Induction of DNA topoisomerase II-mediated DNA cleavage by β-lapacphone and related naphthoquinones

Recent studies have suggested that 3,4-dihydro-2,2-dimethyl-2H- naphtho[1,2-b]pyran-5,6-dione (β-lapachone) inhibits DNA topoisomerase I by a mechanism distinct from that of camptothecin. To study the mechanism of action of β-lapachone, a series of β-lapachone and related naphthoquinones were synthesized, and their activity against drug-sensitive and resistant cell lines and purified human DNA topoisomerases as evaluated. Consistent with the previous report, β-lapachone does not induce topoisomerase I- mediated DNA breaks. However, β-lapachone and related naphthoquinones, like menadione, induce protein-linked DNA breaks in the presence of purified human DNA topoisomerase IIα. Poisoning of topoisomerase IIα by β-lapachone and related naphthoquinones is independent of ATP and involves the formation of reversible cleavable complexes. The structural similarity between menadione, a para-quinone, and β-lapachone, an ortho-quinone, together with their similar activity in poisoning topoisomerase IIα, suggests a common mechanism of action involving chemical reactivity of these quinones. Indeed, both quinones form adducts with mercaptoethanol, and β-lapachone is 10-fold more reactive. There is an apparent correlation between the rates of the adduct formation with thiols and of the topoisomerase II-poisoning activity of the aforementioned quinones. In preliminary studies, β-lapachone and related naphthoquinones are found to be cytotoxic against a panel of drug-sensitive tumor cell lines, including MDR1-overexpressing cell lines, camptothecin- resistant cell lines, and the atypical multidrug-resistant CEM/V-1 cell line.