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.

Utility of Coproporphyrin-I Determination in First-in-Human Study for Early Evaluation of OATP1B Inhibitory Potential Based on Investigation of Ensitrelvir, an Oral SARS-CoV-2 3C-Like Protease Inhibitor

Coproporphyrin-I (CP-I) has been investigated as an endogenous biomarker of organic anion transporting polypeptide (OATP) 1B. Here, we determined the CP-I concentrations in a cocktail drug-drug interaction (DDI) study of ensitrelvir to evaluate the OATP1B inhibitory potential because ensitrelvir had increased plasma concentrations of rosuvastatin in this study, raising concerns about breast cancer resistance protein and OATP1B inhibition. Furthermore, CP-I concentrations were compared between active and placebo groups in a first-in-human (FIH) study of ensitrelvir to verify whether the OATP1B inhibitory potential could be estimated at an early drug development stage. In the cocktail DDI study, CP-I did not differ between with/without administration of ensitrelvir, indicating that ensitrelvir has no OATP1B inhibitory effect. Although there were some individual variabilities in CP-I concentrations among the treatment groups in the FIH study, the normalization of CP-I concentrations with pre-dose values minimized these variabilities, suggesting that this normalized method would be helpful for comparing the CP-I from different participants. Finally, we concluded that CP-I concentrations were not affected by ensitrelvir in the FIH study. These results suggested that the CP-I determination in an FIH study and its normalized method can be useful for an early evaluation of the OATP1B-mediated DDI potential in humans.

Assessing Trans-Inhibition of OATP1B1 and OATP1B3 by Calcineurin and/or PPIase Inhibitors and Global Identification of OATP1B1/3-Associated Proteins

Organic anion transporting polypeptide (OATP) 1B1 and OATP1B3 are key determinants of drug-drug interactions (DDIs). Various drugs including the calcineurin inhibitor (CNI) cyclosporine A (CsA) exert preincubation-induced trans-inhibitory effects upon OATP1B1 and/or OATP1B3 (abbreviated as OATP1B1/3) by unknown mechanism(s). OATP1B1/3 are phosphoproteins; calcineurin, which dephosphorylates and regulates numerous phosphoproteins, has not previously been investigated in the context of preincubation-induced trans-inhibition of OATP1B1/3. Herein, we compare the trans-inhibitory effects exerted on OATP1B1 and OATP1B3 by CsA, the non-analogous CNI tacrolimus, and the non-CNI CsA analogue SCY-635 in transporter-overexpressing human embryonic kidney (HEK) 293 stable cell lines. Preincubation (10-60 min) with tacrolimus (1-10 µM) rapidly and significantly reduces OATP1B1- and OATP1B3-mediated transport up to 0.18 ± 0.03- and 0.20 ± 0.02-fold compared to the control, respectively. Both CsA and SCY-635 can trans-inhibit OATP1B1, with the inhibitory effects progressively increasing over a 60 min preincubation time. At each equivalent preincubation time, CsA has greater trans-inhibitory effects toward OATP1B1 than SCY-635. Preincubation with SCY-635 for 60 min yielded IC50 of 2.2 ± 1.4 µM against OATP1B1, which is ~18 fold greater than that of CsA (0.12 ± 0.04 µM). Furthermore, a proteomics-based screening for protein interactors was used to examine possible proteins and processes contributing to OATP1B1/3 regulation and preincubation-induced inhibition by CNIs and other drugs. A total of 861 and 357 proteins were identified as specifically associated with OATP1B1 and OATP1B3, respectively, including various protein kinases, ubiquitin-related enzymes, the tacrolimus (FK506)-binding proteins FKBP5 and FKBP8, and several known regulatory targets of calcineurin. The current study reports several novel findings that expand our understanding of impaired OATP1B1/3 function; these include preincubation-induced trans-inhibition of OATP1B1/3 by the CNI tacrolimus, greater preincubation-induced inhibition by CsA compared to its non-CNI analogue SCY-635, and association of OATP1B1/3 with various proteins relevant to established and candidate OATP1B1/3 regulatory processes.

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.

Advances in the Evaluation of Gastrointestinal Absorption Considering the Mucus Layer

Because of the increasing sophistication of formulation technology and the increasing polymerization of compounds directed toward undruggable drug targets, the influence of the mucus layer on gastrointestinal drug absorption has received renewed attention. Therefore, understanding the complex structure of the mucus layer containing highly glycosylated glycoprotein mucins, lipids bound to the mucins, and water held by glycans interacting with each other is critical. Recent advances in cell culture and engineering techniques have led to the development of evaluation systems that closely mimic the ecological environment and have been applied to the evaluation of gastrointestinal drug absorption while considering the mucus layer. This review provides a better understanding of the mucus layer components and the gastrointestinal tract's biological defense barrier, selects an assessment system for drug absorption in the mucus layer based on evaluation objectives, and discusses the overview and features of each assessment system.

Structure of human drug transporters OATP1B1 and OATP1B3

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

Preincubation Time-Dependent, Long-Lasting Inhibition of Drug Transporters and Impact on the Prediction of Drug-Drug Interactions

Transporter-mediated drug-drug interaction (DDI) is of clinical concern, and the quantitative prediction of DDIs is an indispensable part of drug development. Cell-based inhibition assays, in which a representative probe substrate and a potential inhibitor are coincubated, are routinely performed to assess the inhibitory potential of new molecular entities on drug transporters. However, the inhibitory effect of cyclosporine A (CsA) on organic anion transporting polypeptide (OATP) 1B1 is substantially potentiated with CsA preincubation, and this effect is both long-lasting and dependent on the preincubation time. This phenomenon has also been reported with transporters other than OATP1Bs, but it is considered more prevalent among OATP1Bs and organic cation transporters. Regulatory agencies have also noted this preincubation effect and have recommended that pharmaceutical companies consider inhibitor preincubation when performing in vitro OATP1B1 and OATP1B3 inhibition studies. Although the underlying mechanisms responsible for the preincubation effect are not fully understood, a trans-inhibition mechanism was recently demonstrated for OATP1B1 inhibition by CsA, in which CsA inhibited OATP1B1 not only extracellularly (cis-inhibition) but also intracellularly (trans-inhibition). Furthermore, the trans-inhibition potency of CsA was much greater than that of cis-inhibition, suggesting that trans-inhibition might be a key driver of clinical DDIs of CsA with OATP1B substrate drugs. Although confidence in transporter-mediated DDI prediction is generally considered to be low, the predictability might be further improved by incorporating the trans-inhibition mechanism into static and dynamic models for preincubation-dependent inhibitors of OATP1Bs and perhaps other transporters. SIGNIFICANCE STATEMENT: Preincubation time-dependent, long-lasting inhibition has been observed for OATP1B1 and other solute carrier transporters in vitro. Recently, a trans-inhibition mechanism for the preincubation effect of CsA on OATP1B1 inhibition was identified, with the trans-inhibition potency being greater than that of cis-inhibition. The concept of trans-inhibition may allow us to further understand the mechanism of transporter-mediated DDIs not only for OATP1B1 but also for other transporters and to improve the accuracy and confidence of DDI predictions.

Multitargeting in cardioprotection: An example of biaromatic compounds

A multitarget drug design approach is actively developing in modern medicinal chemistry and pharmacology, especially with regard to multifactorial diseases such as cardiovascular diseases, cancer, and neurodegenerative diseases. A detailed study of many well-known drugs developed within the single-target approach also often reveals additional mechanisms of their real pharmacological action. One of the multitarget drug design approaches can be the identification of the basic pharmacophore models corresponding to a wide range of the required target ligands. Among such models in the group of cardioprotectors is the linked biaromatic system. This review develops the concept of a "basic pharmacophore" using the biaromatic pharmacophore of cardioprotectors as an example. It presents an analysis of possible biological targets for compounds corresponding to the biaromatic pharmacophore and an analysis of the spectrum of biological targets for the five most known and most studied cardioprotective drugs corresponding to this model, and their involvement in the biological effects of these drugs.

Characterization of Bile Acid Sulfate Conjugates as Substrates of Human Organic Anion Transporting Polypeptides

Drug interactions involving the inhibition of hepatic organic anion transporting polypeptides (OATPs) 1B1 and OATP1B3 are considered important. Therefore, we sought to study various sulfated bile acids (BA-S) as potential clinical OATP1B1/3 biomarkers. It was determined that BA-S [e.g., glycochenodeoxycholic acid 3-O-sulfate (GCDCA-S) and glycodeoxycholic acid 3-O-sulfate (GDCA-S)] are substrates of OATP1B1, OATP1B3, and sodium-dependent taurocholic acid cotransporting polypeptide (NTCP) transfected into human embryonic kidney 293 cells, with minimal uptake evident for other solute carriers (SLCs) like OATP2B1, organic anion transporter 2, and organic cation transporter 1. It was also shown that BA-S uptake by plated human hepatocytes (PHH) was inhibited (≥96%) by a pan-SLC inhibitor (rifamycin SV), and there was greater inhibition (≥77% versus ≤12%) with rifampicin (OATP1B1/3-selective inhibitor) than a hepatitis B virus myristoylated-preS1 peptide (NTCP-selective inhibitor). Estrone 3-sulfate was also used as an OATP1B1-selective inhibitor. In this instance, greater inhibition was observed with GDCA-S (76%) than GCDCA-S (52%). The study was expanded to encompass the measurement of GCDCA-S and GDCA-S in plasma of SLCO1B1 genotyped subjects. The geometric mean GDCA-S concentration was 2.6-fold (90% confidence interval 1.6, 4.3; P = 2.1 × 10^-4) and 1.3-fold (1.1, 1.7; P = 0.001) higher in individuals homozygous and heterozygous for the SLCO1B1 c.521T > C loss-of-function allele, respectively. For GCDCA-S, no significant difference was noted [1.2-fold (0.8, 1.7; P = 0.384) and 0.9-fold (0.8, 1.1; P = 0.190), respectively]. This supported the in vitro data indicating that GDCA-S is a more OATP1B1-selective substrate (versus GCDCA-S). It is concluded that GCDCA-S and GDCA-S are viable plasma-based OATP1B1/3 biomarkers, but they are both less OATP1B1-selective when compared to their corresponding 3-O-glucuronides (GCDCA-3G and GDCA-3G). Additional studies are needed to determine their utility versus more established biomarkers, such as coproporphyrin I, for assessing inhibitors with different OATP1B1 (versus OATP1B3) inhibition signatures.

Differential Preincubation Effects of Nicardipine on OATP1B1- and OATP1B3-Mediated Transport in the Presence and Absence of Protein: Implications in Assessing OATP1B1- and OATP1B3-Mediated Drug-Drug Interactions

Impaired transport activity of hepatic OATP1B1 and OATP1B3 due to drug-drug interactions (DDIs) often leads to increased systemic exposure to substrate drugs (e.g., lipid-lowering statins). Since dyslipidemia and hypertension frequently coexist, statins are often concurrently used with antihypertensives, including calcium channel blockers (CCBs). OATP1B1/1B3-related DDIs in humans have been reported for several CCBs. To date, the OATP1B1/1B3-mediated DDI potential of CCB nicardipine has not been assessed. The current study was designed to assess the OATP1B1- and OATP1B3-mediated DDI potential of nicardipine using the R-value model, following the US-FDA guidance. IC50 values of nicardipine against OATP1B1 and OATP1B3 were determined in transporter-overexpressing human embryonic kidney 293 cells using [3H]-estradiol 17β-D-glucuronide and [3H]-cholecystokinin-8 as substrates, respectively, with or without nicardipine-preincubation in protein-free Hanks' Balanced Salt Solution (HBSS) or in fetal bovine serum (FBS)-containing culture medium. Preincubation with nicardipine for 30 min in protein-free HBSS buffer produced lower IC50 and higher R-values for both OATP1B1 and OATP1B3 compared to in FBS-containing medium, yielding IC50 values of 0.98 and 1.63 µM and R-values of 1.4 and 1.3 for OATP1B1 and OATP1B3, respectively. The R-values were higher than the US-FDA cut-off value of 1.1, supporting that nicardipine has the potential to cause OATP1B1/3-mediated DDIs. Current studies provide insight into the consideration of optimal preincubation conditions when assessing the OATP1B1/3-mediated DDIs in vitro.

Reimagining the Framework Supporting the Static Analysis of Transporter Drug Interaction Risk; Integrated Use of Biomarkers to Generate Pan‐Transporter Inhibition Signatures

Solute carrier (SLC) transporters present as the loci of important drug-drug interactions (DDIs). Therefore, sponsors generate in vitro half-maximal inhibitory concentration (IC₅₀ ) data and apply regulatory agency-guided "static" methods to assess DDI risk and the need for a formal clinical DDI study. Because such methods are conservative and high false-positive rates are likely (e.g., DDI study triggered when liver SLC R value ≥ 1.04 and renal SLC maximal unbound plasma (C_max,u )/IC₅₀ ratio ≥ 0.02), investigators have attempted to deploy plasma- and urine-based SLC biomarkers in phase I studies to de-risk DDI and obviate the need for drug probe-based studies. In this regard, it was possible to generate in-house in vitro SLC IC₅₀ data for various clinically (biomarker)-qualified perpetrator drugs, under standard assay conditions, and then estimate "% inhibition" for each SLC and relate it empirically to published clinical biomarker data (area under the plasma concentration vs. time curve (AUC) ratio (AUCR, AUC_inhibitor /AUC_reference ) and % decrease in renal clearance (ΔCL_renal )). After such a "calibration" exercise, it was determined that only compounds with high R values (> 1.5) and C_max,u /IC₅₀ ratios (> 0.5) are likely to significantly modulate liver (AUCR > 1.25) and renal (ΔCL_renal  > 25%) biomarkers and evoke DDI risk. The % inhibition approach supports integration of liver and renal SLC data and allows one to generate pan-SLC inhibition signatures for different test perpetrators (e.g., SLC % inhibition ranking). In turn, such signatures can guide the selection of the most appropriate individual (or combinations of) biomarkers for testing in phase I studies.

Hepatic Expression of the Na+-Taurocholate Cotransporting Polypeptide Is Independent from Genetic Variation

The hepatic Na+-taurocholate cotransporting polypeptide NTCP/SLC10A1 is important for the uptake of bile salts and selected drugs. Its inhibition results in increased systemic bile salt concentrations. NTCP is also the entry receptor for the hepatitis B/D virus. We investigated interindividual hepatic SLC10A1/NTCP expression using various omics technologies. SLC10A1/NTCP mRNA expression/protein abundance was quantified in well-characterized 143 human livers by real-time PCR and LC-MS/MS-based targeted proteomics. Genome-wide SNP arrays and SLC10A1 next-generation sequencing were used for genomic analyses. SLC10A1 DNA methylation was assessed through MALDI-TOF MS. Transcriptomics and untargeted metabolomics (UHPLC-Q-TOF-MS) were correlated to identify NTCP-related metabolic pathways. SLC10A1 mRNA and NTCP protein levels varied 44-fold and 10.4-fold, respectively. Non-genetic factors (e.g., smoking, alcohol consumption) influenced significantly NTCP expression. Genetic variants in SLC10A1 or other genes do not explain expression variability which was validated in livers (n = 50) from The Cancer Genome Atlas. The identified two missense SLC10A1 variants did not impair transport function in transfectants. Specific CpG sites in SLC10A1 as well as single metabolic alterations and pathways (e.g., peroxisomal and bile acid synthesis) were significantly associated with expression. Inter-individual variability of NTCP expression is multifactorial with the contribution of clinical factors, DNA methylation, transcriptional regulation as well as hepatic metabolism, but not genetic variation.

Utilizing Endogenous Biomarkers to Derisk Assessment of Transporter Mediated Drug-Drug Interactions: A Scientific Perspective

Comprehensive characterization of transporter mediated drug-drug interactions (DDIs) is important to formulate clinical management strategies and ensure the safe and effective use of concomitantly administered drugs. The potential of a drug to inhibit transporters is predicted by comparing the ratio of the relevant concentration (depending on the transporter) and the half maximum inhibitory concentration (IC₅₀ ) to a pre-defined "cut off" value. If the ratio is greater than the cut off value, modeling approaches such as Physiologically Based Pharmacokinetic (PBPK) Modeling or a clinical DDI trial may be recommended. Because false positive (in vitro data suggests the potential for a DDI, whereas no significant DDI is observed in vivo) and false negative (in vitro data does not suggest the potential for a DDI, whereas significant DDI is observed in vivo) outcomes have been observed, there is interest in exploring additional approaches to facilitate prediction of transporter mediated DDIs. The idea of assessing changes in the concentration of endogenous biomarkers (which are substrates of clinically relevant transporters) to gain insight on the potential for a drug to inhibit transporter activity has received widespread attention. This brief report describes how endogenous biomarkers may help to expand the DDI assessment toolkit, highlights some current knowledge gaps, and outlines a conceptual framework that may complement the current paradigm of predicting the potential for transporter mediated DDIs. This article is protected by copyright. All rights reserved.

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

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

Recent advances in the translation of drug metabolism and pharmacokinetics science for drug discovery and development

Drug metabolism and pharmacokinetics (DMPK) is an important branch of pharmaceutical sciences. The nature of ADME (absorption, distribution, metabolism, excretion) and PK (pharmacokinetics) inquiries during drug discovery and development has evolved in recent years from being largely descriptive to seeking a more quantitative and mechanistic understanding of the fate of drug candidates in biological systems. Tremendous progress has been made in the past decade, not only in the characterization of physiochemical properties of drugs that influence their ADME, target organ exposure, and toxicity, but also in the identification of design principles that can minimize drug-drug interaction (DDI) potentials and reduce the attritions. The importance of membrane transporters in drug disposition, efficacy, and safety, as well as the interplay with metabolic processes, has been increasingly recognized. Dramatic increases in investments on new modalities beyond traditional small and large molecule drugs, such as peptides, oligonucleotides, and antibody-drug conjugates, necessitated further innovations in bioanalytical and experimental tools for the characterization of their ADME properties. In this review, we highlight some of the most notable advances in the last decade, and provide future perspectives on potential major breakthroughs and innovations in the translation of DMPK science in various stages of drug discovery and development.

2021 White Paper on Recent Issues in Bioanalysis: Mass Spec of Proteins, Extracellular Vesicles, CRISPR, Chiral Assays, Oligos; Nanomedicines Bioanalysis; ICH M10 Section 7.1; Non-Liquid & Rare Matrices; Regulatory Inputs (Part 1A - Recommendations on Endogenous Compounds, Small Molecules, Complex Methods, Regulated Mass Spec of Large Molecules, Small Molecule, PoC & Part 1B - Regulatory Agencies' Inputs on Bioanalysis, Biomarkers, Immunogenicity, Gene & Cell Therapy and Vaccine)

The 15th edition of the Workshop on Recent Issues in Bioanalysis (15th WRIB) was held on 27 September to 1 October 2021. Even with a last-minute move from in-person to virtual, an overwhelmingly high number of nearly 900 professionals representing pharma and biotech companies, contract research organizations (CROs), and multiple regulatory agencies still eagerly convened to actively discuss the most current topics of interest in bioanalysis. The 15th WRIB included 3 Main Workshops and 7 Specialized Workshops that together spanned 1 week in order to allow exhaustive and thorough coverage of all major issues in bioanalysis, biomarkers, immunogenicity, gene therapy, cell therapy and vaccines. Moreover, in-depth workshops on biomarker assay development and validation (BAV) (focused on clarifying the confusion created by the increased use of the term "Context of Use - COU"); mass spectrometry of proteins (therapeutic, biomarker and transgene); state-of-the-art cytometry innovation and validation; and, critical reagent and positive control generation were the special features of the 15th edition. This 2021 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop, and is aimed to provide the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2021 edition of this comprehensive White Paper has been divided into three parts for editorial reasons. This publication (Part 1A) covers the recommendations on Endogenous Compounds, Small Molecules, Complex Methods, Regulated Mass Spec of Large Molecules, Small Molecule, PoC. Part 1B covers the Regulatory Agencies' Inputs on Bioanalysis, Biomarkers, Immunogenicity, Gene & Cell Therapy and Vaccine. Part 2 (ISR for Biomarkers, Liquid Biopsies, Spectral Cytometry, Inhalation/Oral & Multispecific Biotherapeutics, Accuracy/LLOQ for Flow Cytometry) and Part 3 (TAb/NAb, Viral Vector CDx, Shedding Assays; CRISPR/Cas9 & CAR-T Immunogenicity; PCR & Vaccine Assay Performance; ADA Assay Comparabil ity & Cut Point Appropriateness) are published in volume 14 of Bioanalysis, issues 10 and 11 (2022), respectively.

Effect of a Ketohexokinase Inhibitor (PF-06835919) on In Vivo OATP1B Activity: Integrative Risk Assessment Using Endogenous Biomarker and a Probe Drug

PF-06835919 is a first-in-class ketohexokinase inhibitor (KHKi), recently under development for the treatment of metabolic and fatty liver diseases, which inhibited organic anion transporting polypeptide (OATP)1B1 in vitro and presented drug-drug interaction (DDI) risk. This study aims to investigate the dose-dependent effect of KHKi on OATP1B in vivo activity. We performed an open-label study comparing pharmacokinetics of atorvastatin (OATP1B probe) dosed alone (20 mg single dose) and coadministered with two dose strengths of KHKi (50 and 280 mg once daily) in 12 healthy participants. Additionally, changes in exposure of coproporphyrin-I (CP-I), an endogenous biomarker for OATP1B, were assessed in the atorvastatin study (1.12-fold and 1.49-fold increase in area under the plasma concentration-time profile (AUC) with once-daily 50 and 280 mg, respectively), and a separate single oral dose study of KHKi alone (100-600 mg, n = 6 healthy participants; up to a 1.80-fold increase in AUC). Geometric mean ratios (90% confidence interval) of atorvastatin (area under the plasma concentration - time profile from time 0 extrapolated to infinite time) AUC_inf following 50 and 280 mg KHKi were 1.14 (1.00-1.30) and 1.54 (1.37-1.74), respectively. Physiologically-based pharmacokinetic modeling of CP-I plasma exposure following a single dose of KHKi predicted in vivo OATP1B inhibition from about 13% to 70% over the 100 to 600 mg dose range, while using the in vitro inhibition potency (1.9 µM). Model-based analysis correctly predicted "no-effect" (AUC ratio < 1.25) at the low dose range and "weak" effect (AUC ratio < 2) on atorvastatin pharmacokinetics at the high dose range of KHKi. This study exemplified the utility of biomarker-informed model-based approach in discerning even small effects on OATP1B activity in vivo, and to project DDI risk at the clinically relevant doses.

Evaluation of the Effect of Abrocitinib on Drug Transporters by Integrated Use of Probe Drugs and Endogenous Biomarkers

Abrocitinib is an oral Janus kinase 1 (JAK1) inhibitor currently approved in the United Kingdom for the treatment of moderate‐to‐severe atopic dermatitis (AD). As patients with AD may use medications to manage comorbidities, abrocitinib could be used concomitantly with hepatic and/or renal transporter substrates. Therefore, we assessed the potential effect of abrocitinib on probe drugs and endogenous biomarker substrates for the drug transporters of interest. In vitro studies indicated that, among the transporters tested, abrocitinib has the potential to inhibit the activities of P‐glycoprotein (P‐gp), breast cancer resistance protein (BCRP), organic anion transporter 3 (OAT3), organic cation transporter 1 (OCT1), and multidrug and toxin extrusion protein 1 and 2K (MATE1/2K). Therefore, subsequent phase I, two‐way crossover, open‐label studies in healthy participants were performed to assess the impact of abrocitinib on the pharmacokinetics of the transporter probe substrates dabigatran etexilate (P‐gp), rosuvastatin (BCRP and OAT3), and metformin (OCT2 and MATE1/2K), as well as endogenous biomarkers for MATE1/2K (N¹‐methylnicotinamide (NMN)) and OCT1 (isobutyryl‐_L‐carnitine (IBC)). Co‐administration with abrocitinib was shown to increase the plasma exposure of dabigatran by ~ 50%. In comparison, the plasma exposure and renal clearance of rosuvastatin and metformin were not altered with abrocitinib co‐administration. Similarly, abrocitinib did not affect the exposure of NMN or IBC. An increase in dabigatran exposure suggests that abrocitinib inhibits P‐gp activity. By contrast, a lack of impact on plasma exposure and/or renal clearance of rosuvastatin, metformin, NMN, or IBC suggests that BCRP, OAT3, OCT1, and MATE1/2K activity are unaffected by abrocitinib.

Prediction of drug-drug interaction potential mediated by transporters between dasatinib and metformin, pravastatin, and rosuvastatin using physiologically based pharmacokinetic modeling

Purpose

Recent in vitro studies demonstrated that dasatinib inhibits organic cation transporter 2 (OCT2), multidrug and toxin extrusion proteins (MATEs), and organic anion transporting polypeptide 1B1/1B3 (OATP1B1/1B3). We developed a physiologically based pharmacokinetic (PBPK) model to assess drug–drug interaction (DDI) potential between dasatinib and known substrates for these transporters in a virtual population.

Methods

The dasatinib PBPK model was constructed using Simcyp^® Simulator by combining its physicochemical properties, in vitro data, in silico predictions, and pharmacokinetic (PK) results from clinical studies. Model validation against three independent clinical trials not used for model development included dasatinib DDI studies with ketoconazole, rifampin, and simvastatin. The validated model was used to simulate DDIs of dasatinib and known substrates for OCT2 and MATEs (metformin) and OATP1B1/1B3 (pravastatin and rosuvastatin).

Results

Simulations of metformin PK in the presence and absence of dasatinib, using inhibitor constant (K_i) values measured in vitro, produced estimated geometric mean ratios (GMRs) of the maximum observed concentration (C_max) and area under the concentration–time curve (AUC) of 1.05 and 1.06, respectively. Sensitivity analysis showed metformin exposure increased < 30% in both AUC and C_max when dasatinib K_i was reduced by tenfold for OCT2 and MATEs simultaneously, and < 40% with a 20-fold K_i reduction. The estimated GMRs of C_max and AUC for pravastatin and rosuvastatin with co-administration of dasatinib were unity (1.00).

Conclusions

This PBPK model accurately described the observed PK profiles of dasatinib. The validated PBPK model predicts low risk of clinically significant DDIs between dasatinib and metformin, pravastatin, or rosuvastatin.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00280-021-04394-z.

Biomarker-Informed Model-Based Risk Assessment of Organic Anion Transporting Polypeptide 1B Mediated Drug-Drug 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 (IC₅₀ )). 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 IC₅₀ 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 /IC₅₀ ) 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 IC₅₀ 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.

A novel hydrophilic interaction chromatography assay characterization of 4-pyridoxic acid, an emergent renal organic anion transporter 1/3 transporter biomarker

Aim: 4-pyridoxic acid (PDA) has been proposed as an endogenous biomarker for renal organic anion transporter 1/3 (OAT1/3) inhibition. Clinical data are needed to support the proposal. Materials & methods: A hydrophilic interaction chromatography (HILIC)-LC/MS/MS assay was developed and characterized to support clinical drug-drug interaction (DDI) studies. Results: A HILIC-LC/MS/MS assay was successfully developed. PDA was measured in two clinical DDI studies; one where no significant OAT1/3 inhibition was observed and a second where a known inhibitor of the transporter was dosed. In both clinical studies, PDA plasma concentrations correlate to OAT1/3 function. Conclusion: The analysis of study samples from two clinical DDI studies using a HILIC-LC/MS/MS assay contributes further evidence that PDA is an endogenous biomarker for OAT1/3 inhibition.

Is It Time to Use Modeling of Cellular Transporter Homeostasis to Inform Drug-Drug Interaction Studies: Theoretical Considerations

Mathematical modeling has been an important tool in pharmaceutical research for 50 + years and there is increased emphasis over the last decade on using modeling to improve the efficiency and effectiveness of drug development. In an earlier commentary, we applied a multiscale model linking 6 scales (whole body, tumor, vasculature, cell, spatial location, time), together with literature data on nanoparticle and tumor properties, to demonstrate the effects of nanoparticle particles on systemic disposition. The current commentary used a 4-scale model (cell membrane, intracellular organelles, spatial location, time) together with literature data on the intracellular processing of membrane receptors and transporters to demonstrate disruption of transporter homeostasis can lead to drug-drug interaction (DDI) between victim drug (VD) and perpetrator drug (PD), including changes in the area-under-concentration-time-curve of VD in cells that are considered significant by the US Food and Drug Administration (FDA). The model comprised 3 computational components: (a) intracellular transporter homeostasis, (b) pharmacokinetics of extracellular and intracellular VD/PD concentrations, and (c) pharmacodynamics of PD-induced stimulation or inhibition of an intracellular kinetic process. Model-based simulations showed that (a) among the five major endocytic processes, perturbation of transporter internalization or recycling led to the highest incidence and most extensive DDI, with minor DDI for perturbing transporter synthesis and early-to-late endosome and no DDI for perturbing transporter degradation and (b) three experimental conditions (spatial transporter distribution in cells, VD/PD co-incubation time, extracellular PD concentrations) were determinants of DDI detection. We propose modeling is a useful tool for hypothesis generation and for designing experiments to identify potential DDI; its application further aligns with the model-informed drug development paradigm advocated by FDA.

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

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

Modulation of Urate Transport by Drugs

BACKGROUND

Serum urate (SU) levels in primates are extraordinarily high among mammals. Urate is a Janus-faced molecule that acts physiologically as a protective antioxidant but provokes inflammation and gout when it precipitates at high concentrations. Transporters play crucial roles in urate disposition, and drugs that interact with urate transporters either by intention or by accident may modulate SU levels. We examined whether in vitro transporter interaction studies may clarify and predict such effects.

METHODS

Transporter interaction profiles of clinically proven urate-lowering (uricosuric) and hyperuricemic drugs were compiled from the literature, and the predictive value of in vitro-derived cut-offs like C_max/IC₅₀ on the in vivo outcome (clinically relevant decrease or increase of SU) was assessed.

RESULTS

Interaction with the major reabsorptive urate transporter URAT1 appears to be dominant over interactions with secretory transporters in determining the net effect of a drug on SU levels. In vitro inhibition interpreted using the recommended cut-offs is useful at predicting the clinical outcome.

CONCLUSIONS

In vitro safety assessments regarding urate transport should be done early in drug development to identify candidates at risk of causing major imbalances. Attention should be paid both to the inhibition of secretory transporters and inhibition or trans-stimulation of reabsorptive transporters, especially URAT1.

Evaluation of Ipatasertib Interactions with Itraconazole and Coproporphyrin I and III in a Single Drug Interaction Study in Healthy Subjects

Ipatasertib is a pan-AKT inhibitor in development for the treatment of cancer. Ipatasertib was metabolized by CYP3A4 to its major metabolite, M1 (G-037720), and was a P-gp substrate and OATP1B1/1B3 inhibitor in vitro. A phase I drug-drug interaction (DDI) study (n = 15) was conducted in healthy subjects to evaluate the effect of itraconazole (200-mg solution QD, 4 days), a strong CYP3A4 and P-gp inhibitor, on pharmacokinetics of ipatasertib (100-mg single dose). Itraconazole increased the C_max and AUC_{0 -∞} of ipatasertib by 2.3- and 5.5-fold, respectively, increased the half-life by 53%, and delayed the t_max by 1 hour. The C_max and AUC_0-72h of its metabolite M1 (G-037720) reduced by 91% and 68%, respectively. This study confirmed that CYP3A4 plays a major role in ipatasertib clearance. Furthermore, the interaction of ipatasertib with coproporphyrin (CP) I and CPIII, the two endogenous substrates of OATP1B1/1B3, was evaluated in this study. CPI and CPIII plasma levels were unchanged in the presence of ipatasertib, both at exposures of 100 mg and at higher exposures in combination with itraconazole. This indicated no in vivo inhibition of OATP1B1/1B3 by ipatasertib. Additionally, it was shown that CPI and CPIII were not P-gp substrates in vitro, and itraconazole had no effect on CPI and CPIII concentrations in vivo. The latter is an important finding because it will simplify interpretation of future DDI studies using CPI/CPIII as OATP1B1/1B3 biomarkers. SIGNIFICANCE STATEMENT: This drug-drug interaction study in healthy volunteers demonstrated that CYP3A4 plays a major role in ipatasertib clearance, and that ipatasertib is not an organic anion transporting polypeptide 1B1/1B3 inhibitor. Furthermore, it was demonstrated that itraconazole, an inhibitor of CYP3A4 and several transporters, did not affect CPI/CPIII levels in vivo. This increases the understanding and application of these endogenous substrates as well as itraconazole in complex drug interaction studies.

Assessing OATP1B1- and OATP1B3-Mediated Drug-Drug Interaction Potential of Vemurafenib Using R-Value and Physiologically-Based Pharmacokinetic Models

Organic anion transporting polypeptides (OATP) 1B1 and OATP1B3 are important determinants of transporter-mediated drug-drug interactions (DDIs). Current studies assessed the OATP1B1 and OATP1B3-mediated DDI potential of vemurafenib, a kinase inhibitor drug with high protein binding and low aqueous solubility, using R-value and physiologically-based pharmacokinetic (PBPK) models. The total half-maximal inhibitory concentration (IC50,total) values of vemurafenib against OATP1B1 and OATP1B3 were determined in 100% human plasma in transporter-overexpressing human embryonic kidney 293 stable cell lines. The unbound fraction of vemurafenib in human plasma before (fu,plasma) and after addition into the uptake assay plate (fu,plasma,inc) were determined by rapid equilibrium dialysis. There was no statistically significant difference between fu,plasma and fu,plasma,inc. Vemurafenib IC50,total values against OATP1B1 and OATP1B3 are 175 ± 82 and 231 ± 26 μM, respectively. The R-values [R = 1 + fu,plasma × Iin,max/(fu,plasma,inc × IC50,total)] were then simplified as R = 1+Iin,max/IC50,total, and were 1.76 and 1.57 for OATP1B1 and OATP1B3, respectively. The simulated pravastatin AUC ratio was 1.28 when a single dose of pravastatin (40 mg) was co-administered with vemurafenib (960 mg, twice daily) at steady-state, compared to pravastatin alone. Both R-value and PBPK models predict that vemurafenib has the potential to cause OATP1B1- and OATP1B3-mediated DDIs.

Coproporphyrin I Can Serve as an Endogenous Biomarker for OATP1B1 Inhibition: Assessment Using a Glecaprevir/Pibrentasvir Clinical Study

Organic anion transporting polypeptide (OATP) 1B1 and OATP1B3 are involved in the disposition of a variety of commonly prescribed drugs. The evaluation of OATP1B1/1B3 inhibition potential by investigational drugs is of interest during clinical drug development due to various adverse events associated with increased exposures of their substrates. Regulatory guidance documents on the in vitro assessment of OATP1B1/1B3 inhibition potential are conservative with up to a third of predictions resulting in false positives. This work investigated the utility of OATP1B1/1B3 endogenous biomarkers, coproporphyrin (CP)‐I and CP‐III, to assess clinical inhibition of OATP1B1/1B3 and potentially eliminate the need for prospective clinical drug‐drug interaction (DDI) studies. Correlations between CP‐I exposures and various OATP1B1 static DDI predictions were also evaluated. Glecaprevir/pibrentasvir (GLE/PIB) 300/120 mg fixed‐dose combination is known to cause clinical inhibition of OATP1B1/1B3. In a clinical study evaluating the relative bioavailability of various formulations of GLE/PIB regimen, CP‐I peak plasma concentration (C_max) ratio and 0–16‐hour area under the concentration‐time curve (AUC_0–16) ratio relative to baseline increased with increasing GLE exposures, whereas there was a modest correlation between GLE exposure and CP‐III C_max ratio but no correlation with CP‐III AUC_0–16 ratio. This suggests that CP‐I is superior to CP‐III as an endogenous biomarker for evaluation of OATP1B1 inhibition. There was a significant correlation between CP‐I and GLE C_max (R² = 0.65; P < 0.001) across individual subjects. Correlation analysis between GLE OATP1B1 R values and CP‐I exposures (C_max ratio and AUC_0–16 ratio) suggests that an R value of > 3 can predict a biologically meaningful inhibition of OATP1B1 when the inhibitor clinical pharmacokinetic parameters are available.

Role of OATP1B1 and OATP1B3 in Drug-Drug Interactions Mediated by Tyrosine Kinase Inhibitors

Failure to recognize important features of a drug's pharmacokinetic characteristics is a key cause of inappropriate dose and schedule selection, and can lead to reduced efficacy and increased rate of adverse drug reactions requiring medical intervention. As oral chemotherapeutic agents, tyrosine kinase inhibitors (TKIs) are particularly prone to cause drug-drug interactions as many drugs in this class are known or suspected to potently inhibit the hepatic uptake transporters OATP1B1 and OATP1B3. In this article, we provide a comprehensive overview of the published literature and publicly-available regulatory documents in this rapidly emerging field. Our findings indicate that, while many TKIs can potentially inhibit the function of OATP1B1 and/or OATP1B3 and cause clinically-relevant drug-drug interactions, there are many inconsistencies between regulatory documents and the published literature. Potential explanations for these discrepant observations are provided in order to assist prescribing clinicians in designing safe and effective polypharmacy regimens, and to provide researchers with insights into refining experimental strategies to further predict and define the translational significance of TKI-mediated drug-drug interactions.

Use of a Bile Salt Export Pump Knockdown Rat Susceptibility Model to Interrogate Mechanism of Drug-Induced Liver Toxicity

Inhibition of the bile salt export pump (BSEP) may be associated with clinical drug-induced liver injury, but is poorly predicted by preclinical animal models. Here we present the development of a novel rat model using siRNA knockdown (KD) of Bsep that displayed differentially enhanced hepatotoxicity to 8 Bsep inhibitors and not to 3 Bsep noninhibitors when administered at maximally tolerated doses for 7 days. Bsep KD alone resulted in 3- and 4.5-fold increases in liver and plasma levels, respectively, of the sum of the 3 most prevalent taurine conjugated bile acids (T3-BA), approximately 90% decrease in plasma and liver glycocholic acid, and a distinct bile acid regulating gene expression pattern, without resulting in hepatotoxicity. Among the Bsep inhibitors, only asunaprevir and TAK-875 resulted in serum transaminase and total bilirubin increases associated with increases in plasma T3-BA that were enhanced by Bsep KD. Benzbromarone, lopinavir, and simeprevir caused smaller increases in plasma T3-BA, but did not result in hepatotoxicity in Bsep KD rats. Bosentan, cyclosporine A, and ritonavir, however, showed no enhancement of T3-BA in plasma in Bsep KD rats, as well as Bsep noninhibitors acetaminophen, MK-0974, or clarithromycin. T3-BA findings were further strengthened through monitoring TCA-d4 converted from cholic acid-d4 overcoming interanimal variability in endogenous bile acids. Bsep KD also altered liver and/or plasma levels of asunaprevir, TAK-875, TAK-875 acyl-glucuronide, benzbromarone, and bosentan. The Bsep KD rat model has revealed differences in the effects on bile acid homeostasis among Bsep inhibitors that can best be monitored using measures of T3-BA and TCA-d4 in plasma. However, the phenotype caused by Bsep inhibition is complex due to the involvement of several compensatory mechanisms.

Static Model-Based Assessment of OATP1B1-Mediated Drug Interactions with Preincubation-Dependent Inhibitors Based on Inactivation and Recovery Kinetics

Quantitative assessment of drug-drug interactions (DDIs) via organic anion transporting polypeptide (OATP) 1B1 is one of the key issues in drug development. Although OATP1B1 inhibition exhibits unique characteristics, including preincubation dependence for some inhibitors, a limited approach has been attempted based on the static model that considers such preincubation dependence in the prediction of DDIs via OATP1B1. The present study aimed to establish the prediction of DDIs via OATP1B1 using preincubation-dependent inhibitors based on the static model and incorporating both inactivation and recovery of OATP1B1 activity. Cyclosporine A was selected as a preincubation-dependent inhibitor, as well as five substrates that include probes and pharmaceuticals. The inhibition ratio (R value) calculated on the basis of a conventional static model, considering inhibition of OATP1B1 and contribution ratio of OATP1B1 to the overall hepatic uptake, was much lower than the reported AUC ratio, even when IC₅₀ values were estimated after preincubation conditions. Conversely, the R value that was estimated by considering inactivation and recovery parameters was closer to the AUC ratio. The R value that was calculated assuming the complete contribution of OATP1B1 was much higher than the AUC ratio, avoiding false-negative prediction. The R value estimated by considering inactivation and recovery for another combination of a preincubation-dependent inhibitor, asunaprevir, and substrate drug, rosuvastatin, was also closer to the AUC ratio. Thus, R values calculated based on such OATP1B1 kinetics would be potential alternative indexes for the quantitative prediction of OATP1B1-mediated DDIs using preincubation-dependent inhibitors, although this prediction is affected by estimation of the contribution ratio of substrates. SIGNIFICANCE STATEMENT: Static model-based quantitative prediction of organic anion transporting polypeptide 1B1-mediated drug-drug interactions induced by preincubation-dependent inhibitors was newly proposed to avoid false-negative prediction.

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

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

Estimation of the Effect of OAT2-Mediated Active Uptake on Meloxicam Exposure in the Human Liver

Active uptake mediated by organic anion transporter 2 (OAT2) has been previously hypothesized as a key player in hepatic disposition of its substrates. Previous studies have shown that another hepatic uptake transporter, organic anion transporting polypeptides (OATP) 1B1, significantly elevates liver concentrations of drugs transported by it. As tissue concentration typically governs pharmacodynamics, drug-drug interactions, and toxicity in the liver, it is important to understand if OAT2 functions similarly to OATP1B1 in raising liver exposure. Since this is a research problem that cannot be easily assessed in clinical studies at this time, here we estimated human liver exposure of an OAT2 substrate meloxicam using a deduction method based on physiologically based pharmacokinetic (PBPK) modeling of clinical systemic exposure data. Although in vitro data suggest that OAT2-mediated active uptake is involved in meloxicam disposition, the modeling result concludes that its unbound liver exposure is unlikely significantly different from its unbound systemic exposure. This conclusion is further supported by data and modeling from a terminal monkey study and in vitro hepatocyte studies with bovine serum albumin. Overall, based on currently available data, we do not expect that OAT2 has a strong impact on the liver exposure of meloxicam.

Dose-Dependent Inhibition of OATP1B by Rifampicin in Healthy Volunteers: Comprehensive Evaluation of Candidate Biomarkers and OATP1B Probe Drugs

To address the most appropriate endogenous biomarker for drug–drug interaction risk assessment, eight healthy subjects received an organic anion transporting polypeptide 1B (OATP1B) inhibitor (rifampicin, 150, 300, and 600 mg), and a probe drug cocktail (atorvastatin, pitavastatin, rosuvastatin, and valsartan). In addition to coproporphyrin I, a widely studied OATP1B biomarker, we identified at least 4 out of 28 compounds (direct bilirubin, glycochenodeoxycholate‐3‐glucuronide, glycochenodeoxycholate‐3‐sulfate, and hexadecanedioate) that presented good sensitivity and dynamic range in terms of the rifampicin dose‐dependent change in area under the plasma concentration‐time curve ratio (AUCR). Their suitability as OATP1B biomarkers was also supported by the good correlation of AUC_0‐24h between the endogenous compounds and the probe drugs, and by nonlinear regression analysis (AUCR⁻¹ vs. rifampicin plasma C_max (maximum total concentration in plasma)) to yield an estimate of the inhibition constant of rifampicin. These endogenous substrates can complement existing OATP1B‐mediated drug–drug interaction risk assessment approaches based on agency guidelines in early clinical trials.

Development of a new Japanese guideline on drug interaction for drug development and appropriate provision of information

Drug interactions, in particular with concomitant drugs having a narrow therapeutic range, sometimes cause serious adverse drug reactions or attenuation of the therapeutic effect. Therefore, evaluation of the characteristics and severities of possible drug interactions in drug development is essential to understand such interactions to help prevent any potential risk for patients. In Japan, a regulatory document which was notified in 2001 to outline the basic principles of drug interaction studies during drug development was revised as a new guideline after 17 years to present general procedures that are currently considered scientifically valid. This article aims to present an overview of development process of the new Japanese guideline for investigating drug interactions and show the impact of implementating this guideline on drug interaction evaluations, thereby providing future perspectives of regulatory activities on drug interactions.

2019 White Paper on Recent Issues in Bioanalysis: Chromatographic Assays (Part 1 - Innovation in Small Molecules and Oligonucleotides & Mass Spectrometric Method Development Strategies for Large Molecule Bioanalysis)

The 2019 13^th Workshop on Recent Issues in Bioanalysis (WRIB) took place in New Orleans, LA, USA on April 1-5, 2019 with an attendance of over 1000 representatives from pharmaceutical/biopharmaceutical companies, biotechnology companies, contract research organizations and regulatory agencies worldwide. WRIB was once again a 5-day, week-long event - a full immersion week of bioanalysis, biomarkers, immunogenicity and gene therapy. As usual, it was specifically designed to facilitate sharing, reviewing, discussing and agreeing on approaches to address the most current issues of interest including both small- and large-molecule bioanalysis involving LCMS, hybrid LBA/LCMS, LBA cell-based/flow cytometry assays and qPCR approaches. This 2019 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop, and is aimed to provide the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2019 edition of this comprehensive White Paper has been divided into three parts for editorial reasons. This publication (Part 1) covers the recommendations on Innovation in Small Molecules and Oligonucleotides & Mass Spec Method Development Strategies for Large Molecules Bioanalysis. Part 2 (2018 FDA BMV Guidance, 2019 ICH M10 BMV Draft Guideline and regulatory agencies' input on bioanalysis, biomarkers, immunogenicity and gene therapy) and Part 3 (New Insights in Biomarkers Assays Validation, Current & Effective Strategies for Critical Reagent Management, Flow Cytometry Validation in drug discovery & development & CLSI H62, Interpretation of the 2019 FDA Immunogenicity Guidance and The Gene Therapy Bioanalytical Challenges) are published in volume 11 of Bioanalysis, issues 23 and 24 (2019), respectively.

Short-lasting inhibition of hepatic uptake transporter OATP1B1 by tyrosine kinase inhibitor pazopanib

Risk assessment of organic anion transporting polypeptide 1B1 (OATP1B1)-mediated drug-drug interactions (DDIs) is an integral part of drug development, but the difficult aspects in DDI prediction include complex mechanism of OATP1B1 inhibition. Pazopanib, an orally available tyrosine kinase inhibitor, exhibits OATP1B1 inhibition and clinically interacts with some OATP1B1 substrates, although quantitative analysis of DDI potential has not yet been performed. The purpose of the present study was to characterize the inhibitory effect of pazopanib on OATP1B1-mediated transport. Inhibition by pazopanib of OATP1B1-mediated uptake of two typical substrates, [³H]estrone-3-sulfate (E₁S) and [³H]estradiol-17β-glucuronide, assessed in HEK293/OATP1B1 cells, was more obvious after preincubation with pazopanib compared with no preincubation. The reduction in IC₅₀ values was 3-7 times greater and was comparable with the preincubation effect of another long-lasting inhibitor, cyclosporine A (CsA). Preincubation with pazopanib and CsA tended to similarly reduce V_max and increase K_m values of E₁S. However, the reduced OATP1B1 activity by preincubation with pazopanib was more rapidly recovered than CsA. In addition, R value, which predicts the maximum increase in the AUC ratio of victim drugs, was calculated to be 1.09. These results suggest that pazopanib is preincubation-dependent but a short-lasting inhibitor against OATP1B1 with low potential of OATP1B1-mediated DDIs.

Complex DDI by Fenebrutinib and the Use of Transporter Endogenous Biomarkers to Elucidate the Mechanism of DDI

Mechanistic understanding of complex clinical drug-drug interactions (DDIs) with potential involvement of multiple elimination pathways has been challenging, especially given the general lack of specific probe substrates for transporters. Here, we conducted a clinical DDI study to evaluate the interaction potential of fenebrutinib using midazolam (MDZ; CYP3A), simvastatin (CYP3A and OATP1B), and rosuvastatin (BCRP and OATP1B) as probe substrates. Fenebrutinib (200 mg) increased the area under the curve (AUC) of these probe substrates twofold to threefold. To evaluate the mechanism of the observed DDIs, we measured the concentration of coproporphyrin I (CP-I) and coproporphyrin III (CP-III), endogenous biomarkers of OATP1B. There was no change in CP-I or CP-III levels with fenebrutinib, suggesting that the observed DDIs were caused by inhibition of CYP3A and BCRP rather than OATP1B, likely due to increased bioavailability. This is the first published account using an endogenous transporter biomarker to understand the mechanism of complex DDIs involving multiple elimination pathways.

Enhanced and Persistent Inhibition of Organic Cation Transporter 1 Activity by Preincubation of Cyclosporine A

Recent pharmacogenetic evidence indicates that hepatic organic cation transporter (OCT) 1 can serve as the locus of drug-drug interactions (DDIs) with significant pharmacokinetic and pharmacodynamic consequences. We examined the impact of preincubation on the extent of OCT1 inhibition in transfected human embryonic kidney 293 (HEK293) cells. Following 30-minute preincubation with an inhibitor, approximately 50-fold higher inhibition potency was observed for cyclosporine A (CsA) against OCT1-mediated uptake of metformin compared with coincubation, with IC₅₀ values of 0.43 ± 0.12 and 21.6 ± 4.5 µM, respectively. By comparison, only small shifts (≤2-fold) in preincubation IC₅₀ versus coincubation were observed for quinidine, pyrimethamine, ritonavir, and trimethoprim. The shift in CsA OCT1 IC₅₀ was substrate dependent since it ranged from >1.2- to 50.2-fold using different experimental substrates. The inhibition potential of CsA toward OCT1 was confirmed by fenoterol hepatocyte uptake experiment. Furthermore, no shift in CsA IC₅₀ was observed with HEK293 cells transfected with OCT2 and organic anion transporter (OAT) 1 and OAT3. Short exposure (30 minutes) to 10 µM CsA produced long-lasting inhibition (at least 120 minutes) of the OCT1-mediated uptake of metformin in OCT1-HEK293 cells, which was likely attributable to the retention of CsA in the cells, as shown by the fact that inhibitory cellular concentrations of CsA were maintained long after the removal of the compound from the incubation buffer. The potent and persistent inhibitory effect after exposure to CsA warrants careful consideration in the design and interpretation of clinical OCT1 DDI studies. SIGNIFICANCE STATEMENT: Preincubation of OATP1B1 and OATP1B3 with their inhibitor may result in the enhancement of the inhibitory potency in a cell-based assay. However, limited data are available on potentiation of OCT1 inhibition by preincubation, which is a clinically relevant drug transporter. For the first time, we observed a 50-fold increase in CsA inhibitory potency against OCT1-mediated transport of metformin following a preincubation step. The CsA preincubation effect on OCT1 inhibition is substrate dependent. Moreover, the inhibition potential of CsA toward OCT1 is confirmed by hepatocyte uptake experiment. This study delivers clear evidences about the potent and persistent inhibitory effect on OCT1 after exposure to CsA. Further studies are needed to assess the effect of CsA on OCT1 drug substrates in vivo.

Preincubation With Everolimus and Sirolimus Reduces Organic Anion-Transporting Polypeptide (OATP)1B1- and 1B3-Mediated Transport Independently of mTOR Kinase Inhibition: Implication in Assessing OATP1B1- and OATP1B3-Mediated Drug-Drug Interactions

Organic anion transporting polypeptides (OATP)1B1 and OATP1B3 mediate hepatic uptake of many drugs including lipid-lowering statins. Current studies determined the OATP1B1/1B3-mediated drug-drug interaction (DDI) potential of mammalian target of rapamycin (mTOR) inhibitors, everolimus and sirolimus, using R-value and physiologically based pharmacokinetic models. Preincubation with everolimus and sirolimus significantly decreased OATP1B1/1B3-mediated transport even after washing and decreased inhibition constant values up to 8.3- and 2.9-fold for OATP1B1 and both 2.7-fold for OATP1B3, respectively. R-values of everolimus, but not sirolimus, were greater than the FDA-recommended cutoff value of 1.1. Physiologically based pharmacokinetic models predict that everolimus and sirolimus have low OATP1B1/1B3-mediated DDI potential against pravastatin. OATP1B1/1B3-mediated transport was not affected by preincubation with INK-128 (10 μM, 1 h), which does however abolish mTOR kinase activity. The preincubation effects of everolimus and sirolimus on OATP1B1/1B3-mediated transport were similar in cells before preincubation with vehicle control or INK-128, suggesting that inhibition of mTOR activity is not a prerequisite for the preincubation effects observed for everolimus and sirolimus. Nine potential phosphorylation sites of OATP1B1 were identified by phosphoproteomics; none of these are the predicted mTOR phosphorylation sites. We report the everolimus/sirolimus-preincubation-induced inhibitory effects on OATP1B1/1B3 and relatively low OATP1B1/1B3-mediated DDI potential of everolimus and sirolimus.

In Vitro Evaluation of the Drug Interaction Potential of Doravirine

Doravirine is a novel nonnucleoside reverse transcriptase inhibitor for the treatment of human immunodeficiency virus type 1 infection. In vitro studies were conducted to assess the potential for drug interactions with doravirine via major drug-metabolizing enzymes and transporters. Kinetic studies confirmed that cytochrome P450 3A (CYP3A) plays a major role in the metabolism of doravirine, with ∼20-fold-higher catalytic efficiency for CYP3A4 versus CYP3A5. Doravirine was not a substrate of breast cancer resistance protein (BCRP) and likely not a substrate of organic anion transporting polypeptide 1B1 (OATP1B1) or OATP1B3. Doravirine was not a reversible inhibitor of major CYP enzymes (CYP1A2, -2B6, -2C8, -2C9, -2C19, -2D6, and -3A4) or of UGT1A1, nor was it a time-dependent inhibitor of CYP3A4. No induction of CYP1A2 or -2B6 was observed in cultured human hepatocytes; small increases in CYP3A4 mRNA (≤20%) were reported at doravirine concentrations of ≥10 μM but with no corresponding increase in enzyme activity. In vitro transport studies indicated a low potential for interactions with substrates of BCRP, P-glycoprotein, OATP1B1 and OATP1B3, the bile salt extrusion pump (BSEP), organic anion transporter 1 (OAT1) and OAT3, organic cation transporter 2 (OCT2), and multidrug and toxin extrusion 1 (MATE1) and MATE2K proteins. In summary, these in vitro findings indicate that CYP3A4 and CYP3A5 mediate the metabolism of doravirine, although with different catalytic efficiencies. Clinical trials reported elsewhere confirm that doravirine is subject to drug-drug interactions (DDIs) via CYP3A inhibitors and inducers, but they support the notion that DDIs (either direction) are unlikely via other major drug-metabolizing enzymes and transporters.

Effect of Rifampicin on the Plasma Concentrations of Bile Acid-O-Sulfates in Monkeys and Human Liver-Transplanted Chimeric Mice With or Without Bile Flow Diversion

The present study examined the significance of enterohepatic circulation and the effect of rifampicin [an inhibitor of organic anion-transporting polypeptide 1B (OATP1B)] on the plasma concentrations of bile acid-O-sulfates (glycochenodeoxycholate-O-sulfate, lithocholate-O-sulfate, glycolithocholate-O-sulfate, and taurolithocholate-O-sulfate) in monkeys and human liver-transplanted chimeric mice (PXB mouse). Rifampicin significantly increased the area under the curve of bile acid-O-sulfates in monkeys (13-69 times) and PXB mice (13-25 times) without bile flow diversion. Bile flow diversion reduced the concentration of plasma bile acid-O-sulfates under control conditions in monkeys and the concentration of plasma glycochenodeoxycholate-O-sulfate in PXB mice. It also diminished diurnal variation of plasma lithocholate-O-sulfate, glycolithocholate-O-sulfate, and taurolithocholate-O-sulfate in PXB mice under control conditions. Bile flow diversion did not affect the plasma concentration of bile acid-O-sulfates in monkeys and PXB mice treated with rifampicin. Plasma coproporphyrin I and III levels were constant in monkeys throughout the study, even with bile flow diversion. This study demonstrated that bile acid-O-sulfates are endogenous OATP1B biomarkers in monkeys and PXB mice. Enterohepatic circulation can affect the baseline levels of plasma bile acid-O-sulfates and modify the effect of OATP1B inhibition.

[Quantitative assessment of the risk of OATP1B1/1B3-mediated drug-drug interactions]

Drug transporters play important roles in determining drug pharmacokinetics. Organic anion transporting polypeptides 1B1/1B3 (OATP1B1/1B3) are transporters mediating hepatic uptake of various anionic drugs. OATP1B1/1B3 activities are changed by genetic mutation and drug-drug interaction (DDI) that could lead to severe adverse reactions. Methods to address the precise DDI risk assessment have been developed in addition to the translational assessment from the results of in vitro studies. Using endogenous substrates as probes is an emerging approach that allows clinical assessment of the DDI risk in the early phase of drug development. Then, the clinical data will be subjected to the pharmacokinetic analysis using physiologically-based pharmacokinetic models to perform the more realistic DDI risk assessment with OATP1B1/1B3 substrate drugs. When drug targets are located inside the hepatocytes, DDI impact on the intrahepatic concentration is critical for their pharmacological actions. Positron emission tomography (PET) allows researchers to determine tissue concentration time profiles of the PET probe upon the inhibition of OATP1B1/1B3, and to estimate the change in kinetic parameter for each intrinsic process of hepatic elimination of PET probe. Integration of the clinical data into the PBPK model realizes more precise prediction of DDI impact on the pharmacokinetics of drugs, and their therapeutic effects.