Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0017636 (glioblastoma)
 18,345 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have associated pharmacological studies to a semi-quantitative evaluation of P-glycoprotein(s) expression, to establish if classical multidrug resistance (MDR) could account for the complete resistance phenotype exhibited by progressively doxorubicin-resistant rat glioblastoma cells. Three resistant variants (C6 0.001, C6 0.1 and C6 0.5) of the C6 glioblastoma cell line (C6 S) were selected by long-term culture in the presence of three concentrations of doxorubicin (0.001, 0.1 and 0.5 microgram.ml-1 respectively). The degree of doxorubicin resistance was respectively 7, 33 and 400, and all the cell variants were cross-resistant to m-AMSA, etoposide and vincristine. Doxorubicin incorporation was reduced similarly in all resistant cells, irrespective of the level of resistance. When exposed to their respective doxorubicin IC50, the 7-fold resistant cells had the same intracellular drug incorporation as the sensitive cells, whereas the 33-fold and 400-fold resistant cells could incorporate respectively 3.7 and 17 times more drug. The ratio of doxorubicin exposures required for 50% DNA synthesis inhibition and 50% growth inhibition was dependent on the degree of resistance; this ratio was 12.8 in C6 S, 11.6 in C6 0.001, 6.3 in C6 0.1 and 1.8 in C6 0.5. P-glycoprotein(s) overexpression was of the same magnitude as the resistance factor in variants C6 0.001 and C6 0.1, but was lower than resistance factor in variant C6 0.5. Reversal of drug incorporation by verapamil was complete in all resistant cell lines; however, reversal of doxorubicin cytotoxicity was complete only in the 7-fold resistant line and was only partial in the most resistant lines, which remained 10-fold and 20-fold resistant to doxorubicin. These results suggest that classical MDR was the first phenotype selected by doxorubicin in C6 0.001, whereas mechanism(s) of doxorubicin resistance other than classical MDR are added in the most resistant lines.
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PMID:P-glycoprotein overexpression cannot explain the complete doxorubicin-resistance phenotype in rat glioblastoma cell lines. 134 23

We studied the capacity of doxorubicin encapsulation in liposomes of various lipid compositions to circumvent multidrug resistance in several variants of the C6 rat glioblastoma cell line in culture, and to inhibit azidopine binding to membranes isolated from these cells. Three formulations of liposomes were prepared: (a) phosphatidylcholine (PC)/phosphatidylserine (PS)/cholesterol (cho) at a 9/24 ratio; (b) PC/cardiolipin (CL)/cho at 10/1/4 ratio; (c) dipalmitoylphosphatidylcholine (DPPC)/cho at 11/4 ratio. Unloaded liposomes presented no cytotoxicity against sensitive or resistant cells. Doxorubicin encapsulated in PC/PS/cho and PC/CL/cho liposomes had a cytotoxic activity close to that of free doxorubicin, whereas doxorubicin encapsulated in DPPC/cho liposomes was significantly less active than free doxorubicin in sensitive as well as in two of the three multidrug resistant cell lines, and as active as free doxorubicin in the third one. Free doxorubicin was able to decrease 50% of [3H]azidopine photolabelling to P-glycoprotein at a concentration of 40 microM; doxorubicin encapsulated in PC/CL/cho or PC/PS/cho liposomes was able to inhibit [3H]azidopine binding similarly as free drug, whereas doxorubicin encapsulated in DPPC/cho liposomes had no significant effect on this parameter. Unloaded liposomes of either lipid composition had no effect on [3H]azidopine binding. Together with physical studies performed in parallel on doxorubicin trapping in liposomes (J Liposome Res 1993, 3, 753-766), these results suggest that doxorubicin leaked out of fluid liposomes (PC/PS/cho or PC/CL/cho), whereas rigid liposomes (DPPC/cho) were able to sequester the drug more efficiently. In that case, however, no availability of the drug to the cells was possible and only a weak cytotoxicity was exhibited, especially without any favourable effect on multidrug resistance. In conclusion, no reversal of doxorubicin resistance was found to occur through liposomal encapsulation of the drug.
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PMID:Failure of liposomal encapsulation of doxorubicin to circumvent multidrug resistance in an in vitro model of rat glioblastoma cells. 778 7

Despite substantial advances in the surgery, radiotherapy and chemotherapy of gliomas, the prognosis of patients with glioblastomas has still not improved. Disappointing results in chemotherapy of glioblastomas resulting from multi-drug resistance (MDR) prompted us to investigate the influence of cytokine gene transfer in glioblastoma cells on the expression of P-glycoprotein and on chemosensitivity of transduced cells. Several investigations have shown that malignant gliomas express P-glycoprotein at high levels. The P-glycoprotein is a product of the multi-drug resistance gene (mdr1) and functions as an energy-dependent efflux pump which decreases drug accumulation and cytotoxicity. Since tumour necrosis factor alpha (TNF alpha) is a powerful anti-cancer agent used in clinical trials and gene therapy protocols, this cytokine gene was chosen for the present investigations. Transduction of the human TNF alpha (hTNF) gene carrying retroviral vector pN2tk-hTNF into U373MG human glioblastoma cells resulted in expression and secretion of biologically active hTNF. Release of transduced hTNF reduces P-glycoprotein expression and is associated with enhanced rhodamine-123 uptake and potentiation of cytotoxicity of the MDR-relevant drugs vincristine and doxorubicin. Furthermore, the transfected cell clones showed a reduced growth rate compared to the parental cells.
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PMID:Gene transfer of human TNF alpha into glioblastoma cells permits modulation of mdr1 expression and potentiation of chemosensitivity. 779 Jan 19

A cell line, GBM, was established from a human malignant glioblastoma and was characterized with particular reference to its response to conventional drugs. The GBM cell line exhibited a 73 +/- 7 h doubling time in monolayer cultures. Expression of glial fibrillary acidic and S-100 proteins was observed. Karyotype analysis of GBM cells at early passages revealed the presence of two near-triploid clones (A and B) with multiple chromosome rearrangements; a 100% frequency for clone B was observed in the established cell line. GBM cells had tumorigenic properties, since the s.c. injection of cultured cells into nude mice gave rise to slowly growing tumors. The morphology of GBM cells was retained during in vitro and in vivo passages, as judged by light microscopy. GBM cells were relatively resistant to most conventional drugs; among the tested drugs, only taxol exhibited a marked cytotoxic effect comparable to that found in cells of a different tumor type. GBM cells were found positive for the epidermal growth factor receptor, HER2-neu and P-glycoprotein by flow cytometry of cells labelled with monoclonal antibodies. In spite of the expression of relatively high gamma-glutamyltransferase activity, the intracellular glutathione level was comparable to that of other chemosensitive tumor cells. This glioblastoma cell line is a suitable model for the identification and preclinical studies of new agents and provides an additional system to explore the molecular basis of the intrinsic drug resistance of glioblastoma.
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PMID:Characterization of an established human, malignant, glioblastoma cell line (GBM) and its response to conventional drugs. 792 29

The immunohistochemical detection of multidrug resistance (MDR1) gene products and their mRNA within brain tumor cells has already been described by Fojo et al. 1987. 63 specimens of astrocytomas and glioblastomas were analysed in the present study (Grading type 1 to 4) by means of the monoclonal antibody JSB1. The endothelial cells were positive only in astrocytic tumors with a grading of 1. Increasing tumor grading resulted in more positive immunological reactions in tumor cells. The most impressive reaction could be found in anaplastic astrocytoma and glioblastoma (G3 and G4). Overexpression of this P-glycoprotein, a plasma membrane component of a relative molecular mass of 170 kDa was not only found in tumor cells of anaplastic astrocytomas, but also in endothelial cells and some non-neoplastic brain diseases. Positive immunological reactions in protoplasmatic astrocytes could be demonstrated in cases of phenylketonuria (1/1), tuberculous leptomeningitis (2/2), SSPE (3/4), X-ray necrosis (1/1) and necrotizing viral encephalitis (1/4). According to this, it seems that astrocytes are able to express P-glycoprotein under the influence of some special metabolic conditions. This underlines the detoxicating function of reactive astrocytes within the total number of cells in the CNS.
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PMID:[Expression of P-glycoprotein as a multidrug resistance gene product in human reactive astrocytes and astrocytoma]. 794 20

We have studied the pharmacological parameters of doxorubicin resistance in three lines of murine cells selected by long-term culture in the presence of this drug or vincristine. A line originating from rat hepatoma spontaneously presented an intrinsic doxorubicin resistance as compared to the other lines, originating from a rat glioblastoma and from simian-virus-40-transformed mouse hepatocytes. This intrinsic resistance, as well as the doxorubicin resistance exhibited by the vincristine-selected glioblastoma variant, could be entirely attribute to decreased drug accumulation due to drug efflux. In contrast, the doxorubicin-selected variants of the three lines exhibited an intracellular tolerance to this drug. Despite a reduction in drug accumulation when exposed to the same amount of doxorubicin, they accumulated 6-12 times more doxorubicin than wild lines when submitted to equitoxic exposures. Verapamil could restore in these lines the doxorubicin accumulation observed in sensitive lines but could not restore doxorubicin cytotoxicity. Quantitative evaluation of P-glycoprotein expression by Western blotting with the C219 antibody indicated that the wild hepatoma line overexpressed P-glycoprotein by a factor of 5 in comparison with the other wild lines, and that the vincristine-selected glioblastoma variant overexpressed this protein almost as much as the doxorubicin-selected variants. These observations favor the existence of P-glycoprotein-independent mechanisms of doxorubicin resistance, which are added to the classical multidrug-resistant phenotype in doxorubicin-selected highly resistant variant cell lines.
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PMID:Pharmacological and molecular characterization of intrinsic and acquired doxorubicin resistance in murine tumor cell lines. 810 Aug 23

We have compared the pharmacological and molecular characteristics of 2 cell lines derived from the C6 rat glioblastoma, and selected for resistance either to doxorubicin (C6 0.5 line) or to vincristine (C6 IV line). Each line displays a preferential 400-fold resistance towards the drug used for selection, the C6 IV line being especially weakly resistant to doxorubicin (13-fold). Verapamil completely restored doxorubicin sensitivity in the C6 IV line as well as vincristine resistance in the C6 0.5 line, but could not completely reverse doxorubicin resistance in the C6 0.5 line or vincristine resistance in the C6 IV line. This suggests that specific mechanisms of resistance against each drug were added to a common P-glycoprotein-mediated multidrug-resistance mechanism. Doxorubicin efflux was total within 2 hr in the C6 IV line, whereas it remained 8 to 10% of drug in the C6 0.5 line 4 hr after drug removal, despite a more rapid efflux of the drug in the first 30 min. This 2-compartment behavior could be related to a special sub-cellular distribution of doxorubicin in C6 0.5 cells. Northern and Western blot analysis of the mdrI gene and of the P-glycoprotein expressed by the 2 resistant cell lines made it possible to quantify their degree of over-expression; when compared with the C6 wild strain, the C6 0.5 line over-expressed both the mdrI gene and the P-glycoprotein to a slightly higher level than the C6 IV line. Northern and Western blot analysis also suggested that C6 0.5 cell preferentially over-expressed the mdrIa gene, whereas the C6 IV cells preferentially over-expressed the mdrIb gene. This differential over-expression was confirmed after polymerase-chain-reaction amplification of the cDNA sequences transcribed from total RNA extracted from the 2 lines. It can be concluded therefore that the mdrIa gene product is more efficient than the mdrIb gene product in extruding anti-cancer drugs from the cells; and that the mdrIb gene product might preferentially extrude vincristine rather than doxorubicin.
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PMID:Differential over-expression of mdr1 genes in multidrug-resistant rat glioblastoma cell lines selected with doxorubicin or vincristine. 810 27

We have studied the cytotoxicity and accumulation of doxorubicin encapsulated in polyisohexylcyanoacrylate nanospheres in a model of doxorubicin-resistant rat glioblastoma variants differing by their degree of resistance to this drug. We observed that the particulate form of doxorubicin was always more cytotoxic than free doxorubicin, whereas coadministration of drug-unloaded nanospheres with free doxorubicin did not modify significantly doxorubicin cytotoxicity. In C6 0.001 cells, which were 6-fold resistant and present a pure multidrug-resistant phenotype, the reversal of doxorubicin resistance was complete. In C6 0.1 cells, which were 60-fold resistant, as with C6 1V cells (selected with vincristine), the reversal of doxorubicin resistance was almost complete, with a residual resistance factor of 2-3. In C6 0.5 cells, which were 600-fold resistant to doxorubicin, the reversal of resistance was only partial and, in all cases, not above the expected participation of P-glycoprotein to the phenotype of resistance. Intracellular drug accumulation after 2-h exposure to 17.2 mumol/l doxorubicin was systematically reduced by a factor of 2-3 when doxorubicin was incubated under the form of nanospheres; doxorubicin accumulation after a 2-h exposure to IC50 was also highly reduced in all cell lines for doxorubicin-loaded nanospheres. This work shows that association of doxorubicin with nanoparticles could provide a useful tool for circumventing multidrug resistance, probably by a bypass of P-glycoprotein rather than by an inhibition of this pump.
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PMID:Enhanced cytotoxicity of doxorubicin encapsulated in polyisohexylcyanoacrylate nanospheres against multidrug-resistant tumour cells in culture. 814 72

We have compared the properties of the novel multidrug resistance modulator, S9788, to a panel of 11 well-known modulators in a model of rat glioblastoma cells resistant to doxorubicin and displaying a P-glycoprotein-mediated multidrug-resistance phenotype complemented by a mechanism of intracellular drug tolerance not yet identified (Br J Cancer 1992, 65, 538-544). S9788, like most modulators, was able to completely restore drug accumulation in the resistant line to the level obtained in the sensitive cells. This was obtained with 10 mumol/l of modulator, which is slightly higher than required for cyclosporine A (3 mumol/l) verapamil and nicardipine (6 mumol/l), but lower than for amiodarone, trifluoperazine and dipyridamole (20 mumol/l), tamoxifen and diltiazem (40 mumol/l), quinine, quinidine and nifedipine (> 100 mumol/l). Complete restoration of drug cytotoxicity was, however, obtained only with amiodarone, and a residual resistance factor of 4 could not be overcome by cyclosporine A or S9788, while other modulators gave residual resistance factors of 5-20 (trifluoperazine, tamoxifen, verapamil, quinine, nicardipine, dipyridamole) or even higher (diltiazem, quinidine, nifedipine). When studying doxorubicin accumulation obtained for an exposure to the IC50 of this drug, it appeared that some modulators were able to decrease this "intracellular IC50" independently of their efficiency in resistance reversal (cyclosporine A, S9788, amiodarone, trifluoperazine, quinine, tamoxifen), thus reversing intracellular drug tolerance, whereas other modulators could not reduce this parameter (verapamil, nicardipine, dipyridamole, diltiazem, quinidine). It is suggested that drugs of the first group could be able to segregate doxorubicin in subcellular compartments from which it could not reach its nuclear targets.
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PMID:Reversal of multidrug resistance by a new lipophilic cationic molecule, S9788. Comparison with 11 other MDR-modulating agents in a model of doxorubicin-resistant rat glioblastoma cells. 839 62

We had previously shown that doxorubicin encapsulation in polyisohexylcyanocrylate nanospheres could circumvent the P-glycoprotein-mediated multidrug resistance (MDR) exhibited by C6 rat glioblastoma in culture. We then investigated what could be the mechanism of such a circumvention. The cytotoxicity of free and encapsulated doxorubicin was evaluated in two MDR variants of the C6 cell line in a device allowing the separation of cells from drugs by a polycarbonate membrane of 0.2 micron pore size. We observed that the progressive disruption of the nanospheres allowed their doxorubicin content to reach the cell monolayer and exert its cytotoxicity in a fashion similar to that exhibited by free doxorubicin. However, no circumvention of MDR is obtained by doxorubicin encapsulation when drug-containing nanospheres are separated from the cells by the polycarbonate membrane. In addition, no effect on azidopine binding to P-glycoprotein-enriched membranes is exerted by unloaded nanospheres, even after their spontaneous degradation in cell-culture medium. Taken together, these results suggest that a physical contact between doxorubicin-containing nanospheres and the cells is required for the circumvention of MDR. The role of degradation products from the nanospheres as modulators of P-glycoprotein activity can be ruled out.
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PMID:On the mechanism of action of doxorubicin encapsulation in nanospheres for the reversal of multidrug resistance. 861 9


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