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)

N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]- phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918) has been selected from a chemical program aimed at identifying an optimized inhibitor of multidrug resistance (MDR). The potency of GF120918 is assessed by dose-dependent sensitization of CHRC5, OV1/DXR and MCF7/ADR cells to the cytotoxicity of doxorubicin and vincristine respectively: GF120918 fully reverses multidrug resistance at 0.05 to 0.1 microM and is half maximally active at 0.02 microM. The spectrum of drugs sensitized by GF120918 coincides with those having the classical MDR phenotype. In CHRC5 cells, 0.01-0.1 microM GF120918 enhances the uptake of [3H]daunorubicin and blocks the efflux from preloaded cells. It is also shown that GF120918 is still active several hours after being taken away from the culture medium showing that it is not, like verapamil, effluxed rapidly by P-glycoprotein. GF120918 effectively competes with [3H]azidopine for binding P-glycoprotein, pointing to this transport membrane protein as its likely site of action. After i.v. administration to mice, GF120918 penetrates thoroughly various organs that have a tissue level/blood level ratio above 10. It is eliminated from organs and blood with a half-time of approximately 2.7 h. It is well absorbed after p.o. administration. In mice implanted i.p. with the MDR P388/Dox tumor, a single i.v. or p.o. dose of GF120918 restores sensitivity of the tumor to a single i.p. dose (5 mg/kg) of doxorubicin administered 1 h later. A statistically significant effect is observed at 1 mg/kg GF120918 i.v. and maximal effect is reached at 5 mg/kg. Similarly, whereas neither drug alone is effective, GF120918 (10 mg/kg i.p.) associated with doxorubicin (5 mg/kg i.p.) inhibits the growth of the moderately MDR C26 tumor implanted s.c. as assessed by tumor size at day 19. GF120918 does not modify significantly the distribution or the elimination of doxorubicin in mice ruling out the possibility that the antitumor effects seen might be explained by pharmacokinetic interactions.
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PMID:In vitro and in vivo reversal of multidrug resistance by GF120918, an acridonecarboxamide derivative. 840 33

1,3,5-Triazacycloheptanes were synthesized and examined for reversal of the multidrug resistance dependent on P-glycoprotein. Most of these compounds increased the intracellular uptake of vinblastine in multidrug-resistant mouse leukemia P388/ADR cells without influence upon the vinblastine accumulation in P388/S cells. The efficacy of 1,5-dibenzyl-1,3,5-triazacycloheptanes in increasing the vinblastine accumulation was in the order of 2,4-dithioxo (5) > 2-oxo-4-thioxo (4) approximately 4-(methylthio)-2-oxo (6) > 2,4-dioxo (2). The efficacy was further increased when the benzyl group was converted to a chlorobenzyl group. Among these compounds, 6c [1,5-bis(4-chlorobenzyl)-1,5,6,7-terahydro-4-(methylthio)-2H-1,3,5 - triazepin-2-one] potentiated the in vitro cell growth-inhibitory effect of vinblastine, adriamycin, and mitomycin C on P388/ADR cells and prolonged the life span of P388/ADR-bearing mice in combined therapy with vinblastine more than vinblastine alone.
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PMID:Novel inhibitors for multidrug resistance: 1,3,5-triazacycloheptanes. 854 83

We have previously established Adriamycin-resistant HOB1 cell lines showing the multidrug resistance (MDR) phenotype. For further study, we analyzed the free-radical scavengers glutathione S-transferase (GST) and glutathione peroxidase (GPX) by enzyme assays and Northern blots. Three cell lines, HOB1/ADR0.1, HOB1/ADR1.0, and HOB1/ADR5.0, represented HOB1 cells resistant to 0.1, 1.0, and 5.0 microM Adriamycin, respectively. The mdr1 transcript was overexpressed in HOB1/ADR0.1 cells, and the amount of its expression reached a maximum between HOB1/ADR1.0 and HOB1/ADR5.0 cell lines. The increases in GST activity and GST-pi expression were observed only in high-level-resistant cell line (HOB1/ADR1.0 and HOB1/ADR5.0), which also showed increased GPX activity and expression. For investigation of the cytotoxic effect of Adriamycin on HOB1 cells prior to the mdr1 overexpression, an appropriate number of parental HOB1 cells were treated with 0.1 microM Adriamycin for 7 days, and the viable cells (HOB1/ADR) were isolated and subjected to analyses for mdr1, GST-pi, and GPX expression and for GST and GPX activity. In comparison with HOB1/ADR0.1 cells, HOB1/ADR cells did not show mdr1 overexpression but had significant increases in the activity and expression of GST and GPX. The current study suggests that in the early phase of Adriamycin treatment, GST and GPX are more important than P-glycoprotein for the development in HOB1 cells of resistance against Adriamycin.
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PMID:Glutathione S-transferase and glutathione peroxidase are essential in the early stage of adriamycin resistance before P-glycoprotein overexpression in HOB1 lymphoma cells. 860 51

The human pancreatic tumour cell line PSN1/ADR, stepwise selected in 17-510 nM doxorubicin, displayed a multidrug resistance not conferred by P-glycoprotein (P-gp). Resistance to 17-51 nM doxorubicin was accompanied by overexpression of the vesicular marker lung resistance-related protein (LRP). Further selection in 170 nM doxorubicin led to the activation of multidrug resistance-associated protein (MRP) and to the development of drug accumulation/retention defects sensitive to verapamil. In addition, these defects were reversible by the vesicular traffic inhibitors brefeldin A, fluoroaluminate and nocodazole. In contrast, in human ovarian H134AD cells that are resistant to 1700 nM doxorubicin and used as P-gp-positive controls, the drug efflux was inhibited only by verapamil. The tyrosine kinase inhibitor genistein was a potent blocker of doxorubicin efflux in the PSN1/ADR cells but showed no activity in the H134 AD cells. The doxorubicin cytotoxicity in the PSN1/ADR cells was enhanced both by verapamil and brefeldin A, whereas in the parental PSN1 cells they demonstrated the opposite effects, being respectively sensitising and protecting. The P-gp-negative PSN1/ADR cells adapted to 510 nM doxorubicin retained brefeldin A-sensitive doxorubicin accumulation defects while MRP declined. The persistence of brefeldin A-responsive phenotype on the background of variable MRP expression suggests this agent as a useful functional probe for non-P-gp-mediated resistance to plasma-achievable doxorubicin concentrations.
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PMID:Low-level doxorubicin resistance in P-glycoprotein-negative human pancreatic tumour PSN1/ADR cells implicates a brefeldin A-sensitive mechanism of drug extrusion. 860 92

Itraconazole is a triazole antifungal agent that inhibits cell membrane serol biosynthesis. Currently, itraconazole is a potent candidate for in vivo use to revert multidrug resistance in acute leukemias, with the added benefit of its antifungal effect. As previously reported, itraconazole, as well as verapamil, reversed adriamycin-resistant K562 cells (K562/ADR) and HL60 cells (HL60/ADR) in dosages compatible to the plasma levels achieved by the therapeutic dosages used for the treatment of fungal infections. By RT-PCR analysis of mdr1, mdr3, and mrp mRNA, these adriamycin-resistant cells showed a higher expression of the transcript of these genes than those of the parent cells. By FACS analysis, both the adriamycin-resistant cells showed a higher expression of P-glycoprotein on their cell surfaces. These results suggested the involvement of itraconazole in the mdr gene and/or mrp gene product-associated resistance. Furthermore, itraconazole partially reversed etoposide resistance in both the K562 and K562/ADR cells. The present study suggests that itraconazole may reverse multidrug resistance, at least in part, via a classical MDR-associated mechanism.
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PMID:Reversal effect of itraconazole on adriamycin and etoposide resistance in human leukemia cells. 860 75

The P-glycoprotein (Pgp) efflux pump can influence the hepatocellular concentration of xenobiotics that are modulators and substrates of cytochrome P4503A (CYP3A). We tested the hypothesis that Pgp is a determinant of drug-inducible expression of CYP3A. The magnitude of CYP3A induction by rifampicin was compared in the human parental colon carcinoma cell line LS 180/WT (wild type) and in two derivative clones overexpressing the human multidrug resistance gene MDR1 (also designated PGY1) because of either drug selection (LS 180/ADR) or transfection with MDRI cDNA (LS 180/MDR). In both MDR1 cDNA-overexpressing clones, rifampicin induction of CYP3A mRNA and protein was decreased and required greater rifampicin concentrations compared with parental cells. The role of Pgp in regulation of CYP3A expression in vivo was analyzed in mice carrying a targeted disruption of the mdr1a mouse gene. Oral treatment with increasing doses of rifampicin resulted in elevated drug levels in the livers of mdr1a (-/-) mice compared with mdr1a (+/+) mice at all doses. Consistent with the enhanced accumulation of rifampicin in mdr1a (-/-) mice, lower doses of rifampicin were required for induction of CYP3A proteins, and the magnitude of CYP3A induction was greater at all doses of rifampicin in mdr1a (-/-) mice compared with mdr1a (+/+) mice. We conclude that Pgp-mediated transport is a critical element influencing the CYP3A inductive response.
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PMID:P-glycoprotein: a major determinant of rifampicin-inducible expression of cytochrome P4503A in mice and humans. 863 5

The present study demonstrated that poly(oxypropylene) and poly(oxyethylene) block copolymer pluronic L61 (L61)-hypersensitized multidrug-resistant CHRC5 Chinese hamster ovary cells and MCF-7/ADR human breast carcinoma cells to the cytotoxic action of doxorubicin (Dox). CHRC5 and MCF-7/ADR cells manifested 290- and 700-fold increases, respectively, in their sensitivity to Dox/L61 formulation compared with free Dox. Their sensitive counterparts Aux-B1 and MCF-7 displayed only marginal or no increase at all in their response to Dox/L61. The study of the drug transport performed by flow cytometry showed that L61 enhanced the drug uptake and reduced the P-glycoprotein-mediated drug efflux. Visualization of Dox subcellular distribution in CHRC5 cells by fluorescent microscopy revealed that Dox was sequestered in cytoplasmic vesicles, whereas incubation of the cells with Dox/L61 altered the drug compartmentalization by releasing the drug from these vesicles and shifting it to the nucleus. These findings suggested that the hypersensitive response of multidrug-resistant cells to the action of Dox/L61 was caused by an increase in the drug accumulation and changes in its subcellular distribution.
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PMID:Hypersensitizing effect of pluronic L61 on cytotoxic activity, transport, and subcellular distribution of doxorubicin in multiple drug-resistant cells. 870 95

Overexpression of P-glycoprotein (Pgp) by tumors results in multidrug resistance (MDR) to structurally unrelated oncolytics. MDR cells may be sensitized to these oncolytics when treated with a Pgp modulator. The present study evaluates LY335979 as a modulator both in vitro and in vivo. LY335979 (0.1 microM) fully restored sensitivity to vinblastine, doxorubicin (Dox), etoposide, and Taxol in CEM/VLB100 cells. LY335979 modulated Dox cytotoxicity even when LY335979 (0.5 microM) was removed 24 h prior to the cytotoxicity assay. LY335979 blocked [3H]azidopine photoaffinity labeling of the M(r) approximately 170,000 Pgp in CEM/VLB100 plasma membranes and competitively inhibited equilibrium binding of [3H]vinblastine to Pgp (Ki of approximately 0.06 microM). Treatment of mice bearing P388/ADR murine leukemia cells with LY335979 in combination with Dox or etoposide gave a significant increase in life span with no apparent alteration of pharmacokinetics. LY335979 also enhanced the antitumor activity of Taxol in a MDR human non-small cell lung carcinoma nude mouse xenograft model. Thus, LY335979 is an extremely potent, efficacious modulator that apparently lacks pharmacokinetic interactions with coadministered anticancer drugs and is, therefore, an exciting new agent for clinical evaluation for reversal of Pgp-associated MDR.
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PMID:Reversal of P-glycoprotein-mediated multidrug resistance by a potent cyclopropyldibenzosuberane modulator, LY335979. 879 88

P-glycoprotein acts as an active drug-efflux pump in multidrug-resistant tumour cells. We studied the capacity of P-glycoprotein to extrude drugs from the cells. For nanomolar concentrations of vinblastine P388/ADR cells, which overexpress P-glycoprotein in the plasma membrane, accumulated vinblastine, at 37 degrees C for 30 min, to a much lower extent than the sensitive cells (P388/S), while in the micromolar range the cellular concentration was similar for both types of cells. When cells were incubated with a low (10 nM) or high concentration (1 microM) of vinblastine while energy deprived, the vinblastine concentration increased only in the resistant cells incubated with the low concentration of vinblastine, and this increased level was lowered to the level under the normal conditions by addition of glucose. In contrast, the cellular concentrations in other cases were increased to the normal level by glucose. After cells were loaded with the low concentration of vinblastine, the cellular vinblastine was extruded more rapidly from the resistant cells than from the sensitive cells. The courses of vinblastine efflux from the cells loaded with the high concentration of vinblastine were similar in both types of cells. NA-382, a reported P-glycoprotein inhibitor, effectively increased the intracellular vinblastine and inhibited the drug efflux only from multidrug-resistant cells, P388/ADR and AH66 cells, which were incubated with the low concentration of vinblastine. Cellular uptake of NA-382 was also less in P388/ADR cells than in P388/S cells in culture with 10 nM but not 1 microM of the agent, and this low level was reversed to the level in the sensitive cells by 10 microM vinblastine. These results indicate that P-glycoprotein as a drug-efflux pump works effectively under low extracellular concentrations of substrates, but does not under the high concentrations.
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PMID:Saturable function of P-glycoprotein as a drug-efflux pump in multidrug-resistant tumour cells. 879 79

We attempted to reverse multidrug resistance (MDR) by treatment with 25-mer antisense phosphorothioate oligonucleotide. The phosphorothioate analogs, the sequences of which are sense or antisense to the initiation codon of mouse mdr1 mRNA, were tested against murine leukemic P388/S and adriamycin-resistant P388/ADR cell lines. A weak inhibitory effect on the growth of P388/S and P388/ADR cells was observed at a sense and antisense oligonucleotide concentration of 30 microM. Using the monoclonal antibody to P-glycoprotein and a flow cytometry technique, we showed that the level of expression of P-glycoprotein in P388/ADR cells treated with antisense oligonucleotide was lower than when treated with sense oligonucleotide. The antisense oligonucleotide potentiated the growth-inhibitory effect of vinblastine on P388/ADR cells, whereas sense oligonucleotide did not. This was accompanied by an increase in vinblastine retention in the cells. The reversal of the resistance by antisense oligonucleotide was increased by the combination with 1 microM verapamil. These results suggest that the antisense oligonucleotide and low dose verapamil may be useful in circumventing the resistance to anticancer drugs of MDR tumors.
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PMID:Reversal of drug sensitivity in MDR subline of P388 leukemia by gene-targeted antisense oligonucleotide. 880 35


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