Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0023467 (acute myeloid leukemia)
 35,200 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Overexpression of P-glycoprotein (PGP), MRP or LRP has been characterized as the 'proximal', while overexpression of the anti-apoptosis Bcl-2 or Bcl-xL relative to the pro-apoptosis Bax protein has been recognized as the 'distal' mechanism of multidrug resistance in human AML cells. In the present studies, we examined whether these mechanisms can co-exist in human AML HL-60 cells. We also determined how these mechanisms would affect the accumulation and cytotoxicity of a PGP substrate, such as Taxol (paclitaxel). For this, immunoblot analyses were performed to determine the expression of PGP, MRP, Myc, Bcl-2, Bcl-xL and Bax on either the multidrug-resistant HL-60 sublines created under the selection pressure of doxorubicin (HL-60/AR), paclitaxel (HL-60/TAX1000) or vincristine (HL-60/VCR), or sublines created by transfection and overexpression of the bcl-2 (HL-60/Bcl-2) or bcl-xL gene (HL-60/Bcl-xL). As compared to the control HL-60, HL-60/AR cells possess high MRP while HL-60/TAX1000 and HL-60/VCR cells express high levels of the mdr-1 encoded PGP. In addition, these multidrug-resistant cells possess 1.5- to 2.5-fold higher Bcl-2, while their Bax and Myc levels are similar to those in the control HL-60 cells. HL-60/TAX1000 and HL-60/VCR cells also express three- and 2.5-fold higher Bcl-xL levels. PGP, but not MRP, overexpression significantly impaired paclitaxel accumulation and paclitaxel-induced apoptosis, as well as reduced its cytotoxic effects as determined by the MTT assay. In contrast, enforced and much higher expression of Bcl-2 in HL-60/Bcl-2 (five-fold) or Bcl-xL in HL-60/Bcl-xL cells (10-fold) significantly reduced paclitaxel-induced apoptosis and the loss of cell viability, without affecting its intracellular accumulation. These results confirm the possibility of co-expression of multiple mechanisms of multidrug resistance in human leukemic cells which had been selected by exposure to a single drug. The results also indicate that MRP overexpression does not confer resistance against paclitaxel. In addition, these findings suggest that, for Bcl-2 and Bcl-xL, enforced overexpression to high levels is necessary to induce paclitaxel resistance in HL-60 cells.
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PMID:Co-expression of several molecular mechanisms of multidrug resistance and their significance for paclitaxel cytotoxicity in human AML HL-60 cells. 900 89

A new human myeloid leukemia cell line, designated KF-19, and its drug resistant sublines have been established. The KF-19 cell line was established from the pericardial effusion of a patient with acute myeloid leukemia clinically resistant to chemotherapy and KF-19 cells were characterized by expression of myeloid markers and differentiation into neutrophil- and macrophage-like cells upon optimal stimulations. KF-19AraC, KF-19ADR and KF-19VCR were established as sublines resistant to cytosine arabinoside (AraC), adriamycin (ADR) and vincristine (VCR), respectively. Efflux of the corresponding drugs was documented in each cell line. Expression of the MDR1 gene and the P-glycoprotein was found only in KF-19ADR, which showed a cross resistance to anthracyclines and vinca alkaloids; this resistance was reversed by verapamil or cyclosporin A. KF-19VCR lacking MDR1 gene and P-glycoprotein expression showed only resistance to vinca alkaloids, which was partially reversed by verapamil and cyclosporin A. Unexpectedly, KF-19ADR and KF-19VCR displayed cross resistance to AraC, despite lack of alterations of deoxycytidine kinase (dCK) and deaminase (dA) activities. KF-19AraC showed an efflux of AraC as well as a decreased level of dCK, but not of dA. In addition, KF-19AraC showed cross resistance to VCR in the efflux assay. The cell lines reported herein will provide new aspects on the mechanisms of drug resistance in leukemic cells.
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PMID:Characterization of newly established human myeloid leukemia cell line (KF-19) and its drug resistant sublines. 900 51

Drug resistance often results in failure of anticancer chemotherapy in leukemias. Several mechanisms of drug resistance are known with multidrug resistance (MDR) being the best characterized one. MDR can be due to enhanced expression of certain genes (MDR1, MRP or LRP), alterations in glutathione-S-transferase activity or GSH levels and to reduction of the amount or the activity of topoisomerase II. Here we review the current status of the clinical significance of the various mechanisms of MDR in leukemias and also discuss possibilities for the reversal of MDR. MDR1 gene expression has been seen in many leukemias, notably in acute myeloid leukemia (AML) and blast crisis of chronic myeloid leukemia. Both MDR1 RNA and P-glycoprotein expression of the leukemic cells have been shown to correlate with poor clinical outcome in AML. However, preliminary results indicate that the MRP gene as well as the LRP gene can be expressed in AML. Thus, drug resistance in leukemias appears to be multifactorial. P-glycoprotein-mediated MDR can be reversed by several drugs. These resistance modifiers are currently evaluated with regard to their clinical efficacy. Despite some encouraging results, reversal of drug resistance and subsequent improvement in clinical outcome remains to be shown.
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PMID:Multidrug resistance in leukemias and its reversal. 903 Oct 75

We compared bcl-2 with P-glycoprotein expression (C494 and JSB1), and both with ex vivo chemosensitivity by Differential Staining Cytotoxicity (DiSC) assay (25 cytotoxic drugs), in 76 fresh haematological specimens, including 51 chronic lymphocytic leukaemias (CLL). Strong correlations were seen between bcl-2 and Pgp expression in both CLL (r = 0.5; p < 0.001) and AML (r = 0.9; p < 0.001) although bcl-2 expression was only raised in Pgp positive cells. However, there was no correlation between high or low marker levels and either ex vivo drug sensitivity (-0.30 < r < 0.37; p all > 0.1) or patient survival (chi 2 < or = 0.1; p > 0.7). One B-CLL, one PLL and one hairy cell leukaemia were negative for both bcl-2 and Pgp, whilst 3 T-cell specimens were bcl-2 negative but strongly positive for Pgp. These results suggest that the expression of Pgp and bcl-2 may be interlinked and related to immunophenotype and that clinical sensitivity to MDR-inducing and/or apoptosis-inducing drugs is best determined by ex vivo chemosensitivity testing rather than measurement of Pgp or bcl-2 expression.
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PMID:Correlation of bcl-2 with P-glycoprotein expression in chronic lymphocytic leukaemia and other haematological neoplasms but of neither marker with ex vivo chemosensitivity or patient survival. 904 70

The aim of the study was to test whether fractionated (weekly) idarubicin administration to multiply pretreated leukemia patients is effective and tolerable for outpatient treatment, and whether idarubicin alone can overcome P-glycoprotein (P-gp)-related resistance. P-gp was assessed with an immunocytological technique using the monoclonal antibody 4E3.16. P-gp. expression was characterized as a percentage of P-gp-positive blasts. Additionally, the function of P-gp was determined with the rhodamine-123 (R-123) accumulation test in combination with or without verapamil and expressed as the R123 accumulation ratio. Fractionated idarubicin (12 mg/m2/week) was given to 36 acute myelogenous leukemia (AML) patients, 12 acute lymphoblastic leukemia (ALL) patients, and eight chronic myelogenous leukemia (CML) patients in blast crisis. Furthermore, 11 AML and four ALL patients were treated with fractionated daunorubicin at a dose of 50 mg/m2/week. All patients had been pretreated with drugs inducing P-gp-related resistance including daunorubicin and/or doxorubicin or vindesine (CML patients). Of 71 pretreated patients, 51 (72%) had a P-gp value between 25 and 98%. Six of these patients with increased P-gp expression had a nonpumping P-gp; four of them were CD34 positive. Of 51 patients with increased P-gp expression, 30 (59%) were CD34 positive. With regard to idarubicin monotherapy, overall response was 33/56 (59%) patients, and 23/33 (70%) responding patients showed a P-gp expression between 25 and 95%. All idarubicin-responding patients with high P-gp expression before treatment showed a clear reduction of P-gp-positive blasts. No patients with P-gp expression between 34 and 85% treated with fractionated daunorubicin showed response or reduction of P-gp-positive blasts in bone marrow. This study demonstrates that P-gp-related resistance can be overcome in multiply pretreated leukemia patients with idarubicin alone, and that the protocol used here is tolerable for outpatient treatment.
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PMID:Idarubicin monotherapy in multiply pretreated leukemia patients: response in relation to P-glycoprotein expression. 906 74

The MDR1 gene is of prognostic significance in acute myeloid leukemia (AML). The relationship of this gene to surface markers largely remains unclear. Therefore, we have studied the association of MDR1 gene expression with the expression of specific surface markers in AML. MDR1 RNA expression of leukemic cells was determined by slot blot analysis. Expression of P-glycoprotein and surface markers (CD7, CD13, CD19, CD34, HLA-DR, TdT, blood group H) was assessed by immunocytochemistry. MDR1 RNA (n = 79) and P-glycoprotein (n = 52) expression were detected in 63% and 63% of the patients, respectively. CD7, CD13, CD19, CD34, HLA-DR, TdT and blood group H were positive in 17%, 84%, 0%, 51%, 82%, 11% and 11% of the patients. MDR1 RNA or P-glycoprotein expression were not associated with the expression of either CD7, CD13, CD19, CD34, TdT or blood group H. However, P-glycoprotein expression was more frequent in HLA-DR positive than in HLA-DR negative patients (47% versus 10%, p = 0,04). Consistent with the latter finding, patients with intermediate or high MDR1 RNA expression expressed HLA-DR more frequently than patients with negative or weak MDR1 RNA expression (96% versus 76%, p = 0,03). In conclusion, MDR1 gene expression of AML cells was independent of surface markers except HLA-DR.
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PMID:Relationship between MDR1 gene and surface markers in acute myeloid leukemia. 906 14

We have used laser-assisted confocal microscopy to evaluate the intracellular distribution of daunorubicin (DNR) in acute myeloid leukemia (AML) cell lines and fresh AML cells according to their differentiation phenotype. In KG1a, KG1, TF-1 and HEL cells, which express the early differentiation marker CD34, DNR was distributed in perinuclear vesicles which could be associated with the Golgi apparatus, as suggested by the distribution of fluorescent probes specific for intracellular organelles. In contrast, U937 and HL-60 cells, which display a more mature phenotype, exhibited nuclear and diffuse cytoplasmic DNR fluorescence. DNR sequestration was not correlated with P-glycoprotein (P-gp) or multidrug resistance protein expression. Furthermore, PSC833, a potent P-gp blocker, had little effect on drug sequestration in CD34+ AML cells. We also tested the effect of metabolic inhibitors, cytoskeleton inhibitors and carboxy-ionophores on DNR distribution in both CD34- and CD34+ AML cells. However, only non-specific metabolic inhibitors restored nucleic/cytoplasmic distribution in CD34+ cells. In these cells, the intracellular distribution of doxorubicin and idarubicin was very similar to that of DNR, while the distribution of methoxymorpholinyl-doxorubicin was nuclear and diffusely cytoplasmic. In fresh AML cells, DNR was also concentrated in the perinuclear region in CD34+ but not in CD34- cells. However, DNR sequestration was not observed in normal CD34+ cells. Finally, our results show that DNR is sequestered in organelles in CD34+ AML cells via an active mechanism which appears to be different from P-gp-mediated transport. Abnormal DNR distribution may account for the natural resistance of immature AML cells to anthracyclines.
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PMID:Altered intracellular distribution of daunorubicin in immature acute myeloid leukemia cells. 913 56

An attempt was made to isolate resistant sublines of acute myelogenous leukemia (OCI/ AML-2) cells by chronic exposure to gradually increasing concentrations of daunorubicin in order to determine the mechanism of its resistance to this drug. Four daunorubicin-resistant sublines, AML-2/D100, /D250, /D500, and /D1,000 were isolated. The values of relative resistance of each daunorubicin-resistant AML subline were about 3, 6, 18, and 23-fold, respectively, as compared to the AML-2 line with an IC50 of 5 nM. The daunorubicin-resistant AML-2 sublines also showed cross resistance to various anticancer drugs including another anthracycline doxorubicin, a Vinca alkaloid vincristine, and an epipodophyllotoxin etoposide. A functional assay using flow cytometry showed decreased accumulation of daunorubicin in these sublines as compared to that of AML-2, which was reversed by cyclosporin A or cyanide. The development of the ATP-dependent multidrug resistant phenotype was due to low to high levels of expression of P-glycoprotein (PGP). The major mechanisms of increased PGP appears to be associated with gene amplification. In addition, other mechanisms such as increased stability of protein or mRNA might be involved depending on the concentration of daunorubicin used for selection. However, a multidrug resistance-associated protein (MRP) was not involved in these resistant sublines. These daunorubicin-resistant AML-2 sublines could provide a useful model for the study of multidrug resistance mediated by PGP.
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PMID:Isolation and characterization of daunorubicin-resistant AML-2 sublines. 916 28

Contemporary therapies for acute myeloid leukemia (AML) commonly fail to cure patients because of the emergence of drug resistance. Drug resistance in AML is multifactorial but can be associated with the overexpression of transmembrane transporter molecules, including P-glycoprotein (Pgp) or the multidrug resistance-associated protein (MRP), or associated with inactivation of the p53 tumor suppressor gene, as well as overexpression of the anti-apoptotic protein bcl-2. We are investigating if novel recombinant biotherapeutics can circumvent these resistance mechanisms to effectively treat refractory AML. To target the lethal action of diphtheria toxin (DT) to high affinity granulocyte-macrophage colony-stimulating factor (GMCSF) receptors on AML blasts, we have produced a recombinant chimeric fusion toxin, DTctGMCSF. Since DTctGMCSF enters and kills its target cells by unique mechanisms (GMCSF-receptor binding and protein synthesis inhibition) and is not similar in structure to Pgp or MRP substrates, we postulated that it would be an active agent against therapy-resistant AML. DTctGMCSF was selectively cytotoxic (IC50 1-10ng/ml) to GMCSF-receptor positive AML cells expressing the Pgp- or MRP-associated multi-drug resistant phenotypes, despite high level resistance to conventional chemotherapeutic agents. DTctGMCSF also efficiently killed AML cells deficient in p53 expression, as well as radiation-resistant AML cells and mixed lineage leukemia cells expressing high levels of bcl-2. In addition, DTctGMCSF killed > 99% of primary leukemic progenitor cells from therapy-refractory AML patients under conditions that we have previously found to not adversely affect the proliferative capacity or differentiation of pluripotent normal hematopoietic progenitor cells. DTctGMCSF may prove useful in treating myeloid leukemias that are otherwise resistant to a wide range of conventional therapies.
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PMID:Granulocyte-macrophage colony-stimulating factor receptor-targeted therapy of chemotherapy- and radiation-resistant human myeloid leukemias. 916 35

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.
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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


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