A Near-Infrared Peptide Probe with Tumor-Specific Excretion-Retarded Effect for Image-Guided Surgery of Renal Cell Carcinoma

Targeted in situ self-assembly augments peptide drug conjugate cell-entry efficiency

Peptide drug conjugate (PDC) has emerged as one of the new generations of targeted therapeutics for cancer, which owns the advantages of improved drug targetability and reduced adverse effects compared with traditional chemotherapy. However, the poor permeability of PDC drugs regarding tumor cells is an urgent problem to be solved. Herein, we design a PDC drug molecule, which is composed of three modules: targeting motif (RGD target), assembly motif (GNNNQNY) and cytotoxic payload (CPT molecule). This PDC in situ forms nanoclusters upon binding cellular receptor, resulting in improved PDC cell-entry efficiency and treatment efficacy. In addition, the PDC shows increased therapeutic efficacy and raises the maximum tolerance dose of the drug in breast and bladder xenografted mice models. This strategy leverages the assembly principle to promote penetration of peptide molecules into cells and increase intracellular drug bioavailability, which is of great significance for the development of PDC drugs in the future.

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.

Near-Infrared Fluorescent Probes for the Detection of Cancer-Associated Proteases

Proteases are enzymes capable of catalyzing protein breakdown, which is critical across many biological processes. There are several families of proteases, each of which perform key functions through the degradation of specific proteins. As our understanding of cancer improves, it has been demonstrated that several proteases can be overactivated during the progression of cancer and contribute to malignancy. Optical imaging systems that employ near-infrared (NIR) fluorescent probes to detect protease activity offer clinical promise, both for early detection of cancer as well as for the assessment of personalized therapy. In this Review, we review the design of NIR probes and their successful application for the detection of different cancer-associated proteases.

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.

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.

Supramolecular Dipeptide-Based Near-Infrared Fluorescent Nanotubes for Cellular Mitochondria Targeted Imaging and Early Apoptosis

Herein, we have designed and synthesized unsymmetrical visible Cy-3 and near-infrared (NIR) Cy-5 chromophores anchoring mitochondria targeting functional group conjugated with a Phe-Phe dipeptide by a microwave-assisted Fmoc solid phase peptide synthesis method on Wang resin. These dipeptide-based Cy-3-TPP/FF as well as Cy-5-TPP/FF molecules self-assemble to form fluorescent nanotubes in solution, and it has been confirmed by TEM, SEM, and AFM. The Cy-3-TPP/FF and Cy-5-TPP/FF molecules in solution exhibit narrow excitation as well as emission bands in the visible and NIR region, respectively. These lipophilic cationic fluorescent peptide molecules spontaneously and selectively accumulate inside the mitochondria of human carcinoma cells that have been experimentally validated by live cell confocal laser scanning microscopy and display a high Pearson's correlation coefficient in a colocalization assay. Live cell multicolor confocal imaging using the NIR Cy-5-TPP/FF in combination with other organelle specific dye is also accomplished. Moreover, these lipophilic dipeptide-based cationic molecules reach the critical aggregation concentration inside the mitochondria because of the extremely negative inner mitochondrial membrane potential [(ΔΨ_m)_cancer ≈ -220 mV] and form supramolecular nanotubes which are accountable for malignant mitochondria targeted early apoptosis. The early apoptosis is arrested using Cy-5-TPP/FF and confirmed by annexin V-FITC/PI apoptosis detection assay.

Ultrasound lighting up AIEgens for potential surgical navigation

Multifunctional contrast-enhanced agents suitable for application in surgical navigation by taking advantage of the merits of their diverse imaging modalities at different surgical stages are highly sought-after. Herein, an amphipathic polymer composed of aggregation-induced emission fluorogens (AIEgens) and Gd³⁺ chelates was successfully synthesized and assembled into ultrasound responsive microbubbles (AIE-Gd MBs) to realize potential tri-modal contrast-enhanced ultrasound (US) imaging, magnetic resonance imaging (MRI), and AIEgen-based fluorescence imaging (FI) during the perioperative period. Through ultrasound targeted microbubble destruction (UTMD) and cavitation effect, the as-prepared AIE-Gd MBs went through a MBs-to-nanoparticles (NPs) conversion, which not only resulted in targeted accumulation in tumor tissues but also led to stronger fluorescence being exhibited due to the more aggregated AIE-Gd molecules in the NPs. As a proof-of-concept, our work proposes a strategy of US-lit-up AIEgens in tumors which could offer a simple and powerful tool for surgical navigation in the future.

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.

Hyperfluorescence Imaging of Kidney Cancer Enabled by Renal Secretion Pathway Dependent Efflux Transport

Renal tubular secretion is an active efflux pathway for the kidneys to remove molecules but has yet to be used to enhance kidney cancer targeting. We report indocyanine green (ICG) conjugated with a 2100 Da PEG molecule (ICG-PEG45) as a renal-tubule-secreted near-infrared-emitting fluorophore for hyperfluorescence imaging of kidney cancers, which cannot be achieved with hepatobiliary- and glomerular-clearable ICG. This pathway-dependent targeting of kidney cancer arises from the fact that the secretion pathway enables ICG-PEG45 to be effectively effluxed out of normal proximal tubules through P-glycoprotein transporter while being retained in cancerous kidney tissues with low P-glycoprotein expression. Tuning elimination pathways and utilizing different efflux kinetics of medical agents in normal and diseased tissues could be a new strategy for tackling challenges in disease diagnosis and treatments that cannot be addressed with passive and ligand-receptor-mediated active targeting.

Peptide-based supramolecular hydrogels for bioimaging applications

Peptide-based supramolecular hydrogels have unique merits in bioimaging applications.

Exploring the Biocompatibility of Near-IR CuInSexS2-x/ZnS Quantum Dots for Deep-Tissue Bioimaging

Near-infrared (NIR) emitting quantum dots (QDs) with emission in the biological transparency windows (NIR-I: 650-950 nm and NIR-II: 1000-1350 nm) are promising candidates for deep-tissue bioimaging. However, they typically contain toxic heavy metals such as cadmium, mercury, arsenic, or lead. We report on the biocompatibility of high brightness CuInSe_xS_2-x/ZnS (CISeS/ZnS) QDs with a tunable emission covering the visible to NIR (550-1300 nm peak emission) and quantify the transmission of their photoluminescence through multiple biological components to evaluate their use as imaging agents. In general, CISeS/ZnS QDs were less cytotoxic to mouse fibroblast cells when compared with commercial CdSe/ZnS and InP/ZnS QDs. Surprisingly, InP/ZnS QDs significantly upregulated expression of apoptotic genes in mouse fibroblast cells, while cells exposed to CISeS/ZnS QDs did not. These findings provide insight into biocompatibility and cytotoxicity of CISeS/ZnS QDs that could be used for bioimaging.

pH/Reduction Dual Stimuli-Triggered Self-Assembly of NIR Theranostic Probes for Enhanced Dual-Modal Imaging and Photothermal Therapy of Tumors

Tumor microenvironment plays a pivotal role in the growth and metastasis of tumors, and has become a promising target for precise diagnosis and treatment of tumors. Herein, a novel smart NIR theranostic probe Cy-1 that can simultaneously respond to low intracellular pH and reductive glutathione (GSH) is reported. This probe has demonstrated to be able to intermolecularly undergo a biologically compatible CBT-Cys condensation reaction to selectively form large nanoaggregates in the tumor microenvironment resulting in its enhanced accumulation and retention in the tumor, which as a consequence significantly improves the sensitivity of NIR/photoacoustic imaging and photothermal therapeutic efficacy of tumors in living mice. We thus believe that this dual stimuli-mediated self-assembly strategy may offer a promising and universal platform for cancer theranostics.

Biomaterials based on noncovalent interactions of small molecules

Unlike conventional materials that covalent bonds connecting atoms as the major force to hold the materials together, supramolecular biomaterials rely on noncovalent intermolecular interactions to assemble. The reversibility and biocompatibility of supramolecular biomaterials render them with diverse range of functions and lead to rapid development in the past two decades. This review focuses on the noncovalent and enzymatic control of supramolecular biomaterials, with the introduction to various triggering mechanism to initiate self-assembly. Representative applications of supramolecular biomaterials are highlighted in four categories: tissue engineering, cancer therapy, drug delivery, and molecular imaging. By introducing various applications, we intend to show enzymatic control and noncovalent interactions as a powerful tool for achieving spatiotemporal control of biomaterials both invitro and in vivo for biomedicine.

Enzymatic Noncovalent Synthesis

Enzymatic reactions and noncovalent (i.e., supramolecular) interactions are two fundamental nongenetic attributes of life. Enzymatic noncovalent synthesis (ENS) refers to a process where enzymatic reactions control intermolecular noncovalent interactions for spatial organization of higher-order molecular assemblies that exhibit emergent properties and functions. Like enzymatic covalent synthesis (ECS), in which an enzyme catalyzes the formation of covalent bonds to generate individual molecules, ENS is a unifying theme for understanding the functions, morphologies, and locations of molecular ensembles in cellular environments. This review intends to provide a summary of the works of ENS within the past decade and emphasize ENS for functions. After comparing ECS and ENS, we describe a few representative examples where nature uses ENS, as a rule of life, to create the ensembles of biomacromolecules for emergent properties/functions in a myriad of cellular processes. Then, we focus on ENS of man-made (synthetic) molecules in cell-free conditions, classified by the types of enzymes. After that, we introduce the exploration of ENS of man-made molecules in the context of cells by discussing intercellular, peri/intracellular, and subcellular ENS for cell morphogenesis, molecular imaging, cancer therapy, and other applications. Finally, we provide a perspective on the promises of ENS for developing molecular assemblies/processes for functions. This review aims to be an updated introduction for researchers who are interested in exploring noncovalent synthesis for developing molecular science and technologies to address societal needs.

Combined Tumor Environment Triggered Self-Assembling Peptide Nanofibers and Inducible Multivalent Ligand Display for Cancer Cell Targeting with Enhanced Sensitivity and Specificity

Many new technologies, such as cancer microenvironment-induced nanoparticle targeting and multivalent ligand approach for cell surface receptors, are developed for active targeting in cancer therapy. While the principle of each technology is well illustrated, most systems suffer from low targeting specificity and sensitivity. To fill the gap, this work demonstrates a successful attempt to combine both technologies to simultaneously improve cancer cell targeting sensitivity and specificity. Specifically, the main component is a targeting ligand conjugated self-assembling monomer precursor (SAM-P), which, at the tumor site, undergoes tumor-triggered cleavage to release the active form of self-assembling monomer capable of forming supramolecular nanostructures. Biophysical characterization confirms the chemical and physical transformation of SAM-P from unimers or oligomers with low ligand valency to supramolecular assemblies with high ligand valency under a tumor-mimicking reductive microenvironment. The in vitro fluorescence assay shows the importance of supramolecular morphology in mediating ligand-receptor interactions and targeting sensitivity. Enhanced targeting specificity and sensitivity can be achieved via tumor-triggered supramolecular assembly and induces multivalent ligand presentation toward cell surface receptors, respectively. The results support this combined tumor microenvironment-induced cell targeting and multivalent ligand display approach, and have great potential for use as cell-specific molecular imaging and therapeutic agents with high sensitivity and specificity.

Peptide-Based Nanoassemblies in Gene Therapy and Diagnosis: Paving the Way for Clinical Application

Nanotechnology approaches play an important role in developing novel and efficient carriers for biomedical applications. Peptides are particularly appealing to generate such nanocarriers because they can be rationally designed to serve as building blocks for self-assembling nanoscale structures with great potential as therapeutic or diagnostic delivery vehicles. In this review, we describe peptide-based nanoassemblies and highlight features that make them particularly attractive for the delivery of nucleic acids to host cells or improve the specificity and sensitivity of probes in diagnostic imaging. We outline the current state in the design of peptides and peptide-conjugates and the paradigms of their self-assembly into well-defined nanostructures, as well as the co-assembly of nucleic acids to form less structured nanoparticles. Various recent examples of engineered peptides and peptide-conjugates promoting self-assembly and providing the structures with wanted functionalities are presented. The advantages of peptides are not only their biocompatibility and biodegradability, but the possibility of sheer limitless combinations and modifications of amino acid residues to induce the assembly of modular, multiplexed delivery systems. Moreover, functions that nature encoded in peptides, such as their ability to target molecular recognition sites, can be emulated repeatedly in nanoassemblies. Finally, we present recent examples where self-assembled peptide-based assemblies with "smart" activity are used in vivo. Gene delivery and diagnostic imaging in mouse tumor models exemplify the great potential of peptide nanoassemblies for future clinical applications.

Quicker, deeper and stronger imaging: A review of tumor-targeted, near-infrared fluorescent dyes for fluorescence guided surgery in the preclinical and clinical stages

Cancer is a public health problem and the main cause of human mortality and morbidity worldwide. Complete removal of tumors and metastatic lymph nodes in surgery is significantly beneficial for the prognosis of patients. Tumor-targeted, near-infrared fluorescent (NIRF) imaging is an emerging field of real-time intraoperative cancer imaging based on tumor-targeted NIRF dyes. Targeted NIRF dyes contain NIRF fluorophores and specific binding ligands such as antibodies, peptides and small molecules. The present article reviews recently updated tumor-targeted NIRF dyes for the molecular imaging of malignant tumors in the preclinical stage and clinical trials. The strengths and challenges of NIRF agents with tumor-targeting ability are also summarized. Smaller ligands, near infrared II dyes, dual-modality dyes and activatable dyes may contribute to quicker, deeper, stronger imaging in the nearest future. In this review, we highlighted tumor-targeted NIRF dyes for fluorescence-guided surgery and their potential clinical translation.

Recent progress of therapeutic peptide based nanomaterials: from synthesis and self-assembly to cancer treatment

This review has described the synthesis, self-assembly and the anti-cancer application of therapeutic peptides and their conjugates, particularly polymer–peptide conjugates (PPCs).