The insulin-like growth factor-I receptor and its role in thyroid-associated ophthalmopathy.

Abstract

Thyroid-associated ophthalmopathy (TAO), an autoimmune component of Graves' disease, remains a disfiguring and potentially blinding condition. Here, the author reviews the role of insulin-like growth factor-I receptor pathway in TAO and how it might be therapeutically targeted. The recent literature is reviewed. TAO involves reactivity of orbital connective tissues and their remodeling. While many of the details concerning the pathogenesis of TAO remain to be determined, several insights have come to light recently. Among them is the apparent involvement of IGF-IR. This receptor protein, a membrane-spanning tyrosine kinase receptor can form both physical and functional complexes with the thyrotropin receptor (TSHR). This is notable because TSHR is the established primary autoantigen in Graves' disease. IGF-IR activity is critical to signaling downstream from both IGF-IR and TSHR. In addition, antibodies against IGF-IR have been detected in patients with Graves' disease and in rodent models of TAO. Evidence has been put forward that these antibodies may act directly on IGF-IR, perhaps in some manner activating the receptor. These experimental observations have led to the development of a novel therapy for active TAO, utilizing a monoclonal anti-IGF-IR inhibitory antibody which had been produced originally as treatment for cancer. The agent, teprotumumab was recently evaluated in aclinical trial and found to be highly effective and relatively well-tolerated. It is currently undergoing assessment in a follow-up trial. Should the current study yield similarly encouraging results, it is possible that teprotumumab will emerge as a paradigm-shifting medical therapy for TAO.