Sialic acid as a biomarker studied in breast cancer cells using fluorescent molecularly imprinted polymers, MIPs

Abstract Sialylations 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. Since high expression of EpCAM in primary tumors often is associated with proliferation and a more aggressive phenotype, the expression and of epithelial cell adhesion molecule (EpCAM) CD44 was initially analyzed. The SA-MIPs were used here for the detection of SA on the cell surface of breast cancer cells. Lectins that specifically bind to the α-2,3 SA and α-2,6 SA variants, respectively, 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 SA-analysis of breast cancer cells.