Ensemble Docking Approach to Mitigate Pregnane X Receptor-Mediated CYP3A4 Induction Risk.

Three structurally closely related dopamine D1 receptor positive allosteric modulators (D1 PAMs) based on a tetrahydroisoquinoline (THIQ) scaffold were profiled for their CYP3A4 induction potentials. It was found that the length of the linker at the C5 position greatly affected the potentials of these D1 PAMs as CYP3A4 inducers, and the level of induction correlated well with the activation of the pregnane X receptor (PXR). Based on the published PXR X-ray crystal structures, we built a binding model specifically for these THIQ-scaffold-based D1 PAMs in the PXR ligand-binding pocket via an ensemble docking approach and found the model could explain the observed CYP induction disparity. Combined with our previously reported D1 receptor homology model, which identified the C5 position as pointing toward the solvent-exposed space, our PXR-binding model coincidentally suggested that structural modifications at the C5 position could productively modulate the CYP induction potential while maintaining the D1 PAM potency of these THIQ-based PAMs.

Current Practices, Gap Analysis, and Proposed Workflows for PBPK Modeling of Cytochrome P450 Induction: An Industry Perspective.

The International Consortium for Innovation and Quality (IQ) Physiologically Based Pharmacokinetic (PBPK) Modeling Induction Working Group (IWG) conducted a survey across participating companies around general strategies for PBPK modeling of induction, including experience with its utility to address various questions, regulatory interactions, and regulatory acceptance. The results highlight areas where PBPK modeling is used with high confidence and identifies opportunities where confidence is lower and further evaluation is needed. To enhance the survey results, the PBPK-IWG also collected case studies and analyzed recent literature examples where PBPK models were applied to predict CYP3A induction-mediated drug-drug interactions. PBPK modeling of induction has evolved and progressed significantly, proving to have great potential to accelerate drug discovery and development. With the aim of enabling optimal use for new molecular entities that are either substrates and/or inducers of CYP3A, the PBPK-IWG proposes initial workflows for PBPK application, discusses future trends, and identifies gaps that need to be addressed.

Physiologically based pharmacokinetic modeling of tadalafil to inform pediatric dose selection in children with pulmonary arterial hypertension.

Tadalafil, a phosphodiesterase 5 inhibitor, is being investigated as a treatment for pulmonary arterial hypertension (PAH) in children aged 6 months to less than 18 years. Tadalafil pharmacokinetic (PK) data in children less than 2 years old are unavailable, therefore a physiologically based pharmacokinetic (PBPK) model was developed to enable estimation of tadalafil doses in children less than 2 years old. The model was verified in adults and extended for use in children by modifying CYP3A-mediated intrinsic clearance to include CYP3A7. To account for co-dosing of the commonly prescribed moderate CYP3A4 inducer bosentan, predicted exposures were increased by a factor of 1.54 based on changes in exposure in adults with PAH. This factor was predictable using a bosentan PBPK model. The tadalafil model was verified in children aged greater than or equal to 2 years by comparing predicted and observed exposures. Tadalafil doses for children less than 2 years old were calculated as target area under the concentration curve from zero to 24 h (AUC0-24 )/predicted AUC0-24 , with target AUC0-24 of 10,000 ng*h/ml based on adult 40 mg single dose exposures determined in patients without bosentan background treatment. These doses were 2 mg, 3 mg, 4 mg, and 6 mg, respectively, for children aged birth to less than 1 month, 1 month to less than 6 months, 6 months to less than 1 year, and 1 to less than 2 years. Due to uncertainties in CYP maturation, a nonmechanistic steady-state volume scalar, and lack of PK data in children less than 2 years old, accumulation of tadalafil to steady-state in children less than 2 years was not verifiable. Safety of proposed doses is supported by postmarketing research and investigator-led trials.

Abemaciclib Does Not Have a Clinically Meaningful Effect on Pharmacokinetics of CYP1A2, CYP2C9, CYP2D6, and CYP3A4 Substrates in Patients with Cancer.

Abemaciclib is an orally administered, potent inhibitor of cyclin-dependent kinases 4 and 6 and is metabolized extensively by CYP3A4. The effects of abemaciclib on several CYPs were qualified in vitro and subsequently evaluated in a clinical study. In vitro, human hepatocytes were treated with vehicle, abemaciclib, or abemaciclib metabolites [N-desethylabemaciclib (M2) or hydroxyabemaciclib (M20)]. mRNA levels for eight CYPs were measured using reverse-transcription quantitative polymerase chain reaction, and, additionally, catalytic activities for three CYPs were determined. In the clinical study, adult patients with cancer received a drug cocktail containing CYP substrates [midazolam (3A), warfarin (2C9), dextromethorphan (2D6), and caffeine (1A2)] either alone or in combination with abemaciclib. Plasma pharmacokinetics (PK) samples were analyzed for all substrates, caffeine metabolite paraxanthine, and abemaciclib; polymorphisms of CYP2C9, CYP2D6, CYP3A4, and CYP3A5 were evaluated. In vitro, downregulation of CYP mRNA, including 1A2, 2B6, 2C8, 2C9, 2D6, and 3A, by abemaciclib and/or M2 and M20 was observed at clinically relevant concentrations. In humans, abemaciclib did not affect the PK of CYP2D6 or CYP2C9 substrates. Minor statistically significant but clinically irrelevant changes were observed for midazolam [area under the concentration versus time curve from zero to infinity (AUC0-inf) (13% lower), Cmax (15% lower)], caffeine [AUC0-inf (56% higher)], and paraxanthine: caffeine [area under the concentration versus time curve from 0 to 24 hours ratio (was approximately 30% lower)]. However, given the magnitude of the effect, these changes are not considered clinically relevant. In conclusion, the downregulation of CYP mRNA mediated by abemaciclib in vitro did not translate into clinically meaningful drug-drug interactions in patients with cancer. SIGNIFICANCE STATEMENT: Despite observations that abemaciclib alters the mRNA of various CYP isoforms in vitro, a clinical study using a drug cocktail approach found no clinically meaningful drug-drug interactions between abemaciclib and a range of CYP substrates [midazolam (CYP3A4), S-warfarin (CYP2C9), dextromethorphan (CYP2D6), and caffeine (CYP1A2)]. This lack of translation suggests greater understanding of mechanisms of CYP downregulation is needed to accurately predict clinical drug-drug interaction risk from in vitro data.

Physiologically-Based Pharmacokinetic Modeling of Atorvastatin Incorporating Delayed Gastric Emptying and Acid-to-Lactone Conversion.

The drug-drug interaction profile of atorvastatin confirms that disposition is determined by cytochrome P450 (CYP) 3A4 and organic anion transporting polypeptides (OATPs). Drugs that affect gastric emptying, including dulaglutide, also affect atorvastatin pharmacokinetics (PK). Atorvastatin is a carboxylic acid that exists in equilibrium with a lactone form in vivo. The purpose of this work was to assess gastric acid-mediated lactone equilibration of atorvastatin and incorporate this into a physiologically-based PK (PBPK) model to describe atorvastatin acid, lactone, and their major metabolites. In vitro acid-to-lactone conversion was assessed in simulated gastric fluid and included in the model. The PBPK model was verified with in vivo data including CYP3A4 and OATP inhibition studies. Altering the gastric acid-lactone equilibrium reproduced the change in atorvastatin PK observed with dulaglutide. The model emphasizes the need to include gastric acid-lactone conversion and all major atorvastatin-related species for the prediction of atorvastatin PK.

Disposition and metabolism of [14C]-galunisertib, a TGF-ßRI kinase/ALK5 inhibitor, following oral administration in healthy subjects and mechanistic prediction of the effect of itraconazole on galunisertib pharmacokinetics.

1. The disposition and metabolism of galunisertib (LY2157299 monohydrate, a TGF-ßRI Kinase/ALK5 Inhibitor) was characterized following a single oral dose of 150 mg of [14C]-galunisertib (100 µCi) to six healthy human subjects. 2. The galunisertib plasma half-life was 8.6 h, while the 14C half-life was 10.0 h. Galunisertib was abundant in circulation (40.3% of the 14C AUC024 h), with 7 additional metabolites detected in plasma. Two metabolites LSN3199597 (M5, mono-oxidation), and M4 (glucuronide of M3) were the most abundant circulating metabolites (10.7 and 9.0% of the 14C AUC024 h respectively). The pharmacological activity of LSN3199597 was tested and found to be significantly less potent than galunisertib. 3. The dose was recovered in feces (64.5%) and in urine (36.8%). Galunisertib was cleared primarily by metabolism, based on low recovery of parent in excreta (13.0% of dose). Due to the slow in vitro metabolism of galunisertib in suspended hepatocytes, a long term hepatocyte system was used to model the human excretion profile. 4. Expressed cytochromes P450 and hepatocytes indicated clearance was primarily CYP3A4-mediated. Mechanistic static modeling that incorporated small non-CYP-mediated metabolic clearance and renal clearance components predicted an AUC ratio of 4.7 for the effect of itraconazole, a strong CYP3A4 inhibitor, on galunisertib.

Evacetrapib: in vitro and clinical disposition, metabolism, excretion, and assessment of drug interaction potential with strong CYP3A and CYP2C8 inhibitors.

Evacetrapib is an investigational cholesteryl ester transfer protein inhibitor (CETPi) for reduction of risk of major adverse cardiovascular events in patients with high-risk vascular disease. Understanding evacetrapib disposition, metabolism, and the potential for drug-drug interactions (DDI) may help guide prescribing recommendations. In vitro, evacetrapib metabolism was investigated with a panel of human recombinant cytochromes P450 (CYP). The disposition, metabolism, and excretion of evacetrapib following a single 100-mg oral dose of (14)C-evacetrapib were determined in healthy subjects, and the pharmacokinetics of evacetrapib were evaluated in the presence of strong CYP3A or CYP2C8 inhibitors. In vitro, CYP3A was responsible for about 90% of evacetrapib's CYP-associated clearance, while CYP2C8 accounted for about 10%. In the clinical disposition study, only evacetrapib and two minor metabolites circulated in plasma. Evacetrapib metabolism was extensive. A mean of 93.1% and 2.30% of the dose was excreted in feces and urine, respectively. In clinical DDI studies, the ratios of geometric least squares means for evacetrapib with/without the CYP3A inhibitor ketoconazole were 2.37 for area under the curve (AUC)(0-∞) and 1.94 for C max. There was no significant difference in evacetrapib AUC(0-τ) or C max with/without the CYP2C8 inhibitor gemfibrozil, with ratios of 0.996 and 1.02, respectively. Although in vitro results indicated that both CYP3A and CYP2C8 metabolized evacetrapib, clinical studies confirmed that evacetrapib is primarily metabolized by CYP3A. However, given the modest increase in evacetrapib exposure and robust clinical safety profile to date, there is a low likelihood of clinically relevant DDI with concomitant use of strong CYP3A or CYP2C8 inhibitors.

CYP-mediated drug-drug interactions with evacetrapib, an investigational CETP inhibitor: in vitro prediction and clinical outcome.

AIMS: Evacetrapib is a cholesteryl ester transfer protein (CETP) inhibitor under development for reducing cardiovascular events in patients with high risk vascular disease. CETP inhibitors are likely to be utilized as 'add-on' therapy to statins in patients receiving concomitant medications, so the potential for evacetrapib to cause clinically important drug-drug interactions (DDIs) with cytochromes P450 (CYP) was evaluated. METHODS: The DDI potential of evacetrapib was investigated in vitro, followed by predictions to determine clinical relevance. Potential DDIs with possible clinical implications were then investigated in the clinic. RESULTS: In vitro, evacetrapib inhibited all of the major CYPs, with inhibition constants (K(i)) ranging from 0.57 µM (CYP2C9) to 7.6 µM (CYP2C19). Evacetrapib was a time-dependent inhibitor and inducer of CYP3A. The effects of evacetrapib on CYP3A and CYP2C9 were assessed in a phase 1 study using midazolam and tolbutamide as probe substrates, respectively. After 14 days of daily dosing with evacetrapib (100 or 300 mg), midazolam exposures (AUC) changed by factors (95% CI) of 1.19 (1.06, 1.33) and 1.44 (1.28, 1.62), respectively. Tolbutamide exposures (AUC) changed by factors of 0.85 (0.77, 0.94) and 1.06 (0.95, 1.18), respectively. In a phase 2 study, evacetrapib 100 mg had minimal impact on AUC of co-administered simvastatin vs. simvastatin alone with a ratio of 1.25 (1.03, 1.53) at steady-state, with no differences in reported hepatic or muscular adverse events. CONCLUSIONS: Taken together, the extent of CYP-mediated DDI with the potential clinical dose of evacetrapib is weak and clinically important DDIs are not expected to occur in patients taking concomitant medications.

Investigational small-molecule drug selectively suppresses constitutive CYP2B6 activity at the gene transcription level: physiologically based pharmacokinetic model assessment of clinical drug interaction risk.

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 µM LY2090314, on average by 64.3% ± 5.0% at 10 µM. 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 µM, 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% ± 1.4%; IC50 = 0.049 ± 0.043 µM), which were significantly correlated with catalytic activity (r(2) = 0.87, slope = 0.77; Imax = 57.0% ± 10.8%, IC50 = 0.057 ± 0.027 µM). Direct inhibition of constitutive androstane receptor by LY2090314 is conceptually consistent with the observed CYP2B6 transcriptional suppression (Imax = 100.0% ± 10.8% and 57.1% ± 2.4%; IC50 = 2.5 ± 1.2 and 2.1 ± 0.4 µM for isoforms 1 and 3, respectively) and may be sufficiently extensive to overcome the weak but potent activation of pregnane X receptor by ≤10 µM LY2090314 (19.3% ± 2.2% of maximal rifampin response, apparent EC50 = 1.2 ± 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.

Disposition and metabolism of LY2603618, a Chk-1 inhibitor following intravenous administration in patients with advanced and/or metastatic solid tumors.

The disposition and metabolism of a Chk-1 inhibitor (LY2603618) was characterized following a 1-h intravenous administration of a single 250-mg dose of [14C]LY2603618 (50 µCi) to patients with advanced or metastatic solid tumors. LY2603618 was well tolerated with no clinically significant adverse events. Study was limited to three patients due to challenges of conducting ADME studies in patients with advanced cancer. Plasma, urine and feces were analyzed for radioactivity, LY2603618 and metabolites. LY2603618 had a half-life of 10.5 h and was the most abundant entity in plasma, accounting for approximately 69% of total plasma radioactivity. The second most abundant metabolites, H2 and H5, accounted for <10% of total circulating radioactivity. The major route of clearance was via CYP450 metabolism. The mean total recovery of radioactivity was 83%, with approximately 72% of the radioactivity recovered in the feces and approximately 11% in the urine. LY2603618 represented approximately 6% and 3% of the administered dose in feces and urine, respectively. A total of 12 metabolites were identified. In vitro phenotyping indicated that CYP3A4 was predominantly responsible for the metabolic clearance of LY2603618. Additionally, aldehyde oxidase was involved in the formation of a unique human and non-human primate metabolite, H5.

Disposition and metabolism of LY2452473, a selective androgen receptor modulator, in humans.

The disposition and metabolism of isopropyl N-[(2S)-7-cyano-4-(2-pyridylmethyl)-2,3-dihydro-1H-cyclopenta[b]indol-2-yl]carbamate (LY2452473; a selective androgen receptor modulator) in humans was characterized after a single 15-mg (100 µCi) oral dose of [¹4C]LY2452473 to six healthy male subjects. LY2452473 was absorbed rapidly (time to reach maximum plasma concentration for both LY2452473 and total radioactivity was 2-3 h) and cleared slowly (plasma terminal t(½) of 27 h for LY2452473 and 51 h for the total radioactivity). LY2452473 and metabolites S5 (acetylamine) and S12 (hydroxylation on the cyclopentene) were major circulating entities in plasma, accounting for approximately 42, 21, and 35% of the total radioactivity exposure, respectively, as calculated from relative area under the concentration versus time curves from zero to 48 h derived from the plasma radiochromatograms. The radioactive dose was almost completely recovered after 312 h with 47.9% of the dose eliminated in urine and 46.6% in feces. Minimal LY2452473 was detected in excreta, indicating that metabolic clearance was the main route of elimination. Multiple metabolic pathways were observed with no single metabolic pathway accounting for more than 30% of the dose in excreta. Metabolite S10 (a diol across the cyclopenta-indole linkage) was the largest excretory metabolite (approximately 14% of the dose). S10 displayed interesting chemical and chromatographic properties, undergoing conversion to the corresponding epoxide under acidic conditions and conversion back to the diol under neutral conditions. An in vitro phenotyping approach indicated that CYP3A4 was the largest contributor to LY2452473 depletion.

Interactions of two major metabolites of prasugrel, a thienopyridine antiplatelet agent, with the cytochromes P450.

The biotransformation of prasugrel to R-138727 (2-[1-2-cyclopropyl-1-(2-fluorophenyl)-2-oxoethyl]-4-mercapto-3-piperidinylidene]acetic acid) involves rapid deesterification to R-95913 (2-[2-oxo-6,7-dihydrothieno[3,2-c]pyridin-5(4H)-yl]-1-cyclopropyl-2-(2-fluorophenyl)ethanone) followed by cytochrome P450 (P450)-mediated formation of R-138727, the metabolite responsible for platelet aggregation. For identification of the P450s responsible for the formation of the active metabolite, the current studies were conducted with R-95913 as the substrate. Incubations required supplementation with reduced glutathione. Hyperbolic kinetics (K(m) 21-30 microM), consistent with a single enzyme predominating, were observed after incubations with human liver microsomes. Correlation analyses revealed a strong relationship between R-138727 formation and CYP3A-mediated midazolam 1'-hydroxylation (r(2) = 0.98; p < 0.001) in a bank of characterized human liver microsomal samples. The human lymphoblast-expressed enzymes capable of forming R-138727, in rank order of rates, were CYP3A4>CYP2B6>CYP2C19 approximately CYP2C9>CYP2D6. A monoclonal antibody to CYP2B6 and the CYP3A inhibitor ketoconazole substantially inhibited R-138727 formation, whereas inhibitors of CYP2C9 (sulfaphenazole) and CYP2C19 (omeprazole) did not. Scaling of in vitro intrinsic clearance values from expressed enzymes to the whole liver using a relative abundance approach indicated that either CYP3A4 alone or CYP3A4 and CYP2B6 are the major contributors to R-138727 formation. R-95913 and R-138727 were also examined for their ability to inhibit metabolism mediated by five P450s. R-138727 did not inhibit the P450s tested. In vitro, R-95913 inhibited CYP2C9, CYP2C19, CYP2D6, and CYP3A, with K(i) values ranging from 7.2 microM to 82 microM, but did not inhibit CYP1A2. These K(i) values exceed circulating concentrations in humans by 3.8- to 43-fold. Therefore, neither R-95913 nor R-138727 is expected to substantially inhibit the P450-mediated metabolism of coadministered drugs.