Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:5.99.1.2 (topoisomerase)
9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Factors that reduce the intracellular concentration of triphosphorylated cytarabine (ara-CTP), the active form of cytarabine (ara-C), may induce chemoresistance in acute myeloid leukaemia (AML) patients. These factors include reduced influx of ara-C by the hENT1 transporter, reduced phosphorylation by deoxycytidine kinase (dCK), and increased degradation by high Km cytoplasmic 5'-nucleotidase (5NT) and/or cytidine deaminase (CDD). Increased levels of DNA polymerase alpha (DNA POL) and reduced levels of topoisomerase I (TOPO I) and topoisomerase II (TOPO II) have also been detected in ara-C-resistant cell lines. To determine whether these factors are implicated in clinical ara-C resistance, we analysed the expression of these parameters at diagnosis, using reverse transcription polymerase chain reaction, in the blast cells of 123 AML patients treated with ara-C. At diagnosis, hENT1, dCK, CDD, 5NT, TOPO I, TOPO II, DNA POL and MDR1 were expressed in 83%, 22%, 7%, 37%, 59%, 37%, 39% and 16% of patients respectively. In univariate analysis, patients with expression of 5NT or DNA POL at diagnosis had significantly shorter disease-free survival (DFS). In multivariate analysis, DNA POL positivity and hENT1 deficiency were related to a shorter DFS. In univariate analysis, patients with 5NT-positive blasts had significantly shorter overall survival (OS). In multivariate analysis, shorter OS was related to DNA POL positivity. These results suggest that expression of DNA POL, 5NT and hENT1 at diagnosis may be resistance mechanisms to ara-C in AML patients.
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PMID:In vivo mechanisms of resistance to cytarabine in acute myeloid leukaemia. 1206 Jan 21

Studies on multidrug resistance (MDR) require a sensitive and quantitative assay of mRNA expression in clinical tumor samples. Based on the small size, heterogenity, and the possibility of partial degradation of clinical specimens, unambiguous data are often difficult to obtain. The aim of the present study was to develop a multiplex polymerase chain reaction (PCR) in combination with nested PCR for quantitative analyses of mRNA expression of MDR1, MRP (multidrug resistance protein), and DNA topoisomerase IIalpha in small amounts of tumor tissue. RNA samples extracted from the human cell line RPMI 8226 and its MDR sublines 8226/Dox6 and DOXint40c, that overexpress MDR1 and MRP, respectively, were used as model substrates. In the first step, cDNAs of the three genes as well as of the housekeeping gene beta-actin were simultaneously amplified in single tubes using 20 cycles of PCR after random-primed reverse transcription. When necessary, a second amplification step of the preamplified PCR products was employed using nested primer pairs. Primer competition was evaluated by analyses of serially diluted amounts of cDNA and at different numbers of PCR cycles. Based on the results obtained, this multiplex/nested PCR approach may provide a base for quantitative analyses of MDR1, MRP, and topoisomerase IIalpha mRNA expression in clinical tumor biopsies.
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PMID:A diagnostic tool for monitoring multidrug resistance expression in human tumor tissues. 1223 60

We have synthesized two podophyllotoxin-acridine conjugates-pACR6 and pACR8. In these compounds an 9-acridinyl moiety is beta linked to the C4 carbon of the four ring system in 4'-demethylepipodophyllotoxin (epiDPT) via eighter an N-6-aminohexanylamide linker (pACR6) or via an N-8-aminooctanylamide linker containing two more carbon atoms (pACR8). The acridine-linker moiety occupies the position where different glucoside moieties, dispensable for activity, are normally linked to epiDPT in the well known epipodophyllotoxins VP-16 and VM-26. As with VP-16 and VM-26, pACR6 and pACR8 show evidence of being topoisomerase II poisons as they stimulate topoisomerase II mediated DNA cleavage in vitro and induce DNA damage in vivo. This in vivo DNA damage, as well as pACR6/pACR8 mediated cytotoxicity, is antagonized by the catalytic topoisomerase II inhibitors ICRF-187 and aclarubicin, demonstrating that topoisomerase II is a functional biological target for these drugs. Despite their structural similarities, pACR6 was more potent than pACR8 in stimulating topoisomerase II mediated DNA cleavage in vitro as well as DNA damage in vivo and pACR6 was accordingly more cytotoxic towards various human and murine cell lines than pACR8. Further, marked cross-resistance to pACR6 was seen among a panel of multidrug-resistant (MDR) cell lines over-expressing the MDR1 (multidrug resistance protein 1) ABC drug transporter, while these cell lines remained sensitive towards pACR8. pACR8 was also capable of circumventing drug resistance among at-MDR (altered topoisomerase II MDR) cell lines not over-expressing drug transporters, while pACR6 was not. Two resistant cell lines, OC-NYH/pACR6 and OC-NYH/pACR8, were developed by exposure of small cell lung cancer (SCLC) OC-NYH cells to gradually increasing concentrations of pACR6 and pACR8, respectively. Here, OC-NYH/pACR6 cells were found to over-express MDR1 and, accordingly, displayed active transport of 3H-labeled vincristine, while OC-NYH/pACR8 cells did not, further suggesting that pACR6, but not pACR8, is a substrate for MDR1. Our results show that the spatial orientation of podophyllotoxin and acridine moieties in hybrid molecules determine target interaction as well as substrate specificity in active drug transport.
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PMID:Linker length in podophyllotoxin-acridine conjugates determines potency in vivo and in vitro as well as specificity against MDR cell lines. 1237 83

Intrinsic and acquired multidrug-resistance (MDR) and the activity of the enzyme telomerase have been demonstrated in human melanoma. A direct regulation of the MDR pathways and of telomerase by interpheron-alpha (IFN-alpha), which is currently used in the therapy of advanced cutaneous melanoma, has also been hypothesized. In this study, we used five melanoma cell lines not selected in vitro for drug resistance (Me665/2/21, Me665/2/60, HT-144, SK-MEL-28, and SK-MEL-5), which in a previous study, had shown different responses to IFN-alpha in terms of proliferation, apoptosis, telomerase activity and expression of mRNA for the human telomerase reverse transcriptase (hTERT). We investigated the expression of the multidrug resistance (MDR1) gene, multidrug resistance protein (MRP), lung resistance protein (LRP), topoisomerase IIalpha (Topo IIalpha), hTERT, and telomerase-associated protein (TEP1), which is shared by telomerase and vault MDR proteins at the mRNA expression level, using the reverse transcription-PCR (RT-PCR). All cell lines showed an intrinsic expression of hTERT, TEP1, and MDR gene transcripts (only MDR1 mRNA was under the detection level in SK-MEL-28 cells). After IFN-alpha exposure, we observed either no effect, a trend towards a decrease of hTERT, MRP, and Topo IIalpha, or an increase of TEP1, MDR1, and LRP mRNA expression in some cell lines. Effects were usually temporary and not always significant. No correlation was found between hTERT and TEP1 mRNA expression, whereas significant positive correlations were found between TEP1 and MDR1 mRNA, and between TEP1 and LRP mRNA. IFN-alpha modulates differently MDR gene transcripts in human melanoma cell lines. Positive correlation between TEP1 and LRP also seems to identify them as common targets of IFN-alpha effects.
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PMID:Evaluation of MDR1, LRP, MRP, and topoisomerase IIalpha gene mRNA transcripts before and after interferon-alpha, and correlation with the mRNA expression level of the telomerase subunits hTERT and TEP1 in five unselected human melanoma cell lines. 1279 96

Multidrug resistance (MDR) is a complex phenomenon that includes the expression of many different genes regulating drug transport or metabolism, cellular repair or detoxification mechanisms. The co-expression of several genes could be at the basis of the resistant phenotype in vivo. In order to test a possible prognostic role of the expression and co-expression of several MDR-related genes (MDR1, topoisomerase IIalpha, topoisomerase IIbeta, MRP, GSTpi, LRP), 35 patients affected by acute myeloid leukemia (AML) were tested by RT-PCR assays. In our series, topoisomerase IIbeta was significantly co-expressed with MRP (p = 0.05), GSTpi (p = 0.017) and LRP (p = 0.005). GSTpi was co-expressed with LRP (p = 0.03) and MRP (p = 0.007); on the other hand, 53.8% of patients were LRP and MRP-positive (p = 0.02). The PCR-positivity did not differ according to biological/clinical characteristics of patients, including age; this latter was the only parameter conditioning the response and overall survival. Neither the expression nor the co-expression of the tested genes was significantly correlated with the response to the induction treatment and long-term outcome.
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PMID:The clinical relevance of the expression of several multidrug-resistant-related genes in patients with primary acute myeloid leukemia. 1296 66

XR11576 (MLN576) is a novel monophenazine with a mechanism of action that includes interaction with both topoisomerase (Topo) I and II. The aim of this study was to evaluate its cytotoxicity against fresh tumor cells taken from patients with a variety of solid tumors. Cells were obtained from 89 patients and exposed for 6 days to XR11576 alone, or in combination with doxorubicin, cisplatin, treosulfan, paclitaxel or vinorelbine. Cell survival was measured using the ATP-Tumor Chemosensitivity Assay (ATP-TCA). Immunohistochemical staining of Topo I, Topo IIalpha and MDR1 was performed on paraffin-embedded blocks in those tumors for which tissue was available (n = 49). Overall, the median IC90 and IC50 values of XR11576 in tumor-derived cells were 242 and 110 nM, respectively. In all samples XR11576 was more potent than the other cytotoxics tested. Breast and gynecological malignancies were most sensitive to XR11576, while the potency of this compound was slightly attenuated in gastrointestinal tumors, in which the median IC90 and IC50 values were 308 and 212 nM, respectively. Cases of synergism were identified when combining XR11576 with vinorelbine (nine of 30 samples) and doxorubicin (12 of 38 samples), while the addition of paclitaxel resulted in an antagonistic effect (CI50>1.2) in 38 of 42 tumors. A very modest correlation by linear regression analysis was found between the intensity of MDR1 staining and the IC50 of XR11576 (r = 0.311, p = 0.0312), but not with the IC90 (r = 0.247, NS). These data support the rapid introduction of XR11576 to clinical trials and suggest that it may be effective against a broad spectrum of tumor types.
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PMID:Ex vivo characterization of XR11576 (MLN576) against ovarian cancer and other solid tumors. 1545 25

Three parental neuroblastoma cell lines and nine derived lines resistant to Vincristin, Doxorubicin and Cisplatin, respectively, using CGH were studied. CGH profiles of all three parental cell lines were obtained using DNA from a healthy volunteer as reference DNA. Labeled DNA from each of the drug resistant daughter cell lines and labeled DNA from their parental sensitive cell lines were hybridized to obtain a comparison of gains and losses that accompanied the development of resistance for that particular drug. All three parental cell lines were characterized by typical findings for high risk neuroblastoma: N-myc amplification, gain of 17q, and loss of 1p36.2-36.3. Acquired drug resistance in the neuroblastoma cell lines appeared to be accompanied by a large array of DNA sequence copy number changes. The regions frequently affected in chemo-resistant cell lines included gains of 13q14.1-32, and 7q11.2-31.3, 4 q. Amplifications were seen at 7q 21.1 consistent with MDR1 amplification in UKF-NB-2 VCR, UKF-NB-3 DOXO, UKF-NB-4 VCR, and UKF-NB-4 DOXO, but not in any Cisplatin resistant line. All Cisplatin and Doxorubicin and two Vincristin resistant line (UKF-NB-2 VCR and UKF-NB-4 VCR) had a deletion of part of 19q or the whole 19 chromosome. All lines resistant to Vincristin or Doxorubicin and two Cisplatin resistant lines (UKF-NB-2 CDDP and UKF-NB-4 CDDP) had a deletion of at least part of 17q, UKF-NB-4 DOXO had deletion of the whole chromosome 17. The loss of 17q may cause chemoresistance by deletion of topoisomerase IIalpha gene. Deletion of 19 q in all but one chemo-resistant lines may influence of cytochromes P450 genes which are located on 19q13.2. Also gains of 15q 22, which were detected in UKF-NB-4 VCR, UKF-NB-2 DOXO and UKF-NB-4 DO X O, may affect other cytochromes P450 genes.
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PMID:Characterization of drug-resistant neuroblastoma cell lines by comparative genomic hybridization. 1615 87

Multidrug resistance (MDR) is a major obstacle to successful application of cancer chemotherapy and also a basic problem in cancer biology. Studies on the molecular basis of MDR have revealed that a number of proteins over express in multidrug resistant cells viz., multidrug resistant MDR1 gene product P-glycoprotein, the multidrug resistance-associated protein (MRP) and enzymes associated with the glutathione (GSH) metabolism. Decreased expression or altered activity of topoisomerase II has also been implicated in MDR. In the present investigation a number of changes in phase II detoxification parameters have been noticed in drug resistant cells but the novel aspect of the present report is the observation that the metal copper is involved in drug resistance. Although copper plays important roles in many human and other biological systems and even in the treatment of cancer but the relation of Cu and drug resistance has not so far been studied in detailed. The present report describes the novel findings that the level of copper increases with the development of drug resistance in Ehrlich ascites carcinoma and in Lewis lung carcinoma cells and also in serum of mice bearing drug resistant cancer cells compared to mice bearing drug sensitive cells; the work indicates the important aspect of treating drug resistant cancer patients by lowering Cu level in the cancerous cells and serum prior to treatment.
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PMID:The role of copper in development of drug resistance in murine carcinoma. 1678 40

Based on the topoisomerase IIalpha catalytic inhibitory activity of a previous hit compound, NSC35866, we screened 40 substituted purines or purine-like compounds from the National Cancer Institute repository for their ability to inhibit the ATPase activity of human topoisomerase IIalpha. Several compounds, including NSC348400, NSC348401 and NSC348402, were inhibitory at submicromolar concentrations. Three-dimensional quantitative structure-activity relationship models using comparative molecular field and comparative molecular similarity indices analyses were constructed using 24 of these compounds. The ability of 10 selected compounds to inhibit the complete DNA strand passage reaction of topoisomerase IIalpha correlated well with their potency as ATPase inhibitors. None of the 40 compounds significantly increased levels of the topoisomerase IIalpha-DNA covalent complex, suggesting that they functioned as catalytic topoisomerase II inhibitors and not as topoisomerase II poisons. Although some of these compounds could antagonize the effect of etoposide on the level of topoisomerase IIalpha-DNA covalent complex formation in vitro, in contrast to NSC35866, they were not capable of antagonizing etoposide-induced cytotoxicity and DNA strand breaks in cells. Two independently selected human SCLC cell lines with reduced topoisomerase IIalpha expression displayed cross-resistance to NSC348400, NBSC348401, and NSC348402, whereas an MDR1 line was fully sensitive. These results suggest that topoisomerase IIalpha is a functional cellular target for most of these substituted purine compounds and that these compounds do not display MDR1 liability.
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PMID:A three-dimensional quantitative structure-activity relationship study of the inhibition of the ATPase activity and the strand passing catalytic activity of topoisomerase IIalpha by substituted purine analogs. 1688 Feb 87

The results of multidrug resistance determinants expression analysis on leukemic cells of 56 acute myeloid leukemia (AML) patients by immunophenotyping are presented. Of these, there were 21 persons exposed to ionizing radiation due to the Chemobyl accident with radiation-associated AML and 35 patients with spontaneous leukemia. The aim of this study was to determine if transport proteins (P-glycoprotein, LRP, and MDR1), apoptosis-related proteins (Fas, Bcl-2, Bax, p53, and Bcl-X(L)), and topoisomerase IIalpha expression in AML patients with the history of radiation exposure differed from those in spontaneous AML cases. Leukemic cells in patients with radiation-associated diseases compared to spontaneous AML more often overexpressed antiapoptotic oncoprotein Bcl-2 (12/21 vs. 6/35, p < 0.005) and less often demonstrated expression of Fas receptor (12/21 vs. 30/35, p < 0.05). Moreover, leukemic cells were simultaneously Fas negative and Bcl-2 positive in 4 out of 21 patients exposed to ionizing radiation but none of spontaneous cases had similar phenotype (p < 0.05). Leukemic cells in patients with radiation-associated AML compared to spontaneous cases more often were P-glycoprotein positive (12/20 vs 9/31, p < 0.05). P-glycoprotein overexpression significantly correlated with resistant disease in patients with radiation-associated AML (r = 0.47, p < 0.05), but was not a prognostic variable for the treatment outcome in terms of overall survival. Defects in pathways of drug-induced apoptosis and function of pump, that actively effluxes drugs could contribute significantly to developing drug resistance in radiation-associated AML.
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PMID:[Multidrug resistance determinants in acute myeloid leukemia developed in persons exposed to ionizing radiation due to the Chernobyl accident]. 1713 22


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