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

Executive Summary: G-1 (CAS 881639-98-1) is a synthetic, high-affinity agonist for the G protein-coupled estrogen receptor GPR30 (GPER1), showing minimal off-target activity even at micromolar concentrations [APExBIO product page]. It is well characterized for its ability to selectively activate GPR30-mediated intracellular calcium and PI3K signaling pathways, distinct from classical nuclear estrogen receptors ERα and ERβ (Peng Wang et al., 2021). G-1 efficiently inhibits cell migration in SKBr3 and MCF7 breast cancer cell lines at sub-nanomolar concentrations. In vivo, chronic G-1 administration in ovariectomized rat heart failure models reduces brain natriuretic peptide, attenuates cardiac fibrosis, and improves cardiac contractility. These validated effects support its wide utility in cardiovascular, endocrine, and oncology research.

Biological Rationale

Estrogen signaling is mediated by both nuclear and membrane-associated receptors. GPR30 (also known as GPER1) is a G protein-coupled receptor that localizes primarily to the endoplasmic reticulum membrane and mediates rapid, non-genomic estrogen responses (Peng Wang et al., 2021). Classical nuclear estrogen receptors, ERα and ERβ, regulate gene transcription, but GPR30 triggers distinct intracellular signaling cascades. G-1 (CAS 881639-98-1) enables selective activation of GPR30 without significant activation of ERα or ERβ, providing a tool to disentangle non-classical estrogen pathways in research models. This specificity is essential for studying rapid estrogen effects in cardiovascular, immune, and oncological contexts (G-1: Reference Compound for Rapid Estrogen Signaling). Unlike endogenous estrogen, which activates all estrogen receptors, G-1 allows for targeted investigation of GPR30’s physiological roles.

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

G-1 binds to GPR30/GPER1 with an affinity (Ki) of approximately 11 nM, while showing negligible binding to ERα or ERβ even at 10 μM (APExBIO). Upon G-1 binding, GPR30 undergoes conformational changes leading to activation of G protein–mediated pathways. This triggers increases in intracellular Ca²⁺ (EC50 ≈ 2 nM) and nuclear accumulation of phosphatidylinositol (3,4,5)-trisphosphate (PIP3) via PI3K activation (Peng Wang et al., 2021). These signaling events modulate cell proliferation, migration, and survival. In immune cells, GPR30 activation by G-1 normalizes CD4⁺ T lymphocyte proliferation post-hemorrhagic shock by reducing endoplasmic reticulum stress. In cardiac tissue, G-1 modulates β-adrenergic receptor profiles, reduces fibrosis, and improves contractility in animal models. The selective engagement of GPR30 by G-1, without activating ERα/β, ensures that observed effects are due to rapid, non-nuclear estrogen signaling.

Evidence & Benchmarks

• G-1 displays high affinity for GPR30 (Ki ≈ 11 nM) and negligible activity at ERα/ERβ at concentrations up to 10 μM (APExBIO).
• G-1 induces intracellular Ca²⁺ elevation in GPR30-expressing cells with EC50 = 2 nM (Peng Wang et al., 2021).
• In SKBr3 and MCF7 breast cancer cell lines, G-1 inhibits cell migration with IC50 values of 0.7 nM and 1.6 nM, respectively (APExBIO).
• Chronic G-1 administration in ovariectomized female Sprague-Dawley rats with heart failure reduces brain natriuretic peptide, attenuates cardiac fibrosis, and improves cardiac contractility by modulating β-adrenergic receptor expression (Peng Wang et al., 2021).
• G-1 reverses hemorrhagic shock-induced CD4⁺ T cell dysfunction through GPR30 activation and endoplasmic reticulum stress inhibition (Figure 1).
• Validated for use in cardiovascular, endocrine, and cancer biology research as a reference compound for GPR30-mediated signaling (Reference Compound for Rapid Estrogen Signaling).

Applications, Limits & Misconceptions

G-1 is widely used to dissect rapid, membrane-initiated estrogen signaling in cardiovascular, breast cancer, and immunological research. Its high selectivity allows researchers to attribute observed cellular effects specifically to GPR30 activation, excluding confounding nuclear estrogen receptor pathways (Lab Assay Guide for G-1 (B5455)). This article extends prior practical guides by integrating mechanistic insights and cross-validated animal and cellular benchmarks.

Common Pitfalls or Misconceptions

• G-1 does not activate ERα or ERβ at experimental concentrations (≤10 μM); observed effects in such contexts are not due to nuclear estrogen receptor signaling (Peng Wang et al., 2021).
• G-1 is insoluble in water and ethanol; improper solvent usage can cause precipitation and assay failure (APExBIO).
• Long-term storage of G-1 solutions at room temperature or above -20°C leads to degradation and loss of activity.
• G-1’s effects are mediated only in GPR30-expressing systems; lack of response in GPR30-negative cells or tissues is not a negative control for estrogen signaling in general.
• It should not be used to infer ERα/ERβ biology or nuclear estrogenic responses.

Workflow Integration & Parameters

G-1 is supplied as a crystalline solid (molecular weight: 412.28; chemical formula: C₂₁H₁₈BrNO₃) by APExBIO under SKU B5455. It is soluble in DMSO at concentrations ≥41.2 mg/mL but not in water or ethanol. For experimental use, prepare stock solutions at ≥10 mM in DMSO, using gentle warming or an ultrasonic bath to enhance solubility. Store aliquots at -20°C and avoid repeated freeze-thaw cycles. Do not store solutions long-term. For cell-based assays, titrate final DMSO concentrations below 0.1% (v/v) to minimize solvent toxicity. G-1’s validated benchmarks include robust inhibition of cancer cell migration and reproducible modulation of immune and cardiac parameters in animal models. Detailed scenario-driven protocols and troubleshooting strategies are discussed in Solving Lab Assay Challenges with G-1 and Empowering Cell Assays with G-1, which this article updates by integrating new mechanistic and in vivo data.

Conclusion & Outlook

G-1 (CAS 881639-98-1) is a rigorously validated, selective GPR30 agonist essential for studies of rapid estrogen signaling in cardiovascular, immune, and cancer research. By providing precise, receptor-specific activation, it enables researchers to dissect GPR30-mediated pathways distinct from classical nuclear estrogen receptors. Ongoing research continues to expand its translational relevance, particularly in immune normalization after hemorrhagic shock and attenuation of cardiac fibrosis. For up-to-date technical details, benchmarks, and ordering information, visit the G-1 (CAS 881639-98-1) product page at APExBIO.