Authors: Katarina Elefantova, Boris Lakatos, Jana Kubickova...

JC-1, a cationic fluorescent dye when added to living cells, is known to be localized exclusively in mitochondria, particularly in good physiological conditions characterized by sufficient mitochondrial membrane potential (ΔΨ). The accumulation of JC-1 in these organelles leads to the formation J-aggregates (with a specific red fluorescence emission maximum at 590 nm), which is in addition to the typical green fluorescence of J-monomers (emission maximum of ∼529 nm). The lack of mitochondrial ΔΨ leads to the depression of JC-1 mitochondrial accumulation and a decrease in J-aggregate formation. Therefore, the ratio between the red and green fluorescence of cells loaded with JC-1 is often used for the detection of the mitochondrial membrane potential. However, JC-1 represents a suitable substrate of the multidrug transporter P-glycoprotein (P-gp). Therefore, the depression of the JC-1 content in intracellular space and particularly in the mitochondria to a level that is inefficient for J-aggregate formation could be expected in P-gp-positive cells. In the current paper, we proved this behavior on parental P-gp-negative L1210 (S) cells and their P-gp-positive variants obtained by either selection with vincristine (R) or transfection with the human gene encoding P-gp (T). P-glycoprotein inhibitors cyclosporine A and verapamil fail to restore JC-1 loading of the R and T cells to an extent similar to that observed in S cells. In contrast, the noncompetitive high affinity P-gp inhibitor tariquidar fully restored JC-1 accumulation and the presence of the typical red fluorescence of J-aggregates. In the presence of tariquidar, measurement of the JC-1 fluorescence revealed similar levels of mitochondrial membrane potential in P-gp-negative (S) and P-gp-positive cells (R and T).

Topics: ATP Binding Cassette Transporter, Subfamily B; Animals; Benzimidazoles; Carbocyanines; Cell Line; Cyclosporine; Fluorescent Dyes; Humans; Membrane Potential, Mitochondrial; Mice; Mitochondria; Quinolines; Verapamil

PubMed: 29986516
DOI: 10.3390/ijms19071985

Review

Authors: Ilza K Pajeva, Michael Wiese

The review summarizes the most recent achievements in structure-activity relationship (SAR) studies of tariquidar and its analogs. Tariquidar is one of the most promising representatives of the third generation of multidrug resistance (MDR) modulators created so far. This fact determines the strong interest of different research groups in the development of tariquidar-like structures as selective inhibitors of MDR transporters in resistant human cancer cells. After the discovery of tariquidar, a number of analogs have been synthesized and pharmacologically tested, thus supplying good data for comprehensive analyses of their structure-activity relationships. In the review, the structural and pharmacological data of newly synthesized tariquidar-like compounds are first presented. Next, the main achievements in the SAR studies are described focusing on two main transport proteins: P-glycoprotein and breast cancer resistance protein. The reported results are discussed from the point of view of their significance and importance for future directions in the rational design of effective MDR modulators.

Topics: Drug Resistance, Multiple; Models, Molecular; Quinolines; Structure-Activity Relationship

PubMed: 19504188
DOI: 10.1208/s12248-009-9118-z

Authors: Yae Eun Chong, Manting Chiang, Kiran Deshpande...

Ondansetron, a widely used antiemetic agent, is a P-glycoprotein (P-gp) substrate and therefore expression of P-gp at the blood-brain barrier limits its distribution to the central nervous system (CNS), which was observed to be reversed by coadministration with P-gp inhibitors. Tariquidar is a potent and selective third-generation P-gp inhibitor, and coadministration with ondansetron has shown improved ondansetron distribution to the CNS. There is currently no reported bioanalytical method for simultaneously quantifying ondansetron with a third-generation P-gp inhibitor. Therefore, we aimed to develop and validate a method for ondansetron and tariquidar in rat and human plasma samples. A full validation was performed for both ondansetron and tariquidar, and sample stability was tested under various storage conditions. To demonstrate its utility, the method was applied to a preclinical pharmacokinetic study following coadministration of ondansetron and tariquidar in rats. The presented method will be valuable in pharmacokinetic studies of ondansetron and tariquidar in which simultaneous determination may be required. In addition, this is the first report of a bioanalytical method validated for quantification of tariquidar in plasma samples.

Topics: Animals; Chromatography, High Pressure Liquid; Humans; Limit of Detection; Linear Models; Male; Ondansetron; Quinolines; Rats; Rats, Sprague-Dawley; Reproducibility of Results; Spectrophotometry, Ultraviolet

PubMed: 31322284
DOI: 10.1002/bmc.4653

Authors: Irene Hernández Lozano, Martin Bauer, Beatrix Wulkersdorfer...

P-Glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) in the canalicular membrane of hepatocytes mediate the biliary excretion of drugs and drug metabolites. To measure hepatic ABCB1 and ABCG2 activity, we performed positron emission tomography (PET) scans with the ABCB1/ABCG2 substrate [C]tariquidar in healthy volunteers and wild-type, , , and mice without and with coadministration of unlabeled tariquidar. PET data were analyzed with a three-compartment pharmacokinetic model. [C]Tariquidar underwent hepatobiliary excretion in both humans and mice, and tariquidar coadministration caused a significant reduction in the rate constant for the transfer of radioactivity from the liver into bile (by -74% in humans and by -62% in wild-type mice), suggesting inhibition of canalicular efflux transporter activity. Radio-thin-layer chromatography analysis revealed that the majority of radioactivity (>87%) in the mouse liver and bile was composed of unmetabolized [C]tariquidar. PET data in transporter knockout mice revealed that both ABCB1 and ABCG2 mediated biliary excretion of [C]tariquidar. experiments indicated that tariquidar is not a substrate of major hepatic basolateral uptake transporters (SLCO1B1, SLCO1B3, SLCO2B1, SLC22A1, and SLC22A3). Our data suggest that [C]tariquidar can be used to measure hepatic canalicular ABCB1/ABCG2 transport activity without a confounding effect of uptake transporters.

Topics: ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily G, Member 2; Adult; Animals; Bile; Carbon Isotopes; Gallbladder; Humans; Liver; Male; Mice; Mice, Knockout; Neoplasm Proteins; Positron-Emission Tomography; Quinolines; Radiopharmaceuticals; Tissue Distribution

PubMed: 31790256
DOI: 10.1021/acs.molpharmaceut.9b01060

Clinical Trial

Authors: Martin Bauer, Matthias Blaickner, Cécile Philippe...

UNLABELLED

(11)C-elacridar and (11)C-tariquidar are new PET tracers to assess the transport activity of P-glycoprotein (adenosine triphosphate-binding cassette subfamily B, member 1 [ABCB1]) and breast cancer resistance protein (adenosine triphosphate-binding cassette subfamily G, member 2 [ABCG2]). This study investigated the whole-body distribution and radiation dosimetry of both radiotracers in humans.

METHODS

Twelve healthy volunteers (6 women, 6 men) underwent whole-body PET/CT imaging over the 90 min after injection of either (11)C-elacridar or (11)C-tariquidar. Radiation doses were calculated with OLINDA/EXM software using adult reference phantoms.

RESULTS

Biodistribution was consistent with a major elimination route of hepatobiliary excretion, which may be mediated by ABCB1 and ABCG2. High radioactivity uptake was seen in liver, followed by spleen and kidneys, whereas brain uptake was lowest. Effective doses were 3.41 ± 0.06 μSv/MBq for (11)C-elacidar and 3.62 ± 0.11 μSv/MBq for (11)C-tariquidar.

CONCLUSION

Our data indicate that both (11)C-elacridar and (11)C-tariquidar are safe radiotracers, for which an injected activity of 400 MBq corresponds to a total effective dose of approximately 1.5 mSv.

Topics: Acridines; Adult; Carbon Radioisotopes; Humans; Metabolic Clearance Rate; Organ Specificity; Positron-Emission Tomography; Quinolines; Radiation Dosage; Radiopharmaceuticals; Tetrahydroisoquinolines; Tissue Distribution; Whole-Body Counting

PubMed: 27081167
DOI: 10.2967/jnumed.116.175182

Authors: Laura Braconi, Silvia Dei, Marialessandra Contino...

New 2,5- and 1,5-disubstituted tetrazoles, and 2,5-disubstituted-1,3,4-oxadiazoles were synthesized as tariquidar and elacridar derivatives and studied as multidrug resistance (MDR) reversers. Their behaviour on the three ABC transporters P-gp, MRP1 and BCRP was investigated. All compounds inhibited the P-gp transport activity in MDCK-MDR1 cells overexpressing P-gp, showing EC values even in the low nanomolar range (compounds 15, 22). Oxadiazole derivatives were able to increase the antiproliferative effect of doxorubicin in MDCK-MDR1 and in HT29/DX cells confirming their nature of P-gp modulators, with derivative 15 being the most potent in these assays. Compound 15 also displayed a dual inhibitory effect showing good activities towards both P-gp and BCRP. A computational study suggested a common interaction pattern on P-gp for most of the potent compounds. The bioisosteric substitution of the amide group of lead compounds allowed identifying a new set of potent oxadiazole derivatives that modulate MDR through inhibition of the P-gp efflux activity. If compared to previous amide derivatives, the introduction of the heterocycle rings greatly enhances the activity on P-gp, introduces in two compounds a moderate inhibitory activity on MRP1 and maintains in some cases the effect on BCRP, leading to the unveiling of dual inhibitor 15.

Topics: Antineoplastic Agents; ATP Binding Cassette Transporter, Subfamily G, Member 2; Drug Resistance, Neoplasm; Structure-Activity Relationship; Neoplasm Proteins; Drug Resistance, Multiple; Tetrazoles; Amides

PubMed: 37573829
DOI: 10.1016/j.ejmech.2023.115716

Clinical Trial

Pharmacokinetic and pharmacodynamic study of tariquidar (XR9576), a P-glycoprotein inhibitor, in combination with doxorubicin, vinorelbine, or docetaxel in children and adolescents with refractory solid tumors.

Authors: Elizabeth Fox, Brigitte C Widemann, Devang Pastakia...

PURPOSE

P-glycoprotein (Pgp), an ATP-dependent transport protein, confers multidrug resistance in cancer cells. Tariquidar binds and inhibits Pgp. To assess the toxicity, pharmacokinetics (PK), and pharmacodynamics of tariquidar, we conducted a phase I trial of tariquidar in combination with doxorubicin, docetaxel, or vinorelbine in children and adolescents with recurrent or refractory solid tumors.

METHODS

Patients less than 19 years of age with refractory or recurrent solid tumors were eligible. Tariquidar (1, 1.5, or 2 mg/kg) was administered alone and in combination with doxorubicin, docetaxel, or vinorelbine. PK of tariquidar and cytotoxic drugs was performed. Pgp function was assessed by a rhodamine efflux assay and (99m)Tc-sestamibi scintigraphy. Tumor Pgp expression was assessed by immunohistochemistry. Response was assessed using Response Evaluation Criteria in Solid Tumors.

RESULTS

Twenty-nine subjects were enrolled. No tariquidar-related dose-limiting toxicity (DLT) was observed. DLT related to cytotoxic drugs occurred in 12 % of subjects receiving tariquidar 2 mg/kg. When administered in combination with tariquidar, the clearance of docetaxel and vinorelbine was reduced compared to prior studies. Inhibition of rhodamine efflux was dose dependent. After tariquidar administration, (99m)Tc-sestamibi accumulation in tumor increased by 22 %. Objective responses (1 complete, 2 partial) were observed. There was no association between tumor Pgp expression and response.

CONCLUSION

A tolerable and biologically active dose of tariquidar was established in children and adolescents. This trial demonstrates that modulators of resistance can be evaluated in combination with chemotherapy, and pharmacokinetic and pharmacodynamic endpoints can be useful in determination of recommended dose in children and adolescents.

Topics: ATP Binding Cassette Transporter, Subfamily B; Adolescent; Anemia; Antineoplastic Combined Chemotherapy Protocols; Area Under Curve; Child; Child, Preschool; Docetaxel; Dose-Response Relationship, Drug; Doxorubicin; Drug Resistance, Neoplasm; Female; Humans; Male; Metabolic Clearance Rate; Neoplasms; Neutropenia; Quinolines; Taxoids; Treatment Outcome; Vinblastine; Vinorelbine; Vomiting

PubMed: 26486517
DOI: 10.1007/s00280-015-2845-1

Randomized Controlled Trial

Authors: Martin Bauer, Rudolf Karch, Markus Zeitlinger...

UNLABELLED

The adenosine triphosphate-binding cassette transporters P-glycoprotein (Pgp) and breast cancer resistance protein (BCRP) are 2 major gatekeepers at the blood-brain barrier (BBB) that restrict brain distribution of several clinically used drugs. In this study, we investigated the suitability of the radiolabeled Pgp/BCRP inhibitors (11)C-tariquidar and (11)C-elacridar to assess Pgp density in the human brain with PET.

METHODS

Healthy subjects underwent a first PET scan of 120-min duration with either (11)C-tariquidar (n = 6) or (11)C-elacridar (n = 5) followed by a second PET scan of 60-min duration with (R)-(11)C-verapamil. During scan 1 (at 60 min after radiotracer injection), unlabeled tariquidar (3 mg/kg) was intravenously administered. Data were analyzed using 1-tissue 2-rate-constant (1T2K) and 2-tissue 4-rate-constant (2T4K) compartment models and either metabolite-corrected or uncorrected arterial input functions.

RESULTS

After injection of (11)C-tariquidar or (11)C-elacridar, the brain PET signal corrected for radioactivity in the vasculature was low (~0.1 standardized uptake value), with slow washout. In response to tariquidar injection, a moderate but statistically significant rise in brain PET signal was observed for (11)C-tariquidar (+27% ± 15%, P = 0.014, paired t test) and (11)C-elacridar (+21% ± 15%, P = 0.014) without changes in plasma activity concentrations. Low levels of radiolabeled metabolites (<25%) were detected in plasma up to 60 min after injection of (11)C-tariquidar or (11)C-elacridar. The 2T4K model provided better data fits than the 1T2K model. Model outcome parameters were similar when metabolite-corrected or uncorrected input functions were used. There was no significant correlation between distribution volumes of (11)C-tariquidar or (11)C-elacridar and distribution volumes of (R)-(11)C-verapamil in different brain regions.

CONCLUSION

The in vivo behavior of (11)C-tariquidar and (11)C-elacridar was consistent with that of dual Pgp/BCRP substrates. Both tracers were unable to visualize cerebral Pgp density, most likely because of insufficiently high binding affinities in relation to the low density of Pgp in human brain (∼1.3 nM). Despite their inability to visualize Pgp density, (11)C-tariquidar and (11)C-elacridar may find use as a new class of radiotracers to study the interplay of Pgp and BCRP at the human BBB in limiting brain uptake of dual substrates.

Topics: ATP Binding Cassette Transporter, Subfamily B, Member 1; ATP Binding Cassette Transporter, Subfamily G, Member 2; ATP-Binding Cassette Transporters; Acridines; Adult; Blood-Brain Barrier; Carbon Radioisotopes; Humans; Male; Neoplasm Proteins; Positron-Emission Tomography; Protein Binding; Quinolines; Tetrahydroisoquinolines

PubMed: 23833270
DOI: 10.2967/jnumed.112.118232

Authors: Diana Peña-Solórzano, Matthias Scholler, Günther Bernhardt...

ABC transporters, including ABCG2, play a vital role in defending the human body against the vast range of xenobiotics. Even though this is beneficial for human health, these protein transporters have been implicated in the emerging resistance of cancer cells to a variety of structurally and functionally diverse anticancer drugs. In order to investigate their role in resistance, potent and selective ABCG2 modulators have been described in the literature. A leading class of modulators are the tariquidar analogues; however, their susceptibility to hydrolysis limits their applicable use. To overcome this, we synthesized a novel series of chalcone- and ketone-based compounds inspired by reported tariquidar analogues. Compounds were characterized and evaluated for their ABCG2 modulatory activity and ABC transporter selectivity. When compared to transporters ABCB1 and ABCC1, the chalcone-based compounds exhibited selectivity for ABCG2, while the ketone-based compounds showed only a slight preference for ABCG2. From the former series, chalcone (UR-DP48) displayed similar activity to the reference fumitremorgin C, both producing comparable maximal effects. The compound exhibited marked antiproliferative activity, while cytotoxicity was less pronounced for the most active compound from the ketone series. Chalcone-containing tariquidar analogues are promising modulators to aid in functional investigations of ABCG2 transporters.

PubMed: 30128080
DOI: 10.1021/acsmedchemlett.8b00289

Authors: Yingjie Gao, Caiyan Wei, Lanxin Luo...

The human multidrug transporter P-glycoprotein (P-gp) is physiologically essential and of key relevance to biomedicine. Recent structural studies have shed light on the mode of inhibition of the third-generation inhibitors for human P-gp, but the molecular mechanism by which these inhibitors enter the transmembrane sites remains poorly understood. In this study, we utilized all-atom molecular dynamics (MD) simulations to characterize human P-gp dynamics under a potent inhibitor, tariquidar, bound condition, as well as the atomic-level binding pathways in an explicit membrane/water environment. Extensive unbiased simulations show that human P-gp remains relatively stable in tariquidar-free and bound states, while exhibiting a high dynamic binding mode at either the drug-binding pocket or the regulatory site. Free energy estimations by partial nudged elastic band (PNEB) simulations and Molecular Mechanics Generalized Born Surface Area (MM/GBSA) method identify two energetically favorable binding pathways originating from the cytoplasmic gate with an extended tariquidar conformation. Interestingly, free tariquidar in the lipid membrane predominantly adopts extended conformations similar to those observed at the regulatory site. These results suggest that membrane lipids may preconfigure tariquidar into an active ligand conformation for efficient binding to the regulatory site. However, due to its conformational plasticity, tariquidar ultimately moves toward the drug-binding pocket in both pathways, explaining how it acts as a substrate at low concentrations. Our molecular findings propose a membrane-assisted mechanism for the access and binding of the third-generation inhibitors to the binding sites of human P-gp, and offer deeper insights into the molecule design of more potent inhibitors against P-gp-mediated drug resistance.

PubMed: 38560519
DOI: 10.3389/fmolb.2024.1364494