Importance of Hepatic Transporters in Clinical Disposition of Drugs and Their Metabolites

Transporter-mediated drug-drug interactions: regulatory guidelines, in vitro and in vivo methodologies and translation, special populations, and the blood-brain barrier

This review, part of a special issue on drug-drug interactions (DDIs) spearheaded by the International Society for the Study of Xenobiotics (ISSX) New Investigators, explores the critical role of drug transporters in absorption, disposition, and clearance in the context of DDIs. Over the past two decades, significant advances have been made in understanding the clinical relevance of these transporters. Current knowledge on key uptake and efflux transporters that affect drug disposition and development is summarized. Regulatory guidelines from the FDA, EMA, and PMDA that inform the evaluation of potential transporter-mediated DDIs are discussed in detail. Methodologies for preclinical and clinical testing to assess potential DDIs are reviewed, with an emphasis on the utility of physiologically based pharmacokinetic (PBPK) modeling. This includes the application of relative abundance and expression factors to predict human pharmacokinetics (PK) using preclinical data, integrating the latest regulatory guidelines. Considerations for assessing transporter-mediated DDIs in special populations, including pediatric, hepatic, and renal impairment groups, are provided. Additionally, the impact of transporters at the blood-brain barrier (BBB) on the disposition of CNS-related drugs is explored. Enhancing the understanding of drug transporters and their role in drug disposition and toxicity can improve efficacy and reduce adverse effects. Continued research is essential to bridge remaining gaps in knowledge, particularly in comparison with cytochrome P450 (CYP) enzymes.

Survey of Pharmaceutical Industry's Best Practices around In Vitro Transporter Assessment and Implications for Drug Development: Considerations from the International Consortium for Innovation and Quality for Pharmaceutical Development Transporter Working Group

The International Consortium for Innovation and Quality in Pharmaceutical Development Transporter Working Group had a rare opportunity to analyze a crosspharma collation of in vitro data and assay methods for the evaluation of drug transporter substrate and inhibitor potential. Experiments were generally performed in accordance with regulatory guidelines. Discrepancies, such as not considering the impact of preincubation for inhibition and free or measured in vitro drug concentrations, may be due to the retrospective nature of the dataset and analysis. Lipophilicity was a frequent indicator of crosstransport inhibition (P-gp, BCRP, OATP1B, and OCT1), with high molecular weight (MW ≥500 Da) also common for OATP1B and BCRP inhibitors. A high level of overlap in in vitro inhibition across transporters was identified for BCRP, OATP1B1, and MATE1, suggesting that prediction of DDIs for these transporters will be common. In contrast, inhibition of OAT1 did not coincide with inhibition of any other transporter. Neutrals, bases, and compounds with intermediate-high lipophilicity tended to be P-gp and/or BCRP substrates, whereas compounds with MW <500 Da tended to be OAT3 substrates. Interestingly, the majority of in vitro inhibitors were not reported to be followed up with a clinical study by the submitting company, whereas those compounds identified as substrates generally were. Approaches to metabolite testing were generally found to be similar to parent testing, with metabolites generally being equally or less potent than parent compounds. However, examples where metabolites inhibited transporters in vitro were identified, supporting the regulatory requirement for in vitro testing of metabolites to enable integrated clinical DDI risk assessment. SIGNIFICANCE STATEMENT: A diverse dataset showed that transporter inhibition often correlated with lipophilicity and molecular weight (>500 Da). Overlapping transporter inhibition was identified, particularly that inhibition of BCRP, OATP1B1, and MATE1 was frequent if the compound inhibited other transporters. In contrast, inhibition of OAT1 did not correlate with the other drug transporters tested.

Utilization of OATP1B Biomarker Coproporphyrin-I to Guide Drug-Drug Interaction Risk Assessment: Evaluation by the Pharmaceutical Industry

Drug-drug interactions (DDIs) involving hepatic organic anion transporting polypeptides 1B1/1B3 (OATP1B) can be substantial, however, challenges remain for predicting interaction risk. Emerging evidence suggests that endogenous biomarkers, particularly coproporphyrin-I (CP-I), can be used to assess in vivo OATP1B activity. The present work under the International Consortium for Innovation and Quality in Pharmaceutical Development was aimed primarily at assessing CP-I as a biomarker for informing OATP1B DDI risk. Literature and unpublished CP-I data along with pertinent in vitro and clinical DDI information were collected to identify DDIs primarily involving OATP1B inhibition and assess the relationship between OATP1B substrate drug and CP-I exposure changes. Static models to predict changes in exposure of CP-I, as a selective OATP1B substrate, were also evaluated. Significant correlations were observed between CP-I area under the curve ratio (AUCR) or maximum concentration ratio (Cmax R) and AUCR of substrate drugs. In general, the CP-I Cmax R was equal to or greater than the CP-I AUCR. CP-I Cmax R < 1.25 was associated with absence of OATP1B-mediated DDIs (AUCR < 1.25) with no false negative predictions. CP-I Cmax R < 2 was associated with weak OATP1B-mediated DDIs (AUCR < 2). A correlation was identified between CP-I exposure changes and OATP1B1 static DDI predictions. Recommendations for collecting and interpreting CP-I data are discussed, including a decision tree for guiding DDI risk assessment. In conclusion, measurement of CP-I is recommended to inform OATP1B inhibition potential. The current analysis identified changes in CP-I exposure that may be used to prioritize, delay, or replace clinical DDI studies.

Structure of human drug transporters OATP1B1 and OATP1B3

The organic anion transporting polypeptides OATP1B1 and OATP1B3 are membrane proteins that mediate uptake of drugs into the liver for subsequent conjugation and biliary excretion, a key step in drug elimination from the human body. Polymorphic variants of these transporters can cause reduced drug clearance and adverse drug effects such as statin-induced rhabdomyolysis, and co-administration of OATP substrates can lead to damaging drug-drug interaction. Despite their clinical relevance in drug disposition and pharmacokinetics, the structure and mechanism of OATPs are unknown. Here we present cryo-EM structures of human OATP1B1 and OATP1B3 bound to synthetic Fab fragments and in functionally distinct states. A single estrone-3-sulfate molecule is bound in a pocket located in the C-terminal half of OATP1B1. The shape and chemical nature of the pocket rationalize the preference for diverse organic anions and allow in silico docking of statins. The structure of OATP1B3 is determined in a drug-free state but reveals a bicarbonate molecule bound to the conserved signature motif and a histidine residue that is prevalent in OATPs exhibiting pH-dependent activity.

Progress in the Quantitative Assessment of Transporter-Mediated Drug-Drug Interactions Using Endogenous Substrates in Clinical Studies

Variations in drug transporter activities, caused by genetic polymorphism and drug-drug interactions (DDIs), alter the systemic exposure of substrate drugs, leading to differences in drug responses. Recently, some endogenous substrates of drug transporters, particularly the solute carrier family transporters such as OATP1B1, OATP1B3, OAT1, OAT3, OCT1, OCT2, MATE1, and MATE2-K, have been identified to investigate variations in drug transporters in humans. Clinical data obtained support their performance as surrogate probes in terms of specificity and reproducibility. Pharmacokinetic parameters of the endogenous biomarkers depend on the genotypes of drug transporters and the systemic exposure to perpetrator drugs. Furthermore, the development of physiologically based pharmacokinetic models for the endogenous biomarkers has enabled a top-down approach to obtain insights into the effect of perpetrators on drug transporters and to more precisely simulate the DDI with victim drugs, including probe drugs. The endogenous biomarkers can address the uncertainty in the DDI prediction in the preclinical and early phases of clinical development and have the potential to fulfill regulatory requirements. Therefore, the endogenous biomarkers should be able to predict disease effects on the variations in drug transporter activities observed in patients. This mini-review focuses on recent progress in the identification and use of the endogenous drug transporter substrate biomarkers and their application in drug development. SIGNIFICANCE STATEMENT: Advances in analytical methods have enabled the identification of endogenous substrates of drug transporters. Changes in the pharmacokinetic parameters (Cmax, AUC, or CLR) of these endogenous biomarkers relative to baseline values can serve as a quantitative index to assess variations in drug transporter activities during clinical studies and thereby provide more precise DDI predictions.

Drug-drug interactions that alter the exposure of glucuronidated drugs: Scope, UDP-glucuronosyltransferase (UGT) enzyme selectivity, mechanisms (inhibition and induction), and clinical significance

Drug-drug interactions (DDIs) arising from the perturbation of drug metabolising enzyme activities represent both a clinical problem and a potential economic loss for the pharmaceutical industry. DDIs involving glucuronidated drugs have historically attracted little attention and there is a perception that interactions are of minor clinical relevance. This review critically examines the scope and aetiology of DDIs that result in altered exposure of glucuronidated drugs. Interaction mechanisms, namely inhibition and induction of UDP-glucuronosyltransferase (UGT) enzymes and the potential interplay with drug transporters, are reviewed in detail, as is the clinical significance of known DDIs. Altered victim drug exposure arising from modulation of UGT enzyme activities is relatively common and, notably, the incidence and importance of UGT induction as a DDI mechanism is greater than generally believed. Numerous DDIs are clinically relevant, resulting in either loss of efficacy or an increased risk of adverse effects, necessitating dose individualisation. Several generalisations relating to the likelihood of DDIs can be drawn from the known substrate and inhibitor selectivities of UGT enzymes, highlighting the importance of comprehensive reaction phenotyping studies at an early stage of drug development. Further, rigorous assessment of the DDI liability of new chemical entities that undergo glucuronidation to a significant extent has been recommended recently by regulatory guidance. Although evidence-based approaches exist for the in vitro characterisation of UGT enzyme inhibition and induction, the availability of drugs considered appropriate for use as 'probe' substrates in clinical DDI studies is limited and this should be research priority.

The implication of Mycobacterium tuberculosis-mediated metabolism of targeted xenobiotics

Drug metabolism is generally associated with liver enzymes. However, in the case of Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), Mtb-mediated drug metabolism plays a significant role in treatment outcomes. Mtb is equipped with enzymes that catalyse biotransformation reactions on xenobiotics with consequences either in its favour or as a hindrance by deactivating or activating chemical entities, respectively. Considering the range of chemical reactions involved in the biosynthetic pathways of Mtb, information related to the biotransformation of antitubercular compounds would provide opportunities for the development of new chemical tools to study successful TB infections while also highlighting potential areas for drug discovery, host-directed therapy, dose optimization and elucidation of mechanisms of action. In this Review, we discuss Mtb-mediated biotransformations and propose a holistic approach to address drug metabolism in TB drug discovery and related areas.

Mycobacterium tuberculosis-mediated metabolism of xenobiotics poses an important research question for antitubercular drug discovery. Identification of the metabolic fate of compounds can inform requisite structure–activity relationship strategies early on in a drug discovery programme towards improving the properties of the compound.

Fluorescence-based methods for studying activity and drug-drug interactions of hepatic solute carrier and ATP binding cassette proteins involved in ADME-Tox

In humans, approximately 70% of drugs are eliminated through the liver. This process is governed by the concerted action of membrane transporters and metabolic enzymes. Transporters mediating hepatocellular uptake of drugs belong to the SLC (Solute carrier) superfamily of transporters. Drug efflux either toward the portal vein or into the bile is mainly mediated by active transporters of the ABC (ATP Binding Cassette) family. Alteration in the function and/or expression of liver transporters due to mutations, disease conditions, or co-administration of drugs or food components can result in altered pharmacokinetics. On the other hand, drugs or food components interacting with liver transporters may also interfere with liver function (e.g., bile acid homeostasis) and may even cause liver toxicity. Accordingly, certain transporters of the liver should be investigated already at an early stage of drug development. Most frequently radioactive probes are applied in these drug-transporter interaction tests. However, fluorescent probes are cost-effective and sensitive alternatives to radioligands, and are gaining wider application in drug-transporter interaction tests. In our review, we summarize our current understanding about hepatocyte ABC and SLC transporters affected by drug interactions. We provide an update of the available fluorescent and fluorogenic/activable probes applicable in in vitro or in vivo testing of these ABC and SLC transporters, including near-infrared transporter probes especially suitable for in vivo imaging. Furthermore, our review gives a comprehensive overview of the available fluorescence-based methods, not directly relying on the transport of the probe, suitable for the investigation of hepatic ABC or SLC-type drug transporters.

[Pharmacokinetics and pharmacodynamics of rebamipide. New possibilities of therapy: A review]

The MedLine database contains 570 publications, including 71 randomized clinical trials and 6 meta-analyses on the rebamipide molecule in 2022. Indications for the use of rebamipide are gastric ulcer, chronic gastritis with hyperacidityin the acute stage, erosive gastritis, prevention of damage to the gastrointestinal mucosa while taking non-steroidal anti-inflammatory drugs, eradication of Helicobacter pylori. Currently trials are studying the efficacy and safety of the drug in gouty and rheumatoid arthritis, osteoarthritis, Sjögren's syndrome, bronchial asthma, vitiligo, atherosclerosis, diseases of the kidneys and liver; using in traumatology to accelerate bone regeneration; in ophthalmology to improve the regeneration of corneal epithelium; in oncology to reduce inflammatory changes in the oral mucosa after chemoradiotherapy. The review article is about the main pharmacokinetic and pharmacodynamic characteristics of rebamipide. A detailed understanding of pharmacodynamics and pharmacokinetics allows for individual selection of therapy based on the characteristics of the patient's body - gender, age, comorbidities; choose the optimal route of administration and dosing regimen; predict adverse effects and drug interactions; be determined with new clinical indications.

Hepatic Transporters Alternations Associated with Non-alcoholic Fatty Liver Disease (NAFLD): A Systematic Review

BACKGROUND AND OBJECTIVES

Non-alcoholic fatty liver disease (NAFLD) is a progressive liver disorder and is usually accompanied by obesity, metabolic syndrome, and diabetes mellitus. NAFLD progression can lead to impaired functions of hepatocytes such as alternations in expression and function of hepatic transporters. The present study aimed to summarize and discuss the results of clinical and preclinical human studies that investigate the effect of NAFLD on hepatic transporters.

METHODS

The databases of PubMed, Scopus, Embase, and Web of Science were searched systematically up to 1 March 2022. The risk of bias was assessed for cross-sectional studies through the Newcastle-Ottawa Scale score.

RESULTS

Our review included ten cross-sectional studies consisting of 485 participants. Substantial alternations in hepatic transporters were seen during NAFLD progression to non-alcoholic steatohepatitis (NASH) in comparison with control groups. A significant reduction in expression and function of several hepatic uptake transporters, upregulation of many efflux transporters, downregulation of cholesterol efflux transporters, and mislocalization of canalicular transporter ABCC2 are associated with NAFLD progression.

CONCLUSION

Since extensive changes in hepatic transporters could alter the pharmacokinetics of the drugs and potentially affect the safety and efficacy of drugs, close monitoring of drug administration is highly suggested in patients with NASH.

Pharmacokinetic and pharmacodynamic considerations of antibiotics and antifungals in liver transplantation recipients

The liver plays a major role in drug metabolism. Liver transplantation impacts the intrinsic metabolic capability and extrahepatic mechanisms of drug disposition and elimination. Different levels of inflammation and oxidative stress during transplantation, the process of liver regeneration, and the characteristics of the graft alter the amount of functional hepatocytes and activity of liver enzymes. Binding of drugs to plasma proteins is affected by the hyperbilirubinemia status and abnormal synthesis of albumin and alpha-1-acid glycoproteins. Postoperative intensive care complications such as biliary, circulatory, and cardiac also impact drug distribution. Renally eliminated antimicrobials commonly present reduced clearance due to hepatorenal syndrome and the use of nephrotoxic immunosuppressants. In addition, liver transplantation recipients are particularly susceptible to multidrug-resistant infections due to frequent manipulation, multiple hospitalizations, invasive devices, and frequent use of empiric broad-spectrum therapy. The selection of appropriate anti-infective therapy must consider the pathophysiological changes after transplantation that impact the pharmacokinetics and pharmacodynamics of antibiotics and antifungal drugs.

Analysis of Time-Dependent Pharmacokinetics Using In Vitro-In Vivo Extrapolation and Physiologically Based Pharmacokinetic Modeling

SCR430, a sorafenib derivative, is an investigational drug exhibiting anti-tumor action. This study aimed to have a mechanistic understanding of SCR430's time-dependent pharmacokinetics (TDPK) through an ex vivo study combined with an in vitro-in vivo extrapolation (IVIVE) and physiologically based pharmacokinetic (PBPK) modeling. A non-compartmental pharmacokinetic analysis was performed after intravenous SCR430 administration in female Sprague-Dawley rats for a control group (no treatment), a vehicle group (vehicle only, 14 days, PO), and a repeated-dosing group (SCR430, 30 mg/kg/day, 14 days, PO). In addition, hepatic uptake and metabolism modulation were investigated using isolated hepatocytes from each group of rats. The minimal PBPK model based on IVIVE was constructed to explain SCR430's TDPK. Repeated SCR430 administration decreased the systemic exposure by 4.4-fold, which was explained by increased hepatic clearance (4.7-fold). The ex vivo study using isolated hepatocytes from each group suggested that the increased hepatic uptake (9.4-fold), not the metabolic activity, contributes to the increased hepatic clearance. The minimal PBPK modeling based on an ex vivo study could explain the decreased plasma levels after the repeated doses. The current study demonstrates the TDPK after repeated dosing by hepatic uptake induction, not hepatic metabolism, as well as the effectiveness of an ex vivo approach combined with IVIVE and PBPK modeling to investigate the TDPK.

Determination of the endogenous OATP1B biomarkers glycochenodeoxycholate-3-sulfate and chenodeoxycholate-24-glucuronide in human and mouse plasma by a validated UHPLC-MS/MS method

Glycochenodeoxycholate-3-sulfate (GCDCA-S) and chenodeoxycholate-24-glucuronide (CDCA-24G) are bile acid metabolites that potentially serve as endogenous biomarkers for drug-drug interactions mediated by the hepatic uptake transporters OATP1B1 and OATP1B3. We developed and validated a novel UHPLC-MS/MS method for the quantitative determination of GCDCA-S and CDCA-24G in mouse and human plasma with a lower limit of quantitation of 0.5 ng/mL. Chromatographic separation was achieved on an Accucore aQ column (50 mm × 2.1 mm, dp = 2.6 μm) maintained at 20 °C and a gradient mobile phase comprising 2 mM ammonium acetate in water and methanol. The extraction recoveries of GCDCA-S and CDCA-24G were >80 %, and linear (r2 > 0.99) calibration curves ranged 0.5-100 ng/mL (CDCA-24G and GCDCA-S in mouse plasma) or 0.5-1000 ng/mL (GCDCA-S in mouse plasma). Values for precision (CV < 11.6 %) and accuracy bias (10.9 %) of analyte-spiked quality control samples verified that water was an acceptable matrix to prepare calibrators. This method was successfully applied to establish baseline activity of OATP1B1/OATP1B3 in humans and mice and establish the in vivo effects of OATP1B1/OATP1B3 inhibitors rifampin and micafungin.

Metabolic clearance of select opioids and opioid antagonists using hepatic spheroids and recombinant cytochrome P450 enzymes

The opioid crisis is a pressing public health issue, exacerbated by the emergence of more potent synthetic opioids, particularly fentanyl and its analogs. While competitive antagonists exist, their efficacy against synthetic opioids is largely unknown. Furthermore, due to the short durations of action of current antagonists, renarcotization remains a concern. In this study, metabolic activity was characterized for fentanyl‐class opioids and common opioid antagonists using multiple in vitro systems, namely, cytochrome P450 (CYP) enzymes and hepatic spheroids, after which an in vitro‐in vivo correlation was applied to convert in vitro metabolic activity to predictive in vivo intrinsic clearance. For all substrates, intrinsic hepatic metabolism was higher than the composite of CYP activities, due to fundamental differences between whole cells and single enzymatic reactions. Of the CYP isozymes investigated, 3A4 yielded the highest absolute and relative metabolism across all substrates, with largely negligible contributions from 2D6 and 2C19. Comparative analysis highlighted elevated lipophilicity and diminished CYP3A4 activity as potential considerations for the development of more efficacious opioid antagonists. Finally, antagonists with a high degree of molecular similarity exhibited comparable clearance, providing a basis for structure‐metabolism relationships. Together, these results provide multiple screening criteria for early stage drug discovery involving opioid countermeasures.

Functional Expression of Multidrug-Resistance (MDR) Transporters in Developing Human Fetal Brain Endothelial Cells

There is little information about the functional expression of the multidrug resistance (MDR) transporters P-glycoprotein (P-gp, encoded by ABCB1) and breast cancer resistance protein (BCRP/ABCG2) in the developing blood−brain barrier (BBB). We isolated and cultured primary human fetal brain endothelial cells (hfBECs) from early and mid-gestation brains and assessed P-gp/ABCB1 and BCRP/ABCG2 expression and function, as well as tube formation capability. Immunolocalization of the von Willebrand factor (marker of endothelial cells), zonula occludens-1 and claudin-5 (tight junctions) was detected in early and mid-gestation-derived hfBECs, which also formed capillary-like tube structures, confirming their BEC phenotype. P-gp and BCRP immunostaining was detected in capillary-like tubes and in the cytoplasm and nucleus of hfBECs. P-gp protein levels in the plasma membrane and nuclear protein fractions, as well as P-gp protein/ABCB1 mRNA and BCRP protein levels decreased (p < 0.05) in hfBECs, from early to mid-gestation. No differences in P-gp or BCRP activity in hfBECs were observed between the two age groups. The hfBECs from early and mid-gestation express functionally competent P-gp and BCRP drug transporters and may thus contribute to the BBB protective phenotype in the conceptus from early stages of pregnancy.

Structural Modification in Anesthetic Drug Development for Prodrugs and Soft Drugs

Among the advancements in drug structural modifications, the increased focus on drug metabolic and pharmacokinetic properties in the anesthetic drug design process has led to significant developments. Drug metabolism also plays a key role in optimizing the pharmacokinetics, pharmacodynamics, and safety of drug molecules. Thus, in the field of anesthesiology, the applications of pharmacokinetic strategies are discussed in the context of sedatives, analgesics, and muscle relaxants. In this review, we summarize two approaches for structural optimization to develop anesthetic drugs, by designing prodrugs and soft drugs. Drugs that both failed and succeeded during the developmental stage are highlighted to illustrate how drug metabolism and pharmacokinetic optimization strategies may help improve their physical and chemical properties.

Systemic Ablation of Camkk2 Impairs Metastatic Colonization and Improves Insulin Sensitivity in TRAMP Mice: Evidence for Cancer Cell-Extrinsic CAMKK2 Functions in Prostate Cancer

Despite early studies linking calcium-calmodulin protein kinase kinase 2 (CAMKK2) to prostate cancer cell migration and invasion, the role of CAMKK2 in metastasis in vivo remains unclear. Moreover, while CAMKK2 is known to regulate systemic metabolism, whether CAMKK2's effects on whole-body metabolism would impact prostate cancer progression and/or related comorbidities is not known. Here, we demonstrate that germline ablation of Camkk2 slows, but does not stop, primary prostate tumorigenesis in the TRansgenic Adenocarcinoma Mouse Prostate (TRAMP) genetic mouse model. Consistent with prior epidemiological reports supporting a link between obesity and prostate cancer aggressiveness, TRAMP mice fed a high-fat diet exhibited a pronounced increase in the colonization of lung metastases. We demonstrated that this effect on the metastatic spread was dependent on CAMKK2. Notably, diet-induced lung metastases exhibited a highly aggressive neuroendocrine phenotype. Concurrently, Camkk2 deletion improved insulin sensitivity in the same mice. Histological analyses revealed that cancer cells were smaller in the TRAMP;Camkk2-/- mice compared to TRAMP;Camkk2+/+ controls. Given the differences in circulating insulin levels, a known regulator of cell growth, we hypothesized that systemic CAMKK2 could promote prostate cancer cell growth and disease progression in part through cancer cell-extrinsic mechanisms. Accordingly, host deletion of Camkk2 impaired the growth of syngeneic murine prostate tumors in vivo, confirming nonautonomous roles for CAMKK2 in prostate cancer. Cancer cell size and mTOR signaling was diminished in tumors propagated in Camkk2-null mice. Together, these data indicate that, in addition to cancer cell-intrinsic roles, CAMKK2 mediates prostate cancer progression via tumor-extrinsic mechanisms. Further, we propose that CAMKK2 inhibition may also help combat common metabolic comorbidities in men with advanced prostate cancer.

Effect of Cyclosporin A and Impact of Dose Staggering on OATP1B1/1B3 Endogenous Substrates and Drug Probes for Assessing Clinical Drug Interactions

This study was designed to assess the quantitative performance of endogenous biomarkers for organic anion transporting polypeptide (OATP) 1B1/1B3‐mediated drug‐drug interactions (DDIs). Ten healthy volunteers orally received OATP1B1/1B3 probe cocktail (0.2 mg pitavastatin, 1 mg rosuvastatin, and 2 mg valsartan) and an oral dose of cyclosporin A (CysA, 20 mg and 75 mg) separated by a 1‐hour interval (20 mg (−1 hour), and 75 mg (−1 hour)). CysA 75 mg was also given with a 3‐hour interval (75 mg (−3 hours)) to examine the persistence of OATP1B1/1B3 inhibition. The area under the plasma concentration‐time curve ratios (AUCRs) were 1.63, 3.46, and 2.38 (pitavastatin), 1.39, 2.16, and 1.81 (rosuvastatin), and 1.42, 1.77, and 1.85 (valsartan), at 20 mg, 75 mg (−1 hour) and 75 mg (−3 hours) of CysA, respectively. CysA effect on OATP1B1/1B3 was unlikely to persist at the dose examined. Among 26 putative OATP1B1/1B3 biomarkers evaluated, AUCR and maximum concentration ratio (C_maxR) of CP‐I showed the highest Pearson’s correlation coefficient with CysA AUC (0.94 and 0.93, respectively). Correlation between AUCR of pitavastatin, and C_maxR or AUCR of CP‐I were consistent between this study and our previous study using rifampicin as an OATP1B1/1B3 inhibitor. Nonlinear regression analysis of AUCR⁻¹ of pitavastatin and CP‐I against CysA C_max yielded K_{i,OATP1B1/1B3,app} (109 ± 35 and 176 ± 42 nM, respectively), similar to the K_{i,OATP1B1/1B3} estimated by our physiologically‐based pharmacokinetic model analysis described previously (107 nM). The endogenous OATP1B1/1B3 biomarkers, particularly C_maxR and AUCR of CP‐I, corroborates OATP1B1/1B3 inhibition and yields valuable information that improve accurate DDI predictions in drug development, and enhance our understanding of interindividual variability in the magnitude of DDIs.

Pharmacokinetic Imaging Using 99mTc-Mebrofenin to Untangle the Pattern of Hepatocyte Transporter Disruptions Induced by Endotoxemia in Rats

Endotoxemia-induced inflammation may impact the activity of hepatocyte transporters, which control the hepatobiliary elimination of drugs and bile acids. ^99mTc-mebrofenin is a non-metabolized substrate of transporters expressed at the different poles of hepatocytes. ^99mTc-mebrofenin imaging was performed in rats after the injection of lipopolysaccharide (LPS). Changes in transporter expression were assessed using quantitative polymerase chain reaction of resected liver samples. Moreover, the particular impact of pharmacokinetic drug–drug interactions in the context of endotoxemia was investigated using rifampicin (40 mg/kg), a potent inhibitor of hepatocyte transporters. LPS increased ^99mTc-mebrofenin exposure in the liver (1.7 ± 0.4-fold). Kinetic modeling revealed that endotoxemia did not impact the blood-to-liver uptake of ^99mTc-mebrofenin, which is mediated by organic anion-transporting polypeptide (Oatp) transporters. However, liver-to-bile and liver-to-blood efflux rates were dramatically decreased, leading to liver accumulation. The transcriptomic profile of hepatocyte transporters consistently showed a downregulation of multidrug resistance-associated proteins 2 and 3 (Mrp2 and Mrp3), which mediate the canalicular and sinusoidal efflux of ^99mTc-mebrofenin in hepatocytes, respectively. Rifampicin effectively blocked both the Oatp-mediated influx and the Mrp2/3-related efflux of ^99mTc-mebrofenin. The additive impact of endotoxemia and rifampicin led to a 3.0 ± 1.3-fold increase in blood exposure compared with healthy non-treated animals. ^99mTc-mebrofenin imaging is useful to investigate disease-associated change in hepatocyte transporter function.

Nanomedicine Strategies for Management of Drug Resistance in Lung Cancer

Lung cancer (LC) is one of the leading causes of cancer occurrence and mortality worldwide. Treatment of patients with advanced and metastatic LC presents a significant challenge, as malignant cells use different mechanisms to resist chemotherapy. Drug resistance (DR) is a complex process that occurs due to a variety of genetic and acquired factors. Identifying the mechanisms underlying DR in LC patients and possible therapeutic alternatives for more efficient therapy is a central goal of LC research. Advances in nanotechnology resulted in the development of targeted and multifunctional nanoscale drug constructs. The possible modulation of the components of nanomedicine, their surface functionalization, and the encapsulation of various active therapeutics provide promising tools to bypass crucial biological barriers. These attributes enhance the delivery of multiple therapeutic agents directly to the tumor microenvironment (TME), resulting in reversal of LC resistance to anticancer treatment. This review provides a broad framework for understanding the different molecular mechanisms of DR in lung cancer, presents novel nanomedicine therapeutics aimed at improving the efficacy of treatment of various forms of resistant LC; outlines current challenges in using nanotechnology for reversing DR; and discusses the future directions for the clinical application of nanomedicine in the management of LC resistance.

The Role of Uptake and Efflux Transporters in the Disposition of Glucuronide and Sulfate Conjugates

Glucuronidation and sulfation are the most typical phase II metabolic reactions of drugs. The resulting glucuronide and sulfate conjugates are generally considered inactive and safe. They may, however, be the most prominent drug-related material in the circulation and excreta of humans. The glucuronide and sulfate metabolites of drugs typically have limited cell membrane permeability and subsequently, their distribution and excretion from the human body requires transport proteins. Uptake transporters, such as organic anion transporters (OATs and OATPs), mediate the uptake of conjugates into the liver and kidney, while efflux transporters, such as multidrug resistance proteins (MRPs) and breast cancer resistance protein (BCRP), mediate expulsion of conjugates into bile, urine and the intestinal lumen. Understanding the active transport of conjugated drug metabolites is important for predicting the fate of a drug in the body and its safety and efficacy. The aim of this review is to compile the understanding of transporter-mediated disposition of phase II conjugates. We review the literature on hepatic, intestinal and renal uptake transporters participating in the transport of glucuronide and sulfate metabolites of drugs, other xenobiotics and endobiotics. In addition, we provide an update on the involvement of efflux transporters in the disposition of glucuronide and sulfate metabolites. Finally, we discuss the interplay between uptake and efflux transport in the intestine, liver and kidneys as well as the role of transporters in glucuronide and sulfate conjugate toxicity, drug interactions, pharmacogenetics and species differences.

Molecular Properties of Drugs Handled by Kidney OATs and Liver OATPs Revealed by Chemoinformatics and Machine Learning: Implications for Kidney and Liver Disease

In patients with liver or kidney disease, it is especially important to consider the routes of metabolism and elimination of small-molecule pharmaceuticals. Once in the blood, numerous drugs are taken up by the liver for metabolism and/or biliary elimination, or by the kidney for renal elimination. Many common drugs are organic anions. The major liver uptake transporters for organic anion drugs are organic anion transporter polypeptides (OATP1B1 or SLCO1B1; OATP1B3 or SLCO1B3), whereas in the kidney they are organic anion transporters (OAT1 or SLC22A6; OAT3 or SLC22A8). Since these particular OATPs are overwhelmingly found in the liver but not the kidney, and these OATs are overwhelmingly found in the kidney but not liver, it is possible to use chemoinformatics, machine learning (ML) and deep learning to analyze liver OATP-transported drugs versus kidney OAT-transported drugs. Our analysis of >30 quantitative physicochemical properties of OATP- and OAT-interacting drugs revealed eight properties that in combination, indicate a high propensity for interaction with "liver" transporters versus "kidney" ones based on machine learning (e.g., random forest, k-nearest neighbors) and deep-learning classification algorithms. Liver OATPs preferred drugs with greater hydrophobicity, higher complexity, and more ringed structures whereas kidney OATs preferred more polar drugs with more carboxyl groups. The results provide a strong molecular basis for tissue-specific targeting strategies, understanding drug-drug interactions as well as drug-metabolite interactions, and suggest a strategy for how drugs with comparable efficacy might be chosen in chronic liver or kidney disease (CKD) to minimize toxicity.

Pharmacokinetics and ADME Characterization of Intravenous and Oral [14C]-Linerixibat in Healthy Male Volunteers

Linerixibat, an oral small-molecule ileal bile acid transporter inhibitor under development for cholestatic pruritus in primary biliary cholangitis, was designed for minimal absorption from the intestine (site of pharmacological action). This study characterized the pharmacokinetics, absorption, metabolism, and excretion of [¹⁴C]-linerixibat in humans after an intravenous microtracer concomitant with unlabeled oral tablets and [¹⁴C]-linerixibat oral solution. Linerixibat exhibited absorption-limited flip-flop kinetics: longer oral versus intravenous half-life (6-7 hours vs. 0.8 hours). The short intravenous half-life was consistent with high systemic clearance (61.9 l/h) and low volume of distribution (16.3 l). In vitro studies predicted rapid hepatic clearance via cytochrome P450 3A4 metabolism, which predicted human hepatic clearance within 1.5-fold. However, linerixibat was minimally metabolized in humans after intravenous administration: ∼80% elimination via biliary/fecal excretion (>90%-97% as unchanged parent) and ∼20% renal elimination by glomerular filtration (>97% as unchanged parent). Absolute oral bioavailability of linerixibat was exceedingly low (0.05%), primarily because of a very low fraction absorbed (0.167%; fraction escaping first-pass gut metabolism (fg) ∼100%), with high hepatic extraction ratio (77.0%) acting as a secondary barrier to systemic exposure. Oral linerixibat was almost entirely excreted (>99% recovered radioactivity) in feces as unchanged and unabsorbed linerixibat. Consistent with the low oral fraction absorbed and ∼20% renal recovery of intravenous [¹⁴C]-linerixibat, urinary elimination of orally administered radioactivity was negligible (<0.04% of dose). Linerixibat unequivocally exhibited minimal gastrointestinal absorption and oral systemic exposure. Linerixibat represents a unique example of high CYP3A4 clearance in vitro but nearly complete excretion as unchanged parent drug via the biliary/fecal route. SIGNIFICANCE STATEMENT: This study conclusively established minimal absorption and systemic exposure to orally administered linerixibat in humans. The small amount of linerixibat absorbed was eliminated efficiently as unchanged parent drug via the biliary/fecal route. The hepatic clearance mechanism was mispredicted to be mediated via cytochrome P450 3A4 metabolism in vitro rather than biliary excretion of unchanged linerixibat in vivo.

Non-uniformity of Changes in Drug-Metabolizing Enzymes and Transporters in Liver Cirrhosis: Implications for Drug Dosage Adjustment

Liver cirrhosis is a chronic disease that affects the liver structure, protein expression, and overall metabolic function. Abundance data for drug-metabolizing enzymes and transporters (DMET) across all stages of disease severity are scarce. Levels of these proteins are crucial for the accurate prediction of drug clearance in hepatically impaired patients using physiologically based pharmacokinetic (PBPK) models, which can be used to guide the selection of more precise dosing. This study aimed to experimentally quantify these proteins in human liver samples and assess how they can impact the predictive performance of the PBPK models. We determined the absolute abundance of 51 DMET proteins in human liver microsomes across the three degrees of cirrhosis severity (n = 32; 6 mild, 13 moderate, and 13 severe), compared to histologically normal controls (n = 14), using QconCAT-based targeted proteomics. The results revealed a significant but non-uniform reduction in the abundance of enzymes and transporters, from control, by 30–50% in mild, 40–70% in moderate, and 50–90% in severe cirrhosis groups. Cancer and/or non-alcoholic fatty liver disease-related cirrhosis showed larger deterioration in levels of CYP3A4, 2C8, 2E1, 1A6, UGT2B4/7, CES1, FMO3/5, EPHX1, MGST1/3, BSEP, and OATP2B1 than the cholestasis set. Drug-specific pathways together with non-uniform changes of abundance across the enzymes and transporters under various degrees of cirrhosis necessitate the use of PBPK models. As case examples, such models for repaglinide, dabigatran, and zidovudine were successful in recovering disease-related alterations in drug exposure. In conclusion, the current study provides the biological rationale behind the absence of a single dose adjustment formula for all drugs in cirrhosis and demonstrates the utility of proteomics-informed PBPK modeling for drug-specific dose adjustment in liver cirrhosis.

Elucidation of Metabolic and Disposition Pathways for Maribavir in Nonhuman Primates through Mass Balance and Semi-Physiologically Based Modeling Approaches

Maribavir is in phase 3 clinical development for treatment of cytomegalovirus infection/disease in transplant recipients. Previous research conducted using only intact cynomolgus monkeys indicated biliary secretion as the primary elimination pathway for maribavir and that maribavir undergoes enterohepatic recirculation (EHR). To clarify the exact mechanisms of maribavir's EHR behavior, we studied its clearance pathways using intravenously administered ¹⁴C-labeled maribavir in intact and bile duct-cannulated (BDC) monkeys and constructed a semi-physiologically based pharmacokinetic (PBPK) model. Total radioactivity metabolite profiles in plasma and excreta were quantitatively determined along with plasma maribavir concentrations. Intact animals showed significantly lower clearance and longer half-lives in both total radioactivity and parent concentration in plasma than BDC monkeys. The primary in vitro and in vivo metabolic pathway for maribavir in monkey is direct glucuronidation; N-dealkylation and renal clearance are minor pathways. In BDC monkeys, 73% of dose was recovered as maribavir glucuronides in bile, and 3% of dose was recovered as parent in bile and feces; in intact animals' feces, 58% of dose was recovered as parent, and no glucuronides were detected. Therefore, EHR of maribavir occurs through biliary secretion of maribavir glucuronides, and this is followed by hydrolysis of glucuronides in the gut lumen and subsequent reabsorption of parent. A semi-PBPK model constructed from physiologic, in vitro, and in vivo BDC monkey data is capable of projecting maribavir's pharmacokinetic and EHR behavior in intact animals after intravenous or oral dosing and could be applied to modeling other xenobiotics that are subject to similar EHR processes. SIGNIFICANCE STATEMENT: Through both mass balance and semi-physiologically based pharmacokinetic (semi-PBPK) modeling approaches, this study mechanistically and quantitatively elucidates maribavir's enterohepatic recirculation (EHR) behavior in monkeys, which occurs via extensive direct glucuronidation, biliary secretion of these glucuronides, luminal hydrolysis of glucuronides to parent, and subsequent reabsorption of the parent. The study also identifies important drug- and animal-specific parameters that determine the EHR kinetics, and the semi-PBPK model is readily applicable to other drugs that undergo similar metabolic and recirculation mechanisms.

Pharmacokinetic and Pharmacodynamic Principles for Toxicology

Pharmacokinetic and pharmacodynamic interactions between drugs and the body play a vital role in the therapeutic effects of drugs as well as their toxicity. Toxic effects may evolve from high doses of drugs or from alterations in the absorption, distribution, metabolism, and excretion of those drugs. The effective dose of a drug is influenced by the initial dose, route of administration, drug formulation, and bioavailability. This effective dose, in conjunction with the frequency of dosing, duration of exposure, and pharmacodynamic variability, directly affects the toxicity experienced in the body.

Effects of Single Dose Rifampin on the Pharmacokinetics of Fluvastatin in Healthy Volunteers

The objective of this study was to determine the effects of the OATP inhibitor rifampin on pharmacokinetic of Biopharmaceutics Drug Disposition Classification System Class 1 compound fluvastatin. A crossover study was carried out in 10 healthy subjects who were randomized to 2 phases to receive fluvastatin 20 mg orally alone and following a 30-minute 600 mg i.v. infusion of rifampin. The results demonstrated that i.v. rifampin increased the mean area under the plasma fluvastatin concentration-time curve (AUC0-∞ ) by 255%, mean peak plasma concentration (Cmax ) by 254%, decreased oral volume of distribution by 71%, whereas the mean elimination terminal half-life (T1/2 ), mean absorption time (MAT), and time to peak concentration (Tpeak ) of fluvastatin did not significantly change. The study demonstrated that rifampin exhibited a significant drug interaction with fluvastatin. The mechanism of the increased plasma concentrations is likely due to inhibition of OATP transporters in hepatocytes.

Repurposing 99mTc-Mebrofenin as a Probe for Molecular Imaging of Hepatocyte Transporters

Hepatocyte transporters control the hepatobiliary elimination of many drugs, metabolites, and endogenous substances. Hepatocyte transporter function is altered in several pathophysiologic situations and can be modulated by certain drugs, with a potential impact for pharmacokinetics and drug-induced liver injury. The development of substrate probes with optimal properties for selective and quantitative imaging of hepatic transporters remains a challenge. 99mTc-mebrofenin has been used for decades for hepatobiliary scintigraphy, but the specific transporters controlling its liver kinetics have not been characterized until recently. These include sinusoidal influx transporters (organic anion-transporting polypeptides) responsible for hepatic uptake of 99mTc-mebrofenin, and efflux transporters (multidrug resistance-associated proteins) mediating its canalicular (liver-to-bile) and sinusoidal (liver-to-blood) excretion. Pharmacokinetic modeling enables molecular interpretation of 99mTc-mebrofenin scintigraphy data, thus offering a widely available translational method to investigate transporter-mediated drug-drug interactions in vivo. 99mTc-mebrofenin allows for phenotyping transporter function at the different poles of hepatocytes as a biomarker of liver function.

Factors Influencing Plasma Coproporphyrin-I Concentration as Biomarker of OATP1B Activity in Patients With Rheumatoid Arthritis

Organic anion transporting polypeptides (OATPs) 1B are drug transporters mainly expressed in the sinusoidal membrane. In previous reports, genetic factor, 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF), which is one of the uremic toxins, inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) decreased OATP1B1 activity in vitro, but in vivo effects of these factors have not been elucidated. Plasma coproporphyrin-I (CP-I) is spotlighted as a highly accurate endogenous substrate of OATP1B. This study focused on patients with rheumatoid arthritis (RA) and evaluated the influence of several factors comprising gene polymorphisms, uremic toxins, and inflammatory cytokines on OATP1B activity using plasma CP-I concentration. Thirty-seven outpatients with RA who satisfied the selection criteria were analyzed at the time of recruitment (baseline) and at the next visit. OATP1B1*15 carriers tended to have higher CP-I concentration compared with noncarriers. Plasma CP-I correlated positively with CMPF concentration, but did not correlate with IL-6 or TNF-α concentration. Multiple logistic regression analysis by stepwise selection identified plasma CMPF concentration and OATP1B1*15 allele as significant factors independently affecting plasma CP-I concentration at baseline and at the next visit, respectively. In conclusion, the present results suggest that inflammatory cytokines do not have clinically significant effects on OATP1B activity, whereas the effects of genetic polymorphisms and uremic toxins should be considered.

UPLC-MS/MS method for the simultaneous quantification of pravastatin, fexofenadine, rosuvastatin, and methotrexate in a hepatic uptake model and its application to the possible drug-drug interaction study of triptolide

A rapid and specific UPLC-MS/MS method with a total run time of 3.5 min was developed for the determination of pravastatin, fexofenadine, rosuvastatin, and methotrexate in rat primary hepatocytes. After protein precipitation with 70% acetonitrile (containing 30% H2 O), these four analytes were separated under gradient conditions with a mobile phase consisting of 0.03% acetic acid (v/v) and methanol at a flow rate of 0.50 mL/min. The linearity, recovery, matrix effect, accuracy, precision, and stability of the method were well validated. We evaluated drug-drug interactions based on these four compounds in freshly suspended hepatocytes. The hepatic uptake of pravastatin, fexofenadine, rosuvastatin, and methotrexate at 4°C was significantly lower than that at 37°C, and the hepatocytes were saturable with increased substrate concentration and culture time, suggesting that the rat primary hepatocyte model was successfully established. Triptolide showed a significant inhibitory effect on the hepatic uptake of these four compounds. In conclusion, this method was successfully employed for the quantification of pravastatin, fexofenadine, rosuvastatin, and methotrexate and was used to verify the rat primary hepatocyte model for Oatp1, Oatp2, Oatp4, and Oat2 transporter studies. Then, we applied this model to explore the effect of triptolide on these four transporters.

Divergent Regulation of OCT and MATE Drug Transporters by Cadmium Exposure

Coordinated transcellular transport by the uptake via organic cation transporters (OCTs) in concert with the efflux via multidrug and toxin extrusion proteins (MATEs) is an essential system for hepatic and renal drug disposition. Despite their clinical importance, the regulation of OCTs and MATEs remains poorly characterized. It has been reported that cadmium (Cd²⁺) increase the activities of OCTs while being a substrate of MATEs. Here, we found that human (h) OCT2 protein, as compared with hMATE1, was more active in trafficking between the plasma membrane and cytoplasmic storage pool. Cd²⁺ exposure could significantly enhance the translocation of hOCT2 and hOCT1, but not hMATE1, to the plasma membrane. We further identified that candesartan, a widely prescribed angiotensin II receptor blocker, behaved similarly toward OCT2 and MATE1 as Cd²⁺ did. Importantly, Cd²⁺ and candesartan treatments could lead to an enhanced accumulation of metformin, which is a well-characterized substrate of OCTs/MATEs, in mouse kidney and liver, respectively. Altogether, our studies have uncovered possible divergent regulation of OCTs and MATEs by certain xenobiotics, such as Cd²⁺ and candesartan due to the different cellular trafficking of these two families of transporter proteins, which might significantly affect drug disposition in the liver and kidney.

Overcoming the shortcomings of the extended-clearance concept: a framework for developing a physiologically-based pharmacokinetic (PBPK) model to select drug candidates involving transporter-mediated clearance

Introduction:Human pharmacokinetic (PK) prediction can be a significant challenge to drug candidates undergoing transporter-mediated clearance, when only animal data and in vitro human parameters are available in the drug discovery stage.Areas covered:The extended clearance concept (ECC) that incorporates the processes of hepatic uptake, passive diffusion, metabolism and biliary secretion has been adapted to determine the rate-determining process of hepatic clearance and drug-drug interactions (DDIs). However, since the ECC is derived from the well-stirred model and does not consider the liver as a drug distribution organ to reflect the time-dependent variation of drug concentrations between the liver and plasma, it can be misused for compound selection in drug discovery.Expert opinion:The PBPK model consists of a set of differential equations of drug mass balance, and can overcome the shortcomings of the ECC in predicting human PK. The predictability, relevance and reliability of the model and the scaling factors for IVIVE must be validated using either the measured liver concentrations or DDI data with known transporter inhibitors, or both, in monkeys. A human PBPK model that incorporates in vitro human data and SFs obtained from the validated monkey PBPK model can be used for compound selection in the drug discovery phase.

A Critical Review on Advancement in Analytical Strategies for the Quantification of Clinically Relevant Biological Transporters

Success of a drug discovery program is highly dependent on rapid scientific advancement and periodic inclusion of sensitive and specific analytical techniques. Biological membrane transporters can significantly alter the bioavailability of a molecule in its actual site of action. Expression of transporter proteins responsible for drug transport is extremely low in the biological system. Therefore, proper scientific planning in selection of their quantitative analytical technique is essential. This article discusses critical advancement in the analytical strategies for quantification of clinically relevant biological transporters for the drugs. Article cross-talked key planning and execution strategies concerning analytical quantification of the transporters during drug discovery programs.

Effects of Probenecid on Hepatic and Renal Disposition of Hexadecanedioate, an Endogenous Substrate of Organic Anion Transporting Polypeptide 1B in Rats

The aim of the present study was to investigate changes in plasma concentrations and tissue distribution of endogenous substrates of organic anion transporting polypeptide (OATP) 1B, hexadecanedioate (HDA), octadecanedioate (ODA), tetradecanedioate (TDA), and coproporphyrin-III, induced by its weak inhibitor, probenecid (PBD), in rats. PBD increased the plasma concentrations of these four compounds regardless of bile duct cannulation, whereas liver-to-plasma (K_p,liver) and kidney-to-plasma concentration ratios of HDA and TDA were reduced. Similar effects of PBD on plasma concentrations and K_p,liver of HDA, ODA, and TDA were observed in kidney-ligated rats, suggesting a minor contribution of renal disposition to the overall distribution of these three compounds. Tissue uptake clearance of deuterium-labeled HDA (d-HDA) in liver was 16-fold higher than that in kidney, and was reduced by 80% by PBD. This was compatible with inhibition by PBD of d-HDA uptake in isolated rat hepatocytes. Such inhibitory effects of PBD were also observed in the human OATP1B1-mediated uptake of d-HDA. Overall, the disposition of HDA is mainly determined by hepatic OATP-mediated uptake, which is inhibited by PBD. HDA might, thus, be a biomarker for OATPs minimally affected by urinary and biliary elimination in rats.

Hepatic transporter-mediated pharmacokinetic drug-drug interactions: Recent studies and regulatory recommendations

Transporter-mediated drug-drug interactions are one of the major mechanisms in pharmacokinetic-based drug interactions and correspondingly affecting drugs' safety and efficacy. Regulatory bodies underlined the importance of the evaluation of transporter-mediated interactions as a part of the drug development process. The liver is responsible for the elimination of a wide range of endogenous and exogenous compounds via metabolism and biliary excretion. Therefore, hepatic uptake transporters, expressed on the sinusoidal membranes of hepatocytes, and efflux transporters mediating the transport from hepatocytes to the bile are determinant factors for pharmacokinetics of drugs, and hence, drug-drug interactions. In parallel with the growing research interest in this area, regulatory guidances have been updated with detailed assay models and criteria. According to well-established preclinical results, observed or expected hepatic transporter-mediated drug-drug interactions can be taken into account for clinical studies. In this paper, various methods including in vitro, in situ, in vivo, in silico approaches, and combinational concepts and several clinical studies on the assessment of transporter-mediated drug-drug interactions were reviewed. Informative and effective evaluation by preclinical tools together with the integration of pharmacokinetic modeling and simulation can reduce unexpected clinical outcomes and enhance the success rate in drug development.

Transporter Gene Regulation in Sandwich Cultured Human Hepatocytes Through the Activation of Constitutive Androstane Receptor (CAR) or Aryl Hydrocarbon Receptor (AhR)

The induction potentials of ligand-activated nuclear receptors on metabolizing enzyme genes are routinely tested for new chemical entities. However, regulations of drug transporter genes by the nuclear receptor ligands are underappreciated, especially in differentiated human hepatocyte cultures. In this study, gene induction by the ligands of constitutive androstane receptor (CAR) and aryl hydrocarbon receptor (AhR) was characterized in sandwich-cultured human hepatocytes (SCHH) from multiple donors. The cells were treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), omeprazole (OP), 6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde O-(3,4-dichlorobenzyl)oxime (CITCO) and phenobarbital (PB) for three days. RNA samples were analyzed by qRT-PCR method. As expected, CITCO, the direct activator, and PB, the indirect activator of CAR, induced CYP3A4 (31 and 40-fold), CYP2B6 (24 and 28-fold) and UGT1A1 (2.9 and 4.2-fold), respectively. Conversely, TCDD and OP, the activators of AhR, induced CYP1A1 (38 and 37-fold), and UGT1A1 (4.3 and 5.0-fold), respectively. In addition, OP but not TCDD induced CY3A4 by about 61-fold. Twenty-four hepatic drug transporter genes were characterized, and of those, SLC51B was induced the most by PB and OP by about 3.3 and 6.5 fold, respectively. Marginal inductions (about 2-fold) of SLC47A1 and SLCO4C1 genes by PB, and ABCG2 gene by TCDD were observed. In contrast, SLC10A1 gene was suppressed about 2-fold by TCDD and CITCO. While clinical relevance of SLC51B gene induction or SLC10A1 gene suppression warrants further investigation, the results verified that the assessment of transporter gene inductions are not required for new drug entities, when a drug does not remarkably induce metabolizing enzyme genes by CAR and AhR activation.

Drug-induced liver injury after switching from tamoxifen to anastrozole in a patient with a history of breast cancer being treated for hypertension and diabetes

Anastrozole is a selective non-steroidal aromatase inhibitor that blocks the conversion of androgens to estrogens in peripheral tissues. It is used as adjuvant therapy for early-stage hormone-sensitive breast cancer in postmenopausal women. Significant side effects of anastrozole include osteoporosis and increased levels of cholesterol. To date, seven case reports on anastrozole hepatotoxicity have been published. We report the case of an 81-year-old woman with a history of breast cancer, arterial hypertension, type 2 diabetes mellitus, hyperlipidemia, and chronic renal insufficiency. Four days after switching hormone therapy from tamoxifen to anastrozole, icterus developed along with a significant increase in liver enzymes (measured in the blood). The patient was admitted to hospital, where a differential diagnosis of jaundice was made and anastrozole was withdrawn. Subsequently, hepatic functions quickly normalized. The observed liver injury was attributed to anastrozole since other possible causes of jaundice were excluded. However, concomitant pharmacotherapy could have contributed to the development of jaundice and hepatotoxicity, after switching from tamoxifen to anastrozole since several the patient’s medications were capable of inhibiting hepatobiliary transport of bilirubin, bile acids, and metabolized drugs through inhibition of ATP-binding cassette proteins. Telmisartan, tamoxifen, and metformin all block bile salt efflux pumps. The efflux function of multidrug resistance protein 2 is known to be reduced by telmisartan and tamoxifen and breast cancer resistance protein is known to be inhibited by telmisartan and amlodipine. Moreover, the activity of P-glycoprotein transporters are known to be decreased by telmisartan, amlodipine, gliquidone, as well as the previously administered tamoxifen. Finally, the role of genetic polymorphisms of cytochrome P450 enzymes and/or drug transporters cannot be ruled out since the patient was not tested for polymorphisms.

SLCO1B1 variants as predictors of methotrexate-related toxicity in children with juvenile idiopathic arthritis

Objectives: Methotrexate (MTX) administered at the dose 10-15 mg/m² is currently recommended as the first line therapy in most juvenile idiopathic arthritis (JIA) subtypes. Gastrointestinal side effects and hepatotoxicity are the most prevalent manifestations of MTX intolerance, frequently leading to discontinuation of otherwise effective treatment. Genetic variability within solute carrier organic anion transporter family member 1B1 (SLCO1B1), encoding a hepatic MTX membrane transporter, has been associated with high-dose MTX efficacy and toxicity in paediatric patients with acute lymphoblastic leukaemia. The aim of our study was to determine the association between single-nucleotide polymorphisms in the SLCO1B1 gene (rs4149056, rs2306283) on the disease activity and presence of side effects of MTX therapy in patients with JIA.Method: The study recruited 100 children with JIA of all subtypes treated with MTX. Demographic and clinical parameters were collected at the baseline of MTX therapy and on a control visit 4-6 months after starting MTX. Genotyping was performed using genomic DNA isolated from peripheral blood samples.Results: In comparison to wild-type allele, SLCO1B1 rs4149056 CT/CC variant was significantly associated with higher odds ratio of MTX gastrointestinal side effects occurrence (OR=4.55, 95%CI 1.37-15.13; p=0.013). SLCO1B1 rs4149056 TT subjects were more likely than CT/CC individuals to develop hepatotoxicity (17.86% vs 4.76%, p = 0.046).Conclusion: SLCO1B1 rs4149056 may serve as a determinant of MTX treatment toxicity in children with JIA.

Real-time fluorometric evaluation of hepatoblast proliferation in vivo and in vitro using the expression of CYP3A7 coding for human fetus-specific P450

The fields of drug discovery and regenerative medicine require large numbers of adult human primary hepatocytes. For this purpose, it is desirable to use hepatocyte-like cells (HLCs) differentiated from human pluripotent stem cells (PSCs). Premature hepatoblast-like cells (HB-LCs) differentiated from PSCs provide an intermediate source and steady supply of newly mature HLCs. To develop an efficient HB-LC induction method, we constructed a red fluorescent reporter, CYP3A7R, in which DsRed is placed under the transcriptional control of CYP3A7 coding for a human fetus-type P450 enzyme. Before using this reporter in human cells, we created transgenic mice using mouse embryonic stem cells (ESCs) carrying a CYP3A7R transgene and confirmed that CYP3A7R was specifically expressed in fetal and newborn livers and reactivated in the adult liver in response to hepatic regeneration. Moreover, we optimized the induction procedure of HB-LCs from transgenic mouse ESCs using semi-quantitative fluorometric evaluation. Activation of Wnt signaling together with chromatin modulation prior to Activin A treatment greatly improved the induction efficiency of HB-LCs. BMP2 and 1.7% dimethyl sulfoxide induced selective proliferation of HB-LCs, which matured to HLCs. Therefore, CYP3A7R will provide a fluorometric evaluation system for high content screening of chemicals that induce HB-LC differentiation, hepatocyte regeneration, and hepatotoxicity when it is introduced into human PSCs.

Effect of P-glycoprotein (P-gp) Inducers on Exposure of P-gp Substrates: Review of Clinical Drug-Drug Interaction Studies

Understanding transporter-mediated drug-drug interactions (DDIs) for investigational agents is important during drug development to assess DDI liability, its clinical relevance, and to determine appropriate DDI management strategies. P-glycoprotein (P-gp) is an efflux transporter that influences the pharmacokinetics (PK) of various compounds. Assessing transporter induction in vitro is challenging and is not always predictive of in vivo effects, and hence there is a need to consider clinical DDI studies; however, there is no clear guidance on when clinical evaluation of transporter induction is required. Furthermore, there is no proposed list of index transporter inducers to be used in clinical studies. This review evaluated DDI studies with known P-gp inducers to better understand the mechanism and site of P-gp induction, as well as the magnitude of induction effect on the exposure of P-gp substrates. Our review indicates that P-gp and cytochrome P450 (CYP450) enzymes are co-regulated via the pregnane xenobiotic receptor (PXR) and the constitutive androstane receptor (CAR). The magnitude of the decrease in substrate drug exposure by P-gp induction is generally less than that of CYP3A. Most P-gp inducers reduced total bioavailability with a minor impact on renal clearance, despite known expression of P-gp at the apical membrane of the kidney proximal tubules. Rifampin is the most potent P-gp inducer, resulting in an average reduction in substrate exposure ranging between 20 and 67%. For other inducers, the reduction in P-gp substrate exposure ranged from 12 to 42%. A lower reduction in exposure of the P-gp substrate was observed with a lower dose of the inducer and/or if the administration of the inducer and substrate was simultaneous, i.e. not staggered. These findings suggest that clinical evaluation of the impact of P-gp inducers on the PK of investigational agents that are substrates for P-gp might be warranted only for compounds with a relatively steep exposure-efficacy relationship.

Fluorescent probes for the dual investigation of MRP2 and OATP1B1 function and drug interactions

Detoxification in hepatocytes is a strictly controlled process, in which the governed action of membrane transporters involved in the uptake and efflux of potentially dangerous molecules has a crucial role. Major transporters of hepatic clearance belong to the ABC (ATP Binding Cassette) and Solute Carrier (SLC) protein families. Organic anion-transporting polypeptide OATP1B1 (encoded by the SLCO1B1 gene) is exclusively expressed in the sinusoidal membrane of hepatocytes, where it mediates the cellular uptake of bile acids, bilirubin, and also that of various drugs. The removal of toxic molecules from hepatocytes to the bile is accomplished by several ABC transporters, including P-glycoprotein (ABCB1), MRP2 (ABCC2) and BCRP (ABCG2). Owing to their pharmacological relevance, monitoring drug interaction with OATP1B1/3 and ABC proteins is recommended. Our aim was to assess the interaction of recently identified fluorescent OATP substrates (various dyes used in cell viability assays, pyranine, Cascade Blue hydrazide (CB) and sulforhodamine 101 (SR101)) (Bakos et al., 2019; Patik et al., 2018) with MRP2 and ABCG2 in order to find fluorescent probes for the simultaneous characterization of both uptake and efflux processes. Transport by MRP2 and ABCG2 was investigated in inside-out membrane vesicles (IOVs) allowing a fast screen of the transport of membrane impermeable substrates by efflux transporters. Next, transcellular transport of shared OATP and ABC transporter substrate dyes was evaluated in MDCKII cells co-expressing OATP1B1 and MRP2 or ABCG2. Our results indicate that pyranine is a general substrate of OATP1B1, OATP1B3 and OATP2B1, and we find that the dye Live/Dead Violet and CB are good tools to investigate ABCG2 function in IOVs. Besides their suitability for MRP2 functional tests in the IOV setup, pyranine, CB and SR101 are the first dual probes that can be used to simultaneously measure OATP1B1 and MRP2 function in polarized cells by a fluorescent method.

Validation of Pharmacological Protocols for Targeted Inhibition of Canalicular MRP2 Activity in Hepatocytes Using [99mTc]mebrofenin Imaging in Rats

The multidrug resistance-associated protein 2 (MRP2) mediates the biliary excretion of drugs and metabolites. [^99mTc]mebrofenin may be employed as a probe for hepatic MRP2 activity because its biliary excretion is predominantly mediated by this transporter. As the liver uptake of [^99mTc]mebrofenin depends on organic anion-transporting polypeptide (OATP) activity, a safe protocol for targeted inhibition of hepatic MRP2 is needed to study the intrinsic role of each transporter system. Diltiazem (DTZ) and cyclosporin A (CsA) were first confirmed to be potent MRP2 inhibitors in vitro. Dynamic acquisitions were performed in rats (n = 5-6 per group) to assess the kinetics of [^99mTc]mebrofenin in the liver, intestine and heart-blood pool after increasing doses of inhibitors. Their impact on hepatic blood flow was assessed using Doppler ultrasound (n = 4). DTZ (s.c., 10 mg/kg) and low-dose CsA (i.v., 0.01 mg/kg) selectively decreased the transfer of [^99mTc]mebrofenin from the liver to the bile (k₃). Higher doses of DTZ and CsA did not further decrease k₃ but dose-dependently decreased the uptake (k₁) and backflux (k₂) rate constants between blood and liver. High dose of DTZ (i.v., 3 mg/kg) but not CsA (i.v., 5 mg/kg) significantly decreased the blood flow in the portal vein and hepatic artery. Targeted pharmacological inhibition of hepatic MRP2 activity can be achieved in vivo without impacting OATP activity and liver blood flow. Clinical studies are warranted to validate [^99mTc]mebrofenin in combination with low-dose CsA as a novel substrate/inhibitor pair to untangle the role of OATP and MRP2 activity in liver diseases.

Pharmacokinetic-Based Drug-Drug Interactions with Anaplastic Lymphoma Kinase Inhibitors: A Review

Anaplastic lymphoma kinase (ALK) inhibitors are important treatment options for non-small-cell lung cancer (NSCLC), associated with ALK gene rearrangement. Patients with ALK gene rearrangement show sensitivity to and benefit clinically from treatment with ALK tyrosine kinase inhibitors (ALK-TKIs). To date, crizotinib, ceritinib, alectinib, brigatinib, lorlatinib, and entrectinib have received approval from the US Food and Drug Administration and/or the European Medicines Agency for use during the treatment of ALK-gene-rearrangement forms of NSCLC. Although the oral route of administration is convenient and results in good compliance among patients, oral administration can be affected by many factors, such as food, intragastric pH, cytochrome P450 enzymes, transporters, and p-glycoprotein. These factors can result in increased risks for serious adverse events or can lead to reduced therapeutic effects of ALK-TKIs. This review characterizes and summarizes the pharmacokinetic parameters and drug–-drug interactions associated with ALK-TKIs to provide specific recommendations for oncologists and clinical pharmacists when prescribing ALK-TKIs.

Systematic Investigation of the Effects of Long-Term Administration of a High-Fat Diet on Drug Transporters in the Mouse Liver, Kidney and Intestine

BACKGROUND

Long-term intake of a high-fat diet is a crucial factor contributing to obesity, which has become a global public health problem. Progressive obesity subsequently leads to hepatic injury, renal damage and intestinal atrophy. Transporters expressed in the liver, kidney and intestine play important roles in the deposition of nutrients and drugs, but researchers have not clearly determined whether/how the expression of transporters changes after long-term administration of a High-Fat Diet (HFD). This study aims to explore the effects of the long-term administration of a HFD on the expression of drug transporters in the liver, kidney and intestine in mice and to provide useful information for medical applications in the clinic.

METHODS

Male C57BL/6J mice were fed either a basal diet or HFD for 24 weeks, and oral glucose tolerance tests were performed after 3, 11 and 23 weeks. Serum was obtained to measure lipid metabolism, inflammatory mediators, renal function and hepatic function. Adipose tissues, kidney, pancreas and liver were collected for hematoxylin and eosin (H&E) staining after 4, 12 and 24 weeks. The mRNA and proteins expression of drug transporters in the liver, kidney and intestine were detected using real-time PCR and western blot, respectively.

RESULTS

Compared with the control group, long-term HFD administration significantly increased the adipose index. The serum lipid levels, including Total Cholesterol (TC), Triglyceride (TG), and Low-Density Lipoprotein Cholesterol (LDL-C), as well as the levels of the inflammatory cytokines Interleukin-10 (IL-10) and tumor necrosis factor-α (TNF-α) were significantly elevated in HFD-induced obese mice. H&E staining revealed pathological changes in the adipose cells, liver, kidney and pancreas from the obese group following the long-term administration of the HFD. The liver of the obese group presented increased mRNA expression of the efflux transporter Mrp2 and uptake transporter Oat2 at 24 weeks. The relative expression of Oat2 increased 4.08-fold and the protein expression of Oat2 was upregulated at 24 weeks in HFD-fed mice, while the mRNA expression of the uptake transporters Oct1, Oatp1b2 and Oatp1a4 decreased by 79%, 61% and 19%, respectively. The protein expression of Oct1 was significantly downregulated in obese mice at 12 weeks. The mRNA expression of the efflux transporter Mdr1a was significantly reduced in HFD-fed mice compared with the control group at 24 weeks. Western blot showed that the trend of protein level of Mdr1 was consistent with the mRNA expression. In the kidney, the level of the Oct2 mRNA increased 1.92- and 2.46-fold at 4 and 12 weeks in HFD-fed mice, respectively. The expression of the Oat1 and Oat3 mRNAs was markedly downregulated in the kidneys of mice with HFD-induced obesity at 4 weeks. The decrease of 72% and 21% in Mdr1a mRNA expression was observed in the obese model at 4 weeks and 12 weeks, respectively. Western blot showed that the protein levels of Mdr1 and Oat1 were consistent with the mRNA expression. The qPCR experiments showed a 2.87-fold increase in Bcrp mRNA expression at 24 weeks, and the expression of the Pept1 mRNA increased 2.84-fold in intestines of obese mice subjected to long-term administration of the HFD compared with control mice at 12 weeks. Western blot showed that the trend of protein levels of Mdr1 and Mrp2 were consistent with the mRNA expression.

CONCLUSION

The expression of uptake and efflux transporters mRNAs and protein levels were altered in obese mice compared with control mice, providing scientific evidence for future medical applications in the clinic.

Alteration in the Plasma Concentrations of Endogenous Organic Anion-Transporting Polypeptide 1B Biomarkers in Patients with Non-Small Cell Lung Cancer Treated with Paclitaxel

Paclitaxel has been considered to cause OATP1B-mediated drug-drug interactions at therapeutic doses; however, its clinical relevance has not been demonstrated. This study aimed to elucidate in vivo inhibition potency of paclitaxel against OATP1B1 and OATP1B3 using endogenous OATP1B biomarkers. Paclitaxel is an inhibitor of OATP1B1 and OATP1B3, with K_i of 0.579 ± 0.107 and 5.29 ± 3.87 μM, respectively. Preincubation potentiated its inhibitory effect on both OATP1B1 and OATP1B3, with K_i of 0.154 ± 0.031 and 0.624 ± 0.183 μM, respectively. Ten patients with non-small cell lung cancer who received 200 mg/m² of paclitaxel by a 3-hour infusion were recruited. Plasma concentrations of 10 endogenous OATP1B biomarkers-namely, coproporphyrin I, coproporphyrin III, glycochenodeoxycholate-3-sulfate, glycochenodeoxycholate-3-glucuronide, glycodeoxycholate-3-sulfate, glycodeoxycholate-3-glucuronide, lithocholate-3-sulfate, glycolithocholate-3-sulfate, taurolithocholate-3-sulfate, and chenodeoxycholate-24-glucuronide-were determined in the patients with non-small cell lung cancer on the day before paclitaxel administration and after the end of paclitaxel infusion for 7 hours. Paclitaxel increased the area under the plasma concentration-time curve (AUC) of the endogenous biomarkers 2- to 4-fold, although a few patients did not show any increment in the AUC ratios of lithocholate-3-sulfate, glycolithocholate-3-sulfate, and taurolithocholate-3-sulfate. Therapeutic doses of paclitaxel for the treatment of non-small cell lung cancer (200 mg/m²) will cause significant OATP1B1 inhibition during and at the end of the infusion. This is the first demonstration that endogenous OATP1B biomarkers could serve as surrogate biomarkers in patients. SIGNIFICANCE STATEMENT: Endogenous biomarkers can address practical and ethical issues in elucidating transporter-mediated drug-drug interaction (DDI) risks of anticancer drugs clinically. We could elucidate a significant increment of the plasma concentrations of endogenous OATP1B biomarkers after a 3-hour infusion (200 mg/m²) of paclitaxel, a time-dependent inhibitor of OATP1B, in patients with non-small cell lung cancer. The endogenous OATP1B biomarkers are useful to assess the possibility of OATP1B-mediated DDIs in patients and help in appropriately designing a dosing schedule to avoid the DDIs.

Use of imaging to assess the activity of hepatic transporters

Introduction: Membrane transporters of the SLC and ABC families are abundantly expressed in the liver, where they control the transfer of drugs/drug metabolites across the sinusoidal and canalicular hepatocyte membranes and play a pivotal role in hepatic drug clearance. Noninvasive imaging methods, such as PET, SPECT or MRI, allow for measuring the activity of hepatic transporters in vivo, provided that suitable transporter imaging probes are available.Areas covered: We give an overview of the working principles of imaging-based assessment of hepatic transporter activity. We discuss different currently available PET/SPECT radiotracers and MRI contrast agents and their applications to measure hepatic transporter activity in health and disease. We cover mathematical modeling approaches to obtain quantitative parameters of transporter activity and provide a critical assessment of methodological limitations and challenges associated with this approach.Expert opinion: PET in combination with pharmacokinetic modeling can be potentially applied in drug development to study the distribution of new drug candidates to the liver and their clearance mechanisms. This approach bears potential to mechanistically assess transporter-mediated drug-drug interactions, to assess the influence of disease on hepatic drug disposition and to validate and refine currently available in vitro-in vivo extrapolation methods to predict hepatic clearance of drugs.

Clinically Relevant OATP2B1 Inhibitors in Marketed Drug Space

OATP2B1 is an intestinal and hepatic drug uptake transporter. Intestinal OATP2B1 has been elucidated as the mechanism of unexpected clinical drug-drug interactions (DDIs), where drug exposure was unexpectedly decreased with unchanged half-life. Hepatic OATP2B1 may be an understudied clinical DDI mechanism. The aim of the present work was to understand the prevalence of clinically relevant intestinal and hepatic OATP2B1 inhibitors in marketed drug space. HEK293 cells stably overexpressing human OATP2B1 or vector control were generated and cultured for 72 h in a 96-well format. OATP2B1-mediated uptake of dibromofluorescein (DBF) was found to be optimal at 10 μM concentration and 30 min incubation time. A total of 294 drugs (top 300 marketed drugs, excluding biologics and restricted drugs, supplemented with ∼100 small-molecule drugs) were screened for OATP2B1 inhibition at 10 μM. Drugs demonstrating ≥50% inhibition in this screen were advanced for IC₅₀ determination, which was extrapolated to clinical intestinal and hepatic OATP2B1 inhibition as per 2017 FDA DDI guidance. Of the 294 drugs screened, 67 elicited ≥50% inhibition of OATP2B1-mediated DBF uptake at 10 μM screening concentration. For the 67 drugs flagged in the single-concentration inhibition screen, upon evaluation of a full concentration range, IC₅₀ values could be determined for 58 drugs. OATP2B1 IC₅₀ values established for these 58 drugs were extrapolated as potentially clinically relevant at the intestinal level for 38 orally administered drugs (I_gut/IC₅₀ ≥ 10), and 17 were flagged as potential clinical inhibitors of hepatic OATP2B1 uptake (1 + I_in,max,u/IC₅₀ ≥ 1.1). This analysis of 294 drugs demonstrated prevalence of clinically relevant intestinal and hepatic OATP2B1 inhibitors to be 13 and 6%, respectively. As OATP2B1-inhibitor drugs are not exceedingly rare, these results suggest that clinical OATP2B1 DDIs have been rarely observed because OATP2B1 is uncommonly the predominant determinant of drug disposition.