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)

A carcinogen-transformed rat hepatoma cell line (Reuber H-35) was utilized as a model system for investigation of the biochemical factors which may limit the effectiveness of chemotherapy in intrinsically resistant tumors such as hepatocellular carcinoma. Northern blotting demonstrated expression of mRNA coding for the P-170 membrane-glycoprotein associated with the multi-drug resistance phenotype, while Western blotting identified the P-170 glycoprotein in the hepatoma cell membrane. Consistent with these observations, tumor cell sensitivity to the vinca alkaloids, vincristine and vinblastine, to the anthracycline antibiotics, Adriamycin and daunorubicin, and to the demethylepipodophyllotoxin derivative, VM-26, was enhanced by continuous incubation in the presence of the calcium channel antagonist, verapamil. Verapamil produced a minimal change in cell sensitivity to the demethylepipodophyllotoxin derivative, VP-16, and to the aminoacridine, m-AMSA. Relatively high detoxification potential via the glutathione metabolic pathway was also observed in the hepatoma cell. The capacity of topoisomerase II in nuclear extracts from the hepatoma cell to mediate cleavable complex formation stimulated by VM-26, VP-16 and m-AMSA appeared to be at least comparable to, if not greater than that from drug-sensitive HL-60 cells, suggesting that drug resistance may not occur at the level of this enzyme. Consistent with findings in a number of tumor cell lines resistant to antineoplastic drugs, the antiproliferative activity of the topoisomerase II inhibitors VM-26, VP-16 and m-AMSA appeared to be dissociable from the induction of DNA strand breaks, suggesting that such lesions in DNA may fail to fully account for the antiproliferative activity of these agents in the hepatoma cell.
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PMID:Components of intrinsic drug resistance in the rat hepatoma. 131 Aug 53

We have isolated a multidrug-resistant derivative of Chinese hamster ovary CHO-K1 cells by exposure to progressively increasing concentrations of Adriamycin. This cell line, designated CHO-Adrr, was 27-fold more resistant than the parental line to Adriamycin and showed similar degrees of cross-resistance to several other topoisomerase II (topo II) inhibitors, including mitoxantrone, daunomycin and etoposide. CHO-Adrr cells showed a lower (4-fold) level of cross-resistance to vincristine and colchicine, drugs associated with the multidrug-resistant phenotype. While CHO-Adrr cells showed no enhanced resistance to several mono- and bi-functional alkylating agents or to UV and ionizing radiation, they were greater than 80-fold resistant to mitomycin C (MMC). There was a 5-fold decreased level of daunomycin accumulation in CHO-Adrr cells compared to CHO-K1 cells and this was associated with increased drug efflux. The resistant cells had amplified multidrug resistance gene (mdr) sequences and overexpressed (mdr) mRNA. Verapamil was able to completely reverse Adriamycin resistance but reversal of MMC resistance was only partial, with residual 23-fold resistance. CHO-Adrr cells expressed a 4-fold reduced level of topo II protein but overexpressed an alpha class (basic) glutathione S-transferase (GST). Analysis of cell hybrids showed that while the level of resistance to Adriamycin dropped by a factor of 3 in CHO-K1/CHO-Adrr hybrids compared to CHO-Adrr/CHO-Adrr hybrids, resistance to MMC dropped 10-fold. Thus, CHO-Adrr cells appear to exhibit simultaneously several different drug resistance mechanisms including MDR and GST overexpression, and topo II reduction.
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PMID:Reduced topoisomerase II and elevated alpha class glutathione S-transferase expression in a multidrug resistant CHO cell line highly cross-resistant to mitomycin C. 131 88

N-Benzyladriamycin-14-valerate (AD 198) is a highly lipophilic analogue of Adriamycin with novel cytotoxic mechanisms, greater in vivo antitumor activity, and the ability to circumvent multidrug resistance due to P-glycoprotein-mediated drug efflux or decreased topoisomerase II activity. To identify the mechanism(s) which may confer AD 198 resistance, J774.2 mouse macrophage-like cells were selected for growth in cytotoxic levels of AD 198 (AD 198R). AD 198R cells exhibited over-expression of the mdr1b (P-glycoprotein) gene, cross-resistance to Adriamycin and vinblastine, and potentiation of drug cytotoxicity by verapamil. However, net intracellular accumulation of AD 198 in AD 198R cells was unchanged compared to parental cells, while Adriamycin and vinblastine accumulations were reduced 40% and 95%, respectively. AD 198 was localized in the perinuclear region of the cytoplasm in both parental and AD 198R cells, with additional vesicular compartmentalization in AD 198R cells. Verapamil-induced reversal of AD 198 resistance coincided with some drug redistribution from cytoplasmic vesicles, but without redistribution of AD 198 into the nucleus. These results suggest that AD 198 resistance was not conferred through a P-glycoprotein-mediated reduction in intracellular drug accumulation but through other cytoplasmic mechanisms, including, but not limited to, drug compartmentalization.
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PMID:Resistance to N-benzyladriamycin-14-valerate in mouse J774.2 cells: P-glycoprotein expression without reduced N-benzyladriamycin-14-valerate accumulation. 135 Jul 53

We have previously shown that the multidrug-resistant EHR2/DNR+ cells, which overexpress P-glycoprotein, accumulate only about 20-30% of daunorubicin at steady state compared to the sensitive cells. These cells have been thought to be a "pure" P-glycoprotein cell line. We now report that the EHR2/DNR+ cells exhibit decreased DNA topoisomerase II catalytic activity. We also found that the amount of immunoreactive DNA topoisomerase II from these cells is about one-third that seen in the drug-sensitive cell line. In agreement with the decreased activity and amount of topoisomerase II, the number of DNA-protein complexes stabilized by teniposide (VM-26) was reduced by about 50% in nuclear extracts from EHR2/DNR+ cells. Furthermore, using an intact cell assay for DNA protein complexes, we found that the VM-26-stimulated complexes formed in the drug-resistant cells never reached the level seen in the drug-sensitive cells. Verapamil and Cremophor EL block P-glycoprotein-mediated efflux of "natural product" drugs and increase their accumulation in resistant cells. Coincubation of the EHR2/DNR+ cells with VM-26 and either of these modulators increased the number of complexes formed in the resistant cells. However, neither modulator increased the number of topoisomerase II-DNA complexes in the drug-resistant cells to the level seen in the EHR2 cells. We conclude that the resistance of EHR2/DNR+ cells is due in part to reduced amounts of DNA topoisomerase II. Furthermore, we note that a single cell line can express features of both P-glycoprotein-associated multidrug resistance and altered topoisomerase II-associated multidrug resistance.
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PMID:Decreased DNA topoisomerase II in daunorubicin-resistant Ehrlich ascites tumor cells. 167 12

We have developed three adriamycin (ADR)-resistant K562 sublines with different degrees of resistance. These sublines show a decreased accumulation and an increased efflux of ADR in proportion to the degree of resistance. Two membrane proteins (mol. wt 170,000 and 230,000) reactive with monoclonal antibody against P-glycoprotein were highly expressed in both the K562/ADR200 and the K562/ADR500 subline. Less resistant K562/ADR80 cells contained only small amounts of mol. wt 230,000 protein. Thus, the level of P-glycoprotein expression was not proportionate to the degree of ADR efflux. Verapamil treatment could not completely reverse ADR resistance. No significant change of glutathione-s-transferase activity nor in the level of DNA topoisomerase II was detected in resistant sublines. In our sublines it seems that P-glycoprotein is one of the mechanisms for resistance, but additional mechanisms may be involved.
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PMID:Mechanisms involved in the development of adriamycin resistance in human leukemic cells. 197 51

9-OH-Ellipticine (9-OH-E)-resistant cells are not only resistant to the DNA topoisomerase II inhibitors, but also to some other antitumor agents, such as actinomycin D (AD), adriamycin (ADM), daunorubicin and vincristine. It was previously shown that a decreased uptake accounts for the cross-resistance of these cells to AD and ADM which then suggested that the 9-OH-E-resistant cells might display some of the properties usually associated with the multidrug resistance phenotype. In this work, we have examined the effects of verapamil, a drug which is known to overcome the multidrug resistance, on the toxicity and the cellular accumulation of four cytotoxic agents: 9-OH-E, 2N-methyl-9-hydroxy-ellipticinium (NMHE), AD and ADM, either on 9-OH-E resistant cells or on a multidrug resistant subline derived from the same sensitive parental cells. Verapamil inhibited the cellular accumulation of the ellipticine derivatives in the sensitive DC-3F cells, and the toxicity of these drugs on these cells was correspondingly decreased. On either one of the resistant cell lines, verapamil had no effect on the toxicity and the cellular accumulation of 9-OH-E. In contrast, in the presence of verapamil, the cellular accumulation of NMHE by the 9-OH-E and the multidrug resistant cells was about 50% and 300% increased, respectively. The increased NMHE cellular concentration in the multidrug resistant cells was associated with an 8-fold increased toxicity. The major structural characteristics which might account for this difference between the sensitivities of both ellipticine derivatives to the effects of verapamil on the multidrug resistant cells is the presence of a positive charge on the nitrogen in position 2 of the 6H-pyridocarbazole molecule. Finally, verapamil circumvented partially the cross-resistance of DC-3F/9-OH-E cells to AD and ADM by increasing the accumulation of these drugs inside the cells.
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PMID:Effects of verapamil on the cellular accumulations and toxicity of several antitumor drugs in 9-hydroxy-ellipticine-resistant cells. 334 98

Azatoxin (NSC 640737), a synthetic molecule, was rationally designed as a topoisomerase-II inhibitor and was shown to be a potent cytotoxic agent that inhibits both tubulin and topoisomerase II. A structure-activity relationship study allowed to select 3 derivatives that inhibit either tubulin (methylazatoxin) only or topoisomerase II (fluoroanilinoazatoxin and nitroanilino-azatoxin) in MTT assays performed on K562 and K562/ADM cells; the latter, expressing P-glycoprotein, indicated cross-resistance of K562/ADM cells to all 4 compounds. DNA double-strand breaks induced by the 3 azatoxins that inhibit topoisomerase II in vitro were decreased in K562/ADM as compared with K562 cells. Nitroanilino-azatoxin was the only compound for which resistance and reduced DNA damage observed in K562/ADM cells was partially reversed by verapamil, suggesting that nitroanilinoazatoxin was a substrate for P-glycoprotein. These results were confirmed by testing the cytotoxic activity of azatoxins on P-glycoprotein-expressing rat colon-carcinoma DHDK12/TRb cells in the absence and the presence of verapamil. Cell-cycle and mitotic-index studies indicated that azatoxin- and methyl-azatoxin-induced M-phase arrest was less in K562/ADM than in K562 cells. The G2 block induced by fluoro- and nitroanilinoazatoxins was delayed in K562/ADM cells. Verapamil increased cell-cycle inhibition induced by nitroanilinoazatoxin in K562/ADM cells without modifying cell-cycle effects of fluoroanilinoazatoxin. These results (i) are consistent with the specific inhibition of topoisomerase II or tubulin by azatoxin derivatives in cells; (ii) indicate that the nitro group of nitroanilinoazatoxin allows recognition and efflux by the P-glycoprotein; and (iii) suggest that cross-resistance of K562/ADM cells to other azatoxin derivatives is not mediated by P-glycoprotein.
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PMID:Cellular pharmacology of azatoxins (topoisomerase-II and tubulin inhibitors) in P-glycoprotein-positive and -negative cell lines. 759 Dec 16

The in vitro cytotoxic effects of docetaxel (Taxotere; RP56976, NSC688503) proved both time and concentration dependent. Amongst thirteen human cell lines from various tumor types, exposure to increasing concentrations of docetaxel over 24 hrs resulted in a plateau-shaped dose response curve, suggesting that increased cell kill becomes more dependent on increased exposure duration than on concentration. IC50 concentrations (reducing survival by 50%) ranged from 0.13-3.3 ng/ml, with three neuroblastoma lines proving most sensitive and three breast and two colon carcinoma lines showing least sensitivity. There was significant cross-resistance to docetaxel in the classic multidrug resistant (MDR) Chinese hamster ovarian (CHO) CHRC5 line and the human lymphoblastoid CCRF-CEMVLB1000 line, as well as in two vincristine (VCR)-selected MDR MCF-7 sublines. All four of these MDR sublines overexpress P-glycoprotein (Pgp), as did a 6-fold docetaxel-selected resistant CHO subline. As an apparent corollary, in two human teratoma lines selected for etoposide resistance and showing some cross-resistance to VCR and in two CHO sublines expressing low levels of VCR resistance, yet all proving Pgp positive, no docetaxel cross-resistance was identified. Verapamil modulated docetaxel resistance only in sublines expressing resistance to the drug and overexpressing Pgp. Four other human tumor sublines selected for resistance to 5-fluorouracil, cisplatin or teniposide, showed a lack of cross-resistance to docetaxel. Furthermore, cross-resistance to docetaxel was not apparant in four epipodophyllotoxin-selected resistant sublines with alterations in topoisomerase II, indicating its effectiveness against tumor cells expressing the topoisomerase II-related MDR phenotype. Our observation that docetaxel cross-resistance was not automatically expressed by classic MDR tumour cells appears of interest and of potential clinical relevance.
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PMID:Differential cytotoxic effects of docetaxel in a range of mammalian tumor cell lines and certain drug resistant sublines in vitro. 789 35

Inhibitors of P-glycoprotein (P-gp) or chemosensitizers, such as verapamil, are used to reverse multi-drug resistance (MDR) in cancer patients. Clinical studies in patients with myeloma have shown that some patients with P-gp-positive cancer cells respond to the chemosensitizing effect of verapamil. However, this response is short-lived and tumor cells ultimately become resistant to chemosensitizers. To study mechanisms of resistance to chemosensitizers, a human myeloma cell line, 8226/MDR10V, was selected from a P-gp-positive cell line, 8226/Dox40, in the continuous presence of doxorubicin and verapamil. MDR10V cells are consistently more resistant to MDR drugs than parent cells, Dox40. Chemosensitizers, including verapamil and cyclosporin A, were less effective in reversing resistance in MDR10V compared with Dox40 cells. Verapamil and cyclosporin A were only partially effective in blocking P-gp drug efflux in MDR10V compared to Dox40 cells. Despite higher resistance to cytotoxic agents, MDR10V cells express less P-gp in the plasma membrane than do its parent cells, Dox40. [3H]Azidopine photoaffinity labeling of P-gp and its binding competition with unlabeled verapamil showed similar affinity for P-gp between Dox40 and MDR10V cell lines. Non-P-gp-mediated mechanisms of drug resistance, including over-expression of MRP and alterations in topoisomerase II, were not different for MDR10V cells compared with Dox40 cells.
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PMID:Resistance to the chemosensitizer verapamil in a multi-drug-resistant (MDR) human multiple myeloma cell line. 863 66

A wild type strain of Mycobacterium smegmatis mc2 155 was serially adapted to 64 fold of minimal inhibitory concentration of an antimycobacterial agent, ciprofloxacin. This clone (CIPr) exhibited cross resistance to ofloxacin and ethidium bromide. The rate of drug efflux was accelerated in CIPr compared to the wild type strain. Verapamil, a calcium channel blocker, enhanced the drug accumulation in CIPr by diminishing the efflux and thus reversed the resistant phenotype. Additionally, a missense mutation was detected in the quinolone resistance determining region of the DNA-gyrase A subunit of CIPr. Taken together, these results suggest that drug efflux plays a major role in conferring such a high level of resistance in CIPr, in addition to the mutation in the DNA-gyrase locus.
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PMID:Involvement of an efflux system in mediating high level of fluoroquinolone resistance in Mycobacterium smegmatis. 880 41


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