Discovery of M5049: A Novel Selective TLR7/8 Inhibitor for Treatment of Autoimmunity.

Vlach, Jaromir; Bender, Andrew T; Przetak, Melinda; Pereira, Albertina; Deshpande, Aditee; Johnson, Theresa; Reissig, Sonja; Tzvetkov, Evgeni; Musil, Djordje; Tahmassian-Morse, Noune; Haselmayer, Phillip; Favre-Zimmerli, Simone; Okitsu, Shinji L; Walsky, Robert L; Sherer, Brian

Toll-like receptors 7 and 8 (TLR7/8) are transmembrane receptors that recognize single-stranded RNA. Activation of these receptors results in immune cell stimulation and inflammatory cytokine production which is normally a protective host response. However, aberrant activation of TLR7/8 is potentially pathogenic and linked to progression of certain autoimmune diseases such as lupus. Thus, we hypothesize that an inhibitor that blocks TLR7/8 would be an effective therapeutic treatment. Prior efforts to develop inhibitors of TLR7/8 have been largely unsuccessful due to the challenge of producing a small molecule inhibitor for these difficult targets. Here, we report the characterization of M5049 and Compound 2, molecules which were discovered in a medicinal chemistry campaign to produce dual TLR7/8 inhibitors with drug-like properties. Both compounds showed potent and selective activity in a range of cellular assays for inhibition of TLR7/8 and block molecule synthetic ligands and natural endogenous RNA ligands such as microRNA and Alu RNA. M5049 was found to be potent in vivo and TLR7/8 inhibition efficaciously treated disease in several murine lupus models and, interestingly, was efficacious in a disease context where TLR7/8 activity has not previously been considered a primary disease driver. Furthermore, M5049 had greater potency in disease models than expected based on its in vitro potency and pharmacokinetic/pharmacodynamic properties. With preferential accumulation in tissues, and the ability to block multiple TLR7/8 RNA ligands, M5049 may be efficacious in treating autoimmunity and has the potential to provide benefit to a variety of patients with varying disease pathogenesis. Significance Statement We report discovery of a novel toll-like receptor 7 and 8 (TLR7/8) inhibitor (M5049), characterize its binding mode, potency/selectivity, pharmacokinetic and pharmacodynamic properties, and demonstrate its potential for treating autoimmune diseases in two mouse lupus models. TLR7/8 inhibition is unique in that it may block both innate and adaptive autoimmunity and thus we believe that M5049 has the potential to benefit patients with autoimmune diseases.