Clinical Drug Interaction Studies Research Articles

Ligand- and Structure-based Approaches for Transmembrane Transporter Modeling.

The study of transporter proteins is key to understanding the mechanism behind multidrug resistance and drug-drug interactions causing severe side effects. While ATP-binding transporters are well-studied, solute carriers illustrate an understudied family with a high number of orphan proteins. To study these transporters, in silico methods can be used to shed light on the basic molecular machinery by studying protein-ligand interactions. Nowadays, computational methods are an integral part of the drug discovery and development process. In this short review, computational approaches, such as machine learning, are discussed, which try to tackle interactions between transport proteins and certain compounds to locate target proteins. Furthermore, a few cases of selected members of the ATP binding transporter and solute carrier family are covered, which are of high interest in clinical drug interaction studies, especially for regulatory agencies. The strengths and limitations of ligand-based and structure-based methods are discussed to highlight their applicability for different studies. Furthermore, the combination of multiple approaches can improve the information obtained to find crucial amino acids that explain important interactions of protein-ligand complexes in more detail. This allows the design of drug candidates with increased activity towards a target protein, which further helps to support future synthetic efforts.

Alternatives to rifampin: A perspective on conducting clinical drug interaction studies

Alternatives to rifampin: A perspective on conducting clinical drug interaction studies

Utilization of Rosuvastatin and Endogenous Biomarkers in Evaluating the Impact of Ritlecitinib on BCRP, OATP1B1, and OAT3 Transporter Activity

PurposeRitlecitinib, an inhibitor of Janus kinase 3 and tyrosine kinase expressed in hepatocellular carcinoma family kinases, is in development for inflammatory diseases. This study assessed the impact of ritlecitinib on drug transporters using a probe drug and endogenous biomarkers.MethodsIn vitro transporter-mediated substrate uptake and inhibition by ritlecitinib and its major metabolite were evaluated. Subsequently, a clinical drug interaction study was conducted in 12 healthy adult participants to assess the effect of ritlecitinib on pharmacokinetics of rosuvastatin, a substrate of breast cancer resistance protein (BCRP), organic anion transporting polypeptide 1B1 (OATP1B1), and organic anion transporter 3 (OAT3). Plasma concentrations of coproporphyrin I (CP-I) and pyridoxic acid (PDA) were assessed as endogenous biomarkers for OATP1B1 and OAT1/3 function, respectively.ResultsIn vitro studies suggested that ritlecitinib can potentially inhibit BCRP, OATP1B1 and OAT1/3 based on regulatory cutoffs. In the subsequent clinical study, coadministration of ritlecitinib decreased rosuvastatin plasma exposure area under the curve from time 0 to infinity (AUCinf) by ~ 13% and maximum concentration (Cmax) by ~ 27% relative to rosuvastatin administered alone. Renal clearance was comparable in the absence and presence of ritlecitinib coadministration. PK parameters of AUCinf and Cmax for CP-I and PDA were also similar regardless of ritlecitinib coadministration.ConclusionRitlecitinib does not inhibit BCRP, OATP1B1, and OAT3 and is unlikely to cause a clinically relevant interaction through these transporters. Furthermore, our findings add to the body of evidence supporting the utility of CP-I and PDA as endogenous biomarkers for assessment of OATP1B1 and OAT1/3 transporter activity.

Combined oral contraceptives as victims of drug interactions.

Combined oral contraceptives (COCs) are widely used in women of reproductive age in the United States. Metabolism plays an important role in the elimination of estrogens and progestins contained in COCs. It is unavoidable that a woman using COCs may need to take another drug to treat a disease. If the concurrently used drug induces enzymes responsible for the metabolism of progestins and/or estrogens, unintended pregnancy or irregular bleeding may occur. If the concurrent drug inhibits the metabolism of these exogenous hormones, there may be an increased safety risk such as thrombosis. Therefore, for an investigational drug intended to be used in women with reproductive potential, evaluating its effects on the pharmacokinetics of COCs is important to determine if additional labeling is necessary for managing drug-drug interactions between the concomitant product and the COCs. It is challenging to determine when this clinical drug interaction study is needed, whether an observed exposure change of progestin/estrogen is clinically meaningful, and if the results of a clinical drug interaction study with one COC can predict exposure changes of unstudied COCs to inform labeling. In this review, we summarize the current understanding of metabolic pathways of estrogens and progestins contained in commonly used COCs, known interactions of these COCs as victim drugs, and discuss possible mechanisms of interactions for unexpected results. We also discuss recent advances, knowledge gaps, and future perspectives on this important topic. The review will enhance the understanding of DDIs with COCs and improve the safe and effective use of COCs. Significance Statement This minireview provides an overview of the metabolic pathways of ethinyl estradiol (EE) and progestins contained in commonly used COCs and significant drug interactions of these COCs as victims. It also discusses recent advances, knowledge gaps, and future perspectives and provides insights on potential mechanisms for unexpected results of clinical drug interaction studies of COCs. This minireview will help the reader understand considerations when evaluating the drug interaction potential with COCs for drugs that are expected to be used concurrently.

Acalabrutinib CYP3A-mediated drug-drug interactions: Clinical evaluations and physiologically based pharmacokinetic modelling to inform dose adjustment strategy.

Clinical drug interaction studies with itraconazole and rifampicin have demonstrated that acalabrutinib is a sensitive substrate of CYP3A. A physiologically based pharmacokinetic (PBPK) model was developed based on the data of these studies. One of the active CYP3A metabolites, ACP-5862, was identified but never studied in a drug interaction scenario. This study aims to evaluate both parent and metabolite exposure change with coadministration of moderate CYP3A inhibitors and its impact on safety and efficacy. In an open label, randomized, 2-period study, we investigated the effect of coadministration of fluconazole or isavuconazole on the pharmacokinetics of acalabrutinib. Bruton tyrosine kinase receptor occupancy and safety were compared between different treatments. Experimental data were compared to PBPK simulation results. Least square means of acalabrutinib maximum plasma concentration and area under the curve increased 1.37 (1.14-1.64) and 1.60 (1.45-1.77)-fold in the presence of isavuconazole and 1.48 (1.10-1.98) and 2.16 (1.94-2.40)-fold in the presence of fluconazole, respectively. For ACP-5862, these values are 0.72 (0.63-0.82) and 0.91 (0.86-0.97) fold for isavuconazole and 0.65 (0.49-0.87) and 0.95 (0.91-0.99) fold for fluconazole coadministration. The PBPK model was able to recover acalabrutinib and ACP-5862 PK profiles in the study. Bruton tyrosine kinase receptor occupancy change was minimal in the presence of isavuconazole. There were no deaths, serious adverse events (AEs), or subject discontinuation due to AEs in this study. Only mild (Grade 1) AEs were reported during the study, by 17% of the study population. Our results demonstrate the impact of fluconazole and isavuconazole on the pharmacokinetics of acalabrutinib and ACP-5862, and suggest that no dose adjustment is needed for concomitant administration with moderate CYP3A inhibitors. the current PBPK model can be used to propose dose adjustment for drug interactions via CYP3A.

Mechanism of dasabuvir inhibition of acetaminophen glucuronidation.

Acetaminophen (APAP) (paracetamol) is a widely used non-prescription drug for pain relief and antipyretic effects. The clearance of APAP is mainly through phase-2 biotransformation catalysed by UDP-glucuronosyl transferases (UGT). Dasabuvir is an anti-hepatitis C drug reported to inhibit several UGT isoforms. The study evaluated the in-vitro inhibitory capacity of dasabuvir versus APAP glucuronidation. Procedures included human liver microsomal incubations with APAP and isoform-selective probe substrates. Dasabuvir inhibited APAP metabolism by a reversible, mixed-type (competitive and non-competitive) partial inhibition, with an inhibition constant Ki = 3.4 µM. The index constant 'a' was 6.7, indicating the relative contribution of competitive and non-competitive inhibition. The enzyme-inhibitor complex was still able to catalyse the reaction by 12% of the control capacity. Dasabuvir produced strong partial inhibition effect of UGT1A1 and UGT1A9 and relatively complete inhibition of UGT1A6. Consistent with previous reports, dasabuvir inhibits the activity of 3 UGT isoforms associated with APAP metabolism. In-vitro to in-vivo scaling by 2 different approaches showed identical results, predicting an increased AUC of APAP by a factor of 1.3-fold with coadministration of dasabuvir. Until the findings are confirmed in clinical drug interaction studies, APAP dosage should not exceed 3 g per day in dasabuvir-treated patients to avoid potentially hepatotoxic APAP exposures.

Effects of sedative psychotropic drugs combined with oxycodone on respiratory depression in the rat.

Following a decision to require label warnings for concurrent use of opioids and benzodiazepines and increased risk of respiratory depression and death, the US Food and Drug Administratioin (FDA) recognized that other sedative psychotropic drugs may be substituted for benzodiazepines and be used concurrently with opioids. In some cases, data on the ability of these alternatives to depress respiration alone or in conjunction with an opioid are lacking. A nonclinical in vivo model was developed that could detect worsening respiratory depression when a benzodiazepine (diazepam) was used in combination with an opioid (oxycodone) compared to the opioid alone based on an increased arterial partial pressure of carbon dioxide (pCO2). The current study used that model to assess the impact on respiration of non‐benzodiazepine sedative psychotropic drugs representative of different drug classes (clozapine, quetiapine, risperidone, zolpidem, trazodone, carisoprodol, cyclobenzaprine, mirtazapine, topiramate, paroxetine, duloxetine, ramelteon, and suvorexant) administered alone and with oxycodone. At clinically relevant exposures, paroxetine, trazodone, and quetiapine given with oxycodone significantly increased pCO2 above the oxycodone effect. Analyses indicated that most pCO2 interaction effects were due to pharmacokinetic interactions resulting in increased oxycodone exposure. Increased pCO2 recorded with oxycodone‐paroxetine co‐administration exceeded expected effects from only drug exposure suggesting another mechanism for the increased pharmacodynamic response. This study identified drug‐drug interaction effects depressing respiration in an animal model when quetiapine or paroxetine were co‐administered with oxycodone. Clinical pharmacodynamic drug interaction studies are being conducted with these drugs to assess translatability of these findings.

Case Study 7: Transporters Case Studies-In Vitro Solutions for Translatable Outcomes.

Assessing the interactions of a new drug candidate with transporters, either as a substrate, inhibitor, or inducer, is no simple matter. There are many clinically relevant transporters, as many as nine to be evaluated for an FDA submission and up to 11 for the EMA as of 2020. Additionally, it is likely that if a compound is a substrate or inhibitor of one transporter, it will be so for other transporters as well. There are practically no specific substrates or inhibitors, presumably because the specificities of drug transporters are so broad and overlapping, and even fewer clinically relevant probes that can be used to evaluate transporter function in humans. In the case of some transporters, it is advisable to evaluate an NCE with more than one test system and/or more than one probe substrate in order to convince oneself (and regulatory authorities) that a clinical drug interaction study is not warranted. Finally, each test system has its own unique set of advantages and disadvantages. One has to appreciate the nuances of the available tools (test systems, probe substrates, etc.) to select the most relevant tools for the study and design the optimal in vitro experiment. In this chapter, several examples are used to illustrate the successful interpretation of in vitro data for both efflux and uptake transporters. Some data presented in this chapter are unpublished at the time of the compilation of this book. It has been included in this chapter to provide a sense of the complexities in transporter kinetics to the reader.

Abstract 3016: Tucatinib inhibits CYP3A, CYP2C8 and P-gp-mediated elimination and is impacted by CYP2C8 inhibition in healthy volunteers

Abstract Background: Tucatinib is a potent, highly selective HER2 tyrosine kinase inhibitor in development for the treatment of patients with HER2+ metastatic breast cancer. In vitro metabolism studies suggest that drug metabolizing enzymes CYP2C8 and CYP3A play a role in tucatinib metabolism. Tucatinib exhibits competitive inhibition of CYP2C8, CYP2C9, CYP3A, and P-gp, and metabolism-dependent inactivation of CYP3A in vitro. ONT-380-012 was a clinical drug interaction study conducted to evaluate the magnitude of potential enzyme and transporter interactions for tucatinib (both as a victim and perpetrator), and the safety of healthy subjects when administered tucatinib doses at therapeutic levels (300 mg BID). Methods: Healthy volunteers (n=116) at multiple centers were enrolled in the study. Parts A-C evaluated the effects of a strong CYP2C8 inhibitor (gemfibrozil), a strong CYP3A inhibitor (itraconazole), and a CYP3A/CYP2C8 inducer (rifampin) on single-dose tucatinib (300 mg) PK. Parts D and E assessed the effects of steady-state tucatinib (300 mg BID) on single-dose PK of substrate probes for CYP2C8 (repaglinide), CYP2C9 (tolbutamide), CYP3A (midazolam), and P-gp (digoxin). Plasma samples were collected for PK analysis and drug concentrations were measured using validated LC-MS/MS methods. Results: A strong CYP3A inhibitor (itraconazole) increased tucatinib AUCinf and Cmax 1.3-fold. A CYP3A/CYP2C8 inducer (rifampin) decreased tucatinib AUCinf and Cmax 48% and 37%, respectively. A strong CYP2C8 inhibitor (gemfibrozil) increased tucatinib AUCinf and Cmax 3.1- and 1.6-fold, respectively. Tucatinib increased the AUCinf and Cmax of the CYP3A substrate (midazolam) 5.7- and 3.0-fold, respectively, the AUCinf and Cmax of the CYP2C8 substrate (repaglinide) 1.7-fold, and the AUCinf of the P-gp substrate (digoxin) 1.5-fold. Tucatinib had no impact on the PK of the CYP2C9 substrate (tolbutamide). Overall, tucatinib was well tolerated in healthy volunteers when administered 300 mg BID. Conclusions: Together, these data indicate tucatinib is metabolized primarily by CYP2C8 and to a lesser extent via CYP3A. Tucatinib was found to be a strong inhibitor of CYP3A, a weak inhibitor of CYP2C8 and P-gp, and had no impact on CYP2C9-mediated metabolism in vivo. Citation Format: Ariel R. Topletz-Erickson, Anthony Lee, Hao Sun, JoAl Mayor, Luke Walker, Christopher J. Endres. Tucatinib inhibits CYP3A, CYP2C8 and P-gp-mediated elimination and is impacted by CYP2C8 inhibition in healthy volunteers [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3016.

What Do We Know About Remdesivir Drug Interactions?

The global pandemic of severe acute respiratory syndrome coronavirus 2 (SARS‐Co‐V‐2) has resulted in a critical need to rapidly develop new pharmacologic interventions and disseminate information. This has led to confusing and conflicting information on drug efficacy. Remdesivir has emerged as a promising treatment for SARS‐Co‐V‐2 infection yet published clinical pharmacology and drug interaction studies are limited. Additional studies of the disposition of remdesivir, its active metabolite (GS‐441524), and its triphosphate metabolite (GS‐443902) are needed.

Intravenous formulation of Panax notoginseng root extract: human pharmacokinetics of ginsenosides and potential for perpetrating drug interactions.

XueShuanTong, a lyophilized extract of Panax notoginseng roots (Sanqi) for intravenous administration, is extensively used as add-on therapy inthe treatment of ischemic heart and cerebrovascular diseases and comprises therapeutically active ginsenosides. Potential for XueShuanTong-drug interactions was determined; the investigation focused on cytochrome P450 (CYP)3A induction and organic anion-transporting polypeptide (OATP)1B inhibition. Ginsenosides considerably bioavailable for drug interactions were identified by dosing XueShuanTong in human subjects and their interaction-related pharmacokinetics were determined. The CYP3A induction potential was determined by repeatedly dosing XueShuanTong for 15 days in human subjects and by treating cryopreserved human hepatocytes with circulating ginsenosides; midazolam served as a probe substrate. Joint inhibition of OATP1B by XueShuanTong ginsenosides was assessed in vitro, and the data were processed using the Chou-Talalay method. Samples were analyzed by liquid chromatography/mass spectrometry. Ginsenosides Rb1, Rd, and Rg1 and notoginsenoside R1 were the major circulating XueShuanTong compounds; their interaction-related pharmacokinetics comprised compound dose-dependent levels of systemic exposure and, for ginsenosides Rb1 and Rd, long terminal half-lives (32‒57 and 58‒307 h, respectively) and low unbound fractions in plasma (0.8%‒2.9% and 0.4%‒3.0%, respectively). Dosing XueShuanTong did not induce CYP3A. Based on the pharmacokinetics and inhibitory potency of the ginsenosides, XueShuanTong was predicted to have high potential for OATP1B3-mediated drug interactions (attributed chiefly to ginsenoside Rb1) suggesting the need for further model-based determination of the interaction potential for XueShuanTong and, if necessary, a clinical drug interaction study. Increased awareness of ginsenosides' pharmacokinetics and XueShuanTong-drug interaction potential will help ensure thesafe use of XueShuanTong and coadministered synthetic drugs.

Mechanistic Physiologically Based Pharmacokinetic Modeling of the Dissolution and Food Effect of a Biopharmaceutics Classification System IV Compound—The Venetoclax Story

Venetoclax, a selective B-cell lymphoma-2 inhibitor, is a biopharmaceutics classification system class IV compound. The aim of this study was to develop a physiologically based pharmacokinetic (PBPK) model to mechanistically describe absorption and disposition of an amorphous solid dispersion formulation of venetoclax in humans. A mechanistic PBPK model was developed incorporating measured amorphous solubility, dissolution, metabolism, and plasma protein binding. A middle-out approach was used to define permeability. Model predictions of oral venetoclax pharmacokinetics were verified against clinical studies of fed and fasted healthy volunteers, and clinical drug interaction studies with strong CYP3A inhibitor (ketoconazole) and inducer (rifampicin). Model verification demonstrated accurate prediction of the observed food effect following a low-fat diet. Ratios of predicted versus observed Cmax and area under the curve of venetoclax were within 0.8- to 1.25-fold of observed ratios for strong CYP3A inhibitor and inducer interactions, indicating that the venetoclax elimination pathway was correctly specified. The verified venetoclax PBPK model is one of the first examples mechanistically capturing absorption, food effect, and exposure of an amorphous solid dispersion formulated compound. This model allows evaluation of untested drug-drug interactions, especially those primarily occurring in the intestine, and paves the way for future modeling of biopharmaceutics classification system IV compounds.

Estimation of the Contribution of CYP2C8 and CYP3A4 in Repaglinide Metabolism by Human Liver Microsomes Under Various Buffer Conditions

We have previously reported that the microsomal activities of CYP2C8 and CYP3A4 largely depend on the buffer condition used in in vitro metabolic studies, with different patterns observed between the 2 isozymes. In the present study, therefore, the possibility of buffer condition dependence of the fraction metabolized by CYP2C8 (fm2C8) for repaglinide, a dual substrate of CYP2C8 and CYP3A4, was estimated using human liver microsomes under various buffer conditions. Montelukast and ketoconazole showed a potent and concentration-dependent inhibition of CYP2C8-mediated paclitaxel 6α-hydroxylation and CYP3A4-mediated triazolam α-hydroxylation, respectively, without dependence on the buffer condition. Repaglinide depletion was inhibited by both inhibitors, but the degree of inhibition depended on buffer conditions. Based on these results, the contribution of CYP2C8 in repaglinide metabolism was estimated to be larger than that of CYP3A4 under each buffer condition, and the fm2C8 value of 0.760, estimated in 50 mM phosphate buffer, was the closest to the value (0.801) estimated in our previous modeling analysis based on its concentration increase in a clinical drug interaction study. Researchers should be aware of the possibility of buffer condition affecting the estimated contribution of enzyme(s) in drug metabolism processes involving multiple enzymes.

Evaluation of Pharmacokinetic Interactions Between Lesinurad, a New Selective Urate Reabsorption Inhibitor, and CYP Enzyme Substrates Sildenafil, Amlodipine, Tolbutamide, and Repaglinide.

Lesinurad is a selective uric acid reabsorption inhibitor approved for the treatment of hyperuricemia associated with gout in combination with xanthine oxidase inhibitors. In vitro assays indicate that lesinurad is an inducer of CYPs in the order CYP3A > CYP2C8 > CYP2C9 > CYP2C19 > CYP2B6 and an inhibitor of CYP2C8 and CYP2C9. To investigate the drug interaction potential of lesinurad, clinical drug interaction studies were conducted. Open-label studies in volunteers investigated the effects of single-/multiple-dose lesinurad on the pharmacokinetics of sildenafil and amlodipine (CYP3A4 induction), tolbutamide (CYP2C9 inhibition/induction), and repaglinide (CYP2C8 inhibition/induction). There was no apparent induction of CYP2C8 and CYP2C9 following repeated lesinurad administration, although no inhibition of CYP2C9 and modest inhibition of CYP2C8 were observed following single-dose lesinurad. Consistent with in vitro observations, lesinurad (200 mg once daily) was an inducer of CYP3A based on the effects on sildenafil exposure. Sildenafil exposure decreased by approximately 34% for Cmax and AUC when administered with multiple-dose lesinurad 200 mg and allopurinol 300 mg, relative to sildenafil alone. During lesinurad therapy, the possibility of reduced efficacy of concomitant drugs that are CYP3A substrates should be considered and their efficacy monitored because of induction of CYP3A by lesinurad.

Validation of a microdose probe drug cocktail for clinical drug interaction assessments for drug transporters and CYP3A.

A microdose cocktail containing midazolam, dabigatran etexilate, pitavastatin, rosuvastatin, and atorvastatin has been established to allow simultaneous assessment of a perpetrator impact on the most common drug metabolizing enzyme, cytochrome P450 (CYP)3A, and the major transporters organic anion-transporting polypeptides (OATP)1B, breast cancer resistance protein (BCRP), and MDR1 P-glycoprotein (P-gp). The clinical utility of these microdose cocktail probe substrates was qualified by conducting clinical drug interaction studies with three inhibitors with different in vitro inhibitory profiles (rifampin, itraconazole, and clarithromycin). Generally, the pharmacokinetic profiles of the probe substrates, in the absence and presence of the inhibitors, were comparable to their reported corresponding pharmacological doses, and/or in agreement with theoretical expectations. The exception was dabigatran, which resulted in an approximately twofold higher magnitude for microdose compared to conventional dosing, and, thus, can be used to flag a worst-case scenario for P-gp. Broader application of the microdose cocktail will facilitate a more comprehensive understanding of the roles of drug transporters in drug disposition and drug interactions.

In Vitro and Clinical Evaluations of the Drug-Drug Interaction Potential of a Metabotropic Glutamate 2/3 Receptor Agonist Prodrug with Intestinal Peptide Transporter 1.

Despite peptide transporter 1 (PEPT1) being responsible for the bioavailability for a variety of drugs, there has been little study of its potential involvement in drug-drug interactions. Pomaglumetad methionil, a metabotropic glutamate 2/3 receptor agonist prodrug, utilizes PEPT1 to enhance absorption and bioavailability. In vitro studies were conducted to guide the decision to conduct a clinical drug interaction study and to inform the clinical study design. In vitro investigations determined the prodrug (LY2140023 monohydrate) is a substrate of PEPT1 with Km value of approximately 30 µM, whereas the active moiety (LY404039) is not a PEPT1 substrate. In addition, among the eight known PEPT1 substrates evaluated in vitro, valacyclovir was the most potent inhibitor (IC50 = 0.46 mM) of PEPT1-mediated uptake of the prodrug. Therefore, a clinical drug interaction study was conducted to evaluate the potential interaction between the prodrug and valacyclovir in healthy subjects. No effect of coadministration was observed on the pharmacokinetics of the prodrug, valacyclovir, or either of their active moieties. Although in vitro studies showed potential for the prodrug and valacyclovir interaction via PEPT1, an in vivo study showed no interaction between these two drugs. PEPT1 does not appear to easily saturate because of its high capacity and expression in the intestine. Thus, a clinical interaction at PEPT1 is unlikely even with a compound with high affinity for the transporter.

Development of a Physiologically Based Pharmacokinetic Model to Predict Disease-Mediated Therapeutic Protein-Drug Interactions: Modulation of Multiple Cytochrome P450 Enzymes by Interleukin-6.

Disease-mediated therapeutic protein-drug interactions have recently gained attention from regulatory agencies and pharmaceutical industries in the development of new biological products. In this study, we developed a physiologically based pharmacokinetic (PBPK) model using SimCYP to predict the impact of elevated interleukin-6 (IL-6) levels on cytochrome P450 (CYP) enzymes and the treatment effect of an anti-IL-6 monoclonal antibody, sirukumab, in patients with rheumatoid arthritis (RA). A virtual RA patient population was first constructed by incorporating the impact of systemic IL-6 level on hepatic and intestinal expression of multiple CYP enzymes with information from in vitro studies. Then, a PBPK model for CYP enzyme substrates was developed for healthy adult subjects. After incorporating the virtual RA patient population, the PBPK model was applied to quantitatively predict pharmacokinetics of multiple CYP substrates in RA patients before and after sirukumab treatment from a clinical cocktail drug interaction study. The results suggested that, compared with observed clinical data, changes in systemic exposure to multiple CYP substrates by anti-IL-6 treatment in virtual RA patients have been reasonably captured by the PBPK model, as manifested by modulations in area under plasma concentration versus time curves for midazolam, omeprazole, S-warfarin, and caffeine. This PBPK model reasonably captured the modulation effect of IL-6 and sirukumab on activity of CYP3A, CYP2C9, CYP2C19, and CYP1A2 and holds the potential to be utilized to assess the modulation effect of sirukumab on the metabolism and pharmacokinetics of concomitant small-molecule drugs in RA patients.

Application of Micropatterned Cocultured Hepatocytes to Evaluate the Inductive Potential and Degradation Rate of Major Xenobiotic Metabolizing Enzymes.

Long-term coculture models of hepatocytes are promising tools to study drug transport, clearance, and hepatoxicity. In this report we compare the basal expression of drug disposition genes and the inductive response of prototypical inducers (rifampin, phenobarbital, phenytoin) in hepatocyte two-dimensional monocultures and the long-term coculture model (HepatoPac). All the inducers used in the study increased the expression and activity of CYP3A4, CYP2B6 and CYP2C enzymes in the HepatoPac cultures. The coculture model showed a consistent and higher induction of CYP2C enzymes compared with the monocultures. The EC50 of rifampin for CYP3A4 and CYP2C9 was up to 10-fold lower in HepatoPac than the monocultures. The EC50 of rifampin calculated from the clinical drug interaction studies correlated well with the EC50 observed in the HepatoPac cultures. Owing to the long-term stability of the HepatoPac cultures, we were able to directly measure a half-life (t1/2) for both CYP3A4 and CYP2B6 using the depletion kinetics of mRNA and functional activity. The t1/2 for CYP3A4 mRNA was 26 hours and that for the functional protein was 49 hours. The t1/2 of CYP2B6 was 38 hours (mRNA) and 68 hours (activity), which is longer than CYP3A4 and shows the differential turnover of these two proteins. This is the first study to our knowledge to report the turnover rate of CYP2B6 in human hepatocytes. The data presented here demonstrate that the HepatoPac cultures have the potential to be used in long-term culture to mimic complex clinical scenarios.

Key Findings from Preclinical and Clinical Drug Interaction Studies Presented in New Drug and Biological License Applications Approved by the Food and Drug Administration in 2014.

Regulatory approval documents contain valuable information, often not published, to assess the drug-drug interaction (DDI) profile of newly marketed drugs. This analysis aimed to systematically review all drug metabolism, transport, pharmacokinetics, and DDI data available in the new drug applications and biologic license applications approved by the U.S. Food and Drug Administration in 2014, using the University of Washington Drug Interaction Database, and to highlight the significant findings. Among the 30 new drug applications and 11 biologic license applications reviewed, 35 new molecular entities (NMEs) were well characterized with regard to drug metabolism, transport, and/or organ impairment and were fully analyzed in this review. In vitro, a majority of the NMEs were found to be substrates or inhibitors/inducers of at least one drug metabolizing enzyme or transporter. In vivo, when NMEs were considered as victim drugs, 16 NMEs had at least one in vivo DDI study with a clinically significant change in exposure (area under the time-plasma concentration curve or Cmax ratio ≥2 or ≤0.5), with 6 NMEs shown to be sensitive substrates of cytochrome P450 enzymes (area under the time-plasma concentration curve ratio ≥5 when coadministered with potent inhibitors): paritaprevir and naloxegol (CYP3A), eliglustat (CYP2D6), dasabuvir (CYP2C8), and tasimelteon and pirfenidone (CYP1A2). As perpetrators, seven NMEs showed clinically significant inhibition involving both enzymes and transporters, although no clinically significant induction was observed. Physiologically based pharmacokinetic modeling and pharmacogenetics studies were used for six and four NMEs, respectively, to optimize dosing recommendations in special populations and/or multiple impairment situations. In addition, the pharmacokinetic evaluations in patients with hepatic or renal impairment provided useful quantitative information to support drug administration in these fragile populations.

Liver-selective distribution in rats supports the importance of active uptake into the liver via organic anion transporting polypeptides (OATPs) in humans

Organic anion transporting polypeptide (OATP) 1B1 and 1B3 are key molecules that are involved in hepatic uptake related to drug elimination, and OATP-mediated drug interactions are of clinical concern. In this study, with an aim to determine a cutoff value for the potential involvement of OATP, we collected data on the distribution of 12 human OATP and 24 non-OATP radiolabeled substrates in rats. The OATP substrates exhibited a higher tissue-to-plasma ratio (Kp) in the liver than that in the other tissues. As an index of liver-specific distribution, a hepatic Kp ratio (the ratio of Kp in the liver to that in other tissues) was introduced, and a hepatic Kp ratio <10 was proposed as a criterion for excluding the involvement of OATP in vivo. Approximately 20% of the non-OATP substrates as well as 100% of the OATP substrates exceeded the cutoff value of 10; therefore, further in vitro transport studies will be required to decide whether to conduct clinical drug interaction studies. Since distribution studies are usually conducted in rats during drug development, the use of a hepatic Kp ratio is practical and could refine the current decision tree for selecting OATP substrates in the drug interaction guidance/guidelines.