###### Abstract  
Sialyations are post-translational modifications of proteins and lipids that play important roles in many cellular events, including cell-cell interactions, proliferation, and migration. Tumor cells express high levels of sialic acid (SA), which are often associated with the increased invasive potential in clinical tumors, correlating with poor prognosis. To overcome the lack of natural SA-receptors, such as antibodies and lectins with high enough specificity and sensitivity, we have used molecularly imprinted polymers (MIPs), or \"plastic antibodies\", as nanoprobes. Because high expression of epithelial cell adhesion molecule (EpCAM) in primary tumors is often associated with proliferation and a more aggressive phenotype, the expression of EpCAM and CD4 was initially analyzed. The SA-MIPs were used for the detection of SA on the cell surface of breast cancer cells. Lectins that specifically bind to the a-2,3 SA and a-2,6 SA variants were used for analysis of SA expression, with both flow cytometry and confocal microscopy. Here we show a correlation of EpCAM and SA expression when using the SA-MIPs for detection of SA. We also demonstrate the binding pattern of the SA-MIPs on the breast cancer cell lines using confocal microscopy. Pre-incubation of the SA-MIPs with SA-derivatives as inhibitors could reduce the binding of the SA-MIPs to the tumor cells, indicating the specificity of the SA-MIPs. In conclusion, the SA-MIPs may be a new powerful tool in the diagnostic analysis of breast cancer cells. breast cancer; epithelial cell adhesion molecule; molecularly imprinted polymers; nanoparticles; sialic acid +
Footnote †: journal:  
Accepted: 1 April 2021  
Footnote †: journal:
culating tumor cells (CTCs) released from primary tumors are considered to have the capability to initiate distant metastasis. Detection and isolation of CTCs using the Food and Drug Administration (FDA)-approved CellSearch platform is based on automated immunomagnetic sorting and on expression of the epithelial cell adhesion molecule (EpCAM) and cytokeratin [5]. The expression of EpCAM in primary tumors is often associated with proliferation and a more aggressive phenotype, if it is considered as high [6]. Alternative methods are definitely needed for the detection of CTCs that are able to recognize a broader spectrum of phenotypes. Alterations in protein glycosylation have a role in the transformation to cellular malignancy and cancer progression [7]. Sialic acid (SA), or 5-N-acetylneuraminic acid (Neu5 Ac), is a monosaccharide that plays an important role in many biological processes in the cells [8]. SA is chemically bound to galactose (Gal) or N-acetylgalactosamine (GalNAc) and the underlying glycan via \(\alpha\) -2,3 or \(\alpha\) -2,6 glycosidic linkage [8]. For detection of \(\alpha\)-2,3 SA, the lectin _Maackia amurensis_ I (MAL I) is commonly used, and for detection of \(\alpha\)-2,6 SA, the lectin _Sambucus nigra_ (SNA) is used. \(\alpha\)-2,6-SA can be found on the basolateral cell membrane, whereas \(\alpha\)-2,3-SA seems to be more prominent on the apical cell membrane [9]. Increased levels of SA on tumor cells have been connected with poor prognosis of clinical tumors and increased invasive potential [10]. It has been shown that a high SA expression enhances migration and invasion by increasing integrin interaction and preventing immune cell recognition [11]. The upregulation of sialyltransferase expression is upregulated and results in the accumulation of SA on the surface of cells [12; 13]. Available lectins and glycan specific antibodies for detection of SA containing glycosoconjugates do not perform well in, e.g., analytics of glycoproteins and appropriate high-throughput cellular imaging technologies [14]. Therefore, the studies by us and others are of high importance to develop novel tools for glycan detection [15; 16; 17]. One such tool to prepare saccharide selective receptors is molecular imprinting [18].