81 A new series of biologically active DNA minor groove binders based on bisbenzimidazole and benzimidazole-pyrrole motives

Abstract

As we reported earlier, dimeric bisbenzimidazoles DB(n) (Ivanov et al., 2011a) were able to noncovalently bind in the DNA minor groove and displayed inhibitory activity at low concentrations toward three different DNA-dependent enzymes (Susova et al., 2010; Ivanov et al., 2011b; Cherepanova et al., 2011; Tunitskaya et al., 2011). However, these compounds had a substantial drawback: a low solubility in water solutions, which prevent their potential use in vivo as biologically active preparations. Therefore, for the new minor groove binder series, additional groups were added into the molecule structures for the sake of hydrophility and DNA affinity improvement. A DBP(n) series contains piperazine cycle in the oligomethylene linker which connects bisbenzimidazole fragments of molecule together. A DBPy(n) series have a pyrrole and benzimidazole cycles combination in their structure (Figure 1). DBP(n) (n = 1–4) compounds were studied as inhibitors of calf thymus DNA topoisomerase I (topo-I). All of them inhibited topo-I activity at 1–5 μM concentrations, besides, at concentrations over 5 μM, the inhibitory activities of DBP(n) were few times higher than that of DB(n). It was found that dimeric bisbenzoimidazoles DBP(1–3) were not mutagenic. They were inactive in the point mutagenesis assessment using the Ames test (with Salmonella Typhimurium bacteria as the tested object) and did not display mutagenic or recombinogenic properties in the Drosophila wing somatic mutation and recombination test (SMART). All the compounds of series were evaluated for cytotoxicity in the MTT test on breast cancer MCF-7, large bowel adenocarcinoma HCT-116, noncancer HEK-293 cell lines and on primary murine fibroblasts. All the tested DBP( n ) were not toxic up to concentrations of 100 μM. Contrary, the one tested compound from DBPy(n) series, DBPy(4) (n = 4), showed substantial cytotoxicity against cancer HCT-116 and human leukemic K-562 cell lines with an IC₅₀ of 1–2 μM. Judging by the combination of such criterions as water solubility, topo-I inhibition activity and mutagenicity, it would be safe to assume that dimeric bisbenzoimidazoles of DBP(n) series are more perspective minor groove binders than previously synthesized DB( n ).