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Organic anion transporting polypeptide (OATP1B) plays a key role in the hepatic clearance of a majority of high molecular weight (MW) acids and zwitterions. Here, we evaluated the role of OATP1B-mediated uptake in the clearance of novel hypoxia-inducible factor prolyl hydroxylase inhibitors ("Dustats"), which are typically low MW (300-400 daltons) aliphatic carboxylic acids. Five acid dustats, namely daprodustat, desidustat, enarodustat, roxadustat and vadadustat, showed specific transport by OATP1B1/1B3 in transporter-transfected HEK293 cells. Neutral compound, molidustat, was not a substrate to OATP1B1/1B3. None of the dustats showed transport by other hepatic uptake transporters, including NTCP, OAT2 and OAT7. In the primary human hepatocytes, uptake of all acids was significantly reduced by rifampin (OATP1B inhibitor); with an estimated fraction transported by OATP1B ( f t ,OATP1B ) of up to >80% (daprodustat). Molidustat uptake was minimally inhibited by rifampin; and low permeability acids (desidustat and enarodustat) also showed biliary efflux in sandwich culture human hepatocytes. In vivo, intravenous pharmacokinetics of all 5 acids was significantly altered by a single-dose rifampin (30 mg/kg) in Cynomolgus monkey. Hepatic clearance (non-renal) was about 4-fold (vadadustat) to >11-fod (daprodustat and roxadustat) higher in control group compared to rifampin-treated subjects. In vivo f t ,OATP1B was estimated to be ~70-90%. In the case of molidustat, rifampin had a minimal effect on overall clearance. Rifampin also considerably reduced volume of distribution of daprodustat and roxadustat. Overall, OATP1B significantly contribute to the hepatic clearance and pharmacokinetics of several dustats, which are low MW carboxylic acids. OATP1B activity should therefore by evaluated in this property space. Significance Statement Our in vitro and in vivo results suggest that OATP1B-mediated hepatic uptake play a significant role in the pharmacokinetics of low MW acidic dustats, which are being developed or approved for the treatment of anemia in chronic kidney disease. Significant active uptake mechanisms are not apparent for the neutral compound, molidustat. Characterization of uptake mechanisms is therefore important in predicting human pharmacokinetics and evaluating drug-drug interactions for low MW acids., (Copyright © 2024 American Society for Pharmacology and Experimental Therapeutics.)

Organic anion transporter 2 (OAT2 or SLC22A7 ) plays an important role in the hepatic uptake and renal secretion of several endogenous compounds and drugs. The goal of this work is to understand the structure activity of OAT2 inhibition and assess clinical drug interaction risk. A single-point inhibition assay using OAT2-transfected HEK293 cells was employed to screen about 150 compounds; and concentration-dependent inhibition potency (IC 50 ) was measured for the identified "inhibitors". Acids represented about 65% of all inhibitors, and the frequency of bases-plus-zwitterions approximately doubled for "non-inhibitors". Interestingly, 9 of 10 most potent inhibitors (low IC 50 ) are acids (p K a ∼ 3-5). Additionally, inhibitors are significantly larger and lipophilic than non-inhibitors. In silico (binary) models were developed to identify inhibitors and non-inhibitors. Finally, in vivo risk assessed via static drug-drug interaction models identified several inhibitors with potential for renal and hepatic OAT2 inhibition at clinical doses. This is the first study assessing the global pattern of OAT2-ligand interactions.

Quantitative prediction of drug-drug interactions (DDIs) involving organic anion transporting polypeptide (OATP)1B1/1B3 inhibition is limited by uncertainty in the translatability of experimentally determined in vitro inhibition potency (half-maximal inhibitory concentration (IC 50 )). This study used an OATP1B endogenous biomarker-informed physiologically-based pharmacokinetic (PBPK) modeling approach to predict the effect of inhibitor drugs on the pharmacokinetics (PKs) of OATP1B substrates. Initial static analysis with about 42 inhibitor drugs, using in vitro IC 50 values and unbound liver inlet concentrations (I in,max,u ), suggested in vivo OATP1B inhibition risk for drugs with R-value (1+ I in,max,u /IC 50 ) above 1.5. A full-PBPK model accounting for transporter-mediated hepatic disposition was developed for coproporphyrin I (CP-I), an endogenous OATP1B biomarker. For several inhibitors (cyclosporine, diltiazem, fenebrutinib, GDC-0810, itraconazole, probenecid, and rifampicin at 3 different doses), PBPK models were developed and verified against available CP-I plasma exposure data to obtain in vivo OATP1B inhibition potency-which tend to be lower than the experimentally measured in vitro IC 50 by about 2-fold (probenecid and rifampicin) to 37-fold (GDC-0810). Models verified with CP-I data are subsequently used to predict DDIs with OATP1B probe drugs, rosuvastatin and pitavastatin. The predicted and observed area under the plasma concentration-time curve ratios are within 20% error in 55% cases, and within 30% error in 89% cases. Collectively, this comprehensive study illustrates the adequacy and utility of endogenous biomarker-informed PBPK modeling in mechanistic understanding and quantitative predictions of OATP1B-mediated DDIs in drug development., (© 2021 The Authors. Clinical Pharmacology & Therapeutics © 2021 American Society for Clinical Pharmacology and Therapeutics.)

Prospective predictions of human hepatic clearance for anionic/zwitterionic compounds, which are oftentimes subjected to transporter-mediated uptake, are challenging in drug discovery. We evaluated the utility of preclinical species, rats and cynomolgus monkeys [nonhuman primates (NHPs)], to predict the human hepatic clearance using a diverse set of acidic/zwitterionic drugs. Preclinical clearance data were generated following intravenous dosing in rats/NHPs and compared to the human clearance data ( n = 18/27). Single-species scaling of NHP clearance with an allometric exponent of 0.50 allowed for good prediction of human clearance (fold error ∼2.1, bias ∼1.0), with ∼86% predictions within 3-fold. In comparison, rats underpredicted the clearance of lipophilic acids, while overprediction was noted for hydrophilic acids. Finally, an in vitro clearance assay based on human hepatocytes, which is routinely used in discovery setting, markedly underpredicted human clearance (bias ∼0.12). Collectively, this study provides insights into the usefulness of the preclinical models in enabling pharmacokinetic optimization for acid/zwitterionic drug candidates.

Introduction : Transporters and enzymes play an important role in absorption, distribution, clearance and elimination of drugs. Areas covered : This review provides an overview of the extended clearance concept and usefulness of extended clearance classification system (ECCS) in early identification of predominant clearance mechanisms. Clinical studies demonstrating transporter-enzyme interplay, challenges in scaling clearance from in vitro systems, utility of animal models and modeling approaches for evaluating hepatic clearance and drug-drug interactions are reviewed. Expert opinion : Clinical evidence exists supporting organic anion transporting peptide (OATP)1B and drug metabolizing enzymes involvement in clearance of ECCS class 1B drugs. Emerging evidence point toward contribution of organic cation transporter (OCT)1 to hepatic uptake of cationic drugs. Although, limited clinical evidence is presented, preclinical studies and modeling suggests organic anion transporter (OAT)2-enzyme interplay in clearance of class 1A drugs. Data from in vitro assays and preclinical models coupled with physiologically based modeling approaches are key for understanding transporter-enzyme interplay, enabling prediction of pharmacokinetics, tissue exposure and drug interactions. Current methodologies incur limitations and emphasis should be placed on the development of physiologically relevant in vitro models and characterize in vivo animal models to inform mechanistic modeling and improve confidence in prospective predictions.

Nicotinic acid (NA) and nicotinamide (NAM) are biosynthetic precursors of nicotinamide adenine dinucleotide (NAD + ) - a physiologically important coenzyme that maintains the redox state of cells. Mechanisms driving their entry into cells are not well understood. Here we evaluated the hepatic uptake mechanism(s) of NA and NAM using transporter-transfected cell systems and primary human hepatocytes. NA showed robust organic anion transporter (OAT)2-mediated transport with an uptake ratio (i.e., ratio of accumulation in transfect cells to wild-type cells) of 9.7 ± 0.3, and a Michaelis-Menten constant (K m ) of 13.5 ± 3.3 µM. However, no transport was apparent via other major hepatic uptake and renal secretory transporters, including OAT1/3/4, organic anion transporting polypeptide (OATP)1B1/1B3/2B1, sodium-taurocholate co-transporting polypeptide, organ cation transporter 1/2/3. OAT2-specific transport of NA was inhibited by ketoprofen and indomethacin (known OAT2 inhibitors) in a concentration-dependent manner. Similarly, NA uptake into primary human hepatocytes showed pH- and concentration-dependence and was subject to inhibition by specific OAT2 inhibitors. Unlike NA, NAM was not transported by the hepatic and renal solute carriers upon assessment in transfected cells, although its uptake into human hepatocytes was significantly inhibited by excess unlabelled NAM and a pan-SLC inhibitor (rifamycin SV 1 mM). In conclusion, these studies demonstrate, for the first time, a specific transport mechanism for NA uptake in the human liver and suggest that OAT2 (SLC22A7) has a critical role in its physiological and pharmacological functions., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Organic anion transporting polypeptides (OATPs), expressed in human liver (OATP1B1, OATP1B3, and OATP2B1) and intestine (OATP2B1), govern the pharmacokinetics (PK) of drugs (e.g., statins) and endogenous substrates (e.g., coproporphyrin I [CPI]). Their expression is known to be modulated (e.g., disease, age, and environmental factors), and they also present as the loci of clinically relevant polymorphisms and drug interactions involving inhibition. In comparison, relatively few clinical reports describe the induction of OATPs, although the effect of inducers (e.g., rifampicin [RIF], carbamazepine [CBZ]) on OATP biomarker plasma levels and statin PK has been reported. Of note, available human tissue (e.g., biopsy) protein and messenger RNA expression profiling data indicate that OATPs in gut and liver are not induced by prototypical inducers such as RIF when compared with cytochrome P450 3A4 (CYP3A4), P-glycoprotein (Pgp), multidrug resistance-associated protein 2 (MRP2), and breast cancer resistance protein (BCRP). Such results are consistent with in vitro human hepatocyte data. Therefore, the observed impact of RIF, and possibly CBZ, on statin PK (>20% decrease in the area under the plasma concentration vs. time curve) cannot be ascribed to OATP induction with certainty. In fact, most statins and CPI have been shown to present variously as substrates of RIF-inducible proteins such as CYP3A4, Pgp, MRP2, and BCRP. Interpretation of multidose RIF data is further complicated by its autoinduction, which likely leads to decreased inhibition of OATP. In the absence of more conclusive OATP induction data, caution is needed when modeling drug-drug interactions involving multidose inducers such as RIF. SIGNIFICANCE STATEMENT: Presently, there is limited direct clinical evidence supporting the notion that human liver and gut organic anion transporting polypeptides (OATPs) are inducible by agents like rifampicin (RIF). Such data need to be reconciled and will pose challenges for attempting to incorporate OATP induction into physiologically based pharmacokinetics models. Although disparate sets of tissue biopsy (atorvastatin and carbamazepine) and in vitro hepatocyte (phenobarbital, chenodeoxycholate, and amprenavir) data present OATP messenger RNA induction (≥2-fold) by agents beyond RIF, the clinical relevance of such data needs to be determined., (Copyright © 2020 by The American Society for Pharmacology and Experimental Therapeutics.)

Drug-drug interactions (DDIs) involving drug-metabolizing enzymes and membrane transporters can lead to alteration in substrate drug (victim) exposure, and can influence the pharmacological and toxicological effects. In order to predict DDI potential, it is important to quantitatively characterize the major enzyme(s) and/or transporter(s) involved in the clearance of drugs, in terms of fraction metabolized (f m ) and fraction transported (f t ). In this review, we discuss a strategy using Extended Clearance Classification System (ECCS) to identify the clearance mechanism(s) early in drug discovery, and subsequently rational staging of in vitro characterization to determine f m and f t . In addition, the examples of complex DDIs due to involvement of transporter-enzyme interplay in the hepatic clearance are discussed., Competing Interests: Declaration of competing interest There are no conflict of interest pertaining to the content of this manuscript., (Copyright © 2019 The Japanese Society for the Study of Xenobiotics. Published by Elsevier Ltd. All rights reserved.)

PF-04991532 ((S)-6-(3-Cyclopentyl-2-(4-(trifluoromethyl)-1H-imidazol-1-yl) propanamido) nicotinic acid) is a glucokinase activator designed to achieve hepato-selectivity via organic anion-transporting polypeptides (OATP)s, so as to minimize systemic hypoglycemic effects. This study investigated the effect of OATP1B1/1B3 inhibition and renal impairment on PF-04991532 oral pharmacokinetics. Cyclosporine (600 mg single dose) increased mean area under the plasma curve (AUC) of PF-04991532 by approximately threefold in healthy subjects. In a renal impairment study, PF-04991532 AUC values were ~ 2.3-fold greater in subjects with mild, moderate, and severe kidney dysfunction, compared with healthy subjects. Physiologically-based pharmacokinetic (PBPK) model parameterizing hepatic and renal transporter-mediated disposition based on in vitro inputs, and verified using first-in-human data, indicated the key role of OATP-mediated hepatic uptake in the systematic and target-tissue exposure of PF-04991532. Mechanistic evaluation of the clinical data suggest reduced hepatic OATPs (~ 35%) and renal organic anion transporter (OAT)3 (80-90%) function with renal impairment. This study illustrates the adequacy and utility of the PBPK approach in assessing the impact of drug interactions and kidney dysfunction on transporter-mediated disposition., (© 2019 Pfizer Inc. Clinical Pharmacology & Therapeutics © 2019 American Society for Clinical Pharmacology and Therapeutics.)

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 µ M) inhibits three OATPs, while rifampicin (5 µ M) inhibits OATP1B1/1B3 only. Further, hepatitis B virus myristoylated-preS1 peptide (0.1 µ M), quinidine (100 µ M), and ketoprofen (100-300 µ M) 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., (Copyright © 2019 by The American Society for Pharmacology and Experimental Therapeutics.)

The aim of the present study was to quantitatively evaluate the drug-drug interactions (DDIs) of maraviroc (MVC) with various perpetrator drugs, including telaprevir (TVR), using an in vitro data-informed physiologically based pharmacokinetic (PBPK) model. MVC showed significant active uptake and biliary excretion in sandwich-cultured human hepatocytes, and biphasic organic anion transporting polypeptide (OATP)1B1-mediated uptake kinetics in transfected cells (high-affinity K m ∼5 µ M). No measureable active uptake was noted in OATP1B3- and OATP2B1-transfceted cells. TVR inhibited OATP1B1-mediated MVC transport in vitro, and also exhibited CYP3A time-dependent inhibition in human hepatocytes (inactivation constant, K I = 2.24 µ M, and maximum inactivation rate constant, k inact ) was approximately 34-fold lower in human hepatocytes compared with liver microsomes. A PBPK model accounting for interactions involving CYP3A, P-glycoprotein (P-gp), and OATP1B1 was developed based on in vitro mechanistic data. MVC DDIs with ketoconazole (inhibition of CYP3A and P-gp), ritonavir (inhibition of CYP3A and P-gp), efavirenz (induction of CYP3A), rifampicin (induction of CYP3A and P-gp; inhibition of OATP1B1), and TVR (inhibition of CYP3A, P-gp, and OATP1B1) were well described by the PBPK model with optimized transporter -1 ). The inactivation efficiency ( k inact / K I ) was approximately 34-fold lower in human hepatocytes compared with liver microsomes. A PBPK model accounting for interactions involving CYP3A, P-glycoprotein (P-gp), and OATP1B1 was developed based on in vitro mechanistic data. MVC DDIs with ketoconazole (inhibition of CYP3A and P-gp), ritonavir (inhibition of CYP3A and P-gp), efavirenz (induction of CYP3A), rifampicin (induction of CYP3A and P-gp; inhibition of OATP1B1), and TVR (inhibition of CYP3A, P-gp, and OATP1B1) were well described by the PBPK model with optimized transporter K i values implying that OATP1B1-mediated uptake along with CYP3A metabolism determines the hepatic clearance of MVC, and P-gp-mediated efflux limits its intestinal absorption. In summary, MVC disposition involves intestinal P-gp/CYP3A and hepatic OATP1B1/CYP3A interplay, and TVR simultaneously inhibits these multiple mechanisms leading to a strong DDI-about 9.5-fold increase in MVC oral exposure., (Copyright © 2019 by The American Society for Pharmacology and Experimental Therapeutics.)

Chronic kidney disease (CKD) differentially affects the pharmacokinetics (PK) of nonrenally cleared drugs via certain pathways (e.g., cytochrome P450 (CYP)2D6); however, the effect on CYP2C8-mediated clearance is not well understood because of overlapping substrate specificity with hepatic organic anion-transporting polypeptides (OATPs). This study used physiologically based pharmacokinetic (PBPK) modeling to delineate potential changes in CYP2C8 or OATP1B activity in patients with CKD. Drugs analyzed are predominantly substrates of CYP2C8 (rosiglitazone and pioglitazone), OATP1B (pitavastatin), or both (repaglinide). Following initial model verification, pharmacokinetics (PK) of these drugs were simulated in patients with severe CKD considering changes in glomerular filtration rate (GFR), plasma protein binding, and activity of either CYP2C8 and/or OATP1B in a stepwise manner. The PBPK analysis suggests that OATP1B activity could be decreased up to 60% in severe CKD, whereas changes to CYP2C8 are negligible. This improved understanding of CKD effect on clearance pathways could be important to inform the optimal use of nonrenally eliminated drugs in patients with CKD., (2018 The Authors. Clinical Pharmacology and Therapeutics published by Wiley Periodicals, Inc on behalf of the American Society for Clinical Pharmacology and Therapeutics.)

High-permeability-low-molecular-weight acids/zwitterions [i.e., extended clearance classification system class 1A (ECCS 1A) drugs] are considered to be cleared by metabolism with a minimal role of membrane transporters in their hepatic clearance. However, a marked disconnect in the in vitro-in vivo (IVIV) translation of hepatic clearance is often noted for these drugs. Metabolic rates measured using human liver microsomes and primary hepatocytes tend to underpredict. Here, we evaluated the role of organic anion transporter 2 (OAT2)-mediated hepatic uptake in the clearance of ECCS 1A drugs. For a set of 25 ECCS 1A drugs, in vitro transport activity was assessed using transporter-transfected cells and primary human hepatocytes. All but two drugs showed substrate affinity to OAT2, whereas four (bromfenac, entacapone, fluorescein, and nateglinide) also showed OATP1B1 activity in transfected cells. Most of these drugs (21 of 25) showed active uptake by plated human hepatocytes, with rifamycin SV (pan-transporter inhibitor) reducing the uptake by about 25%-95%. Metabolic turnover was estimated for 19 drugs after a few showed no measurable substrate depletion in liver microsomal incubations. IVIV extrapolation using in vitro data was evaluated to project human hepatic clearance of OAT2-alone substrates considering 1) uptake transport only, 2) metabolism only, and 3) transporter-enzyme interplay (extended clearance model). The transporter-enzyme interplay approach achieved improved prediction accuracy (average fold error = 1.9 and bias = 0.93) compared with the other two approaches. In conclusion, this study provides functional evidence for the role of OAT2-mediated hepatic uptake in determining the pharmacokinetics of several clinically important ECCS 1A drugs., (Copyright © 2018 by The American Society for Pharmacology and Experimental Therapeutics.)

Organic anion transporter (OAT) 2 and OAT7 were recently shown to be involved in the hepatic uptake of drugs; however, there is limited understanding of the population variability in the expression of these transporters in liver. There is also a need to derive relative expression-based scaling factors (REFs) that can be used to bridge in vitro functional data to the in vivo drug disposition. To this end, we quantified OAT2 and OAT7 surrogate peptide abundance in a large number of human liver tissue samples ( n = 52), as well as several single-donor cryopreserved human hepatocyte lots ( n = 30) by a novel, validated liquid chromatography tandem mass spectrometry (LC-MS/MS) method. The average surrogate peptide expression of OAT2 and OAT7 in the liver samples was 1.52 ± 0.57 and 4.63 ± 1.58 fmol/μg membrane protein, respectively. While we noted statistically significant differences ( p < 0.05) in hepatocyte and liver tissue abundances for both OAT2 and OAT7, the differences were relatively small (1.8- and 1.5-fold difference in median values, respectively). Large interindividual variability was noted in the hepatic expression of OAT2 (16-fold in liver tissue and 23-fold in hepatocytes). OAT7, on the other hand, showed less interindividual variability (4-fold) in the livers, but high variability for the hepatocyte lots (27-fold). A significant positive correlation in OAT2 and OAT7 expression was observed, but expression levels were neither associated with age nor sex. In conclusion, our data suggest marked interindividual variability in the hepatic expression of OAT2/7, which may contribute to the pharmacokinetic variability of their substrates. Because both transporters were less abundant in hepatocytes than livers, a REF-based approach is recommended when scaling in vitro hepatocyte transport data to predict hepatic drug clearance and liver exposure of OAT2/7 substrates.

This work explores the utility of the cynomolgus monkey as a preclinical model to predict hepatic uptake clearance mediated by organic anion transporting polypeptide (OATP) transporters. Nine OATP substrates (rosuvastatin, pravastatin, repaglinide, fexofenadine, cerivastatin, telmisartan, pitavastatin, bosentan, and valsartan) were investigated in plated cynomolgus monkey and human hepatocytes. Total uptake clearance and passive diffusion were measured in vitro from initial rates in the absence and presence of the OATP inhibitor rifamycin SV , respectively. Total uptake clearance values in plated hepatocytes ranged over three orders of magnitude in both species, with a similar rank order and good agreement in the relative contribution of active transport to total uptake between cynomolgus monkey and human. In vivo hepatic clearance for these nine drugs was determined in cynomolgus monkey after intravenous dosing. Hepatic clearances showed a range similar to human parameters and good predictions from respective hepatocyte parameters (with 2.7- and 3.8-fold bias on average, respectively). The use of cross-species empirical scaling factors (determined from cynomolgus monkey data either as the data set average or individual drug values) improved prediction (less bias, better concordance) of human hepatic clearance from human hepatocyte data alone. In vitro intracellular binding in hepatocytes also correlated well between species. It is concluded that the minimal species differences observed for the current data set between cynomolgus monkey and human hepatocyte uptake, both in vitro and in vivo, support future use of this preclinical model to delineate drug hepatic uptake and enable prediction of human in vivo intrinsic hepatic clearance., (Copyright © 2018 by The American Society for Pharmacology and Experimental Therapeutics.)

Targeted protein quantification using liquid chromatography-tandem mass spectrometry with stable isotope-labeled standards is recognized as the gold standard of practice for protein quantification. Such assays, however, can only cover a limited number of proteins, and developing targeted methods for larger numbers of proteins requires substantial investment. Alternatively, large-scale global proteomic experiments along with computational methods such as the "total protein approach" (TPA) have the potential to provide extensive protein quantification. In this study, we compared the TPA-based quantitation of seven major hepatic uptake transporters in four human liver tissue samples using global proteomic data obtained from two multiplexed tandem mass tag experiments (performed in two independent laboratories) to the quantitative data from targeted proteomic assays. The TPA-based quantitation of these hepatic transporters [sodium-taurocholate cotransporting polypeptide (NTCP/SLC10A1), organic anion transporter 2 (OAT2/SLC22A7), OAT7/SLC22A9, organic anion-transporting polypeptide 1B1 (OATP1B1/SLCO1B1), OATP1B3/SLCO1B3, OATP2B1/SLCO2B1, and organic cation transporter (OCT1/SLC22A1)] showed good-to-excellent correlations (Pearson r = 0.74-1.00) to the targeted data. In addition, the values were similar to those measured by targeted proteomics with 71% and 86% of the data sets falling within 3-fold of the targeted data. A comparison of the TPA-based quantifications of enzyme abundances to available literature data showed that the majority of the enzyme quantifications fell within the reference data intervals. In conclusion, these results demonstrate the capability of multiplexed global proteomic experiments to detect differences in protein expression between samples and provide reasonable estimations of protein expression levels., (Copyright © 2018 by The American Society for Pharmacology and Experimental Therapeutics.)

Tolbutamide is primarily metabolized by CYP2C9, and, thus, is frequently applied as a clinical probe substrate for CYP2C9 activity. However, there is a marked discrepancy in the in vitro-in vivo extrapolation of its metabolic clearance, implying a potential for additional clearance mechanisms. The goal of this study was to evaluate the role of hepatic uptake transport in the pharmacokinetics of tolbutamide and to identify the molecular mechanism thereof. Transport studies using singly transfected cells expressing six major hepatic uptake transporters showed that tolbutamide is a substrate to organic anion transporter 2 (OAT2) alone with transporter affinity [Michaelis-Menten constant ( K m )] of 19.5 ± 4.3 µ M. Additionally, OAT2-specific transport was inhibited by ketoprofen (an OAT2 inhibitor) and 1 mM rifamycin SV (pan inhibitor), but not by cyclosporine and rifampicin (OAT polypeptides/Na + -taurocholate cotransporting polypeptide inhibitors). Uptake studies in primary human hepatocytes confirmed the predominant role of OAT2 in the active uptake with significant inhibition by rifamycin SV and ketoprofen, but not by the other inhibitors. Concentration-dependent uptake was noted in human hepatocytes with active transport characterized by K m and V max values of 39.3 ± 6.6 µ M and 426 ± 30 pmol/min per milligram protein, respectively. Bottom-up physiologically based pharmacokinetic modeling was employed to verify the proposed role of OAT2-mediated hepatic uptake. In contrast to the rapid equilibrium (CYP2C9-only) model, the permeability-limited (OAT2-CYP2C9 interplay) model better described the plasma concentration-time profiles of tolbutamide. Additionally, the latter well described tolbutamide pharmacokinetics in carriers of CYP2C9 genetic variants and quantitatively rationalized its known drug-drug interactions. Our results provide first-line evidence for the role of OAT2-mediated hepatic uptake in the pharmacokinetics of tolbutamide, and imply the need for additional clinical studies in this direction., (Copyright © 2018 by The American Society for Pharmacology and Experimental Therapeutics.)