Abstract
Human telomeric DNA consists of tandem repeats of the sequence d(TTAGGG) with a 3′ 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 DNA-binding 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.
Footnotes
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This work was supported by grants from the “Ligue Nationale Contre le Cancer, Equipe labelisée 2006” (to J.F.R.), by the Association pour la Recherche contre le Cancer 3365 (to J.L.M.), and from the European Union FP6 “MolCancerMed” program (LSHC-CT-2004-502943 to J.L.M.). D.G. and B.B. have been supported by a postdoctoral fellowship from the Institut de Chimie des Substances Naturelles/Centre National de la Recherche Scientifique. N.T.-S. is supported by a doctoral fellowship from the “Région Champagne Ardenne”.
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Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
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doi:10.1124/mol.107.036574.
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ABBREVIATIONS: hTERT, human telomerase reverse transcriptase; PCR, polymerase chain reaction; POT1, protection of telomere 1; TBE, Tris-borate-EDTA; DAPI, 4,6-diamidino-2-phenylindole; TRF, terminal restriction fragment; steroid FG, a funtumine derivative substituted witha guanylhydrazone moiety; EtBr, ethidium bromide; TRF, telomere repeat factor.
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↵1 Current affiliation: Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 5089, Toulouse, France.
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↵2 Current affiliation: Laboratoire de Physiologie Cellulaire Végétale, Institut de Recherches en Technologie et Sciences pour le Vivant, Commissariat à l'Energie Atomique Grenoble, Grenoble, France.
- Received March 29, 2007.
- Accepted June 20, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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