RS1805

RS1805 is a potent and highly selective small molecule inhibitor of Janus kinase 1 (JAK1) developed by Rui Stone Biopharmaceutical for the treatment of inflammatory bowel diseases, specifically ulcerative colitis. By selectively targeting the JAK1 isoform over JAK2, JAK3, and TYK2, RS1805 aims to modulate the signaling pathways of key pro-inflammatory cytokines, such as interleukin-6 (IL-6) and interferon-gamma (IFN-γ), while minimizing off-target effects associated with broader JAK inhibition, such as anemia or neutropenia. The drug is designed for oral administration and is currently being evaluated in Phase 2 clinical trials to determine its efficacy and safety in patients with moderate-to-severe active ulcerative colitis.