Study on the interactions between B-norcholesteryl benzimidazole compounds with ct-DNA.

The study of molecule-DNA interaction is very important for designing an improved therapeutic agent. In previous studies, we synthesized some B-norcholesteryl benzimidazole compounds, and the tests on cancer cells showed that these compounds had good in vitro anti-cancer activities. In order to further investigate mechanism of their actions, three different B-norcholesteryl benzimidazole compounds were selected and interaction of these compounds with the calf thymus DNA (ct-DNA) was monitored by using various methods including UV-Vis and fluorescence spectroscopic techniques, viscosity measurement, and circular dichroism (CD). The results proved a hypochromic effect accompanied with a slight red-shift due to the interaction of the molecules with ct-DNA. According to the UV-Vis and fluorescence spectra, the mentioned compounds were bound to DNA, preferentially through partial intercalation into the DNA helix. Moreover, the ethidium bromide (EB) and Hoechst 33258 competitive binding experiments were also used to confirm the interaction mode of the compounds with ct-DNA. In the Hoechst 33258 displacement experiment, no significant change in the fluorescence intensity was observed. Additional assays such as iodide quenching, viscosity, and CD spectroscopy further confirmed that intercalation should be the major binding mode of the selected compounds with DNA. The cytotoxicity of these three compounds was also evaluated by MTT method, and the results confirmed that binding ability of these compounds to DNA was consistent with their cytotoxicity behavior. The experimental results indicated a higher binding affinity for compound 3 compared to the other compounds. This research provided a better understanding on the molecular mechanism of the interaction between B-norcholesteryl benzimidazole compounds and tumor cells, and offered a beneficial perspective to the designation of novel B-norsteroidal anticancer compounds.