Development of a Selective Modulator of Aryl Hydrocarbon (Ah) Receptor Activity that Exhibits Anti-Inflammatory Properties

Abstract

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that mediates the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin. However, the role of the AHR in normal physiology is still an area of intense investigation. For example, this receptor plays an important role in certain immune responses. We have previously determined that the AHR can mediate repression of acute-phase genes in the liver. For this observation to be therapeutically useful, selective activation of the AHR would likely be necessary. Recently, the selective estrogen receptor ligand WAY-169916 has also been shown to be a selective AHR ligand. WAY-169916 can efficiently repress cytokine-mediated acute-phase gene expression (e.g. SAA1), yet fail to mediate a dioxin response element-driven increase in transcriptional activity. The goals of this study were to structurally modify WAY-169916 to block binding to the estrogen receptor and increase its affinity for the AHR. A number of WAY-169916 derivatives were synthesized and subjected to characterization as AHR ligands. The substitution of a key hydroxy group for a methoxy group ablates binding to the estrogen receptor and increases its affinity for the AHR. The compound 1-allyl-7-trifluoromethyl-1H-indazol-3-yl]-4-methoxyphenol (SGA 360), in particular, exhibited essentially no AHR agonist activity, yet was able to repress cytokine-mediated SAA1 gene expression in Huh7 cells. SGA 360 was tested in a 12-O-tetradecanoylphorbol-13-acetate (TPA)-mediated ear inflammatory edema model using C57BL6/J and Ahr−/− mice. Our findings indicate that SGA 360 significantly inhibits TPA-mediated ear swelling and induction of a number of inflammatory genes (e.g. Saa3, Cox2, Il6) in C57BL6/J mice. In contrast, SGA 360 had no effect on TPA-mediated ear swelling or inflammatory gene expression in Ahr−/− mice. Collectively, these results indicate that SGA 360 is a selective Ah receptor modulator (SAhRM) that exhibits anti-inflammatory properties in vivo.

Identification of a High-Affinity Ligand That Exhibits Complete Aryl Hydrocarbon Receptor Antagonism

“…TCDD was kindly provided by Dr. Stephen Safe (Texas A&M University, College Station, TX). 1-Allyl-3-(3,4-dimethoxyphenyl)-7-(trifluoromethyl)-1H-indazole (SGA360) was synthesized as described previously (Murray et al, 2010b). ␣NF and 6,2Ј,4Ј-trimethoxyflavone (TMF) were acquired from Indofine Chemicals (Hillsborough, NJ).…”

“…Sequences of primers used for quantitative PCR have been described previously (Murray et al, 2010b). PerfeCTa SYBR Green SuperMix for iQ (Quanta Biosciences, Gaithersburg, MD) was used to determine mRNA levels, and analysis was conducted using MyIQ software, in conjunction with a MyIQ-single-color PCR detection system (Bio-Rad Laboratories, Hercules, CA).…”

“…Mouse ear edema assays were conducted as described previously (Murray et al, 2010b). In brief, 6-week-old male C57BL6/J mice (wild type) were anesthetized.…”

“…These compounds, classified as selective AHR modulators (SAhRMs) 1 , are interesting in a therapeutic sense, in that the effects of DRE-mediated AHR activity would be repressed while the potentially beneficial anti-inflammatory properties would be retained (Murray et al, 2010c). Two distinct compounds have been characterized as SAhRM, SGA360, and 3Ј,4Ј-dimethoxy ␣-naphthoflavone (␣NF); collectively, they have been shown to repress a variety of cytokine-induced acute-phase genes, including SAA1, CRP, LBP, C3, C1S, and C1R (Murray et al, 2010b(Murray et al, , 2011. Others also use the term SAhRM in another context, that of a compound that may be used therapeutically in the treatment of breast cancer through AHR-estrogen receptor ␣ cross-talk, this compound exhibits partial agonist activity (Safe and McDougal, 2002).…”

FOXA1 Is Essential for Aryl Hydrocarbon Receptor–Dependent Regulation of Cyclin G2

“…AHR plays important roles in development and differentiation, as well as in the immune and the reproductive systems (1,2). Moreover, AHR has recently emerged as a therapeutic target for inflammatory and autoimmune diseases, as well as for the treatment of breast cancer (3,4). We and others have shown that AHR activation inhibits estrogen receptor-a (ERa) signaling through direct interaction with ERa and through the modulation of ERa target genes (5-7).…”