Inhibitor Report for: Vinblastine

Human arylacetamide deacetylase (AADAC) plays a role in the detoxification or activation of drugs and is sometimes involved in the incidence of toxicity by catalyzing hydrolysis reactions. AADAC prefers compounds with relatively small acyl groups, such as acetyl groups. Eslicarbazepine acetate, an antiepileptic drug, is a prodrug rapidly hydrolyzed to eslicarbazepine. We sought to clarify whether AADAC might be responsible for the hydrolysis of eslicarbazepine acetate. Eslicarbazepine acetate was efficiently hydrolyzed by human intestinal and liver microsomes and recombinant human AADAC. The hydrolase activities in human intestinal and liver microsomes were inhibited by epigallocatechin gallate, a specific inhibitor of AADAC, by 82% and 88% of the control, respectively. The hydrolase activities in liver microsomes from 25 human livers were significantly correlated (r = 0.87, P < 0.001) with AADAC protein levels, suggesting that the enzyme AADAC is responsible for the hydrolysis of eslicarbazepine acetate. The effects of genetic polymorphisms of AADAC on eslicarbazepine acetate hydrolysis were examined by using the constructed recombinant AADAC variants with T74A, V172I, R248S, V281I, N366K, or X400Q. AADAC variants with R248S or X400Q showed lower activity than wild type (5% or 21%, respectively), whereas those with V172I showed higher activity than wild type (174%). Similar tendencies were observed in the other 4 substrates of AADAC; that is, p-nitrophenyl acetate, ketoconazole, phenacetin, and rifampicin. Collectively, we found that eslicarbazepine acetate is specifically and efficiently hydrolyzed by human AADAC, and several AADAC polymorphic alleles would be a factor affecting the enzyme activity and drug response. Significance Statement This is the first study to clarify that AADAC is responsible for the activation of eslicarbazepine acetate, an antiepileptic prodrug, to eslicarbazepine, an active form, in the human liver and intestines. In addition, we found that several AADAC polymorphic alleles would be a factor affecting the enzyme activity and drug response.

Esterases catalyze the hydrolysis of therapeutic drugs containing esters or amides in their structures. Human carboxylesterase (CES) and arylacetamide deacetylase (AADAC) are the major enzymes that catalyze the hydrolysis of drugs in the liver. Characterization of the enzyme(s) responsible for drug metabolism is required in drug development and to realize optimal drug therapy. Because multiple enzymes may show a metabolic potency for a given compound, inhibition studies using chemical inhibitors are useful tools to determine the contribution of each enzyme in human tissue preparations. The purpose of this study was to find specific inhibitors for human CES1, CES2, and AADAC. We screened 542 chemicals for the inhibition potency toward hydrolase activities of p-nitrophenyl acetate by recombinant CES1, CES2, and AADAC. We found that digitonin and telmisartan specifically inhibited CES1 and CES2 enzyme activity, respectively. Vinblastine potently inhibited both AADAC and CES2, but no specific inhibitor of AADAC was found. The inhibitory potency and specificity of these compounds were also evaluated by monitoring the effects on hydrolase activity of probe compounds of each enzyme (CES1: lidocaine, CES2: CPT-11, AADAC: phenacetin) in human liver microsomes. Telmisartan and vinblastine strongly inhibited the hydrolysis of CPT-11 and/or phenacetin, but digitonin did not strongly inhibit the hydrolysis of lidocaine, indicating that the inhibitory potency of digitonin was different between recombinant CES1 and liver microsomes. Although we could not find a specific inhibitor of AADAC, the combined use of telmisartan and vinblastine could predict the responsibility of human AADAC to drug hydrolysis.