Discovery of Nanomolar Desmuramylpeptide Agonists of the Innate Immune Receptor Nucleotide-Binding Oligomerization Domain-Containing Protein 2 (NOD2) Possessing Immunostimulatory Properties

Muramyl dipeptide (MDP), a fragment
of bacterial peptidoglycan,
has long been known as the smallest fragment possessing adjuvant activity,
on the basis of its agonistic action on the nucleotide-binding oligomerization
domain-containing protein 2 (NOD2). There is a pressing need for novel
adjuvants, and NOD2 agonists provide an untapped source of potential
candidates. Here, we report the design, synthesis, and characterization
of a series of novel acyl tripeptides. A pivotal structural element
for molecular recognition by NOD2 has been identified, culminating
in the discovery of compound 9, the most potent desmuramylpeptide
NOD2 agonist to date. Compound 9 augmented pro-inflammatory
cytokine release from human peripheral blood mononuclear cells in
synergy with lipopolysaccharide. Furthermore, it was able to induce
ovalbumin-specific IgG titers in a mouse model of adjuvancy. These
findings provide deeper insights into the structural requirements
of desmuramylpeptides for NOD2-activation and highlight the potential
use of NOD2 agonists as adjuvants for vaccines.