32P-post-labeling analysis of DNA adduct formation by antitumor drug nitracrine (Ledakrin) and other nitroacridines in different biological systems.

A 32P-post-labeling method has been employed to detect DNA adducts formed by derivatives of nitro-9-aminoacridine in both cellular and non-cellular systems. The treatment of HeLa S3 cells in culture or Ehrlich ascites tumor cells in vivo with nitracrine and two other antitumor 1-nitro-9-aminoacridines, denoted C-857 and C-1006, resulted in covalent binding of these compounds to cellular DNA. Each derivative studied gave rise to a distinct pattern of adduct spots and the similarity of the respective adduct profiles was noted for the both cellular models. Calf thymus DNA samples modified in vitro with nitracrine and C-857 in the presence of either rat hepatic microsomal fraction or dithiothreitol yielded chromatographic profiles resembling those obtained in the cellular systems, suggesting similarity in the DNA adduct structures. There were also neither qualitative nor quantitative differences in calf thymus DNA modification by these two 1-nitro derivatives between aerobic and anaerobic conditions, thus the reduction of a nitro group seems not to be the only determinant of covalent binding to DNA in vitro. No DNA adduct formation was detected in the cellular systems used with 2-nitro and 4-nitro isomers of nitracrine that are devoid of cytotoxic activity, which provides further evidence that both covalent binding and DNA crosslinking, but not intercalation, are responsible for cytotoxic and antitumor properties of 1-nitro-9-aminoacridines.