PT  - JOURNAL ARTICLE
AU  - Collette D. Linder
AU  - Nicole A. Renaud
AU  - J. Matthew Hutzler
TI  - Is 1-Aminobenzotriazole an Appropriate in Vitro Tool as a Nonspecific Cytochrome P450 Inactivator?
AID  - 10.1124/dmd.108.024075
DP  - 2009 Jan 01
TA  - Drug Metabolism and Disposition
PG  - 10--13
VI  - 37
IP  - 1
4099  - http://dmd.aspetjournals.org/content/37/1/10.short
4100  - http://dmd.aspetjournals.org/content/37/1/10.full
SO  - Drug Metab Dispos2009 Jan 01; 37
AB  - 1-Aminobenzotriazole (1-ABT) is generally considered to be a nonselective mechanism-based inactivator of both human and non-human cytochrome P450 (P450) enzymes. Thus, 1-ABT is routinely used when conducting in vitro reaction phenotyping studies with new chemical entities in drug discovery to decipher P450 from non-P450-mediated metabolism. Experiments with pooled human liver microsomes (HLMs) demonstrated that carbon monoxide binding, although substantially reduced after a 30-min preincubation with 1-ABT, was still measurable. Thus, remaining activity of nine major human P450s (1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A4) in HLMs was determined using established selective probe substrates after 30-min preincubation with either 1-ABT (1 mM), a positive control time-dependent inhibitor, or a competitive inhibitor. Whereas P450 2A6 and 3A4 activity was essentially eliminated upon 30-min pretreatment with 1-ABT, the other human P450s were less affected, with at least 20% activity remaining after pretreatment. In contrast, most of the known P450 selective time-dependent inhibitors were more effective inactivators than 1-ABT at lower concentrations. A particularly interesting finding was that 1-ABT was quite ineffective at inactivating P450 2C9, with roughly 60% activity remaining after pretreatment, which suggests that 1-ABT is much less selective for certain human P450s. This collection of data clearly demonstrates that assuming 1-ABT is a nonselective P450 inhibitor in vitro is risky, and false conclusions regarding remaining metabolic activity being non-P450 mediated after 1-ABT pretreatment may be made. The American Society for Pharmacology and Experimental Therapeutics