G-1 (CAS 881639-98-1): Selective GPR30 Agonist for Cardiovascular and Cancer Research

Executive Summary: G-1 (CAS 881639-98-1) is a potent, selective agonist for the G protein-coupled estrogen receptor GPR30 (GPER1), demonstrating a Ki of ~11 nM and negligible affinity for classical estrogen receptors (ERα, ERβ) at micromolar concentrations (APExBIO). In vitro, G-1 robustly inhibits migration of SKBr3 and MCF7 breast cancer cell lines at nanomolar IC50 values and elevates intracellular calcium at EC50 = 2 nM. In vivo, chronic G-1 administration (120 μg/kg, 14 days) in ovariectomized rat models of heart failure reduces brain natriuretic peptide, attenuates cardiac fibrosis, and normalizes β-adrenergic receptor expression (Wang et al., DOI). G-1 is DMSO-soluble, chemically stable under prescribed conditions, and empowers mechanistic studies of rapid, estrogen receptor-independent signaling.

Biological Rationale

GPR30 (GPER1) is a membrane-bound, G protein-coupled receptor distinct from nuclear estrogen receptors ERα and ERβ. It mediates rapid, non-genomic estrogen signaling, influencing intracellular calcium, PI3K/Akt pathway activation, and downstream cell migration, immune, and cardiac functions (Wang et al., 2021). Endogenous ligands for GPR30 include estradiol and aldosterone; however, selective pharmacological tools are required to dissect GPR30-specific pathways independently of classical estrogen receptor activity. G-1 achieves this by displaying high affinity for GPR30 with minimal cross-reactivity to ERα/ERβ, even at 1000-fold higher concentrations. This selectivity allows for precise modulation of GPR30 signaling in cardiovascular, oncological, and immunological models (see related analysis—this article extends the mechanistic discussion by providing new quantitative benchmarks).

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

G-1 binds the GPR30 receptor with a dissociation constant (Ki) of approximately 11 nM (APExBIO). Upon receptor activation, G-1 induces a rapid increase in intracellular Ca²⁺ (EC50 = 2 nM), a hallmark of non-genomic estrogenic signaling. This Ca²⁺ influx triggers PI3K-dependent nuclear accumulation of phosphatidylinositol (3,4,5)-trisphosphate (PIP3), modulating cell migration and survival pathways. Downstream, G-1-mediated GPR30 activation affects β-adrenergic receptor regulation in cardiac tissue, and inhibits endoplasmic reticulum (ER) stress-driven immune dysfunction in splenic CD4+ T lymphocytes post-hemorrhagic shock (Wang et al., 2021). These effects occur independently of ERα or ERβ, as G-1 displays negligible binding to these nuclear receptors even at micromolar concentrations. This mechanism distinguishes G-1 from classical estrogen agonists and enables targeted investigation of rapid, membrane-initiated estrogen signaling in experimental systems (see comparative application—our current article provides updated in vivo performance data).

Evidence & Benchmarks

• G-1 binds GPR30 selectively with Ki ≈ 11 nM, showing <0.3% cross-reactivity for ERα/ERβ at 10 μM (APExBIO).
• G-1 elevates intracellular Ca²⁺ with EC50 = 2 nM in GPR30-expressing cells (APExBIO).
• G-1 (0.7 nM IC50) inhibits migration of SKBr3 breast cancer cells; MCF7 migration IC50 = 1.6 nM—both co-express GPR30 and estrogen receptors (APExBIO).
• Chronic G-1 (120 μg/kg/day, 14 days, i.p.) reduces cardiac fibrosis, normalizes β1-adrenergic receptor, and upregulates β2-adrenergic receptor expression in ovariectomized rat models of heart failure (Wang et al., 2021).
• G-1 reverses hemorrhagic shock-induced CD4+ T cell dysfunction via GPR30 activation and ER stress inhibition; effect is abolished by GPR30 antagonist G15 (Wang et al., 2021).
• G-1 is DMSO-soluble at ≥41.2 mg/mL, but insoluble in water and ethanol; solid at RT (molecular weight: 412.28 Da; formula: C₂₁H₁₈BrNO₃) (APExBIO).
• Stock solutions remain stable at -20°C; warming and ultrasonic treatment improve solubility above 10 mM in DMSO (APExBIO).

Applications, Limits & Misconceptions

G-1 (CAS 881639-98-1) is designed for mechanistic and translational studies that require selective activation of GPR30, particularly in models where rapid, non-genomic estrogen signaling is implicated. Common applications include:

• Breast cancer cell migration assays to probe GPR30-mediated motility and invasion.
• Cardiovascular disease models (heart failure, cardiac fibrosis) to dissect rapid estrogenic remodeling effects.
• Immune modulation studies, e.g., in hemorrhagic shock, to assess ER stress and T cell proliferation.

This article extends the scope of Unlocking the Power of GPR30 Signaling by providing new in vivo quantitative benchmarks and clarifying storage/handling for robust experimental design.

Common Pitfalls or Misconceptions

• G-1 is not an agonist for ERα or ERβ; effects in these pathways require alternative ligands (Wang et al., 2021).
• G-1 is insoluble in water and ethanol; DMSO is required for stock solution preparation (APExBIO).
• G-1 is for research use only; it is not approved for diagnostic or medical applications (APExBIO).
• G-1's effects depend on GPR30 expression and may not manifest in GPR30-null systems or where GPR30 antagonists (e.g., G15) are present (Wang et al., 2021).
• Stock solutions can degrade at room temperature or with repeated freeze-thaw; always aliquot and store at -20°C (APExBIO).

Workflow Integration & Parameters

For experimental reproducibility, G-1 should be prepared as follows:

• Prepare stock solutions at ≥10 mM in DMSO. Warm and use ultrasonic treatment for complete dissolution.
• Aliquot and store at -20°C; avoid repeated freeze-thaw cycles.
• For in vitro assays, dilute stock solutions in cell culture medium containing ≤0.1% DMSO final concentration.
• For in vivo use (e.g., rat models), inject 120 μg/kg/day intraperitoneally for 14 days, as validated in heart failure protocols (Wang et al., 2021).
• Shipping requires blue ice for thermal stability.

For more detailed, protocol-ready workflows and troubleshooting, see G-1: Selective GPR30 Agonist Empowering Cardiovascular and Oncology Research, which our article updates with new immune modulation benchmarks.

Conclusion & Outlook

G-1 (CAS 881639-98-1) from APExBIO is a robust, highly selective GPR30 agonist. It enables targeted, reproducible interrogation of rapid estrogen signaling in cardiovascular, oncology, and immunological models. Its distinct selectivity profile, potent activity, and validated in vivo efficacy set a new standard for non-classical estrogen receptor research. Continued mechanistic dissection of GPR30 signaling—empowered by G-1—promises to unlock new strategies for disease modeling and therapeutic discovery.