Studies on substituted 5H-dibenzo[c,h][1,6]naphthyridin-6-ones and 6H-dibenzo[c,h][2,6]naphthyridin-5-ones have demonstrated that hydrophilic substituents at the 2-position of an ethyl group at the 5- and 6-positions, respectively, can enhance biological activity. The compatibility of such hydrophilic groups at other sites with either TOP1-targeting activity or potent cytotoxic activity has not been explored. The present study examines the influence on biological activity of either a 2-(N,N-dimethylamino)ethyl or a N,N-dimethylacetamide derivative of 8- or 9-amino-5H-dibenzo[c,h]naphthyridin-6-ones that have a 5-butyl- or 5-[2-(N,N-dimethylamino)ethyl]-substituent.