The mechanism of alkylation of DNA by 5-(3-methyl-l-triazeno) imidazole-4-carboxamide (MIC), a metabolite of dic (NSC-45388) non-involvement of diazomethane

doi:10.1016/0009-2797(74)90046-5

Chemico-Biological Interactions

Volume 8, Issue 6, June 1974, Pages 403-413

https://doi.org/10.1016/0009-2797(74)90046-5 Get rights and content

Abstract

Comparison of the nuclear magnetic resonance spectra of chemically synthesized methyl-d₁-methanol with the methanol produced in the solvolytic decompostion of 5-(3-methyl-1-triazeno)imidazole-4-carboxamide (MIC) in D₂O under acidic, basic or neutral conditions indicated that no deuterium was exchanged for the hydrogens on the methyl group. Diazomethane can therefore be ruled out as an intermediate in this reaction.

The methyl-d₃-guanine isolated after incubation of methyl-d₃-MIC with calfthymus DNA in vitro displayed, on chemical ionization mass spectrometry, a quasimolecular ion (MH⁺) at m/e 169, which was 3 mass units higher than the quasimolecular ion for an undeuterated 7-methylguanine standard. The major fragment ions for 7-methyl-d₃-guanine on electron impact mass spectrometry likewise were situated at positions 3 mass units higher than the fragment ions for 7-methylguanine itself.

These data indicate that the methylation of biological macromolecules by MIC must involve the transfer of an intact methyl group.

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5-(3-Methyl-1-triazeno)imidazole-4-carboxamide (NSC-407347, MTIC), an active intermediate in the metabolism of 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide (NSC-45388, DTIC), was investigated for its effect on DNA. When [³H]MTIC was added to an aqueous solution of calf thymus DNA, it was rapidly hydrolyzed, and less than 0.5 per cent of the added ³H was recovered in DNA as methyl groups attached to its base and phosphate constituents. It was estimated that the hydrolysis of phosphotriesters in methylated DNA released 0.5 per cent of total bound ³H of DNA in the experiment in vitro, and 5.7 per cent in vivo. When MTIC was added to tissue culture cells which had been prelabeled with [³H]thymidine, there was a large and immediate increase in acid-soluble radioactivity of both the cell media and the cells. At the same time, there was an accelerated drop in the specific activity of DNA, indicating that degeneration of DNA had occurred; MTIC at 10⁻³ M had a greater effect than at 10⁻⁵ M. Paper chromatographic studies showed that the acid-soluble radioactivity was predominantly in the form of thymidine. MTIC at 10⁻⁴ M induced repair synthesis of DNA but inhibited semi-conservative replication. The extent of repair synthesis was greater at 30 min than after 5 min. Treatment of cells with MTIC at 10⁻³ M irreversibly reduced the sedimentation of DNA in alkaline sucrose gradient. At 10⁻⁵ M, the reduction was reversible, and a normal pattern was restored in 30 min. Comparison of these results with those of sedimentation analysis of DNA in formamide gradient at neutral pH indicated that single strand breaks which were apparent in alkaline sucrose were probably the result of exposure of alkali-labile lesions in DNA to high pH.

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The mechanism of alkylation of DNA by 5-(3-methyl-l-triazeno) imidazole-4-carboxamide (MIC), a metabolite of dic (NSC-45388) non-involvement of diazomethane

Abstract

European J. Cancer

Biochem. Pharmacol.

Biochem. Pharmacol.

Biochem. Pharmacol.

Tox. Appl. Pharmacol.

Chem.-Biol. Interactions

Advan. Cancer Res.

Biochim. Biophys. Acta

Imidazoles. II. 5(or 4)-monosubstituted triazenoimidazole-4-(or 5)-carboxamides

J. Med, Chem.

Antitumor activity of triazenoimidazoles

Biochem. Pharmacol.

Further investigation on the carcinostatic activity of 4(or 5)-aminoimidazole-5(or 4)-carboxamide derivatives: structure-activity relationship

Gann

Antitumor activity of 4(or 5)-aminoimidazole-5(or 4)-carboxamide derivatives

Gann

Carcinogenicity and possible mode of action of 4(5)-(3,3-dimethyl-l-triazeno)imidazole-5(4)-carboxamide (NSC-45388, DIC)

Carcinogenicity of 4(5)-(3,3-dimethyl-1-triazeno)imidazole-5(4)-carboxamide (NSC-45388, DIC) and related chemicals in rats

Disposition of 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide, a new antitumor agent

J. Pharmacol Exp. Ther.

n-Demethylation of the antineoplastic agent 4(5)-(3,3-dimethyl-1-triazeno)imidazoIe-5(4)-carboxamide by rats and man

Cancer Res.

Metabolism of 5-(3,3-dimethyl-l-triazeno)imidazole-4-carboxamide (NSC-45388) in human and animal tumor tissue

Cancer Chemother. Rep.