Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.2 (topoisomerase)
 9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The expression of different genes potentially involved in DNA repair and in cell responses to chemotherapy was evaluated in 33 previously untreated ovarian cancer patients. In biopsies of the same patients the expression of repair genes O6-methylguanine DNA methyltransferase (MGMT), 3-methyladenine DNA glycosylase (MAG), ERCC1, MDR-1, DNA topoisomerase I, DNA topoisomerase IIalpha, and glutathione S-transferase-pi (GST-pi) was assessed by Northern blot analysis. No direct statistical correlation was found between the expression of these genes and the response to chemotherapy (mainly platinum-based with or without doxorubicin and cyclophosphamide). Univariate analysis showed a weak negative correlation (P = 0.037) between the expression of ERCC1 and mortality, whereas no statistically significant correlation was found for other parameters. The MDR-1 gene encoding for the P-glycoprotein P-170 was mostly undetectable in these patients (as assessed by Northern blotting), whereas relatively high levels of MAG and MGMT were found in the majority of patients. A statistically significant correlation was found between the expression of DNA topoisomerase I and the expression of either ERCC1 (P = 0.0026) or GST-pi (P = 0.0279).
 ...
PMID:Expression of genes of potential importance in the response to chemotherapy and DNA repair in patients with ovarian cancer. 910 2

The heterogeneous nature of an adriamycin-selected human MDR squamous lung cell line, DLKP-A, was investigated by isolating and characterising 9 of its clonal subpopulations. The DLKP-A cell line exhibits resistance to the classical MDR drugs, overexpresses P-glycoprotein and displays reduced topoisomerase II amounts. The clonal cell lines exhibit a wide range of resistance extents, with the most resistant clone displaying 9 times the extent of adriamycin resistance observed in the least resistant clone. A number of clones exhibit sensitivity to the concentration of adriamycin in which the parental cell line was selected, possibly indicating cooperation between the more and less resistant cells. Detailed analysis of 4 of the clonal subpopulations revealed broadly similar drug resistance mechanisms. Alterations in expression of the MDR-associated genes MDR1 and Topo IIalpha were observed, with no detectable changes in the expression of MDR3, MRP, GSTpi, Topo IIbeta, Topo I and CYP1A1 noted. However, each clonal cell line displayed a distinct extent of expression of MDR1 and Topo IIalpha and further characterisation of the clones indicated that other modes of drug resistance may exist in at least one of the cell lines. In particular, 2 of the clones (DLKPA6B and DLKPA11B) which have almost identical drug resistance profiles appear to have quite different mechanisms of resistance. The clonal subpopulations possess individual growth rates, amounts of adriamycin accumulation and susceptibility to toxicity-enhancement by MDR-modulating agents. It was possible to generate a cell line with a drug toxicity profile similar to DLKP-A by mixing some of the clonal subpopulations. Our results provide evidence of heterogeneity within an MDR human cell population with respect to resistance and expression of MDR-associated genes.
 ...
PMID:Isolation from a human MDR lung cell line of multiple clonal subpopulations which exhibit significantly different drug resistance. 918 Jan 64

Variants of the human ovarian carcinoma cell line, OAW42, exhibiting low-level intrinsic resistance (OAW42-SR) and drug-induced higher-level resistance (OAW42-A1 & OAW42-A), were studied along with a sensitive clonal population (OAW42-S) which was isolated from OAW42-SR. Expression of the MDR-associated protein P-170, the more recently discovered LRP (lung resistance-related protein) and MRP (multidrug resistance-associated protein), topoisomerase II alpha and beta, GST pi and the cytoskeletal proteins, cytokeratin 8 and vimentin, were studied (using immunocytochemistry and Western blotting techniques) in conjunction with drug (doxorubicin) accumulation and subcellular distribution. Expression of mRNA for P-170, MRP, topoisomerase 11 alpha and beta and GST pi was studied using RT-PCR (reverse transcriptase polymerase chain reaction). Results indicate differential co-expression of four MDR-associated parameters (P-170, MRP, LRP and reduced topoisomerase II alpha and beta) in the OAW42-SR and OAW42-A1 variants, whereas resistance in the OAW42-A variant appeared to be mainly P-170 mediated. Comparable amounts of MRP and greater amounts of LRP were detected in the OAW42-S cells compared to the OAW42-SR variant (which showed increased resistance compared to the OAW42-S cells), but all cell lines expressed similar low-level amounts of MRP mRNA (by RT-PCR). GST pi levels did not differ markedly between variants. Increased levels of the cytoskeletal proteins were observed with increasing levels of resistance. The relative resistance of the variants, OAW42-SR and OAW42-A1, compared with OAW42-S was seen to change during increased serial passaging of the cells. There was greater drug accumulation by the sensitive OAW42-S cell line compared with that of the resistant variants, particularly the most highly resistant OAW42-A cells. Both verapamil and cyclosporin A effectively restored the accumulation defects seen in the resistant variants, cyclosporin A being the more effective of the two. Sub-cellular location of drug was predominantly in the nucleus with maximum levels seen in the sensitive OAW42-S variant and minimum levels in the most resistant OAW42-A clone.
 ...
PMID:Co-expression of MDR-associated markers, including P-170, MRP and LRP and cytoskeletal proteins, in three resistant variants of the human ovarian carcinoma cell line, OAW42. 927 50

The thioether phospholipid ilmofosine (BM 41 440) is a new anti-cancer drug presently undergoing phase II clinical trials. Because resistance to anti-tumour drugs is a major problem in cancer treatment, we investigated the resistance of different cell lines to this compound. Here we report that the multidrug-resistant cell lines MCF7/ADR, CCRFNCR1000, CCRF/ADR500, CEM/VLB100 and HeLa cell lines transfected with a wild-type and mutated (gly/val185) multidrug resistance 1 gene (MDR1) are cross-resistant to ilmofosine compared with the sensitive parental cell lines. In CEMNM-1 cells, in which the resistance is associated with an altered topoisomerase II gene, no cross-resistance to ilmofosine was observed. Ilmofosine is not capable of modulating multidrug resistance and neither does it reduce the labelling of the P-glycoprotein (P-gp) by azidopine nor alter ATPase activity significantly. The resistance to ilmofosine in multidrug-resistant CCRF/VCR1000 cells cannot be reversed by the potent multidrug resistance modifier dexniguldipine-HCI (B8509-035). A tenfold excess of ilmofosine does not prevent the MDR-modulating effect of dexniguldipine-HCl. Treatment of cells with ilmofosine does not alter the levels of MDR1 mRNA. Long-term treatment of an ilmofosine-resistant Meth A subline with the drug does not induce multidrug resistance, indicating that ilmofosine does not increase the level of P-gp. Determination of the MDR2 mRNA levels in the cells revealed that the resistance pattern to ilmofosine is not correlated with the expression of this gene. It is concluded, therefore, that multidrug-resistant cells are cross-resistant to ilmofosine and that the compound is not a substrate of Pgp. No association between the expression of the MDR2-encoded P-gp and resistance to ilmofosine was observed. It is supposed that MDR1-associated alterations in membrane lipids cause resistance to ilmofosine.
 ...
PMID:Resistance to the new anti-cancer phospholipid ilmofosine (BM 41 440). 932 44

The efficacy of all chemotherapeutic agents is limited by the occurrence of drug resistance. For etoposide (VP-16), increased expression of MDR-1 or MRP and alterations in topoisomerase IIalpha have been shown to confer tolerance. To further understand resistance to VP-16, three sublines, designated MCF-7-VP17, ZR-75B-VP13, and MDA-MB-231-VP7, were initially isolated as single clones from parental cells by exposure to VP-16. Subsequently, a population of cells from each subline was exposed to 3-fold higher drug concentrations, allowing stable sublines to be established at higher extracellular drug concentrations. Characterization of the resistant sublines demonstrates the adaptation that occurs with advancing drug concentrations during in vitro selections. Reduced topoisomerase II mRNA and protein levels were observed in the initial isolates. This reduction was accompanied by a decrease in topoisomerase II activity and cellular growth rate and was associated with 6-314-fold resistance to topoisomerase II poisons. With advancing resistance, MRP expression increased and VP-16 accumulation decreased. This adaptation allowed for partial restoration of topoisomerase II activity as a result of increased expression (MCF-7-VP17 and ZR-75B-VP13) or hyperphosphorylation (MDA-MB-231-VP7), with a resultant increase in growth rate. In MDA-MB-231-VP7 cells, hyperphosphorylation coincided with increased casein kinase II mRNA and protein levels, suggesting a role for this kinase in the acquired hyperphosphorylation. In this cell line, hyperphosphorylation mediated the increased activity despite a fall in topoisomerase IIalpha protein levels secondary to an acquired 600-bp deletion in one topoisomerase IIalpha allele, which resulted in reduced protein levels. In all three sublines, high levels of resistance were attained as a result of synergism between the reduced topoisomerase IIalpha levels and MRP overexpression. These studies demonstrate how cellular adaptation to increasing drug pressure occurs and how more than one mechanism can contribute to the resistant phenotype when increasing selecting pressure is applied. Reduced expression of topoisomerase II is sufficient to confer substantial resistance early in the selection process, with synergy from MRP overexpression helping to confer high levels of resistance.
 ...
PMID:Cellular adaptation to drug exposure: evolution of the drug-resistant phenotype. 937 7

We have established an in vivo etoposide-resistant glioma cell line (C6/VP) from C6 rat glioma cells by stepwise exposure to increasing doses of etoposide. The C6/VP cells were 10 times more resistant to etoposide than the parental C6 cells. In addition C6/VP cells demonstrated cross-resistance to vincristine and vinblastine, but not to ADM or m-AMSA. Interestingly, the cells had collateral sensitivity to ACNU, cisDDP and Ara-C. The C6/VP cells did not express the MDR gene or p-glycoprotein, while they showed 16 times less topoisomerase II catalytic activity compared to the C6 cells. Although there was no significant difference between C6 and C6/VP cells in amounts of topoisomerase II in nuclear extracts, the C6/VP cells had 2.9 times higher amounts of the enzyme than C6 cells in nuclear scaffold prepared from a relatively low-salt buffer (0.5 M NaCl). Northern blot analysis demonstrated that mRNAs of topoisomerase IIalpha isoforms were expressed both in C6 and C6/VP cells, and that the amounts of topoisomerase IIalpha in C6/VP cells were 14 times greater than in C6 cells. The total uptake of etoposide in tumor tissues derived from C6/VP cells was 3 times less than those derived from parental C6 cells. These results indicate that the C6/VP acquired a multi-drug resistance phenotype by a reduction of the catalytic activity of topoisomerase II and/or diminished accumulation of drugs. This phenotype did not involve the p-glycoprotein. Alterations of topoisomerase II in the C6/VP cells also were accompanied by an increased amount of the topoisomerase IIalpha isoform, most of which was localized in the nuclear scaffold (matrix). This suggests that altered binding of topoisomerase II to topologically organized DNAs in the nuclear scaffold may be the molecular basis of this multi-drug resistance phenotype.
 ...
PMID:In vivo etoposide-resistant C6 glioma cell line: significance of altered DNA topoisomerase II activity in multi-drug resistance. 952 24

Non-small-cell lung cancer (NSCLC) and small-cell lung cancer (SCLC) differ significantly in their clinical response to topoisomerase IIalpha (topo-IIalpha)-directed drugs, such as etoposide and teniposide, as NSCLC is virtually insensitive to single-agent therapy, while SCLC responds in two-thirds of cases. Preclinical studies have indicated that resistance to topo-IIalpha drugs depends on topo-IIalpha content and/or activity, the altered-topo-II multidrug resistance phenotype (at-MDR) and/or one of two different drug efflux pumps, P-glycoprotein (P-gp) and the multidrug resistance protein (MRP). Immunohistochemical analysis on paraffin-embedded tissue from 27 cases of untreated NSCLC and 29 cases of untreated SCLC (of which additional tumour biopsies after treatment with topo-IIalpha-directed drugs were available in ten cases) yielded the following results: NSCLC had significantly less topo-IIalpha than SCLC (P < 0.0001), as only 5 out of 27 NSCLC cases had > 5% positive cells compared with 28 out of 29 SCLC, and 0 out of 27 NSCLC had > 25% positive cells compared with 26 out of 29 SCLC. P-gp was detected in > 5% of cells in only 3 out of 27 NSCLC and in 6 out of 29 SCLC, and MRP in 5 out of 27 of NSCLC and 9 out of 29 SCLC. After treatment of patients with SCLC with either etoposide or teniposide, which are topo-IIalpha-directed drugs, there was an increase in MRP (P < 0.1) and P-gp (P < 0.05) positivity, while topo-IIalpha decreased (P < 0.05). In conclusion, the major difference between untreated NSCLC and SCLC was in topo-IIalpha content. In the small series of ten patients treated for SCLC, all three MDR phenotypes appeared to increase.
 ...
PMID:Immunohistochemical detection of DNA topoisomerase IIalpha, P-glycoprotein and multidrug resistance protein (MRP) in small-cell and non-small-cell lung cancer. 965 63

KB/7D cells represent a multidrug-resistant subclone of human nasopharyngeal carcinoma KB cells generated by continuous exposure to the topoisomerase II inhibitor VP-16 (etoposide). KB/7D cells also show cross-resistance to doxorubicin and vincristine. Phenotypic traits of the cell line include a 2-fold decrease in topoisomerase II levels and a decrease in the uptake of VP-16 without an increase in the rate of drug efflux or expression of P-glycoprotein, suggesting a novel mechanism associated with the uptake of anticancer drugs. This study demonstrated that the multidrug-resistance associated protein (MRP) is overexpressed in KB/7D cells, and that the loss of resistance in revertant cells correlates with the loss of MRP. The resistance to VP-16 and doxorubicin could be overcome, partially, and resistance to vincristine could be overcome completely, by the L-enantiomer of verapamil, but not by the D-enantiomer or by BIBW 22 (4-[N-(2-hydroxy-2-methyl-propyl)-ethanolamino]-2,7-bis[cis-2,6-++ +dimethylmorpholino)-6-phenylpteridin), an inhibitor of MDR-1. L-Verapamil was shown to be significantly more potent than D-verapamil in modulating the accumulation defect in KB/7D cells towards doxorubicin, as measured by flow cytometry and confocal microscopy, and towards VP-16, as measured by increases in protein-linked DNA strand breaks. This suggests that KB/7D cells are multidrug resistant due to decreases in topoisomerase II levels and the overexpression of MRP, that MRP leads to a decrease in drug accumulation, and that L-verapamil can modulate the MRP-associated accumulation defect and drug-resistance phenotype. This contrasts with previous studies that suggest that MRP causes multidrug resistance by exporting cytotoxic drugs out of the cell and that did not show modulation of MRP by verapamil.
 ...
PMID:Decreased drug accumulation without increased drug efflux in a novel MRP-overexpressing multidrug-resistant cell line. 971 74

TAS-103 is a novel anticancer agent targeting both topoisomerase (Topo) I and Topo II, that stabilizes cleavable complexes of Topo-DNA at the cellular level. In this study, the in vitro antitumor effects of TAS-103 were compared with those of other known Topo I and Topo II inhibitors. TAS-103 inhibited DNA synthesis more strongly than RNA and protein synthesis, and induced an increase of cell population in the S-G2/M phase. The cytotoxicity of TAS-103 was strongest against S-phase cells, but its cell cycle phase specificity was not clear, and depended on drug concentration and exposure time. The cytotoxicity of TAS-103 (IC50: 0.0030-0.23 microM) against various tumor cell lines was much stronger than that of VP-16 and comparable to that of SN-38. The cytotoxicity of TAS-103 seemed to be more related to the amount of protein-DNA complexes than to the accumulation of TAS-103 in the cells. P-Glycoprotein (P-gp)-mediated MDR, CDDP-resistant and 5-FU-resistant cell lines did not show cross-resistance to TAS-103. Although PC-7/CPT cells bearing a Topo I gene mutation showed cross-resistance to TAS-103, the sensitivity of P388/CPT, HT-29/CPT and St-4/CPT cells, showing decreased Topo I expression, was not changed. KB/VM4 and HT-29/Etp cells, showing decreased Topo II expression, were slightly cross-resistant to TAS-103. These results suggest that TAS-103 may act as an inhibitor of both Topo I and Topo II at the cellular level. This property may be responsible for its strong antitumor effect and broad-spectrum, growth-inhibitory effect on drug-resistant cell lines.
 ...
PMID:In vitro antitumor activity of TAS-103, a novel quinoline derivative that targets topoisomerases I and II. 1039 Oct 99

In a series of 40 neuroblastomas we analyzed the relative mRNA levels of the MDR associated genes encoding MDR1/P-glycoprotein (MDR1), multidrug resistance associated protein (MRP), lung cancer resistance related protein (LRP) and topoisomerase IIalpha (TOPO IIalpha) by cDNA-PCR. Cyclin A (CYCA) was included to examine cellular proliferation activity. MYCN gene expression was analyzed as it was recently shown to be associated with enhanced MRP gene expression in neuroblastomas. We found that tumors with MYCN gene amplification exhibit significantly increased MYCN and MRP gene expression levels. Tumors with an allelic loss of the chromosomal 1p region showed significant (P<0.05) lower MDR1 gene expression (MDR1: 50+/-29, n=4) than tumors without (MDR1: 117+/-81, P<0.05, n=36). Moreover, significant positive correlations were found for MYCN/TOPO IIalpha (P<0.0001), MYCN/CYCA (P<0.05), TOPO IIalpha/CYCA (P<0.01), MRP/CYCA (P<0.0001) and MRP/LRP (P<0.05). Our results give evidence that MDR in neuroblastomas might be caused by multiple resistance factors and that a higher proliferation rate of neuroblastoma cells possibly based on altered MYCN gene expression is associated with enhanced MRP, CYCA and TOPO IIalpha gene expression.
 ...
PMID:Expression analysis of multidrug resistance associated genes in neuroblastomas. 1042 16


<< Previous 1 2 3 4 5 6 Next >>