New Glucosamine-Based TLR4 Agonists: Design, Synthesis, Mechanism of Action, and In Vivo Activity as Vaccine Adjuvants

We disclose here a panel of small-molecule TLR4 agonists
(the FP20 series) whose structure is derived from previously
developed
TLR4 ligands (FP18 series). The new molecules have increased
chemical stability and a shorter, more efficient, and scalable synthesis.
The FP20 series showed selective activity as TLR4 agonists
with a potency similar to FP18. Interestingly, despite
the chemical similarity with the FP18 series, FP20 showed a different mechanism of action and immunofluorescence microscopy
showed no NF-κB nor p-IRF-3 nuclear translocation but rather
MAPK and NLRP3-dependent inflammasome activation. The computational
studies related a 3D shape of FP20 series with agonist
binding properties inside the MD-2 pocket. FP20 displayed
a CMC value lower than 5 μM in water, and small unilamellar
vesicle (SUV) formation was observed in the biological activity concentration
range. FP20 showed no toxicity in mouse vaccination experiments
with OVA antigen and induced IgG production, thus indicating a promising
adjuvant activity.