Structure-Based Design of Potent TLR7/8/9 Triple Antagonists: Overcoming High Tissue Distribution and Reactive Metabolite Liabilities

Sustained activation of endosomal Toll-like receptors (TLR) 7, 8, and 9 by self-nucleic acids is considered to be a key driver for autoimmune diseases, e.g., systemic lupus erythematosus (SLE). We report the discovery of a novel series of potent, orally bioavailable TLR7/8/9 triple antagonists featuring a unique "N-aryl-N" pharmacophore. Guided by TLR8 cocrystal structures and TLR7/9 homology models, we systematically optimized the series to balance pan-TLR potency with drug-like properties. Strategic modulation of lipophilicity and basicity successfully reduced the high volume of distribution (Vss) observed in mouse for early leads. Further compound optimization eliminated a reactive metabolite (GSH) liability. The resulting lead, compound 41, demonstrated robust dose-dependent inhibition of TLR7 and TLR9 pathways in mouse challenging models, supporting the potential of a TLR7/8/9 triple antagonist for treating autoimmune diseases.