete amphiphilic co-oligomers with the same composition but different building blocks in a semirigid backbone. These sequence-defined oligomers possess two primary amine groups on the side chain of the azobenzene building block, and hence, they become amphipathic due to quaternization of the amine groups when protonated in acidic aqueous solution. These oligomer isomers assembled into different nanoparticles, including nanofibers, hollow vesicles and spherical micellar complexes, in a THF/water/HCl mixture under the same conditions. UV-vis absorption spectra, differential scanning calorimetry (DSC) and X-ray scattering (XRD) experiments combined with theoretical calculations reveal that the sequence-controlled co-oligomers induce different molecular packing conformations and arrangement modes of building blocks in self-assembly. Furthermore, these self-assembled nanoparticles demonstrate photoresponsive morphological transformation and fluorescence emission under UV light irradiation due to trans-to-cis photoisomerization of azobenzene. This work demonstrates that customizing functional nanoparticles can be achieved by controlling the sequence structure in synthetic co-oligomers.

Synthetic Monosaccharide Channels: Size-Selective Transmembrane Transport of Glucose and Fructose Mediated by Porphyrin Boxes

Here we report synthetic monosaccharide channels built with shape-persistent organic cages, porphyrin boxes (PBs), that allow facile transmembrane transport of glucose and fructose through their windows. PBs show a much higher transport rate for glucose and fructose over disaccharides such as sucrose, as evidenced by intravesicular enzyme assays and molecular dynamics simulations. The transport rate can be modulated by changing the length of the alkyl chains decorating the cage windows. Insertion of a linear pillar ligand into the cavity of PBs blocks the monosaccharide transport. In vitro cell experiment shows that PBs transport glucose across the living-cell membrane and enhance cell viability when the natural glucose transporter GLUT1 is blocked. Time-dependent live-cell imaging and MTT assays confirm the cyto-compatibility of PBs. The monosaccharide-selective transport ability of PBs is reminiscent of natural glucose transporters (GLUTs), which are crucial for numerous biological functions.

Facile synthesis of monocyclic, dumbbell-shaped and jellyfish-like copolymers using a telechelic multisite hexablock copolymer

A heterofunctional hexablock copolymer comprising alternating reactive and non-reactive blocks is designed to generate cyclic, dumbbell-shaped and jellyfish-like copolymers.

AIE Featured Supramolecular Tubisomes for Imaging-Guided Drug Delivery

Polymeric cylinders, a fascinating type of nanostructures with high surface area, internal volume and rigidity, have been exploited as novel drug delivery vehicles over the past decade. However, it's still an open challenge to afford cylindrical nanostructures using polymeric building blocks via traditional self-assembly processes. Herein, we report a hierarchical self-assembly strategy of preparing cylindrical aggregates (tubisomes) from an amphiphilic supramolecular bottlebrush polymer in which cyclic peptide nanotube is employed as the noncovalent backbone. Additionally, aggregation induced emission effect was introduced into the tubisomes to endow them with excellent fluorescent property. Intriguingly, encapsulation of anticancer drug doxorubicin (DOX) can inactivate the fluorescence of both tubisome and DOX due to the energy transfer relay (ETR). The release of DOX can interrupt the ETR effect and light up the silenced fluorescence, thereby permitting the in-situ visualization of drug release. The supramolecular tubisomes described here paves an alternative way for fabricating polymeric cylindrical nanostructures, and holds great potential in imaging-guided drug delivery.

Molecular Self-Assembly and Supramolecular Chemistry of Cyclic Peptides

This Review focuses on the establishment and development of self-assemblies governed by the supramolecular interactions between cyclic peptides. The Review first describes the type of cyclic peptides able to assemble into tubular structures to form supramolecular cyclic peptide nanotubes. A range of cyclic peptides have been identified to have such properties, including α-peptides, β-peptides, α,γ-peptides, and peptides based on δ- and ε-amino acids. The Review covers the design and functionalization of these cyclic peptides and expands to a recent advance in the design and application of these materials through their conjugation to polymer chains to generate cyclic peptide-polymer conjugates nanostructures. The Review, then, concentrates on the challenges in characterizing these systems and presents an overview of the various analytical and characterization techniques used to date. This overview concludes with a critical survey of the various applications of the nanomaterials obtained from supramolecular cyclic peptide nanotubes, with a focus on biological and medical applications, ranging from ion channels and membrane insertion to antibacterial materials, anticancer drug delivery, gene delivery, and antiviral applications.

Molecular Plumbing to Bend Self-Assembling Peptide Nanotubes

Light-induced molecular piping of cyclic peptide nanotubes to form bent tubular structures is described. The process is based on the [4+4] photocycloaddition of anthracene moieties, whose structural changes derived from the interdigitated flat disposition of precursors to the corresponding cycloadduct moieties, induced the geometrical modifications in nanotubes packing that provokes their curvature. For this purpose, we designed a new class of cyclic peptide nanotubes formed by β- and α-amino acids. The presence of the former predisposes the peptide to stack in a parallel fashion with the β-residues aligned along the nanotube and the homogeneous distribution of anthracene pendants.

Molecular engineering of antimicrobial peptide (AMP)-polymer conjugates

As antimicrobial resistance becomes an increasing threat, bringing significant economic and health burdens, innovative antimicrobial treatments are urgently needed. While antimicrobial peptides (AMPs) are promising therapeutics, exhibiting high activity against resistant bacterial strains, limited stability and toxicity to mammalian cells has hindered clinical development. Attaching AMPs to polymers provides opportunities to present AMPs in a way that maximizes bacterial killing while enhancing compatibility with mammalian cells, stability, and solubility. Conjugation of an AMP to a linear hydrophilic polymer yields the desired improvements in stability, mammalian cell compatibility, and solubility, yet often markedly reduces bactericidal effects. Non-linear polymer architectures and supramolecular assemblies that accommodate multiple AMPs per polymer chain afford AMP-polymer conjugates that strike a superior balance of antimicrobial activity, mammalian cell compatibility, stability, and solubility. Therefore, we review the design criteria, building blocks, and synthetic strategies for engineering AMP-polymer conjugates, emphasizing the connection between molecular architecture and antimicrobial performance to inspire and enable further innovation to advance this emerging class of biomaterials.

100th Anniversary of Macromolecular Science Viewpoint: User's Guide to Supramolecular Peptide-Polymer Conjugates

This Viewpoint highlights the design principles and development of peptide-based supramolecular polymers. Here we delve deep into the practicalities of synthesizing and characterizing these macromolecular structures and provide a thorough overview of the benefits and challenges that come with these systems. This Viewpoint emphasizes to beginners and experts alike the importance of understanding the fundamental behavior and self-assembly processes when designing these complex and dynamic functional materials.

Double Orthogonal Click Reactions for the Development of Antimicrobial Peptide Nanotubes

A new class of amphipathic cyclic peptides, which assemble in bacteria membranes to form polymeric supramolecular nanotubes giving them antimicrobial properties, is described. The method is based on the use of two orthogonal clickable transformations to incorporate different hydrophobic or hydrophilic moieties in a simple, regioselective, and divergent manner. The resulting cationic amphipathic cyclic peptides described in this article exhibit strong antimicrobial properties with a broad therapeutic window. Our studies suggest that the active form is the nanotube resulted from the parallel stacking of the cyclic peptide precursors. Several techniques, CD, FTIR, fluorescence, and STEM, among others, confirm the nanotube formation.

A reversible single-molecule ligand-gating ion transportation switch of ON–OFF–ON type through a photoresponsive pillar[6]arene channel complex

A reversible pseudo-single-ligand-gated ion transportation switch of ON–OFF–ON type was achieved through host–guest complexation with pillar[6]arene (P[6]) as the ion channel, and a photoresponsive azobenzene as the dual-role (open and close) ligand.

A reversible pseudo-single-ligand-gated ion transportation switch of ON–OFF–ON type through pillar[6]arene and photoresponsive azobenzene as dual-role ligand.

Comparative Study of the Cellular Uptake and Intracellular Behavior of a Library of Cyclic Peptide-Polymer Nanotubes with Different Self-Assembling Properties

Particle shape has been described as a key factor in improving cell internalization and biodistribution among the different properties investigated for drug-delivery systems. In particular, tubular structures have been identified as promising candidates for improving drug delivery. Here, we investigate the influence of different design elements of cyclic peptide–polymer nanotubes (CPNTs) on cellular uptake including the nature and length of the polymer and the cyclic peptide building block. By varying the composition of these cyclic peptide–polymer conjugates, a library of CPNTs of lengths varying from a few to over a 150 nm were synthesized and characterized using scattering techniques (small-angle neutron scattering and static light scattering). In vitro studies with fluorescently labeled CPNTs have shown that nanotubes comprised of a single polymer arm with a size between 8 and 16 nm were the most efficiently taken up by three different mammalian cell lines. A mechanistic study on multicellular tumor spheroids has confirmed the ability of these compounds to penetrate to their core. Variations in the proportion of paracellular and transcellular uptake with the self-assembling potential of the CPNT were also observed, giving key insights about the behavior of CPNTs in cellular systems.

Engineering of stimuli-responsive lipid-bilayer membranes using supramolecular systems

The membrane proteins found in nature control many important cellular functions, including signal transduction and transmembrane ion transport, and these, in turn, are regulated by external stimuli, such as small molecules, membrane potential and light. Membrane proteins also find technological applications in fields ranging from optogenetics to synthetic biology. Synthetic supramolecular analogues have emerged as a complementary method to engineer functional membranes. This Review describes stimuli-responsive supramolecular systems developed for the control of ion transport, signal transduction and catalysis in lipid-bilayer-membrane systems. Recent advances towards achieving spatio-temporal control over activity in artificial and living cells are highlighted. Current challenges, the scope, limitations and future potential to exploit supramolecular systems for engineering stimuli-responsive lipid-bilayer membranes are discussed.

Supramolecular polymer bottlebrushes

The field of supramolecular chemistry has long been known to generate complex materials of different sizes and shapes via the self-assembly of single or multiple low molar mass building blocks. Matching the complexity found in natural assemblies, however, remains a long-term challenge considering its precision in organizing large macromolecules into well-defined nanostructures. Nevertheless, the increasing understanding of supramolecular chemistry has paved the way to several attempts in arranging synthetic macromolecules into larger ordered structures based on non-covalent forces. This review is a first attempt to summarize the developments in this field, which focus mainly on the formation of one-dimensional, linear, cylindrical aggregates in solution with pendant polymer chains - therefore coined supramolecular polymer bottlebrushes in accordance with their covalent equivalents. Distinguishing by the different supramolecular driving forces, we first describe systems based on π-π interactions, which comprise, among others, the well-known perylene motif, but also the early attempts using cyclophanes. However, the majority of reported supramolecular polymer bottlebrushes are formed by hydrogen bonds as they can for example be found in linear and cyclic peptides, as well as so called sticker molecules containing multiple urea groups. Besides this overview on the reported motifs and their impact on the resulting morphology of the polymer nanostructures, we finally highlight the potential benefits of such non-covalent interactions and refer to promising future directions of this still mostly unrecognized field of supramolecular research.

Hierarchical Self-Assembled Photo-Responsive Tubisomes from a Cyclic Peptide-Bridged Amphiphilic Block Copolymer

Typically, the morphologies of the self-assembled nanostructures from block copolymers are limited to spherical micelles, wormlike micelles and vesicles. Now, a new generation of materials with unique shape and structures, cylindrical soft matter particles (tubisomes), are obtained from the hierarchical self-assembly of cyclic peptide-bridged amphiphilic diblock copolymers. The capacity of obtained photo-responsive tubisomes as potential drug carriers is evaluated. The supramolecular tubisomes pave an alternative way for fabricating polymeric tubular structures, and will expand the toolbox for the rational design of functional hierarchical nanostructures.

A guide to supramolecular polymerizations

Supramolecular polymers are non-covalent assemblies of unimeric building blocks connected by secondary interactions and hold great promises due to their dynamic nature.

Helically shaped cation receptor: design, synthesis, characterisation and first application to ion transport

An helicene-like receptor is able to transport K⁺ across lipid membrane.

Reversible Click Chemistry for Ultrafast and Quantitative Formation of Protein-Polymer Nanoassembly and Intracellular Protein Delivery

Construction of polymer-protein nanoassemblies is a challenge as reactions between macromolecules, especially those involving proteins, are inherently inefficient due to the sparse reactive functional groups and low concentration requirements. We address this challenge using an ultrafast and reversible click reaction, which forms the basis for a covalent self-assembly strategy between side-chain functionalized polymers and surface-modified proteins. The linkers in the assembly have been programmed to release the incarcerated proteins in its native form, only when subjected to the presence of a specific trigger. The generality and the versatility of the approach have been demonstrated by showing that this strategy can be used for proteins of different sizes and isoelectric points. Moreover, simple modifications in the linker chemistry offers the ability to trigger these assemblies with various chemical inputs. Efficient formation of nanoassemblies based on polymer-protein conjugates has implications in a variety of areas at the interface of chemistry with materials and biology, such as in the generation of active surfaces and in delivery of biologics. As a demonstration of utility in the latter, we have shown that these conjugates can be used to transport functional proteins across cellular membranes.

Stimuli-responsive membrane activity of cyclic-peptide-polymer conjugates

Cyclic peptide nanotubes (CPNT) consisting of an even number of amino acids with an alternating chirality are highly interesting materials in a biomedical context due to their ability to insert themselves into cellular membranes. However, unwanted unspecific interactions between CPNT and non-targeted cell membranes are a major drawback. To solve this issue we have synthetized a series of CPNT-polymer conjugates with a cleavable covalent connection between macromolecule and peptide. As a result, the polymers form a stabilizing and shielding shell around the nanotube that can be cleaved on demand to generate membrane active CPNT from non-active conjugates. This approach enables us to control the stacking and lateral aggregation of these materials, thus leading to stimuli responsive membrane activity. Moreover, upon activation, the systems can be adjusted to form nanotubes with an increased length instead of aggregates. We were able to study the dynamics of these systems in detail and prove the concept of stimuli responsive membrane interaction using CPNT-polymer conjugates to permeabilize liposomes as well as mammalian cell membranes.

Switchable length nanotubes from a self-assembling pH and thermosensitive linear l,d-peptide-polymer conjugate

Preparation and characterization of a pH and thermosensitive linear l,d-octapeptide-poly(dimethylamino ethyl methacrylate) ((l-Val-d-Val)₄-PDMAEMA) conjugate is reported. The hydrophobic uncharged linear (l-Val-d-Val)₄ octapeptide was designed to self-assemble in nanotubes by exploiting the tubular self-assembling properties of linear peptides with regularly alternating enantiomeric sequences. pH and thermosensitive PDMAEMA was obtained by atom transfer radical polymerization (ATRP). The conjugate was prepared by click-chemistry on the solid phase synthetized peptide. Because of the strong interactions between the peptide moieties, long single channel nanotubes (0.2-1.5 μm) are formed also at acidic pH with the fully charged polymer. At 25 °C and basic pH the size of the nanotubes did not change significantly. In basic conditions and temperature above the PDMAEMA lower critical solution temperature (LCST) a significant increase of the length of the nanotubes up to several micrometers is observed. The size is retained for several days after cooling back to room temperature. Sonication significantly reduces the nanotube length (0.2-0.5 μm) forming low polydisperse nanotubes. The elongation of the nanotubes is fully reversible by restoring acidic pH. This is the first example, to our knowledge, of thermosensitive peptide-polymer single channel nanotubes with length that can be varied from hundreds of nanometers to several micrometers.

A reversible ion transportation switch of ON–OFF–ON type by a ligand-gated calix[6]arene channel

Calix[6]arene (CX6) was found to be an efficient ion transmembrane channel, which could be blocked by methylene blue (MB) through host–guest interactions.

Supramolecular assembly of functional peptide–polymer conjugates

The following review gives an overview about synthetic peptide–polymer conjugates as macromolecular building blocks and their self-assembly into a variety of supramolecular architectures, from supramolecular polymer chains, to anisotropic 1D arrays, 2D layers, and more complex 3D networks.

New self-assembling peptide nanotubes of large diameter using δ-amino acids

Here we show that 4-aminocyclohexanecarboxylic acid is a rigid stretcher building block for the preparation of cyclic peptides that self-assemble to form peptide nanotubes with large diameter and hydrophobic pores. The hydrophobic properties of the resulting nanotubes provided by the two methylene groups per δ-residue allow the encapsulation of C60 moieties forming a new type of bionanopeapod structure.

Polynucleotide transport through lipid membrane in the presence of starburst cyclodextrin-based poly(ethylene glycol)s

Symmetrical cyclodextrin-based 14-arm star polymers with poly(ethylene glycol) PEG branches were synthesized and characterized. Interactions of the star polymers with lipid bilayers were studied by the "black lipid membrane" technique in order to demonstrate the formation of monomolecular artificial channels. The conditions for the insertion are mainly based on dimensions and amphiphilic properties of the star polymers, in particular the molar mass of the water-soluble polymer branches. Translocation of single-strand DNA (ssDNA) through those synthetic nanopores was investigated, and the close dimension between the cross-section of ssDNA and the cyclodextrin cavity led to an energy barrier that slowed down the translocation process.

Systematic study of the structural parameters affecting the self-assembly of cyclic peptide-poly(ethylene glycol) conjugates

Self-assembling cyclic peptides (CP) consisting of amino acids with alternating d- and l-chirality form nanotubes by hydrogen bonding, hydrophobic interactions, and π-π stacking in solution. These highly dynamic materials are emerging as promising supramolecular systems for a wide range of biomedical applications. Herein, we discuss how varying the polymer conformation (linear vs. brush), as well as the number of polymer arms per peptide unimer affects the self-assembly of PEGylated cyclic peptides in different solvents, using small angle neutron scattering. Using the derived information, strong correlations were drawn between the size of the aggregates, solvent polarity, and its ability to compete for hydrogen bonding interactions between the peptide unimers. Using these data, it could be possible to engineer cyclic peptide nanotubes of a controlled length.

Ring-Expansion/Contraction Radical Crossover Reactions of Cyclic Alkoxyamines: A Mechanism for Ring Expansion-Controlled Radical Polymerization

Macrocyclic polymers present an important class of macromolecules, displaying the reduced radius of gyration or impossibility to entangle. A rare approach for their synthesis is the ring expansion-controlled radical "vinyl" polymerization, starting from a cyclic alkoxyamine. We here describe ring-expansion radical crossover reactions of cyclic alkoxyamines which run in parallel to chain-propagation reactions in the polymerization system. The radical crossover reactions extensively occurred at 105⁻125 °C, eventually producing high molecular weight polymers with multiple inherent dynamic covalent bonds (NOC bonds). A subsequent ring-contraction radical crossover reaction and the second ring-expansion radical crossover reaction are also described. The major products for the respective three stages were shown to possess cyclic morphologies by the molecular weight profiles and the residual ratios for the NOC bonds (φ in %). In particular, the high φ values ranging from ca. 80% to 98% were achieved for this cyclic alkoxyamine system. This result verifies the high availability of this system as a tool demonstrating the ring-expansion "vinyl" polymerization that allows them to produce macrocyclic polymers via a one-step vinyl polymerization.

Supramolecular functional assemblies: dynamic membrane transporters and peptide nanotubular composites

The fabrication of functional molecular devices constitutes one of the most important current challenges for chemical sciences. The complex processes accomplished by living systems continuously demand the assistance of non-covalent interactions between molecular building blocks. Additionally, these building blocks (proteins, membranes, nucleotides) are also constituted by self-assembled structures. Therefore, supramolecular chemistry is the discipline required to understand the properties of the minimal self-assembled building blocks of living systems and to develop new functional smart materials. In the first part of this feature article, we highlight selected examples of the preparation of supramolecular membrane transporters with special emphasis on the application of dynamic covalent bonds. In the second section of the paper we review recent breakthroughs in the preparation of peptide nanotube hybrids with functional applications. The development of these devices constitutes an exciting process from where we can learn how to understand and manipulate supramolecular functional assemblies.

Cyclic peptide-poly(HPMA) nanotubes as drug delivery vectors: In vitro assessment, pharmacokinetics and biodistribution

Size and shape have progressively appeared as some of the key factors influencing the properties of nanosized drug delivery systems. In particular, elongated materials are thought to interact differently with cells and therefore may allow alterations of in vivo fate without changes in chemical composition. A challenge, however, remains the creation of stable self-assembled materials with anisotropic shape for delivery applications that still feature the ability to disassemble, avoiding organ accumulation and facilitating clearance from the system. In this context, we report on cyclic peptide-polymer conjugates that self-assemble into supramolecular nanotubes, as confirmed by SANS and SLS. Their behaviour ex and in vivo was studied: the nanostructures are non-toxic up to a concentration of 0.5 g L^-1 and cell uptake studies revealed that the pathway of entry was energy-dependent. Pharmacokinetic studies following intravenous injection of the peptide-polymer conjugates and a control polymer to rats showed that the larger size of the nanotubes formed by the conjugates reduced renal clearance and elongated systemic circulation. Importantly, the ability to slowly disassemble into small units allowed effective clearance of the conjugates and reduced organ accumulation, making these materials interesting candidates in the search for effective drug carriers.

Sensing, Transport and Other Potential Biomedical Applications of Pseudopeptides

Pseudopeptides are privileged synthetic molecules built from the designed combination of peptide-like and abiotic artificial moieties. Consequently, they are benefited from the advantages of both families of chemical structures: modular synthesis, chemical and functional diversity, tailored three-dimensional structure, usually high stability in biological media and low non-specific toxicity. Accordingly, in the last years, these compounds have been used for different biomedical applications, ranging from bio-sensing, ion transport, the molecular recognition of biologically relevant species, drug delivery or gene transfection. This review highlights a selection of the most remarkable and recent advances in this field.

Macrocyclization of Interferon-Poly(α-amino acid) Conjugates Significantly Improves the Tumor Retention, Penetration, and Antitumor Efficacy

Cyclization and polymer conjugation are two commonly used approaches for enhancing the pharmacological properties of protein drugs. However, cyclization of parental proteins often only affords a modest improvement in biochemical or cell-based in vitro assays. Moreover, very few studies have included a systematic pharmacological evaluation of cyclized protein-based therapeutics in live animals. On the other hand, polymer-conjugated proteins have longer circulation half-lives but usually show poor tumor penetration and suboptimal pharmacodynamics due to increased steric hindrance. We herein report the generation of a head-to-tail interferon-poly(α-amino acid) macrocycle conjugate circ-P(EG₃Glu)₂₀-IFN by combining the aforementioned two approaches. We then compared the antitumor pharmacological activity of this macrocycle conjugate against its linear counterparts, N-P(EG₃Glu)₂₀-IFN, C-IFN-P(EG₃Glu)₂₀, and C-IFN-PEG. Our results found circ-P(EG₃Glu)₂₀-IFN to show considerably greater stability, binding affinity, and in vitro antiproliferative activity toward OVCAR3 cells than the three linear conjugates. More importantly, circ-P(EG₃Glu)₂₀-IFN exhibited longer circulation half-life, remarkably higher tumor retention, and deeper tumor penetration in vivo. As a result, administration of the macrocyclic conjugate could effectively inhibit tumor progression and extend survival in mice bearing established xenograft human OVCAR3 or SKOV3 tumors without causing severe paraneoplastic syndromes. Taken together, our study provided until now the most relevant experimental evidence in strong support of the in vivo benefit of macrocyclization of protein-polymer conjugates and for its application in next-generation therapeutics.

Functional polymer materials affecting cell attachment

This review discusses the functional polymer materials effect on the cell adhesion. The applied polymer materials for the cell adhesion purpose was prepared based on organic fibers and biocompatible hydrogel. On the other hand, the active peptides are incorporated into the polymer materials substrate via the cysteine-containing peptides and N-hydroxysuccinimide-active group. Cancer cells and normal cells were presented for the selective adhesion via the introduced polymer materials substrate containing active peptides including Arginine-Glycine-Aspartic and Isoleucine-Lysine-Valine-Alanine-Valine sequence peptides. This selectivity is revealed by a significant cooperativity between specific and non-specific cell adhesion. This study is of a great impact for the design of the polymeric structures for cell attachment.

One-Pot Synthesis of Thermoresponsive Amyloidogenic Peptide-Polymer Conjugates via Thio-Bromo "Click" Reaction of RAFT Polymers

A synthetic strategy to efficiently prepare main-chain peptide-polymer conjugates probing their aggregation in solution is described. An in situ tandem reaction based on aminolysis/thio-bromo "click" reaction is performed to tether an amyloidogenic peptide fragment amyloid-β_17-20 (Leu-Val-Phe-Phe (LVFF)) to the ω-chain end of poly(diethylene glycol methyl ether acrylate) (PDEGA), prepared via reversible addition fragmentation chain transfer polymerization. Structural confirmation of the constructed conjugates PDEGA-LVFF (M_n,SEC = 5600, Ð = 1.21), (M_n,SEC = 7600, Ð = 1.16), and (M_n,SEC = 8900, Ð = 1.15) is successfully made by combined studies of ¹ H NMR, size-exclusion chromatography, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and electrospray ionization time-of-flight (ESI-TOF) mass spectrometry. The effect of the peptidic constituent on the thermoresponsive behavior of the polymer is examined by UV-vis spectroscopy, and the self-assembly behavior of the amphiphilic conjugate is further exploited, exhibiting micellar morphology in aqueous solution.