Podophyllotoxin aza-analogue, a novel DNA topoisomerase II inhibitor

The pendant E-ring moiety of the podophyllotoxin aza-analogue 1 that is a p otent inhibitor of microtubule assembly was modified in order to acquire in hibitor? activity of DNA topoisomerase II. The monophenolic analogue 2 did not exhibit human topoisomerase II inhibition, while the ortho-quinone 3 th at was obtained by oxidation of 2 inhibited its catalytic activity (decaten ation) in a dose-dependent manner and stimulated double strand DNA breaks i n supercoiled circular plasmid DNA, resulting in the production of linear D NA. These results showed that the topoisomerase II inhibition of the ortho- quinone 3 is due to stabilization of the topoisomerase II-DNA covalent bina ry complex. On the other hand, the ortho-quinone 3 did not inhibit the rela xation process of supercoiled DNA by topoisomerase 1 at concentrations up t o 100 mu M, nor was intercalation observed in unwinding measurements of 3. Therefore, the ortho-quinone 3 was shown to be a novel nonintercalative top oisomerase II specific inhibitor that stabilizes the cleavable complex. The present results suggest that the 4'-free hydroxyl group on the E-ring and the sugar moiety on the C-ring are not a prerequisite for topoisomerase II inhibition by podophyllotoxin derivatives.