Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.3.44 (P-glycoprotein)
13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Decreased accumulation of the fluorescent dye BCECF [2', 7'-bis-(2-carboxyethyl)-5-(6)- carboxyfluorescein] characterized murine and human multidrug-resistant cell lines overexpressing the multidrug resistance protein (MRP). Indomethacin (10 microM), a known cyclo-oxygenase and glutathione-S-transferase inhibitor as well as a modulator of anion transport, increased accumulation and blocked efflux of BCECF in MRP-expressing murine and human cells. The drug did not affect P-glycoprotein (P-gp)-mediated export of rhodamine 123. The indomethacin effect on BCECF efflux was not reversed by the addition of exogenous prostaglandins, suggesting that the drug acts by a mechanism other than decreasing prostaglandin synthesis. Indomethacin also increased multidrug susceptibility of both murine and human cell lines overexpressing MRP, but not those displaying P-gp-associated resistance. In addition, indomethacin modulated the decreased vincristine accumulation in cells expressing MRP, but not in those expressing P-gp. These data suggest that indomethacin is a specific inhibitor of MRP, possibly functioning by inhibition of glutathione-S-transferase or, alternatively, by direct competition with the drug at the transport site.
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PMID:Indomethacin-mediated reversal of multidrug resistance and drug efflux in human and murine cell lines overexpressing MRP, but not P-glycoprotein. 906

The present study characterized the response of P-glycoprotein (P-gp) and multidrug resistance-associated protein (MRP1) to chronic ritonavir (RIT) exposure by assessing increases in P-gp and MRP1 protein expression and activity. LS-180V intestinal carcinoma cells were exposed for 3 days to 1-100 microM RIT concurrently with controls. P-gp and MRP1 protein was quantified by Western blot analysis. Cell accumulation assays, using the P-gp substrate rhodamine 123 (RH123), the P-gp/MRP1 substrate doxorubicin (DOX), and the MRP substrate carboxyfluorescein (CBF), were performed as a measure of transporter activity. RIT strongly induced P-gp and MRP1 expression (maximum 6-fold and 3-fold increases, respectively) in a concentration-dependent fashion. Following extended exposure to RIT (> 10 microM), cells accumulated < 50% of the RH123 and DOX compared with controls, whereas accumulation of CBF was decreased by 30% at 30 microM. Differences in cell accumulation of RH123 could be eliminated with verapamil (100 microM; a P-gp inhibitor), whereas decreased DOX cell accumulation was only partially reversed by verapamil. Indomethacin (100 microM; an MRP1 inhibitor) had no significant effect on RH123 or DOX accumulation, suggesting limited MRP1-mediated activity. Thus, RIT induced protein expression of P-gp and MRP1 and increased cellular drug exclusion of RH123, DOX, and CBF. Similar in vivo phenomena may occur during anti-HIV drug therapy, explaining potential decrements in therapeutic efficacy due to decreases in bioavailability or alterations in drug distribution.
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PMID:Ritonavir induces P-glycoprotein expression, multidrug resistance-associated protein (MRP1) expression, and drug transporter-mediated activity in a human intestinal cell line. 1174 41

The aim of our study was to investigate the functional expression of P-glycoprotein (Pgp) and multidrug resistance-associated proteins (MRPs) in 2 distinct glioma cells (GL15 and 8MG) from patients with glioblastoma multiforme. MDR1 gene and Pgp expression was not detected in either cell line by RT-PCR and Western blotting, respectively. In contrast, MRP1 was detected at both mRNA and protein level in both cell lines, with a higher expression in the 8MG cells that occur predominantly at the cell membrane. Three other MRPs (MRP3, MRP4 and MRP5) were detected by RT-PCR in both cell lines, whereas MRP2 was not expressed. In addition, MRP3 protein was also detected by immunocytochemistry in both GL15 and 8MG cell lines. Indomethacin and probenecid, 2 modulators of MRPs activity, increased the accumulation of vincristine and etoposide, 2 substrates of MRPs, by both cell lines. These modulators also decreased the efflux of vincristine from both cell lines with a more pronounced effect in 8MG cells. In conclusion, our results show functional expression of MRPs leading to a decrease in the intracellular vincristine and etoposide concentrations in human glioblastoma cell lines. Furthermore, our results that exhibit protein expression of MRP1 and MRP3 and gene expression of MRP4 and MRP5 in these 2 glioblastoma cell lines suggest new mechanisms that could lead to a MDR phenotype of tumour cells in patients with glioblastoma multiforme.
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PMID:Molecular and functional MDR1-Pgp and MRPs expression in human glioblastoma multiforme cell lines. 1185 4

The accumulation of glutamate in the extracellular space in the central nervous system (CNS) plays a major part in ischemic and anoxic damage. In this study, we examined the effect of glutamate on the expression and activity of P-glycoprotein (P-gp) in rat brain microvessel endothelial cells (RBMECs) making up the blood-brain barrier (BBB). The level of P-gp expression significantly increased in RBMECs after the treatment of 100 microM glutamate. At this concentration, glutamate also enhanced rat mdr1a and mdr1b mRNA levels determined by RT-PCR analysis. Flow cytometry was used to study P-gp activity by analysis of intracellular rhodamine123 (Rh123) accumulation. Overexpression of P-gp resulted in a decreased intracellular accumulation of Rh123 in RBMECs. Glutamate-induced increase of intracellular reactive oxygen species (ROS) was observed by using the 2',7'-dichlorofluorescein (2',7'-DCF) assay. MK-801, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, and ROS scavenger N-acetylcysteine obviously blocked ROS generation and attenuated the changes of both expression and activity of P-gp induced by glutamate in RBMECs. These data suggested that glutamate up-regulated P-gp expression in RBMECs by an NMDA receptor-mediated mechanism and that glutamate-induced generation of ROS was linked to the regulation of P-gp expression. Therefore, transport of P-gp substrates in BBB appears to be affected during ischemic and anoxic injury.
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PMID:Glutamate up-regulates P-glycoprotein expression in rat brain microvessel endothelial cells by an NMDA receptor-mediated mechanism. 1523 89

Drug resistance continues to be a serious problem in cancer therapy. We investigated whether indomethacin, which inhibited cyclooxygenases, would overcome doxorubicin resistance in K562/ADR leukemia cells. Indomethacin at 10 muM increased the cytotoxicity of doxorubicin, as well as vincristine in K562/ADR. Both multi-drug resistant protein1 (MRP1) and P-glycoprotein were overexpressed in K562/ADR cells when compared with K562 parent cells (K562/P). Expression of MRP1 mRNA and protein, but not P-glycoprotein, was significantly decreased in K562/ADR cells after indomethacin treatment. Indomethacin treatment increased 5(6)-carboxyfluorescein diacetate (CFDA) efflux, as well as decreased accumulation in K562/ADR cells. The activity of the MRP1 promoter decreased after indomethacin treatment in Hela cells. These data strongly suggest that the cyclooxygenase inhibitor, indomethacin, increased the cytotoxicity of doxorubicin with decreasing expression of MRP1 through inhibition of MRP1 promoter activity.
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PMID:Indomethacin overcomes doxorubicin resistance with inhibiting multi-drug resistance protein 1 (MRP1). 1633 95

P-glycoprotein (Pgp/ABCB1) and multidrug resistance related protein 1 (MRP1/ABCC1) were first described in multidrug resistant tumor cells. It is presently known that both proteins are also expressed in a variety of normal cells, including lymphocytes. ABCB1 activity has already been detected in subpopulations of murine thymocytes, but there was little information on the expression or activity of ABCC1 in these cells. The present work studied in mice the expression of both proteins by RT-PCR and immunofluorescence. It was possible to identify the presence of ABCB1 and to detect the expression of ABCC1 in these cells. The functional activities of these proteins were also studied in vivo and in vitro measuring the extrusion of fluorescent dyes in association with MDR modulators. Cyclosporine A, verapamil and trifluoperazine inhibited the activity of thymic ABCB1. Indomethacin, probenecid and MK571 were effective in inhibiting ABCC1 activity by thymic cells. ABCB1 was only active in a small percentage of thymocytes being present in the immature double negative (not CD4 nor CD8) subpopulation and the mature single positive (CD4 or CD8) subpopulations. The functional activity of ABCC1, on the other hand, was more homogeneously distributed being found in all thymocyte subpopulations. Possible physiological roles for these transporters on thymocytes are discussed.
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PMID:In vivo and in vitro modulation of MDR molecules in murine thymocytes. 1639 25

The possible involvement of P-glycoprotein (P-gp) and cytochrome P450 (CYP) 3A4 in risperidone transport was investigated using in vitro and in vivo models. Firstly, uptake studies were performed on a Caco-2/TC7 cell monolayer; the effects of 1 microg ml(-1) risperidone on apparent permeability were determined for secretory and absorptive directions, in the presence or absence of various P-gp and CYP3A4 inhibitors (verapamil, ketoconazole, erythromycin), and of an associated multidrug-resistant protein inhibitor (indomethacin). Secondly, on a conscious rat model, risperidone pharmacokinetic parameters, notably absorption parameters, were determined using compartmental and deconvolution methods. Three groups of seven rats received respectively an IV risperidone dose, an oral risperidone dose (PO group) and the same oral risperidone dose after verapamil administration (POV group). No formation of 9-hydroxyrisperidone was observed on Caco-2 cells after risperidone administration; there was no evidence that intestinal CYP3A4 is involved in risperidone metabolising. Risperidone secretory permeation was higher than absorptive permeation. Verapamil increased risperidone absorption permeation and decreased its secretory permeation. Indomethacin did not modify these permeation values. In rats, verapamil led to an increase in both risperidone and 9-hydroxyrisperidone plasmatic concentrations. The fraction absorbed in the verapamil group was 3.18 times higher than in the oral group (65.9% and 20.7% for POV group and PO group). The absorption rate constant was lower in the verapamil group. Our results indicate that P-gp decreases the intestinal absorption of risperidone and that intestinal CYP3A4 is not involved in risperidone metabolism.
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PMID:P-glycoprotein and cytochrome P450 3A4 involvement in risperidone transport using an in vitro Caco-2/TC7 model and an in vivo model. 1733 19

Cyclosporin A induces closure of the mitochondrial permeability transition pore. We aimed to investigate whether this closure results in concomitant increases in mitochondrial membrane potential (DeltaPsim) and the production of reactive oxygen species. Fluorescent probes were used to assess DeltaPsim (JC-1, 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl-benzimidazolyl-carbocyanine iodide), reactive oxygen species [DCF, 5- (and 6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester] and [Ca2+][Fluo-3, glycine N-[4-[6-[(acetyloxy)methoxy]-2,7-dichloro-3-oxo-3H-xanthen-9-yl]-2-[2-[2-[bis[2-[(acetyloxy)methoxy]-2-oxyethyl]amino]-5-methylphenoxy]ethoxy]phenyl]-N-[2-[(acetyloxy)methoxy]-2-oxyethyl]-(acetyloxy)methyl ester] in human kidney cells (HK-2 cells) and in a line of human small cell carcinoma cells (GLC4 cells), because these do not express cyclosporin A-sensitive P-glycoprotein. We used transfected GLC4 cells expressing P-glycoprotein as control for GLC4 cells. NIM811 (N-methyl-4-isoleucine-cyclosporin) and PSC833 (SDZ-PSC833) were applied as selective mitochondrial permeability transition pore and P-glycoprotein blockers, respectively. To study the effect of cyclosporin A on mitochondrial function, we isolated mitochondria from fresh pig livers. Cyclosporin A and PSC833 induced a more than two-fold increase in JC-1 fluorescence in HK-2 cells, whereas NIM811 had no effect. None of the three substances induced a significant increase in JC-1 fluorescence in GLC4 cells. Despite this, cyclosporin A, NIM811 and PSC833 induced a 1.5-fold increase in DCF fluorescence (P<0.05) and a two-fold increase in Fluo-3 fluorescence (P<0.05). Studies in isolated mitochondria showed that blockage of mitochondrial permeability transition pores by cyclosporin A affected neither DeltaPsim, ATP synthesis, nor respiration rate. The mitochondrial permeability transition pore blockers cyclosporin A and NIM811, but also the non-mitochondrial permeability transition pore blocker PSC833, induced comparable degrees of reactive oxygen species production and cytosolic [Ca2+]. Neither mitochondria, effects on P-glycoprotein nor inhibition of calcineurin therefore play a role in cyclosporin A-induced oxidative stress and disturbed Ca2+ homeostasis.
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PMID:Cyclosporin A-induced oxidative stress is not the consequence of an increase in mitochondrial membrane potential. 1750 81

Doxorubicin is a chemotherapeutic drug widely used for the treatment of hepatocellular carcinoma but its efficacy is restricted by multidrug resistance. Non-steroidal anti-inflammatory drugs (NSAIDs) and cyclooxygenase (COX)-2-selective inhibitors exhibit anti-cancer properties as well as abilities to overcome drug resistance. In the present study, indomethacin (a NSAID) and SC236 (a COX-2-selective inhibitor) enhanced the cytotoxicity of doxorubicin in the hepatocellular carcinoma cell line HepG2 and its drug-resistant sub-line R-HepG2. Both drugs increased the intracellular accumulation and retention of doxorubicin in vitro. The effects were not reversed by prostaglandin E(2), implicating a COX-independent mechanism. Indomethacin and SC236 partially reversed the increase in expression of P-glycoprotein (P-gp) and multidrug resistance-associated protein 1 (MRP1) induced by doxorubicin in R-HepG2 cells. In conclusion, indomethacin and SC236 increased the intracellular accumulation and retention of doxorubicin and thus its cytotoxicity in HepG2 and drug-resistant HepG2 cells. These effects, mediated through decrease in P-gp and MRP1 expression and/or direct inhibition of P-gp activity, may improve multidrug resistant-cancer chemotherapy.
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PMID:Indomethacin and SC236 enhance the cytotoxicity of doxorubicin in human hepatocellular carcinoma cells via inhibiting P-glycoprotein and MRP1 expression. 2137 66

Multidrug resistance (MDR) is a major obstacle in cancer treatment. More than half of human cancers express multidrug-resistant P-glycoprotein (Pgp), which correlates with a poor prognosis. Intriguingly, through an unknown mechanism, some drugs have greater activity in drug-resistant tumor cells than their drug-sensitive counterparts. Herein, we investigate how the novel anti-tumor agent di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT) overcomes MDR. Four different cell types were utilized to evaluate the effect of Pgp-potentiated lysosomal targeting of drugs to overcome MDR. To assess the mechanism of how Dp44mT overcomes drug resistance, cellular studies utilized Pgp inhibitors, Pgp silencing, lysosomotropic agents, proliferation assays, immunoblotting, a Pgp-ATPase activity assay, radiolabeled drug uptake/efflux, a rhodamine 123 retention assay, lysosomal membrane permeability assessment, and DCF (2',7'-dichlorofluorescin) redox studies. Anti-tumor activity and selectivity of Dp44mT in Pgp-expressing, MDR cells versus drug-sensitive cells were studied using a BALB/c nu/nu xenograft mouse model. We demonstrate that Dp44mT is transported by the lysosomal Pgp drug pump, causing lysosomal targeting of Dp44mT and resulting in enhanced cytotoxicity in MDR cells. Lysosomal Pgp and pH were shown to be crucial for increasing Dp44mT-mediated lysosomal damage and subsequent cytotoxicity in drug-resistant cells, with Dp44mT being demonstrated to be a Pgp substrate. Indeed, Pgp-dependent lysosomal damage and cytotoxicity of Dp44mT were abrogated by Pgp inhibitors, Pgp silencing, or increasing lysosomal pH using lysosomotropic bases. In vivo, Dp44mT potently targeted chemotherapy-resistant human Pgp-expressing xenografted tumors relative to non-Pgp-expressing tumors in mice. This study highlights a novel Pgp hijacking strategy of the unique dipyridylthiosemicarbazone series of thiosemicarbazones that overcome MDR via utilization of lysosomal Pgp transport activity.
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PMID:Di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT) overcomes multidrug resistance by a novel mechanism involving the hijacking of lysosomal P-glycoprotein (Pgp). 2572 Apr 91


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