Topoisomerase II-mediated DNA damage produced by 4'-(9-acridinylamino)methanesulfon-m-anisidide and related acridines in L1210 cells and isolated nuclei: relation to cytotoxicity.

4'-(9-Acridinylamino)methanesulfon-m-anisidide (m-AMSA) is a DNA intercalating 9-aminoacridine with clinical activity in adult acute leukemia. m-AMSA has been shown to produce protein-linked DNA strand breaks in mammalian cells through an interaction with the nuclear enzyme DNA topoisomerase II. We have compared the effects of m-AMSA and several acridine analogues (9-aminoacridine; A, NSC 343499; B, SN 16507; C, NSC 140701; D, SN 13553) on DNA integrity and cell survival in L1210 leukemia in vitro. Cells (or isolated nuclei) were treated with drugs (0.1-50 microM) for 0.5-1.0 h and subsequently analyzed using the alkaline elution technique. All drugs, except Compound D, produced DNA-protein cross-links (DPC) in L1210 cells. At 1 microM, potency was in the order, C greater than m-AMSA greater than B greater than A much greater than 9-aminoacridine. In isolated nuclei, DPC and single-strand breaks were produced in essentially a 1:1 ratio, which is consistent with topoisomerase II-mediated protein-linked DNA breaks. Potency differences were less pronounced in nuclei than in cells. In isolated nuclei, Compound D produced extensive DPC not associated with single-strand breaks, which suggests a more complex activity for this compound. Colony formation assays demonstrated the cytotoxicity of most of these acridine analogues (C greater than B greater than A approximately equal to m-AMSA much greater than D = 9-aminoacridine). Correlation of DPC with cell kill gave similar curves for each compound. These results are evidence for a causal relationship between drug-induced topoisomerase II-mediated DNA breaks and cytotoxicity.