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

Executive Summary: G-1 (CAS 881639-98-1) is a highly selective G protein-coupled estrogen receptor (GPR30/GPER1) agonist with nanomolar affinity (Ki ~11 nM) and negligible activity at classical estrogen receptors ERα and ERβ, even at micromolar concentrations [product]. G-1 mediates rapid, non-genomic estrogen signaling, including PI3K-dependent PIP3 accumulation and intracellular calcium elevation (EC50 = 2 nM), producing functional outcomes such as inhibition of breast cancer cell migration and attenuation of cardiac fibrosis in vivo [Wang et al. 2021, DOI]. Experimental protocols require solubilization in DMSO (≥41.2 mg/mL), with avoidance of water or ethanol due to insolubility. APExBIO’s G-1 (SKU B5455) is referenced in multiple peer-reviewed studies and is a benchmark tool for dissecting GPR30-mediated signaling in diverse biological models (see comparison).

Biological Rationale

The G protein-coupled estrogen receptor (GPR30, also known as GPER1) mediates rapid, non-classical estrogen responses, distinct from the slower genomic actions of ERα and ERβ [Wang et al. 2021]. GPR30 is predominantly localized to the endoplasmic reticulum and plasma membrane, enabling fast intracellular signaling upon activation by select agonists. G-1 was developed to provide a highly selective tool for dissecting GPR30-mediated pathways without off-target activation of classical estrogen receptors. This selectivity is essential for unambiguous mechanistic studies in cardiovascular, immune, and oncology research (cf. gold-standard review). By isolating GPR30-specific effects, G-1 enables researchers to link rapid estrogen signaling to outcomes such as immune modulation, anti-fibrotic responses, and inhibition of cancer cell migration.

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

G-1 exhibits high affinity for GPR30 (Ki ~11 nM) and negligible binding to ERα or ERβ, even at concentrations exceeding 1 μM [product]. Upon binding, G-1 induces conformational changes in GPR30, triggering intracellular signaling cascades:

• PI3K pathway activation: G-1 promotes PI3K-dependent nuclear accumulation of phosphatidylinositol (3,4,5)-trisphosphate (PIP3), a key signaling lipid in cell growth and survival [Wang et al. 2021].
• Calcium mobilization: G-1 elevates intracellular Ca²⁺ levels with an EC50 of 2 nM, contributing to fast, non-genomic estrogen responses.
• Regulation of adrenergic receptors: In vivo, chronic G-1 administration normalizes β1-adrenergic receptor expression and upregulates β2-adrenergic receptor expression in heart failure models.

These mechanisms underpin physiological effects such as inhibition of cell migration in breast cancer lines, attenuation of cardiac fibrosis, and immunomodulation following hemorrhagic shock [Figure 1].

Evidence & Benchmarks

• G-1 binds GPR30 with Ki ≈ 11 nM and shows minimal affinity for ERα or ERβ, even at 1 μM concentrations (product data).
• In SKBr3 breast cancer cells, G-1 inhibits cell migration with an IC50 of 0.7 nM; in MCF7 cells, IC50 is 1.6 nM (product data).
• G-1 elevates intracellular calcium in GPR30-expressing cells with EC50 = 2 nM under standard buffer conditions (product data).
• Chronic G-1 administration in ovariectomized, heart failure rat models reduces brain natriuretic peptide (BNP), inhibits cardiac fibrosis, and improves contractility (Wang et al. 2021, DOI).
• G-1’s beneficial immune effects after hemorrhagic shock are abrogated by the GPR30 antagonist G15, indicating GPR30-specificity (Wang et al. 2021, Figure 1).

This article extends the mechanistic focus of prior reviews by integrating new in vivo results and practical experimental guidance.

Applications, Limits & Misconceptions

G-1 enables precise investigation of GPR30-mediated signaling in several model systems:

• Cardiovascular research: Used in heart failure and fibrosis models to dissect rapid estrogenic cardioprotection.
• Oncology: Applied for inhibition of breast cancer cell migration and proliferation studies.
• Immunology: Used to study estrogen’s non-genomic effects on T cell proliferation and immune recovery post-trauma (Wang et al. 2021).
• Endocrine signaling: Disentangles rapid, membrane-initiated estrogen signaling from nuclear receptor pathways.

This scope builds on scenario-driven applications discussed in previous product-focused articles, providing expanded mechanistic and control parameter clarity.

Common Pitfalls or Misconceptions

• G-1 is insoluble in water or ethanol; attempts to prepare aqueous stock solutions result in precipitation and loss of activity.
• Long-term storage of G-1 solutions at temperatures above -20°C may cause degradation; freshly prepared solutions are recommended.
• G-1 does not activate classical nuclear estrogen receptors (ERα, ERβ); observed effects via these receptors are not attributable to G-1.
• In vivo effects require chronic administration and appropriate animal models (e.g., ovariectomized rats); acute dosing may not replicate published outcomes.
• Immunological effects of G-1 are context-dependent and may not generalize across all trauma or shock models.

Workflow Integration & Parameters

G-1 is supplied as a crystalline solid (C21H18BrNO3, MW 412.28, SKU B5455 from APExBIO). For experimental use, dissolve G-1 in DMSO to ≥41.2 mg/mL; ultrasonic bath and mild warming (up to 37°C) enhance dissolution. Stock solutions (>10 mM) should be aliquoted and stored at -20°C. Avoid repeated freeze-thaw cycles and use within a few weeks for maximal activity. For cell-based assays, dilute G-1 into culture medium immediately before use, maintaining final DMSO concentrations ≤0.1% (v/v) to minimize cytotoxicity. In vivo studies require vehicle-matched controls and careful attention to administration route and dosing frequency. Further practical guidance is available in the comparative workflow articles here (expanding on translational applicability) and here (focused on oncology models).

Conclusion & Outlook

G-1 (CAS 881639-98-1) is the gold standard for selective GPR30 activation, enabling precise, reproducible studies in cardiovascular, cancer, and immune signaling. Its nanomolar potency, robust selectivity, and well-documented in vivo efficacy underpin its widespread adoption. APExBIO’s G-1 (B5455) offers researchers a validated, reliable reagent for dissecting non-classical estrogen receptor biology. Ongoing research will further clarify GPR30’s translational potential in disease models and therapeutic innovation. For detailed product specifications and safety data, see the official product page.