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

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.