Tuning G-Quadruplex Nanostructures with Lipids. Towards Designing Hybrid Scaffolds for Oligonucleotide Delivery.

Two G-quadruplex forming oligonucleotides [d(TGT) and d(TGT)] were selected as two tetramolecular quadruplex nanostructures because of their demonstrated ability to be modified with hydrophobic molecules. This allowed us to synthesize two series of G-quadruplex conjugates that differed in the number of G-tetrads, as well as in the terminal position of the lipid modification. Both solution and solid-phase syntheses were carried out to yield the corresponding lipid oligonucleotide conjugates modified at their 3'- and 5'-termini, respectively. Biophysical studies confirmed that the presence of saturated alkyl chains with different lengths did not affect the G-quadruplex integrity, but increased the stability. Next, the G-quadruplex domain was added to an 18-mer antisense oligonucleotide. Gene silencing studies confirmed the ability of such G-rich oligonucleotides to facilitate the inhibition of target luciferase without showing signs of toxicity in tumor cell lines.