Clinical Probes and Endogenous Biomarkers as Substrates for Transporter Drug-Drug Interaction Evaluation: Perspectives From the International Transporter Consortium

New Biomarkers for Renal Transporter-Mediated Drug-Drug Interactions: Metabolomic Effects of Cimetidine, Probenecid, Verapamil, and Rifampin in Humans

The inhibition of renal transport proteins organic cation transporter 2 (OCT2), multidrug and toxin extrusion proteins (MATE1, MATE2-K), and organic anion transporters (OAT1, OAT3) causes clinically relevant drug-drug interactions (DDI). Endogenous biomarkers could be used to improve risk prediction of such renal DDIs. While a number of biomarkers for renal DDIs have been described so far, multiple criteria for valid biomarkers have frequently not been investigated, for example, specificity, metabolism, or food effects. Therefore, there is a need for novel biomarkers of renal DDIs. Here, we investigated the global metabolomic effects following the administration of two classical inhibitors of renal transport proteins [cimetidine (OCT2/MATEs), probenecid (OATs)] in human plasma and urine of healthy volunteers. Additionally, we investigated metabolomic effects of two inhibitors of other transporters [verapamil (P-glycoprotein), rifampin (organic anion transporting polypeptides)] as controls. This analysis shows that both cimetidine and probenecid affect compounds involved in caffeine metabolism, carnitines, and sulfates. Hierarchical cluster analysis of the effects of all four inhibitors on endogenous compounds identified multiple promising new sensitive and specific biomarker candidates for OCT2/MATE- or OAT-mediated DDIs. For OCT2/MATEs, 5-amino valeric acid betaine (median log2-fold change of estimated renal elimination: -3.62) presented itself as a promising candidate. For OATs, estimated renal elimination of 7-methyluric acid and cinnamoylglycine (median log2-fold changes -3.10 and -1.92, respectively) was both sensitive and specific. This study provides comprehensive information on metabolomic effects of transport protein inhibition in humans and identifies putative new sensitive and specific biomarkers for renal transporter-mediated DDIs.

Endogenous plasma riboflavin is not a viable BCRP biomarker in human

Recent reports suggest that plasma riboflavin may serve as a biomarker for BCRP inhibition in humans. However, the clinical data supporting this claim have been limited, with only two studies showing modest increases in riboflavin levels after administration of a BCRP inhibitor. We have recently demonstrated that co-administration of 375 mg once daily (q.d.) cedirogant, an in vitro BCRP inhibitor, significantly increased rosuvastatin (an OATP1B1/1B3 and BCRP substrate) exposures but did not change the levels of the OATP1B endogenous biomarker coproporphyrin-I, demonstrating that cedirogant is a clinical BCRP inhibitor. Samples from this same cedirogant clinical drug-drug interaction study were utilized to test the hypothesis that endogenous plasma riboflavin is a biomarker of BCRP inhibition. Plasma riboflavin levels in the absence of cedirogant ranged from 1 to 10 ng/mL across the 11 participants analyzed with minimal (<20%) intrasubject variability over a 24-hour interval. Contrary to expectations, 375 mg q.d. oral administration of cedirogant did not increase riboflavin levels. These data strongly suggest that endogenous plasma riboflavin is not a viable biomarker for BCRP inhibition in humans.

Tracing the Evolution: A Comprehensive Bibliometric Analysis of Drug Interaction Clinical Studies

This study aims to meticulously map the bibliometric landscape of drug-drug interactions (DDIs) in clinical research. This represents the first use of bibliometric analysis to comprehensively highlight the evolutionary trends and core themes in this critical field of pharmacology. An exhaustive bibliometric search was performed within the Web of Science Core Collection, aiming to comprehensively gather literature on DDIs in clinical settings. A combination of sophisticated analytical tools including DIKW, VOSviewer, and Citespace was utilized for an in-depth exploration of bibliometric patterns and trends. Of the 3421 initially identified articles, 2622 were considered relevant. The analysis revealed a marked escalation in DDIs publications, with a peak observed in 2020. Five principal thematic clusters emerged: Safety and Adverse Reactions, Drug Metabolism and Efficacy, Disease and Drug Treatment, Research Methods and Practices, and Special Populations and Combined Medication. Key insights included the escalating significance of drug metabolism in pharmacokinetics, heightened focus on cardiovascular and antiviral therapeutics, and the advancing frontier of personalized medicine. Additionally, the analysis underscored the necessity for strategic attention to vulnerable populations and innovative methodological approaches. This study calls for the global harmonization of research methods in DDIs clinical investigations, advocating for the integration of personalized medicine paradigms and the implementation of cutting-edge computational analytics. It highlights the imperative for inclusive and collaborative research approaches to adeptly address the intricate challenges of contemporary pharmacotherapy.

A close examination of BCRP's role in lactation and methods for predicting drug distribution into milk

Breastfeeding is the most complete nutritional method of feeding infants, but several impediments affect the decision to breastfeed, including questions of drug safety for medications needed during lactation. Despite recent FDA guidance, few labels provide clear dosing advice during lactation. Physiologically based pharmacokinetic modeling (PBPK) is well suited to mechanistically explore pharmacokinetics and dosing paradigms to fill gaps in the absence of extensive clinical studies and complement existing real-world data. For lactation-focused PBPK (Lact-PBPK) models, information on system parameters (e.g., expression of drug transporters in mammary epithelial cells) is sparse. The breast cancer resistance protein (BCRP) is expressed on the apical side of mammary epithelial cells where it actively transports drugs/substrates into milk (reported milk: plasma ratios range from 2 to 20). A critical review of BCRP and its role in lactation was conducted. Longitudinal changes in BCRP mRNA expression have been identified in women with a maximum reached around 5 months postpartum. Limited data are available on the ontogeny of BCRP in infant intestine; however, data indicate lower BCRP abundance in infants compared to adults. Current status of incorporation of drug transporter information in Lact-PBPK models to predict active secretion of drugs into breast milk and consequential exposure of breast-fed infants is discussed. In addition, this review highlights novel clinical tools for evaluation of BCRP activity, namely a potential non-invasive BCRP biomarker (riboflavin) and liquid biopsy that could be used to quantitatively elucidate the role of this transporter without the need for administration of drugs and to inform Lact-PBPK models.

Ticagrelor modestly raises plasma riboflavin concentration in humans and inhibits riboflavin transport by BCRP and MRP4

Riboflavin (vitamin B2) has been proposed as a biomarker for breast cancer resistance protein (BCRP) activity. In recent studies in mice, cynomolgus monkeys, and humans, BCRP-inhibiting drugs increased the plasma concentration of riboflavin. We showed recently that ticagrelor inhibits BCRP and raises the plasma concentrations of the BCRP substrate rosuvastatin in healthy volunteers. In the same drug-drug interaction study, we now investigated whether ticagrelor affects the plasma concentrations of riboflavin. Intake of 90 mg ticagrelor increased the ratio between the peak plasma riboflavin concentration and the fasting riboflavin concentration before ticagrelor administration by 1.20-fold (90% confidence interval, 1.10-1.32; P = 0.006) compared to placebo. In vitro, riboflavin was transported by BCRP and multidrug-resistance-associated protein 4 (MRP4) but no clear transport was observed by MRP2, MRP3, or the P-glycoprotein. Moreover, ticagrelor inhibited the transport of riboflavin in BCRP- and MRP4-expressing membrane vesicles with unbound 50% inhibitory concentrations of 0.020 and 1.1 μM, respectively. Based on vesicle and tissue protein expression data, the small intestinal MRP4-mediated efflux clearance of riboflavin (1.2-1.4 nL/min/mg) was estimated to be similar to that mediated by BCRP (0.23-1.3 nL/min/mg). As MRP4 is expressed in the basolateral membrane of enterocytes, it may facilitate the absorption of riboflavin and impair the utility of riboflavin as a biomarker of intestinal BCRP. To conclude, ticagrelor modestly raises the plasma concentration of riboflavin probably by inhibiting intestinal BCRP. Inhibition of intestinal MRP4 may have reduced the absorption of riboflavin and limited the effect of ticagrelor on riboflavin levels.

Pseudo-Worsening of Kidney Function Due to Inhibition of Renal Creatinine Secretion: Quality of Information Provided in Prescribing Information/SmPC

Determination of serum creatinine concentrations and subsequent calculation of estimated glomerular filtration rates (eGFR) is a cornerstone of clinical medicine. Crucial clinical decisions such as drug treatment discontinuations are based on eGFR calculated from serum creatinine measurements. However, creatinine is not only filtered in the kidneys, but also actively secreted into urine. Creatinine transporters such as OCT2, OCT3, MATE1, MATE2-K, and OAT2 expressed in proximal tubular cells are responsible for active renal secretion of creatinine. Multiple drugs (e.g., oral antitumor drugs) inhibit these transporters thereby causing a pseudo-worsening of kidney function with an increase in serum creatinine concentrations and a decrease in eGFR while other methods for eGFR determination (e.g., by cystatin C) reveal normal kidney function. Since US Prescribing Information (PI) and European Summaries of Product Characteristics (SmPCs) are the most relevant source of information for physicians, we investigated the quality of information in US PI/German SmPCs of drugs with clear evidence for pseudo-worsening of kidney function. 514 drugs putatively interacting with creatinine transporters were identified. For 149 of those drugs, an increase in serum creatinine concentrations has been described. Available data confirmed the existence of pseudo-worsening of kidney function for 30 of those drugs, for the remaining 119 drugs existing data are insufficient. Only 23.5% (12/51) of the 30 drugs' PI/SmPCs contained unambiguous statements on this proven pseudo-worsening of kidney function and gave clear recommendations for clinical management. Taken together, inadequate information provided in PI or SmPCs on the pseudo-worsening of kidney function poses patients at unnecessary risks.

Coproporphyrin-I as a Selective OATP1B Biomarker Can Be Used to Delineate the Mechanisms of Complex Drug-Drug Interactions: Cedirogant Case Study

Cedirogant is an inverse agonist of retinoic acid-related orphan receptor gamma thymus developed for the treatment of chronic plaque psoriasis. Cedirogant induces cytochrome P450 (CYP) 3A4 while inhibiting P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), organic anion transporting polypeptide (OATP) 1B1, and OATP1B3 in vitro. Static drug-drug interactions (DDIs) predictions suggested possible clinical induction of CYP3A4, and inhibition of P-gp, BCRP, and OATP1B1, leading to challenges in interpreting DDI studies between cedirogant and substrates of CYP3A, P-gp, BCRP, and OATP1B1/3. Here the effects of cedirogant on the pharmacokinetics of two statin drugs were investigated in healthy participants. Coproporphyrin-I (CP-I), a selective endogenous OATP1B biomarker, was used to assess the impact of cedirogant on OATP1B. Cedirogant (375 mg once daily) increased rosuvastatin maximum plasma concentration (Cmax) and area under the plasma concentration curve (AUCtau) by 141% and 55%, respectively when co-administered, whereas atorvastatin Cmax increased by 40% with no effect on its AUCtau compared with administration of rosuvastatin/atorvastatin alone. Cedirogant did not increase CP-I exposures, indicating no clinical OATP1B inhibition. The increased rosuvastatin exposure and minimal change in atorvastatin exposure with co-administration of cedirogant is attributed to BCRP inhibition and interplay between P-gp/BCRP inhibition and CYP3A induction, respectively. Correlation analysis with data from two investigational drugs (glecaprevir and flubentylosin) demonstrated that OATP1B1 R-value of > 1.5 and [Cmax,u]/[OATP1B1 IC50] of > 0.1 are associated with > 1.25-fold increase in CP-I Cmax ratio. This demonstrates the utility of CP-I in disentangling mechanisms underlying a complex DDI involving multiple transporters and enzymes and proposes refined criteria for static OATP1B inhibition predictions.

Drug transporters in drug disposition - highlights from the year 2023

Drug transporter field is rapidly evolving with significant progress in in vitro and in vivo tools and, computational models to assess transporter-mediated drug disposition and drug-drug interactions (DDIs) in humans. On behalf of all coauthors, I am pleased to share the fourth annual review highlighting articles published and deemed influential in the field of drug transporters in the year 2023. Each coauthor independently selected peer-reviewed articles published or available online in the year 2023 and summarized them as shown previously (Chothe et al. 2021; Chothe et al. 2022, 2023) with unbiased perspectives. Based on selected articles, this review was categorized into four sections: (1) transporter structure and in vitro evaluation, (2) novel in vitro/ex vivo models, (3) endogenous biomarkers, and (4) PBPK modeling for evaluating transporter DDIs (Table 1). As the scope of this review is not to comprehensively review each article, readers are encouraged to consult original paper for specific details. Finally, I appreciate all the authors for their time and continued support in writing this review.

Significant increases in detection capability for assessment of organic anion transporting polypeptide-mediated drug-drug interaction in cynomolgus monkeys by modifying pretreatment of Coproporphyrin I and III, and glycochenodeoxycholate-3-sulfate in plasma

BACKGROUND

Coproporphyrin I (CP-I), Coproporphyrin III (CP-III), and glycochenodeoxycholate-3-sulfate (GCDCA-S) act as endogenous substrates of Organic Anion Transporting Polypeptide (OATP) 1B and have been considered for application in OATP1B-mediated drug‒drug interaction (DDI) risk assessments. Prior assays of the endogenous OATP substrates might exhibit reduced DDI detection capability and possibly overlook low DDI risk. We pioneered a simultaneous assay of the three substrates in monkey plasma using ultra-performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS) and applied it to monkey studies to identify lower DDI risk.

RESULTS

The methodology development indicated that precursors of CP-I/III were oxidized to form CP-I/III, diminishing the detection capability in DDI risk assessments. A precursor eliminated analytical (PEA) method was developed to eliminate the precursors through solid-phase extraction. This method aimed to prevent the oxidation of CP-I/III precursors by incorporating edaravone. For comparison, a precursor oxidized analytical (POA) method was also developed, wherein the precursors of CP-I/III were fully oxidized to CP-I/III. The PEA method achieved high sensitivity for CP-I/III and GCDCA-S, with lower quantification limits of 0.01 ng mL-1 and 0.5 ng mL-1, respectively. Both methods ensured that the validation parameters met the acceptance criteria. The two methods were applied to a monkey study, with CP-I/III showcasing notably enhanced DDI detection capabilities through the novel PEA method in comparison to the POA method.

SIGNIFICANCE

This study's methodology has future implications for OATP-mediated DDI risk assessment using endogenous substrates. The novel PEA method can identify lower OATP-mediated DDI risks for drugs that the current methods cannot detect. Our method is likely applicable in clinical settings, and its utility should be assessed in clinical trials.

In Vivo Activity of Intestinal P-Glycoprotein and Hepatic Organic Anion Transporters Polypeptide in Pregnancy and Postpartum

This study investigates the influence of pregnancy on the in vivo activity of the intestinal P-glycoprotein (P-gp) and hepatic organic anion transporters polypeptide (OATP/BCRP) using, respectively, fexofenadine and rosuvastatin as probe drugs. Eleven healthy participants were investigated during the third trimester of pregnancy (Phase 1, 28 to 38 weeks of gestation) and in the postpartum period (Phase 2, 8 to 12 weeks postpartum). In both phases, after administration of a single oral dose of fexofenadine (60 mg) and rosuvastatin (5 mg), serial blood samples were collected for up to 24 h. Rosuvastatin and fexofenadine in plasma were analyzed by LC-MS/MS using previously validated methods. The pharmacokinetic parameters of fexofenadine and rosuvastatin (Phoenix WinNonLin software) with normal distribution (Shapiro-Wilk test) are presented as geometric mean and 90% confidence interval. Phases 1 and 2 were compared using the t test (P < .05). Fexofexadine AUC0-24 values do not differ (P-value: .0715) between Phase 1 (641.9 ng h/mL [500.6-823.1]) and Phase 2 (823.8 ng h/mL [641.5-1057.6]) showing that pregnancy (third trimester) does not alter intestinal P-gp activity. However, rosuvastatin AUC0-24 values are higher (P-value: .00005) in Phase 1 (18.7 ng h/mL [13.3-26.4]) when compared to Phase 2 (9.5 ng h/mL [6.7-13.4]), suggesting inhibition of OATP1B1/OATP1B3 transporters. In conclusion, pregnancy assessed during the third trimester does not alter the intestinal P-gp activity but reduces the activity of hepatic OATP1B1/OATP1B3 transporters. Therefore, adjustments in dosage regimens may be necessary for drugs with low therapeutic index, substrates of the OATP1B1/OATP1B3 transporters, administered during the third trimester of pregnancy.

Development and validation of an UPLC-MS/MS method for the simultaneous determination of fexofenadine and olmesartan in human serum: Application to in vivo pharmacokinetic studies

A sensitive, reproducible, robust, high-throughput ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and validated for the simultaneous quantification of fexofenadine and olmesartan in human serum. Samples (50 µL) undergo protein precipitation prior to UPLC-MS/MS analysis. The analytes were separated using an Acquity BEH C18 column (2.1 mm × 50 mm, 1.7 µm) at a flow rate of 0.5 mL/min using a gradient elution with a total run time of 4 min. The analytes were detected in positive ion mode and selected reaction monitoring (SRM) was used for quantitation. The standard curve concentration range was 1.0-500.0 ng/mL for both analytes and each analyte showed excellent linearity with correlation coefficients (R2 > 0.99). The intra- and inter-day accuracy and precision were ±15% for each analyte, and excellent recovery was demonstrated (93-98%) for both analytes. The method is well suited for high-throughput quantitative determination of fexofenadine and olmesartan simultaneously and was successfully applied to an in vivo pharmacokinetic and transporter phenotyping study in humans.

Innovative Approaches to Optimize Clinical Transporter Drug-Drug Interaction Studies

Of the 450 cell membrane transporters responsible for shuttling substrates, nutrients, hormones, neurotransmitters, antioxidants, and signaling molecules, approximately nine are associated with clinically relevant drug-drug interactions (DDIs) due to their role in drug and metabolite transport. Therefore, a clinical study evaluating potential transporter DDIs is recommended if an investigational product is intestinally absorbed, undergoes renal or hepatic elimination, or is suspected to either be a transporter substrate or perpetrator. However, many of the transporter substrates and inhibitors administered during a DDI study also affect cytochrome P450 (CYP) activity, which can complicate data interpretation. To overcome these challenges, the assessment of endogenous biomarkers can help elucidate the mechanism of complex DDIs when multiple transporters or CYPs may be involved. This perspective article will highlight how creative study designs are currently being utilized to address complex transporter DDIs and the role of physiology-based -pharmacokinetic (PBPK) models can play.

A Pilot Study To Assess the Suitability of Riboflavin As a Surrogate Marker of Breast Cancer Resistance Protein in Healthy Participants

We recently showed that riboflavin is a selected substrate of breast cancer resistance protein (BCRP) over P-glycoprotein (P-gp) and demonstrated its prediction performance in preclinical drug-drug interaction (DDI) studies. The aim of this study was to investigate the suitability of riboflavin to assess BCRP inhibition in humans. First, we assessed the substrate potential of riboflavin toward other major drug transporters using established transfected cell systems. Riboflavin is a substrate for organic anion transporter (OAT)1, OAT3, and multidrug and toxin extrusion protein (MATE)2-K, with uptake ratios ranging from 2.69 to 11.6, but riboflavin is not a substrate of organic anion-transporting polypeptide (OATP)1B1, OATP1B3, organic cation transporter (OCT)2, and MATE1. The effects of BMS-986371, a potent in vitro inhibitor of BCRP (IC 50 0.40 μM), on the pharmacokinetics of riboflavin, isobutyryl carnitine, and arginine were then examined in healthy male adults (N = 14 or 16) after oral administration of methotrexate (MTX) (7.5 mg) and enteric-coated (EC) sulfasalazine (SSZ) (1000 mg) alone or in combination with BMS-986371 (150 mg). Oral administration of BMS-986371 increased the area under the plasma concentration-time curves (AUCs) of rosuvastatin and immediate-release (IR) SSZ to 1.38- and 1.51-fold, respectively, and significantly increased AUC(0-4h), AUC(0-24h), and C max of riboflavin by 1.25-, 1.14-, and 1.11-fold (P-values of 0.003, 0.009, and 0.025, respectively) compared with the MTX/SSZ EC alone group. In contrast, BMS-986371 did not significantly influence the AUC(0-24h) and C max values of isobutyryl carnitine and arginine (0.96- to 1.07-fold, respectively; P > 0.05). Overall, these data indicate that plasma riboflavin is a promising biomarker of BCRP that may offer a possibility to assess drug candidate as a BCRP modulator in early drug development. SIGNIFICANCE STATEMENT: Endogenous compounds that serve as biomarkers for clinical inhibition of breast cancer resistance protein (BCRP) are not currently available. This study provides the initial evidence that riboflavin is a promising BCRP biomarker in humans. For the first time, the value of leveraging the substrate of BCRP with acceptable prediction performance in clinical studies is shown. Additional clinical investigations with known BCRP inhibitors are needed to fully validate and showcase the utility of this biomarker.

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.

Expanding Role of Endogenous Biomarkers for Assessment of Transporter Activity in Drug Development: Current Applications and Future Horizon

The evaluation of transporter-mediated drug-drug interactions (DDIs) during drug development and post-approval contributes to benefit-risk assessment and helps formulate clinical management strategies. The use of endogenous biomarkers, which are substrates of clinically relevant uptake and efflux transporters, to assess the transporter inhibitory potential of a drug has received widespread attention. Endogenous biomarkers, such as coproporphyrin (CP) I and III, have increased mechanistic understanding of complex DDIs. Other endogenous biomarkers are under evaluation, including, but not limited to, sulfated bile acids and 4-pyridoxic acid (PDA). The role of endogenous biomarkers has expanded beyond facilitating assessment of transporter-mediated DDIs and they have also been used to understand alterations in transporter activity in the setting of organ dysfunction and various disease states. We envision that endogenous biomarker-informed approaches will not only help to formulate a prudent and informed DDI assessment strategy but also facilitate quantitative predictions of changes in drug exposures in specific populations.

Utilising Endogenous Biomarkers in Drug Development to Streamline the Assessment of Drug-Drug Interactions Mediated by Renal Transporters: A Pharmaceutical Industry Perspective

The renal secretion of many drugs is facilitated by membrane transporters, including organic cation transporter 2, multidrug and toxin extrusion protein 1/2-K and organic anion transporters 1 and 3. Inhibition of these transporters can reduce renal excretion of drugs and thereby pose a safety risk. Assessing the risk of inhibition of these membrane transporters by investigational drugs remains a key focus in the evaluation of drug-drug interactions (DDIs). Current methods to predict DDI risk are based on generating in vitro data followed by a clinical assessment using a recommended exogenous probe substrate for the individual drug transporter. More recently, monitoring plasma-based and urine-based endogenous biomarkers to predict transporter-mediated DDIs in early phase I studies represents a promising approach to facilitate, improve and potentially avoid conventional clinical DDI studies. This perspective reviews the evidence for use of these endogenous biomarkers in the assessment of renal transporter-mediated DDI, evaluates how endogenous biomarkers may help to expand the DDI assessment toolkit and offers some potential knowledge gaps. A conceptual framework for assessment that may complement the current paradigm of predicting the potential for renal transporter-mediated DDIs is outlined.

An Isolated Perfused Rat Liver Model: Simultaneous LC-MS Quantification of Pitavastatin, Coproporphyrin I, and Coproporphyrin III Levels in the Rat Liver and Bile

The isolated perfused rat liver (IPRL) model provides a mechanistic understanding of the organic-anion-transporting polypeptide (OATP/Oatp)-mediated pharmacokinetics in the preclinical evaluation, which often requires the use of control substrates (i.e., pitavastatin) and monitoring endogenous biomarkers (coproporphyrin I and III). This study aimed to develop and validate an LC-MS method allowing the simultaneous quantification of pitavastatin, coproporphyrin I (CPI), and coproporphyrin III (CPIII) in rat liver perfusion matrices (perfusate, liver homogenate, bile). The analysis was performed on a C18 column at 60 °C with 20 μL of sample injection. The mobile phases consisted of water with 0.1% formic acid and acetonitrile with 0.1% formic acid with a gradient flow of 0.5 mL/min. The assay was validated according to the ICH M10 Bioanalytical Method Validation Guideline (2022) for selectivity, calibration curve and range, matrix effect, carryover, accuracy, precision, and reinjection reproducibility. The method allowing the simultaneous quantification of pitavastatin, CPI, and CPIII was selective without having carryover and matrix effects. The linear calibration curves were obtained within various calibration ranges for three analytes in different matrices. Accuracy and precision values fulfilled the required limits. After 60 min perfusion with pitavastatin (1 μM), the cumulative amounts of pitavastatin in the liver and bile were 5.770 ± 1.504 and 0.852 ± 0.430 nmol/g liver, respectively. CPIII was a more dominant marker than CPI in both liver (0.028 ± 0.017 vs 0.013 ± 0.008 nmol/g liver) and bile (0.016 ± 0.011 vs 0.009 ± 0.007 nmol/g liver). The novel and validated bioanalytical method can be applied in further IPRL preparations investigating Oatp-mediated pharmacokinetics and DDIs.

Membrane transporters in drug development and as determinants of precision medicine

The effect of membrane transporters on drug disposition, efficacy and safety is now well recognized. Since the initial publication from the International Transporter Consortium, significant progress has been made in understanding the roles and functions of transporters, as well as in the development of tools and models to assess and predict transporter-mediated activity, toxicity and drug-drug interactions (DDIs). Notable advances include an increased understanding of the effects of intrinsic and extrinsic factors on transporter activity, the application of physiologically based pharmacokinetic modelling in predicting transporter-mediated drug disposition, the identification of endogenous biomarkers to assess transporter-mediated DDIs and the determination of the cryogenic electron microscopy structures of SLC and ABC transporters. This article provides an overview of these key developments, highlighting unanswered questions, regulatory considerations and future directions.

Assessing Pleiotropic Effects of a Mixed-Mode Perpetrator Drug, Rifampicin, by Multiple Endogenous Biomarkers in Dogs

Rifampicin (RIF) is a mixed-mode perpetrator that produces pleiotropic effects on liver cytochrome P450 enzymes and drug transporters. To assess the complex drug-drug interaction liabilities of RIF in vivo, a known probe substrate, midazolam (MDZ), along with multiple endogenous biomarkers were simultaneously monitored in beagle dogs before and after a 7-day treatment period by RIF at 20 mg/kg per day. Confirmed by the reduced MDZ plasma exposure and elevated 4β-hydroxycholesterol (4β-HC, biomarker of CYP3A activities) level, CYP3A was significantly induced after repeated RIF doses, and such induction persisted for 3 days after cessation of the RIF administration. On the other hand, increased plasma levels of coproporphyrin (CP)-I and III [biomarkers of organic anion transporting polypeptides 1b (Oatp1b) activities] were observed after the first dose of RIF. Plasma CPs started to decline as RIF exposure decreased, and they returned to baseline 3 days after cessation of the RIF administration. The data suggested the acute (inhibitory) and chronic (inductive) effects of RIF on Oatp1b and CYP3A enzymes, respectively, and a 3-day washout period is deemed adequate to remove superimposed Oatp1b inhibition from CYP3A induction. In addition, apparent self-induction of RIF was observed as its terminal half-life was significantly altered after multiple doses. Overall, our investigation illustrated the need for appropriate timing of modulator dosing to differentiate between transporter inhibition and enzyme induction. As further indicated by the CP data, induction of Oatp1b activities was not likely after repeated RIF administration. SIGNIFICANCE STATEMENT: This investigation demonstrated the utility of endogenous biomarkers towards complex drug-drug interactions by rifampicin (RIF) and successfully determined the optimal timing to differentiate between transporter inhibition and enzyme induction. Based on experimental evidence, Oatp1b induction following repeated RIF administration was unlikely, and apparent self-induction of RIF elimination was observed.

Quantitative prediction of transporter-mediated drug-drug interactions using the mechanistic static pharmacokinetic (MSPK) model

Guidance/guidelines on drug-drug interactions (DDIs) have been issued in Japan, the United States, and Europe. These guidance/guidelines provide decision trees for conducting metabolizing enzyme-mediated clinical DDI studies; however, the decision trees for transporter-mediated DDIs lack quantitative prediction methods. In this study, the accuracy of a net-effect mechanistic static pharmacokinetics (MSPK) model containing the fraction transported (ft) of transporters was examined to predict transporter-mediated DDIs. This study collected information on 25 oral drugs with new active reagents that were used in clinical DDI studies as perpetrators (42 cases) from drugs approved in Japan between April 2016 and June 2020. The AUCRs (AUC ratios with and without perpetrators) of victim drugs were predicted using the net-effect MSPK model. As a result, 83 and 95% of the predicted AUCRs were within 1.5- and 2-fold error in the observed AUCRs, respectively. In cases where the victims were statins in which pharmacokinetics several transporters are involved, 70 and 91% of the predicted AUCRs were within 1.5- and 2-fold errors, respectively. Therefore, the net-effect MSPK model was applicable for predicting the AUCRs of victims, which are substrates for multiple transporters.

The Effect of BI 730357 (Retinoic Acid-Related Orphan Receptor Gamma t Antagonist, Bevurogant) on the Pharmacokinetics of a Transporter Probe Cocktail, Including Digoxin, Furosemide, Metformin, and Rosuvastatin: An Open-Label, Non-randomized, 2-Period Fixed-Sequence Trial in Healthy Subjects

Evaluating Drug-Drug Interactions (DDIs) for new investigational compounds requires several trials evaluating different drugs with different transporter specificities. By using a cocktail of drugs with different transporter specificities, a single trial could evaluate the pharmacokinetics (PKs) of each cocktail drug simultaneously, reducing the number of clinical DDI trials required for clinical development. We aimed to investigate the effect of steady-state Boehringer Ingelheim (BI) 730357 (bevurogant) on the PKs of a validated and optimized 4-component transporter cocktail. This open-label, non-randomized, 2-period fixed-sequence phase I trial compared transporter cocktail (0.25 mg digoxin/1 mg furosemide/10 mg metformin hydrochloride/10 mg rosuvastatin) with and without BI 730357 in healthy subjects aged 18-55 years with body mass index 18.5-29.9 kg/m2 . During reference treatment/period 1, transporter cocktail was administered 90 minutes after breakfast. After a washout period, during test treatment/period 2, BI 730357 was dosed twice daily for 13 days, with transporter cocktail administered on day 1. The primary endpoints were the area under the concentration-time curve of the analyte in plasma over the time interval from 0 extrapolated to infinity (AUC0-∞ ) and the maximum measured concentration of the analyte in plasma (Cmax ), and the secondary endpoint was the area under the concentration-time curve of the analyte in plasma over the time interval from 0 to the last quantifiable data point (AUC0-tz ). Steady-state BI 730357 increased digoxin (+48% to +94%), minimally affected metformin (-2% to -9%), furosemide (+12% to +18%), and rosuvastatin (+19% to +39%) exposure. Therefore, no clinically relevant inhibition of transporters OCT2/MATE-1/MATE-2K, OAT1/OAT3, OATP1B1/OATP1B3 was observed. Potential inhibition of breast cancer resistance protein noted as PK parameters of coproporphyrin I/III (OATP1B1/OATP1B3 biomarkers) remained within bioequivalence boundaries while rosuvastatin PK parameters (AUC0-∞ /Cmax /AUC0-tz ) exceeded the bioequivalence boundary. BI 730357 was safe and well tolerated. This trial confirms the usefulness and tolerability of the transporter cocktail consisting of digoxin, furosemide, metformin, and rosuvastatin in assessing drug-transporter interactions in vivo.

Effect of probenecid on blood levels and renal elimination of furosemide and endogenous compounds in rats: Discovery of putative organic anion transporter biomarkers

Transporter-mediated drug-drug interactions (DDIs) are assessed using probe drugs and in vitro and in vivo models during drug development. The utility of endogenous metabolites as transporter biomarkers is emerging for prediction of DDIs during early phases of clinical trials. Endogenous metabolites such as pyridoxic acid and kynurenic acid have shown potential to predict DDIs mediated by organic anion transporters (OAT1 and OAT3). However, these metabolites have not been assessed in rats as potential transporter biomarkers. We carried out a rat pharmacokinetic DDI study using probenecid and furosemide as OAT inhibitor and substrate, respectively. Probenecid administration led to a 3.8-fold increase in the blood concentrations and a 3-fold decrease in renal clearance of furosemide. High inter-individual and intra-day variability in pyridoxic acid and kynurenic acid, and no or moderate effect of probenecid administration on these metabolites suggest their limited utility for prediction of Oat-mediated DDI in rats. Therefore, rat blood and urine samples were further analysed using untargeted metabolomics. Twenty-one m/z features (out of >8000 detected features) were identified as putative biomarkers of rat Oat1 and Oat3 using a robust biomarker qualification approach. These m/z features belong to metabolic pathways such as fatty acid analogues, peptides, prostaglandin analogues, bile acid derivatives, flavonoids, phytoconstituents, and steroids, and can be used as a panel to decrease variability caused by processes other than Oats. When validated, these putative biomarkers will be useful in predicting DDIs caused by Oats in rats.

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.

Development of 4-Pyridoxic Acid PBPK Model to Support Biomarker-Informed Evaluation of OAT1/3 Inhibition and Effect of Chronic Kidney Disease

Monitoring endogenous biomarkers is increasingly used to evaluate transporter-mediated drug-drug interactions (DDIs) in early drug development and may be applied to elucidate changes in transporter activity in disease. 4-pyridoxic acid (PDA) has been identified as the most sensitive plasma endogenous biomarker of renal organic anion transporters (OAT1/3). Increase in PDA baseline concentrations was observed after administration of probenecid, a strong clinical inhibitor of OAT1/3 and also in patients with chronic kidney disease (CKD). The aim of this study was to develop and verify a physiologically-based pharmacokinetic (PBPK) model of PDA, to predict the magnitude of probenecid DDI and predict the CKD-related changes in PDA baseline. The PBPK model for PDA was first developed in healthy population, building on from previous population pharmacokinetic modeling, and incorporating a mechanistic kidney model to consider OAT1/3-mediated renal secretion. Probenecid PBPK model was adapted from the Simcyp database and re-verified to capture its dose-dependent pharmacokinetics (n = 9 studies). The PBPK model successfully predicted the PDA plasma concentrations, area under the curve, and renal clearance in healthy subjects at baseline and after single/multiple probenecid doses. Prospective simulations in severe CKD predicted successfully the increase in PDA plasma concentration relative to healthy (within 2-fold of observed data) after accounting for 60% increase in fraction unbound in plasma and additional 50% decline in OAT1/3 activity beyond the decrease in glomerular filtration rate. The verified PDA PBPK model supports future robust evaluation of OAT1/3 DDI in drug development and increases our confidence in predicting exposure and renal secretion in patients with CKD.

A Metabolomic Analysis of Sensitivity and Specificity of 23 Previously Proposed Biomarkers for Renal Transporter-Mediated Drug-Drug Interactions

Endogenous biomarkers are discussed as tools for detection of drug-drug interactions (DDIs) mediated by renal transport proteins, such as organic cation transporter 2 (OCT2), multidrug and toxin extrusion proteins (MATE1 and MATE2-K) and organic anion transporters (OAT1 and OAT3). Whereas sensitivity of some endogenous biomarkers against at least one clinical transporter inhibitor has frequently been shown, intra-study comparisons of the extent of effects of inhibitors on different biomarkers are frequently lacking. Moreover, in vivo specificity of such discussed biomarkers has frequently not been studied. We therefore investigated changes of 10 previously described putative biomarkers for inhibition of OCT2/MATEs, as well as 15 previously described putative biomarkers for OATs in human plasma and urine samples of healthy volunteers in response to treatment with 4 inhibitors of transport proteins [verapamil (P-glycoprotein), rifampin (organic anion transporting polypeptides), cimetidine (OCT2/MATEs), and probenecid (OATs)]. Two of the putative biomarkers had been suggested for both OCT2/MATEs and OATs. All substances were unequivocally identified in an untargeted metabolomics assay. The OCT2/MATE biomarkers choline and trimethylamine N-oxide were both sensitive and specific (median log2-fold changes -1.18 in estimated renal elimination and -0.85 in urinary excretion, respectively). For renal OATs, indoleacetyl glutamine and indoleacetic acid (median log2-fold changes -3.77 and -2.85 in estimated renal elimination, respectively) were the candidates for sensitive and specific biomarkers with the most extensive change, followed by taurine, indolelactic acid, and hypoxanthine. This comprehensive study adds further knowledge on sensitivity and specificity of 23 previously described biomarkers of renal OCT2/MATE- and OAT-mediated DDIs.

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

PURPOSE

Ritlecitinib, an inhibitor of Janus kinase 3 and tyrosine kinase expressed in hepatocellular carcinoma family kinases, is in development for inflammatory diseases. This study assessed the impact of ritlecitinib on drug transporters using a probe drug and endogenous biomarkers.

METHODS

In vitro transporter-mediated substrate uptake and inhibition by ritlecitinib and its major metabolite were evaluated. Subsequently, a clinical drug interaction study was conducted in 12 healthy adult participants to assess the effect of ritlecitinib on pharmacokinetics of rosuvastatin, a substrate of breast cancer resistance protein (BCRP), organic anion transporting polypeptide 1B1 (OATP1B1), and organic anion transporter 3 (OAT3). Plasma concentrations of coproporphyrin I (CP-I) and pyridoxic acid (PDA) were assessed as endogenous biomarkers for OATP1B1 and OAT1/3 function, respectively.

RESULTS

In vitro studies suggested that ritlecitinib can potentially inhibit BCRP, OATP1B1 and OAT1/3 based on regulatory cutoffs. In the subsequent clinical study, coadministration of ritlecitinib decreased rosuvastatin plasma exposure area under the curve from time 0 to infinity (AUCinf) by  ~ 13% and maximum concentration (Cmax) by  ~ 27% relative to rosuvastatin administered alone. Renal clearance was comparable in the absence and presence of ritlecitinib coadministration. PK parameters of AUCinf and Cmax for CP-I and PDA were also similar regardless of ritlecitinib coadministration.

CONCLUSION

Ritlecitinib does not inhibit BCRP, OATP1B1, and OAT3 and is unlikely to cause a clinically relevant interaction through these transporters. Furthermore, our findings add to the body of evidence supporting the utility of CP-I and PDA as endogenous biomarkers for assessment of OATP1B1 and OAT1/3 transporter activity.

Determination of furosemide and its glucuronide metabolite in plasma, plasma ultrafiltrate and urine by HPLC-MS/MS with application to secretion and metabolite formation clearances in non-pregnant and pregnant women

Furosemide (FUR) has been used in probe drugs cocktails for in vivo evaluation of the renal transporters OAT1 and OAT3 activities in studies of drug-drug interactions (generally using probenecid as an inhibitor) and drug-disease interactions. The objective of this study was to develop and validate methods for FUR and its glucuronide metabolite (FUR-GLU) analysis in plasma, plasma ultrafiltrate and urine for application in pharmacokinetics studies: a pilot drug-drug interaction study in pregnant women (n = 2), who received a single oral dose of FUR (40 mg) and in another occasion a single oral dose of probenecid (750 mg) before a single oral dose of FUR (40 mg), and in non-pregnant women participants (n = 12), who only received a single oral dose of FUR (40 mg). The samples preparation for FUR in 50 µL of plasma and plasma lysate were carried by acidified liquid-liquid extraction, while 50 µL of urine and 200 µL of plasma ultrafiltrate were simply diluted with the mobile phase. The methods presented linearities in the range of 0.50 - 2500 ng/mL of plasma and plasma lysate, 0.125 - 250 ng/mL of plasma ultrafiltrate, and 50 - 20,000 ng/mL of urine. FUR-GLU methods presented linearities in the range of 0.125 - 250 ng/mL of plasma ultrafiltrate and 50 - 20,000 ng/mL of urine. Precision and accuracy evaluations showed coefficients of variation and relative errors < 15%. In the pregnant women participants, the mean values of FUR CLrenal, CLsecretion, CLformation. FUR-GLU and CLnon-renal were all reduced when probenecid was administered with FUR (8.24 vs 2.89 L/h, 8.15 vs 2.80 L/h, 3.86 vs 1.75 L/h, 48.26 vs 22.10 L/h, respectively). Non-pregnant women presented similar values of FUR CLrenal, CLsecretion, CLformation. FUR-GLU to the pregnant women who received FUR only. Finally, FUR fraction unbound (fu) resulted in values of approximately 1% in pregnant women and to 0.22% in non-pregnant women. These developed and validated methods for FUR and FUR-GLU quantification in multiple matrices can allow the further investigation of UGT1A9/1A1 and the fu when FUR is administered as an OAT 1 and 3 in vivo probe.

Albumin-bound kynurenic acid is an appropriate endogenous biomarker for assessment of the renal tubular OATs-MRP4 channel

Renal tubular secretion mediated by organic anion transporters (OATs) and the multidrug resistance-associated protein 4 (MRP4) is an important means of drug and toxin excretion. Unfortunately, there are no biomarkers to evaluate their function. The aim of this study was to identify and characterize an endogenous biomarker of the renal tubular OATs-MRP4 channel. Twenty-six uremic toxins were selected as candidate compounds, of which kynurenic acid was identified as a potential biomarker by assessing the protein-binding ratio and the uptake in OAT1-, OAT3-, and MRP4-overexpressing cell lines. OAT1/3 and MRP4 mediated the transcellular vectorial transport of kynurenic acid in vitro. Serum kynurenic acid concentration was dramatically increased in rats treated with a rat OAT1/3 (rOAT1/3) inhibitor and in rOAT1/3 double knockout (rOAT1/3-/-) rats, and the renal concentrations were markedly elevated by the rat MRP4 (rMRP4) inhibitor. Kynurenic acid was not filtered at the glomerulus (99% of albumin binding), and was specifically secreted in renal tubules through the OAT1/3-MRP4 channel with an appropriate affinity (Km) (496.7 μM and 382.2 μM for OAT1 and OAT3, respectively) and renal clearance half-life (t1/2) in vivo (3.7 ± 0.7 h). There is a strong correlation in area under the plasma drug concentration-time curve (AUC0-t) between cefmetazole and kynurenic acid, but not with creatinine, after inhibition of rOATs. In addition, the phase of increased kynurenic acid level is earlier than that of creatinine in acute kidney injury process. These results suggest that albumin-bound kynurenic acid is an appropriate endogenous biomarker for adjusting the dosage of drugs secreted by this channel or predicting kidney injury.

A 20-Year Research Overview: Quantitative Prediction of Hepatic Clearance Using the In Vitro-In Vivo Extrapolation Approach Based on Physiologically Based Pharmacokinetic Modeling and Extended Clearance Concept

Understanding the extended clearance concept and establishing a physiologically based pharmacokinetic (PBPK) model are crucial for investigating the impact of changes in transporter and metabolizing enzyme abundance/functions on drug pharmacokinetics in blood and tissues. This mini-review provides an overview of the extended clearance concept and a PBPK model that includes transporter-mediated uptake processes in the liver. In general, complete in vitro and in vivo extrapolation (IVIVE) poses challenges due to missing factors that bridge the gap between in vitro and in vivo systems. By considering key in vitro parameters, we can capture in vivo pharmacokinetics, a strategy known as the top-down or middle-out approach. We present the latest progress, theory, and practice of the Cluster Gauss-Newton method, which is used for middle-out analyses. As examples of poor IVIVE, we discuss "albumin-mediated hepatic uptake" and "time-dependent inhibition" of OATP1Bs. The hepatic uptake of highly plasma-bound drugs is more efficient than what can be accounted for by their unbound concentration alone. This phenomenon is referred to as "albumin-mediated" hepatic uptake. IVIVE was improved by measuring hepatic uptake clearance in vitro in the presence of physiologic albumin concentrations. Lastly, we demonstrate the application of Cluster Gauss-Newton method-based analysis to the target-mediated drug disposition of bosentan. Incorporating saturable target binding and OATP1B-mediated hepatic uptake into the PBPK model enables the consideration of nonlinear kinetics across a wide dose range and the prediction of receptor occupancy over time. SIGNIFICANCE STATEMENT: There have been multiple instances where researchers' endeavors to unravel the underlying mechanism of poor in vitro-in vivo extrapolation have led to the discovery of previously undisclosed truths. These include 1) albumin-mediated hepatic uptake, 2) the target-mediated drug disposition in small molecules, and 3) the existence of a trans-inhibition mechanism by inhibitors for OATP1B-mediated hepatic uptake of drugs. Consequently, poor in vitro-in vivo extrapolation and the subsequent inquisitiveness of scientists may serve as a pivotal gateway to uncover hidden mechanisms.

Evaluation of the Selectivity of Several Organic Anion Transporting Polypeptide 1B Biomarkers Using Relative Activity Factor Method

In recent years, some endogenous substrates of organic anion transporting polypeptide 1B (OATP1B) have been identified and characterized as potential biomarkers to assess OATP1B-mediated clinical drug-drug interactions (DDIs). However, quantitative determination of their selectivity to OATP1B is still limited. In this study, we developed a relative activity factor (RAF) method to determine the relative contribution of hepatic uptake transporters OATP1B1, OATP1B3, OATP2B1, and sodium-taurocholate co-transporting polypeptide (NTCP) on hepatic uptake of several OATP1B biomarkers, including coproporphyrin I (CPI), coproporphyrin I CPIII, and sulfate conjugates of bile acids: glycochenodeoxycholic acid sulfate (GCDCA-S), glycodeoxycholic acid sulfate (GDCA-S), and taurochenodeoxycholic acid sulfate (TCDCA-S). RAF values for OATP1B1, OATP1B3, OATP2B1, and NTCP were determined in cryopreserved human hepatocytes and transporter transfected cells using pitavastatin, cholecystokinin, resveratrol-3-O-β-D-glucuronide, and taurocholic acid (TCA) as reference compounds, respectively. OATP1B1-specific pitavastatin uptake in hepatocytes was measured in the absence and presence of 1 µM estropipate, whereas NTCP-specific TCA uptake was measured in the presence of 10 µM rifampin. Our studies suggested that CPI was a more selective biomarker for OATP1B1 than CPIII, whereas GCDCA-S and TCDCA-S were more selective to OATP1B3. OATP1B1 and OATP1B3 equally contributed to hepatic uptake of GDCA-S. The mechanistic static model, incorporating the fraction transported of CPI/III estimated by RAF and in vivo elimination data, predicted several perpetrator interactions with CPI/III. Overall, RAF method combined with pharmacogenomic and DDI studies is a useful tool to determine the selectivity of transporter biomarkers and facilitate the selection of appropriate biomarkers for DDI evaluation. SIGNIFICANCE STATEMENT: The authors developed a new relative activity factor (RAF) method to quantify the contribution of hepatic uptake transporters organic anion transporting polypeptide (OATP)1B1, OATP1B3, OATP2B1, and sodium taurocholate co-transporting polypeptide (NTCP) on several OATP1B biomarkers and evaluated their predictive value on drug-drug interactions (DDI). These studies suggest that the RAF method is a useful tool to determine the selectivity of transporter biomarkers. This method combined with pharmacogenomic and DDI studies will mechanistically facilitate the selection of appropriate biomarkers for DDI prediction.

Emerging Roles of Uremic Toxins and Inflammatory Cytokines in the Alteration of Hepatic Drug Disposition in Patients with Kidney Dysfunction

Patients with kidney dysfunction exhibit distinct pharmacokinetic profiles compared to those with normal kidney function. Hence, it is desirable to monitor the drug efficacy and toxicity caused by fluctuations in plasma drug concentrations associated with kidney dysfunction. Recently, pharmacokinetic information of drugs excreted mainly through the urine of patients with kidney dysfunction has been reported via drug-labeling information. Pharmacokinetic changes in drugs mainly eliminated by the liver cannot be overlooked as drug metabolism and/or transport activity in the liver may also be altered in patients with kidney dysfunction; however, the underlying mechanisms remain unclear. To plan an appropriate dosage regimen, it is necessary to clarify the underlying processes of functional changes in pharmacokinetic proteins. In recent years, uremic toxins have been shown to reduce the activity and/or expression of renal and hepatic transporters. This inhibitory effect has been reported to be time-dependent. In addition, inflammatory cytokines, such as interleukin-6, released from immune cells activated by uremic toxins and/or kidney injury can reduce the expression levels of drug-metabolizing enzymes and transporters in human hepatocytes. In this mini-review, we have summarized the renal and hepatic pharmacokinetic changes as well as the potential underlying mechanisms in kidney dysfunction, such as the chronic kidney disease and acute kidney injury. SIGNIFICANCE STATEMENT: Patients with kidney dysfunction exhibit distinct pharmacokinetic profiles compared to those with normal kidney function. Increased plasma concentrations of uremic toxins and inflammatory cytokines during kidney disease may potentially affect the activities and/or expression levels of drug-metabolizing enzymes and transporters in the liver and kidneys.

Targeting a xenobiotic transporter to ameliorate vincristine-induced sensory neuropathy

Vincristine is a widely used chemotherapeutic drug for the treatment of multiple malignant diseases that causes a dose-limiting peripheral neurotoxicity. There is no clinically effective preventative treatment for vincristine-induced sensory peripheral neurotoxicity (VIPN), and mechanistic details of this side effect remain poorly understood. We hypothesized that VIPN is dependent on transporter-mediated vincristine accumulation in dorsal root ganglion neurons. Using a xenobiotic transporter screen, we identified OATP1B3 as a neuronal transporter regulating the uptake of vincristine. In addition, genetic or pharmacological inhibition of the murine orthologue transporter OATP1B2 protected mice from various hallmarks of VIPN - including mechanical allodynia, thermal hyperalgesia, and changes in digital maximal action potential amplitudes and neuronal morphology - without negatively affecting plasma levels or antitumor effects of vincristine. Finally, we identified α-tocopherol from an untargeted metabolomics analysis as a circulating endogenous biomarker of neuronal OATP1B2 function, and it could serve as a companion diagnostic to guide dose selection of OATP1B-type transport modulators given in combination with vincristine to prevent VIPN. Collectively, our findings shed light on the fundamental basis of VIPN and provide a rationale for the clinical development of transporter inhibitors to prevent this debilitating side effect.

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.

Interactions of human drug transporters with chemical additives present in plastics: Potential consequences for toxicokinetics and health

Human membrane drug transporters are recognized as major actors of pharmacokinetics; they also handle endogenous compounds, including hormones and metabolites. Chemical additives present in plastics interact with human drug transporters, which may have consequences for the toxicokinetics and toxicity of these widely-distributed environmental and/or dietary pollutants, to which humans are highly exposed. The present review summarizes key findings about this topic. In vitro assays have demonstrated that various plastic additives, including bisphenols, phthalates, brominated flame retardants, poly-alkyl phenols and per- and poly-fluoroalkyl substances, can inhibit the activities of solute carrier uptake transporters and/or ATP-binding cassette efflux pumps. Some are substrates for transporters or can regulate their expression. The relatively low human concentration of plastic additives from environmental or dietary exposure is a key parameter to consider to appreciate the in vivo relevance of plasticizer-transporter interactions and their consequences for human toxicokinetics and toxicity of plastic additives, although even low concentrations of pollutants (in the nM range) may have clinical effects. Existing data about interactions of plastic additives with drug transporters remain somewhat sparse and incomplete. A more systematic characterization of plasticizer-transporter relationships is needed. The potential effects of chemical additive mixtures towards transporter activities and the identification of transporter substrates among plasticizers, as well as their interactions with transporters of emerging relevance deserve particular attention. A better understanding of the human toxicokinetics of plastic additives may help to fully integrate the possible contribution of transporters to the absorption, distribution, metabolism and excretion of plastics-related chemicals, as well as to their deleterious effects towards human health.

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.

Glycochenodeoxycholate and glycodeoxycholate 3-O-glucuronides, but not hexadecanedioate and tetradecanedioate, detected weak inhibition of OATP1B caused by GDC-0810 in humans

Endogenous biomarkers of drug transporters are promising tools to evaluate in vivo transporter function and potential alterations in the pharmacokinetics of their substrates. We have previously reported that coproporphyrin I/III captured the weak inhibition of OATP1B transporters by GDC-0810. In this study, we measured plasma concentrations of additional biomarkers, namely fatty acids, bile acids and their sulphate or glucuronide conjugates in the presence and absence of GDC-0810. Concentrations of hexadecanedioate and tetradecanedioate did not increase in the presence of GDC-0810. Among bile acids and their conjugates, glycochenodeoxycholate and glycodeoxycholate 3-O-glucuronides (GCDCA-3G and GDCA-3G) showed C_max increases with geometric mean ratio (95% confidence interval) of 1.58 (1.13-2.22) and 1.49 (1.21-1.83), consistent with previous reports from low-dose rifampin co-administration and pharmacogenetic studies. These results suggest that GCDCA-3G and GDCA-3G are two more promising biomarkers that may capture weak OATP1B inhibition in addition to coproporphyrin I/III.

P-Glycoprotein and Organic Anion Transporter Polypeptide 1B/Breast Cancer Resistance Protein Drug Transporter Activity in Pregnant Women Living With HIV

This study evaluates the influence of pregnancy and HIV infection in conjunction with the use of raltegravir, lamivudine, and tenofovir disoproxil fumarate (combined antiretroviral therapy [cART]) on intestinal P-glycoprotein (P-gp) and hepatic organic anion transporter polypeptide (OATP) 1B1/1B3 and/or breast cancer resistance protein (BCRP) drug transporter activity using rosuvastatin (OATP1B/BCRP) and fexofenadine (P-gp) probes. Single oral doses of 5-mg rosuvastatin and 60-mg fexofenadine were administered to women living with HIV under cART in the third trimester of gestation (n = 15) and postpartum period (n = 10). A control group of 12 healthy nonpregnant women also was investigated. Pharmacokinetic parameters were estimated by using a noncompartmental method and evaluated by t test (P < .05). The rosuvastatin area under the plasma concentration-time curve from time 0 to the last quantifiable concentration (AUC_0-last ) value was higher in the third trimester of pregnancy (19.5 [95%CI, 16.8-22.3] ng • h/mL] when compared to postpartum (13.3 [95%CI, 9.3-17.5] ng • h/mL), while the fexofenadine AUC_0-last values did not differ between the third trimester of pregnancy (738.0 [95%CI, 611.4-864.6] ng • h/mL) and postpartum period (874.9 [95%CI, 408.2-1342.0] ng• h/mL). The rosuvastatin AUC_0-last values did not differ between healthy nonpregnant women (13.8 [95%CI, 10.0-17.6] ng • h/mL) and women living with HIV in the postpartum period (13.3 [95%CI, 9.3-17.5] ng • h/mL), and the fexofenadine AUC_0-last values did not differ between the 2 investigated groups (603.6 [95%CI, 467.5-739.7] ng • h/mL vs 874.9 [95%CI, 408.2-1342.0] ng • h/mL). It is suggested that gestation inhibits the hepatic OATP1B1/1B3 and/or BCRP activity but does not alter intestinal P-gp activity. The influence of HIV infection in conjunction with use of cART on OATP1B/BCRP and intestinal P-gp activity was not observed.

Translatability of in vitro Inhibition Potency to in vivo P-Glycoprotein Mediated Drug Interaction Risk

P-glycoprotein (P-gp) may limit oral drug absorption of substrate drugs due to intestinal efflux. Therefore, regulatory agencies require investigation of new chemical entities as possible inhibitors of P-gp in vitro. Unfortunately, inter-laboratory and inter-assay variability have hindered the translatability of in vitro P-gp inhibition data to predict clinical drug interaction risk. The current study was designed to evaluate the impact of potential IC₅₀ discrepancies between two commonly utilized assays, i.e., bi-directional Madin-Darby Canine Kidney-MDR1 cell-based and MDR1 membrane vesicle-based assays. When comparing vesicle- to cell-based IC₅₀ values (n = 28 inhibitors), non-P-gp substrates presented good correlation between assay formats, whereas IC₅₀s of P-gp substrates were similar or lower in the vesicle assays. The IC₅₀s obtained with a cell line expressing relatively low P-gp aligned more closely to those obtained from the vesicle assay, but passive permeability of the inhibitors did not appear to influence the correlation of IC₅₀s, suggesting that efflux activity reduces intracellular inhibitor concentrations. IC₅₀s obtained between two independent laboratories using the same assay type showed good correlation. Using the G-value (i.e., ratio of estimated gut concentration-to-inhibition potency) >10 cutoff recommended by regulatory agencies resulted in minimal differences in predictive performance, suggesting this cutoff is appropriate for either assay format.

Clinical assessment of gepotidacin (GSK2140944) as a victim and perpetrator of drug-drug interactions via CYP3A metabolism and transporters

Gepotidacin is a novel triazaacenaphthylene antibiotic in phase III development. Based on nonclinical in vitro characterization of gepotidacin metabolism, two phase I studies were conducted in healthy participants to investigate clinical drug-drug interactions (DDIs). We assessed gepotidacin as a DDI victim with a potent cytochrome P450 (CYP) 3A4/P-glycoprotein (P-gp) inhibitor (itraconazole), potent CYP3A4 inducer (rifampicin), and nonspecific organic cation transporter (OCT)/multidrug and toxic extrusion transporter (MATE) renal transport inhibitor (cimetidine) via single doses of gepotidacin before and after co-administration with multiple doses of the modulator drugs. Gepotidacin DDI perpetrator potential for P-gp inhibition (digoxin) and CYP3A4 inhibition (midazolam) was evaluated via single doses of the two-drug cocktail without and with gepotidacin. The DDI magnitudes were interpreted based on area under the concentration-time curve (AUC). A weak DDI (AUC increase 48%-50%) was observed for gepotidacin co-administered with itraconazole. A clinically significant decrease in gepotidacin plasma AUC (52%) was observed with rifampicin coadministration, indicating a moderate DDI. There was no DDI for gepotidacin with cimetidine; a unique biomarker approach showed increased serum creatinine (24%), decreased renal clearance of creatinine (21%), and N1-methylnicotinamide (39%), which confirmed extensive MATE inhibition and partial OCT2 inhibition. Gepotidacin was not a P-gp DDI perpetrator, although the maximum plasma concentration of digoxin increased (53%) and is potentially clinically relevant given its narrow therapeutic index. Gepotidacin demonstrated weak CYP3A4 inhibition with midazolam (<2-fold AUC increase). There were no new safety-risk profile findings. These results will inform the safe and efficacious clinical use of gepotidacin when co-administered with other drugs.

Role of Hepatocyte Transporters in Drug-Induced Liver Injury (DILI)-In Vitro Testing

Bile acids and bile salts (BA/BS) are substrates of both influx and efflux transporters on hepatocytes. Canalicular efflux transporters, such as BSEP and MRP2, are crucial for the removal of BA/BS to the bile. Basolateral influx transporters, such as NTCP, OATP1B1/1B3, and OSTα/β, cooperate with canalicular transporters in the transcellular vectorial flux of BA/BS from the sinusoids to the bile. The blockage of canalicular transporters not only impairs the bile flow but also causes the intracellular accumulation of BA/BS in hepatocytes that contributes to, or even triggers, liver injury. In the case of BA/BS overload, the efflux of these toxic substances back to the blood via MRP3, MRP4, and OST α/β is considered a relief function. FXR, a key regulator of defense against BA/BS toxicity suppresses de novo bile acid synthesis and bile acid uptake, and promotes bile acid removal via increased efflux. In drug development, the early testing of the inhibition of these transporters, BSEP in particular, is important to flag compounds that could potentially inflict drug-induced liver injury (DILI). In vitro test systems for efflux transporters employ membrane vesicles, whereas those for influx transporters employ whole cells. Additional in vitro pharmaceutical testing panels usually include cellular toxicity tests using hepatocytes, as well as assessments of the mitochondrial toxicity and accumulation of reactive oxygen species (ROS). Primary hepatocytes are the cells of choice for toxicity testing, with HepaRG cells emerging as an alternative. Inhibition of the FXR function is also included in some testing panels. The molecular weight and hydrophobicity of the drug, as well as the steady-state total plasma levels, may positively correlate with the DILI potential. Depending on the phase of drug development, the physicochemical properties, dosing, and cut-off values of BSEP IC₅₀ ≤ 25-50 µM or total C_ss,plasma/BSEP IC₅₀ ≥ 0.1 may be an indication for further testing to minimize the risk of DILI liability.

Predicting transporter mediated drug-drug interactions via static and dynamic physiologically based pharmacokinetic modeling: A comprehensive insight on where we are now and the way forward

The greater utilization and acceptance of physiologically-based pharmacokinetic (PBPK) modeling to evaluate the potential metabolic drug-drug interactions is evident by the plethora of literature, guidance's, and regulatory dossiers available in the literature. In contrast, it is not widely used to predict transporter-mediated DDI (tDDI). This is attributed to the unavailability of accurate transporter tissue expression levels, the absence of accurate in vitro to in vivo extrapolations (IVIVE), enzyme-transporter interplay, and a lack of specific probe substrates. Additionally, poor understanding of the inhibition/induction mechanisms coupled with the inability to determine unbound concentrations at the interaction site made tDDI assessment challenging. Despite these challenges, continuous improvements in IVIVE approaches enabled accurate tDDI predictions. Furthermore, the necessity of extrapolating tDDI's to special (pediatrics, pregnant, geriatrics) and diseased (renal, hepatic impaired) populations is gaining impetus and is encouraged by regulatory authorities. This review aims to visit the current state-of-the-art and summarizes contemporary knowledge on tDDI predictions. The current understanding and ability of static and dynamic PBPK models to predict tDDI are portrayed in detail. Peer-reviewed transporter abundance data in special and diseased populations from recent publications were compiled, enabling direct input into modeling tools for accurate tDDI predictions. A compilation of regulatory guidance's for tDDI's assessment and success stories from regulatory submissions are presented. Future perspectives and challenges of predicting tDDI in terms of in vitro system considerations, endogenous biomarkers, the use of empirical scaling factors, enzyme-transporter interplay, and acceptance criteria for model validation to meet the regulatory expectations were discussed.

Studying the right transporter at the right time: an in vitro strategy for assessing drug-drug interaction risk during drug discovery and development

INTRODUCTION

Transporters are significant in dictating drug pharmacokinetics, thus inhibition of transporter function can alter drug concentrations resulting in drug-drug interactions (DDIs). Because they can impact drug toxicity, transporter DDIs are a regulatory concern for which prediction of clinical effect from in vitro data is critical to understanding risk.

AREA COVERED

The authors propose in vitro strategies to assist mitigating/removing transporter DDI risk during development by frontloading specific studies, or managing patient risk in the clinic. An overview of clinically relevant drug transporters and observed DDIs are provided, alongside presentation of key considerations/recommendations for in vitro study design evaluating drugs as inhibitors or substrates. Guidance on identifying critical co-medications, clinically relevant disposition pathways and using mechanistic static equations for quantitative prediction of DDI is compiled.

EXPERT OPINION

The strategies provided will facilitate project teams to study the right transporter at the right time to minimise development risks associated with DDIs. To truly alleviate or manage clinical risk, the industry will benefit from moving away from current qualitative basic static equation approaches to transporter DDI hazard assessment towards adopting the use of mechanistic models to enable quantitative DDI prediction, thereby contextualising risk to ascertain whether a transporter DDI is simply pharmacokinetic or clinically significant requiring intervention.

Cluster Gauss-Newton method analyses of PBPK model parameter combinations of coproporphyrin-I based on OATP1B-mediated rifampicin interaction studies

Coproporphyrin I (CP-I) is an endogenous biomarker supporting the prediction of drug-drug interactions (DDIs) involving hepatic organic anion transporting polypeptide 1B (OATP1B). We previously constructed a physiologically-based pharmacokinetic (PBPK) model for CP-I using clinical DDI data with an OATP1B inhibitor, rifampicin (RIF). In this study, PBPK model parameters for CP-I were estimated using the cluster Gauss-Newton method (CGNM), an algorithm used to find multiple approximate solutions for nonlinear least-squares problems. Eight unknown parameters including the hepatic overall intrinsic clearance (CL_int,all ), the rate of biosynthesis (v_syn ), and the OATP1B inhibition constant of RIF(K_i,u,OATP ) were estimated by fitting to the observed CP-I blood concentrations in two different clinical studies involving changing the RIF dose. Multiple parameter combinations were obtained by CGNM that could well capture the clinical data. Among those, CL_int,all , K_i,u,OATP , and v_syn were sensitive parameters. The obtained K_i,u,OATP for CP-I was 5.0- and 2.8-fold lower than that obtained for statins, confirming our previous findings describing substrate-dependent K_i,u,OATP values. In conclusion, CGNM analyses of PBPK model parameter combinations enables estimation of the three essential parameters for CP-I to capture the DDI profiles, even if the other parameters remain unidentified. The CGNM also clarified the importance of appropriate combinations of other unidentified parameters to enable capture of the CP-I concentration time course under the influence of RIF. The described CGNM approach may also support the construction of robust PBPK models for additional transporter biomarkers beyond CP-I.

Development and validation of an LC-MS/MS method to quantify kynurenic acid in human plasma

Background: Monitoring levels of endogenous biomarkers has become an alternative approach to assess transporter-mediated drug-drug interactions in clinical trials. Among the biomarkers of interest, kynurenic acid is effective for the human organic anion transporters OAT1 and OAT3. Here, a simple and robust bioanalytical method was developed using LC-MS/MS to quantify kynurenic acid in human plasma. Results: This method achieved a LLOQ of 10 nm with acceptable signal-to-noise ratio (S/N >5). In addition, an interfering agent, tryptophan, was identified and separated chromatographically. A full method validation was performed in the spirit of GLP. Conclusion: This method can serve as a tool readily available to assess potential drug-drug interactions mediated by inhibition of OAT1 and OAT3 activities.

A Metabolomics Approach for Predicting OATP1B-Type Transporter-Mediated Drug–Drug Interaction Liabilities

In recent years, various endogenous compounds have been proposed as putative biomarkers for the hepatic uptake transporters OATP1B1 and OATP1B3 that have the potential to predict transporter-mediated drug–drug interactions (DDIs). However, these compounds have often been identified from top–down strategies and have not been fully utilized as a substitute for traditional DDI studies. In an attempt to eliminate observer bias in biomarker selection, we applied a bottom–up, untargeted metabolomics screening approach in mice and found that plasma levels of the conjugated bile acid chenodeoxycholate-24-glucuronide (CDCA-24G) are particularly sensitive to deletion of the orthologous murine transporter Oatp1b2 (31-fold increase vs. wild type) or the entire Oatp1a/1b(−/−)cluster (83-fold increased), whereas the humanized transgenic overexpression of hepatic OATP1B1 or OATP1B3 resulted in the partial restoration of transport function. Validation studies with the OATP1B1/OATP1B3 inhibitors rifampin and paclitaxel in vitro as well as in mice and human subjects confirmed that CDCA-24G is a sensitive and rapid response biomarker to dose-dependent transporter inhibition. Collectively, our study confirmed the ability of CDCA-24G to serve as a sensitive and selective endogenous biomarker of OATP1B-type transport function and suggests a template for the future development of biomarkers for other clinically important xenobiotic transporters.

Development and implementation of urinary transporter biomarkers to facilitate assessment of drug-drug interaction

Aim: Novel urinary biomarker evaluation approaches to support inhibition assessment for renal transporters (e.g., OCT2, multidrug and toxin extrusion proteins [MATEs]). Methods: Highly sensitive and robust hydrophilic interaction chromatography-MS/high-resolution MS assays, for urine and plasma, were developed and characterized to evaluate transporter biomarkers including N¹-methyladenosine and N¹-methylnicotinamide. Results: The assays were simple and reliable with good selectivity and sensitivity, and successfully supported a clinical drug-drug interaction study with a drug candidate that presented in vitro inhibition of OCT2 and MATEs. Conclusion: The multiplexed assays enable a performance comparison, including biomarker specificity and sensitivity, that should increase the confidence in early clinical OCT2/MATEs drug-drug interaction risk assessment.

New and Emerging Research on Solute Carrier and ATP Binding Cassette Transporters in Drug Discovery and Development: Outlook From the International Transporter Consortium

Enabled by a plethora of new technologies, research in membrane transporters has exploded in the past decade. The goal of this state-of-the-art article is to describe recent advances in research on membrane transporters that are particularly relevant to drug discovery and development. This review covers advances in basic, translational, and clinical research that has led to an increased understanding of membrane transporters at all levels. At the basic level, we describe the available crystal structures of membrane transporters in both the solute carrier (SLC) and ATP binding cassette superfamilies, which has been enabled by the development of cryogenic electron microscopy methods. Next, we describe new research on lysosomal and mitochondrial transporters as well as recently deorphaned transporters in the SLC superfamily. The translational section includes a summary of proteomic research, which has led to a quantitative understanding of transporter levels in various cell types and tissues and new methods to modulate transporter function, such as allosteric modulators and targeted protein degraders of transporters. The section ends with a review of the effect of the gut microbiome on modulation of transporter function followed by a presentation of 3D cell cultures, which may enable in vivo predictions of transporter function. In the clinical section, we describe new genomic and pharmacogenomic research, highlighting important polymorphisms in transporters that are clinically relevant to many drugs. Finally, we describe new clinical tools, which are becoming increasingly available to enable precision medicine, with the application of tissue-derived small extracellular vesicles and real-world biomarkers.