G-Quadruplex DNA as a Macromolecular Target for Semi-Synthetic Isoflavones Bearing B-Ring Tosylation

Abstract

Guanine-rich sequences of nucleic acids, including DNA and RNA, are known to fold into non-canonical structures named G-quadruplexes (G4s). Such arrangements of these macromolecular polymers are mainly located in telomeres and in promoter regions of oncogenes and, for this reason, they represent a potential target for compounds with therapeutic applications. In fact, the ligand-mediated stabilization of G4s inhibits telomerase and the activity of transcriptional machinery and counteracts cancer cell immortalization. Flavonoids, along with other classes of small molecules, have been previously tested for their ability to stabilize G4s, but the mechanism of their interaction has not been fully elucidated. In the current work, we report a multi-technique investigation on the binding of tosylated isoflavones obtained by the B-ring modification of compounds from Maclura pomifera to a telomeric DNA sequence. Our study demonstrates that such derivatization leads to compounds showing lower binding affinity but with an increased selectivity toward G4 with respect to double-stranded DNA. The binding mode to the macromolecular target G4 was studied by combining results from electrospray mass spectrometry binding studies, nuclear magnetic resonance experiments and computational simulations. Overall, our findings show that tosylation influences the selectivity toward the macromolecular target by affecting the interaction mode with the nucleic acid.