Selective light-up of dimeric G-quadruplex forming aptamers for efficient VEGF detection.

To develop efficient anticancer theranostic systems, we studied the interaction between a cyanine dye, analogue of thiazole orange (named CyOH), and two G-quadruplex-forming aptamers, V7t1 and 3R02, recognizing the Vascular Endothelial Growth Factor 165 (VEGF) - an angiogenic protein overexpressed in cancer cells, responsible for the rapid growth and metastases of solid tumours. We demonstrated, by exploiting different biophysical techniques - i.e. gel electrophoresis, circular dichroism (CD), UV-vis and fluorescence spectroscopy - that this cyanine interacted with both aptamers giving a marked fluorescence light-up only when bound to their dimeric forms. Interestingly, both oligonucleotides recognized VEGF with higher affinity when adopting dimeric G-quadruplexes, largely prevalent over their monomeric forms in pseudo-physiological conditions. Notably, the fluorescence light-up produced by the probe was maintained when the dimeric aptamer-CyOH complexes bound to the target protein. These complexes, tested on MCF-7 cancer cells using non-tumorigenic MCF-10A cells as control, were effectively internalized in cells and colocalized with a fluorescently-labelled anti-VEGF-A antibody, allowing both recognition and detection of the target. Our experiments showed that the studied systems are promising tools for anticancer theranostic strategies, combining the therapeutic potential of the G4-forming anti-VEGF aptamers with the diagnostic efficacy of the cyanine selective fluorescence light-up.