Construction of photofunctional peptide conjugates through selective modification of N-terminal cysteine with cyclometallated iridium(III) 2-formylphenylboronic acid complexes for organelle-specific imaging, enzyme activity sensing and photodynamic therapy

Luminescent cyclometallated iridium(III) complexes bearing a 2-formylphenylboronic acid moiety were designed; one of the complexes was utilised to modify peptides containing an N-terminal cysteine to afford luminescent conjugates with selective organelle-targeting or furin-responsive properties.

Furin-Catalyzed Enhanced Magnetic Resonance Imaging Probe for Differential Diagnosis of Malignant Breast Cancers

Molecular magnetic resonance imaging (mMRI) of biomarkers is essential for accurate cancer detection in precision medicine. However, the current clinically used contrast agents provide structural magnetic resonance imaging (sMRI) information only and rarely provide mMRI information. Here, a tumor-specific furin-catalyzed nanoprobe (NP) was reported for differential diagnosis of malignant breast cancers (BCs) in vivo. This NP with a compact structure of Fe3O4@Gd-DOTA NPs (FFG NPs) contains an "always-on" T2-weighted MR signal provided by the magnetic Fe3O4 core and a furin-catalyzed enhanced T1-weighted MR signal provided by the Gd-DOTA moiety. The FFG NPs were found to produce an activated T1 signal in the presence of furin catalysis and an "always-on" T2 signal, providing mMRI and sMRI information simultaneously. Ratiometric mMRI:sMRI intensity can be used for differential diagnosis of malignant BCs MDA-MB-231 and MCF-7, where the furin levels relatively differ. The proposed probe not only provides structural imaging but also enables real-time molecular differential visualization of BC through enzymatic activities of cancer tissues.

Self-indicating polymers: a pathway to intelligent materials

Self-indicating polymers have emerged as a promising class of smart materials that possess the unique ability to undergo detectable variations in their physical or chemical properties in response to various stimuli. This article presents an overview of the most important mechanisms through which these materials exhibit self-indication, including aggregation, phase transition, covalent and non-covalent bond cleavage, isomerization, charge transfer, and energy transfer. Aggregation is a prevalent mechanism observed in self-indicating polymers, where changes in the degree of molecular organization result in variations in optical or electrical properties. Phase transition-induced self-indication relies on the transformation between different phases, such as liquid-to-solid or crystalline-to-amorphous transitions, leading to observable changes in color or conductivity. Covalent bond cleavage-based self-indicating polymers undergo controlled degradation or fragmentation upon exposure to specific triggers, resulting in noticeable variations in their structural or mechanical properties. Isomerization is another crucial mechanism exploited in self-indicating polymers, where the reversible transformation between the different isomeric forms induces detectable changes in fluorescence or absorption spectra. Charge transfer-based self-indicating polymers rely on the modulation of electron or hole transfer within the polymer backbone, manifesting as changes in electrical conductivity or redox properties. Energy transfer is an essential mechanism utilized by certain self-indicating polymers, where energy transfer between chromophores or fluorophores leads to variations in the emission characteristics. Furthermore, this review article highlights the diverse range of applications for self-indicating polymers. These materials find particular use in sensing and monitoring applications, where their responsive nature enables them to act as sensors for specific analytes, environmental parameters, or mechanical stress. Self-indicating polymers have also been used in the development of smart materials, including stimuli-responsive coatings, drug delivery systems, food sensors, wearable devices, and molecular switches. The unique combination of tunable properties and responsiveness makes self-indicating polymers highly promising for future advancements in the fields of biotechnology, materials science, and electronics.

TPE conjugated islet amyloid polypeptide probe for detection of peptide oligomers

Islet amyloid polypeptide (IAPP), also known as amylin, is a polypeptide hormone co-secreted with insulin by pancreatic β-cells. In general, IAPP is soluble and lacks a defined structure. However, under certain conditions, these peptides tend to aggregate into soluble oligomers, eventually forming insoluble amyloid fibrils with typical cross-β-sheet structures. Amylin aggregates, therefore, have been regarded as one of the hallmarks of type II diabetes (T2D). Among these aggregated species, oligomers were shown to exhibit significant cytotoxicity, leading to impaired β-cell function and reduced β-cell mass. Monitoring of oligomer appearance during IAPP fibrillation is of particular interest. In this study, we successfully grafted an aggregation-induced emission molecule, tetraphenylethylene (TPE), at the N-terminus of IAPP. By mixing a small amount of TPE-labeled IAPP with unlabeled IAPP, we were able to detect an increase in TPE fluorescence during the nucleation phase of IAPP aggregation in vitro. It may enable real-time monitoring of IAPP oligomer formation and is further applied in the diagnosis of T2D.

Dual Aggregations of a Near-Infrared Aggregation-Induced Emission Luminogen for Enhanced Imaging of Alzheimer's Disease

Aggregation-induced emission (AIE) enables "Turn-On" imaging generally through single aggregation of the AIE luminogen (AIEgen). Dual aggregrations of the AIEgen might further enhance the imaging intensity and the consequent sensitivity. Herein, we rationally designed a near-infrared (NIR) AIEgen Ac-Trp-Glu-His-Asp-Cys(StBu)-Pra(QMT)-CBT (QMT-CBT) which, upon caspase1 (Cas1) activation, underwent a CBT-Cys click reaction to form cyclic dimers QMT-Dimer (the first aggregation) and assembled into nanoparticles (the second aggregation), turning the AIE signal "on" for enhanced imaging of Alzheimer's disease (AD). Molecular dynamics simulations validated that the fluorogen QMT in QMT-NPs stacked much tighter with each other than in the single aggregates of the control compound Ac-Trp-Glu-His-Asp-Cys(tBu)-Pra(QMT)-CBT (QMT-CBT-Ctrl). Dual aggregations of QMT rendered 1.9-, 1.7-, and 1.4-fold enhanced fluorescence intensities of its single aggregation in vitro, in cells, and in a living AD mouse model, respectively. We anticipate this smart fluorogen to be used for sensitive diagnosis of AD in the clinic in the near future.

Aggregation-induced emission for the detection of peptide ligases with improving ligation efficiency

BACKGROUND

Monitoring peptide ligase activity is of great significance for biological research, medical diagnosis, and drug discovery. The current methods for the detection of peptide ligases suffer from the limitations of high background signal, elaborate design of substrate, and high reversibility of ligation reaction. In this work, we proposed a simple and sensitive method for ligase detection with reducing ligation reversibility on the basis of aggregation-induced emission (AIE) mechanism.

RESULTS

The peptide probes labeled with AIE luminogens (AIEgens) were water-soluble and emitted weak fluorescence. After ligation reaction, the enzymatic products with AIEgens showed high hydrophobicity and could readily assembly into aggregates, thus lighting up the fluorescence. More interestingly, the formation of aggregates pushed the equilibrium to the generation of the desired ligation products, thus improving the catalytic efficiency by driving the reaction towards completion. The ligation reaction conversion rate (>80 %) is significantly higher than that without blocking the reversibility with additional treatment. With sortase A (SrtA) as the analyte example, the detection limit of this method was found to be 0.01 nM with a linear range of 0-50 nM. The system was applied to evaluate the inhibition efficiency of berberine chloride and quercetin and determine the activity of SrtA in serum, lysate and Staphylococcus aureus with satisfactory results.

SIGNIFICANCE

This study indicated that the ligation efficiency and detection sensitivity can be improved by reducing ligation reversibility through AIE phenomenon. The proposed strategy could be used for the detection of other peptide ligases by adopting sequence-specific peptide substrates.

A Smart Intracellular Self-Assembling Bioorthogonal Raman Active Nanoprobe for Targeted Tumor Imaging

Inspired by the principle of in situ self-assembly, the development of enzyme-activated molecular nanoprobes can have a profound impact on targeted tumor detection. However, despite their intrinsic promise, obtaining an optical readout of enzyme activity with high specificity in native milieu has proven to be challenging. Here, a fundamentally new class of Raman-active self-assembling bioorthogonal enzyme recognition (nanoSABER) probes for targeted tumor imaging is reported. This class of Raman probes presents narrow spectral bands reflecting their vibrational fingerprints and offers an attractive solution for optical imaging at different bio-organization levels. The optical beacon harnesses an enzyme-responsive peptide sequence, unique tumor-penetrating properties, and vibrational tags with stretching frequencies in the cell-silent Raman window. The design of nanoSABER is tailored and engineered to transform into a supramolecular structure exhibiting distinct vibrational signatures in presence of target enzyme, creating a direct causality between enzyme activity and Raman signal. Through the integration of substrate-specific for tumor-associated enzyme legumain, unique capabilities of nanoSABER for imaging enzyme activity at molecular, cellular, and tissue levels in combination with machine learning models are shown. These results demonstrate that the nanoSABER probe may serve as a versatile platform for Raman-based recognition of tumor aggressiveness, drug accumulation, and therapeutic response.

Advancements in Biosensors Based on the Assembles of Small Organic Molecules and Peptides

Over the past few decades, molecular self-assembly has witnessed tremendous progress in a variety of biosensing and biomedical applications. In particular, self-assembled nanostructures of small organic molecules and peptides with intriguing characteristics (e.g., structure tailoring, facile processability, and excellent biocompatibility) have shown outstanding potential in the development of various biosensors. In this review, we introduced the unique properties of self-assembled nanostructures with small organic molecules and peptides for biosensing applications. We first discussed the applications of such nanostructures in electrochemical biosensors as electrode supports for enzymes and cells and as signal labels with a large number of electroactive units for signal amplification. Secondly, the utilization of fluorescent nanomaterials by self-assembled dyes or peptides was introduced. Thereinto, typical examples based on target-responsive aggregation-induced emission and decomposition-induced fluorescent enhancement were discussed. Finally, the applications of self-assembled nanomaterials in the colorimetric assays were summarized. We also briefly addressed the challenges and future prospects of biosensors based on self-assembled nanostructures.

An AIEgen-based "turn-on" probe for sensing cancer cells and tiny tumors with high furin expression

Peptide-aggregation-induced emission (AIE) luminogen (AIEgen) conjugates are widely used in the bioimaging field for their good resistance to photobleaching, red and near-infrared light emission, good biocompatibility, etc. However, their peptides are mainly negatively charged and the positively charged peptide-AIEgen conjugates are rarely used in in vivo imaging due to their high non-specific interaction with protein to cause "false-positive" results and their potential risk of triggering hemolysis. Herein, we introduce a black hole quencher 3 (BHQ3) to RVRRGFF-AIE (FA) to build a "turn-on" probe, named BHQ3-RVRRGFF-AIE (BFA). Compared with FA, BFA has advantages in the anti-interference ability for different proteins and many solution environments. But, both BFA and FA have high risks of inducing hemolysis, which restricts their further application. Through co-assembly with poly-γ-glutamic acid (γ-PGA), molecular probes BFA and FA are formed into PGA-BFA and PGA-FA nanoparticles with high biocompatibility and suppressed phototoxicity. Cell studies show that PGA-BFA can discriminate cancer cells with high furin expression from low furin-expressed cancer cells and normal cells. In vivo studies show that PGA-BFA can light up tiny tumors in the abdominal cavity with a better tumor-to-intestine ratio (3.14) than that of PGA-FA (1.47), which is helpful for the accurate excision of tiny tumors. This study will advance the development of constructing good biosafety probes with a high signal-to-noise ratio for fluorescence image-guided cancer surgery.

Aggregation-induced emission of a bis(imino)acenaphthene zinc complex with tetraphenylethene units

Using bis(imino)acenaphthene (BIAN) zinc(II) and palladium(II) complexes with tetraphenylethene (TPE) units as bulky aryl groups, Zn-2 and Pd-2 have been designed and developed, and their photophysical properties in solution and in the solid state have been investigated. Both in solution and in the solid state Zn-2 and Pd-2 show two photoabsorption bands in the ranges of 300 nm to 350 nm and 450 nm to 600 nm, which are assigned to the π-π* transition originating from both the TPE units and naphthalene units and the intraligand charge transfer (ILCT) between the TPE units and the BIAN unit, respectively. Density functional theory (DFT) calculations demonstrated that for Zn-2 the highest occupied molecular orbitals (HOMO) are localized on the TPE units, while the lowest unoccupied molecular orbitals (LUMO) are localized on the BIAN unit, leading to the appearance of a photoabsorption band on the ILCT. The emission from Zn-2 was quenched in solution, but appeared as phosphorescence at around 600 nm by photoexcitation at the ILCT band in the solid state as well as in the aggregated state, which was formed by the addition of n-hexane as a poor solvent to the dichloromethane (DCM) solution. The aggregate formation of Zn-2 in the DCM/n-hexane (10 wt%/90 wt%) solution was confirmed by the Tyndall scattering and scanning electron microscopy (SEM) measurements, demonstrating the aggregation-induced emission (AIE) characteristics of Zn-2. On the other hand, Pd-2 was non-emissive in the solid state and in the aggregated state as well as in solution. Moreover, the DCM-inclusion complexes of Zn-2 and Pd-2 were obtained and their photophysical properties were investigated. It was found that the photoluminescence quantum yield (Φ_PL-solid) values of Zn-2 and Zn-2-DCM in the solid state are less than 1%. Single-crystal X-ray structural analysis of Zn-2-DCM revealed the absence of intermolecular π-π interactions. Consequently, it was suggested that the low Φ_PL-solid value of Zn-2 is mainly due to the radiationless relaxation of the excitons by dynamic rotation of the phenyl groups of the TPE units, even in the solid state and in the aggregation state.

Modular Peptide Probe for Protein Analysis

The analysis and regulation of proteins are of great significance for the development of disease diagnosis and treatment. However, complicated analytical environment and complex protein structure severely limit the accuracy of their analysis results. Nowadays, ascribing to the editability and bioactivity of peptides, peptide-based probes could meet the requirements of good selectivity and high affinity to overcome the challenges. In this review, we summarize the advances in the use of modular peptide probes for proteins analysis. It focuses on how to design and optimize the structure of probes, as well as their performance. Then, the strategies and application to improve the analysis result of modular peptide probes are introduced. Finally, we also discuss current challenge and provide some ideas for the future direction for modular peptide probes, hoping to accelerate their clinical transformation.

Recent Advances in the Enzyme-Activatable Organic Fluorescent Probes for Tumor Imaging and Therapy

The exploration of advanced probes for cancer diagnosis and treatment is of high importance in fundamental research and clinical practice. In comparison with the traditional "always-on" probes, the emerging activatable probes enjoy advantages in promoted accuracy for tumor theranostics by specifically releasing or activating fluorophores at the targeting sites. The main designing principle for these probes is to incorporate responsive groups that can specifically react with the biomarkers (e. g., enzymes) involved in tumorigenesis and progression, realizing the controlled activation in tumors. In this review, we summarize the latest advances in the molecular design and biomedical application of enzyme-responsive organic fluorescent probes. Particularly, the fluorophores can be endowed with ability of generating reactive oxygen species (ROS) to afford the photosensitizers, highlighting the potential of these probes in simultaneous tumor imaging and therapy with rational design. We hope that this review could inspire more research interests in the development of tumor-targeting theranostic probes for advanced biological studies.

Recent applications of CBT-Cys click reaction in biological systems

Click chemistry is a hot topic in many research fields. A biocompatible reaction from fireflies has attracted increasing attention since 2009. Herein, we focus on the firefly-sourced click reaction between cysteine (Cys) and 2-cyanobenzothiazole (2-CBT). This reaction has many excellent properties, such as rapidity, simplicity and high selectivity, which make it successfully applied in protein labeling, molecular imaging, drug discovery and other fields. Meanwhile, its unique ability to form nanoparticles expands its applications in biological systems. We review its principle, development, and latest applications in the past 5 years and hope this review provides more profound and comprehensive insights to its further application.

Programmable design and self assembly of peptide conjugated AIEgens for biomedical applications

Aggregation-induced emission luminogens (AIEgens) possess enhanced fluorescence in highly aggregated states, thus enabling AIEgens as a promising module for highly emissive fluorescence biomaterials. So far, AIEgens-based nanomaterials and their hybrids have been reported for biomedical applications. Benefiting from the intrinsic biocompatibility and biofunction-editing properties of peptides, peptide-AIEgens hybrid biomaterials reveal unlimited possibilities including target capacity, specificity, stimuli-responsiveness, self-assembly, controllable structural transformation, etc.. In the last two decades, peptide-AIEgens hybrid nanomaterials with a unique design concept in aggregated states have achieved various biomedical applications such as biosensing, bioimaging, imaging-guided surgery, drug delivery and therapy. More recently, programmable design of peptide-AIEgens for in situ self-assembly provides a unique strategy for constructing intelligent entities with defined biological functions. In this review, we summarize the basic design principle of programmable peptide-AIEgens, structure-effect relationship and their unusual biomedical effects. Finally, an outlook and perspective toward future challenges and developments of peptide-AIEgens nanomaterials are concluded.

Peptide probes for proteases - innovations and applications for monitoring proteolytic activity

Proteases are excellent biomarkers for a variety of diseases, offer multiple opportunities for diagnostic applications and are valuable targets for therapy. From a chemistry-based perspective this review discusses and critiques the most recent advances in the field of substrate-based probes for the detection and analysis of proteolytic activity both in vitro and in vivo.

Tetraphenylethene–anthracene-based fluorescence emission sensor for detection of water with photo-induced electron transfer and aggregation-induced emission characteristics

As a fluorescent sensor for water over a wide range from low to high water content regions in organic solvents, we have designed and developed a PET (photo-induced electron transfer)/AIE...

Imidazopyridine–fluoride interaction: solvent-switched AIE effects via S⋯O conformational locking

Imidazopyridine-based carboxamide exhibiting the aggregation-induced emission phenomenon works effectively in fluoride ion detection through H-bond interaction and subsequent deprotonation.

Progress and Perspective of Solid-State Organic Fluorophores for Biomedical Applications

Fluorescent organic dyes have been extensively used as raw materials for the development of versatile imaging tools in the field of biomedicine. Particularly, the development of solid-state organic fluorophores (SSOFs) in the past 20 years has exhibited an upward trend. In recent years, studies on SSOFs have focused on the development of advanced tools, such as optical contrast agents and phototherapy agents, for biomedical applications. However, the practical application of these tools has been hindered owing to several limitations. Thus, in this Perspective, we have provided insights that could aid researchers to further develop these tools and overcome the limitations such as limited aqueous dispersibility, low biocompatibility, and uncontrolled emission. First, we described the inherent photophysical properties and fluorescence mechanisms of conventional, aggregation-induced emissive, and precipitating SSOFs with respect to their biomedical applications. Subsequently, we highlighted the recent development of functionalized SSOFs for bioimaging, biosensing, and theranostics. Finally, we elucidated the potential prospects and limitations of current SSOF-based tools associated with biomedical applications.

Solid-State Nanochannel with Multiple Signal Outputs for Furin Detection Based on the Biocompatible Condensation Reaction

Utilizing ionic current and fluorescent dual-signal-output nanochannels to achieve the detection of specific target species has received much attention. The introduction of an optical signal could not only improve the selectivity of the detection systems, but also make it possible to observe the reduction of the ionic current that originated from stimulus-triggered nanochannel changes. However, the resolution of an optical signal can only verify issues of the presence or absence and cannot precisely analyze the detailed chemical structural changes within nanochannels. Here, we employed a biocompatible condensation reaction between 2-cyanobenzothiazole (CBT) and d-cysteine, and synthesized molecules PCTC that can be polymerized by cutting off short peptide sequences in the presence of furin to realize the detection of furin with multiple signal outputs. Through the introduction of a UV light-sensitive DNA sequence to the capture probes (CPs) inside the nanochannels, the blocking of the nanochannels can be confirmed to the formed oligomers by mass spectrometry analysis.

Scratching the Surface of Unventured Possibilities with In Situ Self-Assembly: Protease-Activated Developments for Imaging and Therapy

In situ self-assembly has attracted increasing research interest for applications in imaging and therapy in recent years. Particularly for protease-activated developments, inspiration is drawn from the innate specificity of their catalytic activities, rapid discovery of the various roles they play in the proliferation of certain diseases, and inherent susceptibility of small molecule peptide conjugates to proteolytic digestion in vivo. The overexpression of a disease-related protease of interest can be exploited as an endogenous stimulus for site-specific self-assembly to largely amplify a molecular event happening at the cellular level. This holds great potential for applications in early stage disease detection, long-term disease monitoring, and sustained therapeutic effects. This review summarizes the recent developments in protease-activated self-assemblies for imaging and therapeutic applications toward the manifestation of tumors, bacterial infections, neurodegenerative disorders, and wound recovery.

Functional CT Contrast Nanoagents for the Tumor Microenvironment

Understanding the detailed tumor microenvironment (TME) is essential to achieve effective treatment of tumor, because TME has an extremely profound influence on the occurrence, development, invasion, and metastasis of tumor. It is of great significance to realize accurate diagnosis of the TME by using functional computed tomography (CT) contrast nanoagents (FCTNAs). Here, an overview of FCTNAs that respond to the overexpressed receptors, acidic microenvironment, overexpressed glutathione and enzymes, and hypoxia in tumor is provided, and also prospects the advance of novel spectral CT technique to detect the TME precisely. Utilizing FCTNAs is expected to achieve accurate monitoring of the TME and further provide guidance for the effective personalized tumor treatment in clinic.

Pathological environment directed in situ peptidic supramolecular assemblies for nanomedicines

Peptidic self-assembly provides a powerful method to build biomedical materials with integrated functions. In particular, pathological environment instructed peptidic supramolecular have gained great progress in treating various diseases. Typically, certain pathology related factors convert hydrophilic precursors to corresponding more hydrophobic motifs to assemble into supramolecular structures. Herein, we would like to review the recent progress of nanomedicines based on the development of instructed self-assembly against several specific disease models. Firstly we introduce the cancer instructed self-assembly. These assemblies have exhibited great inhibition efficacy, as well as enhanced imaging contrast, against cancer models both in vitro and in vivo. Then we discuss the infection instructed peptidic self-assembly. A number of different molecular designs have demonstrated the potential antibacterial application with satisfied efficiency for peptidic supramolecular assemblies. Further, we discuss the application of instructed peptidic self-assembly for other diseases including neurodegenerative disease and vaccine. The assemblies have succeeded in down-regulating abnormal Aβ aggregates and immunotherapy. In summary, the self-assembly precursors are typical two-component molecules with (1) a self-assembling motif and (2) a cleavable trigger responsive to the pathological environment. Upon cleavage, the self-assembly occurs selectively in pathological loci whose targeting capability is independent from active targeting. Bearing the novel targeting regime, we envision that the pathological conditions instructed peptidic self-assembly will lead a paradigm shift on biomedical materials.

Fluorescence sensors for detection of water based on tetraphenylethene–anthracene possessing both solvatofluorochromic properties and aggregation-induced emission (AIE) characteristics

TPE-(An-CHO)4 has been developed as an SFC (solvatofluorochromism)/AIEE (aggregation-induced emission enhancement)-based fluorescence sensor for detection of water over a wide range from low to high water content regions in solvents.

Responsive Fluorophore Aggregation Provides Spectral Contrast for Fluorescence Lifetime Imaging

Fluorophores experience altered emission lifetimes when incorporated into and liberated from macromolecules or molecular aggregates; this trend suggests the potential for a fluorescent, responsive probe capable of undergoing self-assembly and aggregation and consequently altering the lifetime of its fluorescent moiety to provide contrast between the active and inactive probes. We developed a cyanobenzothioazole-fluorescein conjugate (1), and spectroscopically examined the lifetime changes caused by its reduction-induced aggregation in vitro. A decrease in lifetime was observed for compound 1 in a buffered system activated by the biological reducing agent glutathione, thus suggesting a possible approach for designing responsive self-aggregating lifetime imaging probes.

Furin-instructed molecular self-assembly actuates endoplasmic reticulum stress-mediated apoptosis for cancer therapy

Protein quality control and proteostasis are essential to maintain cell survival as once disordered, they will trigger endoplasmic reticulum (ER) stress and even initiate apoptosis. Severe ER stress-mediated apoptosis is the cause of neurodegenerative diseases and expected to be a new target for cancer therapy. In this study, we designed a small molecule of 1-Nap to execute furin-instructed molecular self-assembly for selectively inhibiting the growth of MDA-MB-468 cells in vitro and in vivo. According to the results of transmission electron microscopy (TEM) and HPLC tracing analysis, 1-Nap is capable of self-assembling upon furin-instructed cleavage that transforms 1-Nap nanoparticles to 1-Nap nanofibers. Fluorescence imaging and Western-blot analysis results indicate that the furin-instructed self-assembly of 1-Nap rather than its ER-targeting interaction is indispensable for the ER stress and activation of apoptosis. The furin-instructed self-assembly of 1-Nap is associated with both the ER (1-Nap's targeting location) and the trans-Golgi network (furin's location); this inspired us to reasonably believe that the blocking of ER-to-Golgi traffic in the secretory pathway by molecular self-assembly may be the intrinsic motivation for controlling cell fate. This work provides a new way for the targeted disturbance of the proteostasis of cells through molecular self-assembly for developing cancer therapeutics.

In situ construction of a self-assembled AIE probe for tumor hypoxia imaging

This communication reported a hypoxia-responsive fluorescent probe based on the in situ concept, which combines a water-soluble azobenzene containing copolymer with a carbamate linkage and an anionic water-soluble aggregation-induced emission fluorogen (AIEgen) tetraphenylethene (TPE). The water-soluble copolymer can be transformed into a protonated primary amine containing polymer by the reduction of the azo bond and through a 1,6-self elimination cascade reaction under hypoxic conditions. The transition of anionic TPE from the molecular dispersed state to the aggregation state induced by self-assembly with the cationic polymer would lead to an obvious increase in fluorescence according to the AIE characteristics.

One-step 18F-fluorination of smart positron emission tomography tracer for sensing furin activity in tumors

INTRODUCTION

Peptide analogues have attracted considerable attention in the field of developing novel positron emission tomography (PET) imaging agents due to their unique properties. Nevertheless, the complicated radiolabeling process and fast metabolism usually pose challenges to the clinical applications of peptide-based molecular probes. Herein a novel PET tracer containing a specific peptide sequence Arg-Val-Arg-Arg (RVRR), Acetyl-Arg-Val-Arg-Arg-Cys(StBu)-Gly(AMB[¹⁸F]F₃)-CBT ([¹⁸F]1), was designed and radiosynthesized using a simple and convenient one-step ¹⁸F-fluorination procedure. The smart tracer can be activated by the protease furin and then undergoes an intermolecular cyclization reaction in tumor cells, leading to improved PET imaging efficiency of tumor.

METHODS

The radiosynthesis of the target tracer [¹⁸F]1 and the control tracer [¹⁸F]1-ctrl was performed under facile conditions in pyridazine-HCl buffer (pH~2.5) at 80 °C within 30 min. The enzyme-controlled condensation was studied for non-radioactive compound 1 in the human breast cancer cell lysates (MDA-MB-468). The cellular uptake of [¹⁸F]1 and [¹⁸F]1-ctrl was studied and compared by measuring the activity in MDA-MB-468 cells using a γ-counter after incubation with 37 kBq of [¹⁸F]1 or [¹⁸F]1-ctrl, respectively. In vivo behavior of [¹⁸F]1 was examined through PET imaging of MDA-MB-468 tumor-bearing mice and compared with that of [¹⁸F]1-ctrl as well as that of [¹⁸F]1 co-injected with non-radioactive compound 1.

RESULTS

The tracer [¹⁸F]1 was obtained with a high radiochemical yield (RCY) of 42.5 ± 1.47% and an excellent radiochemical purity (RCP > 99%). Under the activation of furin and GSH, the tracer suffered a condensation reaction to form dimers and then self-assembled into nanoparticles to produce enduring signal. The cellular uptake of [¹⁸F]1 and [¹⁸F]1-ctrl was determined to be 10.2 ± 0.37 and 1.19 ± 0.25%ID at 120 min, respectively. For in vivo PET imaging, [¹⁸F]1 exhibited the optimum tumor uptake of 2.39 ± 0.31%ID/g and the tumor-to-muscle uptake ratio of 2.93 ± 0.92 at 10 min post injection. Co-injection of [¹⁸F]1 and non-radioactive compound 1 produced a high tumor uptake ranging from 2.83 ± 0.23%ID/g to 3.40 ± 0.18%ID/g at 10 min and 60 min post injection, respectively.

CONCLUSIONS

The one-step labeling method of tracer [¹⁸F]1 showed advantage in simplifying the radiolabeling process with high RCY, which could enable a real kit process for the synthesis of ¹⁸F-radiopharmaceuticals and was significant for the large-scale production of tracers for clinical applications. PET imaging results suggested that the tracer [¹⁸F]1 had good tumor uptake and the co-injection strategy of [¹⁸F]1 with 1 could enhance the imaging signal in tumor.

Aggregation-Induced Emission Photosensitizers: From Molecular Design to Photodynamic Therapy

Photodynamic therapy (PDT) has emerged as a promising noninvasive treatment option for cancers and other diseases. The key factor that determines the effectiveness of PDT is the photosensitizers (PSs). Upon light irradiation, the PSs would be activated, produce reactive oxygen species (ROS), and induce cell death. One of the challenges is that traditional PSs adopt a large flat disc-like structure, which tend to interact with the adjacent molecules through strong π-π stacking that reduces their ROS generation ability. Aggregation-induced emission (AIE) molecules with a twisted configuration to suppress strong intermolecular interactions represent a new class of PSs for image-guided PDT. In this Miniperspective, we summarize the recent progress on the design rationale of AIE-PSs and the strategies to achieve desirable theranostic applications in cancers. Subsequently, approaches of combining AIE-PS with other imaging and treatment modalities, challenges, and future directions are addressed.

Modular Design of Peptide- or DNA-Modified AIEgen Probes for Biosensing Applications

Fluorophore probes are widely used for bioimaging in cells, tissues, and animals as well as for monitoring of multiple biological processes in complex environments. Such imaging properties allow scientists to make direct visualizations of pathological events and cellular targets. Conventional fluorescent molecules have been developed for several decades and achieved great successes, but their emissions are often weakened or quenched at high concentrations that might suffer from the aggregation-caused quenching (ACQ) effect, which reduces the efficiencies of their applications. In contrast to the ACQ effect, aggregation-induced emission (AIE) luminogens (AIEgens) display much higher fluorescence in aggregated states and possess various advantages such as low background, long-term tracking ability, and strong resistance to photobleaching. Therefore, AIEgens are employed as unique fluorescence molecules and building blocks for biosensing applications in the fields of ions, amino acids, carbohydrates, DNAs/RNAs, peptides/proteins, cellular organelles, cancer cells, bacteria, and so on. Quite a few of the above biosensing missions are accomplished by modular peptide-modified AIEgen probes (MPAPs) or modular DNA-modified AIEgen probes (MDAPs) because of the multiple capabilities of peptide and DNA modules, including solubility, biocompatibility, and recognition. Meanwhile, both electrostatic interactions and coupling reactions could provide efficient methods to construct different MPAPs and MDAPs, finally resulting in a large variety of biosensing probes. Those probes exhibit leading features of detecting nucleic acids or proteins and imaging mass biomolecules. For example, under modular design, peptide modules possessing versatile recognition abilities enable MPAPs to detect numerous targets, such as integrin α_vβ₃, aminopeptidase N, MMP-2, MPO, H₂O₂, and so forth; MDAP could allow the imaging of mRNA in cells and tissue chips, suggesting the diagnostic functions of MDAP in clinical samples. Modular design offers a novel strategy to generate AIEgen-based probes and expedites functional biomacromolecules research. In this vein, here we review the progress on MPAPs and MDAPs in the most recent 10 years and highlight the modular design strategy as well as their advanced biosensing applications including briefly two aspects: (1) detection and (2) imaging. By the use of MPAPs/MDAPs, multiple bioanalytes can be efficiently analyzed at low concentrations and directly visualized through high-contrast and luminous imaging. Compared with MPAPs, the quantities of MDAPs are limited because of the difficult synthesis of long-length DNA strands. In future work, multifunctional of DNA sequences are needed to explore varieties of MDAPs for diverse biosensing purposes. At the end of this Account, some deficiencies and challenges are mentioned for briging more attention to accelerate the development of AIEgen-based probes.

Furin-Guided Intracellular 68Ga Nanoparticle Formation Enhancing Tumor MicroPET Imaging

Positron-emission tomography (PET) is routinely used in the clinic for tumor imaging with ultrahigh sensitivity, but tumor-targeted PET imaging probes are quite few. In this work, we rationally designed a furin-responsive radiotracer Acetyl-Arg-Val-Arg-Arg-Cys(StBu)-Lys(DOTA-⁶⁸Ga)-CBT (CBT-⁶⁸Ga) and demonstrated that coinjection of the radiotracer with its cold analogue CBT-Ga instructed the formation of ⁶⁸Ga nanoparticles in furin-overexpressing MDA-MB-468 cancer cells, which significantly enhanced microPET imaging of the tumor in vivo. In vitro results showed that CBT-Ga subjected to furin-initiated CBT-Cys condensation reaction and self-assembly to form the nanoparticles CBT-Ga-NPs with an average diameter of 258.3 nm. In vivo microPET imaging results indicate that the mice coinjected with CBT-⁶⁸Ga and CBT-Ga, which warrants ⁶⁸Ga nanoparticle formation in their MDA-MB-468 tumors, had a tumor/liver ratio 9.1-fold of that of the mice only injected with CBT-⁶⁸Ga. We envisioned that, by replacing the RVRR substrate of CBT-⁶⁸Ga with other enzyme-specific ones and using the strategy of intracellular nanoparticle formation, a series of radioactive probes could be developed for more sensitive and precise tumor microPET imaging in the near future.

Aggregation-Induced Emission Luminogens for Activity-Based Sensing

Fluorescent sensing has emerged as a powerful tool for detecting various analytes and visualizing numerous biological processes by virtue of its superb sensitivity, rapidness, excellent temporal resolution, easy operation, and low cost. Of particular interest is activity-based sensing (ABS), a burgeoning sensing approach that is actualized on the basis of dynamic molecular reactivity rather than conventional lock-and-key molecular recognition. ABS has been recognized to possess some distinct advantages, such as high specificity, extraordinary sensitivity, and accurate signal outputs. A majority of ABS sensors are constructed by modifying conventional fluorogens, which are strongly emissive when molecularly dissolved in solvents but experience emission quenching upon aggregate formation or concentration increase. The aggregation-caused quenching (ACQ) phenomenon leads to a limited amount of labeling of the analyte with the sensor and low photobleaching resistance, which could impede practical applications of the ABS protocol. As an anti-ACQ phenomenon, aggregation-induced emission (AIE) provides a straightforward solution to the ACQ problem. Thanks to their intrinsic advantages, including high photobleaching threshold, high signal-to-noise ratio, fluorescence turn-on nature, and large Stokes shift, AIE-active luminogens (AIEgens) represent a class of extraordinary fluorogen alternatives for the ABS protocol. The use of AIEgen-involved ABS can integrate the advantages of AIEgens and ABS, and additionally, the AIE process offers some unique properties to the ABS approach. For instance, in some cases of water-soluble AIEgen-involved ABS, chemical reaction not only leads to a chang in the emission color of the AIEgens but also causes solubility variations, which could result in specific "light-up" signaling. In this Account, the basic concepts and mechanistic insights of the ABS approach involving the AIE principle are briefly summarized, and then we highlight the new breakthroughs, seminal studies, and trends in the area that have been most recently reported by our group. This emerging sensing protocol has been successfully utilized for detecting an array of targets including ions, small molecules, biomacromolecules, and microenvironments, all of which closely relate to human health, medical, and public concerns. These detections are smoothly achieved on the basis of various reactions (e.g., hydrolysis, boronate cleavage, dephosphorylation, addition, cyclization, and rearrangement reactions) through different sensing principles. In these studies, the AIEgen-involved ABS strategy generally shows good biocompatibility, high selectivity, excellent reliability and high signal contrast, strongly indicating its great potential for high-tech innovations in the sensing field, among which bioprobing is of particular interest. With this Account, we hope to spark new ideas and inspire new endeavors in this emerging research area, further promoting state-of-the-art developments in the field of sensing.

Parallel Induction of CH505 B Cell Ontogeny-Guided Neutralizing Antibodies and tHIVconsvX Conserved Mosaic-Specific T Cells against HIV-1

The aim of this work was to start collecting information on rational combination of antibody (Ab) and T cell vaccines into single regimens. Two promising candidate HIV-1 vaccine strategies, sequential isolates of CH505 virus Envs developed for initiation of broadly neutralizing antibody lineages and conserved-mosaic tHIVconsvX immunogens aiming to induce effective cross-clade T cell responses, were combined to assess vaccine interactions. These immunogens were delivered in heterologous vector/modality regimens consisting of non-replicating simian (chimpanzee) adenovirus ChAdOx1 (C), non-replicating poxvirus MVA (M), and adjuvanted protein (P). Outbred CD1-SWISS mice were vaccinated intramuscularly using either parallel CM8M (tHIVconsvX)/CPPP (CH505) or sequential CM16M (tHIVconsvX)/CPPP (CH505) protocols, the latter of which delivered T cell CM prior to the CH505 Env. CM8M (tHIVconsvX) and CPPP or CMMP (CH505) vaccinations alone were included as comparators. The vaccine-elicited HIV-1-specific trimer-binding and neutralizing Abs and CD8+/CD4+ T cell responses induced by the combined and comparator regimens were not statistically separable among regimens. The Ab-lineage immunogen strategy was particularly suited for combined regimens for its likely less potent induction of Env-specific T cell responses relative to homologous epitope-based vaccine strategies. These results inform design of the first rationally combined Ab and T cell vaccine regimens in human volunteers.

Biomacromolecule-Functionalized AIEgens for Advanced Biomedical Studies

The advances in bioinformatics and biomedicine have promoted the development of biomedical imaging and theranostic systems to respectively extend the endogenous biomarker imaging with high contrast and enhance the therapeutic effect with high efficiency. The emergence of biomacromolecule-functionalized aggregation-induced emitters (AIEgens), utilizing AIEgens, and biomacromolecules (nucleic acids, peptides, glycans, and lipids), displays specific targeting ability to cancer cell, improved biocompatibility, reduced toxicity, enhanced therapeutic effect, and so forth. This review summarizes the rational design of biomacromolecule-functionalized AIEgens and their biomedical applications in recent ten years, including high-resolution optical imaging of cell, tissue, and small animal model with low background; the biomarker detection for early diagnosis and prognosis; the delivery and monitoring of prodrugs; image-guide photodynamic therapy and its combination with chemotherapy. Through illustrating their functional mechanisms and application, it is hoped that this review would open up a completely new train of research thought for attracted researchers in various fields.

Fluorometric detection of sulfate-reducing bacteria via the aggregation-induced emission of glutathione-gold(I) complexes

It is reported that gold(I)-thiolate complexes can display aggregation-induced emission (AIE) similar to organic fluorogens. On addition of lead(II) to glutathione-gold(I) complexes, a supermolecular structure of type GSH-Au(I)-Pb(II) is formed through strong coordination between Pb(II) and GSH. Its fluorescence is quenched by sulfide due to the formation of PbS which destroys the GSH-Au(I)-Pb(II) complex. The finding was used to design a method for fluorometric detection of sulfate-reducing bacteria (SRB) which produce sulfide. The time needed to reduce fluorescence to 10% of its initial intensity linearly dependent on the logarithm of the SRB concentrations in the ranging from 10 to 1 × 10^7 cfu mL^-1. The assay time is also reduced down to 4 days even if the SRB concentration is as low as 10 cfu mL^-1. Graphical abstract Schematic presentation of aggregation-induced emission (AIE)-active GSH-Au(I) complexes based fluorescence detection of SRB. The GSH-Au(I) complexes turn into aggregation and display strong emissive property in the presence of Pb²⁺. Then the fluorescence of GSH-Au(I)-Pb(II) complexes can be quenched by S^2- generated by SRB.

Efficient cell surface labelling of live zebrafish embryos: wash-free fluorescence imaging for cellular dynamics tracking and nanotoxicity evaluation

Imaging the dynamics and behaviors of plasma membranes is at the leading edge of life science research. We report here the development of a universal red-fluorescent probe Chol-PEG-Cy5 for wash-free plasma membrane labelling both in vitro and in vivo. In aqueous solutions, the fluorescence of Chol-PEG-Cy5 is significantly quenched due to the intermolecular resonance energy transfer (RET) between neighbouring Cy5 moieties; however, upon membrane anchoring, the probes undergo lateral diffusion in lipid bilayers, resulting in weakened RET and turn-on fluorescence emission. We demonstrate that Chol-PEG-Cy5 enables rapid, stable and high-quality in vitro cell surface imaging in a variety of mammalian cells. Additionally, with the assistance of three-dimensional (3D) image reconstruction, we achieve for the first time the whole-mount in situ fluorescence imaging of the epidermal cell surfaces of live zebrafish embryos, which cannot be realized by conventional plasma membrane probes due to the presence of the surface-covering mucus barrier. This novel technique encourages us to track the cellular dynamics of the epidermis during embryonic development with 3D visualization. Moreover, we also develop a new method to evaluate the epidermal toxicity of nanomaterials (e.g., gold nanoparticles and graphene oxide nanosheets) toward zebrafish embryos using this fluorescent probe.

Self-Assembly of Amphiphilic Peptides for Recognizing High Furin-Expressing Cancer Cells

Self-assembled nanostructures of amphiphilic peptides have a wide range of applications in bioimaging and delivery systems. In this study, we design and synthesize a biocompatible amphiphilic peptide (C-3) consisting of an RVRRFFF sequence and a nitrobenzoxadiazole fluorophore that can self-assemble into stable micelles for specifically detecting furin, a kind of proprotein convertase with promoting tumor progression. The self-assembly of C-3 with a β-sheet nanostructure is capable of a rapid and specific response to furin in only 5 min in aqueous solution because of the existence of the RVRR motif in the C-3 molecule. The C-3 nanostructures thus can selectively distinguish high furin-expressing cancer cells, like MDA-MB-231 cells, a kind of human breast cancer cells, from normal cells. Furthermore, the C-3 self-assembly can stay in living cells for a long time and are capable of durable detection of intracellular furin, being good for tracer analysis. To our knowledge, this is the first example of self-assembly of a soluble amphiphilic peptide that can selectively detect furin in high furin-expressing live cells.

Fluorogenic probes for disease-relevant enzymes

Traditional biochemical methods for enzyme detection are mainly based on antibody-based immunoassays, which lack the ability to monitor the spatiotemporal distribution and, in particular, the in situ activity of enzymes in live cells and in vivo. In this review, we comprehensively summarize recent progress that has been made in the development of small-molecule as well as material-based fluorogenic probes for sensitive detection of the activities of enzymes that are related to a number of human diseases. The principles utilized to design these probes as well as their applications are reviewed. Specific attention is given to fluorogenic probes that have been developed for analysis of the activities of enzymes including oxidases and reductases, those that act on biomacromolecules including DNAs, proteins/peptides/amino acids, carbohydrates and lipids, and those that are responsible for translational modifications. We envision that this review will serve as an ideal reference for practitioners as well as beginners in relevant research fields.

Self-Assembly of Aggregation-Induced-Emission Molecules

The last decade has witnessed rapid developments in aggregation-induced emission (AIE). In contrast to traditional aggregation, which causes luminescence quenching (ACQ), AIE is a reverse phenomenon that allows robust luminescence to be retained in aggregated and solid states. This makes it possible to fabricate various highly efficient luminescent materials, which opens new paradigms in a number of fields, such as imaging, sensing, medical therapy, light harvesting, light-emitting devices, and organic electronic devices. Of the various important features of AIE molecules, their self-assembly behavior is very attractive because the formation of a well-defined emissive nanostructure may lead to advanced applications in diverse fields. However, due to the nonplanar topology of AIEgens, it is not easy for them to self-assemble into well-defined structures. To date, some strategies have been proposed to achieve the self-assembly of AIEgens. Herein, we summarize the most recent approaches for the self-assembly of AIE molecules. These approaches can be sorted into two classes: 1) covalent molecular design and 2) noncovalent supramolecular interactions. We hope this will inspire more excellent work in the field of AIE.