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

## TL;DR

A new aptamer called YC3 treats Graves' ophthalmopathy by inhibiting a receptor in a novel way, offering a promising therapy for this autoimmune eye disease.

## Contribution

YC3 is a novel TSHR-targeting aptamer that inhibits receptor activation via a previously unidentified allosteric site.

## Key findings

- YC3 suppresses TSAbs-driven hyperactivation in human orbital fibroblasts in vitro.
- YC3 alleviates ocular symptoms in a mouse model of Graves' ophthalmopathy.
- YC3 binds to a novel allosteric site on the TSHR, inhibiting receptor activation.

## 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.

This study presents YC3, a novel inhibitory TSHR‐targeting aptamer, as a promising therapeutic for Graves' ophthalmopathy (GO). YC3 suppresses pathological phenotypes in human orbital fibroblasts and improves outcomes in GO mice by binding to a previously unidentified allosteric site on TSHR, demonstrating the potential of aptamers in advancing targeted therapy, discovering cryptic druggable sites, and uncovering receptor mechanisms.