Aryl Hydrocarbon Receptor (AHR)-Active Pharmaceuticals Are Selective AHR Modulators in MDA-MB-468 and BT474 Breast Cancer Cells

Abstract

Leflunomide, flutamide, nimodipine, mexiletine, sulindac, tranilast, 4-hydroxytamoxifen, and omeprazole are pharmaceuticals previously characterized as aryl hydrocarbon receptor (AHR) agonists in various cell lines and animal models. In this study, the eight AHR-active pharmaceuticals were investigated in highly aggressive aryl hydrocarbon (Ah)-responsive BT474 and MDA-MB-468 breast cancer cell lines, and their effects on AHR protein, CYP1A1 (protein and mRNA), CYP1B1 (mRNA), and cell migration were determined. 2,3,7,8-Tetrachlorodibenzo-pdioxin (TCDD) was used as a positive control. The AHR agonist activities of the pharmaceuticals depended on structure, response, and cell context. Most compounds induced one or more AHR-mediated responses in BT474 cells, whereas in Ah-responsive MDA-MB-468 cells effects of the AHR-active pharmaceuticals were highly variable. 4-Hydroxytamoxifen, mexiletine, and tranilast did not induce CYP1A1 in MDA-MB-468 cells; moreover, in combination with TCDD, mexiletine was a potent AHR antagonist, tranilast was a partial antagonist, and 4-hydroxytamoxifen also exhibited some AHR antagonist activity. Omeprazole and, to a lesser extent, sulindac and leflunomide were full and partial AHR agonists, respectively, in both breast cancer cell lines. These data indicate that the AHRactive pharmaceuticals are selective AHR modulators, and applications of these drugs for targeting the AHR must be confirmed by studies using the most relevant cell context.

Microbiome-Derived Tryptophan Metabolites and Their Aryl Hydrocarbon Receptor-Dependent Agonist and Antagonist Activities

“…Confirmation of the AHR agonist/antagonist activity of the tryptophan metabolites was determined in MDA-MB-468 and MDA-MB-231 cells, which we have previously used to investigate the activities of several AHR-active pharmaceuticals (Jin et al, 2012). Figure 4A shows that the pattern of CYP1A1 induction by tryptamine was similar in both breast cancer cell lines.…”

“…Moreover, in CaCo-2 cells we also examined the effects of 3-indoxyl sulfate, which has previously been characterized as an AHR agonist . TCDD served as a prototypical agonist, and we also compared the effects of TCDD versus the tryptophan metabolites on proteasomedependent downregulation of the AHR protein, which is observed for some (e.g., TCDD) but not all AHR ligands (Davarinos and Pollenz, 1999;Kawajiri et al, 2009;Jin et al, 2012). All the tryptophan metabolites exhibit full or partial (indole) AHR agonist activity in CaCo-2 cells and induced CYP1A1 mRNA and protein, whereas induction of CYP1B1 was highly variable.…”

“…Tissue-and responsespecific agonist or antagonist activity of receptor ligands is due to several factors, including different ligand-induced conformational changes in the receptor and differential expression of cofactors in various tissues/cells. We previously observed the SAhRM-like activity for a series of AHR-active pharmaceuticals in breast cancer cells (Jin et al, 2012).…”

“…For example, a-naphthoflavone and 39-methoxy-49-nitroflavone were initially characterized as AHR antagonists, but subsequent studies showed that they exhibit both agonist and antagonist activity (Lu et al, 1996;Zhou and Gasiewicz, 2003). The AHR-active pharmaceutical mexiletine induces hepatic CYP1A1 in vivo and in vitro and binds the AHR (Hu et al, 2007); however, in MDA-MB-468 breast cancer cells, mexiletine inhibits induction of CYP1A1 by TCDD and is an AHR antagonist (Jin et al, 2012), and this is typical of a tissue-specific selective AHR modulator (SAhRM).…”

Aryl Hydrocarbon Receptor Activity of Tryptophan Metabolites in Young Adult Mouse Colonocytes

“…The cell context-and gene-specific AhR agonist and antagonist activities of the tryptophan metabolites are not unique and have been observed for other AhR ligands including 6-methyl-1,3,8-trichlorobenzofuran, flavonoids, and pharmaceuticals (Astroff et al, 1988;Lu et al, 1996;McDougal et al, 2001;Zhou and Gasiewicz, 2003;Jin et al, 2012;Safe et al, 2012). We also observed that the AhR antagonist CH inhibited Cyp1a1 induction by TCDD and the tryptophan metabolites, indicating that CH inhibited induction of Cyp1a1 by a diverse spectrum of AhR ligands, as previously reported elsewhere (Choi et al, 2012).…”