Aptamer-based Targeted Delivery of a G-quadruplex Ligand in Cervical Cancer Cells

AS1411 is a G-rich DNA oligonucleotide that functions as an aptamer of the protein nucleolin, found at high levels on the surface of cancer cells but not on the surface of normal cells. Herein, we have studied AS1411 as a supramolecular carrier for the delivery of an acridine-based G-quadruplex ligand, C₈, to HeLa cancer cells. Two AS1411 derivatives, LNA-AS1411 and U-AS1411, were also tested, in an attempt to compare AS1411 pharmacological properties. The results showed that AS1411-C₈ complexation was made with great binding strength and that it lowered the ligand's cytotoxicity towards non-malignant cells. This effect was suggested to be due to a decreased internalization of the complexed versus free C₈ as shown by flow cytometry. The AS1411 derivatives, despite forming a stable complex with C₈, lacked the necessary tumour-selective behaviour. The binding of C₈ to AS1411 G-quadruplex structure did not negatively affect the recognition of nucleolin by the aptamer. The AS1411-C₈ repressed c-MYC expression at the transcriptional level, possibly due to C₈ ability to stabilize the c-MYC promoter G-quadruplexes. Overall, this study demonstrates the usefulness of AS1411 as a supramolecular carrier of the G-quadruplex binder C₈ and the potential of using its tumour-selective properties for the delivery of ligands for cancer therapy.