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 pi value or the sigma meta and sigma 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 pi values for the various substituents evaluated and cytotoxic activity. Experimentally determined log P values did not correlate well with either cytotoxicity or pi values. Capacity factors (log k') as determined by high pressure liquid chromatography did correlate well with the pi 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.