New Anti-Telomerase Anti-Cancer Agents

The unlimited proliferative potential of cancer cells depends on telomere maintenance. Optimal telomerase activity requires in chromosomal DNA an unfolded single-stranded telomeric overhang. This overhang may adopt an unusual structure called G-quadruplex, composed of guanine G-quartet which forms in the presence of cations. Therefore, ligands that selectively bind to and stabilize telomeric G-quadruplex structures could act as telomerase inhibitors. However, the development of a new class of anticancer drugs based on targeting the telomeric G-quadruplex structure is hampered by a lack of any structural information about the full length overhang because its size is refractory to structure determination by NMR and crystallography. To date there are no reported thermodynamic binding studies for drug interactions with the functionally relevant higher-order telomeric quadruplex structures. Current literature studies on Gquadruplexes formed by telomeric DNA and their interaction with pharmacologically interesting molecules are mostly limited to the analysis of the oligonucleotide formed by only four TTAGGG repeats (such as d(TTAGGG)4 sequences or slight variants thereof), able to fold into a single quadruplex structure. A telomeric single-stranded overhang is actually constituted of tens of TTAGGG repeats, hence it is able to form several consecutive quadruplex structures (multimers) in the overhang region. Recently obtained, unpublished experimental data from our lab have indicated that the binding properties of longer telomeric sequence (n>4) could be different from the those obtained with the short DNA telomeric sequence (n=4). The need of a systematic study of the structure and binding properties of the longer telomeric DNA sequences is thus compelling. We thus first propose an innovative approach to obtain reliable structural models for the long telomeric DNA overhang that can be used as new targets for chemotherapy. Second, we propose a consistent structure-based strategy to design and test (in vitro and in vivo) ligands that specifically bind to these physiological relevant structures. In summary, the research program consists of the following four main steps: 1) Determination of the structure and stability of the single-stranded telomeric DNA overhang. 2) Rational design of ligands using virtual screening. 3) Experimental determination of the affinity in vitro of the potential ligands (designed according to the step 2) for the target structures. 4) Biological testing of the more promising ligands derived from the analysis of the step 2 and 3.