Cytotoxicity of the traditional chinese medicine (TCM) plumbagin in its copper chemistry

The anticancer traditional Chinese medicine (TCM), plumbagin (PLN), was isolated from Plumbago Zeylanica. Reaction of plumbagin with CuII salt, afforded [Cu(PLN)2]·2H2O (1). With 2,2′-bipyridine (bipy) as a co-ligand, PLN reacts with CuII to give [Cu(PLN)(bipy)(H2O)]2(NO3)2·4H2O (2). 1 and 2 were characterized by elemental analysis, IR, ESI-MS spectra. Their crystal structures were determined by single crystal X-ray diffraction methods. The in vitro cytotoxicity of PLN, 1 and 2 against seven human tumour cell lines was assayed. The metal-based compounds exhibit enhanced cytotoxicity vs. that of free PLN, suggesting that these compounds display synergy in the combination of metal ions with PLN. The binding properties of PLN, 1 and 2 to DNA were investigated through UV-vis, fluorescence, CD spectra, and gel mobility shift assay, which indicated that 1 and 2 were non-covalent binding and mainly intercalated the neighboring base pairs of DNA. PLN, 1 and 2 exhibit inhibition activity to topoisomerase I (TOPO I), but 1 and 2 were more effective than PLN.