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:5.99.1.3 (topoisomerase)
9,911 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

By contrast with other DNA minor groove binders, Hoechst 33258 inhibited topoisomerase-mediated activity in intact cells. To determine whether specific structural alterations could modify the topoisomerase reactivity of this drug, a series of analogs of Hoechst 33258 (compound 1) was examined. When the relative DNA binding affinities (Ka) of these agents were determined, compound 1 had the highest Ka while agents with substitutions in either of the benzimidazole moieties showed reduced affinity. Whether these changes in DNA binding correlated with topoisomerase inhibitory potency was next examined. In isolated nuclei, 25 microM of agents 1, 5 and 7 reduced VM-26 induced cross-links by 64, 65 and 83%, compared with 15 to 25% reductions by agents 2, 3, 4 and 6, respectively. The structural modification common to the less active compounds was the substitution of an oxygen for nitrogen at either position 1 or 2. On the basis of these results, agents 1, 2, 3 and 7, representing a range of inhibitory potency, were chosen for further analyses. Cross-link induction by m-AMSA and camptothecin in isolated nuclei, as well as by VM-26 in intact cells, was inhibited to a greater extent by agents 1 and 7 than 2 or 3. Additionally, all four drugs inhibited relaxation of pBR 322 DNA induced by both topoisomerases, although topoisomerase I was 2 to 5-fold more sensitive than topoisomerase II. A linear correlation was observed between the logarithms of the Ka value of compounds 1, 2 and 3 and their IC25 values for both topoisomerases, suggesting a strong dependence on DNA binding affinity for enzyme inhibition. Nevertheless, agent 7, despite having less affinity for calf thymus DNA than 1, was the most potent topoisomerase inhibitor tested in intact cells and in isolated enzyme systems. Thus, retention of nitrogen at positions 1 and 2 as well as the addition of nitrogen at position 16 was associated with increased topoisomerase inhibitory potency.
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PMID:Effects of analogs of the DNA minor groove binder Hoechst 33258 on topoisomerase II and I mediated activities. 137 46

Although the stabilization of topoisomerase II cleavable complexes by etoposide (VP-16) has been recognized to be important for cell killing, the lethal events following the formation of cleavable complexes remain to be elucidated. In an attempt to characterize the biochemical requirements for VP-16-induced cytotoxicity, we examined the effects of calcium depletion in Chinese hamster DC3F cells. Four-hour preincubation in calcium-free medium or in complete medium containing 5 mM [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA) protected against the cytotoxicity of VP-16. Under these same conditions, the VP-16-induced DNA single-strand break frequency in calcium-depleted cells remained similar to that of control cells. Cell-cycle analysis and thymidine pulse incorporation indicated that calcium depletion did not alter DNA synthesis and cell cycle distribution. Drug-induced cytotoxicity was restored progressively within 4-8 hr after calcium-depleted cells were refed with calcium-containing medium. Calcium depletion also protected against the cytotoxicity of camptothecin, hyperthermia and, to a lesser extent, nitrogen mustard and gamma radiation in DC3F cells. Similar results were obtained in human colon carcinoma HT-29 cells. Our results suggest that topoisomerase II-mediated DNA breaks are only potentially lethal and that calcium-dependent cellular processes are required for the cytotoxicity of topoisomerase inhibitors.
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PMID:Cell death induced by topoisomerase inhibitors. Role of calcium in mammalian cells. 164 24

A number of new 4'-O-demethylepipodophyllotoxin derivatives possessing various 4 beta-N- or 4 beta-O-benzyl groups have been synthesized and evaluated for their inhibitory activity against the human DNA topoisomerase II as well as for their activity in causing cellular protein-linked DNA breakage. The 4 beta-N-benzyl derivatives 9-22 are, in general, as active or more active than etoposide (1). The most active compounds are 14, 16, and 17, which are more than 2-fold more potent than 1. The results indicated that a basic unsubstituted 4 beta-benzylamino moiety is structurally required for the enhanced activity. Replacement of the benzyl nitrogen with oxygen gave compounds (23 and 24) which are inactive. The ability of these compounds to inhibit human DNA topoisomerase II and to cause protein-linked DNA breakage appears to have no direct correlation with cytotoxicity in KB cells.
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PMID:Antitumor agents. 120. New 4-substituted benzylamine and benzyl ether derivatives of 4'-O-demethylepipodophyllotoxin as potent inhibitors of human DNA topoisomerase II. 166 24

Cytotoxic effects and topoisomerase II-mediated DNA breaks induced in vitro by ellipticine derivatives were examined in connection with 1H NMR and circular dichroism (CD) studies on molecular structures and interactions of drugs with DNA. The compounds included four 9-hydroxyellipticine and two 7-hydroxyisoellipticine derivatives. Structure-activity relationships indicated that a change in nitrogen atom position in the pyridinic ring greatly affected drug effects both on topoisomerase II action and cytotoxicity to L1210 cells. The four 9-hydroxyellipticine derivatives yielded bell-shaped curves in in vitro topoisomerase II-mediated DNA break assays, whereas the two 7-hydroxyisoellipticine derivatives demonstrated an almost linear increase at the same concentration (0-10 microM). In both cases, the intensity of cleavage was modulated by the position and the degree of methylation on the pyridinic ring, and results were correlated with cytotoxic activity expressed as the in vitro ID50 values for L1210 leukemia cells. 1H NMR experiments performed on free drug molecules in solution revealed that the two protons (alpha and beta) contiguous to the biologically important hydroxy group were sensitive to changes in electron distribution produced by the distant chemical modifications and methylations of the pyridinic ring. A linear relationship was observed between the differences in chemical shifts of alpha and beta protons (delta delta alpha-beta) versus ID50 values. CD experiments indicated that, at weak ionic strength I = 0.02 and at pH 7, drugs interact with the poly[d(A-T)] duplex according to a "three-mode binding model" which is governed by the drug structure and the drug to DNA ratio. The intercalation mode was related to the induction of topoisomerase II-mediated DNA cleavage, while the external binding mode consecutive to intercalation was related to cleavage suppression. These two modes concerned the good intercalators 9-hydroxyellipticines. The third was found for the weak intercalators 7-hydroxyisoellipticines and was characterized by self-stacked molecules bound "outside" DNA, presumably in the minor groove. Ligands either could be intercalated partially or linked at the edge of bases with a small number of molecules filling intercalation sites, for the second alternative. In addition to having different binding modes, 9-hydroxyellipticines were better inducers of DNA distortions than 7-hydroxyisoellipticines. The incidence of the drug binding modes on DNA-topoisomerase II recognition was discussed in connection with the in vitro cytotoxic activity exhibited by the drugs.
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PMID:DNA-drug recognition and effects on topoisomerase II-mediated cytotoxicity. A three-mode binding model for ellipticine derivatives. 184 65

A number of 4'-O-demethylepipodophyllotoxin derivatives possessing various 4 beta-N-, 4 beta-O- or 4 beta-S-aromatic rings have been synthesized and evaluated for their inhibitory activity against the human DNA topoisomerase II as well as for their activity in causing cellular protein-linked DNA breakage. The results indicated, that for DNA topoisomerase II, a basic unsubstituted 4 beta-anilino moiety is structurally required for the enhanced activity. Substitution on this moiety with CN, COOCH3, COOC2H5, OH and COOCH3, OCH3, COCH3, CH2OH, OCH2O, OCH2CH2O, phenoxy, morpholino, NO2, and NH2 either at the para and/or the meta position yielded compounds which are as potent or more potent than etoposide. Substitution with COOC2H5 and OH at the ortho position afforded inactive compounds. Replacement of the aryl nitrogen with oxygen or sulfur gave compounds which are much less active or inactive. However, replacement of the phenyl ring with a pyridine nucleus furnished compounds which are as active or slightly more active than etoposide. There is a lack of correlation between the ability of these compounds in inhibiting DNA topoisomerase II and in causing protein-linked DNA breaks.
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PMID:Antitumor agents. 113. New 4 beta-arylamino derivatives of 4'-O-demethylepipodophyllotoxin and related compounds as potent inhibitors of human DNA topoisomerase II. 216 85

Human colorectal and pulmonary carcinomas have been shown to contain high levels of opioid peptides and their corresponding membrane-bound receptors. Therefore possible targeted drugs, consisting of modified enkephalins linked to cytotoxic drugs, were designed. Such conjugates were expected to be specifically internalized within opioid receptor-bearing cells. As a model to this approach, we have synthesized enkephalin-ellipticinium conjugates in which the D-Ala2-D-Leu5-enkephalin (DADLE) was coupled to the 2-nitrogen of either ellipticine or 9-hydroxyellipticine, two drugs acting through different mechanisms of cytotoxicity. These conjugates, DADLE-ellipticinium (NME) and DA-DLE-9-hydroxyellipticinium (NMHE), respectively, were previously shown to retain in vitro both opioid receptors and DNA affinities close to those of the parent compounds. In this paper, we first show that each individual moiety in the complexes remains capable of recognizing its cellular targets. Thus, pretreatment of NG108-15 cells containing delta-opioid receptors by the DADLE-ellipticinium conjugates induced a loss of opioid receptor (down-regulation), while the smaller peptide conjugates, tyrosinyl-D-alanylglycine-ellipticinium, prepared as control, do not. On the other hand, peptide-NMHE conjugates were able to induce DNA topoisomerase II-associated DNA strand breaks suggesting that they have a mode of action similar to that of their parent molecule, NMHE. We then examined whether or not these molecules could exert a specific toxicity on opioid receptor-bearing cells. However, when tested on NG108-15 tumor cells and L-fibroblasts as control, the enkephalin-ellipticinium conjugates (DADLE-NME and DADLE-NMHE) proved to be similarly more cytotoxic on both cell lines than their ellipticinium (NME and NMHE) precursors. In order to understand this apparent lack of specificity we examined the cellular accumulation and distribution of DADLE-NME by fluorescence techniques. These experiments revealed that an important intracellular overconcentration caused by a nonspecific process is probably masking the specific targeted effect of the conjugates. Hence, the project of linking DADLE to highly cytotoxic molecules which cannot cross the plasma membrane without site-directed targeting is discussed.
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PMID:Attempts to target antitumor drugs toward opioid receptor-rich mouse tumor cells with enkephalin-ellipticinium conjugates. 253 35

A human Burkitt's lymphoma cell line (Raji-HN2) made resistant to nitrogen mustard, a bifunctional alkylating agent, was used to study the mechanism of resistance to nitrogen mustard. A comparative study of Raji-HN2 and the parental sensitive Raji cell lines revealed the following: (1) The DNA of Raji-HN2 cells was crosslinked by nitrogen mustard to a lower extent than Raji DNA; (2) once interstrand crosslinks were formed, they were repaired at the same rate in both cell lines; (3) DNA crosslink formation in Raji-HN2, but not in Raji cells, was enhanced by novobiocin, a topoisomerase II inhibitor; (4) Raji-HN2 cells had elevated topoisomerase II activity and were hypersensitive to topoisomerase inhibitors (amsacrine, novobiocin, teniposide); (5) similar amounts of topoisomerase I were found in both cell lines; and (6) the chromatin of Raji-HN2 but not of Raji cells, was hypersensitive to DNase I digestion. The relationship between DNA repair, topoisomerase II activity, chromatin structure and drug resistance is discussed.
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PMID:Elevated topoisomerase II activity and altered chromatin in nitrogen mustard-resistant human cells. 281 39

A human Burkitt lymphoma cell line, Raji-HN2, made 10-fold more resistant to nitrogen mustard (HN2) than the parental Raji cell line, exhibited the following characteristics when compared to the parental Raji cells: (i) decreased HN2-induced DNA interstrand crosslinking; (ii) increased (3-fold) DNA topoisomerase II [DNA topoisomerase (ATP-hydrolyzing), EC 5.99.1.3] activity; (iii) increased (4- to 11-fold) sensitivity to topoisomerase II inhibitors; (iv) increased (2-fold) glutathione content; and (v) increased (2-fold) cell doubling time. The resistant phenotype was unstable and was maintained by weekly treatment of the cells with HN2. Growing the resistant cells in the absence of HN2 resulted in a time-dependent decrease in both resistance to HN2 and topoisomerase II activity and an increase in DNA interstrand crosslinking induced by HN2. We hypothesize that HN2 resistance is due to enhanced monoadduct repair with resultant decreased DNA crosslinking and that this process is mediated by topoisomerase II.
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PMID:Elevated DNA topoisomerase II activity in nitrogen mustard-resistant human cells. 282 70

A Rhodopseudomonas capsulata nifH::lacZ gene fusion was used to isolate constitutive mutants of R. capsulata, unable to repress nif gene transcription anaerobically with every fixed-nitrogen source tested. When these nifc strains were grown aerobically, nif gene transcription was repressed. These results indicate that the regulation of nif gene transcription by fixed nitrogen is different from the regulation by oxygen. Under anaerobic conditions, nif gene transcription in both R. capsulata and Klebsiella pneumoniae is specifically prevented by inhibitors of DNA gyrase [DNA topoisomerase type II (ATP-hydrolyzing), EC 5.99.1.3]. A recent study has shown that anaerobically grown Salmonella typhimurium have high DNA gyrase activity, whereas aerobically grown cells have high DNA topoisomerase type I (EC 5.99.1.2) activity and DNA that is more relaxed [Yamamoto, N. & Droffner, M. L. (1985) Proc. Natl. Acad. Sci. USA 82, 2077-2081]. In view of these results, we suggest that the control of nif gene transcription in response to oxygen is determined by the action of DNA gyrase and DNA topoisomerase I. Thus, although nitrogen control of nif gene expression requires the products of regulatory genes for which constitutive mutations can be isolated, oxygen appears instead to prevent the adoption of a DNA conformation necessary, directly or indirectly, for nif gene transcription.
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PMID:Anaerobic regulation of nitrogen-fixation genes in Rhodopseudomonas capsulata. 301 47

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


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