Comparison of substrate specificity among human arylacetamide deacetylase and carboxylesterases

Human arylacetamide deacetylase (AADAC) is an esterase responsible for the hydrolysis of some drugs, including flutamide, indiplon, phenacetin, and rifamycins. AADAC is highly expressed in the human liver, where carboxylesterase (CES) enzymes, namely, CES1 and CES2, are also expressed. It is generally recognized that CES1 prefers compounds with a large acyl moiety and a small alcohol or amine moiety as substrates, whereas CES2 prefers compounds with a small acyl moiety and a large alcohol or amine moiety. In a comparison of the chemical structures of known AADAC substrates, AADAC most likely prefers compounds with the same characteristics as does CES2. However, the substrate specificity of human AADAC has not been fully clarified. To expand the knowledge of substrates of human AADAC, we measured its hydrolase activities toward 13 compounds, including known human CES1 and CES2 substrates, using recombinant enzymes expressed in Sf21 cells. Recombinant AADAC catalyzed the hydrolysis of fluorescein diacetate, N-monoacetyldapsone, and propanil, which possess notably small acyl moieties, and these substrates were also hydrolyzed by CES2. However, AADAC could not hydrolyze another CES2 substrate, procaine, which possesses a moderately small acyl moiety. In addition, AADAC did not hydrolyze several known CES1 substrates, including clopidogrel and oseltamivir, which have large acyl moieties and small alcohol moieties. Collectively, these results suggest that AADAC prefers compounds with smaller acyl moieties than does CES2. The role of AADAC in the hydrolysis of drugs has been clarified. For this reason, AADAC should receive attention in ADMET studies during drug development.