DiMNF

Selective aryl hydrocarbon receptor (AHR) modulator (SAhRM). Suppresses expression of CD55 and CD46 induced by IL-1β in an inflammatory tumor cell microenvironment; exhibits no effect on basal CD55 or CD46 expression.

Selective aryl hydrocarbon receptor modulator-mediated repression of CD55 expression induced by cytokine exposure.[Pubmed:22553215]

J Pharmacol Exp Ther. 2012 Aug;342(2):345-55.

Modulation of aryl hydrocarbon receptor (AHR) activity by a class of ligands termed selective AHR modulators (SAhRMs) has been demonstrated to attenuate proinflammatory gene expression and signaling, including repression of cytokine-mediated induction of acute-phase genes (e.g., Saa1). These effects are observed to occur through an AHR-dependent mechanism that does not require canonical signaling through dioxin response elements. Previously, we have demonstrated that the SAhRM 3',4'-dimethoxy-alpha-naphthoflavone (DiMNF) can repress the cytokine-mediated induction of complement factor genes. Here, we report that the activation of the AHR with DiMNF can suppress cytokine-mediated induction of the membrane complement regulatory protein CD55. When CD55 is expressed on host cells, it facilitates the decay of the complement component 3 (C3) convertase, thereby protecting the cell from complement-mediated lysis. Tumor cells often exhibit elevated CD55 expression on the cell surface in the inflammatory microenvironment of the tumor, and such enhanced expression could represent a means of escaping immune surveillance. DiMNF can repress the cytokine-mediated induction of CD55 mRNA and protein. Luciferase reporter analysis has identified possible response elements on the CD55 promoter, which may be targets for this repression. A C3 deposition assay with [(125)I]C3 revealed that repression of cytokine-mediated CD55 expression by DiMNF led to an increase of C3 deposition on the surface of Huh7 cells, which would likely stimulate the formation of the membrane attack complex. These results suggest that SAhRMs such as DiMNF have therapeutic potential in regulating the immune response to tumor formation.

Distinct roles for aryl hydrocarbon receptor nuclear translocator and ah receptor in estrogen-mediated signaling in human cancer cell lines.[Pubmed:22235307]

PLoS One. 2012;7(1):e29545.

The activated AHR/ARNT complex (AHRC) regulates the expression of target genes upon exposure to environmental contaminants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Importantly, evidence has shown that TCDD represses estrogen receptor (ER) target gene activation through the AHRC. Our data indicates that AHR and ARNT act independently from each other at non-dioxin response element sites. Therefore, we sought to determine the specific functions of AHR and ARNT in estrogen-dependent signaling in human MCF7 breast cancer and human ECC-1 endometrial carcinoma cells. Knockdown of AHR with siRNA abrogates dioxin-inducible repression of estrogen-dependent gene transcription. Intriguingly, knockdown of ARNT does not effect TCDD-mediated repression of estrogen-regulated transcription, suggesting that AHR represses ER function independently of ARNT. This theory is supported by the ability of the selective AHR modulator 3',4'-dimethoxy-alpha-naphthoflavone (DiMNF) to repress estrogen-inducible transcription. Furthermore, basal and estrogen-activated transcription of the genes encoding cathepsin-D and pS2 are down-regulated in MCF7 cells but up-regulated in ECC-1 cells in response to loss of ARNT. These responses are mirrored at the protein level with cathepsin-D. Furthermore, knock-down of ARNT led to opposite but corresponding changes in estrogen-stimulated proliferation in both MCF7 and ECC-1 cells. We have obtained experimental evidence demonstrating a dioxin-dependent repressor function for AHR and a dioxin-independent co-activator/co-repressor function for ARNT in estrogen signalling. These results provide us with further insight into the mechanisms of transcription factor crosstalk and putative therapeutic targets in estrogen-positive cancers.

Suppression of cytokine-mediated complement factor gene expression through selective activation of the Ah receptor with 3',4'-dimethoxy-alpha-naphthoflavone.[Pubmed:21127131]

Mol Pharmacol. 2011 Mar;79(3):508-19.

We have characterized previously a class of aryl hydrocarbon receptor (AHR) ligand termed selective AHR modulators (SAhRMs). SAhRMs exhibit anti-inflammatory properties, including suppression of cytokine-mediated acute phase genes (e.g., Saa1), through dissociation of non-dioxin-response element (DRE) AHR activity from DRE-dependent xenobiotic gene expression. The partial AHR agonist alpha-naphthoflavone (alphaNF) mediates the suppressive, non-DRE dependent effects on SAA1 expression and partial DRE-mediated CYP1A1 induction. These observations suggest that alphaNF may be structurally modified to a derivative exhibiting only SAhRM activity. A screen of alphaNF derivatives identifies 3',4'-dimethoxy-alphaNF (DiMNF) as a candidate SAhRM. Competitive ligand binding validates DiMNF as an AHR ligand, and DRE-dependent reporter assays with quantitative mRNA analysis of AHR target genes reveal minimal agonist activity associated with AHR binding. Consistent with loss of agonist activity, DiMNF fails to promote AHR binding to DRE probes as determined through electromobility shift assay. Importantly, mRNA analysis indicates that DiMNF retains the suppressive capacity of alphaNF regarding cytokine-mediated SAA1 expression in Huh7 cells. Interestingly, predictive docking modeling suggests that DiMNF adopts a unique orientation within the AHR ligand binding pocket relative to alphaNF and may facilitate the rational design of additional SAhRMs. Microarray studies with a non-DRE binding but otherwise functional AHR mutant identified complement factor C3 as a potential SAhRM target. We confirmed this observation in Huh7 cells using 10 muM DiMNF, which significantly repressed C3 mRNA and protein. These data expand the classes of AHR ligands exerting DRE-independent anti-inflammatory SAhRM activity, suggesting SAhRMs may have application in the amelioration of inflammatory disorders.