Synthesis and biological evaluation of bisindenoisoquinolines as topoisomerase I inhibitors.

The indenoisoquinolines represent a class of non-camptothecin topoisomerase I (Top1) inhibitors that exert cytotoxicity by trapping the covalent complex formed between DNA and Top1 during relaxation of DNA supercoils. As an ongoing evaluation of Top1 inhibition and anticancer activity, indenoisoquinolines were linked via their lactam side chains to provide polyamines end-capped with intercalating motifs. The resulting bisindenoisoquinolines were evaluated for cytotoxicity in the National Cancer Institute's human cancer cell screen and for Top1 inhibition. Preliminary findings suggested that the 2-3-2 and 3-3-3 linkers, referring to the number of carbons between nitrogen atoms, were optimal for both potent Top1 inhibition and cytotoxicity. Using optimized linkers, bisindenoisoquinolines were synthesized with nitro and methoxy substituents on the aromatic rings. The biological results for substituted compounds revealed a disagreement between the structure-activity relationships of monomeric indenoisoquinolines and bisindenoisoquinolines as Top1 inhibitors, but cytotoxicity was maintained for both series of compounds.