SLC15A4 Inhibition by NTX-348 Suppresses Endolysosomal Toll-like Receptor Signaling, IRF5 Activation, and Type I Interferon Induction 2249463

Abstract Introduction Recent studies have revealed that nucleic acid sensing by the endolysosomal TLRs (TLR7, TLR8, and TLR9) requires coordinated activity of the lysosomal peptide transporter SLC15A4. This peptide transporter interacts with the adaptor protein TASL and is necessary for the recruitment and activation of the transcription factor IRF5. The importance of this signaling pathway in the pathogenesis of autoimmune disease has been highlighted by human genetic variants in SLC15A4, TASL, and IRF5 that are associated with elevated risk of developing systemic lupus erythematosus (SLE), while pre-clinical studies in mouse have shown that genetic knock-out of these genes is protective in multiple autoimmune or inflammatory disease models. Methods Using structure-based drug design, we have developed a series of novel small molecule SLC15A4 inhibitors. Further optimization of the potency and drug-like properties of these molecules has led to discovery of potential first-in-class lead compounds that exhibit nanomolar cellular potency, favorable in vitro ADME and off-target profiles, and suitable PK properties in mouse that allow for once-daily oral dosing. Results In vitro studies show that SLC15A4 inhibition results in the intracellular degradation of the TASL adapter protein and blockade of inflammatory cytokine production in response to TLR7/8/9 agonists. Using in vivo mouse models of TLR-driven acute cytokine production, treatment with an advanced tool compound NTX-348 results in complete suppression of IRF5 phosphorylation and type I interferon production in response to TLR7 or TLR9 agonist treatment. Conclusion These results highlight our early progress developing novel, drug-like inhibitors of SLC15A4. SLC15A4 inhibition represent a novel therapeutic approach that may provide clinical benefit as an oral therapy for SLE and other immune-mediated diseases. Funding Source All authors are employees or contractors of Nimbus Therapeutics Topic Categories Therapeutic Approaches to Autoimmunity (THER)