In vitro screening model for compound interactions with human and dairy animal BCRP orthologs.

Orthologs of breast cancer resistance protein (BCRP/ABCG2), an ATP-binding cassette (ABC) efflux transmembrane transporter, are present in several species. The list of compounds known to interact with BCRP is growing, and many questions remain concerning species-specific variations in substrate specificity and affinity and the potency of inhibitors. As the most abundant efflux transporter known to be present in the blood-milk barrier, BCRP can increase the elimination of certain xenobiotics to milk, posing a risk for suckling offspring and dairy product consumers. Here we developed a model that can be employed to investigate species-specific differences between BCRP substrates and inhibitors. Membrane vesicles were isolated from transiently transduced human embryonic kidney (HEK) 293 cells, overexpressing BCRP, with human, bovine, caprine, and ovine cDNA sequences. To confirm BCRP transport activity in the transduced cells, D-luciferin efflux was measured and to confirm transport activity in the membrane vesicles, [3H] estrone-3-sulfate ([3H]E1S) influx was measured. We also determined the Michaelis-Menten constant (Km) and Vmax of [3H]E1S for each species. We have developed an in vitro transport model to study differences in compound interactions with BCRP orthologs from milk-producing animal species and humans. BCRP transport activity was demonstrated in the species-specific transduced cells by a reduced accumulation of D-luciferin compared with the control cells, indicating BCRP-mediated efflux of D-luciferin. Functionality of the membrane vesicle model was demonstrated by confirming ATP-dependent transport and by quantifying the kinetic parameters, Km and Vmax for the model substrate [3H]E1S. The values were not significantly different between species for the model substrates tested. This model can be insightful for appropriate inter-species extrapolations and risk assessments of xenobiotics in lactating woman and dairy animals.

Effects of allopurinol and febuxostat on uric acid transport and transporter expression in human umbilical vein endothelial cells.

Uric acid induces radical oxygen species formation, endothelial inflammation, and endothelial dysfunction which contributes to the progression of atherosclerosis. Febuxostat inhibits BCRP- and allopurinol stimulates MRP4-mediated uric acid efflux in human embryonic kidney cells. We hypothesized that endothelial cells express uric acid transporters that regulate intracellular uric acid concentration and that modulation of these transporters by febuxostat and allopurinol contributes to their different impact on cardiovascular mortality. The aim of this study was to explore a potential difference between the effect of febuxostat and allopurinol on uric acid uptake by human umbilical vein endothelial cells. Febuxostat increased intracellular uric acid concentrations compared with control. In contrast, allopurinol did not affect intracellular uric acid concentration. In line with this observation, febuxostat increased mRNA expression of GLUT9 and reduced MRP4 expression, while allopurinol did not affect mRNA expression of these uric acid transporters. These findings provide a possible pathophysiological pathway which could explain the higher cardiovascular mortality for febuxostat compared to allopurinol but should be explored further.

Transporter-Mediated Cellular Distribution of Tyrosine Kinase Inhibitors as a Potential Resistance Mechanism in Chronic Myeloid Leukemia.

Chronic myeloid leukemia (CML) is a hematologic neoplasm characterized by the expression of the BCR::ABL1 oncoprotein, a constitutively active tyrosine kinase, resulting in uncontrolled growth and proliferation of cells in the myeloid lineage. Targeted therapy using tyrosine kinase inhibitors (TKIs) such as imatinib, nilotinib, dasatinib, bosutinib, ponatinib and asciminib has drastically improved the life expectancy of CML patients. However, treatment resistance occurs in 10-20% of CML patients, which is a multifactorial problem that is only partially clarified by the presence of TKI inactivating BCR::ABL1 mutations. It may also be a consequence of a reduction in cytosolic TKI concentrations in the target cells due to transporter-mediated cellular distribution. This review focuses on drug-transporting proteins in stem cells and progenitor cells involved in the distribution of TKIs approved for the treatment of CML. Special attention will be given to ATP-binding cassette transporters expressed in lysosomes, which may facilitate the extracytosolic sequestration of these compounds.

Mitochondrial complex III activity: from invasive muscle biopsies to patient-friendly buccal swab analysis.

Drug-induced mitochondrial dysfunction is a common adverse effect, particularly in case of statins-the most prescribed drugs worldwide. These drugs have been shown to inhibit complex III (CIII) of the mitochondrial oxidative phosphorylation process, which is related to muscle pain. As muscle pain is the most common complaint of statin users, it is crucial to distinguish it from other causes of myalgia to prevent unnecessary cessation of drug therapy. However, diagnosing CIII inhibition currently requires muscle biopsies, which are invasive and not practical for routine testing. Less invasive alternatives for measurement of mitochondrial complex activities are only available yet for complex I and IV. Here, we describe a non-invasive spectrophotometric method to determine CIII catalytic activities using buccal swabs, which we validated in a cohort of statin and non-statin users. Our data indicate that CIII can be reliably measured in buccal swabs, as evidenced by reproducible results above the detection limit. Further validation on a large-scale clinical setting is recommended.

Metabolic impact of genetic and chemical ADP/ATP carrier inhibition in renal proximal tubule epithelial cells.

Mitochondrial dysfunction is pivotal in drug-induced acute kidney injury (AKI), but the underlying mechanisms remain largely unknown. Transport proteins embedded in the mitochondrial inner membrane form a significant class of potential drug off-targets. So far, most transporter-drug interactions have been reported for the mitochondrial ADP/ATP carrier (AAC). Since it remains unknown to what extent AAC contributes to drug-induced mitochondrial dysfunction in AKI, we here aimed to better understand the functional role of AAC in the energy metabolism of human renal proximal tubular cells. To this end, CRISPR/Cas9 technology was applied to generate AAC3-/- human conditionally immortalized renal proximal tubule epithelial cells. This AAC3-/- cell model was characterized with respect to mitochondrial function and morphology. To explore whether this model could provide first insights into (mitochondrial) adverse drug effects with suspicion towards AAC-mediated mechanisms, wild-type and knockout cells were exposed to established AAC inhibitors, after which cellular metabolic activity and mitochondrial respiratory capacity were measured. Two AAC3-/- clones showed a significant reduction in ADP import and ATP export rates and mitochondrial mass, without influencing overall morphology. AAC3-/- clones exhibited reduced ATP production, oxygen consumption rates and metabolic spare capacity was particularly affected, mainly in conditions with galactose as carbon source. Chemical AAC inhibition was stronger compared to genetic inhibition in AAC3-/-, suggesting functional compensation by remaining AAC isoforms in our knockout model. In conclusion, our results indicate that ciPTEC-OAT1 cells have a predominantly oxidative phenotype that was not additionally activated by switching energy source. Genetic inhibition of AAC3 particularly impacted mitochondrial spare capacity, without affecting mitochondrial morphology, suggesting an important role for AAC in maintaining the metabolic spare respiration.

Perfluoroalkyl substances (PFASs) are substrates of the renal human organic anion transporter 4 (OAT4).

Poly- and perfluoroalkyl substances (PFASs) are omnipresent in the environment and have been shown to accumulate in humans. Most PFASs are not biotransformed in animals and humans, so that elimination is largely dependent on non-metabolic clearance via bile and urine. Accumulation of certain PFASs in humans may relate to their reabsorption from the pre-urine by transporter proteins in the proximal tubules of the kidney, such as URAT1 and OAT4. The present study assessed the in vitro transport of 7 PFASs (PFHpA, PFOA, PFNA, PFDA, PFBS, PFHxS and PFOS) applying URAT1- or OAT4-transfected human embryonic kidney (HEK) cells. Virtually no transport of PFASs could be measured in URAT1-transfected HEK cells. All PFASs, except PFBS, showed clear uptake in OAT4-transfected HEK cells. In addition, these in vitro results were further supported by in silico docking and molecular dynamic simulation studies assessing transporter-ligand interactions. Information on OAT4-mediated transport may provide insight into the accumulation potential of PFASs in humans, but other kinetic aspects may play a role and should also be taken into account. Quantitative information on all relevant kinetic processes should be integrated in physiologically based kinetic (PBK) models, to predict congener-specific accumulation of PFASs in humans in a more accurate manner.

A proof of concept using the Ussing chamber methodology to study pediatric intestinal drug transport and age-dependent differences in absorption.

Little is known about the impact of age on the processes governing human intestinal drug absorption. The Ussing chamber is a system to study drug transport across tissue barriers, but it has not been used to study drug absorption processes in children. This study aimed to explore the feasibility of the Ussing chamber methodology to assess pediatric intestinal drug absorption. Furthermore, differences between intestinal drug transport processes of children and adults were explored as well as the possible impact of age. Fresh terminal ileal leftover tissues from both children and adults were collected during surgery and prepared for Ussing chamber experiments. Paracellular (enalaprilat), transcellular (propranolol), and carrier-mediated drug transport by MDR1 (talinolol) and BCRP (rosuvastatin) were determined with the Ussing chamber methodology. We calculated apparent permeability coefficients and efflux ratios and explored their relationship with postnatal age. The success rate for the Ussing chamber experiments, as determined by electrophysiological measurements, was similar between children (58%, N = 15, median age: 44 weeks; range 8 weeks to 17 years) and adults (67%, N = 13). Mean serosal to mucosal transport of talinolol by MDR1 and rosuvastatin by BCRP was higher in adult than in pediatric tissues (p = 0.0005 and p = 0.0091). In contrast, within our pediatric cohort, there was no clear correlation for efflux transport across different ages. In conclusion, the Ussing chamber is a suitable model to explore pediatric intestinal drug absorption and can be used to further elucidate ontogeny of individual intestinal pharmacokinetic processes like drug metabolism and transport.

Effects of tumor necrosis factor on undifferentiated and syncytialized placental choriocarcinoma BeWo cells.

Tumor necrosis factor (TNF) regulates trophoblast turnover during the formation of the placental syncytium and can be a potentially relevant target for adverse effects of xenobiotics. We mimicked syncytialization in vitro by stimulating BeWo cells with 50 µM forskolin. Undifferentiated and syncytialized BeWo cells were exposed to TNF (10 pg/mL-10 ng/mL) for 48 h after which cell viability, progesterone release and gene expression of a selected set of markers representative for placental function were assessed. In undifferentiated BeWo cells, high TNF levels (1-10 ng/mL) increased gene expression of TNF, NF-κB, and TNFRSF1B to maximally 99 ± 17, 2.2 ± 0.2, and 3.0 ± 0.4 of control values, respectively (p < 0.001). These effects were also found in syncytialized BeWo cells but less pronounced. Additionally, TNF may induce syncytialization in BeWo cells as it upregulated ERVW-1 expression by 1.55 ± 0.14-fold (p < 0.05). On the contrary, TNF levels of 10 and 100 pg/mL did not affect gene expression in both undifferentiated and syncytialized BeWo cells, but did enhance cell viability in syncytialised BeWo cells (p < 0.001). In conclusion, we found that high TNF levels (1-10 ng/mL) increased gene expression of TNF, NF-κB, and TNFRSF1B especially in undifferentiated BeWo cells, while physiological TNF concentrations positively affected cell viability and while there was no effect on any of the investigated functional markers.

Ontogeny of Small Intestinal Drug Transporters and Metabolizing Enzymes Based on Targeted Quantitative Proteomics.

Most drugs are administered to children orally. An information gap remains on the protein abundance of small intestinal drug-metabolizing enzymes (DMEs) and drug transporters (DTs) across the pediatric age range, which hinders precision dosing in children. To explore age-related differences in DMEs and DTs, surgical leftover intestinal tissues from pediatric and adult jejunum and ileum were collected and analyzed by targeted quantitative proteomics for apical sodium-bile acid transporter, breast cancer resistance protein (BCRP), monocarboxylate transporter 1 (MCT1), multidrug resistance protein 1 (MDR1), multidrug resistance-associated protein (MRP) 2, MRP3, organic anion-transporting polypeptide 2B1, organic cation transporter 1, peptide transporter 1 (PEPT1), CYP2C19, CYP3A4, CYP3A5, UDP glucuronosyltransferase (UGT) 1A1, UGT1A10, and UGT2B7. Samples from 58 children (48 ileums, 10 jejunums, age range: 8 weeks to 17 years) and 16 adults (8 ileums, 8 jejunums) were analyzed. When comparing age groups, BCRP, MDR1, PEPT1, and UGT1A1 abundance was significantly higher in adult ileum as compared with the pediatric ileum. Jejunal BCRP, MRP2, UGT1A1, and CYP3A4 abundance was higher in the adults compared with children 0-2 years of age. Examining the data on a continuous age scale showed that PEPT1 and UGT1A1 abundance was significantly higher, whereas MCT1 and UGT2B7 abundance was lower in adult ileum as compared with the pediatric ileum. Our data contribute to the deeper understanding of the ontogeny of small intestinal drug-metabolizing enzymes and drug transporters and shows DME-, DT-, and intestinal location-specific, age-related changes. SIGNIFICANCE STATEMENT: This is the first study that describes the ontogeny of small intestinal DTs and DMEs in human using liquid chromatography with tandem mass spectrometry-based targeted quantitative proteomics. The current analysis provides a detailed picture about the maturation of DT and DME abundances in the human jejunum and ileum. The presented results supply age-related DT and DME abundance data for building more accurate PBPK models that serve to support safer and more efficient drug dosing regimens for the pediatric population.

Toxicity of anticancer drugs in human placental tissue explants and trophoblast cell lines.

The application of anticancer drugs during pregnancy is associated with placenta-related adverse pregnancy outcomes. Therefore, it is important to study placental toxicity of anticancer drugs. The aim of this study was to compare effects on viability and steroidogenesis in placental tissue explants and trophoblast cell lines. Third trimester placental tissue explants were exposed for 72 h (culture day 4-7) to a concentration range of doxorubicin, paclitaxel, cisplatin, carboplatin, crizotinib, gefitinib, imatinib, or sunitinib. JEG-3, undifferentiated BeWo, and syncytialised BeWo cells were exposed for 48 h to the same drugs and concentrations. After exposure, tissue and cell viability were assessed and progesterone and estrone levels were quantified in culture medium. Apart from paclitaxel, all compounds affected both cell and tissue viability at clinically relevant concentrations. Paclitaxel affected explant viability moderately, while it reduced cell viability by 50% or more in all cell lines, at 3-10 nM. Doxorubicin (1 µM) reduced viability in explants to 83 ± 7% of control values, whereas it fully inhibited viability in all cell types. Interference with steroid release in explants was difficult to study due to large variability in measurements, but syncytialised BeWo cells proved suitable for this purpose. We found that 1 µM sunitinib reduced progesterone release to 76 ± 6% of control values, without affecting cell viability. While we observed differences between the models for paclitaxel and doxorubicin, most anticancer drugs affected viability significantly in both placental explants and trophoblast cell lines. Taken together, the placenta should be recognized as a potential target organ for toxicity of anticancer drugs.

Rifampicin Transport by OATP1B1 Variants.

Single nucleotide polymorphisms in the OATP1B1 transporter have been suggested to partially explain the large interindividual variation in rifampicin exposure. HEK293 cells overexpressing wild-type (WT) or OATP1B1 variants *1b, *4, *5, and *15 were used to determine the in vitro rifampicin intrinsic clearance. For OATP1B1*5 and *15, a 36% and 42% reduction in intrinsic clearance, respectively, compared to WT was found. We consider that these differences in intrinsic clearance most likely have minor clinical implications.

Human multidrug resistance protein 4 (MRP4) is a cellular efflux transporter for paracetamol glutathione and cysteine conjugates.

Paracetamol (acetaminophen, APAP) overdose is a leading cause of acute drug-induced liver failure. APAP hepatotoxicity is mediated by the reactive metabolite N-acetyl-p-benzoquinone imine (NAPQI). NAPQI is inactivated by conjugation with glutathione (GSH) to APAP-GSH, which is further converted into its cysteine derivative APAP-CYS. Before necrosis of hepatocytes occurs, APAP-CYS is measurable in plasma of the affected patient and it has been proposed as an early biomarker of acetaminophen toxicity. APAP-GSH and APAP-CYS can be extruded by hepatocytes, but the transporters involved are unknown. In this study we examined whether ATP-binding cassette (ABC) transporters play a role in the cellular efflux of APAP, APAP-GSH, and APAP-CYS. The ABC transport proteins P-gp/ABCB1, BSEP/ABCB11, BCRP/ABCG2, and MRP/ABCC1-5 were overexpressed in HEK293 cells and membrane vesicles were produced. Whereas P-gp, BSEP, MRP3, MRP5, and BCRP did not transport any of the compounds, uptake of APAP-GSH was found for MRP1, MRP2 and MRP4. APAP-CYS appeared to be a substrate of MRP4 and none of the ABC proteins transported APAP. The results suggest that the NAPQI metabolite APAP-CYS can be excreted into plasma by MRP4, where it could be a useful biomarker for APAP exposure and toxicity. Characterization of the cellular efflux of APAP-CYS is important for its development as a biomarker, because plasma concentrations might be influenced by drug-transporter interactions and upregulation of MRP4.

Assessment of Placental Disposition of Infliximab and Etanercept in Women With Autoimmune Diseases and in the Ex Vivo Perfused Placenta.

Tumor necrosis factor (TNF) inhibitors are increasingly applied during pregnancy without clear knowledge of the impact on placenta and fetus. We assessed placental transfer and exposure to infliximab (n = 3) and etanercept (n = 3) in women with autoimmune diseases. Furthermore, we perfused healthy term placentas for 6 hours with 100 µg/mL infliximab (n = 4) or etanercept (n = 5). In pregnant women, infliximab transferred into cord blood but also entered the placenta (cord-to-maternal ratio of 1.6 ± 0.4, placenta-to-maternal ratio of 0.3 ± 0.1, n = 3). For etanercept, a cord-to-maternal ratio of 0.04 and placenta-to-maternal ratio of 0.03 was observed in one patient only. In ex vivo placenta perfusions, the extent of placental transfer did not differ between the drugs. Final concentrations in the fetal compartment for infliximab and etanercept were 0.3 ± 0.3 and 0.2 ± 0.2 µg/mL, respectively. However, in placental tissue, infliximab levels exceeded those of etanercept (19 ± 6 vs. 1 ± 3 µg/g, P < 0.001). In conclusion, tissue exposure to infliximab is higher than that of etanercept both in vivo as well as in ex vivo perfused placentas. However, initial placental transfer, as observed ex vivo, does not differ between infliximab and etanercept when administered in equal amounts. The difference in placental tissue exposure to infliximab and etanercept may be of clinical relevance and warrants further investigation. More specifically, we suggest that future studies should look into the occurrence of placental TNF inhibition and possible consequences thereof.

Effects of clofibrate and KH176 on life span and motor function in mitochondrial complex I-deficient mice.

Mitochondrial complex I (CI), the first multiprotein enzyme complex of the OXPHOS system, executes a major role in cellular ATP generation. Consequently, dysfunction of this complex has been linked to inherited metabolic disorders, including Leigh disease (LD), an often fatal disease in early life. Development of clinical effective treatments for LD remains challenging due to the complex pathophysiological nature. Treatment with the peroxisome proliferation-activated receptor (PPAR) agonist bezafibrate improved disease phenotype in several mitochondrial disease mouse models mediated via enhanced mitochondrial biogenesis and fatty acid ß-oxidation. However, the therapeutic potential of this mixed PPAR (α, δ/ß, γ) agonist is severely hampered by hepatotoxicity, which is possibly caused by activation of PPARγ. Here, we aimed to investigate the effects of the PPARα-specific fibrate clofibrate in mitochondrial CI-deficient (Ndufs4-/-) mice. Clofibrate increased lifespan and motor function of Ndufs4-/- mice, while only marginal hepatotoxic effects were observed. Due to the complex clinical and cellular phenotype of CI-deficiency, we also aimed to investigate the therapeutic potential of clofibrate combined with the redox modulator KH176. As described previously, single treatment with KH176 was beneficial, however, combining clofibrate with KH176 did not result in an additive effect on disease phenotype in Ndufs4-/- mice. Overall, both drugs have promising, but independent and nonadditive, properties for the pharmacological treatment of CI-deficiency-related mitochondrial diseases.

Flow stimulates drug transport in a human kidney proximal tubule-on-a-chip independent of primary cilia.

BACKGROUND: Kidney disease modeling and assessment of drug-induced kidney injury can be advanced using three-dimensional (3D) microfluidic models that recapitulate in vivo characteristics. Fluid shear stress (FSS) has been depicted as main modulator improving in vitro physiology in proximal tubule epithelial cells (PTECs). We aimed to elucidate the role of FSS and primary cilia on transport activity and morphology in PTECs. METHODS: Human conditionally immortalized PTEC (ciPTEC-parent) was cultured in a microfluidic 3D device, the OrganoPlate, under a physiological peak FSS of 2.0 dyne/cm2 or low peak FSS of 0.5 dyne/cm2. Upon a 9-day exposure to FSS, albumin-FITC uptake, activity of P-glycoprotein (P-gp) and multidrug resistance-associated proteins 2/4 (MRP2/4), cytotoxicity and cell morphology were determined. RESULTS: A primary cilium knock-out cell model, ciPTEC-KIF3α-/-, was successfully established via CRISPR-Cas9 genome editing. Under physiological peak FSS, albumin-FITC uptake (p = .04) and P-gp efflux (p = .002) were increased as compared to low FSS. Remarkably, a higher albumin-FITC uptake (p = .03) and similar trends in activity of P-gp and MRP2/4 were observed in ciPTEC-KIF3α-/-. FSS induced cell elongation corresponding with the direction of flow in both cell models, but had no effect on cyclosporine A-induced cytotoxicity. CONCLUSIONS: FSS increased albumin uptake, P-gp efflux and cell elongation, but this was not attributed to a mechanosensitive mechanism related to primary cilia in PTECs, but likely to microvilli present at the apical membrane. GENERAL SIGNIFICANCE: FSS-induced improvements in biological characteristics and activity in PTECs was not mediated through a primary cilium-related mechanism.

Uremic solutes modulate hepatic bile acid handling and induce mitochondrial toxicity.

Chronic kidney disease (CKD) is accompanied by accumulating levels of uremic solutes in the circulation. Changes in the size and composition of the bile acid pool have also been observed. We investigated via which mechanisms uremic solutes may interfere with hepatocyte function and thus contribute to altered bile acid handling. We studied interference on the level of bile acid synthesis by cytochrome P450 7A1 (CYP7A1), explored effects on hepatic bile acid transporters, and investigated effects on mitochondrial function. In HEK293 cells overexpressing bile salt transporters, we observed that p-cresyl sulfate inhibited Na+-taurocholate cotransporting polypeptide (NTCP)-mediated uptake of taurocholic acid (TCA), whereas organic anion-transporting polypeptide 1B1 (OATP1B1)-mediated TCA uptake was increased. Assays in transporter-overexpressing membrane vesicles revealed that kynurenic acid inhibited TCA transport via the bile salt efflux pump (BSEP), whereas p-cresyl glucuronide and hippuric acid increased TCA efflux via multidrug resistance-associated protein 3 (MRP3). Moreover, indoxyl sulfate decreased mRNA expression of NTCP, OATP1B3 and CYP7A1 in primary human hepatocytes. Transport studies confirmed a decreased TCA uptake in indoxyl sulfate-exposed hepatocytes. Decreased hepatocyte viability was found for all seven uremic solutes tested, whereas five out of seven also decreased intracellular ATP levels and mitochondrial membrane potential. In conclusion, uremic solutes affect hepatic bile acid transport and mitochondrial function. This can contribute to the altered bile acid homeostasis observed in CKD patients.

Screening of Drug-Transporter Interactions in a 3D Microfluidic Renal Proximal Tubule on a Chip.

Drug-transporter interactions could impact renal drug clearance and should ideally be detected in early stages of drug development to avoid toxicity-related withdrawals in later stages. This requires reliable and robust assays for which current high-throughput screenings have, however, poor predictability. Kidney-on-a-chip platforms have the potential to improve predictability, but often lack compatibility with high-content detection platforms. Here, we combined conditionally immortalized proximal tubule epithelial cells overexpressing organic anion transporter 1 (ciPTEC-OAT1) with the microfluidic titer plate OrganoPlate to develop a screenings assay for renal drug-transporter interactions. In this platform, apical localization of F-actin and intracellular tight-junction protein zonula occludens-1 (ZO-1) indicated appropriate cell polarization. Gene expression levels of the drug transporters organic anion transporter 1 (OAT1; SLC22A6), organic cation transporter 2 (OCT2; SLC22A2), P-glycoprotein (P-gp; ABCB1), and multidrug resistance-associated protein 2 and 4 (MRP2/4; ABCC2/4) were similar levels to 2D static cultures. Functionality of the efflux transporters P-gp and MRP2/4 was studied as proof-of-concept for 3D assays using calcein-AM and 5-chloromethylfluorescein-diacetate (CMFDA), respectively. Confocal imaging demonstrated a 4.4 ± 0.2-fold increase in calcein accumulation upon P-gp inhibition using PSC833. For MRP2/4, a 3.0 ± 0.2-fold increased accumulation of glutathione-methylfluorescein (GS-MF) was observed upon inhibition with a combination of PSC833, MK571, and KO143. Semi-quantitative image processing methods for P-gp and MRP2/4 was demonstrated with corresponding Z'-factors of 0.1 ± 0.3 and 0.4 ± 0.1, respectively. In conclusion, we demonstrate a 3D microfluidic PTEC model valuable for screening of drug-transporter interactions that further allows multiplexing of endpoint read-outs for drug-transporter interactions and toxicity.

Expression of Organic Anion Transporter 1 or 3 in Human Kidney Proximal Tubule Cells Reduces Cisplatin Sensitivity.

Cisplatin is a cytostatic drug used for treatment of solid organ tumors. The main adverse effect is organic cation transporter 2 (OCT2)-mediated nephrotoxicity, observed in 30% of patients. The contribution of other renal drug transporters is elusive. Here, cisplatin-induced toxicity was evaluated in human-derived conditionally immortalized proximal tubule epithelial cells (ciPTEC) expressing renal drug transporters, including OCT2 and organic anion transporters 1 (OAT1) or 3 (OAT3). Parent ciPTEC demonstrated OCT2-dependent cisplatin toxicity (TC50 34 ± 1 µM after 24-hour exposure), as determined by cell viability. Overexpression of OAT1 and OAT3 resulted in reduced sensitivity to cisplatin (TC50 45 ± 6 and 64 ± 11 µM after 24-hour exposure, respectively). This effect was independent of OAT-mediated transport, as the OAT substrates probenecid and diclofenac did not influence cytotoxicity. Decreased cisplatin sensitivity in OAT-expressing cells was associated directly with a trend toward reduced intracellular cisplatin accumulation, explained by reduced OCT2 gene expression and activity. This was evaluated by Vmax of the OCT2-model substrate ASP+ (23.5 ± 0.1, 13.1 ± 0.3, and 21.6 ± 0.6 minutes-1 in ciPTEC-parent, ciPTEC-OAT1, and ciPTEC-OAT3, respectively). Although gene expression of cisplatin efflux transporter multidrug and toxin extrusion 1 (MATE1) was 16.2 ± 0.3-fold upregulated in ciPTEC-OAT1 and 6.1 ± 0.7-fold in ciPTEC-OAT3, toxicity was unaffected by the MATE substrate pyrimethamine, suggesting that MATE1 does not play a role in the current experimental set-up. In conclusion, OAT expression results in reduced cisplatin sensitivity in renal proximal tubule cells, explained by reduced OCT2-mediated uptake capacity. In vitro drug-induced toxicity studies should consider models that express both OCT and OAT drug transporters.

Development of a mechanistic biokinetic model for hepatic bile acid handling to predict possible cholestatic effects of drugs.

Drug-induced liver injury (DILI) is a common reason for drug withdrawal from the market. An important cause of DILI is drug-induced cholestasis. One of the major players involved in drug-induced cholestasis is the bile salt efflux pump (BSEP; ABCB11). Inhibition of BSEP by drugs potentially leads to cholestasis due to increased (toxic) intrahepatic concentrations of bile acids with subsequent cell injury. In order to investigate the possibilities for in silico prediction of cholestatic effects of drugs, we developed a mechanistic biokinetic model for human liver bile acid handling populated with human in vitro data. For this purpose we considered nine groups of bile acids in the human bile acid pool, i.e. chenodeoxycholic acid, deoxycholic acid, the remaining unconjugated bile acids and the glycine and taurine conjugates of each of the three groups. Michaelis-Menten kinetics of the human uptake transporter Na+-taurocholate cotransporting polypeptide (NTCP; SLC10A1) and BSEP were measured using NTCP-transduced HEK293 cells and membrane vesicles from BSEP-overexpressing HEK293 cells. For in vitro-in vivo scaling, transporter abundance was determined by LC-MS/MS in these HEK293 cells and vesicles as well as in human liver tissue. Other relevant human kinetic parameters were collected from literature, such as portal bile acid levels and composition, bile acid synthesis and amidation rate. Additional empirical scaling was applied by increasing the excretion rate with a factor 2.4 to reach near physiological steady-state intracellular bile acid concentrations (80µM) after exposure to portal vein bile acid levels. Simulations showed that intracellular bile acid concentrations increase 1.7 fold in the presence of the BSEP inhibitors and cholestatic drugs cyclosporin A or glibenclamide, at intrahepatic concentrations of 6.6 and 20µM, respectively. This simplified model provides a tool for a first indication whether drugs at therapeutic concentrations might cause cholestasis by inhibiting BSEP.

Prediction of Fetal Darunavir Exposure by Integrating Human Ex-Vivo Placental Transfer and Physiologically Based Pharmacokinetic Modeling.

BACKGROUND: Fetal antiretroviral exposure is usually derived from the cord-to-maternal concentration ratio. This static parameter does not provide information on the pharmacokinetics in utero, limiting the assessment of a fetal exposure-effect relationship. OBJECTIVE: The aim of this study was to incorporate placental transfer into a pregnancy physiologically based pharmacokinetic model to simulate and evaluate fetal darunavir exposure at term. METHODS: An existing and validated pregnancy physiologically based pharmacokinetic model of maternal darunavir/ritonavir exposure was extended with a feto-placental unit. To parameterize the model, we determined maternal-to-fetal and fetal-to-maternal darunavir/ritonavir placental clearance with an ex-vivo human cotyledon perfusion model. Simulated maternal and fetal pharmacokinetic profiles were compared with observed clinical data to qualify the model for simulation. Next, population fetal pharmacokinetic profiles were simulated for different maternal darunavir/ritonavir dosing regimens. RESULTS: An average (±standard deviation) maternal-to-fetal cotyledon clearance of 0.91 ± 0.11 mL/min and fetal-to-maternal clearance of 1.6 ± 0.3 mL/min was determined (n = 6 perfusions). Scaled placental transfer was integrated into the pregnancy physiologically based pharmacokinetic model. For darunavir 600/100 mg twice a day, the predicted fetal maximum plasma concentration, trough concentration, time to maximum plasma concentration, and half-life were 1.1, 0.57 mg/L, 3, and 21 h, respectively. This indicates that the fetal population trough concentration is higher or around the half-maximal effective darunavir concentration for a resistant virus (0.55 mg/L). CONCLUSIONS: The results indicate that the population fetal exposure after oral maternal darunavir dosing is therapeutic and this may provide benefits to the prevention of mother-to-child transmission of human immunodeficiency virus. Moreover, this integrated approach provides a tool to prevent fetal toxicity or enhance the development of more selectively targeted fetal drug treatments.