A New Steroid Derivative Stabilizes G-Quadruplexes and Induces Telomere Uncapping in Human Tumor Cells

Abstract

Human telomeric DNA consists of tandem repeats of the sequence d(TTAGGG) with a 3Ј single-stranded extension (the G-overhang). The stabilization of G-quadruplexes in the human telomeric sequence by small-molecule ligands inhibits the activity of telomerase and results in telomere uncapping, leading to senescence or apoptosis of tumor cells. Therefore, the search for new and selective G-quadruplex ligands is of considerable interest because a selective ligand might provide a telomere-targeted therapeutic approach to treatment of cancer. We have screened a bank of derivatives from natural and synthetic origin using a temperature fluorescence assay and have identified two related compounds that induce G-quadruplex stabilization: malouetine and steroid FG. These steroid derivatives have nonplanar and nonaromatic structures, different from currently known G-quadruplex ligands. Malouetine is a natural product isolated from the leaves of Malouetia bequaaertiana E. Woodson and is known for its curarizing and DNAbinding properties. Steroid FG, a funtumine derivative substituted with a guanylhydrazone moiety, interacted selectively with the telomeric G-quadruplex in vitro. This derivative induced senescence and telomere shortening of HT1080 tumor cells at submicromolar concentrations, corresponding to the phenotypic inactivation of telomerase activity. In addition, steroid FG induced a rapid degradation of the telomeric G-overhang and the formation of anaphase bridges, characteristics of telomere uncapping. Finally, the expression of protection of telomere 1 (POT1) induced resistance to the growth effect of steroid FG. These results indicate that these steroid ligands represent a new class of telomere-targeted agents with potential as antitumor drugs.

Design, synthesis and evaluation of 4,7-diamino-1,10-phenanthroline G-quadruplex ligands

“…A preferred role of the guanidinium group in quadruplex ligands is supported by two independent dynamic combinatorial libraries targeting quadruplex DNA, which both identified the guanidinium-containing compounds as the favored library members, 43,44 and by the higher efficiency of the guanidinium-containing steroid FG exhibited compared to the analogous trimethylammonium steroid maouetine. 45 …”

G‐Quadruplexes: Targets in Anticancer Drug Design

“…[59] Recently, some G-quadruplex ligands have been found to interfere with the conformation and length of the telomeric G-overhang; [60] other studies have also shown that some G-quadruplex ligands may function by dissociation of the telomere binding proteins POT1 (protection of telomeres 1) and TRF2 (telomeric repeat binding factor 2) and uncapping telomeres to make them available for extension. [61][62][63][64] Additionally, the biological functions of telomeres are likely to be dependent on the nature of their various structural states. For example, hybrid quadruplexes can occur within a 3'-end overhang, and the subsequent packaging enables the formation of a so-called t-loop at the end of the chromosome, which is likely to provide flexibility for responding to such environmental changes as protein binding.…”

Power from the Garden: Plant Compounds as Inhibitors of the Hallmarks of Cancer

“…Telomere capping alterations have been associated with G-quadruplex formation. Brassart et al screened natural and synthetic derivatives and identified two natural compounds as potent inducers of G-quadruplex configuration [119]. Both, malouetine (34) isolated from leaves of Malouetia bequaaertiana E. Woodson and a funtumine derivative called funtumine guanylhydrazone (35) from the leaves of Funtuna latifolia stapf induced G-quadruplex stabilization.…”