Highly Selective and Sensitive Chemiluminescent Probe for Leucine Aminopeptidase Detection in Vitro, in Vivo and in human Liver Cancer Tissue

PaAP-Activatable NIR Probe for Diagnosing, Imaging, and Discovering Small-Molecule Therapeutics against Implant-Associated Biofilm Infections

Biofilm formation on medical implants causes implant-associated infections (IAIs), leading to high morbidity and mortality. Developing molecular tools for precise biofilm detection, along with novel strategies and agents to target biofilm-related IAIs, is crucial for improving treatment options and patient outcomes. Pseudomonas aeruginosa aminopeptidase (PaAP), a key biofilm-associated virulence factor, is a promising target for combating infections. Here, we developed a PaAP-activatable near-infrared (NIR) fluorescent probe, Hcy-NEO-Leu, for real-time, specific, and sensitive detection of PaAP activity. This probe enables noninvasive imaging of the P. aeruginosa biofilm in vitro and in vivo. The probe also identified LY-58, a lycorine derivative that disrupts biofilm formation without affecting bacterial growth or mammalian cell viability, enhancing tobramycin penetration and overcoming antibiotic resistance. This study introduces LY-58 as a promising adjunctive therapy. In conclusion, the PaAP-activatable NIR imaging probe, combined with LY-58, offers innovative tools for the early diagnosis and effective treatment of IAIs.

Biocompatible Flash Chemiluminescent Assay Enabled by Sterically Hindered Spiro-Strained-Oxetanyl-1,2-Dioxetane

Chemiluminescence is the emission of light that occurs as a result of a chemical reaction. Depending on the rate of chemiexcitation, light emission can occur as a long-lasting, low-intensity, glow-type reaction or a rapid, highly intense flash-type reaction. Assays using a flash-type mode of action provide enhanced detection sensitivity compared to those using a glow-type mode. Recently, our group discovered that applying spiro-strain to 1,2-dioxetanes significantly increases their chemiexcitation rate, thereby transforming glow-type chemiluminescence into flash-type chemiluminescence. However, further examination of the structure-activity relationships revealed that the spiro-strain severely compromises the chemical stability of the 1,2-dioxetanes. We hypothesized that a combination of spiro-strain, steric hindrance, and an electron-withdrawing effect, will result in a chemically stable spiro-strained dioxetane with an accelerated chemiexcitation rate. Indeed, spiro-fused tetramethyl-oxetanyl exhibited a 128-fold faster chemiexcitation rate compared to adamantyl while maintaining similar chemical stability, with a half-life of over 400 hours in PBS 7.4 buffer at room temperature. Turn-on probes composed of tetramethyl-oxetanyl spiro-dioxetane exhibited significantly improved chemical stability in bacterial and mammalian cell media compared to previously developed dioxetane probes fused to a cyclobutyl unit. The superior chemical stability enables a tetramethyl-oxetanyl dioxetane probe to detect β-Galactosidase (β-gal) activity with enhanced sensitivity in Escherichia coli (E. coli) bacterial assays and leucine aminopeptidase activity in tumoral cell lines. Overall, the development of the tetramethyl-oxetanyl dioxetane luminophore enables us to enhance the detection sensitivity of chemiluminescent probes while maintaining high chemical stability. The results obtained in this study should assist in designing improved chemiluminescent probes and underscore the significance of strain-release techniques in enhancing the detection sensitivity of chemiluminescence assays.

Ultrasensitive Chemiluminescence Probes Designed from Covalent Inhibitors for SRAS-CoV-2 Mpro Detection

In the postpandemic era, the emergence of "long COVID" from SARS-CoV-2 has brought ongoing negative impacts on individual health and society. The development of more efficient methods for drug screening and monitoring viral activity remains a critical need. The main protease (Mpro), due to its important role in the virus lifecycle, high conservation, and specificity, is considered an ideal biomarker for SARS-CoV-2. Herein, we have developed several chemiluminescence probes based on different substrates modified from covalent inhibitors targeted at Mpro. Among these, the best probe, MPCL-2, exhibits a rapid response (<20 min), an extremely low limit of detection (LoD; 0.11 nM), great selectivity, and chemical stability. After validating the probe's mechanism of action, MPCL-2 can also be used for real-time, in-situ imaging of enzymes in cells infected with the authentic virus and has the potential for real-time, in-situ Mpro imaging in vivo. Compared to other methods reported to date, the probe demonstrates superior performance and broader applicability, such as in drug screening or virus activity monitoring. Further, the unique design strategy for the substrate can be adopted to develop sensitive probes for other pathogens.

Phenoxy-1,2-dioxetane-based activatable chemiluminescent probes: tuning of photophysical properties for tracing enzymatic activities in living cells

The use of chemiluminophores for tracing enzymatic activities in live-cell imaging has gained significant attention, making them valuable tools for diagnostic applications. Among various chemiluminophores, the phenoxy-1,2-dioxetane scaffold exhibits significant structural versatility and its activation is governed by the chemically initiated electron exchange luminescence (CIEEL) mechanism. This mechanism can be initiated by enzymatic activity, changes in pH, or other chemical stimuli. The photophysical properties of phenoxy-1,2-dioxetanes can be fine-tuned through the incorporation of different substituents on the phenolic ring and by anchoring them with specific triggers. This review discusses the variations in physicochemical properties, including emission maxima, quantum yield, aqueous solubility, and pKa, as influenced by structural modifications, thereby establishing a comprehensive structure-activity relationship. Furthermore, it categorises the probes based on different enzyme classes, such as hydrolase-sensitive probes, oxidoreductase-responsive probes, and transferase-activatable phenoxy-1,2-dioxetanes, offering a promising platform technology for the early diagnosis of diseases and disorders. The summary section highlights key opportunities and limitations associated with applying phenoxy-1,2-dioxetanes in achieving precise and effective enzyme assays.

Pretheranostic agents with extraordinaryNIRF/photoacoustic imaging performanceand photothermal oncotherapy efficacy

Cervical cancer, the most common gynecological malignancy, significantly and adversely affects women's physical health and well-being. Traditional surgical interventions and chemotherapy, while potentially effective, often entail serious side effects that have led to an urgent need for novel therapeutic methods. Photothermal therapy (PTT) has emerged as a promising approach due to its ability to minimize damage to healthy tissue. Connecting a biothiol detection group to PTT-sensitive molecules can improve tumor targeting and further minimize potential side effects. In this study, we developed a near-infrared fluorescence (NIRF)/photoacoustic (PA) dual-mode probe, S-NBD, which demonstrated robust PTT performance. This innovative probe is capable of activating NIRF/PA signals to enable the detection of biothiols with high emission wavelength (838 nm) and large Stokes shift (178 nm), allowing for in vivo monitoring of cancer cells. Additionally, the probe achieved an outstanding photothermal conversion efficiency of 67.1%. The application of laser irradiation (660 nm, 1.0 W/cm2, 5 min) was able to achieve complete tumor ablation without recurrence. In summary, this seminal study presents a pioneering NIRF/PA dual-mode dicyanoisophorone-based probe for biothiol imaging, incorporating features from PTT for the first time. This pioneering approach achieves the dual objectives of improving tumor diagnosis and treatment.

Activatable Fluorescence and Bio/Chemiluminescence Probes for Aminopeptidases: From Design to Biomedical Applications

Aminopeptidases are exopeptidases that catalyze the cleavage of amino acid residues from the N-terminal fragment of protein or peptide substrates. Owing to their function, they play important roles in protein maturation, signal transduction, cell-cycle control, and various disease mechanisms, notably in cancer pathology. To gain better insights into their function, molecular imaging assisted by fluorescence and bio/chemiluminescence probes has become an indispensable method to their superiorities, including excellent sensitivity, selectivity, and real-time and noninvasive imaging. Numerous efforts are made to develop activatable probes that can effectively enhance efficiency and accuracy as well as minimize the side effects. This review is classified according to the type of aminopeptidases, summarizing some recent works on the design, work mechanism, and sensing, imaging, and theranostic performance of their activatable probe. Finally, the current challenges are outlined in developing activatable probes for aminopeptidases and provide possible solutions for future advancements.

Dual-reporter fluorescent probe for precise identification of liver cancer by sequentially responding to carboxylesterase and polarity

Early treatment significantly improves the survival rate of liver cancer patients, so the development of early diagnostic methods for liver cancer is urgent. Liver cancer can develop from viral hepatitis, alcoholic liver, and fatty liver, thus making the above diseases share common features such as elevated viscosity, reactive oxygen species, and reactive nitrogen species. Therefore, accurate differentiation between other liver diseases and liver cancer is both a paramount practical need and challenging. Numerous fluorescent probes have been reported for the diagnosis of liver cancer by detecting a single biomarker, but these probes lack specificity for liver cancer in complex biological systems. Obviously, using multiple liver cancer biomarkers as the basis for judgment can dramatically improve diagnostic accuracy. Herein, we report the first fluorescent probe, LD-TCE, that sequentially detects carboxylesterase (CE) and lipid droplet polarity in liver cancer cells with high sensitivity and selectivity, with linear detection of CE in the range of 0-6 U/mL and a 65-fold fluorescence enhancement in response to polarity. The probe first reacts with CE and releases weak fluorescence, which is then dramatically enhanced due to the decrease in lipid droplet polarity in liver cancer cells. This approach allows the probe to enable specific imaging of liver cancer with higher contrast and accuracy. The probe successfully achieved the screening of liver cancer cells and the precise identification of liver cancer in mice. More importantly, it is not disturbed by liver fibrosis, which is a common pathological feature of many liver diseases. We believe that the LD-TCE is expected to be a powerful tool for early diagnosis of liver cancer.

Stimuli-responsive linkers and their application in molecular imaging

Molecular imaging is a non-invasive imaging method that is widely used for visualization and detection of biological events at cellular or molecular levels. Stimuli-responsive linkers that can be selectively cleaved by specific biomarkers at desired sites to release or activate imaging agents are appealing tools to improve the specificity, sensitivity, and efficacy of molecular imaging. This review summarizes the recent advances of stimuli-responsive linkers and their application in molecular imaging, highlighting the potential of these linkers in the design of activatable molecular imaging probes. It is hoped that this review could inspire more research interests in the development of responsive linkers and associated imaging applications.

A novel near-infrared fluorescent probe for real-time monitoring of leucine aminopeptidase activity and metastatic tumor progression

This article discusses the importance of early tumor detection, particularly in liver cancer, and the role of leucine aminopeptidase (LAP) as a potential marker for liver cancer diagnosis and prognosis assessment. The article highlights the limitations of current tumor markers and the need for new markers and multi-marker approaches to improve accuracy. The authors introduce a novel near-infrared fluorescent probe, NTAP, designed for LAP detection. They describe the synthesis of the probe and evaluate its spectral properties, including the LOD was 0.0038 U/mL, and QY was 0.32 %. The kinetic properties of NTAP, such as the relationship between LAP concentration (0-0.08 U/mL), reaction time (3 min), and fluorescence excitation spectra (475 nm) and emission spectra (715 nm) are investigated. The article also discusses the stability and selectivity of the probe and its ability to detect LAP in complex samples. Cellular imaging experiments demonstrate the NATP specificity and selectivity in detecting LAP activity and its inhibition. Animal models of liver and lung metastasis are used to evaluate the probe's imaging capabilities, showing its ability to accurately locate and detect metastatic lesions. The article concludes by emphasizing the potential applications of the NTAP probe in early tumor diagnosis, treatment monitoring, and the study of tumor metastasis mechanisms.

Design, synthesis, and evaluation of a carboxylesterase detection probe with therapeutic effects

In this study, a lysosomal targeting fluorescent probe recognition on CEs was designed and synthesized. The obtained probe BF2-cur-Mor demonstrated excellent selectivity, sensitivity, pH-independence, and enzyme affinity towards CEs within 5 min. BF2-cur-Mor could enable recognition of intracellular CEs and elucidate that the CEs content of different cancer cells follows the rule of HepG2 > HCT-116 > A549 > HeLa, and the CEs expression level of hepatoma cancer cells far exceeds that of normal hepatic cells, being in good agreement with the previous reports. The ability of BF2-cur-Mor to monitor CEs in vivo was confirmed by zebrafish experiment. BF2-cur-Mor exhibits some pharmacological activity in that it can induce apoptosis in hepatocellular carcinoma cells but is weaker in normal hepatocyte cells, being expected to be a potential "diagnostic and therapeutic integration" tool for the clinical diagnosis of CEs-related diseases.

A highly sensitive and selective chemiluminescent probe for peroxynitrite detection in vitro, in vivo and in human liver cancer tissue

Peroxynitrite (ONOO-) is one of the important active nitrogen/reactive oxygen species that plays various roles in biological processes, such as inducing apoptosis and necrosis. Recent studies have shown that a significant increases in ONOO- content during tumor development, which is closely related to the level of oxidative stress within the tumor. It has been found that herbicide paraquat (PQ) can significantly increase the level of ONOO- in cells. Therefore, accurate monitoring abnormal changes in ONOO- caused by environmental hazardous materials and tumors is helpful in promoting the diagnosis and treatment of oxidative stress diseases (tumors), evenly environmental detection. Currently, traditional fluorescent probes for ONOO- detection have background interference. To address this, we developed a chemiluminescent probe (CL-1) and a fluorescent probe (Flu-1), using diphenyl phosphonate as a recognition group. CL-1 shows extremely sensitivity (9.8 nM), a high signal-to-noise(S/N) ratio (502), and excellent bioimaging capabilities compared to fluorescent probe (Flu-1). We have successfully used CL-1 to detect ONOO- produced by PQ stimulated cells, as well as endogenous ONOO- in tumor cells, mice, and human liver cancer tissues. Therefore, CL-1 can not only be a valuable tool for visualizing tumor and studying the role of ONOO- in tumor pathology, but the probe has the potential to be a powerful molecular imaging tool for exploring the complex biological role of ONOO- in a variety of biological Settings.

Enzyme-responsive design combined with photodynamic therapy for cancer treatment

Photodynamic therapy (PDT) is a noninvasive cancer treatment that has garnered significant attention in recent years. However, its application is still hampered by certain limitations, such as the hydrophobicity and low targeting of photosensitizers (PSs) and the hypoxia of the tumor microenvironment. Nevertheless, the fusion of enzyme-responsive drugs with PDT offers novel solutions to overcome these challenges. Utilizing the attributes of enzyme-responsive drugs, PDT can deliver PSs to the target site and selectively release them, thereby enhancing therapeutic outcomes. In this review, we spotlight recent advances in enzyme-responsive materials for cancer treatment and primarily delineate their application in combination with PDT.

Near-Infrared Fluorescence Probe with a New Recognition Moiety for the Specific Detection of Cysteine to Study the Corresponding Physiological Processes in Cells, Zebrafish, and Arabidopsis thaliana

Cysteine (Cys), as one of the biological thiols, is related to many physiological and pathological processes in humans and plants. Therefore, it is necessary to develop a sensitive and selective method for the detection and imaging of Cys in biological organisms. In this work, a novel near-infrared (NIR) fluorescent probe, Probe-Cys, was designed by connecting furancarbonyl, as a new recognition moiety, with Fluorophore-OH via the decomposition of IR-806. The use of the furan moiety is anticipated to produce more effective fluorescence quenching because of the electron-donating ability of the O atom. Probe-Cys has outstanding properties, such as a new recognition group, an emission wavelength in the infrared region at 710 nm, a linear range (0-100 μM), a low detection limit of 0.035 μM, good water solubility, excellent sensitivity, and selectivity without the interference of Hcy, GSH, and HS-. More importantly, Probe-Cys could achieve the detection of endogenous Cys by reacting with the stimulant 1,4-dimercaptothreitol (DTT) and the inhibitor N-ethylmaleimide (NEM) in HepG2 cells and zebrafish. Ultimately, it was successfully applied to obtain images of Arabidopsis thaliana, revealing that the content of Cys in the meristematic zone was higher than that in the elongation zone, which was the first time that the NIR fluorescence probe was used to obtain images of Cys in A. thaliana. The superior properties of the probe exhibit its great potential for use in biosystems to explore the physiological and pathological processes associated with Cys.

Enzymatic Activity Profiling Using an Ultrasensitive Array of Chemiluminescent Probes for Bacterial Classification and Characterization

Identification and characterization of bacterial species in clinical and industrial settings necessitate the use of diverse, labor-intensive, and time-consuming protocols as well as the utilization of expensive and high-maintenance equipment. Furthermore, while cutting-edge identification technologies such as mass spectrometry and PCR are highly effective in identifying bacterial pathogens, they fall short in providing additional information for identifying bacteria not present in the databases upon which these methods rely. In response to these challenges, we present a robust and general approach to bacterial identification based on their unique enzymatic activity profiles. This method delivers results within 90 min, utilizing an array of highly sensitive and enzyme-selective chemiluminescent probes. Leveraging our recently developed technology of chemiluminescent luminophores, which emit light under physiological conditions, we have crafted an array of probes designed to rapidly detect various bacterial enzymatic activities. The array includes probes for detecting resistance to the important and large class of β-lactam antibiotics. The analysis of chemiluminescent fingerprints from a diverse range of prominent bacterial pathogens unveiled distinct enzymatic activity profiles for each strain. The reported universally applicable identification procedure offers a highly sensitive and expeditious means to delineate bacterial enzymatic activity fingerprints. This opens new avenues for characterizing and identifying pathogens in research, clinical, and industrial applications.

Activatable fluorescent probes for early diagnosis and evaluation of liver injury

With the increase in people's living standards, the number of patients suffering from liver injury keeps on increasing. Traditional diagnostic methods can no longer meet the needs of early and accurate diagnosis due to their limitations in application. However, fluorescent probes based on different fluorophores and nanomaterials have been gradually lighting up medical research due to their unique properties, such as high specificity and non-invasiveness. In addition, accurate identification of the different types of liver injury biomarkers can significantly improve the level of early diagnosis. Therefore, this review reviews the fluorescent probes used in the detection of biomarkers of liver injury over recent years and briefly summarizes the corresponding biomarkers of different types of liver injury. Impressively, this review also lists the structures and the response mechanisms of the different probes, and concludes with an outlook, suggesting directions in which improvements can be made. Finally, we hope that this review will contribute to the further development of fluorescent probes for the early diagnosis and assessment of liver injury.

Recent Progress of Activity-Based Fluorescent Probes for Imaging Leucine Aminopeptidase

Leucine aminopeptidase (LAP) is an important protease that can specifically hydrolyze Leucine residues. LAP occurs in microorganisms, plants, animals, and humans and is involved in a variety of physiological processes in the human body. In the physiological system, abnormal levels of LAP are associated with a variety of diseases and pathological processes, such as cancer and drug-induced liver injury; thus, LAP was chosen as the early biochemical marker for many physiological processes, including cancer. Considering the importance of LAP in physiological and pathological processes, it is critical that high-efficiency and dependable technology be developed to monitor LAP levels. Herein, we summarize the organic small molecule fluorescence/chemiluminescence probes used for LAP detection in recent years, which can image LAP in cancer, drug-induced liver injury (DILI), and bacteria. It can also reveal the role of LAP in tumors and differentiate the serum of cirrhotic, drug-induced liver injury and normal models.

Thiol-Chromene "Click" Reaction-Activated Chemiluminescent Probe for Thiol Detection In Vitro and In Vivo

Biothiols are biomolecules found in a higher content in cancer cells compared to normal cells, marking them useful cancer biomarkers. Chemiluminescence is widely used in biological imaging due to its excellent sensitivity and signal-to-noise ratio (SNR). In this study, we designed and prepared a chemiluminescent probe that is activated by a thiol-chromene "click" nucleophilic reaction. This probe is initially chemiluminescent but turned off and releases extremely strong chemiluminescence in the presence of thiols. It has high selectivity to thiol compared with other analytes. Real-time imaging of mice tumor sites showed significant chemiluminescence after the probe was injected, and the chemiluminescence of osteosarcoma tissues was also significantly stronger than that in adjacent tissues. We conclude that this chemiluminescent probe has potential to detect thiol, diagnose cancer, especially in its early stages, and aid in the development of related cancer drugs.

Combination of changeable π-conjugation and hydrophilic groups for developing water-soluble small-molecule NIR-II fluorogenic probes

Small-molecule probes emitting in the second near-infrared window (NIR-II) are attracting great attention because of their deep-tissue imaging ability. However, developing NIR-II fluorogenic (off-on) probes with good water solubility remains a great challenge due to the lack of a facile approach. Herein we first report the combination of changeable π-conjugation and hydrophilic groups as an effective strategy for developing water-soluble NIR-II fluorogenic probes. With the strategy, new water-soluble NIR-II fluorophores are prepared, among which NIR-II-F2 and NIR-II-F3 show superior stability and bright fluorescence in aqueous media, and are thus used to design two water-soluble NIR-II fluorogenic probes for leucine aminopeptidase (LAP). The excellent performance in real aqueous bio-environments is demonstrated by imaging mouse vasculatures and organs with NIR-II-F2, and LAP in drug-induced liver injury mice with one of the enzymatic probes; however, water-insoluble dyes cannot achieve such in vivo imaging under the same conditions. Our strategy may be helpful for further developing water-soluble organic NIR-II fluorogenic probes for in vivo imaging of other analytes.

Selective detection of carboxylesterase 2 activity in cancer cells using an activity-based chemiluminescent probe

Carboxylesterase 2 (CES2) has crucial roles in both xenobiotic metabolism and formation of pathogenic states including cancer. Thus, it is highly critical to monitor intracellular CES2 activity in living cancer cells. Here, we report a CES2 activatable phenoxy 1,2-dioxetane based chemiluminescent agent (CL-CES2). The probe exhibited a selective turn-on response in the presence of CES2 enzyme and enabled detection of CES2 activity in three different cancer cells that possess varying enzyme concentrations with high signal to noise ratios. In contrast no signal was obtained with CES1, an isoform of CES2 enzyme. CL-CES2 marks the first ever example of a CES2-responsive chemiluminescent luminophore and holds a great potential in further understanding the roles of CES2 activity in tumorogenesis.

Defective Site Modulation Strategy for Preparing Single Atom-Dispersed Catalysts as Superior Chemiluminescent Signal Probes

Single atom-dispersed catalysts (SADCs) with highly exposed active sites can be used as sensitive signal probes because of their superior catalytic efficiency. However, the dispersed atoms tend to aggregate, restricting the loading capacity of metal atoms. Herein, the defective sites on Zr-oxo clusters of metal-organic frameworks (MOFs) UiO-66-NH₂ were modulated by excessive acetic acid and utilized for confining metal atoms with high loading capacity. To verify the feasibility of the designed strategy, the Co element was loaded onto MOFs UiO-66-NH₂ to prepare SADCs with desirable Fenton-like activity. The prepared Co SADCs at a low concentration of 1.0 μg mL^-1 are found to boost chemiluminescent (CL) emission for 3700 times due to the significantly improved Co content of 5.55 wt %. The superior CL enhancement efficiency is ascribed to reactive oxygen species generated by the accelerated decay of H₂O₂. To verify the application potential in CL assay, they were used as signal probes to establish an immunoassay method for carbendazim with a dynamic range of 1.0 pg mL^-1 to 25 ng mL^-1 and a limit of detection of 0.33 pg mL^-1. This defective site modulation strategy paves an avenue for preparing SADCs with a high CL response by improving the loading capacity of metal atoms.

A Molecular Logic Gate for Developing "AND" Logic Probes and the Application in Hepatopathy Differentiation

Accurate diagnosis and therapy are challenging because most diseases lack a single biomarker that distinguishes them from other disorders. A solution would enhance targeting accuracy by using AND-gated combinations of two disease-associated stimuli. Here, we report a novel "AND" molecular logic gate, enabling a double-controlled release of intact functional molecules. Benefiting from a significant difference in intramolecular cyclization rate, cargo release occurs notably faster with the presence of both stimuli. According to this finding, several AND logic probes have been developed that respond to a broad scope of stimuli and show remarkably improved signal-to-background contrast compared to those of monoresponsive probes. In addition, an AND logic probe that is responsive to monoamine oxidase (MAO) and leucine aminopeptidase (LAP) has been constructed for hepatopathy diagnosis. It works efficiently in living cells and mouse models. Of note, this probe can successfully differentiate cirrhotic from hepatitis B by testing the blood samples from patients.