The Intestinal First-pass Metabolism of Substrates of CYP3A4 and P-glycoprotei—Quantitative Analysis Based on Information from the Literature

Clinical Trial Data-Driven Risk Assessment of Drug-Drug Interactions: A Rapid and Accurate Decision-Making Tool

BACKGROUND

In clinical practice, the vast array of potential drug combinations necessitates swift and accurate assessments of pharmacokinetic drug-drug interactions (DDIs), along with recommendations for adjustments. Current methodologies for clinical DDI evaluations primarily rely on basic extrapolations from clinical trial data. However, these methods are limited in accuracy owing to their lack of a comprehensive consideration of various critical factors, including the inhibitory potency, dosage, and type of the inhibitor, as well as the metabolic fraction and intestinal availability of the substrate.

OBJECTIVE

This study aims to propose an efficient and accurate clinical pharmacokinetic-mediated DDI assessment tool, which comprehensively considers the effects of inhibitory potency and dosage of inhibitors, intestinal availability and fraction metabolized of substrates on DDI outcomes.

METHODS

This study focuses on DDIs caused by cytochrome P450 3A4 enzyme inhibition, utilizing extensive clinical trial data to establish a methodology to calculate the metabolic fraction and intestinal availability for substrates, as well as the concentration and inhibitory potency for inhibitors ( K i ork inact / K I ). These parameters were then used to predict the outcomes of DDIs involving 33 substrates and 20 inhibitors. We also defined the risk index for substrates and the potency index for inhibitors to establish a clinical DDI risk scale. The training set for parameter calculation consisted of 73 clinical trials. The validation set comprised 89 clinical DDI trials involving 53 drugs. which was used to evaluate the reliability of in vivo values of K i andk inact / K I , the accuracy of DDI predictions, and the false-negative rate of risk scale.

RESULTS

First, the reliability of the in vivo K i andk inact / K I values calculated in this study was assessed using a basic static model. Compared with values obtained from other methods, this study values showed a lower geometric mean fold error and root mean square error. Additionally, incorporating these values into the physiologically based pharmacokinetic-DDI model facilitated a good fitting of the C-t curves when the substrate's metabolic enzymes are inhibited. Second, area under the curve ratio predictions of studied drugs were within a 1.5 × margin of error in 81% of cases compared with clinical observations in the validation set. Last, the clinical DDI risk scale developed in this study predicted the actual risks in the validation set with only a 5.6% incidence of serious false negatives.

CONCLUSIONS

This study offers a rapid and accurate approach for assessing the risk of pharmacokinetic-mediated DDIs in clinical practice, providing a foundation for rational combination drug use and dosage adjustments.

Quantitative analysis of the impact of membrane permeability on intestinal first-pass metabolism of CYP3A substrates

The aim of this study was firstly to investigate the effect of membrane permeability on the intestinal availability (Fg ) of 10 cytochrome P450 3A4 substrates with differing permeability (Papp ) and metabolic activity (CLint ) using Madin-Darby canine kidney II (MDCKII) cells expressing human CYP3A4 (MDCKII/CYP3A4 cells), and secondly to confirm the essential factors by simulations. A membrane permeation assay using MDCKII/CYP3A4 cells showed a significant correlation between human intestinal extraction ratio (ER) (Eg (=1 - Fg )) and in vitro cellular ER (r = 0.834). This relationship afforded better predictability of Eg values than the relationship between Eg and CLint,HIM values obtained from human intestinal microsomes (r = 0.598). An even stronger correlation was observed between 1 - Fa ·Fg and ER (r = 0.874). Simulation with a cellular kinetic model indicated that ER is sensitive to changes of PSpassive and CLint values, but not to the intracellular unbound fraction (fu,cell ) or P-gp-mediated efflux (PSP - gp ). It may be concluded that, based on the concentration-time profile of drugs in epithelial cells, transmembrane permeability influences Fg (or ER) and drug exposure time to metabolizing enzymes for P450 substrate.

Physiologically based pharmacokinetic model analysis of the inhibitory effect of vonoprazan on the metabolic activation of proguanil

We previously reported that repeated oral administration of vonoprazan (VPZ) followed by oral administration of proguanil (PG) in healthy adults increased blood concentration of PG and decreased blood concentration of its metabolite cycloguanil (CG) compared with administration of PG alone. In this study, we investigated whether this interaction can be quantitatively explained by VPZ inhibition of PG metabolism. In an in vitro study using human liver microsomes, VPZ inhibited CG formation from PG in a concentration-dependent manner, and the inhibition was enhanced depending on preincubation time. Then, a physiologically based pharmacokinetic (PBPK) model analysis was performed incorporating the obtained inhibition parameters. By fitting the blood concentration profiles of VPZ and PG/CG after VPZ and PG were orally administered alone to our PBPK model, parameters were obtained which can reproduce their concentration profiles. In contrast, when the VPZ inhibition parameters for CG formation from the in vitro study were incorporated, the predicted blood PG and CG concentrations were unchanged; the apparent dissociation constant had to be set to about 1/23 of the obtained in vitro value to reproduce the observed interaction. Further comprehensive evaluation is required, including the possibility that mechanisms other than metabolic inhibition may be involved.

Challenges and Opportunities for In Vitro-In Vivo Extrapolation of Aldehyde Oxidase-Mediated Clearance: Toward a Roadmap for Quantitative Translation

Underestimation of aldehyde oxidase (AO)-mediated clearance by current in vitro assays leads to uncertainty in human dose projections, thereby reducing the likelihood of success in drug development. In the present study we first evaluated the current drug development practices for AO substrates. Next, the overall predictive performance of in vitro-in vivo extrapolation of unbound hepatic intrinsic clearance (CLint,u) and unbound hepatic intrinsic clearance by AO (CLint,u,AO) was assessed using a comprehensive literature database of in vitro (human cytosol/S9/hepatocytes) and in vivo (intravenous/oral) data collated for 22 AO substrates (total of 100 datapoints from multiple studies). Correction for unbound fraction in the incubation was done by experimental data or in silico predictions. The fraction metabolized by AO (fmAO) determined via in vitro/in vivo approaches was found to be highly variable. The geometric mean fold errors (gmfe) for scaled CLint,u (mL/min/kg) were 10.4 for human hepatocytes, 5.6 for human liver cytosols, and 5.0 for human liver S9, respectively. Application of these gmfe's as empirical scaling factors improved predictions (45%-57% within twofold of observed) compared with no correction (11%-27% within twofold), with the scaling factors qualified by leave-one-out cross-validation. A road map for quantitative translation was then proposed following a critical evaluation on the in vitro and clinical methodology to estimate in vivo fmAO In conclusion, the study provides the most robust system-specific empirical scaling factors to date as a pragmatic approach for the prediction of in vivo CLint,u,AO in the early stages of drug development. SIGNIFICANCE STATEMENT: Confidence remains low when predicting in vivo clearance of AO substrates using in vitro systems, leading to de-prioritization of AO substrates from the drug development pipeline to mitigate risk of unexpected and costly in vivo impact. The current study establishes a set of empirical scaling factors as a pragmatic tool to improve predictability of in vivo AO clearance. Developing clinical pharmacology strategies for AO substrates by utilizing mass balance/clinical drug-drug interaction data will help build confidence in fmAO.

Quantitative Prediction of Intestinal Absorption of Drugs from In Vitro Study: Utilization of Differentiated Intestinal Epithelial Cells Derived from Intestinal Stem Cells at Crypts

Prediction of intestinal absorption of drugs in humans is one of the critical elements in the development process for oral drugs. However, it remains challenging, because intestinal absorption of drugs is influenced by multiple factors, including the function of various metabolic enzymes and transporters, and large species differences in drug bioavailability hinder the prediction of human bioavailability directly from in vivo animal experiments. For the screening of intestinal absorption properties of drugs, a transcellular transport assay with Caco-2 cells is still routinely used by pharmaceutical companies because of its convenience, but the predictability of the fraction of the oral dose that goes to the portal vein of metabolic enzyme/transporter substrate drugs was not always good because the cellular expression of metabolic enzymes and transporters is different from that in the human intestine. Recently, various novel in vitro experimental systems have been proposed such as the use of human-derived intestinal samples, transcellular transport assay with induced pluripotent stem-derived enterocyte-like cells, or differentiated intestinal epithelial cells derived from intestinal stem cells at crypts. Crypt-derived differentiated epithelial cells have an excellent potential to characterize species differences and regional differences in intestinal absorption of drugs because a unified protocol can be used for the proliferation of intestinal stem cells and their differentiation into intestinal absorptive epithelial cells regardless of the animal species and the gene expression pattern of differentiated cells is maintained at the site of original crypts. The advantages and disadvantages of novel in vitro experimental systems for characterizing intestinal absorption of drugs are also discussed. SIGNIFICANCE STATEMENT: Among novel in vitro tools for the prediction of human intestinal absorption of drugs, crypt-derived differentiated epithelial cells have many advantages. Cultured intestinal stem cells are rapidly proliferated and easily differentiated into intestinal absorptive epithelial cells simply by changing the culture media. A unified protocol can be used for the establishment of intestinal stem cell culture from preclinical species and humans. Region-specific gene expression at the collection site of crypts can be reproduced in differentiated cells.

Identification of the perpetrator imperatorin in Xin-yi-san-theophylline interaction: observed and predicted herb-drug interaction in rats

OBJECTIVES

Theophylline is a bronchodilator with a narrow therapeutic index and primarily metabolised by cytochrome P450 (CYP) 1A2. Xin-yi-san (XYS) is a herbal formula frequently used to ameliorate nasal inflammation. This study aimed to investigate the effects of XYS and its ingredient, imperatorin, on theophylline pharmacokinetics in rats.

METHODS

The kinetics of XYS- and imperatorin-mediated inhibition of theophylline oxidation were determined. Pharmacokinetics of theophylline were analysed. Comparisons were made with the CYP1A2 inhibitor, fluvoxamine.

KEY FINDINGS

XYS extract and its ingredient, imperatorin, non-competitively inhibited theophylline oxidation. Fluvoxamine (50 and 100 mg/kg) and XYS (0.5 and 0.9 g/kg) significantly prolonged the time to reach the maximum plasma concentration (tmax) of theophylline by 3-10 fold. In a dose-dependent manner, XYS and imperatorin (0.1-10 mg/kg) treatments significantly decreased theophylline clearance by 27-33% and 19-56%, respectively. XYS (0.9 g/kg) and imperatorin (10 mg/kg) significantly prolonged theophylline elimination half-life by 29% and 142%, respectively. Compared with the increase (51-112%) in the area under curve (AUC) of theophylline by fluvoxamine, the increase (27-57%) by XYS was moderate.

CONCLUSIONS

XYS decreased theophylline clearance primarily through imperatorin-suppressed theophylline oxidation. Further human studies are essential for the dose adjustment in the co-medication regimen.

Integrated Use of In Vitro and In Vivo Information for Comprehensive Prediction of Drug Interactions Due to Inhibition of Multiple CYP Isoenzymes

BACKGROUND

Mechanistic static pharmacokinetic (MSPK) models are simple, have fewer data requirements, and have broader applicability; however, they cannot use in vitro information and cannot distinguish the contributions of multiple cytochrome P450 (CYP) isoenzymes and the hepatic and intestinal first-pass effects appropriately. We aimed to establish a new MSPK analysis framework for the comprehensive prediction of drug interactions (DIs) to overcome these disadvantages.

METHODS

Drug interactions that occurred by inhibiting CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A in the liver and CYP3A in the intestine were simultaneously analyzed for 59 substrates and 35 inhibitors. As in vivo information, the observed changes in the area under the concentration-time curve (AUC) and elimination half-life (t1/2), hepatic availability, and urinary excretion ratio were used. As in vitro information, the fraction metabolized (fm) and the inhibition constant (Ki) were used. The contribution ratio (CR) and inhibition ratio (IR) for multiple clearance pathways and hypothetical volume (VHyp) were inferred using the Markov Chain Monte Carlo (MCMC) method.

RESULT

Using in vivo information from 239 combinations and in vitro 172 fm and 344 Ki values, changes in AUC, and t1/2 were estimated for all 2065 combinations, wherein the AUC was estimated to be more than doubled for 602 combinations. Intake-dependent selective intestinal CYP3A inhibition by grapefruit juice has been suggested. By separating the intestinal contributions, DIs after intravenous dosing were also appropriately inferred.

CONCLUSION

This framework would be a powerful tool for the reasonable management of various DIs based on all available in vitro and in vivo information.

Separate Evaluation of Fraction Absorbed and Intestinal Availability after Oral Administration of Drugs Based on the Measurement of Portal and Systemic Plasma Concentrations and Luminal Concentration

There are several experimental methods to estimate the product of the fraction absorbed (Fa) and intestinal availability (Fg) in vivo after oral administration of drugs. Metabolic enzyme inhibitors are typically used to separate Fg from Fa·Fg. Since Fa·Fg can be regarded as Fa under metabolism-inhibited conditions, Fg can be isolated by dividing Fa·Fg by Fa. However, if the inhibition of intestinal metabolism is insufficient, Fa is overestimated, which results in an underestimation of Fg compared to the actual value. In this study, to avoid this problem, an experimental method for the separate estimation of Fa and Fg in rats without utilizing metabolic enzyme inhibitors was established. Buspirone, a CYP3A substrate, and ribavirin, a substrate of purine nucleoside phosphorylase and adenosine kinase, were selected as models. Following oral administration of the drugs with fluorescein isothiocyanate dextran 4000 (FD-4, an unabsorbable marker), Fa·Fg was pharmacokinetically calculated from portal and systemic plasma concentration-time profiles of model drugs and Fa was calculated from the difference in the ileal concentration profiles of the drugs and FD-4. Fg was evaluated by dividing Fa·Fg by Fa. Following oral administration, buspirone was not detected in any segment of the small intestine, indicating that the administered buspirone was completely absorbed. In addition, buspirone was extensively metabolized in enterocytes (Fg = 20.1). Ribavirin was primarily absorbed in the upper segment of the small intestine, and 64.4% of the ribavirin was absorbed before it reached the ileum. In addition, it was revealed that ribavirin was metabolized more extensively in the intestine than in the liver. Our method may be effective in quantitatively assessing Fa and Fg in vivo, which can help in the formulation design and prediction of drug-drug interactions.

The history, mechanism, and perspectives of nirmatrelvir (PF-07321332): an orally bioavailable main protease inhibitor used in combination with ritonavir to reduce COVID-19-related hospitalizations

The rapid development of effective vaccines to combat the SARS-CoV-2 virus has been an effective counter measure to decrease hospitalization and the mortality rate in many countries. However, with the risk of mutated strains decreasing the efficacy of the vaccine, there has been an increasing demand for antivirals to treat COVID-19. While antivirals, such as remdesivir, have had some success treating COVID-19 patients in hospital settings, there is a need for orally bioavailable, cost-effective antivirals that can be administered in outpatient settings to minimize COVID-19-related hospitalizations and death. Nirmatrelvir (PF-07321332) is an orally bioavailable M^pro (also called 3CL^pro) inhibitor developed by Pfizer. It is administered in combination with ritonavir, a potent CYP3A4 inhibitor that decreases the metabolism of nirmatrelvir. This review seeks to outline the history of the rational design, the target selectivity, synthesis, drug resistance, and future perspectives of nirmatrelvir.

An oral SARS-CoV-2 Mpro inhibitor clinical candidate for the treatment of COVID-19

[Figure: see text].

Pharmacokinetics and safety of rilpivirine in healthy Japanese subjects and exploration of ethnic sensitivity of rilpivirine pharmacokinetics with physiologically based pharmacokinetic model approach

Rilpivirine is a non-nucleoside reverse transcriptase inhibitor, used for the treatment of human immunodeficiency virus type-1 infection. An open label study was conducted to investigate the pharmacokinetics (PK) and safety of a single oral dose of rilpivirine 25 mg in Japanese healthy adult subjects. No adverse events were reported. The mean C_max (144.3 ng/mL) and AUC_inf (4542 ng h/mL) in Japanese subjects were approximately 30 % higher than those reported from a similar study in Caucasian healthy subjects, whereas the median t_max and mean t_1/2 values were comparable between studies. A simple physiologically based PK model was developed to characterize the rilpivirine PK profile. The model adequately described rilpivirine PK profiles, and well-predicted drug-drug interactions. With exploration using the model, body size and CYP3A4 abundance were identified as factors which explained the observed inter-ethnic difference in rilpivirine exposure. The inter-ethnic difference in rilpivirine exposure was however considered not clinically relevant, since inter-individual variabilities of those intrinsic factors are larger than inter-ethnic ones; and the observed AUC_inf in Japanese subjects was within the range of AUC_tau associated with efficacy and safety in Phase 3 studies. This study results support the use of rilpivirine without dose modification specific to Japanese patients.

Classification of drugs for evaluating drug interaction in drug development and clinical management

During new drug development, clinical drug interaction studies are carried out in accordance with the mechanism of potential drug interactions evaluated by in vitro studies. The obtained information should be provided efficiently to medical experts through package inserts and various information materials after the drug's launch. A recently updated Japanese guideline presents general procedures that are considered scientifically valid at the present moment. In this review, we aim to highlight the viewpoints of the Japanese guideline and enumerate drugs that were involved or are anticipated to be involved in evident pharmacokinetic drug interactions and classify them by their clearance pathway and potential intensity based on systematic reviews of the literature. The classification would be informative for designing clinical studies during the development stage, and the appropriate management of drug interactions in clinical practice.

Cytochrome P450 expression, induction and activity in human induced pluripotent stem cell-derived intestinal organoids and comparison with primary human intestinal epithelial cells and Caco-2 cells

Human intestinal organoids (HIOs) are a promising in vitro model consisting of different intestinal cell types with a 3D microarchitecture resembling native tissue. In the current study, we aimed to assess the expression of the most common intestinal CYP enzymes in a human induced pluripotent stem cell (hiPSC)-derived HIO model, and the suitability of that model to study chemical-induced changes in CYP expression and activity. We compared this model with the commonly used human colonic adenocarcinoma cell line Caco-2 and with a human primary intestinal epithelial cell (IEC)-based model, closely resembling in vivo tissue. We optimized an existing protocol to differentiate hiPSCs into HIOs and demonstrated that obtained HIOs contain a polarized epithelium with tight junctions consisting of enterocytes, goblet cells, enteroendocrine cells and Paneth cells. We extensively characterized the gene expression of CYPs and activity of CYP3A4/5, indicating relatively high gene expression levels of the most important intestinal CYP enzymes in HIOs compared to the other models. Furthermore, we showed that CYP1A1 and CYP1B1 were induced by β-naphtoflavone in all three models, whereas CYP3A4 was induced by phenobarbital and rifampicin in HIOs, in the IEC-based model (although not statistically significant), but not in Caco-2 cells. Interestingly, CYP2B6 expression was not induced in any of the models by the well-known liver CYP2B6 inducer phenobarbital. In conclusion, our study indicates that hiPSC-based HIOs are a useful in vitro intestinal model to study biotransformation of chemicals in the intestine.

Quantitative Contribution of Six Major Transporters to the Hepatic Uptake of Drugs: "SLC-Phenotyping" Using Primary Human Hepatocytes

Hepatic uptake transporters [solute carriers (SLCs)], including organic anion transporting polypeptide (OATP) 1B1, OATP1B3, OATP2B1, sodium-dependent taurocholate cotransporting polypeptide (NTCP), and organic anion (OAT2) and organic cation (OCT1) transporters, play a key role in determining the systemic and liver exposure of chemically diverse drugs. Here, we established a phenotyping approach to quantify the contribution of the six SLCs, and passive diffusion, to the overall uptake using plated human hepatocytes (PHHs). First, selective inhibitor conditions were identified by screening about 20 inhibitors across the six SLCs using single-transfected human embryonic kidney 293 cells. Data implied rifamycin SV (20 µM) inhibits three OATPs, while rifampicin (5 µM) inhibits OATP1B1/1B3 only. Further, hepatitis B virus myristoylated-preS1 peptide (0.1 µM), quinidine (100 µM), and ketoprofen (100-300 µM) are relatively selective against NTCP, OCT1, and OAT2, respectively. Second, using these inhibitory conditions, the fraction transported (f_t ) by the individual SLCs was characterized for 20 substrates with PHH. Generally, extended clearance classification system class 1A/3A (e.g., warfarin) and 1B/3B compounds (e.g., statins) showed predominant OAT2 and OATP1B1/1B3 contribution, respectively. OCT1-mediated uptake was prominent for class 2/4 compounds (e.g., metformin). Third, in vitro f_t values were corrected using quantitative proteomics data to obtain "scaled f_t " Fourth, in vitro-in vivo extrapolation of the scaled OATP1B1/1B3 f_t was assessed, leveraging statin clinical drug-drug interaction data with rifampicin as the perpetrator. Finally, we outlined a novel stepwise strategy to implement phenotypic characterization of SLC-mediated hepatic uptake for new molecular entities and drugs in a drug discovery and development setting.

Understanding the relevance of herb-drug interaction studies with special focus on interplays: a prerequisite for integrative medicine

Integrative medicine refers to the blending of conventional and evidence-based complementary medicines and therapies with the aim of using the most appropriate of either or both modalities for ultimate patient benefits. One of the major hurdles for the same is the chances of potential herb–drug interactions (HDIs). These HDIs could be beneficial or harmful, or even fatal; therefore, a thorough understanding of the eventualities of HDIs is essential so that a successful integration of the modern and complementary alternative systems of medicine could be achieved. Here, we summarize all the important points related to HDIs, including types, tools/methods for study, and prediction of the HDIs, along with a special focus on interplays between drug metabolizing enzymes and transporters. In addition, this article covers future perspective, with a focus on background endogenous players of interplays and approaches to predict the drug–disease–herb interactions so as to fetch the desired effects of these interactions.

Oral coadministration of elacridar and ritonavir enhances brain accumulation and oral availability of the novel ALK/ROS1 inhibitor lorlatinib

Lorlatinib, a novel generation oral anaplastic lymphoma kinase (ALK) and ROS1 inhibitor with high membrane and blood-brain barrier permeability, recently received accelerated approval for treatment of ALK-rearranged non-small-cell lung cancer (NSCLC), and its further clinical development is ongoing. We previously found that the efflux transporter P-glycoprotein (MDR1/ABCB1) restricts lorlatinib brain accumulation and that the drug-metabolizing enzyme cytochrome P450-3A (CYP3A) limits its oral availability. Using genetically modified mouse models, we investigated the impact of targeted pharmacological inhibitors on lorlatinib pharmacokinetics and bioavailability. Upon oral administration of lorlatinib, the plasma AUC_0-8h in CYP3A4-humanized mice was ∼1.8-fold lower than in wild-type and Cyp3a^-/- mice. Oral coadministration of the CYP3A inhibitor ritonavir caused reversion to the AUC_0-8h levels seen in wild-type and Cyp3a^-/- mice, without altering the relative tissue distribution of lorlatinib. Moreover, simultaneous pharmacological inhibition of P-glycoprotein and CYP3A4 with oral elacridar and ritonavir in CYP3A4-humanized mice profoundly increased lorlatinib brain concentrations, but not its oral availability or other relative tissue distribution. Oral lorlatinib pharmacokinetics was not significantly affected by absence of the multispecific Oatp1a/1b drug uptake transporters. The absolute oral bioavailability of lorlatinib over 8 h in wild-type, Cyp3a^-/-, and CYP3A4-humanized mice was 81.6%, 72.9%, and 58.5%, respectively. Lorlatinib thus has good oral bioavailability, which is markedly restricted by human CYP3A4 but not by mouse Cyp3a. Pharmacological inhibition of CYP3A4 reversed these effects, and simultaneous P-gp inhibition with elacridar boosted absolute brain levels of lorlatinib by 16-fold without obvious toxicity. These insights may help to optimize the clinical application of lorlatinib.

Mechanisms and the clinical relevance of complex drug-drug interactions

As a result of an increasing aging population, the number of individuals taking multiple medications simultaneously has grown considerably. For these individuals, taking multiple medications has increased the risk of undesirable drug–drug interactions (DDIs), which can cause serious and debilitating adverse drug reactions (ADRs). A comprehensive understanding of DDIs is needed to combat these deleterious outcomes. This review provides a synopsis of the pharmacokinetic (PK) and pharmacodynamic (PD) mechanisms that underlie DDIs. PK-mediated DDIs affect all aspects of drug disposition: absorption, distribution, metabolism and excretion (ADME). In this review, the cells that play a major role in ADME and have been investigated for DDIs are discussed. Key examples of drug metabolizing enzymes and drug transporters that are involved in DDIs and found in these cells are described. The effect of inhibiting or inducing these proteins through DDIs on the PK parameters is also reviewed. Despite most DDI studies being focused on the PK effects, DDIs through PD can also lead to significant and harmful effects. Therefore, this review outlines specific examples and describes the additive, synergistic and antagonistic mechanisms of PD-mediated DDIs. The effects DDIs on the maximum PD response (E_max) and the drug dose or concentration (EDEC₅₀) that lead to 50% of E_max are also examined. Significant gaps in our understanding of DDIs remain, so innovative and emerging approaches are critical for overcoming them.

Assessment of Transporter-Mediated and Passive Hepatic Uptake Clearance Using Rifamycin-SV as a Pan-Inhibitor of Active Uptake

The use of in vitro data for the quantitative prediction of transporter-mediated clearance is critical. Central to this evaluation is the use of hepatocytes, since they contain the full complement of transporters and metabolic enzymes. In general, uptake clearance (CL_uptake) is evaluated by measuring the appearance of compound in the cell. Passive clearance (CL_pd) is often determined by conducting parallel studies at 4 °C or by attempting to saturate uptake pathways. Both approaches have their limitations. Recent studies have proposed the use of Rifamycin-SV (RFV) as a pan-inhibitor of hepatic uptake pathways. In our studies, we confirm that transport activity of all major hepatic uptake transporters is inhibited significantly by RFV at 1 mM (OATP1B1, 1B3, and 2B1 = NTCP (80%), OCT1 (65%), OAT2 (60%)). Under these incubation conditions, we found that the free intracellular concentration of RFV is ∼175 μM and that several major CYPs and UGTs can be reversibly inhibited. Using this approach, we also determined CL_uptake and CL_pd of nine known OATP substrates across three different lots of human hepatocytes. The scaling factors generated for these compounds at 37 °C with RFV and 4 °C were found to be similar. The CL_pd of passively permeable compounds like metoprolol and semagacestat were found to be higher at 37 °C compared to 4 °C, indicating a temperature effect on these compounds. In addition, our data also suggests that incorporation of medium concentrations into CL_uptake and CL_pd calculations may be critical for highly protein bound and highly lipophilic drugs. Overall, our data indicate that RFV, instead of 4 °C, can be reliably used to measure CL_uptake and CL_pd of drugs.

Advancements in the oral delivery of Docetaxel: challenges, current state-of-the-art and future trends

The oral delivery of cancer chemotherapeutic drugs is challenging due to low bioavailability, gastrointestinal side effects, first-pass metabolism and P-glycoprotein efflux pumps. Thus, chemotherapeutic drugs, including Docetaxel, are administered via an intravenous route, which poses many disadvantages of its own. Recent advances in pharmaceutical research have focused on designing new and efficient drug delivery systems for site-specific targeting, thus leading to improved bioavailability and pharmacokinetics. A decent number of studies have been reported for the safe and effective oral delivery of Docetaxel. These nanocarriers, including liposomes, polymeric nanoparticles, metallic nanoparticles, hybrid nanoparticles, dendrimers and so on, have shown promising results in research papers and clinical trials. The present article comprehensively reviews the research efforts made so far in designing various advancements in the oral delivery of Docetaxel. Different strategies to improve oral bioavailability, prevent first-pass metabolism and inhibition of efflux pumping leading to improved pharmacokinetics and anticancer activity are discussed. The final portion of this review article presents key issues such as safety of nanomaterials, regulatory approval and future trends in nanomedicine research.

Evaluation of Alteration in Hepatic and Intestinal BCRP Function In Vivo from ABCG2 c.421C>A Polymorphism Based on PBPK Analysis of Rosuvastatin

Polymorphism c.421C>A in the ABCG2 gene is thought to reduce the activity of breast cancer resistance protein (BCRP), a xenobiotic transporter, although it is not clear which organ(s) contributes to the polymorphism-associated pharmacokinetic change. The aim of the present study was to estimate quantitatively the influence of c.421C>A on intestinal and hepatic BCRP activity using a physiologically based pharmacokinetic (PBPK) model of rosuvastatin developed from clinical data and several in vitro studies. Simultaneous fitting of clinical data for orally and intravenously administered rosuvastatin, obtained in human subjects without genotype information, was first performed with the PBPK model to estimate intrinsic clearance for hepatic elementary process. The fraction of BCRP activity in 421CA and 421AA (f_ca and f_aa values, respectively) with respect to that in 421CC subjects was then estimated based on extended clearance concepts and simultaneous fitting to oral administration data for the three genotypes (421CC, 421CA, and 421AA). On the assumption that c.421C>A affects both intestinal and hepatic BCRP, clinical data in each genotype were well reproduced by the model, and the estimated terminal half-life was compatible with the observed values. The assumption that c.421C>A affects only either intestinal or hepatic BCRP gave poorer agreement with observed values. The f_aa values obtained on the former assumption were 0.48-0.54. Thus, PBPK model analysis enabled quantitative evaluation of alteration in BCRP activity owing to c.421C>A, and BCRP activity in 421AA was estimated as half that in 421CC.

A comparative evaluation of models to predict human intestinal metabolism from nonclinical data

Extensive gut metabolism is often associated with the risk of low and variable bioavailability. The prediction of the fraction of drug escaping gut wall metabolism as well as transporter-mediated secretion (F_g ) has been challenged by the lack of appropriate preclinical models. The purpose of this study is to compare the performance of models that are widely employed in the pharmaceutical industry today to estimate F_g and, based on the outcome, to provide recommendations for the prediction of human F_g during drug discovery and early drug development. The use of in vitro intrinsic clearance from human liver microsomes (HLM) in three mechanistic models - the ADAM, Q_gut and Competing Rates - was evaluated for drugs whose metabolism is dominated by CYP450s, assuming that the effect of transporters is negligible. The utility of rat as a model for human F_g was also explored. The ADAM, Q_gut and Competing Rates models had comparable prediction success (70%, 74%, 69%, respectively) and bias (AFE = 1.26, 0.74 and 0.81, respectively). However, the ADAM model showed better accuracy compared with the Q_gut and Competing Rates models (RMSE =0.20 vs 0.30 and 0.25, respectively). Rat is not a good model (prediction success =32%, RMSE =0.48 and AFE = 0.44) as it seems systematically to under-predict human F_g . Hence, we would recommend the use of rat to identify the need for F_g assessment, followed by the use of HLM in simple models to predict human F_g . © 2017 Merck KGaA. Biopharmaceutics & Drug Disposition Published by John Wiley & Sons, Ltd.

Pharmacokinetic interactions of curcuminoids with conventional drugs: A review

ETHNOPHARMACOLOGICAL RELEVANCE

Herb-drug interactions are of great concern in health practices. Curcumin is a natural polyphenol extracted from turmeric, a spice widely used all over the world. Curcumin is clinically used due to its acceptable safety profile and therapeutic efficacy.

AIM OF THE STUDY

Current paper aims to highlight the effect of curcumin on concomitantly used drugs.

METHODS

Electronic databases including PubMed, Scopus and Science Direct were searched with the keywords "curcumin" in the title/abstract and "drug interaction," "drug metabolism," "cytochrome," "P-glycoprotein" and "P450" in the whole text.

RESULTS

Curcumin can induce pharmacokinetic alterations such as changes in C_max and AUC when concomitantly used with pharmacological agents like cardiovascular drugs, antidepressants, anticoagulants, antibiotics, chemotherapeutic agents, and antihistamines. The underlying mechanisms of these interactions include inhibition of cytochrome (CYP) isoenzymes and P-glycoprotein. There is only one clinical trial which proved a significant alteration of conventional drugs in concomitant use with curcumin indicating the need for further human studies.

CONCLUSIONS

Although in vitro and in vivo studies do not provide enough evidence to judge the clinical drug interactions of curcumin, physicians must remain cautious and avoid drug combinations which may lead to curcumin-drug interactions.

Development of Caco-2 cells co-expressing CYP3A4 and NADPH-cytochrome P450 reductase using a human artificial chromosome for the prediction of intestinal extraction ratio of CYP3A4 substrates

The Caco-2 cells co-expressing cytochrome P450 (CYP) 3A4 and NADPH-cytochrome P450 reductase (CPR) were developed using a human artificial chromosome (HAC) vector. The CYP3A4 and CPR genes were cloned into the HAC vector in CHO cells using the Cre-loxP system, and the microcell-mediated chromosome transfer technique was used to transfer the CYP3A4-CPR-HAC vector to Caco-2 cells. After seeding onto semipermeable culture inserts, the CYP3A4-CPR-HAC/Caco-2 cells were found to form tight monolayers, similar to the parental cells, as demonstrated by the high transepithelial electrical resistance (TEER) value and comparable permeability of non-CYP3A4 substrates between parent and CYP3A4-CPR-HAC/Caco-2 cell monolayers. The metabolic activity of CYP3A4 (midazolam 1'-hydroxylase activity) in the CYP3A4-CPR-HAC/Caco-2 cells was constant from 22 to 35 passages, indicating that HAC vectors conferred sufficient and sustained CYP3A4 activity to CYP3A4-CPR-HAC/Caco-2 cells. The strong relationship between the metabolic extraction ratios (ER) obtained from the CYP3A4-CPR-HAC/Caco-2 cells and calculated intestinal extraction ratios in humans (Eg) from reported intestinal availability (Fg) was found for 17 substrates of CYP3A4 (r² = 0.84). The present study suggests that the CYP3A4-CPR-HAC/Caco-2 cell monolayer can serve as an in vitro tool that facilitates the prediction of intestinal extraction ratio (or availability) in humans.

Predicting Drug Extraction in the Human Gut Wall: Assessing Contributions from Drug Metabolizing Enzymes and Transporter Proteins using Preclinical Models

Intestinal metabolism can limit oral bioavailability of drugs and increase the risk of drug interactions. It is therefore important to be able to predict and quantify it in drug discovery and early development. In recent years, a plethora of models-in vivo, in situ and in vitro-have been discussed in the literature. The primary objective of this review is to summarize the current knowledge in the quantitative prediction of gut-wall metabolism. As well as discussing the successes of current models for intestinal metabolism, the challenges in the establishment of good preclinical models are highlighted, including species differences in the isoforms; regional abundances and activities of drug metabolizing enzymes; the interplay of enzyme-transporter proteins; and lack of knowledge on enzyme abundances and availability of empirical scaling factors. Due to its broad specificity and high abundance in the intestine, CYP3A is the enzyme that is frequently implicated in human gut metabolism and is therefore the major focus of this review. A strategy to assess the impact of gut wall metabolism on oral bioavailability during drug discovery and early development phases is presented. Current gaps in the mechanistic understanding and the prediction of gut metabolism are highlighted, with suggestions on how they can be overcome in the future.

Systematic and quantitative assessment of the effect of chronic kidney disease on CYP2D6 and CYP3A4/5

Recent reviews suggest that chronic kidney disease (CKD) can affect the pharmacokinetics of nonrenally eliminated drugs, but the impact of CKD on individual elimination pathways has not been systematically evaluated. In this study we developed a comprehensive dataset of the effect of CKD on the pharmacokinetics of CYP2D6‐ and CYP3A4/5‐metabolized drugs. Drugs for evaluation were selected based on clinical drug–drug interaction (CYP3A4/5 and CYP2D6) and pharmacogenetic (CYP2D6) studies. Information from dedicated CKD studies was available for 13 and 18 of the CYP2D6 and CYP3A4/5 model drugs, respectively. Analysis of these data suggested that CYP2D6‐mediated clearance is generally decreased in parallel with the severity of CKD. There was no apparent relationship between the severity of CKD and CYP3A4/5‐mediated clearance. The observed elimination‐route dependency in CKD effects between CYP2D6 and CYP3A4/5 may inform the need to conduct clinical CKD studies with nonrenally eliminated drugs for optimal use of drugs in patients with CKD.

Stable isotope-labelled intravenous microdose for absolute bioavailability and effect of grapefruit juice on ibrutinib in healthy adults

AIMS

Ibrutinib, an inhibitor of Bruton's tyrosine kinase, is used in the treatment of mantle cell lymphoma or chronic lymphocytic leukaemia. Ibrutinib undergoes extensive rapid oxidative metabolism mediated by cytochrome P450 3A both at the level of first pass and clearance, which might result in low oral bioavailability. The present study was designed to investigate the absolute bioavailability (F) of ibrutinib in the fasting and fed state and assess the effect of grapefruit juice (GFJ) on the systemic exposure of ibrutinib in order to determine the fraction escaping the gut (Fg ) and the fraction escaping hepatic extraction (Fh ) in the fed state.

METHODS

All participants received treatment A [560 mg oral ibrutinib, under fasting conditions], B (560 mg PO ibrutinib, fed, administered after drinking glucose drink) and C (140 mg oral ibrutinib, fed, with intake of GFJ before dosing). A single intravenous (i.v.) dose of 100 μg (13) C6 -ibrutinib was administered 2 h after each oral dose.

RESULTS

The estimated 'F' for treatments A, B and C was 3.9%, 8.4% and 15.9%, respectively. Fg and Fh in the fed state were 47.0% and 15.9%, respectively. Adverse events were mild to moderate in severity (Grade 1-2) and resolved without sequelae by the end of the study.

CONCLUSION

The absolute oral bioavailability of ibrutinib was low, ranging from 3.9% in the fasting state to 8.4% when administered 30 min before a standard breakfast without GFJ and 15.9% with GFJ. Ibrutinib was well tolerated following a single oral and i.v. dose, under both fasted and fed conditions and regardless of GFJ intake status.

Quantitative Rationalization of Gemfibrozil Drug Interactions: Consideration of Transporters-Enzyme Interplay and the Role of Circulating Metabolite Gemfibrozil 1-O-β-Glucuronide

Gemfibrozil has been suggested as a sensitive cytochrome P450 2C8 (CYP2C8) inhibitor for clinical investigation by the U.S. Food and Drug Administration and the European Medicines Agency. However, gemfibrozil drug-drug interactions (DDIs) are complex; its major circulating metabolite, gemfibrozil 1-O-β-glucuronide (Gem-Glu), exhibits time-dependent inhibition of CYP2C8, and both parent and metabolite also behave as moderate inhibitors of organic anion transporting polypeptide 1B1 (OATP1B1) in vitro. Additionally, parent and metabolite also inhibit renal transport mediated by OAT3. Here, in vitro inhibition data for gemfibrozil and Gem-Glu were used to assess their impact on the pharmacokinetics of several victim drugs (including rosiglitazone, pioglitazone, cerivastatin, and repaglinide) by employing both static mechanistic and dynamic physiologically based pharmacokinetic (PBPK) models. Of the 48 cases evaluated using the static models, about 75% and 98% of the DDIs were predicted within 1.5- and 2-fold of the observed values, respectively, when incorporating the interaction potential of both gemfibrozil and its 1-O-β-glucuronide. Moreover, the PBPK model was able to recover the plasma profiles of rosiglitazone, pioglitazone, cerivastatin, and repaglinide under control and gemfibrozil treatment conditions. Analyses suggest that Gem-Glu is the major contributor to the DDIs, and its exposure needed to bring about complete inactivation of CYP2C8 is only a fraction of that achieved in the clinic after a therapeutic gemfibrozil dose. Overall, the complex interactions of gemfibrozil can be quantitatively rationalized, and the learnings from this analysis can be applied in support of future predictions of gemfibrozil DDIs.

Development of a Physiologically-Based Pharmacokinetic Model for Sirolimus: Predicting Bioavailability Based on Intestinal CYP3A Content

Sirolimus is an inhibitor of mammalian target of rapamycin (mTOR) and is increasingly being used in transplantation and cancer therapies. Sirolimus has low oral bioavailability and exhibits large pharmacokinetic variability. The underlying mechanisms for this variability have not been explored to a large extent. Sirolimus metabolism was characterized by in vitro intrinsic clearance estimation. Pathway contribution ranked from CYP3A4 > CYP3A5 > CYP2C8. With the well stirred and Q_gut models sirolimus bioavailability was predicted at 15%. Interindividual differences in bioavailability could be attributed to variable intestinal CYP3A expression. The physiologically-based pharmacokinetics (PBPK) model developed in Simcyp predicted a high distribution of sirolimus into adipose tissue and another elimination pathway in addition to CYP-mediated metabolism. PBPK model predictive performance was acceptable with C_max and area under the curve (AUC) estimates within 20% of observed data in a dose escalation study. The model also showed potential to assess the impact of hepatic impairment and drug–drug interaction (DDI) on sirolimus pharmacokinetics.

In vivo assessment of the impact of efflux transporter on oral drug absorption using portal vein-cannulated rats

The purpose of this study was to evaluate the impact of intestinal efflux transporters on the in vivo oral absorption process. Three model drugs-fexofenadine (FEX), sulfasalazine (SASP), and topotecan (TPT)-were selected as P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and P-gp and BCRP substrates, respectively. The drugs were orally administered to portal vein-cannulated rats after pretreatment with zosuquidar (ZSQ), P-gp inhibitor, and/or Ko143, BCRP inhibitor. Intestinal availability (Fa·Fg) of the drugs was calculated from the difference between portal and systemic plasma concentrations. When rats were orally pretreated with ZSQ, Fa·Fg of FEX increased 4-fold and systemic clearance decreased to 75% of the control. In contrast, intravenous pretreatment with ZSQ did not affect Fa·Fg of FEX, although systemic clearance decreased significantly. These data clearly show that the method presented herein using portal vein-cannulated rats can evaluate the effects of intestinal transporters on Fa·Fg of drugs independently of variable systemic clearance. In addition, it was revealed that 71% of FEX taken up into enterocytes underwent selective efflux via P-gp to the apical surface, while 79% of SASP was effluxed by Bcrp. In the case of TPT, both transporters were involved in its oral absorption. Quantitative analysis indicated a 3.5-fold higher contribution from Bcrp than P-gp. In conclusion, the use of portal vein-cannulated rats enabled the assessment of the impact of efflux transporters on intestinal absorption of model drugs. This experimental system is useful for clarifying the cause of low bioavailability of various drugs.

Quantitative prediction of intestinal glucuronidation of drugs in rats using in vitro metabolic clearance data

UDP-glucuronosyltransferase (UGT) is highly expressed in the small intestine and catalyzes the glucuronidation of small molecules, which may affect the oral bioavailability of drugs. However, no method of predicting the in vivo observed fraction of absorbed drug (F(a)F(g)) affected by UGT has yet been established. Here, we investigated the relationship between F(a)F(g) and in vitro clearance of nine UGT substrates (ketoprofen, tolcapone, telmisartan, raloxifene, entacapone, resveratrol, buprenorphine, quercetin, and ezetimibe) via UGT in intestinal microsomes (CL(int, UGT)) in rats. F(a)F(g) was calculated from pharmacokinetic parameters after intravenous and oral administration or using the portal-systemic concentration difference method, with values ranging from 0.027 (ezetimibe) to 1 (tolcapone). Glucuronides of model compounds were observed in the portal plasma after oral administration, with CL(int, UGT) values ranging from 57.8 (tolcapone) to 19,200 µL/min/mg (resveratrol). An inverse correlation between F(a)F(g) and CL(int, UGT) was observed for most compounds and was described using a simplified intestinal availability model reported previously. This model gave accurate predictions of F(a)F(g) values for three in-house compounds. Our results show that F(a)F(g) in rats is affected by UGT and can be predicted using CL(int, UGT). This work should hasten the development of a method to predict F(a)F(g) in humans.

Prediction of the intestinal first-pass metabolism of CYP3A and UGT substrates in humans from in vitro data

This study aimed to establish a practical and simplified method of predicting intestinal availability in humans (F(g,human)) at the drug discovery stage using in vitro metabolic clearance values and permeability clearance values. A prediction model for F(g,human) of 19 CYP3A substrates and 5 UGT substrates was constructed based on the concept that the permeability clearance values mean the permeability across the basal membrane with a pH of 7.4 on both sides. Permeability clearance values were obtained by parallel artificial membrane permeability assay (PAMPA) at pH 7.4. PAMPA is widely used in the pharmaceutical industry as the earliest primary screening stage and enables estimation of the kinetics of transport by passive diffusion. For CYP3A substrates, the metabolic clearance was obtained from in vitro intrinsic clearance values in human intestinal or hepatic microsomes (CL(int,HIM) or CL(int,HLM), respectively). Using metabolic clearances corrected by the ratio of CL(int,HIM) to CL(int,HLM), HLM showed equivalent predictability to that of HIM for CYP3A substrates. For UGT substrates, the clearance was obtained from alamethicin-activated HIM using one incubation with both NADPH and UDPGA cofactors. The method proposed in this study could predict F(g,human) for the compounds investigated and represents a simplified method based on a new concept applicable to lower permeability compounds.