Synthetic Peptides with Genetic-Codon-Tailored Affinity for Assembling Tetraspanin CD81 at Cell Interfaces and Inhibiting Cancer Metastasis

Probing biomolecular interactions at cellular interfaces is crucial for understanding and interfering with life processes. Although affinity binders with site specificity for membrane proteins are unparalleled molecular tools, a high demand remains for novel multi-functional ligands. In this study, a synthetic peptide (APQQ) with tight and specific binding to the untargeted extracellular loop of CD81 evolved from a genetically encoded peptide pool. With tailored affinity, APQQ flexibly accesses, site-specifically binds, and forms a complex with CD81, enabling in-situ tracking of the dynamics and activity of this protein in living cells, which has rarely been explored because of the lack of ligands. Furthermore, APQQ triggers the relocalization of CD81 from diffuse to densely clustered at cell junctions and modulates the interplay of membrane proteins at cellular interfaces. Motivated by these, efficient suppression of cancer cell migration, and inhibition of breast cancer metastasis were achieved in vivo.

Smart exosomes enhance PDAC targeted therapy

Exosomes continue to attract interest as a promising nanocarrier drug delivery technology. They are naturally derived nanoscale extracellular vesicles with innate properties well suited to shuttle proteins, lipids, and nucleic acids between cells. Nonetheless, their clinical utility is currently limited by several major challenges, such as their inability to target tumor cells and a high proportion of clearance by the mononuclear phagocyte system (MPS) of the liver and spleen. To overcome these limitations, we developed "Smart Exosomes" that co-display RGD and CD47p110-130 through CD9 engineering (ExoSmart). The resultant ExoSmart demonstrates enhanced binding capacity to αvβ3 on pancreatic ductal adenocarcinoma (PDAC) cells, resulting in amplified cellular uptake in in vitro and in vivo models and increased chemotherapeutic efficacies. Simultaneously, ExoSmart significantly reduced liver and spleen clearance of exosomes by inhibiting macrophage phagocytosis via CD47p110-130 interaction with signal regulatory proteins (SIRPα) on macrophages. These studies demonstrate that an engineered exosome drug delivery system increases PDAC therapeutic efficacy by enhancing active PDAC targeting and prolonging circulation times, and their findings hold tremendous translational potential for cancer therapy while providing a concrete foundation for future work utilizing novel peptide-engineered exosome strategies.

Advances in targeted tracking and detection of soluble amyloid-β aggregates as a biomarker of Alzheimer's disease

Misfolding and aggregation of amyloid-β (Aβ) peptides are key hallmarks of Alzheimer's disease (AD). With accumulating evidence suggesting that different Aβ species have varied neurotoxicity and implications in AD development, the discovery of affinity ligands and analytical approaches to selective distinguish, detect, and monitor Aβ becomes an active research area. Remarkable advances have been achieved, which not only promote our understanding of the biophysical chemistry of the protein aggregation during neurodegeneration, but also provide promising tools for early detection of the disease. In view of this, we summarize the recent progress in selective and sensitive approaches for tracking and detection of Aβ species. Specific attentions are given to soluble Aβ oligomers, due to their crucial roles in AD development and occurrence at early stages. The design principle, performance of targeting units, and their cooperative effects with signal reporters for Aβ analysis are discussed. The applications of the novel targeting probes and sensing systems for dynamic monitoring oligomerization, measuring Aβ in biosamples and in vivo imaging in brain are summarized. Finally, the perspective and challenges are discussed regarding the future development of Aβ-targeting analytical tools to explore the unknown field to contribute to the early diagnosis and treatment of AD.

AIEgen-Peptide Bioprobes for the Imaging of Organelles

Organelles are important subsystems of cells. The damage and inactivation of organelles are closely related to the occurrence of diseases. Organelles’ functional activity can be observed by fluorescence molecular tools. Nowadays, a series of aggregation-induced emission (AIE) bioprobes with organelles-targeting ability have emerged, showing great potential in visualizing the interactions between probes and different organelles. Among them, AIE luminogen (AIEgen)-based peptide bioprobes have attracted more and more attention from researchers due to their good biocompatibility and photostability and abundant diversity. In this review, we summarize the progress of AIEgen-peptide bioprobes in targeting organelles, including the cell membrane, nucleus, mitochondria, lysosomes and endoplasmic reticulum, in recent years. The structural characteristics and biological applications of these bioprobes are discussed, and the development prospect of this field is forecasted. It is hoped that this review will provide guidance for the development of AIEgen-peptide bioprobes at the organelles level and provide a reference for related biomedical research.

Self-assembly of Peptide dendrimers and their bio-applications in theranostics

Nanotechnology has brought revolutionized advances in disease diagnosis and therapy. Self-assembled peptide dendrimers own novel physicochemical properties through the synergistic effects of the polypeptide chain, dendrimer and nano-structure, exhibiting great potential in theranostic. This review provides comprehensive insights into various peptide dendrimers for self-assembly. Their nanosize, morphology and composition are presented to understand self-assembly behaviors precisely. We further introduce the emerging theranostic applications based on specific imaging and efficient delivery recently.

Recent Progress of Exosome Isolation and Peptide Recognition-Guided Strategies for Exosome Research

Exosomes are membrane extracellular vesicles secreted by almost all kinds of cells, which are rich in proteins, lipids, and nucleic acids. As a medium of intercellular communication, exosomes play important roles in biological processes and are closely related to the occurrence, and development of many diseases. The isolation of exosomes and downstream analyses can provide important information to the accurate diagnosis and treatment of diseases. However, exosomes are various in a size range from 30 to 200 nm and exist in complex bio-systems, which provide significant challenges for the isolation and enrichment of exosomes. Different methods have been developed to isolate exosomes, such as the “gold-standard” ultracentrifugation, size-exclusion chromatography, and polymer precipitation. In order to improve the selectivity of isolation, affinity capture strategies based on molecular recognition are becoming attractive. In this review, we introduced the main strategies for exosome isolation and enrichment, and compared their strengths and limitations. Furthermore, combined with the excellent performance of targeted peptides, we summarized the application of peptide recognition in exosome isolation and engineering modification.

Engineering Peptide-Functionalized Biomimetic Nanointerfaces for Synergetic Capture of Circulating Tumor Cells in an EpCAM-Independent Manner

Broad-spectrum detection and long-term monitoring of circulating tumor cells (CTCs) remain challenging due to the extreme rarity, heterogeneity, and dynamic nature of CTCs. Herein, a dual-affinity nanostructured platform was developed for capturing different subpopulations of CTCs and monitoring CTCs during treatment. Stepwise assembly of fibrous scaffolds, a ligand-exchangeable spacer, and a lysosomal protein transmembrane 4 β (LAPTM4B)-targeting peptide creates biomimetic, stimuli-responsive, and multivalent-binding nanointerfaces, which enable harvest of CTCs directly from whole blood with high yield, purity, and viability. The stable overexpression of the target LAPTM4B protein in CTCs and the enhanced peptide-protein binding facilitate the capture of rare CTCs in patients at an early stage, detection of both epithelial-positive and nonepithelial CTCs, and tracking of therapeutic responses. The reversible release of CTCs allows downstream molecular analysis and identification of specific liver cancer genes. The consistency of the information with clinical diagnosis presents the prospect of this platform for early diagnosis, metastasis prediction, and prognosis assessment.

Spatial Order of Functional Modules Enabling Diverse Intracellular Performance of Fluorescent Probes

To overcome a series of challenges in tumor therapy, modular-agent probes (MAPs) comprised of various functional modules have been proposed. Researchers have tried to optimize the MAPs by exploiting the new modules or increasing the numbers of module, while neglecting the configuration of various modules. Here, we focus on the different spatial arrangements of existing modules. By utilizing a tetraphenylethylene (TPE) derivative with stereochemical structure and dual modifiable end-group sites as small molecule scaffold, two MAPs with same modular agents (module T for enhancing the internalization of MAPs by tumor cells and module M for causing mitochondrial dysfunction) but different spatial arrangements (on the one side, TM-AIE, and two sides, T-AIE-M, of the molecule scaffold) are designed. T-AIE-M with larger RGD binding angle performed higher specificity, while TM-AIE characterizing longer α-helix structure displayed superior toxicity.

Construction of biodegradable core cross-linked nanoparticles from near infrared dyes encoded in polyprodrug amphiphiles and investigation of their synergistic anticancer activity

Amphiphilic polyprodrugs with reduction-responsive camptothecin prodrug and photothermal converted IR780 dyes was performed via core cross-linking protocol. The nanoparticles could be served as a nanocarrier and presented severe cytotoxicity to HeLa cells.

Tandem Detection of Sub-Nano Molar Level CN- and Hg2+ in Aqueous Medium by a Suitable Molecular Sensor: A Viable Solution for Detection of CN- and Development of the RGB-Based Sensory Device

An inimitable urea-based multichannel chemosensor, DTPH [1,5-bis-(2,6-dichloro-4-(trifluoromethyl)phenyl)carbonohydrazide], was examined to be highly proficient to recognize CN- based on the H-bonding interaction between sensor -NH moiety and CN- in aqueous medium with explicit selectivity. In the absorption spectral titration of DTPH, a new peak at higher wavelength was emerged in titrimetric analytical studies of CN- with the zero-order reaction kinetics affirming the substantial sensor-analyte interaction. The isothermal titration calorimetry (ITC) experiment further affirmed that the sensing process was highly spontaneous with the Gibbs free energy of -26 × 104 cal/mol. The binding approach between DTPH and CN- was also validated by more than a few experimental studies by means of several spectroscopic tools along with the theoretical calculations. A very low detection limit of the chemosensor toward CN- (0.15 ppm) further instigated to design an RGB-based sensory device based on the colorimetric upshots of the chemosensor in order to develop a distinct perception regarding the presence of innocuous or precarious level of the CN- in a contaminated solution. Moreover, the reversibility of the sensor in the presence of CN- and Hg2+ originated a logic gate mimic ensemble. Additionally, the real-field along with the in vitro CN- detection efficiency of the photostable DTPH was also accomplished by using various biological specimens.

Controlled assembly of AIEgens based on a super-quadruplex scaffold for detection of plasma membrane proteins

Quantification of plasma membrane proteins (PMPs) is crucial for understanding the fundamentals of cellular signaling systems and their related diseases. In this work, a super-quadruplex scaffold was designed to regulate assembly of oligonucleotide-grafted AIEgens for detection of PMPs. The nonfluorescence oligonucleotide-grafted AIEgen (Oligo-AIEgen) was firstly synthesized by attaching the AIEgen to 3'-terminus of the oligonucleotide through click chemistry. Meanwhile, the tetramolecular hairpin-conjugated super-quadruplex (THP-G4) as cleavage element and signal enhancement scaffold composited of three elements: a substrate sequence of DNAzyme in the loop region, partial hybridization region in the stem, and six guanine nucleotides to form G-quadruplex. Once the DNAzyme was anchored on the specific PMPs through aptamer-protein recognition, the substrate sequence on the loop of THP-G4 was cleaved by DNAzyme with the aid of cofactor Mn^II, resulting in the conformation switch of THP-G4 to the activated G-quadruplex scaffold. The latter could assemble Oligo-AIEgens to generate aggregation-induced emission (AIE) enhancement, resulting in a simple and sensitive strategy for detection of membrane proteins. Moreover, the DNAzyme continuously cut the next THP-G4 to achieve recycling amplification. Under the optimized conditions, this AIE-based strategy exhibited good linear relationship with the logarithm of MUC1 concentration from 0.01 to 10 μg mL^-1 with the limit of detection down to 4.3 ng mL^-1. The G4-assembled AIEgens provides a universal platform for detecting various biomolecules and a proof-of concept for AIE biosensing.

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.

Biomimetic Sensing System for Tracing Pb2+ Distribution in Living Cells Based on the Metal-Peptide Supramolecular Assembly

Metal-peptide interactions provide plentiful resource and design principles for developing functional biomaterials and smart sensors. Pb²⁺, as a borderline metal ion, has versatile coordination modes. The interference from competing metal ions and endogenous chelating species greatly challenges Pb²⁺ analysis, especially in complicated living biosystems. Herein, a biomimetic peptide-based fluorescent sensor GSSH-2TPE was developed, starting from the structure of a naturally occurring peptide glutathione. Lewis acid-base theory was employed to guide the molecular design and tune the affinity and selectivity of the targeting performance. The integration of peptide recognition and aggregation-induced emission effect provides desirable sensing features, including specific turn-on response to Pb²⁺ over 18 different metal ions, rapid binding, and signal output, as well as high sensitivity with a detection limit of 1.5 nM. Mechanism investigation demonstrated the balance between the chelating groups, and the molecular configuration of the sensor contributes to the high selectivity toward Pb²⁺ complexation. The ion-induced supramolecular assembly lights up the bright fluorescence. The ability to image Pb²⁺ in living cells was exhibited with minimal interference from endogenous biothiols, no background fluorescence, and good biocompatibility. With good cell permeability, GSSH-2TPE can monitor changes in Pb²⁺ levels and biodistribution and thus predict possible damage pathways. Such metal-peptide interaction-based sensing systems offer tailorable platforms for designing bioanalytical tools and show great potential for studying the cell biology of metal ions in living biosystems.

Photosensitizers with Aggregation-Induced Emission: Materials and Biomedical Applications

Photodynamic therapy is arising as a noninvasive treatment modality for cancer and other diseases. One of the key factors to determine the therapeutic function is the efficiency of photosensitizers (PSs). Opposed to traditional PSs, which show quenched fluorescence and reduced singlet oxygen production in the aggregate state, PSs with aggregation-induced emission (AIE) exhibit enhanced fluorescence and strong photosensitization ability in nanoparticles. Here, the design principles of AIE PSs and their biomedical applications are discussed in detail, starting with a summary of traditional PSs, followed by a comparison between traditional and AIE PSs to highlight the various design strategies and unique features of the latter. Subsequently, the applications of AIE PSs in photodynamic cancer cell ablation, bacteria killing, and image-guided therapy are discussed using charged AIE PSs, AIE PS molecular probes, and AIE PS nanoparticles as examples. These studies have demonstrated the great potential of AIE PSs as effective theranostic agents to treat tumor or bacterial infection. This review hopefully will spur more research interest in AIE PSs for future translational research.