Theranostic potential of a novel aptamer specifically targeting HER2 in breast cancer cells

Approximately 20% of human breast cancers are characterized by the overexpression of human epidermal growth factor receptor 2 (HER2), which regulates cellular survival and proliferation.HER2-directed monoclonal antibodies (such as pertuzumab and trastuzumab) along with targeted cytotoxic drug delivery through HER2 receptor antibody-drug conjugates (such as trastuzumab deruxtecan and trastuzumab emtansine) have demonstrated some success in targeting HER2 molecules (Ghosh et al., 2011;Krop and Winer, 2014;Gampenrieder et al., 2020;Kunte et al., 2020).However, these drug therapies have significant limitations.Apart from notable adverse drug reactions, they also lead to the rapid development of drug resistance in HER2-positive breast cancer patients (Dent et al., 2013;Kümler et al., 2014;Kumar et al., 2020).These drawbacks could be overcome with the development of selective agents targeting HER2 at the molecular level.When antibodies are employed as imaging tools, they are poorly tolerated due to their native antigenicity and large size, which limits their ability to penetrate tumors with high degrees of compaction.Consequently, over the past decade, many aptamers designed to target cell surface biomarkers have emerged as high-affinity ligands capable of overcoming the limitations of antibodies for both therapeutic and diagnostic applications (Keefe et al., 2010;Li and Lee, 2019;Zhang et al., 2019).Aptamers, which are short synthetic single-stranded RNA or DNA molecules typically consisting of 20-60 oligonucleotides, exhibit high affinity for binding to various molecular targets, including small molecules, nucleic acids, tissues, cells, and proteins (Kumar et al., 2020).They possess several advantageous properties, being chemically stable, modifiable, nonimmunogenic, Background/aim: The overexpression of HER2 is correlated with poorer outcomes and therapeutic resistance in breast cancer patients.While HER2-targeted therapies have shown improvement, prognosis remains poor for HER2-positive breast cancer patients, and these treatments have limitations.Therefore, it is crucial to explore effective molecular strategies for early detection and treatment of HER2positive breast cancers. Materials and methods:In this study, we employed the cell-SELEX method to generate a selective aptamer capable of recognizing HER2 in its native conformation within breast cancer cells, for theranostic applications.Utilizing an adherent cell-SELEX approach, we developed and explored a DNA aptamer, named HMAP7, which can specifically target HER2 in the MDA-MB-453 and SK-BR-3 human breast cancer cell lines.After sequencing, the binding affinities of 10 candidate aptamers to HER2 receptors were evaluated by measuring fluorescence intensities within intact cells using near-infrared optical imaging.The dissociation constant of HMAP7 was determined to be in the nanomolar range in both cell lines.Results: The cell-SELEX-derived aptamer sequence, HMAP7 (41-mer), exhibited the highest binding affinity and specificity for HER2.HMAP7 was rapidly internalized into breast cancer cells overexpressing HER2 but showed no uptake in the HER2 receptor-deficient breast cancer cell line MDA-MB-231.Moreover, HMAP7 demonstrated remarkable selectivity for HER2, rendering it suitable for use in complex biological systems.Conclusions: Our findings suggest that the novel DNA aptamer HMAP7 holds promise for both therapeutic and diagnostic applications, enabling selective delivery of therapeutic agents or imaging of HER2-positive breast tumors.