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)

Multidrug resistance (MDR) is characterized by the overexpression of P-glycoprotein (Pgp), which is responsible for decreasing drug uptake and/or increasing drug efflux in resistant cells. Although Pgp has a broad-spectrum specificity, this protein seems to react preferentially with amphiphilic and cationic molecules. Rhodamine 123 (R123) is widely used as a marker for mitochondria in living cells and its uptake is dependent on plasma and mitochondrial membrane potential. More recently, cross-resistance to R123 in cells resistant to adriamycin has been demonstrated and a correlation between expression of Pgp and reduced intracellular accumulation of R123 has been shown. The measurement of R123 uptake or efflux allows the characterization of cells displaying a MDR phenotype with overexpression of Pgp, even with low levels of resistance. Other proteins have now been identified which play a role in resistance and in drug transport, including MRP. For this reason we need to determine if R123 is transported only by Pgp or if R123 is a substrate for transport by other drug resistance proteins as well. We also discuss the possibilities of using several techniques based on fluorescence with R123 in order to fully characterize cells by measuring both Pgp activity and its presence/localization.
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PMID:[Use of rhodamine 123 for the detection of multidrug resistance]. 853 26

P-glycoprotein 170 encoded by the MDR-1 gene mediates export of substrates including some immunosuppressive drugs. Rapamycin was compared to cyclosporine A for its ability to inhibit P-glycoprotein on normal human peripheral blood mononuclear cells (PBMC). Rhodamine 123 dye efflux measures P-glycoprotein activity and inhibition of P-glycoprotein results in dye retention. Normal CD4+, CD8+ and B cells include a substantial subset with cyclosporine A-sensitive rhodamine efflux. Rh123 dye efflux is also inhibited by rapamycin at comparable drug levels used in transplant models. CsA is approximately 100-fold more effective on inhibition of PBMC P-gp than is RAPA. P-glycoprotein inhibition of ex vivo lymphocytes with three multi-drug resistant T-cell lines showed susceptibility of P-glycoprotein to rapamycin dependent on the cell type. Compared to cyclosporine A, the reduced ability of rapamycin to inhibit P-glycoprotein reflects a reduced avidity in its binding to P-glycoprotein and perhaps increased access to the cell interior. The increased efficiency of RAPA as an immunosuppressive may in part be a result of its relatively low avidity for P-glycoprotein. The authors speculate that interactions with P-glycoprotein may partially modulate the immunosuppressive effects of rapamycin.
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PMID:Inhibition by rapamycin of P-glycoprotein 170-mediated export from normal lymphocytes. 866 25

In the present study we analyze peripheral blood lymphocytes (PBL) from patients with human immunodeficiency virus (HIV) infection for both phenotypic expression and function of P-glycoprotein (P-170). This transmembrane efflux pump is known to be one of the mechanisms responsible for the multidrug resistance (MDR) in cancer therapy and it is also constitutively expressed in normal PBL. P-170 function, evaluated as Rhodamine 123 (Rh123) efflux in flow cytometry, was found to be significantly reduced in CD16+ natural killer (NK) cells from patients with HIV infection. Interestingly, this reduced efflux significantly correlates with the decreased NK cytotoxicity observed in HIV+ patients, as evaluated against the NK-specific K562 target cell line. These results support a possible role of the P-170-related pump in specific immunological lymphocyte function such as NK cell-mediated cytotoxicity.
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PMID:P-170 glycoprotein (P-170) is involved in the impairment of natural killer cell-mediated cytotoxicity in HIV+ patients. 874 23

The fluorescent dye, rhodamine 123, was used to evaluate the functional activity of the P-glycoprotein (P-gp) efflux transport system in primary cultured bovine brain microvessel endothelial cell (BBMEC) monolayers. Rhodamine 123 accumulation was increased significantly in BBMEC monolayers treated with the P-gp modifying agent, cyclosporin A (CSA). Rhodamine 123 accumulation was also increased by other P-gp modifying agents. The rank effectiveness of these agents in increasing rhodamine 123 accumulation in BBMEC monolayers was CSA = dipyridamole > verapamil = quinidine. The maximal increase in rhodamine 123 accumulation in CSA treated. BBMEC monolayers was approximately 3 fold greater than in control monolayers and was qualitatively similar to that observed with 3H-vincristine. Comparison of functional activity with the biochemical expression of P-gp in BBMEC monolayers and in an established tumor cell line that over-expresses P-gp indicate that functional activity may be a more descriptive measure of the importance of this drug efflux system than protein expression. Furthermore, these studies suggest that accumulation of rhodamine 123 in BBMEC monolayers can be used to quantitatively examine P-gp activity in the blood-brain barrier.
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PMID:Use of rhodamine 123 to examine the functional activity of P-glycoprotein in primary cultured brain microvessel endothelial cell monolayers. 889 Sep 33

In this study the ability of the new pure anti-estrogen ICI 182,780 to modulate the cytotoxic action of adriamycin (ADR) on parental and ADR-resistant MCF-7 (MCF-7 ADRr) human breast-cancer cells was investigated and compared with that of tamoxifen (TAM). TAM enhanced ADR cytotoxicity in MCF-7 ADRr cells in a dose-related manner, but this effect was slight or absent in MCF-7 WT. In contrast, ICI 182,780 was able to enhance ADR toxicity both in MCF-7 ADRr and in the parental cell line. ICI 182,780 was up to 2.5-fold more effective than TAM in reducing the IC50 of ADR in MCF-7 ADRr cells. Analysis of the data by the isobole method showed that the combination ADR/TAM and ADR/ICI 182,780 produced synergistic anti-proliferative activity in MCF-7 ADRr cells. Because ADR resistance in these cells is associated with the expression of high levels of P-glycoprotein (Pgp), we evaluated the effect of anti-estrogens on Pgp expression and activity. Both ICI 182,780 and TAM failed to modulate Pgp expression as assessed by flow cytometry and Western-blot analysis, performed using the monoclonal antibodies MM4.17 and C 219, which are specific for an external or an internal determinant respectively. Pgp activity was investigated by flow cytometry measuring the extrusion of ADR and the cationic dye Rhodamine 123 (Rh 123). ICI 182,780, but not TAM, reduced the activity of Pgp in MCF-7 ADRr cells. Flow cytometry was also used to investigate cell-cycle modifications induced by ADR in MCF-7 ADRr cells, both in the presence and in the absence of anti-estrogens. After 72 hr, higher doses induced an arrest of cells at the G2/M phase. The same effect was visible when lower doses of ADR were combined with ICI 182,780 or TAM. In terms of cell-cycle-blocking activity ICI 182,780 was largely more effective than TAM.
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PMID:Modulatory effect of tamoxifen and ICI 182,780 on adriamycin resistance in MCF-7 human breast-cancer cells. 890 76

Rhodamine 123 has been shown to be a substrate for P-glycoprotein in multidrug resistant cells. In the present investigation the disposition of rhodamine 123 was studied in the isolated perfused rat kidney. After exposing the kidneys to perfusate concentrations ranging from 10 to 1000 ng/ml, the renal clearance was 4-1 times the clearance by glomerular filtration, respectively, indicating active and saturable secretion of rhodamine 123. The rate-limiting step in secretion was found to be membrane passage from cell to tubular lumen. Suprisingly, renal clearance was not influenced by the P-glycoprotein inhibitors cyclosporin A or digoxin. However, pretreatment of the kidneys with verapamil and quinidine (inhibitors of both P-glycoprotein and organic cation transport) or cimetidine (organic cation transport inhibitor) resulted in a significantly reduced rhodamine 123 clearance, indicating that the renal organic cation carrier may be involved in active secretion. Rhodamine 123 accumulated extensively in the isolated perfused rat kidney; tissue concentrations of 270-360 times the perfusate concentration were determined. Similar accumulation ratios at different perfusate concentrations were found, suggesting that the compound enters the tubular cells by (facilitated) diffusion. In conclusion, rhodamine 123 accumulated extensively in the isolated perfused rat kidney and active renal secretion appears to be preferentially mediated by the organic cation carrier and not by P-glycoprotein.
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PMID:Rhodamine 123 accumulates extensively in the isolated perfused rat kidney and is secreted by the organic cation system. 908 43

We have shown previously that the mouse CD4 memory cell subset can be divided into two subpopulations based on differential expression of P-glycoprotein. Cells with high levels of P-glycoprotein can be detected by extrusion of the fluorochrome Rhodamine 123; they are referred to as R123lo cells. These R123lo T cells increase with age and have been shown not to respond to anti-CD3 and IL-2 by proliferation or IL-4 production. We report here (a) that the failure of the R123lo CD4 memory population to respond to anti-CD3/IL-2 stimulation cannot be overcome by addition of anti-CD28, PMA, IL-4 or IL-12, alone or in various combinations, and (b) that this age-dependent subset exhibits impaired production of IL-5 and IL-10 as well as decreased proliferation. R123lo CD4 memory cells from young mice are also deficient in IFN gamma secretion by this subset. Although the R123lo cells respond poorly to receptor-dependent agonists, they can be triggered to proliferate and produce IFN gamma by the combination of PMA and ionomycin. In addition to increasing the proportion of R123lo cells in the memory CD4 pool, aging also leads to a decline in the ability of R123hi cells to produce IL-5 and IL-10. Thus, the accumulation of R123lo cells cannot by itself account for the poor proliferation and Th2 cytokine production of aged T cells in cytokine-supplemented culture conditions.
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PMID:Cytokine production by subsets of CD4 memory T cells differing in P-glycoprotein expression: effects of aging. 915 47

The MDR1 gene product, P-glycoprotein (P-gp), works as a transmembrane efflux pump for several cytotoxic products, representing a major cause for cancer treatment failure. Rhodamine 123 (Rh123), a low toxic fluorescent probe commonly used to assess mitochondrial bioenergetics in living cells, has also been used to measure the efflux activity of P-gp in both normal and malignant cells. Analysis of variation in cellular fluorescence by measuring the rates of Rh123 influx and efflux, together with the effect of mdr reversing agents, allows the investigation of drug-resistant phenotypes in cancer samples. We have studied the functional activity of P-gp in human leukemic cell lines using flow cytometry, taking into consideration that variables such as Rh123 cytotoxicity, culture conditions, cell membrane integrity, as well as the effect of specific P-gp modulators, can impair the resolution of the Rh123-efflux measurements. The studies show that: (1)optimal non-cytotoxic concentrations of Rh123 which allow appropriate color compensation are in the range of 50-200 ng/ml; (2) life-gating allows accurate measurement on the 50% average rate of Rh123 efflux; (3) relative efficiency of P-gp inhibitors was PSC-833 > cyclosporin A > verapamil; and (4) the presence or absence of fetal calf serum had no effect on the bioavailability of chemosensitizer agents, with the exception of serum-free experiments, which showed a significant decrease in P-gp activity under the presence of PSC-833 (P = 0.05). Hence, we recommend this experimental strategy for clinical practice better to study the cellular drug resistance phenotype.
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PMID:Flow cytometric analysis of P-glycoprotein function using rhodamine 123. 920 1

The development of multidrug resistance (MDR) in heterogeneous cell sensitive and resistant populations to a variety of clinically important cytotoxic drugs poses a major obstacle to cancer chemotherapy. The MDR phenotype is characterized by a decrease the intracellular drug accumulation and by an overexpression of the MDR1 gene which encodes the membrane protein, P-glycoprotein (Pgp). To evaluate the MDR phenotype, rationale investigations of the cytotoxic processes and effect,s of Adriamycin (ADR) were done to obtain information on individual cells. Such information could be obtained through a multiparametric approach involving multiwavelength microfluorometry and numerical image analysis on single living cells. To achieve this, cells should be simultaneously stained with Hoechst 33342 (nuclear staining), Rhodamine 123 (mitochondria staining) and Nile Red (cell contour delineation). Changes in the biological parameters accessible from R123, Ho33342 and C-SNARF-1/AM (probe used for the pHi measurements) labelling were found more informative than changes in morphological parameters for the discrimination of sensitive and resistant cells. Furthermore, this approach allows the discrimination between two resistant cell lines expressing different mechanisms of resistance.
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PMID:Multiwavelength videomicrofluorometric study of some human leukemic lymphoblasts: effect of adriamycin on some biological parameter. 961 71

We reviewed mechanisms of multidrug resistance (MDR) phenotype in tumor cells and evaluated analytical methods for detection of clinical MDR. A well-recognized mechanism of MDR phenotype is the induction and increased expression of P-glycoprotein (P-gp) which is a 170 kDa cellular transmembrane protein encoded by a multidrug-resistance 1 gene (MDR1) and works as a drug efflux pump. Cellular MDR phenotype through P-gp/MDR1 can be detectable at protein level by: (1) using immunohistochemical method, flow cytometric assay and Western blot analysis with monoclonal antibodies against human P-gp, and (2) measuring Rhodamine 123 dye-efflux as a functional assay of P-gp. Molecular knowledge and recent technical progress enable to determine MDR1 gene expression by RT-PCR-based analytical methods as well as conventional quantification methods of gene expression such as Northern blot analysis. In the evaluation of P-gp/MDR1 expression in clinical samples, in which amount of materials was limited, utilization of simple and sensitive methods like competitive RT-PCR assay might be efficacious for its quantitative detection in clinical laboratories. Evidences which showed the positive correlation between the expression of P-gp/MDR1 and clinical resistance or refractoriness of tumor cells to anticancer drugs involved in MDR have been accumulated and support the clinical importance of its detection to circumvent resistance with alternate use of non-MDR drugs.
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PMID:[Mechanisms of multidrug resistance in tumor cells and analytical methods for its detection]. 976 Aug 26


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