Novel dications with unfused aromatic systems: Trithiophene and trifuran derivatives of furimidazoline

We report the synthesis, interaction with DNA, topoisomerase II inhibition, and cytotoxicity of two novel unfused aromatic dications derived from the antimicrobial agent furimidazoline. The central diphenylfuran core of furim idazoline has been replaced with a trithiophene (DB358) or a trifuran (DB66 9) unit and the terminal imidozoline groups were preserved. The strength an d.-mode of binding of the drugs to nucleic acids were investigated by compl ementary spectroscopic techniques including spectrophotometric, surface pla smon resonance, circular and linear dichroism,measurements. The trifuran de rivative forms intercalation complexes with double-stranded DNA, whereas th e mode of binding of the trithiophene derivative varies depending on the dr ug/DNA ratio, as independently confirmed by NMR spectroscopic studies perfo rmed with (A-T)(7) and (G-C)(7) oligomers. Two-dimensional NMR data provide d a molecular model for the binding of DB358 within the minor groove of the AATT sequence of the decanucleotide d(GCGAATTCGC)(2). DNase I footprinting experiments confirmed the sequence-dependent binding of DB358 to DNA. The trithiophene derivative interacts preferentially with AT-rich sequences at low, concentrations, but can accomodate GC sites at,higher, concentrations. DNA relaxation assays revealed that DB358 stimulated DNA cleavage by topoi somerase II, in contrast to DB669. The substitution of N-alkylamidines for the imidazoline terminal groups, abolished the capacity of the drug to pois on topoisomerase II. At the cellular level, flow cytometry analysis indicat ed that DB358, which is about six times more cytotoxic than the trifuran an alogue, induced a significant accumulation,of HL-60 human leukemia cells, i n the G2/M phase. The incorporation of thiophene heterocycles appears as a convenient procedure to limit the strict AT selectivity of dications contai ning on extended unfused aromatic system and to design cytotoxic DNA,interc alating agents acting as poisons for human topoisomerase II.