Abstract
Nearly half of prescription medicines are metabolized by human cytochrome P450 (CYP) 3A. CYP3A4 and 3A5 are two major isoforms of human CYP3A and share most of the substrate spectrum. A very limited previous study distinguished the activity of CYP3A4 and CYP3A5, identifying the challenge in predicting CYP3A-mediated drug clearance and drug-drug interaction. In the present study, we introduced gomisin A (GA) with a dibenzocyclooctadiene skeleton as a novel selective probe of CYP3A4. The major metabolite of GA was fully characterized as 8-hydroxylated GA by LC-MS and NMR. CYP3A4 was assigned as the predominant isozyme involved in GA 8-hydroxylation by reaction phenotyping assays, chemical inhibition assays, and correlation studies. GA 8-hydroxylation in both recombinant human CYP3A4 and human liver microsomes followed classic Michaelis-Menten kinetics. The intrinsic clearance values indicated that CYP3A4 contributed 12.8-fold more than CYP3A5 to GA 8-hydroxylation. Molecular docking studies indicated different hydrogen bonds and π-π interactions between CYP3A4 and CYP3A5, which might result in the different catalytic activity for GA 8-hydroxylation. Furthermore, GA exhibited a stronger inhibitory activity towards CYP3A4 than CYP3A5, which further suggested a preferred selectivity of CYP3A4 for the transformation of GA. More importantly, GA has been successfully applied to selectively monitor the modulation of CYP3A4 activities by the inducer rifampin in hepG2 cells, which is consistent with the level change of CYP3A4 mRNA expression. In summary, our results suggested that GA could be used as a novel probe for the selective sensing of CYP3A4 in tissue and cell preparations.