Cell line selectivity and DNA breakage properties of the antitumour agent N-[2-(dimethylamino)ethyl]acridine-4-carboxamide: role of DNA topoisomerase II.

N-[2-(Dimethylamino)ethyl]acridine-4-carboxamide (NSC 601316) is a DNA intercalating experimental antitumour agent which is curative against the Lewis lung carcinoma in mice. Its action has been compared with amsacrine, its inactive isomer oAMSA, the solid tumour active derivative CI-921 (NSC 343499), a C-6 methylene chain-linked bisacridine (NSC 210733), 9-aminoacridine and quinacrine. All compounds inhibited the unknotting of phage P4 DNA by topoisomerase II in nuclear extracts prepared from L1210 cells. NSC 601316 inhibited growth of cultured L1210, P388, P/AMSA (P388 resistant to amsacrine) and P/ACTD (resistant to actinomycin D) cell lines at concentrations of 87, 150, 2020 and 150 nM respectively. A 1 h drug exposure to 0.85 microM NSC 601316 killed 50% of L1210 cells. L1210 cells treated for 1 h with NSC 601316 accumulated DNA breaks and protein-DNA cross-links. There was a good correlation between DNA breakage and cytotoxicity, but the relationship between drug concentration and number of protein-DNA cross-links was non-linear and differed from that of amsacrine and CI-921. There was also a positive correlation between the degree of cross-resistance of P/AMSA cells (which have altered topoisomerase II function) and ability to induce DNA breakage or protein-DNA complexes. The results suggest that topoisomerase II is the target of action of NSC 601316.