Investigating the Effect of Mono- and Dimeric 360A G-Quadruplex Ligands on Telomere Stability by Single Telomere Length Analysis (STELA)

Telomeresare nucleoproteinstructures that cap and protect the natural ends of chromosomes. TelomericDNA G-rich strands can form G-quadruplex(or G4) structures. Ligands that bind to and stabilize G4 structures can lead to telomeredysfunctions by displacing shelterinproteins and/or by interfering with the replication of telomeres. We previously reported that two pyridine dicarboxamide G4 ligands, 360A and its dimeric analogue (360A)2A, were able to displace in vitro hRPA (a single-stranded DNA-binding proteinof the replication machinery) from telomericDNA by stabilizing the G4 structures. In this paper, we perform for the first time single telomerelength analysis (STELA) to investigate the effect of G4 ligands on telomerelength and stability. We used the unique ability of STELA to reveal the full spectrum of telomerelengths at a chromosome terminus in cancer cells treated with 360A and (360A)2A. Upon treatment with these ligands, we readily detected an increase of ultrashort telomeres, whose lengths are significantly shorter than the mean telomerelength, and that could not have been detected by other methods.