Description
Summary Abstract
GC-1 (Sobetirome; 3,5-dimethyl-4-(4′-hydroxy-3′-isopropylbenzyl)phenoxy acetic acid; CAS 211110-63-3) is a synthetic thyromimetic compound first synthesized in 1998 as a selective thyroid hormone receptor-beta (TRβ) agonist. Because TRβ mediates thyroid hormone’s lipid-lowering, hepatic, and central nervous system (CNS) actions while TRα predominantly governs cardiac rate, contractility, and bone turnover, GC-1’s receptor subtype selectivity produces the metabolic and CNS benefits of thyroid hormone without the cardiac and skeletal adverse effects associated with systemic hyperthyroidism. Preclinical data demonstrate 600- to 1,400-fold greater LDL cholesterol-lowering potency than atorvastatin in rodent and primate models; 41% LDL reduction was observed in early human clinical data at 100 µg/day. GC-1 is also investigated as a promoter of CNS remyelination in X-linked adrenoleukodystrophy (X-ALD) models and in preclinical peripheral neuropathy studies.
Clinical Indications
GC-1 (Sobetirome) spans lipid, metabolic, and neurological research programs:
- Dyslipidemia and Atherosclerosis: Preclinical studies demonstrate LDL reduction of 54% versus 24% for atorvastatin at comparable doses in high-fat/high-cholesterol mouse models; early human data show approximately 41% LDL reduction at 100 µg/day.
- X-Linked Adrenoleukodystrophy (X-ALD): GC-1 and its prodrug QRX431 have been investigated for induction of CNS remyelination by promoting oligodendrocyte differentiation and maturation via TRβ signaling, providing a non-hormonal thyromimetic strategy for demyelinating disease.
- Hepatic Steatosis / Non-Alcoholic Fatty Liver Disease (NAFLD): TRβ activation in the liver reduces hepatic triglyceride and LDL production; hepatocyte proliferation and lipid metabolism normalization have been documented in rodent models, supporting GC-1 as a tool compound for NAFLD research.
Contraindications
- Cardiac Endpoint Studies: GC-1 has markedly reduced activity at TRα, the receptor isoform governing cardiac chronotropy and inotropy; however, at high doses or in chronically treated models, residual TRα binding may affect heart rate; cardiac monitoring is appropriate in all in vivo protocols.
- Bone Density Endpoints: TRα-mediated effects on osteoblast/osteoclast balance are minimized with GC-1 relative to T3; nonetheless, studies with skeletal endpoints should include DEXA or histomorphometric controls in chronic in vivo studies.
- HPT Axis Suppression: As a thyromimetic, GC-1 will suppress TSH via hypothalamic-pituitary-thyroid (HPT) axis feedback; in vivo study designs that require intact HPT signaling must account for this pharmacological effect.
Mechanism of Action (MOA)
GC-1 replicates the metabolic and CNS actions of thyroid hormone T3 through selective TRβ engagement:
TRβ Selectivity Over TRα
GC-1 binds thyroid hormone receptor-beta (TRβ) with high affinity while demonstrating markedly reduced affinity for TRα. Structural basis studies (BMC Structural Biology, 2008) reveal that GC-1 fits the TRβ ligand-binding pocket through a benzyl linker architecture that clashes sterically with TRα’s His435 residue, which is replaced by Asn331 in TRβ. This single-residue difference underlies the receptor subtype selectivity.
Hepatic LDL and Cholesterol Lowering
TRβ activation in hepatocytes drives LDL receptor (LDLR) upregulation, accelerating LDL clearance from circulation. Simultaneously, TRβ-mediated activation of cholesterol 7α-hydroxylase (CYP7A1) increases bile acid synthesis from hepatic cholesterol, a second route of cholesterol disposal. Combined, these produce 600–1,400-fold greater LDL-lowering potency than atorvastatin per milligram in rodent studies.
CNS Remyelination
Thyroid hormone is a critical regulator of oligodendrocyte differentiation and myelination. GC-1, by selectively activating TRβ in oligodendrocyte precursor cells (OPCs), drives their differentiation into mature myelin-producing oligodendrocytes. This mechanism is being explored in X-ALD and other demyelinating conditions as a non-immunosuppressive, pro-myelination strategy.
Triglyceride and VLDL Reduction
GC-1 reduces serum triglycerides by approximately 75% in high-cholesterol diet mouse models, exceeding the ~30% HDL reduction that represents the one adverse lipid effect (shared with T3). Hepatic VLDL secretion is reduced by TRβ-mediated upregulation of apoAV and suppression of SREBP-1c-driven triglyceride synthesis, providing a mechanistically distinct triglyceride-lowering profile from fibrates or niacin.
Key Features & Specifications
GC-1 is provided as 100 mcg capsules for TRβ-selective thyromimetic research applications:
Chemical Analysis
| Property | Specification Reference Data |
|---|---|
| IUPAC Name | 3,5-Dimethyl-4-(4′-hydroxy-3′-isopropylbenzyl)phenoxy acetic acid |
| CAS Number | 211110-63-3 |
| Molecular Formula | C20H24O4 |
| Molecular Weight | 328.40 g/mol |
| Synonyms | GC-1; Sobetirome; QRX431; UNII-XQ31741E9Q |
| Form / Variation | 100 MCG Capsules (SKU C-014, $184.00) |
Storage, Safety, and Handling
Storage Protocol
Store GC-1 capsules at −20 °C in a sealed, moisture-protected container. GC-1 is stable in DMSO at concentrations ≥10 mM. For aqueous assays, prepare stock solutions in DMSO and dilute immediately before use; aqueous solubility is limited. Protect from prolonged light exposure to prevent phenolic oxidation of the 4′-hydroxy group.
Handling & Compliance
Handle with standard PPE. GC-1 (Sobetirome) has been evaluated in Phase 1 clinical trials but has no approved therapeutic indication. As a thyroid hormone receptor agonist, it falls within WADA’s prohibited Hormone and Metabolic Modulators (S4) category. Appropriate institutional and regulatory approvals are required for any in vivo use.