Boronic Acid Materials for Glycoprotein Recognition and Enhanced Cellular Delivery

Cell surface glycans, typically in the form of glycoproteins or glycolipids, are commonly aberrant in diseases and can serve as biomarkers that facilitate diagnostics, selective cellular labeling and delivery. Boronic acids have been extensively utilized for the detection and separation of carbohydrates through reversible formation of boronate esters in the binding of diol moieties on glycans. However, the biological application of this sensing group is challenged by its relatively low binding affinity in aqueous media. Through the research described in this dissertation, we designed and synthesized boronic acid materials that can enhance its avidity towards glycan through multivalent binding interactions to achieve biological applications including glycoprotein detection and cellular delivery.In the second chapter of this dissertation, a boronic acid microplate assay for sensitive and high-throughput detection of the cancer-associated glycoprotein mucin-1 was developed. For this purpose, a multivalent surface for glycoprotein recruitment and detection was achieved by immobilizing biotinylated boronic acid onto streptavidin-coated microplates. In the third chapter, novel boronic acid lipids were synthesized and incorporated into liposomes as a drug delivery platform. We validated carbohydrate-responsive liposome efficacy by demonstrating dose-dependent release of encapsulated hydrophobic or hydrophilic fluorophores upon titration with the polysaccharide heparin. Cellular delivery and labeling were visualized by confocal microscopy indicating a dramatic enhancement in fluorescence signal, showcasing the prospects of boronic acid lipids for drug delivery. In the last chapter, bisboronic acid lipids containing a small library of spacers of varying length between two boronic acid units have been synthesized to study selective binding interactions towards sialic acids. Enhanced binding affinity towards N-acetylneuraminic acid and the sialic acid-rich glycoprotein porcine mucin were observed using bisboronic acid lipids, particularly when usinga meta-xylene spacer. This was detected via dye displacement competitive fluorescence assays as well as through liposomal triggered release studies. Finally, dose-dependent fluorescence cellular labelling was visualized using bisboronic acid liposomes. Collectively, these studies show that the incorporation of boronic acids into complex architectures including microplate surfaces and liposomes is effective for advancing applications such as the detection of disease-associated carbohydrates in complex biological samples and the delivery of therapeutic agents to cells.