The synthesis, characterization, inhibitory activity against topoisomerase I, and biological evaluation of a series of oligopeptide-substituted bisindolylmaleimides 7-12 are described. Compounds 7-9, which contain a basic C-terminus function such as (dimethylamino)propyl and bind to DNA with C(50) values of 200, 160, and 135 microM, respectively, exhibited inhibition of topoisomerase I in a concentration dependent manner. Also, the relative order of observed topoisomerase I inhibition is 9 > 8 > 7 at < or = 100 microM concentration, corresponding to the increase of the number of pyrrole units in the oligopeptide moiety. Compounds 10-12, which contain an electrostatically neutral moiety, such as methyl ester, did not bind to DNA templates nor inhibit topoisomerase I. However, the cytotoxicity activities of these compounds were 1.5 times greater than those of compounds 7-9.