Bio-orthogonally Deciphered Binary Nanoemitters for Tumor Diagnostics

Minimized background tumor imaging through self-assembled disulfide dicyanine nanoparticles

Fluorescence imaging holds great potential as a powerful diagnostic tool for tumor cell visualization. However, a significant challenge in fluorescence imaging is the high background signal, which obscures the tumor-specific signal and reduced the signal-to-noise ratio (SNR) of imaging, thereby reducing the accuracy of tumor detection and delineation. In this research, we designed and synthesized an amphiphilic disulfide dicyanine ss-diCy7, which can self-assemble into nanoparticles with uniform dispersion in aqueous environments. The fluorescence intensity of these nanoparticles is significantly reduced by 96% due to aggregation-induced quenching arising from π-π stacking. The nanoparticles exhibit a highly specific response to glutathione (GSH) in vitro, resulting in a substantial enhancement of fluorescence intensity by a 24-fold. The enhancement was also achieved in cell and mouse imaging experiments. In addition, in the mouse tumor model, ss-diCy7 nanoparticles demonstrated superior performance compared to traditional mono-cyanine dyes, offering a reduced background signal and prolonged fluorescence duration. This work is anticipated to contribute to the high-resolution tumor imaging.

Intracellular Formation of Synthetic Peptide Nanostructures Causes Mitochondrial Disruption and Cell Death in Tumor Spheroids

Supramolecular assemblies found in nature demonstrate the concept of creating functionality through structure formation. In recent years, these complex natural architectures have inspired the development of materials for the formation of synthetic nanostructures within living cells. These intracellular assemblies have the potential to modulate cellular processes, yet their specific effects on cellular metabolism and 3D cell networks, such as tumor spheroids, still remain underexplored. Herein, the study correlates the glutathione-induced formation of synthetic nanostructures inside MDA-MB-231 triple-negative breast cancer cells to the metabolic disruption and mitochondrial degradation observed in 2D cell culture, as well as to cell death and size decrease in a 3D tumor spheroid model. In 2D cell culture, material-cell interactions are examined through live-cell imaging and by quantifying changes in mitochondrial respiration. By studying the interplay between glutathione-responsive cytosolic peptide assembly and the implications on the integrity of the mitochondrial network, as well as on 3D cell networks, the work advances the understanding of how synthetic intracellular nanofibers impact vital functions of living cells.

Nanostructured Heterogeneous Catalysts for Bioorthogonal Reactions

Bioorthogonal chemistry has inspired a new subarea of chemistry providing a powerful tool to perform novel biocompatible chemospecific reactions in living systems. Following the premise that they do not interfere with biological functions, bioorthogonal reactions are increasingly applied in biomedical research, particularly with respect to genetic encoding systems, fluorogenic reactions for bioimaging, and cancer therapy. This Minireview compiles recent advances in the use of heterogeneous catalysts for bioorthogonal reactions. The synthetic strategies of Pd-, Au-, and Cu-based materials, their applicability in the activation of caged fluorophores and prodrugs, and the possibilities of using external stimuli to release therapeutic substances at a specific location in a diseased tissue are discussed. Finally, we highlight frontiers in the field, identifying challenges, and propose directions for future development in this emerging field.

Pyrene-Based AIE Active Materials for Bioimaging and Theranostics Applications

Aggregation-induced emission (AIE) is a unique research topic and property that can lead to a wide range of applications, including cellular imaging, theranostics, analyte quantitation and the specific detection of biologically important species. Towards the development of the AIE-active materials, many aromatic moieties composed of tetraphenylethylene, anthracene, pyrene, etc., have been developed. Among these aromatic moieties, pyrene is an aromatic hydrocarbon with a polycyclic flat structure containing four fused benzene rings to provide an unusual electron delocalization feature that is important in the AIE property. Numerous pyrene-based AIE-active materials have been reported with the AIE property towards sensing, imaging and theranostics applications. Most importantly, these AIE-active pyrene moieties exist as small molecules, Schiff bases, polymers, supramolecules, metal-organic frameworks, etc. This comprehensive review outlines utilizations of AIE-active pyrene-based materials on the imaging and theranostics studies. Moreover, the design and synthesis of these pyrene-based molecules are delivered with discussions on their future scopes.

Designing bioresponsive nanomaterials for intracellular self-assembly

Supramolecular assemblies are essential components of living organisms. Cellular scaffolds, such as the cytoskeleton or the cell membrane, are formed via secondary interactions between proteins or lipids and direct biological processes such as metabolism, proliferation and transport. Inspired by nature’s evolution of function through structure formation, a range of synthetic nanomaterials has been developed in the past decade, with the goal of creating non-natural supramolecular assemblies inside living mammalian cells. Given the intricacy of biological pathways and the compartmentalization of the cell, different strategies can be employed to control the assembly formation within the highly crowded, dynamic cellular environment. In this Review, we highlight emerging molecular design concepts aimed at creating precursors that respond to endogenous stimuli to build nanostructures within the cell. We describe the underlying reaction mechanisms that can provide spatial and temporal control over the subcellular formation of synthetic nanostructures. Showcasing recent advances in the development of bioresponsive nanomaterials for intracellular self-assembly, we also discuss their impact on cellular function and the challenges associated with establishing structure–bioactivity relationships, as well as their relevance for the discovery of novel drugs and imaging agents, to address the shortfall of current solutions to pressing health issues.

Creating artificial nanostructures inside living cells requires the careful design of molecules that can transform into active monomers within a complex cellular environment. This Review explores the recent development of bioresponsive precursors for the controlled formation of intracellular supramolecular assemblies.

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

Image-guided surgery plays a crucial role in realizing complete tumor removal, reducing postoperative recurrence and increasing patient survival. However, imaging of tumor lesion in the typical metabolic organs, e.g., kidney and liver, still has great challenges due to the intrinsic nonspecific accumulation of imaging probes in those organs. Herein, we report an in situ self-assembled near-infrared (NIR) peptide probe with tumor-specific excretion-retarded (TER) effect in tumor lesions, enabling high-performance imaging of human renal cell carcinoma (RCC) and achieving complete tumor removal, ultimately reducing postoperative recurrence. The NIR peptide probe first specifically recognizes α_vβ₃ integrin overexpressed in renal cancer cells, then is cleaved by MMP-2/9, which is up-regulated in the tumor microenvironment. The probe residue spontaneously self-assembles into nanofibers that exhibit an excretion-retarded effect in the kidney, which contributes to a high signal-to-noise (S/N) ratio in orthotopic RCC mice. Intriguingly, the TER effect also enables precisely identifying eye-invisible tiny lesions (<1 mm), which contributes to complete tumor removal and significantly reduces the postoperative recurrence compared with traditional surgery. Finally, the TER strategy is successfully employed in high-performance identification of human RCC in an ex vivo kidney perfusion model. Taken together, this NIR peptide probe based on the TER strategy is a promising method for detecting tumors in metabolic organs in diverse biomedical applications.

Probing two PESIN-indocyanine-dye-conjugates: significance of the used fluorophore

Peptide-dye-conjugates hold a great promise in application for biological and medical imaging of cellular processes and in delineation and characterization of human tumors. In particular, indocyanine dyes are of great interest due to their reported superior properties such as absorption and emission in the near-infrared (NIR) spectral range, favorable Stokes shifts and their well-studied safety profile in humans. In this study, we investigated and describe the influence of indocyanine dyes on different properties of the final peptide-dye-conjugates. As a target peptide, PESIN, a bombesin derivative, was used as a model peptide which addresses GRP receptors overexpressed on different malignancies. Here, we map similarities and differences of the fluorescent conjugates and by this elucidate the influence of the dyes on different properties of the formed conjugates. We performed the dye syntheses, subsequent bioconjugation reactions and in the following investigated the optical properties, water/octanol distribution coefficients and target receptor affinities by in vitro competitive binding studies on PC-3 cells. The obtained results give a handrail to medical and biological researchers planning studies involving indocyanine dye biomolecule conjugates.

Bispyrene-Based Self-Assembled Nanomaterials: In Vivo Self-Assembly, Transformation, and Biomedical Effects

Self-assembled nanomaterials show potential high efficiency as theranostic agents for high-performance imaging and therapy. However, superstructures and properties of preassembled nanomaterials are somewhat compromised under complicated physiological conditions. Given the advantages of the dynamic nature and adaptive behavior of self-assembly systems, we propose an "in vivo self-assembly" strategy for in situ construction of nanomaterials in living objects. For the proof-of-concept study of in vivo self-assembly, we developed a bispyrene (BP) molecule as a multifunctional building block. BP molecules show nonfluorescence in the monomeric state. Quantum-chemical calculations indicate that BP forms twisted intramolecular charge transfer states, which are separated into two orthogonal units, preventing the fluorescence emission. Interestingly, the typical excimeric emission of BP is observed with the formation of J-type aggregates, as confirmed by single-crystal X-ray diffraction. Packing of the BP molecules generates parallel pyrene units that interact with adjacent ones in a slipped face-to-face fashion through intermolecular π-π interactions. BP and/or its amphiphilic derivatives are capable of self-aggregating into nanoparticles (NPs) in aqueous solution because of the hydrophobic and π-π interactions of BP. Upon specific biological stimuli, BP NPs can be transformed into variable self-assembled superstructures. Importantly, the self-assembled BP NPs exhibit turn-on fluorescence signals that can be used to monitor the self-assembly/disassembly process in vitro and in vivo. On the basis of the photophysical properties of BP and its aggregates, we synthesized a series of designed BP derivatives as building blocks for in situ construction of functional nanomaterials for bioimaging and/or therapeutics. We observed several new biomedical effects, e.g., (i) the assembly/aggregation-induced retention (AIR) effect, which shows improved accumulation and retention of bioactive nanomaterials in the regions of interests; (ii) the transformation-induced surface adhesion (TISA) effect, which means the BP NPs transform into nanofibers (NFs) on cell surfaces upon binding with specific receptors, which leads to less uptake of BP NPs by cells via traditional endocytosis pathway; and (iii) transformation of the BP NPs into NFs in the tumor microenvironment, showing high accumulation and long-term retention, revealing the transformation-enhanced accumulation and retention (TEAR) effect. In this Account, we summarize the fluorescence property and emission mechanism of BP building blocks upon aggregation in the biological environment. Moreover, BP-derived compounds used for in vivo self-assembly and transformation are introduced involving modulation strategies. Subsequently, unexpected biomedical effects and applications for theranostics of BP based nanomaterials are discussed. We finally conclude with an outlook toward future developments of BP-based self-assembled nanomaterials.

Self-Assembled Fluorescent Organic Nanomaterials for Biomedical Imaging

Fluorescent nanomaterials, self-assembled from building blocks through multiple intermolecular interactions show diversified structures and functionalities, and are potential fluorescence contrast agents/probes for high-performance biomedical imaging. Self-assembled nanomaterials exhibit high stability, long circulation time, and targeted biological distribution. This review summarizes recent advances of self-assembled nanomaterials as fluorescence contrast agents/probes for biomedical imaging. The self-assembled nanomaterials are classified into two groups, i.e., ex situ and in situ construction of self-assembled nanomaterials. The advantages of ex situ as well as in situ constructed nanomaterials for biomedical applications are discussed thoroughly. The directions of future developments for self-assembled nanomaterials are provided.

In situ construction of nanonetworks from transformable nanoparticles for anti-angiogenic therapy

Tumor metastasis as the most common reason of death from cancer has always been a great challenge in both clinical and scientific research, where angiogenesis plays a necessary role. Herein, we report an extracellularly transformable nanomaterial for in situ construction of defensive networks on interaction with vascular endothelial growth factor (VEGF) for anti-angiogenic therapy of tumor. The fibrous networks exhibit transformation-enhanced accumulation and retention (TEAR) effects (over 72 h), and bind and intercept cell-secreted VEGF over particulate and molecular anti-angiogenic agents with high efficiency, leading to anti-angiogenesis. This study demonstrates that angiogenesis is positively related to tumor growth as well as tumor metastasis; the anti-angiogenic therapy inhibits tumor metastasis with an inhibition rate of 65.9%. In addition, this extracellular strategy of transformation may be utilized to bind huge amounts of cell-secreted biomolecules/factors or receptors on cell surfaces and inhibit their functionalities for cancer therapy.

Recent Advances in Nanotechnology for Autophagy Detection

Autophagy is closely related to various diseases, and is a diagnostic and therapeutic target for some diseases. In recent years, tremendous efforts have been made to develop excellent probes for detection of autophagy. Nanostructure-based probes are interesting and promising approaches for in vivo biological imaging due to their unique structural and functional characteristics, e.g., modulating pharmacokinetics property by biocompatible coatings, multimodality capacity by delivering multiple imaging agents and highly specific targeting by antibody ligands. In this Review, we first introduce recent advancements in the development of nanostructure-based probes for detection of autophagy, including inorganic hybrid nanomaterials and self-assembled peptide polymeric nanoparticles. Meanwhile, a nanoprobe based on a "in vivo self-assembly" strategy is highlighted. The "in vivo self-assembly" endows nanoprobes with higher accumulation, and longer and better signal stability for in vivo detection of autophagy. Furthermore, this novel strategy could be widely used for biomedical imaging/diagnostics and therapeutics, which would attract more attention to this research area.

General Approach of Stimuli-Induced Aggregation for Monitoring Tumor Therapy

Intracellular construction of nanoaggregates from synthetic molecules to mimic natural ordered superstructures has gained increasing attention recently. Here, we develop an endogenous stimuli-induced aggregation (eSIA) approach to construct functional nanoaggregates for sensing and monitoring cellular physiological processes in situ. We design a series of thermosensitive polymer-peptide conjugates (PPCs), which are capable of constructing nanoaggregates in cells based on their isothermal phase transition property. The PPCs are composed of three moieties (i.e., a thermoresponsive polymer backbone, a grafted peptide, and a signal-molecule label). The bioenvironment-associated phase transition behavior of PPCs are carefully studied by consideration of various crucial parameters such as chain length, hydrophilicity, ratio of grafted peptides, and concentration. Intriguingly, under the specific intracellular stimulus, the PPCs are tailored and simultaneously form nanoaggregates exhibiting long-term retention effect, which enables specific identification and quantification of endogenous factors. This general approach is expected for high-performance in situ sensing and dynamic monitoring of disease progression in living subjects.