Discovery of Butyrylcholinesterase-Activated Near-Infrared Fluorogenic Probe for Live-Cell and In Vivo Imaging.

Butyrylcholinesterase (BChE) is widely distributed in various tissues and highly implicated in several important human diseases, especially Alzheimer's disease (AD). However, the role of BChE in AD is still controversial, which may be partially attributed to the lack of a direct tool for real-time and noninvasive monitoring of BChE in in vivo. Here, we report three rationally designed near-infrared fluorogenic probes that possess excellent discrimination for butyrylcholinesterase (BChE) over the related enzyme acetylcholinesterase (AChE). The refined probe, BChE-NIRFP, not only functions as an exquisite substrate for BChE in in vitro assays but also represents a superb "signal-on" imaging tool to real-time track BChE levels in human cells, zebrafish, and a mouse model of AD. A further application of BChE-NIRFP to identify the cellular mechanism reveals that Aß fibrils and insulin resistance may be important contributors to the abnormally elevated BChE levels observed during AD progression. Based on the results from the present study, this new probe is a valuable tool for basic and clinical research designed to obtain a complete understanding of the physiological roles of BChE in diverse human diseases, particularly AD.

Discovery of a butyrylcholinesterase-specific probe via a structure-based design strategy.

We report herein the structure-based design and application of a fluorogenic molecular probe (BChE-FP) specific to butyrylcholinesterase (BChE). This probe was rationally designed by mimicking the native substrate and optimized stepwise by manipulating the steric feature and the reactivity of the designed probe targeting the structural difference of the active pockets of BChE and AChE. The refined probe, BChE-FP, exhibits high specificity toward BChE compared to AChE, producing about 275-fold greater fluorescence enhancement upon the catalysis by BChE. Thus, BChE-FP is a specific BChE probe identified by the structure-based design and it can discriminate BChE from AChE. Furthermore, it has been successfully applied for imaging the endogenous BChE in living cells, as well as BChE inhibitor screening and characterization under physiological conditions.

Nonpeptide-Based Small-Molecule Probe for Fluorogenic and Chromogenic Detection of Chymotrypsin.

We report herein a nonpeptide-based small-molecule probe for fluorogenic and chromogenic detection of chymotrypsin, as well as the primary application for this probe. This probe was rationally designed by mimicking the peptide substrate and optimized by adjusting the recognition group. The refined probe 2 exhibits good specificity toward chymotrypsin, producing about 25-fold higher enhancement in both the fluorescence intensity and absorbance upon the catalysis by chymotrypsin. Compared with the most widely used peptide substrate (AMC-FPAA-Suc) of chymotrypsin, probe 2 shows about 5-fold higher binding affinity and comparable catalytical efficiency against chymotrypsin. Furthermore, it was successfully applied for the inhibitor characterization. To the best of our knowledge, probe 2 is the first nonpeptide-based small-molecule probe for chymotrypsin, with the advantages of simple structure and high sensitivity compared to the widely used peptide-based substrates. This small-molecule probe is expected to be a useful molecular tool for drug discovery and chymotrypsin-related disease diagnosis.

Detection of Intracellular Selenol-Containing Molecules Using a Fluorescent Probe with Near-Zero Background Signal.

Selenocysteine (Sec), encoded as the 21st amino acid, is the predominant chemical form of selenium that is closely related to various human diseases. Thus, it is of high importance to identify novel probes for sensitive and selective recognition of Sec and Sec-containing proteins. Although a few probes have been reported to detect artificially introduced selenols in cells or tissues, none of them has been shown to be sensitive enough to detect endogenous selenols. We report the characterization and application of a new fluorogenic molecular probe for the detection of intracellular selenols. This probe exhibits near-zero background fluorescence but produces remarkable fluorescence enhancement upon reacting with selenols in a fast chemical reaction. It is highly specific and sensitive for intracellular selenium-containing molecules such as Sec and selenoproteins. When combined with flow cytometry, this probe is able to detect endogenous selenols in various human cancer cells. It is also able to image endogenous selenol-containing molecules in zebrafish under a fluorescence microscope. These results demonstrate that this molecular probe can function as a useful molecular tool for intracellular selenol sensing, which is valuable in the clinical diagnosis for human diseases associated with Sec-deficiency or overdose.

A Highly Sensitive and Selective Fluorescent Probe for Thiophenol Designed via a Twist-Blockage Strategy.

A benzoquinolizine coumarin-based fluorescent probe was developed for detecting thiophenols, demonstrating the superior fluorescence properties caused by the decay of the twisting effect of N,N-diethylamino group of coumarin. It discriminated thiophenols from various analytes including aliphatic thiols with good selectivity and displayed ∼700-fold fluorescence intensity enhancement and a remarkable limit of detection (4.5 nM). The new probe also can be applied to quantitative determine the concentrations of thiophenol in water samples and living cells.

A coumarin-based fluorescent probe for selective and sensitive detection of thiophenols and its application.

The development of probes for specific thiophenol detection is of great importance, due to the toxicity of thiophenols and their derivatives in the environment. In the present study, a novel fluorescent probe was rationally designed for detecting thiophenols via an intramolecular charge transfer mechanism. The developed probe selectively and sensitively distinguished thiophenols from aliphatic thiols. It displayed a large Stokes shift (145 nm) and >280-fold fluorescence enhancement. Moreover, the new probe not only displayed excellent cell permeability for the successful detection of thiophenol in HEK293 cells but also quantitatively measured thiophenols in water samples with good recovery (more than 90%), indicating that it has promising prospects for application for thiophenol sensing in environmental and biological sciences.