A series of amidino-substituted benzimidazoles, related to furyl-phenyl- and thienyl-phenyl-acrylates, naphthofurans and naphthothiophenes were prepared, their antitumor evaluation and interactions with ct-DNA have been investigated. All tested compounds show differential and strong antitumor activity without apparent difference depending on their structures. Interestingly, the MCF-7 tumor cell line is highly sensitive to all compounds. Compounds 6-9 showed noticeable selectivity in regard to normal fibroblasts (WI 38). Compounds 4-9 interact with ct-DNA by more binding modes, whose mutual distribution is dependent on the compound/DNA ratio. The "acyclic"4-6 and "cyclic" compound 7 interact mostly within the minor groove of DNA, although partial intercalation of 6 and 7 cannot be excluded. The "cyclic" compounds 8 and 9 intercalate between DNA base pairs at high excess of DNA over compounds.