Inhibition of Endotoxin Response by Synthetic TLR4 Antagonists

Endotoxin, from the outer membrane of Gram-negative bacteria, has been implicated as the etiological agent of a variety of pathologies ranging from relatively mild (fever) to lethal (septic shock, organ failure, and death). While endotoxin (also known as lipopolysaccharide or LPS) is a complex heterogeneous molecule, the toxic portion of LPS (the lipid A portion) is relatively similar across a wide variety of pathogenic strains of bacteria, making this molecule an attractive target for the development of an LPS antagonist. Research over the past fifteen years focused on the design of various lipid A analogs including monosaccharide, acyclic and disaccharide compounds has lead to the development of E5564, an advanced, unique and highly potent LPS antagonist. E5564 is a stable, pure LPS antagonist that is selective against endotoxin-mediated activation of immune cells in vitro and in animal models. In Phase I clinical trials, we have developed an ex vivo endotoxin antagonism assay that has provided results on pharmacodynamic activity of E5564 in addition to the more typical safety and pharmacokinetic evaluations. Results from these assays have been reinforced by analysis of in vivo antagonistic activity using a human endotoxemia model. Results from all of these studies indicate that E5564 is an effective in vivo antagonist of endotoxin, and may prove to be of benefit in a variety of endotoxin-mediated diseases. This review discusses the evolution of synthetic LPS antagonists with emphasis on the SAR and development of E5564 and its precursors.