Dmd057018 1008..1015

The glycogen synthase kinase-3 inhibitor LY2090314 specifically impaired CYP2B6 activity during in vitro evaluation of cytochrome P450 (P450) enzyme induction in human hepatocytes. CYP2B6 catalytic activity was significantly decreased following 3-day incubation with 0.1–10 mM LY2090314, on average by 64.3%6 5.0% at 10 mM. These levels of LY2090314 exposure were not cytotoxic to hepatocytes and did not reduce CYP1A2 and CYP3A activities. LY2090314 was not a time-dependent CYP2B6 inhibitor, did not otherwise inhibit enzyme activity at concentrations £10 mM, and was not metabolized by CYP2B6. Thus, mechanism-based inactivation or other direct interaction with the enzyme could not explain the observed reduction in CYP2B6 activity. Instead, LY2090314 significantly reduced CYP2B6 mRNA levels (Imax = 61.9% 6 1.4%; IC50 = 0.049 6 0.043 mM), which were significantly correlated with catalytic activity (r = 0.87, slope = 0.77; Imax = 57.0% 6 10.8%, IC50 = 0.057 6 0.027 mM). Direct inhibition of constitutive androstane receptor by LY2090314 is conceptually consistent with the observed CYP2B6 transcriptional suppression (Imax = 100.0% 6 10.8% and 57.1% 6 2.4%; IC50 = 2.5 6 1.2 and 2.1 6 0.4 mM for isoforms 1 and 3, respectively) and may be sufficiently extensive to overcome the weak but potent activation of pregnane X receptor by £10 mM LY2090314 (19.3% 6 2.2% of maximal rifampin response, apparent EC50 = 1.2 6 1.1 nM). The clinical relevance of these findings was evaluated through physiologically based pharmacokinetic model simulations. CYP2B6 suppression by LY2090314 is not expected clinically, with a projected <1% decrease in hepatic enzyme activity and <1% decrease in hydroxybupropion exposure following bupropion coadministration. However, simulations showed that observed CYP2B6 suppression could be clinically relevant for a drug with different pharmacokinetic properties from LY2090314.