Proliferation dependence of topoisomerase II mediated drug action

The Antibacterial Activity and Mechanism of Action of Luteolin Against Trueperella pyogenes

Purpose

This research aimed to investigate the antibacterial activity and potential mechanism of luteolin against T. pyogenes.

Materials and Methods

The broth microdilution method was used to determine the minimum inhibitory concentrations (MICs) of luteolin against various T. pyogenes strains. The potential mechanism of action of luteolin was elucidated through testing and analysing the luteolin-induced alterations of T. pyogenes in several aspects, including cell wall, cell membrane, protein expression, nucleic acid content, topoisomerase activity and energy metabolism.

Results

The MIC values of luteolin against various T. pyogenes isolates and ATCC19411 were 78 µg/mL. The increased cell membrane permeability, destruction of cell wall integrity and TEM images after exposure to luteolin showed that the cell wall and membrane were damaged. The content of total protein and nucleic acid in T. pyogenes decreased significantly after treatment with luteolin (1/2 MIC) for 12, 24, and 36 h. Moreover, a hypochromic effect was observed in the absorption spectrum of luteolin when deoxyribonucleic acid (DNA) was added. In addition, after treatment with luteolin, a decrease in nicked or relaxed DNA content, which was catalysed by T. pyogenes-isolated DNA topoisomerase, was observed. In addition, the adenosine triphosphate (ATP) content in cells and the activity of succinate dehydrogenase (SDH) both decreased when T. pyogenes was exposed to different concentrations (1/4 MIC, 1/2 MIC, 1 MIC, 2 MIC) of luteolin for 1 h.

Conclusion

Luteolin showed distinct antibacterial activity against T. pyogenes by multiple actions, which mainly include destroying the integrity of the cell wall and cell membrane, influencing the expression of proteins, inhibiting nucleic acid synthesis, and interfering with energy metabolism.

TOP2B: The First Thirty Years

Type II DNA topoisomerases (EC 5.99.1.3) are enzymes that catalyse topological changes in DNA in an ATP dependent manner. Strand passage reactions involve passing one double stranded DNA duplex (transported helix) through a transient enzyme-bridged break in another (gated helix). This activity is required for a range of cellular processes including transcription. Vertebrates have two isoforms: topoisomerase IIα and β. Topoisomerase IIβ was first reported in 1987. Here we review the research on DNA topoisomerase IIβ over the 30 years since its discovery.

Coenzyme Q10 for Prevention of Anthracycline-Induced Cardiotoxicity

Preclinical and clinical studies suggest that anthracycline-induced cardiotoxicity can be prevented by administering coenzyme Q10 during cancer chemotherapy that includes drugs such as doxorubicin and daunorubicin. Studies further suggest that coenzyme Q10 does not interfere with the antineoplastic action of anthracyclines and might even enhance their anticancer effects. Preventing cardiotoxicity might allow for escalation of the anthracycline dose, which would further enhance the anticancer effects. Based on clinical investigation, although limited, a cumulative dose of doxorubicin of up to 900 mg/m2, and possibly higher, can be administered safely during chemotherapy as long as coenzyme Q10 is administered concurrently. The etiology of the dose-limiting cardiomyopathy that is induced by anthracyclines can be explained by irreversible damage to heart cell mitochondria, which differ from mitochondria of other cells in that they possess a unique enzyme on the inner mitochondrial membrane. This enzyme reduces anthracyclines to their semiquinones, resulting in severe oxidative stress, disruption of mitochondrial energetics, and irreversible damage to mitochondrial DNA. Damage to mitochondrial DNA blocks the regenerative capability of the organelle and ultimately leads to apoptosis or necrosis of myocytes. Coenzyme Q10, an essential component of the electron transport system and a potent intracellular antioxidant, appears to prevent damage to the mitochondria of the heart, thus preventing the development of anthracycline-induced cardiomyopathy.

Reversing chromatin accessibility differences that distinguish homologous mitotic metaphase chromosomes

BACKGROUND

Chromatin-modifying reagents that alter histone associating proteins, DNA conformation or its sequence are well established strategies for studying chromatin structure in interphase (G1, S, G2). Little is known about how these compounds act during metaphase. We assessed the effects of these reagents at genomic loci that show reproducible, non-random differences in accessibility to chromatin that distinguish homologous targets by single copy DNA probe fluorescence in situ hybridization (scFISH). By super-resolution 3-D structured illumination microscopy (3D-SIM) and other criteria, the differences correspond to 'differential accessibility' (DA) to these chromosomal regions. At these chromosomal loci, DA of the same homologous chromosome is stable and epigenetic hallmarks of less accessible interphase chromatin are present.

RESULTS

To understand the basis for DA, we investigate the impact of epigenetic modifiers on these allelic differences in chromatin accessibility between metaphase homologs in lymphoblastoid cell lines. Allelic differences in metaphase chromosome accessibility represent a stable chromatin mark on mitotic metaphase chromosomes. Inhibition of the topoisomerase IIα-DNA cleavage complex reversed DA. Inter-homolog probe fluorescence intensity ratios between chromosomes treated with ICRF-193 were significantly lower than untreated controls. 3D-SIM demonstrated that differences in hybridized probe volume and depth between allelic targets were equalized by this treatment. By contrast, DA was impervious to chromosome decondensation treatments targeting histone modifying enzymes, cytosine methylation, as well as in cells with regulatory defects in chromatid cohesion. These data altogether suggest that DA is a reflection of allelic differences in metaphase chromosome compaction, dictated by the localized catenation state of the chromosome, rather than by other epigenetic marks.

CONCLUSIONS

Inhibition of the topoisomerase IIα-DNA cleavage complex mitigated DA by decreasing DNA superhelicity and axial metaphase chromosome condensation. This has potential implications for the mechanism of preservation of cellular phenotypes that enables the same chromatin structure to be correctly reestablished in progeny cells of the same tissue or individual.

Antibacterial mechanism of fraxetin against Staphylococcus aureus

Fraxetin is one of the main constituents of the traditional medicinal plant Fraxinus rhynchophylla. The inhibitory effect of fraxetin on various bacterial strains has been extensively reported, however, its mechanism of action on bacterial cells remains to be elucidated. In the present study, the antibacterial mechanism of fraxetin on Staphylococcus aureus was systematically investigated by examining its effect on cell membranes, protein synthesis, nucleic acid content and topoisomerase activity. The results indicated that fraxetin increased the permeability of the cell membrane but did not render it permeable to macromolecules, such as DNA and RNA. Additionally, the quantity of protein, DNA and RNA decreased to 55.74, 33.86 and 48.96%, respectively following treatment with fraxetin for 16 h. The activity of topoisomerase I and topoisomerase II were also markedly inhibited as fraxetin concentration increased. The result of the ultraviolet‑visible spectrophotometry demonstrated that the DNA characteristics exhibited a blue shift and hypochromic effect following treatment with fraxetin. These results indicated that fraxetin had a marked inhibitory effect on S.aureus proliferation. Further mechanistic studies showed that fraxetin could disrupt nucleic acid and protein synthesis by preventing topoisomerase from binding to DNA.

Mechanisms regulating resistance to inhibitors of topoisomerase II

Inhibitors of topoisomerase II (topo II) are clinically effective in the management of hematological malignancies and solid tumors. The efficacy of anti-tumor drugs targeting topo II is often limited by resistance and studies with in vitro cell culture models have provided several insights on potential mechanisms. Multidrug transporters that are involved in the efflux and consequently reduced cytotoxicity of diverse anti-tumor agents suggest that they play an important role in resistance to clinically active drugs. However, in clinical trials, modulating the multidrug-resistant phenotype with agents that inhibit the efflux pump has not had an impact. Since reduced drug accumulation per se is insufficient to explain tumor cell resistance to topo II inhibitors several studies have focused on characterizing mechanisms that impact on DNA damage mediated by drugs that target the enzyme. Mammalian topo IIα and topo IIβ isozymes exhibit similar catalytic, but different biologic, activities. Whereas topo IIα is associated with cell division, topo IIβ is involved in differentiation. In addition to site specific mutations that can affect drug-induced topo II-mediated DNA damage, post-translation modification of topo II primarily by phosphorylation can potentially affect enzyme-mediated DNA damage and the downstream cytotoxic response of drugs targeting topo II. Signaling pathways that can affect phosphorylation and changes in intracellular calcium levels/calcium dependent signaling that can regulate site-specific phosphorylation of topoisomerase have an impact on downstream cytotoxic effects of topo II inhibitors. Overall, tumor cell resistance to inhibitors of topo II is a complex process that is orchestrated not only by cellular pharmacokinetics but more importantly by enzymatic alterations that govern the intrinsic drug sensitivity.

Secondary leukemia associated with the anti-cancer agent, etoposide, a topoisomerase II inhibitor

Etoposide is an anticancer agent, which is successfully and extensively used in treatments for various types of cancers in children and adults. However, due to the increases in survival and overall cure rate of cancer patients, interest has arisen on the potential risk of this agent for therapy-related secondary leukemia. Topoisomerase II inhibitors, including etoposide and teniposide, frequently cause rearrangements involving the mixed lineage leukemia (MLL) gene on chromosome 11q23, which is associated with secondary leukemia. The prognosis is extremely poor for leukemias associated with rearrangements in the MLL gene, including etoposide-related secondary leukemias. It is of great importance to gain precise knowledge of the clinical aspects of these diseases and the mechanism underlying the leukemogenesis induced by this agent to ensure correct assessments of current and future therapy strategies. Here, I will review current knowledge regarding the clinical aspects of etoposide-related secondary leukemia, some probable mechanisms, and strategies for treating etoposide-induced leukemia.

The endonuclease Ankle1 requires its LEM and GIY-YIG motifs for DNA cleavage in vivo

The LEM domain (for lamina-associated polypeptide, emerin, MAN1 domain) defines a group of nuclear proteins that bind chromatin through interaction of the LEM motif with the conserved DNA crosslinking protein, barrier-to-autointegration factor (BAF). Here, we describe a LEM protein annotated in databases as 'Ankyrin repeat and LEM domain-containing protein 1' (Ankle1). We show that Ankle1 is conserved in metazoans and contains a unique C-terminal GIY-YIG motif that confers endonuclease activity in vitro and in vivo. In mammals, Ankle1 is predominantly expressed in hematopoietic tissues. Although most characterized LEM proteins are components of the inner nuclear membrane, ectopic Ankle1 shuttles between cytoplasm and nucleus. Ankle1 enriched in the nucleoplasm induces DNA cleavage and DNA damage response. This activity requires both the catalytic C-terminal GIY-YIG domain and the LEM motif, which binds chromatin via BAF. Hence, Ankle1 is an unusual LEM protein with a GIY-YIG-type endonuclease activity in higher eukaryotes.

Antibacterial mechanism of soybean isoflavone on Staphylococcus aureus

Effects of different flavonoids on various bacterial strains have been extensively reported; however, the mechanism(s) of their action on bacterial cells remain largely elusive. In this study, the antibacterial mechanism of soybean isoflavone (SI) on Staphylococcus aureus is systematically investigated using 4'6-diamidino-2-phenylindole (DAPI) staining, pBR322DNA decatenation experiment mediated by topoisomerase and agarose gel electrophoresis for direct decatenation. The results of fluorescence microscopy and fluorescence spectrophotometer indicated that DAPI was integrated in Staphylococcus aureus. Additionally, the quantity of both DNA and RNA reduced to 66.47 and 60.18%, respectively, after treated with SI for 28 h. Effects of SI on topoisomerase I and II were also investigated. SI completely inhibited the pBR322DNA unwinding mediated by topoisomerase I and topoisomerase II at the concentration of 6.4 mg/ml and could denature the plasmid DNA at the concentration of 12.8 mg/ml. These results indicate that topoisomerase I and II are the most important targets by SI to restrain bacterial cell division.

Synthesis and biological evaluation of novel naphthoquinone fused cyclic aminoalkylphosphonates and aminoalkylphosphonic monoester

A series of novel naphthoquinone fused cyclic alpha-aminophosphonates, 2-alkoxy-3,4-dihydro-2H-naphtho[2,3-e][1,4,2]oxazaphosphinane-5,10-dione 2-oxide 3-17 and naphthoquinone fused cyclic alpha-aminophosphonic monoester 18 were synthesized for the first time. These cyclic alpha-aminophosphonates were evaluated for antitumor activity on four human tumor cell lines, and three of them showed significant cytotoxicity (IC(50): 0.019-5.15 microM) comparable to that of the reference drug doxorubicin. Furthermore, inhibition assays for topoisomerase II-mediated relaxation of supercoiled DNA indicated that the naphthoquinone fused cyclic aminophosphonates were catalytic inhibitors of topoisomerase II.

Expression dynamics and functional implications of DNA topoisomerase II beta in the brain

Mammalian DNA topoisomerase II beta is a type II DNA topoisomerase that catalyses topological transformations of genomic DNA by the transport of one DNA double helix through another. The II beta enzyme is highly expressed in cells that have undergone the final cell division and committed to differentiate into neuronal cells. The II beta enzyme in the differentiating neuronal cells is located in the nucleoplasm and is actively engaged in its catalytic reaction in vivo. When enzyme action is interfered with a specific inhibitor in vitro, transcriptional induction of a subset of genes fails to occur during neuronal differentiation. Detailed analyses of developing rat cerebellum and the cerebrum of mice with disrupted II beta genes have revealed that DNA topoisomerase II beta is necessary for the developmentally regulated expression of certain genes in cells committed to a neuronal fate after the final division. Herein, we review a dynamic aspect of DNA topoisomerase II beta in the brain with special emphasis on developing cerebellar neurons.

The cell cycle phases of DNA damage and repair initiated by topoisomerase II-targeting chemotherapeutic drugs

Although cytostasis and cytotoxicity induced by cancer chemotherapy drugs targeting topoisomerase II (topoII) arise in specific cell cycle phases, it is unknown whether the drug-initiated DNA damage triggering these responses, or the repair (reversal) of this damage, differs between cell cycle phases or between drug classes. Accordingly, we used a flow cytometric alkaline unwinding assay to measure DNA damage (strand breakage (SB)) and SB repair in each cell cycle compartment of human cancer cell lines treated with clinically relevant concentrations of doxorubicin, daunomycin, etoposide, and mitoxantrone. We found that treated HeLa and A549 cells exhibited the greatest SB in G2/M phase, the least in G1 phase, and generally an intermediate amount in S phase. The cell cycle phase specificity of the DNA damage appeared to be predictive of the cell cycle phase of growth arrest. Furthermore, it appeared to be dependent on topoIIalpha expression as the extent of SB did not differ between cell cycle compartments in topoIIalpha-diminished A549(VP)28 cells. HeLa cells were apparently unable to repair doxorubicin-initiated SB. The rate of repair of etoposide-initiated SB in HeLa cells and of mitoxantrone-initiated SB in HeLa and A549 cells was similar in each cell cycle compartment. In A549 cells, the rate of repair of doxorubicin and etoposide-initiated SB differed between cell cycle phases. Overall, these results indicate that the cell cycle phase specificity of cytostasis and cytotoxicity induced in tumor cells by topoII-targeting drugs may be directly related to the cell cycle phase specificity of the drug-initiated DNA damage. Analysis by cell cycle compartment appears to clarify some of the intercellular heterogeneity in the extent of drug-initiated DNA damage and cytotoxicity previously observed in cancer cells analyzed as a single population; this approach might be useful in resolving inconsistent results reported in investigations of tumor cell topoII content versus response to topoII-targeting drugs.

Modulation of cell cycle by graded expression of MLL-AF4 fusion oncoprotein

Acute lymphoblastic leukemia (ALLs) expressing MLL-AF4, the fusion product of t(4;11)(q21;q23), show marked leucocytosis and extramedullary disease in multiple organs, respond poorly to chemotherapy and have poor prognosis. In vitro, leukemic cells with the t(4;11) show resistance to serum deprivation-induced or interferon gamma-regulated CD95-mediated apoptosis. In addition, t(4;11) cells have prolonged doubling time and lower percentage of cells in cycle compared to non-t(4;11) B lineage cell lines. In this study, we examine the time- and level-dependent effects of MLL-AF4 conditional expression on cell cycle and differentiation of myelomonocytic leukemia cell line U937. By varying the concentration of tetracycline in growth media, we found that increasing levels of MLL-AF4 expression result in a progressive decrease in growth rate and fraction of S phase cells, paralleled by an increase in percentage of cells expressing CD11b. Our results demonstrate a dosage-dependent effect of MLL-AF4 fusion oncoprotein on cell cycle progression, with increasing expression levels resulting in the accumulation in G1, prolonged doubling time, both findings that might be responsible for the increased resistance to etoposide-mediated cytotoxicity. We propose the cell cycle control exerted by MLL-AF4 may be responsible of resistance to cell-death promoting stimuli in leukemia carrying the t(4;11) translocation.

The cytoplasmic trafficking of DNA topoisomerase IIalpha correlates with etoposide resistance in human myeloma cells

In this study we have investigated the role of topoisomerase (topo) IIalpha trafficking in cellular drug resistance. To accomplish this, it was necessary to separate the influence of cell cycle, drug uptake, topo protein levels, and enzyme trafficking on drug sensitivity. Thus, we developed a cell model (called accelerated plateau) using human myeloma H929 cells that reproducibly translocates topo IIalpha to the cytoplasm. Compared to log-phase cells, the cytoplasmic redistribution of topo IIalpha in plateau-phase cells correlated with a 10-fold resistance to VP-16 and a 40-60% reduction in the number of drug-induced double-strand DNA breaks. In addition, 7-fold more VP-16 was necessary to achieve 50% topo IIalpha band depletion, suggesting that there are fewer drug-induced topo-DNA complexes formed in quiescent cells than in log-phase cells. The total cellular amount of topo IIalpha and topo IIbeta protein in log- and plateau-phase cells was similar as determined by Western blot analysis. There was a 25% reduction in S-phase cell number in plateau cells (determined by bromodeoxyuridine (BrdU) incorporation), while there was no significant difference in the equilibrium concentrations of [(3)H]-VP-16 when log cells were compared with plateau cells. Furthermore, the nuclear/cytoplasmic ratio of topo IIalpha is increased 58-fold in accelerated-plateau H929 cells treated with leptomycin B (LMB) when compared to untreated cells. It appears that the nuclear-cytoplasmic shuttling of topo IIalpha, which decreases the amount of nuclear target enzyme, is a major mechanism of drug resistance to topo II inhibitors in plateau-phase myeloma cells.

Chromosomal aberrations induced by 5-azacytidine combined with VP-16 (etoposide) in CHO-K1 and XRS-5 cell lines

A cytogenetic study was carried out with 5-azacytidine (5-azaC) and etoposide (VP-16) in CHO-K1 and XRS-5 (mutant cells deficient for double-strand break rejoining) cell lines to verify the interaction effects of the drugs in terms of induction of chromosomal aberrations. 5-azaC is incorporated into DNA causing DNA hypomethylation, and VP-16 (inhibitor of topoisomerase II enzyme) is a potent clastogenic agent. Cells in exponential growth were treated with 5-azaC for 1 h, following incubation for 7 h, and posttreatment with VP16 for the last 3 h. In K1 cells, the combined treatments induced a significant reduction in the aberrations induced in the X and "A" (autosome) chromosomes, which are the main target for 5-azaC. However, in XRS-5 cells, the drug combination caused a significant increase in the aberrations induced in those chromosomes, but with a concomitant reduction in the randomly induced-aberrations. In addition, each cell line presented characteristic cell cycle kinetics; while the combined treatment induced an S-arrest in K1 cells, alterations in cell cycle progression were not found for XRS-5, although each drug alone caused a G2-arrest. The different cell responses presented by the cell lines may be explained on the basis of the evidence that alterations in chromatin structure caused by 5-aza-C probably occur to a different extent in K1 and XRS-5 cells, since the mutant cells present a typical hyper-condensed chromosome structure (especially the X- and "A" chromosomes), but, alternatively, 5-aza-C could induce reactivation of DNA repair genes in XRS-5 cells.

Elongation by RNA polymerase II on chromatin templates requires topoisomerase activity

Transcription on chromatin by RNA polymerase II (pol II) is repressed as compared with transcription on histone-free DNA. In this study, we show that human topoisomerase I (topo I) and yeast topoisomerase II (topo II), each of which relax both positive and negative superhelical tension, reverse the transcriptional repression by chromatin. In the presence of bacterial topo I, which can relax only negative superhelical tension, the transcription is repressed on chromatin templates. The data together show that the relaxation of positive superhelical tension by these enzymes was the key property required for RNA synthesis from chromatin templates. In the absence of topoisomerase, transcriptional repression on chromatin depended on RNA length. The synthesis of transcripts of 100 nt or shorter was unaffected by chromatin, but repression was apparent when the RNA transcript was 200 nt or longer. These findings suggest that transcription on chromatin templates results in the accumulation of positive superhelical tension by the elongating polymerase, which in turn inhibits further elongation in the absence of topoisomerase activity.

Reduction in drug-induced DNA double-strand breaks associated with beta1 integrin-mediated adhesion correlates with drug resistance in U937 cells

We previously showed that adhesion of myeloma cells to fibronectin (FN) by means of beta1 integrins causes resistance to certain cytotoxic drugs. The study described here found that adhesion of U937 human histiocytic lymphoma cells to FN provides a survival advantage with respect to damage induced by the topoisomerase (topo) II inhibitors mitoxantrone, doxorubicin, and etoposide. Apoptosis induced by a topo II inhibitor is thought to be initiated by DNA damage. The neutral comet assay was used to determine whether initial drug-induced DNA damage correlated with cellular-adhesion-mediated drug resistance. Cellular adhesion by means of beta1 integrins resulted in a 40% to 60% reduction in mitoxantrone- and etoposide-induced DNA double-strand breaks. When the mechanisms regulating the initial drug-induced DNA damage were examined, a beta1 integrin-mediated reduction in drug-induced DNA double-strand breaks was found to correlate with reduced topo II activity and decreased salt-extractable nuclear topo IIbeta protein levels. Confocal studies showed changes in the nuclear localization of topo IIbeta; however, alterations in the nuclear-to-cytoplasmic ratio of topo IIbeta in FN-adhered cells were not significantly different. Furthermore, after a high level of salt extraction of nuclear proteins, higher levels of topo IIbeta-associated DNA binding were observed in FN-adhered cells than in cells in suspension. Together, these data suggest that topo IIbeta is more tightly bound to the nucleus of FN-adhered cells. Thus, FN adhesion by means of beta1 integrins appears to protect U937 cells from initial drug-induced DNA damage by reducing topo II activity secondarily to alterations in the nuclear distribution of topo IIbeta.

Drug resistance-associated factors in primary and secondary glioblastomas and their precursor tumors

Malignant gliomas are largely resistant to current chemotherapeutic strategies often displaying a multidrug-resistant phenotype. Mechanisms involved in drug resistance are reduced cellular drug accumulation through membrane efflux pumps, drug detoxification as well as alterations in drug target specificity. In 27 primary and 17 secondary glioblastomas and their astrocytic precursor tumors, we studied the immunohistochemical expression profile of P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP), lung resistance-related protein (LRP), metallothionein, and topoisomerase II alpha. Glial tumor cells in all glioblastomas showed constant up-regulation of LRP, MRP, and topoisomerase II alpha. P-gp was found in 90% of the primary and 60% of the secondary glioblastomas. In precursor tumors, these drug resistance-related factors were expressed in varying proportions. Metallothionein, also found in normal and activated astrocytes, was retained in all neoplastic phenotypes. Furthermore, metallothionein, P-gp, LRP, and topoisomerase II alpha were strongly expressed by normal and neoplastic vessels which may confer to impaired penetration of therapeutic agents through the blood-brain and blood-tumor barrier. However, the expression profiles of drug resistance-related proteins neither differed between primary and secondary glioblastomas nor revealed any correlation to precursor or recurrent tumors. Nevertheless, inhibition of these factors may be promising approaches to the management of malignant gliomas.

Cell density-dependent VP-16 sensitivity of leukaemic cells is accompanied by the translocation of topoisomerase IIalpha from the nucleus to the cytoplasm

The resistance of several leukaemic and myeloma cell lines (CCRF, L1210, HL-60, KG-1a and RPMI 8226) to VP-16 was found to increase with cell density and to be maximal (3.5- to 39-fold) in plateau phase cell cultures, as measured by clonogenic and MTT assays. Non-transformed confluent Flow 2000 human fibroblasts and Chinese hamster ovary (CHO) cells were also five- and 15-fold resistant to VP-16 respectively. The transition from log to plateau phase was accompanied by a drastic decrease in topoisomerase (topo) IIalpha content in CHO cells and human fibroblasts, while the leukaemic cells maintained constant cellular levels of topo IIalpha and topo IIbeta. However, the nuclear topo IIalpha content was found to decrease as a result of translocation of the enzyme to the cytoplasmic compartment in the leukaemic cells. This was confirmed by subcellular fractionation experiments, Western blotting analyses and immunocytochemistry studies. The quantity of topo IIalpha in plateau phase cytoplasmic fractions ranged from 18% in L1210 cells to 50% in HL-60 and 8226 cells, as measured by both immunoblotting and quantification of the label in immunofluorescent images. The cytoplasmic fraction from plateau phase cells retained topo II catalytic activity, as measured by the decatenation of kinetoplast DNA. The nuclear-cytoplasmic ratio of topo IIalpha may be critical in determining the sensitivity of leukaemic cells to topo II inhibitors. Cytoplasmic trafficking of topo IIalpha was observed in plasma cells obtained from patients with multiple myeloma, and perhaps contributes to drug resistance in this disease.

Influence of teniposide (VM-26) on radiation-induced damage to mouse spermatogenesis: a flow cytometric evaluation

The effect of teniposide (VM-26) 0.05 mg/kg body weight treatment on spermatogenesis of mice exposed to 0, 0.5, 1, 2, and 3 Gy gamma-radiation was evaluated flow cytometrically. Whole body irradiation with 1 to 3 Gy resulted in a significant decline in testis weight from Day 14 to 35 post-irradiation depending on the exposure dose. Treatment of mice with teniposide before irradiation advanced the decline in testicular weight by several days, especially at 3 Gy, where a significant decline in testicular weight was observed at Day 7 post-irradiation when compared with the double distilled water (DDW)+irradiation group. The relative percentage of the 2C population declined significantly in the VM-26+irradiation group in comparison with the DDW+irradiation group at various post-irradiation time periods depending on the exposure dose. A significant depletion in the relative percentage of S-phase cells was observed as early as Day 1 post-irradiation in the VM-26+irradiation group when compared with the DDW+irradiation group after exposure to 1 to 3 Gy. This decline continued up to Day 21 post-irradiation after exposure to 2 Gy. The relative percentage of primary spermatocytes showed a consistent decline after exposure to various doses of gamma-radiation in the VM-26+irradiation group when compared with the DDW+irradiation group at different time periods, with a few exceptions, especially at higher doses. The pattern of decline in the relative percentage of round spermatids was similar to that of primary spermatocytes, where a significant decline was observed at various post-irradiation time periods in the VM-26+irradiation group in comparison with the DDW+irradiation group. These changes in the relative germ cell percentages are manifested as alterations in the ratios of various germ cell populations. The 4C:2C ratio declined consistently from Day 1 to Day 70 post-irradiation in the VM-26+irradiation group at all exposure doses. Similarly, the 4C:S-phase ratio in the VM-26+irradiation group also showed a significant decline at different post-irradiation time periods when compared with the DDW+irradiation group depending on the exposure dose. The reduction observed in the relative percentages of various cell populations was higher in the combination group when compared with the DDW+irradiation controls, indicating potentiation of damage to male germ cells by teniposide treatment before irradiation.

Enhanced sensitivity to topoisomerase inhibitors in synchronous CHO cells pre-treated with 5-azacytidine

Multidrug combination has been shown to be very useful to improve antitumor activity as well as to reduce the toxicity of different anti-cancer drugs. We have evaluated the interaction between the hypomethylating agent 5-azacytidine and the topoisomerase I and topoisomerase II inhibitors Camptothecin (CPT) and 4'-(9-acridinylamino) methanesulfon-m-anisidide (m-AMSA) respectively, based on the hypothesis that through the alteration of chromosome replication timing following DNA hypomethylation, the number of replication forks in early S phase might increase, so enhancing the probability of a collision between a blocked cleavable complex (DNA-topo I-CPT or DNA-topo II-m-AMSA) and a replication fork. We have tested the capacity of CPT and m-AMSA to induce chromosomal aberrations as well as reproductive cell death in synchronous cultured Chinese hamster ovary cells after a pretreatment with 5-azacytidine with positive results.

Cellular resistance to topoisomerase-targeted drugs: from drug uptake to cell death

DNA topoisomerase inhibitors are important antineoplastic agents used in the treatment of both leukemias and solid tumors, such as breast, lung and colon cancers. Their clinical usefulness is limited by both natural and acquired tumor cell resistance, which almost always is multifactorial in nature. The resistance can be due to pretarget events, such as drug accumulation, metabolism and intracellular drug distribution, or due to reduced drug-target interaction. More recently, post-target events, such as macromolecular synthesis, cell cycle progression, DNA repair/recombination and regulation of cell death, have been shown to play an important role in the sensitivity toward topoisomerase inhibitors. The different mechanisms involved in the cellular resistance toward clinically used topoisomerase inhibitors will be reviewed in this article with particular emphasis on post-target events.

Expression and cellular localization of Trypanosoma cruzi type II DNA topoisomerase

Topoisomerases are enzymes that participate in many cellular functions involving topological manipulation of DNA strands. There are two types of topoisomerases in the cell: (a) type I topoisomerases; and (b) type II topoisomerases (topo II). Previously we have cloned and sequenced the gene encoding Trypanosoma cruzi topo II (TcTOP2). This study group has raised an antiserum against recombinant type II DNA topoisomerase (TctopoII) to study the expression of this gene during T. cruzi differentiation and to determine the cellular location of the enzyme. Western blot analysis showed that T. cruzi TctopoII is expressed in the replicative epimastigotes but not in the infective and non-replicative trypomastigotes. However, slot blot analysis of RNAs extracted from epimastigotes and metacyclic trypomastigotes showed that the mRNA encoding the enzyme is present in both developmental stages of the parasite. Confocal laser microscopy using the antiserum raised against recombinant TctopoII showed that the enzyme is located exclusively in the nucleus of the parasite. Similar results were obtained by immunofluorescence analysis of Crithidia fasciculata. However, monoclonal antisera against the corresponding enzyme extracted from C. fasciculata recognizes a kinetoplast protein in both T. cruzi and Crithidia.

Eukaryotic DNA topoisomerase II beta

Type II DNA topoisomerase activity is required to change DNA topology. It is important in the relaxation of DNA supercoils generated by cellular processes, such as transcription and replication, and it is essential for the condensation of chromosomes and their segregation during mitosis. In mammals this activity is derived from at least two isoforms, termed DNA topoisomerase II alpha and beta. The alpha isoform is involved in chromosome condensation and segregation, whereas the role of the beta isoform is not yet clear. DNA topoisomerase II beta was first reported in 1987. Here we review the research on DNA topoisomerase II beta over the last 10 years.

Untangling the role of DNA topoisomerase II in mitotic chromosome structure and function

DNA topoisomerase II (topo II) is involved in chromosome structure and function, although its exact location and role in mitosis are somewhat controversial. This is due in part to the varied reports of its localization on mitotic chromosomes, which has been described at different times as uniformly distributed, axial on the chromosome arms and predominantly centromeric. These disparate results are probably due to several factors, including use of different preparation and fixation techniques, species differences and changes in distribution during the cell cycle. Recently, several papers have re-investigated the distribution of topo II on chromosomes as a function of cell cycle and species(1-3). The new studies suggest that Topo II has a dynamic pattern of distribution on the chromosomes, in general becoming axial as chromosomes condense during prophase and then concentrating at centromeres during metaphase. These experiments suggest a novel role for topo II in centromere structure and function.

Topoisomerase II alpha mRNA and tumour cell proliferation in non-Hodgkin's lymphoma

AIMS

To elucidate potential mechanisms of drug resistance, levels of topoisomerase II alpha mRNA, a target for cytostatic drugs, were measured in cryopreserved tumour tissue from 36 patients with non-Hodgkin's lymphoma. To evaluate the potential association between topoisomerase II alpha and cell proliferation, Ki-67 immunostaining was also assessed.

METHODS

The study population comprised 13 patients with low grade and 20 with high grade non-Hodgkin's lymphoma. Three patients had recurrent disease. Topoisomerase II alpha mRNA was quantitated by using reverse transcription polymerase chain reaction (RT-PCR) and the PCR product measured by using HPLC. The MIB-1 monoclonal antibody was used for Ki-67 immunostaining.

RESULTS

Levels of topoisomerase II alpha mRNA correlated strongly with the Ki-67 labelling index and were higher in high grade than in low grade lymphomas. Patients in complete clinical remission of high grade lymphoma had a higher Ki-67 labelling index and tended to have higher topoisomerase II alpha mRNA levels.

CONCLUSIONS

Although topoisomerase II alpha mRNA levels may be indicative of sensitivity to drugs, it is more likely that they reflect the proliferation status of the cell, which in turn involves a large number of additional molecular systems that influence response to treatment.

Sequence of treatment is important in the modification of camptothecin induced cell killing by hyperthermia

We investigated the modification of camptothecin (CPT)-induced cell killing by hyperthermia in a radioresistant human melanoma (Sk-Mel-3) and a human normal (AG1522) cell line. CPT, a topoisomerase (topo) I inhibitor, was given as a 1 h exposure at variable doses up to 34 microM; hyperthermia was given either before or following CPT treatment. Hyperthermia was given either as a treatment of 41 degrees C for 8 h (termed lower temperature hyperthermia, LTH) or 45 degrees C for 15 min (termed higher temperature hyperthermia, HTH). LTH preceding CPT treatment had no effect on Sk-Mel-3 but potentiated killing of AG1522 cells. HTH preceding CPT treatment, however, almost completely abrogated the toxicity of CPT to both Sk-Mel-3 and AG1522 cells. These results therefore provided evidence for a lack of enhancement of CPT toxicity towards Sk-Mel-3 cells when hyperthermia preceded treatment with CPT. There was also no potentiation of killing of both cell lines when LTH followed treatment with CPT. In contrast, the killing of Sk-Mel-3 cells was slightly potentiated, whereas that of AG1522 cells was reduced, when HTH followed CPT. These results therefore suggested a potential for enhancement of killing of Sk-Mel-3 relative to AG1522 cells when HTH, but not LTH, followed CPT treatment. In addition, we found that a preceding exposure ot HTH did not affect either accumulation or efflux of[3H]CPT in both cell lines. Thus the significantly reduced cytotoxicity observed under those conditions was not related simply to a modification of accumulation or efflux of CPT. We found no significant differences in the atalytic activities of topo I extracted from the nuclei of Sk-Mel-3 and AG1522 cells that were either heated under HTH conditions or that were no subjected to such treatment. These results therefore suggested that the substantial reduction of cytotoxicity seen when HTH preceded CPT treatment was also not due to an effect on topo I catalytic activity. Our results therefore demonstrate that the sequence of application of hyperthermia and CPT is very important in determining the amount and, possibly, selective potentiation of tumour relative to normal cell cytotoxicity.

Reduction of etoposide induced cell killing by hyperthermia can occur without changes in etoposide transport or DNA topoisomerase II activity

We investigated the modification of etoposide (i.e. VP-16)-induced cell killing by hyperthermia in a radioresistant human melanoma (Sk-Mel-3) and a human normal (AG1522) cell line. VP-16, a DNA topo II poison, was given as a 1 h exposure at variable doses up to 35 microM; hyperthermia was given either before or following VP-16 treatment. Hyperthermic treatment comprised one of the following: 41 degrees C for 8 h, 42 degrees C for 2 h or 45 degrees C for 15 min. Hyperthermia preceding VP-16 treatment reduced the cytotoxicity of the latter; the reduction of VP-16 cytotoxicity was directly proportional to the severity of the hyperthermic treatment. For a particular combination of hyperthermic dose and VP-16 concentration, generally similar responses were seen in both cell lines. There were no effects on VP-16 cytotoxicity when both Sk-Mel-3 and AG1522 cells were heated at 41 degrees C for 8 h following treatment with VP-16. However, heating both cell lines at 45 degrees C for 15 min following VP-16 treatment again reduced the amount of cytotoxicity associated with VP-16. In addition, we found that a preceding exposure to 45 degrees C, 15 min heating did not affect either cellular accumulation or efflux of [3H]VP-16 in both cell lines. This suggested that the reduction in VP-16 cytotoxicity observed under those conditions was not due to a modification of VP-16 transport. We found no differences between the catalytic activities of topo II extracted from nuclei of Sk-Mel-3 and AG1522 cells that were either heated at 45 degrees C for 15 min or that were not subjected to such treatment. These results therefore suggested that the substantial reduction of cytotoxicity seen when 45 degrees C, 15 min heating preceded VP-16 treatment was also not due to an effect on topo II catalytic activity. Our results therefore demonstrate that hyperthermia, given either before or after VP-16, can actually reduce the amount of VP-16 cytotoxicity and that this can occur without any overt changes in VP-16 accumulation and efflux or in topo II catalytic activity.

Epidermal Growth Factor Regulates Topoisomerase II Activity and Drug Sensitivity in Human KB Cells

Because of its unique DNA-cleaving and strand-passing activities, topoisomerase II is involved in many aspects of DNA metabolism, including replication, transcription, recombination, and repair. The cytotoxic potential of topoisomerase II–targeted drugs, such as etoposide, is related to their ability to stabilize covalently linked enzyme-DNA complexes, which are intermediates in the enzyme's catalytic cycle. Epidermal growth factor receptor is expressed on the cell surface of the majority of squamous cell carcinomas, and epidermal growth factor binding is known to stimulate a number of cellular transduction pathways, including tyrosine kinase, protein kinase C, and phospholipase C. Because topoisomerase II is a proliferation-dependent protein and has been shown to be a high-affinity substrate for many of these cellular transduction pathways, the effects of epidermal growth factor on cellular regulation and sensitivity to etoposide were studied with the human oral cavity squamous cell line, KB. Topoisomerase II catalytic activity was rapidly and transiently inhibited after the addition of epidermal growth factor to the cellular growth media. Western blot on nuclear extracts did not demonstrate alterations in topoisomerase II polypeptide levels to account for changes in catalytic activity. Epidermal growth factor treatment also led to the formation of stabilized, covalently linked enzyme-DNA complexes. Furthermore, epidermal growth factor-induced, topoisomerase II–mediated DNA strand breaks were additive to those induced by etoposide. This study indicates that epidermal growth factor specifically regulates the catalytic and DNA-cleaving activities of topoisomerase II in KB cells. This may direct clinical strategies for circumventing the intrinsic cellular resistance to chemotherapy commonly observed in squamous cell carcinomas of the head and neck.

Verapamil suppresses the emergence of P-glycoprotein-mediated multi-drug resistance

Selection protocols were designed to determine whether non-cytotoxic chemomodifiers can influence the evolution of the drug-resistant phenotype. To this end, the human multiple myeloma cell line RPMI 8226 (8226/S) was selected with either doxorubicin, verapamil or doxorubicin plus verapamil. Using this approach low-level multi-drug-resistant (MDR) cell lines were obtained when 8226/S was selected with doxorubicin only or doxorubicin plus verapamil but not with verapamil only. The MDR phenotypes obtained were mechanistically distinct. In doxorubicin only-selected cells (8226/dox4), drug resistance was mediated by over-expression of the MDR1 gene and its cognate protein P-glycoprotein. In contrast, the drug resistance seen in the doxorubicin plus verapamil-selected cells was mediated through decreases in topoisomerase II protein levels and catalytic activity and not by P-glycoprotein over-expression. Cells selected with verapamil alone did not become resistant to any of the drugs tested. None of the 3 selected cell lines showed any changes in MRP gene expression when compared with 8226/S. Our results indicate that the inclusion of verapamil during drug selection with doxorubicin influences the drug-resistant phenotype by preventing the selection of MDR1/P-glycoprotein-positive cells.

Clinical trial of daily low-dose oral etoposide for patients with residual or recurrent cancer of the ovary or uterus

OBJECTIVE

To determine the efficacy of long-term therapy of oral etoposide in patients with residual or recurrent gynecological malignancies.

METHODS

Twenty-five Japanese patients with resistant or recurrent carcinoma of the uterus or ovary were treated with oral etoposide at a dose of 25 mg/day/body for 21 consecutive days, and cycles were repeated every 4 weeks. The residual or recurrent lesion could be objectively evaluated in all patients by measuring it directly.

RESULTS

The response rate after 6 cycles of therapy was 40% for the group of all patients, and 42.8%, 28.6% and 50% for those with ovarian carcinoma, cervical carcinoma, and endometrial carcinoma, respectively. Side effects of etoposide treatment included gastrointestinal discomfort in 14 patients and leukopenia of grade 3 or higher in 2 patients. However, these side effects were mild, and all patients could continue treatment.

CONCLUSION

These findings indicate that long-term, low-dose oral etoposide was effective for and well-tolerated by patients with refractory or recurrent carcinoma of the ovary or uterus.

Biomodulation by hyperthermia of topoisomerase II-targeting drugs in human colorectal cancer cells

We examined whether heat stress could enhance the sensitivity of human colon cancer WiDr cells to topoisomerase II-targeting anticancer agents, etoposide (VP-16) and teniposide (VM-26), and also determined the most effective timing for the drug administration after exposure to hyperthermia. Both topoisomerase II contents and topoisomerase II activity were significantly increased in WiDr cells 3 to 12 h after heat stress at 43 degrees C for 1 h, in comparison with those immediately after the heat stress. Cytotoxicity by VP-16 was most significantly enhanced 3 to 12 h after exposure to 43 degrees C for 1 h, but no synergistic effect was observed when the drug was administered immediately after the heat stress. A combination of VM-26 with heat stress, but not that of a topoisomerase I-targeting camptothecin derivative (CPT-11), or vincristine, showed a synergistic cytotoxic effect on WiDr cells. VP-16 alone induced cellular accumulation at the G2 + M phase, whereas the combination of VP-16 and heat stress further increased the cell population at the G2 + M phase, and decreased S-phase cells. A possible application of the combination of VP-16 and hyperthermia in clinical use is discussed.

Mechanism of action of DNA topoisomerase inhibitors

DNA topoisomerases are enzymes that regulate DNA topology and are essential for the integrity of the genetic material during transcription, replication and recombination processes. Inhibitors of the mammalian enzymes are widely used antitumor drugs. They stabilize topoisomerase-DNA cleavable complexes by hindering the DNA relegating step of the catalytic reaction, thus resulting in DNA cleavage stimulation. Investigations on the sequence selectivity of DNA cleavage stimulated by chemically unrelated compounds established that specific nucleotides flanking strand cuts are required for drug action. Moreover, structure-activity relationship studies have identified structural determinants of drug sequence specificities, thus eventually allowing the design of new agents targeted at selected genomic regions. The initial cellular lesion, i.e., the drug-stabilized cleavable complex, is a reversible molecular event; however, how it may lead to cell death remains to be fully clarified. Several laboratories focused in past years on molecular and genetic aspects of drug-activated apoptosis. Irreversible double-stranded DNA breaks, generated from collisions between cleavable complexes and advancing replication forks, were suggested to increase p53 protein levels, thus triggering the cell death program. Other genes were also shown to cooperate in modulating the cell response to drug treatments. Recently, several groups have evaluated the possible prognostic value of topoisomerase II levels in solid tumors and hematopoietic neoplasms. Topoisomerase II inhibitors may also have genotoxic effects. Secondary leukemias, characterized by a translocation between chromosomes 11 and 9, have been reported in disease-free patients after treatments with drug regimens that included anti-topoisomerase II agents. It has been proposed that an impairment of topoisomerase activity may be involved in the molecular pathogenesis of secondary leukemias.

Decreased cytotoxic effects of doxorubicin in a human ovarian cancer-cell line expressing wild-type p53 and WAF1/CIP1 genes

The cytotoxicity of Doxorubicin and cis-dichloro-diammine-platinum (DDP) was evaluated in clones, obtained from a human ovarian cancer cell line transfected with a temperature-sensitive p53 mutant, which express mutant p53 at 37 degrees C and wild-type-like p53 at 32 degrees C. DDP was equally active in cells not expressing p53 (SKN) or cells expressing a mutated form of p53 (SK23a kept at 37 degrees C) or a wild-type-like form of p53 (SK23a cells kept at 32 degrees C). In contrast, Doxorubicin was less cytotoxic in cells expressing wild-type p53 than in cells expressing no p53 or mutated p53. This reduction was not due to a decreased intracellular accumulation or to a faster efflux of Doxorubicin. Topoisomerase II was found to be present in the same amount in all the systems utilized and to be functionally active, thus not accounting for the observed effect of Doxorubicin. A clear induction of WAF1/CIP1 and GADD45 genes in cells expressing wild-type p53 after Doxorubicin treatment was found. DDP, which was equally active in the cells utilized, caused an increase in the transcription only of GADD45 gene but not of WAF1/CIP1 gene. Doxorubicin was also able to induce the transcription of WAF1/CIP1 gene in SKN cells (not expressing p53) or in SK23a cells at 37 degrees C (expressing mutated p53), indicating that the expression of this gene also, in some tumor-cell lines, is not necessarily or uniquely induced by wild-type p53.

Messenger RNA expression of resistance factors and their correlation to the proliferative activity in childhood acute lymphoblastic leukemia

In this report we analyzed the mRNA expression of the resistance-related enzymes DNA topoisomerase II (Topo II), thymidylate synthase (TS), glutathione S-transferase-pi (GST-pi) and glutathione peroxidase (GP) in childhood acute lymphoblastic leukemia (ALL) and their correlation to the proliferative activity, determined by Ki-67. RNA of blast cells from 54 children with untreated ALL were examined by dot blot hybridization. We found a significant positive correlation between Topo II and TS and cell proliferation. No significant correlation was detected between the mRNA expression of the glutathione-dependent enzymes GST-pi or GP and Ki-67. The results were substantiated by a semiquantitative RT-PCR-assay and by immunocytochemistry.

Abundance of nuclear DNA topoisomerase II is correlated with proliferation in Arabidopsis thaliana

Topoisomerase II (TOPII) is an important enzyme involved in DNA replication and chromosome condensation. The level of TOPII expression has been correlated with the proliferative state of eukaryotic cells. Here we report the cloning and characterization of a cDNA clone AtTopII encoding the first reported TOPII from higher plants. AtTopII is 4603 base pairs (bp) in length and encodes an open reading frame of 1473 amino acid residues. One interesting feature of AtTopII is the presence of a 110 bp direct repeat in the last one-third of the cDNA. Analysis of the genomic sequence within this region by PCR revealed that this duplication includes a small intron of 89 bp. Conservation of sequences within this repeated intron suggests that this in-frame duplication may be a relatively recent event. The deduced amino acid sequence of AtTopII shows strong homologies to TOPII sequences reported from other eukaryotes, particularly in the regions that are highly conserved among different species. Southern blot analysis with Arabidopsis DNA indicates that AtTopII is a single-copy gene while Northern blots detected a 5.0 kb transcript, the level of which is substantially higher in young seedlings than in mature plants. Using a polyclonal antiserum raised against the C-terminal one-third of AtTOPII, we found that the protein is localized in the nucleus and its level is correlated with the proliferative state of the particular tissue.

Interaction between adriamycin cytotoxicity and hyperthermia: growth-phase-dependent thermal sensitization

Thermal sensitization of adriamycin cytotoxicity was studied in vitro and in vivo using tumour cells originated from a spontaneous mouse fibrosarcoma, FSa-II. The adriamycin dose-cell survival curve for exponentially growing cells was biphasic with the initial sensitive portion followed by a resistant tail. The survival curves determined in vitro as a function of treatment time at various temperatures were also biphasic. With increasing temperatures the initial portion became steeper and the resistant fraction decreased. At a temperature of 43 degrees C, which gives lethal damage to cells by itself, the cell survival decreased rapidly during the initial 30 min of treatment and became relatively constant for subsequent treatment times up to 180 min. The tumour response determined by the median tumour growth time for one-half of treated tumours to reach 1000 mm3 from the treatment day (35 mm3) indicated that the tumour response to adriamycin was independent of temperature. Hyperthermia at 43.5 degrees C for 60 min prolonged the tumour growth time without showing chemosensitization. The maximum drug dose used was 12 mg/kg that is < LD10 or the drug dose that kills animals with < 10% probability. The dose-response curves (tumour growth versus drug dose) showed identical slopes at room temperature, 41.5 and 43.5 degrees C. Further studies were conducted in vitro. Plateau phase cells were treated with graded adriamycin doses for 60 min at 37 degrees C, or with a constant adriamycin dose of 0.25 microgram/ml for various times at 37 or 43 degrees C. The dose-cell survival curves for both exponential and plateau phase cells were biphasic, but the plateau phase cells were more resistant to adriamycin at 37 degrees C than the exponential phase cells. The survival curve for plateau phase cells, determined as a function of treatment time, showed an initial shoulder followed by an exponential portion. Compared with the heat survival curve at 43 degrees C, the survival curve for the drug treatment at 43 degrees C was identical to that for the heat alone treatment for the first 60 min and then became steeper than the heat alone survival curve. These results suggest that adriamycin cytotoxicity may be enhanced at elevated temperatures only when tumours are treated for a prolonged time or possibly with a large drug dose.

The gene encoding topoisomerase II from Plasmodium falciparum

The gene for topoisomerase II has been isolated from genomic libraries of strain K1 of the human malarial parasite, Plasmodium falciparum. The sequence reveals an open reading frame of 4194 nucleotides which predicts a polypeptide of 1398 amino acids. There are apparently no introns. The sequence is present as a single copy which has an identity of 47.4% and a similarity of 65.4% with its human homologue. Sequences conserved in topoisomerase II from other species are present in Pftopoisomerase II but in addition it has two adjacent asparagine-rich insertions which are unique to it. We have also detected asparagine-rich regions in the gene for PfDNA polymerase alpha. The gene for Pftopoisomerase II has been localised to chromosome 14 and northern analysis reveals a transcript of 5.8 kb. Two independent antisera raised in mice against glutathione-S-transferase fusion proteins containing the amino terminal portion of the malarial protein detect a weak band on western blots at about 160kDa, the expected size of the protein. Use of the same antisera for immunofluorescence analysis suggests that the protein is present at all stages of intraerythrocytic growth of the parasite.

A case of recurrent intramural uterine stromal tumor with epithelial differentiation effectively treated with oral low-dose administration of etoposide

A 66-year-old woman was diagnosed as having myoma of the uterus and total hysterectomy with bilateral salpingo-oophorectomy was performed. The histopathological findings were puzzling, and the case was finally diagnosed as intramural uterine stromal tumor with epithelial differentiation. Three years after the operation, a firm tumor developed in the pelvic cavity. Laparotomy failed to remove the tumor and neither CAP (cyclophosphamide 500 mg, adriamycin 50 mg, CDDP 70 mg) therapy nor radiation therapy was effective. Oral administration of etoposide (25 mg/day), however, showed PR (50% decrease) as determined by CT scanning, and ultrasonography, and no metastatic lesions were found. This tumor was coincident with the endometrial stromal tumor with epithelial elements classified by Clement and Scully. The histological feature of the tumors and the efficacy of oral etoposide therapy are discussed in this study.

Differential expressions of the topoisomerase II alpha and II beta mRNAs in developing rat brain

Distributions of the topoisomerase II alpha and II beta mRNAs were examined in the developing rat brain, by in situ hybridization with isoform-specific oligonucleotide probes. Intense signals for the topoisomerase II alpha mRNA were detected in the ventricular zone of each brain region at embryonic day 13-15 (E13-E15), and in the external granular layer of the cerebellum at postnatal day 7-14 (P7-P14). Thereafter, the signals rapidly decreased in levels and eventually disappeared from respective regions. Administration of bromodeoxyuridine (BrdU) into embryos at E13 showed that the topoisomerase II alpha mRNA was expressed in the BrdU-incorporated region and its ventricular side of the neural wall, suggesting that transcription of this isoform occurs in neurons from S-phase through M-phase. On the other hand, the topoisomerase II beta mRNA was distributed throughout the brain from E13 through P21, irrespective of the ventricular and mantle zones. Signal levels of the topoisomerase II beta mRNA were much stronger during early developmental stages than at mature stages in various brain regions. The characteristic and differential spatio-temporal expressions suggest that the topoisomerase II alpha is involved in the proliferation, while the topoisomerase II beta is closely related to differentiation and maturation of neurons.

Chronic oral etoposide in advanced breast cancer

Chronic oral etoposide has shown activity in some metastatic refractory tumors. To test its activity in previously treated metastatic breast cancer patients, we started a study in 18 consecutive patients given etoposide orally at 50 mg/m2 daily for 21 days. A partial response was observed in 4 of 18 patients (22%); of the responding patients, 3 had visceral metastases and 1 had multiple bone metastases. Leukopenia of grade 3 or 4 was the main hematological toxic effect (23% of patients) and alopecia was the most important nonhematological toxicity. Chronic oral etoposide shows some activity in pretreated patients with metastatic breast cancer, with tolerance being good and toxicity, acceptable. Further studies of this drug given as first-line chemotherapy or in combination with other drugs can establish all its potential activity in this cancer.

Doxorubicin-induced DNA breaks, topoisomerase II activity and gene expression in human melanoma cells

We have analyzed five human melanoma cell lines, displaying variable doxorubicin resistance (1- to 6-fold), for drug-induced DNA breaks, topoisomerase II activity and mRNA expression. Enhanced drug efflux was not the reason for doxorubicin resistance of these tumor cells although they overexpressed the transmembrane 170 kDa P-glycoprotein. Doxorubicin-induced DNA lesions (2-fold) and topoisomerase II activity (7-fold) were higher in HM-1 and G361 cells than in the less doxorubicin-sensitive NH and FCCM-9 cells. Topoisomerase II mRNA expression was also 2-fold higher in HM-1 and G361 cells. Doxorubicin-induced DNA breaks and topoisomerase II activity inversely correlated with the degree of doxorubicin sensitivity. Southern blot analysis showed variation in the hybridization pattern of topoisomerase II gene in doxorubicin-resistant cells when compared to sensitive cells. This study portrays the low doxorubicin sensitivity of NH and FCCM-9 cells as "atypical" and emphasizes the importance of DNA damage and topoisomerase II activity in cellular low doxorubicin resistance.

Cell killing and DNA damage by etoposide in Chinese hamster V79 monolayers and spheroids: influence of growth kinetics, growth environment and DNA packaging

Cells from V79 multicell spheroids must be exposed to approximately 50 times more etoposide than exponentially growing monolayers in order to produce the same amount of cell killing. A part of this difference in sensitivity is readily explained by the decrease in growth fraction of large spheroids, and by the protection afforded by nutrient deprivation which also reduces cellular ATP. However, cells composing the outer 10% of large (approximately 600 microns diameter) V79 spheroids, although actively cycling, were still ten times more resistant to etoposide than exponentially growing monolayers, regardless of whether cells were exposed in situ in spheroids or dispersed by trypsin immediately prior to exposure to the drug. Four cell doublings (48 h) as monolayers were required before the outer cells of spheroids regained drug sensitivity equivalent to that of exponentially growing monolayers. No differences in uptake/efflux of 3H-etoposide or in levels of p-glycoprotein were observed between monolayers and the outer cells of spheroids. In addition, topoisomerase II protein measured by immunoblotting and topoisomerase II activity measured by decatenation of kinetoplast DNA were not reduced in the outer cells of spheroids compared to monolayers. DNA strand breakage measured in individual cells using the DNA precipitation and comet assays correlated well with cell killing with one exception: DNA damage was not affected when cells were incubated with etoposide in phosphate-buffered saline, although the etoposide concentration required to produce a given amount of cell killing was increased approximately 7-fold compared to cells incubated with the drug in complete medium. These results indicate that etoposide toxicity towards V79 spheroids is influenced not only by proliferative status of the cells but also by factors which may include DNA packaging and the growth environment of the cell prior to and during treatment.