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)

Chemotherapy failure remains a significant medical problem in the treatment of neoplastic disease and is thought to be due to many different factors including membrane transport, p-glycoprotein in multidrug resistance, glutathione and its related enzymes, topoisomerase II and DNA repair. Glutathione is a major constituent of non-protein thiol and participates in detoxification of chemotherapy and radiation. Thus, glutathione concentration is correlated with sensitivity to alkylating agents and radiation, and increased in resistant cell lines. Buthionine sulfoximine (BSO) is an inhibitor of glutathione biosynthesis and may increase cytotoxicities of alkylating agents, including melphalan and cisplatin, and radiation in sensitive and resistant cell lines. We studied effects on cellular glutathione levels and cytotoxicities of cisplatin, carboplatin and radiation by BSO treatment in human stomach cancer cell line (SNU-1) and ovarian cancer cell line (OVCAR-3). The results were as follow: 1) After BSO treatment of 1 mM and 2 mM for 2 days, the intracellular thiol concentration was depleted to 75.7% and 76.2% in SNU-1, and 74.1% and 63.0% in OVCAR-3, respectively. 2) The intracellular thiol concentration in SNU-1 was depleted to 33.4% after BSO 2 mM for only 2 hours incubation and 71.5% after small amount of BSO (0.02 mM) for 2 days. 3) The recovery of intracellular thiol concentration required more than 3 days after BSO removal. 4) BSO inhibited partially the growth of SNU-1 and OVCAR-3. 5) The cytotoxicities of cisplatin and carboplatin were markedly enhanced both in SNU-1 and OVCAR-3 by BSO treatment. 6) The cytotoxicities of radiation was increased in OVCAR-3 and SNU-1 by BSO treatment. Therefore, it is concluded that BSO can deplete effectively the intracellular thiol concentration and enhance the cytotoxicities of cisplatin, carboplatin and radiation.
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PMID:Effects of buthionine sulfoximine treatment on cellular glutathione levels and cytotoxicities of cisplatin, carboplatin and radiation in human stomach and ovarian cancer cell lines. 130 72

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

The development of tumor drug resistance is the major obstacle to successful systemic chemotherapy. Therefore, devising methods for reversing drug resistance is a high priority and could lead to significant improvements in cancer treatment. The mechanisms of tumor drug resistance are manifold and are not well understood. The phenomenon of multidrug resistance (MDR) represents the development of resistance to most drugs, regardless of their chemical structure. Several types of MDR are known, for example, the overexpression of a cell membrane glycoprotein (P-170), increased activity of glutathione S-transferase, elevated levels of glutathione (GSH), and alterations in topoisomerase action. A partial reversal of tumor drug resistance has been achieved by the use of competitive inhibitors for the function of glycoprotein P-170, or by the inhibition of GSH synthesis; however, this strategy has not been substantially successful for improving the response of human tumors to clinical therapy. We have recently used electroporation, in conjunction with the cytotoxic drug, cisplatin (cDDP), in an attempt to circumvent drug resistance in cDDP-resistant mouse tumor cells (RIF/Ptr1). Electroporation is the application of a high-voltage electric shock which is known to create transient pores in plasma membranes of cultured cells. Electroporation plus cDDP treatment increased intracellular cDDP concentration and reversed cellular resistance to cDDP-induced cell killing.
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PMID:New approaches to the study of tumor drug resistance. 136 47

The conventional laboratory approach to study the mechanisms of drug resistance has been the selection of drug-resistant cell lines by continuous exposure to cytotoxic agents. Such lines, which are selected for resistance to a single agent, frequently display cross-resistance to a number of cytotoxic agents that are unrelated in both structure and proposed mechanism of action. Multidrug-resistant cells display reduced drug accumulation, which is the result of overexpression of a surface glycoprotein (P170). Although resistance to multiple antitumor agents is a common clinical problem in the treatment of cancer, the precise role of the P-glycoprotein-mediated mechanism in human tumors remains to be established. Many alterations in multidrug-resistant cells selected in vitro have been identified. The concomitant expression of multiple phenotypic differences, which appear to be favored by continued and prolonged drug exposure, makes analysis of critical individual resistance pathways more difficult. However, multiple factors may also be involved in the development of clinical resistance. Recent studies have identified alterations in DNA topoisomerase II activity and function as an alternative mechanism that contributes to the multidrug-resistance phenomenon or is responsible for a different type of drug resistance. The precise nature of these changes remains unclear. Available evidence supports the view that expression of the enzyme is an important determinant of cell sensitivity to DNA topoisomerase poisons, but that other changes involved in regulation of enzyme function and/or in the cellular processing of drug-induced DNA damage may be critical in determining the differential pattern of cell response to antitumor agents.
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PMID:The role of topoisomerase II in drug resistance. 164 58

We have previously shown that Chinese hamster lung cells resistant to 9-hydroxyellipticine, DC-3F/9-OH-E, display multiple phenotypical alterations including cross-resistance to a variety of drugs as well as loss of tumorigenicity. We now analyze a DC-3F/9-OH-E subline that has been maintained for a prolonged period of time in drug-free medium in order to clarify the relationships between the various phenotypic traits. The absence of selection resulted in a partial recovery of the ability to form colonies in soft agar as well as of the tumorigenicity in nude mice. In contrast, no change was observed with respect to population-doubling time. Our results also show that the resistance to 9-hydroxyellipticine, which is associated with an altered topoisomerase II activity, is stable in the absence of drug for more than 1 year. In contrast, the cross-resistance to doxorubicin is partially reversible and the cross-resistance to vincristine is totally reversible in the absence of selection. The cross-resistance to vincristine and doxorubicin is accompanied by a decreased drug uptake. Northern blot analysis shows that the multidrug resistance-associated Mr 170,000-180,000 glycoprotein is overexpressed in the DC-3F/9-OH-E cells and that the overexpression is lost in the absence of selection. We conclude that (a) the DC-3F/9-OH-E cells exhibit multiple mechanisms of resistance which can be dissociated, (b) the tumorigenicity and the altered topoisomerase activity are independent biochemical events whereas the oncogenic potential appears to follow the expression of the multidrug resistance, and (c) the multidrug resistance phenotype may be induced by a drug which is not itself recognized by the multidrug resistance mechanism such as 9-hydroxyellipticine.
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PMID:Multiple resistance mechanisms in Chinese hamster cells resistant to 9-hydroxyellipticine. 258 53

The alkaloid derivative 4'-demethylepipodophyllotoxin 9-(4,6-O-ethylidene)-beta-D-glucopyranoside (etoposide, VP-16) is believed to exert cytotoxicity by causing double-stranded DNA breaks through interruption of the breaking-resealing reaction of topoisomerase II (topo II). Thus it was conceivable that cells could become resistant to VP-16 by a decrease in topo II enzyme level, since this would lead to fewer DNA breaks. As well, given the structure of VP-16, it was also possible that a pleiotropic mechanism of resistance could decrease sensitivity to this drug. To study these possibilities, a series of VP-16-resistant human KB cell lines was established by stepwise selection. The concentrations of VP-16 required to inhibit cell proliferation by 50% in the parent line and KB/1c, KB/7d, KB/20a, and KB/40a lines were, respectively, 0.16, 4.7, 24, 31, and 47 microM. These cell lines expressed cross-resistance to 4'-(9-acridinylamino)methanesulfon-m-anisidide, doxorubicin, vincristine, and methotrexate, although the pattern of relative drug sensitivity was quite different from that of pleiotropic resistant cell lines reported elsewhere. The resistance to vincristine and methotrexate did not increase above the level of the KB/1c cells, and resistance to VP-16, doxorubicin, and especially vincristine was unstable in VP-16-resistant cells cultured in the absence of drug. Although the drug resistance marker Mr 180,000 glycoprotein could not be detected in any of our cell lines, cellular accumulation of [3H]VP-16 was reduced 50-75% in the resistant lines compared with parent KB. With increasing VP-16 resistance, the level of topo II protein, detected by antibody staining, decreased at each step of selection, concomitant with a general decrease in topo II unknotting activity. Sensitivity of the topo II unknotting assay to inhibition by VP-16 was the same for the parent and all resistant cell lines. The level of topo I activity and enzyme increased slightly in the resistant cells. Thus, these cell lines are resistant to VP-16 by virtue of at least two mechanisms: (a) reduced levels of topo II, which confers cross-resistance to other compounds which are topo II-dependent cytotoxic agents; and (b) reduced accumulation of drug, which is likely also responsible for vincristine and methotrexate resistance. However, the possible existence of other mechanisms of resistance cannot be ruled out.
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PMID:Combined modalities of resistance in etoposide-resistant human KB cell lines. 284 93

The ability of malignant cells to develop resistance to cytotoxic drugs poses a major obstacle to the ultimate success of cancer therapy. While some mechanisms of resistance allow cells to survive exposure to a single agent, the phenomenon of multidrug resistance (MDR) confers upon cells the ability to withstand exposure to lethal doses of many structurally unrelated antineoplastic agents. MDR has been strongly linked to the overexpression of a membrane-associated glycoprotein, P-glycoprotein, which appears to play a role in drug efflux. However, several lines of evidence suggest that other mechanisms of resistance are involved in MDR; biochemical similarities observed in a human breast cancer cell line after the acquisition of MDR and in carcinogen-induced rat preneoplastic hepatic nodules indicate that changes in regulation of phase I and phase II drug-metabolizing enzymes may also play a role in MDR. An atypical pattern of MDR has been characterized and related to altered topoisomerase activity. Improvement in current cancer chemotherapy may be achieved by interfering with the regulation and expression of mechanisms of MDR.
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PMID:Multidrug resistance. 289 43

30 years ago an anthracycline antibiotic was shown to have antineoplastic activity. This led to the development of well over 1000 analogues with a vast spectrum of biochemical characteristics. Many biological actions have been described. The original anthracyclines are active against many types of cancer and are an integral part of several curative combinations. They are ineffective against other tumours. Although some analogues show an altered spectrum of activity or an improved therapeutic index relative to the older agents, it is not clear that cardiotoxicity can be totally avoided with these agents. Primary and secondary resistance to anthracyclines remain major clinical problems. Pharmacokinetic studies have been of limited help in explaining this. Overexpression of a surface-membrane permeability glycoprotein (Pgp) was identified in ovarian cancer of patients who had clinical multidrug resistance in 1985. This led the way for the discovery of a number of resistance mechanisms in vitro. Some of these have been found in more than 1 type of cell line, and more than 1 mechanism may exist in a single cell. Additional resistance proteins have been identified, qualitative and quantitative alterations of topoisomerase II have been described, and some mechanisms in other systems have not yet been identified. Some of these may prove to be important in clinical drug resistance. Drugs such as calcium antagonists and cyclosporin, studied initially for their ability to block the Pgp pump, appear to be heterogeneous in this capacity and may have additional sites of action. It will be critical for clinical studies to define the precise resistance mechanism(s) that must be reversed. To date this has been difficult, even in trials ostensibly dealing with the original Pgp. Liposomes can potentially alter toxicity and target drug delivery to specific sites. In addition, they may permit the use of lipophilic drugs that would otherwise be difficult to administer systemically. Resistant tumours may be sensitive to anthracyclines delivered by liposomes. To reduce cardiac toxicity, administering doxorubicin (adriamycin) by slow infusion through a central-venous line should be considered whenever feasible. Monitoring of cardiac ejection fraction and the use of endomyocardial biopsy will permit patients to be treated safely after they reach the dose threshold at which heart failure begins to be a potential risk. A number of structurally modified anthracyclines with the potential advantages of decreased cardiotoxicity and avoidance of multidrug resistance mechanisms are entering clinical trials. Meanwhile, the vast weight of clinical experience leaves doxorubicin as a well tolerated and effective choice for most potentially anthracycline-sensitive tumours.
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PMID:Anthracycline antibiotics in cancer therapy. Focus on drug resistance. 751 99

Resistance to the classical anthracyclines may be due to one or several mechanisms, most notably p-glycoprotein (pGP) associated multidrug resistance (mdr1, "typical mdr") and altered activity of topoisomerase II (topo II) ("atypical mdr"). Modulators of mdr1 will be of limited value in case of combined forms of resistance. A Friend murine erythroleukemia cell line (F4-6R) carrying both mdrl and topo II mediated anthracycline resistance was used to determine the efficacy of structurally altered anthracyclines against such extended multidrug resistance. Proliferation assays showed that 3'N-morpholinyl substituted anthracyclines were able to retain much of their activity even in this setting. MX2 (KRN8602; 3'-deamino-3'-[4-morpholinyl]-13-deoxo-10-hydroxycarminomycin+ ++), which is 9-alkylated in addition to carrying a 3'N-morpholinyl group, was the most promising agent tested.
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PMID:Structurally modified anthracyclines retain activity in a cell line with simultaneous typical and atypical multidrug resistance. 765 9

The nuclear enzymes topoisomerase I and II are critical for DNA function and cell survival, and recent studies have identified these enzymes as cellular targets for several clinically active anticancer drugs. Topoisomerase II inhibitors (anthracyclines, epipodophyllotoxins, etc.) are active against several types of tumours. However, treatment with these drugs often results in the development of the multi-drug resistance. Because topoisomerase II-active drugs have several different modes of action, different mechanisms of resistance, including decreased activation and increased detoxification by glutathione-dependent enzymes, have also been implicated. Unlike topoisomerase II, topoisomerase I is not a cell cycle-dependent enzyme and, therefore, it is a more desirable cellular target for anticancer drug development. Topoisomerase I inhibitors, such as camptothecin and its derivatives, have shown significant activity against a broad range of tumours and, in general, are not substrates for either the multi-drug-resistance P-170 glycoprotein or the multi-drug-resistance-associated protein. Because of manageable toxicity and encouraging activity against solid tumours, topoisomerase I-active drugs offer promise in the clinical management of human tumours.
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PMID:Topoisomerase inhibitors. A review of their therapeutic potential in cancer. 770 11


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