“Influenza viruses are responsible for human flu epidemics and pandemics causing hundreds of thousands of deaths each year, or sometimes long-term sequelae. The infectious process is based notably on two proteins, hemagglutinins and neuraminidases. The first allow the adhesion of the virus on the epithelial cells of the human respiratory system by the interaction with sialylated oligosaccharides. The second are enzymes hydrolyzing the α-glycosidic bonds of the terminal sialic acids allowing the spreading of the virions in the organism. At present, the fight against influenza infections is based on vaccination and the use of antivirals, but these two strategies face the emergence of resistant viral strains that can limit their effectiveness. An antiadhesive therapy consisting in neutralizing viruses with sialosides recognized by hemagglutinins and resistant to hydrolysis by neuraminidases is a promising alternative. To be effective, these decoys must be assembled in a multivalent way on supramolecular supports to prevent the attachment of the virus to the epithelial cells. However, the development of this strategy requires the availability of efficient methods for the production of sialylated oligosaccharides and glycomimetics.
Firstly, this thesis work describes the chemo-enzymatic synthesis of 6-sialyllactose (6SL) and analogues incorporating a sialic acid modified from N-acyl-mannosamines, in strains of E. coli modified by metabolic engineering, using a process developed at CERMAV. These analogs show the same affinity for the SNA-I lectin of Sambucus nigra as the natural 6SL, and are stable competitive inhibitors of the neuraminidase of Vibrio cholerae. Subsequently, two strategies enabled the multivalent presentation of sialyllactose on the surface of Lipidots™, nanostructured lipid particles developed by CEA-LETI. The first consists in synthesizing a glycolipid then anchoring it in the amphiphilic crown of the nanoparticles. The second approach is based on the covalent grafting of sialyllactose onto functionalized Lipidots™. The recognition of these particles by the SNA-I lectin as well as their ability to inhibit Influenza infection have been studied in vitro.
Key words: glycoconjugate, sialic acid, lipid nanoparticles, metabolic engineering of E. coli, Influenza