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

Abstract

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.

Review: Current trends, challenges, and success stories in adjuvant research

“…Subsequent generations of what we now know to be TLR4 agonists (such as GLA/PHAD 2 , INI-2002 3 , or CRX-601 ( 4 )) are synthetic derivatives of MPL from which non-essential components have been removed. Minor modifications of the TLR4 agonists’ structures are able to significantly alter the resulting receptor signals ( 5 ). The latest generation of TLR4 agonists ( e.g ., 2B182c 4 or neoseptin ( 6 )) are small molecules that do not share structural similarities with the canonical receptor agonists.…”

Rational Vaccine Design in Times of Emerging Diseases: The Critical Choices of Immunological Correlates of Protection, Vaccine Antigen and Immunomodulation

“…Thus, GSK Biologicals developed aminoalkyl glucosaminide phosphates (AGPs) where the proximal GlcN ring of lipid A was omitted furnishing in this way a polar head group with rationalized structure [ 137 ]. Variable β-hydroxyacyl and alkyl chains were chemically attached to the polar head group and selected AGPs reached pre-clinical/clinical development which highlighted RC-529 as a potent vaccine adjuvant ( Figure 3 ) [ 138 ]. Lipid A mimetics containing pentaerythritol in place of proximal GlcN residue were developed by Biomira Inc. (Edmonton, AB, Canada) as potent cytokine secreting agonists.…”

Diamino Allose Phosphates: Novel, Potent, and Highly Stable Toll-like Receptor 4 Agonists

“…23−26 These monosaccharide compounds consist of three fatty acyl chains that are N-and O-linked to an O-glucosaminyl ethylamine or serine backbone (e.g., 1a−c, Figure 1). We demonstrated that minor structural modifications to synthetic TLR4 agonists could alter signaling selectivity 27,28 (MyD88 vs TRIF bias in TLR4 agonists) and convert agonist to antagonist responses. 25 Engineered to specifically trigger an innate immune response with varying degrees of specificity, potency, and safety attributes, some of these agonists, in addition to showing promise as vaccine adjuvants, 29−33 were also capable of eliciting nonspecific protection against a wide range of infectious pathogens.…”

“…In the course of our own structure–activity studies on a detoxified but complex form of lipid A known as 3- O -desacyl monophosphoryl lipid A (MPLA), a disaccharide TLR4 agonist, we developed a new class of synthetic monosaccharide TLR4-active glycolipids known as aminoalkyl glucosaminide 4-phosphates (AGPs), capable of eliciting robust innate and adaptive immune responses. − These monosaccharide compounds consist of three fatty acyl chains that are N - and O -linked to an O -glucosaminyl ethylamine or serine backbone (e.g., 1a – c , Figure ). We demonstrated that minor structural modifications to synthetic TLR4 agonists could alter signaling selectivity , (MyD88 vs TRIF bias in TLR4 agonists) and convert agonist to antagonist responses . Engineered to specifically trigger an innate immune response with varying degrees of specificity, potency, and safety attributes, some of these agonists, in addition to showing promise as vaccine adjuvants, − were also capable of eliciting nonspecific protection against a wide range of infectious pathogens. − As evidence of the validity of this approach, the TLR4 agonist RC-529 was approved for human use in a recombinant HBV vaccine and another highly active TLR4 agonist, GSK1795091 (agonist 1c ), completed a phase I clinical trial for safety evaluation …”

“…Previously, we demonstrated that the C2 symmetry of AGPs, synthetic TLR 4 agonists, allowed them to possibly enter the MD-2 pocket in a LPS-like (agonist) or in an Eritoran-like (antagonist, 180°rotation) orientation modulating the immune response. 28 Given the pseudo-C2 symmetry of the DAP series, it is likely that the DAP ligands could be inserted into the pseudosymmetry of MD2 in both orientations as well.…”