Ionic polypeptides with unusual helical stability

Synthetic multi-layer nanoparticles for CRISPR-Cas9 genome editing

The clustered regularly interspaced short palindromic repeat (CRISPR) has great potential to revolutionize biomedical research and disease therapy. The specific and efficient genome editing strongly depends on high efficiency of delivery of the CRISPR payloads. However, optimization of CRISPR delivery vehicles still remains a major obstacle. Recently, various non-viral vectors have been utilized to deliver CRISPR tools. Many of these vectors have multi-layer structures assembled. In this review, we will introduce the development of CRISPR-Cas9 systems and their general therapeutic applications by summarizing current CRISPR-Cas9 based clinical trials. We will highlight the multi-layer nanoparticles (NPs) that have been developed to deliver CRISPR cargos in vitro and in vivo for various purposes, as well the potential building blocks of multi-layer NPs. We will also discuss the challenges in making the CRISPR tools into viable pharmaceutical products and provide potential solutions on efficiency and biosafety issues.

Rational designs of in vivo CRISPR-Cas delivery systems

The CRISPR-Cas system initiated a revolution in genome editing when it was, for the first time, demonstrated success in the mammalian cells. Today, scientists are able to readily edit genomes, regulate gene transcription, engineer posttranscriptional events, and image nucleic acids using CRISPR-Cas-based tools. However, to efficiently transport CRISPR-Cas into target tissues/cells remains challenging due to many extra- and intra-cellular barriers, therefore largely limiting the applications of CRISPR-based therapeutics in vivo. In this review, we summarize the features of plasmid-, RNA- and ribonucleoprotein (RNP)-based CRISPR-Cas therapeutics. Then, we survey the current in vivo delivery systems. We specify the requirements for efficient in vivo delivery in clinical settings, and highlight both efficiency and safety for different CRISPR-Cas tools.

"Metaphilic" Cell-Penetrating Polypeptide-Vancomycin Conjugate Efficiently Eradicates Intracellular Bacteria via a Dual Mechanism

Infections by intracellular pathogens are difficult to treat because of the poor accessibility of antibiotics to the pathogens encased by host cell membranes. As such, a strategy that can improve the membrane permeability of antibiotics would significantly increase their efficiency against the intracellular pathogens. Here, we report the design of an adaptive, metaphilic cell-penetrating polypeptide (CPP)-antibiotic conjugate (VPP-G) that can effectively eradicate the intracellular bacteria both in vitro and in vivo. VPP-G was synthesized by attaching vancomycin to a highly membrane-penetrative guanidinium-functionalized metaphilic CPP. VPP-G effectively kills not only extracellular but also far more challenging intracellular pathogens, such as S. aureus, methicillin-resistant S. aureus, and vancomycin-resistant Enterococci. VPP-G enters the host cell via a unique metaphilic membrane penetration mechanism and kills intracellular bacteria through disruption of both cell wall biosynthesis and membrane integrity. This dual antimicrobial mechanism of VPP-G prevents bacteria from developing drug resistance and could also potentially kill dormant intracellular bacteria. VPP-G effectively eradicates MRSA in vivo, significantly outperforming vancomycin, which represents one of the most effective intracellular antibacterial agents reported so far. This strategy can be easily adapted to develop other conjugates against different intracellular pathogens by attaching different antibiotics to these highly membrane-penetrative metaphilic CPPs.

Peptides as a material platform for gene delivery: Emerging concepts and converging technologies

Successful gene therapies rely on methods that safely introduce DNA into target cells and enable subsequent expression of proteins. To that end, peptides are an attractive materials platform for DNA delivery, facilitating condensation into nanoparticles, delivery into cells, and subcellular release to enable protein expression. Peptides are programmable materials that can be designed to address biocompatibility, stability, and subcellular barriers that limit efficiency of non-viral gene delivery systems. This review focuses on fundamental structure-function relationships regarding peptide design and their impact on nanoparticle physical properties, biologic activity, and biocompatibility. Recent peptide technologies utilize multi-dimensional structures, non-natural chemistries, and combinations of peptides with lipids to achieve desired properties and efficient transfection. Advances in DNA cargo design are also presented to highlight further opportunities for peptide-based gene delivery. Modern DNA designs enable prolonged expression compared to traditional plasmids, providing an additional component that can be synergized with peptide carriers for improved transfection. Peptide transfection systems are poised to become a flexible and efficient platform incorporating new chemistries, functionalities, and improved DNA cargos to usher in a new era of gene therapy.

Synthetic Polypeptide Polymers as Simplified Analogues of Antimicrobial Peptides

Antimicrobial peptides (AMPs) are naturally occurring macromolecules made of amino acids that are potent broad-spectrum antibiotics with potential as novel therapeutic agents. This review aims to summarize the fundamental principles concerning the structure and mechanism of action of these AMPs, in order to guide the design of polymeric analogues that organic chemistry can generate. Among those simplified analogues, this review particularly focuses on those made of amino acids called polypeptide polymers: they are showing great potential by providing one of the best biomimetic and bioactive structures for further biomaterials science applications.

Effect of pH and Molecular Length on the Structure and Dynamics of Linear and Short-Chain Branched Poly(ethylene imine) in Dilute Solution: Scaling Laws from Detailed Molecular Dynamics Simulations

Atomistic molecular dynamics (MD) simulations are carried out to examine the effect of molecular weight M_w (= 0.6, 0.86, 1.12, and 2.15 kDa) and pH (or equivalently, degree of ionization, α⁺ = 0, 50, and 100%) on the structure, state of hydration, and dynamics of linear and branched poly(ethylene imine) (PEI) chains in infinitely dilute salt-free aqueous solutions. It is found that the degree of ionization is the key factor determining the type of molecular conformation adopted by PEI, regardless of molecular architecture and chain length, resulting in a stable trans conformation for fully ionized solutions and in a stable gauche⁺/gauche^- state for neutral or alternate ionized ones; in the latter case, a strong electrolyte behavior is verified for both linear and branched PEI. Linear PEI is observed to be significantly stiffer than branched PEI of the same molecular weight at 100% degree of ionization, but the effect subsides as the degree of ionization decreases. Also, linear PEI diffuses markedly slower than branched PEI of the same M_w. From the MD results, scaling exponents are deduced and reported for the conformation, solvent-accessible surface area, and dynamics of the two different PEI structures with M_w.

Monitoring the Hierarchical Evolution from a Double-Stranded Helix to a Well-Defined Microscopic Morphology Based on a Turbine-like Aromatic Molecule

1H-Indazolo[1,2-b]phthalazine-5,10-dione IPDD with an approximate turbine-like spatial structure, primary assembled double-stranded helices at the first level, was predicted by quantum chemical calculations and confirmed by atomic force microscopy. The higher-dimensional hierarchical architectures including fibrils, helical fibers, spherical shells, and porous prismatic structures were observed in sequence by the scanning electron microscopy technique. The final porous prismatic structures sensitive to NH₃ vapors have the potential to be applied in gas sensing and absorbing materials.

Amphiphilic Nucleobase-Containing Polypeptide Copolymers-Synthesis and Self-Assembly

Nucleobase-containing polymers are an emerging class of building blocks for the self-assembly of nanoobjects with promising applications in nanomedicine and biology. Here we present a macromolecular engineering approach to design nucleobase-containing polypeptide polymers incorporating thymine that further self-assemble in nanomaterials. Diblock and triblock copolypeptide polymers were prepared using sequential ring-opening polymerization of γ-Benzyl-l-glutamate N-carboxyanhydride (BLG-NCA) and γ-Propargyl-l-glutamate N-carboxyanhydride (PLG-NCA), followed by an efficient copper(I)-catalyzed azide alkyne cycloaddition (CuAAc) functionalization with thymidine monophosphate. Resulting amphiphilic copolymers were able to spontaneously form nanoobjects in aqueous solutions avoiding a pre-solubilization step with an organic solvent. Upon self-assembly, light scattering measurements and transmission electron microscopy (TEM) revealed the impact of the architecture (diblock versus triblock) on the morphology of the resulted nanoassemblies. Interestingly, the nucleobase-containing nanoobjects displayed free thymine units in the shell that were found available for further DNA-binding.

Helical polymers for biological and medical applications

Helices are the most prevalent secondary structure in biomolecules and play vital roles in their activity. Chemists have been fascinated with mimicking this molecular conformation with synthetic materials. Research has now been devoted to the synthesis and characterization of helical materials, and to understand the design principles behind this molecular architecture. In parallel, work has been done to develop synthetic polymers for biological and medical applications. We now have access to materials with controlled size, molecular conformation, multivalency or functionality. As a result, synthetic polymers are being investigated in areas such as drug and gene delivery, tissue engineering, imaging and sensing, or as polymer therapeutics. Here, we provide a critical view of where these two fields, helical polymers and polymers for biological and medical applications, overlap. We have selected relevant polymer families and examples to illustrate the range of applications that can be targeted and the impact of the helical conformation on the performance. For each family of polymers, we briefly describe how they can be prepared, what helical conformations are observed and what parameters control helicity. We close this Review with an outlook of the challenges ahead, including the characterization of helicity through the process and the identification of biocompatibility.

Synthetic macromolecules as therapeutics that overcome resistance in cancer and microbial infection

Synthetic macromolecular antimicrobials have shown efficacy in the treatment of multidrug resistant (MDR) pathogens. These synthetic macromolecules, inspired by Nature's antimicrobial peptides (AMPs), mitigate resistance by disrupting microbial cell membrane or targeting multiple intracellular proteins or genes. Unlike AMPs, these polymers are less prone to degradation by proteases and are easier to synthesize on a large scale. Recently, various studies have revealed that cancer cell membrane, like that of microbes, is negatively charged, and AMPs can be used as anticancer agents. Nevertheless, efforts in developing polymers as anticancer agents has remained limited. This review highlights the recent advancement in the development of synthetic biodegradable antimicrobial polymers (e.g. polycarbonates, polyesters and polypeptides) and anticancer macromolecules including peptides and polymers. Additionally, strategies to improve their in vivo bioavailability and selectivity towards bacteria and cancer cells are examined. Lastly, future perspectives, including use of artificial intelligence or machine learning, in the development of antimicrobial and anticancer macromolecules are discussed.

Copolymacrolactones Grafted with l-Glutamic Acid: Synthesis, Structure, and Nanocarrier Properties

The enzymatic ring-opening copolymerization (eROP) of globalide (Gl) and pentadecalactone (PDL) was performed in solution from mixtures of the two macrolactones at ratios covering the whole range of comonomeric compositions. The resulting P(Glx-r-PDLy) random copolyesters were aminofunctionalized by thiol-ene reaction with aminoethanethiol. ROP of γ-benzyl-l-glutamate N-carboxyanhydride initiated by P(Glx-r-PDLy)-NH2 provided neutral poly(γ-benzyl-l-glutamate)-grafted copolyesters, which were converted by hydrolysis into negatively charged hybrid copolymers. Both water-soluble and nonsoluble copolymers were produced depending on copolymer charge and their grafting degree, and their capacity for self-assembling in nano-objects were comparatively examined. The emulsion solvent-evaporation technique applied to the chloroform-soluble copolymers grafted with benzyl glutamate rendered well-delineated spherical nanoparticles with an average diameter of 200-300 nm. Conversely, micellar solutions in water were produced from copolyesters bearing grafted chains composed of at least 10 units of glutamic acid in the free form. The copolymer micelles were shown to be able to load doxorubicin (DOX) efficiently through electrostatic interactions and also to release the drug at a rate that was markedly pH dependent.

Tumor microenvironment-induced structure changing drug/gene delivery system for overcoming delivery-associated challenges

Nano-drug/gene delivery systems (DDS) are powerful weapons for the targeted delivery of various therapeutic molecules in treatment of tumors. Nano systems are being extensively investigated for drug and gene delivery applications because of their exceptional ability to protect the payload from degradation in vivo, prolong circulation of the nanoparticles (NPs), realize controlled release of the contents, reduce side effects, and enhance targeted delivery among others. However, the specific properties required for a DDS vary at different phase of the complex delivery process, and these requirements are often conflicting, including the surface charge, particle size, and stability of DDS, which severely reduces the efficiency of the drug/gene delivery. Therefore, researchers have attempted to fabricate structure, size, or charge changeable DDS by introducing various tumor microenvironment (TME) stimuli-responsive elements into the DDS to meet the varying requirements at different phases of the delivery process, thus improving drug/gene delivery efficiency. This paper summarizes the most recent developments in TME stimuli-responsive DDS and addresses the aforementioned challenges.

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.

Synthesis of modifiable photo-responsive polypeptides bearing allyloxyazobenzene side-chains

A photo-responsive and modifiable polypeptide with stable helical conformation was synthesized. The self-assembly and liquid crystalline phase structure were subsequently studied.

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.

Selective Regulation of Neurons, Glial Cells, and Neural Stem/Precursor Cells by Poly(allylguanidine)-Coated Surfaces

Poly(allylguanidine) (PAG) was synthesized and characterized as a polycationic coating material for culturing neurons, glial cells, and neural stem/precursor cells (NSPCs) to apply PAG for neural tissue engineering. For comparison, poly-d-lysine (PDL), the golden benchmark of the neuron cell culture system, was also used in this study. When PAG was subjected to a mixed culture of neurons and glial cells, cell adhesion and neurite extension of neuronal cells were clearly observed but only few glial cells could be found alongside the neurons. Compared to PDL, the significantly lower density of the glial fibrillary acidic protein-positive cells implied that PAG suppressed the glial cell development. Likewise, PAG was demonstrated to dominate the differentiation of NSPCs principally into neurons. To investigate whether the different effects of PAG and PDL on neuron and glial cell behaviors resulted from the difference of guanidinium cations and ammonium cations, poly-l-arginine (PLA) was included and compared in this study. Similar to PDL, PLA supported high neuron and glial cell viability simultaneously. Consequently, glial cell growth and viability restrained on PAG was not only affected by the side-chain guanidino groups but also by the backbone structure property. The absence of the peptide structure in the backbone of PAG and the conformation of coated PAG on tissue culture polystyrene possibly determined the polycationic biomaterial to limit the growth of glial cells.

Electrostatically Driven Encapsulation of Hydrophilic, Non-Conformational Peptide Epitopes into Liposomes

Since the first use of liposomes as carriers for antigens, much work has been done to elucidate the mechanisms involved in the encapsulation of vaccine-relevant biomolecules. However, only a few studies have specifically investigated the encapsulation of hydrophilic, non-conformational peptide epitopes. We performed comprehensive and systematic screening studies, in order to identify conditions that favor the electrostatic interaction of such peptides with lipid membranes. Moreover, we have explored bi-terminal sequence extension as an approach to modify the isoelectric point of peptides, in order to modulate their membrane binding behavior and eventually shift/expand the working range under which they can be efficiently encapsulated in an electrostatically driven manner. The findings of our membrane interaction studies were then applied to preparing peptide-loaded liposomes. Our results show that the magnitude of membrane binding observed in our exploratory in situ setup translates to corresponding levels of encapsulation efficiency in both of the two most commonly employed methods for the preparation of liposomes, i.e., thin-film hydration and microfluidic mixing. We believe that the methods and findings described in the present studies will be of use to a wide audience and can be applied to address the ongoing relevant issue of the efficient encapsulation of hydrophilic biomolecules.

Recent advances in polymeric materials for the delivery of RNA therapeutics

Introduction: The delivery of nucleic acid therapeutics through non-viral carriers face multiple biological barriers that reduce their therapeutic efficiency. Despite great progress, there remains a significant technological gap that continues to limit clinical translation of these nanocarriers. A number of polymeric materials are being exploited to efficiently deliver nucleic acids and achieve therapeutic effects. Areas covered: We discuss the recent advances in the polymeric materials for the delivery of nucleic acid therapeutics. We examine the use of common polymer architectures and highlight the challenges that exist for their development from bench side to clinic. We also provide an overview of the most notable improvements made to circumvent such challenges, including structural modification and stimuli-responsive approaches, for safe and effective nucleic acid delivery. Expert opinion: It has become apparent that a universal carrier that follows 'one-size' fits all model cannot be expected for delivery of all nucleic acid therapeutics. Carriers need to be designed to exhibit sensitivity and specificity toward individual targets diseases/indications, and relevant subcellular compartments, each of which possess their own unique challenges. The ability to devise synthetic methods that control the molecular architecture enables the future development that allow for the construction of 'intelligent' designs.

Therapeutic Protein PEPylation: The Helix of Nonfouling Synthetic Polypeptides Minimizes Antidrug Antibody Generation

Polymer conjugation is a clinically proven approach to generate long acting protein drugs with decreased immune responses. Although poly(ethylene glycol) (PEG) is one of the most commonly used conjugation partners due to its unstructured conformation, its therapeutic application is limited by its poor biodegradability, propensity to induce an anti-PEG immune response, and the resultant accelerated blood clearance (ABC) effect. Moreover, the prevailing preference of unstructured polymers for protein conjugation still lacks strong animal data support with appropriate control reagents. By using two biodegradable synthetic polypeptides with similar structural compositions (l-P(EG₃Glu) and dl-P(EG₃Glu)) for site-specific protein modification, in the current study, we systematically investigate the effect of the polymer conformation on the in vivo pharmacological performances of the resulting conjugates. Our results reveal that the conjugate l_20K-IFN, interferon (IFN) modified with the helical polypeptide l-P(EG₃Glu) shows improved binding affinity, in vitro antiproliferative activity, and in vivo efficacy compared to those modified with the unstructured polypeptide analogue dl-P(EG₃Glu) or PEG. Moreover, l_20K-IFN triggered significantly less antidrug and antipolymer antibodies than the other two. Importantly, the unusual findings observed in the IFN series are reproduced in a human growth hormone (GH) conjugate series. Subcutaneously infused l_20K-GH, GH modified with l-P(EG₃Glu), evokes considerably less anti-GH and antipolymer antibodies compared to those modified with dl-P(EG₃Glu) or PEG (dl_20K-GH or PEG_20K-GH). As a result, repeated injections of dl_20K-GH or PEG_20K-GH, but not l_20K-GH, result in a clear ABC effect and significantly diminished drug availability in the blood. Meanwhile, immature mouse bone marrow cells incubated with the helical l_20K-GH exhibit decreased drug uptake and secretion of proinflammatory cytokines compared to those treated with one of the other two GH conjugates bearing unstructured polymers. Taken together, the current study highlights an urgent necessity to systematically reassess the pros and cons of choosing unstructured polymers for protein conjugation. Furthermore, our results also lay the foundation for the development of next-generation biohybrid drugs based on helical synthetic polypeptides.

Melamine-mediated supramolecular assembly of nucleobase-modified poly(l-lysine)

Melamine (M) was used to drive the supramolecular assembly of thymine (T)-modified poly(l-lysine) into fibers or spherical micelles through simply adjusting the substitution degree of T and the concentration of M.

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.

Nanoparticle-Based Delivery of CRISPR/Cas9 Genome-Editing Therapeutics

The recent progress in harnessing the efficient and precise method of DNA editing provided by CRISPR/Cas9 is one of the most promising major advances in the field of gene therapy. However, the development of safe and optimally efficient delivery systems for CRISPR/Cas9 elements capable of achieving specific targeting of gene therapy to the location of interest without off-target effects is a primary challenge for clinical therapeutics. Nanoparticles (NPs) provide a promising means to meet such challenges. In this review, we present the most recent advances in developing innovative NP-based delivery systems that efficiently deliver CRISPR/Cas9 constructs and maximize their effectiveness.

Hypoxia-responsive block copolymer radiosensitizers as anticancer drug nanocarriers for enhanced chemoradiotherapy of bulky solid tumors

Radiosensitizers play an important role in the clinical radiotherapy of hypoxic solid tumors to improve therapeutic efficacy. However, the in vivo performance of clinically used small-molecule radiosensitizers is commonly compromised by low bioavailability in hypoxic tumor regions. Herein, amphiphilic block copolymer radiosensitizers are prepared from clinically approved poly(ethylene glycol)-block-poly(l-glutamic acid) (PEG-b-PLG) and metronidazole (MN) to obtain MN-grafted PEG-b-PLG (PEG-b-P(LG-g-MN)) via condensation reaction, which can self-assemble into core-shell micelles as nanoparticle-formulated radiosensitizers in aqueous solution. The radiosensitizers are demonstrated to possess significantly higher sensitization enhancement ratio (SER) of 2.18 and potent in vivo tumor ablation capability upon exposure to electron beam irradiation compared with clinically used sodium glycididazole (GS) with SER of 1.32. Moreover, after optimizing the ratios of carboxyl and MN groups, PEG-b-P(LG-g-MN) micelles can be used to encapsulate doxorubicin (DOX@HMs) efficiently. Hypoxia-responsive structural transformation of MN into hydrophilic aminoimidazole triggers fast DOX release from DOX@HMs. After intravenous injection of DOX@HMs, potent ablation capability against bulky solid tumors (∼500 mm³) is realized at a low radiation dose (4 Gy) via enhanced chemoradiotherapy. Therefore, the developed novel amphiphilic block copolymer radiosensitizers can be concurrently used as high-efficiency radiosensitizers and hypoxia-responsive DOX nanocarriers for enhanced chemoradiotherapy.

Stimuli-Responsive Polypeptides for Biomedical Applications

Stimuli-responsive polypeptides have gained attention because desirable bioactive properties can be easily imparted to them while keeping their biocompatibility and biodegradability intact. In this review, we summarize the most recent advances in various stimuli-responsive polypeptides (pH, reduction, oxidation, glucose, adenosine triphosphate (ATP), and enzyme) over the past five years. Various synthetic strategies exploited for advanced polypeptide-based materials are introduced, and their applicability in biomedical fields is discussed. The recent polypeptides imparted with new stimuli-responsiveness and their novel chemical and physical properties are explained in this review.

A polypeptide based podophyllotoxin conjugate for the treatment of multi drug resistant breast cancer with enhanced efficiency and minimal toxicity

Podophyllotoxin (PPT) is a chemotherapeutic agent which has shown significant activity against P-glycoprotein (P-gp) mediated multi drug resistant cancer cells. However, because of the poor aqueous solubility and high toxicity, PPT cannot be used in clinical cancer therapy. In order to enhance the efficiency and reduce side effect of PPT, a polypeptide based PPT conjugate PLG-g-mPEG-PPT was developed and used for the treatment of multi drug resistant breast cancer. The PLG-g-mPEG-PPT was prepared by conjugating PPT to poly(l-glutamic acid)-g-methoxy poly(ethylene glycol) (PLG-g-mPEG) via ester bonds. The PPT conjugates self-assembled into nanoparticles with average sizes about 100 nm in aqueous solution. Western blotting assay showed that the PLG-g-mPEG-PPT could effectively inhibit the expression of P-gp in the multiple drug resistant MCF-7/ADR cells. In vitro cytotoxicity assay indicated that the resistance index (RI) values of PLG-g-mPEG-PPT on different drug-resistant cancer cell lines exhibited 57-270 folds reduction than of traditional microtubule inhibitor chemotherapeutic drug PTX or DTX. Hemolysis assay demonstrated that the conjugation greatly decreased the hemolytic activity of free PPT. Maximum tolerated dose (MTD) of PLG-g-mPEG-PPT increased greatly (13.3 folds) as compared to that of free PPT. In vivo study showed that the PLG-g-mPEG-PPT conjugate remarkably enhanced the antitumor efficacy against MCF-7/ADR xenograft tumors with a tumor suppression rate (TSR) of 82.5%, displayed significantly improved anticancer efficacy as compared to free PPT (TSR = 37.1%) with minimal toxicity when both of the two formulations were used in MTD.

STATEMENT OF SIGNIFICANCE

The development of multiple drug resistance (MDR) of cancer cells is the main cause of chemotherapy failure. The over-expression of P-glycoprotein (P-gp) has been recognized to be the most important cause of MDR in cancer. Podophyllotoxin (PPT) is a chemotherapeutic agent which has shown strong activity against P-gp mediated multidrug resistant cancer cells by simultaneously inhibiting the over-expression of P-gp and the growth of cancer cells. However, PPT can not be used in clinical cancer treatment due to its poor aqueous solubility and high toxicity. Herein, we developed a polypeptide based PPT conjugate PLG-g-mPEG-PPT by conjugating PPT to poly(l-glutamic acid)-g-methoxy poly(ethylene glycol). The PLG-g-mPEG-PPT shows significantly decreased hemolytic activity, greatly improved maximum tolerated dose and remarkably enhanced antitumor efficacy against MCF-7/ADR xenograft tumors as compared to free PPT.

Investigation on the Linker Length of Synthetic Zwitterionic Polypeptides for Improved Nonfouling Surfaces

Zwitterionic polymers are outstanding nonfouling materials widely used for surface modification. However, works that systematically evaluate the structure-activity relationship of the side chain linker effect with related antifouling abilities are sparse. Here, we generate a series of well-defined zwitterionic polypeptides bearing oligoethylene glycol (EG) linkers in the side chain (P(CB-EG _xGlu), x = 1-3) and anchor them on gold surfaces via the grafting-to approach to compare their antifouling performances. The surface properties are characterized by X-ray photoelectron spectroscopy (XPS), circular dichroism spectroscopy (CD), variable angle spectroscopic ellipsometry (VASE), static water contact angle (SCA), and atomic force microscopy (AFM). By use of quartz crystal microbalance with dissipation (QCM-D), confocal microscopy, and scanning electron microscope, our results convincingly demonstrate the excellent antifouling performance of all zwitterionic polypeptides. Importantly, the surface coated with P(CB-EG₃Glu), the one with the longest EG linker, exhibits the best resistance to single protein (below the detection limit of QCM) and blood serum (∼96-98% reduction) adsorption, which largely outperforms those of the PEG positive control and the two P(CB-EG _xGlu) analogues with shorter EG _x linkers. The same P(CB-EG₃Glu) surface also gives the highest degree of prevention of cell/platelet/bacterial attachment (∼99% reduction) among all samples tested. Together, our study highlights the linker effect to the nonfouling performance of zwitterionic polypeptides, and the results strongly support P(CB-EG₃Glu) as a robust nonfouling material for numerous applications.

Nonviral gene editing via CRISPR/Cas9 delivery by membrane-disruptive and endosomolytic helical polypeptide

Effective and safe delivery of the CRISPR/Cas9 gene-editing elements remains a challenge. Here we report the development of PEGylated nanoparticles (named P-HNPs) based on the cationic α-helical polypeptide poly(γ-4-((2-(piperidin-1-yl)ethyl)aminomethyl)benzyl-l-glutamate) for the delivery of Cas9 expression plasmid and sgRNA to various cell types and gene-editing scenarios. The cell-penetrating α-helical polypeptide enhanced cellular uptake and promoted escape of pCas9 and/or sgRNA from the endosome and transport into the nucleus. The colloidally stable P-HNPs achieved a Cas9 transfection efficiency up to 60% and sgRNA uptake efficiency of 67.4%, representing an improvement over existing polycation-based gene delivery systems. After performing single or multiplex gene editing with an efficiency up to 47.3% in vitro, we demonstrated that P-HNPs delivering Cas9 plasmid/sgRNA targeting the polo-like kinase 1 (Plk1) gene achieved 35% gene deletion in HeLa tumor tissue to reduce the Plk1 protein level by 66.7%, thereby suppressing the tumor growth by >71% and prolonging the animal survival rate to 60% within 60 days. Capable of delivering Cas9 plasmids to various cell types to achieve multiplex gene knock-out, gene knock-in, and gene activation in vitro and in vivo, the P-HNP system offers a versatile gene-editing platform for biological research and therapeutic applications.

Non-viral gene delivery systems for tissue repair and regeneration

Critical tissue defects frequently result from trauma, burns, chronic wounds and/or surgery. The ideal treatment for such tissue loss is autografting, but donor sites are often limited. Tissue engineering (TE) is an inspiring alternative for tissue repair and regeneration (TRR). One of the current state-of-the-art methods for TRR is gene therapy. Non-viral gene delivery systems (nVGDS) have great potential for TE and have several advantages over viral delivery including lower immunogenicity and toxicity, better cell specificity, better modifiability, and higher productivity. However, there is no ideal nVGDS for TRR, hence, there is widespread research to improve their properties. This review introduces the basic principles and key aspects of commonly-used nVGDSs. We focus on recent advances in their applications, current challenges, and future directions.

Secondary structures of synthetic polypeptide polymers

Synthetic peptide-based polymers can fold into different secondary structures in the same way as do proteins. This review article presents how tuning the polypeptide secondary structure could be a key step to modulate various properties in advanced polymeric materials (size, rigidity, self-assembly,etc.).

Self-assembly of Filamentous Cell Penetrating Peptides for Gene Delivery

Cell penetrating peptides (CPPs) have been proven to be an effective vector to deliver a variety of membrane-impermeable macromolecules, such as DNAs, siRNAs, and proteins. Conventional single-chain CPPs typically suffer from severe protease degradation and fast clearance rate for in vivo therapeutic delivery application. In this chapter, we show that supramolecular assembly of de novo designed cationic multidomain peptides (MDPs) leads to nanostructured filaments with increased proteolytic stability and potent membrane activity necessary for improved transfection efficiency.

Secondary structures in synthetic polypeptides from N-carboxyanhydrides: design, modulation, association, and material applications

This article highlights the conformation-specific properties and functions of synthetic polypeptides derived from N-carboxyanhydrides.

Zwitterionic polypeptides bearing carboxybetaine and sulfobetaine: synthesis, self-assembly, and their interactions with proteins

Zwitterionic polypeptides bearing carboxybetaine and sulfobetaine were synthesized and their self-assembly and protein interactions were evaluated.

Cd2+ coordination: an efficient structuring switch for polypeptide polymers

Stimuli-responsive polypeptides have practical applications in devices and therapeutic delivery. Here we report that coordination to Cd²⁺ metal species can be used as a robust stimulus to control both, α-helix and β-sheet secondary structuring of polypeptide polymers.

Cell-Penetrating Peptides: Design Strategies beyond Primary Structure and Amphipathicity

Efficient intracellular drug delivery and target specificity are often hampered by the presence of biological barriers. Thus, compounds that efficiently cross cell membranes are the key to improving the therapeutic value and on-target specificity of non-permeable drugs. The discovery of cell-penetrating peptides (CPPs) and the early design approaches through mimicking the natural penetration domains used by viruses have led to greater efficiency of intracellular delivery. Following these nature-inspired examples, a number of rationally designed CPPs has been developed. In this review, a variety of CPP designs will be described, including linear and flexible, positively charged and often amphipathic CPPs, and more rigid versions comprising cyclic, stapled, or dimeric and/or multivalent, self-assembled peptides or peptido-mimetics. The application of distinct design strategies to known physico-chemical properties of CPPs offers the opportunity to improve their penetration efficiency and/or internalization kinetics. This led to increased design complexity of new CPPs that does not always result in greater CPP activity. Therefore, the transition of CPPs to a clinical setting remains a challenge also due to the concomitant involvement of various internalization routes and heterogeneity of cells used in the in vitro studies.