Quantitative structure-activity relationships on 5-substituted terbenzimidazoles as topoisomerase I poisons and antitumor agents

Several 5-substituted terbenzimidazoles were synthesized and evaluated as mammalian topoisomerase I poisons and for cytotoxicity against a human lymphoblastoma cell line, RPMI-8402. No correlation was observed between topoisomerase I poisoning activity and the Hansch π value or the σ(meta) and σ(para) values associated with each substituent. These data suggest that electronic effects and relative lipophilicity of substituents at the 5-position of these terbenzimidazoles do not have a significant effect upon intrinsic topoisomerase I poisoning activity. There was, however, a good correlation between the relative π values for the various subtituents evaluated and cytotoxic activity. Experimentally determined log P values did not correlate well with either cytotoxicity or π values. Capacity factors (log k') as determined by high pressure liquid chromatography did correlate well with the π values of varied substituents and cytotoxicity. These data indicate that the relative lipophilic activity of substituents at the 5-position of these terbenzimidazoles can strongly influence relative cytotoxic activity.