Spectrophotometric analysis of flavonoid-DNA interactions and DNA damaging/protecting and cytotoxic potential of flavonoids in human peripheral blood lymphocytes.

The ability of luteolin, kaempferol and apigenin to bind to calf thymus (ct)-DNA, mode of action and stability of flavonoids in buffer were investigated. Spectrophotometric analysis revealed a rapid degradation of apigenin in an aqueous medium, while kaempferol and luteolin were stable for 24h upon dissolution in water. Spectrophotometric study of the interactions of kaempferol and luteolin with calf thymus DNA suggests classic intercalation as their dominant binding mode to DNA. Cytotoxicity/genotoxicity and cytoprotective/genoprotective effects of flavonoids in non-stressed and hydrogen peroxide stressed human peripheral lymphocytes were investigated using the fluorescent dye exclusion method and alkaline comet assay. Flavonoids revealed significant genoprotective effects in hydrogen peroxide stressed cells and in cells submitted to longer incubation in the cell culture medium. Luteolin, followed by apigenin and kaempferol, was shown to be the most effective in protecting DNA from oxidative damage induced by hydrogen peroxide. However, the investigated flavonoids also induced DNA damage, indicating their prooxidative capacity. The balance between the protection of DNA from oxidative damage and prooxidative effects was strongly dependent on flavonoid concentration and the incubation period.

Minor structural differences of monomethine cyanine derivatives yield strong variation in their interactions with DNA, RNA as well as on their in vitro antiproliferative activity.

Comparison of binding properties of a series of monomethine cyanine derivatives to ds-DNA and ds-RNA revealed significant impact of the properties of substituent attached to the longer axis of aromatic core. Namely, it seems that only compounds 7, 8 characterised by length of longer axis not exceeding the length of longer axis of basepairs could intercalate into ds-DNA and ds-RNA, while the increased substituent length and additional possibility of hydrogen bonds formation directed binding of 1-6 into ds-DNA minor groove. Consequent ds-RNA over ds-DNA selectivity of 7 and 8 is the most appealing and rather rare property among small molecules. The interactions of 1-8 with ss-RNA were strongly dependent on both, structure of compound and base composition of RNA. The cytotoxicity screening of compounds 1-8 by MTT test revealed considerable antiproliferative activity against solid tumours and especially toward haematological malignancies (IC(50)=0.001-6.6 microM), whereby normal human aortic endothelial cells (HAEC) were significantly less affected (IC(50)=1-200 microM). The cells of chronic myeloid leukaemia in blast crisis (K562) were especially sensitive to all tested compounds (IC(50)=0.001-0.6 microM), while normal lymphocytes were more resistant (IC(50)=0.01-1 microM). Results of uptake and intracellular distribution of compounds 1 and 2 in the living cells showed that they do not bind primarily to nuclear DNA but their fluorescence is scattered through the whole cells. A detailed mechanism of antitumor activity of tested molecules remains to be investigated.