Molecular basis for galectin-ligand interactions : Design, synthesis and analysis of ligands

Sammanfattning: Galectins are a class of β-galactoside-binding proteins that bind glycoconjugates and have been implicated in cancer, regulation of immunity and inflammation. Design and synthesis have achieved highly potent and selective galectin ligands that can inhibit interactions with glycoproteins and have consequent cellular effects. These ligands can be used as tools to further elucidate the roles of galectins in biological processes, and also, potentially, to diagnose and treat diseases. The present theis is about further development of such galectin ligands. A more robust synthetic route to 3-azido-3-deoxy-β-D-galactopyranosides, key intermediates in the synthesis of previous galectin ligands, has been developed. Bis-3-(4-aryl-1,2,3-triazol-1-yl)-thiodigalactosides are potent galectin-1 and galectin-3 ligands and by screening different aryl groups, the affinities and selectivities for galectin-1 and galectin-3 were improved. In case of galectin-1, the aryl group binds in a smaller binding pocket than in galectin-3, thus five-membered heterocycles were screened with the 2-thiazole having the highest galectin-1 affinity. In case of galectin-3, substituted phenyls were screened with the 3,4,5-trifluorophenyl having the highest galectin-3 affinity. Introducing these aryl groups onto thiodigalactosides resulted in ligands with single-digit nM affinity and 10-50 fold selectivity towards either of galectin-1 or galectin-3. Structural analysis of the galectin-3 ligands identified orthogonal multipolar fluorine-amide interactions and cation-π interactions as main contributors to the high affinity. Based on these findings, monosaccharide derivatives with high selectivity and low nM galectin-3 affinities were developed. Galectin-3 is a biomarker used to diagnose heart failure and through immobilization of a highly potent galectin-3 ligand in a microtiter plate, an assay has been developed that binds both intact and truncated galectin-3 C-terminal domain.