A highly selective ratiometric fluorescent probe for in vitro monitoring and cellular imaging of human carboxylesterase 1

A practical strategy to design and develop an isoform-specific fluorescent probe for a target enzyme: CYP1A1 as a case study

The development of isoform-specific probe(s) for a target enzyme with multiple homologs is always challenging. Herein, a practical strategy was used to design and develop an isoform-specific probe for CYP1A1, a key cytochrome P450 isoenzyme involved in xenobiotic metabolism and bioactivation. On the basis of the subtle differences in 3D structure and substrate preference between CYP1A1 and its homolog CYP1A2, we proposed that it was possible to design a CYP1A1-specific probe via local modification of the reaction site on known CYP1A substrates. To validate this hypothesis, 4-hydroxy-1,8-naphthalimide (HN) was selected as the basic fluorophore due to its excellent optical properties, while a series of O-alkylated HN derivatives were prepared to evaluate their specificity towards CYP1A1. Our results revealed that the introduction of a chloroethyl to HN could get the best isoform selectivity towards CYP1A1 over other CYPs including CYP1A2. The newly developed probe NBCeN exhibited excellent specificity, high sensitivity, and a ratiometric fluorescence response following CYP1A1-catalyzed O-dechloroethylation. NBCeN was successfully used to real-time monitor the activity of CYP1A1 in complex biological samples and to rapidly screen CYP1A1 modulators in living systems. NBCeN could also be used for two-photon imaging of intracellular CYP1A1 in living cells and tissues with high ratiometric imaging resolution and deep tissue penetration. All these findings demonstrated that local modification of non-specific substrates was a practical strategy to develop an isoform-specific probe for a target isoenzyme, while NBCeN could serve as a specific imaging tool to explore the biological functions of CYP1A1 in complex biological systems.

A carboxylesterase-selective ratiometric fluorescent two-photon probe and its application to hepatocytes and liver tissues

Carboxylesterases (CEs) are widely distributed enzymes in the human body that catalyze hydrolysis of various endogenous and exogenous substrates. They are directly linked to hepatic drug metabolisms and steatosis, and their regulations are important issues in pharmacological and clinical applications. In this work, we have developed an emission ratiometric two-photon probe (SE1) for quantitatively detecting CE in situ. This probe is based on a translation of intramolecular charge transfer character upon reaction with CE. It shows a sensitive blue-to-yellow emission change in response to human CE activity, easy loading into cells, insensitivity to pH and other metabolites including ROS and RNS, high photostability, and low cytotoxicity. Using live hepatocytes and liver tissues, we found that ratiometric two-photon microscopic imaging with SE1 is an effective tool for monitoring CE activities at the subcellular level in live tissues. This probe will find useful applications in biomedical research, including studies of hepatic steatosis and drug developments.

Monomolecular pyrenol-derivatives as multi-emissive probes for orthogonal reactivities

Chameleons in a test tube: up to four easily distinguishable emission colors result from conversion by two hydrolytic enzymes at opposite reaction sites.

A bioluminescent sensor for highly selective and sensitive detection of human carboxylesterase 1 in complex biological samples

A highly selective and sensitive bioluminescent sensor (DME) for real-time monitoring of human carboxylesterase 1 (hCE1) activities in complex biological samples and bio-imaging of endogenous hCE1 in living cells.

A highly selective marker reaction for measuring the activity of human carboxylesterase 1 in complex biological samples

NMHN hydrolysis was found to be a highly selective marker reaction for sensing the activity of human carboxylesterase 1 (hCE1).

An optimized ratiometric fluorescent probe for sensing human UDP-glucuronosyltransferase 1A1 and its biological applications

This study aimed to develop a practical ratiometric fluorescent probe for highly selective and sensitive detection of human UDP-glucuronosyltransferase 1A1 (UGT1A1), one of the most important phase II enzymes. 4-Hydroxy-1,8-naphthalimide (HN) was selected as the fluorophore for this study because it possesses intramolecular charge transfer (ICT) feature and displays outstanding optical properties. A series of N-substituted derivatives with various hydrophobic, acidic and basic groups were designed and synthesized to evaluate the selectivity of HN derivatives toward UGT1A1. Our results demonstrated that the introduction of an acidic group to HN could significantly improve the selectivity of UGT1A1. Among the synthesized fluorescent probes, NCHN (N-3-carboxy propyl-4-hydroxy-1,8-naphthalimide) displayed the best combination of selectivity, sensitivity and ratiometric fluorescence response following UGT1A1-catalyzed glucuronidation. UGT1A1-catalyzed NCHN-4-O-glucuronidation generated a single fluorescent product with a high quantum yield (Φ=0.688) and brought remarkable changes in both color and fluorescence in comparison with the parental substrate. The newly developed probe has been successfully applied for sensitive measurements of UGT1A1 activities in human liver preparations, as well as for rapid screening of UGT1A1 modulators, using variable enzyme sources. Furthermore, its potential applications for live imaging of endogenous UGT1A1in cells have also been demonstrated.

Fructus Psoraleae contains natural compounds with potent inhibitory effects towards human carboxylesterase 2

Fructus Psoraleae (FP) is an edible Chinese herbal which is widely used in Asia for the treatment of various diseases including asthma, diarrhea, and osteoporosis. This study aimed to investigate the inhibitory effects of the crude ethanol extract from FP on human carboxylesterase 2 (hCE2), as well as to identity and characterize the naturally occurring inhibitors of hCE2 in FP. Our results demonstrated that the ethanol extract of FP displayed potent inhibitory effects towards hCE2, while five major bioactive constitutes in FP were efficiently identified by LC-DAD-ESI-MS/MS, with the aid of LC-based activity profiling. The identified bioactive compounds including neobavaisoflavone, isobavachalcone, bavachinin, corylifol A and bakuchiol were found to be naturally occurring potent inhibitors of hCE2, with low Ki values ranging from 0.62μM to 3.89μM. This is the first report of the chemical constitutes in FP as potent inhibitors of hCE2.

In vivo imaging and detection of nitroreductase in zebrafish by a new near-infrared fluorescence off-on probe

A new near-infrared fluorescence off-on probe is developed and applied to fluorescence imaging of nitroreductase in zebrafish in vivo. The probe is readily prepared by connecting 4-nitrobenzene as a quenching and recognizing moiety to a stable hemicyanine skeleton that can be formed via the decomposition of IR 780. The fluorescence off-on response of the probe to nitroreductase is based on the enzyme-catalyzed reduction of the 4-nitrobenzene moiety, followed by the 1,6-rearrangement-elimination and the fluorophore release. Compared with the existing nitroreductase probes, the proposed probe exhibits superior analytical performance such as near-infrared fluorescence emission over 700 nm as well as high selectivity and sensitivity, with a detection limit of 14 ng/mL. More importantly, the probe has been successfully applied to visualize the distribution of nitroreductase in living zebrafish in vivo, revealing that nitroreductase might mainly exist in zebrafish yolk sac. The superior properties of the probe make it of great potential use in other biosystems and in vivo studies.

A highly selective long-wavelength fluorescent probe for the detection of human carboxylesterase 2 and its biomedical applications

A highly selective long-wavelength fluorescent probe for the detection of human carboxylesterase 2 (hCE2) has been developed and well characterized. The probe can be used for measuring the real activities of hCE2 in complex biological systems.