S1423 RIPK2 Scaffolding Inhibitors are a Novel Approach to Block RIPK2 Signaling, a Hallmark of Inflammatory Bowel Disease

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Introduction: Intestinal microbiota is an established driver of pathogenic immune activation in inflammatory bowel disease (IBD). Receptor-interacting protein kinase 2 (RIPK2) is a key signaling node in microbe-driven inflammation and therefore an attractive therapeutic target to block a key driver of IBD. RIPK2 controls immune activation by peptidoglycan (PGN), a component of all bacterial cell walls, and amplification of pro-inflammatory responses to a range of microbiota-derived byproducts. Here we describe an orally bioavailable, small molecule inhibitor that blocks RIPK2 scaffolding function by preventing its binding to XIAP, an essential adaptor protein, critical for full inhibition of RIPK2. Methods: RIPK2 scaffolding inhibition was assessed by surface plasmon resonance and in cells with a NanoBRET assay. Pathway inhibition was evaluated by measuring cytokine production by cells stimulated with PGN or heat-killed bacteria. Gene expression in human IBD biopsies was analyzed using bulk and single-cell RNA sequencing data. Intestinal tissue biopsies from IBD patients and from mice with colitis was evaluated ex vivo to determine the effects of a RIPK2 scaffolding inhibitor on RNA expression, a panel of fibrosis markers, and cytokine production. Results: An RNA expression signature was developed as a biomarker to report RIPK2 activation. Expression analysis showed increased RIPK2 activity in IBD, and levels correlating with disease severity. In biopsies from patients on anti-TNF or anti-integrin therapy, RIPK2 activity remained elevated only in non-responders. Healthy and disease-derived innate immune cells stimulated with PGN or bacteria produce proinflammatory cytokines (e.g., TNF, IL-23, and TL1A) which are inhibited by treatment with the RIPK2 scaffolding inhibitor. Treating organ cultures of inflamed intestinal biopsies with the RIPK2 scaffolding inhibitor suppressed spontaneous inflammatory cytokine production and reduced expression of fibrosis markers demonstrating the central role of RIPK2 in driving intestinal inflammation. Conclusion: In response to microbiota-derived signals, RIPK2 scaffolding inhibitor blocks the production of cytokines that are validated IBD therapeutic targets, including TL1A, TNF, and IL-23. The relationship between RIPK2 activity and severity of IBD as well as non-responsiveness to biologic therapies suggests RIPK2 activity may underlie therapy resistance and provides rationale to develop a RIPK2 scaffolding inhibitor for monotherapy or combination treatment of IBD.

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