In vivo imaging of β-galactosidase stimulated activity in hepatocellular carcinoma using ligand-targeted fluorescent probe

A near-infrared fluorescent probe toward β-Gal with dual-targeting potential of hepatocytes and lysosomes: Design, synthesis, and evaluation

In this work, a novel near-infrared fluorescent probe of benzopyranonitrile toward β-Gal was developed with high selectivity and low detection limits. DCM-Mor-Gal could effectively distinguish hepatocellular cells (HepG2) from SGC7901, HeLa, A549, and human normal liver cells (HL-7702) under the mediation of the galactose group, and effectively aggregate in the lysosomes under the acidity-alkalinity attraction, showing a notable dual-targeting potential of hepatocytes and lysosomes. The zebrafish experiments confirmed the utility of DCM-Mor-Gal in detecting β-Gal in vivo, which is expected to be an effective tool for the clinical detection of related diseases.

A NIR fluorescent probe based on tricyanofuran for the detection of β-galactosidase in living ovarian tumor cells and in vivo

β-Galactosidase (β-Gal) as an important glycoside hydrolase plays an important role in the early diagnosis of ovarian cancer. It is important to accurately and conveniently detect β-Gal in organisms. In this study, we developed a fluorescent probe TCF-GAL based on the tricyanofuran structure, which is linked to β-galactose through ether bonds for β-Gal detection. Probe TCF-GAL exhibited satisfactory selectivity and sensitivity toward β-Gal with the calculated LOD of 1.45 × 10-4 U/mL. Moreover, it can be applied to image endogenous β-Gal in living SKOV3 cells with low cytotoxicity. Importantly, probe TCF-GAL was successfully employed in monitoring β-Gal in the mouse subcutaneous model of ovarian cancer. These results indicated that this probe had great potential for diagnosing β-Gal related diseases.

β-Galactosidase- and Photo-Activatable Fluorescent Probes for Protein Labeling and Super-Resolution STED Microscopy in Living Cells

We report on the synthesis of two fluorescent probes which can be activated by β-Galactosidase (β-Gal) enzymes and/or light. The probes contained 2-nitro-4-oxybenzyl and 3-nitro-4-oxybenzyl fragments, with β-Gal residues linked to C-4. We performed the enzymatic and photoactivation of the probes in a cuvette and compared them, prior to the labeling of Vimentin-Halo fusion protein in live cells with overexpressed β-galactosidase. The dye fluorescence afforded the observation of enzyme activity by means of confocal and super-resolution optical microscopy based on stimulated emission depletion (STED). The tracing of enzymatic activity with the retention of activated fluorescent products inside cells was combined with super-resolution imaging as a tool for use in biomedicine and life science.

NIR-II Fluorescence Imaging for In Vivo Quantitative Analysis

In vivo real-time qualitative and quantitative analysis is essential for the diagnosis and treatment of diseases such as tumors. Near-infrared-II (NIR-II, 1000-1700 nm) bioimaging is an emerging visualization modality based on fluorescent materials. The advantages of NIR-II region fluorescent materials in terms of reduced photon scattering and low tissue autofluorescence enable NIR-II bioimaging with high resolution and increasing depth of tissue penetration, and thus have great potential for in vivo qualitative and quantitative analysis. In this review, we first summarize recent advances in NIR-II imaging, including fluorescent probe selection, quantitative analysis strategies, and imaging. Then, we describe in detail representative applications to illustrate how NIR-II fluorescence imaging has become an important tool for in vivo quantitative analysis. Finally, we describe the future possibilities and challenges of NIR-II fluorescence imaging.

Recent advances in ratiometric fluorescence imaging of enzyme activity in vivo

Among molecular imaging modalities that can monitor enzyme activity in vivo, optical imaging provides sensitive, molecular-level information at low-cost using safe and non-ionizing wavelengths of light. Yet, obtaining quantifiable optical signals in vivo poses significant challenges. Benchmarking using ratiometric signals can overcome dependence on dosing, illumination variability, and pharmacokinetics to provide quantitative in vivo optical data. This review highlights recent advances using fluorescent probes that are processed by enzymes to induce photophysical changes that can be monitored by ratiometric imaging. These diverse strategies include caged fluorophores that change photophysical properties upon enzymatic cleavage, as well as multi-fluorophore systems that are triggered by enzymatic cleavage to alter optical outputs in one or more fluorescent channels. The strategies discussed here have great potential for further development as well as potential broad applications for targeting diverse enzymes important for a wide range of human diseases.

A Radical-Generating Probe to Release Free Fluorophores and Identify Artemisinin-Sensitive Cancer Cells

The smart light-up probes have been extensively developed to image various enzymes and other bioactive molecules. Upon activation, these probes result in light-up fluorophores that exist in a protein-bound or a free form. The difference between these two forms has not yet been reported. Here, we present a pair of smart light-up probes that generate a protein-bound fluorophore and a free fluorophore upon activation by heme. Probe 8 generated a radical-attached fluorophore that predominantly existed in the free form, while probe 10 generated an α,β-unsaturated ketone-attached fluorophore that showed extensive labeling of proteins. In live-cell imaging, probe 8 showed greater fluorescence intensity than probe 10 when low concentrations (0.1-5 μM) of the probes were used, but probe 8 was less fluorescent than probe 10 when the concentrations of the probes were high (10 μM). Finally, probe 8 was used to reflect the activation level of the endoperoxide bond in cancer cells and to effectively distinguish ART-sensitive cancer cells from ART-insensitive ones.

Cellular senescence imaging and senolysis monitoring in cancer therapy based on a β-galactosidase-activated aggregation-induced emission luminogen

Cellular senescence is a permanent state of cell cycle arrest characterized by increased activity of senescence associated β-galactosidase (SA-β-gal). Notably, cancer cells have been also observed to exhibit the senescence response and are being considered for sequential treatment with pro-senescence therapy followed by senolytic therapy. However, there is currently no effective agent targeting β-galactosidase (β-Gal) for imaging cellular senescence and monitoring senolysis in cancer therapy. Aggregation-induced emission luminogen (AIEgen) demonstrates strong fluorescence, good photostability, and biocompatibility, making it a potential candidate for imaging cellular senescence and monitoring senolysis in cancer therapy when endowed with β-Gal-responsive capabilities. In this study, we introduced a β-Gal-activated AIEgen named QM-β-gal for cellular senescence imaging and senolysis monitoring in cancer therapy. QM-β-gal exhibited good amphiphilic properties and formed aggregates that emitted a fluorescence signal upon β-Gal activation. It showed high specificity towards the activity of β-Gal in lysosomes and successfully visualized DOX-induced senescent cancer cells with intense fluorescence both in vitro and in vivo. Encouragingly, QM-β-gal could image senescent cancer cells in vivo for over 14 days with excellent biocompatibility. Moreover, it allowed for the monitoring of senescent cancer cell clearance during senolytic therapy with ABT263. This investigation indicated the potential of the β-Gal-activated AIEgen, QM-β-gal, as an in vivo approach for imaging cellular senescence and monitoring senolysis in cancer therapy via highly specific and long-term fluorescence imaging. STATEMENT OF SIGNIFICANCE: This work reported a β-galactosidase-activated AIEgen called QM-β-gal, which effectively imaged DOX-induced senescent cancer cells both in vitro and in vivo. QM-β-gal specifically targeted the increased expression and activity of β-galactosidase in senescent cancer cells, localized within lysosomes. It was cleared rapidly before activation but maintained stability after activation in the DOX-induced senescent tumor. The AIEgen exhibited a remarkable long-term imaging capability for senescent cancer cells, lasting over 14 days and enabled monitoring of senescent cancer cell clearance through ABT263-induced apoptosis. This approach held promise for researchers seeking to achieve prolonged imaging of senescent cells in vivo.

A COX2-targeting cancer-specific fluorescent probe for hydrogen sulfide detection in living cells, Caenorhabditis elegans, and zebrafish

A novel cyclooxygenase-2 (COX-2) targeted H2S-activated cancer-specific fluorescent probe, namely, COX2-H2S, was designed and synthesized, with naphthalimide as the fluorophore and indomethacin as the targeting group. This H2S-sensing probe was developed to differentiate tumor cells from normal cells and was tested in living cells, Caenorhabditis elegans (C. elegans), and zebrafish. The probe could successfully be used for imaging endogenous and exogenous H2S in living cells, demonstrating high sensitivity and specificity and strong anti-interference. COX2-H2S had the ability to not only discern cancer cells from normal cells but also specifically recognize 9L/lacZ cells from other glioblastoma cells (U87-MG and LN229). It could also be successfully applied for the fluorescent live imaging of H2S in both C. elegans and zebrafish.

Design strategies and biological applications of β-galactosidase fluorescent sensor in ovarian cancer research and beyond

Beta-galactosidase (β-galactosidase), a lysosomal hydrolytic enzyme, plays a critical role in the catalytic hydrolysis of glycosidic bonds, leading to the conversion of lactose into galactose. This hydrolytic enzyme is used as a biomarker in various applications, including enzyme-linked immunosorbent assays (ELISAs), gene expression studies, tuberculosis classification, and in situ hybridization. β-Galactosidase abnormalities are linked to various diseases, such as ganglioside deposition, primary ovarian cancer, and cell senescence. Thus, effective detection of β-galactosidase activity may aid disease diagnoses and treatment. Activatable optical probes with high sensitivity, specificity, and spatiotemporal resolution imaging capabilities have become powerful tools for visualization and real time tracking in vivo in the past decade. This manuscript reviews the sensing mechanism, molecular design strategies, and advances of fluorescence probes in the biological application of β-galactosidase, particularly in the field of ovarian cancer research. Current challenges in tracking β-galactosidase and future directions are also discussed.

Recent advances in small-molecule fluorescent probes with the function of targeting cancer receptors

Cancer is "the sword of Damocles" that threatens human life and health. Therefore, the diagnosis and treatment of cancer have been receiving much attention. Many overexpressed receptors on the surface of cancer cells provide us with an effective way to specifically identify the cancer cells, and receptor targeting strategies are becoming one of the hot ideas to enhance the ability of fluorescent probes to target tumors. Fluorescent probes connected to ligands are targeted at cancer cell surfaces through receptor-mediated endocytosis. Receptor-targeting probes can image and track cancer cells, determine tumor boundaries, monitor deep lesions, and play a role in clinical medicine, such as fluorescent imaging-guided surgery. In this review, based on the perspective of small molecule fluorescent probes, we reviewed the design ideas, photophysical properties, and applications of receptor-targeting probes for detecting biomarkers in imaging and tracing cancer cells and prospected the future developmental direction of such probes. We hope that this review will provide more ideas for the design and development of active targeting probes for receptors and lead to more applications in the medical field.

Smart nanoparticles for cancer therapy

Smart nanoparticles, which can respond to biological cues or be guided by them, are emerging as a promising drug delivery platform for precise cancer treatment. The field of oncology, nanotechnology, and biomedicine has witnessed rapid progress, leading to innovative developments in smart nanoparticles for safer and more effective cancer therapy. In this review, we will highlight recent advancements in smart nanoparticles, including polymeric nanoparticles, dendrimers, micelles, liposomes, protein nanoparticles, cell membrane nanoparticles, mesoporous silica nanoparticles, gold nanoparticles, iron oxide nanoparticles, quantum dots, carbon nanotubes, black phosphorus, MOF nanoparticles, and others. We will focus on their classification, structures, synthesis, and intelligent features. These smart nanoparticles possess the ability to respond to various external and internal stimuli, such as enzymes, pH, temperature, optics, and magnetism, making them intelligent systems. Additionally, this review will explore the latest studies on tumor targeting by functionalizing the surfaces of smart nanoparticles with tumor-specific ligands like antibodies, peptides, transferrin, and folic acid. We will also summarize different types of drug delivery options, including small molecules, peptides, proteins, nucleic acids, and even living cells, for their potential use in cancer therapy. While the potential of smart nanoparticles is promising, we will also acknowledge the challenges and clinical prospects associated with their use. Finally, we will propose a blueprint that involves the use of artificial intelligence-powered nanoparticles in cancer treatment applications. By harnessing the potential of smart nanoparticles, this review aims to usher in a new era of precise and personalized cancer therapy, providing patients with individualized treatment options.

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.

Activatable probes with potential for intraoperative tumor-specific fluorescence-imaging guided surgery

Owing to societal development and aging population, the impact of cancer on human health and quality of life has increased. Early detection and surgical treatment are the most effective approaches for most cancer patients. As the scope of conventional tumor resection is determined by auxiliary examination and surgeon experience, there is often insufficient recognition of tiny tumors. The ability to detect such tumors can be improved by using fluorescent tumor-specific probes for surgical navigation. This review mainly describes the design principles and mechanisms of activatable probes for the fluorescence imaging of tumors. This type of probe is nonfluorescent in normal tissue but exhibits obvious fluorescence emission upon encountering tumor-specific substrates, such as enzymes or bioactive molecules, or changes in the microenvironment, such as a low pH. In some cases, a single-factor response does not guarantee the effective fluorescence labeling of tumors. Therefore, two-factor-activatable fluorescence imaging probes that react with two specific factors in tumor cells have also been developed. Compared with single biomarker testing, the simultaneous monitoring of multiple biomarkers may provide additional insight into the role of these substances in cancer development and aid in improving the accuracy of early cancer diagnosis. Research and progress in this field can provide new methods for precision medicine and targeted therapy. The development of new approaches for early diagnosis and treatment can effectively improve the prognosis of cancer patients and help enhance their quality of life.

β-Galactosidase-activated nitroxyl (HNO) donors provide insights into redox cross-talk in senescent cells

The cross-talk among reductive and oxidative species (redox cross-talk), especially those derived from sulfur, nitrogen and oxygen, influence several physiological processes including aging. One major hallmark of aging is cellular senescence, which is associated with chronic systemic inflammation. Here, we report a chemical tool that generates nitoxyl (HNO) upon activation by β-galactosidase, an enzyme that is over-expressed in senescent cells. In a radiation-induced senescence model, the HNO donor suppressed reactive oxygen species (ROS) in a hydrogen sulfide (H2S)-dependent manner. Hence, the newly developed tool provides insights into redox cross-talk and establishes the foundation for new interventions that modulate levels of these species to mitigate oxidative stress and inflammation.

Cancer Cell-Specific Fluorescent Prodrug Delivery Platforms

Targeting cancer cells with high specificity is one of the most essential yet challenging goals of tumor therapy. Because different surface receptors, transporters, and integrins are overexpressed specifically on tumor cells, using these tumor cell-specific properties to improve drug targeting efficacy holds particular promise. Targeted fluorescent prodrugs not only improve intracellular accumulation and bioavailability but also report their own localization and activation through real-time changes in fluorescence. In this review, efforts are highlighted to develop innovative targeted fluorescent prodrugs that efficiently accumulate in tumor cells in different organs, including lung cancer, liver cancer, cervical cancer, breast cancer, glioma, and colorectal cancer. The latest progress and advances in chemical design and synthetic considerations in fluorescence prodrug conjugates and how their therapeutic efficacy and fluorescence can be activated by tumor-specific stimuli are reviewed. Additionally, novel perspectives are provided on strategies behind engineered nanoparticle platforms self-assembled from targeted fluorescence prodrugs, and how fluorescence readouts can be used to monitor the position and action of the nanoparticle-mediated delivery of therapeutic agents in preclinical models. Finally, future opportunities for fluorescent prodrug-based strategies and solutions to the challenges of accelerating clinical translation for the treatment of organ-specific tumors are proposed.

Chemosensor with Ultra-High Fluorescence Enhancement for Assisting in Diagnosis and Resection of Ovarian Cancer

Fluorescence imaging-guided diagnostics is one of the most promising approaches for facile detection of tumors in situ owing to its simple operation and non-invasiveness. As a crucial biomarker for primary ovarian cancers, β-galactosidase (β-gal) has been demonstrated to be the significant molecular target for visualization of ovarian tumors. Herein, a membrane-permeable fluorescent chemosensor (namely, LAN-βgal) was synthesized for β-gal-specific detection using the d-galactose residue as a specific recognition unit and LAN-OH (Φ_F = 0.47) as a fluorophore. After β-gal was digested, the fluorescence of the initially quenched LAN-βgal (Φ_F < 0.001) was enhanced by up to more than 2000-fold, which exceeded the fluorescence enhancement of other previously reported probes. We also demonstrated that the chemosensor LAN-βgal could visualize endogenous β-gal and distinguish ovarian cancer cells from normal ovarian cells. Further, the chemosensor LAN-βgal was successfully applied to visualize the back tumor-bearing mouse model and peritoneal metastatic ovarian cancer model in vivo. More importantly, through in situ spraying, the proposed chemosensor was successfully employed to assist in the surgical resection of ovarian cancer tumors due to its high tumor-to-normal (T/N) tissue fluorescence ratio of 218. To the best of our knowledge, this is the highest T/N tissue fluorescence ratio ever reported. We believe that the LAN-βgal chemosensor can be utilized as a new tool for the clinical diagnosis and treatment of ovarian cancer.

Progress on Multifunction Enzyme-Activated Organic Fluorescent Probes for Bioimaging

Bioimaging techniques are of increasing importance in clinical and related fields, which also have been successfully applied in the in vivo/in vitro imaging system. Due to the vital factor of enzymes in biological systems, enzyme-activated fluorophores, which could turn “on” the fluorescence signal from an “off” state, offer non-invasive and effective potential for the accurate bioimaging of particular cells, tissues, or bacteria. Comparing with the traditional imaging probes, enzyme-activated organic small fluorophores can visualize living cells within small animals with high sensitivity, high imaging resolution, non-invasiveness, and real-time feedback. In this mini review, well-designed enzyme-activated organic fluorescent probes with multiple functions are exclusively reviewed through the latest development and progress, focusing on probe design strategy, fluorescence property, enzyme activation process, and bioimaging applications. It is worth noting that multi-enzyme-activated strategies, which could avoid the production of “false-positive” signals in complex biological systems, effectively provide high selective and real-time bioimaging, indicating the exciting potential of intraoperative fluorescence imaging and diagnosis tools.

Enhancing the Contrast of Tumor Imaging for Image-Guided Surgery Using a Tumor-Targeting Probiotic with the Continuous Expression of a Biomarker

Tumor recurrence commonly results from tumor-positive resection margins and metastatic lesions. The complete removal of tumor-positive margins is particularly essential in clinics. Thus, we designed a strategy based on Escherichia coli Nissle 1917 (EcN) nitroreductase (NTR) with a polyethylene glycol (PEG) polymer coating (PC-EcN-NTR) to specifically target and colonize in tumors for high-contrast tumor imaging by providing a large amount of NTR as biomarkers in situ. NTR is a favorable biomarker for tumor detection and imaging. The nfsB-encoding plasmid with a 16S promoter was transfected into EcN for the continuous and stable expression of NTR (E. coli. NfsB). PC-EcN-NTR can accumulate and proliferate for a long time in tumors to substantially express NTR. When the NTR-activated fluorescence (FL) probe was sprayed on the tumor, the tumor region showed fluorescence signals within 5 min. Compared to the tumor without colonization with bacteria, the PC-EcN-NTR-colonized tumors displayed 3.15× enhanced fluorescence signals. Furthermore, the fluorescence signals of the whole tumor can last at least 3 h, which is suitable for a long and meticulous surgical operation. More importantly, in the PC-EcN-NTR-harboring tumor, obvious FL appeared even at the very edge (approximately 200 μm away from the edge) of the tumor tissue. A TCF-Based near-infrared-II fluorescent probe (probe 2) was designed and synthesized. Results similar to those of probe 1 were observed when probe 2 was used for in vivo tumor imaging, which further proved the generality of the enhancing ability of the tumor-targeting probiotic. This strategy will hopefully guide the surgical resection of tumors via monitoring intense NTR activity. It may spur the use of tumor-targeting probiotic and enzyme-activated fluorescent probes for the processes of tumor diagnosis and image-guided surgery.

β-Galactosidase-activated theranostic for hepatic carcinoma therapy and imaging

A β-galactosidase activatable fluorescent turn-on theranostic Gal-CGem exhibits gemcitabine release specifically in β-galactosidase overexpressing hepatic carcinoma cells. The cytotoxicity of Gal-CGem in cancer cells is achieved through the apoptotic cell death pathway. Overall, Gal-CGem is a new frontline prodrug in cancer therapy that has provided antineoplastic information through fluorescence imaging.

A turn on fluorescent assay for real time determination of β-galactosidase and its application in living cell imaging

In recent years, fluorescent probes based on chemical reactions have been widely investigated as a powerful and noninvasive method for the diagnosis of diseases. β-Galactosidase (β-gal), a typical lysosomal glycosidase, over expressed in senescent cells and primary ovarian cancer cells, which has been considered as an important biomarker cell senescence and primary ovarian cancers. Fluorescent probes for the determination of β-gal provide an excellent choice for visualization of cell senescence. In this work, a turn on fluorescent probe (HBT-gal) for β-gal activity was developed based on the enzymatic hydrolysis of glycosidic bonds. HBT-gal showed little fluorescence in aqueous buffer excited at 415 nm, while emitted green fluorescence centered at ∼ 492 nm upon incubated with β-gal. The sensing scheme showed high selectivity and sensitivity for β-gal activity with a limit of detection calculated as low as 0.19 mU/mL. Moreover, HBT-gal was successfully applied to image β-gal activity in senescent Hep G2 cells treated with H₂O₂. Therefore, probe HBT-gal demonstrated a potential usage for the determination of cell senescence using β-gal as a biomarker.

New Chemical Biology Tools for the Histamine Receptor Family

The histamine research community has in the last decade been very active and generated a number of exciting new chemical biology tools for the study of histamine receptors, their ligands, and their pharmacology. In this paper we describe the development of histamine receptor structural biology, the use of receptor conformational biosensors, and the development of new ligands for covalent or fluorescent labeling or for photopharmacological approaches (photocaging and photoswitching). These new tools allow new approaches to study histamine receptors and hopefully will lead to better insights in the molecular aspects of histamine receptors and their ligands.

Recent research progress in galactose-based fluorescent probes for detection of biomarkers of liver diseases

This highlight illustrates the challenges and latest progress in galactose-based fluorescent probes for early diagnosis of liver diseases.

Glycosidase activated prodrugs for targeted cancer therapy

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

Advanced NIR ratiometric probes for intravital biomedical imaging

Near-infrared (NIR) fluorescence imaging technology (NIR-I region, 650-950 nm and NIR-II region, 1000-1700 nm), with deeper tissue penetration and less disturbance from auto-fluorescence than that in visible region (400-650 nm), is playing a more and more extensive role in the field of biomedical imaging. With the development of precise medicine, intelligent NIR fluorescent probes have been meticulously designed to provide more sensitive, specific and accurate feedback on detection. Especially, recently developed ratiometric fluorescent probes have been devoted to quantify physiological and pathological parameters with a combination of responsive fluorescence changes and self-calibration. Herein, we systemically introduced the construction strategies of NIR ratiometric fluorescent probes and their applications in biological imagingin vivo, such as molecular detection, pH and temperature measurement, drug delivery monitoring and treatment evaluation. We further summarized possible optimization on the design of ratiometric probes for quantitative analysis with NIR fluorescence, and prospected the broader optical applications of ratiometric probes in life science and clinical translation.

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.

Highly Stable Red-Emissive Ratiometric Probe for Monitoring β-Galactosidase Activity Using Fluorescence Microscopy and Flow Cytometry

β-Galactosidase (β-gal), well known as a useful reporter enzyme, is a potent biomarker for various diseases such as colorectal and ovarian cancers. We have developed a highly stable red-emissive ratiometric fluorescent probe (CCGal1) for quantitatively monitoring the β-gal enzyme activity in live cells and tissues. This ratiometric probe showed a fast emission color change (620-662 nm) in response to β-gal selectively, which was accompanied by high enzyme reaction efficacy, cell-staining ability, and outstanding stability with minimized cytotoxicity. Confocal fluorescence microscopy ratiometric images, combined with fluorescence-activated cell sorting flow cytometry, demonstrated that CCGal1 could provide useful information for the diagnosis, prognosis, and treatment of β-gal enzyme activity-related diseases such as colorectal and ovarian cancers. Further, it may yield meaningful strategies for designing and modifying multifunctional bioprobes with different biomedical applications.

Activatable Second Near-Infrared Fluorescent Probes: A New Accurate Diagnosis Strategy for Diseases

Recently, second near-infrared (NIR-II) fluorescent imaging has been widely applied in biomedical diagnosis, due to its high spatiotemporal resolution and deep tissue penetration. In contrast to the "always on" NIR-II fluorescent probes, the activatable NIR-II fluorescent probes have specific targeting to biological tissues, showing a higher imaging signal-to-background ratio and a lower detection limit. Therefore, it is of great significance to utilize disease-associated endogenous stimuli (such as pH values, enzyme existence, hypoxia condition and so on) to activate the NIR-II probes and achieve switchable fluorescent signals for specific deep bioimaging. This review introduces recent strategies and mechanisms for activatable NIR-II fluorescent probes and their applications in biosensing and bioimaging. Moreover, the potential challenges and perspectives of activatable NIR-II fluorescent probes are also discussed.

Fluorescent probes for visualizing ROS-associated proteins in disease

Abnormal expression of proteins, including catalytic and expression dysfunction, is directly related to the development of various diseases in living organisms. Reactive oxygen species (ROS) could regulate protein expression by redox modification or cellular signal pathway and thus influence the development of disease. Determining the expression level and activity of these ROS-associated proteins is of considerable importance in early-stage disease diagnosis and the identification of new drug targets. Fluorescence imaging technology has emerged as a powerful tool for specific in situ imaging of target proteins by virtue of its non-invasiveness, high sensitivity and good spatiotemporal resolution. In this review, we summarize advances made in the past decade for the design of fluorescent probes that have contributed to tracking ROS-associated proteins in disease. We envision that this review will attract significant attention from a wide range of researchers in their utilization of fluorescent probes for in situ investigation of pathological processes synergistically regulated by both ROS and proteins.

Methods of detection of β-galactosidase enzyme in living cells

The application of β-galactosidase enzyme ranges from industrial use as probiotics to medically important application such as cancer detection. The irregular activities of β-galactosidase enzyme are directly related to the development of cancers. Identifying the location and expression levels of enzymes in cancer cells have considerable importance in early-stage cancer diagnosis and monitoring the efficacy of therapies. Most importantly, the knowledge of the efficient method of detection of β-galactosidase enzyme will help in the early-stage treatment of the disease. In this review paper, we provide an overview of recent advances in the detection methods of β-galactosidase enzyme in the living cells, including the detection strategies, and approaches in human beings, plants, and microorganisms such as bacteria. Further, we emphasized on the challenges and opportunities in this rapidly developing field of development of different biomarkers and fluorescent probes based on β-galactosidase enzyme. We found that previously used chromo-fluorogenic methods have been mostly replaced by the new molecular probes, although they have certain drawbacks. Upon comparing the different methods, it was found that near-infrared fluorescent probes are dominating the other detection methods.

Enzyme-activatable fluorescent probes for β-galactosidase: from design to biological applications

β-Galactosidase (β-gal), a typical hydrolytic enzyme, is a vital biomarker for cell senescence and primary ovarian cancers. Developing precise and rapid methods to monitor β-gal activity is crucial for early cancer diagnoses and biological research. Over the past decade, activatable optical probes have become a powerful tool for real-time tracking and in vivo visualization with high sensitivity and specificity. In this review, we summarize the latest advances in the design of β-gal-activatable probes via spectral characteristics and responsiveness regulation for biological applications, and particularly focus on the molecular design strategy from turn-on mode to ratiometric mode, from aggregation-caused quenching (ACQ) probes to aggregation-induced emission (AIE)-active probes, from near-infrared-I (NIR-I) imaging to NIR-II imaging, and from one-mode to dual-mode of chemo-fluoro-luminescence sensing β-gal activity.

In Situ Generated Novel 1H MRI Reporter for β-Galactosidase Activity Detection and Visualization in Living Tumor Cells

For wide applications of the lacZ gene in cellular/molecular biology, small animal investigations, and clinical assessments, the improvement of noninvasive imaging approaches to precisely assay gene expression has garnered much attention. In this study, we investigate a novel molecular platform in which alizarin 2-O-β-d-galactopyranoside AZ-1 acts as a lacZ gene/β-gal responsive 1H-MRI probe to induce significant 1H-MRI contrast changes in relaxation times T 1 and T 2 in situ as a concerted effect for the discovery of β-gal activity with the exposure of Fe3+. We also demonstrate the capability of this strategy for detecting β-gal activity with lacZ-transfected human MCF7 breast and PC3 prostate cancer cells by reaction-enhanced 1H-MRI T 1 and T 2 relaxation mapping.

Activatable NIR-II Fluorescent Probes Applied in Biomedicine: Progress and Perspectives

With the advantage of inherent responsiveness that can change the spectroscopic signals from "off" to "on" state in responding to targets (e. g. biological analytes/microenvironmental factors), activatable fluorescent probes have attracted extensive attention and made significant progress in the field of bioimaging and biosensing. Due to the high depth of tissue penetration, minimal tissue damage and negligible background signal at longer wavelengths, the development of second near-infrared window (NIR-II) fluorescent materials provides a new opportunity to develop activable fluorescent probes. Here, we summarized properties, advantages and disadvantages of mainly NIR-II fluorophores (such as rare earth-doped nanoparticles, quantum dots, single-walled carbon nanotubes, small molecule dyes, conjugated polymers and gold nanoclusters), then overviewed current role and development of activatable NIR-II fluorescent probes (AFPs) for biomedical applications including biosensing, bioimaging and therapeutic. The potential challenges and perspectives of AFPs in deep-tissue imaging and clinical application are also discussed.

Increase of tyrosinase activity at the wound site in zebrafish imaged by a new fluorescent probe

Tyrosinase plays a pivotal role in the hyperpigmentation of wounds. Here, we develop a new fluorescent probe and with it, we reveal an increase of tyrosinase activity at the wound site in zebrafish.

Nanoplatforms for Targeted Stimuli-Responsive Drug Delivery: A Review of Platform Materials and Stimuli-Responsive Release and Targeting Mechanisms

To achieve the promise of stimuli-responsive drug delivery systems for the treatment of cancer, they should (1) avoid premature clearance; (2) accumulate in tumors and undergo endocytosis by cancer cells; and (3) exhibit appropriate stimuli-responsive release of the payload. It is challenging to address all of these requirements simultaneously. However, the numerous proof-of-concept studies addressing one or more of these requirements reported every year have dramatically expanded the toolbox available for the design of drug delivery systems. This review highlights recent advances in the targeting and stimuli-responsiveness of drug delivery systems. It begins with a discussion of nanocarrier types and an overview of the factors influencing nanocarrier biodistribution. On-demand release strategies and their application to each type of nanocarrier are reviewed, including both endogenous and exogenous stimuli. Recent developments in stimuli-responsive targeting strategies are also discussed. The remaining challenges and prospective solutions in the field are discussed throughout the review, which is intended to assist researchers in overcoming interdisciplinary knowledge barriers and increase the speed of development. This review presents a nanocarrier-based drug delivery systems toolbox that enables the application of techniques across platforms and inspires researchers with interdisciplinary information to boost the development of multifunctional therapeutic nanoplatforms for cancer therapy.

A ratiometric fluorescent probe based on quinoline for monitoring and imaging of Leucine aminopeptidase in liver tumor cells

Leucine aminopeptidase (LAP) is known as an important potential biomarker for liver malignancy and it is urgent to develop an intuitive and effective method to monitor the activity of LAP in liver cancer. Although, numerous LAP fluorescent probes had been developed, it is still a challenge to detect LAP activity in liver cancer. Herein, combained with the DFT, we reported a novel galactose-appended hepatoma-specific ratiometric fluorescent probe (Gal-QL-Leu) based on quinoline group for imaging and tracing LAP in liver tumor cells. Probe Gal-QL-Leu demonstrated a obvious ratiometric characteristics, better selectivity, good biocompatibility and high sensitivity. Moreover, the selective imaging of LAP in HepG2, HCT116, A549 and HeLa cells had been achieved with probe Gal-QL-Leu, demonstrating good application prospect in the detection of LAP activity in liver tumor cells.

Fluorescent Probe for Monitoring Hydrogen Peroxide in COX-2-Positive Cancer Cells

Hydrogen peroxide (H₂O₂), an important marker for oxidative stress, plays a vital role in cellular biological functions. Overproduction of H₂O₂ causes oxidative damage to cellular functions and promotes cancer and other neurodegenerative diseases. Also, cyclooxygenase-2 (COX-2) enzyme is known to be expressed in several cancer types and exerts multifaceted roles in carcinogenesis and resistance to cancer treatment. Hence, it is important to monitor the H₂O₂ concentration changes in the COX-2-expressing cancer cells. Herein, we have developed a molecular fluorescent ratiometric H₂O₂-responsive probe (NPDIN) composed of indomethacin (COX-2 inhibitor) conjugated with 1,8-napthalimide boronate ester as fluorescent reporter through a chemical linker. The probe was capable of imaging the endogenous H₂O₂ in COX-2 overexpressing cancer cell lines (A549, LoVo, HT29, and Caco-2). Further studies revealed the critical role of the indomethacin moiety in the cellular uptake behavior of NPDIN in COX-2-overexpressing cancer cells. Collectively, our results demonstrated NPDIN as a COX-2-positive cancer-targeting sensitive ratiometric fluorescent probe (I₅₅₄/I₃₉₈) for H₂O₂ imaging and showed its promising biological applications in the future.

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.

A sensitive fluorescent probe for β-galactosidase activity detection and application in ovarian tumor imaging

The development of non-invasive and sensitive optical probes for in vivo bioimaging of cancer-related enzymes is desirable for early diagnosis and effective cancer therapy. β-galactosidase (β-gal) is regarded as a key ovarian cancer biomarker, owing to its overexpression in primary ovarian cancer. Herein, we designed a sensitive near-infrared (NIR) probe (DCMCA-βgal) for the detection and real-time imaging of β-gal activity in ovarian tumors, thereby achieving the visualization of ovarian tumors by β-gal activity detection. DCMCA-β-gal could be triggered by β-gal, resulting in the release of a NIR chromophore, DCM-NH₂; the linear range of fluorescent response to β-gal concentration was 0-1.2 U with a low detection limit of 1.26 × 10^-3 U mL^-1. We used DCMCA-β-gal to detect and visualize β-gal activity in SKOV3 human ovarian cancer cells, as well as for real-time imaging of β-gal activity in ovarian cancer mouse models. DCMCA-β-gal possessed high sensitivity, "turn-on" NIR emission, a large spectral shift, and high photostability in a dynamic living system and thus could serve as a highly sensitive sensor for real-time tracking of β-gal activity in vivo and ovarian tumor imaging.

A ratiometric fluorescent probe for the detection of β-galactosidase and its application

Herein, a coumarin fluorescent probe (Probe 1) was developed for the ratiometric detection of β-galactosidase (β-gal) activity. The detection range was 0–0.1 U mL⁻¹ and 0.2–0.8 U mL⁻¹, and the limit of detection (LOD) was 0.0054 U mL⁻¹. Moreover, the luminous intensity of Probe 1 increased gradually with increase in β-gal activity. It could be observed under 254 nm UV irradiation by the naked eye. Furthermore, this method only required a small amount of sample (20 μL) and a short analytical time (30 min) for the detection of β-gal activity with a low LOD. Probe 1 was successfully used to detect β-gal activity in real fruit samples, and can be applied to the quantitative and qualitative detection of β-gal activity.

A ratiometric fluorescent probe was successfully used as a tool to determine β-galactosidase activity in fruits.

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.