Unr, a cytoplasmic RNA-binding protein with cold-shock domains, is involved in control of apoptosis in ES and HuH7 cells

Unr (upstream of N-ras) is a cytoplasmic RNA-binding protein involved in the regulation of messenger RNA stability and internal initiation of translation. We have used Unr-deficient murine embryonic stem (ES) cells to analyse Unr role in cell proliferation and response to stress. Disruption of both unr gene copies had no effect on ES cell proliferation. However, after ionizing radiation (IR), clonogenic survival of unr(-/-) ES cells was approximately 3-fold enhanced as compared to unr(+/+) cells. We further determined that IR-induced apoptosis was decreased in unr(-/-) ES cells, and that reintroduction of the unr gene in unr(-/-) cells restored normal IR-induced apoptosis. Three pro-apoptotic genes, p53, caspase-3 and Gadd45gamma, were downregulated in unr(-/-) ES cells, indicating that Unr, as other cytoplasmic RNA-binding proteins, regulates a complex genetic program, promoting cell death after IR. In contrast, in the human hepatoma cell line HuH7, Unr knockdown using unr-specific small interfering RNAs induced apoptosis, both in untreated and gamma-irradiated cells. Thus, our results establish that Unr acts as a positive or negative regulator of cell death, depending on the cell type. Manipulating the level of Unr may constitute a specific approach to sensitize cancer cells to anticancer treatments.

Cellular resistance to the antitumor DNA topoisomerase II inhibitor S16020-2: importance of the N-[2(Dimethylamino)ethyl]carbamoyl side chain

The new olivacine derivative S16020-2 (NSC-659687) is a DNA topoisomerase II inhibitor endowed with a remarkable antitumor activity against various experimental tumors. In vitro physicochemical properties of this compound, in particular its interaction with DNA and DNA topoisomerase II, were very similar to those of ellipticine derivatives, except for a strictly ATP-dependent mechanism of cleavable complex induction. From the Chinese hamster lung fibroblast cell line DC-3F, a subline resistant to S16020-2, named DC-3F/S16, was selected by adding stepwise increasing concentrations of the drug to the cell growth medium. Whereas DC-3F/9-OH-E cells, a DC-3F subline resistant to 9-hydroxy-ellipticine, are cross-resistant to S16020-2, DC-3F/S16 cells are only very weakly cross-resistant to ellipticine derivatives, indicating that, despite their structural similarity, these compounds may differ in their mechanisms of action. Uptake and efflux rates of S16020-2 were identical in the resistant and the sensitive cells. Topoisomerase IIalpha was expressed at the same level in both sensitive and resistant cells, whereas expression of the beta-enzyme was approximately 50% lower in the resistant cells. Sequencing of both alpha- and beta-isoform cDNAs revealed a point mutation that converts Arg(486) to a Gly in the alpha cDNA, whereas the beta cDNA was not modified. This amino acid substitution in a highly conserved sequence of the enzyme appears to be responsible for the resistance to S16020-2. Comparative analysis of the properties of the ellipticine and S16020-2-resistant cells suggests that S16020-2, which is a DNA intercalator, might also interact with this enzyme amino acid sequence through its side chain.

Modified alkaline elution allows the measurement of intact apurinic sites in mammalian genomic DNA

The presence of apurinic/apyrimidinic (AP) sites in cell genomes is known to be toxic and mutagenic. These lesions are therefore repaired in cells by efficient enzymatic systems. However, a report (Nakamura and Swenberg, Cancer Res. 59 (1999) 2522-2526) indicates an unexpected high rate of endogenous apurinic/apyrimidinic (AP) sites in genomic DNA in mammalian tissues. The technology used does not allow the authors to distinguish between intact AP sites and 3'cleaved AP sites. The corresponding values range between 2 and 4 sites per million of nucleotides in various human and rat tissues. Using a modified alkaline elution method we show here that the stationary level of intact AP sites is about 0.16 per million of nucleotides in leukemic mouse L1210 cells.

Hematologic recovery in mice transplanted with bone marrow stem cells expressing anti-human immunodeficiency virus genes

We have used a mouse bone marrow transplantation (BMT) model to study the safety of retrovirus-mediated transfer of anti-HIV genes (RevM10 and HIV-1 pol antisense) into hematopoietic stem/progenitor cells (HSPCs). In particular, we have monitored the hematologic recovery post-BMT and transgene expression in myeloid and lymphoid lineages, and analyzed tissue sections for evidence of any transgene-related pathological condition. Expression of anti-HIV genes had no effect on kinetics of hematologic recovery post-BMT. The average time to reach 20% of normal cell counts was 15-17 days for white blood cells and 12-14 days for platelets, and the average time to reach complete recovery was 42-56 days for leukocytes and 104-161 days for platelets. Hematocrit levels were not significantly affected by irradiation and transplantation procedures. Donor chimerism was uniformly > or =90% in all transplanted animals. At 4-5 weeks post-BMT transgene expression was detected in peripheral blood leukocytes in 100% of the animals and ranged from 4.5 to 44.7%. In a majority of the animals the percentage of transgene-expressing cells in circulation decreased over time but remained detectable for the length of the study (>6 months). Expression was detected in all analyzed cell lineages (RBCs, platelets, monocytes, granulocytes, and T and B cells). Relative counts of various leukocytes (Mac1+ monocytes, Gr1+ granulocytes, CD3+ T cells, and B220+ B cells) were normal. There were no treatment-related histopathological changes in a wide range of tissues examined. In addition, there were no treatment effects on differential leukocyte counts, and morphology of peripheral blood and bone marrow brush smears. In summary, transfer and expression of the RevM10 and the HIV-1 antisense genes into hematopoietic stem/progenitor cells in vivo appears safe. We propose that the mouse bone marrow transplantation model could be used to evaluate some safety aspects of HSPC-based gene therapies.

Transfection of 9-hydroxyellipticine-resistant Chinese hamster fibroblasts with human topoisomerase IIalpha cDNA: selective restoration of the sensitivity to DNA religation inhibitors

In the Chinese hamster lung cell line DC-3F/9-OH-E, selected for resistance to 9-OH-ellipticine and cross-resistant to other topoisomerase II inhibitors, the amount of topoisomerase IIalpha is 4-5-fold lower than in the parental DC-3F cells, whereas topoisomerase IIbeta is undetectable. Cloning and sequencing of topoisomerase IIalpha cDNAs from DC-3F and DC-3F/9-OH-E cells revealed an allele polymorphism, one allele differing from the other by the presence of seven silent mutations and three mutations in the noncoding region. In addition, the mutated allele contains three missense mutations located close to the ATP binding site (Thr371Ser) or to the catalytic site (Ala751Gly; Ile863Thr). To analyze the contribution of these topoisomerase IIalpha alterations to their resistance phenotype, DC-3F/9-OH-E cells were transfected with an eukaryotic expression vector containing the human topoisomerase IIalpha cDNA. In one transfected clone, the amount of topoisomerase IIalpha isoform and the catalytic activity were similar to that in the parental DC-3F cells. These cells, which contain only topoisomerase IIalpha, are then a unique mammalian cell line to analyze the physiological and pharmacological properties of this enzyme. However, the restoration of a nearly normal topoisomerase IIalpha activity in the DC-3F/9-OH-E cells did not have the same effect on their sensitivity to different enzyme inhibitors; a 75% reversion of the resistance, associated with a 2-3-fold increased stabilization of the cleavable complex, was observed with both etoposide and m-AMSA, two drugs that inhibit the DNA religation step in the enzyme catalytic cycle; in contrast, the transfected cells remained fully resistant to ellipticine derivatives that did not induce the stabilization of the cleavable complex. We hypothesized that a trans-acting factor, inhibiting the induction of cleavable complex formation by drugs that are not religation inhibitors, might be present in the resistant cells. However, such a factor was not detected in in vitro experiments, and other hypotheses are discussed.

Menadione (vitamin K3) enhances the mitogenic signal of epidermal growth factor via extracellular signal-regulated kinases

The effects of vitamin K3 (VK3) on DNA synthesis, cell proliferation and mitogen-activated protein kinase pathway were investigated in G0-arrested NIH 3T3 fibroblasts. VK3 (5 microM) alone stimulates DNA synthesis by 40% and moderately increases the mitogenic effects of EGF, which is preceded by a rapid phosphorylation of the extracellular signal-regulated kinases (ERKs). At 20 microM, VK3 had an antiproliferative effect. VK3 alone (5 and 50 microM) or in concert with EGF increases the activity of ERK2 (by 2.5 and 5 fold, respectively). Our studies demonstrate that the activation of ERKs by VK3 alone, or VK3 plus EGF can promote either stimulatory or inhibitory effects on the mitogenic signal.

DNA topoisomerases as repair enzymes: mechanism(s) of action and regulation by p53

DNA topoisomerases regulate the organization of DNA and are important targets for many clinically used antineoplastic agents. In addition, DNA topoisomerases modulate the cellular sensitivity toward a number of DNA damaging agents. Increased topoisomerase II activities were shown to contribute to the resistance of both nitrogen mustard- and cisplatin-resistant cells. Similarly, cells with decreased topoisomerase II levels show increased sensitivity to cisplatin, carmustine, mitomycin C and nitrogen mustard. Recent studies propose that topoisomerases may be involved in damage recognition and DNA repair at several different levels including: 1) the initial recognition of DNA lesions; 2) DNA recombination; and 3) regulation of DNA structure. The stress-activated oncogene suppressor protein p53 can modulate the activity of at least three different human topoisomerases, either directly by molecular associations or by transcriptional regulation. Since DNA topoisomerases have considerable recombinase activities, inappropriately activated topoisomerases in tumor cells lacking functional p53 may contribute to the genetic instability of these cells.

DNA topoisomerases as repair enzymes: mechanism(s) of action and regulation by p53

DNA topoisomerases regulate the organization of DNA and are important targets for many clinically used antineoplastic agents. In addition, DNA topoisomerases modulate the cellular sensitivity toward a number of DNA damaging agents. Increased topoisomerase II activities were shown to contribute to the resistance of both nitrogen mustard- and cisplatin-resistant cells. Similarly, cells with decreased topoisomerase II levels show increased sensitivity to cisplatin, carmustine, mitomycin C and nitrogen mustard. Recent studies propose that topoisomerases may be involved in damage recognition and DNA repair at several different levels including: 1) the initial recognition of DNA lesions; 2) DNA recombination; and 3) regulation of DNA structure. The stress-activated oncogene suppressor protein p53 can modulate the activity of at least three different human topoisomerases, either directly by molecular associations or by transcriptional regulation. Since DNA topoisomerases have considerable recombinase activities, inappropriately activated topoisomerases in tumor cells lacking functional p53 may contribute to the genetic instability of these cells.

S16020-2, a new highly cytotoxic antitumor olivacine derivative: DNA interaction and DNA topoisomerase II inhibition

S16020-2 (NSC-659687) is a new olivacine derivative that is highly cytotoxic in vitro and displays remarkable antitumor activity against various experimental tumors, especially some solid tumor models. Its antitumor activity is notably higher than that of 2-methyl-9-hydroxy-ellipticinium (NMHE) and comparable to that of doxorubicin HCl, although with a different tumor specificity. S16020-2 is being tested in phase I clinical trials. A study of the interaction of S16020-2 with DNA showed that it binds through intercalation between adjacent DNA base pairs, inducing an unwinding of 10 degrees of the double helix. Its DNA affinity is approximately equal to that of NMHE and decreases as a function of the salt concentration, indicating a significant electrostatic contribution to the overall binding free energy. S16020-2 did not interfere with the catalytic cycle of DNA topoisomerase I but stimulated DNA topoisomerase II-mediated DNA cleavage via a strictly ATP-dependent mechanism. The interactions of S16020-2 and NMHE with DNA topoisomerase II in vitro are very similar. Both drugs have the same DNA sequence specificity of cleavage and the same biphasic dose-effect response, and neither drug inhibited the rate of DNA religation. In contrast with these observations, in in vivo experiments, S16020-2 was able to induce topoisomerase II-mediated DNA strand breaks at concentrations 500-fold lower than NMHE. We conclude that DNA topoisomerase II most likely is the cellular target involved in the mechanism of cytotoxicity of S16020-2. Its higher biological activity and potency to induce cellular DNA cleavage suggest the involvement of as-yet-unidentified cellular factors.

Genistein resistance in human leukaemic CCRF-CEM cells: selection of a diploid cell line with reduced DNA topoisomerase II beta isoform

Genistein, an isoflavonoid derivative initially described as an in vitro protein tyrosine kinase inhibitor, also inhibits mammalian DNA topoisomerase II both in vitro and in vivo. From a human leukaemic T cell line (CCRF-CEM), two genistein-resistant cell lines, which grow in the presence of 50 and 150 microM genistein, respectively, were selected and designated CEM/GN50 and CEM/GN150. Flow cytometry and karyotype analyses revealed that more than 95% of the parental cells were tetraploid whereas both resistant sublines were essentially diploid and were likely derived from the diploid fraction in the initial population. The CEM/GN cells were 3- to 4-fold resistant to genistein, and highly cross-resistant to certain metabolic inhibitors such as cytosine-arabinoside (50-fold) and 5-fluoro-2'-deoxyuridine (5000-fold). This resistance was associated with a markedly decreased uptake of thymidine and a 10-fold reduction in thymidine kinase activity. The CEM/GM cells were also 15- to 30-fold cross-resistant to topoisomerase inhibitors (etoposide, m-AMSA, 2-Me-9-OH-ellipticinium). Comparison of topoisomerase II activities in the sensitive and resistant cells showed: (i) an approximately 2-fold reduced decatenation activity in nuclear extracts from the resistant cells; (ii) an approximate 30% reduction in DNA-protein cross-links in etoposide-treated resistant cells; and (iii) a markedly reduced expression of the topoisomerase II beta isoform. These data, consistent with our previous results, indicate that the cytotoxicity of genistein is at least in part related to its capacity to inhibit DNA topoisomerase II.

Inhibition of DNA topoisomerases I and II and induction of apoptosis by erbstatin and tyrphostin derivatives

Inhibitors of protein tyrosine kinases (PTK) and DNA topoisomerases are potential antitumour agents. Drugs which bind to the ATP site of PTK, such as genistein, are common inhibitors to both types of enzymes. Eleven erbstatin and tyrphostin derivatives, which inhibit epidermal growth factor receptor PTK activity by competing with both the peptide substrate and ATP were tested for their capacity to inhibit DNA topoisomerases I and II. Erbstatin, two synthetic derivatives with a modified side chain and the tyrphostin AG 786 inhibited both topoisomerases in the same range of concentrations (20-50 microM). The tyrphostin AG 213 inhibited only topoisomerase II. In this series, absence of PTK inhibitory effect was correlated with the absence of DNA topoisomerase inhibition, while the detection of PTK inhibition may or may not be associated with DNA topoisomerase inhibition. In contrast to genistein, none of these molecules induced the stabilization of the topoisomerase-DNA cleavable complex, either in vitro or in vivo. Alcaline elution analysis revealed that erbstatin did not induce the formation of protein associated DNA strand breaks. However, an extensive degradation of the cellular DNA was observed which was shown to result from an internucleosomal fragmentation. Furthermore, typical morphological modifications associated with apoptosis were observed in the erbstatin treated cells by electron microscopy. These data indicate that erbstatin induces an apoptotic cell death.

[Cellular resistance to DNA-topoisomerase II inhibitors]

Chinese hamster lung cells resistant to 9-OH-ellipticine (DC-3F/9-OH-E) present a complex phenotype. These cells, which are about 150-fold resistant to 9-OH-E, display a cross-resistance to other topo-II inhibitors, such as m-AMSA or VP-16, which stabilize the cleavable complex. In addition, these cells display also a cross-resistance to suramin, which is also a topo-II inhibitor, but does not stabilize the cleavable complex. Finally, DC-3F/9-OH-E present a multidrug-resistant phenotype (MDR) which confers a cross-resistance to natural products such as actinomycin D, taxol or vincristine, due to a decrease of cellular accumulation of these drugs. Analysis of expression of the genes encoding topo-II alpha and beta, and the evaluation of both enzyme forms by immunoblotting, revealed that DC-3F cells contained about 20-fold less of the beta form than of the alpha form. The alpha form was decreased by about 4-5-fold in DC-3F/9-OH-E, whereas the beta form became undetectable. Purification and characterization of topo-II activities in sensitive and resistant cells is presently in progress. Analysis of the expression of pgp1, 2, 3 genes, involved in the MDR phenotype in hamster, by Northern blotting or by immunoblotting, has shown that the MDR phenotype in DC-3F/9-OH-E cells is due to the overexpression of pgp1 gene. In these cells, pgp3 expression is positively regulated by myc oncogene expression. Overexpression of the myc gene is followed by an overexpression of the pgp3 gene and is associated to a reversal of the MDR phenotype.

Suramin is an inhibitor of DNA topoisomerase II in vitro and in Chinese hamster fibrosarcoma cells

The antitrypanosomal and antifiliarial drug suramin is currently under investigation for treatment of advanced malignancies including prostatic cancer, adrenocortical cancer, and some lymphomas and sarcomas. Here we show that suramin is a potent inhibitor of the nuclear enzyme DNA topoisomerase II. Suramin inhibited purified yeast topoisomerase II with an IC50 of about 5 microM, as measured by decatenation or relaxation assays. Suramin did not stabilize the covalent DNA-topoisomerase II reaction intermediate ("cleavable complex"), whereas other inhibitors of this enzyme, such as amsacrine, etoposide, and the ellipticines, are known to stabilize the intermediate. In contrast, the presence of suramin strongly inhibited the cleavable-complex formation induced by amsacrine or etoposide. Accumulation of the endogenous cleavable complex was also inhibited. Suramin entered the nucleus of DC-3F Chinese hamster fibrosarcoma cells exposed to radiolabeled suramin for 24 hr as shown by both optic and electron microscopy. The suramin present in the nucleus seemed to interact with topoisomerase II, since suramin reduced the number of amsacrine-induced protein-associated DNA strand breaks in DC-3F cells and protected these cells from the cytotoxic action of amsacrine. Cells resistant to 9-hydroxyellipticine, which have been shown to have an altered topoisomerase II activity, are about 7-fold more resistant to suramin than the sensitive parental cells as shown by 72-hr growth inhibition assay. Our results suggest that DNA topoisomerase II is a target of suramin action and that this action may play a role in the cytotoxic activity of suramin.

Potentiation of TNF-mediated cell killing by VP-16: relationship to DNA single-strand break formation

Interaction between tumor necrosis factor (TNF) and the DNA topoisomerase II inhibitor, etoposide VP-16, in cell killing has been studied. To accurately investigate the nature of DNA damage during the cell killing process, experiments were assessed using the highly TNF-sensitive WEHI164.13 murine fibrosarcoma clone and DNA filter elution methodology. Concomitant treatment of cells with combination of TNF/VP-16 resulted in marked enhancement of cell lysis. Using the alkaline elution technique, we show that TNF fails to induce DNA single-strand breaks as compared to those generated by VP-16. In addition, the potentiating effect of VP-16 on TNF-mediated WEHI164.13 cell killing was not associated with an increase in its intrinsic activity with respect to DNA single-strand break formation. While the 2 phospholipase A2 inhibitors, quinacrine and dexamethasone, were efficient in inhibiting TNF-mediated cell lysis, only quinacrine was efficient in selectively abrogating the TNF/VP-16 cell killing pathway. The inhibitory effect of quinacrine on VP-16/TNF-mediated cell lysis was accompanied by a marked decrease in VP-16-mediated DNA single-strand break generation. Taken together, our findings suggest that TNF and TNF/VP-16 treatments may involve different events during cell killing and support the hypothesis that 2 signals are required for optimal induction of cell lysis by the combination of VP-16/TNF: one signal provided by VP-16 resulting in topoisomerase II inhibition and subsequent DNA single-strand break generation, and a second signal involving TNF.

Effects of morpholinyl doxorubicins, doxorubicin, and actinomycin D on mammalian DNA topoisomerases I and II

The effect of cyanomorpholinyldoxorubicin, morpholinyldoxorubicin, doxorubicin, and Actinomycin D were studied on purified mouse leukemia (L1210) DNA topoisomerases I and II. DNA unwinding and cross-linking were also studied. It was found that 1) morpholinyldoxorubicin, cyanomorpholinyldoxorubicin, and Actinomycin D (but not doxorubicin) stimulated DNA topoisomerase I-induced cleavage at specific DNA sites; 2) only doxorubicin and Actinomycin D stimulated DNA cleavage by DNA topoisomerase II; 3) at higher drug concentrations, DNA intercalators suppressed enzyme-mediated DNA cleavage induced by DNA topoisomerase I, as well as topoisomerase II; 4) only cyanomorpholinyldoxorubicin produced DNA-DNA cross-links; no DNA unwinding could be observed; and 5) DNA intercalation (unwinding) potency of morpholinyldoxorubicin was about 2-fold less than that of doxorubicin. The data indicate that some DNA intercalators are not only inhibitors of DNA topoisomerase II but act also on DNA topoisomerase I. The stabilization of cleavage intermediates by intercalators may have a common mechanism for DNA topoisomerase I and DNA topoisomerase II.

DNase I susceptibility of bent DNA and its alteration by ditercalinium and distamycin

The bending of kinetoplast DNA from Crithidia fasciculata is thought to be related to the periodic distribution of AA or TT cluster sequences. The sensitivity to DNase I of the two strands of this DNA was analyzed at nucleotide resolution by sequencing gel electrophoresis. The effect on the DNase I cleavage pattern of two drugs, ditercalinium and distamycin, that are able to remove bending was analyzed. The same analysis was done on a pBR 322 DNA fragment of random sequence as a control. The periodic distribution of the AA or TT clusters in the bent DNA fragment was first analyzed by computing the autocorrelation function of the AA or TT clusters in the bent DNA fragment. It is shown that the AT tracts are on average 10.5 base pairs apart. This value is almost identical with that of the B-DNA helix pitch in solution [10.5 (Wang, 1979); 10.6 +/- 0.1 (Rhodes & Klug, 1980)]. To reveal the periodic pattern of DNase I cleavage on this bent DNA, alone or in presence of drugs, the cross correlation between the different bands obtained from DNAse I cleavage and the presence of AA or TT sequences was computed. This shows that GC and mixed sequences are the most sensitive regions. These data also suggest that there is a periodic fluctuation in the width of the minor groove in the bent fragment. Ditercalinium and distamycin alter the DNase I cutting pattern of the bent DNA fragment but in an inverse fashion.(ABSTRACT TRUNCATED AT 250 WORDS)

Low concentrations of acridine dimers inhibit micrococcus AP endonuclease through interaction with apurinic sites in DNA

The effect of dimeric DNA intercalating compounds was assayed on a purified AP endonuclease from Microccoccus luteus using apurinic supercoiled PM2 DNA as a substrate. Binding on apurinic sites was estimated through the competition with the intercalating compound, 9-NH2-ellipticine, which displays great specificity for apurinic sites. An acridine dimer with a spermine linker is at 0.1 microM the best inhibitor of cleavage at the apurinic site induced either by the AP endonuclease or by 9-NH2-ellipticine. Bisintercalating agents are more effective inhibitors of AP endonuclease than monointercalating ones. Most effective inhibitors among dimers have acridine residues.

Inhibitory effects of the tyrosine kinase inhibitor genistein on mammalian DNA topoisomerase II

Tyrosine phosphorylation plays a crucial role in cell proliferation and cell transformation which suggests that tyrosine kinase-specific inhibitors might be used as anticancer agents. When the cytotoxic effect of the potent tyrosine kinase inhibitor genistein on various cell lines was studied, we observed that 9-hydroxyellipticine-resistant Chinese hamster lung cells (DC-3F/9-OH-E) were markedly more resistant to genistein than the parental cell line (DC-3F). The DC-3F/9-OH-E cells have been shown to have an altered DNA topoisomerase II activity. We therefore examined the effects of genistein on DNA topoisomerase II-related activities of nuclear extracts from DC-3F cells as well as on purified DNA topoisomerase II from calf thymus. Our results show that genistein (a) inhibits the decatenation activity of DNA topoisomerase II and (b) stimulates DNA topoisomerase II-mediated double strand breaks in pBR322 DNA on sites different from those of 4'-(9-acridinylamino)methanesulfon-m-anisidide, etoposide, and 2-methyl-9-hydroxyellipticinium. Structure-activity studies with six chemically related compounds show that only genistein has an effect on the cleavage activity of DNA topoisomerase II in the concentration range studied. Finally, genistein treatment of DC-3F cells results in the occurrence of protein-linked DNA strand breaks as shown by DNA filter elution. Viscometric (lengthening) studies demonstrate that genistein is not a DNA intercalator. Genistein is therefore an interesting compound because it induces cleavable complexes without intercalation. Taken together, our results show that genistein is an inhibitor of both protein tyrosine kinases and mammalian DNA topoisomerase II. This could be accounted for by the sharing of a common structure sequence between the two proteins at the ATP binding site.

A monoclonal anti-double-stranded DNA autoantibody binds to a 94-kDa cell-surface protein on various cell types via nucleosomes or a DNA-histone complex

A crude supernatant of hybridoma secreting a monoclonal anti-double-stranded (ds)DNA antibody (PME77 mAb), used to stain fibroblasts (CVI cells) in immunofluorescence, gives a punctuated staining of variable intensity. We had suggested that anti-DNA antibodies bind to cell-surface protein(s) of several cells. When the mAb of this crude supernatant was purified on a dsDNA-cellulose column and a histone-Trisacryl column, the mAb no longer bound to the cell surface. Only when dsDNA plus purified histones was added to the purified antibody did the immune complex strongly and uniformly stain again the cell surface of CVI cells. No significant staining was observed if either DNA or histones were omitted. A signal 94-kDa protein from membrane fractions of CVI, Raji, and RINm cell lines was visualized in immunoblots when mAb-DNA-histone complexes were applied to the nitrocellulose strips. No polypeptide was seen if one component was omitted. This 94-kDa protein behaved like a plasma membrane protein since it required the use of detergent to be solubilized and was quantitatively recovered in the Triton X-114 detergent-rich phase. Moreover, a brief treatment of living cells with trypsin cleared off this protein. Purified nucleosomes could be substituted to DNA-histone complexes, giving rise to identical results. Finally, purified polyclonal anti-DNA antibodies from sera of systemic lupus erythematosus patients labeled a 94-kDa protein provided that DNA-histone complexes were added. Anti-DNA autoantibodies could be pathogenic when they are bound to nucleosomes.

Acridine dimers: influence of the intercalating ring and of the linking-chain nature on the equilibrium and kinetic DNA-binding parameters

The rigidity of the linking chain of bifunctional intercalators in the ditercalinium series was shown to be critical for antitumor activity. In order to study the influence of the rigidity of the linking chain on the DNA-binding properties of DNA bifunctional intercalators, fluorescent 9-aminoacridine and 2-methoxy-6-chloro-9-aminoacridine analogues with chains of variable rigidity were synthesized. 1H-NMR studies show that the conformation of 9-aminoacridine dimers is almost independent of the nature of the linking chain. A strong self-stacking of the aromatic rings of the 2-methoxy-6-chloro-9-aminoacridine is observed for dimers with flexible chains but not for those with rigid chains. All the dimers having a linking chain long enough to bisintercalate in DNA according to the excluded site model are indeed bisintercalators. The kinetic association constant of all monomers and dimers for poly[d(A-T)].poly[d(A-T)] are in the same range (2-4 x 10(7) M-1 s-1). The large increase of DNA binding affinity observed for the dimers is always associated with the expected decrease of the dissociation rate constant. The effect of chain rigidity and pH on the calf thymus DNA binding of 9-aminoacridine and 2-methoxy-6-chloro-9-aminoacridine dimers is quite different. In the series of 9-aminoacridine the pKa of the dimers remains high and therefore no difference of DNA-binding affinity is observed between pH 5 and 7.4. The rigidity of the linking chain does not significantly alter the DNA-binding affinity. In the 2-methoxy-6-chloro-9-aminoacridine series, the pKa of all dimers became smaller than the physiological pH and a dramatic decrease of DNA-binding affinity is observed when the pH is increased from pH 5 to 7.4. This decrease appears significantly smaller for dimers with rigid chains. A similar dramatic decrease of binding affinity at pH 7.4 is not observed for poly[d(A-T)].poly[d(A-T)]. This factor makes these dimers strongly specific for the alternating polymer at pH 7.4.

DNA binding, cytotoxicity and inhibitory effect on RNA synthesis of two new 1-nitro-9-aminoacridine dimers

Two 1-nitro-9-aminoacridine dimers were prepared: one bearing a spermine flexible linking chain, compound 4, the other a rigid dipiperidine-type linker, compound 7. Both dimers elicited a higher affinity constant for DNA than the parent monomeric drug nitracrine 2. This affinity was several orders lower than what was found for other dimeric compounds having the same linkers and no nitro group on the acridine ring (3, 5, 6 and 8). Bisintercalation was evidenced for compound 4 by viscosimetric measurements. In the absence of dithiothreitol, an inhibitory effect of RNA synthesis in vitro was observed for all the tested compounds except 2 and 7. In the presence of dithiothreitol, 4 and 7 formed irreversible complexes with DNA of decreased template properties. The level of the dimers binding was lower than that of the parent compound 2. Cross-links were detected by means of hydroxylapatite chromatography in a complex of the dimer bearing a flexible linking chain, compound 4 with DNA, while the compound 7-DNA complex eluted in the single-stranded DNA region. The extent of cytotoxicity of the two 1-nitro-9-aminoacridine dimers against L1210 cultured cells was different.

Role of DNA intercalation in the inhibition of purified mouse leukemia (L1210) DNA topoisomerase II by 9-aminoacridines

An attempt was made to analyze the mechanism by which 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA) inhibits mammalian DNA topoisomerase II. The effects of various 9-aminoacridine derivatives differing by their DNA affinities and DNA sequence selectivity of binding were compared in the presence of purified mouse leukemia L1210 DNA topoisomerase II. No correlation was found between DNA unwinding and topoisomerase II inhibition. 9-Aminoacridine was inactive as a topoisomerase II inhibitor and o-AMSA was only weakly active. The location of L1210 topoisomerase II mediated DNA breaks produced in the absence or presence of 9-aminoacridines were studied in [32P]-end-labeled pBR 322 DNA. All 9-aminoacridines, even those differing by their DNA sequence selectivity of binding, produced similar DNA cleavage patterns. Most drug-induced topoisomerase II mediated DNA breaks appeared at sites that were already cleaved by the enzyme in the absence of drug. The present results suggest that 9-aminoacridines inhibit L1210 DNA topoisomerase II by interacting at or near enzyme-DNA complexes by some unknown DNA effect or by direct protein interaction.

DNA unwinding and inhibition of mouse leukemia L1210 DNA topoisomerase I by intercalators

The DNA unwinding effects of some 9-aminoacridine derivatives were compared under reaction conditions that could be used to study drug-induced topoisomerase II inhibition. An assay was designed to determine drug-induced DNA unwinding by using L1210 topoisomerase I. 9-aminoacridines could be ranked by decreasing unwinding potency: compound C greater than or equal to 9-aminoacridine greater than o-AMSA greater than or equal to compound A greater than compound B greater than m-AMSA. Ethidium bromide was more potent than any of the 9-aminoacridines. This assay is a fast and simple method to compare DNA unwinding effects of intercalators. It led to the definition of a drug intrinsic unwinding constant (k). An additional finding was that all 9-aminoacridines and ethidium bromide inhibited L1210 topoisomerase I. Enzyme inhibition was detectable at low enzyme concentrations (less than or equal to 1 unit) and when the kinetics of topoisomerase I-mediated DNA relaxation was studied. Topoisomerase I inhibition was not associated with DNA swivelling or cleavage.

Topoisomerase II-mediated DNA breaks and cytotoxicity in relation to cell proliferation and the cell cycle in NIH 3T3 fibroblasts and L1210 leukemia cells

The DNA intercalator, 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA) and the nonintercalator, etoposide (VP-16) produce topoisomerase II-mediated protein-linked DNA strand breaks. This function of topoisomerase II was investigated in relation to cell proliferation and cell cycle. Mouse fibroblasts NIH 3T3 and mouse leukemia L1210 cells stop proliferation when they reach a certain density. Nuclei were isolated from proliferative or quiescent cells and then treated with drug for 30 min. DNA modifications were assayed by alkaline elution. We found that the frequencies of m-AMSA- or VP-16-induced DNA-protein links were higher in nuclei from exponentially growing than in those from quiescent cells in both the 3T3 and the L1210 lines. Drug-induced protein-associated DNA breaks were also studied as a function of the cell cycle in 3T3 cells that had been arrested by contact inhibition in medium containing 1% calf serum and then stimulated to proliferate by raplating at a lower cell density in medium containing 10% serum. In these synchronized cells, a large peak of [3H]thymidine incorporation occurred 18-30 h after replating. The yield of DNA-protein cross-links produced by 30-min drug treatments of nuclei isolated at various times after growth initiation increased concomitantly with the peak of the DNA synthesis. The topoisomerase II activity of nuclear extracts, as measured by kinetoplast DNA decatenation followed a similar pattern. Using colony-forming assays, we also observed that m-AMSA and VP-16 were most cytotoxic in proliferative cells and during DNA synthesis. These results suggest that alkaline elution measurement of m-AMSA- or VP-16-induced protein-linked DNA breaks reflects the association of topoisomerase II with DNA. This association is increased during DNA replication, making the cells more vulnerable to m-AMSA and VP-16 at this time.

Effects of the bifunctional antitumor intercalator ditercalinium on DNA in mouse leukemia L1210 cells and DNA topoisomerase II

Ditercalinium, a 7H-pyridocarbazole dimer (bisintercalator) belongs to a new class of antineoplastic intercalating agents. To investigate its mechanism of cytotoxicity, the effects of ditercalinium on DNA were assessed using normal (L1210) and drug-resistant (L1210/PyDi1) mouse leukemia cells. Alkaline elution assays demonstrated that ditercalinium produced no DNA strand breaks, DNA-protein cross-links, or DNA-DNA cross-links, eliminating these effects as cytotoxic lesions. This result sets ditercalinium apart from other intercalating agents with respect to its interaction with DNA. Nucleoids (histone-depleted chromatin) from ditercalinium-treated L1210 cells were considerably more compact than those from untreated cells, as determined by sedimentation in neutral sucrose gradients. In contrast, nucleoids from ditercalinium-treated L1210/PyDi1 (resistant) cells were similar in compactness to those from control cells. Thus, ditercalinium altered chromatin structure in vivo. The effect of the bisintercalator on purified DNA topoisomerase II, an intracellular target of monointercalators, was measured in vitro. Ditercalinium (5 X 10(-7) M) completely inhibited both the formation of covalent complexes between this enzyme and simian virus 40 DNA and the enzyme-induced DNA cleavage. In addition, ditercalinium induced DNA catenation in the presence of topoisomerase II and adenosine triphosphate. Thus, the cytotoxicity of ditercalinium may derive from a mechanism that, although involving topoisomerase II, is manifested by condensation of DNA rather than by the induction of protein-associated DNA strand breaks.

Synthesis of 11H-pyridocarbazoles and derivatives. Comparison of their DNA binding and antitumor activity with those of 6H- and 7H-pyridocarbazoles

The 8-methoxy- and 8-hydroxy-11H-pyrido[2,3-a]-, -[3,4-a]-, -[4,3-a]-, and [3,2-a]carbazoles were synthesized as potential DNA intercalating antitumor drugs. The structure of these compounds was confirmed by 1H NMR study including NOE experiments. The DNA binding properties of substituted and unsubstituted (8-H) heterocycles were determined by using their hydrochlorides or methiodides. These derivatives are able to bind to DNA with an affinity varying from 2.0 X 10(4) to 1.0 X 10(6) M-1, but most of them are unable to intercalate in contrast with the behavior of 6H- and 7H-pyridocarbazole analogues. The cytotoxicity of 11H-pyridocarbazoles, measured on L1210 cells in vitro, is much lower than those of 6H- and 7H-pyridocarbazole analogues.

Trypanosomiasis and laryngeal paralysis in a dog

Laryngeal paralysis and trypanosomiasis were diagnosed in a 12-year-old Labrador Retriever. Bilateral vocal fold resection and partial excision of the left aryepiglottic fold resolved the dog's respiratory difficulty. Trypomastigotes resembling Trypanosoma cruzi were seen in blood smears during hospitalization. In spite of treatment with nifurtimox and dexamethasone, the dog died. Histologic examination of tissues did not reveal amastigotes of T cruzi or granulomatous myositis previously described in canine trypanosomiasis reported from North America. The lack of granulomatous myositis and amastigotes in muscle is unusual and suggests a strain variation in the behavior of T cruzi.

DNA tris-intercalation: first acridine trimer with DNA affinity in the range of DNA regulatory proteins. Kinetic studies

A trimer made up of three acridine chromophores linked by a positively charged poly(aminoalkyl) chain was synthesized as a potential tris-intercalating agent. The length of the linking chain was selected to allow intercalation of each chromophore according to the excluded site model. 1H NMR studies have shown that, at 5 mM sodium, pH 5, the acridine trimer occurred under a folded conformation stabilized by stacking interactions between the three aromatic rings. DNA tris-intercalation of the dye at a low dye/base pair ratio was shown by measurements of both the unwinding of PM2 DNA and the lengthening of sonicated rodlike DNA. The trimer exhibits a high DNA affinity for poly[d(A-T)] (Kapp = 8 X 10(8) M-1, 1 M sodium) as shown by competition experiments with ethidium dimer. Kinetic studies of both the association with poly[d(A-T)] and the exchange between poly[d(A-T)] and sonicated calf thymus DNA have been performed as a function of the ionic strength. In 0.3 M sodium the on-rate constant (k1 = 2.6 X 10(7) M-1 s-1) is similar to that reported for other monoacridines or bis(acridines), whereas the off-rate constant is much smaller (k-1 = 1.2 X 10(-4) s-1), leading to an equilibrium binding constant as large as Kapp = 2.2 X 10(11) M-1. A plot of log (k1/k-1) as a function of log [Na+] yielded a straight line whose slope shows that 5.7 ion pairs (out of 7 potential) are formed upon the interaction with DNA. From this linear relationship a Kapp value of 10(14) M-1 in 0.1 M sodium can be estimated. Such a value reaches and even goes beyond that of some DNA regulatory proteins. This acridine trimer appears to be the first synthetic ligand with such a high DNA affinity.

Encephalitis attributed to dactylariosis in Japanese quail chicks (Coturnix coturnix japonica)

Dactylaria gallopava was isolated from brain tissue of 1-to-3-week-old quail chicks. Successive batches demonstrated elevated (15-20%) mortality preceded by incoordination and lateral recumbency. Chicks exhibited cerebellar and cerebral encephalitis characterized by brown-red discoloration of affected brain tissue. Decontamination of setters and hatchers resulted in abrupt cessation of mortality in subsequent placements, implicating incubators as the source of infection.

Effect of B-Z transition and nucleic acid structure on the conformational dynamics of bound ethidium dimer measured by hydrogen deuterium exchange kinetics

Ethidium dimer is shown to bind by intercalation, almost equally well, to the B and Z form of poly[(dG-m5dC)].poly[(dG-m5dC)], whereas the ethidium monomer shows a strong preference for the B form. The hydrogen-deuterium (H-D) exchange kinetics of the ethidium dimer bound to the B and Z form of poly [(dG-m5dC)].poly[(dG-m5dC)] could then be compared. The kinetics of the H-D exchange were strikingly slower when the dye was bound to Z DNA as compared to B DNA. The exchange kinetics were also modified when ethidium dimer was bound to tRNA and to a triple stranded structure. It is proposed that a dynamic fluctuation at the level of the nucleic acid could modulate the dynamic fluctuation at the level of the bound ligand.

DNA polyintercalation: comparison of DNA binding properties of an acridine dimer and trimer

The DNA binding characteristics of a mono-, di- and trimeric derivative of 9-aminoacridine were studied. The length of the linking carboxamidoalkyl chains was selected to allow bis- or tris-intercalation according to the excluded-site model. Measurements of DNA unwinding angle using closed circular DNA showed that the trimeric derivative behaves as a tris-intercalating agent. Nevertheless the increase of DNA binding affinity on going from dimer to trimer was found to be relatively small. This is probably related to the large structural constraint for DNA binding of the trimeric derivative. The nature of the linking chain for the design of high-affinity DNA poly-intercalating agents appears therefore critical.

Dynamic structure of DNA complexes. Fluorometric measurement of hydrogen-deuterium exchange kinetics of dna-bound ethidium dimer and acridine-ethidium dimer

The hydrogen-deuterium (H-D) exchange kinetics of free and DNA-bound ethidium dimer and acridine-ethidium heterodimer were measured by stopped flow using fluorescence detection. This technique allowed a very accurate measurement of the exchange process. The H-D exchange kinetics were measured in various environments. In some cases, it was observed that the H-D exchange was much faster than the dissociation rate of dimer-DNA complexes. This showed that the exchange was taking place directly from the bound state. Furthermore, the action of a catalyst (imidazolium ion) on the rate of H-D exchange showed that a dynamic structural fluctuation of the ligand in its DNA complex was a necessary step on the exchange process.

Hydrogen bonding in deoxyribonucleic acid base recognition. 1. Proton nuclear magnetic resonance studies of dinucleotide-acridine alkylamide complexes

For studies on the possible involvement of hydrogen bonding in base recognition from the outside of the nucleic acid double helix, 2-methoxy-6-chloro-9-aminoacridine derivatives bearing a carboxamide side chain were examined by 1H NMR spectroscopy. The study of the interaction of these derivatives with CpG or GpC demonstrated that (i) the 2-methoxy-6-chloro-9-aminoacridine ring intercalates preferentially in the minihelix formed by CpG, which indicates a relative pyrimidine-(3'-5')-purine sequence specificity that contrasts with the simple 9-aminoacridine ring wherein Reuben et al. [Reuben, J., Baker, B. M., & Kallenbach, N. R. (1978) Biochemistry 17, 2916-2919] did not observe any sequence preference (ii) the geometry of the intercalated minihelical complex of the 2-methoxy-6-chloro-9-[(5-carbamolypentyl)-amino]acridine with CpG as deduced from isoshielding curves resembles that found in the crystalline complexes of proflavin, with several autocomplementary dinucleoside monophosphates, (iii) the terminal carboxamide group borne by the side chain of 2-methoxy-6-chloro-9-[(5-carbamoylpentyl)amino]acridine (5) intercalated in CpG lies in the small groove and seems to interact through hydrogen bonds with the adjacent guanine.

Hydrogen bonding in deoxyribonucleic acid base recognition. 2. Deoxyribonucleic acid binding studies of acridine alkylamides

A series of derivatives of 2-methoxy-6-chloro-9-aminoacridine bearing side chains terminated by various groups, such as carboxamide, N-methylcarboxamide, N,N-dimethylcarboxamide, methyl ester, and methyl were synthesized. The interaction of these intercalating dyes with DNA of various GC content was studied comparatively by using equilibrium dialysis and fluorescence spectroscopy. The results showed that the compounds bearing a chain terminated by a free carboxamide group could interact specifically with GC-rich DNA provided that the length and conformation of the side chain were appropriate. From these results in hand as well as those reported in the preceding paper (NMR studies at the minihelix level) it is thought that the G specificity of these compounds arises from their ability to form hydrogen bonds between the terminal carboxamide group borne by their side chain and the NH2 and N3 of the adjacent guanine located in the small grove.