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)

Resistance of tumor cells to doxorubicin is a multifactorial phenomenon. In the present investigation, the ability of resistance modifiers against different resistance mechanisms was analysed. Substances which block P-glycoprotein (P-170) function circumvented resistance of doxorubicin-resistant sarcoma 180 (S180) cells completely (verapamil, thioridazine) or partially (hycanthone), whereas inhibitors of glutathione S-transferase (ethacrynic acid, N-ethylmaleimide, buthionine sulfoximine), and protein kinase C (staurosporine, acridine orange) caused only a partial reversion of resistance. In contrast, an inhibitor of alkaline phosphatase (levamisole) did not overcome doxorubicin-resistance. These results indicate that P-glycoprotein blockers might be more effective to modulate doxorubicin-resistance of S180 cells as compared to other modifiers. Further investigations using other MDR cell lines are required to clarify the generality of these findings.
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PMID:Reversal of doxorubicin-resistance in sarcoma 180 tumor cells by inhibition of different resistance mechanisms. 810 93

The expression of alkaline phosphatase (AP) was analyzed in multidrug-resistant (MDR) tumor cells (sarcoma 180, lung carcinoma, and renal cell carcinoma cell lines) by means of immunocytochemistry. MDR cell cultures showed an overexpression of AP and a cross-resistance to 6-thioguanine (6-TG, CAS 154-42-7). Significant correlations between AP expression and doxorubicin or vincristine resistance and P-glycoprotein (P-170) expression were found in these cell cultures. A specific AP inhibitor, levamisole, reversed resistance to 6-TG, but not to doxorubicin. This indicates that 6-TG resistance is certainly associated to P-170 but a causal function of AP for the development of MDR does not exist.
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PMID:Increase of alkaline phosphatase in multidrug-resistant tumor cells and their cross-resistance to 6-thioguanine. 826 80

Anthracyclines and etoposide have been implicated in the multi-drug resistance phenotype. The mdr 1 gene encodes for the transmembrane protein P-glycoprotein. P-glycoprotein expression was measured in the fresh blast cells from 19 patients with acute myeloid leukemia using three monoclonal antibodies, C219, JSB-1 and MRK 16, and immunocytochemistry with the enzyme alkaline phosphatase as marker. Drug resistance can be identified in vitro using the predictive chemosensitivity test, the MTT (3-4,5-dimethylthiazol-2,5-diphenyl tetrazolium bromide) assay. In order to assess cell viability after drug exposure, this technique utilises the ability of cellular dehydrogenase enzymes to reduce the tetrazolium salt MTT to formazan. In vitro resistance to multi-drug resistance related cytotoxic agents was identified in the blast cells from these patients. This study showed no correlation between the results of the MTT assay and P-glycoprotein expression in this disease, suggesting either that more sensitive techniques are required to measure P-glycoprotein expression or that other drug resistance mechanisms may be involved.
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PMID:Comparison of P-glycoprotein expression with in vitro drug sensitivity in fresh blast cells from acute myeloid leukaemia patients. 852 96

P-glycoprotein is an adenosine triphosphate-dependent drug-efflux pump that extrudes drugs from cells and causes drug-resistance. P-glycoprotein is believed to mediate drug-resistance in a wide variety of tumors. In this study, we developed two P-glycoprotein-positive, murine osteosarcoma cell lines that were resistant to Adriamycin (doxorubicin) (MOS/ADR1 and MOS/ADR2). We created the cell lines by short-term pulse exposures of the parent cell line to Adriamycin followed by single-cell cloning. The MOS/ADR1 and MOS/ADR2 cells were sevenfold and eighteenfold more resistant to Adriamycin than the cells from the parent line. Expression of P-glycoprotein, as examined with an immunofluorescence method, was detected in most of the MOS/ADR1 and MOS/ADR2 cells but not in the parent cells. After the cells had been incubated with Adriamycin for one hour, there was less accumulation of the drug in the resistant cell lines than in the parent cell line. The reduced accumulation was due to the increased efflux of Adriamycin. The Adriamycin-resistant cell lines demonstrated greater alkaline phosphatase activity than the parent cell line and produced more differentiated osteoblastic sarcomas in mice. Dose survival studies with use of a tetrazolium colorimetric assay showed that the MOS/ADR1 cells were cross-resistant to vincristine, vinblastine, etoposide, bleomycin, mitomycin C, and actinomycin D but not to dacarbazine, cisplatin, carboplatin, cytosine arabinoside, carmustine, cyclophosphamide, ifosfamide, methotrexate, and 5-fluorouracil. Although the MOS/ADR2 cells exhibited a similar spectrum of cross-resistance, they were more resistant than the MOS/ADR1 cells. We also tested the effect of three different resistance-modifying agents on the reversal of resistance to Adriamycin. We found that verapamil and trifluoperazine substantially reversed resistance to Adriamycin in the P-glycoprotein positive cell lines, whereas cyclosporin A was relatively ineffective. Because these cell lines retain the histological and biochemical features of bone-producing sarcomas and display the multidrug-resistant phenotype, they may be useful models for additional investigations of drug resistance in osteosarcoma.
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PMID:Experimental models for the study of drug resistance in osteosarcoma: P-glycoprotein-positive, murine osteosarcoma cell lines. 861 43

1. Morphine-6-glucuronide is one of the major metabolites of morphine. The potent analgesic action of this compound together with its potential lower apparent toxicity in man, when compared with morphine, indicated its clinical importance. 2. Primary cultures of porcine brain capillary endothelial cells were used to study brain penetration of morphine-6-glucuronide. Biochemical characterization of the cell cultures revealed a marked enrichment in enzymatic activity of alkaline phosphatase (56 fold) and angiotensin converting enzyme (230 fold) as compared to whole brain tissue. By immunostaining the presence of vimentin, factor VIII, the tight junction associated protein ZO-1, and P-glycoprotein was shown. Functional characterization revealed that the carrier system responsible for transport of neutral amino acids was intact. 3. Uptake and transport of morphine-6-glucuronide was marginal and in the range of the extracellular marker sucrose. However, uptake of morphine-6-glucuronide was enhanced significantly (P < 0.0001) in presence of the inhibitors of P-glycoprotein, verapamil or vincristine. The finding that morphine-6-glucuronide may serve as a substrate for P-glycoprotein was confirmed in multidrug-resistant P388 tumour cells. 4. We conclude that penetration of the blood-brain barrier by morphine-6-glucuronide may depend on the expression of the product of the multidrug-resistance (MDR) gene in brain capillary endothelial cells.
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PMID:Evidence for P-glycoprotein-modulated penetration of morphine-6-glucuronide into brain capillary endothelium. 886 18

1. The liver has an important role in the detoxification of organic cations from the circulation. [3H]-1-methyl-4-phenylpyridinium ([3H]-MPP+), a low molecular weight organic cation, is efficiently taken up and accumulated by rat hepatocytes through mechanisms partially unknown. 2. The aim of the present work was to characterize further the uptake of MPP+ by rat isolated hepatocytes. The putative interactions of a wide range of drugs, including inhibitors/substrates of P-glycoprotein, were studied. 3. The uptake of MPP+ was investigated in rat freshly isolated hepatocytes (incubated in Krebs-Henseleit medium with 200 nM [3H]-MPP+ for 5 min) and in the rat liver in situ (perfused with Krebs-Henseleit/BSA medium with 200 nM [3H]-MPP+ for 30 min). [3H]-MPP+ accumulation in the cells and in tissue was determined by liquid scintillation counting. 4. Verapamil (100 microM), quinidine (100 microM), amiloride (1 mM), (+)-tubocurarine (100 microM), vecuronium (45 microM), bilirubin (200 microM), progesterone (200 microM), daunomycin (100 microM), vinblastine (100 microM), cyclosporin A (100 microM) and cimetidine (100 microM) had a significant inhibitory effect on the accumulation of [3H]-MPP+ in isolated hepatocytes. Tetraethylammonium (100 microM) had no effect. 5. In the rat perfused liver, both cyclosporin A (100 microM) and verapamil (100 microM) had much less marked inhibitory effects as compared to their effects on isolated hepatocytes (0% against 35% and 45% against 96% of inhibition, respectively). 6. Inhibition of alkaline phosphatase activity by increasing or decreasing the pH of the incubation medium or by the presence of vanadate (1 mM) or homoarginine (500 microM) led to a significant increase in the accumulation of [3H]-MPP+ in isolated hepatocytes. 7. It was concluded that, in addition to the type I organic cation hepatic transporter, [3H]-MPP+ is taken up by rat hepatocytes through P-glycoprotein, a canalicular transport system that usually excretes endobiotics and xenobiotics. We proposed that the reversal of transport through P-glycoprotein may be related to the loss of efficacy of alkaline in isolated hepatocytes.
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PMID:Inward transport of [3H]-1-methyl-4-phenylpyridinium in rat isolated hepatocytes: putative involvement of a P-glycoprotein transporter. 898 96

Multidrug resistance in leukemic cells is associated with decreased drug accumulation. A resistant cell line and cells from 11 patients with chronic lymphoid leukemia B were used for the evaluation of intracellular accumulation of daunorubicin (DNR), idarubicin (IDA), epirubicin (EPI) and rhodamine-123 (Rh-123). Cyclosporin A (CSA) and verapamil were used to test their modulatory effects on anthracyclines and the fluorescent dye. In leukemic samples there was a tendency for a lower accumulation index in samples tested with Rh-123 as compared to anthracyclines. IDA was a poorer substrate to P-glycoprotein (Pgp) than two of its analogues, e.g. DNR and EPI. A good correlation (80%) was found between Rh-123 accumulation and Pgp expression by phosphatase-anti-alkaline phosphatase. A strict correlation (100%) was found between modulation by CSA of Rh-123 accumulation and immunoreactivity to Pgp. Two discordant results were seen suggesting that other mechanisms of resistance could be present. The Rh-123 accumulation test seems to give a better indication than anthracyclines, however, it is not selective and may allow the detection of other drug-transport pumps.
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PMID:Comparison between anthracyclines and rhodamine-123 accumulation in chronic lymphoid leukemia: effect of cyclosporin A and verapamil. 942 81

A recent study of multidrug resistance (MDR) 1 gene transfected osteosarcoma cells found a cause-effect relationship between increased expression of P-glycoprotein (P-gp) and a low aggressive phenotype. However, several experimental and clinical studies have observed contradictory findings in that P-gp expression has been associated with tumour progression. In the present study, we characterized P-gp-positive and P-gp-negative single-cell clones of a murine osteosarcoma, to further investigate the relationship between P-gp expression and changes in cell phenotype. Although these clones were all selected by doxorubicin (DOX) exposure, they were heterogeneous with respect to MDR1 gene expression. The P-gp-positive clones revealed MDR phenotype, whereas the P-gp-negative clones showed no resistance to drugs. Morphological and functional analysis showed that both the P-gp-positive and P-gp-negative clones were more differentiated than the parent cells in terms of enhanced activity of cellular alkaline phosphatase, an increase in well-organized actin stress fibres and enhanced osteogenic activity. Moreover, these subclones all displayed a decrease in malignant potential such as oncogenic activity, tumour growth rate and metastatic ability, regardless of their P-gp status. These results indicate that the observed osteoblastic differentiation and less aggressive phenotype in DOX-selected osteosarcoma cells may not only be explained by the direct effect of P-gp, and accordingly, consideration of the effect of DOX, as well as P-gp, appears to be important.
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PMID:Osteoblastic differentiation and P-glycoprotein multidrug resistance in a murine osteosarcoma model. 1075 9

Alkaline phosphatases (orthophosphoric-monoester phosphohydrolase, E. C. 3.1.3.1) are a group of nonspecific phosphomonoesterases located primarily in the plasma membrane of the cells in which they occur [1]. It was recently demonstrated that alkaline phosphatase (ALP) concentration in different tissues is positively correlated with the extent of exchange surface per unit volume of the tissue, suggesting an association between ALP and transport systems [2]. Moreover, several groups [3,4,5] obtained evidence of an involvement of ALP in the modulation of P-glycoprotein activity in hepatocytes. The aim of the present study was to determine the putative influence of compounds known to modulate P-glycoprotein-mediated transport on hepatic ALP activity, by using primary cultured rat hepatocytes. The K(m) and V(max) values of ALP were determined (657.2 microM (306.8-933.1) and 32.0+/-1.5 nmol mg protein(-1) min(-1), respectively). Vanadate and corticosterone concentration-dependently reduced ALP activity, producing maximal reductions of 79% (100 microM) and 71% (100 microM), respectively. The IC50's were found to be 7.9 microM (2.1-29.5 microM) and 2.4 microM (0.2-35.2 microM), respectively. Cyclosporin A, verapamil, octreotide, kaempferol, daunomycin and genistein produced a concentration-dependent increase in ALP activity. ALP activity was maximally increased to 253%, 390%, 180%, 487%, 449% and 193% of control in the presence of 100 microM cyclosporin A, 50 microM verapamil, 10 microM octreotide, 100 microM kaempferol, 100 microM daunomycin and 1 microM genistein, respectively. The results show that all P-glycoprotein modulators tested were able to significantly affect the activity of hepatic-ALP. These effects on ALP activity may contribute to the modulation of P-glycoprotein activity by these drugs.
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PMID:Effect of P-glycoprotein modulators on alkaline phosphatase activity in cultured rat hepatocytes. 1109 29

Five immortalized brain capillary endothelial cell lines (TM-BBB1-5) were established from 3 transgenic mice harboring temperature-sensitive simian virus 40 large T-antigen gene (Tg mouse). These cell lines expressed active large T-antigen and grew well at 33 degrees C with a doubling time of about 20 to 30 hours. TM-BBBs also grew at 37 degrees C but not at 39 degrees C. However, growth was restored when the temperature of the culture was lowered to 33 degrees C. Although significant amounts of large T-antigen were shown to be present in the cell culture at 33 degrees C, there was less of this complex at 37 degrees C and 39 degrees C. TM-BBBs expressed the typical endothelial marker, von Willebrand factor, and exhibited acetylated low-density lipoprotein uptake activity. The alkaline phosphatase and gamma-glutamyltranspeptidase activity in TM-BBBs were -10% and 50% to 80% of brain capillary fraction of normal mice, respectively. D-mannitol transport in the both apical-to-basal and basal-to-apical directions across the TM-BBB was 2-fold greater than for inulin. TM-BBBs were found to express GLUT-1 but not GLUT-3, and exhibited concentration-dependent 3-O-methyl-D-glucose (3-OMG) uptake activity with a Michaelis-Menten constant of 6.59 +/- 1.16 mmol/l. Moreover, P-glycoprotein (P-gp) with a molecular weight of -170 kDa was expressed in all TM-BBBs. Both mdr1a and mdr1b mRNA were detected in TM-BBB4 using reverse transcription-polymerase chain reaction (RT-PCR) analysis. [3H]-Cyclosporin A uptake by TM-BBB was significantly increased in the presence of 100 micromol/l verapamil and vincristine, suggesting that TM-BBB exhibits efflux transport activity via P-gp. In conclusion, conditional brain capillary endothelial cell lines were established from Tg mice. This cell line expresses endothelial markers and transporters at the BBB and is able to regulate cell growth, due to the amount of active large T-antigen in the cell, by changing the culture temperature.
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PMID:Conditionally immortalized brain capillary endothelial cell lines established from a transgenic mouse harboring temperature-sensitive simian virus 40 large T-antigen gene. 1174 Dec 43


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