P-glycoprotein-based loperamide-cyclosporine drug interaction at the rat blood-brain barrier: prediction from in vitro studies and extrapolation to humans

Applicability of MDR1 Overexpressing Abcb1KO-MDCKII Cell Lines for Investigating In Vitro Species Differences and Brain Penetration Prediction

Implementing the 3R initiative to reduce animal experiments in brain penetration prediction for CNS-targeting drugs requires more predictive in vitro and in silico models. However, animal studies are still indispensable to obtaining brain concentration and determining the prediction performance of in vitro models. To reveal species differences and provide reliable data for IVIVE, in vitro models are required. Systems overexpressing MDR1 and BCRP are widely used to predict BBB penetration, highlighting the impact of the in vitro system on predictive performance. In this study, endogenous Abcb1 knock-out MDCKII cells overexpressing MDR1 of human, mouse, rat or cynomolgus monkey origin were used. Good correlations between ERs of 83 drugs determined in each cell line suggest limited species specificities. All cell lines differentiated CNS-penetrating compounds based on ERs with high efficiency and sensitivity. The correlation between in vivo and predicted Kp,uu,brain was the highest using total ER of human MDR1 and BCRP and optimized scaling factors. MDR1 interactors were tested on all MDR1 orthologs using digoxin and quinidine as substrates. We found several examples of inhibition dependent on either substrate or transporter abundance. In summary, this assay system has the potential for early-stage brain penetration screening. IC50 comparison between orthologs is complex; correlation with transporter abundance data is not necessarily proportional and requires the understanding of modes of transporter inhibition.

Optimization of dose and route of administration of the P-glycoprotein inhibitor, valspodar (PSC-833) and the P-glycoprotein and breast cancer resistance protein dual-inhibitor, elacridar (GF120918) as dual infusion in rats

Transporters can play a key role in the absorption, distribution, metabolism, and excretion of drugs. Understanding these contributions early in drug discovery allows for more accurate projection of the clinical pharmacokinetics. One method to assess the impact of transporters in vivo involves co‐dosing specific inhibitors. The objective of the present study was to optimize the dose and route of administration of a P‐glycoprotein (P‐gp) inhibitor, valspodar (PSC833), and a dual P‐gp/breast cancer resistance protein (BCRP) inhibitor, elacridar (GF120918), by assessing the transporters’ impact on brain penetration and absorption. A dual‐infusion strategy was implemented to allow for flexibility with dose formulation. The chemical inhibitor was dosed intravenously via the femoral artery, and a cassette of known substrates was infused via the jugular vein. Valspodar or elacridar was administered as 4.5‐hour constant infusions over a range of doses. To assess the degree of inhibition, the resulting ratios of brain and plasma concentrations, Kp's, of the known substrates were compared to the vehicle control. These data demonstrated that doses greater than 0.9 mg/hr/kg valspodar and 8.9 mg/hr/kg elacridar were sufficient to inhibit P‐gp‐ and BCRP‐mediated efflux at the blood‐brain barrier in rats without any tolerability issues. Confirmation of BBB restriction by efflux transporters in preclinical species allows for subsequent prediction in humans based upon the proteomic expression at rodent and human BBB. Overall, the approach can also be applied to inhibition of efflux at other tissues (gut absorption, liver clearance) or can be extended to other transporters of interest using alternate inhibitors.

Impact of In Vitro Passive Permeability in a P-gp-transfected LLC-PK1 Model on the Prediction of the Rat and Human Unbound Brain-to-Plasma Concentration Ratio

PURPOSE

More accurate prediction of the extent of drug brain exposure in early drug discovery and understanding potential species differences could help to guide medicinal chemistry and avoid unnecessary animal studies. Hence, the aim of the current study was to validate the use of a P-gp transfected LLC-PK1 model to predict the unbound brain-to-plasma concentration ratio (Kp_uu,brain) in rats and humans.

METHODS

MOCK-, Mdr1a- and MDR1-transfected LLC-PK1 monolayers were applied in a transwell setup to quantify the bidirectional transport for 12 specific P-gp substrates, 48 UCB drug discovery compounds, 11 compounds with reported rat in situ brain perfusion data and 6 compounds with reported human Kp_uu,brain values. The in vitro transport data were introduced in a minimal PBPK model (SIVA®) to determine the transport parameters. These parameters were combined with the differences between in vitro and in vivo passive permeability as well as P-gp expression levels (as determined by LC-MS/MS), to predict the Kp_uu,brain.

RESULTS

A 10-fold difference between in vitro and in vivo passive permeability was observed. Incorporation of the differences between in vitro and in vivo passive permeability and P-gp expression levels resulted in an improved prediction of rat (AAFE 2.17) and human Kp_uu,brain (AAFE 2.10).

CONCLUSIONS

We have succesfully validated a methodology to use a P-gp overexpressing LLC-PK1 cell line to predict both rat and human Kp_uu,brain by correcting for both passive permeability and P-gp expression levels.

Role of P-glycoprotein in the brain disposition of seletalisib: Evaluation of the potential for drug-drug interactions

Seletalisib is an orally bioavailable selective inhibitor of phosphoinositide 3-kinase delta (PI3Kδ) in clinical development for the treatment of immune-mediated inflammatory diseases. The present study investigated the role of P-gp in seletalisib disposition, especially brain distribution, and the associated risks of interactions. Seletalisib was found to be actively transported by rodent and human P-gp in vitro (transfected LLC-PK1 cells; K_m of ca. 20 µM), with minimal or no affinity for the other tested transporters. A distribution study in knockout rats (single oral dosing at 750 mg kg^-1) showed that P-gp restricts the brain disposition of seletalisib while having minimal effect on its intestinal absorption. Restricted brain penetration was also observed in cynomolgus monkeys (single oral dosing at 30 mg kg^-1) using brain microdialysis and cerebrospinal fluid sampling (K_p,uu of 0.09 and 0.24, respectively). These findings opened the question of potential pharmacokinetic interaction between seletalisib and P-gp inhibitors. In vitro, CsA inhibited the active transport of seletalisib with an IC₅₀ of 0.13 µM. In rats, co-administration of high doses of CsA (bolus iv followed by continuous infusion) increased the brain distribution of seletalisib (single oral dosing at 5 mg kg^-1). The observed data were found aligned with those predicted by in vitro-in vivo extrapolation. Based on the same extrapolation method combined with literature data, only very few P-gp inhibitors (i.e. CsA, quinine, quinidine) were predicted to increase the brain disposition of seletalisib in the clinical setting (maximal 3-fold changes).

Immunosuppressive drugs and the gastrointestinal tract in renal transplant patients

Gastrointestinal (GI) discomfort is common after renal transplantation and can be caused by the use of various immunosuppressive drugs. GI symptoms affect the quality of life, lead to an impaired graft survival and an increased mortality. Moreover, diseases and disturbances of the GI tract also affect the pharmacokinetics of immunosuppressive drugs. This review addresses the interaction between immunosuppressive agents and GI disorders. The GI tract is involved in the metabolism of several immunosuppressive drugs. Calcineurin inhibitors, mTor inhibitors, and corticosteroids are subjected to metabolism by the intestinal cytochrome P450 (CYP3A) and by the drug efflux pump ABCB1. Mycophenolate is partly metabolized in the stomach and intestine and undergoes enterohepatic recirculation. Gastrointestinal disturbances can lead to a modified exposure to immunosuppressive drugs. In the first and second part of this review, we focus on the role of the GI tract in the pharmacokinetics of the immunosuppressive drugs and how to adjust immunosuppressive therapy in patients with vomiting, need for tube feeding, delayed gastric emptying, intestinal resection, and diarrhea. In the third part, we review the GI adverse effects of the various immunosuppressive drugs, with special attention for diarrhea and dyspepsia. Finally, we discuss the effects of drugs used for relief of GI complaints on the exposure to immunosuppressive agents.

Modulation of Opioid Transport at the Blood-Brain Barrier by Altered ATP-Binding Cassette (ABC) Transporter Expression and Activity

Opioids are highly effective analgesics that have a serious potential for adverse drug reactions and for development of addiction and tolerance. Since the use of opioids has escalated in recent years, it is increasingly important to understand biological mechanisms that can increase the probability of opioid-associated adverse events occurring in patient populations. This is emphasized by the current opioid epidemic in the United States where opioid analgesics are frequently abused and misused. It has been established that the effectiveness of opioids is maximized when these drugs readily access opioid receptors in the central nervous system (CNS). Indeed, opioid delivery to the brain is significantly influenced by the blood-brain barrier (BBB). In particular, ATP-binding cassette (ABC) transporters that are endogenously expressed at the BBB are critical determinants of CNS opioid penetration. In this review, we will discuss current knowledge on the transport of opioid analgesic drugs by ABC transporters at the BBB. We will also examine how expression and trafficking of ABC transporters can be modified by pain and/or opioid pharmacotherapy, a novel mechanism that can promote opioid-associated adverse drug events and development of addiction and tolerance.

Interspecies comparison of putative ligand binding sites of human, rat and mouse P-glycoprotein

Prior to the clinical phases of testing, safety, efficacy and pharmacokinetic profiles of lead compounds are evaluated in animal studies. These tests are primarily performed in rodents, such as mouse and rats. In order to reduce the number of animal experiments, computational models that predict the outcome of these studies and thus aid in prioritization of preclinical candidates are heavily needed. However, although computational models for human off-target interactions with decent quality are available, they cannot easily be transferred to rodents due to lack of respective data. In this study, we assess the transferability of human P-glycoprotein activity data for development of in silico models to predict in vivo effects in rats and mouse using a structure-based approach. P-glycoprotein (P-gp) is an ATP-dependent efflux transporter that transports xenobiotic compounds such as toxins and drugs out of cells and has a broad substrate and inhibitor specificity. Being mostly expressed at barriers, it influences the bioavailability of drugs and thus contributes also to toxicity. Comparison of the binding site interaction profiles of human, rat and mouse P-gp derived from docking studies with a set of common inhibitors suggests that the inhibitors share potentially similar binding modes. These findings encourage the use of in vitro human P-gp data for predicting in vivo effects in rodents and thus contributes to the 3Rs (Replace, Reduce and Refine) of animal experiments.

P-glycoprotein Restricts Ocular Penetration of Loperamide across the Blood-Ocular Barriers: a Comparative Study in Mdr1a Knock-out and Wild Type Sprague Dawley Rats

The current research was undertaken to determine the existence and magnitude of P-glycoprotein (P-gp) expression on the blood-ocular barriers by studying the ocular penetration of loperamide, a specific P-gp substrate, in P-gp (Mdr1a) knock-out (KO) and wild type (WT) Sprague Dawley rats. A clear, stable, sterile solution of loperamide (1 mg/mL), for intravenous administration, was formulated and evaluated. Ocular distribution was studied in P-gp KO and WT rats following intravenous administration of loperamide (at two doses). The drug levels in plasma, aqueous humor (AH), and vitreous humor (VH) samples were determined with the aid of UHPLC-Q-TOF-MS/MS, and the AH/plasma (D _AH ) and VH/plasma (D _VH ) distribution ratios were estimated. Electroretinography (ERG), ultrastructural analyses, and histology studies were carried out, in both KO and WT rats, to detect any drug-induced functional and/or structural alterations in the retina. Dose-related loperamide levels were observed in the plasma of both WT and KO rats. The loperamide concentrations in the AH and VH of KO rats were significantly higher compared to that observed in the WT rats, at the lower dose. However, a marked increase in the D _AH and D _VH was noted in the KO rats. ERG, ultrastructure, and histology studies did not indicate any drug-induced toxic effects in the retina under the test conditions. The results from these studies demonstrate that P-gp blocks the penetration of loperamide into the ocular tissues from the systemic circulation and that the effect is more pronounced at lower plasma loperamide concentrations.

A Conformationally Gated Model of Methadone and Loperamide Transport by P-Glycoprotein

P-glycoprotein (Pgp) is a multidrug resistance transporter that limits the penetration of a wide range of neurotherapeutics into the brain including opioids. The diphenylpropylamine opioids methadone and loperamide are structurally similar, but loperamide has about a 4-fold higher Pgp-mediated transport rate. In addition to these differences, they showed significant differences in their effects on Pgp-mediated adenosine triphosphate (ATP) hydrolysis. The activation of Pgp-mediated ATP hydrolysis by methadone was monophasic, whereas loperamide activation of ATP hydrolysis was biphasic implying methadone has a single binding site and loperamide has 2 binding sites on Pgp. Quenching of tryptophan fluorescence with these drugs and digoxin showed competition between the opioids and that loperamide does not compete for the digoxin-binding site. Acrylamide quenching of tryptophan fluorescence to probe Pgp conformational changes revealed that methadone- and loperamide-induced conformational changes were distinct. These results were used to develop a model for Pgp-mediated transport of methadone and loperamide where opioid binding and conformational changes are used to explain the differences in the opioid transport rates between methadone and loperamide.

Increasing nerve agent treatment efficacy by P-glycoprotein inhibition

One of the shortcomings of current treatment of nerve agent poisoning is that not all drugs effectively penetrate the blood-brain barrier (BBB), whereas most nerve agents easily do. P-glycoprotein (Pgp) efflux transporters at the BBB may contribute to this aspect. It was previously shown that Pgp inhibition by tariquidar enhanced the efficacy of nerve agent treatment when administered as a pretreatment. In the present study soman-induced seizures were also substantially prevented when the animals were intravenously treated with tariquidar post-poisoning, in addition to HI-6 and atropine. In these animals, approximately twice as much AChE activity was present in their brain as compared to control rats. The finding that tariquidar did not affect distribution of soman to the brain indicates that the potentiating effects were a result of interactions of Pgp inhibition with drug distribution. In line with this, atropine appeared to be a substrate for Pgp in in vitro studies in a MDR1/MDCK cell model. This indicates that tariquidar might induce brain region specific effects on atropine distribution, which could contribute to the therapeutic efficacy increase found. Furthermore, the therapeutic enhancement by tariquidar was compared to that of the less specific and less potent Pgp inhibitor cyclosporine A. This compound appeared to induce a protective effect similar to tariquidar. In conclusion, treatment with a Pgp inhibitor resulted in enhanced therapeutic efficacy of HI-6 and atropine in a soman-induced seizure model in the rat. The mechanism underlying these effects should be further investigated. To that end, the potentiating effect of nerve agent treatment should be addressed against a broader range of nerve agents, for oximes and atropine separately, and for those at lower doses. In particular when efficacy against more nerve agents is shown, a Pgp inhibitor such as tariquidar might be a valid addition to nerve agent antidotes.

Cyclosporine-inhibitable cerebral drug transport does not influence clinical methadone pharmacodynamics

BACKGROUND

Interindividual variability and drug interaction studies suggest that blood-brain barrier drug transporters mediate human methadone brain biodistribution. In vitro and animal studies suggest that methadone is a substrate for the efflux transporter P-glycoprotein, and that P-glycoprotein-mediated transport influences brain access and pharmacologic effect. This investigation tested whether methadone is a transporter substrate in humans [corrected].

METHODS

Healthy volunteers received oral (N=16) or IV (N=12) methadone in different crossover protocols after nothing (control) or the validated P-glycoprotein inhibitor cyclosporine (4.5 mg/kg orally twice daily for 4 days, or 5 mg/kg IV over 2 h). Plasma and urine methadone and metabolite concentrations were measured by mass spectrometry. Methadone effects were measured by miosis and thermal analgesia (maximally tolerated temperature and verbal analog scale rating of discreet temperatures).

RESULTS

Cyclosporine marginally but significantly decreased methadone plasma concentrations and apparent oral clearance, but had no effect on methadone renal clearance or on hepatic N-demethylation. Cyclosporine had no effect on miosis or on R-methadone concentration-miosis relationships after either oral or IV methadone. Peak miosis was similar in controls and cyclosporine-treated subjects after oral methadone (1.4±0.4 and 1.3±0.5 mm/mg, respectively) and IV methadone (3.1±1.0 and 3.2±0.8 mm, respectively). Methadone increased maximally tolerated temperature, but analgesia testing was confounded by cyclosporine-related pain.

CONCLUSIONS

Cyclosporine did not affect methadone pharmacodynamics. This result does not support a role for cyclosporine-inhibitable transporters mediating methadone brain access and biodistribution.

Changing faces in virology: the dutch shift from oncogenic to oncolytic viruses

Viruses have two opposing faces. On the one hand, they can cause harm and disease. A virus may manifest directly as a contagious disease with a clinical pathology of varying significance. A viral infection can also have delayed consequences, and in rare cases may cause cellular transformation and cancer. On the other hand, viruses may provide hope: hope for an efficacious treatment of serious disease. Examples of the latter are the use of viruses as a vaccine, as transfer vector for therapeutic genes in a gene therapy setting, or, more directly, as therapeutic anticancer agent in an oncolytic-virus therapy setting. Already there is evidence for antitumor activity of oncolytic viruses. The antitumor efficacy seems linked to their capacity to induce a tumor-directed immune response. Here, we will provide an overview on the development of oncolytic viruses and their clinical evaluation from the Dutch perspective.

Coadministration of P-glycoprotein modulators on loperamide pharmacokinetics and brain distribution

The efflux transporter P-glycoprotein, expressed at high levels at the blood-brain barrier, exerts a profound effect on the disposition of various therapeutic compounds in the brain. A rapid and efficient modulation of this efflux transporter could enhance the distribution of its substrates and thereby improve central nervous system pharmacotherapies. This study explored the impact of the intravenous coadministration of two P-glycoprotein modulators, tariquidar and elacridar, on the pharmacokinetics and brain distribution of loperamide, a P-glycoprotein substrate probe, in rats. After 1 hour postdosing, tariquidar and elacridar, both at a dose of 1.0 mg/kg, increased loperamide levels in the brain by 2.3- and 3.5-fold, respectively. However, the concurrent administration of both P-glycoprotein modulators, each at a dose of 0.5 mg/kg, increased loperamide levels in the brain by 5.8-fold and resulted in the most pronounced opioid-induced clinical signs. This phenomenon may be the result of a combined noncompetitive modulation by tariquidar and elacridar. Besides, the simultaneous administration of elacridar and tariquidar did not significantly modify the pharmacokinetic parameters of loperamide. This observation potentially allows the concurrent use of low but therapeutic doses of P-gp modulators to achieve full inhibitory effects.

Predicting the outer boundaries of P-glycoprotein (P-gp)-based drug interactions at the human blood-brain barrier based on rat studies

Using positron emission tomography (PET), (11)C-verapamil as the P-gp substrate, and cyclosporine A (CsA) as the P-gp inhibitor, we showed that the magnitude of P-gp-based drug interactions at the human blood-brain barrier (BBB) is modest. However, such interactions at clinically relevant CsA blood concentrations may be greater for substrates where P-gp plays an even larger role (fractional contribution of P-gp, ft > 0.97) in preventing the CNS entry of the drug (e.g., nelfinavir). Since we have shown that the rat is an excellent predictor of the verapamil-CsA interaction at the human BBB, we determined the magnitude of drug interaction at the rat BBB between nelfinavir and CsA. Under isoflurane anesthesia, male Sprague-Dawley rats were coadministered IV infusions of nelfinavir and escalating doses of CsA to achieve pseudo steady-state plasma/blood and brain concentrations of both drugs (blood CsA ranged 0-264.9 μM, n = 3-6/group). The percent increase in the brain:blood nelfinavir concentration ratio (determined by LC/MS) was described by the Hill equation with Emax = 6481%, EC50 = 12.3 μM, and γ = 1.6. Then, using these data, as well as in vitro data in LLCPK1 cells expressing the human P-gp, we predicted that CsA (at clinically relevant blood concentration of 1.5 μM) will increase the distribution of nelfinavir into the human brain by 236%. Collectively, our data suggest that clinically significant P-gp based drug interactions at the human BBB are possible for P-gp substrates highly excluded from the brain (ft > 0.97) and should be investigated using noninvasive approaches (e.g., PET).

Cyclosporine-inhibitable blood-brain barrier drug transport influences clinical morphine pharmacodynamics

BACKGROUND

The blood-brain barrier is richly populated by active influx and efflux transporters influencing brain drug concentrations. Morphine, a drug with delayed clinical onset, is a substrate for the efflux transporter P-glycoprotein in vitro and in animals. This investigation tested whether morphine is a transporter substrate in humans.

METHODS

Fourteen healthy volunteers received morphine (0.1 mg/kg, 1-h IV infusion) in a crossover study without (control) or with the infusion of validated P-glycoprotein inhibitor cyclosporine (5 mg/kg, 2-h infusion). Plasma and urine morphine and morphine glucuronide metabolite concentrations were measured by mass spectrometry. Morphine effects were measured by miosis and analgesia.

RESULTS

Cyclosporine minimally altered morphine disposition, increasing the area under the plasma morphine concentration versus time curve to 100 ± 21 versus 85 ± 24 ng/ml·h (P < 0.05) without changing maximum plasma concentration. Cyclosporine enhanced (3.2 ± 0.9 vs. 2.5 ± 1.0 mm peak) and prolonged miosis, and increased the area under the miosis-time curve (18 ± 9 vs. 11 ± 5 mm·h), plasma effect-site transfer rate constant (k(e0), median 0.27 vs. 0.17 h(-1)), and maximum calculated effect-site morphine concentration (11.5 ± 3.7 vs. 7.6 ± 2.9 ng/ml; all P < 0.05). Analgesia testing was confounded by cyclosporine-related pain.

CONCLUSIONS

Morphine is a transporter substrate at the human blood-brain barrier. Results suggest a role for P-glycoprotein or other efflux transporters in brain morphine access, although the magnitude of the effect is small, and unlikely to be a major determinant of morphine clinical effects. Efflux may explain some variability in clinical morphine effects.

Capsaicin pretreatment increased the bioavailability of cyclosporin in rats: involvement of P-glycoprotein and CYP 3A inhibition

Capsaicin (CAP), the main ingredient responsible for the hot pungent taste of chilli peppers. This study investigated the effect of CAP on the pharmacokinetics of Cyclosporin A (CyA) in rats and the mechanism of this food-drug interaction. The results indicated that after 7 days of low or middle dose of CAP (0.3 or 1.0 mg/kg), the blood concentration of CyA was not significantly changed compared with that of vehicle-treated rats, whereas the blood concentration of CyA in high dose group (3.0 mg/kg) was significantly increased. The total clearance (CL/F) of CyA was decreased, and the bioavailability was significantly increased to about 1.44-fold of that in vehicle-treated rats after 7 days of high dose CAP treatment. At this time, the P-gp and CYP3A1/2 in the liver and intestine were decreased at both the mRNA and protein levels. These results demonstrated that chronic ingestion of high doses of CAP will increase the bioavailability of CyA to a significant extent in rats and the food-drug interaction between CAP and CyA appears to be due to modulation of P-gp and CYP3A gene expression by CAP, with differential dose-dependence.

The use of microdialysis techniques in mice to study P-gp function at the blood-brain barrier

An integrated assay system involving dual/triple-probe microdialysis techniques in rats was developed earlier for testing interactions with P-glycoprotein (P-gp) at the blood-brain barrier using quinidine/PSC-833 as a P-gp substrate/inhibitor combination. The aim of the present study was to expand our assay system to mice using microdialysis with simultaneous sampling of blood and brain and to compare the result with a primary mouse brain endothelial cell monolayer (pMBMEC) assay. Brain penetration of quinidine was dose dependent in both anesthetized and awake mice after intraperitoneal drug administration. PSC-833 pretreatment caused a 2.5- to 3.4-fold increase in quinidine levels of brain dialysate samples in anesthetized or awake animals, after single or repeated administration of PSC-833. In pMBMEC, a 2.0- to 2.5-fold efflux ratio was observed in the transcellular transport of quinidine. The P-gp-mediated vectorial transport of quinidine was eliminated by PSC-833. These results indicate that quinidine with PSC-833 is a good probe substrate-reference inhibitor combination for testing drug-drug interactions with P-gp in the in vivo and in vitro mouse systems. With increasing number of humanized transgenic mice, a test system with mouse microdialysis experimentation becomes more important to predict drug-drug interactions in humans.