Novel Derivatives of Pyridylbenzo[b]thiophene-2-carboxamides and Benzo[b]thieno[2,3-c]naphthyridin-2-ones: Minor Structural Variations Provoke Major Differences of Antitumor Action Mechanisms

Novel cyano- and 2-imidazolinyl-substituted derivatives of pyridylbenzo[b]thiophene-2-carboxamides 4, 5, 10-13 and benzo[b]thieno[2,3-c]naphthyridin-2-ones 6, 7, 14-17 were prepared. All derivatives showed a prominent antiproliferative effect. Extensive DNA binding studies and additional biological evaluations point to various modes/targets of action. The results strongly support intercalation into DNA as a dominant binding mode of fused analogues, which was substantiated using topoisomerase I inhibition assay. Most intriguingly, only minor structural difference between "nonfused" compounds 12 and 13 has strong impact on the interactions with DNA; while 13 binds within the DNA minor groove in the form of dimer, 12 does not form significant interactions with DNA. The assumption that severe mitotic impairment (G2/M phase arrest) induced by 12 could point to tubulin, another important target, was confirmed by its obvious anti-tubulin activity observed in immunofluorescence assay, whereby treated cells showed disruption of microtubule formation comparable to the effect obtained by paclitaxel. a well-known tubulin antagonist chemotherapeutic.