title: beta-Lapachone, a novel DNA topoisomerase I inhibitor with a mode of action different from camptothecin.
abstract: beta-Lapachone is a plant product that has been found to have many pharmacological effects. To date, very little is known about its biochemical target. In this study, we found that beta-lapachone inhibits the catalytic activity of topoisomerase I from calf thymus and human cells. But, unlike camptothecin, beta-lapachone does not stabilize the cleavable complex, indicating a different mechanism of action. beta-Lapachone inhibits topoisomerase I-mediated DNA cleavage induced by camptothecin. Incubation of topoisomerase I with beta-lapachone before adding DNA substrate dramatically increases this inhibition. Incubation of topoisomerase I with DNA prior to beta-lapachone makes the enzyme refractory, and treatment of DNA with beta-lapachone before topoisomerase has no effect. These results suggest a direct interaction of beta-lapachone with topoisomerase I rather than DNA substrate. beta-Lapachone does not inhibit binding of enzyme to DNA substrate. In cells, beta-lapachone itself does not induce a SDS-K(+)-precipitable complex, but it inhibits complex formation with camptothecin. We propose that the direct interaction of beta-lapachone with topoisomerase I does not affect the assembly of the enzyme-DNA complex but does inhibit the formation of cleavable complex.
authors.affiliation: Division of Cell Growth and Regulation, Dana-Farber Cancer Institute, Boston, Massachusetts.
authors.forename: C J
authors.initials: CJ
authors.lastname: Li
authors.forename: L
authors.initials: L
authors.lastname: Averboukh
authors.forename: A B
authors.initials: AB
authors.lastname: Pardee
mesh_terms: D000818:Animals; D002166:Camptothecin / Q000494:pharmacology*; D002417:Cattle; D002460:Cell Line; D018105:DNA, Kinetoplast / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D015473:Leukemia, Promyelocytic, Acute; D008961:Models, Structural; D015394:Molecular Structure; D009285:Naphthoquinones / Q000494:pharmacology*; D009690:Nucleic Acid Conformation; D010957:Plasmids; D011485:Protein Binding; D013379:Substrate Specificity; D013950:Thymus Gland / Q000201:enzymology; D059004:Topoisomerase I Inhibitors; D014407:Tumor Cells, Cultured
chemical_list: D018105:DNA, Kinetoplast; D009285:Naphthoquinones; D059004:Topoisomerase I Inhibitors; C014638:beta-lapachone; D002166:Camptothecin