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

---

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

An actinomycin D selected, multidrug-resistant (MDR) hamster CHO subline showed strong expression of the P-glycoprotein and sorcin genes together with several other alterations such as a: (i) reduced growth rate, (ii) lowered topoisomerase II, (iii) lowered glutathione-S-transferase-P gene expression, and (iv) the emergence of a 15.5 kDa protein. Besides high resistances to adriamycin, actinomycin D, and vincristine, we observed a lowered sensitivity towards bleomycin, a rather hydrophilic drug usually not involved in P-glycoprotein associated MDR. Moreover, the MDR subline showed a pronounced collateral (enhanced) sensitivity towards the sterically pure dihydropyridine anticancer drug dexniguldipine-HCl (B859-35) preventing its characterization for MDR modulation here. At a non-cytotoxic dose (10 microM) the immunosuppressive cyclic peptide cyclosporin A completely abolished the resistance to vincristine, partially reversed the resistance to teniposide and strongly enhanced the sensitivity towards bleomycin, while not influencing the drug sensitivities of the parental cell line. Buthionine sulfoximine (BSO), an agent depleting cellular glutathione levels, distinctly increased the sensitivity towards teniposide at nontoxic doses (50 microM) exclusively in the MDR subline, while it did not alter vincristine or bleomycin cytotoxicity.
...
PMID:MDR hamster cells exhibiting multiple altered gene expression: effects of dexniguldipine-HCl (B859-35), cyclosporin A and buthionine sulfoximine. 128 2

Although cellular drug resistance is considered to be an important cause of the poor prognosis of children with relapsed acute lymphoblastic leukaemia (ALL), the knowledge of drug resistance in these patients is very limited. Different aspects of drug resistance were studied in 17 children with relapsed ALL. The in vitro sensitivity profile was determined using the MTT assay. Cells from relapsed children were significantly more resistant to 6-thioguanine, prednisolone, cytosine arabinoside, daunorubicin (DNR), mustine-HCl and mafosfamide but not to L-asparaginase and vincristine (VCR) than cells from 41 children with ALL at initial diagnosis. Some relapsed patients showed a general drug resistance while others were resistant to only 1-3 drugs. The relevance of the multidrug resistance (MDR) model was analysed: In all DNR- and VCR resistant cases a co-resistance to drugs not involved in the MDR model was found. P-glycoprotein was not detected in any of 28 untreated and 14 relapsed samples tested. VCR- and DNR accumulation in the most resistant cells were not lower than in sensitive cells. Resistance modifiers did not potentiate the cytotoxicity of VCR and DNR. We conclude that resistance to anthracyclines and vinca alkaloids in childhood relapsed ALL is not due to P-glycoprotein mediated MDR. Different types of drug resistance varying from a resistance to only one drug to a general chemoresistance, can be detected in children with relapsed ALL. VCR and L-asparaginase seemed to be only infrequently involved in drug resistance. Knowledge of drug resistance might lead to more effective and less toxic therapies for children with relapsed ALL.
...
PMID:Different types of non-P-glycoprotein mediated multiple drug resistance in children with relapsed acute lymphoblastic leukaemia. 135 Feb 7

Plasma membranes were prepared from the P-glycoprotein expressing human breast cancer cell line MCF-7 ADR. [3H]Vinblastine bound to these membranes saturably with a Bmax of 24 pmol/mg of protein and KD of 23 nM. In contrast, membranes from the parent cells MCF-7 WT, which do not express P-glycoprotein, did not bind [3H]vinblastine with high affinity. Cytotoxics known to be transported by P-glycoprotein inhibited the binding of [3H]vinblastine, as did multidrug reversing agents including the 1,4-dihydropyridine, dexniguldipine-HCl (Ki, 15 nM). In dissociation kinetic experiments, dexniguldipine-HCl accelerated the dissociation of [3H]vinblastine from P-glycoprotein, indicating a negative heterotropic allosteric mechanism of action through a drug binding site distinct from that of vinblastine. Other 1,4-dihydropyridines tested also accelerated [3H]vinblastine dissociation from P-glycoprotein, however, multidrug reversing drugs of different chemical classes, including quinidine, verapamil and cyclosporin A did not. These results suggest that P-glycoprotein of MCF-7 ADR cell membranes possesses at least two drug acceptor sites which are allosterically coupled: receptor site-1 which binds vinca alkaloids, and receptor site-2 which binds 1,4-dihydropyridines such as dexniguldipine-HCl, which had the highest affinity of the tested derivatives.
...
PMID:Allosteric regulation of [3H]vinblastine binding to P-glycoprotein of MCF-7 ADR cells by dexniguldipine. 759 47

P-glycoprotein is an energy-dependent drug extrusion pump for a variety of anticancer drugs and is involved in the development of multidrug resistance in cancer. Dexniguldipine-HCl is a potent chemosensitizer for P-glycoprotein-mediated multidrug resistance in vitro, and clinical phase I/II trials are underway. To investigate the mechanisms of chemosensitization and to identify the binding sites for dexniguldipine-HCl on target proteins involved in chemosensitization, [3H]B9209-005, an azido derivative of dexniguldipine-HCl, was synthesized and used as a photoaffinity ligand. In two models of multidrug resistance reversal, i.e., sensitization to vincristine and modulation of rhodamine-123 uptake, B9209-005 and dexniguldipine-HCl showed identical biological activities. Photoaffinity labeling experiments with [3H]B9209-005 in cell membranes from multidrug-resistant CCRF ADR-5000 cells, in comparison with labeling experiments with [3H]azidopine (an established photoaffinity ligand for P-glycoprotein), showed that [3H]B9209-005 labeled two proteins, with apparent molecular masses of 170 and 95 kDa. The pharmacological specificity of labeling was demonstrated by inhibition of photoincorporation by several cytostatic drugs transported by P-glycoprotein, as well as by chemosensitizers. Immunoprecipitation of the labeled proteins with the P-glycoprotein-specific monoclonal antibody C 219 and with a site-directed polyclonal antibody to the amino-terminal sequence of P-glycoprotein (amino acids 389-406) identified these proteins as intact P-glycoprotein and the amino-terminal fragment thereof. No specific labeling was obtained in the drug-sensitive parent cell line CCRF-CEM, which is devoid of significant P-glycoprotein expression. Maximal labeling of 17 pmol of the 170-kDa protein/mg of crude membrane protein was obtained. The affinity of [3H]B9209-005 for binding to and photoincorporation into P-glycoprotein was 5-fold greater than that of [3H]azidopine, and photoincorporation of [3H]B9209-005 showed a different photoincorporation pattern, compared with [3H]azidopine, in that the latter compound was incorporated specifically into the carboxyl-terminal 55-kDa fragment of P-glycoprotein. In contrast to [3H]azidopine, no specific labeling of this fragment was obtained with [3H]B9209-005, indicating different binding sites for or different photoincorporation of the two dihydropyridine ligands. Because B9209-005 carries the photoreactive azido group in the dihydropyridine moiety, whereas the azido group of azidopine is located in the side chain, these results suggest that the dihydropyridine moiety of the two compounds probably interacts with the amino-terminal part of P-glycoprotein, whereas the side chains react preferentially with the carboxyl-terminal 55-kDa fragment.(ABSTRACT TRUNCATED AT 400 WORDS)
...
PMID:B9209-005, an azido derivative of the chemosensitizer dexniguldipine-HCl, photolabels P-glycoprotein. 762 71

Cell membranes were prepared from the multidrug resistant, P-glycoprotein expressing human lymphoblastoid cell line CCRF-ADR 5000. The P-glycoprotein of these membranes possessed high affinity binding sites for [3H]vinblastine, with a Kd of 8 +/- 2 nM and Bmax of 17 +/- 8 pmol/mg of protein. The binding of [3H]vinblastine to P-glycoprotein was not ATP-dependent, and was inhibited by cytotoxic drugs with the following potency order; vincristine > doxorubicin > etoposide. The 1,4-dihydropyridine and multidrug resistance reversing agent, dexniguldipine-HCl, inhibited binding with a Ki value of 37 nM. The multidrug resistance reversing agent cyclosporin A, and the cytotoxics doxorubicin and etoposide did not alter the kinetics of [3H]vinblastine dissociation from P-glycoprotein; however, the 1,4-dihydropyridines dexniguldipine-HCl and nicardipine accelerated dissociation of [3H]vinblastine. These data suggest that P-glycoprotein possesses at least two allosterically coupled drug acceptor sites; receptor site 1 which binds vinblastine, doxorubucin, etoposide and cyclosporin A, and receptor site 2 which binds dexniguldipine-HCl and other 1,4-dihydropyridines.
...
PMID:Dexniguldipine-HCl is a potent allosteric inhibitor of [3H]vinblastine binding to P-glycoprotein of CCRF ADR 5000 cells. 770 62

It has previously been shown that dexniguldipine-HCl (B8509-035) is a potent chemosensitizer in multidrug resistant cells [Hofmann et al., J Cancer Res Clin Oncol 118: 361-366, 1992]. It is shown here that dexniguldipine-HCl causes a dose-dependent reduction of the labeling of the P-glycoprotein by azidopine, indicating a competition of dexniguldipine-HCl with the photoaffinity label for the multidrug resistance gene 1 (MDR-1) product. Exposure to dexniguldipine-HCl results in a dose-dependent accumulation of rhodamine 123 in MDR-1 overexpressing cells. In the presence of 1 microM dexniguldipine-HCl, rhodamine 123 accumulated in multidrug resistant cells to similar levels as in the sensitive parental cell lines. At this concentration, dexniguldipine-HCl enhances the cytotoxicities of Adriamycin and vincristine. The resistance modulating factors (RMF), i.e. IC50 drug/IC50 drug + modulator, were found to be proportional to the expression of MDR-1, ranging from 8 to 42 for Adriamycin and from 16 to 63 for vincristine. Transfection with the MDR-1 gene was found to be sufficient to sensitize cells to the modulation by dexniguldipine-HCl. The compound does not affect the expression of the MDR-1 gene. Dexniguldipine-HCl has no effect on a multidrug resistant phenotype caused by a mutation of topoisomerase II. It is concluded that dexniguldipine-HCl modulates multidrug resistance by direct interaction with the P-glycoprotein.
...
PMID:Mechanism of action of dexniguldipine-HCl (B8509-035), a new potent modulator of multidrug resistance. 788 74

Multidrug-resistant tumor cells can be resensitized by combined application of the selecting cytostatic drug and a chemosensitizer, such as cyclosporin A (CsA) or a calcium channel blocker. Since clinical trials on the circumvention of multidrug resistance (MDR) with chemosensitizers report disparate results, we investigated whether tumor cells of the MDR phenotype can develop additional resistance to the cytostatic chemosensitizer combination. Thus, the Adriamycin(ADR)-selected, P-glycoprotein-positive MDR Friend leukemia cell line F4-6RADR was exposed to stepwise increased concentrations of CsA at a constant level of 0.05 microgram/ml ADR. The initial CsA concentration (plus 0.05 microgram/ml ADR) to inhibit cell growth of F4-6RADR cells by 50% (IC50) was 0.04 microgram/ml. By continuous incubation for more than 6 months, the IC50 for CsA (at constant ADR) was elevated to 3.6 micrograms/ml (90-fold), thus generating the variant F4-6RADR-CsA. The F4-6RADR-CsA cells were cross-resistant for cyclosporin H (CsH), a non-immunosuppressive derivative of CsA. As shown by immunocytochemistry as well as by the polymerase chain reaction and by Western blotting including densitometry, P-glycoprotein was preserved in the F4-6RADR-CsA variant and was expressed at a 4-fold higher level than in F4-6RADR cells. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis analysis could detect no new proteins in F4-6RADR-CsA as compared to F4-6RADR. Interestingly, resistance of F4-6RADR-CsA cells remained reversible for the calcium antagonists verapamil and dihydropyridine B859-35 (dexniguldipine-HCl), indicating that CsA and these compounds interfere with the P glycoprotein function by different pharmacodynamic mechanisms. Transport studies with [14C]ADR, performed in the presence and absence of chemosensitizers, confirmed the good correlation of P-glycoprotein function with the pattern of resistance found in proliferation assays. Cellular accumulation of [3H]cyclosporin was reduced to 71% of that of the F4-6 controls in F4-6RADR-CsA cells, but remained at the level of controls in F4-6RADR cells. Results indicate that increased amounts of the P-glycoprotein--besides other, perhaps more important mechanisms that are as yet unknown--partially mediate CsA resistance in F4-6RADR-CsA cells. We have designated this new form of resistance "secondary combined resistance" (SCR). The results suggest that at least some clinical cases of insensitivity to chemosensitizers or of relapse after reversing therapy could be explained by SCR, and that resensitizing treatment of tumor patients should be based on the consideration of several chemosensitizers of different pharmacodynamics.
...
PMID:Secondary combined resistance to the multidrug-resistance-reversing activity of cyclosporin A in the cell line F4-6RADR-CsA. 790 33

A variety of agents are capable of overcoming P-glycoprotein-mediated multidrug resistance (MDR) in vitro. However, the clinical potential of these compounds is often limited due to high plasma protein binding. We compared the efficacy of several MDR-reversing compounds in serum-free culture medium and under serum conditions by means of a functional assay. Using flow cytometry the efflux of the fluorescent dye rhodamine 123 (Rh123) was measured from normal peripheral blood CD8+ T-lymphocytes which express low levels of P-glycoprotein. Inhibition of Rh123 efflux by R-verapamil, dexnigludipine-HCl, cyclosporin A, SDZ PSC833 and the protein kinase C (PKC) inhibitor CGP 41251 was determined in serum-free medium and in serum at concentrations from 0.1 to 50 mumol/l. With the exception of SDZ PSC833 all MDR modulators showed an insufficient or suboptimal modulation of P-glycoprotein under serum conditions at concentrations achievable in vivo. The highest potency under serum conditions demonstrated SDZ PSC833: even at a concentration of 0.5 mumol/l a sufficient inhibitory effect was observed. Subsequently this approach was applied to patients suffering from B-cell chronic lymphocytic leukaemia (B-CLL; n = 3) and acute myeloid leukaemia (AML; n = 2) which were positive in the Rh123 efflux assay. As for normal CD8+ T-lymphocytes, much higher drug concentrations were required under serum conditions to effectively inhibit Rh123 efflux from the leukaemic cells. Thus the interpretation of results of clinical 'modulator' trials should consider the decreased bioavailability of MDR-reversing agents.
...
PMID:Decreased potency of MDR-modulators under serum conditions determined by a functional assay. 855 69

Inhibition of protein kinase C (PKC) is discussed as a new approach for overcoming multidrug resistance (MDR) in cancer chemotherapy. For evaluation of this concept we applied the bisindolylmaleimide GF 109203X, which shows a highly selective inhibition of PKC isozymes alpha, beta 1, beta 2, gamma, delta and epsilon in vitro. The efficacy of this compound in modulation of MDR was examined using several P-glycoprotein (P-gp)-overexpressing cell lines including a MDR1-transfected HeLa clone, and was compared with the activities of dexniguldipine-HCI (DNIG) and dexverapamil-HC1 (DVER), both of which essentially act via binding to P-gp. As PKC alpha has been suggested to play a major role in P-gp-mediated MDR, cell lines exhibiting different expression levels of this PKC isozyme were chosen. On crude PKC preparations or in a cellular assay using a cfos(-711)CAT-transfected NIH 3T3 clone, the inhibitory qualities of the bisindolylmaleimide at submicromolar concentrations were demonstrated. At up 1 microM final concentrations of the PKC inhibitor GF 109203X, a concentration at which many PKC isozymes should be blocked substantially, no cytotoxic or MDR-reversing effects whatsoever were seen, as monitored by 72 h tetrazolium-based colorimetric MTT assays or a 90 min rhodamine 123 accumulation assay. Moreover, depletion of PKC alpha by phorbol ester in HeLa-MDR1 transfectants had no influence on rhodamine 123 accumulation after 24 or 48 h. MDR reversal activity of GF 109203X was seen at higher final drug concentrations, however. Remarkably, [3H]vinblastine-sulphate binding competition experiments using P-gp-containing crude membrane preparations demonstrated similar dose dependencies as found for MDR reversion by the three modulators, i.e. decreasing efficacy in the series dexniguldipine-HCl > dexverapamil-HCl > GF 109203X. Similar interaction with the P-gp in the micromolar concentration range was revealed by competition of GF 109203X with photoincorporation of [3H]azidopine into P-gp-containing crude membrane preparations. No significant effect of the PKC inhibitor on MDR1 expression was seen, which was examined by cDNA-PCR. Thus, the bisindolylmaleimide GF 109203X probably influences MDR mostly via direct binding to P-gp. Our work identifies the bisindolylmaleimide GF 109203X as a new type of drug interacting with P-gp directly, but does not support the concept of a major contribution of PKC to a P-gp-associated MDR, at least using the particular cellular model systems and the selective, albeit general, PKC inhibitor GF 109203X.
...
PMID:Effects of the selective bisindolylmaleimide protein kinase C inhibitor GF 109203X on P-glycoprotein-mediated multidrug resistance. 882 55

The thioether phospholipid ilmofosine (BM 41 440) is a new anti-cancer drug presently undergoing phase II clinical trials. Because resistance to anti-tumour drugs is a major problem in cancer treatment, we investigated the resistance of different cell lines to this compound. Here we report that the multidrug-resistant cell lines MCF7/ADR, CCRFNCR1000, CCRF/ADR500, CEM/VLB100 and HeLa cell lines transfected with a wild-type and mutated (gly/val185) multidrug resistance 1 gene (MDR1) are cross-resistant to ilmofosine compared with the sensitive parental cell lines. In CEMNM-1 cells, in which the resistance is associated with an altered topoisomerase II gene, no cross-resistance to ilmofosine was observed. Ilmofosine is not capable of modulating multidrug resistance and neither does it reduce the labelling of the P-glycoprotein (P-gp) by azidopine nor alter ATPase activity significantly. The resistance to ilmofosine in multidrug-resistant CCRF/VCR1000 cells cannot be reversed by the potent multidrug resistance modifier dexniguldipine-HCI (B8509-035). A tenfold excess of ilmofosine does not prevent the MDR-modulating effect of dexniguldipine-HCl. Treatment of cells with ilmofosine does not alter the levels of MDR1 mRNA. Long-term treatment of an ilmofosine-resistant Meth A subline with the drug does not induce multidrug resistance, indicating that ilmofosine does not increase the level of P-gp. Determination of the MDR2 mRNA levels in the cells revealed that the resistance pattern to ilmofosine is not correlated with the expression of this gene. It is concluded, therefore, that multidrug-resistant cells are cross-resistant to ilmofosine and that the compound is not a substrate of Pgp. No association between the expression of the MDR2-encoded P-gp and resistance to ilmofosine was observed. It is supposed that MDR1-associated alterations in membrane lipids cause resistance to ilmofosine.
...
PMID:Resistance to the new anti-cancer phospholipid ilmofosine (BM 41 440). 932 44


1 2 3 Next >>

---