Novobiocin-mediated inhibition of polymerization and ligation of DNA in vitro

Comparison of lesions induced by intra-articular injections of quinolones and compounds damaging cartilage components in rat femoral condyles

Twenty-five microliters of a 2% saline solution of levofloxacin (LVFX) or ciprofloxacin (CPFX) was injected every other day for 2 wk into the knee joint space of CD rats (weighing 62.7-86.7 g) from the age of 3 wk. Early in the course of injection, histologic examination revealed chondrocyte necrosis without marked matrix change in the articular cartilage of the femoral condyles adjacent to the intercondylar groove. After 7 injections, the surface and intermediate zones of the articular cartilage showed extensive necrosis, sometimes with cavity formation in the center of the same portion. Papain completely depleted matrix basophilia in all zones throughout the condyle and caused cartilage necrosis with cavity formation. One injection of iodoacetic acid caused necrosis of almost all chondrocytes over the entire condyle, but chondrocytes sometimes remained alive in the portion where cavity formation was induced by quinolones. Chondroitinase depleted the matrix basophilia, and sometimes produced necrotic areas. DNA synthesis inhibitors n-ethylmaleimide, CPT-11, and etoposide (VP-16) caused chondrocyte necrosis, but never caused cavities in the articular cartilage. The DNA synthesis inhibitors n-ethylmaleimide, CPT-11, and hydroxyurea were administered concurrently with po LVFX administration and significantly increased the incidence of LVFX-induced cavity formation. n-Ethylmaleimide was the most effective of all the inhibitors. The quinolone-induced cavity formation is suggested to be site specific in the articular cartilage of rat femoral condyles. The depletion of matrix proteoglycans and chondrocyte necrosis may be necessary, although insufficient, to produce such lesions. Disruption of the collagen framework is suspected to contribute to their development. Involvement of altered DNA metabolism may play a role in the chondrocyte necrosis that occurs early in the specific sites.

Response of V79 cells to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) treatment: inhibition of poly(ADP-ribose) and topoisomerase activity

MNNG-induced killing of V79 cells has been found to be enhanced on inhibition of topoisomerase II activity by nalidixic acid and poly(ADP-ribose) polymerase synthesis by benzamide. Using these 2 inhibitors in conjunction after MNNG treatment, some overlap in the functions of these 2 enzymes was observed. Nalidixic acid and benzamide were found to suppress the yields of mutations and SCEs induced by MNNG. Benzamide was more effective in suppressing the mutation yield whereas nalidixic acid was more effective in suppressing SCEs. A model based on the relative requirement of topoisomerase and poly(ADP-ribose) for the repair of different types of damage has been proposed to explain the results.

The effects of inhibitors of topoisomerase II and quinacrine on ultraviolet-light-induced DNA incision in normal and xeroderma pigmentosum fibroblasts

The aim of our work was to investigate whether DNA topoisomerase II participates in the repair-specific incision of UV-irradiated genomic DNA. Therefore, the influence upon DNA incision of the topoisomerase II inhibitors (nalidixic and oxolinic acid, novobiocin and coumermycin A1) as well as the intercalating agent quinacrine has been measured in normal human fibroblasts using the alkaline elution technique. In addition, inhibition by novobiocin has been determined in fibroblast strains from 11 normal donors and from 16 xeroderma pigmentosum (XP) patients belonging to the complementation groups A, C, D, E, and XP variant. Nalidixic and oxolonic acid did not inhibit endonucleolytic cleavage, whereas novobiocin was a potent inhibitor of DNA incision. It was observed that in normal and in all XP strains 50% inhibition by novobiocin occurred on average in the dose range 315-590 microM. Since inhibition by novobiocin was not paralleled by that with the other topoisomerase II inhibitors nalidixic and oxolinic acid, it must be concluded that reduction of enzyme-catalysed breaks was not due to the participation of topoisomerase II in the incision step, but to the displacement of ATP at the binding site of the DNA-incising enzyme. This enzyme absolutely requires ATP as a cofactor for endonucleolytic cleavage. Quinacrine, however, inhibited DNA incision in normal fibroblasts at a mean Ki of 318 microM. Inhibition by this intercalating agent seems to be caused by structural perturbations in DNA, which render it a poor substrate for endonucleolytic cleavage.

Stimulation of DNA repair synthesis of rat thymocytes by novobiocin and nalidixic acid in vitro without detectable DNA damage

Scheduled (SDS) and unscheduled (UDS) DNA synthesis as well as nucleoid sedimentation was investigated in vitro under the influence of novobiocin (NB) and nalidixic acid (NA) using intact thymic (T-cells) and splenic (S-cells) rat cells and cells which were exposed to X-rays, UV irradiation, methyl methanesulfonate (MMS), and DNA polymerase inhibitors. At concentrations of greater than or equal to 56.25 (S-cells) and greater than or equal to 225 micrograms/ml (T-cells), respectively, NB inhibited SDS in a dose-dependent manner. Within a concentration range of greater than or equal to 225-900 micrograms NB/ml, UDS of S-cells decreased to values far below the tracer ([3H-methyl]-thymidine) incorporation of control cells, whereas UDS of T-cells increased by at least 200%. Within a concentration range of 450-1800 micrograms/ml, NA enhanced SDS and UDS by about 30% in S-cells and by 100% in T-cells. The stimulating activity of NB and/or NA could be eliminated specifically by the DNA polymerase beta inhibitor 2',3'-dideoxythymidine. Enhanced nucleoid sedimentation was observed at NB concentrations greater than or equal to 750 micrograms/ml; S-cells revealed a higher sedimentation rate than T-cells. It is suggested that NB (and NA) influence DNA topology in a rather cell specific manner, stimulating UDS of T-cells by a DNA polymerase beta - dependent repair-like mechanism.

Novobiocin enhances alkylating agent cytotoxicity and DNA interstrand crosslinks in a murine model

DNA-DNA crosslinks are the lethal cellular mechanism of bifunctional alkylating agent cytotoxicity. Novobiocin, an inhibitor of DNA topoisomerase II, impairs eukaryotic DNA repair of alkylating agent adducts and may increase the number of adducts and their resultant cytotoxicity in malignant cells. The effect of novobiocin on clonogenic survival and DNA crosslinking due to cisplatin (cDDP) and carmustine (BCNU) was studied. Novobiocin caused synergistic cytotoxicity in Chinese hamster ovary cells exposed to cDDP or BCNU. Novobiocin and cDDP increased the formation of DNA-DNA interstrand crosslinks six-fold greater than cDDP alone. The effect was schedule dependent. Novobiocin and cDDP or BCNU markedly reduced in vivo growth of a murine fibrosarcoma without increased host toxicity. As a modulating agent of cytotoxicity due to DNA-DNA crosslinking, novobiocin may enhance the clinical effectiveness of the alkylating agents in human cancer and offer insight into new therapeutic strategies.

Pyrimidine dimers in Drosophila chromatin become increasingly accessible after irradiation

A prokaryotic DNA-repair enzyme has been utilized as a probe for changes in the accessibility of pyrimidine dimers in Drosophila chromatin following UV irradiation. The results demonstrate a rapid cellular response to physiologically relevant doses of radiation which results in at least a 40% increase in accessible dimers. This increase occurs in two incision-deficient mutants which indicates that the excision-repair process, at or beyond the incision step, is not required or responsible for the increase. In the absence of excision the increase in accessibility persists for at least 2 days following irradiation. The observed increase in accessibility is inhibited by both novobiocin and coumermycin. These inhibitors do not inhibit the initial rate of incision, but do reduce dimer excision measured over more extended periods. A pre-incision process is proposed which actively exposes DNA lesions to excision repair. A fraction of the genome is postulated to be accessible without the intervention of that process.

Chromatid aberrations in a novobiocin-resistant subline of Chinese hamster V79 cells after exposure to novobiocin

We examined effects of novobiocin alone or in combination with gamma-irradiation, on the frequencies of chromatid-type aberrations in a novobiocin-resistant subline of Chinese hamster V79 cells (NOVOr-1). NOVOr-1 cells were significantly resistant to novobiocin, as compared to wild-type V79 (WT) cells, with respect to cell survival and DNA synthesis. Survival responses of WT and NOVOr-1 cells to gamma-rays in the range 2-10 Gy differed only slightly and the number of chromatid aberrations produced by irradiation at 1 Gy was fairly comparable in the two cell types. Post-irradiation treatment of cells with novobiocin at concentrations exceeding 200 micrograms/ml significantly increased the number of chromatid gaps plus breaks in WT cells as compared with NOVOr-1 cells. With 200 micrograms/ml the increase was 1.2-fold (t-test, P less than 0.05) and with 400 micrograms/ml, 2.3-fold (P less than 0.01) the number produced in NOVOr-1 cells.

Role for topoisomerases in the release of DNA into the detergent-soluble fraction of eukaryotic cells

Detergent-soluble DNA is the fraction (2-4%) of DNA that is released into the supernate upon mild detergent lysis. It is nonmitochondrial in origin. It labels efficiently with deoxy[3H]ribonucleosides and the labeling is prevented by inhibitors of polymerase alpha and ribonucleotide reductase. In previous publications we have characterized detergent-soluble DNA from splenocytes of immunologically activated mice. In this publication we show that incorporation of [3H]thymidine into detergent-soluble DNA is prevented by pretreatment with novobiocin, 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA), and teniposide (VM26), three inhibitors of type II topoisomerases. Camptothecin, an inhibitor of type I topoisomerases, also reduces incorporation of [3H]thymidine but only to 50% of control levels. In addition to affecting incorporation of [3H]thymidine, preincubation with the topoisomerase II inhibitors m-AMSA and VM26 alters the amount of DNA recovered in the detergent-soluble fraction. At low concentrations of m-AMSA the amount of detergent-soluble DNA increases somewhat, whereas at higher drug concentrations a marked decrease is observed. Treatment with VM26 results in diminished amounts of DNA being released into the detergent-soluble fraction as well. However, maximal inhibition of detergent-soluble DNA release by VM26 requires the presence of camptothecin. Therefore, we suggest that topoisomerases play an important role in making a small part of lymphocyte chromatin detergent labile. Furthermore, these results are consistent with recent studies demonstrating a role for topoisomerases in yeast replication. Thus, the newly synthesized portion of detergent-soluble DNA may arise as DNA replication intermediates not yet stabilized into mature chromatin.

Effect of 4-quinolones and novobiocin on calf thymus DNA polymerase alpha primase complex, topoisomerases I and II, and growth of mammalian lymphoblasts

The influence of ciprofloxacin, nalidixic acid, norfloxacin, novobiocin, and ofloxacin on elements of eucaryotic DNA replication was investigated in vitro. Each of the 4-quinolones, when present in amounts of more than 100 micrograms/ml, reversibly inhibited the DNA synthesis performed by the 95 DNA polymerase alpha primase complex from calf thymus. Novobiocin at 500 micrograms/ml or at higher concentrations irreversibly inactivated DNA polymerase alpha primase complex. The accuracy of in vitro DNA synthesis in the absence of repair mechanisms was determined from amber-revertant assays with phi X174am16(+) DNA as template. The antimicrobial agents did not significantly increase the frequencies of base pairing mismatches during the course of replication, indicating that the basal mutation rate is not affected by novobiocin and the 4-quinolones. The Ki values of 50% inhibition of DNA topoisomerases from calf thymus by ciprofloxacin, norfloxacin, novobiocin, nalidixic acid, and ofloxacin were 300, 400, 1,000 or more, 1,000 or more, and 1,500 or more micrograms/ml, respectively, in the case of topoisomerase I, and the Ki values were 150, 300, 500, 1,000, and 1,300 micrograms/ml, respectively, in the case of topoisomerase II. The procaryotic topoisomerase II is approximately 100-fold more sensitive to inhibition by ciprofloxacin, norfloxacin, and ofloxacin than is its eucaryotic counterpart. Growth curves of lymphoblasts were recorded in the presence of ofloxacin and ciprofloxacin. Neither 1 nor 10 micrograms of ciprofloxacin or of ofloxacin per ml affected cell proliferation. Ofloxacin and ciprofloxacin at 100 micrograms/ml inhibited cell growth; 1,000 micrograms/ml led to cell death. No correlation exists between the antimicrobial and cytotoxic activities of the 4-quinolones.

Effect of novobiocin on the frequencies of chromatid-type aberrations and sister-chromatid exchanges following gamma-irradiation

The effect of novobiocin on the frequencies of chromatid-type aberrations and SCEs was examined in Chinese hamster V79 cells which were exposed to gamma-rays and post-treated with novobiocin. While no chromatid aberrations were induced in the unirradiated cells by novobiocin, the frequency of SCEs was slightly increased by treatment with novobiocin alone. Irradiation of G2 cells produced multiple chromatid-type aberrations and post-treatment of the irradiated cells with novobiocin resulted in a significant increase of the aberrations, including chromatid gaps and breaks. In contrast, novobiocin failed to increase the frequency of SCEs induced by gamma-rays when the irradiated cells were post-treated with novobiocin.