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PubMedDate not supplied

The role of ring D in the antitumour antibiotic streptonigrin: metal complexation, DNA binding and topoisomerase inhibition by ABC ring analogues of streptonigrin.

interaction of 7-amino-2-(6'-carboxy-2'-pyridyl)-6-methoxy-5,8-quinolinedione, an ABC ring analogue of the antitumour antibiotic streptonigrin, with zinc(II), oligonucleotides and DNA in the presence of zinc(II), and on the relaxation of DNA by topoisomerase II, has been studied. This ligand contains the key functional groups present in streptonigrin required for biological activity, but lacks the phenolic ring D which confers optical activity on streptonigrin. Variable temperature NMR experiments showed that in the presence of zinc(II) triflate, the methyl ester of the ligand forms a mixture of 1:1 and 1:2 metal:ligand bipyridyl complexes, whose relative stabilities are temperature dependent. Titrations of the water-soluble ligand with zinc(II) nitrate at room temperature showed that the predominant species present in aqueous solution at physiological pH is the 1:1 bipyridyl complex. The interaction of the ligand with the hexanucleotides d(GCATGC)2 and d(ATGCAT)2 was studied by 1H- and 31P-NMR spectroscopy. In the presence of 1 equiv of zinc(II) nitrate and 1 equiv of the ligand, small changes in chemical shifts of the proton resonances associated with the purine resonances were detected consistent with a weak interaction of the zinc(II) complex of the ligand with the oligonucleotides, possibly via a groove binding mechanism. UV-VIS titrations showed a weak interaction of the ligand with calf thymus DNA and poly(dG-dC)2 in the presence of zinc(II) but negligible interaction with poly(dA-dT)2. Gel electrophoresis experiments showed that, in contrast to streptonigrin, the ligand did not inhibit the relaxation of plasmid DNA by human topoisomerase II. These results show that the interaction of the ABC ligand with zinc(II), oligonucleotides, DNA and topoisomerase II is different to streptonigrin and hence the design of biologically active ABC ring analogues of streptongrin that operate via different mechanisms should be possible.

Antibiotics, Antineoplastic↗
PubMed1992

Transformation of streptonigrin into streptonigrone; synthesis and biological evaluation of antibiotics streptonigrin and streptonigrone alkyl ethers.

A method of synthesis of antibiotic streptonigrin 8'-O-alkyl ethers by alkylation of streptonigrin diphenylmethyl ester and consequent deprotection of carboxylic group with CF3COOH is developed. An attempt to deblock carboxylic group of 8'-O-methylstreptonigrin diphenylmethyl ester by hydrogenation over Pd produced 8'-O-methylstreptonigrone. Similarly streptonigrin was transformed into streptonigrone over Pd-black in H2 stream. Methylation of streptonigrone afforded 5',5'-N-dimethyl-2',8'-O-dimethylstreptonigrone and 1',5',5'-tri-N-trimethyl-8'-O-methylstreptonigrone. Alkyl streptonigrin ethers demonstrated lower antibacterial activity in vitro than the parent antibiotic.

Alkylation↗
PubMed1987

Streptonigrin and lavendamycin partial structures. Probes for the minimum, potent pharmacophore of streptonigrin, lavendamycin, and synthetic quinoline-5,8-diones.

The preparation and evaluation of 7-amino-5,8-dioxo-2-(2'-pyridyl)quinoline-6'-carboxylic acid (5a) and 7-amino-2-(2'-aminophenyl)-5,8-dioxoquinoline-5'-carboxylic acid (6a) constituting potential minimum, potent pharmacophores of streptonigrin (1a) and lavendamycin (2a), two structurally related naturally occurring antitumor antibiotics, are detailed. In contrast to observations associated with streptonigrin and lavendamycin in which the C-ring C-6' carboxylic acid potentiates the antitumor, antimicrobial, and cytotoxic properties of the naturally occurring, substituted 7-aminoquinoline-5,8-dione AB ring systems, the C-6'/C-5' carboxylic acid of 5a/6a diminishes the observed antimicrobial and cytotoxic properties of the 2-(2'-pyridyl)- and 2-(2'-aminophenyl)-7-aminoquinoline-5,8-diones. A direct comparison of the antimicrobial and cytotoxic properties of a complete set of streptonigrin and lavendamycin partial structures is detailed in efforts to define the role peripheral substituents play in potentiating the biological properties of the naturally occurring and synthetic agents bearing the 7-aminoquinoline-5,8-dione AB ring system and in efforts to define the minimum, potent pharmacophore of the naturally occurring antitumor antibiotics. The relationship of these observations to a chemical mechanism of cellular toxicity is discussed.

Animals↗
PubMed1992

[Preparation and biological activities of monoclonal antibody-streptonigrin immunoconjugates].

The clinic use of streptonigrin (114B), a highly active antitumor antibiotic, is limited by its detrimental effects on normal tissues. In an attempt to improve its specificity streptonigrin was conjugated to anti-human hepatoma monoclonal antibody 3A5 by four different chemical linkage methods. The first method was via water-soluble carbodiimide (EDCI) to create conjugates (1); in the second, an active ester of streptonigrin was applied as a reactive intermediate (2); and in the other two, spacers were put to use for coupling streptonigrin to McAb 3A5-Dextran T-40 (3) or McAb 3A5-bovin serum albumin (BSA) (4). The conjugates showed biological activities and UV spectral characteristics of streptonigrin and 3A5. As determined by clonogenic assay with human hepatoma BEL-7402 cells for 1 hour exposure, the IC50 for conjugate (2), conjugate (3) and streptonigrin were 0.355 ng/ml, 1.23 ng/ml and 22.4 ng/ml, respectively. The potency of conjugates (2) and (3) were 63-fold and 18-fold stronger than that of free streptonigrin. Clonogenic assay with KB cells which weakly react with 3A5 by Elisa showed that the potency of conjugate (2) and (3) were 11-fold and 13-fold weaker than free streptonigrin, respectively. The results suggest that the conjugates of McAb 3A5 and streptonigrin show specific cytotoxicity to target liver cancer cails. The linkage groups of streptonigrin were also discussed.

Antibodies, Monoclonal↗
PubMed1997

Interaction of the antitumour antibiotic streptonigrin with DNA and oligonucleotides.

The interaction of the aminoquinone antitumour antibiotic streptonigrin with plasmid DNA, calf thymus DNA and oligonucleotides, in the presence and absence of metal ions, has been studied using circular dichroism, NMR spectroscopy and gel electrophoresis experiments. In the absence of metal ions, streptonigrin does not interact with DNA. Incubation of the two enantiomers of streptonigrin with calf thymus DNA, in the presence of excess zinc(II), showed no evidence of selective interaction of the natural enantiomer, (R)-streptonigrin, with the DNA by circular dichroism. The interaction of streptonigrin with the hexanucleotide d(GCATGC)2 was studied by 1H- and 31P-NMR spectroscopy. In the presence of four equivalents of zinc(II) nitrate and one equivalent of streptonigrin, small changes in chemical shifts of the proton resonances associated with T4 and G5 were detected as well as P4 and P5, consistent with a weak interaction of the zinc(II)-streptonigrin complex with the most accessible binding sites, involving the phosphate groups and guanine N7, at either end of the duplex. In contrast, no significant interaction between the metal complex and d(ATGCAT)2 was detected. Gel electrophoresis experiments were carried out to probe the sequence specificity of the interaction of the non-covalent streptonigrin-metal complexes with DNA, the DNA cleavage reaction of supercoiled DNA, and the specificity of the cleavage reaction. DNase I footprinting showed no sequence specific interactions. Zinc(II), copper(II) and manganese(II) enhanced the cleavage of supercoiled DNA into nicked and linear forms of DNA, while magnesium showed no cleavage reactions under identical conditions. The DNA cleavage reaction of streptonigrin and NADH in the presence and absence of metal ions was studied. Overall, little sequence specificity was observed, but slightly different cleavage patterns suggest that the DNA cleavage can be influenced by the nature of the metal ions.

Animals↗
PubMed1982

Inhibition of phosphoenolpyruvate carboxykinase by streptonigrin.

Streptonigrin, an antibiotic with antineoplastic activity, inhibited rat liver phosphoenolpyruvate carboxykinase with an I50 of 0.3 microM when excess FeCl2 was present. No inhibition occurred in the absence of added metal ion. Inhibition was partial and noncompetitive versus ITP and oxalacetic acid. The enzyme was more susceptible to inhibition by streptonigrin in the absence of substrates. Fe2+ supported inhibition by streptonigrin to a greater extent than did Fe3+, while Mn2+ activated the enzyme in the presence of streptonigrin. For maximum inhibition, at least a 3-fold molar excess of iron over streptonigrin was required. The methyl ester of streptonigrin was also an inhibitor (I50 = 4 microM) while the fragment containing the C and D rings was not, indicating that inhibition did not depend solely on the presence of the picolinic acid moiety. When oxalacetate synthesis was measured, streptonigrin plus iron had no more effect on enzymatic activity than iron alone, and Mn2+ was capable of stimulating the streptonigrin-Fe2+ inhibited enzyme.

Animals↗
PubMed1984

Changes in streptonigrin lethality during adaptation of Escherichia coli to picolinic acid. Correlation with intracellular picolinate and iron uptake.

Uptake studies with [14C]picolinate and 55Fe3+ have provided an explanation for the change in streptonigrin killing on adaptation of Escherichia coli to picolinate, in terms of the available iron within the cell. When picolinic acid is added to a growing culture of E. coli an interval of bacteriostasis ensues; this adaptation period is followed by resumption of exponential growth. Addition of picolinate (4 mM) to a log phase culture of strain W3110 gave protection from the lethal action of streptonigrin (30 microM) when the two agents were added simultaneously. In contrast streptonigrin killed cells that had adapted to picolinate; however, a preincubation of adapted W3110 with phenethyl alcohol protected the cells from streptonigrin lethality. [14C]Picolinate uptake studies showed that initially picolinate entered the cells, but that it was excluded from adapted cells; addition of phenethyl alcohol permitted the entry of picolinate into adapted W3110. The changes in streptonigrin killing parallel the changes in concentration of intracellular picolinate, which can chelate the iron required by streptonigrin for its bactericidal action. 55Fe3+ uptake studies showed that initially picolinate prevented iron accumulation by strain W3110, whereas adapted cells did take up iron in the presence of picolinate. Addition of phenethyl alcohol prevented any observed uptake of iron by adapted W3110. This modulation of iron transport by picolinate also affects streptonigrin lethality. Experiments with iron transport mutants showed that picolinate acted on both the enterochelin and citrate routes of uptake. Therefore picolinate affects the concentration of available iron within the cell both by (a) its intracellular presence resulting in chelation of iron and (b) its action on iron uptake; these effects explain the change in streptonigrin killing on adaptation of E. coli to picolinate.

Escherichia coli↗
PubMed1987

Role of extracellular iron in the action of the quinone antibiotic streptonigrin: mechanisms of killing and resistance of Neisseria gonorrhoeae.

The quinone antibiotic streptonigrin is believed to kill bacteria by promoting formation of oxygen radicals. This antibiotic has also been used to select resistant bacterial mutants, some of which vary in iron utilization. We examined the effects of streptonigrin on Neisseria gonorrhoeae and several types of gonococcal mutants. Streptonigrin (0.025 microgram/ml) efficiently killed gonococcal strain FA1090, and this effect depended on iron. Streptonigrin-resistant mutant FA6271 had normal iron uptake but was moderately deficient in total iron. Resistance most likely resulted from failure of FA6271 to divert electrons to streptonigrin, as demonstrated by a reduction in KCN-insensitive respiration (a hallmark of the action of quinones) and superoxide formation. Other mutants selected for inability to use human iron-binding proteins (strains FA6273 and FA6275) had no increase in streptonigrin MIC and no decrease in KCN-insensitive respiration. Mutants did not demonstrate an increase in superoxide dismutase or catalase. Streptonigrin killing of gonococci depended on a reaction(s) in which extracellular iron was important, presumably because iron was required for catalysis of hydroxyl radical. The results suggest that a membrane component may be a target for the actions of streptonigrin.

Catalase↗
PubMed1982

Streptonigrin toxicity in Escherichia coli: oxygen dependence and the role of the intracellular oxidation--reduction state.

The bacterial physiology of streptonigrin toxicity was further investigated. An optimal oxygen concentration for toxicity was inferred from data showing that streptonigrin at 5 micrograms/mL was rapidly lethal to aerobic cultures of Escherichia coli K12JF361, but was without effect on anaerobic cultures and was bacteriostatic to cultures inhibited in 5 atm of oxygen plus 1 atm of air (5 atm O2 plus air) (1 atm = 101.325 kPa). Escherichia coli were protected from a potentially lethal concentration of streptonigrin during anaerobic incubation, whether previously grown anaerobically, aerobically, or in 5 atm O2 plus air. Superoxide dismutase activity increased with increasing oxygen tension in the medium, but was not significantly changed by a lethal concentration of streptonigrin. Although the superoxide dismutase activity was four times greater in E. coli grown in 5 atm O2 plus air than those grown in air alone, the aerobic survival in 5 micrograms/mL streptonigrin was identical, which suggested that superoxide dismutase was not rate limiting for toxicity. Escherichia coli K12 strains deficient in glutathione (KMBL54-129, AB1157-821, and AB1157-830) were protected from streptonigrin poisoning. Dithiothreotol (5.0 mM), diamide (1 mM), methyl viologen (1 mM), and cyanide (10 mM) protected aerobic E. coli from 5 micrograms/mL streptonigrin. These data are also consistent with a model of in vivo streptonigrin toxicity that requires a favorable intracellular oxidation--reduction state and an optimal concentration of molecular oxygen.

Cells, Cultured↗
PubMed1990

Ammonium effects on streptonigrin biosynthesis by Streptomyces flocculus.

A defined medium containing glucose and ammonium as the sole carbon and nitrogen sources was developed to support growth and streptonigrin production. In this defined medium, increased initial levels of ammonium resulted in increased growth suggesting that nitrogen is the growth limiting nutrient. In some cases, increased initial ammonium levels resulted in decreased specific streptonigrin productivity, suggesting that nitrogen regulatory mechanisms may adversely affect streptonigrin biosynthesis. This suggestion that nitrogen regulation adversely affects antibiotic biosynthesis is further supported by results from two studies in which the ammonium supply to the cells was controlled. In the first study, streptonigrin productivity and final titer were enhanced by the addition of an ammonium trapping agent. In the second experiment, when ammonium chloride was fed slowly throughout the course of cultivation, the production phase was lengthened and the maximum antibiotic concentration was enhanced compared to the batch controls containing either the same initial or the same total ammonium chloride levels. Although our results indicate streptonigrin production may be subject to nitrogen regulatory mechanisms, the effect of nitrogen on streptonigrin production cannot be strictly correlated to the extracellular ammonium concentration. In fact, we observed that when ammonium was depleted from the medium, streptonigrin production ceased.

Ammonium Chloride↗
PubMed1984

DNA interaction and nucleotide sequence cleavage of copper-streptonigrin.

The copper-accelerated DNA binding and cleavage of streptonigrin have been investigated by 1H-NMR, ESR spectrometry and nucleotide sequence analysis. In the DNA breakage by the streptonigrin-Cu(II)-NADPH system, the somewhat preferred cleavage sites were several cytosine bases adjacent to purine bases such as GCGG(5'----3'), ACGC(5'----3') and GGCG(5'----3') sequences. The proton chemical shifts for the streptonigrin-Cu(I)-poly(dA-dT) complex demonstrated the interaction between the pyridine ring of the drug and the purine bases of the nucleic acid. Indeed, the temperature profile of adenine H-2 proton clearly showed the Tm to shift from 70 degrees C in the binary streptonigrin-poly(dA-dT) system to 75 degrees C in the ternary streptonigrin-Cu(I)-poly(dA-dT) system. The interaction of the streptonigrin-Cu(II) complex with DNA also induced the apparent change of ESR parameters. The tricyclic phenanthidium ring system including the copper chelate ring appears to significantly contribute to the present DNA interaction and cleavage of copper-streptonigrin.

Base Sequence↗
PubMed1982

Iron requirement in the bactericidal mechanism of streptonigrin.

Mutants of Escherichia coli K-12 that are unable to make use of the enterochelin transport system were used to confirm that streptonigrin requires iron for its bactericidal action. Correlation of viability studies and 55Fe3+ uptake experiments showed that killing by streptonigrin increased with an increase in 55Fe3+ uptake by the cells. Streptonigrin did not kill iron-starved mutants that were unable to import iron. The level of iron uptake by these mutants was manipulated by agents such as (i) the enterochelin biosynthetic precursors 2,3-dihydroxybenzoic acid (2 x 10(-5) M) and shikimic acid (2 x 10(-4) M), (ii) citrate (10(-2) M), which promotes iron uptake by an independent pathway, and (iii) the chelating agents desferrioxamine (2 x 10(-4) M) and orthophenanthroline (10(-4) M). Addition of the precursors shikimate and dihydroxybenzoate to strain AB2847 (aroB) and dihydroxybenzoate to strain AN193 (entA), allowing these strains to make enterochelin, resulted in an increase in Fe3+ uptake and a corresponding sharp increase in killing by streptonigrin. Addition of enterochelin itself (10(-6) M) caused an even more pronounced effect. Studies on the effect of citrate in strain AN102 (fep) showed that this mutant was not killed by streptonigrin (4 x 10(-5) M), even in the presence of citrate; however, overnight growth in citrate induced Fe3+ uptake by means of the ferric citrate transport system and resulted in killing by streptonigrin. These studies showed a clear correlation between the change in levels of intracellular iron and the bactericidal effectiveness of streptonigrin.

Bacteria↗
PubMed2004

Antitumor antibiotic streptonigrin and its derivatives as inhibitors of nitric oxide-dependent activation of soluble guanylyl cyclase.

The influence of streptonigrin on the activity of human platelet guanylyl cyclase was investigated. Streptonigrin (0.1-5 microM) had no effect on the basal activity of the enzyme, but inhibited in a concentration-dependent manner the sodium nitroprusside-induced activation of human platelet soluble guanylyl cyclase with an IC(50) value of 4.16 microM. Streptonigrin (10 microM) also inhibited (by 28%) the activation of the enzyme by the direct nitric oxide (NO) donor-spermine-NONO (100 microM), but had no influence on the stimulation of soluble guanylyl cyclase by protoporphyrin IX. The absence of a correlation between the inhibition of NO-stimulated guanylyl cyclase activity by streptonigrin (I) and its derivatives (streptonigrone (IV), streptonigrone-2'-imine (V), amide of 1 and 2'-deoxy-2'-amino-D-glucose (VI), amide of 1 and 2'-deoxy-2'-amino-2'-D-galactose (VII), amide of 1 and 1-O-methyl-6-deoxy-6-amino-D-glucose (VIII), diphenylmethyl ester of I (IX), conjugate of I and daunorubicin (X)), and the level of cytotoxic effects of these compounds excludes the involvement of guanylyl cyclase in the mechanism of antitumor action of streptonigrin. Inhibition of guanylyl cyclase activation by NO donors but not by protoporphyrin IX represents a new biochemical effect of streptonigrin, which should be taken into account in addition to its antitumor action.

Antibiotics, Antineoplastic↗
PubMed1993

[Cytotoxicity to hepatoma BEL-7402 cells of an antitumor monoclonal antibody-streptonigrin conjugate].

Streptonigrin, a highly active antitumor antibiotic, was covalently conjugated to anti-human hepatoma monoclonal antibody 3A5 via the active ester method. The conjugate showed biological activities and UV spectra characteristics of streptonigrin and McAb 3A5. The molar ratio of streptonigrin to 3A5 was 2-6:1, with protein recovery of 76%. The conjugate retained 12.5% of drug activity and nearly full antibody activity, though as the number of streptonigrin molecules in the conjugate increased, the antibody activity of the conjugate decreased. As determined by clonogenic assay with human hepatoma BEL-7402 cells in vitro, the inhibitory potency of the conjugate was 63-fold stronger than that of free streptonigrin. For KB cells (which react weakly with 3A5) the cytotoxicity was 11-fold weaker. The results indicate that the McAb 3A5-streptonigrin conjugate is selective for target cells.

Antibodies, Monoclonal↗
PubMed1994

Streptonigrin-induced topoisomerase II sites exhibit base preferences in the middle of the enzyme stagger.

The non DNA intercalator streptonigrin was shown to inhibit topoisomerase II by stabilizing cleavable complexes (Yamashita et al, Cancer Res. 1990, 50, 5841). Streptonigrin-induced topoisomerase II cleavage sites were mapped in the c-myc proto-oncogene DNA. Streptonigrin induced a unique cleavage pattern. Its cleavage sites were less frequent than those induced by other topoisomerase II inhibitors. Strongly preferred bases were found in the middle of topoisomerase II DNA stagger, with thymine at position +2 and adenine at position +3, position +1 being the nucleotide covalently linked to topoisomerase II. Preference for bases not immediately flanking the cleavage sites has not been reported previously and indicates that a mechanism other than "drug stacking" within the DNA break is taking place with streptonigrin to stabilize cleavable complexes. An alternative model taking into account the unusual DNA binding properties of streptonigrin is proposed.

Base Sequence↗
PubMed1994

Selective killing of tumor cells in vitro by immunotoxin composed of antitumor antibiotic streptonigrin and polyclonal specific antibodies.

Streptonigrin N-hydroxysuccinimide ester (STN-COONSu) was obtained by carbodiimide synthesis. Poly-L-lysine (PLL) was loaded with STN-COONSu and conjugated to polyclonal rabbit immunoglobulin G (IgG) activated with sodium periodate. Non-specific IgG and IgG against Ehrlich carcinoma cells were used to construct non-specific and specific immunotoxins. Immunotoxins contained 100 molecules of streptonigrin per 1 molecule of IgG. The streptonigrin concentration that caused 50% of inhibition of [3H]thymidine incorporation in Ehrlich carcinoma cells (IC50) was 0.8 micrograms/ml for specific immunotoxin, 16 micrograms/ml for non-specific immunotoxin, and 20 micrograms/ml for the poly-L-lysine-streptonigrin conjugate (PLL-STN) used as the initial water-soluble form of antibiotic. Our results demonstrate that the toxicity for target cells of streptonigrin conjugated to specific IgG was 25 times higher than that of the initial water soluble form of antibiotic. This specific immunotoxin was non-toxic for non-target cells.

Animals↗