Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0023418 (leukemia)
 93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thirty-six French centres are involved in an evaluation of the techniques used for MDR phenotype measurement. Until now, 14 samples of various kinds of leukemia (mainly acute myelogenous leukemia) and three cell lines with different levels of resistance were sent by one centre and tested. MRK16 antibody was used for flow cytometry and immunocytochemistry, RNA was measured by RT-PCR, rhodamine or anthracyclin efflux were tested for functional assay. Wide discrepancies were observed in the results, mainly with flow cytometry, specially for the samples with a probable low level of MDR1 expression. The importance of histogram interpretation was documented by the comparative analysis of results obtained on cells already marked with MRK16, fixed and sent to all centers. The use of the ratio of the mean of fluorescence, instead of percentage, should help for standardization. The use of only one control RNA (used at different dilutions) for standardisation of RT-PCR could help in decreasing the discrepancies observed. The mean of fluorescence should also be used for expressing the rhodamine cell content.
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PMID:[Multicentric evaluation of MDR phenotype in leukemia: intermediate analysis of the French study]. 886 43

We studied the cytotoxic effects of two ether lipids, a relatively new class of anticancer drugs, on multidrug-resistant (MDR1) leukemia cells of patients with acute leukemias who had failed induction treatment. The cytotoxicity of ether lipids was determined by the elimination of clonogenic leukemia cells from leukemic cultures or, in case of failure to generate leukemic cultures, by the inhibition of 3[H]thymidine incorporation in leukemic blasts. At dose levels of 50 microg/ml, a plasma level that can be achieved after oral intake, the MDR1-positive blasts were killed, both of patients with drug-resistant acute myeloid leukemia (AML) and of patients with drug-resistant acute lymphoblastic leukemia (ALL). The leukemic blasts were killed by the induction of apoptosis. These data suggest that ether lipids may be effective antileukemic drugs and that their cytotoxic function is not affected by MDR1.
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PMID:Ether lipids are effective cytotoxic drugs against multidrug-resistant acute leukemia cells and can act by the induction of apoptosis. 902 84

Sixty-hertz electric fields have been shown to affect biological systems in a variety of ways, but the mechanisms by which electric fields influence cell function remain uncertain. We have investigated the effects of electric fields on cellular protein kinase C (PKC) activity and on the regulation of the multidrug resistance gene (MDR1), which is responsible for a major form of drug resistance in cancer. We found that exposure of H9 human leukemia cells to 60-Hz sinusoidal electric fields (330 or 750 mV/cm for 60 min) resulted in significantly decreased PKC activity in the cytosolic fraction, whereas electric fields at higher (1250 and 3000 mV/cm) or lower (10 mV/cm) intensities had no effect on PKC activity. Exposure of these cells to electric fields (330 or 750 mV/cm for 17 h) inhibited up-regulation of MDR1 expression by treatment with 25 microM 1-beta-D-arabinofuranosylcytosine (AraC). Again, lower or higher field strengths had little or no effect on the levels of AraC-induced MDR1 mRNA. Similarly, exposure of intact cells to staurosporine (100 nM), a potent PKC inhibitor, significantly reduced cytosolic PKC activity, but not that of the particulate fraction. Staurosporine also prevented AraC-induced MDR1 overexpression. These data show that intermediate-strength electric fields inhibit cytosolic PKC and suggest that electric fields and pharmacological inhibitors of PKC, such as staurosporine, affect cytosolic PKC activity and AraC-induced MDR1 overexpression through related mechanisms. Our findings also suggest the possible utility of 60-Hz electric fields for modulating multidrug resistance in tumor cells.
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PMID:60-Hz electric fields inhibit protein kinase C activity and multidrug resistance gene (MDR1) up-regulation. 905 85

The cells from approximately 70% patients with acute myeloblastic leukaemia exhibit autonomous growth characteristics in vitro, which have been associated with a poor response to therapy. We have previously shown that leukaemic cells with autonomous growth characteristics express high levels of bcl-2 and are relatively resistant to apoptosis. As bcl-x(L) is a bcl-2-related gene with anti-apoptotic activity which also confers resistance to cytotoxic drugs we have studied its expression in AML in relation to cellular growth characteristics and to the expression of P-glycoprotein. Cells from 15 patients were studied. Immunoblotting demonstrated bands at 31 kDa corresponding to bcl-x(L) from the cells of all patients. Bcl-x(S) was not detected in any sample. Using standardised, quantitative flow cytometry, bcl-x(L) expression ranged from 0.25 x 10(5) to 4.24 x 10(5) bound FITC molecules, (median 1.35 x 10[5]). AML blasts with autonomous growth in vitro expressed more bcl-x(L) (median 1.76 x 10[5]) than those which did not (median 0.86 x 10(5), P=0.01). Quantitative bcl-x(L) expression strongly correlated with that of P-glycoprotein, also measured by quantitative flow cytometry using the MRK16 antibody (r=0.95, P < 0.001), but not with MRPr1. These results provide a further explanation for the poor prognosis associated with autonomous in vitro growth of AML blasts and illustrate that these cells may coexpress different modalities of resistance to cytotoxic drug therapy involving both anti-apoptotic pathways (bcl-x(L), bcl-2) and classic multidrug resistance (MDR1). The implication of these findings is that the use of agents to reverse MDR1 function in AML may be unsuccessful in the absence of strategies to reduce resistance to apoptosis.
Leukemia 1997 Jul
PMID:Bcl-x(L) is heterogenously expressed by acute myeloblastic leukaemia cells and is associated with autonomous growth in vitro and with P-glycoprotein expression. 920 73

Increased expression of MDR1 is strongly implicated in the appearance of chemotherapeutic drug resistance in cancer, especially hematological malignancies. We therefore examined the potential of antisense oligonucleotides to inhibit MDR1 and restore sensitivity to drug-resistant human lymphoblastic cells (CCRF-CEM). Treatment with two different phosphorothioate-modified antisense sequences as well as a DNA-RNA hybrid sequence resulted in a 30 to 45% decrease in MDR1 expression as determined by staining with the monoclonal antibody MRK16 followed by flowcytometry (FCM) analysis. Further, inhibition of MDR1 expression persisted for 3 days after removal of oligonucleotides. Increased accumulation of rhodamine 123 and nearly a three-fold sensitization of cells to vincristine paralleled the reduction in staining with MRK16. Reversed or scrambled control sequences had no effect in any of the assays. During the course of these studies, we observed a 25 to 75% increase in MRK16 staining of cells treated with the chemotherapeutic agents daunorubicin and vincristine as well as by the resistance reversal agents verapamil and cyclosporin. Treatment of cells with antisense oligonucleotides prior to exposure to daunorubicin or cyclosporin reduced the increase in MRK16 staining. These results indicate that antisense targeted to MDR1 can sensitize drug-resistant leukemia cells and suggest that antisense treatment may prevent the emergence of MDR1-mediated drug resistance.
Leukemia 1997 Jul
PMID:Sensitization of multidrug-resistant human leukemia cells with MDR1-targeted antisense and inhibition of drug-mediated MDR1 induction. 920 74

Accurate measurement of P-glycoprotein (P-170) expression in clinical samples still remains a controversial issue. In this study tumor cell P-170 expression was assessed in 29 patients suffering from acute leukemia (17 acute myeloid leukemia (AML) and 12 acute lymphoblastic leukemia (ALL)) using three different techniques: flow cytometry measuring rhodamine 123 (Rh123) efflux (functional level), immunocytochemistry (protein level) and RT-PCR (mRNA level). Rh123 efflux was detectable in 10/29 (34%) of all cases, in 9/17 (53%) of AML and in 1/12 (8%) of ALL samples. In AML patients a significant association of CD34 expression and P-170 activity was observed (P < 0.02). All AML patients with the FAB subtype M5 were Rh123 negative (P < 0.007). Cytospin preparations were analyzed for staining with monoclonal antibodies JSB1 and MM4.17. Eight of 16 (50%) AML and 0/9 (0%) ALL cases expressed the multidrug resistance (MDR) protein assessed by JSB1. With MM4.17 87% of AML and 50% of ALL patients were scored positive. Agreement between both antibodies was found in only 13/23 (57%) samples. Extracted RNA from 12 patients was analyzed by RT-PCR to evaluate the expression of MDR1 and multidrug resistance-associated protein (MRP) mRNA. An increased level of MDR1 mRNA was detectable in 4/7 AML and 0/5 ALL cases. MRP expression was found in 3/7 AML and 0/5 ALL patients. Comparison of Rh123 assay and immunocytochemistry revealed a very good correlation when using MoAb JSB1 (P < 0.004) but not with MM4.17 (not significant (NS)). JSB1 also showed a much better association with the PCR results (P < 0.05) than MM4.17 (NS). Finally, we compared the results of the functional Rh123 assay and RT-PCR and observed a high correlation for Rh123/MDR1 (r = 0.819, P < 0.001) but low for Rh123/MRP (r = 0.562, NS). We conclude that measurement of Rh123 efflux and immunocytochemical staining of cytospin preparations with JSB1 allows the accurate monitoring of P-170 expression in acute leukemia. The simplicity of these two MDR assays suggests their use for routine MDR screening.
Leukemia 1997 Jul
PMID:Multidrug resistance in acute leukemia: a comparison of different diagnostic methods. 920 93

Immunocytochemical detection of the expression of the MRP gene and the MDR1 gene in clinical specimens might be affected by several factors. Thus, we studied the impact of monoclonal antibodies, sample source (peripheral blood vs bone marrow) and disease status on the expression of multidrug resistance-associated protein (MRP) as well as P-glycoprotein (P-gp) in leukemic cells of patients with acute myeloid leukemia (AML). MRP expression was determined by means of anti-MRP antibodies (QCRL-1, QCRL-3, QCRL-1/QCRL-3 or MRPr1). In the case of P-gp, monoclonal antibodies C219 and MRK16 were used. High MRP expression ranged from 5 to 35% and high P-gp expression from 5 to 14% of the specimens. A fair correlation between results obtained with QCRL-1/QCRL-3 and those obtained with MRPr1, as well as a moderate correlation between C219 and MRK16, were seen. MRP and P-gp expression of peripheral blood blasts were similar to those of bone marrow blasts in the majority of cases. The degrees of MRP expression at the time of diagnosis were also similar to the degrees of expression at relapse, albeit an analysis of sequential MRP expression in 13 patients indicated an increase of expression at relapse in six patients as compared to the time of diagnosis.
Leukemia 1997 Jul
PMID:Immunocytochemical detection of the multidrug resistance-associated protein and P-glycoprotein in acute myeloid leukemia: impact of antibodies, sample source and disease status. 920 94

The problem of tumor cell drug resistance remains a barrier to the successful treatment of many neoplastic diseases. Problems of tumor cell heterogeneity and expression of multiple mechanisms of drug resistance complicate treatment strategies. Indeed, even that form of resistance to natural product anticancer agents, multidrug resistance (MDR), can have multiple mechanisms. Compounding these problems is the use of different methodologies and different reagents to assess expression of the most widely studied form of MDR, that due to increased expression of the MDR1 gene and its product, P-glycoprotein (Pgp). In this paper, we discuss problems associated with assay variability and accurate measurement of markers of drug resistance, and summarize consensus findings of the St Jude Workshop on methods to detect Pgp in tumors.
Leukemia 1997 Jul
PMID:Methods to detect P-glycoprotein and implications for other drug resistance-associated proteins. 920 98

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.
Leukemia 1997 Jul
PMID:Flow cytometric analysis of P-glycoprotein function using rhodamine 123. 920 1

Multiple myeloma is a disease which is generally considered responsive to chemotherapy; however, essentially all patients who respond to drug treatment will relapse and die of drug-resistant disease. This disease is therefore considered a paradigm for studying the development of acquired drug resistance in the clinic. Natural product agents are frequently used in the treatment of myeloma, especially vincristine and doxorubicin. Studies using human myeloma cell lines have shown that the MDR1 gene product, P-glycoprotein (Pgp), is responsible for conferring drug resistance to natural products and glucocorticoids. We have developed assays to measure the expression of MDR1/Pgp in human myeloma specimens. These assays include immunocytochemistry, flow cytometry, and RT/PCR. Human myeloma cell lines, 8226/Dox, that are resistant to natural product agents and overexpress MDR1/Pgp are important for standardizing results and offer a means of comparing inter- and intra-patient results. Assays which measure both the presence and function of Pgp are necessary to determine the role of Pgp in clinical drug resistance in patients with myeloma.
Leukemia 1997 Jul
PMID:Detection of multidrug resistance gene expression in multiple myeloma. 920 7


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