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

Executive Summary: G-1 (CAS 881639-98-1) is a highly selective agonist for GPR30/GPER1, a G protein-coupled estrogen receptor mediating rapid non-genomic estrogen signaling [Product page]. It binds GPR30 with a Ki of ~11 nM and demonstrates negligible affinity for classical estrogen receptors ERα and ERβ at micromolar concentrations, ensuring functional specificity (Wang et al. 2021). Upon activation, G-1 triggers intracellular calcium elevation (EC50 = 2 nM) and PI3K-dependent PIP3 accumulation. These pathways underlie effects such as inhibition of breast cancer cell migration (e.g., SKBr3 IC50 = 0.7 nM) and attenuation of cardiac fibrosis in vivo. G-1 is a crystalline solid (C21H18BrNO3, MW 412.28) soluble in DMSO, and is used in cardiovascular, endocrine, and oncology research to clarify GPR30-specific mechanisms.

Biological Rationale

GPR30/GPER1 is a seven-transmembrane G protein-coupled receptor that mediates rapid, non-classical estrogen signaling [DOI]. Unlike nuclear receptors ERα and ERβ, GPR30 is primarily localized to the endoplasmic reticulum membrane. It is implicated in diverse physiological processes, including cardiovascular function, immune modulation, and cancer cell migration. Estradiol-induced benefits such as normalization of immune function and inhibition of endoplasmic reticulum stress are linked to GPR30 activation, as demonstrated in trauma and shock models (Wang et al. 2021). Selective ligands such as G-1 allow precise dissection of GPR30's distinct signaling from classical estrogenic pathways.

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

G-1 binds to GPR30/GPER1 with high affinity (Ki ~11 nM), activating the receptor at nanomolar concentrations. The activation triggers G protein-dependent intracellular signaling cascades, including:

• Elevation of cytosolic calcium concentrations (EC50 = 2 nM) via G protein-coupled pathways [DOI].
• PI3K activation and nuclear translocation of PIP3, promoting downstream kinase signaling.
• Inhibition of cell migration in GPR30-expressing breast cancer cell lines (e.g., SKBr3 and MCF7) with IC50 values of 0.7 nM and 1.6 nM, respectively.
• Minimal binding to ERα and ERβ, even at micromolar concentrations, minimizing off-target effects [More detail].

G-1 does not activate classical nuclear estrogen receptors, ensuring specificity for rapid signaling mechanisms. This distinguishes its effects from those of estradiol or ERα/ERβ agonists.

Evidence & Benchmarks

• G-1 selectively activates GPR30/GPER1 with a Ki of ~11 nM and shows minimal activity at ERα/ERβ up to 10 μM (Wang et al. 2021, DOI).
• Activation by G-1 causes a rapid intracellular calcium increase with an EC50 of 2 nM in GPR30-expressing cells (Wang et al. 2021, DOI).
• In SKBr3 breast cancer cells, G-1 inhibits cell migration with an IC50 of 0.7 nM; in MCF7, IC50 is 1.6 nM (APExBIO, product page).
• In vivo, chronic G-1 administration in ovariectomized, heart failure rat models reduces brain natriuretic peptide, inhibits cardiac fibrosis, and improves contractility (Wang et al. 2021, DOI).
• Beneficial cardiac effects are mediated by normalization of β1-adrenergic receptor expression and upregulation of β2-adrenergic receptor expression (Wang et al. 2021, DOI).
• Estradiol’s immune benefits post-hemorrhagic shock are abolished by GPR30 antagonism, confirming G-1’s pathway specificity (Wang et al. 2021, DOI).

This article provides a detailed, mechanistic update on G-1 compared to existing overviews, such as this summary and this translational review, by emphasizing validated quantitative benchmarks and evidence from peer-reviewed models.

Applications, Limits & Misconceptions

G-1 is widely adopted in research exploring:

• Cardiovascular disease models, especially heart failure and cardiac fibrosis attenuation.
• Oncology, notably inhibition of breast cancer cell migration and signaling.
• Endocrine research, focusing on rapid estrogenic signaling distinct from nuclear receptor activity.
• Immunomodulation, as demonstrated in trauma/hemorrhage models with normalization of CD4+ T cell function (Wang et al. 2021).

For practical laboratory guidance on cell-based assay design, see our update over this protocol-focused article—here, we add context on translational endpoints and mechanistic selectivity.

Common Pitfalls or Misconceptions

• G-1 does not activate classical nuclear estrogen receptors (ERα or ERβ); it is functionally selective for GPR30 [DOI].
• G-1 is insoluble in water and ethanol; only DMSO or compatible organic solvents are suitable for stock preparation [APExBIO].
• Long-term storage of G-1 solutions is not recommended; stability is optimal at -20°C and for short durations.
• G-1’s effects are context- and model-dependent; its activity requires GPR30/GPER1 expression and may not generalize to all estrogen-responsive models.
• Inhibition of cell migration is not universal; only validated for specific breast cancer lines with known GPR30 expression.

Workflow Integration & Parameters

G-1 is supplied as a crystalline solid (MW 412.28, C21H18BrNO3) by APExBIO (SKU B5455). Stock solutions can be prepared in DMSO at concentrations of >10 mM; warming and sonication can improve solubility. For cell-based assays, final DMSO concentration should not exceed 0.1% v/v to avoid cytotoxicity. G-1 is stable in DMSO at -20°C for short-term use. It is insoluble in water and ethanol. Standard protocols recommend titrating G-1 in the 0.1 nM to 100 nM range for cellular assays. In vivo models typically use chronic administration via validated routes (e.g., intraperitoneal). For further optimization in viability and migration assays, see the practical discussion in this scenario-based guide, which this article extends by providing mechanistic and benchmarking data.

For purchase and detailed documentation, see G-1 (CAS 881639-98-1), a selective GPR30 agonist at APExBIO.

Conclusion & Outlook

G-1 is the reference standard for selective, high-affinity GPR30/GPER1 activation. Its defined mechanism, reproducible in vitro and in vivo benchmarks, and broad adoption across cardiovascular, endocrine, and cancer biology research validate its utility. APExBIO's G-1 (B5455) offers robust, peer-reviewed support for dissecting rapid estrogenic signaling and its physiological impact. Proper handling, storage, and model selection are essential for reliable results. Future work may expand G-1’s translational scope and clarify additional GPR30-mediated signaling axes. For comprehensive product information and acquisition, visit the APExBIO product page.