Quantitative Targeted Absolute Proteomics of Transporters and Pharmacoproteomics-Based Reconstruction of P-Glycoprotein Function in Mouse Small Intestine

Prediction of drug-drug interaction risk of P-glycoprotein substrate in drug discovery

We aimed at predicting the drug-drug interaction (DDI) risk of P-glycoprotein (P-gp) substrates by using P-gp expressing LLC-PK1 cells and its knockout mice (KO). The area under the curve (AUC) of 16 marketed drugs and plasma concentration (Cplasma) of 207 screening compounds, with corrected efflux ratio (CER) ≥ 2, were compared between P-gp KO mice and wild type mice (WT). At permeability (Papp) ≥ 10 × 10-6 cm/s in parent LLC-PK1 cells, AUC ratios (KO/WT) and Cplasma ratios (KO/WT) of these compounds were within 3-fold. AUC ratios (KO/WT) of clinical P-gp substrates, with human AUC ratios with and without P-gp inhibitor administration ≥2, were higher than 8.7. These observations led us to establish a work-flow of P-gp substrate assessment with the threshold AUC ratio (KO/WT) ≥ 9 leading to a DDI risk of AUC ratio (human) ≥ 2. A screening compound showing high CER (=57.6) was found, but its AUC ratio (KO/WT) was 3.7, had been presumed to be a weak risk and its AUC ratio (human) was 1.2 in a later clinical DDI study. Our proposed workflow should be useful for predicting the DDI risk of P-gp substrates in drug discovery.

Organic anion-transporting polypeptide 2B1 knockout and humanized mice; insights into the handling of bilirubin and drugs

Organic anion transporting polypeptide 2B1 (OATP2B1/SLCO2B1) facilitates uptake transport of structurally diverse endogenous and exogenous compounds. To investigate the roles of OATP2B1 in physiology and pharmacology, we established and characterized Oatp2b1 knockout (single Slco2b1^-/- and combination Slco1a/1b/2b1^-/-) and humanized hepatic and intestinal OATP2B1 transgenic mouse models. While viable and fertile, these strains exhibited a modestly increased body weight. In males, unconjugated bilirubin levels were markedly reduced in Slco2b1^-/- compared to wild-type mice, whereas bilirubin monoglucuronide levels were modestly increased in Slco1a/1b/2b1^-/- compared to Slco1a/1b^-/- mice. Single Slco2b1^-/- mice showed no significant changes in oral pharmacokinetics of several tested drugs. However, markedly higher or lower plasma exposure of pravastatin and the erlotinib metabolite OSI-420, respectively, were found in Slco1a/1b/2b1^-/- compared to Slco1a/1b^-/- mice, while oral rosuvastatin and fluvastatin behaved similarly between the strains. In males, humanized OATP2B1 strains showed lower conjugated and unconjugated bilirubin levels than control Slco1a/1b/2b1-deficient mice. Moreover, hepatic expression of human OATP2B1 partially or completely rescued the impaired hepatic uptake of OSI-420, rosuvastatin, pravastatin, and fluvastatin in Slco1a/1b/2b1^-/- mice, establishing an important role in hepatic uptake. Expression of human OATP2B1 in the intestine was basolateral and markedly reduced the oral availability of rosuvastatin and pravastatin, but not of OSI-420 and fluvastatin. Neither lack of Oatp2b1, nor overexpression of human OATP2B1 had any effect on fexofenadine oral pharmacokinetics. While these mouse models still have limitations for human translation, with additional work we expect they will provide powerful tools to further understand the physiological and pharmacological roles of OATP2B1.

Quantitative prediction of P-glycoprotein-mediated drug-drug interactions and intestinal absorption using humanized mice

BACKGROUND AND PURPOSE

P-glycoprotein (P-gp) exhibits a broad substrate specificity and affects pharmacokinetics, especially intestinal absorption. However, prediction, in vivo, of P-gp-mediated drug-drug interaction (DDI) and non-linear absorption at the preclinical stage, is challenging. Here we evaluate the use of human MDR1 mouse artificial chromosome (hMDR1-MAC) mice carrying human P-gp and lacking their own murine P-gp to quantitatively predict human P-gp-mediated DDI and non-linear absorption.

EXPERIMENTAL APPROACH

The P-gp substrates (aliskiren, betrixaban, celiprolol, digoxin, fexofenadine and talinolol) were administered orally to wild-type, Mdr1a/b-knockout (KO) and hMDR1-MAC mice, and their plasma concentrations were measured. We calculated the ratio of area under the curve (AUCR) in mice (AUC_Mdr1a/b-KO /AUC_wild-type or AUC_Mdr1a/b-KO /AUC_hMDR1-MAC ) estimated as attributable to complete P-gp inhibition and the human AUCR with and without P-gp inhibitor administration. The correlations of AUCR_human with AUCR_wild-type and AUCR_hMDR1-MAC were investigated. For aliskiren, betrixaban and celiprolol, the K_m and V_max values for P-gp in hMDR1-MAC mice and humans were optimized from different dosing studies using GastroPlus. The correlations of K_m and V_max for P-gp between human and hMDR1-MAC mice were investigated.

KEY RESULTS

A better correlation between AUCR_human and AUCR_hMDR1-MAC (R²  = 0.88) was observed. Moreover, good relationships of K_m (R²  = 1.00) and V_max (R²  = 0.98) for P-gp between humans and hMDR1-MAC mice were observed.

CONCLUSIONS AND IMPLICATIONS

These results suggest that P-gp-mediated DDI and non-linear absorption can be predicted using hMDR1-MAC mice. These mice are a useful in vivo tool for quantitatively predicting P-gp-mediated disposition in drug discovery and development.

Quantitative Proteomics-Based Blood-Brain Barrier Study

From the viewpoint of drug discovery, it is an important issue to elucidate the drug permeability at the human central nervous system (CNS) barriers and the molecular mechanisms in the cells forming CNS barriers especially during CNS diseases. I introduced quantitative proteomics techniques into the blood-brain barrier (BBB) study, then quantitatively investigated the transport system at the human BBB and clarified the quantitative differences in protein expression levels and functions of transporters and receptors between animals and humans, or in vitro and in vivo. Based on the difference in the absolute expression level of transporters between in vitro and in vivo, I demonstrated that the drug efflux activity of P-glycoprotein (P-gp) at in vivo BBB can be accurately reconstructed from the in vitro system, not only in mouse models but also monkeys similar to humans and pathological conditions. Furthermore, I discovered Claudin-11 as another tight junction molecule expressed at the CNS barriers, and clarified that it contributes to the disruption of the CNS barriers in multiple sclerosis. Furthermore, it was also elucidated that the P-gp dysfunction causes excessive brain entry of glucocorticoid which causes a nerve damage in cerebral infarct, and it can be suppressed by targeting Abl/Src kinases. These suggest that targeting the tight junctions and transporters, which are important molecules at the CNS barriers, would potentially lead to the treatment of CNS diseases. In this review, I would like to introduce a new CNS barrier study opened by quantitative proteomics research.

Proteomics-Informed Prediction of Rosuvastatin Plasma Profiles in Patients With a Wide Range of Body Weight

Rosuvastatin is a frequently used probe to study transporter‐mediated hepatic uptake. Pharmacokinetic models have therefore been developed to predict transporter impact on rosuvastatin disposition in vivo. However, the interindividual differences in transporter concentrations were not considered in these models, and the predicted transporter impact was compared with historical in vivo data. In this study, we investigated the influence of interindividual transporter concentrations on the hepatic uptake clearance of rosuvastatin in 54 patients covering a wide range of body weight. The 54 patients were given an oral dose of rosuvastatin the day before undergoing gastric bypass or cholecystectomy, and pharmacokinetic (PK) parameters were established from each patient’s individual time‐concentration profiles. Liver biopsies were sampled from each patient and their individual hepatic transporter concentrations were quantified. We combined the transporter concentrations with in vitro uptake kinetics determined in HEK293‐transfected cells, and developed a semimechanistic model with a bottom‐up approach to predict the plasma concentration profiles of the single dose of rosuvastatin in each patient. The predicted PK parameters were evaluated against the measured in vivo plasma PKs from the same 54 patients. The developed model predicted the rosuvastatin PKs within two‐fold error for rosuvastatin area under the plasma concentration versus time curve (AUC; 78% of the patients; average fold error (AFE): 0.96), peak plasma concentration (C_max; 76%; AFE: 1.05), and terminal half‐life (t_1/2; 98%; AFE: 0.89), and captured differences in the rosuvastatin PKs in patients with the OATP1B1 521T<C polymorphism. This demonstrates that hepatic uptake clearance determined in transfected cell lines, together with proteomics scaling, provides a useful tool for prediction models, without the need for empirical scaling factors.

Quantitative and targeted proteomics-based identification and validation of drug efficacy biomarkers

Proteomics refers to the large-scale study of proteins, providing comprehensive and quantitative information on proteins in tissue, blood, and cell samples. In many studies, proteomics utilizes liquid chromatography-mass spectrometry. Proteomics has developed from a qualitative methodology of protein identification to a quantitative methodology for comparing protein expression, and it is currently classified into two distinct methodologies: quantitative and targeted proteomics. Quantitative proteomics comprehensively identifies proteins in samples, providing quantitative information on large-scale comparative profiles of protein expression. Targeted proteomics simultaneously quantifies only target proteins with high sensitivity and specificity. Therefore, in biomarker research, quantitative proteomics is used for the identification of biomarker candidates, and targeted proteomics is used for the validation of biomarkers. Understanding the specific characteristics of each method is important for conducting appropriate proteomics studies. In this review, we introduced the different characteristics and applications of quantitative and targeted proteomics, and then discussed the results of our recent proteomics studies that focused on the identification and validation of biomarkers of drug efficacy. These findings may enable us to predict the outcomes of cancer therapy and drug-drug interactions with antibiotics through changes in the intestinal microbiome.

Electrochemical analysis of uric acid excretion to the intestinal lumen: Effect of serum uric acid-lowering drugs and 5/6 nephrectomy on intestinal uric acid levels

Recently, extensive efforts have been made to understand the importance of the extra-renal uric acid (UA) excretion pathways and their contribution to UA-related diseases. However, the method typically used to measure UA concentrations in the intestinal lumen is difficult to real time and dynamic analysis. In this study, UA excretion in the rat intestinal lumen was measured in real time using an electrochemical method. A sensitive electrode to detect UA was constructed using a gold electrode modified with a mixed self-assembled monolayer. Excretion rate of UA in the intestine was calculated using time course data. A decrease in UA excretion rate was observed in the intestine after administration of serum UA-lowering drugs (benzbromarone, febuxostat, and topiroxostat). Inhibition of ATP-binding cassette transporter G2 (ABCG2) which has been reported as an important exporter of UA was suggested by administration of these drugs. On the other hand, an increase in excretion rate of UA was observed in the intestine of 5/6 nephrectomy rats. Upregulation of mRNA expression of the UA transporter organic anion transporter OAT3, which is related to the secretion at the basal membrane, suggested an enhancement of UA excretion by ABCG2, a high-capacity UA exporter. Observed urate excretion dynamics and mRNA expression of UA transporters in the intestine upon administration of serum UA-lowering drugs and 5/6 nephrectomy improve our understanding of the underlying mechanisms of intestinal UA excretion.

Increased Expression of Renal Drug Transporters in a Mouse Model of Familial Alzheimer's Disease

It is well established that the expression and function of drug transporters at the blood-brain barrier are altered in Alzheimer's disease (AD). However, we recently demonstrated in a mouse model of AD that the expression of key drug transporters and metabolizing enzymes was modified in peripheral organs, such as the small intestine and liver, suggesting that systemic drug absorption may be altered in AD. The purpose of this study was to determine whether the expression of drug transporters in the kidneys differed between 8- to 9-month-old wild-type mice and APPswe/PSEN1dE9 (APP/PS1) transgenic mice, a mouse model of familial AD, using a quantitative targeted absolute proteomics approach. The protein expression of the drug transporters-multidrug resistance-associated protein 2, organic anion transporter 3, and organic cation transporter 2-was upregulated 1.6-, 1.3-, and 1.4-fold, respectively, in kidneys from APP/PS1 mice relative to wild-type mice. These results suggest that in addition to modified oral absorption of certain drugs, it is possible that the renal excretion of drugs that are multidrug resistance-associated protein 2, organic anion transporter 3, and organic cation transporter 2 substrates could be altered in AD. These changes could affect the interpretation of studies conducted during drug development using this mouse model of AD and potentially impact dosage regimens of such drugs prescribed in this patient population.

Characterization of P-Glycoprotein Humanized Mice Generated by Chromosome Engineering Technology: Its Utility for Prediction of Drug Distribution to the Brain in Humans

P-glycoprotein (P-gp), encoded by the MDR1 gene in humans and by the Mdr1a/1b genes in rodents, is expressed in numerous tissues and performs as an efflux pump to limit the distribution and absorption of many drugs. Owing to species differences of P-gp between humans and rodents, it is difficult to predict the impact of P-gp on pharmacokinetics and the tissue distribution of P-gp substrates in humans from the results of animal experiments. Therefore, we generated a novel P-gp humanized mouse model by using a mouse artificial chromosome (MAC) vector [designated human MDR1-MAC (hMDR1-MAC) mice]. The results showed that hMDR1 mRNA was expressed in various tissues of hMDR1-MAC mice. Furthermore, the expression of human P-gp was detected in the brain capillary fraction and plasma membrane fraction of intestinal epithelial cells isolated from hMDR1-MAC mice, although the expression levels of intestinal P-gp were extremely low. Thus, we evaluated the function of human P-gp at the blood-brain barrier of hMDR1-MAC mice. The brain-to-plasma ratios of P-gp substrates in hMDR1-MAC mice were much lower than those in Mdr1a/1b-knockout mice, and the brain-to-plasma ratio of paclitaxel was significantly increased by pretreatment with a P-gp inhibitor in hMDR1-MAC mice. These results indicated that the hMDR1-MAC mice are the first P-gp humanized mice expressing functional human P-gp at the blood-brain barrier. This mouse is a promising model with which to evaluate species differences of P-gp between humans and mice in vivo and to estimate the brain distribution of drugs in humans while taking into account species differences of P-gp.

Altered Expression of Small Intestinal Drug Transporters and Hepatic Metabolic Enzymes in a Mouse Model of Familial Alzheimer's Disease

Drug transporter expression and function at the blood-brain barrier is altered in Alzheimer's disease (AD). However, the impact of AD on the expression of transporters and metabolizing enzymes in peripheral tissues has received little attention. The current study evaluated the expression of drug transporters and metabolizing enzymes in the small intestine and liver from 8- to 9-month-old female wild-type (WT) and APPswe/PSEN 1dE9 (APP/PS1) transgenic mice, a widely used AD model, using a quantitative targeted absolute proteomics (QTAP) approach. Furthermore, the general morphological appearance of the liver was assessed by immunohistochemistry, and lipid content was visualized using Oil Red O staining. The small intestines of APP/PS1 mice exhibited a significant 2.3-fold increase in multidrug resistance-associated protein 2 (Mrp2), a 1.9-fold decrease in monocarboxylate transporter 1 (Mct1), and a 3.6-fold increase in UDP-glucuronosyltransferase (Ugt) 2b5 relative to those from WT mice based on QTAP analysis. While the liver from APP/PS1 mice exhibited no changes in drug transporter expression, there was a 1.3-fold elevation in cytochrome P450 (Cyp) 51a1 and a 1.2-fold reduction in Cyp2c29 protein expression, and this was associated with morphological alterations including accumulation of hepatocyte lipids. These studies are the first to demonstrate that the protein expression of transporters and metabolizing enzymes important in oral drug absorption are modified in a mouse model of familial AD, which may lead to altered disposition of some orally administered drugs in AD.

Augmentation of Anticancer Drug Efficacy in Murine Hepatocellular Carcinoma Cells by a Peripherally Acting Competitive N-Methyl-d-aspartate (NMDA) Receptor Antagonist

The most common solid tumors show intrinsic multidrug resistance (MDR) or inevitably acquire such when treated with anticancer drugs. In this work, we describe the discovery of a peripherally restricted, potent, competitive NMDA receptor antagonist 1l by a structure-activity study of the broad-acting ionotropic glutamate receptor antagonist 1a. Subsequently, we demonstrate that 1l augments the cytotoxic action of sorafenib in murine hepatocellular carcinoma cells. The underlying biological mechanism was shown to be interference with the lipid signaling pathway, leading to reduced expression of MDR transporters and thereby an increased accumulation of sorafenib in the cancer cells. Interference with lipid signaling pathways by NMDA receptor inhibition is a novel and promising strategy for reversing transporter-mediated chemoresistance in cancer cells.