Studies related to antitumor antibiotics. Part XIV. Reactions of mitomycin B with DNA

1978 ◽  
Vol 56 (5) ◽  
pp. 296-304 ◽  
Author(s):  
J. William Lown ◽  
Gordon Weir
Keyword(s):  
Mitomycin C ◽  
Ph Dependence ◽  
Cross Linking ◽  
Antitumor Antibiotic ◽  
Antitumor Antibiotics ◽  
Previous Suggestion ◽  
Aziridine Ring ◽  
Strand Breakage ◽  
Radical Traps

The reactions of the antitumor antibiotic mitomycin B with DNA were examined using ethidium fluorescence assays. The following three aspects of mitomycin B action have been studied to compare its behavior with that of mitomycin C: (a) interstrand cross-linking events, (b) alkylation without necessarily cross-linking, and (c) strand breakage. The greater pKa value of 4.3 found for mitomycin B compared with that of mitomycin C, i.e., 3.2, together with the greater pH dependence of DNA alkylation and interstrand cross-linking and the faster and more extensive cross-linking by mitomycin B at low pH in the absence of reduction, support the suggestion that the aziridine moiety is involved in the initial alkylation of DNA. Mitomycin B, reduced in situ with NaBH4, nicks covalenty closed circular (CCC) PM2 DNA rapidly but less efficiently than mitomycin C in a reaction which is suppressed by (i) superoxide dismutase, (ii) catalase, and (iii) free radical traps showing the intermediacy of O−2∙, H2O2, and OH∙. DNA is cleaved by mitomycin B to which it is covalently attached as well as by the free antibiotic. The addition of intercalated ethidium bromide to DNA prior to treatment with reduced mitomycin B inhibits interstrand cross-linking but not strand scission. The reduced aziridine ring-opened mitomycin B (which lacks the 7-NH2 group of mitomycin C) alkylates DNA and thus provides evidence confirming a previous suggestion that the second covalent link to the DNA is formed at position 10 of the antibiotic.

Studies related to antitumor antibiotics. Part IX. Reactions of carzinophillin with DNA assayed by ethidium fluorescence

1977 ◽  
Vol 55 (6) ◽  
pp. 630-635 ◽  
Author(s):  
J. William Lown ◽  
Krishna C. Majumdar
Keyword(s):  
Ph Dependence ◽  
Cross Linking ◽  
Antitumor Antibiotic ◽  
Antitumor Antibiotics ◽  
Covalent Linkage ◽  
Cytosine Residue ◽  
Cross Links ◽  
Pyrimidine Bases ◽  
The Cross ◽  
Intercalating Agents

The reactions of the antitumor antibiotic carzinophillin (CZ) with native DNAs and synthetic polynucleotides have been examined by an ethidium fluorescence assay. CZ rapidly produces covalent linkage of the complementary strands of a variety of DNAs without activation. This process is accompanied by extensive alkylation, as detected by reduced fluorescence due to destruction of potential intercalation sites for ethidium. These processes which occur without loss of purine or pyrimidine bases show a preference for bonding to guanine groups (but not at the N-7 position). Examination of the reversibility of the cross-links suggests they involve one 'permanent' link to guanine and a second weaker linkage, possibly to a cytosine residue. Both cross-linking and alkylation show strong pH dependence and are favored at lower pH, suggesting that reactive sites on the antibiotic are basic. The addition of intercalating agents to DNA before treatment with CZ inhibits the cross-linking.

Studies Related to Antitumor Antibiotics. Part VI. Correlation of Covalent Cross-linking of DNA by Bifunctional Aziridinoquinones with their Antineoplastic Activity

1975 ◽  
Vol 53 (19) ◽  
pp. 2891-2905 ◽  
Author(s):  
M. Humayoun Akhtar ◽  
Asher Begleiter ◽  
Douglas Johnson ◽  
J. William Lown ◽  
Larry McLaughlin ◽  
...  
Keyword(s):  
Mitomycin C ◽  
Physiological Activity ◽  
Ph Dependence ◽  
Antitumor Agent ◽  
Antineoplastic Activity ◽  
Cross Linking ◽  
Antitumor Antibiotics ◽  
Cross Link ◽  
Covalent Crosslinking ◽  
Cross Links

Certain bisaziridinopyrrolidinoquinone analogs, which contain the structural moieties essential for physiological activity in the parent antitumor agent mitomycin C, have been synthesized. These compounds efficiently induce covalent cross-links in DNA as shown by the ethidium fluorescence assay which was confirmed by an independent S1-endonuclease assay. The interaction of clinically active and structurally related antitumor aziridinoquinones with DNA have been examined similarly. The aziridinoquinones cross-link DNA efficiently with a marked pH dependence. Parallel dependence is observed on pH and concentration of alkylating species in the concomitant alkylation which does not result in cross-linking as measured by the suppression of the before heat fluorescence. The latter phenomenon was shown by the application of radiolabelled polynucleates not to be accompanied by depurination. A direct correlation exists between the extent of covalent cross-linking and (G + C) content of various DNA's of comparable molecular weight as in the case of mitomycin C. Estimates of the average number of cross-links per DNA molecule range from 0.61 to 1.71 depending on (G + C) content. The rate of acid assisted opening of a model aziridinoquinone measured spectrophotometrically at different pH values parallels the observed rate of covalent cross-linking and alkylation. It was shown independently that the intermediate 2,5 bis(2-acetoxyethyl-amino)-3,6-dimethoxy-1,4-benzoquinone does not cross-link DNA. A correlation is made of antineoplastic activity against a variety of tumors with covalent crosslinking ability using λ-DNA.

Studies related to antitumor antibiotics. Part V. Reactions of mitomycin C with DNA examined by ethidium fluorescence assay

1976 ◽  
Vol 54 (2) ◽  
pp. 110-119 ◽  
Author(s):  
J. Wlliam Lown ◽  
Asher Begleiter ◽  
Douglas Johnson ◽  
A. Richard Morgan
Keyword(s):  
Superoxide Dismutase ◽  
Free Radical ◽  
Mitomycin C ◽  
Free Radical Scavengers ◽  
Heat Denaturation ◽  
Cross Linking ◽  
Cytotoxic Action ◽  
Antitumor Antibiotic ◽  
The Cross ◽  
High Concentrations

The cytotoxic action of the antitumor antibiotic mitomycin C occurs primarily at the level of DNA. Using highly sensitive fluorescence assays which depend on the enhancement of ethidium fluorescence only when it intercalates duplex regions of DNA, three aspects of mitomycin C action on DNA have been studied: (a) cross-linking events, (b) alkylation without necessarily cross-linking, and (c) strand breakage. Cross-linking of DNA is determined by the return of fluorescence after a heat denaturation step at alkaline pH's. Under these conditions denatured DNA gives no fluorescence. The cross-linking was independently confirmed by St-endonuclease (EC 3.1.4.–) digestion. At relatively high concentrations of mitomycin the suppression of ethidium fluorescence enhancement was shown not to be due to depurination but rather to alkylation, as a result of losses in potential intercalation sites. A linear relationship exists between binding ratio for mitomycin and loss of fluorescence. The proportional decrease in fluorescence with pH strongly suggests that the alkylation is due to the aziridine moiety of the antibiotic under these conditions. A parallel increase in the rate and overall efficiency of covalent cross-linking of DNA with lower pH suggests that the cross-linking event, to which the primary cytotoxic action has been linked, occurs sequentially with alkylation by aziridine and then by carbamate. Mitomycin C, reduced chemically, was shown to induce single strand cleavage as well as monoalkylation and covalent cross-linking in PM2 covalently closed circular DNA. The inhibition of this cleavage by superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6), and by free radical scavengers suggests that the degradation of DNA observed to accompany the cytotoxic action of mitomycin C is largely due to the free radical [Formula: see text]. In contrast to the behavior of the antibiotic streptonigrin, mitomycin C does not inactivate the protective enzymes superoxide dismutase or catalase. Lastly, mitomycin C is able to cross-link DNA in the absence of reduction at pH 4. This is consistent with the postulated cross-linking mechanisms.

Studies Relating to Aziridine Antitumor Antibiotics. Part II. 13C and 1H Nuclear Magnetic Resonance Spectra of Mitomycin C and Structurally Related Streptonigrin

1974 ◽  
Vol 52 (12) ◽  
pp. 2331-2336 ◽  
Author(s):  
J. William Lown ◽  
Asher Begleiter
Keyword(s):  
Mitomycin C ◽  
Chemical Shifts ◽  
Coupling Constants ◽  
Antitumor Antibiotic ◽  
Antitumor Antibiotics ◽  
Nuclear Magnetic Resonance Spectra ◽  
1H Nuclear Magnetic Resonance ◽  
The Common

Double irradiation experiments in the 100 MHz n.m.r. spectrum of mitomycin C allowed determination of vicinal coupling constants which provide information on the conformation of the antibiotic in solution. The natural abundance 13C spectrum and comparison with selected model compounds allowed assignment of the carbon resonances of mitomycin C. The 13C chemical shifts of the quinone ring carbons in mitomycin C have a bearing on the proposed stabilization in vivo. Similar studies on the antitumor antibiotic streptonigrin bearing the common aminoquinone moiety gave indications of conjugative interactions similar to those established for mitomycin C.

Studies Related to Antitumor Antibiotics. Part III. Syntheses of 1,2,3,4,5,6-Hexahydro-2,3-benzazocin-5-ones as Possible Intermediates in the Biosynthesis of Mitomycins

1975 ◽  
Vol 53 (6) ◽  
pp. 960-969 ◽  
Author(s):  
J. William Lown ◽  
Tsuneo Itoh
Keyword(s):  
Mitomycin C ◽  
Pyrrolizidine Alkaloids ◽  
Ring System ◽  
Antitumor Antibiotic ◽  
Antitumor Antibiotics ◽  
Transannular Interaction

The synthesis of 8-methoxy-9-methyl-N-p-toluenesulfonyl-1,2,3,4,5,6-hexahydro-2,3-benzazocin-5-one (23) and its conversion via transannular interaction to the 2,3-dihydro-lH-pyrrolo[1,2-a]indole ABC parent ring system of the antitumor antibiotic mitomycin C is described. The possible implication of this result in the biosynthesis of the mitosanes and the connection with the structurally and pharmacologically related pyrrolizidine alkaloids is discussed.

Electrochemical oxidation of the antitumor antibiotic mitomycin C and in situ evaluation of its interaction with DNA using a DNA-electrochemical biosensor

2017 ◽  
Vol 133 ◽  
pp. 81-89 ◽  
Author(s):  
Evellin Enny S. Bruzaca ◽  
Ilanna C. Lopes ◽  
Elizaura Hyeda C. Silva ◽  
Paulina Andréa V. Carvalho ◽  
Auro A. Tanaka
Keyword(s):  
Electrochemical Oxidation ◽  
Mitomycin C ◽  
Electrochemical Biosensor ◽  
Antitumor Antibiotic ◽  
Dna Electrochemical Biosensor

scholarly journals Interfacial engineering of lithium‐polymer batteries with in situ UV cross‐linking

InfoMat ◽  
2021 ◽  
Author(s):  
Ramin Rojaee ◽  
Samuel Plunkett ◽  
Md Golam Rasul ◽  
Meng Cheng ◽  
Vahid Jabbari ◽  
...  
Keyword(s):  
Cross Linking ◽  
Lithium Polymer Batteries ◽  
Interfacial Engineering

Stabilization of Peptide-Based Vesicles via in situ Oxygen-Mediated Cross-Linking

2012 ◽  
Vol 12 (9) ◽  
pp. 1220-1231 ◽  
Author(s):  
Adrian Sulistio ◽  
Anton Blencowe ◽  
Jiapei Wang ◽  
Gary Bryant ◽  
Xiaoqing Zhang ◽  
...  
Keyword(s):  
Cross Linking

Palladium immobilized on in situ cross-linked chitosan superfine fibers for catalytic application in an aqueous medium

2018 ◽  
Vol 42 (13) ◽  
pp. 11023-11030 ◽  
Author(s):  
Lulu Liang ◽  
Li Nie ◽  
Minjuan Jiang ◽  
Fusheng Bie ◽  
Linjun Shao ◽  
...  
Keyword(s):  
Aqueous Medium ◽  
Itaconic Acid ◽  
Cross Linking ◽  
Catalytic Application ◽  
Chitosan Composite

Chitosan composite superfine fibers with a diameter of 321 ± 99 nm were prepared by electrospinning with PEO as the co-spinning polymer and itaconic acid as the in situ cross-linking agent.

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