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Biomedical subjects

Y Pommier

Publications and source records attributed to Y Pommier.

At least 181 records · Page 10Linked to original sources
PubMed1993

Dual inhibition of topoisomerase II and tubulin polymerization by azatoxin, a novel cytotoxic agent.

Azatoxin (NSC 640737) is a synthetic molecule that was rationally designed as a topoisomerase II inhibitor (Leteurtre et al., Cancer Res 52: 4478-4483, 1992). The present study was undertaken in order to investigate the molecular pharmacology and the cytotoxic activity of azatoxin in human tumor cells. Alkaline elution experiments performed in HL-60 cells demonstrated that: (1) azatoxin induces DNA-protein cross-links and protein-linked DNA single- and double-strand breaks characteristics of topoisomerase II inhibition in HL-60 cells; and (2) the potency of azatoxin is comparable to that of etoposide (VP-16). Testing of azatoxin in 45 human cell lines in the National Cancer Institute (NCI) in vitro Drug Screening Program indicated that azatoxin was potent (mean IC50 = 0.13 microM), but that its cell line sensitivity profile was correlated with that of tubule inhibitors rather than that of topoisomerase II inhibitors. These data led us to investigate the anti-tubulin activity of azatoxin. We found that azatoxin inhibited tubulin polymerization in vitro and was a mitotic inhibitor at 1 microM and above in the human colon cancer cell line KM20L2. In these cells topoisomerase II inhibition, as detected by the induction of protein-linked DNA strand breaks, required azatoxin concentrations of at least 10 microM. In summary, azatoxin is a potent cytotoxic agent that inhibited both tubulin and topoisomerase II. At lower azatoxin concentrations the former activity prevailed whereas at higher concentrations topoisomerase II inhibition became prominent.

Cell Death↗
PubMed1993

In vitro cytotoxicity, cellular pharmacology, and DNA lesions induced by annamycin, an anthracycline derivative with high affinity for lipid membranes.

Annamycin (AN) is an anthracycline antibiotic with high affinity for lipid membranes which is being developed for clinical studies formulated in liposomes. We studied the in vitro cytotoxicity, cellular pharmacology, and DNA damage induced by AN in P388 cells sensitive and resistant to doxorubicin (DOX). AN was as cytotoxic as DOX against P388-sensitive cells and about 50 times more cytotoxic than DOX against P388-resistant cells (resistance index 5 for AN versus 250 for DOX). Cellular uptake of AN by sensitive cells was 2-3-fold higher than that of DOX. In resistant cells, cellular uptake of AN and DOX was approximately 65% and 30%, respectively, of the cellular uptake in sensitive cells. As a result, cellular uptake of AN by resistant cells was higher than uptake of DOX by sensitive cells. DOX was fully retained in sensitive cells while it was effluxed rapidly from resistant cells. In contrast, efflux of AN was similar in sensitive and resistant cells, thus suggesting that it is not mediated by P-glycoprotein. AN was more effective than DOX in inducing single DNA breaks, double DNA breaks, and DNA-protein cross-links, both in sensitive and resistant cells, although DNA damage was lower in resistant cells than in sensitive cells. DNA lesions induced by AN in resistant cells were similar to or greater than those induced by DOX in sensitive cells. These studies indicate that the lack of cross-resistance between DOX and AN appears to be related, at least in part, to the relatively higher cellular uptake of AN compared with DOX and is associated with the ability of AN to induce significant DNA damage in resistant cells.

Animals↗
PubMed1993

Inhibitors of human immunodeficiency virus integrase.

In an effort to further extend the number of targets for development of antiretroviral agents, we have used an in vitro integrase assay to investigate a variety of chemicals, including topoisomerase inhibitors, antimalarial agents, DNA binders, naphthoquinones, the flavone quercetin, and caffeic acid phenethyl ester as potential human immunodeficiency virus type 1 integrase inhibitors. Our results show that although several topoisomerase inhibitors--including doxorubicin, mitoxantrone, ellipticines, and quercetin--are potent integrase inhibitors, other topoisomerase inhibitors--such as amsacrine, etoposide, teniposide, and camptothecin--are inactive. Other intercalators, such as chloroquine and the bifunctional intercalator ditercalinium, are also active. However, DNA binding does not correlate closely with integrase inhibition. The intercalator 9-aminoacridine and the polyamine DNA minor-groove binders spermine, spermidine, and distamycin have no effect, whereas the non-DNA binders primaquine, 5,8-dihydroxy-1,4-naphthoquinone, and caffeic acid phenethyl ester inhibit the integrase. Caffeic acid phenethyl ester was the only compound that inhibited the integration step to a substantially greater degree than the initial cleavage step of the enzyme. A model of 5,8-dihydroxy-1,4-naphthoquinone interaction with the zinc finger region of the retroviral integrase protein is proposed.

Antibiotics, Antineoplastic↗
PubMed1993

Differential induction of apoptosis in undifferentiated and differentiated HL-60 cells by DNA topoisomerase I and II inhibitors.

The effects of monocytic/macrophage and granulocytic differentiation induced by phorbol myristate acetate (TPA) and all-trans retinoic acid, respectively, were tested on the induction of apoptosis in human promyelocytic leukemia HL-60 cells treated with topoisomerase I and II inhibitors. Using a filter-binding assay, we observed a strong inhibition of DNA fragmentation induced by 3- and 24-hour continuous exposure to camptothecin, VP-16, VM-26, and m-AMSA in TPA-differentiated cells. The inhibition of the typical internucleosomal DNA fragmentation was confirmed by agarose gel electrophoresis. By contrast, drug-induced DNA fragmentation was not inhibited in retinoic acid-differentiated cells, and apoptosis occurred in these cells after 4 to 5 days in the absence of drug treatment. The TPA inhibitory effect was maximal after 24 hours of treatment and was correlated with differentiation, because phorbol dibutyrate ester was active, whereas 4-alpha-TPA, a nontumor promoter that does not induce differentiation, was not active. Using alkaline elution, we observed that TPA and retinoic acid differentiation were associated with changes in topoisomerase-mediated DNA breaks that were not correlated with their differential effects on drug-induced DNA fragmentation. Moreover, TPA also inhibited DNA fragmentation induced by vinblastine, cycloheximide, calphostin C, and x-rays. Using a cell-free system, we observed that DNA fragmentation was not inhibited in nuclei from TPA-differentiated cells. Rather, inhibition of apoptosis seemed to take place in the cytoplasm. We conclude that phenotypic changes associated with TPA-induced differentiation include inactivation of a cytoplasmic activity that can induce DNA fragmentation associated with apoptosis.

Amsacrine↗
PubMed1993

Effects of base mutations on topoisomerase II DNA cleavage stimulated by mAMSA in short DNA oligomers.

DNA cleavage by topoisomerase II in the absence or presence of mAMSA, and VM-26 was investigated in a series of oligonucleotides of 36 and 42 base pairs, which were derived from the DNA sequence of the major topoisomerase II cleavage site in the matrix-associated region of SV40 DNA. Topoisomerase II introduced strand cuts at several sites in the oligonucleotides, and the sequence selectivities of DNA cleavage with and without drugs were the same as in larger SV40 DNA fragments. A time course analysis showed that mAMSA specifically stimulated DNA cleavage at the 4263/4266 site, while DNA cleavage was specifically induced at the 4265/4268 site by the enzyme without drug or with VM-26. In agreement with recent findings on local nucleotide requirements in order for mAMSA to stimulate DNA cleavage, the 4263/4266 site had adenines at the two positions +1. This nucleotide requirement was challenged by mutating the bases 4263 and 4266 of the oligonucleotide representing the natural SV40 DNA sequence. New cleavage sites were not observed in the mutated oligonucleotides, and base mutations had an effect on DNA cleavage induced with and without the two drugs. This general effect was likely due to the sensitivity of topoisomerase II itself to the local DNA sequence. Nevertheless, effects of base mutations were more pronounced for mAMSA than for VM-26. Point mutations of either base 4263 or 4266, representing the two positions +1, reduced markedly the stimulative effect of DNA cleavage at the 4263/4266 site by mAMSA, and mutations of both bases completely abolished it.(ABSTRACT TRUNCATED AT 250 WORDS)

Amsacrine↗
PubMed1993

Small deletion and insertion mutations induced by the topoisomerase II inhibitor teniposide in CHO cells and comparison with sites of drug-stimulated DNA cleavage in vitro.

Sixty-five teniposide-induced mutations at the hemizygous aprt locus of CHO D422 cells were analyzed by polymerase chain reaction and DNA sequencing. Most (63%) of the mutations were deletions, duplications and insertions of various sizes, with the majority being less than 20 base-pairs. The remaining mutations were base substitutions, the majority of which were transversions. A significant correspondence was found between the teniposide-induced small deletion/duplication mutations and sites of teniposide-stimulated DNA strand cleavage by topoisomerase II in vitro. In particular, sequences which were deleted in one or more of the mutants showed a much higher incidence of strong cleavage sites than sequences not involved in deletions. However, the exact positioning of the cleavage sites with respect to the deletion termini was variable. The data did not suggest any unified model to account for all the mutations, but most of the deletions and duplications could be accounted for by one of three mechanisms: (1) double-strand break repair nonhomologous end-joining; (2) replication slippage/misalignment; and (3) addition or deletion of a few nucleotides at free 3' ends left by topoisomerase II, as previously suggested for similar mutations in phage T4. There was no evidence that topoisomerase II subunit exchange was a significant mechanism of mutagenesis in this system.

Animals↗
PubMed1993

Apoptosis and its modulation in human promyelocytic HL-60 cells treated with DNA topoisomerase I and II inhibitors.

Electron microscopy studies demonstrate unequivocally that the observed oligonucleosome-sized secondary DNA fragmentation in human promyelocytic HL-60 cells treated with the topoisomerase inhibitors camptothecin and teniposide is correlated with the morphological changes in cell structure typical of programmed cell death (apoptosis). Since apoptosis has been associated with potential involvement of intracellular signaling linked to the Ca2+/calmodulin and protein kinase C transduction pathways, we also investigated the effects of signaling modulators on camptothecin- and teniposide-induced secondary DNA fragmentation in HL-60 cells. Neither calcium chelators, calcium/calmodulin inhibitors (calmidazolium or cyclosporine A), protein kinase C stimulation by TPA, protein phosphatase inhibition by okadaic acid, protein kinase inhibition by staurosporine, calphostin C, genistein or H7, nor cell cycle alterations by caffeine had any detectable effect. Interestingly, most of these intracellular signaling modulators were able to induce DNA fragmentation in HL-60 cells by themselves. These results may suggest that even though modulation of these signaling pathways was unable to prevent topoisomerase inhibitor-induced apoptosis, their sole deregulations could induce apoptosis in HL-60 cells. In contrast, aphidicolin blocked camptothecin-induced secondary DNA fragmentation, indicating that replication-induced DNA damage is required for camptothecin- but not teniposide-induced secondary DNA fragmentation. Zinc, 3-aminobenzamide, and spermine also modulated both camptothecin- and teniposide-induced secondary DNA fragmentation without significant alteration of topoisomerase-mediated primary DNA strand breaks. Hence, poly(ADP-ribosyl)ation and chromatin structure may be important in modulating oligonucleosome-sized DNA fragmentation associated with apoptosis in HL-60 cells treated with topoisomerase inhibitors.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1993

Dual topoisomerase I and II inhibition by intoplicine (RP-60475), a new antitumor agent in early clinical trials.

The mechanisms of action of intoplicine (RP-60475), a 7H-benzo[e]pyrido[4,3-b]indole derivative that is presently in early clinical trials, have been investigated. Intoplicine induced both topoisomerase I- and II-mediated DNA strand breaks, using purified topoisomerases. The topoisomerase cleavage site patterns induced by intoplicine were unique, relative to those of camptothecin, 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA), and other known topoisomerase inhibitors. Both topoisomerase I- and II-induced DNA breaks decreased at drug concentrations higher than 1 microM, which is consistent with the DNA-intercalating activity of intoplicine. DNA damage was investigated in KB cells in culture by using alkaline elution. Intoplicine induced single-strand breaks (SSB) in a bell-shaped manner with respect to drug concentration (maximum frequency at 1 microM approximately 220 rad-equivalents). SSB formation was fast, whereas reversal after drug removal was slow. Similar bell-shaped curves were obtained for DNA double-strand breaks (DSB) and DNA-protein cross-links. SSB and DNA-protein cross-link frequencies were approximately equal, and no protein-free breaks were detectable, indicating the protein concealment of the breaks, as expected for topoisomerase inhibition. Comparison of SSB and DSB frequencies indicated that intoplicine produced a significant amount of SSB not related to DSB, which is consistent with concomitant inhibition of both DNA topoisomerases I and II in cells. Data derived from resistant cell lines indicated that multidrug-resistant cells were cross-resistant to intoplicine but that m-AMSA- and camptothecin-resistant cells were sensitive to intoplicine. Hence, intoplicine might circumvent topoisomerase I-mediated and topoisomerase II-mediated resistance by poisoning both enzymes simultaneously.

Animals↗
PubMed1992

Overexpression of P-glycoprotein and alterations in topoisomerase II in P388 mouse leukemia cells selected in vivo for resistance to mitoxantrone.

The overexpression of P-glycoprotein (PGP) and alterations in DNA topoisomerase II (TOPO II) were evaluated in mouse leukemia P388 cells selected in vivo for mitoxantrone (MTT) resistance (P388/MTT) and compared to doxorubicin (DOX) resistant (P388/DOX) or vincristine (VCR) resistant (P388/VCR) models. Among a panel of TOPO II inhibitors which included etoposide (VP-16), DOX, MTT and 4'-[(9-acridinyl)-amino]methanesulfon-m-anisidide (m-AMSA), the relative resistance compared to parental sensitive P388/S cells was: P388/DOX greater than P388/MTT greater than P388/VCR. All the resistant sublines exhibited minimal cell kill (less than 20%) at vincristine concentrations greater than 100-fold the IC50 for P388/S cells. In a soft-agar colony-forming assay, the modulation of cytotoxicity in P388/MTT cells by the calmodulin inhibitor trifluoperazine following a 3-hr drug treatment demonstrated a marked potentiation in cell kill with MTT, VP-16, DOX and m-AMSA but not VCR. Immunoblotting data revealed that while PGP was not detectable in P388/S cells, the overexpression of PGP was apparent in P388/MTT cells and the relative expression between the resistant sublines was: P388/DOX greater than P388/MTT greater than P388/VCR. Although the amount and DNA cleavage activity of TOPO II in nuclear extracts from P388/VCR cells were comparable to those in P388/S cells, they were markedly lower in both P388/DOX and P388/MTT cells. However, decatenation activity of TOPO II in nuclear extracts was comparable between the sensitive (P388/S) and resistant sublines (P388/MTT, P388/DOX, and P388/VCR). Results from the present study demonstrated that P388 cells selected for resistance to mitoxantrone exhibit changes in TOPO II and overexpression of PGP similar to P388/DOX cells, while vincristine resistant cells only overexpress PGP. Since therapeutic strategies are primarily designed to interfere with PGP-mediated drug efflux, the choice of agents for modulating resistance in tumors which overexpress PGP versus tumors which overexpress PGP with altered TOPO II could be different.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1992

Rational design and molecular effects of a new topoisomerase II inhibitor, azatoxin.

Azatoxin [NSC 640737-M; 5.R,11aS-1H,6H,3-one-5,4,11,11a-tetrahydro-5-(3,5-dimethoxy-4-hydr oxyphenyl) oxazolo (3',4':1,6)pyrido-(3,4-b)indole] was rationally designed from a model for the pharmacophore of drugs with topoisomerase II inhibition activity. This pharmacophore has at least 2 domains: a quasiplanar polycyclic ring system proposed to bind between the DNA base pairs and a pendant substituent proposed to interact with the enzyme and/or to the DNA grooves. The present study shows that, in cell free systems, azatoxin induces a large number of double strand-breaks in linear Simian virus 40 and human c-myc DNA. These breaks yield cleavage patterns that are different from those of well established topoisomerase II inhibitors (epipodophyllotoxins, amsacrine, mitoxantrone). Azatoxin also inhibits the catalytic activity of purified topoisomerase II, and is a nonintercalator. The structure-activity relationship of 3 isomers and 6 derivatives of azatoxin shows a stringent stereochemical requirement for activity. The effects of azatoxin pendant ring substitution on topoisomerase II mediated DNA cleavage activity were similar to the relationship observed for etoposide.

DNA↗
PubMed1992

Depletion of poly(ADP-ribose) polymerase by antisense RNA expression results in a delay in DNA strand break rejoining.

The effects of inducible expression of poly(ADP-ribose) polymerase (PADPRP) antisense RNA in HeLa cells were determined in order to gain further insight into the biological roles of the poly(ADP-ribosyl)ation modification of nuclear proteins. A recombinant expression plasmid was prepared with the mouse mammary tumor virus (MMTV) promoter upstream of the antisense-oriented PADPRP cDNA. Expression of the antisense RNA was under strict control, with negligible effects on cell growth being apparent in the absence of inducer. Consistent with the previously described stability of PADPRP (half-life of at least 2 days, in vivo), 48-72 h were required after induction of antisense RNA expression by dexamethasone for the abundant concentration of PADPRP, normally present in HeLa cells, to be reduced by greater than 80%. The depletion of endogenous PADPRP as mediated by induced antisense RNA expression was established by: (i) a progressive synthesis of antisense transcripts in cells as assessed by Northern analysis; (ii) an 80% decrease in activity of the enzyme; and (iii) a greater than 90% reduction in the cellular content of PADPRP protein, as demonstrated by both immunoblotting and immunohistochemical analysis in intact cells. Several biological parameters were monitored in cells depleted of PADPRP. The chromatin of PADPRP-depleted cells was shown to have an altered structure as assessed by deoxyribonuclease I susceptibility. Cell morphology was also altered, with multinucleated aggregates being evident 72 h after induction of antisense RNA expression. Cells depleted of PADPRP were not able to commence DNA strand break joining of damaged DNA. However, DNA repair capacity was re-established at later time periods, indicating that PADPRP may contribute to alterations in chromatin structure that occur initially in DNA strand break rejoining and that the concentration of the enzyme in nuclei exceeds the requirement for DNA repair/replication.

Cloning, Molecular↗
PubMed1992

Differential effects of amsacrine and epipodophyllotoxins on topoisomerase II cleavage in the human c-myc protooncogene.

Amsacrine and demethylepipodophyllotoxins (etoposide and teniposide) are potent topoisomerase II inhibitors which have optimum activity in different cancers. To investigate whether these differences are due to different activity on cellular oncogenes, drug-induced topoisomerase II cleavage sites were mapped and sequenced in the human c-myc protooncogene. In the presence of purified murine L1210 topoisomerase II, amsacrine induces prominent cleavage in the P2 promoter (site 2499/2502). Footprinting experiments indicate that topoisomerase II binds to the entire promoter region (approximately 20 base pairs on the sides of the P2 site). In the case of teniposide or etoposide, cleavage is more diffuse and markedly less at the P2 site. Mapping of cleavage sites in human small cell lung carcinoma cells (NCI N417) also shows that cleavage in the P2 promoter region is induced preferentially by amsacrine but not by demethylepipodophyllotoxins. Thus, selective gene damage among topoisomerase II inhibitors may contribute to differential anticancer activity.

Amsacrine↗
PubMed1992

Topoisomerase I alteration in a camptothecin-resistant cell line derived from Chinese hamster DC3F cells in culture.

Camptothecin-resistant DC3F Chinese hamster lung fibroblast cell lines were obtained after mutagenic treatment with ethylmethanesulfonate and subsequent exposure to 1 microM camptothecin (CPT). The most resistant cell line, which was obtained after exposure to CPT for 10 days, was designated DC3F/C-10. Comparison of 50% inhibitory concentration values after 8-h CPT treatments showed that DC3F/C-10 cells were 134-fold resistant to CPT. Resistance was associated with marked reduction of CPT-induced DNA single-strand breaks and DNA-protein cross-links. This reduction was not due to reduced amounts of immunoreactive DNA topoisomerase I protein, although nuclear extracts from DC3F/C-10 cells had less enzyme catalytic activity than those from DC3F cells. Also, fast protein liquid chromatography-purified DNA topoisomerase I from DC3F/C-10 had lower specific catalytic activity than that from DC3F cells. DNA topoisomerase I from DC3F/C-10 was resistant to inhibition of catalytic activity and induction of DNA cleavage by CPT. These results suggest that CPT resistance in DC3F/C-10 cells is due to qualitative alteration of DNA topoisomerase I.

Animals↗
PubMed1992

Acquisition of a growth-inhibitory response to phorbol ester involves DNA damage.

TPA (12-O-tetradecanoylphorbol-13-acetate), a potent tumor promoter, has been shown to stimulate or inhibit cell growth depending on the cell type investigated. We recently found that RT101 cells, a transformed mouse JB6 epidermal cell line, acquired a greater growth inhibition response to TPA during conventional subcultivation. The growth of low-passage RT101 cells was slightly inhibited by TPA in monolayer culture but stimulated in soft agar. In contrast, the growth of high-passage cells was greatly inhibited by TPA in both monolayer culture and in soft agar. Inhibition was dose dependent, directly correlated with protein kinase C-activating activities of tumor promoters, and was found to be reversible. TPA-treated high-passage cells were greatly reduced in volume, showed extensive abnormal mitoses, and were more susceptible to detachment. High-passage cells were also found to be less tumorigenic as indicated by in vivo tumorigenicity assay in nude mice. TPA treatment rendered cells still less tumorigenic in the case of both cell lines. The mechanism for acquisition of increased sensitivity to TPA of RT101 cells during subculture was investigated; it involved nonrandom DNA damage and detachment of nonviable cells. The results suggest the possibility that early-passage RT101 cells contained two subpopulations, one TPA-sensitive and one TPA-resistant population. Conventional subcultivation may have selected for the former subpopulation. The sensitive subpopulation may have been irreversibly inhibited as a result of TPA-induced cell killing, possibly apoptosis.

Animals↗
PubMed1992

Radiolabeling of DNA can induce its fragmentation in HL-60 human promyelocytic leukemic cells.

Incorporation of radiolabeled thymidine is commonly used to investigate DNA damage. Using a filter-binding assay, we observed that the addition of various doses of [methyl-3H]thymidine (0.2 and 2 microCi/ml) or [2-14C]thymidine (0.02 and 0.2 microCi/ml) in the culture medium for 2 days, a standard method for cell-labeling, induces DNA fragmentation in HL-60 human promyelocytic cells. This effect was dose- and time-dependent and the DNA fragments were not protein-linked since the levels of DNA fragmentation were identical in the presence and in the absence of proteinase K (0.5 mg/ml). Radiolabeled thymidine-induced DNA fragmentation was associated with an inhibition of cell growth, but cells remained able to exclude trypan blue, suggesting that plasma membrane integrity was conserved, except at very high doses of [methyl-3H]thymidine (2 microCi/ml). By agarose-gel electrophoresis, the DNA-fragmentation was demonstrated to be internucleosomal with a typical ladder pattern. Addition of unlabeled thymidine to the culture medium prevented DNA fragmentation in a dose-dependent manner, indicating that radiolabeled thymidine incorporation in DNA was directly responsible for DNA fragmentation. We conclude that radiolabeling of DNA using thymidine incorporation can induce DNA fragmentation in some cell lines such as HL-60. This observation must be taken into account in methods using radiolabeling to study DNA damage in these cells.

Apoptosis↗
PubMed1992

Sequential administration of camptothecin and etoposide circumvents the antagonistic cytotoxicity of simultaneous drug administration in slowly growing human colon carcinoma HT-29 cells.

We compared the cytotoxicity of simultaneous and sequential combination chemotherapy with camptothecin and etoposide, in slowly growing human colon carcinoma, HT-29 cells. Simultaneous treatments of HT-29 cells with etoposide and camptothecin produced no marked enhancement of cytotoxicity over single agent administration. This finding demonstrates antagonism of one drug's cytotoxicity over the other. When these studies were repeated in sequential treatment protocols, we observed that antagonism could be circumvented if the period between individual drug administration was separated by 6-8 h. The cytotoxicity that was observed with this approach was never more than additive and the order of camptothecin or etoposide administration did not significantly affect the extent of combined cytotoxicity observed. The protective effect of simultaneous camptothecin and etoposide exposure was not due to reduced formation or alterations in the rate of cleavable complex reversal, and protection persisted for a considerably longer period of time than DNA strand breaks. Protection correlated with the kinetics of DNA and RNA synthesis inhibition produced by either drug. Remarkably, full cytotoxic protection could be afforded by one drug over the other, in the presence of only partial inhibition of DNA or RNA synthesis (50-60%). Our findings suggest that sequential rather than simultaneous administration of topoisomerase I and II inhibitors in future cancer chemotherapy schedules will enhance cytotoxicity over single-agent administration.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1991

Distribution of topoisomerase II cleavage sites in simian virus 40 DNA and the effects of drugs.

The distributions of DNA cleavage sites induced by topoisomerase II in the presence or absence of specific drugs were mapped in the simian virus 40 genome. The drugs studied were 5-iminodaunorubicin, amsacrine (m-AMSA), teniposide (VM-26) and 2-methyl-9-hydroxyellipticinium; each produced a distinctive pattern of enhanced cleavage. Consistently intense cleavage, both in the presence and in the absence of drugs, occurred in the nuclear matrix-associated region. Since topoisomerase II is a major constituent of the nuclear matrix, and cleavage complexes include a covalent link between topoisomerase II and DNA, the findings suggest that topoisomerase II may function to attach DNA to the nuclear matrix. Cleavage usually occurred on both DNA strands with the expected four base-pair 5' stagger, and strong sites tended to occur within A/T runs such as have been associated with binding to the nuclear scaffold. Intense cleavage was present also in the replication termination region, but was absent from the vicinity of the replication origin. Cleavage intensities were found to change with time in a manner that depended both on the site and on the drug, suggesting that topoisomerase II can move along the DNA from a kinetically preferred site to a thermodynamically preferred site.

Amsacrine↗