PT  - JOURNAL ARTICLE
AU  - Bolles, Amanda K.
AU  - Fujiwara, Rina
AU  - Briggs, Erran D.
AU  - Nomeir, Amin A.
AU  - Furge, Laura Lowe
TI  - Mechanism-Based Inactivation of Human Cytochrome P450 3A4 by Two Piperazine-Containing Compounds
AID  - 10.1124/dmd.114.060459
DP  - 2014 Dec 01
TA  - Drug Metabolism and Disposition
PG  - 2087--2096
VI  - 42
IP  - 12
4099  - http://dmd.aspetjournals.org/content/42/12/2087.short
4100  - http://dmd.aspetjournals.org/content/42/12/2087.full
SO  - Drug Metab Dispos2014 Dec 01; 42
AB  - Human cytochrome P450 3A4 (CYP3A4) is responsible for the metabolism of more than half of pharmaceutic drugs, and inactivation of CYP3A4 can lead to adverse drug-drug interactions. The substituted imidazole compounds 5-fluoro-2-[4-[(2-phenyl-1H-imidazol-5-yl)methyl]-1-piperazinyl]pyrimidine (SCH 66712) and 1-[(2-ethyl-4-methyl-1H-imidazol-5-yl)methyl]-4-[4-(trifluoromethyl)-2-pyridinyl]piperazine (EMTPP) have been previously identified as mechanism-based inactivators (MBI) of CYP2D6. The present study shows that both SCH 66712 and EMTPP are also MBIs of CYP3A4. Inhibition of CYP3A4 by SCH 66712 and EMTPP was determined to be concentration, time, and NADPH dependent. In addition, inactivation of CYP3A4 by SCH 66712 was shown to be unaffected by the presence of electrophile scavengers. SCH 66712 displays type I binding to CYP3A4 with a spectral binding constant (Ks) of 42.9 ± 2.9 µM. The partition ratios for SCH 66712 and EMTPP were 11 and 94, respectively. Whole protein mass spectrum analysis revealed 1:1 binding stoichiometry of SCH 66712 and EMTPP to CYP3A4 and a mass increase consistent with adduction by the inactivators without addition of oxygen. Heme adduction was not apparent. Multiple mono-oxygenation products with each inactivator were observed; no other products were apparent. These are the first MBIs to be shown to be potent inactivators of both CYP2D6 and CYP3A4.