Glycosidase activated release of fluorescent 1,8-naphthalimide probes for tumor cell imaging from glycosylated 'pro-probes'

Carbohydrate-Functionalized Anthracene Carboximides as Multivalent Ligands and Bio-Imaging Agents

Anthracene carboximides (ACIs) conjugated with gluco-, galacto- and mannopyranosides are synthesized, by glycosylation of N-hydroxyethylanthracene carboximide acceptor with glycosyl donors. Glycoconjugation of anthracene carboximide increases the aq. solubility by more than 3-fold. The glycoconjugates display red-shifted absorption and emission, as compared to anthracene. Large Stokes shift (λabs/λem=445/525 nm) and high fluorescence quantum yields (Φ) of 0.86 and 0.5 occur in THF and water, respectively. The ACI-glycosides undergo facile photodimerization in aqueous solutions, leading to the formation of the head-to-tail dimer, as a mixture of syn and anti-isomers. Solution phase and solid-state characterizations by dynamic light scattering (DLS), microscopic imaging by atomic force (AFM) and transmission electron (TEM) microscopies reveal self-assembled vesicle structures of ACI glycosides. These self-assembled structures act as multivalent glycoclusters for ligand-specific lectin binding, as evidenced by the binding of Man-ACI to Con A, by fluorescence and turbidity assays. The conjugates do not show cellular cytotoxicity (IC50) till concentrations of 50 μM with HeLa and HepG2 cell lines and are cell-permeable, showing strong fluorescence inside the cells. These properties enable the glycoconjugates to be used in cell imaging. The non-selective cellular uptake of the glycoconjugates suggests a passive diffusion through the membrane.

Selection of Galectin-Binding Ligands from Synthetic Glycopeptide Libraries

Galectins, a class of carbohydrate-binding proteins, play a crucial role in various physiological and disease processes. Therefore, the identification of ligands that efficiently bind these proteins could potentially lead to the development of new therapeutic compounds. In this study, we present a method that involves screening synthetic click glycopeptide libraries to identify lectin-binding ligands with low micromolar affinity. Our methodology, initially optimized using Concanavalin A, was subsequently applied to identify binders for the therapeutically relevant galectin 1. Binding affinities were assessed using various methods and showed that the selected glycopeptides exhibited enhanced binding potency to the target lectins compared to the starting sugar moieties. This approach offers an alternative means of discovering galectin-binding ligands as well as other carbohydrate-binding proteins, which are considered important therapeutic targets.

Fluorescent Probes for Disease Diagnosis

The identification and detection of disease-related biomarkers is essential for early clinical diagnosis, evaluating disease progression, and for the development of therapeutics. Possessing the advantages of high sensitivity and selectivity, fluorescent probes have become effective tools for monitoring disease-related active molecules at the cellular level and in vivo. In this review, we describe current fluorescent probes designed for the detection and quantification of key bioactive molecules associated with common diseases, such as organ damage, inflammation, cancers, cardiovascular diseases, and brain disorders. We emphasize the strategies behind the design of fluorescent probes capable of disease biomarker detection and diagnosis and cover some aspects of combined diagnostic/therapeutic strategies based on regulating disease-related molecules. This review concludes with a discussion of the challenges and outlook for fluorescent probes, highlighting future avenues of research that should enable these probes to achieve accurate detection and identification of disease-related biomarkers for biomedical research and clinical applications.

De Novo Access to BODIPY C-Glycosides as Linker-Free Nonsymmetrical BODIPY-Carbohydrate Conjugates

Recent years have witnessed an increasing interest in the synthesis and study of BODIPY-glycoconjugates. Most of the described synthetic methods toward these derivatives involve postfunctional modifications of the BODIPY core followed by the covalent attachment of the fluorophore and the carbohydrate through a "connector". Conversely, few de novo synthetic approaches to linker-free carbohydrate-BODIPY hybrids have been described. We have developed a reliable modular, de novo, synthetic strategy to linker-free BODIPY-sugar derivatives using the condensation of pyrrole C-glycosides with a pyrrole-carbaldehyde derivative mediated by POCl3. This methodology allows labeling of carbohydrate biomolecules with fluorescent-enough BODIPYs within the biological window, stable in aqueous media, and able to display singlet oxygen generation.

Research Progress on Structure-Activity Relationship of 1,8-Naphthalimide DNA Chimeras Against Tumor

The development of 1,8-naphthalimide derivatives as cell probes, DNA targeting agents, and anti-tumor drugs is one of the research hotspots in the field of medicine. Naphthalimide compounds are a kind of DNA embedder, which can change the topological structure of DNA by embedding in the middle of DNA base pairs, and then affect the recognition and action of topoisomerase on DNA. Aminofide and mitonafide are the first 2 drugs to undergo clinical trials. They have good DNA insertion ability, can embed DNA double-stranded structure, and induce topoisomerase II to cut part of pBR322DNA, but not yet entered the market due to their toxicity. In this paper, the design and structure-activity relationship of mononaphthalimide and bisaphthalimide compounds were studied, and the relationship between the structure of naphthalimide and anti-tumor activity was analyzed and discussed. It was found that a variety of structural modifications were significant in improving anti-tumor activity and reducing toxicity.

Fidelity-oriented fluorescence imaging probes for beta-galactosidase: From accurate diagnosis to precise treatment

Beta-galactosidase (β-gal), a typical glycosidase catalyzing the hydrolysis of glycosidic bonds, is regarded as a vital biomarker for cell senescence and cancer occurrence. Given the advantages of high spatiotemporal resolution, high sensitivity, non-invasiveness, and being free of ionizing radiations, fluorescent imaging technology provides an excellent choice for in vivo imaging of β-gal. In this review, we detail the representative biotech advances of fluorescence imaging probes for β-gal bearing diverse fidelity-oriented improvements to elucidate their future potential in preclinical research and clinical application. Next, we propose the comprehensive design strategies of imaging probes for β-gal with respect of high fidelity. Considering the systematic implementation approaches, a range of high-fidelity imaging-guided theragnostic are adopted for the individual β-gal-associated biological scenarios. Finally, current challenges and future trends are proposed to promote the next development of imaging agents for individual and specific application scenarios.

Anthracenemethyl Glycosides as Supramolecular Synthons for Chiral Self-Assembly and as Probes in Cell Imaging

Chiral self-assembly of molecules warrants optimal structural features of synthons that promote formation of such self-assembled structures. A polyaromatic moiety coupled with hydrophilic, chiral-rich carbohydrates leads to segmentation of the regions and the self-assembly to supramolecular structures. Thermodynamic stability is augmented further through chiral self-assembly of the molecules, and formation of the desired chiral supramolecular structures is achieved. In the present study, we develop anthracene glycosides as efficient synthons that, in aqueous solutions, undergo facile self-assembly and lead to chiral supramolecular structures. Anthracenemethyl O-glycosides, installed with mono- and disaccharides, are studied for their self-assembly properties. Emerging chiral structures follow the configuration of the attached sugar moiety. Monosaccharide d- and l-glycopyranoside-containing derivatives alternate between left- and right-handed chiral structures, respectively. Disaccharide-containing derivatives do not exhibit chirality, even when self-assembly occurred. Photochemical [4π + 4π] cycloaddition occurs in the self-assembled structure in aqueous solution. Cell viability assay using HeLa cells shows above 80% viable cells at a concentration of 50 μM. Bioimaging assays reveal a significant imaging of HeLa cells for anthracenemethyl d-glucopyranoside; bright imaging was observed at the perinuclear region of the cells, suggestive of an active transport of the molecules through the cell membrane. d-Galactopyranoside and l-glucopyranoside-containing derivatives show weak imaging potencies.

Photoinduced electron transfer (PeT) based fluorescent probes for cellular imaging and disease therapy

Typical PeT-based fluorescent probes are multi-component systems where a fluorophore is connected to a recognition/activating group by an unconjugated linker. PeT-based fluorescent probes are powerful tools for cell imaging and disease diagnosis due to their low fluorescence background and significant fluorescence enhancement towards the target. This review provides research progress towards PeT-based fluorescent probes that target cell polarity, pH and biological species (reactive oxygen species, biothiols, biomacromolecules, etc.) over the last five years. In particular, we emphasise the molecular design strategies, mechanisms, and application of these probes. As such, this review aims to provide guidance and to enable researchers to develop new and improved PeT-based fluorescent probes, as well as promoting the use of PeT-based systems for sensing, imaging, and disease therapy.

Selective synthesis of α- and β-glycosides of N-acetyl galactosamine using rare earth metal triflates

Structures containing galactose and GalNAc residues are specifically recognized by asialoglycoprotein receptors, allowing them to selectively internalize by hepatocytes for drug-targeting delivery. However, methods for direct synthesis of GalNAc glycosides are still challenging due to the poor participating group of 2-acetamido. Here, we develop a facile strategy to synthesize various GalNAc glycosides by employing a series of rare earth metal triflates, and the results demonstrate that both α-glycosides and β-glycosides of GalNAc can be obtained by conducting with Hf(OTf)4 and Sc(OTf)3, respectively. These applicable results indicate that any interested GalNAc-containing substrates could be prepared by this simple strategy.

Enhancing cellular sulfane sulfur through β-glycosidase-activated persulfide donors: mechanistic insights and oxidative stress mitigation

Sulfane sulfur species such as persulfides and polysulfides along with hydrogen sulfide protect cells from oxidative stress and are key members of the cellular antioxidant pool. Here, we report perthiocarbamate-based prodrugs that are cleaved by β-glycosidases to produce persulfide and relatively innocuous byproducts. The β-glucosidase-activated persulfide donor enhances cellular sulfane sulfur and protects cells against lethality induced by elevated reactive oxygen species (ROS).

Glycosidase activated prodrugs for targeted cancer therapy

In this review glycosidase activated prodrugs that target cancer cells are discussed.

Fluorescence Microscopy-An Outline of Hardware, Biological Handling, and Fluorophore Considerations

Fluorescence microscopy has become a critical tool for researchers to understand biological processes at the cellular level. Micrographs from fixed and live-cell imaging procedures feature in a plethora of scientific articles for the field of cell biology, but the complexities of fluorescence microscopy as an imaging tool can sometimes be overlooked or misunderstood. This review seeks to cover the three fundamental considerations when designing fluorescence microscopy experiments: (1) hardware availability; (2) amenability of biological models to fluorescence microscopy; and (3) suitability of imaging agents for intended applications. This review will help equip the reader to make judicious decisions when designing fluorescence microscopy experiments that deliver high-resolution and informative images for cell biology.

A general strategy to the intracellular sensing of glycosidases using AIE-based glycoclusters

Glycosidases, which are the enzymes responsible for the removal of residual monosaccharides from glycoconjugates, are involved in many different biological and pathological events. The ability to detect sensitively the activity and spatiotemporal distribution of glycosidases in cells will provide useful tools for disease diagnosis. However, the currently developed fluorogenic probes for glycosidases are generally based on the glycosylation of the phenol group of a donor-acceptor type fluorogen. This molecular scaffold has potential drawbacks in terms of substrate scope, sensitivity because of aggregation-caused quenching (ACQ), and the inability for long-term cell tracking. Here, we developed glycoclusters characterized by aggregation-induced emission (AIE) properties as a general platform for the sensing of a variety of glycosidases. To overcome the low chemical reactivity associated with phenol glycosylation, here we developed an AIE-based scaffold, which is composed of tetraphenylethylene conjugated with dicyanomethylene-4H-pyran (TPE-DCM) with a red fluorescence emission. Subsequently, a pair of dendritic linkages was introduced to both sides of the fluorophore, to which six copies of monosaccharides (d-glucose, d-galactose or l-fucose) were introduced through azide-alkyne click chemistry. The resulting AIE-active glycoclusters were shown to be capable of (1) fluorogenic sensing of a diverse range of glycosidases including β-d-galactosidase, β-d-glucosidase and α-l-fucosidase through the AIE mechanism, (2) fluorescence imaging of the endogenous glycosidase activities in healthy and cancer cells, and during cell senescence, and (3) glycosidase-activated, long-term imaging of cells. The present study provides a general strategy to the functional, in situ imaging of glycosidase activities through the multivalent display of sugar epitopes of interest onto properly designed AIE-active fluorogens.

Real-Time Multi-Photon Tracking and Bioimaging of Glycosylated Theranostic Prodrugs upon Specific Enzyme Triggered Release

Real-time tracking of prodrug uptake, delivery and activation in vivo represents a major challenge for prodrug development. Herein, we demonstrate the use of novel glycosylated theranostics of the cancer pharmacophore Amonafide in highly-selective, enzymatic triggered release. We show that the use of endogenous enzymes for activated release of the therapeutic component can be observed, in real time, and monitored using one and two-photon bioimaging, offering unique insight into the prodrug pharmacokinetic profile. Furthermore, we demonstrate that the potent cytotoxicity of Amonafide is preserved using this targeted approach.

Fluorescent 4-amino-1,8-naphthalimide Tröger's bases (TBNaps) possessing (orthogonal) 'α-amino acids', esters and di-peptides and their solvent dependent photophysical properties

The synthesis of fifteen luminescent bis-naphthalimide based Tröger's bases (TBNaps) derived from 4-amino-1,8-naphthalimide (4-Amino-Nap) precursors is described; these scaffolds possess α-amino acids, esters or di-peptides conjugated at the imide site and show minor fluorescence in aqueous solution while being highly emissive in organic solvents. The investigation shows that these TBNaps possessing ICT excited state properties are capable of generating either positive or negative solvatochromic effects in response to changes in polarity and/or the hydrogen bonding capabilities of the medium.

Cu(I)-Catalyzed Click Chemistry in Glycoscience and Their Diverse Applications

Copper(I)-catalyzed 1,3-dipolar cycloaddition between organic azides and terminal alkynes, commonly known as CuAAC or click chemistry, has been identified as one of the most successful, versatile, reliable, and modular strategies for the rapid and regioselective construction of 1,4-disubstituted 1,2,3-triazoles as diversely functionalized molecules. Carbohydrates, an integral part of living cells, have several fascinating features, including their structural diversity, biocompatibility, bioavailability, hydrophilicity, and superior ADME properties with minimal toxicity, which support increased demand to explore them as versatile scaffolds for easy access to diverse glycohybrids and well-defined glycoconjugates for complete chemical, biochemical, and pharmacological investigations. This review highlights the successful development of CuAAC or click chemistry in emerging areas of glycoscience, including the synthesis of triazole appended carbohydrate-containing molecular architectures (mainly glycohybrids, glycoconjugates, glycopolymers, glycopeptides, glycoproteins, glycolipids, glycoclusters, and glycodendrimers through regioselective triazole forming modular and bio-orthogonal coupling protocols). It discusses the widespread applications of these glycoproducts as enzyme inhibitors in drug discovery and development, sensing, gelation, chelation, glycosylation, and catalysis. This review also covers the impact of click chemistry and provides future perspectives on its role in various emerging disciplines of science and technology.

Chromo-fluorogenic probes for β-galactosidase detection

β-Galactosidase (β-Gal) is a widely used enzyme as a reporter gene in the field of molecular biology which hydrolyzes the β-galactosides into monosaccharides. β-Gal is an essential enzyme in humans and its deficiency or its overexpression results in several rare diseases. Cellular senescence is probably one of the most relevant physiological disorders that involve β-Gal enzyme. In this review, we assess the progress made to date in the design of molecular-based probes for the detection of β-Gal both in vitro and in vivo. Most of the reported molecular probes for the detection of β-Gal consist of a galactopyranoside residue attached to a signalling unit through glycosidic bonds. The β-Gal-induced hydrolysis of the glycosidic bonds released the signalling unit with remarkable changes in color and/or emission. Additional examples based on other approaches are also described. The wide applicability of these probes for the rapid and in situ detection of de-regulation β-Gal-related diseases has boosted the research in this fertile field.

Dual modal fluorescent colposcope combined with near-infrared fluorescent dye TMTP1-PEG4-ICG to detect cervical lesions

To examine the cervical lesions by using the tumor-targeted near-infrared (NIR) fluorescent dyes TMTP1-PEG4-ICG, a dual modal colposcope with visible reflectance imaging and fluorescence imaging was developed. NIR fluorescence imaging and visible light reflectance imaging were integrated together on a colposcope by designing the specific optics and adopting a dual sensor charge coupled device (CCD) camera. Patients with squamous cell carcinoma, adenocarcinoma, cervical intraepithelial neoplasia (CIN) and cervicitis were examined using this dual modal colposcope to validate its potential of cervical cancer detection. Fluorescent dye TMTP1-PEG4-ICG was applied to the cervix 30 minutes before inspection. The fluorescence images were collected after wiping the unbound fluorescent dye using normal saline. Signal to back ratios (SBR) of the fluorescence images were analyzed and compared with the histological analysis. The results suggest that the fluorescent colposcope combined with tumor-specific near-infrared fluorescent dyes TMTP1-PEG4-ICG could help to evaluate cervical lesions in real time.

The Role of NIR Fluorescence in MDR Cancer Treatment: From Targeted Imaging to Phototherapy

BACKGROUND

Multidrug Resistance (MDR) is defined as a cross-resistance of cancer cells to various chemotherapeutics and has been demonstrated to correlate with drug efflux pumps. Visualization of drug efflux pumps is useful to pre-select patients who may be insensitive to chemotherapy, thus preventing patients from unnecessary treatment. Near-Infrared (NIR) imaging is an attractive approach to monitoring MDR due to its low tissue autofluorescence and deep tissue penetration. Molecular NIR imaging of MDR cancers requires stable probes targeting biomarkers with high specificity and affinity.

OBJECTIVE

This article aims to provide a concise review of novel NIR probes and their applications in MDR cancer treatment.

RESULTS

Recently, extensive research has been performed to develop novel NIR probes and several strategies display great promise. These strategies include chemical conjugation between NIR dyes and ligands targeting MDR-associated biomarkers, native NIR dyes with inherent targeting ability, activatable NIR probes as well as NIR dyes loaded nanoparticles. Moreover, NIR probes have been widely employed for photothermal and photodynamic therapy in cancer treatment, which combine with other modalities to overcome MDR. With the rapid advancing of nanotechnology, various nanoparticles are incorporated with NIR dyes to provide multifunctional platforms for controlled drug delivery and combined therapy to combat MDR. The construction of these probes for MDR cancers targeted NIR imaging and phototherapy will be discussed. Multimodal nanoscale platform which integrates MDR monitoring and combined therapy will also be encompassed.

CONCLUSION

We believe these NIR probes project a promising approach for diagnosis and therapy of MDR cancers, thus holding great potential to reach clinical settings in cancer treatment.

Stimulus-Responsive Nanomedicines for Disease Diagnosis and Treatment

Stimulus-responsive drug delivery systems generally aim to release the active pharmaceutical ingredient (API) in response to specific conditions and have recently been explored for disease treatments. These approaches can also be extended to molecular imaging to report on disease diagnosis and management. The stimuli used for activation are based on differences between the environment of the diseased or targeted sites, and normal tissues. Endogenous stimuli include pH, redox reactions, enzymatic activity, temperature and others. Exogenous site-specific stimuli include the use of magnetic fields, light, ultrasound and others. These endogenous or exogenous stimuli lead to structural changes or cleavage of the cargo carrier, leading to release of the API. A wide variety of stimulus-responsive systems have been developed-responsive to both a single stimulus or multiple stimuli-and represent a theranostic tool for disease treatment. In this review, stimuli commonly used in the development of theranostic nanoplatforms are enumerated. An emphasis on chemical structure and property relationships is provided, aiming to focus on insights for the design of stimulus-responsive delivery systems. Several examples of theranostic applications of these stimulus-responsive nanomedicines are discussed.

A trifunctional Pt(II) complex alleviates the NHEJ/HR-related DSBs repairs to evade cisplatin-resistance in NSCLC

Cisplatin, a representative of platinum-based drug, is clinically and widely used in the treatment of various types of malignant cancer. However, its non-selectivity to almost all the cell lines and resistance in long-term use severely limit its scope of use. As biotin-specific uptake systems are overexpressed in many types of tumors but rarely occur in normal tissues, making biotin a promising target for cancer treatment. In the study, we synthesized the Pt(II) complex C2 and determined its biological activities. The existence of biotin enhanced the ability of the complex to target tumors, while the introduction of a naphthalimide compound makes it possible to diagnose tumors and monitor their progress. We have also introduced a known Pt(II) complex DN604, which not only retains the excellent cytotoxicity of platinum drugs, but also inhibits the expression of DNA double-strand breaks (DSBs) repair-related NHEJ protein Ku70 and HR protein Rad51. In summary, we report a novel trifunctional Pt(II) complex that could target tumor cells, monitor tumor progression, and reverse DSBs repair-induced cisplatin-resistance.

Towards dual SPECT/optical bioimaging with a mitochondrial targeting, 99mTc(i) radiolabelled 1,8-naphthalimide conjugate

A series of six different 1,8-naphthalimide conjugated dipicolylamine ligands (L1-6) have been synthesised and characterised. The ligands possess a range of different linker units between the napthalimide fluorophore and dipcolylamine chelator which allow the overall lipophilicity to be tuned. A corresponding series of Re(i) complexes have been synthesised of the form fac-[Re(CO)3(L1-6)]BF4. The absorption and luminescence properties of the ligands and Re(i) complexes were dominated by the intramolecular charge transfer character of the substituted fluorophore (typically absorption ca. 425 nm and emission ca. 520 nm). Photophysical assessments show that some of the variants are moderately bright. Radiolabelling experiments using a water soluble ligand variant (L5) were successfully undertaken and optimised with fac-[99mTc(CO)3(H2O)3]+. Confocal fluorescence microscopy showed that fac-[Re(CO)3(L5)]+ localises in the mitochondria of MCF-7 cells. SPECT/CT imaging experiments on naïve mice showed that fac-[99mTc(CO)3(L5)]+ has a relatively high stability in vivo but did not show any cardiac uptake, demonstrating rapid clearance, predominantly via the biliary system along with a moderate amount cleared renally.

BODIPYs as Chemically Stable Fluorescent Tags for Synthetic Glycosylation Strategies towards Fluorescently Labeled Saccharides

A series of fluorescent boron-dipyrromethene (BODIPY, 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes have been designed to participate, as aglycons, in synthetic oligosaccharide protocols. As such, they served a dual purpose: first, by being incorporated at the beginning of the process (at the reducing-end of the growing saccharide moiety), they can function as fluorescent glycosyl tags, facilitating the detection and purification of the desired glycosidic intermediates, and secondly, the presence of these chromophores on the ensuing compounds grants access to fluorescently labeled saccharides. In this context, a sought-after feature of the fluorescent dyes has been their chemical robustness. Accordingly, some BODIPY derivatives described in this work can withstand the reaction conditions commonly employed in the chemical synthesis of saccharides; namely, glycosylation and protecting-group manipulations. Regarding their photophysical properties, the BODIPY-labeled saccharides obtained in this work display remarkable fluorescence efficiency in water, reaching quantum yield values up to 82 %, as well as notable lasing efficiencies and photostabilities.

Fluorescent glycoconjugates and their applications

Fluorescent glycoconjugates are discussed for their applications in biology in vitro, in cell assays and in animal models. Advantages and limitations are presented for each design using a fluorescent core conjugated with glycosides, or vice versa.

Fluorescent supramolecular hierarchical self-assemblies from glycosylated 4-amino- and 4-bromo-1,8-naphthalimides

The investigation into the self-assembly formation of the glycan based 4-amino- and 4-bromo-1,8-naphthalimide (Nap) structures1–3is presented.

An alternative modular 'click-SNAr-click' approach to develop subcellular localised fluorescent probes to image mobile Zn2+

Zn2+ is involved in a number of biological processes and its wide-ranging roles at the subcellular level, especially in specific organelles, have not yet been fully established due to a lack of tools to image it effectively. We report a new and efficient modular double 'click' approach towards a range of sub-cellular localised probes for mobile zinc. Through this methodology, endoplasmic reticulum, mitochondria and lysosome localised probes were successfully prepared which show good fluorescence responses to mobile Zn2+in vitro and in cellulo whilst a non-targeting probe was synthesized as a control. The methodology appears to have wide-utility for the generation of sub-cellular localised probes by incorporating specific organelle targeting vectors for mobile Zn2+ imaging.

In vivo ratiometric tracking of endogenous β-galactosidase activity using an activatable near-infrared fluorescent probe

Herein, we developed a dual-channel and light-up near-infrared fluorescent probe for ratiometric sensing of β-galactosidase (β-gal) activity. The well-designed probe, which shows ratiometric optical response with a significant red-shift (from 575 nm to 730 nm), was successfully applied to detect endogenous β-gal activity in SKOV-3 cells and tumor-bearing mice.

Enhancing Cytotoxicity of a Monofunctional Platinum Complex via a Dual-DNA-Damage Approach

Mitochondrial DNA (mtDNA) is an attractive cellular target for anticancer agents in addition to nuclear DNA (nDNA). The cationic platinum(II) complex cis-[Pt(NP)(NH₃)₂Cl]NO₃ (PtNP, NP = N-(2-ethylpyridine)-1,8-naphthalimide) bearing the DNA-intercalating moiety NP was designed. The structure of PtNP was fully characterized by single-crystal X-ray crystallography, NMR, and HRMS. PtNP is superior to cisplatin in both in vitro and in vivo anticancer activities with low systemic toxicity. The interaction of PtNP with CT-DNA demonstrated that PtNP could effectively bind to DNA through both covalent and noncovalent double binding modes. In addition to causing significant damage to nDNA and remarkable inhibition to DNA damage repair, PtNP also distributed in mitochondria, inducing mtDNA damage and affecting the downstream transcriptional level of mitochondrion-encoded genes. In addition, PtNP disturbed the physiological processes of mitochondria by reducing the mitochondrial membrane potential and promoting the generation of reactive oxygen species. Mechanistic studies demonstrate that PtNP induced apoptosis via mitochondrial pathways by upregulating Bax and Puma and downregulating Bcl-2 proteins, leading to the release of cytochrome c and activation of caspase-3 and caspase-9. As a dual-DNA-damage agent, PtNP is able to improve the anticancer activity by damaging both nuclear and mitochondrial DNA, thus providing a new anticancer mechanism of action for the naphthalimide monofunctional platinum(II) complexes.

A Malonyl-Based Scaffold for Conjugatable Multivalent Carbohydrate-BODIPY Presentations

A concise synthetic route from methylmalonate to a tetravalent aliphatic scaffold has been developed. The ensuing tetra-tethered derivative is equipped with two hydroxyl groups, as well as orthogonal alkene and alkyne functionalities. The usefulness of the scaffold has been demonstrated with the preparation of two representative multivalent derivatives: (i) a tetravalent compound containing two D-mannose units, one fluorescent boron-dipyrromethene (BODIPY) dye and a suitably functionalized amino acid and (ii) by way of dimerization and saponification, a water-soluble tetramannan derivative containing two fluorescent BODIPY units. Additionally, photophysical measurements conducted on these derivatives support the viability of the herein designed single and double BODIPY-labeled carbohydrate-based clusters as fluorescent markers.

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.

Amphiphilic triphenylamine–benzothiadiazole dyes: preparation, fluorescence and aggregation behavior, and enzyme fluorescence detection

Change of aggregate stabilization based on removal of the galactopyranose moiety leads to an emission enhancement to detect β-galactosidase activity.

Glycosylated naphthalimides and naphthalimide Tröger's bases as fluorescent aggregation probes for Con A

We report the synthesis of glycosylated naphthalimide compounds and their application as fluorescent probes for Concanavalin A (Con A) lectin.

1,1′-Bi(2-naphthol-4,5-dicarboximide)s: blue emissive axially chiral scaffolds with aggregation-enhanced emission properties

Novel electron-deficient 1,1′-binaphthol derivatives bearing two dicarboximide groups at the peri-positions show intense blue luminescence and aggregation-enhanced emission characteristics.

Unveiling the Potential of Unfused Bichromophoric Naphthalimide To Induce Cytotoxicity by Binding to Tubulin: Breaks Monotony of Naphthalimides as Conventional Intercalators

In the development of small-molecule drug candidates, naphthalimide-based compounds hold a very important position as potent anticancer agents with considerable safety in drug discoveries. Being synthetically and readily accessible, naphthalimide compounds with planar architecture have been developed mostly as DNA-targeting intercalators. However, in this article, it is demonstrated, for the first time, that an unfused naphthalimide-benzothiazole bichromophoric compound 2-(6-chlorobenzo[ d] thiazol-2-yl)-1 H-benzo[ de] isoquinoline-1,3(2 H)-dione (CBIQD), seems to expand the bioactivity of naphthalimide as anti-mitotic agent also. Preliminary studies demonstrate that CBIQD interferes with human lung cancer (A549) cell proliferation and growth and causes cellular morphological changes. However, the underlying mechanism of its antitumor action and primary cellular target in A549 cells remained skeptical. Confocal microscopy in A549 cells revealed disruption of interphase microtubule (MT) network and formation of aberrant multipolar spindle. Consistent with microscopy results, UV-vis, steady-state fluorescence, and time-resolved fluorescence (TRF) studies demonstrate that CBIQD efficiently binds to tubulin ( K_b = 2.03 × 10⁵ M^-1 ± 1.88%), inhibits its polymerization, and depolymerizes preformed microtubules (MTs). Low doses of CBIQD have also shown specificity toward tubulin protein in the presence of a nonspecific protein like bovine serum albumin as well as other cytoskeleton component, actin. The in vitro determination of binding site coupled with in silico studies suggests that CBIQD may prefer to occupy the colchicine binding site. Further, CBIQD perturbed tubulin conformation to some extent and protected ∼1.4 cysteine residues toward chemical modification by 5,5'-dithiobis-2-nitrobenzoic acid. We also suggest the possible mechanism underlying CBIQD-induced cancer cell cytotoxicity: CBIQD, when bound to tubulin, may prevent it to maintain a straight conformation; consequently, the α- and β-heterodimers might be no longer available for MT growth. Thus, the consolidated spectroscopic research described herein explores the potential of CBIQD as a new paradigm in the design and development of novel unfused or nonring-fused naphthalimide-based antimitotic cancer therapeutics in medicinal chemistry research.

Eu/Tb luminescence for alkaline phosphatase and β-galactosidase assay in hydrogels and on paper devices

Simple technologies for efficient detection of important (bio)molecules are always in great demand. We now report the detection and assay of two biologically important enzymes, alkaline phosphatase and β-galactosidase, in Eu- or Tb-based cholate hydrogels, respectively, and on filter paper discs coated with such hydrogels. Pro-sensitizers derived from 1-hydroxypyrene and 2,3-dihydroxynaphthalene were incorporated into Eu or Tb cholate hydrogels, respectively. Upon enzyme action, these artificial substrates liberate free sensitizers both in the gel and on gel-coated discs, resulting in turn-on luminescence, red/magenta for Eu, and green for Tb. The detection of enzymes was also demonstrated in natural/biological samples using low-cost systems.

A Lucifer-Based Environment-Sensitive Fluorescent PNA Probe for Imaging Poly(A) RNAs

Fluorescence‐based oligonucleotide (ON) hybridization probes greatly aid the detection and profiling of RNA sequences in cells. However, certain limitations such as target accessibility and hybridization efficiency in cellular environments hamper their broad application because RNAs can form complex and stable structures. In this context, we have developed a robust hybridization probe suitable for imaging RNA in cells by combining the properties of 1) a new microenvironment‐sensitive fluorescent nucleobase analogue, obtained by attaching the Lucifer chromophore (1,8‐naphthalimide) at the 5‐position of uracil, and 2) a peptide nucleic acid (PNA) capable of forming stable hybrids with RNA. The fluorescence of the PNA base analogue labeled with the Lucifer chromophore, when incorporated into PNA oligomers and hybridized to complementary and mismatched ONs, is highly responsive to its neighboring base environment. Notably, the PNA base reports the presence of an adenine repeat in an RNA ON with reasonable enhancement in fluorescence. This feature of the emissive analogue enabled the construction of a poly(T) PNA probe for the efficient visualization of polyadenylated [poly(A)] RNAs in cells—poly(A) being an important motif that plays vital roles in the lifecycle of many types of RNA. Our results demonstrate that such responsive fluorescent nucleobase analogues, when judiciously placed in PNA oligomers, could generate useful hybridization probes to detect nucleic acid sequences in cells and also to image them.

Dendron-Grafted Polylysine-Based Dual-Modal Nanoprobe for Ultra-Early Diagnosis of Pancreatic Precancerosis via Targeting a Urokinase-Type Plasminogen Activator Receptor

Pancreatic ductal adenocarcinoma (PDAC) is one of the leading causes of cancer death. Early detection of precancerous pancreatic intraepithelial neoplasia (PanIN) tissues is an urgent challenge to improve the PDAC prognosis. Here, a urokinase-type plasminogen activator receptor (uPAR)-targeted magnetic resonance (MR)/near-infrared fluorescence (NIRF) dual-modal nanoprobe dendron-grafted polylysine (DGL)-U11 for ultra-early detection of pancreatic precancerosis is reported. Because of its good biocompatibility and biodegradability, globular architecture, and well-defined reactive groups, the DGL is chosen as the platform to load with a pancreatic tumor-targeting peptide U11, a magnetic resonance contrast agent Gd3+ -diethylene triamine pentaacetic acid, and a near-infrared fluorescent cyanine dye Cy5.5. The nanoprobe DGL-U11 has several preferable characteristics, such as active peptide targeting to activator receptor, good biocompatibility, dual-modal imaging diagnosis, and well controlled diameter in a range of 15-25 nm. Upon incorporation of the active U11 peptide target to the overexpressed activator receptor uPAR, the targeted nanoprobe DGL-U11 can increase to the earlier PanIN-II stage through in vivo NIRF imaging. Labeled with both MR and NIRF bioimaging reporters, the uPAR-targeted dual-modal nanoprobe is very effective in the targeted imaging of precancerous PanINs and PDAC lesions with high sensitivity and spatial resolution, providing a promising platform to the ultra-early detection of PDAC.

Stimuli-Responsive Nanomedicines for Overcoming Cancer Multidrug Resistance

Chemotherapy is still a main option for cancer therapy, but its efficacy is often unsatisfying due to multidrug resistance (MDR). The tumor microenvironment is considered a dominant factor causing MDR. Stimuli-responsive nanomedicines exhibit many superiorities for reversal of MDR. As smart systems, stimuli-responsive nanomedicines are desirable for achieving site-specific accumulation and triggered drug release in response to slight changes in physicochemical properties in pathological conditions or to exogenous stimuli. In this review, we highlight the current progress of various nanomedicines with different stimuli-responsive capabilities for overcoming MDR. The materials, design, construction as well as efficacy in overcoming MDR of these nanomedicines are discussed. Eventually, we look forward to forthcoming intelligent nanoparticle systems with new mechanisms to deliver drugs for practical applications in conquering cancer MDR.

Naphthalimide-Based Fluorophore for Soft Anionic Interface Monitoring

A naphthalimide-based low-molecular-mass fluorophore (NA) was designed and synthesized by introducing an azetidine unit onto the aromatic ring of the compound as an electron-donating structure, and a hydrophilic (2-(2-aminoethyl-amino)ethanol) moiety into the "N-imide site" of the core structure. UV-vis absorption and fluorescence measurements revealed that the fluorophore is soluble in water and shows a fluorescent quantum yield of ∼20% and lifetime of ∼3.7 ns in the solvent within a wide pH range. Moreover, the fluorescence emission and anisotropy of the fluorophore as produced are both dependent upon the viscosity and polarity of the medium. Further studies demonstrated that NA can be used as a selective probe to monitor the aggregation of anionic surfactants owing to its accumulation onto the anionic surfaces of the aggregates as formed. Inspired by the discovery, NA was successfully applied for detection of cell membranes and E. coli via monitoring of their negatively charged surfaces, which is important for fast checking of biological contamination of water. Importantly, all the tests could be performed in a visualized manner. We believe that the new, low-molecular-mass fluorophore as created may find applications in chemical and biochemical sensing and imaging.

Fluorescent chemosensors: the past, present and future

Fluorescent chemosensors for ions and neutral analytes have been widely applied in many diverse fields such as biology, physiology, pharmacology, and environmental sciences. The field of fluorescent chemosensors has been in existence for about 150 years. In this time, a large range of fluorescent chemosensors have been established for the detection of biologically and/or environmentally important species. Despite the progress made in this field, several problems and challenges still exist. This tutorial review introduces the history and provides a general overview of the development in the research of fluorescent sensors, often referred to as chemosensors. This will be achieved by highlighting some pioneering and representative works from about 40 groups in the world that have made substantial contributions to this field. The basic principles involved in the design of chemosensors for specific analytes, problems and challenges in the field as well as possible future research directions are covered. The application of chemosensors in various established and emerging biotechnologies, is very bright.

Real time detection of ESKAPE pathogens by a nitroreductase-triggered fluorescence turn-on probe

The identification of bacterial pathogens is the critical first step in conquering infection diseases. A novel turn-on fluorescent probe for the selective sensing of nitroreductase (NTR) activity and its initial applications in rapid, real-time detection and identification of ESKAPE pathogens have been reported.