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)

The effects of GSH depletion in a human breast cancer cell line and a multi-drug resistant subline (ADRr) were determined in a number of experimental conditions. The ADRr cells contained lower GSH concentration which cannot be explained solely on the basis of differences in cell kinetics, and yet the rate-limiting synthetic enzyme gamma-glutamylcysteine synthetase was increased 2-fold. Inhibition of GSH synthesis by BSO resulted in more rapid and more pronounced GSH depletion in ADRr compared to the wild-type cells, suggesting that enhanced GSH utilization and efflux in the resistant cells account for the lowered basal concentration. In addition, the gamma-glutamyl moiety salvage enzyme gamma-glutamyltranspeptidase was reduced markedly in the ADRr cell line. Since these cells have overexpression of the efflux pump protein P-glycoprotein, we examined the effects on cellular GSH of inhibition of the pump's function by verapamil. We found that verapamil significantly depleted cellular GSH. In a rat mammary carcinoma cell line selected in Adriamycin for multi-drug resistance, a similar molecular phenotype has been described including diminished cellular GSH concentration. Verapamil treatment of these cells also resulted in significant depletion of cellular GSH. These results are consistent with the recent report that combined treatment of BSO and verapamil has an additive effect on cytotoxicity. It is likely that decreased basal GSH concentration is due to oxidation and conjugation of it in reactions catalyzed by the enhanced peroxidase and GST found in these cells.
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PMID:Glutathione depletion in human and in rat multi-drug resistant breast cancer cell lines. 199 9

We report the immunohistochemical detection of the 170-180 kDa multi-drug-resistance-related P-glycoprotein in human tumor cells with a low level of resistance. A series of human squamous lung cancer cell lines with increasing levels of resistance to doxorubicin (DOX) was developed and stained for P-glycoprotein, using the JSB-IMAb. Subline SW1573/50A with a 4- to 6-fold cross-resistance to daunorubicin (DNR) and vincristine (VCR) showed rather uniform positive staining for P-glycoprotein apparently at cytoplasmic sites. Only in cells with higher degrees of resistance (greater than 10-fold) could plasma-membrane-associated P-glycoprotein be made visible. DNR efflux was increased in SW1573/50A as compared to the parent line SW1573 (52 and 70% DNR were retained during 3 min efflux respectively). Verapamil partially reversed DNR and VCR resistance in SW1573/50A. Cells obtained from a metastasized renal cell carcinoma and cultured in vitro stained in a similar way to SW1573/50A and showed some sensitivity to verapamil modulation of VCR cytotoxicity. Our results suggest that weakly resistant cancer cells obtained from patients can be routinely detected with JSB-I on cytospins, and implicate that in such weakly resistant cells P-glycoprotein may be present, while plasma membrane expression is not yet readily detectable.
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PMID:Immunohistochemical detection of P-glycoprotein in human tumor cells with a low degree of drug resistance. 256 22

The B-cell neoplasms, multiple myeloma and non-Hodgkin's lymphoma, frequently become drug resistant, despite initial responses to chemotherapeutic drugs. Tumor cells from eight patients with clinically drug-refractory disease were evaluated by immuno-histochemical staining for monoclonal immunoglobulin (Ig) expression, nuclear proliferation antigen, P-glycoprotein (P-gly) expression, and other cellular antigens. P-gly was detected on tumor cells from six of eight patients with drug-resistant disease. Of the six patients with P-gly-positive tumors, five patients had advanced multiple myeloma and one had a drug-refractory non-Hodgkin's lymphoma. Cellular RNA analysis confirmed the over-expression of P-gly. In an effort to overcome drug resistance, a pilot study evaluated possible verapamil enhancement of chemotherapy in these eight patients. All patients had developed progressive disease while receiving a regimen containing vincristine and doxorubicin, and seven of eight patients had previously received continuous infusion vincristine and doxorubicin plus oral dexamethasone (VAD). At the time of progressive disease, continuous infusion verapamil was added to the VAD regimen. Three of the eight patients who were refractory to vincristine and doxorubicin alone responded when verapamil was added to VAD. The three patients who responded had P-gly-positive tumors. Verapamil increased the intracellular accumulation of doxorubicin and vincristine in vitro for both a P-gly-positive myeloma cell line and tumor cells from two patients with end-stage myeloma which over-expressed P-gly. The dose-limiting side effect associated with the addition of verapamil to chemotherapy was temporary impairment of cardiac function, manifest as hypotension and cardiac arrhythmia. We conclude that P-gly expression occurs in drug-refractory B-cell neoplasms and may contribute to the development of clinical drug resistance. However, other factors, such as the proliferative activity of the tumor, may also play a role in determining response to chemotherapy. The administration of verapamil along with VAD chemotherapy may partially circumvent drug resistance in patients whose tumors over-express P-gly.
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PMID:Drug-resistance in multiple myeloma and non-Hodgkin's lymphoma: detection of P-glycoprotein and potential circumvention by addition of verapamil to chemotherapy. 277 86

We show that drugs, such as verapamil, which reverse multidrug resistance (MDR), in P-glycoprotein-overexpressing tumor cells, increased the rate of lactate production in four human MDR cell lines, but not in the parent, sensitive cell lines. The effect on glycolytic rate was maximal at a medium concentration of 2 microM verapamil. The glycolytic rate in sensitive (A2780) and MDR 2780AD) cells showed the same pH dependence, but the effect of verapamil was seen only in 2780AD cells at all pH values investigated (6.6, 7.4 and 8.2). A series of drugs such as nigericin, oligomycin, amiloride and monensin had similar effects in the two cells. Phorbol myristate acetate increased lactate formation in neither cell line. Verapamil induced an extra amount of ATP consumption in P-glycoprotein-expressing 2780AD cells of approx. 25 pmol/s per 10(6) cells, which was estimated to be about 10% of cellular energy turnover.
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PMID:Glycolysis in P-glycoprotein-overexpressing human tumor cell lines. Effects of resistance-modifying agents. 256 23

We have examined the ability of eight compounds to enhance adriamycin (ADM) sensitivity of two human tumour cell lines (a small cell lung cancer cell line, NCI-H69, and a fibrosarcoma cell line, HT1080) and their multidrug-resistant variants. The resistant cell lines (H69AR and HT1080/DR4) do not overexpress P-glycoprotein. Verapamil, nicardipine, perhexiline maleate, chloroquine, tamoxifen, clomiphene, prenylamine and trifluoperazine were tested alone and in combination with ADM for their cytotoxic effects. No major differences in sensitivity between the parent and resistant cell lines were noted when these agents were tested alone, except for HT1080/DR4 cells which exhibited a slight collateral sensitivity to nicardipine and H69AR cells which showed cross-resistance to chloroquine and clomiphene. When the chemosensitisers were combined with ADM no enhanced cytotoxicity of either parent cell line was observed. In HT1080/DR4 cells, verapamil showed only a modest dose-dependent chemosensitising effect while the other compounds had no effect. Verapamil and nicardipine enhanced ADM cytotoxicity in H69AR cells slightly but these effects were not dose-dependent. These results demonstrate that the reversal of drug resistance by verapamil and other calcium antagonists in a dose-dependent fashion is not an invariable property of multidrug-resistant tumour cells.
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PMID:Effect of calcium antagonists on the chemosensitivity of two multidrug-resistant human tumour cell lines which do not overexpress P-glycoprotein. 256 25

Trimetrexate (TMQ) is a lipophilic antifolate shown to have antitumor activity in humans. TMQ-resistant sublines of the MOLT-3 human acute lymphoblastic leukemia cell line were developed and were designated as MOLT-3/TMQ200, MOLT-3/TMQ800, and MOLT-3/TMQ2500 based on degrees of resistance to TMQ. The TMQ resistance was accompanied by 5- to 7-fold increases in dihydrofolate reductase activity and markedly reduced cellular TMQ accumulation. Methotrexate accumulation was not impaired in TMQ-resistant cells. TMQ retention (efflux) was unchanged in these TMQ-resistant cells. Verapamil enhanced the TMQ accumulation in the resistant cells to the level seen in the parent cells but had no effects on the TMQ retention. These sublines were cross-resistant not only to methotrexate but also to vincristine, doxorubicin, daunorubicin, and mitoxantrone. There was no cross-resistance to bleomycin or cisplatin. Resistance to vincristine, doxorubicin, daunorubicin, and mitoxantrone was reversed by verapamil. TMQ resistance was only minimally reversed by verapamil and methotrexate resistance not affected at all. Both cellular accumulation and retention of vincristine and daunorubicin in the TMQ-resistant cells were markedly decreased. Verapamil enhanced both accumulation and retention of the drug. Plasma membrane fractions of the TMQ-resistant cells analyzed by urea-sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by staining with Coomassie Blue revealed the presence of a distinct band with a molecular weight of 170,000. Immunoblot analysis with 125I-labeled monoclonal antibody raised against P-glycoprotein of multidrug-resistant Chinese hamster ovary cells (C219) cross-reacted with the Mr 170,000 protein of the TMQ-resistant cells. These results show that the TMQ-resistant cells displayed not only decreased TMQ uptake and increased dihydrofolate reductase but also characteristics associated with a classical multidrug-resistant phenotype. Multidrug resistance includes lipophilic antifolate.
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PMID:Multidrug resistance in a human leukemic cell line selected for resistance to trimetrexate. 257 16

Verapamil sensitizes multidrug-resistant cell lines to various heterocyclic anticancer drugs by inhibition of energy-dependent release of drug, presumably by interaction with membrane glycoproteins involved in drug efflux. This work assessed verapamil sensitization of human multidrug-resistant lymphocytic and myeloid leukemic cell lines (CEM/VLB100, HL-60/AR) to vincristine during exposures of short duration (4 h). When cells were transferred to drug-free medium immediately after simultaneous 4-h exposures to vincristine and verapamil, the antiproliferative activity of vincristine was not altered in CEM/VLB100 cells and was only moderately increased in HL-60/AR cells. In contrast, when cells were transferred to verapamil-containing medium, vincristine activity was greatly increased against both CEM/VLB100 and HL-60/AR cells. Verapamil enhanced accumulation and inhibited release of [3H]vincristine by CEM/VLB100 and HL-60/AR cells, indicating that the sensitization was due to an increase in cell-associated vincristine after transfer of cells to vincristine-free medium. Slot blot analysis of cellular RNA with the pMDR1 probe revealed high levels of expression of the mdr1 gene in CEM/VLB100 cells but no detectable expression in HL-60/AR cells. Consistent with this finding, polypeptides (Mr 170,000 to 180,000) that were recognized by a monoclonal antibody (C219) against P-glycoprotein were greatly overexpressed in CEM/VLB100 cells, but were expressed at low levels, if at all, in HL-60/AR cells. These results demonstrate the importance of duration of exposure to verapamil in reversing multidrug resistance, not only in cells that overexpress P-glycoprotein but also in cells, such as HL-60/AR, that express little, if any, P-glycoprotein.
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PMID:Effect of duration of exposure to verapamil on vincristine activity against multidrug-resistant human leukemic cell lines. 279 Jul 92

We previously described the cross-resistance patterns and cellular pharmacology of a human leukemic cell line, CEM/VM-1, selected for resistance to the epipodophyllotoxin teniposide (M. K. Danks et al., Cancer Res., 47: 1297-1301, 1987). Compared to CEM/VLB100, which is a well characterized "classic" multidrug-resistant (MDR) cell line, the CEM/VM-1 cells display "atypical" multidrug resistance (at-MDR) in that they are cross-resistant to a wide variety of natural product antitumor drugs, except the Vinca alkaloids, and they are not impaired in their ability to accumulate radiolabeled epipodophyllotoxin. We have extended our characterization of this at-MDR cell line in the present study. In comparison to CEM/VLB100 cells, we found that CEM/VM-1 cells are not cross-resistant to either actinomycin D or colchicine. Verapamil and chloroquine, which enhance the cytotoxicity of vinblastine in CEM/VLB100 cells, had little or no ability to do so in the CEM/VM-1 cells. Membrane vesicles of the two resistant sublines were examined for overexpression of the MDR-associated plasma membrane protein (P-glycoprotein, Mr 170,000 protein, or 180,000 glycoprotein) by photoaffinity labeling with the vinblastine analogue N-(p-azido[3-125I]salicyl)-N'-beta-aminoethylvindesine. We were unable to visualize the MDR-associated protein in the CEM/VM-1 membranes with this photoaffinity probe under conditions in which the P-glycoprotein was readily seen in the membranes of CEM/VLB100 cells. Furthermore, no hybridization of the pMDR1 complementary DNA was seen in slot-blot analyses of the RNA from at-MDR cells, indicating that the mdr gene coding for P-glycoprotein is not overexpressed as is the case in the classic MDR cells. However, cytogenetic analysis indicated that the CEM/VM-1 cells contained an abnormally banded region on chromosome 13q, suggesting that a gene other than mdr may be amplified in these cells. Thus, despite the two cell lines having approximately equal degrees of resistance to epipodophyllotoxins, our data indicate that the mechanism(s) responsible for at-MDR is different from that for classic, P-glycoprotein-associated MDR.
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PMID:Pharmacological, molecular, and cytogenetic analysis of "atypical" multidrug-resistant human leukemic cells. 288 32

A human colon carcinoma cell line selected for a 21-fold resistance to mitoxantrone was cross-resistant to the anthracycline, doxorubicin, but not to the anthracene, bisantrene. A 2-fold resistance was observed with vinblastine, another drug associated with multidrug resistance. Net intracellular mitoxantrone and doxorubicin accumulation were decreased at 1 h for all dose levels in the resistant cell line compared to the sensitive cell line. Although the resistant cells were more resistant to mitoxantrone than doxorubicin, the net accumulation of mitoxantrone was only 19% less than the sensitive cell line; whereas doxorubicin accumulation was decreased by 49%. No significant difference between the sensitive and resistant cell lines was observed in the initial accumulation of mitoxantrone; however, the efflux of mitoxantrone was increased in the resistant cell line. Verapamil did not overcome the resistance to mitoxantrone and did not increase the net accumulation of drug. No alterations in the electrophoretic mobility of membrane proteins were observed. Using immunoblotting techniques, the resistant cell line did not express P-glycoprotein which is frequently observed for cells resistant to anthracycline antibiotics. Cytogenetic analysis showed a putative homogenously staining region on the short arm of chromosome 7 in the resistant cell line. The limited cross-resistant phenotype, lack of verapamil reversal, nondetection of P-glycoprotein, and cytogenetic evidence of gene amplification suggests the involvement of a novel drug-resistant gene associated with resistance to mitoxantrone.
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PMID:Cytogenetic and phenotypic analysis of a human colon carcinoma cell line resistant to mitoxantrone. 289 93

Cyclosporin accumulation was reduced by 50% or more in multidrug- resistant CHRC5 CHO cells with high levels of P-glycoprotein expression compared to drug sensitive AuxB1 CHO cells. This difference could be overcome by verapamil which is known to interact with P-glycoprotein and reverse multidrug resistance. The difference in cyclosporin accumulation between sensitive and resistant cells decreased with increasing cyclosporin concentrations suggesting that cyclosporine itself regulated its own accumulation through interaction with P-glycoprotein. Indeed, cyclosporin also reversed differences in vinblastine accumulation between resistant and sensitive cell lines. Since P-glycoprotein is highly expressed in the kidney which is also a target for cyclosporin toxicity, the effects of verapamil on cyclosporin accumulation were studied in two renal cell lines, rat mesangial cells and LLCPK1, cells. Verapamil increased cyclosporin accumulation by approximately 70%. These results suggest that cellular cyclosporine accumulation is regulated at least in part by its interaction with P-glycoprotein.
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PMID:Reduced cyclosporin accumulation in multidrug-resistant cells. 289


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