Impact of endogenous esterase activity on in vitro p-glycoprotein profiling of dabigatran etexilate in Caco-2 monolayers

Differential Tissue Abundance of Membrane-Bound Drug Metabolizing Enzymes and Transporter Proteins by Global Proteomics

Protein abundance data of drug-metabolizing enzymes and transporters (DMETs) are useful for scaling in vitro and animal data to humans for accurate prediction and interpretation of drug clearance and toxicity. Targeted DMET proteomics that relies on synthetic stable isotope-labeled surrogate peptides as calibrators is routinely used for the quantification of selected proteins; however, the technique is limited to the quantification of a small number of proteins. Although the global proteomics-based total protein approach (TPA) is emerging as a better alternative for large-scale protein quantification, the conventional TPA does not consider differential sequence coverage by identifying unique peptides across proteins. Here, we optimized the TPA approach by correcting protein abundance data by the sequence coverage, which was applied to quantify 54 DMETs for characterization of 1) differential tissue DMET abundance in the human liver, kidney, and intestine, and 2) interindividual variability of DMET proteins in individual intestinal samples (n = 13). Uridine diphosphate-glucuronosyltransferase 2B7 (UGT2B7), microsomal glutathione S-transferases (MGST1, MGST2, and MGST3) carboxylesterase 2 (CES2), and multidrug resistance-associated protein 2 (MRP2) were expressed in all three tissues, whereas, as expected, four cytochrome P450s (CYP3A4, CYP3A5, CYP2C9, and CYP4F2), UGT1A1, UGT2B17, CES1, flavin-containing monooxygenase 5, MRP3, and P-glycoprotein were present in the liver and intestine. The top three DMET proteins in individual tissues were: CES1>CYP2E1>UGT2B7 (liver), CES2>UGT2B17>CYP3A4 (intestine), and MGST1>UGT1A6>MGST2 (kidney). CYP3A4, CYP3A5, UGT2B17, CES2, and MGST2 showed high interindividual variability in the intestine. These data are relevant for enhancing in vitro to in vivo extrapolation of drug absorption and disposition and can be used to enhance the accuracy of physiologically based pharmacokinetic prediction of systemic and tissue concentration of drugs. SIGNIFICANCE STATEMENT: This study quantified the abundance and compositions of drug-metabolizing enzymes and transporters in pooled human liver, intestine, and kidney microsomes as well as individual intestinal microsomes using an optimized global proteomics approach. The data revealed large intertissue differences in the abundance of these proteins and high intestinal interindividual variability in the levels of cytochrome P450s (e.g., CYP3A4 and CYP3A5), uridine diphosphate-glucuronosyltransferase 2B17, carboxylesterase 2, and microsomal glutathione S-transferase 2. These data are applicable for the prediction of first-pass metabolism and tissue-specific drug clearance.

The pharmacokinetics of dabigatran in a rat model of hyperlipidaemia induced by poloxamer 407

Various pharmacokinetic changes have been reported in experimental hyperlipidemic (HL) animal models. To evaluate whether P-glycoprotein (P-gp) activity was affected in HL rats, we assessed the pharmacokinetics of dabigatran after oral administration of dabigatran etexilate (DABE); this is a dabigatran prodrug and a well-known P-gp substrate.HL and control rats exhibited similar area under the plasma concentration-time curve (AUC), total body clearance (CL), and steady state volume of distribution (Vss) values following intravenous administration of dabigatran (1 mg/kg). This suggested that the distribution and elimination of dabigatran were similar in control and HL rats.The hepatic and intestinal P-gp protein levels did not differ significantly between control and HL rats. The dabigatran AUC and extent of absolute oral bioavailability (F) values were similar in control and HL rats following oral administration of DABE (10 mg/kg as dabigatran). Therefore, there was no apparent change in intestinal P-gp activity in HL rats compared to control rats.This study revealed no significant change in P-gp expression or activity in the intestine or liver of HL rats, and similar pharmacokinetics of dabigatran. Hyperlipidaemia may not directly affect the oral absorption of P-gp substrate drugs.

Assessing the relative contribution of CYP3A-and P-gp-mediated pathways to the overall disposition and drug-drug interaction of dabigatran etexilate using a comprehensive mechanistic physiological-based pharmacokinetic model

Dabigatran etexilate (DABE) is a clinical probe substrate for studying drug-drug interaction (DDI) through an intestinal P-glycoprotein (P-gp). A recent in vitro study, however, has suggested a potentially significant involvement of CYP3A-mediated oxidative metabolism of DABE and its intermediate monoester BIBR0951 in DDI following microdose administration of DABE. In this study, the relative significance of CYP3A- and P-gp-mediated pathways to the overall disposition of DABE has been explored using mechanistic physiologically based pharmacokinetic (PBPK) modeling approach. The developed PBPK model linked DABE with its 2 intermediate (BIBR0951 and BIBR1087) and active (dabigatran, DAB) metabolites, and with all relevant drug-specific properties known to date included. The model was successfully qualified against several datasets of DABE single/multiple dose pharmacokinetics and DDIs with CYP3A/P-gp inhibitors. Simulations using the qualified model supported that the intestinal CYP3A-mediated oxidation of BIBR0951, and not the gut P-gp-mediated efflux of DABE, was a key contributing factor to an observed difference in the DDI magnitude following the micro-versus therapeutic doses of DABE with clarithromycin. Both the saturable CYP3A-mediated metabolism of BIBR0951 and the solubility-limited DABE absorption contributed to the relatively modest nonlinearity in DAB exposure observed with increasing doses of DABE. Furthermore, the results suggested a limited role of the gut P-gp, but an appreciable, albeit small, contribution of gut CYP3A in mediating the DDIs following the therapeutic dose of DABE with dual CYP3A/P-gp inhibitors. Thus, a possibility exists for a varying extent of CYP3A involvement when using DABE as a clinical probe in the DDI assessment, across DABE dose levels.

Developing an adult stem cell derived microphysiological intestinal system for predicting oral prodrug bioconversion and permeability in humans

Microphysiological systems (MPS) incorporating human intestinal organoids have shown the potential to faithfully model intestinal biology with the promise to accelerate development of oral prodrugs. We hypothesized that an MPS model incorporating flow, shear stress, and vasculature could provide more reliable measures of prodrug bioconversion and permeability. Following construction of jejunal and duodenal organoid MPS derived from 3 donors, we determined the area under the concentration-time (AUC) curve for the active drug in the vascular channel and characterized the enzymology of prodrug bioconversion. Fosamprenavir underwent phosphatase mediated hydrolysis to amprenavir while dabigatran etexilate (DABE) exhibited proper CES2- and, as anticipated, not CES1-mediated de-esterification, followed by permeation of amprenavir to the vascular channel. When experiments were conducted in the presence of bio-converting enzyme inhibitors (orthovanadate for alkaline phosphatase; bis(p-nitrophenyl)phosphate for carboxylesterase), the AUC of the active drug decreased accordingly in the vascular channel. In addition to functional analysis, the MPS was characterized through imaging and proteomic analysis. Imaging revealed proper expression and localization of epithelial, endothelial, tight junction and catalytic enzyme markers. Global proteomic analysis was used to analyze the MPS model and 3 comparator sources: an organoid-based transwell model (which was also evaluated for function), Matrigel embedded organoids and finally jejunal and duodenal cadaver tissues collected from 3 donors. Hierarchical clustering analysis (HCA) and principal component analysis (PCA) of global proteomic data demonstrated that all organoid-based models exhibited strong similarity and were distinct from tissues. Intestinal organoids in the MPS model exhibited strong similarity to human tissue for key epithelial markers via HCA. Quantitative proteomic analysis showed higher expression of key prodrug converting and drug metabolizing enzymes in MPS-derived organoids compared to tissues, organoids in Matrigel, and organoids on transwells. When comparing organoids from MPS and transwells, expression of intestinal alkaline phosphatase (ALPI), carboxylesterase (CES)2, cytochrome P450 3A4 (CYP3A4) and sucrase isomaltase (SI) was 2.97-, 1.2-, 11.3-, and 27.7-fold higher for duodenum and 7.7-, 4.6-, 18.1-, and 112.2-fold higher for jejunum organoids in MPS, respectively. The MPS approach can provide a more physiological system than enzymes, organoids, and organoids on transwells for pharmacokinetic analysis of prodrugs that account for 10% of all commercial medicines.

Mechanisms and Clinical Significance of Pharmacokinetic Drug Interactions Mediated by FDA and EMA-approved Hepatitis C Direct-Acting Antiviral Agents

The treatment of patients infected with the hepatitis C virus (HCV) has been revolutionised by the development of direct-acting antiviral agents (DAAs) that target specific HCV proteins involved in viral replication. The first DAAs were associated with clinical problems such as adverse drug reactions and pharmacokinetic drug-drug interactions (DDIs). Current FDA/EMA-approved treatments are combinations of DAAs that simultaneously target the HCV N5A-protein, the HCV N5B-polymerase and the HCV NS3/4A-protease. Adverse events and DDIs are less likely with these DAA combinations but several DDIs of potential clinical significance remain. Much of the available information on the interaction of DAAs with CYP drug-metabolising enzymes and influx and efflux transporters is contained in regulatory summaries and is focused on DDIs of likely clinical importance. Important DDIs perpetrated by current DAAs include increases in the pharmacokinetic exposure to statins and dabigatran. Some mechanistic information can be deduced. Although the free concentrations of DAAs in serum are very low, a number of these DDIs are likely mediated by the inhibition of systemic influx transporters, especially OATP1B1/1B3. Other DDIs may arise by DAA-mediated inhibition of intestinal efflux transporters, which increases the systemic concentrations of some coadministered drugs. Conversely, DAAs are victims of DDIs mediated by cyclosporin, ketoconazole, omeprazole and HIV antiretroviral drug combinations, especially when boosted by ritonavir and, to a lesser extent, cobicistat. In addition, concurrent administration of inducers, such as rifampicin, carbamazepine and efavirenz, decreases exposure to some DAAs. Drug-drug interactions that increase the accumulation of HCV N3/4A-protease inhibitors like grazoprevir may exacerbate hepatic injury in HCV patients.

The Potentially Significant Role of CYP3A-Mediated Oxidative Metabolism of Dabigatran Etexilate and Its Intermediate Metabolites in Drug-Drug Interaction Assessments Using Microdose Dabigatran Etexilate

Dabigatran etexilate (DABE), a double ester prodrug of dabigatran, is a probe substrate of intestinal P-glycoprotein (P-gp) commonly used in clinical drug-drug interaction (DDI) studies. When compared with its therapeutic dose at 150 mg, microdose DABE (375 µg) showed approximately 2-fold higher in DDI magnitudes with CYP3A/P-gp inhibitors. In this study, we conducted several in vitro metabolism studies to demonstrate that DABE, at a theoretical gut concentration after microdosing, significantly underwent NADPH-dependent oxidation (~40%-50%) in parallel to carboxylesterase-mediated hydrolysis in human intestinal microsomes. Furthermore, NADPH-dependent metabolism of its intermediate monoester, BIBR0951, was also observed in both human intestinal and liver microsomes, accounting for 100% and 50% of total metabolism, respectively. Metabolite profiling using high resolution mass spectrometry confirmed the presence of several novel oxidative metabolites of DABE and of BIBR0951 in the NADPH-fortified incubations. CYP3A was identified as the major enzyme catalyzing the oxidation of both compounds. The metabolism of DABE and BIBR0951 was well described by Michaelis-Menten kinetics, with Km ranging 1-3 µM, significantly below the expected concentrations following the therapeutic dose of DABE. Overall, the present results suggested that CYP3A played a significant role in the presystemic metabolism of DABE and BIBR0951 following microdose DABE administration, thus attributing partly to the apparent overestimation in the DDI magnitude observed with the CYP3A/P-gp inhibitors. Therefore, DABE at the microdose, unlike the therapeutic dose, would likely be a less predictive tool and should be considered as a clinical dual substrate for P-gp and CYP3A when assessing potential P-gp-mediated impacts by dual CYP3A/P-gp inhibitors. SIGNIFICANT STATEMENT: This is the first study demonstrating a potentially significant role of cytochrome P450-mediated metabolism of the prodrug DABE following a microdose but not a therapeutic dose. This additional pathway, coupled with its susceptibility to P-glycoprotein (P-gp), may make DABE a clinical dual substrate for both P-gp and CYP3A at a microdose. The study also highlights the need for better characterization of the pharmacokinetics and metabolism of a clinical drug-drug interaction probe substrate over the intended study dose range for proper result interpretations.

Influence of ABCB1, CYP3A5 and CYP3A4 gene polymorphisms on prothrombin time and the residual equilibrium concentration of rivaroxaban in patients with non-valvular atrial fibrillation in real clinical practice

OBJECTIVE

The study of ABCB1 and CYP3A4/3A5 gene polymorphism genes is promising in terms of their influence on prothrombin time variability, the residual equilibrium concentration of direct oral anticoagulants (DOACs) in patients with atrial fibrillation and the development of new personalized approaches to anticoagulation therapy in these patients. The aim of the study is to evaluate the effect of ABCB1 (rs1045642) C>T; ABCB1 (rs4148738) C>T and CYP3A5 (rs776746) A>G, CYP3A4*22(rs35599367) C>T gene polymorphisms on prothrombin time level and residual equilibrium concentration of rivaroxaban in patients with atrial fibrillation.

METHODS

In total 86 patients (42 men and 44 female), aged 67.24 ± 1.01 years with atrial fibrillation were enrolled in the study. HPLC mass spectrometry analysis was used to determine rivaroxaban residual equilibrium concentration. Prothrombin time data were obtained from patient records.

RESULTS

The residual equilibrium concentration of rivaroxaban in patients with ABCB1 rs4148738 CT genotype is significantly higher than in patients with ABCB1 rs4148738 CC (P  = 0.039). The analysis of the combination of genotypes did not find a statistically significant role of combinations of alleles of several polymorphic markers in increasing the risk of hemorrhagic complications when taking rivaroxaban.

CONCLUSION

Patients with ABCB1 rs4148738 CT genotype have a statistically significantly higher residual equilibrium concentration of rivaroxaban in blood than patients with ABCB1 rs4148738 CC genotype, which should be considered when assessing the risk of hemorrhagic complications and risk of drug-drug interactions. Further studies of the effect of rivaroxaban pharmacogenetics on the safety profile and efficacy of therapy are needed.

Application of a gut-liver-on-a-chip device and mechanistic modelling to the quantitative in vitro pharmacokinetic study of mycophenolate mofetil

Microphysiological systems (MPS) consisting of multiple linked organ-on-a-chip (OoC) components are highly promising tools with potential to provide more relevant in vitro to in vivo translation of drug disposition, efficacy and toxicity. A gut-liver OoC system was employed with Caco2 cells in co-culture with HT29 cells in the intestinal compartment and single donor primary hepatocytes in the hepatic compartment for the investigation of intestinal permeability, metabolism (intestinal and hepatic) and potential interplay of those processes. The prodrug mycophenolate mofetil was tested for quantitative evaluation of the gut-liver OoC due to the contribution of both gut and liver in its metabolism. Conversion of mycophenolate mofetil to active drug mycophenolic acid and further metabolism to a glucuronide metabolite was assessed over time in the gut apical, gut basolateral and liver compartments. Mechanistic modelling of experimental data was performed to estimate clearance and permeability parameters for the prodrug, active drug and glucuronide metabolite. Integration of gut-liver OoC data with in silico modelling allowed investigation of the complex combination of intestinal and hepatic processes, which is not possible with standard single tissue in vitro systems. A comprehensive evaluation of the mechanistic model, including structural model and parameter identifiability and global sensitivity analysis, enabled a robust experimental design and estimation of in vitro pharmacokinetic parameters. We propose that similar methodologies may be applied to other multi-organ microphysiological systems used for drug metabolism studies or wherever quantitative knowledge of changing drug concentration with time enables better understanding of biological effect.

SLC4A4, FRAS1, and SULT1A1 Genetic Variations Associated With Dabigatran Metabolism in a Healthy Chinese Population

Background: The purpose of this study was to identify genetic variations associated with the metabolism of dabigatran in healthy Chinese subjects, with particular focus given to pharmacokinetics (PK) and pharmacodynamics (PD).

Methods: Healthy Chinese adults aged 18–65 years with unknown genotypes from a bioequivalence trial were included according to the protocol registered at ClinicalTrial.org (NCT03161496). All subjects received a single dose (150 mg) of dabigatran etexilate. PK (main outcomes: area under the concentration-time, AUC0-t, of total and free dabigatran) and PD (main outcomes: anti-FIIa activity, APTT, and PT) parameters were evaluated. Whole-exome sequencing and genome-wide association analyses were performed. Additionally, candidate gene association analyses related to dabigatran were conducted.

Results: A total of 118 healthy Chinese subjects were enrolled in this study. According to the p-value suggestive threshold (1.0 × 10−4), the following three SNPs were found to be associated with the AUC0–t of total dabigatran: SLC4A4 SNP rs138389345 (p = 5.99 × 10−5), FRAS1 SNP rs6835769 (p = 6.88 × 10−5), and SULT1A1 SNP rs9282862 (p = 7.44 × 10−5). Furthermore, these SNPs were also found to have significant influences on the AUC0–t of free dabigatran, maximum plasma concentration, and anti-FIIa activity (p < 0.05). Moreover, we identified 30 new potential SNPs of 13 reported candidate genes (ABCB1, ABCC2, ABCG2, CYP2B6, CYP1A2, CYP2C19, CYP3A5, CES1, SLCO1B1, SLC22A1, UGT1A1, UGT1A9, and UGT2B7) that were associated with drug metabolism.

Conclusion: Genetic variations were indeed found to impact dabigatran metabolism in a population of healthy Chinese subjects. Further research is needed to explore the more detailed functions of these SNPs. Additionally, our results should be verified in studies that use larger sample sizes and investigate other ethnicities.

Biopharmaceutics considerations for direct oral anticoagulants

Vitamin K antagonists (VKA) and direct oral anticoagulants (DOACs) have been clinically used in the treatment of coagulation disorders. There are four DOACs approved since 2010 (dabigatran etexilate, rivaroxaban, apixaban, and edoxaban), and they were designed to overcome the practical limitations of VKA. This review summarized biopharmaceutics considerations about DOACs, which are critically discussed, applying risk analyses to subside the further classification of these drugs according to the Biopharmaceutics Classification System (BCS). These discussions included data compiled about physicochemical properties, equilibrium solubility, permeability, and drug dissolution of DOACs. From the biopharmaceutics characteristics is possible to identify critical variables related to the absorption process, which can help in the design of new formulations. The data were compared with the criteria recommended by regulatory agencies for the biopharmaceutics classification according to the BCS. From that, these data may be used to discuss the approval of generic medicines by the BCS-based biowaiver, and the clinical risks arising from novel formulations with DOACs. However, although there are indications of biopharmaceutics classifications for DOACs, conclusive information to classify these compounds according to the BCS is lacking, requiring more experimental studies to achieve this aim. Conclusive information is essential for a safe decision about the biowaiver, as well as to guide the development of new formulations containing the DOACs.

Monolayer platform using human biopsy-derived duodenal organoids for pharmaceutical research

The human small intestine is the key organ for absorption, metabolism, and excretion of orally administered drugs. To preclinically predict these reactions in drug discovery research, a cell model that can precisely recapitulate the in vivo human intestinal monolayer is desired. In this study, we developed a monolayer platform using human biopsy-derived duodenal organoids for application to pharmacokinetic studies. The human duodenal organoid-derived monolayer was prepared by a simple method in 3-8 days. It consisted of polarized absorptive cells and had tight junctions. It showed much higher cytochrome P450 (CYP)3A4 and carboxylesterase (CES)2 activities than did the existing models (Caco-2 cells). It also showed efflux activity of P-glycoprotein (P-gp) and inducibility of CYP3A4. Finally, its gene expression profile was closer to the adult human duodenum, compared to the profile of Caco-2 cells. Based on these findings, this monolayer assay system using biopsy-derived human intestinal organoids is likely to be widely adopted.

Reduced physiologically-based pharmacokinetic model of dabigatran etexilate-dabigatran and its application for prediction of intestinal P-gp-mediated drug-drug interactions

BACKGROUND

Dabigatran etexilate (DABE) has been suggested as a clinical probe for intestinal P-glycoprotein (P-gp)-mediated drug-drug interaction (DDI) studies and, as an alternative to digoxin. Clinical DDI data with various P-gp inhibitors demonstrated a dose-dependent inhibition of P-gp with DABE. The aims of this study were to develop a joint DABE (prodrug)-dabigatran reduced physiologically-based-pharmacokinetic (PBPK) model and to evaluate its ability to predict differences in P-gp DDI magnitude between a microdose and a therapeutic dose of DABE.

METHODS

A joint DABE-dabigatran PBPK model was developed with a mechanistic intestinal model accounting for the regional P-gp distribution in the gastrointestinal tract. Model input parameters were estimated using DABE and dabigatran pharmacokinetic (PK) clinical data obtained after administration of DABE alone or with a strong P-gp inhibitor, itraconazole, and over a wide range of DABE doses (from 375 µg to 400 mg). Subsequently, the model was used to predict extent of DDI with additional P-gp inhibitors and with different DABE doses.

RESULTS

The reduced DABE-dabigatran PBPK model successfully described plasma concentrations of both prodrug and metabolite following administration of DABE at different dose levels and when co-administered with itraconazole. The model was able to capture the dose dependency in P-gp mediated DDI. Predicted magnitude of itraconazole P-gp DDI was higher at the microdose (predicted vs. observed median fold-increase in AUC_+inh/AUC_control (min-max) = 5.88 (4.29-7.93) vs. 6.92 (4.96-9.66) ) compared to the therapeutic dose (predicted median fold-increase in AUC_+inh/AUC_control = 3.48 (2.37-4.84) ). In addition, the reduced DABE-dabigatran PBPK model predicted successfully the extent of DDI with verapamil and clarithromycin as P-gp inhibitors. Model-based simulations of dose staggering predicted the maximum inhibition of P-gp when DABE microdose was concomitantly administered with itraconazole solution; simulations also highlighted dosing intervals required to minimise the DDI risk depending on the DABE dose administered (microdose vs. therapeutic).

CONCLUSIONS

This study provides a modelling framework for the evaluation of P-gp inhibitory potential of new molecular entities using DABE as a clinical probe. Simulations of dose staggering and regional differences in the extent of intestinal P-gp inhibition for DABE microdose and therapeutic dose provide model-based guidance for design of prospective clinical P-gp DDI studies.

Drug Disposition in the Lower Gastrointestinal Tract: Targeting and Monitoring

The increasing prevalence of colonic diseases calls for a better understanding of the various colonic drug absorption barriers of colon-targeted formulations, and for reliable in vitro tools that accurately predict local drug disposition. In vivo relevant incubation conditions have been shown to better capture the composition of the limited colonic fluid and have resulted in relevant degradation and dissolution kinetics of drugs and formulations. Furthermore, drug hurdles such as efflux transporters and metabolising enzymes, and the presence of mucus and microbiome are slowly integrated into drug stability- and permeation assays. Traditionally, the well characterized Caco-2 cell line and the Ussing chamber technique are used to assess the absorption characteristics of small drug molecules. Recently, various stem cell-derived intestinal systems have emerged, closely mimicking epithelial physiology. Models that can assess microbiome-mediated drug metabolism or enable coculturing of gut microbiome with epithelial cells are also increasingly explored. Here we provide a comprehensive overview of the colonic physiology in relation to drug absorption, and review colon-targeting formulation strategies and in vitro tools to characterize colonic drug disposition.

Pharmacogenetics of Direct Oral Anticoagulants: A Systematic Review

Dabigatran, rivaroxaban, apixaban, edoxaban, and betrixaban are direct oral anticoagulants (DOACs). Their inter-individual variability in pharmacodynamics and pharmacokinetics (transport and metabolism) is high, and could result from genetic polymorphisms. As recommended by the French Network of Pharmacogenetics (RNPGx), the management of some treatments in cardiovascular diseases (as antiplatelet agents, oral vitamin K antagonists, and statins) can rely on genetic testing in order to improve healthcare by reducing therapeutic resistance or toxicity. This paper is a review of association studies between single nucleotide polymorphisms (SNPs) and systemic exposure variation of DOACs. Most of the results presented here have a lot to do with some SNPs of CES1 (rs2244613, rs8192935, and rs71647871) and ABCB1 (rs1128503, rs2032582, rs1045642, and rs4148738) genes, and dabigatran, rivaroxaban, and apixaban. Regarding edoxaban and betrixaban, as well as SNPs in the CYP3A4 and CYP3A5 genes, literature is scarce, and further studies are needed.

Evaluation of In Vitro Models for Assessment of Human Intestinal Metabolism in Drug Discovery

Although intestinal metabolism plays an important role in drug disposition, early predictions of human outcomes are challenging, in part because of limitations of available in vitro models. To address this, we have evaluated three in vitro models of human intestine (microsomes, permeabilized enterocytes, and cryopreserved intestinal mucosal epithelium) as tools to assess intestinal metabolism and estimate the fraction escaping gut metabolism (f g) in drug discovery. The models were tested with a chemically diverse set of 32 compounds, including substrates for oxidoreductive, hydrolytic, and conjugative enzymes. Liquid chromatography-high-resolution mass spectrometry was used to quantify substrate disappearance [intrinsic clearance (CLint)] and qualify metabolite formation (quantitative-qualitative bioanalysis). Fraction unbound in the incubation (f u,inc) was determined by rapid equilibrium dialysis. Measured in vitro results (CLint and f u,inc) were supplemented with literature data [passive Caco-2 apical to basolateral permeability, enterocyte blood flow, and intestinal surface area (A)] and combined using a midazolam-calibrated Q gut model to predict human f g values. All three models showed reliable CYP and UDP-glucuronosyltransferase activities, but enterocytes and mucosa may offer advantages for low-clearance compounds and alternative pathways (e.g., sulfation, hydrolases, and flavin-containing monooxigenases). Early predictions of human f g values were acceptable for the high-f g compounds (arbitrarily f g > 0.7). However, predictions of low- and moderate-f g values (arbitrarily f g < 0.7) remain challenging, indicating that further evaluation is needed (e.g., saturation effects and impact of transporters) but not immediate compound avoidance. Results suggest that tested models offer an additional value in drug discovery, especially for drug design and chemotype evaluation. SIGNIFICANCE STATEMENT: We found that cellular models of the human gut (permeabilized enterocytes and cryopreserved intestinal mucosa) offer an alternative to and potential advantage over intestinal microsomes in studies of drug metabolism, particularly for low-clearance compounds and alternative pathways (e.g., sulfation, hydrolases, and flavin-containing monooxigenases). The predictivity of human fraction escaping gut metabolism for common CYP and UDP-glucuronosyltransferase substrates based on the Q gut model is still limited, however, and appropriate further evaluation is recommended.

A composite nanocarrier to inhibit precipitation of the weakly basic drug in the gastrointestinal tract

For weakly basic drugs, the sharp decrease of drug solubility and the following drug precipitation after drugs transferring from the gastric fluid to the intestinal fluid in the gastrointestinal (GI) tract is a main reason for the poor oral bioavailability of drugs. Here, an anticoagulant dabigatran etexilate (DE) was used as a model drug, and a composite nanocarrier system of DE was developed to improve the drug dissolution by decreasing the drug leakage in the stomach and inhibiting the drug precipitation in the intestinal tract. With the encapsulation of drugs in nanocarriers, the precipitation percentage of DE in composite nanocarriers was 22.25 ± 3.88% in simulated intestinal fluid, which was far below that of the commercial formulation. Moreover, the relative bioavailability of DE-loaded composite nanocarriers (456.58%) was greatly enhanced and the peak of its activated partial thromboplastin time was also significantly prolonged (p < .01) compared with the commercial formulation, indicating that the anticoagulant effect of DE was effectively improved. Therefore, the designed composite nanocarrier system of DE presents great potentials in improving the therapeutic efficiency and expanding the clinical applications of poorly water-soluble weakly basic drugs.

In-Depth Characterization of EpiIntestinal Microtissue as a Model for Intestinal Drug Absorption and Metabolism in Human

The Caco-2 model is a well-accepted in vitro model for the estimation of fraction absorbed in human intestine. Due to the lack of cytochrome P450 3A4 (CYP3A4) activities, Caco-2 model is not suitable for the investigation of intestinal first-pass metabolism. The purpose of this study is to evaluate a new human intestine model, EpiIntestinal microtissues, as a tool for the prediction of oral absorption and metabolism of drugs in human intestine. The activities of relevant drug transporters and drug metabolizing enzymes, including MDR1 P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), CYP3A4, CYP2J2, UDP-glucuronosyltransferases (UGT), carboxylesterases (CES), etc., were detected in functional assays with selective substrates and inhibitors. Compared to Caco-2, EpiIntestinal microtissues proved to be a more holistic model for the investigation of drug absorption and metabolism in human gastrointestinal tract.

Drug-Drug Interactions with Direct Oral Anticoagulants

A large body of evidence suggests that not only direct anticoagulant effects but also major bleeding events and stroke prevention depend on plasma concentrations of direct oral anticoagulants (DOACs). Concomitant drugs that cause drug–drug interactions (DDIs) alter DOAC exposure by increasing or decreasing DOAC bioavailability and/or clearance; hence, they might affect the efficacy and safety of DOAC therapy. Patients with renal impairment already receive smaller DOAC maintenance doses because avoidance of elevated DOAC exposure might prevent serious bleeding events. For other causes of increased exposure such as DDIs, management is often less well-defined. Considering that DOAC patients are often older and have multiple co-morbidities, polypharmacy is highly prevalent. However, the effect of multiple drugs on DOAC exposure, and especially the impact of DDIs when concurring with drug–disease interactions as observed in renal impairment, has not been thoroughly elucidated. In order to provide effective and safe anticoagulation with DOACs, understanding the mechanisms and magnitude of DDIs appears relevant. Instead of avoiding drug combinations with DOACs, more DDI trials should be conducted and new strategies such as dose adjustments based on therapeutic drug monitoring should be investigated. However, dose adjustments based on concentration measurements cannot currently be recommended because evidence-based data are missing.

Renal Excretion of Dabigatran: The Potential Role of Multidrug and Toxin Extrusion (MATE) Proteins

Following oral administration, dabigatran etexilate (DABE) is rapidly hydrolyzed to its active form, dabigatran. DABE, but not dabigatran, presents as a P-glycoprotein (P-gp) substrate and has increasingly been used as a probe drug. Therefore, although dosed as DABE, a P-gp drug-drug interaction (DDI) is reported as a dabigatran plasma concentration ratio (perpetrator versus placebo). Because the majority of a DABE dose (80 to 85%) is recovered in urine as unchanged dabigatran (renal active secretion is ∼25% of total clearance), dabigatran was evaluated in vitro as a substrate of various human renal transporters. Active (pyrimethamine-sensitive) dabigatran uptake was observed with human embryonic kidney (HEK) 293 cells expressing multidrug and toxin extrusion protein 1 (MATE1) and 2K (MATE2K), with Michaelis-Menten constant (K_m) values of 4.0 and 8.0 μM, respectively. By comparison, no uptake of 2 μM dabigatran (versus mock-transfected HEK293 cells) was evident with HEK293 cells transfected with organic cation transporters (OCT1 and OCT2) and organic anion transporters (OAT1, 2, 3, and 4). The efflux ratios of dabigatran across P-gp- and BCRP (breast cancer resistance protein)-MDCK (Madin-Darby canine kidney) cell monolayers were 1.5 and 2.0 (versus mock-MDCK cell monolayers), suggesting dabigatran is a relatively poor P-gp and BCRP substrate. Three of five drugs (verapamil, ketoconazole, and quinidine) known to interact clinically with dabigatran, as P-gp inhibitors, presented as MATE inhibitors in vitro (IC₅₀ = 1.0 to 25.2 μM). Taken together, although no basolateral transporter was identified for dabigatran, the results suggest that apical MATE1 and MATE2K could play an important role in its renal clearance. MATE-mediated renal secretion of dabigatran needs to be considered when interpreting the results of P-gp DDI studies following DABE administration.

Application of Intestinal Epithelial Cells Differentiated from Human Induced Pluripotent Stem Cells for Studies of Prodrug Hydrolysis and Drug Absorption in the Small Intestine

Cell models to investigate intestinal absorption functions, such as those of transporters and metabolic enzymes, are essential for oral drug discovery and development. The purpose of this study was to generate intestinal epithelial cells from human induced pluripotent stem cells (hiPSC-IECs) and then clarify whether the functions of hydrolase and transporters in them reflect oral drug absorption in the small intestine. The hiPSC-IECs showed the transport activities of P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and peptide transporter 1 (PEPT1), revealed by using their probe substrates ([3H]digoxin, sulfasalazine, and [14C]glycylsarcosine), and the metabolic activities of CYP3A4, CES2, and CES1, which were clarified using their probe substrates (midazolam, irinotecan, and temocapril). The intrinsic clearance by hydrolysis of six ester prodrugs into the active form in hiPSC-IECs was correlated with the plasma exposure (Cmax , AUC, and bioavailability) of the active form after oral administration of these prodrugs to rats. Also, the permeability coefficients of 14 drugs, containing two substrates of P-gp (doxorubicin and [3H]digoxin), one substrate of BCRP (sulfasalazine), and 11 nonsubstrates of transporters (ganciclovir, [14C]mannitol, famotidine, sulpiride, atenolol, furosemide, ranitidine, hydrochlorothiazide, acetaminophen, propranolol, and antipyrine) in hiPSC-IECs were correlated with their values of the fraction of intestinal absorption (Fa) in human clinical studies. These findings suggest that hiPSC-IECs would be a useful cell model to investigate the hydrolysis of ester prodrugs and to predict drug absorption in the small intestine.

BCRP/ABCG2 and high-alert medications: Biochemical, pharmacokinetic, pharmacogenetic, and clinical implications

The human breast cancer resistance protein (BCRP/ABCG2) is an ATP-binding cassette efflux transporter that uses ATP hydrolysis to expel xenobiotics from cells, including anti-cancer medications. It is expressed in the gastrointestinal tract, liver, kidney, and brain endothelium. Thus, ABCG2 functions as a tissue barrier to drug transport that strongly influences the pharmacokinetics of substrate medications. Genetic polymorphisms of ABCG2 are closely related to inter-individual variations in therapeutic performance. The common single nucleotide polymorphism c.421C>A, p.Q141K reduces cell surface expression of ABCG2 protein, resulting in lower efflux of substrates. Consequently, a higher plasma concentration of substrate is observed in patients carrying an ABCG2 c.421C>A allele. Detailed pharmacokinetic analyses have revealed that altered intestinal absorption is responsible for the distinct pharmacokinetics of ABCG2 substrates in genetic carriers of the ABCG2 c.421C>A polymorphism. Recent studies have focused on the high-alert medications among ABCG2 substrates (defined as those with high risk of adverse events), such as tyrosine kinase inhibitors (TKIs) and direct oral anti-coagulants (DOACs). For these high-alert medications, inter-individual variation may be closely related to the severity of side effects. In addition, ethnic differences in the frequency of ABCG2 c.421C>A have been reported, with markedly higher frequency in East Asian (∼30-60%) than Caucasian and African-American populations (∼5-10%). Therefore, ABCG2 polymorphisms must be considered not only in the drug development phase, but also in clinical practice. In the present review, we provide an update of basic and clinical knowledge on genetic polymorphisms of ABCG2.

Clinical Implications of P-Glycoprotein Modulation in Drug-Drug Interactions

Drug-drug interactions (DDIs) occur commonly and may lead to severe adverse drug reactions if not handled appropriately. Considerable information to support clinical decision making regarding potential DDIs is available in the literature and through various systems providing electronic decision support for healthcare providers. The challenge for the prescribing physician lies in sorting out the evidence and identifying those drugs for which potential interactions are likely to become clinically manifest. P-glycoprotein (P-gp) is a drug transporting protein that is found in the plasma membranes in cells of barrier and elimination organs, and plays a role in drug absorption and excretion. Increasingly, P-gp has been acknowledged as an important player in potential DDIs and a growing body of information on the role of this transporter in DDIs has become available from research and from the drug approval process. This has led to a clear need for a comprehensive review of P-gp-mediated DDIs with a focus on highlighting the drugs that are likely to lead to clinically relevant DDIs. The objective of this review is to provide information for identifying and interpreting evidence of P-gp-mediated DDIs and to suggest a classification for individual drugs based on both in vitro and in vivo evidence (substrates, inhibitors and inducers). Further, various ways of handling potential DDIs in clinical practice are described and exemplified in relation to drugs interfering with P-gp.

Improved oral bioavailability and therapeutic efficacy of dabigatran etexilate via Soluplus-TPGS binary mixed micelles system

The clinical use of dabigatran etexilate (DABE) is limited by its poor absorption and relatively low bioavailability. Our study aimed to explore the potential of a mixed micelle system composed of Soluplus^® and D-alpha tocopheryl polyethylene glycol 1000 succinate (TPGS) to improve the oral absorption and bioavailability of DBAE. DBAE was first encapsulated into Soluplus/TPGS mixed micelles by a simple thin film hydration method. The DBAE loaded micelles displayed an average size distribution of around 83.13 nm. The cellular uptake of DBAE loaded micelles in Caco-2 cell monolayer was significantly enhanced by 2-2.6 fold over time as compared with DBAE suspension. Both lipid raft/caveolae and macropinocytosis-mediated the cell uptake of DBAE loaded micelles through P-glycoprotein (P-gp)-independent pathway. Compared with the DBAE suspension, the intestinal absorption of DBAE from DBAE mixed micelles in rats was significantly improved by 8 and 5-fold in ileum at 2 h and 4 h, respectively. Moreover, DBAE mixed micelles were absorbed into systemic circulation via both portal vein and lymphatic pathway. The oral bioavailability of DBAE mixed micelles in rats was 3.37 fold higher than that of DBAE suspension. DBAE mixed micelles exhibited a comparable anti-thrombolytic activity with a thrombosis inhibition rate of 63.18% compared with DBAE suspension in vivo. Thus, our study provides a promising drug delivery system to enhance the oral bioavailability and therapeutic efficacy of DBAE.

Association of Oseltamivir Activation with Gender and Carboxylesterase 1 Genetic Polymorphisms

Oseltamivir, an inactive anti-influenza virus prodrug, is activated (hydrolysed) in vivo by carboxylesterase 1 (CES1) to its active metabolite oseltamivir carboxylate. CES1 functions are significantly associated with certain CES1 genetic variants and some non-genetic factors. The purpose of this study was to investigate the effect of gender and several CES1 genetic polymorphisms on oseltamivir activation using a large set of individual human liver samples. CES1-mediated oseltamivir hydrolysis and CES1 genotypes, including the G143E (rs71647871), rs2244613, rs8192935, the -816A>C (rs3785161) and the CES1P1/CES1P1VAR, were determined in 104 individual human livers. The results showed that hepatic CES1 protein expression in females was 17.3% higher than that in males (p = 0.039), while oseltamivir activation rate in the livers from female donors was 27.8% higher than that from males (p = 0.076). As for CES1 genetic polymorphisms, neither CES1 protein expression nor CES1 activity on oseltamivir activation was significantly associated with the rs2244613, rs8192935, -816A>C or CES1P1/CES1P1VAR genotypes. However, oseltamivir hydrolysis in the livers with the genotype 143G/E was approximately 40% of that with the 143G/G genotype (0.7 ± 0.2 versus 1.8 ± 1.1 nmole/mg protein/min, p = 0.005). In summary, the results suggest that hepatic oseltamivir activation appears to be more efficient in females than that in males, and the activation can be impaired by functional CES1 variants, such as the G143E. However, clinical implication of CES1 gender differences and pharmacogenetics in oseltamivir pharmacotherapy warrants further investigations.

Pharmacogenetics in Oral Antithrombotic Therapy

Certain antithrombotic drugs exhibit high patient-to-patient variability that significantly impacts the safety and efficacy of therapy. Pharmacogenetics offers the possibility of tailoring drug treatment to patients based on individual genotypes, and this type of testing has been recommended for 2 oral antithrombotic agents, warfarin and clopidogrel, to influence use and guide dosing. Limited studies have identified polymorphisms that affect the metabolism and activity of newer oral antithrombotic drugs, without clear evidence of the clinical relevance of such polymorphisms. This article provides an overview of the current status of pharmacogenetics in oral antithrombotic therapy.

Antithrombotic triple therapy and coagulation activation at the site of thrombus formation: a randomized trial in healthy subjects

BACKGROUND

Patients with acute coronary syndrome and concomitant atrial fibrillation may require antithrombotic triple therapy but clinical evidence of safety and efficacy is poor. We have therefore studied the combination of different antithrombotic medicines for coagulation activation in an in vivo model in the skin microvasculature.

METHODS AND RESULTS

Platelet activation (β-thromboglobulin [β-TG]) and thrombin generation (prothrombin fragment 1 + 2 [F1+2 ], thrombin-antithrombin complex [TAT]) were studied in an open-label, randomized, parallel group trial in 60 healthy male subjects (n = 20 per group) who received ticagrelor and acetylsalicylic acid (ASA) in combination with dabigatran (150 mg bid), rivaroxaban (20 mg od) or phenprocoumon (INR 2.0-3.0). Coagulation biomarkers in shed blood were assessed at 3 h after monotherapy with the medicines under study, at 3 h after triple therapy dosing and at steady state trough conditions. Single doses of ticagrelor, dabigatran or rivaroxaban caused comparable decreases in shed blood β-TG and were more pronounced than phenprocoumon at an INR of 2.0-3.0. In contrast, thrombin generation was more affected by rivaroxaban and phenprocoumon than by dabigatran. During triple therapy a similarly sustained inhibition of platelet activation and thrombin generation with a maximum decrease of β-TG, F1+2 and TAT at 3 h post-dosing was noted, which remained below pre-dose levels at trough steady state.

CONCLUSION

A triple therapy at steady state with ticagrelor plus ASA in combination with dabigatran or rivaroxaban is as effective as a combination with phenprocoumon for platelet activation and thrombin generation in vivo.

Brain penetration of WEB 2086 (Apafant) and dantrolene in Mdr1a (P-glycoprotein) and Bcrp knockout rats

Transporter gene knockout rat models are attracting increasing interest for mechanistic studies of new drugs as transporter substrates or inhibitors in vivo. However, limited data are available on the functional validity of such models at the blood-brain barrier. Therefore, the present study evaluated Mdr1a [P-glycoprotein (P-gp)], Bcrp, and combined Mdr1a/Bcrp knockout rat strains for the influence of P-gp and breast cancer resistance protein (BCRP) transport proteins on brain penetration of the selective test substrates [(14)C]WEB 2086 (3-[4-(2-chlorophenyl)-9-methyl-6H-thieno[3,2-f][1,2,4]triazolo-[4,3-a][1,4]-diazepin-2-yl]-1-(4-morpholinyl)-1-propanon) for P-gp and dantrolene for BCRP. Brain-to-plasma concentration ratios (BPR) were measured after intravenous coinfusions of 5.5 µmol/kg per hour [(14)C]WEB 2086 and 2 µmol/kg per hour dantrolene for 2 hours in groups of knockout or wild-type rats. Compared with wild-type controls, mean BPR of [(14)C]WEB 2086 increased 8-fold in Mdr1a knockouts, 9.5-fold in double Mdr1a/Bcrp knockouts, and 7.3-fold in zosuquidar-treated wild-type rats, but was unchanged in Bcrp knockout rats. Mean BPR of dantrolene increased 3.3-fold in Bcrp knockouts and 3.9-fold in double Mdr1a/Bcrp knockouts compared with wild type, but was unchanged in the Mdr1a knockouts. The human intestinal CaCo-2 cell bidirectional transport system in vitro confirmed the in vivo finding that [(14)C]WEB 2086 is a substrate of P-gp but not of BCRP. Therefore, Mdr1a, Bcrp, and combined Mdr1a/Bcrp knockout rats provide functional absence of these efflux transporters at the blood-brain barrier and are a suitable model for mechanistic studies on the brain penetration of drug candidates.

Calibration of in vitro multidrug resistance protein 1 substrate and inhibition assays as a basis to support the prediction of clinically relevant interactions in vivo

The multidrug resistance protein 1 (MDR1) is known to limit brain penetration of drugs and play a key role in drug-drug interactions (DDIs). Theoretical cut-offs from regulatory guidelines are used to extrapolate MDR1 interactions from in vitro to in vivo. However, these cut-offs do not account for interlaboratory variability. Our aim was to calibrate our experimental system to allow better in vivo predictions. We selected 166 central nervous system (CNS) and non-CNS drugs to calibrate the MDR1 transport screening assay using Lewis lung cancer porcine kidney 1 epithelial cells overexpressing MDR1 (L-MDR1). A threshold efflux ratio (ER) of 2 was established as one parameter to assess brain penetration in lead optimization. The inhibitory potential of 57 molecules was evaluated using IC50 values based on the digoxin ER-IC50(ER)-or apparent permeability-IC50(Papp)-in L-MDR1 cells. Published clinical data for 68 DDIs involving digoxin as the victim drug were collected. DDI risk assessments were based on intestinal concentrations ([I2]) as well as unbound [I1u] and total plasma [I1T] concentrations. A receiver operating characteristic analysis identified an [I2]/IC50(ER) of 6.5 as the best predictor of a potential interaction with digoxin in patients. The model was further evaluated with a test set of 11 digoxin DDIs and 16 nondigoxin DDIs, resulting in only one false negative for each test set, no false positives among the digoxin DDIs, and two among the nondigoxin DDIs. Future refinements might include using cerebrospinal fluid to unbound plasma concentration ratios rather than therapeutic class, better estimation of [I2], and dynamic modeling of MDR1-mediated DDIs.

In vitro predictability of drug-drug interaction likelihood of P-glycoprotein-mediated efflux of dabigatran etexilate based on [I]2/IC50 threshold

Dabigatran etexilate, an oral, reversible, competitive, and direct thrombin inhibitor, is an in vitro and in vivo substrate of P-glycoprotein (P-gp). Dabigatran etexilate was proposed as an in vivo probe substrate for intestinal P-gp inhibition in a recent guidance on drug-drug interactions (DDI) from the European Medicines Agency (EMA) and the Food and Drug Administration (FDA). We conducted transcellular transport studies across Caco-2 cell monolayers with dabigatran etexilate in the presence of various P-gp inhibitors to examine how well in vitro IC50 data, in combination with mathematical equations provided by regulatory guidances, predict DDI likelihood. From a set of potential P-gp inhibitors, clarithromycin, cyclosporin A, itraconazole, ketoconazole, quinidine, and ritonavir inhibited P-gp-mediated transport of dabigatran etexilate over a concentration range that may hypothetically occur in the intestine. IC50 values of P-gp inhibitors for dabigatran etexilate transport were comparable to those of digoxin, a well established in vitro and in vivo P-gp substrate. However, IC50 values varied depending whether they were calculated from efflux ratios or permeability coefficients. Prediction of DDI likelihood of P-gp inhibitors using IC50 values, the hypothetical concentration of P-gp inhibitors, and the cut-off value recommended by both the FDA and EMA were in line with the DDI occurrence in clinical studies with dabigatran etexilate. However, it has to be kept in mind that validity of the cut-off criteria proposed by the FDA and EMA depends on in vitro experimental systems and the IC50-calculation methods that are employed, as IC50 values are substantially influenced by these factors.