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

The effect of the aging processes of Ulva prolifera-derived dissolved organic nitrogen associated with green tide on the diatoms-dinoflagellates succession in the Southern Yellow Sea, China

Multitudinous dissolved organic nitrogen (DON) enters seawater from Ulva prolifera green tides impacting phytoplankton community structure in the Yellow Sea. Field investigations and cultural experiments on U. prolifera-derived DON aging revealed its regulatory effects. The green-tide outbreak area of the Southern Yellow Sea exhibits a seasonal cycle where dominance shifts from diatoms to dinoflagellates effected by young to aging U. prolifera-derived DON from summer to spring. Diatom abundance rose significantly following the summer green tide outbreak, fueled by young, protein-rich DON released by U. prolifera. After autumn and winter aging, U. prolifera-derived DON was dominant from protein-like to humic-like components, and dinoflagellates bloomed in the green tide outbreak area. An aging U. prolifera-derived DON adding culture experiment of Chaetoceros curvisetus and Prorocentrum minimum proved that old and young DON promoted dinoflagellate and diatom growth, respectively. Diatoms preferred 0 and 12 days-aged DON (DON0 and DON12) with tyrosine B and tryptophan T components, whereas dinoflagellate favored 80 days-aged DON (DON80) with humic acid E and UV fulvic acid A components. DON0 and DON12 can be absorbed by diatoms with higher uptake (kup) and growth (kG) constants than by dinoflagellates under low leucine aminopeptidase (LAP) conditions. Dinoflagellates absorb old DON with higher kup and kG values under higher LAP concentrations than diatoms. This was consistent with the loop of U. prolifera-derived DON turning over the seasonal succession of diatom dinoflagellates in the green-tide outbreak area. This study revealed mechanism of seasonal dinoflagellate-U. prolifera-diatom cycle, and provided new insights for impacts of U. prolifera green tides on phytoplankton regime shift, thus, acting as a basis for marine management strategies.

Fluorescence Turn-On Sensing of Leucine Using Bimetallic Cu-Ag Nanoclusters: A Potential Non-Invasive Biomarker for Cancer Detection

This study investigates the use of bimetallic copper-silver nanoclusters (Cu-AgNCs) for fluorescence turn-on sensing of leucine, a potential biomarker for cancer detection. These nanoclusters exhibit high fluorescence tunability and specificity, with Fe3+ serving as a quencher to facilitate leucine detection. The fluorescence recovery mechanism is attributed to the interaction of leucine with Fe3+, alleviating the quenching effect on the metal nanoclusters. This bimetallic nanocluster is a promising platform for biomarker identification in cancer diagnosis. The fluorescence enhancement upon leucine binding provides a measurable signal, confirming the feasibility of these nanoclusters as noninvasive sensors for cancer biomarkers. The sensor achieves a detection limit of 0.58 μM and demonstrates a linear response within the range of 110-657 μM. This approach offers a promising method for noninvasive cancer diagnostics using saliva and urine samples. Additionally, the method's reproducibility and robustness further support its potential in clinical applications, providing a cost-effective and accessible technique for early cancer detection.

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.

Recent Advances of Aminopeptidases-Responsive Small-Molecular Probes for Bioimaging

Aminopeptidases, enzymes with critical roles in human body, are emerging as vital biomarkers for metabolic processes and diseases. Aberrant aminopeptidase levels are often associated with diseases, particularly cancer. Small-molecule probes, such as fluorescent, fluorescent/photoacoustics, bioluminescent, and chemiluminescent probes, are essential tools in the study of aminopeptidases-related diseases. The fluorescent probes provide real-time insights into protein activities, offering high sensitivity in specific locations, and precise spatiotemporal results. Additionally, photoacoustic probes offer signals that are able to penetrate deeper tissues. Bioluminescent and chemiluminescent probes can enhance in vivo imaging abilities by reducing the background. This comprehensive review is focused on small-molecule probes that respond to four key aminopeptidases: aminopeptidase N, leucine aminopeptidase, Pyroglutamate aminopeptidase 1, and Prolyl Aminopeptidase, and their utilization in imaging tumors and afflicted regions. In this review, the design strategy of small-molecule probes, the variety of designs from previous studies, and the opportunities of future bioimaging applications are discussed, serving as a roadmap for future research, sparking innovations in aminopeptidase-responsive probe development, and enhancing our understanding of these enzymes in disease diagnostics and treatment.

Activity-Based Fluorescence Diagnostics for Cancer

Fluorescence imaging is one of the most promising approaches to achieve intraoperative assessment of the tumor/normal tissue margins during cancer surgery. This is critical to improve the patients' prognosis, and therefore various molecular fluorescence imaging probes have been developed for the identification of cancer lesions during surgery. Among them, "activatable" fluorescence probes that react with cancer-specific biomarker enzymes to generate fluorescence signals have great potential for high-contrast cancer imaging due to their low background fluorescence and high signal amplification by enzymatic turnover. Over the past two decades, activatable fluorescence probes employing various fluorescence control mechanisms have been developed worldwide for this purpose. Furthermore, new biomarker enzymatic activities for specific types of cancers have been identified, enabling visualization of various types of cancers with high sensitivity and specificity. This Review focuses on recent advances in the design, function and characteristics of activatable fluorescence probes that target cancer-specific enzymatic activities for cancer imaging and also discusses future prospects in the field of activity-based diagnostics for cancer.