From Hit to Lead: Discovery of Novel Selective RIPK1 Inhibitor with Pyridoimidazole Scaffold for the Treatment of Autoimmune Diseases through Phenotypic Screening and Structural Optimization

Autoimmune diseases remain challenging to treat due to the limitations of TNFα-targeted biologics and the inefficacy of small molecules directly targeting TNFα. RIPK1, a central mediator of TNFα-driven inflammation and necroptosis, offers a promising alternative therapeutic target. Using drug repurposing and phenotype-based high-content screening of 378 clinical-stage kinase inhibitors, TAK-117 (a PI3Kα inhibitor) was identified as a RIPK1 hit compound with a novel pyridoimidazole scaffold. Guided by structure-based optimization and four iterative SAR cycles, WJH-C19 was developed, exhibiting >1000-fold increased RIPK1 potency (IC₅₀ = 5.7 nM) and negligible PI3Kα activity (IC₅₀ > 10 μM). Mechanistically, WJH-C19 suppressed the RIPK1/RIPK3/MLKL signaling axis, attenuating inflammatory responses. Oral administration of WJH-C19 achieved robust efficacy in DSS-induced colitis and CFA-induced arthritis models, with favorable pharmacokinetics and no observable toxicity. These results establish WJH-C19 as a potent lead and highlight the pyridoimidazole scaffold as a privileged chemotype for RIPK1-targeted drug discovery in autoimmune diseases.