Response to Krieger et al. re: "TSHR/IGF-1R Cross-Talk, Not IGF-1R Stimulating Antibodies, Mediates Graves' Ophthalmopathy Pathogenesis" (Thyroid 2017;27:746-747)

Teprotumumab Divergently Alters Fibrocyte Gene Expression: Implications for Thyroid-associated Ophthalmopathy

CONTEXT

Teprotumumab, an IGF-I receptor (IGF-IR) inhibitor, is effective in thyroid-associated ophthalmopathy (TAO). The drug can modulate induction by TSH of IL-6 and IL-8 in CD34+ fibrocytes and their putative derivatives, CD34+ orbital fibroblasts (CD34+ OF). Fibrocytes express multiple thyroid autoantigens and cytokines implicated in TAO, which are downregulated by Slit2. Inflammation and disordered hyaluronan (HA) accumulation occur in TAO. Whether teprotumumab alters these processes directly in fibrocytes/CD34+ OF remains uncertain.

OBJECTIVE

Determine teprotumumab effects on expression/synthesis of several TAO-relevant molecules in fibrocytes and GD-OF.

DESIGN/SETTING/PARTICIPANTS

Patients with TAO and healthy donors were recruited from an academic endocrine and oculoplastic practice.

MAIN OUTCOME MEASURES

Real-time PCR, specific immunoassays.

RESULTS

Teprotumumab attenuates basal and TSH-inducible autoimmune regulator protein, thyroglobulin, sodium iodide symporter, thyroperoxidase, IL-10, and B-cell activating factor levels in fibrocytes. It downregulates IL-23p19 expression/induction while enhancing IL-12p35, intracellular and secreted IL-1 receptor antagonists, and Slit2. These effects are mirrored by linsitinib. HA production is marginally enhanced by teprotumumab, the consequence of enhanced HAS2 expression.

CONCLUSION

Teprotumumab affects specific gene expression in fibrocytes and GD-OF in a target-specific, nonmonolithic manner, whereas IGF-IR control of these cells appears complex. The current results suggest that the drug may act on cytokine expression and HA production systemically and locally, within the TAO orbit. These findings extend our insights into the mechanisms through which IGF-IR inhibition might elicit clinical responses in TAO, including a potential role of Slit2 in attenuating inflammation and tissue remodeling.

It Takes Two to Tango: IGF-I and TSH Receptors in Thyroid Eye Disease

CONTEXT

Thyroid eye disease (TED) is a complex autoimmune disease process. Orbital fibroblasts represent the central orbital immune target. Involvement of the TSH receptor (TSHR) in TED is not fully understood. IGF-I receptor (IGF-IR) is overexpressed in several cell types in TED, including fibrocytes and orbital fibroblasts. IGF-IR may form a physical and functional complex with TSHR.

OBJECTIVE

Review literature relevant to autoantibody generation in TED and whether these induce orbital fibroblast responses directly through TSHR, IGF-IR, or both.

EVIDENCE

IGF-IR has traditionally been considered a typical tyrosine kinase receptor in which tyrosine residues become phosphorylated following IGF-I binding. Evidence has emerged that IGF-IR possesses kinase-independent activities and can be considered a functional receptor tyrosine kinase/G-protein-coupled receptor hybrid, using the G-protein receptor kinase/β-arrestin system. Teprotumumab, a monoclonal IGF-IR antibody, effectively reduces TED disease activity, proptosis, and diplopia. In addition, the drug attenuates in vitro actions of both IGF-I and TSH in fibrocytes and orbital fibroblasts, including induction of proinflammatory cytokines by TSH and TED IgGs.

CONCLUSIONS

Although teprotumumab has been proven effective and relatively safe in the treatment of TED, many questions remain pertaining to IGF-IR, its relationship with TSHR, and how the drug might be disrupting these receptor protein/protein interactions. Here, we propose 4 possible IGF-IR activation models that could underlie clinical responses to teprotumumab observed in patients with TED. Teprotumumab is associated with several adverse events, including hyperglycemia and hearing abnormalities. Underpinning mechanisms of these are being investigated. Patients undergoing treatment with drug must be monitored for these and managed with best medical practices.

Is Estrogen a Missing Culprit in Thyroid Eye Disease? Sex Steroid Hormone Homeostasis Is Key to Other Fibrogenic Autoimmune Diseases - Why Not This One?

Sex bias in autoimmune disease (AID) prevalence is known, but the role of estrogen in disease progression is more complex. Estrogen can even be protective in some AIDs; but in systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and systemic sclerosis (SSc), estrogen, its metabolites, and its receptors have been demonstrated to play critical, localized inflammatory roles. Estrogen is instrumental to the fibrosis seen in RA, SLE, SSc and other disease states, including breast cancer and uterine leiomyomas. Fibrotic diseases tend to share a common pattern in which lymphocyte-monocyte interactions generate cytokines which stimulate the deposition of fibrogenic connective tissue. RA, SLE, SSc and thyroid eye disease (TED) have very similar inflammatory and fibrotic patterns-from pathways to tissue type. The thorough investigations that demonstrated estrogen's role in the pathology of RA, SLE, and SSc could, and possibly should, be carried out in TED. One might even expect to find an even greater role for estrogen, and sex steroid homeostasis in TED, given that TED is typically sequalae to Graves' disease (GD), or Hashimoto's disease (HD), and these are endocrine disorders that can create considerable sex steroid hormone dysregulation. This paper highlights the pathophysiology similarities in 4 AIDs, examines the evidence of sex steroid mediated pathology across 3 AIDs and offers a case study and speculation on how this may be germane to TED.

Teprotumumab: The Dawn of Therapies in Moderate-to-Severe Thyroid-Associated Ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is a potentially sight-threatening ocular disease. About 3-5% of patients with TAO have severe disease with intense pain, inflammation, and sight-threatening corneal ulceration or compressive optic neuropathy. The current treatments of TAO are often suboptimal, mainly because the existing therapies do not target the pathogenesis of the disease. TAO mechanism is unclear. Ocular fibrocytes express relatively high levels of the functional TSH receptor (TSHR), and many indirect evidences support its participation. Over expression of insulin-like growth factor-1 receptor (IGF-IR) in fibroblasts, leading to inappropriate expression of inflammatory factors, production of hyaluronic acid and cell activation in orbital fibroblasts are also possible mechanisms. IGF-1R and TSHR form a physical and functional signaling complex. Inhibition of IGF-IR activity leads to the attenuation of signaling initiated at either receptor. Teprotumumab (TMB) is a human immunoglobulin G1 monoclonal antibody, binding to IGF-IR. Recently two TMB clinical trials had been implemented in TAO patients, indicating dramatic reductions in disease activity and severity, which approved its use for the treatment of TAO in the US. This review summarizes the treatments of TAO, focusing on the pathogenesis of IGF-1R in TAO and its application prospects.

Putative protective role of autoantibodies against the insulin-like growth factor-1 receptor in Graves' Disease: results of a pilot study

BACKGROUND

The insulin-like growth factor-1 receptor (IGF-1R) is a key element in the pathogenesis of Graves' Orbitopathy (GO), but the role of IGF-1R autoantibodies (IGF-1RAbs) has not been established.

METHODS

We designed a cross-sectional investigation to measure IGF-1RAbs in patients with Graves' disease (GD), with or without GO, who underwent radioiodine therapy followed by glucocorticoids (GC). Twenty-nine patients were included, 15 of which with GO. Patients were evaluated at baseline and three and 6 months after radioiodine. The primary objective was the prevalence of positive tests for IGF-1RAbs. The secondary objectives were: (1) IGF-1RAbs concentrations and their variations; (2) relationship between IGF-1RAbs and the features of GO; (3) relationship between IGF-1RAbs and anti-thyroid autoantibodies.

RESULTS

IGF-1RAbs above the cut-off value were found only in one patient with GD without GO. IGF-1RAb levels were greater in patients with GD without GO, at baseline (P < 0.0001), and after three (P < 0.0001) and six (P = 0.0001) months. No correlations were observed between IGF-1RAbs and the features of GO, nor between IGF-1RAbs and anti-thyroglobulin or anti-thyroperoxidase autoantibodies. There was an inverse correlation between anti-TSH receptor autoantibodies (TRAbs) and IGF-1RAb levels in GD patients with GO at 6 months (P = 0.03).

CONCLUSIONS

IGF-1RAbs appear to be greater in patients with GD without GO compared with those with GO, suggesting a putative protective role of IGF-1RAbs on the development of GO, in line with the beneficial effects of Teprotumumab on GO. The inverse correlation between IGF-1RAbs and TRAbs 6 months after radioiodine may reflect antigen spreading and/or GC treatment.

Modulating TSH Receptor Signaling for Therapeutic Benefit

Autoimmune thyroid-stimulating antibodies are activating the thyrotropin receptor (TSHR) in both the thyroid and the eye, but different molecular mechanisms are induced in both organs, leading to Graves' disease (GD) and Graves' orbitopathy (GO), respectively. Therapy with anti-thyroid drugs to reduce hyperthyroidism (GD) by suppressing the biosynthesis of thyroid hormones has only an indirect effect on GO, since it does not causally address pathogenic TSHR activation itself. GO is thus very difficult to treat. The activated TSHR but also the cross-interacting insulin-like growth factor 1 receptor (IGF-1R) contribute to this issue. The TSHR is a heptahelical G-protein-coupled receptor, whereas the IGF-1R is a receptor tyrosine kinase. Despite these fundamental structural differences, both receptors are phosphorylated by G-protein receptor kinases, which enables β-arrestin binding. Arrestins mediate receptor internalization and also activate the mitogen-activated protein kinase pathway. Moreover, emerging results suggest that arrestin plays a critical role in the cross-interaction of the TSHR and the IGF-1R either in their common signaling pathway and/or during an indirect or potential TSHR/IGF-1R interaction. In this review, novel pharmacological strategies with allosteric small-molecule modulators to treat GO and GD on the level of the TSHR and/or the TSHR/IGF-1R cross-interaction will be discussed. Moreover, monoclonal antibody approaches targeting the TSHR or the IGF-1R and thereby preventing activation of either receptor will be presented. Another chapter addresses the immunomodulation to treat GO using TSHR-derived peptides targeting the human leukocyte antigen DR isotope (HLA-DR), which is a feasible approach to tackle GO, since HLA-DR and TSHR are overexpressed in orbital tissues of GO patients.

Serum antibodies against the insulin-like growth factor-1 receptor (IGF-1R) in Graves' disease and Graves' orbitopathy

BACKGROUND

A role of the insulin-like growth factor-1 receptor (IGF-1R) in the pathogenesis of Graves' orbitopathy (GO) has been proposed, but the existence and function of anti-IGF-1R-antibodies (IGF-1R-Abs) are debated.

METHODS

We designed a cross-sectional investigation to measure serum IGF-1R-Abs by a commercial assay in consecutive patients with Graves' disease (GD) compared with healthy subjects and patients with autoimmune thyroiditis (AT). A total of 134 subjects were screened including 27 healthy subjects, 80 GD patients (54 of whom with GO), and 27 AT patients. The main outcome measure was the prevalence of positive serum IGF-1R-Abs in GO, compared with GD without GO and with the other study groups.

RESULTS

Having established a cut-off value at 55.2 ng/ml for positive tests, positive IGF-1R-Abs were more frequent in GD (25%), than in AT (3.7%, P = 0.003) and healthy subjects (0%, P = 0.006). Within GD, there was no difference between patients with or without GO. Serum levels of IGF-1R-Abs differed across the study population (P < 0.0001), reflecting their higher concentrations in GD (P < 0.0001 vs both AT and healthy subjects), but with no difference between patients with or without GO. In patients with GO, there was an inverse correlation between serum IGF-1R-Abs and CAS (R = - 0.376, 95% CI: from - 0.373 to - 0.631; P = 0.005), the significance of which remains to be investigated.

CONCLUSIONS

Serum autoantibodies against the IFG-1R are present in one-fourth of GD patients, regardless of the presence of GO. Further functional studies are needed to investigate the significance of their inverse correlation with GO activity.

Insulin-like Growth Factor-I Receptor and Thyroid-Associated Ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is a complex disease process presumed to emerge from autoimmunity occurring in the thyroid gland, most frequently in Graves disease (GD). It is disfiguring and potentially blinding, culminating in orbital tissue remodeling and disruption of function of structures adjacent to the eye. There are currently no medical therapies proven capable of altering the clinical outcome of TAO in randomized, placebo-controlled multicenter trials. The orbital fibroblast represents the central target for immune reactivity. Recent identification of fibroblasts that putatively originate in the bone marrow as monocyte progenitors provides a plausible explanation for why antigens, the expressions of which were once considered restricted to the thyroid, are detected in the TAO orbit. These cells, known as fibrocytes, express relatively high levels of functional TSH receptor (TSHR) through which they can be activated by TSH and the GD-specific pathogenic antibodies that underpin thyroid overactivity. Fibrocytes also express insulin-like growth factor I receptor (IGF-IR) with which TSHR forms a physical and functional signaling complex. Notably, inhibition of IGF-IR activity results in the attenuation of signaling initiated at either receptor. Some studies suggest that IGF-IR-activating antibodies are generated in GD, whereas others refute this concept. These observations served as the rationale for implementing a recently completed therapeutic trial of teprotumumab, a monoclonal inhibitory antibody targeting IGF-IR in TAO. Results of that trial in active, moderate to severe disease revealed dramatic and rapid reductions in disease activity and severity. The targeting of IGF-IR with specific biologic agents may represent a paradigm shift in the therapy of TAO.

Evidence That Graves' Ophthalmopathy Immunoglobulins Do Not Directly Activate IGF-1 Receptors

BACKGROUND

Graves' ophthalmopathy (GO) pathogenesis involves thyrotropin (TSH) receptor (TSHR)-stimulating autoantibodies. Whether there are autoantibodies that directly stimulate insulin-like growth factor 1 receptors (IGF-1Rs), stimulating insulin-like growth factor receptor antibodies (IGFRAbs), remains controversial. This study attempted to determine whether there are stimulating IGFRAbs in patients with GO.

METHODS

Immunoglobulins (Igs) were purified from normal volunteers (NV-Igs) and patients with GO (GO-Igs). The effects of TSH, IGF-1, NV-Igs, and GO-Igs on pAKT and pERK1/2, members of pathways used by IGF-1R and TSHR, were compared in orbital fibroblasts from GO patients (GOFs) and U2OS-TSHR cells overexpressing TSHRs, and U2OS cells that express TSHRs at very low endogenous levels. U2OS-TSHR and U2OS cells were used because GOFs are not easily manipulated using molecular techniques such as transfection, and U2OS cells because they express TSHRs at levels that do not measurably stimulate signaling. Thus, comparing U2OS-TSHR and U2OS cells permits specifically distinguishing signaling mediated by the TSHR and IGF-1R.

RESULTS

In GOFs, all GO-Igs stimulated pERK1/2 formation and 69% stimulated pAKT. In U2OS-TSHR cells, 15% of NV-IGs and 83% of GO-Igs stimulated increases in pERK1/2, whereas all NV-Igs and GO-Igs stimulated increases in pAKT. In U2OS cells, 70% of GO-Igs stimulated small increases in pAKT. Knockdown of IGF-1R caused a 65 ± 6.3% decrease in IGF-1-stimulated pAKT but had no effect on GO-Igs stimulation of pAKT. Thus, GO-Igs contain factor(s) that stimulate pAKT formation. However, this factor(s) does not directly activate IGF-1R.

CONCLUSIONS

Based on the findings analyzing these two signaling pathways, it is concluded there is no evidence of stimulating IGFRAbs in GO patients.