Neutrophil-hitchhiking HAT nanodrug silences SYK, reducing RA joint damage without impairing host defense

Rheumatoid arthritis (RA) is a debilitating chronic autoimmune disease characterized by persistent synovial inflammation and progressive joint destruction. Current antirheumatic drugs often provide insufficient efficacy or lead to significant systemic adverse reactions, notably increasing infection risk due to broad immunosuppression. A critical gap exists in therapies that can specifically curb pathogenic neutrophil activity, a central driver of RA pathogenesis, without compromising the host's essential immune defenses. This study investigates spleen tyrosine kinase (SYK) as a key upstream regulator of neutrophil hyperactivation in RA, proposing a targeted nanodrug approach to address this therapeutic challenge.

Researchers engineered a novel HSA-AAPV-TKI (HAT) nanodrug, comprising human serum albumin (HSA) conjugated to a SYK-targeted tyrosine kinase inhibitor (TKI) via an AAPV (Ala-Ala-Pro-Val) peptide linker, which is cleavable by neutrophil elastase. The nanodrug was tested in a collagen-induced arthritis (CIA) mouse model. HAT was designed for preferential internalization by circulating neutrophils, trafficking with them to inflamed joints, and locally releasing the TKI in response to neutrophil activation. Primary endpoints included assessing joint swelling, arthritis scores, structural joint damage, and the preservation of host antimicrobial function.

In RA patients, spleen tyrosine kinase (SYK) was identified as a key upstream regulator whose aberrant activation drives neutrophil hyperactivation, NET formation, inflammatory mediator release, and delayed apoptosis, while preserving antimicrobial function. The engineered HAT nanodrug demonstrated preferential internalization by circulating neutrophils in CIA mice, effectively trafficking with them to inflamed joints. Upon local neutrophil activation, the AAPV linker was cleaved, releasing the SYK inhibitor and thereby attenuating SYK signaling and pathogenic neutrophil functions. This targeted approach successfully reconciled potent anti-inflammatory efficacy with immune safety.

In the collagen-induced arthritis (CIA) mouse model, treatment with the HAT nanodrug significantly reduced joint swelling, arthritis scores, and structural joint damage without impairing host defense mechanisms.