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)

The in vitro cytotoxic effects of docetaxel (Taxotere; RP56976, NSC688503) proved both time and concentration dependent. Amongst thirteen human cell lines from various tumor types, exposure to increasing concentrations of docetaxel over 24 hrs resulted in a plateau-shaped dose response curve, suggesting that increased cell kill becomes more dependent on increased exposure duration than on concentration. IC50 concentrations (reducing survival by 50%) ranged from 0.13-3.3 ng/ml, with three neuroblastoma lines proving most sensitive and three breast and two colon carcinoma lines showing least sensitivity. There was significant cross-resistance to docetaxel in the classic multidrug resistant (MDR) Chinese hamster ovarian (CHO) CHRC5 line and the human lymphoblastoid CCRF-CEMVLB1000 line, as well as in two vincristine (VCR)-selected MDR MCF-7 sublines. All four of these MDR sublines overexpress P-glycoprotein (Pgp), as did a 6-fold docetaxel-selected resistant CHO subline. As an apparent corollary, in two human teratoma lines selected for etoposide resistance and showing some cross-resistance to VCR and in two CHO sublines expressing low levels of VCR resistance, yet all proving Pgp positive, no docetaxel cross-resistance was identified. Verapamil modulated docetaxel resistance only in sublines expressing resistance to the drug and overexpressing Pgp. Four other human tumor sublines selected for resistance to 5-fluorouracil, cisplatin or teniposide, showed a lack of cross-resistance to docetaxel. Furthermore, cross-resistance to docetaxel was not apparant in four epipodophyllotoxin-selected resistant sublines with alterations in topoisomerase II, indicating its effectiveness against tumor cells expressing the topoisomerase II-related MDR phenotype. Our observation that docetaxel cross-resistance was not automatically expressed by classic MDR tumour cells appears of interest and of potential clinical relevance.
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PMID:Differential cytotoxic effects of docetaxel in a range of mammalian tumor cell lines and certain drug resistant sublines in vitro. 789 35

A single amino acid substitution, Gly185-->Val, in the human P-glycoprotein (Pgp) was previously shown to cause an altered pattern of drug resistance in cell lines transfected with the MDR1 cDNA carrying this mutation. To further define the function of amino acid 185 in the Pgp, the wild-type and the mutant Val185 Pgps were expressed in Sf9 insect cells, and their biochemical properties were compared. Verapamil- and colchicine-stimulated ATPase activities were markedly increased with concomitant increase in affinity for these compounds with Gly185-->Val substitution in the Pgp. However, the vinblastine-stimulated ATPase activities of the wild-type and Val185 Pgps were nearly identical. Because transport substrate-induced ATP hydrolysis is generally thought to reflect transport function, these data suggest that colchicine and verapamil are transported at an increased rate with Gly185-->Val substitution in the Pgp. These results also indicate that amino acid 185 is involved in verapamil and colchicine, but not in vinblastine, binding/transport. Kinetic analyses indicate that cyclosporin A, an inhibitor of Pgp, binds to the verapamil and vinblastine binding/transport site(s) in the Pgp. Taken together, the results presented herein reveal that the verapamil and vinblastine binding/transport site(s) are in close proximity and that the cyclosporin A binding site spans the common region of these two drug binding/transport site(s) in the Pgp molecule.
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PMID:Mutation of glycine 185 to valine alters the ATPase function of the human P-glycoprotein expressed in Sf9 cells. 789 10

A rat colon carcinoma cell line, CC531, was exposed to stepwise increasing concentrations of colchicine. A cell line, CC531mdr+, which grows in the presence of 0.2 microM of colchicine was obtained. A revertant cell line, CC531rev was isolated upon colchicine withdrawal. The CC531mdr+ displayed a multidrug-resistant phenotype. Marked resistance to the selecting agent colchicine, was found (RF = 37.5) as well as to vinblastine (RF = 11.3) and actinomycin D (RF = 2.6). Cross resistance to doxorubicin (RF = 8) and daunorubicin (RF = 13.3) was demonstrated. Verapamil was able to reverse drug resistance to colchicine and daunorubicin. The revertant cell line, CC531rev, showed increased sensitivity to colchicine (RF = 0.43), vinblastine (RF = 0.13), doxorubicin (RF = 0.28) and daunorubicin (RF = 0.56). Marked cross resistance to cis-platinum (RF = 6.9) was also induced in CC531mdr+ and was maintained in CC531rev. We conclude that CC531 displays an intrinsic low-level multidrug-resistant phenotype, which was amplified in the CC531mdr+ variant. This correlates with a higher level of expression of P-glycoprotein. CC531rev lacks the multidrug-resistant phenotype and can be used as the drug-sensitive counterpart of the latter two cell lines. Furthermore, it has been shown that in these cell lines cis-platinum resistance is mediated through a mechanism independent of the multidrug-resistant phenotype, since the revertant cell line CC531rev has lost the multidrug-resistant phenotype while retaining the concomitantly induced cis-platinum resistance of the multidrug-resistant variant CC531mdr+.
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PMID:Multidrug resistance in rat colon carcinoma cell lines CC531, CC531mdr+ and CC531rev. 790 65

Verapamil, cyclosporin A (CsA), the cyclosporin derivative SDZ PSC 833 and the novel cyclopeptolide SDZ 280-446 were tested for their capacity to chemosensitize a P-glycoprotein (Pgp)-expressing multi-drug resistant (MDR) variant of the CEM human T lymphoblastoid cell subline (CCRF ACTD 400+). That MDR-CEM cell subline had been previously selected for MDR by actinomycin D and displayed a very high resistance phenotype: 3700-fold for actinomycin D, 3900-fold for vincristine, 1200-fold for taxol, 1000-fold for daunomycin (DAU) and 400-fold for colchicine. Interestingly, these MDR-CEM cells displayed little chemosensitization by resistance-modulating agents (RMA) which presumably work by inhibiting Pgp function. These MDR-CEM cells displayed virtually no chemosensitization by 1 microM verapamil or 1 microgram/ml (about 0.8 microM) CsA, whereas their chemosensitization for different anti-cancer drugs (ACD) was rather stable (from 51- to 82-fold) with 1 microgram/ml (about 0.8 microM) SDZ 280-446, while being very unbalanced (from 5- to 38-fold) with 1 microgram/ml (about 0.8 microM) SDZ PSC 833. Exposure of the MDR-CEM cells to Pgp-directed RMAs, during their loading with DAU (DAU-loading phase), hardly restored DAU retention: SDZ 280-446 being as poorly active as SDZ PSC 833, and about only 3- and 4-fold more active than CsA and verapamil. In contrast, SDZ PSC 833 treatment of human MDR-KB and MDR-LoVo cell lines under the same conditions could restore most or all the DAU retention shown by the parental (Par) cells, in spite of their high level of resistance. By keeping the MDR-CEM cells in the presence of RMA throughout the experiment (both DAU-loading and DAU-efflux phases), a better DAU retention could be restored by the different RMAs used, their order of relative restoration activity being SDZ 280-446 3- to 4-fold > SDZ PSC 833 3- to 10-fold > CsA 2- to 4-fold > verapamil. Nevertheless, the level of DAU retention restored in the MDR-CEM cells reached a plateau at 50% of the Par-CEM cell level. Therefore, although the MDR-CEM cells expressed easily detectable membranous Pgp molecules and probably used them for DAU efflux, they displayed an additional efflux mechanism that was not sensitive to the Pgp inhibitors.
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PMID:Atypical multi-drug resistance (MDR): low sensitivity of a P-glycoprotein-expressing human T lymphoblastoid MDR cell line to classical P-glycoprotein-directed resistance-modulating agents. 790

The interaction of rat renal P-glycoprotein with various drugs and a hydrophobic component found in rat urine was studied to gain an understanding of both its transport function in kidney and its potential role in drug secretion and drug-induced nephrotoxicity. Rat kidney brush-border membranes (BBM) were photolabeled with [3H]azidopine, a calcium-channel blocker that covalently labeles P-glycoprotein. P-glycoprotein was immunoprecipitated with a rabbit polyclonal antibody against the human MDR1 protein (multidrug resistance gene class 1). The amount of [3H]azidopine incorporated into P-glycoprotein was quantitated following gel electrophoresis and fluorography. Photolabeling inhibition assays were conducted with a panel of drugs known to interact with P-glycoprotein in multidrug-resistant cells. Verapamil or quinidine [half-maximal inhibition constant (K0.5) = 1 microM], vinblastine (K0.5 = 3 microM), and doxorubicin or daunomycin (K0.5 = 10 microM) all blocked [3H]azidopine photolabeling of renal P-glycoprotein. Of the drugs tested, the immunosuppressant drug, cyclosporin A, interacted with kidney P-glycoprotein with the highest affinity (K0.5 = 50 nM). However, the cardiac glycoside, digoxin, failed to inhibit P-glycoprotein photolabeling. A hydrophobic rat urine extract prepared by reverse-phase chromatography also blocked photolabeling of renal P-glycoprotein. Our current hypothesis is that various drugs may inhibit urinary excretion of an endogenous substrate by virtue of their ability to bind with high affinity to P-glycoprotein. A hypothesis of drug-induced nephrotoxicity based on the interaction of various compounds like cyclosporin A with P-glycoprotein is presented.
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PMID:Interaction of rat kidney P-glycoprotein with a urinary component and various drugs including cyclosporin A. 790 14

Multidrug-resistance of the tumor cells is the main cause for failure of chemotherapy. Such resistance is correlated to P-glycoprotein 170, which can pump the chemotherapeutic agent out of the tumor cells. This action could be reversed by verapamil through competition for closely related binding sites on P-glycoprotein. Twenty-four postoperative cases of superficial bladder tumors were treated by intravesical instillation of combined adriamycin and verapamil, and they were followed up for 17-35 months (average 24.5 months). Two cases (8.7%) had recurrence. NO marked toxicity and side-effects were observed. Verapamil working as a drug-resistance reversing agent might be used in some other tumors not sensitive to chemotherapy.
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PMID:[Intravesical instillation of combined adriamycin and verapamil in preventing recurrence of superficial bladder tumor]. 790 17

P-glycoprotein was purified from multidrug-resistant Chinese hamster ovary CHRB30 cells by a combination of anion exchange and immunoaffinity chromatography. The P-glycoprotein was about 90% pure and had a Vmax for ATP hydrolysis in detergent solution of 321 nmol/min/mg with a Km of 0.94 mM. The ATPase activity was inhibited by low concentrations of vanadate and N-ethylmaleimide, but unaffected by azide or ouabain. When the purified P-glycoprotein was reconstituted into phospholipid bilayer membranes, the ATPase activity became highly stimulated by several chemosensitizers and drugs involved with multidrug resistance. Verapamil, a potent chemosensitizer, increased the Vmax for ATP hydrolysis by 22-fold and the Km for ATP by 5.4-fold. This effect of verapamil on P-glycoprotein has not previously been observed. These results demonstrate that purified P-glycoprotein has an intrinsic ATPase activity with unique properties. This activity appears sufficient to account for the ATP-dependent reduction in intracellular drug accumulation of P-glycoprotein-expressing multidrug-resistant cells.
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PMID:ATPase activity of purified and reconstituted P-glycoprotein from Chinese hamster ovary cells. 790 70

Verapamil-stimulated ATP hydrolysis by Chinese hamster P-glycoprotein in plasma membranes was shown to occur at a site(s) which is conformationally flexible and of relatively low affinity and specificity. Such properties distinguish P-glycoprotein from other transport ATPases. 8-Azido-ATP and 2-azido-ATP were excellent substrates, confirming that both analogs are suitable photoaffinity labels for investigating the catalytic site(s). Inactivation of ATPase activity occurred coincident with covalent incorporation of approximately two 8-azido-ATP/P-glycoprotein, with the incorporated analog distributed equally between N- and C-terminal halves of the molecule. N-Ethylmaleimide potently inactivated in an ATP-protected, dithiothreitol-irreversible manner, with maximal inactivation occurring coincident with incorporation of approximately two N-ethyl-maleimide/P-glycoprotein. The critical catalytic site sulfhydryls were shown to be located equally in N- and C-terminal halves of the molecule. Sulfhydryl-substituted purines also gave substantial inhibition of P-glycoprotein ATPase activity, which was dithiothreitol reversible. The data provide guidelines for beginning investigation of catalytic site architecture by protein chemistry approaches.
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PMID:Covalent inhibitors of P-glycoprotein ATPase activity. 790 96

P-glycoprotein, a multidrug transporter protein, exists in the brain capillary endothelium. To study the function of P-glycoprotein in brain capillary endothelium as a barrier against cyclosporin A, we examined the interaction of cyclosporin A with P-glycoprotein expressed in cultured brain capillary endothelial cells (MBEC4). P-glycoprotein of MBEC4 specifically bound [125I]iodoaryl azidoprazosin, and the binding was inhibited by cyclosporin A and vincristine. Intracellular accumulation of cyclosporin A in MBEC4 was about one-third the amount accumulated in mouse aortic endothelial cells (MAEC3), a cell line that did not express P-glycoprotein. The reduced accumulation of cyclosporin A in MBEC4 was increased by verapamil, a competitive inhibitor of transport function of P-glycoprotein. Cyclosporin A was preferentially transported from basal to apical side when the cell monolayer of MBEC4 was formed; however this transendothelial transport was not observed across cell monolayer of MAEC3. Verapamil inhibited the transendothelial transport of cyclosporin A across the MBEC4 monolayer. Thus P-glycoprotein in brain capillary endothelium could transport cyclosporin A across the endothelium from the basal to the apical side. These observations suggest that P-glycoprotein is involved in the complex function of the blood-brain barrier as a secretory detoxifying transporter of cyclosporin A.
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PMID:Transport of cyclosporin A across the brain capillary endothelial cell monolayer by P-glycoprotein. 791 24

The relationship between multidrug resistance (MDR) P-glycoprotein expression and swelling-activated Cl- and K+ conductance was investigated in mouse NIH/3T3 fibroblasts and their colchicine-selected counterparts (COL1000, high P-glycoprotein). Whole cell patch-clamp and isotopic flux experiments confirmed that swelling-activated Cl- currents were induced by 20-30% bath dilution only in the MDR-expressing cell line. However, at bath dilutions > 30%, both cell lines developed Cl- currents that reached similar large magnitudes at higher dilution levels. Thus the apparent absolute difference in cell lines at lower dilutions is due to a shift in the response curve relating hypotonicity to Cl- conductance. At all dilutions and in both cell lines, the swelling-activated Cl- currents were outwardly rectifying, active at negative cell voltages, and inactivated at positive voltages. Verapamil (100 microM) and 1,9-dideoxyforskolin (100 microM), which inhibit P-glycoprotein drug transport, did not significantly inhibit the swelling-activated Cl- conductance efflux in the COL1000 cells also showed a leftward shift in the response curve to hypotonicity. These results indicate that response curve to hypotonicity. These results indicate that colchicine-selection for increased P-glycoprotein expression did not lead to the expression of swelling-activated Cl- channels, but instead enhanced a step in the pathway from bath dilution to regulatory volume decrease that is common to both K+ and Cl- channels.
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PMID:Selection for MDR1/P-glycoprotein enhances swelling-activated K+ and Cl- currents in NIH/3T3 cells. 791 92


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