A Gq Biased Small Molecule Active at the TSH Receptor

Area of Science:

• Endocrinology and Pharmacology
• Molecular and Cellular Biology

Background:

• G protein-coupled receptors (GPCRs), including the TSH receptor (TSHR), can initiate distinct signaling pathways.
• Selective modulation of TSHR signaling offers potential for targeted therapeutic interventions.
• Understanding TSHR's ability to engage different G proteins is crucial for drug discovery.

Purpose of the Study:

• To identify and characterize novel small molecule agonists that selectively activate specific G protein pathways of the TSHR.
• To investigate the functional consequences of selective Gq/11 pathway activation at the TSHR.
• To explore the therapeutic potential of Gq-biased TSHR agonists for modulating thyroid cell proliferation.

Main Methods:

• Utilized a transcriptional-based luciferase assay system in CHO-TSHR cells to screen for selective TSHR modulators.
• Assayed for activation of Gαs, Gαi, Gβγ, and Gα12/13 pathways using specific response elements (CRE, NFAT, SRF, SRE).
• Characterized the identified Gq/11 agonist (MSq1) for its potency (EC50), signaling profile, and effects on thyrocyte proliferation and differentiation markers.

Main Results:

• Identified MSq1, a novel small molecule agonist, which selectively activates the TSHR Gq/11 pathway with high potency (EC50= 8.3 × 10^-9 M).
• MSq1 demonstrated a significant anti-proliferative effect on TSH-induced thyrocyte proliferation, mediated through protein kinase C (PKC) activation.
• MSq1 did not induce upregulation of key thyroid-specific differentiation markers in rat thyroid cells (FRTL5).

Conclusions:

• A novel Gq/11-biased agonist (MSq1) for the TSHR was identified and characterized.
• Selective Gq/11 activation of TSHR can suppress proliferative signals induced by the orthosteric ligand.
• Gq-biased TSHR agonists represent a potential therapeutic strategy for modulating thyroid growth.