Multivalent Fucosides with Nanomolar Affinity for the Aspergillus fumigatus Lectin FleA Prevent Spore Adhesion to Pneumocytes

Abstract

FleA (or AFL), a fucose lectin, was recently identified in the opportunistic mold Aspergillus fumigatus, which causes fatal lung infections in immunocompromised patients. We designed di‐, hexa‐ and octavalent fucosides with various spacer arm lengths to block the hexameric FleA through chelation. Microcalorimetry measurements showed that the ethylene glycol (EG) spacer arm length has a strong influence on the binding affinity of the divalent fucosides. The relationship between the EG length and chelate binding efficiency to FleA was explored according to polymer theory. Hexa‐ and octavalent compounds based on cyclodextrin and octameric silsesquioxane scaffolds were nanomolar FleA inhibitors, surpassing their monovalent fucose analogue by more than three orders of magnitude. Importantly, some of the fucosides were highly efficient in preventing fungal spore adhesion to bronchoepithelial cells, with half maximal inhibitory concentration values in the micromolar range. We propose that the synergistic antiadhesive effect observed can be ascribed to chelate binding to FleA and to the formation of conidium aggregates, as observed by optical microscopy. These fucosides are promising tools that can be used to better understand the role of FleA in conidia pathogenicity and host defenses against invasive aspergillosis.

Fucosylated ubiquitin and orthogonally glycosylated mutant A28C: conceptually new ligands for Burkholderia ambifaria lectin (BambL)

“…The two binding sites of BambL were previously reported to have similar affinity towards fucose, but different behavior towards the H type 2 blood group trisaccharide 9 and towards compound 1. 13 The control experiments with αMeFuc are in agreement with those previously reported, 9,13,15,22 and this validates the presence of two equivalent fucose binding sites with an affinity for fucose of approx. 1 µM in each BambL monomer.…”

Polyvalent Transition‐State Analogues of Sialyl Substrates Strongly Inhibit Bacterial Sialidases**

“…CD can be easily derivatized at the primary rim, a feature largely exploited for the design of glycoclusters. [29][30][31] These size-controlled DANA-clusters were completed by two different types of DANA polymers 9 and 10 obtained by RAFT polymerization and ROMP, respectively. Glycopolymers designed for lectin inhibition have already been shown to provide large affinity enhancements for their targets due to their high density sugar contents, large distance spanning, and high adaptability.…”

“…The synthesis of mono-azido-EG 3 20, di-azido-EG 11, 27 21, 22 and peracetylated azido-EG 3 -CD 23 (Scheme 3) was described in previous articles. [29,31] The two polyvalent azides 17 and 19 were obtained as depicted in Scheme 2. 2-Vinyl-4,4dimethyl-5-oxazolone (VDM) [38,39] was polymerized by reversible addition-fragmentation chain transfer (RAFT) polymerization to form the poly(VDM) 54 16 with 35% conversion (the conversion of the monomer was deliberately limited in order to access well-defined polymers [38,39] ) after precipitation in hexane (M n,NMR = 7800 g.mol -1 , DP n,NMR = 54, M n,SEC THF = 8300 g.mol -1 and Ð = 1.14).…”

PNA-Based Dynamic Combinatorial Libraries (PDCL) and screening of lectins

“…[40][41][42] There are current fungicides against A. fumigatus, [43][44] however, the increasing resistance of A. fumigatus strains to these treatments urges alternative approaches targeting different pathways. [45][46][47][48] The best ligand reported to date is a hexavalent cluster with Kd of 18 nM. 48 The bacterial lectin from Ralstonia solanacearum (RSL) has strong similarity with AFL and almost identical fucose binding sites.…”