Metal-based glycoconjugates as molecular sensors for lectins and anti-adhesives

Wojtczak, Karolina
The anti-microbial resistance crisis has been inexorably developing at ever more alarming levels in the 21st century. The WHO regularly updates a list of bacterial and fungal critical priority pathogens for which new treatment strategies and diagnostic tools are urgently needed. We postulate that exploiting the ubiquitous nature of carbohydrate-ligand interactions in infection processes, along with the unique and underutilised properties of metal complexes could give us access to new molecular sensors and therapeutic agents against a variety of pathogens. Chapter 1 sets the context of this project, including a comprehensive literature review of inhibitors known for P. aeruginosa’s carbohydrate-binding proteins. This thesis presents the development of glycoconjugate ligands with known metal binding motifs as targeted inhibitors for bacterial lectin LecA in order to exploit the highly specific nature of the carbohydrate-protein interaction for sensing and/or anti-biofilm inhibition properties as a diagnostic or theranostic tools. To this end, in Chapter 2, the first known lanthanide glycoconjugate complex capable of reliably sensing unlabelled bacterial lectin LecA is reported, as part of a completely new sensing paradigm. With a four-fold “switch-on” increase in emission intensity, low micromolar affinity to its target lectin, and no bacteriostatic or bactericidal properties. Derived compounds in complex with transition and lanthanide metal ions are described in Chapter 3, which demonstrated anti-biofilm activity towards P. aeruginosa of up to 50% and anti-adhesion activity against C. albicans of 60% at 0.1 μM, two pathogens of critical importance for the development of new anti-microbial treatments and strategies. This includes the first known, easily accessible, glycoconjugate complex to act as adhesion inhibitor against C. albicans infection of human buccal epithelial cells and an uncommon low micromolar Gal-Tz inhibitor for LecA. Furthermore, in Chapter 4, an extensive derivatisation of glycoconjugate ligands by a variety of critically-informed structural modifications is presented, to achieve higher affinity to the target lectin and probe into the mechanism of action of the above sensing paradigm. Six total ligands were assessed as lectin binders by three different techniques (fluorescence polarisation assy, isothermal calorimetry and surface plasmon resonance), with most demonstrating low micromolar affinities (under 10 μM). Of this library of glycoconjugates, two were earmarked as very high affinity ligands for further development (0.5 and 0.3 μM by SPR respectively). We conclude that metal glycoconjugates are an underexplored class of molecules with promising applications; that lanthanide glycoconjugates give us access to a completely new direct sensing paradigm of unlabelled bacterial lectins; that simple glycoconjugate ligands when complexed to metals give us access to non-lethal treatments for two priority pathogens thus demonstrating the importance of metal complexation in assembling higher complexity functional systems from simple building blocks; and finally, that affinity to a target lectin can be increased in a variety of ways to hopefully expand the sensing capabilities of the corresponding lanthanide complexes as valuable tools in the fight against antimicrobial resistance.
NUI Galway
Publisher DOI
Attribution-NonCommercial-NoDerivs 3.0 Ireland