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Molecular Pharmaceutics Nov 2023P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are two ATP-binding cassette efflux transporters that are coexpressed at the human blood-brain barrier...
P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are two ATP-binding cassette efflux transporters that are coexpressed at the human blood-brain barrier (BBB) and blood-retina barrier (BRB). While pharmacological inhibition of P-gp and/or BCRP results in increased brain distribution of dual P-gp/BCRP substrate drugs, such as the tyrosine kinase inhibitor erlotinib, the effect of P-gp and/or BCRP inhibition on the retinal distribution of such drugs has hardly been investigated. In this study, we used positron emission tomography (PET) imaging to assess the effect of transporter inhibition on the distribution of [C]erlotinib to the human retina and brain. Twenty two healthy volunteers underwent two PET scans after intravenous (i.v.) injection of a microdose (<5 μg) of [C]erlotinib, a baseline scan, and a second scan either with concurrent i.v. infusion of tariquidar to inhibit P-gp ( = 5) or after oral intake of single ascending doses of erlotinib (300 mg, 650 mg, or 1000 mg, = 17) to saturate erlotinib transport. In addition, transport of [H]erlotinib to the retina and brain was assessed in mice by in situ carotid perfusion under various drug transporter inhibition settings. In comparison to the baseline PET scan, coadministration of tariquidar or erlotinib led to a significant decrease of [C]erlotinib total volume of distribution () in the human retina by -25 ± 8% ( ≤ 0.05) and -41 ± 16% ( ≤ 0.001), respectively. In contrast, erlotinib intake led to a significant increase in [C]erlotinib in the human brain (+20 ± 16%, ≤ 0.001), while administration of tariquidar did not result in any significant changes. In situ carotid perfusion experiments showed that both P-gp and BCRP significantly limit the distribution of erlotinib to the mouse retina and brain but revealed a similar discordant effect at the mouse BRB and BBB following co-perfusion with tariquidar and erlotinib as in humans. Co-perfusion with prototypical inhibitors of solute carrier transporters did not reveal a significant contribution of organic cation transporters (e.g., OCTs and OCTNs) and organic anion-transporting polypeptides (e.g., OATP2B1) to the retinal and cerebral distribution of erlotinib. In conclusion, we observed a dissimilar effect after P-gp and/or BCRP inhibition on the retinal and cerebral distribution of [C]erlotinib. The exact mechanism for this discrepancy remains unclear but may be related to the function of an unidentified erlotinib uptake carrier sensitive to tariquidar inhibition at the BRB. Our study highlights the great potential of PET to study drug distribution to the human retina and to assess the functional impact of membrane transporters on ocular drug distribution.
Topics: Humans; Mice; Animals; Female; Erlotinib Hydrochloride; ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP Binding Cassette Transporter, Subfamily G, Member 2; Neoplasm Proteins; Brain; ATP Binding Cassette Transporter, Subfamily B; Blood-Brain Barrier; ATP-Binding Cassette Transporters; Blood-Retinal Barrier; Membrane Transport Proteins; Breast Neoplasms
PubMed: 37883694
DOI: 10.1021/acs.molpharmaceut.3c00715 -
Journal of Experimental & Clinical... Jul 2009Imatinib, a tyrosine kinase inhibitor currently approved for treatment of several malignancies, has been shown to be a substrate for multiple efflux-transporter...
BACKGROUND
Imatinib, a tyrosine kinase inhibitor currently approved for treatment of several malignancies, has been shown to be a substrate for multiple efflux-transporter proteins, including ABCB1 (P-glycoprotein) and ABCG2 (BCRP). The effect of inhibiting these transporters on tissue exposure to imatinib remains unclear.
OBJECTIVE
To assess the role of these transporters on drug disposition, 50 mg/kg imatinib was administered to Balb/C mice, 30 minutes after receiving tariquidar (10 mg/kg), an inhibitor of both ABCB1 and ABCG2, or vehicle, via oral gavage.
METHODS
Quantitative determination of imatinib in mouse plasma, liver and brain was performed using a newly-developed and validated liquid-chromatography-mass spectrometric method.
RESULTS
Exposure to imatinib was 2.2-fold higher in plasma, liver and brain in mice that received tariquidar, as compared to those that received the vehicle (P = 0.001). The peak plasma concentration did not increase substantially, suggesting that tariquidar is affecting the distribution, metabolism and/or excretion of imatinib, rather than absorption. Though tariquidar increased the absolute exposure of imatinib, the brain-to-plasma ratio of imatinib was unaffected.
CONCLUSION
This study suggests that intentional inhibition of ABCB1 and ABCG2 function at the blood-brain barrier is unlikely to significantly improve clinical outcome of imatinib with currently used dosing regimens.
Topics: ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Administration, Oral; Animals; Antineoplastic Agents; Benzamides; Imatinib Mesylate; Male; Mice; Mice, Inbred BALB C; Piperazines; Protein Kinase Inhibitors; Pyrimidines; Quinolines
PubMed: 19591692
DOI: 10.1186/1756-9966-28-99 -
The Journal of Pharmacology and... Sep 2021Inhibition of acetylcholinesterase (AChE) by certain organophosphates (OPs) can be life-threatening and requires reactivating antidote accessibility to the peripheral...
Inhibition of acetylcholinesterase (AChE) by certain organophosphates (OPs) can be life-threatening and requires reactivating antidote accessibility to the peripheral and central nervous systems to reverse symptoms and enhance survival parameters. In considering dosing requirements for oxime antidotes in OP exposures that inactivate AChE, clearance of proton ionizable, zwitterionic antidotes is rapid and proceeds with largely the parent antidotal compound being cleared by renal transporters. Such transporters may also control disposition between target tissues and plasma as well as overall elimination from the body. An ideal small-molecule antidote should access and be retained in primary target tissues-central nervous system (brain), skeletal muscle, and peripheral autonomic sites-for sufficient periods to reactivate AChE and prevent acute toxicity. We show here that we can markedly prolong the antidotal activity of zwitterionic antidotes by inhibiting P-glycoprotein (P-gp) transporters in the brain capillary and renal systems. We employ the P-gp inhibitor tariquidar as a reference compound and show that tissue and plasma levels of RS194B, a hydroxyl-imino acetamido alkylamine reactivator, are elevated and that plasma clearances are reduced. To examine the mechanism, identify the transporter, and establish the actions of a transport inhibitor, we compare the pharmacokinetic parameters in a P-glycoprotein knockout mouse strain and see dramatic enhancements of short-term plasma and tissue levels. Hence, repurposed transport inhibitors that are candidate or Food and Drug Administration-approved drugs, should enhance target tissue concentrations of the zwitterionic antidote through inhibition of both renal elimination and brain capillary extrusion. SIGNIFICANCE STATEMENT: We examine renal and brain capillary transporter inhibition as means for lowering dose and frequency of dosing of a blood-brain barrier permanent reactivating antidote, RS194B, an ionizable zwitterion. Through a small molecule, tariquidar, and gene knockout mice, CNS antidote concentrations are enhanced, and total body clearances are concomitantly diminished. RS194B with repurposed transport inhibitors should enhance reactivation of central and peripheral OP-inhibited acetylcholinesterase. Activities at both disposition sites are a desired features for replacing the antidote, pralidoxime, for acute OP exposure.
Topics: Acetylcholinesterase; Kinetics; Organophosphates; Pralidoxime Compounds
PubMed: 34145064
DOI: 10.1124/jpet.121.000715 -
Chemical Science Apr 2021P-glycoprotein (Pgp) is a major efflux pump in humans, overexpressed in a variety of cancers and associated with the development of multi-drug resistance. Allosteric...
P-glycoprotein (Pgp) is a major efflux pump in humans, overexpressed in a variety of cancers and associated with the development of multi-drug resistance. Allosteric modulation by various ligands (, transport substrates, inhibitors, and ATP) has been biochemically shown to directly influence structural dynamics, and thereby, the function of Pgp. However, the molecular details of such effects, particularly with respect to the role and involvement of the surrounding lipids, are not well established. Here, we employ all-atom molecular dynamics (MD) simulations to study the conformational landscape of Pgp in the presence of a high-affinity, third-generation inhibitor, tariquidar, in comparison to the nucleotide-free (APO) and the ATP-bound states, in order to characterize the mechanical effects of the inhibitor that might be of relevance to its blocking mechanism of Pgp. Simulations in a multi-component lipid bilayer show a dynamic equilibrium between open(er) and more closed inward-facing (IF) conformations in the APO state, with binding of ATP shifting the equilibrium towards conformations more prone to ATP hydrolysis and subsequent events in the transport cycle. In the presence of the inhibitor bound to the drug-binding pocket within the transmembrane domain (TMD), Pgp samples more open IF conformations, and the nucleotide binding domains (NBDs) become highly dynamic. Interestingly, and reproduced in multiple independent simulations, the inhibitor is observed to facilitate recruitment of lipid molecules into the Pgp lumen through the two proposed drug-entry portals, where the lipid head groups from the cytoplasmic leaflet penetrate into and, in some cases, translocate inside the TMD, while the lipid tails remain extended into the bulk lipid environment. These "wedge" lipids likely enhance the inhibitor-induced conformational restriction of the TMD leading to the differential modulation of coupling pathways observed with the NBDs downstream. We suggest a novel inhibitory mechanism for tariquidar, and potentially for related third-generation Pgp inhibitors, where lipids are seen to enhance the inhibitory role in the catalytic cycle of membrane transporters.
PubMed: 34084427
DOI: 10.1039/d0sc06288j -
Clinical Pharmacology and Therapeutics Feb 2012Using positron emission tomography (PET) imaging we assessed, in vivo, the interaction between a microdose of (R)-[(11)C]verapamil (a P-glycoprotein (Pgp) substrate) and... (Comparative Study)
Comparative Study
Using positron emission tomography (PET) imaging we assessed, in vivo, the interaction between a microdose of (R)-[(11)C]verapamil (a P-glycoprotein (Pgp) substrate) and escalating doses of the Pgp inhibitor tariquidar (3, 4, 6, and 8 mg/kg) at the blood-brain barrier (BBB) in healthy human subjects. We compared the dose-response relationship of tariquidar in humans with data obtained in rats using a similar methodology. Tariquidar was equipotent in humans and rats in its effect of increasing (R)-[(11)C]verapamil brain uptake (expressed as whole-brain volume of distribution (V(T))), with very similar half-maximum-effect concentrations. Both in humans and in rats, brain V(T) approached plateau levels at plasma tariquidar concentrations >1,000 ng/ml. However, Pgp inhibition in humans led to only a 2.7-fold increase in brain V(T) relative to baseline scans (before administration of tariquidar) as compared with 11.0-fold in rats. The results of this translational study add to the accumulating evidence that there are marked species-dependent differences in Pgp expression and functionality at the BBB.
Topics: ATP Binding Cassette Transporter, Subfamily B, Member 1; Animals; Blood-Brain Barrier; Brain; Calcium Channel Blockers; Carbon Radioisotopes; Dose-Response Relationship, Drug; Humans; Positron-Emission Tomography; Quinolines; Rats; Species Specificity; Verapamil
PubMed: 22166851
DOI: 10.1038/clpt.2011.217 -
Journal of Nuclear Medicine : Official... Dec 2009Tariquidar, a potent, nontoxic, third-generation P-glycoprotein (P-gp) inhibitor, is a possible reversal agent for central nervous system drug resistance. In animal... (Clinical Trial)
Clinical Trial
UNLABELLED
Tariquidar, a potent, nontoxic, third-generation P-glycoprotein (P-gp) inhibitor, is a possible reversal agent for central nervous system drug resistance. In animal studies, tariquidar has been shown to increase the delivery of P-gp substrates into the brain by severalfold. The aim of this study was to measure P-gp function at the human blood-brain barrier (BBB) after tariquidar administration using PET and the model P-gp substrate (R)-(11)C-verapamil.
METHODS
Five healthy volunteers underwent paired (R)-(11)C-verapamil PET scans and arterial blood sampling before and at 2 h 50 min after intravenous administration of tariquidar (2 mg/kg of body weight). The inhibition of P-gp on CD56-positive peripheral lymphocytes of each volunteer was determined by means of the (123)Rh efflux assay. Tariquidar concentrations in venous plasma were quantified using liquid chromatography/mass spectrometry.
RESULTS
Tariquidar administration resulted in significant increases (Wilcoxon test for paired samples) in the distribution volume (DV, +24% +/- 15%) and influx rate constant (K(1), +49% +/- 36%) of (R)-(11)C-verapamil across the BBB (DV, 0.65 +/- 0.13 and 0.80 +/- 0.07, P = 0.043; K(1), 0.034 +/- 0.009 and 0.049 +/- 0.009, P = 0.043, before and after tariquidar administration, respectively). A strong correlation was observed between the change in brain DV after administration of tariquidar and tariquidar exposure in plasma (r = 0.90, P = 0.037). The mean plasma concentration of tariquidar achieved during the second PET scan (490 +/- 166 ng/mL) corresponded to 100% inhibition of P-gp function in peripheral lymphocytes.
CONCLUSION
Tariquidar significantly increased brain penetration of (R)-(11)C-verapamil-derived activity due to increased influx. As opposed to peripheral P-gp function, central P-gp inhibition appeared to be far from complete after the administered tariquidar dose.
Topics: ATP Binding Cassette Transporter, Subfamily B, Member 1; Adult; Blood-Brain Barrier; Carbon Radioisotopes; Humans; Kinetics; Male; Pilot Projects; Positron-Emission Tomography; Quinolines; Verapamil
PubMed: 19910428
DOI: 10.2967/jnumed.109.063289 -
Epilepsia Nov 2012Overexpression of the multidrug efflux transporter P-glycoprotein (Pgp) at the blood-brain barrier (BBB) is thought to be involved in pharmacoresistance in epilepsy by... (Review)
Review
Overexpression of the multidrug efflux transporter P-glycoprotein (Pgp) at the blood-brain barrier (BBB) is thought to be involved in pharmacoresistance in epilepsy by extruding antiepileptic drugs (AEDs) from their target site. To explore this hypothesis, positron emission tomography (PET) scans were performed with the Pgp substrate-verapamil (VPM) in animal models before and after status epilepticus (SE) and in patients with temporal lobe epilepsy (TLE) and healthy controls. In addition to baseline scans, a second VPM-PET scan was performed after administration of the Pgp inhibitor tariquidar (TQD), showing that VPM uptake at baseline and its increase after Pgp inhibition are reduced in animals following SE compared to baseline, and in refractory TLE relative to healthy controls. In animal models, brain regions with increased Pgp expression (cerebellum, thalamus, and hippocampus) showed reduced influx rate constants from blood to brain, K(1), of the radiolabeled Pgp substrate relative to control animals. In human studies, preliminary findings are lower K(1) values in refractory compared to seizure-free patients and attenuated increase of K(1) for temporal lobe regions in patients with TLE compared to healthy controls. In summary, there is lower brain uptake of the Pgp substrate VPM in Pgp-rich areas of animals 2 days following SE, as well as lower increase in VPM brain uptake after TQD in patients with refractory TLE compared to healthy controls, supporting the hypothesis of increased cerebral Pgp function following prolonged seizures and as a mechanism contributing to drug resistance in refractory epilepsy. The observation of reduced VPM uptake in refractory compared to seizure-free patients with TLE is consistent with multiple mechanisms affecting Pgp function, including uncontrolled seizures.
Topics: ATP Binding Cassette Transporter, Subfamily B, Member 1; Animals; Blood-Brain Barrier; Carbon Radioisotopes; Epilepsy, Temporal Lobe; Humans; Positron-Emission Tomography; Vasodilator Agents; Verapamil
PubMed: 23134497
DOI: 10.1111/j.1528-1167.2012.03704.x -
In Silico Pharmacology 2021P-glycoprotein (P-gp), which was first identified in cancer cells, is an ATP-dependent efflux transporter that expels a wide variety of cytotoxic compounds out of cells....
P-glycoprotein (P-gp), which was first identified in cancer cells, is an ATP-dependent efflux transporter that expels a wide variety of cytotoxic compounds out of cells. This transporter can decrease the bioavailability of therapeutic drugs by preventing their sufficient intracellular accumulation. Over expression of P-gp in cancer cells lead to multidrug resistance (MDR) phenotype that is one of the main reasons for the failure of chemotherapy. Hence, P-gp inhibition is a favorable method to reverse MDR. In this study, the lignanamides from were docked against P-gp to recognize potential binding affinities of these phytochemicals. Tariquidar and zosuquidar, two well-known P-gp inhibitors, were selected as the control ligands. It was observed that cannabisin M and cannabisin N exhibited higher binding affinities (- 10.2 kcal/mol) to drug-binding pocket of P-gp when compared with tariquidar and zosuquidar that showed binding affinities of - 10.1 and - 9.6 kcal/mol, respectively. Based on these findings, cannabisin M and cannabisin N could be good drug candidates against P-gp.
PubMed: 33442533
DOI: 10.1007/s40203-020-00066-7 -
Nuclear Medicine and Biology Mar 2019The serotonin 1B receptor subtype is of interest in the pathophysiology and treatment of depression, anxiety, and migraine. Over recent years 5-HT receptor binding in...
INTRODUCTION
The serotonin 1B receptor subtype is of interest in the pathophysiology and treatment of depression, anxiety, and migraine. Over recent years 5-HT receptor binding in human brain has been examined with PET using radioligands that are partial but not full agonists. To explore how the intrinsic activity of a PET radioligand may affect imaging performance, two high-affinity full 5-HT receptor agonists (AZ11136118, 4; and AZ11895987, 5) were selected from a large compound library and radiolabeled for PET examination in non-human primates.
METHODS
[C]4 was obtained through Pd(0)-mediated insertion of [C]carbon monoxide between prepared iodoarene and homochiral amine precursors. [C]5 was obtained through N-C-methylation of N-desmethyl precursor 6 with [C]methyl triflate. [C]4 and [C]5 were studied with PET in rhesus or cynomolgus monkey. [C]4 was studied with PET in mice and rats to measure brain uptake and specific binding. Ex-vivo experiments in rats were performed to identify whether there were radiometabolites in brain. Physiochemical parameters for [C]4 (pKa, logD and conformational energetics) were evaluated.
RESULTS
Both [C]4 and [C]5 were successfully produced in high radiochemical purity and in adequate amounts for PET experiments. After intravenous injection of [C]4, brain radioactivity peaked at a low level (0.2 SUV). Pretreatment with tariquidar, an inhibitor of the brain P-gp efflux transporter, increased brain exposure four-fold whereas pretreatment with a high pharmacological dose of the 5-HT antagonist, AR-A000002, had no effect on the binding. Ex-vivo experiments in rats showed no radiometabolites entering brain. [C]5 also failed to enter monkey brain under baseline conditions.
CONCLUSIONS
[C]4 and [C]5 show too low brain uptake and specific binding to be useful PET radioligands. Low brain uptake is partly ascribed to efflux transporter action as well as unfavorable conformations.
Topics: Animals; Brain; Chemistry Techniques, Synthetic; Hydrophobic and Hydrophilic Interactions; Image Processing, Computer-Assisted; Ligands; Macaca mulatta; Positron-Emission Tomography; Radiochemistry; Rats; Receptor, Serotonin, 5-HT1B; Serotonin 5-HT1 Receptor Agonists
PubMed: 30811975
DOI: 10.1016/j.nucmedbio.2019.01.005 -
ACS Chemical Neuroscience Feb 2011Tariquidar was developed as a specific inhibitor of the efflux transporter ABCB1. Recent positron emission tomographic brain imaging studies using [(11)C]tariquidar to...
Tariquidar was developed as a specific inhibitor of the efflux transporter ABCB1. Recent positron emission tomographic brain imaging studies using [(11)C]tariquidar to measure ABCB1 (P-gp, P-glycoprotein) density in mice indicate that the inhibitor may not be as specific as previously thought. We examined its selectivity as an inhibitor and a substrate for the human transporters P-gp, breast cancer resistance protein (BCRP, ABCG2), and multidrug resistance protein 1 (MRP1, ABCC1). Our results show that at low concentrations, tariquidar acts selectively as an inhibitor of P-gp and also as a substrate of BCRP. At much higher concentrations (≥100 nM), tariquidar acts as an inhibitor of both P-gp and BCRP. Thus, the in vivo specificity of tariquidar depends on concentration and the relative density and capacity of P-gp vs BCRP.
Topics: ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Breast Neoplasms; Cell Line, Tumor; Drug Resistance, Multiple; Female; HEK293 Cells; Humans; Neoplasm Proteins; Quinolines; Substrate Specificity
PubMed: 22778859
DOI: 10.1021/cn100078a