Targeting HER2 with DNA Aptamers for Efficient Anticancer Drug Delivery: A Combined Experimental and Computational...

Targeted delivery of cytostatic drugs is a powerful approach to achieving tumor tissue selectivity, reducing systemic toxicity, and ultimately improving the efficacy of anticancer chemotherapy. Targeting can be achieved using a wide range of molecular ligands, with DNA aptamers being a promising representative. In this work, we employed flow cytometry, a AuNP-aptasensor, and atomic-scale computer modeling to assess the affinity of several DNA aptamers (Anti-HER2, HB5, Apt-6, HeA2_1, and HeA2_3) for human epidermal growth factor receptor 2 (HER2), which is known to be one of the factors that promote the growth of breast cancer cells. Flow cytometry showed that short aptamers (HeA2_1 and HeA2_3) had a higher affinity for HER2 on MDAMB453 cancer cells than longer aptamers (HB5, Apt-6). HER2-negative MDA-MB-231 cells served as the negative control. The HeA2_3 aptamer has a high average affinity (HeA2_3:23.6, HeA2_1:13.1, Apt-6:3.6; HB5:3.5; Anti-HER2:3.2) and a nearly Gaussian distribution across the cells, while HeA2_1 forms a fraction of cells with a relatively high fluorescence signal intensity (HeA2_1:11.6; HeA2_3:5.9; Apt-6:3.4; HB5:3.1; Anti-HER2:2.1). Most of the findings for cancer cells also hold for the HER2-positive small extracellular vesicles studied using the AuNP-aptasensor. Computer simulations confirmed that short aptamers are characterized by stronger binding to the extracellular domain of HER2. A detailed analysis of the free energy allowed us to show for the first time that tight binding to HER2 correlates with well-separated hot and cold spots on the protein surface. For the aptamers that meet these criteria (HeA2_1, HeA2_3, and Anti-HER2), favorable interactions with HER2 are driven by the local attraction of nucleotides to arginine and lysine residues of HER2 and possibly stabilized by intermolecular hydrogen bonds. For longer aptamers (Apt-6 and HB5), hot and cold spots on the HER2 surface overlap and the aptamers show much weaker binding. Overall, our findings show that binding of DNA aptamers to HER2 cannot be characterized merely by the dissociation equilibrium constant. A more sophisticated approach that combines experimental and computational methods allowed us to unlock the molecular mechanisms behind the aptamer-HER2 bindings. The results of our study also suggest that computer modeling has become a reliable and accurate tool for aptamer prescreening prior to laboratory experiments.