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

Nanourchin-like Uricase-Poly(L-proline) Conjugate with Retained Enzymatic Activity, Mitigated Immunogenicity, and Sustained Efficacy Upon Repeated Administrations

The poor half-life and strong immunogenicity of proteins such as uricase (UOx), a therapeutic enzyme for chronic refractory gout and hyperuricemia, are pressing clinical challenges. Although conjugation of poly(ethylene glycol) (PEGylation) of UOx can improve the pharmacokinetics, preexisting or induced anti-PEG antibodies, which lead to accelerate blood clearance (ABC) and reduced response rate, have been a major clinical hurdle. Herein, we report the facile "grafting-from" preparation of a nanourchin-like uricase-poly(L-proline) conjugate, namely UOx-PLP, with high grafting-density, enhanced thermal, lyophilization, freeze-thaw, and proteolytic stability. Through a transient preblocking strategy in the synthesis, the UOx-PLP overcomes activity loss and retains ~82 % enzyme activity. In Sprague-Dawley rats, UOx-PLP stimulates minimum complement activation and anti-UOx antibodies. Unlike PEG-UOx gave a significantly reduced half-life after repetitive administrations, UOx-PLP shows no sign of ABC effect. Moreover, the half-life of UOx-PLP remain almost unchanged when cross-administrated to rats previously received PEG-UOx and with high titers of anti-UOx antibodies. Finally, UOx-PLP shows minimum loss of efficacy after five straight administrations in a UOx knock-out hyperuricemia mice model, whereas PEG-UOx experiences sharp loss of efficacy upon the same treatment. Overall, the simple preparation and outstanding nonclinical results highlight the enormous potential of UOx-PLP for future clinical translation.

Open-vessel polymerization of N-carboxyanhydride (NCA) for polypeptide synthesis

Synthetic polypeptides, also known as poly(α-amino acids), have the same polyamide backbone structures as natural proteins and peptides. As an important class of biomaterials, polypeptides have been widely used because of their biocompatibility, bioactivity and biodegradability. Ring-opening polymerization of N-carboxyanhydride (NCA) is a classical and widely used method for the synthesis of polypeptides. The dominantly used primary amine-initiated NCA polymerization can yield well-defined polymers and complex macromolecular architectures, but the reaction is slow and sensitive to moisture, making it necessary to use anhydrous solvents and a glovebox. One solution is to use lithium hexamethyldisilazide (LiHMDS) as the initiator, as described in this protocol. LiHMDS-initiated NCA polymerization is less sensitive to moisture and can be carried out in an open vessel outside the glovebox. It is also very fast; the reaction can be complete within 5 min to produce 30-mer polypeptides. In this protocol, poly(γ-benzyl-L-glutamate) is prepared as an example, but the protocol can easily be adapted to the synthesis of other polypeptides by generating NCAs from different amino acids, making it particularly suitable for the efficient parallel synthesis of polypeptide libraries. We provide detailed procedures for NCA synthesis and purification, the method of polymer end-group modification and measurement of polymerization kinetics and reactivity ratio. The procedure for synthesis of monomers and polymerization to form polypeptides requires <1 d. The superfast and open-vessel NCA polymerization method described here will probably enable a wide range of applications in the synthesis and functional study of polypeptide biomaterials.

Application of Sortase-Mediated Ligation for the Synthesis of Block Copolymers and Protein-Polymer Conjugates

Sortase-mediated ligation (SML) has become a powerful tool for site-specific protein modification. However, sortase A (SrtA) suffers from low catalytic efficiency and mediates an equilibrium reaction. Therefore, ligations with large macromolecules may be challenging. Here, the synthesis of polymeric building blocks for sortase-mediated ligation constituting peptide-polymers with either the recognition sequence for sortase A (LPX1TGX2) or its nucleophilic counterpart (Gx) is demonstrated. The peptide-polymers are synthesized by solid-phase peptide synthesis followed by photo-iniferter (PI) reversible addition-fragmentation chain-transfer (RAFT) polymerization of various monomers. The building blocks are subsequently utilized to investigate possibilities and limitations when using macromolecules in SML. In particular, diblock copolymers are obtained even when using the orthogonal building blocks in equimolar ratio by exploiting a technique to shift the reaction equilibrium. However, ligations of two polymers can not be achieved when the degree of polymerization exceeds 100. Subsequently, C-terminal protein-polymer conjugates are synthesized. Several polymers are utilized that can replace the omnipresent polyethylene glycol (PEG) in future therapeutics. The conjugation is exemplified with a nanobody that is known for efficient neutralization of SARS-CoV-2. The study demonstrates a universal approach to polymer-LPX1TGX2 and Gx-polymer building blocks and gives insight into their application in SML.

Engineering interferons for cancer immunotherapy

Interferons are a family of cytokines that are famously known for their involvement in innate and adaptive immunity. Type I interferons (IFNs) exert pleiotropic effects on various immune cells and contribute to tumor-intrinsic and extrinsic mechanisms. Their pleiotropic effects and ubiquitous expression on nucleated cells have made them attractive candidates for cytokine engineering to deliver to largely immunosuppressive tumors. Type III interferons were believed to play overlapping roles with type I IFNs because they share a similar signaling pathway and induce similar transcriptional programs. However, type III IFNs are unique in their cell specific receptor expression and their antitumor activity is specific to a narrow range of cell types. Thus, type III IFN based therapies may show reduced toxic side effects compared with type I IFN based treatment. In this review, we focus on the development of IFN-based therapeutics used to treat different tumors. We highlight how the development in cytokine engineering has allowed for efficient delivery of type I and type III IFNs to tumor sites and look ahead to the obstacles that are still associated with IFN-based therapies before they can be fully and safely integrated into clinical settings.

Probing the Topological Effects on Stability Enhancement and Therapeutic Performance of Protein Bioconjugates: Tadpole, Macrocycle versus Figure-of-Eight

Chemical topology provides a unique dimension for making therapeutic protein bioconjugates with native structure and intact function, yet the effects of topology remain elusive. Herein, the design, synthesis, and characterization of therapeutic protein bioconjugates in three topologies (i.e., tadpole, macrocycle, and figure-of-eight), are reported. The interferon α2b (IFN) and albumin binding domain (ABD) are selected as the model proteins for bioconjugation and proof-of-concept. The biosynthesis of these topological isoforms is accomplished via direct expression in cells using SpyTag-SpyCatcher chemistry and/or split-intein-mediated ligation for topology diversification. The corresponding topologies are proven with combined techniques of LC-MS, SDS-PAGE, and controlled proteolytic digestion. While the properties of these topological isoforms are similar in most cases, the figure-of-eight-shaped bioconjugate, f8-IFN-ABD, exhibits the best thermal stability and anti-aggregation properties along with prolonged half-life and enhanced tumor retention relative to the tadpole-shaped control, tadp-IFN-ABD, and the macrocyclic control, c-IFN-ABD, showcasing considerable topological effects. The work expands the topological diversity of proteins and demonstrates the potential advantages of leveraging chemical topology for functional benefits beyond multi-function integration in protein therapeutics.

Organ/Cell-Selective Intracellular Delivery of Biologics via N-Acetylated Galactosamine-Functionalized Polydisulfide Conjugates

Biologics, including proteins and antisense oligonucleotides (ASOs), face significant challenges when it comes to achieving intracellular delivery within specific organs or cells through systemic administrations. In this study, we present a novel approach for delivering proteins and ASOs to liver cells, both in vitro and in vivo, using conjugates that tether N-acetylated galactosamine (GalNAc)-functionalized, cell-penetrating polydisulfides (PDSs). The method involves the thiol-bearing cargo-mediated ring-opening polymerization of GalNAc-functionalized lipoamide monomers through the so-called aggregation-induced polymerization, leading to the formation of site-specific protein/ASO-PDS conjugates with narrow dispersity. The hepatocyte-selective intracellular delivery of the conjugates arises from a combination of factors, including first GalNAc binding with ASGPR receptors on liver cells, leading to cell immobilization, and the subsequent thiol-disulfide exchange occurring on the cell surface, promoting internalization. Our findings emphasize the critical role of the close proximity of the PDS backbone to the cell surface, as it governs the success of thiol-disulfide exchange and, consequently, cell penetration. These conjugates hold tremendous potential in overcoming the various biological barriers encountered during systemic and cell-specific delivery of biomacromolecular cargos, opening up new avenues for the diagnosis and treatment of a range of liver-targeting diseases.

On the origin of the low immunogenicity and biosafety of a neutral α-helical polypeptide as an alternative to polyethylene glycol

Poly(ethylene glycol) (PEG) is a prominent synthetic polymer widely used in biomedicine. Despite its notable success, recent clinical evidence highlights concerns regarding the immunogenicity and adverse effects associated with PEG in PEGylated proteins and lipid nanoparticles. Previous studies have found a neutral helical polypeptide poly(γ-(2-(2-(2-methoxyethoxy)ethoxy)ethyl l-glutamate), namely L-P(EG3Glu), as a potential alternative to PEG, displaying lower immunogenicity. To comprehensively assess the immunogenicity, distribution, degradation, and biosafety of L-P(EG3Glu), herein, we employ assays including enzyme-linked immunosorbent assay, positron emission tomography-computed tomography, and fluorescent resonance energy transfer. Our investigations involve in vivo immune responses, biodistribution, and macrophage activation of interferon (IFN) conjugates tethered with helical L-P(EG3Glu) (L20k-IFN), random-coiled DL-P(EG3Glu) (DL20k-IFN), and PEG (PEG20k-IFN). Key findings encompass: minimal anti-IFN and anti-polymer antibodies elicited by L20k-IFN; length-dependent affinity of PEG to anti-PEG antibodies; accelerated clearance of DL20k-IFN and PEG20k-IFN linked to anti-IFN and anti-polymer IgG; complement activation for DL20k-IFN and PEG20k-IFN but not L20k-IFN; differential clearance with L20k-IFN kidney-based, and DL20k-IFN/PEG20k-IFN accumulation mainly in liver/spleen; enhanced macrophage activation by DL20k-IFN and PEG20k-IFN; L-P(EG3Glu) resistance to proteolysis; and safer repeated administrations of L-P(EG3Glu) in rats. Overall, this study offers comprehensive insights into the lower immunogenicity of L-P(EG3Glu) compared to DL-P(EG3Glu) and PEG, supporting its potential clinical use in protein conjugation and nanomedicines.

Nanovaccine Based on a Biepitope Antigen to Potentiate the Immunogenicity of a Neoantigen

Specific neoantigens are promising candidates for personalized cancer vaccines and immunotherapies, whereas the low immunogenicity and physicochemical variability are the main challenges in clinical trials. Herein, based on the rational design of neoantigens, we developed biepitope nanovaccines via integrating CD4⁺ with CD8⁺ T cell epitopes. A class of amphiphilic peptides composed of biepitope and hydrophilic amino acids can form well-defined nanostructures, thus incorporating functional sequences into an artificial platform. Cellular uptake studies demonstrated the enhanced endocytosis of biepitope neoantigens in dendritic cells (DCs). Such designed biepitopes can further stimulate the maturation of DCs, as validated by the upregulation of costimulatory molecules and secreted proinflammatory cytokines, which show the potential ability to prime T cells and evoke specific cellular immunity. The inspiring prophylactic and therapeutic efficacy of biepitope nanovaccines was evaluated in murine colon cancer. In contrast to individual CD8⁺ T cell epitopes, the rationally designed biepitope nanovaccines can efficiently provoke immune activation and potentiate antitumor immunity both in vitro and in vivo, presenting an alternative strategy for neoantigen vaccines.

An immunomodulatory polypeptide hydrogel for osteochondral defect repair

Osteochondral injury is a common and frequent orthopedic disease that can lead to more serious degenerative joint disease. Tissue engineering is a promising modality for osteochondral repair, but the implanted scaffolds are often immunogenic and can induce unwanted foreign body reaction (FBR). Here, we prepare a polypept(o)ide-based PAA-RGD hydrogel using a novel thiol/thioester dual-functionalized hyperbranched polypeptide P(EG₃Glu-co-Cys) and maleimide-functionalized polysarcosine under biologically benign conditions. The PAA-RGD hydrogel shows suitable biodegradability, excellent biocompatibility, and low immunogenicity, which together lead to optimal performance for osteochondral repair in New Zealand white rabbits even at the early stage of implantation. Further in vitro and in vivo mechanistic studies corroborate the immunomodulatory role of the PAA-RGD hydrogel, which induces minimum FBR responses and a high level of polarization of macrophages into the immunosuppressive M2 subtypes. These findings demonstrate the promising potential of the PAA-RGD hydrogel for osteochondral regeneration and highlight the importance of immunomodulation. The results may inspire the development of PAA-based materials for not only osteochondral defect repair but also various other tissue engineering and bio-implantation applications.

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A polypept(o)ide-based hydrogel.

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Prominent and early osteochondral repair.

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Minimized immunogenicity.

Chemical Approaches to Synthetic Drug Delivery Systems for Systemic Applications

Poor water solubility and low bioavailability of active pharmaceutical ingredients (APIs) are major causes of friction in the pharmaceutical industry and represent a formidable hurdle for pharmaceutical drug development. Drug delivery remains the major challenge for the application of new small-molecule drugs as well as biopharmaceuticals. The three challenges for synthetic delivery systems are: (i) controlling drug distribution and clearance in the blood; (ii) solubilizing poorly water-soluble agents, and (iii) selectively targeting specific tissues. Although several polymer-based systems have addressed the first two demands and have been translated into clinical practice, no targeted synthetic drug delivery system has reached the market. This Review is designed to provide a background on the challenges and requirements for the design and translation of new polymer-based delivery systems. This report will focus on chemical approaches to drug delivery for systemic applications.

Mechano-bioconjugation Strategy Empowering Fusion Protein Therapeutics with Aggregation Resistance, Prolonged Circulation, and Enhanced Antitumor Efficacy

Bioconjugation is a powerful protein modification strategy to improve protein properties. Herein, we report mechano-bioconjugation as a novel approach to empower fusion protein therapeutics and demonstrate its utility by a protein heterocatenane (cat-IFN-ABD) containing interferon-α2b (IFN) mechanically interlocked with a consensus albumin-binding domain (ABD). The conjugate was selectively synthesized in cellulo following a cascade of post-translational events using a pair of heterodimerizing p53dim variants and two orthogonal split-intein reactions. The catenane topology was proven by combined techniques of LC-MS, SDS-PAGE, SEC, and controlled proteolytic digestion. Not only did cat-IFN-ABD retain activities comparable to those of the wild-type IFN and ABD, the conjugate also exhibited enhanced aggregation resistance and prolonged circulation time over the simple linear and cyclic fusions. Consequently, cat-IFN-ABD potently inhibited tumor growth in the mouse xenograft model. Therefore, mechano-bioconjugation by catenation accomplishes function integration with additional benefits, providing an alternative pathway for developing advanced protein therapeutics.

Peptide/protein-based macrocycles: from biological synthesis to biomedical applications

Living organisms have evolved cyclic or multicyclic peptides and proteins with enhanced stability and high bioactivity superior to their linear counterparts for diverse purposes. Herein, we review recent progress in applying this concept to artificial peptides and proteins to exploit the functional benefits of these macrocycles. Not only have simple cyclic forms been prepared, numerous macrocycle variants, such as knots and links, have also been developed. The chemical tools and synthetic strategies are summarized for the biological synthesis of these macrocycles, demonstrating it as a powerful alternative to chemical synthesis. Its further application to therapeutic peptides/proteins has led to biomedicines with profoundly improved pharmaceutical performances. Finally, we present our perspectives on the field and its future developments.

Cyclic topology enhances the killing activity of polycations against planktonic and biofilm bacteria

Bacterial biofilms, as a fortress to protect bacteria, enhance resistance to antibiotics because of their limited penetration, which has become a major threat to current anti-infective therapy. Antimicrobial polycations have received wide attention to kill planktonic bacteria because of their unique antimicrobial mechanism without drug resistance but it is still hard to kill the bacteria in the deep of the biofilm. Unlike linear polymers, the cyclic topology has been demonstrated with enhanced penetration in tissues, which is attributed to the lack of end groups, constrained conformation and a smaller hydrodynamic volume, opening a new sight of polycations in the antibacterial application against biofilms. Here, polycations with different topologies including linear and cyclic polycations were synthesized and their killing activity against planktonic and biofilm bacteria was studied. The experimental results showed the enhanced antibacterial activity of cyclic polycations for planktonic bacteria, which is presumably attributed to their smaller hydrodynamic volume, higher local density of positive charge and more interactions between cation units and the bacterial membrane than their linear analogues. Besides, cyclic polycations exhibit enhanced killing effect for biofilm bacteria and inhibition effect for biofilms with 5-7 times and 2-3 times enhancements than the linear polycations, respectively. Furthermore, an Escherichia coli infection model on mice was established and the therapeutic effects of cyclic and linear polycations were evaluated. Compared with the linear polycations, the cyclic polycations exhibited enhanced antibacterial activity with an ∼4 times increase, promoting the healing of the infected wounds. This work provides a new perspective in the development of antimicrobial polycations, which are promising therapeutic agents to kill planktonic and biofilm bacteria without drug resistance.

Polymer-drug conjugates: Design principles, emerging synthetic strategies and clinical overview

Adagen, an enzyme replacement treatment for adenosine deaminase deficiency, was the first protein-polymer conjugate to be approved in early 1990s. Post this regulatory approval, numerous polymeric drugs and polymeric nanoparticles have entered the market as advanced or next-generation polymer-based therapeutics, while many others have currently been tested clinically. The polymer conjugation to therapeutic moiety offers several advantages, like enhanced solubilization of drug, controlled release, reduced immunogenicity, and prolonged circulation. The present review intends to highlight considerations in the design of therapeutically effective polymer-drug conjugates (PDCs), including the choice of linker chemistry. The potential synthetic strategies to formulate PDCs have been discussed along with recent advancements in the different types of PDCs, i.e., polymer-small molecular weight drug conjugates, polymer-protein conjugates, and stimuli-responsive PDCs, which are under clinical/preclinical investigation. Current impediments and regulatory hurdles hindering the clinical translation of PDC into effective therapeutic regimens for the amelioration of disease conditions have been addressed.

Water-Assisted and Protein-Initiated Fast and Controlled Ring-Opening Polymerization of Proline N-Carboxyanhydride

The production of polypeptides via the ring-opening polymerization (ROP) of N-carboxyanhydride (NCA) is usually conducted under stringent anhydrous conditions. The ROP of proline NCA (ProNCA) for the synthesis of poly-_L-proline (PLP) is particularly challenging due to the premature product precipitation as polyproline type I helices, leading to slow reactions for up to one week, poor control of the molar mass and laborious workup. Here, we report the unexpected water-assisted controlled ROP of ProNCA, which affords well-defined PLP as polyproline II helices in 2–5 minutes and almost-quantitative yields. Experimental and theoretical studies together suggest the as-yet-unreported role of water in facilitating proton shift, which significantly lowers the energy barrier of the chain propagation. The scope of initiators can be expanded from hydrophobic amines to encompass hydrophilic amines and thiol-bearing nucleophiles, including complex biomacromolecules such as proteins. Protein-mediated ROP of ProNCA conveniently affords various protein-PLP conjugates via a grafting-from approach. PLP modification not only preserves the biological activities of the native proteins, but also enhances their resistance to extreme conditions. Moreover, PLP modification extends the elimination half-life of asparaginase (ASNase) 18-fold and mitigates the immunogenicity of wt ASNase >250-fold (ASNase is a first-line anticancer drug for lymphoma treatment). This work provides a simple solution to a long-standing problem in PLP synthesis, and offers valuable guidance for the development of water-resistant ROP of other proline-like NCAs. The facile access to PLP can greatly boost the application potential of PLP-based functional materials for engineering industry enzymes and therapeutic proteins.

Higher Order Protein Catenation Leads to an Artificial Antibody with Enhanced Affinity and In Vivo Stability

The chemical topology is a unique dimension for protein engineering, yet the topological diversity and architectural complexity of proteins remain largely untapped. Herein, we report the biosynthesis of complex topological proteins using a rationally engineered, cross-entwining peptide heterodimer motif derived from p53dim (an entangled homodimeric mutant of the tetramerization domain of the tumor suppressor protein p53). The incorporation of an electrostatic interaction at specific sites converts the p53dim homodimer motif into a pair of heterodimer motifs with high specificity for directing chain entanglement upon folding. Its combination with split-intein-mediated ligation and/or SpyTag/SpyCatcher chemistry facilitates the programmed synthesis of protein heterocatenane or [n]catenanes in cells, leading to a general and modular approach to complex protein catenanes containing various proteins of interest. Concatenation enhances not only the target protein's affinity but also the in vivo stability as shown by its prolonged circulation time in blood. As a proof of concept, artificial antibodies have been developed by embedding a human epidermal growth factor receptor 2-specific affibody onto the [n]catenane scaffolds and shown to exhibit a higher affinity and a better pharmacokinetic profile than the wild-type affibody. These results suggest that topology engineering holds great promise in the development of therapeutic proteins.

A moisture-tolerant route to unprotected α/β-amino acid N-carboxyanhydrides and facile synthesis of hyperbranched polypeptides

A great hurdle in the production of synthetic polypeptides lies in the access of N-carboxyanhydrides (NCA) monomers, which requires dry solvents, Schlenk line/gloveboxe, and protection of side-chain functional groups. Here we report a robust method for preparing unprotected NCA monomers in air and under moisture. The method employs epoxy compounds as ultra-fast scavengers of hydrogen chloride to allow assisted ring-closure and prevent NCA from acid-catalyzed decomposition under moist conditions. The broad scope and functional group tolerance of the method are demonstrated by the facile synthesis of over 30 different α/β-amino acid NCAs, including many otherwise inaccessible compounds with reactive functional groups, at high yield, high purity, and up to decagram scales. The utility of the method and the unprotected NCAs is demonstrated by the facile synthesis of two water-soluble polypeptides that are promising candidates for drug delivery and protein modification. Overall, our strategy holds great potential for facilitating the synthesis of NCA and expanding the industrial application of synthetic polypeptides.

Polypeptides-Drug Conjugates for Anticancer Therapy

Polypeptides are an important class of biodegradable polymers that have been widely used in drug delivery field. Owing to the controllable synthesis and robust side chain-functionalization ability, polypeptides have long been ideal candidates for conjugation with anticancer drugs. The chemical conjugation of anticancer drugs with polypeptides, termed polypeptides-drug conjugates, has demonstrated several advantages in improving pharmacokinetics, enhancing drug targeting, and controlling drug release, thereby leading to enhanced therapeutic outcomes with reduced side toxicities. This review focuses on the recent advances in the design and preparation of polypeptides-drug conjugates for enhanced anticancer therapy. Strategies for conjugation of different types of drugs, including small-molecule chemotherapeutic drugs, proteins, vascular disrupting agents, and gas molecules, onto polypeptides backbone are summarized. Finally, the challenges and future perspectives on the development of innovative polypeptides-drug conjugates for clinical cancer treatment are also presented.

Biological applications of water-soluble polypeptides with ordered secondary structures

Water-soluble polypeptides are a class of synthetic polymers with peptide bond frameworks imitating natural proteins and have broad prospects in biological applications. The regulation and dynamic transition of the secondary structures of water-soluble polypeptides have a great impact on their physio-chemical properties and biological functions. In this review article, we briefly introduce the current strategies to synthesize polypeptides and modulate their secondary structures. We then discuss the factors affecting the conformational stability/transition of polypeptides and the potential impact of side-chain functionalization on the ordered secondary structures, such as α-helix and β-sheet. We then summarize the biological applications of water-soluble polypeptides such as cell penetration, gene delivery, and antimicrobial treatment, highlighting the important roles of ordered secondary structures therein.

Cytokine engineering for targeted cancer immunotherapy

Cytokines are key modulators of the immune responses and represent promising therapeutics for a variety of cancers. However, successful translation of cytokine-based therapy to the clinic is limited by, among others, severe toxicities and lack of efficacy due to cytokine pleiotropy and off-target activation of cells. Engineering cytokines with enhanced therapeutic properties has emerged as a promising strategy to overcome these challenges. Advances in protein engineering and protein-polymer conjugate technologies have fostered the generation of cytokines with enhanced target cell specificity and longer half-life than the native ones. These novel cytokines exhibit reduced systemic toxicities while focusing the activities at the tumor site, thus, enhancing antitumor immunity. The growing toolbox of cytokine engineering strategies will further stimulate the development of smart cytokine-based immunotherapies with enhanced efficacy and safety profiles.

Self-Distinguishing and Stimulus-Responsive Carrier-Free Theranostic Nanoagents for Imaging-Guided Chemo-Photothermal Therapy in Small-Cell Lung Cancer

Lack of tumor targeting and low drug payload severely impedes various nanoagents further employed in small-cell lung cancer (SCLC). Therefore, how to develop a new targeting ligand and enhance drug payload has been an urgent need for SCLC therapy. Herein, we first sift and verify that capreomycin (Cm) has a high affinity toward CD56 receptors overexpressed on SCLC cells. Motivated by the concept of self-targeted drug delivery, Cm is selected as the specific targeting ligand toward CD56 receptors and chemodrug doxorubicin (Dox) is adopted to be covalently linked via the redox-responsive disulfide linkage. The synthesized self-distinguishing prodrug (Dox-ss-Cm) and FDA-approved photosensitizer indocyanine green (ICG) as structural motifs can be self-assembled into theranostic nanoagents (ICG@Dox-ss-Cm NPs) within an aqueous solution. Such carrier-free nanoagents with high drug payload can exert targeted on-demand drug release under multiple stimuli of intracellular lysosomal acidity, glutathione (GSH), and an external near-infrared (NIR) laser. Besides, our nanoagents can be specifically self-targeted to SCLC sites in vivo and self-distinguishing via SCLC cells in vitro; thus, they decrease the undesirable effects on normal tissues and organs. Further in vitro and in vivo studies uniformly confirm that such nanoagents show highly synergistic effects for SCLC chemo-photothermal therapy (PTT) under the precise guidance of NIR fluorescence (NIRF)/photoacoustic (PA) imaging. Taken together, our work can provide a novel and promising strategy for the targeted treatment of SCLC.

Dual drug-paired polyprodrug nanotheranostics reverse multidrug resistant cancers via mild photothermal-cocktail chemotherapy

Combating multidrug resistance (MDR) of tumors is still challenging for clinical chemotherapy, cocktail chemotherapy (CCT), and currently widely-studied nanodrug-based treatments. Inspired by different MDR-overcoming and antitumor mechanisms of CCT and photothermal therapy (PT), a dual drug-paired polyprodrug nanoparticle (PDCN25-CDDP) was constructed to achieve the combination therapy PT-CCT for reversing MDR and combating multidrug resistant cancers. The PT-CCT treatment can greatly downregulate the P-gp expression level and achieve utmost MDR-reversal and antitumor efficacy by both a cocktail effect of CCT and a synergistic effect of CCT with PT; meanwhile, PT can inhibit the expression of heat shock protein 90 and enhance the thermosensitivity of cancer cells. Upon NIR irradiation, PDCN25-CDDPin vivo produced a selective tumor accumulation effect and relatively deep tumor penetration, as evidenced by fluorescent and photoacoustic imaging and CLSM. The mild PT-CCT treatment completely eradicated MCF-7/ADR and OVCAR-3/DDP tumors without skin damage or tumor recurrence for 30 days, exhibiting synergistic MDR-reversal and superior antitumor efficacy in vivo. Importantly, this work provides an innovative strategy for reversing MDR and combating DOX-resistant breast and CDDP-resistant ovarian cancers.

Temperature-triggered micellization of interferon alpha-diblock copolypeptide conjugate with enhanced stability and pharmacology

Polypeptides are useful in designing protein-polypeptide conjugates for therapeutic applications; however, they are not satisfactory in improving the stability of therapeutic proteins and extending their in vivo half-life. Here we show that thermally-induced self-assembly (TISA) of elastin-like polypeptide diblock copolymer fused interferon alpha (IFNα-ELP_diblock) into a spherical micelle can dramatically enhance the proteolytic stability of IFNα. Notably, the circulation half-life of IFNα-ELP_diblock micelle (54.7 h) is 124.3-, 5.7-, and 1.4-time longer than those of free IFNα (0.44 h), freely soluble IFNα-ELP (9.6 h), and PEGylated IFNα (39.0 h), respectively. Importantly, in a mouse model of ovarian tumor, IFNα-ELP_diblock micelle exhibited significantly enhanced tumor retention and antitumor efficacy over free IFNα, freely soluble IFNα-ELP, and even PEGylated IFNα. These findings provide a thermoresponsive supramolecular strategy of TISA to design protein-diblock copolypeptide conjugate micelles with enhanced stability and pharmacology.

Tumor extravasation and infiltration as barriers of nanomedicine for high efficacy: The current status and transcytosis strategy

Nanotechnology-based drug delivery platforms have been explored for cancer treatments and resulted in several nanomedicines in clinical uses and many in clinical trials. However, current nanomedicines have not met the expected clinical therapeutic efficacy. Thus, improving therapeutic efficacy is the foremost pressing task of nanomedicine research. An effective nanomedicine must overcome biological barriers to go through at least five steps to deliver an effective drug into the cytosol of all the cancer cells in a tumor. Of these barriers, nanomedicine extravasation into and infiltration throughout the tumor are the two main unsolved blockages. Up to now, almost all the nanomedicines are designed to rely on the high permeability of tumor blood vessels to extravasate into tumor interstitium, i.e., the enhanced permeability and retention (EPR) effect or so-called "passive tumor accumulation"; however, the EPR features are not so characteristic in human tumors as in the animal tumor models. Following extravasation, the large size nanomedicines are almost motionless in the densely packed tumor microenvironment, making them restricted in the periphery of tumor blood vessels rather than infiltrating in the tumors and thus inaccessible to the distal but highly malignant cells. Recently, we demonstrated using nanocarriers to induce transcytosis of endothelial and cancer cells to enable nanomedicines to actively extravasate into and infiltrate in solid tumors, which led to radically increased anticancer activity. In this perspective, we make a brief discussion about how active transcytosis can be employed to overcome the difficulties, as mentioned above, and solve the inherent extravasation and infiltration dilemmas of nanomedicines.

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.

Secondary structure drives self-assembly in weakly segregated globular protein–rod block copolymers

Imparting secondary structure to the polymer block can drive self-assembly in globular protein–helix block copolymers, increasing the effective segregation strength between blocks with weak or no repulsion.

Effect of conjugated (EK)10 peptide on structural and dynamic properties of ubiquitin protein: a molecular dynamics simulation study

Peptide conjugation modulates the stability and biological acitivty of proteins via the allosteric effect.

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.

Broadening the scope of sortagging

Sortases are enzymes occurring in the cell wall of Gram-positive bacteria. Sortase A (SrtA), the best studied sortase class, plays a key role in anchoring surface proteins with the recognition sequence LPXTG covalently to oligoglycine units of the bacterial cell wall. This unique transpeptidase activity renders SrtA attractive for various purposes and motivated researchers to study multiple in vivo and in vitro ligations in the last decades. This ligation technique is known as sortase-mediated ligation (SML) or sortagging and developed to a frequently used method in basic research. The advantages are manifold: extremely high substrate specificity, simple access to substrates and enzyme, robust nature and easy handling of sortase A. In addition to the ligation of two proteins or peptides, early studies already included at least one artificial (peptide equipped) substrate into sortagging reactions - which demonstrates the versatility and broad applicability of SML. Thus, SML is not only a biology-related technique, but has found prominence as a major interdisciplinary research tool. In this review, we provide an overview about the use of sortase A in interdisciplinary research, mainly for protein modification, synthesis of protein-polymer conjugates and immobilization of proteins on surfaces.

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.

Achieving traceless ablation of solid tumors without recurrence by mild photothermal-chemotherapy of triple stimuli-responsive polymer–drug conjugate nanoparticles

We put forward an innovative strategy to leverage hyperthermia and a high drug-loading capacity for mild PT-CT, which achieved traceless ablation of solid MCF-7 tumors without recurrence within 50 days.

Lithium hexamethyldisilazide initiated superfast ring opening polymerization of alpha-amino acid N-carboxyanhydrides

Polypeptides have broad applications and can be prepared via ring-opening polymerization of α-amino acid N-carboxyanhydrides (NCAs). Conventional initiators, such as primary amines, give slow NCA polymerization, which requires multiple days to reach completion and can result in substantial side reactions, especially for very reactive NCAs. Moreover, current NCA polymerizations are very sensitive to moisture and must typically be conducted in a glove box. Here we show that lithium hexamethyldisilazide (LiHMDS) initiates an extremely rapid NCA polymerization process that is completed within minutes or hours and can be conducted in an open vessel. Polypeptides with variable chain length (DP = 20–1294) and narrow molecular weight distribution (Mw/Mn = 1.08–1.28) were readily prepared with this approach. Mechanistic studies support an anionic ring opening polymerization mechanism. This living NCA polymerization method allowed rapid synthesis of polypeptide libraries for high-throughput functional screening.

Ring-opening polymerizations of α-amino acid N-carboxyanhydrides to form polypeptides are usually sensitive to moisture, slow and can undergo side reactions. Here the authors use lithium hexamethyldisilazide to initiate α-amino acid N-carboxyanhydride polymerizations that is very fast and can be conducted in an open vessel.

A S-Sn Lewis Pair-Mediated Ring-Opening Polymerization of α-Amino Acid N-Carboxyanhydrides: Fast Kinetics, High Molecular Weight, and Facile Bioconjugation

The rapid and controlled generation of polypeptides with ultrahigh molecular weight (MW) and well-defined chain end functionality has been a great challenge. To tackle this problem, we report here an initiation system based on a S-Sn Lewis pair, trimethylstannyl phenyl sulfide (PhS-SnMe₃), for the ring-opening polymerization (ROP) of α-amino acid N-carboxyanhydrides (NCAs). This initiator displays a strong solvent effect, and can yield polypeptides with high MW (>1.0 × 10⁵ g·mol^-1) and low polydispersity index within a few hours. The MWs of the obtained polypeptides are strongly dependent on the THF/DMF ratio. The polymerization follows a typical first-order kinetic character with respect to the monomer concentration in mixed THF and DMF. Moreover, a highly reactive phenyl thioester is in situ generated at the C-terminus of the polypeptides, which is readily accessible for native chemical ligation affording high MW and site-specific protein-polypeptide conjugates. Together, this initiator sheds light on regulating the ROP of NCAs via appropriate Lewis pair and solvent selection, and is particularly useful in preparing ultrahigh MW polypeptides within a short period of time.

Super-Temporal-Resolved Microscopy Reveals Multistep Desorption Kinetics of α-Lactalbumin from Nylon

Insight into the mechanisms driving protein-polymer interactions is constantly improving due to advances in experimental and computational methods. In this study, we used super-temporal-resolved microscopy (STReM) to study the interfacial kinetics of a globular protein, α-lactalbumin (α-LA), adsorbing at the water-nylon 6,6 interface. The improved temporal resolution of STReM revealed that residence time distributions involve an additional step in the desorption process. Increasing the ionic strength in the bulk solution accelerated the desorption rate of α-LA, attributed to adsorption-induced conformational changes. Ensemble circular dichroism measurements were used to support a consecutive reaction mechanism. Without the improved temporal resolution of STReM, the desorption intermediate was not resolvable, highlighting both STReM's potential to uncover new kinetic mechanisms and the continuing need to push for better time and space resolution.