PT  - JOURNAL ARTICLE
AU  - Chi-Chi Peng
AU  - Wei Shi
AU  - Justin D. Lutz
AU  - Kent L. Kunze
AU  - Jun O. Liu
AU  - Wendel L. Nelson
AU  - Nina Isoherranen
TI  - Stereospecific Metabolism of Itraconazole by CYP3A4: Dioxolane Ring Scission of Azole Antifungals
AID  - 10.1124/dmd.111.042739
DP  - 2012 Mar 01
TA  - Drug Metabolism and Disposition
PG  - 426--435
VI  - 40
IP  - 3
4099  - http://dmd.aspetjournals.org/content/40/3/426.short
4100  - http://dmd.aspetjournals.org/content/40/3/426.full
SO  - Drug Metab Dispos2012 Mar 01; 40
AB  - Itraconazole (ITZ) is a mixture of four cis-stereoisomers that inhibit CYP3A4 potently and coordinate CYP3A4 heme via the triazole nitrogen. However, (2R,4S,2′R)-ITZ and (2R,4S,2′S)-ITZ also undergo stereoselective sequential metabolism by CYP3A4 at a site distant from the triazole ring to 3′-OH-ITZ, keto-ITZ, and N-desalkyl-ITZ. This stereoselective metabolism demonstrates specific interactions of ITZ within the CYP3A4 active site. To further investigate this process, the binding and metabolism of the four trans-ITZ stereoisomers by CYP3A4 were characterized. All four trans-ITZ stereoisomers were tight binding inhibitors of CYP3A4-mediated midazolam hydroxylation (IC50 16–26 nM), and each gave a type II spectrum upon binding to CYP3A4. However, instead of formation of 3′-OH-ITZ, they were oxidized at the dioxolane ring, leading to ring scission and formation of two new metabolites of ITZ. These two metabolites were also formed from the four cis-ITZ stereoisomers, although not as efficiently. The catalytic rates of dioxolane ring scission were similar to the dissociation rates of ITZ stereoisomers from CYP3A4, suggesting that the heme iron is reduced while the triazole moiety coordinates to it and no dissociation of ITZ is necessary before catalysis. The triazole containing metabolite [1-(2,4-dichlorophenyl)-2-(1H-1,2,4-triazol-1-yl)ethanone] also inhibited CYP3A4 (IC50 >15 μM) and showed type II binding with CYP3A4. The dioxolane ring scission appears to be clinically relevant because this metabolite was detected in urine samples from subjects that had been administered the mixture of cis-ITZ isomers. These data suggest that the dioxolane ring scission is a metabolic pathway for drugs that contain this moiety.