TSHR‐Targeting Nucleic Acid Aptamer Treats Graves' Ophthalmopathy via Novel Allosteric Inhibition

Abstract Graves' ophthalmopathy (GO) is an autoimmune disorder marked by orbital inflammation and tissue remodeling, leading to irreversible disfigurement and vision loss. The current first‐line glucocorticoid therapy remains palliative, underscoring the critical need for mechanism‐based interventions. Autoantibodies against thyrotropin receptor (TSHR) in GO patients highlight its therapeutic potential, yet TSHR inhibitor development faces challenges, including low potency, off‐target effects, and mechanistic constraints. To overcome this therapeutic void, YC3, a TSHR‐targeting nucleic acid aptamer, has been developed through an innovative approach that combines protein‐targeting cell‐SELEX with functional selection. YC3 exhibits nanomolar affinity alongside robust pharmacodynamic efficacy. In vitro, YC3 significantly reverses thyroid‐stimulating antibodies (TSAbs)‐driven hyperactivation in primary human orbital fibroblasts, thereby suppressing pathogenic hallmarks of fibroblasts. In vivo, therapeutic administration of YC3 significantly alleviates ocular symptoms in a GO mouse model. Mechanistic investigations reveal that YC3 binds to a previously unidentified allosteric site within the leucine‐rich repeat domain of TSHR, consequently inhibiting receptor activation. Collectively, this study not only identifies YC3 as a promising TSHR‐targeting therapeutic candidate but also unveils a novel allosteric site for next‐generation inhibitors. These findings highlight the potential of aptamers in both dissecting receptor mechanisms and uncovering cryptic druggable sites, thereby bridging structural biology with targeted drug development.