Methyl-substituted diindolylmethanes as inhibitors of estrogen-induced growth of T47D cells and mammary tumors in rats

A new class of peroxisome proliferator-activated receptor γ (PPARγ) agonists that inhibit growth of breast cancer cells: 1,1-Bis(3′-indolyl)-1-(p-substituted phenyl)methanes

1,1-Bis(3′-indolyl)-1-(p-trifluoromethylphenyl)methane (DIM-C-pPhCF3) and several p-substituted phenyl analogues have been investigated as a new class of peroxisome proliferator-activated receptor γ (PPARγ) agonists. Structure-activity studies in PPARγ-dependent transactivation assays in MCF-7 breast cancer cells show that 5–20 μm concentrations of compounds containing p-trifluoromethyl, t-butyl, cyano, dimethylamino, and phenyl groups were active, whereas p-methyl, hydrogen, methoxy, hydroxyl, or halogen groups were inactive as PPARγ agonists. Induction of PPARγ-dependent transactivation by 15-deoxy-Δ12,14-prostaglandin J2 (PGJ2) and DIM-C-pPhCF3 was inhibited in MCF-7 cells cotreated with the PPARγ-specific antagonist N-(4′-aminopyridyl)-2-chloro-5-nitrobenzamide. In mammalian two-hybrid assays, DIM-C-pPhCF3 and PGJ2 (5–20 μm) induced interactions of PPARγ with steroid receptor coactivator (SRC) 1, SRC2 (TIFII), and thyroid hormone receptor-associated protein 220 but not with SRC3 (AIB1). In contrast, DIM-C-pPhCF3, but not PGJ2, induced interactions of PPARγ with PPARγ coactivator-1. C-substituted diindolylmethanes inhibit carcinogen-induced rat mammary tumor growth, induce differentiation in 3T3-L1 preadipocytes, inhibit MCF-7 cell growth and G0/G1-S phase progression, induce apoptosis, and down-regulate cyclin D1 protein and estrogen receptor α in breast cancer cells. These compounds are a novel class of synthetic PPARγ agonists that induce responses in MCF-7 cells similar to those observed for PGJ2.

Activation of the aryl hydrocarbon receptor by structurally diverse exogenous and endogenous chemicals

The induction of expression of genes for xenobiotic metabolizing enzymes in response to chemical insult is an adaptive response found in most organisms. In vertebrates, the AhR is one of several chemical/ligand-dependent intracellular receptors that can stimulate gene transcription in response to xenobiotics. The ability of the AhR to bind and be activated by a range of structurally divergent chemicals suggests that the AhR contains a rather promiscuous ligand binding site. In addition to synthetic and environmental chemicals, numerous naturally occurring dietary and endogenous AhR ligands have also been identified. In this review, we describe evidence for the structural promiscuity of AhR ligand binding and discuss the current state of knowledge with regards to the activation of the AhR signaling pathway by naturally occurring exogenous and endogenous ligands.

Increased arylhydrocarbon receptor expression offers a potential therapeutic target for pancreatic cancer

The arylhydrocarbon receptor (AhR) was initially identified as a member of the adaptive metabolic and toxic response pathway to polycyclic aromatic hydrocarbons and to halogenated dibenzo-p-dioxins and dibenzofurans. In the present study, we sought to determine the functional significance of the AhR pathway in pancreatic carcinogenesis. AhR expression was analysed by Northern blotting. The exact site of AhR expression was analysed by in situ hybridization and immunohistochemistry. The effects of TCDD and four selective AhR agonists on pancreatic cancer cell lines were investigated by growth assays, apoptosis assays, and induction of the cyclin-dependent kinase inhibitor p21. There was strong AhR mRNA expression in 14 out of 15 pancreatic cancer samples, weak expression in chronic pancreatitis tissues, and faint expression in all normal pancreata. In pancreatic cancer tissues, AhR mRNA and protein expression were localized in the cytoplasm of pancreatic cancer cells. TCDD and the four AhR agonists inhibited pancreatic cancer cell growth in a dose-dependent manner, and decreased anchorage-independent cell growth. DAPI staining did not reveal nuclear fragmentation and CYP1A1 and was not induced by TCDD and AhR agonists. In contrast, TCDD and AhR agonists induced the expression of the cyclin-dependent kinase inhibitor p21. In conclusion, the relatively non-toxic AhR agonists caused growth inhibition in pancreatic cancer cells with high AhR expression levels via cell cycle arrest. In addition, almost all human pancreatic cancer tissues expressed this receptor at high levels, suggesting that these or related compounds may play a role in the therapy of pancreatic cancer in the future.