A small-sized c-MYC promoter G-quadruplex selective fluorescent BZT-Indolium binding ligand was demonstrated for the first time as a highly target-specific and photostable probe for in vitro staining and live cell...

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A series of fluorescent ligands, which were systematically constructed from thiazole orange scaffold, was investigated for their interactions with G-quadruplex structures and antitumor activity. Among the ligands, compound 3 was identified to exhibit excellent specificity toward telomere G4-DNA over other nucleic acids. The affinity of 3-Htg24 was almost 5 times higher than that of double-stranded DNA and promoter G4-DNA. Interaction studies showed that 3 may bind to both G-tetrad and the lateral loop near the 5′-end. The intracellular colocalization with BG4 and competition studies with BRACO19 reveal that 3 may interact with G4-structures. Moreover, 3 reduces the telomere length and downregulates hTERC and hTERT mRNA expression in HeLa cells. The cytotoxicity of 3 against cancer cells (IC50 = 12.7–16.2 μM) was found to be generally higher than noncancer cells (IC50 = 52.3 μM). The findings may support that the ligand is telomere G4-DNA specific and may provide meaningful insights for anticancer drug design.

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