Age- and sex-related expression and activity of carboxylesterase 1 and 2 in mouse and human liver

Regulation of Human Hydrolases and Its Implications in Pharmacokinetics and Pharmacodynamics

Hydrolases represent an essential class of enzymes indispensable for the metabolism of various clinically essential medications. Individuals exhibit marked differences in the expression and activation of hydrolases, resulting in significant variability in the pharmacokinetics (PK) and pharmacodynamics (PD) of drugs metabolized by these enzymes. The regulation of hydrolase expression and activity involves both genetic polymorphisms and nongenetic factors. This review examines the current understanding of genetic and nongenetic regulators of six clinically significant hydrolases, including carboxylesterase (CES)-1 CES2, arylacetamide deacetylase (AADAC), paraoxonase (PON)-1 PON3, and cathepsin A (CTSA). We explore genetic variants linked to the expression and activity of the hydrolases and their effects on the PK and PD of their substrate drugs. Regarding nongenetic regulators, we focus on the inhibitors and inducers of these enzymes. Additionally, we examine the developmental expression patterns and gender differences in the hydrolases when pertinent information was available. Many genetic and nongenetic regulators were found to be associated with the expression and activity of the hydrolases and PK and PD. However, hydrolases remain generally understudied compared with other drug-metabolizing enzymes, such as cytochrome P450s. The clinical significance of genetic and nongenetic regulators has not yet been firmly established for the majority of hydrolases. Comprehending the mechanisms that underpin the regulation of these enzymes holds the potential to refine therapeutic regimens, thereby enhancing the efficacy and safety of drugs metabolized by the hydrolases. SIGNIFICANCE STATEMENT: Hydrolases play a crucial role in the metabolism of numerous clinically important medications. Genetic polymorphisms and nongenetic regulators can affect hydrolases' expression and activity, consequently influencing the exposure and clinical outcomes of hydrolase substrate drugs. A comprehensive understanding of hydrolase regulation can refine therapeutic regimens, ultimately enhancing the efficacy and safety of drugs metabolized by the enzymes.

Regulation of carboxylesterases and its impact on pharmacokinetics and pharmacodynamics: an up-to-date review

INTRODUCTION

Carboxylesterase 1 (CES1) and carboxylesterase 2 (CES2) are among the most abundant hydrolases in humans, catalyzing the metabolism of numerous clinically important medications, such as methylphenidate and clopidogrel. The large interindividual variability in the expression and activity of CES1 and CES2 affects the pharmacokinetics (PK) and pharmacodynamics (PD) of substrate drugs.

AREAS COVERED

This review provides an up-to-date overview of CES expression and activity regulations and examines their impact on the PK and PD of CES substrate drugs. The literature search was conducted on PubMed from inception to January 2024.

EXPERT OPINION

Current research revealed modest associations of CES genetic polymorphisms with drug exposure and response. Beyond genomic polymorphisms, transcriptional and posttranslational regulations can also significantly affect CES expression and activity and consequently alter PK and PD. Recent advances in plasma biomarkers of drug-metabolizing enzymes encourage the research of plasma protein and metabolite biomarkers for CES1 and CES2, which could lead to the establishment of precision pharmacotherapy regimens for drugs metabolized by CESs. Moreover, our understanding of tissue-specific expression and substrate selectivity of CES1 and CES2 has shed light on improving the design of CES1- and CES2-activated prodrugs.

Silicon Ether Ionizable Lipids Enable Potent mRNA Lipid Nanoparticles with Rapid Tissue Clearance

The advent of mRNA for nucleic acid (NA) therapeutics has unlocked many diverse areas of research and clinical investigation. However, the shorter intracellular half-life of mRNA compared with other NAs may necessitate more frequent dosing regimens. Because lipid nanoparticles (LNPs) are the principal delivery system used for mRNA, this could lead to tolerability challenges associated with an accumulated lipid burden. This can be addressed by introducing enzymatically cleaved carboxylic esters into the hydrophobic domains of lipid components, notably, the ionizable lipid. However, enzymatic activity can vary significantly with age, disease state, and species, potentially limiting the application in humans. Here we report an alternative approach to ionizable lipid degradability that relies on nonenzymatic hydrolysis, leading to a controlled and highly efficient lipid clearance profile. We identify highly potent examples and demonstrate their exceptional tolerability in multiple preclinical species, including multidosing in nonhuman primates (NHP).

Physiologically Based Pharmacokinetics Modeling in the Neonatal Population-Current Advances, Challenges, and Opportunities

Physiologically based pharmacokinetic (PBPK) modeling is an approach to predicting drug pharmacokinetics, using knowledge of the human physiology involved and drug physiochemical properties. This approach is useful when predicting drug pharmacokinetics in under-studied populations, such as pediatrics. PBPK modeling is a particularly important tool for dose optimization for the neonatal population, given that clinical trials rarely include this patient population. However, important knowledge gaps exist for neonates, resulting in uncertainty with the model predictions. This review aims to outline the sources of variability that should be considered with developing a neonatal PBPK model, the data that are currently available for the neonatal ontogeny, and lastly to highlight the data gaps where further research would be needed.

Deciphering the species differences in CES1A-mediated hydrolytic metabolism by using a bioluminescence substrate

Carboxylesterases 1A (CES1A) is a key enzyme responsible for the hydrolytic metabolism of a great deal of endogenous and exogenous substrates bearing ester- or amide-bond(s). This study aimed to decipher the species difference in CES1A-mediated hydrolytic metabolism by using a newly developed bioluminescence CES1A sensor (termed NLMe) as the probe substrate, while the liver microsomes from six different mammalian species (human, cynomolgus monkey, dog, minipig, rat and mouse) were used as the enzyme sources. Metabolite profiling demonstrated that all tested liver microsomes from various species could catalyze NLMe hydrolysis, but significant difference in hydrolytic rate was observed. Kinetic plots of NLMe hydrolysis in liver microsomes from different species showed that the inherent clearance rates (C_lint) of NLMe in human liver microsomes (HLM), cynomolgus monkey liver microsomes (CyLM), and pig liver microsome (PLM) were comparable, while the C_lint values of NLMe in dog liver microsomes (DLM), mouse liver microsomes (MLM), and rat liver microsomes (RLM) were relatively small. Moreover, chemical inhibition assays showed that NLMe hydrolysis in all tested liver microsomes could be competently inhibited by BNPP (a potent broad-spectrum inhibitor of CES), but CUA (a selective inhibitor of human CES1A) only inhibited NLMe hydrolysis in human liver microsomes and dog liver microsomes. In summary, the species differences in CES1A-catalyzed NLMe hydrolysis were carefully investigated from the views of the similarities in metabolite profile, hydrolytic kinetics and inhibitor response. All these findings provide new insights into the species differences in CES1A-mediated hydrolytic metabolism and suggest that it is necessary for the pharmacologists to choose appropriate animal models to replace humans for evaluating the in vivo effects of CES1A inhibitors.

Enalapril and Enalaprilat Pharmacokinetics in Children with Heart Failure Due to Dilated Cardiomyopathy and Congestive Heart Failure after Administration of an Orodispersible Enalapril Minitablet (LENA-Studies)

Angiotensin-converting enzyme inhibitors (ACEI), such as enalapril, are a cornerstone of treatment for pediatric heart failure which is still used off-label. Using a novel age-appropriate formulation of enalapril orodispersible minitablets (ODMTs), phase II/III open-label, multicenter pharmacokinetic (PK) bridging studies were performed in pediatric patients with heart failure due to dilated cardiomyopathy (DCM) and congenital heart disease (CHD) in five participating European countries. Children were treated for 8 weeks with ODMTs according to an age-appropriate dosing schedule. The primary objective was to describe PK parameters (area under the curve (AUC), maximal concentration (Cmax), time to reach maximal concentration (t-max)) of enalapril and its active metabolite enalaprilat. Of 102 patients, 89 patients (n = 26, DCM; n = 63 CHD) were included in the primary PK endpoint analysis. Rate and extent of enalapril and its active metabolite enalaprilat were described and etiology and age could be identified as potential PK modifying factors. The dosing schedule appeared to be tolerated well and did not result in any significant drug-related serious adverse events. The PK analysis and the lack of severe safety events supports the applied age-appropriate dosing schedule for the enalapril ODMTs.

Toxicokinetic studies of di-isobutyl phthalate focusing on the exploration of gender differences in rats

Due to the use of di-isobutyl-phthalate (DiBP) in the production of soft-polyvinyl chloride articles, it is currently a hazardous substance prevalent in human daily life. However, reports on DiBP's toxicokinetics are still very scarce. And no studies have been reported on gender differences in DiBP toxicokinetics. Therefore, this study was conducted in accordance with these research needs. DiBP of 100 mg/kg has been exposed to male and female rats single or multiple times. DiBP and its major metabolite, mono-isobutyl-phthalate (MiBP), were quantified from various biological samples obtained from rats administered with DiBP. Based on these results, several toxicokinetic parameters were estimated. Toxicokinetic results between genders were compared, and from this, existence and extent of gender differences in DiBP's toxicokinetics were explored. Investigation of presence and extent of subacute toxicity in male and female rats following multiple exposures to DiBP were also conducted. This study provided comprehensive information on DiBP toxicity and gender differences that have not been reported in detail. Results of these studies imply that subacute toxicity in liver, kidney, lung, and testis of rats at 100 mg/kg of DiBP is modest and that there is little difference in toxicokinetics between genders. And in both male and female rats, the metabolism of DiBP (to MiBP) was significant, and excretion of MiBP into urine was a major indicator of DiBP exposure.

Human carboxylesterases and fluorescent probes to image their activity in live cells

Human carboxylesterases (CESs) are serine hydrolases that are responsible for the phase I metabolism of an assortment of ester, amide, thioester, carbonate, and carbamate containing drugs. CES activity is known to be influenced by a variety of factors including single nucleotide polymorphisms, alternative splicing, and drug-drug interactions. These different factors contribute to interindividual variability of CES activity which has been demonstrated to influence clinical outcomes among people treated with CES-substrate therapeutics. Detailed exploration of the factors that influence CES activity is emerging as an important area of research. The use of fluorescent probes with live cell imaging techniques can selectively visualize the real-time activity of CESs and have the potential to be useful tools to help reveal the impacts of CES activity variations on human health. This review summarizes the properties of the five known human CESs including factors reported to or that could potentially influence their activity before discussing the design aspects and use considerations of CES fluorescent probes in general in addition to highlighting several well-characterized probes.

Impact of carboxylesterase 1 genetic polymorphism on trandolapril activation in human liver and the pharmacokinetics and pharmacodynamics in healthy volunteers

Trandolapril, an angiotensin-converting enzyme inhibitor prodrug, needs to be activated by carboxylesterase 1 (CES1) in the liver to exert its intended therapeutic effect. A previous in vitro study demonstrated that the CES1 genetic variant G143E (rs71647871) abolished CES1-mediated trandolapril activation in cells transfected with the variant. This study aimed to determine the effect of the G143E variant on trandolapril activation in human livers and the pharmacokinetics (PKs) and pharmacodynamics (PDs) in human subjects. We performed an in vitro incubation study to assess trandolapril activation in human livers (5 G143E heterozygotes and 97 noncarriers) and conducted a single-dose (1 mg) PK and PD study of trandolapril in healthy volunteers (8 G143E heterozygotes and 11 noncarriers). The incubation study revealed that the mean trandolapril activation rate in G143E heterozygous livers was 42% of those not carrying the variant (p = 0.0015). The clinical study showed that, relative to noncarriers, G143E carriers exhibited 20% and 15% decreases, respectively, in the peak concentration (Cmax ) and area under the curve from 0 to 72 h (AUC0-72 h ) of the active metabolite trandolaprilat, although the differences were not statistically significant. Additionally, the average maximum reductions of systolic blood pressure and diastolic blood pressure in carriers were ~ 22% and 23% less than in noncarriers, respectively, but the differences did not reach a statistically significant level. In summary, the CES1 G143E variant markedly impaired trandolapril activation in the human liver under the in vitro incubation conditions; however, this variant had only a modest impact on the PK and PD of trandolapril in healthy human subjects.

Development and Application of a Life-Stage Physiologically Based Pharmacokinetic (PBPK) Model to the Assessment of Internal Dose of Pyrethroids in Humans

To address concerns around age-related sensitivity to pyrethroids, a life-stage physiologically based pharmacokinetic (PBPK) model, supported by in vitro to in vivo extrapolation (IVIVE) was developed. The model was used to predict age-dependent changes in target tissue exposure of 8 pyrethroids; deltamethrin (DLM), cis-permethrin (CPM), trans-permethrin, esfenvalerate, cyphenothrin, cyhalothrin, cyfluthrin, and bifenthrin. A single model structure was used based on previous work in the rat. Intrinsic clearance (CLint) of each individual cytochrome P450 or carboxylesterase (CES) enzyme that are active for a given pyrethroid were measured in vitro, then biologically scaled to obtain in vivo age-specific total hepatic CLint. These IVIVE results indicate that, except for bifenthrin, CES enzymes are largely responsible for human hepatic metabolism (>50% contribution). Given the high efficiency and rapid maturation of CESs, clearance of the pyrethroids is very efficient across ages, leading to a blood flow-limited metabolism. Together with age-specific physiological parameters, in particular liver blood flow, the efficient metabolic clearance of pyrethroids across ages results in comparable to or even lower internal exposure in the target tissue (brain) in children than that in adults in response to the same level of exposure to a given pyrethroid (Cmax ratio in brain between 1- and 25-year old = 0.69, 0.93, and 0.94 for DLM, bifenthrin, and CPM, respectively). Our study demonstrated that a life-stage PBPK modeling approach, coupled with IVIVE, provides a robust framework for evaluating age-related differences in pharmacokinetics and internal target tissue exposure in humans for the pyrethroid class of chemicals.

Effect of CES1 genetic variation on enalapril steady-state pharmacokinetics and pharmacodynamics in healthy subjects

AIMS

Enalapril is a prodrug and needs to be activated by carboxylesterase 1 (CES1). A previous in vitro study demonstrated the CES1 genetic variant, G143E (rs71647871), significantly impaired enalapril activation. Two previous clinical studies examined the impact of G143E on single-dose enalapril PK (10 mg); however, the results were inconclusive. A prospective, multi-dose, pharmacokinetics and pharmacodynamics (PK/PD) study was conducted to determine the impact of the CES1 G143E variant on enalapril steady-state PK and PD in healthy volunteers.

METHODS

Study participants were stratified to G143E non-carriers (n = 15) and G143E carriers (n = 6). All the carriers were G143E heterozygotes. Study subjects received enalapril 10 mg daily for seven consecutive days prior to a 72 hour PK/PD study. Plasma concentrations of enalapril and its active metabolite enalaprilat were quantified by an established liquid chromatography-tandem mass spectrometry (LC-MS/MS) method.

RESULTS

The CES1 G143E carriers had 30.9% lower enalaprilat C_max (P =  0.03) compared to the non-carriers (38.01 vs. 55.01 ng/mL). The carrier group had 27.5% lower AUC_0-∞ (P =  0.02) of plasma enalaprilat compared to the non-carriers (374.29 vs. 515.91 ng*h/mL). The carriers also had a 32.3% lower enalaprilat-to-enalapril AUC_0-∞ ratio (P =  0.003) relative to the non-carriers. The average maximum reduction of systolic blood pressure in the non-carrier group was approximately 12.4% at the end of the study compared to the baseline (P =  0.001). No statistically significant blood pressure reduction was observed in the G143E carriers.

CONCLUSIONS

The CES1 loss-of-function G143E variant significantly impaired enalapril activation and its systolic blood pressure-lowering effect in healthy volunteers.

Ontogeny of Hepatic Transporters and Drug-Metabolizing Enzymes in Humans and in Nonclinical Species

The liver represents a major eliminating and detoxifying organ, determining exposure to endogenous compounds, drugs, and other xenobiotics. Drug transporters (DTs) and drug-metabolizing enzymes (DMEs) are key determinants of disposition, efficacy, and toxicity of drugs. Changes in their mRNA and protein expression levels and associated functional activity between the perinatal period until adulthood impact drug disposition. However, high-resolution ontogeny profiles for hepatic DTs and DMEs in nonclinical species and humans are lacking. Meanwhile, increasing use of physiologically based pharmacokinetic (PBPK) models necessitates availability of underlying ontogeny profiles to reliably predict drug exposure in children. In addition, understanding of species similarities and differences in DT/DME ontogeny is crucial for selecting the most appropriate animal species when studying the impact of development on pharmacokinetics. Cross-species ontogeny mapping is also required for adequate translation of drug disposition data in developing nonclinical species to humans. This review presents a quantitative cross-species compilation of the ontogeny of DTs and DMEs relevant to hepatic drug disposition. A comprehensive literature search was conducted on PubMed Central: Tables and graphs (often after digitization) in original manuscripts were used to extract ontogeny data. Data from independent studies were standardized and normalized before being compiled in graphs and tables for further interpretation. New insights gained from these high-resolution ontogeny profiles will be indispensable to understand cross-species differences in maturation of hepatic DTs and DMEs. Integration of these ontogeny data into PBPK models will support improved predictions of pediatric hepatic drug disposition processes. SIGNIFICANCE STATEMENT: Hepatic drug transporters (DTs) and drug-metabolizing enzymes (DMEs) play pivotal roles in hepatic drug disposition. Developmental changes in expression levels and activities of these proteins drive age-dependent pharmacokinetics. This review compiles the currently available ontogeny profiles of DTs and DMEs expressed in livers of humans and nonclinical species, enabling robust interpretation of age-related changes in drug disposition and ultimately optimization of pediatric drug therapy.

Delayed-Release Dimethyl Fumarate Safety and Efficacy in Pediatric Patients With Relapsing-Remitting Multiple Sclerosis

Background: Pediatric multiple sclerosis (MS) is rare: only 1.5-5% of MS cases are diagnosed before 18 years of age, and data on disease-modifying therapies (DMTs) for pediatric MS are limited. The CONNECTED study assessed the long-term safety and efficacy of treatment with delayed-release dimethyl fumarate (DMF), an oral MS DMT, in pediatric patients with MS. Methods: CONNECTED is the 96-week extension to FOCUS, a 24-week phase 2 study of patients aged 13-17 years; participants received DMF 240 mg twice daily. Endpoints included (primary) incidence of adverse events (AEs), serious AEs, and DMF discontinuations due to an AE, and (secondary) T2 hyperintense lesion incidence by magnetic resonance imaging and annualized relapse rate (ARR). Results: Twenty participants [median (range) age, 17 (14-18) years; 65% female] who completed FOCUS enrolled into CONNECTED; 17 (85%) completed CONNECTED. Eighteen participants (90%) experienced AEs: the most frequent was flushing (25%). None experienced infections or fever related to low lymphocyte counts. Three participants experienced four serious AEs; none led to DMF discontinuation. Twelve of 17 participants (71%) had no new/newly enlarged T2 lesions from weeks 16-24, two (12%) had one, and one each (6%) had two, three, or five or more lesions [median (range), 0 (0-6)]. Over the full 120-week treatment period, ARR was 0.2, an 84.5% relative reduction (n = 20; 95% confidence interval: 66.8-92.8; p < 0.0001) vs. the year before DMF initiation. Conclusions: The long-term safety and efficacy observed in CONNECTED was consistent with adults, suggesting pediatric and adolescent patients with MS might benefit from DMF treatment.

Hydrolytic biotransformation of the bumetanide ester prodrug DIMAEB to bumetanide by esterases in neonatal human and rat serum and neonatal rat brain-A new treatment strategy for neonatal seizures?

OBJECTIVES

The loop diuretic bumetanide has been proposed previously as an adjunct treatment for neonatal seizures because bumetanide is thought to potentiate the action of γ-aminobutyric acid (GABA)ergic drugs such as phenobarbital by preventing abnormal intracellular accumulation of chloride and the subsequent "GABA shift." However, a clinical trial in neonates failed to demonstrate such a synergistic effect of bumetanide, most likely because this drug only poorly penetrates into the brain. This prompted us to develop lipophilic prodrugs of bumetanide, such as the N,N-dimethylaminoethyl ester of bumetanide (DIMAEB), which rapidly enter the brain where they are hydrolyzed by esterases to the parent compound, as demonstrated previously by us in adult rodents. However, it is not known whether esterase activity in neonates is sufficient to hydrolyze ester prodrugs such as DIMAEB.

METHODS

In the present study, we examined whether esterases in neonatal serum of healthy term infants are capable of hydrolyzing DIMAEB to bumetanide and whether this activity is different from the serum of adults. Furthermore, to extrapolate the findings to brain tissue, we performed experiments with brain tissue and serum of neonatal and adult rats.

RESULTS

Serum from 1- to 2-day-old infants was capable of hydrolyzing DIMAEB to bumetanide at a rate similar to that of serum from adult individuals. Similarly, serum and brain tissue of neonatal rats rapidly hydrolyzed DIMAEB to bumetanide.

SIGNIFICANCE

These data provide a prerequisite for further evaluating the potential of bumetanide prodrugs as add-on therapy to phenobarbital and other antiseizure drugs as a new strategy for improving pharmacotherapy of neonatal seizures.

ADHD medication and the inverted U-shaped curve: A pharmacological study in female mice performing the rodent Continuous Performance Test (rCPT)

BACKGROUND

The rodent Continuous Performance Test (rCPT) is an analogue of human CPTs where mice have to discriminate between target and non-target stimuli. The rCPT offers a readout of attentional performance and impulsive behaviour. This study aimed to determine if female C57BL/6 J mice could be trained in the rCPT since previously published rCPT studies have only used male mice and to study whether the effects of methylphenidate (MPH), atomoxetine (ATX), and dexamphetamine (AMPH) on attention and impulsivity depend on baseline (reference) levels of performance.

METHODS

48 female mice underwent rCPT training. Effects of MPH (1, 2, and 3 mg/kg), ATX (1, 3, and 5 mg/kg) and AMPH (0.3, 0.6, and 1 mg/kg) were assessed in a variable stimulus duration probe. Drugs were administered intraperitoneally and sequentially tested following a Latin-square design. Data were analysed using a repeated measurements mixed effect model and reference-dependent effects were studied.

RESULTS

ATX and AMPH improved performance as seen by increases in discriminability. These improvements were a result of a decreased false-alarm rate. AMPH showed a reference-dependent effect, improving the task performance of low-performing mice and decreasing the performance of high-performing mice. MPH also showed this reference-dependent effects, albeit to a lesser extent. ATX and AMPH decreased premature responses and increased response criterion, but no reference-dependent effects were observed for these parameters.

CONCLUSION

This study presents a novel method to analyse baseline-dependent effects. It shows that the rCPT can be successfully used in pharmacological studies in female mice and demonstrates that the effect of ADHD medication is in line with the inverted U-shape theory of performance-arousal relationship.

Carboxylesterase 1 and Precision Pharmacotherapy: Pharmacogenetics and Nongenetic Regulators

Carboxylesterase (CES) 1 is the most abundant drug-metabolizing enzyme in human livers, comprising approximately 1% of the entire liver proteome. CES1 is responsible for 80%-95% of total hydrolytic activity in the liver and plays a crucial role in the metabolism of a wide range of drugs (especially ester-prodrugs), pesticides, environmental pollutants, and endogenous compounds. Expression and activity of CES1 vary markedly among individuals, which is a major contributing factor to interindividual variability in the pharmacokinetics (PK) and pharmacodynamics (PD) of drugs metabolized by CES1. Both genetic and nongenetic factors contribute to CES1 variability. Here, we discuss genetic polymorphisms, including single-nucleotide polymorphisms (SNPs), and copy number variants and nongenetic contributors, such as developmental status, genders, and drug-drug interactions, that could influence CES1 functionality and the PK and PD of CES1 substrates. Currently, the loss-of-function SNP G143E (rs71647871) is the only clinically significant CES1 variant identified to date, and alcohol is the only potent CES1 inhibitor that could alter the therapeutic outcomes of CES1 substrate medications. However, G143E and alcohol can only explain a small portion of the interindividual variability in the CES1 function. A better understanding of the regulation of CES1 expression and activity and identification of biomarkers for CES1 function in vivo could lead to the development of a precision pharmacotherapy strategy to improve the efficacy and safety of many CES1 substrate drugs. SIGNIFICANCE STATEMENT: The clinical relevance of CES1 has been well demonstrated in various clinical trials. Genetic and nongenetic regulators can affect CES1 expression and activity, resulting in the alteration of the metabolism and clinical outcome of CES1 substrate drugs, such as methylphenidate and clopidogrel. Predicting the hepatic CES1 function can provide clinical guidance to optimize pharmacotherapy of numerous medications metabolized by CES1.

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.

The Impact of Carboxylesterases in Drug Metabolism and Pharmacokinetics

BACKGROUND

Carboxylesterases (CES) play a critical role in catalyzing hydrolysis of esters, amides, carbamates and thioesters, as well as bioconverting prodrugs and soft drugs. The unique tissue distribution of CES enzymes provides great opportunities to design prodrugs or soft drugs for tissue targeting. Marked species differences in CES tissue distribution and catalytic activity are particularly challenging in human translation.

METHODS

Review and summarization of CES fundamentals and applications in drug discovery and development.

RESULTS

Human CES1 is one of the most highly expressed drug metabolizing enzymes in the liver, while human intestine only expresses CES2. CES enzymes have moderate to high inter-individual variability and exhibit low to no expression in the fetus, but increase substantially during the first few months of life. The CES genes are highly polymorphic and some CES genetic variants show significant influence on metabolism and clinical outcome of certain drugs. Monkeys appear to be more predictive of human pharmacokinetics for CES substrates than other species. Low risk of clinical drug-drug interaction is anticipated for CES, although they should not be overlooked, particularly interaction with alcohols. CES enzymes are moderately inducible through a number of transcription factors and can be repressed by inflammatory cytokines.

CONCLUSION

Although significant advances have been made in our understanding of CESs, in vitro - in vivo extrapolation of clearance is still in its infancy and further exploration is needed. In vitro and in vivo tools are continuously being developed to characterize CES substrates and inhibitors.

Effects of methylphenidate on the aggressive behavior, serotonin and dopamine levels, and dopamine-related gene transcription in brain of male Nile tilapia (Oreochromis niloticus)

The occurrence of pharmaceuticals in the aquatic environment has increased considerably in the last decades, causing negative biochemical, physiological, and behavioral effects in aquatic organisms. In this study, we evaluated the effects of methylphenidate (MPH) on the aggressive behavior, dopamine-related gene transcript levels, monoamine levels, and carboxylesterase transcript levels and activity in the brain of male Nile tilapia (Oreochromis niloticus). Carboxylesterase activity was also measured in the liver and gills. Fish were exposed for 5 days to MPH at 20 and 100 ng L^-1. Fish exposed to 100 ng L^-1 of MPH showed increased aggressiveness and decreased dopamine (DA) and serotonin (5-HT) levels. No changes were observed in plasma testosterone levels and in the transcript levels of D1 and D2 dopamine receptors, dopamine transporter (DAT), and carboxylesterase 2 (CES2). Exposure to 100 ng L^-1 of MPH caused a decrease in the transcript levels of carboxylesterase 3 (CES3) and an increase in tyrosine hydroxylase (TH), while exposure to 20 ng L^-1 of MPH increased the transcript levels of D5 dopamine receptor. Carboxylesterase activity was unchanged in the brain and liver and increased in the gills of fish exposed to 20 ng L^-1. These results indicate that MPH at 100 ng L^-1 increases aggressiveness in Nile tilapia, possibly due to a decrease in 5-HT levels in the brain and alterations in dopamine levels and dopamine-related genes.

Functional Study of Carboxylesterase 1 Protein Isoforms

Carboxylesterase 1 (CES1) is a primary human hepatic hydrolase involved in hydrolytic biotransformation of numerous medications. Considerable interindividual variability in CES1 expression and activity has been consistently reported. Four isoforms of the CES1 protein are produced by alternative splicing (AS). In the current study, the activity and expression of each CES1 isoform are examined using transfected cell lines, and CES1 isoform composition and its impact on CES1 activity in human livers are determined. In transfected cells, isoforms 3 and 4 show mRNA and protein expressions comparable to isoforms 1 and 2, but have significantly impaired activity when hydrolyzing enalapril and clopidogrel. In individual human liver samples, isoforms 1 and 2 are the major forms, contributing 73-90% of the total CES1 protein expression. In addition, the protein expression ratios of isoforms 1 and 2 to isoforms 3 and 4 are positively associated with CES1 activity in the liver, suggesting that CES1 isoform composition is a factor contributing to the variability in hepatic CES1 function. Further investigations of the regulation of CES1 AS would improve the understanding of CES1 variability and help develop a strategy to optimize the pharmacotherapy of many CES1 substrate medications.

Breed Differences in Pig Liver Esterase (PLE) between Tongcheng (Chinese Local Breed) and Large White Pigs

Human carboxylesterases has been proven to be age and race-related and a sound basis of clinical medication. PLE involve in signal transduction and highly catalyze hydrolysis. Therefore, the expression level of PLE most probably exist age and breed difference and lead to significant differences of pharmacology and physiology. Four age groups of Tongcheng (TC) and Large White (LW) pigs were selected to explore PLE breed and age differences, and it was found that PLE mRNA was most abundant in liver in both breeds. In liver, PLE levels and hydrolytic activities increased with age, and PLE levels (except for 3 month) and the hydrolytic activities were higher in LW than in TC across all age groups. Abundance of PLE isoenzymes was obvious different between breeds and among age groups. The most abundant PLE isoenzyme in LW and TC pigs was PLE-A1 (all age groups) and PLE-B9 (three early age groups) or PLE-G3 (adult groups), respectively. 103 new PLE isoenzymes were found, and 55 high-frequency PLE isoenzymes were accordingly classified into seven categories (A-G). The results of this research provide a necessary basis not only for clinical medication of pigs but also for pig breeding purposes.

The impact of ABCB1 (rs1045642 and rs4148738) and CES1 (rs2244613) gene polymorphisms on dabigatran equilibrium peak concentration in patients after total knee arthroplasty

BACKGROUND

Non-vitamin K oral anticoagulants (NOACs) are commonly used for prophylaxis of venous thromboembolism (VTE) in orthopedic patients. Despite known safety and high potency of NOACs, potential interactions of NOACs with genetic polymorphisms are poorly understood. Dabigatran etexilate is one of the most commonly prescribed direct thrombin inhibitors for the prevention of VTE. The objectives of this study were to assess the effect of ABCB1 (rs1045642 and rs4148738) and CES1 (rs2244613) polymorphisms on dabigatran pharmacokinetics in patients after total knee arthroplasty.

PATIENTS AND METHODS

A total of 60 patients, aged 37-81 years, who underwent surgery for knee replacement have been included in the study. VTE prophylaxis was conducted via administration of dabigatran etexilate 220 mg once daily. Genotyping for carrier state of polymorphic variants such as rs1045642 and rs4148738 of the ABCB1 gene and rs2244613 of the CES1 gene was carried out using real-time polymerase chain reaction (PCR). We also measured the peak and trough concentrations of plasma dabigatran by using high-performance liquid chromatography (HPLC).

RESULTS

Our study revealed that TT genotype of rs1045642 polymorphism of the ABCB1 gene was associated with higher dabigatran equilibrium peak concentrations and the higher risk of bleeding than the presence of CC genotype (p<0.008). There was no statistically significant genotype-dependent difference in the trough concentrations between rs1045642 and rs4148738 of the ABCB1 gene and rs2244613 of the CES1 gene.

CONCLUSION

Our findings indicate that the polymorphisms of ABCB1 rs1045642 may have a prominent contribution to the safety of dabigatran in patients after knee surgery. Moreover, TT genotype may be associated with the higher risk of hemorrhagic complications in this population. There were no influence of polymorphism of ABCB1 rs4148738 and CES1 rs2244613 on dabigatran peak and through concentrations. Larger studies are needed to confirm our observations.

A physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) model of the histone deacetylase (HDAC) inhibitor vorinostat for pediatric and adult patients and its application for dose specification

PURPOSE

This study aimed at recommending pediatric dosages of the histone deacetylase (HDAC) inhibitor vorinostat and potentially more effective adult dosing regimens than the approved standard dosing regimen of 400 mg/day, using a comprehensive physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) modeling approach.

METHODS

A PBPK/PD model for vorinostat was developed for predictions in adults and children. It includes the maturation of relevant metabolizing enzymes. The PBPK model was expanded by (1) effect compartments to describe vorinostat concentration-time profiles in peripheral blood mononuclear cells (PBMCs), (2) an indirect response model to predict the HDAC inhibition, and (3) a thrombocyte model to predict the dose-limiting thrombocytopenia. Parameterization of drug and system-specific processes was based on published and unpublished in silico, in vivo, and in vitro data. The PBPK modeling software used was PK-Sim and MoBi.

RESULTS

The PBPK/PD model suggests dosages of 80 and 230 mg/m² for children of 0-1 and 1-17 years of age, respectively. In comparison with the approved standard treatment, in silico trials reveal 11 dosing regimens (9 oral, and 2 intravenous infusion rates) increasing the HDAC inhibition by an average of 31%, prolonging the HDAC inhibition by 181%, while only decreasing the circulating thrombocytes to a tolerable 53%. The most promising dosing regimen prolongs the HDAC inhibition by 509%.

CONCLUSIONS

Thoroughly developed PBPK models enable dosage recommendations in pediatric patients and integrated PBPK/PD models, considering PD biomarkers (e.g., HDAC activity and platelet count), are well suited to guide future efficacy trials by identifying dosing regimens potentially superior to standard dosing regimens.

A Comprehensive Functional Assessment of Carboxylesterase 1 Nonsynonymous Polymorphisms

Carboxylesterase 1 (CES1) is the predominant human hepatic hydrolase responsible for the metabolism of many clinically important medications. CES1 expression and activity vary markedly among individuals; and genetic variation is a major contributing factor to CES1 interindividual variability. In this study, we comprehensively examined the functions of CES1 nonsynonymous single nucleotide polymorphisms (nsSNPs) and haplotypes using transfected cell lines and individual human liver tissues. The 20 candidate variants include CES1 nsSNPs with a minor allele frequency >0.5% in a given population or located in close proximity to the CES1 active site. Five nsSNPs, including L40Ter (rs151291296), G142E (rs121912777), G147C (rs146456965), Y170D (rs148947808), and R171C (rs201065375), were loss-of-function variants for metabolizing the CES1 substrates clopidogrel, enalapril, and sacubitril. In addition, A158V (rs202121317), R199H (rs2307243), E220G (rs200707504), and T290M (rs202001817) decreased CES1 activity to a lesser extent in a substrate-dependent manner. Several nsSNPs, includingL40Ter (rs151291296), G147C (rs146456965), Y170D (rs148947808), and R171C (rs201065375), significantly reduced CES1 protein and/or mRNA expression levels in the transfected cells. Functions of the common nonsynonymous haplotypes D203E-A269S and S75N-D203E-A269S were evaluated using cells stably expressing the haplotypes and a large set of the human liver. Neither CES1 expression nor activity was affected by the two haplotypes. In summary, this study revealed several functional nsSNPs with impaired activity on the metabolism of CES1 substrate drugs. Clinical investigations are warranted to determine whether these nsSNPs can serve as biomarkers for the prediction of therapeutic outcomes of drugs metabolized by CES1.

Methylphenidate for Treating ADHD: A Naturalistic Clinical Study of Methylphenidate Blood Concentrations in Children and Adults With Optimized Dosage

Background

Methylphenidate (MPH), along with behavioral and psychosocial interventions, is the first-line medication to treat attention-deficit hyperactivity disorder (ADHD) in Sweden. The dose of MPH for good symptom control differs between patients. However, studies of MPH concentration measurement in ADHD treatment are limited.

Objective

To describe blood and oral fluid (OF) concentrations of MPH after administration of medication in patients with well-adjusted MPH treatment for ADHD, and to identify the most suitable matrix for accurate MPH concentration during treatment.

Methods

Patients were recruited from Child and Adolescent Psychiatry (CAP), General Psychiatry (GP), and the Department of Dependency (DD). Blood and OF samples were collected in the morning before MPH administration as well as 1 and 6 h after administration of the prescribed morning dose of MPH.

Results

Fifty-nine patients aged between 9 and 69 years, 76 % males. The daily dose of MPH varied from 18 to 180 mg, but the median daily dose per body weight was similar, approximately 1.0 mg/kg body weight. The median MPH concentration in blood 1 and 6 h after the morning dose was 5.4 and 9.3 ng/mL, respectively. Highly variable OF-to-blood ratios for MPH were found at all time points for all three groups.

Conclusions

Weight is a reliable clinical parameter for optimal dose titration. Otherwise, MPH blood concentration might be used for individual dose optimization and for monitoring of the prescribed dose. Relying only on the outcome in OF cannot be recommended for evaluation of accurate MPH concentrations for treatment monitoring.

The novel carboxylesterase 1 variant c.662A>G may decrease the bioactivation of oseltamivir in humans

Background

Human carboxylesterase 1 (CES1) is a serine esterase that hydrolyses various exogenous and endogenous compounds including oseltamivir, a prodrug used to treat influenza. A novel CES1 c.662A>G single nucleotide polymorphism (SNP) was predicted to decrease CES1 enzymatic activity in an in silico analysis. This study evaluated the effect of the c.662A>G SNP on the pharmacokinetics (PK) of oseltamivir in humans.

Methods

A single oral dose of oseltamivir at 75 mg was administered to 20 healthy subjects, 8 heterozygous c.662A>G carriers (c.662AG) and 12 non-carriers (c.662AA). The concentrations of oseltamivir and its active metabolite, oseltamivir carboxylate, were measured in plasma and urine using a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. The PK parameters were calculated using a noncompartmental method. The geometric mean ratios (GMR, c.662AG to c.662AA) of the PK parameters and their 90% confidence intervals (CI) were calculated.

Results

The systemic exposure to oseltamivir, as assessed by the AUC_0-48h of oseltamivir, was increased by 10% in c.662AG subjects, whereas the AUC_0-48h of oseltamivir carboxylate was 5% lower in c.662AG subjects. The GMR and 90% CI of the metabolic ratio (AUC_{0-48h, Oseltamivir carboxylate}/AUC_{0-48h, Oseltamivir}) was 0.87 (0.66–1.14). The amount of unchanged oseltamivir excreted in the urine was increased by 15% in subjects with the c.662AG genotype.

Conclusions

This result suggests that CES1 enzymatic activity may be decreased in these heterozygous allele carriers, although further studies are warranted to investigate the clinical implications of this genetic variation on CES1 substrate drugs.

Trial registration

ClinicalTtrials.gov NCT01902342

Methylphenidate effects in the young brain: friend or foe?

Attention deficit hyperactivity disorder (ADHD) is one of the most prevalent neuropsychiatry disorders in children and adolescents, and methylphenidate (MPH) is a first-line stimulant drug available worldwide for its treatment. Despite the proven therapeutic efficacy, concerns have been raised regarding the possible consequences of chronic MPH exposure during childhood and adolescence. Disturbances in the neurodevelopment at these crucial stages are major concerns given the unknown future life consequences. This review is focused on the long-term adverse effects of MPH to the brain biochemistry. Reports conducted with young and/or adolescent animals and studies with humans are reviewed in the context of long-term consequences after early life-exposure. MPH pharmacokinetics is also reviewed as there are differences among laboratory animals and humans that may be relevant to extrapolate the findings. Studies reveal that exposure to MPH in laboratory animals during young and/or adolescent ages can impact the brain, but the outcomes are dependent on MPH dose, treatment period, and animal's age. Importantly, the female sex is largely overlooked in both animal and human studies. Unfortunately, human reports that evaluate adults following adolescent or child exposure to MPH are very scarce. In general, human data indicates that MPH is generally safe, although it can promote several brain changes in early ages. Even so, there is a lack of long course patient evaluation to clearly establish whether MPH-induced changes are friendly or foe to the brain and more human studies are needed to assess the adult brain changes that arise from early MPH treatment.

The Promises of Quantitative Proteomics in Precision Medicine

Precision medicine approach has a potential to ensure optimum efficacy and safety of drugs at individual patient level. Physiologically based pharmacokinetic and pharmacodynamic (PBPK/PD) models could play a significant role in precision medicine by predicting interindividual variability in drug disposition and response. In order to develop robust PBPK/PD models, it is imperative that the critical physiological parameters affecting drug disposition and response and their variability are precisely characterized. Currently used PBPK/PD modeling software, for example, Simcyp and Gastroplus, encompass information such as organ volumes, blood flows to organs, body fat composition, glomerular filtration rate, etc. However, the information on the interindividual variability of the majority of the proteins associated with PK and PD, for example, drug metabolizing enzymes, transporters, and receptors, are not fully incorporated into these PBPK modeling platforms. Such information is significant because the population factors such as age, genotype, disease, and gender can affect abundance or activity of these proteins. To fill this critical knowledge gap, mass spectrometry-based quantitative proteomics has emerged as an important technique to characterize interindividual variability in the protein abundance of drug metabolizing enzymes, transporters, and receptors. Integration of these quantitative proteomics data into in silico PBPK/PD modeling tools will be crucial toward precision medicine.

Role of farnesoid X receptor in establishment of ontogeny of phase-I drug metabolizing enzyme genes in mouse liver

The expression of phase-I drug metabolizing enzymes in liver changes dramatically during postnatal liver maturation. Farnesoid X receptor (FXR) is critical for bile acid and lipid homeostasis in liver. However, the role of FXR in regulating ontogeny of phase-I drug metabolizing genes is not clear. Hence, we applied RNA-sequencing to quantify the developmental expression of phase-I genes in both Fxr-null and control (C57BL/6) mouse livers during development. Liver samples of male C57BL/6 and Fxr-null mice at 6 different ages from prenatal to adult were used. The Fxr-null showed an overall effect to diminish the “day-1 surge” of phase-I gene expression, including cytochrome P450s at neonatal ages. Among the 185 phase-I genes from 12 different families, 136 were expressed, and differential expression during development occurred in genes from all 12 phase-I families, including hydrolysis: carboxylesterase (Ces), paraoxonase (Pon), and epoxide hydrolase (Ephx); reduction: aldoketo reductase (Akr), quinone oxidoreductase (Nqo), and dihydropyrimidine dehydrogenase (Dpyd); and oxidation: alcohol dehydrogenase (Adh), aldehyde dehydrogenase (Aldh), flavin monooxygenases (Fmo), molybdenum hydroxylase (Aox and Xdh), cytochrome P450 (P450), and cytochrome P450 oxidoreductase (Por). The data also suggested new phase-I genes potentially targeted by FXR. These results revealed an important role of FXR in regulation of ontogeny of phase-I genes.

Association of Oseltamivir Activation with Gender and Carboxylesterase 1 Genetic Polymorphisms

Oseltamivir, an inactive anti-influenza virus prodrug, is activated (hydrolysed) in vivo by carboxylesterase 1 (CES1) to its active metabolite oseltamivir carboxylate. CES1 functions are significantly associated with certain CES1 genetic variants and some non-genetic factors. The purpose of this study was to investigate the effect of gender and several CES1 genetic polymorphisms on oseltamivir activation using a large set of individual human liver samples. CES1-mediated oseltamivir hydrolysis and CES1 genotypes, including the G143E (rs71647871), rs2244613, rs8192935, the -816A>C (rs3785161) and the CES1P1/CES1P1VAR, were determined in 104 individual human livers. The results showed that hepatic CES1 protein expression in females was 17.3% higher than that in males (p = 0.039), while oseltamivir activation rate in the livers from female donors was 27.8% higher than that from males (p = 0.076). As for CES1 genetic polymorphisms, neither CES1 protein expression nor CES1 activity on oseltamivir activation was significantly associated with the rs2244613, rs8192935, -816A>C or CES1P1/CES1P1VAR genotypes. However, oseltamivir hydrolysis in the livers with the genotype 143G/E was approximately 40% of that with the 143G/G genotype (0.7 ± 0.2 versus 1.8 ± 1.1 nmole/mg protein/min, p = 0.005). In summary, the results suggest that hepatic oseltamivir activation appears to be more efficient in females than that in males, and the activation can be impaired by functional CES1 variants, such as the G143E. However, clinical implication of CES1 gender differences and pharmacogenetics in oseltamivir pharmacotherapy warrants further investigations.

Evaluation of a New Molecular Entity as a Victim of Metabolic Drug-Drug Interactions-an Industry Perspective

Under the guidance of the International Consortium for Innovation and Quality in Pharmaceutical Development (IQ), scientists from 20 pharmaceutical companies formed a Victim Drug-Drug Interactions Working Group. This working group has conducted a review of the literature and the practices of each company on the approaches to clearance pathway identification (fCL), estimation of fractional contribution of metabolizing enzyme toward metabolism (fm), along with modeling and simulation-aided strategy in predicting the victim drug-drug interaction (DDI) liability due to modulation of drug metabolizing enzymes. Presented in this perspective are the recommendations from this working group on: 1) strategic and experimental approaches to identify fCL and fm, 2) whether those assessments may be quantitative for certain enzymes (e.g., cytochrome P450, P450, and limited uridine diphosphoglucuronosyltransferase, UGT enzymes) or qualitative (for most of other drug metabolism enzymes), and the impact due to the lack of quantitative information on the latter. Multiple decision trees are presented with stepwise approaches to identify specific enzymes that are involved in the metabolism of a given drug and to aid the prediction and risk assessment of drug as a victim in DDI. Modeling and simulation approaches are also discussed to better predict DDI risk in humans. Variability and parameter sensitivity analysis were emphasized when applying modeling and simulation to capture the differences within the population used and to characterize the parameters that have the most influence on the prediction outcome.

CES1P1 variant -816A>C is not associated with hepatic carboxylesterase 1 expression and activity or antihypertensive effect of trandolapril

PURPOSE

The majority of angiotensin-converting enzyme inhibitors (ACEIs) are synthesized as ester prodrugs that must be converted to their active forms in vivo in order to exert therapeutic effects. Hepatic carboxylesterase 1 (CES1) is the primary enzyme responsible for the bioactivation of ACEI prodrugs in humans. The genetic variant -816A>C (rs3785161) is a common variant located in the promoter region of the CES1P1 gene. Previous studies report conflicting results with regard to the association of this variant and therapeutic outcomes of CES1 substrate drugs. The purpose of this study was to determine the effect of the variant -816A>C on the activation of the ACEI prodrug trandolapril in human livers and the blood pressure (BP)-lowering effect of trandolapril in hypertensive patients.

METHODS

The -816A>C genotypes and CES1 expression and activity on trandolapril activation were determined in 100 individual human liver samples. Furthermore, the association of the -816A>C variant and the BP lowering effect of trandolapril was evaluated in hypertensive patients who participated in the International Verapamil SR Trandolapril Study (INVEST).

RESULTS

Our in vitro study demonstrated that hepatic CES1 expression and activity did not differ among different -816A>C genotypes. Moreover, we were unable to identify a clinical association between the BP lowering effects of trandolapril and -816A>C genotypes.

CONCLUSIONS

We conclude that the -816A>C variant is not associated with interindividual variability in CES1 expression and activity or therapeutic response to ACEI prodrugs.

Age-Dependent Human Hepatic Carboxylesterase 1 (CES1) and Carboxylesterase 2 (CES2) Postnatal Ontogeny

Human hepatic carboxylesterase 1 and 2 (CES1 and CES2) are important for the disposition of ester- and amide-bond-containing pharmaceuticals and environmental chemicals. CES1 and CES2 ontogeny has not been well characterized, causing difficulty in addressing concerns regarding juvenile sensitivity to adverse outcomes associated with exposure to certain substrates. To characterize postnatal human hepatic CES1 and CES2 expression, microsomal and cytosolic fractions were prepared using liver samples from subjects without liver disease (N = 165, aged 1 day to 18 years). Proteins were fractionated, detected, and quantitated by Western blotting. Median microsomal CES1 was lower among samples from subjects younger than 3 weeks (n = 36) compared with the rest of the population (n = 126; 6.27 vs. 17.5 pmol/mg microsomal protein, respectively; P < 0.001; Kruskal-Wallis test). Median cytosolic CES1 expression was lowest among samples from individuals between birth and 3 weeks of age (n = 36), markedly greater among those aged 3 weeks to 6 years (n = 90), and modestly greater still among those older than 6 years (n = 36; median values = 4.7, 15.8, and 16.6 pmol/mg cytosolic protein, respectively; P values < 0.001 and 0.05, respectively; Kruskal-Wallis test). Median microsomal CES2 expression increased across the same three age groups with median values of 1.8, 2.9, and 4.2 pmol/mg microsomal protein, respectively (P < 0.001, both). For cytosolic CES2, only the youngest age group differed from the two older groups (P < 0.001; median values = 1.29, 1.93, 2.0, respectively). These data suggest that infants younger than 3 weeks of age would exhibit significantly lower CES1- and CES2-dependent metabolic clearance compared with older individuals.

Sacubitril Is Selectively Activated by Carboxylesterase 1 (CES1) in the Liver and the Activation Is Affected by CES1 Genetic Variation

Sacubitril was recently approved by the Food and Drug Administration for use in combination with valsartan for the treatment of patients with heart failure with reduced ejection fraction. As a prodrug, sacubitril must be metabolized (hydrolyzed) to its active metabolite sacubitrilat (LBQ657) to exert its intended therapeutic effects. Thus, understanding the determinants of sacubitril activation will lead to the improvement of sacubitril pharmacotherapy. The objective of this study was to identify the enzyme(s) responsible for the activation of sacubitril, and determine the impact of genetic variation on sacubitril activation. First, an incubation study of sacubitril with human plasma and the S9 fractions of human liver, intestine, and kidney was conducted. Sacubitril was found to be activated by human liver S9 fractions only. Moreover, sacubitril activation was significantly inhibited by the carboxylesterase 1 (CES1) inhibitor bis-(p-nitrophenyl) phosphate in human liver S9. Further incubation studies with recombinant human CES1 and carboxylesterase 2 confirmed that sacubitril is a selective CES1 substrate. The in vitro study of cell lines transfected with wild-type CES1 and the CES1 variant G143E (rs71647871) demonstrated that G143E is a loss-of-function variant for sacubitril activation. Importantly, sacubitril activation was significantly impaired in human livers carrying the G143E variant. In conclusion, sacubitril is selectively activated by CES1 in human liver. The CES1 genetic variant G143E can significantly impair sacubitril activation. Therefore, CES1 genetic variants appear to be an important contributing factor to interindividual variability in sacubitril activation, and have the potential to serve as biomarkers to optimize sacubitril pharmacotherapy.

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).

Ontogenic expression of human carboxylesterase-2 and cytochrome P450 3A4 in liver and duodenum: postnatal surge and organ-dependent regulation

Human carboxylesterase-2 (CES2) and cytochrome P450 3A4 (CYP3A4) are two major drug metabolizing enzymes that play critical roles in hydrolytic and oxidative biotransformation, respectively. They share substrates but may have opposite effect on therapeutic potential such as the metabolism of the anticancer prodrug irinotecan. Both CES2 and CYP3A4 are expressed in the liver and the gastrointestinal tract. This study was conducted to determine whether CES2 and CYP3A4 are expressed under developmental regulation and whether the regulation occurs differentially between the liver and duodenum. A large number of tissues (112) were collected with majority of them from donors at 1-198 days of age. In addition, multi-sampling (liver, duodenum and jejunum) was performed in some donors. The expression was determined at mRNA and protein levels. In the liver, CES2 and CYP3A4 mRNA exhibited a postnatal surge (1 versus 2 months of age) by 2.7 and 29 fold, respectively. CYP3A4 but not CES2 mRNA in certain pediatric groups reached or even exceeded the adult level. The duodenal samples, on the other hand, showed a gene-specific expression pattern at mRNA level. CES2 mRNA increased with age but the opposite was true with CYP3A4 mRNA. The levels of CES2 and CYP3A4 protein, on the other hand, increased with age in both liver and duodenum. The multi-sampling study demonstrated significant correlation of CES2 expression between the duodenum and jejunum. However, neither duodenal nor jejunal expression correlated with hepatic expression of CES2. These findings establish that developmental regulation occurs in a gene and organ-dependent manner.

Distribution and quantification of irinotecan and its active metabolite SN-38 in colon cancer murine model systems using MALDI MSI

Tissue distribution and quantitative analysis of small molecules is a key to assess the mechanism of drug action and evaluate treatment efficacy. The prodrug irinotecan (CPT-11) is widely used for chemotherapeutic treatment of colorectal cancer. CPT-11 requires conversion into its active metabolite SN-38 to exert the desired pharmacological effect. MALDI-Fourier transform ion cyclotron resonance (FT-ICR) and MALDI-time-of-flight (TOF) mass spectrometry imaging (MSI) were performed for detection of CPT-11 and SN-38 in tissue sections from mice post CPT-11 injection. In-depth information was gained about the distribution and quantity of drug compounds in normal and tumor tissue. The prodrug was metabolized, as proven by the detection of SN-38 in liver, kidney and digestive tract. In tumors from genetic mouse models for colorectal cancer (Apc (1638N/wt) x pvillin-Kras (V12G) ), CPT-11 was detected but not the active metabolite. In order to correlate drug distribution relative to vascularization, MALDI data were superimposed with CD31 (PECAM-1) immunohistochemistry. This analysis indicated that intratumoral access of CPT-11 mainly occurred by extravasation from microvessels. The present study exploits the power of MALDI MSI in drug analysis, and presents a novel approach to monitor drug distribution in relation to vessel functionality in preclinical and clinical research.