In an attempt to create more effective chemotherapeutic compounds, the naphthoquinone adduct 12,13-dihydro-N-methyl-6,11,13-trioxo-5H-benzo[4,5]cyclohepta[1,2-b]naphthalen-5,12-imine (hereafter called TU100) was synthesized. Cell viability studies revealed TU100 is specific for eukaryotes and induces cell death. Based on its structural similarities to the anthracyclines and isoquinolines, the ability of TU100 to inhibit topoisomerase I and II was examined. TU100 was an effective inhibitor of both enzymes, as indicated by its ability to prevent topoisomerase-mediated relaxation of supercoiled plasmid DNA. The mechanism of action does not involve TU100 intercalation into DNA, unlike anthracyclines. Pre-incubation of topoisomerase with TU100 dramatically decreased the IC50, suggesting the drug is a novel slow acting topoisomerase inhibitor that works in the absence of DNA. Taken together these results indicate the novel naphthoquinone adduct TU100 is a dual topoisomerase I/II inhibitor with a unique mechanism of action and chemotherapeutic potential.