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)

Continuous monitoring of fluorescence (CMF) has been used to examine doxorubicin efflux from intact human myeloma cells. The time resolution of these measurements has enabled detailed comparison of the initial rates of efflux for the drug-sensitive myeloma line RPMI 8226 and a series of sequentially derived multidrug-resistant (MDR) lines expressing different amounts of human MDR protein (P-glycoprotein). Cells that are 3-, 10-, 60-, or 120-fold resistant to doxorubicin export approximately 10, 20, 30, or 33% more doxorubicin than the parental sensitive cells, respectively, when all are preloaded to the same level of total intracellular drug. Remarkably, however, when cells are loaded to the same level of exchangeable drug the initial rates of efflux are found to be virtually identical. This agreement between rates is apparently not dependent on the drug concentration. Approximately 50% of the increase in the steady-state level of doxorubicin efflux for the resistant cells is abolished upon glucose starvation. However, surprisingly, the apparent initial rates of efflux from the treated and untreated cells are found to be virtually the same. Pretreatment of the resistant cells with verapamil reduces the steady-state level of efflux but increases the apparent initial rate at some concentrations. Conversely, vincristine does not alter steady state but slows the initial rate of efflux from both sensitive and resistant cells by approximately the same extent. Finally, quite interestingly, a nearly linear relationship between pHi and relative steady state of efflux is found for the series of cell lines. These data are interpreted in terms of existing models for MDR.
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PMID:Analysis of the steady-state and initial rate of doxorubicin efflux from a series of multidrug-resistant cells expressing different levels of P-glycoprotein. 136 58

Induction of P-glycoprotein-related multi-drug-resistance (MDR) has been shown in normal and malignant tissues to result from environmental stresses such as heat shock, exposure to carcinogens or X-ray irradiation. To identify conditions under which MDR is enhanced during anti-neoplastic chemotherapy, a cell line showing low-level intrinsic MDR was investigated. In the pleural mesothelioma cell line, PXF1118, less than 1% of cells expressed P-glycoprotein (P-gp), as shown by immunocytochemical staining with monoclonal antibody (MAb) MRK16. Exposure of PXF1118 to vincristine, vindesine, vinblastine or doxorubicin for 2-3 weeks led to an increase in the MDR cell fraction of up to 15-28% during 2 to 3 weeks. For doxorubicin and vindesine, dose-dependence was observed: drug concentrations not capable of eliciting cytotoxicity failed to induce significant P-gp expression. Nutrient starvation in aging medium, exposure to activated cyclophosphamide (even at high concentrations) or cisplatin caused only negligible MDR induction. After exposure to vindesine for 6 weeks, tumor colonies exhibited highly enhanced resistance to Vinca alkaloids, doxorubicin, etoposide and dacarbacine, whereas their sensitivity to mitomycin, activated cyclophosphamide or cisplatin remained unchanged. As determined by [3H]-thymidine uptake and proliferation antigen expression, induction of MDR phenotype was observed at minimal proliferative activity with no change in cell count during exposure to anti-cancer drugs, thus suggesting that the drug treatments changed the phenotype of the cells rather than selecting for a resistant sub-population. In addition, changes in cell differentiation were observed during MDR induction. Induction of P-gp during exposure to anti-cancer drugs thus provides a model for MDR development during initially successful chemotherapy. of P-gp during exposure to anti-cancer drugs thus provides
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PMID:Induction of multiple-drug resistance during anti-neoplastic chemotherapy in vitro. 191 65

The multidrug transporter, initially identified as a multidrug efflux pump responsible for resistance of cultured cells to natural product cytotoxic drugs, is normally expressed on the apical membranes of excretory epithelial cells in the liver, kidney, and intestine. This localization suggests that the multidrug transporter may have a normal physiological role in transporting cytotoxic compounds or metabolites. In the liver, hepatectomy or treatment with chemical carcinogens increases expression of the MDR1 gene which encodes the multidrug transporter. To evaluate conditions which increase MDR1 gene expression, we have investigated the induction of the MDR1 gene by physical and chemical environmental insults in the renal adenocarcinoma cell line HTB-46. There are two strong heat shock consensus elements in the major MDR1 gene promoter. Exposure of HTB-46 cells to heat shock, sodium arsenite, or cadmium chloride led to a 7- to 8-fold increase in MDR1 mRNA levels. MDR1 RNA levels did not change following glucose starvation or treatment with 2-deoxyglucose and the calcium ionophore A23187, conditions which are known to activate the expression of another family of stress proteins, the glucose-regulated proteins. The levels of the multidrug transporter, P-glycoprotein, as measured by immunoprecipitation, were also increased after heat shock and sodium arsenite treatment. This increase in the level of the multidrug transporter in HTB-46 cells correlated with a transient increase in resistance to vinblastine following heat shock and arsenite treatment. These results suggest that the MDR1 gene is regulatable by environmental stress.
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PMID:Heat shock and arsenite increase expression of the multidrug resistance (MDR1) gene in human renal carcinoma cells. 196 74

Daunorubucin (DNR) accumulation studies as functional tests of the multidrug resistance (MDR1) gene product P-glycoprotein have produced diverging results when correlated to response to chemotherapy in acute leukaemia. To investigate possible reasons for this diversity a starvation experiment, based upon prolongation of medium exchange, was set up in the multidrug resistant cell line CEM/VBL100. DNR accumulation (1 microgram/ml) was measured flow cytometrically in the presence or absence of Verapamil (10 micromol/l). In cells permanently kept under ideal growth conditions, addition of Verapamil resulted in an average 90% increase in DNR enhancement in five successive experiments. In contrast, DNR accumulation increased by only 26% when the medium exchange was prolonged by 30 h to 42 h. This effect was not accompanied by changes in the MDR1 gene expression at the RNA or protein level. Consequently, 53 leukaemic blast samples of 30 newly diagnosed and 18 relapsed or refractory patients with acute leukaemia (ALL-18, AML-37) were processed without any delay and under the most stringent conditions possible. Evidence of the classical MDR phenotype was arbitrarily defined by a greater than 20% enhancement in DNR accumulation in response to Verapamil (10 micromol/l) or Cyclosporin A (3 micromol/l). Using this cutoff point for analysis of newly diagnosed leukaemia we found DNR uptake better correlated to response to treatment (p = 0.002) than P-gp detection by means of immunocytochemistry, using a panel of monoclonal antibodies (p = 0.03). We conclude that DNR accumulation studies are a sensitive method for predicting therapy outcome in acute leukaemia when performed with necessary precautions.
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PMID:Prolongation of medium exchange is associated with a decrease in function but not expression of the P-glycoprotein pump in leukaemic cells. 859 88

Multidrug resistance (MDR) is a phenomenon by which tumor cells exposed to a single anti-proliferative agent acquire resistance to other structurally and functionally unrelated drugs. The classical form of MDR is caused by a plasma-membrane protein currently named P-glycoprotein or P-170 encoded by the human mdr-1 gene in its functional isoform. In vitro cell lines expressing P-170 usually also present phenotypic and functional alterations. In the present study we report that the cytotoxicity mediated by tumor necrosis factor alpha (TNF alpha) in MDR variants of the human T-lymphoblastoid CEM cell line is associated with apoptosis (programmed cell death). Susceptibility of MDR cells to apoptosis was increased upon cycloheximide + TNF alpha sequential treatment, whereby the impairment of protein synthesis due to the former agent was followed by the effect of cytokine exposure. Massive apoptosis of P-170-positive cells, but not of controls, was also obtained by depletion of nutrients (i.e., serum starvation). In contrast, TNF-alpha exerted a similar apoptotic effect in epithelial (MCF-7) or myeloma (S8226) drug-sensitive/ -resistant cell pairs. However, the MDR variant of myeloma S8226 was more sensitive to the cytostatic effect of TNF alpha than the parental drug-sensitive cell line. These results suggest that the presence of the MDR phenotype may be associated with increased histotype-dependent cell susceptibility to specific, protein-synthesis-independent, apoptotic pathways.
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PMID:Tumor necrosis factor alpha is a powerful apoptotic inducer in lymphoid leukemic cells expressing the P-170 glycoprotein. 876 May 94

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

Here we report that 2-deoxyglucose/Na azide treatment and free/conjugated doxorubicin are synergistic in cell killing. As demonstrated by fluorescence confocal microscopy, KB-V1 cells retained more conjugated doxorubicin than free doxorubicin. Verapamil or 2-deoxyglucose/Na azide enhanced only the retention of the free drug and the small (<70 kDa) conjugates, indicating that P-glycoprotein (P-gp) is not effective against large conjugates. Conjugated doxorubicin was excluded from nuclei. Initially both free and conjugated doxorubicin accumulated in cytoplasmic organelles. Upon 2-deoxyglucose/Na azide treatment, fluorescence labeling of organelles dissipated. Prolonged (24 h) incubation of conjugate-preloaded cells resulted in redistribution of some of the organelle-associated fluorescence to nuclei, suggesting decoupling. The appearance of free doxorubicin was confirmed by capillary electrophoresis. 2-Deoxyglucose/Na azide treatment also retarded decoupling. Our results suggest that energy starvation, in addition to increasing cellular retention of P-gp substrates, may affect cellular fate of conjugated drugs with a possible enhancing effect in cancer cell killing.
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PMID:Synergism of energy starvation and dextran-conjugated doxorubicin in the killing of multidrug-resistant KB carcinoma cells. 1021 47

Multidrug resistance (MDR) is often characterized by the expression of P-glycoprotein (P-gp), a 170-kd ATP-dependent drug efflux protein. As well as effluxing xenotoxins, functional P-gp can confer resistance to caspase-dependent apoptosis induced by a range of different stimuli, including Fas ligand, tumor necrosis factor, UV irradiation, and serum starvation. However, P-gp-positive cells remain sensitive to caspase-independent death induced by cytotoxic T-cell granule proteins, perforin, and granzyme B. It is, therefore, possible that agents that induce cell death in a caspase-independent manner might circumvent P-gp-mediated MDR. We demonstrated here that hexamethylene bisacetamide (HMBA) induced equivalent caspase-independent cell death in both P-gp-positive and -negative cell lines at concentrations of 10 mmol/L and above. The HMBA-induced death pathway was marked by release of cytochrome c from the mitochondria and reduction of Bcl-2 protein levels. In addition, we show that functional P-gp specifically inhibits the activation of particular caspases, such as caspases-8 and -3, whereas others, such as caspase-9, remain unaffected. These studies greatly enhance our understanding of the molecular cell death events that can be regulated by functional P-gp and highlight the potential clinical use of drugs that function via a caspase-independent pathway for the treatment of MDR tumors.
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PMID:HMBA induces activation of a caspase-independent cell death pathway to overcome P-glycoprotein-mediated multidrug resistance. 1073 10

The influence of antibiotics, particularly ofloxacin (OF), a commonly used antimicrobial fluoroquinolone, on the multidrug resistance (MDR) phenotype of the HCT-8 cell line was studied. This cell line was grown in OF containing medium for several months and the expression of the MDR phenotype was followed through the analysis of the expression and functionality of the P-glycoprotein (Pgp), the chemosensitivity to daunorubicin (DNR), and the mRNA expression of mdr-1, multidrug resistance-associated protein (MRP), and topoisomerase IIalpha and IIbeta genes. Replacement of OF by penicillin streptomycin (PS) resulted in a significant decrease in mdr-1 mRNA expression, which was found to correlate with a decrease in the expression and functionality of the Pgp. After antibiotic starvation for 4 weeks, cells grown in antibiotic-free medium were then exposed to PS or OF; these cells showed an increase in mdr-1 mRNA/Pgp and MRP mRNA expression without a decrease in DNR cytotoxicity. OF cultured cells exhibited a significant increase in Pgp expression without evidence of the functionality of the Pgp. An increase in topoisomerase IIalpha mRNA expression was observed with time and with the number of passages of the cell line without any relationship to the presence of antibiotics in the culture medium. These results showed that extensive use of antibiotics, particularly the quinolones, can modify the phenotype of the HCT-8 colon adenocarcinoma cell line.
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PMID:Influence of the fluoroquinolone ofloxacin on the intrinsic expression of multidrug resistance phenotype in HCT-8 human colon carcinoma cells. 1080 41

Regulation of P-glycoprotein (Pgp) expression occurs not only at the DNA and mRNA level but also at the protein level. We showed previously that Pgp was stabilized when multidrug-resistant CH(R)C5 and SKVCR 2.0 ovarian cell lines were subjected to serum-starved or high-cell-density growth conditions, whereas Pgp turnover in a leukemic multidrug-resistant cell line, CEMVLB0.1, was not affected by serum starvation (Muller et al., 1995). On further analysis, we have observed that the majority of the CH(R)C5 and SKVCR 2.0 cells under these conditions were in the G1/G0 phase of the cell cycle, whereas the cell cycle of CEMVLB0.1 cells was not affected. Pgp in CEMVLB0.1 cells was stabilized only when the cell cycle was delayed in the G1/G0 phase by using amino acid-deficient growth medium. In CH(R)C5 cells, Pgp half-life was also considerably increased when the cell cycle of these ovary-derived cells was delayed in the G1/G0 phase by using high concentrations of progesterone under normal serum growth conditions. In contrast, Pgp stability was not greatly affected if these cells were delayed in the S or G2/M phase of the cell cycle with Ara-C, cisplatin, or colchicine under the same conditions. Insulin-like growth factors could release the serum-starved CH(R)C5 and SKVCR2.0 cells from the G1/G0 phase and destabilized Pgp. These results indicate that Pgp turnover is a cell-cycle-related process in MDR cells.
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PMID:Cell-cycle-dependent turnover of P-glycoprotein in multidrug-resistant cells. 1082 30


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