Sugar Concentration and Arrangement on the Surface of Glycopolymer Micelles Affect the Interaction with Cancer Cells.

Glycopolymer-coated nanoparticles have attracted significant interest over the past few years, because of their selective interaction with carbohydrate receptors found on the surface of cells. While the type of carbohydrate determines the strength of the ligand-receptor interaction, the presentation of the sugar can be highly influential as the carbohydrate needs to be accessible in order to display good binding. To shine more light on the relationship between nanoparticle structure and cell uptake, we have designed several micelles based on fructose containing block copolymers, which are selective to GLUT5 receptors found on breast cancer cell lines. The polymers were based on poly-D,L-lactide (PLA), poly(2-hydroxyethyl) acrylate (PHEA), and poly(1-O-acryloyl-beta-D-fructopyranose) (P[1-O-AFru]). A set of six micelles was synthesized based on four fructose containing micelles (PLA(242)-b-P[1-O-AFru](41), PLA(242)-b-P[1-O-AFru](179), PLA(242)-b-P[1-O-AFru(46)-c-HEA(214)], PLA(242)-b-PHEA(280)-b-P[1-O-AFru](41)) and two neutral controls (PLA(247)-b-PHEA(53) and PLA(247)-b-PHEA(166)). SAXS analysis revealed that longer hydrophilic polymers led to lower aggregation numbers and larger hydrophilic shells, suggesting more glycopolymer mobility. Cellular uptake studies via flow cytometry and confocal laser scanning microscopy (CLSM) confirmed that the micelles based on PLA(242)-b-P[1-O-AFru](179) show, by far, the highest uptake by MCF-7 and MDA-MB-231 breast cancer cell lines while the uptake of all micelles by RAW264.7 cell is negligible. The same micelle displayed was far superior in penetrating MCF-7 cancer spheroids (three-dimensional (3D) model). Taking the physicochemical characterization obtained by SAXS and the in vitro results together, it could be concluded that the glycopolymer chains on the surface of micelle must display high mobility. Moreover, a high density of fructose was found to be necessary to achieve good biological activity as lowering the epitope density led immediately to lower cellular uptake. This work showed that it is crucial to understand the micelle structure in order to maximize the biological activity of glycopolymer micelles.