A new small-molecule antagonist inhibits Graves' disease antibody activation of the TSH receptor

Context: Graves' disease (GD) is caused by persistent, unregulated stimulation of thyrocytes by thyroid-stimulating Antibodies (TSAbs) that activate the TSH Receptor (TSHR). We previously reported the first small-molecule antagonist of human TSHR and showed that it inhibited receptor signaling stimulated by sera from four patients with GD.

Objective: Our objective was to develop a better TSHR antagonist and use it to determine whether inhibition of TSAb activation of TSHR is a general phenomenon.

Design: We aimed to chemically modify a previously reported small-molecule TSHR ligand to develop a better antagonist and determine whether it inhibits TSHR signaling by 30 GD sera. TSHR signaling was measured in two in vitro systems: model HEK-EM293 cells stably overexpressing human TSHRs and primary cultures of human thyrocytes. TSHR signaling was measured as cAMP production and by effects on thyroid peroxidase mRNA.

Results: We tested analogs of a previously reported small-molecule TSHR inverse agonist and selected the best NCGC00229600 for further study. In the model system, NCGC00229600 inhibited basal and TSH-stimulated cAMP production. NCGC00229600 inhibition of TSH signaling was competitive even though it did not compete for TSH binding; that is, NCGC00229600 is an allosteric inverse agonist. NCGC00229600 inhibited cAMP production by 39 ± 2.6% by all 30 GD sera tested. In primary cultures of human thyrocytes, NCGC00229600 inhibited TSHR-mediated basal and GD sera up-regulation of thyroperoxidase mRNA levels by 65 ± 2.0%.

Conclusion: NCGC00229600, a small-molecule allosteric inverse agonist of TSHR, is a general antagonist of TSH Receptor activation by TSAbs in GD patient sera.