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Carboxylesterase (CE) inhibition assay

Understand if your compound is an inhibitor of carboxylesterases.

Carboxylesterase (CE) inhibition is a non-CYP mediated metabolism assay within our portfolio of in vitro ADME screening services. Cyprotex deliver consistent, high quality data with the flexibility to adapt protocols based on specific customer requirements.

Determining potential inhibition of carboxylesterase enzymes

  • Human carboxylesterases (CE) are Phase I drug metabolizing enzymes of the serine hydrolase superfamily. They hydrolyze a variety of ester containing drugs and prodrugs.
  • hCE1 and hCE2 are the most extensively studied of the human CEs. They differ in their substrate specificity and tissue distribution. hCE1 is expressed in many organs especially in the liver, with low expression in the gastrointestinal tract. CE2 protein is also expressed in many extrahepatic tissues, especially in the gastrointestinal tract and at lower levels in the liver.
  • Carboxylesterase inhibitors may play a role in improved efficacy of compounds inactivated by this class of enzymes and/or reduce the toxicity of agents that are activated by these enzymes.
  • Cyprotex’s carboxylesterase inhibition assay identifies if your compound is an inhibitor of the carboxylesterase (CE) isoforms, hCE1 or hCE2.
CE inhibitors potentially have dual roles in modulating drug action, by both reducing induced toxicity and/or increasing molecule half-life.

1Hatfield M.J. and Potter P.M. (2011) Expert Opin Ther Patents 21(8); 1159-1171


Carboxylesterase inhibition assay protocol

Test System hCE1-b, hCE1-c, hCE2 expressed enzymes
Substrates Trandolapril (hCE1)
Irinotecan (hCE2)
Metabolites Trandolaprilat (hCE1)
7-Ethyl-10-hydroxycamptothecin (hCE2)
Test Article Concentrations 0, 0.4, 1, 4, 10, 40 and 100 µM (different concentrations available)
Positive Control Inhibitors Benzil (hCE1)
Loperamide (hCE2)
Test Article Requirements 100 µL of a 40 mM DMSO solution (or equivalent amount in solid)
Analysis Method LC-MS/MS
Data Delivery IC50
Standard error of IC50
% Control at each concentration


Data from the carboxylesterase (CE) inhibition assay

carboxylesterase inhibition
Figure 1
Inhibition of trandolapril (hCE1 substrate) and irinotecan (hCE2 substrate) metabolism in recombinant hCE isoforms by rivastigmine.

The experimental design in Figure 1 can be used to identify specificity of hCE inhibitors. For example, it can be shown that rivastigmine demonstrates greater potency (>500 times) for hCE2 than hCE1 isoform.


1Hatfield M.J. and Potter P.M. (2011), Expert Opin Ther Patents 21(8); 1159-1171

Learn More

Learn more about drug metabolism in chapter 3 of our popular Everything you need to know about ADME guide. 

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