Induction of DNA topoisomerase II-mediated DNA cleavage by beta-lapachone and related naphthoquinones.

Recent studies have suggested that 3,4-dihydro-2,2-dimethyl-2H-naphtho[1,2-b]pyran-5,6-dione (beta-lapachone) inhibits DNA topoisomerase I by a mechanism distinct from that of camptothecin. To study the mechanism of action of beta-lapachone, a series of beta-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, beta-lapachone does not induce topoisomerase I-mediated DNA breaks. However, beta-lapachone and related naphthoquinones, like menadione, induce protein-linked DNA breaks in the presence of purified human DNA topoisomerase IIalpha. Poisoning of topoisomerase IIalpha by beta-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 beta-lapachone, an ortho-quinone, together with their similar activity in poisoning topoisomerase IIalpha, suggests a common mechanism of action involving chemical reactivity of these quinones. Indeed, both quinones form adducts with mercaptoethanol, and beta-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, beta-lapachone and related naphthoquinones are found to be cytotoxic against a panel of drug-sensitive and drug-resistant tumor cell lines, including MDR1-overexpressing cell lines, camptothecin-resistant cell lines, and the atypical multidrug-resistant CEM/V-1 cell line.

Selection of natural treatment processes for algae removal from stabilisation ponds effluents in Brasilia, using multicriterion methods.

A multicriterion methodology is used in the evaluation and selection of the most appropriate alternative(s) for removing algae from stabilisation ponds effluents in a case study in Brasilia. For this purpose, five different natural treatment processes are tested at pilot scale: rock filter, sand filter, floating aquatic plants, constructed wetlands, and overland flow. These pilot units were constructed in Brasilia and set in parallel, each one receiving a portion of the effluent that comes from an existing wastewater treatment plant composed of preliminary treatment, UASB reactors, and high-rate stabilisation ponds. Several evaluation criteria are used in order to relate the capabilities of the post-treatment processes to the multiple objectives in this case. Two multicriterion decision-aid methods--compromise programming and ELECTRE-III--are used to select the most satisfying processes. The top ranking alternatives are indicated for subsequent studies, considering the possible implementation of these technologies to existing plants.

Reaction of beta-lapachone and related naphthoquinones with 2-mercaptoethanol: a biomimetic model of topoisomerase II poisoning by quinones.

1,2-Naphthoquinones, such as beta-lapachone, 4-alkoxy-1,2-naphthoquinones, and tetrahydrofuran-1,2-naphthoquinones, react rapidly with 2-mercaptoethanol in benzene to give 1,4-, 1,2-, 1,3- and 1,6-Michael-type adducts that are formed by the addition of the thiol group to the quinone ring. Menadione (2-methyl-1,4-naphthoquinone) reacts with the thiol reagent very slowly under the same reaction conditions. Although the formation of the adducts can be followed by 1H-NMR, attempts to isolate the adducts failed due to their retroconversion to the starting products. On addition of a Lewis acid, however, the adducts undergo cyclization reactions that give stable derivatives that can be isolated and characterized. Determination of the structures of the derivatives allowed for the identification of the adducts from which they originated. Thus, beta-lapachone and 2,3-dinordunnione underwent 1,4- and 1,2-Michael type additions to the quinone ring, while 4-pentyloxy-1,2-naphthoquinone underwent two simultaneous Michael additions to the quinone ring of the naphthoquinone. Menadione underwent a single 1,3-addition. The alkylation rates of the thiol group of 2-mercaptoethanol by the naphthoquinones parallel the naphthoquinones efficiencies in inducing DNA cleavage through DNA-bound topoisomerase II. These results support our hypothesis that the cytotoxic effect of the naphthoquinones derive, at least in part, from their alkylation of exposed thiol residues on the topoisomerase II-DNA complex.