Abstract
The carbazole ligand 3 was synthesized, characterized and its binding interactions with human telomeric (22HT) G-quadruplex DNA in Na+ and K+-containing buffer were investigated by ultraviolet-visible (UV-Vis) spectrophotometry, fluorescence, circular dichroism (CD) spectroscopy, and DNA melting. The results showed that the studied carbazole ligand interacted and stabilized the intramolecular G-quadruplexes formed by the telomeric sequence in the presence of sodium and potassium ions. In the UV-Vis titration experiments a two-step complex formation between ligand and G-quadruplex was observed. Very low fluorescence intensity of the carbazole derivative in Tris HCl buffer in the presence of the NaCl or KCl increased significantly after addition of the 22HT G4 DNA. Binding stoichiometry of the ligand/G-quadruplex was investigated with absorbance-based Job plots. Carbazole ligand binds 22HT with about 2:1 stoichiometry in the presence of sodium and potassium ions. The binding mode appeared to be end-stacking with comparable binding constants of ~105 M−1 as determined from UV-Vis and fluorescence titrations data. The carbazole ligand is able to induce formation of G4 structure of 22HT in the absence of salt, which was proved by CD spectroscopy and melting studies. The derivative of carbazole 3 shows significantly higher cytotoxicity against breast cancer cells then for non-tumorigenic breast epithelial cells. The cytotoxic activity of ligand seems to be not associated with telomerase inhibition.
Highlights
It is known that human genomic DNA contains guanine rich sequences capable of building stable four-stranded structures called G-quadruplexes (G4s) [1]
G-quadruplex are important in promoter regions of oncogenes such as c-MYC [9,10], c-KIT [11,12], bcl-2 [13,14], RET [15,16], or VEGF [17], as well as in human telomeres [18]
The telomeres end with a single-stranded DNA of the repeatable sequence (TTAGGG)n that exists at both ends of eukaryotic chromosomes in human cells
Summary
It is known that human genomic DNA contains guanine rich sequences capable of building stable four-stranded structures called G-quadruplexes (G4s) [1]. They are made of two or more stacks of four co-planar guanines connected by Hoogsteen-type hydrogen bonds. The interest in G-quadruplexes has increased after the publication of reports on the existence of G-quadruplex structures in human cells [5,6,7], and their supposed regulatory roles in biology [8]. G-quadruplex formed by a telomeric sequence in the presence of sodium and potassium. G-quadruplex formed by a telomeric sequence in the presence of sodium and potassium ions.
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