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)

Newly synthesized 1,4-dihydropyridine derivatives possessing alkyl chains at the 4-position screened whether they could overcome P-glycoprotein-mediated multidrug resistance in cultured cancer cells and also leukemia-bearing animals. Of these derivatives, some could overcome drug resistance to doxorubicin and vincristine in multidrug resistant human cancer cell lines. Combined administration of vincristine and some of the derivatives significantly increased the life span of P-glycoprotein overexpressing multidrug-resistant P388 leukemia-bearing mice. The calcium antagonistic activities, an undesirable effects, were weaker than that of verapamil. These results suggested that the introduction of alkyl groups at the 4-position were effective for both overcoming multidrug resistance and reducing the calcium antagonistic activity.
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PMID:Newly synthesized dihydropyridine derivatives as modulators of P-glycoprotein-mediated multidrug resistance. 988 Nov 13

The supernatant from a suspension of Ehrlich cells exposed to centrifugation at 700xg for 45 s induced a transient increase in the intracellular concentration of free, cytosolic Ca2+, [Ca2+]i, as well as activation of an outwardly rectifying whole-cell current when added to a suspension of non-stimulated cells. These effects were inhibited by suramin, a non-specific P2 receptor antagonist, and mimicked by ATP. Reversed phase HPLC analysis revealed that the supernatant from Ehrlich cells exposed to centrifugation contained 2. 6+/-0.2 microM ATP, and that the mechanical stress-induced release of ATP was inhibited by glibenclamide and verapamil, non-specific inhibitors of the cystic fibrosis transmembrane conductance regulator and P-glycoprotein, respectively. After trypan blue staining, less than 0.5% of the cells were unable to extrude the dye. Addition of extracellular ATP induced a suramin-sensitive, transient, concentration-dependent increase in [Ca2+]i, activation of an outwardly rectifying whole-cell current and a hyperpolarization of the plasma membrane. The ATP-induced hyperpolarization of the plasma membrane was strongly inhibited in the presence of charybdotoxin (ChTX), an inhibitor of several Ca2+-activated K+ channels, suggesting that stimulation of P2 receptors in Ehrlich cells evokes a Ca2+-activated K+ current. The relative potencies of several nucleotides (ATP, UTP, ADP, 2-MeSATP, alpha,beta-MeATP, bzATP) in eliciting an increase in [Ca2+]i, as well as the effect of repetitive addition of nucleotides were investigated. The results lead us to conclude that mechanical stimulation of Ehrlich cells leads to release of ATP, which in turn stimulates both P2Y1 and P2Y2 receptors, resulting in Ca2+ influx as well as release and activation of an outwardly rectifying whole-cell current.
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PMID:Mechanical stress induces release of ATP from Ehrlich ascites tumor cells. 988 82

Previous work has established that aging in mice leads to an accumulation of T cells that express high levels of P-glycoprotein, a plasma membrane pump that mediates multiple drug resistance in tumor cells but whose function in normal T cells is still obscure. Pgp+ cells seem to be functionally defective: isolated from the CD4 memory population of young mice, they are unresponsive to T cell receptor-dependent stimuli in tests for proliferation and cytokine production. The proliferative defect can, however, be overcome by exposure to PMA plus the calcium ionophore ionomycin, suggesting that the Pgp+ cells may have a specific defect in calcium signal generation. We show here that Pgp+ T cells, from young or old mice, do indeed show smaller changes in intracellular calcium ion concentration than Pgp- cells, when activated either by Con A, anti-CD3 antibodies, or ionomycin. The difference between Pgp+ and Pgp- cells is apparent even in experiments on isolated CD4 memory T cells from young mice and thus is not simply a consequence of the age-dependent increase in memory cell numbers. Although the molecular basis for the abnormality in calcium signal generation by Pgp+ cells is still uncertain, our data suggest that the effect could be due to inter-subset differences in levels of sorcin, a 22 kDa cytoplasmic protein that is co-expressed with P-glycoprotein in many tumor cells and which binds free calcium ion with high affinity. Sorcin levels are higher in Pgp+ CD4 cells than in Pgp- CD4 cells of young mice and increase with age in CD4 cells, consistent with the hypothesis that sorcin interferes with calcium signals in the age-sensitive Pgp+ T cell subset.
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PMID:Calcium signal abnormalities in murine T lymphocytes that express the multidrug transporter P-glycoprotein. 1022 45

Experiments were undertaken using an ovarian adenocarcinoma cell line (A2780) and a drug-resistant strain (A2780.ad) derived from this line. P-glycoprotein could not be detected in A2780 cells but was essentially ubiquitous in A2780.ad cells, although removing the selective pressure for drug resistance led to reduced expression. However, the amount of P-glycoprotein present was used to predict the capacity of these cells to extrude rhodamine-123 (R-123) and their resistance to adriamycin, a cytotoxic drug. This accords with the role of P-glycoprotein as a drug pump. Although hypotonic solutions increased anion efflux from A2780 and A2780.ad cells, larger responses occurred in the parental line. Moreover, R-123 extrusion and anion efflux appeared to be mutually independent processes and so these data do not support the view that P-glycoprotein is involved in the control of volume-sensitive anion channels. Hypotonic solutions increased intracellular free calcium ([Ca2+]i) in drug-resistant cells but not in the parental line, and so establishing a drug-resistant strain may affect the control of [Ca2+]i during osmotic swelling. This could account for effects that were previously attributed to P-glycoprotein.
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PMID:Drug extrusion, 125I- efflux and the control of intracellular [Ca2+] in drug-resistant ovarian epithelial cells. 1022 71

To determine whether individual protein kinase C (PKC) isozymes differentially phosphorylate sites in the linker region of human P-glycoprotein (P-gp), we used a synthetic peptide substrate, PG-2, exactly corresponding to amino acid residues spanning the region 656-689 of the multidrug resistance gene (MDRI). All tested PKC isozymes phosphorylated PG-2. The maximum phosphate incorporation by calcium-dependent PKC isozymes alpha, betaI, betaII, and gamma was 3, 2, 2, and 3 mol phosphate/mol PG-2, respectively. The maximum phosphate incorporation by calcium-independent isozymes delta, epsilon, eta, and zeta was 1.5, 0.5, 1.5, and 1.5 mol phosphate/mol PG-2, respectively. Two-dimensional tryptic phosphopeptide mapping indicated differential phosphorylation of the PKC consensus sites Ser-661, Ser-667, and Ser-671 by individual isozymes, which may be functionally significant. These data suggest that differential phosphorylation by PKC isoenzymes of PKC sites within the P-gp linker region may play a role in modulating P-gp activity.
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PMID:Differential phosphorylation of sites in the linker region of P-glycoprotein by protein kinase C isozymes alpha, betaI, betaII, gamma, delta, epsilon, eta, and zeta. 1053 49

Natural killer (NK) cells express the highest amount of P-glycoprotein (Pgp), a product of the multidrug resistance (MDR) 1 gene, among lymphoid cells, and our previous studies demonstrated that Pgp is required for NK cell-mediated cytotoxicity. In this study we examined the role of Pgp in NK cell-mediated cytotoxicity using a human NK-like cell line, i.e., YTN cells and two MDR reversing agents, nicardipine and its structural analog, AHC-93. These two agents inhibited the Pgp function (rhodamine-123 excretion) as well as cell-mediated cytotoxicity, confirming that Pgp is critical for NK cell-mediated cytotoxicity. As revealed by video-rate ultraviolet laser-scanning confocal microscopy, AHC-93 did not inhibit the increase in the intracellular calcium concentration upon binding to target cells, whereas nicardipine did, as reported previously. These two reagents relocated acridine orange dye from lysosomes to the cytoplasm at concentrations similar to those required for the inhibition of cell-mediated cytotoxicity. These results suggest that Pgp is directly or indirectly involved in pH regulation in lysosomes, but not in calcium homeostasis.
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PMID:Role of P-glycoprotein in human natural killer-like cell line-mediated cytotoxicity. 1058 62

The development of anthelmintic resistance is making parasite control in small ruminants problematic. Following the discovery that the drug transporter P-glycoprotein may be involved in macrocyclic lactone resistance in Haemonchus contortus, we determined the effect of two multidrug-resistance modulators, verapamil and CL347,099, on the efficacy of ivermectin and moxidectin against unselected and drug-selected strains of H. contortus. CL347,099 is an analog of verapamil that has multidrug-resistance properties but weaker calcium-channel-blocking activity than the parent drug. The combinations of verapamil with either ivermectin or moxidectin significantly reduced worm counts of the selected strains as compared with the untreated controls, whereas ivermectin or moxidectin alone did not significantly reduce worm counts as compared with the untreated controls. The CL347,099 plus moxidectin combination was significantly more efficacious than moxidectin alone against the ivermectin-selected strain. The drug-combination regimes were without adverse effect on the jirds. However, higher levels of verapamil (> or =40 mg/kg) produced some toxicity.
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PMID:Effects of the multidrug-resistance-reversing agents verapamil and CL 347,099 on the efficacy of ivermectin or moxidectin against unselected and drug-selected strains of Haemonchus contortus in jirds (Meriones unguiculatus). 1059 24

The presence of the cellular multidrug resistance (MDR1) gene and its product, P-glycoprotein (Pgp), is thought to be a mechanism for the failure of chemotherapy in cancer patients. Calcium channel blockers have been shown to sensitise cancer cells to anticancer drugs by reversing Pgp expression in cell lines. The interactions between anticancer drugs such as carmustine (BCNU), vincristine (VCR) and procarbazine (PCB) and calcium channel blockers such as nimodipine and verapamil on cultured cells of glioblastoma from eight patients were therefore tested. Pgp expression was examined immunohistochemically using C219 monoclonal antibody in cytospin preparation. The cytotoxicity of the drugs was screened using microculture tetrazolium assay. The cells from five patients showed positive immunoreaction for Pgp. Nimodipine showed growth-inhibitory activity against glioblastoma cells at a rate of 16.55-26.88% (P < 0.05), but a similar effect was not observed with verapamil. While antiproliferative effects of BCNU were around 20.91-45.09% (P < 0.05) on the cells from seven patients, VCR was the most effective agent in inhibition of cell growth at a rate of 26.43-48.47% (P < 0.05). The response of the cells from five patients to PCB was from 11.98 to 16.32% (P < 0.05). When used together, nimodipine further enriched cytotoxicity of the anticancer drugs up to 11.14-40.85% (P < 0.05) without relation to Pgp expression. In conclusion, the enhancement of cytotoxicity of anticancer drugs by nimodipine suggests that there might be a synergy between anticancer drugs and nimodipine in the inhibition of glioma cell growth.
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PMID:The effects of anticancer drugs in combination with nimodipine and verapamil on cultured cells of glioblastoma multiforme. 1062 52

The anti-drug resistance effect of three derivatives (AR-1, AR-2 and AR-3) of [1,2,5-trimethyl-4-phenyl-4-beta-(N,N-disubstituted-ethylamino)] piperidines, that were evaluated as calcium and calmodulin antagonists, was studied on doxorubicin (ADM) and vincristine (VCR) resistant Sarcoma-45 inoculated rats. Treatment with ADM (5 mg/kg) or VCR (3 mg/kg) alone, as well as with AR-1, AR-2 or AR-3 (50 mg/kg) alone, had no effect on tumor growth. However, AR-2 in dose 50 mg/kg (calmodulin antagonist), but not AR-1 and AR-3 (calcium channel blocker), administered with ADM (5 mg/kg) or VCR (3 mg/kg), significantly suppressed tumor growth 80% and 70%, respectively. Two rats treated with ADM/AR-2 and one treated with VCR/AR-2 were cured. 170 kDa protein was purified from sarcoma-45 tumor cells to apparent homogeneity by successive steps of phosphocellulose, DEAE-cellulose, and AR-2-coupled sepharose chromatography. The protein proved to be immunopositive with the P-glycoprotein-specific monoclonal antibody. It is concluded that the effect of AR-2 can be explained by both hydrophobic and electrostatic interaction with a protein target (170 kDa P-glycoprotein) in resistant sarcoma-45 tumor cell's membrane.
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PMID:Reversal of drug resistance in sarcoma-45 by the new calmodulin antagonist--trihydrochloride of [1,2,5-trimethyl-4-phenyl-4-beta-[N-(beta-ethylamino)-N-4'-methoxybe nzy l]-ethylamino] piperidine (AR-2). 1063 81

Drug interactions occur when the efficacy or toxicity of a medication is changed by administration of another substance. Pharmacokinetic interactions often occur as a result of a change in drug metabolism. Cytochrome P450 (CYP) 3A4 oxidises a broad spectrum of drugs by a number of metabolic processes. The location of CYP3A4 in the small bowel and liver permits an effect on both presystemic and systemic drug disposition. Some interactions with CYP3A4 inhibitors may also involve inhibition of P-glycoprotein. Clinically important CYP3A4 inhibitors include itraconazole, ketoconazole, clarithromycin, erythromycin, nefazodone, ritonavir and grapefruit juice. Torsades de pointes, a life-threatening ventricular arrhythmia associated with QT prolongation, can occur when these inhibitors are coadministered with terfenadine, astemizole, cisapride or pimozide. Rhabdomyolysis has been associated with the coadministration of some 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors ('statins') and CYP3A4 inhibitors. Symptomatic hypotension may occur when CYP3A4 inhibitors are given with some dihydropyridine calcium antagonists, as well with the phosphodiesterase inhibitor sildenafil. Excessive sedation can result from concomitant administration of benzodiazepine (midazolam, triazolam, alprazolam or diazepam) or nonbenzodiazepine (zopiclone and buspirone) hypnosedatives with CYP3A4 inhibitors. Ataxia can occur with carbamazepine, and ergotism with ergotamine, following the addition of a CYP3A4 inhibitor. Beneficial drug interactions can occur. Administration of a CYP3A4 inhibitor with cyclosporin may allow reduction of the dosage and cost of the immunosuppressant. Certain HIV protease inhibitors, e.g. saquinavir, have low oral bioavailability that can be profoundly increased by the addition of ritonavir. The clinical importance of any drug interaction depends on factors that are drug-, patient- and administration-related. Generally, a doubling or more in plasma drug concentration has the potential for enhanced adverse or beneficial drug response. Less pronounced pharmacokinetic interactions may still be clinically important for drugs with a steep concentration-response relationship or narrow therapeutic index. In most cases, the extent of drug interaction varies markedly among individuals; this is likely to be dependent on interindividual differences in CYP3A4 tissue content, pre-existing medical conditions and, possibly, age. Interactions may occur under single dose conditions or only at steady state. The pharmacodynamic consequences may or may not closely follow pharmacokinetic changes. Drug interactions may be most apparent when patients are stabilised on the affected drug and the CYP3A4 inhibitor is then added to the regimen. Temporal relationships between the administration of the drug and CYP3A4 inhibitor may be important in determining the extent of the interaction.
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PMID:Pharmacokinetic-pharmacodynamic consequences and clinical relevance of cytochrome P450 3A4 inhibition. 1066 58


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