G-1 (CAS 881639-98-1): A Selective GPR30 Agonist for Precision Rapid Estrogen Signaling

Executive Summary: G-1 (CAS 881639-98-1) is a potent and selective agonist for the G protein-coupled estrogen receptor GPR30/GPER1, exhibiting high affinity (Ki ≈ 11 nM) and minimal off-target activity at classical estrogen receptors ERα and ERβ even at micromolar concentrations (APExBIO). Upon GPR30 activation, G-1 induces rapid intracellular calcium mobilization (EC50 ≈ 2 nM) and triggers PI3K-dependent nuclear PIP3 accumulation, central to non-genomic estrogen signaling (Wang et al., 2021). G-1 robustly inhibits breast cancer cell migration at sub-nanomolar IC50 values and demonstrates in vivo cardioprotective effects by modulating β-adrenergic receptor expression and attenuating cardiac fibrosis in heart failure models. The compound, distributed by APExBIO, is widely used in cardiovascular, endocrine, and cancer biology research. Its solubility, storage, and workflow parameters are well-characterized, supporting reproducible experimental design.

Biological Rationale

Estrogenic signaling is classically mediated by nuclear receptors ERα and ERβ, modulating gene transcription over hours to days. However, non-classical rapid estrogen actions, occurring within seconds to minutes, are mediated by membrane-associated receptors, including GPR30 (also known as GPER1) (Wang et al., 2021). GPR30 is a G protein-coupled receptor localized primarily to the endoplasmic reticulum, and it orchestrates acute signal transduction events such as calcium flux and PI3K activation. These pathways are implicated in immune modulation, cardiovascular protection, and cancer cell behavior. G-1, as a highly selective GPR30 agonist, enables the dissection of these rapid, non-genomic estrogen effects without confounding activation of ERα or ERβ (APExBIO).

Mechanism of Action of G-1 (CAS 881639-98-1), a selective GPR30 agonist

G-1 binds to GPR30/GPER1 with a reported inhibition constant (Ki) of approximately 11 nM, demonstrating >1000-fold selectivity over ERα and ERβ. Upon ligand binding, GPR30 undergoes conformational changes that activate heterotrimeric G proteins, leading to downstream signaling. Key events include:

• Rapid increase in intracellular calcium concentration (EC50 ≈ 2 nM) upon G-1 exposure in cellular models.
• Activation of phosphoinositide 3-kinase (PI3K) pathway and nuclear accumulation of PIP3, supporting cell survival and migration control.
• Regulation of β-adrenergic receptor expression in cardiac myocytes, linked to improved contractility and reduced fibrosis in heart failure models.
• Suppression of endoplasmic reticulum stress (ERS) in immune cells, normalizing CD4+ T lymphocyte function after hemorrhagic shock (Wang et al., 2021).

Unlike estradiol, G-1 does not significantly activate nuclear ERα or ERβ at concentrations up to 1 μM, ensuring mechanistic specificity in experimental systems.

Evidence & Benchmarks

• G-1 binds selectively to GPR30 (Ki ≈ 11 nM) and shows negligible binding to ERα/ERβ at up to 1 μM (APExBIO technical data, product page).
• G-1 induces a rapid rise in intracellular calcium levels with EC50 ≈ 2 nM in GPR30-expressing cells (Wang et al., 2021, Fig. 1).
• In breast cancer cell lines (SKBr3, MCF7), G-1 inhibits cell migration with IC50 values of 0.7 nM and 1.6 nM, respectively (see also summary).
• Chronic G-1 administration in ovariectomized Sprague-Dawley rats with heart failure reduces brain natriuretic peptide, inhibits cardiac fibrosis, and normalizes β-adrenergic receptor expression (Wang et al., 2021).
• G-1 suppresses endoplasmic reticulum stress and restores CD4+ T lymphocyte proliferation in hemorrhagic shock models (Wang et al., 2021, Table 1).

Applications, Limits & Misconceptions

G-1 is widely employed in cardiovascular, endocrine, immune, and oncology research as a tool compound to elucidate GPR30-mediated signaling. Its robust selectivity supports mechanistic studies of rapid estrogen signaling, immune cell regulation after trauma, attenuation of cardiac fibrosis, and inhibition of breast cancer cell migration. For an in-depth mechanistic perspective, see this article, which G-1's workflow advances by providing updated preclinical benchmarks and solubility guidance. Recent reviews, such as BMX-IN-1, focus on G-1's integration into translational research; this article provides updated in vivo benchmarks and workflow integration parameters.

Common Pitfalls or Misconceptions

• G-1 is not an ERα or ERβ agonist: Experimental evidence shows negligible activity at these nuclear receptors at standard concentrations (Wang et al., 2021).
• G-1 is insoluble in water and ethanol: Stock solutions must be prepared in DMSO, typically at >10 mM, with warming/sonication as required (APExBIO).
• Not suitable for long-term solution storage: Prepared solutions are stable at -20°C short-term; repeated freeze-thaw cycles or room temperature exposure can reduce potency.
• Not a pan-estrogen receptor probe: G-1's utility is restricted to GPR30; it does not report on classical estrogen receptor signaling.
• In vivo dosing parameters must be optimized by species/model: Pharmacokinetics and target engagement can vary by animal model and administration route.

Workflow Integration & Parameters

G-1 (CAS 881639-98-1, B5455) is delivered as a crystalline solid (molecular weight 412.28 g/mol; formula C21H18BrNO3). For in vitro use, dissolve in DMSO at ≥41.2 mg/mL (≥100 mM), with gentle warming and ultrasonic bath to accelerate dissolution. For cell-based assays, dilute DMSO stock into pre-warmed media; final DMSO concentration should not exceed 0.1% (v/v) unless otherwise validated. For in vivo rodent studies, G-1 can be administered via intraperitoneal injection; dose, vehicle, and frequency require model-specific optimization. Stock solutions are stable at -20°C for short-term storage. Avoid multiple freeze-thaw cycles. See the APExBIO product page for detailed protocols.

For advanced integration strategies, consult this strategic review, which this article extends with new evidence on post-shock immune normalization and PI3K signaling benchmarks.

Conclusion & Outlook

G-1 (CAS 881639-98-1) is a validated, highly selective G protein-coupled estrogen receptor agonist suitable for mechanistic studies of rapid, non-classical estrogen signaling. Its robust performance in cardiac, immune, and oncology models, along with clarity of workflow integration and storage guidelines, make it a standard tool for GPR30 research. APExBIO provides comprehensive technical documentation and distribution for G-1, supporting reproducible, high-precision experimentation. Ongoing research is expanding its translational potential in cardioprotection, immune modulation, and tumor biology, with emerging evidence connecting GPR30 activation to novel therapeutic strategies (Wang et al., 2021).