ctDNA interaction of Co-containing Keggin polyoxomolybdate and in vitro antitumor activity of free and its nano-encapsulated derivatives

Polyoxometalates (POMs) are negatively charged clusters consisting of transition metals and oxygen atoms. The antiviral and antitumor activities are the dominant activities of POMs in pharmacology and medicine. Based on Co-containing Keggin polyoxomolybdate (K6[SiMo11O39Co(H2O)].nH2O), nanosized starch, and lipid-encapsulated derivatives (abbreviated as SiMo11Co, SEP and LEP, respectively) were synthesized and characterized by FT-IR spectroscopy, ICP, TG analysis, SEM and TEM images. The results show that the SiMo11Co retains its parent structure after encapsulation by starch and lipid nanoparticles. The biological activity of SiMo11Co has been evaluated by investigating its binding ability to calf thymus DNA (ctDNA), using UV–Vis absorption spectroscopy, fluorescence quenching and fluorescence Scatchard plots. The obtained results of absorption titration rule out the intercalating binding mode and propose the groove or outside stacking binding for SiMo11Co. These results were authenticated by fluorescence quenching experiments and scatchard plots. Absorption spectral traces reveal 10.21 % hyperchromism for SiMo11Co. The value of 7.6 × 103 M−1 was obtained for binding constant (Kb) of SiMo11Co to ctDNA. Furthermore, the in vitro antitumor activity of SiMo11Co and nano-encapsulated forms was investigated using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay that was carried out on two types of human cancer cells, MCF-7 (breast cancer cells) and HEK-293 (Human Embryonic Kidney). The results represent the enhancement of cell penetration and antitumor activity of SiMo11Co due to its encapsulation in starch or lipid nanoparticles. However, this observed enhancement for the lipid relative to the starch nanocapsule can be attributed to its smaller size.