ctDNA binding affinity and in vitro antitumor activity of three Keggin type polyoxotungestates

•The POMs bind to ct-DNA via groove or outside stacking mode.•POMs have an intense inhibitory effect on the growth of MCF-7 and HEK-293 cancer cells.•The binding affinity of POMs to ctDNA is highly depended to their metal substituted.•CoWCpFe showed the highest antitumor activity in vitro. The ctDNA-binding properties and in vitro antitumor activity of three water soluble Keggin type polyoxometalates (POMs): K6H[CoW11O39CpZr]⋅nH2O, K6H[CoW11O39CpTi]⋅nH2O and K7H2[CoW11O39CpFe]⋅nH2O (abbreviated as CoWCpZr, CoWCpTi and CoWCpFe, respectively) were investigated using UV–Vis absorption spectroscopy, fluorescence spectrophotometry, cyclic voltammetry and MTT assay. The results of UV–Vis, fluorescence and cyclic voltammetry rule out intercalating binding mode and propose the groove or outside stacking binding of these POMs with ctDNA. The values of 1.30×104M−1, 1.15×104M−1 and 3.10×103M−1 were obtained for binding constant of CoWCpZr, CoWCpTi and CoWCpFe to ctDNA, respectively. The redox potential of POMs shift to more negative values in the presence of ctDNA which can be related to domination of electrostatic interaction in this system. The antitumor activity tests of these polyoxometalates (POMs) were carried out on two types of human cancer cells, MCF-7 and HEK-293 by MTT method. The results show the higher antitumor activity of CoWCpFe respect to two other that is related to its highest penetrating effectiveness for MCF-7 cells. Therefore, the antitumor activity of these POMs depends not only on their affinity to ctDNA but also strongly on their penetration ability to the cell membrane.