In vitro antitumor activity of parent and nano-encapsulated mono cobalt-substituted Keggin polyoxotungstate and its ctDNA binding properties

• The free and encapsulated SiW11Co have a strong inhibitory on the two cell lines.
• The SEP and LEP showed the higher antitumor activity than the parent POM in vitro.
• The SiW11Co bind to ctDNA via groove or outside stacking mode.
• The binding affinity of SiW11Co to ctDNA is highly depended to [SiW11Co]/[ctDNA].

The parent and nanosized starch, and lipid encapsulated K6[SiW11O39Co(H2O)]·nH2O (abbreviated as SEP, LEP and SiW11Co, respectively), as potent antitumor candidates, were synthesized and characterized by FT-IR spectroscopy, ICP, TG analysis, SEM and TEM images. The results show that the SiW11Co retains its parent structure after encapsulation by starch and lipid nanoparticles. Antitumor activity tests of SiW11Co and its encapsulated forms were carried out on two types of human cancer cells, MCF-7 and HEK-293 by MTT method. The encapsulated forms exhibited the higher antitumor activity compared to the parent SiW11Co. However, this observed enhancement for the lipid encapsulated form is more than the starch counterpart, which can be related to its smaller size. These results showed that these compounds can be novel antitumor candidates. The calf thymus DNA (abbreviated as ctDNA) binding ability of SiW11Co was also investigated, using UV–Vis absorption spectroscopy, fluorescence quenching and fluorescence Scatchard plots. Absorption spectra tracing reveal 10% hyperchromism for SiW11Co. The values of 1.8 × 104 and 1.2 × 104 M−1 were obtained for association binding constant of SiW11Co to ctDNA at R ⩾ 1 and R < 1, respectively (R is defined as the mole ratio of SiW11Co to ctDNA). It was shown that the interaction of SiW11Co with ctDNA depended on the R values. The obtained results of absorption titration rejected the intercalating binding mode and suggest the groove or outside stacking binding for SiW11Co. These results were authenticated by fluorescence quenching experiments and scatchard plots.