TOPOISOMERASE-II MEDIATED DNA LESIONS INDUCED BY ACRIDINE-4-CARBOXAMIDE AND 2-(4-PYRIDYL)QUINOLINE-8-CARBOXAMIDE

Acridine-4-carboxamide and 2-(4-pyridyl)quinoline-8-carboxamide repres ent a new generation of antitumor intercalators related to amsacrine ( m-AMSA), a classic topoisomerase II-targeted drug. We examined the abi lity of these tricyclic carboxamides to induce DNA lesions that reflec t the stabilization of topoisomerase II cleavage complexes. DNA-protei n cross-links (DPC) and DNA double-strand breaks (DSB) were assessed i n mouse fibrosarcoma cells (line 935.1). DPC were rapidly formed and r eadily reversible. A bell-shape concentration dependence suggested a s elf-inhibition of DPC at higher drug levels. In isolated nuclei, DPC f ormation by 2-(4-pyridyl)quinoline-8-carboxamide required ATP and was inhibited by novobiocin, a topoisomerase II inhibitor. Acridine-4-carb oxamide and 2-(4-pyridyl)quinoline-8-carboxamide were also potent indu cers of DSB. In contrast to DPC, however, DNA breaks continued to incr ease with drug concentration. These DSB were masked (presumably by non -covalently associated proteins) when analyzed by nucleoid sedimentati on. Thus, while both DPC and DSB seemed to be topoisomerase mediated, at least some DSB appeared to lack t e enzyme bound covalently. DNA le sions by tricyclic carboxamides occurred, in general, at drug concentr ations comparable to those needed to inhibit cell survival. Also, the tricyclic carboxamides inhibited the catalytic activity of isolated to poisomerase II. The results indicate that tricyclic carboxamides inter fere with the action of topoisomerase II. However, the mechanisms of e nzyme inhibition by these drugs differ from the classical trapping of topoisomerase in covalent cleavage complex m-AMSA.