A physiologically based pharmacokinetic modeling approach to predict disease-drug interactions: suppression of CYP3A by IL-6.

Elevated cytokine levels are known to downregulate expression and suppress activity of cytochrome P450 enzymes (CYPs). Cytokine-modulating therapeutic proteins (TPs) used in the treatment of inflammation or infection could reverse suppression, manifesting as TP-drug-drug interactions (TP-DDIs). A physiologically based pharmacokinetic model was used to quantitatively predict the impact of interleukin-6 (IL-6) on sensitive CYP3A4 substrates. Elevated simvastatin area under the plasma concentration-time curve (AUC) in virtual rheumatoid arthritis (RA) patients, following 100 pg/ml of IL-6, was comparable to observed clinical data (59 vs. 58%). In virtual bone marrow transplant (BMT) patients, 500 pg/ml of IL-6 resulted in an increase in cyclosporine AUC, also in good agreement with the observed data (45 vs. 39%). In a different group of BMT patients treated with cyclosporine, the magnitude of interaction with IL-6 was underpredicted by threefold. The complexity of TP-DDIs highlights underlying pathophysiological factors to be considered, but these simulations provide valuable first steps toward predicting TP-DDI risk.

Preclinical assessment of the absorption, distribution, metabolism and excretion of GDC-0449 (2-chloro-N-(4-chloro-3-(pyridin-2-yl)phenyl)-4-(methylsulfonyl)benzamide), an orally bioavailable systemic Hedgehog signalling pathway inhibitor.

GDC-0449 (2-chloro-N-(4-chloro-3-(pyridin-2-yl)phenyl)-4-(methylsulfonyl)benzamide) is a potent, selective Hedgehog (Hh) signalling pathway inhibitor being developed for the treatment of various cancers. The in vivo clearance of GDC-0449 was estimated to be 23.0, 4.65, 0.338, and 19.3 ml min(-1) kg(-1) in mouse, rat, dog and monkeys, respectively. The volume of distribution ranged from 0.490 in rats to 1.68 l kg(-1) in mice. Oral bioavailability ranged from 13% in monkeys to 53% in dogs. Predicted human clearance using allometry was 0.096-0.649 ml min(-1) kg(-1) and the predicted volume of distribution was 0.766 l kg(-1). Protein binding was extensive with an unbound fraction less than or equal to 6%, and the blood-to-plasma partition ratio ranged from 0.6 to 0.8 in all species tested. GDC-0449 was metabolically stable in mouse, rat, dog and human hepatocytes and had a more rapid turnover in monkey hepatocytes. Proposed metabolites from exploratory metabolite identification in vitro (rat, dog and human liver microsomes) and in vivo (dog and rat urine) include three primary oxidative metabolites (M1-M3) and three sequential glucuronides (M4-M6). Oxidative metabolites identified in microsomes M1 and M3 were formed primarily by P4503A4/5 (M1) and P4502C9 (M3). GDC-0449 was not a potent inhibitor of P4501A2, P4502B6, P4502D6, and P4503A4/5 with IC50 estimates greater than 20 microM. K(i)'s estimated for P4502C8, P4502C9 and P4502C19 and were 6.0, 5.4 and 24 microM, respectively. An evaluation with Simcyp suggests that GDC-0449 has a low potential of inhibiting P4502C8 and P4502C9. Furthermore, GDC-0449 (15 microM) was not a potent P-glycoprotein/ABCB1 inhibitor in MDR1-MDCK cells. Overall, GDC-0449 has an attractive preclinical profile and is currently in Phase II clinical trials.

Efficient assessment of the utility of immortalized Fa2N-4 cells for cytochrome P450 (CYP) induction studies using multiplex quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) and substrate cassette methodologies.

Induction of cytochrome P450 (CYP) 1A2, CYP2B6, and CYP3A4 by 22 prototypical inducers was evaluated in the Fa2N-4 immortalized human hepatic cell line. To facilitate this a duplex one-step quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) assay for CYP1A2 and CYP3A4 and a substrate cassette allowing simultaneous monitoring of CYP1A2, CYP2B6, CYP2C9, and CYP3A4 activity were developed. CYP1A2 messenger RNA (mRNA) and activity were induced by the prototypical aryl hydrocarbon receptor (AhR) ligand beta-naphthoflavone (E(max) = 217- and 11-fold, respectively, and EC(50) = 8 microM). CYP3A4 mRNA and activity were induced by the prototypical pregnane X receptor (PXR) ligands, rifampicin (E(max) = 36- and 6-fold, respectively, and EC(50) = 4 microM) and phenobarbital (E(max) = 12- and 4-fold, respectively, and EC(50) = 205 microM). No induction of CYP2B6 was detected with several prototypical constitutive androstane receptor (CAR) ligands. A large mRNA-activity E(max) ratio was observed for some time-dependent inhibitors of CYP3A4, whereas EC(50) determinations appeared to be independent of the endpoint. In conclusion, Fa2N-4 cells are a good surrogate for primary human hepatocytes for assessing AhR and PXR-mediated CYP1A2 and CYP3A4 induction, respectively, but not for CAR-mediated CYP2B6 induction. The sensitive and selective methodologies presented in this paper afford maximal data generation and enhanced throughput capability and are readily transferable to primary human hepatocytes or alternate cellular systems.

Pharmacokinetic consequences of time-dependent inhibition using the isolated perfused rat liver model.

Mathematical models exist to describe the pharmacokinetic changes caused by time-dependent inhibition (TDI) and these have been reported to predict accurately for several marketed drugs. However, their robustness using in-depth, carefully controlled pre-clinical studies has yet to be established. In the current study, the isolated perfused rat liver was employed to investigate the effects of TDI under carefully controlled conditions. A five-compartmental model was used to describe the observed data and bring context to in vitro TDI data (kinact and KI). Co-administration of midazolam with troleandomycin, mifepristone, erythromycin and the discovery compound, AZ-X, increased midazolam area under the curve (AUC) 3.2-, 2.5-, 1.6- and 1.0-fold, respectively, compared with AUC increases of 1.8-, 1.4-, 1.2- and 1.1-fold predicted by the model. These experimental findings, whilst modest in overall effect, support the use of this model in the rat and it is proposed that projections can be made for the likely clinical impact of novel time-dependent inhibitors in man based on predicted human pharmacokinetics and TDI potency determined in vitro.