Characterization of TRIF selectivity in the AGP class of lipid A mimetics: Role of secondary lipid chains.

TLR4 agonists that favor TRIF-dependent signaling and the induction of type 1 interferons may have potential as vaccine adjuvants with reduced toxicity. CRX-547 ( 4 ), a member of the aminoalkyl glucosaminide 4-phosphate (AGP) class of lipid A mimetics possessing three ( R )-3-decanoyloxytetradecanoyl groups and d -relative configuration in the aglycon, selectively reduces MyD88-dependent signaling resulting in TRIF-selective signaling, whereas the corresponding secondary ether lipid 6a containing ( R )-3-decyloxytetradecanoyl groups does not. In order to determine which secondary acyl groups are important for the reduction in MyD88-dependent signaling activity of 4 , the six possible ester/ether hybrid derivatives of 4 and 6a were synthesized and evaluated for their ability to induce NF-κB in a HEK293 cell reporter assay. An ( R )-3-decanoyloxytetradecanoyl group on the 3-position of the d -glucosamine unit was found to be indispensable for maintaining low NF-κB activity irrespective of the substitutions (decyl or decanoyl) on the other two secondary positions. These results suggest that the carbonyl group of the 3-secondary lipid chain may impede homodimerization and/or conformational changes in the TLR4–MD2 complex necessary for MyD88 binding and pro-inflammatory cytokine induction. [ABSTRACT FROM AUTHOR]