Characterization of recombinant human carboxylesterases: fluorescein diacetate as a probe substrate for human carboxylesterase 2

Alisol B alleviates MASLD by activating liver autophagy and fatty acid oxidation via Ces2a

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a prevalent global health issue characterized by excessive fat accumulation in the liver, often linked to obesity and metabolic syndrome. Despite advancements in understanding its pathogenesis, effective therapeutic strategies remain limited. This study investigates the potential of Alisol B, a natural compound from traditional Chinese medicine, in modulating lipid metabolism and autophagy in hepatocytes. We employed a combination of in vivo and in vitro approaches, including mouse models, cell culture assays, and transcriptomic profiling, to evaluate Alisol B's therapeutic efficacy against MASLD and elucidate its underlying mechanisms. Our findings reveal that Alisol B significantly reduces lipid accumulation and enhances fatty acid metabolism by upregulating Ces2a, a key regulator of lipid catabolism, as confirmed by RNA sequencing and Western blot analyses. Additionally, transcriptomic analysis indicates that Alisol B activates critical signaling pathways related to fatty acid metabolism and autophagy, including AMPK signaling. Importantly, in vitro studies demonstrate that Alisol B effectively reduces triglyceride levels in hepatocytes without compromising cell viability. Pharmacological inhibition of Ces2a further underscores its essential role in mediating Alisol B's therapeutic effects. These results suggest that Alisol B holds promise as a novel therapeutic agent for MASLD, warranting further exploration of its clinical applications and potential as a targeted treatment for metabolic disorders.

Compared Inhibitory Activities of Tamoxifen and Avenanthramide B on Liver Esterase and Correlation Based on the Superimposed Structure Between Porcine and Human Liver Esterase

Exposure to tamoxifen can exert effects on the human liver, and esterases process prodrugs such as antibiotics and convert them to less toxic metabolites. In this study, the porcine liver esterase (PLE)-inhibitory activity of tamoxifen has been investigated. PLE showed inhibition of a PLE isoenzyme (PLE5). In addition, avenanthramides, which have a similar structure to that of tamoxifen, have been used to determine the PLE-inhibitory effect. Among the avenanthramide derivatives, avenanthramide B has been shown to inhibit PLE. Avenanthramide B interacts with Lys284 of PLE, whereas avenanthramide A and C counteract with Lys284. Avenanthramide B has shown a similar inhibitory effect to that of tamoxifen. Given that avenanthramide B can modulate the action of PLE, it can be used in pharmaceutical and industrial applications for modulating the effects of PLE. Based on superimposed structures between PLE and human liver esterase, the impact of tamoxifen use in humans is discussed. In addition, this study can serve as a fundamental basis for future investigations regarding the potential risk of tamoxifen and other drugs. Thus, this study presents an insight into the comparison of structurally similar tamoxifen and avenanthramides on liver esterases, which can have implications for the pharmaceutical and agricultural industries.

Activity-Based Dicyanoisophorone Derivatives: Fluorogenic Toolbox Enables Direct Visualization and Monitoring of Esterase Activity in Tumor Models

The visualization and spatiotemporal monitoring of endogenous esterase activity are crucial for clinical diagnostics and treatment of liver diseases. Our research adopts a novel substrate hydrolysis-enzymatic activity (SHEA) approach using dicyanoisophorone-based fluorogenic ester substrates DCIP-R (R = R1-R6) to evaluate esterase preferences on diverse substrate libraries. Esterase-mediated hydrolysis yielded fluorescent DCIP-OH with a nanomolar detection limit in vitro. These probes effectively monitor ester hydrolysis kinetics with a turnover number of 4.73 s-1 and catalytic efficiency (kcat/Km) of 106 M-1 s-1 (DCIP-R1). Comparative studies utilizing two-photon imaging have indicated that substrates containing alkyl groups (DCIP-R1) as recognition elements exhibit enhanced enzymatic cleavage compared to those containing phenyl substitution on alkyl chains (DCIP-R4). Time-dependent variations in endogenous esterase levels were tracked in healthy and liver tumor models, especially in diethylnitrosamine (DEN)-induced tumors and HepG2-transplanted liver tumors. Overall, fluorescence signal quantifications demonstrated the excellent proficiency of DCIP-R1 in detecting esterase activity both in vitro and in vivo, showing promising potential for biomedical applications.

Discovery of the FXR/CES2 dual modulator LE-77 for the treatment of irinotecan-induced delayed diarrhea

Irinotecan (CPT-11) is a widely utilized topoisomerase I inhibitor in the treatment of colorectal cancer and other malignant tumors. However, severe and even life-threatening dose-limiting toxicity-delayed diarrhea affects the clinical application of CPT-11. The standard treatment for CPT-11-induced delayed diarrhea is prompt use of loperamide (LPA), however LPA can also cause constipation, diarrhea and even intestinal obstruction and has a high failure rate. Carboxylesterase 2 (CES2) is the main enzyme in the intestinal transformation of CPT-11, which can convert CPT-11 into toxic metabolite SN-38 and produce intestinal toxicity. Inhibiting CES2 activity can block the hydrolysis process of CPT-11 in the intestine and reduce SN-38 accumulation. Additionally, Farnesoid X receptor (FXR) agonists have anti-inflammatory, anti-secretory, and protective functions on intestinal barrier integrity that could potentially alleviate diarrhea. In this study, we investigated for the first time the anti-delayed diarrhea effect of FXR agonists, and the first time identified LE-77 as a potent dual modulator that activates FXR and inhibits CES2 through high-throughput screening. In the CPT-11-induced delayed diarrhea model, LE-77 demonstrated a dual modulator mechanism by activating FXR and inhibiting CES2, thereby reducing the accumulation of SN-38 in the intestine, alleviating intestinal inflammation, preserving intestinal mucosal integrity, and ultimately alleviating delayed diarrhea.

Pyrazolone compounds could inhibit CES1 and ameliorates fat accumulation during adipocyte differentiation

Carboxylesterase 1 (CES1), a member of the serine hydrolase superfamily, is involved in a wide range of xenobiotic and endogenous substances metabolic reactions in mammals. The inhibition of CES1 could not only alter the metabolism and disposition of related drugs, but also be benefit for treatment of metabolic disorders, such as obesity and fatty liver disease. In the present study, we aim to develop potential inhibitors of CES1 and reveal the preferred inhibitor structure from a series of synthetic pyrazolones (compounds 1-27). By in vitro high-throughput screening method, we found compounds 25 and 27 had non-competitive inhibition on CES1-mediated N-alkylated d-luciferin methyl ester (NLMe) hydrolysis, while compound 26 competitively inhibited CES1-mediated NLMe hydrolysis. Additionally, Compounds 25, 26 and 27 can inhibit CES1-mediated fluorescent probe hydrolysis in live HepG2 cells with effect. Besides, compounds 25, 26 and 27 could effectively inhibit the accumulation of lipid droplets in mouse adipocytes cells. These data not only provided study basis for the design of newly CES1 inhibitors. The present study not only provided the basis for the development of lead compounds for novel CES1 inhibitors with better performance, but also offered a new direction for the explore of candidate compounds for the treatment of hyperlipidemia and related diseases.

New insight on porcine carboxylesterases expression and activity in lung tissues

Over the course of the last twenty years, there has been a growing recognition of the pig's potential as a valuable model for studying human drug metabolism. This study aimed to investigate the expression, enzymatic activity, inhibitory susceptibility, and cellular localization of carboxylesterases (CES) in porcine lung tissue not yet explored. Our results showed that CESs hydrolysis activity followed Michaelis-Menten kinetics in both cytosolic and microsomal fractions of porcine lung tissues (N = 8), with comparable hydrolysis rates for tested substrates, namely 4-nitrophenyl acetate (pNPA), 4-methylumbelliferyl acetate (4-MUA), and fluorescein diacetate (FD). We also determined the CESs hydrolysis activity in a representative sample of the porcine liver that, as expected, displayed higher activity than the lung ones. The study demonstrated variable levels of enzyme activities and interindividual variability in both porcine lung fractions. Inhibition studies used to assess the CESs' involvement in the hydrolysis of pNPA, 4-MUA, and FD suggested that CESs may be the enzymes primarily involved in the metabolism of ester compounds in the pig lung tissue. Overall, this study provides insight into the distribution and diversity of CES isoforms involved in substrate hydrolysis across different cellular fractions (cytosol and microsomes) in porcine lungs.

Ocular drug-metabolizing enzymes: focus on esterases

This review describes current knowledge on the expression of ocular phase I and II drug-metabolizing enzymes in the main animal species used in ocular drug development and in humans, with a focus on ocular esterases and their prodrug substrates. The eye possesses a unique metabolic profile, exhibiting a lower and restricted expression of major cytochrome P450s (CYPs) and most transferases apart from glutathione S-transferases (GST) when compared to the liver. In contrast, hydrolytic enzymes are abundant in many ocular tissues. These enzymes have attracted interest because of their role in prodrug activation and drug elimination. A literature survey suggests profound variations in tissue expression levels and activities between different species but also points out significant gaps in knowledge. These uncertainties highlight a need for more detailed characterization of enzymes in individual ocular tissues and across species to aid future translational studies in ophthalmic drug research. Thus, an in-depth analysis of ocular drug metabolism and species differences is crucial for ocular drug development.

Evaluation of the inhibitory effects of antigout drugs on human carboxylesterases in vitro

Gout is an immune-metabolic disease that frequently coexists with multiple comorbidities such as chronic kidney disease, cardiovascular disease and metabolic syndrome, therefore, it is often treated in combination with these complications. The present study aimed to evaluate the inhibitory effect of antigout drugs (allopurinol, febuxostat, topiroxostat, benzbromarone, lesinurad and probenecid) on the activity of the crucial phase I drug-metabolizing enzymes, carboxylesterases (CESs). 2-(2-benzoyl-3-methoxyphenyl) benzothiazole (BMBT) and fluorescein diacetate (FD) were utilized as the probe reactions to determine the activity of CES1 and CES2, respectively, through in vitro culturing with human liver microsomes. Benzbromarone and lesinurad exhibited strong inhibition towards CESs with Ki values of 2.16 and 5.15 μM for benzbromarone towards CES1 and CES2, respectively, and 2.94 μM for lesinurad towards CES2. In vitro-in vivo extrapolation (IVIVE) indicated that benzbromarone and lesinurad might disturb the metabolic hydrolysis of clinical drugs in vivo by inhibiting CESs. In silico docking showed that hydrogen bonds and hydrophobic interactions contributed to the intermolecular interactions of antigout drugs on CESs. Therefore, vigilant monitoring of potential drug-drug interactions (DDIs) is imperative when co-administering antigout drugs in clinical practice.

Role of carboxylesterase and arylacetamide deacetylase in drug metabolism, physiology, and pathology

Carboxylesterases (CES1 and CES2) and arylacetamide deacetylase (AADAC), which are expressed primarily in the liver and/or gastrointestinal tract, hydrolyze drugs containing ester and amide bonds in their chemical structure. These enzymes often catalyze the conversion of prodrugs, including the COVID-19 drugs remdesivir and molnupiravir, to their pharmacologically active forms. Information on the substrate specificity and inhibitory properties of these enzymes, which would be useful for drug development and toxicity avoidance, has accumulated. Recently,in vitroandin vivostudies have shown that these enzymes are involved not only in drug hydrolysis but also in lipid metabolism. CES1 and CES2 are capable of hydrolyzing triacylglycerol, and the deletion of their orthologous genes in mice has been associated with impaired lipid metabolism and hepatic steatosis. Adeno-associated virus-mediated human CES overexpression decreases hepatic triacylglycerol levels and increases fatty acid oxidation in mice. It has also been shown that overexpression of CES enzymes or AADAC in cultured cells suppresses the intracellular accumulation of triacylglycerol. Recent reports indicate that AADAC can be up- or downregulated in tumors of various organs, and its varied expression is associated with poor prognosis in patients with cancer. Thus, CES and AADAC not only determine drug efficacy and toxicity but are also involved in pathophysiology. This review summarizes recent findings on the roles of CES and AADAC in drug metabolism, physiology, and pathology.

Functional roles and localization of hydrolases in the Japanese mitten crab Eriocheir japonica

The Japanese mitten crab Eriocheir japonica inhabits rivers throughout Japan and is being cultivated for food. To conduct aquaculture efficiently, it is crucial to comprehend the physiological functions of the target organisms. However, there is a lack of fundamental information on Japanese mitten crabs. In this study, hydrolases were extracted from the midgut glands of Japanese mitten crabs and their metabolic activities were analyzed. An enzyme with hydrolytic activity was discovered within the cytosol of the midgut gland. Western blot analysis also revealed that the Japanese mitten crab contains a hydrolase with cross-reactivity to human carboxylesterase 1 (hCES1) antibodies. The substrate specificity of the S9 fraction of the midgut gland was investigated and, interestingly, it was revealed that it reacts well with indomethacin phenyl ester and fluorescein diacetate, which are substrates of hCES2, not substrates of hCES1. Furthermore, this enzyme was observed to metabolize the ester derivative of astaxanthin, which is a red pigment inherent to the Japanese mitten crab. These findings underscore the significance the midgut gland in the Japanese mitten crab as an important organ for metabolizing both endogenous and exogenous ester-type compounds.

Human intestinal organoid-derived PDGFRα + mesenchymal stroma enables proliferation and maintenance of LGR4 + epithelial stem cells

BACKGROUND

Intestinal epithelial cells derived from human pluripotent stem cells (hPSCs) are generally maintained and cultured as organoids in vitro because they do not exhibit adhesion when cultured. However, the three-dimensional structure of organoids makes their use in regenerative medicine and drug discovery difficult. Mesenchymal stromal cells are found near intestinal stem cells in vivo and provide trophic factors to regulate stem cell maintenance and proliferation, such as BMP inhibitors, WNT, and R-spondin. In this study, we aimed to use mesenchymal stromal cells isolated from hPSC-derived intestinal organoids to establish an in vitro culture system that enables stable proliferation and maintenance of hPSC-derived intestinal epithelial cells in adhesion culture.

METHODS

We established an isolation protocol for intestinal epithelial cells and mesenchymal stromal cells from hPSCs-derived intestinal organoids and a co-culture system for these cells. We then evaluated the intestinal epithelial cells and mesenchymal stromal cells' morphology, proliferative capacity, chromosomal stability, tumorigenicity, and gene expression profiles. We also evaluated the usefulness of the cells for pharmacokinetic and toxicity studies.

RESULTS

The proliferating intestinal epithelial cells exhibited a columnar form, microvilli and glycocalyx formation, cell polarity, and expression of drug-metabolizing enzymes and transporters. The intestinal epithelial cells also showed barrier function, transporter activity, and drug-metabolizing capacity. Notably, small intestinal epithelial stem cells cannot be cultured in adherent culture without mesenchymal stromal cells and cannot replaced by other feeder cells. Organoid-derived mesenchymal stromal cells resemble the trophocytes essential for maintaining small intestinal epithelial stem cells and play a crucial role in adherent culture.

CONCLUSIONS

The high proliferative expansion, productivity, and functionality of hPSC-derived intestinal epithelial cells may have potential applications in pharmacokinetic and toxicity studies and regenerative medicine.

Inhibitory effects of phthalate esters (PAEs) and phthalate monoesters towards human carboxylesterases (CESs)

Phthalate esters (PAEs), accompanied by phthalate monoesters as hydrolysis metabolites in humans, have been widely used as plasticizers and exhibited disruptive effects on the endocrine and metabolic systems. The present study aims to investigate the inhibition behavior of PAEs and phthalate monoesters on the activity of the important hydrolytic enzymes, carboxylesterases (CESs), to elucidate the toxicity mechanism from a new perspective. The results showed significant inhibition on CES1 and CES2 by most PAEs, but not by phthalate monoesters, above which the activity of CES1 was strongly inhibited by DCHP, DEHP, DiOP, DiPP, DNP, DPP and BBZP, with inhibition ratios exceeding 80%. Kinetic analyses and in vitro-in vivo extrapolation were conducted, revealing that PAEs have the potential to disrupt the metabolism of endogenous substances catalyzed by CES1 in vivo. Molecular docking results revealed that hydrogen bonds and hydrophobic contacts formed by ester bonds contributed to the interaction of PAEs towards CES1. These findings will be beneficial for understanding the adverse effect of PAEs and phthalate monoesters.

Rationally Engineered hCES2A Near-Infrared Fluorogenic Substrate for Functional Imaging and High-Throughput Inhibitor Screening

Human carboxylesterase 2A (hCES2A) is an important endoplasmic reticulum (ER)-resident enzyme that is responsible for the hydrolytic metabolism or activation of numerous ester-bearing drugs and environmental toxins. The previously reported hCES2A fluorogenic substrates suffer from limited emission wavelength, low specificity, and poor localization accuracy, thereby greatly limiting the in situ functional imaging of hCES2A and drug discovery. Herein, a rational ligand design strategy was adopted to construct a highly specific near-infrared (NIR) substrate for hCES2A. Following scaffold screening and recognition group optimization, HTCF was identified as a desirable NIR fluorophore with excellent photophysical properties and high ER accumulation ability, while several HTCF esters held a high potential to be good hCES2A substrates. Further investigations revealed that TP-HTCF (the tert-pentyl ester of HTCF) was an ideal substrate with ultrahigh sensitivity, excellent specificity, and a substantial signal-to-noise ratio. Upon the addition of hCES2A, TP-HTCF could be rapidly hydrolyzed to release HTCF, a chemically stable product that emitted bright fluorescent signals at around 670 nm. A TP-HTCF-based biochemical assay was then established for the high-throughput screening of potent and cell-active hCES2A inhibitors from an in-house compound library. Furthermore, TP-HTCF displayed high imaging resolution for imaging hCES2A in living cells as well as mouse liver slices and tumor-xenograft mice. Collectively, this study demonstrates a rational strategy for developing highly specific fluorogenic substrates for an ER-resident target enzyme, while TP-HTCF can act as a practical tool for sensing hCES2A in living systems.

Discovery of novel carboxylesterase 2 inhibitors for the treatment of delayed diarrhea and ulcerative colitis

Human carboxylesterase 2 (hCES2) is an enzyme that metabolizes irinotecan to SN-38, a toxic metabolite considered a significant source of side effects (lethal delayed diarrhea). The hCES2 inhibitors could block the hydrolysis of irinotecan in the intestine and thus reduce the exposure of intestinal SN-38, which may alleviate irinotecan-associated diarrhea. However, existing hCES2 inhibitors (except loperamide) are not used in clinical applications due to lack of validity or acceptable safety. Therefore, developing more effective and safer drugs for treating delayed diarrhea is urgently needed. This study identified a lead compound 1 with a novel scaffold by high-throughput screening in our in-house library. After a comprehensive structure-activity relationship study, the optimal compound 24 was discovered as an efficient and highly selective hCES2 inhibitor (hCES2: IC50 = 6.72 μM; hCES1: IC50 > 100 μM). Further enzyme kinetics study indicated that compound 24 is a reversible inhibitor of hCES2 with competitive inhibition mode (Ki = 6.28 μM). The cell experiments showed that compound 24 could reduce the level of hCES2 in living cells (IC50 = 6.54 μM). The modeling study suggested that compound 24 fitted very well with the binding pocket of hCES2 by forming multiple interactions. Notably, compound 24 can effectively treat irinotecan-induced delayed diarrhea and DSS-induced ulcerative colitis, and its safety has also been verified in subtoxic studies. Based on the overall pharmacological and preliminary safety profiles, compound 24 is worthy of further evaluation as a novel agent for irinotecan-induced delayed diarrhea.

Discovery of seven-membered ring berberine analogues as highly potent and specific hCES2A inhibitors

Human carboxylesterase 2A (hCES2A) is a key serine hydrolase responsible for the metabolic clearance of large number of compounds bearing the ester- or amide-bond(s). Inhibition of hCES2A can relieve the chemotherapy-induced toxicity and alter the pharmacokinetic bahaviors of some orally administrate esters-containing agents. However, most of the hCES2A inhibitors show poor cell-membrane permeability and poor specificity. Herein, guided by the structure activity relationships (SAR) of fifteen natural alkaloids against hCES2A, fifteen new seven-membered ring berberine analogues were designed and synthesized, and their anti-hCES2A activities were evaluated. Among all tested compounds, compound 28 showed potent anti-hCES2A effect (IC₅₀ = 1.66 μM) and excellent selectivity over hCES1A (IC₅₀ > 100 μM). The SAR analysis revealed that the seven-membered ring of these berberine analogues was a crucial moiety for hCES2A inhibition, while the secondary amine group of the ring-C is important for improving their specificity over other serine hydrolases. Inhibition kinetic analyses and molecular dynamic simulation demonstrated that 28 strongly inhibited hCES2A in a mixed-inhibition manner, with an estimated K_i value of 1.035 μM. Moreover, 28 could inhibit intracellular hCES2A in living HepG2 cells and exhibited suitable metabolic stability. Collectively, the SAR of seven-membered ring berberine analogues as hCES2A inhibitors were studied, while compound 28 acted as a promising candidate for developing highly selective hCES2A inhibitors.

An endoplasmic reticulum-specific ratiometric fluorescent probe for imaging esterase in living cells

Esterase is primarily distributed in the endoplasmic reticulum (ER) and often overexpressed in cancer cells. Therefore, the detection of esterase in ER is significant for monitoring the metabolic process of various esters and evaluating the efficacy of chemotherapeutic prodrugs. However, only few fluorescent probes can detect esterase in the ER due to the lack of ER-specificity. More seriously, these probes are often limited by low pearson's colocalization coefficient and one single wavelength emission. To solve those problems, an ER-specific ratiometric fluorescent probe (ER-EST) is designed for detecting esterase in living cells. The ER-EST shows a ratiometric and red-shifted emission (125 nm) from 435 to 560 nm after hydrolysis by esterase. The fluorescence intensity ratio of ER-EST displays quantitative response to the esterase activity (0-0.5 U/mL) with low detection limit of 1.8 × 10^-4 U/mL. Importantly, the ER-EST with good biocompatibility and excellent ER-targeted ability was successfully employed to ratiometric image the endogenous endoplasmic reticulum esterase in living cells.

Rational design of a turn-on near-infrared fluorescence probe for the highly sensitive and selective monitoring of carboxylesterase 2 in living systems

In vivo selective fluorescence imaging of carboxylesterase 2 (CES2) remains a great challenge because existing fluorescence probes can potentially suffer from interference by other hydrolases. In addition, some fluorescent probes that have been separately reported for measuring CES2 activity in vitro are affected by autofluorescence and absorption of the biological matrix due to their limited emission wavelength or short Stokes shift. Herein, based on the substrate preference and catalytic performance of CES2, a novel and NIR fluorescent probe was developed, in which a hemi-cyanine dye ester derivative was used as the basic fluorescent group. In the presence of CES2, the probe was hydrolyzed to expose the fluorophore CZX-OH (λ_abs ∼ 675 nm, λ_em ∼ 850 nm), which led to a notable red-shift in the fluorescence (∼175 nm) spectrum. Confocal imaging of cells and live mice demonstrated that the fluorescent signal of this probe was related to the real activities of CES2 in cancer cells. All these results will powerfully promote the screening of CES2 regulators and the analysis of CES2-related physiological and pathological processes.

In vitro metabolic fate of the synthetic cannabinoid receptor agonists (quinolin-8-yl 4-methyl-3-(morpholine-4-sulfonyl)benzoate [QMMSB]) and (quinolin-8-yl 4-methyl-3-((propan-2-yl)sulfamoyl)benzoate [QMiPSB]) including isozyme mapping and carboxylesterases activity testing

The synthetic cannabinoid receptor agonists (SCRAs) (quinolin-8-yl 4-methyl-3-(morpholine-4-sulfonyl)benzoate [QMMSB]) and (quinolin-8-yl 4-methyl-3-((propan-2-yl)sulfamoyl)benzoate [QMiPSB], also known as SGT-46) are based on the structure of quinolin-8-yl 4-methyl-3-(piperidine-1-sulfonyl)benzoate (QMPSB) that has been identified on seized plant material in 2011. In clinical toxicology, knowledge of the metabolic fate is important for their identification in biosamples. Therefore, the aim of this study was the identification of in vitro Phase I and II metabolites of QMMSB and QMiPSB in pooled human liver S9 fraction (pHLS9) incubations for use as screening targets. In addition, the involvement of human monooxygenases and human carboxylesterases (hCES) was examined. Analyses were performed by liquid chromatography coupled with high-resolution tandem mass spectrometry. Ester hydrolysis was found to be an important step in the Phase I metabolism of both SCRAs, with the carboxylic acid product being found only in negative ionization mode. Monohydroxy and N-dealkyl metabolites of the ester hydrolysis products were detected as well as glucuronides. CYP2C8, CYP2C9, CYP3A4, and CYP3A5 were involved in hydroxylation. Whereas enzymatic ester hydrolysis of QMiPSB was mainly catalyzed by hCES1 isoforms, nonenzymatic ester hydrolysis was also observed. The results suggest that ester hydrolysis products of QMMSB and QMiPSB and their glucuronides are suitable targets for toxicological screenings. The additional use of the negative ionization mode is recommended to increase detectability of analytes. Different cytochrome P450 (CYP) isozymes were involved in the metabolism; thus, the probability of drug-drug interactions due to CYP inhibition can be assessed as low.

In Vitro Metabolic Fate of the Synthetic Cannabinoid Receptor Agonists 2F-QMPSB and SGT-233 Including Isozyme Mapping and Carboxylesterases Activity Testing

Quinolin-8-yl 3-(4,4-difluoropiperidine-1-sulfonyl)-4-methylbenzoate (2F-QMPSB) and 3-(4,4-difluoropiperidine-1-sulfonyl)-4-methyl-N-(2-phenylpropan-2-yl)benzamide (SGT-233) belong to a new group of synthetic cannabinoid receptor agonists containing a sulfamoyl benzoate or sulfamoyl benzamide core structure. 2F-QMPSB was identified in herbal material seized in Europe in 2018. The aims of this study were the identification of in vitro Phase I and II metabolites of 2F-QMPSB and SGT-233 to find analytical targets for toxicological screenings. Furthermore, the contribution of different monooxygenases and human carboxylesterases to Phase I metabolism was investigated. Liquid chromatography coupled to high-resolution tandem mass spectrometry was used for analysis. Ester hydrolysis was found to be an important step in the metabolism of 2F-QMPSB, which was catalyzed mainly by human carboxylesterases (hCES)1 isoforms. Additionally, nonenzymatic ester hydrolysis was observed in case of 2F-QMPSB. Notably, the carboxylic acid product derived from ester hydrolysis and metabolites thereof were only detectable in negative ionization mode. In case of SGT-233, mono- and dihydroxy metabolites were identified, as well as glucuronides. The cytochrome P450 (CYP) isozymes CYP2C8, CYP2C9, CYP2C19, CYP3A4 and CYP3A5 were found to be involved in the hydroxylation of both compounds. The results of these in vitro experiments suggest that the ester hydrolysis products of 2F-QMPSB and their glucuronides are suitable targets for toxicological screenings. In the case of SGT-233, the mono- and dihydroxy metabolites were identified as suitable screening targets. The involvement of various CYP isoforms in the metabolism of both substances reduces the likelihood of drug-drug interactions due to CYP inhibition.

A fast fluorescent probe for tracing endoplasmic reticulum-located carboxylesterase in living cells

Carboxylesterase (CEs), mainly localized in endoplasmic reticulum (ER), are responsible for hydrolyzing compounds containing various ester bonds. They have been closely associated with drug metabolism and cellular homeostasis. Although some CE fluorescent probes have been developed, there are still a lack of probes that could target to the ER. Here, we developed a novel fluorescent probe CR with a specific ER anchor for monitoring CEs. In CR, p-toluenesulfonamide was chosen for precise ER targeting. A simple acetyl moiety was used as the CE response site and fluorescence modulation unit. During the spectral tests, CR displayed a fast response speed (within 10 s) towards CEs. In addition, it showed high sensitivity [limit of detection (LOD) = 5.1 × 10^-3 U/ml] and high selectivity with CEs. In biological imaging, probe CR could especially locate in the ER in HepG2 cells. After cells were treated with orilistat, CR succeeded in monitoring the changes in the CEs. Importantly, CR also had the ability to trace the changes in CEs in a tunicamycin-induced ER stress model. Therefore, probe CR could be a powerful molecular tool for further investigating the functions of CEs in the ER.

Activity and Expression of Carboxylesterases and Arylacetamide Deacetylase in Human Ocular Tissues

As a multitissue organ, the eye possesses unique anatomy and physiology, including differential expression of drug-metabolizing enzymes. Several hydrolytic enzymes that play a major role in drug metabolism and bioactivation of prodrugs have been detected in ocular tissues, but data on their quantitative expression is scarce. Also, many ophthalmic drugs are prone to hydrolysis. Metabolic characterization of individual ocular tissues is useful for the drug development process, and therefore, seven individual ocular tissues from human eyes were analyzed for the activity and expression of carboxylesterases (CESs) and arylacetamide deacetylase (AADAC). Generic and selective human esterase substrates 4-nitrophenyl acetate (most esterases), D-luciferin methyl ester (CES1), fluorescein diacetate and procaine (CES2), and phenacetin (AADAC) were applied to determine the enzymes' specific activities. Enzyme kinetics and inhibition studies were performed with isoform-selective inhibitors digitonin (CES1) and verapamil and diltiazem (CES2). Enzyme contents were determined using quantitative targeted proteomics, and CES2 expression was confirmed by western blotting. The expression and activity of human CES1 among ocular tissues varied by >10-fold, with the highest levels found in the retina and iris-ciliary body. In contrast, human CES2 expression appeared lower and more similar between tissues, whereas AADAC could not be detected. Inhibition studies showed that hydrolysis of fluorescein diacetate is also catalyzed by enzymes other than CES2. This study provides, for the first time, quantitative information on the tissue-dependent expression of human ocular esterases, which can be useful for the development of ocular drugs, prodrugs, and in pharmacokinetic modeling of the eye. SIGNIFICANCE STATEMENT: Novel and comprehensive data on the protein expression and activities of carboxylesterases from individual human eye tissues are generated. In combination with previous reports on preclinical species, this study will improve the understanding of interspecies differences in ocular drug metabolism and aid the development of ocular pharmacokinetics models.

Going deeper into the toxicokinetics of synthetic cannabinoids: in vitro contribution of human carboxylesterases

Synthetic cannabinoids (SC) are new psychoactive substances known to cause intoxications and fatalities. One reason may be the limited data available concerning the toxicokinetics of SC, but toxicity mechanisms are insufficiently understood so far. Human carboxylesterases (hCES) are widely known to play a crucial role in the catalytic hydrolysis of drugs (of abuse). The aim of this study was to investigate the in vitro contribution of hCES to the metabolism of the 13 SC 3,5-AB-5F-FUPPYCA, AB-5F-P7AICA, A-CHMINACA, DMBA-CHMINACA, MBA-CHMINACA, MDMB-4F-BINACA, MDMB-4en-PINACA, MDMB-FUBICA, MDMB-5F-PICA, MMB-CHMICA, MMB-4en-PICA, MMB-FUBINACA, and MPhP-5F-PICA. The SC were incubated with recombinant hCES1b, hCES1c, or hCES2 and analyzed by liquid chromatography-ion trap mass spectrometry to assess amide or ester hydrolysis in an initial activity screening. Enzyme kinetic studies were performed if sufficient hydrolysis was observed. No hydrolysis of the amide linker was observed using those experimental conditions. Except for MDMB-5F-PICA, ester hydrolysis was always detected if an ester group was present in the head group. In general, SC with a terminal ester bearing a small alcohol part and a larger acyl part showed higher affinity to hCES1 isozymes. Due to the low hydrolysis rates, enzyme kinetics could not be modeled for the SC with a tert-leucine-derived moiety, but hydrolysis reactions of MPhP-5F-PICA and of those containing a valine-derived moiety followed classic Michaelis-Menten kinetics. In conclusion, drug-drug/drug-food interactions or hCES polymorphisms may prolong the half-life of SC and the current results help to estimate the risk of toxicity in the future after combining them with activity and clinical data.

Carbonate-Based Fluorescent Chemical Tool for Uncovering Carboxylesterase 1 (CES1) Activity Variations in Live Cells

Carboxylesterase 1 (CES1) plays a key role in the metabolism of endogenous biomolecules and xenobiotics including a variety of pharmaceuticals. Despite the established importance of CES1 in drug metabolism, methods to study factors that can vary CES1 activity are limited with only a few suitable for use in live cells. Herein, we report the development of FCP1, a new CES1 specific fluorescent probe with a unique carbonate substrate constructed from commercially available reagents. We show that FCP-1 can specifically report on endogenous CES1 activity with a robust fluorescence response in live HepG2 cells through studies with inhibitors and genetic knockdowns. Subsequently, we deployed FCP-1 to develop a live cell fluorescence microscopy-based approach to identify activity differences between CES1 isoforms. To the best of our knowledge, this is the first application of a fluorescent probe to measure the activity of CES1 sequence variants in live cells.

Optical substrates for drug-metabolizing enzymes: Recent advances and future perspectives

Drug-metabolizing enzymes (DMEs), a diverse group of enzymes responsible for the metabolic elimination of drugs and other xenobiotics, have been recognized as the critical determinants to drug safety and efficacy. Deciphering and understanding the key roles of individual DMEs in drug metabolism and toxicity, as well as characterizing the interactions of central DMEs with xenobiotics require reliable, practical and highly specific tools for sensing the activities of these enzymes in biological systems. In the last few decades, the scientists have developed a variety of optical substrates for sensing human DMEs, parts of them have been successfully used for studying target enzyme(s) in tissue preparations and living systems. Herein, molecular design principals and recent advances in the development and applications of optical substrates for human DMEs have been reviewed systematically. Furthermore, the challenges and future perspectives in this field are also highlighted. The presented information offers a group of practical approaches and imaging tools for sensing DMEs activities in complex biological systems, which strongly facilitates high-throughput screening the modulators of target DMEs and studies on drug/herb‒drug interactions, as well as promotes the fundamental researches for exploring the relevance of DMEs to human diseases and drug treatment outcomes.

Differences in Hydrolase Activities in the Liver and Small Intestine between Marmosets and Humans

For drug development, species differences in drug-metabolism reactions present obstacles for predicting pharmacokinetics in humans. We characterized the species differences in hydrolases among humans and mice, rats, dogs, and cynomolgus monkeys. In this study, to expand the series of such studies, we attempted to characterize marmoset hydrolases. We measured hydrolase activities for 24 compounds using marmoset liver and intestinal microsomes, as well as recombinant marmoset carboxylesterase (CES) 1, CES2, and arylacetamide deacetylase (AADAC). The contributions of CES1, CES2, and AADAC to hydrolysis in marmoset liver microsomes were estimated by correcting the activities by using the ratios of hydrolase protein levels in the liver microsomes and those in recombinant systems. For six out of eight human CES1 substrates, the activities in marmoset liver microsomes were lower than those in human liver microsomes. For two human CES2 substrates and three out of seven human AADAC substrates, the activities in marmoset liver microsomes were higher than those in human liver microsomes. Notably, among the three rifamycins, only rifabutin was hydrolyzed by marmoset tissue microsomes and recombinant AADAC. The activities for all substrates in marmoset intestinal microsomes tended to be lower than those in liver microsomes, which suggests that the first-pass effects of the CES and AADAC substrates are due to hepatic hydrolysis. In most cases, the sums of the values of the contributions of CES1, CES2, and AADAC were below 100%, which indicated the involvement of other hydrolases in marmosets. In conclusion, we clarified the substrate preferences of hydrolases in marmosets. SIGNIFICANCE STATEMENT: This study confirmed that there are large differences in hydrolase activities between humans and marmosets by characterizing marmoset hydrolase activities for compounds that are substrates of human CES1, CES2, or arylacetamide deacetylase. The data obtained in this study may be useful for considering whether marmosets are appropriate for examining the pharmacokinetics and efficacies of new chemical entities in preclinical studies.

In Vitro Metabolic Fate of the Synthetic Cannabinoid Receptor Agonists QMPSB and QMPCB (SGT-11) Including Isozyme Mapping and Esterase Activity

Quinolin-8-yl 4-methyl-3-(piperidine-1-sulfonyl)benzoate (QMPSB) and quinolin-8-yl 4-methyl-3-(piperidine-1-carbonyl)benzoate (QMPCB, SGT-11) are synthetic cannabinoid receptor agonists (SCRAs). Knowing their metabolic fate is crucial for the identification of toxicological screening targets and to predict possible drug interactions. The presented study aimed to identify the in vitro phase I/II metabolites of QMPSB and QMPCB and to study the contribution of different monooxygenases and human carboxylesterases by using pooled human liver S9 fraction (pHLS9), recombinant human monooxygenases, three recombinant human carboxylesterases, and pooled human liver microsomes. Analyses were carried out by liquid chromatography high-resolution tandem mass spectrometry. QMPSB and QMPCB showed ester hydrolysis, and hydroxy and carboxylic acid products were detected in both cases. Mono/dihydroxy metabolites were formed, as were corresponding glucuronides and sulfates. Most of the metabolites could be detected in positive ionization mode with the exception of some QMPSB metabolites, which could only be found in negative mode. Monooxygenase activity screening revealed that CYP2B6/CYP2C8/CYP2C9/CYP2C19/CYP3A4/CYP3A5 were involved in hydroxylations. Esterase screening showed the involvement of all investigated isoforms. Additionally, extensive non-enzymatic ester hydrolysis was observed. Considering the results of the in vitro experiments, inclusion of the ester hydrolysis products and their glucuronides and monohydroxy metabolites into toxicological screening procedures is recommended.

Discovery and Characterization of the Biflavones From Ginkgo biloba as Highly Specific and Potent Inhibitors Against Human Carboxylesterase 2

Human carboxylesterase 2 (CES2), one of the most abundant hydrolases distributed in the small intestine, has been validated as a key therapeutic target to ameliorate the intestinal toxicity caused by irinotecan. This study aims to discover efficacious CES2 inhibitors from natural products and to characterize the inhibition potentials and inhibitory mechanisms of the newly identified CES2 inhibitors. Following high-throughput screening and evaluation of the inhibition potency of more than 100 natural products against CES2, it was found that the biflavones isolated from Ginkgo biloba displayed extremely potent CES2 inhibition activities and high specificity over CES1 (>1000-fold). Further investigation showed that ginkgetin, bilobetin, sciadopitysin and isoginkgetin potently inhibited CES2-catalyzed hydrolysis of various substrates, including the CES2 substrate-drug irinotecan. Notably, the inhibition potentials of four biflavones against CES2 were more potent than that of loperamide, a marketed anti-diarrhea agent used for alleviating irinotecan-induced intestinal toxicity. Inhibition kinetic analyses demonstrated that ginkgetin, bilobetin, sciadopitysin and isoginkgetin potently inhibited CES2-catalyzed fluorescein diacetate hydrolysis via a reversible and mixed inhibition manner, with K _i values of less than 100 nM. Ensemble docking and molecular dynamics revealed that these biflavones could tightly and stably bind on the catalytic cavity of CES2 via hydrogen bonding and π-π stacking interactions, while the interactions with CES1 were awfully poor. Collectively, this study reports that the biflavones isolated from Ginkgo biloba are potent and highly specific CES2 inhibitors, which offers several promising lead compounds for developing novel anti-diarrhea agent to alleviate irinotecan-induced diarrhea.

Carboxylesterases and arylacetamide deacetylase comparison in human A549, H460, and H727 pulmonary cells

AIMS

Human carboxylesterases (CESs) and arylacetamide deacetylase (AADAC) are serine-esterase enzymes catalyzing the hydrolysis of many compounds containing esters, amides, thioesters, or acetyl groups. This study aimed to investigate the presence, kinetic parameters, and inhibition of CES1, CES2, and AADAC in A549, H460, and H727 pulmonary cells in both living cells and S9 fractions.

MATERIALS AND METHODS

The p-nitrophenyl acetate (pNPA) and 4-methylumbelliferyl acetate (4-MUA) were used as non-selective esterase substrates, whereas phenacetin as selective AADAC substrate. CESs activities were also investigated in living cells by cellular bioimaging using selective fluorescent probes.

KEY FINDINGS

AADAC gene was detected in A549 and H460 cells; nevertheless, arylesterase activity was not found in relative S9 fractions. Besides, CES1 and CES2 were expressed to a different extent by all lung cells, and enzymatic activities were quite overlapping each other. All enzymes exhibited a typical Michaelis-Menten saturation curve and, regarding 4-MUA, similar K_m values were found in both living cells and S9 fractions. Conversely, kinetic parameters relative to the pNPA hydrolysis by S9 fractions were significantly lower than those detected in living cells. Inhibition studies revealed that 4-MUA hydrolysis was inhibited by bis-p-nitrophenyl phosphate and phenylmethanesulfonyl fluoride more than loperamide; on the contrary, pNPA hydrolysis inhibition was limited with similar inhibition profiles being obtained in both living cells and S9 fractions. The presence of carboxylesterases was definitely confirmed by cellular bioimaging.

SIGNIFICANCE

These findings add information to esterase knowledge in pulmonary cells that could be used as in vitro models for toxicological and pharmacological studies.

A broad-spectrum substrate for the human UDP-glucuronosyltransferases and its use for investigating glucuronidation inhibitors

Strong inhibition of the human UDP-glucuronosyltransferase enzymes (UGTs) may lead to undesirable effects, including hyperbilirubinaemia and drug/herb-drug interactions. Currently, there is no good way to examine the inhibitory effects and specificities of compounds toward all the important human UGTs, side-by-side and under identical conditions. Herein, we report a new, broad-spectrum substrate for human UGTs and its uses in screening and characterizing of UGT inhibitors. Following screening a variety of phenolic compound(s), we have found that methylophiopogonanone A (MOA) can be readily O-glucuronidated by all tested human UGTs, including the typical N-glucuronidating enzymes UGT1A4 and UGT2B10. MOA-O-glucuronidation yielded a single mono-O-glucuronide that was biosynthesized and purified for structural characterization and for constructing an LC-UV based MOA-O-glucuronidation activity assay, which was then used for investigating MOA-O-glucuronidation kinetics in recombinant human UGTs. The derived K_m values were crucial for selecting the most suitable assay conditions for assessing inhibitory potentials and specificity of test compound(s). Furthermore, the inhibitory effects and specificities of four known UGT inhibitors were reinvestigated by using MOA as the substrate for all tested UGTs. Collectively, MOA is a broad-spectrum substrate for the human UGTs, which offers a new and practical tool for assessing inhibitory effects and specificities of UGT inhibitors.

Carboxylesterase Activities and Protein Expression in Rabbit and Pig Ocular Tissues

Hydrolytic reactions constitute an important pathway of drug metabolism and a significant route of prodrug activation. Many ophthalmic drugs and prodrugs contain ester groups that greatly enhance their permeation across several hydrophobic barriers in the eye before the drugs are either metabolized or released, respectively, via hydrolysis. Thus, the development of ophthalmic drug therapy requires the thorough profiling of substrate specificities, activities, and expression levels of ocular esterases. However, such information is scant in the literature, especially for preclinical species often used in ophthalmology such as rabbits and pigs. Therefore, our aim was to generate systematic information on the activity and expression of carboxylesterases (CESs) and arylacetamide deacetylase (AADAC) in seven ocular tissue homogenates from these two species. The hydrolytic activities were measured using a generic esterase substrate (4-nitrophenyl acetate) and, in the absence of validated substrates for rabbit and pig enzymes, with selective substrates established for human CES1, CES2, and AADAC (d-luciferin methyl ester, fluorescein diacetate, procaine, and phenacetin). Kinetics and inhibition studies were conducted using these substrates and, again due to a lack of validated rabbit and pig CES inhibitors, with known inhibitors for the human enzymes. Protein expression levels were measured using quantitative targeted proteomics. Rabbit ocular tissues showed significant variability in the expression of CES1 (higher in cornea, lower in conjunctiva) and CES2 (higher in conjunctiva, lower in cornea) and a poor correlation of CES expression with hydrolytic activities. In contrast, pig tissues appear to express only CES1, and CES3 and AADAC seem to be either low or absent, respectively, in both species. The current study revealed remarkable species and tissue differences in ocular hydrolytic enzymes that can be taken into account in the design of esterase-dependent prodrugs and drug conjugates, the evaluation of ocular effects of systemic drugs, and in translational and toxicity studies.

Investigating the mechanism of action of aggregation-inducing antimicrobial Pept-ins

Aggregation can be selectively induced by aggregation-prone regions (APRs) contained in the target proteins. Aggregation-inducing antimicrobial peptides (Pept-ins) contain sequences homologous to APRs of target proteins and exert their bactericidal effect by causing aggregation of a large number of proteins. To better understand the mechanism of action of Pept-ins and the resistance mechanisms, we analyzed the phenotypic, lipidomic, and transcriptomic as well as genotypic changes in laboratory-derived Pept-in-resistant E. coli mutator cells. The analysis showed that the Pept-in resistance mechanism is dominated by a decreased Pept-in uptake, in both laboratory-derived mutator cells and clinical isolates. Our data indicate that Pept-in uptake involves an electrostatic attraction between the Pept-in and the bacterial membrane and follows a complex mechanism potentially involving many transporters. Furthermore, it seems more challenging for bacteria to become resistant toward Pept-ins that are less dependent on electrostatic attraction for uptake, suggesting that future Pept-ins should be selected for this property.

Macrophage imaging and subset analysis using single-cell RNA sequencing

Macrophages have been associated with drug response and resistance in diverse settings, thus raising the possibility of using macrophage imaging as a companion diagnostic to inform personalized patient treatment strategies. Nanoparticle-based contrast agents are especially promising because they efficiently deliver fluorescent, magnetic, and/or radionuclide labels by leveraging the intrinsic capacity of macrophages to accumulate nanomaterials in their role as professional phagocytes. Unfortunately, current clinical imaging modalities are limited in their ability to quantify broad molecular programs that may explain (a) which particular cell subsets a given imaging agent is actually labeling, and (b) what mechanistic role those cells play in promoting drug response or resistance. Highly multiplexed single-cell approaches including single-cell RNA sequencing (scRNAseq) have emerged as resources to help answer these questions. In this review, we query recently published scRNAseq datasets to support companion macrophage imaging, with particular focus on using dextran-based nanoparticles to predict the action of anti-cancer nanotherapies and monoclonal antibodies.

Discovery of hCES2A inhibitors from Glycyrrhiza inflata via combination of docking-based virtual screening and fluorescence-based inhibition assays

An integrated strategy via combination of chemical profiling, docking-based virtual screening and fluorescence-based high-throughput inhibitor screening assays was used to efficiently identify natural hCES2A inhibitors from herbal medicines.

Rapalogues as hCES2A Inhibitors: In Vitro and In Silico Investigations

BACKGROUND AND OBJECTIVE

Rapamycin and its semi-synthetic analogues (rapalogues) are frequently used in combination with other prescribed medications in clinical settings. Although the inhibitory effects of rapalogues on cytochrome P450 enzymes (CYPs) have been well examined, the inhibition potentials of rapalogues on human esterases have not been investigated. Herein, the inhibition potentials and inhibitory mechanisms of six marketed rapalogues on human esterases are investigated.

METHODS

The inhibitory effects of six marketed rapalogues (rapamycin, zotarolimus, temsirolimus, everolimus, pimecrolimus and tacrolimus) on three major esterases, including human carboxylesterases 1 (hCES1A), human carboxylesterases 2 (hCES2A) and butyrylcholinesterase (BuChE), were assayed using isozyme-specific substrates. Inhibition kinetic analyses and docking simulations were performed to investigate the inhibitory mechanisms of the rapalogues with strong hCES2A inhibition potency.

RESULTS

Zotarolimus and pimecrolimus displayed strong inhibition of human hCES2A but these agents did not inhibit hCES1A or BuChE. Further investigation demonstrated that zotarolimus could strongly inhibit intracellular hCES2A in living HepG2 cells, with an estimated IC₅₀ value of 4.09 µM. Inhibition kinetic analyses revealed that zotarolimus inhibited hCES2A-catalyzed fluorescein diacetate hydrolysis in a mixed manner, with the K_i value of 1.61 µM. Docking simulations showed that zotarolimus could tightly bind on hCES2A at two district ligand-binding sites, consistent with its mixed inhibition mode.

CONCLUSION

Our findings demonstrate that several marketed rapalogues are potent and specific hCES2A inhibitors, and these agents can serve as leading compounds for the development of more efficacious hCES2A inhibitors to modulate the pharmacokinetic profiles and toxicity of hCES2A-substrate drugs (such as the anticancer agent irinotecan).

Synthesis and Structure-Activity Relationships of 3-Arylisoquinolone Analogues as Highly Specific hCES2A Inhibitors

Mammalian carboxylesterases (CES) are key enzymes that participate in the hydrolytic metabolism of various endogenous and exogenous substrates. Human carboxylesterase 2A (hCES2A), mainly distributed in the small intestine and colon, plays a significant role in the hydrolysis of many drugs. In this study, 3-arylisoquinolones 3 h [3-(4-(benzyloxy)-3-methoxyphenyl)-7,8-dimethoxyisoquinolin-1(2H)-one] and 4 a [3-(4-(benzyloxy)-3-methoxyphenyl)-4-bromo-7,8-dimethoxyisoquinolin-1(2H)-one] were found to have potent inhibitory effects on hCES2A (IC₅₀ =0.68 μΜ, K_i =0.36 μΜ) and excellent specificity (more than 147.05-fold over hCES1 A). Moreover, 4 a exhibited threefold improved inhibition on intracellular hCES2A in living HepG2 cells relative to 3 h, with an IC₅₀ value of 0.41 μΜ. Results of inhibition kinetics studies and molecular docking simulations demonstrate that both 3 h and 4 a can bind to multiple sites on hCES2A, functioning as mixed inhibitors. Structure-activity relationship analysis revealed that the lactam moiety on the B ring is crucial for specificity towards hCES2A, while a benzyloxy group is optimal for hCES2A inhibitory potency; the introduction of a bromine atom may enhance cell permeability, thereby increasing the intracellular hCES2A inhibitory activity.

Discovery of natural alkaloids as potent and selective inhibitors against human carboxylesterase 2

Human Carboxylesterase 2A (hCES2A), one of the most important serine hydrolases, plays crucial roles in the hydrolysis and the metabolic activation of a wide range of esters and amides. Increasing evidence has indicated that potent inhibition on intestinal hCES2A may reduce the excessive accumulation of SN-38 (the hydrolytic metabolite of irinotecan with potent cytotoxicity) in the intestinal tract and thereby alleviate the intestinal toxicity triggered by irinotecan. In this study, more than sixty natural alkaloids have been collected and their inhibitory effects against hCES2A are assayed using a fluorescence-based biochemical assay. Following preliminary screening, seventeen alkaloids are found with strong to moderate hCES2A inhibition activity. Primary structure-activity relationships (SAR) analysis of natural isoquinoline alkaloids reveal that the benzo-1,3-dioxole group and the aromatic pyridine structure are beneficial for hCES2A inhibition. Further investigations demonstrate that a steroidal alkaloid reserpine exhibits strong hCES2A inhibition activity (IC₅₀ = 0.94 μM) and high selectivity over other human serine hydrolases including hCES1A, dipeptidyl peptidase IV (DPP-IV), butyrylcholinesterase (BChE) and thrombin. Inhibition kinetic analyses demonstrated that reserpine acts as a non-competitive inhibitor against hCES2A-mediated FD hydrolysis. Molecular docking simulations demonstrated that the potent inhibition of hCES2A by reserpine could partially be attributed to its strong σ-π and S-π interactions between reserpine and hCES2A. Collectively, our findings suggest that reserpine is a potent and highly selective inhibitor of hCES2A, which can be served as a promising lead compound for the development of more efficacious and selective alkaloids-type hCES2A inhibitors for biomedical applications.

Design, synthesis and biological evaluation of indanone-chalcone hybrids as potent and selective hCES2A inhibitors

Human carboxylesterase 2 (hCES2A), one of the major serine hydrolases distributed in the small intestine, plays a crucial role in hydrolysis of ester-bearing drugs. Accumulating evidence has indicated that hCES2A inhibitor therapy can modulate the pharmacokinetic and toxicological profiles of some important hCES2A-substrate drugs, such as the anticancer agent CPT-11. Herein, a series of indanone-chalcone hybrids are designed and synthesized to find potent and highly selective hCES2A inhibitors. Inhibition assays demonstrated that most indanone-chalcone hybrids displayed strong to moderate hCES2A inhibition activities. Structure-hCES2A inhibition activity relationship studies showed that introduction of a hydroxyl at the C4' site and introduction of an N-alkyl group at the C6 site were beneficial for hCES2A inhibition. Particularly, B7 (an N-alkylated 1-indanone-chalcone hybrid) exhibited the most potent inhibition on hCES2A and excellent specificity (this agent could not inhibit other human esterases including hCES1A and butyrylcholinesterase). Inhibition kinetic analyses demonstrated that B7 potently inhibited hCES2A-mediated FD hydrolysis in a mixed inhibition manner, with a calculated K_i value of 0.068 μM. Furthermore, B7 was capable of inhibiting intracellular hCES2A in living cells and displayed good metabolic stability. Collectively, our findings show that indanone-chalcone hybrids are good choices for the development of hCES2A inhibitors, while B7 is a promising candidate for the development of novel anti-diarrhea agents to ameliorate irinotecan-induced intestinal toxicity.

Per- and polyfluoroalkyl substances exert strong inhibition towards human carboxylesterases

PFASs are highly persistent in both natural and living environment, and pose a significant risk for wildlife and human beings. The present study was carried out to determine the inhibitory behaviours of fourteen PFASs on metabolic activity of two major isoforms of carboxylesterases (CES). The probe substrates 2-(2-benzoyl-3-methoxyphenyl) benzothiazole (BMBT) for CES1 and fluorescein diacetate (FD) for CES2 were utilized to determine the inhibitory potentials of PFASs on CES in vitro. The results demonstrated that perfluorododecanoic acid (PFDoA), perfluorotetradecanoic acid (PFTA) and perfluorooctadecanoic acid (PFOcDA) strongly inhibited CES1 and CES2. The half inhibition concentration (IC₅₀) value of PFDoA, PFTA and PFOcDA for CES1 inhibition was 10.6 μM, 13.4 μM and 12.6 μM, respectively. The IC₅₀ for the inhibition of PFDoA, PFTA and PFOcDA towards CES2 were calculated to be 9.56 μM, 17.2 μM and 8.73 μM, respectively. PFDoA, PFTA and PFOcDA exhibited noncompetitive inhibition towards both CES1 and CES2. The inhibition kinetics parameters (K_i) were 27.7 μM, 26.9 μM, 11.9 μM, 4.04 μM, 29.1 μM, 27.4 μM for PFDoA-CES1, PFTA-CES1, PFOcDA-CES1, PFDoA-CES2, PFTA-CES2, PFOcDA-CES2, respectively. In vitro-in vivo extrapolation (IVIVE) predicted that when the plasma concentrations of PFDoA, PFTA and PFOcDA were greater than 2.77 μM, 2.69 μM and 1.19 μM, respectively, it might interfere with the metabolic reaction catalyzed by CES1 in vivo; when the plasma concentrations of PFDoA, PFTA and PFOcDA were greater than 0.40 μM, 2.91 μM, 2.74 μM, it might interfere with the metabolic reaction catalyzed by CES2 in vivo. Molecular docking was used to explore the interactions between PFASs and CES. In conclusion, PFASs were found to cause inhibitory effects on CES in vitro, and this finding would provide an important experimental basis for further in vivo testing of PFASs focused on CES inhibition endpoints.

How to Study the Metabolism of New Psychoactive Substances for the Purpose of Toxicological Screenings-A Follow-Up Study Comparing Pooled Human Liver S9, HepaRG Cells, and Zebrafish Larvae

The new psychoactive substances (NPS) market continues to be very dynamic. A large number of compounds belonging to diverse chemical groups continue to emerge. This makes their detection in biological samples challenging for clinical and forensic toxicologists. Knowledge of the metabolic fate of NPS is crucial for developing comprehensive screening procedures. As human studies are not feasible due to ethical concerns, the current study aimed to compare the NPS' metabolic pattern in incubations with pooled human liver S9 fraction (pHLS9), human liver HepaRG cells, and zebrafish larvae. The latter model was recently shown to be a promising preclinical surrogate for human hepatic metabolism of a synthetic cannabinoid. However, studies concerning other NPS classes are still missing and therefore an amphetamine-based N-methoxybenzyl (NBOMe) compound, a synthetic cathinone, a pyrrolidinophenone analog, a lysergamide, as well as another synthetic cannabinoid were included in the current study. Liquid chromatography coupled to Orbitrap-based high-resolution tandem mass spectrometry was used to analyze metabolic data. Zebrafish larvae were found to produce the highest number of phase I but also phase II metabolites (79 metabolites in total), followed by HepaRG cells (66 metabolites). Incubations with pHLS9 produced the least metabolites (57 metabolites). Furthermore, the involvement of monooxygenases and esterases in the metabolic phase I transformations of 4F-MDMB-BINACA was elucidated using single-enzyme incubations. Several cytochrome P450 (CYP) isozymes were shown to contribute, and CYP3A5 was involved in all CYP-catalyzed reactions, while amide and ester hydrolysis were catalyzed by the human carboxylesterase (hCES) isoforms hCES1b and/or hCES1c. Finally, metabolites were compared to those present in human biosamples if data were available. Overall, the metabolic patterns in HepaRG cells provided the worst overlap with that in human biosamples. Zebrafish larvae experiments agreed best with data found in human plasma and urine analysis. The current study underlines the potential of zebrafish larvae as a tool for elucidating the toxicokinetics of NPS in the future.

Construction and application of a high-content analysis for identifying human carboxylesterase 2 inhibitors in living cell system

Human carboxylesterase 2 (hCE2), one of the most principal drug-metabolizing enzymes, catalyzes the hydrolysis of a variety of endogenous esters, anticancer agents, and environmental toxicants. The significant roles of hCE2 in both endobiotic and xenobiotic metabolism sparked great interest in the discovery and development of efficacious and selective inhibitors. However, the safe and effective inhibitors of hCE2 are scarce, due to the lack of efficient screening and evaluation systems for complex biological systems. To offer a solution to this problem, a high-content analysis (HCA)-based cell imaging and multiparametric assay method was constructed for evaluating the inhibitory effect and safety of hCE2 inhibitors in living cell system. In this study, we first established a cell imaging-based method for identifying hCE2 inhibitors at the living cell level with hCE2 fluorescent probe NCEN. Meanwhile, two nuclear probes, Hoechst 33342 and PI, were integrated to evaluate the potential cytotoxicity of compounds simultaneously. Then, the accuracy of the HCA-based method was verified by the LC-FD-based method with a positive inhibitor BNPP, and the results showed that the HCA-based method exhibited excellent precision, robustness, and reliability. Finally, the newly established HCA-based multiparametric assay panel was successfully applied to re-evaluate a series of reported hCE2 inhibitors in living cells. In summary, the HCA-based multiparametric method could serve as an efficient tool for the accuracy measurement inhibitory effect and cytotoxicity of compounds against hCE2 in living cell system. Graphical abstract.

Endoplasmic Reticulum Targeting Ratiometric Fluorescent Probe for Carboxylesterase 2 Detection in Drug-Induced Acute Liver Injury

Carboxylesterase 2 (CES2), an endoplasmic reticulum (ER) located phase I enzyme, plays a vital role in the metabolism of various endogenous and exogenous substances, and is regarded as an important target for the design of prodrugs. Unfortunately, superior highly selective ER targeting fluorescent probes for monitoring of CES2 are not currently available. Herein, we report an ER targeting CES2 selective and sensitive ratiometric fluorescent probe ERNB based on the ER localizing group p-toluenesulfonamide. ERNB possessed high specificity, sensitivity, and exhibited excellent subcellular localization when compared to commercial ER tracker, and was used to image CES2 in the ER of living cells. Additionally, using ERNB we evaluated the CES2 regulation under d,l-dithiothreitol and tunicamycin-induced ER stress. Furthermore, we determined the down regulation of CES2 activity and expression in the acetaminophen-induced acute liver injury model. On the basis of these results, we conclude that ERNB is a promising tool for highlighting the role of CES2 in the ER and in exploring the role of CES2 in the development of diseases associated with ER stress.

Dynamics of the Cellular Metabolism of Leptosperin Found in Manuka Honey

Leptosperin (methyl syringate β-d-gentiobioside) is abundantly found in manuka honey, which is widely used because of its antibacterial and possible anti-inflammatory activities. The aim of this study was to examine the molecular mechanism underlying the metabolism of leptosperin. Five phytochemicals (leptosperin, methyl syringate (MSYR), glucuronate conjugate of MSYR (MSYR-GA), sulfonate conjugate of MSYR (MSYR-S), and syringic acid (SYR)) were separately incubated with HepG2 and Caco-2 cells. After incubation, we found that the concentration of MSYR decreased, whereas the concentrations of SYR, MSYR-GA, and MSYR-S increased. By profiling with inhibitors and carboxylesterases (CES1, 2), we found that the conversion from MSYR to SYR was mediated by CES1. Lipopolysaccharide-stimulated RAW264.7 cells restored MSYR-GA to MSYR possibly by the secreted β-glucuronidase. All of the mice administered with leptosperin, MSYR, or manuka honey showed higher MSYR (13.84 ± 11.51, 14.29 ± 9.19, or 6.66 ± 2.30 nM) and SYR (1.85 ± 0.66, 6.01 ± 1.20, or 8.16 ± 3.10 nM) levels in the plasma compared with that of the vehicle controls (3.33 ± 1.45 (MSYR) and 1.85 ± 0.66 (SYR) nM). The findings of our study indicate that the unique metabolic pathways of these compounds may account for possible functionalities of manuka honey.

Inhibition of Human Liver Carboxylesterase (hCE1) by Organophosphate Ester Flame Retardants and Plasticizers: Implications for Pharmacotherapy

Organophosphate ester (OPE) flame retardants and plasticizers, consumer product additives with widespread human exposure, were evaluated for their effect on the activity of purified human liver carboxylesterase (hCE1). Four of the 15 OPEs tested had IC50 values lower than 100 nM, including triphenyl phosphate (TPHP), 2-ethylhexyl diphenyl phosphate (EHDPHP), 4-isopropylphenyl diphenyl phosphate (4IPPDPP), and 4-tert-butylphenyl diphenyl phosphate (4tBPDPP), as did 4 of the commercial flame retardant mixtures tested. Because hCE1 is critical for the activation of imidapril, an angiotensin-converting enzyme-inhibitor prodrug prescribed to treat hypertension, the most potent inhibitors, TPHP and 4tBPDPP, and an environmentally relevant mixture (house dust) were further evaluated for their effect on imidapril bioactivation in vitro. TPHP and 4tBPDPP were potent inhibitors of hCE1-mediated imidapril activation (Ki = 49.0 and 17.9 nM, respectively). House dust extracts (100 µg/ml) also caused significant reductions (up to 33%) in imidapril activation. Combined, these data suggest that exposure to OPEs may affect pharmacotherapy.

Measuring human carboxylesterase 2 activity in pancreatic cancer patient-derived xenografts using a ratiometric fluorescent chemosensor

Irinotecan-based therapy is a common treatment for pancreatic cancer. To elicit its anticancer activity, the drug requires first the hydrolysis action of the enzyme human carboxylesterase 2 (hCES2). It has been established that pancreatic cancer patients have various levels of hCES2, whereby patients having low levels respond poorer to Irinotecan than patients with higher levels, suggesting that hCES2 can be used to predict response. However, current methods that measure hCES2 activity are inaccurate, complex or lengthy, thus being incompatible for use in a clinical setting. Here, we developed a small molecule ratiometric fluorescent chemosensor that accurately measures hCES2 activity in a single-step within complex mixtures. Our chemosensor is highly selective for hCES2 over hCES1, cell permeable and can measure hCES2 activity in pancreatic cancer patient-derived xenografts. Given the simplicity, accuracy and tissue compatibility of our assay, we anticipate our chemosensor can be used to predict patient response to Irinotecan-based therapy.