Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.3 (topoisomerase)
 9,911 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

VP-16 resistant cells, designated VP-16K6-1 (K6-1) were isolated from human acute lymphoblastic leukemia cell line RPMI 8402. IC50 value against VP-16 were 11-fold higher than their sensitive parental cell line. The membrane permeability of the drug was not responsible for resistance in K6-1 cells. K6-1 cells showed resistance in drug-induced DNA strand breaks (single strand breaks) determined by the alkaline sucrose gradient sedimentation method. Dot-blot analysis of RNA extracted from 2 cell lines showed that the mRNA levels of DNA topoisomerase II in K6-1 cells decreased slightly compared with that of parent cells. However, Topo II activities were similar in wild-type and K6-1 cells. In addition, K6-1 cells exhibited cross-resistance only to VM-26. These data suggest that a reduced intracellular Topo II level may contribute to drug resistance as an important factor in K6-1 cells.
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PMID:Isolation and characterization of VP-16 resistant human leukemia cell line. 136 90

In the accompanying paper (K. Tanabe, Y. Ikegami, R. Ishida, and T. Andoh, Cancer Res., 51: 4903-4908, 1991), we showed that ICRF-154 and -193, dioxopiperazine derivatives, inhibited the activity of purified topoisomerase II, without formation of a cleavable DNA-protein complex. In order to see whether ICRF-154 and ICRF-193 affect cellular topoisomerase II in situ or not, we examined the effect of these drugs on etoposide (VP-16)-induced, topoisomerase II-mediated DNA breaks in RPMI 8402 cells by alkaline sedimentation analysis. When RPMI 8402 cells were exposed to VP-16 in the presence of ICRF-154 or ICRF-193 for 1 h, VP-16-induced DNA strand breaks were greatly inhibited by both ICRF compounds. In parallel with this observation, VP-16-induced growth inhibition was also reversed by ICRF-193. Exposure of cells to ICRF-154 resulted in a progressive accumulation of cells with 4C DNA content. Although mitotic index did not significantly increase, mitotic abnormalities were seen in cells exposed to ICRF-193 or ICRF-154: all mitotic cells exhibited early mitotic figures with fewer condensed and entangled chromosomes. The most sensitive phase of the cell cycle to ICRF-154 was the G2-M. ICRF-154 did not affect the spindle formation. However, abnormally oriented spindles were observed in drug-treated cells in parallel with the appearance of multinucleated cells. The results suggest that ICRF-154 and -193 inhibit topoisomerase II activity in RPMI 8402 cells, and this effect resulted in the appearance of cells in G2 and early M phase with fewer condensed and entangled chromosomes and of cells with multilobed nuclei.
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PMID:Inhibition of intracellular topoisomerase II by antitumor bis(2,6-dioxopiperazine) derivatives: mode of cell growth inhibition distinct from that of cleavable complex-forming type inhibitors. 165 5

The nuclear enzyme, topoisomerase II, is the major site of action for cancer chemotherapy agents such as etoposide, teniposide, and a variety of intercalating agents. These compounds cause the enzyme to cleave DNA, forming a DNA-protein complex that may be a key step leading to cell death. It is apparently unique as a chemotherapy target, since drug potency diminishes with decreasing enzyme activity. It was thus of interest to examine the topoisomerase content and drug-induced DNA cleavage in freshly obtained human leukemia cells and to compare the obtained data with the results of similar studies performed in well-characterized human leukemia cell lines. The human T-lymphoblast line, CCRF-CEM, was more than 100-fold more sensitive to the DNA-cleavage effect of etoposide than the cells of the 13 leukemic patients examined. One of the leukemia lines (HL-60) and a lymphoblastoid line (RPMI-7666) were somewhat less sensitive than cells of the CCRF-CEM cells, but were still 10-fold more sensitive than the patients studied. The relative insensitivity of the freshly obtained cells could not be accounted for by differences with respect to drug uptake but were associated with markedly reduced topoisomerase-II content as assayed by immunoblotting using a mouse polyclonal serum against topoisomerase II. Heterogeneity was observed in the sensitivities of patients' cells with respect to both drug-induced DNA cleavage and enzyme content. The observed differences between cultured cell lines and patients' cells may have been related to their proliferative status. Etoposide potency in normal resting lymphocytes resembles that observed in circulating leukemia cells. However, following mitogenesis with phytohemagglutinin and interleukin-2, proliferating lymphocytes become as sensitive to etoposide as cultured cell lines with regard to DNA cleavage. This effect was accompanied by an increase in topoisomerase-II content. Our data thus support the hypothesis that topoisomerase-II content may be an important determinant of cell sensitivity to certain classes of chemotherapy agents. Efforts to stimulate topoisomerase-II content may improve the therapeutic efficacy of these drugs.
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PMID:Etoposide-induced DNA cleavage in human leukemia cells. 282 74

Hoechst dye 33342 (Ho33342), like many other DNA minor groove binding ligands and its parent compound Hoechst dye 33258 (Ho33258), nonspecifically inhibits the catalytic activities of many DNA enzymes. However, both Ho33258 and Ho33342 also specifically interrupt the breakage/reunion reaction of mammalian DNA topoisomerase I by trapping reversible topoisomerase I cleavable complexes. The enhanced membrane permeability of Ho33342 over its parent compound Ho33258 has allowed studies of the cellular action of Ho33342. Our results suggest that Ho33342 also traps topoisomerase I but not topoisomerase II into reversible cleavable complexes in human KB cells. Although Ho33342 shares a similar mechanism of action with camptothecin, a prototypic topoisomerase I poison, in trapping topoisomerase I cleavable complexes, Ho33342 differs from camptothecin in its effect on drug-resistant cells. Different from camptothecin, Ho33342 was shown to be about 200-fold less cytotoxic in MDR1-overexpressing human KB V1 cells relative to parental human KB 3-1 cells. Ho33342 is only 5-fold less cytotoxic for camptothecin-resistant CPT-K5 cells, which expresses a highly camptothecin-resistant from of topoisomerase I, than for the wild type human lymphoblast RPMI 8402 cells. Our studies suggest a potential use of Hoechst 33342 as a new topoisomerase I poison in antitumor chemotherapy.
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PMID:A new mammalian DNA topoisomerase I poison Hoechst 33342: cytotoxicity and drug resistance in human cell cultures. 838 8

Selection protocols were designed to determine whether non-cytotoxic chemomodifiers can influence the evolution of the drug-resistant phenotype. To this end, the human multiple myeloma cell line RPMI 8226 (8226/S) was selected with either doxorubicin, verapamil or doxorubicin plus verapamil. Using this approach low-level multi-drug-resistant (MDR) cell lines were obtained when 8226/S was selected with doxorubicin only or doxorubicin plus verapamil but not with verapamil only. The MDR phenotypes obtained were mechanistically distinct. In doxorubicin only-selected cells (8226/dox4), drug resistance was mediated by over-expression of the MDR1 gene and its cognate protein P-glycoprotein. In contrast, the drug resistance seen in the doxorubicin plus verapamil-selected cells was mediated through decreases in topoisomerase II protein levels and catalytic activity and not by P-glycoprotein over-expression. Cells selected with verapamil alone did not become resistant to any of the drugs tested. None of the 3 selected cell lines showed any changes in MRP gene expression when compared with 8226/S. Our results indicate that the inclusion of verapamil during drug selection with doxorubicin influences the drug-resistant phenotype by preventing the selection of MDR1/P-glycoprotein-positive cells.
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PMID:Verapamil suppresses the emergence of P-glycoprotein-mediated multi-drug resistance. 863 68

As a continuation of our structure--activity relationship study of substituted 2-phenyl-4-quinolones and flavonoids as antitumor and antiviral agents, a series of 5,6,7,8-substituted-2-phenylthiochromen-4-ones has been synthesized by condensation of substituted thiophenols and ethyl benzoylacetates. Target compounds were evaluated for biological activity. Among them, compounds 7, 10, 12, and 13 displayed significant growth inhibitory action against a panel of tumor cell lines including human ileocecal carcinoma (HCT-8), murine leukemia (P-388), human melanoma (RPMI), and human central nervous system tumor (TE671) cells. Compounds 10, 12, and 19 displayed DNA topoisomerase I inhibitory activity in vitro and compound 11 was an in vitro, inhibitor of DNA topoisomerase II. Compound 11 was most active (ED50 value, 0.65 microM) against HIV in acutely infected H9 lymphocytes and had a therapeutic index of about 5.
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PMID:Antitumor agents. 166. Synthesis and biological evaluation of 5,6,7,8-substituted-2-phenylthiochromen-4-ones. 864 56

DNA topoisomerases are nuclear enzymes responsible for modifying the topological state of DNA. The development of agents capable of poisoning topoisomerases has proved to be an attractive approach in the search for novel cancer chemotherapeutics. Coralyne, an antileukemic alkaloid, has appreciable structural similarity to the potent topoisomerase I and II poison, nitidine. Analogues of coralyne were synthesized and evaluated for their activity as topoisomerase I and topoisomerase II poisons. These analogues were also evaluated for cytotoxicity in the human lymphoblast cell line, RPMI 8402, and its camptothecin-resistant variant, CPT-K5. The pharmacological activity of these analogues exhibited a strong dependence on the substitution pattern and the nature of substituents. Several 1-benzylisoquinolines and 3-phenylisoquinolines were also synthesized. These compounds, which incorporate only a portion of the ring structure of coralyne, were evaluated as topoisomerase poisons and for cytotoxicity. These structure-activity studies indicate that the structural rigidity associated with the coralyne ring system may be critical for pharmacological activity. The presence of a 3,4-methylenedioxy substituent on these coralyne analogues was generally associated with enhanced activity as a topoisomerase poison. 5,6-Dihydro-3,4-methylenedioxy-10,11-dimethoxydibenzo[a,g]quinoliz inium chloride was the most potent topoisomerase I poison among the coralyne analogues evaluated, having similar activity to camptothecin. This analogue also possessed exceptional potency as a topoisomerase II poison. Despite the pronounced activity of several of these coralyne derivatives as topoisomerase I poisons, none of these compounds had cytotoxic activity similar to camptothecin. Possible differences in cellular absorption between these coralyne analogs, which possess a quaternary ammonium group, and camptothecin may be responsible for the differences observed in their relative cytotoxicity.
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PMID:Coralyne and related compounds as mammalian topoisomerase I and topoisomerase II poisons. 881 27

Drug-resistance in cell lines and in malignant human tumours is associated with dysregulation of several genes including mdr1, MRP1, GST-pi, bcl-2, DNA topoisomerase II alpha and beta, and thymidine kinase I. mRNA expression was evaluated by quantitative RT-PCR coupled with HPLC in three human tumour cell lines and drug-resistant (DR)-sublines. DR sublines from RPMI-8226 and KB cells specifically overexpressed the mdr1 gene without major changes observed in other putative DR-associated genes. In contrast, the DR-H69 cells exhibited a 34-fold overexpression of the MRP gene accompanied by significant down-regulation of both DNA topoisomerase II alpha and bcl-2 mRNA gene expression, by factors of 43 and 13 respectively. These results demonstrate the concomitant down regulation of topoisomerase II alpha and bcl-2 genes in response to DR. Furthermore, differential patterns of gene dysregulations appear to vary depending upon both the drug used to select resistance and cellular origin.
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PMID:Assessment of drug-induced dysregulations among seven resistance-associated genes in human tumour cell lines. 904 17

The purpose of the present study was to evaluate whether intermittent exposure to a constant dose of doxorubicin selects for multidrug resistance (MDR) in RPMI 8226 human myeloma cells and, if so, to determine the molecular mechanism. In an attempt to approximate clinical doxorubicin treatment in vitro, cells were exposed to a fixed dose of doxorubicin for 4 d alternating with growth in drug-free medium for 17 d. An MDR subline emerged, termed 8226/DOXint5, which was 3-4-fold resistant to doxorubicin, etoposide and m-AMSA, and 1.6-fold resistant to vincristine. Sensitivity to docetaxel, melphalan and cisplatin was normal. Verapamil normalized vincristine sensitivity but had little effect on resistance to the other agents. Cellular uptake and retention of daunorubicin and vincristine were reduced by approximately 10%. The 8226/DOXint5 cells showed diminished DNA topoisomerase IIalpha expression and increased expression of the multidrug resistance protein MRP. Expression of MDR1/P-glycoprotein was not detected. Immunostaining showed 70% of the cells to over-express the lung-resistance protein LRP. This new MDR myeloma cell line may prove to be a useful model for the development of strategies to overcome low-level, multifactorial MDR, which might be a common phenomenon in clinical myeloma treated with doxorubicin.
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PMID:Intermittent exposure to doxorubicin in vitro selects for multifactorial non-P-glycoprotein-associated multidrug resistance in RPMI 8226 human myeloma cells. 913 43

Decreased topoisomerase II (Topo II) activity results in resistance to antineoplastic agents targeting this enzyme. Dox1V derived from human multiple myeloma RPMI 8226 demonstrated a 4-fold resistance to doxorubicin in the absence of MDR1 overexpression or topo II mutations (Futscher B.W., Foley N., Gleason-Guzman M., Meltzer P.S., Sullivan D.M., and Dalton W.S., Int'l. J. Cancer, 66: 520-5, 1996.). Consistent with its drug resistant phenotype, a 2- to 3-fold decrease in topo II expression was identified. To investigate the molecular basis for decreased topo II expression in Dox1V, a semi-quantitative analysis of Topo II activity, protein level and mRNA transcript were performed. The results demonstrated that reduced Topo II activity is due to a decreased mRNA level. Southern blot and sequencing experiments revealed wild-type sequence of the topo II promoter in the drug resistant cells. Transient gene expression assays demonstrated that topo II is transcriptionally down-regulated in Dox1V independent of the promoter sequence of the endogenous alleles. Instead, the activity of a ubiquitous transcription factor CP-1 (NF-Y) interacting with the topo II promoter is decreased. The decrease in CP-1/NF-Y activity in Dox1V is correlated well with the decrease in topo II transcriptional activity, transcript level, Topo II protein and enzyme activity. Therefore, transcriptional down-regulation resulted from a reduced CP-1/NF-Y activity is responsible for decreased topo II expression in Dox1V cells.
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PMID:Decreased CP-1 (NF-Y) activity results in transcriptional down-regulation of topoisomerase IIalpha in a doxorubicin-resistant variant of human multiple myeloma RPMI 8226. 926 89


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