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)

We compared the influence of exogenous N-ras oncogene and treatment with PKC agonist 12-O-tetradecanoylphorbol-13-acetate (TPA) on P-glycoprotein (Pgp) function in various human, rat and dog cell lines. Two approaches were used: (a) flow cytometry analysis of Rhodamine 123 (Rh123) exclusion; and (b) sensitivity to cytotoxic action of colchicine. We have found that in Rat1 fibroblasts, rat IAR2 epithelial cells and rat McA RH 7777 (hepatoma), ras activates Pgp function, while in MDCK (dog kidney), K562 (human chronic myelogenous leukaemia) and LIM1215 (human colon carcinoma) cells it either has no effect or even acts in opposite direction. TPA-induced Pgp function shows dissimilar pattern of cell specificity. It is assumed that PKC and ras oncogene regulate mdr1 gene expression through at least partially distinct signalling pathways.
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PMID:Cell-specific effects of RAS oncogene and protein kinase C agonist TPA on P-glycoprotein function. 762 41

The huge discrepancies in the proportion of tumors positive for P-gp observed in the literature limit any definite conclusions, except for the urgent need for standardized methods to compare results. It is well known by scientists that only positive results are published. For this reason, the frequency of P-gp expression in leukemia and lymphoma may be overestimated. The role of the MDR phenotype in clinical resistance is also not clearly demonstrated, because of the frequent association of other markers of bad prognosis on the same subset of cells (CD34, CD7 in leukemia). Hematologic malignancies are the most extensively studied tumors for drug resistance, and they could be a model for the therapeutic use of modifier agents. Many clinical trials are now ongoing in myeloma, acute leukemia, and lymphoma, with new modifier agents. The standardization of methods for P-gp, permitting large multicentric studies, and the results of randomized studies with modifier agents will help us know if mdr1 gene overexpression is of clinical importance in hematologic malignancies.
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PMID:P-glycoprotein in adult hematologic malignancies. 764 63

A novel multidrug resistance modulator, RS-33295-198, circumvented drug resistance in human, mouse, and Chinese hamster cell lines overexpressing P-glycoprotein. It enhanced the antiproliferative activity of doxorubicin, vincristine, etoposide, and paclitaxel and increased doxorubicin retention in multidrug-resistant hamster CHRC5 cells. RS-33295-198 modulated doxorubicin resistance in a murine P388/ADR leukemia model when administered ip via continuous minipump delivery, ip by bolus injection, and orally; it also improved the efficacy of vincristine toward P388/VCR leukemia when given ip or po. RS-33295-198 showed weak activity in enhancing doxorubicin efficacy against a multidrug-resistant human sarcoma xenograft.
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PMID:RS-33295-198: a novel, potent modulator of P-glycoprotein-mediated multidrug resistance. 764 63

A set of multidrug resistant (MDR) murine leukemia P388 sublines processing 30-50-fold mdr1 gene amplification was obtained as a result of experimental chemotherapy with rubomycin, ruboxyl, vinblastine, vincristine, or combination of rubomycin and vincristine. Significant differences of developed MDR sublines in response to treatment with cisplatin, tiophosphamide, sarcolysin, and dopad were found. Strong correlation between drug sensitivity and a copy number of gene coding for 19-22 kDa calcium-binding sorcin gene co-amplification were hypersensitive to cisplatin and alkylating agents, the cell sublines showing amplification of sorcin DNA sequences did not possess such collateral sensitivity and even acquired cross-resistance. The dependence of sensitivity to cisplatin on sorcin gene co-amplification was confirmed by analysis of Djungarian hamster DM15 cell sublines that selected for MDR in vitro by colchicine.
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PMID:Decreased sensitivity of multidrug-resistant tumor cells to cisplatin is correlated with sorcin gene co-amplification. 765 86

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.
Leukemia 1995 May
PMID:Lack of correlation between expression and function of P-glycoprotein in acute myeloid leukemia cell lines. 776 42

We have characterised sites of photodamage catalysed by the cationic photosensitiser tetrabromorhodamine 123, using P388 murine leukaemia cells and a subline (P388/ADR) which has a multidrug resistance phenotype and hyperexpresses mdr1 mRNA for P-glycoprotein. Fluorescence emission spectra were consistent with sensitiser localisation in hydrophobic regions of the P388 cell, and in more aqueous loci in P388/ADR. Subsequent irradiation resulted in photodamage to the P388 cells, resulting in loss of viability. In contrast, P388/ADR cells were unaffected except for an irreversible inhibition of P-glycoprotein, leading to enhanced accumulation of daunorubicin and rhodamine 123 and a corresponding increase in daunorubicin cytotoxicity. These results are consistent with the premise that substrates for P-glycoprotein are confined to membrane loci associated with the transporter, and indicate a very limited migration of cytotoxic photo-products in a cellular environment.
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PMID:Selective photodynamic inactivation of a multidrug transporter by a cationic photosensitising agent. 784 Oct 45

In a series of 60 ALL samples drawn during different stages of the disease we used a cDNA-PCR approach to analyse the relative mRNA levels of the MDR-associated genes encoding mdr1/P-glycoprotein, mrp, and the topoisomerase II isozymes alpha and beta. Expression analysis of the cyclin A gene was included to examine cellular proliferation activity. The expression of gapdh served as an internal standard. Calculating the mean values we found: (i) a distinctly lower mdr1 gene expression in primary ALL and first relapses compared to bone marrow from healthy donors, (ii) no change in mdr1 and mrp, but a decreased topoisomerase II alpha gene expression in first relapses of ALL compared to the primary leukaemia, and (iii) increased mdr1 and mrp levels combined to decreased topoisomerase II alpha levels in recurrent relapses of ALL showing significant correlations (mdr1/mrp: rs = +0.6833, P < 0.05; mdr1/topoII alpha: rs = -0.6727, P < 0.05). The expression of the topoisomerase II alpha gene was correlated to that of cyclin A, indicating a link of its expression to cellular proliferation. Our findings suggest that a multifactorial MDR including mrp appears particularly in recurrent relapses of ALL, which often do not respond to chemotherapy. Nonetheless, some individual samples showed gene expression levels very different from the mean values calculated for a particular state of the leukaemia, indicating the need of an individual expression analysis of MDR-associated genes.
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PMID:Expression of mdr1, mrp, topoisomerase II alpha/beta, and cyclin A in primary or relapsed states of acute lymphoblastic leukaemias. 787 86

P glycoprotein, the product of multidrug resistance (mdr1) gene, is frequently expressed in advanced myelodysplastic syndromes (MDS) with an excess of bone marrow blasts and could explain their frequent resistance to chemotherapy. P53 gene mutations are also found in 10 to 15% of advanced MDS. Because it has recently been suggested that normal p53 suppressed, but that mutated p53 activated, the mdr1 gene promoter, we tried to correlate p53 mutations and P glycoprotein expression in 34 patients with MDS and an excess of bone marrow blasts (> 5%). P glycoprotein expression was assessed by immunocytochemistry using JSB1 monoclonal antibody and was found positive in 13 out of the 34 patients. p53 mutations were detected both by immunocytochemistry using three different monoclonal antibodies and by single stranded conformation polymorphism (SSCP) analysis of exons 5 to 8 of the P53 gene. Both methods detected a point mutation in 5 out of the 34 patients. Only one out of the 5 patients with a p53 mutation expressed P glycoprotein, as compared to 12 out of the 29 patients without p53 mutations. This suggested the mutant and normal p53 are not major determinants of the regulation of mdr1 expression in vivo, at least in MDS.
Leukemia 1993 Nov
PMID:Relationship between p53 gene mutations and multidrug resistance (mdr1) gene expression in myelodysplastic syndromes. 790 57

Murine leukaemia P388 and L1210 cell sublines with varying degrees of resistance to the anthracycline daunomycin (DNM) have been used to monitor (i) intracellular accumulation of DNM, (ii) expression of the drug efflux pump P-glycoprotein (pgp) and (iii) cytoplasmic pH changes. Drug-resistant L1210/65 cells (65-fold resistance), overexpress pgp, and display decreased intracellular accumulation of DNM and identical intracellular pH as compared to the parental drug-sensitive L1210 cell line. On the other hand, moderately drug-resistant P388/20 cells (20-fold resistance), which also exhibit a decreased intracellular drug accumulation with respect to drug-sensitive P388/S cells, display only moderate pgp-encoding mdr1 gene transcription without detectable levels of pgp protein, and undergo cytoplasmic alkalinisation (up to approximately 0.2 pH units). A further increase in the level of drug resistance (P388/100 cells, 100-fold resistance), results in a more pronounced decrease in drug accumulation, significant pgp expression and slightly higher intracellular alkalinisation. Alterations in the degree of protonation of DNM have been shown previously to influence processes such as the rate of uptake and the intracellular accumulation of the drug. On this basis, we propose that the changes in intracellular pH, observed at low levels of drug resistance (P388/20 cells), could constitute an early cellular response aimed at decreasing the intracellular accumulation of ionisable anti-neoplastics. As the level of resistance increases (P388/100), the cells seem to require more efficient mechanisms of defense against the drug, such as that represented by the expression of pgp. Since there is no apparent correlation between the extent of the changes in intracellular pH and the level of pgp expression in DNM-resistant P388 cell sublines, it is suggested that these two cellular responses contributing to drug resistance could operate independently.
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PMID:Possible coexistence of two independent mechanisms contributing to anthracycline resistance in leukaemia P388 cells. 790 76

Expression of the multidrug resistance gene mdr1 is reported to be an important determinant of responsiveness to therapy and survival in some cancers. Many different methods have been used to evaluate mdr1 expression in these studies. This paper compares four methods for determination of mdr1 expression. We studied the mdr1 gene expression in 36 freshly established cell lines from 28 children with acute lymphoblastic leukemia (16 T-ALL, six BCP-ALL, two B-ALL (L3), two biphenotypic leukemias, two Burkitt's lymphomas). Leukemic specimens were obtained at the time of diagnosis in 16 cases, and after chemotherapy in 20 cases. In all the samples, mdr1 mRNA was measured by slot blotting and reverse transcriptase polymerase chain reaction (rt-PCR), and the presence of the mdr1 product, P-glycoprotein, was detected by immunohistochemistry with the MRK-16 monoclonal antibody. In situ mdr1 RNA hybridization was performed in 30 cases. Complete agreement was noted between all the techniques in 14 cases (39%). Results differed on a single test result in another 39% of the cases. These 78% of cases were considered assessable, and the consensus result was presumed to be correct. By this consensus criterion, immunohistochemistry yields both false negative (11%), and false positive (11%) results. RNA slot blotting has a high (21%) false positive rate. In situ mRNA hybridization and rt-PCR have the highest concordance, 80%. The 28 patients from whom these cell lines were derived appear to represent a very poor prognosis group, since there are only two patients (with Burkitt's lymphoma) who are long-term survivors. Nonetheless, a complete clinical response to therapy was correlated with absence of mdr1 expression in assessable cases (p = 0.04). These four methods of determining mdr1 expression often yield discordant results. Therefore, the use of at least two methods for evaluating mdr1 expression is advisable. Rt-PCR is recommended because of its relative simplicity and specificity. This should be supplemented by a technique (immunohistochemistry or flow cytometry) able to detect heterogeneity of P-glycoprotein expression among cells.
Leukemia 1994 Feb
PMID:Mdr1 gene expression in childhood acute lymphoblastic leukemias and lymphomas: a critical evaluation by four techniques. 790 44


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