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)

Azatoxin (NSC 640737), a synthetic molecule, was rationally designed as a topoisomerase-II inhibitor and was shown to be a potent cytotoxic agent that inhibits both tubulin and topoisomerase II. A structure-activity relationship study allowed to select 3 derivatives that inhibit either tubulin (methylazatoxin) only or topoisomerase II (fluoroanilinoazatoxin and nitroanilino-azatoxin) in MTT assays performed on K562 and K562/ADM cells; the latter, expressing P-glycoprotein, indicated cross-resistance of K562/ADM cells to all 4 compounds. DNA double-strand breaks induced by the 3 azatoxins that inhibit topoisomerase II in vitro were decreased in K562/ADM as compared with K562 cells. Nitroanilino-azatoxin was the only compound for which resistance and reduced DNA damage observed in K562/ADM cells was partially reversed by verapamil, suggesting that nitroanilinoazatoxin was a substrate for P-glycoprotein. These results were confirmed by testing the cytotoxic activity of azatoxins on P-glycoprotein-expressing rat colon-carcinoma DHDK12/TRb cells in the absence and the presence of verapamil. Cell-cycle and mitotic-index studies indicated that azatoxin- and methyl-azatoxin-induced M-phase arrest was less in K562/ADM than in K562 cells. The G2 block induced by fluoro- and nitroanilinoazatoxins was delayed in K562/ADM cells. Verapamil increased cell-cycle inhibition induced by nitroanilinoazatoxin in K562/ADM cells without modifying cell-cycle effects of fluoroanilinoazatoxin. These results (i) are consistent with the specific inhibition of topoisomerase II or tubulin by azatoxin derivatives in cells; (ii) indicate that the nitro group of nitroanilinoazatoxin allows recognition and efflux by the P-glycoprotein; and (iii) suggest that cross-resistance of K562/ADM cells to other azatoxin derivatives is not mediated by P-glycoprotein.
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PMID:Cellular pharmacology of azatoxins (topoisomerase-II and tubulin inhibitors) in P-glycoprotein-positive and -negative cell lines. 759 Dec 16

The purpose of this study was to determine what proportion of drug resistance of MDR cell variant K562/Dox was attributed to the reduced steady state intracellular drug accumulation related to overexpression of P-glycoprotein. K562/Dox was derived from repeated exposure of human erythroleukaemic cell line K562 cell to doxorubicin. As assessed with MTT assay, the resistance of K562/Dox to 7 cytotoxic drugs increased variably in the range between 1200 and 11 folds. K562/Dox cells were positively stained with anti-human p-glycoprotein monoclonal antibody JSB-1, indicating overexpression of P-gp. Intracellular drug accumulation in K562/Dox, though significantly reduced as compared with that in K562 cells, was maximally restored by concurrent exposure of cells to 6 mumol/L verapamil and 1.72 mumol/L either of the doxorubicin, epirubicin or daunorubicin. Similar results were obtained by exposure of cells to 12 mumol/L verapamil and 8.62 mumol/L drug, indicating that restoration of intracellular drug accumulation in MDR cells was dependent on the relative concentrations of verapamil to drug. However, the resistances of K562/Dox cells to epirubicin and daunorubicin still remained for about 5.6 and > 6.6 folds, respectively, even at verapamil concentration of 6 mumol/L, suggesting at least a relatively big fraction of drug resistance was not directly related to the altered cellular pharmacokinetics associated with overexpression of P-glycoprotein.
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PMID:[Reduced intracellular drug accumulation related to overexpression of P-glycoprotein cannot explain the complete drug resistance in MDR cell variant K562/Dox]. 765 12

In a panel of acute myeloblastic leukemia (AML) cell lines, representative of distinct differentiation stages, we investigated the possible correlation between drug-resistance and both expression and function of the multidrug resistance (MDR)-related P-glycoprotein (P-gp). The AML cell lines were KG1a, KG1, TF1, HEL, ML1, and two non drug-selected P-gp positive subclones originating from HL-60 (HL-60JD) and U937 (U937AQ). All these cells overexpressed the mdr1 gene (analyzed by RT-PCR) and displayed variable levels of P-gp expression. Flow cytometric semi-quantitative evaluation of P-gp with two P-gp specific monoclonal antibodies (MRK16 and UIC2) showed the following P-gp expression hierarchy: TF1 < KG1a < HEL < KG1 < HL-60JD < ML1 < U937AQ; the latter expressing 13 times more P-gp than TF1. When P-gp function was assessed by Rhodamine 123 (Rh123) efflux kinetics, we found that only KG1a and KG1 cells, which have an early (immature) CD34+ CD33- CD38- phenotype, and to a lesser extent TF1, with an intermediate (CD34+ CD33+ CD38+) phenotype, displayed significant P-gp activity which could be inhibited by both verapamil and SDZ PSC 833. In contrast, the other more mature CD33+ CD34- AML cell lines presented no Rh123 efflux capacity although they expressed higher P-gp levels. Daunorubicin (DNR) accumulation studies showed that inhibitors of P-gp increased DNR accumulation only in the immature AML cells whereas they had no impact on the mature AML cell lines. MTT drug cytotoxicity assay confirmed that the immature AML cells were 10-15-fold more resistant to DNR than the mature AML cells. Although P-gp inhibitors were able to increase the cytotoxicity of DNR in AML cells which displayed functional P-gp, they could not increase DNR cytotoxicity to levels comparable to that of the CD34- CD33+ cells, suggesting that DNR resistance of immature AML cells may not solely be related to P-gp. With drug-selection, AML subclones displayed higher levels of P-gp expression and higher extruding capacities, and therefore chemoresistance, and this independently of their initial differentiation phenotype. Finally, this study provides evidence for a lack of correlation between expression and function of P-gp in AML cells; this relationship being dependent upon leukemic cell differentiation in unselected myeloid leukemic cells.
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PMID:Lack of correlation between expression and function of P-glycoprotein in acute myeloid leukemia cell lines. 776 42

The purpose of this study was to screen 24 anti-cancer drugs, either in use or in clinical study, using four cell lines, all of which originated from poorly-differentiated gastric cancers. The MTT assay was used at 1, 6, 24 or 72 h exposure times as the chemosensitivity test. We also examined P-glycoprotein expression, mdr-1 gene amplification and the modifier effect of verapamil. All four cell lines generally showed the same chemosensitivity pattern, while GCIY cells showed mdr-1 gene amplification and P-glycoprotein expression, and KATOIII cells showed the multidrug resistant pattern without P-glycoprotein expression. Both cell lines acquired higher chemosensitivity after verapamil addition. All IC50 data (with or without verapamil) were multiplied by exposure time (delta IC50) and compared with the clinical 'area under the concentration curve (AUC)'. SN-38 with/without verapamil, cisplatin with verapamil and pirarubicin with/without verapamil seemed to be the best candidates for poorly-differentiated gastric cancer chemotherapy. Plant alkaloids could also be candidates. With further experiments, we may be able to deduce commonly effective chemotherapy for poorly-differentiated gastric cancer from these drugs.
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PMID:Selection of three out of 24 anti-cancer agents in poorly-differentiated gastric cancer cell lines, evaluated by the AUC/delta IC50 ratio. 779 77

The newly identified drug transporter MRP is functionally linked to a multiple drug resistance independent from P-glycoprotein. Resistance modifiers for this type of MDR are rare at present. We analyzed the modulating effect of the highly selective bisindolylmaleimide PKC inhibitor GF 109203X on the MRP overexpressing human MDR sublines HL60/AR and GLC4/ADR. Applying a 72 hour MTT-assay we demonstrate a complete reversal of the vincristine resistance of HL60/AR cells. Adriamycin resistance of HL60/AR, or vincristine resistance of GLC4/ADR were partially reversed. Furthermore, rhodamine 123 efflux from HL60/AR was strongly modulated by GF 109203X. Since the PKC inhibitor did not significantly influence MRP gene expression at the mRNA level which was examined by cDNA-PCR, our results suggest either a direct interaction of the compound with MRP or/and an indirect influence on MRP activity via altering the phosphorylation status of the transporter.
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PMID:The specific bisindolylmaleimide PKC-inhibitor GF 109203X efficiently modulates MRP-associated multiple drug resistance. 781 10

The multidrug resistant cell lines HL60/AR and GLC4/ADR show high overexpression of the gene encoding the multidrug resistance associated protein MRP compared to their drug sensitive parental counterparts. This and the virtual absence of mdr1/P-glycoprotein gene expression was proven by a complementary DNA polymerase chain reaction (cDNA-PCR) approach. Applying a 72-hour tetrazolium based colorimetric MTT-assay we demonstrate on both MDR sublines a dose-dependent modulation of drug resistances by the leukotriene LTD4 receptor antagonist MK571. A complete reversal of vincristine resistances was achieved at final MK571 concentrations of 30 microM (HL60/AR) or 50 microM (GLC4/ADR) which by itself did not disturb cellular proliferation. The drug resistance of a mdr1/P-gp overexpressing multidrug-resistant HL60 subline, in contrast, was not significantly affected by MK571. Similar effects were seen using the glutathione (GSH) synthesis inhibitor buthionine sulfoximine (BSO). Our results point to a relationship between MRP and a conjugate transporter and identify MK571 as a new tool structure for developing modulators specific for a MRP associated multidrug resistance.
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PMID:The leukotriene LTD4 receptor antagonist MK571 specifically modulates MRP associated multidrug resistance. 788 49

The expression of P-glycoprotein (Pgp), which is associated with multidrug resistance (MDR), was investigated in 20 B-cell chronic lymphocytic leukaemia (B-CLL) patients by flow cytometry using two Pgp-specific monoclonal antibodies (mAb), MRK-16 which recognizes an extracellular epitope, and JSB-1 which recognizes an intracellular epitope. Sixteen (80%) patients were positive with MRK-16 whereas all patients were positive with JSB-1. The proportion of Pgp-positive lymphocytes from each patient sample varied from 2-94% for MRK-16 and 20-93% for JSB-1. There was no correlation between the level of positivity and disease stage or treatment history. In vitro drug resistance to vincristine (VCR) and doxorubicin (DOX) was determined by the colorimetric MTT assay. All patients were resistant to one or both drugs being consistent with the expression of Pgp. There was no correlation between the level of resistance and disease stage or drug treatment. We investigated the expression of Pgp in the normal counterpart of the B-CLL cells, CD5+CD19+ B-lymphocytes. A minor subpopulation (3%) of CD5+CD19+ lymphocytes isolated from normal controls expressed Pgp suggesting that these cells may be the potential precursors to the B-CLL cell. We conclude that Pgp expression and drug resistance are inherent characteristics of the B-CLL lymphocyte.
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PMID:Common expression of the multidrug resistance marker P-glycoprotein in B-cell chronic lymphocytic leukaemia and correlation with in vitro drug resistance. 790 53

We compared the effectiveness of two flow cytometric methods for the detection of the multidrug resistance (MDR) phenotype. The sensitivity of both methods depended on the ability to discriminate low resistance cells from sensitive ones. Therefore, K562 cells with decreasing vinblastine (VLB) resistance levels were examined, the lowest resistance level being nonmeasurable with a colorimetric MTT assay. The fluorescent drug daunorubicin (DNR) was measured in combination with two modulators of MDR, cyclosporin-A (CsA) and verapamil (Vp) in a functional flow cytometric assay. When compared to sensitive cells, DNR uptake levels at steady state were reduced in all resistant cell lines, except for the lowest resistant cell line. The effect of modulator, CsA, on DNR uptake was seen in all resistant sublines, compared to sensitive cells, except for the lowest resistant cells. In another assay, the P-glycoprotein (Pgp) expression was analysed with monoclonal antibodies, MRK16 and C219. MRK16 was found to be the most sensitive antibody to screen for MDR+ cells, since we could show Pgp hyperexpression in all resistant cells. C219 reactivity became evident in cells possessing resistance factors higher than 5. These results indicate that both the functional assay and the Pgp assay are sensitive to be used for screening of MDR+ cells.
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PMID:Evaluation of flow cytometry for multidrug resistance detection in low resistance K562 cells using daunorubicin and monoclonal antibodies. 790 31

A subline (PC-9/VCR) of the human lung adenocarcinoma cell line (PC-9), derived by in vitro exposure to vincristine (VCR), exhibited a 10-12-fold resistance to VCR by MTT and HTCA assay. Compared to the parental cell line (PC-9), PC-9/VCR-resistant cells displayed a reduced accumulation of VCR. The rate of VCR efflux was shown to be enhanced by PC-9/VCR. Unlike multidrug resistance, this efflux was independent of P-glycoprotein overexpression as determined by the Northern blotting method. In addition, PC-9/VCR showed no collateral sensitivity to verapamil. This resistant subline only showed 6.9-fold and 2.5-fold cross resistance to colchicine and vinblastine, respectively. This preliminary result indicates that defective drug accumulation in PC-9/VCR is due to other mechanisms possibly involving the microtubule assembly.
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PMID:[The efflux of intracellular vincristine in drug-resistant human lung cancer cells is not mediated by P-glycoprotein]. 790 99

We describe the selection of 3 new multidrug-resistant cell lines derived from tumor cells of different metastatic phenotypes within the Dunning R3327 model of rat prostatic carcinoma. Cell lines of weak (AT2) and strong (AT3 and MAT-LyLu) metastatic behavior were cultured in vitro and challenged with doxorubicin at progressively increasing concentrations. Chemosensitivity was determined colorimetrically by release of precipitated formazan pigment (MTT assay). Expression of the multidrug-resistance glycoprotein (P-170) was monitored immunocytochemically and by Western blotting using monoclonal antibody C219. The behavior of the parental and resultant drug-resistant cells was assessed by their growth in syngeneic rats. Doxorubicin challenge of the initially drug-sensitive parental prostatic carcinoma cell lines resulted in the rapid development of multidrug resistance together with simultaneous expression of P-glycoprotein. While lung and lymph-node metastases developed in host animals inoculated with parental AT3 and MAT-LyLu cells, no metastases developed in the multidrug-resistant progeny of these cell lines. This study has shown that Dunning rat prostate-carcinoma cell lines, previously sensitive to different cytotoxic agents, rapidly become multidrug-resistant and express P-glycoprotein following exposure to doxorubicin. Furthermore, development of multidrug resistance is associated with a less aggressive tumor phenotype and loss of metastatic potential. Nevertheless, it is unlikely that the non-metastatic phenotype of Dunning rat prostatic carcinoma cells is solely associated with expression of P-glycoprotein. These new multidrug-resistant cell lines exhibiting an altered behavioral phenotype will provide a valuable model with which to analyze the relationship between expression of P-glycoprotein and the metastatic phenotype of prostatic carcinoma cells.
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PMID:Establishment and in vivo characterization of multidrug-resistant dunning R3327 rat prostate-carcinoma cell-lines. 791 Aug 10


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