Is 1-aminobenzotriazole an appropriate in vitro tool as a nonspecific cytochrome P450 inactivator?
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 rem
