E5531

E5531 is a synthetic small molecule endotoxin antagonist developed as a potential therapeutic agent for septic shock and Gram-negative bacterial sepsis. It is a stabilized lipid A derivative based on the structure of nontoxic Rhodobacter capsulatus lipid A. E5531 potently antagonizes lipopolysaccharide (LPS)-mediated cellular activation by blocking LPS-induced release of pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) in human monocytes and whole blood. The drug acts specifically as an antagonist at the Toll-like receptor 4 (TLR4), which mediates immune responses to LPS from Gram-negative bacteria. In preclinical studies, E5531 protected mice from LPS-induced lethality and enhanced survival in models of lethal Escherichia coli infection when combined with antibiotics. Despite promising results in early studies, clinical development for indications such as sepsis was discontinued after reaching phase 2 trials.

Other names

162679-36-9