Targeting hTERT core promoter with specific G-quadruplex ligands

In mammalian somatic cells telomeres shorten at each replication till they reach a critical length that leads to cell replicative senescence. Cancer cells overcome this limit by acquiring the capability to maintain functional telomeres. In most cases, this is due to upregulation of the expression of hTERT, encoding the proteic moiety of telomerase. Therefore, several anti-cancer strategies that target telomerase activity and hTERT expression are being developed. One of these strategies is based on ligands that induce the formation of a G-quadruplex structure at the ends of chromosomes, thus preventing telomerase elongation. Recently, it has been reported that the hTERT core promoter contains a G-rich region able to form multiple G-quadruplex structures, representing a possible target for G-quadruplex ligands. By means of circular dichroism (CD) spectroscopy and DNA polymerase stop assay we report that a series of perylene derivatives with different hydrophilic side chains (HPDIs, hydrosoluble perylene diimides) are able to specifically stabilize G-quadruplex structures and superstructures on the hTERT promoter and to inhibit DNA replication. These data suggest that ligand-induced G-quadruplex formation on hTERT promoter could affect hTERT expression. An analysis of HPDIs effect on hTERT promoter activity by luciferase reporter assay is in progress. An attractive hypothesis is that G-quadruplex ligands could inhibit telomerase activity not only by targeting the terminal telomeric G-tails but also by inducing G-quadruplex structures on the hTERT promoter.