Enzyme‐Instructed Self‐Assembly Enabled Monomer–Excimer Transition to Construct Higher Ordered Luminescent Supramolecular Assembly for Activity‐based Bioimaging

Adaptive enzyme-responsive self-assembling multivalent apelin ligands for targeted myocardial infarction therapy

Microvascular dysfunction following myocardial infarction exacerbates coronary flow obstruction and impairs the preservation of ventricular function. The apelinergic system, known for its pleiotropic effects on improving vascular function and repairing ischemic myocardium, has emerged as a promising therapeutic target for myocardial infarction. Despite its potential, the natural apelin peptide has an extremely short circulating half-life. Current apelin analogs have limited receptor binding efficacy and poor targeting, which restricts their clinical applications. In this study, we utilized an enzyme-responsive peptide self-assembly technique to develop an enzyme-responsive small molecule peptide that adapts to the expression levels of matrix metalloproteinases in myocardial infarction lesions. This peptide is engineered to respond to the high concentration of matrix metalloproteinases in the lesion area, allowing for precise and abundant presentation of the apelin motif. The changes in hydrophobicity allow the apelin motif to self-assemble into a supramolecular multivalent peptide ligand-SAMP. This self-assembly behavior not only prolongs the residence time of apelin in the myocardial infarction lesion but also enhances the receptor-ligand interaction through increased receptor binding affinity due to multivalency. Studies have demonstrated that SAMP significantly promotes angiogenesis after ischemia, reduces cardiomyocyte apoptosis, and improves cardiac function. This novel therapeutic strategy offers a new approach to restoring coronary microvascular function and improving damaged myocardium after myocardial infarction.

Self-assembly of peptides in living cells for disease theranostics

The past few decades have witnessed substantial progress in biomedical materials for addressing health concerns and improving disease therapeutic and diagnostic efficacy. Conventional biomedical materials are typically created through an ex vivo approach and are usually utilized under physiological environments via transfer from preparative media. This transfer potentially gives rise to challenges for the efficient preservation of the bioactivity and implementation of theranostic goals on site. To overcome these issues, the in situ synthesis of biomedical materials on site has attracted great attention in the past few years. Peptides, which exhibit remarkable biocompability and reliable noncovalent interactions, can be tailored via tunable assembly to precisely create biomedical materials. In this review, we summarize the progress in the self-assembly of peptides in living cells for disease diagnosis and therapy. After a brief introduction to the basic design principles of peptide assembly systems in living cells, the applications of peptide assemblies for bioimaging and disease treatment are highlighted. The challenges in the field of peptide self-assembly in living cells and the prospects for novel peptide assembly systems towards next-generation biomaterials are also discussed, which will hopefully help elucidate the great potential of peptide assembly in living cells for future healthcare applications.

Transformable Supramolecular Self-Assembled Peptides for Cascade Self-Enhanced Ferroptosis Primed Cancer Immunotherapy

Immunotherapy has received widespread attention for its effective and long-term tumor-eliminating ability. However, for immunogenic "cold" tumors, such as prostate cancer (PCa), the low immunogenicity of the tumor itself is a serious obstacle to efficacy. Here, this work reports a strategy to enhance PCa immunogenicity by triggering cascade self-enhanced ferroptosis in tumor cells, turning the tumor from "cold" to "hot". This work develops a transformable self-assembled peptide TEP-FFG-CRApY with alkaline phosphatase (ALP) responsiveness and glutathione peroxidase 4 (GPX4) protein targeting. TEP-FFG-CRApY self-assembles into nanoparticles under aqueous conditions and transforms into nanofibers in response to ALP during endosome/lysosome uptake into tumor cells, promoting lysosomal membrane permeabilization (LMP). On the one hand, the released TEP-FFG-CRAY nanofibers target GPX4 and selectively degrade the GPX4 protein under the light irradiation, inducing ferroptosis; on the other hand, the large amount of leaked Fe2+ further cascade to amplify the ferroptosis through the Fenton reaction. TEP-FFG-CRApY-induced immunogenic ferroptosis improves tumor cell immunogenicity by promoting the maturation of dendritic cells (DCs) and increasing intratumor T-cell infiltration. More importantly, recovered T cells further enhance ferroptosis by secreting large amounts of interferon-gamma (IFN-γ). This work provides a novel strategy for the molecular design of synergistic molecularly targeted therapy for immunogenic "cold" tumors.

Peptide Self-Assembly Facilitating DNA Transfection and the Application in Inhibiting Cancer Cells

Non-viral vectors have been developing in gene delivery due to their safety and low immunogenicity. But their transfection effect is usually very low, thus limiting the application. Hence, we designed eight peptides (compounds 1-8). We compared their performances; compound 8 had the best transfection efficacy and biocompatibility. The transfection effect was similar with that of PEI, a most-widely-employed commercial transfection reagent. Atomic force microscope (AFM) images showed that the compound could self-assemble and the self-assembled peptide might encapsulate DNA. Based on these results, we further analyzed the inhibitory result in cancer cells and found that compound 8 could partially fight against Hela cells. Therefore, the compound is promising to pave the way for the development of more effective and less toxic transfection vectors.

Cathepsin B Responsive Peptide-Purpurin Conjugates Assembly-Initiated in Situ Self-Aggregation for Cancer Sonotheranostics

Sonodynamic therapy (SDT) was hampered by the sonosensitizers with low bioavailability, tumor accumulation, and therapeutic efficiency. In situ responsive sonosensitizer self-assembly strategy may provide a promising route for cancer sonotheranositics. Herein, an intelligent sonotheranostic peptide-purpurin conjugate (P18-P) is developed that can self-assemble into supramolecular structures via self-aggregation triggered by rich enzyme cathepsin B (CTSB). After intravenous injection, the versatile probe could achieve deep tissue penetration because of the penetration sequence of P18-P. More importantly, CTSB-triggered self-assembly strongly prolonged retention time, amplified photoacoustic imaging signal for sensitive CTSB detection, and boosted reactive oxygen species for advanced SDT, evoking specific CTSB responsive sonotheranostics. This peptide-purpurin conjugate may serve as an efficient sonotheranostic platform for the early diagnosis of CTSB activity and effective cancer therapy.

Enzymatic Dimerization-Induced Self-Assembly of Alanine-Tyramine Conjugates into Versatile, Uniform, Enzyme-Loaded Organic Nanoparticles

Herein, we report a novel enzymatic dimerization-induced self-assembly (e-DISA) procedure that converts alanine-tyramine conjugates into highly uniform enzyme-loaded nanoparticles (NPs) or nanocontainers by the action of horseradish peroxidase (HRP) in an aqueous medium under ambient conditions. The NP formation was possible with both enantiomers of alanine, and the average diameter could be varied from 150 nm to 250 nm (with a 5-12 % standard deviation of as-prepared samples) depending on the precursor concentration. About 60 % of the added HRP enzyme was entrapped within the NPs and was subsequently utilized for post-synthetic modification of the NPs with phenolic compounds such as tyramine or tannic acid. One-pot multi-enzyme entrapment of glucose oxidase (GOx) and peroxidase (HRP) within the NPs was also achieved. These GOx-HRP loaded NPs allowed multimodal detection of glucose, including that present in human saliva, with a limit of detection (LoD) of 740 nM through fluorimetry. The NPs exhibited good cytocompatibility and were stable to changes in pH (acidic to basic), temperature, ultrasonication, and even the presence of organic solvent (EtOH) to a certain extent, since they are stabilized by intermolecular hydrogen bonding, π-π, and CH-π interactions. The proposed e-DISA procedure can be widely expanded through the design of diverse enzyme-responsive precursors.

Structural Determinants of Stimuli-Responsiveness in Amphiphilic Macromolecular Nano-assemblies

Stimuli-responsive nano-assemblies from amphiphilic macromolecules could undergo controlled structural transformations and generate diverse macroscopic phenomenon under stimuli. Due to the controllable responsiveness, they have been applied for broad material and biomedical applications, such as biologics delivery, sensing, imaging, and catalysis. Understanding the mechanisms of the assembly-disassembly processes and structural determinants behind the responsive properties is fundamentally important for designing the next generation of nano-assemblies with programmable responsiveness. In this review, we focus on structural determinants of assemblies from amphiphilic macromolecules and their macromolecular level alterations under stimuli, such as the disruption of hydrophilic-lipophilic balance (HLB), depolymerization, decrosslinking, and changes of molecular packing in assemblies, which eventually lead to a series of macroscopic phenomenon for practical purposes. Applications of stimuli-responsive nano-assemblies in delivery, sensing and imaging were also summarized based on their structural features. We expect this review could provide readers an overview of the structural considerations in the design and applications of nanoassemblies and incentivize more explorations in stimuli-responsive soft matters.

Supramolecular self-assembled peptide-engineered nanofibers: A propitious proposition for cancer therapy

Cancer is a devastating disease that causes a substantial number of deaths worldwide. Current therapeutic interventions for cancer include chemotherapy, radiation therapy, or surgery. These conventional therapeutic approaches are associated with disadvantages such as multidrug resistance, destruction of healthy tissues, and tissue toxicity. Therefore, there is a paradigm shift in cancer management wherein nanomedicine-based novel therapeutic interventions are being explored to overcome the aforementioned disadvantages. Supramolecular self-assembled peptide nanofibers are emerging drug delivery vehicles that have gained much attention in cancer management owing to their biocompatibility, biodegradability, biomimetic property, stimuli-responsiveness, transformability, and inherent therapeutic property. Supramolecules form well-organized structures via non-covalent linkages, the intricate molecular arrangement helps to improve tissue permeation, pharmacokinetic profile and chemical stability of therapeutic agents while enabling targeted delivery and allowing efficient tumor imaging. In this review, we present fundamental aspects of peptide-based self-assembled nanofiber fabrication their applications in monotherapy/combinatorial chemo- and/or immuno-therapy to overcome multi-drug resistance. The role of self-assembled structures in targeted/stimuli-responsive (pH, enzyme and photo-responsive) drug delivery has been discussed along with the case studies. Further, recent advancements in peptide nanofibers in cancer diagnosis, imaging, gene therapy, and immune therapy along with regulatory obstacles towards clinical translation have been deliberated.

Autohydrolysis of Diglycine-Activated Succinic Esters Boosts Cellular Uptake

Rapid cellular uptake of synthetic molecules remains a challenge, and the motif frequently employed to generate prodrugs, succinic ester, unfortunately lowers the efficacy of the desired drugs due to their slow ester hydrolysis and low cell entry. Here we show that succinic ester-containing diglycine drastically boosts the cellular uptake of supramolecular assemblies or prodrugs. Specifically, autohydrolysis of the diglycine-activated succinic esters turns the nanofibers of the conjugates of succinic ester and self-assembling motif into nanoparticles for fast cellular uptake. The autohydrolysis of diglycine-activated succinic esters and drug conjugates also restores the efficacy of the drugs. 2D nuclear magnetic resonance (NMR) suggests that a "U-turn" of diglycine favors intramolecular hydrolysis of diglycine-activated succinic esters to promote autohydrolysis. As an example of rapid autohydrolysis of diglycine-activated succinic esters for instant cellular uptake, this work illustrates a nonenzymatic bond cleavage approach to develop effective therapeutics for intracellular targeting.

Peptide Assemblies for Cancer Therapy

Supramolecular assemblies made by the self-assembly of peptides are finding an increasing number of applications in various fields. While the early exploration of peptide assemblies centered on tissue engineering or regenerative medicine, the recent development has shown that peptide assemblies can act as supramolecular medicine for cancer therapy. This review covers the progress of applying peptide assemblies for cancer therapy, with the emphasis on the works appeared over the last five years. We start with the introduction of a few seminal works on peptide assemblies, then discuss the combination of peptide assemblies with anticancer drugs. Next, we highlight the use of enzyme-controlled transformation or shapeshifting of peptide assemblies for inhibiting cancer cells and tumors. After that, we provide the outlook for this exciting field that promises new kind of therapeutics for cancer therapy.

Functional Nucleic Acid Probes Based on Two-Photon for Biosensing

Functional nucleic acid (FNA) probes have been widely used in environmental monitoring, food analysis, clinical diagnosis, and biological imaging because of their easy synthesis, functional modification, flexible design, and stable properties. However, most FNA probes are designed based on one-photon (OP) in the ultraviolet or visible regions, and the effectiveness of these OP-based FNA probes may be hindered by certain factors, such as their potential for photodamage and limited light tissue penetration. Two-photon (TP) is characterized by the nonlinear absorption of two relatively low-energy photons of near-infrared (NIR) light with the resulting emission of high-energy ultraviolet or visible light. TP-based FNA probes have excellent properties, including lower tissue self-absorption and autofluorescence, reduced photodamage and photobleaching, and higher spatial resolution, making them more advantageous than the conventional OP-based FNA probes in biomedical sensing. In this review, we summarize the recent advances of TP-excited and -activated FNA probes and detail their applications in biomolecular detection. In addition, we also share our views on the highlights and limitations of TP-based FNA probes. The ultimate goal is to provide design approaches for the development of high-performance TP-based FNA probes, thereby promoting their biological applications.

Constructing lipid droplet-targeting photosensitizers based on coumarins with NIR emission

The development of photosensitizers (PSs) with subcellular targeting capability has raised interest for photodynamic therapy (PDT) research. In this work, two coumarin-based photosensitizers (C-S-2 and C-S-3) were designed and synthesized via expanding their π-conjugation, introducing strong electron-donor and acceptor groups, and adopting sulfur substitution strategy. These sulfured-coumarins exhibited near-infrared emission (greater than 650 nm), lipid droplet-targeting ability and obvious photocytotoxicity under laser irradiation. In particular, C-S-3 exhibited better photostability, superior lipid droplet-targeting capability, and stronger photodynamic effect on cancer cells than C-S-2.

A Cascade-Targeted Enzyme-Instructed Peptide Self-Assembly Strategy for Cancer Immunotherapy through Boosting Immunogenic Cell Death

Immunogenic cell death (ICD) approaches by encumbering mitochondrial functions provide great promise for the treatment of malignant tumors, but these kinds of ICD strategies are still in their infancy. Here, one multifunctional drug-loaded, cascade-targeted, and enzyme-instructed self-assembling peptide nanomedicine (Comp. 4) for ICD-based cancer therapy is constructed. Comp. 4 consists of 1) lonidamine (LND) that specifically interferes with mitochondrial functions; 2) a programmed death ligand 1 (PD-L1) binding peptide sequence (NTYYEDQG) and a mitochondria-specific motif (triphenylphosphonium, TPP) that can sequentially control the cell membrane and mitochondria targeting capacities, respectively; and 3) a -G^D F^D Fp^D Y- assembly core to in situ organize peptide assemblies responsive to alkaline phosphatase (ALP). Comp. 4 demonstrates noticeable structural and morphological transformations in the presence of ALP and produces peptide assemblies in mouse colon cancer cells (CT26) with high expressions of both ALP and PD-L1. Moreover, the presence of PD-L1- and mitochondria-specific motifs can assist Comp. 4 for effective endocytosis and endosomal escape, forming peptide assemblies and delivering LND into mitochondria. Consequently, Comp. 4 shows superior capacities to in vivo induce abundant mitochondrial oxidative stress, provoke robust ICD responses, and produce an immunogenic tumor microenvironment, successfully inhibiting CT26 tumor growth by eliciting a systemic ICD-based antitumor immunity.

Fluorescent probes for the detection of chemical warfare agents

Chemical warfare agents (CWAs) are toxic chemicals that have been intentionally developed for targeted and deadly use on humans. Although intended for military targets, the use of CWAs more often than not results in mass civilian casualties. To prevent further atrocities from occurring during conflicts, a global ban was implemented through the chemical weapons convention, with the aim of eliminating the development, stockpiling, and use of CWAs. Unfortunately, because of their relatively low cost, ease of manufacture and effectiveness on mass populations, CWAs still exist in today's world. CWAs have been used in several recent terrorist-related incidents and conflicts (e.g., Syria). Therefore, they continue to remain serious threats to public health and safety and to global peace and stability. Analytical methods that can accurately detect CWAs are essential to global security measures and for forensic analysis. Small molecule fluorescent probes have emerged as attractive chemical tools for CWA detection, due to their simplicity, ease of use, excellent selectivity and high sensitivity, as well as their ability to be translated into handheld devices. This includes the ability to non-invasively image CWA distribution within living systems (in vitro and in vivo) to permit in-depth evaluation of their biological interactions and allow potential identification of therapeutic countermeasures. In this review, we provide an overview of the various reported fluorescent probes that have been designed for the detection of CWAs. The mechanism for CWA detection, change in optical output and application for each fluorescent probe are described in detail. The limitations and challenges of currently developed fluorescent probes are discussed providing insight into the future development of this research area. We hope the information provided in this review will give readers a clear understanding of how to design a fluorescent probe for the detection of a specific CWA. We anticipate that this will advance our security systems and provide new tools for environmental and toxicology monitoring.

Self-Assembled Peptide-Based Nanodrugs: Molecular Design, Synthesis, Functionalization, and Targeted Tumor Bioimaging and Biotherapy

Functional nanomaterials as nanodrugs based on the self-assembly of inorganics, polymers, and biomolecules have showed wide applications in biomedicine and tissue engineering. Ascribing to the unique biological, chemical, and physical properties of peptide molecules, peptide is used as an excellent precursor material for the synthesis of functional nanodrugs for highly effective cancer therapy. Herein, recent progress on the design, synthesis, functional regulation, and cancer bioimaging and biotherapy of peptide-based nanodrugs is summarized. For this aim, first molecular design and controllable synthesis of peptide nanodrugs with 0D to 3D structures are presented, and then the functional customization strategies for peptide nanodrugs are presented. Then, the applications of peptide-based nanodrugs in bioimaging, chemotherapy, photothermal therapy (PTT), and photodynamic therapy (PDT) are demonstrated and discussed in detail. Furthermore, peptide-based drugs in preclinical, clinical trials, and approved are briefly described. Finally, the challenges and potential solutions are pointed out on addressing the questions of this promising research topic. This comprehensive review can guide the motif design and functional regulation of peptide nanomaterials for facile synthesis of nanodrugs, and further promote their practical applications for diagnostics and therapy of diseases.

Granzyme B Turns Nanoparticle Fluorescence "On" for Imaging Cytotoxic T Lymphocyte Activity in Vivo

Cytotoxic T lymphocytes (CTLs) are important immune cells, and their activation is a key step for cancer immunotherapy. Precise evaluation of CTL activity in vivo provides a powerful tool for monitoring cancer-immunotherapeutic outcomes, yet it faces tremendous challenges. Herein, by rationally designing a near-infrared (NIR) fluorescence probe Cys(StBu)-Ile-Glu-Phe-Asp-Lys(Cy5.5)-CBT (Cy5.5-CBT) and employing a reduction-instructed CBT-Cys click condensation reaction, we developed the fluorescence "dual quenched" nanoparticles Cy5.5-CBT-NPs for imaging of granzyme B (GraB), a biomarker tightly associated with the tumoricidal activity of CTLs. Upon GraB cleavage, Cy5.5-CBT-NPs disassembled, subtly turning the fluorescence signal "on". With this fluorescence "turn-on" property, Cy5.5-CBT-NPs enabled sensitive and real-time monitoring of GraB-mediated CTL responses against cancer cells in vitro. Animal experiments demonstrated that, at 16 h post injection, the fluorescence imaging signal of Cy5.5-CBT-NPs showed a 3.1-fold increase on the tumor sites of mice treated by an immune-activating drug S-(2-boronoethyl)-L-cysteine hydrochloride. We envision that Cy5.5-CBT-NPs may provide a powerful tool for noninvasive and sensitive evaluation of immunotherapeutic efficacy of cancer in the near future.

Intranuclear Nanoribbons for Selective Killing of Osteosarcoma Cells

Herein, we show intranuclear nanoribbons formed upon dephosphorylation of leucine-rich L- or D-phosphopeptide catalyzed by alkaline phosphatase (ALP) to selectively kill osteosarcoma cells. Being dephosphorylated by ALP, the peptides are first transformed into micelles and then converted into nanoribbons. The peptides/assemblies first aggregate on cell membranes, then enter cells via endocytosis, and finally accumulate in nuclei (mainly in nucleoli). Proteomics analysis suggests that the assemblies interact with histone proteins. The peptides kill osteosarcoma cells rapidly and are nontoxic to normal cells. Moreover, the repeated stimulation of the osteosarcoma cells by the peptides sensitizes the cancer cells rather than inducing resistance. This work not only illustrates a novel mechanism for nucleus targeting, but may also pave a new way for selectively killing osteosarcoma cells and minimizing drug resistance.

Intracellular Enzyme-Instructed Self-Assembly of Peptides (IEISAP) for Biomedical Applications

Despite the remarkable significance and encouraging breakthroughs of intracellular enzyme-instructed self-assembly of peptides (IEISAP) in disease diagnosis and treatment, a comprehensive review that focuses on this topic is still desirable. In this article, we carefully review the advances in the applications of IEISAP, including the development of various bioimaging techniques, such as fluorescence imaging, photoacoustic imaging, magnetic resonance imaging, positron-emission tomography imaging, radiation imaging, and multimodal imaging, which are successfully leveraged in visualizing cancer tissues and cells, bacteria, and enzyme activity. We also summarize the utilization of IEISAP in disease treatments, including anticancer, antibacterial, and antiinflammation applications, among others. We present the design, action modes, structures, properties, functions, and performance of IEISAP materials, such as nanofibers, nanoparticles, nanoaggregates, and hydrogels. Finally, we conclude with an outlook towards future developments of IEISAP materials for biomedical applications. It is believed that this review may foster the future development of IEISAP with better performance in the biomedical field.

Peptide-Based Low Molecular Weight Photosensitive Supramolecular Gelators

Over the last couple of decades, stimuli-responsive supramolecular gels comprising synthetic short peptides as building blocks have been explored for various biological and material applications. Though a wide range of stimuli has been tested depending on the structure of the peptides, light as a stimulus has attracted extensive attention due to its non-invasive, non-contaminant, and remotely controllable nature, precise spatial and temporal resolution, and wavelength tunability. The integration of molecular photo-switch and low-molecular-weight synthetic peptides may thus provide access to supramolecular self-assembled systems, notably supramolecular gels, which may be used to create dynamic, light-responsive “smart” materials with a variety of structures and functions. This short review summarizes the recent advancement in the area of light-sensitive peptide gelation. At first, a glimpse of commonly used molecular photo-switches is given, followed by a detailed description of their incorporation into peptide sequences to design light-responsive peptide gels and the mechanism of their action. Finally, the challenges and future perspectives for developing next-generation photo-responsive gels and materials are outlined.

FAP-α-Instructed Coumarin Excimer Formation for High Contrast Fluorescence Imaging of Tumor

Emissive excimers, which are formed by planar polycyclic aromatic fluorophores (e.g., coumarin), enable high contrast tumor imaging. However, it is still challenging to "turn on" excimer fluorescence in physiological dilute solutions. The biocompatible CBT-Cys click condensation reaction enables both intra- and intermolecular aggregations of the as-loaded fluorophores on the probe molecules, which may promote the generation of emissive excimers in a synergistic manner. As a proof-of-concept, we herein design a fluorescence probe Cbz-Gly-Pro-Cys(StBu)-Lys(coumarin)-CBT (Cbz-GPC(StBu)K(Cou)-CBT), which can be activated by FAP-α under tumor-inherent reduction conditions, undergo a CBT-Cys click reaction, and self-assemble into coumarin nanoparticle Cou-CBT-NP to "turn on" the excimer fluorescence. In vitro and in vivo studies validate that this "smart" probe realizes efficient excimer fluorescence imaging of FAP-α-overexpressed tumor cells with high contrast and enhanced accumulation, respectively. We anticipate that this probe can be applied for diagnosis of FAP-α-related diseases in the clinic in near future.

Enzyme-manipulated hydrogelation of small molecules for biomedical applications

Enzyme-manipulated hydrogelation based on self-assembly of small molecules is an attractive methodology for development of functional biomaterials. Upon the catalysis of enzymes, small-molecular precursors are converted into assemblable building blocks, which arrange into high-ordered nanofibers via non-covalent interactions at the molecular level, and further trap water to form hydrogels at the macroscopic level. Such approach has numerous advantages of region- and enantioselectivity, and mild reaction conditions for encapsulation of biomedications or cells that are fragile to environmental change. In addition to the common applications as drug reservoirs or cell scaffolds, the utilization of endogenous enzymes as stimuli to initiate self-assembly in the living cells and tissue is considered as an intelligent spatiotemporally controllable hydrogelation strategy for biomedical applications. The enzyme-instructed in situ self-assembly and hydrogelation can modulate the cell behavior, and even present therapeutic bioactivities, which provides a new perspective in the field of disease treatment. In this review, we categorize distinct enzymatic stimuli and elaborate substrate design, catalytic characteristics, and mechanisms of self-assembly and hydrogelation. The biomedical applications in drug delivery, tissue engineering, bioimaging, and in situ gelation-produced bioactivity are outlined. Advantages and limitations regarding the state-of-the-art enzyme-driven hydrogelation technologies and future perspectives are also discussed. STATEMENT OF SIGNIFICANCE: Hydrogel is a semi-solid soft material containing a large amount of water. Due to the features of adjustable flexibility, extremely porous architecture, and the high similarity of structure to natural extracellular matrices, the hydrogel has broad application prospects in biomedicine. In recent 20 years, enzyme-manipulated hydrogelation based on self-assembly of small molecules has developed rapidly as an attractive methodology for the construction of functional biomaterials. Upon the catalysis of enzymes, small-molecular precursors are converted into assemblable building blocks, which arrange into high-ordered nanofibers via non-covalent interactions at the molecular level, and further trap water to form hydrogels at the macroscopic level. This review summarized the characteristics of enzymatic hydrogel, as well as the traditional application and emerging prospect of enzyme-instructed self-assembly and hydrogelation.

Constructing ECM-like Structure on the Plasma Membrane via Peptide Assembly to Regulate the Cellular Response

This feature article introduces the design of self-assembling peptides that serve as the basic building blocks for the construction of extracellular matrix (ECM)-like structure in the vicinity of the plasma membrane. By covalently conjugating a bioactive motif, such as membrane protein binding ligand or enzymatic responsive building block, with a self-assembling motif, especially the aromatic peptide, a self-assembling peptide that retains bioactivity is obtained. Instructed by the target membrane protein or enzyme, the bioactive peptides self-assemble into ECM-like structure exerting various stimuli to regulate the cellular response via intracellular signaling, especially mechanotransduction. By briefly summarizing the properties and applications (e.g., wound healing, controlling cell motility and cell fate) of these peptides, we intend to illustrate the basic requirements and promises of the peptide assembly as a true bottom-up approach in the construction of artificial ECM.

A dual-targeting peptide facilitates targeting anti-inflammation to attenuate atherosclerosis in ApoE-/- mice

We report a peptidic dual-targeting drug delivery platform (integrins targeting and self-assembly instructed by matrix metalloproteinases) towards inflamed endothelial cells, which improved the anti-inflammatory ability of the loaded drug (i.e., puerarin) in vitro and thus improved the antiatherogenic effect of the loaded drug (i.e., puerarin) in vivo.

Nano-bio interactions: A major principle in the dynamic biological processes of nano-assemblies

Controllable nano-assembly with stimuli-responsive groups is emerging as a powerful strategy to generate theranostic nanosystems that meet unique requirements in modern medicine. However, this prospective field is still in a proof-of-concept stage due to the gaps in our understanding of complex-(nano-assemblies)-complex-(biosystems) interactions. Indeed, stimuli-responsive assembly-disassembly is, in and of itself, a process of nano-bio interactions, the key steps for biological fate and functional activity of nano-assemblies. To provide a comprehensive understanding of these interactions in this review, we first propose a 4W1H principle (Where, When, What, Which and How) to delineate the relevant dynamic biological processes, behaviour and fate of nano-assemblies. We further summarize several key parameters that govern effective nano-bio interactions. The effects of these kinetic parameters on ADMET processes (absorption, distribution, metabolism, excretion and transformation) are then discussed. Furthermore, we provide an overview of the challenges facing the evaluation of nano-bio interactions of assembled nanodrugs. We finally conclude with future perspectives on safe-by-design and application-driven-design of nano-assemblies. This review will highlight the dynamic biological and physicochemical parameters of nano-bio interactions and bridge discrete concepts to build a full spectrum understanding of the biological outcomes of nano-assemblies. These principles are expected to pave the way for future development and clinical translation of precise, safe and effective nanomedicines with intelligent theranostic features.

An injectable co-assembled hydrogel blocks reactive oxygen species and inflammation cycle resisting myocardial ischemia-reperfusion injury

The overproduction of reactive oxygen species (ROS) and burst of inflammation following cardiac ischemia-reperfusion (I/R) are the leading causes of cardiomyocyte injury. Monotherapeutic strategies designed to enhance anti-inflammatory or anti-ROS activity explicitly for treating I/R injury have demonstrated limited success because of the complex mechanisms of ROS production and induction of inflammation. Intense oxidative stress leads to sustained injury, necrosis, and apoptosis of cardiomyocytes. The damaged and necrotic cells can release danger-associated molecular patterns (DAMPs) that can cause the aggregation of immune cells by activating Toll-like receptor 4 (TLR4). These immune cells also promote ROS production by expressing NADPH oxidase. Finally, ROS production and inflammation form a vicious cycle, and ROS and TLR4 are critical nodes of this cycle. In the present study, we designed and prepared an injectable hydrogel system of EGCG@Rh-gel by co-assembling epigallocatechin-3-gallate (EGCG) and the rhein-peptide hydrogel (Rh-gel). The co-assembled hydrogel efficiently blocked the ROS-inflammation cycle by ROS scavenging and TLR4 inhibition. Benefited by the abundant noncovalent interactions of π-π stacking and hydrogen bonding between EGCG and Rh-gel, the co-assembled hydrogel had good mechanical strength and injectable property. Following the injection EGCG@Rh-gel into the damaged region of the mice's heart after I/R, the hydrogel enabled to achieve long-term sustained release and treatment, improve cardiac function, and significantly reduce the formation of scarring. Further studies demonstrated that these beneficial outcomes arise from the reduction of ROS production, inhibition of inflammation, and induction of anti-apoptosis in cardiomyocytes. Therefore, EGCG@Rh-gel is a promising drug delivery system to block the ROS-inflammation cycle for resisting myocardial I/R injury. STATEMENT OF SIGNIFICANCE: 1. Monotherapeutic strategies designed to enhance anti-inflammatory or anti-ROS effects for treating I/R injury have demonstrated limited success because of the complex mechanisms of ROS and inflammation. 2. ROS production and inflammation form a vicious cycle, and ROS and TLR4 are critical nodes of this cycle. 3. Here, we designed an injectable hydrogel system of EGCG@Rh-gel by co-assembling epigallocatechin-3-gallate (EGCG) and a rhein-peptide hydrogel (Rh-gel). EGCG@Rh-gel efficiently blocked the ROS-inflammation cycle by ROS scavenging and TLR4 inhibition. 4. EGCG@Rh-gel achieved long-term sustained release and treatment, improved cardiac function, and significantly reduced the formation of scarring after I/R. 5. The beneficial outcomes arise from reducing ROS production, inhibiting inflammation, and inducing anti-apoptosis in cardiomyocytes.

Self-Amplifying Assembly of Peptides in Macrophages for Enhanced Inflammatory Treatment

Enzyme-regulated in situ self-assembly of peptides represents one versatile strategy in the creation of theranostic agents, which, however, is limited by the strong dependence on enzyme overexpression. Herein, we reported the self-amplifying assembly of peptides precisely in macrophages associated with enzyme expression for improving the anti-inflammatory efficacy of conventional drugs. The self-amplifying assembling system was created via coassembling an enzyme-responsive peptide with its derivative functionalized with a protein ligand. Reduction of the peptides by the enzyme NAD(P)H quinone dehydrogenase 1 (NQO1) led to the formation of nanofibers with high affinity to the protein, thereby facilitating NQO1 expression. The improved NQO1 level conversely promoted the assembly of the peptides into nanofibers, thus establishing an amplifying relationship between the peptide assembly and the NQO1 expression in macrophages. Utilization of the amplifying assembling system as vehicles for drug dexamethasone allowed for its passive targeting delivery to acute injured lungs. Both in vitro and in vivo studies confirmed the capability of the self-amplifying assembling system to enhance the anti-inflammatory efficacy of dexamethasone via simultaneous alleviation of the reactive oxygen species side effect and downregulation of proinflammatory cytokines. Our findings demonstrate the manipulation of the assembly of peptides in living cells with a regular enzyme level via a self-amplification process, thus providing a unique strategy for the creation of supramolecular theranostic agents in living cells.

In Situ Self-Assembly of Bispecific Peptide for Cancer Immunotherapy

Precise and effective manipulation of protein functions still faces tremendous challenges. Herein we report a programmable peptide molecule, consisted of targeting and self-assembly modules, that enables specific and highly efficient assembly governed by targeting receptor proteins. Upon binding to the cell membrane receptor, peptide conformation is somewhat stabilized along with decreased self-assembly activation energy, promoting peptide-protein complex oligomerization. We first design a GNNQQNY-RGD peptide (G7-RGD) to recognize integrin α_V β₃ receptor for proof-of-concept study. In the presence of α_V β₃ protein, the critical assembly concentration of free G7-RGD decreases from 525 to 33 μM and the resultant G7-RGD cluster drives integrin receptor oligomerization. Finally, a bispecific assembling peptide antiCD3-G7-RGD is rationally designed for cancer immunotherapy, which validates CD3 oligomerization and concomitant T cell activation, leading to T cell-mediated cancer cell cytolysis.

Peptide Assembled in a Nano-confined Space as a Molecular Rectifier for the Availability of Ionic Current Modulation

Bioinspired nanochannels have emerged as a powerful tool for bioengineering and biomedical research due to their robust mechanical and controllable chemical properties. Inspired by inward-rectifier potassium (K⁺) channels, herein, the charged peptide assembly has been introduced into a nano-confined space for the modulation of ion current rectification (ICR). Peptide-responsive reaction-triggered sequence changes can contribute to polarity conversion of the surface charge; therefore, ICR reversal (ICRR) is generated. Compared with other responsive elements, natural charged peptides show the merit of controllable charge polarity. By electrochemically monitoring the ICRR as an output signal, one can utilize the peptide assembly-mediated ICRR to construct an ionic sensory platform. In addition, a logic gate has been established to demonstrate the availability of an ionic sensory platform for inhibitor screening. As peptide nanoassemblies may also have various structures and functions due to their diverse properties, the ionic modulation system can provide alternatives for the assay of peptide-associated biotargets with biomedical applications.

Supramolecular Nanomedicines of In-Situ Self-Assembling Peptides

Nanomedicines provide distinct clinical advantages over traditional monomolecular therapeutic and diagnostic agents. Supramolecular nanomedicines made from in-situ self-assembling peptides have emerged as a promising strategy in designing and fabricating nanomedicines. In-situ self-assambly (SA) allows the combination of nanomedicines approach with prodrug approach, which exhibited both advantages of these strategies while addressed the problems of both and thus receiving more and more research attention. In this review, we summarized recently designed supramolecular nanomedicines of in-situ SA peptides in the manner of applications and design principles, and the interaction between the materials and biological environments was also discussed.

Tumour enzyme affinity mediated peptide molecular crowding for targeted disruption of hyperactivated glucose uptake

An unconventional environment-responsive molecular crowding via specific binding between small molecule peptide inhibitor derivatives and an overexpressed tumour enzyme has been developed. Assemblies of such short peptides selectively localize on tumour surfaces and exhibited unique functions in disrupting hyperactivated glucose uptake, providing novel insights towards strategic tumour treatment.

Handedness inversion of the self-assemblies of lipotetrapeptides regulated by the shift of the methyl group

Four lipotetrapeptides containing three glycines and one l-alanine self-assembled into twisted nanoribbons. Handedness inversion was observed with the movement of l-alanine.

Organelle-inspired supramolecular nanomedicine to precisely abolish liver tumor growth and metastasis

Organelles are responsible for the efficient storage and transport of substances in living systems. A myriad of extracellular vesicles (EVs) acts as a bridge to exchange signaling molecules in cell–cell communication, and the highly dynamic tubulins and actins contribute to efficient intracellular substance transport. The inexhaustible cues of natural cargo delivery by organelles inspire researchers to explore the construction of biomimetic architectures for “smart” delivery carriers. Herein, we report a 10-hydroxycamptothecin (HCPT)-peptide conjugate HpYss that simulates the artificial EV-to-filament transformation process for precise liver cancer therapy. Under the sequential stimulus of extracellular alkaline phosphatase (ALP) and intracellular glutathione (GSH), HpYss proceeds via tandem self-assembly with a morphological transformation from nanoparticles to nanofibers. The experimental phase diagram elucidates the influence of ALP and GSH contents on the self-assembled nanostructures. In addition, the dynamic transformation of organelle-mimetic architectures that are formed by HpYss in HepG2 cells enables the efficient delivery of the anticancer drug HCPT to the nucleus, and the size–shape change from extracellular nanoparticles (50–100 nm) to intracellular nanofibers (4–9 nm) is verified to be of key importance for nuclear delivery. Nuclear targeting of HpYss amplifies apoptosis, thus significantly enhancing the inhibitory effect of HCPT (>10-fold) to HepG2 cells. Benefitting from the spatiotemporally controlled nanostructures, HpYss exhibited deep penetration, enhanced accumulation, and long-term retention in multicellular spheroid and xenograft models, potently abolishing liver tumor growth and preventing lung metastasis. We envision that our organelle-mimicking delivery strategy provides a novel paradigm for designing nanomedicine to cancer therapy.

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An organelle-inspired nanomedicine for precise liver cancer therapy is proposed.

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The delivery process mimics the transport of extracellular vesicles and filaments.

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The extra- and intracellular tandem self-assembly influence the nanostructures.

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The dynamic size–shape change of nanomedicine actuates the nuclear delivery.

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Spatiotemporally controlled nanomedicine abolishes liver tumor growth and lung metastasis.

Enzyme-instructed self-assembly enabled fluorescence light-up for alkaline phosphatase detection

Alkaline phosphatase (ALP) exists in both normal and pathological tissues. Spatiotemporal variations in ALP levels can reveal its potential physiological functions and changes that occur during pathological conditions. However, it is still challenging to exploit fluorescent probes that can measure ALP activity under good spatial and temporal resolutions. Herein, enzyme-instructed self-assembly (EISA) was used to construct a high-performing analytical tool (MN-pY) to probe ALP activity. MN-pY alone (free state) showed negligible fluorescence but presented an almost 13-fold increase in fluorescence intensity in the presence of ALP (assembly state). Mechanism study indicated the increase in fluorescence intensity was due to hydrogelation and formation of supramolecular fibrils, mainly consisting of dephosphorylated MN-Y. The dephosphorylation and further fibrillation of MN-pY could induce the formation of a "hydrophobic pocket", leading to a further increase in fluorescence intensity. Moreover, MN-pY could selectively illuminate HeLa cells with a higher ALP expression but not LO2 cells with lower ALP levels, promising a potential application in cancer diagnosis.

A mini-review on peptide-based self-assemblies and their biological applications

Peptide-based supramolecular self-assembly from peptide monomers into well-organized nanostructures, has attracted extensive attentions towards biomedical and biotechnological applications in recent decades. This spontaneous and reversible assembly process involving non-covalent bonding interactions can be artificially regulated. In this review, we have elaborated different strategies to modulate the peptide self-assembly through tuning the physicochemical and environmental conditions, includingpH, light, temperature, solvent, and enzyme. Detailed introduction of biological applications and future potential of the peptide-based nano-assemblies will also be given.

In Vivo Self-Assembly Induced Cell Membrane Phase Separation for Improved Peptide Drug Internalization

Therapeutic peptides have been widely concerned, but their efficacy is limited by the inability to penetrate cell membranes, which is a key bottleneck in peptide drugs delivery. Herein, an in vivo self-assembly strategy is developed to induce phase separation of cell membrane that improves the peptide drugs internalization. A phosphopeptide KYp is synthesized, containing an anticancer peptide [KLAKLAK]₂ (K) and a responsive moiety phosphorylated Y (Yp). After interacting with alkaline phosphatase (ALP), KYp can be dephosphorylated and self-assembles in situ, which induces the aggregation of ALP and the protein-lipid phase separation on cell membrane. Consequently, KYp internalization is 2-fold enhanced compared to non-responsive peptide, and IC₅₀ value of KYp is approximately 5 times lower than that of free peptide. Therefore, the in vivo self-assembly induced phase separation on cell membrane promises a new strategy to improve the drug delivery efficacy in cancer therapy.

Self-assembly of peptide nanofibers for imaging applications

Pathological stimuli-responsive self-assembly of peptide nanofibers enables selective accumulation of imaging agent cargos in the stimuli-rich regions of interest. It provides enhanced imaging signals, biocompatibility, and tumor/disease accessibility and retention, thereby promoting smart, precise, and sensitive tumor/disease imaging both in vitro and in vivo. Considering the remarkable significance and recent encouraging breakthroughs of self-assembled peptide nanofibers in tumor/disease diagnosis, this reivew is herein proposed. We emphasize the recent advances particularly in the past three years, and provide an outlook in this field.

In situ self-assembled peptide nanofibers for cancer theranostics

Self-assembled nanofibers hold tremendous promise for cancer theranostics owing to their in situ assembly, spatiotemporal responsiveness, and diverse bioactivity. Herein, this review summarizes the recent advances of self-assembled peptide nanofibers and their applications in biological systems, focusing on the dynamic process of capturing cancer cells from the outside-in. (1) In situ self-assembly in response to pathological or physiological changes. (2) Diverse functions at different locations of tumors, such as forming thrombus in tumor vasculature, constructing a barrier on the cancer cell membrane, and disrupting the cancer organelles. Of note, with the assembly/aggregation induced residence (AIR) effect, the nanofibers could form a drug depot in situ for sustained release of chemotherapeutic drugs to increase their local concentration and prolong the residence time. Finally, perspectives toward future directions and challenges are presented to further understand and expand this exciting field.