CH 223191: Benchmark Aryl Hydrocarbon Receptor Antagonist

Executive Summary: CH 223191 is a highly selective aryl hydrocarbon receptor (AhR) antagonist validated at nanomolar potency. It blocks TCDD-induced transcriptional activation with an IC50 of ~30 nM in cell-based assays and suppresses cytochrome P450 1A1 (CYP1A1) induction both in vitro and in vivo (product information). In murine models, CH 223191 mitigates hepatic enzyme elevation and weight loss caused by dioxin exposure. It is an essential tool for probing AhR signaling pathways and dioxin toxicity mechanisms, as confirmed by recent ovarian toxicology studies (Neff et al., 2024). The compound's solubility profile and storage recommendations make it well-suited for laboratory workflows in environmental toxicology and mechanistic research.

Biological Rationale

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor central to the cellular response to environmental toxins such as dioxins, including 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and phthalates (Neff et al., 2024). Upon activation, AhR regulates the expression of xenobiotic-metabolizing enzymes, notably cytochrome P450 1A1 (CYP1A1) and CYP1B1, which facilitate the detoxification and elimination of harmful compounds. Dysregulation of this pathway is implicated in reproductive toxicity, hepatic damage, and pathophysiological processes resulting from environmental contaminant exposure (related article). CH 223191, developed and supplied by APExBIO, is a small molecule designed to selectively block AhR-mediated transcription, providing a targeted approach to dissecting toxicological mechanisms.

Mechanism of Action of CH 223191

CH 223191 (CAS 301326-22-7) acts as a competitive antagonist of the aryl hydrocarbon receptor. It binds to the AhR ligand-binding domain, thereby preventing the receptor's activation by exogenous ligands such as TCDD and endogenous ligands like tryptophan metabolites (product data). This inhibition blocks AhR translocation to the nucleus and the subsequent upregulation of target genes, including CYP1A1 and CYP1B1. In cell-based assays, CH 223191 exhibits an inhibitory concentration (IC50) of approximately 30 nM for AhR-mediated transcriptional activation. In vivo, the antagonist reduces hepatic CYP1A1 expression and significantly attenuates dioxin-induced toxic endpoints, such as elevations in plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT), as well as body weight loss (Neff et al., 2024).

Evidence & Benchmarks

• CH 223191 inhibits TCDD-induced AhR activation with an IC50 of ~30 nM in cellular reporter assays (product information).
• In mouse ovarian antral follicles, CH 223191 (1 μM) blocks MEHP-induced upregulation of CYP1A1 and CYP1B1, preventing disruption of follicle growth and steroidogenesis (Neff et al., 2024).
• CH 223191 suppresses hepatic CYP1A1 expression and prevents TCDD-induced plasma AST/ALT elevation and weight loss in vivo (product specification).
• Solubility is ≥33.3 mg/mL in DMSO and ≥2.31 mg/mL in ethanol; the compound is insoluble in water (product data).
• Validated batch purity exceeds 98% by HPLC and NMR analyses (product certificate).

This article extends the protocol focus of 'CH 223191: Applied AhR Antagonism in Toxicology & Regeneration' by providing quantitative in vitro and in vivo benchmarks and clarifying limitations in reproductive models.

Applications, Limits & Misconceptions

CH 223191 is primarily used as a selective AhR pathway inhibitor in environmental toxicology, reproductive biology, and mechanistic dioxin studies. It enables investigators to parse the direct contributions of AhR signaling in toxicant-induced responses, such as those mediated by TCDD or phthalate metabolites. For example, co-culture experiments demonstrate that CH 223191 can counteract MEHP-induced inhibition of follicle growth and estrogen production in mouse ovarian follicles (Neff et al., 2024). Its high selectivity distinguishes it from broader CYP inhibitors, minimizing off-target effects.

However, CH 223191 does not reverse all toxicant-induced effects, particularly those mediated by AhR-independent pathways, and its application should be limited to well-characterized models of AhR activation. The compound is not suitable for long-term solution storage due to potential degradation, and its use in aqueous systems is precluded by insolubility in water (APExBIO).

Common Pitfalls or Misconceptions

• Not a pan-CYP inhibitor: CH 223191 does not broadly inhibit cytochrome P450 enzymes; it selectively targets AhR-mediated transcription.
• Insoluble in water: It cannot be used in purely aqueous buffers; DMSO or ethanol is required for dissolution.
• Not effective for all dioxin-like compounds: Effectiveness is limited to toxicants that activate AhR; it will not block effects mediated by other receptors.
• Not a therapeutic agent: The compound is for research use only and not for clinical application.
• Short solution stability: Solutions should be prepared fresh and used promptly; long-term stock storage is discouraged.

This article deepens the mechanistic context provided by 'CH 223191: Translational Leverage for AhR Axis Discovery', particularly in reproductive and toxicology models.

Workflow Integration & Parameters

• Stock Preparation: Dissolve CH 223191 at concentrations up to 33.3 mg/mL in DMSO or 2.31 mg/mL in ethanol. Do not attempt to dissolve in water (specification).
• Working Solution: Dilute to final concentrations (e.g., 1 μM for cell culture) directly into the assay medium containing a compatible organic solvent carrier.
• Storage: Store the solid at -20°C in a desiccated environment. Use solutions immediately after preparation; avoid repeated freeze-thaw cycles.
• In Vitro Assays: For AhR pathway inhibition in cell-based assays, preincubate cells with CH 223191 for 30–60 minutes before toxicant exposure, as validated in ovarian follicle studies (Neff et al., 2024).
• In Vivo Dosing: Consult the primary literature for dosing regimens compatible with the model species and endpoint; typical protocols employ dosing sufficient to achieve target plasma concentrations based on in vitro potency.

For protocol troubleshooting and advanced workflows, see the supplemental analysis in 'CH 223191: Precision Aryl Hydrocarbon Receptor Antagonist in Toxicology', which this article updates with new ovarian model data.

Conclusion & Outlook

CH 223191 is a validated, potent aryl hydrocarbon receptor antagonist that enables precise investigation of AhR-driven toxicity and signaling. Its high selectivity and robust inhibitory profile make it a reference standard for dissecting environmental toxicology mechanisms, particularly those associated with dioxins and phthalates. Recent data underscore its utility in reproductive models, where it blocks AhR-mediated inhibition of follicle growth and estrogen production (Neff et al., 2024). Ongoing research will further define its role in cross-domain settings, but its use should remain focused on well-characterized AhR-dependent pathways. The compound, available from APExBIO, is integral for laboratories investigating dioxin toxicity mechanisms and AhR-regulated gene expression.