Synthesis, antitumor activity and G-quadruplex DNA/ct-DNA binding property of a cationic platinum(II) complex of 2-(4-nitro)-imidazo-[5,6-f][1,10]-phenanthroline

A cationic platinum(II) complex (1), [Pt(4-NOIP)(en)]·Cl2 (4-NOIP = 2-(4-nitro)-imidazo-[5,6-f][1,10]-phenanthroline, en = 1,2-ethylenediamine), has been synthesized and characterized by IR, UV-vis, ESI-MS and element analysis. The interaction of complex (1) with ct-DNA and human telomeric G-quadruplex DNA [Htel-21] has been investigated by circular dichroism absorption and UV–vis absorption titration as well as fluorescent intercalator displacement assay. The circular dichroism absorption data shows that complex (1) can induce linear human telomeric DNA to transform into antiparallel G-quadruplex structure. The binding contants for complex (1) bound to Htel-21 and ct-DNA are 6.89×10 and 7.53×10 M, respectively, indicating that complex (1) interacts with Htel-21 more intensively than ct-DNA. The FID assay suggests that complex (1) intercalates into ct-DNA and Htel-21 quite strongly. CD and UV–vis data together with FID experiments have shown that the complex can intercalate more intensely into Htel-21 and ct-DNA and induce formation and stabilization of antiparallel G-quadruplex. The anticancer activity of the complex have been tested against four different cancer cell lines and normal cell line HL-7702; the complex shows a higher activity than cisplatin and only weak cytotoxicity to HL-7702.