Identification of Novel Quadruplex Ligands from Small Molecule Libraries by FRET-Based High-Throughput Screening

Abstract

Guanosine-rich nucleic acid sequences can fold into noncanonical higher order structures named G quadruplexes (GQPs). These folds are stabilized by eight Hoogsteen hydrogen bonds per tetrad and p–p stacking interactions between the tetrads.[1] Due to their stability quadruplexes occurring in promoter regions of genes [2] or at the telomeric ends of eukaryotic chromosomes have been suspected to play regulatory roles in gene expression and cell cycle control. [3] In addition, compounds binding to quadruplexes have been studied intensively because of their potential in anticancer treatment.[4] Telomeric DNA comprises thousands of double-stranded tandem repeats of the sequence d(GGGTTA)[5] and a single stranded G rich 3’ overhang of about 100–200 nucleotides.[6] During the life time of a somatic cell telomeres are permanently shortened because of the end-replication problem. At a critical length this leads to induction of cell cycle arrest or even to cell death. [7] However, in about 80–85% of all cancer cells this problem is circumvented as the telomere length is maintained by activation of telomerase,[8] an enzyme that is inactive in somatic cells. [9] By addition of telomeric repeats to the single stranded 3’ overhang, cancer cells can become immortal.[10] Several compounds have been shown to induce quadruplexes, disturbing the telomeric structure and function providing a promising anticancer treatment.