Structure-dependent activation of NR4A2 (Nurr1) by 1,1-bis(3'-indolyl)-1-(aromatic)methane analogs in pancreatic cancer cells

NR4A2 (Nurr1) is an orphan nuclear receptor with no known endogenous ligands and is highly expressed in many cancer cell lines including Panc1 and Panc28 pancreatic cancer cells. Structure-dependent activation of NR4A2 by a series of 1,1-bis(3'-indolyl)-1-(aromatic)methane (C-DIM) analogs was determined in pancreatic cancer cells transfected with yeast GAL4-Nurr1 chimeras and a UASx5-luc reporter gene or constructs containing response elements that bind NR4A2. Among 23 different structural analogs, phenyl groups containing p-substituted trifluoromethyl, t-butyl, cyano, bromo, iodo and trifluoromethoxy groups were the most active compounds in transactivation assay. The p-bromophenyl analog (DIM-C-pPhBr) was used as a model for structure-activity studies among a series of ortho-, meta- and para-bromophenyl isomers and the corresponding indole 2- and N-methyl analogs. Results show that NR4A2 activation was maximal with the p-bromophenyl analog and methylation of the indole NH group abrogated activity. Moreover, using GAL4-Nurr1 (full length) or GAL-Nurr1-A/B and GAL4-Nurr1-(C-F) chimeras expressing N- and C-terminal domains of Nurr1, respectively, DIM-C-pPhBr activated all three constructs and these responses were differentially affected by kinase inhibitors. DIM-C-pPhBr also modulated expression of several Nurr1-regulated genes in pancreatic cancer cells including vasoactive intestinal peptide (VIP), and the immunohistochemical and western blot analyses indicated that DIM-C-pPhBr activates nuclear NR4A2.