G-15: Selective GPR30 Antagonist for Estrogen Signaling Research

Executive Summary: G-15 (CAS 1161002-05-6) is a highly selective antagonist for G protein-coupled estrogen receptor 30 (GPR30), exhibiting a binding affinity (Ki) of ~20 nM and minimal cross-reactivity with classical estrogen receptors ERα/ERβ, even at high concentrations [APExBIO]. It blocks estrogen- and G-1-induced intracellular calcium mobilization and PI3K/Akt signaling in vitro, with a reported IC50 of 185 nM in SKBr3 cells for calcium mobilization inhibition [Peng Wang et al., 2021]. In vivo, G-15 impairs spatial learning in ovariectomized rats and reverses estrogen's immunomodulatory effects, confirming its utility for probing GPR30 function [DOI]. G-15 is insoluble in water/ethanol but dissolves in DMSO (≥37 mg/mL), with recommended storage at -20°C. APExBIO provides G-15 as SKU B5469 for research in estrogen signaling, neurobiology, and cancer biology [APExBIO].

Biological Rationale

Estrogen signaling involves both classical nuclear receptors (ERα, ERβ) and the membrane-bound G protein-coupled estrogen receptor 30 (GPR30). GPR30 mediates rapid, non-genomic responses to estradiol, including intracellular calcium mobilization and PI3K/Akt pathway activation [Wang et al., 2021]. GPR30 is primarily localized in the endoplasmic reticulum and is essential for modulating immune cell proliferation, neurobiological processes, and certain cancer cell pathways. Selective inhibition of GPR30 using antagonists like G-15 allows researchers to precisely dissect these non-classical estrogen-mediated effects, independent of ERα or ERβ activity [Review]. This capability is crucial for advancing mechanistic insights in estrogen signaling research, immune modulation, neurodegenerative disease models, and cancer biology.

Mechanism of Action of G-15

G-15 acts as a highly selective GPR30 antagonist. Its binding affinity (Ki) for GPR30 is approximately 20 nM, allowing potent inhibition at low concentrations [APExBIO]. G-15 does not significantly inhibit or bind classical ERα/ERβ, even at elevated concentrations. In vitro, G-15 blocks both estrogen (E2)- and G-1-induced intracellular calcium mobilization and PI3K activation, thereby reducing downstream Akt phosphorylation [Wang et al., 2021]. In SKBr3 cells, G-15 inhibits G-1-mediated calcium responses with an IC50 of about 185 nM. This antagonism is dose-dependent and reversible. In animal models, subcutaneous administration of G-15 (5–10 μg/day) impairs estrogen-induced neuroprotection and immune normalization, confirming its efficacy in vivo [DOI].

Evidence & Benchmarks

• G-15 binds GPR30 with a Ki of ~20 nM; no significant activity on ERα/ERβ at >100-fold higher concentrations (APExBIO).
• In SKBr3 cell assays, G-15 inhibits G-1-induced calcium mobilization with an IC50 of ~185 nM (Wang et al. 2021).
• G-15 reverses G-1-induced proliferation of breast cancer cells in vitro (DOI).
• In ovariectomized rats, G-15 (5–10 μg/day, s.c.) abolishes estradiol-mediated restoration of CD4+ T cell proliferation and cytokine production after hemorrhagic shock (Wang et al. 2021).
• G-15 impairs spatial learning acquisition in estrogen-dependent behavioral paradigms in vivo (DOI).
• G-15 is insoluble in water/ethanol but soluble in DMSO at concentrations ≥37 mg/mL; stable at -20°C if protected from moisture (APExBIO).

This article updates and extends 'G-15: Advanced Dissection of GPR30 Antagonism in Estrogen...' by providing consolidated quantitative benchmarks and a workflow-focused synopsis for practitioners. It also clarifies technical specifics that are only briefly outlined in 'G-15: Selective GPR30 Antagonist for Estrogen Signaling R...', with new data and protocol advice.

Applications, Limits & Misconceptions

G-15 is widely used to dissect the specific roles of GPR30-mediated signaling in estrogen biology, particularly where rapid, non-genomic effects are of interest. This includes:

• Immune modulation and T cell function studies, especially post-trauma or in inflammatory models (Wang et al. 2021).
• Neurobiological research, including estrogen-dependent neuroprotection and cognitive function assays.
• Cancer biology, especially breast, ovarian, and endometrial cancer models relying on GPR30 signaling (Further reading).
• Dissecting PI3K/Akt and calcium signaling cascades downstream of GPR30.

Common Pitfalls or Misconceptions

• G-15 does NOT antagonize classical estrogen receptors (ERα/ERβ) at physiologically relevant or experimental concentrations; do not use as a pan-estrogen antagonist.
• The compound is insoluble in water and ethanol; improper solvent use results in precipitation or loss of activity.
• Long-term storage of G-15 solutions is not advised; stock instability may impact reproducibility.
• G-15 activity is specific to GPR30; it does not block other GPCRs or unrelated signaling pathways.
• High DMSO concentrations in biological assays can affect cell viability; ensure proper dilution.

Workflow Integration & Parameters

G-15 is supplied as a solid by APExBIO (SKU B5469), with a molecular weight of 370.24 (C₁₉H₁₆BrNO₂). It should be dissolved in DMSO at concentrations ≥37 mg/mL. Stock solutions (>10 mM) are recommended for experimental use and should be stored at -20°C. Avoid repeated freeze-thaw cycles and long-term solution storage. If solubility issues arise, warm to room temperature and apply ultrasonic treatment. For in vitro assays (e.g., calcium mobilization, PI3K/Akt), titrate G-15 from 10 nM to 1 μM. For in vivo studies, doses of 5–10 μg/day (s.c.) have been validated [DOI]. For additional troubleshooting and advanced application strategies, see 'G-15: Selective GPR30 Antagonist for Precision Estrogen S...', which offers workflow-embedded guidance not present in this general overview.

Conclusion & Outlook

G-15 is a rigorously validated, selective GPR30 antagonist that enables precise interrogation of non-genomic estrogen signaling. Its specificity, reproducibility, and solubility profile make it a staple reagent for estrogen signaling research across neurobiology, immunology, and cancer biology. Future directions include expanded use in translational models of neurodegenerative disease and immune dysfunction. For more details and purchasing information, refer to the APExBIO G-15 product page.