Targeted Rheumatoid Arthritis Therapy Using a Smart Nitric Oxide‐Responsive JAK Inhibition

Abstract Rheumatoid arthritis (RA) is a chronic autoimmune disease marked by persistent synovial inflammation, which leads to cartilage degradation and bone erosion. While Janus kinase (JAK) inhibitors, such as Tofacitinib (Tofa), have shown clinical efficacy in RA treatment, their broad immunosuppressive effects increase the risk of systemic toxicity. To address this challenge, NOR‐Tofa, a Nitric oxide (NO)‐responsive JAK inhibitor conjugate, designed for selective activation in inflamed joints are developed. NOR‐Tofa incorporates an o ‐phenylenediamine ( o‐ PD) moiety, allowing for NO‐mediated drug release at inflammation sites. Structural characterization confirmed the successful synthesis and NO‐responsiveness of NOR‐Tofa, which exhibited potent JAK inhibition upon activation. In vitro studies using LPS‐stimulated macrophages demonstrated that NOR‐Tofa effectively suppressed JAK‐STAT signaling and reduced the expression of pro‐inflammatory cytokines. In vivo, a collagen‐induced arthritis (CIA) mouse model revealed that NOR‐Tofa treatment significantly alleviated arthritis symptoms and preserved joint structure, with dose‐dependent therapeutic efficacy. Pharmacokinetic analysis indicated that NOR‐Tofa minimized systemic exposure to tofacitinib while selectively activating in inflamed joints, thereby reducing off‐target effects. Moreover, hematological and acute toxicity assessments confirmed the improved safety profile of NOR‐Tofa compared to Tofacitinib. These findings establish NO‐responsive drug activation as a promising strategy for RA treatment, offering a more targeted and safer alternative to conventional JAK inhibitors.