title: In vitro and in silico identification and characterization of thiabendazole as a mechanism-based inhibitor of CYP1A2 and simulation of possible pharmacokinetic drug-drug interactions.
abstract: Thiabendazole (TBZ) and its major metabolite 5-hydroxythiabendazole (5OH-TBZ) were screened for potential time-dependent inhibition (TDI) against CYP1A2. Screen assays were carried out in the absence and presence of NADPH. TDI was observed with both compounds, with k(inact) and K(I) values of 0.08 and 0.02 min(-1) and 1.4 and 63.3 microM for TBZ and 5OH-TBZ, respectively. Enzyme inactivation was time-, concentration-, and NADPH-dependent. Inactivation by TBZ was irreversible by dialysis and oxidation by potassium ferricyanide, and there was no protection by glutathione. 5OH-TBZ was a weak TDI of CYP1A2, and enzyme activity was recovered by dialysis. IC(50) determination of TBZ and 5OH-TBZ showed both compounds to be potent inhibitors, with IC(50) values of 0.83 and 13.05 microM, respectively. IC(50) shift studies also demonstrated that TBZ was a TDI of CYP1A2. In silico methods identified the thiazole group as a TDI fragment and predicted it as the site of metabolism. The observation pointed to epoxidation of the thiazole and the benzyl rings of TBZ as possible routes of metabolism and mechanisms of TDI. Drug-drug interaction (DDI) simulation studies using SimCyp showed good predictions for competitive inhibition. However, predictions for mechanism-based inhibition (MBI)-based DDI were not in agreement with clinical observations. There was no TBZ accumulation upon chronic administration of the drug. The in vitro MBI findings might therefore not be capturing the in vivo situation in which the proposed bioactivation route is minor. This might be the case for TBZ in which, in vivo, UDP glucuronosyltransferases and sulfanotransferase metabolize and eliminate the 5OH-TBZ.
authors.affiliation: Department of Drug Metabolism and Pharmacokinetics/PD and Toxicology, African Institute of Biomedical Science and Technology, Harare, Zimbabwe.
authors.forename: Roslyn S
authors.initials: RS
authors.lastname: Thelingwani
authors.forename: Simbarashe P
authors.initials: SP
authors.lastname: Zvada
authors.forename: Hugues
authors.initials: H
authors.lastname: Dolgos
authors.forename: Anna-Lena B
authors.initials: AL
authors.lastname: Ungell
authors.forename: Collen M
authors.initials: CM
authors.lastname: Masimirembwa
mesh_terms: D020134:Catalytic Domain; D019388:Cytochrome P-450 CYP1A2 / Q000737:chemistry / Q000378:metabolism; D065609:Cytochrome P-450 CYP1A2 Inhibitors; D004353:Drug Evaluation, Preclinical; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D008862:Microsomes, Liver / Q000187:drug effects* / Q000201:enzymology; D015394:Molecular Structure; D010084:Oxidation-Reduction; D013827:Thiabendazole / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D013844:Thiazoles; D013997:Time Factors
chemical_list: D065609:Cytochrome P-450 CYP1A2 Inhibitors; D004791:Enzyme Inhibitors; D013844:Thiazoles; C035151:5-hydroxythiabendazole; D019388:Cytochrome P-450 CYP1A2; D013827:Thiabendazole