Modulating TSH Receptor Signaling for Therapeutic Benefit

PET Imaging of Differentiated Thyroid Cancer with TSHR-Targeted [89Zr]Zr-TR1402

Thyroid cancer is the most common endocrine cancer, with differentiated thyroid cancers (DTCs) accounting for 95% of diagnoses. While most DTC patients are diagnosed and treated with radioiodine (RAI), up to 20% of DTC patients become RAI refractory (RAI-R). RAI-R patients have significantly reduced survival rates compared to patients who remain RAI-avid. This study explores [89Zr]Zr-TR1402 as a thyroid-stimulating hormone receptor (TSHR)-targeted PET radiopharmaceutical for DTC. [89Zr]Zr-TR1402 was synthesized with a molar activity of 25.9 MBq/nmol by conjugating recombinant human TSH (rhTSH) analogue TR1402 to chelator p-SCN-Bn-deferoxamine (DFO) in a molar ratio of 3:1 (DFO/TR1402) and radiolabeling with 89Zr (t1/2 = 78.4 h, β+ = 22.7%). As TSHR is absent in commonly available DTC-derived cell lines, TSHR was reintroduced via stable transduction by delivering a lentivirus containing the full-length coding region of the human TSHR gene. Receptor-mediated uptake of [89Zr]Zr-TR1402 was evaluated in vitro in stably transduced TSHR+ and wild-type TSHR- DTC cell lines. In vivo PET imaging was performed on Days 1-3 postinjection in male and female athymic nude mice bearing TSHR+ and TSHR- xenografts, along with ex vivo biodistribution on Day 3 postinjection. In vitro uptake of 1 nM [89Zr]Zr-TR1402 was significantly higher in TSHR+ THJ529T (P < 0.0001) and FTC133 (P < 0.01) cells than in TSHR- THJ529T and FTC133 cells. This uptake was shown to be specific in both TSHR+ THJ529T (P < 0.0001) and TSHR+ FTC133 (P < 0.0001) cells by blocking uptake with 250 nm DFO-TR1402. In vivo PET imaging showed accumulation of [89Zr]Zr-TR1402 in TSHR+ tumors, which was the highest on Day 1. In the male FTC133 xenograft model, ex vivo biodistribution confirmed a significant difference (P < 0.001) in uptake between FTC133+ (1.3 ± 0.1%ID/g) and FTC133- (0.8 ± 0.1%ID/g) tumors. A significant difference (P < 0.05) in uptake was also seen in the male THJ529T xenograft model between THJ529T+ (1.8 ± 0.6%ID/g) and THJ529T- (0.8 ± 0.4%ID/g) tumors. The in vitro and in vivo accumulation of [89Zr]Zr-TR1402 in TSHR-expressing DTC cell lines support the continued preclinical optimization of this approach.

Increased thyroid stimulating hormone (TSH) as a possible risk factor for atherosclerosis in subclinical hypothyroidism

Primary hypothyroidism (PHT) is associated with an increased risk for the development of atherosclerosis (AS) and other cardiovascular disorders. PHT induces atherosclerosis (AS) through the induction of endothelial dysfunction, and insulin resistance (IR). PHT promotes vasoconstriction and the development of hypertension. However, patients with subclinical PHT with normal thyroid hormones (THs) are also at risk for cardiovascular complications. In subclinical PHT, increasing thyroid stimulating hormone (TSH) levels could be one of the causative factors intricate in the progression of cardiovascular complications including AS. Nevertheless, the mechanistic role of PHT in AS has not been fully clarified in relation to increased TSH. Therefore, in this review, we discuss the association between increased TSH and AS, and how increased TSH may be involved in the pathogenesis of AS. In addition, we also discuss how L-thyroxine treatment affects the development of AS.

[Interdisciplinary Management of Orbital Diseases]

Diagnosis and therapy of orbital diseases is an interdisciplinary challenge, in which i.e. otorhinolaryngologists, ophthalmologists, radiologists, radiation therapists, maxillo-facial surgeons, endocrinologists, and pediatricians are involved. This review article describes frequent diseases which both, otolaryngologists and ophthalmologists are concerned with in interdisciplinary settings. In particular the inflammatory diseases of the orbit including orbital complications, autoimmunological diseases of the orbit including Grave´s orbitopathy, and primary and secondary tumors of the orbit are discussed. Beside describing the clinical characteristics and diagnostic steps the article focusses on the interdisciplinary therapy. The review is completed by the presentation of most important surgical approaches to the orbit, their indications and possible complications. The authors tried to highlight the relevant facts despite the shortness of the text.

Current Therapeutic Approaches for Graves' Orbitopathy - are Targeted Therapies the Future?

Graves' orbitopathy is an autoimmune disease of the orbit that most frequently occurs with Graves' hyperthyroidism. The occurrence of autoantibodies directed against the TSH receptor (TRAb) is of central importance for the diagnosis and pathogenesis. These autoantibodies are mostly stimulating, and induce uncontrolled hyperthyroidism and tissue remodelling in the orbit and more or less pronounced inflammation. Consequently, patients suffer to a variable extent from periocular swelling, exophthalmos, and fibrosis of the eye muscles and thus restrictive motility impairment with double vision. In recent decades, therapeutic approaches have mainly comprised immunosuppressive treatments and antithyroid drug therapy for hyperthyroidism to inhibit thyroid hormone production. With the recognition that TRAb also activates an important growth factor receptor, IGF1R (insulin-like growth factor 1 receptor), biological agents have been developed. Teprotumumab (an inhibitory IGF1R antibody) has already been approved in the USA and the therapeutic effects are enormous, especially with regard to the reduction of exophthalmos. Side effects are to be considered, especially hyperglycaemia and hearing loss. It is not yet clear whether the autoimmune reaction (development of the TRAb/attraction of immunocompetent cells) is also influenced by anti-IGF1R inhibiting agents. Recurrences after therapy show that the inhibition of antibody development must be included in the therapeutic concept, especially in severe cases.

Somatostatin Receptor Type 2 and Thyroid-Stimulating Hormone Receptor Expression in Oncocytic Thyroid Neoplasms: Implications for Prognosis and Treatment

Somatostatin receptor type 2 (SSTR2) and thyroid-stimulating hormone receptor (TSHR) display variable expression in primary thyroid tumors and have been implicated as theranostic targets. This study was designed to explore the differential expression of SSTR2 and TSHR in oncocytic (Hurthle cell) carcinoma (OC) vs oncocytic adenoma (OA). We performed a retrospective review for oncocytic neoplasms treated at our institution from 2012 to 2019. Formalin-fixed paraffin-embedded tissue blocks were used for tissue microarray construction. Tissue microarray blocks were cut into 5-μm sections and stained with anti-SSTR2 and anti-TSHR antibodies. Immunostains were analyzed by 3 independent pathologists. χ2 and logistic regression analysis were used to analyze clinical and pathologic variables. Sixty-seven specimens were analyzed with 15 OA and 52 OC. The mean age was 57 years, 61.2% were women, and 70% were White. SSTR2 positivity was noted in 2 OA (13%) and 15 OC (28%; 10 primary, 4 recurrent, and 1 metastatic) (P = .22). TSHR positivity was noted in 11 OA (73%) and 32 OC (62%; 31 primary and 1 metastatic) (P = .40). Those who presented with or developed clinical recurrence/metastasis were more likely to be SSTR2-positive (50% vs 21%; P = .04) and TSHR-negative (64.3% vs 28.9%; P = .02) than primary OC patients. Widely invasive OC was more likely to be SSTR2-positive compared to all other OC subtypes (minimally invasive and angioinvasive) (P = .003). For all patients with OC, TSHR positivity was inversely correlated with SSTR2 positivity (odds ratio, 0.12; CI, 0.03-0.43; P = .006). This relationship was not seen in the patients with OA (odds ratio, 0.30; CI, 0.01-9.14; P = .440). Our results show that recurrent/metastatic OC was more likely to be SSTR2-positive and TSHR-negative than primary OC. Patients with OC displayed a significant inverse relationship between SSTR2 and TSHR expression that was not seen in patients with OA. This may be a key relationship that can be used to prognosticate and treat OCs.

Azathioprine as an adjuvant therapy in severe Graves' disease: a randomized controlled open-label clinical trial

Introduction

Azathioprine (AZA) interferes with the activation of T and B lymphocytes, which are the main cells involved in the pathogenesis of Graves' disease (GD). The aim of this study was to investigate the effectiveness of AZA as an adjuvant therapy to antithyroid drugs (ATDs) for moderate and severe GD. In addition, we conducted an incremental cost-effectiveness analysis of AZA to determine its cost-effectiveness.

Methods

We conducted a randomized, open-label, and parallel-group clinical trial. We randomized untreated hyperthyroid patients with severe GD into three groups. All patients received 45-mg carbimazole (CM) as the starting dose and propranolol 40-120 mg daily. The first group (AZA1) received an additional 1 mg/kg/day AZA, the second group (AZA2) received an additional 2 mg/kg/day AZA, and the third group (control group) received only CM and propranolol. We measured thyroid-stimulating hormone (TSH) and TSH-receptor antibody (TRAb) levels at baseline and every 3 months, while free triiodothyronine (FT3) and free thyroxine (FT4) levels were measured at the time of diagnosis, 1 month after initiation of therapy, and every 3 months thereafter until 2 years after remission. Thyroid volume (TV) was assessed by ultrasound at baseline and 1 year after remission.

Results

A total of 270 patients were included in this trial. By the end of follow-up, there was higher remission rate in the AZA1 and AZA2 groups compared with controls (87.5% and 87.5% vs. 33.4%, p = 0.002). Throughout the course of follow-up, FT3, FT4, TSH, and TRAb were significantly different between the AZA groups and the control group, but there was no significant difference regarding TV. The decline in the concentrations of FT4, FT3, and TRAb was significantly faster in the AZA2 group than in the AZA1 group. The relapse rate during the 12-month follow-up was insignificantly higher in the control group than in either the AZA1 or AZA2 group (10, 4.4, and 4.4%, p = 0.05, respectively). The median relapse time was 18 months for the control group and 24 months for the AZA1 and AZA2 groups. The incremental cost-effectiveness ratio for the AZA group compared with the conventional group was 27,220.4 Egyptian pounds per remission reduction for patients using AZA as an adjuvant for ATDs.

Conclusion

AZA could be a novel, affordable, cost-effective, and safe drug offering hope for patients with GD to achieve early and long-lasting medical remission.

Trial registry

The trial is registered at the Pan African Clinical Trial Registry (Registration number: PACTR201912487382180).

Allosteric Regulation of G-Protein-Coupled Receptors: From Diversity of Molecular Mechanisms to Multiple Allosteric Sites and Their Ligands

Allosteric regulation is critical for the functioning of G protein-coupled receptors (GPCRs) and their signaling pathways. Endogenous allosteric regulators of GPCRs are simple ions, various biomolecules, and protein components of GPCR signaling (G proteins and β-arrestins). The stability and functional activity of GPCR complexes is also due to multicenter allosteric interactions between protomers. The complexity of allosteric effects caused by numerous regulators differing in structure, availability, and mechanisms of action predetermines the multiplicity and different topology of allosteric sites in GPCRs. These sites can be localized in extracellular loops; inside the transmembrane tunnel and in its upper and lower vestibules; in cytoplasmic loops; and on the outer, membrane-contacting surface of the transmembrane domain. They are involved in the regulation of basal and orthosteric agonist-stimulated receptor activity, biased agonism, GPCR-complex formation, and endocytosis. They are targets for a large number of synthetic allosteric regulators and modulators, including those constructed using molecular docking. The review is devoted to the principles and mechanisms of GPCRs allosteric regulation, the multiplicity of allosteric sites and their topology, and the endogenous and synthetic allosteric regulators, including autoantibodies and pepducins. The allosteric regulation of chemokine receptors, proteinase-activated receptors, thyroid-stimulating and luteinizing hormone receptors, and beta-adrenergic receptors are described in more detail.

Structure of full-length TSH receptor in complex with antibody K1-70™

Determination of the full-length thyroid-stimulating hormone receptor (TSHR) structure by cryo-electron microscopy (cryo-EM) is described. The TSHR complexed with human monoclonal TSHR autoantibody K1-70™ (a powerful inhibitor of TSH action) was detergent solubilised, purified to homogeneity and analysed by cryo-EM. The structure (global resolution 3.3 Å) is a monomer with all three domains visible: leucine-rich domain (LRD), hinge region (HR) and transmembrane domain (TMD). The TSHR extracellular domain (ECD, composed of the LRD and HR) is positioned on top of the TMD extracellular surface. Extensive interactions between the TMD and ECD are observed in the structure, and their analysis provides an explanation of the effects of various TSHR mutations on TSHR constitutive activity and on ligand-induced activation. K1-70™ is seen to be well clear of the lipid bilayer. However, superimposition of M22™ (a human monoclonal TSHR autoantibody which is a powerful stimulator of the TSHR) on the cryo-EM structure shows that it would clash with the bilayer unless the TSHR HR rotates upwards as part of the M22™ binding process. This rotation could have an important role in TSHR stimulation by M22™ and as such provides an explanation as to why K1-70™ blocks the binding of TSH and M22™ without activating the receptor itself.

Development of Low-Molecular-Weight Allosteric Agonist of Thyroid-Stimulating Hormone Receptor with Thyroidogenic Activity

To normalize the thyroid status in hypothyroidism caused by resistance to thyroid-stimulating hormone (TSH), low-molecular-weight allosteric agonists of TSH receptor can be used. A new compound ethyl-2-(4-(4-(5-amino-6-(tert-butylcarbamoyl)-2-(methylthio)thieno[2,3-d]-pyrimidine-4-yl)phenyl)-1H-1,2,3-triazol-1-yl) acetate (TPY3m), which stimulated the production of thyroxine when administered to rats (25 mg/kg, i.p.) and also increased the expression of thyroidogenic genes in the cultured FRTL-5 thyrocytes (30 μM) and the rat thyroid gland. The in vitro and in vivo treatment with TPY3m did not lead to a decrease in the expression of the TSH receptor gene in thyrocytes, restoring it under the conditions of receptor hyperactivation by the hormone. This determines the retaining and, in some cases, potentiation of the thyroidogenic effects of TSH (FRTL-5) or thyroliberin (rats) when they are coadministered with TPY3m. TPY3m is a prototype drug for correcting thyroid system functions in subclinical hypothyroidism.

MiR-143 Targets IGF-1R to Suppress Autoimmunity in Thyroid-Associated Ophthalmopathy

Objective

Thyroid-associated ophthalmopathy (TAO) is an autoimmune disease that involves the remodeling of orbit and periorbital tissues. Thyroid-stimulating hormone receptor (TSHR) and insulin-like growth factor 1 receptor (IGF-1R) may stimulate the activation of autoimmunity in TAO, but the exact mechanism is unclear. We investigated whether IGF-1R/TSHR modulation in TAO may involve microRNA regulation.

Methods

We conducted microarray analysis using RNA from the orbital connective tissue samples of 3 healthy and 3 patients with TAO. The involvement of differentially regulated microRNA in IGF-1R/TSHR modulation in TAO was evaluated in orbital fibroblasts (OFs) and female BALB/c mice.

Results

Using hierarchical cluster analysis, we identified that miR-143 was downregulated in TAO. The expression levels of miR-143 in OFs were significantly reduced under IL-1B stimulation. However, OF proliferation and inflammatory responses decreased when miR-143 is overexpressed. In contrast, the suppression of miR-143 increased levels of inflammatory markers (IL-6, IL-8, MCP1) and hyaluronan accumulation. Moreover, overexpression of miR-143 significantly lowers levels of IGF-1R and TSHR. A luciferase assay indicated that miR-143 targets the 3′-UTR of IGF-1R. Increases in the expression of IGF-1R increased the expression of the inflammasome marker NLRP3 and apoptotic marker cleaved caspase-1; however, miR-143 overexpression decreased levels of IGF-1R, TSHR, NLRP3, cleaved caspase 1, IL-1B, and IL-18. In a mouse model of TAO, overexpression of miR-143 significantly reduced levels of IGF-1R and attenuated the adipogenesis associated with TAO.

Conclusion

We found that miR-143 directly targets IGF-1R to alleviate the inflammatory response in TAO by indirectly decreasing levels of TSHR and inactivating NLRP3.

[Graves' orbitopathy]

BACKGROUND

 Graves' orbitopathy (GO) is an autoimmune orbital disease which is mostly associated with Graves' disease and requires good interdisciplinary cooperation. To minimize irreversible damages a stage-adapted anti-inflammatory therapy is of great importance.

MATERIAL AND METHODS

 Discussion of the latest results of new findings of the pathogenesis, randomized controlled trials on anti-inflammatory treatments for Graves' orbitopathy and novel therapeutic concepts.

RESULTS

 In all patients with GO achieving euthyroidism, as well as cessation of smoking is very important to avoid prolongated diseases. Mild cases of GO can be treated with selenium supplementation and artificial tears. The moderate-to-severe, active form of GO requires primarily i. v. steroids in combination with orbital irradiation in case of impaired motility. In patients with insufficient therapeutic response after 6 weeks, treatment should be switched to other immunosuppressive agents. In severe sight-threatening cases even high-dose i. v. steroid treatments are often ineffective and bony orbital decompression is necessary. As latest research data have improved our understanding of the pathophysiology of GO, targeted therapies have been developed for GO. Teprotumumab, an IGF-1 receptor antibody, was shown effective in treating GO patients in a phase III trial and should soon be awarded approval for Europe. Inactive patients, who suffer from disturbing exophthalmos should be also treated with bony decompression before eye muscle or lid surgery.

CONCLUSION

 The current concept for Graves' orbitopathy is as follows: first anti-inflammatory therapy then surgical correction of the permanent defects. This might be modified in the future, due to the promising effects of targeted therapies.

Biased and allosteric modulation of bone cell-expressing G protein-coupled receptors as a novel approach to osteoporosis therapy

On the cellular level, osteoporosis (OP) is a result of imbalanced bone remodeling, in which osteoclastic bone resorption outcompetes osteoblastic bone formation. Currently available OP medications include both antiresorptive and bone-forming drugs. However, their long-term use in OP patients, mainly in postmenopausal women, is accompanied by severe side effects. Notably, the fundamental coupling between bone resorption and formation processes underlies the existence of an undesirable secondary outcome that bone anabolic or anti-resorptive drugs also reduce bone formation. This drawback requires the development of anti-OP drugs capable of selectively stimulating osteoblastogenesis and concomitantly reducing osteoclastogenesis. We propose that the application of small synthetic biased and allosteric modulators of bone cell receptors, which belong to the G-protein coupled receptors (GPCR) family, could be the key to resolving the undesired anti-OP drug selectivity. This approach is based on the capacity of these GPCR modulators, unlike the natural ligands, to trigger signaling pathways that promote beneficial effects on bone remodeling while blocking potentially deleterious effects. Under the settings of OP, an optimal anti-OP drug should provide fine-tuned regulation of downstream effects, for example, intermittent cyclic AMP (cAMP) elevation, preservation of Ca²⁺ balance, stimulation of osteoprotegerin (OPG) and estrogen production, suppression of sclerostin secretion, and/or preserved/enhanced canonical β-catenin/Wnt signaling pathway. As such, selective modulation of GPCRs involved in bone remodeling presents a promising approach in OP treatment. This review focuses on the evidence for the validity of our hypothesis.