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)

Many multidrug-resistant (MDR) cell lines overexpress the epidermal growth factor receptor (EGFR) as well as P-glycoprotein (P-gp). However, the role of the increased EGFR in P-gp-mediated drug resistance remains unclear. Since recent studies suggest that activation of phospholipase C (PLC) could increase the phosphorylation of P-gp, and activation of the EGFR would also activate PLC, we investigated whether the effect of epidermal growth factor (EGF) on the phosphorylation of P-gp was mediated through PLC. Treatment of the human MDR breast cancer cell line, MCF-7/AdrR, with EGF increased the phosphorylation of P-gp by 20-50%. The increased phosphorylation of P-gp was accompanied by stimulation of PLC activity, as measured by the production of inositol, 1,4,5-trisphosphate and diacylglycerol, products of phosphatidylinositol-4,5-bisphosphate hydrolysis. Treatment of MDR cells with EGF also had detectable effects on P-gp function. For example, following incubation of MCF-7/AdrR cells with ECF, we observed a consistent decrease in total vinblastine (VBL) accumulation. Kinetic analysis revealed this change to be due to an increase in membrane efflux. The latter was measured by the initial uptake velocity, which was inhibited by EGF. VBL uptake measured at 0-320 sec was inhibited by 20-40%, which was associated with a similar increase in VBL efflux. EGF had no effect on drug accumulation, uptake, or efflux in sensitive MCF-7 cells. These data indicate that EGF can modulate the phosphorylation and function of P-gp, and suggest that this effect may be initiated by the activation of PLC.
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PMID:Regulation of the function of P-glycoprotein by epidermal growth factor through phospholipase C. 926 11

Protein kinase C-alpha (PKC-alpha) activation is an important contributing factor in human breast cancer MCF-7 MDR cell drug resistance. We recently reported the use of N-myristoylated PKC-alpha pseudosubstrate peptides with potent PKC-alpha inhibitory activity as reversal agents of drug resistance in MCF-7 MDR cells. The peptides potently inhibit phosphorylation of the PKC-alpha substrates P-glycoprotein (P-gp), raf kinase and PKC-alpha itself in MCF-7 MDR cells in association with a severalfold induction of intracellular uptake of P-gp substrate chemotherapeutics and a statistically significant twofold increase in cellular chemosensitivity. We now report that the N-myristoylated PKC-alpha pseudosubstrate peptide N-myristoyl-RFARKGALRQKNV (P3) is not a P-gp substrate in MCF-7 MDR cells based on a comparison of the cellular uptake of [125I]-radiolabeled P3 in MCF-7 MDR vs MCF-7 WT cells. The extent of cellular uptake of the radiolabeled peptide in the drug-resistant cell line MCF-7 MDR was either greater than or equivalent to the uptake in the parental drug-sensitive MCF-7 WT cell line over a time course of 30 min to 6 h, and across a peptide concentration range of 25-100 microM. Additionally, treatment of the MCF-7 MDR cells with verapamil (VPL), a known P-gp efflux inhibitor, had no effect on the cellular accumulation of radiolabeled P3. Our results provide direct evidence that the N-myristoylated pseudosubstrate peptide is taken up equivalently by drug-sensitive and MDR cancer cells and therefore has potential value as an MDR reversal agent that operates by a novel mechanism.
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PMID:An N-myristoylated protein kinase C-alpha pseudosubstrate peptide that functions as a multidrug resistance reversal agent in human breast cancer cells is not a P-glycoprotein substrate. 927 25

Sphinxolides, a newly described family of cytotoxins from the New Caledonian sponge Neosiphonia superstes, bear structural resemblance to scytophycins. We now demonstrate that the cytotoxicity of sphinxolides is associated with cell cycle arrest in G2-M and induction of apoptosis. Like scytophycins and cytochalasins, sphinxolides caused rapid loss of microfilaments in cultured cells, without affecting microtubule organization. Microfilament reassembly was very slow after removal of the sphinxolide, consistent with the slow recovery of cellular proliferation. Sphinxolides potently inhibited actin polymerization in vitro and the microfilament-dependent ATPase activity of purified actomyosin, indicating a direct effect on actin. Importantly, sphinxolides were equally cytotoxic toward MCF-7 human breast carcinoma cells and a subline which overexpresses P-glycoprotein (MCF-7/ADR). Similarly, overexpression of the multidrug resistance-associated protein MRP by HL-60 cells did not confer resistance to the sphinxolides. These studies demonstrate that sphinxolides are potent new antimicrofilament compounds that circumvent multidrug resistance mediated by overexpression of either P-glycoprotein or MRP. Therefore, these agents may be useful in the treatment of drug-resistant tumors.
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PMID:Microfilament depletion and circumvention of multiple drug resistance by sphinxolides. 928 83

Clinical chemotherapy of breast carcinomas must be considered insufficient, mainly due to the appearance of drug resistance. The multidrug resistance (MDR) phenotype, either intrinsically occurring or acquired, e.g., against a panel of different antineoplastic drugs, is discussed in relation to several MDR-associated genes such as the MDR-gene mdr1 encoding the P-glycoprotein (PGP), the MRP gene (multidrug resistance protein) encoding an MDR-related protein or the LRP gene encoding the lung resistance protein. Numerous experimental and clinical approaches aiming at reversing resistance require well-characterised in vitro and in vivo models. The aim of our work was to develop multidrug resistant sublines from human xenotransplanted breast carcinomas, in addition to the broadly used line MCF-7 and its multidrug resistant subline MCF-7/AdrR. MDR was induced in vitro with increasing concentrations of Adriablastin (ADR) for several weeks, resulting in a 3.5- to 35-fold increase in IC50 values using the MTT-test. Cell lines were cross-resistant toward another MDR-related drug, vincristine, but remained sensitive to non-MDR-related compounds such as cisplatin and methotrexate. The resistance toward Adriamycin and vincristine was confirmed in vivo by a lack of tumour growth inhibition in the nude mouse system. Gene expression data for the mdr1/PGP, MRP/MRP and LRP/LRP on both the mRNA (RT-PCR) and the protein levels (immunoflow cytometry) demonstrated that induction of mdr1 gene expression was responsible for the acquired MDR phenotype. Rhodamine efflux data, indicated by PGP overexpression, underlined the development of this MDR mechanism in the newly established breast carcinoma lines MT-1/ADR, MT-3/ADR and MaTu/ADR.
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PMID:Development and characterisation of novel human multidrug resistant mammary carcinoma lines in vitro and in vivo. 931 9

Human breast carcinoma MCF-7/AdrVp cells display a novel multidrug resistance phenotype that is characterized by the overexpression of a 95-kDa membrane glycoprotein (p95) and by marked reduction in intracellular anthracycline accumulation, without overexpression of P-glycoprotein or the multidrug resistance protein MRP. p95 is also highly expressed in multidrug-resistant NCI-H1688 cells derived from a human small cell lung carcinoma. Deglycoslyated p95 from NCI-H1688 cells was isolated by two-dimensional gel electrophoresis and then digested with trypsin. The tryptic peptides were analyzed by mass spectrometry and microsequencing. These analyses identified p95 to be identical to NCA-90, the nonspecific cross-reacting antigen related to the carcinoembryonic antigen (CEA). Further confirmation that p95 is indeed NCA-90 was obtained by Northern and Western blot studies using probes or antibodies specific for p95, NCA-90, or CEA family members. Western blot studies also revealed that CEA itself is overexpressed in MCF-7/AdrVp cells compared to parental MCF-7/W cells. The enforced expression of NCA-90 protein in HeLa cells stably transfected with NCA-90 cDNA did not result in increased resistance of the transfected cells to daunorubicin or a decrease in daunorubicin accumulation in the transfected cells compared to cells transfected only with the expression vector. However, a recent report by H. Kawaharata et al. (Int. J. Cancer, 72: 377-382, 1997) of diminished accumulation, retention, and cytotoxicity of doxorubicin in EJNIH3T3 cells in which enforced expression of CEA was accomplished leaves open the possibility that the overexpression of CEA, possibly in combination with that of NCA-90, could account at least in part for the drug resistant phenotype displayed by MCF-7/AdrVp cells.
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PMID:The 95-kilodalton membrane glycoprotein overexpressed in novel multidrug-resistant breast cancer cells is NCA, the nonspecific cross-reacting antigen of carcinoembryonic antigen. 940 50

Resistance of tumor cells to chemotherapeutic drugs can not only be caused by treatment with antineoplastic agents but also by radiotherapy. The aim of this study was to analyze whether ionizing radiation can influence the mRNA expression of proteins which have been found to be involved in drug resistance of tumor cells. Human tumor cell lines (MCF-7, LXF and Sk-Mel) were treated with single doses of irradiation (5, 10 and 20 Gy). The expression of the resistance related proteins glutathione S-transferase-pi (GST-pi), topoisomerase II alpha (Topo II), thymidylate synthase (TS), O6-methylguanine-DNA-methyltransferase (MGMT), P-glycoprotein (Pgp), glutathione peroxidase (GPX) multidrug resistance-associated protein (MRP) and also of the heat-shock protein 70 (HSP 70) were determined at the mRNA level during the time interval from 1.5 to 72 h post-irradiation and compared with their corresponding controls. We also examined whether a relationship exists between these proteins and the proliferative activity (histone 3, Ki-67, statin) of the cells. We found that exposure of MCF-7, LXF and Sk-Mel cells to ionizing radiation increases the expression of the mRNA of GST-pi. Topo II, TS, HSP 70 and proliferation markers were also altered by exposure to ionizing radiation, but there was no common response of the three cell lines. No significant changes were observed in the expression of MGMT, Pgp, GPX and MRP after radiation treatment. Drug resistance tests revealed that irradiated MCF 7 cells were less sensitive to doxorubicin than non-irradiated control cells. Our results indicate that ionizing irradiation modifies the expression of some proteins involved in drug resistance and the response of MCF 7 cells to doxorubicin and may, therefore, play a role in clinical drug response.
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PMID:Messenger RNA expression of resistance factors in human tumor cell lines after single exposure to radiation. 941 87

A phage display library of random decapeptides was used to generate peptide ligands that can bind multidrug-resistance (MDR) drugs mimicking, in this respect, the drug-binding activity of P-glycoprotein. Seven peptide sequences were identified that specifically bound doxorubicin. Five of these sequences expressed the core consensus motif WXXW. The displacement assay showed that the phages expressing these peptides bound MDR type drugs (vinblastine, doxorubicin, verapamil, and genistein) with the same selectivity as P-glycoprotein and did not interact with non-MDR type drugs, such as arabinosylcytosine (Ara-C) and melphalan. One of the selected peptides that showed a highest capacity for the binding (VCDWWGWGIC) was synthesized and displayed competition with the phage for doxorubicin binding. The structure modeling suggested that all the selected sequences contained a hydrophobic envelope in which MDR drugs could be docked with substantial energy minimization. Western blot analysis showed that monospecific antibody obtained against the phage expressing VCDWWGWGIC peptide could specifically recognize P-glycoprotein in the membrane fraction of MDR phenotype MCF-7ADR cells. The MDR drug-binding sequences generated during this work could provide an important tool for design and screening of new chemotherapeutic agents.
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PMID:Multidrug-resistance drug-binding peptides generated by using a phage display library. 949 79

Modulators of P-glycoprotein (P-gp) are often themselves transported out of cells, thereby limiting their effectiveness. It may be possible to develop more effective modulators of multidrug resistance by designing drugs that irreversibly block the function of P-gp. Therefore, we studied the effect of the mustard derivatives of fluphenazine (FPN) and trans-flupenthixol (FPT) on P-gp function. Both fluphenazine-mustard (FPN-M) and trans-flupenthixol-mustard (FPT-M) possessed alkylating activity, as assayed using 4-(p-nitrobenzyl) pyridine. Multidrug-resistant MCF-7/AdrR cells were incubated with FPN or FPN-M, or FPT or FPT-M for 1 h, washed for varying number of times in phosphate-buffered saline (PBS), then resuspended in medium containing [3H]vinblastine (VBL), and assayed for steady-state accumulation of the drug. Washing had far less of an effect on the ability of FPN-M and FPT-M to increase VBL accumulation compared to their parent compounds. After eight washes in excess PBS, the cells initially exposed to FPN or FPT accumulated only 30% and 50% of the initially accumulated drug, whereas the FPN-M- or FPT-M-treated cells accumulated approximately 75% and 90% of the control, respectively. FPN-M and FPT-M also increased the uptake and decreased the efflux of VBL from MDR cells despite repeated washing. We also examined the effects of these modulators on sensitivity of MDR cells to cytotoxic agents. FPN-M and FPT-M sensitized MCF-7/AdrR cells to VBL and doxorubicin to a greater extent than their parent compounds. These studies point out the potential of "irreversible" P-gp modulators to produce prolonged chemosensitization.
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PMID:Inhibitory effect of alkylating modulators on the function of P-glycoprotein. 949 53

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

Multidrug resistance is one of the major obstacles in cancer chemotherapy. In tumor cells, overexpression of the transmembrane P-glycoprotein 170 (P-gp) is associated with the multidrug resistance phenotype and serves as a drug efflux pump. The activation of P-gp has been suggested to occur at the post-translational level. Protein kinase C mediated phosphorylation may be associated with the drug effux mechanism but the overall phosphorylation pathway has not been completely defined. we report the novel finding of an increase in phosphatase 1B (a tyrosine phosphatase) and a decrease in PP1 and PP2A (serine/threonine phosphatases) expression and activity in our series of early (R65) and late (R500) stage adriamycin resistant MCF-7 cells. In addition, we show a decrease in protein kinase A (PKA) activity and an increase in protein kinase C (PKC) in our drug resistant cells. Analyses of PKC isoforms alpha through epsilon revealed that PKCbeta was not expressed and that all other isoforms increased with increasing resistance, except PKCgamma which was detected only in R65 cells. Our findings suggest that in drug resistant cells, there is a pattern consistant with the maintenance of serine and threonine residues in a phosphorylated state.
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PMID:Differential expression and activity of phosphatases and protein kinases in adriamycin sensitive and resistant human breast cancer MCF-7 cells. 962 6


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