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)

Multidrug resistance protein (MRP) and P-glycoprotein (Pgp) are both members of the superfamily of ATP binding cassette plasma membrane drug transport proteins, which may be partly responsible for multidrug resistance of tumor cells. Although MRP has been identified as an organic anion transporter and Pgp as a transporter of certain positively charged compounds, there is considerable overlap in resistance spectrum, suggesting that both proteins transport important anticancer agents such as doxorubicin, etoposide, and vincristine. To obtain more insight in the handling of drugs by both proteins, we performed a detailed kinetic analysis of the efflux of calcein-acetoxymethyl ester (CAL-AM), a common neutral substrate for both proteins and compared it with the kinetics of efflux of calcein (CAL) which is only effluxed by MRP. CAL, the hydrolysis product of the nonfluorescent CAL-AM, is negatively charged and highly fluorescent. For this purpose Pgp+ K562/ADR and MRP+ GLC4/ADR tumor cells were incubated with CAL-AM in ATP-rich or ATP-depleted buffer, and the calcein formation was followed in time by fluorescence development. The intracellular CAL could be distinguished from effluxed (extracellular) CAL by addition to the medium of Co2+, which completely quenched the extracellular CAL fluorescence. The results showed that the Vmax for efflux of CAL-AM and CAL by MRP were very similar (1.0-1.2 x 10(5) molecules/cell/s) but that the Km for CAL-AM was much lower (0.05 microM) than for CAL (268 microM). The latter therefore is much less efficiently transported by MRP than CAL-AM. The Km for CAL-AM transport by Pgp (0.12 microM) was similar to that for MRP. Compared to previously published data for anthracyclines, the kinetic data for MRP-mediated CAL-AM pumping are most similar to those for the neutral hydroxydaunorubicin. These data give a quantitative account of transport properties of MRP for two related but differently charged compounds.
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PMID:Kinetic analysis of calcein and calcein-acetoxymethylester efflux mediated by the multidrug resistance protein and P-glycoprotein. 948 70

Previous studies have demonstrated decreased levels of DNA topoisomerase II alpha protein and messenger RNA in the Adriamycin-resistant P388 murine leukemia cell line P388/ADR/7 compared to the sensitive P388/4 cell line. An allelic fusion event involving the topoisomerase II alpha and the retinoic acid receptor a genes has been identified in these cells that probably contributes to the decreased topoisomerase II activity in P388/ADR/7 cells. However, this allelic mutation may be a minor contributor or even incidental to the resistance phenotype, since these cells display other candidate mechanisms of resistance, including increased P-glycoprotein, increased glutathione-S-transferase activity and an increased onset of DNA repair. To establish a role for topoisomerase II alpha in mediating the Adriamycin resistance phenotype, complementation of the mutant allele was attempted by transfecting the murine P388/ADR/7 cells with a human topoisomerase II alpha expression construct under the control of the human metallothionein IIA promoter. The majority of transfected cell lines that were obtained by selection in hygromycin B contained copies of the integrated expression construct that were rearranged. Only two of thirty-two transfected cell lines were found to contain a single, unrearranged copy of the human topoisomerase II alpha cDNA. P388/ADR/7 cell lines carrying an integrated, intact human topoisomerase II alpha expression vector were more sensitive to Adriamycin, daunorubicin, mitoxantrone, and etoposide, but not to actinomycin D and vincristine compared to control cells transfected with vector alone or cell lines with rearranged topoisomerase II alpha expression constructs. These findings suggest that topoisomerase II alpha is a selective and significant contributor to multifactorial resistance.
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PMID:Selective sensitization of adriamycin-resistant P388 murine leukemia cells to antineoplastic agents following transfection with human DNA topoisomerase II alpha. 949 16

The overexpression of two membrane glycoproteins, P-glycoprotein and multidrug-resistance protein (MRP1) is a major cause of resistance to chemotherapeutic agents in the treatment of human cancers. Both proteins confer a similar multidrug-resistant (MDR) phenotype. 99mTc-MIBI, a myocardial imaging agent, which is also useful for the detection of a variety of tumours, has been shown to be a substrate for P-glycoprotein and MRP1. It thus may provide additional information about the P-glycoprotein and MRP1 status of tumour cells. In order to obtain information on the substrate specificity of these proteins, we have studied the transport kinetics of Tc-MIBI in two cell lines, K562/ADR and GLC4/ADR, which overexpress P-glycoprotein and MRP1, respectively. The mean active efflux coefficient ka, which is proportional to the ratio of maximal efflux rate VM to the apparent Michaelis-Menten constant Km, used to characterise the efficiency of the active efflux, was very similar being 1.9 +/- 0.6 x 10(-11) s(-1) x cells x ml and 1.3 +/- 0.5 x 10(-11) s(-1) x cells x ml for drug-resistant K562 and GLC4, respectively. These values are 50-100-times lower than for daunorubicin and other anthracycline derivatives, strongly suggesting that the efficiency of both transporters to pump Tc-MIBI is by far less than that to efflux anthracyclines. Our data show that (a) P-glycoprotein and MRP transporter efficiencies to wash out Tc-MIBI are similar, in spite of a different suspected mechanism of its transport and (b) that both transporters are less efficient to pump Tc-MIBI than to pump anthracyclines (the ka parameter is about 100-times lower for TC-MIBI than for anthracycline).
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PMID:Comparison of the kinetics of active efflux of 99mTc-MIBI in cells with P-glycoprotein-mediated and multidrug-resistance protein-associated multidrug-resistance phenotypes. 952 23

A human stomach-adenocarcinoma cell line (MKN-45) was selected for resistance to Adriamycin by stepwise exposure to increasing concentrations of this agent. The resulting cell line (MKN/ADR) exhibited a high level of cross-resistance to topoisomerase II (topo II)-targeted drugs such as Adriamycin, mitoxantrone, and etoposide but showed no cross-resistance to other chemotherapeutic agents such as cisplatin, carboplatin, 5-fluorouracil, or mitomycin-C. P-glycoprotein encoded by the mdr-1 gene was not overexpressed in the MKN/ADR cell line. The doubling time of the MKN/ADR cell line (2.1 days) increased only slightly as compared with that of the MKN cell line (1.7 days). The patterns of cross-resistance to various chemotherapeutic agents led us to examine the cellular contents of topo II in both the drug-sensitive and the drug-resistant cells. Extractable topo II enzyme activity was 3-fold lower in MKN/ADR cells as compared with the parental MKN cells. Levels of topoisomerase I (topo I) catalytic activity were similar in both wild-type MKN and drug-resistant MKN/ADR cells. Southern-blot analysis of genomic DNA probed with topo IIalpha or IIbeta showed no sign of either gene rearrangement or hypermethylation. Northern-blot analysis revealed that both topo IIalpha and topo IIbeta mRNA transcripts were essentially identical in the MKN and MKN/ADR cells. In contrast, Western-blot analysis revealed an approximately 20-fold lower level of topo IIalpha in drug-resistant cells as compared with drug-sensitive cells, whereas topo IIbeta levels were similar in both lines. Moreover, the amount of in vivo topo IIalpha-DNA covalent complexes formed in the presence of etoposide was also approximately 20-fold lower in drug-resistant cells. No mutation was detected in the promoter region of the topo IIalpha gene in resistant cells as compared with sensitive cells. Thus, low levels of topo IIalpha polypeptide cannot be ascribed to changes in the mRNA levels. Collectively, the data suggest that a quantitative reduction in topo IIalpha may contribute to the resistance of MKN cells to Adriamycin and other topo II-targeted drugs.
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PMID:Reduced activity of topoisomerase II in an Adriamycin-resistant human stomach-adenocarcinoma cell line. 952 30

When five substituents of hapalosin were placed on D-glucose, molecular modeling revealed that the substituents on mimetics 2 and 3 occupy similar spatial positions as the corresponding substituents on hapalosin. Mimetic 3 and all the glucopyranoside intermediates generated in its synthesis were assessed for their ability to reverse multidrug resistance (MDR) mediated by P-glycoprotein (P-gp) or the multidrug resistance-associated protein (MRP). None of the sugar compounds were as effective as hapalosin in inhibiting P-gp in cytotoxicity and drug accumulation assays using MCF-7/ADR cells. By contrast, four D-glucose compounds exhibited similar efficacy as hapalosin in antagonizing MRP in cytotoxicity assays with HL-60/ADR cells.
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PMID:Design, synthesis, and evaluation of the multidrug resistance-reversing activity of D-glucose mimetics of hapalosin. 952 72

Mevalonate pathway inhibitor lovastatin inhibited proliferation of human multidrug-resistant promyelocytic leukemia HL-60/ADR cells in vitro, with MRP-gene coded p190 mediated drug resistance, to a markedly lesser extent than that of the parental drug sensitive HL-60 cells and also that of the other human multidrug resistant (MDR-1, P-glycoprotein) myeloid leukemia cell line HL-60/VCR. The sensitivity of the examined human leukemia cell lines to the cytostatic activity of lovastatin correlated approximately with the potential of lovastatin to induce the characteristic cell cycle alteration (i.e. the accumulation of lovastatin-treated cells in the G0/G1 phase of the cell cycle). The P-glycoprotein positive HL-60/VCR cells and the parental drug sensitive HL-60 cells were more sensitive to this cell cycle alteration than the HL-60/ADR multidrug resistant leukemia cells with MRP drug resistance. Lovastatin (72 hours, 20 micromol) induced apoptosis and cell necrosis in HL-60 cells, apoptosis but not cell necrosis in HL-60/VCR cells and neither apoptosis nor necrosis in HL-60/ADR cells.
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PMID:Human multidrug-resistant (MRP,p190) myeloid leukemia HL-60/ADR cells in vitro: resistance to the mevalonate pathway inhibitor lovastatin. 960 9

We studied the interaction between the multidrug transporter, P-glycoprotein, and two compounds that interact with it: vinblastine, a classical substrate of the pump, and verapamil, a classical reverser. Steady-state levels of accumulation of these two drugs were determined in a multidrug resistant P388 leukemia cell line, P388/ADR. The time course of accumulation of these drugs, and the effect of energy starvation and the presence of chloroquine on the level of their steady-state accumulation were quite disparate. Vinblastine inhibited the accumulation of verapamil whereas it enhanced the accumulation of daunomycin, another classic substrate of P-glycoprotein. Verapamil did not compete with the intracellular binding sites of vinblastine. In all these aspects, vinblastine behaved as a typical substrate of P-glycoprotein but verapamil did not. Our data suggest that verapamil is a reverser of P-glycoprotein but that its intracellular accumulation is not affected by this membrane-bound transporter.
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PMID:Drug accumulation in the presence of the multidrug resistance pump: dissociation between verapamil accumulation and the action of P-glycoprotein. 960 21

Podophyllotoxin and epipodophyllotoxin react with tubulin at the same binding site as colchicine, but in contrast to colchicine, do not appear to exert their cytotoxicities by mechanisms dependent on P-glycoprotein (Pgp) expression. To investigate structural requirements for Pgp recognition a series of podophyllotoxin and epipodophyllotoxin derivatives have been synthesized. Their interactions with the multidrug resistance-related protein Pgp have been studied by evaluating their relative cytotoxicities versus P388-sensitive murine leukemic cells and a classic multidrug-resistant (MDR) Pgp-overexpressing subline (P388/ADR), and their relative tubulin polymerization inhibitory activities against microtubular proteins have been determined. Based on tridimensional structure-activity relationships within this series of compounds, structural requirements for Pgp recognition have been identified. Moreover, proposals are made for extending these criteria to other chemical classes of anticancer drugs.
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PMID:Requirements for P-glycoprotein recognition based on structure-activity relationships in the podophyllotoxin series. 962 71

To develop a functional assay for the activity of the multidrug resistance protein 1 (MRP1), we tested whether carboxyfluorescein (CF) was specifically transported by MRP and whether this transport pump could be specifically blocked by the leukotriene D4 receptor antagonist MK-571. The activity and expression of MRP1 were studied in several tumor cell lines and in leukemic blasts from patients with acute myeloid leukemia (AML). In the MRP1-overexpressing cell line GLC4/ADR and the MRP1-transfected cell line S1(MRP), MK-571 inhibited CF efflux with high factors [45.9+/-5.8 (mean+/-SD) and 14.4+/-3.2, respectively; n=3; efflux-blocking factors are defined as the ratio of the median fluorescence in presence or absence of MK-571] compared with their MRP1 low-expressing counterparts GLC4 (11.5+/-2.7) and S1 (2.8+/-0.4). In 15 AML cases, the CF efflux-blocking factors of MK-571 varied between 1.9 and 5.2. A good correlation was found between MRP1 protein expression and CF efflux-blocking factors of MK-571 (P=0.013, r=0.39). Besides MRP1, MRP2 was demonstrated with reverse transcription-PCR in 40% of the cases. In contrast to the cell lines, MK-571 also inhibited rhodamine 123 (Rh123) efflux in AML samples. On the other hand, PSC833, a P-glycoprotein specific inhibitor, did not modulate the CF efflux but is efficient in blocking Rh123 efflux. This study demonstrates that AML blasts express MRP1 and MRP2 and that MRP1 activity can be determined by a flow cytometric assay using CF and MK-571.
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PMID:Activity and expression of the multidrug resistance proteins MRP1 and MRP2 in acute myeloid leukemia cells, tumor cell lines, and normal hematopoietic CD34+ peripheral blood cells. 967 48

We synthesized seven acyclic ethylenedisulfonamides and twelve cyclic disulfonamides, 1, 5-bis(arenesulfonyl)-1, 3, 5-triazacycloheptanes, and compared their in vitro anti-multidrug resistance effects in P388/ADR multidrug-resistant cells which overexpress the multidrug transporter P-glycoprotein (P-gp). Acyclic disulfonamides with 4-methoxyphenyl, pyridyl, quinolyl, or isoquinolyl groups hardly influenced the sensitivity of P388/ADR cells to vinblastine (VLB), and cyclic disulfonamides with these aryl groups only slightly increased the sensitivity to VLB. Acyclic or cyclic disulfonamides with 4-chlorophenyl or naphthyl groups moderately potentiated the effect of VLB. The maximum effect was observed with 1, 5-bis(1-naphthale-nesulfonyl)-1, 3, 5-triazacycloheptan (B3). B3 enhanced the effects of vincristine, adriamycin, daunomycin and actinomycin D in P388/ADR cells, but not in sensitive P388 cells. B3 increased intracellular concentrations of VLB and adriamycin in P388/ADR cells. The expression of P-gp in P388/ADR cells was not affected by cultivation with B3 for 72 hours. These results indicated that the anti-multidrug resistance activities of B3 were dependent on its inhibitory effect on P-gp.
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PMID:In vitro anti-multidrug resistance activities of acyclic and cyclic disulfonamides in murine leukemia cells. 971 92


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