Described herein are the synthesis, cytotoxic properties, and
topoisomerase II inhibition assays of benzodiimidazole and dipyrroloimidazobenzimidazole structural variants of the pyrrolo[1, 2-a]
benzimidazole or APBI ring system. These ring variants were designed to inhibit
topoisomerase II, much as the APBIs are able to do. Since only the
quinone form of the APBIs can intercalate
DNA, two-electron reduction to the
hydroquinone by
DT-diaphorase is known to deactivate these compounds. Indeed, the APBIs possess a high inverse correlation with the cellular concentration of
DT-diaphorase. Therefore one feature of the ABPI structural variants is the excessive bulk about the
quinone ring, which was predicted to diminish
DT-diaphorase substrate activity. Another feature is the presence of one or two alkylating centers, which would permit alkylation of
DNA and/or
topoisomerase II. Inhibition assays for
topoisomerase II-mediated relaxation of
supercoiled DNA indicate that the benzodiimidazole and dipyrroloimidazobenzimidazole
quinone ring systems are catalytic inhibitors of
topoisomerase II. Both
quinone systems exhibit cytotoxicity perhaps due to the lack of inactivation by
DT-diaphorase as well as
topoisomerase II inhibition. One
quinone displayed the novel feature of cytotoxicity selectively against
melanoma cell lines. In conclusion, the benzodiimidazole and dipyrroloimidazobenzimidazole
quinone ring systems will be subjected to future analogue development and structure-activity studies.